doc IEEE 802 11 040141 r 0 January

doc. : IEEE 802. 11 -04/0141 r 0 January 2004 Measurements and Modeling for the 5. 9 GHz WAVE Vehicle to Vehicle Channel Prof. Mary Ann Ingram School of Electrical and Computer Engineering Georgia Institute of Technology January 2004 Submission 1 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Objective and Approach • Determine the worst case for the 5. 9 GHz DSRC mobile-to-mobile channel • Channel measurements and literature used to determine extreme channel parameters • Computer simulations and throughput of LINKSYS 802. 11 g link over a channel emulator used to rank channel harshness Submission 2 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Overview of This Talk • Channel parameterization and worst-case trends • Review of Results – – Literature survey Channel measurements SIMULINK simulations Emulator throughput tests • Conclusions • Discuss next steps Submission 3 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Channel Description • • • Vehicle-to-vehicle (V 2 V) All vehicles going 80 mph Range up to 1000 m Small-scale fading only OFDM – 52 subcarriers (48 data, 4 pilots) – 1. 6 ms guard interval – 10 MHz bandwidth Submission 4 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Channel Parameterization N Number of paths Delay of the nth path Gain of the nth path Submission 5 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Current Test Parameters Parameter Description N No. of taps Excess delay of nth tap Path loss tn L Pn Sn ( f ) Kn Submission Normalized tap power distribution PSD of nth tap Rice factor of nth tap Multi. Path Test 2 200 ns Doppler Spread Test 1 0 Min sens. + + 3 d. B Equal 0 d. B (-3 d. B each) Flat d ( f + 2100 Hz) + or d ( f ) d ( f - 2100 Hz) +¥ +¥ 6 Amplitude Variation Test 1 0 Rician Test Min sens. + 3 d. B 0. 5 d ( f + 100 Hz) + 0. 5 d ( f - 100 Hz) +Ad ( f ) +¥ 1 0 6 d. B Classical (“bathtub”) spectrum 10 d. B Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Worst-case Parameter Trends Submission 7 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Definitions of Worst-case Channel • The channel that has the worst-case extreme values for every parameter • A harsh channel that causes a “welldesigned” receiver to nearly fail at a range of 1000 m Submission 8 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Overview of This Talk • Channel parameterization and worst-case trends • Review of Results – – Literature survey Channel measurements SIMULINK simulations Emulator throughput tests • Conclusions • Discuss next steps Submission 9 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Literature Survey • Most papers treat Roadside-to-vehicle • For vehicle-to-vehicle, – Path loss will be higher – Delay spread will be lower – Doppler will be higher – K factor will be lower • Consider overbound for delay spread vs. path loss Submission 10 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Path Loss • 2 -ray model at 1000 m – Roadside-to-vehicle, 2. 6 GHz • Theory: 105 d. B • Measured: 120 d. B – Microcell, antenna ht = 3. 7 m, 1. 9 GHz: 112 d. B – Tokoyo street microcells, 2 GHz: ~112 d. B – Roadside-to-vehicle, 5. 8 GHz, measured agrees well with 2 -ray for uncluttered, LOS channel • Truck or bus diffraction loss: >= 20 d. B Submission 11 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Intersection of Worst-case Environmental Features • Intersections with main-street urban canyons with numerous glass/metallic reflectors, including distant reflectors and clutter near transmitter or receiver • Tall, dumb directional antennas not directed at LOS with no downtilt • Relatively large TX-RX separations Submission 12 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Platoon Vehicle-to-vehicle Delay Spread Summary • Delay spreads are small because in the platoon application vehicles are crowded Submission 13 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Delay Spread Overbound vs. Path Loss • 1. 9 GHz • Microcell • V 2 V delay spead will be lower Up to 13. 3 m antenna height 3. 