SYSTEM FOR EXTENDING BI-DIRECTIONAL SATELLITE RADIO COMMUNICATIONS IN TUNNELS
The invention relates to a communication system that relays a satellite signal inside tunnels and relays the signals transmitted inside said tunnels towards the satellite, in such a way as to assure to vehicles transiting inside the tunnels a perfect transmission and reception quality even in the absence of satellite visibility.
The system is based on a fixed terminal, for gallery illumination, connected to a fixed satellite station, and on a mobile terminal installed on the vehicle, connected to a mobile satellite terminal.
The system automatically effects a switching action between satellite channel and radio channel in the tunnel, and vice versa, to assure the continuity of the vehicle-satellite link.
The system finds elective application for railway vehicles.
FIELD OF APPLICATION
The invention enables to exchange digital and/or analogue signals by means of a radio link between a mobile terminal apparatus positioned on a vehicle and a satellite, in the absence of vehicle-satellite visibility. The invention enables to overcome the problems of total interruption of the vehicle-satellite link when the vehicle enters a gallery.
The invention finds application in the railway industry to assure to one or more trains the continuity of the transmission and reception of analogue and/or digital signals even while travelling in tunnels. Its use can also be extended to other vehicles and/or urban areas characterised by the presence of obstacles that prevent the visibility of the satellite. The invention is particularly advantageous for via satellite links from and to the train, because it enables: a) to provide services without interruptions, even broadband, e.g. multi-channel digital television, or which require interaction between passenger and terrestrial network (e.g. Internet, email), even when the train travels through tunnels and, more in general, in areas where the satellite is not visible; b) to exchange data between train and terrestrial service centre, e.g. data for managing the train's travel, even during travel through tunnels and, more in general, in areas where the satellite is not visible.
STATE OF THE ART
A known system for communicating via radio in tunnels is GSM-R, which allows solely the telephony service based on the well known standard GSM. This system, by its intrinsic nature, is not able to support broadband services, which are instead delivered even inside runnels thanks to the invention described herein.
The GSM-R system allows to transmit via radio only signals transiting through its terrestrial network nodes: therefore, it does not enable to relay satellite signals from/to trains transiting through tunnels, which instead is made possible thanks to the invention described herein. Moreover, GSM-R enables exclusively to transmit digital signals in GSM format, whereas the invention described herein enables to retransmit digital signals of any format, e.g. of the family of the Digital Video Broadcasting (DVB) standards or GSM, UMTS and other future standards, and of analogue signals.
The invention described in the patent JP2171037 (Satellite communication system in tunnel) has the object of extending to the interior of a tunnel a terrestrial radio communication to a mobile object. In the patent JP2171037, the signal transmitted by a terrestrial base station and received by the train outside the gallery is simultaneously transmitted also to a satellite and relayed thereby to a repeater positioned in proximity to the tunnel. The train inside the tunnel receives the signal retransmitted by said repeater. Unlike the solution described in the patent JP2171037, the present invention confronts the problem of assuring the extension of a satellite communication, which engages the train in satellite visibility areas, even when the train enters into and transits through a tunnel. The patent JP2171037 only confronts the case of one-directional communication to the train, whilst the present invention also supports two-directional communications, which would not be obtainable with the apparatus of the patent JP2171037. The invention disclosed herein is based on a particular configuration of the transceiver apparatus equipping the mobile object, which enables to support two-directional communication both in areas with satellite visibility and during travel in tunnels. Moreover, the invention disclosed herein is also based on a method for the automatic switching from the satellite channel to the radio channel available in the tunnel, and vice versa, with related method for managing the carrier frequencies of the channels, in order to assure the extension of two-directional communication also to multiple trains simultaneously transiting inside the same tunnel, avoiding interference phenomena between the channels used by different trains. These functionalities of two-direction communication and management of the automatic
switching between channels cannot be obtained with the solution of the patent JP2171037.
