Showing papers on "Wi-Fi array published in 1994"

MACAW: a media access protocol for wireless LAN's

Abstract: In recent years, a wide variety of mobile computing devices has emerged, including portables, palmtops, and personal digital assistants. Providing adequate network connectivity for these devices will require a new generation of wireless LAN technology. In this paper we study media access protocols for a single channel wireless LAN being developed at Xerox Corporation's Palo Alto Research Center. We start with the MACA media access protocol first proposed by Karn [9] and later refined by Biba [3] which uses an RTS-CTS-DATA packet exchange and binary exponential back-off. Using packet-level simulations, we examine various performance and design issues in such protocols. Our analysis leads to a new protocol, MACAW, which uses an RTS-CTS-DS-DATA-ACK message exchange and includes a significantly different backoff algorithm.

Adaptation and mobility in wireless information systems

Abstract: The author begins by discussing the background, defining key terms and showing how wireless information systems can be viewed as a natural evolution of computing's relentless march toward greater distribution and ubiquity of access. Next, the research issues faced by designers of wireless information systems are detailed, and some large-scale engineering challenges for such designers are presented. The existing cellular system architecture, evolved from telephony, is compared with an alternative architecture more closely integrated with a computer networking view of wireless systems. Existing wireless systems are reviewed, and the final section presents the author's summary and conclusions, and charts the future of wireless information systems. >

Mobile users: to update or not to update?

Abstract: Tracking strategies for mobile users in wireless networks are studied. In order to save the cost of using the wireless links mobile users should not update their location whenever they cross boundaries of adjacent cells. The paper focuses on three natural strategies in which the mobile users make the decisions when and where to update: the time-based strategy, the number of movements-based strategy, and the distance-based strategy. The authors consider both memoryless movement patterns and movements with Markovian memory along a topology of cells arranged as a ring. They analyze the performance of each one of the three strategies under such movements, and show the performance differences between the strategies. >

Privacy and authentication for wireless local area networks

Abstract: Wireless networks are being driven by the need for providing network access to mobile or nomadic computing devices. Although the need for wireless access to a network is evident, new problems are inherent in the wireless medium itself. Specifically, the wireless medium introduces new opportunities for eavesdropping on wireless data communications. Anyone with an appropriate wireless receiver can eavesdrop, and this kind of eavesdropping is virtually undetectable. Furthermore, since the wireless medium cannot be contained by the usual physical constraints of walls and doors, active intrusions through the wireless medium are also made easier. In order to prevent this unauthorized access to the network, the authors present the design of a secure communication protocol that provides for both the privacy of wireless data communications and the authenticity of communicating parties. The placement of the protocol in the overall protocol stack and issues relevant to wireless links and mobile computing devices are discussed. They also present proof of the security of the protocol using the logic of authentication formalism developed by Burrows, Abadi, and Needham (1990). >

Communication network providing wireless and hard-wired dynamic routing

Abstract: A data communication network for providing dynamic routing through both wireless and wired subnetworks to support wireless communication devices and wired remote stations is disclosed. In the wireless network, the wireless communication devices can be mobile RF terminals, while the wired remote stations might be personal computers attached to a wired subnet, such as an ethernet coaxial cable. The wireless network architecture utilizes a spanning tree configuration which provides for transparent bridging between wired subnets and the wireless subnets. The spanning tree configuration provides dynamic routing to and from wireless communication devices and remote stations attached to standard IEEE 802 LANs.

Method and apparatus for bridging wireless LAN to a wired LAN

Abstract: An internetworking node for providing internetworking services for mobile wireless nodes is disclosed. Each mobile wireless node is registered withat the most one internetworking node. Each mobile wireless node emits a topologybroadcast identifying itself and other nodes it has heard. Each internetworking node uses these topology broadcasts to construct a table tracking each mobile node within its range, whether that mobile node is registered to that internetworking node and also a list of which other nodes that mobile wireless node can hear. The internetworking node determines which of these wireless nodes it will register. The internetworking node will then act for all wireless nodes registered to it in relaying messages between wireless nodes or between a wired LAN and the wireless nodes.

Broadcast/Multicast Filtering by the Bridge-Based Access Point

Abstract: In communication systems which include high speed wired local area networks (LANs) and low speed wireless LANs, the bandwidth of the wireless LANs can be severely impacted. It has been found that many broadcast or multicast messages which are forwarded to the wireless LANs are not required as the mobile terminals which would receive the messages are not required to act on them. The present invention provides a means and method to filter out unneeded messages so that they do not impact the bandwidth of the wireless network. Each access point for each wireless LAN maintains a table of parameters for each associated mobile terminal in the connected wireless LAN. The parameters in that table are compared to the parameters in message frames received by the access point and only those messages having parameters found in the table are put on the wireless LAN. The level of filtering can be controlled by specifying which parameters are to be used for filtering messages. The tables at each access point are maintained current by moving table entries from access point to access point as mobile terminals move from wireless LAN to wireless LAN and by removing inactive table entries from the table when a predetermined interval of inactivity is encountered and a terminal is determined to be no longer in active contact with the access point.

