Expressnet: A High-Performance Integrated-Services Local Area Network

Expressnet is a local area communication network comprising an inbound channel and an outbound channel to which the stations are connected. Stations transmit on the outbound channel and receive on the inbound channel. The inbound channel is connected to the outbound channel so that all signals transmitted on the outbound channel are duplicated on the inbound channel, thus achieving broadcast communication among the stations. In order to transmit on the bus, the stations utilize a distributed access protocol which achieves a conflict-free round-robin scheduling. This protocol is more efficient than existing round-robin Schemes as the time required to switch control from one active user to the next in a round is minimized (on the order of a carrier detection time), and is independent of the end-to-end network propagation delay. This improvement is particularly significant when the channel data rate is so high, or the end-to-end propagation delay is so large, Or the packet size is so small as to render the end-to-end propagation delay a significant fraction of, or larger than, the transmission time of a packet. Moreover, some features of Expressnet make it particularly suitable for voice applications. In view of integrating voice and data, a simple access protocol is described which meets the bandwidth requirement and maximum packet delay constraint for voice communication at all times, while guaranteeing a minimum bandwidth requirement for data traffic. Finally, it is noted that the voice/data access protocol constitutes a highly adaptive allocation scheme of channel bandwidth, which allows data users to recover the bandwidth unused by the voice application. It can be easily extended to accommodate any number of applications, each with its specific requirements.     

End-To-End Performance Modeling of Local Area Networks

This paper presents a generic modeling framework for synthesizing existing modeling techniques into a hierarchical structure for representing the end-to-end path between subscriber devices on local area networks (LAN's). The modeling framework is based on analytical queueing network models in a hierarchical decomposition along the layers of communications protocols in the LAN. The methodology can be used during the various phases of LAN system design as well as for capacity planning during the operational phase. The level of system detail that can be examined using the methdology ranges from the architectural level to the component level. A survey of existing LAN models is given and their applicability to the heirarchical framework is discussed. The methodology is described and a case study is presented.     

Throughput-Delay Performance of Interconnected CSMA Local Area Networks

The interconnection of two local area networks, each of which connects a large population of users via a carrier-sense multipleaccess (CSMA) channel is considered. In each network, a bridge node receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link; the bridge node of the destination network queues these internetwork packets for subsequent broadcasting to the local users. For the multiplexing of the user transmissions and the bridge node transmissions on the available broadcast channel in each network, frequency division, and contention are considered. The throughput-delay characteristics of the interconnected system operating under the above multiplexing techniques are found and comparisons are made. It is shown that contention multiplexing can yield system performance comparable to that of frequency division multiplexing, while requiring no hardware or software modification of either network in the interconnected system.     

Saturation Performance of IEEE 802.11 Broadcast Networks

In this letter, saturation performance of broadcast service in IEEE 802.11 is studied analytically and by simulation. Having investigated the features of the broadcast service, we point out that the analytic models for saturation performance evaluation of IEEE 802.11 unicast communication cannot be simply reduced for analysis of broadcast service. Under realistic assumptions, we construct an analytic model to characterize operation of the backoff counter for broadcast, thus obtain closed form solutions to the saturation throughput and packet delivery ratio. Simulation validates the proposed model. Numerical results reveal characteristics of the broadcast service.     

Performance of a CSMA/CD Protocol for Local Area Networks

In this paper we present a performance analysis of a CSMA/CD protocol designed to effectively resolve collisions in a local area network such as Ethernet. We give expressions for the average time required to resolve a collision involvingkstations and the average time for a particular station involved in ak-way collision to send its packet successfully. We also consider the efficiency of this protocol and give a lower bound for the maximum efficiency. The above analysis is independent of any particular packet arrival distribution other than the assumptions that in a successful transmission each station is equally likely to be the one transmitting, that in a collision each station is equally likely to be a participant, and that the probability of the simultaneous arrival of packets is zero.     

