Configuration

1xBTS uses a per-node config directory plus an optional radio-config override:

cargo run --release -p cdma-nib -- --config-dir config --radio-config config/radio_bladerf_micro2.json

The default config directory contains bts.json, bsc.json, msc.json, pcf.json, pdsn.json, hlr.json, smsc.json, and management.json.

Node Configuration

Local Overrides

The configs in config/ are shared defaults. To customize one for your own setup without touching the checked-in file, drop a sibling <name>.local.json next to it:

config/bts.json          # shared default (in git)
config/bts.local.json    # your overrides (gitignored)

At load time the BTS reads the base file, merges your local file on top, and validates the result. Your local file only needs the fields you’re changing — anything you omit keeps the value from the base.

For example, to switch to a different CDMA channel and bump TX gain without touching anything else in bts.json:

{
  "channel": {
    "band_class": "bc0",
    "band_subclass": 0,
    "cdma_channel": 283
  },
  "radio": {
    "tx_gain_db": 60
  }
}

The BTS derives both TX and RX center frequencies from channel (via C.S0057-F band-class formulas). To force a non-standard TX tune for loopback or development work, set runtime.tx_freq_hz_override.

The same convention works for every config in config/: bts.json, bsc.json, msc.json, pcf.json, pdsn.json, hlr.json, smsc.json, management.json, voice-gw.json, and the radio profiles (e.g. radio_bladerf_micro2.local.json).

Merge behavior

• Nested objects are merged field by field; fields you don’t set keep the base value.
• Arrays in your local file replace the base array (they’re not appended).
• Setting a field to null removes it, falling back to the struct default.

The stock BTS settings are for Verizon devices. Want to try Sprint? See Carrier Profiles to switch with one CLI flag while keeping your normal local configuration.

BTS Runtime

{
  "channel": {
    "band_class": "bc0",
    "band_subclass": 0,
    "cdma_channel": 384
  },
  "runtime": {
    "spreading_rate": "sr1",
    "chip_rate_hz": 1228800,
    "tx_digital_backoff": 0.5,
    "realtime": {
      "enabled": true,
      "tx_priority": 80,
      "rx_priority": 75,
      "driver_priority": 70,
      "tx_cpu": null,
      "rx_cpu": null,
      "driver_cpu": null
    }
  }
}

channel is the single source of truth for RF tuning. The BTS supports all 23 band classes defined in C.S0057-F (bc0–bc22, except bc17 and bc22 which are “Not specified” in the spec). The band_subclass selects which spectrum-allocation profile is broadcast in handoff messages. The default (BC0 / subclass 0 / N=384) maps to 881.520 MHz TX / 836.520 MHz RX. See the Configuration Reference for the full per-band formula table.

The BTS also derives the SDR sample rates and RF bandwidths at startup. 1x-only uses a 4x chip-rate clock with 1.5 MHz bandwidth. When EV-DO is enabled in the default composite mode, the runtime chooses the smallest 4x, 8x, or 16x span that fits the configured 1x and HRPD carriers. HRPD-only mode is supported for EV-DO-only deployments and uses the 4x/1.5 MHz profile.

Real-time scheduling is enabled by default for the radio I/O threads. On Linux, grant the process permission to use SCHED_FIFO if you want the configured priorities to take effect; otherwise the BTS logs a warning and continues with normal scheduling. Optional CPU fields pin the corresponding thread by zero-based Linux CPU index. Leave them null unless you are tuning a dedicated host.

Downlink Channels

Extended System Parameters in bts.json carry the advertised MCC and IMSI_11_12 defaults as decimal digit strings, for example "mcc": "310" and "imsi_11_12": "55". The BTS encodes those strings into the C.S0005-E bit fields, and the BSC uses the same overhead values to reconstruct a complete class-0 registration IMSI when the mobile only sends the short IMSI fields on the access channel.

BSC / MSC / Packet Parameters

For SO33 packet-data downlink, bsc.traffic_assignment.enable_f_sch enables F-SCH and f_sch_rate_bps selects 19200, 38400, 76800, or 153600.

RC2 must be present in both BSC supported-RC lists for QCELP 13K calls. The MSC voice.supported_service_options list controls which implemented codecs may be proposed for mobile-terminated calls; the first recognized option is the default.

For EV-DO, bts.evdo.enabled starts the HRPD carrier, AN service, PCF A9 service, and PDSN A11 service in the integrated runtime. bts.evdo.channel is required when EV-DO is enabled, and bts.evdo.mode selects the default composite 1x + HRPD carrier mode or the supported hrpd_only EV-DO-only deployment mode. For EV-DO-only deployments, channels 589, 630, and 770 are good starting points. bts.evdo.advertise_on_1x controls whether hybrid 1x/EV-DO devices are told about the HRPD carrier on the 1x paging channel.

Access Channel

Radio Configuration

Hardware-specific SDR parameters.

UHD (USRP B200/B210)

{
  "kind": "uhd",
  "device": "type=b200,num_recv_frames=1024,num_send_frames=1024",
  "channel": 0,
  "antenna": "TX/RX",
  "tx_gain_db": 65.0,
  "rx_antenna": "RX2",
  "rx_gain_db": 30.0,
  "rx_power_adj": 0.0,
  "rx_sample_delay": 50
}

LimeSDR (Native)

{
  "kind": "lime",
  "device": "",
  "channel": 0,
  "tx_antenna": "BAND1",
  "tx_gain_db": 80,
  "rx_antenna": "LNAW",
  "rx_gain_db": 50,
  "rx_power_adj": 5.0,
  "rx_sample_delay": 97
}

rx_sample_delay compensates for LimeSDR-specific timing offsets in the receive path.

bladeRF (Native)

{
  "kind": "blade_rf",
  "device": "",
  "channel": 0,
  "tx_antenna": "TXA",
  "rx_antenna": "A_BALANCED",
  "tx_gain_db": 60,
  "rx_gain_db": 35,
  "rx_reference_dbm": null,
  "rx_power_adj": 0.0,
  "rx_sample_delay": 82,
  "rx_batch_pcgs": 2,
  "num_buffers": 16,
  "buffer_size": 8192,
  "num_transfers": 8,
  "stream_timeout_ms": 3500
}

tx_antenna and rx_antenna select bladeRF RF ports; the current Micro 2.0 example uses TXA and A_BALANCED.

Environment Variables

Next Steps

• First Registration — Start the BTS and register a handset
• Configuration Reference — Full parameter reference