Cognitive relay is considered as a remarkable technology that increases the network coverage and raises the system spectral utilization by exploiting those detected spectrum holes. We mainly investigate a multi-hop scenario that is more complex than a dual-hop network because of the high correlation between hops. In this article, we consider an energy-constrained network which includes a source node, a destination node and a group of network clusters each consisting of several cognitive relay nodes. To accomplish data transmission from source to destination, the best path including nodes with optimal power is selected to maximize the network capacity using proposed efficient algorithms, taking into account the sensing results of relay nodes, the channel gains and the connectivity of links. In addition, these algorithms can also be adopted in the situation of selecting two relay paths by making only a few slight modifications, which means that the scheme provides good expansibility. Simulation results illustrate the strategies of relay selection and power allocation constrained by different energy consumptions and compare the performance between one-path and two-paths selection.
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