Reducing idle listening time in pipeline-forwarding MAC protocols of wireless sensor networks

In order to reduce the end-to-end delay in duty-cycle MAC protocols of Wireless Sensor Networks (WSNs), the pipeline-forwarding technique has been proposed. According to this technique, sensor nodes along the forwarding path are scheduled with sequential wakeup time slots. Even though the previous pipeline-forwarding protocols such as P-MAC and PRI-MAC showed a good result in term of reducing end-to-end delay, a significant per-hop delay is remained due to the unnecessary idle listening of sensor nodes in each cycle. In this paper, we propose a new pipeline-forwarding technique which tries to resolve this problem. In the proposed protocol, the RTS/CTS handshaking procedure is shortened by taking advantage of ACK mechanism. By waking up right before the upstream node sends ACK frame and overhearing it, a sensor node can be aware of the possibility of receiving data without waiting for and listening RTS frame. Therefore, the unnecessary idle listening can be reduced. When comparing with the existing solution PRI-MAC using QualNet simulator, our protocol shows the significant improvement in term of end-to-end delay and energy consumption.