Method for changing connections between stations of a station group and an associated station group

Abstract

Method for changing connections between stations of a station group and associated station group. The present invention relates to a method for changing connections between stations (16-1, 16-2, 16-3) of a station group (14), between a first state, in which each station (16-1, 16-2, 16-3) of the station group (14) is connected to a first satellite (20-1) of a plurality of satellites, and a second state, in which each station (16-1, 16-2, 16-3) of the station group (14) is connected to a second satellite of the plurality of satellites, distinct from the first satellite (20-1), each satellite (20-1) being mobile relative to a geographical area in which the stations (16-1, 16-2, 16-3) of said station group (14) are positioned, each station (16-1, 16-2, 16-3) being capable of establish a connection with each satellite (20-1) for a predetermined period of presence of said satellite (20-1), considered for said geographical area,The change process includes an election phase and a switchover phase. Figure for the abbreviation: Figure 1,

Description

Title of the invention: Method for changing connections between stations of a group of stations and associated group of stations

[0001] The present invention relates to a method for changing connections between stations of a group of stations.

[0002] The invention further relates to a group of stations comprising several stations.

[0003] The invention lies in the field of satellite communications, in particular communications of several stations forming a group via mobile satellites relative to a geographical area.

[0004] Mobile satellites are satellites moving in non-geostationary orbit, for example in medium Earth orbit (MEO) or in low Earth orbit (LEO). Mobile satellites can be used, for a predefined duration and at a predefined time, as communications relays for communications between stations located in a given geographical area. This duration and this time are predefined by the ephemeris.

[0005] Before the mobile satellite disappears over the horizon, that is to say before this satellite becomes inaccessible for communication between the stations of the group via this satellite, it is appropriate to switch the communication of the stations to another mobile satellite in order to ensure continuity of service.

[0006] In the context of communications within a group of stations, it is particularly important to coordinate the switchover from one satellite to another for all the stations in the group, since the absence of switchover of one or more stations in the group breaks the unity of the communication group. This is likely to result in the loss of communication, temporary or permanent, between the stations in the group. Also, the present invention aims to avoid this drawback by allowing continuity of communications between the members of the group, including when they are present under a constellation of satellites involving a periodic change of satellite acting as a relay.

[0007] To coordinate the switchover of the group of stations, generally an orchestrator dedicated to this switchover is predefined, also called a "hub" in English. The predefined orchestrator is typically located at a fixed position on the ground and sends switchover commands.

[0008] However, in some cases it is complicated, or even impossible, to position the predefined orchestrator in the geographical area, for example given geographical constraints, for example in maritime areas far from the coasts.

[0009] Furthermore, during unavailability or failure of the predefined orchestrator, the switchover is not implemented. Consequently, communication between the stations of the group is likely to be interrupted when the moving satellite disappears over the horizon and thus becomes inaccessible for communication.

[0010] Finally, for example, when adding stations to the group, it is necessary to reconfigure the predefined orchestrator to also control the failover of this station, making this solution complicated and inflexible.

[0011] One aim of the invention is thus at least to reduce the aforementioned drawbacks.

[0012] In particular, the invention aims to obtain a method for changing connections of a group comprising several stations which is more reliable and / or more flexible.

[0013] For this purpose, the invention relates to a method for changing connections between stations of a group of stations, between a first state, in which each station of the group of stations is connected to a first satellite of a plurality of satellites, and a second state, in which each station of the group of stations is connected to a second satellite of the plurality of satellites, distinct from the first satellite, during the initialization of the change method, the stations being in the first state, each satellite being mobile relative to a geographical area in which the stations of said group of stations are positioned, each station being able to establish a connection with each satellite during a predetermined duration of presence of said satellite, considered for said geographical area, the change method comprising:

[0014] - a phase of election of at least one station among the stations of the group of stations, depending on at least one characteristic relating to a satellite antenna of said station, to obtain at least one elected station, the or each elected station being configured to control a switch between the first state and the second state;

[0015] - a switching phase, comprising a diffusion step, by the or each elected station to the other stations in the station group, an instruction to switch the connection from the first satellite to the second satellite.

[0016] Indeed, the change method makes it possible to obtain a switchover of the group of stations between a first and a second satellite which is more flexible and / or reliable.

[0017] By electing the station(s) configured to control the switchover according to the invention, the characteristic(s) of the antenna is / are taken into account, such as a switchover capability. Therefore, the station(s) are elected based on their ability to form an orchestrator for the change of connections between the first and second satellites.

[0018] This thus makes it possible to obtain a reliable switchover. Indeed, one or more of the stations can play the role of an orchestrator for the switchover according to the invention.

