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Waveform Modulated Low Rate UWB System - Proposal for 15.4a alt PHY

This document describes a proposal for a waveform modulated ultra-wideband system for IEEE 802.15 TG4a. It discusses the use of short duration impulses in the time domain, low complexity digital processing, high location accuracy, and adaptive frequency band usage.

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Waveform Modulated Low Rate UWB System - Proposal for 15.4a alt PHY

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  1. doc.: IEEE 802.15-05-0028-00-004a • doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [WAVEFORM MODULATED LOW RATE UWB SYSTEM - Proposal for 15.4a alt PHY] Date Submitted: [Jan., 2005] Source: [Soo-Young Chang] Company [California State University, Sacramento] Address [6000 J Street, Dept. EEE, Sacramento, CA 95819-6019 ] Voice:[916 278 6568], FAX: [916 278 7215], E-Mail:[sychang@ecs.csus.edu] Re: [This submission is in response to the IEEE P802.15.4a Alternate PHY Call for Proposal ] Abstract: [This document describes the waveform modulated UWB proposal for IEEE 802.15 TG4a.] Purpose: [For discussion by IEEE 802.15 TG4a.] 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. NOTE: Update all red fields replacing with your information; they are required. This is a manual update in appropriate fields. All Blue fields are informational and are to be deleted. Black stays. After updating delete this box/paragraph. NOTE: Update all red fields replacing with your information; they are required. This is a manual update in appropriate fields. All Blue fields are informational and are to be deleted. Black stays. After updating delete this box/paragraph. Submission Slide 1 Soo-Young Chang, CSUS

  2. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 WAVEFORM MODULATED LOW RATE UWB SYSTEM- Proposal for 15.4a alt PHY- Soo-Young Chang California State University Submission Slide 2 Soo-Young Chang, CSUS

  3. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 INTRODUCTION • Use short duration impulses: purely processed in time domain, not in frequency domain • Simple concept • Simple digital processing  Low complexity  low cost • No components for processing frequency information (e.g. filter, osc., etc.) • High location accuracy and fast ranging with very short duration pulses • Stealth mode of operation possible with relatively small RF signature by coding frequency subbands with orthogonal codes • Excellent co-existence capability due to adaptive frequency band usage Submission Slide 3 Soo-Young Chang, CSUS

  4. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 PLAUSIBLE MYTHS • Myth 1 • ‘Low rate needs less power consumption.’  With high rates, low power consumption can be achieved. • Myth 2 • ‘Digital implementation needs more complexity and is not easily realizable with the state-of-the art technologies.’  Digital implementation can be realized with less complexity and provide more flexibility. • Myth 3 • ‘Higher frequency is not easy to manage or implement.’  Unless high power is not considered, digital processing method can be applied for higher frequency band. • Myth 4 • ‘Since this technology was not realizable yesterday, today also it is not easy to realize.’  Since technologies advances rapidly, more sophisticated and conceptual ideas should be considered for future applications. Submission Slide 4 Soo-Young Chang, CSUS

  5. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 CONSIDERATIONS FOR LOW RATE UWB (1) • Frequency band • Enjoy full frequency band assigned: 3.1 – 10.6 GHz in the US • Only max power spectral density is limited: Transmitted power is proportional to the bandwidth • Pulse width is inversely proportional to bandwidth: more accurate ranging possible for time based ranging • Large bandwidth entails low fading • High rate sampling is needed • To overcome this problem, new processing method should be devised • Transmit power • Enjoy full power transmitted under frequency mask if waveforms have the spectrum similar to frequency mask • Max power will be -41.3dBm/MHz*7500MHz = -2.54dBm = 0.5mW • More transmit power needs more power consumption ???  New waveform is needed to fit exactly to frequency mask Submission Slide 5 Soo-Young Chang, CSUS

  6. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 CONSIDERATIONS FOR LOW RATE UWB (2) • Data rate • In TRD, “low rate” is suggested with expectation to reduce power consumption and complexity/cost • Power consumption is mainly proportional to the time of signal transmission and processing • No need to reduce data rates if higher rates possible with the same cost/efforts • with higher data rate, less probability of conflict with other transmissions for CSMA and higher success rate with ack • More pulses may be transmitted for the same information with higher rates: more redundancy can be achieved • The amount of information delivered is the key issue for any communication systems • The higher the data rate is, the less time it takes to deliver.  More sophisticated signal processing for higher rate is inevitable. • Full digital processing • Provide full flexibility for any change in signal environments, system concepts and requirements • May also be compatible with a variety of complex digital modulation schemes • Eliminate the cost and complexity of a down conversion stage  Sophisticated digital signal processing technologies needed including high speed ADCs and DACs with sampling rate > 1 Gsamples/sec Submission Slide 6 Soo-Young Chang, CSUS

