BER improvement of multilevel CPM in the mobile radio environment

An attractive modulation scheme, named accelerated phase-quaternary continuous phase modulation (AP-QCPM), is proposed for digital mobile radio applications. As AP-QCPM is a constant envelope modulation scheme, it is well suited to nonlinear power amplifier use in mobile equipment and handheld equipment of wireless LAN applications. The error performance of multilevel low-deviation frequency-shift keying (FSK) is severely degraded in the Rayleigh fading channel. On the other hand, the degradation of phase-shift keying (PSK) remains within a moderate amount. The paper is an attempt to clarify what kind of modification could be added to the conventional four-level FSK to achieve an error probability comparable with the QDPSK in the Rayleigh fading channel. The error probability of the proposed scheme and the power spectral characteristics are obtained to reveal critical values of the modification parameter. The analytical results are confirmed by the hardware simulation at 900 MHz.