The first use of Audio-Animatronics was for Walt Disney’s Enchanted Tiki Room in Disneyland, which opened in June, 1963. The Tiki birds were operated using digital controls; that is, something that is either on or off. Tones were recorded onto tape, which on playback would cause a metal reed to vibrate. The vibrating reed would close a circuit and thus operate a relay. The relay sent a pulse of energy (electricity) to the figure’s mechanism which would cause a pneumatic valve to operate, which resulted in the action, like the opening of a bird’s beak. Each action (e.g., opening of the mouth) had a neutral position, otherwise known as the “natural resting position” (e.g., in the case of the Tiki bird it would be for the mouth to be closed). When there was no pulse of energy forthcoming, the action would be in, or return to, the natural resting position.

This digital/tone-reed system used pneumatic valves exclusively–that is, everything was operated by air pressure. Audio-Animatronics’ movements that were operated with this system had two limitations. First, the movement had to be simple–on or off. (e.g., The open and shut beak of a Tiki bird or the blink of an eye, as compared to the many different positions of raising and lowering an arm.) Second, the movements couldn’t require much force or power. (e.g., The energy needed to open a Tiki Bird’s beak could easily be obtained by using air pressure, but in the case of lifting an arm, the pneumatic system didn’t provide enough power to accomplish the lift.) Walt and WED knew that this this pneumatic system could not sufficiently handle the more complicated shows of the World’s Fair. A new system was devised.
In addition to the digital programming of the Tiki show, the Fair shows required analog programming. This new “analog system” involved the use of voltage regulation. The tone would be on constantly throughout the show, and the voltage would be varied to create the movement of the figure. This “varied voltage” signal was sent to what was referred to as the “black box.” The black boxes had the electronic equipment that would receive the signal and then activate the pneumatic and hydraulic valves that moved the performing figures. The use of hydraulics allowed for a substantial increase in power, which was needed for the more unwieldy and demanding movements. (Hydraulics were used exclusively with the analog system, and pneumatics were used only with the tone-reed/digital system.)

There were two basic ways of programming a figure. The first used two different methods of controlling the voltage regulation. One was a joystick-like device called a transducer, and the other device was a potentiometer (an instrument for measuring an unknown voltage or potential difference by comparison to a standard voltage–like the volume control knob on a radio or television receiver). If this method was used, when a figure was ready to be programmed, each individual action–one at a time– would be refined, rehearsed, and then recorded. For instance, the programmer, through the use of the potentiometer or transducer, would repeatedly rehearse the gesture of lifting the arm, until it was ready for a “take.” This would not include finger movement or any other movements, it was simply the lifting of an arm. The take would then be recorded by laying down audible sound impulses (tones) onto a piece of 35 mm magnetic film stock. The action could then instantly be played back to see if it would work, or if it had to be redone. (The machines used for recording and playback were the 35 mm magnetic units used primarily in the dubbing process for motion pictures. Many additional units that were capable of just playback were also required for this process. Because of their limited function these playback units were called “dummies.”)

Eventually, there would be a number of actions for each figure, resulting in an equal number of reels of 35 mm magnetic film (e.g., ten actions would equal ten reels). All individual actions were then rerecorded onto a single reel–up to ten actions, each activated by a different tone, could be combined onto a single reel. For each action/reel, one dummy was required to play it back. Thus for ten actions, ten playback machines and one recording machine were required to combine the moves onto a new reel of 35 mm magnetic film.
“Sync marks” (synchronization points) were placed at the front end of each individual action reel and all of the dummies were interlocked. This way, during the rerecording, all of the actions would start at the proper time. As soon as it was finished, the new reel could be played back and the combined actions could be studied. Wathel, and often times Marc Davis (who did a lot of the programming and animation design for the Carousel show) would watch the figure go through the motions of the newly recorded multiple actions. If it was decided that the actions didn’t work together, or something needed to be changed, the process was started over; either by rerecording the individual action, or by combining the multiple actions again. If the latter needed to be done, say the “arm lift action” came in too early, it would be accomplished by unlocking the dummy that had the “arm-lift reel” on it. The film would then be hand cranked, forward or back, a certain number of frames, which changed the start time of the arm lift in relation to the other actions. The dummies would be interlocked, and the actions, complete with new timing on the arm lift, would be recorded once again.
With this dummy system, the dialogue and music could also be interlocked and synched-up with the actions. Then the audio could be listened to as the figure went through the actions. This was extremely helpful in getting the gestures and actions to match the dialogue.
The other method used for programming a figure was the control harness. It was hooked up so that it would control the voltage regulation relative to the movements of the harness. Wathel tells horror stories of sitting in the harness for hours upon end, trying to keep every movement in his body to a minimum, except for the several movements they wanted for the figure. This method had the advantage of being able to do several actions at once, but obviously due to the complexities, a great deal of rehearsal was required.

There was also a harness for the mouth movements. Ken O’Brien, who was responsible for programming most of the mouth movements, used a transducer at first for the mouth programming. Later they designed a harness for his head that controlled the movement of the jaw,” remembered Gordon Williams, recording engineer on the AA figures for the Fair. “It was easier for him to coordinate the movement, because he could watch the movement at the same time that he was doing it.”

2. WHAT IS ANIMATRONICS
Animatronics is a combination of animation and electronics. What exactly is an animatronic? Basically, an animatronic is a mechanized puppet. It may be preprogrammed or remotely controlled. The animatronic may only perform a limited range of movements or it may be incredibly versatile. The scare created by  the Great White coming out of the water in “Jaws” and the tender otherworldliness of “E.T.” are cinematic effects that will not be easily forgotten. Later animatronics was used together with digital effects. Through the precision, ingenuity and dedication of their creators, animatronic creatures often seem as real to us as their flesh-and-blood counterparts

3. FORMATION OF ANIMATRONICS

Step 1: Design Process

During the design process, the client and the company developing the animatronics decide what the character will be,its appearance total number of  moves, quality of moves, and what each specific move will be. Budgets ,time lines and  check points are established. Many years have been spent to ensure that this critical step is as simple as possible. Once this critically important stage is solidified and a time line is agreed upon, the project moves to the sculpting department.

Step 2: Sculpting

The sculpting department is responsible for converting two-dimensional ideas into three-dimensional forms. This team can work from photos, artwork, videos, models, statuettes and similar likenesses. Typically, the client is asked to approve the sculpting before it goes to the molding department.

Step 3: Moldmaking

The molding department takes the form created by the sculptor and creates the molds that will ultimately produce the character skins. Molds can be soft or hard, single or multiple pieces, and reusable or non-reusable. To get the sculptor’s exact interpretation, mold making is both an art form and an elaborate technical process. The process can be very time-consuming and complicated. It can be so unnerving that some animation mold makers even refer to it as “black magic.”

After the mold is finished and cured, it is ready for skin making. Fiberglass shells are simultaneously being laid up to form the body and limb shapes. Some of these shapes are reusable stock pieces, but the majority of shells are custom made for each character.

Step 4: Armature Fabrication

Meanwhile, various body armatures are being created and are assembled in the welding metal-fabricating areas. Each of the robot’s movements axis points must have an industrial-rated bearing to provide action and long life. Each individual part requires a custom design and fabrication. These artisans are combining both art and technology to achieve realistic, lifelike moves.

As the armature takes shape, the actuators, valves, flow controls and hoses are installed by the animation department. The technicians select those components carefully in order to ensure the durability and long life. As it’s assembled, each robotic move is individually tested and adjusted to get that perfect movement.

Step 5: Costuming

The costume, if there is one, is usually tailored to the character and its movements. Animation tailoring can be a very difficult tedious process considering the variables. The outfit has to allow for easy acces to the character’s operating mechanisms. It must also “look” normal after movement has taken place. The costume must be designed to provide hundreds of thousands of operations without wearing out and without causing the skin areas(i.e. around the necks or wrists) to breakdown as well.

Step 6: Programming

Finally, if it is an animated character the electronic wizard move in to connect the control system into valve assembly in the preparation for programming. Programming is the final step, and for some animations it is the most rewarding. Programming can be done either at the manufacturing facility or at the final installation site. In programming, all the individual moves are coordinated into complex animated actions and nuances that bring the character to “life.”

4. JURASSIC PARK

Long before digital effects appeared, animatronics were making cinematic history. But it was in Jurassic park that the best possible combination of animatronics and digital effects were used together. Spinosaurus was  a new dinosaur animatronic created for “Jurassic Park III” by Stan Winston Studio (SWS). SWS worked with Universal Studios and the film’s production team to develop the Spinosaurus design. Below lies the discussion of the amazing process that creates and controls a huge animatronic like this dinosaur!

Ø  Jurassic Machines

Ø  Dinosaur Evolution

Ø  In the Beginning

Ø  Creature Creation

Ø  Putting it together

Ø  Making it Move

Ø  Monster Mash

4.1. Jurassic Machines

The “Jurassic Park” series is known for the realism of its creatures, both the animatronic and digital versions. When the original “Jurassic Park” came out in 1993, it set a new standard for the realistic portrayal of dinosaurs, creatures that have never been seen alive by man. “Jurassic Park II: The Lost World” continued to improve the vision, and “Jurassic Park III,” the latest movie in the series, raised the bar once again.

An animatronic of the legendary Tyrannosaurus rex (T. rex) being built
The animatronic Spinosaurus in action

Most of the dinosaur animatronics used in “Jurassic Park III” are new. For example, the Velociraptors were redesigned to more closely resemble what paleontologists think a Velociraptor looked like. The Tyrannosaurus rex was redone too, but is no longer the star of the franchise. That distinction now passes to Spinosaurus, a monster that dwarfs even the mighty T. rex. This is the largest animatronic SWS has ever built, even bigger than the T. rex that Winston’s team built for the original “Jurassic Park”!

Below lies the  amazing Spinosaurus statistics:

Ø  It is 43.5 feet (13.3 m) long — almost as long as a bus — and weighs 24,000 pounds (10,886.2 kg/12 tons).

Ø  It is powered entirely by hydraulics, even down to the blinking of the eyes. This is because the creature was made to work above and below water.

Ø  There are 42 hydraulic cylinders and approximately 2,200 feet (671 m) of hydraulic hoses.

Ø  The creature moves on a track that is 140 feet (43 m) long and made from a pair of 12-inch (30.48 cm) steel I-beams.

Ø  All pivots use roller-bearing construction.

Ø  All large steel pieces were cut using waterjets.

Ø  The creature is completely remote-controlled.

4.2. Dinosaur Evolution

The Spinosaurus, which is the largest meat-eating dinosaur ever discovered, is based on a real dinosaur that paleontologists have recently discovered. This basis in reality can be both good and bad for the design crew. The good side is that they have a solid foundation to start with. The bad side is that it provides a very specific set of criteria that must be matched.  Building the Spinosaurus, or any other animatronic, requires several major steps:

Ø  Put it on paper.

Ø  Build a maquette (miniature model).

Ø  Build a full-size sculpture.

Ø  Create a mold (from the sculpture) and cast the body.

Ø  Build the animatronic components.

Ø  Put it all together.

Ø  Test it and work out any bugs.

A complicated animatronic could take up to two years from conception to completion. However, deadlines and budgets typically don’t allow for a timeline like that. According to John Rosengrant, SWS effects supervisor for “Jurassic Park III,” the Spinosaurus took less than a year to go from the drawing board to the finished product. Rosengrant supervised a crew of about 75 SWS designers, engineers and artists who worked on “Jurassic Park III” animatronics, and approximately 30 of them worked on developing the Spinosaurus.

4.3. In the Beginning

The first two steps in creating an animatronic are the sketches and the miniature model.

Put it on Paper

The first thing that happens with any animatronic is that an artist creates preliminary sketches of the creature. The Spinosaurus sketches were developed by working closely with expert paleontologist Jack Horner and the crew working on “Jurassic Park III.” The sketches are analyzed and changes are suggested. Eventually, the artist creates a detailed illustration of the creature. In the case of Spinosaurus, SWS went from preliminary sketch to final design in about three weeks.

Build a Maquette

From the final paper design, a miniature scale model called a maquette is created. Fashioned out of clay, the first maquette SWS made of Spinosaurus was one-sixteenth scale. This initial maquette is used to verify that the paper design is accurate. If there are any problems, they are corrected and a new paper design is made.

Jurassic Park III Director Joe Johnston and the one-fifth-scale maquette of the Spinosaurus

Next, a one-fifth-scale maquette is made. This sounds small, until you realize the sheer size of the Spinosaurus. The one-fifth-scale model was about 8 feet (2.4 m) long! The larger maquette allows the designers to add more surface detail. This maquette is then used to produce the full-size sculpture.

Big as Life

Once the sketches and models are done, the full-size building begins.

Build a Full-size Sculpture

For the animatronic dinosaurs in the original “Jurassic Park,” SWS had to build the full-size sculpture by hand, a time-consuming and laborious process. Advances in computer-aided manufacturing (CAM) allow them to automate a significant part of this step.

The maquette is taken to Cyber F/X, where it is scanned by a 3-D digitizer. This is nothing like a normal computer scanner. There are a variety of methods used in 3-D digitizers, but the one that was used for Spinosaurus is called laser scanning.

