WO2020128135A1

WO2020128135A1 - A method for adjusting parameters of a network element

Info

Publication number: WO2020128135A1
Application number: PCT/FI2018/050937
Authority: WO
Inventors: Pasi KOIVISTO
Original assignee: Teleste Oyj
Priority date: 2018-12-18
Filing date: 2018-12-18
Publication date: 2020-06-25

Abstract

A method for adjusting upstream parameters of a CATV network element comprising a plurality of components arranged to form an upstream signal path and a plurality of components arranged to form a downstream signal path, the method comprising sending one or more upstream pilot signals via the upstream signal path to a distributed CCAP architecture (DCA) node (200); measuring levels of the one or more upstream pilot signals in the DCA node (202); determining a plurality of downstream pilot signals, wherein a first downstream pilot signal is a reference signal, and any subsequent downstream pilot signal is associated with one of said upstream pilot signals, wherein at least one parameter value of the subsequent downstream signals is determined based on the reference signal and a difference between a measured level and expected level of the associated upstream pilot signal (204); sending the plurality of downstream pilot signals via the downstream signal path to a spectrum analyzer (206); measuring differences between values of said at least one parameter of the reference signal and each of the subsequent downstream pilot signals (208); and providing information, based on the differences of values of said at least one parameter, for adjusting one or more upstream parameters of the CATV network element (210).

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 upstream parameters of a CATV network element.

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.

Adjusting the upstream parameters of the CATV network elements in HFC networks has traditionally been performed by sending measured parameter values to the headend and receiving instructions from the headend for adjusting the upstream parameters correctly. However, the introduction of DCA nodes may lead to a situation where there is no direct signal path from a network element to the headend, whereupon the traditional way of adjusting the upstream parameters is no longer available. DOCSIS 3.1 standard tries to address this issue by establishing out-of- band (OOB) signalling channels, via which DCA nodes may be managed by a plurality of CCAP Core (i.e. headend) functionalities. A logical NDR (Narrowband Digital Return) channel may be established to send measured upstream parameter values of a network element to a Reverse OOB CCAP Core. Another CCAP Core functionality is then used to send the instructions for adjusting the upstream parameters to the DCA node, which then controls the network element to adjust the upstream parameters correctly.

It is evident that such signalling is a complex and cumbersome way of adjusting the upstream parameters of the CATV network elements.

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, an apparatus 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 upstream parameters of a cable television (CATV) network element comprising a plurality of components arranged to form an upstream signal path and a plurality of components arranged to form a downstream signal path, the method comprising sending one or more upstream pilot signals via the upstream signal path to a distributed CCAP architecture (DCA) node; measuring levels of the one or more upstream pilot signals in the DCA node; determining a plurality of downstream pilot signals, wherein a first downstream pilot signal is a reference signal, and any subsequent downstream pilot signal is associated with one of said upstream pilot signals, wherein at least one parameter value of the subsequent downstream signals is determined based on the reference signal and a difference between a measured level and an expected level of the associated upstream pilot signal; sending the plurality of downstream pilot signals via the downstream signal path to a spectrum analyzer; measuring differences between values of said at least one parameter of the reference signal and each of the subsequent downstream pilot signals; and providing information, based on the differences of values of said at least one parameter, for adjusting one or more upstream parameters of the CATV network element.

According to an embodiment, said at least one parameter value comprises a level of the one or more downstream pilot signals.

According to an embodiment, said at least one parameter value comprises a frequency of the one or more downstream pilot signals.

According to an embodiment, the method further comprises configuring a predetermined set of pilot signal parameters in a pilot signal generator and in said DCA node prior to sending the upstream pilot signals.

According to an embodiment, the predetermined set of pilot signal parameters comprises one or more of the following:

- measurement frequencies and expected levels of the upstream pilot signals to be configured in said DCA node;

- frequencies of the downstream pilot signals and the level of the reference signal to be configured in said DCA node;

- frequencies and levels of the upstream pilot signals to be configured in said pilot signal generator;

- frequencies of the downstream pilot signals to be configured in said spectrum analyzer.

According to an embodiment, the pilot signal generator and the spectrum analyzer are integrated in a common node, which is connected to the CATV network element via a test point. According to an embodiment, the method further comprises adjusting an attenuator and/or an equalizer of the upstream signal path of the CATV network element for adjusting said one or more upstream parameters.