[0019] Even when one of the stations in the group is lost or unavailable, the switchover is implemented by another station elected for this purpose.

[0020] In particular, the change method makes it possible to obtain a switchover in the absence of a predefined orchestrator. Thus, the switchover function is implemented by the elected station(s) of the group itself.

[0021] According to other advantageous aspects of the invention, the changing method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0022] - the characteristic relating to the satellite antenna of the station includes a duration switching between the connection to the first satellite and the connection to the second satellite of said station and / or includes a capability for establishing connections simultaneously with the first satellite and the second satellite by said station;

[0023] - the election phase includes the election of the or each station elected further in depending on a computing capability of said station, preferably the computing capability comprising a capability to estimate a transit time of a signal transmitted via the second satellite and / or a capability to estimate the Doppler effect of the signal transmitted via the second satellite;

[0024] - the election phase includes:

[0025] - a first step of determination, by each station, of a marking attributed to this station, among a plurality of predetermined markings, depending on the characteristic relating to the satellite antenna of said station;

[0026] - a second determination step, during which each station determines, at less depending on the marking at this station, an eligibility to form an elected station of the elected station(s);

[0027] - each station determines the marking assigned to this station from among:

[0028] - a first marking, called preferential marking, when the satellite antenna of said station is configured to simultaneously establish a connection with the first satellite and the second satellite;

[0029] - a second marking, called secondary marking, when the satellite antenna of said station is configured to establish a connection, at a given time, only with one of the first satellite and the second satellite, and when the satellite antenna further has a switching duration of the connection between the first satellite and the second satellite less than or equal to a predetermined threshold;

[0030] - a third marking, called unsuitable marking, when the satellite antenna of said station is configured to establish a connection, at a given time, only with one of the first satellite and the second satellite, and when the satellite antenna further has a switching duration of the connection between the first satellite and the second satellite strictly greater than the predetermined threshold;

[0031] - the election phase further comprises a reception step, by one of the stations of the group of stations, called the station in question, of a message comprising the marking of one of the stations of the group of stations other than the station in question, called the other station, and in which, during the second determination step, the station in question determines its eligibility to form an elected station of the station(s) elected furthermore according to said message;

[0032] - during the second determination step, the station considered determines its eli eligibility according to at least one of the following criteria:

[0033] - if the marking of the station considered is the secondary marking and the message includes the preferential marking of the other station, the station in question determines that it is not eligible to form an elected station of the elected station(s),

[0034] - if the marking of the station considered is the secondary marking and the message includes the secondary marking of the other station, the station in question determines that it is eligible to form an elected station of the elected station(s) only if the switching duration is among the N stations having the shortest switching duration among the switching durations of all the stations in the group of stations, N being a predetermined integer,

[0035] - if the marking of the station considered is the preferential marking, the station considered determines that it is eligible to form an elected station of the elected station(s), preferably independently of the message;

[0036] - the switchover phase includes a one-hour planning step between the connection to the first satellite and the connection to the second satellite for each station, depending on the ephemerides of at least the first and second satellites, and

[0037] wherein the failover instruction comprises the failover time;

[0038] - the switching phase includes a step of verifying the presence of the second satellite, wherein the or each elected station transmits a beacon signal to the second satellite, and receives a response to the beacon signal from the second satellite when said second satellite is present, preferably, the broadcasting step being implemented only upon receipt of said response;

[0039] - during the broadcasting step, the or each elected station broadcasts the instruction from below ically via the first satellite to the other stations in the station group.

[0040] The present invention also relates to a group of stations comprising several stations configured to change connections between the stations, between a first state, in which each station of the group of stations is connected to a first satellite of a plurality of satellites, and a second state, in which each station of the group of stations is connected to a second satellite of the plurality of satellites, distinct from the first satellite, each satellite being movable relative to a geographical area in which the stations of said group of stations are positioned, each station being able to establish a connection with each satellite during a predetermined duration of presence of said satellite, considered for said geographical area, the group of stations being configured to elect at least one station from among the stations of the group of stations, based on at least one characteristic relating to a satellite antenna of said station, to obtain at least one elected station, the or each elected station being configured to command a switch between the first state and the second state, the or each elected station being configured to broadcast, to the other stations of the group of stations, an instruction to switch the connection from the first satellite to the second satellite.

