WO2025101153A1

WO2025101153A1 - Resource allocation method for satellite communication

Info

Publication number: WO2025101153A1
Application number: PCT/TR2024/051141
Authority: WO
Inventors: Raşit TUTGUN; Ozan KÖROĞLU
Original assignee: Plan S Uydu Ve Uzay Teknolojileri AS
Current assignee: Plan S Uydu Ve Uzay Teknolojileri AS
Priority date: 2023-11-06
Filing date: 2024-10-03
Publication date: 2025-05-15
Anticipated expiration: 2026-05-06
Also published as: TR2023014380A1

Abstract

The method according to the present invention comprises the steps of; receiving the up-to- date time-frequency schedule; initializing it; receiving request to send messages (RTS) from the satellite access terminals (SAT) and creating a demand matrix; updating the demand matrix order and making a reservation for the updated demand matrix performed on the satellite (S). The reservation process is performed in a way that the highest priority is given to the data packets whose time is expiring.

Description

DESCRIPTION

RESOURCE ALLOCATION METHOD FOR SATELLITE COMMUNICATION

Relevant Technical Field

The present invention relates to demand-allocated multiple access communication methods and especially to a reservation-based resource allocation method developed for satellite communications and a satellite to which the said method is applied.

Prior Art

Satellite communication basically involves the use of communication satellites to transmit data received from a source (user terminals I loT units) on the ground to a target point (ground stations) on the ground. Data is transmitted from the ground to the satellite via an uplink. Providing satellite communication requires the satellite to be accessed by lots of sources, which requires these sources to share the Uplink. In order for many sources to access the satellite via Uplink without interacting with each other, predetermined protocols must be operated. In the known state of the art, there are various demand-assigned multiple access protocols called DAMA, which were developed as a solution to the problem in question. DAMA protocols are developed to ensure effective use of accessible Uplink resources by allowing many users to use the same Uplink channel.

The patent document numbered EP1021001 B1 describes a method and system for the use of the DAMA protocol, where demand control and resource planning are provided on the satellite. In the system in question, an access controller located on the satellite identifies spaces suitable for data transmission in the Uplink and provides reservation records for these spaces in line with the requests of registered users. In this method, registered users transmit a reservation request to the satellite in order to reserve a time slot for data transmission in a way that does not conflict with another user; the transmitted reservation request includes information on the amount of data to be sent. The controller evaluates the received reservation requests in line with predetermined criteria; as a result of this evaluation, the request can be approved, rejected or delayed. The controller creates a reservation grant message containing the time, frequency and length information to be sent to the requesting user. When the user receives a reservation grant message from the controller it will then wait for its reservation time frequency slot and transmit its data in a non-contentious basis within its reserved time slot. If a return message is not received, the user knows that the reservation request collided with another reservation request, and a retransmission strategy of the reservation request is employed. However, in the said method, certain Uplink resources are assigned to predetermined user groups, and the requests from the users within the said user group are evaluated and a prioritization and reservation process is applied within the relevant Uplink resource. Therefore, a flexible planning solution for the entire resource is not offered. In addition, the method in question cannot provide a solution to guarantee that the data is sent within a certain period of time.

Object of the invention

The object of the present invention is to develop a resource allocation method and system that ensures reliable data transfer between satellite access terminals located on the ground surface and the satellite, without data transmission conflicts and data loss.

Another object of the present invention is to develop a resource allocation method and system in which data transmission is provided in line with the resource planning carried out on the satellite.

Another object of the present invention is to develop a resource allocation method and system that provides fair and efficient resource planning, ensuring efficient resource use through resource planning, ensuring that data is sent within a certain period of time.

Definition of the Figures

Exemplary applications of the resource allocation method and system developed with the present invention are shown in the attached figures;

Figure 1 ; is a representation of the system architecture in which the resource allocation method according to the present invention is applied.

Figure 2; is an illustration of data transmission via the downlink control channel used in the resource allocation method according to the present invention.

Figure 3; is an illustration of data transmission via the uplink control channel used in the resource allocation method according to the present invention.

