WCDMA系统中的呼叫允许控制分析

无线资源管理中的呼叫允许控制是WCDMA的重要组成部分，性能优良的呼叫允许控制策略可以尽可能高地提高网络资源利用率。描述了基于功率、基于干扰和基于LA的呼叫允许控制方案，比较分析了它们的性能。     

Adaptive allocation of resources and call admission control forwireless ATM using genetic algorithms

In wireless ATM-based networks, admission control is required to reserve resources in advance for calls requiring guaranteed services. In the case of a multimedia call, each of its substreams (i.e., video, audio, and data) has its own distinct quality of service (QoS) requirements (e.g., cell loss rate, delay, jitter, etc.). The network attempts to deliver the required QoS by allocating an appropriate amount of resources (e.g., bandwidth, buffers). The negotiated QoS requirements constitute a certain QoS level that remains fixed during the call (static allocation approach). Accordingly, the corresponding allocated resources also remain unchanged. We present and analyze an adaptive allocation of resources algorithm based on genetic algorithms. In contrast to the static approach, each substream declares a preset range of acceptable QoS levels (e.g., high, medium, low) instead of just a single one. As the availability of resources in the wireless network varies, the algorithm selects the best possible QoS level that each substream can obtain. In case of congestion, the algorithm attempts to free up some resources by degrading the QoS levels of the existing calls to lesser ones. This is done, however, under the constraint of achieving maximum utilization of the resources while simultaneously distributing them fairly among the calls. The degradation is limited to a minimum value predefined in a user-defined profile (UDP). Genetic algorithms have been used to solve the optimization problem. From the user perspective, the perception of the QoS degradation is very graceful and happens only during overload periods. The network services, on the other hand, are greatly enhanced due to the fact that the call blocking probability is significantly decreased. Simulation results demonstrate that the proposed algorithm performs well in terms of increasing the number of admitted calls while utilizing the available bandwidth fairly and effectively     

Bandwidth allocation and call admission control in high-speednetworks

The authors discuss the broad issue of bandwidth allocation and call admission control (CAC) in high-speed networks, focusing on asynchronous transfer mode technology. It is maintained that despite the considerable amount of high-quality work carried out in this area, the debate surrounding these issues is not yet resolved. The complexity of dealing with a wide variety of as yet unknown user traffic types, as well as the evolving architecture of networks, means that currently proposed solutions are only an intermediate step of the design process. The authors discuss the nature of user traffic and illustrate how it can impact the debate on the quality of service, concentrating on some “equivalent bandwidth” type CAC strategies. Also discussed is a method which uses diffusion approximations. Finally, the authors discuss the novel issue of evaluating the overload created by the CAC procedure itself on network nodes. The article is complemented by several numerical and simulation results which illustrate the discussion     

CAC-RD: an UMTS call admission control

The third wireless network generation (3G) aims to provide fast Internet access with quality of service (QoS) guarantees, especially to multimedia applications. UMTS (Universal Mobile Telecommunication System) is a kind of 3G networks. To provide QoS, the network must use an efficient admission control mechanism. This mechanism needs to prioritize network access to critical classes of applications. This work proposes an UMTS admission control mechanism, called CAC-RD (Call Admission Control—based on Reservation and Diagnosis). It is based on network diagnosis and on channel reservation for handovers. These techniques are associated with new calls blocking when the network reaches utilization thresholds. CAC-RD is a tool that prioritises handovers and conversational applications. The main CAC-RD goals are the handovers blocking reduction and the acceptable performance levels guarantee. Simulation results show that the CAC-RD channel reservation and the diagnosis techniques associated with the intrinsic network signal power control effectively reduces blockings while guarantying performance levels. Due to computational resource limits, simulations cannot answer related to admission control in big networks with thousands of users. This work presents a method to extrapolate scientific questions like CAC’s behavior with thousands of users and many antennas. An artificial neural network approach for CAC-RD in UMTS 3G networks is presented as an extension of the work.     

