V2X Content Distribution Using Batched Network Code
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Content distribution is one of the most popular applications in intelligent transportation system to assist vehicles in acquiring information and achieving mobile entertainment. In this paper, we consider content distribution from a single roadside infrastructure to a group of vehicles passing by it. To combat the short connection time and the lossy channel, the downloaded contents need to be further shared among vehicles after the broadcasting phase. To this end, we introduce an efficient V2X, i.e., joint vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) scheme by using batched sparse (BATS) code to minimize the traffic overhead and reduce the total downloading delay. Specifically, the roadside unit (RSU) encodes the original large-size file into a number of batches in a rateless manner, each containing a fixed number of encoded packets, which are then sequentially broadcast during the connection time. After vehicles moving out of the coverage area of the RSU, they actively help each other with the file recovery via efficient network-coded P2P transmissions. To maximize the usefulness of each transmission, and hence reduce the total transmission cost, a utility-based distributed algorithm is proposed to obtain the optimal broadcasting sequence at each individual vehicle. Furthermore, we derive a closed-form expression for the expected channel rank distribution observed at the bottleneck vehicle, which is then used to optimize BATS coding parameters. The performance of the proposed content distribution scheme is evaluated by extensive simulations and shown to significantly outperform the existing content distribution protocols.
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