KR102336688B1 - Apparatus and method for controlling beam width of low orbit satellite to improve QoS performance - Google Patents

Abstract

The present invention provides an apparatus and method for automatically optimizing a beamwidth of a low-orbit satellite to ensure high QoS in a low-orbit satellite communication system in which handover occurs frequently. According to the present invention, the apparatus comprises: a beamwidth adjustment unit increasing or decreasing a currently set beamwidth in a predetermined adjustment unit; a failure probability calculation unit calculating the total handover failure probability for each of the current beamwidth and the increased or decreased beamwidth in a predetermined manner, comparing a change failure probability, which is the total handover failure probability for the adjusted beamwidth, with a failure probability, which is the total handover failure probability for the current beamwidth, updating the adjusted beamwidth to the current beamwidth to request beamwidth adjustment to the beamwidth adjustment unit when the change failure probability is less than the failure probability, and outputting the failure probability corresponding to the last updated beamwidth when the change failure probability is greater than the failure probability; a call holding time control unit reducing a preset call holding time by preset adjustment unit when the failure probability output from the failure probability calculation unit is greater than a predetermined reference total handover failure probability and transmitting the reduced call holding time to the failure probability calculation unit to request recalculation of the failure probability; and a beamwidth determination unit determining the last updated beamwidth as the beamwidth of the low-orbit satellite communication system when the call holding time control unit determines that the failure probability is smaller than the reference total handover failure probability.

Description

Apparatus and method for controlling beam width of low orbit satellite to improve QoS performance

The present invention relates to an apparatus and technique for controlling a beam width, and to an apparatus and technique for controlling a beam width of a low-orbit satellite.

The satellite communication system can be divided according to the altitude of the orbit where the satellite is located, and can be divided into Geostationary Earth Orbit (GEO), Medium Earth Orbit (MEO), and Low Earth Orbit (LEO) satellites.

1 is a diagram for explaining a satellite communication system according to altitude.

Geostationary orbiting satellites (GEOs) are called geostationary satellites because they are located at an altitude of about 36,000 km and rotate at the same speed as the Earth's rotation speed and always appear stationary when viewed from the ground. Medium orbiting satellites (MEOs) are artificial satellites located at an altitude of about 10,000 km. Low orbital satellites (LEOs) are artificial satellites that mainly rotate in orbits of 500 km or more and 1,500 km or less, and move very fast enough to rotate at a speed of 26,000 km at an altitude of 700 km.

Geostationary orbiting satellites (GEOs) theoretically can cover the entire earth with just three satellites, but since the distance from the ground to the artificial satellite is about 36,000 km, transmission delay occurs and high power output is required, making it portable. It is operated based on terrestrial base stations rather than transceivers. From a military point of view, since the location of the geostationary orbiting satellite (GEO) is fixed, it has the disadvantage of being exposed to the threat of electronic warfare such as jamming by enemy jammers.

Intermediate orbiting satellites (MEO) are located at an intermediate altitude between geostationary orbiting satellites (GEO) and low orbiting satellites (LEO). Therefore, the number of handovers is reduced.

Low-orbit satellites (LEOs) have low radio wave attenuation and propagation delay time because of their low altitude, so the terminal can be miniaturized and the frequency can be reused using multiple satellites, which has the advantage of increasing the overall system capacity. However, since the beam coverage is small and the relative speed of the satellite is high, the handover phenomenon frequently occurs.

Low orbiting satellites (LEOs) can use not only radio frequency (RF) but also free space optics (FSO) due to their low altitude. spot) Since the beam coverage is small due to the beam width, handover occurs frequently.

Korean Patent Publication No. 2017-0129143 (published on November 24, 2017)

It is an object of the present invention to provide an apparatus and method for controlling a beamwidth of a low-orbit satellite that can adaptively adjust a beamwidth to ensure high QoS in a changing traffic situation.

