Overloaded array processing with spatially reduced search joint detection

An antenna array is overloaded when the number of cochannel signals in its operating environment exceeds the number of elements. This paper proposes a n iterative joint detection technique, spatially reduced search joint detec tion (SRSJD), that well approximates the joint maximum likelihood (JML) rec eiver, while reducing its computational complexity by several orders of mag nitude. This complexity reduction is achieved by first exploiting spatial s eparation between interfering signals with a linear preprocessing stage, an d second, performing iterative joint detection with a reduced-state trellis formed over space instead of time. These novel joint detection trellises a re possibly tail-biting and vary in structure from stage to stage. Through simulation, SRSJD is shown to demodulate over 2M synchronous quaternary pha se-shift keying signals of zero excess bandwidth with an M element circular array. The channels of all users are assumed known.