一种新型的异构无线网络呼叫接纳控制算法研究

在CDMA2000蜂窝网络和WLAN组成的异构无线网络中,呼叫接纳控制算法对于提高系统资源的利用率有着非常重要的作用。根据WLAN的网络负载情况和移动用户的速度来判决是否接入WLAN;提出一种基于概率机制的CAC算法,WLAN能够限制来自于蜂窝网的VHO呼叫,减少不必要的VHO处理负荷;对新呼叫阻塞率和DVHO呼叫阻塞率进行理论分析和推导。仿真结果表明,该CAC算法能够减少不必要的重复上下垂直切换,同时将DVHO呼叫阻塞率控制在可接受的范围内。算法保证了较高的系统吞吐量,提高了系统整体性能。     

无线通信网络呼叫接纳控制策略研究综述

呼叫接纳控制（CAC）是无线通信网络无线资源管理中一个重要的组成部分,CAC策略依据一定的准则决定呼叫到达请求的允许接入或拒绝接入,其中策略设计的好坏直接影响着网络的性能和资源利用率。20多年来,CAC策略得到了广泛地研究,极大地改善了网络呼损率、中断率、分组延时、丢包率和吞吐率等性能。简要介绍了无线通信网络中与CAC的一些相关背景及CAC策略的功能定位与作用,重点介绍了近年来CAC研究的一些新的成果,并分析了这些成果仍然存在的一些问题,最后给出了对于CAC进一步研究的探讨。     

WLAN中基于混合模式的接纳控制算法

针对WLAN标准IEEE 802.11e中 EDCA不能提供定量的服务质量(QoS)的问题,提出了一种混合模式(基于模型和测量)的接纳控制算法。通过建立退避实例的各个状态转移的Markov模型,利用贝塞尔削减规则得出网络性能指标的解析表达式,并根据测量的信道的实时状况预测新业务流可获得的吞吐量,最后提出了一种基于吞吐量的接纳控制算法。实验结果表明,该算法保证了已经接入业务流的服务质量,同时接纳了更多的新业务流,提高了网络的吞吐量。     

Elastic threshold-based admission control for QoS satisfaction with reward optimization for servicing multiple priority classes in wireless networks

We analyze performance characteristics of a class of call admission control (CAC) algorithms designed for servicing multiple priority classes in wireless networks with the goal of quality of service (QoS) satisfaction and reward optimization. By reward, we mean some sort of “value” obtained by the system as a result of servicing multiple priority classes. In this paper we design and evaluate the performance of a new algorithm, elastic threshold-based CAC, in terms of the maximum reward obtainable with QoS satisfaction from servicing multiple priority classes with distinct QoS requirements, and compare it with existing partitioning, threshold, and spillover CAC algorithms. We also develop a heuristic-based search method to determine the best threshold-value sets used for multiple service classes by sequentially adjusting these thresholds based on the reward and rejection rate obtainable vs. QoS constraints of each service class. We demonstrate through test cases and simulation that elastic threshold-based CAC outperforms existing CAC algorithms for QoS satisfaction and reward optimization in solution optimality for serving multiple QoS service classes in wireless networks.     

Optimal NT policies for M/G/1 system with a startup and unreliable server

This paper studies the control policies of an M/G/1 queueing system with a startup and unreliable server, in which the length of the vacation period is controlled either by the number of arrivals during the idle period, or by a timer. After all the customers are served in the queue exhaustively, the server immediately takes a vacation and operates two different policies: (i) the server reactivates as soon as the number of arrivals in the queue reaches to a predetermined threshold N or the waiting time of the leading customer reaches T units; and (ii) the server reactivates as soon as the number of arrivals in the queue reaches to a predetermined threshold N or T time units have elapsed since the end of the completion period. If the timer expires or the number of arrivals exceeds the threshold N, then the server reactivates and requires a startup time before providing the service until the system is empty. Furthermore, it is assumed that the server breaks down according to a Poisson process and his repair time has a general distribution. We analyze the system characteristics for each scheme. The total expected cost function per unit time is developed to determine the optimal thresholds of N and T at a minimum cost.     

