JPH02132985A - Transmitting system for character broadcasting signal - Google Patents

Abstract

PURPOSE:To secure the reproduction of a clock signal and a framing timing at a receiver side by relating the clock frequency of a character signal multiplexed to a PAL system television signal to a color sub-carrier frequency. CONSTITUTION:An aimed signal is obtained by a PLL circuit composed of a color sub-carrier frequency-divider 107 of a PAL system television signal and a VCO 110. The signal is adjusted so that the phase of a data output signal can be correctly outputted, by a phase adjusting device 111. For the signal, every frame bucket signal is outputted by the same timing for the horizontal synchronizing timing. With the output as a clock signal, a DMA controller 113 is controlled by a frame timing and an H synchronization, the data are outputted by the above-mentioned timing, and as such, an address signal and the control signal are outputted. By the signal from the controller 113, the data, which is already accumulated in a memory 114, are outputted and multiplexed by a multiplexer 117.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a teletext signal transmission system, and in particular to a PAL
This invention relates to a transmission system that has enhanced error correction capabilities for teletext broadcasting.

[Summary of the Invention] The present invention relates to a teletext signal transmission system,
In the conventional PAL television multiplex teletext broadcasting, it is a powerful error correction code used in Japanese teletext broadcasting (
272, 190) code could not be applied, we extracted a teletext clock signal with a simple frequency relationship from the color subcarrier of the PAL signal, and also reduced the block length of the signal part of one packet to 272 bits. It is the same error correction code as the Japanese system (272
, 190) codes can be applied, thereby providing a powerful error correction effect.

Furthermore, regarding the encoding and other aspects of the present invention, since the block length is the same as that in Japan, there is an advantage that the same system can be used as is.

[Conventional technology] Conventional PAL teletext broadcasting employs a British system called System B by CCIR.

Since this method does not place much emphasis on error correction, it is unsuitable for reception systems in locations with severe reception conditions, or for systems in countries such as China that use ideograms.

On the other hand, since the Japanese system has been developed with the emphasis on error correction from the beginning of system development, (272
, 190) code, we were able to complete a system that is extremely robust against errors.

In this Japanese system, the continuity of the clock signal and the phase continuity of the framing code are maintained between each packet. ) code correction ability could not be fully utilized, but by detecting the framing code timing using forward protection and backward protection, the correction ability of the (272, 190) code can be activated. There is.

Therefore, impulse noise and random noise
Even if a detection error occurs in the framing code, the framing timing can be secured as long as detection errors do not occur continuously.

On the other hand, in systems in countries such as the UK, signal processing is performed only within one packet, so the clock frequency has no simple frequency relationship with the color subcarrier frequency, and errors may occur in the framing code. If the framing timing cannot be obtained, all signals in that packet will be lost. Moreover, for error correction codes, we only use extended codes (8.4) that have the ability to correct errors in 1 bit out of 8 bits for highly important codes or codes for program selection. , the other code parts only use an error detection code that detects an error in 1 bit out of 8 bits.

Therefore, there have been problems such as incorrect characters being reproduced or important information not being sent at locations with severe reception conditions.

[Problems to be Solved by the Invention] The drawbacks of the above-mentioned PAL teletext will be described in detail below.

For text broadcasting multiplexed onto the conventionally known PAL television signal, the British-developed "C:ee"
There is a teletext broadcast called "Fax".In this system, the 6th
As shown in the figure, the teletext signal is 6.9375Mbps.
The first 16 bits are a clock run-in signal for bit synchronization, and the following 8 bits are a framing signal consisting of a fixed pattern to identify signal breaks.
Furthermore, it consists of a 336-bit information section, which is the contents of the signal. The IH period is exactly 444 bits.

For this reason, the British system does not specify a direct frequency relationship between the clock rate and the color sub-galleria.

In addition, although there is a certain frequency relationship between the clock rate and the horizontal synchronization signal frequency, reproducing the clock signal from the horizontal synchronization signal means that: ■ The gain of the APC circuit cannot be obtained.
This is difficult because the horizontal synchronization timing immediately after vertical synchronization causes subtle phase jitter.

For the above reasons, Ceefax adopts a reception method in which signal processing is performed on a packet-by-packet basis without taking into account the frequency relationship with the television signal. Therefore, it is not necessary to match the phases of the leading bits of the packet signals for each H as the sending number 3, and there is no problem even if the packet signals are multiplexed with different phases.

That is, on the receiving side, clock synchronization is achieved using the first 16 bits of the packet signal, and a framing pattern is extracted. When there is a 1-bit error in the framing pattern, it is possible to extract the timing, but when there is an error of 2 or more bits, the timing cannot be extracted, and the packet signal cannot be used at all.

