Re: [Discuss-gnuradio] On the convolutional code performance of gr-ieee802-11

[Ron Economos]

Made a mistake. The DVB-T receiver is not part of the 3.7.8 release. It's a recent commit on the master branch (3.7.9git).

Ron

On 09/15/2015 01:31 AM, Ron Economos wrote:

The author of gr-dvbt looked at this issue when he developed the DVB-T receiver. Here's a blog entry on his findings.

http://yo3iiu.ro/blog/?p=1393

He benchmarked the IT++ decoder in last place.

IT++ = 2-3 Mbps
gr-trellis = 5 Mbps
Karn C = 7-8 Mbps
gr-dvbt = 39-40 Mbps

The gr-dvbt receiver is now part of GNU Radio as of the last release, 3.7.8. The SSE2 viterbi decoder module is here:

https://github.com/gnuradio/gnuradio/blob/master/gr-dtv/lib/dvbt/dvbt_viterbi_decoder_impl.cc

In addition, I believe there's another decoder in gr-fec. I'm not very familiar with it, so maybe someone else can comment on it. Looks like it's in this module:

https://github.com/gnuradio/gnuradio/blob/master/gr-fec/lib/cc_decoder_impl.cc

Ron

On 09/15/2015 12:47 AM, Jeon wrote:

I've measured time taken by convolutional decoding in gr-ieee802-11. The module is using Punctured Convolutional Code class from IT++ library (http://itpp.sourceforge.net/4.3.0/classitpp_1_1Punctured__Convolutional__Code.html)

I've used chrono (chrono.h, chrono) to measure time taken. You can see how I made it from the following page (https://gist.github.com/gsongsong/7c4081f44e88a7f4407a#file-ofdm_decode_mac-cc-L252-L257)

I've measure time with a loopback flow graph (w/o USRP; examples/wifi_loopback.grc)

The result says that it takes from 5,000 to 30,000 us, which is 5 to 30 ms to decode a signal with a length of 9,000 samples (samples are either 1 or -1.)

* Test environment: Ubuntu 14.04 on VMWare, 2 CPUs and 4 GB RAM allocated

* Host environmetn: Windows 7 with i7-3770 3.7 GHz

Since I am not familiar with error correcting codes, I have no idea how large the order of time taken is. But I think that one of the most efficient decoding algorithm is Viterbi and that IT++ must use it.'

Then I  can deduce that CC decoding takes a quite long time even though the algorithm (Viterbi) is very efficient. And is it a natural limitation of software decoding and SDR?

Another question comes that, the commercial off the shelf (COTS) Wi-Fi device achieves really high throughput and that must be based on super faster CC decoding. Is that because COTS is using heaviliy optimized FPGA and dedicated decoding chips?

Regards,

Jeon.