Laser scanning takes precise measurements of the maquette by bouncing beams of laser light off its surface. As the laser scanner moves around the maquette, it sends over 15,000 beams per second. The reflected light from the beams is picked up by high-resolution cameras positioned on either side of the laser. These cameras create an image of the slice (cross section) of the object that the laser is scanning. A custom computer system collects the cross sections and combines them to create a perfect, seamless computer model of the maquette.

Cyber F/X then used the computer model to mill the life-size model of the Spinosaurus from polyurethane foam. This very rigid foam is cut to the correct shape through a proprietary process called CNC-Sculpting®. This process, developed by Cyber F/X, takes the data from the full-scale computer model and divides the model into manageable chunks. The data for each chunk is then sent to the foam-sculpting machine, where a life-size section of the dinosaur is created by whittling away pieces of foam from a large, solid block using tiny spinning blades. Once all the sections are done, the SWS team assembles the pieces like a giant 3-D jigsaw puzzle. This creates a very basic full-sized model. A lot of work still needs to be done and it is handled by a team of sculptors at Stan Winston Studio. They hand-carve the foam to add all the incredible details that make it seem real.

Molding and Casting

A set of molds are made of the full-sized sculpture. The molds are made from an epoxy that is very durable and has strong bonding characteristics.

Once the components of the animatronic are ready, much of the frame work is test fitted inside the molds before the foam rubber skin is cast. In conjunction with this step is the fabrication of the foam-running core, which is created by lining the inside of the mold with precise layers of clay to represent the skin thickness. When the clay lay-up is completed, the surface of the clay is fiberglassed to create the foam-running core. After the clay is cleaned out, the foam-running core is bolted into the mold and creates a negative space between the foam-running core and detailed surface of the mold. When filled with foam rubber, this negative space becomes the skin.

The purpose of this process is twofold:

Ø  It makes the skin movement seem more natural

Ø  It controls the skin’s thickness and weight

4.4. Creature Creation

Build the animatronic components

Building the various components used in the animatronic usually takes the longest time. Most of the creatures that are developed at Stan Winston Studio require parts that you’re not going to find at your local hardware store. This means that SWS has to build almost everything themselves. They do take advantage of any existing products when possible, usually by repurposing parts of a common device to fill some of their uncommon needs.
Working on the head of Tyrannosaurus rex

Basically, there are four main categories that the work splits into, with development happening simultaneously across the categories:

Mechanical –

SWS engineers design and build the mechanical systems, which includes everything from basic gears to sophisticated hydraulics. An interesting fact about the Spinosaurus animatronic is that nearly all of the mechanical systems used in it are hydraulic.

Electronic –

Another group develops the electronic control systems needed to operate the animatronic. Typically starting from scratch and creating their own custom circuit boards, these engineers are essentially building giant remote-controlled toys. Almost all of the movement of the Spinosaurus will be manipulated by specialized remote-control systems known as telemetry devices.

All hydraulic systems are installed and checked.

Structural –

All of the electronic and mechanical components need something to attach to and control, and the skin must have a frame to maintain its shape. This is done by building a plastic and steel frame. To increase the realism, and because it is the natural way to design it, the frame of the Spinosaurus, as well as most other creatures made by SWS, resembles the actual skeleton of the beast. This skeletal frame is largely comprised of graphite, a synthetic material known for its strength and lightness.

Surface –

The “skin” of the Spinosaurus is made from foam rubber, which is a very light, spongy rubber that is made by mixing air with liquid latex rubber and then curing (hardening) it. While there are other compounds, such as silicone and urethane, that are stronger and last longer, foam rubber is used because it is much easier to work with. The solution is poured into each mold and allowed to cure. As mentioned earlier, parts of the frame are embedded with the foam rubber at certain points. To further strengthen the skin, a piece of fabric is cut to size and embedded in the foam rubber after it is poured into the mold. Once cured, each piece of skin is pulled from its mold.

4.5. Putting it Together

When all the components are done, it’s time to build the Spinosaurus. The frame is put together and then the mechanical systems are put in place. As each component is added, it is checked to ensure that it moves properly and doesn’t interfere with other components. Most of the electronic components are then connected to the mechanical systems they will control. The controls have been tested with the mechanical systems prior to final assembly, but the systems are checked again.

The “skeleton” of the Spinosaurus

Parts of the skin that have embedded pieces of the frame in them are put in place when the frame is assembled. The other skin pieces are fastened in place on the frame once the mechanical and electronic components are installed. Assembling the skin is a very laborious process. As each piece is added, the team has to check to make sure there are no problems – such as unwanted folds buckling, stretching, too tight.

Whenever one of these problems occurs, the skin must be adapted or attached differently. Also, there are places where you do want the skin to fold or hang loose or travel in a certain way, and it must be adjusted to achieve that effect. One of the tricks that SWS uses to make the Spinosaurus and other dinosaurs seem more realistic is to attach bungee cords between areas of skin and the frame. During movement, these bungee cords simulate tendons under the skin, bunching and stretching.

Painting the skin

The skin is mostly “painted” before it is attached to the frame. Stan Winston Studio does not use actual paint, though. Instead, a specially formulated mixture that is akin to rubber cement is used. Tints are added to the mixture to get the correct color. Rosengrant says that they use this mixture in place of traditional paint because it bonds more strongly with the foam rubber and stretches with it as the animatronic moves. Once the animatronic is complete, the team has to test it and work out any problems.

Making it Move

The people that control an animatronic are called puppeteers, because that is all that an animatronic is — a sophisticated puppet. These puppeteers are skilled actors in their own right and will spend some time with the animatronic learning its range of movements. Rosengrant calls this “finding the performance.” The puppeteers are determining what movements make the animatronic look angry, surprised, hungry or any other emotions or moods that are called for in the script.

The telemetry device for controlling the arms

Eight puppeteers operate the Spinosaurus:

Ø  Basic head/body – swivels head, opens and closes jaws, moves neck back and forth, makes body sway from side to side

Ø  Tongue slide levers – moves tongue up and down, side to side and in or out

Ø  Eye joystick control – eyes move, eyelids blink and eye ridge moves

Ø  Front arms – full range of motion; hands open and close

Ø  Cart/body – moves creature back and forth on track

Ø  Breathing potentiometer – inflated bladder inside chest cavity simulates breathing

Ø  Tail – full range of motion

Ø  Body raise slider – raises and lowers body

Rosengrant was the coordinator, and he made sure that all of the other puppeteers are working in concert to create a realistic and believable motion. The telemetry devices used to control the Spinosaurus range from simple handheld units, reminiscent of a video-game joystick, to bizarre contraptions you wouldn’t find anywhere else. For example, the puppeteer who controls the arms has a device that he straps onto his own arms. He then acts out the movement he wants the Spinosaurus to make, and the telemetry device translates his motion into a control signal that is sent to the circuit board controlling the mechanical components that comprise the arm system of the Spinosaurus

4.6. Monster Mash

Because the Spinosaurus animatronic is controlled by radio-frequency (RF) devices, certain precautions must be taken when it is in use. Any other device, such as a cell phone, that operates using RF technology must be turned off in the vicinity of the animatronic. Otherwise, improper signals can interfere with the control signals. This could have disastrous effects when dealing with a 12-ton monster. Clean power is important for the same reason. The Spinosaurus has a dedicated uninterruptible power supply (UPS) so that a power surge or brownout would not cause it to go out of control.

Rosengrant calls the Spinosaurus a “hot rod” animatronic. Everything on the Spinosaurus has more power than usual. The hydraulics have larger cylinders than normal and provide approximately 1,000 horsepower. The Spinosaurus is such a powerful machine that it can literally tear a car apart. When the tail is whipped from one side to the other, it reaches 2 Gs at the tip (1 G is the force of Earth’s gravity).

5. BUILDING YOUR OWN ANIMATRONICS

WHAT IS AN ANIMATRONICS KIT?

Everything you need (except batteries and imagination) is included in our easy-to-use kit. Connect the cable to your PC’s serial port, install the software and you’re ready to start. No soldering or programming skills required. If you can use Windows you can use this Animatronics Kit . The software allows you to record the movements of hobby servos (up to two billion moves) and play them back exactly as recorded. Make your creation come to life!

Kit Includes:	System Requirements:
Servo controller circuit board	486 or higher processor (Pentium recommended)
Two Hitech HS-300 hobby servos	8 megabytes of RAM (32 recommended)
Mini SSC Panel v1.2 software	3.5″ 1.44MB floppy
Battery Pack	Windows 3.x, 95, 98 or NT
Two servo horn assembly packs	Available serial port
Illustrated Instruction manual	20 Megabytes of hard drive space

Mini SSC Panel v1.2 software

The Mini SSC Panel v1.2 software is a Windows based computer program that allows you to explore the exciting world of animatronics (a combination of animation and electronics) with ease. With this program, you can control the movements of standard hobby servos attached to just about any creation you can imagine. Create robot figures that move on your command or puppets that seem to come alive. The possibilities are endless.

What is the Mini SSC Panel?

The Mini SSC Panel is a graphical user interface allowing you to easily control standard hobby servos attached to a serial servo controller (SSC) circuit board. This interface provides setup, movement control and movement recording/playback features.

What’s new in the Freelance Edition?
New features include:

Ø  “Sleep” Mode

Ø  Playback Looping

Ø  Editable recordings

Ø  “Script Manager”

Ø  Servo Labeling

Ø  Recording and Playback step readout

Ø  Smoother Playback

Ø  Enhanced user guide and help system

Using the Software:

The Control Panel

The Control Panel is the first screen to contain servo motion controls. You use common Windows scroll bars to control the servos attached to your SSC(s). The Control Panel is an excellent tool to calibrate your animatronic creation.

Use the Control Panel to:

Ø  Test SSC/servo connections and functionality

Ø  Test the minimum bounds of your servos

Ø  Test the maximum bounds of your servos

Ø  Determine the “Home” position of your servos

Ø  Experiment with different speeds

Ø  Devise recording strategies and positioning techniques

The Recorder

The  interface to record animatronic projects is a flexible and easy-to-use. With the Mini SSC Panel v1.2 Freelance Edition you can combine small sub-recordings into larger more robust animatronic productions using our “Script Manager.” By creating smaller recordings and compiling them into larger “Scripts” you can focus on each detail of your animation. For instance, once you have the gripper on your robotic arm working exactly the way you want, you can use that piece over and over again in your final script to keep your movements consistent.

Script Manager

One of the most exciting features of the Mini SSC Panel v1.2 Freelance Edition is the Script Manager. The Script Manager allows you to group smaller sub-recordings into larger, more robust animation productions.

Satellites have been used for years to provide communication network links.  Historically, the use of satellites in the Internet can be divided into two generations. In the first generation, satellites were simply used to provide commodity links (e.g., T1) between countries. Internet Protocol (IP) routers were attached to the link endpoints to use the links as single-hop alternatives to multiple terrestrial hops. Two characteristics marked these first-generation systems: they had limited bandwidth, and they had large latencies that were due to the propagation delay to the high orbit position of a geosynchronous satellite.

In the second generation of systems now appearing, intelligence is added at the satellite link endpoints to overcome these characteristics.  This intelligence is used as the basis for a system for providing Internet access engineered using a collection or fleet of satellites, rather than operating single satellite channels in isolation. Examples of intelligent control of a fleet include monitoring which documents are delivered over the system to make decisions adaptively on how to schedule satellite time; dynamically creating multicast groups based on monitored data to conserve satellite bandwidth; caching documents at all satellite channel endpoints; and anticipating user demands to hide latency.

This paper examines several key questions arising in the design of a satellite-based system:

Ø  Can international Internet access using a geosynchronous satellite be competitive with today’s terrestrial networks?

Ø  What elements constitute an “intelligent control” for a satellite-based Internet link?

Ø  What are the design issues that are critical to the efficient use of satellite channels?

The paper is organized as follows. The next section, Section 2, examines the above questions in enumerating principles for second-generation satellite delivery systems. Section 3 presents a case study of the Internet Delivery System (IDS), which is currently undergoing worldwide field trials.

2. Issues in second-generation satellite link control

We discuss in this section each of the questions raised in this paper’s introduction.

Can international Internet access using a geosynchronous satellite be competitive with today’s terrestrial networks?

The first question is whether it makes sense today to use geosynchronous satellite links for Internet access. Alternatives include wired terrestrial connections, low earth orbiting (LEO) satellites, and wireless wide area network technologies (such as Local Multipoint Distribution Service or 2.4-GHz radio links in the U.S.).

We see three reasons why geosynchronous satellites will be used for some years to come for international Internet connections. The first reason is obvious: it will be years before terrestrial networks are able to provide adequate bandwidth uniformly around the world, given the explosive growth in Internet bandwidth demand and the amount of the world that is still unwired. Geosynchronous satellites can provide immediate relief. They can improve service to bandwidth-starved regions of the globe where terrestrial networks are insufficient and can supplement terrestrial networks elsewhere.

Second, geosynchronous satellites allow direct single-hop access to the Internet backbone, bypassing congestion points and providing faster access time and higher net throughputs. In theory, a bit can be sent the distance of an international connection over fiber in a time on the order of tens of microseconds. In practice today, however, international connections via terrestrial links are an order of magnitude larger. For example, in experiments we performed in December 1998, the mean round trip time between the U.S. and Brazil (vt.edu to embr.net.br) over terrestrial links were 562.9 msec (via teleglobe.net) and 220.7. In contrast, the mean latency between the two routers at the two endpoints of a satellite link between Bangladesh and Singapore measured in February 1999 was 348.5 msec. Therefore, a geosynchronous satellite has a sufficiently large footprint over the earth that it can be used to create wormholes in the Internet: constant-latency transit paths between distant points on the globe [Chen]. The mean latency of an international connection via satellite is competitive with today’s terrestrial-based connections, but the variance in latency can be reduced.

