Ultra Wide Band communication system

Ultra Wide Band (UWB) is a revolutionary technology with incomparable potential in terms of throughput, performance and low cost implementation. The uniqueness of UWB is that it transmits across extremely wide bandwidth of several GHz, around a low center frequency, at very low power levels.UWB is fundamentally different from existing radio frequency technology. For radios today, picture a guy watering his lawn with a garden hose and moving the hose up and down in a smooth vertical motion. You can see a continuous stream of water in an undulating wave. Nearly all radios, cell phones, wireless LANs and so on are like that: a continuous signal that's overlaid with information by using one of several modulation techniques.

Now picture the same guy watering his lawn with a swiveling sprinkler that shoots many, fast, short pulses of water. That's typically what UWB is like: millions of very short, very fast, precisely timed bursts or pulses of energy, measured in nanoseconds and covering a very wide area. By varying the pulse timing according to a complex code, a pulse can represent either a zero or a one: the basis of digital communications.

UWB is almost two decades old, but is used mainly in limited radar or position-location devices. Only recently has UWB been applied to business communications. It's a different type of transmission that will lead to low-power, high-bandwidth and relatively simple radios for local- and personal-area network interface cards and access points. At higher power levels in the future, UWB systems could span several miles or more.

Wireless technologies such as 802.11b and short-range Bluetooth radios eventually could be replaced by UWB products that would have a throughput capacity 1,000 times greater than 802.11b (11M bit/sec). Those numbers mean UWB systems have the potential to support many more users, at much higher speeds and lower costs, than current wireless LAN systems. Current UWB devices can transmit data up to 100Mbps, compared to the 1Mbps of Blue-tooth and the 11Mbps of 802.11b. Best of all, it costs a fraction of current technologies such as Blue-tooth, WLANs and Wi-Fi.

UWB

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HISTORY OF UWB

Ultra wide band communication is not anew technology, infect it was first employed by Guglielmo Marconi in 1901 to transmit Morse Code sequences across the Atlantic ocean using spark gap radio transmitters.

However the benefit of a large bandwidth & capability of implementing Multi-user system provided by electromagnetic pulses were never Considered of that time.Approximately fifty year after Marconi, modern pulse based transmission Gained momentum in military applications in the form of impulse radar. Some of the pioneers of modern UWB communication in the united state from the late 1960s are Henning Harmuth of catholic university of America & Sperry Rand Corporation. From the 1960s to the 1990s this Technology was restricted to military & Department of Defense (DOD) Applications under he classified programs such as highly secure Communications. However the recent advancement in micro processing & fast switching in semiconductor technology has made UWB ready for Commercial applications, therefore it is more appropriate to consider UWB As a new name for a long existing technology. As interest in commercialization of UWB has increased over the past several Years, developers of UWB system began pressuring the FCC to approve UWB for commercial use. In February 2002 the FCC approved the first Report & order (R&O) for commercial use of UWB technology under strict Power emission limits for various devices. & worldwide regulation of UWB Technology.

Federal Communication Commission (FCC):FCC opened spectrum from 3.1GHz –10.6GHz, Handheld emission mask 41.3dBm/MHz& Minimum channel bandwidth 500MHz.FCC’s UWB definition

Instantaneous bandwidth ≥ 500 MHz Fractional bandwidth ≥ 20%

Power spectral density limits in the current FCC NPRAM

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Summarizes the development time of UWB as:

2002 FCC report & order for part 15 acceptance of UWB systems

1998 FCC notice for inquiry for part 15 usage of UWB systems

1994 First unclassified communication system for UWB

1989 US department of defense applied the term “ULTRA WIDEBAND”

1965 G. ROSS- Seperry research development of UWB technology

1963 G. ROSS- Ph.D. Thesis on time domain electromagnetism

1962 HP developed the sampling oscilloscope measured impulse response Of the microwave network

1940s Impulse radio system patents were field & frozen

1924 Spark gap radio was forbidden

1910 Ernst. F.W.Alexanderson introduced continuous RF waves

1887 Henrich Hertz Spark discharges to generate EM waves.

UWB communication proposals:

•Time Hopped UWB (probably IEEE802.15.4a)–First proposals–Old concept (radar)–Impulse Radio (IR-UWB)–Low/moderate data rate•DS-CDMA UWB (IEEE802.15.3a)–High data rate–UWB Forum supporting DS-UWB•Multi-Band OFDM UWB (IEEE802.15.3a, ECMA-368)

