Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:Mitsubishi-electrics-time-hopping-impulse-radio-standards-presentation Date Submitted: November 15, 2004 Source:Andreas F. Molisch et al., Mitsubishi Electric Research Laboratories Address MERL, 201 Broadway Cambridge, MA, 02139, USA Voice: +1 617 621 7558, FAX: +1 617 621 7550, E-Mail: Andreas.Molisch@ieee.org Re:[Response to Call for Proposals] Abstract: Purpose:[Proposing a PHY-layer interface for standardization by 802.15.4a] 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. Molisch et al., Preliminary Proposal

2. Ultra WideBand Mitsubishi Electric Proposal Impulse Radio A. F. Molisch, Z. Sahinoglu, P. Orlik, J. Zhang Mitsubishi Electric Research Lab M. Z. Win Massachusetts Institute of Technology S. Gezici Princeton University Y. G. Li Princeton University Molisch et al., Preliminary Proposal

3. Contents • Proposal overview • Goals • Impulse radio basics • Proposed hybrid modulation • Physical-layer details • Ranging • Simulation results • Summary and conclusions Molisch et al., Preliminary Proposal

4. Goals • Provide a system that can work with different modulation and detection methods • Allows trade-offs among transmitter and receiver complexity/cost/performance • Works with a variety of signaling (modulation) methods and pulse shapes • Enables different receiver structures: coherent, differential, incoherent • Specific proposal built on novel technologies for impulse radio transceivers • Share ideas with other 4a members in the hope of working together. Molisch et al., Preliminary Proposal

5. Impulse Radio Basics Molisch et al., Preliminary Proposal

6. Time Hopping Impulse Radio (TH-IR) +1 Tc Tf Ts -1 • Each symbol represented by sequence of very short pulses • Each user uses different sequence (Multiple access capability) • Bandwidth mostly determined by pulse shape Molisch et al., Preliminary Proposal

7. TH-IR Coherent RAKE Receiver Rake Receiver Finger 1 AGC Rake Receiver Finger 2 Convolutional Decoder Summer Data Sink Rake Receiver Finger Np Optimum receiver for multipath channels Molisch et al., Preliminary Proposal

8. 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 Molisch et al., Preliminary Proposal

9. Transmitted Reference Receiver – Differentially Coherent Convolutional Decoder Td Advantage: Simple receiver Molisch et al., Preliminary Proposal

10. Proposal – Hybrid TR and TH-IR Modulation Molisch et al., Preliminary Proposal

11. Motivation • Different applications require different performance • Vendors want to differentiate themselves • 802.15.4 already has different device types • We provide proposal that allows trade-offs among complexity/capability/cost and performance • Enables simple receivers without penalizing more complex ones Molisch et al., Preliminary Proposal

12. Td Proposed Transmitter Rake Receiver Finger 1 Rake Receiver Finger 2 Summer BPSK symbol mapper Delay Pulse Gen. TH Seq Multiplexer Rake Receiver Finger Np BPSK symbol mapper Central Timing Control One Transmitter Enables Multiple Receiver Types Molisch et al., Preliminary Proposal

13. Proposed Transmitter Structure – Sample Waveform 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 Data Pulse Polarity Ts Molisch et al., Preliminary Proposal

14. Physical Layer Details Molisch et al., Preliminary Proposal

15. 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 Molisch et al., Preliminary Proposal

16. 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 Molisch et al., Preliminary Proposal

17. Channel Estimation • Swept delay correlator • Principle: estimating only one channel sample per symbol. Similar concept as STDCC channel sounder of Cox (1973). • Sampler, AD converter operating at SYMBOL rate • Requires longer training sequence • Two-step procedure for estimating coefficients: • With lower accuracy: estimate at which taps energy is significant • With higher accuracy: determine tap weights • “Silence periods”: for estimation of interference Molisch et al., Preliminary Proposal

18. Multiple Access • Multiple access: • Combination of pulse-position-hopping and polarity hopping for multiple access • More degrees of freedom for design of good hopping sequence than pure pulse-position-hopping • Short or long hopping sequences possible • Long hopping sequence == period of sequence > Number of frames in a symbol. Molisch et al., Preliminary Proposal

19. 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) Molisch et al., Preliminary Proposal

20. 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 Molisch et al., Preliminary Proposal

21. Spectral Shaping & Polarity Scrambling Td = 10 ns Td = 20 ns W/O Polarity Scrambling W/ Polarity Scrambling Molisch et al., Preliminary Proposal

22. Adaptive frame duration • Advantage of large number of pulses per symbol: • Smaller peak-to-average ratio • Increased possible number of SOPs • Disadvantage: • Increased interframe interference • In TR: also increased interference from reference pulse to data pulse • Depends on • Solution: adaptive frame duration • Feed back delay spread and interference to transmitter • Depending on those parameters, TX chooses frame duration Molisch et al., Preliminary Proposal

23. PER Performance Coherent Reception 608 Kbps, Td = 20ns, 20 Frames per symbol Molisch et al., Preliminary Proposal

24. PER Performance Differential Reception 608 Kbps, Td = 20ns, 20 Frames per symbol Molisch et al., Preliminary Proposal

25. Link Budget Molisch et al., Preliminary Proposal

26. Ranging Molisch et al., Preliminary Proposal

27. Two Step Ranging Algorithm • Step-I: • Estimate rough TOA of the incoming signal in a time window by detecting received signal energy • Step-II: • Determine the arrival time of the first signal path by using hypothesis testing (change detection) Symbol rate sampling is sufficient Molisch et al., Preliminary Proposal

