Linearly constrained direct-sequence spread-spectrum interference rejection

A constrained least-squares technique is presented that utilizes a modified optimality criterion which enhances the detection capabilities of direct sequence spread spectrum systems. The standard least-squares rejection filter adds distortion to the decision variable at the output of the despreading operation. Constraints are introduced into the least-squares solution of the rejection filter which reduce the self-noise of the filter while simultaneously retaining its interference rejection properties. Two types of constraint conditions are considered. The first is a correlation matching property for the rejection filter output. This constraint induces the filter to pass the chip sequence undistorted. The second type of constraint is energy reduction, which induces the filter to achieve minimal energy. Both constraint types are successful at increasing the output signal-to-noise ratio (SNR). Simulation results are presented which demonstrate the output SNR improvement by using the constrained rejection filter