WO2010097682A2 - Non-interfering satellite communication system for broad-band communication services on board a train - Google Patents

Abstract

The present invention relates to a satellite communication system (30; 30') of a train configured to communicate with a satellite in a given radiofrequency band and to transmit signals to the satellite with a transmission power. The satellite communication system (30; 30') is characterized in that it is also configured to determine a condition of interference indicating the presence of a terrestrial radio- communication system that transmits and/or receives signals in the given radiofrequency band, and to control, as long as said condition of interference persists, the transmission power in such a way that it does not exceed a pre-defined power. The pre-defined power is such that a signal transmitted by the satellite communication system (30; 30') to the satellite with said pre-defined power does not create interference with said terrestrial radio-communication system.

Description

NON-INTERFERING SATELLITE COMMUNICATION SYSTEM FOR BROAD-BAND COMMUNICATION SERVICES ON BOARD A TRAIN

TECHNICAL FIELD

The present invention relates to a satellite communication system of a train capable of operating without causing any interference with other terrestrial telecommunications systems .

BACKGROUND ART

As is known, in many countries, such as, for example, Italy, France, and Germany, there currently exist various activities of development of broad-band-communications services based upon the Internet Protocol (IP) for high-speed trains. It is expected, in fact, that these services will soon become a specific characteristic both of high-speed trains and of traditional trains .

Examples of services that can be exploited by means of a satellite communication system of a train may be:

• services based upon Voice-over-IP (VoIP) technology;

• video-surveillance services;

• use of video contents in streaming, for example on demand;

• digital television, for example according to the standards Digital Video Broadcasting - Satellite (DVB-S) or Digital Video Broadcasting - Handheld (DVB-H) ;

• Internet netsurfing;

• e-mail services;

• Instant Messaging (IM) services;

• consultation of electronic archives and/or databases; and

• services based upon the File Transfer Protocol (FTP) .

Broadly speaking and according to the known art, a satellite communication system of a train comprises : • a highly directive satellite antenna, set on the roof of the train and configured to communicate bi-directionally with at least one geostationary satellite;

• an on-board communication network, either wired or wireless, installed inside the train and configured to communicate bi-directionally with a plurality of electronic devices present inside the train, for example portable computers or smartphones, in order to enable users of said electronic devices to exploit one or more of the services listed above; and

• a central control unit coupled with said satellite antenna and with said on-board communication network and configured to function as gateway of the satellite communication system by managing and routing at output through the satellite antenna the various traffic flows of the various users connected to the on-board communication network and, likewise, managing and routing towards the various users connected to the on-board communication network the corresponding traffic flows received at input through the satellite antenna.

In particular, as is known, the satellite antenna is built and installed on the roof of the train so as to be continuously aligned with the geostationary satellite, i.e., so as to present a continuous pointing to the geostationary satellite, in order to guarantee a seamless bi-directional communication with the geostationary satellite as the speed and position of the train vary.

In addition, the geostationary satellite enables the aforesaid satellite communication system on board the train to connect remotely up to terrestrial telecommunications networks, for example, the Internet.

In fact, the geostationary satellite is remotely connected not only to the satellite communication system of the train, but also to a ground station that operates as gateway towards a plurality of terrestrial telecommunications networks, thus enabling bi-directional communications between the satellite communication system of the train and said terrestrial telecommunications networks .

In this regard, Figure 1 is a schematic illustration of the scenario of operation just above described.

In particular, Figure 1 shows a train 11 installed on board which is a satellite communication system (not shown) of the type previously described, which comprises a satellite antenna 12 installed on the roof of the train 11 and remotely connected to a geostationary satellite 13. The geostationary satellite 13 is in turn remotely connected to a ground station 14 connected, in turn, to two terrestrial telecommunications networks, designated in Figure 1 by 15 and 16, respectively.

Consequently, the satellite communication system on board the train 11 is remotely connected, via the satellite antenna 12, the geostationary satellite 13, and the ground station 14, to the terrestrial telecommunications networks 15 and 16.

