Merged UWB Proposal for IEEE 802.15.4a Alt-PHY

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Merged UWB proposal for IEEE 802.15.4a Alt-PHY] Date Submitted: [14 Mar 2005] Source: [(1) Andy Molisch, (2) Francois Chin] Company: [(1) MERL, 201 Broadway, Boston, USA, (2)Institute for Infocomm Research, Singapore] Voice: [(1) +1 617 621 7500, (2) +65-68745687] E-Mail: [(1) molisch@merl.com (2) chinfrancois@i2r.a-star.edu.sg] Re: [Response to the call for proposal of IEEE 802.15.4a, Doc Number: 15-04-0380-02-004a ] Abstract: [Merged Proposal to IEEE 802.15.4a Task Group] Purpose: [For presentation and consideration by the IEEE802.15.4a committee] 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. Authors Institute for Infocomm Research: Francois Chin, Xiaoming Peng, Sam Kwok, Zhongding Lei, Kannan, Yong-Huat Chew, Chin-Choy Chai, Rahim, Manjeet, T.T. Tjhung, Hongyi Fu, Tung-Chong Wong General Atomics: Naiel Askar, Susan Lin Thales & Cellonics: Serge Hethuin, Isabelle Bucaille, Arnaud Tonnerre, Fabrice Legrand, Joe Jurianto KERI & SSU & KWU: Kwan-Ho Kim, Sungsoo Choi, Youngjin Park, Hui-Myoung Oh, Yoan Shin, Won cheol Lee, and Ho-In Jeon Create-Net & China UWB Forum: Zheng Zhou, Frank Zheng, Honggang Zhang, Xiaofei Zhou, Iacopo Carreras, Sandro Pera, Imrich Chlamtac Staccato Communications: Roberto Aiello, Torbjorn Larsson Wisair: Gadi Shor, Sorin Goldenberg

3. Authors CWC: Ian Oppermann, Alberto Rabbachin AetherWire: Mark Jamtgaard, Patrick Houghton CEA-LETI: Laurent Ouvry, Samuel Dubouloz, Sébastien de Rivaz, Benoit Denis, Michael Pelissier, Manuel Pezzin et al. STMicroelectronics: Gian Mario Maggio, Chiara Cattaneo, Philippe Rouzet & al. MERL: Andreas F. Molisch, Philip Orlik, Zafer Sahinoglu Harris: Rick Roberts Time Domain: Vern Brethour, Adrian Jennings French Telecom R&D: Patricia Martigne, Benoit Miscopein, Jean Schwoerer

4. Proposal Main Features • Impulse-radio based (pulse-shape independent) • Support for different receiver architectures (coherent/non-coherent) • Flexible modulation format • Support for multiple rates • Enables accurate ranging/positioning • Support for multiple SOP

5. Motivation: • Supports homogenous and heterogeneous network architectures • Different classes of nodes, with different reliability requirements (and cost) must inter-work

6. UWB Technology • Impulse-Radio (IR) based: • Very short pulses  Reduced ISI • Robustness against fading • Episodic transmission (for LDR) allowing long sleep-mode periods and energy saving • Low-complexity implementation

7. Modulation Features • Simple, scalable modulation format • Flexibility for system designer • Modulation compatible with multiple coherent/non-coherent receiver schemes

8. Types of Receivers Supported • Coherent Detection: The phase of the received carrier waveform is known, and utilized for demodulation • Differential Chip Detection: The carrier phase of the previous signaling interval is used as phase reference for demodulation • Non-coherent Detection: The carrier phase information (e.g.pulse polarity) is unknown at the receiver

9. Pros (+) and 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 Differential (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

10. Overview • Basic waveform that simultaneously supports demodulation by either coherent or non-coherent receiver • Non-coherent receiver can use either 2-PPM or OOK demodulation • Coherent receiver can also resolved phase of pulse and benefits from additional coding gain • Differential / Transmit reference (TR) receiver can get information form phase difference between data pulse and reference pulse • Main idea: • Common preamble signaling for different classes of nodes / type of receivers (coherent / differential / non-coherent)

11. Example System Parameters ** To be determined

12. Multiple access Multiple access within piconet: TDMA+CSMA/CA same as 15.4 Multiple access across piconets: CDM + FDM Different Piconet uses different Base Sequence & different 500 MHz band

