Abstract of Doctoral Dissertation 成 層 圏 飛 翔 体 通 信 における 無 線 通 信 路 及 びその 性 能 に 関 する 研 究

Transcription

1 Graduate School of Global Information and Telecommunication Studies, Waseda University Abstract of Doctoral Dissertation Wireless Channel Characteristic and Its Performance for Stratospheric Platform Communication 成 層 圏 飛 翔 体 通 信 における 無 線 通 信 路 及 びその 性 能 に 関 する 研 究 Iskandar 4204A503-8 Global Information and Telecommunication Studies (Wireless Communication and Satellite Communication) January 2007

2 A high altitude platform station (HAPS) or known in different name as a stratospheric platform (SPF) has recently been proposed as a new means of wireless delivery method. The SPF is envisaged to provide wireless links that are complementary to conventional satellite or terrestrial radio system. It is based on reusable unmanned or manned aeronautical vehicles located quasi-stationary at the stratosphere at altitudes of approximately km above the earth surface. These unique altitudes could give a significant advantage of the link budget suffered by the satellites system and a much wider coverage area than the terrestrial system. Because of unique altitude of the SPF, its channel characteristic is inherently different compared with those of the conventional terrestrial or satellite wireless channel. A more detailed study of SPF communication link characteristic is therefore required in order to put this system into real implementation and to provide a proper system design. This study aims at evaluating SPF communication channel and its performance within frequency band of 2 GHz, which is allocated for mobile services. Firstly, we propose a definition and describe an analysis of the wireless channel between SPF and terrestrial mobile users based on experiment in which the measurement is only performed for line of sight (LOS) situation in a semi-urban environment. A proper data processing is performed to find channel parameters such as Ricean factor (K factor) and local mean received power over a wide range of elevation angles ranging from 10 0 to We then evaluate average bit error probability utilizing the proposed channel model to examine the channel performance. For the environment in which the measurements were conducted, we find that elevation angles greater than 40 0 yield better performance. The users, however, may also be served by the SPF under the condition of non-line of sight (NLOS) or shadowed situation. Therefore, our next study is devoted to evaluate propagation characteristic under the condition of LOS and NLOS in a typical urban low rises environment in which many mobile users communicate with the SPF in this area. A typical area under test model for urban area is developed and then ray tracing technique is employed to obtain propagation parameters. Virtual ray tracing technique

3 that generates many numbers virtual transmitter around the area under test is utilized to overcome the path length problem, i.e. the distance from SPF to mobile user. Based on the obtained propagation parameters we estimate power transmit requirement by the SPF for application of IMT-2000 services. We consider various elevation and azimuth angles in ray tracing simulation. Different scenarios, which mean different azimuth angles, clearly show the critical limitations for mobile communication using a concept of stratospheric platform. We found in very low elevation angle the required transmit power was too high and thus perhaps unable to be implemented for the case of SPF mobile communication system. SPF channel characteristic and its propagation parameters in both semi-urban as well as urban low rises environment have been shown depending on elevation and azimuth angle in many cases. Channel performance in term of bit error rate probability in case of semi-urban area has been shown utilizing the experimental result. The downlink channel performance, however, for the SPF link in urban area is our next target in this study. Based on the evaluation result of ray tracing technique we then utilize the propagation parameters to estimate the SPF downlink performance. A simulation model is developed to estimate bit error rate probability taking account propagation loss and Ricean factor obtained from ray tracing simulation. Several services delivered in IMT-2000 system are assumed to be transmitted in the downlink direction in order to evaluate the channel performance under different information bit rate. Finally, in this study, multibeam SPF CDMA capacity analysis is performed under comprehensive multiple access interference considering fading and imperfect power control. The proposed SPF channel fading characteristic is used in the interference analysis to estimate cell capacity carrying IMT-2000 services, which basically employs CDMA system. We examine a reverse link capacity evaluation of CDMA system employing single and multiple SPF in terms of outage probability as a function of number of users. An overlapped region is introduced in the case of multiple platform scenarios. It is shown that overlapped region cannot be neglected in the interference

4 analysis. The increasing minimum elevation angle is then proposed to reduce interference effects generated by the user in the overlapped region. The result shows a non-trivial improvement in capacity due to this method, however the number of the SPF might be increased because of the coverage area become smaller. This problem, therefore, would be not only costly but also environmentally unacceptable. To cope with this problem we propose to use adaptive antenna array onboard the platform. With this technique the capacity of multiple SPF is increased at approaching to the capacity of single SPF.

5 List of Academic Achievements Category Articles in Refereed Journals Presentations at International conferences 1. Iskandar and Shigeru Shimamoto, Channel characterization and performance evaluation of mobile communication employing stratospheric platform, IEICE Transactions on Communications, vol. E89-B, no. 3, pp , March Iskandar and Shigeru Shimamoto, On the performance of IMT-2000 communication link based on stratospheric platforms, Indonesian Journal (Makara) Series on Technology, vol. 10, no. 1, pp. 1-10, April Iskandar and Shigeru Shimamoto, Analysis of CDMA capacity for multiple stratospheric platform mobile communications under imperfect power control and fading, in Proceedings IEEE Wireless Communications and Networking Conference (WCNC), Hong Kong, China, March Iskandar and Shigeru Shimamoto, On the Downlink Performance of Stratospheric Platform Mobile Communications Channel, in Proceedings IEEE Global Telecommunications Conference (GLOBECOM), San Francisco, USA, November Iskandar and Shigeru Shimamoto, Prediction of propagation path loss for stratospheric platforms mobile communications in urban site LOS/NLOS environment, in Proceedings IEEE International Conference on Communications (ICC), Istanbul, Turkey, June Iskandar and Shigeru Shimamoto, Ray tracing for urban site propagation in stratospheric platform mobile communications, in Proceedings of the 11th IEEE Asia-Pacific Conference on Communications (APCC), pp , Perth, Australia, October Iskandar and Shigeru Shimamoto, Urban site path loss prediction for mobile communications employing stratospheric platforms, in Proceedings of the 8th IEEE International Symposium on Signal Processing and Its Application (ISSPA), vol. 1, pp , Sydney, Australia, August 2005.

6 8. Iskandar and Shigeru Shimamoto, The channel characterization and performance evaluation of mobile communication employing stratospheric platform, in Proceedings of IEEE/ACES Wireless Communications and Applied Computational Electromagnetics (WCACEM), pp , Hawaii, USA, April Iskandar and Shigeru Shimamoto, The channel characterization of mobile communication employing stratospheric platform, in Proceedings of the 12th International Conference on Telecommunication System Modeling and Analysis (ICTSM), pp , Monterey, USA, July 2004.