It's not CDMA vs. GSM
Background
Have you ever been annoyed to see something incorrect spouted over and over again? Someone who doesn't know what they are talking about mentions something in the wrong way, and then it catches on with clueless people repeating the original incorrect source. It's one of my pet peeves. Sometimes it doesn't matter, sometimes it does. With phones it matters, because the tech. specs are, well, technical.
I've seen this a lot recently with phones in general, and particularly the iPhone, with many people mentioning "GSM Version" vs. the "CDMA Version".
A little history
There have been four major versions of cell phone technology up until now.
1. AMPS - This was the original analog cell phone standard. This is what you can see in old movies like "Wall Street", where someone is logging around a giant brick.
2. D-AMPS - This is the digital version of AMPS. This used TDMA.
3. GSM - This is a world-wide standard, which originally also used TDMA, but newer versions use CDMA.
4. CDMA2000 - This is what Sprint and Verizon in the US use, and was the first large scale network to use CDMA.
Basically, #3 and #4 are still alive and being upgraded, the simplified progression goes like this:
CDMA2000: cdmaOne→1x→EV-DO r0→EV-DO rA→EV-DO rB
GSM: GSM→GPRS→Edge→W-CDMA/UTMS→HSPA→LTE
A Primer on Cell Phone Technology
So what are CDMA and TDMA, and what makes them different?
Basically TDMA is an older technique which allows multiple phones to use a single tower by allocating time-slots for each handset. As a simplification, you can immagine that every second in time is divided into 100 slots of 10ms each. If each phone only needed one 10ms slot per second to communicate with the tower, the tower could support up to 1000 phones. The main problem with TDMA is that it's not very efficient, since if only 1 phone is in use, it may still receive 1 slot per second from the tower, leaving the rest of the tower's capacity idle. Another issue is that TDMA suffers from "hard" capacity. If the tower can support 1000 phones, it can support 1000, but not 1001. There is no gradual degradation of quality as the tower becomes crowded, it just reaches a limit, and then can't accept any more calls.
CDMA works differently in that it allows all handsets to transmit continuously instead of waiting for a pre-allocated time-slot. Since all phones can transmit at the same time, the tower has to listen carefully and separate out the signals, much as one might be able to separate out several voices when multiple people are talking to you at the same time. Each handset is identified by a unique code, thus the term "Code division multiple access". CDMA makes more efficient use of bandwidth than TDMA, and allows a more graceful degradation of signal quality when cells become overloaded ("Soft capacity"), but it is more complex to implement than TDMA, which is why it only became popular later on.
Conclusion
TDMA and CDMA are single multiplexing methods, and not entire protocols. The latest versions of both of the major systems in place in the US use CDMA multiplexing, so it's not "CDMA" vs. anything. One could say "CDMA2000 vs. W-CDMA", and the conversation would make a lot more sense.
Lest you think I am being pedantic, realize that in countries like Japan, TDMA was never supported in the GSM tree, and started out with W-CDMA. All carriers have been CDMA, but not CDMA2000.
A more annoying trend is trying to differentiate the phones by carrier. (i.e. "AT&T iPhone" vs. "Verizon iPhone"). While this might be practical in a sense for end-users, it doesn't make a lot of sense for those who might be using other carriers, particularly people in other countries, who are likely to say "What is AT&T?" If you buy an official unlocked phone, one can bet that it uses CDMA, but that won't tell you which carrier it will work on - hence the need to actually be accurate in terminology.
One more thing to note: The CDMA2000 line has hit it's end, because even the standard's creator has decided to join the W-CDMA camp, and start working on LTE for the next generation.
Have you ever been annoyed to see something incorrect spouted over and over again? Someone who doesn't know what they are talking about mentions something in the wrong way, and then it catches on with clueless people repeating the original incorrect source. It's one of my pet peeves. Sometimes it doesn't matter, sometimes it does. With phones it matters, because the tech. specs are, well, technical.
I've seen this a lot recently with phones in general, and particularly the iPhone, with many people mentioning "GSM Version" vs. the "CDMA Version".
A little history
There have been four major versions of cell phone technology up until now.
1. AMPS - This was the original analog cell phone standard. This is what you can see in old movies like "Wall Street", where someone is logging around a giant brick.
2. D-AMPS - This is the digital version of AMPS. This used TDMA.
3. GSM - This is a world-wide standard, which originally also used TDMA, but newer versions use CDMA.
4. CDMA2000 - This is what Sprint and Verizon in the US use, and was the first large scale network to use CDMA.
Basically, #3 and #4 are still alive and being upgraded, the simplified progression goes like this:
CDMA2000: cdmaOne→1x→EV-DO r0→EV-DO rA→EV-DO rB
GSM: GSM→GPRS→Edge→W-CDMA/UTMS→HSPA→LTE
A Primer on Cell Phone Technology
So what are CDMA and TDMA, and what makes them different?
Basically TDMA is an older technique which allows multiple phones to use a single tower by allocating time-slots for each handset. As a simplification, you can immagine that every second in time is divided into 100 slots of 10ms each. If each phone only needed one 10ms slot per second to communicate with the tower, the tower could support up to 1000 phones. The main problem with TDMA is that it's not very efficient, since if only 1 phone is in use, it may still receive 1 slot per second from the tower, leaving the rest of the tower's capacity idle. Another issue is that TDMA suffers from "hard" capacity. If the tower can support 1000 phones, it can support 1000, but not 1001. There is no gradual degradation of quality as the tower becomes crowded, it just reaches a limit, and then can't accept any more calls.
CDMA works differently in that it allows all handsets to transmit continuously instead of waiting for a pre-allocated time-slot. Since all phones can transmit at the same time, the tower has to listen carefully and separate out the signals, much as one might be able to separate out several voices when multiple people are talking to you at the same time. Each handset is identified by a unique code, thus the term "Code division multiple access". CDMA makes more efficient use of bandwidth than TDMA, and allows a more graceful degradation of signal quality when cells become overloaded ("Soft capacity"), but it is more complex to implement than TDMA, which is why it only became popular later on.
Conclusion
TDMA and CDMA are single multiplexing methods, and not entire protocols. The latest versions of both of the major systems in place in the US use CDMA multiplexing, so it's not "CDMA" vs. anything. One could say "CDMA2000 vs. W-CDMA", and the conversation would make a lot more sense.
Lest you think I am being pedantic, realize that in countries like Japan, TDMA was never supported in the GSM tree, and started out with W-CDMA. All carriers have been CDMA, but not CDMA2000.
A more annoying trend is trying to differentiate the phones by carrier. (i.e. "AT&T iPhone" vs. "Verizon iPhone"). While this might be practical in a sense for end-users, it doesn't make a lot of sense for those who might be using other carriers, particularly people in other countries, who are likely to say "What is AT&T?" If you buy an official unlocked phone, one can bet that it uses CDMA, but that won't tell you which carrier it will work on - hence the need to actually be accurate in terminology.
One more thing to note: The CDMA2000 line has hit it's end, because even the standard's creator has decided to join the W-CDMA camp, and start working on LTE for the next generation.
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