WO2020157370A1 - A method for adjusting parameters of a network element - Google Patents
A method for adjusting parameters of a network element Download PDFInfo
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- WO2020157370A1 WO2020157370A1 PCT/FI2019/050072 FI2019050072W WO2020157370A1 WO 2020157370 A1 WO2020157370 A1 WO 2020157370A1 FI 2019050072 W FI2019050072 W FI 2019050072W WO 2020157370 A1 WO2020157370 A1 WO 2020157370A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/2801—Broadband local area networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
- H04B10/25751—Optical arrangements for CATV or video distribution
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client
- H04N21/61—Network physical structure; Signal processing
- H04N21/6106—Network physical structure; Signal processing specially adapted to the downstream path of the transmission network
- H04N21/6118—Network physical structure; Signal processing specially adapted to the downstream path of the transmission network involving cable transmission, e.g. using a cable modem
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/10—Adaptations for transmission by electrical cable
- H04N7/102—Circuits therefor, e.g. noise reducers, equalisers, amplifiers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N7/17309—Transmission or handling of upstream communications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04H—BROADCAST COMMUNICATION
- H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
- H04H20/65—Arrangements characterised by transmission systems for broadcast
- H04H20/76—Wired systems
- H04H20/77—Wired systems using carrier waves
- H04H20/78—CATV [Community Antenna Television] systems
Definitions
- the invention relates to cable television (CATV) networks, and especially to an arrangement for adjusting downstream parameters of a CATV network element containing a DCA node.
- CATV cable television
- CATV networks may be implemented with various techniques and network topologies, but currently most cable television networks are implemented as so-called HFC networks (Hybrid Fiber Coax), i.e. as combinations of a fibre network and a coaxial cable network.
- Data Over Cable Service Interface Specification DOCSIS
- DOCSIS is a CATV standard providing specifications for high-bandwidth data transfer in an existing CATV system.
- the latest version DOCSIS 3.1 enables the cable network operators to maximize both the downstream and upstream data throughput using the existing HFC networks.
- DCA Distributed CCAP Architecture
- DAA Distributed Access Architecture
- RPD Remote PHY Device
- RMD Remote-MACPHY Device
- FDX Full Duplex
- At least the first generation RPD/RMD nodes will most likely be designed such that a conventional HFC node is provided with an RPD/RMD unit or module.
- the downstream signals of the traditional CATV broadcast and the RPD/RMD-related services are obtained from separate input paths, but they are combined to a common signal path for downstream transmission.
- the components of the common signal path are typically adjusted in terms of an optimal signal level for the CATV broadcast downstream transmission. It is evident that parameter values of components, which have been optimized for the CATV broadcast downstream transmission, may not necessarily be optimal for the RPD/RMD-related service signals, but they may rather cause distortion to the RPD/RMD- related service signals.
- a method for adjusting downstream parameters of a cable television (CATV) network element comprising a first input arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA- related service signals, the method comprising measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and adjusting, based on said frequency response, one or more parameters of said DCA- related service signals in said DCA module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
- CATV cable television
- the method further comprises storing the values of the adjusted one or more parameters in a memory functionally connected to the DCA module.
- said parameters comprise one or more of the following: signal level, temperature compensation, slope, linear/cable slope and flatness.
- the method further comprises adjusting, prior to said measuring, one or more parameter of said plurality of components forming the downstream signal path of CATV broadcast signals in terms of desired frequency response of the CATV broadcast signal levels.
- the method further comprises measuring a frequency response of signal levels of the CATV broadcast signals from the second input to an output of the common downstream signal path; and adjusting the parameters of said DCA-related service signals in said DCA module based on detected changes in the frequency response of signal levels of the CATV broadcast signals.
- a second aspect relates to a CATV network element comprising a first input arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; a combiner for combining the CATV broadcast signals and the DCA- related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals; means for measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and means for adjusting, based on said frequency response, one or more parameters of said DCA-related service signals in said DCA module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
- DCA distributed CCAP architecture
- Fig. 1 shows the general structure of a typical HFC network
- Fig. 2 shows a simplified example of a DCA node
- Figs. 3a, 3b shows frequency responses of the signal level measured for the signal path of the DCA-related service channel signals
- Fig. 4 shows a flow chart of a method according to an embodiment of the invention.
- Fig. 5 shows the frequency response of the signal level compensated according to an embodiment of the invention.
- FIG. 1 shows the general structure of a typical HFC network.
- Program services are introduced from the main amplifier 100 (a so- called headend) of the network via an optical fibre network 102 to a fibre node 104, which converts the optical signal to an electric signal to be relayed further in a coaxial cable network 106.
- this coaxial cable segment typically comprises one or more broadband amplifiers 108, 110 for amplifying program service signals in a heavily attenuating coaxial media.
- the cable network 112 of a smaller area such as a distribution network of an apartment building, which are typically implemented as coaxial tree or star networks comprising signal splitters for distributing the program service signals to each customer.
