关于CATV系统中交调互调指标的分析

1前言随着CATV行业的逐步发展,我区有线电视网中的频道数越来越多,在系统性能指标中,交扰调制、相互调制等非线性失真将会给基带信号引入固定的干扰。因此,对有线电视工程技术人员而言,对交调、互调两项指标的理解显得尤为重要。2交调、互调的定义及公式交扰交调是指需要的调制信号电平的峰峰值和其它频道转移过来的调制信号电平的峰值比。CM=交扰调制比是表示由于系统非线性而造成各个频道的调制信号相互转移,影响用户正常收看的一项技术指标。载波互调是指载波电平有效值和互调产物电平有效值比。IM=载波互调比是表示由于系统存…     

射频放大器互调失真检测和载波抵消的研究

采用高功率射频信号内部互调失真的包络特性检测与比较技术,对射频功率带外信号进行检测和估计。设计用于高功率射频放大器前馈技术线性化的一个带外信号检测器。探讨如何进行射频载波抵消以及检测放大器互调失真信号。     

多模光纤线路的组合二阶失真分析

在多模光纤线路上传输多路射频模拟信号会带来谐波失真和互调失真.文章通过推导多模光纤线路的谐波失真和互调失真表达式,分析了影响组合二阶失真的因素,进而得到接收功率的频谱特性.结果表明:在中短距离传输的多模光纤线路上,如果组合二阶失真的值小于-50 dBc,可以采用副载波复用技术传输多路射频信号.     

基于MATLAB的RF功率放大器互调失真仿真分析

应用Matlab仿真平台对RF功率放大器的互调失真(inter-modulation—IMD)进行了分析。结果表明:在输入信号峰值或峰值功率不变时,可以用输入为两个或三个正弦信号情况下的互调失真指标来估计输入为宽频带、高密度信号情况下的互调失真指标;通过降低输入功放信号的峰值功率可以降低互调失真分量的相对幅度。     

宽带多载波微波光链路多源非线性数字补偿方法

随着数据通信容量需求的不断增长，微波光子技术在未来宽带卫星通信发展中具有良好的应用潜力。针对宽带多载波微波光链路系统中多种非线性失真共存问题，提出了一种数字线性化方法，通过在数字域进行非线性失真算法补偿，实现了系统多载波射频信号的互调非线性失真、三阶交调非线性失真的共同抑制。实验证明了所提方法的有效性。     

多载波线性功放的SystemView仿真

在第三代移动通信系统中,多媒体业务要求信道能够灵活分配带宽,采用多载波线性功放既为按需分配带宽提供了条件,也解决了单载波功放信号合成时产生较大功耗的问题。为了提高多载波功放的线性指标,消除互调干扰,目前采用前馈技术和预失真技术。在讨论这两种技术的基础上,提出了前馈对消技术和预失真补偿技术的设计方案,并给出了SystemView的仿真结果。     

电缆电视系统的非线性失真及其影响

电缆电视系统的非线性失真及其影响戴建明载噪比、交扰调制比、载波互调比是电缆电视系统中最重要的三项技术指标，载噪比决定了系统工作的下限电平，由系统非线性失真５！起的交扰调制失真和载波相互调制失真则决定了系统工作的上限电平。上述三项技术指标是电缆电视系统...     

GSM二次谐波和二阶无源互调IM2与三阶无源互调IM3的研究

正1引言互调干扰在移动通信系统中很常见,若处理不当,将影响移动通信系统的服务质量和信噪比,从而影响通信系统的容量。以下结合案例数据,对GSM二次谐波和二阶无源互调IM2与三阶无源互调系统进行分析。无源互调是指非线性射频线路中,在大功率条件下,在输入两个及以上载波时,因为微波部件的非线性产生载波不同谐波和/或差频信号现象。无源非线性会引起射频信号产生许多谐波信号,二阶、三阶互调产物是因为通信系统中无源器件非线性引起互调干扰。这会对移动通信系统接收机造成严重干扰,尤其是在多系统     

基于自适应射频预失真的多载波功率放大器线性化技术

用高功率放大器放大线性调制信号 (包络波动变化 ) ,必然会产生失真和互调成分。而基于扩频技术的第三代无线通信系统中的功率放大器必须要有很好的线性性能。本文提出一种线性化射频多载波高功率放大器的自适应射频预失真器。     

