High-capacity digital microwave radio systems

The design problems associated with high-capacity digital microwave radio systems and their present status are reviewed. Nonmilitary systems having transmission capabilities of about 90 Mbit/s or greater per radio bearer have been considered, those known to be under development operating within the approximate frequency range 8¿21 GHz. At the lower-frequency end, repeater spacings are limited by multipath effects to about 60 km, whereas at the higher-frequency end, spacings are dominated by rain attenuation and are limited to a few kilometres. The effects of both types of fading and the calculation of repeater spacings are considered. Bandwidth utilisation is very important for digital systems, and the design criteria for suitable filtering schemes are discussed leading to possible overall radio-frequency-channel arrangements. Constraints imposed by the system design are discussed, and the consideration of available components leads to outlines of possible repeater arrangements.