simulation_capacity_users.m

多用户检测器的matlab仿真模型

function [SNR] = simulation_capacity_users
% Shows the BER as a function of the number of users in the system 
% AWGN channel
% single path
SNR = 8;
N = 16; %  the length of spread code
T = 50000;
alpha = 1;
SNR_dec = 10.^(SNR / 10);
Matcodes = no_orth_spreadcode(N);%非正交的
% C1=C1(:,1:K);

ku = 1;
% Matched filter
k=1;
for K=1:2:15  %K is the number of users
    %A=floor((0:(K-1))*5/K)+1;% what
    A=ones(K,1)*alpha;
    A=A*ones(1,T);%vector(1,5000)
    Aavg = sum(A.^2,2)/T;%
    C = Matcodes(:,1:K);
    Eb = C(:,ku)' * C(:,ku)*Aavg(ku);
    mf = C(:,ku);
    disp('loop');
    sigma = Eb/SNR_dec(k)/2;
    Sentbit = sign(randn(K,T));
    Y=C*(A.*Sentbit) + sqrt(sigma)*randn(N,T);
    % matched    
    Receivedbit1 = sign(mf'*Y);
    Perr1(K) = sum(abs(Receivedbit1-Sentbit(ku,:)))/2/T;
    % decorrelator
    Receivedbit2 = sign(inv(C'*C)*C'*Y);
    Perr2(K) = sum(abs(Receivedbit2(ku,:)-Sentbit(ku,:)))/2/T;
    % MMSE
    Receivedbit3 = sign(inv(C'*C+sigma*diag(1./Aavg))*C'*Y);
    Perr3(K) = sum(abs(Receivedbit3(ku,:)-Sentbit(ku,:)))/2/T;
    % SIC  逐级干扰对消（串行）
    Z=C'*Y;
    for j=K:-1:1
        Z2=Z(j,:);
        sent_bit=sign(Z2);
        R=C'*C;
        Z = Z - R(:,j)*(A(j,:).*sent_bit);%abs(Z2)
        Receivedbit4(j,:)=sent_bit;
    end
    Perr4(K) = sum(abs(Receivedbit4(ku,:)-Sentbit(ku,:)))/2/T;
    % DFD  决策反馈
    F=chol(C'*C);
    Finv=inv(F');
    Yfb = Finv*C'*Y;
    for j=K:-1:1
        sent_bit=sign(Yfb(j,:));
        Yfb=Yfb-F(:,j)*(A(j,:).*sent_bit);%abs(Yfb(j,:))
        Receivedbit5(j,:)=sent_bit;
    end
    Perr5(K) = sum(abs(Receivedbit5(ku,:)-Sentbit(ku,:)))/2/T;
    % PIC（并行）
    Z3=inv(C'*C)*C'*Y;
    Receivedbit6 = sign(Z3);% decorrelator
    B=C'*C-triu(tril(C'*C));%去除对角上的元素，留下的是可认为是相互干扰的成分
    Z3=C'*Y-B*(A.*Receivedbit6);
    %vector ones(1,5000)
    %triu(tril(Z3))
    Receivedbit6 = sign(Z3);
    Perr6(K) = sum(abs(Receivedbit6(ku,:)-Sentbit(ku,:)))/2/T;
end
if (nargout==0)
    semilogy(1:2:15, Perr1(1:2:15), 'bx-');hold on;
    xlabel('number of users');
    ylabel('BER');
    semilogy(1:2:15, Perr2(1:2:15), 'ro-');hold on;
    semilogy(1:2:15, Perr3(1:2:15), 'm+-');hold on;
    semilogy(1:2:15, Perr4(1:2:15), 'k*-');hold on;
    semilogy(1:2:15, Perr5(1:2:15), 'cs-');hold on;
    semilogy(1:2:15, Perr6(1:2:15), 'bv-');hold on;
    hold on;
    legend('Matched filter', 'Decorrelator','MMSE','SIC','DFD','PIC')
end


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function [codeMatrix] = no_orth_spreadcode(SF)
% This function returns a matrix whose lignes are code vectors. These codes are 
% not orthonormal
C1=hadamard(SF);            % Generates a matrix with orthogonal vectors
C2=sign(randn(SF,1));       % Generates a cell code to ensure spreading
C3=diag(C2)*C1/sqrt(SF);    % Matrix normalized
C4=(rand(SF,SF)-.5)/3;      % Generates a noise matrix
codeMatrix = C4+C3;         % Sums the code and the noise to have non-orthogonal codes
%end function
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