decoding_coherent_test.m

source Matlab traites the UWB

%
%
clear all;
%
% Necessary path
addpath ../
addpath ../rng;
addpath ../util;
addpath ../pulse;
addpath ../receiver;
addpath ../data_signal;

% Some parameters
FS_CONT = 8e9;
PACKET_LENGTH = 128*8;
TC = 2e-9;
Eb = 1;
snr_dB = 5:1:15;
% Receiver
T_INT = 1e-9;
N_INT = 1;
% From SNR in dB to the variance of the noise
snr = 10.^(snr_dB/10);
s2 = Eb ./ (2*snr);
% Simulation
L = 200;

dt = 1/FS_CONT;
%samples_per_unit = 1e-9*FS_CONT;
samples_per_unit = 1e-9*FS_CONT;
samples_per_chip = TC * FS_CONT;

% Get a pulse
chip_span = 0.5;
[monopulse,t] = get_monopulse(1,chip_span,1e-9,TC,samples_per_chip);
monopulse = monopulse(1:end-1);

% Normalize
monopulse = Eb*monopulse./norm(monopulse);
% $$$ % Better?
% $$$ monopulse = Eb*monopulse/sqrt(dt*sum(monopulse.^2));


% Create the signal to be transmitted
tx_signal = conv(monopulse,upsample(ones(1,PACKET_LENGTH),2*samples_per_chip));
tx_signal = tx_signal(1:2*PACKET_LENGTH*samples_per_chip);

% Indices for the energy receiver
signal_start_0 = cumsum(ones(1,PACKET_LENGTH)*(2*samples_per_chip))-(2* ...
						  samples_per_chip);

% Coherent receiver and decoding;
template = repmat(monopulse,1,PACKET_LENGTH);
n = length(monopulse);

signal_idx_0 = repmat(signal_start_0,n,1)+repmat((0:n-1)',1,PACKET_LENGTH) + 1;
signal_idx_1 = signal_idx_0 + samples_per_chip;

% Parameters for the generation of the Gaussian noise
ALPHA = PACKET_LENGTH;
T     = TC;
Nt    = T*FS_CONT;
B     = 1e9;

Scale = (2*B)/FS_CONT;;

for l = 1:length(snr_dB)
  fprintf('SNR = %d [dB]\n',snr_dB(l));
  for k = 1:L
    % Add the noise
% $$$     noise = ...
% $$$     sqrt(s2(l))*randn(1,PACKET_LENGTH*2*samples_per_chip);
    [noise_0 noise_1] = ...
    randn_bl(ALPHA,T,Nt,B,s2(l)*Scale);
    rx_signal = tx_signal + [noise_0 noise_1];

    % Coherent receiver
    rx_0 = coherent_receiver( ...
        rx_signal(reshape(signal_idx_0,1, PACKET_LENGTH*n)),n,template);
    rx_1 = coherent_receiver( ...
        rx_signal(reshape(signal_idx_1,1, PACKET_LENGTH*n)),n,template);
    rx_down = rx_0-rx_1;


    idx_dec0 = find(rx_down>0);
    idx_dec1 = find(rx_down<0);
    idx_unknown = find(rx_down==0);

    decoded = [];
    decoded(idx_dec0) = 0;
    decoded(idx_dec1) = 1;
    decoded(idx_unknown) = round(rand(1,length(idx_unknown)));

    % Compute the BER
    [num_err,ber_sim(l,k)] = symerr(decoded,zeros(1,PACKET_LENGTH));
    end
end

semilogy(snr_dB,mean(ber_sim,2),'.');
% Achtung, orthogonal modulation scheme
ber_bppm = 0.5*erfc( sqrt(snr) / sqrt(2));
ber_bpsk = 0.5*erfc( sqrt(2*snr) / sqrt(2));
hold on;
semilogy(snr_dB,ber_bppm,'r',snr_dB,ber_bpsk,'r--');
hold off;