In 2022, GPS is all around us – maybe even more so than some people are comfortable with. Short for “Global Positioning System,” GPS is the hallmark technology used for locating and tracking people and things, and for that reason, surrounds our everyday lives.
We can not only access detailed route guidance from San Diego to San Francisco, but we can also search for generic term like “food” and see only relevant, nearby restaurants recommended to us. Even mobile applications can utilize GPS to offer us a streamlined experience.
But how exactly does GPS work? And what does the technology really do? Without any knowledge on the subject one might assume that it utilizes the Internet to find its location. I know I did at first. I mean, every innovation nowadays comes from the Internet, right?
Let’s consider the GPS navigation systems in our car sand on our phones. Cars – at least for the moment – generally do not connect to the Internet. However, in-car GPS systems have existed for over 20 years. And in phones/mobile devices, our Maps route does not crash or quit once we enter an area with no service. By those two examples alone, we can see that “Internet” does not hold up as the answer to our question. In a practical sense too, if GPS relied on the Internet to function, it would be a huge limitation to the technology. Imagine being in a remote location and losing your route because of weak connection or having your route buffer right before a turn in a busy city. The limitations could be dangerous.
But if not thanks to the Internet, then how does GPS work?
At its core, GPS is a system that includes 31 satellites that orbit the Earth and send out information that devices receive and use to determine their (the device’s) location. There are 31 satellites to ensure that GPS devices can be anywhere on Earth and still pick up signals from at least 4 satellites (more on this below). This process breaks down into five major steps:
STEP 1: Satellites send a signal via radio wave that includes location and time data
STEP 2: Radio signal travels from space to Earth for devices to receive
STEP 3: GPS device (smartphone, tracking unit, etc.) receives signal and notes the
exact time the signal was received
STEP 4: GPS device calculates distance from the satellite
STEP 5: GPS device repeats steps 1-4 for four satellites, and uses geometry to find
GPS: A Closer Look
Let’s take a closer look at each step to better understand this process.
Step 1: Satellites send out a radio wave signal
Starting at step 1, each of the 31 satellites is constantly sending out a unique, repeating code in the form of radio signals. These signals are sent out regardless of any action on the receiving end. In other words, GPS devices do not request data from a satellite; satellites send out signals and GPS devices receive when needed. So, if all GPS devices were shut down, these satellites would still be transmitting the signal, they would just not be received by anything. This allows for maximum coverage from the GPS system because it does not rely on the device being able to reach the satellite. If every GPS device had to communicate with each of the 31 satellites, these satellites would be overloaded, and the system would either crash or be extremely slow. Instead, satellites send out their signals into open space and devices that pick up the signal determine whether or not they need the information. This is just like our FM & AM radio stations. Each radio station will send out its signal regardless of who is listening, and it will be up to us to “tune in” to that signal and receive the data. But even if we do not tune in, that signal is still being sent out.
Looking at the image below, we can see that a satellite can send its data to many different GPS devices at once, because it sends out one wave into the open space, and GPS devices choose whether or not to receive the signal.
Step 2: Radio Signal Travels from Space to Earth
As mentioned above, these radio signals are not directed towards any particular device. So, when the satellite sends out a radio wave, it travels to Earth and is picked up by whatever devices can find the signal and want to pick it up. The key thing to note in this step is the rate at which the signal travels. These radio waves travel at the speed of light (c), which is 3x10^8 meters per second.
Steps 3 & 4: GPS Device Receives Signal and Calculates Distance
In these steps, the device detects the satellite signal and then tracks the beginning and end of the regular sequence sent by the satellite. From there the receiver can determine how long the radio wave took to travel from the satellite to the receiver. Now, using this calculated time and the fixed speed of the signal, the speed of light, we can calculate the distance between the GPS device and the satellite using the following formula:
Distance = rate * time
Step 5: Use Distances from 4 Satellites to Find Location
While it seems like we solved our equation after step 4, we are still not quite there. Knowing the distance from our GPS device to the satellite is great information, but in the end the distance does not tell us our location. However, we can utilize distances from multiple satellites to calculate the device location.
If we have the distance from four different satellites, we can use geometry to figure out the location of the receiver. Each satellite creates a sphere with a radius of its respective distance, and then intersection of the four spheres will be where the GPS tracker is located.
The reason that four satellites are needed is because we are trying to find a unique intersection point in three dimensional space. You make think three dimensions means three satellites, but in actuality four satellites are needed to find a distinct, single intersection point. Let us consider the 2D space to see why this happens. Looking at the diagram below, you can see that with two circles, there are two points of intersection. However, bringing in a third circle will eliminate one of those points and narrow down to only one point of intersection.
Using that same logic, we can extend that line of thinking to the 3D space. Having only three satellites will lead to two intersecting results: one on the surface, and one approximately 12,500+ miles off of Earth's surface. So, bringing in the fourth satellite will narrow the results down to the true location of the GPS device.
In reality, there are many more computations, factors, and nuances at play in the process of calculating location using GPS, but this description provides the foundation. Overall, GPS is incredibly accurate at telling time and location, and is utilized in many different ways across many different industries. GPS is a critical factor at play in telematics, and allows solutions like Positioning Universal’s FT7500 to provide reliable, accurate data to fleet managers, no matter the surrounding conditions. And for fleets that traverse many thousands of miles through all sorts of terrains, this means safety and security for their drivers.