Handover method using high altitude platforms in non-terrestrial networks and a system

Abstract

Invention is a handover method realized by a system (100) having plurality of satellites (120) for serving user equipment (130) via cells (140) where a satellite (120) serving to a user equipment (130) is defined as source satellite (121) and a satellite (120) that will serve user equipment (130) after handover operation is defined as a target satellite; (122) at least a high altitude platform which is configured to communicate with user equipment (130) and said satellites (120) characterized in that comprising steps of: by said HAPS (110) receiving metric report from user equipment; (130) by HAPS (110) determining user equipment (130) that will be subjected to a handover operation based on metric report; by HAPS (110) transmitting handover request from each target satellite (122) for each related determined user equipment; (130) by each target satellite (122) and each source satellite (121) realizing handover procedure for related user equipment (130).

Description

[0001] HANDOVER METHOD USING HIGH ALTITUDE PLATFORMS IN NON-TERRESTRIAL NETWORKS AND A SYSTEM

[0002] TECHNICAL FIELD

[0003] Invention relates to a system and a method for realizing handover of user equipment in a nonterrestrial network.

[0004] BACKGROUND

[0005] A non-terrestrial network (NTN) is a communication network that operates outside the Earth's terrestrial (land-based) infrastructure. It encompasses various communication systems and technologies that are deployed in space, the stratosphere, the Earth's atmosphere, or other non-terrestrial environments. NTN is a broad and evolving field that includes satellite networks, high-altitude platform stations (HAPS), drone networks, and other emerging technologies designed to provide wireless connectivity and communication services.

[0006] Handover in non-terrestrial networks (NTN) refers to the process of transferring an active communication session from one non-terrestrial platform or network component to another without disrupting the ongoing communication. This transfer is essential to ensure seamless connectivity as mobile devices or users move across different coverage areas or when the network needs to balance the load among various non-terrestrial platforms. Handover mechanisms in NTN are designed to maintain the quality of service, minimize signal disruptions, and optimize the use of network resources. Various parameters, such as signal strength and network congestion, are considered to initiate and execute handovers effectively, ensuring continuous and reliable communication for users in non-terrestrial environments.

[0007] Handover is decided and realized by satellites that are part of NTN. Satellites receive signal strength metrics from user equipment, and they realize handover when conditions are met. Signaling, in the context of networks, means the exchange of control information that manages the main user data traffic (e.g., setting up and tearing down connections, handovers, and status updates). When an overwhelming amount of signaling traffic is present in a wireless network, it is called signaling storm. Signaling storms can degrade network performance and potentially lead to network failures. All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0008] BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a handover method and a system to eliminate the above- mentioned disadvantages and bring new advantages to the relevant technical field.

[0010] An object of the invention is to reduce signaling between UE and source and target satellite during handover in non-terrestrial networks.

[0011] Another object of the invention is to reduce computational load on target and source satellites.

[0012] Another object of the invention is to reduce repeated unnecessary handovers.

[0013] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to A handover method realized by a system having plurality of satellites for serving user equipment via cells where a satellite serving to a user equipment is defined as source satellite and a satellite that will serve user equipment after handover operation is defined as a target satellite; at least a high altitude platform which is configured to communicate with user equipment and said satellites. Accordingly, it is characterized by comprising steps of:

[0014] - by said HAPS receiving metric report from user equipment;

[0015] - by HAPS determining user equipment that will be subjected to a handover operation based on the metric report;

[0016] - by HAPS transmitting handover request from each target satellite for each related determined user equipment;

[0017] - by each target satellite and each source satellite realizing handover procedure for related user equipment. Thus, signal load on satellites are significantly reduced.

[0018] A possible embodiment of the invention is characterized in that the step “by each target satellite and each source satellite realizing handover procedure for related user equipment.” comprising sub-steps steps of:

[0019] - by each target satellite transmitting handover acknowledgement message to each related source satellite; - by each source satellite, after receiving handover acknowledgement message, radio resource control reconfiguration to user equipment and comprising the step of:

[0020] - by user equipment transmitting radio resource control reconfiguration completion message to target satellite.

[0021] Another possible embodiment of the invention is characterized in that wherein the metric report comprises hysteresis margin generated based on signal power metric and user equipment location. Thus, unnecessary handovers are significantly reduced.

[0022] Another possible embodiment of the invention is characterized in that wherein signal power metric is reference signal received power (RSRP).

[0023] Another possible embodiment of the invention is characterized in that user equipment location metric is the distance between center of serving cell and user equipment.

