JP4484718B2 - Data receiving apparatus and data receiving method - Google Patents

Description

  The present invention relates to a data receiving apparatus and a data receiving method used in a system for transmitting a stream such as an MPEG2 transport stream (TS) in real time.

  As a conventional data reception method, a time stamp (hereinafter referred to as “time information”) is added to the head of a TS packet on the data transmission side, and data transmission is performed using the time information added to the TS packet in the data reception device. There is one that corrects the fluctuation of the clock of the data receiving device with respect to the clock on the side (see, for example, Patent Document 1). In this data receiving apparatus, data is read from a storage unit provided in the data receiving apparatus based on time information included in the TS packet. This data receiving apparatus controls the voltage control oscillator based on the time information and corrects the fluctuation of the clock. However, the following method is also used for cost reduction and simplification of the circuit.

  For example, the data reception device has a free-running clock generator that is not synchronized with the clock of the data transmission device, and the output value of a timer that operates with this clock and the time information included in the received TS packet This is a method of comparing and reading packet data from a storage unit provided in the data receiving device at a timing based on the comparison result.

Japanese Patent Laying-Open No. 2003-258894 (paragraphs 0044-0047, FIG. 8)

  In the above method, since the clocks of the data transmission device and the data reception device are not synchronized, an overflow or an underflow may occur in the storage unit of the data reception device. Therefore, a method of adjusting the frequency of reading data from the storage unit of the data receiving apparatus by adding / subtracting an offset value to / from the update value of the timer so as to keep the remaining amount of data in the storage unit of the data receiving apparatus constant.

  However, for example, when the content of the transmission data relates to special reproduction such as fast-forwarding of digital video or a DVD player, the data transmission rate from the data transmission device to the data reception device is significantly reduced, and the data reception device The remaining amount of data in the storage unit decreases. Then, the data reception device attempts to delay the timer count-up by subtracting the offset value from the timer update value in order to keep the remaining data amount in the storage unit constant. As a result, there is a problem that the time during which data is not read out from the storage unit of the data receiving apparatus becomes long and data reading fails.

  Therefore, the present invention has been made to solve the above-described problems of the prior art, and can stably transmit packet data from a data receiving apparatus even if the data transmission rate is drastically reduced. An object of the present invention is to provide a data receiving apparatus and a data receiving method capable of performing the above.

  In order to achieve the above object, a data receiving device according to the present invention includes a storage unit that stores packet data including time information transmitted from a data transmission device via a network, and a data remaining in the storage unit. A data reception device having a storage state detection unit for detecting a quantity, a timer for measuring an internal time, and a control unit, wherein the timer adds or subtracts an offset value to the update value, thereby the data transmission device The control unit extracts a change in the remaining amount of data detected by the storage state detection unit, the change is greater than a predetermined threshold, and When the change is a monotonous change, the update value of the timer is not changed, and the data is read from the storage unit using the internal time measured by the timer. It is configured to generate a data read timing signal to provide a ring.

  In order to achieve the above object, a data receiving method according to the present invention stores packet data including time information sent from a data transmitting device to a data receiving device via a network, Detecting the remaining amount of stored data; measuring the internal time by a timer; and adding / subtracting an offset value to / from the updated value of the timer, A step of correcting a deviation of a reference time, extracting a change in the remaining amount of data, and if the change is larger than a predetermined threshold and the change is a monotonous change, The updated value of the timer in the step of correcting a deviation is stored in the internal time measured by the timer without being changed. And it generates a data read timing signal to provide a timing to read the over data.

  In the data receiving apparatus and the data receiving method of the present invention, by monitoring the remaining amount of data in the storage unit, it is detected that the content of the transmission data is a low rate signal such as a special reproduction image. When it is detected that the content of the transmission data is a low rate signal, the predetermined value of the packet data is read from the storage unit using the internal time measured by the timer without changing the update value of the timer. A timing signal that gives the timing to be generated is generated. Therefore, according to the data receiving apparatus and the data receiving method of the present invention, it is possible to prevent the data reading from the storage unit from failing even if the packet data is a low rate signal. Can be transmitted without interruption.

Embodiment 1 FIG.
FIG. 1 is a block diagram schematically showing a configuration of a packet data transmission / reception system including a data receiving apparatus according to Embodiment 1 of the present invention (that is, an apparatus capable of executing the data receiving method according to Embodiment 1). . As shown in FIG. 1, the packet data transmission / reception system according to the first embodiment includes a data transmission device 100 and a data reception device 200. Packet data transmitted from the data transmission device 100 is transmitted to the data reception device 200 via the network 300.

