A root-CMA algorithm for multi-user separation

Constant modulus algorithms often offer candidate solutions for problems related to wireless communication systems that use antenna arrays and also for MIMO radar. The classical constant modulus adaptive array, however, fails at locking onto a single mode, and instead, it equalizes the full band spectrum. In this paper, we develop a novel approach for the separation of multiple users in a frequency-reuse radio system making use of the original constant modulus adaptive (CMA) algorithm. Based on the observation that the differential filter weights resemble a superposition of the array steering vectors, we cast the original task to a direction-of-arrival estimation problem. With rigorous theoretical analysis of the array response based on the discrete- space Fourier transform we elaborate a solution that solves the problem by finding the roots of a polynomial equation. We give an illustrative numerical example to demonstrate the validity of the approach under high SNR conditions.