Numerology
The set of OFDM parameters (subcarrier spacing, cyclic prefix length, slot duration) used in 5G NR. NR supports multiple numerologies (mu = 0 to 4) with SCS from 15 kHz to 240 kHz.
Numerology is NR's flexible OFDM, and it's one of the biggest departures from LTE, which was locked to a single 15 kHz spacing. NR scales the spacing by powers of two: numerology mu = 0 is 15 kHz, mu = 1 is 30 kHz, and so on up to 120 kHz (mu = 3) for data and 240 kHz for SSB only. Wider subcarriers also mean shorter symbols and shorter slots — a slot is 1 ms at 15 kHz but just 0.125 ms at 120 kHz.
That coupling is the whole point. Low spacings give long symbols with generous cyclic prefixes, good for large cells and lower bands. High spacings give short slots — useful for low latency and essential at mmWave, where phase noise and Doppler punish narrow subcarriers. You pick numerology to fit the band and the use case, and different numerologies can even coexist on one carrier through separate BWPs. The trade is overhead: a longer CP eats more of each symbol, so you're balancing resilience against efficiency.
Frequently asked questions
- Why does 5G support multiple numerologies when LTE only had one?
- Because 5G spans a far wider range of bands and use cases. A 700 MHz macro cell and a 28 GHz mmWave small cell have very different needs — the former wants long symbols and a long cyclic prefix for coverage, the latter wants short slots to fight phase noise and Doppler and to hit low-latency targets. A single fixed subcarrier spacing can not serve both well, so NR makes it scalable.
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