WO2020204816A1

WO2020204816A1 - Method of controlling access to a satellite uplink channel in a vhf data exchange system (vdes) and system thereof

Info

Publication number: WO2020204816A1
Application number: PCT/SG2020/050164
Authority: WO
Inventors: Tung Chong David Wong; Xiaoming Peng; Qian Chen
Original assignee: Agency For Science, Technology And Research
Priority date: 2019-03-29
Filing date: 2020-03-25
Publication date: 2020-10-08

Abstract

There is provided a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite. The method includes: obtaining position information of a plurality of vessels with respect to the plurality of cells; configuring time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information; generating satellite uplink channel configuration information for the satellite uplink channel, the satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel; and transmitting the satellite uplink channel configuration information to the plurality of cells for the plurality of vessels to access a frame of the satellite uplink channel based on the satellite uplink channel configuration information. There is also provided a corresponding system for controlling access to a satellite uplink channel to a satellite in VDES.

Description

METHOD OF CONTROLLING ACCESS TO A SATELLITE UPLINK CHANNEL IN A VHF DATA EXCHANGE SYSTEM (VDES) AND SYSTEM

THEREOF

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore Patent Application No. 10201902837W, filed on 29 March 2019, the content of which being hereby incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

[0002] The present invention generally relates to a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) and a system thereof, and more particularly, with respect to a plurality of cells within a coverage area of the satellite.

BACKGROUND

[0003] Automatic Identification System (AIS) is an existing solution to provide one way reporting of the position information (or location information) of vessels (or ships). However, the existing AIS faced severe overloading problem over Very High Frequency (VHF) channels, especially over crowded waters. In view of the overloading problem faced by the existing AIS, the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA), the International Maritime Organization (IMO) and the International Telecommunication Union (ITU) developed a new generation VHF Data Exchange System (VDES) to offer two-way data exchange, thus enabling new features such as broadcasting critical maritime information instead of only one-way reporting. The VDES seeks to alleviate the overloading problem suffered by the existing AIS. For example, by offering ship-to-ship, ship-to-shore, shore-to-ship, ship-to-satellite and satellite-to-ship communications, the VDES also supports the Global Maritime Distress and Safety System (GMDSS).

[0004] In particular, the VDES is a maritime communication system comprising different communication subsystems, namely, AIS, Applicant-Specific Messages (ASM) and VHF Data Exchange (VDE). FIG. 1 depicts a schematic overview of the VDES, including the current allocation of various frequency bands for the channels in VDES. In the VDES, ASM channels decreases the load of AIS channels, and the VDE allows higher rate communications as well as being highly flexible to be able to support a variety of services, such as relating to weather, regional hydrology, aids to navigation, risk warning, traffic management and route information. Therefore, the VDES does not only support direct ship-to-ship and ship-to-shore communications, but also support ship- to-satellite and satellite-to-ship communications based on the satellite component of VDES (which may be referred to herein as satellite VDES).

[0005] For example, International Telecommunications Union Recommendation (ITU-R) M.1371 -5 has defined a standard for one-way reporting of position information over VHF AIS channels. In particular, two carrier frequencies were allocated for AIS, namely, 161.975 MHz and 162.025 MHz, each having a channel bandwidth of 25 KHz. The VDES provides data exchange between ship-to-ship and ship-to-shore via the use of more channels with higher channel bandwidth of up to 100 KHz.

[0006] The recent progress for New Space that leverages on disruptive technologies for small satellites operating in 600 km orbit opens up an opportunity to explore the use of small satellites to achieve timely data access from space. Small satellites can offer a low-cost solution with lower entry barrier for AIS and VDES satellites forming a constellation to connect ship-to-ship and ship-to-shore for a global coverage. This is an effective means to extend the AIS and VDES to areas outside of coastal coverage.

[0007] Conventionally, access to channels by each ship is accomplished through a variant of the conventional time division multiple access (TDMA) technique but without having a central controller to coordinate the multiple access to the channel. For each channel, the frame length is one minute in duration and each frame consists of 2,250 time slots which AIS messages may be transmitted. All AIS transmitters are synchronised to the Coordinated Universal Time (UTC) such that the start of each time slot is universally known. In essence, whenever a message is sent from a ship, the transmitter announces the next intended time slots that it will be transmitting. This information is contained within the message sent. Thus, message collisions may be largely mitigated within the areas of reception for terrestrial transmission. [0008] However, due to the large footprint (or coverage area) of a satellite, for example, a message collision over the same time slot may occur from AIS and/or VDES satellite uplink signals because multiple ships which are outside of respective reception areas (i.e., out of sight (field of view) of each other) may transmit messages over the same time slots. The implication of a message collision is that most, if not all, of the messages involved in the collision would be lost. Solutions to recover these collided messages have been studied in the past to de-collide the interference using an interference cancellation method with Doppler diversity and Crossed Dipoles Antennas. In the interference cancellation method, a bank of parallel receivers operating at different frequency offsets are used to enhance the signals corresponding with the considered frequency offset while attenuating the other signals. In the event that the Doppler shifts of two or more signals are not separable by the receiver bank, then interference cancellation would be invoked. This interference cancellation leads to high computational power which may not be acceptable or suitable for satellites, especially small satellites, due to their power budget constraints.

[0009] A need therefore exists to provide a method of controlling access to a satellite uplink channel to a satellite in a VDES and a system thereof that seek to overcome, or at least ameliorate, one or more of the deficiencies in conventional methods and systems for controlling access to a satellite uplink channel, such as but not limited to, reducing or minimizing message collisions in accessing a satellite uplink channel to the satellite in the VDES by multiple vessels, thereby improving the throughput of the satellite in the VDES. It is against this background that the present invention has been developed.

SUMMARY

[0010] According to a first aspect of the present invention, there is provided a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, using at least one processor, the method comprising:

obtaining position information of a plurality of vessels with respect to the plurality of cells; configuring time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information;

generating satellite uplink channel configuration information for the satellite uplink channel, the satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel; and transmitting the satellite uplink channel configuration information to the plurality of cells for the plurality of vessels to access a frame of the satellite uplink channel based on the satellite uplink channel configuration information.

[0011] According to a second aspect of the present invention, there is provided a system for controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, the system comprising:

a memory; and

at least one processor communicatively coupled to the memory and configured to: obtain position information of a plurality of vessels with respect to the plurality of cells;

configure time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information;

generate satellite uplink channel configuration information for the satellite uplink channel, the satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel; and

transmit the satellite uplink channel configuration information to the plurality of cells for the plurality of vessels to access a frame of the satellite uplink channel based on the satellite uplink channel configuration information.

