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
Performance - Data
I noted a few times that I tried the device at two different residences, both for completeness sake and because they're completely different coverage-wise. Location one is relatively urban and already had excellent signal and performance; I regularly see speedtests over HSPA of nearly 5 Mbps. The internet connection here is a 20 Mbps downstream, 4 Mbps upstream DOCSIS 3.0 Cox Cable connection shared using a WRT54G-TM running Tomato. I sat in the same room as where the AT&T MicroCell was installed, my office. There's some irony in using T-Mobile's branded router (as it's sold expressly for UMA), however I use it because it has double the RAM and ROM of the WRT54GL.
Location two is more rural and doesn't have good performance or signal coverage; there are more than a few dead zones throughout the house, and I chose what I perceived to be the worst one. Internet here is Comcast Cable with 6.6 Mbps downstream, 1.1 Mbps upstream shared using a m0n0wall router running on a WRAP PC Platforms board.
I installed the microcell at both locations and let it sit for an hour. I assigned a static DHCP IP address, and then set that IP to maximum QoS priority for both upstream and downstream. For testing, I used four iPhone 3GSes, including my daily device, which is jailbroken so I can report RSSI. This is the relative signal strength reported by the baseband in arbitrary units, though still in dB. If you're rusty, remember that every factor of two change in power corresponds to 3 dB - if we go down 3 dB, we're at almost exactly half the signal. If we go up 3 dB, we're at double the power. In this case, RSSI is not dBm. As an aside, this is a much better way to gauge signal at a glance than the vague signal bar visualization; the iPhone seems to show a very optimistic moving average in its bar metric.
On the iPhone, -113 dB is effectively zero to one "bars." In fact, this seems to be the bare minimum in practice before the radio disconnects. Similarly, -51 is absolute maximum. If you put the phone next to the microcell, you'll see this, or if you're standing within line of sight very close to a macrocell. Thus in the following plot, closer to 0 is better.
For testing bandwidth, I ran tests using speedtest.net on the iPhone over 3G with and without the microcell, and over WiFi for a comparison point of my network bandwidth. Of course, we're limited to 802.11b (11 Mbps) rates on the iPhone over WiFi.
One thing that stands out doing lots of tests is that upstream performance is arbitrarily capped at exactly 58-60 kilobits/s on the MicroCell. Remember that 256 kilobits/s requirement earlier? It's obvious now where they derived that 60 kilobit/s cap from: 60 * 4 is roughly 240 kilobits/s. Add in some overhead fudge factor, and you've got 256 kilobits/s. So in the worst case, where there was previously almost no signal at all, we can now get a pretty speedy 3G data connection over the microcell. However, in the best case, at location 1, we're actually slower than before.
Remember again that AT&T's MicroCell currently only supports HSDPA speeds of up to 3.6 Mbps - at location 1 it's obvious that AT&T is running HSDPA at 7.2 Mbps, as I regularly see results like these:
Oh yeah, I'm always up that late doing bandwidth tests
Location 2 Before and After
But performance is still a function of signal strength even with the MicroCell. As you move away, you'll see speeds go from being ideal for HSDPA 3.6 Mbps all the way down to a respectable but less than ideal 1.2 Mbps.
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atiller - Thursday, April 1, 2010 - link
Thanks for the excellent and detailed report. One comment - your view of picocells is rather out of date. Just like femtocells, today's picocells use IP backhaul and can be installed without any specialist skills. Some people call them 'enterprise femtocells', but they have a larger capacity and range than a femto.Brian Klug - Thursday, April 1, 2010 - link
Awesome tip, thanks, I definitely didn't know about these. Do you know what kind of carrier interaction is required for installing one of those? I mean, are they carrier agnostic, some common brand, and can anyone just buy them?I think there's definitely a market for malls and large shopping centers that want to improve coverage indoors - it seems to be a systemic problems for large buildings with high population density inside.
-Brian Klug
Paulman - Thursday, April 1, 2010 - link
Except that I was reading an 4/1/2010 post on a friend's blog which made me wonder when the tech sites would start posting their crazy stories, and then I realized... wait a second...Before realizing this, I had read up to page 4 (Inside the Networking), at which point I was like, "I'm done with this article - I was just really curious to see if this was a 3G signal repeater, or if it got the data through a broadband connection and then just broadcast it locally over 3G". Lol.
TGressus - Thursday, April 1, 2010 - link
...by failed handovers on AT&T.In southern California we as a community drive a lot (serious understatement), and many careers involve driving throughout the work day. Certain devices and occupations have moved my colleagues and family to AT&T at times, including the present. Everyone I know is regularly affected by the worst case handover scenarios you were surprised about in your article.
