NL2006821C2

NL2006821C2 - Method for monitoring and/or correcting signal quality in a branched bidirectional telecommunications network, and related system, command and evaluation unit and corrective and measuring unit.

Info

Publication number: NL2006821C2
Application number: NL2006821A
Authority: NL
Inventors: Peter Turksma; Wouterus Leegwater
Original assignee: Communicatie Techniek Hoogland B V
Priority date: 2011-05-20
Filing date: 2011-05-20
Publication date: 2012-11-21
Also published as: WO2012161573A1

Abstract

A method is disclosed for monitoring and/or correcting signal quality in a branched bidirectional telecommunications network comprising a number of network links and stations, which method comprises the following steps (a) and (b): (a) individually monitoring of the signal transmission performance of a number of different signal paths in the network, by(1) providing a test signal on a first position in the network system in a signal path from the first position in the network system to a second position in the network system, (2) measuring a signal quality parameter value at the second position, and(3) evaluating the measured value of the signal quality parameter, (b) correcting a signal transmission performance parameter of one or more of the monitored signal paths in the network, wherein at least one of the steps (a) and (b) comprises the switching and/or adjusting components in one of the monitored signal paths, automatically controlled from a remote position. The steps (a) and (b) are precededby the step of detecting a failure in the regular signal transmission of the network. The signal quality parameter value may represent a signal property derived from other information than digital information encoded in the signal. Also disclosed are a network system, and a correction- and measuring unit.

Description

- 1 -

Method for monitoring and correcting signal quality in a branched bidirectional telecommunications network, and related system, command and evaluation unit and corrective 5 and measuring unit

The present invention relates to a method for monitoring and correcting signal quality in a branched 10 bidirectional telecommunications network comprising a number of network links and stations according to the preamble of claim 1. The invention also relates to a corresponding telecommunications network system, and a corrective and measuring unit thereof.

15 In this document, the term 'station' refers to equipment serving the regular signal transport in a telecommunications network, such as signal processing equipment, such as amplifiers, network switches and routers. The term 'link' refers to a connection of two stations with 20 respect to signal transmission between these stations.

Methods for monitoring and/or correcting signal quality of the described type are known, and are typically executed manually. For instance, in a CATV (CAble Television) network carrying analog radio and television, digital radio, 25 interactive digital television, internet and digital telephone signals, it is common to send a technician to several downstream stations in the network, when at an upstream station, such as a hub connecting the CATV network to an internet backbone and/or a television reception 30 station, a failure in the upstream signal transport is detected. The technician will trace the cause of the failure and repair the network. It is also known to correct, or adjust, upstream signal transmission performance of a newly installed electronic amplifier near the downstream end of a 35 so-called hybrid fiber copper (HFC) network system, by - 2 - stopping services in the branch containing the electronic amplifier and then sending a test signal through the amplifier to an upstream station and evaluating and adjusting the quality of the received signal.

5 The PCT application WO 2011/0569667 A1 on the name of

General Instrument Corporation discloses, applied in a cable television network having two-way communication of digital services using a version of the DOCSIS standard, a method for detecting instability resulting from non-linear impairments 10 and resetting at least one equalizer of an end device using a communications device, wherein the method comprises: retrieving an equalization instability threshold from a data storage device; monitoring an equalization parameter for the end 15 device; and determining whether the equalization parameter exceeds the equalization instability threshold, and in response to the equalization parameter exceeding the equalization instability threshold, resetting the equalizer 20 to a lower value of the equalization parameter. The equalization instability threshold is a pre-set value, indicating a level for the equalization parameter above which the equalizer is expected, or predicted, to become instable. The same document also discloses a corresponding 25 communications device.

The known method according to the preamble works well only in a limited number of situations. In particular, it may prevent failures by avoiding a specific cause for failure, being an equalization filter setting that is likely to cause 30 equalization instability. Thus, it reduces the periods in which a loss of services occurs.

However, other causes exist for failure of the network, in the sense of entirely loosing transfer of the regular transmission of the digital signal in at least one signal 35 path.

- 3 - A disadvantage of the known method is that recovery from such loss is laborious and time-consuming for the network provider, and meanwhile a substantial fraction of the users of the network experiences significant periods of loss 5 of services.

In order to reduce these disadvantages, the invention aims at providing an improved method for testing and correcting a signal quality of the aforementioned type. In particular, the invention aims at providing such a system in 10 which the loss of network functionality is reduced, in terms of length in time of reduced services.

