WO2011053226A1

WO2011053226A1 - Converter for a satellite reception system and such system

Info

Publication number: WO2011053226A1
Application number: PCT/SE2010/051125
Authority: WO
Inventors: Dan Sahlin
Original assignee: Raycore Fiber Optic Solutions Ab
Priority date: 2009-10-26
Filing date: 2010-10-18
Publication date: 2011-05-05
Also published as: SE0901377A1; SE534823C2; EP2494722A1

Abstract

The invention, concerns a converter (1) for a satellite reception system comprising:- an electrical signal port, - an optical signal port wherein the converter (1) is adapted to convert an optical satellite communications signal, received from the optical signal port, to an electrical satellite communications signal and. to transmit the electrical satellite communications signal via the electrical signal port. The converter (1) is distinguished by that it is adapted to convert also an electrical satellite receiver (4) control signal, received from the electrical signal port, to an optical satellite receiver (4) control signal and fcransmit said optical satellite receiver (4) control signal via the optical signal port, The invention also concerns a further converter (11), a satellite reception system and a use of a converter (1,11).

Description

Fiald of th« invention

The present invention concerns a converter for a satellite reception system according to the preamble of claim 1.

Further, it concerns a second converter for a satellite reception system according to the preamble of claim 8, a satellite reception system according to claim 9 and a use of converter according to claim 10.

Background art

It is previously known to have satellite TV receivers

connected, via a switch, to a plurality of frequency bands containing different TV channels. Such frequency bands may originate from a plurality of polarisations of a satellite dish receptor head a.k.a. low-noise block converter (LNB) , from one or more such LNBs, and from one or more satellite dishes carrying one or more LNBs. In fig. 1, an installation is shown where a single satellite receiver is connected via a switch using a protocol called Digital Satellite Equipment Control (DiSEqC) . The switch is connected to two satellite dishes, each having an LNB.

When the user switches TV channels on the satellite receiver, a DC/DiSEqC (DC as in Direct Current) signal goes from the satellite receiver to the DiSEqC switch selecting the correct dish and LNB. The DC/DiSEqC control signal is also decoded by the LNB so that the correct polarisation is chosen (using DC 13V or 18V) and high or low band (using the 22 kHz DiSEqC signal) .

There are LNBs with a built-in DiSEqC switch for two or four satellite receivers.

The DiSEqC¹" signalling system is developed by Eutelsat. All cables shown in fig. 1 are coaxial cables, typically with a 0.8, 1.0 or 1.6 mm centre core. The LNBs convert the

satellite signals from 10-12 GHz to 0.950-2.1 GHz. This lower frequency is less attenuated on the coaxial cable. However, at 2.2 GH2 the typical attenuation is 34 dB/100 m. This means that the cable preferably should not be more than 50 m. Fig. 2 illustrates a multi-switched system. In such a system, several satellite receivers may share a group of satellite dishes. The so-called multi-switch allows a number of users to individually select their satellite dish, polarisation and high or low band.

A multi-switched net uses coaxial cable, and as for the single user the maximum cable length should not be more than 50 m. There are amplifiers that can extend this range once, but even with those amplifiers it is hard to go a longer distance than 100 m. Thus, a multi-switched net is normally limited to a single building, or just a part of a larger building. The number of users is seldom larger than 40.

A problem of the background art is a problem common to all technology, namely how to improve upon an existing design. Summary of th« invention

It is an object of the present invention to propose a solution for or a reduction of the problems of prior art. A main object is consequently to provide a technical improvement over the prior art.

According to the invention this is accomplished with a device having the features of claim 1. Such a device can be connected between a multiswi ten and a satellite receiver, close to the receiver, for instance in a system according to fig. 2. If the device has a counterpart converter connected also between the satellite receiver and the multiswitch but at the multiswitch end, both converters can communicate via an optical fibre connected between them. Thus, instead of the coaxial cable of fig. 2 the communication is taking place on an optical fibre. In this way, it is made possible to distribute a satellite reception signal over a fibre infrastructure in housing, using existing multiswitch- receiver technology. This is achievable since the control signal from the satellite receiver is converted to an optical counterpart and can be distributed upstream to the multiswitch while the satellite video signal is propagated downstream.

