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UBC Theses and Dissertations

Performance study of the IEEE 802.11 wireless media access control protocols Cheung, William K. W.


The performance of the IEEE Project 802.11 Wireless Media Access Control (WMAC) protocols for wireless local area networks (WLANs) is studied. In particular, the asynchronous data service in the contention period of the protocol is simulated in both adhoc and infrastructure network topologies. Ptolemy, a powerful mixed-mode and object-oriented simulator, is used as the engine for all discrete-event computer simulations. The sensitivity of network geometry, traffic flow, queueing size, channel models, hardware, and backoff parameters on performance is extensively studied. Moreover, the "hidden terminal problem" is also examined. It turns out that the connectivity and the hidden terminal parameter, P[sub h], can be used to predict the performance of the system with different geometries. In the worst case considered in this thesis where both the connectivity and P[sub h] are high, the throughput performance for the Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) protocol using RTS/CTS and ACK frames drops down to 16% of the data rate. However, the throughput is kept steady even when the system load is twice the data rate. Various other parameters used in the simulation can also affect the performance to some extent. Near optimal values for the queueing size, the receiver sensitivity, the carrier sense threshold, the contention window size, and the maximum retransmission value can be found through computer simulations. On the whole, it appears that the performance of the CSMA/CA basic access protocol in the 802.11 standard is acceptable even under adverse channel conditions.

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