Figure 4; is an illustration of data transmission via the uplink service channel used in the resource allocation method according to the present invention.

Figure 5; is a flow chart showing the process steps of the resource allocation method according to the present invention.

The elements in the figures and their relevant reference numbers are stated below:

Satellite (S)

Satellite access terminal (SAT)

Coverage area (A)

Communication link (L) Beacon signal (BC)

Request to send message (RTS)

Clear to send message (CTS)

Data package (DP)

Uplink control channel (UCC)

Downlink control channel (DCC)

Uplink service channel (USC)

Get time schedule (1)

Initialize time-frequency schedule (2)

Receive new request to send messages (3)

Will there be fair resource allocation? (4)

Update lower limit value according to fair resource allocation (5)

Is there an upper limit? (6)

Update demand matrix based on upper limit (7)

Are there any data packages that are expiring? (8)

Update demand matrix based on expiring data packets (9)

Sort by priority (10)

Sort priority groups randomly within themselves (11)

Find the emptiest service channel (12)

Allocate resources for the demand at the top of the demand matrix (13)

Delete the allocated demand from the demand matrix (14)

Is RTS over (15)

Has the time schedule changed? (16)

Description of the Invention

With the present invention, which was developed to solve the above-mentioned technical problems and whose exemplary applications are represented in the attached figures, a resource allocation method for satellite communication and a satellite on which the said method is applied are provided. The method according to the invention provides data transmission reservation for satellite access terminals that communicate with the satellite via multiple access method.

Figure 1 shows an exemplary representation of the system architecture in which the method of the invention is applied. As shown in Figure 1 , the satellite (S) communicates with many satellite access terminals (SAT) within the coverage area (A) via a communication link (L). The communication link (L) between the satellite (S) and the satellite access terminals (SAT) provides two-way half-duplex communication. The communication link (L) in question comprises at least one downlink control channel (DCC) through which signal transmission is provided from the satellite (S) to the satellite access terminals (SAT) within the coverage area (A), by broadcast method; at least one uplink control channel (UCC) where multiple access is provided through random access from the ground to the satellite (S) (from the satellite access terminals (SAT) to the satellite (S)) and multiple uplink service channels (USC) through which reservation-based multiple access from the satellite access terminals (SAT) to the satellite (S) is provided in line with the resource allocation. In these uplink service channels (USC), timefrequency slices are obtained by using time division multiple access TDMA and frequency division multiple access FDMA methods together. With the method of the invention, reservation-based multiple access is provided, where each of the time-frequency slots is used for the transmission of a data packet from only one satellite access terminal (SAT).

The satellite (S) periodically sends a beacon signal (BC) from the downlink control channel (DCC) to the satellite access terminals (SAT) entering the coverage area (A). The period mentioned here may have a predetermined fixed period duration or a variable period duration. In preferred embodiments of the invention, the period duration in question can be changed in line with the number of satellite access terminals (SAT) on the ground, the data density requested to be transmitted and similar criteria; It is preferably determined so as not to exceed the time between the first moment of entry of a satellite access terminal (SAT) on the ground into the satellite coverage area (A) and the moment of exit from the satellite coverage area (A). Satellite access terminals (SAT) transmit request to send messages (RTS) to the satellite (S) over the uplink control channel (UCC) as soon as they receive the beacon signal (BC) coming from the satellite (S). By evaluating the incoming request to send messages (RTS), the satellite allocates the time slots suitable for data transmission of the uplink service channels (USC) to the requesting satellite access terminals (SAT) and transmits a clear to send message (CTS), which is the information message regarding the allocation process, through the downlink control channel (DCC) to satellite access terminals (SAT) located within the coverage area (A). Satellite access terminals (SAT) transmit data packets (DP) within the specified time period, through the uplink service channel (USC) determined for them, in line with the clear to send message (CTS). Figures 2 to 4 show the signals transmitted over the downlink control channel (DCC), uplink control channel (UCC) and uplink service channels (USC), respectively.

An exemplary application of the time-frequency schedule of the communication link (L) in question is shown in Table 1.

