Ultra-Wideband (UWB) Wireless Communications

Transcription

1 Ultra-Wideband (UWB) Wireless Communications Associate Professor Center for Manufacturing/ ECE Department nological University Presented at Virginia Tech Nov. 20,

2 Outline Introduction UWB Principles UWB Propagation Mechanisms Time Domain UWB based IEEE a Multi-band OFDM Per-Path Path Pulse Distortion Physics-based System Modeling Conclusion 2

3 Mobile Devices Market Segmentation odules - mbedded Apps elematics / elemetry dd-on evices ata Devices / Integral ireless usiness / mart hones asic hones Nokia 3330 PDQ Smart Phone Ericsson R380 RIM Blackberry HP Jornada 720 w/ PC Card Palm HandSpring Visor, Spring Board Modules Greater Multi-Media Capability Larger Displays / Touch-Screens and Keyboards Multi Wireless Modes & Generally Higher Data Rates 3

4 3G & UWB Combining Air Interface Complementing Technologies 3G Local Area Network Personal Area Network WLAN UWB WCDMA EDGE CDMA2000 Wide Area Network Not to Scale 1 Wide Area cell = ~ WLAN cells 4

5 Supporte UWB OFDM Alliance Authors 5

6 UWB Applications 6

7 UWB Applications (IEEE a) WPAN (range<10m) for multimedia digital stream ( Mbps) Home Entertainment Devices Home Network Devices PC Enterprise Business Market HandSpring Visor, Spring Board Modules 7

8 UWB Communications & Sensor Networks Environments Real-time Distributed Dynamic Hostile Applications Remote surveillance, threat detection Video to the foxhole/battlefield High-resolution location services Key Technologies Ultra-wide band systems Mobile, adhoc networks Data fusion / synthesis Open Research Issues System and protocol design Analysis, performance modeling Test-bed development / trials 8

9 What Is Ultra-Wideband (UWB)? Definition (In radar,etc) f u -f l =25% f u +f l Where: f u = upper 10 db down point f l = lower 10 db down point Or greater than 500 MHz (FCC Feb 2002) At FCC Part 15 powers (a few tens of microwatts total - across several GHz), cannot be reliably measured below 10 db down points 9

10 .5 GHz UWB Spectrum Allocated by FCC 02/200 10

11 FCC Feb Ruling 11

12 Time Modulated Ultra-Wideband Wideband An Not a sinewave,, but millions of pulses per second Example 500 ps Time coded to make noise-like Channelization Anti-jam Smooths spectrum Amplitude Randomized Time Coding Time 0 1 Power Spectral Density (db) Frequency (GHz) Random noise signal Frequency (GHz) Pulse position modulation δ δ δ = 125 ps 12

13 UWB with PPM An Example d = data sequence, addition binary pulse position Tennessee modulation Tech 13

14 UWB Impulse Radio (simplified) Example free space UWB XMIT 1 µw /MHz 1 ns (time) 1 foot (space) Channel=Filter UWB RCV 0 1 GHz 2 GHz 3 GHz Radio Frequency Power Spectra 14

15 Propagation Measurement Received Signal (mv) MHz Impulse at 12 meters in an Office Building Direct Path Pulse Multipath Pulses Pulse Generator 2 MHz -6 Time (nanoseconds) 650 Impulse Signal at 3 meters in an Office Building 0 Trigger line PC Computer Antenna Signal Power (db) Multipath Effects UHF TV Ambient RF Cellular Frequency (MHz) HP54120B Digital Oscilloscope LNA Source: Robert Schultz, USC 15

16 Physics of UWB scattering - Multipath Fading Immunity Benefits Path-1 Deep Fade Path Time (nanoseconds) Frequency (MHz) Wide bandwidth means signal and correlator outputs can be short in time Result is that multipath components can be separately resolved time domain paradigm shift Each component can have full bandwidth Narrowband systems can confuse multipath with attenuation The two top charts are time & frequency duals Fading immunity means channel model closely follows R 2 (free space) rather than R 3.5 or R 4 Leads to robust in-building operation Bottom chart shows actual signal strength measured in a typical office environment (blue) along with reference R 3.5 (red) and R 2 (green) traces Range (feet) Multipath fading immune Exceeds specified delay spread Reduces Required Link Budget 16