As quality-of-service (QoS) guarantees are introduced by carriers, the mean and variance in latency should go down for international connections, reducing the appeal of geosynchronous satellites. However, although QoS may soon be widely available within certain countries, it may be some time until it is available at low cost between most countries of the world.

A third reason for using geosynchronous satellites is that the Internet’s traffic distribution is not uniform worldwide: clients in all countries of the world access content (e.g., Web pages, streaming media) that today is chiefly produced in a few regions of the world (e.g., North America).  This implies that a worldwide multicast architecture that caches content on both edges of the satellite network (i.e., near the content providers as well as near the clients) could provide improved response time to clients worldwide. We use this traffic pattern in the system described in the case study (Section 3).

One final point of interest is to ask whether LEO satellites that are being deployed today will displace the need for geosynchronous satellites.  The low orbital position makes the LEO footprint relatively small.  Therefore, international connections through LEOs will require multiple hops in space, much as today’s satellite-based wireless phone systems operate.  The propagation delay will eliminate any advantage that LEOs have over geosynchronous satellites. On the other hand, LEOs have an advantage:  they are not subject to the constraint in orbital positions facing geosynchronous satellite operators. So the total available LEO bandwidth could one day surpass that of geosynchronous satellites.

What elements constitute an “intelligent control” for a satellite-based Internet link?

The basic architecture behind intelligent control for a satellite fleet is to augment the routers at each end of a satellite link with a bank of network-attached servers that implement algorithms appropriate for the types of traffic carried over the links. We use certain terminology in our discussion. First, given the argument above for asymmetric traffic, our discussion is framed in terms of connecting content providers (in a few countries) to end users (in all countries). In some cases (e.g., two-way audio), however, the traffic may be symmetrical.  Second, we refer to the content-provider endpoint of a satellite link as a warehouse, and the end-user endpoint as a kiosk. The architecture of warehouses and kiosks must be scalable: The number of servers, storage capacity, and throughput of warehouses and kiosks must scale as the number and bandwidth of satellite links, content providers, and end users grows.

Figure 1 illustrates the generic architecture.  Content providers are connected via the terrestrial Internet to a router inside a warehouse. The router also connects to a local area network that interconnects various servers. The router also connects to the earth station for the satellite. Within the footprint of the satellite are many groundstations, each connected to a router within a kiosk. The kiosk is similar to the warehouse in that it connects to a local area network that interconnects servers, and optionally, to a terrestrial Internet connection. The kiosk also acts as the head end for Internet service providers (ISPs) that provide network connections to end users.  More details are given in the case study in Section 3.
Figure 1: Intelligent control resides in warehouses and kiosks

Intelligent controls reside in the warehouse and kiosk and are required to share limited satellite bandwidth among many users and to hide the quarter-second latency of a geosynchronous satellite. The controls are a distributed algorithm, in which part runs on warehouses and part runs on kiosks. All warehouses and kiosks must cooperate and must coordinate the use of satellite resources. Multicast groups are defined to allow communication between cooperating entities (e.g., between a warehouse and multiple kiosks).

To identify which controls make sense, it is useful to look at the characteristics of Internet traffic. Figure 2 is a taxonomy of traffic with six categories. Three of them represent Web pages: pages that are popular for months or longer (e.g., a news service such as cnn.com); pages that are popular for a short time (e.g., hours, days, or weeks, such as those resulting from Olympic games); and pages that are accessed only a few times. One of the facts known about this traffic is that most of the requests and most of the bytes transferred in client workloads come from a small number of servers. For example, in a study of proxy or client uniform resource locator (URL) reference traces from Digital Equipment Corporation (DEC), America Online, Boston University, Virginia Tech, a gateway to South Korea, and one high school, 80% to 95% of the total accesses went to 25% of the servers.

The next category of traffic in Figure 2 is push channels. This consists of a collection of media that a content provider assembles and distributes, for example using the proposed World Wide Web Consortium (W3C) Information and Content Exchange (ICE) protocol. The remaining two categories are real-time traffic, such as streaming audio or video from a teleconference, and what we call timely but not real time.  This last category includes information that is updated periodically and has a certain lifetime, such as financial quotes and Network News Transfer Protocol (NNTP).
Figure 2: Categorization of Internet traffic

The point of categorizing traffic is that different intelligent controls are needed for different categories of traffic. The following are mechanisms used in the case study of Section 3:

• Caching of both categories of popular URLs and push channels should be done at both the warehouse and the kiosk. Caching at the kiosk side obviously avoids the satellite delay when an end-user requests a popular document. Caching at the warehouse is desirable to decouple the process of retrieving documents from the content providers (i.e., the path between content providers and the warehouse in Figure 1) and the process of scheduling multicast transmission of documents from a warehouse via satellite to kiosks. In addition, the warehouse reduces cache consistency traffic, because consistency traffic occurs only between the content providers and the warehouse. The kiosks do not need consistency checks, because they rely on the warehouse to send them updated pages when the warehouse detects inconsistency.
• Feedback of logs of documents, channel content, real-time streams, and timely documents are requested from the kiosk end of satellite connections by the warehouse side for use in adaptive algorithms.
• Unpopular pages may be cached at an individual kiosk only, and retrieved from the Internet using a terrestrial link if available. Only if feedback from the kiosk logs sent to the warehouse shows that a document is popular among multiple kiosks does the document get reclassified as “popular for short term” and hence cached at the warehouse.
• To hide latency, pages and updates to the content of changed pages could be preemptively delivered across the satellite link based on the feedback of logs.
• Push channels could be dynamically constructed by identifying which Web documents have become popular.
• Multicast could be used to deliver push channels, real-time streams and timely documents based on subscriptions.
• The bandwidth available on satellite links could be allocated based on traffic categories.

What are the design issues that are critical to using satellite channels efficiently?

The overall system must achieve a balance between the throughput of the terrestrial Internet connection going into the warehouse, the throughput of the warehouse itself, the throughput of the satellite link, the throughput of each kiosk, and the throughput of the connection between a kiosk and its end users. In addition, a balance among the number of end users, the number of kiosks, and the number of warehouses is required.

Consider some examples. As the number of end users grows, so will the size of the set of popular Web pages that must be delivered, and the bandwidth required for push, real time, and timely traffic. Let’s look at Web traffic in detail. Analysis of end-user traffic to proxy servers at America Online done at Virginia Tech shows that an average user requests one URL about every 50 seconds, which indicates a request rate of 0.02 URLs per second.  (This does not mean that a person clicks on a link or types a new URL every 50 seconds; instead, each URL requested typically embeds other URLs, such as images. The average rate of the individual URLs requested either by a person or indirectly as an embedded object is one every 50 seconds.) Thus, a kiosk supporting 1,000 concurrent users must handle a request rate of 200 per second. The median file size from the set of traces cited above (DEC, America Online, etc.) is 2 kilobytes. Thus, the kiosk Hypertext Transfer Protocol (HTTP)-level throughput to end users must be 400 kilobytes per second.  At the other end, the warehouse has a connection to the Internet.  The bandwidth of this connection must exceed that of the satellite connection, because the warehouse generates cache consistency traffic. The servers within the warehouse and kiosk have limited throughput, for example, the throughput at which the cache engines can serve Web pages. To do multicast transmission, a collection of content (Web pages, pushed documents) must be bundled up at the application layer at the warehouse into a unit for transmission to a multicast group, then broken down into individual objects at the kiosk. This assembly and disassembly process also limits throughput.

A second issue is how to handle Web page misses as kiosks. If the kiosk has no terrestrial Internet connection, then these situations obviously must be satisfied over the satellite channel. This reduces the number of kiosks that a satellite link can handle. On the other hand, if the kiosk does have a terrestrial connection, an adaptive decision might be to choose the satellite over the terrestrial link if there is unused satellite capacity and if the performance of the territorial link is erratic.

A third issue is how to handle Domain Name System (DNS) lookups. A DNS server is necessary at kiosks to avoid the delay of sending lookups over a satellite.  However, how should misses or lookups of invalidated entries in the kiosk’s DNS server be handled? One option is for the DNS traffic to go over a terrestrial link at the kiosk, if one is available. An alternative is for the warehouse to multicast DNS entries to the kiosks, based on host names encountered in the logs transmitted from the kiosks to the warehouse.

A fourth issue is fault tolerance. If a kiosk goes down and reboots, or a new kiosk is brought up, there must be a mechanism for that kiosk to obtain information missed during the failure.

3. Case study: Internet delivery system

IDS uses

• multicast transmission to share channel bandwidth with users in many counties
• caching (e.g., Table 1) at both ends of the satellite to hide or avoid latency, in the form of large (terabyte-size) content warehouses and kiosks
• automated monitoring of user behavior to dynamically create multicast push channels of content
• proactive content refreshing that updates inconsistent cached documents before users request those documents

The objective of the IDS is to provide fast and economical Internet connectivity worldwide. IDS also facilitates Internet access to parts of the globe that have poor terrestrial connectivity. IDS achieves this goal by two means:

1.      creating satellite-based wormholes [Chen], from content providers to geographically distant service providers, thus providing a fast path from one edge of the network to the other

2.      caching content such as HTTP, File Transfer Protocol (FTP), NNTP, and streaming media at the content-provider end as well as the service-provider end, thus conserving bandwidth

The idea for the IDS was conceived at INTELSAT, an international organization that owns a fleet of geostationary satellites and sells space segment bandwidth to its international signatories. Work on the prototype started in February 1998. In February 1999, the prototype system stands poised for international trials involving ten signatories of INTELSAT. A commercial version of IDS will be released in May 1999.

The building blocks of IDS are warehouses and kiosks. A warehouse is a large repository (terabytes of storage) of Web content. The warehouse is connected to the content-provider edge of the Internet by a high-bandwidth link. Given the global distribution of Web content today, an excellent choice for a warehouse could be a large data-center or large-scale bandwidth reseller situated in the U.S. The warehouse will use its high-bandwidth link to the content providers to crawl and gather Web content of interest in its Web cache. The warehouse uses an adaptive refreshing technique to assure the freshness of the content stored in its Web cache. The Web content stored in the warehouse cache is continuously scheduled for transmission via a satellite and multicast to a group of kiosks that subscribe to the warehouse.

The centerpiece of the kiosk architecture is also a Web cache. Kiosks represent the service-provider edge of the Internet and can therefore reside at national service providers or ISPs. The storage size of a kiosk cache can therefore vary from a low number of gigabytes to terabytes. Web content multicast by the warehouse is received, is filtered for subscription, and is subsequently pushed in the kiosk cache. The kiosk Web cache also operates in the traditional pull mode. All user requests for Web content to the service provider are transparently intercepted and redirected to the kiosk Web cache. The cache serves the user request directly if it has the requested content; otherwise, it uses its link to the Internet to retrieve the content from the origin Web site. The cache stores a copy of the requested content while passing it back to the user who requested it.

The layout for an IDS prototype warehouse and kiosk is shown in Figure 1 . The prototype warehouse consists of two server class Pentium II based machines, namely an application server and a  cache server. The cache server houses a Web cache and other related modules.  The Web cache at the warehouse has 100 gigabytes of storage. The application server is host to a transmitter application, a relational database, and a Java-based management application. These servers reside on a dedicated subnet of the warehouse network. This subnet is connected to a multicast-enabled router that routes all multicast traffic to a serial interface for uplinking to the INTELSAT IDR system [Intelsat]. The INTELSAT IDR system provides IP connectivity, over a 2-Mbps satellite channel, between the warehouse and kiosks.

The prototype kiosk also contains a Pentium II-based application server and a Pentium II-based cache server. The kiosk cache server houses a Web cache with 50 gigabytes of storage. The application server is host to a receiver application, a relational database, and a Java-based configuration and management application. These servers reside on a dedicated subnet of the kiosk network. This subnet is connected to a multicast-enabled router. An important part of the prototype kiosk is a layer-4 server switch [Williams], which is used to transparently redirect all HTTP (Transmission Control Protocol/port 80) user traffic to the kiosk cache server.

IDS treats Web content as composed of six traffic categories as categorized in Figure 2. These categories are summarized in Table 1 below. Type A traffic consists of HTTP Web content that is identified by a human operator as content that should remain popular over a long time (e.g., months). This may include popular news Web sites such as the Cable News Network (CNN) Web site. Type B traffic refers to HTTP Web content directly pushed into the warehouse by subscribing content providers. Type E traffic refers to unicast HTTP user request-reply traffic that passes though the kiosk and is not cached at the kiosk. The reply for a type E request is cached at the kiosk on its return path from the origin server. As requests for a particular URL accumulate at multiple kiosks, such a hot-spot URL is converted from type E to type C. Type D traffic refers to real-time streaming traffic. Type F traffic refers to semi-real-time reliable traffic such as financial quotes and NNTP. Traffic of types A, B, C, D, or F is multicast to all kiosks and pushed to subscribing kiosks.

