Sunday, October 01, 2017

Microcell through a mobile hotspot

I accidentally acquired a tree farm 20 minutes outside of town. For utilities, it gets electricity and basic phone. It doesn't get water, sewer, cable, or DSL (i.e. no Internet). Also, it doesn't really get cell phone service. While you can get SMS messages up there, you usually can't get a call connected, or hold a conversation if it does.

We have found a solution -- an evil solution. We connect an AT&T "Microcell", which provides home cell phone service through your Internet connection, to an AT&T Mobile Hotspot, which provides an Internet connection through your cell phone service.

Now, you may be laughing at this, because it's a circular connection. It's like trying to make a sailboat go by blowing on the sails, or lifting up a barrel to lighten the load in the boat.

But it actually works.

Since we get some, but not enough, cellular signal, we setup a mast 20 feet high with a directional antenna pointed to the cell tower 7.5 miles to the southwest, connected to a signal amplifier. It's still an imperfect solution, as we are still getting terrain distortions in the signal, but it provides a good enough signal-to-noise ratio to get a solid connection.

We then connect that directional antenna directly to a high-end Mobile Hotspot. This gives us a solid 2mbps connection with a latency under 30milliseconds. This is far lower than the 50mbps you can get right next to a 4G/LTE tower, but it's still pretty good for our purposes.

We then connect the AT&T Microcell to the Mobile Hotspot, via WiFi.

To avoid the circular connection, we lock the frequencies for the Mobile Hotspot to 4G/LTE, and to 3G for the Microcell. This prevents the Mobile Hotspot locking onto the strong 3G signal from the Microcell. It also prevents the two from causing noise to the other.

This works really great. We now get a strong cell signal on our phones even 400 feet from the house through some trees. We can be all over the property, out in the lake, down by the garden, and so on, and have our phones work as normal. It's only AT&T, but that's what the whole family uses.

You might be asking why we didn't just use a normal signal amplifier, like they use on corporate campus. It boosts all the analog frequencies, making any cell phone service works.

We've tried this, and it works a bit, allowing cell phones to work inside the house pretty well. But they don't work outside the house, which is where we spend a lot of time. In addition, while our newer phones work, my sister's iPhone 5 doesn't. We have no idea what's going on. Presumably, we could hire professional installers and stuff to get everything working, but nobody would quote us a price lower than $25,000 to even come look at the property.

Another possible solution is satellite Internet. There are two satellites in orbit that cover the United States with small "spot beams" delivering high-speed service (25mbps downloads). However, the latency is 500milliseconds, which makes it impractical for low-latency applications like phone calls.

While I know a lot about the technology in theory, I find myself hopelessly clueless in practice. I've been playing with SDR ("software defined radio") to try to figure out exactly where to locate and point the directional antenna, but I'm not sure I've come up with anything useful. In casual tests, it seems rotating the antenna from vertical to horizontal increases the signal-to-noise ratio a bit, which seems counter intuitive, and should not happen. So I'm completely lost.

Anyway, I thought I'd write this up as a blogpost, in case anybody has better suggestion. Or, instead of signals, suggestions to get wired connectivity. Properties a half mile away get DSL, I wish I knew who to talk to at the local phone company to pay them money to extend Internet to our property.

Phone works in all this area now


Unknown said...

I had a similar issue, but instead of connecting to a remote cell site, I found a neighbor within a few kilometers who had a "rural broadband initiative" fiber connection, which was dumb luck. I put up a 100' tower and just looked around once it was up and started to canvass properties that I could see, and I got lucky. Two Mikrotik 5ghz APs and I was off to the races. The new ATT microcells work well, but the old orange/white ones are pretty much doorstops at this point. Looks like your property is in Oregon, or at least the PNW, very similar to mine. I've had poor luck with amplifiers, as you have - microcell seems like the best (only) solution for truly robust coverage.

Greg Nation said...

Have you considered IP over Avian Carriers? It may not meet your latency requirements...

As for rotating the antenna, from my limited experience with SDR, every damn thing can cause interference: light bulbs, people, computers, computer monitors, cables, birds (including Avian Carriers), the day of the week, your mother-in-law's birthday, etc, etc. Were there any other variables that changed when you rotated from horizontal to vertical?