GPS, GLONASS or GNSS: what the difference is and what works in Azerbaijan

When a fleet manager in Baku asks "so is it GPS or GLONASS you have?", there is usually a specific problem behind the question. The tracker lost vehicles in the narrow courtyards of the old city, drew the track across the rooftops in the dense development of the centre, dropped out on the mountain road towards Quba and Qusar. And so the person goes looking for the "right" system that will finally work.

The short answer is a multi-system GNSS receiver. But to understand what it solves and what it does not, let us take it in order.

Why "GPS" is not what you think it is

The word "GPS" has become a generic term, the way "Xerox" stands in for any photocopier. Technically GPS (Global Positioning System) is one specific satellite system, run by the United States. It was built for military purposes and later opened up for civilian use.

The general term for satellite navigation as a whole is GNSS, or Global Navigation Satellite System. It covers four global systems. For vehicles in Azerbaijan it is useful for a tracker to receive several of them at once.

The four global systems

GPS (United States)

Satellites in medium Earth orbit at an altitude of about 20,200 km; the constellation is designed around a minimum of 24 working satellites. In open country — the M-2 motorway, the Kur-Araz lowland, Gobustan — GPS alone is usually enough. In dense development and in gorges the number of visible satellites falls, and accuracy falls with it.

GLONASS (Russia)

GLONASS orbits have an inclination of about 64.8°, greater than that of GPS (around 55°). At middle and northern latitudes that adds satellites high above the horizon. Azerbaijan lies roughly between 38° and 42° north, and the extra satellites help where part of the sky is shut off by buildings or slopes.

Galileo (European Union)

The only one of the four built as a civilian system from the outset. Its open service gives good accuracy, and on modern trackers Galileo is an ordinary part of multi-system reception.

BeiDou (China)

A system with global coverage, some of whose satellites sit in geosynchronous orbits over Asia. Above our region it increases the number of available satellites. How noticeable that is in practice depends on the receiver in the particular tracker.

Official descriptions of the systems are published by their operators: gps.gov (GPS), the GLONASS information and analysis centre, the European agency EUSPA (Galileo) and the official BeiDou site. For the exact specifications of trackers, consult the manufacturer's documentation — the Teltonika Wiki for the FMB models, for instance; the ones we fit are gathered in our catalogue.

How it works: the physics in three minutes

The satellite receiver in a tracker is a radio receiver: it sends nothing to the satellite, it only listens.

Each satellite continuously transmits a signal carrying its own number and the exact time. The tracker measures the delay with which the signal arrives, works out the distance to the satellite and "builds" a sphere around it.

One satellite gives a sphere. Two give a circle. Three give two points. Four give an exact position in three dimensions, with a correction for the receiver's clock.

So the more satellites are visible at once, and the wider they are spread across the sky, the more stable the fix. A multi-system receiver picks the best signals out of several constellations.

Receiving coordinates and transmitting data are two different things

This distinction explains most of the "disappearances" from the map.

• Receiving the coordinates happens from the satellites. It determines where the tracker "thinks" the vehicle is. This is where GNSS helps.
• Transmitting the data happens over the mobile network (Azercell, Bakcell, Nar) to the server of the Wialon platform. With no network the tracker carries on fixing its coordinates and accumulating points in memory, but on the map the vehicle "freezes" until the connection comes back.

Hence a practical conclusion: if a vehicle vanishes from the map in the mountains beyond Quba and the track then appears in full, satellite reception was working normally — there was no mobile coverage. Swapping GPS for GNSS will not help here; a multi-operator SIM and the right buffer settings will, and that is the responsibility of technical support.

Real problems in Azerbaijani conditions

Baku: the "urban canyon" effect

The glass facades of the towers in central Baku reflect the radio signal. The reflected signal arrives with a delay, the receiver calculates the distance wrongly, and the point shifts by tens of metres — the track "jumps" across the rooftops. Antenna quality and the right mounting position for the tracker both help. On top of that the platform can snap the track to the roads.

Mountain roads

On the hairpins of the road to Lahij, or on the passes of the Quba-Qusar district, a tracker that writes a point once every 30 seconds "cuts" the corners straight through the hillside. Trackers with adaptive logging add points when the heading changes, and the track then follows the road. Getting that right is a matter of system configuration, not of the choice of satellite system.

Underground car parks and covered markets

Concrete and metal block the satellite signal completely. Some trackers can in that case work out an approximate position from the base stations of the mobile network (LBS). Accuracy drops to hundreds of metres, but at least it is clear that the vehicle has driven into a particular shopping centre rather than disappeared.

A tracker against a smartphone

Every second client asks this. The difference comes down to several things.

• Logging frequency. A smartphone saves its battery and updates its position rarely in the background. A tracker writes points by set rules: by time, by distance and by change of heading.
• Protection against jammers. When a GPS jammer is switched on, a smartphone simply loses navigation in silence. Many professional trackers can register jamming: the event arrives once the connection is restored, or over a backup channel, depending on the model and the settings. Under a configured scenario the tracker can also prevent the engine from starting.
• Offline memory. The tracker holds points in memory while there is no network and uploads them once the connection is back. A smartphone with an app behaves differently depending on its settings and its charge.
• Power and control. The tracker is wired into the on-board electrics and does not depend on whether the driver took his phone with him or switched location services off.

In summary: what to choose for a fleet

Limitations

• Multi-system reception does not rescue a poor mounting position: a tracker under metal, or with a shaded antenna, will work worse whatever the number of systems.
• Underground, the satellite signal does not get through at all.
• The accuracy of an individual point in the city is metres and tens of metres, not centimetres: enough for keeping account of vehicles, not enough for surveying.

A checklist for choosing a tracker

• the documentation states reception of several GNSS systems;
• there is internal memory for working without a connection, and it is clear how many points it holds;
• adaptive logging by heading and by distance is supported;
• there is detection of jamming and of the power being cut;
• the contractor offers a multi-operator SIM for districts with weak coverage.

Saving money on a simple single-system tracker often ends in a loss of trust in the data. Models with multi-system reception are in our equipment catalogue, and the engineer chooses the position of the antenna during the fitting. Further on the subject: how the fitting works and what the cost of monitoring is made of.