The invention realizes these goals by providing a system with the characterizing features of claim 1.

By performing the steps (a) and (b) after the step of 15 detecting a failure in the regular signal transmission of the network, the recovery of the lost services is enhanced, in fact automated to a great extent - no longer requiring human intervention.

In an embodiment, the individually monitoring of the 20 signal transmission performance of different signal paths in the network comprises the monitoring of individual components in stations, from an input of the respective component to an output of that component. Often, a failure or poor signal transmission performance, are caused with a single component 25 in a station. By monitoring individual components, it becomes possible to identify, and subsequently eliminate, the cause of failures or poor signals relatively easily.

In another embodiment, the network system is wired, and the control of said monitoring and/or correcting occurs via 30 communication at one or more frequencies or frequency ranges having no overlap with the frequency range(s) used for the transmission of the regular signals used in the telecommunication network. Such a frequency range may also be an unused frequency range within the overall frequency range 35 used for the transmission of regular signals used in the - 4 - network system, at an unused frequency subrange. At such frequency ranges, the monitoring and possibly correcting, make use of the network system itself, thereby reducing the associated costs.

5 In yet another embodiment, the test signal lies at one or more frequencies or frequency ranges having no overlap with the frequency range (s) used for the transmission of the regular signals used in the telecommunication network. This may, for example, be used in measuring the so-called Common 10 Path Distortion (CPD) at an unused frequency, in a signal channel that has signal transmission behavior similar to that of the channels carrying regular signals.

In another embodiment, the test signal is the regular signal in only the channels being monitored. This approach 15 causes minimal disturbance of the regular signals occurring in the network system. Under conditions, regular signals may be useful for making measurements, in addition to or as an alternative to dedicated test signals injected in an otherwise empty signal path or channel.

20 In another embodiment, the test signal is an altered, in particular suppressed or switched off, version of the regular upstream signal in only the channels being monitored. This in particular allows for performing noise measurements.

A further embodiment has in normal use of the system 25 only signals within the frequency range(s) of regular signals transmitted and signals at other frequencies are filtered out or blocked, and during monitoring, at least part of the time thereof, signals at one or more other frequencies than the regular signals are left to pass through the monitored signal 30 path and the test signal lies at the one or more other frequencies than the regular signals. This allows for measuring without affecting regular signals, even when the regular signals are not suited for measuring the performance of the respective signal path. For instance, the regular 35 signals may be absent or may be heavily distorted, both due - 5 - to a failure.

The invention further relates to a telecommunications network system according to claim 7 and an embodiment thereof according to claim 8. The advantages are similar to those 5 offered in the methods according to the invention, as described above

Finally, the invention relates to a corrective and measuring unit for a branched bidirectional communications network system according to claim 9 and embodiments thereof 10 according to claims 10-14. The corrective unit is capable of performing the monitoring and corrective steps according to the method of claim 1 and its dependant claims, in cooperation with a command and evaluation unit according to the invention, and suits the system of claims 7 and 8, thus 15 contributes to making the advantages of this method and system possible.

In a particular embodiment, in the corrective and measuring unit - the means capable of providing a test signal in a signal 20 path are capable of providing a test signal at the input of the signal path in the unit, - the means capable of measuring at least one signal quality parameter value in the signal path are capable of measuring the signal parameter value at the output of the signal path 25 in the unit, and the unit also comprises means capable of evaluating the measured signal quality parameter value and adjusting at least one signal transmission performance parameter of the signal path from an input to an output of the unit in a local 30 control loop.

In this manner the unit may easily be made capable of adjusting itself, and in particular of providing a calibrated test signal suited for measuring the signal transmission performance in a further signal path, outside the unit. This 35 is in particular the case if the corrective and measuring - 6 - unit also comprises an electrical upstream signal amplifier with remotely adjustable amplification factor in the signal path from the input to the output, and switching and/or filtering means for positioning the signal amplifier either 5 in or out of the control loop.

In another embodiment, the corrective and measuring unit comprises switching and/or filtering means for passing signals within the frequency range(s) of regular signals and, according to a setting controlled remotely, either filtering 10 out or blocking of other signals or passing other signals at one or more other frequencies than the regular signal. By using a number of such units in a network system according to the invention, the provision of a test signal becomes relatively simple.

15 The invention will now be described on the basis of the attached drawing, in which corresponding parts in different figures are provided with identical reference characters.

