ATM traffic management in an LMDS wireless access network

We investigate the capacity of LMDS to support ATM services in the local loop. In particular, we evaluate the performance of a MAC protocol for this system when transporting voice and IP traffic using the VBR and GFR service categories of ATM, respectively. Our results show that the MAC protocol is well suited for voice traffic but in general lacks efficient bandwidth management mechanisms to support the more dynamic bandwidth requirements of IP traffic     

Broadband access: comparing alternatives

Capital investments by network providers to develop broadband access for the information superhighway have inherent risks. Nevertheless, potential rewards to telephone companies, cable TV companies, and others for serving the end consumer in an expanding information economy make such investments a business imperative. This article focuses on the incumbent terrestrial access providers, the telephone local exchange carriers (LECs) and cable multiple system operators (MSOs). First, it cites the business environment and the information highway services that are driving local telephone and cable companies to invest in broadband access, as evolving technology and relaxing regulation enable the convergence of these two industries. Broadband access technologies are then reviewed and evolutionary paths from the respective embedded bases are considered, with respect to both today's choices and the long-term vision. The two choices for broadband access are loosely termed hybrid fiber-coax (HFC) and switched digital video (SDV). The thrust of this article is to explain why these two alternatives overshadow all others and to highlight the decision factors facing network providers in choosing between them     

不同运营商间多媒体消息业务互通关键问题

多媒体消息业务(MMS)逐渐成为运营商继短信业务后又一重要的收入增长点.不同运营商的MMS的互通有助于MMS产业快速发展,更好满足用户的通信需求.本文探讨、分析了MMS网间互联互通时,网间承载协议、媒体格式、终端支持、网间互联架构等关键问题.比较了MMSC,IWGW合设、分设,全国一点互联、分省多点互联的优缺点,在此基...     

IEEE 1547 series of standards: interconnection issues

IEEE 1547 2003 standard for interconnecting distributed resources with electric power systems is the first in the 1547 series of planned interconnection standards. Major issues and a wealth of constructive dialogue arose during 1547 development. There was also a perceived increased vitality in updating complementary IEEE standards and developing additional standards to accommodate modern electrical and electronics systems and improved grid communications and operations. Power engineers and other stakeholders looking to the future are poised to incorporate 1547 into their knowledge base to help transform our nation's aging distribution systems while alleviating some of the burden on existing transmission systems.     

LMDS系统及应用实例

近年新兴的宽带无线接入技术本地多点分配业务（ＬＭＤＳ）具备带宽高、覆盖面积大及双向数据传输等特点,可提供高质话音、高速Ｉｎｔｅｒｎｅｔ访问、帧中继、ＶＰＮ等业务。最后本文给出了国内电信运营商的ＬＭＤＳ试验网的应用实例。     

Architectural issues for robust optical access

Optical access networks are beginning to be deployed at the edge of the optical backbone network to support access by the high-end users that drive increased bandwidth demands. This development in the applications of optical networking poses new challenges in the areas of medium access, topology design, and network management. In particular, since optical access networks carry high volumes of critical traffic, the level of reliability and robustness traditionally reserved for core applications must be implemented in access networks. We survey access network architectures and outline the issues associated with providing reliability for these architectures. In the area of architecture design, two main approaches emerge. The first considers dedicated optical access networks, such as stars or folded buses, to implement optical access LANs and MANs. The second is overlay architectures, which use existing network infrastructure. Overlay architectures seek to replicate, on a smaller scale, logical topologies akin to those of backbone networks, or may instead create architectures specifically designed for access purposes     

光码分多址相位编/解码器

介绍了几种基于相干光的光码分多址(OCDMA)相位编/解码器.分别给出了采用空间光调制器(SLM)、平面光波导(PLC)、超结构光纤布喇格光栅(SSFBG)技术的OCDMA编/解码器的工作原理及最新研究进展,并分析了它们的特点.基于SSFBG的编/解码器在产生超长光学码方面是最好的;平面光波导编/解码器由于可实现单片集成,也是一种很有前途的器件.     

LMDS应用及其发展

对宽带无线接入的基本概念作了介绍，对本地多点分配业务（LMDS）的原理、体系结构和协议、技术特点进行了较为详细的分析，并对其技术的优缺点、发展现状和前景进行了探讨。     

Bandwidth- and power-efficient multicarrier multiple access

Orthogonal frequency-division multiple access (OFDMA) gains increasing attention for broadband, high data rate wireless communications. We develop a novel unitary precoded (UP) OFDMA scheme that is particularly appealing for the uplink, because it offers high bandwidth efficiency, and constant modulus transmissions for each user. Theoretical analysis of UP-OFDMA with channel coding shows the performance improvement introduced by unitary precoding. It provides useful guidelines for practical system designs, and also quantifies the performance of UP-OFDMA relative to the single-user bound. Simulations confirm that UP-OFDMA improves performance considerably relative to conventional OFDMA.     

