工作点偏移对光纤AMCATV外调制传输性能的影响

对于光纤ＡＭＣＡＴＶ外调制传输，调制器的偏置工作点设置是非常重要的。通过理论分析得出：当工作点偏离最佳偏置点时，主要对系统的组合二次失真ＣＳＯ（ＣｏｍｐｏｓｉｔｅＳｅｃｏｎｄＯｒｄｅｒｄｉｓ－ｔｏｒｔｉｏｎ）产生影响，并导出相应的公式。对于ＰＡＬ／Ｄ制５５０ＭＨｚＣＡＴＶ系统，要保证ＣＳＯ小于－７０ｄＢｃ，工作点的偏移不能大于１０ｍＶ；实验结果和理论分析一致。     

宁波GSM系统LAC调整方案

宁波ＧＳＭ系统ＬＡＣ状况 目前宁波ＧＳＭ系统共有ＬＡＣ区２２个,每个ＢＳＣ分配一个ＬＡＣ（除市区ＢＳＣ２３,ＢＳＣ２４外）,这样,某些ＢＳＣ的Ｌｏｃａｔｉｏｎ－Ｕｐｄａｔｅ占ＯＫ－ＡＣＣ－ＰＲＯＣ的比例（后称ＬＵ－ＲＡＴＥ）相当高,如余姚ＢＳＣ８,其ＬＵ－ＲＡＴＥ高达７９．４２％,其ＳＤＣＣＨ负荷相当重,且已导致ＳＤＣＣＨ拥塞,具体每个ＢＳＣ的ＬＵ次数,ＬＵ－ＲＡＴＥＰＡＧＥ－ＲＥＱＵＥＳＴＳ／ＰＡＧＥ－ＲＥＳＰＯＮＳＥ,ＰＡＧＥＳ－ＰＥＲ－ＳＥＣＯＮＤ,ＳＤ－ＣＯＮＧＥＳＴＩＯＮ－ＲＡＴＥ,…     

一种新型结构的LB膜化学场效应晶体管的气敏特性研究

合成了新型的有机半导体ＬＢ膜气敏材料（ＣＯＴＤＭＡＰＰ），其ＬＢ多层膜拉制在场效应晶体管上，形成了具有ＬＢ－ＯＳＦＥＴ结构的化学场效应晶体管（ＣｈｅｒｎＦＥＴ），该器件置于ＮＯ２，ＮＨ３，ＣＯ和Ｈ２Ｓ等有害气体中，结果表明在ＮＯ２气氛中元件漏电流ＩＤＳ发生变化，并可检测到２ｐｐｍ的ＮＯ２．这种器件的气敏特性在于ＦＥＴ的电流放大作用及ＬＢ膜的有序性的影响．     

WSi_2栅和Si栅CMOS／BESOI的高温特性分析

用厚膜ＢＥＳＯＩ（ＢｏｎｄｉｎｇａｎｄＥｔｃｈ－ｂａｃｋＳｉｌｉｃｏｎ－Ｏｎ－Ｉｎｓｕｌａｔｏｒ）制备了ＷＳｉ２栅和Ｓｉ栅４００７ＣＭＯＳ电路，在室温～２００℃的不同温度下测量了其Ｐ沟、Ｎ沟ＭＯＳＦＥＴ的亚阈特性曲线，分析了阈值电压和泄漏电流随温度的变化关系。     

CCETT的测试与测量仪器

ＣＣＥＴＴ的ＩＲＤ－Ｐｒｏ是一种集成的数字地面电视接收机解码器。它具有测量和监测特点,主要用来满足ＤＶＢ－Ｔ网络的使用和维修人员的需要。测量结果通过友好的用户屏幕显示（ＯＳＤ）接口直接在ＴＶ屏上显示。这种的测量包括信号的相关性、信通响应、校正前后的信号群和误码率。ＣＣＥＴＴ相信,客户将会发现,ＩＲＤ－Ｐｒｏ的性能在进行ＤＶＢ－Ｔ移动现场试验中会特别有用。 据ＣＣＥＴＴ称,数字音频和数字视频序列的ＴＯＣＡＤＥ音频和ＴＯＣＡＤＥ视频客观质量分析仪也适用于测试和测量。它们可以在各种类型的广播网上对传输…     

