LINC digital component separator for single and multicarrier W-CDMA signals

An implementation of a digital component separator for a linear amplification using nonlinear components (LINC) system on a field-programmable gate array is presented. It employs a flexible upconversion architecture, which can be easily configured as an image-reject or direct-upconversion architecture for transmission of single or combined multicarrier wireless code-division multiple-access (W-CDMA) signals and uses the phase-modulation method. Four direct digital synthesizers are applied as phase modulators, operating first on a low IF carrier varying from 0 to 1/4 of the sampling frequency. The sampling frequency can be chosen up to 32 times (122.88 MHz) the symbol rate of the W-CDMA chip rate of 3.84 Mbit/s. The system allows a flexible frequency assignment and spacing of one or two independent W-CDMA channels. This paper outlines how the envelope and phase information of two combined W-CDMA channels may be pre-calculated in real time. This information may be used for the generation of two phase-modulated signals, which are then supplied to a single LINC transmitter. The achieved performance is demonstrated for single and multicarrier application utilizing direct and/or image-reject upconversion including simulated and experimental data (adjacent channel power ratio, complementary cumulative distribution function, error vector magnitude).