Cooperative Communication Protocol based on Relay Node Grouping in Wireless Networks

IEEE 802.11a/b/g standards support multiple data rates. Although the use of multiple data rates increases the capacity of wireless networks, it can lead to a performance anomaly problem. Cooperative communication for wireless networks has attracted considerable interest owing to its ability to mitigate this performance anomaly problem. In cooperative communication, a number of relay nodes support a source node in the forwarding of data packets to a destination node. If the direct transmission of a data packet between a source node and a destination node is not successful, the overheard data packet from the source node is forwarded by relay nodes to the destination node. Several MAC (Medium Access Control) protocols have been proposed for cooperative communication in wireless networks. A number of these can result in collisions among the relay nodes in a dense network. Further, cooperative communication can be interrupted by other nodes. To resolve these problems, we propose a new cooperative protocol. In the proposed protocol, relay nodes are divided into several groups based on their data rates. Then, to limit the number of contending relay nodes, only the relay nodes in the highest group are selected. Collisions among the selected relay nodes are resolved based on a backoff mechanism. The proposed protocol ensures that cooperative communication is not interrupted by other nodes by implementing a busy signal and NAV (Network Allocation Vector). The proposed protocol can reduce the collision probability and increase the network performance. Performance evaluation is conducted using simulation, and confirms that the proposed protocol significantly outperforms the previous protocol in terms of throughput, collision probability, and delay. Keyword-Cooperative communication, MAC protocol, Relay node grouping, WLAN