Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Mitubishi Electric Pro

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:Mitubishi Electric Proposal Time-Hopping Impulse Radio Date Submitted: May 5th, 2003 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: We present a standards proposal for a high-data-rate physical layer of a Personal Area Network, using ultrawideband transmission. The air interface is based on time-hopping impulse radio, using BPSK for the modulation, and in addition polarity randomization of the pulses within the symbol. Combinations of delayed and weighted pulses allow an efficient shaping of the spectrum. This provides good suppression of interference, and guarantees fulfillment of coexistence requirements. The system is designed to have A/D conversion and digital processing only at the symbol rate, not the chip rate. Costs are comparable to Bluetooth. Purpose:[Proposing a PHY-layer interface for standardization by 802.15.3a] 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., Time Hopping Impulse Radio

2. Ultra WideBand Mitsubishi Electric Proposal Time-Hopping Impulse Radio A. F. Molisch, Y.-P. Nakache, P. Orlik, J. Zhang Mitsubishi Electric Research Lab S. Y. Kung, Y. Wu, H. Kobayashi, S. Gezici, V. Poor Princeton University Y. G. Li Georgia Institute of Technology H. Sheng, A. Haimovich New Jersey Institute of Technology Molisch et al., Time Hopping Impulse Radio

3. Contents • System overview • Physical-layer details • Performance evaluation • Signal robustness • Coexistence • Cost analysis • Summary and conclusions Molisch et al., Time Hopping Impulse Radio

4. Goals and Solutions • Commonly used technology Time hopping impulse radio • Fulfillment of spectral mask, but full exploitation of allowed power. Interference suppression  Linear combination of basis pulses • Cheap implementation, robustness to multipath  Few Rake fingers, all A/D conversion and computation done at 200MHz • Scalability  Multi-code transmission Molisch et al., Time Hopping Impulse Radio

5. Creation of Proposal • Proposal based on • Scientific experience of leading research groups (Princeton, Georgia Tech, MERL, MELCO) • Practical experience of high-quality product development team of Mitsubishi in USA and Japan • Experience in hardware (RF components, antennas, semiconductor, applications,…..) and applications design Molisch et al., Time Hopping Impulse Radio

6. Transmitter Structure Sync. & Training Sequence Central Timing Control Convolutional Code Multiplexer Timing Logic Pulse Gen. TH Seq.-1 Polarity Scrambler Power Control Demultiplexer Data Source Convolutional Code Multiplexer Polarity Scrambler Timing Logic Pulse Gen. TH Seq.-N Molisch et al., Time Hopping Impulse Radio

7. Receiver Structure Synchronization Channel Estimation Timing Control Rake Receiver Finger 1 AGC Rake Receiver Finger 2 Demultiplexer MMSE Equalizer Convolutional Decoder Summer Data Sink Rake Receiver Finger Np Molisch et al., Time Hopping Impulse Radio

8. Contents • System overview • Physical-layer details • acquisition • channel estimation • polarity hopping • spectral shaping • Rake structure • Performance evaluation • Summary and conclusions Molisch et al., Time Hopping Impulse Radio

9. Fast acquisition • template signal and received signal need to be aligned • standard method: serial search (chip by chip) • but: chip duration very short in UWB, takes long time • our solution: • Beacon provides rough timing estimation (within runtime of the piconet diameter) • new “block search” methods for actual acquisition Molisch et al., Time Hopping Impulse Radio

10. Block Search Algorithms • Steps in acquisition: • Find delay region where signal is likely to exist • After finding it, search in more detail for first significant path • Block search algorithm • Sequantial block search (SBS): integrate output of detector over delay region (block), search for block with significant energy. Best for LOS • Average block search (ABS): average over absolute values of detector output. Best for NLOS Molisch et al., Time Hopping Impulse Radio

11. Sequential Block Search 1) Check the bth block using the first template signal (t). 2) If the output of the bth block is not higher than a block threshold, τb, then, go to step 6. 3) If the output of the bth block is higher than the block threshold, τb, then search the block in more detail, i.e., cell-by-cell serial search with a signal threshold τs, using the second template signal (t). 4) If no signal cell is detected in the block, go to step 6. 5) If the signal cell is detected in the block, DONE. 6) Set b = (b mod B) + 1 and go to step 1. Molisch et al., Time Hopping Impulse Radio

