一种新的基于多业务的移动通信系统切换策略

针对目前移动通信系统大部分信道切换策略中新呼叫阻塞率高的问题,提出了一种新的呼叫延迟切换策略,该策略是让即将占用最后一个空闲信道的新呼叫短暂延迟后再占用空闲信道,切换呼叫则直接占用空闲信道,缩短了信道被全部占用的时间,增加了新呼叫和切换呼叫占用信道的机会。该策略同时考虑了数据业务之间的优先级,只有当高优先级数据队列中的数据包为空时,低优先级队列中的数据包才能够占用信道。给出了切换呼叫掉话率、新呼叫阻塞率及数据包掉包率的理论公式。与预留信道策略和可移动边界策略的对比表明,新策略既提高了新呼叫进入系统的概率,又有效降低了切换呼叫的掉话率,同时也减少了高优先级数据的掉包率。     

An efficient approach for distributed dynamic channel allocation with queues for real-time and non-real-time traffic in cellular networks

We are witnessing these days a rapid growth of mobile users. Therefore, frequency spectrum must be efficiently utilized, as available frequency spectrum is limited. This paper proposes a channel allocation scheme with efficient bandwidth reservation, which initially reserves some channels for handoff calls, and later reserves the channels dynamically, based on the user mobility. The direction of user mobility may not be straight always, but the user may also go left, right or backwards. Thus, QoS can be improved, if the channel reservation is made based upon the user mobility and the location of the user. We devise here a new algorithm that deals with multiple traffic systems by modifying the existing DDCA algorithm [Krishna, P.V., Iyengar, N.Ch.S.N., 2008. Optimal channel allocation algorithm with efficient channel reservation for cellular networks. International Journal of Communication Networks and Distributed Systems 1 (1), 33-51]. This algorithm reserves more channels for hot cells, less number of channels for cold cells and an average number of channels for the medium cells. Furthermore, we maintain queues for all types of calls. We model the system by a three-dimensional Markov Chain and compute the QoS parameters in terms of the blocking probability of originating calls and the dropping probability of handoff calls. The results indicate that the proposed channel allocation scheme exhibits better performance by considering the above mentioned user mobility, type of cells, and maintaining of the queues for various traffic sources. In addition, it can be observed that our approach reduces the dropping probability by using reservation factor.     

Predictive channel reservation for handoff prioritization in wireless cellular networks

In wireless cellular networks, a roaming mobile station (MS) is expected to move from one cell to another. In order to ensure that ongoing calls are not dropped while the owner mobile stations roam among cells, handoff calls may be admitted with a higher priority than newly generated calls. Predictive channel reservation (or pre-reservation) schemes allow the reservation of a channel for an ongoing call in an adjacent cell before its owner MS moves into that cell, so that the call is sustained when the MS moves into the adjacent cell. Pre-reservations are made when the MS is within some distance of the new cell boundary. This distance determines the area in which the MS can make channel reservations. In this paper, we study the effect of the pre-reservation area size on handoff performance in wireless cellular networks. Our studies show that if the reserved channels are strictly mapped to the MSs that made the corresponding reservations, as we increase the pre-reservation area size, the system performance (in terms of the probability that the handoff calls are dropped) improves initially. However, beyond a certain point, the performance begins to degrade due to a large number of false reservations. The optimal pre-reservation area size is closely related to the traffic load of the network and the MSs’ mobility pattern (moving speed). We provide an analytical formulation that furthers understanding with regard to the perceived behavior in one-dimensional networks (in which all cells are along a line).With the objective of improving handoff performance and alleviating this sensitivity to the area size, we propose an adaptive channel pre-reservation scheme. Unlike prior pre-reservation methods, the key idea in our scheme is to send a channel pre-reservation request for a possible handoff call to a neighboring cell not only based on the position and orientation of the owner MS, but also as per its speed towards the target cell. The newly proposed scheme uses GPS measurements to determine when channel pre-reservation requests are to be made. Simulation results show that the adaptive channel pre-reservation scheme performs better in all typical scenarios than a previously proposed popular pre-reservation method that does not take mobility into account.     

A hybrid channel allocation algorithm with priority to handoff calls in mobile cellular networks

This paper proposes and investigates a novel analytical model of a hybrid channel allocation algorithm within wireless cellular networks. Each cell of the network consists of a predesigned fixed number of channels and the network may approve the request for extra channels for both new and handoff calls if all predesigned channels are occupied. This approval depends on the types of new and handoff calls, as well as the number of approved additional channels in the cell. If a request is denied for the arriving new call, this call will be blocked and cleared from the system. However, if a request is denied for an arriving handoff call, this call will not be blocked immediately but rather put on hold in a buffer with finite space. The implication behind this is to give priority to handoff calls. For this proposed hybrid channel allocation scheme, we first obtain the stationary distribution of each cell when there are i calls connecting to the system and j calls holding on in the buffer. We then derive new and handoff call blocking probabilities, the average number of borrowed channels, and the average delay period of handoff calls. The numerical results show that the proposed hybrid algorithm is more efficient than other approaches, specifically, in comparison with methods without a borrowing capability for new calls and those without a reserved buffer priority for handoff calls. The idea and results presented in this paper are expected to provide guidelines for field data processing within current wireless and mobile network design and performance evaluation.     

