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Wideband Communications

This lecture presents an overview of Ultra Wideband (UWB) communications, including its principles, applications, and technical specifications. It covers the basics of impulse radio technology, the vast bandwidth allocated for commercial use (3-10.5 GHz), and the stringent power limits of UWB systems (less than 0.5 mW). You'll explore UWB's high data rates (100-1000 Gbps), its short range capabilities (1-10 m), and various modulation techniques like time hopping and direct sequence spread spectrum. Learn about key concepts such as processing gain and interference mitigation, crucial for reliable communication.

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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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