Spatially superposed M-ary QAM wireless communication system

We present a spatially superposed Mary-quadrature amplitude modulation (QAM) communication system that can provide efficient use of frequency resources and transmitted power. The system incorporates multiple conventional quaternary phase shift key (QPSK) modulators and combines their output signals spatially with a specially tailored antenna array to produce an M-ary QAM signal. Thus, it can operate on power amplifiers driven in the high efficiency region and relax the strict requirements for the hardware as compared to conventional M-ary QAM systems. The proposed system, however, is sensitive to superposition error. A novel antenna array system is presented that can minimize the superposition error.