Friday, 14 October 2016

CAT 16, LimeSDR competition and all that jazz

For those that have not seen it here is the talk I gave at CAT16. I also have it on my
YouTube channel but the BATC version includes the Q&A at the end.

Since that talk was given I have been adding some more features to the program.
I have added better filtering in the FPGA for low symbol rates on DVB-S2,
unfortunately to make that change I had to remove support for the tighter roll-off
filters as there was no room left in the FPGA.

I plan to add a couple of more features to the program in the next couple of weeks
then put the software into maintenance mode so I can work on other projects.

As some of you know my entry was selected for the latest
LimeSDR design challenge
The last few days I have been researching how actually to implement an RF
channel simulator. I now have some ideas on how to generate random
numbers and how to give them a normal distribution. I also now
know the difference between Rayleigh and a Rician fading channels.  
The first is a channel where there is no direct path
(for example an HF ionospheric channel) and the latter is where there is a
direct line of sight path as well as other reflected paths. The Rician
channel is more like the type of channels we see with terrestrial DATV.

Originally I hoped to do most of the maths in the FPGA but now I am beginning to
think a better solution might be to move a lot of the maths into the host and do the
hard real time stuff on the FPGA. There appears to be a lot of log, sine and cosine
operations involved in producing the fading models and while Altera provide mega
functions to do these things they consume quite a lot of space and valuable multipliers.
At the end of the day what will be needed will be a trade-off between precision,
bandwidth, number of paths and ease of development.

It is an interesting project never the less and should make use of some of the maths
I learn't when I took some O.U courses a few years ago. At least I can
understand most of the concepts that are described in the various internet articles
I have found on the subject. I am sure if I get really stuck I can get help with the
maths. Anyone that helps will get a credit on the project! I may have an A level
in maths, studied Electronics at University and taken some O.U refresher courses
but that doesn't make me an expert.

I plan first to simply produce software than can set the S/N of a signal. That is not
actually as simple as it first seems but it will be a start. 

1 comment:

  1. Hello Charles,

    Thank you for the informative presentation. Looking forward to the LimeSDR implementation along with the ARM board for portable use.

    Mike KM7MH