On the Joint Beamforming and Power Control in Cellular Systems: Algorithm and Stochastic Model

The increasing demand for mobile communications has led to a spectrum shortage that severely limits the expansion of cellular systems. An attractive approach to cope with this problem is to use beamforming techniques for improving the signal-to-interference-plus-noise ratio (SINR), which in turn allows reducing the transmission power and increasing the system capacity. In this context, a novel approach for joint beamforming and power control in cellular systems is discussed. Regarding the beamforming, an adaptive algorithm is devised, aiming to overcome an important implementation challenge of the constrained stochastic gradient (CSG) and improved CSG (ICSG) algorithms, namely the requirement to estimate each interfering signal individually. The proposed beamforming algorithm, called adaptive-projection CSG (AP-CSG), provides both enhanced SINR performance and reduced computational burden as compared with the standard CSG algorithms. Concerning the power control, a real-time algorithm designed to operate jointly with the AP-CSG is also developed, which allows reducing the transmission power while maintaining acceptable SINR levels. Moreover, a stochastic model for the proposed joint beamforming and power control algorithm is derived, allowing the prediction of its behavior accurately. Numerical simulation results are shown, confirming the effectiveness of the new algorithm and the accuracy of the proposed model.