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Review of Proposed UWB-PHY Modulation Schemes and Selection Criteria

This document provides a review of various modulation/waveform options for the UWB-PHY standard and proposes selection criteria for further investigation and selection.

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Review of Proposed UWB-PHY Modulation Schemes and Selection Criteria

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: TG4a Review of Proposed UWB-PHY Modulation Schemes and Selection Criteria Date Submitted: June 30th, 2005 Source: Gian Mario Maggio & Philippe Rouzet (STMicroelectronics) Contact: Gian Mario Maggio Voice: +41-22-929-6917, E-Mail: gian-mario.maggio@st.com Abstract: Review of modulations/waveforms for TG4a UWB-PHY standard and proposed selection criteria Purpose: To provide information for further investigation on and selection of the modulation/waveforms for the UWB-PHY 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. Gian Mario Maggio & Philippe Rouzet (STM)

  2. IEEE 802.15.4a:UWB-PHY Modulation UWB-PHY Modulation Subgroup Gian Mario Maggio & Philippe Rouzet Gian Mario Maggio & Philippe Rouzet (STM)

  3. List of Contributors/Documents • Gian Mario Maggio & Philippe Rouzet - STMicroelectronics (#15-05-0217-00-004a, #15-05-0243-00-004a, #15-05-0325-00-004a) • Laurent Ouvry et al. – CEA-LETI (#15-05-0354-01-004a) • Michael Mc Laughlin – Decawawe (#15-05-0359-00-004a) • Matt Welborn – Freescale (#15-05-0240-02-004a) • Francois Chin et al. – I2R (#15-05-0231-03-004a) • Huang-Ban Li et al. – NICT (#15-05-0300-00-004a) • Ismail Lakkis & Saeid Safavi – Wideband Access (#15-05-0250-03-004a, #15-05-0355-00-004a) • Phil Orlik, Andy Molisch et al. - MERL (#15-05-0291-00-004a) Gian Mario Maggio & Philippe Rouzet (STM)

  4. Topics for Discussion • Pulse shaping • Modulation formats • Waveform design • Design parameters • Adaptive modulation & coding • Selection Criteria • Receiver Architecture • Simulation Results ACTION LIST UWB-PHY GROUP Gian Mario Maggio & Philippe Rouzet (STM)

  5. UWB-PHY: Introduction • Impulse-radio based (pulse-shape independent) • Support for different RX architectures: • Coherent • Differentially-coherent • Non-coherent • Support for multiple rates • Support for SOP Gian Mario Maggio & Philippe Rouzet (STM)

  6. Gian Mario Maggio & Philippe Rouzet (STM)

  7. One Pulse PULSE: shortest waveform One Chip Illustration of Pulse and Chip Definitions CHIP: closest allowable distance between successive pulses Gian Mario Maggio & Philippe Rouzet (STM)

  8. Symbol Duration Burst Duration Pulse Duration Pulse Burst (1 or more pulses) Symbol (1 or more bursts) Signal in time domain Pulse Repetition Interval (PRI, assuming one burst per symbol) 3 dB BW Inverse Relation PRF Effective Pulse Duration Chip Duration -3 dB -10 dB -20 dB -30 dB Spectrum -40 dB -50 dB -60 dB Inverse Relation -70 dB 10 dB BW Gian Mario Maggio & Philippe Rouzet (STM)

  9. Pulse Shaping Pulse shape: a) Gaussian b) Raised cosine c) Chaotic d) Chirp …. • Optional: Variable pulse shapes with SSA (Soft Spectrum Adaptation) Pulse duration: Lower bound set by bandwidth occupation (e.g. 500 MHz); Upper bound may be set according to design considerations Pulse amplitude: Peak-to-peak voltage limited by CMOS technology Gian Mario Maggio & Philippe Rouzet (STM)

