WLAN Environment Research Articles

Genetic Algorithm based Approach to Enhance Network Performance in Multi-rate WLANs

In a multi-rate 802.11 WLAN environment, the users’ fairness and network throughput is a trade-off problem. Although there are many valuable research papers related to this optimization problem, up to date, none of those researches could offer a rational, clearly designed mathematical model which can be easily and widely implemented using the well known AI algorithms. Thus our research aims to fill such gap. In this paper we define the problem as an informed search NP-hard problem in a practical scenario, and then we will propose a new intuitive simplified mathematical model called Simplified Coefficient of Variation (SCV), by using Genetic Algorithm to implement the SCV model, through controlling the power of Access Points to optimize and enhance the performance of the network. The simulation gives excellent results that indicate our model is efficient and superior to existing method. After the experiment analysis, we use software SAS to further reveal the relationships of three indicators to illustrate the essence of our algorithm and an existing algorithm.

Fast Directional Handoff and lightweight retransmission protocol for enhancing multimedia quality in indoor WLANs

More and more mobile devices such as smartphones are being used with IEEE 802.11 wireless LANs (WLANs or Wi-Fi). However, mobile users are still experiencing poor service quality on the move due to the large handoff delay and packet loss problem. In order to reduce the delay, a new handoff scheme using the geomagnetic sensor embedded in mobile devices is proposed in this paper. The proposed scheme predicts the movement direction of a Mobile Station (MS) from the currently associated Access Point (AP) and performs active scanning with a reduced number of channels. In terms of the packet loss, a lightweight retransmission protocol is also proposed to minimize lost packets on Wi-Fi without producing a lot of acknowledgement packets. The proposed approaches are implemented on Android smartphones, and their performance is evaluated in a real indoor WLAN environment. The evaluation results demonstrate that the proposed schemes maintain seamless quality for real-time video even in an environment with frequent handoffs. Note that the proposed schemes are a client-only solution and do not require modification of the existing APs, which renders them very practical.

Enhancing Performance of Multi-Rate WLANs: Ant Colony Approach

The trade-off between users’ fairness and network throughput may be unacceptable in a multi-rate 802.11 WLAN environment. In this paper, we will design a new intuitive simplified mathematical model called simplified coefficient of variation (SCV) to closely reflect our topic. Through controlling the power of Access Points, SCV can optimize and improve the performance. Since our topic is a NP-hard problem, we use Ant Colony Algorithm to solve our model in a practical scenario. The simulation shows excellent results indicating that our model is efficient and superior to an existing method. Also we use software SAS to further reveal the relationships among the three indicators to illustrate the essence of our approach and an existing algorithm.

Device-free Localization Technique for Indoor Detection and Tracking of Human Body: A Survey

The extensive usages of WLANs and mobile devices have increased the interest in Indoor localization systems for wireless environments. In the context of wireless-based localization system, researchers have always focused on device-based localization system, in which tracked entities must have a device attached. This practice for many years developed localization systems like Global Positioning System; Radio Frequency based system, Ultrasonic bases system and Infrared base systems. These all location based systems need a device to be attached with tracked entity, in order to run part of localization algorithm. Thus, all these systems are called as active device-based location systems. Recently a new concept device-free localization system is introduced; this system can detect and track any entity without carrying any radio device or participating actively in the localization process. A human body is detected in the device-free localization system by observing the changes in the received signal strength of WLAN environment. This paper presents a comprehensive survey of various techniques of the device-free localization system.

무선랜 침입탐지를 위한 경량 시스템 설계 및 구현

스마트폰 사용이 일반화되고 스마트워크, BYOD(Bring Your Own Device) 트렌드가 확산되면서 국내 무선랜 사용이 가속화되고 이로 인해 보안위협도 크게 증가하고 있다. 시스코시스템즈, 아루바네트웍스 등 무선랜 업체들은 WIPS(침입탐지), MDM(모바일단말관리), DLP 등 다양한 제품들을 출시해오고 있지만 비용이나 관리적인 측면에서 소규모 기업에서는 도입하기가 쉽지 않다. 본 논문에서는 고가의 H/W 장비를 도입하지 않고 무선랜 환경에서 패킷분석, AP, Station관리, 보안취약점을 분석할 수 있는 무선랜 침입탐지 시스템을 제안하고자 한다. Smartphones have become commonplace to use smart, BYOD (Bring Your Own Device) spread the trend of domestic WLAN use is intensifying as a result, the security threat will be greatly increased. Even though WLAN vendors such as Cisco Systems Inc,. Aruba networks released WIPS, MDM, DLP etc, however, these solutions can not be easily introduced for small business due to high cost or administrative reasons. In this paper, without the introduction of expensive H/W equipment, in WLAN environments, packet analysis, AP, Station management, security vulnerabilities can be analyzed by the proposed intrusion detection system.