12. Average Block Search 1) Check difference between successive averages wi mod B- w(i-1) mod B. 2) If the difference is not higher than a first threshold go to step 6. 3) If the difference is higher than, check z(i mod B)K+1, …, z(i mod B)+1)K serially, comparing to a second threshold, . 4) If no signal cells detected, go to step 6. 5) If signal cell(s) are detected, DONE. 6) Set i = (i + 1) mod B, and go to step 1. Molisch et al., Time Hopping Impulse Radio

13. 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 frequency • Requires longer training sequence • Three-step procedure for estimating coefficients: • With lower accuracy: estimate at which taps energy is significant • With higher accuracy: determine tap weights • Determine effective channel seen by equalizer • “Silence periods”: for estimation of interference Molisch et al., Time Hopping Impulse Radio

14. Channel Estimator – Block Diagram Adj.Weight Multiplier & Low-Pass Filter Σ Rake receiver Output Rake Finger 1 Programmable Training Waveform Gen. EQ Output ReceiverFront End MMSE Equalizer Multiplier & Low-Pass Filter Adj.Weight Programmable Training Waveform Gen. Rake Finger 2 Coefficients Adj.Weight Multiplier & Low-Pass Filter Equalizer Estimator Programmable Training Waveform GEN. Rake Finger N Channel Estimator EQ Training Sequence Timing Controller Channel Estimation Output Molisch et al., Time Hopping Impulse Radio

15. Estimator algorithm evaluation of one sample per 5ns interval, offset by Tc Molisch et al., Time Hopping Impulse Radio

16. Estimator • Multi-step procedure • estimate which taps have significant weights • estimate tap weights for L significant taps • determine Rake receiver weights via minimum mean square error criterion • determine equivalent (symbol-spaced) channel from transmitter to output Rake receiver • find equalizer for this equivalent channel (MMSE) Molisch et al., Time Hopping Impulse Radio

17. Modulation and 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 hopping sequences, to make equalizer implementation easier • Modulation: BPSK • Channel coding: • rate ½ convolutional code; • requires 4dB SNR for 10^-5 BER • Improvement by 3dB possible by turbo codes Molisch et al., Time Hopping Impulse Radio

18. Spectral Shaping & Interference Suppression • Basis pulse: fifth derivative of Gaussian pulse • Drawbacks: • Loses 3dB 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 Magnitude of p(t) Time (s) frequency (Hz) Molisch et al., Time Hopping Impulse Radio

19. 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., Time Hopping Impulse Radio

20. Initialization • find “modified” mask that follows FCC and required interference suppression (e.g., 20dB for 802.11a • approximate “optimum filling of mask” as • solution of this in closed form (eigenvector belonging to largest eigenvalue) Molisch et al., Time Hopping Impulse Radio

21. Iterative Refinement • backpropagating neural network Molisch et al., Time Hopping Impulse Radio

22. Rake Receiver • Main component of Rake finger: pulse generator • A/D converter: 3-bit, operating at 220Msamples/s • No adjustable delay elements required Molisch et al., Time Hopping Impulse Radio

23. Contents • System overview • Physical-layer details • Performance evaluation • Signal robustness • Coexistence • Cost analysis • Summary and conclusions Molisch et al., Time Hopping Impulse Radio

24. Link Budget Molisch et al., Time Hopping Impulse Radio

25. 110Mbps: PER as Function of Distance Sensitivity: AWGN 13m cm1 6.8 cm2 6.2 cm3 5.3 cm4 5.0 Molisch et al., Time Hopping Impulse Radio

26. 110Mbps: Probability of Link Success Molisch et al., Time Hopping Impulse Radio

27. 110Mbps: Outage vs. SNR Molisch et al., Time Hopping Impulse Radio

28. 110Mbps: Single co-channel interferer separation distance In AWGN: PER < 8% at less than 1 m Molisch et al., Time Hopping Impulse Radio

