Directionally constrained adaptive beam forming to enhance interference nulling in direct-sequence spread-spectrum communication systems

The authors examine a direct-sequence spread-spectrum communication system using an adaptive antenna array to null interference. The system model is a modification of Compton´s (1990) system, using a digital implementation and a directional constraint. One of the primary roles of spread-spectrum modulation in the system is to remove the desired signal from the adaptive beam forming process. The simulated results of this directed system indicate that nulling of a tone jammer occurs without respect to direct-sequence code acquisition and that nulling of the desired signal occurs very slowly. Theoretical results are also obtained by using the system covariance matrix, and incorporating the effects of spread-spectrum filtering, to compute the system response as a function of time. These results show that the system may be made to null the jammer quickly and consistently, by using the auxiliary beam output power as a parameter in the least mean-squares (LMS) adaptive beam-forming algorithm