A method for dynamically adjusting handover thresholds

Abstract

A method for operating a high altitude platform station (HAPS) (200) realized by a control unit (100) associated with the HAPS (200) where the HAPS (200) provide a coverage area (300) having plurality of cells (310) plurality of user equipment (400) and where said user equipment (400) initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold characterized in that comprising the step of determining a source handover threshold; and comprising following steps which are repeated in each time slot; for each cell (310) determining a handover frequency, a swing angle, and average signal strength for current time slot; updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell (310) to center of HAPS (200); transmitting updated source handover threshold to user equipment (400) to be used in next time slot.

Description

[0001] DESCRIPTION

[0002] A METHOD FOR DYNAMICALLY ADJUSTING HANDOVER THRESHOLDS

[0003] TECHNICAL FIELD

[0004] A method for operating a high altitude platform station (HAPS) realized by a control unit associated with the HAPS where the HAPS provide a coverage area having plurality of cells plurality of user equipment and where said user equipment initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold.

[0005] PRIOR ART

[0006] High altitude platform station (HAPS) are a communication platforms that uses unmanned aircraft or airships, typically stationed at high altitudes in the Earth's stratosphere to provide various communication services.

[0007] High Altitude Platform Stations (HAPS) are an innovative advancement in telecommunications, offering extensive cellular coverage over vast areas. However, their operation presents a unique challenge due to the inherent instability of these platforms. The swinging or swaying motion of HAPS often leads to unnecessary handovers between cells within the same coverage area. This issue, specific to HAPS, results in degraded service quality and network efficiency, marking it as a critical concern in cellular communication.

[0008] Existing solutions like those disclosed in CN103596227A and US2010056149A1 , while addressing network handovers in traditional cellular networks, do not adequately cater to the unique challenges posed by HAPS. CN103596227A outlines a method for selecting target cells based on preset network types and signal measurements. However, this method does not account for the dynamic shifts in coverage cells unique to HAPS, thus failing to address the problem of unnecessary handovers caused by their swinging motion. Similarly, US2010056149A1 describes a dynamic threshold determination method for hard handoffs in cellular networks but does not extend to the unique challenges of HAPS, particularly in managing conditional handovers influenced by the platforms' physical movements and signal strength fluctuations. In summary, while these references contribute to the field of network handovers, they fall short in addressing the specific challenges associated with HAPS-based systems. Their lack of effective mechanisms for managing conditional handovers in the context of the unstable movements of HAPS underscores a significant gap in the current state of technology in this area.

[0009] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field.

[0012] An object of the invention is provide a method that dynamically adjusting handover threshold.

[0013] The objective of the invention is to present a method that prevents frequent and unnecessary handovers between cells of the same HAPS caused by the unstable movements of the HAPS.

[0014] The objective of the invention is to present a method that prevents and reduces Radio Link Failures (RLFs).

[0015] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method for operating a high altitude platform station (HAPS) realized by a control unit associated with the HAPS where the HAPS provide a coverage area having plurality of cells plurality of user equipment and where said user equipment initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold. It is characterized by comprising the step of determining a source handover threshold; and comprising following steps which are repeated in each time slot; for each cell determining a handover frequency, a swing angle, and average signal strength for current time slot; updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell to center of HAPS; transmitting updated source handover threshold to user equipment to be used in next time slot. Thus, A possible embodiment of the invention is characterized in that the step “for each cell determining a handover frequency, a swing angle, and average signal strength for current time slot” comprises sub-step of for each cell also determining radio link failure rate and rate of change in signal strength for current time slot and updated source handover threshold is determined considering also link failure rate and rate of change in signal strength is also considered in step “updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell to center of HAPS”. This allows threshold to be dynamically updated, thus reducing unnecessary handovers between cells in a coverage area of a HAPS.

[0016] Another possible embodiment of the invention is characterized in that updating the source handover threshold is realized using below formulas co = p x / (swing angle, nr) + y x g(handover frequency) + 6 x k(average signal strength); updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm, f, g, k are predetermined functions, nr is the distance of cell n to center of HAPS.

