Loosely coupled interworking WLAN/cellular system has attracted a lot of attention recently, since the WLAN bandwidth is not restricted by the cellular network. In this kind of systems, a handoff from the WLAN to the cellular network is considered as a new call and therefore incurs a significant delay. Hence, the mobile station (MS) has to accomplish the handoff ahead of losing the WLAN coverage. In many cases the MS enters a region with a low bit rate before completing the handoff. This paper tries to aid the handoff by allocating the requested WLAN bandwidth to maintain the MS link with the serving access point as much as possible. In the case of WLAN bandwidth shortage, the handoff is assisted by using MS’s as ad hoc relay stations (RS’s) to extend the WLAN coverage. In a low-density WLAN, usually the handoff is accomplished by the aid of WLAN bandwidth. In contrast, in a high-density WLAN, the chance of finding a proper RS is high while the amount of available WLAN bandwidth is low. As a result, generally the handoff is accomplished by the assistance of potential RS’s. Both analytical and simulation results are provided to validate the effectiveness of the proposed method in terms of decreasing the call dropping probability.

由于WLAN带宽不受蜂窝网络的限制，松散耦合的互操作WLAN /蜂窝系统最近引起了很多关注。在这种系统中，从WLAN到蜂窝网络的切换被认为是一个新的呼叫，因此会产生很大的延迟。因此，移动站（MS）必须在失去WLAN覆盖范围之前完成切换。在许多情况下，MS在完成切换之前进入比特率较低的区域。本文试图通过分配请求的WLAN带宽来帮助切换，以尽可能多地维护与服务访问点的MS链路。在WLAN带宽不足的情况下，通过将MS用作临时中继站（RS）来扩展WLAN覆盖范围，从而辅助切换。在低密度WLAN中，通常，切换是借助WLAN带宽来完成的。相反，在高密度WLAN中，找到合适的RS的机会很高，而可用WLAN带宽的数量却很低。结果，通常通过潜在RS的协助来完成切换。分析和仿真结果均被提供以验证所提方法在降低呼叫掉话概率方面的有效性。