Intermodulation improvement for multichannel television distribution by appropriate channel allocations and the use of 1/3rd line offsets

In addition to the use of frequency plans to reduce intermodulation interference between carriers, in the case of television distribution further improvement can be obtained by using? line-rate frequency offsets. Some results are tabulated.     

Intermodulation distortion improvement by active compensation in impatt amplifiers

The letter discusses how the intermodulation distortion in impatt diode amplifiers can be improved significantly by active compensation. Theoretical evaluation based on a large-signal impatt diode model predicts considerable improvement in the intermodulation behaviour; in particular, the improvement in the third-order intercept point is found to be in excess of 12 dB.     

Intermodulation distortion improvement by active compensation in an X-band IMPATT amplifier

The intermodulation products generated in an actively compensated X-band IMPATT amplifier have been measured and compared with the corresponding uncompensated amplifier. The 3rd-order intercept point increases from 11.5 dB to 23 dB, giving an improvement of 11.5 dB.     

Intermodulation generation by electron tunneling through aluminum-oxide films

The generation of intermodulation (IM) interference by nonlinear conduction mechanisms in normally passive hardware components can lead to severe degradation in the performance of multi-carrier communication systems in satellites, space probes, and ship-board systems. This paper describes an investigation of the generation of IM due to nonlinear conduction by electron tunneling through aluminum-oxide films. Details are presented regarding the fabrication of Al-Al2O3-Al junctions, the current-voltage and capacitance characteristics, and the measurement of IM power levels. The IM is correlated with the junction circuit parameters and with tunneling theory. Results are also presented on preliminary experiments to beneficially modify such nonlinear conduction by implantation of metallic ions in the oxide film.     

Reduction of Mixer Intermodulation by Neutral RF Biasing

The introduction of a neutral RF signal to a nonlinear resistance diode mixer as a means of reducing the effects of undesired intermodulation is described.     

Intermodulation products generated by a p-i-n diode switch

Values are reported for the odd-order intermodulation products originating from a p-i-n diode in a UHF SPST switch which is tied to a transmission line carrying two signals. Included are their dependence on power levels, bias, and ambient temperature.     

Intermodulation effects induced on parallel wires by transientexcitation

The analysis of the transient response of a five-wire planar array of identical thin wire scatterers is presented. The transient current induced on the individual wires comprising the array exhibits inherent intermodulation effects. This particular effect is explained in terms of the excitation of several of the natural frequencies obtained by applying the singularity expansion method (SEM) to the multiple-wire arrays. The natural frequencies group themselves into layers that can each be associated with the natural singularities of the isolated thin-wire scatterers, that constitute the individual elements in the array. Calculation of the coupling coefficients associated with the natural modes corresponding to the natural frequencies illustrates the manner in which different intermodulation frequencies appear in the transient response of the array as a function of the excitation orientation and polarization. Tables and curves illustrating the pertinent parameters determining these intermodulation effects are presented for one-, two-, three-, four-, and five-wire arrays     

Intermodulation in parametric amplifiers

Third-order intermodulation products due to the charge-voltage nonlinearity of the varactor diode in a parametric amplifier have been computed. Some experimental data obtained from a two-carrier measurement have been reported. Finally, the noise power density in a telephone channel due to parametric amplifier intermodulation has been calculated as a function of total input power into the amplifier.     

互调干扰信号的特征识别

在复杂电磁信号环境中,实际存在为数不少的互调干扰信号,对这类信号的有效分析识别,是无线电监测工作需要重点关注解决的难题。对互调干扰信号在幅度特征和频谱峰值特征两个方面的特性进行了分析,给出了互调干扰信号识别的思路。     

Fiber Optic Intermodulation Distortion

In analog frequency-division multiplexed fiber optic systems, laser nonlinearities transfer energy between the different carriers, resulting in intermodulation distortion and interference. A third-order polynomial without memory is used to model the nonlinearity. The FM frequency-division multiplexed (FM/FDM) signal consists of a set of FM carriers at frequencies.N_{omega 0}, whereN = L, L + 1, L +2, ... , M. The video distortion introduced by the nonlinearity is determined for various types of second- and third-order intermodulation terms. The intermodulation distortion frequency spectrum is determined for FM signals with assumed Gaussian spectra.     

Performance improvement of TCP in ad hoc networks by mitigating channel contention

In ad hoc networks, the spatial reuse property limits the number of packets which can be spatially transmitted over a path. In standard Transmission Control Protocol (TCP), however, a TCP sender keeps transmitting packets without taking into account this property. This causes heavy contention for the wireless channel, resulting in the performance degradation of TCP flows. Hence, two techniques have been proposed independently in order to reduce the contention. First, a TCP sender utilizes a congestion window limit (CWL), by considering the spatial reuse property. This prevents the TCP sender from transmitting more than CWL number of packets at one time. Second, a delayed ack (DA) strategy is exploited in order to mitigate the contention between the TCP ACK and DATA packets. Recently, although TCP‐DAA (Dynamic Adaptive Acknowledgment) attempts to utilize a CWL‐based DA strategy, TCP‐DAA overlooks a dynamic correlation between these two techniques. This paper, therefore, reveals the dynamic correlation and also proposes a protocol which not only reduces the frequency of the TCP ACK transmissions but also determines a CWL value dynamically, according to network conditions. Simulation studies show that our protocol performs the best in various scenarios, as compared to TCP‐DAA and standard TCP (such as TCP‐NewReno). Copyright © 2009 John Wiley & Sons, Ltd.     