29. 110Mbps: Single co-channel interferer separation distance Molisch et al., Time Hopping Impulse Radio

30. 110Mbps: Single co-channel interferer separation distance Molisch et al., Time Hopping Impulse Radio

31. 110Mbps: Single co-channel interferer separation distance Molisch et al., Time Hopping Impulse Radio

32. 200Mbps: PER as Function of Distance Sensitivity: AWGN 9.2m cm1 4.5 cm2 3.2 Molisch et al., Time Hopping Impulse Radio

33. 200Mbps: Probability of Link Success Molisch et al., Time Hopping Impulse Radio

34. 200Mbps: Outage vs. SNR Molisch et al., Time Hopping Impulse Radio

35. 200Mbps: Single co-channel interferer separation distance In AWGN: PER < 8% at less than 1 m Molisch et al., Time Hopping Impulse Radio

36. 200Mbps: Single co-channel interferer separation distance Molisch et al., Time Hopping Impulse Radio

37. 200Mbps: Single co-channel interferer separation distance Molisch et al., Time Hopping Impulse Radio

38. 200Mbps: Single co-channel interferer separation distance Test link uncoordinated piconet d int AWGN AWGN < 1 m st 20 first re alizations of cm1 21 realization of cm1 1.5 m st 20 first realizations of cm2 21 realization of cm1 1.3 m st 20 first realizations of cm 1 21 realization of cm3 1.6 m st 20 first realizations of cm2 21 realization of cm3 1.7 m st 20 first realizations of cm1 21 realizati on of cm4 1.4 m st 20 first realizations of cm2 21 realization of cm4 1.4 m Molisch et al., Time Hopping Impulse Radio

39. Susceptibility to Interference • Piconets • 20 first realizations of the 4 channel model and AWGN • Desired user: 6dB above sensitivity • admissible distance of interferer: less than 2m for 110 and 200Mbps • 802.11a: influence only when interferer less than 2m distance, in CM2 for test link and interferer at 200Mbps • 802.11b: no noticeable influence (even at less than 1m distance of interferers) in all cases Molisch et al., Time Hopping Impulse Radio

40. At 110Mbps: Susceptibility to Interference Channel of test link : AWGN and cm1 Channel of test link: cm2 Molisch et al., Time Hopping Impulse Radio

41. At 200Mbps: Susceptibility to Interference Channel of test link : AWGN and cm1 Channel of test link: cm2 Molisch et al., Time Hopping Impulse Radio

42. Coexistence (at 1m) Molisch et al., Time Hopping Impulse Radio

43. Cost Estimates (for 110Mbit/s mode) • TX • Digital: • Coders 100k gates • timing logic <100k gates • RF • Pulse generators (4): 0.6mm2 • Polarity scramblers 0.04mm2 • Summers 0.04mm2 Molisch et al., Time Hopping Impulse Radio

44. Cost Estimates (for 110Mbit/s mode) • RX • Digital: • Viterbi Decoder 100k gates • timing logic <100k gates • MMSE equalizer 50k gates • Rake finger weighting and summing <50k gates • RF • LNA (11dB SNR) 0.05mm2 • Pulse generators (2*10): 3.2mm2 • Polarity descramblers 0.04mm2 • Low-pass filters 0.48mm2 • Summers 0.04mm2 Molisch et al., Time Hopping Impulse Radio

45. Cost Estimates - Summary • RF part: • total die size <10mm2 – less than Bluetooth • 0.18mu CMOS technology sufficient • Digital part: • Less than 500k gates • Operation at 220Mbit/s • Antenna: cavity-backed spiral antenna • Total costs comparable to Bluetooth Molisch et al., Time Hopping Impulse Radio

46. Self-Evaluation (I) Molisch et al., Time Hopping Impulse Radio

47. Self-Evaluation (II) Molisch et al., Time Hopping Impulse Radio

48. Summary and Conclusions • TH-IR based standards proposal • Meets targets of 802.15.3a for LOS • Innovative way 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 • Scaleable • Multicode / multirate system. Molisch et al., Time Hopping Impulse Radio