WLC24-4: The Destructive Effect of Acknowledgment Traffic in WLANs

We investigate the interaction between data and acknowledgment (ACK) traffic in Wireless LANs (WLANs) with hidden nodes. The multiple access protocols considered are Carrier Sense Multiple Access (CSMA) and Request-To-Send- Clear-To-Send (RTS-CTS), with access priority given to ACK packets over data packets, as in the IEEE 802.11 standard. The priority given to ACK packets protects them from being destroyed by data packets. We show the converse to hold under RTS-CTS, but not under CSMA, i.e., under the latter protocol ACK packets can destroy data packets. The resulting system capacity is much lower than that predicted by most of the existing studies, where this effect is not accounted for. To boost the performance of CSMA WLANs, we propose and evaluate a technique for grouping ACKs pertaining to different data packet transmissions. Our conclusions are substantiated by an analytical model and further corroborated by simulation.