In order to achieve the above object, an apparatus for controlling a beamwidth of a low orbit satellite according to an embodiment of the present invention includes: a beamwidth adjusting unit for increasing or decreasing a currently set beamwidth by a predetermined adjustment unit; Calculate the total handover failure probability for each of the current beamwidth and the increased or decreased adjusted beamwidth in a predetermined manner, and the change failure probability, which is the total handover failure probability for the adjusted beamwidth, and the total handover failure probability for the current beamwidth The failure probability is compared, and if the change failure probability is less than the failure probability, the adjusted beamwidth is updated to the current beamwidth and the beamwidth adjustment is requested to the beamwidth adjuster. If the failure probability is greater than the failure probability, the failure probability corresponding to the last updated beamwidth a failure probability calculator that outputs; If the failure probability output from the failure probability calculation unit is greater than a predetermined reference total handover failure probability, the predetermined call holding time is reduced by a predetermined adjustment unit, and the reduced call maintenance time is transmitted to the failure probability calculation unit to fail. a call holding time control unit for recalculating the probability; and a beamwidth determiner configured to determine the last updated beamwidth as the beamwidth of the low-orbit satellite communication system when the call holding time controller determines that the failure probability is smaller than the reference total handover failure probability.

The failure probability calculation unit when the change failure probability for the adjusted beam width is reduced than the failure probability for the current beam width, updates the adjusted beam width to the current beam width and requests the beam width adjustment unit to further adjust the beam width in the adjustment direction, the failure If the probability is greater than or equal to the probability, the beamwidth adjuster requests to change the adjustment direction for the beamwidth, and if the failure probability for the applied beamwidth due to additional adjustment or change adjustment is greater than or equal to the failure probability for the updated current beamwidth, it corresponds to the last updated beamwidth You can print the failure probability.

The failure probability calculator may request a change to increase the beamwidth if the updated beamwidth is updated by decreasing the last updated beamwidth, and may request a change to increase the beamwidth if the updated beamwidth is adjusted by increasing the last updated beamwidth.

The failure probability calculator calculates the failure probability (P _ns ) with respect to the beam width (R) by the equation

(Here, P _b1 represents the blocking probability of a new call attempt within a cell, P _b2 represents the handover failure probability when a mobile subscriber moves between cells, and P _drop is the probability that a maintained call will be disconnected due to a handover failure. ) can be calculated according to

The low orbit satellite communication system includes a fixed channel allocation (FCA) method in which channels are previously allocated to each of a plurality of cells, and a queuing handover in which a handover queue is allocated to each cell to process a handover call. : It is possible to provide a communication service according to the QH) technique.

In the low-orbit satellite communication system, a handover queue allocated to each cell according to the QH technique is an infinite queue, and M/M/S (First In First Out: FIFO) for performing a service. M: Poission arrival process / M: service time exponentially distributed / S: number of channels assigned per cell) A queuing model may be applied.

In order to achieve the above object, a low-orbit satellite beamwidth control method according to another embodiment of the present invention includes: setting a reference total handover failure probability as a required QoS; increasing or decreasing the currently set beamwidth by a predetermined adjustment unit; calculating a total handover failure probability for each of the current beamwidth and the increased or decreased beamwidth in a predetermined manner; By comparing the change failure probability, which is the total handover failure probability for the adjusted beamwidth, with the failure probability, which is the total handover failure probability for the current beamwidth, if the change failure probability is less than the failure probability, the adjusted beamwidth is updated to the current beamwidth. repeatedly calculating the failure probability by further adjusting the beam width; If the failure probability is greater than or equal to the failure probability, the failure probability corresponding to the last updated beamwidth is compared with the reference total handover failure probability, and the predetermined call holding time is adjusted in a predetermined adjustment unit according to the comparison result to recalculate the failure probability. to readjust the beam width; and if the failure probability is smaller than the reference total handover failure probability, determining the last updated beamwidth as the beamwidth of the low-orbit satellite communication system.

Accordingly, the apparatus and method for controlling a beamwidth of a low-orbit satellite according to an embodiment of the present invention extracts an optimal beamwidth capable of guaranteeing high QoS even in a situation in which traffic changes in a low-orbit satellite communication system in which handover occurs frequently Thus, handover performance can be improved by controlling the beam width of a radio signal or an optical signal of a low-orbit satellite.

