Research And Design Of Efficient FIR Filter In Software Radio System

The technical core of the software radio is analog-digital (A/D) and digital-analog (D/A) wideband conversion as near as possible to the antenna, so that to construct an opening and flexible mobile communications system. Such system, the signal sample frequency is very high, under the condition of high sample rate, can't adopt the method of the normal regulations to carry on the design of the filter of narrow-band FIR. This paper designs the filter of narrowband FIR based on theories of the sampling rate signal processing of the software radio , and as to it's really carried on the MATLAB to emulation mode.The realization of the filter of narrow-band FIR under the condition of high sample rate of the software radio, is mainly application much the theories of the sampling rate signal processing carries on sample to the signal, such as decimator, interpolator, the effect transformation and many stages sampling rate conversion, etc. By decimation to slow down the sampling rate, under the condition of the low sampling rate, design the filter of FIR that meet the function request. Then, the sampling rate can be increased a ideal valaue . In the design, when the conversion factor(the factor of decimator D or the factor of interpolator I) of the sampling rate conversion will lead to fault, in other words, completing once the sampling rate conversion work is not realistic, which put forward the higher request for hardware of speed and saving capability. Therefore, carry out multilevel sampling rate conversions through twice orabove to convert.In the design, the implement of multilevel decimation and interpolation based on cascaded integrator comb (CIC) filters and half band filters (HBF), the main reason lies in cascaded integrator comb filters not to need the multiplication unit, the coefficients of half band filters equal to zero. The advantage of this method is not only to improve the efficiency of computing, and to build a good foundation for the realization of the programmable logic chips.This paper analyses the components of narrow-band FIR filters, based on these analyses, gives the full structure of narrow-band FIR filters and analyses its characteristics. At last, the paper designs an example which analyses its characteristics, such as frequencies response, antialiasing and anti-image. The results indicates that this method can efficiently control the performance of narrow band FIR filters which conclude width of pass-band , attenuation of pass-band, rectangular coefficient and attenuation of stop-band.