Performance of EGPRS incremental redundancy in interference limited environments

Incremental Redundancy (IR), an established Hybrid-ARQ technique, has been proposed as an adaptive link level mechanism in third-generation and evolved second-generation wireless systems such as the Enhanced General Packet Radio Service (EGPRS). In this paper, three alternative EGPRS Incremental Redundancy ARQ algorithms of low (IR-ARQ1), medium (IR-ARQ2) and high (IR-ARQ3) computational complexity are specified. The relative downlink performance of the specified algorithms is evaluated for interference-limited mobile radio environments with pedestrian (5 km/h) and vehicular (50 km/h) mobile speeds, using a high-speed link level simulator. For comparison, a basic Selective-Repeat ARQ algorithm (SR-ARQ) is also implemented. The algorithms are compared in terms of their throughput performance, transmission delay performance, and processing requirements. It is shown that the most significant performance improvement is from SR-ARQ to IR-ARQ1 (up to about 2dB at 5 km/h, and 5 dB at 50 km/h). The performance gains from IR-ARQ1 to IR-ARQ2, and from IR-ARQ2, to IR-ARQ3 are negligible. Overall, the results suggest that implementing a low-complexity Incremental Redundancy ARQ algorithm gives the optimal performance/complexity trade-off.