We continually hear people complain about their cell service being slow, weak or otherwise unacceptable even though they live near a cell tower. Of course, the simplest response is to question whether or not the tower they can see is actually used by the cellular carrier they have an account with. Even if you can access the fence around most towers, you can’t always tell from the signage which carrier(s) are using that tower. Towers are often owned by third parties and any particular carrier may or may not be broadcasting from any particular tower.
Assuming that you are correct and the tower near your location has an antenna for the carrier you use, the next question is whether or not the beam from the antenna is pointed in your direction. Although we may, conceptually think of antennas as radiating in all directions, cell phone towers don’t operate that way.
Figure 1 is a screenshot from an Android app called Network Cell Info Lite. The app is reporting how my Verizon Pixel 5 is connecting to the network. For the moment we’re going to ignore the numbers at the top of the picture and will only look at the map. My location is shown as the blue dot and the tower I am connected to is to my south.
Notice that there are two yellow circles with signal strength bars just to my north. Those are Verizon-owned towers which the app has in its database. But notice that I’m not connected to either of them even though they seem closer.
The answer to that question, most likely comes from the beam pattern of those antennas compared to the one I am connected to. The antennas in the yellow circles are positioned to service the towns of Rockport and Fulton and their beam patterns are, most likely optimize to the urban areas around them. The tower my phone is connected to is probably optimized to service State highway 35 that lies just to the west of our location. It makes sense that that tower would have an “elongated” footprint roughly parallel with the highway.
I happen to know from my own testing that my location is in a particularly poor spot because we are far away enough from the highway to be in the edge of the serving tower’s beam but too far away from the in-town towers to receive their signals.
So now if you think you can guess the tower that serves you by knowing its beam pattern, you are only partly correct. That’s only the first-tier decision process; the next step comes about when your phone or hotspot determines which of the towers in your area actually provides the best usable signal. Notice that I didn’t say which tower provides the “strongest” signal. Lots of people make the mistake of focusing solely on signal strength. But that’s not always the same as which tower provides the best usable signal.
To answer that question, we need to look at the “dials” and numbers at the top of the picture. They depict the cell I am connected (on the left) and the “neighboring cell” on the right. That might seem odd; why should we care about the signal from a neighboring cell that we’re not connected to? That’s because our phone is always “looking” for a better connection and if it can find it in a neighboring cell it will shift our connection to that cell. That’s what happens when you are driving along the highway; your phone is continuously checking the neighboring cells for signal strength and quality. When it finds a better combination of the two it will switch your connection to that cell?
Let’s now look at the dials at the top of the screenshot. In the left dial the large number tells us that the signal strength is -104 dBm (decibels). In “cell phone lingo” that’s called the RSRP. If you haven’t heard this before, decibels are a logarithmic measurement and signal strength is measured in negative decibels so a smaller negative number will represent a stronger signal. In our case the signal strength is -104 dB which Is not a particularly good signal strength but it’s what I have at my location. But the reason that I don’t have much of a problem using that weak signal is embedded in that little “-10 dB” that you can see to the right of the -104. That -10 dB is what is called the RSRQ and it’s a measure of what engineers call the “signal to noise ratio.” We’re not going to worry about how the RSRQ is calculated, we’re simply going to accept the fact that an RSRQ of -10 dB is rather good. Notice that just above the dial it notes that we are connected using Band 13.
Figure 2 is a table published by Quectel, a major manufacturer of cellular modems. The table provides comparative “ratings” of RSRP and RSRQ values. My -104 dBm RSRP value is weak, but my RSRQ of -10 dB is rated as excellent (a value equal to or greater than -10). That makes it possible for my phone to provide excellent performance despite the weak signal. Would I benefit by boosting the strength of the signal; maybe not because the signal quality is already as good as it can be. For those of us raised on analog signals, this is one of the oddities of working with digital signals; they only need to be “strong enough” to be quite usable. Making them stronger doesn’t necessarily improve the situation.
So now let’s look at the dial on the top right side of the first figure. It shows the RSRP and RSRQ for our neighboring cell. We can see that the RSRP (the signal strength) is -112 dBm. Because of the logarithmic nature of decibels, a reduction of 6 dBm in signal strength is a factor of 4. The neighboring cell is definitely weaker. In addition, when we look at the RSRQ we see that it is -11 dB which means that the signal to noise ratio is not quite as good as we have in the cell we are connected to. In this instance, there is no question but that we’ll stay connected to the cell we’re in. But these numbers can and will vary over time and every once in a while, even without moving my location, the connection will switch to the other cell. Notice that in this case the evaluation of the signal was made using Band 2 compared to Band 13 used in the first case.
If all of this seems a bit confusing, I can assure you that this has been an extremely simplified discussion of how your phone selects a tower and a band to use for your phone conversation or internet connection. And think about the fact that it is constantly re-evaluating that “decision” multiple times per second in order to give you the highest speeds and best voice conversation quality possible. So the next time someone says to you “how come my cell service is so poor even though I live next to a tower?” you can tell them that “there’s more to it than you might have thought!”
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