SOME UNCONVENTIONAL SIGNAL PROCESSING APPLICATIONS OF MULTIRATE TECHNIQUES

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INTRODUCTION
Multirate digital signal processing systems are characterized
by unequal sampling rates at various stages in the system. In
recent years, there has been a growing interest in the design
and applications of such systems. In most cases, the multirate
concepts have been used in some conventional applications
such as subband coding of signals, transfer of data to
and from systems with differing sampling rates, interconnection
of frequency-division multiplex and time-division
multiplex telecommunication systems, etc. In this paper, we
outline some unconventional applications of multirate concepts
recently developed by us and others, and point out their
usefulness in developing efficient signal processing systems.


EFFICIENT DECIMATOR AND INTERPOLATOR STRUCTURES

The structural subband decomposition-based structure can be
computationally more efficient than the conventional polyphase
decomposition-based structure in realizing decimators
and interpolators that employ linear-phase Nyquist-type lowpass
filters. To this end, it is necessary to use transform matrices
that transfer the filter-coefficient symmetry to the subfilters.
Figure 3 shows the implementation of a factor-of-4
down-sampler utilizing a length 12 linear phase FIR Nyquist
lowpass filter and realized using a 4-branch Hadamard transform
based subband decomposition. The realization shown
requires only 6 multipliers in contrast to the 12 multipliers
needed in the conventional polyphase decomposition-based
structure. Similar savings are also obtained in the implementation
of an interpolator.