Radio resource management in wireless LANs

Some chief information officers and information technology managers are reluctant to deploy wireless LANs. Among their concerns are reliability, availability, performance, and deployment. Each of these concerns can be directly addressed through the radio resource management techniques used in a new generation of wireless LAN equipment. The new capabilities include dynamic channel assignment, dynamic power control, and load sharing. Changing from the relatively static radio resource management techniques generally in use today to dynamic methods like those highlighted in this article helps to increase the capacity and improve the performance of large-scale wireless LANs.     

Performance analysis of a large interconnected network bydecomposition techniques

A study that models the possible configurations of a proposed packet-transport-equipment (PTE)-based university campus network is reported. The function of these PTEs is to receive/forward data packets from/to remote LANs or workstations. The objective is to determine whether the traffic capacity of the proposed network can handle the projected university workload, how different applications impact network load, and where the potential system bottlenecks are. The modeling approach taken treats the interconnected LANs as a hierarchy with the fiber (backbone) ring as the apex. Both analytical and simulation models are developed, with simulation being preferred as the workloads approach saturation conditions     

Analysis and Evaluation of Mobile IPv6 Handovers over Wireless LAN

In this paper, we analyze the IPv6 handover over wireless LANs. Mobile IPv6 is designed to manage mobile nodes movements between wireless IPv6 networks. Nevertheless, a mobile node cannot receive IP packets on its new point of attachment until the handover completes. Therefore, a number of extensions to Mobile IPv6 have been proposed to reduce the handover latency and the number of lost packets. We focus on Fast Mobile IPv6 which is an extension of Mobile IPv6 that allows the use of L2 triggers to anticipate the handover. We compare the handover latency in four specific cases: basic Mobile IPv6, the forwarding method of Mobile IPv6, the Anticipated method, and the Tunnel-Based Handover. The results of the handover latency are calculated with the L2 properties of IEEE 802.11b. In particular, we take into account the L2 handover for different configurations of the wireless network.     

A New Scheme to Avoid Collisions for Broadcast Packets in Wireless LANs

This paper proposes a new approach to avoiding collisions for broadcast packets in distributed wireless LANs. The basic idea is to use in-band pulses to convey the medium access control information for broadcast packets. The new approach extends the basic functionality of the IEEE 802.11 distributed coordination function (DCF) from the unicast case to the broadcast case and significantly improves the broadcasting efficiency in wireless LANs.     

Efficient detection of missing tags for passive RFID systems

One of the most interesting radio‐frequency identification applications is the detection of missing tags along with the objects they are attached to. This process must be executed in a fast and efficient way. A monitoring function may need to be periodically executed in order to implement a reliable detection system, therefore raising the need to optimize its performance, in terms of both time and reliability. The contribution of this paper is twofold; on one hand, we provide a protocol taxonomy for the missing‐tag detection problem, which up to our best knowledge is the first of its class, and on the other hand, we propose two novel protocols for a fast detection of the missing tags in a passive radio‐frequency identification system. By increasing the length of the packets exchanged among the reader and the tags, our protocols are able to reduce the time needed to detect the missing tags, by decreasing the number of broadcast messages in the network. Our results show that our proposals outperform the most recent protocols in the literature, obtaining improvements on the execution time going from 25% to 75%. Copyright © 2016 John Wiley & Sons, Ltd.     

Extended bridge algorithms for large networks

A network bridge is a device that operates at the ISO data link level and routes packets across extended networks, commonly composed of multiple local area networks (LANs) and bridges. A set of algorithms that greatly extends the application of the network bridge is presented. This multitree bridge algorithm allows networks of arbitrary topology and capacity to use bridge routing. The reduced broadcast bridge algorithm alleviates the problem of extraneous broadcasting in large networks built from bridges and packet switches. A method for routing to network users who change their location rapidly, as in mobile cellular radio systems, is presented. An algorithm for efficient multicasting in bridges is given. Application of this technology to the broadband integrated services digital network (BISDN) is proposed     

Optimal Transmission Ranges for Randomly Distributed Packet Radio Terminals

In multihop packet radio networks with randomly distributed terminals, the optimal transmission radii to maximize the expected progress of packets in desired directions are determined with a variety of transmission protocols and network configurations. It is shown that the FM capture phenomenon with slotted ALOHA greatly improves the expected progress over the system without capture due to the more limited area of possibly interfering terminals around the receiver. The (mini)slotted nonpersistent carrier-sense-multiple-access (CSMA) only slightly outperforms ALOHA, unlike the single-hop case (where a large improvement is available), because of a large area of "hidden" terminals and the long vulnerable period generated by them. As an example of an inhomogeneous terminal distribution, the effect of a gap in an otherwise randomly distributed terminal population on the expected progress of packets crossing the gap is considered. In this case, the disadvantage of using a large transmission radius is demonstrated.     

