why do I get this error while using qammod? "Expected input number 1, X, to be an array with all of the values < 4."

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Hanojhan Rajahrajasingh 2022-9-28

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https://ww2.mathworks.cn/matlabcentral/answers/1813550-why-do-i-get-this-error-while-using-qammod-expected-input-number-1-x-to-be-an-array-with-all-of

评论： Hanojhan Rajahrajasingh 2023-2-9

N=256;
% Number of subcarriers or size of IFFT/FFT
N_data_symbol=128;
% Number of symbol to IFFT
GI=N/4;
% Guard interval 1/4,1/8,1/16,. . .
M=4;
% Modulation 2:BPSK, 4:QPSK, (8,16,32,64,128,256):QAM
L=16;
% Channel length
N_Iteration=500;
% Number of iteration
SNR=[0:1:15];
% Signal to Noise Ratio in dB
for i=1:length(SNR)
    snr=SNR(i)
    for (k=1:N_Iteration)
        tx_bits=randi(N_data_symbol,1,M);
        % Input Bit Streams to Transmit
        % Modulation
        tx_bits_Mod=qammod(tx_bits,M);
        input_symbol=[zeros((N-N_data_symbol)/2,1); 
            tx_bits_Mod;
            zeros((N-N_data_symbol)/2,1)];
        
        % IFFT and Circular Prefix Addition
        ofdm_symbol_ifft=ifft(input_symbol,N);
        % Guard Interval insertion (CP)
        guard_symbol=ofdm_symbol_ifft(N-GI+1:N);
        % Add the cyclic prefix to the ofdm symbol
        ofdm_symbol=[guard_symbol; ofdm_symbol_ifft];
        %sig_pow=ofdm_symbol'.*conj(ofdm_symbol);
        ofdm_spectrum=ofdm_symbol;
        %ofdm_spectrum=[ofdm_spectrum; ofdm_symbol];
        % h=randn(L,1)+j*randn(L,1); % Generate random channel
        h(1:L,1)
        %h=h./sum(abs(h)); % Normalization
        h=1; %AWGN
        y1=filter(h,1,ofdm_symbol);
        %y=x*h
        % Adding AWGN Noise
        y=awgn(y1,snr,'measured');
        %y=x*h+n
        % Remove Cyclic prefix
        rx_symbol=y(GI+1:N+GI);
        % The FFT of the time domain signal after the removal of
        cyclic prefix
        rx_symbol_fft=fft(rx_symbol,N);
        % Equalization
        %H_f=fft(h,N);
        %G=1./H_f;
        rx_equalized_zp=rx_symbol_fft;
        rx_equalized=rx_equalized_zp(((N-N_data_symbol)/2)+1:(N+N_data_symbol)/2);
        % Demodulate
        rx_bits_zp=qamdemod(rx_equalized,M);
        rx_bits=rx_bits_zp;
        % Comparison
        % Bit Error Rate computation
        [nErr bErr(i,k)]=symerr(tx_bits,rx_bits);
    end
end
snr_theo=10.^(SNR/10);
Theory_awgn=0.5*erfc(sqrt(snr_theo));
semilogy(SNR,mean(bErr'),'b',SNR,Theory_awgn,'ro–');

The errors I'm getting are as follows:

Error using qammod

Expected input number 1, X, to be an array with all of the values < 4.

Error in qammod>validateInput (line 288)

validateattributes(x, {'numeric'}, {'real','integer','>=',0,'<',M}, mfilename, 'X', 1);

Error in qammod (line 95)

validateInput(x, M, bitInput, outputDataType);

Error in Experimental_DCOFDM_2 (line 21)

tx_bits_Mod=qammod(tx_bits,M);

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Answer 1

Chunru 2022-9-28

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1813550-why-do-i-get-this-error-while-using-qammod-expected-input-number-1-x-to-be-an-array-with-all-of#answer_1062205

在 MATLAB Online 中打开

A few bugs in program. The major one is generating input signa which should bel: tx_bits=randi([0 M-1], [N_data_symbol,1]);

N=256;

% Number of subcarriers or size of IFFT/FFT

N_data_symbol=128;

% Number of symbol to IFFT

GI=N/4;

% Guard interval 1/4,1/8,1/16,. . .

M=4;

% Modulation 2:BPSK, 4:QPSK, (8,16,32,64,128,256):QAM

L=16;

% Channel length

N_Iteration=500;

% Number of iteration

SNR=[0:1:15];

% Signal to Noise Ratio in dB

for i=1:length(SNR)

snr=SNR(i)

for (k=1:N_Iteration)

%tx_bits=randi(N_data_symbol,1,M);

tx_bits=randi([0 M-1], [N_data_symbol,1]);

% Input Bit Streams to Transmit

% Modulation

tx_bits_Mod=qammod(tx_bits,M);

input_symbol=[zeros((N-N_data_symbol)/2,1);

tx_bits_Mod;

zeros((N-N_data_symbol)/2,1)];

% IFFT and Circular Prefix Addition

ofdm_symbol_ifft=ifft(input_symbol,N);

% Guard Interval insertion (CP)

guard_symbol=ofdm_symbol_ifft(N-GI+1:N);

% Add the cyclic prefix to the ofdm symbol

ofdm_symbol=[guard_symbol; ofdm_symbol_ifft];

%sig_pow=ofdm_symbol'.*conj(ofdm_symbol);

ofdm_spectrum=ofdm_symbol;

%ofdm_spectrum=[ofdm_spectrum; ofdm_symbol];

% h=randn(L,1)+j*randn(L,1); % Generate random channel

%h(1:L,1)

%h=h./sum(abs(h)); % Normalization

h=1; %AWGN

y1=filter(h,1,ofdm_symbol);

%y=x*h

% Adding AWGN Noise

y=awgn(y1,snr,'measured');

%y=x*h+n

% Remove Cyclic prefix

rx_symbol=y(GI+1:N+GI);

% The FFT of the time domain signal after the removal of

% cyclic prefix

rx_symbol_fft=fft(rx_symbol,N);

% Equalization

%H_f=fft(h,N);

%G=1./H_f;

rx_equalized_zp=rx_symbol_fft;

rx_equalized=rx_equalized_zp(((N-N_data_symbol)/2)+1:(N+N_data_symbol)/2);

% Demodulate

rx_bits_zp=qamdemod(rx_equalized,M);

rx_bits=rx_bits_zp;

% Comparison

% Bit Error Rate computation

[nErr bErr(i,k)]=symerr(tx_bits,rx_bits);

end

snr = 0

snr = 1

snr = 2

snr = 3

snr = 4

snr = 5

snr = 6

snr = 7

snr = 8

snr = 9

snr = 10

snr = 11

snr = 12

snr = 13

snr = 14

snr = 15

snr_theo=10.^(SNR/10);

Theory_awgn=0.5*erfc(sqrt(snr_theo));

semilogy(SNR,mean(bErr'),'b', SNR,Theory_awgn, 'ro-');

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Hanojhan Rajahrajasingh 2022-9-28

Thank you so much.

Hanojhan Rajahrajasingh 2023-2-9

In the above code channel is set to 1 (h), if I try to uncomment the below line of code and generate a random channel then blue curve representing the simulated value becomes a straight line. What is causing this issue? Why can't the channel be used?

% h=randn(L,1)+j*randn(L,1); % Generate random channel

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