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PN Offset Question

Discussion in 'GENERAL Wireless Discussion' started by ChaosThyre81, Apr 7, 2005.

  1. larry

    larry Sprint loyalist and former mod
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    I believe the CDMA system is simply not as good as the GSM system for incoming call reliabilty because of pilot pollution and too much PN offset switching. But it beats GSM in other categories such as capacity and seamless handoffs.
     
  2. MeatChicken

    MeatChicken Senior Member
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    Yes, just last night at 6PM here, I placed a call while idle on 800Mhz ch 384, & the system switched me over to 1900Mhz 825 for the call. Upon hang up I was then Idle & continued to be using on 825. My "guess" is that sector @ freq 384 was not "full", but the system is probably set to start moving/rebalacing users when it reaches some set #, such as 70% or whatever.
    I have never experienced "excessive" P/N switching, & have never heard of that as any sort of "CDMA Problem", & CDMA is actually designed to "like" P/N switching & handoffs, unlike analog or GSM, & it is not uncommon to have dozens of seamelss handoffs / PN switches within a few seconds, something that would be havoc on TDMA/GSM.
    Pilot pollution is probably less of a problem in most markets as compared to Co-Channel Interference on GSM networks.
    Both "problems" can be minimized by putting metal screens around the cell panels & giving them more of a downward tilt, to minimize the problem (.. while reducing the effective range of the sector).
    In my market of NY/NJ, I actually can Identify many of the ATT/CING sites by their downward tilt & screens, which is almost common now, but very rare on the VZW panels. Remember, while a CDMA network is designed for a phone to see multiple cells using the same channel / freq, this same situation could destroy a GSM phones ability to make / hold a call.
     
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  3. Andy

    Andy Diamond Senior Member
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    So that's what the metal shielding on CDMA sites are for, to reduce the effective range of the sector. I've always wondered that, since in my area, some sectors of a site will have those shieldings and other won't.
    I have definitely experienced Pilot Pullution where my phone will switch from 4 bars to 1 in a specific area because there's two pilots with about the same db reading, but one of them is much more polluted(ec/io in the -20's since it's further away), but the phone will keep switching between the two. This is definitely, though, much more noticable on LG phones, Nokias tend to perform better in this category.
    Thanks for the great info,
    Andy
     
  4. ChaosThyre81

    ChaosThyre81 Member
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    I noticed today that when I placed a call on both my phone and my brothers, both PN Offsets were 128 but I was on channel 450 while he was on channel 500. Does a sector use more than one channel? Also, does each sector have it's own paging channel? Or how does that work?

    M.
     
  5. MeatChicken

    MeatChicken Senior Member
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    Each Freq channel has it's own paging & voice channels. All freqs assigned to a sector will use the same p/n offset numbering sequence for each sectors. There can be many freq channels per sector, each with their own paging & voice channels.
    For example, the system here "hashes" or defaults my phone to ch 384, while my wife's hashes to ch 425.
    At home in the house we are both using p/n offset 204, the closest sector, although we are each on different freq assignments, w/ different paging channels.
    The paging channel sends various system messages to the phones at regular intervals, including the Time, neighbor list, a list of system parameters including what freq channels are on the system, incomming call message, re-direction messages (to switch to another channel), ect...

    I like Analogies :O :

    Imagine a large ballroom, w/3 seperate colored sections (3 CDMA Freq channels) of a dozen chairs each, Red-White-Blue.
    In front of each section is a guy w/ a bullhorn shouting messages (He's the paging channel), & the chairs are the voice channels.
    Behind the chairs are standing 3 dozen people in each section ( the "idle" phones). Day after day they report & stand in their same assigned (hashed), section behind their color.
    Idle standers can only "hear" their section's pager. He shouts various messages direct to everyone in his section, such as, "The time is 2PM", "The blue section is to the right, & the red section is to the left"..... & he also shouts messages to specific Idles, "Person # 212-555-1212, go sit in chair # 4, you will receive an incomming call there".
    If all the chairs in his section are "full" he can shout, " Person #212-555-1212, Go to the blue section & sit in chair # 8, there is a call waiting for you there."
    Once the call is established in the new section, that "person" now is listening to, & can only hear the Pager from that new section.
    If one day, a bus drops off 18 additional blue people, the blue bullhorn may say " Everyone standing with a number ending in 6,7 or 8 move over behind the red chairs", to keep a balance.
    The chairs in each section, although different colors w/ different pager, use the same numbering system (P/N offset #).
    The Ballroom may decide to add another section (additional spectrum channel), "Green", if the other 3 start getting too crowded. The owner of the ballroom ( System engineers, the pager's "boss"), "may" decide that no one "reports" (hashes) directly to the green section, it is only used for overflow, & you must be sent there by your regular sections pager, or it may be treated the same as the others.
     
