Got two minutes? Then we have a Phase 4 Ground video report for you! :+)
Phase 4 Ground and GNU Radio
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, and GNU Radio Companion can help us do this. 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 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.
GNU Radio comes with a very large number blocks included. When you install GNU Radio, these blocks come for free! The first type of block is a source block. This brings the digital samples, from the radio hardware attached to the computer, into the GNU Radio flow graph. The second type of block is a sink block, which consumes signals. Sink blocks include things like saving a signal to disk, an audio output, oscilloscopes, spectrum analyzers, time sequences, or video. In between the sources and the sinks are all the radio functions that we need to make our radios work. Filters, amplifiers, decoders, demodulators, counters, constellations, costas loops, synchronizers, and more! You can make your own custom blocks or modify an existing block.
If you install GNU Radio using PYBOMBs, then you can add additional blocks from outside GNU Radio very easily. PYBOMBS works on Linux.
One of the most useful GNU Radio Recipes for our community is gr-satellites, by Dr. Daniel Estévez. There are a lot of satellites supported in this module. For an introduction, please see the source code repository here: https://github.com/daniestevez/gr-satellites.
The introduction also covers how to submit telemetry to the projects that have requested this.
Other great open source satellite communications projects include Dan Cajacob’s base station network, Alexandru Csete’s gqrx and gpredict programs, Libre Space Foundation’s SatNOGs (satellite network on the ground) with RTL-SDR and GNU Radio, and PE4WJ Es’Hail2 (QO-100) uplink, beacon tracker and LNB drift correction flowgraphs.
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 the received signal. We don’t know what the transmitter clock is doing! We will not be coordinated with it. We may even be off a bit 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 well-known 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.
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 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.
One of the proposals coming out of JAMSAT 2019 was localization of GNU Radio Companion for the Japanese language. Work has begun. The first step is to make sure that all Japanese characters can be displayed in GNU Radio Companion. This means going through the codebase and removing anything that prevents Japanese characters from being freely displayed. GNU Radio project leadership is very supportive of the project. We will do our best on this! We will need help reviewing and perfecting the language support in GNU Radio Companion.
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. 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 mailing list can be found at our website https://openresearch.institute/ Write Michelle Thompson [email protected] to join our Slack account. This is where daily engineering discussions take place.
Dear friends and fans of GNU Radio,
GNU Radio Conference celebrates and showcases the substantial and remarkable progress of the world’s best open source digital signal processing framework for software-defined radios. In addition to presenting GNU Radio’s vibrant theoretical and practical presence in academia, industry, the military, and among amateurs and hobbyists, GNU Radio Conference 2019 will have a very special focus.
Summer 2019 marks the 50th anniversary of NASA’s Apollo 11 mission, which landed the first humans on the Moon. GNU Radio Conference selected Huntsville, AL, USA as the site for GNU Radio Conference 2019 in order to highlight and celebrate space exploration, astronomical research, and communication.
Space communications are challenging and mission critical. Research and development from space exploration has had and continues to have far-reaching effect on our communications gear and protocols.
Please join us September 16-20, 2019 at the “Huntsville Marriott at the Space & Rocket Center” hotel for the best technical conference of the year.
Registration and an online and mobile-friendly schedule will be posted at the conference web site:
Call for All!
We invite developers and users from the GNU Radio Community to present your projects, presentations, papers, posters, and problems at GNU Radio Conference 2019. Submit your talks, demos, and code! Please share this Call for All with anyone you think needs to read it.
To submit your content for the conference, visit our dedicated conference submission site at:
If you have questions or need assistance with OpenConf, or have content that doesn’t quite fit and you want to talk it over, please write [email protected]
Topics may include but are not limited to:
Space (including ground stations)*
Digital Signal Processing
*special focus awards given to all accepted work with Space as a topic.
Please visit our booth in the expo area at HamCation in Orlando, Florida 8-10 February 2019.
Thank you to European Space Agency and MyriadRF for giving Open Research Institute the opportunity to get LimeSDR Minis into the hands of some very amazing people doing open source space communications research and development.
