JPH1032806A - Cable television system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect movement of a terminal unit which is lent out to a new subscriber's house of a CATV system and to prevent unauthorized viewing. SOLUTION: In a bi-directional CATV system, a center unit 1 transmits a terminal response request command to a terminal unit 2 which is lent out to a new subscriber, and the unit 2 returns a response command to the terminal response request command to the unit 1 side. The unit 1 stores the time which is taken by the response command to be returned as an initial response delay time of the unit 2 in a response delay amount storage database 10. The unit 1 requests the unit 2 to return the response command at each fixed time, compares the time that is taken by the response command to be returned with the initial response delay time, decides that the unit 2 has moved when the difference in both becomes a prescribed time or more, and executes viewing restrictive processing such as stopping of transmitting program data, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable television system having a terminal response function, and more particularly, to detecting a terminal device moved out of a subscriber's home to prevent unauthorized viewing. It relates to a cable television system.

[0002]

2. Description of the Related Art A general cable television system (CATV system) is a so-called addressable system in which a unique identification code (ID code) is assigned to each terminal device. A terminal device is connected by a downlink for transmitting data from the center device to each terminal device and an uplink for transmitting data from the terminal device to the center device.

In such a CATV system, when the center device monitors the status of the terminal device,
The center device polls each terminal device using the ID code. The terminal device corresponding to the ID code that has received the polling command returns a response command to the center device side via the uplink. The center device monitors the terminal device based on the returned response command.

On the other hand, recent CATV systems include a so-called video on demand (VOD).
d) In order to realize interactive functions such as services and online shopping, or to realize communication functions accompanying the deregulation of telephones and the like, the above-mentioned up line and down line are used together with a single cable. A two-way communication system in which a center device and each terminal device are connected is employed.

[0005] This two-way communication type CATV system (two-way CATV system) includes a center device 500 provided in a cable television station and a plurality of terminal devices 600 provided in respective homes, as shown in FIG. It is configured by connecting in parallel or in a tree shape via a bidirectional cable 550.

The center device 500 includes a video supply unit 5
01, a communication unit 511, and a data multiplexing unit (MUX). The video supply unit 501 includes a video server 502 for transmitting a plurality of programs such as movies and news to the terminal device 600; A database 503 such as a magneto-optical disk, a semiconductor memory, or a video tape recorder in which a plurality of programs such as the movie and news are stored.
And a plurality of modulators (MODs) 504 provided for the number of channels that can be viewed on the terminal device 600 side.

The communication unit 511 includes a communication control unit 512
A storage unit 513 storing subscriber management data for managing the subscribers of the CATV system; and a plurality of units for performing predetermined modulation processing on data transmitted from the center device 500 to the terminal device 600. Modulator (MOD) 51
4, and a plurality of demodulators (DEM) 515 for demodulating data transmitted from the terminal device 600 to the center device 500.
It is composed of

The video supply unit 501 and the communication unit 511
Is connected via an internal bus line 520, and communicates between the units 501 and 511 while communicating with the terminal device 60.
It accepts transmission requests from the 0 side, transmits programs, and the like.

The video supply unit 501 and the communication unit 511 have a function of connecting to an external video / news server and a function of connecting to a public network (such as a telephone line network). When a subscriber receives a video / news distribution request not stored in the video DB 503, the data is acquired from an external server. Further, when a telephone request to the outside of the CATV network is made from the subscriber to the communication unit 511, the communication unit 511 relays the request and connects to the public network.

Next, the terminal device 600 installed in each home or the like is provided, for example, in the vicinity of the television device 602 in the home, and inside the terminal device 600, a predetermined modulation process is performed on data to be transmitted. And a demodulator for receiving and demodulating program data and the like transmitted from the center device 500 and supplying the demodulated data to the television device 602. ing.

The modulator 514 provided on the center device 500 and the modulator provided on the terminal device 600 can easily synchronize with each other and can perform stable communication even on a low C / N transmission line. Therefore, QPSK (Quadrature Phase Shift Keying) modulation processing is performed on the data to be transmitted. The center device 500
The demodulator 515 provided on the side and the demodulator provided on the terminal device 600 side perform QPSK demodulation processing on received data corresponding to the modulator for performing the QPSK modulation processing. .

The modulator 504 provided on the center device 500 side needs to transmit large-capacity data such as video data by efficiently using the transmission band of a high-speed and large-capacity transmission line. Therefore, 64QAM modulation processing is performed, and a demodulator for performing 64QAM demodulation processing is provided on the terminal device 600 side correspondingly.

[0013] Such a bidirectional CATV system uses a so-called time division multiple access communication system (TDMA).
Communication device) and the center device 500 and each terminal device 60
0 is communicated.

Here, in such a two-way CATV system, the terminal device 600 usually has a rental contract of one unit per home, but family members in each home can individually obtain desired rental contracts. In some cases, even in the home, a rental contract may be made for a plurality of terminal devices in order to view a program or to record a counterprogram. In this case, for example, if the rental fee for the first terminal device is 4000 yen, the rental fee for the second and subsequent terminal devices is 400 yen, which is 1/10 of the rental fee for the first terminal device. In many cases, the second terminal device and the following terminal devices are set at a lower price than the first rental fee.

[0015]

However, when a subscriber having a rental contract for such a plurality of terminal devices lends one of the terminal devices to a neighbor who has not made a rental contract, This neighbor can illegally view the broadcast program even though he has not subscribed to the CATV system. However, the conventional CATV system can detect the movement of the terminal device lent by the rental contract. Therefore, there has been a problem that such unauthorized viewing cannot be detected.

Such unauthorized viewing can be prevented to some extent by constantly checking the number of terminal devices lent to each subscriber's home as part of field maintenance of the CATV system. It requires a lot of work, cost and time and is unrealistic.

The present invention has been made in view of the above problems, and has as its object to provide a cable television system capable of detecting movement of a lent terminal device and preventing unauthorized viewing. .

[0018]

A cable television system according to the present invention is a cable television system of a bidirectional communication system for performing bidirectional communication between a center device and a plurality of terminal devices. In order to solve the problem, the center unit is provided with the following units.

That is, when the center device transmits terminal response request data requesting a response to each terminal device from the center device, response data corresponding to the terminal response request data is returned from each terminal device. Response time detecting means for detecting a response time, which is the time required until, and a storage means for storing the response time of each terminal device detected at a predetermined time by the response time detecting means as an initial response time.

In addition, the center device, together with the means, controls the response time detecting means so as to detect the response time of each terminal device after detecting the initial response time; When the response detection control means detects the response time of each terminal device after the detection of the time, the response time is compared with the initial response time stored in the storage means. And a movement detecting means for detecting that the terminal device has been moved when there is an error.

In such a cable television system, for example, when there is a new subscriber to the cable television system and a terminal device is installed at the subscriber's house (for example, when time has elapsed since the terminal device was installed). First, the response time detecting means transmits the terminal response request data to the terminal device, and detects the time until the response data is returned from the terminal device in response thereto. The storage means stores the response time as an initial response time.

The response time detecting means detects the response time of each terminal device at predetermined time intervals, for example, once a day or once a week. When a response time is detected after the detection of the initial response time, the movement detection means reads out the initial response time of the terminal device corresponding to the response time from the storage means and compares the two.

If the terminal device is moved improperly, there is a difference in the transmission distance at the time of initial installation, so that a difference also occurs in the response time. For this reason, the movement detecting means detects that the terminal device has been moved when there is a difference between the two by a predetermined time or more as a result of the comparison.

When the movement of the terminal device is detected, the center device stops program delivery and data transmission to the terminal device, and rejects the request from the terminal device.
Alternatively, take measures such as dispatching a maintenance man to confirm movement. Thereby, unauthorized viewing due to unauthorized movement of the terminal device can be prevented.

Next, the cable television system according to the present invention is provided with viewing restriction means in addition to the above-described configuration. When the movement of the terminal device is detected, the viewing restriction means restricts viewing by the terminal device. Specifically, for example, the transmission of the program data is stopped on the center device side, or the terminal device is controlled so that the center device does not decode the program data.

Thus, unauthorized viewing due to unauthorized movement of the terminal device can be automatically prevented without dispatching the maintenance man or the like.

