Digital quasi-impulse shaping for multi-level QAM and QPRS systems

Digital quasi-impulse-shaped signals for the transmission of Nyquist-shaped raised-cosine filtered signals and partial response signals are considered. Quasi-impulse signals do not require conventionally used phase-equalized x/sin(x)-shaped aperture equalizers. A simple logic circuit reduces the pulse-width of the conventional NRZ format, binary or multi-level input data. The finite pulse-width duration of these signals, as compared with the theoretically infinite impulse duration, permits a practical realization with negligible performance degradation. Experimental and computer simulation results demonstrate that pulse-widths of 25% for 225-QPRS class I, 18.75% for 64-QAM and 12.5% for 256-QAM lead to a performance degradation of only 0.2 dB at a P_e = 10^-8.