An efficient frequency sampling design of FIR raised-cosine filters for software radio applications

An important requirement in the design of data transmission filters is the minimization of intersymbol interference (ISI), which is zero if the overall impulse response (transmitter filter, channel and receiver filter) satisfies the Nyquist criterion, i.e. it has uniformly spaced zero-crossings. An important class of transfer functions, satisfying the Nyquist criterion, is the so-called raised-cosine filter family. In this paper, a design method is given to find the coefficients of couples of linear-phase transmitter/receiver FIR filters, that cascaded have raised-cosine amplitude. The design is based on Frequency Sampling techniques, and the filter parameters are chosen in order to obtain maximum stopband attenuation. The filter coefficients can be easily evaluated and the optimal filter parameters can be obtained with tables. The design method is very simple and suited for non-filter-oriented users. The main advantages of this design approach concerns its simplicity, flexibility, and efficiency by which the receiver and transmitter filters can be generated. Furthermore, the design method may be efficiently developed in the software radio systems, based on architectures using general-purpose processors, such as DSP or FPGA platforms.