Here, two subscribers are neighbors of an apartment house, one subscriber contracts for a paid A channel, the other subscriber contracts for a paid B channel, and the other subscriber contracts for a paid B channel. Is rented by one of its neighbors to view channel A, the terminal device is rented to the neighbor's house through a wall in an apartment house such as an apartment house or apartment house. Since the distance is only about a meter, there is no significant difference in the response time of the terminal device of each subscriber, and there is a concern that even if such an illegal act is performed, it cannot be detected.

In view of the above, the cable television system according to the present invention, in addition to the above-described configuration, has a pass band rejection for preventing the transmission of data in different frequency bands, for example, for each branch line of each terminal device. Means are provided.
Then, the center device and each terminal device perform communication by using the assigned bands other than the pass band of the pass band blocking means of the terminal device.

In the above example, the passband rejection means for the terminal device of one of the subscribers is set with a rejection frequency band so as to reject the first frequency, and the terminal of the other subscriber is rejected. In the passband rejection means for the device, a rejection frequency band is set so as to reject the second frequency. And
The terminal device of the one subscriber communicates with the center device using a frequency band blocked by the pass band blocking means for the terminal device of the other subscriber, and the terminal device of the other subscriber. Communicates with the center device using the frequency band rejected by the passband rejection means for the terminal device of one subscriber.

[0030] Thus, when the terminal device of one subscriber is illegally lent to the other subscriber as described above, the response data from the terminal device of the one subscriber is transmitted to the other subscriber. Since the signal is returned using the frequency band blocked by the pass band blocking means for the terminal device, it is blocked by the pass band blocking means for the terminal device of the other subscriber and is not transmitted to the center device side. Becomes

When the center device detects that the response data is not returned, it determines that the terminal device has been improperly moved, and executes the above-described viewing restriction processing. With this, even a small movement of several meters in distance,
The legitimate movement in the subscriber's home can be accurately distinguished and detected, and illegal viewing can be prevented.

Next, the cable television system according to the present invention, as another means for detecting the above-mentioned slight movement, adds a predetermined unique word to terminal response request data transmitted from the center device to each terminal device. It has a unique word adding means for adding. This unique word adding means is provided, for example, at each branch line or node of each terminal device. The unique word is preferably information capable of identifying the terminal device, and includes, for example, an identification code of the terminal device.

In this case, when each of the terminal devices receives the terminal response request data to which the unique word is added by the unique word adding means, the terminal device adds the unique word to the response data and returns it to the center device.

If the terminal device is not moved improperly, the response data should be returned with a predetermined unique word added thereto. Therefore, the center device detects the unique word added back to the response data and returned, thereby detecting the transmission path on which the response data is returned. When the unique word is added by another unique word adding means, the response command is transmitted via another transmission path, that is, the terminal device is moved. It is determined that there is, and the above-described viewing restriction processing is executed.

Thus, as in the case where the above-mentioned pass band blocking means is provided, even a slight movement of several meters in distance can be accurately distinguished from a legitimate movement in the subscriber's home and detected. This can prevent unauthorized viewing.

Next, if the unique word adding means is provided for each branch point for each terminal device, the cost increases. For this reason, the cable television system according to the present invention adds a unique word changing means for changing a unique word formed by the unique word adding means to the unique word adding means in response to a command from the center device. Provided. Then, this is provided at a node or the like connected to the main communication line by integrating branch lines from the center device side or each terminal device.

In this case, the center device changes the unique word for each terminal device and transmits the terminal response request data. As a result, the transmission path of each terminal device can be detected, and unauthorized movement of the terminal device can be detected.

Next, the cable television system according to the present invention is provided with scramble processing means for scrambling the terminal response request data transmitted from the center device based on the unique word. And
When each terminal device receives the terminal response request data scrambled by the scramble processing means, the terminal device decodes the terminal response request data by using information unique to the terminal device, adds the decoded data to the response data, and adds Return to the center device.

In this case, since the center device can recognize in advance the terminal device which has issued the terminal response request and the result of the scramble processing by the unique word, the terminal response added to the response data and returned is returned. By detecting the decoding result of the request data, the transmission path to which the response data is returned is detected. Then, when the transmission path is for a terminal device other than the terminal device, the terminal device detects that the terminal device has been moved. As a result, the transmission path of each terminal device can be detected, and unauthorized movement of the terminal device can be detected.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a cable television system according to the present invention will be described below in detail with reference to the drawings.

First, a cable television system (CATV system) according to the present invention is a bidirectional CATV system capable of bidirectional communication between a center device and a terminal device. Video-on-video transmission of the program data desired by the subscribed subscriber
It can be applied to a demand system (VOD system).

The VO according to the first embodiment of the present invention
In the D system, as shown in FIG. 1, a center device 1 provided in a cable television station and a plurality of terminal devices 2 provided in respective homes and the like are connected in parallel via one communication line 3. It consists of.

The center device 1 is composed of a video supply unit 4 and a communication unit 5. The video supply unit 4 transmits a plurality of programs such as movies and news to the terminal device 2. And a database 6 such as a magnetic disk (HDD: hard disk), a magneto-optical disk, a semiconductor memory, a video tape recorder, etc., in which a plurality of program data such as the above-mentioned movies and news are stored. It comprises a plurality of modulators (MOD) 8 provided for the number of channels.

The communication section 5 includes a management data storage database 10 storing subscriber management data for managing the subscribers of the VOD system, and each response of the terminal device 2 lent to each subscriber. A database for storing the response delay amount in which the delay times are stored, the management data and the response delay time, and a management for detecting the movement (illegal viewing) of each terminal device 2 based on the response delay time. A communication control unit 11, a plurality of modulators (MOD) 12 for performing predetermined modulation processing on data transmitted from the center device 1 to the terminal device 2, and data transmitted from the terminal device 2 to the center device 1 Demodulators (D
EM) 13.

The video supply unit 4 and the communication unit 5 are connected via an internal bus line 15 to receive a transmission request from the terminal device 2 while communicating between the units 4 and 5 and to transmit program data. And so on.

The video supply unit 4 and the communication unit 5
Have a function of connecting to an external video / news server and a function of connecting to a public network (such as a telephone line network). Is received from a subscriber, the data is obtained from an external server. Further, when a telephone request to the outside of the CATV network is made from the subscriber to the communication unit 5, the communication unit 5 relays the request and connects to the public network.

Next, the terminal device 2 installed in each home or the like is provided, for example, in the vicinity of the television device 16 in the home, and will be described in detail later. And a modulator for performing predetermined modulation processing on the data and transmitting the modulated data to the center device 1 side, and the center device 1
A demodulator and the like for receiving and demodulating program data and the like transmitted from the side and supplying the demodulated data to the television device 16 are provided. Also, the terminal device 2 can be connected to a home telephone 17 and can communicate with a desired party via a telephone line connected to the center device 1.

The modulator 12 provided on the center device 1 side and the modulator provided on the terminal device 2 side can easily synchronize, and stable communication can be performed even on a low C / N transmission line. Because it is possible, QPS
K (Quadrature Phase Shift Keying) modulation processing is performed. The demodulator 13 provided on the center device 1 side and the demodulator provided on the terminal device 2 side perform QPSK demodulation processing on received data in correspondence with the modulator for performing the QPSK modulation process. Is to be applied.

Also, the modulator 8 provided on the center device 1 side needs to transmit large-capacity data such as video data by efficiently using the transmission band of a high-speed and large-capacity transmission line. For this reason, 64QAM modulation processing is performed, and the terminal device 2 has 6
A demodulator for performing 4QAM demodulation processing is provided.

In such a VOD system, communication is performed between the center device 1 and each terminal device 2 using a so-called time division multiple access communication system (TDMA communication system).

Specifically, of the data (uplink data) transmitted from the terminal device 2 to the center device 1, the time slot (TS) allocation request frame is as shown in FIG.
As shown in (a), each frame has a data length of 2 msec, and is transmitted at a transmission speed of 8.192 Mbps. The uplink data of one frame is stored in a time slot (TS0, T0) of a predetermined number of bit strings allocated to each terminal device having a transmission request.
S1, TS2,...). Each of the time slots is variably assigned for the purpose of, for example, allocating only to the terminal device having a transmission request to improve communication efficiency. However, when starting communication, each terminal device 2 first assigns the time slot. In order to make a request, an empty slot is detected from the TS allocation request slots (A0, A1, A2,...). Then, T
An S allocation request is stored and transmitted to the center device 1.

On the side of the center device 1, each time slot (A0, A1, A2,.
.), The corresponding T in the downlink control frame
Using S, a time slot is designated for each of the requested terminal devices. Thereafter, communication is started using the assigned time slot.