Thus, this provides a signal transportation infrastructure over optical fibre that is transparent to the multiswitch and the digital receiver. Therefore, in housing where there is already a redundant optical fibre, this fibre can be used without further investment besides the converter according to the invention. Also, standard multiswitches and standard receivers can be used at a longer distance from each other, due to less attenuation in the optical fibre, compared to coaxial cable. Further, an object of the present invention is accomplished with a device having the features of claim 8. Such a device will provide similar benefits as the previous device and constitutes the apparatus that can be connected at the

multiswitch end in the above anticipated system. Further, an object of the present invention is accomplished with a system having the features of claim 9. Such a system corresponds to the system anticipated above in relation to the device of claim 1 and provides similar benefits. Further, an object of the present invention is accomplished with a use of a device in accordance with claim 10. Using such a converter to connect a satellite receiver to a multiswitch over a fibre optical link provides the benefits mentioned above. There are known systems designed for transportation of

satellite signals on fibre, e.g. systems from British company Global Invacom. Such systems are intended to provide an infrastructure to transport all satellite signals from a certain satellite dish position on a single fibre and to do this potentially over longer distances than is possible with coaxial cable. A single satellite dish position originates four signals: vertical polarisation/low band, vertical

polarisation/high band, horizontal position/low band,

horizontal position/high band. Each of these signals is between 1 and 2 GHz, and thus occupying a bandwidth of 1 GHz each. In the system from Global Invacom the four signals are stacked, so that they occupy the frequency range 1-5 GHz. This signal is then fed from an LNB into an optical fibre. At the other end of the fibre there is a special kind of multiswitch, capable of handling this optical signal. By using an optical splitter, the same signal can be fed to multiple

multiswitches.

However, these systems do not provide any support for a transportation of a control signal, such as a DiSEqC signal, from a satellite receiver upstream. Thus, this kind of known system is unable to provide the benefit of the present

invention, namely that multiple of user receivers can be connected over great distances via optical fibre with one central multiswitch and where this optical transport is completely transparent to the multiswitch and the receivers. Brief description of the drawing*

Embodiments exemplifying the invention will now be described, by means of the appended drawings/ on which

Pig. 1 illustrates schematically a single satellite receiver connected via a DiSEqC switch to two satellite dishes

according to prior art,

Fig. 2 illustrates a multi-switched satellite reception system according to prior art,

Fig. 3 illustrates a satellite reception system according to the invention including converters according to the invention. Fig. 4 illustrates an embodiment of a converter according to the invention, and

Fig. 5 illustrates another embodiment of a converter according to the invention. Detailed description of the invention

In figure 3, an embodiment of the invention is illustrated. As can be seen, the transportation of satellite reception signals from a multiswitch to several satellite receivers can be effected by the use of optical fibre and converters according to the invention. According to the invention there should be two types of converters, namely one converter 1 that can be connected to the satellite receiver 4 side and one converter 11 that can be connected to the multiswitch 5 side. The main idea is now that the converters 1, 11, in addition to being able to convert an electrical satellite reception signal to an optical counterpart and vice versa, also can convert an electrical satellite receiver control signal to an optical counterpart and vice versa. This additional receiver control signal is a signal mainly intended to be sent from a satellite receiver 4 to the multiswitch 5 in order to control the raultiswitch as to what signal bands it should transmit

downstream to the receiver 4 .

Below, we describe more closely the workings of the converters of the invention. First, the converter 1 intended for the satellite receiver side is described together with some different embodiments and then the converter 11, intended for the multiswitch side, is described.

Such a converter 1 for a satellite reception system comprises an electrical signal port 2 and an optical signal port 3, to provide for the connectivity. Such ports can be ordinary coaxial cable connectors and optical cable connectors

respectively. The converter 1 is adapted to convert an optical satellite communications signal, received from the optical signal port 3, to an electrical satellite communications signal and to transmit the electrical satellite communications signal via the electrical signal port 2. Further, the

converter is adapted to convert also an electrical satellite receiver control signal, received from the electrical signal port 2, to an optical satellite receiver control signal and transmit said optical satellite receiver control signal via the optical signal port 3.

