Ambulance Sensor Networks

1 Overview and operating context

An ambulance is a road vehicle with three data domains: the chassis (engine, speed, battery, tyres), the vehicle-mounted emergency and cabin equipment (lights, siren, doors, cot, oxygen, patient-compartment climate, drug fridge), and the clinical devices (monitor/defibrillator, ventilator, infusion pump) that feed an electronic patient care record (ePCR). A telematics unit or mobile data terminal (MDT) carries position and status to the dispatch system (CAD) over cellular.

Unlike a bus or truck, an ambulance is idle for much of its day and then switches abruptly into high-rate operation on dispatch. Utilisation is 20-45% busy in a typical urban system, and a 12-hour shift sees about 1.5-3 calls in rural areas and 6-10 in busy urban ones. Call volume peaks 10:00-20:00 with Friday and Saturday night spikes. Planning figures for the ambulance telemetry stream: one publish every 5-30 s (1 s on dispatch), 0.5-3 kB per publish, 1-15 records/s bursty, 3-30 MB per day and 100-600 MB per month.

Data provenance: values come from the research notes, where they are tagged either as confirmed from a cited source or as domain-knowledge estimates. In this report, items without a source tag are tunable defaults from the research, and anything the report author derived is labelled "inference".

2 Sensor inventory

2.1 Vehicle CAN, J1939 and OBD-II

Heavy chassis use J1939 on CAN at 250 kbit/s. Light chassis (for example Ford Transit, E-450, Sprinter) use OBD-II over ISO 15765 at 500 kbit/s. Signal and PGN names are source-confirmed; scaling factors are domain-knowledge defaults to verify against the DBC or J1939DA.

OBD-II polling by a telematics dongle (ISO 15765-4) runs at 1-10 Hz over 5-20 PIDs: 0x0C RPM (1/4 rpm per bit), 0x0D speed (km/h), 0x05 coolant (A-40 degC), 0x11 throttle %, 0x2F fuel level %, 0x42 module voltage.

2.2 GNSS position

2.3 Cabin, vehicle equipment and cold chain

2.4 Oxygen

2.5 Medical devices and vitals

These are generator parameters for synthetic patients only. Default alarm limits marked "Mindray" are from the cited bedside monitor checklist; the rest are domain-knowledge defaults.

3 Networks and messaging standards

3.1 Messaging standards

The research flags LOINC and MDC codes it could not confirm (an EtCO2 LOINC code and the EtCO2 MDC code). The codes in the table above are the ones the research treats as well known or as nomenclature examples; do not rely on any code without a terminology lookup.

3.2 Cellular behaviour

3.3 Bridge-layer facts relevant to ambulances

• Telematics boxes (CAN-to-MQTT/TCP, for example Teltonika, CalAmp, Geotab, Samsara) record at 1-10 s and batch every 30-300 s over 4G Cat-1/Cat-4 or LTE-M.
• Time batching: 10 s live, 60 s typical, 300 s economy; flush on ignition-off or at 70-80% buffer fill. Deadband filtering removes 60-90% of samples (speed 1 km/h, coolant 1 degC, fuel 0.5%, GPS 10-50 m or 15-30 deg heading). Report by exception with a 30-300 s heartbeat; tiered rates run 1 Hz when running and one report per 600 s when parked.
• MQTT QoS 0 drops on any link loss; QoS 1 gives duplicates (0.1-2% on lossy cellular, 5-15% of in-flight messages around reconnects) and can be overtaken by newer messages; QoS 2 doubles round trips and is rare on cellular. Use keepalive of 60 s or less because cellular NAT timeouts are 30-300 s; reconnect backoff is 1-60 s with jitter. The cloud dedupe key is (device_id, boot_id, seq).
• LTE-M: round trip 100-300 ms, up to about 1 Mbps, with power-saving wake delays of seconds to minutes.
• The bridge research gives a one-line ambulance coverage pattern: mostly urban, alarms prioritised, reconnect bursts. Tunnels cause 30 s to 10 min of total loss with GNSS also lost and data buffered.
• Store-and-forward: RAM ring plus flash; FIFO drop-oldest is silent loss; keep a priority lane for alarms and DTCs; replay at 1-10 times real time interleaves with live data and causes out-of-order arrival; after 6-72 h offline at 1 Hz, records are dropped and a sequence gap is visible.
• J1939 multi-frame messages (DM1 with more than one DTC, VIN): BAM has no retry, so one lost frame drops the whole message; 0.5-3% of multi-frame messages fail.
• Typical J1939 rates: EEC1 20 ms, CCVS 100 ms, ET1 1 s, DM1 1 s while a fault is active.

4 Mission profiles

CAD timestamps for a call: call received, call answered, location verified, dispatched, en route (turnout), on scene, patient contact, depart scene, arrive hospital, transfer of care, clear, return or available. CAD status codes: Available, Dispatched, En route, On scene, Transporting, At hospital, Clear, Out of service. Status changes are either manual (crew button on the MDT) or automatic (geofence arrival, speed).

