Some aspects of the need for redundancy in telecommunication transmission systems

The high inherent reliability of the electronic equipment as well as the greatly simplified replacement of functional units makes all duplication superfluous in a multiplex terminal on the apparatus level. An economically justifiable availability of a telecommunication network can be achieved, however, by appropriate planned transmission systems with automatic or manual re-routing possibilities in combination with an adequate maintenance and well-considered stock of spares.     

Improvement of interference immunity of telemetry transmission systems based on the use of the Hamming code

A telemetry transmission system is described. This system appeared as a model which was used to check the propagation conditions and the noise immunity of the transmitted signal. Based on the obtained data a modeling was performed in the MATLAB environment in order to realize a better degree of noise immunity of the given signal. With this aim after the upgrade of the hardware part of the encoder the use of the simplest and the most noise immune codes (15/11 Hamming) and checking its work under the influence of the pulse interference were suggested. The results coincided with the theoretical estimations.     

The reliability of silicon avalanche photodiodes for use in optical-fiber transmission systems

Thermal overstress tests on silicon avalanche photodiodes (APD's) from two manufacturers have shown that APD's, despite their complexity, can have adequate reliability for use in optical-fiber transmission systems in telecommunications networks. However, two failure mechanisms were observed on the APD's from one manufacturer, namely increased surface leakage currents and localized premature breakdown, which would have caused either increased error rates or complete system failure. The results indicate that procurement specifications are required to guard against the use of unreliable APD's in transmission systems, and procedures are recommended.     

Reliability of optical components for use in submarine optical fiber transmission systems

This paper presents the reliability test results for LD modules, optical couplers, and APD modules, which are fabricated through methods for achieving and assuring a high degree of reliability for use in 400-Mbit/s submarine optical fiber transmission systems. In particular, the paper presents methods for evaluating the optical component reliability as well as an investigation into the degradation factors in the coupling circuits. From the reliability test results obtained, the paper also discusses the mechanism and test acceleration of wear-out degradation following reliability tests conducted for more than 8000 h on the fabricated optical components. These optical components are consequently confirmed to be highly reliable for a system life of 25 years.     

Transfer characteristics of Brillouin fibre amplifiers for use in self-homodyne coherent optical transmission systems

Presents for the first time, the basic input-output characteristics of a Brillouin fibre amplifier, and shows that these are in good agreement with the first experimental results reported recently by other workers on a novel and potentially very important application of Brillouin amplification in a coherent optical fibre transmission system. For this type of application, theoretical results are also presented on the optical pump power dependence of the amplifier gain per unit optical pump power.<>     

A survey on estimating the timing constraints of hard real-time systems

A real-time computer system must interact with its environment in terms that are dictated by the occurrence of a significant event or simply by the passage of time. The computational activities triggered by these stimuli are expected to provide the correct results at the right time, since a real-time controller must meet the timing constraints that are dictated by its particular environment. If a computer controller fails to meet these time constraints, the controlled system may suffer a behavioural degradation from where, in some cases, a catastrophe can emerge. Thus, the correct estimation and handling of the timing constraints of a controlled system are central issues for the specification, development and test of a real-time computer controller, in a job that requires the scientific contribution of system engineers and real-time computer designers.In this paper we survey proposed solutions and concepts for estimating the timing constraints and the behavioural degradation of a controlled system when it suffers the impact of a timing failure. Although it is universally agreed that these are central issues for the development of predictable real-time controllers, this study shows that, except for a few cases, current literature does not place on them as much emphasis as one could expect. Moreover, a systematic method for evaluating the timing constraints of a controlled system does not seem to actually exist.     

Optimal transmission of high definition video transmission in WiMedia systems

WiMedia systems are developed for indoor high-data-rate wireless systems. The H.264/AVC, a high-efficiency video coding technique, is considered for high definition (HD) video application. Considering the transmission of H.264/AVC based HD video over WiMedia, in this paper, we will propose a cross-layer architecture and an analytical model to calculate the optimal payload length with the constraints in error criteria, retransmission mechanism, and the delay budget. Besides, the required minimum reservation slots in WiMedia are also investigated to optimize the transmission performance of HD video.     

Some comments on the use of markov models in communications

In their recent article Feng, Field and Haykin rediscovered an approach to the channel modelling based on stochastic differential equations (SDE). In the following we would like to bring readers attention to a body of literature which deals with similar subjects using SDE approach.     

