ultrawide band wikipedia

8/12/2019 Ultrawide Band Wikipedia

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Ultra-wideband

From Wikipedia, the free encyclopedia

Ultra-wideband(also known as UWB, ultra-wide bandand ultraband) is a radio technologypioneered byRobert A. Scholtzand others which may be used at a very low energy level for

short-range, high-bandwidth communications using a large portion of the radio spectrum.[1]

UWB has traditional applications innon-cooperative radar imaging.Most recent applicationstarget sensor data collection, precision locating and tracking applications.

[2]

Similar tospread spectrum,UWB communications transmit in a manner which does not interfere

with conventionalnarrowbandandcarrier waveused in the same frequency band.

Ultra-wideband is a technology for transmitting information spread over a large bandwidth(>500MHz); this should, in theory and under the right circumstances, be able to share spectrum

with other users. Regulatory settings by theFederal Communications Commission(FCC) in theUnited States intend to provide an efficient use of radio bandwidth while enabling high-data-ratepersonal area network(PAN) wireless connectivity; longer-range, low-data-rate applications; and

radar and imaging systems.

Ultra wideband was formerly known as "pulse radio", but the FCC and theInternational

Telecommunication UnionRadiocommunication Sector (ITU-R)currently define UWB in terms

of a transmission from an antenna for which the emitted signal bandwidth exceeds the lesser of500 MHz or 20% of the center frequency. Thus, pulse-based systemswhere each transmitted

pulse occupies the UWB bandwidth (or an aggregate of at least 500 MHz of narrow-band carrier;

for example,orthogonal frequency-division multiplexing(OFDM)can gain access to the UWB

spectrum under the rules. Pulse repetition rates may be either low or very high. Pulse-basedUWB radars and imaging systems tend to use low repetition rates (typically in the range of 1 to

100 megapulses per second). On the other hand, communications systems favor high repetition

rates (typically in the range of one to two gigapulses per second), thus enabling short-rangegigabit-per-second communications systems. Each pulse in a pulse-based UWB system occupies

the entire UWB bandwidth (thus reaping the benefits of relative immunity tomultipath fading,

but notintersymbol interference), unlikecarrier-basedsystems which are subject to deep fadingand intersymbol interference.

[3]

Contents

1 Theory 2 Technology

o 2.1 Antenna systems 3 Applications 4 Regulation 5 Technology groups 6 See also 7 References
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e_note-1http://en.wikipedia.org/wiki/Robert_A._Scholtz


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8 External links

Theory

A significant difference between conventional radio transmissions and UWB is that conventional

systems transmit information by varying the power level, frequency, and/or phase of a sinusoidalwave. UWB transmissions transmit information by generating radio energy at specific time

intervals and occupying a large bandwidth, thus enablingpulse-positionor time modulation. The

information can also be modulated on UWB signals (pulses) by encoding the polarity of the

pulse, its amplitude and/or by using orthogonal pulses. UWB pulses can be sent sporadically atrelatively low pulse rates to support time or position modulation, but can also be sent at rates up

to the inverse of the UWB pulse bandwidth. Pulse-UWB systems have been demonstrated at

channel pulse rates in excess of 1.3 gigapulses per second using a continuous stream of UWB

pulses (Continuous Pulse UWB orC-UWB), supporting forward error correction encoded datarates in excess of 675 Mbit/s.

[4]

A valuable aspect of UWB technology is the ability for a UWB radio system to determine the"time of flight" of the transmission at various frequencies. This helps overcomemultipath

propagation,as at least some of the frequencies have aline-of-sighttrajectory. With a

cooperative symmetric two-way metering technique, distances can be measured to highresolution and accuracy by compensating for local clock drift andstochasticinaccuracy.

[5]

Another feature of pulse-based UWB is that the pulses are very short (less than 60 cm for a500 MHz-wide pulse, less than 23 cm for a 1.3 GHz-bandwidth pulse), so most signal reflections

do not overlap the original pulse and the multipath fading of narrowband signals does not exist.

However, there is still multipath propagation and inter-pulse interference to fast-pulse systemswhich must be mitigated by coding techniques.

[citation needed]

Technology

One performance measure of a radio in applications such as communication, locating, tracking

and radar is thechannel capacityfor a given bandwidth and signaling format. Channel capacity is

the theoretical maximum possible number of bits per second of information which may beconveyed through one or more links in an area. According to theShannonHartley theorem,the

channel capacity of a properly encoded signal is proportional to the bandwidth of the channel

and the logarithm of thesignal-to-noise ratio(SNR) (assuming the noise isadditive white

Gaussian noise). Thus channel capacity increases linearly by increasing the channel's bandwidthto the maximum value available, or (in a fixed-channel bandwidth) by increasing the signal

power exponentially. By virtue of the large bandwidths inherent in UWB systems, large channel

capacities could be achieved in principle (given sufficient SNR) without invokinghigher-ordermodulationsrequiring a very high SNR. Ideally, the receiver signal detector should match the

transmitted signal in bandwidth, signal shape and time. A mismatch results in loss of margin for

the UWB radio link. Channelization (sharing the channel with other links) is a complex issue,subject to many variables. Two UWB links may share the same spectrum by using orthogonal
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time-hopping codes for pulse-position (time-modulated) systems, or orthogonal pulses and

orthogonal codes for fast-pulse-based systems.