An HMM-based call admission control policy for supporting QoS in wireless cellular networks

The multimedia services are getting to become the major trend in next-generation cellular networks. Call admission control (CAC) plays the key role for guaranteeing the quality of service (QoS) in cellular networks. The goal which keeps both the call dropping probability (CDP) and call blocking probability (CBP) below a certain level is more difficult owing to user indeterminate mobility. In this paper, the Hidden Markov Models (HMMs) concept which is suitable for solving a dynamic situation is introduced and applied to the call admission control policy. The prediction of user mobility can be modeled and resolved as the decoding problem of the HMMs. According to the prediction result, the proposed CAC method can reserve appropriate bandwidths for a handoff call beforehand. Thus, the call dropping probability can be kept below a lower level. Moreover, the call blocking probability is not sacrificed too much since the proposed method can reserve the suitable bandwidths in the appropriate cells but not reserve stationary ones which are always adopted by traditional CAC methods. Therefore, the proposed method not only can satisfy both CDP and CBP issues, but also improve the system utilization.     

Routing with admission control in ATM networks

An optimal control parameter, , was developed by optimal control theory for Asynchronous Transfer Mode (ATM) networks. The parameter is related to link utilization, buffer occupancy, system throughput and cell rejection characteristics and is applied to routing and admission control in simulation of a network carrying multiclass traffic. Simulation results show that the parameter produces better performance with respect to cell rejection rate characteristics compared with the traditional control parameter for utilization, .This research has been supported by the ATI as part of the Navy Contract N00140-94-C-BC03. Some parts of the paper were presented at Globecom'94.     

基于最优功率控制和马尔可夫链优化的异构无线网络

为了提高异构无线网络的资源利用率以及网络吞吐量,提出一种基于最优功率控制和马尔可夫链优化的异构无线网络,通过建立异构网络模型对异构网络的业务负载情况进行分析,采用有限容量下的最优功率控制方法来使业务能够选择合适的接入网络,并采用基于马尔可夫链来进行网络吞吐量优化,在对不同形式的网络进行速率分配时,采用了多权重优化进行求解最优解,可以降低网络的阻塞情况,提高网络的利用效率.实验仿真结果及分析表明,该算法在提高网络吞吐量、减少网络利用效率上具有较好的效果.     

基于马尔可夫链策略的传感器网络节点密度控制算法

如何保证多跳自组织网络的连通性是无线传感器网络研究的核心问题.在正态遮蔽衰退模型的基础上,借助状态转移概率矩阵提出一种基于马尔可夫链策略的节点密度控制算法.该算法利用一步转移概率矩阵求出信号在任意节点对之间互达的迟早概率,并通过令节点间信号互达的迟早概率趋近于1来逼近网络全连通时的最小节点密度.实验结果表明,与R.HEKMAT算法相比,所提出的算法能有效降低数值误差,从而提高算法结果与实验数据的吻合度.     

无线传感器网络多信道协议的调度机制

针对现有无线传感器网络多信道MAC协议没有区分数据业务优先级的问题,提出了一种基于区分服务的多信道协议（DP-McMAC）。该协议采用优先级调度策略和区分服务机制,对不同数据业务设置不同的退避参数和竞争窗口,并对提出的协议进行数学建模及延迟分析。仿真结果表明,该协议在高优先级数据的传输时延和吞吐量等性能方面比现有的协议均有所提高,并且保证了高优先级数据传输的实时性要求。     

Energy-efficient topology control algorithm for maximizing network lifetime in wireless sensor networks with mobile sink

Uneven energy consumption is an inherent problem in wireless sensor networks characterized by multi-hop routing and many-to-one traffic pattern. Such unbalanced energy dissipation can significantly reduce network lifetime. In this paper, we study the problem of prolonging network lifetime in large-scale wireless sensor networks where a mobile sink gathers data periodically along the predefined path and each sensor node uploads its data to the mobile sink over a multi-hop communication path. By using greedy policy and dynamic programming, we propose a heuristic topology control algorithm with time complexity O(n(m + n log n)), where n and m are the number of nodes and edges in the network, respectively, and further discuss how to refine our algorithm to satisfy practical requirements such as distributed computing and transmission timeliness. Theoretical analysis and experimental results show that our algorithm is superior to several earlier algorithms for extending network lifetime.     