[0041] These characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

[0042] - [Fig.l] [Fig.l] is a schematic view of a communication system comprising a group of stations according to the invention and a constellation of satellites, of which only a first satellite of the constellation, accessible for communication with the stations, is represented, the communication system being in a first state, in which each station is connected to the first satellite;

[0043] - [Fig.2] [Fig.2] is a schematic view of the communication system of the [Fig.l], in which the first satellite and a second satellite of the constellation, accessible for communication, are represented, the communication system being in an intermediate failover state;

[0044] - [Fig.3] [Fig.3] is a schematic view of the communication system of the Figures 1 and 2, in which only the second satellite of the constellation, accessible for communication, is shown, the communication system being in a second state, in which each station is connected to the second satellite, and the first satellite is in particular inaccessible; and

[0045] - [Fig.4] [Fig.4] is a flowchart of a change process according to the invention, implemented by the group of stations of the communication system of Figures 1 to 3.

[0046] With reference to Figures 1 to 3, a communication system 10 comprises a constellation 12 of satellites and a group of stations 14 comprising several stations 16-1, 16-2, 16-3 configured to communicate with each other using the constellation 12 of satellites.

[0047] The constellation 12 comprises N satellites 20-1 to 20-N mobile relative to a geographical area in which the stations 16-1, 16-2, 16-3 of the group of stations 14 are positioned. The number N is greater than 2, advantageously greater than 10 and preferably greater than 50. Generally, the number N can be between 2 and 1000. In some embodiments, the number N is between 2 and 10,000. In still other embodiments, the number N is greater than 10,000.

[0048] By "mobile satellite" is meant in particular a satellite moving in a non-geostationary orbit, such as low Earth orbit or medium Earth orbit. In Figures 1 to 3, examples of movement of the satellites are illustrated by arrows 21.

[0049] In the examples of Figures 1 to 3, only the satellites 20-1 to 20-N accessible to the group of stations 14 for communication are shown. For example, in [Fig. 1], only a first satellite 20-1 of the constellation 12 is shown, in [Fig. 2], the first satellite and a second satellite 20-2 of the constellation 12 are shown, and in [Fig. 3], only the second satellite 20-2 is shown.

[0050] Each satellite 20-1 to 20-N forms in particular a communications relay between all the stations 16-1, 16-2, 16-3 of the group of stations 14, all notably located in the geographical area, and this in particular for a predefined duration and at a predefined time. This duration and this time are predefined by the ephemerides.

[0051] Each satellite 20-1 to 20-N comprises a payload 22 comprising all of its electronic components enabling it to ensure its communication functions with the group of stations 14 and optionally with the other satellites.

[0052] The payloads 22 of the satellites 20-1 to 20-N are for example substantially similar to each other.

[0053] For example, each payload 22 comprises, not shown, a radiofrequency signal receiver / transmitter configured to receive and transmit radiofrequency signals comprising the communications of the group of stations 14. Each payload 22 further comprises, for example, at least one circuit for controlling and operating the transmitter / receiver. The transmitter / receiver defines at least one spot 24, in which communication between the groups of stations 14 via the corresponding satellite 20-1 to 20-N is implemented. In particular, no communication between the group of stations 14 positioned outside the spot 24 and the corresponding satellite 20-1 to 20-N is possible.

[0054] The group of stations 14 comprises M stations 16-1 to 16-M. The number M is greater than 2. According to the example of Figures 1 to 3, the group of stations 14 comprises three stations 16-1, 16-2, 16-3.

[0055] Each station 16-1 to 16-M of the group 14 is configured to communicate, via one of the satellites 20-1 to 20-N with the other stations 16-1 to 16-M of the group 14.

[0056] Each station 16-1 to 16-M is a ground station. By “ground station” is meant in particular a station positioned on the surface of the earth or in the atmosphere. In particular, the ground station is distinct from a station on board a satellite.

[0057] Each station 16-1 to 16-M is for example a fixed ground station, or a mobile station.

[0058] When the station 16-1 to 16-M is a mobile station, it is preferably mobile within the geographic area. For example, the mobile station is on board a land vehicle, a sea vehicle or an aircraft.

[0059] Each station 16-1 to 16-M comprises at least one control module 30, a satellite transmitter / receiver 32 and at least one satellite antenna 34, 36 connected to the satellite transmitter / receiver 32 for establishing communications with the other stations 16-1 to 16-M of the group 14 via the intermediary of the satellite 20-1 to 20-N.

[0060] The control module 30 comprises a memory and a processor, not shown. The control module 30 is in particular configured to determine messages of the communication implemented between the stations 16-1 to 16-M via the satellite transmitter / receiver 32 and the satellite antenna 34, 36.

[0061] The satellite transceiver 32 comprises, for example, a modem. The satellite transceiver 32 is in particular configured to convert digital signals from the control module 30 into analog signals for transmission via the satellite antenna 34, 36 to the satellite(s) 20-1 to 20-N. The satellite transceiver 32 is further configured to convert analog signals received by the satellite antenna 34, 36 into digital signals and transmit them to the control module 30.