[0017] Another possible embodiment of the invention is characterized in that updating the source handover threshold is realized using below formulas; co = p x / (swing angle, nr) + y x g(handover frequency) + 6 x k(radio link failure rate, rate of change in signal strength, average signal strength) ; updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm, / , g, k are predetermined functions, nr is the distance of cell n to center of HAPS.

[0018] Also the present invention relates to a method for operating a high altitude platform station (HAPS) realized by a control unit associated with the HAPS where the HAPS provide a coverage area having plurality of cells plurality of user equipment and where said user equipment initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold. It is characterized by comprising the step of determining a source handover threshold; and comprising following steps which are repeated in each time slot; for each cell determining a handover frequency, a swing angle, and radio link failure rate and change in signal strength for current time slot; updating the source handover threshold based on radio link failure rate and change in signal strength and the distance of cell to center of HAPS; transmitting updated source handover threshold to user equipment to be used in next time slot. Another possible embodiment of the invention is characterized in that characterized in that updating the source handover threshold is realized using below formulas; co = P x / (swing angle, nr) + y * g(handover frequency) + 5 x k(radio link failure rate, rate of change in signal strength); updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm, f, g, k are predetermined functions, nr is the distance of cell n to center of HAPS.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a drawing illustrating top schematic view of the system.

[0021] Figure 2 is a drawing illustrating top schematic view of HAPS and coverage area.

[0022] Figure 3 is a drawing illustrating schematic view of a subject embodiment matter method comprises below steps.

[0023] Figure 4 is a drawing illustrating schematic view of different scenarios for signal strength changes and new threshold.

[0024] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0025] 100 Control unit

[0026] 200 HAPS

[0027] 300 Coverage area

[0028] 310 Cell

[0029] 400 User equipment

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] 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.

[0032] Invention is a method to be applied by high altitude platform stations (HAPSs (200)) that utilizes real time measurements in a time window in order to determine and update a handover threshold in a next time window. Handover threshold is determined in such way that it reduces unnecessary handovers. Conditional handover refers to a type of handover in a wireless communication system where a user equipment (400) transitions from one cell (310) to another based on specific conditions. These conditions typically rely on factors such as signal strength, cell capacity, traffic density, or other performance metrics.

[0033] Conditional handover can occur when the communication conditions in the cell (310) to which the user is connected fall below a certain threshold or exceed a specific level. This enables the user to transition to a cell (310) associated with factors like a stronger signal or better cell capacity.

[0034] Referring to figure 2a and 2b each HAPS (200) provide a coverage area (300) to plurality of user equipment (400). Coverage areas (300) comprise plurality of cells (310).

[0035] Referring to figure 1 , the system that implements subject matter method comprises plurality of HAPS (200). The method is realized by a control unit (100). Said control unit (100) is associated with the HAPS (200). Said control unit (100) may be a processing unit (not shown) that executes instructions stored in a memory (not shown). For instance, control unit may be a processor, microprocessor, CPU, GPU etc. Control unit (100) may be provided in HAPS (200) or it may be in communication with HAPS (200) in order to realize subject matter method. Control unit (100) may be a processor of HAPS (200). Control unit (100) may be a network controller, in particular non-terrestrial network controller.

[0036] Referring to figure 2a, high altitude platform station (HAPS (200)) is a base station in the Earth’s stratosphere. Due to their positioning at high altitudes, (HAPS (200)) have a wide coverage area (300). This makes them suitable for extending communication services to remote or hard-to-reach areas. HAPS (200) provides network service to user equipment (400).

[0037] Referring to figure 2b, the coverage area (300) of HAPS (200) consists of hexagonal cells (310). The effect of swing motion increases as we move from the center to the edges of the coverage area (300) and therefore the probability of handover increases. The distance between a cell’s (310) center and HAPS (200) is defined as nr. Cells (310) are arranged on imaginary co-centric rings starting from coverage area (300) center to edges of coverage area (300). nr may depict which ring a cell (310) is on, and distance may be calculated based on the ring number since radius of rings are predetermined.