一种用于提高802. 15. 4网络性能的区分服务模型

IEEE802. 15. 4作为低速率、低功耗的无线传感器网络标准,其媒体接入控制(MAC)协议的竟争接入时段(CAP)对所有数据帧和节点都采用相同的竞争参数,不能为某些需要服务区分的应用提供很好的服务。针对这一问题,提出了一种基于区分服务的改进IEEE802. 15. 4机制以支持高QoS要求。该机制的主要思想是根据服务质量要求(时延及吞吐量)为不同的数据流分配不同的优先级,对不同优先级数据设置不同的数据帧长度和竟争参数来达到区分服务的目的。与此同时提出一种区分服务的不饱和马尔科夫链模型来分析所提出的机制。该模型评佑了采用此简单但有效的区分服务机制后两种优先级数据的信道接入概率、吞吐量、时延及能耗等性能。分析结果表明,此模型对区分服务起到了很好的效果。     

无线传感器网络中平均时延约束的自适应休眠机制

针对流量动态变化的无线传感器网络,提出了具有平均时延约束的自适应休眠机制.在休眠阶段,节点采取自适应地周期性休眠和苏醒来节省能量且保证平均传输延迟.在苏醒周期的节点没有数据发送或者收到目的地址为其他节点的RTS/CTS帧后进入休眠周期.通过建立马尔科夫链模型分析可得到该机制中平均时延约束下休眠周期的优化值.     

Cell-related location area planning for 4G PCS networks with variable-order Markov model

Location management is a critical issue in personal communication service (PCS) networks, tracking the location of user equipment (UE) with the goal of minimizing total signaling cost. Previous work can be classified into two categories: static and dynamic. Static schemes partition networks into fixed size LAs. However, these schemes are inefficient because they do not take UEs’ mobility and the call arrival rate into account. On the other hand, focusing on individual UEs, dynamic schemes have minimized the location management cost. However, they are difficult to implement because recording the individual information of numerous UEs and planning each of their LAs consume uncontrollable cost. Because of these reasons, we propose a cell-based scheme between static and dynamic schemes. Considering people usually stay in specific zones for long periods and the movement of UEs usually presents a strong moving direction in areas, this study presents a distributed algorithm by employing variable-order Markov models to find the mobility characteristic shared by UEs to plan better LAs with lower location management cost. When the order of Markov model is set to 1, our method is equal to a pure cell-centric LAP scheme; while the order of Markov model is high, it is more like a profile-based dynamic scheme. So, the setting of the order actually is a trade-off problem between the overall location management cost and the computing complexity. We present to retrieve a balance by using the expected location management cost and the number of total states of Markov models. In simulations, the origin–destination matrix (O–D matrix) from the Taipei Rapid Transit Corporation is used for representing the association between two cells. Simulation results demonstrate that the proposed scheme achieves good performance.     

Efficient link scheduling for online admission control of real-time traffic in wireless mesh networks

Link scheduling is used in wireless mesh networks (WMNs) to guarantee interference-free transmission on the shared wireless medium in a time division multiple access approach. Several papers in the literature address the problem of link scheduling guaranteeing a minimum throughput to the flows traversing the WMN. However, none of the existing works address the problem of computing a schedule that guarantees that pre-specified end-to-end delay constraints are met. In this paper, we make a first step forward in this direction by defining a link scheduling algorithm that works in sink-tree WMNs, i.e. those whose traffic is routed towards a common sink (i.e. the Internet gateway). Our iterative algorithm exploits a delay-based admission control procedure, devised through Network Calculus, which solves an optimization problem and tests the feasibility of a schedule from the point of view of delay guarantees. Thanks to a clever solution approach for the optimization problem, the iterative algorithm computes feasible solutions in affordable times for networks of several tens of nodes, and is thus amenable to online admission control of real-time traffic.     

Dynamic adaptation of CSMA/CA MAC protocol for wide area wireless mesh networks

Though the popular IEEE 802.11 DCF is designed primarily for Wireless LAN (WLAN) environments, today it is being widely used for wide area wireless mesh networking. The protocol parameters of IEEE 802.11 such as timeout values, interframe spaces, and slot durations, sufficient for a general WLAN environment, need to be modified in order to efficiently operate in wide area wireless mesh networks. The current wide area wireless mesh network deployments use manual configuration of these parameters to the upper limit which essentially makes the networks operate at lower system efficiency. In this paper, we propose d802.11 (dynamic 802.11) which dynamically adapts the protocol parameters in order to operate at varying link distances. In fact, in 802.11, a transmitter can face ACK/CTS timeout even when it started receiving ACK/CTS packet before the timeout value. We present three strategies, (i) multiplicative timer backoff (MTB), (ii) additive timer backoff (ATB), and (iii) link RTT memoization (LRM), to adapt the ACK_TIMEOUT in d802.11 in order to provide better adaptation for varying link dimensions. Through extensive simulation experiments we observed significant performance improvement for the proposed strategies. We also theoretically modeled the maximum link throughput as a function of the link dimension for the proposed system. Our results show that the LRM technique provides the best adaptation compared to all other schemes.     

