Packet combining strategies for EGPRS

Packet combining techniques are used to improve the performance of the hybrid ARQ mechanisms. This paper assesses the impact of several variations of packet combining, in its two basic forms (diversity combining and code combining), on a selective-repeat ARQ mechanism in an EGPRS wireless system. These variations range from the application of no packet combining at all, to the application of both diversity combining and code combining on all possible combinations of available packets. A link-level simulator for the EGPRS downlink in a typical urban mobile radio propagation environment is implemented. Mobile speeds of 5 km/h and 50 km/h are considered. It is shown that packet combining can significantly improve performance and has a greater impact at the higher speed. Furthermore, a packet combining strategy of moderate complexity is shown to be optimal in terms of the trade-off between performance, on the one hand, and the associated decoding-related processing load at the receiver, on the other.