WP2 Communications Links and Networking

This workpackage addresses various aspects related to communication links between HAPs as a central point in the network and ground nodes and satellites.

Much of the activity will concentrate on the high-speed vehicle application.

This demanding application will require the development of a suitable access standard, which should be based on the most suitable of the existing or developing standards with the necessary adaptations as required.

The HeliNet project carried out a review of standards for the fixed broadband application, and found that IEEE 802.16 was most suitable. This work will form the starting point of this new selection process new requirements will be taken into account such as highspeed mobility and available equipment.

Appropriate standards for different system segments and scenarios will be selected from the list of candidate standards offering some of the targeted characteristics (bit-rate, mobility), e.g. IEEE 802.16, IEEE 802.20, , HIPERACCESS, DVB-S, DVB-RCS, DVB-T, the critical aspects will be emphasised and possible technological constraints will be investigated, and these will form the basis of the future work.

A detailed understanding of the propagation environment is vital to the success of broadband delivery from this new architecture. Propagation measurements will concentrate on the HAP architecture specific aspects and to avoid duplication, will take into account relevant previous measurements in satellite and terrestrial links.

The HeliNet project has carried out a detailed assessment of the rain attenuation mechanisms and how they affect fixed nodes. Work here will extend these analyses, looking at short-term rain outage mitigation strategies, including time diversity, and caching.

The effects of scintillation will also be examined. This is of particular importance when high rate modulation schemes are used.

Short-term propagation impairments such as multipath (caused by reflections) and Doppler effect will also be investigated. Normally these are unlikely to be significant for static users with highly direction antenna at these frequencies, but may be important when antenna array technology is used on fast moving vehicles.

These studies will be supported by a series of measurements taken from the system testbed throughout the project.

The development of an efficient radio interface for the future high-speed application will be addressed. This will be based around existing/developing access standards, and will use work developed by HeliNet for the fixed application.

The main objective will be to illustrate what changes will be required to support this new application and architecture, and this will be input into the relevant standards/regulatory bodies by the relevant partners.

Cutting edge technologies will be explored including the use of MIMO as a platform diversity technique, advanced signal processing algorithms that minimise the processing power requirements, cope with the high aggregate data rates and are computationally efficient, and with the envisaged multipath/Doppler environment.

Advanced software radio signal processing techniques will be investigated in detail, concentrating specifically on aspects pertinent to an aerial platform architecture. Their performance gains achievable for aerial platform applications will be assessed through the implementation of selected algorithms on a DSP platform.

HeliNet has proposed several resource management strategies to support broadband communications to fixed users with both single and multiple platform architectures.

The combination of high-speed mobility and platform movement present a significant challenge in maintaining adequate communication links in the mobile train scenario, with rapid and frequent handover required to maintain adequate quality of service for delay sensitive broadband applications.

Novel resource allocation strategies will be developed for both the user and backhaul links of a single HAP, to mitigate the effects of mobility and interference and provide both efficient spectrum utilisation and adequate QoS. They will encompass resource and mobility management (interaction of channel assignment, medium access control, inter-beam and inter-platform handoff, caching, and prioritisation), and will be designed to be harmonious with broadband transmission standards.

The potential of multiple HAP constellations combined with highly directional user antennas to enhance capacity by means of overlapped or co-located regions of coverage will be investigated further, and this work will be extended to determine how diversity may be exploited to increase service availability. The platform constellations offering the best capacity and/or diversity benefits will be determined.

The work will additionally focus on spectrum sharing, as the present radio regulatory environment in Europe will require that the 28/31GHz frequency bands are shared with terrestrial and satellite operators.

Interoperability issues will be examined to determine the viability of the coexistence of HAP systems with other wireless/satellite technologies.

End-to-end networking and interworking with other technologies will be of paramount importance when delivering "Broadband for All". Users will wish to see a common set of applications, services and configurations when they are in the office, at home in a rural area, or on board a high-speed train.

These issues will be tackled here, and a network architecture that maintains diverse quality of service requirements will be developed based on existing/future standards such as IPv6. This will be based on work undertaken in HeliNet which looked at network provision for the fixed application.