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PRINCIPLE OF UWB

This concept doesn't stand for a definite standard of wireless communication. This is a method of modulation and data transmission which can entirely change the wireless picture in the near future. The diagram given below demonstrates the basic principle of the UWB:

The UWB is above and the traditional modulation is below which is called here Narrow Band (NB), as opposed to the Ultra Wideband. On the left we can see a signal on the time axis and on the right there is its frequency spectrum, i.e. energy distribution in the frequency band. The most modern standards of data transmission are NB standards - all of them work within a quite narrow frequency band allowing for just small deviations from the base (or carrier) frequency. Below on the right you can see a spectral energy distribution of a typical 802.11b transmitter. It has a very narrow (80 MHz for one channel) dedicated spectral band with the reference frequency of 2.4 GHz. Within this narrow band the transmitter emits a considerable amount of energy necessary for the following reliable reception within the designed range of distance (100 m for the 802.11b). The range is strictly defined by FCC and other regulatory bodies and

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Requires licensing. Data are encoded and transferred using the method of frequency modulation (control of deviation from the base frequency) within the described channel.

Now take a look at the UWB - here the traditional approach is turned upside down. In the time space the transmitter emits short pulses of a special form which distributes all the energy of the pulse within the given, quite wide, spectral range (approximately from 3 GHz to 10 GHz). Data, in their turn, are encoded with polarity and mutual positions of pulses. With much total power delivered into the air and, therefore, a long distance of the reliable reception, the UWB signal doesn't exceed an extremely low value (much lower than that of the NB signals) in each given spectrum point (i.e. in each definite licensed frequency band). As a result, according to the respective FCC regulation, such signal becomes allowable although it also takes spectral parts used for other purposes:

So, the most part of energy of the UWB signal falls into the frequency range from 3.1 to 10.6 GHz. below 3.1 GHz the signal almost disappears. The more ideal the form of a pulse formed with the transmitter, the less the energy goes out of the main range. The spectral range lower than 3.1 GHz is avoided not to create problems for GPS systems. However, UWB is accurate to within 10 centimeters -- much better than the Global Positioning System satellites and because it spans the entire frequency spectrum (licensed and unlicensed), it can be used indoors and underground, unlike GPS. UWB could replace communications of all types, ending forever our dependence on wires and making worthless theOwnership of radio frequencies.

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The total energy of the transmitter which can fit into this band is defined by the area of the spectral characteristic (see filled zones on the previous picture). In case of the UWB it's much greater compared to the traditional NB signals such as 802.11b or 802.11a. So, with the UWB we can send data for longer distances, or send more data, especially if there are a lot of simultaneously working devices located close to each other. Here is a diagram with the designed maximum density of data transferred per square meter:

Density of transferred data able to coexist on the same square meter is much higher for the UWB compared to the popular NB standards. That is, it will be possible to use the UWB for the intersystem communication or even for an interchip communication within one device! In case of the NB a frequency and width of the dedicated spectral range for the most part (though the real situation is much more complicated) defines a bandwidth of the channel, and the transmitter's power defines a distance range. But in the UWB these two concepts intertwine and we can distribute our capabilities between the distance ranges and bandwidth. Thus, at small distances, for example, in case of an inter chip communication, we can get huge throughput levels without increasing the total transferred power and without cluttering up the air, i.e. other devices are not impeded. Look at how the throughput of data transferred in the UWB modulation depends on distance:

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While the traditional NB standard 802.11a uses an artificially created dependence of throughput on distance (a fixed set of bandwidths discretely switched over as the distance increases), the UWB realizes this dependence in a much more natural way. At short distances its throughput is so great that it makes our dreams on the inter chip communication real, but at the longer distances the UWB loses to the NB standard. On the one hand, a theoretical volume of the energy transferred, and therefore, the maximum amount of data, is higher. On the other hand, we must remember that in a real life information is always transferred in large excess. Beside the amount of energy, there is the design philosophy which also has an effect. For example, a character of modulation, i.e. how stably and listlessly it is received and detected by the receiver. Let's compare the classical:

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USB TRANSCEIVERS:

The classical transceiver contains a reference oscillator (synth) which, as a rule, is stabilized with some reference crystal element (Ref Osc). Further, in case of reception this frequency is subtracted from the received signal, and in case of transmission it is added to the data transferred. For the UWB the transmitter looks much unsophisticated – we just form a pulse of a required shape and send it to the antenna. In case of reception we amplify the signal, pump it through the band filter which selects our working spectrum range and... That’s all - here is our ready pulse.