A second aspect relates to a CATV network element implementing a distributed CCAP architecture (DCA) node, said network element comprising means for receiving one or more upstream pilot signals via an upstream signal path of a second network element in a same network segment; means for measuring levels of the one or more upstream pilot signals; means for determining a plurality of downstream pilot signals, wherein a first downstream pilot signal is a reference signal, and any subsequent downstream pilot signal is associated with one of said upstream pilot signals, wherein at least one parameter value of the subsequent downstream signals is determined based on the reference signal and a difference between a measured level and an expected level of the associated upstream pilot signal; means for sending the plurality of downstream pilot signals via a downstream signal path of the second network element to a spectrum analyzer.

A third aspect relates to an apparatus comprising functionalities for implementing a pilot signal generator and a spectrum analyzer, the apparatus comprising means for sending one or more upstream pilot signals via an upstream signal path of a CATV network element to a distributed CCAP architecture (DCA) node in a same network segment; means for receiving a plurality of downstream pilot signals from the DCA via a downstream signal path of the CATV network element, wherein the downstream pilot signals comprise a reference signal and at least one subsequent downstream pilot signal; means for measuring differences between values of at least one parameter of the reference signal and each of the subsequent downstream pilot signals; and means for providing information, based on the values of said at least one parameter differences, for adjusting one or more upstream parameters of the CATV network element. 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 flow chart of a method according to an embodiment of the invention;

Fig. 3 shows an example of upstream pilot signaling in a process for adjusting upstream parameters of a CATV network element connected to the same network segment with a DCA node;

Figs 4a - 4c illustrate an example of determining the signal level of the downstream pilot signals according to an embodiment of the invention;

Fig. 5 shows an example of downstream pilot signaling in a process for adjusting upstream parameters of a CATV network element connected to the same network segment with a DCA node; and

Figs. 6a, 6b show an example of adjusting the upstream parameters of a CATV network element based on the signal levels of the received downstream pilot signals 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.

Adjusting the upstream parameters of the CATV network elements in HFC networks has traditionally been performed by sending measured parameter values to the headend and receiving instructions from the headend for adjusting the upstream parameters correctly. However, the introduction of DCA nodes may lead to a situation where there is no direct signal path from a network element to the headend, whereupon the traditional way of adjusting the upstream parameters is no longer available.

DOCSIS 3.1 standard tries to address this issue by establishing out-of- band (OOB) signalling channels, via which DCA nodes may be managed by a plurality of CCAP Core (i.e. headend) functionalities. A logical NDR (Narrowband Digital Return) channel may be established to send measured upstream parameter values of a network element to a Reverse OOB CCAP Core. Another CCAP Core functionality is then used to send the instructions for adjusting the upstream parameters to the DCA node, which then controls the network element to adjust the upstream parameters correctly.

Naturally, such signalling involving establishing physical OOB channels and logical channels therein between a plurality of CCAP Core functionalities is a complex and cumbersome way of adjusting the upstream parameters of the CATV network elements.

Therefore, an improved procedure is needed for adjusting upstream parameters of a CATV network element.

According to an aspect, a method for adjusting upstream parameters of a cable television (CATV) network element is now introduced, wherein the CATV network element comprises a plurality of components arranged to form an upstream signal path and a plurality of components arranged to form a downstream signal path. An exemplified flowchart of the method is illustrated in Figure 2, wherein the method comprises sending (200) one or more upstream pilot signals via the upstream signal path to a distributed CCAP architecture (DCA) node; measuring (202) levels of the one or more upstream pilot signals in the DCA node; determining (204) a plurality of downstream pilot signals, wherein a first downstream pilot signal is a reference signal, and any subsequent downstream pilot signal is associated with one of said upstream pilot signals, wherein at least one parameter value of the subsequent downstream signals is determined based on the reference signal and a difference between a measured value of said parameter and an expected level of the associated upstream pilot signal; sending (206) the plurality of downstream pilot signals via the downstream signal path to a spectrum analyzer; measuring (208) differences between values of said at least one parameter of the reference signal and each of the subsequent downstream pilot signals; and providing (210) information, based on the differences of values of said at least one parameter, for adjusting one or more upstream parameters of the CATV network element.

