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curve of BER in ldpc codes in matlab

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electronical

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hello every body.
I wrote a plan for ldpc code an get these result but it is different ehit result that recived from papaers.can any boby tell me why the result is different?
 

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zorro

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Hi electronical,

Please provide mode details about your code and what result do you expect.
By the way, it would be better to place this post in the "Digital Communication" forum.
Regards

Z
 

electronical

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hello .
I wrote these code for n=1210 and frame_num=2000, code rate=0.5;
I used these code for channel
[m,n]=size(H);
sigma=sqrt(10^(-SNRindB1/10));
msg = randint(1,n-m);
c=rem(msg*G,2);
modObj = modem.pskmod('M',2,'InputType','Bit');
modulatedsig = modulate(modObj, c);
receivedsig = awgn(modulatedsig, SNRindB1(I), 0); ...
% Compute log-likelihood ratios (AWGN channel)
demodObj = modem.pskdemod(modObj,'DecisionType','LLR', ...
'NoiseVariance',sigma);
LLR = demodulate(demodObj, receivedsig);

and I expect nearly these result :at low value SNR ,bit error rate value be about 10^(-1)
 

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zorro

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Hi,

it would be necessary to check the results against theory for this particular code (have you the theoretical result?)
Nevertheless, your first result seems to give a result better to the theoretical capacity limit for AWGN channel with rate=1/2 at Eb/No=0dB (see figure).
I would check the simulation.
Regards

Z
 

electronical

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thanks zorro
my result is nearly linear but the result of theoretical is nonlinear.
I want to know my recieved result is true?
if not can you tell me why ?
the problem is about channel or my code?
my code is simple
by regegards
 
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zorro

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Hi electronical,

You result seems to violate an information theory limit (see my previous post).
In order to see if your simulation of the channel is correct, you should check its performance without coding (i.e. pure BPSK) and compare with the result of theory.
Regards

Z
 
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