1 is a diagram for explaining a satellite communication system according to altitude.
2 is a diagram for explaining the concept of a fixed channel allocation scheme.
3 is a diagram for explaining the concept of a dynamic channel allocation scheme.
4 is a diagram for explaining an overlapping area to which a queuing handover technique can be applied.
5 shows handover probabilities of a source cell and a transition cell according to mobility parameters of a mobile subscriber.
6 shows the relationship between the average number of handovers as the altitude of the low-orbit satellite decreases.
7 shows an example of an FCA-QH model.
8 shows a schematic configuration of a low orbit satellite beamwidth control apparatus according to an embodiment of the present invention.
9 shows a low-orbit satellite beamwidth control method according to an embodiment of the present invention.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the accompanying drawings. However, the present invention may be embodied in various different forms, and is not limited to the described embodiments. In addition, in order to clearly explain the present invention, parts irrelevant to the description are omitted, and the same reference numerals in the drawings indicate the same members.

Throughout the specification, when a part "includes" a certain component, it does not exclude other components, unless otherwise stated, meaning that other components may be further included. In addition, terms such as "...unit", "...group", "module", and "block" described in the specification mean a unit that processes at least one function or operation, which is hardware, software, or hardware. and a combination of software.

2 is a diagram for explaining the concept of a fixed channel allocation scheme.

A channel allocation method used in a low-orbit satellite communication system can be roughly divided into a fixed channel allocation (FCA) method and a dynamic channel allocation (DCA) method.

In the FCA scheme, channels are allocated to each cell in advance so that channel interference does not occur, and when a channel allocation request occurs, an unused channel is allocated among channels previously allocated to the current cell.

In FIG. 2, a case in which a low orbit satellite (LEO) divides a beam coverage area (BCA) into 7 cells and allocates channels is illustrated as an example. As in the example of FIG. 2, when a channel is allocated by dividing the beam coverage area (BCA) into 7 cells, the set F(K) of channels allocated to the k-th cell is to be allocated using the remainder operator as shown in Equation 1 can

where m is the total number of channels.

And when a new call is made to a specific cell (x) among the divided cells, if there is no channel available in the cell (x), the call is blocked. Similarly, when a handover call is transferred from an adjacent cell to a cell (x), if there is no channel available in the cell (x), the call is stopped. That is, blocking and interruption of a call is determined by the presence or absence of an available channel in the cell in which the call is made.

Compared to DCA, FCA has a simple system configuration, and there is no information exchange between adjacent cells or information exchange between adjacent satellites, and it shows excellent performance in a high traffic situation.

3 is a diagram for explaining the concept of a dynamic channel allocation scheme.

The DCA method can use all channels in the system that are not being used within an adjacent distance from any cell in which the user terminal is located. When a channel used within a certain distance is reused, interference occurs and call quality deteriorates. Due to this interference, a set of channels usable in a specific cell continues to change. Here, a set of 18 surrounding cells that cause interference in a specific cell (x) is called an interference belt (I(x)).

When a new call is made to a specific cell (x), if there is no available channel in the cell (x) and the interference belt (I(x)), the call is blocked. Similarly, in this case, when a handover call is transferred from an adjacent cell, the call is stopped. That is, call blocking and interruption are determined by the cell in which the call originates and the presence or absence of an available channel in the interference belt of the cell.

On the other hand, in all mobile communication systems including the low-orbit satellite communication system, it is more fatal for a subscriber to interrupt a call in a call due to a handover failure than to block a new call. Therefore, a handover priority method should be considered. As a technical method, there are a method of using a dedicated channel for a handover call, a method of using a queue to process a handover, and the like. This is called a queuing handover (QH) technique.

4 is a diagram for explaining an overlapping area to which a queuing handover technique can be applied.

As shown in FIG. 4 , an area in which adjacent cell areas overlap and a subscriber can receive service from both adjacent cells is referred to as an overlap area (OA). In order to apply the QH technique, such an overlapping area (OA) must exist.

In the overlapping area (OA) of two adjacent cells, the UE can use the channels of the two cells at the same time. The length of the overlapping area OA is determined according to the antenna characteristics of the subscriber's moving direction satellite, radio wave conditions, and the like.

In the QH technique, each cell has a handover queue to process a handover call. The handover queue is an infinite queue and is serviced in a First In First Out (FIFO) method.

When the QH technique is applied, a handover request is made at the moment the terminal enters the overlapping area (OA). Therefore, as the length of the overlapping area (OA) becomes longer, the handover failure rate is lowered, so it becomes a variable directly affecting system performance. In general, the average length is calculated as R/5.

