[amsat-bb] JAMSAT report, language support for GRC, Phase 4 Ground update+strategy+test plan, GNU Radio Conference

Sat May 11 17:02:19 UTC 2019

LoRA is super cool! We've been following FossaSat with great interest and
were very fortunate to have an opportunity to hear Julian Fernandez present
about the project in person.

We have several options for supporting modes other than our "native" 4-ary
minimum shift keying uplink. We anticipate channels about 100kHz wide. More
bandwidth needed, you bond them together. If you want, for example, a
number of narrowband modes supported within that channel, then each channel
can be treated like a band that can be subdivided into subchannels.

If we approach this like it's a subdivided band, traffic needs to be
recognized and properly transmitted through the system.

The set of technologies for that on Phase 4 Ground is called "ARAP" or
amateur radio access point. The number of modes recognized depends on how
ambitious we get with the number and type of signals recognized, and that
depends on how much horsepower we have in the payload receiver. The basic
requirement is to support FM HTs and P25 radios. We want to digitize and
then tag these signals as legacy FM traffic and pass them through the
system.

We have demonstrated this type of approach at Symposium in the past, where
traditional HT traffic is digitized, turned into tagged CODEC2 frames, and
then the multiple HT traffic is combined and repeated as a single digital
signal. The receiver selects one of the channels present in the composite
signal. You're not necessarily limited to selecting only one channel. If
you want a conference, then multiple channels would be selected. This leads
right to a need for a good user interface.

Being able to recognize, digitize, and include a variety of signal types?
Sounds awesome to me! To mean it means we need to take on autonomous signal
identification, see what machine learning can do for us, and all sorts of
other really neat stuff that is in the domain of cognitive radio. We have a
solid beginning here and some working code. There's an excellent
implementation of modulation type recovery using machine learning that we
expect to rely upon. Books like Signal Analysis for Radio Monitoring by
Roland Proesch and the Autonomous Receiver book from JPL provide a lot of
leverage here too!

The most important question to me is "What would you like to see the end
result do?" When you think about a successful LoRA integration, what does
that look like?

-Michelle W5NYV

On Sat, May 11, 2019 at 9:30 AM Pedro Converso <pconver at gmail.com> wrote:

