MIMO Precoding and Power Control based on 1-bit Feedback

This paper proposes a novel solution to the problem of beamforming and power control in the downlink of a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system. This solution is developed in two steps. First, we describe an adaptive beamforming technique that, using a stochastic gradient method, maximizes the power delivered to a mobile terminal In the proposed solution, perturbed precoding matrices are time multiplexed in the information signal transmitted to a mobile terminal; then, the mobile terminal informs the transmitter, via a single feedback bit, about the perturbation delivering the larger power. This approach does not need pilot symbols and uses quasi-Monte Carlo methods to generate the required perturbations. Then, we propose a novel power control algorithm that, selecting a proper transmission energy level from a set of possible values, aims at minimizing the average bit error rate. This set of levels is generated on the basis of the channel statistics and of a long term constraint on the average transmission power. Numerical results evidence the robustness of the proposed algorithms in a dynamic fading environment