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COMPARISION WITH WIRELESS TECHNOLOGIES

A comparison table of the characteristics:

Range Versus Data Rate:

Distance Frequency Channel Throughput

UWB

Up to 50 (atPresent) 3.1 to 10.6

GHz The sameHundreds of

Mbit

802.11b 100 2.4 GHz 80 MHz Up to 11 Mbit

802.11a 50 5 GHz 200 MHz Up to 54 Mbit

Bluetooth 10 2.4 GHz Up to 1 Mbit

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REGULATIONS & STANDARDS

A major landmark in the development of UWB has been the publication in early 2002 of the Federal Communication Commission (FCC) Order and Report deregulating the use of UWB systems in the USA. The FCC has defined a UWB system as having bandwidths greater than 20% of the centre frequency, measured at points 10 dB down from the peak level, or RF bandwidths greater than 500 MHz, whichever is smaller. There are a number of key points to the related emission regulations (US 47 CFR Part 15(f)). Firstly, to avoid inadvertent jamming of existing systems such as GPS satellite signals, the lowest band edge for UWB for communication purposes is set at 3.1GHz, with the highest frequencies 10.6GHz. Within this operational band, emission must be below –43 dBm/MHz EIRP- a limit the FCC has stated to be conservative. Importantly, the FCC deregulation does not specify nor imply any particular implementation technology. There are currently at least five identifiable UWB technologies that have been designed to comply with the FCC legal limits (as indicated in the previous section). Each has is proponents and detractors, each has its own technical benefits and restrictions and none are mutually compatible! It should also be noted that the FCC has deregulated UWB technology for other applications as well as communications- for example various types of imaging and vehicular applications. The defined allowable spectrum is different for different applications. While this deregulation has obviously had a major impact on the USA’s development of UWB, other countries are also progressing the regulatory framework. Of particular note is Singapore, which has established an aggressive schedule for deregulation. Experimental licenses have been granted for UWB with an EIRP limit 6dB higher than the FCC specification. These will be assessed before the final deregulation standard is formalised. Japan has granted experimental licenses for the demonstration of UWB with deregulation stated for a 2004/5 timeframe. The ITU is preparing reports in a similar timeframe. The legal situation in Europe has generally yet to be clarified. There is, however, very substantial activity. Of considerable

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concern has been the system co-existence issue of potentially a large number of UWB users operating with existing licensed spectrum users. It may be that the European deregulation will modify the spectral mask of UWB around fixed link operational frequencies (approximately 3 to 5 GHz ) with a 20dB reduction over the FCC mask in these areas. With this as a background, UWB has generated an enormous interest within various standard forums. A UWB physical layer is under development within the IEEE 802 LAN/WAN forum, group 3a of IEEE P802.15 where UWB has been considered for an alternative radio physical layer for the emerging Wireless Personal Area Network (W-PAN ) standard. This is seen as a key standard and has been the subject of much controversy over competing technology such that, at the time of writing this standard has not yet been decided. Competing alternative technologies are very different. Each technology can provide the targets data rates of at least 110 Mbps to 480 Mbps over a personal area network distance from to 2 to 10 m. Which ever standard is eventually adopted, UWB systems can significantly out-perform competing wireless communications systems operating in license-free spectrum by virtue of the large available bandwidth despite the significantly lower EIRP levels. They also have unique and interesting propagation characteristics. UWB systems can also provide opportunity for distance and position finding information. As such these are likely to be considered as possible physical layer definition by the IEEE 802.15.4 a group. This is also under consideration, with longer range (up to 100m) applications in mind, and includes wireless sensor networks with high power efficiency requirements.

