700 MHz Explained in 10 Steps

113 thoughts on “700 MHz Explained in 10 Steps”

  1. Rob,

    while there seem to be some trade offs, I am not exactly sure on the bandwidth limitations and have a few phone calls out and will answer your question after I get a chance to report some more on this.

    Appreciate your patience!

  2. Rob,

    Absolutely there is a tradeoff in bandwidth. Coverage and penetration are phenomenal, but 700MHz is damn near useless for anything even approaching even the low end of “broadband”. Raindeer explained this very well here, I thought:

    http://gigaom.com/2007/03/09/google-ebay-yahoo-700mhz/#comments

    With similar factors to weigh, this is why so many municipalities and terminals have upgraded from 900 to 2.4 and/or 4.9

    Nice post Om, very informative info on the spectrum. Thanks!
    -Michael

  3. Some basic spectrum tradeoffs:

    • Lower frequencies propagate better and penetrate better
    • Lower frequencies are more spectrally efficient (support more bits/Hertz)

    The flip side of better propagation is that lower frequencies make for a more difficult or more broadly spaced out sprectral re-use plan. Modern mobile networks maximize their spectrum by re-using the same frequency blocks/pairs in non-adjacent cells.

    The physics lead to economics. The UHF band is best suited to sparse and distributed demand sets or broadcast type applications. Thus the discussions about public safety (smaller demand set, lower cost network, value of broad coverage and penetration) and broadcast to mobile devices.

  4. Om, I don’t know who you are calling, but as an actual RF Engineer who has designed and optimized netowrks at 800 MHz, 1.9 GHz, 2.4 GHz, 2.6 GHz, and other frequencies, I can tell you that the above post by H is pretty much spot on as a generality.

  5. Jesse

    First of all you really got to take me off your spam list. I know i trouble you a lot but then, so does everyone else.

    I emailed folks from some of the vendors to get a better sense of the spectrum potential, and also some carriers in case you were interested.

    Also, there might be an email waiting for you somewhere in your trash folder.

    H: thanks for your kind comments and feedback.

  6. OM, does this mean that the GOOG / YHOO / DISH / DTV / EBAY consortium, which was set-up to petition the FCC on the upcoming 700 mhz spectrum auction is just a waste of time (as goes broadband)? In other words, that group, or a sub-set of that group can’t team up to build a broadband network in the 700 mhz band b/c the 700 mhz spectrum doesn’t work well for broadband? If that’s the case, then why would they be petitioning the FCC on it?

  7. If anybody could give some concrete calculations on how much bandwidth one could stuff in 60Mhz of spectrum I would be much obliged. I only have a degree in Public Administration, so for most people I’m not worthy to sharpen pencills 😉 But my understanding has been that jamming more than two bits in the 700 Mhz spectrum is a bit tough, which leave at most 120Mbits in 60Mhz block. One has to share this and therefore as our good friend H sais. Broadcast or maybe, emergency services. Both ofcourse being limited, though probably firefighters would be very happy with having indoor coverage.

  8. Just a quick note to clarify my points earlier.
    700Mhz can be used for traditional commercial mobile type applications. The original US and Canadian cellular networks are at 800MHz so the economics and performance can be reasonable. However, a 700Mhz network is more complex to design and can be more expensive and less efficient, because of spectral reuse challenges, for high demand urban environments than a 1.7Ghz to 2.1Ghz type design. It can be done with a positive business case but it’s not the ideal spectrum for a high traffic dense urban demand set.

    I would think that a greater question regarding the Ebay/Google/etc. interest is whether the US market can support a 5th, 6th, or 7th service provider in a capital intensive business.

  9. Raindeer, 60 MHz is plenty of spectrum for a single carrier and could probably support 2 carriers just fine. BUT there is not 60 MHz of spectrum available, there is only 36 MHz that is going to be auctioned off. The 24 MHz that is going to public safety has all kinds of weird rules applied to how it can be channelized that make it unsuitable for things like WiMAX and LTE. This channelization was done so that voice oriented networks would have a consistent set of channels nationwide, but like most things the FCC does, it is based on the technology of 10 years ago, not the technology of today or 5 years from now.

    By the way, here is how I would estimate per cell throughput: Expected efficiency at N=3 reuse is 2 bits/Hz. N=3 reuse means 1/3 of total spectrum per cell. So, for 60 MHz of spectrum, per cell throughput would be 40 Mbps. Once you factor in Layer 2 and 3 overhead you are down to about 30-35 Mbps (note that this is aggregate, not full-duplex).

    PS Om, you are not on MY spam list. I don’t see any e-mails from you in my Comcast screened mail, either. Internet gremlins?

  10. Jesse, you calculations do not take into consideration the fact that 60 MHz is available for uplink and downlink. If we consider 70:30 for downlink/uplink, the thruput would be even lesser.

    Is there a way to reduce the frequency re-use factor to 2 or 1 ? Smart Antennas may allow a better reuse factor.

    I feel there is no way content providers would bid for beachfront spectrum. Their business model and investors will not allow them to do that (as of today).