The problem of extending a mobile radio communication in tunnels by means of radio repeaters is also confronted in the patent JP 11112409 (Radio relay system for mobile communication). However, said patent only considers terrestrial radio signals transmitted from base stations with visibility of the repeater system that operates in tunnels. The invention disclosed in the patent JPl 1112409 does not provide for use of the satellite and, moreover, it does not propose solutions for the automatic switching of the mobile terminal between the two radio channels present outside and inside the tunnel; consequently, the solution described in the patent JPl 1112409 cannot support satellite communications, which instead are assured also inside tunnels thanks to the invention described herein.
The patent application JP2001230718 (Gap filler device for satellite broadcasting system and satellite broadcasting system) proposes a satellite communication system for areas with poor reception of satellite signals, which uses a receiving satellite apparatus and a transmitter apparatus connected by means of coaxial cable. Said system supports only one-directional communications (broadcast signals) and provides no solutions to the problem of the configuration of mobile terminals which have to operate in such a context. Moreover, the application JP2001230718 proposes no solutions for the automatic switching of the terminal from the satellite radio channel to the radio channel relayed by the gap filler system, and vice versa. All these problems are instead solved by the invention described herein.
Similar considerations can also be repeated for the patent application JP2001308765 (Gap filler system for tunnel, and device for reception and device for transmission used in the gap filler system). Said patent proposes a solution for extending a satellite signal broadcast inside tunnels through a communication system formed by a satellite receiver antenna, positioned outside the tunnel, and a plurality of ratio transmitter units inside the tunnel with fibre optic connection.
Solutions for relaying broadcast satellite signals are also proposed in the patent applications US2005059343 (Apparatus and method for identifying a gap filler in a satellite broadcasting system) and JP2004312349 (Satellite mobile broadcasting system and ground repeater). These solutions provide only receiving terminals and hence do not solve the problem of assuring two-directional communications from and to a mobile terminal. The systems for relaying the satellite signal are based on a regenerative approach comprising signal demodulation and re-modulation operations, and therefore the solutions
are only valid for digital signals using particular and specific wave forms. The solution proposed herein instead is based on a transparent approach which adopts only amplification, carrier frequency conversion and signal filtering operations and therefore can support both analogue and digital signals with generic wave form, which allows an evident improvement and expansion of functionality with respect to the aforementioned patents. Moreover, the inventions described in the applications US2005059343 and JP2004312349 do not solve the problem of the automatic switching of the mobile terminal from the radio channel of the satellite signal to the radio channel of the relayed signal, and vice versa, which are instead solved with the invention described herein. The above considerations also apply for the patent application JP2005123901 (Gap filler system) which proposes a regenerative system for relaying only one-directional digital signals which provide for the use of particular and specific wave forms, whereas the invention described herein enables to support both analogue and digital signals with generic wave form, allows to use two-directional signals and communications and solves the problem of automatic switching between the radio channel of the satellite signal and the radio channel of the relayed signal, hence providing new and extended functionalities which axe not otherwise obtainable.
Additional solutions for relaying satellite signals to mobile terminals located in areas of non visibility of the satellite are described in the patent application JP2003332964 (Satellite broadcast system, gap filler, monitor, auxiliary unit and satellite broadcasting method), in the patent JPl 1261999 (Satellite-mobile object broadcasting system, repeater and reception terminal) and in the patent application JP2002050993 (Satellite broadcasting system). AU three satellite signal repeater systems described therein are proposed to operate with receiving-only mobile terminals and broadcast satellite transmissions. Therefore the described solutions do not solve the problem of supporting two-directional communications from and to a mobile terminal, which are instead assured by the invention described herein.
Lastly, also with respect to the patent applications JP2002190760 (Satellite digital sound broadcasting system, and ground station, satellite and earth station in this system) and JP2002190758 (Multi-antenna system for mobile object), which described broadcast satellite signal repeater systems which exclusively support one-directional communications, considerations similar to the previous ones apply, in that the present invention enables to operate on a far broader range of signals and types of
Communications, such as two-directional and/or interactive communications, with an evident improvement over the prior art.
