Implementation of a 64-QAM modem for 140 Mbit/s digital radio

The authors describe a newly developed 64-QAM (quadrature amplitude modulation) modem for use in microwave terrestrial radio systems at 140 Mbit/s. Digital signal processing and LSI technology are extensively used in the implementation of several modem functions to ensure compactness, high reliability, and low power consumption in the equipment. In particular, a seven-tap baseband digital equalizer (BDE) is employed to counteract multipath fading, and forward error correction (FEC) is adopted to eliminate residual bit errors caused by modem imperfections. Finally, BDE and FEC are jointly exploited to provide monitoring capability in early error detection and protection switching.<>