A modern driver cannot imagine his trip without an electronic map, which shows the location and routes in real time. GPS is an acronym that we hear every day, but few people think about the complex physical processes that allow your smartphone or navigator to accurately determine where you are. The Global Positioning System has become so familiar that we have ceased to be surprised by its accuracy, although behind it lies the work of dozens of satellites orbiting the Earth at enormous speed.
The principle of operation of this technology is based on radio signals that are transmitted from orbit to a receiver in your device. Global Positioning System was developed by the US Department of Defense, but has long been available for civilian use around the world. Understanding exactly how satellites “communicate” with your car will help you better navigate situations where navigation fails and consciously choose additional equipment for your car.
In this article, we will analyze the structure of the system, answer the question “what is GPS?” and find out why the signal may disappear in a tunnel or among high-rise buildings. You will learn how a civilian signal differs from a military one, and what factors influence the accuracy of coordinate determination. This knowledge is necessary for everyone who values their time and plans routes in advance.
How satellite navigation works
The whole system is based on triangulation, or, more precisely, trilateration. A constellation of 24 main satellites is constantly in Earth’s orbit, distributed in such a way that at any point on the planet the receiver “sees” at least four of them. Satellite continuously transmits a radio signal containing information about its exact location and the time the message was sent. Receiver, whether in your phone or on-board computer Toyota, catches these signals.
The key parameter here is time. The radio signal travels at the speed of light, and the receiver calculates the distance to each satellite by multiplying the signal's travel time by that speed. If you know the distance to three satellites, you can determine the coordinates on the plane, but to obtain the altitude above sea level and synchronize the clocks, a signal from the fourth satellite is needed. Atomic clock on board spacecraft provide incredible accuracy, since even a microscopic error in time will lead to a huge shift in coordinates on the ground.
⚠️ Attention: Positioning accuracy directly depends on time synchronization. If the clocks in the receiver and satellite are out of sync by even one millisecond, the error in position determination will be about 300 kilometers!
The process of calculating coordinates occurs in a fraction of a second, but in practice there are delays caused by the signal passing through the atmosphere. The ionosphere and troposphere can slow down radio waves, introducing additional errors. Modern receivers use complex algorithms to compensate for these effects, but physics is physics - perfect accuracy cannot be achieved under certain conditions.
What does a global positioning system consist of?
Many people mistakenly believe that GPS is just an app on your phone. In fact, this is a complex infrastructure complex consisting of three segments: space, control and user. The space segment is the same satellites that rotate at an altitude of about 20,000 kilometers. They are constantly in motion and require periodic orbital correction.
The control segment is a network of ground stations scattered around the globe. These stations monitor the status of satellites, correct their orbits and check the time on the on-board atomic clocks. Without constant monitoring by operators, the system would quickly lose its accuracy and become useless. Ground stations they also download new almanacs - data on the position of all satellites in the system.
The user segment is all the devices that we hold in our hands or install in our cars. These could be smartphones based on Android or iOS, car navigators Garmin, trackers for transport control or even smart watches. All of them are equipped with a GPS receiver that is capable of decoding signals coming from orbit. This segment is growing the fastest, becoming an integral part of our lives.
To improve signal reception in the car, try not to cover the location where the navigator is installed with metal objects or a thick layer of plastic, as metal shields radio waves.
Accuracy of coordinate determination and influencing factors
Under ideal conditions, in open areas with clear skies, civilian receivers provide an accuracy of 3 to 10 meters. This is quite enough for navigation on public roads. However, there are factors that can significantly worsen this indicator. Error can grow to tens of meters if the signal passes through dense clouds, tree foliage, or is reflected from surfaces.
