Working Kerr effect; PDM; speedups; removed unused files

[4yp.git] / CDCompensation.m

function [yCDComp, kstart] = CDCompensation(y, D, lambda, z, Tsamp)
  %% Chromatic dispersion compensation.
  %% Params:
  %%  - y: received waveform with CD
  %%  - D: dispersion coefficient (ps / (nm km))
  %%  - lambda: wavelength (nm)
  %%  - z: length of fibre (km)
  %%  - Tsamp: sampling time (s)
  %% Output:
  %%  - yCDComp: y after performing CD compensation

  %% Convert everything to SI base units
  c = 299792458; % m/s
  D = D * 1e-6; % s/m^2
  lambda = lambda * 1e-9; % m
  z = z * 1e3; % m

  %% Implementing Eq. (9) in [1].
  N = 2 * floor(abs(D) * lambda^2 * z / (2 * c * Tsamp^2)) + 1;
  k = -floor(N / 2) : floor(N / 2);
  kstart = -floor(N/2);

  % h: FIR filter
  h = exp(-j * pi * c * Tsamp^2 * k .^ 2 / (D * lambda^2 * z));

  len_fft = max(length(y), length(h));
  H = fft(h, len_fft);
  Y = fft(y, len_fft);

  yCDComp = ifft(H.' .* Y);
  l = (length(h) - 1) / 2;
  if l > 0
    yCDComp = [yCDComp(l:end); yCDComp(1:l-1)];
  else
    yCDComp = [yCDComp(end); yCDComp(1:end-1)];
  end

end
%% References
%% [1]: S.J. Savory, Digital filters for coherent optical receivers, 2008.