ATM交换机设计

本文提出一种宽带交换的新设计思想,它以异步传送模式为前提,能够保证各种宽带和窄带业务的综合交换。     

S12的新一代交换机—P3S

在全球电信市场向宽带业务发展的同时,如何保存现有的窄带通信设备,并使其在新的领域中继续发挥作用,正成为一个日益引起人们重视的问题。上海贝尔Ｐ３Ｓ产品的适时推出,为电信商提供了一个满意的解决方案,既保护了电信商在窄带通信领域中已投入的设备资产,又能够将...     

Hicom 300E数字程控交换机系统的维护

Hicom 300E数字程控交换机是德国西门子公司生产的，是全数字、时分、A律编码的交换系统，是集话音交换、数字传输、计算机通信和微电子技术为一体，具有综合数据业务网（ISDN）的新一代通信设备。我局于1999年开通运行，经过几年的使用，我们总结出该交换机维护的重点是：系统的启动、系统的维护和系统的管理。     

ALCATEL移动交换机模块负荷高的故障处理

ＡＬＣＡＴＥＬ移动交换机的软／硬件结构与上海贝尔Ｓ１２４０设备相似 ,由一个内部交换网络和连接在网络上的不同模块所构成。其中 ,ＰＳＡＣＥ模块完成呼叫处理部分字冠分析功能。ＩＳＶＣＥ模块完成Ｒ２信令及收发ＤＴＭＦ信号功能。松原的ＡＬＣＡＴＥＬ移动交换机曾出现这两种模块负荷异常的障碍。我将障碍处理经过具体叙述如下 ,希望对同类机型维护人员有所帮助。１故障一松原移动交换机共有４块ＰＳＡＣＥ模块 ,２０００年７月２４日至２８日 ,此类模块的忙时负荷值从１５%开始 ,每天以１０个百分点递增 ,升至５５% ,且凌晨闲时负荷…     

宽带交换机概述

就上海贝尔公司生产的宽带交换机来阐述下一代交换机是如何实现宽带接入的。     

交换机技术综述

从常见的交换技术，交换机的分类及功能，交换机的选择，交换机的应用，新一代交换技术概述等方面，详细地介绍了有关交换机的技术。     

宽带E波段无线传输系统

本实验采用74 GHz本振源与一对矩形喇叭天线实现了非归零开关键控(NRZ-OOK)信号在室内环境下的传输。在实验中还研究了不同传输距离和速率对系统性能的影响。结果表明误码率性能随着距离和速率的增加而下降,使用前向纠错编码(FEC)的5 Gbit/s和6 Gbit/s信号可以在3.6 m内实现无误码传输,而7 Gbit/s信号只能在2.4 m内实现无误码传输。     

Downlink transmission of broadband OFCDM systems-part III: turbo-coded

Orthogonal frequency and code-division multiplexing (OFCDM) systems have been introduced for high-speed data transmission in future wireless mobile communications. In this paper, a hybrid multicode interference cancellation (MCI) and minimum mean-square error (MMSE) detection scheme is presented for the turbo-coded OFCDM systems. Channel estimation based on a code-multiplexed pilot channel is employed. The weights of the hybrid detection are derived theoretically and an effective method to generate the weights in practical applications is proposed. By means of computer simulation, the effects of system parameters on the performance are studied extensively. It is shown that the hybrid detection outperforms pure MMSE detection in various channel conditions, especially for high-level modulation schemes. To carry out interference regeneration for the hybrid detection, the conventional turbo decoding algorithm which only decodes systematic bits should be extended to decode parity bits as well. Moreover, two iterations in turbo decoding are sufficient to provide good performance for the system with the multistage hybrid detection. Finally, given time-domain spreading factor N/sub T/, the system performance improves with frequency-domain spreading factor N/sub F/. However, the frequency diversity gain is saturated when N/sub F/ is large (i.e., N/sub F//spl ges/16).     

Digital video transmission for broadband networks

The information society to come is characterized by a large information flow in the integrated broadband network. Today it is the distribution of TV programmes that requires high transmission capacity. This leaves the cable operator with a problem. How should the CATV network of today be constructed? It must fulfil the need for distribution now and it must be prepared for new services to come. Some aspects of the above problem are discussed in this paper. It is emphasized that digital techniques as well as optical fibre transmission should be included in a modern cable network. The Danish DOCAT network concept is presented as one way to accomplish this. DOCAT combines optical fibre transmission in the trunk network with conventional coaxial techniques in the subscriber network.     

PCBX：新一代个人电脑控制用户交换机

ＰＣＢＸ：新一代个人电脑控制用户交换机谢国河（台湾景阳电信股份有限公司总经理）ＰＣＢＸ：ＰＣＣｏｎｔｒｏｌｌｅｄＳｍａｒｔＰＡＢＸ￥ＸｉｅＧｕｏｈｅ（Ｄｉｒｅｃｔｏｒ，ＵＮＩＷＯＲＬＤＥｌｅｃｔｒｏｎｉｃｓＣｏ．，ＬＴＤ．）ＰＣ个人电脑工业的诞生．大...     

