Local network as part of cabletelecasting system

FIELD: cabletelecasting.

SUBSTANCE: proposed local network 10 has subscriber leads 21 coupled with cabletelecasting head station 11 in desired carrier band. Network 10 also has noise suppression unit 21 whose input 24 is connected to leads 21 and output, to station 11. Unit 23 has band filters 28 - 31 connected to input 24 and using different passbands and transducers 32 - 35 designed for comparing output signal level of respective filter 28 - 31 with preset reference level and for feeding comparison result dependent logic signals to logic control unit 36 that functions to find out if these signals comply with conditions stored in unit 36 so as to convey control signal to unitized interlocking circuit 26 inserted in separate line 25 used to transfer signals from input 24 to output 27. Circuit 26 passes signals when logic signals received by unit 36 meet conditions stored therein.

EFFECT: provision for integrating interlocking means of noise-suppression unit in unitized interlocking circuit common for all carrier passbands.

9 cl, 2 dwg

 

The present invention relates to a local network, which is part of cable TV systems.

More specifically the invention relates to such a local network, which allows you to transmit signals in the opposite direction from the subscriber conclusions contained in the network head-end station specified CATV system within a predetermined band of carrier frequencies used for transmitting signals in a specified opposite direction, while in the specified local network has a block noise reduction designed to reduce the noise transmitted in the opposite direction from that of the local network.

The local network of the specified type are used in cable television systems, which in addition to the distribution of television signals broadcast from the headend system to subscribers connected to different local networks of this system can be used for bidirectional transmission of signals between subscribers and head station system.

In such cable television systems in the band of carrier frequencies used for transmitting signals in the opposite direction, you may experience strong interference due to noise generated in local networks or falling into them through the subscriber conclusions or lines associated with these conclusions, and nakaplivat what's consistent passing through the system towards the head-end station. That's why it was proposed to provide each local network special block noise reduction to reduce noise transmitted in the opposite direction from the network.

The invention relates to a local network, in which there is block noise with the input, which is connected with the subscriber conclusions; output, which is connected to the parent station; a set of bandpass filters that are associated with the specified input and have different bandwidth, lying within a specified band of carrier frequencies; a corresponding number of sensors each of which is connected with one of these filters and compares the power level of the signal coming from the corresponding filter, at least one predetermined reference level; and locking means functionally associated with these sensors and designed to permit or prohibiting transmission of signals from the specified input to the specified output depending on the result of comparison performed by the specified sensors. In the present description, the term "signal-strength" refers to the instantaneous value of the signal power at the output of the filter, measured over short time intervals of a given duration.

Block noise reduction of the specified type described in the application for the European patent EP 0859514 A2, 7 In this famous block noise reduction locking means is formed by a separate tool lock for each individual bandwidth, each of these locking means is controlled by the output signal from the sensor corresponding to the bandwidth. However, such design of the block noise reduction is unsatisfactory for several reasons. First, different bandwidth should be at some distance from each other, which in turn leads to inefficient use of bandwidth back channel as a whole. In addition, later turns out to be difficult to shift or change the used bandwidth so that they can be used for purposes different from the original.

The aim of the invention is the creation of a local network with the above-described block noise reduction, in which the aforementioned disadvantages can be eliminated or at least significantly reduced.

The network, which according to the invention proposed to achieve this goal, differs primarily from the fact that at least one group of adjacent bandwidths, these locking means are formed only locking scheme, which is common for all bandwidths within the specified group, included in a separate line is used for transmitting signals within these bandwidths from the specified input to the specified output, and is functionally connected with each of the output from the sensors, corresponding to the specified group bandwidths.

Through the use of a single circuit block, the total for all bandwidths in this group, there is no need to pass different bandwidth in the group at some distance from each other. Instead, these bandwidth can be chosen so that they collectively blocked the entire frequency range in which they are located. Different bandwidth may slightly mutually overlap.

According to a preferred variant implementation of the present invention, the bandwidth may include all of the bandwidth within the band of carrier frequencies used for transmitting signals in the opposite direction.

