Showing papers on "Wi-Fi array published in 2004"

An overview of MIMO communications - a key to gigabit wireless

Abstract: High data rate wireless communications, nearing 1 Gb/s transmission rates, is of interest in emerging wireless local area networks and home audio/visual networks. Designing very high speed wireless links that offer good quality-of-service and range capability in non-line-of-sight (NLOS) environments constitutes a significant research and engineering challenge. Ignoring fading in NLOS environments, we can, in principle, meet the 1 Gb/s data rate requirement with a single-transmit single-receive antenna wireless system if the product of bandwidth (measured in hertz) and spectral efficiency (measured in bits per second per hertz) is equal to 10/sup 9/. A variety of cost, technology and regulatory constraints make such a brute force solution unattractive, if not impossible. The use of multiple antennas at transmitter and receiver, popularly known as multiple-input multiple-output (MIMO) wireless, is an emerging cost-effective technology that offers substantial leverages in making 1 Gb/s wireless links a reality. The paper provides an overview of MIMO wireless technology covering channel models, performance limits, coding, and transceiver design.

Wireless Sensor Networks

Abstract: Sensor networks consist of a set of sensor nodes, each equipped with one or more sensors, communication subsystems, storage and processing resources, and in some cases actuators. The sensors in a node observe phenomena such as thermal, optic, acoustic, seismic, and acceleration events, while the processing and other components analyze the raw data and formulate answers to specific user requests. Recent advances in technology have paved the way for the design and implementation of new generations of sensor network nodes, packaged in very small and inexpensive form factors with sophisticated computation and wireless communication abilities. Although still at infancy, these new classes of sensor networks, generally referred to as wireless sensor networks (WSN), show great promise and potential with applications ranging in areas that have already been addressed, to domains never before imagined. In this article we provide an overview of this new and exciting field and a brief discussion on the factors pushing the recent flurry of sensor network related research and commercial undertakings. We also provide overview discussions on architectural design characteristics of such networks including physical components, software layers, and higher level services. At each step, we highlight special characteristics of WSNs and discuss why existing approaches and results from wireless communication networks are not necessarily suitable in WSN domains. We conclude by briefly summarizing the state of the art and the future research directions.

The design space of wireless sensor networks

Abstract: In the recent past, wireless sensor networks have found their way into a wide variety of applications and systems with vastly varying requirements and characteristics. As a consequence, it is becoming increasingly difficult to discuss typical requirements regarding hardware issues and software support. This is particularly problematic in a multidisciplinary research area such as wireless sensor networks, where close collaboration between users, application domain experts, hardware designers, and software developers is needed to implement efficient systems. In this article we discuss the consequences of this fact with regard to the design space of wireless sensor networks by considering its various dimensions. We justify our view by demonstrating that specific existing applications occupy different points in the design space.

Ad Hoc Wireless Networks: Architectures and Protocols

Abstract: Practical design and performance solutions for every ad hoc wireless networkAd Hoc Wireless Networks comprise mobile devices that use wireless transmission for communication. They can be set up anywhere and any time because they eliminate the complexities of infrastructure setup and central administration-and they have enormous commercial and military potential. Now, there's a book that addresses every major issue related to their design and performance. Ad Hoc Wireless Networks: Architectures and Protocols presents state-of-the-art techniques and solutions, and supports them with easy-to-understand examples. The book starts off with the fundamentals of wireless networking (wireless PANs, LANs, MANs, WANs, and wireless Internet) and goes on to address such current topics as Wi-Fi networks, optical wireless networks, and hybrid wireless architectures. Coverage includes: Medium access control, routing, multicasting, and transport protocols QoS provisioning, energy management, security, multihop pricing, and much more In-depth discussion of wireless sensor networks and ultra wideband technology More than 200 examples and end-of-chapter problemsAd Hoc Wireless Networks is an invaluable resource for every network engineer, technical manager, and researcher designing or building ad hoc wireless networks.