[0062] According to one example, the satellite transceiver 32 is configured to simultaneously convert digital signals into analog signals for transmitting signals simultaneously to two of the satellites 20-1 to 20-N simultaneously. Also, the satellite transceiver 32 is for example configured to simultaneously convert analog signals received from the two satellites into digital signals.

[0063] Analog signals are in particular radio frequency signals. For example, radio frequency signals are signals in one or more bands allocated to satellite communications, such as the C, X, Ku, Ka bands, etc.

[0064] The satellite antenna is preferably either a satellite antenna 34 of the type called multiple pointing, or a satellite antenna 36 of the type called single pointing in the present description.

[0065] The multi-pointing type satellite antenna 34 is configured to establish connections simultaneously with at least two satellites among the satellites 20-1 to 20-N, positioned in distinct directions relative to the satellite antenna 34.

[0066] Preferably, the satellite antenna 34 of the multiple pointing type is an electronic antenna, in particular devoid of moving mechanical parts for a re- antenna orientation.

[0067] The single-pointing type satellite antenna 36 is configured to establish, at a given instant, a connection with only one of the satellites 20-1 to 20-N. In particular, the single-pointing type satellite antenna 36 is configured to implement a connection in a single direction, at a given instant.

[0068] The simple pointing type satellite antenna 36 is in particular unable to implement a connection simultaneously with two or more satellites 20-1 to 20-N, positioned in different directions relative to this antenna.

[0069] The single-pointing type satellite antenna 36 is preferably a parabolic antenna. For example, the satellite antenna 36 is configured to be rotated along the direction of the given satellite 20-1 to 20-N to establish the connection.

[0070] According to another example, the simple pointing type satellite antenna 36 is an electronic antenna, in particular without moving mechanical parts for reorientation of the antenna, but capable of establishing, at a given instant, a connection in a single direction with one of the satellites 20-1 to 20-N.

[0071] Preferably, at least one of the stations 16-1 to 16-M of the group comprises the satellite antenna 34 of the multiple pointing type and at least one of the stations 16-1 to 16-M of the group comprises the satellite antenna 36 of the single pointing type.

[0072] For example, with reference to Figures 1 to 3, station 16-1 includes the multi-pointing type satellite antenna 34, and stations 16-2 and 16-3 include the single-pointing type satellite antenna 36. Each satellite antenna 36 is configured to be rotationally oriented to the corresponding satellite 20-1 to 20-N, as illustrated by arrows 38.

[0073] A change method 100 implemented by the communication system 10, and in particular by the stations 16-1 to 16-M of the group of stations 14, is now explained with reference to [Fig.4] showing a flowchart of the steps of this method.

[0074] It is considered that during the implementation of this method, the satellites 20-1 to 20-N are moving along their usual orbit.

[0075] During the scrolling of satellites 20-1 to 20-N, each satellite is accessible for communication with stations 16-1 to 16-M positioned in spot 24 at a predefined time and for a predefined duration.

[0076] The changing method 100 comprises changing the connections of all stations 16-1 to 16-M of the station group 14 between a first state and a second state.

[0077] In the first state, an example of which is illustrated in [Fig.l], each station 16-1 to 16-M of the station group 14 is connected to the same satellite, for example to the first satellite 20-1. Preferably, each station 16-1 to 16-M is not connected to satellites other than the first satellite 20-1 when initiating the change method 100. In the second state, an example of which is illustrated in [Fig. 3], each station 16-1 to 16-M of the station group 14 is connected to a satellite distinct from the first satellite 20-1, namely the second satellite 20-2. In other words, in the first state, all stations 16-1 to 16-M of the station group 14 are connected to the first satellite 20-1, and in the second state, all stations 16-1 to 16-M are connected to the second satellite 20-2.

[0078] When initializing the change method 100, the communication system 10 is in the first state.

[0079] The change method 100 comprises an election phase 110 and a switch phase 120.

[0080] In the election phase 110, at least one station among the plurality of stations 16-1 to 16-M of the station group 14 is elected to control a switch between the first state and the second state. The station(s), which are elected in the election phase 110, is / are called elected station(s).

[0081] The election of the elected station(s) depends on at least one characteristic relating to the satellite antenna 34, 36 of the respective elected station. Examples of the characteristic(s) are described below.

[0082] The election phase 110 comprises for example a first determination step 130, a reception step 135 and a second determination step 140.

[0083] During the first determination step 130, each station 16-1 to 16-M determines a marking assigned to the station, from among a plurality of predetermined markings, at least as a function of the characteristic relating to the satellite antenna 34, 36 of the station 16-1 to 16-M.