Table 1: IDS traffic categories
Traffic Definition	IDS traffic category
Web sites popular over long time	A
Publisher pushed	B
Automatically identified as hot Web sites	C
Kiosk unicast requests	E
Real-time streaming	D
Semi-real time	F

The IDS prototype implements traffic types A, C, and E. Figure 3 below shows the flow of traffic types A, C, and E through the IDS system. Type A traffic is defined by the warehouse operator by entering popular URLs through the warehouse management interface. The warehouse operator also classifies URLs into channels as part of creating type A content. Once created, content belonging to type A is registered in the relational database and subsequently crawled from the Web and stored in the warehouse Web cache. The warehouse refreshes content of type A from the origin servers based on an adaptive refresh algorithm. Content of type A is also continuously multicast by the transmitter application to the kiosks. At the kiosk, the receiver application filters the incoming multicast traffic, thus accepting only the subset of traffic that belongs to channels subscribed at the kiosk. Filtered content is then pushed into the Web cache at the kiosk.

Traffic of type E originates as an HTTP request from kiosk end users. The request is redirected to the layer-4 switch at the kiosk, the kiosk cache. If the requested content is not found in the kiosk cache, then that request is routed to the origin server. The reply from the origin server is cached at the kiosk Web cache on its way back to the end user who made the request. In Figure 2, the path for unicast type E traffic is shown as going through the satellite back channel. It must be noted, however, that type E traffic bypasses all warehouse components and is routed to the Internet.

On a periodic basis, the warehouse polls all subscribing kiosks for hit statistics regarding the type E content in their respective Web caches. Using this information and appropriate business rules specified by the management application at the warehouse, the warehouse converts a subset of type E content to type C. Once type C content has been created, the data flow for this traffic type follows the same path as described above for traffic type A.
Figure 3: IDS data flow

4. IDS architecture

Components at the warehouse

The IDS warehouse is composed of four major components, namely the cache subsystem, transmission subsystem, management subsystem, and  database subsystem. Figure 4 shows the major components of the warehouse along with their interconnections.

The cache subsystem consists of a cluster of standard Web caches that communicate among each other using standard protocols such as Internet Cache Protocol (ICP). For the IDS prototype, we have a single Squid cache. The cache subsystem also consists of refresh and crawl modules that communicate with the Web cache(s) using HTTP and are responsible for proactively refreshing and crawling newly created type A or C content from origin Web servers, respectively. The log module in the cache subsystem parses standard logs from the Web cache and communicates hit-metering data to the database subsystem.

The transmission subsystem contains scheduling and gathering modules. These modules perform the following functions:

• obtain from the database subsystem lists of URLs belonging to content of types A and C that must be transmitted
• obtain objects corresponding to the URLs from the Web cache
• append a bit map denoting kiosks that subscribe to the channel with each URL to the corresponding object
• construct object bundles sized for optimal transmission
• transfer the bundles to the transmitter

The transmitter module, also a part of the transmission subsystem, receives bundles and transmits them using the Multicast File Transfer Protocol from Starburst Communications.

The management subsystem is a Web-based graphical front end that communicates with the database subsystem and provides the warehouse operator with a tool to perform the following types of activities:

• add popular content to the warehouse (traffic type A)
• create channels and manually classify content into channels
• configure system operational parameters such as thresholds for conversion of content from type E to type C

The database subsystem consists of the relational database, the Y module, and the mapper. The relational database contains persistent information about the content stored in the warehouse Web cache as well as URL hit statistics and channel and subscription information. The Y module performs three major tasks:

1.      It periodically requests per-URL hit statistics for type E content stored in the Web caches of all kiosks.

2.      Based on thresholds set at the warehouse, it converts a subset of E content to C.

3.      It automatically channelizes the newly converted C content into the channels available at the warehouse.

Components at the kiosk

Like the warehouse, the IDS kiosk is also composed of four major components: (1) the cache subsystem, (2) the transmission subsystem, (3) the management subsystem, and (4) the database subsystem. Figure 5 shows the major components of the kiosk.

The cache subsystem at the kiosk consists of a cluster of standard Web caches, a layer-4 switch, and a log module. The cache cluster at the kiosk is identical to the one at the warehouse in all respects except one: the Web cache(s) at the kiosk are equipped to accept an HTTP push. The HTTP push method, which is described in detail in [Chen], enables the kiosk to directly push multicast Web content received from the warehouse into the kiosk cache(s). For the IDS prototype, we have a single Squid cache at the kiosk. The kiosk Web cache(s) are connected to the rest of kiosk network through a layer-4 switch. The layer-4 switch at the kiosk is configured to redirect all user HTTP-based traffic transparently to the Web cache(s). The log module accepts log data from the Web cache and inserts hit-metering data into the database subsystem.

The transmission subsystem at the kiosk contains a receiver module and several push clients. The receiver module performs the following functions:

• receives Multicast File Transfer Protocol bundles
• takes the bundles apart into separate HTTP objects
• filters out objects that do not belong to channels subscribed at the kiosk by inspecting associated bit maps
• passes the rest of the objects along with their URLs to the push clients
• The push clients push all objects forwarded to them by the receiver into the Web cache(s) using the HTTP push method.

The management subsystem at the kiosk is a Web-based graphical front end that communicates with the database subsystem and provides the kiosk operator with a tool to perform the following types of activities:

• subscribing to the channels made available by the warehouse
• blocking specific URLs from being pushed into the kiosk Web cache
• configuring system operational parameters

The database subsystem consists of the relational database and the Y module. The relational database contains persistent information about the content stored in the kiosk Web cache as well as URL hit statistics and channel and subscription information. The Y module at the kiosk transmits per-URL hit statistics for E type content stored in its Web cache when requested to do so by the warehouse.

5. Design issues and goals

In this section, we discuss some of the salient design goals that make IDS a unique system that fits its requirements.

Content refresh at the warehouse

Cache consistency techniques for Web caches are a well-debated topic. In the authors describe techniques for maintaining fresh content in Web caches, namely,

• Time to live (TTL) fields, implemented using the “expires” header field in HTTP, and are used by content publishers to set a TTL for objects they create. When the TTL for an object expires, the cache invalidates that object. The next request for that object to the Web cache is directed to the origin server. The caveat in this strategy is that for a significant proportion of Web content, the TTLs are either incorrect or unspecified.

• Client polling is a technique in which caches periodically query the origin server to determine whether an object has changed. The query frequency is a key factor in this technique. The authors used a client-polling scheme based on the assumption that “young files are modified more frequently than old files” on the Alex FTP cache. A well-tuned client-polling algorithm can be more effective than a cache refresh policy based only on TTL.

In the IDS design, the warehouse maintains the freshness of objects residing within IDS (i.e., in the warehouse and kiosk Web caches). The IDS warehouse design includes an adaptive refresh client-polling technique that uses object TTLs as initial estimates for object refresh times. The client-polling technique is encapsulated in the following relationship:

C_i+1 = C_i + f.(C_i – M)

where C_i denotes the time when the ith query to check the freshness of an object was sent to the origin Web server. C_i+1 denotes the estimated query time for the (i + 1)th query. M denotes the time when the object was last modified at the server. Finally, f denotes a constant factor. A desirable value of f can be determined by minimizing the number of queries i, such that a subsequent modification to the object after time M is discovered as quickly as possible. A value of 0.1 for f is suggested in the HTTP 1.1 request for comments.

By having the warehouse refresh all the kiosks, IDS saves the client-polling bandwidth to origin servers. In addition, the refresh mechanism in IDS is sensitive to objects that change too frequently. Such frequently changing documents are tagged as uncacheable by the system.

Content prefetch

The IDS warehouse is designed to prefetch cacheable objects embedded in a cached Web page. The crawler module in IDS proactively parses cached objects for embedded cacheable objects, evaluates the embedded objects against evaluation parameters, and fetches them from their origin servers to be cached. The evaluation parameters, set through the management application, use the heuristic that objects associated with a popular object are likely to be popular also. Thus, caching of prefetched objects leads to better hit rates for the kiosk caches.

Content rerun — kiosk fault tolerance

Along with new and updated Web content, the IDS warehouse constantly multicasts all information cached in its Web cache to the kiosks. This design feature provides an automatic recovery for kiosks that were offline for a certain period of time. It automatically brings new kiosks up-to-date as well.

Push channels

The IDS warehouse is designed to classify all Web content into push channels based on keywords associated with cached objects. Two methods of channelization are present. Manual channelization is offered through the management application at the warehouse. Any object in the warehouse can be manually associated with a channel. Web content brought in by the warehouse crawler module is also automatically channelized based on a keywords discovery algorithm in the crawler. Kiosks subscribe to channels offered by the warehouse. Based on kiosk subscriptions, which are communicated periodically from all kiosks to the warehouse, the warehouse is able to append a subscription bitmap to all objects being multicast out to the kiosks. Kiosks inspect the subscription bitmap and filter out all unwanted traffic.

Portable module interfaces

A specific goal in the design of IDS is to design modules with portable interfaces. This allows flexibility in choosing implementation platforms. All IDS modules within the warehouse and kiosks use Transmission Control Protocol/IP for interprocess communication. Thus, all warehouse (or kiosk) functionality may reside on a single machine or may be distributed among several machines.  In addition, the relational database communicates with other modules through a single set of application programming interfaces.

Transparent redirection of HTTP traffic at kiosk

A hard requirement of the IDS kiosk design is that all HTTP traffic from users to the kiosk must be transparently redirected to the kiosk cache. Thus, the deployment of a kiosk at a national service provider or an ISP will be invisible to the customers of the kiosk. Although transparent redirection has been implemented in software by Netcache and other cache vendors, most service providers choose to deploy a hardware-based solution such as Web Cache Control Protocol running on CISCO cache engines and routers or to use a content-aware layer-4 switch. The IDS design includes a layer-4 switch to implement transparent redirection of HTTP traffic to the kiosk cache.

Content push into Web cache

The Web caches used in IDS are designed to operate in pull as well as push mode. While pull is the default mode of behavior, IDS Web caches are modified to accept object push. The kiosk Web cache accepts objects pushed from the warehouse. The warehouse Web cache can accept objects pushed from content providers.

Minimal modifications to Web cache architecture

A key goal in the IDS design was to keep modification to the Web cache to a minimum, which would allow the Web cache to be used as a pluggable module. The IDS prototype uses the Squid Web cache from the National Laboratory for Applied Network Research; however, the design allows for the substitution of Squid by any commercial Web cache that implements the push protocol.

Persistent storage of Web cache metadata

Web cache metadata including hit-metering statistics for all cached objects is stored in a relational database. This persistent storage provides IDS with the ability to query relevant metadata statistics to enforce business rules.

6. Roadmap for the future

Although the concept of “shortcuts” from the content providers to service providers is not new, this idea has been harnessed only recently. This recent development has resulted from the availability of enabling technologies such as IP multicast/broadcast over satellite, Web caches that accept push, and transparent redirection of layer-4 traffic. While the planet becomes wired through terrestrial and undersea high-bandwidth fiber links, geostationary satellites offer an ideal platform for offering an intelligent and high-performance infrastructure for Internet delivery. The first generation of such intelligent products will be available this year. These products and services will also serve as the proving grounds for several next-generation internet services, such as virtual private networks (VPNs), which offer security as well as guaranteed quality of service from the content providers to the end users.

At the writing of this document the IDS prototype has been tested at INTELSAT labs and is poised for deployment in international trials. The trials will comprise ten signatories of INTELSAT, including Teleglobe International (Canada), Telia (Sweden), British Telecom (UK), French Telecom (France), and Embratel (Brazil). The international trials will have a single warehouse located near Montreal, Canada, and operated by Teleglobe, and 10 kiosks located at participating signatory sites in North America, Europe, and Africa. The trials will last for three months.

Commercial releases of IDS will add functionality to provide the following:

• Content-provider-based push of Web content into the warehouse Web cache. IDS modules within the warehouse as well as the content provider will be developed to implement this feature.
• A transport and proxy for real-time streaming traffic within IDS.
• Security and QoS for all traffic flowing through IDS.
• Billing components for warehouses and kiosks.
• Information mined from warehouse and kiosk databases to content providers and service providers.

The first commercial version of IDS is scheduled for release in May 1999. Two subsequent commercial releases are planned in 1999.

7. CONCLUSION

A new generation of Internet access built around geosynchronous satellites can provide immediate relief. They can improve service to bandwidth-starved regions of the globe where terrestrial networks are insufficient and supplement terrestrial networks elsewhere. This new generation of satellite system manages a set of satellite links using intelligent controls at the link endpoints. Mechanisms controlled include caching, dynamic construction of push channels, use of multicast. and scheduling of satellite bandwidth.

The need for a wireless electrical power supply has spurred an interest in piezoelectric energy harvesting, or the extraction of electrical energy using a vibrating piezoelectric device. Examples of applications that would benefit from such a supply are a capacitively tuned vibration absorber ,a foot-powered radio” tag and a Pico Radio .A vibrating piezoelectric device differs from a typical electrical power source in that its internal impedance is capacitive rather than inductive in nature, and that it may be driven by mechanical vibrating amplitude and frequency. While there have been previous approaches to harvesting energy generated by a piezoelectric device there has not been an attempt to develop an adaptive circuit that maximizes power transfer from the piezoelectric device. The objective of the research described herein was to develop an approach that maximizes the power transferred from a vibrating piezoelectric transducer to an electromechanical battery. The paper initially presents a simple model of piezoelectric transducer. An ac-dc rectifier is added and the model is used to determine the point of optimal power flow for the piezoelectric element. The paper then introduces an adaptive approach to achieving the optimal power flow through the use of a switch-mode dc-dc converter. This approach is similar to the so-called maximum power point trackers used to maximize power from solar cells. Finally, the paper presents experimental results that validate the technique.

