Do Chipset Channels Matter?
When people start comparing different GPS devices, a feature commonly listed among marketing materials is the number of “channels” a GPS has. Inside every GPS device is something known as the “GPS chipset” which is the heart of finding where you are. Different chipsets use a different number of “channels”. So what are these channels, and are they important in determining which GPS to purchase?
First, it might be helpful if you have a basic understanding of how GPS works. While the following video was produced with an audience of kids in mind, sometimes taking it down to this very basic level is helpful.
At the most basic level, think of your GPS as needing one channel for every satellite it is communicating with. (Note that technical GPS whiz people will know there are exceptions, but for this basic article we’re going to ignore that.) So the more channels your GPS’s chipset has, the more satellites it can communicate with at one time.
So the more channels, the better, right? Well– no, not exactly. At any given time there are at least 24, more more often about 30 satellites that make up the GPS system. They orbit the earth about 12,000 miles above us. The system is designed to provide similar levels of service anywhere in the world. So at any given moment of time you won’t be able to “see” all of the sites at one time. At least half of them will be out of view on the other side of the planet. Others could be out of view due to ground obstructions (mountains, buildings, etc).
Many GPS devices have a satellite information screen that will show you how many satellites your GPS is tracking at any given time. If you view this page and take your GPS device somewhere with an unobstructed sky view, you can see how many satellites your GPS is tracking, and thus how many channels are being used.
Take the picture to the right of the paragraph above and you will see that the GPS was tracking 10 satellites, so essentially 10 channels were being used. It is rare for a GPS to be tracking more than 12 satellites at any given time. So in that sense– having a GPS which has more than 12 channels might seem like a waste… and to some degree it is.
But channels can be used for more than just tracking a satellite “right now”. Sometimes channels can be reserved for “searching” as new satellites are predicted to come into your view. If you watch the satellite info screen over a period of an hour or so you will see that some satellites disappear from view while other satellites appear on the horizon. So while your GPS might be tracking only 8 satellites, it might be using a couple of other channels to search for new satellites it is predicting will come into view.
Why More?
So why have 20, 30, or 60 channel receivers? To some degree it is a marketing gimmick. Back in the “old days” of GPS, a receiver might only have 8 channels. Then came along the 12 channel receivers which improved reception and acquisition times dramatically. Then came along 16 channel receivers which also showed some improvement. So where to go from there? Add more channels.
Unfortunately, now that the number of channels a receiver has has exceeded the amount of satellites you can realistically track at any given time, the benefits of a 20+ channel receiver are muddier. This issue is further compounded by the fact that many of the popular 20 channel chipsets such as the SiRFstarIII, have a 20 channel receiver. The SiRFstarIII is a great chipset– without doubt, but its greatness isn’t just because it has 20 channels. (The reasons are more technical and beyond the scope of this article.)
The Bottom Line
The more channels the better– to a point. You can’t simply say that just because one chipset has 16 channels and another has 20 channels that the 20 channel receiver will have more accurate, or faster performance. So for the most part, unless you are doing some sort of activity that needs the highest precision possible in a consumer level GPS (which is rare) I tell people these days to largely ignore the number of channels a GPS device has. Other factors such as the location of the chipset in the device and the materials the device is made from will have a greater impact on signal performance.
