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Wireless LAN & CSMA-CA-(Part 2)

Monday, 01 July 2002   



Tresa Johnson

In the previous issue, we looked at wireless LAN and the limitations that come along with it. The use of CSMA / CA protocol imposes an increasing number of communication capability losses due to frequent inter Frame (IF) spacing delays. In this issue, we'll continue by addressing those limitations.

4. Possible methods of addressing the above limitations [1]

This section shows three methods for increasing the efficiency of IEEE 802.11 MAC protocols over a wireless channel. These methods are the fruit of an extensive research by prof Legand L. Burge III (Systems and Computer Science, Howard University, Washington, DC) and Kevin A. Loney (Aggregate Network Solutions, Washington, DC). The first method is to utilize a real-time adaptive contention window CW boundary-sizing algorithm to determine CW boundary limits. This section shows that this real-time adaptive contention window CW boundary-sizing algorithm increases the network throughput over a dynamic range of channel loads. The second method uses an EPD algorithm to increase the effective channel rate, and is well suited for networks using advanced real-time routing protocols. The third method employs real-time fast fitted alpha-stable distribution for CW scaling. This algorithm minimizes the effects of channel capture on the network, while maintaining the original throughput and media access delay characteristics of the network.

1.Real-time Adaptive Tuning of CW Boundaries

The CWmin and CWmax parameters, by definition, are respectively the minimum and the maximum length by which the CW expands or contracts. By dynamically tuning these values to better suit the network needs, an increase in throughput can be achieved. Both CWmin and CWmax affect channel throughput. CWmin is the domaint tributary attribute. it is clear, that the optimum value of CWmin is the optimum value of CWmin is dependent on the number of greedy nodes. This promotes the fact that the throughput of WLANs can be vastly improved by dynamically choosing the CWmin size at run-time, according to the network traffic load. The adaptive CW tuning algorithm is described below.


Where : eq is service time ~ packet length.


HC=Hold Constant. The CWBoundary Values are set periodically with a period equaling CWhold time.

CWhold time helps to stabilize the systems that maintain

For simulation HC=1500 purposes, and is approximated by detection packets being dropped.

2. Expired Packet Deletion Protocol (EPD)

There are many ways that IEEE 802.11's contention algorithm can be enhanced. The most lucid of potential enhancements is the deletion of packets with an expired transmission deadline (TTL) field; this routine is termed as EPD algorithm. This EPD method (method 2) associates a TTL


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