ORI and Phase 4 Ground are very proud to present the following international recipients. We commit to supporting, enabling, promoting, and publicizing their work.
Sahana Raghunandan, USA
As part of discussions at the 2018 GNU Radio Conference DVB-S2X Block Party, one of the functionalities of the demodulator that was identified as needing additional review and testing was the frame synchronization and symbol timing recovery loop. The goal of targeting LimeSDR is to modify and test existing GNNU Radio flowgraphs related to this subsystem of the demodulator. In order test this functionality independently, it is assumed that signal captures at the input to the baseband demodulator will be available.
Sahana Raghunandan is a researcher at Virginia Tech and an independent consultant focusing on satellite and terrestrial systems engineering including waveform design & implementation and interference analysis for spectrum management. Her experience includes design and FPGA-based implementation of waveforms for satellite broadband modems and satellite ground systems architecture with emphasis on modeling and simulation of cross layer optimization techniques. She has also worked on platforms and architectures for software and cognitive radio networks. Her research experience also includes design of modules for radar data acquisition, system integration of radar depth sounders and application of synthetic aperture radar techniques for ice sheet tomography.
Jeremy Reeve, New Zealand
Jeremy has been working on VHF and L-band LNA designs. He has been running qucs simulations to look at optimum noise matching and stability circles and the like. His goals are to contribute RF hardware and baseband/FPGA content. He expects to be able to work with his educational institution to create a project that will result in quality open source publications.
Edson W. R. Pereira, Brazil
Edson is an open source advocate and extremely active in amateur radio. He implemented a GUI (SDR-Shell) for Bob McGwier’s and Frank Brickle’s DttSP SDR, has contributed code for Joe Taylor’s WSJT-X, and has been a primary contributor on many other projects.
He is a lead maintainer for the Phase 4 Ground polyphase filter bank repository and is heavily involved with Phil Karn KA9Q’s development effort for multicast IP SDR innovations and implementations.
Matias LU9CBL, Argentina
Matias is active in many areas of open source space communications. He is part of a group working to build a ground station design that supports a wide variety of satellite missions.
He has a SatNOGS ground station that is making rapid progress through the development portal. He is working to build and test antennas to add to this station.
He is active in his club station (LU4AA), which plans to run a station with an azimuth and elevation rotor from Yaesu, 2 crossed Yagis for VHF, and 2 crossed Yagis for UHF. Multiple fixed station will be added for remote control, and the station will be added to the SatNOGS network after it is functional.
Matias is active on SatNOGS forums and has a blog at lu9cbl.blogspot.com.
It is critically important to increase the number of stations and people involved in satellite communications from the southern hemisphere. Matias is deeply committed to publishing, sharing, and supporting others that are working in open source space communications.
David Fannin, USA
David Fannin KK6DF works closely with Phase 4 Ground volunteer David Viera and wrote the code for David Viera’s LMX2594 oscillator and CW beacon project. David Viera demonstrated this system at GNU Radio Conference 2018 to great acclaim.
David Fannin has worked on a number of oscillator and SDR projects, his github account is https://github.com/dfannin, and he is committed to open source development in advanced digital communications.
Open Research Institute and Phase 4 Ground are honored to be given the chance to put advanced software defined radio hardware like the LimeSDR Mini into the hands of active developers across the world. We are ready to help make the most of this very generous donation to open source space communications work.
HamSci, or Ham Radio Science Citizen Investigation, advances scientific research and understanding through amateur radio activities. Primary cultural benefits include the development of new technologies along with providing excellent educational opportunities for both the amateur community and the general public.
The HamSci Space Weather System is a HamSci project. HamSci Space Weather Stations form a distributed radio network dedicated to space weather research. HamSci Space Weather Stations produce receiver data from transmitters associated with coordinated observations. Sensors range from ground magnetometers, to ionospheric sounders, to lightning detectors and more. The diversity of sensor types means a wide variety of radios can participate.
