Test Results of Digital Broadcasting Using Pathfinder Plus and a Jet Plane

Abstract

Stratospheric platforms (SPF) are made to stay at about 20 km stratospheric altitude, and used for communications, broadcasting, earth observations, etc. Since they have advantages compared with ground or satellite systems, they are expected to be effective and useful systems. In order to confirm the validity of SPF systems, and obtain data for future practical operations, preliminary flight tests were conducted concerning the following items in 2002. (1) UHF Digital HDTV (High Definition Television) broadcasting and IMT2000 communications tests using Pathfinder Plus, (2) Digital HDTV broadcasting test using a jet plane, and (3) Ka band and mm-wave communications tests using a helicopter. Consequently, while the world's first IMT-2000 and digital HDTV transmission experiments were conducted successfully with practical terminals from the stratosphere of 20km altitude, it was confirmed that 110km radius coverage of HDTV broadcasting can be possible with only nearly 10W RF output. And useful new data have been acquired concerning SPF systems. INTRODUCTION A national project of SPF (or HAPS; High Altitude Platform Stations) systems utilizing airships at a stratospheric altitude of about 20km, as platforms for communications, broadcasting and earth observations was started in 1998 in Japan. Since then, R&D of communications and broadcasting systems using the advantages of HAPS systems have been advanced by CRL and TAO. On the other hand, the R&D of airship is conducted by NAL (National Aerospace Laboratory of Japan). Prior to the final experiments using airships for experiment and demonstration purpose, preliminary flight tests of communications and broadcasting systems were conducted from June to October of 2002, using unmanned solar plane Pathfinder Plus, a jet plane and a helicopter, which were used as substitutes for the test airships. In this paper, the results of the preliminary tests mainly related to broadcasting systems are described. ADVANTAGES OF SPF FOR BROADCASTING SYSTEMS Comparison with Terrestrial Systems As HAPS is located at an altitude of 20km in the stratosphere, which is about 60 times the height of, for example, Tokyo TV Tower of about 330m high, the elevation angle becomes much larger than that of terrestrial systems. Therefore, even near the fringe of a service area, for example, of 110km radius, where elevation angle is nearly 10 degrees, the line-of-sight propagation is possible. Consequently, a larger service area is realized with much smaller transmission power than terrestrial systems. According to a link budget calculation, the output RF power becomes 40dB less than terrestrial transmitter. Moreover, although the number of relay transmission stations necessary in Japan is now more than 15,000, it is expected to decrease remarkably. An example of service area arrangement of 16 HAPS system is shown in Figure 1. Comparison with Satellite Systems In the case of HAPS systems, as the propagation distance is 1/1800 that of geo-stationary satellite, higher speed transmission is realized with less RF *Researcher, Yokosuka Stratospheric Platform Research Center, TAO (Telecommunications Organization Advancement of Japan), Yokosuka, Japan Researcher, CRL (Communications Research Laboratory), Wireless Innovations Systems Group, Yokosuka, Japan Group Leader, Wireless Innovations Systems Group, Senior Researcher, CRL, Yokosuka, Japan General Manager, Yokosuka Stratospheric Platform Research Center, TAO, Yokosuka, Japan Figure 1 Example of service are arrangement for Japan. Altitude 20km