[0012] According to a third aspect of the present invention, there is provided a computer program product, embodied in one or more non-transitory computer-readable storage mediums, comprising instructions executable by at least one processor to perform a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, using at least one processor, the method comprising:

obtaining position information of a plurality of vessels with respect to the plurality of cells;

configuring time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information;

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

FIG. 1 depicts a schematic overview of a VDES, including the current allocation of various frequency bands for the channels in VDES;

FIG. 2 depicts a schematic flow diagram of a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, according to various embodiments of the present invention;

FIG. 3 depicts a schematic block diagram of a system for controlling access to a satellite uplink channel to a satellite in a VDES with respect to a plurality of cells within a coverage area of the satellite, according to various embodiments of the present invention; FIG. 4 depicts a schematic drawing of a VDES for wireless communication, according to various embodiments of the present invention;

FIG. 5 depicts shows a conventional satellite VDES MAC slot access range for a frame of a satellite uplink channel;

FIG. 6 depicts a dynamic satellite VDES partition MAC slot access range based on the satellite VDES partition MAC protocol according to various example embodiments;

FIGs. 7A to 7C depict example frame structures for the coexistence of the SBB- based dynamic slot partition VDES MAC protocol according to various example embodiments and the terrestrial VDES MAC protocol; and

FIG. 8 depicts simulation results of throughputs of various satellite MAC protocols against a range of channel loads.

DETAILED DESCRIPTION

[0014] Various embodiments of the present invention provide a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) and a system thereof, and more particularly, with respect to a plurality of cells within a coverage area of the satellite.

[0015] VDES is a maritime communication system that is known in the art, which comprises different communication subsystems, namely, AIS, Applicant-Specific Messages (ASM) and VHF Data Exchange (VDE). FIG. 1 depicts a schematic overview of a VDES, including the current allocation of various frequency bands for the channels in VDES. It will be appreciated by a person skilled in the art that various functions or frequency usage of the VDES may be subjected to change (e.g., revised or modified) over time as appropriate, such as by the IALA, the IMO, and/or the ITU, without deviating from the scope of the present invention. That is, the present invention is not limited to the VDES having the currently defined functions and frequency usage (such as shown in FIG. 1), but also applies to a VDES having revised or modified functions or frequency usage as appropriate.

[0016] As mentioned in the background, due to the large footprint (or coverage area) of a satellite, message collisions may occur in satellite uplink messages (or signals) from multiple vessels under the VDES which are out of sight (field of view) of each other. As a result, the messages involved in collisions may be lost. There exist conventional techniques for recovering collided messages, but such conventional techniques may not be acceptable or suitable to be employed in satellites, especially small satellites (e.g., having a wet mass under 500 kg), as for example, such conventional techniques require high computational power while satellites may typically have power budget constraints. Accordingly, various embodiments of the present invention provide a method of controlling access to a satellite uplink channel to a satellite in a VDES and a system thereof that seek to overcome, or at least ameliorate, one or more of the deficiencies in conventional methods and systems for controlling access to a satellite uplink channel, such as but not limited to, reducing or minimizing message collisions in accessing a satellite uplink channel to the satellite in the VDES by multiple vessels, thereby improving the throughput of the satellite in the VDES.

[0017] FIG. 2 depicts a schematic flow diagram of a method 200 of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, using at least one processor, according to various embodiments of the present invention. The method 200 comprising: obtaining (at 202) position information of a plurality of vessels with respect to the plurality of cells; configuring (at 204) time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information; generating (at 206) satellite uplink channel configuration information for the satellite uplink channel, the satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel; and transmitting (at 208) the satellite uplink channel configuration information to the plurality of cells for the plurality of vessels to access a frame of the satellite uplink channel based on the satellite uplink channel configuration information.

[0018] In various embodiments, the method 200 is performed or executed by or at one or more of the satellites (e.g., each of the satellites, respectively) in the VDES. The above-mentioned coverage area of the satellite may also be referred to as a field of view (FoV) or a footprint of the satellite. In various embodiments, each cell of the plurality of cells refers to a geographic region or area, such as but not limited to, a circular region. In various embodiments, each of the plurality of cells is a self-organized time division multiple access (SOTDMA) cell. By way of an example only and without limitation, a SOTDMA cell may have a radius of about 40 nm (nautical miles).

[0019] In various embodiments, the satellite uplink channel may be any one of the satellite uplink channels as shown in FIG. 1 , including a VDE satellite uplink channel, an ASM satellite uplink channel or an AIS satellite uplink channel. In various embodiments, the satellite uplink channel may be a VDE satellite uplink channel or an ASM satellite uplink channel. In various embodiments, the satellite uplink channel may be a VDE satellite uplink channel.

[0020] In various embodiments, in relation to the above-mentioned obtaining (at 202) position information of a plurality of vessels, the position information of each vessel may be obtained from the periodic position reporting by the respective vessel, such as via the position reporting and safety related information transmitted by the respective vessel in an AIS message. For example, the position information of each vessel may be based on global positioning system (GPS) or global navigation satellite system (GNSS), that is, may be GPS data or GNSS data. In various embodiments, the position information of each vessel located in each of the plurality of cells may be obtained, that is, all vessels located in the plurality of cells.

[0021] In various embodiments, in relation to the above-mentioned configuring (at 204) time slots in a frame structure for the satellite uplink channel, one respective group of time slots is configured for each of the plurality of cells. Therefore, each of the plurality of cells has a corresponding group of time slots in the frame structure for the satellite uplink channel. In various embodiments, each group of time slots has a size (e.g., the number of time slots) configured for the corresponding cell. In various embodiments, the plurality of groups of time slots in the frame structure are non-overlapping, that is, no group of time slots of the plurality of groups of time slots overlap with another group of time slots of the plurality of groups of time slots. In various embodiments, within each group of time slots of the plurality of groups of time slots, the time slots (i.e., all time slots within the group) are consecutive time slots. In various embodiments, the above- mentioned configuring (at 204) time slots in a frame structure for the satellite uplink channel may be performed iteratively (e.g., periodically) such as once per frame or once per satellite bulletin board so as to be transmitted in the satellite bulletin board. Accordingly, the configuration of the time slots in the frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells may be updated iteratively (e.g., periodically).

[0022] In various embodiments, in relation to the above-mentioned generating (at 206) satellite uplink channel configuration information for the satellite uplink channel and the above-mentioned transmitting (at 208) the satellite uplink channel configuration information, after time slots in the frame structure have been configured into the plurality of groups of time slots, satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel may then be generated and transmitted to the plurality of cells. For example, the satellite uplink channel configuration information may be transmitted to the plurality of cells via a broadcast. Accordingly, each vessel in the plurality of cells may receive the satellite uplink channel configuration information transmitted from the satellite and may thus be informed of the frame structure (i.e., the current frame structure configured as described above) such that the vessel may access a frame of the satellite uplink channel having the frame structure. In particular, each vessel located in a particular cell of the plurality of cells may access a frame of the satellite uplink channel having the frame structure and within a group of time slots configured for that particular cell (i.e., within the corresponding group of time slots).

