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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: [DS-UWB Responses to TG3aVoter NO Comments – Equalizer, SOP, ADC, RFI] Date Submitted: [September 2004] Source: [Matt Welborn, John McCorkle,& Michael McLaughlin] Company [Freescale Semiconductor, Inc & DecaWave, Ltd.] Address [8133 Leesburg Pike] Voice:[703-269-3000], E-Mail:[matt.welborn @freescale.com] Re: [] Abstract: [Response to NO voter comments and feedback regarding the DS-UWB (Merger #2) Proposal] Purpose: [Provide technical information to the TG3a voters regarding DS-UWB (Merger #2) Proposal] 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. Welborn, Freescale & McLaughlin, DecaWave

  2. Topic: Equalization • Typical comments • A single carrier receiver requires a decision based equalizer (DFE) for meeting reasonable performance. Under severe multipath scenarios (non line of sight) such equalizers introduces an error propagation effect • lack of sufficient high fidelity simulations of equalizer performance • Current evidence shows that DFE works well at very high SNRs (9.6 and 12.6 dB). Mustshow evidence that DFE will not suffer from error propagation at realistic operating points such at ~1 dB • I believe that a big application area for UWB will be in personal and portable devices. I have not been convinced that the DS-SS proposal will provide good performance in the face of changing propagation conditions, potential due to device movement or movement of people and objection in the propagation path. I have not seen an explanation and a simulation of how the equalizer will quickly adapt Welborn, Freescale & McLaughlin, DecaWave

  3. Responses: Equalization • Comments – Fully Resolved • There is no need for an adaptive equalizer. The system is assumed to see a psuedo-stationary channel for the duration of the packet.The equalizer re-trained for each packet. • At 110 Mbps, packets will be < 0.1ms in duration • Equalizer performance is demonstrated in system-level simulations • Our simulations show that although error propagation is present, it does not significantly reduce the range achieved by DS-UWB Welborn, Freescale & McLaughlin, DecaWave

  4. DS-UWB in Multipath • Indoor multipath channels provide several challenges for UWB systems • Multipath fading • Inter-symbol interference (ISI) • Energy capture • Effects are well-understood and are analyzed as trade-off between performance versus complexity • DS-UWB minimizes fading and provides scalable energy capture • Other approaches can provide good energy capture at the expense of significant multipath fading Welborn, Freescale & McLaughlin, DecaWave

  5. Compensating for ISI • ISI occurs as a result of non-uniform channel frequency response • Multipath delay spread exceeds the symbol interval • ISI is compensated for using an equalizer • Linear equalizer (digital filter) • Decision-feedback equalizer (DFE) • If left uncompensated, ISI can cause high BER & error floor phenomenon • Equalizer technology is widely used in many types of systems • Telephone modems • WLAN (e.g. 802.11b) • HDTV • OFDM systems use frequency domain equalization to compensate for phase and amplitude response of channel • If delay spread exceeds CP length, residual ISI compensation would require additional time-domain equalization Welborn, Freescale & McLaughlin, DecaWave

  6. Uncoded Equalization Performance on CM3-15, 16 Finger Rake -1 No Equalization 9-Tap Least-Squares DFE AWGN Channel -2 -3 Log10 BER -4 -5 -6 5 10 15 20 Eb/No Example of ISI Effects on BER • Un-equalized system experiences high BER and error floor • 9-tap DFE with 16-finger rake performance approaches AWGN Welborn, Freescale & McLaughlin, DecaWave

  7. Eye diagram at Eb/No = 5 dB Noise dominates ISI Welborn, Freescale & McLaughlin, DecaWave

  8. Eye diagram at Eb/No = 10 dBNoise/ISI at similar levels Welborn, Freescale & McLaughlin, DecaWave

  9. Eye diagram at Eb/No = 15 dB ISI dominates AWGN Welborn, Freescale & McLaughlin, DecaWave

  10. Eye diagram at Eb/No = 20 dB ISI dominates AWGN Welborn, Freescale & McLaughlin, DecaWave

  11. Responses: Equalization • Comments – Fully Resolved • There is no need for an adaptive equalizer. The system is assumed to see a psuedo-stationary channel for the duration of the packet.The equalizer re-trained for each packet. • At 110 Mbps, packets will be < 0.1ms in duration • Equalizer performance is demonstrated in system-level simulations • Our simulations show that although error propagation is present, it does not significantly reduce the range achieved by DS-UWB Welborn, Freescale & McLaughlin, DecaWave