SUMMARY OF THE INVENTION The invention enables to extend the radio link between a moving vehicle and a satellite even in areas in which, due to obstacles of various kinds, the visibility of the satellite is precluded. In the description, reference is made to the railway environment, considering a train transiting along a path characterised by the presence of tunnels. The invention can also be applied to other environments, such as urban areas and / or other vehicles.
The system is based on a fixed terminal, for gallery illumination, connected to a fixed satellite station, and on a mobile terminal installed on a train and connected to a mobile satellite terminal.
In the satellite to train connection, the fixed external satellite station receives the satellite signal transmitted by the satellite and directed to the train and relays it inside the tunnel through the fixed terminal. In the direction of the train-satellite connection, the fixed terminal receives the signal transmitted by the train and directed to the satellite and relays it outside the runnel through the fixed external satellite station.
The train is equipped with a transceiver apparatus, called mobile terminal, connected to the mobile satellite terminal. The latter enables to exchange signals directly with the satellite in the periods when there is visibility between train and satellite, i.e. when the train travels in open spaces without the presence of obstacles. When the train, because of its motion, abandons an area of visibility of the satellite and enters a tunnel, the system automatically accomplishes a switch between the satellite channel and the radio channel available in the tunnel, which carries the same satellite signal, but on a different carrier frequency. Similarly, when the train exits the gallery and enters an area of visibility of the satellite, the system automatically accomplishes a switch between radio channel available in the tunnel and satellite channel.
The switching between channels takes place according to a logic that process the information on the quality of the channels and decides which of them to use.
The carrier frequencies of the satellite channel and of the channel in the tunnel in the satellite-train direction are mutually linked by a defined frequency conversion relationship. Similarly, the carrier frequencies of the satellite channel and of the channel in
the tunnel in the train-satellite direction are mutually linked by a defined frequency conversion relationship.
The system enables to effect the switching between satellite channel and channel in tunnel without loss of information perceptible by the user, for any velocity of travel of the train.
The invention is described herein with reference to an embodiment, which is described for illustrative, non limiting purposes.
DESCRIPTION OF FIGURES FIG. 1 : Block diagram of the fixed transmission and reception system in tunnel.
FIG. 2: Block diagram of the filtering and equalisation device on the return channel.
FIG. 3A: Block diagram of the receiving and transmitting chains of the mobile terminal and of their integration with the mobile satellite terminal, in case of switching on the receiving chain effected on analogue signals.
FIG. 3B: Block diagram of the receiving and transmitting chains of the mobile terminal and of their integration with the mobile satellite terminal, in case of switching on the receiving chain effected on demodulated signals.
FIG. 3C: Block diagram of the receiving and transmitting chains of the mobile terminal and of their integration with the mobile satellite terminal, in case of switching on the receiving chain effected on decoded and formatted signals.
FIG. 4A: Operating logic flow of the switching control device, for switching on the receiving chain effected on analogue or demodulated signals.
FIG. 4B: Operating logic flow of the switching control device, for switching on the receiving chain effected on decoded and formatted signals.
DETAILED DESCRIPTION OF THE INVENTION IN ONE OF ITS REALIZATION FORM
Figure 1 illustrates the block diagram of the transmission and reception system relating to the fixed terminal, which extends the satellite connection in tunnel, connected to the external fixed satellite station. The system is able:
• to receive from the mobile terminals installed on the trains a number N of signals on N carrier frequencies (FRAl, FRA2,..., FRAN) and to relay them to the satellite
on N different carrier frequencies (FRDl, FRD2, ..., FRDN);
• to receive from the satellite a number M of signals on M carrier frequencies (FFAl, FFA2,...,FFAM) and to relay them to mobile terminals installed on the trains on M different carrier frequencies (FFDl, FFD2,...,FFDM). The system is described herein with reference to the case N=3 and M=I (the carrier frequency of the signal transmitted by the satellite is designated FFA and the carrier frequency of the same signal relayed inside the tunnel is designated FFD); however, the invention is compatible with a higher number of signals N and number of signals M.