In this way, an existing, presently redundant, fibre

infrastructure can be used to distribute satellite video signals using existing multiswitch-receiver technology. Such a redundant fibre infrastructure can for instance present itself in block of flats where a pair of fibres has been deployed. Such a pair may have been intended for an uplink and downlink internet connection respectively, but such uplink and downlink may have been realised on only one of the fibres leaving the second one unused. Of course, deploying new fibre

infrastructure in buildings lacking fibres is of course also an alternative. In any of these cases, the invention allows for a central deployment of a multiswitch that connects satellite receivers that can be scattered around in different buildings at much longer distances from the multiswitch than is possible with coaxial fibre. At the same time, the

multiswitch and the receivers can be off-the-shelf, standard products that do not have to be adapted in any way.

In order to convert the electrical control signal to the optical counterpart, there are several alternatives. For instance, the converter 1 can be adapted to convert the electrical control signal by using an analogue representation of the electrical control signal to modulate an optical energy source. I.e., the electrical control signal itself or a modified version (voltage compression, voltage expansion, frequency translation, etc.) is used to modulate the optical energy source. In this way, the control signal can change (new protocol etc.) but the converter still works since it does not decode the control signal. To carry out such a direct

modulation, one way would e.g. be to provide the electric control signal as input to a voltage controlled oscillator and then use this frequency modulated signal to drive a laser light emitting diode. A small bias may have to be imposed, such that the electrical control signal never becomes

negative. This may be necessary when the light source is a diode that only generates light for positive input voltages.

As an alternative to direct modulation, the converter 1 could be adapted to convert the electrical control signal by digitising the electrical control signal and then using the digitised electrical control signal to modulate an optical energy source. This would provide the benefit of digitisation, namely better control over the signal and its properties.

Thus, if there for instance would be a problem with high noise levels somewhere in the transmission chain, the electrical control signal could be digitised before being modulated onto the optical energy source. As another alternative to direct modulation, the converter 1 could be adapted to convert the electrical control signal by decoding the control signal and then using the decoded

electrical control signal to modulate an optical energy source. This is also a way to avoid degradation if the control signal is noisy; it may be better to first decode the signal in order to get rid of possible noise.

Above, it was mentioned that the direct modulation could be accomplished with frequency modulation. The same is really true for the converter 1 according to any of the previous approaches to convert the electrical signal to the optical counterpart. That is to say that regardless if an analogue representation of the electrical control signal is used to modulate an optical energy source or if the electrical control signal is digitised first or if it is decoded first, the converter can be adapted to modulate the optical energy source by frequency modulation. Another alternative is pulse width modulation. In one embodiment, in addition to any of the earlier

embodiments of the converter, the converter can be adapted to use a carrier wavelength for the optical control signal that is the same wavelength as the carrier wavelength of the optical satellite communications signal. The electrical control signal itself may be contained in a frequency band below 100 kHz. This is for instance the case for the DC/DiSEqC signal. In such a case the converter of the invention would be adapted to be able to handle that

particular frequency band. As has been noted earlier, in one embodiment of the converter 1 according to the invention, the electrical control signal can be a DC/DiSEqC signal. In that case, certain requirements are imposed on the converter. For instance, the converter must be able to handle the DC-component of that type of signal as well as the frequency range of the DiSEqC signal. Such

requirements on the converter would be apparent from the

DC/DiSEqC protocol specification. Of course, even though the must ubiquitous control signal in satellite reception systems is the DC/DiSEqC signal, the invention is not limited to this type of control signal, but can be adapted to other types. The idea underlying the invention is that the converter 1 provides a transparent transport of a control signal from (or to) a satellite receiver. This implies that satellite receivers and satellite reception multiswitches using coaxial cables can be used over an optical fibre based transport infrastructure without further adjustment of the original receiver or

multiswitch. The counterpart to the converter 1, described above, is a converter 11 to be connected at the multiswitch side (see fig. 3} . Such a converter 11 for a satellite reception system comprises:

