JPS5915388A - Digital signal transmission system using catv line - Google Patents

Abstract

PURPOSE:To realize transmission of a large quantity of digital signals with free division of the corresponding block length, by reducing the redundancy of an error correction code of a CATV system. CONSTITUTION:The digital signals are transmitted to plural channels, and at the same time an error correction code is added to each channel to increase the block length of an information signal and to reduce the redundancy occupied by the error correction code. Thus the block length of the information signal can be used with free division. The figure A shows a stereo channel containing 34 bits in all of an L channel (16 bits), an R channel (16 bits) and the service bit (2 bits). The figure B shows a word containing 162 bits of channels A, B, C and D (34 bits each), a BCH code (16 bits) and a synchronizing (SYNC) code (10 bits). The figure C shows a frame containing 32 words (5184 bits). Thus the signal formats are shown in these figures. The transmission capacity (transmission speed) using 2 series (quadruple level) of such signal formats is within an allowable range. This is possible enough to transmits the digital signals via a transmission line having a band width of a channel of a TV.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a digital signal transmission system using a CATV (cable television) line, and particularly to a digital signal transmission system suitable for transmitting digital audio signals using a CATV line. Regarding signal transmission methods.

1N console technology and its problems Presently, the progress of digital audio technology is remarkable, and in contrast to these technologies, 1gPcM audio (digital audio) has been promoted to meet the expectations of music lovers, such as PCM day recorders and DAD (
Digital audio discs) etc. have been developed.

By the way, such digital audio signals have a high bit rate, that is, a wide bandwidth, and therefore can be transmitted using DBS (satellite broadcasting), etc., which can use a wide band. is considered to have many problems.

It is also considered possible to transmit data using the CAT line, but this has not yet been realized. On the other hand, the signal format that is normally used in digital audio systems generally adds an error code (A1) to each channel, so that data that uses a high-quality transmission line such as a CATV system is Communication lines have a high degree of redundancy.

Purpose of the Invention The present invention focuses on the fact that CATV systems can generally transmit high-quality data with a good S/N ratio and little interference, and is capable of transmitting a variety of data by reducing the redundancy of error correction signals. The present invention provides a digital signal transmission system using a CATV line that can transmit digital signals in multiple formats and freely divide the block length in a signal format suitable for such high quality transmission lines. .

Summary of the Invention The present invention makes it possible to transmit digital signals through multiple channels in a digital signal transmission system using CATV lines, and also increases the block length of information signals by adding error correction codes to each of these multiple channels. , the redundancy occupied by the error correction code is reduced, the block length of the information signal can be freely divided and used, and the signal format is flexible and expandable.
Digital data communication, especially the transmission of digital audio signals, using CATv lines becomes possible.

EXAMPLE Hereinafter, an example of the present invention will be explained in detail based on FIGS. 1 to 7.

In this invention, the circuit components used in the current CA'ff system are utilized as much as possible, and costs can be reduced. Now, if we focus on the input/output comprehensive filter characteristics of the transmission line of the CATV system, we can see the characteristics as shown in Figure 1. In the figure, the color subcarrier fc (3,58M)
If the Nyquist point is set at Iz), the roll-off rate η
is expressed by the following equation.

b 4.5-3.58 η= −= −= 0.25 ・・・・・・(1
) a 3.58, approximately 3 at the color subcarrier level of 3.58MHz
Assuming that a filter with dB attenuation can be obtained,
Transmission speed is 3.5g x 1d x 2 x 2 = 14.32MBPS ・
...(2). Therefore, the maximum data 1 in the 6MHz transmission band, which is equivalent to one television channel,
For example, 16QAM or 4-level VSB (residual sideband) method is preferable for transmitting the signal. Here, the four-level Bell VSB method is considered to be the most preferable for the following reasons. In other words, the C/N ratio of the CATV line is good (sufficiently wide carrier can be used), ICs for television receivers can be used as birdware, and SWF for color television receivers can be used.
(Surface Acoustic Wave Filter) etc. can be easily obtained as the filter.

Although multilevel levels (e.g., 8-level, 16-level) are also possible, 4-level is optimal in consideration of the stability of the transmission line and circuit.

In addition, since the C/N of the CATv line and the interference characteristics of other TV/SOYON signals are sufficiently good, code amount interference is caused by reflected waves caused by deterioration of vSwR, envelope delay characteristics of the transmission line, and amplitude characteristics of the transmission line. This is thought to be due to the deviation from the standard value.

Therefore, in order to keep the code amount interference to a minimum value, a BTF (binary transparsal filter) is inserted on the transmitting side to equalize the input and output filter characteristics.

Figure 2 shows the signal format used in the present invention. A stereo channel consisting of 34 bits, for example, channels A, B,
C and D (both 34 bits), BCT (code (
16 bits), synchronous (5YNC) code (10 bits)
Figure 2C represents the signal format of one word consisting of 162 bits, and one frame consisting of 32 words (5184 bits). And the transmission valley using two series (i.e. 4-level levels) of such signal format... (transmission speed) is 4.4.1 XI O5X ((16X2+2)X4
+16+1. O1x2= 14.2884 MBPS・
...(3).