The information on empty slots is transmitted for each slot in the downlink communication control frame (A0, A1, A2,...).

As shown in FIG. 2C, the downlink frame is a frame dedicated to downlink including video data, and each time slot is assigned to correspond to an uplink time slot.

The upstream data of each frame includes
A delay control slot (DLC) described later, which is provided to correct the transmission distance to the center device 1, is provided.

On the other hand, the communication control frame (downlink control data) transmitted from the center device 1 to the terminal device 2 has a data length of 2 msec for each frame as shown in FIG. 2B. And is transmitted at a transmission speed of 384 kps. The one frame of downlink data is divided into time slots of a predetermined number of bit strings allocated to the respective terminal devices 2,
The center device 1 transmits communication slot control data (A0, A1, A2,...) Of the terminal device 2 in a time slot allocated to each terminal device 2.

The downlink control frame of each frame is provided with a delay control slot (DLC), which will be described later, provided to correct different transmission distances from the center device 1 to each terminal device 2. I have.

Each frame of the downlink data includes:
"Notification" data (BR1, BR2, B, etc.) from the center device, such as the broadcast time of each program, the contents of each program, etc.
R3...).

Next, from the center device 1 to each terminal device 2
The delay control slot (DLC-D) attached to each frame of the downlink data transmitted in FIG.
Has a data length of 128 bits as shown in FIG.
6-bit synchronization data (Sync), 32-bit ID code (STN) assigned to each terminal device 2,
An 8-bit polling ID (ID-EOT) for requesting a response to the terminal device 2 and a frequency (hereinafter referred to as a frequency) set by the terminal device when data is transmitted from the terminal device 2 to the center device 1 ( And 16-bit upstream frequency data (Frq-up) indicating the upstream frequency.

Further, a delay control slot (DLC-D)
Is 12-bit time slot data (TS) for specifying the time slot of the terminal device 2, 4-bit timing data (Tim) for specifying the data transmission timing of the terminal device 2, and Device 2
8-bit amplitude data (Amp) for designating the amplitude of the data, a 16-bit reserved area (Reserve) used when new transmission data increases in the future, and the delay control slot (DLC). -D) a 16-bit error correction code (ER-Det) for performing the entire error correction.

On the other hand, the delay control slot (DLC-U) assigned to each frame of the uplink data transmitted from the terminal device 2 to the center device 1 is shown in FIG.
As shown in (b), it has a data length of 136 bits, and a 4-bit guard band (G) and 1
The 6-bit unique word (Unq-word) and the data transmission output level from the terminal device according to the transmission distance to the center device 1 which differs for each terminal device 2
32-bit level detection data (LV
L-Det).

The delay control slot (DLC-
U) is 32-bit ID data (STN) unique to the terminal device, an 8-bit response code (ID-EOT) indicating that the terminal device has responded to the response request by the polling ID from the center device 1, and the center device 1 The 12-bit time slot data (TS) for confirming the time slot of the terminal device 2 specified by the center device 1 on the side of the center device 1 and the data transmission timing of the terminal device 2 specified by the center device 1 It has 4-bit timing data (Tim) for confirmation at the center device 1 side.

The delay control slot (DLC-
U) is 8-bit amplitude data (Amp) for confirming the data amplitude of the terminal device 2 specified by the center device 1 on the side of the center device 1, and the entire delay control slot (DLC-U). It has a 16-bit error correction code (ER-Det) for performing the error correction of (1) and a 2-bit guard band.

Here, the downlink data transmitted from the center device 1 to each terminal device 2 is continuously transmitted to a plurality of terminal devices 2 that have requested transmission. The upstream data transmitted to the center device 1 is
Since transmission is performed from a plurality of terminal devices 2 to one center device 1, for example, when two terminal devices 2 simultaneously transmit uplink data, the two uplink data are transmitted to the center device 1 in an overlapping manner. In addition, there is a possibility that the terminal device 2 that has requested the transmission cannot be specified on the center device 1 side. For this reason, the delay control slot (D
In LC-U), a 4-bit guard band and a 2-bit guard band are provided at the beginning and end of the delay control slot, respectively, thereby preventing the above two data from overlapping.

In the center device 1 side, in the delay control operation, in order to accurately detect data intermittently transmitted from a plurality of terminal devices 2, the received data is delayed by one symbol and detected. And delay detection is performed. Therefore, the delay control slot (DLC-U) of the uplink data includes the PLL of the center device side.
A 16-bit unique word, which is a data pattern unique to the terminal, for performing phase pull-in by the circuit is added. The center device 1 performs phase pull-in based on the unique word, To play.

Next, the VOD having the above configuration
The operation of the system will be described.

First, in the VOD system, when the terminal device 2 is installed at the subscriber's house by a subscription contract,
The initial delay time of the newly installed terminal device 2 is measured, and the initial delay amount is registered in the response delay amount storage database 10.

That is, at the time of registration of the initial delay amount, the communication unit 5 of the center device 1 transmits a terminal response request command to be transmitted to the newly installed terminal device 2 via the communication line 3. The data is transmitted to the terminal device 2.

More specifically, the communication section 5 has a configuration as shown in FIG.
U) 20 forms a terminal response request command for transmission to the newly installed terminal device 2.

The terminal response request command shown in FIG.
Downlink data delay control slot (DLC-D)
Alternatively, using any of the other time slots, FIG.
The synchronization data (Sync) shown in FIG.
Along with the D code (STN), polling ID (ID-EOT), and uplink frequency (Frq-UP), for example, time slot data (TS) and timing data (Tim) each set to "MAX" as a terminal delay initial value, default It is formed by amplitude data (Amp) set to an initial value of 50%, and the like. The response command transmitted from the terminal device matches the head of the upstream frame synchronized with the head of the received downstream communication control frame.

The MPU 20 supplies such a terminal response request command to the buffer circuit 25 via the local bus (Local Bus) 23 and the data bus (D-Bus) 24.

The buffer circuit 25 is supplied with a write signal (C2) formed by the timing generation circuit 30 based on the frame synchronization signal from the frame synchronization generation circuit 36. , The terminal response request command is written in a period other than the delay control slot (DLC-D) of the downlink data frame shown in FIG.

The buffer circuit 25 is supplied with a read signal (C1) formed by the timing generation circuit 30 based on the frame synchronization signal from the frame synchronization generation circuit 36. Based on the read signal, the terminal response request command is read in a bit-by-bit manner at the timing of the delay control slot (DLC-D) of the downlink data frame shown in FIG. Circuit (P / S conversion circuit) 26.

The P / S conversion circuit 26 converts the terminal response request command supplied as parallel data into serial data, and supplies this to the modulator 12 via the filter 27. The modulator 12 performs QPSK modulation processing on the terminal response request command, and
9. The frequency converter 29 converts the terminal response request command into a downlink transmission channel frequency, and transmits this to the terminal device 2 via the high-pass filter and the multiplexer 14.

The data transmitted via the communication line 3 is, for example, a program request signal transmitted from the terminal device 2 to the center device 1 in ascending order of the transmission frequency band as shown in FIG. The transmission frequency band of uplink data, the transmission frequency band of downlink data such as the terminal response request command transmitted from the center device 1 to the terminal device 2, and the program transmitted from the center device 1 to the terminal device 2 A transmission frequency band is allocated according to the type of data, such as a data transmission frequency band.

Next, the terminal device 2 has a configuration as shown in FIG. 6, and a terminal response request command from the center device 1 is supplied to the frequency converter 44 via the input / output terminal 40. Is done. The frequency converter 44 down-converts the terminal response request command transmitted from the center device 1 into a signal of a frequency handled by the terminal device 2 and supplies the signal to the demodulation circuit 45. The demodulation circuit 45
Q corresponding to the QPSK modulation process performed when transmitted
PSK demodulation processing is performed on the terminal response request command, and the command is supplied to a serial / parallel conversion circuit 46 and a frame synchronization circuit 47. The frame synchronization circuit 47 detects a 16-bit frame synchronization signal added to the head of the terminal response request command, and supplies this to the timing generation circuit 48.

The timing generation circuit 48 supplies a conversion signal to the serial / parallel conversion circuit 46 at the timing when the frame synchronization signal is detected. This allows
In the serial / parallel conversion circuit 46, the terminal response request command supplied as serial data is converted into parallel data and supplied to the command processing circuit 49 and the communication control circuit 50 in the control unit 52.