[0084] The characteristic relating to the satellite antenna 34, 36 of the elected station comprises for example a switching duration between the connection to the first satellite 20-1 and the connection to the second satellite 20-2. For example, when the satellite antenna 36 is of the simple pointing type and the reorientation of the antenna is implemented by rotation of the antenna, the switching duration corresponds to the duration for the reorientation of the satellite antenna 36 between the satellites 20-1 and 20-2.

[0085] According to another example or as an optional addition, the characteristic comprises a capacity for establishing connections simultaneously with the first satellite 20-1 and the second satellite 20-2. For example, when the satellite antenna 34 is of the multiple pointing type, this antenna has the capacity for establishing connections simultaneously with the first satellite 20-1 and the second satellite 20-2.

[0086] During the first determination step 130, the or each station 16-1 to 16-M determines the marking and assigns this marking to itself, for example, from among a first marking, called preferential marking, a second marking, called secondary marking, and a third marking, called unfit marking.

[0087] The or each station 16-1 to 16-M determines and assigns itself the preferential marking, when the satellite antenna 34 of the station 16-1 to 16-M is configured to simultaneously establish a connection with the first satellite 20-1 and the second satellite 20-2. In particular, in this case, the satellite antenna 34 is of the multiple pointing type.

[0088] When station 16-1 to 16-M assigns itself the preferential marking, it considers itself as the preferred station to control the switch between the first state and the second state.

[0089] The or each station 16-1 to 16-M determines and assigns itself the secondary marking, when the satellite antenna 36 of the station 16-1 to 16-M is of the simple pointing type and the switching duration of the connection between the first satellite 20-1 and the second satellite 20-2 is furthermore less than or equal to a predetermined threshold. In other words, the satellite antenna 36 is configured to establish a connection, at a given instant, only with one of the first satellite 20-1 and the second satellite 20-2, that is to say is of the simple pointing type, and furthermore has the switching duration greater than the predetermined threshold.

[0090] The predetermined threshold is in particular chosen so as to guarantee a switchover of the connections of all the stations 16-1 to 16-M from the first satellite 20-1 to the second satellite 20-2 during the switchover phase 120 before the disappearance of the first satellite 20-1 on the horizon, as described in the context of the description of the switchover phase 120.

[0091] When station 16-1 to 16-M assigns itself the secondary marking, it considers itself as a station which is capable of controlling the switching between the first state and the second state, but which is less suitable than each station presenting the preferential marking.

[0092] The or each station 16-1 to 16-M determines and assigns itself the unfit marking, when the satellite antenna 36 of the station 16-1 to 16-M is of the simple pointing type and when the antenna also has a switching duration of the connection between the first satellite and the second satellite strictly greater than the predetermined threshold. In this case, the station 16-1 to 16-M considers itself in particular as unfit to control the switchover.

[0093] According to an example, each station 16-1 to 16-M further determines its marking based on a computing capacity of the station 16-1 to 16-M.

[0094] For example, the computational capability includes, or is defined by, the capability to estimate the Doppler effect of a signal transmitted between station 16-1 to 16-M and the first or second satellite 20-1, 20-2.

[0095] Additionally or alternatively, the computing capability includes, or is defined by, the capability of station 16-1 to 16-M to determine a transit time of a signal transmitted via the first or via the second satellite 20-1, 20-2, for example of a beacon signal.

[0096] The expression "transit time" is understood in particular to mean the duration between the time of transmission, by the station 16-1 to 16-M, of the signal to the corresponding satellite, and the time of reception, by the same station 16-1 to 16-M, of a response from this satellite following the transmission of the signal.

[0097] When the corresponding station 16-1 to 16-M has the calculation capacity to estimate the Doppler effect and / or the transit time of the signal, it assigns itself, for example, the preferential marking.

[0098] Information comprising the estimation of the Doppler effect and / or the transit time makes it possible in particular to establish a connection with the second satellite 20-2 very quickly during the switching phase 120, since the station 16-1 to 16-M switching the connection from the first satellite 20-1 to the second satellite 20-2 is capable of finding the second satellite 20-2 quickly, and thus establishing the connection.

[0099] According to one example, each station 16-1 to 16-M further determines its marking as a function of the transit time of the signal transmitted via the first or via the second satellite 20-1, 20-2, for example by sending and receiving a beacon signal via the corresponding satellite.

[0100] Preferably, the or each station 16-1 to 16-M assigning itself the respective marking, transmits to the other stations 16-1 to 16-M a message comprising an identifier of the station 16-1 to 16-M and this marking.

