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Join Date: Aug 2008
Re: What is CDMA ?
Advantages of using CDMA
- Voice Activities Cycles
CDMA is the only access that takes advantage of the nature of human conversation. In conversation the "voice activity cycle" is 35%, the rest of the time we are listening. In CDMA all the users are sharing one radio channel. Because each channel user has active just 35% of the entire cycle, all others benefit with less interference in a single CDMA radio channel. So, the mutual interference is reduced by 65%; and thus, the channel capacity is increased about three times.
- No Hard Handoff
In CDMA, every cell uses the same radio, the only difference is the code sequences. As a result there is no handoff from one frequncy to another while moving between cells.
- No Guard Time in CDMA
TDMA requires the use of guard time between time slots. Of course, the guard time does occupy the time period for certain bits. This "waste" of bits does not exists in CDMA, because guard time is not needed in CDMA technique.
- Less Fading
Less fading is observed in the wide-band signal while propagating in a mobile ratio environment.
- Capacity Advantage
Within certain parameters, CDMA can have four times the TDMA capacity; and twenty times the FDMA capacity per channel/cell.
- No frequency management or assignment needed
In both TDMA and FDMA the frequency management is always a critical task. Since there is only one channel in CDMA, no frequency management is needed.
- Soft Capacity
Since all CDMA traffic channels share a single CDMA radio channel, we can always add one additional user -- of course the voice quality is there by slightly degraded.
Both systems, analog and CDMA can operate in two different spectras, with no interference at all.
- For Microcell and in-building Systems
CDMA is probably the best system for microcell and in-building systems.
- No Equalizer Needed
When the transmission rate is much higher than 10kb/s in both FDMA and TDMA, an equalizer is required. On the other hand, CDMA only needs a correlator, which is cheaper than the equalizer.