The command processing circuit 49 converts the terminal response request command into an ID code (S
TN) and supplies it to the terminal control circuit 51.
The terminal control circuit 51 compares the self-registered ID code registered in advance with the detected ID code, and forms a response command to which the self-ID code is added only when the two coincide with each other. Is supplied to the parallel / serial conversion circuit 55 via the communication control circuit 50.

The parallel / serial conversion circuit 55 converts a response command supplied as parallel data into serial data, and converts this into an SFT circuit 56 and a filter 57.
To the modulator 58 via The modulator 58 performs QPSK modulation processing on the response command, and supplies this to the frequency converter 60 via the filter 57. The frequency converter 60 up-converts the response command subjected to the QPSK modulation processing to an uplink transmission channel frequency of a designated time slot, and converts the up-converted command into the center device 1 via the input / output terminal 40 and the communication line 3. To be transmitted.

When the terminal device 2 receives the terminal response request command of the downlink data as an agreement between the terminal device 2 and the center device 1, the terminal device 2 transmits the frame to which the terminal response request command is attached. The response command is returned at the beginning of the next frame.

Next, the response command transmitted to the center device 1 is supplied to the frequency conversion circuit 31 shown in FIG. The frequency conversion circuit 31 converts the response command into a signal of a frequency handled by the center device 1 and supplies the signal to the demodulator 13. The demodulator 13 transmits the QP
A QPSK demodulation process is performed on the response command subjected to the SK modulation process, and this is supplied to a delay amount calculation circuit 35 via a carrier detection circuit 34. The delay amount calculation circuit 35 measures the time from the beginning of the frame next to the frame in which the terminal response request command is transmitted to the time when the response command is received as “response time”,
Supply to U20.

That is, the terminal device 2 returns a response command in accordance with the head of the frame next to the frame to which the terminal response request command has been added as described above. For this reason, the delay amount calculation circuit 35
The response time measured by the terminal device 2
The time obtained by adding the delay time when performing communication to the terminal device 2 and the delay time when performing communication from the terminal device 2 to the center device 1 is measured. As a matter of course, in the same transmission path, as the transmission distance from the center device 1 to the terminal device 2 increases, the terminal response time also increases.

The MPU 20 controls each unit such that the terminal response time is measured, for example, 16 times for the newly installed terminal device 2, and is supplied from the delay amount calculation circuit 35 for each measurement. By averaging the measured data, the measurement error is reduced, and initial delay time data indicating the response time (initial delay amount) when the terminal device 2 is newly installed is formed. Then, this initial delay time data is
The registration is controlled in the response delay amount storage database 9.

When the registration of the initial delay time data is completed, based on the terminal response time indicated by the initial delay time data, the information of the information reaching the center device 1 from the newly installed terminal device 2 is determined. The delay setting value for the head of the frame of the uplink data from the newly installed terminal device 2 is calculated so that the symbol phase matches the other terminal devices 2.

The center device 1 calculates the time from the beginning of the frame to the time when the response command is received as a delay correction value of the newly installed terminal device 2.

Here, the delay correction value is a value indicating how much to advance the head of the frame transmitted to the upstream frame from the head of the upstream frame by the terminal device side, and is a value from the shift register and the buffer in the terminal. This is for correcting the read timing. As a result, it is possible to return a response to the next frame received on the terminal device side.

Alternatively, the center device 1 may calculate the time from the time when the response command is received to the time when the end of the frame is received as the delay setting value of the newly installed terminal device 2. Good. In this case, the response data from the newly installed terminal device 2 reaches the receiving end of the center device 1 at the beginning of the frame two frames ahead of the frame for which the terminal response request was made.

The choice depends on the system configuration between the center device and the terminal device and on the matters to be determined in advance. For example, the former is a case where the terminal device side is configured to be able to output uplink data with a phase earlier than the downlink communication control frame received, and the latter is a case where the latter transmits uplink data with a phase delayed from the changed downlink communication control frame. This is the case where it is configured to output. The embodiment will be described below in accordance with the former case.

The center device 1 calculates the delay setting value and, based on the reception level of the response command, changes the reception level of the uplink data from the newly installed terminal device 2 to another terminal device. The terminal response reception level is set so as to be the same as the reception level of the uplink data from the device 2.

The delay set value data and the terminal response reception level are registered and controlled in the subscriber management database 10.

When the initial setting is completed on the side of the center device 1, the terminal device 2 can be substantially used.

After completing the initial setting, when the subscriber requests transmission of a desired program, the subscriber uses the keypad 53 shown in FIG. 6 to input a code corresponding to the desired program. Accordingly, the terminal control unit 51 adds the ID code of the terminal device 2 to the program code specified by the subscriber, and transmits the program code to the center device 1 via the communication control circuit 50. This program code is subjected to QPSK modulation processing by the modulator 58, converted to the frequency of uplink data by the frequency conversion circuit 60, transmitted to the center device 1, and transmitted to the center device 1 shown in FIG. The signal is supplied to the circuit 31.

The frequency conversion circuit 31 converts the program code and the like into a frequency handled by the center device 1 and supplies this to the demodulator 13. The demodulator 13 performs a QPSK demodulation process on the program code and the like, and outputs this through the serial / parallel conversion circuit 32 and the buffer circuit 33 to the MPU 2.
Supply 0. When the program code or the like is supplied, the MPU 20 compares the ID code of the terminal device 2 with the corresponding ID code stored in the subscriber management database 9 to determine whether or not the terminal device 2 is a subscriber. The program code is transmitted together with the ID code to the video server 7 via the internal bus line 15 shown in FIG.

When the program code is supplied, the video server 7 reads and controls the video database 6 so as to read out the program data corresponding to the program code. Then, the program data is transmitted to the subscriber's terminal device 2 indicated by the ID code. The program data is subjected to 64QAM modulation processing by the modulator 8, transmitted to the center device 2 side via the multiplexer 14, and supplied to the tuner unit 41 via the input / output terminal 40 shown in FIG.

The tuner section 41 selects a transmission channel of the program data and supplies it to the demodulator 42. The demodulator 42 performs 64QAM demodulation processing on the program data, and supplies this to the decoding circuit 43. On the side of the center device 1, each program data or the like is stored in, for example, an MPEG format.
(Moving Picture Experts Group), etc., perform high-efficiency compression encoding processing, save the data, and transmit it. For this reason, the decoding circuit 43 converts the program data supplied from the demodulator 42 into the center device 1
The decoding process corresponding to the encoding process performed on the side is performed and reproduced, and the video signal is output via an output terminal 61,
The audio signal is supplied to the television device 16 shown in FIG. Thereby, the video of the program desired by the subscriber is displayed via the television device 16,
The subscriber can watch a desired program.

Here, in the VOD system,
The movement of each terminal device 2 installed at each subscriber's house is detected to prevent unauthorized viewing.

That is, for example, the center device 1
By detecting the response delay time of each terminal device 2 at predetermined time intervals, such as once or multiple times a day, and comparing this with the response time (initial delay amount) registered at the time of terminal installation, The movement of the terminal device 2 is detected.

[0098] Specifically, the center device 1
FIG. 7 shows the configuration including the functional blocks of the PU 20. When the response time of each terminal device 2 is detected (movement is detected), the operation is performed according to the flowchart of FIG. ing.

In the flowchart shown in FIG. 8, the MPU 20 uses the time information from the timer to
Is started by detecting that the response time is detected, and the process proceeds to step S1.

In step S1, the control unit 65 shown in FIG.
Confirms the subscriber management database 10 via the database reading unit 77, so that the initial delay time data of the terminal device 2 currently attempting to detect the response time is stored in the response delay amount storage database 9 It is determined whether or not it is stored in. If the initial delay time data has been registered, an initial value registered flag is set, the initial delay time data of the terminal device is read from the response delay amount storage database 9, and the recording / reproducing memory (RAM) 38 shown in FIG. And control is passed to step S2.

The MPU 20 shown in FIG.
(Counter Timer Controller) and a direct memory access controller (DMAC). The DMAC 22 allows the DMAC 22 to store and read data to and from the RAM 38 for the buffers 25 and 33.
This is performed directly without using U20.

Next, in step S2, the control unit 65
However, in order to poll the terminal device 2,
In order to form the terminal response request command by setting the ID code of the terminal device 2, the time slot position of the uplink data, the uplink frequency, the delay setting value, and the output gain control value, and to transmit the terminal response request command Are set in the down channel setting circuit 69 and the up channel setting circuit 70.
Then, the formed terminal response request command is transmitted to the write signal (C2) supplied from the timing generation circuit 30.
, The write control is performed on the DLC slot area in the buffer circuit 25 having a FIFO (First In First Out) configuration, and the process proceeds to step S3.