  As shown in FIG. 1, the data transmission device 100 includes an input terminal 1, a time information adding unit 2, and a timer 3. For example, a transport stream (TS) packet that is 188-byte data is input to the input terminal 1. The timer 3 measures the internal time in the data transmission device 100. The time information adding unit 2 adds the internal time measured by the timer 3 to the TS packet input from the input terminal 1 as time information. The TS packet to which the time information is added is transmitted via the network 300 from an interface unit (not shown) of the data transmission apparatus 100.

  FIG. 2 is a diagram for explaining a TS packet to which time information is added. In the example shown in FIG. 2, the time information is 4 bytes, the TS packet (packet data body portion) is 188 bytes, and the time information is added to the head of the TS packet.

  As shown in FIG. 1, the data receiving apparatus 200 includes a storage unit 10, a time information separation unit 20, a data read timing generation unit 30, and a storage state detection unit 40.

  The storage unit 10 stores TS packets to which time information transmitted from the data transmission apparatus 100 via the network 300 and received by an interface unit (not shown) of the data reception apparatus 200 is added. The time information separation unit 20 separates the packet data read from the storage unit 10 (that is, a TS packet to which time information is added) into time information and a TS packet (packet data body portion).

  As shown in FIG. 1, the data read timing generation unit 30 includes a comparison unit 31, a timer 32, and a control unit 33. The data read timing generation unit 30 generates a data read timing signal from the storage unit 10. The data read timing signal generated by the control unit 30 is a signal that gives the timing for reading the TS packet to which the time information is added from the storage unit 10 based on the time information separated by the time information separation unit 20. . The timer 32 measures the internal time in the data receiving device 200. The comparison unit 31 compares the time information from the time information separation unit 20 with the internal time from the timer 32. The control unit 33 generates a data read timing signal from the storage unit 10 based on the comparison result of the comparison unit 31. The storage state detection unit 40 measures the remaining amount of data stored in the storage unit 10.

  FIGS. 3A to 3C are diagrams for explaining the transmission state of TS packets in the packet data transmission / reception system of FIG. 3A to 3C show the state of TS packets on transmission paths having different transmission bands. FIG. 3A shows a state of a TS packet that is input to the input terminal 1 of the data transmission apparatus 100. FIG. 3B shows a state of TS packets transmitted over the network 300. FIG. 3C shows the state of a TS packet output from the data receiving apparatus 200. 3A to 3C, the horizontal direction (arrangement direction of TS packets TS1 to TS5) is the time axis direction.

  As shown in FIG. 3A, the packet interval of TS packets input to the input terminal 1 of the data transmitting apparatus 100 is usually different between the respective packets and is not constant.

  In order to correctly reproduce the TS packet in a TS packet reproducing apparatus (not shown) connected to the subsequent stage of the data receiving apparatus 200 and receiving the TS packet output from the data receiving apparatus 200, FIG. The interval between TS packets input to the data transmission device 100 shown in FIG. 3 is substantially equal to the interval between corresponding TS packets output from the data reception device 200 shown in FIG. (However, a slight error of about 50 μs is allowed). That is, each TS packet output from the data receiving apparatus 200 needs to be output with a certain delay amount with respect to each TS packet input to the data transmitting apparatus 100.

  In general, the transmission band of the upstream transmission path of the data transmitting apparatus 100 and the transmission band of the downstream transmission path of the data receiving apparatus 200 are substantially the same. For example, when data transmission is performed using IEEE 1394S400, TS packets are transmitted and received at a maximum transmission rate of 400 Mbps.

  However, the transmission band on the network 300 is different from the transmission band of the previous transmission line of the data transmitting apparatus 100 and the transmission band of the subsequent transmission line of the data receiving apparatus 200. For example, when a wireless LAN is used as the network 300, the execution throughput is about 25 Mbps, which is narrower than the execution throughput (about 400 Mbps) of IEEE1394S400 described above. Even when Ethernet (registered trademark) or the like is used as the network 300, the execution throughput is about 80 Mbps, and the transmission band is very narrow when compared with the execution throughput of IEEE1394S400.