  7. Modulation/demodulation Source coding Channel coding (FEC) ARQ not considered Interleaving Pulse generation Antenna Multiple access Synchronization LNA Message relaying Simultaneously operated piconet (SOP) Localization function Transmit only device • doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 KEY CONSIDERATIONS Submission Slide 7 Soo-Young Chang, CSUS

  8. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 FREQUENCY PLAN • Flexible enough to satisfy any frequency mask and to avoid any forbidden bands  pulse waveforms can be adaptively tailored to any frequency mask applied • With FCC mask, 3.1GHz to 10.6 GHz full frequency band is used to enjoy more transmitted power  3.8 dB more power used than Gaussian pulse’s case in the same frequency band  3.8 dB more margin for link budget Submission Slide 8 Soo-Young Chang, CSUS

  9. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 FREQUENCY SUBBANDS • Whole frequency band under FCC mask is divided into 4 groups • Each group has 4 subbands • BW of a subband = (10.6-3.1) GHz /16 = 469 MHz • Each subband has its own waveform group 2 group 3 group 4 group 1 f 3.1 GHz 10.6 GHz subband 2 subband 3 subband 4 subband 1 f base waveform w23 w24 w21 w22 Submission Slide 9 Soo-Young Chang, CSUS

  10. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 PULSE WAVEFORM OF SUBBAND • Pulse waveform shape • Mathematical derivation/expression • Shape: duration: 9 ns • Spectrum: flat throughout whole band • How can pulses be generated • Digital way? Overlapped with various delays  can be generated with relatively lower sampling rate DACs • 100 samples/waveform: • 16 waveforms/group for binary representation 81 waveforms/group for ternary representation • 1600 or 8100 sample information stored in ROM per group  1.6 or 8.1 Kbytes ROM needed to store waveform information if 8 bits/sample is adopted • Generate waveforms using DACs which has a sampling rate of 1 Gsamples/sec • Analog way? • No idea • 4 digital ways considered in this proposal • How can delay devices for TX and RX be implemented?  Cost/accuracy/step size are the key issues Submission Slide 10 Soo-Young Chang, CSUS

  11. 0.2 2 0 0.15 amplitude in dB -2 0.1 amplitude -4 0.05 -6 0 -8 -0.05 -10 -0.1 -12 -0.15 -14 -0.2 -16 -10 -8 -6 -4 -2 0 2 4 6 8 10 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 frequency time • doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 TYPICAL PULSE WAVEFORM AND ITS SPECTRUM • For each subband, there is one waveform which has flat spectrum as shown in the above. • Group i has four base waveforms: wi1, wi2, wi3 , and wi4 • Group i has 16 waveforms: mi1, mi2, mi3, . . . , mi16 mij,=a* wi1 +b* wi2 +c* wi3 +d* wi4 where a, b, c, and d are determined by modulation method applied Submission Slide 11 Soo-Young Chang, CSUS

  12. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 POSSIBLE MODULATIONS • OOK • Two levels: +1, -1 • Anti-podal: BPSK • Two levels: +1, -1 • OOK + Anti-podal • Three levels: +1, 0, -1 • n level modulation • nQAM Submission Slide 12 Soo-Young Chang, CSUS

  13. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MODULATION/MA EFFICIENCY • Energy or power efficient? joule/sec • Energy=power*time • Power limited by FCC mask • Pmax=-41.3dBm/MHz*7500MHz=-2.54dBm=0.5mW • To use more energy, more time needs to be transmitted  totally related to time • for UWB, BW>500MHz or fractional BW>20% of fc  short duration pulses • use multiple pulses for one bit (or symbol) • need more power under frequency mask to have higher power • power constrained with frequency mask for UWB case • new waveform needed to have more transmitted power • Spectrally efficient? bit/Hz • Not important for UWB because of plenty of bandwidth • Time efficient? bit/sec • For higher rate, more important: for lower rate, less important  more room for flexibility for LR-WPAN • However, as bit duration increases, more power consumption may be required Submission Slide 13 Soo-Young Chang, CSUS