In the drawing,

Figure 1 shows a schematic representation of an embodiment of 20 a CATV telecommunication network system according to the invention,

Figures 2a, 2b and 2c show schematic representations of three types of units in the network system of Figure 1, into more detail, 25 Figure 3 shows a block schematic representation of an embodiment of a corrective and measuring unit of a first type according to the invention,

Figure 4 shows a block schematic representation of a Group Station incorporating a corrective and measuring unit of a 30 second type according to the invention, and

Figure 5 shows a block schematic representation of an End Station incorporating a corrective and measuring unit of a third type according to the invention.

In Figure 1, a part of CATV telecommunication network 35 system S is shown. The network system S provides analogue - 7 - cable television and radio services, digital radio services, interactive digital cable television services, telephone services and internet services to individual households.

The network system S comprises stations 1, each 5 indicated by an open dot, and links 2, each indicated by a line. The dotted lines represent branches of the network that are not further shown.

The network system S is branched, in the form of a tree (hence, from upstream, on the left side, in the downstream 10 direction, to the right side, it only contains branches and does not merge) , becoming wider from left to right in the figure. The various levels, a level being the number of links to the leftmost station along the shortest path, in the tree are indicated by means of vertical lines; stations on the 15 same line are at the same level in the network.

The left side part of the network in figure 1 is called the upstream side, the right side the downstream side. Communication (by signals) from left to right in the network, indicated by the arrow 'D' is called downstream 20 communication, communication from right to left, indicated by the arrow 'U' is called upstream communication. The network system S is capable of bidirectional communication, in the sense that any station is capable of bidirectional transmission of signals between that station and another 25 station, under the condition that the other station is located downstream of the first station. In this embodiment, stations at the same upstream/downstream level are not capable of communicating with each other.

The network system S is a so-called hybrid fiber-copper 30 (HFC) network, having communication via optical signals in glass fiber in the signal paths near the upstream side and in the middle, and communication via electrical signals in the signal paths near the downstream side, i.e. the end users.

Each station comprises signal processing components, 35 such as routers, switches, filters and amplifiers, which - 8 - components are connected to the links and support the bidirectional communication between any pair of upstream-downstream links connected to the station. Each link 2 is a signal connection, in this embodiment comprising of glass 5 fiber data lines (from levels 0 to 1, from 1 to 2, and from 2 to 3) and electrically conducting coax cable (indicated by CC). A link 2 may also include equipment for conditioning the signal, such as amplifiers, as long as it is functionally a link between only two stations.

10 The station at level 0 is a Hub Station, and connected to both a backbone of the internet and a receiver of satellite television signals (not shown). The stations at level 1 are Upper Intermediate Stations, the stations at level 2 are Lower Intermediate stations, and the stations at 15 level 3 are Group stations, at level 4 are End Stations and at level 5 are the stations of individual users.

In the Hub station, at level 0, a command and evaluation unit 3 is provided.

The command and evaluation unit 3 comprises a 20 connection means to a switch unit also present in station 2, which connection means enables communication of a means 6 for communicating in the unit with the downstream network part for the downstream network part. Further, the command and evaluation unit 3 has a means 7 for evaluating a value of the 25 SNR of the upstream signal, which means is capable of storing IDs of network parts. Connected to the command and evaluation unit 3 is an interface unit 101 which connects to administrative computers (not shown) of the network system S. Also connected to the unit is a human-computer interface 102, 30 comprising mouse, keyboard and display (not shown).

In the Upper Intermediate stations (see Figure 2a), a measuring unit 4 is provided, containing a measuring means capable of measuring the SNR of the upstream signal through the station in which the measuring unit 4 is located.

35 In the Group Stations 20 (see Figure 2b), a corrective - 9 - and measuring unit 8 of a second type (see Figure 4) is provided, comprising a signal connection 9 to the amplifier and switch 10, enabling communication of the corrective and measuring unit 8 to the upstream network part and the 5 downstream network part, and a communication and control means 11 capable of exchanging information and control commands for the corrective unit 8 via the link in the upstream part of the network. In this example, each Group Station is connected to eight End Stations, of which in the 10 Figures only three are shown.

In the End Stations 30 (see Figure 2c) , a corrective and measuring unit 12 of a third type (see Figure 5) is provided, comprising a signal connection 13 to the switch 14, enabling communication of the corrective and measuring unit 15 12 to the upstream network part and the downstream network part, and a communication and control means 15 capable of exchanging information and control commands for the corrective and measuring unit 12 via the link in the upstream part of the network.

