Mobile Radio Environment Research Articles

고속철도 지면반사파를 고려한 열차무선 전파모델

고속철도에서의 열차무선전파는 일반적인 이동통신전파와 달리 레일, 침목 및 자갈로 구성된 철로면 반사에 의해 불규칙적으로 수신되는 지면반사파의 영향을 받는다. 본 논문에서는 이와 같이 불규칙적으로 수신되는 철로면 반사파를 랜덤변수로 모의하고, 여기에 송수신간 직접 경로에 의한 직접파를 추가한 열차무선 전파모델을 제안하였다. 제안한 전파모델을 이용한 시뮬레이션 결과 열차무선에서의 경로손실지수는 3.0으로 분석되어, 일반적인 이동통신환경에서의 4.0에 비해 경로손실이 감소하는 것으로 나타났다. 또한, 고속철도 현장에서의 열차무선 수신전력 측정치에서도 동일하게 경로손실지수가 3.0으로 분석되었다. 이상과 같은 시뮬레이션 및 측정결과로부터, 열차무선 전파모델을 검증하고 경로손실지수를 도출할 수 있었으며, 이 결과는 고속철도 열차무선통신망의 커버리지 예측 및 기지국 설계에 응용할 수 있다. Radio propagation in a high-speed railway is affected by ground reflective waves that are due to irregular reflection by the railway track, which consists of rails, sleepers, and gravel. This paper provides a train radio propagation model that simulates an irregular track reflective wave as a random variable. A simulation study using the train radio propagation model shows that the path loss exponent is around 3.0, indicating a reduced path loss compared to the value of 4.0 in the general mobile radio environment. Regressive analysis of the received signal strength indicators measured in the Gyeongbu high-speed railway showed the results identical to those of the simulation. These results confirm the train radio propagation model and can be applied to the coverage estimation and the design of a train radio network.

Group Key Management Protocols for Secure Mobile Multicast Communication: A Comprehensive Survey

Key management is equally important as compared to any other security measure such as encryption and authentication. With the growing usage of mobile devices and the advent of multicast communication, there has been a significant amount of work carried out in developing an optimum group key management protocol for mobile multicast systems. Key management is widely being adopted in securing group communication for both wired and wireless networks. Securing group communication over wired networks is fairly well established; however, wireless networks bring additional challenges due to member mobility and increase in the number of members. This paper presents a comprehensive survey of group key management protocols in wireless mobile environments that employ multicast communication. They are classified into network dependent and independent protocols and further categorized into tree-based and cluster-based key management protocols. The survey clearly outlines the characteristics of each protocol along with highlighting their advantages and limitations with respect to real-world systems. The paper is concluded with a taxonomy of the individual protocols with respect to the defined requirements which provides a strong source of literature reference for researchers in this field.

Dynamic Task Allocation in Multi-Hop Multimedia Wireless Sensor Networks with Low Mobility

This paper presents a task allocation-oriented framework to enable efficient in-network processing and cost-effective multi-hop resource sharing for dynamic multi-hop multimedia wireless sensor networks with low node mobility, e.g., pedestrian speeds. The proposed system incorporates a fast task reallocation algorithm to quickly recover from possible network service disruptions, such as node or link failures. An evolutional self-learning mechanism based on a genetic algorithm continuously adapts the system parameters in order to meet the desired application delay requirements, while also achieving a sufficiently long network lifetime. Since the algorithm runtime incurs considerable time delay while updating task assignments, we introduce an adaptive window size to limit the delay periods and ensure an up-to-date solution based on node mobility patterns and device processing capabilities. To the best of our knowledge, this is the first study that yields multi-objective task allocation in a mobile multi-hop wireless environment under dynamic conditions. Simulations are performed in various settings, and the results show considerable performance improvement in extending network lifetime compared to heuristic mechanisms. Furthermore, the proposed framework provides noticeable reduction in the frequency of missing application deadlines.

