SUMMARYSystem level design considerations for high altitude platforms operating in the mm-wave bands are examined. Propagation e!ects in these bands are outlined, followed by a brief introduction to di!erent platform scenarios. Ground-based and platform-based "xed wireless access scenarios are considered, and it is shown that using a platform, a single base station can supply a much larger coverage area than a terrestrial base station. The e!ects on performance of platform displacement from its desired location with both "xed and steerable antennas are also examined. It is shown that steerable antennas are of most use when "xed stations are immediately below the platform, with no bene"t for "xed stations on the edge of coverage. The bandwidths required to serve several tra$c distributions (suburbs and city centre based) are evaluated using the Shannon equation. It is shown that capacity can be constrained when users are located in the city centres, despite longer line of sight paths to users out in the suburbs. The e!ects of temporal changes in the spatial tra$c distribution are investigated. It is shown that bandwith requirements can be reduced if the platform moves to track these changes.

System level design considerations for high altitude aeronautical platforms operating in the LMDS band are examined. Propagation effects in the LMDS band are outlined, followed by a brief introduction to different platform scenarios. Ground-based and platformbased Fixed Wireless Access scenarios are considered, and it is shown that using a platform, considerably longer link lengths can be used. The effects on performance of platform displacement from its desired location with both fixed and steerable antennas are also examined. It is shown that steerable antennas are of most use when fixed stations are immediately below the platform, with no benefit for fixed stations on the edge of coverage.

With an ever increasing demand for capacity for future generation multimedia applications, service providers are looking to utilise the frequency allocations in the millimetre wave bands, e.g. those specified for Local Multi-Point Distribution Systems (LMDS). In these frequency bands signals are attenuated by rain and line of sight paths are required. A possible solution to these effects is to use High Altitude Platforms (HAPs). HAPs are either airships or planes that operate in the stratosphere, 17-22km above the ground. Such platforms have the potential capability to serve a large number of users, using considerably less communications infrastructure than required by a terrestrial network. They can be considered as either a complimentary or disruptive technology-complementary in the sense that they augment existing infrastructure, or disruptive in the sense that they replace existing infrastructure. This paper provides an overview of the HAP concept, discussing both advantages and critical issues for Broadband Fixed Wireless Access (B-FWA) delivery from HAPs with reference to conventional terrestrial/satellite technologies. Finally, a brief summary is provided of HAP projects underway at the University of York such as the European Framework V HeliNet Project, in which York is leading the broadband communications aspects.

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