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

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Achievable Rates of Transmit- Ref erence Ultra- Wideband Radio with PPM Xiliang Luo

May 5, 2005 Dept . of ECE, Univ. of Minnesot a Email: luoxx026@umn.edu

EE 8510, Project Presentation

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Background …

UWB Impulse Radio: WPAN (short-range, high-rates)

Frequency Emitted power

Narrowband (bandwidth 30KHz) Spread-Spectrum (802.11b) (bandwidth 80MHz) UWB (bandwidth >2GHz) Noise floor

0.2 0.4 0.6 0.8

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• 0.5

0.5 1 Time (ns) Amplitude

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

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PPM-UWB with TR …

Tx Structure Channel Model

Reference Modulated: position index: k

m-ary PPM: block fading:

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• : position index in nth channel use for message w

Random Coding at Tx…

Tx coding M messages N channel uses generate a codebook :

• Tx. message 1:

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Rx Structure:

Rx Structure …

Projection onto the set of bases: Choose system parameters such that: Rx signal vector over nth channel use (w=1 sent): Decision statistics:

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Demodulation and Performance …

Message is sent if: Decision Rule: Error Probability: Detection threshold: How to make the error probability 0 ?

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Achievable Rates…

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

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1GHz UWB system…

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

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Rates achieved by 1GHz UWB radio …

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Free Space Propagation

Bandwidth Scaling …

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Multi-path Fading Channel (20ns RMS delay spread):

Bandwidth Scaling (con’t) …

non-coherent

Rx collects more noise as W

non-coherent

capacity 0 for white-like signal [Telatar-Tse’00] [Medard-Gallager’02]

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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: Find a tighter bound for when collision(s) are present ! In order to increase the rates at high SNR, we need to choose:

Thank You!