As may be readily appreciated, the signal transmission powers used in the communications between a satellite communication system of a train and a geostationary satellite must necessarily be very high to be able to guarantee a seamless connection between the satellite communication system of the train and the geostationary satellite.

In fact, said powers must guarantee that the signals received are still intelligible in spite of all the attenuations and distortions that they may have undergone during uplink or downlink propagation and that, in general, are linked to the distance covered during propagation, to the speed of the train, and to the presence of possible obstacles, such as for example buildings or tunnels, along the path of the train.

On the other hand, the spectrum of the frequencies that can be used for radio communications, i.e., the so-called radiofrequency spectrum, is a finite resource, which, already today, starts to appear inadequate in regard to the ever- increasing number of Radiocommunication systems and of services provided thereby.

Consequently, in the last few years it has become necessary to guarantee a rational, fair, co-ordinate, efficient, and economic use of the radiofrequency spectrum by all the Radiocommunication systems, both existing ones and future ones, including satellite ones.

For this purpose, in the course of various World Radiocommunication conferences, the last of which was held in Geneva in 2007, Radio Regulations have been initially defined and then progressively updated, aimed at guaranteeing an interference-free operation of all the Radiocommunication systems, both existing ones and future ones.

In said Radio Regulations the maximum levels of Power-Flux Density (PFD) have been defined, which must be respected by each Radiocommunication system in order not to create interference with other Radiocommunication systems.

Said maximum levels of PFD are excessively restrictive for satellite communication systems of trains of a known type, in particular in the case where said systems provide services of fast access to the Internet and of digital television, for which it is necessary to use levels of PFD not allowed by the Radio Regulations when the radiofrequency band used by said systems is also used by terrestrial radio-communication systems . In this regard, Figure 2 is a schematic illustration of a scenario in which a satellite communication system (not shown) installed on board a train 21 creates an interference with a terrestrial radio-communication system 22 present along the path of the train 21.

In particular, as shown in Figure 2, the satellite communication system on board the train 21 comprises a satellite antenna 23, installed on the roof of the train 21, which communicates with a satellite 24 in a given radiofreguency band.

In addition, also the terrestrial radio-communication system 22 transmits and receives signals in the given radiofrequency band.

Consequently, the satellite communication system installed on board the train 21 disturbs the communications of the terrestrial radio-communication system 22 when the radiation beam of the satellite antenna 23 is superimposed on the radiation beam of the antenna and/or antennas (in Figure 2 not numbered) of the terrestrial radio-communication system 22.

Consequently, in order to be able to use the levels of PFD necessary for a proper and reliable operation of the satellite communication systems on board trains, currently used are, for said type of systems, "protected" bands, i.e., radiofrequency bands, defined once again in the Radio Regulations, which can be used exclusively by the satellite systems, such as, for example, the radiofrequency band comprised between 14 and 14.25 GHz.

The Applicant has however noted that the use of said protected bands for the satellite communication systems on board trains leads to very high costs for the services provided to users on account of the small number of satellites that are currently equipped with transponders operating in said protected bands .

In fact, in order to be able to provide on the trains one or more services among the ones previously listed it is necessary to:

• make an economic agreement with one or more of the companies that possess satellite transponders (or satellites equipped with satellite transponders) operating in said protected bands in order to hire the use of said transponders for conveying one or more of the services listed above; or else

• launching into orbit a new satellite equipped with at least one transponder operating in said protected bands .

As may be readily appreciated, both solutions entail start-up costs that are very high and inevitably reflect on the fees paid by the users for exploiting said services on board trains .

In addition, the present applicant has moreover noted that, on account of the small number of satellites that are currently equipped with transponders operating in said protected bands and following upon a possible massive demand of use of said transponders by operators of satellite communication services that are already available and differ from the ones provided on board trains, there could even occur unavailability of the protected band for start-up of the broad-band communication services on board trains, this thus giving rise, in this case, to a discrimination between the train and other means of collective transport, for example, ships and aeroplanes, for which, unlike in the case trains, there do not exist, except in circumscribed cases, risks of interference with the terrestrial radio-communication systems.