Hence, the method enables to adjust the upstream parameters of the CATV network element, even if no direct signal path to the headend is available. On the other hand, the complex and cumbersome adjustment process via the NDR channels is avoided by the straightforward implementation of the method. Thus, it is not necessary to establish any kind of connection to the headend, but the upstream parameters may be adjusted e.g. upon installation of the CATV network element.

According to an embodiment, said at least one parameter value comprises a level of the one or more downstream pilot signals. Thus, the DCA node may determine the signal level of the upstream pilot signals and compare them to expected levels of the pilot signals. For example, the signal level may be measured in decibel microvolts (dBpV), whereupon the difference of the measured pilot signals and the expected levels of the corresponding pilot signals may be expressed in dBs. The DCA node may then indicate these differences as proportional signal level differences in the downstream pilot signals, which the spectrum analyzer then measures and determines the information for adjusting the one or more upstream parameters of the CATV network element.

According to an embodiment, said at least one parameter value comprises a frequency of the one or more downstream pilot signals. Hence, after determining the difference of the measured upstream pilot signals and the expected levels of the corresponding pilot signals, the DCA node may create a set of downstream pilot signals, wherein said difference is expressed as frequency difference between the downstream pilot signals. For example, a signal level difference of 1 dB in the measured and expected upstream signals may be indicated as 100 kHz frequency difference in the downstream pilot signals. The spectrum analyzer then measures the frequency difference of the downstream pilot signals and determines the information for adjusting the one or more upstream parameters of the CATV network element.

As a presumption, the downstream signal path of a CATV network element is provided with adjustment, e.g. relating to gain and slope, such that the signal response of the downstream signal path is kept as straight as possible. Using the frequency difference in indicating the signal level differences provides the advantage that the possible effect of such adjustments in the downstream pilot signals can be avoided. Moreover, the downstream pilot signals with the frequency difference may be transmitted using downstream channels close to one or both edges of the usable downstream bandwidth, e.g. close to the frequencies 85 MHz and 862 MHz of the current DOCSIS downstream bandwidth. Thereby, transmission of CATV payload signals, typically transmitted more often on the center channels of the downstream bandwidth, is not disturbed.

According to an embodiment, the level difference of the measured upstream pilot signals and the expected levels of the corresponding upstream pilot signals is indicated as a difference of both level and frequency of the downstream pilot signals. Hence, the above embodiments may be combined, whereupon more variation in the signaled parameters may be achieved. The combined indication also provides more robustness for the spectrum analyzer for interpreting the downstream pilot signals.

According to an embodiment, the method further comprises configuring a predetermined set of pilot signal parameters in a pilot signal generator, in said spectrum analyzer and in said DCA node prior to sending the upstream pilot signals. Thus, by using a pilot signal generator and a spectrum analyzer and providing the DCA node with a predetermined set of pilot signal parameters, the upstream parameters of any CATV network element connected to the same network segment with DCA node can be adjusted. According to an embodiment, the predetermined set of pilot signal parameters comprises one or more of the following:

According to an embodiment, the pilot signal generator and the spectrum analyzer are integrated in a common node, which is connected to the CATV network element via a test point. Thus, the functionalities for initiating the measurements and providing the necessary information for adjusting the upstream parameters may be implemented in a separate device, which can be connected to the test point of the CATV network element under configuration.

Various embodiments relating to the method are further illustrated by referring to Figure 3, which shows an example of adjusting upstream parameters of a CATV network element connected to the same network segment with a DCA node.

In the example of Figure 3, the CATV network element 300 under configuration is an HFC amplifier. Figure 3 shows a strongly simplified structure of the amplifier and therefore Figure 3 does not show all the functional blocks of a typical amplifier. The amplifier 300 comprises a first port 302, which operates as an input port for downstream signals and an output port for upstream signals. A second port 304, correspondingly, operates as an input port for upstream signals and an output port for downstream signals. Diplexers 306, 308 are used to separate the downstream signals and upstream signals to their corresponding signal paths. Between the second port 304 and the diplexer 308, there is a directional coupler 310, which provides a tap for a test point 312. The test point 312 may be used for sampling downstream signal or supplying upstream test signals.

