Title of Invention

CABLE TV SYSTEM OR OTHER SIMILAR COMMUNICATION SYSTEM

Abstract

The invention relates to a cable TV system, which is arranged to permit a transmission of signal in the return direction from local network, included in the system, to a head end of the system within a predetermined carrier frequency band, serving for the transmission of signals in said direction, comprises means for monitoring the system in respect of disturbances occurring within said carrier frequency band. said monitoring means comprise detector means within each local network which are arranged to compare the energy level of signals occurring within said carrier frequency band with at least one predetermined reference level and to generate logic signals, depending upon the result of said comparison, and memory means within each local network which are arranged to store information about time intervals during which said energy level exceeds said reference level, derived form the values of said logic signals at different times. ABSTRACT CABLE TV SYSTEM OR OTHER SIMILAR COMMUNICATION SYSTEM The invention relates to a cable TV system, which is arranged to permit a transmission of signals in the return direction from local networks, included in the system, to a head end of the system within a predetermined carrier frequency band, serving for the transmission of signals in said direction, comprises means for monitoring the system in respect of disturbances occurring within said carrier frequency band. Said monitoring means comprise detector means within each local network which are arranged to compare the energy level of signals occurring within said carrier frequency band with at least one predetermined reference level and to generate logic signals, depending upon the result of said comparison, and memory means within each local network which are arranged to store information about time intervals during which said energy level exceeds said reference level, derived from the values of said logic signals at different times.

