Digital Alias-free Signal Processing

7

Threshold-crossing Sampling

In cases where sampling is being randomized, this is usually done purposefully to take signal sample values at specifically defined time instants in order to achieve some specific desirable effects. When that happens, the sampling process is randomized and is also nonuniform. In fact, randomization of sampling and nonuniform sampling are almost synonymous. However, deliberate randomization of sampling makes sense only if such a complication of this operation is justified by the end results. Apparently there has to be a good reason for randomizing the sampling operation as the equidistant sample value taking procedure has many outstanding positive qualities and is preferable whenever application of it is appropriate. The motivation considered so far for randomizing of sampling has been the widening of the frequency range for fully digital signal processing. That surely is a good enough argument in favour of deliberate direct randomizing of sampling as it leads to the irregularities of the sample taking process vital for elimination of aliasing. However, avoidance of aliasing is not the only possible reason why sometimes it makes sense to use this approach. There might also be some other motivational factors, like complexity reduction of systems for data acquisition, transmission and processing. Specific types of sampling randomizing, indirect randomizing and targeting goals other than suppression of aliases are discussed in this chapter.

The operational ...