Downlink transmission of broadband OFCDM systems-part IV: soft decision

In this paper, the performance of turbo-coded orthogonal frequency and code-division multiplexing (OFCDM) systems is investigated with soft multicode interference (MCI) cancellation and minimum mean-square error (MMSE) detection for downlink transmission in future high-speed wireless communications. To regenerate the soft interference signal, the conventional turbo decoding algorithm must be modified to provide log-likelihood ratio (LLR) values for all coded bits. Based on the LLR outputs of turbo decoder, two soft-decision functions are proposed, called LLR-soft-decision and Gaussian-soft-decision functions. The Gaussian assumptions used for deriving these two soft functions are verified by simulation results, and simple methods are proposed to estimate parameters used in the soft functions in practical systems. By means of computer simulations, the performance of soft MCI cancellation is studied extensively and compared with that of hard ones. It is shown that in a highly frequency-selective channel, soft MCI cancellation and MMSE detection can significantly improve the performance of turbo-coded OFCDM systems. Two iterations in turbo decoding are sufficient for both hard and soft-decision functions. The proposed soft-decision functions outperform the hard-decision function with various channel conditions and system parameters, such as the channel correlation, the quality of channel estimation, the number of iterations in turbo decoding and the frequency-domain spreading factor (N/sub F/). Furthermore, the Gaussian-soft-decision function provides better performance than the LLR-soft-decision function. Finally, although frequency diversity gain is saturated for large channel correlation when N/sub F/ is large as in , the gain increases further with increasing N/sub F/ for small channel correlation even when N/sub F/ is large.     

Downlink transmission of broadband OFCDM Systems-part I: hybrid detection

The broadband orthogonal frequency and code division multiplexing (OFCDM) system with two-dimensional spreading (time and frequency domain spreading) is becoming a very attractive technique for high-rate data transmission in future wireless communication systems. In this paper, a quasianalytical study is presented on the downlink performance of the OFCDM system with hybrid multi-code interference (MCI) cancellation and minimum mean square error (MMSE) detection. The weights of MMSE are derived and updated stage by stage of MCI cancellation. The effects of channel estimation errors and sub-carrier correlation are also studied. It is shown that the hybrid detection scheme performs much better than pure MMSE when good channel estimation is guaranteed. The power ratio between the pilot channel and all data channels should be set to 0.25, which is a near optimum value for the two-dimensional spreading system with time domain spreading factor (N/sub T/) of 4 and 8. On the other hand, in a slow fading channel, a large value of the channel estimation window size /spl gamma/N/sub T/, where /spl gamma/ is an odd integer, is expected. However, /spl gamma/=3 is large enough for the system with N/sub T/=8 while /spl gamma/=5 is more desirable for the system with N/sub T/=4. Although performance of the hybrid detection degrades in the presence of the sub-carrier correlation, the hybrid detection still works well even the correlation coefficient is as high as 0.7. Finally, given N/sub T/, although performance improves when the frequency domain spreading factor (N/sub F/) increases, the frequency diversity gain is almost saturated for a large value of N/sub F/ (i.e., N/sub F/ /spl ges/ 32).     

实用化宽带模拟光纤传输系统

介绍了一种基于半导体激光器调制特性的实用化宽带模拟光纤传输系统及其结构组成和实测性能。该系统的-3dB带宽为30kHz～1.1GHz,非线性小于±5%的动态范围不小于40dB,输出噪声峰峰值小于5mV。具有频带宽、动态范围大、输出噪声低、抗电磁干扰能力强等特点,可用于复杂电磁环境下的亚纳秒脉冲信号传输。     

Multi-rate group-orthogonal OFDMA-CDMA for broadband mobile transmission

In this work, the problem of multi-rate Multi-Carrier (MC) Code Division Multiple Access (CDMA) wireless transmission is addressed. In particular, we investigated the possibility of exploiting subcarrier grouping, already considered in literature for constant bit-rate MC-CDMA, in order to reduce mutual interference among different rate users and to allow the use of theoretically-optimum Maximum-Likelihood Multi-User Detection (ML-MUD) with affordable computational burden. We propose a multi-code Group Orthogonal (GO) OFDMA-CDMA system where the available subcarriers are subdivided into fixed-cardinality orthogonal subcarrier groups. The user’s data stream is selectively multiplexed into a variable number of substreams, which depends on the data-rate. Then, these substreams are transmitted over an orthogonal subcarrier group, univocally assigned to a user rate class. Experimental results obtained by adopting linear multi-user detection show that the proposed GO-OFDMA-CDMA outperforms state-of-the-art Variable Spreading Length (VSL) and multi-code MC-CDMA as far as higher data rate users are concerned. On the other hand, BER performance of lowest-rate users is slightly worse. Orthogonal subcarrier grouping allows to greatly increasing BER performance when using ML-MUD operated over small subcarrier groups. In such a case, the tradeoff to be managed is between achievable performance and computational complexity.     

一种适合低轨卫星通信的宽带传输技术

针对低轨卫星通信过程中功率受限的约束以及宽带业务需求的不断增长,研究了一种宽带传输技术。首先,分析了离散傅里叶变换扩频正交频分复用技术的宽带传输能力以及低峰均比特性;其次,进行了低轨卫星运动场景下的多普勒频移及采样偏差的分析,并在此基础上提出了一种低轨宽带通信的帧结构。仿真结果表明,该技术可有效抗低轨场景下的多普勒残留频偏且能完成高速率的传输任务。