Enhanced High-Performance Distributed Coordination Function for IEEE 802.11 Multi-Rate LANs

To compensate for the effects of fading in wireless channels, IEEE 802.11 systems utilize a rate-adaptation mechanism to accomplish a multi-rate capability. However, the IEEE 802.11 distributed coordination function results in a fundamental performance anomaly in multi-rate networks; namely, when stations with different transmission rates collide, the throughput performance of the high-rate station is significantly degraded by the relatively longer channel occupancy time of the low-rate station. This study resolves this problem through the use of an Enhanced High-performance Distributed Coordination Function (EHDCF) protocol. While most existing solutions to the multi-rate performance anomaly problem have the form of simple contention-based protocols, EHDCF has two modes, namely a contending mode and an active mode.