PoE设计方案分析

以太网供电PoE（PowerOverEthernet）是一种局域网技术,通过现有的Cat5/Cat5e/Cat6以太网电缆给IP终端设备（如IP电话机、无线局域网接入点AP等）同时提供数据的传输和直流电源的供给,能在确保现有结构化布线安全的同时保证现有网络的正常运作,最大限度地降低成本。当前PoE技术已在企业与工业中得到广泛的应用,文中提出几种PoE设计方案,希望对PoE产品的开发有所帮助。     

The Demand Priority MAC protocol

A new technology needs to offer more than just 100 Mb/s. To succeed in the LAN marketplace, a new LAN technology must be very cost competitive with the established LANs, such as Ethernet and Token Ring, while also providing backwards compatibility with existing network software. We describe a new 100-Mb/s LAN technology that has these characteristics This technology is being defined as an open standard within the IEEE Project 802.12 Demand Priority group. Two important objectives were established for this LAN technology: first, it should be able to use the unshielded twisted pair (UTP) wiring found in a large number of installations and, in particular, to use the same wiring as defined for use in 1OBase-T. This objective was later extended to encompass support for the shielded twisted pair (STP) used for IEEE 802.5. This will enable the majority of current LAN users to benefit from their enormous investment in cable plant. The second objective was that the network should support new applications, such as video conferencing and remote training, while also providing backwards compatibility with the massive installed software base. Both objectives have been met. The Demand Priority MAC protocol currently being standardized in IEEE 802.12, offers substantial benefits over the CSMA/CD protocol of IEEE 802.3. By preserving both the current wiring infrastructure and investment in software, and by using the very simple Demand Priority MAC protocol, 100 Mb/s LANs could soon be as low-cost as 10Base-T is today     

Reduction of crosstalk noise in modular jack for high-speeddifferential signal interconnection

Crosstalk noise has become a significant problem in the design of high-speed digital interconnections. In this paper, we demonstrate a crosstalk reduction method, which has been successfully applied to the design of a CAT-5E modular jack. The CAT-5E is a newly adopted cabling and connector standard for advanced cabling network systems to assure more robust, reliable and high-speed operation, which is based on differential mode signal transmission using unshielded twist pair (UTP) cable. The improved design of the modular jack shows minimal crosstalk noise and return loss over a wide range of manufacturing conditions. The improved crosstalk characteristics of the modular jack were accomplished by inserting embedded capacitors on the printed circuit board (PCB) of the modular jack. The embedded capacitors compensate for the unbalanced capacitive crosstalk that occurs in the plug and insert. In particular, the embedded balancing capacitor is designed to have maximum capacitance, with limited PCB area, by using a double-sided PCB design. Less than -45 dB near-end-crosstalk (NEXT) was achieved after the crosstalk noise compensation, satisfying the CAT-5E specification for frequencies up to 100 MHz     

Remarks on standard fibre-optic LANs

This paper explains the importance of standard fibre-optic LANs, and gives an overview of the state of development of the main emerging fibre-optic LAN standards. Fibre-optic enhancements to 802·3, 802·4 and 802·5 are discussed, as well as FDDI and FDDI-2. A brief mention is made of 802·6 and SONET, which are not LANs but are relevant to the discussion. The need for a rational cabling infrastructure is mentioned, as is the need for conformance tests. Some of the practical reasons why it makes sense to have fibre available at the end stations are discussed.     

Open systems cabling as a building utility

Open Systems Interconnection (OSI) is intended to facilitate interworking between data terminal equipments (DTEs) of different designs and from multiple vendors, thus providing the user community with a broad level of independence in the procurement of IT equipment. Whilst OSI local area network (LAN) standards have aimed to fulfil this objective, actual variations in data rates, media types and cabling topographies have hindered progress. The `tree and branch' cabling architecture presented in the paper provides a powerful solution to these problems. Based on twisted-pair and optical-fibre media, it could support today's industry standard LANs, point-to-point communication links such as V24, and circuit-switched telephony within an elegant, integrated cabling system     

5类电缆性能测试的基本指标

结构化布线工程的最后一步是对布线系统的测试和评估，电缆的性能测试经常被忽视，基本指标有：近端串扰，综合近端串扰，衰减串扰比，等效远端串扰，综合等效远端串扰，回波损耗，延迟抖动等。     

智能建筑的AMP综合布线工程

AMP综合布线系统是一种通用型开放的传播平台,其特征是仅以一种传输路线满足多种通信业务终端的技术要求,再加上用多媒体终端集语音、数据、图像于一体的通信应用方式,给用户带来很大方便和经济实用的效果,在智能建筑布线系统中具有广泛的应用价值。文中提供了AMP综合布线标准,对基于此标准的AMP综合布线系统测试工程进行了较为详细的分析和讨论。     