Table 1. Time-frequency schedule

In Table 1 , TI ... TM+2... show consecutive time periods. According to Table 1 , the communication session starts when a satellite (S) within the coverage area sends a beacon signal (BC) in the Ti time period. Due to the half-duplex structure of the communication link (L), during the time slots when the satellite (S) sends a beacon signal (BC) from the downlink control channel (DCC) (for example, in the Ti time slot in Table 1), all uplink channels (UCC, USC) are in closed state. In Table 1 and the following sections, the closed state is shown as “NA”. In the T2 time slot, all satellite access terminals (SAT) that hear the beacon signal (BC) send request to send messages (RTS) via the uplink control channel (UCC) to the satellite (S) via random access, in order to make a reservation for data transmission. During this time period, the downlink control channel (DCC) is in the closed “NA” state. On the uplink service channels (UPCs); satellite access terminals (SAT), which have previously been allocated resources for the relevant time-frequency intervals, send data packets (DP). Using the request to send messages (RTS) received by the satellite (S) in the T2 time slot as input, it creates the resource planning for the time-frequency intervals available for data transmission starting from the T4 time slot and sends the clear to send message (CTS) regarding the allocation process, to the satellite access terminals (SAT) via the downlink control channel (DCC) in the T3 time slot. All satellite access terminals (SAT) in the coverage area (A) receive the clear to send message (CTS). From the T4 time slot to the TM time slot where the resource allocation will be updated, all satellite access terminals (SAT) with resource allocations, send data packets (DP) in the frequency channel and time slots allocated to them via the uplink service channels (USC). Satellite access terminals (SAT) for which resource allocation has not been made continue to request reservations again by sending request to send messages (RTS) over the uplink control channel (UPC). In the TM time slot, the satellite (S); takes into account the reservation request messages (RTS) received between T4 and TM-I time slots and the gaps suitable for data packet (DP) transmission in the time-frequency schedule and reallocates resources, sending the clear to send message (CTS), which is updated in the TM time slot. This cycle continues continuously.

Due to the half-duplex structure of the communication link (L), the time-frequency schedule is divided into downlink communication time slots and uplink communication time slots. Therefore, the time frequency schedule contains the following time periods that are consecutive and repeated cyclically: a downlink time slot during which the beacon signal (BC) is transmitted from the satellite (S) to the satellite access terminals (SAT) located within the coverage area (A); during this time slot all channels except the downlink control channel are in closed state (NA) and until the next beacon signal (BC) is sent, the said time period is repeatedly followed by: o at least one uplink time slot during which request to send messages (RTS) and data packets (DP) of the satellite access terminals (SAT) to which resource is allocated previously, are transmitted to the satellite (S); during this time slot the downlink control channel is closed (NA); o a downlink time slot during which the clear to send message (CTS) is transmitted from the satellite (S) to the satellite access terminals (SAT); during this time slot, all channels except the downlink control channel are closed (NA); o a downlink time slot during which the beacon signal (BC) is transmitted from the satellite (S) to the satellite access terminals (SAT) located within its coverage area (A).

During the process, collected request to send messages (RTS) are evaluated and the resource planning is updated; the updated resource planning is sent to the satellite access terminals (SAT) with the clear to send message (CTS). The resource allocation method that is the subject of the invention implemented in this process is explained in detail below:

The resource allocation method uses the request to send messages (RTS) received by the satellite (S) and the time-frequency slots that are suitable for data packet (DP) transmission in the time-frequency schedule as inputs. The number of time-frequency slots to be allocated to each satellite access terminal (SAT) is determined by taking into account the number of data packets to be sent and the constraints related to the satellite access terminal (SAT). The flow chart of the method is shown in Figure 5. The process steps are explained in detail below.

