Yang Principles of Ultra Wideband Communications

8/13/2019 Yang Principles of Ultra Wideband Communications

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1 NOKIA FILENAMs.PPT/ DATE / NN

P rinc iples of U ltra W ide bandCommunicat ion

Overview

[email protected]


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Introduction

History

What is Ultra wideband technology

Main principlee Difference from WCDMA

Signal & Spectral characteristics

Channel statistical characteristics

Modulation & demodulation

Transceiver

Antenna

Applications

Reference


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D ifference from W C D M A

It is not the traditional spread spectrumtechnique.

Lower interference Without dedicated frequency Inherent covertness in secure Using a unique timing code for a pair of

specific transceivers Multiple pulse comprise each bit, + timing

code make this technology suitable fornoisy radio environment

Same advantage: enhance process gain onreceived signal, operate in the presence ofother higher-powered radio system


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U W B character istics (1)

UWB shares the same spectrum with existingusers

A revolutionary wireless technology

UWB systems make use of narrow pulse(Impulse) and time-domain signal processing.

Transmitting digital data over a wide spectrum offrequency with very low power (Ptx


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P rinciple (1)

Time Domain's founder, Larry Fullertondiscovered that single RFmonocycles could be transmitted through an antenna and by preciselypositioning these monocycles in time and then using a matched receiver torecover the transmissions created a whole new wireless medium.

Utilizing narrow Gaussian mono-pulses and time hopping spread the signalspectrum over a wide frequency range

Pulse timing within the allotted pulse frame is controlled by a time PN code.

The PN code determines the time bin assoiated with each pulses niominaltime.

Time modulation (TM) is utilized to transmit each data bit by preciselycontrolling the timing of each pulse within its designated time bin.

Time hopping spread the signal spectrum -> RF energy to distribute moreuniformly across the frequency band. -> channelization for multiaccesssystems


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P rinciple (2)

In traditional fashion, the communication system alway usesthe some frequency band, and the radio spectrum is dividedinto band and the channel. and then the signal transmitted in

the channel can be tractable, and the signal is said carryingby the carrier.

UWB sysytem operates as spread spectrum systems: i.e.bandwidth>> minimal effective data rate

Very short duration of pulse -> The duration of the pulse istypically short that the interval corresponding to a single bit.

UWB does not rely on a spreading sequence or a hoppingsequence to produce a wide bandwidth signal -> shortduration of basic pulse

It has always been possible to generate the signal withoutthe carrier.

Carrierless -> Anttena is excited with baseband signaldirectly.

UWB works in the power-limited regime.


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It is difficult tpdesign the systemwith traditional RF principle.lower carrier freq. 2-3GHz

UW B sys tem s

Time-domain modulationi.e. impulse radio

UWB system

FrB>0.25

FrB10GHz

Fractional bandwidth (FrB):is the ratioof the bandwidthof a signal to thecenter frequency of transmission.


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S pa tial S pe ctrum

Frequency

Pow

er

spe

ctralde n

sity(P

SD)

Conventional

radio servicetransmission

UWB trnsmission


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S pa tial Cap ac ity


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Signals

A general UWB pulse train signal cab be presented as a sumof pulses shifted in time:

where, s(t)is the UWB signal; p(t)is the basic pulse shape; akand tkare the amplitude and time offset for each individualpulse.

Due to the short duration of the pulse, the spectrum of theUWB signal can be several gigahertz or more in bandwidth.

FCC proposes that UWB system be permitted to operate on anunlicensed basis at extremely low transmit power levels.

==

k

kk ttpats )()(


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S ign al - m on ocycle


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M onocycle in TD and FD


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P ulse train in T D and F D


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N ear-w hite U W B sign al spectrum


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M od ulation (1)B P S K (Binary phase-shift keying) modualtion: if data

sequence is random and i.i.d. with zero mean, the spectrum willvanish. (Spectrum lines will incur the reduction of the total transmitpower.)

P ulse-po sit ion m od ulation(PPM): Timedomainsignal processing:The pulses are not uniformly paced in time.

where, akis the data ak{-1,1}andTis the amount of pulseadvance or delay in time relative to the reference(unmodulated) postion

Whenever 1/is an interger greater that two, then there are

no spectrum lines.

Others: OOK: On-off keying PAM: Pulse-amplitude modulation

=

+=

k

k TakTtpts )()(


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M od ulation (2)

Consider the transmission of a train of pulses equally spaced

in time. the receiver processing determines whether eachreceived pulse is located where expected or arrives early orlate.

With PPM, a slightly retarted pulse could represent a 0and

a slightly advanced pulse could represent a 1whentransmitting digital information.

The important point in Modulations selection is to considerthe spectral properties in order to archieve maximum powerefficiency.

i.e. to select a power efficient modulation scheme with a smooth PSD(power sprectrum density).


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P ulse P os ition M od ulation


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C od ing an d cha nn elization


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C on stallation disgram s

BPSK PPM

Time offsetsfor the pulses

are chosen to make twopossible pulses orthogonalat the receiver.PPM must use 2 times bitenergy to archieve the samebit error rate compared to

BPSK

Greatest inter-symbol distance:

3 dB advantage in efficiency than PPM.It seems the best selection from thisviewpoint.


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Spectrums

2)(

1)( fP

T

fBPSK =

)()(1

)(1

)(

2

2

2

T

kf

T

kP

TfP

Tf

k+=

=

BPSK:

OOK: (PPM: when 1/is an integer greater than two)

where P(f)is the Fourier transform of p(t)(f)is the unit impulse discrete spectral lines


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Demodulat ion

Scheme selection: Target is to reduce the complexity ofstructures.