[0023] Furthermore, when the frame structure is modified, for example, the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure is modified (or updated) based on new (or updated) position information of vessels (e.g., all vessels) in the plurality of cells, vessels in the plurality of cells are also informed of the modified frame structure (via the satellite uplink channel configuration information transmitted from the satellite). Therefore, each vessel located in a particular cell of the plurality of cells may access a frame of the satellite uplink channel having the modified frame structure and within a group of time slots configured for that particular cell (i.e., within the corresponding group of time slots).

[0024] Accordingly, based on the method 200 of controlling access to a satellite uplink channel to a satellite in a VDES according to various embodiments, message collisions in accessing the satellite uplink channel to the satellite in the VDES by multiple vessels are advantageously reduced or minimized, thereby improving the throughput of the satellite VDES. For example, by configuring time slots in the frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information, and transmitting the satellite uplink channel configuration information for the satellite uplink channel to the plurality of cells, vessels located in any particular cell of the plurality of cells would access a frame of the satellite uplink channel within a group of time slots configured for that particular cell (e.g., the group of time slots having a size configured for that particular cell) Therefore, for example, message collisions in accessing the satellite uplink channel amongst such vessels in the particular cell, as well as message collisions amongst such vessels in the particular cell with vessels in other cells of the plurality of cells, can be reduced or minimized, thereby improving the throughput of the satellite VDES. Furthermore, since each group of time slots is configured (e.g., sized) for the corresponding cell based on the position information (e.g., from which the number of vessels in each cell can be determined), the time slots in a frame of the satellite uplink channel can be more efficiently utilized by vessels in the plurality of cells (e.g., a group of time slots may be configured to have a larger size for a cell having more vessels therein), thereby further improving the throughput of the satellite VDES. Still further, each group of time slots may be iteratively (e.g. periodically) configured for the corresponding cell based on new (or updated) position information of vessels (e.g., all vessels) in the corresponding cell at each iteration, thereby dynamically configuring the frame structure (in particular, the configuration of the plurality of groups of time slots for the plurality of cells, respectively) over time for capturing the dynamic state of the plurality of cells (e.g., number of vessels therein may change over time) and enabling the time slots in the frame of the satellite uplink channel to continually be efficiently utilized by vessels in the plurality of cells. [0025] In various embodiments, the above-mentioned configuring (at 204) time slots in the frame structure for the satellite uplink channel comprises partitioning (e.g., dividing) time slots in the frame structure into the plurality of groups of time slots for the plurality of cells, respectively, each of the plurality of groups of time slots having a size determined based on the position information of the plurality of vessels. In various embodiments, the size of a group of time slots refers to the number of time slots in the group of time slots. In various embodiments, each group of time slots partitioned for a corresponding cell may be referred to as partitioned time slots for the corresponding cell.

[0026] In various embodiments, the above-mentioned configuring (at 204) time slots in the frame structure for the satellite uplink channel further comprises assigning the plurality of groups of time slots to the plurality of cells, respectively, for vessels in each of the plurality of cells to access the frame of the satellite uplink channel within the corresponding group of time slots assigned to the cell (in which the vessels are located). That is, each of the plurality of groups of time slots is assigned to a corresponding or respective cell of the plurality of cells, such that vessels (e.g., all vessels) in the corresponding cell access the frame (having the frame structure) of the satellite uplink channel within the assigned group of time slots. In various embodiments, vessels in the corresponding cell may access the frame within the assigned group of time slots based on a satellite VDES media access channel (MAC) protocol, and in particular, a slot carrier- sense TDMA (SCTDMA) MAC protocol). In various embodiments, the above-mentioned information indicating the configuration of the plurality of groups of time slots for the plurality of cells in the frame structure for the satellite uplink channel further indicates the assignment of the plurality of groups of time slots to the plurality of cells, respectively.

[0027] In various embodiments, the method 200 further comprises determining a number of vessels in each of the plurality of cells based on the position information. In this regard, the size of each of the plurality of groups of time slots is determined based on the number of vessels determined in the corresponding cell of the plurality of cells. Accordingly, in various embodiments, each group of time slots may be determined to have a size (e.g., number of time slots) based on the number of vessels determined to be in the corresponding cell. For example, a vessel may be determined to be in a cell if the position information (e.g., GPS or GNSS position) of the vessel is within a geographical region or area of the cell (e.g., defined by the cell).

[0028] In various embodiments, the size of each of the plurality of groups of time slots is selected from a plurality of predetermined sizes (number of time slots) for a plurality of predetermined categories of cells, respectively, based on the number of vessels determined in the corresponding cell of the plurality of cells. In other words, a plurality of sizes (number of time slots) predetermined for a plurality of predetermined categories of cells, respectively, may be provided. By way of an example only and without limitation, the predetermined categories of cells may be a cell having a low load (or a low load cell), a cell having a medium load (or a medium load cell) or a cell having a high load (or a high load cell), and for each of these predetermined categories of cells, the size of the group of time slots assigned thereto (or configured for) is predetermined. Accordingly, each of the plurality of cells may be classified into one of the plurality of predetermined categories (e.g., one of a low load cell, a medium load cell or a high load cell) based on the number of vessels determined to be in the cell, and the size of the group of time slots assigned to (or configured for) the cell is determined to be the size (selected from the plurality of predetermined sizes) predetermined for the category which the cell belongs to.

[0029] In various embodiments, the position information of the plurality of vessels comprises current position information of the plurality of vessels (e.g., latest position information of the plurality vessels received by the satellite), and the number of vessels in each of the plurality of cells is determined based on the current position information of the plurality of vessels.

[0030] In various embodiments, the method 200 is configured to control access to the satellite uplink channel iteratively (e.g., periodically or repeatedly). In this regard, each iteration (or repetition) comprises: the above-mentioned obtaining (at 202) position information of a plurality of vessels with respect to the plurality of cells; the above- mentioned configuring (at 204) time slots in the frame structure for the satellite uplink channel; the above-mentioned generating (at 206) satellite uplink channel configuration information for the satellite uplink channel; and the above-mentioned transmitting (at 208) the satellite uplink channel configuration information to the plurality of cells. In other words, in each iteration, each of the above-mentioned obtaining (at 202) position information of a plurality of vessels with respect to the plurality of cells; the above- mentioned configuring (at 204) time slots in the frame structure for the satellite uplink channel; the above-mentioned generating (at 206) satellite uplink channel configuration information for the satellite uplink channel; and the above-mentioned transmitting (at 208) the satellite uplink channel configuration information to the plurality of cells, may be performed or repeated. Accordingly, each group of time slots may be iteratively (e.g., periodically) configured for the corresponding cell based on new (or updated or latest) position information of vessels (e.g., all vessels) in the corresponding cell at each iteration, thereby dynamically configuring the frame structure (in particular, the configuration of the plurality of groups of time slots for the plurality of cells, respectively) for the satellite uplink channel over time for capturing the dynamic state of the plurality of cells (e.g., number of vessels therein may change over time) and enabling the time slots in the frame of the satellite uplink channel to continually be efficiently utilized by vessels in the plurality of cells.