    Some of the key motivation for differnt players to bid for this spectrum would be :

    Big 4 : reduce their roaming cost by having own towers in rural areas. For T and VZ, they can provide DSL like service to rural areas too

    Rural carriers: They want a piece of it to survive (lot of their revenue come from roaming). But price of spectrum may make it too expensive for them

    Clearwire : Adds greatest value to their business

    MSO : If they really plan to launch wireless service in AWS, then 15MHz would be too less for them. They will want a piece of 700 party too, to reduce their CAPEX on rural coverage

    any thoughts? comments?

  11. I certainly have more confidence in the FCC to allow higher power radios in this space, the abilities of our engineering teams to use the new MIMO antenna technologies to extend bandwidth and reach on any new 700Mhz systems.
    There is a good economic reason for these Big boys bidding on this spectrum. They would not be playing here if they could not expect significant improvement in bandwidth delivery across these networks. Look what MediaFlo is doing with these new Mobile Broadcast TV networks in 700MHz.
    Keep in mind that we thought 802.11b & g were limited to 20-40Mbps at one time then MIMO (which was considered unrealistic) happened and 802.11n came along with 100-200 Mbps.

    Jacomo

  12. I am not an engineer, but I do know some of the physics/maths of this. So my question is, how can this possibly provide broadband to a large number of people?

    With a 1000Sq Mile radius per tower and only 35MBs top speed (from someone’s calculation above) and with the average DSL cable connection at 467kbs, how can this possibly provide more than a couple hundred households per tower (1000sq miles, 35MBs/467kbs– that is a population density of 8 people or so per square mile) Even if you assume rural people will settle for a slower (but faster than dial up) connection, that is still only maybe 1000 households you could serve with this per tower. So it’s only good for the very rural areas.

    Now if you gave people a differnt downlink like satellite, using 700MHz for a reliable uplink, maybe that would work.

    But really, am I missing something? I don’t see how this spectrum could be used for anything more than more cell phones and applications that don’t need significant speed?

    Help me understand this you smart engineers out there.

  13. I would actually prefer to not see the spectrum used for cell service. It just isn’t necessary to have more entrants in that business and it doesn’t support intelligent frequency re-use.

    It has served broadcasters very well for many years and I’d like to see it continue to serve broadcasters in forms such as:

    Terrestrial Subscription Audio Content (Competition to a merged XM/Sirius)

    A Way To Add Additional Local Broadcasters — Ever tried to start a radio station in any major market? The bands could use some breathing room.

    One-Way Data Services To Portable Devices (a la MediaFLO, but additional marketplace competition)

    Positional Services – Additional GPS augmentation/corrections over a localized area for industrial (non-life or death) users. (So we can all have sub-meter directions to the Starbucks.)

  14. I am not sure, but I think that 700 Mhz is in the spectrum in humans absorb the most radio waves. I had a chart handy for that, but I can’t find it…damned.

    There’s still lots of parts of the US without adequate cellular service. This is mostly very rural areas, like northern Maine. There are smaller pockets of inadequate coverage. In these areas, it would be reasonable for cellular to operate.

    In cities, already well-covered by existing cellular infrastructure, it is less reasonable to designate this band for cellular. However, it is useful as it penetrates further into buildings than higher frequencies. I believe that text-messaging services, and other low-bandwidth applications which require high reliability, are the best use of this band. Perhaps part of the 700 mhz could be used for control signals in cellular applications, to help the phone find a working channel in which to send its data (voice content and other high-bandwidth applications such as video).

    In many cities, the part 15 band at 2.4 ghz is completely full. This is a real problem for many wifi users. A small, but dedicated WiFi band within 700 mhz would be a good use of the spectrum, as it provides the most use to the greatest number of people. However, there must be tight regulation of the protocols used within this band to lessen interference. All of these protocols MUST be public domain. I believe that the ever-increasing use of more spectrum for a given wifi connection must be reversed: instead of unreliable “108 mbps” wifi which is a bandwidth hog that doesn’t work, I’d rather see a 1 mbps wifi channel that delivers, throughout difficult conditions, and with low power requirements (to keep laptop batteries running longer).

    There should be channels set aside within this 700 mhz wifi band for rooftop mesh networking. The radios on these bands should be allowed to run at a higher power.

    He have to vocally resist the spectrum-grab by the communications giants. The content providers may find allies in the datacom sector (Cisco, Linksys, Netgear, etc), because a new 700 mhz wifi band would allow them to sell much new equipment. With these combined resources, the communications giants could be more easily defeated.

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  16. So, primarily, this band is best utilized in a One (few) to Many) broadcast scenario. Public service, MediaFLow, etc… How would Google capitalize on this as a competitive entrant against C/AT&T, VZW, Etc…? Also, I guess the rumored GooglePhone would run on 700Mhz.. if So, would it likely be VOIP? which back to bandwidth and uplink speeds, wouldn’t work on this network.. sorry for the random nature of this but I’m very interested in the comments… Thx

  17. You say “The lower band is 48 MHz while upper band is 60 MHz”

    But 794-746 = 48
    Are you sure the spectrum picture above is an upper band picture.