C波段GaAs FET VCO设计的一种方法

在小信号Ｓ参数基础上，提出了一种宽带优化方法，设计了宽调谐、低相噪ＧａＡｓＦＥＴＶＣＯ。用该方法设计的Ｃ波段ＧａＡｓＦＥＴＶＣＯ用变容二级管调谐，其电压调谐范围在０～１５Ｖ，在调谐带宽为５００ＭＨｚ范围内ＶＣＯ的调谐线性度为１：１．５，带内相位噪声优于－８２ｄＢｃ（偏离１００ｋＨｚ处）输出功率大于２０ｍＷ，功率起伏小于±１ｄＢ。     

低通滤波器结构的改进分析及模拟

在高频域，ＭＯＳＦＥＴ的分布参数对全集成ＭＯＳＦＥＴ－Ｃ滤波器的特性有很大影响，本文应用ＳＰＩＣＥ（Ⅱ）通用模拟电路程序，采用非理想运算放大器单极点电路模型，考虑到ＭＯＳＦＥＴ的寄生电容，对一个六阶切比雪夫低通滤波器全ＭＯＳＦＥＴ－Ｃ平衡结构应用传输线模型进行了仿真分析。     

时间色散信道中格形编码的正交频分复用(TC-OFDM)技术

本文提出了一种格形编码的正交频分复用（ＴＣ－ＯＦＤＭ）方案，研究把正交频分复用（ＯＦＤＭ）和格形编码（ＴＣＭ）有机地结合，来克服时间色散信道中的频率选择性和多径衰落。文中对码率２／３格形编码的８ＤＰＳＫ－ＯＦＤＭ在时间色散信道中的误码率性能进行了分析和模拟，并讨论了不同正交载波数情况下格形编码的设计。结果表明，在比特误码率ＢＥＲ为１０－３时采用ＴＣ－ＯＦＤＭ方案与未编码系统相比可以提供６ｄＢ的编码增益。     

S12用户交换机统计方法的比较

对用户交换机进行详细的话务统计和分析可以帮助提高用户交换机的维护质量 ,提高全网接通率。下面结合实际对Ｓ１２用户交换机统计的方法进行比较。１一般统计（ＧＥＮＥＲＡＬＳＴＡＴＩＣＴＩＳ）采用一般统计法对Ｓ１２用户交换机进行统计 ,可分为两种方法。（１）对非商业性用户交换机群的一般统计（ＣＯＵＮＴＥＲＳＰＥＲＮＯＮＢＵＳＩＮＥＳＳＣＯＭＭＵＮＩＣＡＴＩＯＮＧＲＯＵＰＰＡＢＸ）这种方法使用的计数器有 :１２２６:ＴＥＲＭＡＴＴ-ＰＢＸＧ１２２８:ＴＥＲＭＣＯＮＧ -ＰＢＸＧ１２４０:ＴＥＲＭ -ＯＣＣ -ＰＢＸＧ１２…     

雷卡1X—AIME CDMA信令测试仪

雷卡１Ｘ－ＡＩＭＥ（Ａｉｒ Ｉｎｔｅｒｆａｃｅ Ｍｏｎｉｔｏｒ／Ｅｍｕｌａ－ｔｏｒ）系统是专门为手机的ｃｄｍａＯｎｅ及 ｃｄｍａ２０００ １Ｘ信令测试而设计的，广泛应用于新产品开发、兼容测试、评估和服务支持，是手机生产研发时必不可少的测试工具。 目前，１Ｘ－ＡＩＭＥ系统可支持ｃｄｍａＯｎｅ＋ｃｄｍａ２０００的标淮，包括：ＩＳ９５Ａ、ＩＳ９５Ｂ、Ｊ－ＳＴＤ－００８、ＡＲＩＢ－Ｔ５３、ＫＯＲＥＡＮ ８００ＭＨＺ、ＫＯＲＥＡＮ ＰＣＳ、ＩＳ－２０００ １Ｘ等，并且兼容ＣＤＧ２２、ＣＤＧ５３及ＣＤＧ５７的第二阶…     

