function  [ber] = imdd_simulation_minimal(varargin)
% BASIC IMDD Model...

% varargin is either empty or a struct, i.e.:
%    optionalvars = struct('bitrate',300e9,'M',6);
% then:
%    imdd_simulation_minimal(optionalvars)
% replaces the respective variables -> nice for looping parameter sets
    
    curFolder = pwd;
    funcFolder=fileparts(mfilename('fullpath'));
    if ~isempty(funcFolder)
        cd(funcFolder);
    end
    
    % TX
    M               = 4;
    fsym            = 112e9;
    apply_pulsef    = 1;
    fdac            = 256e9;
    fadc            = 256e9;
    random_key      = 1;
    db_precode      = 0;
    db_encode       = 0;
    rcalpha         = 0.05;
    kover           = 16;
    vbias_rel       = 0.5;
    u_pi            = 2.9;
    vbias           = -vbias_rel*u_pi;

    laser_wavelength    = 1310;
    laser_linewidth     = 0;
    tx_bw_nyquist       = 0.95;
    
    % Channel
    link_length     = 1; %km
    
    % RX
    rop = -7;
    rx_bw_nyquist = 0.9;
    
    % EQ
    vnle_order=[50,7,7];
    dfe_order = [2 0 0];
    
    len_tr = 4096*2;
    mu_ffe = [0.0004 0.0004 0.0004];
    mu_dfe = 0.0004;
    mu_dc = 0.00;
    
    % Replace optional input arguments if there are any
    if ~isempty(varargin)
        var_s = varargin{1};
        if isstruct(var_s)
            fields = fieldnames(var_s);
            for i = 1:numel(fields)
                eval([fields{i}, ' = ',  num2str( var_s.(fields{i}) ), ';']);
                fprintf("%s <-- %.2f \n", fields{i}, var_s.(fields{i}));
            end
        else
            error('Optional variables should be passed as a struct.');
        end
    end

    fsym_ = floor( bitrate*1e-9./log2(M) ).*1e9;
    if fsym_ ~= fsym
        fsym = fsym_;
        fprintf('Adapted symbolrate to %d GBd, to match provided bitrate of %d GBit/s using PAM %d \n',fsym.*1e-9,bitrate.*1e-9, M);
    end
    f_nyquist       = fsym/2;
    
    %%%% TX Signal
    Pform       = Pulseformer("fsym",fsym,"fdac",4*fsym,"pulse","rrc","pulselength",16,"rrcalpha",rcalpha);
    
    [Digi_sig,Tx_symbols,Tx_bits] = PAMsource(...
        "fsym",fsym,"M",M,"order",18,"useprbs",1,...
        "fs_out",fdac,...
        "applyclipping",0,"clipfactor",1.5,...
        "applypulseform",apply_pulsef,"pulseformer",Pform,...
        "randkey",random_key,...
        "db_precode",db_precode,"db_encode",db_encode,...
        "mrds_code",0,"mrds_blocklength",512).process();
    
    Digi_sig.spectrum("displayname",'Digital Spectrum at TX','fignum',10,'normalizeTo0dB',1);
    
    %%%%% AWG
    % El_sig = M8199A("kover",kover).process(Digi_sig);
    El_sig = AWG("fdac",fdac,"f_cutoff",fsym,"lpf_active",1,"kover",kover,"bit_resolution",12).process(Digi_sig);
    % El_sig.spectrum("displayname",'Digi Spectrum','fignum',100,'normalizeTo0dB',0);
    El_sig = El_sig.setPower(0,"dBm");

    El_sig.eye(fsym,M,"fignum",11,'displayname','Rx Eye');
    
    %%%%% Low-pass el. components %%%%%%
    El_sig = Filter('filtdegree',4,"f_cutoff",75e9,"fs",fdac*kover,"filterType",filtertypes.butterworth,"active",true).process(El_sig);
    
    %%%%% Electrical Driver Amplifier %%%%%%
    El_sig = Amplifier("amp_mode","ideal_no_noise","gain_mode","gain","amplification_db",3).process(El_sig);
    
    %%%%% MODULATE E/O CONVERSION %%%%%%
    [Opt_sig] = EML("mode",eml_mode.im_cosinus,"power",3,"fsimu",El_sig.fs,"lambda",laser_wavelength,"bias",vbias,"u_pi",u_pi,"linewidth",laser_linewidth,"randomkey",random_key+1).process(El_sig);
    