> Hello Michelle,
>
> Impresive information, thanks! for sharing.
>
> Do you know if some decoder is or will be implemented for LoRa ?.
>
> This due the growing activity, future satellites on LoRa & Balloon
> usage of LoRa.
>
> Thanks in advance,
>
> 73, LU7ABF, Pedro
>
> On 5/11/19, Michelle Thompson via AMSAT-BB <amsat-bb at amsat.org> wrote:
> > My daughter Geneva and I had a wonderful time at JAMSAT Symposium in
> March
> > 2019! There was a wide variety of talks about so many different
> payloads, a
> > very special banquet dinner, adventures in Kyoto and Osaka, visits to ham
> > radio stores, getting to see a new ICOM radio up close, lots of Pokemon,
> a
> > Fire Festival, and making so many new friends. We were welcomed and will
> > never forget the hospitality.
> >
> > A big part of Symposium was the GNU Radio Workshop by Imamura-san. It was
> > an honor to share how we on Phase 4 Ground use GNU Radio in our
> > presentation on Sunday morning.
> >
> > GNU Radio is a digital signal processing framework for software-defined
> > radio. It’s the software that tells the hardware in your radio what to
> do.
> > We need to be able to quickly and easily set up a software-defined radio
> to
> > do whatever modulation and coding we want during development of new
> > payloads and new ground stations. In many cases, GNU Radio is the exact
> > right tool for this job.
> >
> > GNU Radio Companion is a Graphical User Interface that allows us to drag
> > and drop functions onto a canvas. We click block outputs to connect to
> > block inputs. When we do this, it creates a directed graph that
> implements
> > radio functions. The signals flow from beginning to end. Each block
> > modifies the signal, as if it was part of a circuit. The flow graph looks
> > something like a block diagram combined with a software flowchart. GNU
> > Radio has software variables. It can adapt to signal conditions and user
> > input.
> >
> > The workshop at JAMSAT was held after the last talk on Sunday. It was
> > several hours of hands-on training. Participants brought their own
> > computers, installed GNU Radio, and created useful radio flow graphs that
> > worked with real hardware. Several experiments were done in order.
> > Imamura-san kept everything organized through a set of projected slides
> > that had clear instructions. Optimizations and customizations were made
> so
> > that participants could see how they can use GNU Radio to achieve their
> > goals. The hardware included RTL-SDRs and Plutos. Imamura-san also
> > demonstrated a live video transmission from the podium.
> >
> > Something that I noticed in the workshop was how much easier it would be
> if
> > this community could use the software if it was in Japanese. I decided to
> > see what was required. After some homework and reading, I got a very
> simple
> > example working and understood the basic workflow. I asked JAMSAT if they
> > were interested in a localized version of GNU Radio Companion. JAMSAT
> > responded positively and work began in earnest! It started to become
> clear
> > that after this initial groundwork, that additional languages would be
> much
> > easier. I reached out to AMSAT-DL next, and got an enthusiastic response
> > there too. As of today, both German and Japanese are in progress! I
> > received an inquiry about Portuguese following the initial announcement
> > that the main menus had successful translations in testing. It's now on
> the
> > list after we fully test localization for German and Japanese.
> >
> > While at JAMSAT, I was able to give a status update for Phase 4 Ground.
> >
> > Phase 4 Ground is a broadband digital microwave system for both
> terrestrial
> > and space use. It complies with both ITAR and EAR open source and public
> > domain carve-outs, so it’s open to participation worldwide. All
> engineering
> > is published as it’s created. All are welcome to participate.
> >
> > Phase 4 Ground is best suited for GEO and HEO satellite missions. The
> > uplink is frequency division multiple access. We use a 5GHz uplink. The
> > regenerative repeater payload receives the uplink signals, digitizes
> them,
> > multiplexes them, and processes them into DVB-S2 and DVB-S2X frames. The
> > downlink is 10GHz. DVB-S2 is Digital Video Broadcasting Satellite 2nd
> > edition. The X stands for extensions down in to Very Low SNR modulation
> and
> > codings. Very Low SNR is of interest to hams, so we include the extension
> > to the main standard DVB-S2.
> >
> > We use both pilots and short frame lengths in order to make the receiver
> > implementation as easy as possible. Pilot tones are optional, and there
> are
> > medium and long frames available in the standard.
> >
> > There is a recommended order to receive DVB-S2/X frames. The first stage
> of
> > the demodulator is symbol timing recovery. We have to figure out the best
> > possible time to measure, or take a snapshot, of the received signal. The
> > receiver does not know the phase of the transmitter clock. We will not be
> > automatically coordinated with it. It's not just a problem with phase,
> > either. The receiver and transmitter may disagree in terms of the period
> of
> > the clocks, or we might have jitter, or we might have drift. We have to
> > analyze the received waveform and synchronize our receiver clock to the
> > transmitter clock that is “hidden” in the received signal. Then, once we
> > are synchronized, we sample that symbol and report the results.
> >
> > Doing this gives us a reliable value for the received symbol. Now that we
> > have a series of received symbols, we have to figure out the start of the
> > frame. This is done in DVB-S2 (and many other protocols) by sending a
> fixed
> > pattern at the start of every frame. For DVB-S2, this is called a
> Physical
> > Layer Start of Frame sequence. It’s 26 symbols long. This is what we look
> > for. Once we see it, we know where the start of the frame is!
> >
> > Frame synchronization can be done in several ways. There are two
> different
> > methods described in the implementation guidelines for DVB-S2/X. One is
> > relatively simple, using shift registers. The other is bit more complex,
> > using state machines. There are advantages to using the state machine
> > method, but it’s more complicated and expensive. The shift registers is
> > simple and cheap, but gives up a bit of performance. This is the constant
> > balance in digital communications. Performance comes at a cost!
> >
> > Right after frame synchronization, we correct for carrier frequency
> error.
> > First we do a coarse correction. This can be done with a
> delay-and-multiply
> > frequency error detector. Then we do a fine correction. This can be done
> > with something like a feed-forward estimation algorithm. Coarse
> correction
> > is in the MHz, and fine correction is the hundreds of kHz.
> >
> > Next, we do phase recovery. This is to fix any residual frequency offset
> > from the coarse and fine frequency offsets. Phase 4 Ground will support
> all
> > the modulation and codings of DVB-S2/X, but we expect lower order