ANALYSIS AND SOLUTION FOR MULTI-BAND ORTHOGONAL FREQUENCY-DIVISION MULTIPLEXING ULTRA WIDE BAND SYSTEM IN REAL ENVIRONMENT FOR VEHICLE TO INFRASTRUCTURE APPLICATION

Many researches in the world deal with driving on the road to ensure optimum safety. In this context, several telecommunication technologies are often used to connect the vehicles via continuous wireless communication with the infrastructure, exchange data and information relevant to increase overall road safety and enable cooperative traffic management. These systems are not reliable for all situations and the difficulties encountered by the drivers. We have been proposed the Multi-band Orthogonal Frequency- Division Multiplexing system based on Ultra Wide Band (MB-OFDM UWB) as a good candidate to insure a Vehicle to Infrastructure (V2I) communication with high data rate and good performances in terms of Bit Error Rate (BER). However, Inter-Carrier Interference (ICI) resulting from Doppler shift phenomenon degrades MB-OFDM UWB system performance and raises a significant challenge in wireless mobile environment. In this study, V2I communication based on the MB-OFDM UWB technology is studied and analyzed for 200 Mbit/s, over multipath channel using the IEEE802.15.4a channel model with Doppler shift for different speeds. The theoretical formulas of BER in Additive White Gaussian Noise (AWGN) and Rayleigh channels are calculated and are compared to the simulation results in MB-OFDM UWB system. The comparison shows that simulation results are consistent with theoretical formulas. The degradation in the performance of the proposed system solution becomes worse with a high speed 250 Km h1, so it's necessary to use new receiver solutions. The Extended Kalman Filer (EKF) and the Maximum Likelihood (ML) estimation with ZF equalizer have been proposed and have been compared to Zero-Forcing (ZF) in order to combat the ICI effect. For high value of speed (250 Km h1), the EKF method performs better than the ML method, better than the ZF equalizer and offers much improvement in performance in term of BER

Air Indexing for On-Demand XML Data Broadcast

XML data broadcast is an efficient way to disseminate semistructured information in wireless mobile environments. In this paper, we propose a novel two-tier index structure to facilitate the access of XML document in an on-demand broadcast system. It provides the clients with an overall image of all the XML documents available at the server side and hence enables the clients to locate complete result sets accordingly. A pruning strategy is developed to cut down the index size and a two-tier structure is proposed to further remove any redundant information. In addition, two index distribution strategies, namely naive distribution and partial distribution, have been designed to interleave the index information with the XML documents in the wireless channels. Theoretical analysis and simulation experiments are also put forward to show the benefits of our indexing methods.

Wireless Grid and Intruder Detection Server

Wireless Grid is an emerging communication and resource sharing architecture in recent years. It is getting more and more researches and application in mission, industry, business, science research. Wireless grid technique is developing and improving, especially with the storage capacity rising. Storage resource can be managed by wireless grid and ensure the grid availability and reliability by replica, cache prefetch and buffer. Extracting information or discovering knowledge from wireless or mobile grids has become increasingly important issue. Many researches in grid environment only consider data mining time. Other constraints, such as energy consumption and immediate bandwidth that are more important in mobile computing, will physically affect the performance and system availability. If Grid system is integrated with the wireless network devices, Grid applications will soon be popularly and widely deployed in different domains to serve many more people in the world. Wireless Grid-based mobile agent system (WGMAS) which integrates mobile agent techniques and wireless environment with a Grid system, to provide a wireless accessible mobile agent system to users. An Intruder is a person who attempts to gain unauthorized access to a system, to damage that system, or to disturb data on that system. In summary, this person attempts to violate Security by interfering with system Availability, data Integrity or data Confidentiality. The goal of an Intrusion Detection System (IDS) is to identify, preferably in real time, unauthorized use, misuse, and abuse of computer systems by both system insiders and external penetrates. An IDS is used as an alternative (or a complement) to building a shield around the network. The shielding approaches deficient in several ways, including failure to prevent attacks from insiders.

Enhancing content-centric networking for vehicular environments

Content-Centric Networking (CCN) is a new popular communication paradigm that achieves information retrieval and distribution by using named data instead of end-to-end host-centric communications. This innovative model particularly fits mobile wireless environments characterized by dynamic topologies, unreliable broadcast channels, short-lived and intermittent connectivity, as proven by preliminary works in the literature.In this paper we extend the CCN framework to efficiently and reliably support content delivery on top of IEEE 802.11p vehicular technology. Achieved results show that the proposed solution, by leveraging distributed broadcast storm mitigation techniques, simple transport routines, and lightweight soft-state forwarding procedures, brings significant improvements w.r.t. a plain CCN model, confirming the effectiveness and efficiency of our design choices.

