4 Rsym = 2.5e10; % symbol rate (sym/sec)
5 Tsym = 1 / Rsym; % symbol period (sec)
8 span = 6; % filter span
9 sps = 8; % samples per symbol
11 fs = Rsym * sps; % sampling freq (Hz)
14 t = (0 : 1 / fs : numSymbs / Rsym + (1.5 * span * sps - 1) / fs).';
18 power = 10 .^ (power_dBm / 10) * 1e-3; % watts
20 Es = power * Tsym; % joules
21 Eb = Es / log2(M); % joules
23 N0ref_db = 10; % Eb/N0 at power = 1mW
24 %% Fix N0, such that Eb/N0 = N0ref_db at power = 1mW
25 N0 = 1e-3 * Tsym / (log2(M) * 10 ^ (N0ref_db / 10)); % joules
26 %% At current settings, N0 = 0.002 pJ
28 plotlen = length(power);
30 ber = zeros(1, plotlen);
32 data = randi([0 M - 1], numSymbs, 1);
33 %%modData = dpskmod(data, M, 0, 'gray');
34 modData = pskmod(data, M, 0, 'gray');
36 modData(i) = modData(i) * modData(i-1);
40 %% Chromatic dispersion
41 D = 17; % ps / (nm km)
47 linewidthLO = 1e6; % Hz
52 x_P1 = txFilter(modData, rolloff, span, sps);
59 snr = Es(i) / sps / N0;
60 snr_dB = 10 * log10(snr);
62 %%x = txFilter(modData, rolloff, span, sps);
63 %% Now, sum(abs(x) .^ 2) / length(x) should be 1.
64 %% We can set its power simply by multiplying.
65 x = sqrt(power(i)) * x_P1;
67 %% We can now do split-step Fourier.
68 gamma = 1.2; % watt^-1 / km
71 xCDKerr = splitstepfourier(x, D, lambda, z, Tsamp, gamma);
73 xpn = phaseNoise(xCDKerr, linewidthTx, linewidthLO, Tsamp);
75 y = awgn(xpn, snr_dB, 'measured', 'db');
78 r = rxFilter(y, rolloff, span, sps);
82 rCDComp = CDCompensation(r, D, lambda, z, Tsamp);
83 rCDComp = normalizeEnergy(rCDComp, numSymbs * sps, 1);
85 rSampled = rCDComp(2:2:end);
88 [adaptFilterOut, convergeIdx] = adaptiveCMA(rSampled);
90 pncorr = phaseNoiseCorr(adaptFilterOut, M, 0, 40).';
92 demodAdapt = pskdemod(pncorr, M, 0, 'gray');
93 remod = pskmod(demodAdapt, M, 0, 'gray');
94 delayed = [1; remod(1:end-1)];
95 demod = pskdemod(remod .* conj(delayed), M, 0, 'gray');
98 [~, ber(i)] = biterr(data(convergeIdx:end), demod(convergeIdx:end));
100 [~, ber(i)] = biterr...
101 (data(ceil(0.8*numSymbs):end), ...
102 demod(ceil(0.8*numSymbs):end));
112 %% Plot simulated results
113 qp = 20 * log10(erfcinv(2*ber)*sqrt(2));
114 plot(power_dBm, qp, 'Color', [0, 0.6, 0], 'LineWidth', 2);
117 title({'CD + Kerr + CD compensation', ...
118 strcat(['$D = 17$ ps/(nm km), $z = ', num2str(z), '$ km'])});
120 xlabel('Optical power (dBm)');
121 ylabel('$20 \log_{10}\left(\sqrt{2}\mathrm{erfc}^{-1}(2 BER)\right)$');