Local-area networks go wireless

As standards emerge, data rates rise, and laptops seek connectivity, wireless LANs are finding a market niche as extensions to wired networks. Wireless LANs have found homes in buildings where installing wires would expose asbestos or destroy historic architecture. They have also proved valuable to companies that often relocate and want networks they can take with them. Another common use is for connecting wired LANs that are physically separated. The growth has been fueled by the desire to add wireless adjuncts to wired LANs, so that mobile workers can keep in constant contact with corporate networks over short distances. The author discusses the befits of wireless LANs. The radio based wireless LAN is discussed including multipath interference and data bottlenecks. The infrared based wireless LAN is also discussed and an inset discusses standards for wireless LANs     

无线网络中基于混合流的高效可靠机会网络编码算法

Although the wireless network is widely used in many fields, its characteristics such as high bit error rate and broadcast links may block its development. Network coding is an artistic way to exploit its intrinsic characteristics to increase the network reliability. Some people research network coding schemes for inter flow or intra flow, each type with its own advantages and disadvantages. In this paper, we propose a new mechanism, called MM NCOPE, which integrates the idea of inter flow and intra flow coding. On the one hand, MM NCOPE utilizes random liner coding to encode the NCOPE packets while NCOPE is a sub protocol for optimizing the COPE algorithm by iteration. In NCOPE, packets are automatically matched by size to be coded. As a result, it improves the coding gain in some level. On the other hand, we adopt the partial Acknowledgement retransmission scheme to achieve high compactness and robustness. ACK is an independent packet with the highest priority rather than a part of the data packets. Compared with existing works on opportunistic network coding, our approach ensures the reliability of wireless links and improves the coding gain.     

A shared-memory virtual channel queue for ATM broadband terminal adaptors

In order to take advantage of the low entry cost of the future public ATM (asynchronous transfer mode) network with shared facilities, it is highly desirable to interconnect different hosts and local area networks (LANs) to the ATM network. The interface between the computer hosts or LANs and the ATM network, commonly called a broadband terminal adaptor (BTA), provides the necessary format conversion for the data packets and the ATM cells. It is conceivable that multiple packets from different virtual channels are interleaved as they arrive at the receive-end BTA. The BTA must have a sufficiently large buffer, called a virtual channel queue (VCQ), to temporarily store the partially received packets. Once a complete packet has been received, it is forwarded to the host or LAN. Whenever the buffer fills with all incomplete packets, a packet must be discarded to make room for others. In this paper, we first study, through computer simulations, the buffer size requirement of a shared-memory VCQ for different numbers of virtual channels at various packet loss probabilities. We then present two different implementation architectures for the shared-memory VCQ, and compare their hardware complexity. The second architecture with linked-queue approach, adopted in our work, requires less buffer and has better scalability to accommodate a large number of virtual channels. Various possible error conditions, such as cell losses in the ATM network and the VCQ buffer overflow, are considered. Corresponding solutions are proposed and included in the VCQ designs.     

Power control and capacity analysis for a packetized indoormultimedia DS-CDMA network

This paper proposes a packetized indoor wireless system using direct-sequence code-division multiple-access (DS-CDMA) protocol. The indoor radio environment is characterized by slow Rayleigh fading with or without lognormal shadowing. The system supports multimedia services with various transmission rates and quality of service (QoS) requirements and allows for seamless interfacing to asynchronous transfer mode (ATM) broadband networks. All packets are transmitted with forward error correction (FEC) using convolutional code for voice packets and Bose-Chaudhuri-Hocquenghem (BCH) code for data packets with an automatic retransmission request (ARQ) protocol and for video packets without ARQ. A queueing model is used for servicing data transmission requests. A power control algorithm is proposed for the system, which combines closed-loop power control with channel estimation to give the best performance. The cell capacity of each traffic type and various multimedia traffic configurations in both single-cell and multiple-cell networks are evaluated theoretically under the assumption of perfect power control. The effect of power control imperfection on the capacity using the proposed power control algorithm is investigated by computer simulation     