Neighbour peer selection scheme based on effective capacity for mobile Peer-to-Peer streaming

For Peer-to-Peer (P2P) streaming services in mobile networks, the selection of appropriate neighbour peers from candidate peers with demanding data is an important approach to improve Quality-of-Service (QoS). This paper proposes a novel Effective Capacity Peer Selection (ECPS) scheme based on effective capacity. In the ECPS scheme, the neighbour peer selection problem was modeled using the Multiple Attribute Decision Making (MADM) theory, which considered multiple factors of candidate peers, including Signal to Interference and Noise Ratio (SINR), residency time, power level, security, moving speed, and effective capacity. This model could increase the suitability of ECPS for wireless mobile environments. Then, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was used to solve the MADM problem and identify the preferred neighbour peers. Simulation results show that the ECPS scheme can improve the network throughput, reduce packet delay by about 82%, and almost double the packet delivery ratio of the mobile P2P streaming service.

An accelerating handover process scheme for IEEE 802.16j multi-hop relay networks

IEEE 802.16j multi-hop relay network systems provide the mobile wireless communication environment. In such network systems, the handover scanning procedure allows a mobile station (MS) to obtain the information about the handover target base stations (BSs) or relay stations (RSs). The network systems need more time to negotiate the association parameters and to handle scanning the BSs and the RSs when the number of BS and RS increases. It results in more overhead for the handover scanning procedure. In order to accelerate the handover process and reduce the transmission interruption, efficient handover scanning procedure schemes and corresponding algorithms must be developed and designed. A novel relative angle computing algorithm is proposed in this article to accelerate the handover process by taking into account the moving behavior of the MS, and the distances among the MS, the RS, and the BS. The main idea of this algorithm is to reduce the management information overhead and to estimate the potential moving path of the MS in the wireless mobile communication networks. By using the proposed scheme, we eliminate the unnecessary associations and scanning intervals, and reduce the handover scanning procedure efficiently. Simulation result demonstrate the superior performance of our proposed scheme and its ability to strike the appropriate performance in the handover overhead and the message delay for IEEE 802.16j multi-hop relay network systems.

Microcell prediction model based on support vector machine algorithm

A new microcell prediction model for mobile radio environment is presented in this paper. The popular support vector machine algorithm is used as an optimizing tool to build a model. In order to validate the model quality, extensive electric field strength measurements were carried out in the city of Belgrade, for two different test transmitter locations. The analysis of the model has shown that proposed model is fast, accurate (on the order of the local mean measurements uncertainty), reliable, and suitable for computer implementation.

E-CHANET: Routing, forwarding and transport in Information-Centric multihop wireless networks

Information-Centric Networking (ICN) is a promising architecture for the future Internet that focuses on content rather than IP addresses. By leveraging named-data instead of named-hosts, ICN does not need the set up and maintenance of stable paths between end-nodes. This makes ICN particularly convenient in networks characterized by intermittent connectivity and hostile propagation conditions, such as wireless multihop networks like ad hoc and mesh networks.In this paper, we present an information-centric architecture for IEEE 802.11 wireless ad hoc networks, named E-CHANET, which performs routing, forwarding and reliable transport functions, specifically tailored to cope with the limitations and requirements of wireless distributed environments. E-CHANET performance is evaluated through simulations and a comparison with the legacy TCP/IP architecture and the basic CCN model is provided. Achieved results demonstrate the effectiveness of the proposed solution in mobile wireless environments.

Technique for Cross-layer Vertical Handover Prediction in 4G Wireless Networks

Abstract With the increasing deployment of a variety of wireless access networks, wireless devices face the challenge of selecting the most suitable network from a set of available access networks. Some of the weighty issues in 4G wireless networks are fastness and seamlessness in handover process. This paper therefore, proposes a handover technique based on movement prediction in wireless mobile (WiMAX and LTE - Advanced) environment. The technique enables the system to predict signal quality between the mobile User Equipment (UE) and eNodeB stations/access points (APs) in two different networks. Prediction is achieved using dynamic regressive integrated moving average (DRIMA) model by keeping track of the signal strength of mobile users. With the help of the prediction, layer-3 handover activities are able to occur prior to layer-2 handover, and therefore, total handover latency can be reduced. This demonstrates that the proposed method predicts the future signal level accurately and reduces the total handover latency.

