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The last actualizacions for CDMA systems like HSPDA specify higher order modulations like 16QAM. This is what allows UMTS systems to raise the throughput.
However it doesnt mean it is better that QPSK (or that 8PSK is better that QPSK). The problem is that points in the constellation will be closer for 16QAM or 8PSK and they will be more error prone and more power will be needed to sustain a hign SNR. The gain in througput will need an increase in complexity or an increase in power consumption.
The last actualizacions for CDMA systems like HSPDA specify higher order modulations like 16QAM. This is what allows UMTS systems to raise the throughput.
However it doesnt mean it is better that QPSK (or that 8PSK is better that QPSK). The problem is that points in the constellation will be closer for 16QAM or 8PSK and they will be more error prone and more power will be needed to sustain a hign SNR. The gain in througput will need an increase in complexity or an increase in power consumption.
By using QPSK we can code 4 times better than PSK
Maybe you have to understand more about QPSK first
There's a diferent way to code the data when we using UMTS, GSM, etc
Should I explain all of them here?
GMSK is a spectral efficient type of modulation. It helps to make the signal spectrum more narrow. But CDMA is spread spectrum system. It does not need this economy.
QPSK gives the lowest energy per bit for a desired bit error rate. It beats BPSK. You get twice the bit rate with near same BER at the same power as a BPSK.
For transmit, the peak to average power ratio, or peak to min ratio of the resultant waveform of the signal dictates how linear the PA must be to prevent distortion degradation of the signal. The more linear the PA needs to be, the worse its power conversion efficiency (DC power in to RF power output). Offset QPSK or staggered QPSK reduces the amplitude fluxuations somewhat for a slight degradation in energy per bit. The benefit of the reduced amplitude fluxuation is less stringent linearity requirement on power amp which translates to better power conversion efficiency. This helps extend battery life.
GMSK used for GSM does not require a linear PA. 8PSK (used for GSM EDGE) does require a fairly linear PA. LTE requires a very linear PA.
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