LMDS与FSO技术的分析及比较

LMDS技术分析LMDS是提供宽带接入服务的第三代PMP无线通信系统,具有流量突发、流量高度不对称的适应能力。LMDS可以通过各种多址技术提供业务的分配,如:频分多址(FDMA)、时分多址(TDMA)。无线ATM(W-ATM)和无线IP等许多新的传输平台都可以为这些基于端到端网络的服务提供支撑。W-ATM技术可以为按需使用带宽的服务提供可变带宽支持。系统设计主要考虑因素视距通信像FSO一样,LMDS本质上是一个视距通信系统,这是由其使用频段(26GHz)所决定的,在这个频段内信号容易被阻断。视距通信的好处是可以利用方向性天线和极化方式进行扇…     

FSO—本地接入市场新焦点

本地宽带接入技术-自由空间光通信（FSO）是一种视距技术,在太赫兹频段发射激光或光脉冲来传输分组数据。FSO的高带宽、低成本、易安装的优势使其可以作为本地接入一种理想的补充形式,不过FSO需要解决的问题包括由恶劣天气引起的信号衰减（尤其是雾）、由建筑物摆动导致的激光不能对准、安装权限和受地域限制。FSO可以应用于校园局域网、紧急情况备用、灾难恢复以及短途的国际专线。     

智能卡与其它卡片技术的比较

在目前的卡片市场中,除了磁卡和智能卡以外,还有一种被称为“激光卡”的非磁质高密度记录媒体。三种卡的结构和功能比较如下表所示。     

TD-SCDMA与其它CDMA技术的比较

１TD-SCDMA与UTRATDD的比较TD-SCDMA与UTRATDD具有相同的高层信令，一部分物理层技术也相同，但两个标准的设计出发点不同，因此其主要特性和用途也不同。１．１TD-SCDMA与UTRATDD的相同之处（1）使用TDD双工方式；（2）同时使用FDMA/TDMA/CDMA；（3）使用相同的QPSK射频调制解调技术；（4）使用正交可变扩频系数相同的扩频调制方法；（5）超帧和无线帧长度相同；（6）数据复接和分接方法相同；（7）在信道编码和交织方面，使用与3GPP完全相同的技术；（8）CDMATDD将使用完全相同的第二、第三层信令。１．２T…     

FSO宽带接入技术

一、背景近年来,随着通信与信息产业的快速发展和Internet的普及,人们对宽带的需求越来越迫切,而且传统的通信业务也由语音通信向多媒体和高速数据通信发展。为了适应这种需要,出现了多种高速率的接入方式,如光纤电缆混合网(HFC)、数字用户环线(xDSL)、电缆调制解调器、光纤网、直播卫星系统(DBS)和本地多点分配业务LMDS系统等。FSO接入技术以其建设周期短、初期投资少、传输速率高、业务类型丰富而备受人们的关注。二、FSO接入技术简介FSO(Free-SpaceOptical)一般译为无线光通信,也译为自由光通信,也称为FreeSpacePhotonics(F…     

弹性分组环与其它技术的比较

RPR与相关技术的比较RPR与其它技术相比，最大的特点是经济，同时具有可靠的保证语音传送的手段,可充分利用网络带宽，同时简化IP的转发方式。RPR和千兆以太网RPR帧格式类似于千兆以太帧，RPR端口具有千兆以太网端口的经济性，但在信令交换和传送机制上有本质的区别。对以太网来说，它的扫描树不允许多节点组成环形拓扑结构；故障恢复很慢；用户或服务在2层隔离，不便于升级，通常需要MPLS或基于3层的隔离。这样在可靠性、扩展性等方面不能满足大型服务运营商网络的需求，其技术路线的核心为简单地提高传输带宽和交换容量，而在其…     

