NL9101040A - Transmission system for the transmission of satellite signals via a local optical network - Google Patents

Abstract

Optical transmission system for the local network which, in addition to the distribution and exchange of telephony and conventional 'coax-compatible ' signals (45-850 MHz), is furthermore used for the distribution of satellite signals (0.9-2 GHz). These signals are fed via this network to the subscribers where they are converted by a conventional ' satellite tuner ' into signals which are suitable for the TV set. The advantage is an additional service in which the subscribers are connected via the local optical network to centrally located satellite reception antennas of the highest quality. <IMAGE>

Description

Transmission system for the transmission of satellite signals via a local optical network

A. BACKGROUND OF THE INVENTION

The invention relates to an optical transmission system for transmitting signals between a local exchange and subscribers connected to that exchange via a local optical transmission network. The signals exchanged with the subscribers by means of the local optical network can be, for example, telephone signals, TV signals or ATM signals, as is known from EP-337619. These signals can be transmitted at different optical wavelengths or all at the same wavelength. In the latter case, a distinction between the different transmitted signals can be achieved, e.g. by frequency multiplexing (FDM), where the signals are modulated at different carrier frequencies, by time slot multiplexing (TDM), where the signals are in a generally fixed order , are transmitted via time slots, or by asynchronous time-division transmission (ATM), in which the signals are transmitted via data cells, and the data cells belonging to the same signal have the same characteristic 'virtual channel indicator' (VCI) in their 'header'.

In the conventional arrangement, telephone and cable TV signals are both transmitted to subscribers via separate networks. Telephone signals between the local exchange and the telephone subscribers are thereby exchanged via a system of copper wire pairs, belonging to the local telephone network, while TV signals are thereby transmitted to the (cable) TV subscriber via a system of coaxial cables, belonging to the cable -TV net. The telephony signals are thereby exchanged in the speech band (300-3000 Hz), while the (frequency-multiplexed) TV signals are transmitted to the subscribers within a frequency band of 45-860 MHz. Incidentally, these cable TV signals also include FM radio signals (88-108 MHz) and Digital Satellite Radio (118; 132 MHz). The TV signals (PAL or D2-MAC) are AM-VSB modulated signals.

The introduction of optical local networks now makes it possible to integrate the originally separate networks - the local telephone network and the cable TV network - into the same network. Subscribers thus only need to be connected to one network, which offers the same service as the conventionally separated networks. It is also important that the telephone networks, which were originally only intended for the - narrowband - exchange of telephone signals, among other things due to the sharp increase in the use of PCs, 1 telephones, etc., should be made more and more suitable for more broadband applications, especially for exchanging digital information, such as ISDN signals. On the other hand, on the cable TV networks side, there is a tendency to not only distribute (broadband) signals (unidirectional, from exchange to subscribers) via these networks, but also to send control signals from the subscribers to the (cable) networks. TV), for example in need of 'subscriber TV', 'pay per view1 and' tele-video library '. From both networks, a trend can therefore be observed towards a broadband, bidirectional local network. Optical local networks, which are currently being introduced in different countries, thus offer a good opportunity to integrate the originally separated networks into one local network.

B. SUMMARY OF THE INVENTION

The present invention is based on the insight that in the optical local network there is not only room for the transmission of signals originally transmitted via the telephone network and the cable TV network, but that now, due to the considerably larger maximum transmission frequency of the optical network, inherent in the use of optical instead of electric conductors - signals can also be passed on to the subscribers via the optical local network, which hitherto - due to their very high frequencies - are only 'subscribers' outside the telephone network and outside the cable TV network to be received using 'own resources'. This concerns in particular the signals which are broadcast by TV broadcast satellites and which are in a frequency range of approx. 900-2000 MHz (0.9-2 GHz). It has hitherto been common practice to receive these satellite signals via private "subscriber" antennas (satellite dishes) and to supply them to the TV set via a "satellite tuner". It is now already clear that the increasing use of these private satellite dishes will have a disfiguring effect on the streetscape in towns and cities (an effect that was also manifest with regard to conventional TV antennas, before the central antenna systems were introduced; however satellite dishes are more bulky than conventional TV antennas).

