Reusable Software Defined Radio Platform for Micro-satellite

[alexc]

I found this very interesting student thesis

Reusable Software Defined Radio Platform for Micro-satellites
This thesis describes the design and implementation of a software platform for software defined radio (SDR). This platform was to form part of an experimental satellite payload. Several other experiments were also housed on this platfrom and subsequently had to be incorporated into the design. The hardware components of the payload were already determined at the start of the project but firmware had to be created as part of the project. The software platform was based on the Linux kernel. Device drivers had to be designed for the hardware and firmware components. These drivers were designed so that standard Unix utilities could be used to interact with them. This allowed for easy testing of the system and the programs running on it. The use of the platform for modulation and demodulation of analogue signals was demonstrated using a proof-of-concept SDR application.

It's actually flying and has AMSAT designator SO-67. Download the thesis: http://etd.sun.ac.za/handle/10019/1346

[jdp]

Alex,
Do you know if it's flying linux?
(Seems like a power sink).
John

[alexc]

Sorry, I don't have much details about the satellite itself. There is some info here: http://www.amsatsa.org.za/SZASAT.htm
According to that "The Amateur Radio Payload will be operating in conjunction with the University of Stellenbosch Software Defined Receiver project as it will share the VHF receiver and UHF transmitter used by the SDR project." and also other info on the page seems to be consistent with the thesis.

[scasey]

Thanks Alex - good find.

A little background on software-defined radios can be found here:

http://en.wikipedia.org/wiki/Software-defined_radio

It's the increase in single-chip processing power that enables this capability (and the supposed elimination of ancillary radio components).

I know this kind of approach is starting to shape next generation radio instrument for astronomy.

SC

[alexc]

Indeed.
Software defined radios have been around us for quite some time, e.g. WiFi and satellite TV. The exact boundary between software defined radio and hardware defined radio is an active topic of discussion. Some people say that in a true software defined radio analog to digital conversion occurs already at the antenna; however, that definition has little practical use at GHz frequencies with today's technology (remember the Nyquist–Shannon sampling theorem). Thus, for all practical purposes, Wikipedia's definition is a very good one.

It might be a proper time to remind forum members that we have a complete off the shelf, open source software defined radio framework at our disposal:

• GNU Radio – A complete and very mature software development toolkit that provides the signal processing runtime and processing blocks.
• USRP – A flexible and cost efficient hardware platform that can be used with GNU Radio to convert the digital data to radio frequencies (DC to 6 GHz) and vice verse.

Both of these have been mentioned on various occasions here on the forum (see for example Open Source Communication Lab). It's a very exciting cross-disciplanry field where one gets around electronics, RF, mathematics, programming, ... With the open source framework available nothing stands in the way to learn by doing.

[tristancho]

I do like Nyquist stuff, my favorite in telecomm.
Best,
Joshua

[scasey]

Well - what this does is put what previously in the realm of hardware (filters and multipliers) in the realms of software. The first inkling of this was in the development of DSPs. But as processing power has continued to increase (especially in the realm of A/D converters) the radio frequencies for which this technology is applicable has continued to rise (MHz - GHz).

"If a function x(t) contains no frequencies higher than B hertz, it is completely determined by giving its ordinates at a series of points spaced 1/(2B) seconds apart."(1)

Detection of a 100 MHz signal requires sampling the waveform at 200MHz. One does have to worry about the aliasing of high frequencies into the sampled waveform (but I suppose this is accomplished via a low-pass filter at 100 MHz prior to the A/D). With even higher sampling rates, I suppose the low pass filtering is accomplished computationally.

In general, once the problem is cast in the realm of software, it is amenable to open source methodologies.

Aside from WIFI, is there anything in this realm that we can develop and deploy on Monroe's Mark-I lander?

SC

[jdp]

Telemetry might help debug stabilization algorithms.

[alexc]

Detection of a 100 MHz signal requires sampling the waveform at 200MHz. One does have to worry about the aliasing of high frequencies into the sampled waveform (but I suppose this is accomplished via a low-pass filter at 100 MHz prior to the A/D). With even higher sampling rates, I suppose the low pass filtering is accomplished computationally.

Yes, we can get such ADCs for 10-20$, even Giga samples per second, though they are not cheap... There are also other factors to consider, such as computing power. It will sample all frequencies from DC to Nyquist and if you need a high frequency resolution the FFT size will have to be very large for high bandwidth. So it is much more practical to only sample the bandwidth you need and use down conversion / heterodyning instead.

[scasey]

Amazing - USRP is right next door just off of the 101:

http://www.ettus.com/contact

We should think about how this technology is applicable to the mission and on-going prototyping efforts.

SC

[jdp]

We should think about how this technology is applicable to the mission and on-going prototyping efforts.

For completeness... of course Alex's ground station work is based on software defined radio..

[alexc]

We should think about how this technology is applicable to the mission and on-going prototyping efforts.

For completeness... of course Alex's ground station work is based on software defined radio..

Indeed. In fact, it is all based on GNU Radio and USRP-family. You may recall the S-band ground station setup where I added a super low noise preamp to reduce receiver noise figure, but otherwise it was USRP with the DBSRX RF board.

The USRP and GNU Radio can be used as is to create fully functional lab mock-up of a complete TT&C subsystem required for this mission. It can be used for prototyping and experimenting with modulation, error correction, etc. The USRP v1 can function as two independent transceivers and therefore it can provide the functionality of both radios on the lander (one to Earth, one to the rover). Since the hardware is open source, one could later create a flight version should that be feasible.

[alexc]

I moved the ground station discussion to a separate topic – I hope it's okay.

[tristancho]

Sure!
Joshua

[alexc]

The US army also likes GNU Radio: "No-knob" radio: the future of Warfighter communications?

[scasey]

I just noticed that USRP was recently purchased by National Instruments:

- February 5th, 2010 -- Ettus Research LLC has been acquired by National Instruments Corporation. For more information about this exciting development, please see: http://www.ettus.com/ni

That's pretty awesome in my book!

SC

[alexc]

NASA design review passed! We're building three remote satellite control stations and mgmt. center using GNU Radio, Ettus USRP2s, and Linux.

[tristancho]

Yeah!
Joshua