- the cable network 112 such as the distribution network of an apartment, may further comprise a Network Interface Unit (NIU) arranged to divide downstream signals to appropriate home appliances.
- the NIU may operate as a home amplifier. From a wall outlet the signal is further relayed either via a cable modem 114 to a television receiver 116 or a computer 118, or via a so-called set-top box 120 to a television receiver 122.
- NIU Network Interface Unit
- DOCSIS Data Over Cable Service Interface Specification
- HFC hybrid fiber-coaxial
- the headend 100 of the CATV network comprises inputs for signals, such as TV signals and IP signals, a television signal modulator and a cable modem termination system (CMTS).
- CMTS provides high-speed data services to customers thorough cable modems (CM; 114) locating in homes.
- CM cable modems
- the CMTS forms the interface to the IP-based network over the Internet. It modulates the data from the Internet for downstream transmission to homes and receives the upstream data from homes.
- the CMTS additionally manages the load balancing, error correction parameters and the class of service (CoS).
- Signals from the headend 100 are distributed optically (fiber network 102) to the vicinity of individual homes, where the optical signals are converted to electrical signals at the terminating points 104.
- the electrical signals are then distributed to the various homes via the existing 75 ohm coaxial cables 106.
- the maximum data transfer of the coaxial cables is limited due to strong frequency-based attenuation. Therefore, the electrical signals transmitted over coaxial cables must be amplified.
- the amplifiers 108, 110 used for this purpose are suited to a specific frequency range.
- the upstream and downstream must occur over the same physical connection.
- the last part 112 of the coaxial connection between the CMTS and the CMs branches off in a star or a tree structure.
- a CMTS transmits the same data to all CMs located along the same section of cable (one-to-many communications).
- a request/grant mechanism exists between the CMTS and the CMs, meaning that a CM needing to transmit data must first send a request to the CMTS, after which it can transmit at the time assigned to it.
- the upstream channel width may vary between 200 kHz and 3.2 MHz (versions 1.0/1.1 ), and even to 6.4 MHz (version 2.0).
- 64-QAM or 256-QAM modulation is used for downstream data in all versions, but upstream data uses QPSK or 16- level QAM (16-QAM) for DOCSIS 1.x, while QPSK, 8-QAM, 16-QAM, 32-QAM, 64-QAM and 128-QAM are used for DOCSIS 2.0 & 3.0.
- DOCSIS 3.1 specifications support capacities of at least 10 Gbit/s downstream and 1 Gbit/s upstream using 4096 QAM.
- DOCSIS 3.1 rejects the 6 or 8 MHz wide channel spacing and uses narrower orthogonal frequency-division multiplexing (OFDM) subcarriers being 20 kHz to 50 kHz wide, which sub-carriers can be combined within a block spectrum of about 200 MHz wide.
- OFDM orthogonal frequency-division multiplexing
- DOCSIS 3.1 further provides the concept of Distributed CCAP Architecture (DCA), which may also be referred to as Distributed Access Architecture (DAA).
- DCA Distributed CCAP Architecture
- CCAP Converged Cable Access Platform
- DAA Distributed Access Architecture
- CCAP may be defined as an access-side networking element or set of elements that combines the functionality of a CMTS with that of an Edge QAM (i.e. the modulation), providing high-density services to cable subscribers.
- the CCAP functionalities have been implemented in the headend/hub, such as the headend 100 in Figure 1.
- some features of the CCAP are distributed from headend/hub to the network elements closer to the customers, for example to the optical nodes 104 or the broadband amplifiers 108, 110 in Figure 1.
- DOCSIS 3.1 specifies at least two network element concepts, i.e.
- DOCSIS 3.1 also provided Annex F introducing a Full Duplex DOCSIS 3.1 technology, where a new distributed access node called Full Duplex (FDX) Node is determined.
- FDX Full Duplex
- FIG. 2 shows a simplified structure of a DCA node 200, such as an RPD/RMD node. At least the first generation RPD/RMD nodes will most likely be designed such that a conventional HFC node is provided with an RPD/RMD unit or module. Therein, the downstream signals of the traditional CATV broadcast and the RPD/RMD-related services are obtained from separate input paths, but they are combined to a common output path for downstream transmission.
- a DCA module such as an RPD/RMD module 202 is arranged to receive digital downstream multiplexes from the headend via a first input 201.
- the RPD/RMD module 202 comprises various functionalities for implementing the distributed CCAP functionalities.
- the RPD/RMD module 202 generates the RF output signals by modulating the digital signals accordingly and supplies the signals further via an adjustable amplifier 206.
- the CATV broadcast downstream signals are received via a second input 204.
- the CATV receiver unit 208 converts the optical signals into RF signals (208a), which are amplified (208b, 208c) at an appropriate level.
- the RF signals from the amplifier 206 and from the CATV receiver unit 208 are combined in a combiner 210, after which the RF signal share a common downstream signal path.
- the signal path may comprise a plurality of amplifier units, such as a gain control amplifier unit 212 and a slope control amplifier unit 214.