7 m antenna height ~ 1 ms 112 d. B Submission 14 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Doppler Spectra • Theoretical V 2 V flat-fading, based on circle -to-circle scattering model • Measured V 2 V flat-fading • Measured roadside-to-vehicle frequency selective (per-tap spectra) Submission 15 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Circle-to-circle V 2 V Flat-fading Model Single-ring model TX Double-ring model RX TX RX The critical parameter is the ratio of vehicle speeds Submission 16 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Spectra for the Circle-to-circle Model equal velocity • The first few taps of our measured freeway spectra resemble the a=1 spectra Submission V 1=2 V 2 fixedto-veh. 17 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Measured Flat-fading Vehicle-to. Vehicle Spectra Urban Highway Submission 18 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Fixed-to-Vehicle Per-tap Doppler Spectra Submission 19 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Fading Distribution • Flat-fading vehicle-to-vehicle @ 5. 2 GHz: Rician • Per-tap vehicle-to-vehicle @ 900 MHz: Rician 1. 38<K<17. 6, typically 5<K<11 • Per-tap fixed-to-vehicle – LOS: 2 d. B<K<5. 5 d. B on early taps, Rayleigh on late taps – NLOS: -1 d. B on 1 st tap, Rayleigh on late taps Submission 20 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Conclusions From Literature Study • Extreme vehicle-to-vehicle parameter values – Path loss @ 2 GHz, 1000 m = 120 d. B – Delay spread @ 1000 m = 1 ms (pessimistic) • Doppler per tap – All shapes are possible • Fading distribution: K values as low as -1 d. B on 1 st tap, Rayleigh on rest Submission 21 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Overview of This Talk • Channel parameterization and worst-case trends • Review of Results – – Literature survey Channel measurements SIMULINK simulations Emulator throughput tests • Conclusions • Discuss next steps Submission 22 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Channel Measurements in Atlanta, Georgia • Phase I – OTS 802. 11 b sniffer – Delay only – 7 sites identified with large spreads (~300 ns) – Reported in August 20, 2003 presentation • Phase II – Custom DSSS sounding at 2. 4 GHz up to 300 m range – Delay and Doppler – Reported in November 11, 2003 presentation Submission 23 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 News Since November • Low-power intermodulation-like products apparent in post-collection testing of equipment • Phase II delay and most powerful Doppler components deemed reliable Submission 24 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Main Observations of Phase II • Majority of delay profiles are unimodal with no more than 3 significant 50 ns taps • Delay spreads of 300 ns confirmed when Phase I sites were re-visited • An absolute delay of 600 ns was observed • Up to 8 consecutive taps within 7 d. B of each other observed • Repeatable per-tap Doppler profiles, not previously published, measured on freeway Submission 25 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Example of Isolated High Values of Delay Spread From Phase I Peak occurred when passing the intersection in the middle Delay vs. sounding sample delay, nsec RMS Delay Spread of MA (L=10) of Sounding Samples Ignoring L Samples after 35 Threshold = -70 d. Bm 0 30 0 25 0 20 0 15 0 10 0 5 0 0 0 300 ns 0. 5 1 1. 2 5 Sounding 2. 5 3 3. 5 samples Submission 26 Mary Ann Ingram, Georgia Tech 4 x 10 4

doc. : IEEE 802. 11 -04/0141 r 0 Extreme Absolute Delay Spread of 600 ns (301 ns rms) Freeway exit ramp 600 ns (180 m) Submission 27 10 d. B Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Extreme Number of Strong Consecutive Taps T-intersection with tennis courts, parking lots, and 4 -story bldgs Power Delay Profile 10 d. B Eight 50 ns taps Submission 28 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Two Passes Through a Freeway Channel Vehicles going in same direction in slow lane (55 mph) Power Delay Profiles Pass 1 Pass 2 Submission 29 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Short-time (50 ms) and Long-time (0. 7 s) Spectra for Pass 1 -600 Hz +600 Hz -1000 Hz +1000 Hz Tap 1 Submission Tap 2 30 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Taps 3 and 4 400 Hz Tap 4 component is transient Tap 3 Submission 31 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Suspected Origin of 400 Hz Component • Scaled to 5. 825 GHz and 80 mph, this component is 1, 383 Hz • Current Doppler shift in Std is 2100 Hz Path is closing at nearly 110 mph 55 mph Submission Stationary Reflector 55 mph 32 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Tap 6 • Except for DC component, spectrum becomes a shallow bathtub Submission 33 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Short-time (50 ms) and Long-time (0. 