During my Ph.D. work, I had developed a matlab based IEEE 802.11 simulator that we dubbed as SimEleven. I occasionally receive request from students who want to use SmEleven in lieu of more time-consuming simulators such as ns-2, OPNET, Qualnet or OMNeT++. Unfortunately, I no longer maintain SimEleven. However, I found that someone has developed and made freely available another matlab based WiFi simulator which is based on SimEleven. Here is the link:
I have not used this simulator, and as such do not endorse it. But if you are looking for SimEleven, this one might work for you as well.