One of the main enemies of accuracy is the multipath effect. A signal from a satellite may bounce off the wall of a building, a glass façade, or even the surface of the earth before reaching the receiver's antenna. In this case, the device receives a reflected, longer signal path, which introduces an error into the calculations. In the “canyons” of megacities, where tall buildings surround the road on all sides, the navigator may show that you are on the wrong side of the street.
| Influence factor | Description of impact | Impact on accuracy |
|---|---|---|
| Atmospheric conditions | Ionospheric signal delays | Low (2-5 meters) |
| Multipath effect | Reflection from buildings and terrain | Medium (5-15 meters) |
| Satellite geometry | Location of visible satellites | High (up to 50 meters) |
| Tunnels and bridges | Complete signal coverage | Signal loss |
Also important is the geometry of the satellites, known as GDOP (Geometric Dilution of Precision). If all visible satellites are clustered in one part of the sky, accuracy drops sharply. The ideal situation is when the satellites are evenly distributed across the sky. This is why navigation works worse in narrow gorges or between tall buildings than in an open field.
Differences between GPS, GLONASS and other systems
Although the title GPS has become a household word; it refers exclusively to the American system. However, there are other global navigation satellite systems (GNSS) in the world. Russian system GLONASS is a direct analogue and provides coverage of the entire territory of the Earth. European system Galileo and Chinese BeiDou are also actively being developed and used in modern smartphones.
Modern receivers are usually multi-system. This means that they can simultaneously receive signals from GPS, GLONASS and other satellites. The more satellites the device “sees,” the higher the accuracy and reliability of positioning. The use of several systems allows you to compensate for the disadvantages of one at the expense of the advantages of another, especially in difficult urban conditions.
⚠️ Attention: When purchasing a navigator or tracker, pay attention to multi-system support. A GPS-only device will be less accurate in northern latitudes than a combined GPS+GLONASS receiver.
Technically, the systems differ in orbital parameters and signal encoding methods. For example, GLONASS satellites have a slightly different orbital altitude and inclination, which can be advantageous at high latitudes. However, for the average user, the difference lies only in the speed of the “cold start” and the stability of communication in difficult conditions.
Why is the American system called GPS, and the Russian GLONASS?
GPS (Global Positioning System) is the trade name of the American system, which has become a brand. The full technical name is NAVSTAR GPS. GLONASS is an acronym for Global Navigation Satellite System. The difference in names is due to the history of development and marketing promotion of technologies in different countries.
Signal reception problems in an urban environment
Urban environments create unique challenges for satellite navigation. Dense buildings, tunnels, underground parking lots, and even just canopies over bus stops can block the direct path of radio waves. In such cases, the navigator often goes into “dead reckoning” mode, using the accelerometers and gyroscopes of the smartphone or car to roughly determine the location based on inertia.
A common problem is the so-called “cold start”. If you have not used the navigator for a long time or transported it over a long distance while it was turned off, it needs time to load the current satellite almanac. During this period, the device searches for satellites “blindly,” which can take from 30 seconds to several minutes. With a “warm start”, when the approximate coordinates and almanac are already in memory, the start occurs in a few seconds.
The influence of weather should also not be discounted. Although radio waves pass through clouds and rain, heavy thunderstorms or heavy snowfall can weaken the signal. In addition, a wet car roof or a layer of snow on the antenna (if it is external) can also serve as an additional filter that reduces the quality of reception.
☑️ Checking the quality of signal reception
The future of satellite navigation and new technologies
Technologies do not stand still, and the requirements for navigation accuracy are growing. If previously 10 meters was the norm, then for self-driving cars accuracy down to centimeters is required. To achieve this, differential correction systems are being introduced, which use ground-based base stations to transmit corrections to the satellite signal. This allows atmospheric and orbital errors to be corrected in real time.
Navigation integration with other data sources is also being developed. Cell towers, Wi-Fi hotspots and even magnetic field sensors help the device locate where a satellite signal is not available. The future lies in hybrid systems that switch between satellites, cellular networks and sensor data to provide continuous positioning.
An important area is protection against spoofing and signal jamming. As navigation has become a critical infrastructure, devices are emerging that can create false coordinates or block receivers. Developing secure civilian signals and authentication algorithms is one of the main challenges for developers in the coming years.
Modern navigation is a symbiosis of satellite data, cellular networks and inertial sensors, which allows it to maintain accuracy even in dense urban areas.