Inference: the research gives duration ranges per phase but no formal state machine; a generator would chain these phases as a state machine with the listed ranges as dwell-time distributions.

5 Faults and anomaly signatures

5.1 Bridge and gateway failures that also apply

6 Events, alerts and thresholds

6.1 Driver behaviour events

6.2 Equipment alarms and thresholds

Clinical alarm priorities follow IEC 60601-1-8: high (red; for example asystole, VF, SpO2 below 85), medium (yellow) and low (cyan). Technical alarms include lead-off, low battery and cuff leak. Vital-sign limits are in section 2.5.

6.3 Response-time KPIs

Priority classes: P1 (life-threatening), P2, P3 (non-emergent), with some systems using P4 or determinant codes such as MPDS 10-D-1.

7 Generator guidance for the simulator

The parameter sets below are the research values arranged for generation. Where a distribution shape or a formula is stated, it is an inference (marked) because the research gives ranges and not distributions.

8 How the Sense simulator implements this

8.1 Scenario codes (tenant subvariant)

The Fleet tenant's variant ambulance selects the vehicle kind and its subvariant selects the scenario. The three presets of this report are mapped onto the platform's codes: urban BLS is bls, ALS is als, and rural or critical-care transport is critical-care. A tenant with another subvariant runs no ambulance; the simulator's own selector is used only when the tenant has no subvariant.

Mission phases are the same in all scenarios: station idle (engine off 70% of the time), turnout 45-90 s (siren in 60-90% of priority-1 runs and 15% of priority 2), emergency run, on scene (lognormal, median 12.5 / 14 / 22 min; 8% of calls are treated in place), transport (urban 32-55 km/h, siren on 20-30% of transports, twice as often with an unstable patient), hospital handover (median 20 / 25 min, transfer of care at three quarters of the dwell), return, restock 5-15 min, station idle again. The Wialon param trip_state numbers them: 0 station, 1 dispatched or on the run, 2 on scene, 3 transporting, 4 at hospital, 5 returning, 6 restock. In 75% of the ambulances a call is already running at the start.

8.2 Protocols emitted and the one-vehicle-per-tenant model

Wialon input bits: 0 ignition, 1 siren, 2 emergency lights, 3 rear (patient) door; the iButton field carries the driver card in hex. Cadence (+-10% jitter, and at once on dispatch, siren, door, alarm, shock, NIBP, fault and link events): station 60 s with the engine off and 30 s with it on; turnout and run 5 s (als 2 s); on scene 10 s, with a patient 10 s (als 4 s); transport 10 s, with a patient 5 s (als 2 s); handover as on scene; return 15 s; restock 30 s. NMEA and CAN are sent once a second while the engine is on, CAN slow groups every 5 s and the VIN every 600 s. The patient vitals are not HL7 or FHIR messages: they are Wialon params, because Sense reads HL7 v2 only over TCP and the simulator sends UDP only.

8.3 Signals actually emitted

NMEA is as for buses: GGA latitude, longitude, fix quality, satellites and altitude; RMC status, latitude, longitude, speed (knots) and course. Sense makes one reading per OBD-II or J1939 signal and per Wialon param, named as in the tables.

critical-care sends J1939: EEC1 (61444), EEC2 (61443), CCVS (65265) and LFE (65266) every second; ET1 (65262), EFL/P1 (65263), DD (65276, Fuel level), VEP1 (65271), AMB (65269), HOURS (65253), LFC (65257), VD (65248), VDHR (65217), AT1T1I (65110, DEF), TIRE1 (65268, six wheels in turn) and B1 (65274) every 5 s; DM1 (65226) and the address claim (60928) at engine start. Points and units are those of the truck report, without the tachograph group, Cruise control set speed and Cargo ambient temperature. DM1 codes: SPN 110 FMI 16 (coolant over 102 degC), SPN 168 FMI 1 (battery under 11.5 V), SPN 110 FMI 17 (thermostat stuck open), SPN 1761 FMI 18 (DEF under 10%).

8.4 What Sense can and cannot read yet

The state below follows AMBULANCE_POINTS.md section 8 (checked against the working copy of the Sense listener sources, read only) and Sense's BUILD.md.