Wireless sensor and actor networks: research challenges

Abstract: Wireless sensor and actor networks (WSANs) refer to a group of sensors and actors linked by wireless medium to perform distributed sensing and acting tasks. The realization of wireless sensor and actor networks (WSANs) needs to satisfy the requirements introduced by the coexistence of sensors and actors. In WSANs, sensors gather information about the physical world, while actors take decisions and then perform appropriate actions upon the environment, which allows a user to effectively sense and act from a distance. In order to provide effective sensing and acting, coordination mechanisms are required among sensors and actors. Moreover, to perform right and timely actions, sensor data must be valid at the time of acting. This paper explores sensor-actor and actor-actor coordination and describes research challenges for coordination and communication problems.

Centralized channel assignment and routing algorithms for multi-channel wireless mesh networks

Abstract: The IEEE 802.11 Wireless LAN standards allow multiple non-overlapping frequency channels to be used simultaneously to increase the aggregate bandwidth available to end-users. Such bandwidth aggregation capability is routinely used in infrastructure mode operation, where the traffic to and from wireless nodes is distributed among multiple interfaces of an access point or among multiple access points to balance the traffic load. However, bandwidth aggregation is rarely used in the context of multi-hop 802.11-based LANs that operate in the ad hoc mode. Most past research efforts that attempt to exploit multiple radio channels require modifications to the MAC protocol and therefore do not work with commodity 802.11 interface hardware. In this paper, we propose and evaluate one of the first multi-channel multi-hop wireless ad-hoc network architectures that can be built using standard 802.11 hardware by equipping each node with multiple network interface cards (NICs) operating on different channels. We focus our attention on wireless mesh networks that serve as the backbone for relaying end-user traffic from wireless access points to the wired network. The idea of exploiting multiple channels is particularly appealing in wireless mesh networks because of their high capacity requirements to support backbone traffic. To reap the full performance potential of this architecture, we develop a set of centralized channel assignment, bandwidth allocation, and routing algorithms for multi-channel wireless mesh networks. A detailed performance evaluation shows that with intelligent channel and bandwidth assignment, equipping every wireless mesh network node with just 2 NICs operating on different channels can increase the total network goodput by a factor of up to 8 compared with the conventional single-channel ad hoc network architecture.

Information Exchange in Wireless Networks with Network Coding and Physical-layer Broadcast

Abstract: —We show that mutual exchange of independentinformation between two nodes in a wireless network can be effi-ciently performed by exploiting network coding and the physical-layer broadcast property offered by the wireless medium. Theproposed approach improves upon conventional solutions thatseparate the processing of the two unicast sessions, correspondingto information transfer along one direction and the oppositedirection. We propose a distributed scheme that obviates theneed for synchronization and is robust to random packet lossand delay, and so on. The scheme is simple and incurs minoroverhead. I. I NTRODUCTION In this paper, we investigate the mutual exchange of inde-pendent information between two nodes in a wireless network.Let us name the two nodes in consideration a and b, respec-tively. Consider a packet-based communication network withall packets of equal size. The basic problem is very simple: awants to transmit a sequence of packets {X 1 (n)} to b andb wants to transmit a sequence of packets {X

An Energy-Efficient Surveillance System Using Wireless Sensor Networks

Abstract: The focus of surveillance missions is to acquire and verify information about enemy capabilities and positions of hostile targets. Such missions often involve a high element of risk for human personnel and require a high degree of stealthiness. Hence, the ability to deploy unmanned surveillance missions, by using wireless sensor networks, is of great practical importance for the military. Because of the energy constraints of sensor devices, such systems necessitate an energy-aware design to ensure the longevity of surveillance missions. Solutions proposed recently for this type of system show promising results through simulations. However, the simplified assumptions they make about the system in the simulator often do not hold well in practice and energy consumption is narrowly accounted for within a single protocol. In this paper, we describe the design and implementation of a running system for energy-efficient surveillance. The system allows a group of cooperating sensor devices to detect and track the positions of moving vehicles in an energy-efficient and stealthy manner. We can trade off energy-awareness and surveillance performance by adaptively adjusting the sensitivity of the system. We evaluate the performance on a network of 70 MICA2 motes equipped with dual-axis magnetometers. Our results show that our surveillance strategy is adaptable and achieves a significant extension of network lifetime. Finally, we share lessons learned in building such a complete running system.