- the RF signals are highpass filtered (216) and lowpass filtered (218) to a desired frequency range and supplied to an output hybrid amplifier unit 220 before transmission to a network segment via an output 222.
- Figure 2 is only simplified block chart of a DCA node and does not show all the functional blocks of a real DCA node. For example, Figure 2 does not show any functional blocks relating to the CATV upstream signal path.
- the downstream signal level of the CATV broadcast signal is adjusted for the whole downstream signal path from the CATV broadcast input 204 to the output 222, whereupon parameters of the plurality of downstream signal path components (i.e. one or more of the components 208, 212, 214, 220) are adjusted in terms of an optimal signal level for the CATV broadcast downstream transmission.
- the optimal signal level for the CATV broadcast downstream transmission is typically not the same for all frequencies but depending e.g. on the channel raster of the network, signal levels on some frequencies (e.g. containing channels) are emphasized more than other frequencies (containing no or less important channels).
- the adjustment of the downstream signal path components also affects to the signal level of the RPD/RMD-related service channel signals.
- This is illustrated in Figure 3a by the curve 300 showing the frequency response of the signal level measured for the signal path of the RPD/RMD-related service channel signals, i.e. from the input 206 to the output 222, where the signal level varies as a function of the frequency.
- the downstream signal level of the RPD/RMD-related service channels can be adjusted in the RPD/RMD module only.
- the signal levels of the digital signals at the output of the RPD/RMD module are adjusted on an equal level throughout the used frequency range, as illustrated by the straight line 302 in Figure 3a.
- the adjustment may involve adjusting one or more further parameters, such as temperature compensation, slope and flatness.
- the signal levels of the RPD/RMD-related services inevitably become distorted, wherein the distortion reflects the variation in the frequency response of the signal level measured from the RPD/RMD module 202 to the output 222.
- Figure 3b shows how the signal levels of the RPD/RMD-related service channels (the plurality of vertical lines along the frequency axis) vary according to the variation in the the frequency response of the signal level measured from the RPD/RMD module to the output.
- the downstream signal level of at least some of the RPD/RMD- related service channels is significantly lower or higher that originally adjusted. This reduces the accuracy of the RPD/RMD-related service signals and may deteriorate the reception and interpretation of said signals.
- a method for adjusting downstream parameters of a cable television (CATV) network element comprises a first input arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; and a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals.
- DCA distributed CCAP architecture
- FIG. 4 An exemplified flowchart of the method is illustrated in Figure 4, wherein the method comprises providing (400) the above-described CATV network element; measuring (402) a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and adjusting (404), based on said frequency response, one or more parameters of said DCA-related service signals in said DCA module to compensate for deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
- the method enables to provide necessary information for the DCA module, such as the RPD/RMD module, for adjusting the parameters of the DCA-related service signals such that deviations in one or more parameters, detected at the output of the CATV network element and which are caused by the settings of the components of the common downstream signal path within the CATV network element, can be compensated. Since the parameters of the DCA-related service signals can only be adjusted in the DCA module, it is necessary to provide the information, such as frequency response of signal levels of the DCA-related service signal path, to the DCA module.
- the DCA module may comprise a processing unit (CPU) for controlling the operation of the DCA module, such as the RPD/RMD module.
- the processing unit may receive the information, such as frequency response of signal levels of the DCA-related service signal path, and calculate the necessary adjustment for one or more parameters of said DCA-related service signals. As a result, the values of one or more parameters of the DCA-related service signals, as detected at the output of the CATV network element, are re-adjusted to the desired level.
- the measurement of the frequency response of signal levels of the CATV signal path may provide additional or alternative control information for adjust the parameters of said DCA-related service signals in said DCA module, which control information may be used to compensate for deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
- the method further comprises obtaining a signal representing the frequency response from an output of the CATV network element, and providing the signal to an input of the DCA module for said measuring of the frequency response.
- the output of the CATV network element may be provided with coupling means, such as a directional coupler 224 shown in Figure 2, for obtaining the output signal.
- the output signal is supplied via the feedback loop 226 to an input of the the DCA module, such as the RPD/RMD module 200.
- an analog-digital (AD) converter may be used for measuring of the frequency response.
- the one or more parameters of said DCA-related service signals are then adjusted based on the measurement, for example as dynamic adjustment.
- the method further comprises storing the values of the adjusted one or more parameters in a memory functionally connected to the DCA module.
- the CATV network element may comprise a memory, which is functionally connected to the DCA module. Since the measured frequency response of signal levels of the DCA-related service signal path is most dominantly affected by the settings of components of the common part of the downstream signal path, the same adjusted parameter values can typically be used even if the DCA module is changed. Storing the values of the adjusted one or more parameters in the memory is especially beneficial, if the CATV network element lacks the feedback loop 226, which enables the dynamic adjustment of the parameters of said DCA-related service signals. Thus, instead of the dynamically adjusted parameters, the parameters stored in the memory may be used.
- said parameters comprise one or more of the following: signal level, temperature compensation, slope, linear/cable slope and flatness.
