Process for entering a satellite communication network using a hopping beam

Abstract

The present disclosure relates to a procedure for entering a satellite communication network with hop-beams. The invention relates to a method for entering a satellite communication network comprising at least one satellite, the communication of the satellite communication network being organized according to a hop-beam mechanism in which a hop-frame defines an antenna beam configuration of the at least one satellite, wherein resources (101, 102, 103) of the hop-frame are reserved for forming a directional entry beam dedicated to the entry or re-entry of a user terminal into the satellite communication network, at least two directional entry beams having different aiming directions. The invention also relates to a satellite, a user terminal and a communication network configured to implement said method.

Description

Technical Field

[0001] This invention relates to the field of satellite communication transmission, and more specifically to a method for accessing a satellite communication network to a user terminal when communication within the network is organized via a beam-hopping mechanism. This invention can be applied to both geostationary and non-geostationary satellites. Background Technology

[0002] Access to a satellite communication network is a primary function of a satellite communication system. Attention is focused on both the initial access of a user terminal (or satellite communication terminal) to the network and its re-entry after a prolonged loss of connection. The performance of these accesses (the time spent entering or re-entering the system) contributes to the overall network performance.

[0003] The process of a satellite communication user terminal accessing a satellite communication network is well-known to those skilled in the art. It typically involves two stages:

[0004] - In the first phase, the user terminal synchronizes with the satellite in time and frequency and collects signaling data, including information about the structure of uplink frames, so as to be able to send connection requests (login) at the time provided for this purpose.

[0005] - In the second phase, the user terminal receives a connection response with connection information from the task segment and registers with the network.

[0006] Then, knowing the presence and needs of user terminals, the communication network can allocate its resources to their transmission. The largest area illuminated by a satellite on Earth will be referred to as its coverage area. The size of the coverage area depends on the satellite's altitude and the characteristics of one or more of its antennas.

[0007] In the case of a communication network that provides continuous coverage of its coverage area based on one or more multi-point geostationary satellites, network access is straightforward because the satellite locations are known and the user terminal has already established a radio connection with the satellite (regardless of the user terminal's location within the coverage area). The user terminal can then initiate a standard network access procedure based on signaling data transmitted using data services, which includes synchronization and registration with the satellite.

[0008] In the case of non-geostationary satellites illuminating their entire coverage area, such as those in constellations of LEO or MEO satellites (LEO and MEO being abbreviations for Near Earth Orbit and Medium Earth Orbit, respectively), the satellite's position is unknown or determined by information such as ephemeris tables, which are not accurate enough to allow the user terminal's antenna to be directly pointed at the satellite. In such cases, systems such as the Iridium satellite communication system are known where the user terminal does not have a highly directional antenna. This low directivity reduces the link budget and thus the transmission performance. Furthermore, the user terminal's transmission can be partially oriented along the geostationary arc, which is prohibited by regulatory constraints for transmissions intended for LEO or MEO satellites in certain frequency bands.

[0009] Alternatively, for user terminals using directional antennas, it is known to perform a process of searching for and tracking satellite positions before entering the network. The satellite search is conducted in terms of both altitude and azimuth, and, depending on the situation, also in terms of frequency and / or polarization. This search complicates the process and slows down the user terminal's entry into the network.

[0010] If a satellite provides only partial coverage within its coverage area, and if a user terminal is located in an uncovered area, the user terminal can no longer access the satellite communication network. This particular situation occurs when a satellite uses hopping beams for transmission, where the hopping beams illuminate geographic points according to user needs. Certain points not used by active users can then be turned off; user terminals existing in the turned-off areas lack a radio link with the satellite that would allow these user terminals to perform the process of accessing the network.

[0011] One known solution to this problem involves using a specific frequency band to enter the network, with the antenna beam covering the entire coverage area of ​​the satellite used for these transmissions. The frequency band can be selected to avoid the problem of transmitting in the direction of the geostationary arc. However, this solution requires inserting additional equipment into the satellite and using the available frequency bands throughout the coverage area (a frequency tuning problem). Furthermore, the use of a large antenna beam reduces the gain of the radio link. Another solution involves defining a time interval reserved for entering the satellite communication network, during which the satellite uses its antenna beam to cover its entire coverage area. This solution is also unsatisfactory because a large portion of the useful bandwidth within the satellite's entire coverage area is used for entering the network and therefore cannot be used for transmitting data services, and because transmissions from the satellite with a large antenna beam reduce the gain of the radio link.

