Working Kerr effect; PDM; speedups; removed unused files

[4yp.git] / kerr.m

diff --git a/kerr.m b/kerr.m
index c67bbb2..7e534dd 100644 (file)
--- a/kerr.m
+++ b/kerr.m
@@ -1,4 +1,4 @@
-numSymbs = 5e4;
+numSymbs = 2^16;
 M = 4;
 
 Rsym = 2.5e10; % symbol rate (sym/sec)
@@ -6,40 +6,46 @@ Tsym = 1 / Rsym; % symbol period (sec)
 
 rolloff = 0.25;
 span = 6; % filter span
-sps = 2; % samples per symbol
+sps = 8; % samples per symbol
 
 fs = Rsym * sps; % sampling freq (Hz)
 Tsamp = 1 / fs;
 
 t = (0 : 1 / fs : numSymbs / Rsym + (1.5 * span * sps - 1) / fs).';
 
-
-power_dBm = -3:0.25:4;
+power_dBm = -6:1:4;
+%%power_dBm = 0;
 power = 10 .^ (power_dBm / 10) * 1e-3; % watts
 
 Es = power * Tsym; % joules
 Eb = Es / log2(M); % joules
 
-N0ref_dB = 10; % Eb/N0 at power = 1mW
-%% Fix N0, such that Eb/N0 = N0ref_dB at power = 1mW
-N0 = 1e-3 * Tsym / (log2(M) * 10 ^ (N0ref_dB / 10)); % joules
-
+N0ref_db = 10; % Eb/N0 at power = 1mW
+%% Fix N0, such that Eb/N0 = N0ref_db at power = 1mW
+N0 = 1e-3 * Tsym / (log2(M) * 10 ^ (N0ref_db / 10)); % joules
+%% At current settings, N0 = 0.002 pJ
 
 plotlen = length(power);
 
 ber = zeros(1, plotlen);
 
 data = randi([0 M - 1], numSymbs, 1);
-modData = pskmod(data, M, pi / M, 'gray');
+modData = dpskmod(data, M, 0, 'gray');
+%%modData = pskmod(data, M, pi/4, 'gray');
 
 
 %% Chromatic dispersion
 D = 17; % ps / (nm km)
 lambda = 1550; % nm
-z = 600; % km
+z = 100; % km
 
 
+TsampOrig = Tsamp;
+
 for i = 1:plotlen
+  sps = 8;
+  Tsamp = TsampOrig;
+
   snr = Es(i) / sps / N0;
   snr_dB = 10 * log10(snr);
 
@@ -50,58 +56,52 @@ for i = 1:plotlen
 
   %% We can now do split-step Fourier.
   gamma = 1.2; % watt^-1 / km
-  %%stepnum = round(40 * z * gamma); % Nonlinear Fiber optics, App B
-  stepnum = 100;
-  xCD = splitstepfourier(x, D, lambda, z, Tsamp, gamma, stepnum);
 
-  y = awgn(xCD, snr, power(i), 'linear');
-  %%y = xCD;
+
+  xCDKerr = splitstepfourier(x, D, lambda, z, Tsamp, gamma);
+
+  y = awgn(xCDKerr, snr_dB, 'measured', 'db');
+  %y = xCDKerr;
 
   r = rxFilter(y, rolloff, span, sps);
+  sps = 2;
+  Tsamp = Tsamp * 4;
+
   rCDComp = CDCompensation(r, D, lambda, z, Tsamp);
-  rCDComp = normalizeEnergy(rCDComp, numSymbs*sps, 1);
+  rCDComp = normalizeEnergy(rCDComp, numSymbs * sps, 1);
 
-  rSampled = rCDComp(sps*span/2+1:sps:(numSymbs+span/2)*sps);
-  rNoCompSampled = r(sps*span/2+1:sps:(numSymbs+span/2)*sps);
+  rSampled = rCDComp(2:2:end);
 
-  %% rotate rNoCompSampled to match original data
-  theta = angle(-sum(rNoCompSampled .^ M)) / M;
-  %% if theta approx +pi/M, wrap to -pi/M
-  if abs(theta - pi / M) / (pi / M) < 0.1
-    theta = -pi / M;
-  end
-  rNoCompSampled = rNoCompSampled .* exp(-j * theta);
+  %% adaptive filter
+  [adaptFilterOut, convergeIdx] = adaptiveCMA(rSampled);
 
+  demod = dpskdemod(adaptFilterOut, M, 0, 'gray');
+  %%demod = pskdemod(adaptFilterOut, M, pi/4, 'gray');
 
-  %% Not entirely sure why, but after using FFT instead of time-domain
-  %% convolution for simulating CD, we now need to do the same rotation
-  %% for rSampled as well, but this time with a positive rotation.
-  theta = angle(-sum(rSampled .^ M)) / M;
-  if abs(theta + pi / M) / (pi / M) < 0.1
-    theta = +pi / M;
+  if convergeIdx < Inf
+    [~, ber(i)] = biterr(data(convergeIdx:end), demod(convergeIdx:end));
+  else
+    [~, ber(i)] = biterr...
+                    (data(ceil(0.8*numSymbs):end), ...
+                     demod(ceil(0.8*numSymbs):end));
   end
-  rSampled = rSampled .* exp(-1j * theta);
-
+end
 
-  %% adaptive filter
-  adaptFilterOut = adaptiveCMA(rSampled);
+ber
 
-  demodAdapt = pskdemod(adaptFilterOut, M, pi / M, 'gray');
-  [~, ber(i)] = biterr(data, demodAdapt);
-end
 
-figure(1);
+figure;
 clf;
 
 %% Plot simulated results
-semilogy(power_dBm, ber, 'Color', [0, 0.6, 0], 'LineWidth', 2);
+qp = 20 * log10(erfcinv(2*ber)*sqrt(2));
+plot(power_dBm, qp, 'Color', [0, 0.6, 0], 'LineWidth', 2);
 hold on;
 
 title({'CD + Kerr + CD compensation', ...
-       strcat(['$D = 17$ ps/(nm km), $z = ', num2str(z), '$ km']), ...
-       strcat(['$E_b/N_0 = ', num2str(N0ref_dB), '$ dB at 1 mW'])});
+       strcat(['$D = 17$ ps/(nm km), $z = ', num2str(z), '$ km'])});
 grid on;
 xlabel('Optical power (dBm)');
-ylabel('BER');
+ylabel('$20 \log_{10}\left(\sqrt{2}\mathrm{erfc}^{-1}(2 BER)\right)$');
 
 formatFigure;