Full Text

The present invention relates to a cable TV system. More particularly, the invention relates to such a system of the kind which is arranged to permit a transmission of signals in the return direction from local networks, included in the system, to a head end of the system within a predetermined carrier frequency band, serving for the transmission of signals in said direction, and which comprises monitoring means for monitoring the system in respect of disturbances occurring within said carrier frequency band. Cable TV systems of said kind are intended to be used not only for the distribution of TV signals and radio signals from the head end of the system to the subscribers connected to various local networks of the system but also for bi¬directional transmission of different kinds of signals between the subscribers and the head end of the system. In such cable TV systems, within the carrier frequency band utilized for the transmission of signals in the return direction, there may occur severe disturbances due to noise penetrating into the local networks through the subscriber outlets and the lines connected thereto and successively accumulated when passing through the system towards the head end. For this reason, it has been proposed to provide systems of the above kind with means for monitoring the occurrence of disturbances within said carrier frequency band. In systems previously known, said monitoring has been based either on an accurate measurement at the head end of the magnitude and frequency of all signals within the carrier frequency band in question, incoming to the head end, or on a measurement of the magnitude of signals, occurring under certain predetermined short periods of time, effected through a sampling process. However, in practice, both alternatives are unfavourable and they do not make it possible in an easy manner to determine from which local network disturbances within said frequency band emanate. The invention therefore has for its purpose to provide an improved communication system of the kind initially specified which facilitates the detection of disturbances occurring within the frequency band of the return channel as well as the identification of the local network from which the disturbances are transmitted. The system according to the invention proposed for said purpose is primarily characterized in that said monitoring means comprise detector means within each local network which are arranged to compare the energy level of signals occurring within said carrier frequency band with at least one predetermined reference level and to generate logic signals, depending upon the result of said comparison, and memory means within each local network which are arranged to store information about time intervals during which said energy level exceeds said reference level, derived from the values of said logic signals at different times, and fetching in and evaluation means at the head end of the system by which information stored in said memory means of the local netwoks can be fetched in to the head end for evaluation thereof at the head end. The invention makes it possible, within each local network, continuously to detect signals within the frequency band of the return channel, occurring within said network and having an energy level exceeding the reference level and to store information corresponding to the character of said signals for an evaluation thereof later on if and when so required. As a consequence, when disturbances occur within said frequency band, the identification of the local network from which said disturbances emanate will be simplified. Additionally, the invention also makes it possible at the head end of the system to determine from which local network any occurring disturbances emanate. Said memory means may be arranged to store information about said time intervals in the form of information about the starting point and the length of each individual interval. In order to make it possible to reduce the total amount of information that need to be stored in said memory means, said means may however preferably be arranged, at least in respect of certain periods of time, to store information about said time intervals in the form of statistics relating to the number of such intervals occurring during said periods. Said reference level, which should be lower than the lowest level to which a message signal intended to be transmitted to the head end of the system may be expected to amount, may be adjustable, preferably under the control thereof from the head end of the system. In this case, said memory means may suitably be arranged also to store information about the value of the set reference level. In order to make it possible to determine and store information relating to the slope of the front edge of signals occurring within said carrier frequency band, said detector means may be arranged to compare the energy level of said signals with at least two different reference levels. In order to make it possible to monitor the system in a very accurate manner, said detector means may be arranged to effect said comparison and said generation of logic signals, depending upon the result of said comparison, individually for each one of a plurality of different sections of said frequency band, and said memory means may be arranged to store individual information for each of said sections, derived from said signals. In this case, each local network may comprise a plurality of band-pass filters, which divide said carrier frequency band into a corresponding plurality of subbands, and a corresponding plurality of detector means, each serving to compare signals occurring within one of said subbands with said reference level or levels, respectively. Alternatively, each local network may instead comprise a single band-pass filter, having a predetermined pass band width, constituting only a fraction of the total band width of said carrier frequency band, and a single detector means, connected to said filter, in