waterfill_single.m

无线通信系统多天线注水算法

%Single User Waterfilling
%Authors: Screen Lee
%Date:  12/05/06

function [Ex] = waterfill_single(H, p);
%Returns optimal covariance matrix 
%where H is effective channel matrix
%etc.

%Function Inputs
%H:             double indexed channel
%p:             power in linear units

%Function Outputs

%Ex:            double indexed matrices containing the capacity achieving
%               covariance matrices


%Other Variables
%M:  # number of base station antennas in uplink channel
%N:  # number of terminal antennas in uplink channel



[M,N] = size(H);

%Perform SVD of channel
s = svd(H'* H);
channels = length(s);

s = real(s);
%Eliminate zeroes
s = max(s, 1e-10);

noise_vector = 1./s;
% unsortedN = noise_vector;
%Put noise variances in increasing order
noise_vector = sort(noise_vector);  

last = channels;   %index of worst channel allocated non-zero power
loop = 1;

%Find channels allocated non-zero power
while (loop)
    water = noise_vector(last);    %water level
    power = sum(max(water - noise_vector, 0));
    if (power > p)
        last = last - 1;
    else
        loop = 0;
    end;
end; 

%Calculate optimal water level
water = 1/last * (p + sum(noise_vector(1:last)));

% Ex = zeros(N,N,K);
Ex=zeros(N,N);
%Take svd of channel
[u,v,w] = svd(H'* H);
s = svd(H' * H);
s = real(s);
%eliminate zeroes
s = max(s, 1e-10);
noise_vector = 1./s;

Ex = u * diag(max((water- noise_vector),0)) * u';