Method creating dynamic handover free areas for non-terrestrial network

Abstract

A method realized by a control unit (100) for creating buffer zones (400) that provide handover free operation of user equipment (500) in a network having plurality of high altitude platform stations (HAPS) (200) for providing network service to user equipment (500) via coverage areas (300) and having plurality of said user equipment (500) characterized in that using an optimization algorithm, determining initial buffer zones (400) comprising at least a part of intersection areas where two coverage areas (300) of two HAPS (200) intersect based on pre-recorded values of handover parameters of a handover rate parameter where it is defined by frequency of handovers from a HAPS (200) j to said HAPS (200) j's neighboring HAPSs (200), a disconnection rate parameter which is defined by rate of user equipment (500) disconnections from HAPS (200) j, and a swing parameter of HAPS (200) j; and based on reference signal received power (RSRP) parameters received from user equipment (500); acquiring real time handover parameters for each HAPS (200) and adjusting boundaries of buffer zones (400) until values of RSRP parameters deviates from predetermined thresholds or a predetermined number of iterations are executed; signaling user equipment (500) which are in buffer zones (400) to operate in a handover free state.

Description

[0001]DESCRIPTION METHOD CREATING DYNAMIC HANDOVER FREE AREAS FOR NON-TERRESTRIAL NETWORK TECHNICAL FIELD Invention relates to a method realized by a control unit for creating buffer zones that provide handover free operation of user equipment in a network having plurality of high altitude platform stations (HAPS) for providing network service to user equipment via coverage areas and having plurality of said user equipment. PRIOR ART Non-terrestrial networks (NTNs) represent a distinct category of communication and data transfer networks, distinguished by their operation independent of terrestrial infrastructure. Utilizing satellite constellations, these networks face specific challenges in managing handovers - the process of transferring a user's connection from one satellite to another. This handover is crucial for continuous communication and efficient network management. However, in NTNs, complications arise with unnecessary handovers, leading to frequent changes in device connectivity and service interruptions. High-Altitude Platform Stations (HAPS) are a pivotal element in NTNs. Positioned at high altitudes, HAPS provide extensive services including telecommunications, remote sensing, and surveillance over large areas. They have the potential to enhance handover processes due to their broad coverage. However, their movement complicates handover strategies, causing unnecessary handovers, data losses, service interruptions, and increased energy consumption. Recent studies and developments have highlighted additional complexities in the handover process within NTNs. For example, the swing state of HAPS, influenced by stratospheric winds, creates dynamic changes in the cell coverage area on the ground. This variability increases handover frequency, leading to elevated signaling and service disruptions. US2020021974 introduces handover free states for user equipment in order to reduce number of unnecessary handovers. Disclosure focuses on methodology to inform user equipment relating to their handover free state and removing users from said handover free state. Since HAPS operate in swinging angles which may cause handover free user equipment to lose connection to cells due to shifting coverage area. The persistent challenges in handover processes within non-terrestrial networks, particularly those related to the dynamics of High-Altitude Platform Stations, highlight the need for innovation in this technical field. The development of improved handover mechanisms and management strategies in NTNs is thus a critical technological advancement, essential for enhancing network efficiency and user experience in these rapidly evolving communication systems. BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field. An object of the invention is to provide a method that reduces unnecessary handovers of user equipment that are connected to HAPSs. To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method realized by a control unit for creating buffer zones that provide handover free operation of user equipment in a network having plurality of high altitude platform stations (HAPS) for providing network service to user equipment via coverage areas and having plurality of said user equipment. It is characterized by comprising using an optimization algorithm, determining initial buffer zones comprising at least a part of intersection areas where two coverage areas of two HAPS intersect based on pre-recorded values of handover parameters of a handover rate parameter where it is defined by frequency of handovers from a HAPS j to said HAPS j’s neighboring HAPSs, a disconnection rate parameter which is defined by rate of user equipment disconnections from HAPS j, and a swing parameter of HAPS j; and based on reference signal received power (RSRP) parameters received from user equipment; acquiring real time handover parameters for each HAPS and adjusting boundaries of buffer zones until values of RSRP parameters deviates from predetermined thresholds or a predetermined number of iterations are executed; signaling user equipment which are in buffer zones to operate in a handover free state. A possible embodiment of the invention is characterized in that comprising following steps which are repeated until values of RSRP parameters deviates from predetermined thresholds or a predetermined number of iterations are executed. -acquiring real time handover parameters for each HAPS calculating a control parameter Wj for each haps using reference parameters where positive increase of each control parameter’s value, positively effects increase of Wj; -determining a HAPS j* having minimum value of Wj; -enlarging area of buffer zone of HAPS j* towards HAPS js that are neighboring to HAPS j*; -adjusting size of buffer zones based on swinging angles. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a drawing illustrating schematic view of system. Figure 2 is a drawing illustrating schematic view of HAPS and coverage area. Figure 3 is a drawing illustrating schematic view of buffer zone. REFERENCE NUMBERS GIVEN IN THE FIGURE 100 Control unit 200 High altitude platform stations (HAPS) 210 High altitude platform stations 1 (HAPS 1) 220 High altitude platform stations 2 (HAPS 2) 300 Coverage area 400 Buffer zone 500 User equipment DETAILED DESCRIPTION OF THE INVENTION 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. Present invention is a method realized by a control unit (100) for creating buffer zones (400) that provide handover free operation of user equipment (500) in a network having plurality of high altitude platform stations (HAPS) (200) for providing network service to user equipment (500) via coverage areas (300) and having plurality of said user equipment (500). Referring to figure 1, present invention comprises a control unit (100), plurality of high altitude platform stations (HAPS) (200) and plurality of user equipment (500). Said HAPS (200) is a base station in the stratosphere. HAPS (200) provides network service to user equipment (500). Network services may be include internet access, telecommunication services, emergency communications, surveillance, monitoring, environmental monitoring, transportation, and logistics services. High altitude platform stations (HAPS) (200) comprise various technological components placed on platforms in the stratosphere. Said technological components may be include energy sources, communication equipment, observation, detection system, control, management systems, data processing and storage unit. HAPSs (200) are well-known in the art and is not explicitly disclosed herein. User equipment (500) are devices that provide the user to connect to communication networks. UE may be mobile phones, computers and other equipment that use cellular network. User equipment (500) are well-known in the art and is not