JPS60125036A - Communication system of two-way catv system - Google Patents

Abstract

PURPOSE:To improve reliability by sending out packet type data to a down circuit while performing frequency conversion when there is data on an up circuit or modulation based upon a characteristic modulation pattern when there is no data to the down circuit. CONSTITUTION:The data from the up circuit is demodulated temporarily by a receiver 501 and applied to the modulation input terminal of a transmitter 503 while noise is removed by a noise separating circuit 502 to transmit the data to the down circuit. A transmitter 602 sends the up data at a terminal side through a distributor 601, but a CPU modulates the data and also turns on and off a carrier. The data from the down circuit, on the other hand, is demodulated by a receiver 603. A user terminal 605 performs its input, etc. The transmitter detects whether there is a carrier on the up circuit or not from the output of a carrier detecting circuit of the circuit and switches the modulation input so that a down illegal pattern is transmitted when there is no carrier and resending is performed when there is a carrier, thereby descriminating whether the data is within a data area or not.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a data communication system on a two-way 0ATV system.

The CAT'V system operates in such a way that a coaxial cable is laid within a limited area, and each user selects and receives images supplied from a video center using some method.

Compared to normal broadcasting systems that use airwaves, the 0ATV system uses a fixed medium called coaxial cable, so it has a greater degree of freedom in its operation. For example, in the airwaves, transmission is carried out on adjacent channels where there is a risk of interference. This is possible by lowering the level of audio waves that have frequency components close to those of adjacent channels.

In particular, the most distinctive feature of CATV systems is that they can perform bidirectional data communication.

For this reason, a system has been adopted that uses the 0ATV system to pay a fee each time a pay channel is viewed, and as a means of realizing this system, bands (empty channels) that are not used for video signals are used.

Data for billing, video selection, scrambling, etc., data communication for maintaining the so-called 0ATV system, is already widely used, but "C0MM0N-CARRIER" does not limit the content of the data or its usage.
J and T (7) y''-'I communication is considered as a future issue.

Applications of data communication using the OA'TV system include, in addition to the above-mentioned data communication for maintaining the 0ATV system, one-way communication using the VBI part within the video channel such as telex and teletext. communication method,
DOWNLOA of data such as one-way software
Although there is a communication method such as DING SYSTEM, it lacks a degree of freedom in terms of free communication between users.

Now, the technical field intended by the present invention is exclusively the communication system as the above-mentioned rcOMMON-CARRI ERJ.

[Prior art] The network configuration adopted as a communication system applicable to the 0ATV system is a so-called bus type as shown in Figure 1, so it is a communication form similar to that used in a general telephone network. cannot be used, so the form of packet communication is used.

Packet communication is a time division multiplex communication method in which many users are connected to one line, each data is divided into packets, and each user uses the line as if it were exclusive to the line.

The C8MA/CD method (Carrier Sense Multiple Access with Collision Detection) has been proposed as a time division multiplexing method with high line usage efficiency. It is used. Conventionally, LA
The C8MA/CD method used in N, etc. performs communication using a so-called baseband, and various changes are required for application to the 0ATV system.

iX 17) CSMA/CD method 0ATV
The following conditions are required to apply it to the system. FIG. 2 shows an example of the frequency allocation of a general CATV system. Here, the usable frequency band is roughly divided into two, with the lower group of frequency bands used in the upstream direction (from the terminal to the headend), and the upper group used in the downstream direction (from the terminal to the headend).
(from the head end to the terminal). Normally, multiple channels are allocated in order to supply a large number of videos in the downstream direction.The method of dividing this frequency band in the United States is the MID-8PLIT method or the
Examples include the UB-8PLIT system. In this way CA
On a TV system, the direction of data communication is defined by a frequency band, so when applying the C8MA/CD method to the system, it is necessary to have the following configuration.

1. Baseband communication cannot be performed, and communication is performed by modulating the carrier wave using an appropriate carrier layer.

2. Upstream data and downstream data use carrier waves of different frequencies.

A frequency conversion device is required at the end of the uplink and the start of the downlink in the 3.0 ATV system to connect both lines.

If a communication system is constructed on the 0ATV system while satisfying the above conditions, it will be as shown in FIG. Here, the frequency conversion bag [(FC) 101 converts the uplink frequency f1 to the downlink frequency f2.

