NR‑ARFCN vs GSCN — What’s the Difference in 5G NR?
5G NR uses two separate numbering systems to identify frequencies:
- NR‑ARFCN → identifies carrier center frequencies (used for channels like PDSCH, PUSCH, SS/PBCH reference points, etc.)
- GSCN → identifies Synchronization Signal Block (SSB) frequencies (used for initial cell search and synchronization)
Although both map to frequencies, they serve different purposes, have different step sizes, and follow different equations.
1. NR‑ARFCN (Absolute Radio Frequency Channel Number)
NR‑ARFCN uniquely maps any RF channel frequency in the range 0–100 GHz.
The mapping is defined in 3GPP TS 38.104 §5.4.2.1.
Purpose
- Identifies carrier center frequency
- Used in RF channel configuration, RRC signaling
- Used for Point A, BWP, PRB alignment, and scheduling
- Applies to FR1 and FR2
Mapping Formula
(from 3GPP TS 38.104 Table 5.4.2.1‑1)
Depending on the frequency range:
(A) 0 – 3000 MHz
- ΔFGlobal = 5 kHz
- FREF-Offs = 0
- NREF-Offs = 0
NR‑ARFCN=FMHz0.005\text{NR‑ARFCN} = \frac{F_{\text{MHz}}}{0.005}NR‑ARFCN=0.005FMHz
(B) 3000 – 24250 MHz
- ΔFGlobal = 15 kHz
- FREF-Offs = 3000
- NREF-Offs = 600000
NR‑ARFCN=600000+FMHz−30000.015\text{NR‑ARFCN} = 600000 + \frac{F_{\text{MHz}} – 3000}{0.015}NR‑ARFCN=600000+0.015FMHz−3000
(C) 24250 – 100000 MHz
- ΔFGlobal = 60 kHz
- FREF-Offs = 24250.08
- NREF-Offs = 2016667
NR‑ARFCN=2016667+FMHz−24250.080.06\text{NR‑ARFCN} = 2016667 + \frac{F_{\text{MHz}} – 24250.08}{0.06}NR‑ARFCN=2016667+0.06FMHz−24250.08
Key Characteristics
- Very fine resolution (5 kHz / 15 kHz / 60 kHz)
- Covers all NR frequencies (usable for carriers, SSB, etc.)
- Used by both UE and gNB for tuning receivers/transmitters
- Exact alignment needed for spectrum planning and CA
2. GSCN (Global Synchronization Channel Number)
GSCN identifies where SSBs (PSS+SSS+PBCH) can be transmitted.
All SSBs must lie on a global synchronization raster defined in 3GPP TS 38.104 §5.4.3.
Purpose
- Identifies the SSB center frequency, not carrier center
- Used for UE initial synchronization
- Reduces search complexity → UE searches only these discrete frequencies
- Defined differently for FR1 sub‑3 GHz, FR1 ≥3 GHz, and FR2
3. GSCN Frequency Mapping Rules
Mapping depends on the frequency region (above 3 MHz raster):
(A) 0 – 3000 MHz region
fSSB=1.2N+0.05Mf_{\text{SSB}} = 1.2N + 0.05MfSSB=1.2N+0.05M
M ∈ {1,3,5} ― small steps around 50 kHz
GSCN=3N+M−32\text{GSCN} = 3N + \frac{M – 3}{2}GSCN=3N+2M−3
GSCN range: 2 – 7498
(B) 3000 – 24250 MHz (FR1 mid-band)
fSSB=3000+1.44Nf_{\text{SSB}} = 3000 + 1.44N fSSB=3000+1.44N
GSCN=7499+N\text{GSCN} = 7499 + NGSCN=7499+N
GSCN range: 7499 – 22255
(C) 24250 – 100000 MHz (FR2 mmWave)
fSSB=24250.08+17.28Nf_{\text{SSB}} = 24250.08 + 17.28NfSSB=24250.08+17.28N
GSCN=22256+N\text{GSCN} = 22256 + NGSCN=22256+N
GSCN range: 22256 – 26639
4. Summary Comparison Table
| Feature |
NR‑ARFCN |
GSCN |
| Purpose |
Identify carrier frequency |
Identify SSB (sync signal) frequency |
| Used For |
Channel tuning, BWP, PointA, scheduling |
UE initial search, SSB decoding |
| Defined In |
3GPP TS 38.104 §5.4.2.1 |
3GPP TS 38.104 §5.4.3 |
| Step Size |
5 / 15 / 60 kHz |
1.2 / 1.44 / 17.28 MHz |
| Range |
0–3 GHz, 3–24.25 GHz, 24.25–100 GHz |
Sub‑3 GHz, FR1, FR2 |
| Precision |
Very fine raster |
Coarse raster |
| Search Complexity |
High (not used for search) |
Low (UE only checks GSCNs) |
| Links to |
Full carrier grid |
SSB center frequency only |
5. Why 5G Needs Both?
NR‑ARFCN handles everything
- Choosing carrier bandwidth
- Defining scheduling grids
- Setting PointA
- Calculating PRB boundaries
- Required for uplink & downlink channels
GSCN optimizes initial access
- UE doesn’t know bandwidth or numerology
- So it scans only pre‑defined SSB frequencies
- Much faster synchronization
- Reduces battery drain
- Ensures consistent SSB placement across bands
The GSCN raster is a coarse global marker, while
NR‑ARFCN is a fine-granularity universal channel marker.
6. Simple Example: n78 (3300–3800 MHz)
- In this range, SSB frequencies use 1.44 MHz steps
- Example from 3GPP-derived calculators:
- GSCN = 7725 → f = 3325.44 MHz
- But the carrier center frequency will use ARFCN:
- f = 3645.12 MHz → NR‑ARFCN = 643008 (15 kHz raster)
So SSB may not lie at the carrier center, and GSCN ≠ ARFCN.
January 31, 2026