High reliability access point for wireless local area network

Abstract: A high reliability access point for RF communications in a wireless local area network. The high reliability access point includes a central processing unit (CPU) for handling high level protocol functions and for interfacing with the infrastructure of the local area network. The high reliability access point also includes at least two wireless adapters. Each wireless adapter includes a radio, a media access control (MAC) processor for handling low level protocol functions, and at least one antenna. The multiple wireless adapters allow the access point to perform self monitoring, reduce the effects of multipath interference, reduce some occurrences of collisions at the access point and provide infrastructure backup in the event of an infrastructure failure. The access points also allow for wireless network infrastructure communication for connection of one or more remote access points to the infrastructure. A backup power supply for the access point is also shown.

Wireless LAN design alternatives

Abstract: The authors have discussed several alternatives in wireless LAN design: media choice, operating frequency, operating mode, network topology, and access method. Although each technical choice presents both advantages and disadvantages, they argue that there is a design point that provides the best fit with present and future wireless LAN user needs. Considering all factors/spl mdash/including robustness, regulatory considerations, and interference avoidance/spl mdash/using a product based on the slow frequency-hopping spread spectrum, in the 2.4 GHz ISM band, relying on a base station remote station network topology and using a TDMA-based access method is the best way to meet the needs of radio-frequency wireless LAN users. The choices are many, but slow frequency-hopping at 2.4 GHz and TDMA-based medium access control provide the best mix of cost, range, interference, and performance. >

Method of configuring a communication unit using a wireless portable configuration device

Abstract: In a wireless communication system (100), a communication unit (102) may operate therein in the following manner. At power up of the communication unit (102), the communication unit transmits an application request over a second wireless communication path (117) to a configuration device (115). The configuration device (115) determines whether this was a valid request, and if so transmits the appropriate software applications to the communication unit (102) over the second wireless communication path (117). The communication unit (102) stores the application information in volatile memory (119). Having this information stored, the communication unit (102) prepares a service request by requesting configuration information from the configuration device (115). Upon receiving the configuration information from the configuration device (115) via the second wireless communication path (117), the communication unit (102)can access the wireless system (100) via a first wireless communication path (103).

Method and apparatus for preventing wireless fraud

Abstract: The use of stolen mobile identification number (MIN) and electronic serial number (ESN) information to fraudulently place wireless calls is prevented by having the switches of multiple wireless carriers forward or direct, over a telephone connection, all calls placed from selected MINs to a central authentication platform that serves the multiple wireless carriers. The central authentication platform engages in a so-called "challenge-response" authentication with local processors that are interfaced to the wireless telephones from which non-fraudulent calls originate. The challenge-response authentication uses a shared secret key (S-Key) that is not broadcast over the interface, thus preventing the key from being "stolen". A call from a wireless telephone that is not interfaced to a local processor capable of successfully completing the challenge-response authentication is blocked, while a call from a wireless telephone having a local processor capable of successfully completing the challenge-response authentication is completed to the number desired by the customer. Advantageously, since the central authentication platform serves multiple wireless carriers, the need for one wireless carrier to access the database of another is alleviated and the expense of providing additional security is reduced.

Switching Arrangement for Wireless Terminals Connected to a Switch Via a Digital Protocol Channel

Abstract: A digital port comprising a passive bus and, at least, the registration and call transfer features associated with a switch to provide cellular wireless capability. The passive bus allows a base station to be connected to the channel and thereby interface a plurality of wireless terminals to the switch. While only some of the wireless terminals in the neighborhood of a base station can be active concurrently (as is the case in all wireless systems) by way of a digital communication channel that is included in the passive bus, the switch can register and, hence, keep track of, a larger number of wireless terminals that are present in the base station's neighborhood. The passive bus also includes at least one circuit switched channel to allow communication with one or more wired or wireless terminals.

Method and apparatus for facilitating the ultimate making of wireless data transfers

Abstract: Unnecessary expenses associated with exchanging data with wireless data stations that have become unavailable are avoided, in accordance with the principles of the invention, by a) transmitting the data to be transmitted to a store and forward unit; b) marking as unavailable a wireless data station to which the store and forward unit could not successfully complete the data transmission; c) waiting for the wireless data station to register, i.e., signal its availability to receive data transmissions; and d) transmitting the data from the store and forward unit to the data station once a registration is received from the wireless data station. Optionally, any data transfers to the wireless data station during this waiting period are queued at the store and forward data unit and no attempt is made to contact the wireless data station over the wireless service provider's network. Furthermore, if the data station shares communication facilities with a wireless voice telephone, any call attempts to the wireless telephone during the waiting period are disallowed, i.e., no attempt is made to contact the wireless telephone over the wireless service provider's network.