[0024] Another possible embodiment of the invention is characterized in that characterized in that comprising the step of

[0025] - by HAPS grouping user equipment and in step “by HAPS determining user equipment that will be subjected to a handover operation based on metric report;” groups that will be subjected to a handover is determined based on location of group and trajectory of target satellite and source satellite. Thus, computational loads on satellites are reduced.

[0026] Invention is also a system having at least a HAPS, plurality of satellites and user equipment that are configured to realize the above steps.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a drawing illustrating schematic view of the system.

[0029] Figure 2 is a drawing illustrating the flow of steps in the method.

[0030] Figure 3 is a drawing illustrating cell movement and user equipment locations.

[0031] Figure 4 is a drawing illustrating Hysteresis Margin and handover process on said Hysteresis Margin graphic. REFERENCE NUMBERS GIVEN IN THE FIGURE

[0032] 100 System

[0033] 110 HAPS

[0034] 120 Satellite

[0035] 121 Source satellite

[0036] 122 Target satellite

[0037] 130 User equipment

[0038] 140 Cell

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

[0041] Referring to figure 1 , invention is a method realized by a system (100) comprising a high altitude platform Station (HAPS), plurality of satellites (120) that serve plurality of user equipment (130) via cells (140) and said user equipment (130) that are subjected handover procedure. A satellite (120) serving a user equipment (130) is defined as a source satellite (121 ) and a satellite (120) that will take over the serving duty from a source satellite (121 ) is defined as a target satellite (122). HAPS (110) are configured to communicate with both user equipment (130) and satellite (120).

[0042] HAPS are known in the art. HAPS (110) are vehicles that are able to operate in certain altitudes. HAPS (1 10) may be mobile or quasi-stationary. HAPS (110) comprises processing elements (such as processors) in order to realize process steps in subject matter method and have communication components in order to communicate with user equipment (130) and satellites. Satellites and user equipment (130) comprises processing and communication elements as well. Satellites may be LEO satellites. User equipment (130) may be smart phones, computers or other devices that use cell (140) service of satellites. Satellites, HAPS (110) and user equipment (130) are well known in the area of non-terrestrial networks, thus well-known details are not disclosed herein.

[0043] The service mentioned in this description may be communication service, computing service and other services that satellites are known to provide to user equipment (130). Referring to figure 2, the subject matter method provides handover between a source satellite (121 ) and a target satellite (122) using HAPS (1 10).

[0044] Subject matter method comprises following steps:

[0045] - HAPS receives metric reports from user equipment (130).

[0046] - HAPS determines user equipment (130) that will be subjected to a handover operation based on a metric report.

[0047] - HAPS transmits handover requests from each target satellite (122) for each related determined user equipment (130). A target satellite (122) of a certain user equipment (130) may be different from the target satellite (122) of another user equipment (130) since there may be multiple cells (140) to handover to. This message indicates that a handover process will be held for a user equipment (130) from a source satellite (121) to a target satellite (122).

[0048] - Each target satellite (122) and each source satellite (121 ) realizes the handover procedure for related user equipment (130).

[0049] This greatly reduces data traffic between user equipment (130) and satellites relating to handover. Thus, reducing load on satellites and reducing signaling

[0050] HAPS continuously receives metric reports from user equipment (130) and evaluates them for determining handover. In a possible embodiment handover conditions may be predetermined and may be stored in a data storing element.

[0051] In a possible embodiment handover procedure may comprise following steps:

[0052] - After receiving handover request from HAPS (1 10), each target satellite (122) transmits handover acknowledgement message to each related source satellite (121 ). This message acknowledges source satellite (121 ) of the handover process and details thereof.

[0053] - After receiving handover acknowledgement message, source satellite (121 ) transmits radio resource control reconfiguration to user equipment (130). Thus, user equipment (130) is acknowledged of the target cell (140) and target satellite (122) and channel details that it will connect to.

[0054] - User equipment then transmits radio resource control reconfiguration completion message to target satellite (122). Thus, target satellite (122) is acknowledged that user equipment (130) is ready to switch to itself as service providing satellite.

[0055] In a possible embodiment metric report may comprise hysteresis margin generated from signal power metric and location of user equipment (130). Signal power metric may be reference signal received signal received power (RSRP). In a possible embodiment location of user equipment (130) may be the distance between user equipment (130) and center of serving cell (140). Hysteresis margin may be calculated by HAPS (1 10) or user equipment (130). the UE moves closer to the cell (140) border, the hysteresis margin decreases, allowing for smoother handover decisions. In a possible embodiment measuring the distance between the user equipment (130) location and the cell (140) center is realized by using the Haversine distance formula.

