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1.
The quality of service (QoS) support for multimedia communications faces a big challenge in a fading wireless network. On one hand, conventional automatic repeat request (ARQ) schemes are not effective for small-scale fading channels with correlated errors due to consecutive retransmission failures. On the other hand, large-scale fading due to propagation loss or shadowing severely limits transmission range. A novel differentiated cooperative medium access control (MAC) protocol, called DC-MAC, is proposed to enhance the QoS support for multimedia communications while supporting service differentiation based on the IEEE 802.11e architecture. By enabling cooperative ARQ, the retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source. Since unnecessary and useless retransmissions may intensify the node contention and degrade the system performance contrarily, a novel negative acknowledgement feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Extensive simulations are conducted on the OPNET platform to analyse the performances of DC-MAC under both small-scale and large-scale fading. Simulation results show that the proposed scheme significantly improves the performances of both multimedia applications and best-effort data applications in terms of throughput, delay and coverage with moderate user contention. 相似文献
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Control phase plays a critical role in the performance of time-division multiple access (TDMA)-based networks. Within cluster-based wireless sensor networks, a nimble and adaptive control phase algorithm called NACPA to control the control phase of TDMA-based medium access control (MAC) in cluster-based sensor networks is proposed. This algorithm takes advantage of the wireless sensor hardware feature and presents a more accurate although simpler means to calculate the number of contention nodes in one round. On the basis of the analysis of the features of contention probability against the number of contention nodes, this algorithm can significantly reduce its computation complexity, rendering it practically feasible for resource-constrained sensor networks. Detailed analytical evaluation against two typical MAC algorithms (polling and carrier sense multiple access) is presented both in terms of packet transmission delay and average channel utilisation, the results of which, while also matching the simulation observation, have shown its effectiveness and efficiency. 相似文献
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This study deals with the throughput analysis of data services over high-speed downlink packet access (HSDPA) systems. The achievable throughput is calculated with an approximate analytical method based on the Padhye model that has two input parameters: the packet loss probability and the transmission control protocol (TCP) round trip time. The proposed solution is to calculate these parameters with an equivalent queuing network model of the HSDPA system that takes into account the possible congestion points in the system and the protocol layers that have dominant impact on the delay and packet drop. The modelling considerations and the analysis method are described in detail. Finally, the model is validated with a performance study of the HSDPA system that is executed with detailed NS2- based simulations too. The proposed method is found to be reasonably accurate requiring less computational effort than the simulations. 相似文献
4.
The fundamental medium access control mechanism in IEEE 802.11 wireless LANs (WLANs)-distributed coordination function (DCF) only supports the best-effort service and does not support quality-of-service (QoS) differentiation. Enhanced distributed channel access (EDCA) in IEEE 802.11e supports delay differentiation. A new approach, EDCA+ , is proposed to enhance QoS over WLANs. It simultaneously achieves bandwidth, delay and jitter differentiation by distinguishing the minimum contention window, the maximum backoff stage or persistent factor and packet-loss rate differentiation by distinguishing the retry limit. Analytical models are proposed to analyse the performance of EDCA+ in terms of throughput, bandwidth, delay, jitter and packet-loss rate. Extensive simulations are also carried out to evaluate the accuracy of the proposed performance models and to compare the performance of DCF, EDCA and EDCA+. The simulation results show that EDCA+ performs better than DCF and EDCA in ensuring integrated QoS, and that the proposed analytical models are valid. 相似文献
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IEEE 802.16 is a standardisation for a broadband wireless access in metropolitan area networks (MAN). Since the IEEE 802.16 standard defines the concrete quality of service (QoS) requirement, a scheduling scheme is necessary to achieve the QoS requirement. Many scheduling schemes are proposed with the purpose of throughput optimisation and fairness enhancement, however, few scheduling schemes support the delay requirement. In this study, the authors propose a new scheduling scheme reflecting the delay requirement. Specifically, the authors add the delay requirement term in the proportional fair scheduling scheme and the scheduling parameters are optimised with respect to the QoS requirement. Therefore the QoS requirement is achieved without the excessive resource consumption. 相似文献
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The authors propose a new analytical model based on BCMP closed queueing networks in order to evaluate the performance of IEEE 802.11 DCF MAC protocol when all nodes are in the transmission range of each other, that is, a single hop wireless ad hoc network. By the proposed model, some performance metrics such as saturation and non-saturation throughput, distributions of channel access delay and the number of packets in the MAC buffer are derived. An extension of the proposed model is used for the analysis of IEEE 802.11e EDCA and the same performance metrics are evaluated for this protocol. Analytical results on IEEE 802.11e prove that differentiation in service is possible and channel share for each service type may be well assigned by tuning the MAC protocol parameters. Simulation results show consistency with our analytical results. 相似文献
7.