  12. Topic: Simultaneous Piconets (SOP) • Typical comments: • SOP numbers are inconsistent with any of the sanity checks. Please revise numbers via full level simulation. Do not assume that the interference is white Gaussian noise and shift curves. To verify numbers are based on simulations, please provide each curve usedin the averaging process • Isolation between interfering piconets occupying the lower band needs to be better than the stated d_int/d_ref = 0.66 for 2-3 uncoordinated interfering piconets in some applications - I would like to see evidence of how this can be met Welborn, Freescale & McLaughlin, DecaWave

  13. SOP Mechanism • SOP performance values reported for DS-UWB were based on full simulations of all interfering signals (not based on statistical signal distributions) • SOP mechanism is based on spread-spectrum techniques • Other piconet signals look like uncorrelated noise • Analysis results show PHY layer interference ratios • Equivalent to “fully loaded” piconets • Actual MAI will depend on MAC & actual traffic loading • 15.3 MAC co-existence mechanisms (child & neighbor piconets) can allow co-existence at much shorter ranges Welborn, Freescale & McLaughlin, DecaWave

  14. SOP Performance • DS-UWB also has the potential for enhanced SOP performance using advanced receiver architectures • MAI is not truly random noise, but has structure • Different piconet codes & chip rates are known • Multi-user detection (MUD) techniques could allow for significant SOP performance improvements Welborn, Freescale & McLaughlin, DecaWave

  15. AWGN SOP Distance Ratios • AWGN distances for low band • High band ratios expected to be lower • Operates with 2x bandwidth, so 3 dB more processing gain Welborn, Freescale & McLaughlin, DecaWave

  16. Multipath SOP Distance Ratios Test Transmitter: Channels 1-5 Single Interferer: Channels 6-10 Second Interferer: Channel 99 Third Interferer: Channel 100 • High band ratios expected to be lower (3 dB more processing gain) Welborn, Freescale & McLaughlin, DecaWave

  17. Topic: ADC Issues • Typical comments • [DS-UWB must demonstrate] a receiver structure would be suggested that can achieve range comparable with the MBOA proposal, with a digital sampling rate of no more than 528Mbit/s • The Silicon implementation feasibility is substantiated satisfactorily. ----The Silicon implementation size/power/complexity claims of the ADC/DAC/FEC/ Rake/equalizer at high speed do not agree with general knowledge… Welborn, Freescale & McLaughlin, DecaWave

  18. ADC Power Requirements & Scaling • ADC complexity is a function of both sample rate and bit width • Concerns of comments seem to be that ADC requirements are much higher for DS-UWB than for alternative approaches (e.g. MB-OFDM) because clock rate is higher • ADC performance is described by “efficiency quotient” • EQ = power / 2^ (ENOB * BW) • ENOB = effective number of bits & BW = input bandwdith • This agrees with ADC scaling estimates based on MB-OFDM-proposed methodology • Available in IEEE Document 03/343r1 describing MB-OFDM complexity and power consumption • DS-UWB digital receiver architecture can use a fixed bit width for all data rates up to 1.326 Gbps • MB-OFDM proposes to use 4-5 bits at 528 MHz Welborn, Freescale & McLaughlin, DecaWave

  19. ADC Relative Complexity & Bounds • Relative complexity (power) • 528 MHz @ 4 bits  0.8x 1326 MHz @ 3 bits • 528 MHz @ 5 bits  1.6x 1326 MHz @ 3 bits • Both approaches can likely scale to lower resolution ADCs with some sacrifice in performance • Research on the lower bounds for ADC resolution indicates that OFDM-UWB will have “error floors” for low ADC resolution (not true for single-carrier UWB) • “Digital Architecture for an Ultra-Wideband Radio Receiver,” Raul Blazquez, Fred S. Lee, David D. Wentzloff, Puneet P. Newaskar, Johnna D. Powell, Anantha P. Chandrakasan, Microsystems Technology Laboratory, Massachusetts Institute of Technology, VTC 2003 Welborn, Freescale & McLaughlin, DecaWave

  20. Topic: Interference Rejection • Comments • Authors of Merged #2 showed heuristic arguments for performance in the presence of narrowband interferers. The selection criteria ask for simulation results. Authors need to do simulations. • I find the DS approach hard to achieve good performance under narrow band interferers. I will change my vote if I get explanation how this approach can function under narrow band interferers Welborn, Freescale & McLaughlin, DecaWave

  21. Topic: Interference • Comments – Fully Resolved • Selection Criteria clearly ask for analysis or simulation results • Detailed analysis shows that DS-UWB provides robust performance against RFI through UWB processing gain • Additional implementation mechanisms available to significantly improve RFI rejection Welborn, Freescale & McLaughlin, DecaWave

