Can Anyone help me to solve this error?Error using * Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.

here's the full code

numAntennasTx = 256;       % Number of antennasTx
numAntennasRx = 16;        % Number of antennasRx
numBits = 10000000;        % Number of random bits
ModulationOrder = 16;      % 16QAM
snrValues = 0:5:40;        % Range of SNR values

%% Generate Random Bits
bits = randi([0 1], numBits, 1);

%% Convolutional Encoding
trellis = poly2trellis(7, [171 133]); % Example trellis
codedBits = convenc(bits, trellis);

%% Modulation
mod_symbols = qammod(codedBits, ModulationOrder, 'InputType', 'bit', 'UnitAveragePower', true);

%% Ensure the number of symbols can be reshaped properly
numSymbols = length(mod_symbols);
paddingSymbols = mod(numAntennasTx - mod(numSymbols, numAntennasTx), numAntennasTx);
mod_symbols_padded = [mod_symbols; zeros(paddingSymbols, 1)];

%% Reshape modulated symbols to fit Tx antennas
mod_symbols_reshaped = reshape(mod_symbols_padded, numAntennasTx, []);

%% Precoding
H = (randn(numAntennasRx, numAntennasTx) + 1i * randn(numAntennasRx, numAntennasTx)) / sqrt(2*numAntennasRx); % Channel matrix

% Regularized Zero Forcing (RZF) Precoding
lambda = 0.01; % Regularization parameter
WRZF = (H' / (H*H' + lambda*eye(numAntennasRx)));

% Phased Zero Forcing (PZF) Precoding
angle_H = angle(H);
phase_shift = exp(-1i*angle_H);
H_pzf = H .* phase_shift;
WPZF = (H_pzf' / (H_pzf*H_pzf'));

%% Apply Precoding
size(WRZF)

ans = 1x2

256 16

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size(mod_symbols_reshaped)

ans = 1x2

256 19532

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precodedBitsRZF = WRZF * mod_symbols_reshaped; % precoding RZF

Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To operate on each element of the matrix individually, use TIMES (.*) for elementwise multiplication.

precodedBitsPZF = WPZF * mod_symbols_reshaped; % precoding PZF

%% Without Precoding
precodedBitsWP = mod_symbols_reshaped; % No precoding

%% OFDM Modulation with Precoding
OfdmSymbolsRZF = ifft(precodedBitsRZF, [], 2); % OFDM modulation with RZF precoding
OfdmSymbolsPZF = ifft(precodedBitsPZF, [], 2); % OFDM modulation with PZF precoding
OfdmSymbolsWP = ifft(precodedBitsWP, [], 2);   % OFDM modulation without precoding

%% Channel AWGN
berRZF = zeros(1, length(snrValues)); % Initialize BER results for RZF
berPZF = zeros(1, length(snrValues)); % Initialize BER results for PZF
berWP = zeros(1, length(snrValues));  % Initialize BER results for no precoding

for i = 1:length(snrValues)
    snr = snrValues(i); 
    noiseVar = 1 / (10^(snr/10));
    
    % Transmit through channel (AWGN) for RZF
    rxSymbolsRZF = awgn(H * OfdmSymbolsRZF, snr, 'measured') + sqrt(noiseVar/2) * (randn(size(OfdmSymbolsRZF)) + 1i * randn(size(OfdmSymbolsRZF)));
    % Transmit through channel (AWGN) for PZF
    rxSymbolsPZF = awgn(H * OfdmSymbolsPZF, snr, 'measured') + sqrt(noiseVar/2) * (randn(size(OfdmSymbolsPZF)) + 1i * randn(size(OfdmSymbolsPZF)));
    % Transmit through channel (AWGN) without precoding
    rxSymbolsWP = awgn(H * OfdmSymbolsWP, snr, 'measured') + sqrt(noiseVar/2) * (randn(size(OfdmSymbolsWP)) + 1i * randn(size(OfdmSymbolsWP)));
    
    %% OFDM Demodulation
    % Serial to Parallel Conversion
    receivedSymbolsRZFSerial = reshape(rxSymbolsRZF, [], numAntennasRx).'; % Serial to parallel conversion
    receivedSymbolsPZFSerial = reshape(rxSymbolsPZF, [], numAntennasRx).'; % Serial to parallel conversion
    receivedSymbolsWPSerial = reshape(rxSymbolsWP, [], numAntennasRx).'; % Serial to parallel conversion
    