- the measurement of various parameters, as detected at the output of the CATV network element may be performed and the information may be provided to the DCA module.
- the processing unit may then calculate the necessary adjustment for any of said parameters and a re-adjustment of said DCA-related service signals may be carried out.
- the method further comprises adjusting, prior to said measuring, one or more parameter of said plurality of components forming the downstream signal path of CATV broadcast signals in terms of desired frequency response of the CATV broadcast signal levels.
- the components of the CATV element such as the DCA node based on a conventional HFC node, are first adjusted for optimizing the downstream signal path of CATV broadcast signals.
- said parameters can be adjusted to compensate for any deviations caused by the first adjustment.
- the parameters of both the CATV broadcast signals and the DCA-related service signals may be adjusted on an appropriate level.
- the method and the related embodiments may naturally be implemented in a basic DCA node, such as an RPD/RMD node, which is not combined with the HFC node.
- a basic DCA node such as an RPD/RMD node, which is not combined with the HFC node.
- such basic DCA node may lack at least the second input 204, the opto-electric converter 208a, amplifiers 208b, 208c and the combiner 210.
- the design requirements for the components of the downstream signal path 212, 214, 220 are not strict since they do not have to be adjusted in terms of an optimal signal level for the CATV broadcast downstream transmission. Instead, any deviations in said one or more parameters caused by the plurality of components of the downstream signal path may be directly adjusted by the features of the DCA module. Thus, less expensive components may be used in the downstream signal path of such basic DCA node.
- the various embodiments may be implemented in hardware or special purpose circuits or any combination thereof. While various embodiments may be illustrated and described as block diagrams or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
- the implementation may include a computer readable storage medium stored with code thereon for use by an apparatus, such as the network element, which when executed by a processor, causes the apparatus to perform the various embodiments or a subset of them.
- the implementation may include a computer program embodied on a non-transitory computer readable medium, the computer program comprising instructions causing, when executed on at least one processor, at least one apparatus to apparatus to perform the various embodiments or a subset of them.
- an apparatus may comprise circuitry and electronics for handling, receiving and transmitting data, computer program code in a memory, and a processor that, when running the computer program code, causes the apparatus to carry out the features of an embodiment.
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Abstract
A method for adjusting downstream parameters of a CATV network element comprising a first input arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals (400), the method comprising measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path (402); and adjusting, based on said frequency response, one or more parameters of said DCA-related service signals in said DCA module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path (404).
Description
A METHOD FOR ADJUSTING PARAMETERS OF A NETWORK ELEMENT
Field of the invention
The invention relates to cable television (CATV) networks, and especially to an arrangement for adjusting downstream parameters of a CATV network element containing a DCA node.
Background of the invention
CATV networks may be implemented with various techniques and network topologies, but currently most cable television networks are implemented as so-called HFC networks (Hybrid Fiber Coax), i.e. as combinations of a fibre network and a coaxial cable network. Data Over Cable Service Interface Specification (DOCSIS) is a CATV standard providing specifications for high-bandwidth data transfer in an existing CATV system. The latest version DOCSIS 3.1 enables the cable network operators to maximize both the downstream and upstream data throughput using the existing HFC networks.
One issue relating to the introduction of DOCSIS 3.1 is the concept of Distributed CCAP Architecture (DCA), a.k.a. Distributed Access Architecture (DAA), where some features of the headend are distributed to the network elements closer to the customers, such as optical nodes and broadband amplifiers. DOCSIS 3.1 specifies at least three distributed network units, i.e. a Remote PHY Device (RPD) Node, a Remote-MACPHY Device (RMD) and Full Duplex (FDX) Node, which may commonly be referred to as DCA nodes.
At least the first generation RPD/RMD nodes will most likely be designed such that a conventional HFC node is provided with an RPD/RMD unit or module. Therein, the downstream signals of the traditional CATV broadcast and the RPD/RMD-related services are obtained from separate input paths, but they are combined to a common signal path for downstream transmission.
The components of the common signal path are typically adjusted in terms of an optimal signal level for the CATV broadcast downstream transmission. It is evident that parameter values of components, which have been optimized for the CATV broadcast downstream transmission, may not necessarily be optimal for the RPD/RMD-related service signals, but they may rather cause distortion to the RPD/RMD- related service signals.
Brief summary of the invention
Now, an improved arrangement has been developed to reduce the above-mentioned problems. As aspects of the invention, we present a method and a network element of a cable television network, which are characterized in what will be presented in the independent claims.
The dependent claims disclose advantageous embodiments of the invention.
According to an aspect of the invention, there is provided a method for adjusting downstream parameters of a cable television (CATV) network element comprising a first input arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA- related service signals, the method comprising measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and adjusting, based on said frequency response, one or more parameters of said DCA- related service signals in said DCA module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
According to an embodiment, the method further comprises obtaining a signal representing the frequency response from an output of the CATV network element; and providing the signal to an input of the DCA module for said measuring of the frequency response.
According to an embodiment, the method further comprises storing the values of the adjusted one or more parameters in a memory functionally connected to the DCA module.
