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Top message:  850 downfall by 155n8th   Oct 29, 2003, 6:32 PM

Replying to:  Re: 850 downfall by wb   Nov 4, 2003, 12:22 AM

Re: 850 downfall

by Rich Brome (Moderator)    Nov 4, 2003, 1:15 AM

wb said:
Interesting fuss with Nextel, considering that PS used Nextel almost exclusively until just recently, for their cell phone carrier.


Yes and no. Public safety people may use Nextel for cell phone service, but they sure as heck don't use Nextel for dispatch and critical communications. It doesn't seem like you meant that, but I just wanted to clear that up before anyone else reading this confuses that issue.

I will beg to differ. The 800-850 issue is not simply a swath of spectrum but are very specifically assigned frequencies within a given band. Those specific frequencies are assigned to specific users.


Yes. Absolutely.

Just to expound on that a bit more:

Everyone has their own spectrum for any given area. (Spectrum = frequency band(s)). For any given area, Sprint has their spectrum, Verizon has theirs, Nextel has theirs, and public safety has theirs. They don't overlap (in theory).

Digital, analog, 3G... it doesn't matter - each company has their own spectrum, and as long as they stay within it, everything's separate.

For example: Cingular (or rather its pre-merger predecessors) originally ran just AMPS (analog) in the 800 (AKA 850) MHz spectrum they were originally given back when cellular just got started. Now, in most regions, they run AMPS, TDMA, and GSM simultaneously, all in that very same slice of spectrum.

Nextel has its own spectrum, which wasn't originally designated for cellular phone service. It's closer to public safety bands than the cellular 800/850 band used by other companies like Cingular and Verizon. Because it's right "next to" the public safety bands, and because Nextel's iDEN technology has a lot in common with public safety radio systems, there have been unique interference issues.

...I would guess that cell phone companies also have a type of shared frequency activity going on, or it would be impossible for someone calling on one company's frequencies to talk to someone else on a different company's portion of the 1900 swath, but my knowledge on the specifics of this is void.
Rich?


Do you mean when someone with Cingular talks to someone with Verizon, etc? In that case, the frequency of each calling party's phone is irrelevant. It would only matter if the radio signal went directly from phone-to-phone, but it does not. Phones can only connect to towers, and vice-versa.

Therefore, it only matters that a phone can use the same frequency as the nearby tower. From the tower, the call is routed to phone system trunk lines, to the other carrier's network, their tower, and then to the other phone, even if you're standing right next to each other. It's not much different even if you're on the same carrier and standing next to each other - the call still goes through the towers and the network - not phone-to-phone.

As far as how spectrum is split up for carriers/regions, down to individual calls... it's complicated. I can explain it, but we should start a new thread for that... Wink

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