Joint reliability of medium access control and radio link protocol in 3G CDMA systems

In this paper, we study the reliability as offered jointly by the medium access control (MAC) and the radio link protocol (RLP) for third generation (3G) code division multiple access (CDMA) standards. The retransmission mechanism supported at the RLP layer has a considerable amount of delay (80-100 ms) associated with it; hence, it may not be able to support applications with strict delay requirements. On the other hand, if retransmissions are also performed at a lower layer, such as the MAC layer, then the performance of CDMA systems can be improved because of the fast retransmissions at the MAC layer. We show how the performance of RLP improves with respect to three metrics - mean delay, throughput, and RLP recovery -when a finite number of retransmissions is allowed at the MAC layer. Synthetically generated Web traffic is used as the application, the objects of which are fragmented into equal-sized RLP frames. We consider soft packet combining support at the receiver, which effectively lowers the frame error rate. We also consider the possibility of misinterpretations of acknowledgments. Simulation experiments are conducted to verify the performance as offered jointly by the MAC and the RLP, particularly for cdma2000 standard and wideband CDMA (WCDMA) systems. The improvement in the TCP throughput is also evaluated.