  22. Interference Criteria • Interference criteria (03/031r11): • When this interferer is present, using simulation results, analysis, or technical explanations, determine the average received interference power, PI, that can be tolerated by the receiver, after it has executed any interference mitigation algorithms, while still maintaining a PER less than 8% for 1024 byte packets • Minimum criteria: PI - Pd> 3 dB (Pd is the received power which is defined here as 6 dB above the receiver sensitivity level) • Out-of-Band Interference from Intentional or Unintentional Radiators • Proposers should report the minimum out-of-band rejection in dB provided by the proposed system. This will provide a minimum standard for out-of-band interferer immunity Welborn, Freescale & McLaughlin, DecaWave

  23. NarrowBand Interference (NBI)Radio Frequency Interference (RFI)3-Cases Out-of-Band BPF RFI Mild Processing Gain Adequate Moderate LNA does Not saturate Processing Gain inadequate Severe LNA saturates Must Filter DS-UWB 1% (40 MHz) Notch Filter =2% of DS-UWB band No added complexity needed 2% = small impact Welborn, Freescale & McLaughlin, DecaWave

  24. Moderate RFI Moderate LNA does Not saturate Processing Gain inadequate See calculation next page DS-UWB SIR < -3.06 dB MB-OFDM SIR < ? dB Notch Filter Digital RFIExtraction 10+ dB gain Erasure Detection & Erasure decoding (same as turning tone off) LOW COMPLEXITY Only 4 MAC’sper symbolper tone! SIR < -13 dB SIR < -7 dB Welborn, Freescale & McLaughlin, DecaWave

  25. Narrow-Band Interference • DS-UWB receivers with 3-bit ADC architectures • Simulations with no active NBI compensation indicate about 3 dB I-to-S is to be expected • Simple analysis with NO ACTIVE COMPENSATION (worst case): • Required Eb/No is 5.0 dB for rate-½ FEC code • Assume 1.5 dB implementation loss (based on simulation results) • Total noise-per-bit is –87 dBm = -174dBm/Hz + 10log(110MHz) + (6.6 dB NF) • Sensitivity = -87+5+1.5= 80.5 • Sensitivity + 6dB (per spec) = signal power (S) = -74.5 dBm • Allowable (I+N) = -74.5 - 5.0 - 1.5 = -81 dBm (assume I is noise-like at slicer) • Allowable I is therefore 10*log(10^(-81/10)-10^(-87/10)) = -82.24 dBm • At 110 Mbps, processing gain is 12:1 over (I+N) in signal bandwidth  10.8 dB gain (worst case) • Processing gain is a function of tone frequency – depends on pulse shape. At band edges, gain is much higher • Allowable I-to-S is therefore -81.24 + 10.8 -(-74.5) = 3.06 dB I-to-S • Result for high-band operation is 6.0 dB allowable I-to-S • 3 dB better than low band operation because 2x signal bandwidth provides 3 dB more processing gain Welborn, Freescale & McLaughlin, DecaWave

  26. Digital RFI Removal • Real signal and noise from hardware • A/D samples fed into Matlab • 6 bits used to represent basis functions • Data processed in 128 sample blocks After (SNR = 15 dB) Before (SIR = 5 dB) Welborn, Freescale & McLaughlin, DecaWave

  27. Quantized RFI Suppression Performance Vs. Frequency Error Welborn, Freescale & McLaughlin, DecaWave

  28. Spectrum Before Extraction Fd = 114e6 Resolution: Fd/1024 = 111 kHz Welborn, Freescale & McLaughlin, DecaWave

  29. Spectrum After Extraction Fd = 114e6 Resolution: Fd/1024 = 111 kHz Welborn, Freescale & McLaughlin, DecaWave

  30. BACKUP Welborn, Freescale & McLaughlin, DecaWave

  31. Bounds on ADC Resolution • From “Digital Architecture for an Ultra-Wideband Radio Receiver,” Raul Blazquez, Fred S. Lee, David D. Wentzloff, Puneet P. Newaskar, Johnna D. Powell, Anantha P. Chandrakasan, Microsystems Technology Laboratory, Massachusetts Institute of Technology, VTC 2003. Welborn, Freescale & McLaughlin, DecaWave

  32. DS-UWB Avoids the UNII Band • DS-UWB already excludes bands used by most likely high power interferers (UNII bands: WLAN, radars, DSRC, cordless phones, etc Welborn, Freescale & McLaughlin, DecaWave