Low-latency mobile IP handoff for infrastructure-mode wireless LANs

The increasing popularity of IEEE 802.11-based wireless local area networks (LANs) lends them credibility as a viable alternative to third-generation (3G) wireless technologies. Even though wireless LANs support much higher channel bandwidth than 3G networks, their network-layer handoff latency is still too high to be usable for interactive multimedia applications such as voice over IP or video streaming. Specifically, the peculiarities of commercially available IEEE 802.11b wireless LAN hardware prevent existing mobile Internet protocol (IP) implementations from achieving subsecond Mobile IP handoff latency when the wireless LANs are operating in the infrastructure mode, which is also the prevailing operating mode used in most deployed IEEE 802.11b LANs. In this paper, we propose a low-latency mobile IP handoff scheme that can reduce the handoff latency of infrastructure-mode wireless LANs to less than 100 ms, the fastest known handoff performance for such networks. The proposed scheme overcomes the inability of mobility software to sense the signal strengths of multiple-access points when operating in an infrastructure-mode wireless LAN. It expedites link-layer handoff detection and speeds up network-layer handoff by replaying cached foreign agent advertisements. The proposed scheme strictly adheres to the mobile IP standard specification, and does not require any modifications to existing mobile IP implementations. That is, the proposed mechanism is completely transparent to the existing mobile IP software installed on mobile nodes and wired nodes. As a demonstration of this technology, we show how this low-latency handoff scheme together with a wireless LAN bandwidth guarantee mechanism supports undisrupted playback of remote video streams on mobile stations that are traveling across wireless LAN segments.     

Proportional bandwidth allocation with consideration of delay constraint over IEEE 802.11e-based wireless mesh networks

Wireless mesh networks (WMNs) extend the limited transmission coverage of wireless LANs by enabling users to connect to the Internet via a multi-hop relay service provided by wireless mesh routers. In such networks the quality of experience (QoE) depends on both the user location relative to the Internet gateway and the traffic load. Various channel access or queue management schemes have been proposed for achieving throughput fairness among WMN users. However, delay and bandwidth utilization efficiency of such schemes may be unacceptable for real-time applications. Accordingly, the present study proposes a proportional bandwidth allocation scheme with a delay constraint consideration for enhancing the QoE of users of WMNs based on the IEEE 802.11e standard. An analytical model of the proposed scheme is provided. Moreover, the performance of the proposed scheme is systematically compared with that of existing bandwidth allocation methods. The simulation results show that the proposed scheme outperforms previously proposed schemes in terms of both an improved throughput fairness among the WMN users and a smaller end-to-end transmission delay.     

Peak-to-mean power control and error correction for OFDMtransmission using Golay sequences and Reed-Muller codes

A coding scheme for OFDM transmission is proposed, exploiting a previously unrecognised connection between pairs of Golay complementary sequences and second-order Reed-Muller codes. The scheme solves the notorious problem of power control in OFDM systems by maintaining a peak-to-mean envelope power ratio of at most 3 dB while allowing simple encoding and decoding at high code rates for binary, quaternary or higher-phase signalling together with good error correction     

100BASE-T2: a new standard for 100 Mb/s Ethernet transmission overvoice-grade cables

100BASE-T2 is a new physical-layer specification for IEEE 802.3 LANs operating at 100 Mb/s (“Fast Ethernet”). It enables users of the prevailing 10BASE-T Ethernet LAN technology to upgrade their networks from 10 to 100 Mb/s performance while retaining an existing voice-grade cabling infrastructure. 100BASE-T2 transceivers will operate over two pairs in unshielded twisted-pair cables corresponding to EIA/TIA category 3 (UTP-3), as minimally required for 10BASE-T. In a four-pair UTP-3 cable, simultaneous operation of two 100BASE-T2 links, or one 100BASE-T2 and one 10BASE-T link, is permitted. Since voice-grade cables exhibit more signal attenuation and significantly higher crosstalk coupling between adjacent pairs than data-grade cables, sophisticated digital signal processing techniques are needed to achieve reliable duplex 100 Mb/s transmission over two pairs. The 100BASE-T2 standard defines dual-duplex baseband transmission at a modulation rate of 25 Mbaud. During each modulation interval, a four-bit data nibble or Ethernet-specific control information is encoded into a pair of quinary signals. These signals are transmitted simultaneously on the two wire pairs in both signaling directions. In the receivers, adaptive digital filters are required for echo and NEXT cancellation, equalization, and interference suppression     

A low-cost unrestricted fast playback scheme for video streaming

In this brief, we propose a low cost fast-forward and fast-backward playback scheme for video streaming applications. By reshaping the ordinary linear encoded group-of-pictures (GOP) structure into a hierarchical structure, the transmission overhead caused by frame dependencies can be reduced. The resulting video streaming system can provide all directions video playback with any speed-up factor. A set-top box architecture that supports the binary tree structured GOP playback is also described.     