  10. Definitions • Coherent RX: The phase of the received carrier waveform is known, and utilized for demodulation • Differentially-coherent RX: The carrier phase of the previous signaling interval is used as phase reference for demodulation • Non-coherent RX: The phase information (e.g. pulse polarity) is unknown at the receiver - operates as an energy collector - or as an amplitude detector Gian Mario Maggio & Philippe Rouzet (STM)

  11. Pros/Cons of RX Architectures Coherent + : Sensitivity + : Use of polarity to carry data + : Optimal processing gain achievable - : Complexity of channel estimation and RAKE receiver Differentially-Coherent (or using Transmitted Reference) + : Gives a reference for faster channel estimation (coherent approach) + : No channel estimation (non-coherent approach) - : Asymptotic loss of 3dB for transmitted reference (not for DPSK) Non-coherent + : Low complexity + : Acquisition speed - : Sensitivity, robustness to SOP and interferers Gian Mario Maggio & Philippe Rouzet (STM)

  12. Modulation Format(s) • Simple, scalable modulation format • One mandatory mode plus one or more optional modulation modes • Modulation compatible with multiple coherent/non-coherent receiver schemes  Flexibility for system designer • Time hopping (TH) for spectral smoothing and to permit multiple access Gian Mario Maggio & Philippe Rouzet (STM)

  13. Time Hopping-IR: Basics +1 Tc Tf Ts -1 • Each symbol represented by sequence of very short pulses • Each user uses different PN sequences (for multiple access) • Spectrum mostly determined by pulse shape Gian Mario Maggio & Philippe Rouzet (STM)

  14. Waveform Design • Combination of (outer) TH and BPPM, combined with BPSK/DBPSK • Guarantee coexistence of coherent and non-coherent RX architectures: • Non-coherent receivers just look for energy in the early or late slots to decode the bit (BPPM); OOK receiver may be used to demodulate BPPM symbol as well • Coherent and differentially-coherent receivers, in addition, understand the fine symbol structure (BPSK or DBPSK) • Principle: Non-coherent and differentially-coherent modes should not penalize coherent-RX performance Gian Mario Maggio & Philippe Rouzet (STM)

  15. Rake Receiver Finger 1 BPSK symbol mapper Delay Pulse Gen. TH Seq Multiplexer Rake Receiver Finger 2 Summer BPSK symbol mapper Rake Receiver Finger Np Central Timing Control Td ( )2 RX Coexistence Coherent RX TX Differentially-Coherent RX Non-Coherent RX Gian Mario Maggio & Philippe Rouzet (STM)

  16. Mitigation of Peak-Voltage through Multi-Pulses Tf=PPI ppV = peak-to-peak voltage M = 1 IS « EQUIVALENT » TO Tf=PPI M = 4 ppV/2 Tf=PPI M = 2 ppV/sqrt(2) Gian Mario Maggio & Philippe Rouzet (STM)

  17. BPPM Symbol Structure • Doublet-based symbol Realization 1a: TH-IR + TR (the whole TR symbol is BPPM modulated) Realization 2a: TR + Inner TH (apply TH code to each frame) Realization 3a: Diff. encoding + Inner TH (doublets with memory from previous bit) • Burst-based symbol Realization 2a: Generalized TR (one reference pulse, multiple information pulses) Realization 2b: “CDMA-like” burst (burst of pulses, modulated by a spreading code) Gian Mario Maggio & Philippe Rouzet (STM)

  18. data Td +1 Tc Tf reference Ts -1 (1) Transmitted-Reference: Basics • First pulse serves as template for estimating channel distortions • Second pulse carries information • Drawback: Waste of 3dB energy on reference pulses Gian Mario Maggio & Philippe Rouzet (STM)

  19. Ts « 11 » 2-PPM + TR base M = 2 (with two bits/symbol) « 01 » « 10 » « 00 » (1a) Example - Signal Waveforms (coherent decoding possible) 2-PPM + 16 chips 2-ary TH code • Time hopping code is (2,2) code of length 8/16, can be exploited by non-coherent RX • Effectively, 28 or 216 codes to select for channelization for non-coherent scheme Gian Mario Maggio & Philippe Rouzet (STM)