In addition, the sensors corresponding to the specified group bandwidths, preferably can apply logical signals generated by them depending on the comparison result, the logical control unit, which determines whether these signals certain conditions stored in the control unit, and supplies in accordance with this control signal to the locking scheme, allowing the transmission of signals from the specified input to the specified output only when these output signals from the sensors satisfy the specified conditions./p>

The types of conditions stored in the logical control unit, can be very different. As an example we can mention the following conditions: when the logical output signal of one sensor is received by the control unit, changes in direction, svidetelstvuya that the output signal of bandpass filter just changed from a value less specified at least one reference level to a value higher than the specified level, the control unit generates a control signal that enables the transmission of signals through the locking scheme only on the condition that the logical signals received from two or more other sensors, has not changed at the same time in the same way.

Conditions stored in the control unit, can be stored in the specified block constantly unchanged. However, it is preferable that the control unit was programmable and allows you to modify the stored conditions. In this case, the network can be made so as to ensure that such reprogramming of the control unit from the headend of the CATV system.

According to a preferred variant implementation of the present invention, at least one, and preferably each of the sensors belonging to a specified group of bandwidths, is able to compare the level m is snasti output signal, coming from the corresponding bandpass filter, at least two different reference levels. This property of the sensor allows the use of logical control unit for measuring the steepness of the leading edge of the output signal from the specified bandpass filter, and determine whether the front corresponding to the condition stored in the control unit. Since the leading edge of many kinds of interference from external sources, has a slope significantly different from the slope of the leading edge of the signal message transmitted from the subscriber output, the control unit can in this case to generate the control signal, allowing the signal transmission through the locking scheme, only under the condition that the magnitude of the measured slope is within a predetermined allowed range.

The above-mentioned at least one reference level or each of the above-mentioned at least two reference levels can have a fixed value. However, it is preferable that the specified level or, respectively, each of these levels can be adjusted. For this specified level or each of these levels can be generated by the reference level is controlled from the headend of the CATV system.

To omosule management to determine whether received at the input of the squelch signal parameters such that you want to allow passage of the signal through the locking scheme, will inevitably have to spend some time, namely, on the one hand, you want the time to ensure that the specified signal is increased to some reference level, and on the other hand, it takes time to perform the required analysis in the control unit. For this reason, to prevent cutting the initial part of the message signal transmitted from the subscriber conclusion, it is useful to consider inclusion between the input block noise reduction and locking scheme means of signal delay.

After the locks are the result of detection by any of the sensors of the message signal at the input of the block noise reduction switched from the lock status to the status of the transmission, to prevent the return circuit for the lock in the lock state due to any modulation signal messages, and to ensure this return only when the specified signal will actually disappear, it is possible to provide that each sensor after detecting the disappearance of the signal of the message did not change its output signal to a logical control unit, within a predetermined short period of time.

Below the invention is described with reference to soprovojdali the drawings, where:

figure 1 as an example schematic diagram of the local cable television network according to one embodiment of the present invention;

figure 2 shows the structural diagram of the block noise reduction, connected to the specified network and designed to reduce noise transmitted in the opposite direction from the local network.

The cable network, shown in figure 1 and indicated generally by item 10, represents the local network, forming part of the CATV system, and contains the head-end station 11, which performs the functions of the communication node with which the network 10 is connected through a schematically shows a regional network 12 and the backbone network 13, the latter of which is the parent station 11.

The network 10 includes multiple branches 14 which through a bi-directional amplifier 16 and diplexing filter 17 connected with the joint input/output 15 network 10, which, in turn, connected to the network 12. In each leg 14 has a variety of subscriber outlet boxes 18, each of which contains three different conclusion: conclusion 19 for connecting the TV antenna, the output 20 to connect the antenna 20 of radio and conclusion 21 for connecting the target device data.

In the illustrated television system for the transmission of various types signal is in different directions between the parent station 11 and outlet boxes 18 are used in a known manner different band of carrier frequencies. Below, it is assumed that the system uses the first lower band b1 of the carrier frequencies, for example 15-65 MHz, for transmitting signals carrying messages in the reverse direction, for example, to transfer data signals from the terminals 22 of the data connected with the pins 21, the parent station 11; the second, higher frequency, the bandwidth b2 of the carrier frequencies, for example 120-127 MHz for transmission of data signals in a forward direction, i.e. from the headend 11 to target devices 22 data; and two lanes of b3 and b4 of the carrier frequencies, for example 88-108 MHz and 130-860 MHz, respectively, for transmission of radio signals and television signals from the headend to subscribers.

