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CDMA Sites and GPS

Discussion in 'Cell Tower Hunting Club' started by adgsteve, Oct 19, 2005.

  1. adgsteve

    adgsteve Tower Hunting Addict
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    Am I right that all CDMA cell sites have a little white cone shaped GPS antenna/receiver on them?
    Since I read that somewhere I've been checking my local sites and that's been correct, until now. :(
    I just discovered GPS antenna's on two towers I thought were GSM towers :confused:
     
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  2. Yankees368

    Yankees368 Compulsive Signal Checker
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    I think (but i' not sure) that GSM needs it too. I do know that CDMA needs it.
     
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  3. adgsteve

    adgsteve Tower Hunting Addict
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    Hmm, well I've looked at some towers that I know for sure are Cingular and I can't find a GPS antenna anywhere on or near the site. So I was thinking it's only a CDMA thing. If that's true I gotta do some more research on those two towers. ;)
     
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  4. hillbilly44

    hillbilly44 Senior Member
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    The little while cone shaped antennas are for GSM companies like Cingular. They use GPS and antenna triangulation to locate a caller for 911 purposes. Some CDMA carriers use GPS in the handset to do the same thing:cool:
     
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  5. Yankees368

    Yankees368 Compulsive Signal Checker
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    I think you are mistaking. Please correct me if I am wrong, but dont CDMA carriers use the GPS cone to sync timing so that the CDMA protocol can operate?
     
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  6. adgsteve

    adgsteve Tower Hunting Addict
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    Yeah, that's what I read about it.
    After doing some more checking on some of the GSM towers that I am sure of, they do not have a GPS antenna anywhere on them. All of the CDMA towers that I am sure of do have a GPS antenna.
    I can only conclude that GPS antenna are only needed on CDMA sites.
     
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  7. CellSiteGuy

    CellSiteGuy New Member

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    Nope. *All* cell sites use GPS. It is used for time sync on the network, plus to provide the network the location of the site for carriers who are not using handset-based location. (ie to triangulate the users location based on the uplink power level to the 3 cell sites).
     
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  8. adgsteve

    adgsteve Tower Hunting Addict
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    Well, you must be right. I just spent 2 hrs looking up one of the towers I had in question, and it's a T-Mobile site with a GPS antenna on it. I guess the other GSM towers I referred to have the GPS antenna hidden fairly well. (I couldn't find it)
    There went that theory.. Oh well. :O
     
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  9. Yankees368

    Yankees368 Compulsive Signal Checker
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    They could be anywhere on the installation. Could be on the cabinets, on the wiring path from the cabinets to the actuall tower, could be on the tower itself. Ive seem them all over the place.
     
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  10. adgsteve

    adgsteve Tower Hunting Addict
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    Hmm, well there's one Cingular tower that I've examined and done everything except climb the fence around the cabinets and I still can't find the GPS antenna. It must be tucked away inside somewhere below the level of the top of the fence. ;)
     
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  11. Yankees368

    Yankees368 Compulsive Signal Checker
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    Thats what I was thinking. There are some towers that unless you get a birds eye view of, or before they put up the fence, you will never find it.

    Waittttt a minute here. I never remember seeing a GPS cone with the new T-Mobile tower that was installed in my home town. I was around for almost every stage of construction. Before they even put up the cabinets. I never remember seeing a GPS cone.
     
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  12. Andy

    Andy Diamond Senior Member
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    At a local bulding here, there's a NExtel site and an ex-Qwest site. Nextel seems to have their equipment in a shed-like thing on the side of the building and there are two GPS cones there. Qwest's equipment is on the outside of the building right where the panels are and there was at least one GPS cone belonging to Qwest, so we have two different technologies, both using the GPS.
     
