Latest Hackfest

GNU Radio
1

We had our latest GNU Radio Hackfest last week at Ettus R… It was
a
fantastic week with a lot of good work getting done. If you’re
interested
in what we are working on and to get a glimpse of some of the new things
we’ll be rolling out in the next few GNU Radio versions, find our
working
notes here:

http://gnuradio.org/redmine/projects/gnuradio/wiki/Hackfest1403-2

Thanks to everyone who came and hacked with us. Thanks, too, to Ettus
Research for being great hosts for our motley band of developers!

Tom

2

Dear Tom,

I have read about the FEC work done during the Hackfest, so this would
be an appropriate time to bring this up. We have participated in the
Darpa Spectrum Challenge, and developed some good and fast codes.
Specifically, we have a generic convolutional code encoder and decoder
(any R and K is supported, tailbiting can be enabled), with fast SSE
implementation. In the attached BER figure we have used R=1/8, K=9 and
length = 3 bytes = 24 bits for encoding headers. The speed is not much
worse than the spiral generated one. More importantly, we have a
specially crafted version of a repeat accumulate coder/decoder that
can be quickly decoded with SSE. On the figure we have used rates 1/3,
1/2, 1/3 and 4/5 with a payload size of 1440 bytes. On the orbit-lab
machines (core-i7) our SSE code can decode more than 1000 packets per
second on a single core.

I plan to release this code under the GPL (and maybe under an MIT
license as well) after I have a paper written up about it. So the
question would be:

  1. how to incorporate this into gnuradio (separate OOT or built in)
  2. how to deal with puncturing (we have some good generic solution)
  3. how to deal with variable packet lengths and variable rates (have
    some ides)
  4. how mature is the FEC API, can it be modified if needed?

Best,
Miklos

3

On Thu, Apr 3, 2014 at 3:05 PM, Miklos M.
[email protected]wrote:

specially crafted version of a repeat accumulate coder/decoder that
can be quickly decoded with SSE. On the figure we have used rates 1/3,
1/2, 1/3 and 4/5 with a payload size of 1440 bytes. On the orbit-lab
machines (core-i7) our SSE code can decode more than 1000 packets per
second on a single core.

I plan to release this code under the GPL (and maybe under an MIT
license as well) after I have a paper written up about it. So the
question would be:

Miklos,

This sounds like a fantastic result.

  1. how to incorporate this into gnuradio (separate OOT or built in)

If it’s to go into GNU Radio, it would only be license GPLv3, like the
rest
of the code base. Also, we require a copyright transfer from you. We can
discuss and work on that on the side.

Also, with the use of SSE, we’d want to separate the code into a VOLK
kernel with a generic and SSE implementation. That way, we’re not
restricting ourselves to certain platforms. And then, we can extend it
to
other SIMD architectures.

  1. how to deal with puncturing (we have some good generic solution)

We let the FEC API encoder and decoder blocks handle the puncturing and
depuncturing separate from the coders themselves. I think they are
generic
enough, but we’d probably want to update them if they don’t fit every
scenario.

  1. how to deal with variable packet lengths and variable rates (have some
    ides)

The FEC API encoder/decoder blocks don’t care about the packet lengths
as
long as the coders themselves can handle it. Right now, our working
example
uses fixed packet length, but (I don’t think) that’s a requirement.
Might
have to double-check this. Same should go for the rate.

In the FEC API world, there is an FEC encoder and decoder block that
sets
just a few parameters. One of them is the variable that actually defines
the encoder and decoder code, and those variables are designed to work
with
the API. So most of this is on how these variable blocks are built.

  1. how mature is the FEC API, can it be modified if needed?

It’s mature in that we’ve tested it out-of-tree with a number of
situations. But as we’re moving it into GNU Radio, there’s a window here
to
update it. Best done before we merge it into master, though, which will
set
the API until 3.8 of GNU Radio. It’d be great if you could take my
current
github repo branch “fecapi” and see about fitting your coder into it.
That’ll get us some feedback before we merge into master.

Best,
Miklos

Thanks!
Tom

4

On Mon, Apr 7, 2014 at 11:52 AM, Miklos M.
[email protected]wrote:

be an appropriate time to bring this up. We have participated in the
second on a single core.

with a generic and SSE implementation. That way, we’re not restricting
ourselves to certain platforms. And then, we can extend it to other SIMD
architectures.

