Ok, so I've been working on the digital modulations, and everything works
great except when I put in the AGC loop. It jumps up in gain when there is
no signal applied and then takes too long to converge when the signal comes
in. The result is that it almost always misses the first packet before
converging to receive the rest of a burst of packets. Taking the AGC loops
out will work when the transmitter amplitude and receiver gain are set
within a reasonable range, but we're of course loosing dynamic range this
way.
I've played with the rate of the AGC to no avail, and we have a limiter in
there to clamp the gain, but again, if we clamp too much, we'll loose
dynamic range.
The implementation is a straight-forward and simple AGC:
gain += (reference - sqrt(real(y)^2 + imag(y)^2))*rate
Where the reference is the value to converge to (+-1 usually) and the rate
is the slew rate of the loop.
I'm looking at Frerking's "Digital Signal Processing in Communications
Systems" for a possible solution. His AGC circuit is a similar approach to
the one above with a few more parts like a log(), integrator, blah blah
blah. I'm concerned with adding too much more to the AGC loop for
computational concerns, though, but will if it's the best way to go.
Does anyone have any recommendations? Is it worth implementing a more
complicated circuit to improve the acquisition time of the AGC? Or am I
looking in the wrong direction?
Thanks,
Tom
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