Inter-Session Network Coding Schemes for Two Unicast Sessions with Sequential Hard Deadline Constraints

The emerging wireless media delivery services haveplaced greater demands for wireless networks to support high-throughput applications while minimizing the delay of individualpackets. In this paper, we investigate using inter-session networkcoding to send packets wirelessly for two deadline-constrainedunicast sessions. Specifically, each unicast session aims to transmita stored video file, whose packets have hard sequential deadlineconstraints. We first characterize the corresponding deadline-constrained capacity region under heterogeneous channel condi-tions and heterogeneous deadline constraints. We show that thisdeadline-constrained capacity region can be achieved asymptoti-cally by modifying the existing generation-based schemes. Despiteits asymptotic optimality, the generation-based scheme has poorperformance and high complexity in the practical regime small &medium file sizes. To address these problems, we further developnew immediately-decodable network coding (IDNC) schemesthat admit superior performance in the practical regime whilebeing provably optimal in the asymptotic regime. In contrastto the existing delay/deadline-based IDNC results, which focuson a single multicast session (intra-session network coding) withhomogeneous channel conditions, our new IDNC design takes fullaccount of channel heterogeneity and provides the first rigorousasymptotic optimality analysis for two unicasts with (potentiallyheterogeneous) hard deadline constraints.