[0101] During the reception step 135, at least one of the stations 16-1 to 16-M, preferably each station 16-1 to 16-M of the group 14, receives the message comprising the marking of another station 16-1 to 16-M of the group 14. The or each station 16-1 to 16-M receiving the message is called “station considered” in the present description.

[0102] During the second determination step 140, each station determines, at least based on its marking, an eligibility to form the elected station. Preferably, the station considered 16-1 to 16-M determines its eligibility to form the elected station further based on the message received during the reception step 135.

[0103] For example, during the second determination step 140, the station considered 16-1 to 16-M determines its eligibility to form the elected station according to at least one criterion among a first criterion, a second criterion and a third criterion, preferably according to all of these criteria.

[0104] According to the first criterion, the station considered 16-1 to 16-M determines that it is not eligible to form the elected station, if its marking is the secondary marking and the message received from the other station during step 135 includes the preferential marking of the other station.

[0105] According to the second criterion, the considered station 16-1 to 16-M determines that it is eligible to form the elected station, if its marking is the secondary marking and if, in addition, the switching duration is part of the N stations 16-1 to 16-M having the shortest switching duration among the switching durations of all the stations 16-1 to 16-M of the group of stations 14. N is a predetermined integer, and is for example equal to 2 or 3.

[0106] According to the third criterion, the station considered determines that it is eligible to form the elected station, if the marking of the station considered is the preferential marking. In this case, the station considered preferably determines that it is eligible independently of the message. According to an example, in this case, the station considered determines that it is eligible only if a number of other stations of the group of stations 14 considered as eligible, is less than a predetermined number. This makes it possible in particular to limit the number of stations of the group of stations 14 determining that they are eligible to form the elected station.

[0107] The switchover phase 120 comprises the switchover of all the connections of the stations 16-1 to 16-M from the first satellite 20-1, i.e. from the first state, to the second satellite 20-2, i.e. to the second state.

[0108] The switchover phase 120 is preferably implemented when the communication system 10 is in an intermediate switchover state, illustrated in [Fig.2], in which both the first and second satellites 20-1 and 20-2 are accessible for communication.

[0109] The switchover phase 120 comprises in particular a step 145 of planning a switchover time, a step 150 of verifying the presence of the second satellite 20-2, a step 155 of developing a switchover instruction, a step 160 of broadcasting this instruction and a step 165 of applying this instruction.

[0110] During the planning step 145, the elected station 16-1 to 16-M determines a switchover time between the connection to the first satellite 20-1 and the connection to the second satellite 20-2 for each station 16-1 to 16-M. The elected station 16-1 to 16-M determines the switchover time at least as a function of the ephemerides of the first and second satellites 20-1, 20-2.

[0111] During the verification step 150, the elected station 16-1 to 16-M verifies the presence of the second satellite 20-2. In particular, the elected station 16-1 to 16-M transmits a beacon signal to the second satellite 20-2, and receives a response to the beacon signal from the second satellite 20-2 when the second satellite 20-2 is present.

[0112] To do this, if the satellite antenna 34 of the elected station 16-1 to 16-M is of the multiple pointing type, the elected station 16-1 to 16-M transmits the beacon signal to the second satellite 20-2 and continues to be connected to the first satellite 20-1 simultaneously.

[0113] If the satellite antenna 36 of the elected station 16-1 to 16-M is of the simple pointing type, the elected station 16-1 to 16-M interrupts the connection with the first satellite 20-1, reorients the satellite antenna 36 to the second satellite 20-2, for example by rotating the satellite antenna 36, ​​and transmits the beacon signal to the second satellite 20-2. Upon receiving the response to the beacon signal, the elected station 16-1 to 16-M again rotates the satellite antenna 36 towards the first satellite 20-1, in particular before implementing the development step 155 and the broadcasting step 160.

[0114] During the development step 155, the elected station 16-1 to 16-M develops the switchover instruction.

[0115] The switchover instruction comprises a command to switch the connection to the second satellite 20-2. The switchover instruction further comprises, for example, an identifier and time-dependent positions of the second satellite 20-2. Preferably, the switchover instruction further comprises the switchover time.

[0116] When the elected station 16-1 to 16-M has the capability to estimate the Doppler effect of a signal transmitted via the second satellite 20-2, the switchover instruction preferably includes an indication of the estimated Doppler effect for the transmission.

[0117] When the elected station 16-1 to 16-M has the capability to estimate the transit time of a signal transmitted via the second satellite 20-2, the switchover instruction preferably includes this estimated transit time.

[0118] This allows in particular each station 16-1 to 16-M applying the switchover instruction during the application step 165, to establish the connection with the second satellite 20-2 very quickly, since this station knows certain parameters for establishing the connection, namely the Doppler effect and / or the estimated transit time.

