An analytical solution based on mobility and multicriteria optimization for access selection in heterogeneous environment

Providing global connectivity with high speed and guaranteed quality at any place and any time is now becoming a reality due to the integration and co-ordination of different radio access technologies. The internetworking of existing networks with diverse characteristics has been considered attractive to meet the incredible development of interactive multimedia services and ever-growing demands of mobile users. Due to the diverse characteristics of heterogeneous networks, several challenges have to be addressed in terms of quality of service (QoS), mobility management and user preferences. To achieve this goal, an optimal network selection algorithm is needed to select the target network for maximizing the end user satisfaction. The existing works do not consider the integration of utility function with mobile terminal mobility characteristics to minimize ping-pong effects in the integrated networks. An integrated multicriteria network selection algorithm based on multiplicative utility function and residual residence time (RRT) estimation is proposed to keep the mobile users always best connected. Multiplicative weighted utility function considers network conditions, application QoS and user preferences to evaluate the available networks. In this paper, the proposed scheme is implemented with two mainstreams (pedestrian users and high-velocity users). For high-velocity users, RRT and adaptive residence time threshold are also considered to keep the probability of handover failures and unnecessary handovers within the limits. Monte-Carlo simulation results demonstrate that the proposed scheme outperforms against existing approaches.     

Uplink analysis for hierarchical CDMA systems with attenuators applied to microcell under imperfect power control

Under the signal-strength-based power control scheme, the effect of various microcell cluster locations on the uplink average signal-to-interference ratio (also called carrier-to-interference ratio, or CIR) is studied for the hierarchical code-division multiple-access cellular system with attenuators applied to each microcell base station. On the basis of the interference statistics analysis, the influence of power control errors on the uplink average bit error rate (BER) is also studied under the multipath fading and shadowing. Results show that both central macrocell and microcell uplink CIR are almost unaffected by the variations of microcell cluster locations, and that the uplink average BER is evidently affected by the imperfection of power control and the shadowing standard deviations.     

Two-level single-chain pointer forwarding strategy: a new scheme for location management in mobile communication

A new strategy called 'two-level single-chain pointer (TLSCP) Forwarding strategy is proposed to reduce location management cost for mobile users. A two-level hierarchy of level-1 and level-2 pointer forwarding chains that are reduced to a single chain in a distributed database environment to locate a mobile user is used in this strategy. An analytical model is developed to evaluate the signalling and location tracking cost. Performance analysis shows that the proposed TLSCP scheme significantly reduces the network signalling traffic cost for mobile users with low mobility.     

基于接入控制器模式的公共无线局域网安全体系设计

公共无线局域网面临网络安全、用户数据保护、身份认证、移动管理及网络服务等多方面的挑战。将现有的公共无线局域网分为WISP—owned,Operator—owned以及for Enterprise 3种类型,并分别讨论了各种类型的特征及其架构。在此基础上提出一种基于接入控制器模式的通用安全体系,可应用于目前大多数类型的公共无线局域网。提出了一种802．1X和Web认证的混合型认证协议,该协议在进行Web认证时将利用802．1X协商后产生的密钥进行,可有效地抵抗窃取服务、基站伪装、消息窃听等攻击,并与现有公共无线局域网Web认证相兼容。     

Laboratory studies on influence of transverse cracking on chloride-induced corrosion rate in concrete

To clarify the corrosion mechanism of steel induced by transverse crack, a study on the influence of crack widths and epoxy coating on corrosion of steel bars in cracked concrete is presented here. Microcell and macrocell corrosions of bars were investigated on single crack specimens with crack widths of 0.08, 0.26, 0.38 and 0.94 mm. The entire study was carried out in an artificially created chloride ion-induced corrosion environment. The results show that the steel in cracks was activated once the transverse crack occurred on concrete element, and the macrocell corrosion must co-exist with microcell corrosion of reinforcements in test specimens with transverse crack. The macrocell current of steel elements were separated from the crack width, and the wider the transverse crack is, the higher corroded area and the greater microcell current of the rebar is. Oxygen and water go into concrete through crack instead of through concrete cover. The epoxy coating cannot prevent the occurrence and propagation of crack, so it was not effective to prevent corrosion of steel bars in cracked concrete.     

