An innovative approach to the automatic monitoring of signal quality on digital transmission channels such as communication links is presented. A communication channel is said to be experiencing some form of stress when the channel (and hence the signal) is distorted from nominal conditions. The stress may be the result of a variety of sources such as transmitter and receiver equipment errors, ionospheric effects, tropospheric effects, and jamming. A new monitor, the DEGRAD (Digital Eye Gridded Receiver with Arbitrary Degradation) monitor, is developed that is better able to detect and identify channel degradations before a significant change in signal quality is noticed by the end user. >

A method of utilizing the available communication bandwidth efficiently is provided by multi-hphase coding. A receiver structure for joint estimation of data, carrier phase, and symbol timing is derived based on ML estimation techniques and subsequently assessed analytically and by means of Monte Carlo simulation procedures. Results indicate that the receiver structure, although not strictly optimum, yields near-optimum performance on the additive white Gaussian noise channel.

Multi-hschemes are bandwidth-efficient CPM signaling formats which offer means of coding without explicit redundancy. However, the required (optimal) receiver structures tend to be very complex [1], [4], [8] requiring a large number of filters of correlators. Here a reduced complexity receiver for the joint estimation ofM-ary data, carrier phase, and symbol timing is realized through the use of an approximate representation of the likelihood function. Evaluation of receiver performance indicates a fraction of a decibel degradation in coding gain and almost no loss in synchronization performance.