Posts tagged 850

AT&T Bands in Las Vegas – 850 GSM/EDGE, 1900 UMTS/3G

Last time I was in Las Vegas it was for MIX 10 and Windows Phone 7 (back when it included ‘series’ at the end). This time, the reason is CES 2011 with AnandTech and a whole bunch more mobile devices.

I thought it was interesting last time I came that most casino floors in Las Vegas had shockingly poor or non-existant UMTS (3G) coverage on AT&T. I guess I didn’t find it too shocking, since coverage inside buildings in a dense urban environment is probably the most challenging for mobile networks, but it seemed to be a consistent problem. After getting frustrated about 6 hours into my stay, I decided to switch entirely to EDGE for the duration just because of how annoying being constantly handed between GSM/EDGE and UMTS is when you’re trying to do things. For whatever reason, back then I didn’t think to pull up field test on the iPhone 3GS I was currently carrying to see what bands were assigned to which network technology.

Now that I’m back, I decided to check. Thankfully, Apple has restored most if not all of the Field Test data products in iOS 4.2.1, a huge step forward from 4.1 just allowing signal strength in dBm at top left, and a far cry from 4.0 which shipped with no field test whatsoever. To save potential readers some googling, to get here, enter *3001#12345#* from the dialer and hit call – if it hasn’t been removed yet, you’ll get dumped into Field Test on iOS.

In EDGE and tapping on GSM RR Info, it’s immediately obvious why I saw that behavior last time I was here:

ARFCN dictates what channel inside what band we’re on, and 142 just happens to lie inside the GSM 850 band. It’s a number basically used to refer to the FDD pair of frequencies the phone is currently using. You can calculate exactly what frequency downlink and uplink are on with a little math and some reference guide (there’s a good table here), but basically with an ARFCN of 142 we know immediately that GSM/EDGE is on AT&T’s 850 MHz spectrum. Between 128 and 251 is that GSM850 spectrum.

Now, what about UMTS/3G? Enabling 3G (look at how weak that signal is…) and going into UMTS RR info, I saw the following:

Looking at the fields “Downlink Frequency” and “Uplink Frequency” we can see the device’s UARFCN channel numbers. It’s the same thing, but U for UMTS. Again, with a reference aide (read: wikipedia) we can see that UMTS/3G is working in the PCS 1900 MHz band.

Remember that higher frequencies are less effective at propagating through buildings. It’s pretty obvious now why getting good 3G coverage on AT&T is a challenge deep inside a casino in Las Vegas. There’s nothing inherently wrong with putting GSM/EDGE on 850 and UMTS on 1900, it’s just interesting in practice how immediately obvious the difference is walking around. Propagation is a challenge in dense urban environments with lots of people moving around to begin with, I’m sure this doesn’t help in Las Vegas. AT&T promised to put all of its 3G (UMTS) network on the 850 MHz band (wherever it’s licensed to use it) by the end of 2010, but sadly that hasn’t happened quite yet, at least in this market. I’ll keep checking, but thus far it’s been solidly in 1900 PCS. Oh well.

AT&T Observations and Bandwidth

Bandwidth and Latency Data

I’ve always kind of been obsessed with bandwidth. I find myself constantly testing latency, bandwidth, and connection quality (mostly, in fact, through smokeping). Needless to say, that same obsession applies to my mobile habit, and especially given the often-congested perception of AT&T.

It sounds weird, but the two most-run applications on my iPhone are Speedtest.net Speed Test and Xtreme Labs SpeedTest. The Xtreme labs test used to be my favorite, largely because of its superior accuracy and stability. As great as Speedtest.net’s website is for testing, the iPhone app continually fell short. Tests ended before throughput stabilized, often the test would start, then the data would start being calculated a second later (skewing the average), or it’d just crash entirely. I could go on and on about the myriad problems I saw which no doubt contributed negatively to perception of network performance.

A few months ago, I wrote a big review and threw it up on the App Store. In the review, I noted that being able to export data would be an amazing feature. At the time, I had emailed Xtreme Labs and asked whether I could get a sample of my speed test results for analysis (I have yet to hear back). On Feb. 2nd, Ookla finally got around to releasing an update to the Speedtest.net app; it included the ability to export data as CSV.

