Detection and Selective Smoothing of Transmission Errors in Linear PCM

Detection and Selective Smoothing of Transmission Errors in Linear PCM By R. STEELE and D. J. GOODMAN (Manuscript received May 5, 1976) We consider detection of transmission errors in PCM by means of statistical hypothesis testing of the received quantized sequence. When errors are detected, a median filter is used to smooth waveform discontinuities. We describe two error detectors, one (CDC), based on correlation measurements, and the other (DDC), based on sample-tosample difference measurements. While both offer s/n advantages over conventional PCM in the presence of errors, DDC is more promising both in terms of performance and simplicity of implementation. I. INTRODUCTION An acceptable decoded signal-to-noise ratio (s/n) can be maintained in a pulse code modulation (PCM) system in the presence of transmission errors if error detecting and correcting codes are added to the transmitted PCM signal. T h i s approach 1 , 2 when combined with a H u f f m a n coder in juxtaposition to the PCM and channel encoders offers the best theoretical solution, given that the properties of the transmission channel can be specified. By best solution we mean that for a specified channel bandwidth and error rate, the highest decoded s/n can be achieved. However, this approach is not usually justified economically, and partial solutions may be appropriate. One solution is to retain a conventional transmitter and to modify the receiver of a PCM system to make provision for the possibility of transmission errors.