Joint energy-efficient resource allocation and transmission duration for cognitive HetNets under imperfect CSI

Cognitive heterogeneous network (CR-HetNet) has been deemed a promising technique to improve spectral efficiency and system capacity. Designing effective resource allocation (RA) and transmission duration algorithms can further improve energy efficiency (EE) of communication systems. Different from the existing EE RA algorithms, in this paper, we focus on robust EE-based maximization RA problem by jointly optimizing power allocation, subcarrier allocation and transmission duration under the consideration of spectrum sensing errors and channel uncertainties simultaneously. The formulated optimization problem is an NP-hard and non-convex problem that is challenging to solve, especially in the case of a large number of users. A suboptimal algorithm is proposed to achieve subcarrier allocation for each femtocell user, and a Taylor expansion approximation is used to determine the optimal transmission duration. Furthermore, a Bernstain approximation approach is introduced to convert the optimization problem with uncertain constraints into a convex one which is solved by an iteration-based algorithm. Simulation results demonstrate the effectiveness of the proposed algorithm by comparing with the existing algorithms in terms of robustness and EE.