As systems fulfilling technical conditions for “multimedia broadcasting system dedicated to mobile terminals” (i.e., multimedia mobile broadcasting standard (ARIB STD-B46), which is planned to come into use in 2011, ISDB-Tmm system and ISDB-Tsb system have been proposed. Both systems are based on ISDB-T. They are characterized in that a 13-segment transmission wave of the transmission standard for terrestrial digital television broadcasting (ARIB STD-B31) and a 1- or 3-segment transmission wave of the transmission standard for terrestrial digital audio broadcasting (ARIB STD-B29) are used as unit transmission waves, which can undergo concatenated transmission, arranged on the frequency axis, without using guard bands. Both systems can therefore achieve an effective use of frequencies. To accomplish practical concatenated transmission, concatenated signals may be subjected to the batch IFFT process, thereby to generate an OFDM signal.
To save energy and lower the cost, the waves should no longer be transmitted once the broadcasting has been stopped. In the concatenated transmission, however, the wave transmission can hardly be stopped in units of waves, because adjacent waves are concatenated together. In order not to transmit a unit broadcast wave, dummy data must be generated and transmitted in place of the unit broadcast wave. (In many cases, the dummy data is an MPEG2-NULL packet.) The dummy data is subjected to transmission-path coding and is then continuously transmitted. If many unit transmission waves are no transmitted, more signals, each having a large peak amplitude, will be generated than in the ordinary broadcast waves. Consequently, as known in the art, the transmission equipment will be adversely influenced.
This is because each NULL packet inserted in place of the data to be broadcast, as described above, assumes the same data value in any unit transmission wave. In the unit transmission wave, the energy is diffused in order to maintain the sufficient randomness of whichever data input. If the unit transmission waves to be concatenated have the same transmission parameter, they will undergo the same signal processing and become identical output signals. These output signals are added in the same phase. The peak amplitude will inevitably much increase.