text: Multi-packet reception (MPR) has been recognized as a powerful capacity-enhancement technique for randomaccess wireless local area networks (WLANs). As is common with all random access protocols, the wireless channel is often under-utilized in MPR WLANs. In this paper, we propose a novel multi-round contention random-access protocol to address this problem. This work complements the existing randomaccess methods that are based on single-round contention. In the proposed scheme, stations are given multiple chances to contend for the channel until there are a sufficient number of ?winning? stations that can share the MPR channel for data packet transmission. The key issue here is the identification of the optimal time to stop the contention process and start data transmission. The solution corresponds to finding a desired tradeoff between channel utilization and contention overhead. In this paper, we conduct a rigorous analysis to characterize the optimal strategy using the theory of optimal stopping. An interesting result is that the optimal stopping strategy is a simple threshold-based rule, which stops the contention process as soon as the total number of winning stations exceeds a certain threshold. Compared with the conventional single-round contention protocol, the multi-round contention scheme significantly enhances channel utilization when the MPR capability of the channel is small to medium. Meanwhile, the scheme automatically falls back to single-round contention when the MPR capability is very large, in which case the throughput penalty due to random access is already small even with single-round contention.
  @cite_0: With the improvement of the physical layer's ability to decode more than one packets from multiple users, the classical collision model no longer applies and a cross-layer approach should be employed when designing multiple access protocols. This is especially the case for CSMA communications, which previously have not been studied under a multipacket reception (MPR) model. Since CSMA is used in the IEEE 802.11 wireless LAN standards and other wireless networks, improving its performances could have widespread benefits. In here, we investigate the impact of MPR on CSMA and propose a performance-improving cross-layer designed CSMA protocol for wireless networks.
summary: In related work, @cite_0 attempts to enhance the utilization of MPR channels by allowing stations to count down and transmit as long as there are less than @math ongoing transmissions in the air. To do this, one key assumption is that a station is able to detect the number of ongoing transmissions using an energy detector. This assumption, however, is not valid in wireless networks, where the received energy from each transmitting station is random and unknown a priori.