  14. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MODULATION PROPOSED • Proposed Mod (1) • 8 frequency bins are coded with an 8 bit Walsh code and represent one bit using BPSK • Proposed Mod (2) • 4 waveforms of a subgroup are mapped to 2 bit (quaternary) information ex) m1,1(t)  00 m1,6(t)  01 m1,11(t)  10 m1,16(t)  11 • Each user sends information using one subgroup of each group  at one time 8 bit information is delivered • Each waveform is modulated by OOK or BPSK or OOK+BPSK Submission Slide 14 Soo-Young Chang, CSUS

  15. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 WAVEFORMS FOR EACH GROUP group 2 group 3 group 4 group 1 f 3.1 GHz 10.6 GHz m1,1(t) m1,1(t) m1,1(t) m1,1(t) m1,1(t) m1,1(t) m1,1(t) m2,1(t) m3,1(t) m1,1(t) m1,1(t) m1,1(t) m4,1(t) m1,2(t) m1,2(t) m1,2(t) m1,2(t) m2,2(t) m1,2(t) m1,2(t) m1,2(t) m1,2(t) m1,2(t) m1,2(t) m3,2(t) m4,2(t) m1,16(t) m1,16(t) m1,16(t) m1,16(t) m1,16(t) m2,16(t) m1,16(t) m1,16(t) m1,16(t) m1,16(t) m1,16(t) m3,16(t) m4,16(t) Submission Slide 15 Soo-Young Chang, CSUS

  16. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 SUBGROUPS FOR EACH GROUP group 2 group 3 group 4 group 1 f 3.1 GHz 10.6 GHz SG1 SG2 SG3 SG4 Submission Slide 16 Soo-Young Chang, CSUS

  17. 2 1.8 1.6 1.4 1.2 amplitude 1 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 6 7 8 9 10 Frequency( GHz.) • doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 BASE WAVEFORM FOR ONE GROUP • For four subbands – assuming each has 1 GHZ BW • If smaller BW, larger pulse width + + + t (ns) 0 4 Submission Slide 17 Soo-Young Chang, CSUS

  18. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 EXAMPLES OF WAVEFORMS m1,5(t) m1,12(t) m1,16(t) Submission Slide 18 Soo-Young Chang, CSUS

  19. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 CORRELATIONS • # of samples = 180 # of samples = 90 • Correlation ratio = autocorrelation/crosscorrelation Submission Slide 19 Soo-Young Chang, CSUS

  20. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 DATA RATES • 1 Mbps max with 100% overhead  Tb = 1/2 Mbps = 500 ns • Pulse width = 9 ns  Duty cycle = 2 % 500 ns 500 ns Submission Slide 20 Soo-Young Chang, CSUS

  21. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MULTIPLE ACCESS (1) • Possible MAs considered • Frequency hopping (FH) among groups • Not efficient because of uncertainty of FCC’s ruling on FH so far and less usage of power • TDMA • Less time efficient • Direct-sequence (DS) CDMA • Less time efficient and more complex f Group 4 Group 3 Group 2 Group 1 t1 t2 t3 t4 t5 t 16 frequency bins time domain bins Submission Slide 21 Soo-Young Chang, CSUS

  22. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MULTIPLE ACCESS (2) • For each subband, one base waveform exists • 16 base waveforms: w11(t), w12(t), w13(t), w14(t), w21(t), . . . . , w43(t), w44(t) • Each waveform is almost orthogonal to each other • Each group has • 16 waveforms for mod (1) or 81 waveforms for mod (2) • m1,1=0, m1,2= w1, m1,3= w2, . . . . , m4,16= w13+ w14+ w15+ w16 Submission Slide 22 Soo-Young Chang, CSUS

  23. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MULTIPLE ACCESS (3) • Correlation where : kth sample of ith waveform of a subband for N samples • Ratio of correlations = autocorrel/crosscorrel for various N values • Orthogonality holds for sinusoidal waveforms with some conditions (Orthogonality condition, refer to next slide), but the waveforms used here are not sinusoidal with some envelope • At receiver, a processing procedure can be used to make pure sinusoidal for a period • mij*mij=(a* wi1 +b* wi2 +c* wi3 +d* wi4 )(a* wi1 +b* wi2+c* wi3 +d* wi4) where mij is the waveform transmitted and mij is the waveform generated at RX • After integrate for a one waveform duration, only autocorrelation terms remain • Orthogonality can hold at RX during detection • What is the best sampling frequency such that orthogonality can be achievable? Submission Slide 23 Soo-Young Chang, CSUS