20 Each End Stations is connected to two End User

Stations. End User stations serve individual households; in an End Station, the persons in a household connect their television sets, Ethernet and Wifi home networks, telephone sets, and/or radios.

25 The links between Group Stations and End Stations, and between End Stations and End User Stations comprise coaxial electrical cables for the signal transmission. The other links in the network, located more upstream, comprise optical fibres for the signal transmission.

30 The network system S of Figure 1 implements the method of the invention, as follows. We describe two modes of use: a failure correction mode, and a fine tune mode (or adjustment mode).

The regular signals of the CATV network S are in the 35 range of 15-65 MHZ, in this example. The lower range of 5-15 - 10 - MHz is reserved for test signals, and the even lower range of 0-5 MHz serves for the communication used in the control of the method according to the invention, in other words in the control of testing and corrective actions.

5

Failure correction mode

The failure correction mode of the network system S is meant for circumstances in which a failure occurs in the system. Often, failures occur in the downstream part of the 10 network, caused by poor upstream signals from individual households, and propagated upstream. An example of a typical failure is the overloading of an electronic amplifier in the upstream direction of a group node. This results in a distorted output signal, not only in the narrow frequency 15 range of the specific channel, but also in other frequency ranges. As a result, not only the end user or downstream station that causes the failure experiences loss of services, but also other users.

Failures are detected by monitoring the regular 20 upstream signal at two frequencies, in this example at the UIS level. The noise level is monitored (it should be below a predefined value) and the total distortion of the signal (common path distortion; should be below a predefined level) and the signal level (should be above a predefined value); 25 other values may be measured, of course. This monitoring occurs in the measuring unit 4, and is controlled by the command and evaluation unit 3, via communication in the network, over a frequency range below the frequency range of the regular signals. It is obvious, that in a variant of the 30 present example, the measuring unit 4 may be integrated with the command and evaluation unit 3.

When a failure is detected by the command and evaluation unit 3, the next step consists of monitoring individual parts of the network, in order to locate the cause 35 of the failure. The monitoring of different parts of the - 11 - network consists of monitoring the Group Stations one by one, for example by switching one Group Station off at a time, which means providing a zero test signal, measure the signal upstream at the UIS level and evaluate whether the failure is 5 still present, hence whether its cause is still present, and - if so - switching the respective Group Station on again. Instead of switching off the Group Station, a test signal may be provided at a frequency not used for regular signal transmission, and this signal may then be compared to the 10 signal arriving at the measuring unit 4, which gives an indication of the distortion over the entire path from the respective Group Station to the measuring unit 4. As a third way of providing a test signal, a frequency not used for regular signal transmission may be 'opened up', i.e. signals 15 at that frequency, normally blocked, may be left to pass through the station, in order to provide a monitored signal path from a location still further downstream from the Group Station to the measuring unit 4, or to the output of the Group Station, using the signal coming the location further 20 downstream as a test signal (this may be purely noise). As a fourth way of providing a test signal, a signal may be injected at an input of the Group Station and measured at an output thereof, the monitored signal path being located entirely within the Group Station. The signal may be at an 25 unused frequency, or alternatively a frequency normally used for regular signals after effectively cutting off, by a switchable component, e.g. a filter, the regular signals in the respective signal path.

This monitoring is continued until either the Group 30 Station that causes the failure in the network is identified, or, if no such Group Station is found, all relevant parts of the network are tested. The corrective step according to the invention, here consists of leaving the responsible Group Station switched off, or at least a component thereof, such 35 as an amplifier and reporting that the Group is switched off - 12 - and should be repaired.

In an alternative setting of the command and evaluation unit 3, the monitoring of different parts is realized by consecutively switching off more Group Stations, until the 5 regular signal has sufficient quality again, and then switching on Group Stations again one by one, and, as soon as the signal quality drops again, switching the respective Group Station off again, and move on to the next station to be switched on, and so forth until switching on of all 10 switched off stations has been tried. The latter testing method also allows for identifying multiple causes for a failure .

After determination of the Group Station that causes the failure, a repairman may be sent to that Station, and 15 continue the testing and corrective actions manually.

However, the command and evaluation unit 3 also has a setting in which its software continues testing, by testing the downstream End Stations of that particular Group Station, by switching off the upstream signal through End Stations one by 20 one, and measuring the signal quality in the measuring unit 4 - hence, by recursively applying the procedure used for the Group Stations.

