Satellite communication system, leo satellite relaying communications between a geo satellite and terrestrial stations, the uplinks and downlinks using the same frequency band and time-division multiplexing

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 SYSTEM OF COMMUNICATION BY SATELLITE, A SATELLITE in LEO that is RELAYING COMMUNICATIONS BETWEEN A SATELLITE in GEO, AND TERRESTRIAL STATIONS, THE UPLINKS AND DOWNLINKS USING THE SAME FREQUENCY BAND AND TIME-division MULTIPLEXING Field of the invention The invention pertains to the field of data transmission systems at great distance.

It relates more particularly to systems and methods for data communications (data transfer, remote monitoring terminals...) between users with small mobile terminals.

Background of the invention and problem posed The question of the transmission of data to a large distance from or to a mobile device, and is particularly for connections between computers ( machine to machine or M2M).

This area of transmission is characterized by a data rate much lower than that of links of type image or Internet, and/or by the ability to use a link intermittent rather than continuous.

We know a first approach to this problem, followed by existing systems of data transmission, such as Orbcomm and Argos, which use constellations of satellites in low earth orbit (LEO English Low Earth Orbit ).

In this approach, the normal mode of operation of each satellite in low earth orbit LEO requires it to be, on the one hand visibility simultaneous with a ground station for control and connection, and on the other hand of a user terminal.

The satellite then serves as a link of communication between the two parties, and the latency of acknowledgments and messages is a function of the distance between the satellite and the ground station (GES English Gateway Earth Station ).

However, the coverage provided by the network of ground stations systems using satellites in low-earth orbit, such as Orbcomm and Argos, is limited by the deployment of stations soils (GHG) emissions and the existing systems provide only a limited coverage of the Earth in this mode.

Each ground station allows coverage over a radius of about 3000 km, and each of these systems has a twenty ground stations.

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 2 then We find easily that the coverage areas have large areas of white for which the system is not usable.

These areas cover, in particular, a large proportion of the areas of the ocean, or even a significant portion of continental areas such as Africa or Australia.

In the case for which the satellite LEO has no visibility of both the user terminal and the control station ground (GHG) emissions, it is necessary to use a method of communication storage and shipment (known method of skilled in the art under the name store & forward ).

In this method, the message is stored on board the satellite, which continues its travel on its orbit until it overflies the ground station GES to which it delivers the message stored.

With this method of operation, the times of communications are long and make it difficult to make two-way communications on acceptable terms, given that the delays are typically between a few minutes and the 100 to 150 minutes of duration of a complete orbit of the satellite LEO.

We know also examples of telecommunication systems with hybrid for the transmission of data between users.

These hybrid systems are composed of geostationary satellites and a constellation of satellites in low earth orbit.

These include a first patent document US 6208625.

This document describes a network of LEO satellites and geostationary orbit (GEO) can communicate with each other.

On the ground, user terminals are capable of reception / transmission (Rx/Tx) with LEO satellites and GEO.

The component LEO performs a filtering of the traffic received from the terminals, and according to the urgency of the traffic received, it needle this traffic either internally to the LEO or to the GEO.

In a second patent document EP 0883252, it is proposed a satellite communication system allowing a global coverage, a reduction in the transmission delay (Tx), and maximizing the use of the capacity of the system (satellite communication broadband by interconnecting multiple constellations in medium earth orbit ME0 and geostationary-GEO ).

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 3 satellites ME0 and GEO to communicate directly between themselves by inter-satellites, which allows a routing of the traffic (voice and data) on board satellites according to certain rules.

In addition, this paper proposes a sharing and reuse of spectrum between GEO satellites and ME0 to very high frequencies (eg between 40 and 60 GHz), in order to allow the function known under the name of seamless handover for mobile terminals (passage of a mobile network to a fixed network without interruption of communications in progress).

It is clear that the hybrid systems today are of great complexity, synonym of high cost of implementation and use.

Objectives of the invention An objective of the invention is to provide a solution based on satellite transponders as simple as possible, offering good performance (link budget, availability) within the coverage area of each satellite.

Disclosure of the invention According to a first aspect, the present invention relates to a payload of a satellite repeater of a telecommunications system, said satellite repeater being intended to be placed in orbit scrolling above the surface of a celestial body, and the payload being configured to repeat data received from a satellite stationary above the surface of the celestial body towards a terminal substantially at the surface of the celestial body, and to repeat data received from the terminal to the satellite stationary.

Said payload is further configured to :

- use the same frequency band for repeating data towards the satellite is stationary, the so-called broadcast rising , and for repeating data towards the terminal, the so-called show-down , and - multiplex in time the emissions rising emissions and top-down.

Such provisions allow a better sharing of the power onboard the satellite repeater.

In addition, such provisions serve to optimize the architecture of the payload to reduce the manufacturing cost, footprint, and/or the launch mass.

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 4 It is important to note what is meant by terminal substantially at the surface of the celestial body , in particular the terminals of users terrestrial, maritime or aeronautical.

Similarly, these terminals are allowed, for example, be placed in a means of terrestrial, maritime or aeronautical.

We give below, of particular modes of realization of the payload of the satellite repeater. The invention aims also to all the combinations technically possible of these particular modes of realization.

According to a particular mode of implementation, the payload includes at least one power amplifier, and said payload is configured to use said power amplifier both for emissions rising, and for emissions top-down.

According to a particular mode of implementation, the payload includes :

- at least one transmit antenna uplink, - at least one transmitting antenna that is top-down, with the means to route a signal at the output of the power amplifier, representative of data to be repeated, either to said transmitting antenna rising to either said transmitter antenna down.

According to a particular mode of implementation, the payload includes means for multiplexing, at the input of the power amplifier, the signals of emissions rising signals and emissions top-down.

According to a particular mode of implementation, the payload includes :

- multiple transmit antenna downlink, the means to route a signal at the output of the power amplifier, representative of data to be repeated, to any of said transmit antenna backward.

According to a particular mode of realization, the payload is configured to use the same frequency band, used for emissions rising, and the emission top-down, for the reception of data to be repeated from the terminal, said reception uplink , and for reception of data to repeat the satellite stationary, said receiving trough .

According to a particular mode of implementation, the payload includes several receiving antennas uplink, and said payload is configured CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 to receive simultaneously on each of said receiving antennas rising.

According to a particular mode of realization, the payload is configured to multiplex in time the emissions rising and receptions 5 rising, and/or to multiplex in time the emissions down and the receptions top-down.

According to a particular mode of realization, the payload is configured to use a same first sub-frequency band of the frequency band for the receptions rising emissions and rising, and use a same second sub-frequency band of the frequency band for receptions, top down programming top-down.