DISCLOSURE OF INVENTION

Consequently, the aim of the present invention is to provide a satellite communication system of a train that, in general, is able to alleviate the disadvantages just referred to above and, in particular, does not create interference with terrestrial radio-communication systems and does not lead to high costs for the services provided to the users.

The aforesaid purpose is achieved by the present invention in so far as it relates to a satellite communication system of a train, according to what is defined in the annexed claims .

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, some preferred embodiments, which are provided purely by way of explanatory and non-limiting example, will now be illustrated with reference to the annexed drawings (not in scale) , in which:

Figure 1 is a schematic illustration of a scenario of operation of a satellite communication system of a train;

Figure 2 is a schematic illustration of a scenario in which a satellite communication system of a train creates an interference with a terrestrial radio-communication system;

Figure 3 shows a block diagram representing a satellite communication system of a train according to a first preferred embodiment of the present invention; and

Figure 4 shows a block diagram representing a satellite communication system of a train according to a second preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The ensuing description is provided for enabling a person skilled in the sector to implement and use the invention. Various modifications to the embodiments presented will be immediately evident to persons skilled in the sector, and the generic principles disclosed herein could be applied to other embodiments and applications without, however, thereby departing from the sphere of protection of the present invention .

Consequently, the present invention must not be understood as being limited merely to the embodiments described and shown herein, but it must be granted the widest sphere of protection consistently with the principles and characteristics presented herein and defined in the annexed claims .

In the first place, according to the present invention, a satellite communication system of a train is provided, configured to :

• communicate with a satellite in a given radiofrequency band, said given radiofrequency band not being a protected radiofrequency band.

In this way, the realization of the satellite communication system of the train does not lead to high costs for the services provided to users.

On the other hand, as has been said previously, since a satellite communication system of a train that communicates in a non-protected radiofrequency band transmits signals with very high levels of PFD, it creates interference with terrestrial radio-communication systems that communicate in the same radiofrequency band as that of the satellite communication system.

This further technical problem is overcome from the satellite communication system of the train according to the present invention since said satellite communication system of the train is moreover configured to:

• transmit signals to the satellite with a transmission power;

• determine a condition of interference indicating the presence of a terrestrial radio-communication system that transmits and/or receives signals in the given radiofrequency band; and

• as long as said condition of interference persists, control the transmission power in such a way that it does not exceed a pre-defined power, said pre-defined power being such that a signal transmitted by the satellite communication system to the satellite with said pre-defined power does not create interference with said terrestrial radio-communication system.

Preferably, controlling the transmission power in such a way that it does not exceed a pre-defined power as long as said condition of interference persists comprises :

• if the transmission power is greater than said predefined power, reducing the transmission power to said predefined power.

Alternatively, controlling the transmission power in such a way that it does not exceed a pre-defined power as long as said condition of interference persists comprises:

• not transmitting signals to the satellite as long as said condition of interference persists.

Or again alternatively, controlling the transmission power in such a way that it does not exceed a pre-defined power as long as said condition of interference persists may conveniently comprise:

• transmitting signals on a terrestrial radiocommunication network, such as, for example, a cellular phone network of second generation (GSM/GPRS/EDGE) and/or third generation (UMTS/HSDPA/HSUPA) .

Furthermore, illustrated in Figure 3 is a block diagram representing a satellite communication system 30 of a train (not shown) according to a first preferred embodiment of the present invention. In detail, as shown in Figure 3, the satellite communication system 30 comprises:

• a satellite antenna 31 placed on the roof (not shown) of the train, having a radiation pattern such as to guarantee a seamless alignment with said satellite (not shown) and configured to communicate with said satellite in the 'given radiofrequency band and to transmit signals to said satellite with said transmission power;

• an on-board communication network 32, wired or wireless, installed inside the train and configured to communicate with a plurality of electronic devices (not shown) present inside the train, for example portable computers or smartphones ; and

• a central control unit 33, coupled with said satellite antenna 31 and with said on-board communication network 32 and configured to determine said condition of interference and to control, as long as said condition of interference persists, said transmission power of the satellite antenna 31 in such a way as not to exceed said pre-defined power.

