WO2001017143A1

WO2001017143A1 - In-home network using an existing coaxial cable installation

Info

Publication number: WO2001017143A1
Application number: PCT/EP2000/007698
Authority: WO
Inventors: Mark H. Verberkt; Carel J. L. Van Driel; Johannes A. G. Vugts; Pieter J. Snijder; Giovanni Rosi Li
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 1999-08-27
Filing date: 2000-08-08
Publication date: 2001-03-08
Also published as: EP1125385A1; JP2003508963A

Abstract

The communication system (2) according to the invention comprises a gateway (4) and a plurality of stations (6). The gateway (4) and the stations (6) are interconnected via a coaxial cable network (8). The gateway (4) is arranged for receiving broadcast signals (10), e.g. television and/or radio signals, from a transmitter and for distributing the broadcast signals (10) in a broadcast frequency band via the coaxial cable network (8) to the stations (6). The stations (6) are arranged for exchanging information signals via the coaxial cable network (8). The information signals are exchanged in an information frequency band which lies below the broadcast frequency band, e.g. below 65 MHz. In this way, an in-home network is established in which the stations (6) can exchange information via a separate frequency band over already present coaxial cables.

Description

IN-HOME NETWORK USING AN EXISTING COAXIAL CABLE

INSTALLATION

The invention relates to a communication system comprising a gateway and a plurality of stations, the gateway and the stations being interconnected via a coaxial cable network, the gateway being arranged for receiving broadcast signals from a transmitter and for distributing the broadcast signals in a broadcast frequency band via the coaxial cable network to the stations.

The invention also relates to a station for receiving broadcast signals in a broadcast frequency band via a coaxial cable network.

A communication system according to the preamble is known from

International Patent Application WO 97/36404. It is anticipated that, due to the ongoing digitisation and the growing number of digital in-home terminals, the need for digital in-home interconnections between terminals will increase. These interconnections provide new functionality in the home, like for instance resource sharing (e.g. remote usage of a digital VCR, a printer, a security camera etc.) and follow me (when a person moves through the house, the music he is listening to follows his/her movement). To arrive at the anticipated in- home situation, the (digital) in-home equipment has to be interconnected. Within this context, there is currently a lot of interest for digital interconnection technologies like IEEE 1394.1995 and USB. However, the transition from analogue to digital in-home equipment is expected to be a gradual one, which will take a long time (10 to 20 years). The new interconnection technologies like IEEE 1394.1995 and USB all require new cables to be installed in the house. Because there is still analogue equipment in the home for the next period of time, the already installed in-home cables (coaxial cable for analogue and digital TV and/or radio distribution and twisted pair for telephony) will not be removed. This implies that the introduction of digital in-home interconnection technology requires installation of new cables in the house, which will form a substantial barrier for the introduction of in-home digital networks. This problem can be solved, in principle, by using the already existing in-home cables (for distributing the broadcast signals which may include television and/or radio signals) also for the digital in-home interconnections. However, according to the International Patent Application, the in-home coaxial networks are not well suited for sending signals directly from one station to another as these signals are severely attenuated by the splitters in the network.

An object of the invention is to provide a communication system, wherein the information signals can be exchanged over the coaxial network without being severely attenuated. This object is achieved in the communication system according to the invention, which is characterized in that at least two of the stations are arranged for exchanging information signals in an information frequency band via the coaxial cable network, the information frequency band lying below the broadcast frequency band . The invention is based upon the recognition that the splitters commonly used in coaxial cable networks only severely attenuate signals (which are transmitted between the two outputs of those splitters) above a certain threshold frequency, i.e. the attenuation amounts to more than 20 dB for frequencies above approximately 65 MHz. In contrast, for frequencies under 65 MHz the attenuation is smaller than 20 dB. In Europe the broadcast frequency band lies between 85 MHz and 860 MHz, while in the United States the broadcast frequency band lies between 54 MHz and 750 MHz. Hence, severe attenuation of the information signals is prevented by exchanging these information signals in an information frequency band which lies below the lower barrier of the broadcast frequency band, i.e. 65 MHz in Europe and 54 MHz in the US. Part of the frequency spectrum lying below the broadcast frequency band is reserved for upstream signals. In Europe this return channel lies between 5 MHz and 65 MHz, while in the US the return channel lies between 5 MHz and 42 MHz. In the home, (part of) the return channel can be used for the purpose of exchanging the information signals. A first embodiment of the communication system according to the invention is characterized in that the communication system comprises a high pass filter for a station being arranged for reception of the broadcast signals, the high pass filter being arranged for separating the broadcast signals from the information signals, and in that the communication system comprises a low pass filter for a station being arranged for reception of the information signals, the low pass filter being arranged for separating the information signals from the broadcast signals. Experiments with respect to the current coaxial in-home situation have shown that the input impedance of especially televisions (but also video recorders, set-top boxes and radios) is not well matched to the cable impedance, for frequencies which differ from the frequency to which the television tuner is actually tuned to. In the case that the coaxial cable is simultaneously used for the distribution of broadcast signals and digital transmission between devices in the home, this impedance mismatch results in large (more or less complete) reflections of the digital signal. A complicating factor in this is that the maximum delay of these reflections is very large (500 ns), given the bit rates under consideration (in the order of 100 Mbit/s). By using low pass and high pass filters the broadband frequency band and the information frequency band can be completely separated from each other. The high pass filters ensure that the information signals are largely attenuated, which ensures that reflections that are caused by for instance TVs are very small compared to the original signal. Furthermore, as the information signals are largely attenuated by the high pass filters, a relatively large power can be used to transmit the information signals without disturbing the reception of the broadcast signals by the stations. The low pass filters ensure that the information signals do not interfere with the broadcast signals.

A second embodiment of the communication system according to the invention is characterized in that the communication system comprises a diplex filter, the diplex filter comprising the low pass filter and the high pass filter. The diplex filters, which can replace, depending on the structure of the coaxial cable network, some or most of the splitters commonly used in coaxial networks, act as frequency splitters instead of power splitters. This has the advantage that the signal loss introduced by the diplex filters is (almost) negligible, while the standard (power) splitters have an attenuation of approximately 3.5 dB.

The above object and features of the present invention will be more apparent from the following description of the preferred embodiments with reference to the drawings, wherein: Figure 1 shows a block diagram of an embodiment of the communication system according to the invention,

Figure 2 shows the transfer function of a splitter commonly used in coaxial cable networks,

Figures 3 and 4 show further embodiments of the communication system according to the invention.

In the Figures, identical parts are provided with the same reference numbers. Figure 1 shows a block diagram of an embodiment of a communication system 2 according to the invention. The communication system 2 comprises a gateway 4 and a plurality of stations 6. The gateway 4, which can be a plain wall outlet, and the stations 6 are interconnected via a coaxial cable network 8. Alternatively, the gateway 4 can be comprised in one of the stations 6. Broadcast signals 10, such as television signals and/or radio signals, which are received by the gateway 4 from a transmitter (not shown), are distributed by the gateway 4 via the coaxial cable network 8 to the stations 6. The broadcast signals 10 are distributed in a broadcast frequency band, e.g. in Europe the broadcast frequency band may lie between 85 MHz and 860 MHz, while in the United States the broadcast frequency band may lie between 54 MHz and 750 MHz. Some of the stations 6, such as a TV, a VCR, a radio (not shown) and a set-top box (not shown), are arranged for the reception of the broadcast signals. Some of the stations 6, such as a PC and a printer, are arranged for the exchange of (digital) information signals via the coaxial cable network 8. A station, such as a digital TV, a digital radio or a PC with a television receiver card, might also be arranged for the reception of the broadcast signals and for the exchange of the information signals. The information signals, which carry for instance status information or control information, are exchanged in an information frequency band which lies below the broadcast frequency band, i.e. below 85 MHz in Europe or below 54 MHz in the United States. As part of the frequency spectrum lying below the broadcast frequency band is reserved for the transmission of upstream signals via the return channel (in Europe this return channel lies between 5 MHz and 65 MHz, while in the US the return channel lies between 5 MHz and 42 MHz), in the home (part of) this return channel can be used for the purpose of exchanging the information signals.

The coaxial cable network 8 comprises a number of splitters (not shown) for making interconnections between different branches of coax cable. The passive splitters commonly used in coaxial cable networks have a single input and two outputs. These splitters attenuate the broadcast signals which are transmitted from the input to the outputs with approximately 3.5 dB. This attenuation is relatively independent of the frequency of the broadcast signals. For the transmission of the information signals the situation is different. The information signals are transmitted from one output of the splitters to the other output. The transfer function 20 of the splitters, i.e. the attenuation of an information signal that is transmitted from one output to the other output as function of the frequency of that information signal, is shown in Figure 2. From this Figure it is clear that the splitters commonly used in coaxial cable networks only severely attenuate information signals (which are transmitted between the two outputs of those splitters) above a certain threshold frequency, i.e. the attenuation amounts to more than 20 dB for frequencies above approximately 65 MHz. In contrast, for frequencies under 65 MHz the attenuation is smaller than 20 dB.