51.84 Mb/s 16-CAP ATM LAN standard

The paper describes the characteristics and performance of the 16-CAP transmission scheme that has been chosen by the Technical Committee of the ATM Forum as the ATM LAN physical layer interface standard at 51.84 Mb/s for category 3 unshielded-twisted-pair (UTP) wiring. The two most attractive features of the 16-CAP transceiver are its capability of operating in the presence of multiple users in a voice-grade UTP cable and the straightforward way in which it can provide scalability to lower speeds. It is also shown in the paper how the carrierless AM/PM (CAP) modulation scheme used for the ATM LAN standard can be utilized to provide substantially higher data rates than 51 Mb/s when there is only one user in a cable. Under this condition, data rates up to 155 Mb/s can be achieved over category 3 wiring and significantly higher rates can be achieved over high-performance category 5 wiring     

Performance of direct sequence spread spectrum ISM band radio LANs in a multipath time dispersive channel

The results of a Monte Carlo/semianalytic estimation of the performance of DS spread spectrum ISM band radio LANs in a time dispersive channel are presented. The results show that these DS systems have an advantage over FH systems of 4-6 times, depending on diversity scheme, in maximum tolerable delay spread or maximum transmission rate.<>     

大规模MIMO系统多用户PSK调制方案的优化

针对超可靠低时延通信短包传输特征,在大规模多输入多输出( Multiple-Input Multiple-Output,MIMO)上行链路系统中,利用较低导频开销来设计相移键控( Phase Shift Keying,PSK)调制方案,并对该方案进行优化兼顾无线链路传输的可靠性.首先,在接收端构建基于最小欧式距离的非相...     

Bandwidth-efficient digital transmission over unshieldedtwisted-pair wiring

Describes techniques for achieving data rates up to 155 Mb/s over unshielded twisted-pair (UTP) wiring for local area network (LAN) applications in premises distribution systems. Duplex operation at these high data rates is achieved over two pairs of UTP wiring and with a bandwidth utilization that is less than 30 MHz, thus avoiding potential problems with radiation limits. The transmission scheme used for these LAN applications is carrierless AM/PM (CAP), which is a bandwidth-efficient two-dimensional passband encoding scheme. The paper also discusses in some detail a technique called NEXT equalization, which allows several users to share the same cable     

5类线结构化布线系统要求和方法

目前以太网已得到普遍使用,结构化布线系统已成为首要解决的问题.本文全面地介绍了结构化布线系统,5类线的基础知识,并对布线方法及敷设工艺、质量标准等做了详尽的描述,使大家在布线时有一个合理的参考方案.     

Low-Complexity Channel Estimation for Wireless Block Transmission Systems in Time-and Frequency-Selective Rayleigh Fading Channels

Mobility-induced Doppler spread and multipath propagation introduce the time- and frequency-selectivity (doubly selectivity) in fading channels. Based on the complex exponential basis expansion model (BEM) to approximate the doubly selective channel (DSC), a low-complexity channel estimation scheme for block transmission systems over DSC are developed in this paper. Using the developed scheme, the long data block is divided into a few short data subblocks in terms of the maximum normalized Doppler frequency and block length, and each subblock is performed to respective channel estimation. Thus the total calculation complexity is effectively decreased because the number of the BEM channel coefficients to estimate is greatly reduced for each sub-block. Moreover, by utilizing these channel estimation values to refit the true channel, we can obtain better channel estimation. Besides, the normalized mean square error (NMSE) expressions for the developed scheme and the existing scheme are derived in detail, respectively. Compared to the existing scheme, the proposed scheme has lower calculation complexity and superior performance. The simulation results verify the effectiveness of the developed scheme, and the theory values of the derived NMSE accord with corresponding simulation values.     

Distributed Arithmetic Coding

We propose a distributed binary arithmetic coder for Slepian-Wolf coding with decoder side information, along with a soft joint decoder. The proposed scheme provides several advantages over existing schemes, and its performance is equal to or better than that of an equivalent scheme based on turbo codes at short and medium block lengths.     

Structured cabling comes of age

Structured cabling has emerged as a basic building utility, comparable to heating and air conditioning, electricity or plumbing. it forms the essential communications infrastructure of a business's IT system, and is every bit as important as the equipment connected to each end of a piece of cable. Cabling is often overlooked or taken for granted, but a little time and effort in the choice of cabling system will save time, money and frustration in the near term, and, in the longer term, minimise the need for disruptive upgrades. A key objective for any structured cabling system is the capacity to handle with speed and reliability the huge data streams encountered in modern Internet and e-commerce applications. The system should also be capable of fast installation and deployment, which means that cabling components need to be modular, simple to use and, ideally, supplied in pre-qualified form. The author reviews the role of structured cabling in enabling the office IT infrastructure-today and into the future