• Read by the working copy of Sense, not by the released build of 12 Oct 2026: TIRE1 (65268) and B1 (65274); GGA HDOP and the RMC time; the Wialon record time; a Wialon unit name table that includes the vitals and device names of the table above (for example hr, spo2, nibp_*, etco2, o2_bar, fridge_temp, vent_*, pump*_mlh, defib_j). Names the table does not know, flags and states stay without a unit.
• No standard path for vitals and devices: Sense has an HL7 v2 reader but only for TCP (MLLP), so the synthetic vitals travel as Wialon params and not as HL7 ORU^R01 or FHIR Observations; the MDC and LOINC codes of this report are not used. ECG waveforms, 12-lead data (50-300 KB) and CAD status codes cannot be represented as readings; the 12-lead pre-alert is only a counter and the CAD state a number (trip_state).
• Body, cot, light bar, siren, door and oxygen signals have no J1939 or OBD-II group in Sense; they are carried as Wialon params. OBD-II has no PID for tyre pressure, odometer, seat belt, door or gear, so the vans send tpms_1 to tpms_4 as params; the readable PIDs of this report (0C, 0D, 05, 11, 2F, 42) are all read.
• Alarms (vital_alarm, fridge_alarm, o2_low, door_alarm, cot_alarm) arrive as ordinary readings; Sense does not apply the IEC 60601-1-8 priorities or this report's thresholds to them.
• Not read at all: string params and the iButton field of Wialon IPS; the native UDP form of Wialon IPS 2.0; Sense does not use seq or boot_id, so replays and duplicates count as new readings. The heavy-chassis J1939 groups 65270, 61445, 65272, 61441 and 65258, which the document lists as unread, are not sent by the ambulance.
• Vehicle profiles: the Fleet compatibility check chooses a profile by variant and subvariant (bls, als, critical-care); an empty or unknown subvariant uses the plain Ambulance profile.

8.5 Faults and the ground-truth file

Latent traits and the generic faults are those of the bus and truck work (clock ppm, chronic flag, frame loss, bus-off, J1939 or CAN not-available after engine start, spike, encoding error, stuck-at on fuel level, coolant and fridge temperature, drift, GNSS episodes and cold start, link outages with store-and-forward, reboot, TPMS leak, engine overtemperature, VIN transport abort); rates are those of Tables 5.1 and 5.2 of this report, scaled by --ambulance-faults. Specific to ambulances: oxygen leak (cylinder falls 7-12 bar a minute, 1.5% of shifts), drug fridge fault (compressor off 40-100 min, 1.5% of shifts), battery undervoltage (house battery drains 1.4 V an hour for 25-65 min, 0.75% of shifts), thermostat stuck open (coolant at 68 degC for 30-120 min), door open or cot unlocked while moving (0.0003 per 10 minutes of driving), seatbelt unfastened on 3% of trips, harsh braking (55% of traffic stops during the run, none with a patient on board), monitor artifacts (motion artifact 5-25 s in 5-15% of moving time, lead-off, SpO2 dropout, NIBP retry 7.5% in motion), patient deterioration in 10% of the patients, cardiac arrest in critical patients of als and critical-care (VF 55% or asystole, CPR 100-120 per min, shocks every 2 minutes in VF) and a rare panic button.

With --truth FILE the simulator writes JSON lines, each with t, utc, vehicle and type; first run and one vehicle line per ambulance (scenario, identity, calls per shift, siren share). Then the bus and truck labels that apply and, for ambulances: can_na, station, dispatch (call, priority, scene, hospital, transport), on_scene, transport, at_hospital, transfer_of_care, restock, lights_siren, harsh_brake, seatbelt_unfastened, patient (phenotype 0 stable, 1 unstable, 2 critical; rhythm; weight; deterioration; ventilated), deterioration, vital_alarm, defib_shock, rosc, ecg12_prealert, o2_swap, o2_leak, fridge_fault_start and fridge_fault_end, fridge_alarm, battery_undervoltage_start, thermostat_stuck_open, rear_door_open_moving, cot_unlocked_moving and panic_button. Not simulated: crash and rollover (acceleration over 4-6 g), red-light running, geofence status codes of the CAD, HL7 and FHIR messages, ECG waveforms, AVL gaps beyond the generic link outages, and schema or firmware mismatch.

8.6 Measured differences between the scenarios

Slow runs of 13 Oct 2026 (nothing faster than clock 2; 24 simulated minutes each, starting 13:00 IST), default fault rates, 36 ambulances per scenario over two sets. Speeds are from NMEA, fuel from OBD-II PID 5E or the J1939 fuel rate, cadence from the device time stamps of the Wialon records. Every datagram was identified by Sense's protocol handler as NMEA 0183, OBD-II or J1939, or Wialon IPS (none unknown or unreadable); with every fault at 1000 times the rate, 9 of 7,510 critical-care datagrams carrying only address-claim frames were not identified. The runs cover only what fell into a 24-minute window: no P0128, P0217, P0562 or SPN 168 occurred with frames intact, so those codes were checked by feeding the bytes the simulator writes to the same handler (one event each).

Other measured values: cabin temperature 22.5-32.7 degC (door open: ambient), drug fridge 4.2-7.9 degC (the 7.9 comes from the fridge fault), oxygen cylinder 93-152 bar, house battery 12.55-14.28 V (engine off / on). Priority-1 runs with siren: als 6 of 7 (knob 60-90%); transports with siren 12 of 32 over all sets (knob 20-30%, twice as often with an unstable patient). The Wialon cadence of als shows 1-2 s because the 2 s interval is jittered by +-10% and truncated to whole seconds. Over all sets: 43 calls started, 48 scenes, 32 transports, 14 transfers of care, 14 restocks, 20 12-lead pre-alerts, 2 defibrillator shocks.

9 Uncertainty and assumptions