Therefore, Ceefax has a major drawback in that the reception of the framing code is weaker than the Japanese system in which the reception of the framing code is performed using forward protection and backward protection. Naturally, if the reception ability of the framing code is low, no matter how strong the error correction ability of subsequent signals is, it is meaningless.

As described above, Ceefax does not give much consideration to error correction, and the character code after the framing code is simply a 7-bit code with 1 bit of parity added, and has only an error detection function. As mentioned above, PAL television multiplex teletext (Ceefax) is vulnerable to bit errors, and is not suitable for systems that transmit ideographs with many single characters such as Japanese or Chinese, or important A system for sending information. It has the disadvantage that it is not suitable for systems that transmit large amounts of information (for example, telesoftware that transmits computer programs).

Therefore, an object of the present invention is to provide a transmission system that improves the error correction ability of PAL teletext broadcasting.

[A Thousand Steps to Solve the Problem] In order to achieve the above object, the transmission method according to the present invention extracts a color subcarrier signal from a PAL television signal, and extracts a color subcarrier signal from a PAL television signal, and extracts a color subcarrier signal that is in a simple integer ratio with the color subcarrier signal. 16-bit clock run-in for generating clock signals for character signals and synchronizing clocks from a specific vertical blanking period. 8-bit framing code for determining framing timing, 190-bit information. 190
It is characterized by sequentially transmitting a total of 296 bits, such as an 82-bit parity signal calculated from bit information.

[Function] In the present invention, a clock signal having a certain frequency relationship with the color subcarrier of a PAL television signal is adopted, and the continuity of the clock signal is maintained, and the clock frequency itself is different from the IH of the PAL signal. It is designed to carry the same (272,190) code used in Japanese teletext broadcasting, and is intended to have the same strong error correction ability as Japanese teletext broadcasting.

[Example] Hereinafter, the present invention will be explained in detail based on Examples.

First, the basic principle of this embodiment will be explained.

The frequency fsc of the color subcarrier signal in the PAL television signal is defined as fsc"4433618.75Hz.The clock frequency of the teletext signal is defined as fsc"4433618.75Hz.
It is desirable that CL be in the form fCL=1·fSC. However, m and n are simple integers. In the PAL system, the period T of one frame is as follows.

The conditions for maintaining the continuity of the clock signal are as follows.

TcLx N = M x 40x 10-3 However,
N is the number of clocks in the period considered here, M
indicates the number of frames when considered in units of one frame. Therefore, = −x M x 177344.
75m, and N must not satisfy the above formula and must be an integer.

When M=1, that is, the clock signal is continuous in one frame as m/n-12/11.16/11.20
/11, etc., and the bit rate at this time is 4.
．． 836675MHz, 6.44890MHz, 8.0
61125MHz, and 5 1” AL signals can be multiplexed.
272 + 8 + 16 = in a period of about 4 microseconds
It is not permissible to multiplex 296 bits.

Next, in the case of M=2, that is, the clock signal is continuous in two frames is m/n-12/11, 14/11
．． 16/11 etc. Here, the values other than m/n-14/11 are the same as in the case where the frames are continuous in one frame.

The bit rate in the case of m/n=14711 is 5.
The bit rate is 8427875 MHz, which is almost equal to the bit rate of Japanese and Japanese teletext broadcasting, 5.727 M}Iz. Also, the number of bits that can be multiplexed in a period of about 54 microseconds is 304.
It is 7 bits, which is a bit rate that can sufficiently multiplex the necessary 296 bits.

The IH of a PAL signal is exactly 64 microseconds. Therefore, the number of bits that can be multiplexed to IH is 64x5.642
7875 = 361.1384 bits, Japan's 3
The value is approximately equal to 64 bits. If a continuous phase clock at this bit rate is multiplexed into IH by 296 bits, the phase of the first bit will shift by about 1 bit after 8H. The number of bits after 1 frame is 225711.5 bits, and after 2 frames,
Compared to the first frame, the phase is shifted by 0.5 bit. Moreover, after the third frame, the phase becomes the same.

As mentioned above, regarding the method of multiplexing character signals on PAL television signals, in order to obtain the same strong error correction ability as in Japan, the color subcarrier 1471
It is better to use a method in which the frequency of 1 is the bit rate.

