A Channel Sharing Scheme for Cellular Mobile Communications

This paper presents a channel sharing scheme, Neighbor Cell Channel Sharing (NCCS) , based on region partitioning of cell coverage for wireless cellular networks. Each cell is divided into an inner-cell region and an outer-cell region. Cochannel interference is suppressed by limiting the usage of sharing channels in the inner-cell region. The channel sharing scheme achieves a traffic-adaptive channel assignment and does not require any channel locking. Performance analysis shows that using the NCCS scheme leads to a lower call blocking probability and a better channel utilization as compared with other previously proposed channel assignment schemes.     

Space Partitioning Hybrid Channel Assignment Scheme for Cellular Networks

The conventional approach of hybrid channel assignment strategy in cellular networks is rather inefficient due to the fact that it does not take advantage of the FCA scheme to the extreme. In this paper, we divide a cell into two parts: inner cell region and outer cell region, and apply the dynamic channel assignment and the fixed channel assignment schemes to the inner region and out region, respectively, in an attempt to fully utilize the strengths of the channel assignment schemes. In the performance evaluation, we demonstrate that the channel reuse efficiency has been improved compared to the FCA and DCA schemes. We also calculate the probability of an intracell handoff due to the use of the space partitioning. The proposed scheme can be adapted to a multi-tier structure with high/low speed mobile users, and hot spots.     

An Adaptive and Fault-Tolerant Channel Set Allocation Algorithm for Microcell/Macrocell Cellular Networks

Microcell/macrocell architectures are generally deployed in current cellular networks, and involve allocating each cell to a preliminary channel set to support the communications of mobile subscribers. However, cellular networks suffer risks of base transceiver station (BTS) service failure and traffic load variation among BTSs. Both of these conditions impact traffic-carrying capacity and mobile subscriber satisfaction. This investigation presents a dynamic channel set allocation algorithm for ensuring continuous optimization of overall traffic-carrying capacity. This algorithm can tolerate BTSs failure and also resolve the traffic-adaptive problem. Additionally, analytical and simulation results are presented to demonstrate the efficiency of the algorithm.Chyi-Ren Dow was born in 1962. He received the B.S. and M.S. degrees in information engineering from National Chiao Tung University, Taiwan, in 1984 and 1988, respectively, and the M.S. and Ph.D. degrees in computer science from the University of Pittsburgh, U.S.A., in 1992 and 1994, respectively. Currently, he is a Professor in the Department of Information Engineering, Feng Chia University, Taiwan. His research interests include mobile ad-hoc networks, network agents, learning technologies, and embedded systems.Jong-Shin Chen was born in 1972. He received the B.Sc. and Ph.D. degrees in engineering from Feng Chia University, Taiwan, in 1996 and 2003, respectively. His research interests include mobile computing, wireless communications, capacity planning, and systems.Yi-Hsung Li was born in 1979. He received his B.S. degree and M.S. degree in information engineering from Feng Chia University, Taiwan, in 2001 and 2003. He is currently a graduate student for the Ph.D. degree in the Department of Information Engineering and Computer, Feng Chia University, Taiwan. His research interests include personal communications, mobile computing, learning technologies, and network agents.     

Cellular Channel Assignment: A New Localized and Distributed Strategy

As the use of mobile communications systems grows, the need arises for new and more efficient channel allocation techniques. The total number of available channels on a real-world network is in fact a scarce resource, and many assignment heuristics suffer from a clear lack of flexibility (this is the case of Fixed Channel Allocation), or from high computational and communication complexity (as with channel borrowing techniques). Performance can be improved by representing the system with an objective function whose minimum is associated with a good configuration; the various constraints appear as penalty terms in the function. The problem is thus reduced to the search for a minimum, that is often performed via heuristic algorithms like Hopfield neural networks, simulated annealing or reinforcement learning. These strategies usually require a central process to have global information and decide for all cells. We consider an objective-function formulation of the channel assignment problem that has been previously solved by search heuristics; we prove that the search time for the global minimum of the objective function is O(nlogn), and therefore there is no need for search techniques. Finally we show that the algorithm that arises from this formulation can be modified so that global knowledge and synchronization are no longer required, and we give its distributed version. By simulating a cellular network with mobile hosts on a hexagonal cell pattern with uniform call distribution, we show that our technique actually performs better than the best known algorithms.     