LMDS systems and their application

Local multipoint distribution systems (LMDS) represent a new radio-based access technology with cellular architecture offering flexible high-capacity connections to private users and organizations. The systems employ a point-to-multipoint broadcast downlink with a total capacity of 36-38 Mb/s per transport stream, giving high flexibility for inclusion of any type of data. The interactive channel, being a point-to-point connection, may employ different technologies depending on availability and user demand for capacity. This capacity may basically range from a few kilobits per second up to at least 25.6 Mb/s. LMDS performance relative to other broadband access technologies is discussed. A major remaining development task is the establishment and verification of methods for coverage of normally shielded areas. The availability of cheap repeaters and possibly reflectors for increased coverage is a must, which will significantly improve coverage. The LMDS technology, now in its first stage of implementation, is expected to enhance development of broadband services such as e-commerce and tele-teaching     

Reservation CSMA/CD: a multiple access protocol for LAN's

A multiple-access protocol for local area networks is described. It is basically a hybrid of carrier-sense multiple access with collision detection (CSMA/CD) and the broadcast recognizing access method (BRAM). CSMA/CD, which is contention-based, works well under light traffic, but message collisions degrade system performance when the channel becomes heavily loaded. BRAM, which is collision-free, has no longer delays at low load, but its efficiency improves as the load increases. Performance models are developed for the hybrid protocol and for the Ethernet protocol, a proven commercial implementation of CSMA/CD-type protocols. It is found that the hybrid protocol gives better performance for a wide range of scenarios     

UWB多址技术的研究

UWB技术不需载波,能直接调制脉冲信号,产生带宽高达几GHZ的窄脉冲波形,其带宽远远大于目前任何商业无线通信技术所占用的带宽.超宽带系统的成功,很大程度上依赖于有效的多址技术的发展.主要研究内容是超宽带无线通信系统中的多址技术.通过计算机仿真的方法,比较了TH-UWB和DS-UWB两种多址方式的多址性能,得出DS-UWB无论是用户容量还是误比特率都要优于TH-UWB.     

Fair power-level division multiple access

Power-level division multiple access (PDMA) exploits the capture effect to generalize and improve time-division multiple access (TDMA). The original PDMA scheme, however, is not fair because in every cycle one station may capture another station a greater number of times. In this letter, we propose a permutation method to assign transmission power levels and time slots to every station, so that in every cycle any two stations can capture each other the same number of times     

Energy-efficient multiple access protocol design

We provide a systematic approach based on the generalized tree protocol proposed earlier to optimize the power management associated with multiple access schemes given instantaneous feedback available. For the target protocol structure of our interest, we show the individual effect of the power consumption in transmission, reception and standby modes on the optimization, and the divarification between optimizing system utilization and power management     

Ultra-wideband for multiple access communications

Ultra-wideband wireless communications techniques have many merits, including an extremely simple radio that inherently leads to low-cost design, large processing gain for robust operations in the presence of narrowband interference, covert operations, and fine time resolution for accurate position sensing. However, there are a number of challenges in UWB receiver design, such as capturing multipath energy, intersymbol interference especially in a non-line-of-sight environment, and the need for high-sampling-rate analog-to-digital converters. In this article, we provide a comprehensive review of UWB multiple access and modulation schemes, and their comparison with narrowband radios. We also outline the issues with UWB signal reception and detection, and explore various suboptimal low-complexity receiving schemes     

Minislotted packet reservation multiple access

A minislotted packet reservation multiple access (PRMA) protocol is proposed in response to the disadvantage of PRMA wherein an entire slot is wasted in the event of a collision. The proposed protocol is shown to yield improvements over PRMA at the expense of introducing small amounts of additional clipping in some talkspurts.<>     

Feedforward multiple access satellite communications

Satellite communications modeled by a feedforward random multiple-access system are considered. The transmission times of the users are governed by protocol signals. The authors consider the model of a slot-synchronized collision channel without feedback, proposed by J.L. Massey and P. Mathys (1985), augmented by interleavers that are essential for enabling the use of practical short codes. They assess the throughput of the channel on the basis of a short-coding error parameter. The set of parameters of all users characterizes the rate region achievable by employing short block codes with nonideal interleaving. The short-coding error parameter corresponds to a bound on the probability of error which is tighter than the bound expressed with the aid of the conventional cut-off rate. The analysis takes into account practical communication aspects, such as the effect of interleaving span and noise in noninterfered slots