Space-Time Diversity Techniques for WCDMA High Altitude Platform Systems

Third generation mobile systems are gradually being deployed in many developed countries in hotspot areas. However, owing to the amount of new infrastructures required, it will still be some time before 3G is ubiquitous, especially in developing countries. One possible cost effective solution for deployments in these areas is to use High Altitude Platforms (HAPs) (Collela et al., 2000; Djuknic et al., 1997; Grace et al., 2001; 2005; Miura & Oodo, 2002; Park et al., 2002; Steele, 1992; Thornton et al., 2001; Tozer & Grace, 2001) for delivering 3G (WCDMA) communications services over a wide coverage area (Dovis et al., 2002; Falletti & Sellone, 2005; Foo et al., 2000; Masumura & Nakagawa, 2002; Vazquez et al., 2002). HAPs are either airships or planes that will operate in the stratosphere, 17-22 km above the ground. This unique position offers a significant link budget advantage compared with satellites and much wider coverage area than conventional terrestrial cellular systems. Such platforms will have a rapid roll-out capability and the ability to serve a large number of users, using considerably less communications infrastructure than required by a terrestrial network (Steele, 1992). In order to aid the eventual deployment of HAPs the ITU has allocated spectrum in the 3G bands for HAPs (ITU, 2000a), as well as in the mm-wave bands for broadband services at around 48 GHzworldwide (ITU, 2000b) and 31/28 GHz for certain Asian countries (Oodo et al., 2002). Spectrum reuse is important in all wireless communications systems. Cellular solutions for HAPs have been examined in (El-Jabu, 2001; Thornton et al., 2003), specifically addressing the antenna beam characteristics required to produce an efficient cellular structure on the ground, and the effect of antenna sidelobe levels on channel reuse plans (Thornton et al., 2003). HAPs will have relatively loose station-keeping characteristics compared with satellites, and the effects of platform drift on a cellular structure and the resulting inter-cell handover requirements have been investigated (Thornton et al., 2005). Cellular resourcemanagement strategies have also been developed for HAP use (Grace et al., 2002). Configurations of multiple HAPs can also reuse the spectrum. They can be used to deliver contiguous coverage and must take into account coexistence requirements (Falletti & Sellone, 2005; Foo et al., 2000). A technique not widely known is their ability to serve the same