which case the frequency spectrum of the carrier frequency band may be controllably displaceable relatively to the pass band of the band-pass filter in order to permit different sections of the carrier frequency band to be placed within said pass band. In the latter case, it is possible to scan the different sections of the carrier frequency band in a cyclic manner by placing said sections cyclically within the pass band of the band-pass filter. Compared to the use of a plurality of band-pass filters and a corresponding plurality of detector means, the use of a single band-pass filter and a single detector means and means for controllably displacing the frequency spectrum of the carrier frequency band offers the advantage of making it possible to reduce the costs for the hardware required within each local network while simultaneously also making it possible to divide the carrier frequency band in question into an increased number of smaller sections. Below the invention is further described with - relerence to the accompanying drawings, in which- Figure 1 shows a principle diagram of a local cable TV network, forming part oi a cable TV system according to an embodiment of the invention, selected by way of example only and containing a plurality of such local networks, Figure 2 shows a detailed block diagram of a moni¬toring unit, connected in said network and forming part of an equipment for monitoring said system in respect of noise transmitted in the return direction from various local networks, and Figure 3 shows a detailed block diagram of a moni¬toring unit according to an alternative embodiment of the invention. The cable TV network shown in Figure I and general¬ly designated 10 constitutes a local area network, forming part of a cable TV system, including a head end 11 which serves as a communication central and to which network 10 is connected via a diagramatically shown regional network 12 and a trunk network 13, also diagramatically shown and wherein head end 11 is provided. Network 10 includes a plurality ot branch lines 14 which, vra a bi-drrectlonal amplifier 16 find a diplex filter 17, are connected to a combined input and output 15 of network 10 which, in its turn, is connected to network 12. Each branch line 14 has a plurality of sub¬scriber outlet boxes 18, connected thereto, each com¬prising three different outlets, namely a TV antenna outlet 19, a radio antenna outlet 20 and a data terminal outlet 21. In known manner, the illustrated TV system utilizes different carrier frequency bands for the transmission of different kinds of signals and signals in different direc¬tions between head end 11 and outlet boxes 18. Below, it is assumed that the system utilizes a first lower carrier frequency band bl, e.g. 15 - 65 MHz, for the transmission of data signals in the return direction, .1 .e. from data terminals 22, connected to outlets 21, to head end 11, while it utilizes a second higher carrier frequency band b2 , e.g. 120 - 127 MHz, for the transmission of data sig¬nals in a forward direction, i.e. from head end 11 to data terminals 22, and two further carrier frequency bands b3 and b4, e.g. 88 - 108 MHz and 130 - 860 MHz, respectively, for the transmission of radio signals and TV signals from the head end to the subscriber out¬lets. In order to make it possible to monitor network 10 in respect of noise within carrier frequency band b1, i.e. within the carrier frequency band serving for the trans¬mission of data signals in the return drrection, transmit¬ted from said network to network 12 via the combined in¬put and output 15, network 10 is provided with a special noise monitoring unit 23, the more detailed structure of which appears from Figure 2. Unit 23 comprises an input 24, connected to diplex filter 17 and arranged to receive signals within frequen¬cy band bl incoming to said filter from lines 14, and a line 25, having its one end connected to input 2 4 and containing a controllable blocking circuit 2b. If permit¬ted to pass through blocking circuit 26, the signals re¬ceived at input 24 can be delivered from line 25 to an output 27 of unit 23, connected to filter 17, in order then, via said filter and amplifier 16, to pass further in the return direction to output 15 of network 10 and then to head end 11. In Figure 2, reference numeral 28, 29, 30 and 3 I designate four band-pass filters which are connected to input 24 and have mutually different pass bands, located next to each other, and which serve to divide the signals incoming via input 24 on four subbands, together cove¬ring the entire frequency band b1. Furthermore, refe¬rence numeral 32, 33, 3 4 and 3 5 designate Lour detectors which are connected each to the output or one 01 sa.td filters and which serve to compare the energy level or the output signal from the corresponding filter with at least one predetermined reference level and to deliver logic signals, depending upon the result of sard compa¬rison, to a unit 36. Unit 36 contains memory means which are arranged, individually for each of sard subbands, to store informa¬tion about the time intervals, during which said energy level exceeds said reference level, derived from the values of said logic signal at different times. For the purpose of generating and supplying said reference level to the different detectors, there is provided a reference level generator 37. Unit 36, which may contain a processor for proces¬sing the incoming logic signals, may be arranged to store, in a memory of said unit, information about said time in¬tervals in the form of information about the startrng point and the length of each of said time intervals. However, unit 36 may also be arranged to store said in¬formation in any other form, preferably in the form of statistics relating to the number of time intervals of the abovementioned kind occurring during certain periods of time. With the aid of means provided at head end 11, the information stored in unit 36 may be fetched in to the head end for subsequent evalutation thereof