According to an embodiment, said parameters comprise one or more of the following: signal level, temperature compensation, slope, linear/cable slope and flatness.
According to an embodiment, the method further comprises adjusting, prior to said measuring, one or more parameter of said plurality of components forming the downstream signal path of CATV broadcast signals in terms of desired frequency response of the CATV broadcast signal levels.
According to an embodiment, the method further comprises measuring a frequency response of signal levels of the CATV broadcast signals from the second input to an output of the common downstream signal path; and adjusting the parameters of said DCA-related service signals in said DCA module based on detected changes in the frequency response of signal levels of the CATV broadcast signals.
A second aspect relates to a CATV network element comprising a first input arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; a combiner for combining the CATV broadcast signals and the DCA- related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals;
means for measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and means for adjusting, based on said frequency response, one or more parameters of said DCA-related service signals in said DCA module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
These and other aspects, embodiments and advantages will be presented later in the detailed description of the invention.
Brief description of the drawings
The invention will now be described in more detail in connection with preferred embodiments with reference to the appended drawings, in which:
Fig. 1 shows the general structure of a typical HFC network;
Fig. 2 shows a simplified example of a DCA node;
Figs. 3a, 3b shows frequency responses of the signal level measured for the signal path of the DCA-related service channel signals;
Fig. 4 shows a flow chart of a method according to an embodiment of the invention; and
Fig. 5 shows the frequency response of the signal level compensated according to an embodiment of the invention.
Detailed description of the embodiments
Figure 1 shows the general structure of a typical HFC network. Program services are introduced from the main amplifier 100 (a so- called headend) of the network via an optical fibre network 102 to a fibre node 104, which converts the optical signal to an electric signal to be relayed further in a coaxial cable network 106. Depending on the
length, branching, topology, etc. of the coaxial cable network, this coaxial cable segment typically comprises one or more broadband amplifiers 108, 110 for amplifying program service signals in a heavily attenuating coaxial media. From the amplifier the program service signals are introduced to a cable network 112 of a smaller area, such as a distribution network of an apartment building, which are typically implemented as coaxial tree or star networks comprising signal splitters for distributing the program service signals to each customer. The cable network 112, such as the distribution network of an apartment, may further comprise a Network Interface Unit (NIU) arranged to divide downstream signals to appropriate home appliances. The NIU may operate as a home amplifier. From a wall outlet the signal is further relayed either via a cable modem 114 to a television receiver 116 or a computer 118, or via a so-called set-top box 120 to a television receiver 122.
Data Over Cable Service Interface Specification (DOCSIS) is a CATV standard providing specifications for high-bandwidth data transfer in an existing CATV system. DOCSIS may be employed to provide Internet access over existing hybrid fiber-coaxial (HFC) infrastructure of cable television operators. DOCSIS has been evolved through versions 1.0, 1.1 , 2.0 and 3.0 to the latest version of 3.1. DOCSIS provides a lucrative option for cable network providers to maximize both the downstream and upstream data throughput using the existing cable TV network, but without making expensive changes to the HFC network infrastructure.
When implementing the HFC network of Figure 1 according to DOCSIS, the headend 100 of the CATV network comprises inputs for signals, such as TV signals and IP signals, a television signal modulator and a cable modem termination system (CMTS). The CMTS provides high-speed data services to customers thorough cable modems (CM; 114) locating in homes. The CMTS forms the interface to the IP-based network over the Internet. It modulates the data from the Internet for downstream transmission to homes and receives the
upstream data from homes. The CMTS additionally manages the load balancing, error correction parameters and the class of service (CoS).
Signals from the headend 100 are distributed optically (fiber network 102) to the vicinity of individual homes, where the optical signals are converted to electrical signals at the terminating points 104. The electrical signals are then distributed to the various homes via the existing 75 ohm coaxial cables 106. The maximum data transfer of the coaxial cables is limited due to strong frequency-based attenuation. Therefore, the electrical signals transmitted over coaxial cables must be amplified. The amplifiers 108, 110 used for this purpose are suited to a specific frequency range. In addition, the upstream and downstream must occur over the same physical connection. The last part 112 of the coaxial connection between the CMTS and the CMs branches off in a star or a tree structure. A CMTS transmits the same data to all CMs located along the same section of cable (one-to-many communications). A request/grant mechanism exists between the CMTS and the CMs, meaning that a CM needing to transmit data must first send a request to the CMTS, after which it can transmit at the time assigned to it.
Depending on the version of DOCSIS used in the CATV network, there is a great variety in options available for configuring the network. For the downstream channel width, all versions of DOCSIS earlier than 3.1 use either 6 MHz channels (e.g. North America) or 8 MHz channels (so-called "EuroDOCSIS"). However, the upstream channel width may vary between 200 kHz and 3.2 MHz (versions 1.0/1.1 ), and even to 6.4 MHz (version 2.0). 64-QAM or 256-QAM modulation is used for downstream data in all versions, but upstream data uses QPSK or 16- level QAM (16-QAM) for DOCSIS 1.x, while QPSK, 8-QAM, 16-QAM, 32-QAM, 64-QAM and 128-QAM are used for DOCSIS 2.0 & 3.0.