The switching off of the upstream signals through Group Stations and End Stations is done, in this example, by means 25 of bridging a filter in the respective station. This filter normally, when unbridged, cuts off signals below 65 MHz and passes the regular signals in the network. When bridged, all upstream signals are allowed to pass, both the regular signals and signals in the low frequency band, such as the 30 signals for controlling the corrective and measuring units, coming from the command and evaluation unit 3.

Fine tune mode

The fine tune mode is not part of the invention, but 35 described for a better understanding thereof. The fine tune - 13 - mode has similar actions as the failure correction mode, the differences being (1) that the detection of a failure is left away and (2) the corrective action is usually not the switching off of a component in a Station, but adjusting the 5 component.

In the Fine Tune Mode, the network is 'polled' at set intervals, and only if the corrective actions do not succeed, a failure is reported and the failure correction mode is initiated.

10 In this example, the fine tune mode is used for adjusting the amplification factors of electronic amplifiers and switches 10 in Group Stations, one amplifier and switch 10 at a time.

By the control and evaluation unit 3, the respective 15 amplifier and switch 10 is effectively switched off by bridging a filter (see also Figures 4 and 5).

Next, a test signal is applied in the upstream channel of the amplifier. In this example, the test signal lies at a frequency below the frequencies of the regular signals, hence 20 below 65 MHz. However, the signal could also be in the frequency range of the regular signals, for example in an unused channel. In fact, under conditions the signal could even be the regular signal itself.

The signal quality is measured, in this example the 25 quality parameters measured include the Common path distortion, i.e. the distortion of the test signal from where it is applied to where it is measured (at the measuring unit 4), and the Signal-to-Noise Ration (SNR) of the test signal, depending on the setting of the command and evaluation unit 3 30 as determined by an operator of that unit.

When the signal quality is below an acceptable level, as determined by the operator in this example, several actions may be done, one of which is the adjustment of the adjustable amplification factor of the amplifier in the 35 amplifier and switch 10.

- 14 -

The adjustment of the amplification factor of the amplifier may also be preceded by adjusting the amplification factor or attenuators before the test signal is applied, in order to provide a well-defined test signal level. Such 5 initial adjusting of the amplification level or attenuators is possible, for instance, with the aid of an internal control mechanism in the amplification and switch unit 10; the corrective unit 30 of Figure 5 contains such a control mechanism (as described below), but this corrective unit is 10 of a type used in the End Stations.

The steps of selecting a Group Station, suppressing the regular upstream signal, adjusting the amplification factor or attenuators for providing a well-defined test signal, applying a test signal, measuring and evaluating the 15 transmitted test signal, and (again) adjusting the amplification factor of the amplifier, are controlled by the command and evaluation unit 3. This unit contains a computer and software that allow it to do these steps in an automated manner, and to repeat these steps for other Group Stations. 20 In this manner, the network performance is optimized in a manner that costs little human effort, and hardly disturbs the regular network services.

Now turning to the three embodiments of a corrective and measuring unit according to the invention, Figure 3 shows 25 corrective and measuring unit 16 for use in a Station. One or more of these units may be incorporated, each in one signal path. The corrective and measuring unit 16 consists of a directional coupler 16a functioning as a signal splitter, a switch 16b, that has three positions, and a programmable 30 attenuator 16c, a connection 16d to an upstream side in the Station and a connection 16e to a downstream side in the Station, a filter 17 and a controller 18, and wiring between these components.

The switch 16b is controlled remotely, via the 35 controller 18, e.g. by a command and evaluation unit - 15 - according to the invention. The switch 16b has three positions and thereby provides the elementary functions needed in a corrective and measuring unit. In particular, the unit 16 allows for: 5 - passing only the regular signal in the upstream direction, cutting off frequencies below 15 MHz; this is the mode for normal use (switch at 'a'), - passing the signal over the entire frequency range, unfiltered (possibly slightly attenuated); this is the mode 10 for measuring (switch at 'b'), - cutting off the signal; in this mode, a failure can be neutralized, after which a repairman may do manual repairs (switch at 'c'), and - attenuating the signal, by a selected amount (switch at 'a' 15 or 'b') .

In Figure 4, a Group Station 20 (see also Figure 2B) is shown into details. The unit is suitable for use in the network system S of Figure 1, as a branching station. It is relatively basic, in the sense that it contains no amplifier 20 and no local control mechanism, as is present in the end station 30 shown in Figure 5.

