A Unified Analysis on ARQ-Based Broadcast: A Road to the Optimum

This paper presents a unified framework for Automatic Repeat reQuest (ARQ)-based retransmission schemes in multi-user broadcast environments. Two perspectives, namely, coded packet design and the enhancement of the ARQ protocol, are used to establish the unified framework. Consequently, the combined use of index coding and ARQ incorporated with memory is demonstrated to be beneficial toward performance enhancement in terms of transmission efficiency and memory overhead. Specifically, the asymptotic and finite transmission efficiencies of the index-coded ARQ incorporated with memory are analyzed to be close to the optimum over a wide range of packet error probabilities and the number of users, which is validated numerical evaluations. Furthermore, the use of index coding is analyzed to be also favourable in terms of memory overhead in comparison with the memory ARQ. Thus, index-coded ARQ with appropriate use of memory is shown to be a reasonable option in a practical sense, which sheds light on the possibility that multi-user coded ARQ can play a crucial role for a reliable broadcast beyond unicast.