For full suppression of the noise within the bandwidth b1 of the carrier frequencies, that is, within a band of carrier frequencies used for signaling messages in the opposite direction to the network 12 from various branches 14 through the combined inlet/outlet 15, the network 10 has a special unit 23 noise reduction, the structure of which is shown in more detail in figure 2.

The block 23 has an input 24, which is connected with diplexer filter 17 and is designed to receive signals within a band b1 frequencies coming in the specified filter from the line 14, and line 25, one end of which is connected to the input 24 and which includes circuit 26 of the lock control. From line 25 of those signals, topusa input 24, which is allowed to pass through the circuit 26 of the lock, go to the output 27 of the block 23 connected to the filter 17, then through the specified filter and amplifier 16 to go in the opposite direction to the output 15 of the network 10 and then to the parent station 11.

Figure 2 positions 28, 29, 30 and 31 are four bandpass filter, which is connected to the input 24. They have different bandwidth, lying next to each other, and are designed to separate the signals received through the inlet 24 into four sub-bands, together overlying the entire band b1 frequency. To this end, various bandwidth should be selected so that adjacent with each other bandwidth slightly mutually overlap. In addition, positions 32, 33, 34 and 35 indicated four sensors, each of which is connected with the output of one of these filters and is designed to compare the power level of the output signal from the matching filter, at least one predetermined reference level and for supplying logic signals depending on the result of comparison, logical block 36 of the control circuit 26 of the lock. For the formation of one or more reference level and feed it into the various sensors include a generator 37 reference level.

The control unit 36 is designed to determine whether it receives a logical signal which, in certain circumstances, stored in this block, and for filing in the circuit 26 of the lock control signal, which permits the transmission of signals through the specified schema from the inlet 24 to the outlet 27 only when the logic signals received at block 36, satisfy stored in this block conditions.

The width of the bandwidth of the bandpass filters 32-35 in the preferred case, can be chosen such that expected on the basis of the available experience the power level of interference for different bandwidths would be approximately the same. This means that filters with a smaller frequency bandwidth should typically have less bandwidth than filters with greater frequency. If, as mentioned above, the band b1 frequencies covers 15-65 MHz, the bandwidth of the filters 32, 33, 34 and 35, you can choose equal to, for example, 15-24 MHz, 24-34 MHz, 34-47 MHz and 47-65 MHz, respectively.

To enable adjustment of the head-end station 11 of the magnitude of the reference level or levels specified by the generator 37 to reprogram the unit 36 of the control to change the conditions stored in this block, or for temporary service suspension, i.e. temporarily forced the closure of the transmission path of signals through the circuit 26 of the lock, a demodulator 38, the headend 11 through the inlet 39 connected with the connecting line between maximizing the LEM 16 and diplexer filter 17, and through the band-pass filter 40 connected to the specified input 39, may be submitted to the control commands in the frequency band b2.

The operation of such unit 23 noise reduction can be generally described as follows. Using four filters 28-31 signal in the band b1 entering the block noise reduction through the inlet 24, is divided into four different sub-bands. Part of the signal that falls within a respective subrange, enters the sensor 32, 33, 34 or 35, respectively, connected to the filter. The sensor compares the power level of the received signal with at least one reference level and generates an output logic signal depending on a result of the above comparison, in block 36 of the control. In the specified block of logic signals received from various sensors are analyzed to ascertain whether they are stored in the control unit conditions. The control signal for closing transmission channel signals from inlet 24 to the outlet 27 of the circuit 26 of the lock enters the specified circuit block of the block 36 control only when the block 36 come Boolean signals that meet the conditions stored in the specified block. These conditions, which may be of any suitable type, can either reside in the unit 36 in an unchanged form, can either be modified by preprogramming the deposits from the headend 11.

Comparing each sensor, the power level of the signal received from the corresponding filter with two different reference levels, you can easily control circuit 26 of the locking block 36 control not only depending on the levels of signals received at the sensors, but also depending on the speed of changes in the levels of these signals.

