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.     

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.     

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.     

Performance analysis of a threshold based distributed channel allocation algorithm for cellular networks

Rapid advances of the handheld devices and the emergence of the demanding wireless applications require the cellular networks to support the demanding user needs more effectively. The cellular networks are expected to provide these services under a limited bandwidth. Efficient management of the wireless channels by effective channel allocation algorithms is crucial for the performance of any cellular system. To provide a better channel usage performance, dynamic channel allocation schemes have been proposed. Among these schemes, distributed dynamic channel allocation approaches showed good performance results. The two important issues that must be carefully addressed in such algorithms are the efficient co-channel interference avoidance and messaging overhead reduction. In this paper, we focus on our new distributed channel allocation algorithm and evaluate its performance through extensive simulation studies. The performance evaluation results obtained under different traffic load and user mobility conditions, show that the proposed algorithm outperforms other algorithms recently proposed in the literature.     

A hybrid genetic algorithm to optimize device allocation in industrial Ethernet networks with real-time constraints

With the advance of automation technology,the scale of industrial communication networks at field level is growing.Guaranteeing real-time performance of these networks is therefore becoming an increasingly difficult task.This paper addresses the optimization of device allocation in industrial Ethernet networks with real-time constraints (DAIEN-RC).Considering the inherent diversity of real-time requirements of typical industrial applications,a novel optimization criterion based on relative delay is proposed.A hybrid genetic algorithm incorporating a reduced variable neighborhood search (GA-rVNS) is developed for DAIEN-RC.Experimental results show that the proposed novel scheme achieves a superior performance compared to existing schemes,especially for large scale industrial networks.     

A preemptive channel allocation scheme for multimedia traffic in mobile wireless networks

This paper presents a channel allocation model with both partial and full preemptive capabilities for multimedia traffic in mobile wireless networks. The different types of multimedia traffic in transmitting through next-generation networks possess different characteristics and demand an adequate channel allocation scheme to fulfill individual Quality of Service (QoS) requirements. In the proposed model, multimedia traffic is classified into three classes corresponding to different priority levels in a decreasing order. To effectively reduce the dropping probability, a higher-priority handoff call is allowed to fully or partially preempt any lower-priority ongoing calls when the channel capacity becomes insufficient. In addition, to prevent from possible starvation of the lowest-priority traffic, a portion of system channels are purposely reserved. Performance measures, including the dropping probability of handoff calls, the call-interruption probability that an ongoing call is forced to termination due to full preemption, and the bandwidth reduction ratio due to partial preemption, are investigated through an analytical model built with 4-D Markov chains. The numerical results demonstrate the effectiveness of our model.     

一种改进的基于最少信道切换的路由算法

在Ad Hoc网络中,如何基于多信道有效地利用网络中的频谱资源,提高网络的性能,已经成为近几年来研究的热点。在DSDV路由协议的基础上,提出了一种基于减少网络中的信道切换的路由算法——OLCH-DSDV,该算法采用最小切换时延的信道分配策略,尽量减少信道切换产生的时延,从而降低了网络时延,提高了吞吐量。该算法要求源节点通过自身维护的路由和信道使用信息,选择到达目的节点的最优路径,也就是需要最少信道切换的路径。仿真结果表明该路由改进算法在有效提高系统吞吐量的同时,也有效地减少了网络中的传输时延。     

移动互联异构网络下多终端协同的垂直切换决策算法

针对移动互联网用户的多终端协同的垂直切换问题,提出一种UMTS与WLAN异构网络环境下的多终端协同的垂直切换决策算法,其包含切换时间判断与多终端协同算法。首先利用模糊逻辑判断网络切换时机,然后综合考虑主观因素和客观因素,采用AHP（Analytic Hierarchy Process）合理定义权值并结合TOPSIS（Technique for Order Preference by Similarity to an Ideal Solution）实现不同接入策略的性能评价,为用户提供最佳QoE（Quality of Experience）的多终端协同方案。实验结果表明：所提方法和基于迟滞算法相比,切换次数平均降低7.9次,切换失败率平均降低2.25%;网络选择结果与应用需求和用户需求保持较好的一致性。实现了多终端协同用户在异构网络环境下高效实时的垂直切换。     

A weight-aware channel assignment algorithm for mobile multicast in wireless mesh networks

Wireless mesh networks (WMNs) are one of key technologies for next generation wireless networks. In this paper, we propose a heuristic channel assignment algorithm with weight awareness to support mobile multicast in WMNs. To enhance network throughput, our algorithm is based on the path forwarding weight to perform channel assignment. In addition to non-overlapping channels, partially-overlapping channels are also used in channel assignment. To fully exploit all available channels in channel assignment, we devise a new channel selection metric to consider the channel separation and the distance between nodes. In mobile multicast, the multicast tree structure cannot be fixed due to receiver (multicast member) mobility. The change of the multicast tree structure will result in channel re-assignment. The proposed algorithm is based on a critical-event driven manner to reduce the times of channel re-assignment as much as possible. Finally, we perform simulation experiments to show the effectiveness of the proposed channel assignment algorithm.     