Get the time schedule (1): the horizontal and vertical components of the time-frequency schedule described above do not change. The frequency ranges for the uplink and downlink channels and, preferably, the time slots (T1-TM) within each frequency range are fixed. However, the time between two Beacon signals (BC); the number of resource planning updates to be performed between two Beacon signals (BC) and therefore the frequency of the clear to send message (CTS) transmission; the uplink time slot and downlink time slot intervals may vary. These changes are preferably performed by the mentioned processing unit in line with the criteria such as data transmission demand density, system or functional changes, satellite access terminal (SAT) density, etc. Therefore, the resource allocation process starts with the receipt of the current time schedule by the processing unit. Initialize the time-frequency schedule (2): In this process step, the processing unit creates an empty time-frequency schedule in line with the received time schedule and fills the message type information to be included in the downlink control channel (DCC), uplink control channel (UCC) and uplink service channels (USC) with the relevant indicators. An initialized version of an example time-frequency schedule containing seven service channels is shown in Table 2. In the table in question, the control unit fills each time frequency interval with an indicator related to the relevant interval. In the exemplary application in Table 2, the indicators in question are selected as follows: -4: Closed, -3: BC, -2: RTS, -1: CTS, 0: Available.

Table 2. initialized time frequency schedule

Receive new request to send messages (3): The satellite (S) collects request to send messages (RTS) and creates a demand matrix before updating the clear to send message (CTS). An example demand matrix is shown in Table 3.

Table 3. Demand matrix

The “SAT ID” in Table 3 is the satellite access terminal identification number and refers to a unique number contained in each satellite access terminal (SAT). The said identification number is preferably transmitted to the satellite (S) with each request to send message (RTS) generated by the satellite access terminals (SAT), thus enabling the satellite (S) to recognize the relevant satellite access terminal (SAT). Number of data packages indicates the number of data packets (DP) to be sent by the satellite access terminal (SAT) and is transmitted to the satellite (S) with each request to send message (RTS) generated by the satellite access terminals (SAT).

The “Expiring” column shows how many of the data packets (DP) to be sent are about to expire. Data packet expiration occurs when a specified period of time has passed since the data packet (DP) generation time and it has still not been transmitted. To prevent this situation from occurring, priority is given to the transmission of data packets (DP) that are determined as “expiring”. In a preferred embodiment of the invention, the number of data packets in the "expiring" status is transmitted to the satellite (S) by the satellite access terminal with each request to send message (RTS) created. In the mentioned application, the satellite access terminal (SAT) compares the creation time information of the data packets it contains with a threshold value and determines that the data packet is in the "expiring" status if it exceeds the threshold value. The threshold value in question may be the same for each satellite access terminal (SAT), or it may differ depending on the application. In another preferred embodiment of the invention, the number of data packets in the "expiring" status is detected on the satellite. In the embodiment in question, satellite access terminals (SAT) transmit the number of data packets as well as the creation time information of each data packet to the satellite; the satellite compares the incoming data with a threshold value and determines the number of data packets that are “expiring”. The threshold value used here can be a fixed threshold value for all satellite access terminals, or different threshold values can be used for different satellite access terminals.

The priority value indicates which priority the relevant satellite access terminal (SAT) will have in resource scheduling. For example, satellite access terminals (SAT) with a priority value of “1” can have first priority in resource scheduling. Priority value information can be transmitted by the satellite access terminal (SAT) via a request to send message (RTS), or it is preferably determined on the satellite (S). The process in question is performed using a data string previously recorded in the satellite (S) and matching the satellite access terminal identification number with the priority value.

The lower limit represents the number of data packets (DP) guaranteed to be allocated for the relevant satellite access terminal (SAT); the upper limit represents the maximum number of packets that the relevant satellite access terminal (SAT) is allowed to send. As in the case of the priority value, both values can be transmitted by the satellite access terminal (SAT) via a request to send message (RTS), but preferably are determined on the satellite (S) by using a pre-registered data string, matching the satellite access terminal identification number with the lower limit and upper limit values. In the exemplary embodiment shown in Table 3, when the lower limit and upper limit values are specified as “-1”, it means that there is no relevant limit.