DOCSIS 3.1 specifications support capacities of at least 10 Gbit/s downstream and 1 Gbit/s upstream using 4096 QAM. DOCSIS 3.1 rejects the 6 or 8 MHz wide channel spacing and uses narrower orthogonal frequency-division multiplexing (OFDM) subcarriers being
20 kHz to 50 kHz wide, which sub-carriers can be combined within a block spectrum of about 200 MHz wide.
DOCSIS 3.1 further provides the concept of Distributed CCAP Architecture (DCA), which may also be referred to as Distributed Access Architecture (DAA). Converged Cable Access Platform (CCAP) may be defined as an access-side networking element or set of elements that combines the functionality of a CMTS with that of an Edge QAM (i.e. the modulation), providing high-density services to cable subscribers. Conventionally, the CCAP functionalities have been implemented in the headend/hub, such as the headend 100 in Figure 1. In a DCA, some features of the CCAP are distributed from headend/hub to the network elements closer to the customers, for example to the optical nodes 104 or the broadband amplifiers 108, 110 in Figure 1. DOCSIS 3.1 specifies at least two network element concepts, i.e. a Remote PHY Device (RPD) and a Remote-MACPHY Device (RMD), to which some functionalities of the headend can be distributed. A recent version of DOCSIS 3.1 specification also provided Annex F introducing a Full Duplex DOCSIS 3.1 technology, where a new distributed access node called Full Duplex (FDX) Node is determined. These network elements may be commonly referred to as DCA nodes.
Figure 2 shows a simplified structure of a DCA node 200, such as an RPD/RMD node. At least the first generation RPD/RMD nodes will most likely be designed such that a conventional HFC node is provided with an RPD/RMD unit or module. Therein, the downstream signals of the traditional CATV broadcast and the RPD/RMD-related services are obtained from separate input paths, but they are combined to a common output path for downstream transmission.
This is illustrated in Figure 2, where a DCA module, such as an RPD/RMD module 202 is arranged to receive digital downstream multiplexes from the headend via a first input 201. The RPD/RMD module 202 comprises various functionalities for implementing the distributed CCAP functionalities. The RPD/RMD module 202 generates
the RF output signals by modulating the digital signals accordingly and supplies the signals further via an adjustable amplifier 206.
The CATV broadcast downstream signals are received via a second input 204. The CATV receiver unit 208 converts the optical signals into RF signals (208a), which are amplified (208b, 208c) at an appropriate level. The RF signals from the amplifier 206 and from the CATV receiver unit 208 are combined in a combiner 210, after which the RF signal share a common downstream signal path. The signal path may comprise a plurality of amplifier units, such as a gain control amplifier unit 212 and a slope control amplifier unit 214. The RF signals are highpass filtered (216) and lowpass filtered (218) to a desired frequency range and supplied to an output hybrid amplifier unit 220 before transmission to a network segment via an output 222.
A skilled person appreciates that Figure 2 is only simplified block chart of a DCA node and does not show all the functional blocks of a real DCA node. For example, Figure 2 does not show any functional blocks relating to the CATV upstream signal path.
The downstream signal level of the CATV broadcast signal is adjusted for the whole downstream signal path from the CATV broadcast input 204 to the output 222, whereupon parameters of the plurality of downstream signal path components (i.e. one or more of the components 208, 212, 214, 220) are adjusted in terms of an optimal signal level for the CATV broadcast downstream transmission. When evaluated in frequency domain, the optimal signal level for the CATV broadcast downstream transmission is typically not the same for all frequencies but depending e.g. on the channel raster of the network, signal levels on some frequencies (e.g. containing channels) are emphasized more than other frequencies (containing no or less important channels).
The adjustment of the downstream signal path components also affects to the signal level of the RPD/RMD-related service channel signals. This is illustrated in Figure 3a by the curve 300 showing the frequency
response of the signal level measured for the signal path of the RPD/RMD-related service channel signals, i.e. from the input 206 to the output 222, where the signal level varies as a function of the frequency.
On the other hand, the downstream signal level of the RPD/RMD- related service channels can be adjusted in the RPD/RMD module only. Typically, the signal levels of the digital signals at the output of the RPD/RMD module are adjusted on an equal level throughout the used frequency range, as illustrated by the straight line 302 in Figure 3a. In addition to the signal level, the adjustment may involve adjusting one or more further parameters, such as temperature compensation, slope and flatness.
However, due to the common downstream signal path for both the CATV broadcast signals and the RPD/RMD-related service channel signals within the DCA node, the signal levels of the RPD/RMD-related services inevitably become distorted, wherein the distortion reflects the variation in the frequency response of the signal level measured from the RPD/RMD module 202 to the output 222. This is illustrated in Figure 3b, showing how the signal levels of the RPD/RMD-related service channels (the plurality of vertical lines along the frequency axis) vary according to the variation in the the frequency response of the signal level measured from the RPD/RMD module to the output. As a result, the downstream signal level of at least some of the RPD/RMD- related service channels is significantly lower or higher that originally adjusted. This reduces the accuracy of the RPD/RMD-related service signals and may deteriorate the reception and interpretation of said signals.