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  13. adgsteve

    adgsteve Tower Hunting Addict
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    It just seems odd that they would need GPS equipment on every cell site for location finding. I mean after all, when they build a cell site they know the GPS coordinates where they put it, and the tower isn't going to move. Wouldn't it be a lot cheaper to just enter the coordinates in the system when they turn on the site. That would save them having to buy 10's of thousands of GPS units.
    Now the timing signal for the system I can understand.
    Oh well, I'm overthinking again.... :(
     
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  14. CellSiteGuy

    CellSiteGuy New Member

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    The PCS-band carriers (1900 Mhz) usually place the GPS antenna away from the cell site antennas. Reason being is that the GPS rx frequency is close to the 1900 Mhz band. Usually the GPS would be placed on the equipment shelter, or for sites that just use cabinets like T-Mobile, Sprint, and some Cingular sites, they would mount the GPS to one of the ice bridge supports (the metal cable tray that goes from the BTS equipment to the tower and protects it from ice). Or the would place it on the tower, usually around 40' - 50' above ground. If the carrier owns the tower, they'll place it on the tower, otherwise on the equipment/shelter. Reason being is that the tower company will charge them extra for the extra antenna, and the extra length of 1/2" coax that is required for the GPS antenna.
     
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  15. Andy

    Andy Diamond Senior Member
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    INteresting. I didn't know that 1900 carriers needed to place the GPS equipment away from the panels. Then I wonder how come Qwest had their GPS so close to the panels...

    If tower space is leased/rented, the owner will actually charge the carrier for the extra GPS antenna on the tower? I didn't know that...Great information, thank you very much.
     
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  16. adgsteve

    adgsteve Tower Hunting Addict
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    That is interesting, and good information. Thanks CellSiteGuy! :)
     
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  17. bobolito

    bobolito Diamond Senior Member
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    You know that's a very good point you're raising. You got me thinking. :headscrat
     
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  18. CellSiteGuy

    CellSiteGuy New Member

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    They certainly will, vertical real estate, my friend. Think of it this way: You live in an apartment bldg with 5 other apartments. Your Landlord has some storage closets that he will lease sepearatley to his tenants if they want , first come first serve. He'll charge you for it, but you can have it. Tower companies charge by the # of antennas & cables at an elevation (your apartment). If you want to put a GPS on the tower (the storage closet), you need to pay the tower company more.

    The main thing is that the more antennas & cables that you put on a tower, it decreases the structural capacity of the tower - they are only designed for a certain load and they are very co$tly to reenforce.
     
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  19. Andy

    Andy Diamond Senior Member
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    Very good info, thank you!

    Are panels/cables really that heavy that the company would need to reinforce the tower?
     
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  20. CellSiteGuy

    CellSiteGuy New Member

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    On average, the panels are about 17lbs each, plus the mounts, which if you are using a full 12 antenna array mount, weights about 190', so a total new setup could be about 400 lbs. Its not only the weight - alot of it is the windloading. The more surface area (the face of the antenna) the wind has to blow on at the top of the antenna, the more pressure it is putting on the bottom half of the tower and the foundation, which could require reinforcement.
     
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  21. hillbilly44

    hillbilly44 Senior Member
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    Andy,

    Yes the GPS antennas have to be placed away from the antennas, both because of interference concerns and windloading on the tower. Also the FCC requires all carriers to provide coordinates of where the caller is located within a certain radius (300 to 150ft)(this is phase 2 9110. The 911 centers already have the cell sites equipmemt location (it's called phase 1). hope this helps with the explaination:D
     
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  22. Jonathan Kramer

    Jonathan Kramer Telecom Atty/RF Engr.
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    Interesting thread!

    GPS is used for network sync and precise timing purposes, not for site location purposes.

    By using a very high stability timing source (GPS) available to all sites in a large geographic area, you can sync all sites together.

    Precise timing permits noiseless handoffs, and handouts without clipping from re-synch. Precise timing is also useful in triangulation calcs for E911.