According to a particular mode of realization, the payload is configured to perform receptions rising simultaneously to the emissions top-down, and to make the receptions top-down simultaneously with emissions rising.

According to a second aspect, the present invention relates to a telecommunications system, intended for the transfer of data between at least one terminal, situated substantially on the surface of a celestial body, and at least a satellite stationary above the surface of the celestial body.

The system includes one or more satellite transponder signals, said satellite repeater scrolling above the surface of the celestial body and comprising a payload consistent with the invention.

We give below, of particular modes of realization of the telecommunications system. The invention aims also to all the combinations technically possible of these particular modes of realization.

According to a particular mode of realisation, it uses the same frequency band for communications between the terminal and the constellation of satellite transponders for communications between the satellite stationary, and the satellite repeater.

Preferably, when the terminal is in the coverage area of the satellite is stationary, it also uses the same frequency band for direct communications between the terminals and the satellite is stationary.

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 6 This provides a significant advantage compared to solutions of the prior art.

The frequency band used by the system can be located in any of the bands allocated to telecommunications services by satellite (of low frequency bands, for example UHF or VHF, up to high frequencies such as the bands Ka, or Q).

Preferentially, the frequency band used is the L band (between 0.9 and 2.0 GHz) which is more particularly suitable for mobile communications by satellite.

According to a particular mode of implementation, the system includes at least one ground station connection of the satellite stationary.

The communications between the ground and the satellite repeaters are insured by the intermediary of the satellites stationary stations, and connection of these satellites stationary.

These communications include both data exchanges between users and potentially the communication of remote control and telemetry means of rehearsal space.

This embodiment therefore does not require the use of ground station connection assigned to the satellite transponders.

According to a particular mode of realization, at least one satellite repeater is placed in polar orbit or quasi-polar (inclination of the orbit above 70 ) around the celestial body.

According to a particular mode of realization :

- at least one satellite repeater includes means to perform an amplification without translation frequency of the signal received from the satellite stationary, - the air interface used is an interface type CDMA (from the English Code Division Multiple Access) , and at least one terminal comprises means of managing the arrival of two signals with differences of time delay and Doppler.

In this case, preferentially, the means to manage the arrival of two signals with differences in delay and Doppler, the terminal device is a receiver type Rake , the well-known man of the art.

According to a particular mode of realization :

- the air interface type is TDMA, the system uses two separate signals : one for the satellites CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 7 stationary and one for satellite transponders, - a time-division multiplexing is used to distribute the capacity between the satellite stationary satellite and repeaters at intervals of guard and a pre-compensation of the Doppler at the level of the satellite repeaters.

According to a particular mode of realization, at least one terminal includes means to use the spatial diversity techniques or MIMO (Multiple Input Multiple Output) for recombining the signals from both a satellite is stationary, and a satellite repeater.

According to a particular mode of realization :

- at least one satellite repeater relays the signal, transparently or regenerative, with no translation of frequency of the received signal, and - the air interface comprises means of limiting interference at a terminal, between the signals from a satellite-stationary and the signals relayed by a satellite transponder.

According to a particular mode of realization :

- at least one satellite repeater relays the signal, transparently or regenerative, in an adjacent channel, before its retransmission, and the telecommunications system comprises a coordinating entity for coordinating the frequency plans between the satellites stationary and the satellites transponders.

According to a third aspect, the present invention relates to a method of telecommunication intended for the transfer of data between a terminal, situated substantially on the surface of a celestial body and a satellite stationary above the surface of the celestial body, the transfer of data between said terminal and said satellite is stationary is carried through a satellite repeater configured to repeat data received from said satellite is stationary to said terminal and to repeat data received from said terminal to said satellite is stationary.

In addition :

- the satellite repeater uses the same band of cutresult for CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 8 repetition of data to the satellite is stationary, the so-called broadcast rising , and for repeating data towards the terminal, the so-called show-down , - the satellite repeater multiplex in time the emissions rising emissions and top-down.

We give below, of particular modes of implementation of the process of telecommunications. The invention aims also to all the combinations technically possible of these particular modes of implementation.

According to a particular mode of implementation, the satellite repeater uses the same power amplifier for both emissions rising emissions and top-down.

According to a particular mode of implementation, the satellite repeater uses the same frequency band, used for emissions rising, and the emission top-down, for the reception of data to be repeated from the terminal, said reception uplink , and for reception of data to repeat the satellite stationary, said receiving trough .

According to a particular mode of implementation, the satellite repeater multiplex in time the emissions-tops and reception tops, and/or said satellite repeater multiplex in time the emissions down and the receptions top-down.

According to a particular mode of implementation, the satellite repeater at the same time the emissions to the descending and receptions rising, and at the same time emissions are rising and receptions descending.

According to a particular mode of implementation, the satellite repeater uses the same first sub-frequency band of the frequency band for the receptions rising emissions and rising, and uses a same second sub-frequency band of the frequency band for receptions, top down programming top-down.

Brief description of the figures The purposes and advantages of the invention will be better understood on reading the description and the figures of particular modes of implementation, given CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 9 examples are non-limiting, and for which the figures represent :

- Figure 1 : the general architecture of the system, - Figure 2 : illustration of the positions of satellites scrollable LEO and stationary GEO on a planisphere, at a given moment, - Figure 3 : a table of the orders of magnitude of delays between the signals from a satellite and a stationary GEO satellite scrolling LEO for various altitudes of orbits LEO, - Figure 4 : coverage areas of the satellites scrollable LEO and stationary GEO of the constellation described, - Figure 5: an example of the use of a frequency band in a system according to the invention, - Figure 6 : a schematic representation of a payload of a satellite scrolling LEO according to a preferred mode of realization, - Figure 7a and 7b: examples of time-division multiplexing of communications between a user terminal, a satellite, scrolling, LEO, and a satellite stationary GEO - Figure 8 : a schematic representation of a payload according to a variant of the embodiment of figure 6, In these figures, references that are identical denote elements that are identical or similar.

Detailed Description of embodiments of the invention, The architecture of a telecommunications system according to the invention is illustrated by figures 1 and 2.

As we can see on these figures, the proposed system uses two satellite constellations.

The first constellation is composed of one or more satellites in stationary (also called GEO in the remainder of the description).

In this case, the system described here by way of example but not limited to, is based on a constellation of three satellites in stationary GE01, GE02, GE03 placed in geostationary orbit above the three continental areas are the main (eg the longitudes 265 E, 25 E, 145 E, respectively, as shown in figure 2).

The satellites stationary GE01, GE02, GE03 operate in the band dite MSS L (1.5/1.7 GHz).