Therefore, an improved procedure is needed for adjusting downstream parameters of a CATV network element.
According to an aspect, a method for adjusting downstream parameters of a cable television (CATV) network element is now introduced, wherein the CATV network element comprises a first input
arranged to receive distributed CCAP architecture (DCA)-related service signals; a DCA module arranged to adjust one or more parameters of said DCA-related service signals; a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals; and a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals.
An exemplified flowchart of the method is illustrated in Figure 4, wherein the method comprises providing (400) the above-described CATV network element; measuring (402) a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and adjusting (404), based on said frequency response, one or more parameters of said DCA-related service signals in said DCA module to compensate for deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
Hence, the method enables to provide necessary information for the DCA module, such as the RPD/RMD module, for adjusting the parameters of the DCA-related service signals such that deviations in one or more parameters, detected at the output of the CATV network element and which are caused by the settings of the components of the common downstream signal path within the CATV network element, can be compensated. Since the parameters of the DCA-related service signals can only be adjusted in the DCA module, it is necessary to provide the information, such as frequency response of signal levels of the DCA-related service signal path, to the DCA module. The DCA module may comprise a processing unit (CPU) for controlling the operation of the DCA module, such as the RPD/RMD module. The processing unit may receive the information, such as frequency response of signal levels of the DCA-related service signal path, and calculate the necessary adjustment for one or more parameters of said DCA-related service signals. As a result, the values of one or more
parameters of the DCA-related service signals, as detected at the output of the CATV network element, are re-adjusted to the desired level.
This is illustrated in Figure 5, where the signal levels of the DCA- related service channels (the plurality of vertical lines along the frequency axis) no longer vary according to the variation in the frequency response of the signal level measured from the input to the output, but they are detected at an equal level throughout the used frequency range.
It is noted that instead of or in addition to measuring the frequency response of signal levels of the DCA-related service signal path, it is possible to measure the frequency response of signal levels of the CATV signal path and adjust the parameters of said DCA-related service signals in said DCA module based on detected changes in the frequency response of signal levels of the CATV signal path. Thus, the measurement of the frequency response of signal levels of the CATV signal path may provide additional or alternative control information for adjust the parameters of said DCA-related service signals in said DCA module, which control information may be used to compensate for deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
According to an embodiment, the method further comprises obtaining a signal representing the frequency response from an output of the CATV network element, and providing the signal to an input of the DCA module for said measuring of the frequency response. Thus, the output of the CATV network element may be provided with coupling means, such as a directional coupler 224 shown in Figure 2, for obtaining the output signal. The output signal is supplied via the feedback loop 226 to an input of the the DCA module, such as the RPD/RMD module 200. Therein, for example an analog-digital (AD) converter may be used for measuring of the frequency response. The one or more parameters of said DCA-related service signals are then adjusted based on the measurement, for example as dynamic adjustment.
According to an embodiment, the method further comprises storing the values of the adjusted one or more parameters in a memory functionally connected to the DCA module. The CATV network element may comprise a memory, which is functionally connected to the DCA module. Since the measured frequency response of signal levels of the DCA-related service signal path is most dominantly affected by the settings of components of the common part of the downstream signal path, the same adjusted parameter values can typically be used even if the DCA module is changed. Storing the values of the adjusted one or more parameters in the memory is especially beneficial, if the CATV network element lacks the feedback loop 226, which enables the dynamic adjustment of the parameters of said DCA-related service signals. Thus, instead of the dynamically adjusted parameters, the parameters stored in the memory may be used.
According to an embodiment, said parameters comprise one or more of the following: signal level, temperature compensation, slope, linear/cable slope and flatness. Thus, the measurement of various parameters, as detected at the output of the CATV network element, may be performed and the information may be provided to the DCA module. The processing unit may then calculate the necessary adjustment for any of said parameters and a re-adjustment of said DCA-related service signals may be carried out.
According to an embodiment, the method further comprises adjusting, prior to said measuring, one or more parameter of said plurality of components forming the downstream signal path of CATV broadcast signals in terms of desired frequency response of the CATV broadcast signal levels. Thus, the components of the CATV element, such as the DCA node based on a conventional HFC node, are first adjusted for optimizing the downstream signal path of CATV broadcast signals. Owing to the features of the DCA module for adjusting the parameters of said DCA-related service signals, said parameters can be adjusted to compensate for any deviations caused by the first adjustment.
Thereby, the parameters of both the CATV broadcast signals and the DCA-related service signals may be adjusted on an appropriate level.
