In order to address the challenges of cooperation, PHY layer cooperation schemes were proposed and, to a limited extent, medium access control (MAC) layer schemes. On the network layer, the network coding techniques can be viewed as a form of cooperation as well. To the best of our knowledge, there are very few designs that involve multiple layers for cooperative wireless sensor networks. Although the benefits of cooperation is partially achieved in one way or another, these designs have two main issues. Firstly, the relay selection process is implemented in the MAC layer, which would require a significant amount of control packets to provide handshakes between source/destination and relay nodes. Also, even a larger amount of control packets are necessary, when relays fail to deliver the packets. Secondly, the relays are prohibited from transmitting simultaneously, since the CSMA/CA protocol is invoked. Thus, only limited throughput enhancement could be achieved, given that the relays experience robust channel conditions. Cross-layer designs are proposed to combine cooperative diversity at the PHY layer with truncated Automatic Repeat-reQuest at the link layer to improve the throughput performance. Both schemes utilize cooperative diversity only if the destination node receives an erroneous packet from the source node.
In this work, our primary objective is to establish a multi-hop cooperative route from the source to the destination so that diversity can be achieved on a hop-by-hop basis through the entire cooperative path. As the result, the cooperative nodes will be systematically involved from the beginning, hence improving the first transmission attempt under fading channel conditions. The overall design structure is aimed at achieving full cooperative diversity, based on which the PHY, link and network layers of the system are specifically tailored.