Integrating Distributed Channel Allocation and Adaptive Handoff Management for QoS-Sensitive Cellular Networks

Next generation high-speed cellular networks are expected to support multimedia applications, which require QoS provisions. Since frequency spectrum is the most expensive resource in wireless networks, it is a challenge to support QoS using limited frequency spectrum. In the literature, two orthogonal approaches are used to address the bandwidth utilization issue and the QoS provision issue; that is, channel allocation schemes have been proposed to improve bandwidth efficiency, whereas handoff management schemes, based on bandwidth reservation, have been proposed to guarantee a low connection dropping rate. However, little effort has been taken to address both issues together. In this paper, we integrate distributed channel allocation and adaptive handoff management to provide QoS guarantees and efficiently utilize the bandwidth. First, we present a complete distributed distributed channel allocation algorithm and propose techniques to reduce its message complexity and intra-handoff overhead. Second, we integrate the proposed distributed channel allocation algorithm with an adaptive handoff management scheme to provide QoS guarantees and efficiently utilize the bandwidth. Detailed simulation experiments are carried out to evaluate the proposed methodology. Compared to previous schemes, our scheme can significantly reduce the message complexity and intra-handoff overhead. Moreover, the proposed scheme can improve the bandwidth utilization while providing QoS guarantees.     

Robust Packet Scheduling in Wireless Cellular Networks

This paper addresses the following robust scheduling problem: Given that only coarse-grained channel state information (i.e., bounds on channel errors, but not the fine-grained error pattern) is available, how to design a robust scheduler that ensures worst-case optimal performance? To solve this problem, we consider two coarse-grained channel error models and take a zero-sum game theoretic approach, in which the scheduler and the channel error act as non-cooperative adversaries in the scheduling process. Our results show that in the heavy channel error case, the optimal scheduler adopts a threshold form. It does not schedule a flow if the price (the flow is willing to pay) is too small, in order to maximize the system revenue. Among the scheduled flows, the scheduler schedules a flow with a probability inversely proportional to the flow price such that the risk of being caught by the channel error adversary is minimized. We also show that in the mild channel error model, the robust scheduling policy exhibits a balanced trade-off between a greedy decision and a conservative policy. The scheduler is likely to take a greedy decision if it evaluates the risk of encountering the channel error adversary now to be small. Therefore, robust scheduling does not always imply conservative decision. The scheduler is willing to take “risks” to expect higher gain in some scenarios. Our solution also shows that probabilistic scheduling may lead to higher worst-case performance compared to traditional deterministic policies. Finally, the current efforts show the feasibility to explore a probabilistic approach to cope with dynamic channel error conditions.     

基于IP网络的动态部分缓冲共享方案

本文基于IP网络提出了一种分组丢弃控制方案——动态部分缓冲共享.和已有的静态部分缓冲共享方案相比,新方案根据分组丢弃行为对控制阈值进行动态调整,从而对网络流量的变化具有更优的适应性.同时新方案也避免了复杂的阈值设置问题,任意设定的初始阈值都不会影响系统稳态性能.实验结果显示,新方案可以保证稳定的相对丢失率性能,并且在相同的流量条件下比原有方案具有更低的抖动延迟.     

光纤通道交换式网络的虚拟通道分配策略

 为了满足光纤通道(Fibre Channel,FC)交换式网络不断增长的带宽需求,光纤通道协议提出了虚拟通道(Virtual Channel,VC)架构,通过逻辑上的通信通道对整网流量进行合理分配.本文将VC机制由"点到点"扩展为"端到端",并结合网络演算(Network Calculus)理论和信誉量漏桶机制,在强实时条件约束下,提出虚拟通道的分配策略,以减小整网业务流量的端到端延迟时间为优化目标,解决了VC架构的三项技术难题:每种VC数目的确定、每个VC的信誉量(Credit)如何保证、以及每条VC的路径选择.计算机仿真结果表明,随着网络负载强度的不断加大,扩展的VC分配策略具有适应能力,增强了在FC交换式网络中应用VC架构的有效性.     