With reference to Figure 1, the operation of the system is described as follows: 1. The signals RSAl, RSA2, RSA3 transmitted by the mobile terminals on the trains and having band occupation BRl, BR2, BR3 Hertz around the carrier frequencies FRAl, FRA2, FRA3, respectively, are received by the antenna in the tunnel (AG) and made to pass through the low noise amplifier block of the terminal in the tunnel (LNBG) obtaining the signals RSBl, RSB2, RSB3, having the same band occupations BRl, BR2, BR3 Hertz around the carrier frequencies FRBl, FRB2, FRB3 less than FRAl, FRA2, FRA3, respectively.
2. The signals RSBl, RSB2, RSB3 are made to pass through the filtering and equalisation device (FER) obtaining the signals RSCl, RSC2, RSC3 having band occupations BRl, BR2, BR3 Hertz around the carrier frequencies FRCl, FRC2, FRC3 and equal level of power P.
3. The signals RSCl, RSC2, RSC3 are made to pass through the amplifier block of the fixed satellite station (BUGS) obtaining the signals RSDl, RSD2, RSD3 having band occupations BRl, BR2, BR3 Hertz around the carrier frequencies FRDl, FRD2, FRD3 greater than FRCl, FRC2, FRC3, respectively and irradiated to the satellite through the external antenna (AE).
4. The signal FSA transmitted by the satellite and having band occupation BF Hertz around the carrier frequency FFA is received by the external antenna (AE) and made to pass through the low noise amplifier block of the fixed satellite station (LNBS) obtaining the signal FSB having the same band occupation BF Hertz around the carrier frequency FFB less than FFA.
5. The signal FSB is made to pass through the filtering device (FF) obtaining the signal FSC having band occupation BF Hertz around the carrier frequency FFC.
6. The signal FSC is made to pass through the amplifier block of the fixed
terminal in the tunnel (BUCG) obtaining the signal FSD having band occupation BF Hertz around the carrier frequency FFD greater than FFC and irradiated to the mobile terminals on the trains through the antenna in the tunnel (AG).
The carrier frequencies on which the signals RSAl, RS A2, RS A3, FSD are transmitted inside the tunnel (between mobile terminal on the train and fixed terminal installed in the tunnel) and the signals RSDl, RSD2, RSD3, FSA outside the tunnel are linked by the following relationships:
• Satellite-train connection: FFA=FFD+FFfissata where FFfissata indicates a constant quantity. • Train-Satellite connection: FRAl=FRDl+FRfissata, FRA2=FRD2+FRfissata,
FRA3=FRD3+FRfissata where FRfissata indicates a constant quantity.
Figure 2 shows a possible embodiment of the filtering and equalisation device on the train-satellite channel (FER in Figure 1). With reference to Figure 2, the operation of the device is described as follows: • The signals RSBl, RSB2, RSB3 are made to pass through the frequency measuring device (RDF) which determines the carrier frequencies FRBl, FRB2, FRB3 around which the signals were received.
• The signals RSBl5 RSB2, RSB3 are replicated on the three branches Rl5 R2, R3 which connect the frequency measuring device (RDF) to the three power measuring devices (RPl5 RP2, RP3).
• The frequency measuring device (RDF) generates three signals:
The signal SFl that carries the information about the carrier frequency FRBl around which the signal RSBl is transmitted, which is passed on to the power measuring device (RPl) and channel isolator and equaliser (ICEl) devices. - The signal SF2 that carries the information about the carrier frequency
FRB2 around which the signal RSB2 is transmitted, which is passed on to the power measuring device (RP2) and channel isolator and equaliser (ICE2) devices.