explicitly disclosed herein. In a possible embodiment of the invention, the control unit (100) can be provided in HAPS (200). In another possible embodiment of the invention, the control unit (100) can be a network controller. In another possible embodiment, control unit (100) can be provided on satellite. According to the subject matter method comprises below steps, - Control unit (100) creates initial buffer zones (400) comprising at least a part of intersection areas where two coverage areas (300) of two HAPS (200) intersect based on pre-recorded values of handover parameters. The control unit (100) may create initial buffer zones (400) using an algorithm which is fed with historical data. Said historical data comprises at least following parameters: A handover rate parameter which is defined by frequency of handovers from a HAPS (200) to said HAPS’s (200) neighboring HAPSs (200). A disconnection rate parameter is defined by the rate of user equipment (500) disconnections from a HAPS (200) j. A swing parameter which indicates swing movement of HAPS (200) j. Control unit also receives on reference signal received power (RSRP) parameter from user equipment (500). - Control unit then monitors handover parameters in real time for each HAPS (200). Control unit adjusts boundaries of buffer zones (400) until values of RSRP parameters deviates from predetermined thresholds or a predetermined number of iterations are executed. This step may also be realized by an optimization algorithm. - Control unit signals user equipment (500) which is in buffer zones (400) to operate in a handover free state. Thus, a dynamic handover free zone is created. Handover rate parameter refers to a parameter used to determine how frequently the handover process occurs. Said handover rate parameter is a crucial factor influencing the performance of the network in mobile communication systems. Handover processes often occur frequently due to user mobility, such as traveling or moving within the boundaries of a cell. Disconnection rate parameter refers to a parameter when a user device loses its connection with a cell or base station in wireless communication systems. Disconnection rate may be tracked by HAPS (200). HAPS (200) may be move within a specific range due to stratospheric winds or other reasons related to control system of the platform. HAPS (200) movement when HAPS (200) changes its position, the location and orientation of antennas or communication equipment can differ. Therefore swing parameter refers to a parameter the coverage area (300) change of the antenna or communication equipment during the movement of a HAPS (200). Swing parameter may be monitored by sensors located on HAPS (200). Such sensors for instance may be GNSS sensors or gyro type sensors (Bingtuan Gao, Zhenyu Zhu,Jianguo Zhao and Boran Huang A Wireless Swing Angle Measurement Scheme Using Attitude Heading Reference System Sensing Units Based on Microelectromechanical). HAPS (200) may move within a specific range due to stratospheric winds or other reasons related to control system of the platform (figure 2a and 2b). In a possible embodiment algorithm may additionally use data such as network load, user density, and geolocation. Said historical data collected can be used for determining the optimal size of handover-free areas. Then an initial buffer zone on intersection of neighboring handover free areas may be created. This provides proactive adjustments to the system’s configuration based on historically observed conditions. In a possible embodiment adjusting boundaries step may comprise below sub-steps: - Calculating a control parameter Wj for each HAPS (200) using reference parameters where positive increase of each control parameter’s value, positively effects increase of Wj. - Determining a HAPS (200) j* having minimum value of Wj. - Enlarging area of buffer zone (400) of HAPS (200) j* towards HAPS (200) js that are neighboring to HAPS (200) j*. - Adjusting size of buffer zones (400) based on swinging angles. Larger swing angles result in larger buffer zones (400). If the maximum change in the values of Wj is below a certain threshold or the maximum number of iterations is reached, the iterative process stops. The resulting buffer zones (400) are those that balance the need to minimize handovers due to swing, while maintaining signal strength and disconnections within boundaries. Buffer zones (400) are dynamically adjustable and allows bi-directional communication different from handover free regions. In a possible embodiment control parameter Wj is calculated using below formula: Wj = α fj(Handover rate) + β gj (Disconnection rate) + γ hj(Swing parameter) (1); Where fj gj hj are predetermined functions α, β and γ are constrains calculated by an optimization algorithm. The resulting buffer zones (400) are those that balance the need to minimize handovers due to swing and maintaining signal strength and disconnections within boundaries. In a possible embodiment of the invention optimization method may be gradient descent algorithm with above specified parameters. In the buffer zone (400) where UE (500) is in handover-free state, the UE (500) receives an identifier from the control unit (100), which allows the network to recognize it without requiring a new handover each time the UE (500) moves between cells in the handover-free area. This identifier and the UE's (500) connection context are stored both on the UE (500) and control unit (100) (i.e. network device) the network device. Control device (100), sends activation or deactivation messages to UE (500) which indicates activation of handover free operation and deactivation of handover free operation. This may be realized using known methods in the art. For instance, the method described in US2020021974 may be used. In a possible embodiment activation can be initiated either by a command from the network device or according to the a method known in the art as WUS (wake up signal). Deactivation can occur when the UE (500) moves out of the handover-free area, receives a specific paging message, and shifts to cells in different tracking areas. Upon deactivation, the UE (500) can send its handover-free identifier to the network, which then provides a new, dedicated identifier for communication. Thus, UE (500) exits the handover-free state and re-enters the standard connected state, can facilitating immediate data transmission without needing a full new data access process. Said WUS Implementation can utilize the WUS functionality to signal when a UE enters or exits a buffer zone (400) enables real-time, dynamic adjustment of the buffer zones (400), considering the instantaneous network conditions. With the support of WUS, the HAPS (200) may be inactive such as where it does not transmit nor receive signal / channel or where it only transmits and receives limited signals. HAPS (200) can transit to become active for transmitting or receiving a channel / signal upon reception of an uplink signal from the UE Said technique enables the UE (500) to send an uplink wake-up signal to request transitioning of a cell from no or reduced transmission / reception activity to active transmission or reception of a channel / signal. Technique A-3 provides UEs (500) to be located within these buffer zones (400) by reducing the need for constantly active transmit / receive activities. Therefore, technique can save energy during the periods. An example working scenario of the present invention is as follows; In figure 2-a a coverage area (300) of HAPS 1 (210) and HAPS 2 (220) is on time t depicted. Referring to figure 2-b on time t+t1 coverage are of HAPS 1 (210) moves towards coverage (300) area of HAPS (2). Referring to figure 2-c HAPS 1 (210) moves away from HAPS 2 further than it was on time t. This swinging motion causes coverage area (300) to change in time. Figure 2-d depicts intersection between swinging coverage areas. This intersection and its enlarged or shrunk versions define buffer zones (400) for user equipment (500). User equipment (500) are assigned to be handover free while in buffer zones (400). Thus preventing unnecessary handovers between HAPSs (200) is prevented. 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

