Modeling distortion in multichannel communication systems

A behavioral modeling technique suited to capturing the response of wide-band multifunctional and multichannel amplifiers is introduced. The technique is based on the three-box approximation of the Volterra model and takes into account the dependence of the amplifier characteristics on frequency. The model is coupled with a new nonlinear statistical analysis, which enables accurate estimation of intermodulation and cross-modulation distortions of multiple digitally modulated signals. The model parameters can be obtained using simple measurements.     

信道串扰对多信道混沌通信的影响

构建了基于垂直腔面发射激光器(VCSELs)的多信道全光混沌通信系统模型,通过描述其特性的数率方程,研究了信道串扰对系统混沌同步及解码性能的影响。在数值模拟中,使用一个改进型的参数——相似指数作为参考标准来评价同步性能。结果表明,相对注入强度越小,信道间隔越大,系统同步的性能越好;双信道系统的同步质量相比主从式单信道系统会有明显下降,而进一步增加信道数量,同步品质并不发生显著改变。以2.5Gb/s伪随机数字调制下的混沌掩藏方式为例,分析了不同信道条件下系统解码性能。在同步质量足够高时,信号可以得到较好的恢复。     

信道串扰对多信道混沌通信系统的影响

为了研究多信道全光混沌通信系统中信道串扰对系统同步及解码性能的影响,构建了基于垂直腔面发射激光器的多信道混沌通信系统模型.通过利用描述其特性的数率方程模型,采用相似指数作为参考标准来评价同步性能,并进行了2.5Gbit/s混沌掩藏方式的编解码数值模拟.结果表明,相对注入强度越小,信道间隔越大,系统同步的性能越好;双信道系统的同步质量相比主从式单信道系统会有明显下降,而进一步增加信道数量,同步品质并不发生显著改变.在同步质量足够高时,信号可以得到较好的恢复.     

TSK-based decision feedback equalizer using an evolutionary algorithm applied to QAM communication systems

A Takagi-Sugeno-Kang (TSK) fuzzy-based decision feedback equalizer (DFE) applied to detecting a quadrature-amplitude-modulation (QAM) signal is presented. The structure of a TSK fuzzy system may produce many local minimum of involved cost functions for detecting received signals. An evolutionary algorithm is adopted for the proposed TSK fuzzy equalizer to overcome the difficulty for locating global minimum in weight space. Results showed that the performance of the newly designed equalizer is much improved for DFEs with multilayer perceptron or least mean square scheme.     

On the theory of importance sampling applied to the analysis ofdetection systems

Detection systems are designed to operate with optimal or nearly optimal probability of a wrong decision. Analytical solutions of the performance of these systems have been very difficult to obtain. Monte Carlo simulations are often the most tractable method of estimating performance. However, in systems with small probability of error, this technique requires very large amounts of computer time. A technique known as importance sampling substantially reduces the number of simulation trials needed, for a given accuracy, over the standard Monte Carlo method. The theory and application of the importance sampling method in Monte Carlo simulation is considered in a signal detection context. A general method of applying this technique to the optimal detection problem is given. Results show that in cases examined, the gain is approximately proportional to the inverse of the error probability. Applications of the proposed method are not limited to optimum detection systems; analysis, leading to a measure of the gain in using this biasing scheme, shows that in all optimal systems considered, less than 100 trials is needed to achieve estimates with 45% confidence, even for extremely small error probabilities     

Injection lasers for multichannel optical communication

Injection lasers are suitable sources of radiation for optical communication systems. The output characteristics of III-V compound and mixed crystal III-V compound injection lasers for0.64-1.1-muspectral range are described. In order to improve the spectral output (and to increase the threshold for the appearance of adjacent modes) composite cavities were successfully used. Such a cavity contains the diode and a passive transparent flat plate, which serves as an additional selective component in the feedback circuit of the laser. A 96-channel telephone link was tested in the laboratory using four lasers (wavelengths 0.74, 0.78, 0.85, and 0.91μ) in one beam. The method of combining and separating the four spectral channels at the transmitter and receiver, respectively, as well as the results of the experiments are described.     

Source coding theory for cascade and branching communication systems

A source coding problem is considered for cascade and branching communication systems. The achievable rate region is established for the cascade systems and bounds are obtained for the branching systems. Some examples are also included.     

Novel multireceiver communication systems configurations based onoptimal estimation theory

A multireceiver configuration for the purpose of carrier arraying and/or signal arraying is presented. The configuration is arrived at by formulating the carrier and/or signal arraying problem as an optimal estimation problem and consists of two stages. The first stage optimally estimates various phase processes received at different receivers with coupled phase-locked loops, (PLL) wherein the individual PLLs acquire and track their respective receivers' phase processes but are aided by each other in an optimal manner via low-frequency error signals. The coupled PLL estimator is followed by a linear or nonlinear combining of the quadrature-phase components of the mixers from various receivers for the purpose of data detection. The proposed configuration results in the minimization of the effective radio loss as the combiner output and thus maximization of energy per bit to noise power spectral density ratio is achieved. An adaptive algorithm for the estimator of the signal model parameters when these are not known a priori is also presented     