适应三峡库区特殊地形的DP-DB FSO接入系统研究

针对三峡库区的特殊地形,设计了一种适应三峡 库区环境接入应用的偏振复用双二进制自由空间光接入系统。在 天气较好条件下,10 Gb/s偏振复用双二进制信号在1km自由空间光 无线信道中成功进行了收发和传输。测试了该接入系统 中两路偏振复用信号传输前后的光谱、眼图和误码率等指标,测试结果表明: 10 Gb/s偏振复用双二进制信号在晴天条件下 经1km自由空间光无线信道传输后的接收眼图清晰可见,信号接收质量较高,并在误码率为 10－6情况下,测得经偏振解复 用后解调还原的两路数据信号的最佳解调判决点分别为0.5 bit和0.51 bit,系统接收机灵敏度为－2.7 dBm,该接入系统方案具 有良好的收发及传输性能。与常规接入通信方式相比,该方案不仅能够有效提升有限带宽内 的信号光谱效率,还能在三 峡库区的特殊地形区域实现“最后一公里”接入信号的自由空间高速无线传输。     

无线光通信FSO技术

当宽带接入的概念深入到我们身边时,各种接入技术在“最后一公里”的不同位置上争夺着自己的势力范围。但在一些特殊的应用领域或场合下,我们常见的这些接入方案往往在“最后一公里”的某些段落上,存在布设、成本、带宽等许多方面的一些限制,现在,一种结合了无线与光纤技术的宽带连接方案——FSO(Free Space Optics,无线光通信)正悄然兴起,有望能填补宽带接入市场的这些缝隙FSD——现代十大热门电信技术中之一,这种技术已经得到越来越广泛的重视和认可。     

各种有线接入技术比较与应用

所谓接入网是指连接用户和业务节点之间的电信网络,用户通过用户／网络接口（UNI）与它相连,它通过业务节点接口（SNI）与业务节点（SN）相连,并通过Q3接口与电信管理网络（TMN）相连。对于有线接入网络来说,在解决宽带接入时,光纤进一步向用户延伸是不可避免的。就目前的经济、技术和市场来看,FTTB、FTTC、FTTCabinot禾DFTTZ应当是目前采口近期光摄入网络的重点。各种光接入网的结构如图1所示。对于FTTB、FTTC、FTTCabinet和FTTZ方式,在技术上有两个需要解决的问题：一是光纤网络单元（ONU）与光纤线路终端（OL…     

无线光通信FSO技术

当宽带接入的概念深入到我们身边时，各种接入技术在“最后一公里”的不同位置上争夺着自己的势力范围。但在一些特殊的应用领域或场合下，我们常见的这些接入方案往往在“最后一公里”的某些段落上，存在布设、成本、带宽等许多方面的一些限制。现在，一种结合了无线与光纤技术的宽带连接方案——FSO(Free Space Optics，无线光通信)正悄然兴起，有望能填补宽带接入市场的这些缝隙。FSO——现代十大热门电信技术中之一，这种技术已经得到越来越广泛的重视和认可。     

Fixed access network technologies

Telecommunications operators around the world are facing flat or declining revenues in their traditional services and expanding commercial and political demand for ubiquitous broadband access. This creates two opposing pressures — to cut costs radically and to invest heavily in new technology. The traditional fixed access network is central to both of these issues and this paper describes the technology that is being developed to meet these challenges.     

