RADIO ACCESS IN WIRELESS INFORMATION NETWORKS

Jens Zander, KTH Radio Communication Systems

In this project, we will focus on design principles for distributed radio access schemes and evaluate performance of these schemes in wireless information systems. The main emphasis of the project is on packet swithed environments where both moderate speed interactive data communication systems as well as high-speed ATM-based systems for wireless access are considered. Although the study is focused on radio access problems, the close interaction with the fixed infrastructure requires a close scrutiny also of these aspects. The main performance measure in these systems is the achievable transmission rate and/or the spatial capacity, i.e. the achievable data rate per square (or cube!) meter. The performance may also be expressed in average message delay or response time in interactive applications.

The design of a radio access scheme involves the selection of multiplex-scheme (TDMA, CDMA, etc), strategies for the selection of time slot/codes,the selection of proper base station, handoff (if required), etc. A predominant feature of interactive systems is that the main directions of the traffic flow is from the fixed infrastructure to the mobile terminal. In addition, the same information may be exploited by using "intelligent" multi-point ARQ-strategies that allow stations to store all available information that is transmitted on the radio medium that memory constraints allow for possible future use in order to conserve bandwidth.

Other interesting tools in the radio access design could be directional antennas and soft handover /simulcasting schemes. The latter utilize the inherent diversity structure of these systems to provide for smooth transitions from one radio port to another as a mobile moves.A crucial feature of all suggested schemes is that they should allow fordistributed control and implementation. Due to the large number of ports, the systems have a very large complexity and centralized solutions would be impractical. Further, the project should provide an assessment of problems and advantages of the suggested schemes with respect to protocol design and implementation.

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