[0012] Therefore, one object of the present invention is to provide a method for implementing a process for accessing a network when a geostationary satellite or a non-geostationary satellite only provides partial coverage of its coverage area, since the geostationary satellite or the non-geostationary satellite uses hopping beams.

[0013] Another object of the present invention is that the described method allows a terminal to enter the network for a short period of time with minimal impact on network capacity.

[0014] Finally, another objective of the present invention is that, in the case of non-geostationary satellites, the method allows for rapid acquisition of the satellite's position without involving launch in the direction of the geostationary arc. Summary of the Invention

[0015] To this end, the present invention describes a method for accessing a satellite communication network comprising at least one satellite, wherein communication is organized according to a beam-hopping mechanism, in which hopping frames define the antenna beam configuration of at least one satellite. In the method according to the invention, resources of hopping frames are reserved for forming directional access beams dedicated to user terminals entering or re-entering the satellite communication network, at least two of which have different aiming directions.

[0016] According to one embodiment, the directional access beam is used to transmit information about the transmission method of a user terminal's request to enter or re-enter the satellite communication network and to transmit requests to enter or re-enter the satellite communication network by one or more user terminals.

[0017] Advantageously, the amount and arrangement of frame skipping resources reserved for forming a directional entry beam can be dynamically adjusted.

[0018] In one implementation, the directional approach beam is configured such that the frame-skipping beam provides a radio link to all coverage areas of the satellite.

[0019] In one implementation, at least one satellite is a non-geostationary satellite. In this case, the directional approach beam is configured to be visible from Earth at a substantially constant elevation angle.

[0020] Advantageously, the elevation angle at which the directional beam can be seen from Earth is between 10° and 30°, preferably between 15° and 25°, and more preferably substantially equal to 20°.

[0021] Advantageously, the directional entry beam is configured such that multiple directional antenna beams cover an angular aperture that is substantially less than 180°.

[0022] Advantageously, the directional entry beam is oriented such that the transmissions of user terminals entering or re-entering the satellite communication network are not sent in the direction of the geostationary arc.

[0023] Advantageously, the user terminal seeking access to the satellite communication network is configured to search for the satellite by pointing its antenna beam to an elevation angle corresponding to the elevation angle of the incoming beam and by searching for non-geostationary satellites only by azimuth angle. Advantageously, the user terminal uses information about the satellite's position to reduce the azimuth angle search space.

[0024] The present invention also relates to a satellite in a satellite communication network whose communication is organized according to a beam-hopping mechanism, in which frame hopping defines the antenna beam configuration of the satellite. In the satellite according to the invention, the resources of frame hopping are reserved for forming directional access beams dedicated to user terminals entering or re-entering the satellite communication network, at least two of which have different aiming directions.

[0025] The present invention also relates to a user terminal configured to enter or re-enter a satellite communication network comprising at least one non-geostationary satellite, wherein communication of the satellite communication network is organized according to a beam-hopping mechanism, in which a hopping frame defines the antenna beam configuration of at least one non-geostationary satellite, the resources of the hopping frame are reserved for forming a directional entry beam, the directional entry beam being dedicated to the user terminal entering or re-entering the satellite communication network, at least two of the directional entry beams having different aiming directions, and the directional entry beams being configured to be visible from Earth at a substantially constant elevation angle. According to the present invention, the user terminal is configured to enter or re-enter the satellite communication network by:

[0026] - Orient the user terminal's antenna beam elevation angle to the elevation angle of the directional entry beam, and search for satellite positions solely by azimuth angle.

[0027] - Send a request to enter or re-enter the satellite communication network.

[0028] Finally, the present invention relates to a satellite communication network comprising at least one satellite as described above, and at least one user terminal. Attached Figure Description

[0029] The invention will be better understood by reading the following non-limiting description and by means of the accompanying drawings, which are given by way of example, and other features, details and advantages will become more apparent.

