function Rx_Data=AWGN_channel(Tx_data,SNR);

%--------------------
% add AWGN
%--------------------
[nnl,mml]=size(Tx_data);
    Tx_signal_power=0;
    for k=1:nnl
      for b=1:mml
        Tx_signal_power=Tx_signal_power+real(Tx_data(k,b))^2+imag(Tx_data(k,b))^2;
      end
    end
    Tx_signal_power=Tx_signal_power/(nnl*mml);

linear_SNR = 10^( SNR /10) ;
Rx_Data=AWGN(Tx_data,linear_SNR,Tx_signal_power,'linear');