  Therefore, when TS packets pass through transmission paths having different transmission bands, TS jitter occurs in the preceding stage of the data transmitting apparatus 100 and the subsequent stage of the data receiving apparatus 200, and the interval between the TS packets is not compensated. . In general, when TS is transmitted, it is necessary to suppress the TS jitter of the TS output from the data receiving apparatus 200 to a predetermined value (for example, 50 μs) or less. This is due to the following reason. An MPEG decoder device (not shown) arranged at the subsequent stage of the data receiving device 200 separates the TS packet to which PCR (program clock reference) is added from the input TS packet, and uses the input timing and time information as the input timing and time information. Based on this, a PLL (Phase Locked Loop) is applied to the internal reference clock. Therefore, if a large jitter occurs in the TS packet, the PLL of the reference clock does not work, and the decoded image stops or block noise or the like occurs.

  For example, when a wireless LAN (execution throughput of about 25 Mbps) is used for the network 300 and an HD (High Definition) stream of about 20 Mbps is transmitted, the transmission band of the wireless part is equal to the data transmission band of the previous stage of the data transmission device 100 ( For example, when IEEE 1394 S400 is used, it is very narrow compared to 400 Mbps. For this reason, the bit rate in the average radio section of the TS packet is transmitted at a substantially constant interval because the transmission band is very narrow in the radio section even when the input TS packet is VBR (Variable bit rate). (See FIG. 3B). That is, when transmitting a TS packet, the time spent to transmit one TS packet varies depending on the difference in network transmission bands.

  Therefore, the interval between TS packets changes by the amount of time spent for transmitting TS packets. If no adjustment is made in a state where the interval between the TS packets is changed, the interval between the TS packets remains changed after that, and TS jitter is not compensated.

  Therefore, in the subsequent stage of the data receiving apparatus 200, the following processing is performed to restore the interval between TS packets in the previous stage of the data transmitting apparatus 100.

  First, when a TS packet is input from the input terminal 1 of the data transmitting apparatus 100, the time information adding unit 2 adds the reference time in the data transmitting apparatus 100 output from the timer 3 to the TS packet and transmits the packet to the network 300. Data (TS packet to which time information is added) is output (see FIG. 2). The TS packet output from the data transmission device 100 and transmitted via the network 300 is received by the data reception device 200. As described above, the transmission band on the network 300 is different from the transmission band in the previous stage of the data transmission device 100. Therefore, as shown in FIGS. 3A and 3B, the interval between TS packets changes. In the first embodiment, since the transmission band of the previous stage of the data transmitting apparatus 100 is wide and the transmission band on the network 300 is narrow, the interval between corresponding TS packets on the network 300 becomes smaller.

  When the data receiving apparatus 200 receives a TS packet to which time information is added, the TS packet is stored in the storage unit 10. In the first embodiment, the storage unit 10 is configured by 256 bytes × 1024 lines, and TS packets received by the data reception device 200 are stored in the storage unit 10 in units of one line. As shown in FIG. 2, the TS packet is composed of 192 bytes including time information. In the first embodiment, when the next TS packet received is stored, the TS packet is stored in the storage unit 10. It shall be stored from the beginning of the next line. Thereby, the time information is stored at the head of each line in the storage unit 10. Therefore, when the writing of the first TS packet is completed, the control unit 33 outputs the write address for the TS packet input second from the first write address of the next line to the storage unit 10.

  Therefore, every time TS packets to which time information is added are sequentially received by the data receiving apparatus 200, the number of TS packets in the writing state increases unless data is read from the storage unit 10.

  On the other hand, in the data receiving apparatus 200, when a preset data reading start condition is satisfied, a process of reading data stored in the storage unit 10 is started. As a data read start condition, for example, when the number of TS packets stored in the storage unit 10 (referred to as “data remaining amount”) exceeds a predetermined number, the TS packets stored in the storage unit 10 Starts reading. In Embodiment 1, it is assumed that reading of TS packets is started when the storage capacity of the storage unit 10 exceeds half (when TS packets for 512 lines are stored).

  The process of reading data from the storage unit 10 when the data read start condition is satisfied is performed as follows.

  First, when the data read start condition is satisfied, the data read timing generation unit 30 outputs a data read timing signal to the storage unit 10.

  When the storage unit 10 receives the data read timing signal, the storage unit 10 outputs the time information in which the TS packet of the first line is stored. In the first embodiment, it is composed of 4 bytes. Data (time information) read from the storage unit 10 is input to the time information separation unit 20. The time information separation unit 20 determines whether the input data is time information or a TS packet, and if it is time information, inputs it to the comparison unit 31. The comparison unit 31 stores the input time information in a register (not shown), and outputs the time information to the timer 30 in the case of the time information of the first TS packet. When the timer 30 receives the time information to which the first TS packet is added, the timer 30 sets the time information as an initial value in a counter for measuring the internal time, and starts counting the internal time of the data receiving device 200. To do.