A Distributed Fault-tolerant Resource Planning Scheme for Wireless Networks

Efficient management of wireless channels is critical for the performance of cellular systems. Resource planning represents the allocations of system channels into cells. Accordingly, channel assignment strategies respond for using the allocated channels of cells to provide communication services in cells. However, a cellular system that experiences the varying of traffic distributions and the mobile service stations (MSSs) failing to provide communication services or recovered from failures will lessen the utilization of channels to provide communication services. In this paper, we present a distributed fault-tolerant resource planning scheme that can adaptively allocate channels to cells according to above variations in cellular systems. When the MSS of a cell fails to provide communications, its allocated channels can be reallocated to other non-failed MSSs. Our scheme has the advantages of low message overhead and low time delay. Moreover, freedom from deadlock is ensured. Simulation results, which are observed from reducing the overall average call blocking probability and the message overhead with and without applying our resource planning scheme to various channel assignment strategies, demonstrate that our algorithm is very efficient.     

Performance Analysis of Fair Channel Sharing Policies in an Integrated Cellular Voice/Data Network

We study channel sharing in an integrated cellular voice/data network with a finite queue for data call requests that cannot be served immediately upon arrival. Using analytical techniques, a comparison of different fair channel sharing policies is made. As a main result, a closed-form expression is derived for the expected sojourn time (waiting time plus transfer time) of a data call, conditional on its size, indicating that the sojourn time is proportional to the call size. This attractive proportionality result establishes an additional fairness property for the channel sharing policies proposed in the paper. Additionally, as a valuable intermediate result, the conditional expected sojourn time of an admitted data call is obtained, given the system state at arrival, which may serve as an appreciated feedback information service to the data source. An extensive numerical study is included to compare the proposed policies and to obtain insight in the performance effects of the various system and policy parameters.     

在广域网上使用IPX协议访问Oracle分布式数据库

介绍了在局域网上安装Ｏｒａｃｌｅ分布式数据库,各局域网通信路由器使用分组交换网（Ｘ．２５）连成广域网,从而在整个广域网上实现客户机（Ｃｌｉｅｎｔ）对Ｏｒａｃｌｅ服务器（Ｓｅｒｖｅｒ）的访问的方法。并对Ｃｉｓｃｏ路由器的设置、Ｏｒａｃｌｅ分布式数据库的安装和配置以及Ｄａｔａｂａｓｅ Ｌｉｎｋ的创建进行了说明。     

An Authentication Scheme for Ad-hoc Networks using Threshold Secret Sharing

Ad-hoc networks are peer-to-peer self- organized networks that make possible the communication between nodes located in areas, where communication infrastructure is absent or difficult to implement. For such networks, security is a crucial issue, since the wireless medium is vulnerable to various attacks. A centralized solution can be easily compromised, leaving the nodes exposed to threats originating from malicious users. In this paper, a security design for Ad-hoc networks is proposed and studied, providing authentication to the nodes that follow the principles of threshold secret sharing.     

Performance of Channel Carrying for Handoff in a DCA Cellular Network

Channel carrying allows a mobile station to continue the use of its currently occupied channel when it hands off to a new cell. Since in a dynamic channel assignment (DCA) system, generally, any channel can be usedby any cell, channel carrying can be more easily implemented than in a fixed channel assignment (FCA) system which supports channel carrying through borrowing channels or extending channel reuse distance. Therefore, this paperinvestigates different channel carrying strategies maybe used in the distributed timid DCA scheme with the seamless handoff policy (DCA-DT/SLH), namely, channel carrying first (CCF) and channel carrying last (CCL). This study shows that (1) CCL generally outperforms CCF; (2) in DCA-DT/SLH without channel carrying,handoff calls may suffer higher dropping probabilities than new calls if no priority is given to handoff calls while channel carrying can easily avoidsuch undesirable situation; and (3) channel carrying in DCA-DT/SLH is comparableand even better than the guard channel (GC) in FCA and can also slightly improvethe performance of GC in DCA-DT/SLH.     

