Design and implementation of a WLAN/cdma2000 interworking architecture

The combination of 3G and WLAN wireless technologies offers the possibility of achieving anywhere, anytime Internet access, bringing benefits to both end users and service providers. We discuss interworking architectures for providing integrated service capability across widely deployed 3G cdma2000-based and IEEE 802.11-based networks. Specifically, we present two design choices for integration: tightly coupled and loosely coupled, and recommend the latter as a preferred option. We describe in detail the implementation of a loosely coupled integrated network which provides two kinds of roaming services, a SimpleIP service and a Mobile-IP service. We present, in detail, two new components used to build these services: a network element called a WLAN integration gateway deployed in WLAN networks; a client software on the mobile device. For a mobile device with interfaces to both technologies, our system supports seamless handoff in the presence of overlapping radio coverage.     

Effects of Power Amplifier Distortion and Carrier Frequency Offset on the Performance of WLAN System

Due to the efficiency of mitigation multipath delay spread, orthogonal frequency division multiplexing (OFDM) is extensively used in the wireless local area network (WLAN) domain, such as the IEEE 802.11a standard defined by the IEEE 802.11 standardization group and the HIPERLAN/2 defined by the European Telecommunication Standards Institute Project on Broadband Radio Access Networks. OFDM based WLAN system is very sensitive to the power amplifier distortion and the carrier frequency offset. The performance of the OFDM based WLAN system in the presence of the power amplifier distortion and the carrier frequency offset under practical fading channel is researched and analyzed in this paper. A closed form of bit error rate (BER) is derived for the OFDM based WLAN system in the presence of the power amplifier distortion and the carrier frequency offset under practical fading channel. The effects of the power amplifier distortion and the carrier frequency offset on the OFDM based WLAN system performance are comparatively studied by the theoretical method and by the simulation method under practical multipath fading channels. Studies show that the theoretical and simulated results match well.     

5G无线局域网环境下OFDM对无线信道的适应性分析

建立了基于广义平稳不相关散射假设(WSSUS)下的多径时变信道模型。针对无线局域网(WLAN)的特点,从802．11a协议出发,从全信道和子信道两个角度分别建立信道模型,阐述了OFDM利用循环前缀对抗多径信道码间干扰(ISI)的机理,并仿真了不同多普勒频移对系统误码底板影响,结果表明OFDM系统对WLAN具有强大适应性。     

无线局域网中OFDM系统的研究

OFDM是下一代移动通信(NGN)的核心技术之一。论文遵循802.11a标准规范,用SystemView仿真软件搭建了WLAN802.11aOFDM系统仿真电路,为OFDM技术的研究提供了方便,并对OFDM技术性能进行仿真,验证了该技术具有很强的抗多径衰落能力。     

Analog AGC Circuitry for a CMOS WLAN Receiver

The IEEE 802.11a standard uses orthogonal frequency division multiplexing (OFDM) to allow high data rates in multipath WLAN environments. The high peak-to-average power ratio (PAPR) of OFDM signals, along with stringent settling-time constraints, make conventional closed-loop automatic gain control (AGC) schemes impractical for WLAN receivers. In a direct conversion receiver, AGC and channel-select filtering are performed by analog baseband circuitry. A baseband signal processor using a new open-loop analog gain-control algorithm for OFDM is described. The new AGC algorithm uses switched coarse gain-setting steps followed by an analog open-loop fine gain-setting step to set the final gain of variable gain amplifiers (VGAs). The AGC was implemented in a 0.18-$muhbox m$CMOS process using newly designed circuits including linear VGAs, RMS detectors, and current-mode computation circuitry. Simulation and measurement results verify that the new AGC circuit converges with gain error less than 1dB to the desired level within 5.6$muhbox s$.     