Figure 3 shows a simplified block chart of the upstream signal path components, wherein between the diplexers 306, 308 there is only shown an equalizer 314 (a.k.a. signal inclination controller), an attenuator 316, and an amplifier 318. The embodiments are related to the adjustment of upstream parameters, and therefore the downstream signal path is even more simplified to comprise an amplifier 320.

In the example of Figure 3, the pilot signal generator 332 and the spectrum analyzer 334 are shown as an integrated device 330 connected to the test point 312 of the HFC amplifier 300. It is nevertheless noted that the pilot signal generator and the spectrum analyzer may equally be implemented as (a part of) separate devices, or one or both of them may be integrated as a part of the CATV network element under configuration.

In the example of Figure 3, the DCA node 340 is an RPD node. Figure 3 shows a simplified block chart of the RPD node comprising a common port 342 for upstream input signals and downstream output signals. The signal paths of the upstream input signals and the downstream output signals are separated by a diplexer 344. The upstream input signals are input in an RPD module 348 via an analog- digital-converter (ADC; 346) to be processed in digital form. The downstream output signals are converted by a digital-analog-converter (DAC; 350) before transmission to downstream.

Prior to starting the measurements according to the embodiments, a predetermined set of pilot signal parameters are preferably configured in a pilot signal generator 332, in said spectrum analyzer 334 and in the RPD node 340 prior to starting the measurements. The pilot signal parameters may be default settings in any of the pilot signal generator, the spectrum analyzer and/or the RPD node. On the other hand, they may be configured separately for each measurement, if necessary, depending on the CATV network element to be configured. The DCA node, i.e. the RPD node 340 in this example, may be provided with measurement frequencies and expected levels of the upstream pilot signals. Thus, the RPD node knows at which frequencies the upstream pilot signals are expected and what should the signal levels preferably be. Furthermore, the RPD node is preferably provided with information regarding the downstream pilot signals to be generated, i.e. at which frequencies the downstream pilot signals should be generated and what should be the signal level of the reference signal.

Similarly, the pilot signal generator 332 is preferably provided with information regarding the upstream pilot signals to be generated, i.e. at which frequencies the upstream pilot signals should be generated and what should be the signal level of the reference signal. The spectrum analyzer 334, in turn, may be provided with information at which frequencies the downstream pilot signals are expected.

Upon starting the measurement process according to embodiments, the pilot signal generator 332 is preferably connected to the test point 312 of HFC amplifier 300. The pilot signal generator 332 generates one or more upstream pilot signals and input them via the test point 312 to the upstream signal path of the HFC amplifier. The components of the upstream signal path cause some modifications to the pilot signal e.g. due to disturbance, slope changes and attenuation generated by the components. The pilot signals are further transmitted via the upstream output port 302 of the HFC amplifier to the RPD node 340.

The RPD node, e.g. the ADC 346 of the node, measures the signal levels of the one or more upstream pilot signals. The measured signal levels, including the modifications caused by components of the upstream signal path of the HFC amplifier, are compared to the predetermined expected signal levels of the upstream pilot signals. Let N be the number of the upstream pilot signals generated by the pilot signal generator and received by the RPD node. The RPD node now determines M downstream pilot signals, where M=N+1. The first downstream pilot signal is a reference signal, for which the RPD applies the predetermined signal level. Every subsequent downstream pilot signal is associated with one of the upstream pilot signals, preferably such that the second downstream pilot signal is associated with the first upstream pilot signal, the third downstream pilot signal is associated with the second upstream pilot signal, etc. In general, the downstream pilot signals are associated with the upstream pilot signals according to PDS=PUS+ 1 , where PDS and Pus are the order numbers of the downstream pilot signals and the upstream pilot signals, correspondingly.

The RPD node determines the signal level of the subsequent downstream pilot signals, i.e. starting from the second downstream pilot signal, based on the reference signal and the difference between a measured level and an expected level of the associated upstream pilot signal. For example, the signal level may be measured in decibel microvolts (dBpV), whereupon the difference of the subsequent downstream pilot signal and the downstream pilot reference level may be the same in dBs as the difference between the measured level and the expected level of the associated upstream pilot signal in dBs.