Since then, I’ve been using it exclusively. I’ve gathered a bit of data, and thought it relevant to finally go over some of it. This is all from my iPhone 3GS in the Tucson, AZ market, largely in the central area. I’ve gathered a relatively modest 76 data points. Stats follow:

Gathered Statistics

Downstream (kbps)
Upstream (kbps)
Latency (ms)
Average 1880.3 263.3 1029.2
St. Dev. 1179.6 101.6 1140.2
Max 4279.0 356.0 6011.0
Min 82.0 18.0 366.0

These stats really mirror my perceptions. Speeds on UMTS/HSPA vary from extremely fast (over 4.2 megabits/s!) to as slow as 82 kilobits/s, but generally hang out around 1.2 megabits/s. On the whole, this is much faster than the average 600 kilobits/s I used to see when I was on Sprint across 3 different HTC phones.

Next, I became curious whether there was any correlation between time of day and down/up speeds. Given the sensitivity of cellular data networks to user congestion (through cell breathing, strain on backhaul, and of course the air link itself), I expected to see a strong correlation. I decided to plot my data per hour, and got the following:

Downstream and Upstream Bandwidth

Some interesting trends appear…

  1. I apparently sample at roughly the same time each day (given the large vertical lines that are evident if you squint hard enough). Makes sense because I habitually test after class, while walking to the next.
  2. There is a relatively large variation per day for those regular samples, sometimes upwards of a megabit.
  3. There does appear to be a rough correlation between time of day and bandwidth, but the fact that I’m moving around from cell to cell during the day makes it difficult to gauge.
  4. Upstream bandwidth is extremely regular, and relatively fast at that.

I’m still mentally processing what to make of the whole dataset. Obviously, I’m going to continue testing and gathering more data, and hopefully more trends will emerge. You can grab the data here in excel form. I’ve redacted my latitude and longitude, just because my daily trends would be pretty easily extracted from those points, and that’s just creepy.

3G Bands – Where is the 850?

Lately I’ve been getting an interesting number of hits regarding the 850/1900 MHz coverage of AT&T here in Tucson.

To be honest, I’ve read a number of different things; everything from certainty that our market has migrated HSPA (3G) to 850 MHz, to that AT&T doesn’t even have a license for that band in Arizona. For those of you that don’t know, migrating 3G to the 850 MHz bands is favorable because lower frequencies propagate better through walls and buildings compared to the 1900 MHz bands. In general, there’s an industry wide trend to move 3G to lower frequencies for just that reason.

I’ve been personally interested in this myself for some time, and finally decided to take the time to look it up.

Maps, maps, maps…

The data I’ve found is conflicting. Cellularmaps.com shows the following on this page:

AT&T 1900 MHz

AT&T 850 MHz

Note that the entire state of Arizona doesn’t have 850 MHz coverage/licensing.

However, the GSM authority over at GSM World shows three very different maps:

HSPA 3G Coverage (yellow)

AT&T 850 MHz coverage

AT&T 1900 MHz coverage

Note that the 3G data coverage map is labeled ambiguously; HSPA coverage exists, but it could be on either 1900 or 850. However, what we do glean is that (at least according to GSM world) there is equal 850 and 1900 MHz coverage in Tucson and the surrounding area. This contradicts the earlier map.

Then you have maps like these, which are relatively difficult to decipher but supposedly show regions of 800-band coverage from Cingular and AT&T before the merger:

Cingular 800, AT&T 850

Finally, you have websites such as these that claim Arizona is only 1900 MHz.

So what’s the reality? Uncertain at this point.

The map given by cellularmaps.com is sourced from 2008, whereas the GSM world maps are undated, and ostensibly current. The other maps are also undated, but the majority consensus is that AT&T isn’t licensed to use 800 MHz in this market.

If anyone knows about some better resources or information, I’d love to see it.

Update – 3/24/2010

I finally spoke with someone at AT&T, and it turns out that my initial suspicions were correct – Arizona does not have the 850 MHz UMTS Band 5. It’s as simple as that.

Oh well, at least we know now!