FR2806572A1 - MULTIMEDIA SYSTEM AND METHOD FOR DISTRIBUTING WIRELESS AND WIRED CHANNELS IN A CABLE NETWORK IN TWISTED PAIRS - Google Patents

Abstract

The invention relates to a multimedia system for distributing high frequency signals in a twisted pair cable network. This system comprises: - a first impedance matching means for receiving by means of a coaxial cable a high frequency (HF) signal and transmitting on a twisted pair of category 5, 6 or 7 said HF signal; - a second impedance matching means for receiving the HF signal coming from the twisted pair of category 5, 6 or 7 and transmitting the HF signal to a given terminal by means of a coaxial cable. The first impedance matching means is a balun balun which can be passive or active. The second impedance matching means is a desymmetrying balun which can be passive or active with amplification of the HF signal and automatic gain control.

Description

- 1- "Multimedia system and method for distributing channels

  The present invention relates to a multimedia system for distributing radio channels in a cable network in twisted pairs. It also relates to a method implemented

in this system.

  The present invention finds a particularly interesting application in the field of the distribution of television channels in places such as collective or public establishments (education,

hospitals, hotels).

  Television channels can be distributed either over the air using a reception antenna installed on the roof of a hotel, for example, or by cable network (fiber optic or coaxial cable). There are currently television channel distribution systems implementing broadband transmission techniques and using, for example, fiber optic cable or coaxial cable networks. Fiber optics and coaxial cables efficiently transmit high frequency signals such as chain signals

  radio frequencies between 47 megahertz and 850 megahertz.

  There are known, by the present applicant, video signal distribution systems in which a high frequency signal can be conveyed by a category twisted pair from a central server to a plurality of television sets. The twisted pair has the distinction of being cheaper than optical fiber. In addition, networks of twisted pairs are generally pre-installed when the tertiary buildings are constructed. However, such systems require a demodulation of the high frequency signal into a baseband signal carried by the twisted pair and then a symmetrization of the baseband signal to supply the television set. This system is expensive - 2 - due to the investment in devices such as a

switching matrix.

  The present invention aims to remedy the above drawbacks by providing an inexpensive system based on the technology of twisted pairs of category 5, 6 or 7 which can carry signals of several hundred megahertz. In the following, by balun is meant an impedance matching system for connecting a symmetrical twisted pair cable (BALanced) to an asymmetrical coaxial cable (UNbalanced, with ground line); Category 7 cable, qualified for digital signals up to 700 MHz, means a shielded cable made up of four pairs

  individually screened twisted to ISO SC25 / WG3.

  It is recalled that category 5, qualified for digital signals up to 100Mhz, relates to a shielded cable (STP) or unshielded (UTP), composed of four twisted pairs unshielded individually; Category 6, qualified for digital signals up to 250 MHz, concerns a screened cable composed of four screened twisted pairs per group of

two, or individually.

  The above objective is achieved with a multimedia system for distributing high frequency signals in a cable network in twisted pairs, comprising: - a first impedance matching means for receiving by means of a coaxial cable a high signal frequency (HF) and transmit on a twisted pair said HF signal; - a second impedance matching means for receiving the HF signal from the twisted pair and transmitting the HF signal to a given terminal by means of a coaxial cable. In other words, a twisted pair connection is inserted between two coaxial cables. This technical solution is particularly advantageous insofar as the twisted pair is an inexpensive means of transport and generally installed in collective or private premises from the

construction of these premises.

  - 3- According to the invention, the first adaptation means comprises a passive balun balun and the second means

  adapter includes a passive asymmetric balun.

  One can possibly provide, upstream of the passive balun balun, means for amplifying the HF signal

from the coaxial cable.

  The balun balancer is advantageously designed to provide galvanic isolation between the incoming coaxial cable and the twisted pair. It is the same with the desymmetrizing balun which is advantageously designed to provide galvanic isolation between the twisted pair and the outgoing coaxial cable. The twisted pair can be of category 5, 6 or 7. Thanks to this twisted pair, the system makes it possible to distribute high frequency signals which are signals of hertzian and cabled chains ranging between 47 megahertz and 850 megahertz, or any modulated video signal in this frequency band. The multimedia system according to the invention may further comprise means for producing a means for producing a phase shift of 90 between the input signals and the output signals of the balun balancer, as well as rejection means.

noise.

  Furthermore, this system can also include, at the output of the asymmetrizing balun, automatic gain control means to compensate for the weakening of the amplitude of the HF signal.

in the twisted pair.