In the PAL system, teletext can be multiplexed in the vertical blanking period of fields 8H to 25H and their paired fields. Therefore, if 272-bit packet signals are multiplexed sequentially from 8H, the packet period will be 36
By using 2 bits, the multiplexing position will be sequentially shifted for each H (see FIG. 2). The amount of this deviation is
This corresponds to 0.8616 bits. Therefore, the amount of deviation up to 25H is 0.86+6X17=14.6472 hits. The amount of time equivalent to this minute is 14.6472 x
1/5.6427875 = 2.595738365
(u sec). Therefore, by providing this much time margin for the last part of the packet signal multiplexed on the first 8th H, the packet signal multiplexed on each H is 36.
If the data is multiplexed every second bit, handling on the receiving side becomes easier.

However, in this case, from the first bit multiplexed at the 8th H,
The total length as seen on the same H up to the final bit multiplexed on the 25th H is (296+14.6472)/5.81127875-
55.05208197 (μsec).

On the other hand, since it takes 10 microseconds to the end of a color burst in a PAL television signal and 64 microseconds in IH, the maximum multiplexable period is only 54 microseconds. On the other hand, since the amount of deviation exceeds 54 microseconds, multiplexing is impossible as it is.

Next, if packet signals are multiplexed at a period of 361 bits (see FIG. 3), the phase will advance by 0.1384 bits for each H. In this case, 81]
Considering 188 up to 5H, (296 plus 17
X Q. l384)/5.6427875-52.8
73300 [i5 (μsec)], which is included in the above 54 μs. However, since it takes 10 microseconds to the last part of the color par, the time width that can be multiplexed is 54 - 52.8978275 = 1.102172
5 (μsec), and although it is not impossible, there is little margin.

Note that the original length of one packet is 296 bits, which is 296 x
1/5.6427875 = 52.4563436
1 (μsec). In the case of Figure 3 above, 52.87330065-52.45634361-0
．． 41695704 (μsec), which is only slightly longer.

Also, compared to "Ceefax" shown in Figure 6, it is 52
．． 87330065-51.89189189-0.9
8140876 (μsec), which is an extension of the data length of 1 microsecond or less. Therefore, Ceefax
The packet length is almost the same as that of

Furthermore, the beginning of each packet may be changed for each packet. For example, the clock run-in may start from the 361st bit in the 9th H following the 8H, and the clock run-in may start from the 362nd bit in the 108th.

In this way, the clock run-in starts at each H every 361 bits, and the clock run-in starts every 362 bits at each H.
If clock run-in starts at
If it is set every 2 bits, there will be a difference of 6 to 7 times, so
Clock run-in starts every 361 bits H is 6~
After 7H, one packet whose clock run-in starts after 362 bits may be mixed in.

Since the above description is directed to all Hs that can be multiplexed during the vertical retrace period, it goes without saying that if the multiplexed H is to be limited, multiplexing for every 361 bits or 362 bits is sufficient.

Furthermore, even with the above-described method, if there is no margin for color subcarriers, the 272-bit information block may be shortened and used. For example, 272 -8=264
(bits) A block length such as 272-16=256 (bits) is also considered. Also, since the information bits of the (272.190) code are 190 bits and are not in units of bytes, 272 - 6 = 21i6 (bits) 272. -14
=258 (bits), etc., the information bits will be 184 bits each = 23 bytes, and 176 bits = 22 bytes, making it easier to handle. In such a case, it is sufficient to arrange the signals from the clock run-in for each H at 361-bit or 362-bit intervals as described above. The above has described a multiplexing method of multiplexing vertical blanking at the start of one frame, but vertical blanking of the next field must also be considered. If the first line number of the next field is 3138,
The number of H that can be multiplexed is 17H from the 321st H. Figure 4 shows these relationships. However, if the next packet simply continues with 361 bits or 362 bits, the 321st to 8th bits will be significantly shifted, which is inconvenient. Therefore, it is determined that multiplexing is performed after a certain clock length from the 8th H. moreover,
The next field will be multiplexed from the 633rd H, but in this case too, multiplexing will be performed after another fixed clock length. However, in this case, for the first field,
The phase of the clock signal will be shifted by 0.5 bit. This means that the 14/11 X fsc defined here is 2
This is because it has the property of having one period in a frame.

In Fig. 4, considering 8H as the standard, the deviation in pit vine units at 321H in the next field is 313 x 64 x 5.6427875 = 11
3036.3192 (bits). Also, after the next field 312 H, 312 X64/5.6427875 = 112675
．． 1808 (bits) Therefore, the point at the same timing one frame later is 113036.3192+112675.1808-2
The difference is 25711.5 (bits). The deviation of less than 1 bit position at these times is 0.0565677
8675 microseconds, 0.03204090177 7
It takes 7 seconds to cum, 0.08860868852.