17 Shannon s Equation Information Theory Benefits S P0 B P0 C = B log 1 + = B log 1 + = B log 1 + N KTB KT Regulatory limits provide Watts/Hz for UWB P 0 ( ) igh order modulation Allows data rate capacity C to be larger than channel bandwidth B BUT requires high SNR and allows the trades data-rate for range or power at an unfavorable log function with power. ow order modulation and B>>C linearly trades data-rate for range or power allows software controlled integration-gain to push bandwidth into the SNR Allows simple, inexpensive, low-linearity, radio implementation Large BW high capacity with low order modulation & low power Data rate is proportional channel bandwidth B Bandwidth comes from IC process in the proposed solution Moore s Law Radio 17

18 Channel Measurement Test Setup Channel Transmit Ant Rcv Ant & Mount Trigger Cable 50 ft. RG-223/U 21 4 GHz 78 nsec delay DSO TDC SG 10 ns/div 350 Averages Floppy Miteq 30 4 GHz 0.4 nsec delay Preamp NF = 2.2 BC1 50 ft. RG-223/U 21 4 GHz 78 nsec delay Ch.1 Trig HP54750A Ch Vdc P.S. Calex CM BC2 3 ft. RG-223/U GHz 4.5 nsec delay db High Pass Filter, ISM, & PCS Notch f (GHz) 1.0 nsec delay -1.6 db Male to Male SMA HP8494B 0-11 db, 1 db Step Variable Attenuator 4.5" of Semi Rigid HP8495B 0-70 db, 10 db Step Variable Attenuator 1.4 nsec delay GHz at 0 db step BC5 2 ft. RG-223/U GHz 3 nsec delay HP8449B 1.5 nsec delay 37 4 GHz Preamp NF = 9 22 nsec Delay Line HP54008A 2 4 GHz BC6 2 ft. RG-223/U GHz 3 nsec delay 18

19 Transmitted and Received Pulses 3.00E E E E E-02 Amplitude (V) 0.00E E-02 Amplitude (V) 5.0E E E E E Time (ns) -2.5E Time (ns) Transmitted voltage waveform measured at coax input to the horn Received waveform shows a single time differentiationtent n Small Antenna gain 19

20 Representative Measurements II Office Rcvd Blocked LoS Hold Rcvd Clear LoS Hold Rcvd Blkd LoS ns 200 ns ns time (nanoseconds) time (nanoseconds) time (nanoseconds) ns time (nanoseconds) time (nanoseconds) time (nanoseconds) 20

21 IEEE a A A Review What is going on? Technical Issues of Proposals 21

22 Why UWB and why spectrum agility? Why UWB for IEEE a? UWB technology is uniquely suited for high-rate, short range access» Theoretical advantages for approaching high rates by scaling bandwidth» Newly allocated unlicensed spectrum (7.5 GHz) that does not take away from other narrowband systems (licensed or unlicensed)» CMOS implementations now possible at these higher frequencies All CMOS architecture Why spectrum agility for a UWB solution? Just because the FCC allows UWB to transmit on top of other services does not mean we should!» Government regulations should be broader than industry requirements Spectrum usage and interference environment changes by country location, within a local usage area, and over time» Enable adaptive detection and avoidance strategies for better coexistence and possible non-contiguous spectrum allocations for flexible regulations in future Allow for simple backward compatibility and future scalability 22

23 Flexible Spectrum Use Unexpected Interferer Low Frequency Set Group High Frequency Set Group ~ Drop band in Sacrifice sub-band for coexistence Japan Drop band interference Europe mitigation (based on regulation and geographical location) Reserved Center frequencies chosen for ease of implementation 440 MHz band separation for improved flexibility ~538 MHz wide bands to best utilize spectrum 23

