Alex Hills

Large-scale wireless LAN design

The design of a large-scale wireless LAN poses a number of interesting questions. Building the Wireless Andrew network at Carnegie Mellon University has given us the opportunity to deal with these questions. This article describes the approaches we have developed for the design of similar networks. A large-scale wireless LAN must be designed so that all of the target space has radio coverage (i.e., there are no coverage gaps). It must also be designed so that its capacity is adequate to carry the expected load. These requirements generally can be met by using the proper combination of access point locations, frequency assignments, and receiver threshold settings.

Wireless Andrew [mobile computing for university campus]

At Carnegie Mellon University in Pittsburgh, staff and students are using mobile computers for various tasks such as transferring lecture notes, sending e-mails, or surfing the net. This possible due to the installation of a wireless network which will cover all 28 academic and administrative buildings on the 40-hectare campus, and provide service to 10000 people. As long as they are on campus, the university community will be able to take advantage of the network. The high speed wireless infrastructure installed at Carnegie Mellon is called Wireless Andrew. Started as a National Science Foundation-funded research network to support Carnegie Mellons wireless research initiative, the network originally provided coverage in seven campus buildings. The challenges in building such a large network are far from trivial. They include designing the network so that coverage blankets the entire campus, providing enough capacity to handle the campus-wide traffic load. Further, the network must provide highly reliable service. It builds on the universitys wired network infrastructure, which currently provides 10-Mb/s and 100-Mb/s Ethernet service. To supply high-speed wireless service to the campus, Lucent WaveLAN equipment has been installed, which uses direct sequence spread-spectrum radio to provide a raw data rate of 2 Mb/s. For wireless access off campus or otherwise out of the range of the WaveLAN network, cellular digital packet data is used.

Radio resource management in wireless LANs

Some chief information officers and information technology managers are reluctant to deploy wireless LANs. Among their concerns are reliability, availability, performance, and deployment. Each of these concerns can be directly addressed through the radio resource management techniques used in a new generation of wireless LAN equipment. The new capabilities include dynamic channel assignment, dynamic power control, and load sharing. Changing from the relatively static radio resource management techniques generally in use today to dynamic methods like those highlighted in this article helps to increase the capacity and improve the performance of large-scale wireless LANs.

Rollabout: a wireless design tool

Deployment of wireless LANs includes two main design issues: selection of access point locations and access point frequency assignments. Properly solving these issues normally involves a trial and error process, and can be very time consuming. The Rollabout design tool partially automates this process, making it quicker and more efficient. When pushed around on a rolling cart, the system collects data from access points and automatically creates a coverage map. With Rollabout, data collection is much faster, and a much larger set of data can be captured. Furthermore, the design tool predicts the coverage changes that result when access points are moved to different locations. It also can produce an optimal set of frequency assignments for any set of access point locations and corresponding coverage areas.

Spectrum use and carrier costs: a critical trade-off

In making spectrum allocation and assignment decisions, national officials may wish to consider how these decisions will affect the costs experienced by licensees and the prices ultimately paid by customers. With low tier wireless systems as an illustration, this paper uses an engineering-economic model to describe the relationship between the amount of spectrum allocated and the per subscriber investment required of carriers/licensees. This relationship is explored under a variety of assumptions relating to service provision. The paper concludes with the public policy implications of the work and recommendations for policymakers and regulators involved with spectrum allocation. The analysis presented here seems particularly appropriate for extending service to unserved areas.

Teaching information networking

An integrated masters degree program on information networking is described. Business and public policy, as well as computers and telecommunications, are studied in this program. Typical technology courses include such traditional electrical engineering courses as communications engineering and computer architecture, plus courses like circuit and packet switching developed specifically for the program and computer science courses in operating systems and distributed systems. Business principles are covered in an introductory course. Other business courses focus on management information systems, corporate telecommunications networks, and systems design and implementation. A major goal is to prepare students to design the electronic information systems of the future.<<ETX>>

Satellites and mobile phones: Planning a marriage: Dramatic improvements in rural communications may be in the offing as direct service by satellite to mobile phones moves closer to reality

It is pointed out that cellular radio is not well suited for rural areas, where potential users are sparsely distributed. Mobile satellite service is seen as the ideal way to pick up where cellular leaves off, particularly if mobile units are developed that will work with either system. The new system could also provide nationwide two-way voice dispatch services. Interest in the new system is high in rural areas because the divestiture of the American Telephone & Telegraph Co. and the deregulation of the telephone industry are making local telephone service more expensive for rural subscribers. Of particular concern is the high cost of the rural local loop, the cable pair that connects the subscriber to an exchange. Mobile telephone service could replace the expensive local loop by connecting the rural telephone user directly to a large exchange, perhaps far away. A general description of a mobile satellite service is provided. Attention is also given to the regulatory change being considered by the US Federal Communication Commission.

Using wireless technology to provide basic telephone service in the developing world

Low-tier wireless systems offer great promise for the provision of basic telephone service in the developing world. Such systems offer the advantages of rapid deployment, minimal disruption during construction, and low cost. This paper examines the level of investment required to deploy such systems, exploring the question in the context of a number of design constraints and parameters. The analysis shows that the investment required to build a low-tier wireless system compares quite favorably with that of a conventional cable-based system. The paper concludes with some policy implications of the work that are relevant to national governments and telephone carriers in the developing world.

Radio port spacing in low tier wireless systems

The capacity of a low tier wireless system is dependent on the distance between adjacent radio ports (RPs). Maximum port spacing, determined by a RP’s maximum coverage area, is important where population density is low. Minimum port spacing is important where population density is high, as is the case in congested urban areas. Minimum port spacing imposes a significant capacity constraint and has a direct impact on the amount of spectrum needed in a low tier wireless system.

Communications: Alaska's giant satellite network: Telephone services and radio and television broadcasts for virtually every Alaskan community are ensured by the state's satellite

Telephone services and radio and television broadcasts for virtually every Alaskan community are ensured by the states satellite.