On integrating multiple access control and adaptive channel coding for cellular wireless voice and data services

Abstract

In this paper, we introduce a novel technique to exploit the synergy between the multiple access control (MAC) layer and the physical layer of a cellular wireless system with integrated voice and data services. As in a traditional design, the physical layer (channel encoder and modulator) is responsible for providing error protection for transmitting the packets over the hostile radio channel while the MAC layer is responsible for allocating the precious bandwidth to the contending users for voice or data connections. However, a distinctive feature of our proposed design is that in the physical layer, a variable rate adaptive channel encoder is employed to dynamically adjust the amount of FEC according to the time-varying wireless channel state such that the MAC layer, which is a reservation-based TDMA protocol, is able to make informed decisions as to bandwidth allocation. Specifically, based on the channel state information provided by the physical layer, the MAC protocol gives higher priority to users with better channel states. This novel synergistic mechanism between the two protocol layers can utilize the system bandwidth more effectively. The multiple access performance of the proposed scheme is compared with two baseline systems and the well known DRMA protocol. The first baseline system consists of the same reservation-based MAC protocol but with a traditional fixed-rate physical layer. The second system consists of the same reservation-based MAC protocol and the same channel adaptive physical layer but without interaction between the two layers. All four protocols are incorporated with a request queue which stores the previous requests that survive the contention but are not allocated information slots. Our extensive simulation results demonstrate that significant performance gains are achieved through the exploitation of the synergy between the two protocol layers. © 2001 Elsevier Science B.V.