The terminal response request command written in the buffer circuit 25 is read out in synchronization with the frame synchronization signal by the read signal (C1) supplied from the timing generation circuit 30, and the P / P signal shown in FIG. S conversion circuit 2
6 is converted into a serial stream, band-limited by a filter circuit 27, QPSK-modulated by a modulator 12, converted to a frequency of a downlink transmission channel by a frequency converter 29 at a predetermined symbol rate, and transmitted to the communication line 3. Is done.

When the control unit 65 polls such a specific terminal device 2 in step S3, the control unit 65 waits for reception of response data from the terminal device 2 and proceeds to step S4.

In step S 4, the control section 65 starts measuring the terminal response time from the beginning of the frame following the polling operation, and waits for a response command from the terminal device 2.

Next, the terminal device 2 that has received the terminal response request command transmitted by such a polling operation
Is a command processing circuit 49 as described with reference to FIG.
To process the terminal response request command, form a response command corresponding to the command, and transmit it to the center device 1.

[0107] As described above, when the terminal device 2 receives the downlink data terminal response request command as an agreement between the terminal device 2 and the center device 1,
The response command is sent back to the beginning of the frame following the frame to which the terminal response request command is attached.

The transmitted response command is supplied to the upstream data demodulation circuit 13 and the delay amount measurement circuit 35 via the low-pass filter 80.

In step S5, the control unit 65 sets the terminal within the range of the terminal response time slot located in the next frame head area where the polling operation has been performed within a predetermined time after the reception waiting state. It is determined whether there is a response. If there is a terminal response within the predetermined time, the process proceeds to step S6. If there is no terminal response within the predetermined time, it is determined that some trouble has occurred. To make a terminal response request,
Returning to step S1, the routine from step S1 to step S5 is repeatedly executed.

Here, the control section 65 sets a predetermined number m,
If there is no terminal response even if a terminal response request is made, a terminal response request is made to another terminal device.

If the number of repetitions exceeds the predetermined number m in step S5, the next terminal device is set and polling is newly started except for the terminal device concerned.

In step S6, the MPU 20 determines the terminal response time of the terminal device 2 from the start of the next frame after the polling operation until the response command is received from the terminal device 2. And the process proceeds to step S7.

That is, to the delay amount measuring circuit 35 to which the response command returned from the terminal device 2 is supplied, the measurement enable signal (C
3) is supplied, and when the measurement enable signal is supplied, the delay amount measurement circuit 35 resets the measurement time at the head of the frame of the uplink data, and resets the terminal time until the head of the uplink data is detected from this point. The response time is counted. The terminal response measurement result measured by the delay amount measurement circuit 35 is temporarily stored and controlled using the RAM 38 as a buffer, and thereafter the MPU 20 reads out the RAM 38 from the RAM 38 in which the terminal response measurement result is stored, and performs offline time measurement processing. , Averaged. Thereafter, it is stored in another area of the RAM 38.

The measurement of the terminal response time is performed, for example, 16 times for one terminal device 2, and the terminal response time measured each time is stored and controlled in the RAM 38. I have. Therefore, step S
At 7, the control unit 65 determines whether or not the measurement of the terminal response time has been completed a predetermined number of times. If the determination is No, the process returns to step S3. The above routine is repeatedly executed, and in the case of Yes, the process proceeds to step S8.

In step S8, the average of the terminal response times stored and controlled in the RAM 38 is detected by measuring the response times for a predetermined number of times.

That is, when the measurement of the response times for the predetermined number of times is completed, the MPU 20 reads each terminal response time data from the RAM 38 and supplies the data to the averaging processing circuit 72 shown in FIG. The clock (C4) output from the timing generation circuit 30 after the DLC period has been completed a predetermined number of times from the start of the delay measurement is supplied to the averaging processing circuit 72. This clock (C4)
It occurs every time the MPU 20 reads each terminal response time data from the RAM 38. The averaging circuit 72 calculates each terminal response time data read from the RAM 38 at the timing when the DLC period of the upstream frame ends with this clock, calculates an average time, and supplies the average time to the changeover switch 73.

As described above, by detecting the terminal response time a plurality of times and calculating the average thereof, the detection error of the terminal response time can be suppressed, and the detection accuracy of the terminal response time can be improved. it can.

Next, when the terminal response time averaging process is completed and the process proceeds to step S9, the control unit 65
Based on the initial value registered flag, it is determined whether or not the terminal response time detected by the averaging process is detected for the first time after the terminal device 2 is installed.
In the case of es, the process proceeds to step S10, and in the case of No, the process proceeds to step S13.

In step S10, the terminal response time detected by the averaging process is detected only after the terminal device 2 is installed.
Controls the changeover switch 73 so that the terminal response time data is supplied to the DB registration processing circuit 74. Then, the DB registration processing circuit 74 converts the terminal response time data into “initial delay time data” as described above.
Is registered in the data storage area of the response delay amount storage database 9 corresponding to the terminal device, and the process proceeds to step S11.

In step S11, the delay amount calculation setting circuit 75 calculates the output delay timing of the uplink data from the terminal device 2 based on the initial delay time data as described above, and proceeds to step S12.

At step S12, at step S11
The output delay timing of the uplink data calculated in the above is transmitted as a terminal-side delay control amount, together with the terminal setting command and the ID code of the terminal device 2, to the downlink terminal response request time slot, and returns to step S1. The polling process for the next terminal device is performed by setting the ID code and the like of the terminal device.

On the other hand, if it is determined in step S9 that the terminal response time detected by the averaging process is not the first time detected since the terminal device 2 was installed, the control unit 65 sets The switch 73 is controlled so that the terminal response time data is supplied to the comparison circuit 78, and the DB reading circuit 77 is controlled so as to read the initial delay time data of the terminal device 2 from the response delay amount database 9. . This DB
The terminal device 2 read by the reading circuit 77
Is supplied to the comparison circuit 78.

The comparing circuit 78 compares the initial delay time data read from the response delay amount database 9 with the currently detected terminal response time data, and supplies the comparison output to the control unit 65.

Next, in step S14, the control unit 65
Determines whether or not the terminal device 2 has moved based on the comparison output.

More specifically, if the comparison output indicates a time difference exceeding 1/16 symbol, the control section 65 determines that the terminal device 2 has moved, and the comparison output indicates If it indicates a time difference not exceeding 1/16 symbol, it is determined that the terminal device 2 has not moved. When it is determined that the terminal device 2 has not moved, the process proceeds to step S15, and when it is determined that the terminal device 2 has moved, the process proceeds to step S18.

In step S15, since the terminal device 2 has not moved, the delay amount calculation setting circuit 75 updates the initial delay time data to update the previously set delay setting value of the terminal device 2. The output delay timing of the uplink data from the terminal device 2 is calculated based on the
Proceed to 6.

At step S16, the control unit 65
The output delay timing of the uplink data calculated in step S15 is used as the terminal-side delay control amount, and
The terminal setting command and the ID code are re-registered in the subscriber management database 10, and the process proceeds to step S17.

At step S17, the control unit 65
The ID code, delay measurement value, measurement date, time, and other measurement histories of the terminal device are stored in the area for storing the information of the terminal device 2 in the response delay amount storage database 9, and the process proceeds to step S19.

On the other hand, if the movement of the terminal device 2 is detected in step S14, the control section 65 proceeds to step S18, forms a parental control command for the terminal device 2, and sends this to the ID of the terminal device 2. The transmission is performed with the code attached, and the process proceeds to step S19.

The parental control command transmitted to the terminal device 2 is decoded by the command processing unit 49 shown in FIG. 6 and supplied to the terminal control unit 51. When this viewing restriction command is supplied, the terminal control unit 51 performs “viewing restriction” of the terminal device 2 itself.

Specifically, when the terminal control unit 51 receives the parental control command, the terminal control unit 51 uses the so-called “notification” channel of the data transmitted from the center device 1 side in the terminal device 2. Only a certain terminal information notification channel can be received. In addition, the uplink data from the terminal device 2 to the center device 1 is transmitted to the center device 1 such as a response command to the terminal response request command.
Only the response request from the side is allowed.