[0030] Figure 1 An example of a series of beam skipping frames in a method for accessing a satellite communication network according to an embodiment of the present invention is illustrated;

[0031] Figure 2a An example of the total radiation pattern of a satellite antenna in one embodiment of the present invention in the case of a non-geostationary satellite is shown;

[0032] Figure 2b The radiation pattern of a satellite antenna in one embodiment of the invention, in the case of a non-geostationary satellite, is schematically shown.

[0033] Figure 2c The diagram illustrates resource allocation in a hop frame for entering the network in one embodiment of the method according to the invention;

[0034] Figure 2d The diagram illustrates resource allocation in a hop frame for entering the network in one embodiment of the method according to the invention;

[0035] Figure 3 An implementation of a method for a user terminal to access a satellite communication network according to an embodiment of the present invention is illustrated;

[0036] Figure 4a The duration of illumination for a LEO satellite in polar orbit is shown as a function of the elevation angle of the satellite communication beam.

[0037] Figure 4b The duration of illumination of an LEO satellite in an inclined orbit is shown as a function of the elevation angle of the satellite communication beam.

[0038] Figure 5 It is a diagram showing the exchange sequence between a satellite and a user terminal, used to enable the user terminal to access the network according to one embodiment of the present invention. Detailed Implementation

[0039] This invention describes a method for a user terminal to access a satellite communication network, which includes at least one geostationary or non-geostationary satellite using hopping beams.

[0040] Beam hopping is a commonly used mechanism in satellite communications. It allows for complete and instantaneous reconfiguration of satellite coverage via the definition of frames divided into time intervals (called hop frames). Each time interval is associated with one or more antenna beam configurations. These beams are formed using one or more frequencies and one or more polarizations, either with active antennas (which typically allow multiple directional beams to be formed in parallel to illuminate multiple points simultaneously) or multiple directional antennas. Hop frames are dynamically defined as needed to best serve all participants in the network. They can be represented as two input tables that associate the formed antenna beam configuration and the satellite's antenna ports with each time interval.

[0041] The method according to the invention includes: using dedicated resources for user terminal access to the network by forming directional antenna beams in certain resources of the satellite in a frame skipping operation. The fact that directional antenna beams mean the beams only cover a portion of the satellite's coverage area allows for increased link gain between the satellite and the user terminal. The access beams are determined to be either transmit or receive beams based on whether communication between the satellite and the user terminal occurs on the uplink or downlink. They are not used for transmitting data services (useful data) between the user terminal and the satellite, but rather for transmitting signaling information allowing the user terminal to access / re-access the network. This information may be downlink information about the satellite's position (e.g., an ephemeris) and information allowing the user terminal to send connection requests (e.g., information about broadcast channels).

[0042] Figure 1 An example is illustrated in a method for accessing a satellite communication network according to an embodiment of the present invention, comprising a series of beam hopping frames. These hopping frames are divided into multiple time intervals TS1, TS2, ..., TSM. Figure 1 The columns are the various antenna ports of the satellite: Ant 1, Ant 2, ..., Ant N. The number of time intervals per frame hop and the number of antenna ports are given only by illustration. Within a frame hop, for each time interval, an antenna beam configuration is associated with each port.

[0043] This invention includes reserving beams 101, 102, and 103 within a frame skip for forming directional beams, which allows the terminal to access a satellite communication network; these beams are referred to as access beams. The remaining frame skips are unaffected by the method according to the invention. Figure 1 In the example, the incoming beam is reserved on the first antenna port for the first time interval of each hop frame. However, the frequency of the beam dedicated to network access can be increased to accelerate network access, or decreased to consume fewer resources. Beams dedicated to network access must be regularly distributed or on the same antenna port: their distribution is free and depends only on the performance sought. They may also be ad hoc beams formed when satellite resources are available. Therefore, the distribution of the incoming beam in hop frames is a trade-off between the time the user terminal enters the network and its impact on network capacity.

[0044] For example, in a satellite with 24 antenna ports, dividing a 16ms frame skip into 16 1ms time intervals, with each frame retaining an incoming beam, results in a very small decrease in the total system capacity, approximately 0.26%.

