Performance analysis of centralized FH‐CDMA wireless networks

Centralized CDMA networks with unslotted Aloha randomaccess mode are considered. Users communicate with a central node by sharing a finite number of signature sequences assigned to the receivers at the central node. Two methods for sharing preamble codes are considered. In one method a common preamble code is used by all receivers, and in the other method a distinct code is assigned for each receiver. A unified analysis framework for evaluating the performance of centralized FHCDMA networks is developed. Closed form expressions for packet decoding error probabilities are derived. Numerical results show that common preamble codes can support only low traffic levels. However, by appropriately selecting the design parameters, acceptable levels of packet loss probabilities are achievable with the receiverbased preambles.     

Performance analysis of the IEEE 802.16e sleep mode for correlated downlink traffic

In this paper, we evaluate the performance of the IEEE 802.16e sleep mode mechanism in wireless access networks. This mechanism reduces the energy consumption of a mobile station (MS) by allowing it to turn off its radio interface (sleep mode) when there is no traffic present at its serving base station (BS). After a sleep period expires, the MS briefly checks the BS for data packets and switches off for the duration of another sleep period if none are available. Specifically for IEEE 802.16e, each additional sleep period doubles in length, up to a certain maximum. Clearly, the sleep mode mechanism can extend the battery life of the MS considerably, but also increases the delay at the BS buffer. For the performance analysis, we use a discrete-time queueing model with general service times and multiple server vacations. The vacations represent the sleep periods and have a length depending on the number of preceding vacations. Unlike previous studies, we take the (short-range) traffic correlation into account by assuming a D-BMAP arrival process, i.e. the distribution of the number of packet arrivals per slot is modulated by the transitions in a Markov chain with N background states. As results, we obtain the distribution of the number of packets in the queue at various sets of time epochs, the distribution of the packet delay and the antenna activity rate. We apply these results to the IEEE 802.16e sleep mode mechanism with correlated downlink traffic. By means of some examples, we show the influence of both the configuration parameters and the traffic correlation on the delay and the energy consumption.     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

Time-parallel simulation of wireless ad hoc networks

In this paper, we study time-parallel simulation of wireless networks based upon the concept of the perturbation induced by a networking event and present a layer-by-layer analysis of the impact of perturbations on the wireless network. This analysis allows us to propose several methods to improve the accuracy of time-parallel simulation. We describe an implementation based on the widely used ns-2 simulator and on the iterative extension of the warmup period. We introduce a method for initial state approximation which can improve the accuracy of the simulation for table-driven ad hoc routing protocols. A series of experiments show that on typical scenarios time-parallel simulation leads to a significant speedup while maintaining a high level of accuracy.     

Performance analysis of Push-To-Talk over IEEE 802.16e with? sleep mode and idle mode

We investigate how much power saving can be achieved for a Push-To-Talk (PTT) service by employing sleep mode and idle mode in the IEEE 802.16e. In this paper, a mobile station by employing sleep mode during an on-session and idle mode during an off-session of the PTT service is modeled as a semi-Markov chain. We obtain power consumption of the mobile station, call setup delay and talker arbitration delay. Using our mathematical model, we can find the optimal sleep window satisfying the required quality of service (QoS) on call setup delay and talker arbitration delay. The numerical examples show that the sleep mode and idle mode provide a considerable reduction on energy of the mobile stations.     

Scheduling of real‐time traffic in IEEE 802.11 wireless LANs

The desire to provide universal connectivity for mobile computers and communication devices is fueling a growing interest in wireless packet networks. To satisfy the needs of wireless data networking, study group 802.11 was formed under IEEE project 802 to recommend an international standard for Wireless Local Area Networks (WLANs). A key part of the standard are the Medium Access Control (MAC) protocols. Given the growing popularity of real‐time services and multimedia based applications it is critical that the 802.11 MAC protocols be tailored to meet their requirements. The 802.11 MAC layer protocol provides asynchronous, time‐bounded, and contention free access control on a variety of physical layers. In this paper we examine the ability of the point coordination function to support time bounded services. We present our proposal to support real‐time services within the framework of the point coordination function and discuss the specifics of the connection establishment procedure. We conduct performance evaluation and present numerical results to help understand the issues involved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simulation and analysis of node throughput using smart antenna in wireless mesh networks

