Expected input to be a scalar.

this is my cod , i have problem at this ligne :

ofdm_symb_awgn_t=ifft(awgn( fft(ofdm_symb_t) , SNR, 'measured'));

close all;
clear all;

%% Ofdm parameteres %%
mod_order = 4; % Oder da modulaQAM
N =256; % Numero de sinais a ser modulado/tamaho do ODFDM symbol
vec_EbN0_dB_ofdm =0 : 2 : 20 ;
vec_SNR_dB_ofdm		=	vec_EbN0_dB_ofdm + 10 * log10( mod_order );

%SNR=18;
fading= 'yes';

for i=1:length(vec_EbN0_dB_ofdm)
    
        var_ber_soma = 0;
        var_ber(i) = 0;
        iteracao = 0;
        SNR(i)     = vec_EbN0_dB_ofdm(i)+ 10*log10( log2(mod_order)) ;
        while(var_ber_soma < 100)
            i
            iteracao = iteracao + 1
            %tx
            data_tx = randi([0,mod_order-1],N,1);
            qam_symb_tx_f=qammod(data_tx,mod_order, 'UnitAveragePower', true); 
            ofdm_symb_t=ifft(qam_symb_tx_f, N);
            
            if strcmpi(fading,'yes')
                %Rayleigh channel
                h = (randn+1i*randn)/sqrt(2);
                H=fft(h, N).';   
                rayleigh_ofdm_symb= H .* qam_symb_tx_f; 
            elseif strcmpi(fading,'no')         
                h = 1;
                H=fft(h, N).';   
                rayleigh_ofdm_symb= H .* qam_symb_tx_f; 
            end
            
            %Adding AWGN / tem que ser na freq?
            ofdm_symb_awgn_t=ifft(awgn( fft(ofdm_symb_t) , SNR, 'measured'));
            ofdm_symb_awgn= awgn(rayleigh_ofdm_symb , SNR(i));%, 'measured');
            
            %rx
            %data_rx=qamdemod((ofdm_symb_awgn./H),mod_order, 'UnitAveragePower', true);
            data_rx=qamdemod((ofdm_symb_awgn),mod_order, 'UnitAveragePower', true);
            
            %SER
            ser= sum(data_tx~=data_rx);
            [SnumErrors,ser2] = symerr(data_tx,data_rx);
            %BER
            [BnumErrors, ber] = biterr(data_tx,data_rx);

            var_ber_soma = var_ber_soma + ber
            %var_ser(i) = ser2;
        end 
        var_ber(i) = var_ber_soma/iteracao;
        
        
end

%semilogy(SNR,var_ber, 'r', 'MarkerSize', 2 );
semilogy(SNR,var_ber, 'c', 'MarkerSize', 3 );	
ylim( [ 1e-6, 10000 ] ); xlim( [ 0, 20 ] );
grid on;
hold on ;

Answer 1

[Torsten]

            %Adding AWGN / tem que ser na freq?
            ofdm_symb_awgn_t=ifft(awgn( fft(ofdm_symb_t) , SNR, 'measured'));
            ofdm_symb_awgn= awgn(rayleigh_ofdm_symb , SNR(i));%, 'measured');            

In the first line, you most probably mean SNR(i) instead of SNR.