支持多媒体业务的接入控制技术研究进展

如何保障不同类型的多媒体业务在通信过程中的通信服务质量(QoS),是目前接入控制技术中一项热点研究问题。通过对近十几年间相关文献的整理和分析,对支持多媒体业务的接入控制技术的研究进展进行综述,具体内容包括多媒体业务类型的设计、支持多媒体业务的接入控制协议、多信道分配策略等方面,并提出了支持多媒体业务的接入控制技术未来的研究方向。     

基于多码CDMA系统的多级业务接入控制

基于支持多级业务的多码CDMA系统,本文设计了一种适合于多级业务接入的两层控制方案,借助于该方案,实时业务用户一旦被接纳就立刻进行通信,而非实时数据用户的通信过程要受到呼叫层和突发层双重的皎皎接入控制,这样,前者的QoS能够得到保证,而后者则可以充分利用网络暂时闲置的信道容量。     

移动多媒体业务中的无线ATM网络

在有线通信领域，由于服务质量的悬殊差别，传统的语音和数据通信渐渐面临被多媒体通信全面替代的威胁。随着视频编码技术和光纤网络传输能力的不断提高，多媒体的网络传输已逐渐成为现实。加之Internet和Intranet的成功动作，多媒体业务已逐渐成为有线业务的重要组成部分，并有望在不久的将来成为主要的业务类型。现在，初具规模的电子商务、     

CDMA随机多址接入技术研究

CDMA作为一种多址接入技术在无线网络中已广为应用,在多码CDMA和单码CDMA研究的基础上,构造了多码CDMA和单码CDMA在无线分组数据网络中的随机多址接入模型,并且分析了两种系统的吞吐率特性和归一化时延特性。结果证明单码CDMA和多码CDMA具有相同的多址接入性能。     

CDMA网络接入失败原因的分析

详细分析了CDMA移动台接入失败的原因，并提出了相应的解决措施，对CDMA无线网络的网络优化工作有一定的指导作用。     

CDMA无线接入技术

本文重点介绍了中兴新公司最新开发的ＣＤＭＡ无线接入设备－ＺＸＤＷＬＬ系统的实现工，技术特点及其应用，以期促进中国ＣＤＭＡ技术的发展。     

一种新的CDMA系统多业务接入控制算法

文中提出一种新的CDMA系统中多业务接入控制算法。为了提高系统容量,在传统容量干扰受限的CDMA系统接入控制算法的基础上,考虑各种业务的激活因子,计算出系统接入呼叫用户后各个业务的中断概率,根据其中断概率是否满足QoS要求判断业务是否接入。仿真结果表明：所提算法的各种业务的阻塞概率明显低于传统算法,并且系统获得的性能改善随着桌些业务呼叫强度的增加而下降,从而证明了所提算法在系统容量上的优势。     

基于半马尔可夫链的WLAN/CDMA联合呼叫接入控制

下一代网络（NGN）将融合多种异构无线接入网络。为了在满足QoS限制下,最大化网络收益,在对WLAN／CDMA等效带宽的研究基础上,提出一种基于SMDP（半马尔可夫决策规划）的最优的联合呼叫接入控制（JCAC）方案,方案考虑了WLAN和CDMA网络间的相互影响,并将网络连接的联合呼叫控制问题等效成一个半马尔可夫决策过程,仿真表明方案相对于离散时间的MDP和在MDP基础上的JCAC算法具有明显的优势。     

软交换网络中的视频多媒体业务

介绍了支持视频多媒体业务的软交换系统结构，软交换系统的功能要求以及软交换中多媒体视频业务的实现方式等。     

A Novel Effective Bandwidth Based Call Admission Control for Multimedia CDMA Systems

A novel Call Admission Control(CAC)scheme is proposed for multimedia CDMA systems.The effectivebandwidth of real time calls is reserved in the CAC with the consideration of active factors.The admission of non-real timecalls is controlled by the system according to the residual effective bandwidth left from real time calls.Simulation resultshave shown that the novel CAC has greatly enlarged the admission region for real time calls and make the transmission de-lay of non-real time calls under an acceptable level.     

Centralized and distributed power control algorithms for multimedia CDMA networks

We study in this paper both centralized and distributed transmitter power control algorithms for multimedia CDMA networks. In our study, users can have different data rates as well as different quality of service (QoS) requirements characterized by bit energy‐to‐interference ratios. For centralized power control, we derive an optimum power assignment which can be obtained by solving a set of linear equations. For distributed power control (DPC), we study the fully distributed power control (FDPC) algorithm. We modify the FDPC algorithm so that it can be used in a multi‐service environment. We prove that, as long as there are solutions of power levels for all users to meet their QoS requirements, the FDPC algorithm can always find one. A quasi‐centralized power control algorithm with partial link gain measurements is proposed to speed up the process in finding a feasible power set. In the algorithm, a base station measures the link gains for all mobiles connected to it. Numerical results show that quasi‐centralized power control can find a feasible power set much faster than distributed power control. Copyright © 2005 John Wiley & Sons, Ltd.     

Optimized bandwidth allocation with fairness and service differentiation in multimedia wireless networks

In this article we present an optimal Markov Decision‐based Call Admission Control (MD‐CAC) policy for the multimedia services that characterize the next generation of wireless cellular networks. A Markov decision process (MDP) is used to represent the CAC policy. The MD‐CAC is formulated as a linear programming problem with the objectives of maximizing the system utilization while ensuring class differentiation and providing quantitative fairness guarantees among different classes of users. Through simulation, we show that the MD‐CAC policy potentially achieves the optimal decisions. Hence our proposed MD‐CAC policy satisfies its design goals in terms of call‐class‐differentiation, fairness and system utilization. Copyright © 2006 John Wiley & Sons, Ltd.     