The operation from the detection of movement of the terminal device 2 to the restriction on viewing will be described with reference to a specific example. In FIG. 1, two terminal devices 2 are provided to the subscriber A home (Home A) by contract. , 2a are lent, and subscriber A uses one of them 2a due to fraudulent acts.
When the center device 1 measures the transmission delay time of the response command from each of the terminal devices 2 and 2a according to the terminal response request command, the terminal device 2 installed at the subscriber A's home does not move. Although the time difference between the transmission delay times described above is within 1/24 symbol, the terminal device 2a lent to the non-subscriber B home moves from the subscriber A home to the non-subscriber B home. The transmission delay time shows a time difference of 1/16 symbol or more from the initial response time.

In general, the transmission speed of data transmitted on the communication line 3 used in the VOD system is 85 times the speed of light.
%, And the above data is transmitted over the communication line 3 of 1 m.

1 / (3 × 10 ⁸ × 0.85) = 3.92 ns / m

For example, as shown in FIG. 2, if the transmission symbol rate of uplink data is 4.096 MSPS and the time resolution on the center device 1 side is 16 times the symbol rate, detection in 15.3 ns units is performed. It becomes possible.
Therefore, when the terminal device 2a lent to the non-subscriber B's house has moved 3.9 m or more from the subscriber's A's house, the center device 1 can detect the movement. Then, when this movement is detected, the above-mentioned viewing restriction is executed. As a result, unauthorized viewing of unsubscriber B (and improper behavior of subscriber A) can be prevented.

In the case of a system configuration in which the uplink transmission rate is set to about 1 MSPS, the transmission symbol rate of the uplink data is 1.024 MSPS and the time resolution on the center device side is 24 times the symbol rate, as described above. Then, detection in units of 40.7 ns becomes possible, and this is sufficiently effective even when the uplink symbol rate is low. In this case, the movement can be detected when the distance exceeds 11 m.

Next, when such parental control is completed in step S18, when the registration of the initial delay amount of the terminal device 2 is completed in step S12, and when the measurement history is written in step S17. In the case where the process is completed, in step S19 to proceed to, the control unit 65 shown in FIG. 7 determines whether or not the measurement of the transmission delay time for all the terminal devices 2 of all the subscribers of the VOD system is completed. When all the measurements have been completed, FIG.
Are completed. If all the measurements have not been completed, step S
1, the routine from step S1 to step S19 is repeatedly executed for the terminal device 2 designated by the next polling terminal designation circuit 76.

As is clear from the above description, the first
In the VOD system according to the embodiment, the terminal response time of the terminal device 2 installed at the time of contract is stored in the response delay amount database 9 as the initial delay time, and the initial delay time and the terminal response time detected thereafter are stored. By comparing the time with the time, the movement of the terminal device 2 can be detected.
Then, when the movement of the terminal device 2 is detected, by subjecting the terminal device 2 to a viewing restriction process, unauthorized viewing can be prevented.

The VOD system has a response delay amount database 9 for storing the initial delay time.
And a simple configuration that simply causes the control unit 65 to execute a program that periodically measures the delay time of each terminal device 2 and compares the program with the initial delay time. Therefore, the VOD system can be realized at low cost through simplification of the configuration.

If the VOD system according to the first embodiment is operated for a long period of time, the terminal response time changes due to aging of each unit and change in the transmission path, and so on. There is a concern that detection of movement (detection of unauthorized viewing) may be erroneously detected.

However, in the case of the above-mentioned aging of each part, since the aging is a long-term change, the change speed is very slow, and even if this occurs, the reception phase of the uplink data at the time of terminal response changes only slightly. . In addition, since the same transmission line in the same area shows substantially the same change, the control unit 65 observes the history of the change amount, so that the terminal response time suddenly changes due to the intentional movement of the terminal device. It can be distinguished from a change, and does not cause the erroneous detection.

Also, the change of the terminal response time due to the change of the transmission line is handled in the same way as the aging of the above-mentioned parts by managing and observing the changed part and the change time of the transmission line on the center device side. be able to. Regarding the change of the transmission line, a response circuit is added to the HUB, node, tap-off, etc., which are the main points of the distribution line including the communication line 3, and the center device 1 is changed in the same manner as the terminal device 2 described above.
By forming a response command in response to a terminal response request command from the terminal device and returning the response command to the center device 1, the presence or absence of movement of the terminal device 2 can be reliably detected.

Next, although there is almost no problem when the symbol rate of the uplink data from the terminal device is 4 MSPS, the symbol rate of the uplink data is 1.024.
In the MSPS system, when the terminal device 2 moves 11 m or more, the center device 1 can detect the movement for the first time. Therefore, when the present invention is applied to an apartment house or an apartment house where the adjacent house is only a few meters away from the wall, the center device 1 side is used to detect the movement of the terminal device 2 to the adjacent house. In this case, a detection accuracy of 50 to 100 times the symbol rate is required, which is not practical.

Therefore, in addition to the configuration of the above-described first embodiment, the frequency trap devices 85a to 85c or (and) the unique word insertion device 87 as described in the following second and third embodiments will be described. , 88, it is possible to detect the movement between adjacent houses in the apartment house.

In the description of the second and third embodiments, the same reference numerals are given to the portions indicating the same operations as those of the VOD system according to the above-described first embodiment, and duplicate description will be avoided. It shall be.

That is, the VOD system according to the second embodiment of the present invention, in addition to the configuration of the above-described first embodiment, has a frequency for blocking the passage of uplink data of a predetermined frequency as shown in FIG. It is provided with trap devices 85a to 85c. Each of these frequency trap devices 85a-8
Reference numeral 5c is provided outside the subscriber's home such as a service entrance for drawing a line branched from the communication line 3 into the subscriber's home, for example. It has become.

Further, the frequency trap device 85a is
It has a characteristic of blocking passage of only uplink data of the first frequency BWa. Further, the frequency trap device 85b
The frequency trap device 85c has a characteristic of blocking the passage of only the uplink data of the second frequency BWb and the passage of only the uplink data of the third frequency BWc.

In the VOD system according to the second embodiment having such a configuration, when the terminal device 2 is installed in each resident's house adjacent to the multiple dwelling house, the terminal device 2 is installed and the stop band is different. Frequency trap device 8
5a to 85c are installed outside each resident's house.

Specifically, subscriber A's home shown in FIG.
A)-Assuming that the home of the subscriber C (Home C) is adjacent residents in one apartment house, the trap device 85a for the subscriber A sets the first frequency BWa as a stop band, and subscribes. In the trap device 85b for the person B, the second
Is set as the stop band, and the third frequency BWc is set as the stop band in the trap device 85d for the subscriber C.

[0149] Then, for the terminal device at the subscriber A's house, the center device 1 sets, for example, the second frequency BWb, which is a band other than the first frequency BWa, of the stop band at the subscriber A's house as the upstream frequency. The terminal device 2 installed in the subscriber A's home transmits the terminal response request command to the terminal A in response to the terminal response request command, in response to the terminal response request command, in a band other than the first frequency BWa of the stop band of the subscriber A's home. For example, a response command is returned using the second frequency BWb.

On the other hand, the center apparatus 1 transmits the second frequency BW of the stop band of the subscriber B home to the subscriber B home.
The terminal device 2 installed at the subscriber B's home transmits a terminal response request command by designating a third frequency BWc which is a band other than the band b. A response command is returned using BWc.

Further, the center apparatus 1 designates the first frequency BWa which is a band other than the third frequency BWc of the stop band of the subscriber C home for the subscriber C home, and specifies the terminal response request command. Is transmitted, and the terminal device 2 installed at the subscriber C's home receives the first response to the terminal response request command.
A response command is returned using the frequency BWa of

As described above, the center device 1 and each subscriber A
To the subscriber C perform data transmission using a band other than the set stop band BWa to the stop band BWc.

Here, suppose that the subscriber A makes a contract for lending a plurality of terminal devices 2 and moves one of the lent terminal devices 2 to the subscriber B's house. ,
When receiving the terminal response request command from the center device 1, the terminal device 2 moved to the subscriber B home receives the second frequency B which is the communication band allocated to the subscriber A.
The response command is sent back using Wb, and this response command is supplied to the trap device 85b provided for the subscriber B's house.

As described above, the stop band of the trap device 85b provided for the subscriber B's house is the second frequency Bwb allocated to the communication band for the subscriber A's house. For this reason, the response command from the terminal device 2 moved to the subscriber B's home (lostly lent from the subscriber A's home) is sent to the trap device 8 provided for the subscriber B's home.
5b, and is not transmitted to the center apparatus 1 side.