    GPS antennas do not alway constantly update the timing stability. Many sites have high stability time sources that are disciplined (yes, that's the correct technical term) by periodic GPS updates. In other words, the satellites don't have to be visible 24/7 to keep the timing precise. At my own site I have a photo of a Cingular (now T-Mobile) gps antenna that's under a large overhang at a church in Irvine, California (go search the term, "light of christ" and you'll find it).

    As for the distance of the GPS antenna from the panel, it's an issue of reflections. Multipath reception from bounced signals can interfere with the precise timing function. Generally, it's better to have the GPS antenna above the panels, or a distance away from them, but like so many other hard-and-fast rules, this isn't hard-or-fast.

    One type of site that doesn't require GPS is a cellular repeater. Repeaters don't require independent time source information since they rely on the donor cell to handle that function.

    OADM, I'll be uploading some new photos today, including a monopalm that doesn't have visible antennas. I took the photo yesterday in Palm Desert, California. I have a few more goodies to upload, too.

    Best,

    Jonathan
     
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  23. Andy

    Andy Diamond Senior Member
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    Wow, thanks guys! This is some great information from all 3 of you!

    CellSiteGuy: I never thought that panels weigh this much. Lol, oh well. I wish I could personally go inside the base of a cellsite sometime. This stuff is so interesting, but I'm just a 'normal' person. ;)

    HillyBilly: Yes, very helpful as well. Thanks!

    Johnathan: Great explanation as well. It makes complete sense that repeater type antennas don't need GPS since they just 'feed' off the donor cell as you said.

    ~Andy
     
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  24. Scitnor

    Scitnor New Member

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    :confused: I'm new to the forum and would like to ask, What is an "Ice Bridge" and where is it located within a site?
     
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  25. jrip

    jrip Senior Member
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    Any antenna is just a hunk of metal, sheet metal, round stock etc.. Some are wire wound with or without an inductor. Nothing about them is light, unless they are small.
     
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  26. hillbilly44

    hillbilly44 Senior Member
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    Alot of antennas weigh abut 16-18lbs so they're not that heavy. Some are even lighter (4-5lbs) Also what the@#@$@ is an inductor. I've been an engineer for 8-9 years and have never heard of an inductor. Most antennas are NOT wire wound but have circuit boards inside of a fiberglass housing. Also GPS antennas do more than synch the site. They are part of the triangulation system that is used with phase 2 911 systems for location of a mobile phone.:cool:
     
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  27. Jonathan Kramer

    Jonathan Kramer Telecom Atty/RF Engr.
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    This continues to be an interesting thread! Even though I've responded once, I'll chime back in with some additional comments to help explain the technology...

    Some sites do not use GPS antennas because they are repeaters. Repeater sites borrow capacity from another site and relay calls from the pocket area back to the donor site. The repeater relies on the timing data from the donor site.

    Yes, GPS antennas can be almost anywhere. Most configurations don't require timing 100% of the time. The GPS is used to "discipline" the internal site clocks. Now before you start thinking about Charylee's newest avatar (which, I guess, I am...:browani: ), look up the word on dictionary.com.

    If you look at the photos here (and at my site searching on the term GPS) you'll find many examples of partially blocked GPS antennas. It's a bit tricker for the LMU antennas, but that's another post!

    -jlk-
     
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  28. Andy

    Andy Diamond Senior Member
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    So will a repeater site look just like a regular cellsite, other than not having the GPS antenna?
     
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  29. Jonathan Kramer

    Jonathan Kramer Telecom Atty/RF Engr.
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    Andy, a repeater site will normally look like a regular cell site, albeit with a smaller equipment footprint. In some cases, diamond-shaped antennas will be used to link to the donor site. In other cases, data lines (copper or fiber) will be used. In most cases, you won't be 100% sure if the site is a repeater site, or a stand-alone site.

    j
     
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  30. Andy

    Andy Diamond Senior Member
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    Will the PN offsets of the repeater site be the same as the offets of the donor site? I'm not completely sure why a carrier would use a repeater site(unless of course in a rural area that doesn't have access to T1 lines, etc.).

    Sorry I have so many questions.
     
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