Abstract:
An apparatus for transmitting terrestrial digital data using a synchronous-optical-network system or a synchronous-digital-hierarchy system includes a synchronous-difference calculating unit that calculates a synchronous difference between a standard signal used in the synchronous-optical-network system or the synchronous-digital-hierarchy system and a first synchronous signal that synchronizes with a leading position included in image data of the terrestrial digital data; and a transmission processing unit that transmits the synchronous difference together with the terrestrial digital data to a destination.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technology for transmitting a signal for a terrestrial digital broadcasting using synchronous optical network (SONET)/synchronous digital hierarchy (SDH) communication system. 
     2. Description of the Related Art 
     To improve image quality and to achieve advanced features in television, terrestrial digital broadcasting services are being offered. Specifically, terrestrial television broadcasting is digitalized, and then transmitted from towers on the ground (such as Tokyo Tower) to broadcast stations. 
     The mainstream method of transmitting signals of terrestrial digital broadcasting is the wireless signal transmission method (refer to “Digital Terrestrial Television Transmitter System in Tokyo Tower”, Tomohito Ikegami et al., NEC Giho Vol. 57, No.4/2004, pp. 49-54). 
     However, because wireless transmission is used for various purposes other than terrestrial digital broadcasting, many frequencies are competing with each other. Thus, there is a strong demand to transmit signals of terrestrial digital broadcasting by using fixed cables. 
     However, it is very difficult to transmit signals of terrestrial digital broadcasting by using fixed cables, because it entails many advanced specifications of interfaces between devices. Thus, none of the broadcast stations have realistic plans to implement cable signal transmission. 
     One approach is to build new cables dedicated for terrestrial digital broadcasting, connecting the broadcast stations. However, this is unfeasible because enormous costs are required. 
     It is therefore imperative to use existing general-purpose lines so that broadcast stations can realize cable signal transmission for terrestrial digital broadcasting without difficulty. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least solve the problems in the conventional technology. 
     An apparatus according to one aspect of the present invention, which is for transmitting terrestrial digital data using a synchronous-optical-network system or a synchronous-digital-hierarchy system, includes a synchronous-difference calculating unit that calculates a synchronous difference between a standard signal used in the synchronous-optical-network system or the synchronous-digital-hierarchy system and a first synchronous signal that synchronizes with a leading position included in image data of the terrestrial digital data; and a transmission processing unit that transmits the synchronous difference together with the terrestrial digital data to a destination. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a transmitting system according to an embodiment of-the present invention; 
         FIG. 2  is a functional block diagram of a transmitter and an ADM shown in  FIG. 1 ; 
         FIG. 3  is a functional block diagram of a transmission processing unit shown in  FIG. 2 ; 
         FIG. 4  describes how differences between broadcasting TS synchronous signals and 8K synchronous signals are extracted; 
         FIG. 5  describes how differences between synchronous clock signals and the 8K synchronous signals are extracted; 
         FIG. 6  is an example of a data structure mapped in a frame by a VC3 mapping unit; 
         FIG. 7  is a functional block diagram of a reception processing unit shown in  FIG. 2 ; 
         FIG. 8  describes how the broadcasting the TS synchronous signals are reproduced; and 
         FIG. 9  describes how the synchronous clock signals are reproduced. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention will be described-below with reference to accompanying drawings. The present invention is not limited to these embodiments. 
     A transmitter according to the present invention functions as a source transmitter and a destination transmitter. The source transmitter calculates differences between standard synchronous signals in the SONET/SDH communication system, and signals of terrestrial digital broadcasting (hereinafter, “terrestrial digital broadcasting signals”). The calculated differences and the terrestrial digital broadcasting signals are stored in a frame (such as a SONET/SDH frame), and the frame is transmitted to the destination transmitter. 
     The destination transmitter that receives the frame reproduces signals equivalent to the terrestrial digital broadcasting signals of the source transmitter, based on the differences and the terrestrial digital broadcasting signals stored in the frame. 
       FIG. 1  is a block diagram of a transmitting system according to an embodiment of the present invention. In the transmitting system, a transmitter  100  and a transmitter  200  are connected to an add/drop multiplexer (ADM)  300  and an ADM  400 , respectively. The ADM  300  and the ADM  400  are connected through an SDH synchronous network  50 . 
