Adjacent channel interference in overlapping access points of OFDM WLANs

Interference analysis has always been a key issue for WLAN systems, because of the unregulated nature of the Industrial Scientific and Medical (ISM) bands that they operate in. However, an aspect of interference generally not considered is adjacent channel interference (ACI) from a neighboring WLAN operating on a standard defined non-overlapping channel. Because standard defined nonoverlapping channels are not truly non-overlapping but are based on limits set on the transmit signal spectrum, situations may arise where this interference will significantly degrade performance. With escalating deployment of WLANs in overlapping areas and the limited number of valid operating channels available, ACI may become a major hindrance to the optimal functioning of WLANs. In this work we present a detailed analysis of ACI that access points (APs) of OFDM WLANs deployed in overlaying coverage areas may experience when individual APs operate on IEEE 802.1 la defined non-overlapping channels. We investigate scenarios where ACI is most likely to occur. We also investigate the parameters that affect the severity of this interference and how system performance is degraded in the presence of ACI (in terms of physical layer parameters). We use these results to suggest minimum separation distances between APs that would render the effects of ACI negligible. Furthermore, several ACI mitigation techniques are described and their effectiveness for various scenarios is investigated. Results from our analysis may be used to improve network deployment strategies for large scale multi-AP WLANs and to develop routines that allow better coexistence strategies for APs deployed in overlapping coverage areas.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat