MAX17356 supports coherent and differential mode.
To transmit packets in coherent mode, you need to set MAC PIB “macCoherentEnable” (0x0223) = 0x01 and set “Mod Scheme” to 1 in “Neighbor Table” entry
For differential modulation a phase difference for particular tone at current symbol is calculated relative to phase of the same tone of previous symbol.
For coherent modulation this phase difference is relative to the initial phase at beginning of the packet.
A SNR performance of coherent scheme is 2-3 dB better than differential.
But the implementation is more complex and it’s sensitive to clock PPM difference between TX and RX modems.