Disconnection management system for wireless voice communications

Abstract: A communications system is designed to monitor voice communications signals for an initial end-to-end communications link which is comprised of a) a wireless segment which connects a wireless network to a wireless end-user apparatus, and b) a second segment which connects a communications end-user device to the wireless network. When the system detects that the wireless segment is inoperative, it inhibits the release of the second segment. Thereafter, the system sets up a subsequent wireless segment which extends from the wireless network to the wireless end-user apparatus. The subsequent wireless segment is then bridged to the second segment to form a new end-to-end communications link to restore connectivity between the wireless end-user apparatus and the communications end-user device.

Location dependent service for a wireless telephone

Abstract: Using a plurality of terminal service profiles (TSP) that are selected on the basis of the switching system to which a wireless mobile unit is registered. Each TSP defines the operation of features associated with the wireless mobile unit, and a service profile defines features associated with a directory number shared by a stationary station set and the wireless mobile unit. This allows some features to be associated only with the wireless mobile unit and other features to be associated with the shared directory number. These other features are usable by the wireless mobile unit and any other unit sharing the shared directory number. These other features are performed on a permanent switching system to which the shared directory number is assigned. When the wireless mobile unit is not associated with a stationary telephone station set, different TSPs are selected based on the particular switching system to which the wireless mobile unit is registered. ISDN messages are used to provide those features which should appear to be performed on a permanent switching system as if the wireless mobile unit was registered on the permanent switching system.

Secure wireless LANs

Abstract: Mobile computing is a major area of current research. A variety of wirelessly networked mobile devices now make it possible for a physically untethered computer to function in a fully networked manner. Recent research has focussed on providing the mobile user a seamless environment of wired and wireless networks. One of the major hurdles in providing such a seamless environment is that wireless media are inherently less secure.In this paper, we propose a security scheme for wireless media which permits secure communication over a single wireless channel. Our scheme allows both communicating parties to authenticate each other and establish a shared key for secure communication. An unauthorized snooper cannot even discover the identity of the communicating parties. Mobile computers are thus provided a highly secure wireless environment. We describe an efficient practical implementation of the scheme and prove its correctness.

Approaches to layered coding for dual-rate wireless video transmission

Abstract: Visual communications over wireless networks require the efficient and robust coding of video signals for transmission over wireless links having time-varying channel capacity. The authors compare several schemes for encoding video data into two priority streams, thereby enabling the transmission of video data over wireless links to be switched between two bit rates. An H.261 (p/spl times/64) algorithm is modified to implement each candidate scheme. The algorithms are evaluated for a microcellular wireless environment and a clear-channel bit rate of 65 kb/s. The results show that by combining layering with automatic-repeat request (wireless-)link control, almost-wireline visual quality can be achieved. >

Method and apparatus for wireless trunking to private branch exchanges

Abstract: Radio units (112) responsive to a paging signal seize a trunk (114) to connect wireless calls to telephone apparatus (104) serviced by a private branch exchange (106). The radio units (112) can each respond to a different set of mobile identification numbers, or can be configured in a masterslave arrangement or can employ subaddressing. Wireless trunking to a wireless private branch exchange can also be accomplished and a system with multiple hierarchical layers can also be formed.

Plug-in wireless module for operation with portable wireless enabled host equipment

Abstract: A wireless-enabled host electronic equipment includes a built-in antenna and special plug-in receptacles enabling a plug-in wireless communicator to interact with the host and to connect to the built-in antenna for wireless transmission and reception. In accord with the invention the plug-in arrangement is constructed to conform to a standardized plug-in arrangement, such as a PCMCIA standard and to provide additional plug-in capability in addition to the standardized receptacle which does not conflict with the standardized receptacle. The plug-in arrangement is configured to permit use of a plug-in for other purposes in the same standard receptacle.

Adaptive omni-modal radio apparatus and methods for networking the same

Abstract: A frequency and protocol agile wireless communication product, and chipset for forming the same, including a frequency agile transceiver (2, 4, 6, 8, 10, 12), a digital interface circuit for interconnecting the radio transceiver with external devices, protocol agile operating circuit for operating the radio transceiver in accordance with one of the transmission protocols as determined by a protocol signal (38, 40) and an adaptive control circuit for accessing a selected wireless communication network and for generating the frequency control signal (34) and the protocol control signal (38, 40) in response to a user defined criteria. Additionally, a network and method of operating a network of wireless service providers adapted to interact with a plurality of omni-modal wireless products within a given geographic area in a manner to permit the wireless service providers to 'borrow' radio frequencies from other wireless service providers within the same geographic region is disclosed.

