function rxspectrum(scenario, fc, bw, fs, fshift, L)

if( nargin == 0)
    fprintf('Use this function to plot your Receive spectrum\n');
    fprintf('\n');
    fprintf('First argument is to run 8 example scenarios.\n');
    fprintf('rxpsectrum(1) or rxspectrum(2)...to plot and study various scenarios\n');
    fprintf('\n');
    fprintf('For custom numbers function can be called as follows\n');
    fprintf('rxspectrum([], center frequency, data bandwidth, sampling frequency,shift or carrier frequency, x-axis plotting limit(optional arugment)\n');
elseif (nargin == 1)
%% System Parameters
sys          = [];
sys.scenario = scenario;
switch sys.scenario
case 1
    % Good Scenario. Nyquist sampling theorem.
    %
    % The sampling rate of 4 GHz is high enough to satisfy Nyquist sampling
    % theorem.
    %
    % Use Nyquist Zone 1.
    sys.fc     = 1e9;
    sys.bw     = 300e6;
    sys.fs     = 4e9;
    sys.fshift = -1e9;
    L          = 7;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 2
    % Good Scenario. Bandpass sampling theorem.
    %
    % The sampling rate of 3 GHz is not high enough to satisfy Nyquist sampling
    % theorem but it is one of the good sampling rates from bandpass sampling
    % theorem.
    %
    % Use Nyquist Zone 2.
    sys.fc     = 3e9;
    sys.bw     = 300e6;
    sys.fs     = 4e9;
    sys.fshift = 1e9;
    L          = 7;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 3
    % Bad Scenario.
    %
    % Sampling rate does not satisfy Nyquist nor bandpass sampling theorem.
    %
    % Spectrum overlaps (completely or partially).
    sys.fc     = 3e9;
    sys.bw     = 300e6;
    sys.fs     = 2.4e9;       % Complete Overlap
    % sys.fs     = 5.8e9;     % Partial Overlap
    sys.fshift = -0.6e9;
    L          = 10;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 4
    % Bad Scenario.
    %
    % Sampling rate satisifies bandpass sampling theorem but spectra touch each
    % other.
    %
    % Unless we have an ideal brick wall lowpass filter, we cannot recover the
    % signal at 3 GHz.
    sys.fc     = 3e9;
    sys.bw     = 300e6;
    sys.fs     = 5.7e9;
    sys.fshift = 2.7e9;
    L          = 10;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 5
    % Solution to scenario 4. Spectra no longer touch either other.
    %
    % But we cannot use Xilinx hard IP decimate-by-2.
    sys.fc     = 3e9;
    sys.bw     = 300e6;
    sys.fs     = 3.4e9;
    sys.fshift = 0.4e9;
    L          = 8;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 6
    % Solution to scenario 5. Spectra no longer touch either other and we can
    % use Xilinx hard IP decimate-by-2.
    sys.fc     = 3e9;
    sys.bw     = 300e6;
    sys.fs     = 4e9;
    sys.fshift = 1e9;
    L          = 8;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 7
    % Same problem even with Nyquist sampling theorem.
    sys.fc     = 1.5e9;
    sys.bw     = 300e6;
    sys.fs     = 4e9;
    sys.fshift = -1.5e9;
    L          = 7;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
case 8
    sys.fc     = 1.5e9;
    sys.bw     = 300e6;
    sys.fs     = 2e9;
    sys.fshift = -0.5e9;
    L          = 7;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
otherwise
    error('Invalid sys.scenario');
end % switch
end  %if(nargin == 1)
if (nargin == 5)
    %% System Parameters
    sys          = [];
    sys.scenario = scenario;
    sys.fc = fc;
    sys.bw = bw;
    sys.fs = fs;
    sys.fshift = fshift;
    L = 7;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
end
if (nargin == 6)
    %% System Parameters
    sys          = [];
    sys.scenario = scenario;
    sys.fc = fc;
    sys.bw = bw;
    sys.fs = fs;
    sys.fshift = fshift;
    sys.xlim   = [-L L];
    sys.xticks = -L : L;
end
sys.xunit = 'GHz';


%%
if isempty(findobj('Number', sys.scenario))
    figure(sys.scenario)
    set(gcf, 'Position', [27          82        1180         638])
else
    figure(sys.scenario)
    clf
end


%%
Nsubplots = 5;
subplot(Nsubplots, 1, 1);
xlim(sys.xlim);
xticks(sys.xticks);
set(gca, 'Position', [0.04    0.8720    0.9277    0.09])
plotspectrum('asym',      sys.fc, sys.bw, 'r', sys.xunit);
plotspectrum('asymflip', -sys.fc, sys.bw, 'r', sys.xunit);
title(sprintf('Analog Bandpass Signal (Center = %.2f GHz. BW = %d MHz.)', ...
    sys.fc/1e9, sys.bw/1e6), 'FontSize', 12);
plotannotations(sys.fs, 1);
set(get(gca, 'XAxis'), 'FontSize', 11);