2. DESIGN

2.1. OPTIMAL POWER FLOW OF PIEZOELECTRIC DEVICE

fig.1  piezoelectric element model dc-dc converter

To determine its power flow characteristics, a vibrating piezoelectric element is modeled as a sinusoidal current source i_p (t) in parallel wit its internal electrode capacitance Cp. This model will be validated in a later section. The magnitude of the polarization current I_P varies with the mechanical excitation level of the piezoelectric element, but is assumed to be relatively constant regardless of external loading. A vibrating piezoelectric device generates an ac voltage while electromechanical batteries require a dc voltage, hence the first stage needed to be the output harvesting circuit is an ac-dc rectifier connected to the output of the piezoelectric device, as shown in the Fig. 1. In the following analysis, the dc filter capacitor Crect is assumed to be large; enough so that the output voltage Vrect is essentially constant; the load is modeled as a constant current sourceload ; and the diodes are assumed to exhibit ideal behavior.

The voltage and current waveforms associated with the circuit are shown in Fig 2. These waveforms can be divided into two intervals. In interval 1, denoted as u, the polarization current is charging the electrode capacitance of the piezoelectric element. During this time, all diodes are reverse-biased and no current flows to the output. This condition continues until the magnitude of the piezoelectric voltage vp (t) is equal to the output voltage Vrect. At the end of the communication interval, interval 2 begins, and output current flows to the capacitor Crect and the l

By assuming C_rect >> C_p , the majority of the current will be delivered as output current

The dc component of i_o (t) can be shown to be

The output power can be shown to vary with the value of the output voltage V_rect as follows

	+ P (t) ,   =
					(4)

It can then be shown that the peak output power occurs when

			(5)

Or one-half the peak open circuit voltage of the piezoelectric element

Fig.2 Voltage, current waveforms of a piezoelectric device

2.2. ENERGY HARVESTING CIRCUITRY

The magnitude of the polarization current I_p generated by the piezoelectric transducer, and hence the optimal rectifier voltage, may not be constant as it depends upon the vibration level exciting the piezoelectric element. This creates the need for flexibility in the circuit. i.e., the ability to adjust the output voltage of the rectifier to achieve maximum power transfer. To facilitate the attainment of the optimal voltage at the output of the rectifier, a dc-dc converter is shown in Fig. 3. Typically the controller of such a converter is designed to regulate the output voltage [11]; however, in this circuit the converter will be operated to maximize power flow into the battery. If effective, the piezoelectric element would be at peak power, which corresponds to the output voltage of the rectifier V_rect being maintained at its optimal value, approximately one-half the open circuit voltage, as described previously.

The purpose of this circuit is to maximize the power flowing into the battery. As the battery voltage is essentially constant or changes very slowly, this is equivalent to maximizing the current into the battery, I_battery. By sensing this current, the duty cycle can be adjusted to maximize it. A control scheme such as this is general enough to be effective for many dc-dc converter topologies. To illustrate the theoretical principle of maximum power transfer and the control of the converter will be discussed in this paper. Fig. 4 shows a representation of the steady state battery current-duty cycle relationship using a step-down converter.

In order to achieve peak battery current, an appropriate method of controlling the duty cycle is to incrementally increase or decrease the duty cycle as determined by the slope of the battery current curve JI/JD. The duty cycle is now the sum of the present duty cycle and the increment

D_i+1 = D_i + K _sgn (JI/JD)

Where K is the assigned rate of change of the duty cycle and sgn() is the signum function which returns the sign of the quotient JI/JD.

Note a few features of this control: First, as the control algorithm is based upon the sign of a rate of change, the duty cycle must continuously change in practice. Ideally, once the controller has settled, this will amount to small perturbations about the optimal operating point. Furthermore, as the control algorithm is based upon steady-state behavior of piezoelectric element and the dc-dc converter, a two time scale approach must be used when designing the controller [12]. Using two-time-scale analysis techniques, convergence of the controller can be assured provided the dynamics of the control algorithm are set to be “slow” enough such that the piezoelectric device and converter can be assumed to always be operating under steady state conditions. However, this also places limitations on the bandwidth of the controller.

2.3. CONTROL IMPLEMENTATION

fig.5

The adaptive controller is implemented using a dSPACE DS1102 controller board. The board includes a Texas Instruments TMS320C31 floating point digital signal processor(DSP), analog-to-digital (ADC) converter for sampling measurements, and pulse-width modulated (PWM) signal outputs for controlling the converter. The control algorithm was developed in MATLAB 5.3 using the graphical interface Simulink 3.0 and the Real-Time Workshop to generate the controller code for the DSP.

Fig. 5 shows a block diagram of the controller implementation. The initial duty cycle is set at 10% for circuit startup. The resulting battery current is evaluated using a current sense resistor in series with the battery and sampled by an A/D converter. The current signal is then low-pass filtered to attenuate noise and reduce the current ripple effect caused by the switching of the MOSFET. The derivative of the signal is then taken and divided by the derivative of the duty cycle. Dividing the derivative of the current by the derivative of duty cycle provides JI/JD. Which is used to determine the controller’s position n the battery current-duty cycle curve shown in Fig. 4.

The sign of the quotient, JI/JD. is used by a 0-threshold block to increment the duty cycle by a set rate, in our case 21 mill percent /s (21-m%/s). This rate was determined to produce a measurable change in the battery current that could be used to evaluate the effectiveness of the new duty cycle. The resulting sign(+/-) of the division block, not its numerical magnitude, is all that is used by the 0- threshold block to increase or decrease the duty cycle. If either input signal would be zero, resulting in a zero or undefined quotient, the threshold block will decrease the duty cycle as a default. This default decrease allows the control to migrate to lower duty cycle values when the battery current might not be measurably changing, as is the case of circuit startup. Experimentation showed that, at a switching frequency of 1kHz, the current changes little at duty cycles above 10%, whereas optimal duty cycles occurred around 3-5%.

The duty cycle is then filtered and used to generate the PWM signal for the driver circuitry of the step-down converter. The additional filtering of the PWM signal is necessary to slow the rate of change of the duty cycle so the change in current can be measured and evaluated. Without the LPF, the controller is prone to duty cycle oscillations, as the perturbing signal reacts faster than the finite settling time of the battery current signal.

3. EXPERIMENTAL SETUP

A Quickpack® QP20W purchased from Active Control eX-perts(ACX), Cambridge, MA, was used as the piezoelectric energy source. It is a two layer device that generates an ac voltage when vibrated in a direction perpendicular to its mid-plane. Device specifications and diagram are shown along with the piezoelectric element properties.

Fig.7

The experimental setup is shown in Fig 7. The piezoelectric device is secured to an electric-powered shaker, which provides variable mechanical excitation in response to a sine wave input. The magnitude of the mechanical excitation of the piezoelectric element will be characterized by the open-circuit voltage that is measured across the unloaded rectifier capacitor, Voc. A small mass was added to the free tip of the bimorph to enhance the external stress and increase the tip deflection, thus providing a larger open-circuit voltage.

The step-down converter consists of a MOSFET switch with a high breakdown voltage rating, a custom wound inductor with inductance of 10.03 mH, a Schotty diode, and a filter capacitor. The voltage across the current-sense resistor is amplified with a precision op-amp (powered by he 3V battery), and then sampled by the A/D converter on the controller card. The controller card then generates the PWM signals at the calculated duty cycle that is fed to a high side MOSFET driver. The driver was powered by an external dc power supply. Due to the low power levels expected from the piezoelectric element [2] – [4],[6], it is assumed that the converter will operate in discontinuous current condition mode at the chosen because switching losses in the experimental setup comprised a significant fraction of the power flow from the element.

4. RESULTS

Experimental data were taken to illustrate the theories presented in this paper and to demonstrate the performance of the adaptive control algorithm. The first experiment was conducted in order to determine the validity of the piezoelectric model presented in the Fig.1. Various resistive loads were placed across the output of the excited piezoelectric element, as shown in fig. 8., and the output voltage was measured. The frequency of the excitation was adjusted to the resonant mode of the system for each resistor. This was done to ensure a relatively constant mechanical excitation level of the element throughout the experiment as the resistive load has a dampening effect on the amplitude of the mechanical vibrations. The output voltage for the circuit is given by

Ö1+ ( w CpR )2

(7)

R

Ip

Vo =

A least squares fitting of the data to (7)resulted in I_p equal to 2.2 mA_rms and C_p equal to 0.184mF. Substituting these values into(7), the theoretical output voltage of the circuit can be compared to the measured output voltage over a range of load resistance as shown in Fig. 9.

The next experiment was performed to validate the piezoelectric element-rectifier circuit optimal power transfer theory. Fig. 10 shows a plot of the output power versus the voltage maintained at the output rectifier for a vibrating piezoelectric element. The piezoelectric device was driven at a constant frequency of 53.8Hz and resistors of various values were inserted across the rectifier capacitor (see Fig. 1) to provide the load. At open-circuit condition, a voltage of 45.0 V was measured across the rectifier V_rect. The plot of power dissipated in the resistor at various voltages shows that the maximum power of 18.0mW is available with a 24.0kW resistor at a voltage of 20.57 V. this represents the maximum power available for a set level of execution and shows that maximum power occurs at a specific output voltage. The optimal rectifier voltage of the piezoelectric element. A possible reason for this discrepancy is unmodeled loss mechanisms in the piezoelectric device and/or rectifier.

Using the same circuit and conditions, the output current io(t) of the piezoelectric element was measured using a 10W current sense resistor between the rectifier and the capacitor. The waveforms for load resistor of 430 kW to 0.51 kW across the rectifier capacitor. As the resistance is decreased, the communication interval u becomes smaller and the current waveform is closer to a rectified sine wave.

To demonstrate that a dc-dc converter is capable of attaining the point of maximum power transfer, the step-down converter was operated with manually varied duty cycle. Fig. 10 revels that the battery current has a definite maximum with respect to the duty cycle. With a 45.0 V open-circuit voltage, the maximum current of 4.3 mA was measured at a duty cycle of 3.18%. at this point, the voltage at the rectifier bus capacitor was measured at 20.4 V(2V below one-half the open-circuit voltage). The current remained above 4mA for duty cycles between 2.5 and 4.5% and quickly decreased outside this range. The power stored by the 3 V batteries was 13.0 mW at the optimal duty cycle as compared to the previous experiment, which showed 18.0mW of power available with a resistive load. Power converter losses are therefore estimated to be 5mW. For comparison, direct charging of the battery across the rectifier capacitor yielded.5mA or 4.5 mW of power harvested.

The adaptive controller was then used to show that the algorithm could find and maintain the maximum power into the battery at circuit startup and adjust itself aas the excitation varied. The initial duty cycle was set at 10%and the controller decreased the duty cycle linearly as the current increases. With an open-circuit voltage of 45.8 V, the controller settled to the maximum current of 4.3 mA. The controller then maintained maximum power transfer, while pertubing the duty cycle slightly.

The settling time illustrates the duty cycle rate of change, 21-m%/s, and its effects. The value allows meaningful changes to the current to be measured without large oscillations around the maximum power point. This value does limit the controller speed at startup, taking almost 6 min to achieve maximum current, but once the optimum duty cycle is determined, it limits the oscillations that would increase the time away from the optimum duty cycle. Smaller rates of change that were investigated did not allow changes in the current to be reliably measured and larger rates cost inefficient harvesting due to the increased duty cycle oscillations.

5.APPLICATION

SHOE-POWERED RF TAG SYSTEM

To demonstrate the feasibility and utility of scavenged shoe power, we developed a simple application circuit. The design is a self-powered, active radio frequency (RF) tag that transmits a short-range, 12-bit wireless identification (ID) code while the bearer walks. This system has immediate application in a smart environment, in which multiple users transmit their identities to the local surroundings. The IDs, for example, can enable a central server to make dynamic, near-real-time decisions to personalize the environment or route appropriate information to mobile users. Most previous work in this area relied on battery-powered infrared (IR) badges.9 Our RF-based design, however, requires no line of sight to the reader and therefore can be mounted in a shoe, operating without a battery under the power of a piezoelectric insert. Figure 11 shows a functional prototype pair of self-powered RFID sneakers.

Figure 11. Piezoelectric-powered RFID shoes with mounted electronics.

Figure 12 shows the RF tag system schematic. This design uses scavenged energy from either the PVDF or PZT source to encode and transmit a periodic, On/Off-keyed RFID signal using devices developed for automotive keyless entry systems. A local base station receives the transmission and emits an audible chirp upon identifying the transmitter. The signal from the piezoelectric source is full-wave rectified through 500-mA diode bridge D1. As the source signal ramps up, charge transfers to electrolytic bucket capacitor C1 whenever the source voltage overcomes the voltage already supported by this capacitor (plus two diode drops). As C1 charges beyond 12.6 V (the Z1 breakdown voltage plus the diode drop across the base-emitter junction of Q1), Q1 is forced into conduction, in turn activating Q2 and latching Q1. With Q1 on, the high side of C1 now has a current return path to ground and discharges through the Maxim MAX666 low-dropout (LDO) linear regulator U1.