     The transmitter  100  calculates the differences between the terrestrial digital broadcasting signals and the standard synchronous signals, and transmits the calculated differences and the terrestrial digital broadcasting signals to the transmitter  200 . When data is received from the transmitter  100 , the transmitter  200  reproduces signals equivalent to the terrestrial digital broadcasting signals that the transmitter  100  acquired, based on the differences and the terrestrial digital broadcasting signals received. 
     The terrestrial digital broadcasting signals include broadcasting transport stream (TS) signals, broadcasting TS synchronous signals, and synchronous clock signals. The broadcasting TS signals are image data signals of terrestrial digital broadcasting, the broadcasting TS synchronous signals are signals that synchronize with a starting point in each image data in the broadcasting TS signals, and the synchronous clock signals are used when the destination transmitter receives and reproduces terrestrial digital broadcasting signals. 
     The ADM  300  acquires data from the transmitter  100  and stores the data in a frame. The ADM  300  then transmits the frame to the ADM  400  through the SDH synchronous network  50 . When the ADM  300  acquires a frame, the ADM  300  extracts data in the acquired frame, and passes the extracted data to the transmitter  100 . The ADM  300  also passes standard synchronous data received from outside to the transmitter  100 . 
       FIG. 2  is a functional block diagram of the transmitter  100  and the ADM  300  shown in  FIG. 1 . Descriptions of the transmitter  200  and the ADM  400  are omitted because they have the same configurations as those of the transmitter  100  and the ADM  300 . 
     The transmitter  100  includes a phase locked loop (PLL)  110 , an 8K-hertz (Hz)-frame-synchronous-signal generating unit  120 , a transmission processing unit  130 , and a reception processing unit  140 . The ADM  300  includes a virtual concatenation  3  (VC3) mapping unit  310 , an electrical/optical (E/O) processing unit  320 , an optical/electrical (O/E) processing unit  330 , and a VC3 demapping unit  340 . 
     The PLL  110  matches a frequency of an input signal and a frequency of an output signal. Thus, the PLL  110  passes standard synchronous signals input from the ADM  300  to the 8K-frame-synchronous-signal generating unit  120  without changing the frequency. 
     The 8K-frame-synchronous-signal generating unit  120  generates standard synchronous signals of 8 KHz (hereinafter, “8K synchronous signals”), based on the standard synchronous signals received from the PLL  110 . The generated 8K synchronous signals are then passed to the transmission processing unit  130  and the reception processing unit  140 . 
       FIG. 3  is a functional block diagram of the transmission processing unit  130  shown in  FIG. 2 . The transmission processing unit  130  includes an image packet extracting unit  131 , a generic framing procedure (GFP) capsuling unit  132 , a synchronous-signal-difference extracting unit  133 , a synchronous-signal digitalizing unit  134 , a synchronous clock-difference extracting unit  135 , and a synchronous-clock digitalizing unit  136 . 
     The image packet extracting unit  131  extracts an image packet from the broadcasting TS signals, and passes the extracted-image packet to the GFP capsuling unit  132 . The GFP capsuling unit  132  capsules the image packet using a GFP capsuling method, and passes the capsuled image packet (hereinafter, “capsuled image data”) to the ADM  300 . 
     The synchronous-signal-difference extracting unit  133  acquires the broadcasting TS synchronous signals and the 8K synchronous signals, and extracts the differences between each of the broadcasting TS synchronous signals and each of the 8K synchronous signals. The synchronous-signal-difference extracting unit  133  then passes the extracted differences to the synchronous-signal digitalizing unit  1 , 34 . The synchronous-signal digitalizing unit  134  digitalizes the differences, and passes the digitalized differences (hereinafter, “synchronous difference data”) to the ADM  300 . 
