Two-Way Network-Coded Relaying With Delay Constraint
Random channel fading may cause serious channel outage, and automatic repeat-request protocol has been widely used to mitigate packet loss by retransmitting the packet when the receiver fails to decode that packet. To restrict the transmission delay, a single packet might be retransmitted up to a limited number of times. For wireless two-way relay channels, the packet could be retransmitted by the original source node or the relay nodes, and the delay constraint might be imposed in a per-hop manner or end-to-end manner. For single-relay networks, we study the throughput of several relaying strategies including pure relaying and network-coded relaying subject to the delay constraint. We demonstrate that the binary xor-based network coding can greatly improve the system throughput, but the throughput gain is upper bounded. We also develop a near-optimum power allocation scheme to maximize the system throughput. For multirelay networks, we show that using digital network coding alone may cause some throughput loss when the frame length is much smaller than the number of relays, and we develop a hybrid network coding scheme to recover such throughput loss.