Furthermore, once again as shown in Figure 3, the central control unit 33 is also coupled with:

• a receiver 34 of a satellite positioning system (not shown) , for example a GPS (Global Positioning System) or Galileo receiver, said receiver 34 being configured to compute a position of the train; and

• an electronic archive 35, configured to store a plurality of pre-determined geographical areas in which respective terrestrial radio-communication systems are present.

Hence, the central control unit 33 is configured also to:

• determine said condition of interference on the basis of the position of the train computed by the receiver 34 and of said pre-determined geographical areas stored in the electronic archive 35. Preferably, the central control unit 33 determines said condition of interference when the position of the train computed by the receiver 34 is inside one of said predetermined geographical areas stored in the electronic archive 35.

Conveniently, the central control unit 33 is moreover configured to determine said condition of interference also on the basis of the radiation pattern of the satellite antenna 31 and of a speed of the train, it being possible for said speed to be computed and communicated to the central control unit 33 by the receiver 34.

In fact, the higher the speed and/or the higher the angle of elevation of the radiation pattern of the satellite antenna 31, the less said condition of interference will persist, i.e., the shorter the duration of said condition of interference .

Illustrated, instead, in Figure 4 is a block diagram representing a satellite communication system 30' of a train (not shown) according to a second preferred embodiment of the present invention.

In particular, in Figure 4 the components of the satellite communication system 30' that do not differ from those of the satellite communication system 30 are designated by the same reference numbers as the ones used in Figure 3.

In detail, as shown in Figure 4, the satellite communication system 30' comprises:

• said satellite antenna 31;

• said communication network 32 on board the train; and a central control unit 33 ' , coupled with said satellite antenna 31 and with said on-board communication network 32 and configured to determine said condition of interference and to control, as long as said condition of interference persists, said transmission power of the satellite antenna 31 in such a way as not to exceed said predefined power.

Furthermore, once again as shown in Figure 4, the central control unit 33' is also coupled with a low-directivity antenna 36 placed on the roof (not shown) of the train and configured to receive signals in the given radiofrequency band.

Hence, the central control unit 33' is configured also to:

• determine said condition of interference when a power of a signal received by said low-directivity antenna 36 satisfies a given condition.

Preferably, the central control unit 33' determines said condition of interference when the power of the signal received by said low-directivity antenna 36 is higher than or equal to a pre-defined threshold.

Furthermore, as in the satellite communication system 30, also in the satellite communication system 30' the central control unit 33 ' can conveniently determine said condition of interference also on the basis of the speed of the train and of the radiation pattern of the satellite antenna 31.

Moreover, in the case where the satellite communication system of the train does not transmit signals to the satellite as long as said condition of interference persists, the central control unit 33 or 33' is further configured to:

• as long as said condition of interference persists, store data that arrive from said on-board communication network 32 and that are to be transmitted to the satellite; and

• when said condition of interference terminates, transmit to the satellite said stored data.

From the foregoing description the advantages of the present invention may be immediately appreciated.

In particular, the satellite communication system of a train according to the present invention, by not using a protected radiofrequency band, is able to communicate with the majority of the satellites that have so far been launched into orbit and hence does not entail either high initial production costs or consequent high fees for the services provided to users .

Furthermore, another advantage of the present invention is linked to the fact that the satellite communication system according to the present invention does not create interference with possible radio-communication systems present along the path of the train and that use the same radiofrequencies as the satellite communication system on board the train.

A further advantage of the present invention derives from the fact that it is able to exploit far wider radiofrequency bands or bands at a higher frequency as compared to the protected bands that comprise radiofrequency ranges that cannot be modified. Moreover, thanks to this further advantage, the present invention enables an increase in the performance and competitivity of the broad-band communication services offered to passengers on trains .