7 s) Spectra for Pass 2 Tap 1 Submission Tap 2 34 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Taps 3 and 4 Tap 3 Submission Tap 4 35 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Tap 5 Submission 36 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Channel Emulator Settings That Match Highway Pass 1 (Unscaled) Path Number Path Power Delay d. B ns 1 -4. 0 0 2 -0. 0 3 fm Angle-ofarrival Frequency Offset Hz Degrees Hz 11 100 75 0 Rounded 50 30 100 80 0 Flat -5. 0 100 12 150 80 0 Rounded 4 -26 150 7 250 85 0 Classic 3 d. B 5 -25 250 1 375 98 75 Classic 3 d. B Submission Kfactor 37 Spectrum Shape Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Extremes Found in Measurements • RMS delay spread: 301 ns • Number of significant 50 ns taps: 8 • Doppler shape: box (uniform) or shallow bathtub + DC component • Maximum Doppler (scaled): 1, 383 Hz • K-factor: 1 in Highway, 0 elsewhere Submission 38 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Overview of This Talk • Channel parameterization and worst-case trends • Review of Results – – Literature survey Channel measurements SIMULINK simulations Emulator throughput tests • Conclusions • Discuss next steps Submission 39 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Simulation Description • • • Used SIMULINK standard block library DSRC and 802. 11 a specs Includes ½-rate code, interleaving and puncturing Differential modulation Receiver perfectly synchronized to LOS, regardless of delay or Doppler profiles – Gives pessimistic performance because real receiver would not always synchronize to LOS (e. g. when later tap is stronger) Submission 40 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Block Diagram Convolutional Encoder Puncturer D-QPSK Modulator Interleaver Viterbi Decoder Input Data Coding & Modulation OFDM TX Channel OFDM RX Deinterleaver D-QPSK Demodulator De-coding & Output Data Demodulation BER Calculator Submission 41 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Simulation Strategies • Vary an individual channel parameter, while keeping others fixed, to see which are the most critical channel parameters • Try various combinations of channel parameters, for example delay and max Doppler, to find combinations cause the highest BER • Emphasis BER in 10 -5 to 10 -4 range because these correspond to PERs of 10% Submission 42 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 PER Definition • Simulated 1000 -byte “packet” to get PER • Packet error declared if at least one bit in a packet is wrong • In 2 - and 3 -tap simulation with Rayleigh fading and rms delay of 300 ns or 400 ns, 10% PER Submission 10 -5 < BER < 10 -4 43 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Observations from Simulations • RMS delay spread is the most critical parameter • More paths, with fixed rms delay spread is worse • Equal tap powers is worse • Max Doppler on second tap (2 taps total) not so important when powers are equal • Rayleigh per-tap distribution is worse than Rician Submission 44 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Overview of This Talk • Channel parameterization and worst-case trends • Review of Results – – Literature survey Channel measurements SIMULINK simulations Emulator throughput tests • Conclusions • Discuss next steps Submission 45 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Throughput Testing at 2. 4 GHz • Net. IQ’s Chariot 4. 3 software used to measure throughput of a LINKSYS 802. 11 b link over the TAS 4500 RF channel emulator • Usually high SNR (received power = -35 d. Bm) • Performed long (1 GByte) and short (10 Mbytes) tests Submission 46 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Rate and Modulation Differences Between 802. 11 g and DSRC • 802. 11 g – 1 & 2 Mbps DSSS – 5. 5 & 11 Mbps CCK – 5. 5 & 11 Mbps HR/DSSS/PBCC (optional mode replacing CCK) – 22 & 33 Mbps ERP_PBCC (optional) – 6, 9 12, 18 24, 36 48, 54 Mbps OFDM – 6, 9, 12, 18, 24, 36, 48, 54 Mbps DSSS-OFDM (optional) • DSRC – 3, 4. 5, 6, 9, 12, 18, 24, and 27 Mbps, all OFDM Submission 47 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Throughput Test Set-up Submission 48 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Favorable 2 -Path Channel Showing Repeatability 54 Mbps Rate is higher than highest DSRC rate (27 Mbps) • Essentially a 1 -path model with zero Doppler Submission 49 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Unfavorable 2 -Path Channel Showing Repeatability 2 Mbps Rate is lower than lowest DSRC rate (3 Mbps) and is not OFDM • Equal-powered paths, 150 ns rms delay, Rayleigh with classic Doppler, fmax=1000 Hz Submission 50 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 2 -Path Channel Severity Ranking Submission 51 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Conclusions From the 2 -path Study • A two-path channel (Case 18) exists that nearly causes the LINKSYS 802. 