4- You will need to study the document at the end of this problem set, entitled Broadband with altitude. This is a single page news item from the IEE Review, introducing the concept of highaltitude platforms (HAPs) to provide future broadband communication links around TWENTY YEARS AGO but still applicable TODAY. There are several more detailed sources available, but you should be able to produce a good answer by referring only to the source provided here. I want you to be involved in reading technical document and being able to analyze them.

Question.

Summarize briefly the main features, benefits and development opportunities offered by high-altitude platforms in comparison with conventional satellite systems that are evident from the IEE Review news item. What additional difficulties do you think need to be overcome, before HAPs could become widely adopted?

Broadband with altitude

Broadband with altitude, News, IEE Review, Vol. 50, February 2004, p.15

Airships or solar-powered aircraft could provide broadband Internet access to compete with landlines in four years time, according to researchers in a major new research project. High Altitude Platforms (HAPs) are a potentially attractive way of providing broadband access over a wide area. Cheaper than satellite links and without the long time delays, a single HAP operating at a height of around 20 km could provide coverage to isolated rural areas around 60 km in diameter. A constellation of HAPs could hover over urban areas to create a high bandwidth access network to compete with existing ADSL and cable-based operators. However, the technology faces regulatory and technical issues. Capanina, a research project funded under the European Unions Sixth Framework program and led by a team from the Communications Group at the University of York, is designed to resolve some of these. Within Europe, prospects for the early deployment of HAPs are threatened by competing demands for spectrum. Two frequency bands have been allocated to HAPs: 4748 GHz band, available worldwide, and 2831 GHz band, available in all the Americas, much of Asia, but not in Europe. From an operator perspective, reduced attenuation and technology availability make the lower band the better option. However, fears of interference mean that the European terrestrial fixed wireless access lobby is strongly opposed to HAPs deployment in the 2831 GHz band. According to David Grace, a member of the Communications Research Group at the University of York and Capaninas principal scientific officer, establishing the desirability and feasibility of 2831 GHz operations in Europe is one of Capaninas key objectives. It will also study multi-HAP systems with research on the inter-working of wireless and optical links, and the use of steerable antennas. The optical links could be used for air-to-ground links, augmenting wireless and boosting system bandwidth when weather conditions permit, and to interconnect HAP constellations to create an optical network in the sky. Steerable antennas would allow wireless links to be controlled dynamically, according to changing levels of use and attenuation. We have already shown that this will significantly enhance spectrum efficiency, says Grace. The York team will also be investigating the role of steerable antennas in providing broadband access to fast moving trains, probably using an electronically steerable smart antenna on the HAP and a mechanicalelectronic hybrid antenna on the train. The Capanina team envisages commercial deployment within four years, according to Grace. Early systems are likely to rely on tethered aerostats a sort of high-tech barrage balloon. Operating at an altitude of 15,000 feet, they are currently deployed along the USMexican border to spot low-flying aircraft attempting to smuggle drugs into the US. HAPs using airship and aircraft could be as much as a decade away, although Japan is expected to have a prototype system operating by 2008.