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5G gNB Frequency Configuration

Configuring the frequency settings for a 5G gNB involves specifying multiple parameters in the gNB configuration file. This guide outlines the necessary parameters and provides step-by-step instructions for configuration.

Configuration parameters

To configure the gNB with the required frequency and bandwidth, modify following parameters in the configuration file:

gNBs Section

  • absoluteFrequencySSB: ARFCN (frequency number) of the middle frequency of the SSB. This value must align with the NR frequency raster defined in TS 38.104, Section 5.4.3.1.
  • Steps to compute this value are provided below.
  • dl_absoluteFrequencyPointA: ARFCN (frequency number) for Point A, lowest subcarrier of the reference resource block (Common RB 0).
  • Steps to compute this value are provided below.
  • dl_frequencyBand: downlink NR frequency band number.
  • dl_subcarrierSpacing: downlink subcarrier spacing.
  • Allowed values: 0 = 15 kHz, 1 = 30 kHz, 2 = 60 kHz, 3 = 120 kHz
  • dl_carrierBandwidth: number of PRBs for downlink.
  • initialDLBWPlocationAndBandwidth: resource indicator value (RIV) of the initial BWP.
  • Steps to compute this value are provided below.
  • initialDLBWPsubcarrierSpacing: initial downlink BWP subcarrier spacing.
  • Allowed values: 0 = 15 kHz, 1 = 30 kHz, 2 = 60 kHz, 3 = 120 kHz
  • initialDLBWPcontrolResourceSetZero: CORESET0 index (valid configurations, based on SCS and frequency bandwith, are given in TS 38.213, Table 13.1 to Table 13.14).
  • ul_frequencyBand: uplink NR frequency band number.
  • ul_absoluteFrequencyPointA: ARFCN (frequency number) for Point A, lowest subcarrier of the reference resource block (Common RB 0).
  • Set only for FDD configurations.
  • Frequency separation between DL and UL channels for a specific 5G NR band is defined in 38.101-1 5.4.4-1 for FR1 bands and in 38.101-5 5.4.4-1 for FR1 NTN bands. ul_absoluteFrequencyPointA is calculated by substracting the given frequency offset from the dl_absoluteFrequencyPointA.
  • ul_carrierBandwidth: number of PRBs for uplink.
  • initialULBWPlocationAndBandwidth: resource indicator value (RIV) of the initial BWP.
  • Steps to compute this value are provided below.
  • initialULBWPsubcarrierSpacing: initial uplink BWP subcarrier spacing.
  • Allowed values: 0 = 15 kHz, 1 = 30 kHz, 2 = 60 kHz, 3 = 120 kHz
  • subcarrierSpacing: general subcarrier spacing for both DL and UL.
  • Allowed values: 0 = 15 kHz, 1 = 30 kHz, 2 = 60 kHz, 3 = 120 kHz

RUs Section

  • bands: NR frequency band number for RU(s).

Determining the ARFCN value for absoluteFrequencySSB and dl_absoluteFrequencyPointA

Follow these steps to find the ARFCN values for absoluteFrequencySSB, dl_absoluteFrequencyPointA, initialDLBWPlocationAndBandwidth, and initialULBWPlocationAndBandwidth: 1. Convert RU center frequency to ARFCN value * Example tool: 5G NR ARFCN Calculator * Input the center frequency of the RU (in MHz) into the tool to calculate the ARFCN value.

  1. Enter parameters into the online tool for NR Point A computation

    • Example tool: NR Reference Point A Tool
    • Enter the NR frequency band, ARFCN value for center frequency (use the value calculated in step 1), subcarrier spacing, CORESET0 index (initialDLBWPcontrolResourceSetZero in the gNB config file) and bandwidth into the tool.

  2. Obtain required values

    • From the tool’s output, use the following results for your configuration:
    • Arfcn GSCN: This corresponds to absoluteFrequencySSB - value for absoluteFrequencySSB can be selected freely from the table, if Coreset(0) check is “ok”.
    • Point A Arfcnc: This corresponds to dl_absoluteFrequencyPointA.
    • locationAndBandwidth full: Use this value for both initialDLBWPlocationAndBandwidth and initialULBWPlocationAndBandwidth.

  3. Set dl_absoluteFrequencyPointA, absoluteFrequencySSB, initialDLBWPlocationAndBandwidth, and initialULBWPlocationAndBandwidth in the gNB configuration file

Example calculation

  1. Convert RU center frequency to ARFCN value

    • Center frequency = 3450 MHz
    • Center frequency ARFCN = 630000

  2. Enter parameters into the online tool for NR Point A computation

    • Open the NR Reference Point A Tool and input the following values:
    • Frequency band = n78
    • NR Arfcn scan (center frequency) = 630000
    • SCS = 30 kHz
    • Bandwidth = 100 MHz
    • Control ResourceSet Zero = 11

  3. Obtain required values

    • The tool provides following output values:
    • Arfcn GSCN (absoluteFrequencySSB) = 630048
    • Point A Arfcnc (dl_absoluteFrequencyPointA) = 626724
    • locationAndBandwidth full (initialDLBWPlocationAndBandwidth) = 1099
    • locationAndBandwidth full (initialULBWPlocationAndBandwidth) = 1099