Vertical Handoff from WLAN to Cellular Network Based on Relay Environment

Seamless handoff in loosely coupled WLAN/cellular systems is still a challenging issue. Since the cellular network overlaps the WLAN during a handoff from a cellular network to a WLAN, this type of handoff is less complicated. Thus, all the attempts go toward the handoff from the WLAN to the cellular network. In the cellular network, this handoff is considered as a new call. Therefore, it has a significant delay which makes it inappropriate for the real-time services. The worst case occurs when a mobile station (MS) exits a building surrounding the WLAN. In such a case, there might not be enough time for the handoff to be completed due to the abrupt loss of the received signal strength indication. In this paper, the proposed solution uses MSs as relay stations (RSs) and the existing frequency channels dedicated to the RSs to provide the required WLAN coverage during the handoff process. The suggested solution is analyzed using a simple proposed analytical model. Both the analytic and simulation results confirm that the suggested method improves the handoff dropping probability.