一种新的启发式算法在蜂窝网络信道分配中的应用

在蜂窝小区信道分配算法中,排序分配算法是根据待分配小区的难度系数分配信道,收敛速度较快,但很容易陷入排序的自身循环以至于无法找到更好的排序方式。在MAX MIN蚁群算法的基础上提出一种新的启发式算法,通过概率选择避免排序自身循环,再通过判定收敛系数来确定此次迭代是否已停滞,然后重新初始化信息素以寻找更好的排序方式。在对Philadelphia典型问题的测试中,本算法较排序分配算法更接近理论边界值,而且在解的质量相同情况下,其收敛时间也优于其他蚁群算法。     

结合混合式信道分配的Mesh多路径路由协议

为了优化无线Mesh网络中的多接口多信道网络资源,对单接口多路径路由协议和单路径信道分配策略进行了深入的分析研究,提出了与混合式信道分配方式相结合的多路径路由协议(AODV-MP),实现了网络中多条路径的并行传榆,从而提高网络的整体吞吐率.并根据多路径路由协议自身的特性,结合与邻居节点干扰相关的因素--信噪比(SNR),提出了多路径路由的路由度量判决WCETYSNR,同时将该路由度量作为负栽流量分配的比例标准.利用NS2网络仿真平台对该多路径路由协议进行测试,结果显示AODV-MP在网络吞吐率上提高了45%,并在高负载情况下,较大幅度地减少了网络延时.     

Simulation of wireless cellular networks with impatient calls

Algorithms for the approximate calculation of the characteristics of wireless telecommunications with a microcellular structure where new and handover calls form queues with limited length have been developed. It is supposed that calls of both types can leave the queues unserved if their waiting time exceeds some threshold values. The results of numerical calculations are presented.     

Optimum reserved resource allocation scheme for handoff in CDMA cellular system

CDMA cellular systems support two types of handoff: soft handoff and hard handoff. Soft handoff has many advantages over hard handoff. Qualitatively, this feature provides more reliable handoff between base stations as a mobile moves from one cell to the adjacent one. Quantitatively, it considerably increases both the capacity of a heavily loaded multicellular system and the coverage of each individual cell in a lightly loaded system. In this paper, in order to increase the probability of soft handoff at the time of handoff, optimum reserved resource allocation scheme for handoff in CDMA cellular system is proposed, which allocates reserved resource to each frequency channel according to the number of neighbor cells using the same frequency channel. Performance analysis results show that the proposed scheme has higher probability of soft handoff at the time of handoff and higher total call processing performance which is a function of both new calls accepted probability and soft handoff probability than the conventional scheme allocating reserved resource irrelevantly to frequency channels being used by neighbor cells.     

An efficient evolutionary algorithm for channel resource managementin cellular mobile systems

Modern cellular mobile communications systems are characterized by a high degree of capacity. Consequently, they have to serve the maximum possible number of calls while the number of channels per cell is limited. The objective of channel allocation is to assign a required number of channels to each cell such that both efficient frequency spectrum utilization is provided and interference effects are minimized. Channel assignment is therefore an important operation of resource management and its efficient implementation increases the fidelity, capacity, and quality of service of cellular systems. Most channel allocation strategies are based on deterministic methods, however, which result in implementation complexity that is prohibitive for the traffic demand envisaged for the next generation of mobile systems. An efficient heuristic technique capable of handling channel allocation problems is introduced as an alternative. The method is called a combinatorial evolution strategy (CES) and belongs to the general heuristic optimization techniques known as evolutionary algorithms (EAs). Three alternative allocation schemes operating deterministically, namely the dynamic channel assignment (DCA), the hybrid channel assignment (HCA), and the borrowing channel assignment (BCA), are formulated as combinatorial optimization problems for which CES is applicable. Simulations for representative cellular models show the ability of this heuristic to yield sufficient solutions. These results will encourage the use of this method for the development of a heuristic channel allocation controller capable of coping with the traffic and spectrum management demands for the proper operation of the next generation of cellular systems     