       FIG. 4  describes how the differences between the broadcasting TS synchronous signals and the 8K synchronous signals are extracted. A counter circuit (not shown) of a predetermined high-frequency clock starts counting from a leading edge of an 8K synchronous signal of a cycle of 125μseconds. The counting stops when a leading edge of a broadcasting TS synchronous signal is generated. The counted value is the synchronous difference data. If a leading edge of a broadcasting TS synchronous signal is not generated within the 125μ cycle of the 8K synchronous signal, absence of broadcasting TS synchronous signal difference data is notified to the synchronous-signal-difference extracting unit  133 . The absence can be recognized when a next leading edge of the 8K synchronous signal is detected while the counting is in progress. Alternatively, the absence can be recognized when a next leading edge of the 8K synchronous signal is detected, and the counter circuit is reset to start counting again. 
     Returning to  FIG. 3 , the synchronous clock-difference extracting unit  135  acquires the synchronous clock signals and the 8K synchronous signals, extracts differences between the signals, and passes the extracted differences to the synchronous-clock digitalizing unit  136 . The synchronous-clock digitalizing unit  136  digitalizes the differences acquired from the synchronous clock-difference extracting unit  135 , and passes the digitalized differences (hereinafter, “clock difference data”) to the ADM  300 . 
       FIG. 5  describes how the differences between the synchronous clock signals and the 8K synchronous signals are extracted. The counter circuit of a predetermined high-frequency clock starts counting from a leading edge of an 8K synchronous signal of a cycle of 125μ seconds. The counting stops when a first leading edge of a synchronous clock signal is generated. The counted value is the clock difference data. If a leading edge of a synchronous clock signal is not generated within the 125μ cycle of the 8K synchronous signal, absence of synchronous-clock-signal difference data is notified to the synchronous clock-difference extracting unit  135 . The absence can be recognized when a next leading edge of the 8K synchronous signal is detected while the counting is in progress. Alternatively, the absence can be recognized when a next leading edge of the 8K synchronous signal is detected, and then the counter circuit is reset to start counting again. 
     Returning to  FIG. 2 , the VC3 mapping unit  310  acquires the capsuled image data, the synchronous difference data, and the clock difference data from the transmission processing unit  130 . The GFP is used for mapping data in a frame. 
       FIG. 6  is an example of a data structure mapped in a frame by the VC3 mapping unit  310 . The frame includes a section overhead (SOH), a path overhead (POH), a VC3#1, a VC3#2, and a VC3#3. The VC3#1, the VC3#2, and the VC3#3 each includes a mapping region for presence or absence of broadcasting TS synchronous signal difference data/difference value, a mapping region for presence or absence of synchronous-clock-signal difference data/difference value, and a mapping region for broadcasting TS packets. 
     The SOH is a region that stores data required for maintenance and operation of transmission path switching data. The POH is a region that stores data required for maintenance and operation of each unit segment of mapping regions. The mapping region for presence or absence of broadcasting TS synchronous signal difference data/difference value stores the synchronous difference data (the region includes a 16 bit region so that a counted value is input as a binary code). When there is no synchronous difference data, data informing absence of the broadcasting TS synchronous signal difference data is stored. 
     The mapping region for presence or absence of synchronous-clock-signal difference data/difference value stores the clock difference data (the region includes a 16 bit region so that a counted value is input as a binary code). When there is no clock difference data, data informing absence of the synchronous-clock-signal difference data is stored. The mapping region for broadcasting TS packets stores the capsuled image data. 
     Returning to  FIG. 2 , the E/O processing unit  320  acquires the frame in electrical signals from the VC3 mapping unit  310 , converts the frame into optical signals, and transfers the frame in optical signals to the ADM  400  through the SDH synchronous network  50 . 
     When the O/E processing unit  330  receives the frame in optical signals from the SDH synchronous network  50 , the O/E processing unit  330  converts the frame into electrical signals, and passes the frame in electrical signals to the VC3 demapping unit  340 . Upon receiving the standard synchronous signals, the O/E processing unit  330  passes the standard synchronous signals to the PLL  110 . 
     The VC3 demapping unit  340  acquires the frame from the O/E processing unit  330 , extracts the capsuled image data, the synchronous difference data, and the clock difference data from the frame, and passes the extracted data to the reception processing unit  140 . 
