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Effective line-of-sight range of CDMA?

Discussion in 'GENERAL Wireless Discussion' started by TKR, Feb 27, 2006.

  1. wirles

    wirles I'm baaaaaaaaaack
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    The problem with your ability to make a call on a distant BTS even though you had good signal would also be due to, in part, capacity available. You are far away, and handsets that are closer (with a stronger signal connection to the radio) will take priority. You may get some data packets, but won't be able to set up a voice call.

    As for coverage in the sky, you have several factors in play...scatter, skyward propogation, the specific propogation algorithm of the technology (TDMA, CDMA, etc...) and the free space propogation once you get really high in altitude.
     
  2. Deep_Under_Cover

    Deep_Under_Cover New Member

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    Hi All,

    I am new to the forum today but I think I can shed some light on the topic. I work for a Super Regional Cellular 850 /PCS 1900 CDMA carrier. There are many factors that can cause your phone not to work as expected. The only absolute in RF is that there are no absolutes.

    Your phone transmits 23Dbm or 200 mW. Thats just a 8 more DBM than a wifi router. Not much, espceially at 1900 Mhz. Such factors that cause your phone to have connectivity issues on mountain tops are this:

    Path loss, and a few more. These factors can cause poor quality of signal (EC/IO measure of signal quality = energy per chip / noise) wich results in high FER resulting in dropped calls, and call blocking. Most of all, the search window as specified or datafilled differently at each cell site. If you are beyond the search window of the cell site providing service, you will see signal strength but not be able to make calls. The search window unit is a "chip" and 8 chips equal a mile. Also, if you are too far away, you can still recieve virtual Pn's from other mountain top cellular sites far away causing interference because the Pn is not in the neighbor list from a cell site closer that can provide reliable service. Virtual Pn's are Pn's that because of path loss, have been scewed at a few units up and just appear as noise to the phone. The phone then has a poor Ec/IO, high transmitt power to try to "yell" above the raised noise floor, high FER, which usually causes dropped call or ineffective attemps. Sorry to be too technical. By the way, a Pn is psedorandom noise. Since CDMA transmits on one channel only per carrier, a Pn is transmitted by the pilot of each sector to let the phone and other cellsites know who is who as defined by the neighbor list.


    Bottom line is, if your having trouble making a voice call on CDMA if your on a mountain top, put your phone into analog only or analog call and make a call.
     
  3. TKR

    TKR Senior Member
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    Similar experience again this year. Cohutta wilderness area in North Georgia. Up on high enough terrain on a ridge, I could get a Sprint signal and a Verizon CDMA signal. On neither CDMA could I actually place a call. The phone finally reverted to analog and I was able to place a clear analog call on SID 93 (same SID as the CDMA signal, Verizon out of TN) fine on a faily weak signal.
     
  4. larry

    larry Sprint loyalist and former mod
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    I agree with Andy. CDMA phones are all about pilot pollution in high altitudes. It sometimes renders the phone useless even though it appears to have a good signal. I can't see my phone working in an airplane while in the air. How would it single out a PN offset to use and how will it be able to handoff every 5 seconds to other PN offsets not in it's neighbor list? I've always been skeptical about phones working in airplanes. Even GSM with it's hard handoffs doesn't seem like it would work that well. Maybe analog has a better chance?
     
  5. RadioFoneGuy

    RadioFoneGuy Powered by HTC FUZE
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    Some setting in the Switch will bar the phone from working at long distances as well. As a default on a Nortel GSM switch it is approx 20-25 miles. After this approx mileage the timing between the tower and the phone will not sync up. On your display you may read -80 db but if you look at the bar indicator there will be no bars. TDMA and analog did not has the more relaxed timing standards, plus the hard handoff doesnt hurt either.

    One example of this is I was in Lake Michigan approx 30 miles from my nearest tower. I had -80 db on both analog and GSM but could only make a call off the analog.
     
  6. TKR

    TKR Senior Member
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    I guess with analog going dark, it's one of those unfortunate things that the coverage footprint for the fringe areas will be reduced.
     
  7. RadioFoneGuy

    RadioFoneGuy Powered by HTC FUZE
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    Im sure CDMA developers will figure out a fix for this. Im surprised Qualcom hasnt figured this one out. With GSM moving toward WCDMA and the current CDMA 1x platform you would think they would resolve the SID/NID/Pilot flooding issues and the cell shrinkage. It seems like DATA is more important than fixing these issues.

    These are a couple of reasons I favor GSM as a Voice platform.
     
  8. TKR

    TKR Senior Member
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    I thought timing issues limited the effective radius of GSM.
     
  9. larry

    larry Sprint loyalist and former mod
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    I always thought the same thing. I heard that CDMA transmission has more range the GSM because of that very issue.
     
  10. Andy

    Andy Diamond Senior Member
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    You guys probably won't believe me but here I go: I am outside of Boulder, Utah, and I'm picking up a weak Verizon signal off their Navajo Mountain site, which is over 70 miles line of sight to where I am and I can receive calls and make calls fine. My signal is about -104 dbm (no service inside my cabin) and my Ec/Io is always -3 or better. Crazy, isn't it?
     
    #40 Andy, Mar 27, 2007
    Last edited: Mar 27, 2007
  11. larry

    larry Sprint loyalist and former mod
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    70 miles?? No way there must be something closer that you don't know about.
     
  12. Andy

    Andy Diamond Senior Member
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    That's what I thought but there is not anything closer.
    Even on Lake Powell house-boating last year there were times when I was over 20 miles away from the site and my view was blocked by tall mountains and I still held on to a signal...that site must just be way powerful.
     