Also, the operation of the satellite dishes - especially in urban areas - will often be hindered by obstacles, buildings, etc. Furthermore, receiving signals from different satellites is quite difficult, in the sense that - because the different satellites have different azimuth and deviation-- use should be made of as many satellite dishes or of different azimuth and deviation adjustable dishes. In fact, the invention provides a "central satellite antenna system", but exploiting the capabilities of the optical local network, making it not only used as a transmission medium for telephony, data and cable networks. TV signals, but now also for transmitting the output signals of one or more centrally placed satellite dishes. In addition to preventing the proliferation of antenna dishes, this also ensures that the satellite signals offered are of high and constant quality because the central satellite dishes can be of the highest quality and can be optimally arranged.

The invention thus provides a transmission system for transmitting signals between a local exchange and subscribers connected to that exchange via a local optical transmission network, wherein according to the invention it is provided that said local exchange comprises means for receiving signals originating from one or more extraterrestrial broadcasting transmitters, such as satellite broadcasting transmitters, and for transmitting those signals to subscribers via that local optical transmission network. As may have become clear from the foregoing, it is preferably also provided that it comprises local central means for receiving signals from one or more terrestrial broadcasting transmitters and for transmitting those subscribers via that local optical transmission network. signals.

Further elaborated, it may further be provided that the local exchange comprises one or more antennas which are intended and suitable for the reception of signals from satellite and / or terrestrial broadcasting stations, or that the local exchange is connected via a transmission network to one or more receiving stations, comprising one or more antennas for receiving signals from satellite and / or terrestrial broadcasting transmitters, the signals received by those antennas being transmitted to that local exchange via that transmission network.

In particular, the invention - the transport of satellite TV signals over the local optical network - is advantageous in the case that the signals from one or more satellite broadcast stations are FM modulated TV signals. It should be noted that the TV signals transmitted in the lower frequency range — the conventional cable TV area — are usually AM (-VSB) modulated signals. A problem here is that - as a result of a relatively high noise level in optical transmission systems, as a result of the inherent noise of the transmitting lasers used and as a result of optical interference (reflections) - a relatively large transmission signal is required for the transmission of those signals. the more so, if - as also proposed in EP-337619 - the optical network is a passive network, in which the signal distribution takes place exclusively via passive components, in this case 'splitters' and 'couplers', which passive components cause quite a lot of attenuation. AM signals - inherent to their modulation mode - are quite sensitive to signal-to-noise ratios. FM signals, on the other hand, are considerably less sensitive to this, which makes satellite TV signals eminently suitable for transmission via the optical local network. The invention is thus based on the insight that the very high-frequency, frequency-modulated satellite TV signals can be excellently combined with the transmission properties of an optical network, in particular the optical local network.

C. REFERENCES

EP-337619 [BRITISH TELECOM]

D. IMPLEMENTATION EXAMPLES

Figure 1 shows an embodiment of the invention. In a telephone exchange (building) 1, by means of wavelength multiplexers 5, the output signals - with an optical wavelength lambda 2 - of switching equipment located therein are combined with the output signals - with an optical wavelength lambda 1 - of an optical signal splitter 3 to whose input, via a fiber optic connection, the output of an antenna station (TV head-end) 4 is connected. This antenna station 4 is equipped with various antennas, both conventional radio / TV antennas, aimed at 'terrestrial' broadcasting stations, and antennas directed at ('extraterrestrial') broadcasting satellites. The broadcast signals from the satellites are received at a frequency of about 11-12 GHz, which very high frequencies are already converted in the antennas themselves to the frequency band of 0.9-2 MHz. The other signals from the conventional antennas are in the frequency range of 45-850 MHz. The entire spectrum of 45 MHz to 2 GHz thus obtained is - after conversion into an optical signal with a wavelength lambda 1 (eg 850 nm) - transferred to the signal splitter 3 via the said glass fiber. The optical signals from the optical outputs of the switchgear 2 - with a wavelength lambda 2 (eg 1300 nm) - are combined in the multiplexers 5 (one multiplexer per output) with the output signal of the antenna station 4 as it appears at the outputs of the signal splitter 3. The telephone signals to one of the various subscribers are frequency-multiplexed (FDM) within the frequency band 88-108 MHz. The optical signals thus formed - the telephony signals in the band of 88-108 MHz with an optical wavelength lambda 1 and the radio / TV signals in the band of 45 MHz-2 GHz with an optical wavelength lambda 2 - are sent to the side of the subscribers transmitted via a glass fiber 6, which opens into a first passive optical splitter 7, after which the (otherwise attenuated) signal arrives via a second passive optical splitter 8 at the input of the network connection 11 of a subscriber 10. In this network connection 11 - which is shown in more detail in Figure 2 - the signals are split (demultiplexed) to their wavelength, converted into electrical signals which are then split to their frequency band.

