I’ve never been clear what the main purpose of these things is but they do seem to get deployed for trade shows and such. Maybe for natural disasters?
Then there are microcells, which can be privately owned. I worked at a place that had one when I was in mobile. There was a period of time when one of the carriers would sell you one if you were having connectivity issues. It’s possible for instance, living on a hill, to have a cell signal on your roof but not in the rest of the house and they can work as a repeater.
I first heard of CoWs (cell towers on wheels) from Woodstock '99, when they tried to repeat the debacle of Woodstock '94. (AFAIK, the CoW did not work.)
The idea of cellular networks is simple: Put the "source" of the bandwidth near where the people need it.
The idea of CoWs is also simple: It's the same thing, but it's dynamic and flexible.
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There was a time in my life when I was using AT&T as an all-you-can-eat LTE provider through a third party as my home Internet access, because reasons (and hear you me, if DOCSIS had been an option then none of this would have happened).
Armed with a hotspot device that had external antenna connectors, band selection, and a Yagi antenna, I found a cell tower that I thought to be about 14 miles away that had consistently good Internet bandwidth. It was a ton better than several other much-closer towers (some only 1 or two miles away), presumably because it had better backhaul(s).
I made quite a study of things to get that dialed in and working reliably. And it was reliable for months. But then: One day, the signal had turned to shit.
So I did the right thing and I drove over to where I thought that tower was, 14 miles out, to have a peek. And the tower was right where I expected it to be.
But there were men actively working on the tower (with ropes and stuff), and a CoW of much-smaller stature was parked there and providing (rather lesser) backup service.
Which, you know: That explained that.
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They additionally get used some for natural disasters if a tower fails, and also sometimes for other dynamic events like festivals and concerts and such. They're pretty useful when they work, in that a tiny sliver of bandwidth is superior to zero bandwidth. When properly-managed they can reduce contention on neighboring towers so that regular people doing their regular things are less-affected by whatever dynamic event is happening nearby.
Then there are microcells, which can be privately owned. I worked at a place that had one when I was in mobile. There was a period of time when one of the carriers would sell you one if you were having connectivity issues. It’s possible for instance, living on a hill, to have a cell signal on your roof but not in the rest of the house and they can work as a repeater.