21 March 2009

Low-Power GSM in the UK

Back in April 2006, the UK spectrum regulator, Ofcom, did something very rare these days: they auctioned off new spectrum in a standard GSM band.  Specifically, Ofcom auctioned off 12 national licenses in the top 6.6 MHz of the DCS1800 band.  The lucky winners and winning bids are listed on that link, but I'll repeat them here:

  • British Telecommunications PLC £275,112
  • Cable & Wireless UK £51,002
  • COLT Mobile Telecommunications Ltd £1,513,218
  • Cyberpress Ltd £151,999
  • FMS Solutions Ltd £113,000
  • Mapesbury Communications Ltd £76,660
  • O2 Ltd £209,888
  • Opal Telecom Ltd £155,555
  • PLDT Ltd £88,889
  • Shyam Telecom UK Ltd £101,011
  • Spring Mobil AB £50,110
  • Teleware PLC £1,001,880
A national DCS license for less than US$100k.  Damn.  (I bet COLT felt like chumps when they saw that they were spending something like 10x the typical winning bid, too.)

The catch is that transmitted power is limited to 200 mW and mast heights are limited to 10 meters AGL for outdoor installations.  It seems to me that the 200 mW limitation seems overly conservative, given that a typical GSM handset can put out a full Watt, but Ofcom wrote up a report justifying these limitations on the grounds that they were required for limiting interference with other cells.  Clearly, from the assumptions of the report, Ofcom expects these licenses to be used to provide high capacity over small areas, with each licensee having non-exclusive access to the full 6.6 MHz spectrum.  Otherwise, it would have made more sense to give each licensee exclusive use of a more limited bandwidth at much higher power levels, even if that meant fewer licenses.

So I'm assuming this is all about fill-in pico-cells, but maybe I'm wrong.  I'd love to hear reports of what the license holders are actually doing with this spectrum.  I've also heard of similar low power cellular in the Netherlands.  I can't find as much information on that, but welcome any reports of similar openings in other countries.

03 March 2009

The Problem of Spectrum Granularity

[BTW, Greetings from eComm 2009.]

One of the most serious challenges to providing low-cost cellular service in rural areas is the lack of available cellular spectrum. Just about everywhere in the world, all of the spectrum is already locked up by incumbent carriers. So, you might ask, if the spectrum is already held, why don't the people living under it have service? The problem is one of granularity.

Rural areas have lower population density and less infrastructure than urban areas. You need taller towers to get greater range. Your cell sites might not have grid power. The best sites may not be near paved roads. These factors make rural areas more expensive to serve. As the same time, perversely, the people who live in these rural areas have less income, and there are a lot less of them. So if you are a cellular carrier with licenses in both rural and urban areas, you have good motives to concentrate on urban service and ignore the rural areas.

Basic physics shows us that urban and rural areas might require different technical approaches. Basic demographics shows us that expectations of profitability are much lower in rural areas than in urban areas. So how do regulators deal with that? They make it nearly impossible to get a cellular license in a rural area without having to get a license in an urban area at the same time. No, that's not supposed to make sense, but it is true nearly everywhere in the world.

Here in the US, the FCC auctioned most cellular licenses by "metropolitan statistical area" (MSA) or "rural statistical area" (RSA). Despite those promising names, more often than not an MSA or RSA is just a county or group of counties. (Here's the map in PDF.)  That's why I can't get a license for rural Solano County, California, which is mostly sheep pasture and marshes, without getting licenses for several cities totaling nearly 500,000 people at the same time. That's why I can't get a license for Gerlach, Nevada, an isolated town of about 200 people, without getting a license for Reno, a distant city of more than 200,000, in the bargain. What if you want to serve Gerlach but can't afford a license for Reno? TFB (too ... bad). No license for you!

It's bad enough to do business that way in the US, where even the country folk are affluent by world standards, but in developing countries, where the urban-rural disparity is even greater, most licenses are national.  For example, if you want to provide cellular service anywhere in Kenya, you probably need a license for Nairobi.  And since median income in Nairobi is around US$160/mo and the median income in the coutryside is less than US$30/mo, you can imagine what that does for the prospects of a small rural carrier ever happening.

If you wanted a licensing system to discourage rural service, it would be hard to design a more effective spectrum allocation policy.  Some countries are making noises about changing these policies soon.  Let's hope.

02 March 2009

NDA and the Path to Servitude

I have a friend with a consulting client (who will remain unnamed) who is using a digital radio receiver (that will remain unidentified).  They are having a hell of a time getting the receiver to work for this client's application, but for a number of reasons that I won't detail here there's a strong motivation to use this particular receiver, regardless of the difficulties.

The problem appears to be in the receiver device driver.  So the client runs a test, and the receiver interface fails, and they send the results to the radio vendor.  The vendor sends back some questions about the test.  They send some answers.  The vendor recommends another test.  They try it.  The vendor asks more questions.  Since the client and the vendor are in radically different time zones, every step of this little dance takes at least a day.  This has been going on for weeks.

So I ask this friend, "Why wait for the vendor?  Why don't you just look at the source code for the device driver and fix this problem yourself?"  Damned good idea, but they don't have the source code because the interface to the radio is proprietary.  Make a nasally whining noise when you say that: proprietary.  No one is suggesting that the vendor should put everything under GPL and give it out to world in a free download.  Hell, my friend can even sign an NDA. 

Just show them the code.  I seriously doubt there's anything there he hasn't seen before.  He's worked with several of digital radio systems over the years and all of the interfaces look pretty much the same.  You have packets or frames of baseband samples.  The packets or frames are timecoded, maybe with sequence numbers, a sample clock, IRIG, SMPTE, whatever.  You've seen the G.711 steam in RTP?  Most digital radio interfaces look a lot like that.  It's the only approach that makes any sense.

On second though, to hell with the NDA.  Once anyone sees the code under NDA their careers are in mortal danger.  What's the problem?  Suppose you sign that NDA and see this proprietary interface and then go off and design another interface for another digital radio.  And since there's really only one way to build that interface that makes any sense, it will inevitably have similarities to the design you received under NDA.  You may well end up getting sued even though you've done nothing wrong.  Legally, those similarities are justified under the "merger" doctrine, but it's not like you just go stand in front of a judge and say "It's just merger, your honor."  Instead, there's a process, a process that takes many months and costs a frightful amount of money and has an uncertain outcome.  And since your ability to participate in this process is directly related to available funds (and not much else), and since if you fail to participate in the process you lose by default, you can easily get railroaded into signing away your intellectual rights to avoid personal financial ruin.  This can happen.  I've seen it happen.  No thanks.  Let them fix their own driver.

Getting back to the original problem, though, what my friend has isn't really a technical problem with the radio interface so much as a psychological problem with the vendor.  As an engineering consultant, maybe he should start charging double to deal with psychological problems.