2D cubic spline implementation for concurrent dual-band system

This paper presents a 2D cubic-spline (2D C-spline) implementation of digital predistortion (DPD) for the linearization of power amplifier (PA) used in dual band transmitters. The implementation uses a 2D look up table (2D-LUT) for storing the coefficients of the 2D C-spline. The transmitted signals are assumed to be sufficiently spaced wide apart so that only the in-band distortion in both the channels need to be accounted for. The frequency selective technique is used to implement the DPD in each band as it reduces the sampling frequency requirement for the analog to digital converters (ADC) and digital to analog converters (DAC) used in the transmit and feedback paths. An FPGA testbench integrating the concurrent dual band RF system is utilized to verify the linearization performance of the 2D C-spline predistorter. The linearization of two wideband code division multiple access (WCDMA) signals which are 310 MHz apart is investigated. The experimental results shows that the intermodulation distortion products are reduced by 25 dBc for a 10 W dual-band PA.