| 1 | function x = txFilter(modData, rolloff, span, sps) |
| 2 | %% Transmitter pulse-shaping (root raised cosine) filter. |
| 3 | %% Inputs: |
| 4 | %% - modData: modulated data |
| 5 | %% - rolloff: rolloff factor in root raised cosine filter. |
| 6 | %% - span: filter span (number of symbols) |
| 7 | %% - sps: samples per symbol |
| 8 | %% Output: |
| 9 | %% - x: pulse-shaped waveform |
| 10 | |
| 11 | %% Construct filter object |
| 12 | txfilter = comm.RaisedCosineTransmitFilter... |
| 13 | ('Shape', 'Square root', ... |
| 14 | 'RolloffFactor', rolloff, ... |
| 15 | 'FilterSpanInSymbols', span, ... |
| 16 | 'OutputSamplesPerSymbol', sps, ... |
| 17 | 'Gain', sqrt(sps)); % so that output has energy 1 |
| 18 | |
| 19 | %% Extract filter coefficients |
| 20 | coef = coeffs(txfilter); |
| 21 | %% Upsample data and perform filtering in frequency domain |
| 22 | filter_fft = fft(coef.Numerator, length(modData) * sps); |
| 23 | modData_fft = fft(upsample(modData, sps)); |
| 24 | x = ifft(modData_fft .* filter_fft.'); |
| 25 | %% Re-order signal due to circular convolution |
| 26 | l = (length(coef.Numerator) - 1) / 2; |
| 27 | x = [x(l:end); x(1:l-1)]; |
| 28 | end |