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UWB Proposal for 802.15.4a Alt-PHY

This submission proposes an impulse-radio based UWB technology for the IEEE 802.15.4a CFP, supporting flexible modulation formats and multiple rates for accurate ranging and positioning.

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UWB Proposal for 802.15.4a Alt-PHY

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) • Submission Title:STM_CEA-LETI_CWC_AETHERWIRE 15.4aCFP response • Date Submitted: January 4th, 2005 • Source: Ian Oppermann (1), Mark Jamtgaard (2), Laurent Ouvry (3), Philippe Rouzet (4) • Companies: • (1) CWC-University of Oulu, Tutkijantie 2 E, 90570 Oulu, FINLAND • (2) Æther Wire & Location, Inc., 520 E. Weddell Drive, Suite 5, Sunnyvale, CA 94089, USA • (3) CEA-LETI, 17 rue des Martyrs 38054, Grenoble Cedex, FRANCE • (4) STMicroelectronics, CH-1228, Geneva, Plan-les-Ouates,SWITZERLAND • Voice: (1) +358 407 076 344, (2) 408 400 0785 (3) +33 4 38 78 93 88, (4) +41 22 929 58 66 • E-Mail: (1) ian@ee.oulu.fi, (2) mark@aetherwire.com(3) laurent.ouvry@cea.fr, (4) philippe.rouzet@st.com, • Abstract: UWB proposal for 802.15.4a alt-PHY • Purpose: Proposal based on UWB impulse radio for the IEEE 802.15.4a CFP • 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 contributors acknowledge and accept that this contribution becomes the property of IEEE and may be made publicly available by P802.15

  2. List of Authors • CWC– Ian Oppermann, Alberto Rabbachin (1) • AetherWire – Mark Jamtgaard, Patrick Houghton (2) • CEA-LETI – Laurent Ouvry, Samuel Dubouloz, Sébastien de Rivaz, Benoit Denis, Michael Pelissier, Manuel Pezzin et al. (3) • STMicroelectronics – Gian Mario Maggio, Chiara Cattaneo, Philippe Rouzet & al. (4)

  3. Outline • Introduction • Transmitter • Receiver architectures • System performances • Link budget • Framing, throughput • Power Saving • Ranging • Proof of concept • Conclusions

  4. Introduction (1/2) • 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. Introduction (2/2) • Motivation for (2-4): • Supports homogenous and heterogeneous network architectures • Different classes of nodes, with different reliability requirements (and cost) must inter-work

  6. Commonalities with Other Proposals • Many commonalities exist between the CWC/Aetherwire/LETI/STM proposal and other proposals, including FT and Mitsubishi: • UWB technology • Modulation features • Bandwidth usage • Ranging approach • Discussions are under way for future collaborations and merging

  7. 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

  8. Modulation Features • Simple, scalable modulation format • Flexibility for system designer • Modulation compatible with multiple coherent/non-coherent receiver schemes • Time hopping (TH) to achieve multiple access

  9. Bandwidth Usage (1/2) • Flexible use of (multi-)bands depending on application and regulatory environment • Use of TH and/or polarity randomization for spectral smoothing • Noise-like interference towards existing radio services

  10. Bandwidth Usage (2/2) ISM Band ISM Band Upper Band 3 Upper Band 1 Upper Band 2 Lower band 0.96 3.1 5.1 6.0 8.0 8.1 10.1 GHz

  11. Ranging Approach • Signal bandwidth ≥ 1GHz for very good location accuracy • Two-way ranging protocol to avoid synchronization between nodes • Location based on ranging from several nodes on a higher layer

  12. Preliminaries (1/2) • 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

  13. Preliminaries (2/2) • 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

  14. ½ PRP ½ PRP TX: Modulation Formats PRP « 1 » OOK « 0 » D « 1 » TR-BPSK « 0 » « 1 » DBPSK (one pulse per PRP ) « 0 » « 1 » BPPM « 0 »

  15. ½ PRP ½ PRP TX: Multi-pulse Modulation Formats PRP « 1 » OOK « 0 » Scope for Adding more information with multi-pulse D « 1 » TR-BPSK « 0 » « 1 » DBPSK « 0 » « 1 » BPPM « 0 »

  16. 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 • Reference waveform averaging (non-coherent integration); • see also GLRT [Franz, Mitra; Globecom’03, pp. 744-748, Dec 2003] • Implementation challenges: • Analogue: Implementing delay value, • delay mismatch, jitter

  17. D TR Schemes (1/3) • GTR (Generalized Transmitted Reference) BPSK Extension to N-ary TR D « A » « B » « C » « D » PRP • Concept: Multi-level version of the TR scheme, where the energy associated with the reference pulse is “shared” to improve efficiency

