Cooperative Communication to Improve Reliability and Efficient Neighborhood Wakeup in Wireless Sensor Networks

To maximize lifetime of Wireless Sensor Networks, medium access control protocols usually trade off reliability for energy efficiency. Channel errors, collisions, idle listening, and overhearing further aggravate the problem. Our work investigates opportunities to improve reliability in Wireless Sensor Networks under such constraints. We consider a multi-hop data gathering network in which sensor nodes are deployed around a sink. Nodes periodically sense data and forward it to next hop nodes. For such a network, a Medium Access Control protocol, called CPS-MAC, is proposed. This protocol uses cooperative communication to improve reliability by using overhearing to its advantage. In conventional protocols, overhearing causes nodes to receive packets which are not meant for them. Therefore, these packets are discarded and considered a waste of energy. On the contrary, CPS-MAC intentionally wakes up next 1-hop and 2-hop neighbors to improve their chances of overhearing a packet. The overheard packets are buffered and then relayed to the next hop neighbor, combating channel fading by a cooperative spatial diversity gain. By combining multiple copies of the same packet, next hop neighbor is more likely to recover the original packet. Design challenges such as efficiently waking up neighborhood nodes, minimizing energy overhead, and partner selection are addressed. Simulation results show that CPS-MAC significantly decreases packet error rate without expending additional energy.