In the field of communications, an ever-increasing number of system functions is realized in digital form. In this context, the problem of economical analog/digital conversion becomes an important issue. The cost of analog/digital conversion, however, is often dominated by the associated filters required for the prevention of foldover distortion. For this reason, an approach characterized by analog filtering (with relaxed requirements) before A/D conversion, and additional, digital, time-shared filtering after A/D conversion, becomes an attractive solution. In this paper, the signal-to-noise ratio of such a system is analyzed. The analysis includes quantization noise and overload distortion from the analog/digital conversion process, additional noise due to codec imperfections and round-off noise from the digital filters and interpolators. A design example, that was also implemented in hardware, demonstrates that the specifications of the CCITT can be easily met.

This paper presents a numerical technique for the solution of a class of queueing problems having fixed priority assignment, synchronous service, constant service time, and finite number of sources. The analysis yields waiting-time distributions, namely, the probabilities of waiting exactlynWservice cycles or longer. It applies to scanners, multiplexer channels, loop configurations, etc. It is especially useful for worst case design in that it permits the calculation of overflow probabilities. Results are given in the form of curves and are compared with those for exponential service times. A priority scheme is outlined that allows partial elimination of the geometrical priorities inherent to loop multiplexers.