A collaboration between HamSci and Tucson Amateur Packet Radio (TAPR) was proposed at the Digital Communications Conference (DCC) on 14-16 September 2018 in Albuquerque, New Mexico. Discussions about custom software-defined radio hardware designed, built, and sold by TAPR as HamSci Space Weather Stations began at the conference and continued though a Google Group.
HamSci presented at the TAPR DCC Sunday Seminar. Slides introducing possible sensor types from that presentation are reproduced throughout the full document linked above.
The receiver network employs a wide variety of sensor types. Combining sensor data from disparate sources, when the end result has greater certainty, accuracy, or quality than if the data was used individually, is called sensor fusion. The HamSci Space Weather System, as proposed above, can be affordably accomplished through sensor fusion.
For example, a $150 dedicated lightning detector on a Raspberry Pi in Florida, USA can participate in this network with a $6331 USRP X310 station sampling at highest rate and bandwidth in Madrid, Spain. The inexpensive data from the lightning detector may enhance the data from the expensive radio and increase scientific knowledge. Another example is a set of five inexpensive radios configured as ionosondes. The data combined is better than any one station’s individual contribution.
Open Research Institute (ORI) proposed an open source cubesat as part of the network. Observing from ground and space simultaneously provides substantial additional scientific value. The receiver network can be coordinated to make scheduled observations that align with satellite passes. This can be enabled with SatNOGS open source software. See https://satnogs.org/ for more information about this open source satellite network on the ground.
ORI believes that the central challenge of the HamSci Space Weather Station project is not the radio hardware. It is how the radios are interconnected, what metadata is accepted, how observations are scheduled, how the interactions between different sensor data is modeled, and how the large quantity of data is handled, organized, and re-used over time. This is the Data Plane.
We don’t like keeping secrets. However, we do have some secrets.
The Phase 4B payload, and the other related projects that we have actively supported (like CQC) all require launches.
We have a launch with the Wide Field of View payload with the Air Force. The good news is how well we did in getting engineering approval for this launch. We have a ride. The bad news is the cost of the launch. It is $6 million and they can guarantee us about one year and not even guarantee us it will be over the United States. We have decided we cannot ask the community for $6M to support this launch. It’s just not a good deal for US hams.
Fortunately there’s been a lot of work going on behind the scenes for additional launches. This work has been going on for a while.
I can’t share the details. I can say that our prospects have never been better. Anyone following along and helping the project, anyone that has been with us through a lot of challenging experiences, deserves to know that we are absolutely serious, focused, and unrelenting in obtaining multiple launches for this technology.
Traditionally, an amateur launch would be announced and then a payload developed. With modern digital technologies taking significantly longer development time than legacy technologies, and with opportunistic short-notice launches becoming more the norm, this design pattern really can’t work for us. That’s one of the reasons we need to work hard, now, as if the launch was imminent. Howie DeFelice and I wrote an article for QEX about this.
Working hard without a launch date is a lot to ask of people that are not getting paid and in some cases not being given the support or recognition they should be getting.
In the new year, we’ll be doing just that and asking for more in terms of technology demonstration and development from the team. The next big technology demonstration will be HamCation, and the most ambitious goal for that is to have LDPC working on an FPGA with interactive controls. This is the heart of the coding part of the receiver.
A GNU Radio LDPC demonstration can be seen in a recent video report, and the GPU version can be run by anyone with a late model Nvidia GPU.
Until HamCation, our goal is to get the air interface into the best possible shape. We need to capture the excellent progress we’ve made and make it as easy as possible for upcoming payloads to say “Yes!” to Phase 4 Ground.
There’s plenty going on. Progress is good. Launch prospects are part of that good news. A lot of the work is invisible during the negotiating process, but we are working as hard as we can to make it more than worth the wait.
Thanks to the enormous generosity of MyriadRF, Phase 4 Ground has some hardware help!
Five LimeSDR Mini Kits have been given to Phase 4 Ground for open source satellite communications development work.
We want to get these into as many hardworking hands as possible! Write me today with your need and let’s get you up and running.