[0045] Advantageously, the incoming beams can all use the same carrier frequency (or a limited number of carrier frequencies) and / or the same polarization, in order to simplify the steps for user terminals to search for satellites.

[0046] The incoming beam formed by a satellite is a directional beam, which is pointed at a specific geographic area within the satellite's coverage area, thereby intermittently providing a radio link to terminals in areas not covered by the satellite. The size of this area depends on the gain required for transmission, the amount of resources dedicated to the network access, the relative speed of the satellite, and the performance required in terms of the timing of network access. To increase antenna gain, the incoming beam has different aiming directions.

[0047] Compared to known systems (in which frame skipping intervals are used for terminal-to-network access, and during this time, satellites use non-directional antennas to cover their entire coverage area), the method according to the invention uses a directional antenna beam that can be formed in parallel with other directional beams covering other parts of the coverage area, such as... Figure 1 As shown. Therefore, the implementation of the method according to the invention results in a much smaller reduction in system capacity compared to known methods. Furthermore, it has the advantage of being able to define the incoming beam in the same frequency band as the beam dedicated to services, thereby solving the problems of frequency band allocation and the additional hardware required for satellites and user terminals.

[0048] In the first embodiment, the incoming beam is defined to sequentially illuminate each satellite communication point within the satellite's coverage area. In this way, each point within the satellite's coverage area is periodically covered. The radio link between a user terminal located at an uncovered point and the satellite is necessarily periodic, and this period is used to perform the standard procedure for entering the network.

[0049] In another implementation, the incoming beam is defined as illuminating geographical areas not served by the service beam that skips frames. In this case, user terminals located within the satellite's coverage area access the network based on signaling data exchanged in the service beam, while user terminals located outside the service beam's coverage area access the radio link only when the incoming beam points to them.

[0050] In both implementations, the service beam and the access beam allow intermittent coverage of the entire coverage area of ​​the satellite, and thus allow any user located within its coverage area to access the network, even if that user is not covered by the service beam.

[0051] In another embodiment, specifically for non-geostationary satellites, the incoming beam is an antenna beam with a constant elevation angle; that is, a beam that forms a strip when viewed from the ground, within which a radio link exists between the user terminal and the satellite when the user terminal points its antenna to an elevation angle corresponding to the selected elevation angle. Due to the shape of the satellite's antenna radiation pattern, the concept of a constant elevation angle should have a margin, and slight variations may exist around the set elevation angle.

[0052] Figure 2a An example of the total radiation pattern of a satellite antenna in one embodiment of the invention, in the case of a non-geostationary satellite, is illustrated. This representation is given in the satellite's reference frame: it represents the satellite's coverage area and gives the equivalent radiative isotropic power level as a function of the beam direction and elevation angle within that coverage area. The darkest areas correspond to the areas of highest power. Figure 2a In the middle, the satellite has an antenna beam 201, the power of which is concentrated at a constant elevation angle of about 20° in the satellite's reference frame, for an angular aperture of about 150° north.

[0053] Using an antenna beam with a constant elevation angle has several advantages:

[0054] - Associated with the movement of all satellites in the constellation, it allows for systematic and regular coverage of almost all of its coverage areas, and thus provides user terminals not covered by the service beam with the opportunity to access the network;

[0055] - It allows satellite communication terminals to determine the satellite's position simply by scanning the space along the azimuth axis, thereby eliminating limitations on beamforming and / or mechanical movement of the satellite communication terminal and reducing the time spent searching for satellites, thus reducing network access time. Furthermore, since the satellite's elevation angle is known, user terminals can use highly directional antenna beams, which improves link budget;

[0056] - The satellite's antenna beam is directional, which increases the gain of the radio link between the satellite and visible user terminals;

[0057] - The satellite's antenna beam can be oriented to prevent user terminals from transmitting in the direction of the ground stationary arc.

[0058] To improve the link budget of the incoming beam, this invention proposes to divide the incoming beam into multiple beams, which have different aiming azimuth directions and together cover all the angular apertures of the beam 201.

