get_slow_fading.m

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Paper title: Accelerated Projected Gradient Method for the Optimization of Cell-Free Massive MIMO Downlink
% Conference: IEEE PIMRC 2020
% Authors: Muhammad Farooq, Hien Quoc Ngo, and Le Nam Tran
% Written by: Muhammad Farooq
% Email: Muhammad.Farooq@ucdconnect.ie
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function myBeta = get_slow_fading(nAPs,nUsers,nTx,D,d0,d1,sigma_sh)

%Randomly locations of M APs:
AP=unifrnd(-D/2,D/2,nAPs,2);
%Wrapped around (8 neighbor cells)
D1=zeros(nAPs,2);
D1(:,1)=D1(:,1)+ D*ones(nAPs,1);
AP1=AP+D1;

D2=zeros(nAPs,2);
D2(:,2)=D2(:,2)+ D*ones(nAPs,1);
AP2=AP+D2;

D3=zeros(nAPs,2);
D3(:,1)=D3(:,1)- D*ones(nAPs,1);
AP3=AP+D3;

D4=zeros(nAPs,2);
D4(:,2)=D4(:,2)- D*ones(nAPs,1);
AP4=AP+D4;

D5=zeros(nAPs,2);
D5(:,1)=D5(:,1)+ D*ones(nAPs,1);
D5(:,2)=D5(:,2)- D*ones(nAPs,1);
AP5=AP+D5;

D6=zeros(nAPs,2);
D6(:,1)=D6(:,1)- D*ones(nAPs,1);
D6(:,2)=D6(:,2)+ D*ones(nAPs,1);
AP6=AP+D6;

D7=zeros(nAPs,2);
D7=D7+ D*ones(nAPs,2);
AP7=AP+D7;

D8=zeros(nAPs,2);
D8=D8- D*ones(nAPs,2);
AP8=AP+D8;

%Randomly locations of K terminals:
Ter=unifrnd(-D/2,D/2,nUsers,2);



%Create an MxK large-scale coefficients beta_mk
myBeta = zeros(nAPs,nUsers);
dist=zeros(nAPs,nUsers);
for m=1:nAPs
    for k=1:nUsers
    dist(m,k) = min([norm(AP(m,:)-Ter(k,:)), norm(AP1(m,:)-Ter(k,:)),norm(AP2(m,:)-Ter(k,:)),norm(AP3(m,:)-Ter(k,:)),...
        norm(AP4(m,:)-Ter(k,:)),norm(AP5(m,:)-Ter(k,:)),norm(AP6(m,:)-Ter(k,:)),norm(AP7(m,:)-Ter(k,:)),norm(AP8(m,:)-Ter(k,:)) ]); %distance between Terminal k and AP m
    
    if dist(m,k)<d0
         betadB=-nTx - 35*log10(d1) + 20*log10(d1) - 20*log10(d0);
    elseif ((dist(m,k)>=d0) && (dist(m,k)<=d1))
         betadB= -nTx - 35*log10(d1) + 20*log10(d1) - 20*log10(dist(m,k));
    else
    betadB = -nTx - 35*log10(dist(m,k)) + sigma_sh*randn(1,1); %large-scale in dB
    end
    
    myBeta(m,k)=10^(betadB/10); 
    end
end

end