Further, one terminal device (hereinafter referred to as NIU) 102 is provided for each user, and controls data transmission and reception. That is, data from a user terminal connected to the NIU is packetized, modulated at the transmission frequency f1, and transmitted according to the C8MA/CD control method. Also, is the data on the line constantly monitored? R1 is a series of controls such as capturing a packet addressed to the own terminal, analyzing the packet structure, and outputting the data to the user terminal if there is no error. Note that this N
Multiple IUs are connected to one system, and each NIU
(that is, the user terminal connected to rltJ) can communicate with any NIU.

The operation of this NIU is as follows. C3MA/CD
In this system, data can be transmitted only when there is no data on the communication line, but each NIU performs the data detection on its own. In a CATV system, the transmission frequency and reception frequency of each terminal are separated, and the uplink frequency is used for transmission and the downlink frequency is used for reception.
The fact that another terminal is transmitting a data packet can be recognized by receiving the frequency-converted downlink by the frequency conversion device. In other words, in order to transmit data on the uplink, it is necessary to receive the downlink and understand the status of the uplink. Also, C8M
Regarding collision detection, which is a feature of the A/CD system, collisions on the uplink are monitored on the downlink.
I'jlU transmits data to the uplink and at the same time compares the data sent to the downlink to avoid "collision".
must be detected. In other words, it is determined that a "collision" has occurred when the data sent by itself cannot be received correctly.From the above, it can be understood that the downlink needs to accurately reflect the situation of the opposing uplink. .

When the NIU has data to send, it monitors the downlink and begins transmitting data packets to the uplink after confirming that there is no other data.

It then monitors the downlink, receives the data it has transmitted, and compares it with the data it is currently transmitting. If it detects an error during the comparison, it immediately interrupts the transmission even in the middle of transmission. This is important in order to prevent the line from being occupied by meaningless data and to improve the overall usage efficiency of the line.

Next, data formats for uplink and downlink will be explained. The uplink and downlink are not only different in frequency (
, essentially have the following differences: In other words, whereas the downlink has one transmitter and many receivers,
The uplink consists of one receiver for many transmitters. This imposes restrictions on the format of data on the uplink. In other words, in order to perform free data communication, it is necessary to perform time-division communication on the uplink, and each terminal is required to turn on the carrier wave only when necessary, and turn off the carrier wave at other times. In other words, the carrier wave itself is turned on and off according to the length of the data to be transmitted. In this case, if there is some carrier wave leakage in each NIU in the off state, it becomes noise for the NIU that is the source, and appears as the sum of the noise at the input end of the receiver at the center, and is transmitted to the uplink. This results in deterioration of C-/, N.

On the other hand, on the downlink, it is sufficient to reflect the data on the uplink, but the contention for the data line has already been carried out on the uplink, so it is sufficient to simply transmit the data in a broadcast-like format. In other words, the data arriving at the end of the uplink,
By converting the frequency and transmitting it directly to the downlink, it can be implemented as a system.

[Problems with the prior art] In this way, in the 0ATV system, C8MA/CD
When this communication system is adopted, the uplink carrier wave is frequency-converted and transmitted to the downlink, which has the following drawbacks.

(1) In a large-scale 0ATV network, the uplink data reception level is high (varies), so the downlink transmission level also fluctuates.

(2) Uplink noise is directly superimposed on the downlink.

(3) Packets that connect or disconnect the carrier wave are also transmitted on the downlink, so each NILJ needs to receive data with the carrier wave disconnected.

[Object of the present invention] The present invention was made based on the above circumstances, and it maintains a stable transmission level on the downlink without being affected by fluctuations in the reception level of data on the uplink, and also maintains a stable transmission level on the downlink. In addition, the continuity of the carrier wave in the downlink is maintained by controlling whether or not to modulate packets that are connected to or disconnected from the diagnostic wave in the uplink, so as not to introduce noise, and to control whether or not to modulate the packets in the uplink. The present invention aims to provide a communication method in a bidirectional 0ATV system that can improve the quality of NIU mutual communication.

[Summary of the Invention] To this end, the present invention provides that, in a bidirectional CATV system in which upstream and downstream signals are divided into a certain frequency band, a center II unit divides the frequency band into a frequency band for the bidirectional 0ATV system. The packet-shaped data transmitted by connecting or disconnecting the carrier wave is frequency-converted in the section where the data exists on the uplink and is sent to the downlink, and the data is present on the uplink -L. The feature is that the section in which the signal is not transmitted is frequency-modulated with a modulation pattern that cannot appear in the modulated signal on the uplink, and is transmitted to the downlink @line.

