THE DIFFERENTIAL CMA ADAPTIVE ARRAY ANTENNA USING AN EIGEN-BEAMSPACE SYSTEM

This paper addresses approaches to enhancement of performance of the C MA (Constant Modulus Algorithm) adaptive array antenna in multipath en vironments that characterize the mobile radio communications. The cost function of the CMA reveals that it has an AGC (Automatic Gain Contro l) procedure of holding the array output voltage at a constant value. Therefore, if the output voltage by the initial weights is different f rom the object value, then the CMA may suffer from slow convergence be cause suppression of the multipath waves is delayed by the AGC behavio r. Our objective is to improve the convergence characteristics by adop ting the differential CMA for the adaptive array algorithm. First, the basic performance of the differential CMA is clarified via computer s imulation. Next, the differential CMA is incorporated into the eigen-b eamspace system in which the eigenvectors of the correlation matrix of array inputs are used in the BFN (Beam Forming Network). This BFN cre ates the optimum orthogonal multibeams for radio environments and work s helpfully as a preprocessor of the differential CMA. The computer si mulation results have demonstrated that the differential CMA with the eigen-beamspace system has much better convergence characteristics tha n the conventional CMA with the element space system. Furthermore, a m odified algorithm is introduced which gives the stable array output vo ltages after convergence, and it is confirmed that the algorithm can c arry out more successful adaptation even if the radio environments are changed abruptly.