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INNER WORKINGS

UWB uses a kind of pulse modulation. To transfer data, a UWB transmitter emits a single sine wave pulse (called a monocycle) at a time. This monocycle has no data in it. On the contrary, it is the timing between monocycles (the interval between pulses) that determines whether data transmitted is a 0 or a 1. A UWB pulse typically ranges between .2 and 1.5 nanoseconds. If a monocycle is sent early (by 100 Pico seconds), it can denote a 0, while a monocycle sent late (by 100 Pico seconds) can representa 1.Spacing between monocycles changes between 25 to 1000 nanoseconds on a pulse-to-pulse basis, based on a channel code. A channel code allows data to be detected only by the intended receiver. Since pulses are spaced and timing between pulses depends on the channel, it’s already in encrypted form and is more secure than conventional radio waves.

Modulation Methods:

Several modulation techniques can be used to create UWB signals, some more efficiently than others. In its formative years, some of the most popular methods to create UWB pulse streams used mono-phase techniques such as pulse amplitude (PAM), pulse position (PPM), or on-off keying (OOK). In these techniques, a ‘1’ is differentiated from a ‘0’ either by the size of the signal or when it arrives in time – but all the pulses is the same shape. A more efficient approach, bi-phase ultra-wideband, is also being deployed. Bi-phase differentiates a ‘1’ with a ‘right-side-up’ pulse and a ‘0’ with an ‘upside-down’ pulse and works by reading pulses both “backwards” and “forwards,” irrespective of time. Multi-phase UWB is not being deployed today as it is too cost-prohibitive for the consumer and enterprise markets.

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Mono-phase Ultra-wideband:

In this approach, all pulses are right side up, meaning they all look alike. Using pulses in time to create the desired ultra-wideband waveform, mono-phase ultra-wideband technologies are currently used in select military applications under a special license from the FCC. All of these deployed systems are much higher in power and much lower in frequency than the limits published by the FCC in their recent UWB approval guidelines.

The three most popular mono-phase ultra-wideband approaches include:

1. Pulse amplitude (PAM)—PAM works by separating the “tall” and the “short” waves. By varying the amplitude (height of pulse) the receiver can tell the difference between “1” and “0,” thereby encoding data in the signal.

2. Pulse position (PPM)—In PPM, all the pulses (both “1”s and “0”s) are the same height. The receiver distinguishes between a “1” or a “0” by when it arrives in time, or the time lag between pulses. In this case, a long time lag could mean a “1” and a short time lag could mean a “0”.

3. On-Off Keying (OOK)—In OOK, a “1” is a pulse and an absence of a pulse is a “0.”

Bi-phase Ultra-wideband:

In this approach, the pulses can be sent right side up or upside down, which determines whether the pulse is a “1” or a “0”, so pulses can be sent at a much higher rate.

PULSE POSITION MODULATION (PPM)

Encodes information by modifying the position of the pulse

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PULSE AMPLITUDE MODULATON (PAM)

Determines whether a pulse is a ‘1’ or ‘0’ based on the size of the pulse.

ON-OFF KEYING

Determines a ‘0’ by the absence of a pulse and ‘1’ by the presence of a pulse

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BI-PHASE

Reads forward and backward pulses as either ‘0’or ‘1’

WHY UWB IS EFFECTIVE?

Shanon Hartely channel capacity theorem:It may be shown that in a channel which is disturbed by a white Gaussian noise, one can transmit information at a rate of C bits per second, where C is a channel capacity & is expressed as

C =B log2 (1+S/N) = B log2 (1+S/NoB)

Where:C = Max Channel Capacity (bits/sec)B = Channel Bandwidth (Hz)

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S = Signal Power (watts)N = Noise Power (watts)C grows linearly with B, but only logarithmically with S/N. Since B isVery high C also becomes very high.

Few points have given for effectiveness of UWB according to the above theorem Level Below thermal noise floor of input circuitry.

APPLICATION

Ultra Wideband (UWB) devices can be used for precise measurement of distances

or locations and for obtaining the images of objects buried under ground or behind surfaces. UWB devices can also be used for wireless communications, particularly for short-range high-speed data transmissions suitable for broadband access to the Internet.

Communication Applications:UWB devices can be used for a variety of communications applications involving the transmission of very high data rates over short distances without suffering the effects of multi-path interference. UWB communication devices could be used to wirelessly distribute services such as phone, cable, and computer networking throughout a building or home.

Positioning Applications:

Capacity C increases linearly with bandwidth; logarithmically withSignal to noise ratio (S/N) .

To increase throughputs: having a larger bandwidth available allowFor significantly lower RF transmit power.