The Group Station 20 contains eight downstream connections 21, an upstream connection 22, and a communication means 11 that was already described. Each of 25 the eight signal paths from the downstream connections 21 to the upstream connection 22 contains a pair of an attenuator and a switch 23, each pair being capable of both attenuating an input signal and switching it off and on. The signals from the eight pairs of attenuator and switch 23 are combined into 30 a single signal, by seven binary signal combiners 24. The signals in the downstream direction pass through the same physical paths as the signals in the upstream direction, at a different frequency range.

The pairs 23 of attenuator and switch are controlled 35 by, or via, the communication and measuring means 11, - 16 - consisting of a modem 25, a receiver 26, a microprocessor 27 and two multiplexers 28, and interconnections 29 between these components. The communication and measuring means 11 is capable of measuring signal quality parameters at the eight 5 downstream connections 21.

When the network system containing the Station 20 is operative and no corrective action is being taken and no measurements are being made, the attenuators are operative such that the regular upstream signals are passing through 10 the attenuators, and signals between 5 and 15 MHz are being cut-off, while signals below 5 MHz are left to pass. The operation of the attenuator and switch pairs 23 will be clear to persons skilled in the art, and is therefore not further elaborated. By attenuation and/or switching the incoming 15 upstream signals from stations located more downstream than the corrective unit 20, the regular signals may be effectively switched off or adapted to provide test signals, as part of realizing the method according to the invention.

The corrective and measuring unit 8, shown in Figure 20 2B, as a distinct unit, is integrated in the Group Station 20; it consists essentially of the components 11 and 23, and some of the wiring. It has in particular the following functions, controlled remotely: measuring the signal coming from a location at the 25 downstream side of the Station 20, before the pairs of attenuator and switch 23, - measuring at a position in the upstream side of the network system, the signal coming from a position in the downstream side of the network system, typically an End Node or End 30 User. The measured signal may be the regular signal, but also a signal at an unused frequency within the spectrum of the regular signals or below this spectrum. The measured signal originates only from one position in the downstream side of the system, by allowing only the signal from that position to 35 pass through a high-pass filter; this is realized by - 17 - switching the respective filter (by the microprocessor 27) in an 'all-pass' mode, and switching the other filters in a 'high-pass' mode. It is this latter type of measurement that is particularly suited for measuring the individual 5 contribution of stations at the downstream side of Station 20 at a position in the upstream side of the network, and correcting the signals, by setting the adjustable attenuators 22 and 23 in the inputs and output.

An example of this type of measuring and correcting is 10 measuring the common path distortion (CPD) in the upstream signal at the command and evaluation unit, and correcting the downstream attenuation in the station 20 when the CPD is too high.

Due to the specific layout of the Station 20, no 15 corrective and measuring units are required in the layer of Stations immediately downstream of a layer filled with the Stations 20. In realistic CATV network systems, this implies a serious reduction of hardware required and thus a serious reduction of investment costs.

20 In Figure 5, the End Station 30 is shown, suitable for use in the network system S of Figure 1. The End Station 30 has connections 'outl' and 'out2' for downstream stations and a connection 'input' for an upstream station.

Signals in the downstream direction, arriving at the 25 input, pass through diplexer 31, tilt corrector 32 and attenuator 33 as well as downstream amplifier 34, and a diplexer 35, to either outl or out2 with the aid of a splitter 47.

Signals in the upstream direction, arriving at either 30 outl or out2, pass through the diplexer 35, a high-pass filter 36, an attenuator 37 and tilt corrector 38, an upstream amplifier 39, and the diplexer 31 to the input. The signal at the output of the upstream amplifier 39 may also be fed into a filter 40 and rectifier unit 41 for measuring 35 signal strength of the signal directed upstream. The wire - 18 - with indication 'RSSI' connected to the rectifier unit 41 serves to pass the measured strength parameter value on to a microprocessor 42. An oscillator 43 is used to provide a test signal (of 32 MHz) to the filter 36, when needed. A modem 44 5 serves to communicate, via the upstream connection 'input', to a command and evaluation unit 3. A temperature sensor 45 and a receiver 46 are connected to the tilt correctors and attenuators 32, 33, 37 and 38, as well as to the microprocessor 42. The temperature sensor 45 serves to make 10 corrections for distortion with a known temperature dependency.

