In the past, carriers have been guarded if not purposely opaque about things like radio network planning, infrastructure rollouts, and other competitive details. With the smartphone boom well underway, many of those curtains are starting to fall as customers get more and more savvy with air interfaces and asking the important questions. This morning on Reddit, a T-Mobile RF engineer started an AMA, no doubt with official T-Mobile backing, to answer some LTE rollout and network modernization questions. Update: I was dropped a line and notified the AMA is being done without any official T-Mobile backing, but has been confirmed, and is nevertheless very interesting. 

I obviously could not resist the temptation to ask a few questions myself, and got some interesting replies. 

My questions: 

  • Can you talk briefly about how much traffic on GERAN you see from iPhone customers? How much of a catch-22 is that situation for moving that PCS spectrum dedicated to it over to WCDMA?
  • In some markets it seems as though T-Mobile will be unable to run DC-HSDPA on AWS alongside any LTE because of lack of spectrum. Obviously multi-band carrier aggregation (WCDMA carriers on PCS and AWS) is a big part of that future, can you talk about the challenges involved there?
  • Will T-Mobile deploy 3GPP Rel 8, or will you guys go right to Rel 10 for LTE?
  • How much variance in WCDMA utilization do you see across markets? From your point of view, are caps and the end of unlimited data plans really backed up across the board, or just in a few markets? In my AZ markets (Tucson, Phoenix) where I do a lot of testing, I regularly find I have the sector to myself.
  • Traditional PA at bottom architecture, or Remote Radio Head architecture for T-Mobile LTE?
  • This is already somewhat obvious, but could you confirm/discuss T-Mobile LTE channel bandwidths?

T-Mobile RF engineer replies:

  • We have about a million iPhones on our network now. 99.9% of their traffic is 2G/EDGE only right now, so obviously their load is dwarfed by everything else. The iPhone is a significant part of the modernization project. Once implemented, iPhones will work on U1900 at much higher speeds.
  • Spectrum is always a limitation. With the software that exists now, you will not be able to do dual carrier split between AWS and PCS. That's supposed to be fixed in the future, but I don't know a timeline on it.
  • It depends on a lot of things. In general, I think caps are stupid, especially the way that we handle them. Events (concerts, sporting events, malls @ Christmas) crush us though.
  • We're going with remote radios as much as we can, for LTE, UMTS, and GSM.
  • LTE will launch with a single 10 MHz channel, 5 up, 5 down.

So there you have it. Interestingly enough, the 1 million iPhones number seems a bit low, although it's likely this is a ballpark estimate - I suspected an even larger number given the unlocked iPhone 4S sales and AT&T's post-subsidy unlock program. T-Mobile going with Remote Radio Heads (RRH) for LTE, UMTS, and GSM is also interesting - in the USA, AT&T, Sprint, and Clearwire have all gone with RRH deployments which move the power amplifiers up the mast and next to the antennas, dramatically minimizing cable losses which are generally around 2-3 dB depending on length. This leaves Verizon the sole player in the USA using the traditional power amplifier at the bottom of the tower architecture. Finally, there's official confirmation that T-Mobile will be 5 MHz FDD-LTE initially, at launch. For comparison, Verizon is 10 MHz FDD everywhere in the US, and AT&T is 10 MHz FDD or 5 MHz FDD depending on the market. 

Update: The T-Mobile AMA source has dropped a few other interesting tidbits, as the AMA has progressed. Among mundane things like equipment failures, copper theft and vandalism are a major source of problems for T-Mobile in some markets, along with the usual kind of things like animal encroachment. In addition, the source uses a Samsung Galaxy S 3, and noted the use of disguised cell sites

Source: Reddit


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  • Eggrenade - Wednesday, August 8, 2012 - link

    There are 6 questions but only 5 answers. Did you forget one?
  • Brian Klug - Wednesday, August 8, 2012 - link

    Well, he didn't really reply to the Release 8 / Release 10 thing, which is why.

    There are other new responses as well in that thread, he seems to be going at it quite actively.

  • senecarr - Friday, August 10, 2012 - link

    The Release 8 / Release 10 is one you didn't really need to bother asking him. T-Mobile's CTO, Neville Ray, has already said they're going straight to release 10, which will leave them software upgradeable to LTE advanced. They also said they don't foresee doing VoLTE anytime soon (voice just isn't that much of drain on their network).
  • tom1l21 - Wednesday, August 8, 2012 - link

    A little over my head, but interesting nonetheless. I'd love to see a Verizon engineer do one.
  • Brian Klug - Wednesday, August 8, 2012 - link

    That would be interesting. I should note that one of the VZW RF engineers does maintain a useful personal blog:

  • Souka - Wednesday, August 8, 2012 - link

    "Among mundane things like equipment failures, copper theft and vandalism are a major source of problems for T-Mobile in some markets"

    Ahh that explains it.... Verizon, ATT, and Sprint don't have any of those problems, only T-Mobile.


  • Zoomer - Thursday, August 9, 2012 - link

    He can't speak for other companies.
  • Bardia - Wednesday, August 8, 2012 - link

    "In general, I think caps are stupid, especially the way that we handle them. "

    Man I strongly disagree. I'm a TMO customer right now and I love how they do their caps. I don't have to worry about either getting charged or getting caught without any connectivity, you just get throttled.

    I use the 2g plan and I've yet to get throttled. I know some people may exceed that, but they have 5g and 10g plans available as well.
  • Impulses - Thursday, August 9, 2012 - link

    I agree, their soft cap is the next best thing to unlimited IMO... Though I think he may have been alluding to caps in general, not just T-mo's, he was referring to the fact that caps are just meant as a way of preserving network integrity but network integrity is usually only compromised in temporary locations and dates...

    Kinda like when AT&T was throttling the top X percent of people with unlimited plans in all markets even when it meant some people were getting throttled way before reaching 2GB because it was a sparsely loaded location. At the time I remember reading Verizon did some localized throttling on a per tower basis even if you were an unlimited plan, which makes far more sense.
  • sigmatau - Wednesday, August 8, 2012 - link

    Maybe if you are in a large city and rarely wander away does T-mobile work for you. Otherwise they are barely better than Sprint in terms of coverage. To me, who travels statewide and to sorounding states, their 4G is not faster than AT&T's 3G.

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