Beamforming With Multi cell Coordination

Abstract

In this work, we study the optimum multi-cell beamforming and we propose an optimized multi-cell downlink beamforming solution in which our objective is to maximize capacity of a cellular network. We first formulate an optimization problem, maximizing the received signal power of every active user in a cell, subjected to limiting the overall interference observed by other users below a specified level. In addition, we also put constraint on maximum transmit power of the serving base station. Next, we need robust downlink design against the imperfect channel state information. So in order to compute robust beamforming vector we accommodate channel estimation error in our formulation. To model the uncertainity between the true and estimated channel coefficients, we consider channel imperfection as error between true and estimated channel coefficients and we assume error is bounded with in an ellipsoidal set. The resulting formulation is a non-convex optimization problem. Since it is very difficult to solve a non-convex optimization problem we tried to convert non convex problem in to convex optimization problem. So to get a tractable solution for resulting non convex optimization problem, we exploit linear matrix inequality based S-procedure. The final reformulation is solved by using semi definite relaxation. The efficacy of proposed solution in improving cellular capacity and efficient power transmission is shown by simulations.