The receiver 46 serves to measure the signal quality in the downstream direction, and to correct that signal via the tilt correction 32 and the attenuator 33, or to correct the 15 upstream signal transmission performance via the attenuator 37 and tilt correction 38. By correcting the downstream signal, the upstream signal is also positively influenced, because the downstream signal, when of poor quality, yields distortion products in the path downstream of the End Station 20 30 that arrive at the End Station 30 in its upstream channel.

The End Station 30 is capable of providing the following functions, controlled via the modem 44 by a command and evaluation unit upstream in the network: - measuring the signal quality in the upstream direction, 25 using filter 40 and rectifier 41, after the amplifier 39, - correcting the downstream signal in tilt correction 32 or attenuator 33 (using a should-be value of the downstream signal stored in its memory), - correcting the upstream signal in attenuator 37 and/or tilt 30 correction 38 (using a should-be value of the downstream signal stored in its memory), - measuring the signal quality in the downstream direction, in the receiver 46, - for measuring purposes, allowing all upstream signals to 35 pass or cutting off the low frequencies of the upstream - 19 - signals, in filter 36, - for corrective purposes, cutting off or allowing to pass upstream signals by the attenuator 37, and - for measuring purposes, providing a test signal in the 5 upstream path before the upstream amplifier 39, by the oscillator 43.

These functions allow, among other things, for measuring an upstream signal passing through the filter 36, in the following manners: 10 - measuring (a) at the rectifier 41 or (b) at a position upstream of the End Station 20, a signal coming from a position downstream of the End Station 20, the signal being either (1) the regular upstream signal, 15 (2) a test signal, applied by the oscillator 43 at the input side of the filter 36, or a noise level in an unused channel in the regular signal path, or (3) a test signal, applied by the oscillator 43 at the input side of the filter 36, or a noise level in a frequency range 20 below that of the regular signal (the filter 36 allowing to let the signals at lower frequencies pass).

The combination of applying a test signal by the oscillator 43 and measuring its response at the rectifier 41 is used in a local control mechanism of measuring the signal 25 level at and with rectifier unit 41 and then evaluating this level in the microprocessor 42 and, if necessary, adjusting, the level of the test signal coming from the oscillator 43. This local control mechanism allows for adjusting the signal level of the test signal, which results in providing a test 30 signal with a calibrated signal level.

In Figure 5, the corrective and measuring unit 12, shown in Figure 2C as a distinct unit, is integrated in the End Station 3. In addition to the corrective and measuring unit 12, the End Station 3 also comprises two amplifiers, one 35 for downstream signals and one for upstream signals.

- 20 -

The End Station 30 may also be used as a Group Station, after a slight modification thereof. Mainly, a bypass line is needed, as shown dotted, from input to splitter 47, as a signal line for the communication at frequencies below 5 MHz, 5 for passing on commands.

The described and shown embodiments of the invention serve for illustration of the invention. Variations on these embodiments are possible. For example, the network of Figure 1 may have more levels than shown. The command and evaluation 10 station may be capable of testing more than one branch simultaneously, for instance with the unit of Figure 5 sending two test signals simultaneously, and the test signals in the fine tune mode may - instead of being at a lower frequency than the regular signals in the network system - be 15 in-band with the regular upstream communication, e.g. at an unused frequency, as well as out-band at a higher frequency (for example just above the regular signals, between 65 and 70 MHz). Instead of high-pass filters, band-pass filters may be used, or, depending on the situation, on and off switches 20 in a signal path. Although mainly signals in the upstream direction were measured and corrected in the shown embodiments, the invention applies to signals in downstream directions as well. The communication between the command and evaluation unit and the corrective and measuring units in the 25 shown examples occurs via the energy supply lines of these units, but may also take place via the links of the network system.

Claims

A method for monitoring and correcting signal quality in a branched two-way telecommunications network comprising a number of network connections and stations, which method comprises at least one of the following steps (a) and (b): (a) separately monitoring of the signal transfer performance of a number of different signal paths in the network, by (1) providing a test signal at a first position in the network system to a second position in the network system, (2) measuring a signal quality parameter value at the second position, and (3) subsequently evaluating the measured value of the signal quality parameter, (b) correcting a signal transmission performance parameter of one or more of the monitored signal paths in the network, wherein at least one of the steps (a) and (b) switching and / or adjusting components in one of the monitored signal paths, which switching and / or adjusting is automatic is controlled from a remote position, characterized in that steps (a) and (b) are preceded by the step of detecting a failure in the regular signal transmission of the network.

Method according to claim 1, wherein the network system 35 is wired, and the control of said monitoring and / or correction takes place via communication on one or more frequencies or frequency ranges that have no overlap with the frequency range (and ) used for the transmission of the regular signals used in the telecommunications network.