一种应用于无线通信系统的MIMO天线

MIMO系统是通过不同的分集技术,以实现在相同带宽和发射功率的条件下大幅改善系统容量和可靠性,减小信道失真。作为系统关键模块之一的天线,则要求有着好的分集特性,并接收较多的这波。这里提出的MIMO天线工作在2．4GHz,天线单元是等边三角形贴片天线。三角形天线的宽波瓣可以使MIMO天线接收更丰富的多径这波,与天线单元的高增益相结合能较好改善MIMO系统的SNR和抗干扰能力。通过对天线端口间的互耦和相关性分析,该系统能实现好的极化和方向图分集,获得高的分集增益。     

DSP在移动通信中的应用

可编程ＤＳＰ（数字信号处理器）在数字蜂窝电话中已广泛应用。本文阐述了ＤＳＰ在目前标准中的应用情况,展望了未来ＤＳＰ向低功耗方向发展的趋势。     

Dynamics of multichannel feedforward adaptive systems

The role played by reference-signal compensation in the convergence of multichannel feedforward adaptive systems is addressed. Convergence conditions are established, and effects of compensation errors are analyzed. We also explore, by means of altering the reference-signal compensation filtering from the conventional choice, ways to force systems to converge to arbitrary solutions of possible interest other than the standard Wiener solution. This could be useful, for example, if one wished to cancel noise at a very large number of measurement points, which, conventionally, would require a correspondingly complex, possibly prohibitively large, controller. The scheme developed enables very efficient usage of error signals, such that systems with large numbers of disturbance-cancellation points need employ only a relatively small number of error signals in the actual control-system implementation     

Stability of multichannel sound control systems

Sufficient conditions for the stability of decentralised, as well as fully coupled, active multichannel harmonic sound systems are derived. Such systems are being increasingly used to attenuate undesirable noise from harmonic (or narrowband) sources, at specific locations. These conditions are based on generalisations of the Gershgorin theorem. The advantage of using these generalisations is that they yield less conservative results than those based directly on the Gershgorin theorem, and more important, the conditions are applicable to systems where uncertainties in the physical parameters, and/or the frequency of the primary source within a given bandwidth, are assumed. The intuitive assertion that adding to the optimisation cost function a term which prevents using too much control effort is undesirable from the viewpoint of the steady-state error is formally shown. An analysis of the behaviour of the steady-state error as a function of the control effort is provided. A method to determine a small control effort which still guarantees stability of the optimisation algorithm is derived. A simple example is worked out analytically and simulation results for a more complicated example are provided     

Rate-distortion theory applied to automatic object recognition

We consider the problem of recognizing CAD models at arbitrary orientations observed via the projective transformation on an imaging sensor with noise. Bounds on codebook size are established through the rate-distortion curve for a distortion measure derived from the Hilbert-Schmidt norm for elements of the orthogonal group     

Ray-optical techniques applied to antenna admittance theory

It is demonstrated that the admittance of thick tubular antennas can be accurately computed by using a ray-optical technique for finding the reflection from the end. The theory gives good results for a radius as small as 0.2 of a wavelength. The results are compared with a numerical solution by Chang [1].     

The effect of error control coding in multichannel FSK coherentlightwave communication systems influenced by laser phase noise

It has been shown that coherent optical fiber receivers with a two-filter structure (TFS) consisting of a wide-band IF filter and a narrow-band postdetection filter are less susceptible to the influence of phase noise. However, the expanded IF bandwidth required to achieve optimum sensitivity performance is large, particularly in multichannel FSK systems. Forward error control coding can relax the laser linewidth requirement and improve receiver sensitivity. In this paper a multichannel asynchronous FSK scheme equipped with (31, k) Reed-Solomon codes is used to verify the coding benefit. A systematic error probability analysis is developed and a stable and accurate performance evaluation procedure is provided. The sensitivity penalties due to the combined phase noise and interchannel crosstalk for both coded and uncoded systems are calculated for comparison. The results show that the performance reduction due to phase noise can be largely alleviated by choosing a proper code rate and an optimum value of the expanded IF bandwidth     

Bit-error rate computation of optical CDMA communication systems bylarge deviations theory

Recently, there has been a lot of interest in using code-division multiple access (CDMA) for optical fiber communication systems. In this letter, we present a technique for estimating the bit error rate of optical CDMA communication systems employing avalanche photodiode receivers. The proposed technique, which is based on large deviations theory, is featured as a simple, accurate, and flexible method for performance evaluation of such systems     

Angular multiplexing for multichannel communication in a single fiber

A concept of angular multiplexing of several communication channels in a relatively short step-index fiber is described. The angular dependence of the outgoing light flux and the temporal impulse response are calculated for slab waveguides and round fibers in terms of the fiber's length and the excitation conditions. Calculations of the inpulse response in the presence of mode coupling are based on a simple model which is found to be adequate for short fibers. Crosstalk levels are calculated by integrating the flux over the aperture of the detectors. Measurements of angular flux distribution, temporal impulse response, and crosstalk levels agree with theoretical prediction and validate the proposed concepts. To increase light levels, parallel excitation of each channel by several light sources is suggested and tested. Also, light collection efficiency is increased by employing lenses and annular mirrors to deflect and focus the light from each channel to small-area detectors. Given a 25 m long fiber with a coupling constant of 10^-5rad²/m, it is possible to multiplex four channels with cross-talk of about -25 dB and information rates ranging from 10⁹bits/s to 10¹⁰bits/s for each channel.