Channel Management for Multi-Service Traffic in Cellular Wireless Networks

Channel management aims to provide quality of service guarantees for mobile users while efficiently utilize limited radio spectrum. With the increasing demand for diverse services in wireless networks, channel management for multi-service traffic in wireless networks is important. To provide diverse broadband services in limited radio spectrum, previous literature has presented adaptive services which provide mobile users with good quality of services. This study considers channel management for multi-service traffic in wireless networks with adaptive services. A channel management scheme, namely, restricted sharing, is devised to provide multi-class traffic with quality of service guarantees while increase channel utilization as much as possible. An analysis is used to study the performance of the restricted sharing scheme. Three classes are considered in numerical results. Numerical results show that the restricted sharing scheme guarantees quality of service and achieves high channel utilization.     

两跳蜂窝移动系统中继信道分配策略

在频率复用因子为1的两跳固定中继节点的蜂窝移动通信系统中,基于现实移动业务分布的时变性和非均匀性,提出了新的中继信道分配策略。与传统的中继信道分配策略相比,该策略不需要BS之间的协作,也能严格控制相邻小区之间同频RS的干扰距离,降低同信道干扰,在较低的系统复杂度下,实现了无线资源的有效利用。     

一种基于二维细胞自动机的秘密图像共享方案

基于二维细胞自动机提出了一种新的秘密图像共享方案,该方案把秘密图像作为细胞自动机的一个初始配置,通过利用二维n阶可逆存贮细胞自动机进行分解成n为份的影子图像,再利用其逆细胞自动机进行反向迭代来重构所共享的秘密图像.分析表明,该方案实现简单,在计算上是安全的,并且是一个完备的(n,n)方案.     

Dynamic Flow Model for Borrowing Channel Assignment Scheme in Cellular Mobile System

A mathematical model that predicts the dynamic flows in cellular mobile networks that allocate channels using the Borrowing Channel Assignment (BCA) scheme is described in this paper. Two types of handoff procedures – the prioritized and non-prioritized schemes – will be considered in the model. Discrete event simulations were performed and the results were found to be comparable to the results obtained using the mathematical model. Application to comparative study of the dynamic behaviours of the BCA and the Fixed Channel Assignment (FCA) schemes is also presented.     

无线蜂窝网中基于Δ-邻域超图的信道重用模型

信道重用问题是基于频分多址技术的无线蜂窝网络中的一项关键技术,它关系到信道的传输效率,传统的方式是用冲突图模型来表示该问题。但是,由于冲突图模型中只考虑了两个小区之间的干扰,无法反映多个小区之间干扰的情况,又有人用超图模型来描述该问题。超图的建模为指数时间的,为了降低建模的计算复杂度,将该问题描述为Δ-邻域超图模型。性能分析结果表明,该模型既可以在多项式时间内完成建模,又可以充分反映多个小区之间的干扰关系。     

Channel Assignment for Cellular Networks Based on a Local Modified Hopfield Neural Network

In this paper, we propose a modified discrete Hopfield neural networks algorithm for the channel assignment problem. In opposition to previous work, we tried to apply the optimization locally on a per cell basis in order to reduce the CPU processing time and decrease the designed system complexity while obtaining a near-optimum solution. In addition, the research is extended to study the algorithm performance in a more realistic cellular system where the number of requested channels is continuously changing with time. In this paper, the channel assignment problem is formulated as an energy function which is at its minimum when all the defined compatibility constraints are satisfied and the assigned channel number (ACN) is equal to the requested channel number (RCN) in each cell.     

D-CAT: An Efficient Algorithm for Distributed Channel Allocation in Cellular Mobile Networks

We propose a distributed channel allocation algorithm based on a threshold scheme, called D-CAT, for cellular mobile networks. The algorithm employs two thresholds: (i) a heavy threshold for determining whether a cell is heavy, or overloaded, and for triggering the channel allocation algorithm; and (ii) a target threshold for indicating the target number of free channels that a heavy cell intends to acquire. Based on the two-threshold scheme, the D-CAT algorithm can determine the optimal number of free channels as well as the cell(s) from where a heavy cell should import channels in order to satisfy the required channel demand. Simulation experiments and analyses show that the proposed algorithm incurs lower overhead for channel allocation and is more efficient in terms of channel utilization than other distributed channel allocation algorithms. It also outperforms other centralized and distributed algorithms in terms of call blocking probability.