On Average Packet Delay Bounds and Loss Rates of Network-Coded Multicasts over Wireless Downlinks

Latency is a critical concern in interactive or delay-sensitive services such as interactive IPTV and VoIP. This is especially so when using network coding as a means to conserve bandwidth in these bandwidth-hungry services. In practical network coding, packets are coded in batches and thus suffer a large average delay per packet when packets get decoded after the whole batch is received. A larger batch size, however, also gives the highest bandwidth savings. In this paper, we analyze the achievable upper and lower bounds of the average delay per packet as well as packet loss rates due to finite-sized queue in a multicast downlink transmission from the system and client perspectives. We validate our analysis with simulation results and characterize the queueing and transmission delays, and packet loss performance with respect to (i) the maximum size of a batch and (ii) packet arrival rates. We find that random linear coding is an upper bound in delay performance and other hybrid network coding method might achieve better delay gains.