On the Constrained Stochastic Gradient Algorithm: Model, Performance, and Improved Version

KOLODZIEJ, JAVIER ERNESTO; TOBIAS, ORLANDO JOSÉ; SEARA, RUI; MORGAN, DENNIS R.

IEEE TRANSACTIONS ON SIGNAL PROCESSING

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Año: 2009 vol. 57 p. 1304 - 1315

1053-587X

This paper discusses the constrained stochastic gradient (CSG) algorithm used for controlling antenna arrays, aiming to maximize the signal to interference plus noise ratio (SINR) in mobile communications. Firstly, analytical expressions for the first moment of the weight vector and the SINR characteristic of the standard CSG algorithm are derived for two interferer signals, considering small step size conditions and assuming Gaussian signal, interference, and noise. From these model expressions, the CSG algorithm performance is assessed, which predicts undesired behavior (termed here unbalanced behavior, pertaining to an unbalance between maximizing signal power and minimizing interference power) when one or more interference angles of arrival are close to the signal angle of arrival and the angle of arrival spreads of the involved signals are small. Finally, by using the model expressions, an improved CSG (ICSG) algorithm is proposed to compensate the unbalanced behavior of the standard CSG algorithm. The accuracy of the proposed model and the effectiveness of the modified algorithm are assessed through numerical simulations.