Efficiency and speed improvement for network coded file distribution with adaptive request

Content dissemination in Vehicular Ad-Hoc Networks (VANET) has attracted wide interest in the research community. The use of network coding for file sharing has been proved to overcome several problems such as highly dynamic topology and intermittent connectivity. Prior works have originally been designed to work well even with only single hop communication. However, the previous works are not entirely suitable for networks with low node density or low percentage of interested nodes. We, therefore, propose CarCode, an adaptive request mechanism to improve the speed and efficiency of network-coded file distribution in such networks. Each node adaptively requests coded pieces of the file from the source when it does not receive any useful coded piece from its current neighbors within a calculated timeout. Our adaptive timer is proportional to the rate of new incoming neighbors whereas the number of requested pieces is inversely proportional. We have incorporated our approach with CodeTorrent and evaluated its performance on NS-2 simulator. Our result indicates that CarCode can significantly improve the efficiency and download latency of CodeTorrent under investigated scenarios.