In line 25 may be included circuit 41 delays, so that in case of receipt of an acceptable input signal at input 24 to provide some compensation for the delay in locking the transmit path circuit 26 of the lock; this delay is due to the filters 28-31, sensors 32-35 and unit 36 of the control.

In the head-end station 11 system can be provided with means of measuring the level of noise in the input signals in the band b1 of the carrier frequencies. In addition, the headend may include features that allow detection unacceptably high level of noise file from the head-end station control commands in the band b2 of the carrier frequencies to alternately force function block diagrams 26 lock, available in various local networks. In this implementation, the system can quickly determine which of the local networks is a source of excessive noise, and then to block the specified network and to prevent subsequent transmission of its signals, the bandwidth b1 of the carrier frequencies as long while the cause unacceptable noise persists.

The invention is not limited to a variant implementation, which is described above and shown in the drawings. There are other numerous ways of its implementation, within the scope of the present invention defined by the claims.

For example, block noise may contain two or more groups of bandpass filters with the appropriate sensors; in this case, different groups may cover different parts of the band b1 of the carrier frequencies and using a logical control unit, each of these groups can manage a single locking scheme, belong to this group. Furthermore, in addition to one or more such groups block noise may also include one or more separate bandpass filters and sensors, each of which is functionally associated with a respective separate tool lock.

1. Local network (10), which is part of the CATV system and allow the passage of signals in the opposite direction from the subscriber conclusions (21)belonging to a specified network (10)to the head-end station (11) of the said CATV system within a predetermined band of carrier frequencies used for transmitting signals in a specified opposite direction, with the specified local network VK is uchet block (23) noise reduction, designed to reduce noise transmitted in the specified opposite direction from the specified local network (10)having an inlet (24)connected to the subscriber's findings (21), the output (27)connected to the head station (11), a set of bandpass filters (28-31), United with the specified input (24) and having a different bandwidth, lying within a specified band of carrier frequencies corresponding to multiple sensors (32-35), each of which is connected with one of these filters (28-31) and configured to compare the power level the output signal of the filter (28-31) at least one predetermined reference level, and means (26) locks are used to enable or disable transmission of signals from the specified input (24) to the specified output (27) depending on the comparison result produced by the sensors (32-35), characterized in that at least one of the groups neighboring with each other bandwidths, these locks are made in the form of a single circuit (26) lock, which is common for all bandwidths specified group of bandwidths and included in a separate line (25), which provides for transmission of signals within these bandwidths from the specified input (24) to the specified output (27), the sensors (32-35)corresponding to the specified group the voice bandwidth made with a possibility of output logic signals depending on a result of these sensors comparison, logical block (36) control, which is designed with the ability to determine whether these logical signals certain conditions stored in the block (36) control, and ability to supply the control signal depending on the result of this determination, the circuit (26) of the lock to allow the transmission of signals to this circuit from the specified input (24) to the specified output (27) only when these output signals of the sensors (32-35) satisfy the specified conditions.

2. Local network according to claim 1, characterized in that the bandwidth includes all of the bandwidth within a specified band of carrier frequencies.

3. Local network according to claim 1, characterized in that the above conditions are stored in the block (36) management constantly unchanged.

4. Local network according to claim 1, characterized in that the block (36) control is programmable and configured to modify the stored terms.

5. Local network according to claim 1, characterized in that at least one of the sensors (32-35)corresponding to the specified group bandwidth, configured to compare the power level of the output signal from the connected with the floor sensor is spot filter (28-31), at least two different reference levels.

6. Local network according to claim 5, characterized in that the block (36) control performed by measuring the steepness of the leading edge of the output signal of bandpass filter (28-31), connected to the specified at least one sensor (32-35), and determine whether the slope of the corresponding condition, stored in the block (36)of the control.

7. Local network according to claim 6, characterized in that the block (36) control configured to signal permitting the transmission of signals through the circuit (26) lock, only under the condition that the magnitude of the measured slope is within a predetermined allowable range.

8. Local network according to any one of the preceding paragraphs, characterized in that the at least one reference level or each of these reference levels, respectively, is adjustable.

9. Local network according to any one of claims 1 to 7, characterized in that it includes means (41) delay contained in a separate line (25) between the input (24) of block (23) noise reduction scheme (26) locks.



 

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