无线局域通信网

文章介绍了无线局域网的传输技术、网络拓扑、基本网络组成,以及与其他网络集成的技术,并在此基础上简单介绍了其应用与发展前景。     

IEEE 802.11 Wireless Local Area Networks

The draft IEEE 802.11 wireless local area network (WLAN) specification is approaching completion. In this article, the IEEE 802.11 protocol is explained, with particular emphasis on the medium access control sublayer. Performance results are provided for packetized data and a combination of packetized data and voice over the WLAN. Our performance investigation reveals that an IEEE 802.11 network may be able to carry traffic with time-bounded requirements using the point coordination function. However, our findings suggest that packetized voice traffic must be handled in conjunction with an echo canceler     

Multimedia Broadcast Multicast Service Performance and its Enhancements in WCDMA Networks

Multimedia Broadcast Multicast Service (MBMS) in Wideband Code Division Multiple Access (WCDMA) networks is used to transmit information from one source to vast amount of recipients. The MBMS technique eases the load of the network and therefore allows network to serve more subscribers. The very aim of this study is to evaluate the performance of Release 6 MBMS and its performance enhancements in WCDMA networks. Special attention will be focused on macro and receive diversity which are considered in addition to time diversity provided by long interleaving as enhancements on MBMS performance. 3GPP Release 6 specifications for MBMS introduce two macro diversity schemes: soft and selective combining. The effect of those combining scheme concepts together with and without receive diversity provided by multiple receive antennas are examined. Also, a concept closely related to the receive diversity called Rx-switching i.e., turning the another receive antenna off in good channel situations for power saving purposes is studied. The system level performance of MBMS point-to-multipoint (p-t-m) mode is evaluated with dynamic system level tool in which e.g., mobility of users and interactions of the radio resource management functionalities are explicitly taken into account. Our studies indicate that macro diversity brings significant gains to the MBMS performance. Receive diversity together with macro diversity schemes improves the performance even more and therefore enhances the cell throughput that MBMS can offer. Furthermore, based on the findings of this study it seems that 2Rx Rake receiver can operate with a single antenna significant amount of time without sacrificing desired coverage and thus provide clear power saving opportunities.

Radio Planning of Wireless Local Area Networks

In this paper we propose mathematical models to tackle the WLAN planning problem. Our approach aims at maximizing network efficiency by taking into account the inter-AP domain interference and the access mechanism. Both the single-channel and the multiple-channel WLAN planning problems are considered. We give different formulations which capture at different levels of detail the effect of interference on the network efficiency. In order to evaluate the quality of the proposed models, we obtain the optimal solutions for synthetic network instances, and propose heuristics to get suboptimal solutions in a reasonable computing time. We show that the networks planned according to our approach feature higher efficiency than the ones planned using classical models, like the minimum-cardinality set covering problem (SCP), by privileging network solutions with low-power APs installed. The achieved gain reaches 167% in particular network scenarios. Moreover, we test the obtained solutions through simulation and real-life testbed implementation; both analyses show that the networks planned with the proposed approaches are the ones with the highest saturation throughput with respect to those configurations obtained with SCP.     

WDM局域网的数据传送算法

针对单跳波分复用（ＷＤＭ，Ｗａｖｅｌｅｎｇｔｈ Ｄｉｖｉｓｉｏｎ Ｍｕｌｔｉｐｌｅｘｉｎｇ）访问控制协议中的两大难点：可调光器件的调谐时延比较大，以及网络的传播时延相对于单位分组的传输时延比较大，本文提出了几种数据传送算法，这些算法都是以信息最早地无接收碰撞传送为基本目标，本文对这些数据传送算法的基本特性进行了分析，并用大量的计算机模拟结果对算法的性能进行了比较和分析     

Kernel-Based Positioning in Wireless Local Area Networks

The recent proliferation of location-based services (LBSs) has necessitated the development of effective indoor positioning solutions. In such a context, wireless local area network (WLAN) positioning is a particularly viable solution in terms of hardware and installation costs due to the ubiquity of WLAN infrastructures. This paper examines three aspects of the problem of indoor WLAN positioning using received signal strength (RSS). First, we show that, due to the variability of RSS features over space, a spatially localized positioning method leads to improved positioning results. Second, we explore the problem of access point (AP) selection for positioning and demonstrate the need for further research in this area. Third, we present a kernelized distance calculation algorithm for comparing RSS observations to RSS training records. Experimental results indicate that the proposed system leads to a 17 percent (0.56 m) improvement over the widely used K-nearest neighbor and histogram-based methods     

Fiber Optic Configurations for Local Area Networks

A number of fiber optic configurations for a new class of demand assignment multiple-access local area networks requiring a physical ordering among stations are proposed. In such networks, the data transmission and linear-ordering functions may be distinguished and be provided by separate data and control subnetworks. The configurations proposed for the data subnetwork are based on the linear, star, and tree topologies. To provide the linear-ordering function, the control subnetwork must always have a linear unidirectional bus structure. Due to the reciprocity and excess loss of optical couplers, the number of stations that can be accommodated on a linear fiber optic bus is severely limited. Two techniques are proposed to overcome this limitation. For each of the data and control subnetwork configurations, the maximum number of stations as a function of the power margin, for both reciprocal and nonreciprocal couplers, is computed.     