> > modulations to be more heavily used. This means that a pilot-assisted
> > maximum-likelihood (ML) feed-forward estimator will be the most useful.
> If
> > you compute the average phase of each pilot field, then you can subtract
> > this out and improve the signal. Higher-order modulations will need
> another
> > feedback loop.
> >
> > Automatic gain control is next. AGC can be done in many ways. One way to
> do
> > it depends on the pilot symbols in DVB-S2/X standard. These symbols are
> > sent at regular intervals to provide a known easy-to-receive signal. We
> use
> > these known pilot symbols in order to determine the amplitude
> > multiplication factor for the rest of the signal. Pilot symbols are
> > optional in the DVB standard, but Phase 4 Ground requires them. When the
> > pilot symbols are on, the AGC is listening. When the pilot symbols are
> off,
> > the AGC turns off, and the information from the AGC is used.
> >
> > After AGC, the constellation is decoded. DVB-S2 has a lot of them! There
> > are many techniques to get the bits from the constellations. GNU Radio
> has
> > a very versatile and powerful constellation block.
> > Instead of the usual MPEG transport stream (DVB-S2 is for satellite TV,
> so
> > the content is usually broadcast television signals), we use the more
> > flexible Generic Stream Encapsulation standard from DVB.org. This means
> we
> > have less overhead and complexity, and can handle any digital traffic
> that
> > the amateur operator wants to transmit. It’s just a digital pipe.
> >
> > Phase 4 Ground uses GNU Radio extensively in research and development as
> > well as for archiving and publishing our work. GNU Radio is not just a
> tool
> > to figure things out, but is also a way to define a reference design for
> > the radio.
> >
> > Because Phase 4 Ground is not a bent pipe, the payload is more complex.
> > This complexity needs to be fully tested on the ground before risking
> large
> > digital circuits in space.
> >
> > All the uplink channels are received with a polyphase filter bank. The
> > current polyphase filter bank implementation in GNU Radio needs some
> > updates in order to achieve the speeds and performance that we want. This
> > is an active area of research and development. There have been three
> > efforts over the past three years by various groups that have attempted
> to
> > update and improve the existing working polyphase filter bank in GNU
> Radio.
> > There is some recent good news here! EJ Kreinar reported that his open
> > project (Theseus Cores) has an open source FPGA polyphase channelizer!
> This
> > works with RFNoC. We will experiment with this in our payload design.
> This
> > could fill in a big piece of the system that we need. Check it out here:
> > http://gitlab.com/theseus-cores/theseus-cores
> >
> > Ron Economos and Paul Williamson successfully implemented GSE in GNU
> Radio
> > and in Wireshark. This made it possible to do transport layer testing.
> Ron
> > Economos is the lead author of the DVB blocks in GNU Radio. Improvements
> to
> > GSE continue today. The current focus is improving internetworking
> > functions so that large amounts of data can be more easily handled. We
> > intend to use multicast IP as much as possible, and making sure GSE
> > integrates well with multicast IP is important. The path forward with
> that
> > is in our test plan. You can find our test plan here:
> >
> >
> https://github.com/phase4ground/documents/blob/master/Papers_Articles_Presentations/Papers/P4G%20Testbed%20Proposal.md
> >
> > The error correction in DVB-S2/X is state of the art. There are not many
> > other error correcting codes that are better than Low Density Parity
> Check
> > + BCH. This is a concatenated digital code specified by the DVB standard
> > for S2 and T2 transmissions. We have two open source implementations of
> > LDPC decode for DVB-S2/X. The first one is for graphical processing units
> > and was written by Charles Brain. It was demonstrated at 2017 AMSAT-NA
> > Symposium and at several events following.
> >
> > The second open source implementation is in C by Ahmet Inan and can be
> > found here: https://github.com/xdsopl/LDPC
> > This version has been incorporated into GNU Radio by Ron Economos. This
> can
> > be found here: https://github.com/drmpeg/gr-dvbs2rx
> >
> > The next step for LDPC is to implement and publish an open source version
> > for FPGA.
> >
> > GNU Radio is very important for our voice codec work, uplink modulation
> > experiments, and trying out authentication and authorization schemes. GNU
> > Radio allows us to use a wide variety of off the shelf hardware to
> achieve
> > things that were not possible only a few short years ago. The GNU Radio
> > community has been welcoming, helpful, supportive, friendly, and a source
> > of continually amazing software-defined radio advancements.
> >
> > GNU Radio has an annual conference. In 2018, we held a week-long “Block
> > Party” for DVB-S2/X. We had fun, set up multiple demos, explained
> DVB-S2/X,
> > made the case for open source LDPC, and made progress on DVB-S2
> correlates
> > and GSE. Phase 4 Ground made significant progress due to the generous
> > support of the conference organizers and the community.
> >
> > Learn more about the conference here:
> > https://www.gnuradio.org/grcon/grcon19/
> >
> > Registration for 2019 is open. The conference will be held September
> 16-20,
> > 2019 in Huntsville, AL, USA. There is a poster session, proceedings,
> talks,
> > workshops, contests, and social activities. The theme for 2019 is Space
> > Communications! There are special gifts for space themed content. If you
> > have a GNU Radio project that you want to share, consider making a
> > presentation at or sending a poster to GNU Radio Conference 2019.
> >
> > The collaboration between Phase 4 Ground and JAMSAT has been absolutely
> > stellar and we all look forward to continued enjoyment and success. Next
> > generation payloads will be more complicated with multiplexing and
> advanced
> > digital techniques. We all need to be able to work together,
> > internationally. Open source and public domain is the best way forward.
> > Phase 4 Ground and Open Research Institute are entirely dedicated to
> making
> > this happen. We will be keeping the momentum and progress going. ORI is
> > proud to be an affiliate member of Open Source Initiative
> > https://opensource.org/
> >
> > Join the Phase 4 Ground team! Our work benefits all AMSAT organizations.
> > Our mailing list can be found at our website
> https://openresearch.institute/
> >
> > Write me at w5nyv at arrl.net if you want to join our Slack account. This
> is
> > where daily engineering discussions take place.
> >
> > More soon!
> > -W5NYV
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> > to all interested persons worldwide without requiring membership.
> Opinions
> > expressed
> > are solely those of the author, and do not reflect the official views of
> > AMSAT-NA.
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> >
>