9 Comments

Summary:

Earlier this morning I received an email from one of our readers who had some questions about the 700 MHz auction and the high cost of the infrastructure buildout that someone like Google might have to undertake in order to roll out their own network. His […]

Earlier this morning I received an email from one of our readers who had some questions about the 700 MHz auction and the high cost of the infrastructure buildout that someone like Google might have to undertake in order to roll out their own network. His question:

TV broadcasters have been broadcasting 700 mhz signals from their local tv stations for decades. The buildings and towers to send the downstream signal. Which means the infrastructure is already in place to cover the country minus the backhaul/upstream gear? Couldn’t Google (and Apple together, perhaps) buy the backhaul gear and have it installed at these stations and create ad revenue sharing agreements with the owners of these stations?

Given that two networks — broadcast and broadband — will be used for very different purposes, there is a need for new gear. The only thing they share is the slice of the spectrum. Anyway, I decided to put his question out to you, hoping that you can give him more insight into this topic.

  1. Most 700 MHz networks will likely rely on an architecture similar to a cellular system — numerous smaller towers or antennas on buildings — in order to reuse the spectrum many times in a metro area, an architecture that also facilitates receiving uplinked communications from low-powered subscriber units. TV stations, by contrast use a high-power, tall-tower in order to get a single uniform signal spread across as wide an area as possible. That arrangement is not an efficient way to engineer a high-capacity two-way network. However, it may well be a good way to engineer broadcast-like broadband networks that are beaming encoded video out over a metro area, as Qualcomm is doing using its 700 MHz licenses for the former TV channel 55. But this is unlikely to be used for networks oriented toward broadband access.

    Share
  2. I’m not an expert on Radio/TV by any means, though I am a licensed Amateur Radio technician. However, high speed packet radio has been discussed for years

    http://www.qsl.net/vk3jed/future.html

    So what you are suggesting seems entirely possible, though a discussion with Doc Searls led me to believe that there wasn’t enough spectrum to handle it all, but I never did enough research to verify that.

    Also read this Wikipedia page about packet radio and pay attention to the talk of bulletin boards.

    I often think that in the case of a global internet online disaster (if a serious disruption in line transmissions occurred), the world would still communicate via the free spectrum, but with computers, not voice as they did in the last century.

    http://en.wikipedia.org/wiki/Packet_radio

    But one thing seems for certain, the spectrum we do have will be used for much differnt things in the future. It’s too valuable to waster on one way TV transmission, I would think.

    Perhaps Twitter apps like the one I built yesterday will be the emergency communications devices of the future, and take place over radio, not lines. Ehhhhhhh. Could be! http://atlocals.com

    Share
  3. The towers are there – and you can assume they are dispersed correctly to cover most of the country. Using the existing towers and contracts with the land-owners would actually significantly reduce build out costs and shorten the time to market.

    So while the back-end equipment needs replaced, and the antennas may need changing, there is still a potentially huge cost savings in using the existing infrastructure.

    Rob

    Share
  4. While it sounds good in principle, the fact is that the towers are nowhere near close enough to each other to create a functional cell-like system. TV broadcasters transmitted their signals at significantly greater power than mobile devices will and, as a result, the systems will need many, many more cell sites (towers) than currently exist on these systems. They are also located at much higher heights and have larger antennas than the devices that they would be servicing; from a sheer radio physics standpoint these towers would be a good start but wouldn’t come anywhere close to providing all of the coverage that an operator of a wireless system would need.

    The other factor is the capacity… the thing that gives a cellular system its enormous capacity is the ability to reuse spectrum. Having a single tower eliminates any reuse and thus drastically reduces the number of devices that an operator could service.

    Share
  5. Another gentle reader sent this in via email:

    The biggest issue with any two-way low powered
    radiotelephone system is the upstream power you can provide.
    Television station antenna/broadcast towers are used to spew data (in
    the case of HDTV) out at 200,000 Watts. They don’t receive anything. A
    handset transmits at well less than a Watt typically, which travels
    all of about a mile or two in best circumstances. The reason you see
    mobile towers everywhere is because you don’t need or want a lot of
    height. Channels are limited in capacity and throughput, if everyone
    saw a cell and tried to talk on it the whole network would come
    crashing down in a sea of unused bits.

    Simply put you can’t reuse infrastructure from high-power broadcast
    applications in a low-power 2-way application. It won’t work in a
    crowded urban environment.

    Share
  6. Ignacio Berberana Monday, December 10, 2007

    So many reasons for this not to be possible. A few more to those already indicated:

    • The television antennas are much better than those that can be incorporated in a PC or in a portable device. They are usually located in favourable places (p.e., roofs) and are fixed, pointing to the transmitting station. Having television coverage does not mean that mobile or portable coverage is guaranteed.
    • TV stations do not incorporate receiving equipment. Also, a number of functions required for an efficient operation of a cell system are not present: power control, handover support, etc. So you would have to spend some serious money upgrading TV stations.
    Share
  7. [...] Reader Question: 700 MHz & The Buildout – GigaOM Om asks some good questions about the buildout costs of a 700MHz network here in the U.S. (tags: wireless communications technology google om-malik giga-om) [...]

    Share
  8. This begs the question that i have had for years, i too am not a rf engineer, but have always been curious about the cellular foot print….it would seem since sprint, att, etc….own their slice of spectrum and it is a distributed network, why cant they distribute the tower all the way down to the house via a wifi like set top? it would take a great deal of load off the tower giving it more capacity….just a thought that tickles the brain……

    Share
  9. Qualcomm already owns a part of the spectrum and uses it for its mediaflo technology. Its being used as a part of the Verizon VCast offering. AT&T is current running trials to use this technology. The current technology is more suited for broad-casting than up-casting.

    About the gear being already in place. Its not in place with regards to mobility applications. It was there for traditional broadcasting and people moved away from it, not without a reason.

    Share

Comments have been disabled for this post