Calculating the CSO/CTB spectrum of CATV amplifiers and opticalreceivers

The discrete CSO/CTB intermodulation distortion has a big influence on the CATV net quality. This article describes a new method to calculate the composite second order (CSO) and composite triple beat (CTB) intermodulation distortion spectrum for the full frequency range of a coaxial cable CATV amplifier for any input frequency plan. The calculation takes into account the output level ripple and preemphasis, using frequency dependent intermodulation coefficients. These coefficients have been established through CSO/CTB measurements on multichannel test systems for standard frequency plans at 5-8 intermodulation frequencies or on distortion arrays for the two (three) oscillator measuring test system. The defined intermodulation coefficients are unrelated to the frequency plan and the input/output level ripple. It is also possible to calculate the CSO/CTB spectrum caused by analogue channels within digital QAM channels. The results equally apply to optical CATV receivers. Simulation results have been verified using extensive data from multichannel measurement systems     

Signal distortion and noise in AM-SCM transmission systemsemploying the feedforward linearized MQW-EA external modulator

In subcarrier multiplexing (SCM) optical video distribution systems, the nonlinear signal distortion generated by the combined action of laser chirp and fiber dispersion limits the transmission distance. This paper for the first time shows that low-chirp MQW (multiquantum well)-EA (electroabsorption) external modulators are applicable to AM-SCM transmission systems. The feedforward linearization technique is used to compensate the signal distortion due to the nonlinearity in the modulator's L-V (light power versus voltage) characteristic. The effectiveness of this type of modulator for suppressing dispersion-induced distortion is clarified experimentally. A feedforward linearized transmitter with composite second order (CSO) intermodulation distortion <-62 dBc, composite triple beat (CTB) intermodulation distortion <-59 dBc and a carrier-to-noise ratio (CNR) >50.5 dB is successfully constructed. It is shown that the transmitter can achieve a CSO <-59 dBc, a CTB <-57 dBc and a CNR >49.5 dB for a 32 channel AM signal and 10 km transmission. Furthermore, estimations of the signal distortion cancellation and the noise characteristic achieved with feedforward circuit modeling are shown. The results obtained here emphasize that MQW-EA external modulators are applicable to AM-SCM transmission systems     

The impact of CSO/CTB distortion on BER characteristics by hybridmultichannel analog/QAM transmission systems

The FEC limit (uncorrectable errors) with CSO/CTB (composite second order/composite triple beats) distortion presence in a channel is not for modulated lasers only, but for coaxial networks with amplifiers too. The system quality reserve depends not only on CNR, but is more limited on CSO/CTB. It is important, for the definition of the system quality reserve, to calculate the CSO/CTB spectrum caused by analogue channels within analogue and digital QAM channels and also to calculate the changing of CNR from the intermodulation interaction between analog and digital channels in a CATV network     

Second-order distortion of amplified intensity-modulated signalswith chirping in erbium-doped fiber

Second-order distortion produced in an erbium-doped fiber amplifier (EDFA) is investigated theoretically and experimentally. Rate equations for intermodulation products are led by the perturbation method. From numerical calculation, it is shown that optimum combinations of input power to EDFA and signal wavelength exist that give a distortion-free condition, Improvement of the composite second-order (CSO) distortion, which results from the cancellation of the laser distortion and the gain tilt induced distortion, was confirmed for VHF multichannel transmission. Furthermore, CSO distortion-free transmission in cascaded EDFA's has been demonstrated for a 42-channel AM-SCM signal by experimentally determining the optimum operating condition of the EDFA such that each amplifier generates no additive distortion     

Improvement of CSO/CTB performances employing up-converted and polarization modulation techniques

A two-wavelength wavelength-division multiplexing (WDM) community antenna television (CATV) transport system that employed up-converted and polarization modulation techniques to reduce the composite second-order (CSO) distortion and optical nonlinearities is proposed and demonstrated. In contrast to a two-wavelength WDM CATV transport system using the intensity modulation technique, good performances of CSO and composite triple beat were obtained, accompanied by acceptable carrier-to-noise ratio value in our proposed system over a 100-km single-mode fiber transmission.     