When a handover request is made from an adjacent cell to the current cell, if there is no channel available in the current cell, the call in progress enters the handover queue of the current cell and waits. At this time, the maximum waiting time (t _w max) of the handover queue is the time for the subscriber to pass through the overlapping area. If the handover is not processed even if the call in progress enters the handover queue and waits for the maximum waiting time (t _w max), a call blocking phenomenon occurs and the call is removed from the handover queue.

In a low-orbit satellite communication system, the FCA-QH method, which combines the FCA method and the QH method, is mainly used.

As described above, handover occurs very frequently in the low orbit satellite communication system. At this time, a cell in which a new call is generated by a mobile subscriber (MS) is called a source cell, and when the mobile subscriber (MS) moves to an adjacent cell while the call is maintained, the moved adjacent cell is transferred It is called a transit cell. Since the moving speed of the mobile subscriber MS is very small compared to the relative speed of the satellite, the moving speed of the mobile subscriber MS can be calculated as the relative speed of the satellite. Accordingly, a user mobility parameter (α) representing the movement speed characteristic of the mobile subscriber MS can be calculated according to Equation (2).

Here, V _orb represents the relative speed of the satellite, T _m represents the average call duration, time R represents the cell radius.

When applying the QH techniques as described above, a mobile subscriber (MS) when entering the adjacent transfer cell, and transmits an immediate handover request, this time, the maximum wait time for a handover (t _w max) is calculated by equation (3) can be

The maximum waiting time (t _w max) is the maximum value of the waiting time for handover, and in fact, the call may be terminated before passing the overlapping area.

5 shows handover probabilities of a source cell and a transition cell according to mobility parameters of a mobile subscriber.

As shown in FIG. 5 , the probabilities (P _h1 , P _h2 ) of making a handover request in the source cell and the transition cell are different from each other, and can be calculated by Equations 4 and 5, respectively.

_{From Equations 4 and 5, the probability (Q i} ) of the call being maintained during the i handover (i=1,2,...) period is calculated by Equation 6, and the probability that the call is connected even after the i handover (V _i ) is It is calculated by Equation 7, and the probability (B _i ) of call disconnection in the i handover can be calculated by Equation 8.

Here, P _b1 and P _b2 represent a blocking probability and a handover failure probability for a new call attempt, respectively.

_{From Equations (6) and (7), the average number of handovers (n h} ) that the mobile subscriber (MS) must succeed during the time that a mobile subscriber (MS) initiates a new call and maintains the call is calculated by Equation (9).

6 shows the relationship between the average number of handovers as the altitude of the low-orbit satellite decreases. 6 is a simulation result assuming that both the blocking probability (P _b1 ) and the handover failure probability (P _b2 ) for a new call attempt are 0, and the blocking probability (P _b1 ) and handover for a new call attempt Even when the failure probability (P _b2 ) is 0, it can be seen that _{the average number of handovers (n h} ) increases as the altitude of the low orbiting satellite (LEO) decreases.

_{On the other hand, the performance of the communication system to which the QH technique is applied can be expressed as the total handover failure probability (P ns} ), which indicates the probability that a new call attempt is blocked or a call that has been maintained is disconnected due to handover failure, and is calculated by Equation 10 can be

Here, P _drop is the probability that the maintained call will be disconnected because the handover fails.

That is, in order to calculate the total handover failure probability (P _ns ) according to Equation (10), the blocking probability (P _b1 ) and the handover failure probability (P _b2 ) for a new call attempt and the number of times that the maintained call will be disconnected due to handover failure You must acquire a probability (P _{drop ).}

_{A probability (P drop} ) of a call that was maintained first being dropped due to a handover failure may be calculated as in Equation (11).

Meanwhile, in order to calculate the blocking probability (P _b1 ) and the handover failure probability (P _b2 ) for a new call attempt, the average call completion rate (μ) according _{to the call arrival rates (λ, λ h ) needs to be calculated.}

_{First, the average channel holding time (E[t Hi} ]) in each of the source cell (i=1) and the transition cell (i=2) may be expressed by Equation (12).

Assuming that the handover request follows a Poisson distribution, since the new call and the handover call are independent of each other, the ratio between the intra-cell handover call arrival rate (λ _h ) and the new call arrival rate (λ) (λ _h /λ) can be calculated by Equation 13.

That is, the handover call arrival rate (λ _h ) and the new call arrival rate (λ) of Equation 13 can be calculated to be the same as _{the average number of handovers (n h ) of Equation 9.}

The average channel holding time (E[t _Hi ]) in one cell follows an exponential distribution, and the average service time (1/μ) of each cell can be calculated by Equation 14 as the inverse of the average call completion rate (μ) .

7 shows an example of an FCA-QH model.

7, in this embodiment, the FCA-QH model follows the M/M/S (M: Poission arrival process / M: service time exponentially distributed / S: number of channels assigned per cell) queuing model. Assume And, as described above, it is assumed that the handover queue is an infinite queue and the service is performed in a first-in, first-out (FIFO) method. _{The call incomplete rate (μ w} ) that exceeds the maximum waiting time for over (t _w max) and cannot receive service is calculated as the reciprocal of the maximum waiting time (t _w max) (μ _w = 1/t _{w max)} can be And, from the call incomplete rate (μ _{w ), the probability (P n} ) of the existence of n mobile subscribers in the cell can be calculated as in Equation (15).

From Equation (15), the idle state (idle) probability (P ₀ ) can be calculated by Equation (16).

And when there is no channel available for a new call (n ≥ S), the blocking probability (P _b1 ) of blocking a new call attempt may be calculated according to Equation 17.

When a handover request occurs, if an available channel exists (n < S), handover is immediately possible, but if there is no available channel (n ≥ S), it waits in a queue. And when the waiting time in the queue exceeds the maximum waiting time (t _w max = 1/μ _w ), handover fails. Therefore, in the state of n mobile subscribers, the handover failure probability (P _b2|n ) can be calculated by Equation (18).

From Equation (18), the handover failure probability (P _b2 ) is calculated as Equation (19).

Since the relationship between the handover call arrival rate (λ _h ) and the new call arrival rate (λ) _{expressed by Equation 13 is also related to the new call attempt blocking probability (P b1} ) and the handover failure probability (P _b2 ), the new call attempt blocking probability (P _b1 ) and the handover failure probability (P _b2 ) may be obtained using a recursive approach.

8 shows a schematic configuration of a low orbit satellite beamwidth control apparatus according to an embodiment of the present invention.

Referring to FIG. 8 , the low orbit satellite beamwidth control apparatus according to the present embodiment includes a QoS setting unit 110 , a beamwidth control unit 120 , a failure probability calculation unit 130 , a call holding time control unit 140 , and a beam width. A decision unit 150 may be included.

The QoS setting unit 110 sets QoS required in the low orbit satellite communication system. Here, like the FCA-QH model of this embodiment, in a communication system to which the QH technique is applied, the total handover failure probability (P _ns ) is used as a performance evaluation index for determining QoS. Accordingly, the QoS setting unit 110 sets a reference total handover failure probability (P _{ns_th} ) required by the communication system. The QoS setting unit 110 may set the initial call holding time (T _m ) _{together with the reference total handover failure probability (P ns_th ).}

The beamwidth adjusting unit 120 acquires the previously set beamwidth (R) of the satellite by a preset adjustment unit (R _adj ), and transmits the adjusted beamwidth (R ㅁR _adj ) to the failure probability calculator 130 . At this time, the beamwidth control unit 120 receives _{the change in the total handover failure probability (P ns ) calculated by the failure probability calculation unit 130 as feedback, and the beam width (RR adj} ) is reduced by the _{adjustment unit (R adj} ) in the beam width (R). ) or the increased beam width (R+R _adj ) may be repeatedly transmitted to the failure probability calculator 130 .

The failure probability calculation unit 130 calculates the changed total handover failure probability (P _{ns_adj} ) according to Equation 10 according _{to the adjusted beamwidth (RR adj} or R+R _{adj ) applied from the beamwidth control unit 120,} the calculated change the total handover failure probability (P _{ns_adj)} the old compared to the total of the handover failure probability (P _{ns_R)} calculated for the beam width (R), to change the total handover failure probability (P _{ns_adj),} the previous beam width (R ), when it is lower than the calculated total handover failure probability (P _{ns_R} ), the adjusted beamwidth (RR _adj or R+R _adj ) is updated to the current beamwidth and transmitted to the beamwidth adjuster 120, and the beamwidth adjuster 120 to be further adjusted in the previously adjusted direction.