Therefore, the clock run-in phase of the packet signal multiplexed at the 313Hth clock is set to the 113036th clock,
Further after 312H (i.e., after 1 frame)
If the phase of the pit clock is shifted by half a bit after 112674.5 bits (that is, one frame),
! The phase is continuous in the frame period.

FIG. 5 is a diagram showing the relative positions of each packet signal.

FIG. 1 shows a circuit for generating a television signal according to the invention. In the tree diagram, 101 is a color subcarrier (4.43361875MHz) signal, 102 is a frame pulse for shifting the clock phase by half a bit every frame, 103 is a horizontal synchronization signal for counting the number of H, and 104 is a Character data sent from the computer, 105 is a normal PAL television signal, 106 is a line number designation signal for designating multiple H, 107 is a frequency dividing circuit, 108 is a phase difference detection circuit, 10
9 is a frequency dividing circuit, 110 is a voltage controlled oscillator (VCO),
111 is a phase adjustment circuit for adjusting the clock phase;
112 is a phase switching circuit for shifting the clock phase by half a bit for each frame, and 113 is a DM for reading data from the memory 114 at the timing already explained.
A controller, 114 is a memory for temporarily storing transmission data, 115 is an address and control signal for controlling the memory 114, 116 is multiple packet data, and 117 is for multiplexing on a specified line of a television signal. This shows the multiplexing device. Next, we will explain the operation of this signal generator. PL consisting of color subcarrier frequency divider 107 and VCOIIO for PAL television signal
The desired 5.8427875 1z signal is obtained by the L circuit. This signal is adjusted by the phase adjuster 111 so that the phase of the data output signal is correctly output.

This signal is shifted by a half bit for each frame by the frame pulse, so that each frame packet signal is output at the same timing with respect to the horizontal synchronization timing.

Using this output as a clock signal, the DMA controller 1
13 is controlled by frame timing and H synchronization, and the address signal and control signal from the DMA controller 113 are outputted so that data is outputted at the timing described above.

This signal from the DMA controller 113 causes the data already stored in the memory 114 to be output.
The multiplexer 117 multiplexes the television signal onto designated lines. Naturally, since the clock run-in and framing code is a fixed No. 3, it is not output from the memory 114, but rather
It may also be output from a fixed storage area such as OM.

The configuration shown in FIG. 1 is a basic configuration example, and the memory output data 116 is band-limited by a cosine roll-off filter or the like (not shown) at the input section of the multiplexer 117. Of course you should accept it. [Effects of the Invention] As explained above, according to the invention, by associating the clock frequency of the character signal multiplexed with the PAL television signal with the color subcarrier frequency, it is possible to reproduce the clock signal on the receiver side. , the framing timing can be regenerated reliably.

For example, if the clock signal frequency is (14/u)bc, the framing timing of the television signal is (40/u)
By inverting the clock phase every 40 msec), the timing of the beginning of the packet signal can be made to match every 40 msec by shifting by half a bit, thereby making it easier to handle the signal at the receiver. Thus, one packet is 296, which is the same as the Japanese teletext signal.
Bits can be multiplexed and it is a powerful error correction method (272
, 190) codes can now be applied. Also, receive {X
The only difference in the machine is the way it receives signals; other than that, the IC developed by Japan's Teletext Broadcasting Corporation can be used as is. Furthermore, the encoding method can be adopted as is.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a circuit that generates a television signal according to the present invention. Figure 2 is a diagram showing an example of multiplexing each packet at 362-bit intervals. Figure 3 is a diagram showing an example of multiplexing each packet at 361-bit intervals. Figure 4 is a diagram showing vertical blanking of a PAL television signal, Figure 5 is a diagram showing the relative position of each packet signal, and Figure 6 is a teletext broadcast called "Ceefax". FIG. 107... Frequency divider circuit, 108... Phase difference detection circuit, 109... Frequency divider circuit, 110... Voltage controlled oscillator (VCO), 111...
Phase adjustment circuit, 112... Phase switching circuit, 113... DMA controller, 114... Memory, 117... Multiplexer, 118... Television signal multiplexed with character signals.

Claims (1)

[Claims] 1) Extract a color subcarrier signal from a PAL television signal, generate a character signal clock signal having a simple integer ratio with the color subcarrier signal, and generate a clock signal from a specific vertical blanking period. 16-bit clock run-in for synchronization, 8-bit framing code for framing timing, 19
0 bit information, 8 calculated from the 190 bit information
A teletext signal transmission system characterized by sequentially transmitting a total of 296 bits such as a 2-bit parity signal.