Adaptive opportunistic fair scheduling in power-controlled code division multiple access systems

The authors treat the multiuser scheduling problem for practical power-controlled code division multiple access (CDMA) systems under the opportunistic fair scheduling (OFS) framework. OFS is an important technique in wireless networks to achieve fair and efficient resource allocation. Power control is an effective resource management technique in CDMA systems. Given a certain user subset, the optimal power control scheme can be derived. Then the multiuser scheduling problem refers to the optimal user subset selection at each scheduling interval to maximise certain metric subject to some specific physical-layer constraints. The authors propose discrete stochastic approximation algorithms to adaptively select the user subset to maximise the instantaneous total throughput or a general utility. Both uplink and downlink scenarios are considered. They also consider the time-varying channels where the algorithm can track the time-varying optimal user subset. Simulation results to show the performance of the proposed algorithms in terms of the throughput/ utility maximisation, the fairness, the fast convergence and the tracking capability in time-varying environments are presented.     

异构无线网络中基于多用户分集的协作频谱感知算法

研究了协作通信与认知无线电的结合,针对TD-SCDMA系统和WiMAX系统组成的异构无线网络,提出了一种基于多用户分集的协作频谱感知机制.根据该算法,WiMAX用户被分成若干个簇,选择每个簇内瞬时信道条件最好的WiMAX用户协作检测频谱,并利用软硬结合的判决手段,既保证检测性能,又不增加复杂度.分析和仿真表明,该算法一方面保证了频谱检测的可靠性,降低了虚警概率,另一方面减少了通信开销,提高了判决消息传输的可靠性,达到了提升频谱利用率的目的.     

Provision of proportional delay differentiation in wireless LAN using a cross-layer fine-tuning scheduling scheme

The proportional delay differentiation (PDD) is one of the most well-known quality of service (QoS) models and has drawn much attention because of its 'controllable' and 'predictable' characteristics. How to provide PDD in a wireless LAN (WLAN) is addressed and a cross-layer fine-tuning scheduling (CFS) scheme with the goal to maintain PDD among all wireless stations is proposed, while improving performance in a WLAN. CFS additionally considers the time-varying channel capacity to schedule packets, finely tunes the contention window and properly arbitrates the backoff time. Also, it operates in a fully distributed manner among all stations and in a cross-layer approach in each station. The simulation results demonstrate that the CFS scheme can provide more satisfactory PDD and higher performance in a WLAN, compared with 802.1 le.     

Interference-limited resource allocation for cognitive radio in orthogonal frequency-division multiplexing networks

Efficient and fair resource allocation strategies are being extensively studied in current research in order to address the requirements of future wireless applications. A novel resource allocation scheme is developed for orthogonal frequency-division multiplexing (OFDM) networks designed to maximise performance while limiting the received interference at each user. This received interference is in essence used as a fairness metric; moreover, by defining different interference tolerances for different sets of users, the proposed allocation scheme can be exploited in various cognitive radio scenarios. As applied to the scheme, the authors investigate a scenario where two cellular OFDM-based networks operate as primary and secondary systems in the same band, and the secondary system benefits by accessing the unused resources of the primary system if additional capacity is required. The primary system benefits either by charging the secondary system for the use of its resources or by some form of reciprocal arrangement allowing it to use the secondary system's licenced bands in a similar manner, when needed. Numerical results show our interference-limited scheduling approach to achieve excellent levels of efficiency and fairness by allocating resources more intelligently than proportional fair scheduling. A further important contribution is the application of sequential quadratic programming to solve the non-convex optimisation problems which arise in such scenarios.     

Authentication mechanism over the integrated UMTS network and WLAN platform using the cross-layer bootstrap

The 3G mobile data network provides always-on and ubiquitous connectivity for subscribers. Although the service coverage area in wireless local area network (WLAN) is much smaller than that in a 3G mobile data network, the data transmission rate in WLAN can be from 2 to 54 Mbps, which is much faster than 3G mobile network. Obviously, the relationship between the 3G mobile data network and WLAN is complementary in terms of service coverage and data transmission rate. Therefore integration of 3G mobile network and WLAN can offer subscribers higher speed wireless service in hot spots and ubiquitous connectivity in 3G mobile data network. An authentication mechanism over the loose coupled integration mechanism using a cross-layer bootstrap is proposed. The benefits of the proposed mechanism are (a) integrating Universal Mobile Telecommunication System network and WLAN using the existing protocols denned in 3GPP, IETF and IEEE 802. Hi, (b) the use of the Extension Authentication Protocol authentication method is flexible, (c) reduction of the authentication signalling when a subscriber roams from one access point (AP) to another AP and (d) user identity privacy protection.     

