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[Discuss-gnuradio] smooth transition from acquisition to tracking

From: Achilleas Anastasopoulos
Subject: [Discuss-gnuradio] smooth transition from acquisition to tracking
Date: Tue, 06 May 2008 12:04:35 -0400
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

Hi all,

I have the following question that came up in our attempt to implement an GPS receiver.

Suppose samples are coming in from the USRP at a sampling rate of Fs
and in the beginning we grab N such samples (say 2msec worth of data) to process them for initial acquisition of frequency/code epoch. Now suppose that the task of acquisition is quite heavy so that it takes approximately time T (say for example ~10sec) to be completed.
At the end of this process we have an estimate of the code delay "tau"
In the meantime samples are accumulating on the incoming queue of our block.

We see two problems with that:
1) the queues will overflow so samples will start being dropped and
2) once the above happens, then the estimate "tau" is meaningless

One solution that I see to this is during the acquisition task to periodically interupt the processing and consume a known ammount of data (say equal to the code period) so that 1) does not happen and 2) we have a way to relate the estimate "tau" to the incoming data after acquisition.

I wanted to ask
a) if we are on the right track,
b) if there is a simple method to implement such interupts, and
c) if there is an easier way to do that other than the one suggested.


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