A survey of mobility management in next-generation all-IP-based wireless systems

Abstract: Next-generation wireless systems are envisioned to have an IP-based infrastructure with the support of heterogeneous access technologies. One of the research challenges for next generation all-IP-based wireless systems is the design of intelligent mobility management techniques that take advantage of IP-based technologies to achieve global roaming among various access technologies. Next-generation wireless systems call for the integration and interoperation of mobility management techniques in heterogeneous networks. In this article the current state of the art for mobility management in next-generation all-IP-based wireless systems is presented. The previously proposed solutions based on different layers are reviewed, and their qualitative comparisons are given. A new wireless network architecture for mobility management is introduced, and related open research issues are discussed in detail.

The changing usage of a mature campus-wide wireless network

Abstract: Wireless Local Area Networks (WLANs) are now commonplace on many academic and corporate campuses. As "Wi-Fi" technology becomes ubiquitous, it is increasingly important to understand trends in the usage of these networks.This paper analyzes an extensive network trace from a mature 802.11 WLAN, including more than 550 access points and 7000 users over seventeen weeks. We employ several measurement techniques, including syslogs, telephone records, SNMP polling and tcpdump packet sniffing. This is the largest WLAN study to date, and the first to look at a large, mature WLAN and consider geographic mobility. We compare this trace to a trace taken after the network's initial deployment two years ago.We found that the applications used on the WLAN changed dramatically. Initial WLAN usage was dominated by Web traffic; our new trace shows significant increases in peer-to-peer, streaming multimedia, and voice over IP (VoIP) traffic. On-campus traffic now exceeds off-campus traffic, a reversal of the situation at the WLAN's initial deployment. Our study indicates that VoIP has been used little on the wireless network thus far, and most VoIP calls are made on the wired network. Most calls last less than a minute.We saw greater heterogeneity in the types of clients used, with more embedded wireless devices such as PDAs and mobile VoIP clients. We define a new metric for mobility, the "session diameter." We use this metric to show that embedded devices have different mobility characteristics than laptops, and travel further and roam to more access points. Overall, users were surprisingly non-mobile, with half remaining close to home about 98% of the time.

Wireless communications apparatus and method

Abstract: A wireless communication method and apparatus are described for increasing security for communication devices utilizing identification chips for accessing wireless networks and the associated billing for services. One aspect of the invention is an enhanced phone chip and a communications device adapted to engage the enhanced phone chip, which then cannot be installed or removed from the wireless communications device by unauthorized users. In one embodiment a security key mates to the identification chip and is utilized for installing and removing the enhanced phone chip. The security key preferably has a display upon which information about the communication device is displayed prior to removing the security key after installing the enhanced phone chip. Other aspects of the invention include wireless base station communication devices which support wired (dedicated and non-dedicated), and more preferably wireless extensions, while providing sharing of wireless network resources and interconnectivity between base station and extensions.

MultiNet: connecting to multiple IEEE 802.11 networks using a single wireless card

Abstract: There are a number of scenarios where it is desirable to have a wireless device connect to multiple networks simultaneously. Currently, this is possible only by using multiple wireless network cards in the device. Unfortunately, using multiple wireless cards causes excessive energy drain and consequent reduction of lifetime in battery operated devices. We propose a software based approach, called MultiNet, that facilitates simultaneous connections to multiple networks by virtualizing a single wireless card. The wireless card is virtualized by introducing an intermediate layer below IP, which continuously switches the card across multiple networks. The goal of the switching algorithm is to he transparent to the user who sees her machine as being connected to multiple networks. We present the design, implementation, and performance of the MultiNet system. We analyze and evaluate buffering and switching algorithms in terms of delay and energy consumption. Our system is agnostic of the upper layer protocols, and works well over popular IEEE 802.11 wireless LAN cards.

