Continuous phase modulation of spectrally efficient FQPSK signals

A continuous phase modulation (CPM) implementation alternative of a recently standardized class of Feher-patented quadrature phase-shift keying (FQPSK-B) modulation is proposed. It is based on the fact that the FQPSK-B signal has quasi-constant amplitude and continuous phase characteristics, allowing CPM interpretation. Based on this, we derive the modulation index, premodulation filter and alternating change monitor differential encoder for the CPM generated FQPSK-B signal, to be fully compatible with the original I/Q-modulated one. It is shown that the power spectral density and the bit error rate performance of the CPM generated FQPSK-B signal are almost the same as those of the I/Q modulated FQPSK-B signal.