  18. D1 TR Schemes (2/3) • TR-BPPM (with/without BPAM) Extension to N-ary TR « A » D2 « B » « C » Coherent Detection « D » PRP • Concept: Transmitted-reference version of BPPM, with BPAM [Zasowski, Althaus and Wittneben, Proc. IWUWBS/UWBST’04, Kyoto, Japan] • TR-BPPM (non-coherent): Binary symbols restricted to “A” and “B”

  19. D ½ PRP ½ PRP TR Schemes (3/3) • TR-PCTH (pseudo-chaotic time hopping) • [Maggio, Reggiani, Rulkov; IEEE Trans. CAS-I, v. 48, no. 12, p. 1424, Dec 2001] Random inter-pulse interval Extension to N-ary TR « 0 » « 1 » • Concept: Random TH  Smoothes spectral lines in the PSD • Modulation: Pulses in the first ½ PRP correspond to “0” and vice versa for“1” • Demodulation: Similar to PPM, but more flexible (threshold or Viterbi detector)

  20. Transmission • Combine BPPM with more sophisticated TR scheme • Non-coherent receiver sees BPPM with pulse stream per bit • More sophisticated receiver sees BPPM (1 bit) plus bits carried in more sophisticated modulation scheme (e.g. extended TR) • Advantages: • Differential and non-coherent receiver may coexist • reference can be used for synch and threshold estimation • Concept can be generalized to N-ary TR-BPSK

  21. Design Parameters (1/6) • Motivation: • Flexible waveform • Still simple • Compatible with multiple coherent/non-coherent receiver schemes • Limitations (compliant with FCC) • Increased Bandwidth (pros/cons) • (+) High transmit power • (+) High time resolution • (-) Increased design complexity • (-) Less stringent requirements on out of band interference filtering • Signal BW of 500 MHz - 2 GHz in Upper bands Signal BW of 700 MHz in 0 to 960 MHz Lower band (low band) • Increased Pulse Repetition Period (pros/cons) • (+) more energy per pulse (easier to detect single pulse) • (+) Lower inter-channel interference due to channel delay spread • (-) Transmitter peak voltage compatible with technology • (-) Acquisition time  PRP (chip period) Between 250ns and 500ns

  22. TX: Design Parameters (2/6) • Simple modulation schemes: • BPPM combined with Transmitted Reference • min 1 bit/symbol for non-coherent, 2 bits/symbol for TR (more for GTR) • Channelization : • Coherent schemes: Use of TH codes and polarity codes • Non-coherent schemes: Use of TH codes (polarity codes for spectrum smoothing only) • Increased TH code length (pros/cons): • (+) higher processing gain, robustness to SOP operation • (-) Lower bit-rate • (-) Faster acquisition, shorter frame size (synch. phase) • TH code length 8 or 16

  23. TX: Design Parameters (3/6) • Basic Mode - Upper-bands (XH0=250 Kbps): • PRP = 250 ns, binary modulation, TH code length of 16chips • N pulses per symbol (1 < N < 124) • PHY-SAP payload bit rate (Xo) is 250 kbps • Enhanced Mode 1 - Upper-bands (XH1=500 Kbps): • PRP = 250 ns, 4-level modulation, TH code length of 16chips • N pulses per symbol (1 < N < 124) • PHY-SAP payload bit rate (Xo) is 500 kbps • Enhanced Mode 2 - Upper-bands (XH2=1000 Kbps): • PRP = 250 ns, 8-level modulation, TH code length of 16chips • N pulses per symbol (1 < N < 40) • PHY-SAP payload bit rate (Xo) is 1000 kbps

  24. D « 1 1 » « 1 0 » Enhanced Mode 1 «0 1 » «0 0 » « 1 1 1 1» « 1 0 1 0 » Enhanced Mode 2 ½ PRP ½ PRP TX: Design Parameters (4/6) « 1 » Basic Mode « 0 »

  25. Need not fill entire slot « 1 » Basic Mode (as seen by receiver) « 1 1 » Enhanced Mode 1 (randomising code) TX: Design Parameters (5/6) « 1 1 » Enhanced Mode 1 « 1 0 » Position Swap, polarity invert 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 1,1

  26. TX: Design Parameters (6/6) • Basic Mode - Lower-band (XL0=250 Kbps): • PRP = 500 ns, binary modulation, TH code length of 8 chips • N pulses per symbol (1 < N < 120) • PHY-SAP payload bit rate (Xo) is 250 kbps • Enhanced Mode 1 - Lower-band (XL1=500 Kbps): • PRP = 500 ns, 4-level modulation, TH code length of 8 chips • N pulses per symbol (1 < N < 120) • PHY-SAP payload bit rate (Xo) is 500 kbps • Enhanced Mode 2 - Lower-band (XL2=1000 Kbps): • PRP = 500 ns, 8-level modulation, TH code length of 8 chips • N pulses per symbol (1 < N < 40) • PHY-SAP payload bit rate (Xo) is 1000 kbps

