Technique for tracking amplitude fades for multi-amplitude signalling

Abstract

Amplitude variations in a multi-amplitude transmission system are tracked by monitoring amplitude variations over a substantial data time span through the use of a technique in which the percentage of time that a maximum-valued reference amplitude is exceeded is made equal to the percentage of time that a minimum-valued amplitude is not obtained. For this purpose, received data samples are multiplied by an adjustable gain constant to obtain an amplitude product. The amplitude product is then compared with reference values corresponding to the maximum and minimum amplitudes. If the amplitude product exceeds the maximum amplitude reference, the gain constant is decreased, and if the amplitude product is smaller than the minimum amplitude reference, the gain constant is increased. To implement this technique on a percentage basis, a storage device, such as an up/down counter, is loaded with a prescribed number corresponding to the percentage range over which the gain adjustment is measured and the contents of the counter are controllably incremented or decremented depending upon received gain products. Modification of the gain constant can be in accordance with a fixed value or one which is a function of the difference between the amplitude product and the maximum or minimum reference values.