5G NR ARFCN & Frequency Calculator

Architecture of the 3GPP 5G NR Global Frequency Raster

In cellular communications, the radio frequency (RF) raster defines the allowable center frequencies for transmitting carriers. In legacy 4G LTE systems (3GPP TS 36.101), a uniform 100 kHz channel raster was used across all frequency bands. While 100 kHz was convenient for integer arithmetic, it led to noticeable architectural friction with OFDMA subcarrier spacing (SCS). LTE subcarriers are spaced at 15 kHz intervals (7.5 kHz half-shift for uplink). Because 100 kHz is not an integer multiple of 15 kHz (100 / 15 = 6.666...), LTE carrier center frequencies could not align directly with subcarrier centers, requiring intentional DC subcarrier nulling and complex phase adjustments in baseband digital signal processors.

To solve this fundamental limitation and accommodate carrier bandwidths from 5 MHz up to 400 MHz spanning Sub-1 GHz to 100 GHz millimeter-wave spectrum, the 3rd Generation Partnership Project (3GPP) completely overhauled frequency assignment in Release 15 (TS 38.104 Section 5.4). The 5G New Radio (NR) specification defines a globally harmonized frequency raster covering 0 kHz to 100 GHz, governed by the continuous piecewise formula:

The 3GPP global frequency raster segments the electromagnetic spectrum into three distinct operational regimes:

• Range 1 (0 – 3000 MHz): Global raster step ΔF_Global = 5 kHz. Offset frequency F_REF-Offs = 0 MHz, offset channel number N_REF-Offs = 0. Channel numbers span N_REF = 0 to 599,999. The 5 kHz granularity preserves compatibility with legacy low-band refarming (e.g., 700 MHz, 850 MHz, 1800 MHz, 2100 MHz, 2.6 GHz) while providing a common denominator with 15 kHz and 30 kHz subcarrier spacings.
• Range 2 (3000 – 24250 MHz): Global raster step ΔF_Global = 15 kHz. Offset frequency F_REF-Offs = 3000 MHz, offset channel number N_REF-Offs = 600,000. Channel numbers span N_REF = 600,000 to 2,016,666. Because 15 kHz is exactly equal to the base 5G NR numerology subcarrier spacing (μ = 0), and divides evenly into 30 kHz (μ = 1) and 60 kHz (μ = 2), carrier centers in mid-band C-Band (n77, n78) align harmoniously with OFDMA physical resource block (PRB) resource elements.
• Range 3 (24250 – 100000 MHz / mmWave): Global raster step ΔF_Global = 60 kHz. Offset frequency F_REF-Offs = 24250 MHz, offset channel number N_REF-Offs = 2,016,667. Channel numbers span N_REF = 2,016,667 to 3,279,165. This aligns directly with 60 kHz (μ = 2) and 120 kHz (μ = 3) millimeter-wave numerologies used across bands n257, n258, n260, and n261.

Channel Raster vs. Synchronization Raster (SSB Search Mechanics)

One of the most consequential architectural breakthroughs of 5G NR is the complete operational decoupling of the RF Channel Raster from the Synchronization Raster. In 4G LTE, the Primary Synchronization Signals (PSS) and Secondary Synchronization Signals (SSS) were permanently centered in the middle 6 resource blocks (1.08 MHz) of the channel bandwidth. A User Equipment (UE) powering on had to blindly scan every single 100 kHz channel raster step across entire cellular frequency bands, decoding the center of each potential carrier to see if an eNodeB cell was present.

In 5G NR, wideband channels can measure 100 MHz (FR1) or up to 400 MHz (FR2). Scanning a 100 MHz carrier on a fine 5 kHz or 15 kHz channel raster would require testing tens of thousands of candidate frequencies, severely draining UE battery reserves and creating unacceptable initial cell attachment latencies.