伪随机二相编码信号的寄生调幅与相位误差

本文分析了带有寄生调幅与相位误差的0、π调相信号及其对伪随机编码测距系统的影响。文中将失真信号分解为有用的二相调制信号及附加的无调制载波分量,并导出了以此二分量表示的测距关系式。     

Influence of imbalance on distortion in optical push-pull frontends

The influence of imbalance on second-order intermodulation distortion (IMD2) in optical push-pull frontends for subcarrier multiplex CATV applications is investigated theoretically and experimentally. The investigation focuses on imbalance introduced in either the photodiode, the push-pull amplifier, or the output balun, and expressions describing the overall IMD2 cancellation efficiency are derived. The developed theory is used to predict the IMD2 cancellation behavior of an optical push-pull frontend. Commercially available PIN photodiodes for CATV purposes and ferrite core transformers are characterised for phase and amplitude balance up to 1 GHz. The overall IMD2 cancellation efficiency of an optical push-pull frontend based on the best of these devices is calculated. The theory is finally verified experimentally with an optical push-pull frontend designed with the characterised photodiode and transformer. The improvement in IMD2 suppression obtained with the push-pull structure relative to a single-ended structure is in average 29 dB across the band from 47-862 MHz. The total IMD2 suppression obtained for the frontend is between 60 dBc and 79 dBc at an average optical input power of 1 mW and with an optical modulation index (OMI) of 35 percent per carrier in a two-tone setup,     

Cross Cancellation TechniqueEmploying an Error Amplifier

In this letter, we propose a new distortion cancellation mechanism for a balanced power amplifier (PA) structure using the cross cancellation technique employing an error amplifier. The proposed cross cancellation balanced linear PA is implemented in the IMT-2000 ( 2.14GHz) band. With commercial PAs with a peak power of 240 W for base-station application, the proposed system shows 18.6 dB improvement at an average output power of 40 dBm for adjacent channel leakage ratio measurement with wideband code division multiple access 4FA signal. The efficiency of the proposed structure is about 2% higher than the conventional feedforward amplifier for modulated carrier.     

箕舌线变步长LMS/F算法数字域自干扰消除研究北大核心CSCD

自干扰消除技术是实现带内全双工(IBFD)通信的重要前提,其中数字域自干扰消除是带内全双工通信系统中硬件复杂度最低、灵活性最高的自干扰消除技术,并且是自干扰消除的最后一道防线。然而,其消除能力仍需提升,主要是如何处理收敛速度和稳态精度之间的平衡,并且还要具备突变信道的自适应能力。文章提出了一种新的全双工系统的数字自干扰消除方法,发射链路采用数字、模拟预失真技术消除功率放大器的非线性失真,使用辅助接收链获取发射链路信号副本,在数字域中利用重构自干扰信号副本消除接收信号残余自干扰信号和功率放大器残余非线性失真,并通过在接收链与辅助接收链之间共用一个振荡器消除部分接收机相位噪声。仿真表明,该方法与已有变步长LMS消除方法相比,在信噪比为5 dB的条件下,能够在提高收敛速度的同时获得优于变步长LMS方法的消除能力。     

Elimination of signal distortion and crosstalk from carrier densitychanges in the shared semiconductor amplifier of multifrequency signalsources

The signals from multifrequency sources that utilize a shared semiconductor optical amplifier often exhibit distortion and crosstalk due to carrier density changes in the shared amplifier. We propose a technique that eliminates the signal distortion and crosstalk by keeping the carrier density in the shared amplifier constant via feedforward of the electrical drive signals. We demonstrate the technique using a waveguide grating router multifrequency laser     

Effects of Power Amplifier Distortion and Carrier Frequency Offset on the Performance of WLAN System

Due to the efficiency of mitigation multipath delay spread, orthogonal frequency division multiplexing (OFDM) is extensively used in the wireless local area network (WLAN) domain, such as the IEEE 802.11a standard defined by the IEEE 802.11 standardization group and the HIPERLAN/2 defined by the European Telecommunication Standards Institute Project on Broadband Radio Access Networks. OFDM based WLAN system is very sensitive to the power amplifier distortion and the carrier frequency offset. The performance of the OFDM based WLAN system in the presence of the power amplifier distortion and the carrier frequency offset under practical fading channel is researched and analyzed in this paper. A closed form of bit error rate (BER) is derived for the OFDM based WLAN system in the presence of the power amplifier distortion and the carrier frequency offset under practical fading channel. The effects of the power amplifier distortion and the carrier frequency offset on the OFDM based WLAN system performance are comparatively studied by the theoretical method and by the simulation method under practical multipath fading channels. Studies show that the theoretical and simulated results match well.     