Dynamic call admission control in ATM networks

The authors present dynamic call admission control using the distribution of the number of cells arriving during the fixed interval. This distribution is estimated from the measured number of cells arriving at the output buffer during the fixed interval and traffic parameters specified by users. Call acceptance is decided on the basis of online evaluation of the upper bound of cell loss probability, derived from the estimated distribution of the number of calls arriving. QOS (quality of service) standards can be guaranteed using this control when there is no estimation error. The control mechanism is effective when the number of call classes is large. It tolerates loose bandwidth enforcement and loose policing control, and dispenses with modeling of the arrival processes. Numerical examples demonstrate the effectiveness of this control, and implementation is also discussed     

Efficient bandwidth allocation and call admission control for VBR service using UPC parameters

Provision of Quality‐of‐Service (QoS) guarantees is an important and challenging issue in the design of Asynchronous Transfer Mode (ATM) networks. Call Admission Control (CAC) is an integral part of the challenge and is closely related to other aspects of network designs such as traffic characterization and QoS specification. Since the Usage Parameter Control (UPC) parameters are the only standardized traffic characterizations, developing efficient CAC schemes based on UPC parameters is significant for the implementation of CAC on ATM switches. In this paper, we develop a CAC algorithm called TAP (derived from TAgged Probability) as well as two other CAC algorithms using the UPC parameters. These CAC algorithms are based on our observation that the loss‐probability‐to‐overflow‐probability ratio tends to decrease as the number of sources increases. By introducing the loss‐probability‐to‐overflow‐probability ratio K, we find that this ratio sheds light on increasing resource utilization while still guaranteeing QoS. Analysis, simulation, and numerical results have shown that the proposed TAP algorithm is simple and efficient. Copyright © 2000 John Wiley & Sons, Ltd.     

A call admission control scheme for ATM networks using a simplequality estimate

The authors propose a call admission control scheme based on a method of estimating cell loss quality for individual bursty traffic sources. The estimate is expressed in terms of virtual cell loss probability, which may be defined by two traffic characteristic parameters alone: peak and mean rate. The approach is suitable for the estimation of real cell loss probability in heterogeneous and homogeneous traffic models when burst length is larger than buffer capacity. The concept of virtual cell loss probability is extended to the individual call level so as to be able to estimate the quality of service (QOS) provided to individual calls. A virtual bandwidth method is used to develop a practical call admission control system. Quality is ensured by combining a traffic clustering scheme, with a scheme for assigning individual clusters to subcapacities of a link. Priority levels are presented in terms of the class of QOS required, i.e., deterministic or statistical, and the allocation of virtual bandwidth is discussed in terms of both QOS class and traffic characteristics     

Call admission control schemes: a review

Over the last few years, a substantial number of call admission control (CAC) schemes have been proposed for ATM networks. We review the salient features of some of these algorithms. Also, we quantitatively compare the performance of three of these schemes     

Investigation of capacity and call admission control schemes in TD‐SCDMA uplink systems employing smart antenna techniques

Due to the TDMA (time division multiple access)/time division duplex (TDD) specialization in the uplink (UL) of code division multiplex access (CDMA) systems, some advanced techniques, such as smart antenna (SA) and multi‐user detection (MUD), are utilized conveniently in time division‐synchronous code division multiplex access (TD‐SCDMA) systems. These advanced techniques have great impacts on the capacity and radio resource management (RRM) schemes. In this paper, the UL capacity and load models specified for TD‐SCDMA systems are proposed, in which the impacts from SA and MUD techniques are considered, and the UL load can be estimated based on the total received power in the base station. According to the proposed theoretical capacity and load evaluation models, the call admission control (CAC) strategies suitable for TD‐SCDMA systems are presented. Since there are two kinds of SA schemes (i.e., tracking beam antenna (TBA) and switched beam antenna (SBA)) utilized in TD‐SCDMA systems, the efficient CAC algorithms suitable for these two SA schemes are designed and evaluated, which are based on principles of the interference increase estimation. All simulation results show that the proposed CAC strategies can work efficiently and improve performances of TD‐SCDMA systems dramatically. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison of admission control schemes in ATM networks

Asynchronous transfer mode (ATM) offers an efficient means of carrying a wide spectrum of BISDN traffic provided that network congestion is prevented. Unfortunately, efficient congestion control is difficult to achieve in integrated broadband networks, owing to the wide range of traffic characteristics and quality of service (QOS) requirements. We have implemented a network simulator that allows us to evaluate many proposed admission control schemes using many different traffic models. We present the results of several simulation studies, including one study of the performance of the admission control schemes in the presence of traffic sources that exhibit long-term dependence.     