  When the setting of the initial value in the timer 30 is completed and counting of the internal time in the data receiving device 200 is started, the comparison unit 31 outputs the internal time and the time information separating unit of the data receiving device 200 output from the timer 30. The time indicated by the time information added to the head of the TS packet input from 20 is compared, and the internal time of the data receiving apparatus 200 is equal to or greater than the time indicated by the time information. In this case, a control signal is output to the control unit 33 so as to read the leading TS packet data. In the case of the first TS packet, since the internal time is initially set to the time indicated by the first time information, the internal time is equal to the time information. Therefore, the comparison unit 31 outputs a control signal to the control unit 33. When this control signal is input, the control unit 33 outputs a read timing signal for reading the first TS packet data to the storage unit 10. Specifically, the TS packet is composed of 188 bytes as shown in FIG. The control unit 33 outputs a control signal (read address signal or the like) for reading the 188-byte TS packet to the storage unit 10.

  When the reading of the data of the first TS packet is completed, the control unit 33 outputs to the storage unit 10 a read control signal (such as a read address signal) of time information added to the head of the next TS packet. The memory unit 10 reads time information added to the head of the TS packet stored in the next line (second line) based on the read control signal output from the control unit 33 following the reading of the head TS packet. Is read.

  The time information separation unit 20 separates the TS packet output from the storage unit 10 and the time information, and outputs the TS packet from the output terminal. On the other hand, the time information is output to the comparison unit 31. When the time information is input from the time information separation unit 20, the comparison unit 31 stores the time information in a register. When the time information is stored in the register, the comparison unit 31 compares the time information stored in its own register (not shown) with the reference time of the data receiving device 200 output from the timer 32. Normally, when the time information is input, the internal time is smaller than the time indicated by the time information.

  Then, the comparison unit 31 determines that the reference time of the timer 32 is equal to the time indicated by the time information input to the comparison unit 31 (time indicated by the time information = reference time) or the reference time of the timer 32 is The control signal is not output to the control unit 33 until the time indicated by the time information input to the comparison unit 31 is greater than the time indicated by the time information (time indicated by the time information <reference time). Therefore, when the reference time of the timer 32 has not reached the time indicated by the time information input to the comparison unit 31, the time information and TS packet are not newly read from the storage unit 10. Further, the reference time output from the timer 32 becomes equal to the time information stored in the register (not shown) of the comparator 31 (time indicated by the time information = reference time), or is output from the timer 32. When the reference time becomes larger than the time information stored in the register (not shown) of the comparator 31 (time indicated by the time information <reference time), the comparison unit 31 notifies the control unit 33 of the first TS packet. A control signal is output to read data. When this control signal is input, the control unit 33 outputs a read timing signal for reading the TS packet data stored in the second line in the storage unit 10. Then, when the valid data of the TS packet is read from the storage unit 10, the time information separation unit 20 outputs the TS packet to a subsequent TS packet reproduction device (not shown) via the output terminal.

  When the reading of the data of the TS packet of the second line is completed, the control unit 33 outputs a reading control signal (reading address signal or the like) of the time information added to the head of the TS packet of the third line to the storage unit 10. To do. The storage unit 10 is added to the head of the TS packet stored in the next line (third line) based on the read control signal output from the control unit 33 following the reading of the TS packet of the second line. Read time information. Subsequently, the TS packet stored in the storage unit 10 is sequentially read from the storage unit 10 by repeating the above operation.

  Here, the time information added to the TS packet is an output value of the timer 3 when the TS packet is input to the data transmission device 100. Therefore, the read timing signal output from the control unit 33 is output based on the output value of the timer 3 (reference time information of the data transmission device) added by the time information adding unit 2.

  Therefore, the output interval of the read timing signal in the data receiving apparatus 200 is the same as the input interval of the TS packets input to the data transmitting apparatus 100. That is, it is assumed that the main part of each TS packet separated by the time information separation unit 20 is taken out at the output interval of the read timing signal. Then, the packet interval of each TS packet input to the data transmitting device 100 (FIG. 3A) and the packet interval of each corresponding TS packet output from the data receiving device 200 (FIG. 3C) are obtained. Will be equal.

  The above description is a case where the TS signal is input to the data receiving apparatus 200 when the transmission signal is a normal playback image (the transmission rate is constant) on the network 300.