Performance analysis of wireless mobile networks with queueing priority and guard channels

The blocking probability of originating calls and forced termination probability of handoff calls are important criteria in performance evaluation of integrated wireless mobile communication networks. In this paper, we model call traffic in a single cell in an integrated voice/data wireless mobile network by a finite buffer queueing system with queueing priority and guard channels. We categorize calls into three types of service classes: originating voice calls, handoff voice calls and data calls. The arrival streams of calls are mutually independent Poisson processes, and channel holding times are exponentially distributed with different means. We describe the behavior of the system by a three‐dimensional continuous‐time Markov process and present the explicit expression for steady‐state distribution of queue lengths using a recursive approach. Furthermore, we calculate the blocking, forced termination probabilities and derive the Laplace–Stieltjes transform of the stationary distribution of actual waiting times and their arbitrary kth moment. Finally, we give some numerical results and discuss the optimization problem for the number of guard channels.     

An adaptive call admission algorithm for cellular networks

In this paper, we first propose a new continuous action-set learning automaton and theoretically study its convergence properties and show that it converges to the optimal action. Then we give an adaptive and autonomous call admission algorithm for cellular mobile networks, which uses the proposed learning automaton to minimize the blocking probability of the new calls subject to the constraint on the dropping probability of the handoff calls. The simulation results show that the performance of the proposed algorithm is close to the performance of the limited fractional guard channel algorithm for which we need to know all the traffic parameters in advance.     

User mobility oriented predictive call admission control and resource reservation for next-generation mobile networks

This paper addresses the problem of resource reservation (RR) and call admission control (CAC) in wireless mobile networks. A new user mobility oriented predictive scheme called PCAC-RR is proposed for call admission control and resource reservation. The main goal is to reduce the call dropping probability and the call blocking probability, and to maximize the bandwidth utilization. By analyzing the previous movements of the mobile users, we generate local and global mobility profiles for mobile users, which are utilized effectively in the prediction of the future path of a mobile user. Extensive simulation is used to study the performance of the proposed technique and to compare its performance with other two techniques: FR-CAT2 and PR-CAT4. Simulation results show that the proposed scheme has a significantly better performance compared to the other two schemes.     

Optimal prioritized channel allocation in cellular mobile systems

Under the cutoff priority discipline, the optimal prioritized channel allocation problem is formulated, which minimizes the weighted average blocking probability of handoff calls while ensuring the prespecified grade of service for new calls and the co-channel interference constraints. We use the concept of pattern to deal with the problem more conveniently. Using Lagrangean relaxation and subgradient optimization techniques, we obtain high-quality solutions with information about their deviations from true optimal solutions. Computational experiments show that our method works very well.Scope and PurposeChannel allocation is one of the most important problems in the design of cellular mobile systems. Since the number of cells of forthcoming networks will increase rapidly, this problem will be of even greater importance in the future. In cellular mobile systems, a new channel should be assigned by the new base when a call enters an adjacent cell. It provides continuation of ongoing calls as the user travels across cell boundaries, and is called handoff. The handoff call is forced to terminate before completion if there are no channels available in the new cell. However, in many practical situations, the blocking of a handoff call attempt is critical since it will result in a disconnection of the call in the middle of conversation. Thus, for reducing the blocking probability of handoff calls, several algorithms based on the cutoff priority scheme have been introduced in the literature. In the cutoff priority scheme, priority is given to handoff calls by exclusively reserving some channels called guard channels for them. In this article, we formulate a prioritized channel allocation problem under the cutoff priority scheme in general multicell environments, and suggest an efficient algorithm to solve that problem.     

