WO2001050775A2

WO2001050775A2 - Method for increasing data transfer capacity of a data communications network, such as a cable television network

Info

Publication number: WO2001050775A2
Application number: PCT/FI2000/001146
Authority: WO
Inventors: Antti Siitonen; Jarmo Kuru
Original assignee: Elisa Communications Oyj
Priority date: 1999-12-29
Filing date: 2000-12-22
Publication date: 2001-07-12
Also published as: WO2001050775A3; FI19992812A; AU2519201A

Abstract

The invention relates to a method for increasing the data-transmission capacity of a bi-directional telecommunications network. Optical-fibre cables are connected in parallel with optical-fibre cables of an original cable-television network. The signals coming from the supplementary-service signal source, which in the original network were combined in the head end (A) with signals coming from the television signal source, are transmited on these cables and combined with the signals coming from the television signal source in the node stations (B) and (C).

Description

Method for increasing data transfer capacity of a data communications network, such as a cable television network

The present invention relates to a method, according to the preamble to Claim 1, for increasing the data transmission capacity of a cable television network or other 5 telecommunications network.

Methods of this kind are used to increase the data transmission capacity of an existing cable television network implemented using HFC (Hybrid Fibre Coax) technology, in which method a second optical-fibre cable and related devices for signal processing are connected in parallel with an existing optical-fibre cable in an optical-fibre section of 10 the network. Data being transferred is split between these two optical-fibre cables, over the optical-fibre part of the network. In the node stations, in which the optical signal is converted to an electrical signal, the data of the optical-fibre cables is added together and fed to a coaxial network, which extends to domestic households and offices in the vicinity of the node station.

15 The state of the art consists of cable-television networks, by means of which television broadcasts can be transferred to customers. Many cable-television networks are implemented using HFC technology. In an HFC network, data is transferred from the service provider's main repeater (the so-called head end) to node stations, by using an optical-fibre transmitter to feed optical signals to optical-fibre cables leading to the node

20 stations. In the node stations, the optical signal is received by optical-fibre receivers, which convert the optical signal into an electrical signal. The electrical signal is forwarded over coaxial cables to domestic households and offices in the vicinity of the node station in question. Television receivers in the domestic households and offices are connected to the cable television network, allowing television broadcasts to be watched 5 on the television screen. Some channels are provided subject to a charge, in which case customers require a home terminal to be able to receive the channels. The home terminal receives encrypted data from the cable television network and modulates it into a conventional television signal. This television signal is fed to the antenna socket of the television, whereupon the channel in question appears on the television screen. The spread of electronic telecommunications has led to the utilization of cable television networks to provide supplementary services, besides transferring television broadcasts. For example, HFC networks can be used to provide Internet connections and other telecommunications connections, along with other supplementary services. To create an Internet connection, the customer's computer is connected to the HFC network through a separate cable modem and an Ethernet card installed in the computer. The cable modem receives data from the cable television network and modulates it into the form required by the computer. The cable modem correspondingly modulates signals coming from the customer's interface and transfers them through the network to the service provider's head end. The equipment in the head end performs the operations required by the signal sent from the customer's cable modem. The aforesaid other supplementary services can be, for example, interactive repertory information windows, program information windows, or other windows that open on the television screen. New supplementary services can be developed as technology and demand develop. Other forms of two-way telecommunications connection can also be provided using cable television networks. Telecommunications connections and supplementary services are implemented by using one or more television channel locations for data transmission.

In the state of the art, television channel signals and supplementary services' signals are combined in the head end and transferred from it to domestic households and offices over the same optical-fibre and coaxial cables. This means that both television and supplementary service signals travel over nearly the entire network in the same cable. In practice, this takes place by transferring the signals at different frequencies.

A drawback in the state of the art is its limited data transmission capacity. Most existing cable television networks have been designed and dimensioned to meet television- channel transmission requirements. Television-channel transmission is one-way

(distribution type) data transmission, whereas telecommunications connections (e.g. Internet connections) and interactive supplementary services are two-way. Two-way transmission and the diversity of supplementary services place greater demands than before on the data transmission capacity of a network. Demand for Internet connections and other telecommunications services is also expected to increase, thus requiring data transmission capacity to be raised to the level set by demand, to maintain effective service. Factors limiting the data transmission capacity of an optical-fibre section include the lengths, distortion values, and often the routings of the optical-fibre cables.