    % Perform OFDM demodulation for RZF
    rxSymbolsIFFTRZF = fft(receivedSymbolsRZFSerial, [], 2); % FFT
    % Perform OFDM demodulation for PZF
    rxSymbolsIFFTPZF = fft(receivedSymbolsPZFSerial, [], 2); % FFT
    % Perform OFDM demodulation for no precoding
    rxSymbolsIFFTWP = fft(receivedSymbolsWPSerial, [], 2); % FFT
    
    %% Parallel to Serial Conversion
    rxSymbolsDemod_RZF = reshape(rxSymbolsIFFTRZF.', [], 1); % Parallel to serial conversion
    rxSymbolsDemod_PZF = reshape(rxSymbolsIFFTPZF.', [], 1); % Parallel to serial conversion
    rxSymbolsDemod_WP = reshape(rxSymbolsIFFTWP.', [], 1);   % Parallel to serial conversion
    
    % Remove the padded symbols before demodulation
    rxSymbolsDemod_RZF = rxSymbolsDemod_RZF(1:end-paddingSymbols);
    rxSymbolsDemod_PZF = rxSymbolsDemod_PZF(1:end-paddingSymbols);
    rxSymbolsDemod_WP = rxSymbolsDemod_WP(1:end-paddingSymbols);
    
    % QAM demodulation
    demodBitsRZF = qamdemod(rxSymbolsDemod_RZF, ModulationOrder, 'OutputType', 'bit', 'UnitAveragePower', true);
    demodBitsPZF = qamdemod(rxSymbolsDemod_PZF, ModulationOrder, 'OutputType', 'bit', 'UnitAveragePower', true);
    demodBitsWP = qamdemod(rxSymbolsDemod_WP, ModulationOrder, 'OutputType', 'bit', 'UnitAveragePower', true);
    
    % Calculate the Bit Error Rate (BER)
    berRZF(i) = sum(demodBitsRZF ~= codedBits(1:end-paddingSymbols)) / numBits;
    berPZF(i) = sum(demodBitsPZF ~= codedBits(1:end-paddingSymbols)) / numBits;
    berWP(i) = sum(demodBitsWP ~= codedBits(1:end-paddingSymbols)) / numBits;
end

%% Display Results
fprintf('Bit Error Rate (RZF Precoding):\n');
disp(berRZF);
fprintf('Bit Error Rate (PZF Precoding):\n');
disp(berPZF);
fprintf('Bit Error Rate (Without Precoding):\n');
disp(berWP);

%% Plotting the results
figure;
semilogy(snrValues, berRZF, 'bs-', 'LineWidth', 2);
hold on;
semilogy(snrValues, berPZF, 'gs-', 'LineWidth', 2);
semilogy(snrValues, berWP, 'rs-', 'LineWidth', 2);
xlabel('SNR (dB)');
ylabel('Bit Error Rate (BER)');
legend('RZF Precoding', 'PZF Precoding', 'Without Precoding');
title('Massive MIMO 256x16 Antennas with RZF and PZF Precoding');
grid on;

[Gita]

here's the error

Error using *

Incorrect dimensions for matrix multiplication. Check that the number of

columns in the first matrix matches the number of rows in the second matrix.

To perform elementwise multiplication, use '.*'.

Error in Main (line 39)

precodedBitsRZF = WRZF * mod_symbols_reshaped; % precoding RZF

[Shashi Kiran]

Hi @Gita,

Can you provide the reference paper you used for writing this code?

From my initial review, it seems that during pre-coding, you should not use the channel directly. Instead, you should use Singular Value Decomposition of H (16x256) to get the matrix V (256x256) and use V in place of H.

If you could provide some documentation regarding the code, it would be helpful in addressing the issue further.

[Torsten]

@Gita

What do you expect as result when you try to multiply WRZF (256x16) with mod_symbols_reshaped (256x19532) ?

precodedBitsRZF = WRZF.' * mod_symbols_reshaped 

would work, but we don't know if this is what you want.