无线网络时变带宽业务的准入控制性能分析

无线蜂窝网络的通话准入控制方法与通话的 Qo S以及无线信道的利用率密切相关 .使用 Markov过程得出了业务带宽需求时变状况下系统性能 (通话的切换掉线概率、并发掉线概率、阻塞概率以及信道利用率 )的理论模型 .通过数值结果分析了系统负载、用户的移动、通话的持续时间对系统性能的影响     

异构分层无线网络中基于业务和逗留时间的动态流量均衡算法

在异构分层无线网络中使用有效的流量均衡技术，可以给更多的移动用户提供服务。现有的流量均衡算法主要针对同种无线网络，因而不能直接用于异构无线网络。本文提出了一种适用于异构无线网络的基于业务和逗留时间的动态流量均衡算法，该算法首先根据移动模型计算移动用户在小区内的逗留时间，然后基于小区呼叫到达率和重叠覆盖小区的流量状态来确定一个周期内转移的非实时性呼叫数量，最后依据逗留时间门限值将重负载小区中满足条件的呼叫转移到轻负载的重叠覆盖小区中。为降低切换呼叫掉线率，还对异构网间的呼叫切换策略做了改进。仿真实验结果表明．本算法在新呼叫阻寒率和切换呼叫掉线率等性能指标上比传统方法有显著提高．     

A ratioed channel assignment scheme for initial and handoff calls in mobile cellular systems

In this paper, we present two schemes to improve the call completion probability of initial and handoff calls in mobile cellular systems. All the previous schemes give priority to handoff calls over initial calls to avoid the forced termination of calls in progress. We observe that giving priority to handoff calls would not yield better call completion probability in general. Moreover, the proportion of handoff to initial attempts in service will influence the call completion probability if both handoff and initial calls are queued. Our theoretical analysis and the simulation results both show that the proposed schemes are better than the NPS scheme and the FIFO scheme when the performance is measured in terms of call completion probability.     

Completed analysis of cellular networks with PH-renewal arrival call

In this paper, we apply the PH-renewal process to model new call and handoff processes, and apply the matrix-analytic approach to explore the performance measures of the drop and block probabilities. We examine the bursty nature of handoff call drops by means of conditional statistics with respect to alternating block and non-block periods. Five related performance measures are derived from conditional statistics, including the long-term new call block and handoff call drop probabilities, and the three short-term measures of average length of a block period and a non-block period, as well as the conditional handoff call drop probability during a block period. These performance measures greatly assist the priority reservation handoff mechanism in determining a proper threshold guard channel in the cell. Furthermore, we derive the handoff call drop probability from the short-term performance measures of average length of a block period and a non-block period, as well as the conditional handoff call drop probability during a block period. The results presented in this paper can provide guidelines for designing adaptive algorithms to adjust the threshold in the guard channel reservation handoff scheme.     

On utility-fair bandwidth adaptation for multi-class traffic QoS provisioning in wireless networks

The ability to adjust the allocated bandwidth of ongoing calls to cope with wireless network resource fluctuations is becoming increasingly important. In this paper, we describe a utility-based bandwidth adaptation scheme for multi-class traffic quality-of-service (QoS) provisioning in wireless networks. With the proposed scheme, each call is assigned a utility function according to its adaptive characteristics. Depending on the network load the allocated bandwidth of ongoing calls are upgraded or degraded dynamically such that each call receives fair utility. The quantization of utility function by dividing the utility range into a fixed number of equal intervals is a key feature of our proposed utility-fair algorithm. Appropriate call admission control and bandwidth reservation policies are also integrated into the proposed scheme to provide QoS guarantees to the new and handoff calls. Extensive simulation experiments have been conducted to evaluate the performance of the proposed scheme compared with two other existing ones. Results show that our bandwidth adaptation scheme is effective in achieving utility fairness while keeping the call blocking and handoff dropping probabilities substantially low.     

LEO卫星通信系统中信道分配策略仿真

切换是LEO卫星移动通信系统中移动性管理的一个重要组成部分。LEO切换中的信道分配一般采用保护信道和各种排队方法相结合的策略。研究了多业务条件下LEO卫星通信系统越区切换中的信道分配策略，根据数据业务和话音业务的特点，提出了适用于LEO卫星通信系统的保护信道和强占优先相结合的信道分配策略。建立了一个简单而有效的LEO卫星通信系统切换模型，将新策略与传统的保护信道策略进行比较，仿真结果表明新策略以略微增加数据时延为代价换取了话音业务各项性能的极大改善。     

一种自适应的扇型微蜂房式带宽预留通信模式

在目前的跨区域连接方式中,扇型微蜂房式的网络系统比传统的微蜂房式系统有更高的传输速度.文中介绍了一种自适应的带宽预留模式,这种模式使用了一种神经模糊带宽预留估计量的技术,经过证实,这种技术能够减少客户连接时被强行终止的概率.在这种带宽预留模式中,使用一种通道借用技术能够在实时通信时,减少新的呼叫受阻现象的发生.通过分析强行终止的客户连接和呼叫受阻的概率事件,仿真结果表明,采用扇型微蜂房式的网络系统比传统的固定带宽预留模式要有更好的性能.     