A Novel Wireless Positioning System for Seamless Internet Connectivity based on the WLAN Infrastructure

Nowadays, several positioning systems are available for outdoor localization, such as the global positioning system (GPS), assisted GPS (A-GPS), and other systems working on cellular networks, for example, time difference of arrival (TDOA), angle of arrival (AOA) and enhanced observed time difference of arrival (E-OTD). However, with the increasing use of mobile computing devices and an expansion of wireless local area networks (WLANs), there is a growing interest in indoor wireless positioning systems based on the WLAN infrastructure. Wireless positioning systems (WPS) based on this infrastructure can be used for indoor localization to determine the position of mobile users. In this paper, we present a novel wireless positioning system, based on the IEEE 802.11b standard, using a novel access point (AP) with two transceivers to improve the performance of WPS in terms of accuracy of the location estimation and to avoid service connectivity interruption. In our proposed system, the novel AP uses the second transceiver to find information from neighboring mobile stations (STAs) in the transmission range and then sends information in advance to associated APs, which estimate the location of the STA based on an internal database. We also use a TDOA technique to estimate the location of the STA when there is not enough information in the database (in this case, the STA moves into a new area where the system has not run the calibration phase). Using TDOA, the database can be generated and updated automatically. The initial results from our simulations show that the proposed system provides higher accuracy of location estimation than other related work and does not interrupt the Internet connection for end users in contrast with other proposed schemes.

Heterogeneous uncoordinated deployment of WLANs: an evolving problem for current and future Wi‐Fi access

This article addresses the problem of uncoordinated heterogeneous deployment of 802.11 wireless local area networks (WLANs). It is expected that such deployments by different WLAN owners and WiFi providers will become a challenging problem that limits the network performance and quality of service of wireless users. We present results of a real case study that show a need for coordination among WLAN devices in order to avoid current and future problems. We provide potential solution directions. A special focus is given to channel assignment and coordinated channel access problems. Our results show that a new paradigm for designing WLAN devices seems to be crucial. Copyright © 2012 John Wiley & Sons, Ltd.     

A Low-Order DGPS-Based Vehicle Positioning System Under Urban Environment

The vehicle positioning system is a key component in functions such as vehicle guidance, driver alert and assistance, and vehicle automation. Since installing a low-cost global positioning system (GPS) or inertial navigation system (INS) unit is becoming a common practice in vehicle applications, its involvement in vehicle guidance and vehicle safety deserves a closer investigation. Typical vehicle applications require high reliability, low cost, and sufficient accuracy under all operational conditions. For GPS-based positioning, urban driving with its complicated maneuvers, frequent GPS blockage, and multipath, are some of the most difficult driving environments. This paper explores the feasibility of a low-order vehicle positioning system functioning under an urban environment. The equipped vehicle has a midrange differential GPS (DGPS) unit and few relatively simple in-vehicle sensors. A low-order integration is explored by utilizing a vehicle model-based extended Kalman filter (EKF) to incorporate in-vehicle motion sensors and to largely avoid direct integration of INS signals. Further, the characteristics of DGPS measurements under urban environments are investigated, and novel DGPS noise processing techniques are proposed to reduce the chances of exposing the EKF to undesirable DGPS measurements due to common DGPS problems such as blockage and multipath. A resulting fourth order EKF based positioning system is successfully implemented in the test vehicle to demonstrate the feasibility of the proposed design. Experimental results illustrate the ability of the system to meet the accuracy and robustness requirements in the presence of blockage and multipath under a typical urban driving environment.     

The need for access point power saving in solar powered WLAN mesh networks

Wireless LAN mesh networks are now being used to deploy Wi-Fi coverage in a wide variety of outdoor applications. In these types of networks, conventional WLAN mesh nodes must be operated using continuous electrical power connections. This requirement may often be very expensive, especially when the network includes expansive outdoor wireless coverage areas. An alternative is to operate some of the WLAN mesh nodes using an energy sustainable source such as solar or wind power. This eliminates the need for a fixed power connection, making the node truly tetherless and allowing more flexibility in node positioning. In this article we first review the background and recent activities in the area of energy sustainable WLAN mesh networks. These types of networks are provisioned geographically, in that the assigned resources are a function of the geographic region where the network is to be deployed. The theory behind this is briefly described using some sample North American locations. We then discuss the current shortcomings of IEEE 802.1 1 when used in these types of networks. IEEE 802.11 requires that the access point be continuously powered, and this requirement is a major barrier to deploying cost-effective sustainable energy networks in certain applications. Recent work is then reviewed that has begun to address the changes that would be required to the standard to better support these types of networks.     

