Timing recovery in HF

 
 
Hi all
 
We are designing a 128TCM QAM receiver. Our idea is to take advantadge
from the Digital Downconverters (DDC as GC4016 or similar) to convert from
HF to baseband directly ,let's say sampling at 1MHz, then DDC (CIC +
decimation filters), and then a DSP system at 50KHz sampling time where
the complete receiver will be implmented.
 
The problem we are guessing is about timing recovery. If we recover the
timing at baseband (i.e. recover the 50KHz) and multiply it up to the HF
sampling frequency to feed the 1MHz A/D, we will substantially increase
the loop time due to the DDC path (order of milisecs).
 
Therefore we suspect (though we don�t know for sure) that the timing
recovery will fail to converge or at least will significantly worse this
behaviour.
 
Will be in this way? Do you know about any source/paper talking about the
use of DDC in a QAM receiver down to baseband directly? Any other isuue
that we should take care of?
 
Thanks a lot
 
Alex Moreno
Software engineer