topic Re: 7/8 LDPC channel decoding in RF Measurement Devices

7/8 LDPC channel decoding

scnsRF — Wed, 16 May 2012 14:46:52 GMT

Hi,

I'm considering approaching my boss for a copy of the modulation toolbox but I need to determine if it will suit our needs before doing so.

We have recently installed some receivers in support of a new satellite coming on line (proposed launch June,2013) that utilizes the CCSDS 131.1-O-2 recommendation for LDPC encoding and decoding. The RF-ICD specifies a base( 8160,7136) 7/8 rate code with a LDPC codeword message area of 892 octets and a 1024 octet parity.

Will the modulation toolbox allow me to assemble a simulator and decoder that will meet these parameters?

Thanks in advance,

Mike

Re: 7/8 LDPC channel decoding

JVP — Sun, 13 Jul 2025 20:40:29 GMT

Hello Mike,

To evaluate the NI Modulation Toolkit please see the following link:

http://digital.ni.com/demo.nsf/websearch/503ecadcb8968c96862579290053a7ef?opendocument

Best Regards,

Jignesh P

Re: 7/8 LDPC channel decoding

andrewd220 — Mon, 18 Jun 2012 12:46:04 GMT

What did you end up doing with this if you don't mind me asking? =D

I'm downloading the modulation toolkit now but I'm guessing there isn't a 7/8 ldpc decoder contained in it.

Re: 7/8 LDPC channel decoding

JVP — Sun, 13 Jul 2025 20:40:45 GMT

Hello,

If you take a look at the Modulation Toolkit Shipping Examples Developer Zone article you will find all the encoding and decoding examples. LDPC is actually in the list of examples.

Best Regards,

Jignesh P

Applications Engineer

Re: 7/8 LDPC channel decoding

KittF — Tue, 26 Jun 2012 15:13:52 GMT

The LDPC in the Modulcation Toolkit does not allow for even weighting (j must be odd). Many LDPC encoders are even weighted, with 4 being common (two 1's per row, two 1's per column). Standard CCSDS LDPC Encoding and Decoding, specifically the (8160, 7136) flavor in linked spec, is one of these. http://public.ccsds.org/publications/archive/131x1o2e2.pdf

Questions: Why must j be odd? Is this a limitation in the algorithm NI has chosen? Is there an option for even? Is there any means of implementing CCSDS LDPC (8160, 7136) using NI MT?

Thanks.

Re: 7/8 LDPC channel decoding

lis@jiang — Wed, 27 Jun 2012 18:55:26 GMT

Hi Nemo,

I've asked your questions to our R&D team and am waiting for an answer back. I'm not sure that we can provide an answer for "Why must j be odd?" but we'll try to determine if even options are available.

Thanks,

Lisa

Re: 7/8 LDPC channel decoding

scnsRF — Thu, 28 Jun 2012 12:33:10 GMT

May be that the ratio (8160,7136) is a shortened code word to make up for the fact that the entire codeword ratio (8176,7156) is not an even divisible by 32?

it'll be interesting to see what the actual answer is going to be

Re: 7/8 LDPC channel decoding

lis@jiang — Fri, 29 Jun 2012 22:04:04 GMT

Just an update: Still waiting on some developers for an answer. It's possible that the functionality for even will be incorporated in the future, but at this time, there is no timeline for such an event.

I will update with more information whenever I get that.

Thanks,
Lisa J

Re: 7/8 LDPC channel decoding

lis@jiang — Mon, 09 Jul 2012 23:21:48 GMT

I'm still not sure why only odd values are supported, but as far as a workaround goes, can you create your own matrix rather than using the VI to generate one?

Lisa

Re: 7/8 LDPC channel decoding

andrewd220 — Tue, 10 Jul 2012 14:09:39 GMT

I've tried that and the Encode LDPC VI produces no output and no error. Just an empty data stream.

Re: 7/8 LDPC channel decoding

lis@jiang — Tue, 10 Jul 2012 17:23:28 GMT

Can you provide the array you generated? (It might be easiest to attach the VI at this point.)

I've gone ahead and filed a Corrective Action Request to add support for even j values, however, there is currently no timeline for when this will be implemented. I'll take a look at functionality for creating your own matrix.

Thanks,

Lisa J

Re: 7/8 LDPC channel decoding

andrewd220 — Wed, 01 Aug 2012 17:36:12 GMT

Lisa,

Array for parity check matrix can be generated from the spec in the link Nemo provided on 06-26-2012 10:13 AM.

Any updates from your R&D team?

-Andrew

Re: 7/8 LDPC channel decoding

lis@jiang — Thu, 02 Aug 2012 17:01:40 GMT

Hi guys,

I have filed a Corrective Action Request (CAR#: 362571) as per our R&D team's request. While there is no timeline in which this new feature will be implemented and released, they will be looking into the issue.

Thanks,

Lisa J

Re: 7/8 LDPC channel decoding

andrewd220 — Mon, 12 Aug 2013 17:48:42 GMT

Lisa,

Any luck on your corrective action?

I'm still interested in this functionality from a year ago 😃

Has anyone at least looked at it?

Thanks!

Re: 7/8 LDPC channel decoding

Leah-L — Tue, 13 Aug 2013 15:35:43 GMT

Hi andrewd220!

I looked up the status of the CAR that was filed for this bug. Currently R&D is still working on this, however, I am unable to give any details on the timeline for this fix.

Please let me know if you have any additional questions!