Smart antenna technology is introduced to wireless mesh networks. Smart antennas based wider-range access medium access control (MAC) protocol (SWAMP) is used as MAC protocol for IEEE 802.11 mesh networks in this study. The calculation method of node throughput in chain and arbitrary topology is proposed under nodes fairness guarantee. Network scale and interference among nodes are key factors that influence node throughput. Node distribution pattern near the gateway also affects the node throughput. Experiment based on network simulator-2 (NS-2) simulation platform compares node throughput between smart antenna scenario and omni-antenna scenario. As smart antenna technology reduces the bottle collision domain, node throughput increases observably.     

Performance evaluation of path optimization schemes for inter‐switch handoff in wireless ATM networks

One of the major design issues in wireless ATM is the support of inter‐switch handoff. An inter‐switch handoff occurs when a mobile terminal moves to a new base station connecting to a different switch. Recently, a two‐phase handoff protocol has been proposed to support inter‐switch handoff in wireless ATM networks. With the aim of shortening handoff delay while using the network resources efficiently, the two‐phase handoff protocol employs path extension for each inter‐switch handoff, followed by path optimization if necessary. To implement the two‐phase handoff protocol efficiently, we need to determine when to trigger path optimization. In this paper, we propose and analyze three path optimization schemes, namely: periodic, exponential, and Bernoulli, for the two‐phase handoff protocol. The design objective is to determine the time to invoke path optimization such that the average cost per connection is minimized. We develop a discrete time analytical model and a discrete‐event simulation model for comparing the performance of the three path optimization schemes. Results indicate that the Bernoulli path optimization scheme outperforms the other two schemes by providing a lower average cost per connection. The proposed models can also be adapted to analyze other path optimization schemes in general. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design and analysis of low‐power access protocols for wireless and mobile ATM networks

This paper describes the design and analysis of a low‐power medium access control (MAC) protocol for wireless/mobile ATM networks. The protocol – denoted EC‐MAC (energy conserving medium access control) – is designed to support different traffic types with quality‐of‐service (QoS) provisions. The network is based on the infrastructure model where a base station (BS) serves all the mobiles currently in its cell. A reservation‐based approach is proposed, with appropriate scheduling of the requests from the mobiles. This strategy is utilized to accomplish the dual goals of reduced energy consumption and quality of service provision over wireless links. A priority round robin with dynamic reservation update and error compensation scheduling algorithm is used to schedule the transmission requests of the mobiles. Discrete‐event simulation has been used to study the performance of the protocol. A comparison of energy consumption of the EC‐MAC to a number of other protocols is provided. This comparison indicates the EC‐MAC has, in general, better energy consumption characteristics. Performance analysis of the proposed protocol with respect to different quality‐of‐service parameters using video, audio and data traffic models is provided. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simulation comparison of active queue management algorithms in TCP/IP networks

Active Queue Management techniques are recommended to overcome the performance limitations of TCP congestion control mechanisms over drop-tail networks. The main objective of this paper is to present the comparative analysis of the performance of 10 different queue management policies using the OMNeT++ simulator. The AQMs have many parameters which influence their behavior, so some results concerning the parameters selection are given. The algorithms are tested in terms of average queue size, packet delay and packet loss rate in presence of TCP traffic.     

Study of the IEEE 802.16 contention-based request mechanism

Broadband wireless access systems offer a solution for broadband access and QoS-aware multimedia services through a wireless medium. The IEEE 802.16 standards specify the physical and medium access control layers for broadband wireless access systems as well as the various mechanisms to meet the quality of service (QoS) requirements of a wide variety of applications. Among the mechanisms defined by the standards, the bandwidth request and grant mechanisms play a central role on guaranteeing the QoS required by the subscriber stations. In this paper, we undertake the study of the bandwidth request mechanisms defined in the IEEE 802.16 standards. We then propose an approach for reducing the overhead required by the signalling mechanisms. Our simulation results show that our approach outperforms the mechanisms proposed in the IEEE 802.16 standards.     

