Transmitter Power Control in Two-Way Communications System

A typical scatter communications loop consists of two sites, each having transmitters and receivers operating simultaneously over a two-way microwave loop. In tropospheric scatter systems, disturbances in the microwave paths produce dynamic fading of RF signal levels at the receivers. To achieve high system reliability, the current practice is to continuously transmit high power, adequate to maintain RF reception during the presence of severe fading. This wastes power and creates serious radio interference during favorable propagation periods. Feedback control is applied to high reliability systems to vary the transmitted power as a function of the fading and consequently 1) to reduce operating cost by conserving transmitted power, and 2) to reduce interference to other radio networks in the area. Other secondary advantages, including reduction of the dynamic range of received signal strength (which will ease receiver AGC and RF amplifier design), will be apparent to the reader. In order to maintain high system reliability, the automatic control at each site is simultaneous, continuous, and effective for nonreciprocal as well as for reciprocal fading. The system has been referred to as Controlled Carrier Communications.