Fast and reliable two-layer retransmission scheme for CDMA systems

An analytical model of two-layer retransmission scheme is proposed for CDMA systems in which selective repeat automatic repeat request (ARQ) is used at the radio link protocol (RLP) layer and n-channel stop-and-wait hybrid ARQ at the medium access control (MAC) layer. 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, enhance the performance of the system. We show how the joint reliability varies with respect to the maximum retransmission number of RLP layer and MAC layer. We also consider when soft packet combining at the MAC layer of the receiver is supported, which effectively lowers the frame error rate (FER). Compared with the RLP layer ARQ used in IS-99, the two-layer retransmission scheme shows shorter packet transmission delay and lower packet error rate. The results show that it can offer faster and more reliable communication.