+++ Changes +++

+ duobinary_target now supports memoryless decoding (FFE targets DB response without MLSE)
+ PAMmapper.quantize now supports custom constellations for quantization
+ Added a new folder 'Documentations' for pdfs, slides, etc.
+ Added new FSO evaluation scripts in projects/FSO transmission/Evaluation Scripts
+ Added ffe_db (rudimentary module, not important anymore)

Classes/03_electrical/Electrical_Hybrid.m

@@ -0,0 +1,130 @@
+classdef Electrical_Hybrid < handle
+
+    properties(Access=public)
+        file_path
+        plot = 0
+
+        % If true: perform digital residual-echo cancellation using known TX
+        cancel_echo = 1
+
+        % If true: in addition return v_hyb and v_echo_est
+        return_intermediates = 1
+    end
+
+    methods(Access=public)
+
+        function obj = Electrical_Hybrid(options)
+            arguments
+                options.file_path = ''
+                options.plot = 0
+                options.cancel_echo = 1
+                options.return_intermediates = 1
+            end
+
+            fn = fieldnames(options);
+            for n = 1:numel(fn)
+                obj.(fn{n}) = options.(fn{n});
+            end
+        end
+
+        function [v_fe_rec, v_hyb, v_echo_est] = process(obj, v_ne_tx, v_fe_tx)
+            % v_ne_tx : Near-End TX signal object (Port 1)
+            % v_fe_tx : Far-End TX signal object  (Port 2)
+            %
+            % Output:
+            % v_hyb      : physical hybrid differential output (Port4 - Port3)
+            % v_echo_est : estimated residual echo due to local TX only
+            % v_fe_rec   : v_hyb - v_echo_est  (if cancel_echo enabled), else v_hyb
+
+            % --- Load S-Parameters (.s4p) ---
+            net = sparameters(obj.file_path);
+            f_s = net.Frequencies(:);
+            S4  = net.Parameters;
+
+            % Extract needed S-parameters for differential output:
+            % V3 = S31*V1 + S32*V2
+            % V4 = S41*V1 + S42*V2
+            % Vhyb = V4 - V3 = (S41-S31)*V1 + (S42-S32)*V2
+            S31_s = squeeze(S4(3,1,:));
+            S41_s = squeeze(S4(4,1,:));
+            S32_s = squeeze(S4(3,2,:));
+            S42_s = squeeze(S4(4,2,:));
+
+            % --- Time-domain signals ---
+            x1 = v_ne_tx.signal(:);
+            x2 = v_fe_tx.signal(:);
+
+            if length(x2) ~= length(x1)
+                error('Near-end and far-end signals must have the same length.');
+            end
+
+            N  = length(x1);
+            Fs = v_ne_tx.fs;
+
+            % --- Use zero padding to avoid circular convolution artifacts ---
+            Nfft = 2^nextpow2(2*N);  % robust choice
+
+            % --- FFT ---
+            V1 = fft(x1, Nfft);
+            V2 = fft(x2, Nfft);
+
+            % --- Frequency axis for interpolation (signed then abs) ---
+            f_fft = (0:Nfft-1).' * (Fs/Nfft);
+            f_signed = f_fft;
+            idxNeg = f_signed > Fs/2;
+            f_signed(idxNeg) = f_signed(idxNeg) - Fs;      % (-Fs/2, Fs/2]
+            f_pos = abs(f_signed);
+
+            % --- Interpolate S-parameters onto f_pos ---
+            S31 = interp1(f_s, S31_s, f_pos, 'linear', 'extrap');
+            S41 = interp1(f_s, S41_s, f_pos, 'linear', 'extrap');
+            S32 = interp1(f_s, S32_s, f_pos, 'linear', 'extrap');
+            S42 = interp1(f_s, S42_s, f_pos, 'linear', 'extrap');
+
+            % Hermitian symmetry for real time-domain response:
+            % For negative frequencies enforce conj symmetry.
+            S31(idxNeg) = conj(S31(idxNeg));
+            S41(idxNeg) = conj(S41(idxNeg));
+            S32(idxNeg) = conj(S32(idxNeg));
+            S42(idxNeg) = conj(S42(idxNeg));
+
+            % --- Physical hybrid differential output ---
+            % Vhyb = (S41-S31)*V1 + (S42-S32)*V2
+            He = (S41 - S31);              % residual echo transfer from local TX
+            Hr = (S42 - S32);              % transfer from far-end TX to output
+
+            V_hyb = He .* V1 + Hr .* V2;
+
+            % --- Residual echo estimate (digital canceller model) ---
+            V_echo = He .* V1;
+
+            % --- Back to time-domain (take first N samples after padding) ---
+            v_hyb_full = ifft(V_hyb, 'symmetric');
+            v_echo_full = ifft(V_echo, 'symmetric');
+
+            v_hyb = v_hyb_full(1:N);
+            v_echo_est = v_echo_full(1:N);
+
+            % --- Optional cancellation ---
+            if obj.cancel_echo
+                v_fe_rec = v_hyb - v_echo_est;
+            else
+                v_fe_rec = v_hyb;
+            end
+
+            if ~obj.return_intermediates
+                v_hyb = [];
+                v_echo_est = [];
+            end
+
+            % --- Bring output in the correct form ---
+            v_fe_rec = Informationsignal(v_fe_rec,"fs",v_fe_tx.fs);
+            v_hyb = Informationsignal(v_hyb,"fs",v_fe_tx.fs);
+            v_echo_est = Informationsignal(v_echo_est,"fs",v_fe_tx.fs);
+
+            if obj.plot
+                rfplot(net)
+            end
+        end
+    end
+end