The signal SF3 that carries the information about the carrier frequency FRB3 around which the signal RSB3 is transmitted, which is passed on to the power measuring device (RP3) and channel isolator and equaliser (ICE3) devices.
• The power measuring device RPl lets the signal RSBl pass unaltered, determines its power level and communicates it, through the signal SPl, to the channel isolator and equaliser ICEl.
• The power measuring device RP2 lets the signal RSB2 pass unaltered, determines its power level and communicates it, through the signal SP2, to the channel isolator and equaliser ICE2.
• The power measuring device RP3 lets the signal RSB3 pass unaltered, determines its power level and communicates it, through the signal SP3, to the channel isolator and equaliser ICE3.
• The channel isolator and equaliser ICEl isolates the signal RSBl with bandwidth occupation BRl around the carrier frequency FRBl and equalises its power the level P: the resulting signal is RSBleq. • The channel isolator and equaliser ICE2 isolates the signal RSB2 with bandwidth occupation BR2 around the carrier frequency FRB2 and equalises its power the level P: the resulting signal is RSB2eq.
• The channel isolator and equaliser ICE3 isolates the signal RSB3 with bandwidth occupation BR3 around the carrier frequency FRB3 and equalises its power the level P: the resulting signal is RSB3eq.
• The controller and frequency converter device (CCF) combines the three signals RSBleq, RSB2eq, RSB3eq and generates, through a frequency conversion, the signals RSCl, RSC2, RSC3 at the frequencies FRCl, FRC2, FRC3, respectively.
Figure 3 A, Figure 3B and Figure 3 C illustrate three possible embodiments of the block diagram of the transmission and reception system relating to the mobile terminal installed on the trains. In all three embodiments, the system is able:
• to receive from the fixed terminal installed in the tunnel a signal on a carrier frequency (FFD).
• To transmit to the fixed terminal installed in the tunnel a signal on a carrier frequency (FRA).
Figure 3A, Figure 3B and Figure 3C illustrate the possible embodiments of the reception and transmission chains of the mobile terminal and of their integration with the mobile satellite terminal. The three embodiments are possible according to whether the switching on the reception chain takes place on analogue signals (Figure 3A), demodulated digital signals (Figure 3B) or decoded and formatted digital signals (Figure 3C).
With reference to Figure 3 A, the operation of the system is described as follows: 1. The digital signal TX at the output of the formatting and coding device (COD), obtained transforming the Txdec signal, is used to modulate, through a modulator (MOD),
a transmission carrier frequency FTXl obtaining the bandwidth BXl signal TXl .
2. The signal TXl is made to pass through the transmission switching device (TXCOM) which routes the aforesaid signal on the branch Rl which connects the radio frequency block of the mobile satellite terminal (RFS), or on the branch R2 which connects the amplifier block of the mobile terminal in the tunnel (BUC).
3. The transmission switching device (TXCOM) is commanded by a switching control device (CCl) through the control signal SCl which indicates on which branch (Rl or R2) the signal is to be routed.
4. If the selected branch is Rl, the signal TXl is made to pass through the radio frequency block of the mobile satellite terminal (RFS) and thereby converted to the carrier frequency
FTX2S, amplified and irradiated through the antenna of the mobile satellite terminal (ATS) to the satellite.
5. If the selected branch is R2, the signal TXl is made to pass through the amplifier block of the mobile terminal in the tunnel (BUC) and thereby converted to the carrier frequency FTX2G=FRA, amplified and irradiated through the antenna of the. mobile terminal in the tunnel (ATG) to the fixed terminal in the tunnel.
6. The switching control device (CCl) implements the switching logic and decides which transmission and reception chain to use (mobile terminal for tunnel or mobile satellite terminal) according to the channel availability information received from the mobile terminal for tunnel and from the mobile satellite terminal through the signals SC3 and SC4, respectively.