  However, the clock of the data transmission device 100 and the clock of the data reception device 200 are not synchronized. Usually, even when a crystal oscillator or the like is used as a basic clock generation element of the data transmission device 100 and the data reception device 200, the clock frequency deviation is 100 ppm. Therefore, the reference time in the data transmitting apparatus 100 and the reference time in the data receiving apparatus 200 are gradually shifted by the clock frequency deviation. Therefore, the remaining data amount of TS packets stored in the storage unit 10 gradually increases or decreases, and finally overflow or underflow occurs. To prevent this, the storage state detection unit 40 monitors the remaining amount of data in the storage unit 10, and when the remaining amount of data is in a decreasing direction (monotonically decreasing), the update value of the timer 32 is decreased and the timer counts up. Is delayed, the frequency of reading data from the storage unit 10 is decreased, and the remaining amount of data is kept constant.

  Conversely, when the remaining amount of data is in an increasing direction (monotonically increasing), the update value of the timer 32 is increased and the timer counts up to increase the frequency of data reading from the storage unit 10 to increase the data Keep the remaining amount constant. Hereinafter, a method of estimating the reference time in the data transmitting apparatus 100 based on the remaining data in the storage unit 10 and controlling the reference time in the data receiving apparatus 200 will be referred to as “clock synchronization control”.

  However, for example, when the amount of transmission data of a TS packet changes abruptly, the above control causes a delay time until the TS packet at the time when the transmission data rate changes is read. Specifically, a delay time of about 512 TS packets occurs. Hereinafter, a case where high-speed playback is performed during playback of a digital VTR will be described. For example, when high-speed playback is performed during playback of 20 Mbps content, the rate of input TS packets may be about 2 Mbps. Also, when shifting from normal playback to high-speed playback or from high-speed playback to normal playback, TS packets are not output until the servo of the digital VTR tape running system and the tracking system servo are locked (stable). FIG. 4 shows the transmission data rate of TS packets when the digital VTR shifts from normal playback to high-speed playback (special playback) (time t1) and from high-speed playback (special playback) to normal playback (time t3). Shows changes. FIG. 5 shows changes in the number of stored TS packets in the storage unit 10 at that time. As shown in FIG. 5, when the playback mode of the digital VTR shifts (when the data amount of the TS packet greatly changes), the remaining data amount in the storage unit 10 is also significantly reduced (or increased).

  Then, the storage state detection unit 40 updates the timer 32 in an attempt to keep the remaining data amount of the TS packet stored in the storage unit 10 constant (for example, half the storage capacity of the storage unit 10) as described above. Control is performed so that the frequency of reading data from the storage unit 10 decreases by decreasing the value and delaying the count-up of the timer. However, the change in the remaining amount of data stored in the storage unit 10 is not caused by the difference in the reference clock frequency between the data transmission device 100 and the data reception device 200. Therefore, when the reference time in the data receiving apparatus 200 is delayed in response to the change in the remaining amount of data, the TS packet read control from the storage unit 10 fails. Specifically, a phenomenon that the jitter of the TS packet generated on the network 300 cannot be absorbed, and the reproduced image in the subsequent TS packet reproducing device is disturbed.

  Therefore, when a change in the transmission rate of the TS packet input via the network 300 is detected and the transmission rate changes greatly, the data reading in the storage unit 10 is performed by masking the control in the storage state detection unit 40 or the like. It is important to avoid bankruptcy. The apparatus and method according to the embodiment of the present invention are configured to prevent failure of data read control from the storage unit 10 (hereinafter referred to as “data read failure phenomenon”).

  Therefore, in order to avoid the data read failure phenomenon, data receiving apparatus 200 according to Embodiment 1 detects the transmission rate of TS packets input via network 300 as follows. Hereinafter, a method for detecting the transmission rate of TS packets according to Embodiment 1 will be described.

  FIG. 4 shows changes in the transmission rate of TS packets when the digital VTR is switched from normal playback to high-speed playback (time t1), which is special playback, and from high-speed playback to normal playback (time t3). . In FIG. 4, the vertical axis represents the transmission rate and the horizontal axis represents time. During high-speed playback, the transmission rate of TS packets decreases as shown at times t1 to t3 in FIG. FIG. 5 shows the remaining amount of data in the storage unit 10 at that time. At the time of high-speed playback (time t1), the transmission rate of the TS packet decreases, so the frequency of reading data from the storage unit 10 is higher than the frequency of writing data, so the remaining data amount increases rapidly. (Time t1 to t2). During high-speed playback, the remaining amount of data is reduced by the control of the conventional storage state detection unit 40, and the count rate of the reference time of the timer 32 is reduced, so that the remaining amount of data is increased (time t2 to t2). t3). Then, when normal reproduction is resumed (time t4), the transmission rate of the TS packet increases, and the remaining data amount also increases. However, since the reference time in the data receiving apparatus 200 is delayed as described above, the storage capacity of the storage unit 10 temporarily increases toward the target value. At this time, since the TS packet output from the data receiving apparatus 200 cannot sufficiently absorb jitter generated on the network 300, a phenomenon that a reproduced image in a subsequent TS packet reproducing apparatus (not shown) is disturbed occurs.

