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UWB Proposal for IEEE 802.15.4a Alt-PHY

This proposal presents an Ultra-Wideband (UWB) impulse radio based alternative physical layer for IEEE 802.15.4a, supporting different receiver architectures, flexible modulation formats, multiple rates, and accurate ranging/positioning. The document outlines the main features, motivation, modulation, and commonalities with other proposals.

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UWB Proposal for IEEE 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_MITSUBISHI_FTR&D 15.4aCFP response • Date Submitted: January 4th, 2005 • Source: Ian Oppermann (1), Mark Jamtgaard (2), Laurent Ouvry (3), Philippe Rouzet (4), Andreas F. Molisch(5), Philip Orlik(5), Zafer Sahinoglu (5), Rick Roberts (6), Vern Brethour (7), Adrian Jennings (7) , Patricia Martigne (8), Benoit Miscopein (8), Jean Schwoerer (8) • 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 • (5) MERL, 201 Broadway, Boston, USA • (6) Harris, (7)Time Domain, Hansville, Alabama • (8) FT R&D, 28 Chemin des vieux chênes, BP98, 38243 Meylan Cedex • Voice: (1) +358 407 076 344, (2) 408 400 0785 (3) +33 4 38 78 93 88, (4) +41 22 929 58 66 (5) +1 617 621 7500 • E-Mail: (1) ian@ee.oulu.fi, (2) mark@aetherwire.com(3) laurent.ouvry@cea.fr, (4) philippe.rouzet@st.com, (5) {molisch, porlik, zafer}@merl.com, rrober14@harris.com, {vern.brethour, adrian.jennings}@timedomain.com, (8) {patricia.martigne, benoit.miscopein, jean.schwoerer}@francetelecom.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) • MERL– Andreas F. Molisch, Philip Orlik, Zafer Sahinoglu (5) • Harris – Rick Roberts (6) • Time Domain – Vern Brethour, Adrian Jennings (7) • France Telecom R&D – Patricia Martigne, Benoit Miscopein, Jean Schwoerer (8)

  3. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  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 for (2-4): • 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 • Time hopping (TH) to achieve multiple access

  8. Commonalities with Other Proposals • The present document is the result of preliminary merging efforts among the new CWC/STm/LETI/AetherWire/MERL/Harris/FTR&D/TDC group. Work is still ongoing for refining and consolidation of some of the parameters described in this proposal. • Discussions are under way for further collaborations and merging in 802.15.4a.

  9. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  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

  11. 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

  12. Time Hopping Impulse Radio (TH-IR) - Principle +1 Tc Tf Ts -1 • Each symbol represented by sequence of very short pulses (see also Win & Scholtz 2000) • Each user uses different sequence (Multiple access capability) • Bandwidth mostly determined by pulse shape

  13. 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 • Implementation challenges: • Analogue: Implementing delay value, • delay mismatch, jitter

  14. Transmitted Reference data Td +1 Tc Tf reference Ts -1 • First pulse serves as template for estimating channel distortions • Second pulse carries information • Drawback: Waste of 3dB energy on reference pulses

  15. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  16. Design Parameters (1) • Motivation: • Flexible waveform • Simple • Compatible with multiple coherent/non-coherent receiver schemes • Large Bandwidth • (+) Higher transmit power • (+) improved 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) • Long Pulse Repetition Period • (+) more energy per pulse (easier to detect single pulse) • (+) Lower inter-pulse interference due to channel delay spread • (-) Higher peak voltage requirements at transmitter • (-) Longer acquisition time  Frame duration between 40ns (first realization) and 125ns (second realizations). Higher values for the frame duration have been mentioned. Further discussions are required to fix the values

  17. Design Parameters (2) • Simple modulation schemes: • BPPM combined with Transmitted Reference • Channelization : • Coherent schemes: Use of TH codes and polarity codes • Non-coherent schemes: Use of TH codes (polarity codes for spectrum smoothing only) • Long TH code length • (+) higher processing gain, robustness to SOP operation • (-) Lower bit-rate • (-) Longer acquisition time, shorter frame size (synch. phase) • TH code length 8 or 16 TH code : binary position (delay of 0 or τΔ ), bi-phase For first realization, higher-order TH with shorter chip duration (multiples of 2ns) can be used. This is under discussion

  18. Transmission • Basic idea: use modulation scheme that allows coherent, differentially coherent, and incoherent reception • 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: • Coherent, differential and non-coherent receiver may coexist • reference can be used for synch and threshold estimation • Concept can be generalized to N-ary TR system

  19. Waveform Design • Coexistence of coherent and non-coherent architectures • Combine BPPM with BPSK • Divide each symbol into two 125 ns BPPM slots (250 ns symbol) • In either slot transmit a signal that can be received with a variety of receivers: differentially coherent or coherent receivers. • Non-coherent receivers just look for energy in the early or late slots to decode the bit. • Other receivers understand the fine structure of the signal.

