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Multiuser diversity refers to a kind of diversity present across different users in a fading environment. This diversity can be exploited by scheduling transmissions so that users transmit when their channel conditions are favorable. Exploiting multiuser diversity access, called also opportunistic access, conducts to a system efficiency that rises with the number of users. Different opportunistic IEEE 802.11 Medium Access Control (MAC) approaches have been proposed. The efficiency study of these approaches by NS-2 simulation is necessary for a performance comparison. The implementation of any opportunistic IEEE 802.11 MAC approach in NS-2 is based on using different cross-layer interactions between the physical layer and the link layer components which are the interface queue and the MAC sub layer. In this paper, we introduce the work that has been done to create a model for implementing these interactions. We also give the different functions we have implemented in NS-2 on the basis of this model. Any opportunistic approach can thus be implemented using these functions. Our contribution is providing an NS-2 extension that can be used to implement protocols exploiting multiuser diversity. We explain how to use our NS-2 extension by giving two examples showing the implementation of new opportunistic MAC protocols.

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