The constellation of satellites stationary GE01, GE02, GE03 is CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 controlled by one or more control stations land, arranged in order of the satellites stationary GE01, GE02, GE03 they control, which perform control functions and remote control.

The constellation of satellites stationary GE01, GE02, GE03 is connected 5 to telecommunication networks earth by one or more stations of connection to terrestrial GHG, arranged in order of the satellites stationary GE01, GE02, GE03 via a link FL (English Feeder Link) in a manner known in itself.

The system is completed by a second constellation of three 10 satellites scrolling in low earth orbit or medium (also called LEO) satellites, or satellites, MEO), with orbits of altitudes typically between 400 and 20,000 km, acting as satellite transponders.

It is clear that the system can use a number larger or smaller satellites in each of the constellations of satellites scrollable LEO and stationary GEO, the difference being coverage of the Earth more or less complete.

In the example described here, the satellite rolls are assumed to be of the type moving in low orbit (known as LEO), and placed in sun-synchronous orbit at an altitude of 567 km with an inclination of 97.7 in three different orbital paths (with right ascension of the node the ascendant at 0 , 60 and 120 ).

We remind you that the sun-synchronous orbit is defined by the fact that each satellite scrolling returns after several orbits to the same point on the Earth at the same solar local time.

This system uses three satellites in low earth orbit : LE01, LE02, LE03, of which the traces of the orbits are illustrated on figure 2, as the example in no way limiting.

In this example, these three satellites scrolling in low orbit LE01, LE02, LE03, may be of the payloads onboard as a passenger on satellites whose primary payload is dedicated to another mission, such as, for example, the observation of the Earth.

It is clear that the constellation of satellites scrolling LE01, LE02, LE03, may include satellites moving in orbits of altitudes or inclinations different.

These satellites scrolling LE01, LE02, LE03, operate in the same frequency band as the satellites stationary GE01, GE02, GE03, and CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 11 in the present case, in the band MSS L (1.5/1.7 GHz).

The telecommunications system is available to any user, including mobile on the surface of the Earth, and has a terminal transmitter/receiver (also known as terminal REC).

In the example illustrated by figure 1, the system is directed in particular to a user equipped with a terminal transmitting/receiving REC1, transmitting or receiving data to or from another user, possibly himself with a terminal transmitting/receiving REC2, and also possibly mobile on the surface of the Earth. The user REC3 can also be connected to a terrestrial network (IP, PSTN, ...) and be connected to the user REC1 via the GES.

Each user terminal REC1 and REC2 is a transportable terminal, comprising in particular a user interface, e.g. keyboard, touch screen or data link to an electronic equipment, a battery and/or power supply, a processor and/or an electronic control, means of storing programs or data, and the means of transmitting and receiving signals, operating in the frequency band MSS L, in the present example described here, as in no way limiting.

Each user terminal REC1 and REC2 is endowed in this example of an omnidirectional antenna, adapted to receive signals from either of any satellites scrolling LE01, LE02, LE03 low-earth orbit, or any of the satellites stationary GE01, GE02, GE03 in geostationary orbit.

In the implementation described here, each user terminal REC1 and REC2 has to the way to go and a receiver type Rake , the well-known man of the art.

It is reminded that a receiver Rake is a radio receiver, designed originally to compensate for the attenuation due to the multipath of radio waves for terrestrial systems.

It is based on the concept that the reflected signals can be distinguished (typically in the case of a use of a technique of multiplexing CDMA) and thus can be combined in a proper way in taking then advantage of the multiple propagations.

For the way back, the satellites are stationary GEO are CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 12 supposed to be transparent to the receiver and Rake is positioned at the level of the GHG (stations, connection of the GEO satellites).

It is noted, however, that, in the case where the satellites stationary GEO would be regenerative, it would be necessary that they carry a receiver Rake (replacing the receiver placed at the GES).

A communication between two user terminals REC1, REC2 supposed to two satellites scrolling LE01, LE02, respectively, and a single satellite stationary GE01, involves several steps, as schematized in figure 1 :

- the first user terminal REC1 transmits a first signal to the first satellite scrolling LE01 in low-earth orbit - the satellite scrolling LE01, receives and amplifies the signal, If issued by the user terminal REC1 on the ground and transmits it in the form of signal S2 to the satellite stationary GE01 in geostationary orbit, the satellite is stationary GE01 receives the signal S2 and, if conditions allow, the signal If, and retransmits it in the form of a signal S3 toward the second satellite, scrolling LE02 in low orbit, either directly (with routing on board the satellite) or via the docking station EMISSIONS.

The signals Si and S2 are processed by means of a receiver Rake or edge (in the case of a routing edge) or at the level of the station GES (this solution is preferred for reasons of simplification of the implementation).

- the satellite scrolling LE02, receives and amplifies the signal S3 is emitted by the satellite stationary GE01 and transmits it in the form of signal S4 to user terminal REC2 on the ground.

- the user terminal REC2 receives the signal S4, and potentially the signal S3 if conditions permit.

A receiver Rake allows to recombine these two signals at the user terminal.

In a case involving user terminals in view of two satellites in stationary different GE01, GE02, the link between the two terminals CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 13 users also includes a communication segment between these satellites, for example but not limited to, through the stations connection gas (GHG) and links to ground or via a direct link inter-satellite GEO, if it exists.

We understand of course that it is also possible to achieve a communication of a user REC1 having a terminal transmitter/receiver mobile, with another user REC3 connected through a network of telecommunications traditional terrestrial (PSTN, IP, ...) via the docking station EMISSIONS.

In this case :

- the first user terminal REC1 transmits a first signal to the first satellite scrolling LE01 in low-earth orbit - the satellite scrolling LE01, receives and amplifies the signal, If issued by the user terminal REC1 on the ground and transmits it in the form of signal S2 to the satellite stationary GE01 in geostationary orbit, the satellite is stationary GE01 receives the signal S2 and potentially the signal and retransmits it in the form of signal S5 to the station connection GHG, - the docking station GES receives the signal S5 (combining when it is needed the signals Si and S2 contained in S5 by means of a receiver (Rake) and transmits it in the form of signal S6 to the user terminal REC3 on the ground via a ground network classic.

We note that, in figure 1, the direct links between user terminals REC1, REC2 and REC3 and the satellite stationary GE01 are not depicted to simplify the figure.

Different approaches can be envisaged for the repeater space on board a satellite scrolling LE01, LE02, LE03.

Or, preferably, a simple amplification without translation frequency of the signal received from the satellite stationary GEO.