基于OPNET交换式局域网仿真建模与分析

常规局域网存在信道利用率不高、时延较大的问题,用户迫切需求使用一种方便快捷、性能良好的网络。针对这一问题,提出了常规局域网的一种改进方式---交换式局域网（ Switching LAN）。介绍了OPNET仿真软件的主要特性、建模机制及仿真步骤。采用OPNET网络仿真软件设计实验,根据2种网络特点建立不同的场景并进行仿真,并通过对比以太网时延、接收数据包流量、数据包冲突数目在不同场景时的变化,证明了交换式局域网的性能明显优于常规局域网。     

Geometry modeling in cellular network planning

To design a cellular radio network (GSM, UMTS, WiFi …) it is indispensable today to use a radio planning software. In current commercialized tools, radio network planning is based on a numerical evaluation of a set of radio metrics, directly linked to quality of service notion, such as interference, throughput, coverage, capacity … The network configurations produced by such tools are generally faced with the human expert judgment who attaches great importance to the organizational aspects such as cells size and the topology. In other words, all those concepts related to the visual cells shape and geometry. In this article we emphasize the simplicity and the strength by which the geometrical concepts helps to bring out good network properties which are not taken into account by conventional radio criteria. On one hand, well-formed cells lead to reduce the number of handover calls, and to form transition zones between cells allowing proper completion of the handover procedure. On the other hand, cell geometry optimization produce performing network schemes in which the frequencies reuse (frequencies planning in GSM, WiFi) is simplified. We describe in this paper an original and practical modeling of the cellular geometry criteria granting the integration of this concept into the automatic planning process of mobile radio networks. The relevance of this criterion is assessed on three different levels. On a local level, we first establish the correlation between the geometric criteria and the improvement of point-by-point radio quality indicators. We secondly show geometry impact on radio frequency planning and the improving of the handover zones. Finally we analyze the impact of geometric criterion on improving indoor positioning systems.     

A Statistical Method for Reconfiguration of Cognitive Radios

Recent developments in computer technology have enabled radio developers to accomplish in software what traditionally was performed with application-specific integrated circuits. A radio that has the core of its functionality implemented in software is called a software-defined radio. When an SDR has the capability to sense, reason, and dynamically adapt to requirements and environmental change, we call this more capable device a cognitive radio. Many private and public agencies are investing in the promise of CR to improve the utilization of radio frequency spectrum. They envision devices that can sense frequency vacancies and dynamically reconfigure to utilize idle channels. The promise of CR depends on the capability of a radio to change operating frequencies, power, and/or modulation schemes (physical layer flexibility). In addition to this physical layer flexibility, there are a large number of opportunities to capitalize on the interplay of the CR physical layer configuration and other parameters in the radio network protocol stack. At the core of CR functionality is the ability to select from thousands of potential configurations to maximize performance-be it in terms of spectrum use, throughput, or reliability. In this article, we describe a method for selecting from a number of potential configurations to fulfill the communication requirements of a CR network. By using accepted statistical methods, we show how parameters at the physical, data link, network, and application layers interact to affect performance. We build upon this parametric insight with our presentation of a technique for predicting radio performance.     

Congestion control in interconnected LANs

The reasons why congestion control is more difficult in interconnected local area networks (LANs) than in conventional packet nets are examined. The flow and congestion control mechanisms that can be used in an interconnected LAN environment are reviewed. The focus is on congestion control (that is, prevention of internal congestion); however some of the proposed schemes require the interaction of flow and congestion control. The schemes considered are dropping packets; input buffer limit, i.e. a limit on the number of input packets (i.e. packets from local hosts) that can be buffered in the packet switch; the use of choke packets, in which, whenever a bridge or router experiences congestion, it returns to the source a choke packet containing the header of the packet traveling in the congested direction and the source, on receiving the choke packet, declares the destination congested, and slows (or stops altogether, for a period of time) traffic to that destination; backpressure, which is the regulation of flow along a virtual connection; and congestion prevention, whereby a voice or video connection is accepted only if there is enough bandwidth (in a statistical sense) in the network to support it     

A future radio-access framework

This paper discusses the requirements on future radio access and, based on the requirements, proposes a framework for such a system. The proposed system based on orthogonal frequency-division multiplexing supports very low latencies and data rates up to 100 Mb/s with wide area coverage and 1 Gb/s with local area coverage. Spectrum flexibility is identified as one main requirement for future systems, and the proposed framework can be deployed in a wide range of spectrum allocations with bandwidths ranging from 2.5 to 100 MHz. Multihop relaying, useful to extend the range for the high data rates, and multiple-antenna configurations are integral parts of the framework. A packet-centric approach is taken for the dataflow processing, implying that the scheduling mechanism and the retransmission protocol operate on complete packets rather than segments thereof, thus allowing for cross-layer optimization. Finally, numerical evaluations are provided, illustrating the feasibility of future very wideband radio access.     

