Novel Retransmission Methods based on Collision Types for Wireless LANs

Abstract

Wireless local area networks (WLANs) based on the IEEE 802.11 standard have been used widely because of its easy accessibility of the WLANs and high data rate with low cost. To avoid collisions, the IEEE 802.11 medium access control (MAC) with distributed coordination function (DCF) uses predetermined inter-frame spaces and the random back-off process. As the physical data rate increases, the channel utilization of MAC becomes low. This is because most of the time is wasted in the back-off state. Moreover, the number of wireless devices sharply increases and the size of data continues to grow. In this environment, the networks become saturated. In saturated networks, collisions and retransmissions frequently occur, aggravating the network throughput.In this paper, we classify collisions into two types based on their causes: selecting an identical back-off count and hidden station problem. For each cause, we propose novel retransmission methods respectively, to increase network performance. In the first proposed retransmission method, a station that experienced collision transmits additional data after a successful retransmission. The second proposed method detects collisions caused by hidden stations and then allows collision-free retransmission. The analysis and simulations results show that the proposed methods provide greater normalized throughput than DCF. Moreover, proposed methods maintain the fairness and provide a shorter average waiting time than existing schemes.