24 Why did 10 Companies Propose Multi-Band Solutions in March 2003? Some of the reasons include: Spectrum Flexibility / Agility Regulatory regimes may lack large contiguous spectrum allocations Spectrum agility may ease coexistence with existing services Energy collected per RAKE finger scales with longer pulse widths used Fewer RAKE fingers Reduced bandwidth after down-conversion mixer reduces power consumption and linearity requirements of receiver Fully digital solution for the signal processing is more feasible e than a single band solution for the same occupied bandwidth Transmitter pulse shaping made easier Longer pulses easier to synthesize & less distorted by IC package e & antenna properties Have the ability to utilize an FDMA mode for severe near-far scenarios doc.: IEEE /xxxr0 Nov

25 Most of the Multi-Band Proposals in March 03 used Pulses, What Happened? Energy collection under severe multipath (CM3, CM4) required improvement We needed a computationally efficient method of multipath combining Parallel receivers? Infinite RAKE? OFDM? OFDM in each sub-band band was selected as a successor to the pulsed multi-band approaches doc.: IEEE /xxxr0 Nov

26 Why are 34+ Companies Now Supporting the Multi-band OFDM Approach? Multi-band OFDM kept the unique Multi-Band benefits and solved the energy collection problem very elegantly Feasibility studies of FFT and Viterbi cores showed encouraging numbers for gate-count and power consumption Multi-band OFDM suitable for CMOS implementation (all( components) Antenna and pre-select filter are easier to design (can possibly use off-the the-shelf components) Low cost + low power + CMOS integrated solution = early market adoption a Scalability: Digital section complexity/power scales with improvements in technology nodes (Moore( Moore s s Law). Analog section complexity/power scales slowly with technology node Much more can be said in detail about the Multi-band OFDM PHY performance, but first we should review our proposal doc.: IEEE /xxxr0 Nov

27 Overview of OFDM OFDM was invented more than 40 years ago Adopted by numerous standards effort:» Asymmetric Digital Subscriber Line (ADSL) services.» IEEE a/g; IEEE a» Digital Audio Broadcast (DAB); Home Plug» Digital Terrestrial Television Broadcast: DVD in Europe, ISDB in Japan OFDM is also being considered for 4G, IEEE n and OFDM is spectrally efficient. IFFT/FFT operation ensures that sub-carriers do not interfere with each other OFDM has an inherent robustness against narrowband interference. Narrowband interference will affect at most a couple of tones. Information from the affected tones can be erased and recovered via the forward error correction (FEC) codes OFDM has excellent robustness in multi-path environments. Cyclic prefix preserves orthogonality between sub-carriers. Cyclic prefix allows the receiver to capture multi-path energy more efficiently 27

28 Overview of Multi-Band OFDM Basic idea: divide spectrum into several 528 MHz bands Information is transmitted using OFDM modulation on each band OFDM carriers are efficiently generated using an 128-point IFFT/FFT Internal precision is reduced by limiting the constellation size to QPSK Information bits are interleaved across all bands to exploit frequency diversity and provide robustness against multi-path and interference 60.6 ns prefix provides robustness against multi-path even in the worst channel environments 9.5 ns guard interval provides sufficient time for switching between bands Solution is very scalable and flexible Data rates, power scaling, frequency scaling, complexity scaling 28

29 Proposal for IEEE a 29

30 30

31 Per-Path Pulse Distortion Physics-based Modeling 1 c t 2 2 ( ) E( tt, '; rr')=-, δ( t-t') δ( r-r' ) 2 2 Rx 2 2 ( + k ) E( k, rr', ) = δ ( r-r' ) UTD/MOM A B A N αn H( ω) = A ( jω) e h n= 1 n 1 jωτ N α n 1 ( τ ) = An τ δ( τ τn) n= 1 Γ ( α n ) n attering Center [Qiu, 1995] α n = 1 2 for a single edge diffraction Multiple diffraction must be included! 31