Theoretical and experimental study of microcell and macrocell corrosion in patch repairs of concrete structures

Patch repair is commonly used to rectify localized corrosion induced damage in concrete structures. However, inadequate durability in patch repair systems caused by new corrosion attack is prevalent. From the prevailing understanding, the mechanism is attributed to macrocell corrosion formed between repaired area (called patch) and its adjacent unrepaired area (called substrate), and thereby ensuring electrochemical compatibility between the two areas is deemed to be the key element to reduce the corrosion risk and thus to achieve a successful repair. This paper examined the corrosion mechanism and the concept of compatibility in patch repair systems from fundamental electrochemical principles and experimental verification. It was illustrated that both macrocell and microcell corrosion mechanisms could play significant roles, and the total corrosion could be underestimated if the latter is overlooked. Although the incompatibility serves as the driving force for the macrocell corrosion, in light of corrosion kinetics, it was shown that the corrosion magnitude depends more on the individual corrosion kinetics of the anode or cathode.     

Design of an access control module for an instrumentation gateway

This paper describes some of the preliminary work performed on a resource access control module for an instrumentation gateway. The access control module employs a variation of the popular role-based access control (RBAC) scheme described by various authors. The gateway has very little security; hence, any user able to log onto the system is able to control any resource. This module aims to implement a pluggable module whereby users are granted access to various parts of the system depending on their user rights, while giving the administrator a very powerful method of restricting access without sacrificing ease of administration.     

Proxy-Based Hierarchical Distributed Mobility Management for Tactical Networks

An important requirement in a military domain is a highly reliable mobility management method, especially when components of the networks are moving in tactical network environments. To increase reliability, the mobility management technology of the tactical network should be able to reflect the characteristics of the tactical network, such as a limited environment, failure, and hierarchical unit structure. In this paper, we propose a proxy-based hierarchical distributed mobility management scheme, which is highly focused on tactical networks. Considering the characteristics of tactical networks, the proposed scheme is composed of the following: 1) a proxy-based method, 2) a distributed mobility management method that synchronizes a mobility database between entities, and 3) a method of managing mobility by dividing the tactical network into upper and lower layers. Mathematical analysis and modeling and simulation results demonstrate that the method outperforms the existing state-of-the-art method in overcoming entity failure, handover cost, and delay in tactical environments.     

全复用多小区系统下行链路用户调度与功率分配

对全复用多小区系统下行链路用户调度与功率分配问题进行了研究,提出了一种半分布式的用户调度与功率分配方案.首先,各小区根据自身所辖用户的信道与干扰信息,采用最大信干噪比准则进行用户调度,然后各基站将所调度用户的信息上报给中央资源控制器,最后中央资源控制器基于最速下降法的思想,采用贪婪功率分配(GPA)算法为各用户分配相应的发射功率.所提方案利用小区之间的相互协作有效地弱化了小区间干扰,与现有方法相比获得了更好的吞吐量性能和更高的功率效率.     

Proportional Fairness-Based Power Allocation Algorithm for Downlink NOMA 5G Wireless Networks

Non-orthogonal multiple access (NOMA) is one of the key 5G technology which can improve spectrum efficiency and increase the number of user connections by utilizing the resources in a non-orthogonal manner. NOMA allows multiple terminals to share the same resource unit at the same time. The receiver usually needs to configure successive interference cancellation (SIC). The receiver eliminates co-channel interference (CCI) between users and it can significantly improve the system throughput. In order to meet the demands of users and improve fairness among them, this paper proposes a new power allocation scheme. The objective is to maximize user fairness by deploying the least fairness in multiplexed users. However, the objective function obtained is non-convex which is converted into convex form by utilizing the optimal Karush-Kuhn-Tucker (KKT) constraints. Simulation results show that the proposed power allocation scheme gives better performance than the existing schemes which indicates the effectiveness of the proposed scheme.     