Towards the formation of comprehensive SLAs between heterogeneous wireless DiffServ domains

Traffic patterns generated by multimedia services are different from traditional Poisson traffic. It has been shown in numerous studies that multimedia network traffic exhibits self-similarity and burstiness over a large range of time-scales. The area of wireless IP traffic modeling for the purpose of providing assured QoS to the end-user is still immature and the majority of existing work is based on characterization of wireless IP traffic without any coupling of the behaviour of queueing systems under such traffic conditions. Work in this area has either been limited to simplified models of FIFO queueing systems which do not accurately reflect likely queueing system implementations or the results have been limited to simplified numerical analysis studies. In this paper, we advance the knowledge of queueing systems by example of traffic engineering of different UMTS service classes. Specifically, we examine QoS mapping using three common queueing disciplines; Priority Queuing (PQ), Low Latency Queuing (LLQ) and Custom Queueing (CQ), which are likely to be used in future all-IP based packet transport networks. The present study is based on a long-range dependent traffic model, which is second order self-similar. We consider three different classes of self-similar traffic fed into a G/M/1 queueing system and construct analytical models on the basis of non-preemptive priority, low-latency queueing and custom queueing respectively. In each case, expressions are derived for the expected waiting times and packet loss rates of different traffic classes. We have developed a comprehensive discrete-event simulator for a G/M/1 queueing system in order to understand and evaluate the QoS behaviour of self-similar traffic and carried out performance evaluations of multiple classes of input traffic in terms of expected queue length, packet delay and packet loss rate. Furthermore, we have developed a traffic generator based on the self-similar traffic model and fed the generated traffic through a CISCO router-based test bed. The results obtained from the three different queueing schemes (PQ, CQ and LLQ) are then compared with the simulation results in order to validate our analytical models.     

Performance analysis of an ad hoc network for emergency and collaborative environments

Ad hoc networks can be used for quickly set up small spontaneous networks, such as in emergency situations or during sessions of cooperative works as in conferences, teaching rooms or meetings. Real-life tests of such networks are invaluable in order to assess models used in simulation. However, the number of factors affecting the performance of an ad hoc network is high, theoretically infinite. There are, for example, system factors, such as routing protocols, MAC and physical layer protocols and their cross-layer interaction, as well as environment factors, such as the presence of walls, foliage and surrounding moving objects. In order to optimize protocols, it is important both to design repeatable experiments of the network and to identify the parameters which really affect the system behavior. We accomplish the former demand by building a simple network by means of off-the-shelf hardware and software. For the latter point, we propose to use methods of statistical testing theory to identify these parameters in a compact manner. In particular, we use OLSR as a routing protocol. Results from real experiments in outdoor and indoor scenarios confirm the horizon effect of ad hoc multi-hop networks and show that there is a treatment effect caused by the window size of OLSR.     

Protocol for the application of cooperative MIMO based on clustering in sparse wireless sensor networks

Wireless sensor networks (WSN) using cooperative multiple-input multiple-output (MIMO) communication are effective tools to collect data in several environments. However, how to apply cooperative MIMO in WSN remains a critical challenge, especially in sparse WSN. In this article, a novel clustering scheme is proposed for the application of cooperative MIMO in sparse WSN by extending the traditional low-energy adaptive clustering hierarchy (LEACH) protocol. This clustering scheme solves the problem that the cluster heads (CH) cannot find enough secondary cluster heads (SCH), which are used to cooperate and inform multiple-antenna transmitters with CHs. On the basis of this protocol, the overall energy consumption of the networks model is developed, and the optimal number of CHs is obtained. The simulation results show that this protocol is feasible for the sparse WSN. The simulation results also illustrate that this protocol provides significant energy efficiencies, even after allowing for additional overheads.     

User’s mobility effect on the performance of wireless cellular networks serving elastic traffic

The objective of the present paper is to give an analytic approximation of the performance of elastic traffic in wireless cellular networks accounting for user’s mobility. To do so we build a Markovian model for users arrivals, departures and mobility in such networks; which we call WET model. We firstly consider intracell mobility where each user is confined to remain within its serving cell. Then we consider the complete mobility where users may either move within each cell or make a handover (i.e. change to another cell). We propose to approximate the WET model by a Whittle one for which the performance is expressed analytically. We validate the approximation by simulating an OFDMA cellular network. We observe that the Whittle approximation underestimates the throughput per user of the WET model. Thus it may be used for a conservative dimensioning of the cellular networks. Moreover, when the traffic demand and the user speed are moderate, the Whittle approximation is good and thus leads to a precise dimensioning.     

