Issue No. 08 - August (2011 vol. 22)
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/TPDS.2010.176
Hongzi Zhu , Shanghai Jiao Tong University and Shanghai Key Lab of Scalable Computing and Systems, Shanghai
Minglu Li , Shanghai Jiao Tong University and Shanghai Key Lab of Scalable Computing and Systems, Shanghai
Luoyi Fu , Shanghai Jiao Tong University, Shanghai
Guangtao Xue , Shanghai Jiao Tong University and Shanghai Key Lab of Scalable Computing and Systems, Shanghai
Yanmin Zhu , Shanghai Jiao Tong University and Shanghai Key Lab of Scalable Computing and Systems, Shanghai
Lionel M. Ni , The Hong Kong University of Science and Technology, Hong Kong and Shanghai Key Lab of Scalable Computing and Systems, Shanghai
Intercontact time between moving vehicles is one of the key metrics in vehicular ad hoc networks (VANETs) and central to forwarding algorithms and the end-to-end delay. Due to prohibitive costs, little work has conducted experimental study on intercontact time in urban vehicular environments. In this paper, we carry out an extensive experiment involving thousands of operational taxies in Shanghai city. Studying the taxi trace data on the frequency and duration of transfer opportunities between taxies, we observe that the tail distribution of the intercontact time, that is, the time gap separating two contacts of the same pair of taxies, exhibits an exponential decay, over a large range of timescale. This observation is in sharp contrast to recent empirical data studies based on human mobility, in which the distribution of the intercontact time obeys a power law. By analyzing a simplified mobility model that captures the effect of hot areas in the city, we rigorously prove that common traffic influxes, where large volume of traffic converges, play a major role in generating the exponential tail of the intercontact time. Our results thus provide fundamental guidelines on design of new vehicular mobility models in urban scenarios, new data forwarding protocols and their performance analysis.
Vehicular ad hoc networks, intercontact time, exponential tail, mobility model, traffic influx, empirical data analysis.
L. M. Ni, Y. Zhu, G. Xue, L. Fu, H. Zhu and M. Li, "Impact of Traffic Influxes: Revealing Exponential Intercontact Time in Urban VANETs," in IEEE Transactions on Parallel & Distributed Systems, vol. 22, no. , pp. 1258-1266, 2010.