In other words, the permissible amount of transmission speed 1 expressed by the above equation (1)
Nffl, and can be sufficiently transmitted using a transmission line with the bandwidth of one television channel, that is, 6 MHz.

Note that, as will be described later, the same gate signal is configured to have a binary level number upon modulation.

Furthermore, most of the errors in CATV lines are due to noise and other code amount interference in lieu of television signal interference. Therefore, the data format is configured to make it easy to measure error states. In other words, an error correction code is added to each word, and the error correction code is, for example, 2.
(255.239) BCH with bit correction capability
:BCH of (152□, 136) with shortened I-do
A code is used in which 136 bits are information bits and 16 bits are check bits.

Therefore, as shown in Figure 3A, the signal distribution is, for example, J
Channel AK among channels A-D that make up the series
is a digital audio program (stereo) Pi
(16 bits for one channel at 44.1kHz),
Channel B has a digital audio program (stereo) P2 (44.1kHz, one channel)
Announcement information (monaural) (22.1 kHz 8 bit) P3 and guide information (monaural) (22.1 kHz 8 bit) P4 are time-shared on channel C, and facsimile P5 and 7 axim I are on channel D.
JP6 is inserted. Note that when two programs are selected at the same time, P3 and P4 are configured so that one of them is given priority depending on the importance and urgency of the contents. Also, regarding P5 and P6, one may be made i'l-first than the other. The father-sender side is determined by the two-bis bits (SB) of channels C and I].

In addition to the above-mentioned one series of four stereo channels A to channel D, when transmitting another four stereo channels, insert them on the side of Figure 3 B representing the other one series. Make it. Note that, if necessary, pseudo data for measurement may be inserted on the transmitting side as shown in FIG. 3B to contribute to error status checking on the receiving side.

FIG. 4 exemplarily shows the case of obtaining a signal format for transmission at four-value levels.

That is, in Fig. 4A, the signal configuration from channel A to channel D forming an l series (corresponding to Fig. 3A) is arranged, and in Fig. 4B, the signal configuration from channel E to channel H forming another l series is arranged. Arrange the signal configuration (corresponding to FIG. 3B). Then, by converting the binary levels of A and B in Figure 4 to 4-level levels, channels A, E1, B, F1, C, 01, D, and 11 coexist as shown in Figure 4C. so as to constitute one signal format. In this case, error correction for both series (Note 1)
The numbers are also configured to have four levels. In other words, go to Figure 4 〇 BCH1 code and BCH2 code of Figure 4B to Figure 4C
Convert to 4-value level and arrange as shown below. In this case, the synchronizing signal 5YNC is set to a binary level and is not converted to a 4-level level.

FIG. 5 and FIG. 6 show an embodiment of this invention.
FIG. 5 shows the configuration of the transmitting side, and FIG. 6 V shows the configuration of the receiving side.

First, to explain FIG. 5, input terminals (1) to (6)
) are supplied with the information of two consecutive programs P1 to P6, respectively, and audio analog signals from input terminals (1) to (4) are sent to an analog-to-digital converter (hereinafter referred to as A/D converter). An analog signal is converted into a digital signal at (7) to ←0 (referred to as a converter), while facsimile signals, for example, from input terminals (5) and (6) are
The signal is supplied to the multiplexer 09 via facsimile interface circuits 0η to α. Here, these signals are distributed to each corresponding channel as described above, and an error correction gradient signal, a synchronization signal, etc. are added and output. And the output signal from multiplexer 01 is
The digital signal is transmitted through BTF Q→, which is used to adjust the frequency characteristics of the entire transmitting and receiving system to eliminate code amount interference.
The signal is supplied to a 4-value conversion circuit Or9 consisting of an analog converter (hereinafter referred to as a D/A converter), where 7.15
MBPS
It is good to fix the other one series to the level of 1"- or "O". The output signal of the conversion circuit 0υ is supplied to the AMK regulator αQ, where the analogy from oscillator 0 is 38.9 M.
A carrier wave of Hz is produced by the output 1g of the conversion circuit 0υ. Strangely, 14 degrees in this case is, for example, a maximum of 100 degrees when the roll-off rate is 0.25. Therefore, the control device α
A signal with an intermediate frequency fIf-389M)Iz is obtained on the output side of Q, and this signal is passed through a vestigial sideband filter (VSBF).
') is supplied to the mixing circuit 0 through α→, where it is mixed with a signal of a local oscillation frequency, e.g.
It is extracted as an if signal. Note that the local oscillation frequency of the oscillation circuit is 1 higher than the transmission frequency of any channel.
The frequency is set to a higher frequency by 11 minutes. Therefore, the transmission channel is determined by selecting the local oscillator frequency.

The output signal from the mixing circuit (shellfish) is taken out to the output terminal (22I) through the band filter (21), and the signal from this output terminal (2) is sent to the so-called head end (not shown) of the CATV system. The signal from the head end is then supplied to the receiving side via a CATV line (not shown).Note that 1.231 is a pseudo data generation circuit for generating pseudo data for testing. .

