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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [IEEE 802.15.4b High Rate Alt-PHY proposals - Further Performance Comparison] Date Submitted: [27 Oct, 2004] Source: [Francois Chin] Company: [Institute for Infocomm Research, Singapore]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [IEEE 802.15.4b High Rate Alt-PHY proposals - Further Performance Comparison] Date Submitted: [27 Oct, 2004] Source: [Francois Chin] Company: [Institute for Infocomm Research, Singapore] Address: [21 Heng Mui Keng Terrace, Singapore 119613] Voice: [65-68745684] FAX: [65-67768109] E-Mail: [chinfrancois@i2r.a-star.edu.sg] Re: [Response to the call for proposal of IEEE 802.15.4b, Doc Number: 15-04-0239-00-004b] Abstract: [This presentation compares all proposals for the IEEE802.15.4b PHY standard.] Purpose: [Proposal to IEEE 802.15.4b Task Group] 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. Francois Chin, Institute for Infocomm Research (I2R)

  2. Background • Main contribution of current doc is to provide further simulation results based on 1000 channel realisation, for the PHY proposals using coherent detection • Previous comparison used 100 channel realisation, as in IEEE Doc 15-04-0507-04-004b • Performance comparison herein done with • {0,1,2} cyclic chip extension • {1,2,3} RAKE fingers Francois Chin, Institute for Infocomm Research (I2R)

  3. Updates • Corrected 3-RAKE multipath performance for all proposals (due to programme bug in previous version) • Included PSSS performance with Precoding • Stated Recommendation based on corrected simulation results Francois Chin, Institute for Infocomm Research (I2R)

  4. Candidates for Multipath Performance Comparison (using Coherent Chip Despreading) • Source: 15-04-0507-04-004b Francois Chin, Institute for Infocomm Research (I2R)

  5. Comparison Methodology • Multipath robustness performance • Investigation done with • Zero, one and two Cyclic chip(s) extension • One, two & three RAKE fingers • Bandwidth efficiency (bps / Hz) • RF requirement • Memory requirement Francois Chin, Institute for Infocomm Research (I2R)

  6. Multipath Realisations 1000 Channel Realisations at each RMS Delay Spread Francois Chin, Institute for Infocomm Research (I2R)

  7. Multipath Realisations 1000 Channel Realisations at each RMS Delay Spread Francois Chin, Institute for Infocomm Research (I2R)

  8. Proposed Symbol-to-Chip Mapping (8-chip Code Set C8) The sequences are related to each other through cyclic shifts and/or conjugation (i.e., inversion of odd-indexed chip values) Francois Chin, Institute for Infocomm Research (I2R)

  9. Other Root Sequences (8-chip C8for Coherent Despreading only) • The following Root Sequences are found through exhaustive search with identical low cross correlation and autocorrelation, in base 10: 9 18 23 29 33 36 46 58 66 71 72 92 111 113 116 123 132 139 142 144 163 183 184 189 197 209 219 222 226 232 237 246 Francois Chin, Institute for Infocomm Research (I2R)

  10. Decimal Symbol Binary Symbol Chip Values 0 0 0 0 0 0 0 1 1 0 1 0 0 0 1 0 0 0 1 0 0 1 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 1 2 0 1 0 0 0 0 0 0 0 1 1 1 0 1 1 1 0 1 1 1 3 1 1 0 0 0 1 0 1 0 0 1 0 0 0 1 0 0 0 1 0 4 0 0 1 0 0 0 1 1 1 0 1 1 0 1 0 0 1 0 1 1 5 1 0 1 0 0 1 1 0 1 1 1 0 0 0 0 1 1 1 1 0 6 1 1 1 0 0 0 0 0 1 0 0 0 0 1 1 1 1 0 0 0 7 0 1 1 1 0 1 0 1 1 1 0 1 0 0 1 0 1 1 0 1 8 0 0 0 1 0 0 1 1 0 1 0 0 1 0 1 1 1 0 1 1 9 1 0 0 1 0 1 1 0 0 0 0 1 1 1 1 0 1 1 1 0 10 0 1 0 1 0 0 0 0 0 1 1 1 1 0 0 0 1 0 0 0 11 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 1 1 0 1 12 0 0 1 1 0 0 1 1 1 0 1 1 1 0 1 1 0 1 0 0 13 1 0 1 1 0 1 1 0 1 1 1 0 1 1 1 0 0 0 0 1 14 0 1 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 1 15 1 1 1 1 0 1 0 1 1 1 0 1 1 1 0 1 0 0 1 0 DSSS Sequence E16 • Source doc.: IEEE 802.15-04-0314-02-004b Francois Chin, Institute for Infocomm Research (I2R)

  11. PSSS Sequence F31 (15 bit/32 chip) • Source doc.: IEEE 802.15-04-0121-04-004b Francois Chin, Institute for Infocomm Research (I2R)

  12. Proposed Symbol-to-Chip Mapping (16-chip Code Set G16) The sequences are related to each other through cyclic shifts and/or conjugation (i.e., inversion of odd-indexed chip values) Francois Chin, Institute for Infocomm Research (I2R)

  13. Other Root Sequences (8-chip G16for Coherent Despreading only) • The following Root Sequences are found through exhaustive search with identical low cross correlation and autocorrelation, in base 10: 1915 3566 12115 21038 22715 31238 34297 42820 44497 53420 61969 63620 Francois Chin, Institute for Infocomm Research (I2R)

  14. Multipath Performance (COBI 16-chip) For 16-chip COBI Sequence, No cyclic chip is needed when 3 RAKE is used. Francois Chin, Institute for Infocomm Research (I2R)

