IEEE 802.11 LAN 시스템에서의 멀티채널 기반 패킷 전송에 관한 연구

Abstract

Currently, the mobile communication techniques have been developed in the various field due to the advantage of mobility. The researches are continued to provide for supporting various quality of services in the mobile communication environments. Moreover, the explosive growth of the Internet and the continued dramatic increase in demand for all types of wireless services require more effective ways in connection control in IEEE 802.11 WLANs. So, medium access control is an essential part. However, MAC protocols suffer from the problems such as the hidden node problem and the exposed node problem. The problems shown in legacy WLANs have limited the channel efficiency of such systems. In order to solve the problems occurred in legacy WLANs, we propose a new packet transmission protocol based on multi-channel environment. The use of multi channel can provide advantages in improving network efficiency and reducing collisions. If there is no interference between channels, the number of nodes can transmit through the different channels simultaneously. In a multi-channel MAC protocol, the main issue is how to negotiate channels between sender and receiver for packet transmission. One of the critical problems in the WLANs is collisions which occur frequently in the contention mode. The way to mitigate the performance degradation from collisions is to govern the number of multiple users in a slot by employing time-varying access permission probability function. Therefore, in this thesis, we propose a multi-channel MAC protocol in which additional control channel is assigned to the traffic channels. As access to initiate packet transmission is performed through control channel between nodes, collision only occurs in control channel. In order to reduce the collision probability, we propose the collision resolution algorithm with p-persistent channel access probability function. The proposed algorithm assigns different channel access probability function to different QoS classes according to QoS class priority. The node with the traffic of the highest priority always sends the control packet earlier than others. The proposed algorithm is expected to guarantee diverse QoS requirement. We evaluate the performance of simple multi-channel WLAN systems by using NS-2. The results show that our proposed multi-channel scheme increases both per-traffic channel and per-node aggregate throughput.