at said end whenever so desired. Said means may preferably com¬prise a computer 11' at the head end by means of which a process for fetching in information to the head end may be ordered and the information fetched in may be evaluated. In addition, unit 36 may be arranged to serve as a control unit for blocking circuit 26. in a manner described more in detail in Swedish patent application No. 99 04589-0, unit 36 may in this case be arranged to determine whether the received logic signals satisfy certain conditions previously stored in said unit and, via a line 42, indicated by a dash-dotted line, to de¬liver to blocking circuit 26 a control signal ror closing the signal path through said circuit from input 24 to output 27 only when the logic signals received by unit 36 satisfy said conditions. In this case, unit 23 will also function as a ncise reduction unit built-in in the network. The band width of band-pass filters 32 - 35 may preferably be selected in such a manner that the energy level that can be expected to arise from, based on ex¬perience, normally appearing disturbances will be appro¬ximately equal within the different pass bands. This means that filters having lower pass band frequencies should normally have less band width than filters having higher pass band frequencies. In order to make it possible, from head end II, to order an operation for fetching in information stored in unit 36, a reprogramming of the processor contained in said unit, an adjustment of the magnitude of the reference level generated by generator 37 or a temporary compulsory blocking or a temporary compulsory closing of the signal path through blocking circuit 26, there is provided a demodulator 38 to which control commands transmitted from head end 11 within frequency band b2 may be supplied via an input 39, connected to the junc¬tion line between amplifier 16 and diplex filter 17, and a band-pass filter 40, connected to said input. From unit 36, the information stored in said unit may be transmitted to output 27 via a modulator 4 3 in which said information is modulated on a carrier, the frequen¬cy of which may lie between the two frequency bands bl and b2. The manner of operation of the system above described may be summarized as follows. By means of the four filters 28 - 31, a signal within frequency band b1 incoming to unit 23 via input 2 4 is divided into four different subbands. The portion of: the signal falling within a certain subband is supplied to the detector 32, 33, 34 or 35, respectively, connected to the filter in question. The detector compares the energy level of the incoming signal with at least one reference level and delivers a logic signal depending upon said comparison to unit 36. In the processor contained in unit 36, the logic signals delivered from the different detectors are subjected to the required processing to generate the desired information which is then stored in the memory contained in said unit. When a corresponding control command is supplied to unit 36 from head end 11 via input 39, filter 40 and demodulator 38, sard information may then be delivered to the head end via modulator 43 and output 27. In the head end, the fetched in information may then be evalua¬ted in order to determine any required measures. If said evaluation proves that network 10 delivers unac-ceptably high disturbances, it is then possible from the head end to command a compulsory activation ot the blocking function of blocking circuit 26 in order hereby to prevent any continued transmission of signals within carrier frequency band bl from network 10 until the cause of said disturbances has been eliminated. Above it has been assumed that each detector 32, 33, 34 and 35, respectively, is arranged to compare the energy level of the srgnal incoming to the detector from the corresponding filter 28, 29, 30 or 31, respec¬tively, wrth a single reference level. However, each detector may be arranged to compare sard energy level with two different reference levels in order hereby to make it possible also to determine the slope of the front edge of each signal incoming to the detector and to store the corresponding information in unit 36. Unit 36 may also be arranged to effect a certain evaluation of the information stored therein. For in stance, it may be arranged to trigger and send an alarm signal to the head end when said evaluation proves that obviously impermissible conditions exist in network 10. In Figure 3, components of the embodiment of unit 2 3 shown therein which correspond to components of the above-described embodiment according to Figure 2 have been provided with the same reference numerals as in Figure 2. The embodiment according to Figure 3 differs from the embodiment according to Figure 2 primarily in that, instead of the different band-pass filters 28, 29, 30 and 3 1 and the different detectors 32, 33, 34 and 35, connected to said filters, it contains a single band pass filter 44 and a detector 45, connected to the out¬put of said filter. Furthermore, between input 24 and filter 44, there is provided a mixer 46 which is connec¬ted also to an oscillator 47, arranged to deliver a signal of an adjustable frequency to the mixer. Hereby, filter 44 can be supplied with a signal corresponding to the signal at input 24 but having a frequency spectrum that is displaced in relation to said signal in depen¬dence upon the set frequency of the output signal from oscillator 47. The setting of the frequency of the out¬put signal from the oscillator may be controlled from head end 11 of the cable TV system via input 39, filter 40 and demodulator 38. The band width of filter 44 should constitute only a small fraction of the total band width of carrier frequency band bl and, if band b1 covers the frequency range above mentioned by way of example, i.e. 15 - 65 MHz, it may for instance amount to 5 MHz. As a consequence of the composition of unit 2 3 above described, it is possible by controlling the fre¬quency of the output signal from oscillator 47 to dis- place