[0031] In various embodiments, the satellite uplink channel configuration information is transmitted to the plurality of cells in at least one of a bulletin board signalling channel (BBSC) and an announcement signalling channel (ASC). For example, with respect to the BBSC, a satellite bulletin board may define the network configuration parameters such as signaling channels (control channels) and data channel(s), protocol versions and future network configuration, and the satellite uplink channel configuration information may be included in the satellite bulletin board. For example, the satellite bulletin board may be transmitted every frame (every minute) in the VDE satellite downlink exclusive channels (e.g., channel 2014 and 2086). For example, the full satellite bulletin board messages may be transmitted over several frames, and essential information of the satellite bulletin board may be repeated over every frame (every minute).

[0032] In various embodiments, each of the plurality of cells is a self-organized time division multiple access (SOTDMA) cell. A SOTDMA cell is known in the art and thus need to be described in detail herein for conciseness and clarity. [0033] FIG. 3 depicts a schematic block diagram of a system 300 (e.g., which may also be embodied as a device or an apparatus) for controlling access to a satellite uplink channel to a satellite in a VDES with respect to a plurality of cells within a coverage area of the satellite, according to various embodiments of the present invention, such as corresponding to the method 200 of controlling access to a satellite uplink channel to a satellite in a VDES as described hereinbefore with reference to FIG. 2 according to various embodiments. The system 300 comprises: a memory 302; and at least one processor 304 communicatively coupled to the memory 302 and configured to: obtain position information of a plurality of vessels with respect to the plurality of cells; configure time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information; generate satellite uplink channel configuration information for the satellite uplink channel, the satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel; and transmit the satellite uplink channel configuration information to the plurality of cells for the plurality of vessels to access a frame of the satellite uplink channel based on the satellite uplink channel configuration information.

[0034] In various embodiments, the system 300 may be located or provided (e.g., installed or integrated) in one or more of the satellites in the VDES.

[0035] It will be appreciated by a person skilled in the art that the at least one processor 304 may be configured to perform the required functions or operations through set(s) of instructions (e.g., software modules) executable by the at least one processor 304 to perform the required functions or operations. Accordingly, as shown in FIG. 3, the system 300 may comprise a vessel positioning module (or circuit) 306 configured to perform the above-mentioned obtaining position information of a plurality of vessels with respect to the plurality of cells; a frame structure configuring module (or circuit) 308 configured to perform the above-mentioned configuring time slots in a frame structure for the satellite uplink channel into a plurality of groups of time slots for the plurality of cells, respectively, based on the position information; a satellite uplink channel configuration information generating module (or circuit) 310 configured to perform the above-mentioned generating satellite uplink channel configuration information for the satellite uplink channel, the satellite uplink channel configuration information comprising information indicating the configuration of the plurality of groups of time slots for the plurality of cells, respectively, in the frame structure for the satellite uplink channel; and a satellite uplink channel configuration information transmitting module (or circuit) 312 configured to perform the above-mentioned transmitting the satellite uplink channel configuration information to the plurality of cells for the plurality of vessels to access a frame of the satellite uplink channel based on the satellite uplink channel configuration information.

[0036] It will be appreciated by a person skilled in the art that the above-mentioned modules are not necessarily separate modules, and two or more modules may be realized by or implemented as one functional module (e.g., a circuit or a software program) as desired or as appropriate without deviating from the scope of the present invention. For example, two or more of the vessel positioning module 306, the frame structure configuring module 308, the satellite uplink channel configuration information generating module 310, and the satellite uplink channel configuration information transmitting module 312 may be realized (e.g., compiled together) as one executable software program (e.g., software application or simply referred to as an“app”), which for example may be stored in the memory 302 and executable by the at least one processor 304 to perform the functions/operations as described herein according to various embodiments.

[0037] In various embodiments, the system 300 corresponds to the method 200 as described hereinbefore with reference to FIG. 2, therefore, various functions or operations configured to be performed by the least one processor 304 may correspond to various steps of the method 200 described hereinbefore according to various embodiments, and thus need not be repeated with respect to the system 300 for clarity and conciseness. In other words, various embodiments described herein in context of the method 200 are analogously valid for the corresponding system 300, and vice versa.

[0038] For example, in various embodiments, the memory 302 may have stored therein the vessel positioning module 306, the frame structure configuring module 308, the satellite uplink channel configuration information generating module 310, and/or the satellite uplink channel configuration information transmitting module 312, which respectively correspond to various steps of the method 200 as described hereinbefore according to various embodiments, which are executable by the at least one processor 304 to perform the corresponding functions/operations as described herein.

[0039] FIG. 4 depicts a schematic drawing of a VDES 400 for wireless communication, employing the method 200 of controlling access to a satellite uplink channel 404 to a satellite 402 in the VDES 400 with respect to a plurality of cells 408a, 408b, 408c within a coverage area of the satellite 402 as described herein according to various embodiments of the present invention. It will be appreciated by a person skilled in the art in the VDES 400 shown in FIG. 4, only one satellite and three cells are shown by way of example only for simplicity and the VDES 400 is not limited as such. It will be appreciated by a person skilled in the art that the VDES 400 may include additional satellites or cells as appropriate, without deviating from the scope of the present invention. Furthermore, FIG. 4 simply illustrates the existence of a plurality of cells 408a, 408b, 408c but does not illustrate the actual arrangement or configuration (e.g., shape) of the plurality of cells 408a, 408b, 408c. For example, it will be appreciated by a person skilled in the art that the plurality of cells 408a, 408b, 408c may be configured and arranged so as to completely cover an area. Accordingly, if no overlap between the plurality of cells 408a, 408b, 408c is desired, each cell may be configured to have an appropriate shape such as rectangular (e.g., square) or hexagonal and arranged adjacent one another. If some overlap between the plurality of cells 408a, 408b, 408c are acceptable, each cell may be configured to be circular and portions of the plurality of cells 408a, 408b, 408c may overlap in order to completely cover an area. It will also be appreciated by a person skilled in the art that cells may include or also refer to sub-cells.