3. Method as claimed in any of the claims 1-2, wherein the test signal is on one or more frequencies or frequency range (s) that do not overlap with the frequency range (s) used for the transmission of the regular signals used in the telecommunications network.

4. Method as claimed in any of the claims 1-2, wherein the test signal is the regular signal in the upstream direction in only the upstream channels that are monitored.

5. Method as claimed in any of the claims 1-2, wherein the test signal is a modified, in particular suppressed or switched off, version of the regular signal in the upstream direction in only the upstream channels that are monitored.

6. Method as claimed in any of the foregoing claims, why during normal use of the system only signals are transmitted within the frequency range (s) of common signals and signals on other frequencies are filtered out or blocked, and during monitoring, or at least part of the time thereof, signals on one or more frequencies other than the regular signals are passed through the monitored signal path and the test signal on the frequencies deviating from the usual signals.

A telecommunications network system comprising a number of network connections and stations, the network being branched and suitable for bidirectional telecommunication, the network also comprising: - a number of measurement units in the network, 5. a number of correction units in the network a command and evaluation unit, in which the network system is able to (a) separately monitor a number of different signal paths from the network, the monitoring comprising the following 10 steps for each monitored signal path from the network: providing a command from the command and evaluation unit, by a correction unit at the first position, of a test signal at the first position in the network system in a signal path from the first position in the network system to a second position in the network system , measuring, by a measuring unit, a signal quality parameter at the second position, 0. evaluating, by the command and evaluation unit, of the value of the measured signal quality parameter, wherein each of the correction units is capable of correcting a signal transmission performance parameter of one or more of the monitored signal paths in the network, wherein at least one of the steps (a) and (b) comprises switching and / or adjusting correction units or measuring units in one of the monitored signal paths, which switching and / or adjusting is automatically controlled by the command and evaluation unit. characterized in that the measuring unit is suitable for measuring the signal quality parameter even in the presence of a disturbance in the regular signal transmission. - 24 -

A telecommunications network system according to claim 7, characterized in that the network is wired, the command and evaluation unit comprises means of a first type for communicating with each individual correction unit, each of the correction units means of a second type for communicating with the command and evaluation unit, and said first and second type means operate in a frequency range that has no overlap with the frequency range used to transmit the common signals of the network.

9. Correction and measurement unit for a branched two-way telecommunications network system, comprising: 15. communication means capable of exchanging information and / or command for controlling the correction and measurement unit via a connection in the network system, - means in capable of providing a test signal in a signal path, means capable of measuring at least one signal quality parameter value in the signal path, and means capable of adjusting at least one signal transmission performance parameter of the signal from an input to an output of the unit, characterized in that the measuring unit is suitable for measuring the signal quality parameter even in the presence of a disturbance in the regular signal transmission.

10. The correction and measurement unit according to claim 9, further comprising - means for muting or effectively switching off signals.

11. Correction and measurement unit according to claim 9 or 10, wherein the means are capable of providing a test signal in a signal path capable of providing a test signal at the input of the signal path in the unit, 5. the means capable of measuring at least one signal quality parameter value in the signal path capable of measuring the signal parameter value at the output of the signal path in the unit, and also comprising means capable of evaluating the measured signal quality parameter value and adjusting at least one signal transfer performance parameter of the signal path from an input to an output of the unit in a local control loop.

12. Correction and measuring unit for a telecommunications network system according to claim 11, further comprising: - an electrical signal amplifier of the upstream signal with remotely adjustable gain in the signal pass from the input to the output, 20. switching and / or filtering means for positioning the signal amplifier either in the control loop or outside.

13. Correction and measuring unit for a telecommunications network system according to any of claims 9-12, comprising switching and / or filtering means for transmitting signals located within the frequency range (s) of conventional signals and, according to a remote-controlled setting, either filtering out or blocking other signals or passing other signals on one or more frequencies than those of the regular signal.

14. Correction and measuring unit for a telecommunications network system according to one of claims 9-12, comprising: 35. several connections located on the downstream side - 26 - for a downstream side of a network system, - one or more on the upstream side upstream side connections of a network system, wherein the means capable of measuring at least one signal quality parameter value in the signal path are provided with a microprocessor and wiring for measuring a selected copy of the signal quality parameter at one of the downstream side network connections and one of the upstream side network connections, and the choice is made by remote control.