调制解调非理想特性联合补偿数字预失真方法

A Modulation and Demodulation Non-ideal Characteristic Joint Compensation Digital Predistortion Method

针对调制解调非理想特性影响数字预失真效果,导致邻信道功率比性能较差的问题,提出了一种调制端和解调端联合补偿的数字预失真方法。首先,建立了正交调制器、解调器的基带等效模型;然后,基于多项式预失真,利用正交调制器与解调器的特点,结合递归最小二乘法,推导出了联合补偿数字预失真原理,避免了仅通过调制端补偿,或者调制端、解调端分别补偿只能使数字预失真算法收敛到局部最优解的现象出现;最后,以甚高频航空通信常用的差分八相移键控(Differential 8 Phase Shift Keying,D8PSK)调制方式为例进行了仿真和实现验证,邻信道功率比相对无预失真可以改善28 dBc,相对现有联合补偿数字预失真可以改善16 dBc。

In view of the problem that the non-ideal characteristics of modulation and demodulation affect the digital predistortion effect and lead to poor performance of adjacent channel power ratio,a digital predistortion method with joint compensation at the modulation and demodulation ends is proposed.Firstly,the baseband equivalent models of orthogonal modulators and demodulators are established.Then,based on polynomial predistortion and by utilizing the characteristics of orthogonal modulators and demodulators,combined with recursive least squares method,the principle of joint compensation for digital predistortion is derived,avoiding the phenomenon of only compensating the modulation end or compensating the modulation end and demodulation end separately,which can only make the digital predistortion algorithm converge to the local optimal solution.Finally,by taking the commonly used differential 8 phase shift keying(D8PSK)modulation method in very high frequency aviation communication as an example,simulation and implementation verification is conducted,the adjacent channel power ratio can be improved by 28 dBc compared with that of the method without predistortion,and by 16 dBc compared with that of existing joint compensation digital predistortion.