The paper presents a jamming-based MAC with dynamic priority adjustment (JMDPA) for multimedia services in wireless ad hoc networks. The proposed scheme differentiates multimedia traffic into classes with different priority levels. A mobile node is prioritised in frame transmissions by issuing a precalculated length of jamming noise: the one with the longest jamming length can win the frame transmission. The winner immediately broadcasts its current priority level (local priority) to update the global priorities of all the neighbouring nodes. The global priority is used as a contention baseline, which prevents any node with a local priority lower than the baseline from participating in the next contention. One of the innovative designs in the proposed scheme is right, in that the priority of a mobile node can be dynamically adjusted according to network conditions so that any possible starvation of low-priority traffic or any ineffective contention of high-priority traffic can be avoided. A multidimensional Markov model, together with the scalability analysis, is introduced to evaluate the performance of the proposed JMDPA. The analytical results provide very useful guidelines to tune the QoS parameters for supporting prioritised multimedia traffic in wireless ad hoc networks 相似文献
8.
随着分布式仿真系统与Web服务技术的结合日益紧密,以及功能与资源分离的愈加明显,导致大量仿真资源暴露于网络中,传统、单一的访问控制模型已无法应对.为此提出了一种基于属性的针对功能和资源的双重访问控制模型,采用证书代理机制实现功能端单点登录,采用XACML实现资源端多属性的访问控制.详细描述了该模型的访问控制流程,目前已应用到虚拟采办系统中.通过对性能的分析和测试,证明了该双重访问控制模型的可用性和有效性. 相似文献
9.
It is of utmost importance in a wireless body area network (WBAN) to improve the lifetimes of devices, while restricting latencies within allowable limits. These two demands are often conflicting, and a method to ensure fairly good values for these parameters with a view to satisfying the requirements of the WBAN application would be highly desirable. We consider CSMA/CA option of the medium access in 802.15.6 standard, and propose a sleep mechanism for the devices. An M/G/1 queue with repeated inhomogeneous vacations model is used for the medium access in a typical WBAN network in hospital environments to see how the requirements of lifetimes and delays are taken care of. An analytical method for finding the probability generating function of the contention delay for medium access is developed first using Markovian techniques. The results obtained are then used in the queueing model. Comparison of theoretical values with simulations results shows a fairly close match and defines the conditions that affect the interplay of lifetimes and latencies. 相似文献
10.
IEEE 802.lie provides guaranteed quality of service (QoS) by proving different transmission priorities. IEEE 802. lie improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two new channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function-controlled channel access. The available bandwidth and transmission rate may be easily affected by the signal quality, because the communication channel in a wireless environment operates in a random time-variation manner. Generally, a station using a low transmission rate will occupy the communication channel for a long time and degrade system performance, which causes bandwidth waste and unfairness; thus the guaranteed QoS for stations with higher transmission rates cannot be provided. An enhancing EDCAF (E DCAF) is proposed that consolidates the cross-layer concept and the IEEE 802.1 le EDCAF protocol. After simulation experiments, E DCAF obviously improves performance, especially in throughput and fairness. E DCAF scheduling also allows the different QoS requirements to be processed efficiently and flexibly. 相似文献
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In the traditional medium access control (MAC) protocols for wireless sensor networks (WSNs), energy consumption is traded for throughput and delay. However, in future WSNs, throughput and delay performance had better not be sacrificed for energy conservation. Here first, an incompletely cooperative game-theoretic heuristic-based constraint optimisation framework is introduced to achieve the goals of throughput, delay and energy conservation simultaneously. Then a simplified game-theoretic MAC (G-MAC) protocol is presented, which can be easily implemented in WSNs. Simulation results show that compared with two typical MAC protocols for WSNs, sensor MAC and timeout MAC, G-MAC can increase system throughput, and decrease delay and packet-loss-rate, while maintaining relatively low energy consumption. 相似文献
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《IEEE transactions on instrumentation and measurement》2008,57(12):2742-2750
15.
