| 1 | function x = CDCompensation(xCD, D, lambda, z, Tsamp) |
| 2 | %% Chromatic dispersion compensation. |
| 3 | %% Params: |
| 4 | %% - xCD: received waveform with CD |
| 5 | %% - D: dispersion coefficient (ps / (nm km)) |
| 6 | %% - lambda: wavelength (nm) |
| 7 | %% - z: length of fibre (km) |
| 8 | %% - Tsamp: sampling time (s) |
| 9 | %% Output: |
| 10 | %% - x: xCD after performing CD compensation |
| 11 | |
| 12 | %% Convert everything to SI base units |
| 13 | c = 299792458; % m/s |
| 14 | D = D * 1e-6; % s/m^2 |
| 15 | lambda = lambda * 1e-9; % m |
| 16 | z = z * 1e3; % m |
| 17 | |
| 18 | %% Discrete FIR filter: |
| 19 | %% N: filter length; k: filter index; h: filter coefficients. |
| 20 | N = 2 * floor(abs(D) * lambda^2 * z / (2 * c * Tsamp^2)) + 1; |
| 21 | k = -floor(N / 2) : floor(N / 2); |
| 22 | h = exp(-1j * pi * c * Tsamp^2 * k .^ 2 / (D * lambda^2 * z)); |
| 23 | |
| 24 | %% Perform filtering in frequency domain |
| 25 | len_fft = max(length(xCD), length(h)); |
| 26 | H = fft(h, len_fft); |
| 27 | XCD = fft(xCD, len_fft); |
| 28 | x = ifft(H.' .* XCD); |
| 29 | |
| 30 | %% Re-order due to circular convolution |
| 31 | l = (N - 1) / 2; |
| 32 | if l > 0 |
| 33 | x = [x(l:end); x(1:l-1)]; |
| 34 | else |
| 35 | x = [x(end); x(1:end-1)]; |
| 36 | end |
| 37 | end |