Figure 12

The regulator is biased to provide a stable +5 V to the serial ID encoder U2 and RF transmitter U3, as long as C1 has sufficient charge to produce a valid regulator output voltage (Vout). Note that Vout exhibits some ripple when supplying the transmitter during the ID code’s On periods. When Vout swings below approximately 4.5 V (as set by R5 and R6), the low-battery in pin (LBin on U1) is pulled below its threshold, driving the low-battery out pin (LBout) to ground momentarily. This negative pulse through C3 turns Q1 Off, thus deactivating Q2 and renewing the C1 charging cycle. Note that R1, R2, and R3 bias Q1 and Q2 to show C1 a very high load impedance when the Q1-Q2 latch is deactivated. Finally, we included R4 and C2 to better match the load stage to the charging circuit and source impedance; the remaining resistors support the load stage components in other ways.

Figure 13 is a representative graph of signals from the power-conditioning circuitry with the PZT source during a walk. The upper trace shows the voltage across C1 (in this case, 47 F), and the lower trace shows the MAX666 linear regulator’s output. Charge accumulates on the bucket capacitor, increasing with each step until the capacitor stores enough energy to power the transmitter for roughly half a second, generally after three to five steps with the current system. Substituting a high-frequency switching regulator for the MAX666 would further improve the efficiency of this circuit; this line of inquiry led to the results summarized in the following section.

Figure 13. Stored voltage (top) and regulated power output (bottom) waveforms for shoe-powered RFID transmitter while walking.

Have you been to the gas station this week? Considering that we live in a very mobile society, it’s probably safe to assume that you have. While pumping gas, you’ve undoubtedly noticed how much the price of gas has soared in recent years. Gasoline which has been the main source of fuel for the history of cars, is becoming more and more expensive and impractical (especially from an environmental standpoint). These factors are leading car manufacturers to develop cars fueled by alternative energies. Two hybrid cars took to the road in 2000, and in three or four years fuel-cell-powered cars will roll onto the world’s highways.

While gasoline prices in the United States have not yet reached their highest point ($2.66/gallon in 1980), they have climbed steeply in the past two years. In 1999, prices rose by 30 percent, and from December 1999 to October 2000, prices rose an additional 20 percent, according to the U.S. Bureau of Labor Statistics. In Europe, prices are even higher, costing more than $4 in countries like England and the Netherlands. But cost is not the only problem with using gasoline as our primary fuel. It is also damaging to the environment, and since it is not a renewable resource, it will eventually run out. One possible alternative is the air-powered car.

Air powered cars runs on compressed air instead of gasoline. This car is powered by a two cylinder compressed engine. This engine can run either on compressed air alone or act as an IC engine. Compressed air is stored in glass or fiber tanks at a pressure of 4351 psi.

Within the next two years, you could see the first air-powered vehicle motoring through your town. Most likely, it will be the e.Volution car that is being built by Zero Pollution Motors.

The cars have generated a lot of interest in recent years, and the Mexican government has already signed a deal to buy 40,000 e.Volutions to replace gasoline- and diesel-powered taxis in the heavily polluted Mexico City.

2. VEHICLE PARTS

Compressed air tanks
One of the most frequently asked questions is about the safety of the compressed air storage tanks. These tanks hold 90 cubic meters of air compressed to 300 bars. Many people ask whether this system is dangerous in case of an accident and if there is a risk of explosion. The answer is NO. Why? Because these are the same tanks used to carry the liquid gas used by buses for public transport. The tanks enjoy the same technology developed to contain natural gas. They are designed and officially approved to carry an explosive product: methane gas.

In the case of a major accident, where the tanks are ruptured, they would not explode since they are not metal. Instead they would crack, as they are made of carbon fiber. An elongated crack would appear in the tank, without exploding, and the air would simply escape, producing a loud but harmless noise. Of course, since this technology is licensed to transport an inflammable and explosive gas (Natural gas), it is perfectly capable inoffensive and non-flammable air.

It is fitting, therefore, that MDI has reached an agreement with the European leader in aerospace technology Airbus Industries for the manufacture of the compressed air storage tanks. With a remote supervision arrangement, Airbus Industries oversees the making of the storage tanks at each MDI factory. The coiled carbon fibre technology used in the construction of the tanks is complex and requires a substantial quality control process which the multinational company, home of the Airbus aircraft, will provide for our vehicles.
Brake power recovery

The MDI vehicles will be equipped with a range of modern systems. For example, one mechanism stops the engine when the car is stationary (at traffic lights, junctions etc). Another interesting feature is the pneumatic system which recovers about 13% of the power used.
The body

The MDI car body is built with fibre and injected foam, as are most of the cars on the market today. This technology has two main advantages: cost and weight. Nowadays the use of sheet steel for car bodies is only because of cost – it is cheaper to serially produce sheet steel bodies than fibre ones. However, fibre is safer (it doesn’t cut like steel), is easier to repair (it is glued), doesn’t rust etc. MDI is currently looking into using hemp fibre to replace fibre-glass, and natural varnishes, to produce 100% non-contaminating bodywork.

The Air Filter

The MDI engine works with both air taken from the atmosphere and air pre-compressed in tanks. Air is compressed by the on-board compressor or at service stations equipped with a high-pressure compressor.

Before compression, the air must be filtered to get rid of any impurities that could damage the engine. Carbon filters are used to eliminate dirt, dust, humidity and other particles, which unfortunately, are found in the air in our cities.

This represents a true revolution in automobiles – it is the first time that a car has produced minus pollution, i.e. it eliminates and reduces existing pollution rather than emitting dirt and harmful gases. The exhaust pipe on the MDI cars produces clean air, which is cold on exit (between -15º and 0º) and is harmless to human life. With this system the air that comes out of the car is cleaner than the air that went in.
The chassis

Based on its experience in aeronautics, MDI has put together highly resistant, yet light, chasses, aluminium rods glued together. Using rods enables us to build a more shock-resistant chassis than regular chasses. Additionally, the rods are glued in the same way as aircraft, allowing quick assembly and a more secure join than with welding. This system helps to reduce manufacture time.

Electrical system

Guy Nègre, inventor of the MDI Air Car, acquired the patent for an interesting invention for installing electrics in a vehicle. Using a radio transmission system, each electrical component receives signals with a microcontroller. Thus only one cable is needed for the whole car. So, instead of wiring each component (headlights, dashboard lights, lights inside the car, etc), one cable connects all electrical parts in the car. The most obvious advantages are the ease of installation and repair and the removal of the approximately 22 kg of wires no longer necessary. Whats more, the entire system becomes an anti-theft alarm as soon as the key is removed from the car.

3. TECHNOLOGY DESCRIPTION

The following is the technology description of the actual functionality of the motor. A more detailed explanation can be found in U.S. patent no: 6,334,435

PROCESS DESCRIPTION

1. The first piston takes in ambient air and compresses it to approximately 300 psi and 200*f in the compression chamber during the first cycle of the engine.

1. When the piston pause, a small amount of compressed air from the tanks is released into the expansion chamber to create a low pressured, low temperature volume of about 140psi
2. Shortly before the valve to the exhaust cylinder is opened, a high-speed shutter connects the compression and expansion chambers. The sudden pressure and temperature difference between the low chambers creates pressure waves in the expansion chamber, thereby producing work in the exhaust chamber that drives the piston to power the engine.

The air tanks for storing the compressed air are localized underneath the vehicle. They are constructed of reinforced carbon fiber with a thermoplastic liner. Each tank can hold 3,180 ft³ of air at a pressure of up to 4,300 psi. When connected to a special compressor station, the tanks can be recharged within 3-4 minutes. They can also be recharged using the on-board compressor 3-4 hours after connecting to a standard power outlet.

TECHNOLOGY OVERVIEW

These new vehicles incorporate various innovative and novel systems such as storing energy in the form of compressed air, using new materials such as fiberglass to build the car and vegetable oil for the motor lubrication.

Numerous innovations have been integrated in the engine design. As an example, there is a patented system of articulated conrods that allow the piston to pause at top dead center. The following graph indicates this movement of the piston in relation to the driving shaft rotation.

The car engine runs on compressed air and incorporates the three laws of thermodynamics.

1.     The first law states that energy can neither be destroyed nor be wasted.

2.     The second law describes the disorder within substances.

3.     The third law defines that only in crystals at 0^o k, there is absolute disorder.

The car incorporates these laws of thermodynamics in the following way. First, the pressure that is created within on-board tanks during compression is in direct proportion to the energy that has been stored in it. This process is equivalent to the energy stored in a wire spring when it is compressed.

Furthermore, thermal energy is dissipating from the system, thereby lowering the temperature of a compressed gas volume that expands. This process is equivalent to harnessing energy that has been stored.

In turning the shaft, shock waves similar to supersonic waves are created when two gases with very different characteristics are mixed together in a certain fashion. All these effects result in a high-powered air technology.

4. WORKING

Air powered cars run on compressed air instead of gasoline. Since the car is working on air there is no pollution. A two cylinder, compressed air engine, powers the car. The engine can run either on compressed air alone or act as an internal combustion engine. Compressed air is stored in fiber or glass fiber tanks at a pressure of 4351 pounds per square inch. The air is fed through an air injector to the engine and flows into a small chamber, which expands the air. The air pushing down on the piston moves the crankshaft, which gives the vehicle power.

This car is also working on a hybrid version of their engine that can run on hybrid version of their engine that can run on traditional fuel in combination with air. The change of energy source is controlled electronically. When the car is moving at speeds below 60kph,it runs on air. At higher speeds, it runs on a fuel such as gasoline diesel or natural gas.

Air tanks fixed to the underside of the vehicle can hold about 79 gallons (300 litres) of air. This compressed air can fuel the car upto 200km at a top speed of 96.5kph.When the tank nears empty it can be refilled at the nearest air pump. The car motors require a small amount of oil about 0.8 litres worth that have to change just every 50,000km.

4.1 GEAR BOX

Gear changes are automatic, powered by an electronic system device. A computer which controls the speed of the car is effectively continuously changing gears. The latest of many previous versions, this gearbox achieves the objective of seamless changes and minimal energy consumption.

4.2 DISTRIBUTION AND VALVES

To ensure smooth running and to optimize energy efficiency, engines use a simple electromagnetic distribution system which controls the flow of air into the engine. This system runs on very little energy and alters neither the valve phase nor its rise.

4.3 MOTO-ALTERNATOR

The moto-alternator connects the engine to the gearbox. It has many functions:

• It supports the vehicles motor to allow the tanks to be refilled.
• As an alternator it produces brake power

It starts the vehicle and provides extra power when necessary.

BASIC PRINCIPLES OF COMPRESSED AIR TECHNOLOGY ENGINE

It uses an innovative system to control the movement of the second-generation pistons and one single crankshaft. The pistons work in two stages and one intermediate stage of compression and expansion.

The engine has four stage pistons that are 8 compression and or expansion chambers. They have two functions:

1. To compress ambient air
2. To make successive expansions thereby approaching isothermic expansion.

THE DUAL ENERGY SYSTEM

The engine can be equipped with and run on dual engines. Fossil fuels and compressed air and incorporate a reheating mechanism between the storage tank and the engine. This mechanism allows the engine to run exclusively on fossil fuel, which permits compatible autonomy on the road. While the car is running on the fossil fuel, the compressor air tanks. The control system maintains a zero pollution emission in the city at speeds upto 60 km per hour.

THE AIR FILTER

The air compressed engine works on with both air taken from the atmosphere and air pre compressed in tanks. Air is compressed by the on board compressor or at service stations equipped with a high-pressure compressor.

Before compression the air must be filtered to get rid of any impurities that could damage the engine. Carbon filters are used to eliminate dirt, dust, humidity and abundant abrasive particles that unfortunately exist in the air from our cities.

This system eliminates and reduces existing pollution rather than emitting dirt and harmful gases. The exhaust pipe on the air-powered cars produces clean air which is cold on exit (between 15^o and 0^o) and is harmless to human life. With this system the air that comes out of the car is cleaner than the air that went in.

5. CRYOGENIC HEAT ENGINE

Another version of an air-powered car is being developed by researchers at the University of Washington using the concept of a steam engine, except there is no combustion. The Washington researchers use liquid nitrogen as the propellant for their LN2000 prototype air car. The researchers decided to use nitrogen because of its abundance in the atmosphere — nitrogen makes up about 78 percent of the Earth’s atmosphere — and the availability of liquid nitrogen. There are five components to the LN2000 engine:

Ø  A 24-gallon stainless steel tank.

Ø  A pump that moves the liquid nitrogen to the economizer.

Ø  An economizer that heats the liquid nitrogen with leftover exhaust heat.

Ø  A heat exchanger that boils the liquid nitrogen, creating a high pressure gas.

Ø  An expander, which converts nitrogen’s energy into usable power.

The liquid nitrogen, stored at -320 degrees Fahrenheit (-196 degrees Celsius), is vaporized by the heat exchanger. The heat exchanger is the heart of the LN2000′s cryogenic engine, which gets its name from the extremely cold temperature at which the liquid nitrogen is stored. Air moving around the vehicle is used to heat the liquid nitrogen to a boil. Once the liquid nitrogen boils, it turns to gas in the same way that heated water forms steam in a steam engine.