However, this implies the use of an air interface capable of supporting the arrival of two signals with a few differences in delay and Doppler. It is by CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 14 example the case of an air interface type CDMA ( Code Division Multiple Access ) associated with a receiver Rake.

Or, alternatively, the use of two separate signals (one for the satellite and a stationary GEO and one for the satellite scrolling LEO).

For example, it is possible to use an air interface of type TDMA (Time Division Multiple Access), known per se, considering either a tdm to allocate capacity between the satellites scrolling LEO and stationary GEO (with intervals of guard and a pre-compensation of the Doppler at the level of the satellite scrolling LEO).

Alternatively or in addition, it is also possible to use two different channels of the frequency band (one for the satellite and a stationary GEO and one for the satellite scrolling LEO).

In the implementation described here as an example, the first approach has been selected because it offers a simple and effective solution.

It operates, in effect, the diversity of the satellites, since the signals from both satellites scrolling LEO and stationary GEO can be combined in a receiver Rake to obtain a better signal-to-noise ratio.

This technique, improvement of the signal-to-noise ratio, allows to obtain an error rate of transmission ( bit error rate ) lower, a lower transmitted power EIRP (Effective Isotropically Radiated Power), or a greater margin in the link budget.

In addition, for a user terminal REC, in order simultaneously to a satellite scrolling LEO and a satellite stationary GEO, if the propagation conditions result in the loss of a link to one of the satellites to which it is connected (due to the evolution of the geometry of the link with the satellite scrolling LEO varying as a function of time, or due to obstacles in the line of sight of one of the two satellites running LEO and stationary GEO), the other link can help maintain the communication.

This concept is simple amplification without translation frequency of the signal received from the satellite stationary GEO, can be implemented thanks to the possibility offered by the receiver is Rake, which is included in the user terminal REC, to combine different signals from different paths from a satellite scrolling LEO and a satellite stationary GEO.

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 In the scenario of data communications by satellite, which is the subject of this implementation, the component multi-paths is usually negligible.

In this case, the receiver Rake is used simply to combine multiple direct signals from 5 several satellites scrollable LEO and stationary GEO, since the different signals can be considered as components of multipath fictitious.

The received signals may then be combined in the terminal 10 user to the REC according to three main algorithms, known to those skilled in the art and therefore not described further here :

- by selecting the best signal (known under the English term " selection combining ), by a simple combination of equal signals (known as the 15 English term of equal gain combining ), or by a recombination-weighted signals to maximize the signal to total noise (known under the English term of Maximum Ratio Combining, or MRC).

This algorithm is the preferred solution because it is the most efficient in terms of signal-to-noise ratio obtained.

One of the key issues related to the combination of signals is that each path has a length of possibly very different due to the relative position of elements : user - satellite scrolling LEO satellite to a stationary GEO.

In order to balance the difference in propagation time, which also varies in time, buffers, appropriate data must be provided at the receiver Rake.

The sizing of these buffers depends on the difference of time in the worst case between different paths, and the maximum rate of data transfer used.

In the proposed system, the time difference remains less than 5 ms for the constellation of satellites scrolling LE01, LE02, LE03 considered.

The table in figure 3 gives a few orders of magnitude times for different altitudes of low earth orbits relative to a satellite to a stationary GEO in geostationary orbit.

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 16 It should also be noted that communication services envisaged for the system according to the invention, are preferentially transmissions at low data rates.

Because of this, the size of the data buffer needed remains reasonable.

With this approach using a receiver Rake, in the case of a technique of multiplexing, CDMA, satellites scrolling LEO and stationary GEO share the same frequency band (in-band MSS L in the present example) without generating harmful interference.

The frequency planning and coverage issues must also be taken into consideration, since the coverage areas LEO and GEO should be coordinated to ensure correct operation of the system.

In the proposed approach, the coverage of the satellites stationary GEO is composed of a beam global, covering the entire visible surface of the Earth.

This approach allows to avoid or limit the transfer procedures for the satellites scrollable LEO (known by the man of the art under the term hand over ) between different beams from one (or more) satellites stationary GEO.

The cover LEO, therefore, is included in the coverage of the GEO as illustrated in figure 4.

The satellites scrollable LEO turns so just the signals from the satellites stationary GEO in which they are located.

In the example above :

- the satellite scrolling LE01 relays the signals to the satellite and back stationary GE01, - the satellite rolls, LE02 and LE03 relaying the signals to the satellite and back stationary GE02.

There is no satellite scrolling LEO in the coverage of the satellite stationary GE03 at the instant illustrated by figure 4.

In fact, the satellite scrolling LE03 is, at this time, connected to the satellite stationary GE02.

As a satellite scrolling LEO any moves in the coverage area of the satellites stationary GEO, it can be in visibility of different satellites in stationary GEO.

However, it is assumed that at any given time it is connected to a geostationary satellite unique.

When CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 17 several satellites stationary GEO are in the visibility zone of the satellite rolls, LEO, different strategies can be adopted for the choice of the satellite to a stationary GEO in which the satellite scrolling LEO must hang (eg on a criterion for the best signal received at the satellite level scrolling, LEO, or a geometrical criterion of minimization of the distance between satellite scrolling LEO satellite and a stationary GEO, which is predictable in advance on the basis of the ephemerides of the satellites).

In the example above the satellite is scrolling, LEO is connected to the satellite and a stationary GEO providing the best received signal.

With these assumptions, it is not necessary to design complex strategies for planning of frequencies and all satellites (three satellites in stationary GEO and the three satellites scrollable LEO) can operate for example on a single channel of the frequency band used, with a multiplexing of the type CDMA.

In contrast to the approach of the prior art type Orbcomm or Argos, the proposed system is able to provide communications of bi-directional data, based on the fact that the satellite to a stationary GEO relays the communications satellites scrollable LEO.

According to this approach, as soon as the user terminal REC1, REC2 is in the coverage area of a satellite scrolling LE01, LE02, LE03, it is possible to communicate bidirectionally and in real time with him.

There is more requirement of visibility simultaneous satellite scrolling LE01, LE02, LE03, the user terminal REC1, REC2 and a station connection to ground, which then makes it possible to envisage a complete coverage of the Earth.

The time, to communicate with a user terminal REC1 on the ground is then only a function of the frequency of passage of satellites scrolling LE01, LE02, LE03, which depends directly on the orbit chosen for these satellites and the number of these satellites (up to continuous coverage of the entire earth).

Figure 5 represents schematically the use by a telecommunications system according to the invention, of a same frequency band for communications between user terminals REC and satellites CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 18 scrollable LEO, and for communications between the satellite rolls, and LEO satellites stationary GEO.

