How does the opportunistic MAC protocol exploit the multi-packet reception capability in WLANs?

With the development of the advanced signal processing techniques, the Access Point (AP) can separate multiple packets transmitted in the channel at the same time. This property is called multi-packet reception (MPR). Several proposals to take advantage of the MPR capability use the 802.11 medium access control (MAC) protocol with the Request-to-Send/Clear-to-Send (RTS/CTS) access mechanism. However, under multi-rate transmissions, these proposals exhibit the phenomenon known as performance anomaly, which results in MPR being under-utilized. In [8] an opportunistic method of how a strategy might better exploit the MPR capability in a multi-rate scenario is presented. This method provides contending stations without permission to send data packets a second chance after the CTS packet reception via opportunistic probability. In this paper, the objective is to propose an analytical expression and to analyze the conditions where the opportunistic method offers the best performance into a multi-rate scenario via a new form of implementing the second chance. Analytical performance is provided and verified through simulations. Results indicate that the opportunistic method provides a partial improvement in function with the MPR capability, with respect to average throughput when compared to previous approaches.