Figure 2 shows the splitting of the optical signals applied to the network connection 11. The optical signal of wavelength lambda 1 from antenna station 4 is separated by means of an optical wavelength (de) multiplexer from the optical signal of wavelength lambda 2 originating from the telecommunication switching equipment 2. Then both signals are each converted by an O / E converter (optical receiver) into an electrical radio / TV signal and an electrical telephone signal. The radio / TV signal is further split into (electric) passflashes, which have a passband of 45-850 MHz (11.1), 0.9-2 GHz (11.2), 88-108 MHz (11.3) and 118 respectively. 132 MHz (11.4). The output signals 11.1-11.4 are fed but (see figure 1) an analog TV receiver 13, a satellite tuner 14, an FM radio receiver 15 and a DSR receiver (DSR = Digital Satellite Radio).

The electric telephone signal (88-108 MHz) is converted by a (electric) receiver, tuned to a frequency specific for that subscriber (see also patent application EP90200673 in the name of the applicant), converted to a low-frequency signal of 0.3-3KHz.

That low-frequency signal is transferred to a telephone set 17 (Figure 1) via a line unit, which is not further described and which provides for the implementation of the telephony signaling protocol.

The receiver is part of a transceiver, while the E / O converter to which that transceiver is connected is a bidirectional O / E converter (optical transceiver). The electric transceiver and the bidirectional E / O converter thus transmit the signals received from the exchange 2 to the telephone set 17 and the line unit and, conversely, the signals coming from the telephone set and the line unit. for the exchange 2. It is noted that the said wavelength (de) multiplexer, in addition to de-multiplexing the optical signals received from the exchange 2, also serves - in a known manner - for multiplexing the signals sent by the telephone set. and the line unit are generated and destined for the exchange 2.

Continuing with Figure 1, the output signals 11.1 and 11.2 are fed to the TV receiver 13, via an electrical signal coupler 12. Signal 11.1 is fed directly to the coupler 12, the very high-frequency signal 11.2 via a 'satellite tuner' 14, which converts the signals within the 0.9-2MHz band into corresponding signals within the 'conventional' TV band (for which the TV set is suitable). It is also possible to convert the 0.9-2MHz signals into 'baseband' signals (0-5.5MHz) and apply them to the TV receiver.

Claims (8)

Optical transmission system for transmitting signals between a local exchange and subscribers connected to that exchange via a local optical transmission network, characterized in that said local exchange comprises means for receiving signals from one or more extraterrestrial broadcasters such as satellite broadcast transmitters, and for transmitting those signals to subscribers via that local optical transmission network. Optical transmission system according to claim 1, characterized in that it comprises local central means for receiving signals from one or more terrestrial broadcasting transmitters and for transmitting those signals to subscribers via that local optical transmission network. Optical transmission system according to claim 1 or 2, characterized in that the local exchange comprises one or more antennas which are intended and suitable for receiving signals from satellite and / or terrestrial broadcasting stations. Optical transmission system according to claim 1 or 2, characterized in that the local exchange is connected via a transmission network to one or more receiving stations, comprising one or more antennas for receiving signals from satellite and / or terrestrial broadcast stations, wherein the signals received by those antennas are transferred via that transmission network to that local exchange. Optical transmission system according to claim 1, characterized in that the signals from one or more satellite broadcast stations are FM modulated TV signals. Optical transmission system according to claim 5, characterized in that the frequency range of said signals is globally between 900 and 2000 MHz with a global bandwidth of 15 to 40 MHz. Optical transmission system according to claim 1, characterized in that the satellite signals transmitted by the local optical transmission network on the subscriber's side are converted by satellite tuners into input signals suitable for analog TV sets. Optical transmission system according to claim 7, characterized in that on the subscriber's side the end of the local optical transmission network is connected to an opto-electric converter for converting optical signals supplied to the subscriber via the local transmission network and that said satellite tuner converts the electrical satellite signals thus formed into electrical signals in a frequency band suitable for analog TV sets.