AT&T 3G MicroCell: A Comprehensive Exploration
by Brian Klug on April 1, 2010 1:55 AM EST- Posted in
- Smartphones
- AT&T
- Microcell Review
- Mobile
I mentioned earlier that voice and data both work fine, as long as you're inside the MicroCell's coverage radius. So what happens if you step outside? In theory and per advertising, your call is supposed to transition "seamlessly" to the nearest macrosite. In fact, the first time I tried walking out of location 1, it transitioned perfectly! I then proceeded to spend over a half hour trying to repeat my initial success...
The Theory of Handovers
But before I dive into the problems I experienced, let's briefly touch on some of the tech behind it. There are two types of handover that happen on a cellular network: soft and hard handovers. In a soft handover, the phone is continually talking to multiple macrocells at the same time - the transition happens seamlessly because you're already connected and communicating with towers you're going to handover to. This is a make-before-break transition. The transition is simply a matter of choosing which one has the best link quality, and this is generally how most transitions happen because it's robust.
The other case is a hard handover - this is less seamless break-before-make transition that's nearly instantaneous in practice, but still perceptible if you know what to look for. In a hard handover, the phone literally releases its active connection and transitions to another. Also of relevance are so-called vertical handoffs - these are transitions that happen across network technologies, in this case from UMTS to GSM, though other cross-technology handovers are possible as well. There's a huge amount of complexity to these systems; effectively handing off users while maintaining voice and data sessions is a challenging multidimensional problem. One that's often taken entirely for granted because of just how well we're used to it working.
So you can imagine my surprise when I discovered that the handover from femtocell back to public 3G wasn't just rough, it's downright crude. First of all, virtually every femtocell handover is of the hard variety, and in practice almost all of the ones I saw were also vertical, from UMTS (3G) to GSM (2G). During that long provisioning process, I mentioned that the femtocell is building a rough list of all the macrocells it can see. Hopefully, it can see a few of both 3G and 2G variety, which it passes onto the phone in the form of a neighbor list. The phone also builds out its own neighbor list, which you can see some of in the Field Trial (*3001#12345#*) dialer application. It's been gimped significantly since the iPhone 2G, but there's still enough here to get the point across:
Neighbor Cells - Just like advertised
Anyhow, when you leave the femtocell's radius, if there's a macrocell in range and your phone can hard handover to it, the call continues. Hopefully this is what happens, otherwise the call drops. Of course, the big caveat here is that if you're installing the femtocell in a place with little to no signal (why it's there in the first place) handover is going to be a difficult prospect. That's why I tried the AT&T MicroCell both in an area with good existing coverage, and one with poor coverage. The results at both were equally disappointing.
AT&T advertises an effective range of 5000 square feet. This seems about right, but it's signal dependent. Location one is just over of 2000 square feet, and continual femtocell coverage barely makes it across two rooms. Location two is effectively 5000 square feet, and femtocell coverage includes the whole house, guest house, and most of both long driveways. Again, this is largely in part because the femtocell is sitting atop existing 3G spectrum - there's no spectrum overlay just for microcells yet. The result is that if signal is bad where you are, your microcell range is larger. Conversely, if signal is already reasonable, you're not going to see more than a room or two of microcell coverage. It's a complex problem akin to the cell breathing phenomenon, and I think AT&T's 3G MicroCell product is doing a lot of ranging at setup.
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A beautiful mind - Thursday, April 1, 2010 - link
My Nokia N900 already uses the home/office wifi connection to access the internet, with the possibility to receive/make calls from/to skype.There is absolutely no extra functionality that is provided by the femtocell approach.
softdrinkviking - Thursday, April 1, 2010 - link
For you and me, this is true.But not for everyone.
That's the really sad thing about this device. It's designed as a way to nickel and dime poor souls whose homes are in a dead zone and absolutely have to answer their phone for business.
nafhan - Thursday, April 1, 2010 - link
Great article, and you did an excellent job of diving into the tech behind the femtocell.An interesting follow up to this article might be to see what kind of results you get from purchasing an antenna and repeater. I've seen antenna/repeater setups online in the $350 and up range, and wondered how they would do. If they work OK, it might be a viable alternative, especially for people without good internet connections.
gwolfman - Thursday, April 1, 2010 - link
Where is the print article feature on the new site?Maroon - Thursday, April 1, 2010 - link
They've been sneaking these things in Apple stores. No wonder the iPhone feelgood only lasts untill you get out of the store and have to rely on the "standard" AT&T network. LOL.soccerharms - Thursday, April 1, 2010 - link
Are you kiddin' me? I am going to approach this from two angles. The first being that this article is completely fake. ITS APRIL 1st people! The tech community should have an uproar for such a device. We buy internet and it is usually our responsibility to distribute it around the house with a router for wireless and whatnot. HOWEVER, we do not buy a wireless......phone plan with the intention on increasing a carriers crappy signal in our own house out of our pocket. That's ludacris! There is another much cheaper solution...........its called a LAN line with a cordless phone HA!The only company that could profit from a device like this would be Apple. But they would have to make it a little more shiney and put that quarter eaten logo on the side :)
Let the battles begin....
Jaybus - Thursday, April 1, 2010 - link
This is like buying an airline ticket only to find there is no flight. Since they don't have a flight, the airline offers to sell you your own airplane. You have to provide your own pilot, fuel, and maintenance, but you still have to pay them the full price for a ticket whenever you fly your own airplane. So my idea is to start a car rental business that has no cars. Anyone willing to pay AT&T for a microcell that uses their own Internet connection would surely be willing to pay me a rental fee for driving their own car.HotFoot - Thursday, April 1, 2010 - link
Eh... much of this market is iPhone users - people already willing to accept the concept of ecosystem lock-in. By a similar analogy to your car rental company, they're already willing to buy a car from a company that requires that they drive only on roads built or approved by that company, buy gas only at that company's stations, and buy car insurance from that company.Why not charge them for the roadside delivery of a jerry can of gas when the customer finds out the station filled their tank with water instead of fuel?
yacoub - Thursday, April 1, 2010 - link
I give it a year or two before the first cancer danger report comes out. ;)loydcase - Thursday, April 1, 2010 - link
AT&T cell reception at my house is weak in spots. OTOH, if a femtocell allows me to rip out my landlines, it might be worth it. So I'd like to know if a femtocell would be viable for that purpose.