  The balun balancer can advantageously include a plurality of outputs, for example eight outputs, identical each on a twisted pair as well as a ninth output to connect in cascade, by means of a coaxial cable, a second balun balun in order to multiply the number of

outputs on twisted pair.

  The twisted pair connecting the balun balancer and the asymmetrizing balun can be part of a set of four twisted pairs forming an RJ45 type link. A twisted pair of the RJ45 link is used for a telephone connection and two other twisted pairs of the link - 4- RJ45 can for example be used for a

Internet type network.

  Generally, the impedance of coaxial cables is 75 Ohms and that of Category 5, 6 or 7 twisted pairs is 100 Ohms. The present invention also relates to a method of distributing high frequency signals in a cable network in twisted pairs, in which a first impedance matching is carried out between a coaxial cable and a twisted pair so as to transmit a high frequency signal (HF). from the coaxial cable to the twisted pair, and a second impedance matching between the twisted pair and a second coaxial cable connected to a terminal. According to the invention, these first and second impedance adaptations are made respectively by a first and a second passive baluns

  respectively balun and unbalance.

  The second impedance matching can involve an amplification linked to an automatic gain control in order to compensate for the weakening of the HF signal in the pair.

twisted.

  Other advantages and characteristics of the invention

  will appear on examination of the detailed description of a mode

  implementation in no way limiting, and the accompanying drawings, in which: - Figure 1 is a simplified schematic view of the main elements included in the system according to the invention; - Figure 2 is a simplified electronic diagram of the first balun amplifying and symmetrizing the high frequency signal picked up by an antenna; - Figure 3 is a simplified electronic diagram of the second balun performing a desymmetrization or dissymmetrization and an automatic gain control of the high frequency signal transmitted to a television set; - Figure 4 is a simplified schematic view of a distribution system for television channels to a plurality of televisions; - 5- - Figure 5 is a simplified electronic diagram of a balun balancer having a plurality of outputs; - Figure 6 is a simplified schematic view of a multimedia system according to the invention integrating telephony and Ethernet; and - Figure 7 is a simplified electronic diagram of a mode

  particular embodiment of a system according to the invention.

  In Figure 1, we see an antenna 1 for receiving radio channels capable of picking up a high frequency signal between 47 megahertz and 850 megahertz. The HF signal is transmitted to a balun balancer 3 by means of a coaxial cable 2 of impedance 75 Ohms. The balun balancer 3 is arranged so that the HF signal is correctly transmitted in a twisted pair cable 4 of category 7 and of impedance 100 Ohms. To do this, the balun balancer 3 amplifies the HF signal which arrives with a very weak amplitude level, then symmetrizes the amplified HF signal. Symmetrization involves moving from an unbalanced means of transport composed of a conduction line and a ground line (coaxial cable) to a balanced means of transport composed of two conduction lines (pair twisted). The twisted pair 4 is connected to a desymmetrizing balun 5. The desymmetrizing balun 5 makes it possible to transmit the HF signal coming from the twisted pair 4 (balanced) to a coaxial cable 6 (dissymmetrical) with an automatic gain control to compensate for the attenuation amplitude in the twisted pair 4. The length of the twisted pair 4 is for example a maximum of one hundred meters, this makes it possible to have an HF signal at the input of the desymmetrizing balun 5

  the amplitude is not irreversibly weakened.

  However, to increase the length of the twisted pair, two twisted pairs can be connected by means of a sub-distributor (not shown) providing amplification of the HF signal. The coaxial cable 6 is finally

  connected to a television set 7.

  A simplified electronic diagram of the balun balancer 3 is shown in Figure 2 in which are also shown the coaxial cable 2 connected to the antenna 1 and the pair - 6 - twisted 4 carrying the HF signal to the desymmetrizing balun 5. The main functions of the balun balancer 3 are: - amplification of the incoming HF signal; an impedance adaptation, that is to say an input impedance of 75 Ohms and an output impedance of 100 Ohms for example, the impedance values being a function of the type of cables connected to the input and to the output; and galvanic isolation between the coaxial cable 2 and the

twisted pair 4.

  The balun balun 3 has at its input a high pass filter integrating a decoupling capacity 301 and a resistor 302. The amplifier 303 makes it possible to amplify the incoming HF signal. The characteristics of the amplifier 303 are for example an amplification of 20 dB between 47 megahertz and 850 megahertz. The amplifier 303 then supplies a transformer 304 ensuring the galvanic isolation. The primary of transformer 304 is connected to ground and has an impedance of 75 Ohms. The secondary of transformer 304 is connected in parallel to a resistor 305 with a value equal to 100 Ohms. The terminals of the resistor 305 represent the output of the balun balancer 3 on

  which are connected the wires of the twisted pair 4.

  The simplified electronic diagram of the balun balancer 3 differs significantly from that of the asymmetrizing balun 5 represented in FIG. 3. The twisted pair 4 and the coaxial cable 6 connected to the television set 7 are also represented in FIG. 3. The main functions of the balun balancing 5 are: - an automatic gain control to amplify in a controlled manner the amplitude of the HF signal arriving by the twisted pair 4; an impedance adaptation, that is to say an input impedance of 100 Ohms and an output impedance of 75 Ohms for example, the impedance values being a function of the type of cables connected to the input and to the output; and - galvanic isolation between the twisted pair 4 and the

coaxial cable 6.

  - 7 - The two wires of the twisted pair 4 are connected to the primary of a transformer 501 ensuring galvanic isolation between the twisted pair 4 and the coaxial cable 6. The secondary of the transformer 501 is connected to an automatic control device for gain represented by the variable gain amplifier 502, the amplifier 503 and the buffer amplifier 504. The impedance adaptation at the output is carried out by the resistor 505 with a value of 100 Ohms. Resistance

  505 is connected in series to coaxial cable 6.

  In another particular embodiment of a distribution system according to the invention illustrated in FIG. 7, the system comprises a first passive balun placed at the arrival of a coaxial cable and provided for balancing a frequency between 50 and 860 MHz on a twisted pair of a local network, with adaptation of the impedance to the cable

  V.D.I. used and galvanic isolation.

  A second passive balun, identical but inverted with respect to the first balun, placed at the other end of the cable

  V.D.I., is intended to desymmetrize the frequency.

  An amplifier can be placed upstream of the first balun, to supply the V.D.I. a signal of sufficient amplitude for its transport. This amplifier may have power characteristics which are a function of the distance to be traveled, calibrated for example in 5-meter increments. The distances covered are between 1 and 100 meters from the arrival of the HF signal on coaxial cable and its restitution on coaxial cable at a post

reception.

  This system allows the distribution of channels

  over the air, cable, and all audio channels-

  video re-modulated within a local wired V.D.I. (Category 5, 6 or 7 twisted pair), in a frequency band

between 47 and 860 MHz.

  The present invention being for example intended for the distribution of television channels in hotels, we will now describe a system for a plurality of televisions. In such a system, in accordance with FIG. 4, the antenna 1 delivers an HF signal to a balun balun 31 to - 8 - through the coaxial cable 2. The balun balun 31 has eight identical outputs which are respectively connected to the eight twisted pairs 41-48. Each twisted pair is then connected to a desymmetrizing balun 51 ... or 58 followed by a coaxial cable 61. ... or 68 and a television set 71 ... or 78. The baluning balun 31, playing the role of a server, can be of a design identical to that of the balun 3 but with eight outputs obtained with eight secondary windings on the transformer 304. Each winding is provided in parallel with a resistance of 100 Ohms. The HF signal arriving via the coaxial cable 2 is thus dispatched on the eight twisted pairs 41-48 to the eight different televisions 71-78. The balun balun 31 also has an additional output to which a second balun balun 33 is connected by means of a coaxial cable 32. This additional output is for example the output of an amplifier connected upstream of the input capacity of the balun balun 31. The balun 33 is identical to the balun 31 with eight outputs on eight twisted pairs 81-88 each connected in series to a desymmetrizing balun 91 ... or 98, to a coaxial cable 101 ... or 108 and to a television 11l ... or 118. The system thus described makes it possible to distribute television channels on sixteen television sets. You can increase the number by connecting several other symmetrical baluns in a row

balun balun 33.

  In Figure 5 we can see the simplified electronic diagram of the balun balun 31. The identical elements with the balun balun 3 are shown with the same references. The balun balancer 31 therefore comprises, in addition to the balun balancer 3, seven other outputs on twisted pairs from seven other secondary windings on the transformer 304. Balun balun 31 also differs from balun balun 3 by said additional output carried upstream of the capacity 301 by means of an amplifier 313. One of the characteristics of the amplifier 313 can be an amplification gain of 8 dB for example for

  compensate for the losses of the branch on the coaxial cable 32.