When the center device 1 detects that the response command from the terminal device 2 is not returned, the center device 1 transmits the terminal response request command again so as to return the response command on another channel, for example, the first frequency BWa. Transmit. When receiving the terminal response command, the terminal device 2 sets the data transmission frequency to the first frequency BWa specified by the center device 1 and transmits the response command. Since this response command is transmitted at the first frequency BWa, its stop band is changed to the second frequency BWa.
trap device 85b for subscriber B's home set to "b"
And is transmitted to the center device 1 side.
Thereby, it can be detected that the terminal device 2 has been illegally moved to the subscriber B's house. Center device 1
Detects the illegal movement of the terminal device 2 and restricts the viewing described above.

As described above, in the VOD system according to the second embodiment, the trap units 85a to 85c having different stop bands are provided outside the adjacent subscribers' homes, respectively. Then, each trap device 85
By performing communication using a band other than the stop bands a to 85c, even if the terminal device 2 is illegally moved to a neighbor's house of several meters through a wall such as an apartment house, the terminal device 2 can be used. Since the return of the response command from the device is prevented by the trap device, the movement can be detected, and unauthorized viewing can be prevented.

Next, V according to the third embodiment of the present invention will be described.
The OD system will be described.

In the VOD system according to the third embodiment, in addition to the configuration of the above-described first embodiment, a unique word insertion device 87 is added to a node of the communication line 3 as shown by a dashed line in FIG. A unique word insertion device 88 is provided at the tap-off of each terminal device 2.

The unique word insertion device 87 (and unique word insertion device 88) adds a unique word to the terminal response request command transmitted from the center device 1 to each terminal device 2. As shown in FIG. 10, a typical configuration is a band-pass filter (BPF) 8 for extracting a downlink communication frame from the center device 1.
9 and a frequency conversion circuit (DC) 90 for converting the frequency of the downlink communication frame extracted by the BPF 89 to an intermediate frequency handled by the unique word insertion device 87.
And a demodulator 91 for performing QPSK demodulation processing on the downlink communication frame subjected to QPSK modulation processing and transmitted.

The unique word insertion device 87
The output timing of each pulse is determined by a frame synchronization unit 92 that detects a frame synchronization word added to the head of a downlink communication frame subjected to QPSK demodulation processing and a comparison output from a phase comparator (PC) 98 described later. It is controlled so as to detect a reserved area in the downlink communication frame based on the detection output of the frame synchronization word from the frame synchronization section 92 and output this detection pulse, and to perform the detection based on the detection result of the reserved area. And a timing generation circuit 93 for outputting first and second switching pulses for controlling the switching of the first switch 95 and the second switch 97.

Also, the unique word insertion device 87
Is a unique word generating circuit 94 for generating a predetermined unique word based on the detection output of the reserved area from the timing generating circuit 93, and a demodulator 91 in response to a first switching pulse from the timing generating circuit 93.
To switch and output the data of the downstream communication frame supplied from the timing generation circuit 93 and the unique word supplied from the unique word generation circuit 94.
And a modulator 96 for performing QPSK modulation processing on data of the downstream communication frame from the first changeover switch 95.

The unique word insertion device 87
Compares the phase of the data of the downstream communication frame from the BPF 89 with the phase of the data of the downstream communication frame remodulated by the modulator 96, and outputs a comparison output to the timing generation circuit 93. A second switch for switching and outputting data of the downstream communication frame from the BPF 89 and data of the downstream communication frame remodulated by the modulator 96 in response to the second switching pulse from the timing generation circuit 93. 97
A BPF 100 to which data of a downstream communication frame is supplied from the second changeover switch 97;
An HPF 99 to which the data of the downlink communication frame supplied to F89 is supplied, and a low-pass filter (LPF) for passing an uplink frequency from the subscriber terminal device.

Next, the operation of the VOD system according to the third embodiment having the unique word insertion device 87 (or unique word insertion device 88) having such a configuration will be described.

First, when the above-mentioned terminal response request command is output from the center device 1 side, this terminal response request command is supplied to the BPF 89 and HPF 99 in the unique word insertion device 87 via the communication line 3. .

The BPF 89 extracts a downstream communication frame from the terminal response request command, supplies the same to the second changeover switch 97 and the phase comparator 98, and supplies the same to the frequency converter 90. The frequency converter 90 converts the data of the downlink communication frame into an intermediate frequency handled by the unique word insertion device, and supplies this to the demodulator 91. The demodulator 91 performs QPSK demodulation processing on the data of the downlink communication frame, supplies the data to the frame synchronization unit 92, and supplies the data to the first switch 95 via the timing generation circuit 93.

The frame synchronization unit 92 detects a frame synchronization word (Sync shown in FIG. 3A) located at the head of the demodulated downlink communication frame data, and outputs this detection output at the timing. It is supplied to the generator 93. When the detection output of the frame synchronization word is supplied, the timing generator 93 forms a first switching pulse based on the detection output, supplies the first switching pulse to the first switching switch 95, and will be described later. Based on the comparison output from the phase comparator 98, a reserve area (Reserve shown in FIG. 3A) in the downlink communication frame is detected,
This detection output is supplied to a unique word generation circuit 94.

The unique word generating circuit 94 is, for example, a PN code sequence generator having a unique generating polynomial. The unique word generating circuit 94 forms a word unique to the transmission line at the timing when the detection output of the reserved area is supplied. This is supplied to the first changeover switch 95. The data of the downstream communication frame from the demodulator 91 is supplied to the first changeover switch 95. Usually, the first changeover switch 95 outputs the data of the downstream communication frame by the first changeover pulse from the timing generation circuit 93. Switching is controlled. When the reserved area is detected by the timing generation circuit 93, the switching is controlled so that the unique word from the unique word generation circuit 94 is output at this timing. As a result, the first changeover switch 95 outputs data of the downstream communication frame in a form in which the unique word is inserted in the reserved area. This first changeover switch 95
Are supplied to the modulator 96.

The modulator 96 adds QP to the data of the downlink communication frame in which the unique word is inserted in the reserved area.
SK modulation processing is performed, and this is changed to a second changeover switch 9
7 and to a phase comparator 98.

The phase comparator 98 compares the data phase of the downstream communication frame supplied via the BPF 89 with the data phase of the downstream communication frame in which a unique word has been inserted into the reserved area from the modulator 96. The comparison output is supplied to the timing generator 93. The timing generator 93 varies the output timing of each pulse based on the comparison output.

That is, the phase comparator 98 compares the data of the downlink communication frame in which the unique word is inserted in the reserved area with the data of the downlink communication frame in which the unique word is not inserted in the reserved area. Therefore, the comparison output appears during the reserved area period. For this reason, the timing generation unit 93 is a timing at which the comparison output is supplied.
The count value of the internal counter is reset at the detection timing of the reserve area. Then, the internal counter is counted from this reset, and a reserved area detection output for generating a unique word is supplied to the unique word generating circuit 94 during the reserved area period based on the count value, and the unique word is output. The first changeover pulse for selecting the first changeover switch 9
5, and a second switch pulse for selecting data of the downstream communication frame subjected to the QPSK modulation processing by the modulator 96 is supplied to a second switch 97.

The data of the downstream communication frame from the BPF 89 is supplied to the second changeover switch 97. Normally, the data of the downstream communication frame is selected and output. When the second switching pulse is supplied at the timing of detecting the reserved area (timing of resetting the internal counter), the data of the downlink communication frame from the modulator 96 is selected and output.

Thus, it is possible to form a terminal response request command by accurately inserting the unique word into the reserved area of the data of the downlink communication frame supplied from the BPF 89. That is, the modulator 96
As the data of the downstream communication frame subjected to the SK modulation processing, only the unique word is used.

The terminal response request command formed by the switching control of the second switch 97 is BP
It is supplied to the terminal device 2 via F100. Data other than the terminal response request command is supplied to the terminal device 2 via the HPF 99.

Next, upon receiving the terminal response request command, the terminal device 2 forms the response command described above,
This response command is returned to the center device 1 in synchronization with the head of the downstream frame using the upstream channel of the frequency specified by the terminal response request command. At this time, the terminal device 2 returns the unique word inserted in the reserved area of the terminal response request command to the center device 1 side with the response command.

