High-Capacity Microwave System for Digital Data Transmission

A nationwide data network is planned that will employ microwave relay networks for both long-haul and short-haul interconnection. A digital modulation technique has been developed that has the constant level advantage of frequency-shift keying (FSK) systems while retaining the error rate and threshold performance of coherently detected binary or four-phase phase-shift keying (PSK). Occupied spectrum and interference characteristics of a 21.5-Mbit/s data system are compared to the more conventional 600-, 1200-, and 1800-channel message systems.