Partition and Cooperation for Crowded Multi-rate WLANs

Recently, growth in smart devices has increased along with the number of wireless nodes in wireless local area networks (WLANs). The increased number of nodes causes throughput degradation due to frequent collisions between nodes. In multi-rate environments, transmission at low data rates limits the throughput of WLANs, and we call it performance anomaly. The time fairness approach has been proposed to resolve the performance anomaly. However, in the time fairness approach, nodes, which transmit at low data rates, experience lower throughput than in the IEEE 802.11 standard. In this paper, we propose a new medium access control (MAC) protocol, called partition and cooperation based MAC (PCMAC), to simultaneously solve these problems including frequent collisions, performance anomaly, and low throughput under time fairness scheme. First, we calculate the optimum number of nodes, which maximizes the data transmission time, for each data rate. Second, for resolving performance anomaly and reducing collisions, we divide the nodes into several partitions based on the data rate and the optimum number of nodes. Each partition has a different transmission time slot that is proportional to the number of nodes. Finally, we propose a cooperative communication scheme using a relay partition to improve the throughput of nodes with low data rates and to achieve robust cooperative transmission. PCMAC is evaluated through extensive simulation and simulation with measured data. The results show that our scheme effectively improves WLAN performance.