When the response command is returned from the terminal device 2 specified by the terminal response request command, the center device 1
The unique word attached to the response command is detected, and it is determined whether or not the unique word belongs to the unique word insertion device 87 provided on the transmission path of the terminal device 2. Then, the unique word is the terminal device 2
In the case of the unique word insertion device 87 provided on the transmission line of the terminal device 2, it is determined that the terminal device 2 does not move, and the unique word is inserted into the unique word insertion device provided on the transmission line of the terminal device 2. If it is not the device 87, it is determined that the terminal device 2 has been improperly moved, and the above-described viewing restriction is executed.

As described above, in the VOD system according to the third embodiment, a unique word that generates a unique word indicating that a transmission has been made on the transmission line of the terminal device 2 in the transmission line of the terminal device 2 A generating device 87 (88) is provided, and the unique word generated by the unique word generating device 87 is added to the terminal response request command from the center device 1 and transmitted to the terminal device 2 side. Then, the terminal device 2 adds the unique word transmitted together with the terminal response request command to the response command, and
Side, and the center device 1 detects the unique word returned along with the response command.

As a result, it is possible to detect whether or not the data (response command) transmitted from the terminal device 2 is transmitted via the transmission path allocated to the terminal device 2. The movement of the terminal device 2 can be detected.

Specifically, when the unique word insertion device 87 is provided at the node of the distribution line as shown in FIG. 1, the movements of a plurality of terminal devices 2 can be detected collectively.

When the unique word insertion device 88 is provided at the tap-off portion of the distribution line as shown in FIG. 1, the movement of the terminal device 2 at each subscriber's home can be detected separately.

Next, such a unique word insertion device 87, 88 receives the terminal response request command from the demodulator 91 as shown by the dotted line in FIG.
01 (PN code sequence generator) may be provided, and the command processing / word change circuit 101 may supply a different sequence to the unique word generation circuit 94 in accordance with an instruction from the center device 1. Thereby, the center device 1
Different unique words can be generated in response to an instruction from the user (unique word change control), and illegal viewing can be more strongly prevented.

The unique word insertion device 87,
As shown by a dotted line in FIG. 10, a demodulator 88 is provided based on the unique word from the unique word generating circuit 94.
A scramble processing circuit 102 that performs scramble processing on downlink communication data supplied from 1 through the timing generation circuit 93 and supplies the data to the modulator 96 may be provided. The scramble processing circuit 102 can be easily constituted by a logic circuit using a flip-flop and an exclusive OR.

In this case, the unique word from the unique word generation circuit 94 and the data of the downstream communication frame from the demodulator 91 are supplied to the scramble processing circuit 102 to be scrambled, and re-modulated by the modulator 96 to the second
Is supplied to the changeover switch 97. The timing generation circuit 93 controls switching of the second switch 97 so that a terminal response request command in which only the DLC area of the communication frame is scrambled is formed. The terminal response request command thus formed is transmitted to the terminal device 2.

The terminal device 2 that has received the terminal response request command decodes the data in the DLC area with the ID code of the terminal device 2 and returns it to the center device 1 together with the response command.

The center device 1 determines whether or not the data from the terminal device 2 has been returned via a predetermined node based on the decoding result of the terminal device 2 with the ID code. The above-described viewing restriction processing and the like are executed according to the result of this determination.

In this case, the first switch 95
Can be eliminated, and the configuration of the VOD system can be simplified.

The scramble processing circuit 102
May be provided on the center device 1 side. Also,
In the scramble process, the ID code of the target terminal device 2 may be used as a unique word.

Lastly, in the description of each of the above embodiments,
The communication between the center device 1 and each terminal device 2 is performed based on the TDMA system. However, this is because the terminal response time can be measured if at least a terminal response for each frame is possible. The present invention is not limited to the scheme, and for example, a spread spectrum scheme having a code slot divided by a plurality of specific codes, a frequency multiplexing scheme (FDM), or the like may be used instead of a time slot divided by time.

When detecting the initial delay time or the like, 16
The average value of the measurement results of the times is calculated, and if a time difference exceeding 1/16 symbol is detected when the movement of the terminal device 2 is detected, it is determined that the terminal device 2 has moved. Has been described with specific numerical values,
This is just an example for easier understanding, and it goes without saying that various changes can be made according to the design and the like within a range not departing from the technical idea of the present invention.

[0189]

The cable television system according to the present invention can detect the movement of the terminal device of each subscriber. Therefore, unauthorized viewing can be detected.

Further, the cable television system can be realized simply at a low cost by simply providing a storage means for storing an initial response time from the terminal device detected at the time of subscription or the like. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment in which a cable television system according to the present invention is applied to a video on demand system (VOD system).

FIG. 2 is a diagram for explaining an upstream frame, a downstream communication control frame, and a downstream frame of a TDMA system used in the VOD system.

FIG. 3 is a diagram for explaining a configuration of a DLC area provided in the upstream frame and the downstream frame.

FIG. 4 is a block diagram showing a configuration relating to delay control and terminal movement detection on the center device side of the VOD system.

FIG. 5 is a diagram illustrating a communication band in the VOD system.

FIG. 6 is a block diagram showing a configuration of a terminal device side of the VOD system.

FIG. 7 is a detailed block diagram of the center device including a functional block diagram of an MPU provided on the center device side of the VOD system.

FIG. 8 is a flowchart for explaining a communication operation of the VOD system according to the first embodiment.

FIG. 9 is a block diagram of a VOD system according to a second embodiment of the present invention.

FIG. 10 is a block diagram of a main part of a VOD system according to a third embodiment of the present invention.

FIG. 11 is a block diagram of a conventional VOD system.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 center device, 2 terminal device, 3 communication line, 4 video supply unit 5 communication unit, 6 database, 7 video server, 8
... Modulator 9 ... Database for storing management data, 10 ... Database for storing response delay amount 11 ... Management communication control unit, 12 ... Modulator, 13 ... Demodulator,
15 Internal bus lines 85a to 85c Frequency trapping device, 87, 88 Unique word insertion device 94 Unique word generation circuit 101 Command processing / word change circuit 102 Scramble processing circuit

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Keiko Ando 3-3-9, Shimbashi, Minato-ku, Tokyo Inside Toshiba AV EE Co., Ltd.

Claims (6)

[Claims] In a cable television system of a two-way communication system for performing two-way communication between a center device and a plurality of terminal devices, the center device requests a response from the center device to each terminal device. Response time detecting means for detecting a response time, which is a time required until the response data corresponding to the terminal response request data is returned from each terminal device when transmitting the terminal response request data to be transmitted, Means for storing the response time of each terminal device detected at a predetermined time by the means as an initial response time, and controlling the response time detecting means so as to detect the response time of each terminal device after detecting the initial response time. Response detection control means for detecting the response time of each terminal device after the detection of the initial response time. And a movement detection means for comparing the initial response time stored in the storage means and the initial response time stored in the storage means, and when there is a difference of not less than a predetermined time, detecting that the terminal device has been moved. Characterized cable television system. 2. The cable television system according to claim 1, further comprising viewing restriction means for restricting viewing by the terminal device when the movement of the terminal device is detected by the movement detection device. 3. A pass band blocking means provided for each terminal device for blocking the passage of data in different frequency bands, wherein the center device and each terminal device have a pass band of the terminal device. 2. The communication is performed using a band assigned to each of the blocks other than the pass block band of the blocking unit.
Or the cable television system according to claim 2. 4. A unique word adding means for adding a predetermined unique word to terminal response request data transmitted from the center device to each terminal device, wherein each terminal device has a unique word added by the unique word adding device. Upon receiving the added terminal response request data, the unique word is added to the response data and sent back to the center device. The center device detects the returned unique word added to the response data and returns the response word. The transmission path to which data is returned is detected, and when the transmission path is a terminal apparatus other than the terminal apparatus, the terminal apparatus detects that the terminal apparatus has been moved. The cable television system according to claim 2. 5. The cable television system according to claim 4, further comprising a unique word changing means for changing a unique word formed by said unique word adding means in response to a command from said center device. 6. A scramble processing means for performing scramble processing on terminal response request data transmitted from said center device based on said unique word, wherein each terminal device has a terminal scrambled by said scramble processing means. When the response request data is received, the terminal response request data is decoded using the information unique to the terminal device, and the decoded data is added to the response data and returned to the center device. By detecting the decoding result of the added and returned terminal response request data, the transmission path to which the response data is returned is detected, and if this transmission path is that of a terminal device other than the terminal device, 6. The cable television system according to claim 4, wherein the terminal device is detected as being moved. System.