Project Fi Network Selection Explained – Hopefully

Over the course of the past few weeks, I’ve read a lot of comments here and on Google+ with regards to Project Fi and the criteria it uses to select the carrier to use at any given time.  It is an interesting subject and one that I have a fair amount of experience with not only as a Fi subscriber, but in my day job in the communications industry.  The confusion, I think, rests with a user having what appears to be full signal strength in their area on say T-Mobile yet their phone is continually connecting to Sprint which has less signal in that location.  As a general rule, you won’t know which network you are on unless you are using a tool like Signal Spy to check it out.  But the bottom line is that a stronger signal isn’t the only thing that Google is looking for when it comes to selecting the network in Project Fi.

I covered this notion in my post back in December 2015 on how to know if your call is going over Wi-Fi but I am going to go more in depth to hopefully clear up the matter.  First, let’s talk about how Fi chooses a network.  There is a set of criteria involved that includes both signal strength and signal quality.  Signal strength is the easier one to explain as it apparent to everyone.  This is simply how “loud” the signal is reaching your phone.  In theory, the louder the signal (the stronger it is), it should have the best quality for voice and highest throughput for data.  But that isn’t always the case.  Things interfere with that signal such as the structure you are in, the amount of radio frequency (RF) interference between you and the cellular POP and even things like the case you have on your phone.  That’s where the second measurement comes into play.  Signal quality is measuring the throughput of that connection.  That’s where the interference comes into play.  You may have “4 bars” on T-Mobile but if there is a lot of interference, your Nexus may chose Sprint as it doesn’t have as much interference but has a weaker signal.  Compounding this is network congestion.  We tend to think of congestion from a data perspective (my connection is slow) but the same applies to voice communications as well.  If you are connecting to a tower that has a lot of T-Mobile calls going on, Fi will go to Sprint to assure you can get a call out even if that call isn’t the best available.

Clear as mud?

Now why is this all important?  Because if you use a tool like Signal Spy or dialer codes and force your Nexus device to switch between one network to the other, it may appear that one is better than the other but the reality is that the call quality may not be up to Google’s standards.  Thus, on its own, it chose the “weaker” network to assure that you have the best call experience possible.

Project Fi Data Use
Project Fi App

To be fair I am way over simplifying this process but you have the basics of how it works.

For those of you who use Project Fi and are using a tool like Signal Spy or using dialer codes to force your phone to one network or another, keep in mind that you may actually be hurting yourself more over the long run.  Fi is constantly measuring strength and quality for both T-Mobile and Sprint in your area from your Nexus.  That is part of the mechanism by which it switches from one network to another.  By forcing your Nexus to just T-Mobile or just Sprint, the service can’t learn what is best in your area.  Further, Google can’t go back to the carriers and ask/persuade/force them to make any changes without data points to prove that something needs to change.  Do I know this for fact?  No.  I’m not an employee of Google and exactly what types of conversations they have with the carriers is not known to me nor is the algorithm they use to calculate these values.  But I can say I, based on empirical evidence, that this is the case.

When I first signed up for Fi, my signal in Denver was predominantly on Sprint and while weak, did provide me good call quality.  Over the course of the first few weeks however, I noticed that my Nexus 6 was increasingly using T-Mobile in Denver and my signal strength and quality improved.  I noted the same thing in Austin, Texas where I travel frequently and San Francisco, California.  In San Francisco, I noted I almost always connected to T-Mobile but now when I am there, I am usually on Sprint.  In all of these cases, it learned where I was and which provider would give me the best experience based on these criteria and congestion.

I have been focusing on calls on Project Fi for this article but the principles hold true for data throughput as well.  Signal strength and signal quality as just as important here too but they are helped a bit with things like T-Mobile’s 700 MHz Band 12 LTE which can go over further distances and through buildings much easier.  This, fundamentally, is part of the whole discussion around calls going over Wi-Fi too.  It’s all part of the same cake, just different layers in the cake.

All of this, from an engineering perspective is impressive.  As I put in my review of Fi when I first joined up, Doing this is nothing short of engineering gymnastics. To get a device to switch antennas and carrier modes actively is extremely difficult.  Then Google went one step further.  In the Nexus devices it will switch between these two carriers and Wi-Fi.  So now if you have strong, good quality Wi-Fi it will leverage that for your calls and if that signal starts to drop, it will seamlessly hand the call of to one of the carriers so you don’t lose the call.  You, as a user, don’t have to do anything to make this happen.

Hopefully this clears up some things for you on the subject.  The best advice I can give – and it is just that, advice – is that you let Fi figure it out on its own for your area.  That may mean a few challenging weeks when you first sign up but it should improve and when more Fi users get to you area, that is only going to help speed things up.