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1 Abdullah, NF., Piechocki, RJ., & Doufexi, A. (2010). Spatial diversity for IEEE p V2V safety broadcast in a highway environment. In ITU Workshop on Fully Networked Car, Geneva International Telecommunication Union (ITU). Peer reviewed version Link to publication record in Explore Bristol Research PDF-document University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available:

2 Spatial Diversity for IEEE p V2V Safety Broadcast in a Highway Environment 1 Nor Fadzilah Abdullah, Robert Piechocki and Angela Doufexi Centre for Communications Research, University of Bristol, UK.

3 Need for Vehicular Communication 2 o In 2007, the EU recorded ~43,000 deaths and >1.8 million injuries ( 160 billion loss) o Steady growth of car usage and ownership (>200 millions cars in Europe) congestion built-up, unpredictable journey time impact on the economy: significant vehicle operating costs overhead, burden for travellers impact on the environment: harmful emissions, worsen air quality o Allocated bandwidth for C2X services o Lowering cost of WiFi and GPS European Road Safety Observatory, Annual statistical report [Online]

4 Research Contribution 3 o Vehicular communication requires longer communication range (than a/g/n), in extreme multipath and high speed environment Spatial diversity: a low complexity and low cost solution o Accurate and realistic vehicular communication modelling by means of: BER curves from detailed PHY simulator specific to modulation types, vehicular speeds and range of SNR values Integration of PHY simulator and realistic mobility model into network simulator

5 Scenario: Post-crash warning in highway environment 4 D. W. Matolak, I. Sen, W. Xiong, and N. T. Yaskoff, 5GHZ Wireless Channel Characterization for Vehicle to Vehicle Communications, Proceedings of IEEE Military Communications Conference (MILCOM 05), vol. 5, pp , Atlatnic City, NJ, USA, Oct o Realistic mobility traces: 3 lanes bidirectional highway. o 2 types of traffic density models (Low & High). o 2 types of ad-hoc V2V safety messages Emergency message Periodic message o Rayleigh channel with 103ns rms delay spread (ETSI channel B)

6 Correlation coefficient Midamble symbol spacing as a function of channel coherence time, data rate, and packet size 5 Space-time correlation, Midamble spacing chosen: 30 symbols bytes data using IEEE p QPSK 1/2 (6Mbps) Jakes PSD (fd=1100hz) Total pkt duration (84sym=0.672ms) Tc = 0.225ms (28sym) Jakes model PSD (fd=550hz) Tc = 0.44ms (55sym) Time(s) x 10-3

7 Frame Structure for Proposed Multi Antenna System with Midamble Channel Estimation 6 o Channel tracking: reuses long preamble sequence for midamble channel estimation S. I. Kim, H. S. Oh, and H. K. Choi, "Mid-amble Aided OFDM Performance Analysis in High Mobility Vehicular Channel," IEEE Intelligent Vehicles Symposium, Eindhoven, Netherlands, Jun 2008.

8 PER Need for midamble in fast fading vehicular channel 7 o Midamble vs. Preamble at 10 symbols midamble spacing Midamble vs. Preamble at 50 km/h : preamble : midamble STBC 2x2: midamble STBC 4x4: midamble : Single Input Single Output STBC: Space Time Block Codes Modulation: QPSK 1/2 Antenna configuration Rank 1 STBC 2x STBC 4x4 3/ SNR (db)

9 Packet Delivery Ratio (%) Low Density Traffic: Emergency Message Packet Delivery Ratio in Rayleigh channel Emergency broadcast with Interference: Low Density, LoD, no priority, LoD, EDCA STBC 2x2, LoD, no priority STBC 2x2, LoD, EDCA STBC 4x4, LoD, no priority STBC 4x4, LoD, EDCA Low density traffic: 6 vehicles/km/lane Low density No priority STBC 2x2 vs. 60% (200m/125m) EDCA 80% (225m/125m) STBC 4x4 vs. 132% (290m/125m) 164% (330m/125m) Distance (m) * EDCA (Enhanced Distributed Channel Access)