Nitrogen gas formed in the heat exchanger expands to about 700 times the volume of its liquid form. This highly pressurized gas is then fed to the expander, where the force of the nitrogen gas is converted into mechanical power by pushing on the engine’s pistons. The only exhaust is nitrogen, and since nitrogen is a major part of the atmosphere, the car gives off little pollution. However, the cars may not reduce pollution as much as you think. While no pollution exits the car, the pollution may be shifted to another location. As with the e.Volution car, the LN2000 requires electricity to compress the air. That use of electricity means there is some amount of pollution produced somewhere else. Some of the leftover heat in the engine’s exhaust is cycled back through the engine to the economizer, which preheats the nitrogen before it enters the heat exchanger, increasing efficiency. Two fans at the rear of the vehicle draw in air through the heat exchanger to enhance the transfer of heat to the liquid nitrogen.

The Washington researchers have developed a crude prototype of their car, using a converted 1984 Grumman-Olson Kubvan mail truck. The truck has a radial five-cylinder that produces 15 horsepower with the liquid nitrogen fuel. It also features a five-speed manual transmission. Currently, the vehicle is able to go only about two miles (3.2 km) on a full tank of liquid nitrogen, and its top speed is only 22 mph (35.4 kph). However, because a liquid nitrogen-propelled car will be lighter, the researchers think that a 60-gallon (227 liters) tank will give the LN2000 a potential range of about 200 miles (321.8 km). With gas prices soaring, as they have over the past two years, it might not be long before many motorists turn to vehicles powered by alternative fuels. Although air-powered vehicles are still behind their gasoline counterparts when it comes to power and performance, they cost less to operate and are arguably more environmentally friendly, which makes them attractive as the future of highway transportation.

6. PRODUCTION LICENCE FOR MDI’S CAR

A production license for MDI’s (Moteur Development International) compressed-air vehicles has recently been signed in Nice, for markets in Colombia, Peru, Ecuador and Panama. The signatory, MDI Andina S.A is a group of business entities from the Columbian private and public sector.

After a thorough examination of the technical and financial aspects of MDI’s business, the new associates travelled to Spain to meet MDI’s existing licensees. Representatives of MDI Andina S.A. met official representatives of MDI management in Barcelona to negotiate the contract, and then travelled to France to sign the agreement.

With this additional sale there are now 50 fabrication and distribution licenses signed in the world, from a total of 400 available. Some of the countries that have signed agreement include France, Germany, Spain, Portugal, Italy, New Zealand, Israel, South Africa, etc.

As fees for production rights are the only source of financing for the inventor, Mr. Guy Nègre, this new contract, worth almost 10 million Euros, is another major step in bringing MDI’s Zero Pollution car closer to production.

The question that is most frequently asked is “When will these cars be on the streets?” Although a number dates have been released to the media in the past, the programme required some more time to complete. Developing and productionising automobiles is at best a complex, expensive and time-consuming exercise. Guy Negre and his team of dedicated engineers have effectively “reinvented the wheel” within the last 5 years and with the development and introduction of all of this groundbreaking and “new” technology, some delays were inevitable.

Starting factory production of cars that are based on a major technological advance is not easy, and has been made still harder by lack of external financing. So far, the institutions MDI has presented this project to were unprepared to invest in the initial phase of development, while showing great interest in doing so once a car was on the road. Delay in developing this technology has resulted largely from lack of public investment, which has compelled MDI to turn to private investors.

Despite this, the project has made considerable commercial and technological progress. The technology has been shown in London, with the support of the Department of the Environment, and in Sao Paulo, to an audience of over 600. Negotiations are now taking place with investors from all five continents. The first production plant in France is now complete and Guy Nègre’s latest model, the MultiCAT’s, applies the technology in a new direction: commercial and public service vehicles for public and freight transportation.

NEW MODELS, NEW APPLICATIONS:

The MiniCAT’s prototype is featured in the latest edition of the ‘Salon Mondial de l’Automobile Paris 2002′. This model is as ecologically sound as its predecessors and has equally low fuel consumption; one tank of air is enough for 200 km, at a cost of only 2 Euro. Like its “sister” vehicles, the MiniCAT’s emits only clean air at a temperature of -20ºC. A main innovation is that with 2.65 meters in length, and with a three seat configuration (the driver is in the center) the boot is as capacious as a conventional family saloon.

Guy Nègre has also designed a dual-energy vehicle for longer distances, which works on compressed air in the city, and air/petrol on motorways. This vehicle (the RoadCAT’s) can travel more than 2000 km on 100 m3 of air and 50 litres of petrol, so can be used for long journeys and is not an exclusively urban vehicle. Other applications of the technology include power generation, compressing air as a means of storing energy, and powering boats.

MDI also presented the MultiCAT’s concept of a zero pollution urban transportation system which incorporates several important economic advantages. Consisting of a Driver module and up to 4 transport modules, (as in a train with tyres) it has been developed with a view to transporting up to 135 people at a cost of only 2.5 Euros for each 100 km per module, which could allow local and/or national governments to offer practically free urban transport to its citizens. At the moment the sale of the first license to manufacture the MultiCAT’s for the Spanish and Portuguese market is in an advanced stage of negotiation with a group of investors consisting of the MDI license holders for Spain and other companies involved in the transport and energy sectors of those countries.

7. COMPARISON WITH COMPETITION

8. FREQUENTLY ASKED QUESTIONS

How does the air tanks work and are there any issues with their safety?

One of the most frequently asked questions regards the safety of the air tanks, which store 90m3 of air at 300 bars of pressure. Many people ask whether this system is dangerous in case of an accident, and whether there is an explosion risk involved. The answer is NO. Why? Because the tanks are the ones already used to carry liquefied gases on some urban buses, and therefore make use of the technology that is already used to move buses on natural gas. That means that the tanks are prepared and certified to carry an explosive product: methane gas.

In the case of an accident, with air tank breakage, there would be no explosion or shattering, now that the tanks are not metallic. Due to the fact that they are made of glass fibre the tanks would crack longitudinally, and the air would escape, causing a strong buzzing sound with no dangerous factor. It is clear that if this technology has been tested and prepared to carry an inflammable and explosive gas, it can also be used to carry air.

A final matter with reference to the air tanks is the improvement that MDI contributed to the original structure. In order to avoid the so-called ‘rocket effect’, this means to avoid the air escaping through one of the tank’s extremities causing a pressure leak that could move the car, MDI made a small but important change in the design. The valve on the buses’ tanks are placed on one of the extremities. MDI has placed the valve in the middle of the tank reducing the ‘rocket effect’ to a minimum.

It is said to have a 90m3 tank. That is impossible, for it would take up the space of four lorries. There must be a mistake. Yes, there is a mistake. The four tanks have a capacity of 90 litres, and they store 90m3 of air at a pressure of 300 bars.

You refer to an air tank at 200 pressure bars that can be recharged at home with a domestic compressor. With the ones I know about, not only is it impossible, but also it would be dangerous.
The pressure is of 300 bars, not 200. It is not referring to a conventional compressor to refill the tanks. The MDI car has a small compressor designed to fully refill the tanks in 3 to 4 hours.
Which materials are used to produce the body?

The car bodies of the MDI vehicles are made of glass fibre with injected foam, such as many other cars that are on the market nowadays. This technology brings in two main advantages: lower cost and less weight.
What is the weight capacity of the car?

It can carry 450kg of bulk weight, or 4 passengers and the driver.
Is the car noisy?

No, its sound is lower than a normal car’s, now that neither explosion nor combustion takes place in the engine.
What is its maximum range?

The range is dependent on the speed. At 50 km/p/h the range is over 300 km. At 100 kmh it is reduced to one third of that. In an urban environment the car can run for upto 10 hours.

What does the fuel cost?

Around $2 to fill up the air tanks.
How long does the refilling of the tanks take?

In an air-refilling station, it takes between 3 and 4 minutes. At home, with a 220V plug, it takes 3 and half hours.

How does the electrical system works?

Guy Negre, the inventor of the MDI engine, acquired the patent of an interesting invention for the electrical installation of the vehicle. It is a system based on the radio emission picked up by micro controllers installed in each one of the electrical devices of the car, which allows there to be one sole cable for the whole car. That is to say, that instead of using one cable for each device (lights, interior car lights, indicators, etc), it uses one cable for the whole car. The two obvious advantages are the simplicity of installation and repairs of the system, and the reduction of weight by 22kg.
What kind of filter is built in, and how does it work?

The MDI engine works with air taken from the atmosphere and pressurized air in the tanks. The air is compressed by the onboard compressor that is incorporated in each car or in an air-refilling station equipped with a high pressure compressor.

In order for the air to be pressurized, it must be filtered previously, to remove all possible impurities that could damage the compressor. Carboni type filters are used to remove dirt, dust and abundant abrasive particles that unfortunately exist in the air of our cities.

This factor is truly revolutionary in the automotive world, for the first time an engine produces negative contamination, in other words it eliminates and reduces already existent pollution rather than releasing dirt and burnt gases.

The exhaust pipe of the MDI vehicle expels clean air, that comes out fresh (between –30 ºC and 0ºC) and does not cause disruptions to any form of life. Thanks to this system, the air leaves the vehicle cleaner than it entered.

The engine does not take dirty air and miraculously restore purified air. It expels clean air, I guess with a small amount of oil, and it leaves a dirty filter. Yes. In the same way as major industries are forced to use filters in order to avoid polluting, the compressor filters the air, and later these are recycled and the filters decontaminated. There is no magic or miracles.
The exhaust gases are used to cool the car. But, how does the heating work?

The exhaust gases are not as we generally understand them to be as in the common vehicle. What leaves the vehicle is cool air. The heating works using the energy produced by the considerable temperature difference between the head of the piston at 400ºC and the cold air expelled between 0ºC and -30ºC. When a new vehicle is made, it is shown to the media and then to the ordinary citizens.

Although the engine does not expel contaminating gases, the electric energy needed to make the commediaor work has been produced (most probably) throughout some form of contamination.
You are right. But I doubt you have reached the end of the reasoning. The matter is briefly outlined: With regards to pollution: the MDI engine allows “two displacements and one optimization”.

• The first displacement is geographical: the car is urban, and with it we will stop polluting the city centres now that there is NO emission of contaminating gases. It is important to remember that 80% of car displacements are done in urban centres, where precisely the majority of the population lives.
• The second displacement is with regards to the responsibility of the pollution. The car runs on air, but this air is pressurized previously by a compressor that uses electricity. At the same time this electricity is produced by the State, thanks to hydraulic energy of rivers, thermic plants that burn petrol, nuclear energy, solar energy and wind energy. If the general citizen decides to use a car that does not expel any form of pollution, it is not in his/her responsibility to determine the source of the energy production. In each country the matter is different. In Spain, the majority of electricity is produced by burning petrol or nuclear sources. That is to say that most of the energy that the car uses is polluting, the rest is clean. In other countries, these figures are the opposite. On the other hand, MDI has patents to install systems of production of compressed air by using the currents of rivers. The cars that use this method will be 100% non-contaminating. In certain provinces, such as Navarra, electricity is nearly ‘clean’ of pollution, thanks to the use of wind power; the same occurs in areas where wind forms are present, like the Costa del Sol.
• The optimization that the engine brings is simple: it is much more polluting to burn a bit of petrol in each one of the cars in Spain than to produce this energy massively in industrial plants and use its power throughout compressed air. This system is an evident optimization now that it benefits the vehicle’s global energetic profitability.

Environmentally speaking, the restore of a gas to the atmosphere (even if it is air), at a very different temperature (between 0ºC and -30ºC) means an impact on the atmosphere.
Completely true in theory, but in practice it works the other way round: ALL human systems produce great amounts of heat that had not been previewed and that affect the planetary ecosystem since tens of years ago. Releasing small amounts of cool air does not assume any risks. What’s more: in order to compress the air some heat is released in the process…
When will the approval process be finalized?

Towards the end of the year 2002/early 2003.
When will the first cars produced?

In France the first car series are to be produced towards late December 2002 and the first cars will be used to assist float orders.
When will the first cars on the market?

Maybe in a simultaneous way around the same date as above. It all depends on the order of construction of factories throughout the world.
What is the average estimate price?

Between 8.000 and 10.000 $ for the basic vehicle: taxi, van, pick-up truck or “family car”.

The demand for making air traveling more ‘pleasant, secure and productive for passengers is one of the winning factors for airlines and aircraft industry. Current trends are towards high data rate communication services, in particular Internet applications. In an aeronautical scenario global coverage is essential for providing continuous service. Therefore satellite communication becomes indispensable, and together with the ever increasing data rate requirements of applications, aeronautical satellite communication meets an expansive market.

Wireless Cabin (IST -2001-37466) is looking into those radio access technologies to be transported via satellite to terrestrial backbones .  The project will provide UMTS services, W-LAN IEEE 802.11 b and Blue tooth to the cabin passengers. With the advent of new services a detailed investigation of the expected traffic is necessary in order to plan the needed capacities to fulfill the QoS demands. This paper will thus describe a methodology for the planning of such system.

In the future, airliners will provide a variety of entertainment and communications equipment to the passenger. Since people are becoming more and more used to their own communications equipment, such as mobile phones and laptops with Internet connection, either through a network interface card or dial-in access through modems, business travelers will soon be demanding wireless access to communication services.