Forward error correctionused in high-data-rate UWB pulse systemscan provide channel

performance approaching theShannon limit.[3]

OFDM receivers typically fix most errors with a

low density parity check codeinner code followed by some other outer code that fixes theoccasional errors (the "error floor") that get past the LDPC correction inner code even at low bit-

error rates. For example: The Reed-Solomon code with LDPC Coded Modulation (RS-LCM)

adds aReedSolomon error correctionouter code.[6]

The DVB-T2 standard and the DVB-C2standard use aBCH codeouter code to mop up residual errors after LDPC decoding.

[7]WiMedia

over a UWB channel uses aHybrid automatic repeat request:inner error correction using

convolutional and Reed-Solomon coding, outer error correction using a frame check sequence

that, when the check fails, triggers automatic repeat-request (ARQ).[8]

When stealth is required, some UWB formats (mainly pulse-based) may be made to appear like a

slight rise in background noise to any receiver unaware of the signals complex pattern.[3]

Multipath interference(distortion of a signal because it takes many different paths to the receiver

with various phase shift and various polarisation shift) is a problem in narrowband technology. Italso affects UWB transmissions, but according to the Shannon-Hartley theorem and the variety

of geometries applying to various frequencies the ability to compensate is enhanced. Multipath

causes fading, and wave interference is destructive. Some UWB systems use "rake" receivertechniques to recover multipath-generated copies of the original pulse to improve a receiver's

performance. Other UWB systems use channel-equalization techniques to achieve the same

purpose. Narrowband receivers may use similar techniques, but are limited due to the different

resolution capabilities of narrowband systems.

Antenna systems

DistributedMIMO:To increase the transmission range, this system exploits distributedantennas among different nodes.

Multiple-antenna:Multiple-antenna systems (such as MIMO) have been used to increasesystem throughput and reception reliability. Since UWB has almost impulse-like channel

response, a combination of multiple antenna techniques is preferable as well. Coupling

MIMO spatial multiplexing with UWB's high throughput gives the possibility of short-

range networks with multi-gigabit rates.

Applications

Ultra-wideband characteristics are well-suited to short-distance applications, such asPCperipherals.Due to low emission levels permitted by regulatory agencies, UWB systems tend to

be short-range indoor applications. Due to the short duration of UWB pulses, it is easier to

engineer high data rates; data rate may be exchanged for range by aggregating pulse energy perdata bit (with integration or coding techniques). Conventionalorthogonal frequency-division

multiplexing(OFDM) technology may also be used, subject to minimum-bandwidth

requirements. High-data-rate UWB may enablewirelessmonitors,the efficient transfer of data
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from digitalcamcorders,wirelessprintingof digital pictures from a camera without the need for

apersonal computerandfile transfersbetweencell-phonehandsets and handheld devices such as

portable media players.[9]

UWB is used for real-time location systems; its precision capabilitiesand low power make it well-suited for radio-frequency-sensitive environments, such as hospitals.

Another feature of UWB is its short broadcast time.

Ultra-wideband is also used in "see-through-the-wall" precision radar-imaging

technology,[10][11][12]

precision locating and tracking (using distance measurements between

radios), and precision time-of-arrival-based localization approaches.[13]

It is efficient, with aspatial capacityof approximately 10

13bit/s/m.

[citation needed]UWB radar has been proposed as the

active sensor component in anAutomatic Target Recognitionapplication, designed to detect

humans or objects that have fallen onto subway tracks.[14]

UWB has been a proposed technology for use inpersonal area networks,and appeared in the

IEEE 802.15.3a draft PAN standard. However, after several years of deadlock, the IEEE

802.15.3a task group[15]

was dissolved[16]

in 2006. The work was completed by the WiMedia

Alliance and the USB Implementer Forum. Slow progress in UWB standards development, thecost of initial implementation, and performance significantly lower than initially expected are

several reasons for the limited use of UWB in consumer products (which caused several UWBvendors to cease operations in 2008 and 2009).

[17]

Regulation

Ultra-wideband refers to radio technology with abandwidthexceeding the lesser of 500 MHz or

20% of the arithmeticcenter frequency,according to the U.S.Federal Communications

Commission(FCC). A February 14, 2002 FCC Report and Order[18]

authorized the unlicenseduse of UWB in the frequency range from 3.1 to 10.6GHz.The FCC powerspectral density

emission limit for UWB transmitters is 41.3dBm/MHz. This limit also applies to unintentionalemitters in the UWB band (the"Part 15"limit). However, the emission limit for UWB emitters

may be significantly lower (as low as 75dBm/MHz) in other segments of the spectrum.

Deliberations in theInternational Telecommunication UnionRadiocommunication Sector (ITU-R)resulted in a Report and Recommendation on UWB

[citation needed]in November 2005.UK

regulatorOfcomannounced a similar decision[19]

on 9 August 2007. More than four dozen

devices have been certified under the FCC UWB rules, the vast majority of which are radar,imaging or locating systems

[citation needed].

There has been concern over interference between narrowband and UWB signals sharing the

same spectrum; earlier, the only radio technology which operated using pulses werespark-gaptransmitters(which were banned due to interference to medium-wave receivers), but UWB uses

lower power. The subject was extensively covered in the proceedings that led to the adoption of

the FCC rules in the U.S. and in the meetings relating to UWB of the ITU-R leading to its Reportand Recommendations on UWB technology. Commonly used electrical appliances emit

impulsive noise(for example, hair dryers) and the argument was successfully made that thenoise

floorwould not be raised excessively by wider deployment of wideband transmitters using low

power.
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5/5

China allowed 24 GHz UWB Automotive Short Range Radar in Nov 2012.[20]
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