Incremental Localization in WLAN Environment with Timeliness Management

WLAN based localization is becoming an important research topic in mobile Internet field,and the fingerprint methods are the trend.One feature of those methods is that the accuracy is determined by the identification of the training and the testing dataset.However,in the real world,the WiFi data is changing as the time passed,which leads to the reduction of the prediction accuracy.We propose TMELM to handle this problem.On one hand,it meets the requirement of the real application,allowing appending new incremental training data to the prediction model.On the other hand,timeliness management is designed to maximize the contribution of the new training data to the model.The experiments show that compared with several traditional incremental methods,our proposed TMELM performs better on the real WiFi dataset.

Vertical handoff decision in 4G wireless networks using multi attribute decision making approach

Multi-interface terminal in heterogeneous wireless networks will have network access from diverse access technologies. Multiple attribute for decision making including user preference will increase the complexity of handoff process. Various approaches have been proposed to solve the complexity problem of handoff decision. In this paper, multi attribute decision making algorithms Analytic Hierarchy Process (AHP) method, Simple Additive Weighting (SAW), Total Order Preference by Similarity to the Ideal Solution (TOPSIS), and Grey Relational Analysis (GRA) methods have been proposed for handoff decision in a WiMAX–WLAN environment to facilitate user with better quality of service. AHP has been used for calculation of weights of decision parameters. Numerical results show that SAW, TOPSIS and GRA provide almost similar performance. SAW is very simple to implement but probability of error is less in GRA because values of decision attribute are directly used for ranking of alternatives. TOPSIS is sensitive to the attribute with high score.

Evaluating a computer-based simulation program to support wireless network fundamentals

Formal learning on networking basics can reduce motivation and expectations for students who aim to become future professionals on wireless networks. To address this shortcoming, this paper presents an educational methodology to enhance learning by conducting cases studies on Wi-Fi network design. The proposed methodology is supported by a new educational simulation tool, namely WiFiSim, aimed at the generic study of IEEE 802.11-based WLANs in a disciplined way. The interest of this tool, which has been developed by the authors, lies in its ability to simulate realistic and customizable WLAN environments, high interactivity and user-friendly interface, and intuitive and easy-to-interpret 3D graphic results. These help students in wireless network modeling and deployment with improved reach and realism. In order to validate this basis, we tested WiFiSim under different simulation conditions. As a result, the teaching experience has demonstrated the effectiveness of the followed methodology and significantly reduced the gap between theory and practice.

AP 상대위치 정보를 고려한 향상된 WLAN RSSI 기반 실내 측위 알고리즘

With the development of mobile internet, requirements of positioning accuracy for the LBS (Location Based Service) are becoming more and more higher. The LBS is based on the position of each mobile device. So, it requires a proper acquisition of accurate user's indoor position. Thus indoor positioning technology and its accuracy is crucial for various LBS. In general, RSSI (Received Signal Strength Indicator) measurements are used to obtain the position information of mobile unit under WLAN environment. However, indoor positioning error increases as multiple AP's configurations are becoming more complex. To overcome this problem, an enhanced indoor localization method by AP (Access Point) selection criteria adopting DOP (Dilution of Precision) is proposed.

Principal Component Localization in Indoor WLAN Environments

This paper presents a novel approach to building a WLAN-based location fingerprinting system. Our algorithm intelligently transforms received signal strength (RSS) into principal components (PCs) such that the information of all access points (APs) is more efficiently utilized. Instead of selecting APs, the proposed technique replaces the elements with a subset of PCs to simultaneously improve the accuracy and reduce the online computation. Our experiments are conducted in a realistic WLAN environment. The results show that the mean error is reduced by 33.75 percent, and the complexity by 40 percent, as compared to the existing methods. Moreover, several benefits of our algorithm are demonstrated, such as requiring fewer training samples and enhancing the robustness to RSS anomalies.

