Research And Design On Digital Predistortion In Wideband Wireless Communication System

In a wireless communication system, RF power amplifier is a key component of the transmitter and has Inherent nonlinear characteristics; it is the main nonlinear source of system. The nonlinear characteristics of Amplifier lead to the in-band distortion of the output signal and the out-of-band spectral regrowth, which seriously affect the performance of the communication system. In order to get greater system capacity and higher spectral efficiency, high-order modulation technique, such as M-QAM and QPSK, is Commonly used in modern mobile communication system, WCDMA、OFDM Wideband data transmission technology is also widely used. This makes the signals has higher peak to average power ratio and more susceptible to nonlinear characteristics, so RF power amplifier must have higher linearity. Traditional PA linearization technology solution is to back-off the signal power from the PA saturation point; however this method cannot meet the system requirements now, Power amplifier linearization techniques become a hot topic at home and abroad.Digital pre-distortion (DPD) technology becomes the mainstream power amplifier linearization technology solutions, because it is high-performance, low cost and low implementation complexity. In this paper, we do research on digital pre-distortion structure and common design of digital pre-distortion, finally select system design scheme based on lookup table and memory polynomial. The scheme combines the advantages of look-up tables and memory polynomial method to improve efficiency and reduce hardware circuit compensates for the cost of the system. By using algorithm of singular value decomposition (SVD), we solve memory polynomial parameters directly and get the generalized inverse matrix. Different from conventional LMS algorithm and RLS algorithm, this algorithm avoid repeated iteration.System design is completed in Matlab/Simulink and Xilinx ISE/EDK development environment, during system test, we introduced hardware co-simulation test method, creating DPD system hardware co-simulation module by System Generator tool and verifying system software and hardware design based on Xilinx ML605FPGA development board. The test signals generated by MATLAB are16QAM signal with bandwidth of5M and10M respectively. We choose a2.4GHz WLAN integrated power amplifier designed by Research Department of our lab. Test results show that the DPD system could improve ACPR indicators of Simulink amplifier model by30dB.The performance of DPD system should be tested in the actual hardware, so we design hardware-in-the-loop simulation platform based on digital measuring instrument in Simulink simulation environment. Controlling measuring instrument by SCPI programming, we can introduce measuring instruments and amplifiers to DPD system test and realize to compensate actual amplifiers.In order to simultaneously verify the DPD hardware design and the effect of algorithms to compensate for the actual amplifier, we design open-loop DPD system, which combines hardware co-simulation and hardware-in-the-loop simulation. In this way, we realize full hardware test.Test results show that the DPD system could improve ACPR indicators by12dB...