Performance analysis of STT-RAM with cross shaped free layer using Heusler alloys

We have investigated the performance of a spin transfer torque random access memory (STT-RAM) cell with a cross shaped Heusler compound based free layer using micromagnetic simulations. We have designed a free layer using a Cobalt based Heusler compound. Simulation results clearly show that the switching time from one state to the other state has been reduced, also it has been found that the critical switching current density (to switch the magnetization of the free layer of the STT RAM cell) is reduced.     

Performance Comparison of Long-Wavelength Infrared Type II Superlattice Devices with HgCdTe

The InAs/GaSb family of type II superlattices (T2SL) is the only known infrared (IR) detector material having a theoretically predicted higher performance than HgCdTe. The Auger lifetime has been predicted to be much longer, offering the possibility of much lower dark currents. In this paper the present state of the technology for long-wavelength infrared (LWIR) applications is evaluated by examining the dark current density in LWIR T2SL diodes at 78 K as a function of device cutoff wavelength, and comparing it with the HgCdTe benchmark known as Rule 07. The dark current density remains greater than Rule 07, but it has rapidly decreased in recent years with advancing technology, particularly due to innovative barrier structures.     

Bit-per-joule performance of power saving ad hoc networks with a mobile backbone

Energy efficient MAC protocols have been developed for wireless sensor and mobile ad hoc networks so that inactive nodes can transition into sleep state to conserve energy. It has been recognized that maintaining a continuously awake connected dominating set (CDS) serves to reduce the route setup latency. Under the mobile backbone network (MBN) architecture introduced by Rubin et al., a mobile backbone (Bnet) is dynamically constructed to provide a topological covering of the network. The MBN employs a hybrid routing algorithm under which flows that travel a distance longer than a threshold are directed along routes across the Bnet. In turn, a limited span network-wide global route discovery process is applied for routing shorter distance flows. In this paper, we introduce and analyze an MBN based power saving protocol (MBN-PS) that employs this hybrid routing scheme. Under the MBN-PS scheme, dynamically elected backbone nodes are kept awake, while inactive non-backbone nodes can reside in sleep state. We analytically show that, when the number of network flows is above a minimal level, the throughput per watt efficiency attained in an ad hoc network under complete backbone coverage is better than that achieved by a corresponding network that does not form a backbone. We present a model for the calculation of the bit-per-joule performance of the network as a function of the distance threshold. We confirm the validity of our analytical approach through simulations. Using our method, a network designer is able to choose the optimal distance threshold to be used by this scheme, based on traffic loading conditions.     

A Simulation Study on the Throughput Performance of TCP over Wireless Fading Channel

1　Introduction　TransportControlProtocol (TCP )asthewidespreadusedtransportprotocolintheInternetapplicationswasdesignedforwirelinenetworkswherethechannelerrorratesareverylowandcon gestionistheprimarycauseofpacketloss.Howev er ,whenTCPconnectionsextendoverwirelesslinks,manyfactorssuchasinterference,multipathfading ,usermobilityandatmosphericconditionsmaycauseerrorsresultinginframelossesoverthewirelesslinksthustheperformanceofTCPisseverelyaffected .　TheperformanceofTCPthroughputconsideri…     

Impact of XPM on the Performance of Microwave Photonic Switching with NOLM

The impact of XPM on the microwave photonic switching with NOLM is analyzed by the split-step Fourier method (SSFM) that can solve the coupled nonlinear Schr?dinger equation (CNLSE). The simulation results show that XPM induces the distortion of waveforms and the leak of side lobes. And the larger the modulation bandwidth is, the larger the leak of side lobes is. Furthermore, the power transmission function of NOLM Tm is distorted because of the XPM-induced nonreciprocity: Tm decreases when the splitting ratio of the coupler f ∈(0,0.5) and increases when f ∈(0.5,1.0).