WO2001073456A1

WO2001073456A1 - Return path amplifier device for hfc network

Info

Publication number: WO2001073456A1
Application number: PCT/AU2001/000335
Authority: WO
Inventors: Steve Alan Jordan; Michael Thomas Agius; Michael James Cannard
Original assignee: Remote Management Systems Pty Ltd
Priority date: 2000-03-30
Filing date: 2001-03-26
Publication date: 2001-10-04
Also published as: AUPQ657500A0

Abstract

A return path amplifier device (20) for a hybrid fibre coaxial network (1), comprising: a forward path branch (21), a reverse path branch (22, 23), an adjustable gain RF amplifier (24) located in said return path branch, a command signal demodulator (38) for demodulating command signals received on said forward branch path, signal generation means (30) for generating one or more feedback signals for transmission on said return path, and processing means (26) for adjusting the gain of said RF amplifier and selectively causing said signal generation means to generate a desired feedback signal.

Description

RETURN PATH AMPLIFIER DEVICE FOR HFC NETWORK

The present invention relates generally to Hybrid Fibre Coaxial (HFC) networks and in particular to the use of the return path of an HFC network to provide upstream transmissions to a head-end station within the network.

There are a wide variety of cable management solutions available on the market today. Many attempts to address the needs of cable operators and major service operators (MSO's) providing forward path services to customers. As the need for a greater range of interactive services drives the loading of cable networks, the MSO's must look for ways of improving the core infrastructure to deal with this demand.

The most expensive and inefficient areas in the management of cable networks is in provisioning and maintenance. Both areas are extremely labour intensive and drive costs that often cannot be budgeted for accurately. To date, two distinct ways of addressing these concerns have been tried, namely high level network management systems and low level switch installation.

High level network management systems are geared to interface to existing operational support systems and provide middle wear to tie together service management, fault management and accounting management. These systems have a "basic" connection to devices in the field and rely on the limited information supplied to nodes, hubs or termination equipment to present at a higher level. Generally, such systems do not reach far enough into the network to provide critical path alarm data, so that only a false situation becomes reactive. Moreover, such systems are often geared to information gathering, displaying and reporting, but provide no control or ability to manage assets efficiently. These systems can also be unwieldy, processing bound systems which congest the system and slow the overall response to critical field information. Maintenance and fault isolation must still be performed manually, therefore keeping the maintenance costs high and repair times indeterminable. Low level switch installation provides an expensive alternative in the management of the cable network. It involves the installation of a series of intelligent switches from the head end to deep in the distribution network by dividing the network into smaller groups or sections to be monitored. These intelligent switches provide technicians with the ability to remotely isolate areas of the network that are suspected to be causing problems via a software interface. Technical and qualified operations personnel are able to derive important modelling and statistical information through connections to spectrum analysers, or complex analyser software. Although this trending and logging of huge amounts of data can assist a qualified observer to "read" the activity of the network and take action, it only provides "snap shots" at any point in time and still requires interpretation. While this type of system can reduce the isolation of a particular fault, there are still a number of problems associated with this type of system. For example, this system is still reactive and requires technicians to be deplored to confirm the nature of a problem. Ongoing maintenance costs are therefore still high. Moreover, the system is expensive since to ensure that the smallest group or section can be isolated, a large number of switches must be installed both in the network and at the head end. Complex analysis and display software must be installed, tuned and integrated. Accordingly, initial capital rollout costs are high.

It would therefore be desirable to address the aforementioned problems by enabling the assets of a cable network to be efficiently and cost effectively managed.

With this in mind, the present invention provides a return path amplifier device for a hybrid fibre coaxial network, comprising: a forward path branch, a reverse path branch, an adjustable gain RF amplifier located in said return path branch, a command signal demodulater for demodulating command signals received on said forward branch path, signal generation means for generating one or more feedback signals for transmission on said return path, and processing means for adjusting the gain of said RF amplifier and for selectively causing said signal generation means to generate a desired feedback signal.

A return path amplifier device having these features enables the direct feedback and control of return path assets in a cable network. Such a device overcomes the need to manually adjust gain controls in the field and accepts commends from the forward path whilst sending critical device data and test signals along the return path. The enhanced capabilities of such a device allow remote alignment and control of the return path from a head end site, or a centrally located operation centre within a hybrid fibre coaxial network. Typically, the command signal de-modulator includes an FSK receiver and a local oscillator. The signal generation means may be caused by the processing means to selectively act as the local oscillator.

The signal generation means may generate a frequency modulated output signal, the processing means acting to select the frequency of that output signal in response to received command signals on the forward path branch.

The return path amplifier device may further comprise network parameter monitoring means for monitoring, for example, ambient temperature, power supply or like parameters.

The following description refers in more detail to the various features of the return path amplifier device of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the return path amplifier device is illustrated in a preferred embodiment. It is to be understood that the return path amplifier device of the present invention is not limited to the preferred embodiment as illustrated in the drawings.

In the drawings:

Figure 1 is a schematic diagram of an HFC network; and

Figure 2 is a schematic diagram of one embodiment of a return path amplifier device according to the present invention for use in the HFC network of Figure 1.

