Contact Duration Aware Data Replication in DTNs with Licensed and Unlicensed Spectrum

The recent popularization of hand-held mobile devices, such as smartphones, enables the inter-connectivity among mobile users without the support of Internet infrastructure. When mobile users move and contact each other opportunistically, they form a delay tolerant network (DTN), which can be exploited to share data among them. Data replication is one of the common techniques for such data sharing. However, the unstable network topology and limited contact duration in DTNs make it difficult to directly apply traditional data replication schemes. In this paper, we recognize the deficiency of existing data replication schemes which treat the complete data item as the replication unit, and propose to replicate data at the packet level using erasure coding techniques. Our study consists of two cases based on the operating spectrum: unlicensed spectrum and licensed spectrum. For both cases, we analytically formulate the data replication problem as a mixed integer programming problem and propose a practical algorithm which operates in a fully distributed manner. Extensive simulations on both synthetic and realistic traces show that our scheme outperforms other existing replication schemes in terms of successful data retrieval probability in various scenarios.