Experiment 5 : Linear Filtering using OAM/OSM


In this experiment, we learnt about linear FIR filtering methods i.e. OAM and OSM. These are two algorithms that are used to process real-time signals. This is used over Fast Fourier Transform (FFT) because in case of FFT, the entire signal needs to be available at the same time in order to receive the output which isn’t feasible in real-time signals. Here’s where OAM and OSM come into play. In the lab, we implemented the required codes on the DSP board and saw how real-time signals are processed.

Overlap-Add Method (OAM)
Here the input sequence is x(n) and an M point sequence h(n) is considered. The long input signal x(n) is further decomposed into L point sequences. With the formula N = L + M -1, where N is assumed to be a radix 2 value, we get the value of L. After decomposing we perform Linear convolution of each decomposed signal and add all of them to get the final output signal.
Overlap Save Method (OSM)
In this method, again we decompose the signal in the same way as in case of OAM, however here we modify the decomposed signals by making them each an N point sequence. In order to make it N point from L point, the (N-L) points from the previous decomposed signal is added to the start of the next. The signal h(n) is also zero padded and made an N point signal. Here we perform Linear Convolution by Circular Convolution and in the end discard the (N-L) points from each decomposed signal and then add the rest to get the final output signal


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