I have thought about it. I know that all SSE code is currently
separated into a VOLK kernel (with the exception of FFT which is
coming from a separate library). Of course you can do that, but then
most of the gnuradio blocks will be just wrappers around the VOLK
kernels.

Yeah, so what?

Seriously, this is a good thing, not a problem. The more we can wrap up
into volk, the easier it is to use on multiple platforms and reuse in
other
situations. We won’t put any SIMD code into GNU Radio at this point that
doesn’t come through VOLK since VOLK handles the mechanics of dealing
with
multiple platforms and different available SIMD architectures.

blocks and reorders (permutes) them and extends them with zero at
arbitrary places. Basically it takes a map (integer list between -1
and N-1) where -1 means “zero out” and 0 through N-1 means some
element of the input. Probably it is harder to explain than to see it.
Anyhow, the puncturing design is important and you have to omit
encoded (unsigned char) hard bits and insert soft (float) zeros.

Having the block interleaver would be nice. We have the generic
puncturer
block, as I said, but if you have them roped together, seems like (I’m
guessing) it should be easy to use this block as an interleaver and/or a
puncture block.

I’m assuming you have the deinterleaver/depuncture block as well?

In the FEC API world, there is an FEC encoder and decoder block that sets
just a few parameters. One of them is the variable that actually defines
the
encoder and decoder code, and those variables are designed to work with
the
API. So most of this is on how these variable blocks are built.

Do you have a working coder/decoder pair with this API?

https://github.com/trondeau/gnuradio/tree/fecapi

We’re still messing around with things right now, so this is all
work-in-progress right now (in other words, it’s a bit messy).

get

us some feedback before we merge into master.

Probably the best would be to put my code (separate it from the rest)
into a OOT module for you to see it, and then we pick up the
discussion from there.

Miklos

Sure. If you can fit your encoder/decoder blocks into FEC API-style
variables, it’ll be easy to use within our system and would make vetting
it
for incorporation easier, too.

Tom

5

Hi Tom,

On Fri, Apr 4, 2014 at 12:21 AM, Tom R. [email protected] wrote:

(any R and K is supported, tailbiting can be enabled), with fast SSE
license as well) after I have a paper written up about it. So the

If it’s to go into GNU Radio, it would only be license GPLv3, like the rest
of the code base. Also, we require a copyright transfer from you. We can
discuss and work on that on the side.

Also, with the use of SSE, we’d want to separate the code into a VOLK kernel
with a generic and SSE implementation. That way, we’re not restricting
ourselves to certain platforms. And then, we can extend it to other SIMD
architectures.

I have thought about it. I know that all SSE code is currently
separated into a VOLK kernel (with the exception of FFT which is
coming from a separate library). Of course you can do that, but then
most of the gnuradio blocks will be just wrappers around the VOLK
kernels.

  1. how to deal with puncturing (we have some good generic solution)

We let the FEC API encoder and decoder blocks handle the puncturing and
depuncturing separate from the coders themselves. I think they are generic
enough, but we’d probably want to update them if they don’t fit every
scenario.

I have a generic interleaver / puncturer that takes chunks of memory
blocks and reorders (permutes) them and extends them with zero at
arbitrary places. Basically it takes a map (integer list between -1
and N-1) where -1 means “zero out” and 0 through N-1 means some
element of the input. Probably it is harder to explain than to see it.
Anyhow, the puncturing design is important and you have to omit
encoded (unsigned char) hard bits and insert soft (float) zeros.

just a few parameters. One of them is the variable that actually defines the
encoder and decoder code, and those variables are designed to work with the
API. So most of this is on how these variable blocks are built.

Do you have a working coder/decoder pair with this API?

  1. how mature is the FEC API, can it be modified if needed?

It’s mature in that we’ve tested it out-of-tree with a number of situations.
But as we’re moving it into GNU Radio, there’s a window here to update it.
Best done before we merge it into master, though, which will set the API
until 3.8 of GNU Radio. It’d be great if you could take my current github
repo branch “fecapi” and see about fitting your coder into it. That’ll get
us some feedback before we merge into master.

Probably the best would be to put my code (separate it from the rest)
into a OOT module for you to see it, and then we pick up the
discussion from there.

Miklos