[0059] Figure 2bAn implementation is schematically illustrated in which an incoming beam with a constant elevation angle is divided into multiple independent sub-beams. In this example, the incoming beam is divided into four sub-beams 211, 212, 213, and 214, which have the same elevation angle but different aiming directions to... Figure 2a The same applies to all corner apertures.

[0060] This implementation allows for a limitation of the angular aperture at the azimuth angle of the incoming beam, thereby improving the link budget. Figure 2b In the example, dividing the incoming beam into four sub-beams allows for an increase in link budget of approximately 6 dB. The number of sub-beams can be determined based on the expected increase in link budget and the anticipated impact on the overall system capacity.

[0061] Figure 2c and Figure 2d Various embodiments of resource allocation in one or more hop frames are illustrated in some implementations of the method according to the invention. Figure 2c In this process, sub-beams 211 to 214 are formed within each frame. Therefore, within each frame, resources 221 to 224 are attributed to sub-beams 211 to 214 respectively. Figure 1 Compared to the previous implementation, the impact of beam allocation on the total network capacity is multiplied by 4, but the capacity reduction is still less than in the prior art method. It should be noted that the arrangement of resources allocated within a frame skip is not important: they can be equally assigned to individual antenna ports within a given time interval, or any other configuration can be used.

[0062] exist Figure 2d In this context, resources 231 to 234, respectively belonging to the formation of incoming beams 211 to 214, are allocated in each frame skip. Figure 2d In this example, the four sub-beams are distributed across two consecutive frames. Figure 2c Compared to the previous implementation, the impact on network capacity is reduced, but the time that user terminals can observe satellites is divided by 2.

[0063] Figure 2c and Figure 2dThe frame definitions given are merely illustrative, and those skilled in the art will be able to readily modify these definitions according to their operational requirements, and in particular, according to the expected gain in the incoming beams, the visible duration of the satellites, and the expected impact on the overall network capacity. Furthermore, the distribution of resources attributable to the formation of incoming beams can be dynamically adjusted, for example, to form more beams in areas with unfavorable propagation conditions (e.g., around the equator, or under unfavorable weather conditions) to improve link budget. For example, eight incoming beams (four allocated per frame across two consecutive frames) could be defined for transmissions near the equator, while only four incoming beams (two allocated per frame across two consecutive frames) could be defined for transmissions above 50° latitude.

[0064] Figure 3 An example illustrates an implementation of a method for a user terminal to access a satellite communication network according to an embodiment of the present invention in the case of a non-geostationary satellite. A non-geostationary satellite 301 (e.g., a LEO satellite moving in an inclined orbit in direction 302) is configured to form an antenna beam 303 with a constant elevation angle. The coverage area of ​​the antenna beam 303 on the ground is shown as a stripe 304, which is curved due to the curvature of the Earth. The coverage area 304 on the ground corresponds to the sum of the formed entry sub-beams in order to cover a large azimuth angle while benefiting from high antenna gain, such as... Figure 2b As shown. The width of strip 304 depends on the satellite's altitude and the aperture of the antenna beam. Area 304 moves simultaneously with satellite 301. Therefore, a user terminal 305 seeking access to the satellite communication network with its antenna positioned at the correct elevation angle is radio visible to satellite 301 for a period of time, which depends on the satellite's speed, altitude, the configuration of the access beam, the selected elevation angle, and the number of access sub-beams formed. For example, for a non-geostationary LEO satellite forming an access beam with an elevation angle of approximately 20° to the user terminal along its north-south axis and an aperture of 4°, the width of the coverage area 304 on the ground is greater than 300 km. If the satellite is moving in a polar orbit at a speed of 7.4 km / s, it will be visible to the user terminal pointing at a 20° elevation angle for approximately 40 seconds. The user terminal can use this time to detect the satellite by scanning the sky only by azimuth angle for subsequent network access procedures (synchronization and registration).

