The effects of digitization on nonstationary stochastic signals with applications to pulsar signal baseband recording

The process of digitizing a stochastic signal introduces systematic distortions into the resulting digitized data. Further processing of these data may result in the appearance of unwanted artifacts, especially when the input signal was generated by a nonstationary stochastic process. In this paper the magnitude of these distortions are calculated analytically and the results are applied to a specific example found in pulsar signal processing. A pulsar signal is an excellent example of a nonstationary stochastic process. When analyzing pulsar data, the effects of interstellar medium (ISM) dispersion must be removed by digitally filtering the received signal. The distortions introduced through the digitization process cause unwanted artifacts to appear in the final "dedispersed" signal. These artifacts are demonstrated using actual a-bit (4-level) digitized data of the pulsar PSR B0833-45 (Vela). Techniques are introduced that simultaneously minimize these artifacts and maximize the signal-to-noise ratio of the digitized data. The distortion analysis and artifact removal techniques described in this paper hold for an arbitrary number of input digitization thresholds (i.e., number of bits). Also presented are tables of the optimum digitizer thresholds for both uniform and nonuniform input threshold digitizers.