A hybrid MAC protocol for multimedia traffic in wireless networks

Abstract

This paper proposes a new MAC protocol, called request-TDMA/CDMA protocol, for supporting multimedia traffic in wireless networks. The protocol has CDMA laid over TDMA like frame structure which has two kinds of slots, viz., data slots and control slots. The control slot holds the information of the next frame's data slot allocation. Whenever a mobile terminal needs to transmit a message, it sends a request to the base station and enters the contention process. The scheduler at the base station takes into consideration the time of generation of a call, the bit rate requirement and the message length while reserving slots for the entire length of the message generated. Three scheduling algorithms are proposed and their performances are studied for four classes of traffic. We also model our protocol using a two-dimensional Markov chain, and for a given system load we compute the state transition probabilities and derive the average waiting time. By simulation experiments we show that our (hybrid) request-TDMA/CDMA protocol is able to effectively combine the orthogonality of both time and code division multiplexing.