Mitigating false blocking problem in wireless sensor networks

The hidden terminal problem in wireless sensor network (WSN) is one of the main causes of collision. Even though RTS/CTS handshaking has been implemented in CSMA/CA standard to alleviate the problem, it does not solve the collision completely. Moreover, it induces an issue called false blocking problem. Unaware of a busy status of a hidden receiver, adjacent nodes which can be potential senders will keep transmitting RTS packets to obtain a response but in vain. These RTS retransmission will cause other nodes which overhear the RTS packets blindly defer, causing them to be falsely blocked. The false blocking problem can exhaust scarce energy and degrade the network performance especially in a large distributed sensor network with heavy traffic condition. In this paper, we propose and evaluate a scheme that combines both the Block Notification (BN) and Ready-to-Send (RS) packets. The BN packet is used to notify the deferred state to adjacent nodes in order to avoid unnecessary backoff and RTS retransmissions. The RS packet, on the other hand, is used to validate the received RTS packets and in case the BN packets are not received, the node can verify the RTS packets before going to the deferred state too. Simulation results have shown that the proposed scheme can overcome the false blocking problem by reducing both the number of unnecessary RTS retransmissions and energy consumed.