The Effect of Terminal Movement on the Performance of IEEE 802.11 g Wireless LAN Systems in Simulated Radio Channels

The effect of terminal movement on the performance of the IEEE 802.11 g wireless LAN (WLAN) system is evaluated using a measurement set-up including a radio channel simulator. The evaluation is based on laboratory measurements of WLAN PC cards in different simulated radio environments. In the measurements, two different radio channel models are used; the exponential channel model and the UMTS vehicular channel model. The measurement results indicate promising operation of IEEE 802.11 g WLAN systems as such. However, the use of different packet sizes has a significant effect on the system behaviour. With large packets the terminal is more likely to experience channel estimation errors than with small packets. This is due to the fact that the IEEE 802.11 g receiver estimates the channel only once per frame, and uses this estimation over the entire frame. Based on the measurement results we suggest a modification to the medium access control (MAC) layer operation that overcomes this problem: the use of optimized fragmentation.     

Delay analysis for forward signaling channels in wireless cellularnetwork

We consider connection-oriented wireless cellular networks. Such second generation systems are circuit-switched digital networks which employ dedicated radio channels for the transmission of signaling information. A forward signaling channel is a common signaling channel assigned to carry the multiplexed stream of paging and channel-allocation packets from a base station to the mobile stations. Similarly, for ATM wireless networks, paging and virtual-circuit-allocation packets are multiplexed across the forward signaling channels as part of the virtual-circuit set-up phase. The delay levels experienced by paging and channel-allocation packets are critical factors in determining the efficient utilization of the limited radio channel capacity. A multiplexing scheme operating in a “slotted mode” can lead to reduced power consumption at the handsets, but may in turn induce an increase in packet delays. In this paper, focusing on forward signaling channels, we present schemes for multiplexing paging and channel-allocation packets across these channels, based on channelization plans, access priority assignments and paging group arrangements. For such multiplexing schemes, we develop analytical methods for the calculation of the delay characteristics exhibited by paging and channel-allocation packets. The resulting models and formulas provide for the design and analysis of forward signaling channels for wireless network systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of a Two-Hop Centralized Packet Radio Network--Part I: Slotted ALOHA

The design of packet radio systems involves a large number of design variables that interact in a very complex fashion. As this design problem in its general form is quite complex, a viable approach is to analyze some simple but typical configurations in an attempt to understand the behavior of these systems. In this paper, a two-hop centralized configuration is considered in which traffic originates at terminals, is destined to a central station, and requires for its transport the relaying of packets by store-and-forward repeaters. The through-put-delay performance is derived, and its dependence on such key system variables as the network topology, the transmission protocol, and the repeaters' storage capacities, is given. In this part, devices are assumed to be utilizing the slotted ALOHA access mode. Carrier sense multiple access is treated in Part II of this series [1].     

Performance analysis of cognitive radio networks for secondary users with slotted central control

This paper deals with analysis, performance evaluation and optimization of cognitive radio networks with central controller. The main principle of this technology is that secondary users are enabled to make opportunistic use of the spectrum part, which is actually unused by the primary users. The considered network enables heterogeneous slotted structure for the channel, in which the secondary user’s packets are transmitted on a slot basis, while the primary user’s packets are forwarded in super-slots, i.e. in fixed length slot-blocks. This heterogeneous slotted channel structure enables more flexible operation leading to more realistic system model of cognitive radio network. We model the cognitive radio networks by preemptive priority queueing model with two classes of customers. We solve the model by applying Markov chain technique and derive the steady-state distributions of the number of primary user’s packets and secondary user’s packets in the system. We provide the formulas for several performance measures including the interruption rate, loss rate, throughput, and average latency of secondary users. After validating the analysis by simulation the influence of the secondary user’s buffer capacity on various system performance measures is investigated. In the last part of the paper we address the question of optimal design of secondary user’s buffer capacity.