Broadband access using wireless-over-fibre technologies

This paper describes a number of wireless-over-fibre technologies for broadband access which are being investigated in the Photonics Group at University College London (UCL). In particular, the paper will report the asymmetric Fabry-Perot modulator/detector (AFPM), functioning not only as an optical modulator in the uplink direction, but also as a conventional photodetector in the downlink direction in a single device. Compared to the existing waveguide type electro-absorption modulator, the AFPM is polarisation-insensitive to light, simpler to fabricate and uses only a single optical fibre for both uplink and downlink transmissions, and therefore has the potential to lower the costs of future picocell deployments. Direct modulation of a semiconductor laser is the simplest way to generate modulated optical signals. In the presence of multiple large modulation signals, however, intermodulation or inter-channel distortion can easily be generated in the semiconductor laser and affect other lower power neighbouring channels. A feed-forward linearisation technique for directly modulated semiconductor lasers, capable of operating at frequencies above 5 GHz, has been developed and will be described in detail in this paper. Most modern commercial buildings already have a multimode optical fibre (MMF) infrastructure for carrying the Ethernet data. To provide cost-effective and reliable indoor cellular and wireless local area network (WLAN) coverage without dependence on the radio penetration from outside base-stations, it is highly desirable that the same MMF infrastructure be used to carry these additional services between the equipment room and the remote antenna units around the building. Although not previously regarded as having sufficient bandwidth, it has now been shown that MMF can successfully carry microwave modulated optical signals, including GSM1800 and UMTS cellular radio. Use of MMF for multiservice, multioperator in-building radio coverage has been demonstrated in a collaboration between UCL and the University of Cambridge and will be described in this paper. As the number of cellular and broadband WLAN devices increases, the lower parts of the radio spectrum are becoming more and more congested. To meet the demand for ever higher data transmission rates, other parts of the radio spectrum are being considered for these applications, particularly the millimetre-wave region (30 GHz and above). One of the challenges facing such systems is the generation and delivery of a low phase noise precisely synchronised local oscillator signal. In this paper, a simple optical heterodyne source with two injection locked slave lasers and a more environmentally robust source using an optical injection phase lock loop will be described, together with signal distribution using a bidirectional semiconductor optical amplifier in a coarse wavelength division multiplex fibre ring architecture. Finally it will be argued in the conclusions that future broadband wireless-over-fibre access networks will be required to provide multiservice and multi-operator coverage for buildings, and having the required technologies at sufficiently low cost will be the key factor to success.     

An overview of broad-band access technologies

The provision of broad-band services based on either the Internet or the asynchronous transfer mode (ATM) technique requires a new generation of access networks. In the short term, solutions such as x-digital subscriber line (DSL) and hybrid fiber coaxial (HFC), allowing the reuse of existing infrastructures look very promising. For the longer term, new infrastructures based either on radio or on optical access links seem preferable. Three x-DSL techniques aiming at high-bit-rate transmission over twisted pairs are presented: high-bit-rate DSL, asymmetrical DSL, and very-high-bit-rate DSL. An extension of existing cable television networks known as HFC is also described. Two other prospective approaches, wireless in the loop (WITL) and fiber in the loop (FITL), are then presented. Several techniques are considered for WITL: digital enhanced cordless telecommunication local multipoint distribution service, wireless ATM, and low Earth orbit satellite constellations. The various architectural alternatives for the FITL approach are discussed, a special interest being dedicated to the synchronous digital hierarchy self-healing loop and the ATM over a passive optical network. We mention the main experiments and the standardization activities inherent to the domain     

FSO应用实例

一个极有潜力的大客户, 蛇口少有的高层办公楼之一,要求在一周内开通数据及语音业务,带宽要求一次开通8个E1。中国联通深圳分公司与该客户接触最早, 并获得了客户的认可。基础网络部在工程实施前考察时发现,离客户最近的机楼设在蛇口赤湾的炮台旁边, 但从该机楼到客户的大楼没有铺设光缆, 无法直接通过光缆为客户开通业务。深圳联通首先想到租用某运营商的管道资源, 却遭到该运营商的拒绝。继而深圳联通提出采用微波设备,但遭到客户所在大楼物业的阻拦,理由是微波有辐射,客户对微波链路的质量也持怀疑态度。最后,深圳联通与世纪人通讯联系,…     

EPON媒体接入控制的关键技术研究

文章简要介绍了基于以及太网的无源光网络（EPON）这种新型的接入网技术，将其与基于ATM技术的无源光网络（APON）的优缺点进行了比较，并对其媒体接入控制（MAC）的关键技术测距及上行接入进行了讨论，初步提出了光网络单元（ONU）的软、硬件实现方案。     

LTE与其它技术的对比

1 LTE技术与其他技术对比 1.1 调制技术 为了适应不断变化的无线信道,HSDPA,WiMAX 和 LTE 都采用了多种调制方式,同时都可以根据无线信道质量的变化,动态改变调制方式,以使得传输的性能最优.