  20. Ts Outer time hop of Tc = Tf/2 = n*Th Tf Same polarity : bit = 0 Same polarity : bit = 0 « 0 » Th Inner time hop of Tdelta = 2 Th Tdelay Td Tc negative positive (1a) Detailed Symbol Structure Gian Mario Maggio & Philippe Rouzet (STM)

  21. Ts (1b) Example - Signal Waveforms « 11 » 2-PPM + TR base M = 2 One bit/symbol « 01 » « 10 » « 00 » 2-PPM + 16 chips 2-ary TH code or 2-PPM + 8 chips 4-ary TH code (coherent decoding possible) • Time hopping code is (2,2) code of length 8/16, can be exploited by non-coherent RX • Effectively, 28 or 216 codes to select for channelization for non-coherent scheme Gian Mario Maggio & Philippe Rouzet (STM)

  22. negative positive (1b) Detailed Symbol Structure Ts Outer time hop of Tc = Tf/2 = n*Th Tf Same polarity : bit = 0 Same polarity : bit = 0 « 0 » Th Inner time hop of Tdelta = 2 Th + inner polarity hop Td Tdelay Tx Tx Tc Gian Mario Maggio & Philippe Rouzet (STM)

  23. (1c) Differential Encoding: Basics b0 b2 b4 b3 b1 b5 b-1 Tx Bits 0 0 1 1 0 0 1 Reference Polarity -1 -1 +1 +1 -1 -1 +1 -1 +1 -1 +1 -1 Ts Gian Mario Maggio & Philippe Rouzet (STM)

  24. bi-1 = 1, bi = 1 bi-1 = 0, bi = 1 bi-1 = 1, bi = 0 bi-1 = 0, bi = 0 (1c) Example - Signal Waveforms • Use of doublets with memory from previous bit (encoding of reference pulse with previous bit) Gian Mario Maggio & Philippe Rouzet (STM)

  25. τdelay +τΔ D D D « 1 » Basic Mode (as seen by non-coherent) τdelay +τΔ D D D « 1 1 » Enhanced Mode « 1 0 » Pulse Shift, polarity invert τΔ + τdelay τΔ τΔ τdelay τdelay τΔ + τdelay τΔ + τdelay τΔ + τdelay (2a) Generalized TR TH Pattern TH Code 1,1 1,1 0,1 0,0 1,0 0,1 Data 1,1 1,1 1,1 1,1 1,1 0,0 Gian Mario Maggio & Philippe Rouzet (STM)

  26. (2b) “CDMA-Like” Burst Similar signal using 31-pulse sequence Can use coherent or non-coherent receiver Can use PPM/OOK by sending pulse burst in Either first or second bit location One BPPM symbol Gian Mario Maggio & Philippe Rouzet (STM)

  27. (2b) Example 1: 31-Chip Code • Can support both coherent and non-coherent pulse compression • Add 33 zero chips to get baseline mode for non-coherent receivers • Note: In general, careful code design is needed for spectral shaping Gian Mario Maggio & Philippe Rouzet (STM)

  28. (2b) Example 2: Spreading via Scrambling • Scrambling = time varying spreading • Use a single (set) scrambler of length (ex: 32768) and assign a different offset (of 16 or 32) to different nodes • For ternary modulation invert sequence when transmitting a 0 • Number of users supported is 1024 • Perfect co-channel interference rejection • Support virtually any data rate from 16MHz to 32 Kbps for a PRF of 16MHz • Spectrum is virtually flat (no back-off) Gian Mario Maggio & Philippe Rouzet (STM)

  29. (2b) Example 2: Ternary Modulator Gian Mario Maggio & Philippe Rouzet (STM)

  30. (2b) Example 2: Ternary Receiver 1b ADC : requires threshold training during preamble 3b ADC : does not requires thresholding (soft correlator) Gian Mario Maggio & Philippe Rouzet (STM)

  31. (2b) Example 2: BPSK Modulator/Receiver • ADC from 1 bit to multiple bits • BPSK correlator • Time varying spreading improves interference rejection tremendeously Gian Mario Maggio & Philippe Rouzet (STM)

  32. Design Parameters (1/3) • Pulse Repetition Period (PRP) • Realization #1: 1a) PRP = 100 ns 1b) PRP = 40 ns 1c) PRP = 40 ns • Burst Repetition Period (BRP) • Realization #2: 2a) BRP ≥ 200 ns 2b) BRP = 436 ns • Inter-pulse interval: • Minimum: ~5 ns (technology constraint) • Realization #1: ~20 ns • Realization #2(b): ~4.5 ns Note (TR): Max realizable analog delay ~10 ns Gian Mario Maggio & Philippe Rouzet (STM)

  33. Design Parameters (2/3) • Time-hopping: • TH code (outer): 2-ary (or M-ary in general, for better SOP support) of length 4-16; granularity level ~Tf/2 (or Tf/M) • Inner TH code (Realization #1b,c): Apply inner TH code (frame-by-frame) down to 2 ns (or multiples) granularity level • Polarity hopping: May be applied on top, for spectral smoothing purposes and/or signals separation Gian Mario Maggio & Philippe Rouzet (STM)

  34. Design Parameters (3/3) • Channelization • Coherent schemes: Use of TH codes and polarity codes • Non-coherent schemes: Use of TH codes (polarity codes for spectrum smoothing only) • Realization 2b): CDMA • Multi-access capabilities: • Max # of coexisting users within piconet • SOP support: • Up to 6 SOP/band Gian Mario Maggio & Philippe Rouzet (STM)

  35. Adaptive Modulation & Coding • Adaptive modulation: Enhanced modes (available for coherent receiver) • Adaptive PRP: Two PRP values supported • Adaptive processing gain: Variable TH code length (variable number of pulses/bit) • Adaptive coding rate (e.g. by acting on the puncturing associated with a convolutional code) Gian Mario Maggio & Philippe Rouzet (STM)

  36. Optional: Encoding of “Extra”-Bits • Example: Rate-½ convolutional encoder • Produce multiple coded bits from each data bit • Special case of convolutional code is a “systematic” code • First coded bit is same as input data bit • Second coded bit is computed by encoder • Mapping coded bits to waveform • Map first coded bit (systematic bit) into position for BPPM • Map second coded bit into TR symbol • Can be extended to more general (non-systematic) codes very easily x1=bk Convolutional Encoder bk x2 Gian Mario Maggio & Philippe Rouzet (STM)

  37. (3) CS-UWB • Chirp Signaling-UWB can be generated by passing a pulsesignal through a distributed delay line (DDL) such as a SAW DDL: Frequency Time DDL Amplitude Amplitude Time Pulse signal Frequency Gian Mario Maggio & Philippe Rouzet (STM)

  38. (3) Correlated Processing • Correlated processing produces not only high precision ranging but also robustness against noise and multipath Correlated processing Correlator output B: 3-dB bandwidth of chirp T: time interval of chirp Time shift[s] The wide the bandwidth, the sharp the peak. Gian Mario Maggio & Philippe Rouzet (STM)

  39. (3) Advantages of Chirp Signaling • High capacity for SOP • Plenty of source with chirp • Combination with FDM and/or CDM • Additional link margins • Low peak-to-average ratio • Robustness against interference and multipath • Excellent correlation characteristics • Potential high precision ranging. • Excellent correlation characteristics • An selectivity for FFD and RFD • Chirp vs. non-chirp Gian Mario Maggio & Philippe Rouzet (STM)