Figure 3 shows a first embodiment of the commumcation system 2 according to the invention. The commumcation system 2 comprises a wall outlet A, which serves as a gateway, and three stations 6, i.e. a TV and two PCs (PCI and PC2). The wall outlet 4 and the stations 6 are interconnected via a coaxial cable network 8. Broadcast signals 10 are distributed by the wall outlet 4 via the coaxial cable network 8 to the stations 6. The PCI and PC2 stations 6 can exchange (digital) information signals via the coaxial cable network 8. The communication system 2 comprises a high pass filter 30 for those stations 6 which are arranged for the reception of the broadcast signals, i.e. in this embodiment only the TV. The high pass filter 30 separates the broadcast signals from the information signals. The commumcation system 2 further comprises a low pass filter 32 for those stations 6 which are arranged for the reception of the information signals, i.e. in this embodiment PCI and PC2. The low pass filter 32 separates the information signals from the broadcast signals. The communication system 2 comprises a further high pass filter 30 for the gateway 4. The further high pass filter 30 prevents the information signals from being transmitted to the outside world. By using the low pass filters 32 and the high pass filters 30 the broadcast frequency band and the information frequency band are completely separated from each other. The high pass filters 32 ensure that the information signals are largely attenuated, which ensures that reflections that are caused by for instance TVs are very small compared to the original signal. The low pass filters 30 ensure that the information signals do not interfere with the broadcast signals. The cut off frequencies of the low pass filters 32 and the high pass filters 30 depend on the frequency band being used by the information signals and the broadcast signals. For the European situation 65 MHz is a suitable cut off frequency for the low pass filters 32, and 85 MHz is a suitable cut off frequency for the high pass filters 30. For the United States 42 MHz is a suitable cut off frequency for the low pass filters 32, and 54 MHz is a suitable cut off frequency for the high pass filters 30. The low pass filters 32 and the high pass filters 30 can, for example, be included in the coaxial cable network 8, in the stations 6 or in connectors which are used to connect the stations 6 to the coaxial cable network 8. Figure 4 shows a second embodiment of the communication system 2 according to the invention. This second embodiment only differs from the first embodiment as shown in Figure 3 in that each triplet of a low pass filter 32, a high pass filter 30 and a splitter is replaced by a diplex filter 40. Each diplex filter 40 includes a low pass filter 32 and a high pass filter 30. Suitable cut off frequencies for the low pass filters 32 and the high pass filters 30 are as described for Figure 3. The diplex filters 40 can, for example, be included in the coaxial cable network 8 or in connectors which are used to connect the stations 6 to the coaxial cable network 8.

The scope of the invention is not limited to the embodiments explicitly disclosed. The invention is embodied in each new characteristic and each combination of characteristics. Any reference signs do not limit the scope of the claims. The word "comprising" does not exclude the presence of other elements or steps than those listed in a claim. Use of the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1. A communication system (2) comprising a gateway (4) and a plurality of stations (6), the gateway (4) and the stations (6) being interconnected via a coaxial cable network (8), the gateway (4) being arranged for receiving broadcast signals (10) from a transmitter and for distributing the broadcast signals (10) in a broadcast frequency band via the coaxial cable network (8) to the stations (6), characterized in that at least two of the stations (6) are arranged for exchanging information signals in an information frequency band via the coaxial cable network (8), the information frequency band lying below the broadcast frequency band.

2. A commumcation system (2) according to Claim 1 , characterized in that the information frequency band comprises at least part of the return channel band.

3. A communication system (2) according to Claim 1 or 2, characterized in that the information frequency band lies below 65 MHz.

4. A communication system (2) according to any one of the Claims 1 to 3, characterized in that the communication system (2) comprises a high pass filter (30) for a station (6) being arranged for reception of the broadcast signals, the high pass filter (30) being arranged for separating the broadcast signals from the information signals, and in that the communication system (2) comprises a low pass filter (32) for a station (6) being arranged for reception of the information signals, the low pass filter (32) being arranged for separating the information signals from the broadcast signals.

5. A communication system (2) according to Claim 4, characterized in that the communication system (2) comprises a further high pass filter (30) for the gateway (4), the further high pass filter (30) being arranged for separating the broadcast signals from the information signals.

6. A communication system (2) according to Claim 4, characterized in that the commumcation system (2) comprises a diplex filter (40), the diplex filter (40) comprising the low pass filter (32) and the high pass filter (30).

7. A station (6) for receiving broadcast signals (10) in a broadcast frequency band via a coaxial cable network (8), characterized in that the station (6) is arranged for exchanging information signals in an information frequency band via the coaxial cable network (8), the information frequency band lying below the broadcast frequency band.

8. A station (6) according to Claim 7, characterized in that the information frequency band comprises at least part of the return channel band.

9. A station (6) according to Claim 7 or 8, characterized in that the information frequency band lies below 65 MHz.