A-GPS终端一致性测试

A-GPS(Assisted Global Positioning System)是一种通过移动通信网络辅助的全球定位技术,此技术结合了两类位置信息,一类是移动台通过自身GPS接收机获得的,而另一类则是移动台通过移动通信网络获取的。A-GPS技术可以在2G,3G以及未来4G的通信网络中部署应用,移动终端应用A-GPS定位业务,需要增加A-GPS接收机及相应信号处理模块。A-GPS的终端一致性认证,即对于移动终端的A-GPS功能部分进行一致性验证,目前国际上采用的包含A-GPS一致性测试规范有3GPP51.010,3GPP34.171,3GPP34.123,3GPP2C.S0036,3GPP2C.S0059,OMA-ETS-SUPL等,本文对上述规范做了详细介绍。     

A survey of QoS enhancements for IEEE 802.11 wireless LAN

Quality‐of‐service (QoS) is a key problem of today's IP networks. Many frameworks (IntServ, DiffServ, MPLS etc.) have been proposed to provide service differentiation in the Internet. At the same time, the Internet is becoming more and more heterogeneous due to the recent explosion of wireless networks. In wireless environments, bandwidth is scarce and channel conditions are time‐varying and sometimes highly lossy. Many previous research works show that what works well in a wired network cannot be directly applied in the wireless environment. Although IEEE 802.11 wireless LAN (WLAN) is the most widely used IEEE 802.11 wireless LAN (WLAN) standard today, it cannot provide QoS support for the increasing number of multimedia applications. Thus, a large number of 802.11 QoS enhancement schemes have been proposed, each one focusing on a particular mode. This paper summarizes all these schemes and presents a survey of current research activities. First, we analyze the QoS limitations of IEEE 802.11 wireless MAC layers. Then, different QoS enhancement techniques proposed for 802.11 WLAN are described and classified along with their advantages/drawbacks. Finally, the upcoming IEEE 802.11e QoS enhancement standard is introduced and studied in detail. Copyright © 2004 John Wiley & Sons, Ltd.     

Maximizing signal strength for OFDM inside buildings

Propagation inside buildings suffer from large shadowing and high multipath effects. This is a serious problem for wireless local area network (WLAN) systems. This paper shows that shadowing and path loss can be minimized by exploiting the multipath tolerance of orthogonal frequency-division multiplexing (OFDM). This can be achieved by using multiple transmission antennas spread over the area of a WLAN cell. These antennas act as repeaters, transmitting and receiving the same signal at the same time. This decreases the average path loss, but increases the multipath delay spread. Using OFDM allows the advantage of reduced path loss to be utilized without detrimental effects of inter-symbol interference caused by the increased delay spread. The reduced path loss allows an increased system capacity, quality of service, or a decrease in intercellular interference in a cellular WLAN     

Positioning in WLAN environment by use of artificial neural networks and space partitioning

Short range wireless technologies such as wireless local area network (WLAN), Bluetooth, radio frequency identification, ultrasound and Infrared Data Association can be used to supply position information in indoor environments where their infrastructure is deployed. Due to the ubiquitous presence of WLAN networks, positioning techniques in these environments are the scope of intense research. In this paper, the position determination by the use of artificial neural networks (ANNs) is explored. The single ANN multilayer feedforward structure and a novel positioning technique based on cascade-connected ANNs and space partitioning are presented. The proposed techniques are thoroughly investigated on a real WLAN network. Also, an in-depth comparison with other well-known techniques is shown. Positioning with a single ANN has shown good results. Moreover, when utilising space partitioning with the cascade-connected ANNs, the median error is further reduced for as much as 28%.     

Outdoor Mobile Broadband Access with 802.11

The IEEE 802.11 OFDM physical layer was designed primarily for indoor local area networks. Commercially available 802.11 radios suffer greatly reduced performance, even failing completely, when deployed outdoors, where long delay spreads cause self-interference, and vehicular mobility causes fast variations in the radio channel parameters. This article describes an advanced OFDM receiver that overcomes these problems. It works by combining all useful received energy, accounting for inter-symbol interference, and accurately tracking radio channel variations. Complexity and performance advantages arc gained by splitting the processing between the time and frequency domains. Computer simulations show that even for outdoor urban environments at speeds greater than 140 mph, this receiver delivers performance comparable to a non-mobile, indoor system.     

gpsOne定位技术研究

移动通信最显著的特点就是移动,因而自然会衍生一些和位置相关的服务需求.在不远的将来,电子邮件和定位服务将成为移动通信的两大支柱增值产业. 鉴于传统GPS及基于无线网络本身的定位技术在定位精度或定位灵敏度或系统建设或终端方面存在的重大缺陷,目前,世界上较流行的移动定位技术是无线网络辅助GPS技术及混合型定位技术.由于自身技术优势,gpsOne已无可争议的成为移动定位业界的首选技术.     

