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:Mitubishi Electric Proposal Time-Hopping Impulse Radio Date Submitted: March 3rd, 2003 Source:Andreas F. Molisch et al., Mitsubishi Electric Research Laboratories Address MERL Murray Hill558 Central Avenue Murray Hill, NJ 07974, USA Voice: +1 908 363 0524, FAX: +1 908 363 0550, 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, E. Fishler, 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 • Performance evaluation • Achievable coverage • Coexistence • Cost analysis • Summary and conclusions Molisch et al., Time Hopping Impulse Radio

9. 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 Molisch et al., Time Hopping Impulse Radio

10. 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

11. 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 6dB SNR for 10^-5 BER • Improvement by 3dB possible by turbo codes Molisch et al., Time Hopping Impulse Radio

12. 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

13. Synchronization • Combination of MAC-Layer and PHY-Layer approach • Beacon provides rough timing estimation (within runtime of the piconet diameter) • Fine acquisition by transmission of synch pulses • Acceleration of acquisition by Block Search algorithms Molisch et al., Time Hopping Impulse Radio

14. 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 • Serial block search (SBS): integrate output of detector over delay region (block), search for block with significant energy • Average block search (ABS): average over absolute values of detector output Molisch et al., Time Hopping Impulse Radio

15. 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

16. 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

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

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

19. PER as Function of Distance Molisch et al., Time Hopping Impulse Radio

20. Probability of Link Success Molisch et al., Time Hopping Impulse Radio

21. Outage vs. SNR Molisch et al., Time Hopping Impulse Radio

22. Signal Acquisition Time Molisch et al., Time Hopping Impulse Radio

23. Susceptibility to Interference • Piconets • All channels AWGN • Desired user: 6dB above sensitivity • admissible distance of interferer: 2.5m • Desired user: 10m distance • Admissible distance: 6m • 802.11a: influence only when interferer less than 0.4m distance, in CM2 • 802.11b: no noticeable influence (even at 0.3m distance of interferers) in all cases Molisch et al., Time Hopping Impulse Radio

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

25. 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

26. 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

27. 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

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

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

30. 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