Figure 5 represents an example of the use of the L-band for applications of the type MSS.

As illustrated by figure 5, the L-band is organized into sub-bands used, either for the communications uplink (from a user terminal REC to a satellite scrolling LEO and/or a satellite to a stationary GEO, and a satellite scrolling LEO to a satellite and a stationary GEO), or the communications downlink (from a satellite and a stationary GEO to a satellite scrolling LEO and/or a user terminal REC, and a satellite scrolling LEO to a user terminal REC).

In this example, the L-band corresponds to the frequencies between 1.518 GHz and 1.675 GHz, and:

- the sub-band used for the communications top-down corresponds to the frequencies between 1.518 and 1.559 GHz, - the sub-band used for communication uplink corresponds to a frequency range between 1.6265 and 1.6605 GHz, and to frequencies between 1.668 and 1.675 GHz.

The use of sub-frequency bands distinct from the L-band for communications uplinks and communications downlinks corresponds to a multiplexing frequency of such communications uplinks and downlinks, known in the anglo-saxon literature under the name of Frequency Division Duplex (FDD).

We also understand that other types of multiplexing communications uplinks and communications downlinks, such as, for example, a time-division multiplexing or Time Division Duplex (TDD), multiplexing, code division type CDMA, etc

However, the use of multiplexing frequency FDD corresponds to a preferred mode of implementation of the fact that the interference between communications in uplink and downlink are reduced, and since the use of a time-division multiplexing TDD can be complex given the time delays inherent in the systems of telecommunications by satellite.

In the example shown in figure 5, and to a communication CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 19 uplink, a user terminal REC transmits data in a given channel (sub-frequency band of the L-band used for communication uplink, comprising preferentially several such channels) in the direction of a satellite that is running LEO.

Preferably, the satellite scrolling LEO repeat such data, transparent or regenerative, to a satellite and a stationary GEO using the same channel as the one used by the user terminal REC.

As previously indicated, the satellite scrolling LEO may also, in the alternative, to repeat the data in an adjacent channel of the sub-frequency band used for communication uplink.

Similarly, for a communication downlink, a satellite and a stationary GEO emits data in a given channel (the sousbande frequency of the L-band, used for the communications top-down, with preferentially more such channels) in the direction of a satellite that is running LEO.

Preferably, the satellite scrolling LEO repeat such data, transparent or regenerative, to a user terminal REC by using the same channel as that used by the satellite to a stationary GEO.

As previously indicated, the satellite scrolling LEO may also, in the alternative, to repeat the data in an adjacent channel of the sub-frequency band used for communication uplink.

According to one implementation particularly advantageous of the invention, the emissions rising by a satellite scrolling LEO to a destination satellite to a stationary GEO, and emissions top-down, by the said satellite scrolling LEO to a destination user terminal REC are multiplexed in time.

In other words, emissions are rising and emissions descending by a same satellite scrolling LEO are performed during different time intervals.

Indeed, an important constraint on the design of a payload of a communications satellite, and its cost of manufacture, is derived from the instantaneous power emission maximum to be issued.

Due to the time-division multiplexing of emissions rising, and emissions are top-down, the instantaneous power of maximum emission is reduced by CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 compared to the case of emissions up and down simultaneous.

This is all the more advantageous as, in the case of small satellite, the instantaneous power emission maximum available is usually limited (for example of the order of 60 to 150W for a satellite of mass 5 in the range of 100 to 200 kg).

The figure 6 represents schematically a preferred mode of realization of a payload 10 of a satellite repeater scrolling LEO, configured to multiplex in time the emissions uplinks to a satellite 10 stationary GEO and emissions downlink to a user terminal REC.

It is noted that the payload 10 of the satellite and scroll LEO can also include other elements, not represented on the figure 6.

As illustrated by figure 6, the payload 10 includes a floor radio for communications with the satellites stationary 15 GEO, said floor LEO/GEO 100, as well as a floor radio for communications with the user terminals REC, said floor LEO/REC 110.

In the non-limiting example illustrated by figure 6, the floor LEO/GEO 100 includes four antennas 101 which are implemented at 20 for both emissions rising and for entertaining descendant.

Such a use of the antenna 101 to the time for emissions rising and receptions-top-down is made possible by the fact that they are performed in the same frequency band, for example in the sousbandes frequency of the L-band described in reference to figure 5.

The antenna 101 may be of any suitable type, for example antennas horn, antennas, patch, etc

Each antenna 101 is coupled to two paths, a path of emission and reception, for example via a circulator 102, of a type known in itself.

This circulator 102 is able to route signals on the path of emission to the antenna 101, and to route signals received by the antenna to the path of reception.

Each channel of reception comprises a low noise amplifier or LNA 103 (acronym of the English expression Low-Noise Amplifier ), which can CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 21 be of any type known in itself.

In a similar way, the floor LEO/REC 110 includes four antennas 111, which are implemented both for emissions top-down and for the entertaining rising, which may be of any suitable type, for example antennas horn, antennas, patch, etc

Each of the antennas 111 is coupled to two paths, a path of emission and reception, for example by means of a circulator 112, of a type known in itself.

Each channel of reception comprises a low-noise amplifier or LNA 113, which may be of any type known in itself.

In addition, the payload 10 includes a power amplifier or PA 120 (acronym of the English expression Power Amplifier ), which may be of any type known per se, for example an amplifier, SSPA ( Solid State Power Amplifier ), amplifier tubes, etc

In the preferred mode of realization, illustrated by figure 6, the amplifier PA 120 is shared between the floor LEO/GEO 100 and the floor LEO/REC 110.

In other words, the amplifier PA 120 is used both for programming the rising and for emissions top-down.

This is made possible, on the one hand, the fact that emissions are rising emissions and downlink are performed in the same frequency band, for example in the sub-frequency bands of the L band that are described in reference to figure 5.

This is made possible, on the other hand, the fact that those emissions are rising, and the emission downlink are multiplexed in time.

For this purpose, the payload 10 comprises means for routing a signal at the output of the amplifier PA 120, which is representative of data to be repeated, that is, toward the antenna 101 of the floor LEO/GEO 100, or to the antenna 111 of the floor LEO/REC 110.

Such means of router is present in the non-limiting example illustrated by figure 6, in the form of a switch circuit 121.

Also for this purpose, the payload 10 comprises means for multiplexing, at the input of the amplifier PA 120, signals emissions rising signals and emissions top-down.

The said means of multiplexing are presented, in the non-limiting example illustrated by figure 6, also in the form of a switch circuit 122.

CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 22 The payload 10 is also coupled to each of the receiving tracks, circuits, receivers 130, of a type known in itself, the output of which are obtained on two channels in quadrature of phase which are known as channels I and Q.