Non-coherent (an envelope detector) demodulation isbased on Simplify timing requirement Bandwidth required of samplers or A/D converters

UWB has had many properties to reduce the designcomplexity: No requirement on carrier recovery or frequeny translation UWB transmitter will not require a power amplifier.

Coherent demodulation: BPSK must use a coherent demodulation: every pulse looks thesame out of the envelope detection.

Possible to use the optimal RAKE combining to improve the S/I.


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Fo rw ard error correct ion an d co ding

Operation in a power-limited regime has implications

for forward error correction techniques. Signal-space codes, such as Trelli codes, that

increase the alphabet size are good for band-limitedapplications, but not as appropriate for UWB

systems. Appropriate coding technique for power-limited

regime also has the potential to significiantly improvethe UWB system performance.


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Transmitter/receiver

U W B trnsm itter:operates in baseband, no

power amplification, baseband mono-pulse isdirectly apllied to the antenna

UW B receiver:operates in baseband, no IFstage

En tire UW B transceiver system shave beenfabricated on CMOS chips.


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PulseON TM U W B transceiver


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C orrelator O utput

A correlator is a correlation receiver

A correlator multiplies the receivedRF signal with a templetewaveform, and then integrates the

output of that process to yield asingle DC voltage.

This multiply-Integrate processoccurs over the duartion of the pulse

Correlator is an optimal earlt/late

detector:when the received pulse is of apulse early, the output is +1

when the received pulse ise ofpulse late, the output is -1

when the received pulse arrivescentered in the correlation window,the output is 0

The pulse-integration process willpick up the transmitted signal below

the nois e floor


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A n indoo r channel m odel

Indoor communication is the main use of UWB incommunication field now.

The channel can be modeled by the signal (lastslide)

Main parameters to characterize the indoor

channel model Multipath delay spread Multipath idensity profile Multipath fading distribution Multipath arrival times


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Ind oo r U W B channe l statistics (1) A UWB channel can be defined by the SNR of the LOS path.

where, s(n,)is the normalized largest incident signal; N is the numer of time samples wherethe signal is assumed to be nonzero, is the angle-of-arrival, and2is the variance of thenoise floor.

The temporal-spatial distribution of signal energy is charaterised by the firstmoment and the root of second moment of power delay profile:

where, r(n,k)is the kthreceived signal (based on discrete time signals)

dBns

SNR

N

n

2

1

0

2 ),(log10

==

=

=

=

=

=

=

1

0

2

1

0

22

,

1

0

2

1

0

2

),(

),()(

),(),(

N

n

N

n k

kT

N

n

N

nk

knr

knrTn

knrknnrT


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Ind oo r U W B channe l statistics (2)

Delay spread is often reported as the median of the collectionof measurement

The spatial distribution of the signal energy can be measured

by the first and root of second moments of received angularprofile:

wherekis the amplitude of the signal component incident from angle k, is the power-weighte average AOA, and is the RMS AOA

can be interpreted as the energy accumulated at the angle k during the measurement

time window.

=

=

=

=

=

=

1

0

2

1

0

22

1

0

2

1

0

2

)(N

n

N

n k

k

N

n

N

n k

k

k2


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M ultipath com po nen ts

One of potential benefits of UWB radio is itsmultipath resolution.

The multipath components can be distinct identifiedin UWB system, but may not be resolved in morenarrow system.

Traditional spectrum analyzers cannot be used tomeasure the UWB channel response at ameaningful distance. A receiver using a timemodulated ultra-wideband rake receiver concept,scanning receiver, has been deveploing in Time-Domain Ltd.

Diversity is applied for improving the systemperformance


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P ow er delay p rofile


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P ropaga tion prop erties


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Multipath


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M ultipath reflec tion


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Sy stem capac ity

PulsONradio system

Thousands of voice channels per cell without special signalprocessing algorithm

200-1000 simultaneous duplex 64 kbps telephoneconversation per bae station

Using sectored base station antenna technique, more capacity

can be achieved


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Applicat ions

Geo-loaction system

Radar, position locator, tracking, ranging

Indoor wireless communication (short range)with

Unlicensed operation Resistance to multipath interference Low transmit power


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Reference

The temporal and spectral characteristcs of Ultra wideband signals, William A. Kissisck, U.S. Departmentof Commerce, J an. 2001, NTIA report 01-383.

Time Domain Coroperation, www.time-domain.com

Ultra-wideband Working goup, www.uwb.org/standards.htm

Broad is the way, lower power radio, Terry Mitchell, IEE Review J an. 2001.pp. 35-39

Spatio-temporal diversity in Ultra-wideband radio, J .m. Cramer, and etc. IEEE, 1999, pp. 888-892

System considerations for Ultra-Wideband wireless networks, Matthew L. Welborn, XtremeSpectrum, Inc.,IEEE 2001, pp. 5-8

Ultra-Wideband antenna array, Kaveh Heidary, IEEE 2001, pp.472-475

Preliminary results of an ultra-wideband (impulse) scanning receiver, P. Withington, etc, 1999IEEE, 1186-

1190

Impulse Radio: How it works, Moe Z. Win., et al, 1998IEEE, communication letters, Vol 2, No. 2, Feb.1998, pp. 36-38

Ultra-ide bandwidth time-hopping spread-spectrum impulse radio for wireless multi-accesscommunications, Moe, Z. Win, et,al, IEEE, Trans. on Communications, vol. 48, No.4 April 2000, pp. 679-691

Spectral density of random time-hopping spread-spectrum UWB signals with Uniform timing J itter, Moe Z.Win., 1999IEEE, pp.1196-1200

Pseudo-Chaotic time hopping for UWB impulse radio, Gian Mario Maggio, et al, IEEE Trans on Ccircuitsand systems, vol. 48, No. 12, Dec. 2001

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Yang Principles of Ultra Wideband Communications

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