[0065] The elevation angle and aperture of the incoming beam are selected based on the satellite's motion to increase the visibility time for the user terminal and maximize antenna gain. Figure 4a and Figure 4b The duration is shown as a function of the choice of elevation angle of the incoming beam, during which the user terminal can see a non-geostationary LEO satellite moving at a speed of 7.4 km / s using an antenna beam with a 4° aperture along the north-south axis. Figure 4aAssuming the satellite is operating in a polar orbit at an altitude of approximately 1000 km, and Figure 4b Assume the satellite is operating in an inclined orbit at an altitude of approximately 1200 km. For a given application, when the included elevation angle is selected between 15° and 25°, the beamwidth 304 will always be greater than 300 km.

[0066] Ideally, the angular aperture of an antenna beam with a constant elevation angle transmitted by a non-geostationary satellite is a few degrees along the minor axis of its coverage area on the ground, typically -3dB, less than 10°, usually around 4° to 5°, and covers 360° of azimuth to provide radio links to as many user terminals as possible. However, regulators may consider prohibiting user terminals from transmitting in the direction of the geostationary arc within certain frequency bands. For this purpose, it is advantageous to select a sub-beam dedicated to entering the network with an overall azimuth aperture angle slightly less than 180° and pointing towards the poles. This is Figure 2b The example in the diagram shows that the incoming beams corresponding to the four sub-beams 211 to 214 have an aperture with an azimuth angle of approximately 150°. This configuration prevents the user terminal from transmitting along the direction of the geostationary arc within a portion of the Earth.

[0067] By altering the orientation of the equivalent entry beam formed by the individual entry sub-beams during the transit of a non-geostationary satellite, the user terminal's transmission is systematically performed in the direction opposite to the geostationary arc during network access. For example, for a satellite in polar orbit, a beam with a constant elevation angle can be modified as follows:

[0068] - As the satellite moves from the equator toward the North Pole, the various incoming sub-beams form an equivalent incoming beam oriented toward the South Pole (i.e., behind the satellite).

[0069] - As the satellite moves from the North Pole toward the equator, the various incoming sub-beams form an equivalent incoming beam oriented toward the South Pole (i.e., in front of the satellite).

[0070] - As the satellite moves from the equator toward the South Pole, the various incoming sub-beams form an equivalent incoming beam oriented toward the North Pole (i.e., behind the satellite).

[0071] - As the satellite moves from the South Pole toward the equator, various incoming sub-beams form an equivalent incoming beam oriented toward the North Pole (i.e., in front of the satellite).

[0072] Whether in polar orbit or inclined orbit, by switching at least four times during the rotation period, the equivalent entry beam orientation will be aligned to the pole direction, thereby avoiding the satellite communication terminal transmitting in the direction of the geostationary arc.

[0073] Near the poles, when the area outside the region corresponding to the geostationary arc is not visible to the satellite communication terminal, the satellite can oriented the equivalent directional entry beam toward both the front and rear of the satellite, or modify the beam orientation by tilting the satellite, in order to achieve a larger visible coverage area on the ground.

[0074] Figure 5 This is a diagram illustrating the sequence of a user terminal entering a telecommunications network according to one embodiment of the present invention, assuming a non-geostationary satellite with a constant elevation angle and the user is located in an area not covered by the satellite. This diagram is for illustrative purposes only and represents one embodiment.

[0075] The satellite forms an antenna beam with a constant elevation angle in the hop frame resources dedicated to network access, and this access beam is oriented in at least two different directions. Advantageously, the access antenna beam is configured to cover all azimuth angles that are large, but preferably substantially less than 180°, such as... Figure 2b The sub-beams shown are used by satellites to transmit signaling information 511 (e.g., ephemeris tables that allow user terminals to determine their location and the locations of other satellites in the constellation) and information that allows user terminals to send connection requests over the network (e.g., active channels and / or time intervals).

[0076] In part, the user terminal is configured to use an antenna with a directional antenna beam to detect the 502 satellite and to locate the satellite's position only by azimuth, the directional antenna beam being oriented at an elevation angle corresponding to the incoming beam.

[0077] Advantageously, when the satellite is configured to enter the beam in a directional manner to avoid the user terminal transmitting in the direction of the geostationary arc, the user terminal can search for the satellite only in the direction opposite to the geostationary arc with an azimuth angle of less than 180°.