The signals obtained on each of these channels are then digitized by means of analog/digital converters 131, of a type known in itself, in view of a processing by a processing module 150, such as a microcontroller and/or FPGA.

The signals processed by the processing module 150, representative of the data to be repeated and occurring in the form of two channels I and Q to be issued in phase quadrature, are converted into analog signals through d/a converters analog 141.

The signals at the output of said d/a converters analog 141 are then provided at the input of circuits modulators 140, of a type known per se, which are coupled to the switch circuit 122 at the input of the amplifier PA 120.

In addition, although it is not shown in figure 6, the processing module 150 is coupled to the switch circuit 122 at the input of the amplifier PA 120 and the switch circuit 121 at the output of the amplifier PA 120.

The processing module 150 is further configured to control said circuits, the switches 121, 122 in a manner substantially synchronized in order to use said amplifier PA 120 and sometimes for emissions rising, sometimes for emissions top-down.

It is understood that the interest of the preferred mode of realization shown in figure 6 resides particularly in the fact that the same power amplifier PA 120 is used both for emissions rising, sometimes for emissions top-down.

In effect, this helps to reduce the number of power amplifiers to be embedded in a satellite scrolling LEO, which has at least the following advantages :

- the power amplifiers are devices that generally consume a lot of energy, the decrease in the number of power amplifiers needed can reduce the power requirements of the satellite scrolling LEO, CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 23 - the power amplifiers are devices, usually large, the decrease in the number of power amplifiers necessary makes it possible to manufacture satellites scrollable LEO more compact, - this leads to satellites scrollable LEO less expensive to build and to launch.

According to a variant of realization of the payload 10, also illustrated in figure 6, the floor LEO/REC 110 also includes means to route a signal at the output of the amplifier PA, more particularly at the output of the switch circuit 121, to any of said antennas 111 issue backward.

In the non-limiting example illustrated by figure 6, these means of router is present in the form of a switch circuit, said circuit scan 114, for example, controlled by the processing module 150 (control that is not represented in the figure 6).

The fact of the circuit of scan 114, the payload 10 is suitable, for emissions top-down, to enable successively the antenna 111.

For example, if the antennas 111 are directional antennas of directions of sight are different, this allows you to scan different areas on the surface of the Earth to repeat data to the user terminals REC different, while emitting in each of these areas with the instantaneous power of maximum emission.

Preferably, said payload 10 is configured to simultaneously enable reception of each of the antennas 111 of the floor LEO/REC 110.

In other words, during the time intervals during which the payload 10 will receiving uplink data from user terminals REC, all of the antennas 111 are connected by their way of receiving to the processing module 150, which will process the signals received simultaneously from each of antennas 111.

In effect, this will increase the length of time during which signals may be received from user terminals REC.

Nothing precludes, according to particular modes of realization, of having a CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 24 circuit scan 114 more complex to enable multiple antennas 111 (two antennas on four, three antennas out of four, etc), and activate several successive groups of antennas 111.

In addition, nothing precludes, according to particular modes of implementation, also to provide a circuit sweep for the antenna 101 of the floor LEO/GEO 100.

This can be advantageous for example to communicate with different satellites in stationary GEO, the antenna 101 with then of the directions referred to different.

It is to be noted that, in a variant of realization of the payload 10 of figure 6, a same switch circuit with an input coupled to the amplifier PA 120) and five outputs (four outputs coupled respectively to each of the four antennas 111 of the floor LEO/REC 110, and an output coupled to all the antennas 101 of the floor LEO/GEO 100) could be used instead of the switch circuit 121 (the output of the amplifier PA 120) and the circuit of scanning 114.

According to a preferred alternative implementation of the invention, at the level of a satellite scrolling LEO satellite scrolling LEO multiplex in time the emissions-tops and reception tops.

In other words, the satellite scrolling LEO does not receive rising during time intervals when it performs or may perform an emission rising.

Preferably, the satellite scrolling LEO also multiplexes in time the emissions down and the receptions top-down.

In other words, the satellite scrolling LEO performs no reception down during time intervals when it performs or is likely to perform a show down.

According to the invention, the communications between user terminals REC and satellites scrollable LEO, and for communications between the satellite rolls, and LEO satellites stationary GEO, use the same frequency band.

More particularly, if it takes place in the non-limiting example illustrated by the figure 5, the communications uplinks using a first CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 sub-frequency band of the L-band, while the communications downlink using a second sub-frequency band of the l-band.

So, it is understandable that, from a point of view of the satellite scrolling LEO, a broadcast uplink to a satellite stationary GEO can disrupt a 5 receiving uplink simultaneously carried out by this satellite scrolling, LEO, to the extent that these communications are made within the same sub-frequency band of the l-band. This is also the case, from the point of view of the satellite scrolling LEO, for a program top-down simultaneous to a reception down done by the satellite scrolling LEO.

10 Such disruptions could be reduced by insulating the floor LEO/GEO 100 of the floor LEO/REC 110, but this insulation would also include the addition of extra features of insulation and/or remoteness increased antenna 101 of the floor LEO/GEO 100 and the antennas 111 of the floor LEO/REC 110.

By multiplexing in time, at the level of the satellite scrolling 15 LEO, emissions are rising and receptions rising one hand, the emissions down and the receptions downlinks, on the other hand, such disturbances are removed.

This removal is achieved without having to add additional devices to insulation.

In addition, the antenna 101 of the floor LEO/GEO 100 and the antennas 111 of the floor LEO/REC 110 may be 20 spaced, for example, arranged on adjacent sides of the satellite scrolling LEO.

It is to be noted that the time-division multiplexing, at the level of a satellite scrolling LEO, emissions are rising and receptions rising one hand, 25 and emissions top-down banquets and descending on the other hand, allows you to greatly simplify the design floor LEO/GEO 100 and the LEO/REC 110 from a point of view of insulation electromagnetic.

Such provisions could, therefore, be considered independently of the time-division multiplexing of emissions rising, and emissions are top-down, which allow a better sharing of the power onboard the satellite scrolling LEO.

However, we understand that the combination of time-division multiplexing of emissions rising, and emissions are top-down, and multiplexing CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 26 temporal emissions rising and receptions rising one hand, and emissions to the descending and receptions downlinks, on the other hand, allows for the design of satellites scrollable LEO especially compact and with a cost controlled better.

Figures 7a and 7b illustrate two examples of implementation.

In these examples, it is designated by F1 the sub-frequency band used for communication uplink, and by F2 the sub-band of frequency used for the communications top-down.