In this way, the signal transmitted via the CATV line (No. 1 is supplied to the front end (32) from the receiving side input terminal Cl1l shown in FIG. This intermediate frequency signal is supplied to an individual detector, for example, a PLL detector G31, where a four-level baseband signal is demodulated.
However, in order to avoid waveform distortion, it is preferable to use a PLL detector as described above.

The output signal from the PLL detector (33) is connected to the four comparator (
34), where the level is identified where the eye patterns match, the digital data is extracted, and is supplied to the next stage demultiplexer (351).Then, the data is rearranged, error corrected, or the synchronization signal (351) is supplied. No. 48 processing such as extraction of SYNC) is performed. Demultiplexer 6 [
The digital signal from j) is connected to the switch (3G) and 0'
The signals are supplied to the D/A converters (31m and (31m) through II, where the digital signals are converted into analog signals and then output to output terminals (42) and (431), respectively.

When the switch (36) is on the contact a side, program P1 is demultiplexed, when it is on the contact side, program P2 is demultiplexed, while when the switch θ is on the contact a side, program P3 is on the contact side, and when it is on the contact side, program P4 is demultiplexed. It is switched and taken out by the address signal from MG5). On the other hand, the facsimile signal is taken out to the output terminal (44) through the facsimile interface circuit (4υ) via the switch G8). In this case, when the switch C38 is on the contact a side, the program P5 is taken out, and when it is on the contact side, the facsimile signal is taken out. Program P6 is switched and taken out. Q. These switches (36)
-C38) can be arbitrarily selected under control from the transmitting side.

In addition, the pit clock used when processing these signals is
In order to reproduce the bit clock without being affected by jitter, this is done by referring only to the period of the synchronization signal.

That is, on the output side of the PLL detector (33), as shown in FIG.
An output signal as shown in FIG. 7A, which is a signal at a value level and is a signal at a four-value level at times other than time T, is extracted. Therefore, the synchronizing signal 5YNC from the demultiplexer (3(g)) and the data from the level comparator (34J) are supplied to the clock regenerator (451), and the synchronizing signal 5YNC
The data, which is at a binary level only during this period, is extracted as a pit clock and supplied to three demultiplexers. It is possible to reproduce a bit clock with a small number of bit clocks.Also, since the pattern is always constant during this synchronization signal period, the AGC voltage is generated in the AGC circuit (46) by referring to the (Ft voltage) during this synchronization signal period, This is supplied to the front end. This allows stable AGC operation to be obtained at all times.

Application example: In the above-described embodiment, a digital audio signal and a facsimile signal are multiplexed and transmitted, but the present invention can be similarly applied to the case where other different types of digital signals are transmitted. Further, although the case where a BCH code is used as an error correction code has been described as an example, the present invention is not limited to this, and other error correction codes may be used.

Also, the modulation method is not limited to the 4-level VSB method, and examples include 16QAMNPSK, QPSK,
FSK, binary level vsB method, etc. may be used.

Effects of the Invention As described above, according to the present invention, in a digital signal transmission system using a CATV line, a digital signal is transmitted through multiple channels, an error correction code is added to each of these multiple channels, and an information signal is transmitted. By increasing the block length and reducing the redundancy occupied by the error correction code, the predetermined bits, for example 34x4
= 136 bits can be freely divided and used (
For example, 130 bits for data transmission, 6 bits for other data, etc.) The degree of freedom is increased, and a highly expandable signal format can be obtained. It is also effective because it can be used immediately for 4-channel stereo, etc. It is also useful when transmitting facsimile data or other data simultaneously with digital audio signals, and since one error correction code is added to each of multiple channels such as 4 channels, data from all multiple channels can be played back at the same time. In some cases, the decoding circuit configuration has the advantage of being small.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams for explaining this invention;
FIGS. 5 and 6 are block diagrams showing one embodiment of the present invention, and FIG. 7 is a diagram for explaining the sixth operation question. (7) ~Q+j is an analog-digital converter, 0υ,
0 is a facsimile interface circuit, 0;) is a multiplexer, 0 is a pinary transnormal filter (BTF), ao is a 4-level bell conversion circuit, θQ is an AM modulator, 0 is an oscillator, 0→ is the residual sideband filter (VSBF), α is the mixing circuit, (A) is the local oscillation circuit, (21) is the bandpass filter, (23) is the pseudo data generation circuit, (32) is the front end, (33) is a PLL detector, (34) is a level comparator, (3 are demultiplexers, (ate) to (38) are switches, (:
3 (g), (401 is a digital-to-analog converter,
The old one was an interface circuit for Facun Milli, (451 is a clock regeneration circuit, and (Tsukuda is an AGC circuit).

Claims (1)

[Claims] A digital signal transmission method using a CATV line, which is characterized by transmitting digital signals through multiple channels and adding an error correction code to each of the multiple channels. method.