On optimal call admission control in resource-sharing system

In this paper, we consider call admission control of multiple classes without waiting room. We use event-based dynamic programming for our model. We show that sometimes the customer classes can be ordered: if it is optimal to accept a class, then to accept a more profitable class is optimal too. We demonstrate submodularity of the minimum cost for the 2-classes problem and establish some properties of optimal policies. Then we formulate a fluid model that allows us to study the optimal control for the large-capacity case. We show that in the case of same service time distributions, the control problem can be reduced to a model with a one-dimensional (1-D) state space, and a trunk reservation policy is optimal. We present numerical examples that validate our results     

SIR-based call admission control for DS-CDMA cellular systems

Signal-to-interference ratio (SIR)-based call admission control (CAC) algorithms are proposed and studied in a DS-CDMA cellular system. Residual capacity is introduced as the additional number of initial calls a base station can accept such that system-wide outage probability will be guaranteed to remain below a certain level. The residual capacity at each cell is updated dynamically according to the reverse-link SIR measurements at the base station. A 2^k factorial experimental design and analysis via computer simulations is used to study the impact of the parameters used in the algorithms. The influence of these parameters on system performance, namely blocking probability and outage probability, is then examined via simulation. The performance of the algorithms is compared together with that of a fixed call admission control scheme (fixed CAC) under both homogeneous and hot spot traffic loading. The results show that SIR-based CAC always outperforms fixed CAC even under overload situations, which is not the case in FDMA/TDMA cellular systems. The primary benefit of SIR-based CAC in DS-CDMA cellular systems, however, lies in improving the system performance under hot spot traffic     

On optimal call admission control in cellular networks

Two important Quality-of-Service (QoS) measures for current cellular networks are the fractions of new and handoff “calls” that are blocked due to unavailability of “channels” (radio and/or computing resources). Based on these QoS measures, we derive optimal admission control policies for three problems: minimizing a linear objective function of the new and handoff call blocking probabilities (MINOBJ), minimizing the new call blocking probability with a hard constraint on the handoff call blocking probability (MINBLOCK) and minimizing the number of channels with hard constraints on both of the blocking probabilities (MINC). We show that the well-known Guard Channel policy is optimal for the MINOBJ problem, while a new Fractional Guard Channel policy is optimal for the MINBLOCK and MINC problems. The Guard Channel policy reserves a set of channels for handoff calls while the Fractional Guard Channel policy effectively reserves a non-integral number of guard channels for handoff calls by rejecting new calls with some probability that depends on the current channel occupancy. It is also shown that the Fractional policy results in significant savings (20-50\%) in the new call blocking probability for the MINBLOCK problem and provides some, though small, gains over the Guard Channel policy for the MINC problem. Further, we also develop computationally inexpensive algorithms for the determination of the parameters for the optimal policies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Probabilistic call admission control in wireless multiservice networks

A new probabilistic call admission control scheme is proposed for multiservice wireless networks. The new scheme gradually suppresses the admission rate of the new calls and of the calls of each service class (SC) supported considering their priorities independently. The scheme is examined both for a single SC and for multiple SCs under general conditions. The analysis employs Markov chain theory and yields analytical expressions for the call blocking probabilities. The proposed analytical method was validated via simulations employing different distributions for the channel holding time; the simulations demonstrated the accuracy of the proposed framework.     

Optimal call admission control under packet and call level QoS constraints and effect of buffering

For a single network switch allocating link bandwidth to connections of a single class, an optimal call admission control (CAC) policy is found by the solution of a linear programming (LP) problem. Our optimization differs from previous work in that we include the effect of an output buffer in the switch for the temporary storage of packets bound for transmittal across the link. We find a policy that is optimal in the sense of minimizing call blocking subject to a packet level quality of service (QoS) requirement that limits the packet loss ratio. Such a policy's call blocking probability, if it is small enough to satisfy a call level QoS requirement, then establishes the feasibility of satisfying both the packet and call level QoS requirements for a given call request rate. We show with a previously described example that the addition of even a small output buffer can significantly increase the range of call request rates for which there exists a feasible policy, i.e. one that satisfies both QoS requirements. Also presented is an upper bound, valid for any fixed buffer size, on the range of call request rates for which there exists a feasible CAC policy. Copyright © 2003 John Wiley & Sons, Ltd.     