  Therefore, in the first embodiment, as described above, the data transmission rate of the TS packet input to the data transmission apparatus 100 has greatly changed such that the reproduction output of the digital VTR is changed from normal reproduction to high-speed reproduction. The remaining amount of data in the storage unit 10 in the data receiving device 200 changes greatly. In the first embodiment, it is detected that the data transmission rate of the TS packet input to the data transmission device 100 has changed significantly from the change in the remaining amount of data in the storage unit 10, and the data reception in the storage state detection unit 40 is performed. By switching the reference time correction control in the device 200, the TS jitter generated in the network 300 can be compensated. Hereinafter, a method for detecting that the transmission data has become a special reproduction image from the remaining amount of data stored in the storage unit 10 will be described.

  First, the storage state detection unit 40 shown in FIG. 1 calculates the remaining amount of data in the storage unit 10. Specifically, the storage state detection unit 40 calculates the remaining amount of data in the storage unit 10 from the address at which the write process was last performed and the address at which the read process was last performed in the storage unit 10. Can do.

  For example, the memory of the storage unit 10 is configured with 8 lines as shown in FIG. 6 (actually, it is configured with 1096 lines in the first embodiment, but for simplicity of explanation) 8 lines). Note that the address of the lowermost line is “1”, and the address of the line increases by “1” as it goes to the upper stage. Therefore, in FIG. 6, the address of the uppermost line is “8”.

  In the memory having the addressed line as described above, as shown in FIG. 6, the address of the line on which the write process was last performed is “7”, and the line on which the read process was last performed is performed. Consider the case where the address of “3” is “3”.

In this case, the remaining data amount is as follows.
(Remaining data)
= (The address of the line where the last write process was performed)
-(The address of the line that was last read)
= 7-3
= 4

  Further, it is assumed that writing has been completed up to the top level of the memory, and writing processing has been performed again from the bottom level of the memory. In this case, as shown in FIG. 7, the address of the line on which the last write process is performed is “3”, and the address of the line on which the last read process is performed is “6”. Is considered.

In this case, the remaining data amount is as follows.
(Remaining data)
= (Maximum memory address)
+ {(The address of the line where the last write process was performed)
-(Address of the last read-out line)}
= 8 + (3-6)
= 5

As can be seen from the above considerations,
(The address of the line that was last written)
> (Address of the last read-out line)
In this case, the remaining data amount is as follows.
(Remaining data)
= (The address of the line where the last write process was performed)
-(The address of the line that was last read)

Also,
(The address of the line that was last written)
<(The address of the line that was last read)
In this case, the remaining data amount is as follows.
(Remaining data)
= (Maximum memory address)
+ {(The address of the line where the last write process was performed)
-(Address of the last read-out line)}

  By using the above calculation formula, it is possible to obtain the remaining amount of data using the line address even for a memory having a finite amount.

  Next, clock synchronization control in the storage state detection unit 40 will be described. In the first embodiment, the storage state detection unit 40 measures a change in the remaining amount of data in the storage unit 10 for a predetermined period. Specifically, the change in the remaining amount of data is integrated for a predetermined period. Then, a difference value between the integration result measured last time and the integration result measured this time is measured, and the clock synchronization control algorithm is changed depending on the magnitude of the difference value. Here, the reason why the clock synchronization control algorithm is switched depending on the magnitude of the difference value will be described. For example, when a VBR TS packet is input, the amount of data of the TS packet that is input instantaneously changes. Therefore, the change in the remaining amount of data in the storage unit 10 is caused by the change in the data transmission rate of the input TS packet, in addition to that based on the deviation between the reference clocks in the data transmission device 100 and the data reception device 200. Swing. Therefore, even when the difference value of the integration result fluctuates greatly, it may occur because the input TS packet is VBR. Therefore, in the first embodiment, attention is paid to the change in the difference value of the integration result. If the difference value increases greatly because the input TS packet is VBR (for example, when the remaining data amount is large), the average data transmission rate of VBR is almost equal. However, the remaining data amount does not increase monotonously, but the integrated value of the remaining data amount is negative (in the direction in which the remaining data amount decreases) at the next measurement or the next measurement. .

