Lecture 24-27: Ultra Wideband Communications Aliazam Abbasfar

Outline What’s UWB ? Impulse Radio

UWB Very huge band allocated for commercial use 7.5 GHz ( GHz) BW should be > 500 MHz Power is very limited Total < 0.5 mW Density < mask Applications: Short range (1-10 m) High data rate ( Gbps) Indoor Range/data rate trade-off Low cost/high data rate communications Types : Impulse radio Multi-carrier

Impulse radio (IR) Very short duration pulses 100 pico-second Wideband spectrum Very low energy pulses Combine many pulses to have reliable detection Baseband transmission No carrier Simple No continuous transmission Spectrum lines violates power density mask Use Time hopping-pulse position modulation (TH-PPM)

TH-PPM Time hopping spread spectrum N mono-cycles for each data symbol ( = N chips) Processing gain (PG 1 = N) E b /N 0 = PG 1 E c /N 0 Remove line spectrums Pulse selection (for each mono-cycle) Should satisfy the PSD mask Gaussian/Laplacian/Rayleigh/ Hermitian Pulse does not occupy the while mono-cycle(chip) More processing gain (PG 2 = T f /T p ) for interference mitigation PG = PG 1 + PG 2 If delay between pulses > channel spread (T H ) No ISI between pulses  no ISI Resistant to multipath propagation

Pulses Gaussian pulse DC components First derivative Center freq : f 0 = 1/T p 3dB BW = 1.16 f 0 Higher derivatives Lower BW

Modulation PAM BER = Q(2 SNR) OOK BER = Q( SNR) Pulse positioning modulation(PPM) p(t) = v(t – d i ) is chosen based on pulse auto-correlation () Orthogonal case : ()= 0 BER = Q((1-)SNR) Negative  improves BER PSM Different pulses for data Orthogonal pulses BER = Q(SNR)

TX/RX architecture TX : A random offset is added (code) Baseband pulse shaping RX Correlators Data rate vs range Variable SF

Multiple access in TH-PPM Time hopping codes T f = M T c Synchronous # of orthogonal users = M Latin square codes Asynchronous Pseudo-Random codes Very low cross-correlation between codes

DS-UWB Direct sequence spread spectrum N chips for each data symbol ( = N chips) Processing gain (PG = N) E b /N 0 = PG 1 E c /N 0 Remove line spectrums Pseudo-Random spreading Chip pulse selection Should satisfy the PSD mask Gaussian/Raised cosine We have ISI Rake receiver is used in multipath propagation

Modulation BPAM BER = Q(SNR) = Q(N SNR c ) OOK BER = Q(SNR) PPM BER = Q((1-)SNR) Negative  improves BER PSM Different codes/pulses for data BER = Q((1-)SNR)

Multi-carrier MC-CDMA Spread in frequency domain MC-DS-CDMA Spread in time domain Multiband OFDM BW : 500 MHz Band hopping MA: Frequency-time hopping pattern

Reading Opperman 1.1, 3.1, 3.2, and 3.3