- an electrical signal port 13, - an optical signal port 12, wherein the converter 11 is adapted to convert an electrical satellite communications signal, received from the electrical signal port 13, to an optical satellite communications signal and to transmit the optical satellite communications signal via the optical signal port 12. Further, the converter 11 is adapted to convert also an optical satellite receiver control signal, received from the optical signal port 12, to an electrical control signal and transmit said electrical control signal via the electrical signal port 13. This converter 11 for the multiswiten side is really a mirror image of the converter 1 for the satellite receiver side;

therefore all the different embodiments of the converter 1 for the satellite receiver side described above can be adapted to corresponding embodiments for this converter 11 for the multiswitch side. That is to say, that all those earlier described embodiments have a counterpart for the converter 11 and are a part of the invention. For instance, above it is described that in one embodiment of the converter 1, it is adapted to convert the electrical control signal by using an analogue representation of the electrical control signal to modulate an optical energy source. For the converter 11, the counterpart to this

embodiment is the converter 11 as described and further adapted to convert the optical satellite receiver control signal to the electrical control signal, wherein the optical satellite receiver control signal is a signal which has been created by modulation of an optical energy source using an analogue representation of the original electrical control signal. The converter 1, 11 according to the invention may also be bidirectional in regard of converting and transferring a satellite receiver control signal. This may be of use for instance in conjunction with motor controlled satellite dishes, where also control signals are sent downstream to the satellite receiver. The DiSEqC 2.0 standard allows such a bidirectional signal.

In a further development of any of the embodiments of the converter I, 11 according to the invention, the optical transmission could additionally employ Wavelength-division multiplexing (WDM) . In this way, a plurality of channels can be transferred over the same fibre. Each different channel would then occupy respectively a different wavelength λ. The system could be designed so that a WDM version can be

supported for up to, for instance, 8 users on the same fibre. This would enable a single household to have up to 8

receivers, all with an independent choice of channels. As an alternative or complement to WDM, it is conceivable to adapt the converters of the invention to use separate fibres for the upstream and downstream directions. Another

alternative or complement to WDM is to use a single fibre and to transmit upstream and downstream on the same wavelength. This is possible because of the superposition property of light. Of course, transmitting upstream and downstream at different wavelengths on the same fibre is also possible.

In order to provide for a rational physical handling and storage, the converter 11 for the multi-switch side could be adapted to be positioned in a rack. For instance, a standard 19-inch rack. When combining the converter 1 and the converter 11, a

complete satellite reception system is realised. Such a system would comprise:

- a first converter 1 according to any of the embodiments above, wherein said first converter is connected via its electrical signal port 2 to a satellite receiver 4 and

connected via its optical signal port 3 to an optical fibre,

- a second converter 11 according to the embodiment above or any of the counterpart embodiments, connected via its

electrical signal port 13 to a satellite multiswitch 5 and connected via its optical signal port 12 to the optical fibre, wherein the first converter 1 can communicate with the second 11 converter over the optical fibre. The invention also includes the use of a converter 1, 11 according to any of the embodiments described, wherein the converter 1, 11 is used in a satellite reception system to connect a satellite receiver to a multiswitch over a fibre optical link.

Example of specifications for an implementation

A3 an example, some specifications for an embodiment follow. Two types of fibre converters are used: Head End Fibre

converter, to be connected at the multiswitch side, and User Fibre converter, to be connected at the receiver side. A

Single mode, single fibre is used.

Head End Fibre converter

Coaxial side: input 950-2400 MHz - Fibre side: output 1550 nm. Coaxial side: output DC/DiSEqC - Fibre side: input 1310 run.

User Fibre converter

Coaxial side: output 950-2400 MHz - Fibre side: input 1550 rim. Coaxial side: input DC/DiSEqC - Fibre side: output 1310 nm.

Input and output levels of the RF and optical signals are chosen as appropriately.

According to the DiSEqC standard [DiSEqC2.0], the DiSEqC signal is a 22 kHz tone (±20%) with pulses of a minimum duration of 0.5 ms (120%). The nominal amplitude is 650 mV (±250mV) peak-peak. The system should tolerate voltages between 300 mV and 1000 mV and should further ignore voltages below 100 mV.

The DC signal is either 13 V (11 - 15V) or 18 V (18-20V) .

Maximum current drawn from the Head End Fibre converter is 50 mA. There are different options for the OC/DiSEqC signal to be coded onto the fibre, for instance:

1. Direct conversion, i.e. the DC/DiSEqC signal is not

decoded. The conversion to fibre must then be able to handle a signal 0-20V (resolution <100 mV) , 0-50 kHz. As the fibre cannot reliably handle a DC signal, the signal is converted using frequency modulation, pulse width modulation or digital conversion (AD-converter) . 2. Decoded conversion, i.e. the DC/DiSEqC signal is decoded before transmission onto the fibre. A differentiation is made between DC being 11-15V or 18-20 V. The pulses in the DiSEqC signal are decoded. The DiSEqC is sampled with at least 10 kHz whereas it is sufficient to decode the DC signal with just 1 Hz. The decoded signals are transmitted digitally on the fibre, using a suitable decoding.

