MAC layer retransmissions in 1XTREME

We study the joint reliability as offered by the medium access control (MAC) and the radio link protocol (RLP) in CDMA systems, particularly for 1XTREME. The retransmission mechanism in the RLP has considerable amount of delay associated with it which might not be able to sustain real-time communications with strict delay requirements. Retransmissions done at a lower layer, such as the MAC, enhances the performance of the system. We show how the performance varies with respect to delay and throughput as observed from the RLP, for finite number of retransmissions at the MAC. We find that there is a substantial gain in the performance with the incorporation of fast retransmissions at the MAC. Synthetically generated HTTP traffic was used as the application, the objects of which were fragmented into equal sized RLP frames. We consider an I-path Rayleigh fading channel with correlated errors. We also consider that soft packet combining at the receiver is supported, which effectively lowers the frame error rate (FER). Simulation experiments are conducted to verify the performance as offered by the MAC and the RLP.