Embodiments of the present invention will be specifically described below with reference to FIGS. 4 to 12. In FIG. 4, reference numeral 401 indicates the state of the carrier wave transmitted to the uplink, and the carrier wave is made "connected" only when necessary.

Reference numeral 402 indicates a downlink carrier wave, and modulation is applied only when the carrier wave is turned on in the uplink. Further, 403 is downlink modulation data, which matches the uplink carrier wave. For such signal control, a configuration as shown in FIG. 5 is provided on the transmitting side. Here, uplink data is demodulated once by a receiver 501, and uplink noise is removed by a next noise separation circuit 502. Then, this noise-separated data is applied to the modulation input terminal of transmitter 503, and the data is transmitted to the downlink.

Regarding the construction of such a communication system on the sending side,
On the terminal side, a configuration as shown in FIG. 6 is adopted. Here, the signal distribution N6 used for input/output distribution is
Uplink data is transmitted from the transmitter 602 via 01, but in this case, data modulation and "connection" to "disconnection" of the carrier wave are performed in accordance with commands from the central processing unit (CPU).

Also, the data from the downlink is 4! at the receiver 603! tune. In the figure, the symbol @604 is a controller built in a microcomputer, which controls 1. the transmitter 602; Input of sending data.

Data input from receiver 603, analysis, address recognition, control of C8MA/CD procedures, and user terminal 6
Controls communication to 05. User terminal 6 above
05 is a device that performs human interface, and N
It inputs commands to the IU and displays received messages. Further, the user terminal 605 may be a computer or the like. The application of this system can take various forms depending on the configuration of the user terminal, but the explanation here will be limited to the construction of a communication system.

The format of the data signal on the downlink is as shown in FIG. For the downlink signal: Considering the stability of the operation of the receiver at the terminal, the carrier wave is not connected or disconnected, but whether or not it is modulated is controlled. The format of the modulated data is the same as that of the upstream signal, and is shown in FIG. 7(b). An example of the format of this data will be explained within the cylinder. This data is organized in a so-called packet format,
First, a preamble signal is inserted at the beginning. This signal is a signal for performing bit-level synchronization on the receiving side. Next, a flag signal for synchronizing the 7-raming of the packet is inserted, and by correctly receiving this signal, it becomes possible to obtain synchronization at the 7-raming level or byte unit. Next, so-called address information is included. This is usually inserted with the destination address and sender address of this packet-shaped data. Based on this address information, each terminal performs an operation to capture the corresponding packet. Data to be transmitted is inserted after the address information. This length is determined by the packet construction method t
ti is variable depending on the system design and also varies depending on the amount of data required. Additionally, a control byte may be provided at the beginning of this data. Next, an error check code is added to detect data transmission errors, and finally a frame end flag is added.

In this method of receiving packets, the valid data is between the flags, and the address information immediately after the first flag is the only one in the system.
This allows the device to capture only packets that match the given address of its own terminal. here,
The length of the data is not constant and the end of the packet is detected only by the final flag. As a result, the data immediately before the R end flag is detected is the error check code. Further, the data up to just before that is data.

In this way, in packet communication, so-called flags play an important role, and data areas surrounded by flags are recognized. In particular, the HDLC method (High Level Denta Link), which communicates in a similar packet format,
control), set the flag configuration to "01111110"
To prevent erroneous detection of the flag, an 'O' insertion function is provided to prevent six consecutive bits of 1 in the data area included in the flag.If this flag is erroneously recognized, the data Be careful, as it may become impossible to detect the normal end of the data, and the next data may be incorrectly framed.In other words, correct recognition of the flag signal is the key to accurate packet communication. In addition, even if a 5-v framing error is made, correct framing must be restored as soon as possible.

In addition, in the C8MA/CD communication system described above, each terminal determines whether or not other data exists on the line, but for this purpose, each terminal must monitor the line at the same time. , it is necessary to immediately determine the data transmission state and the data-free state (hereinafter referred to as the idle state). However, as mentioned above, the determination based on the "flag signal" sacrifices immediacy.In addition, the transmissions from each user will be concentrated at the end of one packet.

If the above problems are considered in a line having a modulation section 701 and a non-modulation section 702 as shown in FIG. 7, the following problems will arise. That is, in general, when an unmodulated signal is received and demodulated, the following two forms are obtained compared to data modulation.

