## Copyright (C) 2018 Jens Ahrensfeld
## 
## This program is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or
## (at your option) any later version.
## 
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
## 
## You should have received a copy of the GNU General Public License
## along with this program.  If not, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*- 
## @deftypefn {Function File} {@var{retval} =} garage (@var{input1}, @var{input2})
##
## @seealso{}
## @end deftypefn

## Author: Jens Ahrensfeld <ahrensfeld@w2ess001vm>
## Created: 2018-12-06

function bits = garage (varargin)

params = struct ('numSamplesPerSym', 4, 'with_filter', 0, 'k_noise', 0.04);
units = struct ('numSamplesPerSym', 'sps', 'with_filter', '', 'k_noise', '');

% Parse parameters
names = fieldnames(params);
for k=1:nargin-1,
	for n=1:length(names),
		if strcmpi(varargin{k}, names{n})
			params.(names{n}) = varargin{k+1};
		end
	end
end
	
print_parameters(params, units)

k_n = params.k_noise;		% NOise
k_s = 1.0;		% Sym

numSamplesPerSym = params.numSamplesPerSym;
baud = 9600;
fs = baud * numSamplesPerSym;

numSyms = 50;
numBursts = 3;
numSymsPauseBetweenBurst = 50;

syms = rand(numSyms, 1) > 0.5;

bit = 0;
syms_m = [];

% Line coding
for n=1:numSyms,
	if syms(n) == 1
		syms_m = [syms_m bit];
		bit = not(bit);
		syms_m = [syms_m bit];
		bit = not(bit);
	else
		syms_m = [syms_m bit];
		syms_m = [syms_m bit];
		bit = not(bit);
	end
end
	

% Upconvert
x = [];

for k=1:numBursts
	for n=1:2*numSyms,
		for m=1:numSamplesPerSym,
			x = [x syms_m(n)];
		end
	end
	x = [x zeros(1, numSymsPauseBetweenBurst*numSamplesPerSym)];
end

% Channel
[b,a] = butter(2, baud/fs);

if params.with_filter
  x = filter(b, a, x);
end
y = k_s*x + k_n*randn(1, length(x));

y = wavread('seq.wav');

N = length(y);
n = 1:N;


bit = 0;
count = numSamplesPerSym;

smp = [];
smp_n = [];
bits = [];

% Receive
state = "Init";
peakFindCount = 10;
v_min = 0;
v_max = 0;
for n=1:N
	state_next = state;
	v_thr = (v_max - v_min) / 2;
	if y(n) < v_min
		v_min = y(n);
	elseif y(n) > v_max
		v_max = y(n);
	end
	v_min = v_min + 1e-5*(v_thr - v_min);
	v_max = v_max - 1e-5*v_max;
	if strcmp(state, "Init")
		state_next = "Decode";
	elseif strcmp(state, "Decode")
		bit_curr = y(n) > v_thr;
		if (bit ~= bit_curr)
			count = fix(numSamplesPerSym/2);
      bit = bit_curr;
		end
		if count > 0
			count = count - 1;
		else
			count = numSamplesPerSym-1;
			smp = [smp y(n)];
			smp_n = [smp_n n];
			bits = [bits bit_curr];
		end;
		_cnt(n) = count;
	end
		_v_tr(n) = v_thr;
	
	if ~strcmp(state, state_next)
		fprintf(stdout, "Change state: %s => %s\n", state, state_next);
		state = state_next;
	end
end
bits = bits';

n = 1:N;

% Plot
subplot(2, 1, 1)
plot(n, y, '-o', smp_n, smp, 'rx', n, _v_tr, 'y'); grid;
subplot(2, 1, 2)
plot(n, _cnt); grid;

endfunction