Adaptive Parameter Estimation Method for Wireless Localization Using RSSI Measurements

Location-based service (LBS) is becoming an important part of the information technology (IT) business. Localization is a core technology for LBS because LBS is based on the position of each device or user. In case of outdoor, GPS - which is used to determine the position of a moving user - is the dominant technology. As satellite signal cannot reach indoor, GPS cannot be used in indoor environment. Therefore, research and study about indoor localization technology, which has the same accuracy as an outdoor GPS, is needed for "seamless LBS". For indoor localization, we consider the IEEE802.11 WLAN environment. Generally, received signal strength indicator (RSSI) is used to obtain a specific position of the user under the WLAN environment. RSSI has a characteristic that is decreased over distance. To use RSSI at indoor localization, a mathematical model of RSSI, which reflects its characteristic, is used. However, this RSSI of the mathematical model is different from a real RSSI, which, in reality, has a sensitive parameter that is much affected by the propagation environment. This difference causes the occurrence of localization error. Thus, it is necessary to set a proper RSSI model in order to obtain an accurate localization result. We propose a method in which the parameters of the propagation environment are determined using only RSSI measurements obtained during localization.

A study on the influence of transmission errors on WLAN IEEE 802.11 MAC performance

AbstractSince the advent of the first IEEE 802.11 standard for WLANs, several papers have been presented that evaluate the IEEE 802.11 DCF access method. In realistic WLAN environments frame errors usually occur due to non‐ideal channel conditions; in this way, papers including adverse transmission conditions in the evaluation have been published later in the literature. In this paper, we review existent analytical models that include the influence of transmission errors in IEEE 802.11 DCF performance. We modify current models and provide a more accurate analysis, thus allowing the evaluation in single rate and multi‐rate scenarios with stations subject to different link error conditions. Moreover, this paper exposes the unfairness problem that arises in IEEE 802.11 DCF networks with stations subject to different transmission conditions through analytical and simulation results. Stations are not able to distinguish collisions from failed transmissions due to link errors; both result in a missing ACK and, consequently, the transmitting stations apply the exponential backoff algorithm. This fact leads to a lower performance for stations in worse transmission conditions. Copyright © 2010 John Wiley & Sons, Ltd.

Achieving airtime fairness of delay-sensitive applications in multirate IEEE 802.11 wireless LANs

In multirate IEEE 802.11 wireless LANs, performance anomaly is a well-studied problem. Most existing solutions try to solve this problem by achieving airtime fairness. However, these solutions tend to increase the frame delay of some stations. If these stations run delay-sensitive applications, e.g., VoIP and video conferences, their quality of service would be seriously degraded. In this article we introduce and classify the existing solutions. The frame delay of each type of approach is illustrated by analytical results. We also propose an adaptive approach to solve this delay issue. The proposed approach could accurately model the condition of each station and concurrently adjust multiple MAC parameters. Simulation results validate that the proposed approach not only achieves airtime fairness but also improves frame delay. Therefore, the proposed approach could be applied to improve the quality of service of multimedia applications over WLAN environments.

On the feasibility of bandwidth estimation in wireless access networks

Bandwidth estimation refers to the measurement of a bandwidth-related metric over a network path, performed only by the end hosts, without access to the intermediate routers. The problem of fast bandwidth estimation has been extensively studied in the wired Internet. More recently, researchers have shown that tools developed for the wired Internet cannot be used in wireless networks, due to the different characteristics of these networks which invalidate many of the assumptions made for the wired Internet. This observation has led to new tools that take into account the different characteristics of wireless networks. These tools have only been evaluated in controlled environments, under controlled settings and interferers, and only for 802.11 CSMA-based WLANs. In addition, no tool has been reported so far in the literature for cellular networks. This paper presents the first study of the feasibility of fast bandwidth estimation in wireless networks "in the wild", i.e., in deployed operational networks. We discuss the challenges associated with bandwidth measurements in operational networks in contrast to in controlled lab environments. We study the applicability of a state-of-the-art probe-based tool for 802.11 WLANs in a commercial 1 × EVDO network. In addition, we evaluate the accuracy of the tool in three different WLAN environments, i.e., lab, home, and hotspot. Our results show that bandwidth estimation using a probe-based tool can be challenging in certain WLAN environments, and practically infeasible in EVDO cellular networks, due to the short-scale dynamics in this type of networks.