Emerging technologies in wireless LANs: theory, design, and deployment - [book reviews]

This book provides a comprehensive look at the theory and practice of the latest WLAN technologies and applications. It consists of 14 parts, which contain a total of 38 chapters. Some of the topics covered include: an introduction to the IEEE 802.11 standard; quality of service aspects of WLANs; security; hardware design of 802.11 chips and antennas; WiFi hotspots; ultra wideband (UWB) wireless technology; and delivering wireless broadband to the public. This book touches on a wide variety of aspects related to wireless LANs. It does a good job at presenting emerging standards and interesting applications. All chapters have extensive and current references. There is some overlapping material, and the latest version of the WLAN standard, 802.11-2007, is not referenced in the book, but overall this useful book is recommended for postgraduate students, university researchers, and engineers working in the industry.     

Sensor Measurements for Wi-Fi Location with Emphasis on Time-of-Arrival Ranging

Wireless local area network (WLAN) location is the perfect complement to global positioning system (GPS) receivers for providing users with location information. WLAN operates in many areas in which GPS receivers cannot establish a lock, such as in indoor environments and metropolitan (obstruction by tall buildings) areas. There are many references to WLAN location in scientific literature. Most of this literature concentrates on signal-strength-based approaches. The advantage of signal strength approaches is that they are easy to implement, usually only requiring software modifications. In this paper, we discuss a novel time of arrival (TOA) approach that Intel research has developed. Although this approach typically requires minor silicon or firmware modifications to implement, it can deliver significant performance improvements over signal-strength-based measurements, as shown in this paper. Currently, Intel is introducing this method as an approach to add fine-accuracy location into the IEEE WLAN standard, 802.11 v.     

IEEE 802.11s wireless mesh networks: Framework and challenges

Wireless mesh networking based on 802.11 wireless local area network (WLAN) has been actively explored for a few years. To improve the performance of WLAN mesh networks, a few new communication protocols have been developed in recent years. However, these solutions are usually proprietary and prevent WLAN mesh networks from interworking with each other. Thus, a standard becomes indispensable for WLAN mesh networks. To meet this need, an IEEE 802.11 task group, i.e., 802.11s, is specifying a standard for WLAN mesh networks. Although several standard drafts have been released by 802.11s, many issues still remain to be resolved. In order to understand what performance can be expected from the existing framework of 802.11s standard and what functionalities shall be added to 802.11s standard to improve performance, a detailed study on the existing 802.11s standard is given in this paper. The existing framework of 802.11s standard is first presented, followed by pointing out the challenging research issues that still exist in the current 802.11 standard. The purpose of this paper is to motivate other researchers to develop new scalable protocols for 802.11 wireless mesh networks.     

Receiver Algorithms for Multi-stream Data Transmission in WLAN 802.11n Networks

Multiple Input Multiple Output (MIMO) systems employ multiple antennas to provide high spectral efficiency and wireless link reliability thanks to multipath diversity and space multiplexing. This technology is now being implemented into wireless standards such as 802.11n, as well as the 4th generation cellular networks. In this paper we present results of an extensive simulation research in which we compare three receiver models for MIMO WLAN 802.11n system. We investigate maximum-likelihood, zero-forcing and Vertical Bell Laboratories Layered Space Time receivers. Performance of these receivers for a range of 802.11n environments, i.e. for several channel models and different number of transmitter and receiver antennas is evaluated. The results of the comparison highlight the benefits of MIMO technology and show to what extent it is possible to improve the MIMO 802.11n system performance increasing the receiver complexity.     

802.11无线局域网与公用网的连接方式探讨

作为一种有广阔前景的技术，IEEE802．11(简称802．11)无线局域网正在得到越来越多人的关注，而运营商也考虑在热点地区布署无线局域网以作为其接入手段的一种补充。由于早期制定协议时对如何接入公用网考虑得不够完全，因而802．11标准在AAA（authenticate、authority、account)、漫游、加密等方面还存在一些不完备之处。同时，在局域网布署以后将对运营商原有的网络产生影响，运营商也希望能将其纳入至统一的网络管理、规划和业务控制系统中。本描述了目前国际上正在进行的这方面努力，同时提出了原有经营无线业务的运营商在铺设基于802．11的无线局域网时采用的解决方案。最后简要介绍了802．11无线局域网在未来的发展方向。