This paper introduces a family of bandwidth efficient modulation schemes called quadrature multiplexed continuous phase modulation (QM-CPM). QM-CPM can be thought of as an alternative to smooth pulse-shaped quadrature amplitude modulation (QAM). Like pulse-shaped QAM, QM-CPM modulates smooth continuous signals onto the in-phase (I) and the quadrature-phase (Q) channels, but these signals are derived from CPM signals instead of being filtered to attain their desired smoothness and spectral properties. QM-MSK (QMminimum shift keying) is developed and is shown to double the bits/Hz over MSK while maintaining MSK's normalized minimum distance of d 2   min  = 2.0. Classes of M 2 -ary QMCPFSK (QM-continuous phase frequency shift keying) signals are derived from constant envelope M-ary CPFSK signals to construct bandwidth efficient modulation schemes which are comparable to and offer advantages over pulse-shaped QAM.
['John P. Fonseka', 'Eric M. Dowling', 'Chen Chia Teng']
Quadrature multiplexed CPM