Therefore, the above-mentioned data can be partially obtained from the request to send message (RTS), can be partially generated on the satellite (S); and which data is obtained in which way varies according to the embodiments of the invention. In an exemplary implementation, the satellite access terminal identification number (SAT ID), the number of data packets (DP) and the packet creation time information are transmitted to the satellite (S) with the request to send message (RTS). The satellite (S) determines how many of the packets to be transmitted are in the “expiring” status by comparing the time elapsed from the time the data packets (DP) were created to that moment, with a threshold time value. In a preferred embodiment, the satellite access terminal (SAT) is configured to transmit the data packet (DP) with the oldest creation date first. In the embodiment in question, each or some of the priority, lower limit and/or upper limit information is determined in the satellite and used in resource allocation.

Will there be fair resource allocation (4): If the answer to this question is “Yes”, the lower limit value for all satellite access terminals (SAT) requesting a reservation is replaced by a specified number of data packets (DP). The lower limit specifies the number of packets that are guaranteed to be sent.

Update lower limit value according to fair resource allocation (5): If fair resource allocation is to be made, the lower limit value in the demand matrix, whose application example is shown in Table 3, is replaced with a specified "minimum number of packages" value. Table 4 shows an example case where the minimum number of packages for fair resource allocation is “1”.

Table 4. Demand matrix - after the fair resource allocation update

Is there an upper limit (6): In this step, the values in the upper limit column of the demand matrix are checked. The upper limit value is defined in the case where the maximum number of packets that satellite access terminals (SAT) can send is limited. The upper limit values in question can be determined depending on the data density and data need to be sent on a satellite access terminal (SAT) basis depending on the subscription type of the said satellite access terminal (SAT)

Update demand matrix according to upper limit (7): For each satellite access terminal (SAT), if the number of packets it wants to send exceeds the upper limit value, it is limited from above. An example application is shown in Table 5. Accordingly, the number of packets requested by the satellite access terminal numbered “821” (which is “7”) is limited to the upper limit value of the relevant satellite access terminal (SAT) which is “5”.

Are there any data packets that are expiring (8): This is the stage where the data packets requested to be sent by the satellite access terminals (SAT) are checked whether their duration (the time has passed since the said data packet created) has exceeded the threshold value.

Update demand matrix based on expiring data packets (9): Satellite Access Terminals (SAT) with a request to send a data packet (DP) with the status "expiring" are given the highest priority based on the number of data packets with the status "expiring". For data packets of such satellite access terminals that are not in the "expiring" status, their current transmission priorities will be the same. The request of the relevant satellite access terminal will be treated as two separate requests. An example application is shown in Table 6.

Table 6. Demand matrix - after the “expiring” status update

In the example above, there are two satellite access terminals with a request to send a data packet with the status “expiring”: “9641” and “6498”. Since two of the five data packets requested to be sent by the satellite access terminal numbered “9641” were in the “expiring” status, this request was divided into two requests and the priority value for the two packets was set to “0”, which is the highest priority indicator. For the remaining data packets, the priority of the satellite access terminal, which is “3”, is maintained. Similarly, priority identifier number “0” was assigned to five packets of satellite access terminal number “6498”, and the current priority value was maintained for the remaining packet.

Sort by priority (10): The demand matrix is updated according to the values in the “priority” column such that the satellite access terminal (SAT) with the highest priority (lowest priority number) will be at the top (the rows will be ordered according to the priority value). An example application is shown in Table 7.

Table 7. Demand matrix - after the priority order update

Sort priority groups randomly within themselves (11): Requests with the same priority (priority groups) are sorted randomly within themselves. An example application is shown in Table 8.

Table 8. Demand matrix - after “sort priority groups randomly” update

From this point on, starting from the top line, satellite access terminals (SAT) will be placed in time slots suitable for data transmission in the service channels, according to the procedure detailed below. Steps 12 to 15 below will be repeated until all rows in the demand matrix are completed. Find the emptiest service channel (12): In this step, the number of timeslots available for data packet (DP) transmission of each service channel is determined. The service channel with the largest number of “available” time slots will be selected as the emptiest channel. In the initialized form of the time-frequency schedule, an example application of which is shown in Table 2, the service channel time slots with the "Available" status that are suitable for data packet transmission are marked with the "0" indicator. In this step, the time-frequency intervals that have the "0" indicator are determined for each service channel, from the current time slot until the longest predetermined time limit for resource allocation. The maximum predetermined time for resource allocation is a time pre-registered in the satellite processing unit, taking into account the maximum time a satellite terminal can remain in the satellite coverage area.

