Frequency Raster

In 5G NR, the Frequency Raster defines the set of permitted center frequencies for RF channels. Unlike LTE's fixed 100 kHz raster, 5G NR utilizes a more flexible grid to accommodate a wider spectrum range.

1. Global Frequency Raster (NR-ARFCN)

The NR-ARFCN (New Radio Absolute Radio Frequency Channel Number) maps every possible frequency to a unique integer. Per 3GPP TS 38.104, the relationship between the frequency ( $F_{\text{REF}}$ ) and the NR-ARFCN ( $N_{\text{REF}}$ ) is defined by:

F_{\text{REF}} = F_{\text{REF-OFFS}} + \Delta F_{\text{Global}} (N_{\text{REF}} - N_{\text{REF-OFFS}})

Or, solving for $N_{\text{REF}}$ (NR-ARFCN):

N_{\text{REF}} = N_{\text{REF-OFFS}} + \frac{F_{\text{REF}} - F_{\text{REF-OFFS}}}{\Delta F_{\text{Global}}}

Parameters

Frequency Range ( $F_{\text{REF}}$ )	$\Delta F_{\text{Global}}$	$F_{\text{REF-OFFS}}$ (MHz)	$N_{\text{REF-OFFS}}$	NR-ARFCN Range
0 — 3 GHz	5 kHz	0	0	0 — 599000
3 — 24.25 GHz	15 kHz	3000	600000	600000 — 2016666
24.25 — 100 GHz	60 kHz	24250.08	2016667	2016667 — 3279165

2. Channel Raster

The Channel Raster is a band-specific subset of the global grid. While the global grid defines what is physically possible, the Channel Raster defines what is allowed for a specific operating band (e.g., n78).

For each operational band, 3GPP specifies a $\Delta F_{\text{Raster}}$ . This way, if the $\Delta F_{\text{Global}}$ is 5 kHz while the $\Delta F_{\text{Raster}}$ is 100 kHz, the valid NR-ARFCNs will have a step size of 20.

Raster Validation

A frequency is considered valid for a band if it aligns with the required step size ( $\Delta F_{\text{Raster}}$ ).

(N_{\text{REF}} - \text{Start}_{\text{Grid}}) \pmod {\text{Step}_{\text{Band}}} = 0

Off-Raster Scenarios

An off-raster frequency exists on the Global Raster ( $N_{\text{REF}}$ is an integer) but does not align with the band-specific step. The UE will not typically scan for carriers on these positions during initial cell search.

Example: Band n1 ( $\Delta F_{\text{Raster}}$ = 100 kHz / Step Size = 20)

1920.00 MHz ( $N_{\text{REF}} = 384000$ ): Valid. It aligns with the 100 kHz grid.

1920.05 MHz ( $N_{\text{REF}} = 384010$ ): Off-Raster. Although it is a valid NR-ARFCN, it cannot be used as a center frequency for band n1.

The next valid NR-ARFCN for band n1 is $\text{384000 + 20 = 384020 (1920.10 MHz)}$ .