Predistortion in a 12/4 star QAM modulator

摘要

Methods and devices for predistorted 12/4 Quadrature Amplitude Modulation that compensate for distortion from a nonlinear element. Modulator input bits are mapped (40) to a plurality of nonreturn-to-zero (NRZ) modulator control bit (20-30). The mapping is determined by desired points on a 12/4 QAM constellation. At least one phase shift device (4, 6) receives an input signal and at least one of the plurality of modulator control bit. At least two quaternary phase shift keying (QPSK) devices (8, 10) receive phase shifted signals from at least one phase shift device. Each of at least two QPSK devices receives at least one of the plurality of NRZ symbols. An attenuator (32) that attenuates a first QPSK signal outputted from a first QPSK device of the at least two QPSK devices. A summer (34) sums the attenuated first QPSK signal with a second QPSK signal. The second QPSK signal is outputted from a second QPSK device of the two QPSK devices. The summer outputs a predistorted 12/4-QAM signal. The plurality of modulator control bit control the at least one phase shift devices and the two QPSK modulators to achieve the desired points on the 12/4 QAM constellation. <IMAGE>