A semi-Markov decision process-based joint call admission control for inter-RAT cell re-selection in next generation wireless networks

In the next generation wireless networks (NGWNs), where different radio access technologies (RAT) will coexist and work in collaboration to provide ubiquitous access, a mechanism called Joint Call Admission Control (JCAC) will play an important role by deciding whether or not an incoming service request will be accepted according to an admission constraint as well as determining in which RAT (among the available) it will be connected. In this paper, we propose an optimal JCAC for inter-RAT cell re-selection problem also referred to as initial RAT selection in co-located wireless networks, which supports both real-time services and non-real-time services. To properly meet the JCAC goals, we propose a cost function that weigh two criteria: the blocking cost function, which takes into account the priority of each service class in each RAT, and the alternative acceptance cost, which reflects the multiplicity of RATs working in a collaborative fashion, mandatory in NGWN. We use the framework of Semi-Markov Decision Process (SMDP) to formulate the optimization problem and the value iteration algorithm to compute the optimal policy. Our model still takes into consideration the ratio between the radius of the co-located RATs and shows how it may impact on optimal initial RAT selection. Numerical results, supported by an analysis of the structure of the optimal policy, show that the proposed optimal JCAC selects for real-time service class the biggest RAT and for non-real-time service class the smallest one. This optimal JCAC policy is ratified by the current trend in the design of NGWN and also follows the 3rd Generation Partnership Project (3GPP) expectations.     

嵌入式软件系统体系结构可靠性分析方法

AADL是嵌入式领域对SA进行建模、评估的常用方法,但其属于一种半形式化开发语言,无法直接对SA的可靠性进行验证。为此,提出一种基于AADL的可靠性分析框架,对SA的可靠性进行形式化验证。首先通过分析系统体系结构的元素关系,建立AADL可靠性模型;然后设计转换模型及其规则,将AADL模型转换为连续时间马尔科夫链模型;最后采用概率模型检验工具对连续时间马尔科夫链模型进行可靠性定量分析。仿真结果表明,与现有可靠性分析方法相比,该方法在计算效率和转换效率上都有明显的提高。基于AADL的可靠性分析框架实现在软件系统开发早期对SA进行可靠性定量计算,为AADL在嵌入式软件系统可靠性定量分析方面提供了一种新的验证思路。     

Quality of service estimation for soft handoff region ratio and call admission control in CDMA cellular systems

In the operational stage of code division multiple access (CDMA) systems, the soft handoff region ratio (SHRR) is among the important parameters that guarantee the quality of service (QoS) and resource allocation. This paper analytically investigates the effects of the SHRR on QoS. In doing so, we simultaneously take into account the capacity increasing factor and traffic load variation. For this purpose, we propose a new traffic load estimation model using a semi-Markov chain in order to consider the call arrivals influenced by the SHRR under general resident time condition. We also present the calculation algorithm of the QoS measures such as the new call blocking probability (NBP) and forced termination probability (FTP) by applying the proposed model to the prioritized call admission control (CAC). The numerical result illustrates the effects of various soft handoff system parameters. Likewise, it shows that the value of SHRR has a significant impact of the QoS under the normal propagation conditions. Sensitivity analysis is also performed to show the effect of exponential cell resident time assumption. The proposed modeling is expected to provide a practical guide to improve the QoS of CDMA soft handoff systems.     

WLAN中MAC协议性能分析研究

对媒体接入控制(Media Access Control,MAC)协议进行性能分析,可以深入理解MAC协议的操作特点,发现吞吐量、数据包时延与丢失等性能遭受影响的本质原因。对当前马尔可夫链性能分析法加以详细地分析与总结,分别阐述了无线局域网络中分布式协调功能和增强的分布式信道接入两种MAC协议的性能分析研究工作。对进一步的研究工作进行了分析与展望。