[0119] During the broadcasting step 160, the elected station broadcasts the switchover instruction via the first satellite 20-1 to the other stations in the group. For example, the elected station broadcasts the switchover instruction several times, in particular periodically.

[0120] Preferably, the broadcasting step 160 is only implemented following the reception, during the verification step 150, by the elected station 16-1 to 16-M of the response to the beacon signal.

[0121] For example, the elected station broadcasts the switch instruction for a predetermined broadcast duration. Preferably, the elected station begins broadcasting at a given time before the switch time. A time period between this given time and the switch time depends, for example, on the switching duration of the elected station. Preferably, the time period is greater than the sum of the switching duration and the predetermined broadcast duration.

[0122] This allows in particular the elected station, in particular when it includes the simple pointing type satellite antenna 36, ​​to establish the connection with the second satellite 20-2 before the connection of the other stations 16-1 to 16-M to the second satellite 20-2, and thus to monitor the switchover of all stations 16-1 to 16-M to the second satellite 20-2 during the application step 165.

[0123] During the application step 165, each station 16-1 to 16-M of the group 14 receives the switchover instruction, and applies the instruction, by switching the connection from the first satellite 20-1 to the second satellite 20-2.

[0124] The planning 145, verification 150, development 155 and broadcasting 160 steps are implemented by the elected station 16-1 to 16-M, which is elected during the election phase 110. When several stations 16-1 to 16-M are elected, during the election phase 110, to form the elected stations, each of these stations preferably implements the steps 145, 150, 155 and 160.

[0125] For example, when several stations 16-1 to 16-M are the elected stations, each elected station broadcasts for example the switchover instruction during the broadcasting step 160, and each station 16-1 to 16-M, in particular the stations other than the elected stations, applies, during the application step 165, the switchover instruction received first.

[0126] Preferably, the election phase 110 is repeated several times before the implementation of the switchover phase 120.

[0127] Of course, other embodiments may be envisaged. For example, steps 130 to 155 and 165 are optional steps, and / or variants of these steps are conceivable.

Claims

1.

2.

3. Claims A method of changing (100) connections between stations (16-1, 16-2, 16-3) of a group of stations (14), between a first state, in which each station (16-1, 16-2, 16-3) of the group of stations (14) is connected to a first satellite (20-1) of a plurality of satellites (20-1, 20-2), and a second state, in which each station (16-1, 16-2, 16-3) of the group of stations (14) is connected to a second satellite (20-2) of the plurality of satellites (20-1, 20-2), distinct from the first satellite (20-1), upon initialization of the changing method (100), the stations (16-1, 16-2, 16-3) being in the first state, each satellite (20-1, 20-2) being movable relative to a geographical area in which the stations (16-1, 16-2, 16-3) of said group of stations (14) are positioned, each station (16-1, 16-2, 16-3) being able to establish a connection with each satellite (20-1, 20-2) during a predetermined duration of presence of said satellite (20-1, 20-2),considered for said geographical area, the change method (100) comprising: - an election phase (110) of at least one station among the stations (16-1, 16-2, 16-3) of the group of stations (14), as a function of at least one characteristic relating to a satellite antenna (34, 36) of said station (16-1, 16-2, 16-3), to obtain at least one elected station, the or each elected station being configured to command a switch between the first state and the second state;, - a switching phase (120), comprising a broadcasting step (160), by the or each elected station to the other stations (16-1, 16-2, 16-3) of the group of stations (14), of an instruction to switch the connection from the first satellite (20-1) to the second satellite (20-2). The switching method (100) of claim 1, wherein the characteristic relating to the satellite antenna (34, 36) of the station (16-1, 16-2, 16-3) comprises a switching duration between the connection to the first satellite (20-1) and the connection to the second satellite (20-2) of said station (16-1, 16-2, 16-3) and / or comprises a capacity for establishing connections simultaneously with the first satellite (20-1) and the second satellite (20-2) by said station (16-1, 16-2, 16-3). The switching method (100) of claim 1 or 2, wherein the election phase (110) comprises the election of the or each elected station furthermore according to a computing capacity of said station (16-1, 16-2, 16-3), preferably the computing capacity comprising a capacity to estimate a transit time of a signal transmitted via the second satellite (20-2) and / or a capability to estimate the Doppler effect of the signal transmitted via the second satellite (20-2).

4. A method of change (100) according to any one of the preceding claims, wherein the election phase (110) comprises: - a first step of determination (130), by each station (16-1, 16-2, 16-3), of a marking assigned to this station, from among a plurality of predetermined markings, as a function of the characteristic relating to the satellite antenna (34, 36) of said station (16-1, 16-2, 16-3); - a second step of determination (140), during which each station (16-1, 16-2, 16-3) determines, at least as a function of the marking at this station, an eligibility to form an elected station of the elected station(s).

