Xiliang Luo Dept . of ECE, Univ. of Minnesot a Email: - PowerPoint PPT Presentation

May 5, 2005 EE 8510, Project Presentation Achievable Rates of Transmit- Ref erence Ultra- Wideband Radio with PPM Xiliang Luo Dept . of ECE, Univ. of Minnesot a Email: luoxx026@umn.edu 1

Background … � UWB Impulse Radio: WPAN (short-range, high-rates) 1 Emitted power Narrowband (bandwidth 30KHz) 0.5 Amplitude Spread-Spectrum 0 (802.11b) (bandwidth 80MHz) UWB Noise -0.5 floor (bandwidth >2GHz) -1 0 0.2 0.4 0.6 0.8 Frequency Time (ns) � Challenges: � Timing synchronization/Channel estimation � Efficient demodulation � efficient energy collection � Transmitted Reference (TR) [ Hoctor-Tomlinson’02 ] [ Rushforth’64 ] � Non-coherent � bypasses channel estimation � Robust to mistiming 2

PPM-UWB with TR … � Tx Structure Modulated: Reference position index: k � m-ary PPM: � Channel Model � block fading: � 3

Random Coding at Tx… � Tx coding � M messages N channel uses � generate a codebook : � : position index in n th channel use for message w � Tx. message 1: 4

Rx Structure … � Rx Structure: � Choose system parameters such that: � Projection onto the set of bases: � Rx signal vector over n th channel use (w=1 sent): � Decision statistics: 5

Demodulation and Performance … � Decision Rule: � Message is sent if: � Detection threshold: � Error Probability: How to make the error probability � 0 ? 6

Achievable Rates… � Upper Bound on the “Average Error Probability”: � Achievable Rates: 7

1GHz UWB system… � 1GHz UWB radio with 10m Tx-Rx separation: � FCC spectral mask : -41.3dBm/MHz � 1GHz bandwidth � max Tx power: -12dBm � Noise spectral density: -103dBm/MHz : Boltzmann const. : noise figure : link margin � Path loss: 80dB [ IEEE 802.15-02/278r1-SG3a ] � High SNR ( ) benchmark: 70dB � Channel has RMS delay spread 20ns [ IEEE 802.15-02/490r1-SG3 ] � Choose 8

9 Rates achieved by 1GHz UWB radio …

Bandwidth Scaling … � Free Space Propagation 10

Bandwidth Scaling (con’t) … � Multi-path Fading Channel (20ns RMS delay spread): � non-coherent Rx collects more noise as W � non-coherent capacity � 0 for white-like signal [ Telatar-Tse’00 ] [ Medard-Gallager’02 ] 11

Conclusions … � PPM-UWB with TR achieves rates on the order of for practical SNR values. � PPM modulation size should vary depending on SNR � Future Work: � In order to increase the rates at high SNR, we need to choose: Find a tighter bound for when collision(s) are present ! Thank You! 12