JP2696950B2 - Data transmission equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a data transmission device.

2. Description of the Related Art Conventionally, when a video signal is transmitted via a transmission line, a codec (hereinafter, referred to as a codec) converts a baseband video signal to a high signal in order to use the transmission line efficiently. Efficiency coding to reduce its bit rate,
It was adapted to the pit rate of the line.

On the other hand, as a video signal source, there is a video recording / reproducing device of an analog recording system, a so-called analog VTR. Video recording / reproducing apparatuses using a small number of digital recording methods, so-called digital VTRs, have been developed and used. Digital VT
In R, the bit rate is reduced by high-efficiency coding, like the codec in the data transmission system, to increase the recording time. Therefore, the digital VT
When R is used as a video signal source, a system configuration is adopted in which high-efficiency coded digital data is once decoded, high-efficiency coding for video transmission is performed again, and the data is transmitted to a transmission line. Performing transmission processing to a transmission line at the stage of a high-efficiency coded signal in a reproduced signal is advantageous from the viewpoint of signal processing time, hardware, signal distortion, and the like.

Digital VTRs generally include an A / D converter that digitizes analog video signals, a recording processor that mainly performs high-efficiency encoding of digital data by the A / D converter, and an electromagnetic converter that actually performs magnetic recording and reproduction. System, a reproduction processing unit that mainly performs decoding processing corresponding to high-efficiency encoding on the reproduction data by the electromagnetic conversion system, and a D / A conversion unit that converts the reproduction data by the reproduction processing unit into an analog video signal. When considering the connection to the transmission line as
The digital data being processed in the reproduction processing unit or the output data of the reproduction processing unit is connected to a transmission line via a codec (or a high-efficiency encoder for transmission).

[Problems to be solved by the invention]

In general, whether transmitting analog signals or digital data, in an information transmission system the bit rate of the transmission line is first determined and the transmitting device
The information is transmitted according to the bit rate of the transmission line. Therefore, even when the reproduction data of the digital VTR is to be transmitted to the transmission line as described above, the operation of adjusting the bit rate is indispensable. Specifically, if the reproduced data is transmitted as it is on the transmission format of the transmission line, the total bit rate often slightly exceeds the bit rate of the transmission line. Alternatively, encoding has to be performed with higher efficiency, resulting in deterioration of image quality.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a data transmission apparatus capable of adapting reproduced data of a digital VTR to a bit rate of a transmission line without causing signal deterioration.

[Means for solving the problem]

The data transmission apparatus according to the present invention inputs a code string in units of blocks each including a predetermined amount of high-efficiency encoded data, an additional code for restoring the predetermined amount of high-efficiency encoded data, and other codes. Input means, removing means for removing the other code in each block of the code string input by the input means, and additional code for transmission to the code string from which the other code has been removed by the removing means. , And output means for externally outputting the data in a unit amount for transmission.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows the recording format of the magnetic tape of the digital VTR, in which the magnetic tape 10 moves in the direction of arrow 12, at which time the magnetic head mounted on the rotating drum (not shown) scans in the direction of arrow 14, As a result, the magnetic tape 10
A track 16 is formed thereon. Within one track,
Reference numeral 18 denotes a recording area of a pilot signal (hereinafter, referred to as an ATF signal) for taking a tracking servo, 20 denotes a recording area of a CRI (Clock-Run-In) signal for pulling in a PLL, and 22 denotes video data and audio. Data recording area,
Reference numeral 24 denotes a recording area for a CRI signal, 26 denotes an audio data recording area for post-recording, and 28 denotes a recording area for an ATF signal. Guard space areas 30, 32, and 34 are provided between the areas in order to absorb variations in the mechanism of the recording / reproducing apparatus.

FIG. 3 shows details of the video and audio recording area 22 or the audio recording area 26 of the recording format of FIG. That is, a synchronization code SYNC35 and an identification code ID36 indicating position information of image data and the like are added before the recording data 37 for a predetermined number of words, and an error generated in a recording / reproducing process is corrected after the synchronization code SYNC35. And a parity 38 is added, and a single synchronous block 39 is constituted as a whole. Recording area
A plurality of synchronization blocks are recorded in 22,26.

For example, in the case where the actual recording area extends over 180 ° in the winding angle of the magnetic tape around which the magnetic tape is wound around the rotating drum, one synchronous block has a winding angle of about 0.70 °.
The length of each area in this case is represented by the number of synchronous blocks as shown in Table 1. For reference, the corresponding winding angles are also shown.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. A signal reproduced by the reproducing head 40 is amplified by a reproducing amplifier 42 and equalized in waveform by an equalizer 44. PLL circuit 4
6 outputs a clock phase-synchronized with the clock component of the CRI signal in the recording areas 20 and 24.
With the clock from the circuit 46, each data of the output of the equalizer 44 is identified and reproduced. The output of the identification circuit 48 is still highly efficient encoded data.

