Some results on the spectral efficiency improvement in partial response CPM systems

The problem of the determination of the pulse shape in partial-response constant envelope CPM (continuous phase modulation) systems with binary signaling to furnish optimum spectral behavior with a prescribed bit error rate performance is studied. The spectral performance is characterized by the effective bandwidth of the modulated signal. The minimum Euclidean distance is used to measure the error probability. The procedure is based on an approximation which is valid when the minimum Euclidean distance required is small, so that the effective bandwidth can be made particularly narrow. The general shape of the optimum baseband pulse can be expressed in closed form. Numerical results are reported and comparisons with standard pulses are discussed