High Performance Distributed Coordination Function with QoS support in IEEE 802.11e networks

IEEE 802.11e standard is specified to support QoS (Quality of Service) in wireless local area networks for multimedia traffic such as real-time audio and video streaming. It proposes two wireless network access mechanisms to support QoS: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA). EDCA is a contention-based scheme. When the network size is increased, there will be more collisions and idle slots. Therefore, the performance will degrade a lot. To cope with this problem, this study proposed a High Performance Distributed Coordination Function with QoS support (QHDCF) protocol to enhance the performance. In QHDCF, the transmitting station determines the next transmitter according a selection rule from a probability formulation perspective based on the priorities and numbers of stations in different traffic classes. Since, in the proposed QHDCF, stations do not contend for channel access, transmission collisions are reduced a lot, and hence the network throughput is enhanced. Moreover, in EDCA, the high-priority traffic will always get the transmission opportunity and therefore low-priority traffic will suffer starvation. In contrast, in QHDCF, the high-priority traffic has better transmission opportunity on a probability base and hence does not starve the low-priority traffic. Simulation results show that the proposed QHDCF protocol outperform EDCA protocol in different packet sizes and number of stations.