13. Realization #1

14. System Description • Each piconet uses one set of code sequences for different classes of nodes / type of receivers (coherent / differential / non-coherent receivers) • 16 Orthogonal Sequences of code length 32 to represent a 4-bit symbol • PRF (chip rate): 24 MHz (TBD) • Low enough to avoid significant interchip interference (ICI) with all 802.15.4a multipath models • High enough to ensure low pulse peak power • FEC: optional (or low complexity type)

15. Criteria of Code Sequence Design • The sequence Set should have orthogonal (or near orthogonal) cross correlation properties to minimise symbol decision error for all the below receivers • For coherent receiver • For differential chip receiver • For transmitted reference receiver • For non-coherent symbol detection receiver • Energy detection receiver • Each sequence should have good auto-correlation properties

16. Base Sequence Set • 31-chip Ternary Sequence set are chosen • Only one sequence and one fixed band (no hopping) will be used by all devices in a piconet • Logical channels for support of multiple piconets • 6 sequences = 6 logical channels (e.g. overlapping piconets) for each FDM Band • The same base sequence will be used to construct the symbol-to-chip mapping table

17. Symbol-to-Chip Mapping: Gray coded 16-ary Ternary Orthogonal Keying To obtain 32-chip per symbol, cyclic shift the Base Sequence first, then append a ‘0’-chip in front Base Sequence #1

18. Modulation & Coding (Mode 1) Binary data From PPDU Symbol- to-Chip Bit-to- Symbol Symbol Repetition Pulse Generator Mode 1- common signaling for all receivers (e.g. Beacon) Bit to symbol mapping: group every 4 bits into a symbol Symbol-to-chip mapping: Each 4-bit symbol is mapped to one of 16 32-chip sequence, according to 16-ary Ternary Orthogonal Keying Symbol Repetition: for data rate and range scalability Pulse Genarator: • Transmit Ternary pulses at PRF = 24MHz (TBD) {0,1,-1} Ternary Sequence

19. Modulation & Coding (Mode 2) Binary data From PPDU Symbol- to-Chip Pulse Generator Bit-to- Symbol Symbol Repetition Ternary- Binary Mode 2 – for enhanced performance when receiver types are known (except for energy detector) Bit to symbol mapping: group every 4 bits into a symbol Symbol-to-chip mapping: Each 4-bit symbol is mapped to one of 16 32-chip sequence, according to 16-ary Ternary Orthogonal Keying Symbol Repetition: for data rate and range scalability Ternary to Binary conversion: (-1/+1 → 1,0 → -1) Pulse Genarator: • Transmit bipolar pulses at PRF = 24MHz (TBD) {1,-1} Binary Sequence {0,1,-1} Ternary Sequence

20. Code Sequence Properties & Performance • AWGN Performance • Multipath Performance (in Appendix) • For Coherent Symbol Detector • For Non-coherent Symbol Detector • For Differential Chip Detector • For Energy Detector

21. AWGN Performance AWGN performance @ 1% PER

22. Summary The proposed system: • Impulse-radio based system coupled with a Common ternary signaling allows operation among different classes of nodes / type of receivers, with varying cost / power / performance trade-off • Is robust against multipath and SOP interference

23. Realization #2

24. Non-Coherent and Coherent Demodulation X1 = 0, X2 = 0 X1 = 1, X2 = 0 X1 = 1, X2 = 1 X1 = 0, X2 = 1 • Non-coherent receiver only sees position • Demodulates only x1 • No Viterbi decoding required (easy since x1=bk) • Achieves no coding gain, assumes bk = x1  Done. • Coherent receiver demodulates position and phase • Decodes x1 & x2 • Viterbi decoding used to estimate original bit, bk • Achieves coding gain of original rate ½ code

25. 4-BOK (coherent) constellation 2-PPM constellation 2-PPM constellation OOK constellation Non-coherent receiver cannot see these • Encoding two coded bits requires a 4-point signal constellation • Each axis represents one of two possible positions (orthogonal axes) • Phase of pulse determines sign of constellation point on axis  4-BOK • Non-coherent receiver is insensitive to phase – see only two points in constellation  2-PPM • Support for OOK receiver is possible by demodulating only one of the two dimensions (i.e. just look at first position: pulse or not?)

