Comments on 'IEEE 1588 clock synchronization using dual slave clocks in a slave'

In the above letter, Chin and Chen proposed an IEEE 1588 clock synchronization method based on dual slave clocks, where they claim that multiple unknown parameters - i.e., clock offset, clock skew, and master-to-slave delay - can be estimated with only one-way time transfers using more equations than usual. This comment investigates Chin and Chen's dual clock scheme with detailed models for a master and dual slave clocks and shows that the formulation of multi-parameter estimation is invalid, which affirms that it is impossible to distinguish the effect of delay from that of clock offset at a slave even with dual slave clocks.