Digital Signal Processing Reference
In-Depth Information
the distances between the adjacent sampling instants need to be sufficiently short.
When sampling is performed in accordance with the HDS model, the signal
sample values, formed by the outputs of two ADCs connected in parallel, could
be placed much closer than half of the sampling interval characterizing the use
of a single ADC.
Thus five different nonuniform sampling approaches, in addition to periodic
sampling, are studied in the following chapters. It is assumed that the advantages
and drawbacks of periodic sampling are well known. All of the nonuniform
sampling approaches, their typical applications, advantages and limitations are
summarized in Table 3.2.
Apparently the classical way of treating signals digitally is not exclusive. There
are also other different ways of doing that, as shown in this topic and in many
other publications. These alternatives are examined in this topic. Although the
nonuniform sampling techniques differ, all of them are based on taking signal
sample values irregularly in time. That is necessary in order to avoid frequency
overlapping and to avoid aliasing. Theoretically, it is often convenient to as-
sume that the random (pseudo-random) intervals between the sampling instants
are distributed according to one or another distribution, including the exponen-
tial distribution. However, there are practical considerations that impose some
restrictions. Specifically, the interval between two successive sampling instants
should never be shorter than allowed by the operational speed of the used ADC.
By definition, the mean sampling rate of a typical alias-free nonuniform sampling
process covering a certain frequency range is lower than the sampling frequency
of the periodic sampling process that would be used for sampling the same sig-
nals. In other words, a typical nonuniform sampling process is sparse with fewer
sample values taken in a given time interval.
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