7. If the satellite is visible, the signal RX2S irradiated on the carrier frequency FX2S is received by the antenna of the mobile satellite terminal (ATS), transformed by the radio frequency block of the mobile satellite terminal (RFS) into the signal RXlS and passed on the carrier frequency FXlS less than FX2S, through the branch R4, to the reception switching device (RXCOMl).
8. If the satellite is not visible and the mobile terminal is in the area of coverage of the fixed terminal installed in the tunnel, the signal RX2G irradiated on the carrier frequency FX2G=FFD is received by the antenna of the mobile terminal in the tunnel (ATG), transformed by the low noise figure block of the mobile terminal in the tunnel (LNB) into the signal RXlG and passed on the carrier frequency FXlG less than FX2G to the power measuring device (RP).
9. The signal RXlG travels through the power measuring device (RP) which computes its
power level that is communicated through the control signal SC3 to the switching control device (CCl) and reaches, through the branch R3, the reception switching device (RXCOMl).
10. The reception switching device (RXCOM) is commanded by the switching control device (CCl) through the control signal SC2 which indicates which analogue input signal
(branch R3 or branch R4) has to go through to the output (signal RXl).
11. The signal RXl at the output of the reception switching device (RXCOMl) is transformed into the signal RX by the demodulation device (DEM).
12. The signal RX at the output of the demodulation device (DEM) is transformed into the signal RXdec by the decoding and formatting device (DEC).
With reference to Figure 3B, the operation of the system is described indicating its differences with respect to the operation of the system described in Figure 3A. The operation of all the parts of the system that are not specified hereafter is to be construed as identical to what is described with reference to Figure 3 A: 1. The signal RXlS at the output of the radio frequency block of the mobile satellite terminal (RFS) is transformed into the signal RXS by the demodulation device for the satellite channel (DEMS) and passed on the branch R4 to the reception switching device (RXCOM2).
2. The signal RXlG at the output of the power detection device (RP) is transformed into the signal RXG by the demodulation device for the tunnel channel (DEMG) and passed on the branch R3 to the reception switching device (RXCOM2).
3. The reception switching device (RXCOM2) is commanded by the switching control device (CCl) through the control signal SC2 which indicates which analogue input signal (branch R3 or branch R4) has to go through to the output (signal RX). With reference to Figure 3C, the operation of the system is described indicating its differences with respect to the operation of the system described in Figure 3B. The operation of all the parts of the system that are not specified hereafter is to be construed as identical to what is described with reference to Figure 3B:
1. The signal RXS at the output of the demodulation device for the satellite channel (DEMS) is transformed into the signal RXdecS by the decoding and formatting device for the satellite channel (DECS) and passed on the branch R4 to the reception switching device (RXCOM2).
2. The signal RXG at the output of the demodulation device for the tunnel channel
(DEMG) is transformed into the signal RXdecG by the decoding and formatting device for the tunnel channel (DECG)and passed on the branch R3 to the reception switching device (RXC0M2).
3. The reception switching device (RXC0M2) is commanded by the switching control device (CC2) through the control signal SC2 which indicates which analogue input signal
(branch R3 or branch R4) has to go through to the output (signal RXdec).
4. The switching control device (CC2) implements the switching logic and decides which transmission and reception chain to use (mobile terminal for tunnel or mobile satellite terminal) according to the channel availability information received through the signals SC3 and SC4, coming from the decoding and formatting device for the tunnel channel (DECG) and from the decoding and formatting device for the satellite channel (DECS), respectively.
The switching control device (CCl) used in the case of mobile terminal with reception switching effected on analogue signals (Figure 3A) and demodulated signals (Figure 3B) operates according to the logic described in Figure 4A.
The switching control device (CC2) used in the case of mobile terminal with reception switching effected on decoded and formatted signals (Figure 3C) operates according to the logic described in Figure 4B.