The platforms enabling wireless sensor networks

Abstract: All emphasize low-cost components operating on shoestring power budgets for years at a time in potentially hostile environments without hope of human intervention.

Channel surfing and spatial retreats: defenses against wireless denial of service

Abstract: Wireless networks are built upon a shared medium that makes it easy for adversaries to launch denial of service (DoS) attacks. One form of denial of service is targeted at preventing sources from communicating. These attacks can be easily accomplished by an adversary by either bypassing MAC-layer protocols, or emitting a radio signal targeted at jamming a particular channel. In this paper we present two strategies that may be employed by wireless devices to evade a MAC/PHY-layer jamming-style wireless denial of service attack. The first strategy, channel surfing, is a form of spectral evasion that involves legitimate wireless devices changing the channel that they are operating on. The second strategy, spatial retreats, is a form of spatial evasion whereby legitimate mobile devices move away from the locality of the DoS emitter. We study both of these strategies for three broad wireless communication scenarios: two-party radio communication, an infrastructured wireless network, and an ad hoc wireless network. We evaluate several of our proposed strategies and protocols through ns-2 simulations and experiments on the Berkeley mote platform.

Method and apparatus for wireless network hybrid positioning

Abstract: Methods and apparatuses for position determination and other operations. In one embodiment of the present invention, a mobile station uses wireless signals from a plurality of wireless networks (e.g., with different air interfaces and/or operated by different service providers) for position determination (e.g., for data communication, for obtaining time and/or frequency information, for range measurement, for sector or altitude estimation). In one embodiment of the present invention, mobile stations are used to harvest statistical data about wireless access points (e.g., the locations of mobile stations that have received signals from the wireless access points, such as from cellular base stations, wireless local area network access points, repeaters for positioning signals, or other wireless communication transmitters) and to derive location information (e.g., position and coverage area of the wireless access points) for the wireless networks from the collected statistical data.

Reconsidering wireless systems with multiple radios

Abstract: The tremendous popularity of wireless systems in recent years has led to the commoditization of RF transceivers (radios) whose prices have fallen dramatically. The lower cost allows us to consider using two or more radios in the same device. Given this, we argue that wireless systems that use multiple radios in a collaborative manner dramatically improve system performance and functionality over the traditional single radio wireless systems that are popular today. In this context, we revisit some standard problems in wireless networking, including energy management, capacity enhancement, mobility management, channel failure recovery, and last-hop packet scheduling. We show that a systems approach can alleviate many of the performance and robustness issues prevalent in current wireless LAN systems. We explore the implications of the multi-radio approach on software and hardware design, as well as on algorithmic and protocol research issues. We identify three key design guidelines for constructing multi-radio systems and present results from two systems that we have built. Our experience supports our position that a multi-radio platform offers significant ben-efits for wireless systems.

On cross-layer design of wireless networks

Abstract: Summary form only given. The layered architecture is one of the key reasons behind the explosive and continuing growth of the Internet. There are, however, special networks in which cross-layer design is appropriate and may even be necessary. Two such cases are small wireless LAN and large-scale sensor networks. We consider first the design of medium access control (MAC) for a small wireless LAN based on a multiuser physical layer. We present a complete characterization of the throughput region and present conditions under which ALOHA is optimal. Next we consider the estimation of signal field using data collected from a large scale sensor network. The impact of medium access control on estimation is examined. We show that there exists a threshold on sensor outage probability above which a distributed random access protocol (such as ALOHA) outperforms the centralized deterministic schedulers.

