Numerology — The single index μ that sets subcarrier spacing and slot length
The grid and its units
This page is the explanation. numerology, 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
Numerology is the single index $\mu$ that sets everything about the time-frequency grid: subcarrier spacing is $2^{\mu} \times 15$ kHz, and the slot length is $1/2^{\mu}$ ms.
Seven values, 0 to 6, giving 15 to 960 kHz (TS 38.211 Table 4.2-1). One number decides the trade that runs through the whole system:
Wider spacing means shorter symbols, so shorter slots and lower latency, and more tolerance of frequency error and phase noise — which is why high bands use it. Narrower spacing means longer symbols, so a longer cyclic prefix for the same overhead fraction, and better tolerance of echoes — which is why wide-area cells use it.
Only $\mu = 2$ has the extended cyclic prefix as an option.
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: