WO2008040854A1

WO2008040854A1 - Broadband data transfer in a cable television network

Info

Publication number: WO2008040854A1
Application number: PCT/FI2007/050542
Authority: WO
Inventors: Janne Liitola; Olli LEPPÄNEN
Original assignee: Teleste Oyj
Priority date: 2006-10-06
Filing date: 2007-10-04
Publication date: 2008-04-10
Also published as: FI20065644A; FI119313B; FI20065644A0

Abstract

A communication system for relaying a data signal in a coaxial cable network adapted for transferring a cable television signal, which communication system comprises a first data network connection point for entering a baseband broadband data signal to said communication system; a modulating unit for forming a modulated data signal of said baseband broadband data signal, which modulated data signal comprises at least two logically connected but to different data transfer channels modulated signal components; a combiner adapted for said coaxial cable connection for adapting said modulated data signal to its own frequency channel to be relayed with said coaxial cable connection; a separator for separating said modulated data signal to separate signals; a demodulating unit for demodulating and connecting said signal components into a baseband broadband data signal; and a second data network connection point for relaying the baseband broadband data signal further to at least one node point of a data processing device.

Description

BROADBAND DATA TRANSFER IN A CABLE TELEVISION

NETWORK

Field of the invention

The invention relates to an arrangement for relaying a broadband data signal in a cable television network.

Background of the invention

As the use of the Internet is becoming more common and different services are becoming IP-based (Internet Protocol), the demand for broadband data connections is constantly increasing. At the moment, the provided broadband connections are typically either xDSL connections or cable modem connections. Particularly in areas where a television signal is led to homes via a cable network, the cable network provides an existing transfer path for relaying data signals as well.

In a DOCSIS-type (Data-Over-Cable Service Interface Specifications) of a cable television system (CATV, Community Antenna Television), the data signal is modulated to its specific frequency (channel) in the same way as TV signals, in which case the signals can be relayed in the same cable and be separated from each other in the receiving set. A disadvantage for homes is that a special cable modem (CM) for modulating/demodulating signals and for forming a data connection on a computer is required, which causes additional expenses. Cable network operators have the problem that expensive network equipment CMTS (Cable Modem Termination System) used for cable modem connections is only capable of offering a limited number of connections. CMTS controls all the cable modems connected to the cable network within its administrative area, which requires that the CMTS maintains a register of active cable modems and divides the available transfer band between all cable modems. This, in turn, requires that a sufficient time slot must be reserved for each cable modem for stating channel requests in the upstream direction and for controlling parameters (ranging). If a user needs more bandwidth in the upstream direction, it is possible to make a request to the CMTS via the cable modem CM (a so-called request-grant-process) for allocating a greater bandwidth, but this always causes a significant delay before the greater bandwidth is available for use.

In addition, in a DOCSIS system channel allocation between the downstream and upstream channels is typically very asymmetrical, in which case the upstream bandwidth provided by the system easily remains inadequate for using new bidirectional IP-based services, such as VoIP-calls and peer-to-peer-applications, simultaneously with other data services. Providing a greater upstream bandwidth in most cases requires the construction or updating of an expensive, fiber optic network arrangement for a reverse channel. To sum up, a data network centralized to the CMTS according to the DOCSIS system is cumbersome to control, and quite inflexible in relation to expanding its capacity. One CMTS administers thousands of home connections, which share the available data transfer capacity, both frequency-wise and time-wise. When the capacity of the existing CMTS runs out, a new CMTS is again needed for new users, the capacity of which new CMTS is typically underutilized in the beginning.

A further problem is that the "last 100 meters" of the CATV networks are implemented with different network topologies, such as a coaxial- cabled star network or a tree i.e. cascade network. Buildings may also comprise an existing local area network or a twin cabling, for example, a Cat1 or Cat5 cabling, that can be utilized for local area network use, in which case it would be advantageous to be able to utilize this existing cabling. In each of these network topologies and existing local area networks the data connections must be arranged in a different way.