Q Form of data modulation by AC coupling (b) Form of data modulation by DC coupling The demodulated waveforms of each data are shown in Figure 8.0. Φ). FIG. 8 Q shows a case where AC coupling is used, and the section A in the figure is unmodulated, and the section B is a section with data modulation. FIG. 8(b) shows the case where DC coupling is used, and the sections A and B are exactly the same as in the case of (f).

In the case of Q, it is common sense to judge the data modulation at the zero crossing point, which is the method with the least code errors, but in this case, only noise is reproduced as data in the section F. becomes. In other words, in the section F, the potential is output as the determination level itself, so if even a small amount of noise is superimposed, the output of the data determiner will be inconsistent due to its influence. In this situation, it is not possible to determine which data interval is significant and which is an idle interval, so
The above-mentioned idle state cannot be detected.

In addition, in the case of 0, the difficulty of data modulation and demodulation generally increases (it is necessary to transmit up to DC), and
The idle interval will be fixed at a certain level (for example, all '1' or '0'). In this situation, it will be possible to determine the idle interval if a condition is set that some bits are continuous. However, even in this case, in addition to the difficulty of DC modulation as described above, there are technical issues such as minimizing the causes of fluctuations in the DC component.For example, FS
When performing transmission using the K method (frequency shift keying), the frequency stability in the transmitter and receiver must be made stable for all components.

Therefore, it is generally necessary to upgrade the hardware.

Therefore, when implementing the C8MA communication method on a CATV system, simply looping back the data on the upstream line will cause problems in the system configuration on the downstream line.

In this regard, in the present invention, a configuration as shown in FIG. 5 is provided (configuration of the frequency converter), and level variations in the uplink and noise in the uplink can be separated. Furthermore, the downlink carrier wave can be connected or disconnected.
Downlink data is superimposed on the carrier wave depending on whether the data is modulated or not. However, simply the presence or absence of modulation cannot be used to detect an idle period. Therefore, the following method is used.

In other words, the code format of data that has a normal packet format is referred to as the code format of a method that does not follow a specific pattern. This is a code that does not include a DC component, for example Bi P-
L, BPS(Bi-P)IAsESPAGE) or Delayed M0dUIatiOn, etc. may be used, and by this, a continuation of levels longer than a certain length will not occur. This type of code setting is used when the transmission band is considered to be a narrow band, and does not lack film characteristics.

For example, it is especially effective when narrowing the band [) elay
Suppose we adopt a code format of dM odulation (D M ). This is as shown in Figure 9. This code format is created by inverting at the center of the bit length when "1", at O## does not change, however, II Ojl and 8
When 401+ are consecutive, this is done by inverting at the bit length boundary. In this code, the code formed result (
MARK/5PAGE), each with a maximum of 2 pit lengths.

The minimum length is 1 bit and 3/2 bit length. Other mark lengths and space lengths cannot be used. Moreover, this DM code is a data "1" 1. “0”, marks, and spaces do not correspond in level, and are basically differential encoding that transmits changes in data. Furthermore, the fundamental frequency component is the maximum repetition frequency of data (101'O...
), it is a code format that allows efficient transmission.

Considering this in reverse, if the mark length or space length is, for example, 3 pits long, consecutive marks or spaces cannot be determined to be normal data, and it becomes ``illegal''.
It is detected as a pattern with “legal > ”. This judgment is included in a part of the receiving circuit. Therefore, if this illegal pattern is used outside the iEM data area, it must be surrounded by the flags mentioned above. It becomes possible to physically identify the data area that has been used and the other idle state.

In other words, considering the system as a whole, in the uplink, each terminal activates a carrier wave and transmits data when necessary, but this data packet is demodulated once at the receiver at the center, separated from noise, and then sent back to the downlink. It is sent. However, the center transmitter uses the output of the uplink carrier detection circuit to determine whether or not a carrier exists on the uplink, and if there is no carrier, it transmits an illegal pattern to the downlink and detects the carrier wave on the uplink. By switching the modulation input so that the data on the upstream line is retransmitted when there is a problem, it is possible to identify the inside and outside of the data area. On the other hand, on the terminal side, when attempting to make a call, the idle detection operation can be determined based on whether an illegal pattern exists on the downlink. In other words, when an illegal pattern exists, it can be said to be in an idle state, and when there is no illegal pattern, it is a data area, indicating that transmission is not possible.

In the system configured as described above, the C8MA/CD communication method can be changed to C8MA/CD without any problems in terms of efficiency.
It is possible to build grooves on the ATV system.