Finally, it is clear that various modifications may be made to the present invention, all of which fall within the sphere of protection of the invention, as defined in the annexed claims.

Claims

1. A satellite communication system (30; 30') of a train configured to:

• » communicate with a satellite in a given radiofrequency- band; and

• transmit signals to the satellite with a transmission power ; said satellite communication system (30; 30') being characterized in that it is further configured to:

• determine a condition of interference indicating the presence of a terrestrial radio-communication system that transmits and/or receives signals in the given radiofrequency band; and,

• as long as said condition of interference persists, control the transmission power in such a way that it does not exceed a pre-defined power, said pre-defined power being such that a signal transmitted by the satellite communication system (30; 30') to the satellite with said pre-defined power does not create interference with said terrestrial radio- coirmunication system.

2. The system of claim 1, wherein controlling the transmission power in such a way that it does not exceed a pre-defined power as long as said condition of interference persists comprises:

• if the transmission power is greater than said predefined power, reducing the transmission power to said predefined power.

3. The system of claim 1, wherein controlling the transmission power in such a way that it does not exceed a pre-defined power as long as said condition of interference persists comprises:

• as long as said condition of interference persists, not transmitting signals to the satellite.

4. The system of claim 1, wherein controlling the transmission power in such a way that it does not exceed a pre-defined power as long as said condition of interference persists comprises :

• as long as said condition of interference persists, transmitting signals on a terrestrial radiocommunication network .

5. The system according to any preceding claim, comprising:

• a satellite antenna (31) placed on a roof of the train, having a radiation pattern such as to guarantee a seamless alignment with said satellite, and configured to communicate with said satellite in the given radiofrequency band and to transmit signals to said satellite with said transmission power; and

• a central control unit (33; 33'), coupled with said satellite antenna (31) , and configured to determine said condition of interference and to control, as long as said condition of interference persists, said transmission power of the satellite antenna (31) in such a way that it does not exceed said pre-defined power.

6. The system of claim 5, further comprising:

• a receiver (34) of a satellite location system, said receiver (34) being configured to compute a position of the train and being coupled with said central control unit (33); and

• an electronic archive (35) , configured to store a plurality of pre-determined geographical areas in which respective terrestrial radio-communication systems are present, said electronic archive (35) being coupled with said central control unit (33); said central control unit (33) being further configured to:

• determine said condition of interference on the basis of the position of the train computed by the receiver (34) and of said pre-determined geographical areas stored in said electronic archive (35) .

7. The system of claim 6, wherein said central control unit (33) determines said condition of interference when the position of the train computed by the receiver (34) is within one of said pre-determined geographical areas stored in the electronic archive (35) .

8. The system of claim 5, further comprising:

• a low-directivity antenna (36) placed on the roof of the train, configured to receive signals in the given radiofrequency band and coupled with said central control unit (33'); said central control unit (33') being further configured to:

• determine said condition of interference when a power of a signal received by said low-directivity antenna (36) satisfies a given condition.

9. The system of claim 8, wherein said central control unit (33') determines said condition of interference when the power of the signal received by said low-directivity antenna

(36) is higher than or equal to a pre-defined threshold.

10. The system according to any claim 6-9, wherein said central control unit (33; 33') determines said condition of interference also on the basis of a speed of the train and of the radiation pattern of the satellite antenna (31) .

11. The system according to Claim 3 and any one of claims 5-10, further comprising:

• an on-board communication network (32) installed inside the train, coupled with said central control unit (33; 33') and configured to communicate with a plurality of electronic devices present inside the train; said central control unit (33; 33') being further configured to :

• as long as said condition of interference persists, store data that arrive from said on-board communication network (32) and that are to be transmitted to the satellite; and

• when said condition of interference terminates, transmit to the satellite said stored data.

12. An electronic processor configured to implement the central control unit (33; 33') of the satellite communication system (30; 30') according to any claim 5-11.