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Observer
Observer
551 Views
Registered: ‎10-26-2018

LDPC IP simulation and matlab missmatch

I am using the example design for LDPC IP with the following paramters: 
Standard: DoCSIS 

Operation: Decode 

Algorithm: Normalized MinSum

And I am simulating this core against its bit level accurate MATLAB model (provided with the core) 
I am fixinig the configuration between both runs however I am getting missmatch results between MATLAB reference model and IP RTL simulation. Any ideas how to match their results? 

 

 

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Moderator
Moderator
532 Views
Registered: ‎08-01-2007

回复: LDPC IP simulation and matlab missmatch

The C-Model should match IP core simulation, check if the parameters can match, if the data input can match.

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Observer
Observer
519 Views
Registered: ‎10-26-2018

回复: LDPC IP simulation and matlab missmatch

The only thing I am concered about is the input scaling, it is not that clear in the product guide. 
It says that input should be scaled to -7.75 to 7.75 even though each llr is represented in 8 bits(6,2) which spans from -31.75 to 31.75.

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Xilinx Employee
Xilinx Employee
462 Views
Registered: ‎09-18-2018

回复: LDPC IP simulation and matlab missmatch

Hi @momran ,

Can you please specify how the LLR is calculated. LLR should be calculated as mentioned in the PG281. [ LLR = (Pr=1/Pr=0)]

The LLR calculation in MATLAB function is generally inverse to what is mentioned in PG281. [ LLR = (Pr=0/Pr=1)]

The MEX-model have an inbuilt saturation function to limit the LLR within the range, so user may not be concerned about it. Also the sc_idx=12 (0.75) is a good starting point for the decoder operation.

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Observer
Observer
409 Views
Registered: ‎10-26-2018

回复: LDPC IP simulation and matlab missmatch

I have fixed the noramlziation factor for both. 
I will check the LLR calculation in the MATLAB. 

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Observer
Observer
407 Views
Registered: ‎10-26-2018

回复: LDPC IP simulation and matlab missmatch

Also can you specify where in the pg280 it says that LLR in the c or MATLAB model the LLR is calculated as P(0)/P(1)

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Xilinx Employee
Xilinx Employee
401 Views
Registered: ‎09-18-2018

回复: LDPC IP simulation and matlab missmatch

Hi @momran ,

What I meant to say was if the LLR function from MATLAB library is used, then this LLR will be generally inverted to LLR calculation required as in PG281.

LLR calc should be P(1)/P(0) for both IP and Mex model. How is the LLR computed in both these models in your design ?

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Observer
Observer
369 Views
Registered: ‎10-26-2018

回复: LDPC IP simulation and matlab missmatch

I am not using LLR function from MATLAB library. 
I am using the MEX model that comes with the Xilinx LDPC IP and nowhere in the pg280 it says that LLRs are caculated differently, hence they should be the same.

Also the model is bit accurate so it should be matching excatly the hardware output, given the configuration is the same. 

My question about the normalization, if I choose a scaling factor of 12, what effect should it do for the input LLRs

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Visitor
Visitor
256 Views
Registered: ‎07-17-2019

回复: LDPC IP simulation and matlab missmatch

Have you found a solution? I am also getting a mismatch is simulations on the encoder side of things.

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