Allocate resources for the demand in the top row of the demand matrix (13): For the satellite access terminal at the top of the current demand matrix; which matrix is formed as a result of the above-mentioned processes; one time slot for each data package to be sent is reserved on the determined emptiest channel. The reservation process is carried out by reserving consecutive time slots for the relevant satellite access terminal, starting from the first available time slot of the service channel detected. During this process, the longest period mentioned above is taken into account and if a timeout occurs when the entire number of data packets requested for reservation are allocated, the number of packets is limited in a way that does not timeout. For the limitation to be made, the lower limit value, if any, is taken into account and the relevant limitation is carried out in a way that it does not remain below the lower limit.

Since the demands for satellite access terminals with data packets in the "expiring" status are divided into two separate rows in the demand matrix, there is a possibility of a resource planning where the same satellite access terminal will transmit data from two separate service channels in the same time period. The resource planning process is carried out in a way that prevents this possibility. In this regard, a control process is preferably carried out before resource allocation is made for the demand at the top of the demand matrix. The control process in question involves checking whether there are currently reserved time slots for the relevant satellite access terminal. If a reservation has been made for the same satellite access terminal before, resource allocation is ensured in such a way that no new reservations are made during the previous reservation time intervals. In a preferred embodiment, the said control process is performed only for satellite access terminals that have a data packet (DP) in the status of “expiring”.

Delete the allocated demand from the demand matrix (14): The request of the satellite access terminal placed in the time-frequency schedule is deleted from the demand matrix. The next satellite access terminal in the matrix then becomes the next in line for allocation. Is RTS over (15): It is checked whether the entries in the demand matrix are finished (whether the reservation process is completed for all rows in the matrix). If there is no demand left in the demand matrix, go to step 16; otherwise, go back to step 12.

Has the time schedule changed? (16): If the time schedule changes, the time-frequency schedule will need to be re-initialized since the satellite-to-ground and ground-to-satellite transmission times and the reserved time slots in which different message types are sent will change, so we will return to step 1. If the time schedule does not change, the functional flow continues from step 3, where new requests are received.

According to the example application above, the process of resource allocation by applying steps 12 to 15 to the time-frequency diagram shown in Table 2 in line with the demand matrix in Table 8 is shown in the tables below.

In the demand matrix shown in Table 8, the satellite access terminal numbered “6498” is in the first row and the number of data packets appears as 5. According to the time-frequency diagram shown in Table 2, the time slot range from 4th to 10th time slots in all service channels appears to be in the “0” status, i.e. suitable for data packet transmission. Therefore, since all service channels have the same number of available slots, the first service channel in the list, USCi, is selected. Starting from the first available time slot of USCi, time slots equal to the number of data packets are reserved for the satellite access terminal numbered "6498". The process is summarized below:

Selected service channel: USCi

Selected satellite access terminal: 6498

Allocated time slots: T4, T5, Te, T7, Ts

The updated time-frequency schedule as a result of the allocation process is shown in Table 9.

Table 9. Time-frequency diagram - updated version

The operations for the following rows in the demand matrix are shown below, respectively.

Selected service channel: IISC2

Selected satellite access terminal: 9641 Allocated time slots: T4, T5

Table 10. Time-frequency diagram - updated version Selected service channel: IISC3

Selected satellite access terminal: 821

Allocated time slots: T4, T5, Te, T7 Ts

Table 11 . Time-frequency diagram - updated version

Selected service channel: IISC4

Selected satellite access terminal: 5446

Allocated time slots: T4, T5, Te, T7, Ts

Table 12. Time-frequency diagram - updated version

Selected service channel: IISC5 Selected satellite access terminal: 9641

Allocated time slots: Te, T7, Ts

During this process, according to the exemplary embodiment of the invention, since a reservation has been made for the satellite access terminal numbered 9641 in the 4th and 5th time slots, the reservation process is made starting from the 6th time slot in this step.

