Md. Imrul Hassan, Hai L. Vu, and Taka Sakurai Centre for Advanced Internet Architectures, Faculty of ICT Swinburne University, Australia

Transcription

1 Performance Analysis of the IEEE MAC Protocol for DSRC with and without Retransmissions Md. Imrul Hassan, Hai L. Vu, and Taka Sakurai Centre for Advanced Internet Architectures, Faculty of ICT Swinburne University, Australia Outline Overview of DSRC Research Objectives Standardization activities Analytical model Proposed extension Results Discussions Page 2 Swinburne University of Technology 1

2 Overview of DSRC Figure: DSRC applications overview Reference: ETSI Technical Committee Intelligent Transportation System; IntelligentTransportSystems.aspx Page 3 Overview of DSRC Figure: Safety applications for DSRC Reference: Jiang, D., Taliwal, V., Meier, A., Holfelder, W., & Herrtwich, R. (2006). Design of 5.9 GHz DSRC-based vehicular safety communication. IEEE Wireless Communications Page 4 Swinburne University of Technology 2

3 Research Objectives MAC layer constraints Broadcast performance enhancement Disseminate safety messages to all nearby vehicles within time constraint Latency should be kept minimum (100ms ~ 400ms) Packet Delivery Ratio (PDR) > 90% Reference: ASTM (2003). Standard Specification for Telecommunications and Information Exchange Between Roadside and Vehicle Systems 5 GHz Band DSRC MAC and PHY Specifications. Page 5 Research Objectives Hidden terminal problem No RTS/CTS mechanism for IEEE broadcast Potential hidden terminal area is larger Potential hidden terminal area R S R R S R R Tagged Node Transmission Hidden Vulnerable period Node Transmission Collision Unicast Broadcast (b) Vulnerable period (a) Potential hidden terminal area Figure: Hidden terminal problem Page 6 Swinburne University of Technology 3

4 Standardization activities US FCC allocated 75 MHz of spectrum at 5.9 GHz for DSRC ASTM standard for the PHY and the MAC layer IEEE p amendment for DSRC PHY & MAC IEEE a 10MHz OFDM Improved receiver performance requirements MAC layer consists DCF and EDCAF Reduced overhead for efficient group setup ETSI to standardize ITS architecture In Europe Page 7 Assumptions Unsaturated network with each vehicle modelled as an M/G/1 queue Message lengths are constant Linear topology Perfect channel No capture effect Propagation delay is ignored Page 8 Swinburne University of Technology 4

5 Analytical Model Broadcast communications Unsaturated network A vehicle can have a packet to transmit with probability equal to queue utilization factor, p Transmit probability is scaled with p Hidden terminal For successful transmission of tagged node No neighbouring node should transmit at the same slot No hidden node should transmit within the vulnerable period Collision probability is modified to account for hidden terminal Page 9 Analytical Model Model Broadcast Hidden Unsaturated Bianchi et al Malone et al. - - Tickoo et al. - - Rao et al. - Chen at al. - - Tsertou et al. Our model Table: Comparison of our model with the existing models in the literature Page 10 Swinburne University of Technology 5

6 Analytical Model Chen s model Markov chain based model assumes renewal point Hidden terminals are not synchronized No transmission from hidden node in vulnerable period Geometric distribution for transmission probability Transmission probabilities in successive slots are not independent Page 11 Analytical Model Fixed point formulation Direct collision probability Depends on queue utilization factor, p Hidden collision probability Mean total delay Queuing delay Backoff delay Transmission delay Page 12 Swinburne University of Technology 6

7 Analytical Model Performance measures Packet Delivery Ratio (PDR) Mean total delay Parameters (Rd,λ,P) Data rate, Rd Mbps Packet arrival rate, λ packets/sec Packet length, P bytes Network simulation for validation Page 13 Model Validation Figure: Comparison of packet delay with Chen's model using parameter set: (Rd,λ,P) Page 14 Swinburne University of Technology 7

8 Model Validation Figure: Comparison of PDR with Chen's model using parameter set: (Rd,λ,P) Page 15 Retransmission Scheme Sequential retransmissions 1 of safety messages Improve reliability No feedback necessary Fixed number of retransmissions Implementation Same backoff between two attempts Can be implemented in application layer Compatible with IEEE DCF Performance analysis Analytical model easily extended Simulation validates accuracy 1 Reference: Xu, Q.; Mak, T.; Ko, J. & Sengupta, R. (2007). Medium access control protocol design for vehicle --vehicle safety messages. IEEE Transactions on Vehicular Technology Page 16 Swinburne University of Technology 8

9 Results Figure: Total delay for sequential retransmissions with three transmission attempts using parameter set: (Rd,λ,P) Page 17 Results Figure: PDR for sequential retransmissions with three transmission attempts using parameter set: (Rd,λ,P) Page 18 Swinburne University of Technology 9

10 Results Figure: Comparison of the PDR between sequential retransmissions and single transmission using parameter set: (Rd,λ,P) Page 19 Discussions Analytical model formulation Simulation validates accuracy for single transmission Retransmission in low loads improves reliability Channel congestions in higher loads MAC protocol is critical for DSRC safety applications Analytical modelling necessary for approximating the performance achievable Comparison among various enhancements Page 20 Swinburne University of Technology 10

11 References ETSI Technical Committee Intelligent Transportation System; IEEE (2009). Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Amendment : Wireless Access in Vehicular Environments ASTM (2003). Standard Specification for Telecommunications and Information Exchange Between Roadside and Vehicle Systems 5 GHz Band DSRC MAC and PHY Specifications. Jiang, D., Taliwal, V., Meier, A., Holfelder, W., & Herrtwich, R. (2006). Design of 5.9 GHz DSRC-based vehicular safety communication. IEEE Wireless Communications Bianchi, G. (2000). Performance analysis of the IEEE distributed coordination function. IEEE Journal on Selected Areas in Communications Malone, D., Duffy, K., & Leith, D. (2007). Modeling the Distributed Coordination Function in Nonsaturated Heterogeneous Conditions. IEEE/ACM Transactions on Networking Tickoo, O., & Sikdar, B. (2008). Modeling queueing and channel access delay in unsaturated IEEE random access MAC based wireless networks. IEEE/ACM Transactions on Networking Rao, A.; Kherani, A. A. & Mahanti, A. (2008) Performance evaluation of broadcasts for a single cell network with unsaturated nodes. Networking, Springer Tsertou, A. & Laurenson, (2008) D. Revisiting the hidden terminal problem in a CSMA/CA wireless network. IEEE Transactions on Mobile Computing Chen, X., Refai, H. H., & Ma, X. (2007). A quantitative approach to evaluate DSRC highway inter-vehicle safety communication. Proceedings of the IEEE Global Telecommunications Conference Xu, Q.; Mak, T.; Ko, J. & Sengupta, R. (2007). Medium access control protocol design for vehicle --vehicle safety messages. IEEE Transactions on Vehicular Technology Page 21 Q/A Session Page 22 Swinburne University of Technology 11