interpolate using rcosdesign in matlab

To interpolate a signal using rcosdesign in MATLAB, you can follow the following steps:

1. Design the raised cosine filter using the rcosdesign function. The raised cosine filter is a low pass filter used for pulse shaping in digital communication systems. The rcosdesign function is used to design a raised cosine filter with a given filter length, cutoff frequency and roll-off factor.

main.m
span = 10; % Number of symbols the filter spans
k = 4; % Roll-off factor
sps = 4; % Number of samples per symbol
beta = 0.25; % Cutoff frequency

h = rcosdesign(beta, span, sps, 'normal', k); % Design the raised cosine filter
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2. Upsample the signal using the upsample function. Upsampling is the process of adding zeros between the original samples of a signal, thereby increasing the sample rate.

main.m
x = [1 0 0 1]; % Original signal
x_upsampled = upsample(x, sps); % Upsample the signal
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3. Apply the designed filter to the upsampled signal using the filter function. The filter function is used to filter a signal with a given filter.

main.m
y = filter(h, 1, x_upsampled); % Filter the upsampled signal with the raised cosine filter
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4. Downsample the filtered signal using the downsample function. Downsampling is the process of removing samples from a signal, thereby decreasing the sample rate.

main.m
y_downsampled = downsample(y, sps); % Downsample the filtered signal
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The filtered and downsampled signal y_downsampled is the interpolated version of the original signal x.