Abstract :
There has been increasingly widespread use of radio to replace wire and cable in telephone communications systems. Most of it, however, has been applied to telephone trunks between switchboards or for private line application. Use of it on a large scale for subscriber lines into a switchboard has never been considered economically acceptable due to the extravagance of the frequency spectrum requirements, cost of equipment, and numerous undesirable technical problems. The radio central system described in this paper promises to provide radio subscriber lines with sufficient bandwidth economy to make them worthwhile for mobile subscribers. The requirements of such a mobile communications system are discussed with particular attention being given to their effects on the choice of a modulation technique. It is shown that single-sideband techniques are well suited for application to coordinated mobile communication systems, and overcome many of the technical difficulties associated with other methods of modulation. Problems of interference, automatic frequency control, and systems stability are discussed. Methods of reducing the effects of the intermodulation distortion and resulting cross-channel interference that occur in the input stages of a broad-band radio receiver are given. One solution is suggested to selective calling on a single-sideband coordinated communications system having relatively poor frequency stability.