Next, the configuration of the center 41 device suitable for the method of the present invention will be explained as follows.
The configuration of the terminal will be explained with reference to FIG. 0 and FIG. 11, respectively. In FIG. 10, the center frequency conversion device is an uplink channel receiver (which outputs baseband data and the presence or absence of a received carrier signal in I key).
1001, a circuit 1002 for synchronized data reproduction and waveform shaping, and an illegal pattern generator 100 for transmitting an illegal pattern to the downlink channel.
3, a switching circuit 1004 for a pattern that is illegal with this data, and a transmission l111005 for the down channel.

The operation of this device will be explained using timing flags shown in FIG. 12. In the figure, 0 indicates the state of the carrier wave in the uplink. In section A, the carrier wave is completely disconnected, but in section B, one of the many connected terminals starts transmitting a signal, and the receiver at the center detects the carrier wave. demodulation starts. Further, 0) in the figure indicates a state in which the carrier wave detection signal (hereinafter referred to as CD) in the center receiver operates in accordance with the carrier wave from section B. Furthermore, as shown at 0 in the figure, 4! of the upstream signal! Key data is also output from the ward JIB. This demodulated data is
The above-mentioned DM modulation is applied. On the other hand, in Q9,
The output of the illegal pattern generator inside the center is shown, and is a repetitive signal of marks and spaces with a length of "3 bits long" that does not occur in DM modulation.

In addition, (sub) shows the baseband waveform modulated by the downlink signal. Here, the illegal pattern 9 is output when there is no signal in the section, but since the upstream signal is input from section B onwards, the data of the upstream signal is output. For switching between the illegal pattern and II data, it is effective to use the CD signal shown in (v). That is, when there is no upstream signal, the illegal pattern is used as a modulation signal, and when an upstream signal is received, the received data is used as the modulation signal.

The configuration of the center equipment for performing the above operations is as shown in FIG. . This receiver 1001 also outputs a signal @ (the above-mentioned CD) indicating the presence or absence of a carrier wave. The 4I leaked baseband signal is input to a synchronous regeneration and waveform shaping circuit 1002 for noise separation on the uplink. This circuit reproduces data from which jitter and the like generated by data waveforms containing noise have been removed. Various proposals have been made to implement this circuit, and digital P
There are methods using Lm (DPLL), analog locking methods, and rehit methods using a simple counter. Therefore, with this circuit, data from the uplink is free of noise components and is operated with correct lock.

On the other hand, the illegal pattern generation circuit always generates the above-mentioned illegal pattern. This output is driven by a precise lock on the basis of the data to be transmitted on the downlink. This illegal pattern is switched depending on the polarity of the above-mentioned received data and CD signal. This is the AND-OR circuit 1004 in FIG. In order to perform this switching, it is necessary that the received data is synchronized with the illegal pattern at the pin level, and the clock regeneration and waveform shaping circuit 1002
The output of is operated with the same clock as that used for illegal pattern generation circuit 1003. This situation is shown in FIG. 12 (6).

The signal jH created by this AND-OR circuit 1004 is sent to the downlink transmitter 1005 via the buffer circuit 100G.
is added to the modulation input terminal of the signal and sent to the downlink. This signal is output to one line through a circuit for combining with an upstream signal.

As described above, uplink signals are reflected in downlink signals. When there is no upstream signal, an illegal pattern is output to the downstream line, and when there is an upstream signal, the data content is output as is.

The configuration number of the terminal that accepts this downlink signal is number 11.
As shown in the figure. Terminal (t1) detects an illegal pattern on the downlink as described above, recognizes the idle state of the uplink, and starts transmitting data. Therefore, the 0ATV line is branched into two at the splitter 1101, One is connected to a downlink receiver 1102. The output of this receiver 1102 is a signal q containing an illegal pattern and data, and this pattern can be recognized in the DM state. This data and pattern are as shown in Figure 12 (2).Illegal patterns are extracted from this data by detecting consecutive marks or spaces of 3 bits in length.

This determination is possible because normal data only includes marks or spaces up to a maximum length of 2 bits. This illegal pattern determination circuit 1103 is
This can be easily implemented using a counter circuit. Next, the illegal pattern detection signal is sent to the DM-NRZ conversion circuit 1104 (
NRZG, tNON RETUR, N ZERO)
and determines the operating state of the DM-NR2 conversion.