10 Packet Delivery Ratio (%) High Density Traffic: Emergency Message Packet Delivery Ratio in Rayleigh channel Emergency broadcast with Interference: High Density, HiD, no priority, HiD, EDCA STBC 2x2, HiD, no priority STBC 2x2, HiD, EDCA STBC 4x4, HiD, no priority STBC 4x4, HiD, EDCA High density traffic: 11 vehicles/km/lane High density No priority STBC 2x2 vs. 70% (170m/100m) EDCA 50% (195m/130m) Low density No priority STBC 2x2 vs. 60% (200m/125m) EDCA 80% (225m/125m) STBC 4x4 vs. 65% (165m/100m) 138% (310m/130m) STBC 4x4 vs. 132% (290m/125m) 164% (330m/125m) 9 20 High density STBC 2x2 vs. STBC 4x4 vs Distance (m) EDCA improve ment Low density 15% (195m/170m) STBC 2x2 vs. 88% (310m/165m) STBC 4x4 vs. EDCA improve ment 13% (225m/200m) 14% (330m/290m)

11 Conclusion 10 o Performance of safety broadcast messages, for MIMO-STBC vs. in a vehicular environment has been presented. o Spatial diversity increase the communication range: 50-80% for STBC 2x2 and % for STBC 4x4 case. o Traffic prioritization (EDCA) is efficient in high density scenario and extends the communication range by 15% for STBC 2x2 case and 88% for STBC 4x4.

12 Spatial Diversity for IEEE p V2V Safety Broadcast in a Highway Environment 11 Appendix

13 Normalized power (db) Normalized power (db) Vehicular Channel Model 12 o Differing maximum Doppler shifts for low and high density traffic o RMS delay spread of 103ns [Matolak, 2005] Vehicular time-correlated multipath fading channel at fd=550hz 0 path1-2 path2 path3-4 path4 path5-6 path6 path7-8 path8 Vehicular time-correlated multipath fading channel at fd=1100hz path1 path2 path3 path4 path5 path6 path7 path Number of OFDM symbols per frame Number of OFDM symbols per frame D. W. Matolak, I. Sen, W. Xiong, and N. T. Yaskoff, 5GHZ Wireless Channel Characterization for Vehicle to Vehicle Communications, Proceedings of IEEE Military Communications Conference (MILCOM 05), vol. 5, pp , Atlatnic City, NJ, USA, Oct 2005.

14 Physical Layer Simulator Block Diagram 13

15 Numerical Analysis Parameters 14 Physical Layer Tx Frequency: 5.9 GHz Bandwidth: 10 MHz Tx Power: 23 dbm MAC Layer Slot Time: 13 us OFDM symbol: 8 us PLCP: 40 us Receiver threshold: -82 dbm SIFS: 32 us, CWmin: 31 Antenna gain: 0 dbi Antenna height : 1.5 m Channel Model: Rayleigh ECWmin: 7 Modulation scheme: QPSK 1/2 Application Layer DIFS: 58 us, BO = 208 us EDCA: High Priority (EM) AIFS: 58 us, BO = 52 us EDCA: Low priority (PM) Pkt Generation Rate: 10 pkt/s ECWmin: 31 Packet size: 500 bytes AIFS: 123 us, BO = 208 us

16 PER Midamble symbol spacing as a function of channel coherence time, data rate, and packet size 15 Lower SNR requirement for higher spatial diversity and smaller payload size. STBC 4x4 reduces maximum data rate vs MIMO: 100 km/h, with midamble spacing of 30 symbols 10 0 : 100 bytes : 500 bytes : 1000 bytes STBC 2x2: 100 bytes 10-1 STBC 2x2: 500 bytes STBC 2x2: 1000 bytes STBC 4x4: 100 bytes STBC 4x4: 500 bytes STBC 4x4: 1000 bytes SNR (db)

17 BER Midamble symbol spacing as a function of channel coherence time, data rate, and packet size 16 Higher SNR requirement for higher modulations., 100 km/h, with midamble spacing of 30 symbols BPSK 1/2 BPSK 3/4 QPSK 1/2 QPSK 3/4 16QAM 1/2 16QAM 3/4 64QAM 2/3 64QAM 3/ SNR (db)