WLAN bandwidth support for relay-based upward handover in WLAN/cellular systems

Handover from WLAN to a cellular network in loosely coupled WLAN/Cellular systems is considered as a new call and therefore is not given any priority in the cellular network. Hence, it induces a remarkable delay that makes loosely coupled WLAN/Cellular systems inappropriate for online services. Due to this fact, during a handover from a WLAN to a cellular network, a mobile station (MS) may be trapped in a low bit rate region before completing the handover. This paper suggests using relay stations (RS's) during a handover to extend WLAN coverage until the handover is completed. When RS’s are not available, especially in sparse hotspots, allocating a large amount of the WLAN bandwidth to the MS can assist the handover process. In contrast, in a dense hotspot, the probability of finding an appropriate RS is high. Thus, the handover could be completed by using the potential RS's inside the WLAN coverage. It is confirmed, by analytical modeling and simulation, that the proposed method can reduce the call dropping probability and improve the handover performance.