It is to be noted that the examples illustrated by figures 7a and 7b are placed from the point of view of the satellite scrolling LEO.

We note in particular the following points :

- an arrow F1 between a user terminal REC and a satellite scrolling LEO indicates a time interval during which the satellite scrolling LEO performs a reception in the sousbande F1. The absence of such an arrow F1 means that the satellite scrolling LEO performs no reception in the sousbande F1, but does not imply that the user terminal REC emits no signal in said sub-band F1 ; in particular, if the conditions allow it, the user terminal REC can send a signal directly to the attention of the satellite to a stationary GEO (the coexistence of the signals transmitted in the sub-band F1 by the user terminal REC and the satellite scrolling LEO that can be done for example with an air interface to CDMA and use of a receiver Rake to level the ground station connection GHG) emissions ;

- a downward arrow F2 between a satellite and a stationary GEO satellite scrolling LEO indicates a time interval during which the satellite scrolling LEO performs a reception in the sousbande F2. The absence of such a downward arrow F means that said satellite scrolling LEO performs no reception in the sousbande F2, but does not imply that the satellite to a stationary GEO emits no signal in said sub-band F2 ; in particular, if the conditions allow, the satellite to a stationary GEO can CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 27 send a signal directly to the attention of the terminal user (the coexistence of the signals transmitted in the sub-band F2 by the satellite to a stationary GEO satellite and scrolling LEO that can be done for example with an air interface to CDMA and use of a receiver Rake at the level of the user terminal REC).

In the example shown in figure 7a, the time-division multiplexing, at the level of a satellite scrolling LEO, revolves mainly around three time intervals 11, 12 and 13.

During a first time interval 11, the satellite scrolling LEO performs the emissions top-down in the sub-band F2 towards one or more user terminals REC.

During a second time interval 12, the satellite scrolling LEO performs the emissions are rising in the sub-band F1 in the direction of one or more satellites in stationary GEO.

During a third time interval 13, the satellite scrolling LEO performs simultaneously receptions rising in the sub-band F1 and receives downlinks in the sub-band F2.

This sequence of time intervals 11, 12 and 13 is preferably made on a recurring basis.

For example, the duration of each of these time intervals can be of fixed value, predetermined, or variable, to determine according to predefined criteria. For example, the duration of each of these time intervals may be between a few tenths of a second and a few tens of seconds.

In a preferred mode of embodiment, and as illustrated by figure 7b, the payload 10 is configured to perform receptions rising simultaneously to the emissions top-down, and to make the receptions top-down simultaneously with emissions rising.

As illustrated by figure 7b, the time-division multiplexing revolves mainly around two time intervals 11 and 12.

During a first time interval 11, the satellite scrolling LEO performs the emissions top-down in the sub-band F2 in the direction CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 28 or more user terminals REC, as well as receptions rising in the sub-band F1 of the signals possibly issued by one or more user terminals REC.

During a second time interval 12, the satellite scrolling LEO performs the emissions are rising in the sub-band F1 in the direction of one or more satellites in stationary GEO, as well as receptions descending in the sub-band F2 signals that may have been issued by one or more satellites in stationary GEO.

This sequence of time intervals 11 and 12 is preferably performed in a recurring manner.

For example, the duration of each of these time intervals can be of fixed value, predetermined, or variable, to determine according to predefined criteria. For example, the duration of each of these time intervals may be between a few tenths of a second and a few tens of seconds.

Figure 8 represents a variant of realization of the payload of figure 6, adapted for operation of the payload 10 of the satellite repeater scrolling LEO as illustrated by figure 7b.

Compared to the payload 10 illustrated by figure 6, a greater number of components are used both for communications with one or more satellites in stationary GEO and for communications with one or more user terminals REC.

This is made possible by the fact that these communications from the point of view of the satellite scrolling LEO, are multiplexed in time, as highlighted in figure 7b.

Thus, compared to the payload 10 illustrated by figure 6, the following components are shared :

- the circuits modulators 140: the sharing of these components allows to reduce the number from two to one, - digital to analogue converters 141 : the sharing of these components allows to reduce the number from four to two, - the circuits in receivers 130: the sharing of these components allows to reduce the number from eight to four, CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 29 - the analog/digital converters 131 : the sharing of these components allows to reduce the number from sixteen to eight.

Compared to the payload 10 of figure 6, the switch circuit 122 at the input of the amplifier PA 120 has been removed, the multiplexing being performed directly by the processing module 150.

By contrast, circuit switches 160 have been added at the input circuits of receivers 130, controlled by the processing module 150 (control that is not represented in the figure), to connect them both to the floor LEO/GEO 100 and to the floor LEO/REC 110.

Therefore, we can understand that, because of the use of the same frequency band and because of the time-division multiplexing of communications with the satellites stationary and communications with the user terminals, it is possible to obtain a payload of 10 highly optimized.

It is to be noted that other components may also be shared, such as for example the amplifiers LNA 103, 113.

Advantages of the invention, Through the combination of a constellation of satellites scrollable LEO (which allows to provide a better services to the polar regions) and a constellation of satellites in stationary (GEO which provides a quality service to equatorial regions and low latitudes), the average duration of non-visibility of a satellite to a user terminal is canceled or greatly reduced compared to systems of the prior art, particularly when high elevation angles are sought (in the case of mobile communications by satellite, the blocking factor of the signal is reduced at high elevation which leads to better service availability).

It is understood that a system as described which provides an availability significantly increased (by means of a cover quasi-continuous) for the users who need to operate in remote areas and little coverage by the systems of traditional communication. This is the case, for example, the polar areas, through a constellation in polar orbit or quasi polar).

In addition, a multiplexing suitable for various tasks of the transmit/receive payload satellites scrollable LEO allows CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 to simplify greatly the design and reduce the manufacturing cost, while maintaining a high level of performance.

Other advantages of the invention are particularly well 5 when compared to existing solutions, using either low-orbiting satellites or geostationary satellites, or hybrid constellations.

Compared to a solution of satellite communications using a constellation of low-orbiting satellites (such as Orbcomm or Argos for 10 example), the advantages gained by the invention are multiple :

it is not necessary to deploy stations connection for communications between the satellite rolls, LEO, and the network infrastructure on land ; in fact, the station connection or satellite stationary GEO guarantee access to 15 permanent satellites scrollable LEO;

it is not necessary to deploy stations Remote control/Telemetry & Control (TT&C) of the constellation of satellites running, the signals TT&C is also relayed by the satellite stationary GEO; it is understood 20 that the control of the satellites scrollable LEO is made, since the ground stations controlling the satellites stationary GEO, through these satellites, stationary GEO ;

- a design of the satellites scrollable LEO greatly simplified due to an operation of the payloads of these satellites 25 scrollable LEO to share the power board between emissions rising, and the emissions top-down, and to reduce the isolation requirements electromagnetic floor LEO/GEO and floor LEO/REC.

