# HELP! How can i solve this array incompatible size issue

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I was trying to combine two signals and caculate the bit error rate and plot the graph but it shows error at line 30 with Arrays have incompatible sizes for this operation. Can anyone help me please. I am new to matlab. Below is the code.

clc;

clear all;

close all;

% Parameters

fs = 1000; % Sampling frequency

fc = 100; % Carrier frequency for BPSK modulation

T = 1; % Duration of the signals

t = 0:1/fs:T-1/fs; % Time vector

% SNR for channel in dB

SNRdB = 0 : 32;

% Get SNR Valur, SNRdB = 10*log(10) (signalpower/noise power)

SNR = 10.^(SNRdB/10);

%Data bits

N = 10^5;

x = randsrc(1,N,[0,1]);

%BPSK data generation

bpsk_modulated = 1-2*x;

% Generate Interference Signal (e.g., sinusoidal interference)

interference_frequency = 50; % Frequency of the interference signal

interference_amplitude = 0.5; % Amplitude of the interference signal

interference_signal = interference_amplitude * sin(2*pi*interference_frequency*t);

% Combine BPSK Signal with Interference

size(bpsk_modulated)

size(interference_signal)

x_BPSK = bpsk_modulated + interference_signal;

%AWGN noise

n = randn(1,N);

for k=1:length(SNR);

%Assume that noise follow the gaussian distribution, the (0,1). here

%the veriance (sigma squre = 1 and mean = 0), so that noise power = 1

y = (sqrt(SNR(k)) * x_BPSK) + n;

% We need to find which bits has changed with noise ( -1 -> +1 , +1 ->

% -1) in the transmitted channel

noisy_bits = y.*x_BPSK;

% Get indices of the currupted bits by noise

index_currupted = find((noisy_bits)<0);

% Get no of currupted bits by noise

NumOfError_bits(k) = length(find(index_currupted));

end

%BER calculation

ber= NumOfError_bits/N;

%Simulation results

figure;

%Practical

prac = semilogy(SNRdB, ber, 'b*-','linewidth', 1);

hold on;

%Theoritical

theoritical = qfunc(sqrt(SNR));

theo = semilogy(SNRdB,theoritical,' r+-','linewidth',1);

xlabel("SNR in dB");

ylabel("Bit Error Rate(BER)");

legend ([prac theo], {'Practical','Theoritical'});

grid on;

datacursormode on;

##### 2 Comments

Fangjun Jiang
on 27 Mar 2024

see the output of size() prior to the error.

The size of the two matrix is different.

### Accepted Answer

Chunru
on 27 Mar 2024

Make the change: N = length(t);

If you need larger N, thant T in your code to a larger value.

% Parameters

fs = 1000; % Sampling frequency

fc = 100; % Carrier frequency for BPSK modulation

T = 1; % Duration of the signals

t = 0:1/fs:T-1/fs; % Time vector

% SNR for channel in dB

SNRdB = 0 : 32;

% Get SNR Valur, SNRdB = 10*log(10) (signalpower/noise power)

SNR = 10.^(SNRdB/10);

%Data bits

%N = 10^5;

N = length(t);

x = randsrc(1,N,[0,1]);

%BPSK data generation

bpsk_modulated = 1-2*x;

% Generate Interference Signal (e.g., sinusoidal interference)

interference_frequency = 50; % Frequency of the interference signal

interference_amplitude = 0.5; % Amplitude of the interference signal

interference_signal = interference_amplitude * sin(2*pi*interference_frequency*t);

% Combine BPSK Signal with Interference

%whos

x_BPSK = bpsk_modulated + interference_signal;

%AWGN noise

n = randn(1,N);

for k=1:length(SNR);

%Assume that noise follow the gaussian distribution, the (0,1). here

%the veriance (sigma squre = 1 and mean = 0), so that noise power = 1

y = (sqrt(SNR(k)) * x_BPSK) + n;

% We need to find which bits has changed with noise ( -1 -> +1 , +1 ->

% -1) in the transmitted channel

noisy_bits = y.*x_BPSK;

% Get indices of the currupted bits by noise

index_currupted = find((noisy_bits)<0);

% Get no of currupted bits by noise

NumOfError_bits(k) = length(find(index_currupted));

end

%BER calculation

ber= NumOfError_bits/N;

%Simulation results

figure;

%Practical

prac = semilogy(SNRdB, ber, 'b*-','linewidth', 1);

hold on;

%Theoritical

theoritical = qfunc(sqrt(SNR));

theo = semilogy(SNRdB,theoritical,' r+-','linewidth',1);

xlabel("SNR in dB");

ylabel("Bit Error Rate(BER)");

legend ([prac theo], {'Practical','Theoritical'});

grid on;

datacursormode on;

##### 4 Comments

Chunru
on 27 Mar 2024

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