Improved digital signalling on land mobile communication system

Nippon Telegraph & Telephone Public Corporation (NTT) has developed an 800 MHz band high capacity land mobile communications system and put it into service in Tokyo, Osaka and Nagoya. This system, which is similar to AMPS, employs in-band tone signalling in voice channels. It is essential for tone-signalling system to detect tone (control) signals from voice signals correctly. Therefore, it can be said that tone signalling system is not capable enough to add new signals for optional services such as "Hooking signal for call-waiting service", etc. In order to add new signals, NTT has developed the fully digitalized signalling system which has been realized with low cost and high reliability, and evaluated the performance of this system in Nagoya area.