[0038] The HAPS (200) provide a coverage area (300) having plurality of cells (310) plurality of user equipment (400) and where said user equipment (400) initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold. This allows the user to transition to a cell (310) associated with factors such as a stronger signal or better cell capacity.

[0039] User equipment (UE) (400) is equipment used by end-users to access and utilize the services provided by a network. In the context of cellular networks, such as 4G LTE or 5G, the user equipment (400) includes devices like smartphones, tablets, laptops, and other wireless- enabled devices.

[0040] Referring to figure 3, the subject a first embodiment matter method comprises below steps:

[0041] - Determining a source handover threshold. Initial source handover threshold may be selected from predetermined thresholds. In a possible embodiment initial source handover threshold may be calculated by an optimization algorithm. Optimization algorithm may use historical data of parameters such as handover frequency, swing angle and signal strength received from user equipment (400). it further comprises following steps which are repeated in each time slot:

[0042] - For each cell (310) determining a handover frequency, a swing angle and average signal strength for current time slot. HAPS (200) may comprise communication sensors, location sensors (gyroscopes, accelerometers, and GNSS modules), and observation and detection sensors (swing angle measurement, imaging cameras, and radars) to determine handover frequency, swing angle, and average signal strength. Determining handover frequency by HAPS (200) is well known in the art, so it is not further elaborated herein. Swing angle may be determined using GNSS modules, gyroscopes, accelerometers etc. Average signal strength may be calculated based on signal strength reports received from user equipment (400).

[0043] - Updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell (310) to center of HAPS (200).

[0044] - Transmitting updated source handover threshold to user equipment (400) to be used in next time slot.

[0045] User equipment (UE (400)) then monitors signal strength according to handover threshold, and realizes conditional handover procedure from the source cell to the target cell when condition is met. In first embodiment, updating the source handover threshold may be realized using below formulas; co = p x / (swing angle, nr) + y x g(handover frequency) + 6 x k(average signal strength); updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm in formulas, f, g, k are predetermined functions, nr is the distance of cell (310) n to center of HAPS (200).

[0046] In a second embodiment, the step “for each cell (310) determining a handover frequency, a swing angle, and average signal strength for current time slot” comprises sub-step of:

[0047] For each cell (310) also determining radio link failure rate and rate of change in signal strength for current time slot. Radio link failure (RLF) may be determined using known techniques in the art that are not disclosed herein.

[0048] - updated source handover threshold is determined considering also link failure rate and rate of change in signal strength is also considered in step “updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell (310) to center of HAPS (200)”. This ensures a comprehensive assessment when making decisions regarding handover thresholds in the potential configuration of the invention.

[0049] In second embodiment of the invention, updating the source handover threshold may be realized using below formulas: co = P x / (swing angle, nr) + y x g(handover frequency) + 5 x k(radio link failure rate, rate of change in signal strength, average signal strength) ; updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm in formulas. / , g, k are predetermined functions, nr is the distance of cell (310) n to center of HAPS (200).

[0050] In a third embodiment of the method comprises following steps

[0051] - Determining a source handover threshold. it further comprises following steps which are repeated in each time slot: - For each cell (310) determining a handover frequency, a swing angle, radio link failure rate and rate of change in signal strength for current time slot.

[0052] - Updating the source handover threshold based on the handover frequency, the swing angle, radio link failure rate and rate of change in signal strength and the distance of cell (310) to center of HAPS (200).

[0053] - Transmitting updated source handover threshold to user equipment (400) to be used in next time slot.

[0054] In third embodiment the step of updating the source handover threshold may be realized using below formulas: co = P x / (swing angle, nr) + y x g(handover frequency) + 5 x k(radio link failure rate, rate of change in signal strength); updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm in formulas, f, g, k are predetermined functions, nr is the distance of cell (310) n to center of HAPS (200).

