An optimal pulse-shaping filter design for multilevel QAM/QPR digital radio systems

This paper presents a practical optimal pulse-shaping filter design technique for QAM/QPR bandwidth-efficient digital radio systems. The transmit uses a hybrid FIR/analog-filter, and the receive uses either a hybrid analog/FIR (or IIR)-filter or a pure analog-filter. The design starts with the receive filter with a magnitude optimized to a square-root Nyquist shaping to minimize the adjacent channel interference. The impulse response of the cascaded transmit D/A, analog reconstruction filter and receive filter is then used to calculate the matched transmit digital filter. The filter is optimized to minimize the AWGN channel BER, i.e., the intersymbol interference, and to meet the transmit FCC spectral mask requirement. The computer simulations demonstrate that the technique gives a satisfactory result. The flexibility of this technique has made it easily to be adapted particularly to multi-level QAM/QPR digital systems. The technique has been successfully implemented on a Harris 155.52 Mbps (OC-3, STM-1) 128QAM SONET/SDH radio and a 25.8 Mbps (l6T1) 225QPR radio. The radio test results are presented and discussed