  15. Multipath Performance (COBI 8-chip) For 8-chip COBI Sequence, 1 Chip Extension is needed even with 3-RAKE, due to weaker despreading strength (shorter code length). Francois Chin, Institute for Infocomm Research (I2R)

  16. Multipath Performance (DSSS) For DSSS, No cyclic chip is needed when 3 RAKE is used. Francois Chin, Institute for Infocomm Research (I2R)

  17. Multipath Performance (PSSS) For PSSS, best performance with 2 RAKE fingers + 1 chip extension. Precoding (according to 15-04-0121-04-004b) & 3rd RAKE do not seem to help. Francois Chin, Institute for Infocomm Research (I2R)

  18. What happened to PSSS? Neighbouring parallel sequence is using M-Seq with 2 cyclic shifts in PSSS parallel sequence construction • Source doc.: IEEE 802.15-04-0121-04-004b While other schemes enjoy better multipath performance with more RAKE fingers, PSSS can only use up to 2 fingers as the 3rd RAKE is dominated by adjacent parallel bit sequence. PSSS is inter-parallel sequence interference limited Francois Chin, Institute for Infocomm Research (I2R)

  19. Coherent Receiver Multipath Performance • 1 chip extension is NOT necessary for 16-chip sequence (COBI-16 & DSSS) ifsufficient RAKE is used, even in dense multipath environment • 1 chip extension is necessary for 8-chip COBI sequence, due to weaker despreading strength • General performance comparison: • COBI sequence (16 chip) > COBI sequence (8+1 chip) > PSSS (31+1 chip, no Precoding) > DSSS Sequence (16 chip) Francois Chin, Institute for Infocomm Research (I2R)

  20. Coherent Receiver Multipath Performance What leads to Multipath robustness? Frequency selectivity leads to Inter-chip interference, and that is the killer…. To overcome, code must have good autocorrelation properties, i.e. low sidelodes Francois Chin, Institute for Infocomm Research (I2R)

  21. COBI 8-chip autocorrelation matrix COBI 16-chip autocorrelation matrix How these codes achieve Multipath robustness? • COBI, maintain constant module, can at best achieve zero auto-correlation within 2 chips from cor. Peak; that is good enough to handle ICI of upto 2 chip periods • DSSS, comprising Walsh sequences, is not designed with auto-correlation sidelodes in mind • PSSS, uses flexibility in amplitude to achieve low (zero?) auto-correlation throughout for each parallel sequence. However, it is inter-parallel sequence interference limited Francois Chin, Institute for Infocomm Research (I2R)

  22. Multipath Performance Summary (Coherent Chip Despreading) • To combat inter-chip interference due to relatively large channel delay spread (RMS delay spread / chip period ~ 0.6, that is 2us for 868MHz band and 0.6us for 915MHz bands), 2 recommendations are: • RAKE combining (with 3 fingers) for all proposed sequences in receiver to combine path diversity; (this does not affect standard) • One additional chip extension to shorter code e.g. COBI 8-chip sequence to avoid inter-symbol interference • With the 2 recommendations, under large channel delay spread • @ BER = 10-5 (PER ~ 1% @ 127 byte-packet), 16-chip COBI sequence have clear performance superiority (> 4dB better than the rest), followed by COBI (8+1 chip). Francois Chin, Institute for Infocomm Research (I2R)

  23. Candidates for Multipath Performance Comparison (using Coherent Chip Despreading) Note : Red - desirable Francois Chin, Institute for Infocomm Research (I2R)

  24. Coherent Detection Performance (at less channel delay spread) • performance comparison: • Using 2 RAKE + 1 cyclic chip extension, • COBI sequence (16 chip) > DSSS Sequence (16 chip) > • COBI sequence (8+1 chip) > PSSS (31+1 chip) • Again, PSSS can only use up to 2 fingers as the 3rd RAKE is dominated by adjacent parallel bit sequence. PSSS is inter-parallel sequence interference limited. Precoding does give slightly better performance under less channel delay spread Francois Chin, Institute for Infocomm Research (I2R)

  25. Can Non-Coherent Detection be used? • The COBI are designed to give best performance with coherent detection receiver. When the receiver employs non-coherent detection: • Yes, COBI sequence (16 chip) can handle multipath channels upto RMS delay spread / chip period ~ 0.15 (that is 0.5us for 868MHz band using 600kcps and 0.15us for 915MHz bands using 1Mcps), which normally corresponds to short range indoor environment • Yes, COBI sequence (8+1 chip) can handle multipath channels upto RMS delay spread / chip period ~ 0.03 (that is 0.1us for 868MHz band using 600kcps and 0.03us for 915MHz bands using 1Mcps), at even shorter range indoor Francois Chin, Institute for Infocomm Research (I2R)

  26. Code Sequence Recommendations • Multipath robustness vs complexity • As multipath robustness is vital, and differential chip despreading does not perform well under channels with excessive delay spread, coherent chip despreading with RAKE combining is necessary to ensure coverage in large indoor environment, e.g. industry space • One cyclic chip extension is ONLY necessary for shorter code, e.g. 8-chip COBI, to avoid inter-symbol interference under channels with excessive delay spread • 8-chip (+1 chip extension) & 16-chip COBI sequence is recommended for its better multipathh performance, low RF linearity requirement, high bandwidth efficiency and low memory requirement • Differential chip despreading can also be used in shorter range indoor environment,e.g. residential space, where multipath channel RMS delay spread is small Francois Chin, Institute for Infocomm Research (I2R)

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