Performance analysis of RLP over fading channels in CDMA systems

The RLP protocol in CDMA systems is a link layer error control protocol that improve the error performance of the radio link. It uses NAK (negative acknowledgement) based ARQ to recover corrupted frames. The receiver only acknowledges the corrupted frames by sending NAK´s in batch to the sender. Each NAK, if successfully received, will trigger the sender side RLP to retransmit the corresponding corrupt frame. We develop an analytical method to calculate the important RLP performance metrics such as residual frame error rate, goodput, and over-channel delay over fading channels that are modelled by hidden Markov models (HMM). It´s also shown there exists a simple linear relationship between TCP´s stable throughput and RLP´s goodput. Using numerical results, we find that the assumption of error-free NAK´s (it can greatly simplified the calculation method) is good for goodput and delay calculation, but not suitable for calculating residual frame error when the data channel is not highly correlated.