    %%%%%% Fiber %%%%%%
    Opt_sig    = Fiber("fsimu",Opt_sig.fs,"fiber_length",link_length/1000,"alpha",0.3,"D",0,"lambda0",1310,"gamma",0,"Dslope",0.07).process(Opt_sig);
    
    %%%%%% ROP %%%%%%
    Rx_sig = Amplifier("amp_mode","ideal_no_noise","gain_mode","output_power","amplification_db",rop).process(Opt_sig);
    
    %%%%%% PD Square Law %%%%%%
    Rx_sig = Photodiode("fsimu",fdac*kover,"dark_current",2e-08,"responsivity",1,"temperature",20,"nep",1.8e-11).process(Rx_sig);

    Rx_sig.eye(fsym,M,"fignum",30,'displayname','Rx Eye');
    
    %%%%%% Low-pass RX (PD, El. Connectors and Scope %%%%%%
    Rx_sig = Filter('filtdegree',4,"f_cutoff",75e9,"fs",fdac*kover,"filterType",filtertypes.butterworth,"active",true).process(Rx_sig);
    
    %%%%%% Low-pass inside Scope %%%%%%
    Lp_scpe = Filter('filtdegree',4,"f_cutoff",110e9,"fs",fadc,"filterType",filtertypes.butterworth,"active",true);
    
    %%%%%% Scope %%%%%%
    Scpe_sig = Scope("fsimu",fdac*kover,"fadc",fadc,...
        "delay",0,"fixed_delay",0,"filtertype",filtertypes.butterworth,...
        "samplingdelay",0,"rand_samplingdelay",0,"freq_offset",0,"samp_jitter",0,...
        "adcresolution",8,"quantbuffer",0.1,'block_dc',1,'lpf_active',1,'H_lpf',Lp_scpe).process(Rx_sig);
    
    Scpe_sig.spectrum("displayname",'Digital (256 GSa/s) Rx Spectrum','fignum',10,'normalizeTo0dB',1);

    Scpe_sig.normalize("mode","rms").plot("displayname",'Digital (256 GSa/s) Rx Spectrum','fignum',21,'clear',1);
    
    %%%%%% Sample to 2x fsym %%%%%%
    Scpe_sig =  Scpe_sig.resample("fs_in",fadc,"fs_out",2*fsym);
    
    %%%%%% Sync Rx signal with reference %%%%%%
    [Scpe_sig,S] = Scpe_sig.tsynch("reference",Tx_symbols,"fs_ref",fsym);
    
    
    %%% EQUALIZING
    
    %FFE or VNLE
    [Eq_signal,Eq_noise] = EQ("Ne",vnle_order,"Nb",dfe_order,"training_length",len_tr,"training_loops",5,"dd_loops",5,"K",2,"DCmu",mu_dc,"DDmu",[mu_ffe mu_dfe],"DFEmu",0.005,"FFEmu",0,"plotfinal",0,"ideal_dfe",1).process(Scpe_sig,Tx_symbols);
    
    Rx_bits = PAMmapper(M,0).demap(Eq_signal);

    [~,numErrors,ber,~] = calc_ber(Rx_bits.signal,Tx_bits.signal,"skip_front",100,"skip_end",150,"returnErrorLocation",1);

    Eq_signal.normalize("mode","rms").plot("displayname",'Digital (256 GSa/s) Rx Spectrum','fignum',21,'clear',0);

    %%% Visualize EQ Stuff

    figure(40);
    clf
    title(sprintf('PAM %d after EQ ; BER: %1.2e',M, ber ));
    constellation = unique(Tx_symbols.signal);
    received = NaN(numel(constellation),length(Tx_symbols));
    for lvl = 1:numel(constellation)
        %Separate the equalized signal into the
        %respective levels based on the actually
        %transmitted level!
        received(lvl,Tx_symbols.signal==constellation(lvl)) = Eq_signal.signal(Tx_symbols.signal==constellation(lvl));
        intermediate = received(lvl,:);
        cnt(lvl) = numel(intermediate(~isnan(intermediate)));
        hold on
        histogram(received(lvl,:),1000,"EdgeAlpha",0,'DisplayName',['Lvl ',num2str(lvl),' | ',num2str(cnt(lvl)),' entries']);
    end
    legend
    
    fprintf('BER: %.2e \n',ber);

    autoArrangeFigures;
    
    if ~isempty(curFolder)
        cd(curFolder);
    end

end