Quote:
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Originally Posted by PetiteFlower
And what's the difference between GPRS and CDMA again?
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Well, first, GPRS and CDMA aren't equivalent. Let me give you too much of an answer, shall I?
CDMA and TDMA are two different ways of multiplexing multiple calls in a fixed bandwidth of RF spectrum. CDMA stands for "code-division multiple access", which throws many packets in the air from different cell phones and sorts them out by a code attached to each packet, whereas TDMA stands for "time-division multiple access", which allocates each phone a predictable, but short, slot of time. It so turns out that CDMA is much more "spectrally efficient" than TDMA, since it's much better at compressing out situations where people don't talk or data doesn't flow (just stop throwing packets in the air, as opposed to having dedicated timeslices that exist whether or not you use them).
GSM is a consortium standard that currently uses a version of TDMA as its "air interface". It turns out that TDMA classically had no way of doing high-speed data transmission, so GPRS was built as an interim solution that sits on top of TDMA and provides a rudimentary packet layer on top of the time-multiplexed channel. Ultimately, GSM will adopt a form of CDMA, called "wideband CDMA", to support one solution to
real high-speed data.
Now, the form of CDMA in the US is
not wCDMA or any such GSM standard; it's a similar, but not identical, form called IS-95 CDMA, invented by Qualcomm. 1xRTT CDMA is the next version of IS-95 CDMA, that supports GPRS-like speeds; the next standard likely to be adopted is 1xEV-DV CDMA. These, known as a batch as "cdma2000", offer improvements on both voice and data services, as does wCDMA.
So, from a featureset standpoint, GPRS is roughly equivalent to 1xRTT CDMA data, GSM's TDMA is roughly equivalent to IS-95's CDMA, and wCDMA will compete against 1xEV-DV CDMA (cdma2000).
Is that confusing enough?

Because I have one more twist: AT&T's "legacy" network uses an
old form of TDMA, less featureful than GSM's TDMA, called IS-136 TDMA. It has no provision for data services except analog calls, which are
very slow.
--janak