System for integrating an airborne wireless cellular network with terrestrial wireless cellular networks and the public switched telephone network

Abstract: The present non-terrestrial feature transparency system spoofs the Air-to-Ground Network and the ground-based cellular communication network into thinking that the wireless subscriber devices have no special considerations associated with their operation, even though the wireless subscriber devices are located on an aircraft in flight. This architecture requires that the non-terrestrial feature transparency system on board the aircraft replicate the full functionality of a given wireless subscriber device, that has a certain predetermined feature set from a ground-based wireless service provider, at another wireless subscriber device located within the aircraft. The Air-to-Ground Network transmits both the subscriber data (comprising voice and/or other data) as well as feature set data to thereby enable the wireless subscriber devices that are located in the aircraft to receive consistent wireless communication services.

A survey of QoS enhancements for IEEE 802.11 wireless LAN

Abstract: *Summary 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 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.

Method and apparatus for integrated wireless communications in private and public network environments

Abstract: A communication system formed by a private network that includes a private wireless network. The communication system includes a public wireless network using a public wireless protocol, such as GSM, and includes public networks, such as PSTN, ISDN and the Internet, using a wired protocol, such as IP. The private network also includes a local area network (LAN) and the private network connects to the public networks using a wired packet protocol, such as IP. The public and private wireless networks operate with the same public wireless protocol, such as GSM, and the private wireless network additionally operates with a wired packet protocol, such as IP. The communication system permits users to operate freely in both public and private wireless networks using standard mobile stations while achieving high private network data rates. The communication system uses normal wireless handsets or other mobile or fixed stations without need for any modifications.

Portable data unit for communicating with gaming machine over wireless link

Abstract: A method and arrangement for communicating with a gaming machine is disclosed. The gaming machine includes a first wireless transceiver. A portable data unit includes a second wireless transceiver. In response to positioning the portable data unit in proximity to the gaming machine, without inserting the portable data unit into any portion of the gaming machine, a wireless transmission link is established between the first and second wireless transceivers. The wireless transmission link may, for example, be a radio (RF) link or an infrared (IR) link. Information is transmitted between the portable data unit and the gaming machine via the wireless transmission link for such purposes as cashless gaming, player tracking, game customization, and data transfer.

Closed-loop control over wireless networks

Abstract: This article includes an implementation of an 802.11b wireless control loop with high communication rates and a timing scheme that uses clock driven sensing and actuation with event-driven control. The timing scheme was implemented using standard PCs and an 802.11b peer-to-peer wireless network. The control scheme was scaled up to a multimode multiplant arrangement with coordination among loops. To examine the wireless control loop performance, we use the rotating base variation of the linear inverted pendulum. Using the wireless control loop, we can examine a number of the characteristics of UDP data transmission over 802.11b.

Coverage in Wireless Sensor Networks.

Abstract: Recent improvements in affordable and efficient integrated electronic devices have a considerable impact on advancing the state of wireless sensor networks, which constitute the platform of a broad range of applications related to national security, surveillance, military, health care, and environmental monitoring. An important problem receiving increased consideration recently is the sensor coverage problem, centered around a fundamental question: How well do the sensors observe the physical space? The coverage concept is subject to a wide range of interpretations due to a variety of sensors and applications. Different coverage formulations have been proposed, based on the subject to be covered (area versus discrete points), sensor deployment mechanism (random versus deterministic) as well as other wireless sensor network properties (e.g. network connectivity and minimum energy consumption). In this article, we survey recent contributions addressing coverage problems in the context of static wireless sensor networks. We present various coverage formulations and their assumptions, as well as an overview of the solutions proposed.

Method and apparatus for a source-initiated handoff from a source cellular wireless network to a target non-cellular wireless network

Abstract: To address the need for an apparatus and method for handoff from a cellular wireless network to a non-cellular wireless network (WLAN, e.g.), the present application describes an access gateway (214) and a dual mode mobile station (201) that enable such handoffs. Dual mode MSs can determine when a handoff to a non-cellular network is preferred and request a handin (302) from the non-cellular network. The access gateway provides information to the MS (304) so that it can initiate a handoff through the serving cellular network. Triggering handoffs in this manner, allows cellular networks to handle handoffs to non-cellular networks in much the same way they handle inter-MSC handoffs today, i.e., source initiated.