A Comparative Survey of Adaptive Codec Solutions for VoIP over Multirate WLANs: A Capacity versus Quality Performance Trade-Off

In multi-rate WLANs, users can suffer transmission rate changes due to the link adaptation mechanism. This results in a variable capacity channel, which is very hostile for VoIP and can cause serious quality of service (QoS) degradation in all active calls. Various codec adaptation mechanisms have been proposed as a solution to this, as well as to solve congestion problems on WLAN environments. Here, these solutions are presented, categorized according to the adaptation policy and scenario they implement, and evaluated at call-level in terms of the resulting blocking and dropping probabilities, as well as the perceived voice quality. To define a common performance metric, a new index named VGoS-factor is presented, which, by combining these capacity and quality indicators, can provide an overall view of the capacity versus quality trade-off of the proposed mechanisms and consequently help in choosing the adequate policy for each scenario.

Multilayer ANN indoor location system with area division in WLAN environment

Multilayer ANN indoor location system with area division in WLAN environment

Gabor Filter Aided 3D Ultra-Sonography Diagnosis System with WLAN Transmission Consideration

The Gabor filter aided diagnosis system for 3-dimensional ultra-sonography (3DUS) under the WLAN environment is introduced. Due to the important relationship between breast tumour surface features and internal architecture, we applied our system using 3D inter-pixel correlations instead of 2D features. Gabor filters provide a multi-resolution representation of texture, which increases ultrasound technology capability in the differential diagnosis of solid breast tumours. Our experiments show that the performance of the proposed diagnostic method is effective. Moreover, physicians manipulate our diagnostic system using hand-held devices in the hospital. Because WLAN is unstable, our system ensures good transmission quality. We also focus on transmission control strategies that adapt to the time varying wireless network conditions. We analyze strategies that use competitive analysis techniques. The experiments show that the algorithm's performance is effective.

Seamless Handover of IPTV Streams in a Wireless LAN Network

A robust mechanism to enable seamless handover of streamed IPTV in a WLAN is presented. Handover in a wireless network is usually based on signal strength measurements, but that approach does not consider levels of congestion within the network. Here, the case of stationary nodes with varying levels of network congestion is considered. A scheme that analyzes the jitter is used to establish the relationship between congestion and loss in WLANs. This Moving Average of Negative Jitter is used as the basis of a handover scheme which can minimize loss. The handover scheme uses a client with two simultaneous connections to the same server through two separate WLANs, and it is shown that the client can compare the jitter in the two streams to determine which network delivers the best performance; this information is then used to determine when to perform a handover. The proposed scheme is implemented and results are presented that show the successful handover of an RTP over UDP stream in a live WLAN environment. The test scenario used is aimed at ldquoOver-The-Toprdquo service delivery, but the core algorithm is expected to be more broadly applicable.

Goodput analysis of a WLAN with hidden nodes under a non-saturated condition

Hidden nodes may severely degrade the performance of wireless LANs. Focusing on the hidden node effect, we analyze goodput in a single cell WLAN environment with hidden nodes under a non-saturated condition. Uplink and downlink goodputs are analytically derived using an approximation technique and are compared with simulation results.

QoS Differentiation Based Adaptive p-Persistent MAC Scheme for Dynamic Optimization of the Channel Utilization

PDF HTML阅读 XML下载 导出引用 引用提醒 QoS 区分的自适应p-Persistent MAC 算法对信道利用率的动态优化 DOI: 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: Supported by the National High-Tech Research and Development Plan of China under Grant Nos.2005AA123820, 2005AA121122 (国家高技术研究发展计划(863)) QoS Differentiation Based Adaptive p-Persistent MAC Scheme for Dynamic Optimization of the Channel Utilization Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在无线局域网中提供服务质量(QoS)保证的MAC 算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC 算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistent MAC 算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE 802.11 DCF 和IEEE 802.11e EDCA 机制. Abstract:This paper proposes an adaptive p-persistent MAC scheme, named QDA-MAC (QoS differentiation based adaptive MAC scheme), for WLAN to maximize the channel utilization and provide the service differentiation among different traffic stations. Specifically, different from the previous work, the proposed schemedoes not need to estimate the number of active stations for each priority class but still achieves the channelutilization close to its optimal value by exploiting a new parameter, persistent factor, whose optimal value candynamically follow the change of the load based on a simple estimation of the network status. At the same time, thetransmission probability of each priority class can be updated by the optimal persistent factor. Simulation andnumerical results show that QDA-MAC can achieve much higher channel utilization and have shorter delay thanstandard IEEE 802.11 DCF and IEEE 802.11e EDCA in all different WLAN environments. 参考文献 相似文献 引证文献