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To: New2Tech who wrote (1688)6/2/1998 9:40:00 AM
From: Travis Pennington  Read Replies (1) of 5390
 
Another CDMA link:

cdg.org

Contains a very high-level description of AMPS, TDMA, CDMA.

The basic ideas behind the 3 technologies are (excuse me if I'm insulting your intelligence):

AMPS: Allocate a channel to each caller.
Pro: Very simple and mature technology.
Con: Consumes an entire 10 to 30 kHz channel for a call. This is a big problem that has motivated the TDMA and CDMA technologies.

TDMA: Have x number of calls share a channel. For digital calls, a handset will receive its data only 1/x'th of the time and turn the data into an continuous analog signal (i.e, voice coming out of the speaker)
Pro: Better utilization of the RF Spectrum than AMPS and easier to implement than CDMA.
Con: Improvement of RF usage not as good as the theoretical improvement offered by CDMA.

CDMA: Remove the idea of allocating calls to channel. Combine x number of calls into a single ball of data and transmit it as a whole.
The handset receives the huge ball of data, extracts the information it is interested in, and turns the data into an analog signal (voice data).
Pro: Theoretically, offers a better utilization of the RF Spectrum than TDMA.
Con: Extremely difficult technology to implement. Interestingly, a side-effect of this complexity is that CDMA offers better privacy against eavesdroppers than TDMA.

I'm not sure how far along CDMA technology has progressed. Most of the data I've seen touting CDMA's RF utilization improvement over TDMA have been based on theoretical rather than actual data -- Be careful when you come across such comparisons. In contrast, I believe the theoretical improvement involved with TDMA is relatively easy to achieve.
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