11 b link to fail at high SNR • Case 18 has equal power, 600 ns absolute delay, K=7 such that each path has the equal but opposite sign maximum Doppler of 1000 Hz along with the classic 3 d. B spectrum • It doesn’t matter much if the wider Doppler spread is on the first or second path • The maximum phase channel (higher power on second path) is worse than the minimum phase channel, but not much different than the equal-power case • Lower K factors and larger delays are generally worse Submission 52 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Delay Spread Severity Ranking Submission 53 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Conclusions from the Delayspread Study • Increasing the number of paths for a fixed delay spread generally reduces the throughput • Increasing the delay spread generally decreases the throughput Submission 54 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Highway-based Severity Ranking Submission 55 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Scaling Up Doppler: 17 to 14 Mbps Submission 56 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Changing to Classic: 14 to 12. 6 Mbps Submission 57 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Going to Equal Power: 12. 6 to 2. 6 Mbps Submission 58 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Extreme Shape and Delay: 2. 6 to 0. 2 Mbps Submission 59 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Near-Extreme Doppler: 0. 217 to 0. 198 Submission 60 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Conclusions from the Highway Study • The LINKSYS link performs fairly well for the measured and scaled freeway channel • Changing the Doppler spectra to classic 3 d. B decreases the throughput • Moving from the measured power delay profile to the equal-power profile caused a significant drop in throughput • Changing the measured path delays to be equally spaced with the worst case rms delay (350 ns) takes the throughput down to its lowest values Submission 61 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Overview of This Talk • Channel parameterization and worst-case trends • Review of Results – – Literature survey Channel measurements SIMULINK simulations Emulator throughput tests • Summary and Conclusions • Discuss next steps Submission 62 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Summary • Channel measurements provided new extreme parameter values for vehicle-to-vehicle • Simulations and throughput tests provided severity rankings, however these tests do not indicate how a DSRC unit would behave • Channel with nearly all extremes but path loss caused LINKSYS 802. 11 b (lowest rates, not OFDM) to fail 2 out of 3 times Submission 63 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Conclusions • With the extreme values (including path loss) from this study, can define a worstcase 1000 m channel now • This is likely to be a very harsh channel • Not clear how a DSRC unit would perform for that channel, because we could not emulate a channel in the right band nor simulate a realistic DSRC unit Submission 64 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 What is Needed To Test a DSRC Link Over Worst-Case Channel • For simulation of a DSRC receiver, need specification of synchronization and channel estimation algorithms • For channel sounding at Georgia Tech, need new STA with about 24 d. B higher power (to reach 1000 m) and a new down-conversion stage (5. 8 GHz to 2. 4 GHz) in the receiver • For channel emulator PER testing of an 802. 11 a PCI/WLAN card, need a channel emulator that works in DSRC band, Signal Studio for the Agilent E 4438 C RF signal generator (we have) and a commercial 802. 11 a sniffer (~$3, 500) Submission 65 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 Signal Studio to Generate 802. 11 a (No Channel Emulation Shown) Submission 66 Mary Ann Ingram, Georgia Tech

doc. : IEEE 802. 11 -04/0141 r 0 A New Way to Do Channel Emulation • Eliminates expensive stand-alone channel emulator • Requires ESG Arbitrary Waveform Generator, a card for the PC, and Agilent Software for the PC • Has 802. 11 a now Submission 67 Mary Ann Ingram, Georgia Tech