Application of support vector machines to bandwidth reservation in sectored cellular communications

Many mechanisms based on bandwidth reservation have been proposed in the literature to decrease connection dropping probability for handoffs in cellular communications. The handoff events occur at a much higher rate in sectored cellular networks than in traditional cellular systems. An efficient bandwidth reservation mechanism for the neighboring cells is therefore critical in the process of handoff during the connection of multimedia calls to avoid the unwillingly forced termination and waste of limited bandwidth in the sectored cellular communications, particularly when the handoff traffic is heavy. In this paper, a self-adaptive bandwidth reservation scheme, which adopts support vector machines technique, is proposed to reduce the forced termination probability. Meanwhile, a channel-borrowing technique is used to decrease the new call-blocking probability of real-time traffic. The simulation results show that the proposed scheme can achieve superior performance than the representative bandwidth-reserving schemes in sectored cellular networks in the literature when performance metrics are measured in terms of the forced termination probability and the new call- blocking probability.     

Service Adaptability in Multimedia Wireless Networks

Next-generation wireless communication systems aim at supporting wireless multimedia services with different quality-of-service (QoS) and bandwidth requirements. Therefore, effective management of the limited radio resources is important to enhance the network performance. In this paper, we propose a QoS adaptive multimedia service framework for controlling the traffic in multimedia wireless networks (MWN) that enhances the current methods used in cellular environments. The proposed framework is designed to take advantage of the adaptive bandwidth allocation (ABA) algorithm with new calls in order to enhance the system utilization and blocking probability of new calls. The performance of our framework is compared to existing framework in the literature. Simulation results show that our QoS adaptive multimedia service framework outperforms the existing framework in terms of new call blocking probability, handoff call dropping probability, and bandwidth utilization.      

LEO卫星中模拟实时通信量确保保护信道的分配

由于LEO（Low Earth Orbit）卫星网络中不断变化的点波束小区实时通信量负载无法估计,提出了一种根据系统仿真过程中当前通信量状态优化动态保护信道算法（ODGCS）。该分配策略引入呼叫间隔时间和切换呼叫中断间隔时间来获悉系统的实时性能状态,由仿真中通信量状态预测当前系统切换呼叫的中断概率,根据比较计算的呼叫中断概率和预先设定的QoS（Quality of Service）值,动态调整预留给切换呼叫使用的保护信道数。仿真结果表明,与传统的静态预留保护信道的算法相比,该算法能有效提高LEO卫星系统的性能稳定性。在负载较轻时,ODGCS算法保证切换呼叫QoS的同时,降低了新呼叫阻塞概率。     

LACAV: an energy-efficient channel assignment mechanism for vehicular ad hoc networks

Designing an efficient channel assignment system for Vehicular Ad hoc Networks (VANETs), which conserves energy, is a challenging task, primarily because of the high degrees of mobility of nodes in these networks. As the high mobility of nodes in vehicular networks leads to frequent handoffs, channel assignment in VANETs becomes a tedious task. In this paper, we propose a channel assignment mechanism using the concepts of learning automata (LA) and reusability. LA is used to optimize the performance of the proposed system by selecting suitable number of reserved channels for the handoff calls and reusability allows the channel to be reused by the different base stations (BSs) based on the reuse distance. The proposed system is designed to reduce the dropping probability. The proposed system is suitable for network architectures in which it is possible to arrange the BSs with different groups of channels sequentially in a particular order that helps in conserving energy. Our experiments clearly indicate that the system reduces the dropping probability and allows a continuous communication throughout the duration of the call. The performance of proposed algorithm is compared with the Vehicular Fast Handover Scheme (VFHS), and the Cooperative scheme for service channel reservation (CRaSCH) scheme in terms of handoff latency, and it is shown that the proposed algorithm performs better than VFHS and CRaSCH.     

Mobility-based predictive call admission control and bandwidth reservation in wireless cellular networks

This paper presents call admission control and bandwidth reservation schemes in wireless cellular networks that have been developed based on assumptions more realistic than existing proposals. In order to guarantee the handoff dropping probability, we propose to statistically predict user mobility based on the mobility history of users. Our mobility prediction scheme is motivated by computational learning theory, which has shown that prediction is synonymous with data compression. We derive our mobility prediction scheme from data compression techniques that are both theoretically optimal and good in practice. In order to utilize resource more efficiently, we predict not only the cell to which the mobile will handoff but also when the handoff will occur. Based on the mobility prediction, bandwidth is reserved to guarantee some target handoff dropping probability. We also adaptively control the admission threshold to achieve a better balance between guaranteeing handoff dropping probability and maximizing resource utilization. Simulation results show that the proposed schemes meet our design goals and outperform the static-reservation and cell-reservation schemes.