Group Delay Reduction Methods in FIR Digital Filters

Linear-phase finite impulse response (FIR) filters are widely used in digital signal processing applications because of their various advantages. These advantages include the absence of phase distortion, unrestricted stability, and lower filter-coefficient sensitivity. The most important shortcoming of linear-phase FIR filter is that the overall group delay is (N-1)/2 where N is the length of the filter. This quantity becomes large for higher order filters in communication applications. Many algorithms have been proposed to reduce this delay and its distortion. Typically, block convolution techniques such as overlap-add method (OAM) and overlap-save method (OSM) are used for a long input sequence. Yet, with respect to input, by using these methods, the output sequence has a finite group delay. In this thesis, the performance of enhanced modified overlap and save method is investigated. First, the impulse response is made causal and then it is shifted left (circular) by an amount of for odd and for even. Finally, the samples to be excluded from the final convolution are defined. It is expected that this results in a reduction in the causal delay and also in the group delay. Simulations are carried out by MATLAB. The performance of the method is compared with the results obtained from the OSM based filter. Keywords: Impulse Response, FIR Filter, Linear Phase FIR Filter, Group Delay.