FPGA Central

I am implementing the timing recovery model using Gardner timing error
detector and the parabolic interpolator. The model is used in V.29 cabl
modem with 8KHz sampling rate. The model block is as follow:
-->Matched------->interpolator--->Equalizer-->
Filter | |
Garner-------
TED
Loop filter after TED is not used.
The model works well when in flat channel and no symbol rate difference.
When test in fading channel or change symblo rate of input signal(whthi
100ppm) the equalizer disconverge after a while. The same Phenomenon
ocur when Hold the equalizer after converging. It seems that the timin
recovery model is not worked well. The situation is improved when using

the following smoothing filter after TED:
y(n) = y(n-1) + (x(n)-y(n-1))*a; a=1/16;
But the disconverging Phenomenon also occur.
Can anyone tell me how to implement the Loop filter?
Thanks
Regards
aming