[One (M7) Android Development] trjlive:
Information about LTE signal levels

This is just a follow-up about the LTE signal levels issue that some people are experiencing. I did a test and took some screenshots that better illustrate the point I was trying to make in this post, which I think I may have made more confusing than it needs to be. I also talked with a T-Mobile engineer who gave me some more insight to the "low LTE levels" in the United States.

According to my T-Mobile engineer source, due to the type of technology used to deploy LTE, it is possible to have a usable signal with lower dBm to the handsets. LTE is more power-efficient, and doesn't require as strong of a signal to still have usable throughput. This way, the carriers get LTE coverage over the same physical area as HSPA by upgrading essential every other tower (easiest way to think about it), albeit at a lower, though still usable signal level. Then after then get the initial LTE deployment is complete, and they can say they have officially launched LTE in a certain metro area, they can go back through and upgrade the remaining towers, increasing the signal levels to handsets even more.

Edge/HSPA

When I am connected to the Edge network, I get a signal level of about -81 dBm, which is a fairly strong signal. Android displays this level as full bars. When I connect to the HSPA network, I get a signal level of about -87 dBm, which is a little lower than the Edge, but still pretty strong and very usable. Android still displays this level as full bars. When using Edge/HSPA, the lower cutoff for a decent signal is about -102 dBm. Anything stronger than that (smaller number is better) is considered good. Above about -75 dBm is considered excellent. So you can see that my -81 and -87 is pretty middle-of-the-road signal level.

LTE

When I connect to the LTE network, I get a signal of -108 dBm. Since Android considers any signal less than -102 dBm to be a poor signal, it displays only a single bar for my -108 dBm. However, the usable signal levels for LTE are different than Edge/HSPA. Usable LTE signal average ranges from about -80 dBm to about -120 dBm. So my signal of -108 dBm should be in about the same position as my Edge/HSPA signal level, meaning my LTE should be almost full bars, or at least 3/4 of the way to full bars. There is nothing wrong with a LTE signal of -108 dBm, I am still getting plenty fast speed tests (download 20Mbps+), even though Android thinks I have a poor signal level. Just look at the numbers on the scales, the range is different between Edge/HSPA and LTE.

I did these three tests with my phone in the exact same location, at generally the same time (within minutes of each other). My wifi and bluetooth was turned off. You will notice I'm running the GPE rom, but the results are essentially the same with a Sense rom. I'm using firmware 4.06.1540.2 and radio 4T.21.3218.21 on the AT&T network.

Because Android apparently doesn't take this different LTE scale into account, American carriers have taken it upon themselves to modify the signal level icons with signal meters that better reflect the lower but still usable signal levels. That is why changing the device's sku_id to 11 for T-Mobile or 7 for AT&T makes it look like you're getting better signal. You're not really getting any better signal level, the modification just tells the device to display more bars for the same signal level. The mod is basically doing what Android should do by default, which is sliding the scale down so a lower LTE signal still appears to be good.

Hopefully this all makes better sense than my previous post on this issue. I apologize for a long-winded post, but I'm sure there are plenty of people who didn't know this information and were wondering about it. If there are any questions about this that I didn't answer, by all means ask and I can ask my T-Mobile contact.