A previous patent application by the same applicant FI20045502 (also EP 1675288) discloses an arrangement for relaying an Ethernet signal bidirectionally to a subscriber line of a cable network together with a CATV signal. As relaying the baseband data signal does not require modulation/demodulation, it is possible to use passive components for combining and separating the CATV signal and the baseband Ethernet signal. The application in question, however, concentrates on the so- called "last 100 meters", i.e. a CATV network arrangement in the substantial vicinity of home connections from the distribution point (EMT, Ethernet multitap) as a coaxial network until the connection point of a home. The application does not, however, disclose more closely bringing a broadband Ethernet data signal to an Ethernet switch EMT.

Taking these problems into account, it is obvious that there is a need for a network arrangement, which enables a more flexible and effective data connection management universally in such a manner that the limitations set to arranging the data connections by different network topologies are at the same time taken into account.

Summary of the invention

Now, an improved arrangement has been developed to reduce the above-mentioned problems. As different aspects of the invention, we present a communication system, a modulating unit and a demodulating unit, which are characterized in what will be presented in the independent claims. The dependent claims disclose advantageous embodiments of the invention.

The invention is based on that data communication system for relaying data signal is formed in a coaxial cable network adapted for transferring cable television signal, which communication system comprises a coaxial cable connection for distributing cable television signal to a distribution point of a cable television network. In addition, the communication system comprises a first data network connection point for entering baseband broadband data signal to said communication system; a modulating unit for forming a modulated data signal of said baseband broadband data signal, which modulated data signal comprises at least two logically connected but to different data transfer channels modulated signal components; a combiner adapted for said coaxial cable connection for adapting said modulated data signal to its own frequency channel to be relayed with said coaxial cable connection; a separator adapted to said coaxial cable connection for separating said modulated data signal into a separate signal; a demodulating unit for demodulating and connecting said signal components to a baseband broadband data signal; and a second data network connection point for transmitting the baseband broadband data signal further to at least one node point of a data processing device.

In other words, one starting point of the invention is that by forming the above-described communication system, it is possible by means of a coaxial cable segment of a CATV network to advantageously arrange a transfer line for an Ethernet data signal, which can be separated and managed in a manner suitable for the network topology and cabling available for use when distributing the Ethernet signal further to homes. Modulated Ethernet signals are entered instead of an optical fiber to a coaxial cable, which then forms a type of a "virtual" optical fiber from the point of view of the operation of the system.

As substantial aspects from the point of view of modulating the Ethernet signal are also disclosed a modulating unit adaptable to a coaxial cable network, which unit comprises an input interface for entering a baseband broadband data signal to said modulating unit; separator means for separating the baseband broadband data signal to at least two separate signal components, modulating means for modulating said signal components to different data transfer channels; and a control unit for controlling said separator means and modulating means in such a manner that the signal components can be logically combined into one data signal, as well as a demodulating unit adaptable to a coaxial cable network, which comprises at least two input interfaces for entering at least two separate modulated signal components to said demodulating unit, which said signal components can be logically combined into one data signal; demodulating means for demodulating said signal components into baseband signal components; combiner means for combining baseband signal components into a broadband data signal; and a control unit for controlling said demodulating means and combiner means to combine said signal components into one data signal.

These kind of modulating/demodulating units enable the transfer of an Ethernet signal being relayed with a data rate of at least 100 Mbps or even more, in a coaxial cable network without the receiving node having to comprise a cable modem. 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 a simplified block chart of a network arrangement according to the invention,

Fig. 2a shows an advantageous implementation of a network modem according to the invention in a simplified block chart; Fig. 2b shows an advantageous implementation of a terminal modem according to the invention in a simplified block chart; Fig. 3 shows a block chart of an embodiment for applying the network arrangement according to the invention; Fig. 4 shows a block chart of another embodiment for applying the network arrangement according to the invention; and Fig. 5 shows a block chart of a third embodiment for applying the network arrangement according to the invention; and

Fig. 6 shows a block chart of a fourth embodiment for applying the network arrangement according to the invention.

