Joint Optimization of User Association, Subchannel Allocation and Power Allocation in OFDMA Heterogeneous Networks

This paper investigates joint user association, sub-channel assignment, and power allocation in the uplink of multi-user orthogonal frequency division multiple access (OFDMA) of a heterogeneous network (HetNet) where users are subject to maximum transmission power constraints. It is shown that the  underlying problem is a highly non-convex mixed integer non-linear problem. To tackle the problem, the integer variables are relaxed and a penalty function is added to the objective function to make sure that the relaxed variables take binary values. Finally, the objective function is rewritten as the difference of two convex (D.C.) functions and the resulting problem is addressed through using the successive convex  approximation method. It is worth mentioning that, to the best of the author’s knowledge, the problem of joint user association, sub-channel allocation, and power control in the uplink of a heterogeneous network has not been addressed in the literature till now. Simulation results demonstrate the superiority of the proposed method over existing works in terms of achieving higher throughput despite exhibiting a higher complexity.