Abstract

Mos t previous work on code division multiple access (CDMA) considers the bit error ratio (BER) at the physical layer and the frame drop ratio (FDR) at the medium access control layer separately. However, a better system per formance, e.g., in terms of a lower overall frame loss ratio (FLR) , can be achieved i f BER and FDR are jointly optimized.

In this paper , we propose a cross-layer optimization scheme called trafficadaptive scheme for multicode CDMA operating over a time division multiple access (TDMA) channel . Based on the traffic condition and buffer status , this scheme employs a Markov Decision Process (MDP) to determine the optimal value of the maximum number of simultaneous data frames that can be transmitted in each time slot of a TDMA frame so as to minimize the overall FLR of the s ystem.

To facilitate implementation, we also propose an approximation scheme named the rate adaptive scheme to reduce the computation cos t. Simulation and analytical resul ts show that both the traffic-adaptive scheme and rate-adaptive scheme can significantly reduce FLR, increase the s ystem throughput, and optimize the packet access delay of the system. Fur thermore, the rate-adaptive scheme can achieve a per formance close to the traffic-adaptive scheme when the traffic load in the system is high.

INDEX TERMS
Multimedia communication, wi reless, multicode code division multiple access.

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