Detailed description of the invention Figure 1 shows a network arrangement according to the invention by means of a simplified block chart. The network arrangement comprises a termination node 100 of an optical fibre network, which node operates as a television signal generator. An optical cable television signal (CATV) coming from the headend of a CATV network via an optical fiber is entered as input to the node 100, which signal is converted in the node 100 into an electric signal, modulated to the desired frequency and separated further to be entered into several coaxial cable branches. Further the network arrangement comprises an Ethernet tap 102, to which is entered as input, either via a twin cable or optical fibre connection, a very broadband Ethernet signal transferred advantageously at a rate of at least one gigabit (GbE). The Ethernet tap 102 separates the signal to several more narrowband, for example 100 or 200 Mbps, Ethernet signal. Each separated signal (for example, 100 Mbps) comprises data, which is defined dynamically for certain Ethernet MAC target addresses. Thus, each 100 Mbps Ethernet signal can be delivered on their own channel to the mutual distribution point of homes, such as a curbside unit.

Each branch of the separated signal of the Ethernet tap 102 is further connected to a modem 104 for modulating the Ethernet signals before entering to the coaxial cable. The Ethernet signals are modulated with some efficient modulating method, such as 64-QAM modulation or 256- QAM modulation. Thus, the modulation can be performed, for example, in the same manner as in DOCSIS systems using a cable modem. The modulated Ethernet signals are entered to a coaxial cable, which now forms a "virtual" optical fiber from the point of view of the operation of the system. For combining the Ethernet signals and CATV signals the network arrangement comprises, for example, a combiner 106 implemented by means of a bandpass filter (if certain frequency bands are reserved for Ethernet signals). The modem 104 and the combiner 106 can advantageously be implemented as an integrated network device (surrounded by a dashed line), which device can here be called an Ethernet node modem ENM.

By using an 8 MHz bandwidth, which is compatible with the bandwidth of the European PAL television standard, a data rate of 50 Mbps per channel can be reached with a 256-QAM modulation. Figure 2a shows an advantageous implementation of an Ethernet node modem ENM

200 in a simplified block chart, where the incoming baseband 100

Mbps signal 202 is entered to a separator circuit 204, which comprises means for separating the signal into two 50 Mbps signal components.

The separator circuit can be implemented, for example, as a PLD circuit (Programmable Logic Device), such as a FPGA circuit (Field

Programmable Gate Array). From the separator circuit these signal components are taken to modulating units 206, 208, which adapt these two signal components advantageously by 256-QAM modulating to two separate 8 MHz channels. ENM further comprises a MAC unit (Media

Access Control) 210, which controls channel allocation and signal separation into components on the basis of Ethernet MAC addresses. Each signal component is divided into data packets, which are entered to their own channels, the bandwidth and modulation, and thus also the time delay of which channels are substantially the same. This facilitates the synchronization, and combining of signal components at the receiving end significantly.

Again, with reference to figure 1 , the coaxial cable network 108 comprises the necessary number of repeaters and amplifiers 110, whose placement and feature dimensioning are known as such for a person skilled in the art, and are not directly connected to the implementation of the present invention. Before the distribution point 114 of homes (e.g. curbside unit), by means of the separator 112 with a coaxial connection, the modulated Ethernet signals and CATV signals are separated from each other, in which case the signals (50 Mbps) on the Ethernet channels are directed to the modem 116 for demodulation. Correspondingly, the CATV signals are directed typically amplified to the distribution point 114. In figure 1 the separator 112 and the modem 116 are shown as an integrated device (by a dashed line), which can be called an Ethernet amplifier modem EAM.

Figure 2b shows an advantageous implementation of the Ethernet amplifier modem EAM 220 in a simplified block chart, which comprises the corresponding components as the above-described ENM. EAM advantageously comprises two inputs for two 8 MHz channels, which channels comprise the above-described two 50 Mbps signal components 222, 224, which logically belong to one 100 Mbps Ethernet signal. Each signal component is demodulated in separate demodulating units 226, 228 and the thus-formed baseband signal components are taken to the combiner circuit 230, which bundles the signal components into a baseband 100 Mbps signal 232 to be relayed further to the Ethernet MAC addresses specified in the signal. Since each signal component is separated into data packets, which are relayed to the EAM advantageously as two channels with the same features, the data packets of the signals arrive at the EAM in the correct order for bundling, in which case the bundling of the signal components at the combiner circuit of the receiving end is significantly simple. Correspondingly, the combiner circuit can also be implemented, for example, as a PLD circuit (Programmable Logic Device), such as a FPGA circuit (Field Programmable Gate Array). EAM also comprises a MAC unit (Media Access Control) 234, which together with the MAC unit of the ENM controls channel allocation and signal component combination on the basis of Ethernet MAC addresses. The MAC units control the distribution of the combined baseband 100 Mbps Ethernet signal among the IP addresses of the end users, such as home connections, which IP addresses are allocated dynamically to signals according to the Ethernet protocol, i.e. in relation to the cumbersome bandwidth allocation of the DOCSIS system the distribution of the signal among the end users is facilitated significantly.

