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Some basic idea about polar and IQ modulation

Polar modulation is analogous to IQ modulation in the same way that polar coordinates are analogous to Cartesian coordinates.

For Quadrature modulator approach to digital radio transmission requires a linear RF power amplifier, which creates a design conflict between improving power efficiency or maintaining amplifier linearity.

The polar modulation system allows the use of highly non-linear power amplifier such as class E. In a polar modulation system ,the power amplifier input signal only vary in phase, and amplitude modulation is accomplished by directly controlling the gain or modulating the supply voltage.

An good example of the selection of Polar and IQ modulation is about the EDGE system.
EGDE modulation effectively triples transmission rate using the same bandwidth as the earlier Gaussian minimum shift keying modulation, because EDGE introduces amplitude modulation variation(~17dB) as compared to the constant - evelope GMSK modulation format, EDGE radio architecture must deliver better spectral purity and modulation quality in order to deliver the necessary linear performance.

The use of polar transmitter has solved this design conflict between improving power efficiency or maintaining amplifier linearity and is most effective when implemented as a closed loop system.


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