A new Distributed Coordination Function for W-LANs with multiple channel structure

Abstract — IEEE 802.11a/e has become a worldwide wireless local area network (W-LAN) standard, with a rapid development. Many proposals have been made for its further expansion, and some of them focus on multicarrier code division multiple access (MC-CDMA), a novel, high capacity, multicarrier modulation scheme. From the point of view of medium access control (MAC) layer, by the use of MC-CDMA, the frequency channel is divided in many channels separated by different spreading sequences, which we refer to as codechannels (cchs). Previous work [1] has proven the achievements of this approach. The network reaches higher net throughput while the queue and transmission delays are kept low since almost no collisions occur. In this paper we present and evaluate a new distributed coordination function (DCF) for the MAC protocol, best suited for W-LANs with multiple channel structure. Although in this work the new DCF is analysed for the MC-CDMA approach, its functionality is not limited to spread spectrum systems. Scope of the new DCF is to reduce the queue delay and prioritize some mobile stations (MS) by allowing them to start parallel Backoff timers in more than one cch. The outcome is a more symmetric distribution of load among the codechannels, which enhances the network performance, which can be seen from the simulation results