Figures 4a - 4c illustrate an example of determining the signal level of the downstream pilot signals. Figure 4a shows an example of two upstream pilot signals generated by the pilot signal generator. The first pilot signal having a signal level of 75 dBpV is generated at the frequency of 10 MHz and the second pilot signal having a signal level of 73 dBpV is generated at the frequency of 54 MHz.

If the CATV network element, such as the HFC amplifier, had its upstream parameters adjusted correctly, the DCA node, such as the RPD node, would receive the upstream pilot signal at the predetermined expected signal levels stored in the RPD node. For example, the first pilot signal would be received at a signal level of 71 pV dB and the second pilot signal at a signal level of 70 dBpV, as shown in Figure 4b. However, the modifications caused by the components of the upstream signal path of the HFC amplifier have deteriorated the pilot signals more than expected, resulting in receiving the first pilot signal at a signal level of 70 dBpV and the second pilot signal at a signal level of 68 dBpV, as shown in Figure 4b. In other words, the upstream parameters of the HFC amplifier have not been adjusted correctly, and therefore control information for re-adjusting the upstream parameters of the HFC amplifier is created in the RPD node.

In this example, the RPD node indicates the level difference of the measured upstream pilot signals and the expected levels of the corresponding upstream pilot signals as a difference of signal level. It is noted that instead of, or in addition to, this approach, the RPD node may use the frequency difference in the downstream pilot signals for indicating said level difference.

Figure 4c illustrates an example of determining the signal level of three downstream pilot signals based on the measured and expected signal levels of the two upstream pilot signals shown in Figure 4b. The RPD node first generates a reference signal according to the previously configured information. In this example, a reference signal of 85 dBpV is generated at the frequency of 85 MHz. The second downstream pilot signal is associated with the first upstream pilot signal. Since the difference between the expected signal level and the measured signal level of the first upstream pilot signal was -1 dB, the signal level of the second downstream pilot signal to be generated at the frequency of 86 MHz is set at 84 dBpV. Similarly, the third downstream pilot signal is associated with the second upstream pilot signal. Since the difference between the expected signal level and the measured signal level of the second upstream pilot signal was -2 dB, the signal level of the third downstream pilot signal to be generated at the frequency of 87 MHz is set at 83 dBpV.

Figure 5 illustrates the transmission of the downstream pilot signals in the exemplified arrangement of Figure 3. Thus, the RPD node 340 sends the plurality of downstream pilot signals via the downstream signal path to the spectrum analyzer 334 connected to the test point 312 of HFC amplifier. The spectrum analyzer measures the differences between levels of the reference signal and each of the subsequent downstream pilot signals, and based on the level differences, provides information for adjusting one or more upstream parameters of the HFC amplifier. For example, the spectrum analyzer 334 may provide information for adjusting the attenuator 316 and/or the equalizer 314 of the upstream signal path of the HFC amplifier such that the expected signal levels and the measured signal levels of each upstream pilot signals correspond to each other. It is noted that in addition to, or instead of, information for adjusting gain and slope of the HFC amplifier, information for adjusting any other parameters of a CATV network element may be provided based on the analyzed downstream pilot signals. These parameters may include e.g. flatness and temperature compensation of the CATV network element.

Figures 6a and 6b illustrate an example of adjusting the upstream parameters of a CATV network element based on the signal levels of the received downstream pilot signals. Figure 6a shows an example of the received signal levels of the downstream pilot signals generated in Figure 4c. The signal levels of all received downstream pilot signals have degraded by 10 dB. However, the more important information deduced by the spectrum analyzer is that the signal levels of the second and third downstream pilot signal are lower than the signal level of the first, i.e. reference, downstream pilot signal. This implies that the upstream parameters of the HFC amplifier needs to be adjusted, for example by adjusting the attenuator and/or the equalizer of the upstream signal path of the HFC amplifier.

Figure 6b shows the received signal levels of the downstream pilot signals after carrying out an appropriate adjustment of the upstream parameters. Now the signal levels of the second and third downstream pilot signal are equal to the signal level of the reference downstream pilot signal, thereby indicating that the upstream parameters of the HFC amplifier are correctly adjusted.

