Mobile ad hoc relaying for upward vertical handoff in hybrid WLAN/cellular systems

One of the main issues in hybrid wireless networks is vertical handoff. Dropping probability is one of the important parameters that must be considered in planning the wireless communication systems. However, there has not been much effort in dropping rate reduction in loosely coupled hybrid wireless networks. In loosely coupled WLAN/cellular systems the system administrator of the WLAN is different from the cellular one. Therefore, in these situations, reducing the dropping probability based on classical methods such as using reserved guard channels is difficult. A handoff from a WLAN to a cellular system occurs when a multi-mode device moves out of the WLANs coverage area. This is an upward vertical handoff in a hybrid network. In this paper, we propose to employ ad hoc relaying during the upward vertical handoff in a hybrid WLAN/cellular system. Two-hop and multi-hop relaying approaches, which we propose in this paper, improve the dropping probability regardless of the number of reserved channels. Simulation results support the effectiveness of the proposed methods. Also, practical routing protocols are proposed in order to implement the suggested relaying methods.