I'm trying to compare the spectrum of correlatively coded OFDM transmit and uncoded version of the same... I can't figure out what I'm doing wrong..Help!

clc
% Generation of the data matrix.
%Each column represents one symbol. Parallel processing
%So, we have here 100 symbols,each symbol containing 96 data samples each

no_sym=100;
no_bps=96;
data=randint(no_bps,no_sym);

% Modulation: BPSK
for i=1:100
  mod_data1=pskmod(data(:,i),2);
  mod_data(:,i)=mod_data1;
 end
%Correlative coding
corr_data(:,1)=mod_data(:,1);

for i=2:size(mod_data,2)
   corr_data(:,i)=mod_data(:,i-1)+mod_data(:,i);
end

% IFFT Block
ifft_data1=ifft(mod_data);
ifft_data2=ifft(corr_data);

% Parallel to serial Conversion
serial_data1=reshape(ifft_data1,1,no_sym*no_bps);
serial_data2=reshape(ifft_data2,1,no_sym*no_bps);

% % Upsampling 

[num,den] = butter(2, .8 ) ;
txd_Output = filter(num,den,serial_data1);
cor_Output = filter(num,den,serial_data2);

fsMHz = 20;

 [Pxx,W] = pwelch(txd_Output,[],[],4096,20);    
 figure(1);

subplot(1,2,1);plot([-2048:2047]*fsMHz/4096,10*log10(fftshift(Pxx)));
[Pxx1,W] = pwelch(cor_Output,[],[],4096,20);
subplot(1,2,2);plot([-2048:2047]*fsMHz/4096,10*log10(fftshift(Pxx1)));

end