Table 13. Time-frequency diagram - updated version

Selected service channel: USCs Selected satellite access terminal: 1880

Allocated time slots: T4, T5

Table 14. Time-frequency diagram - updated version

Selected service channel: IISC7

Selected satellite access terminal: 8437 Allocated time slots: T4, T5

Table 15. Time-frequency diagram - updated version

Selected service channel: IISC2 Selected satellite access terminal: 6498

Allocated time slots: Tg

Table 16. Time-frequency diagram - updated version

Selected service channel: USCe

Selected satellite access terminal: 7315

Allocated time slots: Te

Table 17. Time-frequency diagram - updated version

With this process, the reservation process for all requests in the demand matrix shown in Table 8 will be completed and the relevant rows will be deleted from the demand matrix. In the following “is RTS over (15)” step, it will be determined that all inputs are finished and “has the time schedule changed? (16)” step will be moved on.

The method, which is the subject of the present invention and whose application examples are explained above, has been developed to provide resource allocation for multiple uplink service channels (USC) included in a communication link (L); which communication link (L) provides communication between at least one satellite (S) having at least one processing unit and the satellite access terminals (SAT) located within the coverage area (A) of the satellite in question. The method comprises the following steps performed on the satellite (S) by the said processing unit: obtaining an up to date time-frequency diagram; initializing the received time-frequency diagram and thus determining the time slots available for data packet (DP) transmission for each uplink service channel (USC); receiving request to send messages (RTS) from satellite access terminals (SAT) located within the coverage area (A) creating a demand matrix by using the received request to send messages (RTS); wherein each row of the demand matrix in question comprises the following data regarding a satellite access terminal (SAT) sending a request to send message (RTS): o satellite access terminal identification number, o number of data packets to be transmitted, o the number of data packets that are expiring and o priority order for the satellite access terminal updating the demand matrix and accordingly: o checking whether there are any expiring data packets (DP) o if any, creating an additional row in the demand matrix for each of the satellite access terminals (SAT) having expiring data packets (DP) and dividing the demand in two so that one row is created for the expiring data packets with the highest priority ranking and one row for the remaining data packets with the current priority ranking of the relevant satellite access terminal (SAT) in the demand matrix; o sorting the demand matrix according to priority value such that the demand row with the highest priority will be at the top; performing reservation for the updated demand matrix and accordingly; o evaluating the initialized time-frequency schedule and determining the uplink service channel (USC) with the highest number of time slots suitable for data packet transmission; o for the satellite access terminal (SAT) at the top of the demand matrix, the number of time slots according to the number of data packets (DP) to be transmitted is reserved on the detected uplink service channel (USC) o deleting the row for which the reservation is completed, from the demand matrix o checking if there are any rows left in the demand matrix o if there is a row to be processed in the demand matrix, returning to the step of determining the service channel with the highest number of time slots suitable for data packet transmission and repeating the following operations, o if there is no row to be processed in the demand matrix, returning to the step of obtaining the current time frequency schedule and repeating the following operations.

Initialization of the received time-frequency schedule preferably comprises creating an empty time-frequency diagram and filling each time-frequency interval with an indicator of the respective interval. The indicator mentioned here is an indicator showing that, the relevant time frequency range is closed (NA), reserved for beacon signaling (BC), reserved for request to send message (RTS) transmission, reserved for clear to send message (CTS) or available for data packet (DP) transmission. In a preferred embodiment of the invention, the method in question further comprises the step of sorting the demand matrix according to the priority value such that the row having the highest priority will be at the top, followed by the step of randomly sorting the rows having the same priority value.

In a preferred embodiment of the invention, the said method also comprises the process step of entering an upper limit value obtained by using incoming request to send messages (RTS) for each row of the created demand matrix and changing the data packet number value in the demand matrix with the said upper limit during the process of updating the demand matrix order in case the number of data packets exceeds the upper limit value.

In a preferred embodiment of the invention, the method in question includes the following process steps in the process of making a reservation for the updated demand matrix: checking if there are already reserved time slots for the satellite access terminal for which resource allocation will be made and if there are, making reservation for time slots other than those slots.

