Joint resource allocation and admission control in OFDMA-based multi-tier cellular networks

We present a joint resource allocation (RA) and admission control (AC) framework for an orthogonal frequency-division multiple access (OFDMA)-based cellular network composed of a macrocell overlaid by small cells. In this framework, the resource allocation problems for both the macrocell and small cells are formulated as optimization problems. The macrocell RA problem is aware of the existence of the small cell tier. On the other hand, the RA and AC problems for the small cells aim at maximizing the number of admitted users while simultaneously minimizing the consumed bandwidth. These optimization problems are shown to be mixed integer nonlinear problems (MINLPs). Techniques are proposed to obtain either the optimal solution or a bound on the optimal solution with reduced complexity through convex relaxation. Dual decomposition technique is also used to have a distributed solution for the small cell tier. Numerical results confirm that the convex relaxations follow a similar behavior to the MINLP formulations. Also, the distributed solution converges to the optimal solution obtained by solving the corresponding convex optimization problem in a centralized fashion.