Research And FPGA Implementation On Two-Dimensional Digital Predistortion Technology

With the continuous development of modern wireless communication systems,in order to maximize the use of spectrum resources to cope with the growing user demand,a series of modulation technologies with high spectrum efficiency such as WCDMA and OFDM are widely used.In order to enable mobile network operators to make full use of the discontinuous spectrum resources,it has become a trend to use transmitters that can simultaneously process signals of different standards and different frequency bands.Using a power amplifier to simultaneously amplify signals in multiple frequency bands has the advantage that it can significantly reduce the number of circuit components and the power consumption of the transmitter.As the core device of the basestation system,the RF Power amplifier consumes the most energy in the entire system.Due to the inherent physical characteristics of the power amplifier,it is difficult for people to achieve high linearity and high efficiency at the same time.As a new type of power amplifier linearization technology,digital predistortion technology as a power amplifier linearization technology has high accuracy,good stability,and low cost and other advantages.With the change of application scenarios and the emergence of dual-band signals,the digital predistortion technology designed for single-band has been unable to effectively respond.Therefore,this thesis focuses on the two-dimensional digital predistortion technology and FPGA implementation of concurrent dual-band power amplifiers.In concurrent dual-band communication systems,due to the large number of two-dimensional memory polynomial model coefficients and the existence of crossmodulation terms,the realization of two-dimensional digital predistorter usually requires huge FPGA hardware resources.To solve this problem,this thesis proposes a new lookup table-based two-dimensional digital predistorter structure.Compared with the traditional two-dimensional digital predistorter,the same band signal shares the same lookup table and complex multiplier between different memory depths through time division multiplexing,which effectively reduces the use of storage resources and multiplier resources.The predistorter designed in this thesis was tested in the RF WebLab.For dual-band OFDM signals,ACPR improved by about 11.5 dB and NMSE improved by about 16.87 dB.In order to cope with the strong nonlinearity exhibited by high-efficiency power amplifiers,this thesis proposes a piecewise predistortion model based on vector quantization.The piecewise model processes the signal partitions according to the twodimensional vector composed of the two-band signal amplitude,and designs and implements it on the FPGA.In this thesis,the designed piecwise model was measured on the Doherty power amplifier.The test results show that ACPR is improved by about 16.94 dB and NMSE is improved by about 12.38 dB.Under the same nonlinear order and memory depth,they are significantly better Traditional two-dimensional predistortion method.