  On the other hand, for example, in the case of the above-described digital VTR (when changing from normal reproduction to high-speed reproduction), the integration result is large and changes monotonously. The first embodiment is configured to detect a change in the data transmission rate of the TS packet input to the data transmitting apparatus 100 based on the change in the difference value.

  Next, processing when it is determined that the data transmission rate of the TS packet has changed will be described. First, when the storage state detection unit 40 determines that the data transmission rate has changed, the storage state detection unit 40 notifies the control unit 33 and the timer 32 accordingly.

  The timer 32 stops adding / subtracting the offset value to / from the update value. That is, the control unit 33 extracts a change in the remaining amount of data detected by the storage state detection unit 40, and when the change is greater than a predetermined threshold and the change is a monotonic change, The update value is not changed, and a data read timing signal that gives a timing for reading data from the storage unit 10 is generated using the internal time measured by the timer 32. The storage state detection unit 40 may set the predetermined threshold according to the magnitude of the change in the remaining amount of data with respect to the average value determined from the change in the remaining amount of data. At this time, the timer 32 performs normal count-up. Therefore, the timer 32 operates regardless of the remaining amount of data in the storage unit 10. The control unit 33 outputs a data read timing signal to the storage unit 10, and time information is first read from the storage unit 10.

  The time information is input to the time information separation unit 20 and then input to the comparison unit 31. The comparison unit 31 compares the time indicated by the time information with the output value of the timer 32 that has started normal count-up, and the time indicated by the time information is equal to the internal time that is the output value of the timer 32 (the time information is If the time indicated by the time information is smaller than the internal time that is an output value of the timer 32 (time indicated by the time information <internal time), the comparison unit 31 sends the control signal to the control unit 33. Output for.

  The control unit 33 outputs a data read timing signal to the storage unit 10 and simultaneously outputs a valid signal to the TS packet reproducing device (not shown).

  The storage unit 10 receives this data read timing signal, outputs a TS packet of 188 bytes, and thereafter updates the data read address to the address of the next time information. A TS packet reproducing device (not shown) that has received the valid signal captures this TS packet.

  In addition, time information of the next TS packet is output to the time information separation unit 20, further output to the comparison unit 31, and compared with the output value of the timer 32.

  The above operation is repeated. When it is determined that the change in the data transmission rate is within a predetermined range, the storage state detection unit 40 determines that the data transmission rate of the input TS packet has converged almost uniformly, and starts the clock synchronization control. A control signal is output to the timer 32. In response to this, the timer 32 returns to the clock synchronization control mode in which the offset value is added to or subtracted from the update value so that the remaining amount of data in the storage unit 10 is maintained in the vicinity of half of the storage capacity.

  As described above, the data reception device 200 according to Embodiment 1 is configured to detect a change in the data transmission rate from the remaining data amount of the data stored in the storage unit 10, and thus the storage state detection unit 40 Thus, the clock synchronization control performed in the network 300 can be controlled without breaking down, and the TS jitter generated in the network 300 can be compensated. Therefore, even when the data transmission rate of the TS packet changes remarkably, there is an effect that the TS packet can be transmitted without causing a phenomenon that the reproduced image in the subsequent TS packet reproducing device is disturbed.

Embodiment 2. FIG.
In the data receiving device according to the first embodiment, the storage state detection unit 40 uses the storage unit 10 to determine the line address that has been last written and the line address that has been last read. The remaining amount of data in the storage unit 10 was calculated. However, in the data receiving device according to the second embodiment, the storage state detection unit 40 determines the data in the storage unit 10 based on the number of times the write process has been performed and the number of times the read process has been performed in the storage unit 10. Calculate the remaining amount. Specifically, the storage state detection unit 40 in the second embodiment adds “1” when writing of data for one TS packet to the storage unit 10 is completed. In addition, when reading of data for one TS packet in the storage unit 10 is completed, “1” is subtracted.

  For example, it is assumed that the number of times data is written to and read from one memory packet in the storage unit 10 is the same. In this case, the difference between the two times is “0”. This means that the remaining amount of data in the storage unit 10 is “0”. If the TS packet has never been read, the number of times data for one TS packet has been written is the remaining data amount in the storage unit 10.

  As described above, the storage state detection unit 40 according to Embodiment 2 stores the storage unit 10 based on the number of times the TS packet has been written to the storage unit 10 and the number of times the read process has been performed. The remaining amount of data is calculated. Therefore, since the storage state detection unit 40 according to the second embodiment can be easily configured with an adder or the like, the circuit configuration can be prevented from becoming more complicated than the storage state detection unit 40 according to the first embodiment. .

