Question about Matlab code in BER OFDM

Code Matlab M - [expand]
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%%%%%%%%%%%%%%%%%%%%%
SP.FFTsize = 64;
% SP.inputBlockSize =16;
N=64;
SP.CPsize=20;
SP.subband = 0;
SP.numRun =10;%10^4;
% Constant CFOs values for each user 
SP.ep1=0.1; %
SP.ep2=-0.1;%-0.1;
SP.ep3=-0.05; %-0.05%;
SP.ep4=0.05;%0.05%;
numSymbols = SP.FFTsize;
% modtype='16QAM'; %'16QAM';modtyp=SP.modtype
ofdm;
% Constant CFOs
A1=exp((1*1i*2*pi*SP.ep1/(numSymbols))*(0:(numSymbols-1)));
A2=exp((1*1i*2*pi*SP.ep2/(numSymbols))*(0:(numSymbols-1)));
CT1=(eye(numSymbols))*diag(A1)*ifft(eye(numSymbols ));
CT2=(eye(numSymbols))*diag(A2)*ifft(eye(numSymbols ));
SP.SNR=0:5:30;
SP.channel=(1/sqrt(8))*(randn(2,8)+1i*randn(2,8))*(1/sqrt(2));%SP.channel=(1/sqrt(7))*(randn(4,7)+1i*randn(4,7))*(1/sqrt(2))
%AWGN channel
 
% H = fft(SP.channel(1,:),SP.FFTsize);
% H_channel2 = fft(SP.channel(2,:),SP.FFTsize);
for n = 1:length(SP.SNR) 
% rng('state',0)
% rng('state',0)
 
for k = 1:SP.numRun
 
SP.channel=(1/sqrt(8))*(randn(2,8)+1i*randn(2,8))*(1/sqrt(2));%SP.channel=(1/sqrt(7))*(randn(4,7)+1i*randn(4,7))*(1/sqrt(2))
%AWGN channel
 
H_channel1 = fft(SP.channel(1,:),SP.FFTsize);
H_channel2 = fft(SP.channel(2,:),SP.FFTsize);
% 
H = diag(fft(H_channel1,SP.FFTsize));
% A_channel2 = diag(fft(H_channel2,SP.FFTsize));
 
data1=randi([0 15],1,48);
data1=data1.';
inputSymbols1=qammod(data1,16);
I1=eye(N);
v_phi=1:4:64;
I1(:,v_phi)=[];
inputSymbols11=I1*inputSymbols1;
% inputSymbols=diag(I1*inputSymbols);
m2=4;
data2=randi([0 15],1,48);
data2=data2.';
inputSymbols2=qammod(data2,16);
I2=eye(N);
v_phi2=2:4:64;
I2(:,v_phi2)=[];
inputSymbols22=I2*inputSymbols2;
% OFDM User 1 
inputSymbols_freq = fft(inputSymbols11).'; 
%OFDM User 2
 
inputSymbols_freq2 = fft(inputSymbols22).'; 
TxSamples_u1= [inputSymbols_freq(numSymbols-SP.CPsize+1:numSymbols) inputSymbols_freq]; % TxSamples_ifdma_u1= [TxSamples_ifdma1(numSymbols-SP.CPsize+1:numSymbols) TxSamples_ifdma1];
 
%CP for User 2 
TxSamples_u2= [inputSymbols_freq2(numSymbols-SP.CPsize+1:numSymbols) inputSymbols_freq2 ]; % TxSamples_ifdma_u2= [TxSamples_ifdma2(numSymbols-SP.CPsize+1:numSymbols) TxSamples_ifdma2];
 
%============================ Noise Generation =====================
 
tmpn = randn(1,numSymbols+SP.CPsize);
complexNoise = tmpn /sqrt(2) ; %complexNoise = (tmpn(1,:) + 1i*tmpn(2,:))/sqrt(2);
noisePower =(10^(-SP.SNR(n)/10));
noise_= sqrt(noisePower)*complexNoise;%noise_= sqrt(noisePower/Q)*complexNoise
 
%=============== Channel and CFO for User 1 ==============================
RxSamples_u1 = filter(SP.channel(1,:), 1, TxSamples_u1); % Multipath Channel
 
RxSamples_u1 = RxSamples_u1.*exp((1i*2*pi*SP.ep1/(numSymbols))*(-SP.CPsize:(numSymbols-1)));
 
%=============== Channel and CFO for User 2 ==============================
 
RxSamples_u2 = filter(SP.channel(2,:), 1, TxSamples_u2); % Multipath Channel
 
RxSamples_u2 = RxSamples_u2.*exp((1i*2*pi*SP.ep2/(numSymbols))*(-SP.CPsize:(numSymbols-1)));
 
%============================= Received signal ============================
% RxSamples_ofdma1 = RxSamples_u1 +noise_;
RxSamples_ofdma1 = RxSamples_u1 + RxSamples_u2+noise_;
%% remove CP
Y_ofdma1 = RxSamples_ofdma1(SP.CPsize+1:numSymbols+SP.CPsize) ;
 
Y_ofdma2=fft(Y_ofdma1);
% %%=============compensation channel and CFO =============
HC=H*CT1;
%% MMSE Equalization
C=inv(HC'*HC+10^(-SP.SNR(n)/10)*eye(N))*HC';
Y_ofdmaC=C*Y_ofdma2.';
 
%% cancel NO-subcarrier
Y_ofdma= I1'*Y_ofdmaC;
 
demodulated_symbol1_conv=qamdemod(Y_ofdma,16);
demodata_ofdma=demodulated_symbol1_conv;
%[Num1,noe_ofdm(k)]=biterr(data1,demodata_ofdma); 
[~,ber_ofdm(k)]=biterr(data1,demodata_ofdma);
% noe_ofdm(k)=sum(abs((data1-demodata_ofdma)));
end
BER_ofdm(n) =mean(ber_ofdm);
% BER_ofdm(n,:) =sum(noe_ofdm)/(SP.numRun*N);
end
 
semilogy(SP.SNR,BER_ofdm,'k--s');
% toc
legend('OFDM')
xlabel('SNR (dB)'); ylabel('BER');
title('MMSE Equalization,QAM')
axis([0 35 1e-4 1 ])
grid