It so predominant that I estimate 1/4 of my calls with AT&T I answer, "sorry, dropped call" rather than, "hello". It is the consensus of the mobile professionals with whom I interact through AT&T that one can not afford to make important phone calls on the road. I know that must seem like the most obvious statement ever, but try and empathize here; the nature of many businesses in massive urban sprawl lends itself to perpetual mobile telephony.
People regularly attribute these issues to the coverage maps and, more recently, smart-phone burden. I'm no cellular techncian, but I suspect it's something more fundamental with GSM and/or AT&T technology. I'm not surprised you noticed this issue. In fact, I'm surprised you are surprised.
Brian Klug - Thursday, April 1, 2010 - link
I can't speak for the load in that area, but migrating calls and handing them over if the adjacent cell sites are overloaded is generally what causes soft handovers to fail. So imagine that you're on a node, being serviced perfectly fine, but migrate (while driving, say) into an adjacent cell that's completely overtaxed. The phone will try to migrate its session, but if it's so overloaded that it can't, the call will fail.It's a sad state of things, but that's probably what's going on if you see that you have good signal but still encounter problems. In fact, I'd say if you don't hear distortion or blocking, but rather just have the call fail (and you're moving) this is probably the case. Of course, that market is one that AT&T is particularly stressed about and focusing on now, hopefully it improves.
Both CDMA2000, GSM, and UMTS are equally robust in the soft handover arena, and it *usually* works flawlessly - this is a technology that's rolled out pretty much everywhere. The technology is robust, but it's entirely carriers prerogative to install it properly and watch out for these load issues. Nothing is going to overcome the laws of physics. ;)
Cheers,
Brian Klug
slyck - Thursday, April 1, 2010 - link
Comments so far are right on. This should be a choice of last resort only for those who are connected to their cell number. If you need internet to make your call there is always VOIP which costs far, far less.sxr7171 - Thursday, April 1, 2010 - link
Firstly pardon my language here. But this is bullshit.These stupid wireless carriers have a lot of nerve trying to extend their wireless coverage off of the customer's dime. On top of the ridiculous prices they charge for voice and data and most importantly: SMS. They have a lot of nerve asking customers to pay for the device and to pay for calls on it.
The only advantage this has over a VOIP solution is basically seamless hand-offs - WHICH THIS CRAP PRODUCT DOES NOT DO.
For GSM users this functionality was built into the standard and has been around for years and was mentioned in the article: SIP. T-mobile uses it but they restrict the devices.
SIP is a feature built into many open unlocked phones like Symbian phones from Nokia and others, but our US carriers don't like such open phones so they would never allow a carrier sponsored phone to have the SIP software intact in the FW/OS. The whole technology was designed around having a choice of cell phone provider and SIP provider - you know choice as in the kind that creates competition. But our carriers will never allow that, and our consumers will always get sucked into carrier contracts and locked phones. This sort of thing is what makes it impossible to launch a phone or technology without the carrier's blessing and it is what makes us indentured to carriers.
That iPhone is not $200 always remember the $1680 of overpriced service that is part of it. An unlocked iPhone costs $999. Think about why that is. It's because with the carriers control the device prices since they control who can buy it and what services must be purchased and how much that service costs. Will wireless ever be a free market in the US?
HotFoot - Thursday, April 1, 2010 - link
Have to agree with you. This is just silly.Where I live, there are two good solutions for the problem this device/service is trying to solve.
1) Rogers has wifi capable cell phones that will switch to using your home 802.11 (or other hotspots) for making calls. When you're on wifi with these phones, you get different rates for calls much more in line with VoIP.
2) Smart phone that will Skype over wifi. I pay $15/mo for my cell phone service plus another $3 to Skype for unlimited calling in North America. That's $18/mo, no contracts. I did pay $600 for my N900, so if that lasts me 3 years add another $18/mo to the total so I pay $36/mo to have basic cell phone service while I'm out and about and unlimited calling while at home, work, or coffee shop/anywhere there's free wifi.
Anyone feeling like this AT&T offer is a load of steaming crap in comparison?
sxr7171 - Thursday, April 1, 2010 - link
But the 2 are open technologies that were supposed to enable seamless hand-offs and choice of service provider.Wayne86 - Thursday, April 1, 2010 - link
I was hoping this article was an April Fools joke. Alas, after Topekaing, it is not. :)