%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% MATLAB design: Time Offset Estimation
%
%% Introduction:
%
% The generated hardware core for this design operates at 1/os_rate 
% where os_rate is the oversampled rate. That is, for 8 oversampled clock cycles 
% this core iterates once. The output is at the symbol rate.
%
% Key design pattern covered in this example:
% (1) Data is sent in a vector format, stored in a register and accessed
% multiple times
% (2) The core also illustrates basic mathematical operations
% 

%   Copyright 2011-2015 The MathWorks, Inc.

%#codegen
function [tauh,q] = mlhdlc_comms_toe(r,mu)

persistent tau
persistent rBuf

os_rate = 8;
if isempty(tau)
    tau = 0;
    rBuf = zeros(1,3*os_rate);
end

rBuf = [rBuf(1+os_rate:end) r];

taur = round(tau);

% Determine lead/lag values and compute offset error
zl = rBuf(os_rate+taur-1);
zo = rBuf(os_rate+taur);
ze = rBuf(os_rate+taur+1);
offsetError = zo*(ze-zl);

% update tau
tau = tau + mu*offsetError;

tauh = tau;

q = zo;

function mlhdlc_comms_toe_tb
%

%   Copyright 2011-2015 The MathWorks, Inc.

os_rate = 8;
Ns = 128;
SNR = 100;
mu = .5; % smoothing factor for time offset estimates

% create simulated signal
rng('default'); % always default to known state  
b = round(rand(1,Ns));
d = reshape(repmat(b*2-1,os_rate,1),1,Ns*os_rate);

x = [zeros(1,Ns*os_rate) d zeros(1,Ns*os_rate)];
y = awgn(x,SNR);

w = fir1(3*os_rate+1,1/os_rate)';
z = filter(w,1,y);
r = z(4:end); % give it an offset to make things interesting

%tau = 0;
Nsym = floor(length(r)/os_rate);
tauh = zeros(1,Nsym-1); q = zeros(1,Nsym-1);
for i1 = 1:Nsym-1
    rVec = r(1+(i1-1)*os_rate:i1*os_rate);
    
    % Call to the Timing Offset Estimation Algorithm
    [tauh(i1),q(i1)] = mlhdlc_comms_toe(rVec,mu);
end

indexes = 1:os_rate:length(tauh)*os_rate;
indexes = indexes+tauh+os_rate-1-os_rate*2;

Fig1Loc=figposition([5 50 90 40]);
H_f1=figure(1); clf;
set(H_f1,'position',Fig1Loc);
subplot(2,1,1)
plot(r,'b');
hold on
plot(indexes,q,'ro');
axis([indexes(1) indexes(end) -1.5 1.5]);
title('Received Signal with Time Correct Detections');
subplot(2,1,2)
plot(tauh);
title('Estimate of Time Offset');

function y=figposition(x)
%FIGPOSITION Positions figure window irrespective of the screen resolution
% Y=FIGPOSITION(X) generates a vector the size of X. 
% This specifies the location of the figure window in pixels
% 
screenRes=get(0,'ScreenSize');
% Convert x to pixels
y(1,1)=(x(1,1)*screenRes(1,3))/100;
y(1,2)=(x(1,2)*screenRes(1,4))/100;
y(1,3)=(x(1,3)*screenRes(1,3))/100;
y(1,4)=(x(1,4)*screenRes(1,4))/100;