The time axis correction circuit (TBC) 50 corrects the time axis of the output of the identification circuit 48 according to the reference clock from the crystal oscillator 52, and applies it to the buffer memory 54. Buffer memory
To 54, data of 258 synchronization frames shown in Table 1 is applied per track.
The filter 54 removes an overhead portion (that is, an ATF signal, a CRI signal, and a portion corresponding to a gap) other than a portion necessary for data recovery on the receiving side, and outputs the signal at a timing according to a reference clock from the crystal oscillator 52. That is, the buffer memory
Numeral 54 outputs the SYNC, ID, data, and parity portions shown in FIG.

The overhead adding circuit 56 is a circuit that processes the output of the buffer memory 54 so as to conform to the transmission standard via the transmission line and adds an overhead section for reception processing. Adds one unit of overhead to a plurality of synchronous blocks output from the buffer memory 54. The output of the overhead adding circuit 56 is sent from an output terminal 58 to a transmission line. FIG. 4 shows the format of the signal at the output terminal 58. In FIG. 4, reference numeral 60 denotes an overhead portion added by an overhead adding circuit, and 61 denotes a user's data portion, which constitutes one frame 62. The signals 35 to 38 of the synchronous block shown in FIG. 3 are allocated in the user's data section 61.

In this embodiment, the ratio of the data transmitted to the transmission line to the total data reproduced from the magnetic tape is (240 + 3)
+3) /258≒0.95, and the bit rate can be reduced by about 5%. At this level of value, the effect seems to be small at first glance, but as explained below, the actual effect is enormous. That is, a digital VTR having a total bit rate of 138 Mbps (Kashida et al., "Experiment of digital recording system for high-definition television signals," Television Society Technical Report vol. 11, No.
24, VR87-34), a transmission line (H4 line) with a user data section 61 bit rate of 135 Mbps
In the case of transmission using, the bit rate on the VTR side is higher than the bit rate of the transmission line, and transmission cannot be performed as it is, but in this embodiment, 138 × 0.95 ≒ 131
(Mbps) and can be transmitted without signal deterioration.

FIG. 5 is a block diagram showing the configuration of another embodiment of the present invention for performing transmission on a transmission line having a lower bit rate. The difference from FIG. 1 is that parity 38 for error correction is used.
Is also eliminated. 5, the same components as those in FIG. 1 are denoted by the same reference numerals. 53 is an error correction circuit
The error correction is performed using the parity 38 with respect to the code string that has been time-axis corrected by the time-axis correction circuit 50, and is applied to the buffer memory 54. The error correction method for the VTR is based on the assumption that the error rate in the VTR is high.For transmission lines whose error rate is relatively low compared to the VTR, the transmission line is overloaded and the transmission frame The error correction function included in the head unit 60 is sufficient. FIG. 6 shows a transmission format according to the embodiment of FIG.

If the overhead section 60 of the transmission frame does not have an error correction function, a low redundancy error correction code corresponding to the error rate of the transmission line is added after the data 37 and transmitted. Is also good.

In the above description, a TV video signal has been described as an example, but the present invention is not limited to this, and other data such as a facsimile signal and a still image signal may be used. The source of the transmission data may be a reproducing device such as an optical disk or a magneto-optical disk.

[Effects of the Invention] As can be easily understood from the above description, according to the present invention, a portion of a code sequence from a data source which is not involved in data reproduction on a receiving side is removed and transmitted. Since the code string is formed, the size of the hardware is not increased and the signal is not deteriorated in order to match the bit rate of the transmission line. Therefore, it is possible to provide a compact transmission device with no or little signal degradation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the format of a track of a digital VTR, FIG. 3 is the contents of one synchronous block in a digital VTR, and FIG. FIG. 5 is a block diagram showing the configuration of a modified embodiment of the present invention, and FIG. 6 is a transmission format according to the embodiment shown in FIG. 40: playback head, 42: playback amplifier, 44: equalizer, 46: PLL circuit, 48: identification circuit, 50: time axis correction circuit, 52: crystal oscillator, 54: buffer memory,
56: Overhead addition circuit, 58: Output terminal

Claims (1)

(57) [Claims] 1. An input means for inputting a code string in units of a block composed of a predetermined amount of high-efficiency encoded data, an additional code for restoring the predetermined amount of high-efficiency encoded data, and a block of other codes. Removing means for removing the other code in each block of the code string input by the input means, and adding an additional code for transmission to the code string from which the other code has been removed by the removing means, An output means for externally outputting the data in a unit amount for transmission.