Nonlinear distortions and compensations of DFB laser diode inAM-VSB lightwave CATV applications

The nonlinear distortions of a directly modulated laser diode applied to AM-VSB lightwave CATV systems are studied from the viewpoint of rate equations. A simple method for calculating composite second-order distortion (CSO) is proposed, which is called the quasidynamic approach. The contribution to nonlinearity from fiber dispersion and laser chirping is also discussed. The dependences on the variations of parameters of rate equations are investigated to determine the dominant factor for CSO degradation. This approach explains quite well the experimental results and suggests a method for constructing a predistortion circuit with at least 10 dB improvement     

Polarization dependent distortion in AM-SCM video transmissionsystems

The second-order intermodulation distortion product, namely composite second-order (CSO) distortion, of an AM-SCM video transmission system can be caused by the optical isolators, cascaded fiber amplifiers, or the fiber transmission cable employed. Moreover, the absolute distortion value depends on the polarization angle of light input to the optical isolators, cascaded fiber amplifiers, and fiber transmission line. The degraded distortion values are measured and their mechanisms are clarified     

The impact of CSO/CTB distortion on BER characteristics by hybridmultichannel analog/QAM transmission systems

This article describes the measurements of composite second order (CSO), composite triple beats (CTB) frequency spectrum and time-varying distortion in the basic bandwidth (BB) (0-4 MHz) of the 64-QAM digital channels by multichannel AM/64-QAM optical and coaxial transmission systems. For any regular standard frequency plans (Europe, USA, NCTA, etc.) there is, for the I and Q components in the BB of the QAM channels, the harmonic series of the CSO/CTB with the first harmonic f ₁. It has been shown that for all the same laser-optics or coaxial transmission systems the CSO/CTB distortions spectrum form in the QAM BB 60-80 μs duration bursts of a series pulse with a pulse period T=1/f₁ and a pulse duration τ≈0.4/f_m, where f_m is the CSO/CTB harmonic with maximum amplitude in the QAM BB. The bursts result in the essential unevenness of error bits in time domain distribution. These bursts can deteriorate essential error correction by the interleaver-deinterleaver and Reed-Solomon (RS) forward error correction (FEC) code of the transmission systems also with a relative low bit error rate (BER) of about 10^-5 before FEC. There is, white Gaussian noise like, intermodulation distortion from interaction of digital-, digital-analog channels too, that have added white Gaussian noise     

光发射机中MZ型波导调制器产生CTB的分析

AM－CATV外调制光发射机中的MZ型波导调制器，其转移特性呈正弦曲线。当多路信号同时调制时，将产生组合二次失真（CSO）和组合三次差拍（CTB）。本文对CTB进行了理论分析，并对我国450、550MHz二种CATV系统调制时的CTB进行了计算。这对非线性补偿电路的设计具有一定的指导价值。     

Analytical formulation of distortion and chirp in CATV DFB lasersincluding spatial hole burning

Analytical formulas for distortions permitting the calculation of composite second order (CSO) and composite triple beat (CTB) in distributed feedback (DFB) laser diodes are given, including gain compression and longitudinal spatial hole burning (LSHB). An improved chirp expression including both effects is also proposed. Gain compression is compared to LSHB over the CATV band: LSHB effects on distortion and chirp are found to be dominant in actual CATV lasers. Nonmonotonous behavior (dips) function of frequency and bias current is verified in second- and third-order distortions in agreement with recent results