The method and the related embodiments may naturally be implemented in a basic DCA node, such as an RPD/RMD node, which is not combined with the HFC node. Compared to the DCA module shown in Figure 2, such basic DCA node may lack at least the second input 204, the opto-electric converter 208a, amplifiers 208b, 208c and the combiner 210. In such basic DCA node, the design requirements for the components of the downstream signal path 212, 214, 220 are not strict since they do not have to be adjusted in terms of an optimal signal level for the CATV broadcast downstream transmission. Instead, any deviations in said one or more parameters caused by the plurality of components of the downstream signal path may be directly adjusted by the features of the DCA module. Thus, less expensive components may be used in the downstream signal path of such basic DCA node.
In general, the various embodiments may be implemented in hardware or special purpose circuits or any combination thereof. While various embodiments may be illustrated and described as block diagrams or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
A skilled person appreciates that any of the embodiments described above may be implemented as a combination with one or more of the other embodiments, unless there is explicitly or implicitly stated that certain embodiments are only alternatives to each other.
The various embodiments can be implemented with the help of computer program code that resides in a memory and causes the relevant apparatuses to carry out the invention. Thus, the implementation may include a computer readable storage medium
stored with code thereon for use by an apparatus, such as the network element, which when executed by a processor, causes the apparatus to perform the various embodiments or a subset of them. In addition, or alternatively, the implementation may include a computer program embodied on a non-transitory computer readable medium, the computer program comprising instructions causing, when executed on at least one processor, at least one apparatus to apparatus to perform the various embodiments or a subset of them. For example, an apparatus may comprise circuitry and electronics for handling, receiving and transmitting data, computer program code in a memory, and a processor that, when running the computer program code, causes the apparatus to carry out the features of an embodiment.
It will be obvious for a person skilled in the art that with technological developments, the basic idea of the invention can be implemented in a variety of ways. Thus, the invention and its embodiments are not limited to the above-described examples but they may vary within the scope of the claims.
Claims
1. A method for adjusting downstream parameters of a cable television (CATV) network element comprising
- a first input arranged to receive distributed CCAP architecture (DCA)-related service signals;
- a DCA module arranged to adjust one or more parameters of said DCA-related service signals;
- a second input arranged to receive CATV broadcast signals;
- a plurality of components arranged to form a downstream signal path of CATV broadcast signals;
- a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals, the method comprising
measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and
adjusting, based on said frequency response, one or more parameters of said DCA-related service signals in said DCA module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
2. The method according to claim 1 , further comprising
obtaining a signal representing the frequency response from an output of the CATV network element; and
providing the signal to an input of the DCA module for said measuring of the frequency response.
3. The method according to claim 1 or 2, further comprising
storing the values of the adjusted one or more parameters in a memory functionally connected to the DCA module.
4. The method according to any preceding claim, wherein said parameters comprise one or more of the following: signal level, temperature compensation, slope, linear/cable slope and flatness.
5. The method according to any preceding claim, further comprising adjusting, prior to said measuring, one or more parameter of said plurality of components forming the downstream signal path of CATV broadcast signals in terms of desired frequency response of the CATV broadcast signal levels.
6. The method according to any preceding claim, further comprising measuring a frequency response of signal levels of the CATV broadcast signals from the second input to an output of the common downstream signal path; and
adjusting the parameters of said DCA-related service signals in said DCA module based on detected changes in the frequency response of signal levels of the CATV broadcast signals.
7. A CATV network element comprising
a first input arranged to receive distributed CCAP architecture (DCA)-related service signals;
a DCA module arranged to adjust one or more parameters of said DCA-related service signals;
a second input arranged to receive CATV broadcast signals; a plurality of components arranged to form a downstream signal path of CATV broadcast signals;
a combiner for combining the CATV broadcast signals and the DCA-related service signals such that at least a part of said plurality of components are arranged to form a common downstream signal path for the CATV broadcast signals and the DCA-related service signals;
means for measuring a frequency response of signal levels of the signal path from the first input to an output of the common downstream signal path; and
means for adjusting, based on said frequency response, one or more parameters of said DCA-related service signals in said DCA
module to compensate deviations in said one or more parameters caused by the plurality of components of the common downstream signal path.
8. The network element according to claim 7, further comprising
means for obtaining a signal representing the frequency response from an output of the CATV network element; and
means for providing the signal to an input of the DCA module for said measuring of the frequency response.
9. The network element according to claim 7 or 8, further comprising means for storing the values of the adjusted one or more parameters in a memory functionally connected to the DCA module.
10. The network element according to any of claims 7 - 9, wherein said parameters comprise one or more of the following: signal level, temperature compensation, slope, linear/cable slope and flatness.
11. The network element according to any of claims 7 - 10, further comprising
means for adjusting, prior to said measuring, one or more parameter of said plurality of components forming the downstream signal path of CATV broadcast signals in terms of desired frequency response of the CATV broadcast signal levels.
12. The network element according to any of claims 7 - 11 , further comprising
means for measuring a frequency response of signal levels of the CATV broadcast signals from the second input to an output of the common downstream signal path; and
means for adjusting the parameters of said DCA-related service signals in said DCA module based on detected changes in the frequency response of signal levels of the CATV broadcast signals.
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