The data transmission capacity of an existing HFC network can be raised by replacing the existing optical-fibre transmitters and receivers with new optical-fibre transmitters and receivers that exploit the bandwidth more efficiently. The problem then becomes the expense of the more powerful receivers and transmitters.

The invention is based on connecting a second optical fibre, and related signal- processing equipment, in parallel with the optical-fibre cables of the optical-fibre part of an existing network. The television signals are transferred over the original cable while the supplementary-service signals are transferred over the new cable. In the node stations, the signals of both optical-fibre cables are converted from an optical form to an electrical form. After conversion, the television and supplementary-service signals are combined by adding and fed into the coaxial cable network. Thus, the television and supplementary-service signals are not combined in the same cable until the signals reach the node station.

More specifically, the method according to the invention for increasing the data transmission capacity of a cable television network or other telecommunications network is characterized by what is stated in the characterizing section of Claim 1.

Considerable advantages are gained with the aid of the invention. By using the method according to the invention, the data transmission capacity of an existing HFC network can be increased, without altering the structure of the original network, by as much as when using an improvement method according to the state of the art. As fewer alterations are made to the original network, the costs will be lower. In addition the purchase of more efficient but expensive optical-fibre transmitters and receivers is also avoided. The break in telecommunications connections caused by the improvement work is also shorter, resulting in less inconvenience to customers. The possibility to use the same frequencies for both television signals and supplementary-service signals over the optical-fibre section of the HFC network can also be seen as an advantage.

In the following, the invention is examined with the aid of examples and with reference to the accompanying figures. Due to the nature of the invention, its implementation is shown with two figures that are related to each other. Figure 1 shows an existing HFC network before the measures that accord to the invention while Figure 2 shows the improved HFC network after the measures that accord to the invention. The example describes the context of the method according to the invention by explaining the operation of systems according to Figures 1 and 2. The actual method that accords to the invention is disclosed at the end of the example.

For clarity, the figures do not show all the details of an HFC cable television network. For example, the origins of the signals of the television channels and the supplementary services are not shown. The signals can, for instance, be produced in, or near the head end, or be transferred from elsewhere to the head end, or be purchased from an external producer. The coaxial networks extending from the node stations to domestic households and offices are not shown in detail. The HFC networks of the figures have only two node stations, though in reality there would usually be very many more.

The examples only show the implementation of downward data transmission, which refers to data traffic from the head end to the node stations, and from the node stations in turn to domestic households and offices. Interactive supplementary services and two- way data traffic require that the system can also be used to implement upward data traffic. Upward data transmission refers to data traffic from domestic households and offices to the node stations, and from the node stations in turn to the head end. Two-way traffic and its implementation are not examined in the example.

Both of systems according to Figures 1 and 2 only include single sources of television and supplementary-service signals. In reality, there may be several sources of both television and supplementary-service signals.

The figures show an optical-fibre cable by a line of medium thickness and a coaxial cable by the thinnest line. Clarity has been improved by using the thickest line to frame

The equipment located in the head end and the equipment located in the node stations have been framed with the thickest line for clarity.

A television signal source refers to any device or cable at all feeding a television signal. A supplementary-service signal source refers to any device or cable at all feeding signals relating to supplementary services.

An adder refers to a device combining the signals travelling in two or more cables and feeding them into a single cable. Thus, the adder's output signal comprises the two signals fed into the adder. Electrical adders combine electrical signals and optical adders combine optical signals. Though the adder does not alter the incoming data, it may alter the form of transmission of the data, for instance, by changing the signal's frequency.

A splitter refers to a device that allows signals from a single cable to be fed unaltered into several cables. Thus, the splitter's output signals are identical to the splitter's input signal. Electrical splitters split electrical signals and optical splitters split optical signals.

An optical-fibre transmitter refers to a device with an input of electrical signals and an output of optical signals, which can be fed to an optical-fibre cable network.

An optical-fibre receiver refers to a device with an input of optical signals and an output of electrical signals, which can be fed, for example, into a coaxial cable network.

Figure 1 shows a block diagram of a typical system for transmission of television and supplementary-service signals, implemented by means of HFC technology.

Figure 2 shows a block diagram of a system for transmission of television and supplementary-service signals, implemented by means of improved HFC technology, which system has been improved applying the method according to the invention.

