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Non-coherent ranging with a-priori knowledge of noise variance

This document presents performance results of non-coherent ranging receivers with accurately estimated noise variance available a-priori.

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Non-coherent ranging with a-priori knowledge of noise variance

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Non-coherent ranging results with a-priori knowledge of noise variance] Date Submitted: [24 June 2005] Source: [Ismail Guvenc, Zafer Sahinoglu, Andy Molisch, Philip Orlik, Mitsubishi Electric] Contact:Zafer Sahinoglu Voice:[+1 617 621 7588, E-Mail: zafer@merl.com] Abstract: [This document provides performance results of non-coherent ranging receivers, under the assumption that noise variance is accurately estimated and available a-priori] Purpose: [To help objectively evaluate ranging proposals under consideration] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

  2. Outline • Signal waveforms • Receiver architectures • Simulations • Summary • Recommendations

  3. Objective • Study feasibility of non-coherent ranging • Evaluate ranging performance of various proposals

  4. Generic Architecture for Ranging • Received signal energy is collected • Energy vector is processed to suppress noise artifacts and enhance signal containing parts • Edge detection is performed channel Signal Signal Energy Collector Channel Characteristics Signal Energy Edge Detector Signal Energy Conditioner Signal Parameters TOA Estimate

  5. Option-III (Ternary Sequences) Pulse Repetition Interval ~ 62.5ns 4 5 6 7 8 1 2 3 30 31 ………………………… Option-IV (Pulse PPM) Tp = 4ns PRP ± TH Tf = ~125ns Proposed System Parameters (With Same # Pulses per unit time) Option-I (Burst PPM) The Other Bit One Bit Always Empty Always Empty Always Empty 4-pulses 4 pulses

  6. Technical Differences and Commonalities

  7. Filtering + Assumption/path selection Time base 1-2ns accuracy Assumption path synchronization Matrix Analog comparator Time stamping "Path-arrival dates" table 1D to 2D Conversion BPF ( )2 LPF / 2-4ns integrator interference suppression Energy image generation Energy combining across symbols 1D-2D Conversion Sliding Correlator 2D-1D Conversion ADC Bipolar template Energy Detection Receiver Architectures FT R&D TOA Estimator I2R MERL Energy image generation Removes interference Length-3 Vertical Median or Minimum Filtering 2D to 1D Conversion with Energy Combining 1D to 2D Conversion

  8. LOS Before and After Square-Law • A 500MHz pulse (4ns duration) is passed through a channel sampled at 8GHz • Received signal energy is collected at 4ns intervals • Strong LOS is lost First arriving and strongest path Channel realization Energy collection at 4ns First arriving energy block Strongest energy block

  9. Another example Channel realization Energy collection at 4ns With a search back window of 32ns, in this realization the first energy block is missed (the error was 4 energy blocks (2ns +3*4ns = 14ns)

  10. Fixed Search Back • Fixed search back window length is not very efficient First threshold crossing within 430 (TOA estimate) Strongest energy block p First signal energy threshold y t x z Fixed search back window

  11. Threshold Selection • Assume that µn and σn2mean and the variance of the noise respectively • Probability that a noise only sample greater than a threshold ε is • Probability of threshold crossing within K consecutive noise only samples • The corresponding threshold is PFA ε

  12. Adaptive and Iterative Search Back • K-iterative search back deals with K consecutive noise only blocks • As long as a cluster is detected backward, the search back continues Iterative search back Strongest energy block z y First signal energy noise dependent threshold x p 3 2 1 0 n+3 n+2 n+1 n Energy block index

  13. Observation window = 512ns TOA Ambiguity = 256ns Ts3 = 2048ns* Simulation Settings Option 3 (16 pulses per 2us) Option 1 ** (16 pulses per 2us) Option 4 (16 pulses per 2us) Ts1 = Ts4 = 512ns * Since option-3 uses 31 chip sequences, 1984ns symbol duration is used for option-3 to have multiples of 4ns sampling duration. However, total energy used within 4ms duration are identical for all cases. ** A training sequence of all 1’s are used. Random training sequence will introduce self interference that will degrade the performance.

  14. Results • PFA = 0.01, TB = 4ns

  15. Results • PFA = 0.005, TB = 4ns

  16. Results • PFA = 0.001, TB = 4ns

  17. Results • PFA = 0.05, TB = 2ns

  18. Results • PFA = 0.01, TB = 2ns

  19. Results • PFA = 0.005, TB = 2ns

  20. Transmitted Time-hopping Sequence Anomaly in Option-4 ACF of the Transmitted Time-hopping Sequence Zero Correlation Zone Multipath components Peak Leading Edge Received energy samples (after processed with the time-hopping code) Search-back the leading edge

  21. Summary • A-priori knowledge of noise variance improved ranging performance • Threshold is set according to the noise variance and probability of missing a block, not according to the percentage of the highest signal energy block • This made option-4 suffered. • Option-1 performed the best both in terms of 3ns confidence level and mean absolute error (MAE). • Increasing the sampling rate gained us 2dB • 3ns 90% confidence level around 13dB at 2ns sampling interval • The MAE is appr. 2ns at 13dB with 2ns sampling interval • In order to have SOP support, symbol duration should be prolonged in option-1 • This lowers the achievable bit rate (<1Mbps) • Coherent processing is faster with burst PPM

  22. Recommendation to the IEEE 802.15.4a TG • Lower the bit rate from 1Mbps to 500Kbps • This will provide • Non-coherent with option-1 with better SOP support • Better non-coherent ranging • Adopt option-1 waveform in preamble

  23. For an Even Better Ranging Performance ~512 ns T1 (time-hopping margin) Multipath tolerance M-chip times TH1 symbol with 0-ns time hopping symbol with TH1 nanosecond burst time hopping • Bursts are coarsely time-hopped • Can be integer multiples of BRI

  24. Backup Slide • EBN0 = 22dB, Interference and desired equidistant to the receiver • Strong SOP interference is easily suppressed by the way the image is created and by means of length-3 minimum filtering (in ranging) Multi-user Interference Desired User Energy MinimumFiltering {Length 3 Vertical} Symbol Index Symbol Index Block Index Block Index

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