shadowing.m

无线仿真Matlab代码

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%   ***************************************************************************
%
%   UMTS-HSDPA channel generator 
%              
%   [S] = shadowing(numTTI,shadow_std,alpha,beta)
%
%   Generate shadow fading
%   The result is translated and normalised such that the resulting mean and
%   standard deviation correspond to 0 and shadow_std. 
%   So, even for short simulations, two UE's that only differ in the 
%   random seed, do have the same statistics.
%
%   At the start of the loop over the number of users in the main file, 
%   the random seed is set to the current user index. First the fast fading 
%   is generated. Next the shadow fading characteristics are generated. 
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


function [S] = shadowing(numTTI,shadow_std,alpha,beta)

% Initialize array in order to speed up the matlab compiler
S = zeros(numTTI,1);

% Draw random values
s_random = randn(numTTI,1);

% Set initial shadowing value
S(1) = s_random(1);

% Include correlation factor (in order to make the next command simple for the compiler);
% beta equals sqrt(1-alpha^2)
s_random = beta*s_random;                     

% Generate correlated fading
for ii = 2:numTTI
    S(ii) = alpha*S(ii-1) + s_random(ii);
end

% Correct the result, such that different random seeds, even for 'short simulations' result in 
% the same statistics for the shadow fading, i.e. a distribution with mean 0 and std shadow_std

meanS=mean(S);
stdS=std(S);
Scorrected=(S-meanS)*shadow_std/stdS;
S=Scorrected;