Performance Analysis And Optimization Of IEEE 802.11 MAC Protocol

In recent years, IEEE 802.11 based WLAN has been widely used for its convenience, flexibility, low cost and easiness to be extended. However, its performance is expected to be lower than the traditional wireline networks. Although it is regarded as an inherent characteristic of wireless networks, the inefficiencies of Medium Access Control (MAC) protocol also contributes to the performance degradation. As such, it is of importance to make research on the improvement of the performance of IEEE 802.11 MAC protocol.With the popularity of the IEEE 802.11 standards, many analysis models for the distributed coordination function (DCF) have been proposed. A careful study at backoff counter decrement rules in the specification allows us to conclude that the slot immediately following a successful transmission can be accessed only by the station that has just successfully transmitted in the previous slot time. Thus, the assumption of uncorrelation and statistical homogeneity between consecutive channel slots is not true generally. The thesis proposes a new DCF analysis model that takes into account such a correlation while being able to retain the simplicity of typical analysis model.In addition, the thesis proposes a new virtual backoff algorithm (VBA), which is based on the sequencing technique for efficient medium access control. The VBA scheme uses fair distributed mechanisms to access a channel. A counter is introduced at each node to keep the transimission discipline of the nodes. The proposed method minimizes the packet collision probability while reducing the MAC delay.Finally, simulations are performed using NS-2 network simulator. The results have shown that the network performance indexes derived from the new DCF analysis model have higher accurasy than that derived from the typical analysis model, and that the VBA backoff algorithm provides better network performance than the standard IEEE 802.11 DCF.