Decoding delay reduction in network coded cooperative systems with intermittent status update

In this paper, we study the problem of decoding delay reduction for instantly decodable network coding (IDNC) in broadcast cooperative systems, where a group of closely located clients cooperate with each other to obtain their missing packets. In such cooperative systems, one of the clients (referred to as the leader) decides the transmitting client and the packet combination for each transmission. We consider intermittent system status update (SSU) at the leader such that all other clients feed back their packet reception status to the leader after several cooperative transmissions. We first introduce an intermittent local IDNC (IL-IDNC) graph to represent all potential packet combinations for a transmitting client. We then formulate the joint client and packet selection problem that results in the minimum expected decoding delay in each cooperative transmission as a maximum weight clique problem over all the IL-IDNC graphs. Since solving the formulated problem is computationally complex, we propose a heuristic algorithm to select the transmitting client and the packet combination that can reduce the decoding delay. Simulation results show that the proposed heuristic algorithm can achieve a tolerable degradation compared to the full SSU performance while using a smaller number of SSUs.