       FIG. 7  is a functional block diagram of the reception processing unit  140 . The reception processing unit  140  includes a broadcasting TS extracting unit  141 , a memory  142 , a synchronous-difference extracting unit  143 , a TS-synchronous-signal reproducing unit  144 , a lead control unit  145 , a clock-difference extracting unit  146 , a synchronous-clock reproducing unit  147 , and a PLL  148 . 
     The broadcasting TS extracting unit  141  acquires the capsuled image data from the ADM  300 , extracts the image packet from the capsuled image data, and stores the image packet in the memory  142 . The memory  142  is a storing unit that stores image packets. 
     The synchronous-difference extracting unit  143  acquires the synchronous difference data from the ADM  300 , extracts the synchronous differences from the synchronous difference data, and passes the synchronous differences to the TS-synchronous-signal reproducing unit  144 . 
     The TS-synchronous-signal reproducing unit  144  acquires the synchronous differences from the synchronous-difference extracting unit  143 , and the 8K synchronous signals from the 8K-frame-synchronous-signal generating unit  120 , respectively. Based on the acquired data, the TS-synchronous-signal reproducing unit  144  reproduces broadcasting TS synchronous signals equivalent to those of a source transmitter. 
       FIG. 8  describes how the broadcasting TS synchronous signals are reproduced. The counter circuit starts counting from a leading edge of an 8K synchronous signal. When a counted value reaches a point that equals the synchronous difference, the point becomes a leading edge of a broadcasting TS synchronous signal. By repeating such a processing, the TS-synchronous-signal reproducing unit  144  reproduces broadcasting TS synchronous signals. The TS-synchronous-signal reproducing unit  144  passes the reproduced broadcasting TS synchronous signals to the lead control unit  145  and a host computer (not shown). 
     Returning to  FIG. 7 , the lead control unit  145  passes the image packets stored in the memory  142  to the host computer, as broadcasting TS signals. The broadcasting TS signals include image data, and each image data includes a plurality of image packets. The lead control unit  145  controls a flow of the image packets to the host computer, so that a leading image packet in an image data synchronizes with a broadcasting TS synchronous signal received from the TS-synchronous-signal reproducing unit  144 . 
     The clock-difference extracting unit  146  acquires the clock difference data from the ADM  300 , extracts the clock differences from the clock difference data, and passes the clock differences to the synchronous-clock reproducing unit  147 . 
     The synchronous-clock reproducing unit  147  acquires the clock differences from the clock-difference extracting unit  146 , and the 8K synchronous signals from the 8K-frame-synchronous-signal generating unit  120 , respectively. Based on the acquired data, the synchronous-clock reproducing unit  147  reproduces synchronous clock signals equivalent to those of the source transmitter. 
       FIG. 9  describes how the synchronous clock signals are reproduced. The counter circuit starts counting from a leading edge of an 8K synchronous signal. When a counted value reaches a point that equals the clock difference, the point becomes a leading edge of a synchronous clock signal. By repeating such a processing, the synchronous-clock reproducing unit  147  reproduces synchronous clock signals. The synchronous-clock reproducing unit  147  passes the reproduced synchronous clock signals to the host computer through the PLL  148 . A description of the PLL  148  is omitted here because it is the same as the PLL  110  shown in  FIG. 2 . 
     In the transmitter  100  according to the present embodiment, the GFP capsuling unit  132  generates the capsuled image data, the synchronous-signal digitalizing unit  134  generates the synchronous difference data, and the synchronous-clock digitalizing unit  136  generates the clock difference data. The transmitter  100  transmits such data to the transmitter  200  through the ADM  300 . 
     In the transmitter  100 , when a frame is received, the broadcasting TS extracting unit  141  extracts the broadcasting TS signals, the TS-synchronous-signal reproducing unit  144  reproduces broadcasting TS synchronous signals, and the synchronous-clock reproducing unit  147  reproduces synchronous clock signals. 
     Thus, cable signal transmission for terrestrial digital broadcasting can be realized by using existing general-purpose lines without difficulty. Specifically, terrestrial digital data can be transmitted without requiring advanced specifications, and without deteriorating image quality. Moreover, the terrestrial digital data can be precisely reproduced. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.