[0040] The satellite 402 comprises the system 300 for controlling access to a satellite uplink channel 404 thereto in the VDES 400 with respect to a plurality of cells 408a, 408b, 408c within a coverage area of the satellite 402 as described herein according to various embodiments of the present invention. Each vessel (e.g., illustrated as rectangular blocks within the plurality of cells in FIG. 4) located in the plurality of cells 408a, 408b, 408c has installed therein a VDES compliant transceiver. As described hereinbefore, the satellite uplink channel configuration information for the satellite uplink channel 404 may be transmitted from the satellite 402 to the vessels in the plurality of cells 408a, 408b, 408c. Therefore, based on the satellite uplink channel configuration information received, vessels located in any particular cell of the plurality of cells 408a, 408b, 408c may access a frame of the satellite uplink channel 404 within a group of time slots configured for that particular cell (e.g., the group of time slots having a size configured for that particular cell). Accordingly, for example, message collisions in accessing the satellite uplink channel 404 amongst such vessels in the particular cell in the particular cell, as well as message collisions amongst such vessels with vessels in other cells of the plurality of cells 408a, 408b, 408c, can be reduced or minimized, thereby improving the throughput of the satellite VDES. Furthermore, since each group of time slots is configured (e.g., sized) for the corresponding cell based on the position information (e.g., from which the number of vessels in each cell can be determined), the time slots in a frame of the satellite uplink channel 404 can be more efficiently utilized by vessels in the plurality of cells (e.g., a group of time slots may be configured to have a larger size for a cell having more vessels therein), thereby further improving the throughput of the satellite VDES.

[0041] A computing system, a controller, a microcontroller or any other system providing a processing capability may be provided according to various embodiments in the present disclosure. Such a system may be taken to include one or more processors and one or more computer-readable storage mediums. For example, the system 300 described hereinbefore may include a processor (or controller) 304 and a computer- readable storage medium (or memory) 302 which are for example used in various processing carried out therein as described herein. A memory or computer-readable storage medium used in various embodiments may be a volatile memory, for example a DRAM (Dynamic Random Access Memory) or a non-volatile memory, for example a PROM (Programmable Read Only Memory), an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or a flash memory, e.g., a floating gate memory, a charge trapping memory, an MRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase Change Random Access Memory).

[0042] In various embodiments, a“circuit” may be understood as any kind of a logic implementing entity, which may be special purpose circuitry or a processor executing software stored in a memory, firmware, or any combination thereof. Thus, in an embodiment, a“circuit” may be a hard-wired logic circuit or a programmable logic circuit such as a programmable processor, e.g., a microprocessor (e.g., a Complex Instruction Set Computer (CISC) processor or a Reduced Instruction Set Computer (RISC) processor). A“circuit” may also be a processor executing software, e.g., any kind of computer program, e.g., a computer program using a virtual machine code, e.g., Java. Any other kind of implementation of the respective functions which will be described in more detail below may also be understood as a“circuit” in accordance with various alternative embodiments. Similarly, a“module” may be a portion of a system according to various embodiments in the present invention and may encompass a “circuit” as above, or may be understood to be any kind of a logic-implementing entity therefrom.

[0043] Some portions of the present disclosure are explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities, such as electrical, magnetic or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated.

[0044] Unless specifically stated otherwise, and as apparent from the following, it will be appreciated that throughout the present specification, discussions utilizing terms such as “obtaining”, “configuring”, “generating”, “transmitting”, “partitioning”, “assigning”,“determining”,“transmitting”,“controlling” or the like, refer to the actions and processes of a computer system, or similar electronic device, that manipulates and transforms data represented as physical quantities within the computer system into other data similarly represented as physical quantities within the computer system or other information storage, transmission or display devices.

[0045] The present specification also discloses a system (e.g., which may also be embodied as a device or an apparatus) for performing the operations/functions of the methods described herein. Such a system may be specially constructed for the required purposes, or may comprise a general purpose computer or other device selectively activated or reconfigured by a computer program stored in the computer. The algorithms presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose machines may be used with computer programs in accordance with the teachings herein. Alternatively, the construction of more specialized apparatus to perform the required method steps may be appropriate.

[0046] In addition, the present specification also at least implicitly discloses a computer program or software/functional module, in that it would be apparent to the person skilled in the art that the individual steps of the methods described herein may be put into effect by computer code. The computer program is not intended to be limited to any particular programming language and implementation thereof. It will be appreciated that a variety of programming languages and coding thereof may be used to implement the teachings of the disclosure contained herein. Moreover, the computer program is not intended to be limited to any particular control flow. There are many other variants of the computer program, which can use different control flows without departing from the spirit or scope of the invention. It will be appreciated by a person skilled in the art that various modules described herein (e.g., the vessel positioning module 306, the frame structure configuring module 308, the satellite uplink channel configuration information generating module 310, and/or the satellite uplink channel configuration information transmitting module 312) may be software module(s) realized by computer program(s) or set(s) of instructions executable by a computer processor to perform the required functions, or may be hardware module(s) being functional hardware unit(s) designed to perform the required functions. It will also be appreciated that a combination of hardware and software modules may be implemented.

[0047] Furthermore, one or more of the steps of a computer program/module or method described herein may be performed in parallel rather than sequentially. Such a computer program may be stored on any computer readable medium. The computer readable medium may include storage devices such as magnetic or optical disks, memory chips, or other storage devices suitable for interfacing with a general purpose computer. The computer program when loaded and executed on such a general-purpose computer effectively results in an apparatus that implements the steps of the methods described herein.

[0048] In various embodiments, there is provided a computer program product, embodied in one or more computer-readable storage mediums (non-transitory computer- readable storage medium), comprising instructions (e.g., the vessel positioning module 306, the frame structure configuring module 308, the satellite uplink channel configuration information generating module 310, and/or the satellite uplink channel configuration information transmitting module 312) executable by one or more computer processors to perform a method 200 of controlling access to a satellite uplink channel to a satellite in a VDES as described hereinbefore with reference to FIG. 2. Accordingly, various computer programs or modules described herein may be stored in a computer program product receivable by a system therein, such as the system 300 as shown in FIG. 3, for execution by at least one processor 304 of the system 300 to perform the required or desired functions.

[0049] The software or functional modules described herein may also be implemented as hardware modules. More particularly, in the hardware sense, a module is a functional hardware unit designed for use with other components or modules. For example, a module may be implemented using discrete electronic components, or it can form a portion of an entire electronic circuit such as an Application Specific Integrated Circuit (ASIC). Numerous other possibilities exist. Those skilled in the art will appreciate that the software or functional module(s) described herein can also be implemented as a combination of hardware and software modules.

[0050] It will be appreciated by a person skilled in the art that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. [0051] In order that the present invention may be readily understood and put into practical effect, various example embodiments of the present invention will be described hereinafter by way of examples only and not limitations. It will be appreciated by a person skilled in the art that the present invention may, however, be embodied in various different forms or configurations and should not be construed as limited to the example embodiments set forth hereinafter. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0052] Various example embodiments of the present invention relate to multiple wireless communication access over a satellite communication network, in particular, a satellite VDES.

