Constant Envelope Rate Compatible Modulation

The conventional rate compatible modulation (RCM) uses the high-order quadrature amplitude modulation (QAM) signal for rateless transmitting. The large size complex constellation with near-Gaussian probability mass function (PMF) produces high peak-to-average power ratio (PAPR). This paper presents a new method aimed at solving the PAPR problem associated with RCM. We transform the RCM signal to a constant envelope signal through concatenating RCM with continuous phase modulation (CPM), which decreases the PAPR to 0 dB. At the receiver, the serial iterative demodulating and decoding procedure is designed to improve the performance of the system. In the presence of nonlinear power amplifier, we simulate the bit error rate and spectral efficiency of the RCM-CPM and the RCM-QAM in additive Gaussian noise channels. The simulation results demonstrate that RCM-CPM outperforms RCM-QAM with input back-off, especially the performance advantage is about 3 dB at high signal-to-noise ratios (SNRs).