jakes_filter.m

通信系统仿真原理与无线应用书中matlab源程序

% File: Jakes_filter.m
% Software given here is to accompany the textbook: W.H. Tranter, 
% K.S. Shanmugan, T.S. Rappaport, and K.S. Kosbar, Principles of 
% Communication Systems Simulation with Wireless Applications, 
% Prentice Hall PTR, 2004.
%
function [impw] = jakes_filter(fd)
% FIR implementation of the Jakes filter (128 points)
n = 512; nn = 2*n;      fs=100;                        % nn is FFT block size
f = 0:fs/64:fs;								% sampling frequency = 16*fd
H = zeros(1,n);									% initialize H(f)
for k=1:(n/8+1)									% psd for k=1:65
   jpsd(k)=[1-cos(pi*(f(k))/fs)]^2;
%    if(jpsd(k))>1000
%       jpsd(k)=1000;
%    end
   H(k)=jpsd(k)^0.5;							% first 65 points of H
end
for k=1:n										% generate negative frequencies
   H(n+k) = H(n+1-k);
end
[inv,time] = linear_fft(H,nn,fs/64);		    % inverse FFT
imp = real(inv(450:577));						% middle 128 points
impw = imp.*hanning(128)';						% apply hanning window
energy = sum(impw.^2);							% compute energy
impw = impw/(energy^0.5);						% normalize
% End of function file.


ts = 1/(16*fs); 			% sampling frequency and time
time = [1*ts:ts:128*ts];		% time vector for plot
subplot(2,1,1)
stem(time,impw,'.'); grid 
xlabel('Time'); ylabel('Impulse Response')


% Square the fft and check the power transfer function.
%
[h fd] = linear_fft(impw,128,ts);    % generate H(f) for filter
subplot(2,1,2)
plot(fd,abs(h.*h)); grid;
xlabel('Frequency'); ylabel('PSD')
%