I am a new one to GnuRadio. Now I am studying some implemented techniques in GnuRadio, one of them is the digital clock recovery. I would like to ask you a question that what are the reference documents or papers you used for the interpolation filter in that task (digital clock recovery). When I traced back the source files - digital_clock_recovery_mm_ff and then gri_mmse_fir_interpolator, I found only a little information:
* This implements a Mininum Mean Squared Error interpolator with 8 taps.
* It is suitable for signals where the bandwidth of interest B = 1/(4*Ts)
* Where Ts is the time between samples.
I find it tough to understand the algorithm you selected, so could you please help me on this problem. I make a guess with the key words " Mininum Mean Squared Error", the implementation may have some link to those below papers:
. G. Watkins, “Optimal Farrow coefficients for symbol timing recovery,” IEEE Communications Letters, vol. 5, no. 9, pp. 381–383, Sep. 2001.
 Daeyoung Kim, M. J. Narasimba, and D. C. Coc, “Design of optimal interpolation filter for symbol timing recovery,” IEEE Transactions on Communications, vol. 45, no. 7, pp. 877–884, Jul. 1997.
I would like to thank you very much in advance,
With best regards,
Nguyen Anh Duc