Cyclic prefix — A copy of the symbol's tail, prepended as a guard
The grid and its units
This page is the explanation. cyclic prefix, live is the working
half — the same quantities computed by 5G Simulation/ while the page loads, so they cannot
drift from what is written here.
Where it sits
What it is
The cyclic prefix is a copy of the symbol's own tail, prepended as a guard interval — not silence, which is the part worth understanding.
Why a copy and not silence. A guard of silence would stop echoes leaking into the next symbol, but it would also break the periodicity that makes the tones orthogonal. Copying the tail makes the received symbol look periodic over the whole observation window, so a delayed echo arrives as a phase rotation the receiver can correct rather than as interference.
It sets the cell's tolerance for echoes, and therefore its size: the guard is worth a distance, and any reflection arriving later than that becomes interference.
Read on
The full treatment is in nr-frame-structure — this page is the definition and the map reference; that note is where the subject is actually developed.
Before this concept, the hierarchy says to learn the following — the full chain, in order: