Blind Detection of Co-channel QPSK Signals: A Phase Precoding-based Approach

Quadrature Phase Shift Keying (QPSK) is one of the important and commonly used modulation formats. Phase precoding was recently proposed as a new approach to achieve blind recovery of co-channel QPSK signals in the CDMA context. In this paper, we propose a new blind receiver for phase precoded QPSK signals, whose performance is significantly better, and close to that of anMMSE receiver. The receiver is derived by exploiting the phase-precoding knowledge, as well as the special structure of the QPSK constellation. Obtained in a closed-form manner, the proposed receiver avoids convergence and initialization problems associated with some of the earlier blind co-channel receivers that were based on the constant modulus (CM) property or finite alphabet (FA) property or Higher Order Statistics (HOS) based receivers. Considering the good performance achieved and the closed-form nature of the detector, phase precoding may be seen as an attractive candidate for co-channel systems employing QPSK signaling to enable efficient blind detection while saving significant data throughput.