Analysis of a Microwave Feedforward Amplifier Using Volterra Series Representation

The use of feedforward correction to reduce nonlinear distortion in a microwave amplifier is investigated, using the Volterra series approach. Expressions are derived for the suppression of main amplifier distortion, in terms of the circuit parameters of the system. It is shown that the gain and phase imbalance in the second interference loop mainly determine the distortion suppression in the feedforward amplifier. An expression is derived for the relationship between amplifier distortion suppression and the degree of gain and phase imbalance in the second interference loop. The effect of the phase imbalance in the second interference loop on the AM-to-AM and AM-to-PM conversion in a feedforward amplifier is discussed; it is shown that the presence of such phase imbalance may cause a substantial difference to exist between the improvement in cross-modulation and that in intermodulation. Further, the gain sensitivity of the feedforward amplifier as a function of gain and phase imbalance is obtained. As an illustrative example, the distortion suppression of a specific IMPATT amplifier with feedforward correction is considered.     

A wide-band feedforward amplifier

The design of a wide-band feedforward amplifier in the frequency range 30-300 MHz is described. Expressions are derived for feedforward amplifier sensitivity, and the effect of imperfect loop cancellation is described. The effect of circuit imbalance on gain and terminal impedances is investigated. The circuit is realized in thin-film hybrid form, and measurements show 20 dB of distortion improvement at 300 MHz. Practical aspects of circuit adjustment and operation are considered.     

Broadband analogue predistortion using a distortion generator based on two-stage RF mixer topology

An analogue predistorter using a distortion generator based on a two-stage radio frequency mixer topology is presented. The proposed distortion generator achieves fundamental signal cancellation without using a signal cancellation loop or a resonant circuit, thus it generates an error signal that predominantly consists of unwanted intermodulation distortion (IMD). Measurements are performed using multi-tones, WLAN- and Terrestrial Trunked Radio (TETRA)-modulated signals. Distortion generator provides high levels of IMD and achieves more than 40 dB fundamental signal cancellation across a bandwidth of 120 MHz. A proof-of-concept predistorter was constructed to validate the usefulness of the proposed distortion generator, which achieves up to 15 dB suppression of IMD and adjacent channel power ratio at the output of a power amplifier. Distortion generator and predistorter gave similar results at multiple frequencies between 920 MHz and 2 GHz, with different test signals having bandwidths ranging from 25 kHz to 120 MHz.     

Adaptive joint linearisation/equalisation with delay alignments fora wideband power amplifier

Tap delay lines are introduced into a power amplifier feedforward lineariser for two purposes: first, to align the delays of the combining branches for both loops. Secondly, to equalise the power amplifier, which reduces the power of the linear distortion signals going through the auxiliary amplifier     

线性Doherty功放的优化设计

设计了一个高效率、高线性度的射频Doherty GSM基站功放。利用Doherty功放的载波放大器与峰值放大器之间的互调对消技术使Doherty功放的三阶互调干扰(IMD3)改善了11dBc;并通过相位补偿延迟线的前置处理进一步提高了功放的效率,使其效率比常用的平衡补偿线方案提高了4%左右。文中利用两个MRF9060功放管制作了一个GSM频段Doherty功放,其实测1dB压缩点功率(P1dB)达到了130W;双音测试表明:经过4.5dB的回退后三阶互调失真(IMD3)优于-35dBc,此时功率附加效率(PAE)高达47.3%;WCDMA 3GPP的测试结果表明:经过6dB回退后,其5MHz偏移量的邻道功率比(ACPR)优于-40.5dBc,PAE为43.5%,比AB类平衡功放的效率提高了17.8%。结果表明:该设计方案较好地解决了射频功放功率与效率之间的矛盾,适用于射频功放的设计。