  13. larry

    larry Sprint loyalist and former mod
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    I know one area where I can use a Sprint signal as much as 30 miles away but that's about the limit.
     
  14. Andy

    Andy Diamond Senior Member
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    I have used a Verizon signal as far as that as well out in the West Desert and the only reason I could not use it further than that is because of the topography (there are huge mountains in the way as you move more than 30 miles away from the site).
    I know for sure that Verizon has no other cell sites where I was, PN Offsets and Neighborhood list matches exactly what I get next to their Navajo Mountain site and my signal improves dramatically whenever I have clear line of sight to Navajo Mountain(which is very tall).
     
  15. Fire14

    Fire14 Easy,Cheap & Sleazy
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    That is simply amazing, I would never have expected to hear someone picking up a digital signal that far.
     
  16. Andy

    Andy Diamond Senior Member
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    I know, I was shocked! I'm still shocked, actually! My bill was just posted online and sure enough, those calls were indeed placed on their Navajo Mountain site.
    I never thought 70 miles would be possible.
     
  17. Fire14

    Fire14 Easy,Cheap & Sleazy
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    Too bad they can't get better coverage in the cities & other rural area's like that.
     
  18. Andy

    Andy Diamond Senior Member
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    I know really. I guess this must just be a very unique setting. I mean you can tell that the signal must be coming from far away, because the second I stepped into my cabin it was gone. When I stepped back out, it came back, weak, but reliable.
     
  19. Gonz

    Gonz Senior Member
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    There supposdly were sites like that once in SE wisconsin (which still are extremely tall). Supposidly they had to turn down power levels to make room for larger call volume in the mid 90's. I was told the long-range tower that once primarilly served the area in which my parents live is a little less than 20 miles away. (Brookfield, WI). For all who know brookfield, it's the huge tower right off I-94 between bluemound and mooreland road. I was told this tower was designed to serve 94 between Oconomowoc and Wauwatosa. Oconomowoc is about 25 miles from the site.

    BTW, on the technologies, VZW Airphone is based on TDMA if I remember correctly, due to the fact that CDMA does have those tower selecting issues when too many are seen.
     
  20. Andy

    Andy Diamond Senior Member
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    So does Airphone work if its a TDMA based system? Do you know, Gonz?
     
  21. Gonz

    Gonz Senior Member
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    I read it somewhere that airphone needs the time division in order to be used in such a manner. Supposidly there are a bunch of hugely wide-area sites which serve the system.

    Aww, according to the verizon site, airphone will be discontinued as of Dec 2008. That's a shame. The system works fine, I used it at the discounted rate for verizon customers plenty of times. Very clear call quality.

    I do remember definetely reading (from verizon) that the technology was very similiar to TDMA, yet, I do not remember the operating band.

    The service probably is too much of a bother to staff for customer service. Shame, airphones will always live on on a bunch of the 9/11 documentaries however.
     
  22. RadioFoneGuy

    RadioFoneGuy Powered by HTC FUZE
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    GSM effective distance is limited by the switch settings. I have made calls off of sites up to 40 miles away before. Im not sure about the CDMA being able to go farther than GSM. This would be a good test for someone out in old Western Wireless area (Alltel that has a CDMA and a GSM test phone)

    I know Nortel GSM pushes 10 more watts than Nortel CDMA 1x. But it would also be line of site. How many calls on the CDMA, is there enuff calls to make the cell shrinkage problem an issue. You have to worry about NID borders. Also have to figure out which band 850/1.9.

    We just turned off our CDMA which was CDMA 1 Motorola that put out more power that some of the newer stuff.

    This would make for a good test.

    On most case in GSM you will lose coverage due to line of sight before distance, at least hear in Michigan.
     
  23. TKR

    TKR Senior Member
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    I can't help but wonder if sometimes the weak link in the chain is the handset and it's power level. If the phone shows it can get a signal from the tower, but it cannot place a call, is that perhaps because the phone's transmission is too weak for the tower to pick up? I doubt I had too many other PN offsets to confuse the phone in the remote location where I was.
     
  24. larry

    larry Sprint loyalist and former mod
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    That's a possibility. I'm sure I remember the older generations of Sprint phones from circa 1998 such as the Samsung SCH-1000 being able to pick up RF better and hold onto calls better in fringe areas. They also used to have better sound quality. Also don't GSM phones generally have higher wattage than CDMA?
     
  25. RadioFoneGuy

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    Not sure on the phone power, probable compare similar phones on makers website. Possible compare Moto razr V3 or some phone that is offered by both technologies. Seems like I saw a setting in our switch that sets the power at 33 dbm for 1900 and 36 dbm for 850.
     
  26. wirles

    wirles I'm baaaaaaaaaack
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    Don't forget the FCC limitations on handset power as well.
     
  27. TKR

    TKR Senior Member
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    Yes, it would be nice if the FCC would allow phones to have a "boost" button (higher power output) just for those remote situations where extra power might make the difference.
     
  28. MicroTACelite

    MicroTACelite New Member

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    As far as making calls from planes on 9.11, you have to remember that most people still had analog handsets back then, or at least dual-mode ones. Even if the CDMA service was unavailable in the air, the analog most likely was.
     
  29. wirles

    wirles I'm baaaaaaaaaack
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    i seem to recall discussing this ad nauseum in another thread. they were also at low altitudes. Flight 93 was in a rural area.
     
  30. larry

    larry Sprint loyalist and former mod
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    Yeah the lower altitudes probably made it much easier to place calls.
     

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