Handoff performance in wireless DS‐CDMA networks

This paper analyses the performance of DS‐CDMA networks in the presence of call handoffs. We show that a handoff may violate the SINR requirements for other users, and thus cause an outage in the target cell. We propose to use the probability of such events as a possible metric for quality of service in networks with multiple traffic types, and derive the corresponding QoS parameters. A two‐level admission policy is defined: in tier 1 policy, the network capacity is calculated on the basis of the bound on outage probability. However, this policy does not suffice to prevent outage events upon handoffs for various traffic types, and henceforth, we propose an extension that reserves extra bandwidth for handoff calls, thus ensuring that handoff calls will not violate the outage probability bound. The overhead imposed by the extension is negligible, as the complete two‐tier admission control algorithm is executed only when a call is admitted into the network. Once admitted, calls can freely execute handoffs using the reserved bandwidth. The modified second‐tier bandwidth reservation policy is adaptive with respect to the traffic intensity and user's mobility and we show that it can provide satisfactory call (flow) quality during its lifetime. Analytical results for the QoS have been verified by the simulations. Copyright © 2002 John Wiley & Sons, Ltd.     

一种改进的CDMA自适应呼叫接纳控制算法

呼叫接纳控制（CAC）是CDMA蜂窝系统无线资源管理的重要功能实体，有效的CAC算法能满足各类业务的不同OoS要求，还能提高资源利用率。文中讨论了一种改进的基于cDMA系统门限的自适应接纳控制算法，仿真结果表明改进后的算法与传统算法相比具有比较好的性能．     

Ratioed power and rate control for CDMA wireless networks

We propose in this paper the ratioed power and rate control (RPRC) algorithm to satisfy the requirements of both the data rate and the signal quality. During the execution of the RPRC algorithm, only the representative user in each cell adjusts its power level according to certain distributed power control algorithm, and the ratio of the power level for the non‐representative user to that for the representative user is kept constant. When the RPRC algorithm is finished, the power levels for all users remain unchanged and the transmission rate is determined by the available rate. We show that the RPRC algorithm can be used for allocating the bandwidth of each cell and achieving the required rate of each user. Furthermore, simulation results reveal that the RPRC algorithm results in larger throughput and finds a feasible power set faster than the other algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

MIMO ARIMA models for handoff resource reservation in multimedia wireless networks

This paper presents a new approach to prediction of resource demand for future handoff calls in multimedia wireless IP networks. Our approach is based on application of multi‐input‐multi‐output (MIMO) multiplicative autoregressive‐integrated‐moving average (ARIMA) (p,d,q)x(P,D,Q)_S models fitted to the traffic data measured in the considered cell itself and on the new call admission control (CAC) algorithm that simultaneously maximizes the system throughput while keeping the handoff call dropping probability (CDP) below the targeted value. The main advantages of the proposed approach are the following: first, the proposed multi‐variable prediction method gives on average better predictions (i.e. narrower prediction confidence interval) for realistic traffic situations, which results in lower new call blocking probability (CBP) at the targeted handoff CDP and second, the model is simple to implement since it does not require communication among the adjacent cells. Simulation results show the superiority of the proposed MIMO prediction approach combined with the proposed call admission control algorithm for some typical nonstationary situations in comparison with univariate models. Copyright © 2004 John Wiley & Sons, Ltd.     

Bandwidth guaranteed call admission in TDMA/CDMA ad hoc wireless networks

This paper first studied the timeslot assignment problem in time division multiple access/code division multiple access (TDMA/CDMA) wireless ad hoc networks. Given a path P, we prove that a timeslot assignment providing one unit of bandwidth on P can be found in O(P) time if such an assignment exists. The results have been extended to the case that P can provide two units of bandwidth. Based on the timeslot assignment for the special cases, an efficient slot assignment algorithm with O(P²k) is proposed for general cases, where k is the number of slots in a TDMA frame. Then, the timeslot assignment algorithm is integrated into a quality of service (QoS) call admission scheme for QoS call requests. Extensive simulations are conducted and the results have demonstrated the superior performance of our method.     

Admission control for variable spreading gain CDMA cellular system with imperfect power control and shadowing

Variable spreading gain (VSG) CDMA is the prime transmission scheme for supporting multiple services for the next generation cellular systems. As different services have different quality of service and data rate requirements, admission control is essential in safeguarding the performance of different services in VSG‐CDMA cellular systems in harsh wireless environment. In this paper, we propose an admission control scheme for multiple services VSG‐CDMA cellular system in a practical multi‐cell environment where there exist adverse effects due to imperfect power control and shadowing. Rather than with a fixed bound as in previous studies, the admission bound in our scheme is based on the probability distribution of total intra‐cell power (P_in) and other‐cell interference power (I_other). This is used to estimate the blocking probability by utilizing a simple and accurate approximation that incorporates the random nature of P_in and I_other. Evaluation of the impact of power control error to the mean and standard deviation of P_in and I_other, we performed and compared the blocking probability with fixed admission bound scheme in an integrated voice/data environment. Our work has enabled the calculation of the blocking probability and capacity of different mobility users having different power control errors under shadowing. Copyright © 2006 John Wiley & Sons, Ltd.