Compared to a solution of satellite communications using a 30 satellite in geostationary orbit, the advantages gained by the invention are :

- an extension of the coverage of the satellite to a stationary GEO to cover for example the polar areas, - low latency for access to the network and for the CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 31 receipt of acknowledgement of receipt.

Compared to a system (included in the prior art) telecommunications satellite hybrid comprising one or more satellites in geostationary orbit and a constellation of low-orbiting satellites, the advantages provided by the invention are :

- the use of a common protocol between the two systems, more efficient than each protocol taken separately.

- a sharing of the frequency band used, with mechanisms to ensure that the interference intra-system are limited.

Because of its design, the concept is particularly suited to the user terminal having a low directivity and not requiring the maintenance of the pointing direction of satellites in low earth orbit.

In effect, it is sufficient that the user terminal points to a satellite to a stationary GEO or running LEO to ensure the communication.

The applications envisaged relate to the improvement of future mobile systems by satellites in geostationary orbit (MSS or " Mobile Satellite Services ), including aeronautical mobile services by satellites such as AMSS ( Aeronautical Mobile Satellite Service ) and AMSRS ( Aeronautical Mobile Satellite Route Services ), in-band UHF, L, S, C or X based on the deployment of a constellation in low earth orbit much less complex than the constellations MSS existing (such as Globalstar or Iridium) for communications of voice, data or message exchanges of machine-to-machine (M2M).

This concept can also apply to delivery systems, mobile satellite data, television or radio (e.g. radio broadcast to the standard S-DAB using a allocation to BSS in the L-band or the broadcast of mobile television in standard DVB-SH using an allocation MSS S-band).

Another use of this concept concerns the data exchanges for navigation applications (maritime or aviation, in particular).

In these applications, known to the man skilled in the art under the name SBAS (CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 32 English Satellite Based Augmentation System ), currently, there is no way to cover the mobile terminals located in the vicinity of the poles.

The invention allows to remedy this problem with a satellite in geostationary orbit, and a satellite in low orbit scrolling to the mobile phone.

Similarly, within a service area of a geostationary satellite there are grey areas for which the geostationary satellite is not in direct visibility of the terminal surface because of phenomena of masking by buildings or natural elements (trees, mountains, ...).

The coverage of a shadow area of these devices of traditional communication is possible, therefore, that this area may come in view of a satellite that is running in a low-earth orbit.

The use of a system or a method for telecommunications, in accordance with the invention thus makes it possible to extend the coverage area of the means of communication with shadow areas, and notably to extend the coverage area of a SBAS system using a geostationary satellite.

In the case where the repeater space transmits in a channel adjacent to that of the satellite to a stationary GEO and regenerative, an advantage of the invention is the possibility of a possible simplification of the exchange protocols between the user terminals and the satellites scrollable LEO.

The satellites scrollable LEO, in particular, can perform a conversion to a protocol of exchanges specific to the GEO (to account, for example, time constraints propagation specific GEO), or an aggregation of messages and optimize the use of bandwidth.

Another important attraction of this concept is the possibility to have a permanent connection and near real-time between the network and control mission and constellation of satellites scrollable LEO through the docking station and relay GEO.

We understand that the system does not necessarily require the deployment of a constellation of satellites scrollable LEO and stationary GEO dedicated.

Indeed, it is possible to use the capabilities of CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 33 transmission available on constellations of satellites stationary GEO already existing.

We choose in this case of course the frequency band of the satellite constellation of stationary GEO used to be a band of working frequency of the satellite rolls, LEO.

This allows to solve the problem of the limited frequency bands available for mobile satellite services using satellites in non-geostationary orbit, and it therefore provides a regulatory interest in the deployment of a constellation of satellites scrollable LEO operating on a secondary basis in the same frequency band as the (or the) satellite to stationary GEO.

Similarly, the functions envisaged for the satellite scrollable LEO can in fact be performed by means of the payloads onboard as passengers on satellites scrollable LEO dedicated primarily to other functions.

In this case, the decisive criterion is the orbit envisaged for the satellite scrolling LEO.

A good choice is that of observation satellites of the Earth, who frequently use a sun-synchronous orbit highly inclined, and thus covering the high latitudes.

This implementation payloads as passengers, and, of course, very advantageous in terms of cost of deployment of the system.

The system described here is therefore a simple and economic solution, in comparison with other possible alternatives such as :

- the deployment of a large number of stations soil to provide a permanent connection between the satellite rolls, the LEO and the ground, which is costly and complex to implement in particular to cover the oceans (the Globalstar constellation is a good illustration of this difficulty) ;

- the use of inter-satellite link to provide a permanent connection between the satellites scrollable LEO and a limited number of stations in the soil ; this solution has the drawback of adding complexity and additional costs at the level of the space segment (the Iridium constellation is a good illustration of this solution).

Finally, the architecture is advantageous and less costly to the payload, CA 02841393 2014-01-10 WO 2012/171809 PCT/EP2012/060359 34 as previously described, allows to reduce the system cost without sacrificing performance.

In this case, the significant reduction in the complexity of satellite platforms repeaters rolls, used to decrease their price and/or increase the number of satellites deployed in the telecommunications system.

Variants of the invention The use of spatial diversity (techniques or MIMO) at the user terminal for recombining the signals from both the satellite and a stationary GEO satellite and scroll LEO can be considered in order to improve the link budget of more way.

The repeater satellite can be a simple analogue repeater transparent, which is the simplest solution but imposes design limitations on the air interface so as to limit the interference at the terminal between the signals from the satellite to a stationary GEO and the signals relayed by the satellite scrolling LEO.

An alternative solution is to relay the signal (transparent or regenerative) in a channel of a same frequency band of the satellite transponder.

This solution requires a coordinating entity for coordinating the frequency plans between the satellites stationary GEO and scrollable LEO.

The constellation of satellites relay can also implement additional functionality ( store & forward , aggregations of signals).

The constellation of satellite transponders can provide coverage of the whole or part of the Land according to the set goals.

The constellation of satellite transponders can provide continuous coverage in time (for services, real-time available at any time) or only access with a certain delay (for non real-time) using constellations with a smaller number of satellites.

It is also clear that the concept described, using the same frequency band for communications between the terminal surface and the satellite repeaters, and for communication between the satellite repeaters and the satellites are stationary, can only apply on the way to go or on the way back or in both directions.