  A general synchronization waveform type that is insensitive to frequency
error for massive Internet-of-Things (mIoT) is derived in "Robust
synchronization waveform design for massive low-power IoT" (IEEE Trans. on
Wireless Commun., vol. 16, no. 11, pp. 7551-7559, Nov. 2017). Detailed issues
such as (1) how to obtain the frequency error information from the waveform;
(2) how to refine the timing estimation; and (3) how to adjust the waveform
parameter to meet various spectral requirements are not addressed in the paper,
and yet are of great importance for a practical application. These issues are
discussed in this comment.

Signal Processing