[0056] The Haversine distance formula calculates the great-circle distance between two points on a sphere, given their longitudes and latitudes. It is commonly used to measure distances on the Earth's surface. The formula is as follows: hav(0)=hav((p_1 -<p_2 )+cos (<p_1 ) cos (cp_2 )hav(A_2-A_1 ) d = r x archav(h) where h = hav{0) where: d represents the distance between the two points in the same units as the radius (r).

[0057] O, and Atdenote the latitude and longitude of the cell center.

[0058] <t>2and A2represent the latitude and longitude of the UE's location.

[0059] By applying the Haversine distance formula, the distance between the cell center and the user equipment can be calculated, aiding in determining the appropriate hysteresis margin based on the UE's proximity to the cell border.

[0060] In a possible embodiment HAPS (110) groups user equipment (130) and determines hand over of the group together. Above steps are realized on a group basis. Handover is realized based on the group's location and the direction of the cell’s (140) motion. Referring to figure 3, since cells (140) are moving, speed of user equipment (130) may be neglected unless relatively high changes occur in the metric report. HAPS (110) receives metric reports and groups user equipment (130) together. By accounting for location data in addition to RSRP, user equipment (130) can be grouped. User equipment (130) that have circular shape and that have elliptical shape belong to different groups. At a given time User equipment (130) ready for Handover are far from the cell center, and UE not ready for Handover are close to the cell center. User equipment (130) movement is negligible compare to cell movement that is unless significant RSRP change occurs, group handover is more efficient than individual handovers in terms of signaling and number of ping-pong handover. Then HAPS (110) determines which groups handover to a target satellite (122). Then HAPS (110) informs target satellite (122) of handover and target satellite (122), source satellite (121 ), user equipment (130) belonging to said group realizes handover. Referring to figure 4 declining continuous line represents received metric values of a group of user equipment (130) of a source cell (140) and increasing continuous line represents received metric values of the group of user equipment (130) of a target cell (140). The vertical line on the left hand side indicates the time when handover conditions are met, the vertical line on the middle represents the start of handover and vertical line on the right hand side represents completion time of handover.

[0061] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1. A handover method realized by a system (100) having plurality of satellites (120) for serving user equipment (130) via cells (140) where a satellite (120) serving a user equipment (130) is defined as source satellite (121 ) and a satellite (120) that will serve user equipment (130) after handover operation is defined as a target satellite; (122) at least a high altitude platform station which is configured to communicate with user equipment (130) and said satellites (120) characterized in that comprising steps of:- by said HAPS (110) receiving metric reports from user equipment (130);- by HAPS (110) determining user equipment (130) that will be subjected to a handover operation based on the metric reports;- by HAPS (110) transmitting handover request from each target satellite (122) for each related determined user equipment (130);- by each target satellite (122) and each source satellite (121 ) realizing the handover procedure.

2. The handover method according to claim 1 , characterized in that the step “by each target satellite (122) and each source satellite (121 ) realizing handover procedure for related user equipment (130) comprising sub-steps of:- by each target satellite (122) transmitting handover acknowledgement message to each related source satellite; (121 )- by each source satellite (121 ), after receiving handover acknowledgement message, radio resource control reconfiguration to user equipment and comprising the step of:- by (130) user equipment (130) transmitting radio resource control reconfiguration completion message to target satellite (122).

3. The handover method according to claim 1 , characterized in that wherein the metric report comprises hysteresis margin generated based on signal power metric and user equipment (130) location.

4. The handover method according to claim 3, characterized in that wherein signal power metric is reference signal received power (RSRP).

5. The handover method according to claim 3, characterized in that user equipment (130) location metric is the distance between center of serving cell (140) and user equipment (130).

6. The handover method according to claim 5, characterized in that the distance between center of serving cell (140) and user equipment (130) is calculated using below Haversine distance formula: hav(0)=hav((p_1 -<p_2 )+cos (<p_1 ) cos (cp_2 )hav(A_2-A_1) d = r x archav(h) where h = hav{0) where: d represents the distance between the two points in the same units as the radius (r).O, and Atdenote the latitude and longitude of the cell center.<t>2and A2represent the latitude and longitude of the UE's location.

7. The handover method according to claim 3 or claim 5, characterized in that comprising the step of- by HAPS (110) grouping user equipment (130) and in step “by HAPS (110) determining user equipment (130) that will be subjected to a handover operation based on metric report; groups that will be subjected to a handover are determined based on location of group and trajectory of target satellite (122) and source satellite (121).

8. Handover system (100) comprising at least a HAPS (110), at least a user equipment (130) and plurality of satellites (120) characterized in that said system (100) is configured to realize method according to claims 1-7.

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