In a preferred embodiment of the invention, the aforementioned process steps are performed only for satellite access terminals whose "expiring" value in the demand matrix is different from 0.

The present invention also provides a satellite (S) comprising at least one processing unit arranged to perform the above-mentioned processing steps. The satellite is preferably a low earth orbit (LEO) satellite.

Claims

1. A method for providing resource allocation for more than one uplink service channel (USC) of a communication link (L) providing the communication between at least one satellite (S) having at least one processing unit and satellite access terminals (SAT) within the coverage area (A) of the satellite; wherein the method comprises the following steps performed by the processing unit on the satellite (S): obtaining an up to date time-frequency diagram; initializing the received time-frequency diagram and thus determining the time slots available for data packet (DP) transmission for each uplink service channel (USC); receiving request to send messages (RTS) from satellite access terminals (SAT) located within the coverage area (A); creating a demand matrix by using the received request to send messages (RTS); wherein each row of the demand matrix in question comprises the following data regarding a satellite access terminal (SAT) sending a request to send message (RTS): o satellite access terminal identification number, o number of data packets to be transmitted, o the number of data packets that are expiring and o priority order for the satellite access terminal updating the demand matrix and accordingly: o checking whether there are any expiring data packets (DP); o if any, creating an additional row in the demand matrix for each of the satellite access terminals (SAT) having expiring data packets (DP) and dividing the demand in two so that one row is created for the expiring data packets with the highest priority ranking and one row for the remaining data packets with the current priority ranking of the relevant satellite access terminal (SAT) in the demand matrix; o sorting the demand matrix according to priority value such that the demand row with the highest priority will be at the top; performing reservation for the updated demand matrix and accordingly; o evaluating the initialized time-frequency schedule and determining the uplink service channel (USC) with the highest number of time slots suitable, for data packet transmission o for the satellite access terminal (SAT) at the top of the demand matrix, reserving a time slot for each data packet (DP) to be transmitted on the detected uplink service channel (USC) o deleting the row for which the reservation is completed, from the demand matrix o checking if there are any rows left in the demand matrix o if there is a row to be processed in the demand matrix, returning to the step of determining the service channel with the highest number of time slots suitable for data packet transmission and repeating the following operations, o if there is no row to be processed in the demand matrix, returning to the step of obtaining the current time frequency schedule and repeating the following operations.

2. A method according to claim 1 , wherein initialization of the received time-frequency schedule comprises; creating an empty time-frequency diagram and filling each timefrequency interval with an indicator of the respective interval.

3. A method according to claim 2, wherein the indicator comprises at least one of the following: an indicator showing that, the relevant time frequency range is closed (NA), an indicator showing that, the relevant time frequency range is reserved for beacon signaling (BC), an indicator showing that, the relevant time frequency range is reserved for request to send message (RTS) transmission, an indicator showing that, the relevant time frequency range is reserved for clear to send message (CTS) or an indicator showing that, the relevant time frequency range is available for data packet (DP) transmission.

4. A method according to any of the preceding claims, comprising the step of randomly sorting the rows having the same priority value, following the step of sorting the demand matrix according to the priority value such that the row having the highest priority will be at the top.

5. A method according to any of the preceding claims, comprising the step of entering an upper limit value obtained by using incoming request to send messages (RTS) for each row of the created demand matrix and changing the data packet number value in the demand matrix with the said upper limit during the process of updating the demand matrix order in case the number of data packets exceeds the upper limit value.

6. A method according to any of the preceding claims, comprising a control phase having the following process steps, in the process of making a reservation for the updated demand matrix: checking if there are already reserved time slots for the satellite access terminal for which resource allocation will be made and if there are, making reservation for time slots other than those slots.

7. A method according to Claim 6 wherein the control phase is performed only for satellite access terminals whose "expiring" value in the demand matrix is different from 0.

8. A satellite comprising at least one processing unit arranged to perform the processing steps of the method according to any of the preceding claims.

9. A satellite according to claim 8 wherein the said satellite is a Low Earth Orbit satellite.