  In the first and second embodiments, the case where IEEE1394 is used as the TS packet input network and the wireless LAN is used as the network 300 has been described. However, the communication method is not limited to the above, and the present invention may be applied to a wired network such as Ethernet (registered trademark), high-speed PLC (power line communication), UWB (ultra-wide band wireless), and the like.

It is a block diagram which shows roughly the structure of the packet data transmission / reception system containing the data receiver which concerns on Embodiment 1 and 2 of this invention. It is a figure for demonstrating the TS packet to which time information is attached. (A)-(c) is a figure for demonstrating the transmission state of TS packet. It is a figure which shows the time change of a data rate roughly. It is a figure which shows roughly the time change of the data remaining amount in a memory | storage part. FIG. 7 is a diagram (No. 1) for describing a remaining data detection process according to the first embodiment; FIG. 10 is a diagram (No. 2) for describing the remaining data detection process according to the first embodiment;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal of data transmission device, 2 Time information addition part of data transmission device, 3 Timer of data transmission device, 10 Storage part, 20 Time information separation part, 30 Data read timing generation part, 31 Comparison part, 32 Timer, 33 Control unit, 40 storage state detection unit, 100 data transmission device, 200 data reception device, 300 network.

Claims (10)

A storage unit for storing packet data including time information transmitted from a data transmission device via a network;
A storage state detection unit for detecting the remaining amount of data in the storage unit;
A timer that measures the internal time,
In a data receiving device having a control unit,
The timer corrects a deviation in the reference time between the data transmitting device and the data receiving device by adding or subtracting an offset value to or from the updated value,
The control unit extracts a change in the remaining amount of data detected by the storage state detection unit, and when the change is greater than a predetermined threshold and the change is a monotonous change, an update value of the timer A data receiving device that generates a data read timing signal that gives a timing for reading the data from the storage unit, using the internal time measured by the timer without changing. A time information separating unit that separates the data read from the storage unit into the time information and the packet data body portion other than the time information;
A comparison unit that compares the internal time measured by the timer with the time indicated by the time information separated by the time information separation unit;
The control unit generates the data read timing signal when the comparison result in the comparison unit indicates that the internal time measured by the timer is equal to or greater than the time indicated by the time information. The data receiving apparatus according to claim 1, wherein the data is read from the storage unit. The storage unit is a memory partitioned by a plurality of lines,
The storage state detection unit is configured to store the remaining data based on an address corresponding to the line of the memory where the data writing process has been performed and an address corresponding to the line of the memory where the data reading process has been performed. The data receiving device according to claim 1, wherein the data receiving device is detected. The storage state detection unit includes the number of times data processing for one packet data is written to the storage unit, and the number of times data processing for one packet data is read from the storage unit. The data receiving device according to claim 1, wherein the remaining amount of data is detected based on the data. The storage state detection unit sets the predetermined threshold according to the magnitude of the change in the remaining amount of data with respect to an average value determined from the change in the remaining amount of data. The data receiving device according to any one of the above. Storing packet data including time information sent from the data transmission device to the data reception device via the network;
Detecting the remaining data amount of the stored data;
Measuring internal time with a timer;
Correcting the deviation of the reference time between the data transmitting device and the data receiving device by adding / subtracting an offset value to / from the updated value of the timer, and
When the change in the remaining amount of data is extracted, and the change is greater than a predetermined threshold value and the change is a monotonous change, the updated value of the timer in the step of correcting the deviation of the reference time is changed. And a data read timing signal that gives a timing for reading the stored data, using the internal time measured by the timer. Reading the stored data and separating the time information and the packet data body other than the time information;
Comparing the internal time with the time indicated by the separated time information;
A step of generating the data read timing signal and reading the stored data when the result of the comparison is that the internal time is equal to or greater than the time indicated by the time information. The data receiving method according to claim 6, wherein: The detection of the remaining amount of data is executed based on an address corresponding to the line of the memory where the data writing process has been performed and an address corresponding to the line of the memory where the data reading process has been performed. The data receiving method according to claim 6, wherein: The detection of the remaining amount of data is executed based on the number of times data writing processing for one packet data is performed and the number of times data reading processing for one packet data is performed. The data receiving method according to claim 6 or 7, characterized in that The data according to any one of claims 6 to 9, wherein the predetermined threshold value is set according to a magnitude of a change in the remaining amount of data with respect to an average value determined from a change in the remaining amount of data. Reception method.

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