A Hybrid Distributed Coordination Function for Scalability and Inter-operability in Large-scale WLANs

The distributed coordination function (DCF) of IEEE 802.11 MAC protocol is not scalable as the number of users on a network increases. We propose two new contention resolution schemes to reduce the number of collisions between a large number of contending mobile stations. The hybrid DCF (H-DCF) scheme splits contention resolution into two phases to improve scalability. Enhanced hybrid DCF (EHDCF) adds fairness with expect to mobile stations using the current IEEE 802.11 MAC and further improves the efficiency of contention resolution. Inter-operability with the IEEE 802.11 DCF is the major advance over previous work. We use an ns-2 simulator to simulate the performance of these new schemes with the IEEE 802.11 DCF. The results show that an improvement in network performance by up to 10∼30%.