5G NR › Fundamentals › Section 1.2
Fundamentals

Numerology &
Frame Structure

5G NR defines five numerologies — μ = 0 through 4 — each doubling the subcarrier spacing of the previous. This section explains what numerology is, why different values exist for different scenarios, and how the 10 ms radio frame divides into subframes, slots, and symbols.

TS 38.211 §4.2 TS 38.211 §4.3

What is numerology?

In 5G NR, numerology refers to the subcarrier spacing and all quantities that scale with it — symbol duration, CP length, and slot duration. All are controlled by a single parameter μ (mu). Doubling μ doubles the SCS and halves the symbol duration.

For the supported transmission numerologies, the subcarrier spacing and cyclic prefix are given in Table 4.2-1. The supported subcarrier spacings are Δf = 2^μ · 15 kHz where μ ∈ {0, 1, 2, 3, 4}.
3GPP TS 38.211, Section 4.2
Numerology table — TS 38.211 Table 4.2-1 TS 38.211 §4.2
μSCS (kHz)Symbol durationCP (normal)Slot durationSlots/subframeTypical use
01566.67 μs4.69 μs1 ms1LTE-compatible, FR1
13033.33 μs2.34 μs0.5 ms2← our example (n78)
26016.67 μs1.17 μs0.25 ms4FR1 high BW, FR2
31208.33 μs0.59 μs0.125 ms8FR2 mmWave data
42404.17 μs0.29 μs0.0625 ms16FR2 reference signals

Why different numerologies?

The choice of SCS is a trade-off between two competing factors:

Large cells, low frequencies (FR1): Delay spreads can reach 10–20 μs. A long CP is needed, which means long symbols (low SCS). Phase noise is low at these frequencies, so narrow subcarriers work fine.

mmWave, small cells (FR2): Delay spreads are tiny (0.1–1 μs) but phase noise is severe. Phase noise rotates subcarriers causing inter-carrier interference — wider SCS reduces this effect. Shorter symbols also mean lower latency.

Low μ
large cells, FR1
Long CP absorbs delay spread. Low phase noise tolerates narrow SCS.
μ = 1
our example (n78)
30 kHz. 0.5 ms slots. Good balance for 3.5 GHz.
High μ
mmWave FR2
Wide SCS tolerates phase noise. Short CP is fine — tiny delay spread.

Radio frame structure

Downlink and uplink transmissions are organized into radio frames with a duration of T_f = 10 ms. Each radio frame consists of 10 subframes with a duration of T_sf = 1 ms. For numerology μ, there are 2^μ slots in each subframe, each containing 14 OFDM symbols with normal cyclic prefix.
3GPP TS 38.211, Section 4.3.2
Frame hierarchy — μ = 1 (30 kHz SCS) TS 38.211 §4.3.2

Slot structure — 14 symbols

Every slot contains 14 OFDM symbols. Symbol 0 has a slightly longer CP (160 vs 144 samples) to keep cumulative slot timing aligned across subframes.

Slot — 14 symbols, μ = 1 TS 38.211 §4.3.2
■ Symbol 0 — longer CP: 160 samples = 2.60 μs ■ Symbols 1–13 — normal CP: 144 samples = 2.34 μs
Complete timing — μ = 1, SCS = 30 kHzTS 38.211 §4.3.2
// Frame hierarchy
Radio frame  = 10 ms    = 10 subframes = 20 slots = 280 symbols
Subframe     = 1 ms     = 2 slots      = 28 symbols
Slot         = 0.5 ms   = 14 symbols   = 30,720 samples @ 61.44 Msps
Symbol 0     = 2208 samples (160 CP + 2048 useful) = 35.94 μs
Symbols 1–13 = 2192 samples (144 CP + 2048 useful) = 35.68 μs

// SFN
SFN range = 0..1023  →  full cycle = 1024 × 10 ms = 10.24 seconds

// Slots per frame for each μ:
μ=0: 10 slots/frame  |  μ=1: 20  |  μ=2: 40  |  μ=3: 80  |  μ=4: 160
Frame structure — μ = 1 key facts
SCS          → 30 kHz (= 2¹ × 15 kHz)
Slot duration → 0.5 ms
Symbols/slot  → 14
Slots/frame   → 20
SFN period    → 10.24 s
← PreviousOFDM & Multicarrier