Information loss on a LDPC decoded bitstream - Modulation Toolkit

[gkhnclk123]

Hi everyone,,

I am using LDPC channel coding in my project. As  you know, The LDPC blocks of labview Modulation toolkit uses parity check matrices at the transmitter and receiver to encode and decode a  bitstream. However, I recognized that there are some inconsistency in terms of the size of the input/output bitstream. For ex, I am using a parity check matrix with size of 144x576. Let’s say that the size of our bitstream to be encoded is 1000 bits. The encoded bitstream  has size of 1152 bits, which is 2 times of 576, in this case. After decoding the 1152 bits, I get a decoded output bitstream with size of 864. The original data is truncated and we are losing about 140 bits of our data. You can check this results by using MT LDPC Encode-Decode example application by changing the parameters.

It is urgent that we have to solve this information loss problem. What do you suggest for this problem?

Best,

[gkhnclk123]

The output of the MT LDPC Encode-Decode  examples is attached.

Thanks,

[fromm8]

Hello gkhnclk123

Why are you using that matrix with size 144X576?

You should use an appropriate LDPC matrix. Please check information about this algorithm and how you should construct this matrix. For this example, if m is a submultiple of Message Bits you are going to get the same number for Decoded Bit count.

Regards

Frank R.

[gkhnclk123]

Hi fromm8,

I have to use this matrix and it is not an ordinary parity check matrix. It is used in the Wimax standart. As far as I understand, the encoded bitstream has a lenght with the multiple of 576-144=432, so that the decoded bit stream has same length with original bitstream.

Thanks,

Gokhan

[fromm8]

Hello gkhnclk123

So you cannot change the LDPC matrix. Can you use 1296 message bits?

Regards

Frank R.