Extending access point service coverage area through opportunistic forwarding in multi-hop collaborative relay WLANs

In multi-hop WLANs, it is more efficient to let some clients relay traffic for the clients whose distances are a bit far away from the AP, which increases the transmission efficiency. The existing solutions for multi-hop WLANs try to choose one or two fixed best relays to forward packets. However, the links between far-away clients and the AP are intermittently connected, and end-to-end paths may not exit. In order to fill this gap, using opportunistic forwarding, our solutions do not fix a relay; the source simply broadcasts its signal, any client who received the signal will relay the traffic. In this paper, our object is to extend the connectivity by opportunistic forwarding for far-away clients in multi-hop WLAN accesses. The original contributions made by this paper include: 1) We develop a general model to analyze the throughput of opportunistic forwarding in multi-hop WLANs. 2) We classify the clients into three groups, and propose a centralized opportunistic routing relay algorithm for each group of clients to achieve the optimal system throughput. 3) We propose a distributed opportunistic routing relay protocol for clients' disconnected and connected actions. Extensive simulations have been done in NS-2. The simulation results show that our protocol can significantly increase the service's coverage and connectivity of the entire network, compared with those methods by traditional one-hop and multi-hop relay.