Maximum likelihood decoding of AMI-coded digital transmission and additive Gaussian disturbance

By the example of the AMI-coded digital signal, the statistical dependence of successive code symbols of redundant digital transmission are used to reduce the error rate occurring in decoding the signal subject to interference. For this purpose, the concepts of the state, the state diagram, the code trellis and the maximum likelihood function are introduced. With respect to the decoding rule resulting from the statistical dependence, it becomes evident that certain code elements are not decoded immediately, but only after the reception of further code elements. It is for this reason that this decoding procedure is called sequential decoding. Since the decoder must be able to store various data for the duration of several code symbols, it may be called decoder with memory. A block diagram of this decoding procedure is included. With the aid of a computer simulation, the error rate is determined as a function of the signal to noise power ratio.