Comparative Study of 802.11 DCF and its Modification in the Presence of Noise

IEEE 802.11 specifies a technology for wireless local area networks (LANs) and mobile networking. In this paper, we present an analytical method of estimating the saturation throughput of a 802.11 wireless LAN in the presence of noise, which distorts transmitted frames. With the Distributed Coordination Function (DCF) being the fundamental access mechanism in the IEEE 802.11 MAC protocol, sequential attempts to transfer by every station are separated by backoff intervals. Besides the standard backoff rule of the DCF, according to which the mean backoff interval is doubled after each failure in order to avoid collisions, we propose and study a modification of the backoff rule. This modification relies on the optional 802.11 tools to recognize a reason of a failure (collision or noise-induced distortion) and does not increase the mean backoff interval if a failure happens due to distortion by noise. In addition to the throughput, our method allows estimating a probability of a packet rejection occurring when the number of packet transmission retries attains its limit. The obtained numerical results of investigating 802.11 LANs by the developed method are validated by simulation and show high estimation accuracy for any values of protocol parameters and bit error rates. We adopt this method to tune the protocol parameters and to compare the proposed modification with the standard backoff rule.