The system shown in Figure 1 includes a head end A, node stations B and C, optical- fibre cables 31a connecting head end A to node stations B and C, and coaxial cable networks 9 and 10 extending into the vicinity of the node stations. Head end A includes a television-signal source 1, a supplementary-service signal source 2, an adder 3, a splitter 4, optical-fibre transmitters 5 and 6, and coaxial cables 30 connecting the aforesaid elements 1 - 6. Node stations B and C include optical-fibre receivers 7 and 8 and coaxial cables 32a connecting optical-fibre receivers 7 and 8 to coaxial cable networks 9 and 10. A system according to Figure 1 for transferring television and supplementary-service signals to a coaxial cable network operates as follows:

101) Signals coming from television signal source 1 and supplementary-service signal source 2 are led by coaxial cables 30 to adder 3.

102) The television and supplementary-service signals are combined in adder 3 and led from there by coaxial cables 30 to splitter 4.

103) In splitter 4 the signal is split unaltered into two coaxial cables 30, which transfer the signal to optical-fibre transmitters 5 and 6.

104) Optical-fibre transmitters 5 and 6 convert the electrical signal into an optical signal and feed it to optical-fibre cables 31 a that transfer the signal to node stations B and C.

105) Optical-fibre receivers 7 and 8 of node stations B and C convert the optical signal into an electrical signal and feed it over coaxial cables 32a to coaxial-cable networks 9 and 10.

As in Figure 1, the system shown in Figure 2 includes a head end A, node stations B and C, optical-fibre cables 31a connecting head end A to node stations B and C, as well as coaxial cable networks 9 and 10 extending into the vicinity of the node stations. As in Figure 1, head end A includes a television signal source 1, a supplementary-service signal source 2, a splitter 4, optical-fibre receivers 5 and 6, and coaxial cables 30 connecting the aforesaid elements 1 - 2 and 4 - 6. As in Figure 1, node stations B and C include optical-fibre receivers 7 and 8 and coaxial cables 32a that forward the signals coming from optical-fibre receivers 7 and 8. In addition to these devices, the system of Figure 2 includes an optical-fibre transmitter 1 1, an optical splitter 12, optical-fibre receivers 13 and 14, optical-fibre cables 31b connecting the aforesaid elements 11 - 14, adders 15 and 16, and coaxial cables 32b connecting the aforesaid devices 13 and 15, and 14 and 16.

The system of Figure 2 is an improved version of the system of Figure 1. The improvement gives the system of Figure 2 a greater data-transmission capacity than the data-transmission capacity of the system of Figure 1. In Figure 2, the original cables that are also in Figure 1 are marked with the reference numbers 30, 31a, and 32a. When following the method according to the invention, the cables to be connected in parallel with the original cables are marked in Figure 2 with the reference numbers 31b and 32b. In reality, some of the original cables may be replaced with new cables if necessary.

In the system below, sub-sections a and b of the section in question are performed simultaneously, sub-section a depicting the progress of television signals through the network and sub-section b depicting the progress of supplementary-service signals through the network.

The system according to Figure 2 for transferring television and supplementary-service signals to a coaxial cable network operates as follows:

201a) Signals coming from television signal source 1 are led over coaxial cables 30 to splitter 4.

201b) Signals coming from supplementary-service signal source 2 are led over coaxial cables 30 to optical-fibre transmitter 11.

202a) In splitter 4 the signal is split, without altering it, to two coaxial cables 30 that transfer the signal to optical-fibre transmitters 5 and 6.

202b) Optical-fibre transmitter 11 converts the electrical signal into an optical signal and feeds it to optical-fibre cable 31b that transfers the signal to optical splitter 12.

203 a) Optical-fibre transmitters 5 and 6 convert the electrical signal into optical signals and feed it to optical-fibre cables 31a that transfer the signal to node stations B and C.

203b) In optical splitter 12 the signal is split without altering it to two optical-fibre cables 31b that transfer the signal to node stations B and C.

204a) Optical-fibre receivers 7 and 8 of node stations B and C convert the optical signal into an electrical signal and feed it over coaxial cables 32a to adders 15 and 16. 204b) Optical-fibre receivers 13 and 14 of node stations B and C convert the optical signal into an electrical signal and feed it over coaxial cables 32b to adders 15 and 16.

205) In adders 15 and 16 the television and supplementary-service signals are combined and then led over coaxial cables 32a to coaxial cable networks 9 and 10.

