One-segment broadcasting is one type of digital terrestrial broadcasting ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), and it is one type of partial segment broadcasting that performs transmission of broadcast waves in which broadcast data are placed in a specific frequency (segment) within a transmission channel and is being used for broadcasting to mobile terminals and the like. A method of broadcasting in a partial segment of the number of all segments in a transmission channel for SDTV (Standard Definition Tele-Vision) broadcasting such as the one-segment broadcasting, so-called digital radio broadcasting (terrestrial digital audio broadcasting) of 3 segs (three segments), educational television broadcasting of 4 segments and the like is called as partial segment broadcasting below.
And, partial segment broadcasting such as one-segment broadcasting is suitable for implementation by SFN (Single Frequency Network) system and implementation by a broadcasting system (area broadcasting) covering a relatively small area with a very low transmission power, and its further expansion of use in the future is expected.
For example, if a large area is tried to be constructed under the SFN environment to construct an area to be covered by digital terrestrial broadcasting, it is necessary to construct the SFN environment by performing multistage relay of broadcast waves.
As shown in FIG. 11, the digital terrestrial broadcasting performs transmission of broadcast waves emitted from a transmission station (master station) by relaying at several relay transmission stations, and it is easy to perform multistage relay of a stable radio wave between transmission stations.
However, for digital terrestrial broadcasting, if the transmission station (master station, higher rank station) or the relay transmission station (relay station) is located in an urban region or a mountain region, as shown in FIG. 12, radio reflections are many due to vehicular traffic in the urban region, buildings or mountains, and it is difficult to construct the SFN environment by multistage relay of broadcast waves. For example, it is difficult for a wraparound canceller to be used in the transmission station of digital terrestrial broadcasting to cancel the wraparound wave stably and continuously to transmit a broadcast wave signal (retransmitted wave) to a subsequent stage because a change in received signal level of broadcast waves due to the influence of radio reflection and a change in a number of multipath waves and a D/U ratio are considerable.
Here, the concept of segment of digital terrestrial broadcasting is described.
As shown in FIG. 13, within a channel (13 segments resulting from 14 divisions of each 6 MHz in the example shown in the drawing) of digital terrestrial broadcasting, one-segment broadcast waves, a method wave in which broadcast data has been placed in one segment (segment number 0) is emitted to provide a broadcasting service. Receivers of one-segment broadcasting receive a broadcast wave of segment number 0 and receive images, sounds and data.
Even when such one-segment broadcasting service of digital terrestrial broadcasting is performed, it is difficult to perform stably a multistage relay in an SFN environment in an urban region or a mountain region similar to the above.
Patent Literature 1 proposes, in order to solve a problem that a broadcasting system (area broadcasting) covering a specific area with a very low transmission power using the one-segment broadcasting system tends to have a dead zone in its service area, a broadcasting method that can be remedy or reduce the dead zone of area broadcasting by so-called frequency diversity by transmitting simultaneously a signal having the same contents in another possible transmission frequency band part of a usable transmission frequency band.
Patent Literature 2 proposes a transmission system in which when plural transmission apparatuses perform radio transmission of a signal using a different segment of the same channel by an OFDM modulation method, one or more transmission apparatuses among the plural transmission apparatuses, in order to improve reception characteristics of the receiving apparatus, receive a predetermined signal from the outside by a receiving means, and controls transmission timing of the OFDM modulated signal by a transmission timing control means at the timing according to the signal received by the receiving means.
Patent Literature 3 proposes a transmission apparatus in order to provide a transmission apparatus capable of determining a segment (frequency) to be output according to an input signal for area broadcasting of for example a digital terrestrial broadcasting system, wherein a channel detection means detects a channel according to information for identifying the channel contained in an input signal for broadcasting, a segment detection means detects a segment according to information for identifying the segment contained in the input signal for broadcasting, and a modulated signal generation means generates a modulated signal in which placed is data for broadcasting contained in the input signal for broadcasting at the position of the segment detected by the segment detection means among plural segments provided in the channel detected by the channel detection means, and outputs the modulated signal generated by the modulated signal detection means.
Patent Literature 4 proposes a transmission apparatus in order to provide a transmission apparatus capable of determining a segment (frequency) to be output according to usage conditions of radio waves of a different frequency in the air for area broadcasting of for example a digital terrestrial broadcasting system, wherein a segment detection means detects a segment corresponding to an unused frequency region to be used for transmission on the basis of a relation of a frequency region to a signal level of the radio wave received by radio, and a transmission signal generation means generates a transmission signal having thereon data for broadcasting included in a signal for broadcasting inputted to the position of a segment detected by the segment detection means, and outputs the transmission signal generated by the transmission signal generation means.
Patent Literature 5 proposes a broadcasting system which is provided with a first transmitter for transmitting a digital terrestrial broadcasting wave of a central segment common to a predetermined region, and other transmitters for transmitting a radio wave for transmitting a digital terrestrial broadcasting wave of a periphery segment to a portion of the predetermined region to make the area broadcasting receivable in the large range, the broadcasting system having a means for controlling at least one of a transmission point arrangement of a central segment and a periphery segment adjacent to the central segment, a transmission electric field, a retransmission electric field, a frequency channel interval, a transmission antenna height, transmission antenna directivity, transmission phase synchronization, a frequency segment interval and a transmission electric field propagating property, and for separating a transmission electric field of the digital terrestrial broadcasting wave of the periphery segment from a receiving electric field of the central segment near the ground in the predetermined region.
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