Mobility / Portability

Time Interleave (Robustness against urban noise, mobility & portability)

In digital transmission system, error correction technologies are adopted to reduce the degradation caused by any kinds of interferences (including thermal noise). ISDB-T also adopts error correction technologies, named concatenated error correction (chain of Convolutional coding/Viterbi decoding + Reed-Solomon (RS) coding/decoding).

Functional block diagram of ISDB-T
Figure 1  Functional block diagram of ISDB-T

Such error correction technologies show the advantage against the random error such as thermal noise, but these does not work well against the burst error like concatenated error. Therefore, the technology for randomization of error is necessary for the error correction technologies called as "Interleave" technology like (1) Bite interleave, (2) Bit interleave, (3) Time interleave and (4) Frequency interleave.

Interleave circuits and these effect
Figure 2  Interleave circuits and these effect

"Time Interleave" is quite effective to improve both the robustness against impulse noise and the performance for mobile/portable reception. Impulse noise caused by car engine and electrical equipment is the dominant degradation factor in urban area. As a result, ISDB-T is significantly superior to ATSC and DVB-T in the reception performance in urban area and mobile/portable reception performance.

As an example, Figure 3 shows the reception performance under impulse noise condition. As shown in the figure, ISDB-T is about 7dB better than other 2 systems in C/N value at around 300 µs pulse noise width. That means 1/5 less power of transmitter, and ISDB-T needs only 200W power of transmitter for the same coverage area as ATSC and DVB-T covers using 1kW power of transmitter.

Reception performance under Impulse noise condition (3 DTTB systems)
Figure 3  Reception performance under Impulse noise condition (3 DTTB systems)