认知无线Mesh网络中基于协作学习自动机的自适应信道分配算法*

在认知无线Mesh网络多信道环境中处理繁重的数据业务是一项具有挑战性的任务。为了解决这个问题,提出了一种新的基于协作学习自动机(Learning automata,LA)的自适应信道分配算法(CLACAA)。在所提出的算法中,LA被部署在邻近的互相协作的次用户上。首先,为了LA能自适应地更新其动作概率向量,设计了一种线性奖赏无为方案;其次,定义了一种新的信道利用率因子用于信道选择,以解决信道冲突发生的问题;最后,给出了当信道由于大量输入请求而过载时的信道切换方案。实验仿真结果表明,该算法在提升网络吞吐量和数据传输率,降低切换时延和缓冲时延上有明显的优势。     

A decomposition-based hybrid multiobjective evolutionary algorithm with dynamic resource allocation

Different crossover operators suit different problems. It is, therefore, potentially problematic to chose the ideal crossover operator in an evolutionary optimization scheme. Using multiple crossover operators could be an effective way to address this issue. This paper reports on the implementation of this idea, i.e. the use of two crossover operators in a decomposition-based multi-objective evolutionary algorithm, but not simultaneously. After each cycle, the operator which has helped produce the better offspring is rewarded. This means that the overall algorithm uses a dynamic resource allocation to reward the better of the crossover operators in the optimization process. The operators used are the Simplex Crossover operator (SPX) and the Center of Mass Crossover operator (CMX). We report experimental results that show that this innovative use of two crossover operators improves the algorithm performance on standard test problems. Results on the sensitivity of the suggested algorithm to key parameters such as population size, neighborhood size and maximum number of solutions to be altered for a given subproblem in the the decomposition process are also included.     

On distributed dynamic channel allocation in mobile cellularnetworks

Distributed dynamic channel allocation (DDCA) is a fundamental resource management problem in mobile cellular networks. It has a flavor of distributed mutual exclusion but is not exactly a mutual exclusion problem. We establish the exact relationship between the two problems. Specifically, we introduce the problem of relaxed mutual exclusion to model one important aspect of the DDCA problem. We develop a general algorithm that guarantees relaxed mutual exclusion for a single resource and prove necessary and sufficient conditions for the information structure. Considering distributed dynamic channel allocation as a special case of relaxed mutual exclusion, we apply and extend the algorithm to further address the issues that arise in distributed channel allocation such as deadlock resolution, dealing with multiple channels, design of efficient information structures, and channel selection strategies. Based on these results, we propose an example distributed channel allocation scheme using one of the information structures proposed. Analysis and simulation results are provided and show that the results of this research can be used to design more efficient distributed channel allocation algorithms     

A disk bandwidth allocation mechanism with priority

Virtualization is a popular technology. Services and applications running on each virtual machine have to compete with each other for limited physical computer or network resources. Each virtual machine has different I/O requirement and special priority. Without proper scheduling resource management, a load surge in a virtual machine may inevitably degrade other’s performance. In addition, each virtual machine may run different kinds of application, which have different disk bandwidth demands and service priorities. When assigning I/O resources, we should deal with each case on demand. In this paper, we propose a dynamic virtual machine disk bandwidth control mechanism in virtualization environment. A Disk Credit Algorithm is introduced to support a fine-gained disk bandwidth allocation mechanism among virtual machines. We can assign disk bandwidth according to each virtual machine’s service priority/weight and its requirement. Related experiments show that the mechanism can improve the VMs’ isolation and guarantee the performance of the specific virtual machine well.     

时变信道正交频分复用系统绿色资源分配算法

传统的基于终端节能的绿色资源分配算法大都忽略了无线信道的时间选择性对能耗与系统性能的影响,为此提出一种结合多用户分集的绿色资源分配算法。在保证用户公平性的基础上引入多用户分集,动态调整多用户分集子模块大小以满足信道时变特性要求;分集子模块内有多个频带可供使用,用户资源尽可能集中在比较少的时隙内传输以降低总的终端接收能耗,通过顶点搜索快速寻找最优解。仿真结果表明,系统吞吐量可以提高13%左右,其稳定性得到改善;同时算法具有计算复杂度低、收敛速度快等特点,保持了良好的终端节能增益。