地上デジタル放送用ガードインターバル越えマルチパス等化器の等化特性改善

概要

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Most digital terrestrial television broadcasting systems including Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) system use the orthogonal frequency division multiplexing (OFDM) scheme, which is robust against echoes (multipath interference) due to the insertion of a guard interval. However, echoes can occur outside the guard interval and degrade the quality of the received signal, especially in single frequency network (SFN). To overcome this problem, a channel equalizer that performs a Fast Fourier transform (FFT) on several OFDM symbols in combination and then equalizes the frequency characteristics in the frequency domain has been shown to be effective. In this paper, we extend this scheme and propose an equalization algorithm using serially concatenated two-frequency domain equalizers. Simulation results showed that the performance was improved, especially when the delay spread was within the guard interval length. We also added an adaptive control method to the leak process part of the channel estimation. Results of a field experiment in a receiving environment with reflection waves from the mountains further demonstrated the effectiveness of the proposed method.