This paper describes the performance of space diversity reception for the digital terrestrial television broadcasting system(ISDB-T). We developed 2-branch diversity OFDM receiver and measured mobile performances of various ISDB-T transmisson parameters. The results of laboratory experiment show that maximum ratio combining diversity is effective to improve 64QAM-OFDM mobile performance. When the ISDB-T parameter is mode2, 64QAM and r=3/4, the required C/N is 18dB in the CSM typical urban area fading channel with maximum Doppler frequency of 70Hz.
The influence of the additive noise is not improved after the equalization in OFDM. To solve this problem, diversity reception using array antennas is effective. However, it requires the hardware in proportion to the number of antennas and the hardware of the receiver becomes complicated. Therefore in this paper, we paid attention to DFT that is used in receiver, an OFDM diversity receiver whose hardware complexity is equal to that of a single antenna receiver is proposed. The proposed receiver combines signals from the intermediate stage of DFT. As the results of computer simulations and theoretical analysis, it is confirmed that the bit error rate characteristics are better than that of the single antenna receiver.
In the reception of an OFDM signal, frequency dips caused by multipath propagation generates burst errors and this leads to a severe degradation of performance. To improve this degradation, an error control code such as trellis coded modulation(TCM)combined with an frequency interleaver is usually used. In this paper, characteristics of data spreading scheme in the frequency domain combined with TCM is analyzed. As the results, better performance of the proposed method is confirmed. Moreover, it is shown that the required number of states of TCM can be made smaller and hardware reduction of decoder is possible.
Stratospheric platform is a long endurance aircraft staying at a constant position in the stratosphere about 20km high. Wireless communications systems using stratospheric platforms will be ideal for broadband FWA, multi-media mobile radio and broadcasting systems because of much lower path loss then satellite systems and less multi-path effect than terrestrial systems. This paper describes the features of the stratospheric wireless systems and R&D activities in Japan and in the world. Also frequency allocation issues are described.