Exploiting the Overheard Information of Coded Caching for Heterogeneous Lossy Channels

Coded caching is a promising technique for reducing traffic load in wireless networks. In this paper, coded caching is studied for heterogeneous lossy channels, where each user independently suffers packet loss with a distinct and fixed probability. In the original MAN transmission [1], each packet is destined for a specific combinational subset of users. When a packet is received by users beyond the destined subset, it is undecodable and will be dropped. We term these packets as the Overheard Packets (OPs). Interestingly, we find that the OPs can be exploited as side information to increase the multicast gain of the retransmitted packets. With this motivation, we propose a reliable coded caching scheme to reduce the retransmission rate over the shared link. This method enables the users to recover their own lost packets (could be different) from one encoded retransmitted packet. Aided by the OPs, the multicast gain of retransmissions can be increased up to K in certain cases, where K represents the number of users. In other cases, retransmission achieves at least the same multicast gain as the original transmission. Two well-known techniques for reliable transmission are employed in coded caching and serve as baseline schemes. Through both simulations and theoretical analysis we show that the proposed scheme significantly outperforms the baseline schemes in terms of the retransmission rate.