Spread Spectrum : transmitting signal bandwidth larger than theRequired bandwidth B in (1) allows receivers to receive input signal

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UWB devices can be used to measure both distance and position. UWB positioning systems could provide real time indoor and outdoor precision tracking for many applications. Some potential uses include locator beacons for emergency services and mobile inventory, personnel and asset tracking for increased safety and security, and precision navigation capabilities for vehicles and industrial and agricultural equipment.

Radar Applications:

1. Disaster rescue: UWB technology has been used for some time in Ground Penetrating Radar (GPR) applications and is now being developed for new types of imaging systems that would enable police, fire and rescue personnel to locate persons hidden behind a wall or under debris in crises or rescue situations. By bouncing UWB pulses, rescuers can detect people through rubble, earth or even walls using equipment similar to radar. Construction and mineral exploration industries may also benefit.

2. Radars: The US military has already been using this technology for military radars and tracking systems for the last 15 years.

3. Collision avoidance: UWB technology can make intelligent auto-pilots in automobiles and other crafts a reality one day.

4. Construction safety: UWB imaging devices also could be used to improve the safety of the construction and home repair industries by locating steel reinforcement bars (i.e., re-bar) in concrete, or wall studs, electrical wiring and pipes hidden inside walls.

5. Automotive safety: UWB devices could improve automotive safety with collision avoidance systems and air bag proximity measurement for safe deployment

6. Medical Application: Potential medical uses include the development of a mattress-installed breathing monitor to guard against Sudden Infant Death Syndrome and heart monitors that measure the heart's actual contractions.

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7. Home safety: Some potential home safety uses include intrusion detection systems that are less susceptible to false alarms, and space heaters that turn themselves off when a child comes nearby.

ADVANTAGES

• Capacity Possibility of achieving high throughput, robustness to co-channel interferenceAnd narrowband jammers, and greater spectrum sharing

• Low Power and Low Cost Can directly modulate a baseband pulse & no need for mixers or PA. High capacity can be achieved with much lower Tx power levels Promising for mobile applications (low cost/low battery usage).

• Fading robustness Wideband nature of the signal reduces time varying amplitude fluctuations(Fading). This reduces fade margin in link budgets.

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• Position location capability Short impulse (wideband signal) allows for accurate delay estimates, which canBe used for accurate position location.

• Flexibility Can easily and dynamically trade-off throughput for distance, making theTechnology compatible for a large number of applications.

• ChallengesReceiver complexity (RAKE combining, synchronization, narrowband jammers) multiple access and modulation schemes to take advantage of capacity

•High processing gain UWB technology’s very wide bandwidth property offers the advantage of potentially high processing gain (cited in reference 2 and elsewhere) that can be applied to low-power, stealthy communications.

Apart from low-power usage, inherent security and minimal noise generation, UWB doesn’t suffer from multi-path interference (where signals reach the receiver after traveling through two or more paths). Something similar happens when your car is at an intersection surrounded by tall buildings. Your radio might not give a clear reception as it’s receiving both direct signals and those that have bounced off the buildings. Often, the static disappears when you move ahead or backwards. Hence, it can be used in densely built-up places, or where numbers of users are more than what is supported by Wi-Fi, Blue-tooth etc.

DISADVANTAGES

UWB technology’s carrierless transmission property has the disadvantage of not supporting super-resolution beam forming .although with UWB pulsed systems there is no carrier and therefore no carrier phase for fine resolution in terms of phase coherency, there is certainly the potential at least for the baseband equivalent of coherency using pulse sequences .

UWB technology’s very short pulse width property has the disadvantage of producing a very large number of multipath components.

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UWB technology’s very short pulse width property has the disadvantage that pulse coding of signals involves relatively long synchronization times.

UWB technology’s multipath persistence property has the disadvantage that there is a significant scatter in the angle of arrival.

UWB technology’s very wide bandwidth property has the disadvantage of causing interference to existing systems and of being subject to interference from existing systems.

The technology too is at an early stage of development and standardization isis incomplete.

UWB is not a long range system for data transmission at higher rate.