[0053] Various example embodiments provide a technique for dynamic allocation of partition access slots (e.g., corresponding to the plurality of groups of time slots as described hereinbefore according to various embodiments) for satellite uplink access based on the position information of the vessels (e.g., the vessels' GNSS positions/locations), and such resource allocation may be announced to the vessels via, for example, a satellite downlink bulletin board. In various example embodiments, vessels transmit in partitioned slots (e.g., a plurality of groups of time slots for a plurality of cells, respectively) in a satellite uplink channel based on their position or location information derived from GNSS to minimize the collisions of messages at the satellite receiver. Accordingly, various example embodiments provide dynamic allocation of the satellite access slots (time slots in a frame structure for the satellite uplink channel) via, for example, a satellite downlink bulletin board information so as to overcome or mitigate imbalance of traffic load among different cells, thereby advantageously enhancing throughput. In this regard, for example, as the satellite downlink bulletin board is already part of the VDES, the dynamic allocation of the satellite access slots according to various example embodiments can advantageously make use of the existing satellite downlink bulletin board in the VDES, thereby simplifying implementation.

[0054] In various example embodiments, a method (or an algorithm) may be performed or executed in or at a satellite for allocating partitioned slots (e.g., configuring and assigning a plurality of groups of time slots to a plurality of cells, respectively) within a frame for a ship vessel's ship-to-satellite transmission. In various example embodiments, the method takes into consideration of (or receives) the safety reporting information including the vessels' locations/positions. In this regard, ship vessels having positions/locations within the same cell are assigned to the same partitioned slots (i.e., assigned to the same group of time slots in the frame structure for the satellite uplink channel). Different groups of time slots are assigned to different cells, respectively. Based on experimental simulations performed, the throughput of the satellite VDE employing the method of controlling access to a satellite uplink channel according to various example embodiments has been found to significantly improve.

[0055] The method of controlling access to a satellite uplink channel according to various example embodiments has a number of advantages, such as but not limited to:

• Dynamic allocation of partitioned slots (e.g., a plurality of groups of time slots for a plurality of cells, respectively) according to the number of ship vessels in the plurality of cells (e.g., in each of a plurality of adjacent cells), which may be announced to the vessels via the satellite bulletin board information for the downlink transmission. This can cater for imbalance of traffic loads in different cells (including sub-cells). As a result, the message collisions at the satellite receiver may be reduced or alleviated, thereby improving the performance of detection and system throughput significantly as compared to, for example, satellite VDES using SCTDMA MAC protocol without the dynamic allocation of partitioned slots according to various example embodiments.

• On-board processing or execution of the method (e.g. algorithm) for the dynamic allocation of partitioned slots can be implemented at VDES satellites, instead of implementing at all ships for ship-to-satellite transmissions.

• Serve as an additional check for the Best MAC protocol, similar to physical sensing and NAV complementary checks in the IEEE 802.11 analogy.

[0056] The VDES MAC protocol may use Slot Carrier-sense TDMA (SCTDMA) for channel access. For example, the VDES MAC protocol allows ship station to announce its occupation for up to three time slots that are randomly selected for their future transmission. The first transmission may select a time slot using a probability persistent (p-persistent) algorithm. Bulletin Board Information (BBI) is used to define control channels and data channels for resource allocation. The satellite and shore-based stations coordinate resource allocation via the BBI and update information in BBI in a regular or periodic basis. More specifically, a VDES satellite uses satellite bulletin board (SBB) to announce the resource allocation for ships (vessels) within its field of view. A shore- based VDES station uses terrestrial bulletin board (TBB) to announce the resource allocation for ships within its control area. It will appreciated by a person skilled in the art that the specific resource allocation method is not defined in the standard and may be implemented by individual vendors.

[0057] Various example embodiments provide a satellite VDES MAC protocol using SBB information. For example, various example embodiments enhance the overall throughput in the satellite VDES for a range of offered loads in cells, including unbalanced traffic loads in different cells (or clusters), for example, as compared to a fixed equal slot partition MAC protocol for all cells (i.e., each cell is respectively assigned a fixed group of time slots having the same size). In various example embodiments, the method of controlling access to a satellite uplink channel may be applied in the field of satellite transmission by ship vessels in an open sea/ocean and in sea ports.

[0058] In various example embodiments, the method of controlling access to a satellite uplink channel seeks to enhance the system throughput for satellite VDES under a range of offered loads in cells, including unbalance traffic loads in different cells, while working cohesively with the terrestrial VDES MAC protocol.

[0059] In various example embodiments, the method of controlling access to a satellite uplink channel may be embodied as a method of media access control (MAC) that relates generally to a satellite VDES MAC protocol and configured for enhancing throughput of the communication system (satellite VDES).

[0060] For better understanding and without limitation, a SBB-based dynamic slot partition VDES MAC (which may also simply be referred to as dynamic slot partition VDES MAC or a satellite VDES partition MAC with dynamic slot partition herein) protocol or method (e.g., corresponding to the method of controlling access to a satellite uplink channel as described hereinbefore) according to various example embodiments of the present invention will now be described. The SBB-based dynamic slot partition VDES MAC protocol may be used by ship vessels for maritime communication via a satellite uplink channel.

[0061] A conventional satellite VDES MAC protocol may be modelled similar to the satellite AIS MAC protocol. For example, the conventional satellite- VDES MAC protocol has the same performance as the satellite slotted aloha protocol under equal channel load conditions in each TDMA frame as illustrated in FIG. 5. In particular, FIG. 5 shows a conventional satellite VDES MAC slot access range for a frame of a satellite uplink channel, whereby the number of total slots in the frame is denoted by N_s. As shown in FIG. 5, based on the conventional satellite VDES MAC protocol, each cell has access to the full range of the total time slots (i.e., full slot access range) in the frame. The conventional satellite VDES MAC protocol may use slot carrier-sense TDMA (SCTDMA) MAC protocol for channel access. In contrast, the SBB-based dynamic slot partition VDES MAC protocol according to various example embodiment only access a portion (e.g., corresponding to a group of time slots as described hereinbefore according to various embodiments) of the total time slots, N_s, in a frame, based on the number of ship vessels in each SOTDMA cell (or cluster).

