[Discuss-gnuradio] Interest in beamforming and GNSS receivers

[Carles Fernandez]

Hi everybody,

I discovered GNU Radio few months ago, in a before-go-to-bed surfing. I found it very interesting, but complicated because of my poor skills in programming Python or C++. I'm doing research on Global Navigation Satellite Systems (GNSS) receivers, and I'm used to code everything in Matlab. Night after night, I've been browsing the documentation and making humble steps: I installed Ubuntu on my laptop, followed the -excellent, also for dummies like me- guide for installing all the software, read diagonally the documentation and played with sample codes. Some Hello Worlds, some problems with the audio module, getting used to read the mailing list, feeling astonished by the intense activity of this community... nothing new, I guess.

Now I want to take it more seriously. I've seen that both python and c++ have very well done matrix algebra libraries, and that's exactly what I need for my research (you can call me naive). I would like to implement a GNSS receiver (in the wide sense) based on an antenna array and play with beamforming algorithms and weird RF front-end architectures (direct RF, IF sampling, etc). My main concern is synchronization, concretely I want to implement some signal processing algorithms in a real receiver in order to assess their impact in the whole system, testing them with real data. I've been working in the development of some algorithms that -theoretically- performs better in multipath environments, but I want to see if this is true beyond classical academic benchmarks.

What is the state of GNSS receivers development in GNU Radio? I have found some expressions of interest in the Internet, but nothing concrete. I'm willing to start it from the scratch, but it is nonsense to reinvent the wheel. I would like to put in contact with other people interested on these topics. Taking advantage of your patience, I have some other questions (and you will see my newbie approach):

- I've seen some statements about "beamforming is possible". To what extend? I'm trying to understand the multi-antenna code example, but it is possible to use the four ADC at the same time? How well are they synchronized? it is possible to compute the weight values in software and perform the multiplication in the FPGA at real time? There is any other major bottleneck than algebraic weight computation time?

- My first target is a "traditional" L1 C/A code GPS receiver. I guess that I can choose between RFX1200 and a BasicRx with an external front-end. Have someone worked in the connection of GNU Radio with gpstk?

- It is 32 MHz the maximum bandwidth available? Will the USRP 2.0 increase this bandwidth? It is possible to decrease the resolution of the ADCs and/or increase their sampling frequency?

- I also would like to work on the Galileo signal structure and the new L2CS GPS signal, mostly on the correlators. I have a background on signal processing, but I'm strongly matlab-shaped in what about programming is concerned. I'm willing to learn, but am I pointing to the right direction? 


If someone could enlighten me in some of this questions, it would be greatly appreciated. Sorry for the long text.


Best regards,
Carles Fernandez