| Research Abstract |
The satellite diversity (Sat.D) system and Time-delayed diversity (TDD) system characteristics for Ku-band and L-band satellite communication and broadcasting systems are obtained by using the GPS satellite signals and the Excel software for overcome signal level degradations caused by rain attenuation or shielding satellite signals by urban buildings and trees etc. The following results can be obtained.
(1)TDD system characteristics for the L-band mobile satellite system
The TDD system is constructed by using two radio channels. The first channel (f1) is real-time broadcast signal and the second channel (f2) is delayed-time (τ) broadcast signal. The mobile receiver receives both channels at a certain location, where satellite broadcasting signals are attenuated by buildings, etc. After several minutes, the mobile receiver receives both channels at different locations; as a result, the satellite broadcast signals are not attenuated. In the mobile receiver, the real-time signal and the de
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layed-time signal are combined or switched to a higher quality channel. By the effect of the TDD system, the availability of digital mobile broadcast satellite system can be improved.
Experiments are carried out in four main cities in Hokkaido, i.e., Sapporo, Asahikawa, Otaru and Hakodate. The experimental data are processed by data process software. From analyzed results, it becomes clear that the optimum delay-times are about 3-6 minutes for TDD system. By using the TDD system, the satellite visibilities can be improved about twice.
(2)Sat.D system characteristics for the L-band mobile satellite system
The Sat.D system is constructed by using two satellites. The orbital separation angle is defined as θs and both mobile receivers are presented in the same location. The mobile receivers receive signal from both satellites at a certain location, where the signal from one satellite is attenuated by buildings, etc.; however, the signal from the other satellite is not attenuated by buildings, etc. Therefore, satellite visibilities can be improved using the Sat. D system. The experimental data are processed by data process software. By using the Sat.D system, the satellite visibilities can be improved about twice and about 90% satellite visibility can be achieved.
(3)Ku-band Sat. D system characteristics
The Ku-band Sat.D system characteristics are obtained by using a measuring system which is constructed with a spectrum analyzer and processing PC. Maximum numbers of measured satellites are seven. The measured data are processed by PC. Better improvement of rain attenuation can be obtained in winter season, because of narrower cloud distribution. More long term measurement will be necessary for more detail propagation data.
(4)Proposal of TDD/Sat.D system
The TDD/Sat.D system is proposed, and this concept is combination of TDD system and Sat.D system. By using the TDD/Sat. D system, almost perfect visibilities would be achieved. Further studies should be continued for the system design of the TDD/Sat.D system.
Above mentioned results are published in the Proc.of the IEEE AP-S (Antenna and Propagation Symposium) or paper of IEICE of Japan, with 37 total paper numbers. Less
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