Dynamic target wireless network selection technique using fuzzy linguistic variables

Even though various wireless Network Access Technologies (NATs) with different specifications and applications have been developed in the recent years, no single wireless technology alone can satisfy the anytime, anywhere, and any service wireless-access needs of mobile users. A real seamless wireless mobile environment is only realized by considering vertical and horizontal handoffs together. One of the major design issues in heterogeneous wireless networks is the support of Vertical Handoff (VHO). VHO occurs when a multi-interface enabled mobile terminal changes its Point of Attachment (PoA) from one type of wireless access technology to another, while maintaining an active session. In this paper we present a novel multi-criteria VHO algorithm, which chooses the target NAT based on several factors such as user preferences, system parameters, and traffic-types with varying Quality of Service (QoS) requirements. Two modules i.e., VHO Necessity Estimation (VHONE) module and target NAT selection module, are designed. Both modules utilize several “weighted” users' and system's parameters. To improve the robustness of the proposed algorithm, the weighting system is designed based on the concept of fuzzy linguistic variables.

An ID-Based Certified E-mail Protocol with STTP Suitable for Wireless Mobile Environments

ID-based public key cryptography is proposed to simplify the management of the certification process and greatly reduce the public key authentication computation as well as communication cost. Certified e-mail protocol is a fair exchange of a message for a receipt between two potentially mistrusting parties over the network. A number of certified e-mail protocols have been studied in recent years. However, most of those protocols used certificated-based cryptography and the the full trusted third party employed ,may not be suitable for wireless networks that own limited resources such as power, computation and bandwidth . In this paper, we propose an improved identity-based signcryption with re-encryption scheme firstly ,then based on the scheme, we develop a novel certified e-mail protocol in Id-based setting that employs an off-line semi-trusted third party STTP for wireless networks,finally the detailed analysis shows that the proposed approach is dynamic, lightweight and scalable.

Efficient service cache management in mobile P2P networks

Service oriented computing is growing as the prominent technology both in the technical and business perspectives. Due to the rapid growth in the volume of service repositories and services, obtaining the appropriate service is becoming tedious in the current scenario. Though advanced techniques are proposed to handle these challenges in conventional environments, still it is in its critical stage in the resource constrained scenarios, particularly in wireless mobile environments. The work presented in this paper proposes a Service Cache Management (SCM) for Mobile Peer-to-Peer (MP2P) networks to facilitate the efficient retrieval of services. We used a communication structure called Distributed Spanning Tree (DST), in which nodes of MP2P are made to form a forest of spanning trees in a distributed fashion. Using the DST structure, fast service cache and retrieval can be achieved within MP2P. Further to enhance the effectiveness of the proposed system, the DST network is optimized with Ant Colony Optimization (ACO), to identify the simplest path between nodes of each layer on the DST. The merits of the proposed techniques are demonstrated in terms of reduced time requirement for cached service search, increased availability, enhanced consistency, scalability and improved hit ratios.

The Replication in Varying Fanout Indexing Technique for Skewed Access Patterns in the Wireless Mobile Environments

Due to limited battery power, the most important issue in mobile computing is energy saving. The energy efficiency can be achieved through indexed data organization over wireless channels. In this paper, we explore the balanced and imbalanced index tree with varying fanout over skewed data. We purpose a varying fanout indexing technique with replication for skewed data over a single wireless communication channel. The proposed indexing technique is compared and analyzed with the fixed fanout indexing technique for skewed data over a single wireless channel. The result shows the decrease in directory miss and the depth of the tree is also reduced.

