Random beamforming based on homogeneous feedback threshold and O(1) feedback constraint for multi-cell systems

In multiple-input single-output (MISO) multi-cell systems, the problem of maximizing downlink sum-rate with random beamforming (RBF) is investigated under O(1) feedback constraint about the average number of feedback users. A sufficient condition is first analyzed to guarantee the single-cell sum-rate as a Schur-concave function, which leads to the optimality of solving this problem by using the homogenous feedback threshold (HFT) policy. Then a new multi-cell RBF algorithm is proposed based on the HFT policy, namely HFT-MRBF in this paper, where an optimal HFT is also derived according to the number of expected feedback users. Finally, various numerical examples are presented to validate the efficiency of the proposed algorithm and the analytical results.