32 Generalized RAKE Receiver δ ( τ ) τ τ 1 τ τ 2 τ τ N j 1 A e φ j 2 A e φ 1 2 j N AN e φ Turin s Model [Since 1956] δ ( τ ) τ τ 1 τ τ 2 j 1 A e φ j 2 A e φ 1 2 τ τ j N AN e φ N N j n h() τ = Ae φ δτ τ n= 1 n ( n 1 Dα τ 2 Dα τ N Dα τ Qiu, Ph.D. Thesis [1995] n = 1 N jφn αn h() τ = Ae D δτ τ n τ ( 32 n

33 Concept of UWB Pulse Distortion due to Diffraction N N N N 1GO 2 GO GTD GO / GTD h( τ ) = A δ( τ τ ) + B R ( τ) δ( τ τ ) + C g ( τ) δ( τ τ ) + D [ R ( τ) g ( τ)] δ( τ τ ) n n n n n n n n n n n n n= 1 n= 1 n= 1 n= 1 Edge Wedge Ground N Distorted Pulse αn jωτn ( ω) = n ( ω) n= 1 N 1 α n 1 ( τ ) = An τ δ( τ τn) n= 1 Γ ( α n ) H A j e h UWB pulse distortion is a physical phenomenon!!! 33

34 Waveform Distortion can be Modeled as the Singularity of Wavefront for a Ray h n ( τ ) C ξ ( τ τ) ( τ τ), τ τ = D η( τ τ) ( τ τ), τ > τ n n α α < α n= 0 n! n n α α α n= 0 n! D 1 n t n t C 1 n t n t Hn( ω) = η( ) t e dt ξ( ) t e dt n 0 n 0 n 0 n!( jω) = jω n!( jω) jω The impulse responses of localized scattering centers in a generalized ray can be modeled as the early-time responses in the time domain or asympotic approximation of time-harmonic fields in the FD! (Kline 1956) 34

35 Exact Solution UWB Diffraction by Half-Plane u = u ± u = A e F( 2kr cos( θ ϕ)) ± A e F( 2kr cos( θ + ϕ)) jkr cos( θ ϕ) jkr cos( θ+ ϕ) u( ω ) 2 r / c cos 2( θ ϕ) cos 2( θ + ϕ) 1 1/2 h( τ) L = τ δ( τ r / c) u0 2 π r r τ + cos( θ ϕ) τ + cos( θ + ϕ) τ r / c c c P ( r, θ ) y H r E π j 4 e 2 j F ( x) = µ e dµ x π r θ o φ Half Plane x 1 F z = erfc e z 2 jπ /4 ( ) ( ) At the wave front a PEC edge has a singularity of α τ α = 1/2 1. τ 35

36 ystem Performance Optimum Receiver λd ( τ ) Pe = Q, d ( τ 0 ) = 1 Rp ( t) p ( t τ )( τ 0) 1 R τ ( τ ) = ptpt ( ) ( τ ) dt pt () pt ( 0 ) 0 0 E p 0 L 1 pt () = p () t ht (), ht () = ah() t δ ( t τ ) TX l l l l= 0 R ( ) p () t p ( t τ )( τ 0) = Rpp( t) h( t) h( t) δ( t τ0) 0 36

37 Diffraction-Based Pulse Shape Transform 1.5 Diffracted Signal d(t)and Template Signal v(t) d(t) and v(t) alpha= -1: 0.25: 0 (bottom to top) alpha=0 <==> Incident Waveform Red dashed Template Pulse v(t) time t (ns) 37

38 Summary UWB is one of the most promising technologies 7.5 GHz unlicensed spectrum from GHz Volume products will be shipped in years UWB is good for both short-range range (10-30m) and long-range ( m) 1000m) Per path pulse distortion in a UWB channel is one of the majo potential problems in system design Experimental measurements needed Physics-based system modeling UWB MIMO is good for extending UWB range 38

39 Thank You! 39