I recently set up a LimeSDR Mini with GNU Radio with one of our list members and it went very well. This is a wonderful SDR. The LimeSuite GUI allows prototyping with what feels like every register setting on the controller. Performance is very good.
For a talk about LimeSDR (and the extended frequency range chip) from Microwave Update 2018 from Mike Seguin N1JEZ, please see https://youtu.be/F76BzezuCmw
LDPC-BCH decode on the FPGA is a current area of great interest for us. LDPC-BCH is the forward error correction for DVB-S2/X. But, we are also interested in doing more with Polar codes. There is at least one open source satellite payload project that has specified Polar forward error correcting codes. There is very little open source work here, it’s cutting edge, and Polar codes are specified for use in 5G communications. Polar codes are the first family of error-correcting codes that achieve the Shannon capacity for a wide range of communication channels with efficient encoding and decoding.
The FPGA on the LimeSDR mini is the Intel MAX 10 (10M16SAU169C8G 169-UBGA). How far can we take it?
What else needs doing? How about a SatNOGS station with the LimeSDR mini? A proof of concept of Phase 4 Ground authentication and authorization scheme? Handling the Generic Stream Encapsulation streams properly from the downlink for amateur communications? Plenty to do! Dive in and we will help you.
Contact Michelle W5NYV [email protected] to sign on and get kitted up.
An open source Low Density Parity Check decode from Phase 4 Ground is working for DVB-S2, DVB-S2X, and DVB-T2 in GNU Radio, thanks to the efforts of Ahmet Inan, Ron Economos, and Charles Brain.
This is a big step forward for open source satellite communications.
Video report here:
Out of Tree (OOT) GNU Radio module by Dr. MPEG here:
Decoder by Ahmet here:
Here’s a demonstration of a 3D printed Cassegrain antenna system for 122GHz amateur radio. It was presented in the demonstration room at Microwave Update 2018.
122 GHz is an amateur radio band. There’s activity and distance records and some contesting. 122GHz has significant attenuation due to atmospheric absorption. Specifically, oxygen gets in the way.
I’ve been working on a 3D printed rig for 122GHz. This was sparked by a request from Alan Devlin VK3XPD for a 3D printed subreflector for a Cassegrain dish. People generally get by with a flat subreflector, but you can get better performance if it’s a hyperbolic curve matched to the feed and parabolic dish.
So what is 122GHz good for? Well, car radar for one thing. That’s what Silicon Radar does. They’re a company in Germany, and they have a radar development board and Millimeter Wave Integrated Circuits (MMICs) for 122GHz. The patch antennas are actually on the chip. The dev boards were used in this experiment. They send out a wide chirped radar signal and measure the return. There is software provided by Silicon Radar that runs the dev board.
The goal for Microwave Update 2018 was to verify a 3D printed Cassegrain antenna design for 122GHz amateur use. This design was adapted from the Customizable Cassegrain dish by drxenocide on Thingiverse. Link is in the show notes.https://www.thingiverse.com/thing:1935824
This thing creates a customizable Cassegrain Reflector dish. It was created using the equations from the paper by Peter Hannan, “Microwave antennas derived from the Cassegrain telescope,” in IRE Transactions on Antennas and Propagation, vol. 9, no. 2, pp. 140-153, March 1961.
The antenna parts were designed, the 3d model specified, the parts were printed, the resulting pieces were metallized (with MG Chemicals conductive paint), and then the parts combined into their final form.
Design files and papers can be found here: https://github.com/Abraxas3d/122GHz
The assemblies were taken to Microwave Update 2018 and set up in the demonstration room. Here’s what happened next.
So what were the results? Here’s some screenshots from the Silicon Radar software with and without the Cassegrain antenna installed over the stock lens in the development board.
And, there’s more. Please read Mike Levelle’s wonderful report on his efforts with the Silicon Radar chip in building a simple 122GHz transceiver. Link is in the show notes.
Mike has a tremendous amount of expertise and enthusiasm for the higher microwave bands and is a fantastic mentor.
What’s next? Building a radio! Stay tuned and stay on the air!