Comparative studies of experimental and numerical techniques in measurement of corrosion rate and time-to-corrosion-initiation of rebar in concrete in marine environments

The evaluation of the corrosion process for estimating the service life of concrete structure is of great importance to civil engineers. In this paper, the effects of different exposure conditions (i.e., tidal and splash zones) on macrocell and microcell corrosion of rebar in concrete were examined on concrete specimens with different w/c ratios in the Persian Gulf region. Experimental techniques such as macrocell corrosion rate measurement, Galvanostatic pulse, electrical resistivity, half-cell potential measurement, and numerical techniques were used to determine the corrosion rate and time-to-corrosion-initiation of rebar. Results showed that corrosion rates in the splash zone were higher than the ones in the tidal zone. This indicates that the propagation of corrosion in the splash zone is faster than the one in the tidal zone. There was also a strong correlation between the experimental results and those obtained from a numerical model in both tidal and splash zones.     

An Adaptive Power Allocation Scheme for Performance Improvement of Cooperative SWIPT NOMA Wireless Networks

Future wireless networks demand high spectral efficiency, energy efficiency and reliability. Cooperative non-orthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) is considered as one of the novel techniques to meet this demand. In this work, an adaptive power allocation scheme called SWIPT based adaptive power allocation (SWIPT-APA-NOMA) is proposed for a power domain NOMA network. The proposed scheme considers the receiver sensitivity of the end users while calculating the power allocation coefficients in order to prevent wastage of power allocated to user in outage and by offering priority to any one of the users to use maximum harvested power. A detailed analysis on the bit error rate (BER) performance of the proposed scheme is done and closed form expression is obtained. Simulations have been carried out with various parameters that influence the receiver sensitivity and the results show that the network achieves better outage and BER performance using the proposed scheme. It is found that the proposed scheme leads to a ten-fold decrease in transmit power for the same error performance of a fixed power allocation scheme. Further, it offers 96.06% improvement in the capacity for a cumulative noise figure and fading margin of 10 dB.     

智能DNS在校园网多链路控制的应用

为了解决校内外用户高速访问高校校园网的内部资源服务器的问题,提出了校园网智能DNS解决方案.智能DNS利用Bind9视图技术,结合F5负载均衡器的虚拟服务器和链路控制原理,能根据网络用户IP的来源,将校内资源服务器的域名动态解析成用户IP对应网络的IP地址,从而提高用户访问校内资源的速度和可靠性.测试结果表明,教科网、电信网和联通网等公网用户和内网用户都能获得最佳的链路以访问校内资源,校内用户访问其他公网资源也能获得更好的体验.     

Robust mobility adaptive clustering scheme with support for geographic routing for vehicular ad hoc networks

There are a number of critical problems related to road safety in intelligent transportation systems (ITS) caused by increased vehicle usage, urbanisation, population growth and density, and faster rates of movements of goods and people. It is envisaged that vehicular ad hoc networks (VANETs) will bring about a substantial change to the way our road transport operates to improving road safety and traffic congestion. A major challenge in VANETs is to provide real-time transfer of information between vehicles within a highly mobile environment. The authors propose a new clustering scheme named robust mobility adaptive clustering (RMAC) to strategically enable and manage highly dynamic VANETs for future ITS. It employs a novel node precedence algorithm to adaptively identify the nearby 1-hop neighbours and select optimal clusterheads based on relative node mobility metrics of speed, locations and direction of travel. Furthermore, the zone of interest concept is introduced for optimised approach to the network structure such that each vehicular node maintains a neighbour table of nodes, beyond its communications range, that reflects the frequent changes on the network and provides prior knowledge of neighbours as they travel into new neighbourhoods. RMAC predominantly employs more reliable unicast control packets and supports geographic routing by providing accurate neighbour information crucial when making routing decisions in multi-hop geographic routing. It is shown by simulations that RMAC on IEEE802.11 ad hoc WLAN protocol is very effective in a highly dynamic VANETs environment, being robust on link failures, and having very high cluster residence times compared to the well known distributed mobility clustering scheme.     

WLAN 802.11/11b数据加密机制的安全分析

在802.11标准中的加密采用WEP协议，用于提供链路层数据传输的安全保护。目前，在原有EP的基础上提出了一些改进方案，能提高WEP的安全性能，但理论上缺少严密的安全分析。笔者通过数学模型对这些解决方案以及原有WEP协议进行量化分析，推导出机制内各模块与整个安全机制间安全性能的对应函数关系，并比较了这些方案间安全性能的差异，证明这些安全机制可以提高原有WEP的安全性能，在理论上为用户提供如何构造满足所需安全性能的WLAN数据加密增强机制。