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Wideband Communications

Wideband Communications . 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 (3-10.5 GHz) BW should be > 500 MHz Power is very limited Total < 0.5 mW Density < mask

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Wideband Communications

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  1. Wideband Communications Lecture 24-27: Ultra Wideband Communications Aliazam Abbasfar

  2. Outline • What’s UWB ? • Impulse Radio

  3. UWB • Very huge band allocated for commercial use • 7.5 GHz (3-10.5 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 (100-1000 Gbps) • Indoor • Range/data rate trade-off • Low cost/high data rate communications • Types : • Impulse radio • Multi-carrier

  4. 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)

  5. TH-PPM • Time hopping spread spectrum • N mono-cycles for each data symbol ( = N chips) • Processing gain (PG1 = N) • Eb/N0 = PG1Ec/N0 • 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 (PG2 = Tf/Tp ) for interference mitigation • PG = PG1 + PG2 • If delay between pulses > channel spread (TH) • No ISI between pulses  no ISI • Resistant to multipath propagation

  6. Pulses • Gaussian pulse • DC components • First derivative • Center freq : f0 = 1/Tp • 3dB BW = 1.16 f0 • Higher derivatives • Lower BW

  7. Modulation • PAM • BER = Q(2 SNR) • OOK • BER = Q( SNR) • Pulse positioning modulation(PPM) • p(t) = v(t – ddi) • is chosen based on pulse auto-correlation r(t) • Orthogonal case : r(t)= 0 • BER = Q((1-r)SNR) • Negative r improves BER • PSM • Different pulses for data • Orthogonal pulses • BER = Q(SNR)

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

  9. Multiple access in TH-PPM • Time hopping codes • Tf = M Tc • Synchronous • # of orthogonal users = M • Latin square codes • Asynchronous • Pseudo-Random codes • Very low cross-correlation between codes

  10. DS-UWB • Direct sequence spread spectrum • N chips for each data symbol ( = N chips) • Processing gain (PG = N) • Eb/N0 = PG1Ec/N0 • 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

  11. Modulation • BPAM • BER = Q(SNR) = Q(N SNRc) • OOK • BER = Q(SNR) • PPM • BER = Q((1-r)SNR) • Negative r improves BER • PSM • Different codes/pulses for data • BER = Q((1-r)SNR)

  12. 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

  13. Reading • Opperman 1.1, 3.1, 3.2, and 3.3

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