Enhancing the Performance of Spectrum Mobility in Cognitive Radio Local Area Networks Using KF-ABF-SRE Estimators

Wireless Personal Communications - This paper aims at improving the performance of spectrum mobility in cognitive radio local area networks under a congested environment. Due to the atmospheric...     

Interconnection of CSMA Local Area Networks: The Frequency Division Approach

This paper considers the interconnection of two local area networks, each of which connects a large population of users via a carrier-sense multiple-access (CSMA) channel. In each network a bridge node receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link; the bridge node of the destination network queues these internetwork packets for subsequent broadcasting to the local users. The available broadcast channel in each of the two networks is frequency divided into a bridge node subchannel, used for bridge node transmissions, and a CSMA user subchannel, used for user transmissions. For the interconnected system, stability conditions, optimal bandwidth allocations, and throughput delay characteristics are found. Also it is shown that the performance of a single CSMA network can be substantially improved by partitioning it into smaller interconnected networks.     

A New Approach for Transmitting Local Content Within Digital Single Frequency Broadcast Networks

Current broadcast networks make use of either a single frequency network (SFN) or a multi frequency network (MFN) approach. In this paper a new scheme is presented which combines the strength of both MFNs and SFNs. Considerations towards the implementation with digital video broadcasting-handheld (DVB-H) are also given. The applicability of this concept is shown by a signal propagation simulation and an efficiency study.     

Load Distribution in Non-homogeneous Wireless Local Area Networks

This paper presents an approach to distributing traffic among capability-varying access points (APs) in wireless Local Area Networks. Under consideration is a non-homogeneous environment where maximum transport rates over radio channels differ from AP to AP. We let each new station associate itself to a best-fit AP, allowing for received signal strength, potential responsiveness, and remaining channel capacity of every AP in range. Our approach is developed for alignment with standard protocols, keeping legacy stations operable while maintaining forward compatibility. Our development augments the functionality of APs such that association is decided by APs collaboratively. Simulation results show that our approach outperforms counterpart schemes by an appreciable amount in terms of throughout, transmission delay, and load distribution. Our approach is also of avail to homogeneous network settings. Featuring simplicity and efficiency, our design lends itself to other types of contention-based wireless network like ZigBee as well.     

Tokenless Protocols for Fiber Optic Local Area Networks

A family of LAN (Local Area Network) protocols is presented. The LAN consists of a pair of unidirectional fiber optic buses to which stations are connected via passive taps. The protocols provide round-robin bounded delay access to all stations. Contrary to most roundrobin access schemes, the protocols do not require transmission of special packets (tokens); rather, they simply rely on the detection of bus activity at each station. The performance of these protocols in various traffic conditions and system configurations is evaluated via analysis and simulation.     

用于无线局域网的扩频技术

无线局域网是计算机通信系统中的一个重要的组成部分，具有传输速率高、安全保密性强，使用灵活方便等特点，扩频技术不仅具有很强的抗干扰性能，而且其多址功能、安全保密、抗多径干扰等功能也备受人们青睐，把扩频技术用于无线局网中，必将使无线局域网的整体性能大大提高，满足各种情况下对系统的要求。     

Spread-Spectrum Access to Mixed Voice-Data Local Area Networks

The various issues relating to the use of direct-sequence (DS) spread-spectrum (SS) modulation as access protocols for a local computer network are investigated. Voice and data messages having different traffic characteristics are packetized and the information bits DPSK modulated, after which spreading by the DS gives the waveform to be transmitted. Each node within the network will have a SS modem, to which all kinds of voice and data sources of different rates can be connected. Each node will be characterized by a certain DS code, thus getting security as a fringe benefit. Except for the code circuit, all SS modems will look the same; moreover, all the DS signals transmitted will have the same spectral properties, thus achieving uniformity and modularity of signals and equipments throughout the network. Among the performance criteria, we choose the signal-to-noise ratio (SNR) at the demodulator, the packet delay, the probability of correct packet detection, and the useful throughput. A new definition is suggested for the network efficiency and all performance criteria for the proposed network are compared to those of a classic FDMA/ALOHA-type network under the same circumstances.     

大洋网与播控系统的发展

文章以南通电视台大洋网制作播出网为例 ,从数字压缩技术、硬盘容量及硬盘控制、管理技术 ,探讨了网络播控系统的方向