When the method according to the invention is used to increase the data-transmission capacity of the HFC network shown in Figure 1 , by altering the structure of the network of Figure 1 to that of the network of Figure 2, the following measures are performed:

I) Optical-fibre transmitter 11 and optical splitter 12 are added to head end A.

II) Optical-fibre receivers 13 and 14, and adders 15 and 16 are added to node stations B and C.

III) Optical-fibre cables 31b are used to connect optical-fibre transmitter 11, optical splitter 12, and optical-fibre receivers 13 and 14, in the manner according to Figure 2.

IV) Optical-fibre cables 32b are used to connect optical-fibre receivers 13 and 14 and adders 15 and 16, in the manner according to Figure 2.

V) Adder 3 is removed and television signal source 1 and splitter 4 are connected by coaxial cable 30.

VI) Supplementary-service signal source 2 is connected to optical-fibre transmitter 11 by coaxial cable 30.

VII) Optical-fibre transmitter 11, optical splitter 12, and optical-fibre receivers 13 and 14 are connected by optical-fibre cables 31b, in the manner according to Figure 2.

VIII) Optical-fibre receivers 13 and 14, and adders 15 and 16 are connected by coaxial cables 32b.

IX) Coaxial cables 32a are cut and connected to adders 15 and 16, in the manner according to Figure 2. Solutions differing from the embodiment disclosed above can also be envisaged within the scope of the invention. The method according to the invention can be implemented in stages. The optical-fibre cables allocated to the transmission of supplementary services can be connected to an existing network in stages, for example, to one node station at a time. The method can also be utilized to increase the data-transmission capacity of a part of an existing HFC network.

The invention can also be applied to increasing the data-transmission capacity of other telecommunications networks. For example, the method can be used in telephone networks in which data is transferred over optical-fibre cables in part of the network. It may also be possible to improve other networks, in which data is transferred by means of two or more technologies, by applying the method according to, or one adapted from the invention.

The method can also be applied so that supplementary-service signals are transferred to the node stations from elsewhere than the head end. Supplementary-service signals can be transferred to the node stations from several different places and over different routes. Supplementary services can also be produced in the node stations, or operations processed in a node station can be included in the supplementary services.

In this application and particularly in the patent claims, the term data-transmission capacity refers to the ability to transfer signals or information. Data-transmission capacity is typically measured in bit/s (bits per second).

In this application and particularly in the patent claims, the term telecommunications network refers to a system for transferring digital or analogue information from at least one physical point to at least one other physical point.

In this application and particularly in the patent claims, the term telecommunications technology refers to a technology permitting the implementation of a system for transferring signals or information from at least one physical point to at least one other physical point. In this application and particularly in the patent claims, the term cable refers to any cable whatever, such as an optical-fibre cable, a coaxial cable, a twin cable, a twistedpair cable, a data cable, or any combination of these.

Claims

Claims:

1. A method for increasing the data-transmission capacity of a telecommunications network, in which method

- an existing telecommunications network (1 - 10, and 30, 31a, and 32a), which exploits two or more telecommunications technologies to for transmission of signals, is altered.

characterized in that

- a separate cable or separate cables (31b) are connected in parallel with one or more of the original cables

- at least some of the signals to be transferred are directed to travel in this separate cable, or in these separate cables.

2. A method according to Claim 1, characterized in that the original existing telecommunications network is an HFC (Hybrid Fibre Coax) network.

3. A method according to Claim 1, characterized in that the original existing telecommunications network is a cable-television network.

4. A method according to one of Claims 1 - 3, characterized in that a separate cable is connected in parallel with the optical-fibre cable or cables in the optical-fibre cable section of the telecommunications network.

5. A method according to one of Claims 1 - 4, characterized in that a separate cable is used for transmission of supplementary-service signals.

6. A method according to one of Claims 1 - 4, characterized in that a separate cable is used for transmission of television signals.

7. A method according to one of Claims 1 - 6, characterized in that the same frequencies are used in both the original existing network and in the cable connected in parallel, or in the cables connected in parallel.

8. A method according to one of Claims 1 - 7, characterized in that in some part of the telecommunications network the signals transferred in different data-transmission channels are combined to travel in the same cable.

9. A method according to one of Claims 1 - 8, characterized in that the signals being transferred are transferred to domestic households and offices.

10. A method according to one of Claims 1 - 9, characterized in that the telecommunications network is two-way.