To eliminate this bottleneck, 3GPP engineered the Global Synchronization Channel Number (GSCN) raster (TS 38.104 Section 5.4.3). The Synchronization Signal and PBCH block (SS/PBCH block, or SSB) does not have to reside in the center of the 5G carrier; it can be placed anywhere within the carrier bandwidth on a sparse, predefined grid of GSCN search points:

• 0 – 3000 MHz: SSB center frequency follows F_SSB = N × 1200 kHz + M × 50 kHz (where N = 1 to 2499, and M ∈ {1, 3, 5}). The corresponding GSCN is given by GSCN = 3N + (M − 3)/2. With typical M = 3, the synchronization search step is 1.2 MHz — 240 times coarser than the 5 kHz channel raster, cutting UE frequency search sweeps by over 99%.
• 3000 – 24250 MHz: SSB center frequency follows F_SSB = 3000 MHz + N × 1.44 MHz (where N = 0 to 14756). The synchronization raster number is GSCN = 7499 + N. The UE searches at 1.44 MHz steps instead of 15 kHz channel steps.
• 24250 – 100000 MHz (FR2 mmWave): SSB center frequency follows F_SSB = 24250.08 MHz + N × 17.28 MHz (where N = 0 to 4383). The synchronization raster number is GSCN = 22256 + N. The synchronization step is a wide 17.28 MHz, enabling ultra-fast beam sweeping and rapid cell acquisition across gigahertz of millimeter-wave spectrum.

Operating Bands: Frequency Range 1 (FR1) vs. Frequency Range 2 (FR2)

3GPP TS 38.104 classifies all 5G operating bands into two major frequency domains, each characterized by radically different radio propagation dynamics, antenna architectures, and numerology structures:

1. Frequency Range 1 (FR1): Sub-7 GHz

Designated from 410 MHz to 7125 MHz, FR1 represents the foundational coverage and capacity tier of global 5G networks. It includes Frequency Division Duplex (FDD) paired spectrum (e.g., Band n28 at 700 MHz, Band n71 at 600 MHz, Band n1 at 2.1 GHz), Time Division Duplex (TDD) unpaired spectrum (e.g., Band n41 at 2.5 GHz, Band n77 at 3.7 GHz, and Band n78 at 3.5 GHz), as well as Supplementary Downlink/Uplink (SDL/SUL) carrier configurations. Sub-carrier spacing in FR1 typically utilizes 15 kHz (μ = 0) for low bands and 30 kHz (μ = 1) for mid-band massive MIMO deployments.

2. Frequency Range 2 (FR2): Millimeter-Wave (mmWave)

Designated from 24.25 GHz up to 71.0 GHz, FR2 comprises FR2-1 (24.25 GHz – 52.6 GHz) and FR2-2 (52.6 GHz – 71.0 GHz). Common allocations include Band n257 (28 GHz), Band n258 (26 GHz), and Band n260 (39 GHz). Due to severe atmospheric attenuation, high diffraction loss, and penetration limits through building facades, FR2 systems deploy massive active phased-array beamforming (hundreds of antenna elements) with 60 kHz (μ = 2) and 120 kHz (μ = 3) subcarrier spacing, supporting wide component carriers of 50, 100, 200, and 400 MHz.

Practical Base Station RF Provisioning and Point A Configuration

In carrier-grade gNodeB commissioning, network engineers must configure not only the nominal RF carrier frequency F_REF, but also the absoluteFrequencyPointA parameter. In 3GPP RRC signaling, Point A serves as the common reference frequency for the entire resource block grid:

• Point A: Represents the center frequency of subcarrier 0 of physical resource block 0 (PRB 0) for subcarrier spacing μ = 0 (15 kHz). Point A is always signaled as an integer NR-ARFCN value.
• Subcarrier Grid Alignment: For an active transmission bandwidth comprising N_PRB resource blocks, the carrier center frequency must satisfy the relationship:
  F_center = F_pointA + (N_PRB × 12 × Δf_SCS) / 2.
• Inter-Carrier Interference (ICI) Avoidance: If the configured ARFCN does not match the channel raster or causes fractional subcarrier misalignments with adjacent carriers in carrier aggregation (CA), severe inter-carrier interference and phase noise degradation will occur. Utilizing the exact TS 38.104 formulas implemented in this calculator ensures mathematical compliance across cell site commissioning and RF drive-test post-processing workflows.

3GPP 5G NR Operating Bands Reference Table (TS 38.104 / TS 38.101-1/2)

The table below compiles key 3GPP 5G New Radio operating bands across FR1 and FR2, detailing duplex modes, frequency allocations, NR-ARFCN ranges, and global raster step sizes: