Subscriber Tracking & Virtual Drive Test

OmniLCS provides two periodic location monitoring features: Subscriber Tracking for single-UE continuous monitoring, and Virtual Drive Test for multi-UE campaigns with combined GPS positioning and signal quality measurements.

Architecture

Subscriber Tracking

Subscriber Tracking periodically locates a single UE using a selected positioning method. Results are persisted in Mnesia and available via the web UI and REST API.

Web UI

Navigate to Subscriber Tracking in the sidebar. Enter an IMSI, polling interval (minimum 5 seconds), and select a positioning method (Cell, E-CID, GNSS, OTDOA). Click Start Watching.

Active watches are displayed in a table showing IMSI, method, interval, fix count, device status (Online/Offline/Error), last fix time, and last result. Click a row to view the fix history. Use the Export CSV or Export KML buttons to download data.

REST API

Method	Path	Description
`GET`	`/api/tracking`	List active tracking sessions
`POST`	`/api/tracking`	Start tracking. Body: `{"imsi": "...", "method": "gnss", "interval": 30}`
`GET`	`/api/tracking/:imsi`	Get tracking history for an IMSI
`DELETE`	`/api/tracking/:imsi`	Stop tracking an IMSI
`GET`	`/api/tracking/:imsi/export/csv`	Download CSV export
`GET`	`/api/tracking/:imsi/export/kml`	Download KML export

Device Status

The tracking session handles device online/offline transitions:

Status	Condition	Behavior
Online	`Engine.locate` succeeds	Fix stored with coordinates
Offline	No connected MME or UE unreachable	Error recorded, session continues polling
Error	Locate failed for other reasons	Error recorded, session continues polling

The session never stops on errors. It continues polling at the configured interval until explicitly cancelled.

Virtual Drive Test

Virtual Drive Test runs multi-IMSI campaigns that combine GNSS positioning (for GPS coordinates) with E-CID measurements (for RSRP, RSRQ, serving cell, PCI, EARFCN). This is the signal quality measurement equivalent of a physical drive test.

How It Works

On each tick, the campaign:

For each IMSI in the campaign (up to 4 concurrent):
- Sends an LPP GNSS Request to the UE via the MME for GPS coordinates
- Sends an LPP E-CID Request to the UE for signal measurements
- Merges the results into a single measurement record
Stores each measurement in Mnesia
Logs to InfluxDB (if configured)
Broadcasts results to the web UI via PubSub

Web UI

Navigate to Virtual Drive Test in the sidebar.

Enter a Campaign Name (e.g., "CBD Coverage Test")
Enter IMSIs (one per line or comma-separated)
Set the Interval (minimum 10 seconds)
Click Start Campaign

The campaigns table shows name, UE count, interval, tick count, and last tick time. Click a campaign row to view measurements. The measurement table shows per-fix data:

Column	Description
Time	Fix timestamp
IMSI	Target UE
Lat/Lon	GPS coordinates from GNSS
PCI	Physical Cell ID from E-CID
RSRP	Reference Signal Received Power (UE-reported)
RSRQ	Reference Signal Received Quality (UE-reported)
GNSS	GNSS status (ok/error)
ECID	E-CID status (ok/error)

RSRP values are color-coded: green (strong), yellow (medium), red (weak).

REST API

Method	Path	Description
`GET`	`/api/drive_test`	List active campaigns
`POST`	`/api/drive_test`	Start campaign. Body: `{"name": "...", "imsis": ["..."], "interval": 30}`
`GET`	`/api/drive_test/:id`	Get campaign measurements. Query: `?limit=200&imsi=filter`
`DELETE`	`/api/drive_test/:id`	Stop a campaign
`GET`	`/api/drive_test/:id/export/csv`	Download CSV with all measurements
`GET`	`/api/drive_test/:id/export/kml`	Download KML with signal-quality color coding

Example API Usage

Start a campaign:

curl -sk -X POST https://omnilcs:8445/api/drive_test \
  -H "Content-Type: application/json" \
  -d '{
    "name": "CBD Coverage Test",
    "imsis": ["001010000000001", "001010000000002"],
    "interval": 30
  }'

Get measurements:

curl -sk https://omnilcs:8445/api/drive_test/<campaign_id>?limit=100

Export KML:

curl -sk https://omnilcs:8445/api/drive_test/<campaign_id>/export/kml -o coverage.kml

E-CID Measurements

The E-CID method requests RSRP, RSRQ, and UE Rx/Tx timing difference directly from the UE via LPP (3GPP TS 36.355). This approach works regardless of eNB LPPa support since the UE performs the measurements locally.

Measurement Fields

Field	Description	Source
`rsrp`	Reference Signal Received Power	UE measurement (mapped value, ~-44 to -140 dBm)
`rsrq`	Reference Signal Received Quality	UE measurement (mapped value, ~-3 to -19.5 dB)
`pci`	Physical Cell ID	Serving cell identifier
`earfcn`	E-UTRAN Absolute Radio Frequency Channel Number	Serving cell frequency
`cell_global_id`	Cell Global Identity (PLMN + Cell ID)	Serving cell
`ue_rx_tx_time_diff`	UE Rx-Tx time difference	Propagation delay estimate

API Response Example

{
  "status": "ok",
  "method": "ecid",
  "imsi": "001010000000001",
  "ecid_measurements": {
    "measurements": [
      {
        "pci": 373,
        "earfcn": 1825,
        "cell_global_id": {
          "cell_id": 4000,
          "plmn": {"mcc": "001", "mnc": "01"}
        },
        "rsrp": 40,
        "rsrq": 25,
        "ue_rx_tx_time_diff": 19
      }
    ]
  }
}

Export Formats

CSV

Comma-separated values with header row. Includes all measurement columns: IMSI, timestamp, coordinates, signal measurements, and status fields. Suitable for import into spreadsheet tools or analysis scripts.

KML

Google Earth / Google Maps compatible. Each fix becomes a Placemark with:

Coordinates (lat/lon/alt)
Timestamp
Description with IMSI, RSRP, RSRQ, PCI
Color-coded icons by RSRP signal strength (green/yellow/red)
Per-IMSI track LineString connecting all fixes

Open in Google Earth, Google Maps, QGIS, or any KML-compatible GIS tool.

InfluxDB Integration

Both Subscriber Tracking and Virtual Drive Test log measurements to InfluxDB when the InfluxDB connection is configured in runtime.exs.

Measurements Written

InfluxDB Measurement	Source	Fields
`subscriber_tracking`	Tracking sessions	latitude, longitude, altitude, device_status
`drive_test`	Drive test campaigns	latitude, longitude, altitude, rsrp, rsrq, serving_pci, uncertainty

Tag	Description
`imsi`	Target UE IMSI
`method`	Positioning method used
`campaign_id`	Drive test campaign identifier (drive test only)

Persistence

All tracking and drive test data is stored in Mnesia disc_copies tables, surviving application restarts.

Mnesia Table	Key	Content
`:mnesia_tracking_history`	`{imsi, monotonic_time}`	Individual tracking fixes
`:mnesia_tracking_config`	`imsi`	Active tracking session configuration
`:mnesia_drive_test_measurements`	`{campaign_id, imsi, monotonic_time}`	Drive test measurements
`:mnesia_drive_test_config`	`campaign_id`	Active campaign configuration

History is automatically trimmed to 1,000 entries per IMSI (tracking) or 10,000 entries per campaign (drive test).

Architecture​