the frequency spectrum of: carrier, frequency band bl in relation to the pass band of: band-pass filter 44 in such a manner that different sections of said fre¬quency band will be placed within the pass band of the filter. Hereby, the different sections of carrier fre¬quency band bl may be scanned in a cyclic fashion by cyclically placing them one at a time within the pass band of filter 44. However, when desired, said cyclic scanning may be interrupted temporarily for a mere de¬tailed investigation of the character of signals occur¬ring within a certain section of said frequency band. One feasible manner of detecting whether a siqnai occurring within frequency band bl consistutes a com¬munication signal or a disturbance signal is to detect whether the signal contains an acceptable preamble. How¬ever, in this case, it is necessary that the detector means contained in the local networks are capable of reacting sufficiently rapidly. The invention is not restricted to the embodiments above described and shown in the drawings. Instead, many other embodiments are feasible within the scope of the invention as defined in the following claims. WE CLAIM: 1. A cable TV system of the kind which is arranged to permit a transmission of signals in the return direction from local networks (10), included in the system, to a head end (11) of the system within a predetermined carrier frequency band, serving for the transmission of signals in said direction, and which comprises monitoring means (11, 23) for monitoring the system in respect of disturbances occurring within said carrier frequency band, characterized in that said monitoring means (11, 23) comprise detector means (32 to 35; 45) within each local network (10) which are arranged to compare the energy level of signals occurring within said carrier frequency band with at least one predetermined reference level and to generate logic signals, depending upon the result of said comparison, and memory means (36) within each local network (10) which are arranged to store information about time intervals during which said energy level exceeds said reference level, derived from the values of said logic signals at different times, and fetching in and evaluation means (11') at the head end (11) of the system by which information stored in said memory means (36) of the local networks (10) can be fetched in to the head end (11) for evaluation thereof at the head end. 2. The cable TV system as claimed in claim 1, wherein said memory means (36) are arranged to store said information in the form of information about the starting point and the length of each individual interval. 3. The cable TV system as claimed in claim 1 or 2, wherein said memory means (36) are arranged in respect of certain periods of time, to store information about said time intervals in the form of statistics relating to the number of such intervals occurring during said periods. 4. The cable TV system as claimed in any one of the preceding claims, wherein said reference level is adjustable, preferably under the control thereof from the head end (11) of the system. 5. The cable TV system as claimed in claim 4, wherein said memory means (36) are arranged also to store information about the value of the set reference level. 6. The cable TV system as claimed in any one of the preceding claims, wherein said detector means (32 to 35; 45) are arranged to compare said energy level with at least two different reference levels. 7. The cable TV system as claimed in any one of the preceding claims, wherein said detector means (32 to 35; 45) are arranged to effect said comparison and said generation of logic signals, depending upon the result of said comparison, individually for each one of a plurality of different sections of said frequency band and that said memory means (36) are arranged to store individual information for each of said sections derived from said signals. 8. The cable TV system as claimed in claim 7, wherein each local network (10) comprises a plurality of band-pass filters (28 to 31), which divide said carrier frequency band into a corresponding plurality of subbands, and a corresponding plurality of detector means (32 to 35), each serving to compare signals occurring within one said subbands with said reference level or levels, respectively. 9. The cable TV system as claimed in claim 7, wherein each local network (10) comprises a single band-pass filter (44), having a predetermined pass band width, constituting only a fraction of the total band width of said carrier frequency band, and a single detector means (45), connected to said filter, the frequency spectrum of the carrier frequency band being controllably displaceable relatively to the pass band of the band-pass filter (44) in order to permit different sections of the carrier frequency band to be placed within said pass band. 10. The cable TV system as claimed in claim 9, wherein the carrier frequency band is arranged to have different sections thereof cyclically placed within the pass band of the band-pass filter (44).

Documents:

in-pct-2002-01250-che abstract.pdf

in-pct-2002-01250-che assignement.pdf

in-pct-2002-01250-che claims.pdf

in-pct-2002-01250-che correspondence-others.pdf

in-pct-2002-01250-che correspondence-po.pdf

in-pct-2002-01250-che description(complete).pdf

in-pct-2002-01250-che drawings.pdf

in-pct-2002-01250-che form-1.pdf

in-pct-2002-01250-che form-18.pdf

in-pct-2002-01250-che form-26.pdf

in-pct-2002-01250-che form-3.pdf

in-pct-2002-01250-che form-5.pdf

in-pct-2002-01250-che form-6.pdf

in-pct-2002-01250-che pct search report.pdf

in-pct-2002-01250-che pct.pdf

in-pct-2002-01250-che petition.pdf

in-pct-2002-1250-che correspondence others.pdf

in-pct-2002-1250-che drawings.pdf

in-pct-2002-1250-che abstract duplicate.pdf

in-pct-2002-1250-che claims duplicate.pdf

in-pct-2002-1250-che correspondence others.pdf

in-pct-2002-1250-che description (complete) duplicate.pdf

in-pct-2002-1250-che drawings duplicate.pdf

in-pct-2002-1250-che drawings.pdf