    I guess the picture is depicting the lower band.

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  19. Will anyone be able to use the upper 60 MHz, more specifically the 36 MHz commercial and the 24 MHz public safety allocation prior to the TV stations vacating the spectrum in February 2009?

    I’m more concerned about the 24 MHz frequency and whether there is or will be any use of that space prior to Feb 2009.

    If so, I’m curious who and what.

    Thanks.

    J.

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  22. Much of the discussion above concerning the improved propogation of 700 MHz is true. However, clearly a lower frequency, all things being equal carries less analog info than a higher one. Depending on coding/modulation techniques and associated quantization that will be employed in the 700 MHz range, both spectral effeciency and hence overall throughput can be improved. While physics puts contraints on what can be done, using different QAM and a myriad of engineering tricks can make a 700 MHz signal carry a receivable signal just as well as 1.9 Ghz and higher. Depending on the POP/AP density, you can arrive at a happy medium of throughput per user. Good luck achieving the same with 2.4 Ghz without 50 – 75 nodes per square mile…

  23. I have been providing 700 MHz wireless broadband access since 2003. I helped test the first 700 MHz transverter for Vyyo. I have deployed multiple sites using both Airspan and Vyyo equipment. The biggest issue I have with 700 MHz is its propagation. It is too good in many instances. Frequency reuse and self interference are a real issue. My company has been particularly plagued by tropospheric ducting (a phenomenon created by atmospheric temperature inversion). The 700 MHz noise floor can raise by 50+ db in a split second. If you are looking into 700 MHz equipment, DO YOUR HOMEWORK. Test the equipment. Make them prove it does all they say. Install one head end and test it thoroughly before buying the whole package. Do some research on tropospheric ducting http://www.dxinfocentre.com/tropo.html

  24. Things are heating up so quickly in large part because of the FCC’s anti-collusion rules which kick into effect on December 3 (the final day to file applications to be in the 700 MHz auction). Once the filing deadline hits, applicants who have not reached (and disclosed) agreements cannot speak to each other about the 700 MHz spectrum until the auction is over and final payments come in. So, while the auction starts January 24, the talking stops on December 3, so everyone is rushing to get their deals made now.

  25. Question: Regarding the auction of the 700MHz band… can someone who aquires this use it for radio broadcast? Is it mandatory cell-related use?

    Would appreciate a reply. Thanks.

    Misty

  26. I hope we start to see more open bands becoming available to the general public in the same way that WiFi has become generally available. Just look at how successful, widely adopted, and useful WiFi is nowadays, and how it is able to be used and shared by everyone. It’s really where we should be heading.

  27. we just got an offer from our mobile carrier. they have a tower on our land that they lease from us. they want to buy the lease for $100,000 for 40 years. even if the carrier merges or collapses, they would still pay us for the lease. is this a good idea, or should we hold out for something better?? just curious. if anyone can help, please. thx.

  28. 700mhz? Too bad it isnt as easy as it was back in the analog days of the 800mhz… heard some very interesting conversations via the radio shack scanner back then. anyone recall those days?

  29. What is with the public safety chunk and so much of it? I do not see were that much is needed. I am upset with the FCC and things like in band digital radio. Never years ago would the FCC have approved HD radio using in band as they have.
    Internet over power lines is another thing they should have laughed at like it was a joke.
    With the digital switch i know many people that have TV now but will not with the TV switch to Digital. They will be forced to go to satellite TV and many people because of trees ect. cannot do that.
    In my home in over 30 years of off air tv i have never had loss of analog signal but now with Digital it cuts out sometimes for hours.
    It is not because i do not have a good antenna because i have the best and a super low noise booster. I have tried many and am using what works best. They were analog UHF channels as are the digital ones.

  30. I haven’t heard so much, yet learned so very little, in quite some time…

    “…maximize their spectrum by re-using the same frequency blocks/pairs in non-adjacent cells.”

    “It can be done with a positive business case but it’s not the ideal spectrum for a high traffic dense urban demand set.”

    “Depending on coding/modulation techniques and associated quantization that will be employed in the 700 MHz range, both spectral effeciency and hence overall throughput can be improved.”

    “Frequency reuse and self interference are a real issue. My company has been particularly plagued by tropospheric ducting (a phenomenon created by atmospheric temperature inversion).”

  31. In cities, already well-covered by existing cellular infrastructure, it is less reasonable to designate this band for cellular. However, it is useful as it penetrates further into buildings than higher frequencies. I believe that text-messaging services, and other low-bandwidth applications which require high reliability, are the best use of this band. Perhaps part of the 700 mhz could be used for control signals in cellular applications, to help the phone find a working channel in which to send its data (voice content and other high-bandwidth applications such as video).

  32. I believe the key in this delima is how we modulate the signals in these particular bands. The modification of MIMO antennas and modification 802.xx protocols using better OPSK modulations will intertwine themselves into the 700mhz ring of play.

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