In other words, when one illegal pattern is detected, DM-
NRZ conversion is not performed, and when an illegal pattern is not detected, DM-NRZ conversion is performed and the received data converted to NRZ is output to the CPLI board 1105. The operation of the CPU board 1105 is to perform carrier sense (O8) for COMA/CD based on the illegal pattern detection signal and determine the data on the line. Also, when the illegal pattern detection signal is off, the data is decoded and the contents of the data packet are determined. The content of each determination is whether or not the packet is addressed to the own terminal at the time of reception, and whether the data being transmitted is being sent correctly (whether or not a collision has occurred) at the time of transmission. If there is further data to be transmitted, after performing C8 above, the transmission data is output to the NRZ-DM converter 110G, and the data converted to DM is sent to the modulation input of the uplink transmitter 1107. It is applied to the terminal and output in the form of modulation on the uplink carrier wave.

The output of this transmission 111107 is applied to the other terminal of the branch B11o1 mentioned above, and output as an upstream signal to the 0ATV line.

The communication method described here is a method for efficiently performing packet communication on a large-scale CAT system, and is different from the communication method developed on a conventional small-scale 0ATV system. For example, installing a receiver and a transmitter in the center equipment may lead to an increase in system cost in a small-scale system, but in a large-scale system, the number of terminals will be on the order of several thousand, The slight increase in the cost of the center equipment can be ignored.Also, as mentioned above, in large-scale ATV systems, it is difficult to deploy receivers and transmitters in the center equipment due to poor uplink quality. This greatly increases the reliability of the data.

On the other hand, in a method in which the center side generates an illegal pattern when the uplink line is vacant, and each terminal detects the idle state of the line based on that signal, the circuit configuration of the center equipment becomes somewhat complicated, but as shown above. This can be ignored in large-scale systems.

A further circuit addition on the terminal side is an illegal pattern detector, but this is not a complex circuit;
The cost is also negligible.

[Effects of the present invention] As detailed above, the present invention provides two-way 0AT when adopting the C8MA/CD method in the 0ATV system.
Packet communication on the V system can be carried out with high reliability, and the advantage is that only a minor circuit configuration is required at the terminal. In addition, the line utilization efficiency is also extremely high.

[Brief explanation of the drawing]

Figure 1 is a diagram conceptually showing a network of a two-way 0ATV system, Figure 2 is a diagram showing an example of frequency allocation of an 0ATV system, and Figure 3 is a communication system constructed between a transmitting side and a receiving side. , FIG. 4 is a diagram showing the signal level of data communication according to the present invention, FIG. 5 is a block diagram of the transmitting side, FIG. 6 is a block diagram of the receiving side, and FIG. 7 is a diagram of the downstream data packet. Figure 8 shows the data demodulation waveform. Figure 9 shows the DM code format.
Figure 0 is a block diagram of the transmitting side showing the essential part of the present invention.
FIG. 11 is a block diagram of the receiving side, and FIG. 12 is a signal waveform diagram in the system operation of the present invention. 101... Frequency conversion device, 102... Terminal device,
401.402...Carrier waveform, 501...Receiver, 502...Noise separation circuit, 50
3...Transmitter, 601...Distributor, 602...Transmitter, 603...
- Receiver, 604...Controller, 605...User terminal, 701...Modulation section, 702...Non-modulation section, 1001...Receiver, 1002...Synchronized reproduction/waveform shaping circuit , 1003... Illegal pattern generator, 1004... Switching circuit, 1005... Transmitter, 1006... Buffer circuit, 1101... Brancher, 1102... Receiver, 11o3... Illegal Pattern determination circuit ζ1104...DM-NRZ conversion circuit, 1105-CP Ll Ho t', 110G-N
RZ-DM conversion circuit, 1107...transmitter. Patent applicant: Pioneer Co., Ltd. Agent: Patent attorney: Shin Kobashi Jundo Patent attorney: Susumu Murai

Claims (1)

[Claims] In a bidirectional 0ATV system where upstream and downstream signals are divided into certain frequency bands, the center WaM is
The carrier wave in the frequency band for the bidirectional 0ATV system is
- Packet-type data transmitted by "cutting off" is frequency-converted in sections where data exists on the uplink and sent to the downlink, and in sections where no data exists on the uplink, it is sent out to the downlink. A bidirectional CAT characterized in that it is configured to frequency-modulate the modulation pattern with a modulation pattern that cannot appear in the modulation signal of the input terminal 1iA't'' and send it to the downlink.
Communication method in the V system.