Thus, by means of a CATV network segment based on a coaxial cable, it is possible to advantageously arrange a transfer line for an Ethernet data signal, which can be separated and managed in a manner suitable for the network topology and cabling available for use when distributing the Ethernet signal further to homes. The examples described hereinbelow illustrate the advantages of using this type of a network arrangement when aiming to avoid the limitations set by different network topologies to arranging data connections. From the point of view of a subscriber interface a great advantage in any case is that no cable modem is needed for data connections and the existing coaxial cable network can still be utilized for broadband data transfer.

From the point of view of a network operator the management of data connections is simplified, because there is no need to maintain a register of active cable modems and the cable modems do not need to reserve time slots for themselves for making upstream channel requests, i.e. the so-called request-grant-process of the DOCSIS system can be left out entirely. Since one modulated data channel relayed in a coaxial cable is allocated for a certain number of target addresses (for example 10 to 20 IP addresses), there is no need to maintain reservations for new users as in CMTS, but the time division of target addresses can be arranged significantly more effectively. In relation to the DOCSIS system also the latency of the system decreases, because the request-grant-process that causes delay can be left out.

In addition, adding new data connections to the system is easy and low-cost. When a certain number of new connection subscribers are added, a new Ethernet branch can be formed for them, and a separate channel is allocated for the broadband Ethernet signal of the branch. In this connection it is possible to re-distribute new and old subscribers among new and existing channels, if in this way the distribution of data signals to different connection subscribers can be optimized. Adding capacity is flexible, and when the existing capacity runs out, no additional and expensive CMTS apparatuses are needed.

The network arrangement according to the invention also provides an upstream data channel from home connections via the connection network to the Ethernet amplifier modem EAM and from that via a coaxial cable connection back to the Ethernet node modem ENM. The Ethernet output modem EAM shown in figure 2b naturally comprises a modulator for the reverse channel used with a coaxial cable connection, and correspondingly, the Ethernet node modem ENM shown in figure 2a comprises a demodulator. Thus, correspondingly by connecting logically two 256-QAM modulated 50 Mbps channels, a symmetrical 100 Mbps capacity is created both ways. If, in turn, the reverse channel does not require as great a bandwidth and data speed as the downstream data channel, in the reverse channel it is possible to use, for example, only one 50 Mbps channel or, like in the DOCSIS standard, a QPSK modulation (or 16-QAM modulation), which offers a smaller data rate but is more reliable.

It is obvious for a person skilled in the art that the above-described examples of the 8 MHz channel and 256-QAM modulation are only one embodiment of the invention. It is obvious that the available bandwidth may vary, for example, according to the TV system (for example, in NTSC 6.4 MHz) and on the other hand, the modulation can be some other, either more efficient or less efficient modulation than 256-QAM modulation. In addition, even though currently and in the near future the broadband data transfer needs can be met cost-effectively by using two signal components for one Ethernet amplifier modem EAM, the number of signal components can also in the future be greater than the two presented now. Thus, due to these several variables the different embodiments of the invention may vary in such a manner that the baseband signal leaving one Ethernet amplifier modem EAM as output can have a greater or smaller data speed than 100 Mbps.

Next, different embodiments for connecting the network arrangement according to the invention to CATV network arrangements implemented in the substantial vicinity of different home connections (the so-called last 100 meters) are disclosed. The invention is not limited solely to the following examples, but their purpose is to illustrate how the network arrangement according to the invention can advantageously be applied to very different types of connection networks.