26. Transmitted Reference (TR) • TR schemes simplify the channel estimation process • Reference waveform available for synchronisation • Potentially more robust (than non-coherent) under SOP operation • Supports both coherent/differentially-coherent demodulation • Multiple pulses can be used to increase throughput • Implementation challenges: • Analogue: Implementing delay value, • delay mismatch, jitter

27. Differential Encoding of Bits 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

28. Multiple access • On top of this modulation scheme: • Polarity hopping: repeat data at regular intervals, but encoded with polarity sequence that is unique for piconet • Alternatives: • Time hopping • Ternary encoding sequence • Note that PPM can be applied on a “per pulse” basis or a “per symbol” basis (see 05-0130 and Backup slides)

29. Positive pulse Negative pulse Symbol Format (1st realization) Td Tc Tf Ts • Non-coherent receiver sees energy in one of the two halves • Differentially coherent receiver sees phase differences • Coherent receiver sees symbols drawn from 2-D signal space:

30. Bandwidth Usage • Flexible use of (multi-)bands • Signal bandwidth may be 500 MHz to 2 GHz • Bandwidth may change depending on application and regulatory environment • Use of polarity randomization for spectral smoothing • Different bandwidth use options being considered

31. Band Plan

32. Option: Linear Pulse Combination • Spectral shaping by linear combination of delayed, weighted pulses • Adaptive determination of weight and delay • Number of pulses and delay range restricted • Can adjust to interferers at different distances (required nulldepth) and frequencies • Weight/delay adaptation in two-step procedure • Initialization as solution to quadratic optimization problem (closed-form) • Refinement by back-propagating neural network • Matched filter at receiver good spectrum helps coexistence and interference suppression

33. Spectral Shaping & Polarity Scrambling Td = 10 ns Td = 20 ns W/O Polarity Scrambling W/ Polarity Scrambling

34. Adaptive Frame Duration • Advantage of large number of pulses per symbol: • Smaller peak-to-average ratio • Increased possible number of SOPs • Disadvantage: • Increased inter-frame interference • In TR: also increased interference from reference pulse to data pulse • Solution: adaptive frame duration • Feed back delay spread and interference to transmitter • Depending on those parameters, TX chooses frame duration

35. Ranging

36. Ranging • Motivation : • Benefit from high time resolution (thanks to signal bandwidth): • Theoretically: 2GHz provides less than 20cm resolution • Practically: Impairments, low cost/complexity devices should support ~50cm accuracy with simple detection strategies (better with high resolution techniques) • Approach : • Use Two Way Ranging between 2 devices with no network constraint (preferred); no need for time synchronization among nodes • Use One Way Ranging and TDOA under some network constraints (if supported) Asynchronous Ranging TOF : Time Of Flight RTT : Round Trip Time SHR : Synchronization Header

37. TOA Delay Estimation - Non-Coherent • Use bank of integrators to determine coarse synchronisation “uncertainty” region • Symbol synchronisation “uncertainty” region given by coarse synchronisation ( e.g., 4ns-20ns) • A refinement search is applied onto the uncertainty region by either • further dividing it into narrower non overlapping regions for non-coherent refinement (e.g., 1ns –> 4ns) or • Coherent search with a template correlation Integrator outputs Detects the coarse “uncertainty region” Energy Analyzer Performed within the selected uncertainty region Leading Edge Search Refinement TRB: the length of uncertainty region Range info

38. TOA Delay Estimation - Non-Coherent (cont’d) • The algorithm selects the maximum value integration window index and then it searches backward to find the first integration value which crosses an adaptively set threshold. • If there are no values crossing the threshold, the peak position is used for the TOA estimation. MES-SB based TOA Estimate Searchback window Strongest Path, energy block Threshold based TOA Estimate Threshold N 2 1 0 Actual TOA Contains leading edge MES: Maximum Energy Search TC: Threshold comparison SB: Search Back MES based TOA Estimate

39. Features- Sequential two-way ranging is executed via relay transmissions- PAN coordinator manages the overall schedule for positioning- Inactive mode processing is required along the positioning- PAN coordinator may transfer all sorts of information such as observed - TDOAs to a processing unit (PU) for position calculationBenefits- It does not need pre-synchronization among the devices- Positioning in mobile environmentis partly accomplished Proposed Positioning Scheme P_FFD3 P_FFD2 TOA 24 TOA 34 RFD PAN coordinator TOA 14 PU P_FFD : Positioning Full Function Device RFD : Reduced Function Device P_FFD1

