147 lines
4.6 KiB
Matlab
147 lines
4.6 KiB
Matlab
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% Minimal IMDD model for investigating FFE noise enhancement.
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% Parameters mirror the current IMDD_base_system/imdd_it.m,
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% IMDD_base_system/imdd_model.m, and the FFE branch in dsp_scope_signal.m.
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clearvars;
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close all;
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%% Sweep parameters from imdd_it.m
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fsym_values = 172e9;%(152:16:200).*1e9;
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precomp = 0;
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laser_wavelength = 1310;
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M = 4;
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link_length = 2;
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channel_alpha = 0.5;
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duob_mode = db_mode.db_precoded;
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decoding_mode = db_decoder.sequencedetection;
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channel_mode = channel_model.physical;
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channel_snr_dB = 20;
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rop = 0;
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%% Inner model parameters from imdd_model.m
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bitrate = [];
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apply_pulsef = 0;
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fdac = 256e9;
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fadc = 256e9;
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random_key = 1;
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rcalpha = 0.05;
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kover = 16;
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vbias_rel = 0.5;
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u_pi = 3;
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vbias = -vbias_rel*u_pi;
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laser_linewidth = 0;
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eml_alpha = 0;
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len_tr = 4096*2;
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pf_ncoeffs = 1;
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mu_dc = 0.005;
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nRates = numel(fsym_values);
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eq_names = ["FFE","VNLE"];
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nEqs = numel(eq_names);
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emptyResult = struct("fsym",[],"ROP",[],"equalizer",[],"BER",[],"SNR",[],"numBitErr",[], ...
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"eq_noise",[],"eq_signal_sd",[],"eq",[],"Rx_sig",[],"Tx_sig",[],"Tx_symbols",[]);
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results = repmat(emptyResult,nRates,nEqs);
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cols = flip(cbrewer2('RdYlBu',nRates+4));
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midIdx = floor(size(cols,1)/2) + (-1:2);
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cols(midIdx,:) = [];
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for i = 1:numel(fsym_values)
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fsym = fsym_values(i);
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fprintf("Running %.0f GBd (%d/%d)\n", fsym*1e-9, i, numel(fsym_values));
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if isempty(bitrate)
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bitrateCurrent = fsym * log2(M);
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end
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Pform = Pulseformer("fsym",fsym,"fdac",4*fsym,"pulse","rc","pulselength",18,"alpha",rcalpha);
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[Digi_sig, Symbols, Bits] = PAMsource( ...
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"fsym",fsym,"M",M,"order",18,"useprbs",0, ...
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"fs_out",fdac, ...
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"applyclipping",0,"clipfactor",1.5, ...
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"applypulseform",apply_pulsef,"pulseformer",Pform, ...
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"randkey",random_key, ...
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"duobinary_mode",duob_mode, ...
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"mrds_code",0,"mrds_blocklength",512).process();
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rateResults = repmat(emptyResult,nEqs);
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Tx_sig = Digi_sig;
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El_sig = M8199B("kover",kover).process(Digi_sig);
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tx_bwl = 85e9;
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El_sig = Filter("filtdegree",4,"f_cutoff",tx_bwl,"fs",fdac*kover, ...
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"filterType",filtertypes.bessel_inp,"active",true).process(El_sig);
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El_sig = El_sig.normalize("mode","oneone");
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scaling = 0.7*(u_pi/2-abs(vbias-u_pi/2));
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El_sig = El_sig .* scaling;
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Opt_sig = EML("mode",eml_mode.im_cosinus,"power",3,"fsimu",El_sig.fs, ...
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"lambda",laser_wavelength,"bias",vbias,"u_pi",u_pi, ...
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"linewidth",laser_linewidth,"randomkey",random_key+1, ...
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"alpha",eml_alpha).process(El_sig);
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Opt_sig = Fiber("fsimu",Opt_sig.fs,"fiber_length",link_length, ...
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"alpha",0.3,"D",0,"lambda0",1310,"gamma",0,"Dslope",0.07).process(Opt_sig);
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Rx_sig = Amplifier("amp_mode","ideal_no_noise","gain_mode","output_power", ...
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"amplification_db",rop).process(Opt_sig);
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Rx_sig = Photodiode("fsimu",fdac*kover,"dark_current",2e-08, ...
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"responsivity",0.6,"temperature",20,"nep",1.8e-11).process(Rx_sig);
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rx_bwl = 90e9;
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Rx_sig = Filter("filtdegree",4,"f_cutoff",rx_bwl,"fs",fdac*kover, ...
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"filterType",filtertypes.butterworth,"active",true).process(Rx_sig);
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Lp_scpe = Filter("filtdegree",4,"f_cutoff",110e9,"fs",fadc, ...
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"filterType",filtertypes.butterworth,"active",true);
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Rx_sig = Scope("fsimu",fdac*kover,"fadc",fadc, ...
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"delay",0,"fixed_delay",0,"filtertype",filtertypes.butterworth, ...
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"samplingdelay",0,"rand_samplingdelay",0,"freq_offset",0, ...
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"samp_jitter",0,"adcresolution",8,"quantbuffer",0.1, ...
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"block_dc",1,"lpf_active",1,"H_lpf",Lp_scpe).process(Rx_sig);
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txPulseformer = [];
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if apply_pulsef
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txPulseformer = Pform;
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end
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Scpe_sig = preprocessSignal(Rx_sig, Symbols, fsym, ...
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"mode","auto", ...
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"tx_pulseformer",txPulseformer, ...
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"debug_plots",0);
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Scpe_sig.signal = Scpe_sig.signal(1:2*Symbols.length);
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Scpe_sig.signal = real(Scpe_sig.signal);
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%%
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% -------------------- VNLE + MLSE --------------------
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pf_ncoeffs = 1;
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ffe_order3 = [50, 0, 0];
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eq_ = FFE("epochs_tr",5,"epochs_dd",5,"len_tr",len_tr, ...
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"mu_dd",1e-3,"mu_tr",0.4,"order",50, ...
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"sps",2,"decide",0,"optmize_mus",0,"dd_mode",1, ...
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"adaption_technique","nlms","dc_tracking_mu",1e-3);
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pf_ = Postfilter("ncoeff",pf_ncoeffs,"useBurg",1);
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mlse_ = MLSE("duobinary_output",0,'M',M,'trellis_states',PAMmapper(M,0).levels);
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[vnle_results, mlse_results] = vnle_postfilter_mlse(eq_, pf_, mlse_, M, Scpe_sig, Symbols, Bits, ...
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"precode_mode", duob_mode, 'showAnalysis', 1, "postFFE", [], "eth_style_symbol_mapping", 0);
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end
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