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UWB-IR Modulation Schemes for WPANs: TG4a Review

This IEEE submission provides information for further investigation and selection of modulation/waveform for UWB Impulse Radio in Wireless Personal Area Networks (WPANs).

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UWB-IR Modulation Schemes for WPANs: TG4a Review

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: TG4a Review of proposed UWB-IR Modulation schemes Date Submitted: 21 April 2005 Source: Philip Orlik, Andy Molisch (Mitsubishi Electric), Gian Mario Maggio (STMicroelectronics), Ian Opperman (University of Oulu) Contact: Philip Orlik Voice: +1 617 621 7570, E-Mail: porlik@merl.com Abstract: Yet another UWB waveform Purpose: To provide information for further investigation on and selection of the modulation /waveform for UWB Impulse Radio (low bit rate plus ranging) 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. P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  2. IEEE 802.15.4a PHY:UWB-IR Modulation for multiple receiver types Many slides stolen from 15-05-0217-00-004a P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  3. 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 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  4. Waveform Design (1/2) • Combination of BPPM with BPSK • Guarantee coexistence of coherent and non-coherent receiver architectures: • Non-coherent receivers just look for energy in the early or late slots to decode the bit (BPPM) • Coherent and differentially-coherent receivers, in addition, understand the fine structure of the signal (BPSK or DBPSK) • Principle: Non-coherent and differentially-coherent modes should not penalize coherent RX performance P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  5. Waveform Design (2/2) • Two possible realizations: 1) The whole symbol (consisting of Nf frames) is BPPM-modulated 2) Apply 2-ary time hopping code, so that each frame has BPPM according to TH code • Coexistence coherent/non-coherent RX: - Special encoding and waveform shaping within each frame - Use of doublets with memory from previous bit (encoding of reference pulse with previous bit) - Proposed 20ns separation between pulses - Extensible to higher order TR for either reducing the penalty in transmitting the reference pulse or increasing the bit rate (see: 15-05-0217-00-004a for detail) - Also possible the use of multi-doublets (see 15-05-0217-00-004a) P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  6. 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 Impulse Radio Modulation Scheme Coherent Receiver Hybrid Transmitter Differentially Coherent Receiver Non-Coherent Receiver P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  7. Pros/Cons of RX Architectures Coherent + : Sensitivity + : Use of polarity to carry data + : Optimal processing gain achievable - : Complexity of channel estimation and RAKE receiver - : Longer acquisition time 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 Non-coherent + : Low complexity + : Acquisition speed - : Sensitivity, robustness to SOP and interferers P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  8. Design Parameters • Pulse Repetition Period (PRP) • Proposed range between 40ns (first realization) and 125ns (second realization) • Channelization (In addition to FDM) • Coherent schemes: Use of TH codes and polarity codes • Non-coherent schemes: Use of TH codes (polarity codes for spectrum smoothing only) • TH code length • Variable TH code length; proposed range: 8-16 • TH code: Binary position, bi-phase Note: For first realization, higher-order TH with shorter chip duration (multiples of 2ns) may be used P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  9. 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 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  10. Example Signal Waveforms for data modulation (1) bi-1 = 1, bi = 1 bi-1 = 0, bi = 1 bi-1 = 1, bi = 0 bi-1 = 0, bi = 0 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  11. Ts Example Signal Waveforms for data modulation (2) « 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 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  12. Ts « 11 » 2-PPM + TR base M = 2 (with two bits/symbol) « 01 » « 10 » « 00 » Example Signal Waveforms for data modulation (3) 2-PPM + 16 chips 2-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 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  13. 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 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  14. 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 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  15. ‘Uncoded’ AWGN Performance 1.5 dB P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  16. ‘Uncoded’ CM8 Performance 1 dB P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  17. Advantages • Coherent RX gets additional benefit from coding inherent in the modulation • Waveform permits polarity scrambling to reduce required back-off • A single waveform for all receiver types P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  18. Coherent view of Hybrid Modulation • Symbols consist of sequences of doublets that have 4 possible forms bi-1 = 1, bi = 1 bi-1 = 0, bi = 1 bi-1 = 1, bi = 0 bi-1 = 0, bi = 0 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  19. Basis functions • Symbols can be decomposed using several equivalent orthogonal basis functions (2-D) ( ) ( ) _ _ , , [1, 0] [1/2, 1/2] [-1, 0] [-1/2, -1/2] [0, 1] [1/2, -1/2] [0, -1] [-1/2, 1/2] P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  20. Matched Filter Outputs (basis 1) Template signals constructed from these 2 basis functions Barker 13 applied to TR doublets bi-1 = 1, bi = 1 bi-1 = 0, bi = 1 bi-1 = 1, bi = 0 bi-1 = 0, bi = 0 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  21. Matched Filter Outputs (basis 2) Template signals constructed from these 2 basis functions Barker 13 applied to doublets _ _ bi-1 = 1, bi = 1 bi-1 = 0, bi = 1 bi-1 = 1, bi = 0 bi-1 = 0, bi = 0 P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  22. Ranging Implications • So what does this mean for ranging? • Really nothing • If we want to transmit a barker sequence (or something else) we can still use our receiver to “look” for the ranging symbol • Basically we can use as a basis and view the compression code as a polarity code applied to the reference pulse and data pulse independently. • Barker 13 = [1 1 1 1 1 -1 -1 1 1 -1 1 -1 1] • Reference code = [1 1 1 -1 1 1 1 ] • Data code = [1 1 -1 1 -1 -1 ] ( ) _ _ , P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

  23. Barker 13 transmission Correlator output Tx waveform P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

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