40. Process of Proposed Positioning Scheme TOA measurement

41. RTT12 = T + 2T12 RTT23 = T + 2T23 RTT13 = T12 + 2T + T23 + T13 More Details for obtaining TDOAs • Distances among the positioning FFDs are calculated from RTT measurements and known time interval T • Using observed RTT measurements and calculated distances, TOAs/TDOAs are updated T12 = (RTT12 – T)/2 T23 = (RTT23 – T)/2 T13 = (RTT13 – T12 – T23 – 2T) RTT34 = T34 + T + T34 TOA34 = (RTT34 - T)/2 RTT24 = T23 + T + T34 + T + T24 TOA24 = (RTT24 - T23 - TOA34 - 2T) TOA14 = (RTT14 - T12 - T23 - TOA34 - 3T) RTT14 = T12 + T + T23 + T + T34 + T + T14 TDOA12 = TOA14 – TOA24 TDOA23 = TOA24 – TOA34

42. Position Calculation using TDOAs • The range difference measurement defines a hyperboloid of constant range difference • When multiple range difference measurements are obtained, producing multiple hyperboloids, the position location of the device is at the intersection among the hyperboloids

43. Conclusions • Proposal based upon UWB impulse radio • High time resolution suitable for precise ranging using TOA • Modulation: • Pulse-shape independent • Robust under SOP operation • Facilitates synchronization/tracking • Supports multiple coherent/non-coherent RX architectures • System tradeoffs • Modulation optimized for several aspects (requirements, performances, flexibility, technology) • Trade-off complexity/performance RX • Flexible implementation of the receiver • Coherent, differential, non-coherent (energy collection) • Analogue, digital • Fits with multiple technologies • Easy implementation in CMOS • Very low power solution (technology, architecture, system level)

44. Backup slides

45. Preamble (32 bits) SFD (8 bits) LEN (8 bits) MHR+MSDU (240 bits) CRC (16 bits) PER in 15.4a Channel Model Non-Coherent (Energy Collection) BPPM Framing format: • Simulations over 1000 channel responses • BW = 2GHz – Integration Time = 80ns • Implementation loss + Noise figure margin : 11 dB • Max range is determined from: • Required Eb/N0, • Implementation margin • Path loss characteristics Case I: 250 kbps – PRP 250 ns with 16 pre-integrations = 4 µs Case II: 250 kbps – PRP 500 ns with 8 post-integrations

46. DBPSK – PER vs. Eb/N0 – 15.4a Channel Models 0 10 X1 X2 X3 X4 -1 10 PER -2 10 -3 10 10 11 12 13 14 15 16 17 18 19 20 Eb/N (dB) 0 PER/BER in 15.4a Channel Model DBPSK (RAKE) Theoretical BER Curves – Integration Time = 50 ns Implementation loss and Noise figure margin : 11 dB Case I: 250 kbps – PRP 250 ns with 16 pre-integration = 4 µs Case II: 250 kbps – PRP 500 ns with 8 post-integrations

47. Link Budget: Non-Coherent (Energy Collection) BPPM

48. Link Budget: DBPSK (RAKE)

49. BP : Beacon Period CAP : Contention Access Period CFP : Contention Free Period IP : Inactive Period (optional) Beacon slot CAP slot CFP slot Octets 4 1 1 32 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 PHY layer Preamble SFD Frame length PSDU = MPDU BP CAP CFP IP SHR PHR PSDU (PHY Service Data Unit) Superframe Duration Beacon Interval PPDU (PHY Protocol Data Unit) Framing – 802.15.4 Compatible

50. Bytes 4 1 1 5 PHY layer Preamble SFD Frame length PSDU SHR PHR PSDU PPDU (PHY Protocol Data Unit) Bytes 4 1 1 32 PHY layer Preamble SFD Frame length PSDU = MPDU SHR PHR PSDU (PHY Service Data Unit) PPDU (PHY Protocol Data Unit) Throughput Data Frame (32 octet PSDU) ACK Frame (5 octet PSDU) Tdata T_ACK Tack IFS • Numerical example (high-band) • Preamble + SFD + PHR = 6 octets • Tdata = 1.216 ms • T_ACK = 50 ms (turn around time requested by IEEE 802.15.4 is 192ms) • Tack = 0.352 ms • IFS = 100μs • Throughput = 32 octets/1.718 ms = 149 kb/s • Average data-rate at receiver PHY-SAP 250 kb/s (Basic Mode)