  20. Waveform Design • Two possible realizations: • The whole symbol (consisting of N_f frames) is BPPM-modulated. • Have a 2-ary time hopping code, so that each frame has BPPM according to TH code

  21. First Realization

  22. « 11 » 2-PPM + TR base M = 2 (with two bits/symbol) One bit/symbol also Possible !!! « 01 » « 10 » « 00 » Second Realization Ts 2-PPM + 16 chips 2-ary TH code (coherent decoding possible) This is a time-hopping that can be exploited by non-coherent receiver Time hopping code is (2,2) code of length 8 or 16 Effectively 28 or 216 codes to select for channelization for non-coherent scheme

  23. 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)

  24. Coexistence of Different Receiver Architectures • Want waveform that allows TR reception without penalizing coherent reception • That is achieved by special encoding and waveform shaping within each frame. Does not affect the co-existence of coherent/non-coherent receivers

  25. Basic Properties • Use of Doublets with memory from previous bit. (Encoding of reference pulse with previous bit) • Agreed on 20ns separation between pulses • Extensible to higher order TR for either reducing the penalty in transmitting the reference pulse or increasing the bit rate? • Also allows the use of multi-DOUBLET

  26. 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 Note: Thisslide is meant to describe the encoding of data on the reference pulse and data pulse in the basic modulation format. For simplicity we have omitted the multipulse/multiframes per symbol structure.

  27. Total Modulation Scheme (First Realization) THE KEY SLIDE OF THE PROPOSAL: this is the modulation format that allows Coherent, differentially coherent, and non-coherent demodulation at once

  28. τdelay +τΔ D D D « 1 » Basic Mode (as seen by non-coherent) τdelay +τΔ D D D « 1 1 » Enhanced Mode 1 « 1 0 » Pulse Shift, polarity invert τΔ + τdelay τΔ τΔ τdelay τdelay τΔ + τdelay τΔ + τdelay τΔ + τdelay Higher-order modulation 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

  29. Comments on Transmitted Signal • Frame period for solution 2 is Tframe = (Np * D) + τΔ + τdelay • Τdelay is some allowance for channel delay spread • Frame period could be dynamic modified dependant on • the estimated channel delay spread or • ability of receiver to cope with delay spread • Symbol period is length of the TH code x Tframe • Upper Band Nominally 250 ns x 16 = 4 µs • Lower Band Nominally 500 ns x 8 = 4 µs • Realistic Receiver structures exist for multi-pulse TR schemes (see back-up slides)

  30. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  31. Proposed RAKE -- Coherent 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

  32. Proposed Transmitted Reference Receiver – Differentially Coherent • Addition of Matched Filter prior to delay and correlate operations improves output signal to noise ratio and reduces noise-noise cross terms Matched Filter Convolutional Decoder Td SNR of decision statistic

  33. Band Matched ADC ADC BPF 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 Tracking Thresholds setting Ranging branch Block index for acquisition reference Energy Analyzer Leading-edge refinement search Range info Recyle this branch for Enhanced Data Rate Modes

  34. 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

  35. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  36. Bandwidth Usage (1/4) • Flexible use of (multi-)bands • Signal bandwidth may be 500 MHz to 2 GHz • Bandwidth may change depending on application and regulatory environment • Optional sub-GHz band 140 MHz to 800 MHz with a center frequency of 470 MHz • Use of TH and/or polarity randomization for spectral smoothing • Different bandwidth use options being considered

  37. Bandwidth Usage – 2GHz option (2/4) 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

  38. Bandwidth Usage -500 MHz Option (3/4) ISM Band ISM Band Upper Bands 5 - 12 Upper Bands 1 - 4 Lower band 0.96 3.1 5.1 6.0 8.0 8.1 10.1 GHz

  39. Bandwidth Usage –Variable Option (4/4) ISM Band ISM Band Upper Bands 5 - 12 Upper Bands 1 - 4 Lower band 0.96 3.1 5.1 6.0 8.0 8.1 10.1 GHz

  40. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  41. Spectral Shaping & Interference Suppression (Optional) • Basis pulse: use simple pulse shape gaussian, raised cosine, chaotic, etc. • Drawbacks: • Possible loss of power compared to FCC-allowed power • Strong radiation at 2.45 and 5.2 GHz Monocycle, 5th derivative of gaussian pulse Power spectral density of the monocycle 10log10|P(f)|2 dB frequency (Hz)

  42. Linear Pulse Combination • Solution: 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

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

  44. 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

  45. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

  46. 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

  47. 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

  48. Outline • Introduction • Background • Transmitted Signal • Receiver Architectures • Bandwidth Usage • Optional Aspects • System performances • Link budget • Framing, throughput • Power Saving • Ranging and Delay Estimation • Feasibility • Conclusions

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

  50. Link Budget: DBPSK (RAKE)

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