  Another advantage of such a device is the simplification of wiring both in collective or private premises and in the field of home automation. Referring to Figure 6, we see that the twisted pair 4 is part of a set of four twisted pairs 4, 401, 402 and 403 forming a cable 400 of category 5, 6 or 7 connected to distributors 405 and 406 The distributors 405 and 406 allow the four twisted pairs 4, 401, 402 and 403 to be separated. The twisted pair 401 is intended for telephony and the twisted pairs 402 and 403 are intended for connection to a network of Ethernet or Internet type. . The distributor 405, on the one hand directs the twisted pair 4 on a connector 404 of RJ45 type inserted in the balun balancer 3, and on the other hand directs the twisted pairs 401, 402 and 403 on a connector 407 of RJ45 type connected to the switched telephone network 408 for example, by means of a link 409. The distributor 406, on the one hand directs the twisted pair 401 on a connector 410 of RJ45 type inserted in the asymmetrizing balun 5, and on the other hand directs the twisted pair 401 on a connector 411 of RJ45 type connected to a telephone 413 and the twisted pairs 402 and 403 on a connector 412

  RJ45 type connected to a 414 microcomputer.

  The present invention therefore makes it possible to distribute television channels on a plurality of televisions installed in a building such as a hotel inexpensively by using inexpensive electrical elements.

  expensive such as twisted pairs and active baluns.

  One can advantageously use the four twisted pairs of category 5, 6 or 7 of RJ45 type to optimize the wiring in a collective or private room, or in a single house. Telephony, Ethernet and distribution are thus integrated into a cable with four twisted pairs

hertzian chains.

  The system according to the invention finds applications in the distribution of hertzian chains, the cable plan, the satellite channels, and / or any modulated source, in the pre-wired individual or collective houses, or

in commercial buildings.

  - 10- Of course, the invention is not limited to the examples which have just been described and numerous arrangements can be made.

  be brought to these examples without departing from the scope of the invention.

- 11-

Claims (13)

  1. Multimedia system for distributing high frequency signals in a cable network in twisted pairs, comprising: - a first impedance matching means for receiving by means of a coaxial cable a high frequency signal (HF) and transmitting over a twisted pair said HF signal; and a second impedance matching means for receiving the HF signal from the twisted pair and transmitting the HF signal to a given terminal by means of a coaxial cable, characterized in that the first matching means comprises a passive balun balun and the second means of adaptation   includes a passive asymmetric balun.   2. System according to claim 1, characterized in that it further comprises, upstream of the passive balun balun,   means for amplifying the HF signal from the coaxial cable.   3. System according to one of claims 1 or 2, characterized   in that the balun balancer is designed to provide galvanic isolation between the incoming coaxial cable and the twisted pair.   4. System according to one of the preceding claims,   characterized in that the asymmetrizing balun is designed to provide galvanic isolation between the twisted pair and the outgoing coaxial cable.   5. System according to one of the preceding claims,   characterized in that it further comprises means for producing means for producing a phase shift of 90 between the input signals and the output signals of the balun balun. - 12-   6. System according to any one of the claims   previous, characterized in that it comprises, at the level of   balun balun, means of noise rejection.   7. System according to any one of the claims   above, characterized in that it further comprises, at the output of the desymmetrizing balun, automatic gain control means to compensate for the attenuation   amplitude of the HF signal in the twisted pair.   8. System according to any one of the claims   previous, characterized in that the balun balun includes eight identical outputs each on a twisted pair as well as a ninth output to connect in cascade, by means of a coaxial cable, a second balun balun in order to multiply the number of outputs on pair twisted.   9. System according to any one of the claims   previous, characterized in that the twisted pair connecting the balun balancer and the asymmetrizing balun is part of a set of four twisted pairs forming a connection RJ45 type.   10. System according to claim 9, characterized in that a twisted pair of the RJ45 link is used for a telephone connection and two other twisted pairs of the RJ45 link are used for a network connection of Internet type.   11. Multimedia system according to one of claims 1 or 2,   characterized in that the high frequency signals are signals from radio and cable channels between 47 MHz and 860 MHz.   12. Method for distributing high frequency signals in a cable network in twisted pairs, in which a first impedance adaptation is made between a coaxial cable and a twisted pair so as to transmit a high frequency signal (HF) from the coaxial cable to the twisted pair, and a second impedance adaptation between the twisted pair and a second coaxial cable connected to a terminal, characterized in5 that these first and second impedance adaptations are made respectively by a first and a second balun   passive respectively balun and unbalanced.   13. The method of claim 12, characterized in that it further comprises an amplification linked to an automatic gain control in order to compensate for the weakening of the HF signal in the twisted pair.