  27. Synchronization Clock Tracking Thresholds setting Channel Estimation Trig ADC Band Matched BPF Buffer LNA Threshold Integration / Decision Estimated CIR Coefficients Coherent Receiver Architecture

  28. Band Matched ADC ADC BPF ADC Dump Latch TR Delay Controlled Integrator BPPM Synch Trigger TR Demodulation branch Differentially-Coherent/Non-Coherent Receiver Architecture Basic Mode and Enhanced Mode 1 BPPM Demodulation branch Controlled Integrator r(t) LNA Dump Latch x2 RAZ RAZ DUMP Synchro Tracking Thresholds setting THRESHOLD Ranging branch Comparator Trigger Integrator Time base Recyle this branch for Enhanced Mode 2

  29. 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 despreading TH Sequence Matched Filter b(t) soft info Bit Demodulation r(t) LNA Case II – Non-coherent / differential TH despreading

  30. 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

  31. 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

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

  33. Link Budget: DBPSK (RAKE)

  34. 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

  35. 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)

  36. Power Saving techniques achieved by combining advantages offered at 3 levels: Technology (best if CMOS) Architecture (flexible schemes provided by the TH+pulse modulation) System level (framing, protocol usage) Selected techniques used in one existing realization (see proof of concept slides) Low-duty cycle Episodic transmission/reception Scheduled wake-up 80ms RTOS tick Ad-hoc networking using multi-hop Special rapid acquisition codes / algorithm Matchmaking further reduces acquisition time Multi-stage time-of-day clock Synchronous counter / current mode logic for highest speed stages Ripple counter / static CMOS for lowest speed stages Compute-intensive correlation done in hardware Saving Power

  37. 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)

  38. TOF Estimation Request Two Way Ranging (TWR) T1 To Terminal A TX/RX Terminal B RX/TX TOF TOF TReply Terminal A Prescribed Protocol Delay and/or Processing Time Terminal B

  39. Main Limitations / Impact of Clock Drift on Perceived Time Two Way Ranging (TWR) Is the frequency offset relative to the nominal ideal frequency • Range estimation is affected by : • Relative clock drift between A and B • Prescribed response delay • Clock accuracy in A and B • Channel response (weak direct path) Example using Imm-ACK SIFS of 15.4 and 15.3 • Relaxing constraints on clock accuracy is possible by • Performing fine drift estimation/compensation • Benefiting from cooperative transactions (estimated clock ratios …) • Adjusting protocol durations(time stamp…)

  40. 20dB SNR, 3ns Integration Non-Coherent Energy Detection TOA estimation with serial search. Parameters: uncertainty region of 13 ns, search region 20 ns, integration window 3 ns, SNR of 20 dB, CM1 (802.15.3a)

  41. TOA Error CDF (CM1 802.15.3a) TOA error CDF for serial search. Integration window of 3 and 4 ns.

  42. 55 mm 40 mm Antenna FeasibilityCapacitive Dipole and Various Bowtie Antennas Bowtie antenna

  43. CWC Oulu “Proof-of-Concept” (1) Non-coherent Transceiver Non-coherent, Energy Collection Receiver 5 Mbps BPPM 350 ps pulse train with long scrambling code

  44. CWC Oulu “Proof-of-Concept” (2) Non-coherent Transceiver UWB-IR BPPM Non-Coherent Transceiver Implementation UWB Transmitter 400 μm x 400 μm 0.35 μm CMOS UWB Transceiver Test architecture <10 mm2 0.35 μm SiGe Bi-CMOS

  45. P-Channel Drivers N-Channel Drivers N-C DelayBuffers “Proof-of-Concept” (3): Transmitter - Lower Band UWB Transmitter chip for generating impulse doublets

  46. LF RTC DACs High-FrequencyReal Time Clock CodeSequenceGenerators DACs PLL Loop Filter 32 Time-IntegratingCorrelators “Rails” for testing analog circuits VGC Amp “Proof-of-Concept” (4): Receiver - Lower Band Coherent UWB Receiver with multiple time integrating correlators

  47. “Proof-of-Concept” (5) High Speed Coherent Circuit Elements RF front end chips in CMOS 0.13mm, 1.2V 20 GHz digitizer for UWB 20 GHz DLL for UWB 3-5 GHz LNA Chip and layout

  48. 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)

  49. Backup Slides

  50. -1 10 -2 10 BER -3 10 -4 10 -5 10 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Eb/N0 BER Performance in AWGN Channel MRC Solution (coherent) Differential Solution Energy Collection solution in OOK Transmitted Reference (one pulse) -3 dB : the “reference” is not in the same PRP ! PER = 1% with 32 bytes PSDU  acceptable BER 4x10-5 with no channel coding

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