KEY ISSUES FOR UWB

UWB technology is attracting as an ultra fast interface for digital appliances. A number of technical issues involved in getting UWB up and running in homes and offices have been uncovered.They can be broken down into five groups namely

1. Reducing interference with other radio systems,2. Complying with electromagnetic regulations of many nations,3. Minimizing erroneous transmissions caused by reflections from walls and Objects (multi-path),and4. Assuring continuous communication between multiple pieces of Equipment (multi-access),

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5. Reducing implementation cost of UWB radio circuitry.6. All of these issues will be vital to the success of UWB.

GOVERNMENT & INDUSTRY INTEREST

The government and commercial industry are expressing great interest in UWB technology. For example, two main UWB applications of interest are the transmission of large amounts of voice and data at very high speeds requiring very little power, and radars capable of penetrating walls and providing detailed views from “behind” the wall. In addition, the ability to define thePrecise location of hidden objects to within1 inch is of interest to military, lawEnforcement, and rescue agencies. In response, the FCC approved limited productions of UWB radars for police and rescue workers.With these new applications, the wireless industry is interested in UWB technologies potential to—

End spectrum congestion: The wireless industry is currently experiencing limited spectrum availability. To compound this Problem, the wireless industry is seeking room in the already congested spectrum to introduce next-generation services. Competition is high for the limited available spectrum, as is the cost for licensing. Users of UWB devices operating in a single channel do not need a license.

Eliminate interference from signals reflecting off buildings or walls and congested cell sites:According to one estimate, with this technology in place, more than 20,000 people can use UWB cell phones in the same square block without interference. UWB devices would be virtually immune to interference because UWB signals can penetrate walls and other obstructions, eliminating a major source of multipath interference.

Provide secure transmissions:UWB devices transmit millions of coded pulses per second at emissions below the noise floor and across an ultra wide bandwidth using receiver/transmitter pairsCommunicating with a unique timing code. These transmissions have a very low radio frequency signature, providing intrinsically secure transmissions with lowProbability of detection and low probability of interception.

Reduce power consumption:

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Dramatically. One vendor, Time Domain, has developed a chip that consumes only 0.05 milliwatts of power compared with the hundreds of milliwatts used by today’s cellphones. This reduced power consumption leads to longer battery life.

CONCLUSION

Ultra wide band has the potential to become a viable and competitive technology for short-range high-rate WPANs as well as lower rate and low-power consuming low-cost devices and networks with the capability to support a truly a pervasive user-centric and thus personal wireless world.UWB is undoubtedly a niche technology which holds promise in a wide area. But, its success depends on scoring against a handful of rival technologies in which companies have invested billions. Those who’ve invested their money will not hasten to consider an upstart rival, even if it offers better services. Now, visualize what happens when you heave a large rock into a small pond. It splashes out the water in one go (as seen with our naked eyes). If captured as a still photo, we’ll see the millions of water droplets that splash out in a fraction of a second and make the

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splash we see. If ripples are like normal transmission of data between wireless devices (as in blue-tooth or Wi-Fi), UWB promises to be the ‘huge rock’ in dataTransmission.UWB and the associated networking protocol efforts are in the early stages of development, and several key deployment scenarios are being defined and evaluated. UWB complements currently deployed wireless networks in the WLAN environment, plus it extends high bit-rate, multimedia connectivity to WPANssupporting PC, CE and cellular devices. This combination will enable true convergence of computers, consumer electronics and mobile communications.Many UWB components and systems are already in the testing and demonstration phases, with actual release dates for final consumer products expected in early 2005. Intel Corporation is working with the industry to enable this exciting technology and help ensure its success.

REFERENCES

1. http://www.cnn.com/2001/TECH/internet/07/12/wireless.government.idg/in dex.html

2. http://www.multispectral.com/presentations/UWB%20Applications/sld018.h3. http://www.timedomain.com4. http://www.timedomain.com/Technology/findout_faqs1.htm5. http://www.developer.intel.com/technology/ijt/q22001/articles/art_4a.h6. http://www.mcommercetimes.com/Technology/117. http://www.nwfusion.com/columnists/2001/04116dzubeck.htm8. http://www.pcworld.com/news/article9. http://www.multispectral.com/presentations/UWB%20Applications/sld005.h10.http://www.multispectral.com/presentations/UWB%20Applications/sld004.h

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11.http://www.sss-mag.com/uwb.htm12.http://www.fcc.gov/oet/waivers13.http://www.ntia.doc.gov/osmhome/reports/UwbGps/NTIASP_01_45.pdf

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