%
% FUNCTION 2.9 : "cp0202_transmitter_2PAM_DS"
%
% Simulation of a UWB transmitter implementing 2PAM with DS
%
% Transmitted Power is fixed to 'Pow'.
% The signal is sampled with frequency 'fc'.
% 'numbits' is the number of bits generated by the source.
% 'Ns' pulses are generated for each bit, and these pulses
% are spaced in time by an average pulse repetition period
% 'Ts'.
% The DS code has periodicity 'Np'.
% Each pulse has time duration 'Tm' and shaping factor
% 'tau'.
%
% The function returns:
% 1) the generated stream of bits ('bits')
% 2) the generated DS code ('DScode')
% 3) the generated signal ('Stx')
% 4) a reference signal without data modulation ('ref')
%
% Programmed by Guerino Giancola
%

function [bits,DScode,Stx,ref]=cp0202_transmitter_2PAM_DS

% ----------------------------
% Step Zero - Input Parameters
% ----------------------------

Pow = -30;      % Average transmitted power (dBm)

fc = 50e9;      % sampling frequency

numbits = 2;    % number of bits generated by the source

Ts = 2e-9;      % frame time, i.e. average pulse repetition
                %  period [s]
Ns = 10;        % number of pulses per bit

Np = 10;        % periodicity of the DS code

Tm = 0.5e-9;    % pulse duration [s]
tau = 0.25e-9;  % shaping factor for the pulse [s]   

G = 1;
% G=0 -> no graphical output
% G=1 -> graphical output

% ----------------------------------------
% Step One - Simulating Transmission Chain
% ----------------------------------------

% binary source
bits = cp0201_bits(numbits);

% repetition coder
repbits = cp0201_repcode(bits,Ns);

% Direct Sequence code
DScode = cp0202_DS(Np);

% Pulse Amplitude Modulation + DS
[PAMDSseq,DSseq] = cp0202_2PAM_DS(repbits,fc,Ts,DScode);

% Shaping filter
power = (10^(Pow/10))/1000;     % average transmitted power
                                % (watt)
Ex = power * Ts;                % energy per pulse
w0 = cp0201_waveform(fc,Tm,tau);% Energy Normalized pulse
                                %  waveform
wtx = w0 .* sqrt(Ex);           % pulse waveform
Sa = conv(PAMDSseq,wtx);      % Output of the filter (with
                              %  modulation)
Sb = conv(DSseq,wtx);         % Output of the filter (no
                              %  modulation)

L = (floor(Ts*fc))*Ns*numbits;
Stx = Sa(1:L);
ref = Sb(1:L);

% ---------------------------
% Step Two - Graphical Output
% ---------------------------

if G
    
F = figure(1);
set(F,'Position',[32 223 951 420]);

tmax = numbits*Ns*Ts;
time = linspace(0,tmax,length(Stx));
P = plot(time,Stx);
set(P,'LineWidth',[2]);
ylow=-1.5*max(wtx);
yhigh=1.5*max(wtx);
axis([0 tmax ylow yhigh]);
AX=gca;
set(AX,'FontSize',12);
X=xlabel('Time [s]');
set(X,'FontSize',14);
Y=ylabel('Amplitude [V]');
set(Y,'FontSize',14);
for j = 1 : numbits
    tj = (j-1)*Ns*Ts;
    L1=line([tj tj],[ylow yhigh]);
    set(L1,'Color',[0 0 0],'LineStyle','--', ...
       'LineWidth',[2]);
    for k = 0 : Ns-1
     if k > 0
       tn = tj + k*Ts;
       L2=line([tn tn],[0.8*ylow 0.8*yhigh]);
       set(L2,'Color',[0.5 0.5 0.5], ...
          'LineStyle','-.','LineWidth',[1]);
     end
    end
end

end % end of graphical output