3GPP 38.300 v19.3.0 — the document's own text
16.23.4.3.2 D2R amble signals
A D2R preamble signal for timing acquisition, timing tracking and channel estimation, and zero or more D2R midamble signal(s) for timing tracking and channel estimation, are inserted in a D2R transmission. A D2R preamble signal is transmitted immediately before a PDRCH.