The authors present an extensive investigation of the performance of the IEEE 802.11 medium access control (MAC) protocol, with respect to throughput and delay. For the protocol analysis, a new model, which describes the protocol's behaviour to a great extent by incorporating and extending the existing models, is proposed. The authors also present a detailed analysis of the end-to-end delay through the study of the MAC delay and the queueing delay. The authors use the Z-transform of backoff duration to obtain the mean value, the variance and the probability distribution of the MAC delay. For the queueing analysis, first the authors consider an M/G/l queue in order to provide a first look at the queueing delay. Second, the authors modify the input process of the queue so that the packet arrival process is described by an ON- OFF model, which expresses the bursty nature of traffic. In the investigations, data rates of 1, 5.5 and 11 Mbps are assumed to highlight the effect of the bit rate on network performance for both Basic and request-to-send/ clear-to-send access mechanisms. The throughput and delay analyses are validated by simulating the distributed coordination function, whereas the models are compared with the existing models based on their results. The accuracy of the analyses was found to be quite satisfactory. 相似文献
16.
高科技产品是科技发展的产物,对发展国家经济和提高人民群众的生活水平起着重要的作用。考虑高科技产品斜坡需求和延迟补货受时间和价格影响的特点,将顾客分为价格偏好者和时间偏好者,构造了2种不同的延迟函数,建立了相应的经济订货批量模型,采用数值仿真分析了系统主要参数对高科技产品订货策略和总利润的影响。研究结果表明:需求增长因子、价格敏感因子以及资金贴现率对订货次数和服务水平的影响比其它因素大;需求增长期长度、价格偏好者比例对服务水平的影响比订货次数大;计划期长度对服务水平的影响比订货次数小。 相似文献
17.
The medium access control of IEEE 802.11e defines a novel coordination function, namely, hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate traffic, packet loss may occur seriously. The authors propose a TXOP allocation scheme to efficiently allocate bandwidth and meet the QoS requirements in terms of both delay bound and packet loss probability. To achieve high bandwidth efficiency, the authors take advantage of not only intra-flow multiplexing gain of traffic flows with large delay bounds, but also inter-flow multiplexing gain of multiple traffic flows with different delay bounds. According to numerical results obtained by computer simulations, the proposed TXOP allocation scheme results in much higher bandwidth efficiency than previous algorithms under the same constraints of delay bounds and packet loss probability. 相似文献
18.
Analytical performance evaluation of ultra-wideband multiple access schemes for different wireless sensor network application environments 总被引:1,自引:0,他引:1
One of the most promising uses for ultra-wideband (UWB) is wireless sensor networks (WSNs). Since WSNs offer a wide variety of services for different application areas, the UWB propagation channel characteristics of each application environment show fundamental differences from each other in many aspects. A reliable and energy-efficient multiple access scheme is thus required to coordinate the transmissions of sensor nodes in these various application channel environments. We develop an analytical framework for evaluating the performance of UWB time-hopping (TH), direct sequence (DS) and orthogonal frequency division multiplexing (OFDM) multiple access schemes with multi-node interference in the following UWB propagation channel environments that have a high importance for WSN applications: residential, office, suburban outdoor, industrial and agricultural. The objective is to determine the most appropriate multiple access scheme to be applied for a particular WSN application channel environment. Performance is evaluated in terms of the average information throughput efficiency, a relevant progress-related measure for multihop WSNs. The mathematical expression of this metric is derived in detail, and is used in numerical evaluations for assessing the performance of the three schemes operating under UWB propagation channel models of the various environments that are characterised by distinct channel parameters and specific valid distance ranges. TH-UWB is shown to be the most suitable multiple access scheme to be adopted for UWB WSNs. It outperforms both the DS-UWB and OFDM-UWB schemes for all application environments and is the most robust and energy efficient. OFDM-UWB is the poorest performing whereas DS-UWB provides similar performance to TH-UWB below a specific threshold number of interfering nodes. 相似文献
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In the construction industry, delivery times of building materials are often delayed to fit the progress of construction, and therefore parts manufacturers are forced to hold extra parts inventory over the period of the delivery delay. To minimise the inventories, two production models, i.e., push and pull type production models can be widely considered. When production lead-time is short and length of delivery delay is long, a pull type may require smaller inventories to keep a certain service level, and a push type may require smaller inventories under the condition of longer production lead-time and shorter length of delivery delay. To examine performance of average inventory level under different system conditions, factors such as ratio of average length of delivery delay to production lead-time, length of production cycle, and coefficient of variation of demand are chosen to define different system conditions. As the performance measure, the ratio of push type inventory to pull type inventory is used in the comparison of the push and pull types, and a quantitative criterion of production model selection is presented. 相似文献