On the impact of channel coding on average packet delay in a multiuser environment

Delay sensitive applications such as gaming and video streaming require relatively low average packet delay, an important higher layer metric which directly affects the user experience. In this paper, we consider a polling based multiple access scheme and study the impact of channel coding on the average packet delay where the link layer employs Automatic Repeat Request (ARQ) to provide error free packet transmission. The communication model assumes that users share a common physical channel and communicate with a central server which polls them for transmission in a cyclic order. Using an average waiting time analysis, we prove that, compared to an uncoded system, it is sufficient for a coding scheme to reduce the average service time in order to achieve lower average packet delay. We use the bounds on the minimum distance of linear codes to choose that code for which the reduction in the number of retransmissions (due to a decrease in probability of packet error) outweighs the increase in packet time (due to an increase in packet length by channel coding) such that the average service time is minimized. We also show that the percentage reduction in average service time by employing channel coding (compared to an uncoded system) results in corresponding reduction in average transmit energy required for successful transfer of a data packet. Numerical examples are provided to highlight the tradeoffs involved in the choice of an appropriate channel coding scheme.