[0062] Various example embodiments seek to reduce message collisions in the satellite uplink channel by configuring (or partitioning) time slots in a frame for each SOTDMA cell’s (e.g., a plurality of groups of time slots for a plurality of cells, respectively) channel access, such as illustrated in FIG. 6. In particular, FIG. 6 shows a dynamic satellite VDES partition MAC slot access range based on the satellite VDES partition MAC protocol with dynamic slot partition according to various example embodiments. As shown in FIG. 6, based on the satellite VDES partition MAC protocol with dynamic slot partition according to various example embodiments, when accessing a satellite uplink channel, each cell has access only to a respective group of time slots (partitioned time slots) assigned thereto in the frame. By way of an example only and without limitation, FIG. 6 illustrates an example whereby there are three different categories of cells, namely, a low load cell category, a medium load cell category and a high load cell category. As shown in FIG. 6, a cell belonging to a low load cell category (which may be referred to as a low load cell) may be assigned thereto a group of time slots having a size predetermined for such a category, a cell belonging to a medium load cell category (which may be referred to as a medium load cell) may be assigned thereto a group of time slots having a size predetermined for such a category, and a cell belonging to a high load cell category (which may be referred to as a high load cell) may be assigned thereto a group of time slots having a size predetermined for such a category. In this regard, as illustrated in FIG. 6, the size (number of time slots) predetermined for a category having a larger load may be larger than the size predetermined for a category having a smaller load. It will be appreciated that the present invention is not limited to specific predetermined categories or number of categories and specific predetermined sizes for the predetermined categories, which may be selected or determined as desired or as appropriate. Furthermore, although FIG. 6 may illustrate the relative sizes (number of time slots) of group of time slots for different categories of cells, it will be appreciated by a person skilled in the art that FIG. 6 does not illustrate the actual number of time slots in a frame. For example, it will be appreciated by a person skilled in the art that for a SOTDMA cell, the frame structure has a total number of time slots of 2250 (i.e., N_s = 2250), and such a specific number of time slots in the frame structure is not shown in FIGs. 5 and 6.

[0063] In various example embodiments, SCTDMA is used by the satellite VDES partition MAC protocol with dynamic slot partition for channel access. As shown in FIG. 6, a plurality of groups of time slots are tied to (or assigned to) a plurality of cells (e.g. SOTDMA cells), respectively, such that vessels in any particular cell access (e.g., based on SCTDMA) the corresponding group of time slots assigned thereto. Accordingly, in various example embodiments, vessels in a cell having assigned thereto a group of time slots, may access the group of time slots (partitioned time slots) based on SCTDMA.

[0064] In various example embodiments, the position or location information of the vessels in each of the plurality of cells may be obtained based on a GNSS positioning subsystem. In various example embodiments, a plurality of groups of slots for a plurality of SOTDMA cells may be determined based on the position information of the plurality of vessels as described hereinbefore, whereby the plurality of groups of slots are non overlapping. For example, by configuring the plurality of groups of slots to be non overlapping, the possibility of message collision in the satellite uplink channel is advantageously reduced, thereby enhancing the overall satellite throughput with respect to the satellite uplink channel. Accordingly, the satellite VDES partition MAC protocol with dynamic slot partition according to various example embodiments may be a position-based MAC protocol. FIGs. 7A to 7C shows example usage of time slots for the satellite VDES partition MACs with dynamic slot partition according to various example embodiments and the terrestrial VDES MACs (ITDMA/RATDMA) working side by side in a frame of a satellite uplink channel. Within each SOTDMA cell, after starting up with random access TDMA (RATDMA), incremental TDMA (ITDMA) is used for subsequent reservation of slots for terrestrial VDES MAC protocol. Terrestrial ITDMA coexists with satellite VDES MAC protocol as well as the satellite VDES partition MAC protocols with dynamic slot partition using additional rules to the existing rules in VDES. For example, the additional rules are used to exclude the partitioned set of satellite access slots (a group of time slots) from the existing terrestrial VDES MAC, such as illustrated in FIGs. 7A to 7C, as well as to accommodate a new set of partitioned satellite access slots when moving from one SOTDMA cell region to another SOTDMA cell region according to the vessel position/location reporting messages sent to the VDES satellite. These messages include GNSS location information of the vessels. In various example embodiments, a technique for next SOTDMA cell projection is provided based on periodic GNSS positioning records. According to various example embodiments, the number of partition access slots for each SOTDMA cell (that is, the number of time slots in each group of time slots assigned to corresponding SOTDMA cell) can be dynamically allocated in the Satellite Downlink Bulletin Board.

[0065] FIG. 6 shows the partitioned slots access ranges (access ranges for the plurality of groups of time slots for the plurality of cells, respectively) for the SBB-based dynamic slot partition VDES MAC protocol according to various example embodiments of the present invention. By way of example only and without limitation, as described hereinbefore, there may be three types or categories of traffic loads, namely, low load, medium load and high load. As an example, the ratio of the traffic loads for low load, medium load and heavy load may be about 1 :2:3. By way of example only and without limitation, the number of partitioned access slots (the size of a group of time slots) for an SOTDMA cell determined to have a low load may be dynamically set at N_Sj! 2 (where N_sf refers to a reference or an average number of time slots), the number of partitioned access slots for an SOTDMA cell determined to have a medium load may be dynamically set at N_sf, and the number of partitioned access slots for an SOTDMA determined to have a high load may be dynamically set at 3N_s 2. The partitioned access slots for each SOTDMA cell (i.e., the configuration of the plurality of groups of time slots for the plurality of cells) may be announced to the vessels in each SOTDMA cell based on information (e.g., corresponding to the satellite uplink channel configuration information) included in the Satellite Downlink Bulletin Board.

[0066] Example frame structures or formats for the coexistence of the SBB-based dynamic slot partition VDES MAC protocol according to various example embodiments and the terrestrial VDES MAC protocol are shown in FIGs. 7A to 7C for a SOTDMA cell determined to have a low load, a SOTDMA cell determined to have a medium load and a SOTDMA cell determined to have a high load, respectively. For example, with the group of time slots assigned to the low load SOTDMA cell based on the dynamic slot partition VDES partition MAC protocol as shown in FIG. 7A, the remaining time slots shown in FIG. 7 A may be made available (e.g., reserved) for channel access based on the terrestrial VDES MAC protocol. Similarly, with the groups of time slots assigned to the medium load SOTDMA cell and high load SOTDMA cell as shown in FIGs. 7B and 7C, respectively, the remaining time slots shown in FIGs. 7B and 7C may be made available for channel access based on the terrestrial VDES MAC protocol.

[0067] The use of satellite downlink bulletin board information (BBI) will now be described according to various example embodiments of the present invention. The satellite may use the bulletin board signalling channel and/or the announcement signalling channel to assign the time and frequency resources (both downlink and uplink) to vessels. The time slots and frequency bands used for the satellite bulletin board signalling channel and the announcement signalling channel are dedicated and reserved, for example, normally a portion of the frame (60 seconds, 2250 slots) on a 50 kHz satellite downlink physical channel. Accordingly, in various example embodiments, the satellite bulletin board signalling channel (via the satellite BBI) and/or the announcement signalling channel are used to coordinate the resource allocation for different SOTDMA cells. It will be appreciated by a person skilled in the art that although the satellite BBI technique may be used as an example to transfer the information of the slot assignment (i.e., the configuration of the plurality of groups of time slots for the plurality of cells) to the ship vessels in the satellite downlink channel, other techniques for achieving the same transfer of information of slot assignment to the ship vessels in the satellite downlink channel may also be employed as desired or as appropriate without deviating from the scope of the present invention.

