CIC filter for sample rate conversion in software defined radio

Software Defined Radio (SDR) or Software Radio is one of the most important technologies for the modern wireless communication system. The vision of SDR is implementing a single radio that can emulate any radio signal of evolving or already existing wireless standards. It can be done simply by updating software without replacing the underlying hardware platform. Again, different air interface requires different sample rate for baseband processing. So, Sample Rate Conversion (SRC) is an important functionality of SDR. SRC includes both sample rate reduction or decimation and sample rate increase or interpolation. But in both the cases Comb Integrator Comb (CIC) filter plays an important role as anti-aliasing filter (in case of decimation) or anti-imaging filter (in case of interpolation). This paper describes the basic structure of CIC filter and illustrates important parameters to characterize this filter. Consequently it focuses on implementation of CIC filter in decimator and interpolator. This paper also tries to find a technique to improve the characteristics of this filter and point out some problems associated with it.