Research On A Key Technology Of Improved Digital Predistortion With Single Feedback Of Phased Array

As a multi-antenna technology,phased array technology has flexible beam scanning ability and high gain,so it has broad prospect in 5G.The linearity of power amplifier in phased array greatly affects the communication quality.The digital pre-distortion(DPD)method is a better linearization technique.The existing training method of phased array digital DPD and the acquisition method of feedback signal have many shortcomings.Through in-depth research,this paper proposes an improved training method of DPD and an improved direct connection single feedback structure for phased array transmitter.The main contents include:Firstly,the phased array digital pre-distortion integral communication framework is presented,the advantages and disadvantages of the existing DPD training methods are analyzed,and an improved DPD training method is proposed.The whole process of phased array digital predistortion is introduced in detail,including the learning structure and parameter extraction of the predistorter.In this paper,several aspects of DPD training methods are studied,and an improved training method is proposed to train DPD at the optimal training angle of 60°.The simulation experiment and result analysis of the improved training method are given.The results show that this method improves the simplicity of DPD training and reduces the calculation amount.Secondly,based on the previous research on the improved DPD training method,an improved direct connection single feedback structure is proposed to obtain feedback signals in the process of DPD training.In theory,this feedback method is equivalent to the method of training DPD by placing receiving antenna over the air(OTA)in the far field to obtain feedback signals.However,in practice,the performance of training DPD is usually better than that of OTA-based feedback structure due to the fact that it uses RF line to transmit signals.In this paper,the two feedback structures are simulated respectively,and the results show that the linearization performance and anti-interference performance of the proposed improved direct connection single feedback structure are better than the OTA feedback structure.Thirdly,the experimental environment of phased array transmitter composed of omnidirectional antenna is built to carry out experimental tests on the improved DPD training method and the improved direct-connected single feedback structure proposed above.The actual test show that the ACPR(Adjacent-Channel Power Rejection)of the signal can be improved from-35 dBc to-45.5 dBc by the DPD coefficient training by using improved DPD training method.On experimental test for improved single feedback structure,we found that the DPD coefficient based on OTA feedback loop can restrain the ACPR from-35 dBc to-44.2 dBc,and the improved feedback loop,namely direct connection single feedback method can restrain ACPR from -35 dBc to -49.4dBc.Experiments shows that the improved feedback structure is superior to the feedback based on OTA structure in the DPD performance.