Research on uplink coordinated transmission schemes in LTE-advanced systems

The investigation of inter-cell interference mitigation techniques is a key area in wireless communications.Coordinated multiple points(CoMP) transmission/reception is a candidate technique for interference cancellation in 3GPP LTE-Advanced system.However,the coordination scheme in CoMP remains a key research problem to be solved,which will have a strong influence on the performance of CoMP.In this paper,a novel coordinated transmission scheme is proposed for the uplink LTE-Advanced system.In our scheme,several base transceiver stations(BTS) and users are selected as coordination partners which form a CoMP cluster.Joint processing is used at the receiver to mitigate interference.From the perspective of coordinated partner selection,our scheme can be divided into static and dynamic coordination which are both considered to fully exploit the throughput gain of CoMP.The proposed schemes are evaluated by system level simulation and compared with the conventional LTE system based upon single cell processing.Our simulation results demonstrate that the proposed schemes attain superior performance as opposed to the conventional system in terms of cell average and cell edge throughput.     

PMD对平均光孤子系统传输性能影响的研究

文章采用计算机系统仿真的方法,通过数值求解简化的基本传输方程和非线性薛定谔方程,研究了采用相敏光纤参量放大器(PSA)作为在线放大器时,偏振模色散(PMD)对系统传输性能的影响.系统传输方案采用平均孤子系统.仿真结果表明:当PMD系数增大时,孤子脉冲出现分裂和展宽,幅度出现衰减,从而导致系统的传输性能下降.     

Expressions for the analysis of digital transmission systems

It is shown that, if the sinusoidal roll-off response commonly used in the analysis of digital transmission systmes is replaced by a trapezoidal response, it is possible to derive algebraic expressions for the signal/noise ratio and error rate in cases of practical importance.     

Reducing the effects of transmission impairments in digital fiberoptic systems

The major impairments in lightwave systems and the signal-processing techniques that can be used to reduce these impairments are discussed. Guidelines for the use of these techniques are presented. These guidelines are used to determine the techniques with the most potential for providing improved performance in long-haul systems, local-area networks, and local loop systems. Although many of the techniques have been previously considered for these applications, few have been implemented in commercial products. Some of the most promising techniques include dispersion-compensating fibers, polarization control, nonlinear cancellation (NLC), and coding for reducing the effect of distortion in long-haul single-frequency-laser direct-detection systems     

准线性光传输系统的非线性噪声研究

采用一阶摄动理论分析了准线性光传输系统的非线性相位噪声,在此基础上得出中置光学相位共轭器的准线性光传输系统的非线性相位噪声的方差的理论表达式,并围绕理论推导得出的非线性相位噪声的性能参数进行数值计算。计算结果表明在光放大器和传输系统的终点到光学相位共轭器等距的情况下,采用光学相位共轭器的色散补偿光传输系统可以完全消除非线性相位噪声对非线性系数的一阶影响。     

Observation of modal noise in single-mode-fibre transmission systems

Modal noise has been observed in overmoded short fibre sections and transmitter pigtails resulting in performance degradation in a single-mode-fibre transmission system. The power penalty becomes negligible when the fibre is sufficiently long or is deployed with a bend to sufficiently attenuate the LP11 mode.     

The experimental evaluation of flat periodic transmission lines for use as an information source in automated transportation systems

A brief summary of some past studies of the use of transmission lines as an information source for automated ground transportation systems is presented. One method, which involves the use of helically wound transmission lines, was found to be promising [6] but such lines are difficult to implement. Here the geometry-dependent properties of the magnetic-field distribution of flat periodic transmission lines is developed. It is found that such lines should be usable as a replacement for helically wound lines. The results of an experimental evaluation of several flat lines are presented with emphasis on triangular-shaped lines. It is found that the performance characteristics are even better than those of the helically wound line.     

基于多物理层损伤限制的光网络RWA算法研究

在透明光网络中,如何在选路过程中自适应地规避物理层损伤进而实现高质量的传输服务是亟待解决的问题.提出了一种面向多物理损伤约束的RWA算法,改进原有损伤感知RWA算法考虑物理损伤单一不够全面的问题,尝试将多个物理损伤作为路径选择的多个约束条件,从而可以选择损伤最小的光路来完成光连接的请求,从而满足未来高传输质量的需求.     

Some statistical remarks on the derivation of BER in amplifiedoptical communication systems

We consider the signal detection problem in amplified optical transmission systems as a statistical hypothesis testing procedure, and we show that the detected signal has a well-known chi-squared distribution. In particular, this approach considerably simplifies the derivation of bit-error rate (BER). Finally, we discuss the accuracy of the Gaussian approximations to the exact distributions of the signal     

具有不同chip波形的DS/SS系统抗单频干扰的精确性能分析

用领域分析的方法，分析了具有不同chip波形的DS／SS系统单频干扰时的误码性能，讨论了chip波形对系统抗单频干扰能力的影响，将Torrieri的改进高斯近似方法推广应用到一般的chip波形。