The Formula · SCS = 2^μ × 15 kHz
μ=0 → 15 kHz (LTE-compatible). μ=1 → 30 kHz. μ=2 → 60 kHz. μ=3 → 120 kHz. μ=4 → 240 kHz. μ=5 → 480 kHz. μ=6 → 960 kHz. Each step doubles the SCS.
Slot Length Inversely Proportional to SCS
Slot length = 1 ms / 2^μ. μ=0: 1 ms (LTE). μ=1: 500 μs. μ=2: 250 μs. μ=3: 125 μs. μ=4: 62.5 μs. μ=5: 31.25 μs. μ=6: 15.625 μs. Slots-per-subframe = 2^μ; 14 OFDM symbols per slot regardless of μ.
Cyclic Prefix Scales With SCS
CP duration = 144 · κ · 2^-μ T_c, where T_c ≈ 0.509 ns and κ = 64. μ=0: 4.69 μs. μ=3: 0.59 μs. μ=6: 0.073 μs (~73 ns). Longer CP = more multipath tolerance = better coverage. Shorter CP = less overhead = higher spectral efficiency.
FR1, FR2, FR2-2 Deployment Defaults
FR1 (sub-6 GHz, 410 MHz – 7.125 GHz): typically μ=0 or μ=1. n78 / 3.5 GHz mid-band uses μ=1 (30 kHz). FR2 (24.25 – 52.6 GHz mmWave): μ=3 (120 kHz). FR2-2 (52.6 – 71 GHz, Rel-17): μ=4, 5, or 6.
Trade-offs Engineers Need to Remember
Higher μ → shorter slot → lower latency. But also: shorter CP (less multipath robustness), tighter Doppler tolerance, shorter coverage range. Lower μ → longer slot, longer CP (better coverage), but slower scheduling and higher latency.
Numerology Per Use Case
eMBB: typically μ=1 in FR1, μ=3 in FR2. URLLC: typically μ=3 to get 125 μs slot, sub-ms decision. mMTC / RedCap: μ=0 or μ=1 for coverage. NTN (satellite): μ=0 for very long delay-spread tolerance. mmWave point-to-point: μ=3 or μ=4.
Extended CP · Only μ=2
In addition to Normal CP (14 sym/slot), NR defines Extended CP (12 sym/slot) — but only at μ=2 (60 kHz SCS). Extended CP duration is 4.17 μs — useful for rural cells, factory halls, and high-delay-spread environments.
Frequently Asked Questions
What does numerology mean in 5G NR?
Numerology is the choice of subcarrier spacing in 5G NR. SCS = 2^μ × 15 kHz, where μ is the numerology index (0 to 6). Different numerologies trade off slot length, cyclic prefix, latency, and coverage.
What is the default numerology for FR1?
FR1 default is μ=1 (30 kHz SCS, 500 μs slot). Older bands sometimes use μ=0 (15 kHz, LTE-compatible) for backward compatibility. C-band (3.5 GHz) and most mid-band 5G uses μ=1.
What is the default numerology for FR2 mmWave?
FR2 default is μ=3 (120 kHz SCS, 125 μs slot). The shorter slot enables URLLC and tighter beam-tracking, while the still-acceptable 0.59 μs CP handles mmWave multipath.
What is FR2-2 in 5G NR?
FR2-2 (Rel-17) extends mmWave to the 52.6 – 71 GHz band. It introduces three new numerologies: μ=4 (240 kHz), μ=5 (480 kHz), μ=6 (960 kHz). At 960 kHz the slot is just 15.625 μs.