  Distributed contention based Medium Access Control (MAC) protocols are the
fundamental components for IEEE 802.11 based Wireless Local Area Networks
(WLANs). Contention windows (CW) change dynamically to adapt to the current
contention level, Upon each packet collision, a station doubles its CW to
reduce further collision of packets. IEEE 802.11 Distributed Coordination
Function (DCF) suffers from a common problem in erroneous channel. They cannot
distinguish noise lost packets from collision lost packets. In both situations
a station does not receive its ACK and doubles the CW to reduce further packet
collisions. This increases backoff overhead unnecessarily in addition to the
noise lost packets, reduces the throughput significantly. Furthermore, the
aggregate throughput of a practical WLAN strongly depends on the channel
conditions. In real radio environment, the received signal power at the access
point from a station is subjected to deterministic path loss, shadowing and
fast multipath fading. In this paper, we propose a new saturation throughput
analysis for IEEE 802.11 DCF considering erroneous channel and capture effects.
To alleviate the low performance of IEEE 802.11 DCF, we introduce a mechanism
that greatly outperforms under noisy environment with low network traffic and
compare their performances to the existing standards. We extend the
multidimensional Markov chain model initially proposed by Bianchi(3) to
characterize the behavior of DCF in order to account both real channel
conditions and capture effects, especially in a high interference radio
environment.
