On Scheduling of Data Dissemination in Vehicular Networks with Mesh Backhaul Liu Zhongyi M.S. Candidate, Peking Univ (To Appear on IEEE ICC08 Vehi-mobi Workshop)

2 Outline Background & Motivation System Model Scheduling Algorithms Performance Evaluation Conclusions and Future Work Problem Metrics Algorithms Evaluation Methodology

3 Background & Motivation -Vehicular Networks Vehicular Networks –Networks for C2C and C2R communications –Based on wireless communication technologies (Ad hoc, multi- channel, etc) Characteristics –Restricted Network Topology and Mobility Pattern –Frequent changes of network topology –Network partition may occur under sparse car density –Multi-path fading effects Applications –Safety applications (collision avoidance, emergency warning) –Internet access on the go –Data collection via sensors on vehicles

4 Background and Motivation -Motivation TIME and SPACE Constraints of Messages Messages should be Disseminated in a specific duration and a given coverage Trade-offs between Reliability And fairness Traffic Congestion Car Accident Road maintenance & Traffic Control Reliability: the quality of service for a single message Fairness: whether different messages are given the same level of chances

5 System Model -Network Architecture Car Accident !! Disseminate event message to left-side and downside areas Attributes of a message Content (x,y) Radius duration Mesh Roadside Unit (MRU) Vehicle

6 System Model -Metrics Reliability Metric Is the message disseminated in all its requested duration? –TRM indicates reliability in the time dimension Is the message disseminated in all its requested area? –SRM depicts reliability in the space dimension Can we specify the level of reliability we want? –K indicates the reliability level

7 System Model -Metrics m1m1 m2m2 m1m1 m2m2 m1m1 t 0 t0+ t0+2* 1.Message input 2. 1st schedule 3. 2nd schedule K=1 K=2 TRM=1/2+1/2=1 TRM=1+0=1 TRM=(1/2)^2+(1/2)^2=1/2 TRM=(1)^2+(0)^2=1 Illustration for Reliability Level

8 System Model -Metrics Fairness Metric Combined Metric

9 Scheduling Algorithms Reliability-oriented algorithms Fairness-oriented algorithms Hybrid Schemes MQIF: Maximum Quality Increment First (using estimated Quality Increment as the selection criteria) LSF: Least Selected First (using the number of scheduling times as the selection criteria) Combine via threshold: conditional-MQIF,conditional-LSF (easy to be adapted to different application scenarios) Combine via hybrid selection criteria:MQILSF

10 Performance Evaluation Simulation Scenario Simulation Parameters The effects of reliability level should be evaluated The effects of threshold values should also be evaluated

11 Performance Evaluation -Comparison of different scheduling algorithms Reliability Metric Fairness MetricCombined Metric Summary: LSF and MQIF achieve the worst reliability and fairness, respectively MQIF does not result in the best reliability. The Reason? Hybrid schemes achieve better reliability and Fairness, therefore better overall performance e.g. The reliability metric of Cond-LSF is about 7% higher than that of LSF; the fairness metric of MQILSF is about 11% higher than that of MQIF

12 Performance Evaluation -Effects of Reliability Level Global Service Ratio (GSR) Average Local Service Ratio (Average-LSR) Fairness Metric Average-LSR is the average of the service ratio of all MRUs Summary: GSR, Average-LSR and FM all decreases as the reliability level increases

13 Performance Evaluation -Effects of Threshold Values In Cond-MQIF, RM decreases as the threshold value increases In Cond-MQIF, FM increases as the threshold value increases Summary: As the threshold value increases, more opportunities are given To the LSF strategy while less are given to MQIF.

14 Conclusions and Future Work We argue that there are trade-offs between reliability and fairness in the data dissemination of vehicular networks Metrics for both reliability and fairness are proposed –RM covers both the SPACE and TIME dimensions and can specify different reliability levels –FM concerns only whether there is a chance for service for a message (without regarding whether the same level of opportunities are given to different messages) One reliability-oriented, one fairness oriented and 3 hybrid algorithms are developed and evaluated Future work –Better fairness metric –Message urgencies not considered –Traffic density not considered in our current metrics and algorithms

15 Q&A

16 Related Work Researches on developing vehicular networks with infrastructure –Mainly focus on one-hop communications Scheduling for data access –Data access within one hop –Considers only upload/download –Fairness not considered Packet Scheduling at MAC layer in wireless Networks –Packet-level Qos –Trade-off between channel utilization and fairness –Focus on one-hop communications

17 References V. Bychkovsky, B. Hull, et al. A measurement study of of vehicular internet access using in situ wi-fi networks. In Proceedings of the 12th annual international conference on mobile computing and networking(mobicom06),pages 50-61, 2006 D. Hadaller, S. Keshav, T. brecht, et.al. Vehicular opportunistic communication under the microscope. In Proceedings of The 5th International Conference on Mobile Systems, Applications, and Services(MobiSys07), 2007 Yang Zhang, Jing Zhao and Guohong Cao. On Scheduling Vehicle-Roadside Data Access. In Proceedings of the fourth ACM international workshop on Vehicular ad hoc networks(VANET07). Pages 9-18, 2007 Haiyun Luo, et.al. A new model for packet scheduling in multihop wireless networks. In Proceedings of the 6th annual international conference on Mobile computing and networking(mobicom00). Pages 76-86,2000.