Added:

- Class folder 'Timing Recovery' with different timing recoveries
- Minimal example for the timing recovery on the FSO data
- New evaluation scripts in the FSO project folder

Classes/04_DSP/Timing Recovery/Godard_Timing_Recovery.m

@@ -0,0 +1,112 @@
+classdef Godard_Timing_Recovery < handle
+
+    properties(Access=public)
+        mode
+        num_blocks
+        fft_length
+        sps
+        rolloff
+        mu
+        Ki
+    end
+
+    methods(Access=public)
+        function obj = Godard_Timing_Recovery(options)
+            arguments(Input)
+
+                options.mode = 0;
+                options.num_blocks = 1;
+                options.fft_length = 1024;
+                options.sps = 2;
+                options.rolloff = 0;
+                options.mu = 0;
+                options.Ki = 1e-3;
+
+            end
+
+            fn = fieldnames(options);
+            for n = 1:numel(fn)
+                obj.(fn{n}) = options.(fn{n});
+            end
+
+            %obj-Initialization here%
+
+        end
+
+        function [data_out, tau_hat] = process(obj, data_in)
+
+            data_out = data_in;
+            output_vector = zeros(length(data_in),1);
+            block_length = length(data_in)/obj.num_blocks;
+            for i = 1:obj.num_blocks
+                i_start = ((i-1)*block_length)+1;
+                i_end = i*block_length;
+                x = data_in.signal(i_start:i_end);
+                beta = obj.rolloff;
+                eta  = obj.sps;
+                R = fft(x,obj.fft_length);
+                R_full = fft(x);
+            
+                if obj.mode == 0 % Classic Godard
+                    % Calculate time shift
+                    k0   = (1:obj.fft_length/2).';
+                    idx1 = k0;
+                    idx2 = k0+(obj.fft_length/2);
+                    tau_hat = sum(imag(R(idx1) .* conj(R(idx2))));
+                elseif obj.mode == 1 || obj.mode == 2 % Modified Godard 1
+                    % Calculate Shift for the received signal
+                    shiftBins = (1 - 1/eta) * obj.fft_length;
+                    if abs(shiftBins - round(shiftBins)) > 1e-12
+                        disp('Warning: shiftBins=(1-1/eta)*fft_length is non-integer. Choose compatible values for fft_length and eta.');
+                    end
+                    shiftBins = round(shiftBins);
+                
+                    % Calculate upper and lower bounds
+                    kStart = ((1-beta)/(2*eta)) * obj.fft_length;
+                    kEnd   = ((1+beta)/(2*eta)) * obj.fft_length - 1;
+                    if abs(kStart - round(kStart)) > 1e-12 || abs(kEnd - round(kEnd)) > 1e-12
+                        disp('Warning: kStart/kEnd are non-integer. Choose compatible values for fft_length, eta, and beta.');
+                    end
+                    kStart = round(kStart);
+                    kEnd   = round(kEnd);
+                
+                    k0   = (kStart:kEnd).';
+                    idx1 = k0 + 1;
+                    idx2 = mod(k0 + shiftBins, obj.fft_length) + 1;
+        
+                    % Calculate time shift 
+                    if obj.mode == 1
+                        tau_hat = sum(imag(R(idx1) .* conj(R(idx2))));
+                    elseif obj.mode == 2
+                        tau_hat = sum(angle(R(idx1))-angle(R(idx2)));
+                    end
+                end
+
+                
+                % % Normalization
+                % denom = floor(log10(abs(tau_hat)));
+                % tau_hat = tau_hat / 10^denom;
+
+                % Calculate mu using a first-order loop filter
+                mu_block = obj.mu + obj.Ki * tau_hat;
+
+                % % Shifting the signal in time domain using interpolation
+                % x_original = linspace(0,length(x)-1,length(x)).';
+                % x_new = x_original + mu_block;
+                % output_vector(i_start:i_end) = interp1(x_original,x,x_new,'linear','extrap');
+    
+                % Shifting the signal in frequency domain
+                k = (0:block_length-1).';
+                phaseRamp = exp(-1j * 2*pi * (k/block_length) * mu_block);
+                R_shifted = R_full .* phaseRamp;
+
+                output_vector(i_start:i_end) = real(ifft(R_shifted));
+
+            end
+            data_out.signal = output_vector;
+        end
+
+
+    end
+end
+