On Optimal Relay Placement for Urban Vehicular Networks

This paper considers the problem of optimal relay placement for urban monitoring in wireless vehicular networks. The placement of relays is greatly impacted by vehicle distribution and mobility, which makes it difficult to determine the optimal locations. We theoretically prove that the relay placement problem (RPP) is NP-hard even when the vehicle traces are assumed as a priori knowledge. We first propose an approximate algorithm for the RPP with given vehicle traces (D-RPP). This algorithm is proved to achieve an approximation ratio of (1-1/ e), where e is the natural logarithm base. To solve the RPP without a priori knowledge about future vehicle traces (N-RPP), we first show that there is strong regularity with vehicle mobility by entropy analysis. Then, we propose an algorithm for solving the N-RPP, which exploits regularity extracted from historical traces. Extensive simulations based on real trace datasets show that the D-RPP algorithm produces performance close to the optimum. Keywords-wireless vehicular networks, wireless relays, optimal placement, approximation algorithms.