  40. Proposed Selection Criteria (in decreasing priority order) • PER (packet error rate) performance @1Mb/s with 15.4a channel models, CMOS-compatible peak-to-peak voltage, rate ½ convolutional code (constraint length up to 5; more needs justification): 1.a) Coherent receiver 1.b) Diff. coherent receiver 1.c) Non-coherent receiver • SOP isolation (at least 2 SOP/band; up to 6 SOP) • Spectrum: SPAR (spectral peak-to-average ratio) • Receiver flexibility: Support for coherent, diff. coherent and non-coherent RX • Scalability: Trade-off performance vs. complexity • Resilience to NBI (narrow-band interference) Gian Mario Maggio & Philippe Rouzet (STM)

  41. ANNEX (Extra-Slides: Support for Discussion) Gian Mario Maggio & Philippe Rouzet (STM)

  42. Coherent Receiver: RAKE Receiver Channel Estimation Rake Receiver Finger 1 Rake Receiver Finger 2 Sequence Detector Demultiplexer Convolutional Decoder Summer Data Sink Rake Receiver Finger Np • Addition of Sequence Detector – Proposed modulation may be viewed as having memory of length 2 • Main component of Rake finger: pulse generator • A/D converter: 3-bit, operating at symbol rate • No adjustable delay elements required Gian Mario Maggio & Philippe Rouzet (STM)

  43. Differentially-Coherent Receiver(for Transmitted Reference) Matched Filter Convolutional Decoder Td • Note: Addition of Matched Filter prior to Delay & Correlation operations improves output SNR and reduces noise-noise cross terms Gian Mario Maggio & Philippe Rouzet (STM)

  44. BPPM Demodulation branch Controlled Integrator Band Matched r(t) LNA Dump Latch x2 RAZ ADC RAZ DUMP BPF Tracking Thresholds setting Non-Coherent Receiver (Energy Collector) Gian Mario Maggio & Philippe Rouzet (STM)

  45. Band Matched Band Matched ADC ADC BPF BPF De-Spreading TH Codes TH Sequence Matched Filter r(t) Bit Demodulation LNA Case I - Coherent TH de-spreading TH Sequence Matched Filter b(t) soft info Bit Demodulation r(t) LNA Case II – Non-coherent / differential TH despreading Gian Mario Maggio & Philippe Rouzet (STM)

  46. “0” r(t) Non-Coherent Detector (Energy Collection) “0” Pulse Matched D f(t) s(t) LNA BPF - Synchro Tracking Thresholds setting “1” Delay D “1” TR-BPSK  Non-Coherent Detection • Idea: Transmitted-reference BPSK symbol can be decoded by a non-coherent detector (like OOK symbol) • Advantages: Differential and non-coherent receiver may coexist • Concept can be generalized to N-ary TR-BPSK Gian Mario Maggio & Philippe Rouzet (STM)

  47. TR-BPPM Schemes Comparison (1/2) Notes: • Results are theoretical calculations • Assumes ideal ”impulse” UWB pulses in AWGN channel • Different TR-BBPM options are considered with different number of pulses per pulse train • Multipath fading simulations can be performed to back up theory Gian Mario Maggio & Philippe Rouzet (STM)

  48. TR-BPPM Schemes Comparison (2/2) • Parameters: • PPI slot - slot inside each TH chip containing a burst of pulses including reference pulses • Np represents the number of pulses in each PPI slot • The energy E per PPI slot is kept constant • The pulse energy Ep = E/Np • TW represent the time-bandwidth product Gian Mario Maggio & Philippe Rouzet (STM)

  49. Pulse Repetition Structures- Scheme 1TR-BPPM with doublets Gian Mario Maggio & Philippe Rouzet (STM)

  50. Pulse Repetition Structures - Scheme 2TR-BPPM single reference Gian Mario Maggio & Philippe Rouzet (STM)

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