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To deliver digital terrestrial broadcasting signals throughout Japan, master station waves must be relayed by relay stations. Broadcast-wave transmission over "geographically complicated" areas such as mountainous regions or to remote islands requires many signal relays. Technologies to minimize the signal degradation caused by the relay process are being developed using digital signal characteristics. |
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Relay system with equalization and symbol decision techniques |
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This system first equalizes the signals received at a relay station to remove distortion in preparation for demodulation. It then determines which "0" and "1" values in the modulated signals have been corrupted by noise and re-modulates them to produce clear "0" and "1"s. This process prevents noise-related distortion from accumulating at individual relay stations, making a broadcast-wave relay network feasible, even for multi-stage relay routes. (Figure 1) |
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Co-channel interference elimination technology (Adaptive array antenna) |
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Since relay stations are built on high ground, such as on the top of a mountain, their receiving antennas receive interference signals from other broadcasting areas. This system combines the signals received with two to four antennas for each OFDM carrier wave, where the entire number of OFDM signals reaches several thousand carrier waves. Receiving signals in a way that minimizes the influence of interference waves on each carrier frequency optimizes the combined beam pattern of the antenna array, contributing to a relay broadcast that has very little interference. (Figure 2) |
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Coupling loop interference (CLI) cancellation technology |
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An SFN relay station re-transmits signals on the same frequency as that of the master station, which can cause interference from the transmitted radio waves feeding back to the receiving antenna. This system realizes an SFN broadcast-wave relay through the electrical elimination of these coupling loop interference waves. Its ability to remove long-delay coupling loop interference waves makes this system appropriate for the various installation environments of the relay stations.
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