Joint energy-efficient power allocation and subcarrier pairing in orthogonal frequency division multiple-based multi-relay networks

In this study, a resource allocation scheme for energy-efficient communication in a cooperative orthogonal frequency division multiple (OFDM) network based on subcarrier pairing is proposed. Different from traditional cooperative OFDM networks, in the concerned network, one subcarrier pair can be forwarded by multiple relays, and the source is allowed to retransmit the signals sent in the first phase. The problem aimed at maximising the system energy efficiency (EE) under total power constraint and minimum spectral efficiency constraint is formulated into a mixed-integer nonlinear programming (MINLP) problem, which in general has intractable complexity because of its combinatorial nature. The authors simplify the optimising model as a typical fractional programming problem to solve the complex the MINLP problem. The simplified fractional programming problem is proved to be quasi-concave, thus Dinkelbach´s method consisting of outer iterations and inner iterations can be used to find the optimal solution to the proposed MINLP problem.