As the Head End Fibre converter must be able to emit a DC signal up to 18 V, it is probably suitable to power the whole unit with at least 18V DC.

The User Fibre converter on the other hand does not need to emit such high voltage. It might be feasible to power this unit using the input DC signal coming on the coaxial cable from the satellite receiver. No separate DC converter would then be needed, and the unit would turn itself off when the satellite receiver is turned off.

A Wavelength-division multiplexing (WDM) scheme could look as follows.

Head End transmission User transmission

User 1 1490 nm 1290 nm

User 2 1510 nm 1310 nm

User 3 1530 nm 1330 nm

User 4 1550 nm 1350 nm

User 5 1570 nm 1370 nm

User 6 1590 nm 1390 nm Figure 4 illustrates a diagrammatical functional block scheme of a converter intended for a multi-switch side according to the invention. Further, Fig. 5 illustrates another embodiment of a converter intended for a satellite receiver side

according to the invention. Of course, fig. 4 and 5 are just examples of an implementation of the converters of the

invention.

As is obvious for a skilled person, a number of other

implementations, modifications, variations and/or additions can be made to the above described exemplary embodiments. It is to be understood that the invention includes all such other implementations, modifications, variations and/or additions which fall within the scope of the claims.

Claims

Converter (1) for a satellite reception system

comprising:

- an electrical signal port (2),

- an optical signal port (3),

wherein the converter (1) is adapted to convert an optical satellite communications signal, received from the optical signal port (3), to an electrical satellite communications signal and to transmit the electrical satellite communications signal via the electrical signal port (2),

characterised in that the converter (1) is adapted to convert also an electrical satellite receiver (4) control signal, received from the electrical signal port (2), to an optical satellite receiver (4) control signal and transmit said optical satellite receiver (4) control signal via the optical signal port (3) .

Converter (1) according to claim 1, wherein the converter (1) is adapted to convert the electrical control signal by using an analogue representation of the electrical control signal to modulate an optical energy source.

Converter (1) according to claim 1, wherein the converter (1) is adapted to convert the electrical control signal by digitising the electrical control signal and then using the digitised electrical control signal to modulate an optical energy source. Converter (1) according to claim 1, wherein the converter (1) is adapted to convert the electrical control signal by decoding the control 3ignal and then using the decoded electrical control signal to modulate an optical energy source.

Converter (1) according to any of claims 2 - 4, wherein the converter (1) is adapted to modulate the optical energy source by frequency modulation or pulse width modulation.

Converter (1) according to any of claims 2 - 5, wherein the converter (1) is adapted to use a carrier wavelength for the optical control signal that is the same

wavelength as the carrier wavelength of the optical satellite communications signal.

Converter (1) according to any of claims 1 - 6, wherein the electrical control signal is a DC/DiSEqC signal. Converter (11) for a satellite reception system

comprising:

- an electrical signal port,

- an optical signal port, wherein the converter (11) is adapted to convert an electrical satellite communications signal, received from the electrical signal port, to an optical satellite communications signal and to transmit the optical satellite communications signal via the optical signal port,

characterised in that the converter (11) is adapted to convert also an optical satellite receiver (4) control signal, received from the optical signal port, to an electrical control signal and transmit said electrical control signal via the electrical signal port. Satellite reception system, comprising:

- a first converter (1) according to any of claims I ~ 7, said first converter (1) connected via its electrical signal port to a satellite receiver (4) and connected via its optical signal port to an optical fibre,

- a second converter (11) according to claim 8 connected via its electrical signal port to a satellite multiswitch and connected via its optical signal port to the optical fibre,

wherein the first converter {1} can communicate with the second converter (11) over the optical fibre. Use of a converter (1, 11) according to any of claims 1- 8, wherein the converter (1, 11) is used in a satellite reception system to connect a satellite receiver (4) to a multiswitch (5) over a fibre optical link.