Ultra-Wideband (UWB) Wireless Communications

Transcription

1 Ultra-Wideband (UWB) Wireless Communications Associate Professor Tennessee Technological University Presented at Georgia Tech Oct. 27,

2 Outline Introduction UWB Principles UWB Propagation Mechanisms Time Domain UWB based IEEE a Multi-band OFDM Per-Path Path Pulse Distortion-- --Challenge 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 UWB Applications 5

6 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 6

7 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 7

8 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 8

9 .5 GHz UWB Spectrum Allocated by FCC 02/200 9

10 FCC Feb Ruling 10

11 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 11

12 UWB with PPM An Example d = data sequence, addition binary pulse position modulation 12

13 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 13

14 Propagation Measurement 650 MHz Impulse at 12 meters in an Office Building 6 Direct Path Pulse Multipath Pulses Received Signal (mv) Pulse Generator 2 MHz -6 Time (nanoseconds) Trigger line Antenna 650 Impulse Signal at 3 meters in an Office Building 0 PC Computer Signal Power (db) Multipath Effects UHF TV Ambient RF Cellular HP54120B Digital Oscilloscope LNA Frequency (MHz) Source: Robert Schultz, USC 14

15 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 15

16 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 16

17 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 17

18 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 18

19 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) 19

20 IEEE a A A Review 20

21 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 21

22 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 22

23 Block Diagram Analog Section Antenna 26mW 24mW 10mW / 20mW UWB Filter T/R LNA + Interferer Rejection + RF VGA Down Conversion + Baseband I Q Analog To Digital 20mW / 32mW Driver 45mW / 55mW MultiBand Generator + Modulator + Shaper Timing & Control Phase Control Active blocks in Transmit Mode TX Data Active blocks in Receive Mode Active blocks in Transmit/Receive Mode Note: Power Consumption for 132 / 264 Mbps 23

24 Proposal for IEEE a 24

25 25

26 MB-OFDM 26

27 er-path Pulse Distortion Based UWB Channel 1 c t 2 2 ( ) E( tt, '; rr')=-, δ( t-t') δ( r-r' ) ( + k ) E( k, rr', ) = δ ( r-r' ) Rx 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 α n = 1 2 for a single edge diffraction Multiple diffraction must be included! 27

28 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 N jφn αn h() τ = Ae D δτ τ n= 1 n τ ( 28 n

29 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 ( ω) = n ( αn ω) jωτn n= 1 N 1 α n 1 ( τ ) = An τ δ( τ τn) n= 1 Γ ( α n ) H A j e h Distorted Pulse UWB pulse distortion is a physical phenomenon!!! 29

30 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) 30

31 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 UWB MIMO is good for extending UWB range 31

32 Thank You! 32