|Subject:||Re: [Discuss-gnuradio] Fwd: Correlation Estimator in 3.7.10|
|Date:||Tue, 4 Oct 2016 14:23:24 -0600|
For what it’s worth, I’ve resorted to two hacks.
1) where the sum of consecutive correlation mag squared samples is compared to 4*detection, I’ve gone to 8*detection. With the block threshold set to 0.999999, this results in threshold levels (compared to the peak correlation value) of 32 to 78 %.
2) I added a variable to track the max cross-correlation magnitude for samples that exceed the 8*detection threshold. Then i compare those (peak) samples to that max/4 and those that are above, I let pass.
I had to do the latter because I was seeing false correlations at the very end of my TDMA packets. I think they are due to the tx-to-rx transient I see with my B200mini. My thought is that the transient is slow (looks like a DC offset) and may create a false peak when part of it is convolved with the reference sync sequence. Anyway, implementing #2 made that problem go away.
The other thought I have for my particular application is to disabled the Correlation Estimator (CE) when I know there will be no sync sequence. Since I have a TDMA system with a GPSDO/clock governing the slot scheme, I can generate an “enable” pulse from my MAC and use it to control the CE block.
The big flaw with my approach in 1) and 2) is that I am not accounting for variable receive power such as you’d expect in a multi-radio TDMA system… first things first, though, gotta see packets received reliably under Tx constant power.
Steven Knudsen, Ph.D., P.Eng.
Der entscheidende Augenblick der menschlichen Entwicklung ist immerwährend. Darum sind die revolutionären geistigen Bewegungen, welche alles Frühere für nichtig erklären, im Recht, denn es ist noch nichts geschehen. - Franz Kafka
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