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GSM |
CDMA |
Primary method of how to divide the finite frequency of airwaves between multiple users at the same time |
TDMA, or the Time Division Multiple Access concept. Each user of the channel takes turns transmitting and receiving in a round-robin fashion. In reality, only one person is actually using the channel at any given moment, but he only uses it for short bursts. GSM (TDMA) does it by chopping up the channel into sequential time slices |
CDMA uses a special type of digital modulation called Spread Spectrum, which takes the user’s voice stream bits and splatters them across a very wide channel in pseudo-random fashion. The receiver undoes the randomization in order to collect the bits together in a coherent order. |
International Mobility |
Very good |
Limited |
Tower communication range |
35 Km |
110 Km |
Phone power output |
Typically 2W |
Typically 200 mW |
Communication time |
Generally higher in a GSM (TDMA) phone due to its pulse nature of transmission |
Could be lower even with lower power output because CDMA phone transmits all the time |
Cell tower handoff |
Hard Handoff, i.e., the phone first stops receiving and transmitting on the old channel, and then commences transmitting and receiving on the new channel. Therefore, if you are making a call during a handoff, the call needs to be dropped. |
Soft Handoff, i.e., when a mobile phone has to choose between two cells, and then shift from one of them to another as you travel, the transition is very smooth |
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56 kbps data transmission speed today, is also catching up very fast, and moving towards the next generation protocols, the GPRS and the EDGE. |
153.6 to 614 kbps. Hence the claim to supply internet at 144 kbps speed. |
Security |
It is possible for someone to put fake base station and it is only a matter of time before a good hacker cracks the mathematical algos. Just like internet is hackable, GSM is clonable. |
More secure than GSM. Since it uses entire spectrum, base station snooping is not possible. |
The number of channels (users) that can be allocated in a given bandwidth |
Lower than CDMA |
Higher than GSM |