Energy‐efficient adaptive power allocation in orthogonal frequency division multiplexing‐based amplify‐and‐forward relay link

Recently, improving energy efficiency has been a new tendency in wireless relay communication. However, the introduction of relay technology may increase the system capacity, but is often followed by a more severe energy‐efficiency problem when compared with traditional single‐hop system. In this study, based on orthogonal frequency division multiplexing‐based frequency‐selective channel of amplify‐and‐forward relay link, a suboptimal two‐step power allocation algorithm of subcarriers is proposed to maximise the energy efficiency. The proposal includes two steps. First, a suboptimal subcarrier matching is achieved for introducing a virtual direct link, which may reduce the dimensionality of the power allocation. Second, the allocation problem of relay network is simplified as that in traditional cellular network. Thus, the optimal power allocation of virtual direct link can be obtained by one‐dimensional search method. Furthermore, the effects of rate and power constraints on the energy‐efficiency problem are analysed. Simulation shows that the suboptimal solution of the proposed algorithm is very close to the optimal solution, and the proposed energy efficient power allocation method can achieve the highest energy efficiency, compared with the rate adaptive and margin adaptive optimisations.