讨论了外调制光传输系统中非线性补偿技术,分析了外调制光发射机存在的非线性失真问题:包括功率放大器引起的失真以及外调制器引起的失真。重点讨论了预失真补偿技术,寻找一种针对整个外调制发射机端非线性失真的补偿方案,设计出适用于外调制光发射机的预失真电路。

This paper discusses the nonlinear compensation of external modulation optical fiber transmission system, analysing the nonlinear distortion of external modulation optical transmitter caused by power amplifi-er and external modulator. Predistortion technique is discussed in detail, and th paper seeks a kind of method which can compensate the whole external modulaton transmitter''s distortion. In the end, the results with pre-distortion circuit are given.

针对基于记忆多项式的预失真方法相关矩阵条件数和复杂度随着阶数的升高而急剧增加,数值计算复杂且失稳的问题,提出一种并行两箱预失真方法,采用非迭代查询表和正交记忆多项式两个并行模块,分别补偿功放高阶非线性失真和低阶记忆非线性失真.两个模块相互补充,预失真精度高,只须对低阶正交记忆多项式系数进行迭代求解,复杂度低.通过仿真验证了该方法对非正弦时域正交调制信号的有效性,并与基于传统多项式的预失真方法以及查询表级联多项式预失真方法进行了比较.仿真结果表明:所提预失真方法收敛速度快,复杂度低,均方误差较传统记忆多项式预失真降低19dB,较级联预失真降低4dB,功率谱和误比特率性能接近原调制信号,均优于其余两种方法.

In predistortion algorithm based on memory polynomial model ,the condition number of correlation matrix and the computation complexity rise drastically as the order of polynomial increa-ses .To overcome the above weakness ,a predistortion algorithm based on parallel two-box model was presented ,which contained two parallel module ,non-iterative look-up-table and orthogonal memory polynomial .The former is to compensate the high order nonlinearity of power amplifier ,while the lat-er is for low order nonlinearity and memorability .Two boxes supplement to each other ,leading to high precision and low complexity .The effectivity of the new method to non-sinusoidal orthogonal modulation signal in time-domain was verified through simulation ,while the performance was com-pared with predistortion algorithm based on conventional polynomial and algorithm based on look-up-table cascaded by memory polynomial .The simulation results show that the new method reduces the mean square error by 19 dB

利用记忆多项式模型来建模预失真和功放的非线性特性，可以不受特定功放模型的约束，具有较好的健壮性。提出了一种新结构的预失真模型，阐述了功放和预失真模型在数学上的关联。由一组功放的输入－输出信号，不难求出预失真器的记忆多项式；仿真结果表明，经过预失真处理之后的信号减少了带外失真，并与理想的线性输出信号的频谱图几乎重合，记忆多项式模型取得了较好的效果。

Power amplifier ( PA) memory effects cannot be ignored in wideband applications.The nonlinearity of PA, as well as predistorter, can be constructed using memory polynomials for the benefits of regardless of particular model of PA, hence it is robust.A new structure of predistorter was proposed to illustrate the mathematical relationship between the PA and predistort-er.With a series of input-output signals, the memory polynomial formula of predistorter was easy to be obtained.Simulation re-sults show that output signals with predistortion can get a better out-band suppression close to the ideal linear output signals;this indicates memory polynomial model works well.

针对记忆多项式数字预失真的问题,构造了一个记忆多项式预失真系统,通过非直接学习结构(ILA)实现系数估计,根据系统特性推导出改进LMS算法。以Matlab为平台,仿真结果表明这种记忆多项式预失真器能够较好地消除失真。

Aiming at the problem of digital pre-distortion in memory polynomial,a memory polynomial pre-distortion system is constructed,which realize the estimate of the coefficients through indirect learning architecture(ILA)approach,and the modi-fication LMS algorithm is derived according to the system characteristics. The results of simulation on Matlab show that the memory polynomial pre-distorter can effectively reduce the distortion.

随着医疗卫生事业的蓬勃发展，医院会计资料也变得越来越复杂。目前，医院的会计信息失真现象仍比较普遍，已严重影响到社会各方对医院业绩的正确评价。本文介绍了会计信息失真的涵义，分析了医院会计信息失真的现状，最后提出医院会计信息失真的防范对策，供广大读者参考与指导。

With the development of health industry, hospital''s accounting information grew more complicated. Currently, distortion of such information is common, and has severely impeded an accurate assessment of hospital''s work. The article introduces the definition of distortion of accounting information, analyzes the status quo of such distortion, and finally proposes preventive countermeasures against it, as reference for the readers.