[0068] An example method of allocation of dynamic partitioned slots over time will now be described according to various example embodiments of the present invention, namely, a directly proportional method. For the directly proportional method, the number of allocated time slots (i.e., the number of time slots in a group of time slots) assigned to a cell may be directly proportional to the number of ship vessels determined to be in the cell. For example, the number of ship vessels in each cell may be obtained from the position reporting messages sent by the ship vessels to the VDES satellite in each SOTDMA frame. In this regard, each SOTDMA frame is 60 seconds, and thus, the dynamic allocation of time slots to each cell may vary over time, depending on the traffic load of the ship vessels in each cell.

[0069] Accordingly, in the various example embodiments, the method of controlling access to a satellite uplink channel to a satellite in a VDES enhances system throughput for Satellite VDES by dynamically partitioning access slots in a frame for channel access in the satellite uplink channel. Operations may also be simplified since the selection of time slots is dynamically allocated within a partial range of time slots as defined by the assigned group of time slots, rather than within the full range of time slots in a frame. The method also caters for imbalance of traffic loads in different cells. Furthermore, on-board processing or execution of the method (e.g. algorithm) for the dynamic allocation of partitioned slots can be implemented at VDES satellites, instead of implementing in all ships for ship-to-satellite transmissions. The method may also serve as an additional check for the Best MAC protocol based on GNSS positioning which is already available in VDES, and there is no need for GNSS additional system integration.

[0070] FIG. 8 shows simulation results of throughputs of various satellite MAC protocols against a range of channel loads. As can be seen in FIG. 9, the simulation results demonstrate that the satellite VDES partition MAC protocol with dynamic slot partitioning according to various example embodiments advantageously achieved the highest throughput across the range of channel loads.

[0071] Accordingly, in various example embodiments, there is provided a method of wireless communication access between terrestrial vessels over a satellite VDES system. The method may comprise determining (at a satellite) a geographical location of the terrestrial vessel; determining (at the satellite) a subset of time slots in a frame of an uplink communication channel of VDES based on the geographical location whereby the subset of time slots corresponds to (or is assigned to) a Self-Organization Time Division Multiple Access (SOTDMA) cell; selecting (at a vessel) dynamically at least one candidate time slot from the subset of time slots based on satellite downlink bulletin board information (received by the vessel from the satellite); and transmitting (at the vessel) a message using the at least one candidate time slot. In various example embodiments, the selecting of the range of partition slot number is based on a dynamic allocation or mapping of the partition slots for channel access in the satellite uplink channel. The satellite downlink bulletin board information may include information indicating the configuration of the plurality of groups of time slots for the plurality of cells obtained based on messages with position/location information transmitted from the ship vessels to the VDES satellites.

[0072] While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

CLAIMS What is claimed is:

1. A method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, using at least one processor, the method comprising:

2. The method according to claim 1 , wherein said configuring time slots in the frame structure for the satellite uplink channel comprises partitioning time slots in the frame structure into the plurality of groups of time slots for the plurality of cells, respectively, each of the plurality of groups of time slots having a size determined based on the position information.

3. The method according to claim 2, wherein said configuring time slots in the frame structure for the satellite uplink channel further comprises assigning the plurality of groups of time slots to the plurality of cells, respectively, for vessels in each of the plurality of cells to access the frame of the satellite uplink channel within the corresponding group of time slots assigned to the cell.

4. The method according to claim 2, further comprising determining a number of vessels in each of the plurality of cells based on the position information,

wherein the size of each of the plurality of groups of time slots is determined based on the number of vessels determined in the corresponding cell of the plurality of cells.

5. The method according to claim 4, wherein the size of each of the plurality of groups of time slots is selected from a plurality of predetermined sizes for a plurality of predetermined categories of cells, respectively, based on the number of vessels determined in the corresponding cell of the plurality of cells.

6. The method according to claim 4, wherein the position information of the plurality of vessels comprises current position information of the plurality of vessels, and the number of vessels in each of the plurality of cells is determined based on the current position information of the plurality of vessels.

7. The method according to claim 1, configured to control access to the satellite uplink channel iteratively, wherein each iteration comprises:

said obtaining position information of a plurality of vessels with respect to the plurality of cells;

said configuring time slots in the frame structure for the satellite uplink channel; said generating satellite uplink channel configuration information for the satellite uplink channel; and

said transmitting the satellite uplink channel configuration information to the plurality of cells.

8. The method according to claim 1, wherein the satellite uplink channel configuration information is transmitted to the plurality of cells in at least one of a bulletin board signalling channel and an announcement signalling channel.

9. The method according to claim 1, wherein each of the plurality of cells is a self- organized time division multiple access (SOTDMA) cell.

10. A system for controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, the system comprising:

a memory; and

P. The system according to claim 10, wherein said configure time slots in the frame structure for the satellite uplink channel comprises partitioning time slots in the frame structure into the plurality of groups of time slots for the plurality of cells, respectively, each of the plurality of groups of time slots having a size determined based on the position information.

12. The system according to claim 11, wherein said configure time slots in the frame structure for the satellite uplink channel further comprises assigning the plurality of groups of time slots to the plurality of cells, respectively, for vessels in each of the plurality of cells to access the frame of the satellite uplink channel within the corresponding group of time slots assigned to the cell.

13. The system according to claim 11, wherein the at least one processor is further configured to determine a number of vessels in each of the plurality of cells based on the position information,

14. The system according to claim 13, wherein the size of each of the plurality of groups of time slots is selected from a plurality of predetermined sizes for a plurality of predetermined categories of cells, respectively, based on the number of vessels determined in the corresponding cell of the plurality of cells.

15. The system according to claim 13, wherein the position information of the plurality of vessels comprises current position information of the plurality of vessels, and the number of vessels in each of the plurality of cells is determined based on the current position information of the plurality of vessels.

16. The system according to claim 10, wherein the at least one processor is configured to control access to the satellite uplink channel iteratively, and wherein each iteration comprises:

said obtain position information of a plurality of vessels with respect to the plurality of cells;

said configure time slots in the frame structure for the satellite uplink channel; said generate satellite uplink channel configuration information for the satellite uplink channel; and

said transmit the satellite uplink channel configuration information to the plurality of cells.

17. The system according to claim 10, wherein the satellite uplink channel configuration information is transmitted to the plurality of cells in at least one of a bulletin board signalling channel and an announcement signalling channel.

18. The system according to claim 10, wherein each of the plurality of cells is a self- organized time division multiple access (SOTDMA) cell.

19. A computer program product, embodied in one or more non-transitory computer- readable storage mediums, comprising instructions executable by at least one processor to perform a method of controlling access to a satellite uplink channel to a satellite in a VHF Data Exchange System (VDES) with respect to a plurality of cells within a coverage area of the satellite, using at least one processor, the method comprising:

20. The computer program product according to claim 19, wherein said configuring time slots in the frame structure for the satellite uplink channel comprises partitioning time slots in the frame structure into the plurality of groups of time slots for the plurality of cells, respectively, each of the plurality of groups of time slots having a size determined based on the position information.