A new variable step-size constant modulus array for signal separation in fast fading channels

The constant modulus array (CMARY) blind beamformer has the main drawback of typically capturing the signal that has the greatest power among the received cochannel signals. Hence, the capture process should be guided by controlling the initial beam steering. The minimum variance distortion less response (MVDR) beamformer is used to estimate the initial beam steering of the CMARY; this combination allows steering the initial beam of CMARY antenna toward the desired user´s direction. Therefore the desired user will have a dominant power at the array output and CMARY will capture it. This technique is called MVDR guided CMARY (GCMARY). In fading channel, the GCMARY does not necessarily still capture on the desired user. This occurs because the CMARY attempts to capture the strongest signals, thus if the desired signal captured by CMARY undergoes a deep fade, the CMARY might release that source. Therefore, the constant modulus algorithm (CMA) is modified to adapt slowly during a deep fade so that the CMARY maintains capture on the same signal throughout the fade and the algorithm is called the Variable Step-Size Constant Modulus VSCMA. Computer simulations show the high efficiency of the proposed GVSCMARY in separating cochannel signals even in the presence of channel fading and multipath propagation. Also, we show that the GVSCMARY can be efficiently used for tracking a fading signals operating with other stationary users.