Advanced wireless access system

Abstract: This paper describes an advanced wireless system which is composed of a wireless access node, a wireless access point, and a multimedia portable terminal. The wireless access node and access point are connected by optical fibers to realize broadband and high quality transmission. The radio frequency spectrum is directly carried on optical fibers using "fiber radio" technologies. This advanced wireless system, the multimedia wireless access system, provides video and data communications as well as voice services.

Time Division Multiple Access Mobile Wireless Telecommunication System

Abstract: In a time division multiple access mobile wireless telecommunication system, a base station has a plurality of frequencies with their priority order previously registered in a memory, selects, upon starting the operation, the frequency having the highest priority from frequencies not used by other wireless telecommunication systems, and initiates communications at the selected frequency. The base station also transmits a pilot signal representative of the priority for using the selected frequency in order to prevent other wireless telecommunication system from interrupting to use the frequency.

A pilot-based dynamic channel assignment scheme for wireless access TDMA/FDMA systems

Abstract: We propose a control architecture for implementing a dynamic channel assignment (DCA) algorithm which optimizes two-way channel quality in a TDMA portable radio system. Computer simulations are used to evaluate the performance of this DCA method. A common control frequency, which is frame-synchronized among base stations, provides (1) beacons for portables to locate base stations and obtain DCA information, (2) broadcast channels for system and alerting information, and (3) pilot signals to permit portables to evaluate downlink interference. This allows low-complexity radio ports and portables to mutually select channels to avoid interference and avoid creating excessive interference. Results from computer simulations demonstrate the good spectrum efficiency of this method and its potential for handling nonuniform traffic demand. This work is targeted toward understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks.

Wireless access to broad-band services through microcellular indoor systems

Abstract: Wireless access to advanced communications services could offer significant advantages to future users requiring high transmission rates and an increased freedom of mobility. The purpose of this paper is to present a view of the nature of broad-band services that will be accessed through future indoor wireless systems based on microcells, as well as the underlying challenges, both architectural and technological.

A 50 Mbit/s Optical Wireless LAN Link Using Novel Optical and Electronic Enabling Technologies

Abstract: Optical wireless transmission is proposed for the implementation of broadband wireless LANs. An optical cellular structure, which uses holograms to define optical cells and high levels of optical concentration in the receivers, will maximise the performance of such a system. The bootstrapping circuit technique can be used in the optical receiver design to give wideband and low noise operation in the presence of a large photodiode capacitance. Results for a 50Mbit/s link that operates over a 5m2 cell size are given.

Functional approach to a hybrid wireless network for mobile stations

Abstract: The limited range of wireless mediums is often compensated for by a cellular topology controlled by base stations interconnected by means of a wired infrastructure. The size of the area covered by such networks varies a lot according to the wireless medium used. They do, however, share certain functionalities which are presented here in the form of a functional model. To simulate this type of hybrid network, it is necessary to identify all parameters involved which may have an influence. This preoccupation led to an Entity model which is detailed in this paper for the case of an infrared wireless LAN for in-house communications. The principal parameters are classified and assigned to entities. The interactions between these entities and the characteristics of the network are identified for a future simulation.

Interoperable licensed and unlicensed wireless access for PCS

Abstract: The FCC allocated 120 MHz of licensed spectrum and 20 MHz of unlicensed spectrum near 2 GHz for personal communications services (PCS). Licensed spectrum is likely to be used for public access in most outdoor and some indoor venues. Unlicensed spectrum is likely to be used for wireless Centrex/PBX, wireless payphone, and private residential wireless access. Network services for PCS will need to provide mobility functions such as registration, roaming, routing, and subscriber validation for a variety of venues and wireless access systems. Small and low complexity terminals can be achieved that provide access to licensed and unlicensed systems in a variety of venues by using wireless systems with a high degree of commonality across the transport and signaling layers for these environments. Low power TDMA can be used in frequency division duplex mode for licensed wireless access and in time division duplex mode for unlicensed wireless access to permit a low complexity terminal. >

The AT&T GIS WaveLAN air interface and protocol stack

Abstract: The AT&T GIS WaveLAN system is the first wireless LAN communication system on the market that can transfer information at a rate of 2 Mbits per second. This paper gives an overview of the aspects of the WaveLAN air interface that are relevant for inter-operability between systems. Emerging areas of application of such a wireless LAN system are medical, transportation or retail vertically integrated systems. The paper covers the physical layer, media access control and also higher level protocols specific for application in the wireless indoor environment.