OFDM信号中的相位分配

Question

我有一个OFDM信号，它给了我一半的功率谱(一半的带宽)。我被告知阶段分配是导致它的原因，但我已经抽搐了好几天....仍然没有正确答案

prp=1e-6;   
fstep=1/prp;   
M = 4;                                 %   QPSK signal constellation   
k = log2(M);                           %  bits per symbol    
fs=4e9;  
Ns=floor(prp*fs);   
no_of_data_points = (Ns/2);            
no_of_points=no_of_data_points;
no_of_ifft_points = (Ns);            %   256 points for the FFT/IFFT  
no_of_fft_points = (Ns);   
nsamp = 1;                          % Oversampling rate   

fl = 0.5e9;   
fu = 1.5e9;     
 Nf=(fu-fl)/fstep;       
phin=zeros(Nf,1);          
dataIn = randint(no_of_data_points*k*2,1,2);  % Generate vector of binary            
data_source = randsrc(1, no_of_data_points*k*2, 0:M-1);
qpsk_modulated_data= modulate(modem.qammod(M),data_source);     
modu_data= qpsk_modulated_data(:)/sqrt(2);           
[theta, rho] = cart2pol(real(modu_data), imag(modu_data));       
A=angle(modu_data);       
theta=radtodeg(theta);        
figure(3);       
plot(modu_data,'o');%plot constellation without noise       
axis([-2 2 -2 2]);      
grid on;       
xlabel('real'); ylabel('imag');       
%%   E:GENERTION        
phin = zeros(Nf,1);      
phin(1:Nf,1)=theta(1:Nf);      

 No = fl/fstep;       
Vn = zeros(Ns,1);       
for r = 1:Nf        
 Vn(r+No,1) = 1*phin(r,1);       
% Vn(r+No,2) = 1*phin(r,2);      
 end       
%%
%------------------------------------------------------     
 %E.     Serial to parallel conversion      
%------------------------------------------------------      
par_data = reshape(Vn,2,no_of_data_points);     
 %%     
 % F.     IFFT Transform each period's spectrum (represented by a row of             
 % time domain via IFFT      

time_domain_matrix =ifft(par_data.',Ns);

Answer 1

你只考虑信号的实部