CLAIMS 1. A method realized by a control unit (100) for creating buffer zones (400) that provide handover free operation of user equipment (500) in a network having plurality of high altitude platform stations (HAPS) (200) for providing network service to user equipment (500) via coverage areas (300) and having plurality of said user equipment (500) characterized in that - using an optimization algorithm, determining initial buffer zones (400) comprising at least a part of intersection areas where two coverage areas (300) of two HAPS (200) intersect based on pre-recorded values of handover parameters of a handover rate parameter where it is defined by frequency of handovers from a HAPS (200) j to said HAPS (200) j’s neighboring HAPSs (200), a disconnection rate parameter which is defined by rate of user equipment (500) disconnections from HAPS (200) j, and a swing parameter of HAPS (200) j; and based on reference signal received power (RSRP) parameters received from user equipment (500); - acquiring real time handover parameters for each HAPS (200) and adjusting boundaries of buffer zones (400) until values of RSRP parameters deviates from predetermined thresholds or a predetermined number of iterations are executed; - signaling user equipment (500) which are in buffer zones (400) to operate in a handover free state.

2. The method according to claim 1, characterized in that comprising following steps which are repeated until values of RSRP parameters deviates from predetermined thresholds or a predetermined number of iterations are executed. - acquiring real time handover parameters for each HAPS (200) calculating a control parameter Wj for each HAPS (200) using reference parameters where positive increase of each control parameter’s value, positively effects increase of Wj; - determining a HAPS (200) j* having minimum value of Wj; - enlarging area of buffer zone (400) of HAPS (200) j* towards HAPS (200) js that are neighboring to HAPS (200) j*; - adjusting size of buffer zones (400) based on swinging angles.

3. The method according to claim 2, characterized in that control parameter Wj is calculated using below formula: Wj = α fj(Handover rate) + β fj (Disconnection rate) + γ fj(Swing parameter);where fjs are predetermined functions α, β and γ are constrains calculated by an optimization algorithm.

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