%%
subplot(Nsubplots, 1, 2);
xlim(sys.xlim);
xticks(sys.xticks);
set(gca, 'Position', [0.04    0.6720    0.9277    0.09])
title(sprintf('Sampling Images (Towards +ve Frequencies). Fs = %.2f GHz.', ...
    sys.fs/1e9), 'FontSize', 12);
for n = 1:8
    f1 = sys.fc  + n*sys.fs;
    f2 = -sys.fc + (n*sys.fs);
    plotspectrum('asym',     f1, sys.bw, 'b', sys.xunit);
    plotspectrum('asymflip', f2, sys.bw, 'b', sys.xunit);
end
set(get(gca, 'XAxis'), 'FontSize', 11);


%%
subplot(Nsubplots, 1, 3);
xlim(sys.xlim);
xticks(sys.xticks);
set(gca, 'Position', [0.04    0.4720    0.9277    0.09])
title(sprintf('Sampling Images (Towards -ve Frequencies). Fs = %.2f GHz.', ...
    sys.fs/1e9), 'FontSize', 12);
for n = -1:-1:-8
    f1 = sys.fc  + n*sys.fs;
    f2 = -sys.fc + (n*sys.fs);
    plotspectrum('asym',     f1, sys.bw, 'c', sys.xunit);
    plotspectrum('asymflip', f2, sys.bw, 'c', sys.xunit);
end
set(get(gca, 'XAxis'), 'FontSize', 11);


%%
subplot(Nsubplots, 1, 4);
xlim(sys.xlim);
xticks(sys.xticks);
set(gca, 'Position', [0.04    0.2720    0.9277    0.09])
title(sprintf('Real Digital Signal (Fs = %.2f GHz. BW %d MHz.)', ...
    sys.fs/1e9, sys.bw/1e6), 'FontSize', 12)
n  = -8:8;
f1 = sys.fc  + n*sys.fs;
f2 = -sys.fc + (n*sys.fs);
plotspectrum('asym',     f1, sys.bw, 'r', sys.xunit);
plotspectrum('asymflip', f2, sys.bw, 'r', sys.xunit);
plotannotations(sys.fs, 0);
set(get(gca, 'XAxis'), 'FontSize', 11);


%%
subplot(Nsubplots, 1, 5);
xlim(sys.xlim);
xticks(sys.xticks);
set(gca, 'Position', [0.04    0.0720    0.9277    0.09])
title(sprintf(['Complex Baseband Signal (Fs = %.2f GHz. BW %d MHz. ', ... 
    'fshift = %.2f GHz)'], sys.fs/1e9, sys.bw/1e6, sys.fshift/1e9), ...
    'FontSize', 12);
f1 = f1 + sys.fshift;
f2 = f2 + sys.fshift;
plotspectrum('asym',     f1, sys.bw, 'r', sys.xunit);
plotspectrum('asymflip', f2, sys.bw, 'r', sys.xunit);
plotannotations(sys.fs, 0);
set(get(gca, 'XAxis'), 'FontSize', 11);
Fs = sys.fs / 1e9;
x  = [-Fs/2, -Fs/4, -Fs/4, Fs/4, Fs/4, Fs/2];
y  = [0.25,  0.25,  0.75,  0.75, 0.25, 0.25];
hold on
plot(x, y, 'k--', 'LineWidth', 2)


end


% ------------------------------------------------------------------------------
%                           Helper Functions
% ------------------------------------------------------------------------------


function plotannotations(fs, zone)

%% Plot DC.
xline(0, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
y = 0.9;
addtext1(0, y, '0')

%% Plot fs/2.
xline(fs/2/1e9, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
xline(-fs/2/1e9, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
addtext1(0 + fs/2/1e9, y, 'Fs/2')
addtext1(0 - fs/2/1e9, y, '-Fs/2')

%% Plot fs.
xline(fs/1e9, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
xline(-fs/1e9, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
addtext1(0 + fs/1e9, y, 'Fs')
addtext1(0 - fs/1e9, y, '-Fs')

%% Plot 3*fs/2.
xline(fs*1.5/1e9, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
xline(-fs*1.5/1e9, 'LineWidth', 3, 'Color', 'g', 'LineStyle', '--')
addtext1(0 + 1.5*fs/1e9, y, '3*Fs/2')
addtext1(0 - 1.5*fs/1e9, y, '-3*Fs/2')

% %% Plot ...
% ntext4(0 + 1.6*fs/1e9, 0.6, '...', 'FontSize', 30, 'FontWeight', 'bold');
% ntext4(0 - 1.7*fs/1e9, 0.6, '...', 'FontSize', 30, 'FontWeight', 'bold');

% %%
% if zone == 1
%     addtext2(0.7,            0.65, {'Nyquist', 'Zone 1'})
%     addtext2(0.7 + fs/2/1e9, 0.65, {'Nyquist', 'Zone 2'})
%     % addtext2(0.7 + fs/1e9,   0.65, {'Nyquist', 'Zone 3'})
% end

end


function addtext1(x, y, t)

h                     = ntext4(x, y, t);
h.FontSize            = 15;
h.FontWeight          = 'bold';
h.HorizontalAlignment = 'center';

end


function addtext2(x, y, t)

h                     = ntext4(x, y, t);
h.FontSize            = 15;
h.FontWeight          = 'bold';
h.Color               = [0    0.4470    0.7410];
h.HorizontalAlignment = 'center';

end