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Cooperative relaying has been proposed as a promising transmission technique that effectively creates spatial diversity through the cooperation among spatially distributed nodes. However, to achieve efficient communications while gaining full benefits from cooperation, more interactions at higher protocol layers, particularly the MAC (Medium Access Control) and network layers, are vitally required. This is ignored in most existing articles that mainly focus on physical (PHY)-layer relaying techniques. In this paper, we propose a novel crosslayer framework involving two levels of joint design-a MACnetwork cross-layer design for forwarder selection (or termed routing) and a MAC-PHY for relay selection-over symbol-wise varying channels. Based on location knowledge and contention processes, the proposed cross-layer protocol, CoopGeo, aims at providing an efficient, distributed approach to select next hops and optimal relays along a communication path. Simulation results demonstrate that CoopGeo not only operates properly with varying densities of nodes, but performs significantly better than the existing protocol BOSS in terms of packet error rate, transmission error probability, and saturated throughput.

In this paper, we propose a novel relay selection scheme based on geographical information, aiming to minimize the symbol error probability (SEP) for wireless ad hoc relay networks. The proposed scheme utilizes only the source-relay and relay-destination distances as selection criteria to choose the best relay. In particular, such geographical information is often available during network initialization. Thus, the proposed scheme does not need extra procedures to examine which relay has the best channel quality and, hence, reduces significantly the computational complexity. By contrast, most existing relay selection schemes rely on strict channel state information (CSI) and coherent time intervals, drastically increasing the difficulty in practical realizations, especially for large relay networks in which the fading channels are sufficiently fast-varying. In our scheme, the accuracy of the distance information is the main factor resulting in non-best relay selection. An ideal scheme (in which the distances between nodes are exact) and a practical scheme (in which there exists distance estimation errors) will be discussed respectively. Simulation results demonstrate the proposed relay selection method can efficiently improve the SEP performance and outperform the random relay selection scheme.Keywords-Cooperative diversity; wireless ad hoc relay networks; relay selection; decode-and-forward (DF); symbol error probability (SEP)

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Most of geographic routing approaches in wireless ad hoc and sensor networks do not take into consideration the medium access control (MAC) and physical layers when designing a routing protocol. In this paper, we focus on a cross-layer framework design that exploits the synergies between network, MAC, and physical layers. In the proposed CoopGeo, we use a beaconless forwarding scheme where the next hop is selected through a contention process based on the geographic position of nodes. We optimize this Network-MAC layer interaction using a cooperative relaying technique with a relay selection scheme also based on geographic information in order to improve the system performance in terms of reliability.