gNB Configuration

⚠️ RF Compliance Warning - Read Before Configuring!

Before configuring and starting the gNB for radio transmission, ensure you have:

1. ✅ Read RF Regulations & Compliance
2. ✅ Prepared an RF shielded box or cable connection + attenuator
3. ✅ Understood the legal consequences of illegal transmission (5-15 days detention)

If you just want to test software functionality, use ZMQ simulation mode without connecting SDR hardware.

This page details the srsRAN gNB configuration parameters.

Configuration File Structure

gNB uses YAML format configuration:

gnb_id: 411
gnb_id_bit_length: 22

cell_cfg:
  # Cell configuration
  
cu_cp:
  # CU-CP configuration
  
ru_sdr:
  # SDR configuration
  
log:
  # Logging configuration

Complete Configuration Example

USRP B210 Configuration

# gNB Identity
gnb_id: 411
gnb_id_bit_length: 22

# Cell Configuration
cell_cfg:
  dl_arfcn: 632628          # n78 band center frequency
  band: 78                   # NR band
  channel_bandwidth_MHz: 20  # Bandwidth
  common_scs: 30             # Subcarrier spacing (kHz)
  plmn: "00101"              # PLMN
  tac: 1                     # Tracking Area Code

  pdcch:
    common:
      ss0_index: 0
      coreset0_index: 12
    dedicated:
      ss2_type: common
      dci_format_0_1_and_1_1: false

  prach:
    prach_config_index: 1

# CU-CP Configuration (Core Network Connection)
cu_cp:
  amf:
    addr: 192.168.1.10       # AMF address
    port: 38412              # NGAP port
    bind_addr: 192.168.1.20  # gNB local address
    n2_bind_addr: 192.168.1.20
    n2_bind_interface: eth0  # Optional

  upf:
    bind_addr: 192.168.1.20  # N3 interface address

# SDR Configuration
ru_sdr:
  device_driver: uhd         # USRP driver
  device_args: type=b200     # Device parameters
  srate: 23.04               # Sample rate (MHz)
  tx_gain: 50                # TX gain (dB)
  rx_gain: 40                # RX gain (dB)
  
  # Clock configuration
  clock: internal            # internal/external/gpsdo
  sync: internal

# Logging Configuration
log:
  filename: /tmp/gnb.log
  all_level: info            # debug/info/warning/error
  phy_level: info
  mac_level: info
  rlc_level: info
  pdcp_level: info
  rrc_level: info
  ngap_level: info

# Performance Configuration
expert:
  phy:
    threads:
      pdsch:
        nof_threads: 2
      pusch:
        nof_threads: 2

Key Parameters

Cell Parameters

Parameter	Description	Common Values
dl_arfcn	Downlink Absolute Radio Frequency Channel Number	See band table
band	NR band number	78, 41, 3, etc.
channel_bandwidth_MHz	Channel bandwidth	10, 20, 40, 100
common_scs	Subcarrier spacing	15, 30 kHz
plmn	Public Land Mobile Network	Must match Open5GS
tac	Tracking Area Code	Must match Open5GS

Band and ARFCN

Common n78 band ARFCNs:

Center Frequency	ARFCN	SCS
3.5 GHz	632628	30 kHz
3.6 GHz	636666	30 kHz
3.7 GHz	640704	30 kHz

Core Network Connection

Parameter	Description
amf.addr	Open5GS AMF IP address
amf.port	NGAP port, default 38412
amf.bind_addr	gNB local IP
upf.bind_addr	N3 interface bind address

Start gNB

# Foreground
sudo gnb -c gnb.yaml

# Background
sudo gnb -c gnb.yaml > /tmp/gnb.log 2>&1 &

Verify Connection

Check AMF Connection

On successful connection, gNB logs show:

[NGAP   ] NG Setup procedure successful
[NGAP   ] AMF connected

Open5GS AMF logs show:

[amf] INFO: gNB-N2 accepted[192.168.1.20]:38412

Troubleshooting

NGAP Connection Failed

[NGAP   ] Failed to connect to AMF

Check:

1. AMF address and port are correct
2. Network connectivity ping 192.168.1.10
3. AMF service is running
4. Firewall rules

PLMN Mismatch

[NGAP   ] NGAP Setup Failure - Unknown PLMN

Ensure plmn matches Open5GS configuration.

Next Steps

• UE Configuration - Configure software terminal
• Open5GS Subscriber - Add subscribers