PROBLEMS OF HIGH CAPACITY DIGITAL TRANSMISSION IN ANALOG FREQUENCY BANDS.

The expansion of the transmission network, as planned in many countries, is based on an increased use of digital techniques. In Italy medium capacity digital radio equipment is already available, and is being installed to cover the needs for local network expansion. However, larger capacity links (at least 70 or 140 Mb/s per carrier) are required, to combine economical and operational advantages, in main trunk connections. In this case the use of existing radio towers and buildings would require the sharing of a frequency band among the existing analog and the future high capacity digital links. Some different solutions could be envisaged, as for instance the overlay of the new radio network to the existing one with a new channelling plan, keeping to a minimum the interference probabilities to the analog routes. In this paper some possible solutions are discussed, taking into account the main parameters influencing the spectrum efficiency and the system performance.