Handoff in WLAN/cellular systems based on a hybrid of WLAN bandwidth and ad hoc relaying strategies

Abstract

The seamless vertical handoff from a wireless local area network (WLAN) to a cellular system yet poses a big challenge. While serving by a WLAN, a mobile node (MN) may enter a region with a low data rate before completing a handoff towards a cellular network. To maintain quality of service, a large amount of WLAN bandwidth must be allocated to compensate for the weakness of MN link. However, this mechanism does not work properly in dense hotspots because of the lack of WLAN bandwidth. An alternative is to employ relay nodes (RN) to remain connected to the AP. This scheme also does not operate well in a low-density hotspot because the chance of finding a suitable RN is low. In this paper, a hybrid solution that uses both WLAN bandwidth and potential RNs is proposed. It uses the trade-off between the WLAN bandwidth and the potential RNs to reach an optimum handoff performance in terms of call dropping probability. Initially, the probability of call dropping in relay mode is theoretically evaluated and compared with the simulation results. Next, the proposed Hybrid approach is modelled by assuming 5% and 10% of nods as the relay nodes. The results show the proposed method can significantly reduce call dropping probability in both low and high-density hotspots when compared with a relay or bandwidth-based approach. It also reduces new call blocking probability of the bandwidth only but slightly worse than the relay only methods.