2.WIRELESS CABIN ARCHITECTURE

So far, GSM telephony is prohibited in commercial aircraft due to the uncertain certification situation and the expected high interference levels of the TDMA technology. With the advent of spread spectrum systems such as UMTS and W-LAN, and low power pico-cell access such as Blue tooth this situation is likely to change, especially if new aircraft avionics technologies are considered, or if the communications technologies are in line with aircraft development as today

When wireless access technologies in aircraft cabins are envisaged for passenger service, the most important standards for future use are considered to be: UMTS with UTRAN air interface, Blue tooth, and W-LAN IEEE 802.11 b. Of course, these access technologies will co-exist with each other, beside conventional IP fixed wired networks. The wireless access solution is compatible with other kinds of IFE, such as live TV on board or provision of Internet access with dedicated installed hardware in the cabin seats. Hence, it should not be seen as an alternative to wired architecture in an aircraft, but as a complementary service for the passengers.

The Wireless Cabin architecture and its components are conceptually depicted in figure 1.

Figure 1.wireless cabin architecture

Several wireless access segments in the aircraft cabin, namely a wireless LAN according to IEEE 802.11 b standard for IP services, an UMTS pico-cell for personal and data communications, and Bluetooth1.1, as well as a standard wired IP LAN.

A satellite segment for interconnection of the cabin with the terrestrial telecom networks. The different cabin services must be integrated and interconnected using a service integrator, that allows the separation and transportation of the services over a single or several satellite bearers. Peculiarities, such as limited bandwidth, asymmetric data rates on satellite up- and down-link, and dynamic traffic demand between the different services and handover between satellite bearers need to be addressed. In order to minimize the cost (satellite resources) for a given QoS efficient interworking between the service integrator and the satellite segment will be required.

An aircom service provider segment supporting the integrated cabin services. The aircom provider segment provides the interconnection to the terrestrial personal and data networks as well as the Internet backbone. For the UMTS cabin service, a subset of the UMTS core network must be available.

The provision of such a heterogeneous access network with collectively mobile users requires the development of new protocol concepts to support

• The integrated services with dynamic bandwidth sharing among the services and asymmetrical data rate;
• IP mobility and virtual private networks (VPN) for the individual passengers in the mobile network; authentication, admission and accounting (AAA) in the mobile network, especially taking into account the necessity to support different pricing concepts for each passenger in the mobile network and the interaction of airline, satellite provider, aircom service provider and terrestrial service providers.

3. SATELLITE CONNECTION

Connection to telecom networks is considered to  be achieved by satellites with large coverage areas especially over oceanic regions during long-haul flights. The service concept needs to take into account today’s peculiarities of satellite communications, thus it must cope with the available or in near future available satellite technology, and interworking must be performed at aircraft interface level with the satellite segment,

• Only restricted satellite data rates will be available in the near future; thus the bandwidth that is requested by standard interfaces of the wireless standards needs to be adapted to the available bandwidth (typically: 432 kb/s in down- link, 144 kb/s up-link (Inmarsat B- GANTM), or 5 Mb/s in down-link, 1.5 Mb/s in up-link (Connexion by Boeing)). Furthermore, dynamic bandwidth management is needed to allocate higher bit rates from temporarily unused services to other service-
• Currently, few geostationary satellites such as the Inmarsat fleet are available for two-way communications, that cover the land masses and the oceans. Ku-band may be used on a secondary allocation basis for aeronautical mobile satellite services (AMSS) but bandwidth is scarce and coverage is mostly provided over continents. K/Ka-band satellites will be launched in the near future, again here continental coverage is mainly intended. The scenario must thus consider

§   the use of different satellite systems, which will probably force the support of different service bearers, and

§   handover between satellite systems.

It is assumed that each satellite segment is connected via terrestrial wide area networks or via the IP backbone to the aircom service provider.

• Asymmetrical data rates in satellite up- and down-links, that may also be caused to operate in conjunction with different satellites systems for up- and down-link. The service portfolio in the cabin and the service integration needs to cope with this possibility.

4. TECHNICAL OVERVIEW

A. UMTS

The Universal Mobile Telecommunication System (UMTS)  is the third generation mobile communications system being developed within the IMT -2000 framework. UMTS will build on and extend the capability of today’s mobile technologies (like digital cellular and cordless) by providing increased capacity, data capability and a far greater range of services.

In January 1998, ETSI reached an agreement concerning the radio access technique to be used for UMTS. This air interface, named UTRAN (UMTS Terrestrial Radio Access) is applicable in the two existent duplexing schemes for UMTS: UMTS-FDD and UMTS- TTD. UMTS-FDD relies on wideband-CDMA (W-CDMA) access technique, while UMTS- TTD uses the TD-CDMA access technique, a combination of CDMA and TDMA technologies.

a) Umts   Structure

B. BLUETOOTH

Bluetooth operates in the unlicensed 2.4–GHz ISM (industrial, scientific and medical) band and uses a frequency- hopping spread spectrum (FHSS) technique to minimise interference. A Bluetooth unit has a nominal range of approximately 10 meters (in the Class 3 defined in the standard, but which can be enlarged by amplifying the transmit power in Class 2 and Class 1 up to 100 m.). Two or more Bluetooth units sharing the same channel form a piconet. Each piconet consists of a master unit and up to seven active slave units. Furthermore, two or more piconets can be interconnected to form a scattemet. To be a part of more than one piconet a unit called inter-piconet unit (gateway) is required.

c. IEEE802.11b

Wireless local area networking (WLAN) radio technology provides superior bandwidth compared to any cellular technology. The IEEE 802.11 b standard offers a maximum throughput of II Mbps (typical 6.5 Mbps) working in the same 2.4- GHz ISM band as B1uetooth by the use of direct sequence spread spectrum (DSSS). WLANs were originally intended to allow local area network (LAN) connections where premises wiring systems were inadequate to support conventional wired LANs, but they were later identified with mobility.

A WLAN cell is formed by an AP and an undefined number of users in a range from approximately 20 to more than 300 m ( 100 m. in indoor environments) that access the AP through network adapters (NAs ), which are available as a PC card that is installed in a mobile computer.

Table 1 summarizes the main parameters of each standard, where only Class 3 of the Bluetooth standard has been considered, as long as the Bluetooth version 1.0 specification focuses primarily on the 10- meter ranger standard radio. Notice that the coverage range in the UMTS case is capacity dependent and it can vary from 200 m. up to 1.4 Km., a phenomena known as “cell breathing”.

	Bit rates		Bw.(MHz)	Band(GHz)	Coverage Range(m.)	Duplexing Scheme	Tx.P. (dBm)	Modulation
	Max	Typ
UMTS	2Mbps	144Kbps	5,10,20	FDD: 1.92-1.90(ul) 2.11-2.17(dl) TDD: 1.90-1.92 2.01-2.025	Depends on capacity	FDD/TDD	20	QPSK(dL) BPSK (uL)
Bluetooth	1Mbps	728 Kbps	1	2.4-2.4835	10	TDD	0	GFSK
IEEE 802.11b	11Mbps	6,5Mbps	26	2.4-2.4835	20-100	TDD	20	Depends on bit rate

5. SERVICE INTEGRATOR

The different wireless access services of UMTS, W-LAN and Bluetooth require an integration of the services over the satellite. The central part of the service portfolio provisioning is the service integrator (SI), cf. Figure 3. The service integrator will provide the interfaces for the wireless and wired service access points in the cabin, as well as the interface to the terrestrial networks at aircom provider site. All services will be bundled and transported between a pair of Service Integrators. It performs the encapsulation of the services and the adaptation of the protocols.

The SI multiplexer is envisaged to assign variable capacities to the streams, controlled by a bandwidth manager that monitors also the QoS requirements of the different service connections. Changes in capacity assignment must be signaled to the SI at the other communication end. The heterogeneous traffic stream is then sent to streaming splitter/combiner. This unit is envisaged to support several satellite segments and to perform handover between them. Asymmetrical data rates in inbound and outbound directions can be managed here. Adaptation to the supported satellite segments are done by medium access controllers (MAC) in a modular manner. Towards the terminal side, the interfaces of the wireless access standards need to interwork with the transport streaming of the SI by specific adaptation layers (AL). These ALs have to be designed according to the analysis of the impact of delay, jitter and restricted / variable bandwidth on the protocol stack. Buffering (to compensate delay jumps at handover) and jitter compensation for real-time services (e.g., voice) must be also provided here.

6. SERVICE DIMENSIONING

This section provides an overview of key issues and steps for the systematic system dimensioning of Wireless Cabin aircom satellite communications system.   We will tackle the satellite constellations as potential candidates for aircom services as well as the gross traffic calculation and assignment process.

Different market entry options and reference business cases must be taken into account in an initial stage of a system design.   The evolutionary path leads from existing L-band systems such as inmarsat GAN (see Figure 5) or
B-Gan in few years up to C/Ku band and existing GEO transponders, whereas the “revolutionary” path may target from the beginning at advanced K/Ka band technology and the design of a tailor-made, potentially non-GEO system.

The system dimensioning process can be structured in several steps:

• Determination of gross traffic per aircraft using the multi-service model
• Determination of the timely and locally varying traffic, depending on the flight path and flight schedule, assuming also a service rool-out scenario for different airlines and aircraft types.
• Identification of potential serving satellites and their coverage areas.
• Mapping and traffic allocation of the aircom traffic to the satellite systems.

Two key observations concerning the “geographic market” are 1) the pronounced asymmetry of market opportunities between northern and southern hemisphere (partly just a result of our earth’s “continental layout”), and the fact  that a significant  share of the addressable market is at higher (northern ) latitudes, especially with the important long-haul intercontinental flight routes between the European, North American and East Asian regions.   Both observations are illustrated in figure 6, although its view is Europe-centric; the underlying flight route investigations have been performed within the European ACTS project ABATE and have been used for design and dimensioning studies of an aeronautical subsystem of the EuroSkyWay satellite communications system

7. INTERFERENCE

Once the above described measurements finish. four types of interferences within the CMHN have to be studied: the co-channel interference among the terminals of the same wireless access segment, the inter- segment interference between terminals of different wireless networks, the cumulative interference of all simultaneous active terminals with the aircraft avionics equipment and the interference of the CMHN into terrestrial networks.

From the co-channel interference analysis the re-use distance and the re-use frequency factor for in-cabin topology planning will be derived. For this reason it is important to consider different AP locations during the measurements.

It is not expected to have major problems due to interference from UMfS towards WLAN and Bluetooth, thanks to the different working frequency. On the other hand, particular interest has to be paid in the interference between Bluetooth and WLAN .Due to the market acceptance of Bluetooth and WLAN, there is a special interest of designers and portable data devices manufacturers to improve the coexistence of the two standards. There are many studies showing the robustness and the reliability of Bluetooth in presence of WLAN and vice versa.

A description of the electromagnetic behaviour of conventional aircraft equipment is necessary to analyse the interference and the EMC of the new wireless network with the avionics systems. The allowed radiated field levels are regulated and must be respected if certification is desired. So far, GSM telephony is prohibited in commercial aircraft due to the uncertain certification situation and the expected high interference levels of the TDMA technology. With the advent of spread spectrum systems such as

8. COLLECTIVELY MOBILE

HETEROGENEOUS NETWORK

The concept of having several users, which are collectively on the move forming a group with different access standards into this group, is called Collectively Mobile Heterogeneous Network (CMHN). In such a scenario [5] one can find two types of mobility and two types of heterogeneity: the mobile group itself and the user mobility inside the group from one side, and heterogeneous access segments and heterogeneous user access standards from the other side. The aircraft cabin represents a CMHN (see Fig. 1) supporting three types of wireless (user mobility) access standards (heterogeneous user access) inside an aircraft (the mobile group) using one or more satellite access segments. The CMHN may cross coverage areas and then inter-/ intra- satellite handover will be required.

The communication infrastructure to support the cabin CMHN is depicted in Fig 2. The architecture consists of (i) several wireless access segments in the aircraft cabin which can coexist with the standard wired IP LAN, (ii) a satellite segment for interconnection of the cabin with the terrestrial telecom networks, and (iii) an aircom service provider segment supporting the integrated cabin services.

9.CONCLUSION

Go meet the increasing and ever changing needs of the most demanding passengers a solution in which passengers, both business and economy, could use their own wireless equipment must be developed. This approach has many advantages. From the users point of view, their service acceptance will be increased by the following facts: they can be reached under their usual telephone number, they may have available telephone numbers or other data stored in their cell phones or PDAs, their laptops have the software they are used to, the documents they need and with their personalized configuration (starting web site, bookmarks, address book). In addition, since users in an aircraft are passengers, the electronic devices they carry with them is wireless, like laptops with WLAN interface. From the airlines point of view there is a huge saving of the investment that would suppose the installation of terminals (screens, stations, wired telephones), the consequent software licenses (in case of PCs) and the further investment due to hardware updating to offer always last technology to their customers. Currently, one of the major IFE costs is due to film copies and delivery expenses of new movies. This could be reduced if other broadband services were offered to passengers via satellite. Anyway, the wireless access solution is not replacing other kinds of IFE, such as TV on board or provision of Internet access with dedicated installed hardware in the cabin seats. Hence, it should not be seen as an alternative to a wired architecture in aircraft, but as an added service for passengers.