[0055] In figure 4 is a drawing illustrating schematic view of different scenarios for signal strength changes and updated handover thresholds.

[0056] Referring to 4-a, the signal strength received by the user from the source cell has dropped below both the initial threshold and the dynamically varying threshold. The signal strength of the target cell has surpassed its threshold. Therefore, the handover occur.

[0057] Referring to 4-b, the signal strength received by the user from the source cell has dropped below the initial threshold, but remains above the dynamically varying threshold. Therefore, a handover does not take place.

[0058] Referring to 4-c, the signal strength received by the user from the source cell does not fall below either the dynamic threshold or the initial threshold. Additionally, the target cell has not surpassed its threshold. Therefore, the handover is not initiated.

[0059] Referring to 4-d, even though the signal strength from the source cell falling below the dynamic threshold, the target cell has not surpassed its threshold. Hence, the handover is not initiated. In the event of a significant drop in signal strength from the source cell, it may lead to Radio Link Failure.

[0060] 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 method for operating a high altitude platform station (HAPS (200)) realized by a control unit (100) associated with the HAPS (200) where the HAPS (200) provide a coverage area (300) having plurality of cells (310) plurality of user equipment (400) and where said user equipment (400) initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold characterized in that comprising the step of: determining a source handover threshold; and comprising following steps which are repeated in each time slot;- for each cell (310) determining a handover frequency, a swing angle, and average signal strength for current time slot;- updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell (310) to center of HAPS (200);- transmitting updated source handover threshold to user equipment (400) to be used in next time slot.

2. The method according to claim 1 , characterized in that the step “for each cell (310) determining a handover frequency, a swing angle, and average signal strength for current time slot” comprises sub-step of:- for each (310) cell also determining radio link failure rate and rate of change in signal strength for current time slot and updated source handover threshold is determined considering also link failure rate and rate of change in signal strength is also considered in step “updating the source handover threshold based on the handover frequency, the swing angle, the average signal strength and the distance of cell (310) to center of HAPS (200)”.

3. The method according to claim 1 , characterized in that updating the source handover threshold is realized using below formulas: co = p x / (swing angle, nr) + y x g(handover frequency) + 5 x k(average signal strength); updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm, f, g, k are predetermined functions, nr is the distance of cell (310) n to center of HAPS (200).

4. The method according to claim 3, characterized in that updating the source handover threshold is realized using below formulas: co = p x / (swing angle, nr) + y * g(handover frequency) + 5 x k(radio link failure rate, rate of change in signal strength, average signal strength) ; updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm, f, g, k are predetermined functions, nr is the distance of cell (310) n to center of HAPS (200).

5. A method for operating a high altitude platform station (HAPS) (200) realized by a control unit (100) associated with the HAPS (200) where the HAPS (200) provide a coverage area (300) having plurality of cells (310) plurality of user equipment (400) and where said user equipment (400) initiates handover from a source cell to a target cell when a signal strength of source cell falls below a source handover threshold and the signal strength of target cell exceeds a target handover threshold characterized in that comprising the step of: determining a source handover threshold; and comprising following steps which are repeated in each time slot;- for each cell (310) determining a handover frequency, a swing angle, and radio link failure rate and change in signal strength for current time slot;- updating the source handover threshold based on radio link failure rate and change in signal strength and the distance of cell (310) to center of HAPS (200);- transmitting updated source handover threshold to user equipment (400) to be used in next time slot.

6. The method according to claim 5, characterized in that updating the source handover threshold is realized using below formulas: co = P x / (swing angle, nr) + y x g(handover frequency) + 5 x k(radio link failure rate, rate of change in signal strength); updated source handover threshold = current source handover threshold - co; where p, y, 5, are coefficients that are determined by an optimization algorithm, / , g, k are predetermined functions, nr is the distance of cell (310) n to center of HAPS (200).

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