System and method for activation of portable and mobile media player devices for wireless lan services

Abstract: A system and a method for activation of portable and mobile media player devices for wireless LAN services have been disclosed. In one embodiment, the system includes a server computer, a wireless transmitter to transmit a signal, and a portable device comprising a wireless receiver to receive the signal and a wireless transceiver to transition from a first state to a second state to perform content synchronization with the server computer in response to the signal, wherein the wireless transceiver consumes less power in the first state than in the second state. Other embodiments have been claimed and described.

A wireless LAN-based indoor positioning technology

Abstract: Context-aware computing is an emerging computing paradigm that can provide new or improved services by exploiting user context information. In this paper, we present a wireless-local-area-network-based (WLAN-based) indoor positioning technology. The wireless device deploys a position-determination model to gather location information from collected WLAN signals. A model-based signal distribution training scheme is proposed to trade off the accuracy of signal distribution and training workload. A tracking-assistant positioning algorithm is presented to employ knowledge of the area topology to assist the procedure of position determination. We have set up a positioning system at the IBM China Research Laboratory. Our experimental results indicate an accuracy of 2 m with a 90% probability for static devices and, for moving (walking) devices, an accuracy of 5 m with a 90% probability. Moreover, the complexity of the training procedure is greatly reduced compared with other positioning algorithms.

A scalable approach for reliable downstream data delivery in wireless sensor networks

Abstract: There exist several applications of sensor networks wherere liability of data delivery can be critical. While the redundancy inherent in a sensor network might increase the degree of reliability, it by no means can provide any guaranteed reliability semantics. In this paper, we consider the problem of reliable sink-to-sensors data delivery. We first identify several fundamental challenges that need to be addressed, and are unique to a wireless sensor network environment. We then propose a scalable framework for reliable downstream data delivery that is specifically designed to both address and leverage the characteristics of a wireless sensor network, while achieving the reliability in an efficient manner. Through ns2 based simulations, we evaluate the proposed framework.

MAR: a commuter router infrastructure for the mobile Internet

Abstract: We introduce MAR, a commuter mobile access router infrastructure that exploits wireless diversity (e.g. channel diversity, network diversity, and technology diversity) to provide improved data performance for wireless data users. Our system design stems from the observation that rather than choosing a single wireless service provider (e.g. Sprint, AT&T, BT, Vodafone), a single technology (e.g. GPRS, UMTS, CDMA, 802.11), or a single wireless channel, users can obtain significant benefits by using the multiplicity of choices available. MAR is a wireless multi-homed device that can be placed in moving vehicles (e.g. car, bus, train) to enable high-speed data access. MAR dynamically instantiates new channels based on traffic demand, aggregates the bandwidth and dynamically shifts load from poor quality to better quality channels. MAR, thus, provides a faster, more stable, and reliable communication channel to mobile users.We have implemented and tested the MAR system in our testbed which spans the networks of three different cellular providers. Through our experiments we have performed a detailed evaluation to quantify the benefits of MAR for different protocols and applications. For example, even in highly mobile environments, MAR, on average, improves the end-user experience of web-browsing and streaming applications by a factor of 2.8 and 4.4 respectively. Our results show that significant benefits can be obtained by exploiting the diversity in coverage offered by many cellular operators, different technology networks (e.g. GPRS, CDMA), and diverse wireless channels.

Load balancing in overlapping wireless LAN cells

Abstract: We propose a load-balancing scheme for overlapping wireless LAN cells. Agents running in each access point broadcast periodically the local load level via the Ethernet backbone and determines whether the access point is overloaded, balanced or under-loaded by comparing it with the received reports. The load metric is the access point throughput. Overloaded access points force the handoff of some stations to balance the load. Only the under-loaded access points accept the roaming stations in minimizing the number of handoffs. We show via experimental evaluation that our balancing scheme increases the total wireless network throughput and decreases the cell delay.