It is important to understand that there are two main technologies behind GPS fleet tracking.  The first is obviously GPS, which stands for Global Positioning system.  This is the technology that allows a device to be able to find the location of a vehicle in your fleet with a tracking device installed on it.  The second is GSM, or Global System for Mobile communications.  This technology is how a GPS device can become a GPS tracking device and represents the method of data delivery from your device to a data processing system.  All fleet tracking devices will have GPS on them, but some will use another method of data delivery than GSM, but since GSM is the most common and widely used in both commercial and consumer grade devices that is the technology that we will spend some time talking about.  Our discussion of GSM will have to wait for another article and with this article we will take  a look at GPS and how it works.

GPS, Fleet Tracking, and Satellites

One of the most important things to understand about the Global Positioning System is that it is a global system.  GPS is global because there are 20+ satellites currently in orbit around the earth that are broadcasting signals constantly.  These signals contain specialized bits of data that can be used by specialized receiving devices to determine the location of that device on the face of the earth.

To help us better understand why so many satellites are needed we should probably take a look at a mathematical principle that is key to understanding GPS fleet tracking technologies: trilateration.  Here is a picture that summarizes in graphical form what goes on when a GPS tracking devices goes through the process of trilateration:


A studied glance at this diagram will give anyone enough information about GPS tracking to give them a solid grasp of how it all works.  In this diagram point B is the location of the GPS receiver – let’s say the M3G-2 system from GPS Fleet Solutions, one of the leading names in the fleet tracking industry.  P1, P2, and P3 all represent satellites in orbit around the earth.  The colored spheres represent the distance that a signal from the satellite has traveled over a specified period of time.  The larger the circle, the longer a signal has traveled from the GPS satellite.  This distance traveled is represented by the r1, r2, and r3 in each corresponding sphere.

Now, at point B the M3G-2 fleet tracking system is able to figure out its exact location based upon the know positions of P1, P2, and p3.  Because P1 … are all satellites in orbit around the earth scientists have developed rather precise predictions about where these satellites will be at any given moment in time.  Using know constants, such as their altitude and velocity, they can tell where any satellite is at any moment.  This information is stored in the GPS device and used by it when it receives a signal from a specific satellite.

The distance of r1, r2, and r3 are calculated using the amount of time takes the signal to reach the M3G-2 GPS fleet tracking system.  Since the speed of the signals is known, all the receiver needs to know is when the signal was transmitted from the satellite.  This piece of information is actually contained within the signal sent by the satellite, so all the receiver has to do is read that data and multiply it by the know speed of the signal since:

Distance = Speed x Time

Now that the GPS tracking receiver knows the position of the satellites that have transmitted the signal as well as the relative distance of the receiver from all the satellites it is able to find out its position in the world.

To sum up, here is a bullet point summary:

  • GPS stands for Global Positioning System
  • There are 20+ satellites in orbit around the globe broadcasting signals all the time
  • GPS receivers use a mathematical process called trilateration to find out where they are
    • Trilateration requires that you have information from at least 3 GPS satellites
    • Using the Distance equation (D=SxT), receivers are able to find out all the information they need to get a location for the receiver using the know location of the satellites in their orbit

From this list, we can see that there are some drawbacks to the GPS system.  We will know turn our attention to these drawbacks.

Potential Problems With GPS Fleet Tracking Receivers

Any owner of a fleet tracking system is going to want to know under what conditions their investment is not going to work.  Hopefully, our discussion of how GPS works will help us get a better understanding of what conditions will prevent proper function of the tracking system.  When your business is on the line, you need to have as much information about what it is you are working with as possible.

TrilaterationOne problem is that you could have too few satellites in range of your GPS receiver.  If one of the circles surrounding P1, P2, or P3 were removed from our image to the right, we would not be able to get a firm location of where B is in the world around us.  For example, imagine for a second that P3 was not a part of our picture – all we have is P1 and P2.  As you look at the picture you will notice that Point A and Point B are both points where the two circles, P1 and P2, intersect.  You will also notice that these two points are very far away from each other!

A GPS tracking receiver would not be able to tell where it was on the surface of the earth and this could have disastrous effects for your business.  Imagine trying to route a vehicle in your fleet from their current location to the next service call when they could be in two different places.  What types of difficulties would you encounter when trying to notify a customer about the arrival of their products or service personnel if the vehicle containing the good could be in two different locations?  These issues and more would be your fate if you were only working with two signals.  The problem is compounded even more if you only had a signal from one satellite.  Needless to say, making sure that a GPS receiver has access to at least 3 signals is pretty important.

There a few different things that could prevent your receiver from receiving the proper number of signals to make it an effective GPS fleet tracking device.  The first is that there are physical obstructions preventing your fleet vehicle from hearing what the satellite has to say.  Things like concrete walls, driving in a tunnel, and even being in the urban canyon created by towering skyscrapers all have been shown to inhibit the working of GPS tracking devices.  These obstructions pose a big problem for mainly urban service and delivery fleets who operate exclusively in city centers.

Another thing that can sometimes prevent a receiver from receiving the proper number of signals is being is a remote area.  While the military tried to create a system that could cover the whole globe, there are some physical feature of the earth that create environments where using the Global Positioning System difficult.  Mountainous areas, deep canyons, heavy forests, and caves all inhibit a receiver’s ability to get a lock on a satellite signal.  Other natural phenomena also can effect this process including heavy rain or snow, heavy fog, or simply heavy cloud cover.  Pretty much any obstruction of a satellite’s signal is going to affect a fleet tracking receiver’s ability to get a fix on its location.

A-GPS Fleet Tracking: As A Solution

In order to help prevent some of these problems from occurring, the GPS fleet tracking industry has made some efforts to improve receiver performance in all sorts of circumstances.  The outcome has been the development of A-GPS fleet tracking.  The A in A-GPS stands for ‘Assisted’ and helps receivers overcome the difficulty that weak satellite signals create for vehicle tracking and fleet management.

TrilaterationWhat A-GPS is able to do is leverage existing cell phone towers and other wireless communication arrays to make up for the loss of one or more signals from a satellite.  For example, let us assume that our example from above is still true – that P1 and P2 represent satellite signals where both A and B are possible locations for a GPS receiver like the M3G-2 GPS fleet tracking system.  Because both A and B are possible outcomes of the trilateration process, the receiver doesn’t know exactly where it is on the face of the earth.

However, the M3G-2 is using A-GPS.  Because of this is is able to tap into some cell phone towers in the area which will give it a point of reference from which to create the circle represented by P3.  Therefore, the A-GPS fleet tracking device is able to perform where a normal tracking device would fail.  A-GPS is certainly superior and has been a major improvement to fleet tracking technology .

Position Finding and Position Communication

In talking about GPS we have discussed the first major part of GPS fleet tracking – position finding.  If you want to be able to track a vehicle in your fleet then you obviously need the vehicle to know where it is in the world.  This is first and most important part of this process and the Global Positioning System provide the technology for this to occur.  Next, we are going to discuss GSM which serves as the position communication technology in most fleet tracking devices.  For once the device knows where it is, it has to find a way to communicate that information to you, the fleet owner or fleet dispatcher.  GSM is where this capability comes from and is an integral part of GPS fleet tracking technologies.

Find out more about GMS and how it affects GPS fleet tracking here: GPS Fleet Tracking Technologies: GSM