Referring now to Figure 1, there is shown generally a hybrid fibre coaxial (HFC) telephony network 1 comprising a (H/E) station 2, a fibre optic network 3 and a coaxial cable network 4. The H/E station 2 collects video, voice, internet or other data from satellite down links, IP networks, telephony networks, etc. and then distributes them over the fibre optic network 3 to fibre nodes 5, 6 and 7 at the boundaries of the fibre optic network 3 and the coaxial cable network 4. The fibre nodes 5 to 7 convert light into electrical signals for downstream transmissions from H E station 2 to subscribers and vice versa for upstream transmissions from subscribers to the H/E station 2 on the coaxial cable network 4. Due to the distance between the fibre nodes 5 to 7 and customers, here referenced 8 to 12, amplifiers, such as that referenced 13, are introduced into the coaxial cable network 4. The amplifiers compensate for signal atenuation and maintain good signal quality. In order to provide for two way data flow over the HFC network 1, the amplifiers 13 are bi-directional and allow for both upstream and downstream transmissions between the customers 8 to 12 and the H/E station 2. The upstream and downstream transmissions are respectively provided on a forward path and a return path within the coaxial cable.

Referring now to Figure 2 there is shown generally a return path amplifier device 20 for connection in a coaxial cable of the coaxial cable network 4. Specifically, the return path amplifier device 20 is provided with a terminal 21 for connection to the forward path, whilst terminals 22 and 23 are connected in line with the return path of the cable. The return path amplifier device 20 includes an adjustable gain digital RF amplifier 24 connected in the return path branch between the terminals 22 and 23. The amplifier 24 acts to amplify feedback signals sent along a coaxial cable to the H/E station 2. Preferably, a band pass filter 25 is connected in series between the terminal 22 and the input of the amplifier 24 to reduce noise on the return path. The return path amplifier device 20 further includes a microcomputer 26 including a central processing unit and memory for storing computer program code to cause the CPU to execute predefined functions. In particular, the microcomputer 26 acts to adjust the gain of the RF amplifier 22 by transmitting an appropriate gain control signal from an output 27 to the gain control input 28 of the RF amplifier 24. In addition, the microcomputer 26 is programmed to supply signals at an output 29 indicative of preselected network parameters and test information. The signals provided at the output 29 are converted into an analogue modulated signal by signal generation means 30, in this case an RF frequency generator. Undesired high frequency components of the output of the RF generator 30 are extracted by a band pass filter 31.

The return path amplifier device further comprises switching means 32 and 33. In a first configuration, as shown in Figure 2, the switching means 32 and 33 enable the output of low pass filter 31 to be injected into the RF return path branch via an RF coupler 34 connected in series between the band path filter 25 and the RF amplifier 24. The switching means 33 is also selectively operable to inject the output of the low pass filter 31 into the RF return path via an RF coupler 35 connected between the output of the RF amplifier 24 and the terminal 23. The microcomputer 26 acts transmit control signals at an output 36 to selectively operate the switching means 33.

The microcomputer 26 also acts to generate a control signal at an output 37 to control the operation of the switching means 32 so that in a first configuration, as shown in Figure 2, the filtered output signal from the RF frequency generated 30 is injected into the RF return path, whereas in a second configuration, the RF frequency generator 30 is connected to an FSK receiver 38. In the second configuration, the RF frequency generator acts as a local oscillator which, together with the FSK receiver 38, form a command signal demodulator for de-modulating command signals received at the terminal 21 of the forward path branch of the return path amplifier device 20. Preferably, a band pass filter 39 is connected in series between the terminal 21 and the input of the FSK receiver 38. Accordingly, modulated command signals sent from the H/E station 2 to the return path amplifier device are de-modulated and provided to the microcomputer 26 at an input 40. The microcomputer 26 acts to either adjust the gain of the RF amplifier 24 or alternatively selectively cause the RF frequency generator 30 to selectively generate a desired feedback signal for injection into the return path branch of the device 20 for transmission to the

H/E station 2.

The return path amplifier device 20 may also be provided with an input

41 for monitoring parameters of a power supply 42 of the return path amplifier device 20, as well as other network parameter monitoring means, such as a temperature monitoring device 43 providing an output signal to the microcomputer 26 at an input 44. Moreover, a memory device 45 for the storage of non-volatile parameters to be used by the microcomputer 26 may be provided and interconnected with the microcomputer 26 via a bus 46. The feedback signals able to be generated by the microcomputer 26, in conjunction with the RF frequency generator 30, may be indicative of the network parameters monitored at the inputs 41 and 44.

The microcomputer 26, in response to appropriate command signals received on the forward path branch, is therefore able to transmit to the H/E station a test signal frequency, an indication of the power supply voltage or other parameter, an indication of the ambient temperature, an indication of the non-volatile parameter configuration and an indication of its presence on the network (otherwise known as "pinging").

Those skilled in the art will appreciate that there may be many variations and modifications of the circuit configuration described herein which are within scope of the present invention.

Claims

The claims defining the invention are as follows:

1. A return path amplifier device for a hybrid fibre coaxial network, comprising: a forward path branch, a reverse path branch, an adjustable gain RF amplifier located in said return path branch, a command signal demodulator for demodulating command signals received on said forward branch path, signal generation means for generating one or more feedback signals for transmission on said return path, and processing means for adjusting the gain of said RF amplifier and selectively causing said signal generation means to generate a desired feedback signal.

2. A return path amplifier device according the claim 1, wherein the command signal demodulator includes an FSK receiver and a local oscillator.

3. A return path amplifier device according to claim 2, wherein the processing means causes the signal generation means to selectively act as the local oscillator.

4. A return path amplifier device according to any one of the preceding claims, wherein the signal generation means generates a frequency modulated output signal, the processing means acting to select the frequency of that output signal in response to received command signals on the forward path branch.

5. A return path amplifier device according to any one of the preceding claims, and further comprising: network parameter monitoring means for monitoring one or more network parameters.

6. A return path amplifier device according to claim 5, wherein said network parameters include ambient temperature or power supply.