Research On Predistortion Algorithm For Broadband DVB-S2X Modulator

Satellite communication continues to develop in the direction of large bandwidth and high spectrum efficiency under the growing demands for networks,services,and high-speed data transmission.The new generation of digital TV broadcasting standard DVB-S2 X has brought more challenges to satellite communication systems.The TWTA in the satellite channel produces strong nonlinearity and unavoidable memory effects.The pre-compensation of the transmitter and the post-compensation of the receiver in the DVB-S2 X system make the system nonlinear distortion is better recovered.To solve the nonlinear distortion of TWTA in the DVB-S2 X satellite system,this paper mainly concentrates on the digital predistortion technology.According to its application scenarios,it is mainly the research about predistortion algorithms in single carrier scenarios and multi-carrier scenarios.The key achievements of this paper are as follows:(1)Taking an investigation about the characteristics of TWTA in the DVB-S2 X system,this paper explored the evaluation scheme of link power back-off.Firstly,the TWTA characteristic curve given in the standard was fitted,and the nonlinear characteristic function suitable for the DVB-S2 X system was given.Secondly,this paper analyzed the distortion components in the nonlinear channel,and calculated the noise variance of the nonlinear channel on the basis of related literature.Finally,by synthesizing the quantified nonlinear distortion,a semi-simulation evaluation scheme for power back-off under nonlinear distortion conditions was proposed,and its correctness was verified by simulating the BER of the nonlinear system.This evaluation scheme exhibited less time complexity than the original method of calculating the total link backoff,and it can be widely used for evaluating predistortion algorithms' compensation performance.(2)The predistortion algorithms in single carrier scenarios of the DVB-S2 X systems are researched.At the first,the evaluation indicators of the predistortion algorithm were described,and several key indicators were listed for the algorithm performance evaluation in the following text.Finally,in view of the resource occupancy rate and performance improvement of the above algorithms,this paper designed an indirectRecursive Least Squares predistortion algorithm based on the memory polynomial model.After simulation and comparison,the algorithm achieved better optimization effects in terms of resource occupancy and performance compared with existing pre-distortion algorithms.(3)The predistortion algorithms in the multi-carrier scenarios of the DVB-S2 X system were studied.First of all,this paper modeled the multi-carrier system and analyzed the input and output components of the satellite transponder by obtaining the expression of the third-order intermodulation terms.In order to solve the problems above,the direct structural predistortion method based on the memory polynomial model was realized which includes independent predistortion and joint predistortion.Our simulation results proved that the performance of the direct structure predistortion is better than that of the indirect structure.Although the joint predistorter has higher implementation complexity,its power degration is lower than that of the independent predistorter.The realized multi-carrier predistortion technology achieved by this paper will has important guiding significance in the DVB-S2 X satellite systems.