抑制空间行波管五阶交调失真的信号注入法

本文全面地研究了信号注入（谐波,三阶交调）对空间行波管（STWT）的五阶交调（IM5）失真分量的抑制情况。首次采用泰勒级数法对IM5理论分析,继而利用计算机仿真,分别注入谐波和三阶交调（IM3）信号来抑制STWT的IM5,并得出最大抑制量及最佳注入信号参数。实验结果表明：谐波和IM3都能够较明显地抑制IM5,IM3注入技术能够得到31.6 dB的IM5抑制量,大于谐波注入技术的最佳抑制量18.3 dB,且IM3注入功率也更低,实验条件较宽松,因此对窄带STWT而言,IM3注入技术比谐波注入技术能更明显地抑制五阶失真分量。     

Improved Intermodulation Rejection in Mixers

Intermodulation is one of the most pernicious forms of spurious response in superheterodyne receivers. This type of interference cannot be completely eliminated by narrowband filters. Improvements in receiver performance can be made only by improving and making more effective use of the mixing element. Intermodulation results from terms of higher order than two in the v-i power series expansion about the dc operating point of the mixing element. The magnitude of these higher order terms must be reduced in order to improve intermodulation rejection. In the work described in this paper, it has been observed that such a reduction in higher order terms can be obtained by proper design of the mixing element and by a proper choice of dc operating point. More than 80 dB intermodulation rejection was obtained with a single ended hot carrier diode mixer. Best performance is obtained by operating two hot carrier diodes at different operating points in a balanced mixer arrangement. Intermodulation ratios greater than 100 dB have been measured for this operating mode. Optimization of performance for IM rejection has little effect on sensitivity or rejection of other spurious responses. A new mixing element, the space-charge-limited resistor (SCLR), was designed to minimize the higher order terms in the current function. A balanced mixer provided the best performance with these mixing elements also. Intermodulation from +5 dBm inputs can be rejected below the mixer noise level. Early models of this device are not as sensitive as hot carrier mixers, but improvement appears to be possible.     

Two-Tone Intermodulation in Diode Mixers

This paper explores, experimentally and theoretically, the problem of minimizing second- and third-order intermodulation distortion in diode mixers. A numerical technique is presented which can be used to calulate internrodulation levels with unprecedented accuracy, and it is used to identify circuit and diode parameters which maximize dynamic range. It is shown that intermorhdation distortion is minimized by using low diode junction capacitance and series resistance, short-circuit embedding impedances, and high local-oscillator level. It is also shown that certain conditions which may optimize conversion loss, such as image enhancement, may severely exacerbate intermodulation.     

混频器双音交调特性分析

分析了混频器的双音交调特性,提出混频器的双音无虚假动态范围受双音四阶交调虚假中频信号的限制。实验验证了理论分析。     

Analysis of Intermodulation Noise in Frequency Converters by Volterra Series

Frequency converters produce intermodulation noise in the desired signal band which may be a serious problem for communications systems using amplitude modulation. In this paper, we introduce the Volterra series with time-varying kernels to treat intermodulation in frequency converters with one two-terminal nonlinearity. The method gives exact results up to the order calculated (third order here) for any nonlinearity expressable as a power series, will treat frequency dependence in the nonlinearity as well as the terminations, and leads to a convenient algorithm for computer calculation. The mathematics provides a physical picture of intermodulation of a specific order as being produced by the modulation of lower order products through the nonlinearity. In fact, the solution for a given order of intermodulation currents or charges is the solution of a set of linear equations where the driving functions are intermodulation currents of lower order. A program has been written for the specific but important case of an abrupt junction varactor upconverter. Results for an upconverter that may be used for single-sideband operation in the common carrier microwave band show that the largest contribution to intermodulation comes from currents which are at the sum and difference frequencies of the input (IF) signal corresponding to currents above the input port in frequency and currents in the bias circuitry. This paper documents previously unpublished work (1972) done as part of the exploratory study of single-sideband modulation on long-haul microwave radio transmission.     

多载波CDMA系统信道估计改进算法研究

首先介绍了基于导频信号的辅助信道估计过程，并据此给出了信道模型。通过对基于导频信号信道估计算法分析，提出改进算法。即在导频位置信道响应处乘以一相位旋转因子以消除插值算法带来的相移影响的改进算法。     

调频广播引起的民航接收机互调干扰信号分析

随着民用航空频率清理整顿工作的不断深入，全国各级无线电管理部门通过积极有效的工作，使民航航空频率的干扰事件大大减少。但是最近笔者在实际工作中发现，由调频广播发射机引起的民航接收机互调干扰问题屡有发生，本文就此问题进行理论分析，解释有关现象产生的原因，为排除民航接收机互调干扰提供支持。     

Intermodulation distortion of cascaded transistors

Intermodulation distortion performance of cascaded transistors is analyzed using a nonlinear frequency-dependent model for the transistor and with Volterra series as an analysis tool. The objective of this study is to determine the optimum cascade that has high gain and good modulation performance especially for higher frequencies. A particular application is in long-haul, analog, solid-state coaxial systems where intermodulation distortion is a critical problem. Both experimental as well as computer results are used in this analysis. It is shown, for example, that certain low distortion configurations can exhibit high distortion when cascaded. A few optimum cascade configurations are discussed in detail.     

Dynamic Theory of Intermodulation Distortion

This paper studies the third-order intermodulation distortion of signals in a reflection amplifier that are separated by an appreciable fraction of the bandwidth. This large separation of input signals requires taking account of the energy interchange between diode and circuit. A theory of intermodulation distortion accounting for this interaction is developed for large-order nonlinearities. Previous analyses of this problem have been limited to small nonlinearities and small separation of the input signals. Experimental verification of the theory developed here is demonstrated for an IMPATT diode reflection amplifier as a function of power level and tone separation.