gmskspec.m

来自「自适应滤波原理_西蒙.赫金_Matlab_源代码 希望能够对学习自适应滤波技术」· M 代码 · 共 49 行

%----------------------------------------------------
%  Compute the spectra of various GMSK signals
%----------------------------------------------------

K    = 20;      % number of blocks to simulate
N    = 32*256;   % number of symbols to simulate
Nsmp = 16;      % number of samples per symbol
h    = 0.5;     % modulation index
L    = 9;       % pulse length in symbol periods
T    = 1;       % symbol length

spec = zeros(N*Nsmp,1);

%------------------------------------------------------------
%  GMSK pulse shape
%------------------------------------------------------------
t  = [0: 1/Nsmp : L*T];  
c1 = sqrt(2*pi/log(2));
W  = 0.30;
g  = c1*W*exp(- c1^2 *pi* W^2 * (t-L*T/2).^2);  % must integrate to 1/2 over one symbol period

% MSK modulation
q0    = filter(g,1,[zeros(1,Nsmp*L*T) ones(1,Nsmp) zeros(1,Nsmp*L*T)]);
q     = cumsum(q0);
qNorm = 0.5/max(q);
%---------------------------------------------------------------
%  Generate signal
%----------------------------------------------------------------
temp = [];
for i=1:K
   d = 2*floor(2*rand(1,N)) - 1;
   d = ones(Nsmp,1) * d;
   dd = d(:);

   freqpulse = filter(g,1,dd);
   phi  = 2*pi*h* cumsum(freqpulse)*qNorm; %/Nsmp;

   signal = exp(j*phi);

   spec = spec + abs(fft(kaiser(length(signal),2).*signal)).^2;
   i
end

%-----------------------------------------------
%  Plot spectrum
%-----------------------------------------------
Fs = 1;
[freq,specdB] = plotspec(spec,Fs,Nsmp,N);