US Digital Cellular Standard
Donald J. Miller
> It has come to my attention that the digital cellular standards
> adopted by US carriers are not going to be compatible with what we
> have adopted in Australia, GSM. I am interested in finding out a bit
> more about the US systems but cant find any FAQ on the subject.
The US Digital Cellular scheme (TDMA) was originally conceived to ease
the bandwidth requirement for a phone conversation by at least 3 to 1.
A 6 to 1 capacity advantage over the regular AMPS service would be
achieved if and when acceptable half-rate voice codecs were available.
Currently, each caall uses two of the six TDMA time slots. The aim
was/is to eventually use only one.
The first TDMA phones were to be dual-mode: that is to say that they
would function as regular AMPS phones as well. The hope WAS that
after 10 to 15 years, the AMPS functionality could be dropped,
resulting in more cost effective phones. A monkey wrench has been
tossed in the works, however.
AFTER the cellular industry chose TDMA as the standard, Qualcomm
proposed the use of a different CDMA technology with promises of even
greater capacity. Some, but not all carriers joined the Qualcomm
camp. The net result is that we now have two digital phone standards.
Motorola proposed a new analog system (NAMPS) with a capacity
advantage of 3 to 1 over AMPS that many hail as a good intermediate
step before full digital cellular implementation.
So, now we have FOUR phone "standards". What about ROAMING?
Well, it looks like the more expensive DUAL-MODE phones are here to
stay. Either of the two digital systems, TDMA or CDMA could have been
cost effective with time and further work on the ICs inside the
phones. The power-wasting RF duplexers required in AMPS phones for
full-duplex operation would not have been needed -- money would be
saved and talk time increased.
Six times the existing bandwidth was not enough. We got greedy.
Don Miller dmi...@crl.com
John Barcomb
> So, now we have FOUR phone "standards". What about ROAMING?
The way I see it, AMPS will always be supported so it will always be
standard to use AMPS in the U.S.
> Well, it looks like the more expensive DUAL-MODE phones are here to
> stay. Either of the two digital systems, TDMA or CDMA could have been
Actually, U S WEST didn't increase our price to the customer when we
started selling dual mode N-AMPS/AMPS (832/2412) phones in our N-AMPS
markets.
> Six times the existing bandwidth was not enough. We got greedy.
When the potential benefit of CDMA is 10-20 times capacity, there is a
good reason to look at that technology. There is also talk about
voice quality issues (Possible improved quality on CDMA -- nothing for
sure yet.)
Just thought I throw my $.02 in ...
John