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在有线电视(CATV)等多频道信号的传输系统中,由于传输机器上用的激光二极管(LD)和放大器等的非线性会产生互调失真。关于这种互调失真对数字调制信号传输特性的影响迄今还不太明确。 本报告是为了明确传输系统产生的干扰波(互调失真+热噪声)与误码率(BER)特性的因果关系,对干扰波的振幅分布及其对数字调制信号的干扰特性进行了测量;其次对干扰波的振幅分布用计算机进行模拟,从而揭示出其模拟结果与测量结果的一致性。由此对以下三点得到了明确: 1.含有互调失真的干扰波的振幅分布,因在某振幅范围内与正规分布有所偏离。所以,对误码率(BER)的影响仅对干扰波功率的总和才能评定。 2.干扰波的振幅分布不仅随干扰波的功率不同而异,而且随互调失真的类别(2次失真、3次失真)失真发生源的波数及载噪比(C/N)的不同而变化。 3.由干扰波振幅分布的测量结果可以推算调制信号的误码率(BER)。
In transmission systems such as CATV, multi-channel signals, intermodulation distortion occurs due to the non-linearity of laser diodes (LDs) and amplifiers used in the transmission equipment. The impact of such intermodulation distortion on the transmission characteristics of digitally modulated signals is not yet clear. This report is intended to clarify the causal relationship between the interference wave (intermodulation distortion + thermal noise) and the error rate (BER) characteristic of the transmission system, and to measure the amplitude distribution of the interference wave and its interference characteristic to the digitally modulated signal. Second, the amplitude distribution of the interfering wave is simulated by computer, which reveals the consistency between the simulation result and the measurement result. The following three points are therefore clear: 1. The amplitude distribution of interfering waves containing intermodulation distortion deviates from the normal distribution over a range of amplitudes. Therefore, the impact on bit error rate (BER) is only evaluated over the sum of the interference wave powers. 2. The amplitude distribution of the interference wave not only varies with the power of the interference wave but also varies with the wave number of the source of distortion and the carrier to noise ratio (C / N) depending on the type of intermodulation distortion (second-order distortion, third-order distortion) Variety. 3. Measured by the interference wave amplitude distribution can be calculated modulation signal bit error rate (BER).