| Cooperative relaying is a viable option for improving the trade off between link reliability and power consumption, since a more reliable point-to-point link usually requires a larger transmitter power for the same rate. It takes advantage of the broadcast nature of the radio channel, often viewed as a drawback to increase the robustness against fading by exploiting the spatial diversity. Similar to conventional relaying (routing), in cooperative relaying a source node transmits its message to an intended destination by the help of other nodes called relays. However, unlike routing, it yields diversity gain while reducing the effective path loss between the source and the destination. The robustness to fading that the diversity gain provided can be translated into an increase in the achieved transmission range (reach), the achievable data rate, or reliability.;In this work the challenges to implementing cooperative relaying in wireless sensor and ad hoc networks are addressed. Specifically, we develop efficient and low overhead cooperative relaying protocols assuming randomly deployed wireless networks. In these protocols the relay nodes are selected in a decentralized fashion which eliminates the need for an authority (e.g., an access point) or for handshaking between the nodes to assign a relay. We first propose stratified cooperative relaying (SCR), a route-free cooperative relaying protocol in which the messages cooperatively propagate toward the destination by the help of randomly-selected relays. We then show how this protocol can be implemented on top of a routing protocol and propose cooperation-augmented routing (CAR) which enables cooperation using an existing route as a backbone. Both protocols have less overhead and yield performances close to those of more complex protocols. |
