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.


  1. The problem in serving rural areas is clearly the cost of the network. I am affraid that even with OpenBTS, GSM will not be competitive there. I see the projects power much more in innovating current and future cellular networks for developed world.

    To be really effective for Africa, you need a network that costs 1000-times less to deploy, not 10-times only. That means you probably want to use whole other frequencies that can still hold only few voice channels.

    I see the future of rural Africa though wireless, but much more static than mobile. If mobility would appear already, the future IEEE Wi-Fi roaming spec could pretty much handle it in my opinion.

  2. Kozuch82, I do not agree with your view. I am working in Africa with gsm networks and in southern, central and west Africa see that even conventional gsm networks are making money. The problem in my view is that it is not spreading fast enough and if a Mega telecommunications company can make profits in Africa then a cheaper simpler GSM network could very easily slip under that ARPS ceiling that exists for them. To develop huge new technologies and focus them on the the lower income bracket is doomed to failure and Wi whatever is going to take several leaps before it can offer any real VOIP solutions. That wireless is the solution for Africa is correct, but using existing technology and making it simplier is the answer. Thus far I agree with the views David holds, I understand his frustration.

  3. I had intended to comment earlier, but I agree with myself, too. ;)

    GSM handsets will probably always cost less than 802.1x. The radios are simpler and they are already produced in huge volumes. I won't even start into a capex/opex comparison between fixed-station VoIP/WiFi and a GSM handset.

    And GSM will always have a larger service radius at equal power, especially in the lower bands. The 2G cellular air interfaces are well designed for long-range rural service and 802.1x air interfaces are not. Given the original design goals of each, that should be no surprise. For example, 802.11 can do 30 km point-to-point links with masts and tight antennas, but GSM can go 35 km MOBILE and well over that to fixed stations if you get creative with antennas and configurations. That's worth a lot in areas with low subscriber density.

  4. You can buy a new simple gsm phone in south africa for under R200 now, less than 20$. Forget about the second hand phone market, I have four functioning old phones in my drawer and they have bluetooth and gprs, needing new batteries, but they work. Show me a transceiver handset that can beat that price and functionality and stores text messages as a minor function. And when that transceiver fails I merely pop that SIM into another phone and I'm on air again. The sims here cost $0.01 now I can get my old number back with a new sim if I loose my phone ( with sim inside ). The 900 band works remarkably well all things considered and ideal for rural environments.

  5. The permanent question of wireless for development is if you need high data throughput (Wifi) or mobility and possibly voice-only (cellular). Over 30 km, you can easily push close to few Mbits/s with Wifi while only few Kbits/s with GSM. So for $6000 you either set up one OpenBTS (spectrum license not included) or 60 Wifi clients for the same area...

    I think lower frequencies are needed or the cellular growth in rural developing world will not be sustainable in the future. CDMA2000 450 is an interesting technology, but probably still way too expensive for Africa.

  6. (1) You will not run a 30 km WiFi link on a $100 subscriber unit, especially in an off-grid environment. You are forgetting the mast, the antenna, the power source and the technician who has to install it all.

    (2) You forget that the main AP for this point-to-multipoint WiFi system will require a site installation almost as expensive as the OpenBTS cell site. And don't say "mesh" because your subscribers are too thin on the the ground to support it.

    (3) In most countries, you'll need a license anyway. Just operating in an unlicensed band will not protect you from regulatory disruption. Look at what happen to Village-Telco in Orange Farm last month.

    (4) You forget that a raw network connection is useless to someone with no computer system.

    Also, since you can use Wi-whatever for OpenBTS backhaul, and since the cellular will only need a small fraction of that backhaul, you can still deploy point-to-multipoint 802.1x very easily once the OpenBTS infrastructure is in place. It doesn't have to be an "exclusive or" deployment. I just think that basic phone service is the "killer app" for this infrastructure.

  7. I must agree that what you say makes sence to me. I just try to employ my imagination and my little technology knowledge to catalyze some more practical GSM4D output here. I really am looking forward to reading from you more often with bits of your valuable cellular knowledge.

  8. "They make it nearly impossible to get a cellular license in a rural area with having to get a license in an urban area at the same time"
    --> without?

  9. Thanks for pointing out the typo.

  10. You can get 200-400Kbps from EDGE on GSM and they're revising the spec all the time - the latest ones are now faster than the first HSDPA ones were.

  11. Have you been in touch with the "Open Spectrum" people ? They seem to be researching practical ways to adress the problem of spectrum granularity : http://manypossibilities.net/what-im-working-on/open-spectrum/

  12. I've been following some of the spectrum reform efforts in South Africa. It is a good start, but I suspect it will take a while before we see meaningful reforms in cellular spectrum.

  13. Maybe the ETSI RRS activity will solve this problem.