[0078] Advantageously, to accelerate satellite search, the user terminal can use information about the satellite's position stored in its memory to reduce the azimuth search area. For example, this information could be an ephemeris that allows it to reconstruct the satellite's position. In this case, the user terminal is able to calculate its azimuth in a fairly accurate manner, allowing it to limit the search to around the satellite's expected position. However, ephemeris have a very short effective duration (a few hours). Advantageously, the present invention proposes using RAAN information (RAAN is an abbreviation for the right ascension of the rising node), which provides the angle of a satellite moving north across the equator. This information allows the determination of the satellite's orbit and, correspondingly, limits the azimuth search area. RAAN information has a much longer effective duration than ephemeris (approximately several years). Therefore, in terms of processing operations, searching for satellite positions is faster and less costly, freeing up time for the process of entering the network itself.

[0079] Once a satellite is detected, the user terminal collects the signaling data transmitted by the satellite, especially the ephemeris and information about the connection method.

[0080] The ephemeris allows user terminals to track satellite positions during their motion within the visible period, thus maintaining radio contact with satellites even if the user terminal's antenna is highly directional. Information about the connection method allows it to know the time and channel dedicated to sending connection requests.

[0081] Then, the user terminal can send a connection request 512 to the satellite. The satellite sends this request to the mission center, which records the existence of the user terminal, allows or disallows the user terminal to join the network, registers the user terminal, and assigns network parameters (such as IP address) to the user terminal. Then, the satellite sends a response 513 to the user terminal, containing information about the user terminal's registration status in the network and its network parameters.

[0082] Once these steps have been performed, the user terminal registers with the satellite communication network, and the network administrator responsible for defining beam-hopping frames takes the user terminal into account during its subsequent designation period.

[0083] Figure 5 All the switching shown can be performed on a single resource dedicated to a hop frame entering the network, or on multiple dedicated resources during one or more channels visible to the satellite.

[0084] The difference in operation of the method of the invention of the geostationary satellite is that the beam does not have a constant elevation angle, and it is not necessary to send information related to the position of the satellite, nor is it necessary to perform the satellite search step 502.

[0085] Therefore, the method for accessing a telecommunications network according to the present invention includes: reserving resources for accessing / re-accessing the network in a beam-hopping frame, wherein during accessing / re-accessing the network, at least one satellite of the network is configured to have the following directional antenna beams:

[0086] - The directional antenna beam is oriented to work in conjunction with the service beam to provide a radio link between the satellite and the entire coverage area; or

[0087] - The directional antenna beam is shaped such that, for non-geostationary satellite networks, the incoming beam is observable from Earth at a constant elevation angle.

[0088] In the access method according to the invention, the access beam can be customized in parallel with the service beam and is in the same frequency band.

[0089] For non-geostationary satellites, the method according to the invention divides the incoming beam into multiple beams with smaller angular apertures transmitted at azimuth angles on different hop frame resources to improve the link budget. Advantageously, the beams can be oriented so that the user terminal does not transmit in the direction of the geostationary arc.

[0090] The present invention also relates to a satellite including means for forming antenna beams, and the satellite being configured to use dedicated resources for frame skipping to form directional approach beams, and to a satellite communication network including such a satellite. According to one embodiment, this addresses the problem of configuring approach beams to be oriented such that these approach beams are visible from Earth at a substantially constant elevation angle for a non-geostationary satellite.

[0091] The present invention also relates to a satellite user terminal configured to search for the presence of non-geostationary satellites by positioning the antenna of the satellite user terminal using a given elevation angle of the incoming beam and by performing a spatial scan based solely on azimuth angle. The user terminal is configured to collect connectivity information and send a request to enter / re-enter the satellite communication network once a satellite has been detected.

Claims

1. A method for accessing a satellite communication network, the satellite communication network comprising at least one satellite (301), the communication of the satellite communication network being organized according to a beam-hopping mechanism, wherein a hopping frame defines the antenna beam configuration of the at least one satellite, the method being characterized in that hopping frame resources (101, 102, 103, 221, 222, 223, 224, 231, 232, 233, 234) of the hopping frame are reserved for forming directional access beams (211, 21...). 2, 213, 214), the directional entry beams (211, 212, 213, 214) are dedicated to the user terminal (305) entering or re-entering the satellite communication network. The directional entry beams are not used to transmit data services between the user terminal and the satellite, but are used to transmit signaling information that allows the user terminal to enter / re-enter the network. At least two of the directional entry beams (211, 212, 213, 214) have different aiming directions.

