Thursday, December 3, 2009

Still alive and working hard


despite not writing anything in here, I have been working on a new version of the dongle and on many other things.

First, I'm now in hardware design: look at the new signal samplers, my personal joy and pride :)

Fig.1: Primo USB dongles: very flexible GNSS data samplers.

These have the same functionality of the old CPLD version, but are more slick and robust. Eheh!

Second, I'm playing with a new platform:

Fig.2: The Gumstix Overo Earth runs our software GNSS receiver.

Above is one of our dongles connected to a Gumstix OVERO earth carrier board. Not only the OMAP3503 can reliably record the raw GNSS stream, but it is also capable of processing 16 GPS -or Galileo BOC(1,1)- channels in real-time, continuously!
To do that, quite some assembly code had to be written (especially for the FFTs!). The NEON core within the Cortex-A8 is a wonderful machine, and the learning curve with gcc is very acceptable. I won't give more details of how we did it, just want to share -again- my joy and pride :)

To finish, this time I HAVE TO thank all my colleagues-friends working hard with me at NSL, and the opensource community of the Beagleboard and the BeagleSDR project.


P.S.: Next post is coming soooon...

Friday, February 20, 2009

Ticking the last box: Glonass L1

We had to wait long enough for some RF filters. Half a hour after receiving them, the Maxim MAX2769 which is fitted on our NSL USB dongle tuned correctly on Glonass frequency. I had to quickly make up a bit of Matlab code, and off I went acquiring Russian birds over Nottingham skies.
Result: 8 satellites. Pictures attached.

Fig. 1: The signal characteristics show some interference peak, and the gain should to be increased a bit.

Fig. 2: The typical histogram of acquired channels. This time is Glonass.

Some details of the channels:

Fig. 3: Details about the individual channels.

I hope the MAX2769 has no secrets any more :)

The next post will be something new, about a new exciting Software Defined Radio GNSS receiver!


Sunday, February 1, 2009

An interesting signal modulation

With GIOVE-B, the second satellite of the IOV Galileo constellation, a new modulation is being experimented, the CBOC(6,1,1/11).
With the CPLD version of NSL dongle and a bit of software, I did get the result below.. is not smooth and as beautiful as Septentrio's one (, but it demonstrates some interesting capabilities already.

Fig.1: Tracking the CBOC(6,1,1/11) with a BOC(1,1) replica, a BOC(6,1) replica, and the sum of of the two.

In a couple of week I would like to show something else... let's see.


Monday, January 19, 2009

Did I mention that...

did I mention that with the CPLD version of the dongle we can receive Beidou-M1, the first satellite of the Chinese global navigation system?
The bird transmits a BPSK(2) on a 1561.098 MHz carrier. Slightly modifying the Matlab code from the book "A Software-Defined GPS and Galileo Receiver. A single frequency approach" by Kai Borre, Dennis M. Akos, Nicolaj Bertelsen, Peter Rinder, and Soren Holdt Jense, I got the following results:

We then decoded some subframes :)


And soon I will publish some more results...