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Re: [Discuss-gnuradio] GPS L2C Implementation on E100 FPGA

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] GPS L2C Implementation on E100 FPGA
Date: Thu, 01 Sep 2011 13:18:19 -0400
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0) Gecko/20110812 Thunderbird/6.0

On 01/09/2011 1:08 PM, Nick Foster wrote:
On Thu, Sep 1, 2011 at 8:42 AM, Wolfarth, Ryan <address@hidden> wrote:
Hi all,

I am generating my masters thesis proposal and I have a few questions about the capabilities of the E100 and the feasibility of my project.  I have read other posts to gather information, but correct me if anything I've determined is wrong.  My goal is to implement an 8 channel GPS L2C receiver on an FPGA.  I am interested in doing this with the E100 since I may be able to take advantage of the ARM processor as well.  Can anyone with experience in this area provide advice?

I would like to use the RFX1200 to receive the L2C signal since it has better performance characteristics than the DBSRX.  This would prevent me from first acquiring L1 signals to aid in acquisition, so I propose using preloaded almanac data to estimate SV position/Doppler frequency.  This would reduce the number computations when acquiring L2 CM code.  The end result only has to go as far as to decode the navigation bits: I will not need a position solution.

The root of my question is: does the FPGA on the E100 have enough space to handle this project?

Does it sound like I'm on the right track?

Sounds like a very interesting project. I have two suggestions:

1. The SBX daughterboard has a better noise figure (5dB vs. 8dB typ.), with better linearity, and would be better suited for GPS work, especially if you aren't using front-end filters. SBX will also receive both the L1 and L2 frequencies.
In the specific case of GPS, most active GPS antennas (which is what most people use) have GPS-optimized LNAs with very low noise figure,
  and easily enough gain to swamp the noise figure of whatever receiving hardware is downstream, so the noise figure of the receiver
  board is largely irrelevant in most cases with GPS active antennae.

In my radio astronomy work (where Tsys is absolutely critical), as long as the downstream receiver has a noise figure below about 15dB or
  so, I generally don't care what it is, since I use a tuned vLNA in front of it.  It's a very similar situation with GPS.

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