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

Claims:

1. A method for adjusting upstream parameters of a cable television (CATV) network element comprising a plurality of components arranged to form an upstream signal path and a plurality of components arranged to form a downstream signal path, the method comprising

sending one or more upstream pilot signals via the upstream signal path to a distributed CCAP architecture (DCA) node;

measuring levels of the one or more upstream pilot signals in the DCA node;

determining a plurality of downstream pilot signals, wherein a first downstream pilot signal is a reference signal, and any subsequent downstream pilot signal is associated with one of said upstream pilot signals, wherein at least one parameter value of the subsequent downstream signals is determined based on the reference signal and a difference between a measured level and an expected level of the associated upstream pilot signal;

sending the plurality of downstream pilot signals via the downstream signal path to a spectrum analyzer;

measuring differences between values of said at least one parameter of the reference signal and each of the subsequent downstream pilot signals; and

providing information, based on the differences of values of said at least one parameter, for adjusting one or more upstream parameters of the CATV network element.

2. The method according to claim 1 , wherein said at least one parameter value comprises a level of the one or more downstream pilot signals.

3. The method according to claim 1 or 2, wherein said at least one parameter value comprises a frequency of the one or more downstream pilot signals.

4. The method according to any preceding claim, further comprising configuring a predetermined set of pilot signal parameters in a pilot signal generator and in said DCA node prior to sending the upstream pilot signals.

5. The method according to claim 4, wherein the predetermined set of pilot signal parameters comprises one or more of the following:

6. The method according to any preceding claim, wherein the pilot signal generator and the spectrum analyzer are integrated in a common node, which is connected to the CATV network element via a test point.

7. The method according to any preceding claim, further comprising adjusting an attenuator and/or an equalizer of the upstream signal path of the CATV network element for adjusting said one or more upstream parameters.

8. A CATV network element implementing a distributed CCAP architecture (DCA) node, said network element comprising

means for receiving one or more upstream pilot signals via an upstream signal path of a second network element in a same network segment;

means for measuring levels of the one or more upstream pilot signals;

means for determining a plurality of downstream pilot signals, wherein a first downstream pilot signal is a reference signal, and any subsequent downstream pilot signal is associated with one of said upstream pilot signals, wherein at least one parameter value of the subsequent downstream signals is determined based on the reference signal and a difference between a measured level and an expected level of the associated upstream pilot signal;

means for sending the plurality of downstream pilot signals via a downstream signal path of the second network element to a spectrum analyzer.

9. The CATV network element according to claim 8, wherein said at least one parameter value comprises a level or a frequency of the one or more downstream pilot signals.

10. The CATV network element according to claim 8 or 9, further comprising

means for configuring a predetermined set of pilot signal parameters prior to receiving the upstream pilot signals.

11. The CATV network element according to claim 10, wherein the predetermined set of pilot signal parameters comprises one or more of the following:

- measurement frequencies and expected levels of the upstream pilot signals to be configured in said CATV network element;

- frequencies of the downstream pilot signals and the level of the reference signal to be configured in said CATV network element.

12. An apparatus comprising functionalities for implementing a pilot signal generator and a spectrum analyzer, the apparatus comprising

means for sending one or more upstream pilot signals via an upstream signal path of a CATV network element to a distributed CCAP architecture (DCA) node in a same network segment;

means for receiving a plurality of downstream pilot signals from the DCA via a downstream signal path of the CATV network element, wherein the downstream pilot signals comprise a reference signal and at least one subsequent downstream pilot signal; means for measuring differences between values of at least one parameter of the reference signal and each of the subsequent downstream pilot signals; and

means for providing information, based on the values of said at least one parameter differences, for adjusting one or more upstream parameters of the CATV network element.

13. The apparatus according to claim 12, wherein said at least one parameter value comprises a level or a frequency of the one or more downstream pilot signals.

14. The apparatus according to claim 12 or 13, further comprising

configuring a predetermined set of pilot signal parameters in the pilot signal generator prior to sending the upstream pilot signals.

15. The apparatus according to claim 14, wherein the predetermined set of pilot signal parameters comprises one or more of the following:

16. The apparatus according to any of claims 12 - 15, further comprising

means for connected the apparatus to the CATV network element via a test point.

17. The apparatus according to any of claims 12 - 16, further comprising

means for adjusting an attenuator and/or an equalizer of the upstream signal path of the CATV network element for adjusting said one or more upstream parameters.