problem with qam

[EDIT: 20110525 12:21 CDT - reformat - WDR]

hi all,

i have a problem with my code for qam

i getting error on line 37

% Define parameters.
M = 16; % Size of signal constellation
k = log2(M); % Number of bits per symbol
n = 3e4; % Number of bits to process = 30,000
Fd=1;Fs=1; %Input message sampling frequency, output message sampling frequency
nsamp = 1; % Oversampling rate
% Signal Source
% Create a binary data stream as a column vector.
x = randint(n,1); % Random binary data stream
% Plot first 40 bits in a stem plot.
stem(x(1:40),'filled');
title('Random Bits');
xlabel('Bit Index'); ylabel('Binary Value');
% Bit-to-Symbol Mapping
% Convert the bits in x into k-bit symbols.
xsym = bi2de(reshape(x,k,length(x)/k).','left-msb');
% Stem Plot of Symbols
% Plot first 10 symbols in a stem plot.
figure; % Create new figure window.
stem(xsym(1:10));
title('Random Symbols');
xlabel('Symbol Index'); ylabel('Integer Value');
% Modulation
odd=real(xsym);
even=imag(xsym);
A=1;
Ts=1;                    %dec
fs=200;                  %Hz
fc=2;                    %Hz
Df=1/Ts;
A=1;                     %volt
S=[];
t1=[];
t=0:1/fs:Ts ;            %sec
for i=1:n/2                % לולאה שמציגה את כל ה-M
     s_t=A*(odd).*(cos(2*pi*fs*t))+(even).*(sin(2*pi*fs*t));
     S=[S,s_t];
     t1=[t1,t];
     t= t( length(t)):1/fs:t(length(t))+Ts ;
end
     figure;
     plot (t1,S)
     xlabel ('t')

       ylabel ('Amp[volt]')
       xlim ( [0,4*Ts] )

[Walter Roberson]

Which line is line 37, and what is the error message?

[Walter Roberson]

By the way,

t= t( length(t)):1/fs:t(length(t))+Ts ;

can be rewritten as

t = t(end):1/fs:t(end)+Ts;

[Sarthak Garg]

xsym = bi2de(reshape(x,k,length(x)/k).','left-msb');

this is the error...Can you fix it?

[Walter Roberson]

I need to know the error message

Answer 1

[Walter Roberson]

bi2de() cannot produce imaginary numbers, so even = imag(xsym) is going to produce a vector of zeros.

Please recheck your code in this regard.

Answer 2

[yossi]

[EDIT: 20110526 07:53 CDT - reformat - WDR]

ok i change the script but now i getting thous error:

??? Error using ==> times
Matrix dimensions must agree.

the script:

Error in ==> qam at 36
     s_t=odd.*cos(2*pi*fs*t)+even.*sin(2*pi*fs*t);

% Define parameters.
M = 16; % Size of signal constellation
k = log2(M); % Number of bits per symbol
n = 3e4; % Number of bits to process = 30,000
Fd=1;Fs=1; %Input message sampling frequency, output message sampling frequency
nsamp = 1; % Oversampling rate
% Signal Source
% Create a binary data stream as a column vector.
x = randint(n,1); % Random binary data stream
% Plot first 40 bits in a stem plot.
stem(x(1:40),'filled');
title('Random Bits');
xlabel('Bit Index'); ylabel('Binary Value');
% Bit-to-Symbol Mapping
% Convert the bits in x into k-bit symbols.
xsym = bi2de(reshape(x,k,length(x)/k).','left-msb');
% Stem Plot of Symbols
% Plot first 10 symbols in a stem plot.
figure; % Create new figure window.
stem(xsym(1:10));
title('Random Symbols');
xlabel('Symbol Index'); ylabel('Integer Value');
% Modulation
odd=xsym(1:2:end, :);
even=xsym(2:2:end, :);
A=1;
Ts=1;                    %dec
fs=200;                  %Hz
fc=2;                    %Hz
Df=1/Ts;
A=1;                     %volt
S=[];
t1=[];
t=0:1/fs:Ts ;            %sec
for i=1:n/2                % לולאה שמציגה את כל ה-M
     s_t=odd.*cos(2*pi*fs*t)+even.*sin(2*pi*fs*t);
     S=[S,s_t];
     t1=[t1,t];
     t= t( length(t)):1/fs:t(length(t))+Ts ;
end
     figure;
     plot (t1,S)
     xlabel ('t')
       ylabel ('Amp[volt]')
       xlim ( [0,4*Ts] )

[Walter Roberson]

cos(2*pi*fs*t) with fs a scalar value, will have the same length as t.

odd will have a very different length.

Similar problems exist for even and the sin() expression.

You cannot use .* to multiply matrices of very different lengths.

Perhaps what you want there is

s_t=odd(i).*cos(2*pi*fs*t)+even(i).*sin(2*pi*fs*t);