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A vehicular communication network (VCN) is composed of low-cost base stations called roadside units (RSUs), 3 where each RSU has limited storage space and are able to wirelessly communicate with fast-moving vehicles. Cellular traffic off-loading to vehicular communication networks benefits from the fact that most of the outdoor traffic originates from portable communication devices within vehicles. Further, modern vehicles may be equipped with processing power and storage space better than that of smartphones or tablets, which, in turn, can facilitate advanced signal processing techniques to mitigate channel impairments and achieve higher throughput. Furthermore, vehicular communication technologies are designed for outdoor environments where high Doppler channel conditions are prevalent, which make them preferable over Wi-Fi networks. In this paper, we investigate a content delivery network, in which cellular traffic is being off-loaded via VCNs.We consider a content delivery network where the central content server is hosted at the base station(s) of a cellular network, and the cache servers are hosted at the RSUs of a VCN. A delay tolerant approach to content delivery is explored with a goal of balancing the end-user service quality against the congestion in the cellular network. Upon the request for a file at the central content server from an end-user application, the central content server returns a search interval. The search interval may be chosen as a function of the delay tolerance of the requesting application. During the search interval, the application requesting the file attempts to download the file from the cache servers that the end-user (vehicle) visits as it travels. If the download is not successful by the end of search interval, then the file is delivered over the cellular network from the main server. Since the majority of file downloads are delay tolerant, this approach can considerably reduce the load of the base station.Given the above content delivery model, we want to minimize the cellular traffic, which in turn means to maximize the average hit ratio, the average fraction of total requests served via the local caches per unit time. Given the popularity of the contents, the traffic patterns of streets, and the location of the cache servers (RSUs) in a geographical area, how shall the files be placed in the local cache servers so as to maximize the average hit ratio? We refer to the above problem by cache content placement (CCP) problem. In this paper, we seek to solve CCP in a distributed fashion: design local algorithms that enable each cache server to autonomously choose its files in response to its own local information such that the average hit ratio is maximized. There are several reasons why we prefer distributed approaches over centralized approaches for solving CCP. First, there are several time-varying parameters in vehicular networks, such as file demands or vehicles mobility model, and distributed approaches adapt faster in these dynamic situations compared to the centralized...

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