28. 1 1 1 2 2 2 … … … NB NB NB Step-I: Energy Detection j = 1 2 N1 i = TRF TRB Y2,2 Y2,1 Y2,N1 i = Ranging Block index Y1 Y2 YNB j = Ranging Frame index max Step-II Molisch et al., Preliminary Proposal Block decision

29. Step-II: Chip Detection • TOA is estimated at chip resolution • Once a ranging block is detected, the chips in that block plus M1 extra chips prior to the ranging block (to prevent errors due to multipath) are searched • Correlations of the received signal with time delayed versions of a template signal are considered • Correlation output is obtained over N2 frames to have sufficient SNR • Solution of first arriving path found by hypothesis testing methods on zi r(t), received signal zi s(t-TC), shifted template signal Molisch et al., Preliminary Proposal

30. Ranging System Settings Molisch et al., Preliminary Proposal

31. Ranging Results • Residential LOS Molisch et al., Preliminary Proposal

32. Ranging Results • AWGN Molisch et al., Preliminary Proposal

33. Two-way Ranging Protocol • Developed for transceivers that can first detect the coarse TOA of a signal and then determine the offset (error) of the coarse estimation • No need to transmit extra information to correct the timing offset or the processing delay • Each node switches between receive and transmit mode every T seconds until the ranging is complete Molisch et al., Preliminary Proposal

34. TOA estimation error T TOA estimation error Second transmission may help filter out clock drifts, if the Tx has a more reliable clock Enhanced Two-way Ranging Protocol Conventional Two-way Ranging Protocol Molisch et al., Preliminary Proposal

35. Acquisition • The first step of the TOA estimation algorithm is also suitable for acquisition • For the second step of the acquisition, a conventional serial search algorithm, or the hypothesis testing based approach can be applied, depending on the complexity and performance constraints • If ranging is performed no separate acquisition step is necessary Molisch et al., Preliminary Proposal

36. Summary and Conclusions • Impulse radio based standards proposal • UWB signaling achieves accurate ranging. • Innovative modulation technique • Admits multiple transmit waveforms • Provides framework for multiple receiver types • Offers trade-off of cost/complexity/performance • Coherent and differentially coherent receivers suppress interference • More users • Innovative ways to manage spectrum • Meet FCC requirements • Improve performance in interference environment • Decrease interference to other systems • Allows cheap implementation • All digital operations at symbol rate, not chip rate Molisch et al., Preliminary Proposal

37. References • Proposal content has been reviewed and published in various technical journals and conferences • S. Gezici, F. Tufvesson, and A. F. Molisch, “On the performance of transmitted-reference impulse radio”, Proc. Globecom 2004, • F. Tufvesson and A. F. Molisch, “Ultra-Wideband Communication using Hybrid Matched Filter Correlation Receivers“, Proc. VTC 2004 spring • A. F. Molisch, Y. G. Li, Y. P. Nakache, P. Orlik, M. Miyake, Y. Wu, S. Gezici, H. Sheng, S. Y. Kung, H. Kobayashi, H.V. Poor, A. Haimovich,and J. Zhang, „A low-cost time-hopping impulse radio system for high data rate transmission“, Eurasip J. Applied Signal Processing, special issue on UWB • S. Gezici, Z. Tian, G. B. Giannakis, H. Kobayashi, A. F. Molisch, H. Vincent Poor and Z. Sahinoglu, "Localization via Ultra-Wideband Radios," IEEE Signal Processing Magazine, invited paper (special issue) • S. Gezici, E. Fishler, H. Kobayashi, H. V. Poor, and A. F. Molisch, “Performance Evaluation of Impulse Radio UWB Systems with Pulse-Based Polarity Randomization in Asynchronous Multiuser Environments”, Proc. WCNC 2004, • S. Gezici, E. Fishler, H. Kobayashi, H. V. Poor, and A. F. Molisch, “Effect of timing jitter on the tradeoff between processing gains, Proc. ICC 2004, in press. F. Tufvesson and A. F. Molisch, “Ultra-Wideband Communication using Hybrid Matched Filter Correlation Receivers“, Proc. VTC 2004 spring Molisch et al., Preliminary Proposal

38. References (Cont) • Z. Sahinoglu, A. Catovic, "A Hybrid Location Estimation Scheme for Wireless Sensor Networks, IEEE ICC'04, June 2004, Paris • S. Gezici, Z. Sahinoglu, H. Kobayashi, H. Vincent Poor, Book Chapter: Ultra Wideband Geolocation, Ultra Wideband Wireless Communications by H. Arslan and Z. N. Chen, John Wiley & Sons, Inc. , February 2005. • S. Gezici, Z. Sahinoglu, H. Kobayashi, H. Vincent Poor, "Impulse Radio Systems with Multiple Types of UWB Pulses," submitted to ICASSP'05. • A. Catovic, Z. Sahinoglu, "The Cramer-Rao Bounds of TOA/RSS and TDOA/RSS Location Estimation Schemes", IEEE Comm. Letters, October 2004 • H. Sheng, A. Haimovich, A. F. Molisch, and J. Zhang, “Optimum combining for time-hopping impulse radio UWB Rake receivers”, Proc. UWBST 2003, in press • Li, Y.G.; Molisch, A.F.; Zhang, J., "Channel Estimation and Signal Detection for UWB", International Symposium on Wireless Personal Multimedia Communications (WPMC), October 2003 • Nakache, Y-P; Molisch, A.F., "Spectral Shape of UWB Signals - Influence of Modulation Format, Multiple Access Scheme and Pulse Shape", IEEE Vehicular Technology Conference (VTC), April 2003 Molisch et al., Preliminary Proposal