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    #35 MeatChicken, Apr 21, 2005
    Last edited: Apr 21, 2005
  6. NYCDru

    NYCDru Sprint Newbie
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    Andy, I noticed the same thing too. My LG's would goback and forth between the two ofsets even though one would have a better db reading by about 5. My Moto found the most viable offset and basically camped on it.
     
  7. Andy

    Andy Diamond Senior Member
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    LG phones are always doing more PN hopping, as I found out in my experiments. Moto and Nokia phones are usually better at staying on the strongest offset, w/out hopping too much. I hope that the VX8100 will be a little better in that respect, otherwise I might go for the moto e815, if it's a lot better, RF wise.
     
  8. larry

    larry Sprint loyalist and former mod
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    Thanks for the tip. I was considering getting an LG soon but now I won't. Next time I'm in the market for a phone I need to find one that's better at staying put on the best PN offset. My Samsung A680 is very bouncy. Too bad Motorola doesn't make more phones for Sprint.
     
  9. TKR

    TKR Senior Member
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    Is it a function of the Qualcomm chip? At one time Nokia and Moto used their own chip design - not sure if they still do.

    Larry - the 125 still is getting consistently good reviews, including RF, so it is still on my "potentials" list.
     
  10. Andy

    Andy Diamond Senior Member
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    I'm not sure if Sprint LG phones are different, but Verizon LG Phones, especially the 6k, sometimes the 6100 series, tend to do that. Not sure how newer LG(Verizon) models compare, nor how Sprint LG's compare.
     
  11. larry

    larry Sprint loyalist and former mod
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    Yes the Nokia and Motorola used to use thier own chip. Not sure if they still do.

    TKR - are you ever going to get a new phone? ;) I know you have had a "potentials" list for a long time now. lol But I don't blame you for holding out since most of Sprint's phones over the past 2 years haven't been winners for one reason or another.
     
  12. NYCDru

    NYCDru Sprint Newbie
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    LG has a point to prove when it comes to Sprint. Sprint wasn't going to let them back till they PROVED that there phones can hang on to that signal. That was the problem last time right? So LG is going to up there game when it comes to them. Verizon likes them so they don't have to TRY as hard.
     
  13. MeatChicken

    MeatChicken Senior Member
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    All the Newer Nokias (6015i, 3589/86/88i ect ) use the newest Nokia Chipsets, which not only get great performance reviews, but they seem to be faster at aquiring the system upon turn on & hang-up, compared to many other phones.
     
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  14. larry

    larry Sprint loyalist and former mod
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    Too bad Nokia can only make basic phones for Sprint instead of a powerhouse.
     
  15. ChaosThyre81

    ChaosThyre81 Member
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    If my phone is using 3 PN offsets, is it receiving instructions from each sectors pilot channels? Or just one?

    M.
     
  16. Andy

    Andy Diamond Senior Member
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    You could say the same thing about Nokia and Verizon ;)
     
  17. ChaosThyre81

    ChaosThyre81 Member
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    If my phone is using 3 PN offsets, is it receiving instructions from each sectors pilot channels? Or just one? How does the phone know whether to use 1,2, or 3 PN offsets?

    Thanks!

    M.
     
  18. MeatChicken

    MeatChicken Senior Member
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    This was explained earlier - During a call the phone scans neighbor pilots, & if any go above signal level "T-Add", the fone requests that this pilot be added to the active set. This is how the phone "knows" whether to use 1, 2 ,3 PN offsets.
    It does receive instructions from all active pilots, but during a call there is a "Master instruction" to avoid paradox/conflicts between sectors -
    For example, When using more than 1 sector, 1 sector may "tell" the phone to reduce power output, causing another to request it to boost output. A master instruction will tell the phone which sector's requests to "ignore", or what power level to not go above/below......
     
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  19. TKR

    TKR Senior Member
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    let's just say I get full value out of my phones!
     
  20. larry

    larry Sprint loyalist and former mod
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    Sprint likes customers like you who keep their phones a long time. Sprint actually loses some money on many new phones they sell to exsisting customers. They prefer old customers to keep their phones for as long as possible.
     

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