5. A switching method (100) according to claim 4, wherein each station (16-1, 16-2, 16-3) determines the marking assigned to this station from among: - a first marking, called preferential marking, when the satellite antenna (34) of said station (16-1, 16-2, 16-3) is configured to simultaneously establish a connection with the first satellite (20-1) and the second satellite (20-2); - a second marking, called secondary marking, when the satellite antenna (36) of said station is configured to establish a connection, at a given instant, only with one of the first satellite (20-1) and the second satellite (20-2), and when the satellite antenna (36) further has a switching duration of the connection between the first satellite (20-1) and the second satellite (20-2) less than or equal to a predetermined threshold;- a third marking, called unsuitable marking, when the satellite antenna (36) of said station is configured to establish a connection, at a given instant, only with one of the first satellite (20-1) and the second satellite (20-2), and when the satellite antenna (36) also has a switching duration of the connection between the first satellite (20-1) and the second satellite (20-2) strictly greater than the predetermined threshold.;

6. A method of change (100) according to claim 4 or 5, wherein the election phase (110) further comprises a step of reception (135), by one of the stations (16-1, 16-2, 16-3) of the group of stations (14), called the station considered, of a message comprising the marking of one of the stations (16-1, 16-2, 16-3) of the group of stations (14) other than the station considered, called other station, and in which, during the second determination step (140), the station considered determines its eligibility to form an elected station of the station(s) further elected according to said message.

7. A method of change (100) according to claim 6, wherein, during the second determination step (140), the station considered determines its eligibility according to at least one of the following criteria: - if the marking of the station considered is the secondary marking and the message includes the preferential marking of the other station, the station considered determines that it is not eligible to form an elected station of the elected station(s);- if the marking of the station in question is the secondary marking and the message includes the secondary marking of the other station, the station in question determines that it is eligible to form an elected station of the elected station(s) only if the switching duration is one of the N stations (16-1, 16-2, 16-3) having the shortest switching duration among the switching durations of all the stations (16-1, 16-2, 16-3) of the group of stations (14), N being a predetermined integer, - if the marking of the station in question is the preferential marking, the station in question determines that it is eligible to form an elected station of the elected station(s), preferably independently of the message.;

8. A switching method (100) according to any preceding claim, wherein the switching phase (120) comprises a step of scheduling (145) a switching time between connection to the first satellite (20-1) and connection to the second satellite (20-2) for each station, based on the ephemeris of at least the first and second satellites (20-1, 20-2), and wherein the switching instruction comprises the switching time.

9. A method of change (100) according to any one of the preceding claims, wherein the switching phase (120) comprises a step of verifying (150) a presence of the second satellite (20-2), during which the or each elected station transmits a beacon signal to the second satellite (20-2), and receives a response to the beacon signal from the second satellite (20-2) when said second satellite (20-2) is present, preferably, the broadcasting step (160) being implemented only upon receipt of said response.

10. A switching method (100) according to any preceding claim, wherein, in the broadcasting step (160), the or each elected station broadcasts the switchover instruction via the first satellite (20-1) to the other stations (16-1, 16-2, 16-3) of the group of stations (14).

11. A station group (14) comprising a plurality of stations (16-1, 16-2, 16-3) configured to change connections between the stations (16-1, 16-2, 16-3) between a first state, in which each station (16-1, 16-2, 16-3) of the station group (14) is connected to a first satellite (20-1) of a plurality of satellites (20-1, 20-2), and a second state, in which each station (16-1, 16-2, 16-3) of the station group (14) is connected to a second satellite (20-2) of the plurality of satellites (20-1, 20-2), distinct from the first satellite (20-1), each satellite (20-1, 20-2) being movable relative to a geographical area in which the stations (16-1, 16-2, 16-3) of said group of stations (14) are positioned, each station (16-1, 16-2, 16-3) being able to establish a connection with each satellite (20-1, 20-2) during a predetermined duration of presence of said satellite (20-1, 20-2), considered for said geographical area,the group of stations (14) being configured to elect at least one station from among the stations (16-1, 16-2, 16-3) of the group of stations (14), as a function of at least one characteristic relating to a satellite antenna (34, 36) of said station (16-1, 16-2, 16-3), to obtain at least one elected station, the or each elected station being configured to command a switch between the first state and the second state, the or each elected station being configured to broadcast, to the other stations (16-1, 16-2, 16-3) of the group of stations (14), an instruction to switch the connection from the first satellite (20-1) to the second satellite (20-2).,

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