Scalable service discovery in ubiquitous and pervasive computing architectures: A percolation-driven approach

The diffusion of ubiquitous and pervasive computing applications, providing advanced services anytime and everywhere across heterogeneous mobile networks, is fostering the development of new architectures and models, based on the emerging peer-to-peer paradigm, to allow the effective use of multiple replicated resources and services without the scalability and adaptiveness limitations characterizing traditional client–server organizations. In this scenario, effective service discovery facilities are needed to minimize the administrative overhead and increase the overall usability and perceived service quality. However, most of the currently available implementations lack efficiency due to the highly dynamic and hierarchically flat nature of the underlying wireless mobile networking environment, that make any traditional solution based on centralized schemes and statically defined roles practically unfeasible. Accordingly we proposed a novel service discovery approach based on a fully distributed and parallel search model, that does not require any centralized intelligence, fixed roles and stable communication infrastructure. It exploits, in a dynamic scale-free scenario characterized by competition for links and balanced node insertion and removal rates, a widely known random walk-based search paradigm benefitting from bond percolation in power law organizations to automatically limit the search space (by shielding low connectivity nodes from search traffic) and drastically reduce the total control overhead. We analyzed the effectiveness and performance of the proposed solution by using discrete event-driven simulation, whose results were satisfactory also in highly mobile ad-hoc environments. This indicates that the proposed ideas are promising and deserve further exploitation by practical application solutions designers.

Analysis of mobility impact on interference in cognitive radio networks

Cognitive radio (CR) technology seems to be a promising candidate for solving the radio frequency (RF) spectrum occupancy problem. CRs strive to utilize the white holes in the RF spectrum in an opportunistic manner. Because interference is an inherent and a very critical design parameter for all sorts of wireless communication systems, many of the recently emerging wireless technologies prefer smaller size coverage with reduced transmit power in order to decrease interference. Prominent examples of short-range communication systems trying to achieve low interference power levels are CR relays in CR networks and femtocells in next generation wireless networks (NGWNs). It is clear that a comprehensive interference model including mobility is essential especially in elaborating the performance of such short-range communication scenarios. Therefore, in this study, a physical layer interference model in a mobile radio communication environment is investigated by taking into account all of the basic propagation mechanisms such as large- and small-scale fading under a generic single primary user (PU) and single secondary user (SU) scenario. Both one-dimensional (1D) and two-dimensional (2D) random walk models are incorporated into the physical layer signal model. The analysis and corresponding numerical results are given along with the relevant discussions.

Cross-Layer Design for Optimized Region of Interest of Ultrasound Video Data Over Mobile WiMAX

The application of advanced error concealment techniques applied as a post-process to conceal lost video information in error-prone channels, such as the wireless channel, demand additional processing at the receiver. This increases the delivery delay and needs more computational power. However, in general, only a small region within medical video is of interest to the physician and thus if only this area is considered, the number of computations can be curtailed. In this paper we present a technique whereby the Region of Interest (ROI) specified by the physician is used to delimit the area where the more complex concealment techniques are applied. A cross layer design approach in mobile WiMAX wireless communication environment is adopted in this paper to provide an optimized Quality of Experience (QoE) in the region that matters most to the mobile physician while relaxing the requirements in the background, ensuring real-time delivery. Results show that a diagnostically acceptable Peak Signal-to-Noise-Ratio (PSNR) of about 36 dB can still be achieved within reasonable decoding time.

A multirate MAC protocol for reliable multicast in multihop wireless networks

Many multicast applications, such as audio/video streaming, file sharing or emergency reporting, are becoming quite common in wireless mobile environment, through the widespread deployment of 802.11-based wireless networks. However, despite the growing interest in the above applications, the current IEEE 802.11 standard does not offer any medium access control (MAC) layer support to the efficient and reliable provision of multicast services. It does not provide any MAC-layer recovery mechanism for unsuccessful multicast transmissions. Consequently, lost frames cannot be detected, hence retransmitted, causing a significant quality of service degradation. In addition, 802.11 multicast traffic is sent at the basic data rate, often resulting in severe throughput reduction.In this work, we address these issues by presenting a reliable multicast MAC protocol for wireless multihop networks, which is coupled with a lightweight rate adaptation scheme. Simulation results show that our schemes provide high packet delivery ratio and when compared with other state-of-the-art solutions, they also provide reduced control overhead and data delivery delay.