  24. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 ORTHOGONALITY OF SINUSOIDS • A key property of sinusids is that they are orthogonal at different frequencies. That is, • This is true whether they are complex or real, and whatever amplitude and phase they may have. All that matters is that the frequencies be different. Note, however, that the sinusoidal durations must be infinity. • For length sampled sinusoidal signal segments exact orthogonality holds only for the hamonics of the sampling rate-divided-by- , i.e., only for the frequencies • These are the only frequencies that have a whole number of periods in samples • Ex. N=100 for 4 ns pulse duration, fs=25 GHz • fk=k*25*10**9/100=2.5*10**8*k=0.25*k GHz • For any integer k, fk can be determined  center frequencies of each subband can be determined http://ccrma.stanford.edu/~jos/r320/Orthogonality_Sinusoids.html Submission Slide 24 Soo-Young Chang, CSUS

  25. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MAPPING FREQUENCY BINS TO WALSH ENCODED SYMBOLS Submission Slide 25 Soo-Young Chang, CSUS

  26. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 MUTIPLE ACCESS (4) • A orthogonal set of 8 8-bit Walsh codes is used • Max autocorrelation, min (or zero) crosscorrelation each other • One code consists of 8 frequency domain bins • Minimal Hamming distance of this code set is 4 • One frequency bin error can be corrected while three bin errors can be detected; works as an ECC code; increases robustness • 8 SOPs case • For one user, one code is assigned • One time domain bin is occupied by two codes • Each code represents one bit; one time domain bin represents two bits; one time domain bit deliver two bits • 64 SOPs case • For one user, two codes (16 bits) are assigned • One time domain bin is occupied by two codes • two codes represent one bit; one time domain bin represents one bit; one time domain bit deliver one bit Submission Slide 26 Soo-Young Chang, CSUS

  27. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 TRANSMITTER STRUCTURE • Simple structure with impulse radio concept • FEC encoder • Interleaver • Pulse generator • Modulator • Antenna antenna This part can be realized using digital processing Data in Data manipulator modulator Source coding Channel coding interleaving Pulse generator Submission Slide 27 Soo-Young Chang, CSUS

  28. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 TRANSMITTER BLOCK DIAGRAM ROM, group 2 S/P converter data manipulator input data encoding interleaving encryption ROM, group 1 DAC waveform transformer DAC waveform transformer ROM, group 3 DAC waveform transformer ROM, group 4 DAC waveform transformer Submission Slide 28 Soo-Young Chang, CSUS

  29. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 RECEIVER STRUCTURE • Simple receiver structure • Antenna - Pulse generator • LNA - Location processor • Demodulator • Data detector • De-interleaver • Channel decoder • Synchronizer location Synch Information retriever Pulse generator demodulator detector Data De-manipulator Data out antenna LNA Submission Slide 29 Soo-Young Chang, CSUS

  30. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 RECEIVING BLOCK received signal correlation pulse generator Time correlator concept ROM waveform conditioner ADC correlator correlation LNA 6 bit Flash Submission Slide 30 Soo-Young Chang, CSUS

  31. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 LINK BUDGET ANALYSIS • AWGN and 0 dBi gain at TX/RX antennas assumed. Fc=5.73GHz Submission Slide 31 Soo-Young Chang, CSUS

  32. doc.: IEEE 802.15-05-0028-00-004a Jan. 2005 WHY THIS PROPOSAL? • More transmit power used under frequency mask • More margin: at least 3 dB more by using full power under any frequency-power constraints with waveforms adaptive to frequency mask  Spectrally efficient / more received signal power  More chance to intercept signals • Very simple architecture • Directly generated pulse waveforms using ROM • Processing in digital methods • No need to have analog devices, i.g., mixers Los, integrator, etc.  low cost / low power consumption • High location accuracy • Wider bandwidth for each waveforms  narrower pulse width  more accurate location information • High adaptability to frequency, data rate, transmit power requirements  high scalability in frequency, data rate, system configuration, waveform, etc. Submission Slide 32 Soo-Young Chang, CSUS

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