In figure 3 the network arrangement is connected to a coaxial access network implemented as a star network, by means of which the Ethernet signal and the CATV signal are distributed further to houses 300, 302, 304 and 306. Thus, it is possible to connect both the output Ethernet signal from the Ethernet amplifier modem EAM and the CATV signal from the CATV network to a shared distribution point EMT (Ethernet Multitap) and to utilize the solution known from publication Fl 20045502. In this solution the Ethernet signal brought to the distribution point via the broadband data network is relayed bidirectionally in the coaxial access network from/to the computer in such a manner that the baseband data signal sent in the cable network is filtered with a bandpass filter and connected to a filtered CATV signal, in which case a combined signal is formed, which can be relayed in the coaxial access network. At the receiving end (in the home connection) of the combined signal, respectively, the baseband data signal and the CATV signal are separated from the combined signal by filters, in which case the data signal is entered to the computer typically via a network adapter interface and the CATV signal to the television. Further, the coaxial access network provides a reverse data channel from the home connection via the distribution point back to the Internet operator. Thus, the coaxial access network can be utilized in relaying both the CATV signal and the data signal directed, for example, to a computer, without a cable modem. As relaying the baseband data signal does not require modulation/demodulation, it is possible to use cheap passive filters in the combining/separating, and thus expensive and capacity consuming cable modems are not needed.

In figure 4 the network arrangement is connected to a coaxial access network implemented as a tree i.e. cascade network, by means of which the Ethernet signal and the CATV signal are distributed further to houses 400, 402, 404 and 406. In this case as well, the Ethernet signal from the Ethernet switch EMT and the CATV signal from the CATV network can be connected to a shared distribution point, but the passive filter solution described in publication Fl 20045502 does not operate in a cascade network, because the connection network comprises several taps before the home connection, in which case the passive components cannot direct the data to the correct target address. Instead, it is possible to use the solution according to publication WO2004/080075 in the access network, according to which transceivers meant for data transfer in an electric network (PLC) are used in connection with the modems to form OFDM-modulated data which can be transferred together with the TV signal in the cable television media.

In figure 5 the network arrangement is utilized in such a manner that the CATV signal is distributed via a coaxial access network and the

Ethernet data signal is taken, for example, to the telephone exchange

500 of a multi-storied building, and from there further to the local area network (LAN) of the building. The local area network can be implemented in a variety of ways. One arrangement suitable for almost all multi-storied buildings is a broadband local area network implemented by means of the HomePNA-technique (standard ITU-

989.1 ), where the Ethernet signal is brought via a HomePNA-switch to the telephone network of the building. The HomePNA-technique does not set great requirements for the cabling of the telephone network, but a common Cat1 twin cable is sufficient for implementing a local area network in the existing telephone network. The HomePNA uses the upper frequencies from 5.5 to 9.5 MHz of the twin cable, in which case the HomePNA-traffic and the telephone services operating in the lower frequencies do not interfere each other. On the other hand, most new multi-storied buildings are built with telephone network cabling (for example Cat5 twin cabling), which enables relaying local area network traffic via the telephone network simultaneously (so-called IRB, Internet-Ready Building). Thus, there may be a local area network concentrator (repeater and/or switch) in connection with the telephone exchange relaying the local area network traffic.

The above-described examples (HomePNA and IRB) are meant to illustrate embodiments, where the existing cabling is aimed to be utilized as far as possible. The network arrangement according to the invention for bringing a broadband data signal to a local area network is naturally not limited to these examples, but it can also be implemented in situations, where new cabling is required between connection points.

Figure 6 shows yet another embodiment for applying the network arrangement according to the invention. By means of the network arrangement shown in it, a broadband Ethernet data connection is brought to the base station 500 of a broadband wireless local area network (WLAN). This type of a solution is especially useful in forming WLAN Hot Spots in places, where there are many potential WLAN users, such as hotels, airports, railway and bus stations, etc.

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 communication system for transferring a data signal in a coaxial cable network adapted for transferring cable television signal, the communication system comprising a coaxial cable connection (108) for distributing a cable television signal to a distribution point (114) of the cable television network, characterized in that the communication system comprises a first data network connection point (102) for entering a baseband broadband data signal (202) to said communication system; a modulating unit (ENM) for forming a modulated data signal of said baseband broadband data signal (202), which modulated data signal comprises at least two logically combined, but to different data transfer channels modulated signal components (212, 214); a combiner (106) adapted to said coaxial cable connection for adapting the signal components of said modulated data signal to their own frequency channels to be relayed with said coaxial cable connection; a separator (112) adapted to said coaxial cable connection for separating the signal components of said modulated data signal to separate signals; a demodulating unit (EAM) for demodulating and combining said signal components (222, 224) into a baseband broadband data signal (232); and a second data network connection point (118) for relaying a baseband broadband data signal further to at least one node point of a data processing device.