WiMax网络中自相似呼叫接纳控制算法研究

针对WiMAX网络业务流的自相似特性,提出用M/Pareto模型来对网络业务流进行建模,通过M/Pareto模型和FBM业务流模型之间统计性质得到2个模型间的参数映射关系,推导出基于M/Pareto模型参数的有效带宽计算公式,据此设计出一个自相似接纳控制算法(SS-CAC)。该算法避免了通过测量的方法来获取FBM业务流模型中参数值,又适应了WiMAX网络流自相似这一特性,使得计算的有效带宽更加精确和方便,提高了系统资源利用率。仿真结果表明,该算法极大地提高网络的带宽利用率,降低了系统的呼叫阻塞率。     

Distributed call admission control in mobile/wireless networks

The major focus of this paper is distributed call admission control in mobile/wireless networks, the purpose of which is to limit the call handoff dropping probability in loss systems or the cell overload probability in lossless systems. Handoff dropping or cell overload are consequences of congestion in wireless networks. Our call admission control algorithm takes into consideration the number of calls in adjacent cells, in addition to the number of calls in the cell where a new call request is made, in order to make a call admission decision. This is done by every base station in a distributed manner without the involvement of the network call processor. The admission condition is simple enough that the admission decision can be made in real time. Furthermore, we show that our distributed call admission control scheme limits the handoff dropping or the cell overload probability to a predefined level almost independent of load conditions. This is an important requirement of future wireless/mobile networks with quality-of-service (QoS) provisioning     

Adaptive call admission control in 3GPP LTE networks

In this article, we propose new methods to reduce the handoff blocking probability in the 3rd Generation Partnership Project Long Term Evolution wireless networks. This reduction is based on an adaptive call admission control scheme that provides QoS guarantees and gives the priority of handoff call over new call in admission. The performance results of the proposed schemes are compared with other competing methods using simulation analysis. Simulation results show the major impact on the performance of the 3rd Generation Partnership Project Long Term Evolution network, which is reflected in increased resource utilization ratio to (99%) and in the ability in satisfying the requirements of QoS in terms of call blocking probability (less than 0.0628 for Voice over IP service) and dropping probability rate (less than 0.0558).Copyright © 2012 John Wiley & Sons, Ltd.     

A call admission control framework for voice over WLANs

In this article a call admission control framework is presented for voice over wireless local area networks (WLANs). The framework, called WLAN voice manager, manages admission control for voice over IP (VoIP) calls with WLANs as the access networks. WLAN voice manager interacts with WLAN medium access control (MAC) layer protocols, soft-switches (VoIP call agents), routers, and other network devices to perform end-to-end (ETE) quality of service (QoS) provisioning and control for VoIP calls originated from WLANs. By implementing the proposed WLAN voice manager in the WLAN access network, a two-level ETE VoIP QoS control mechanism can be achieved: level 1 QoS for voice traffic over WLAN medium access and level 2 QoS for ETE VoIP services in the networks with WLANs as the local access. The implementation challenges of this framework are discussed for both level 1 and level 2. Possible solutions to the implementation issues are proposed and other remaining open issues are also addressed.     

Opportunistic call admission control for wireless broadband cognitive networks

Wireless Broadband Cognitive Networks (WBCN) are new trend to better utilization of spectrum and resources. However, in multiservice WBCN networks, call admission control (CAC) is a challenging point to effectively control different traffic loads and prevent the network from being overloaded and thus provide promised quality of service. In this paper, we propose a CAC framework and formulate it as an optimization problem, where the demands of both WBCN service providers and cognitive subscribers are taken into account. To solve the optimization problem, we developed an opportunistic multivariate CAC algorithm based on a joint optimization of utility, weighted fairness, and greedy revenue algorithms. Extensive simulation results show that, the proposed call admission control framework can meet the expectations of both service providers and subscribers in wireless broadband cognitive networks.