On higher layer protocol performance in CDMA S-ALOHA networks with packet combining in Rayleigh fading channels

Physical layer mechanisms to enhance wireless channel reliability can impact the performance of higher layer protocol techniques in a non-trivial manner. The performance implications of retransmission diversity packet combining on RLC (Radio Link Control)/MAC (Medium Access Control) layer and transport layer protocol performance are investigated for three different heuristic-based RLC/MAC layer access control schemes in a CDMA S-ALOHA network under frequency selective Rayleigh fading. The transport layer protocol here implements a two-level error recovery mechanism for reliable data transmission. Two different transport layer timer control mechanisms are considered. Performance evaluation is also carried out for these access control schemes for single-level error recovery in the case of moderate delay and loss-sensitive data traffic. In addition, implications of some physical layer parameters on system performance are discussed. It is observed that for two-level error recovery through a reliable transport protocol, the achieved throughput is dependent on the transport protocol timer control mechanism and a suitable mechanism can be identified for an underlying RLC/MAC layer access control scheme and a particular physical layer design. The results presented here enable us to get insight into the identification of proper higher layer protocol mechanisms and physical layer design choices which would be required for transmission protocol stack performance optimization in a CDMA-based wireless networking scenario.