2. The method for accessing a satellite communication network according to claim 1, wherein, The directional access beam is used to transmit (511) information about the transmission method of a user terminal’s request to enter or re-enter the satellite communication network by the satellite, and to transmit (512) a request to enter or re-enter the satellite communication network by one or more user terminals.

3. The method for accessing a satellite communication network according to claim 1, wherein, The amount and arrangement of the frame skipping resources reserved for forming a directional entry beam can be dynamically adjusted.

4. The method for accessing a satellite communication network according to claim 1, wherein, The directional approach beam is configured such that the frame skipping beam provides a radio link to all coverage areas of the satellite.

5. The method for accessing a satellite communication network according to any one of claims 1 and 3, wherein, The at least one satellite is a non-geostationary satellite (301), and wherein the directional entry beams (211, 212, 213, 214) are configured to be visible from Earth at a substantially constant elevation angle.

6. The method for accessing a satellite communication network according to claim 5, wherein, The elevation angle at which the directional incoming beam can be seen from Earth is between 10° and 30°, preferably between 15° and 25°, and more preferably substantially equal to 20°.

7. The method for accessing a satellite communication network according to claim 5, wherein, The directional entry beams are configured such that multiple directional antenna beams (211, 212, 213, 214) cover an angular aperture that is substantially less than 180°.

8. The method for accessing a satellite communication network according to claim 5, wherein, The directional entry beam is oriented such that transmissions from user terminals entering or re-entering the satellite communication network are not sent in the direction of the geostationary arc.

9. The method for accessing a satellite communication network according to claim 5, wherein, The user terminal (305) seeking access to the satellite communication network is configured to search (502) the at least one non-geostationary satellite by pointing the antenna beam of the user terminal (305) to an elevation angle corresponding to the elevation angle of the access beam and by searching the at least one non-geostationary satellite only by azimuth angle.

10. The method for accessing a satellite communication network according to claim 9, wherein, The user terminal uses information about the satellite's position to reduce its azimuth search space.

11. A satellite (301) in a satellite communication network, wherein communication of the satellite communication network is organized according to a beam hopping mechanism, wherein a hopping frame defines the antenna beam configuration of the satellite, the satellite being characterized in that the resources (101, 102, 103) of the hopping frame are reserved for forming directional entry beams (211, 212, 213, 214), the directional entry beams (211, 212, 213, 214) being dedicated to user terminals entering or re-entering the satellite communication network, the directional entry beams not being used to transmit data services between the user terminal and the satellite, but rather to transmit signaling information allowing the user terminal to enter / re-enter the network, and at least two of the directional entry beams having different aiming directions.

12. A user terminal (305) configured to enter or re-enter a satellite communication network comprising at least one non-geostationary satellite (301), wherein communication of the satellite communication network is organized according to a beam-hopping mechanism, wherein a hopping frame defines the antenna beam configuration of the at least one non-geostationary satellite, the resources (101, 102, 103) of the hopping frame are reserved for forming directional entry beams (211, 212, 213, 214), the directional entry beams (211, 212, 213, 214) being dedicated to the user terminal entering or re-entering the satellite communication network, at least two of the directional entry beams having different aiming directions, the directional entry beams being configured to be visible from Earth at a substantially constant elevation angle, the user terminal being characterized in that the user terminal is configured to enter or re-enter the satellite communication network by: - Orient the elevation angle of the user terminal's antenna beam (502) to the elevation angle of the directional entering beam, and search for the satellite's position only by azimuth angle. - Send (512) a request to enter or re-enter the satellite communication network, in, The directional entry beam is not used to transmit data services between the user terminal and the satellite, but rather to transmit signaling information allowing the user terminal to enter / re-enter the network.

13. A satellite communication network, characterized in that, The satellite communication network includes at least one satellite as described in claim 11 and at least one user terminal as described in claim 12.

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