Achieving maximum energy-efficiency in multi-relay OFDMA cellular networks: a fractional programming approach

Abstract

In this paper, we consider the joint power and subcarrier allocation problem in the context of maximizing the Energy-Efficiency (EE) of a multi-user, multi-relay Orthogonal Frequency Division Multiple Access (OFDMA) cellular network. Our objective function is formulated as the ratio of the Sum-Rate (SR) over the total power dissipation. We prove that the fractional programming problem considered is quasi-concave and then employ Dinkelbach's method for finding the optimal solution at a low complexity. This method allows us to solve the above-mentioned master problem by solving a series of parameterized concave secondary problems. These secondary problems are solved using a dual decomposition approach, which allows us to further decompose each secondary problem into a number of similar subproblems. We characterize the impact of various system parameters on the attainable EE and Spectral-Efficiency (SE) of the system when employing both EE Maximization (EEM) and SE Maximization(SEM) algorithms. In particular, we observe that increasing the number of relays provides diminishing returns in EE gain, whilst increasing both the number of available subcarriers and the number of active User Equipment~(UE) increases both the EE and SE of the system as a benefit of the increased frequency and multi-user diversity, respectively. Finally, we demonstrate that as expected, increasing the available power tends to improve the SE when using our SEM algorithm. By contrast, given a sufficiently high available power, our EEM algorithm attains the maximum achievable EE and a suboptimal SE.

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ORCID for Lajos Hanzo: orcid.org/0000-0002-2636-5214

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