2. The communication system according to claim 1 , characterized in that the signal components comprise data packets, which are entered to their own frequency channels, the parameters of which channels are selected to create substantially the same time delay for each signal component.

3. The communication system according to claim 1 or 2, characterized in that the modulated data signal comprises two 50 Mbps signal components, which are modulated with a 256-QAM modulation for data transfer channels comprising a bandwidth of 8 MHz.

4. The communication system according to any of the claims 1 to 3, characterized in that said modulated data signal comprises data meant for predetermined target addresses, which data is modulated to its own frequency channel.

5. The communication system according to any of the claims 1 to 4, characterized in that said second data network connection point is integrated to said cable television distribution point, in which case said integrated data network connection point (EMT) is arranged to combine said baseband data signal and the cable television signal and to distribute the combined signal to at least one node point of the cable television network.

6. The communication system according to any of the claims 1 to 4, characterized in that said second data network connection point is integrated to said cable television distribution point, in which case said integrated data network connection point (EMT) is arranged to modulate said baseband data signal with modulation intended for the data transfer of an electric network (PLC) and to relay the modulated data signal and the cable television signal to at least one node point of the cable television network.

7. The communication system according to any of the claims 1 to 4, characterized in that said second data network connection point is arranged to enter said baseband data signal to at least one node point of a telephone network for distributing the data signal via the telephone network to home connections.

SUBSTITUTE SHEET P* SS⁾ 14

7. 6. The communication system according to any of the claims 1 to 4, characterized in that said second data network connection point is arranged to enter said baseband data signal to at least one node point of a telephone network for distributing the data signal via the telephone network to home connections. 15

8. The communication system according to claim 7, characterized in that said at least one node point of the telephone network comprises a HomePNA switch.

9. The communication system according to claim 7, characterized in that said at least one node point of the telephone network comprises a local area network concentrator.

10. A modulating unit adaptable to a coaxial cable network, characterized in that the modulating unit (200) comprises an input interface (202) for entering a baseband broadband data signal to said modulating unit; separating means (204) for separating the baseband broadband data signal into at least two separate signal components, modulating means (206, 208) for modulating said signal components (212, 214) to different data transfer channels; and a control unit (210) for controlling said separating means and modulating means in such a manner that said signal components can be logically combined into one data signal.

11. The modulating unit according to claim 10, characterized in that said modulating means are arranged to enter the data packets comprised by said signal components to their own frequency channels, the parameters of which channels are selected to create substantially the same time delay for each signal component.

12. The modulating unit according to claim 10 or 11 , characterized in that said modulating means are arranged to modulate the data signal to comprise two 50 Mbps signal components, which are modulated with a 256-QAM modulation for data transfer channels comprising a bandwidth of 8 MHz. 16

13. The modulating unit according to any of the claims 10 to 12, characterized in that said control unit is arranged to control the logical combination of said signal components on the basis of the Ethernet MAC addresses.

14. A demodulating unit adaptable to a coaxial cable network, characterized in that the demodulating unit (220) comprises at least two input interfaces for entering at least two separate modulated signal components (222, 224) to said demodulating unit, which said signal components can be logically combined into one data signal; demodulating means (226, 228) for demodulating said signal components into baseband signal components; combiner means (230) for combining baseband signal components into a broadband data signal (232); and a control unit (234) for controlling said demodulating means and combiner means to combine said signal components into one data signal.

15. The demodulating unit according to claim 14, characterized in that said combiner means are arranged to combine the demodulated data packets comprised by said signal components substantially in their order of arrival.

16. The demodulating unit according to claim 14 or 15, characterized in that said signal components comprise 50 Mbps data signal modulated with a 256-QAM modulation for a data transfer channel comprising a bandwidth of 8 MHz.

17. The demodulating unit according to any of the claims 14 to 16, characterized in that said control unit is arranged to control the logical combination of said signal components on the basis of the Ethernet MAC addresses.