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.

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The traditional RTS/CTS handshaking has been widely adopted in wireless ad hoc networks to reduce the hidden terminal problem. However, the handshaking induces the false blocking problem where adjacent nodes are deferred unnecessarily by overhearing the unsuccessful RTS packets. To mitigate these, the Blocking Notification (BN) scheme was proposed previously. In the BN scheme, the hidden and exposed receivers will broadcast the BN packets to inform adjacent nodes of their deferring status to avoid any incoming RTS packets which will not be replied by them. Nevertheless, the BN scheme itself can potentially incur redundant BN packet transmissions, energy wastage and packet collisions. The effectiveness of the BN scheme depends critically on the judicious transmission and successful reception of BN packet. In this paper, we propose an improved BN scheme that is able to dynamically assign strategic nodes the right to broadcast the BN packets. The improved BN scheme with strategic nodes attempts to minimize the BN packet transmissions and avoid collisions while maximizing their successful receptions at the intended nodes. This ensures higher energy efficiency, which is critical in ad hoc networks. Moreover, the proposed BN scheme can be deployed in any arbitrary network topology instead of a simplistic linear topology as assumed in previous works. Simulation results have shown that the proposed BN scheme with strategic nodes can significantly reduce the number of BN packet transmissions and provide energy savings of up to 60%.

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