As an example, if it is determined that the changed total handover failure probability (P _{ns_adj} ) is reduced by reducing and adjusting (RR _adj ) by the previous adjustment unit (R _adj ), the beamwidth adjusting unit 120 additionally reduces and adjusts If it is determined that the changed total handover failure probability (P _{ns_adj} ) has been decreased by increasing and adjusting (R+R _adj ) by the previous adjustment unit (R _adj ), the beamwidth adjuster 120 additionally increases and adjusts it.

However, the failure probability calculation unit 130 determines that the changed total handover failure probability (P _{ns_adj ) according to the adjusted beamwidth (RR adj} or R+R _adj ) is increased, and adjusts the beamwidth to the adjusted beamwidth (RR _adj or R +R _adj ), the total handover failure probability (P _{ns_R} ) calculated from the previous beamwidth (R) is transferred to the call holding time controller 140 .

Call holding time adjusting section 140 compares the total handover failure probability (P _{ns_R)} and the reference total handover failure probability (P _{ns_th)} set at the QoS setting unit (110) passed from the failure probability calculation unit 130 . Call holding time adjusting unit 140 is a total handover failure probability (P _{ns_R)} is based on the total handover failure probability (P _{ns_th)} is greater than, adjusting the retention time previously set number (T _m) Basis unit (T _adj) Adjust the decrease by as much as (T _m -T _adj ). Then, the decrease-adjusted call holding time (T _m -T _adj ) is updated to the current call holding time (T _m ), transmitted to the failure probability calculator 130, and the total handover failure probability (P _{ns_R} ) is calculated again, The failure probability calculation unit 130 requests the beam width adjustment unit 120 to adjust the beam width.

On the other hand, if the total handover failure probability (P _{ns_R} ) is less than or equal to the reference total handover failure probability (P _{ns_th} ), the obtained beamwidth R and call duration T _m are transmitted to the beamwidth determiner 150 .

The beam width determiner 150 determines the transmitted beam width R as the beam width R of the low orbit satellite, and allows the low orbit satellite to form a beam with the determined beam width R. Here, the beam width determining unit 150 may be integrated with the call holding time adjusting unit 140 .

In the above description, the low orbit satellite beamwidth control device has been described on the assumption that the low orbit satellite performs communication based on a radio signal. In the case of using it, the beam width of the low-orbit satellite can be adjusted in the same way.

9 shows a low-orbit satellite beamwidth control method according to an embodiment of the present invention.

Referring to FIG. 8, the low orbit satellite beamwidth control method of FIG. 9 is described. First, a reference total handover failure probability (P _{ns_th} ) is set as QoS required in the low orbit satellite communication system (S11). In this case, the initial call holding time (T _m ) may be set together.

When a required QoS based on the total handover failure probability (P _{ns_th)} is set, the total of the handover failure probability based on the beam width (R) of the currently selected satellite (P _{ns_R)} a reference to Equation 11, 17 and 19 mathematics It is calculated according to Equation 10 (S12).

And the currently set beam width (R) of the satellite is adjusted by increasing or decreasing by a _{predetermined adjustment unit (R adj ) (S13).} Here, it is assumed that the beam width R is reduced to an adjustment unit (R _adj ) (RR _{adj ).}

And by calculating the change total handover failure probability (P _{ns_adj)} according to a controlled beam width (RR _adj) determines whether or not reduced as compared with the total handover failure probability (P _{ns_R)} calculated for the previous beam width (R) (S14). Ten thousand and one changes the total handover failure probability (P _{ns_adj)} has a total of handover failure probability (P _{ns_R)} If it is determined that a reduced more, the controlled beam width (RR _adj) and change the total handover failure probability (P _{ns_adj)} each current beam width (R) and the total handover failure probability (P _{ns_R} ) are updated, and the beamwidth (R) is additionally adjusted by the adjustment unit (R _adj ) in the previous adjustment direction (S15). That is, when the previous beamwidth (R) _{is reduced by the adjustment unit (R adj} ) (RR _adj ), the beamwidth is additionally _{reduced by the adjustment unit (R adj} ). However, when the previous beamwidth (R) _{is increased by the adjustment unit (R adj} ) (R+R _adj ), the beamwidth is additionally _{increased by the adjustment unit (R adj} ).

And it determines whether or not reduced as compared with the total handover failure probability calculated for the additional adjustment of the beam width (R) updated by calculating a change total handover failure probability (P _{ns_adj)} in the beam width (P _{ns_R)} (S16) . Ten thousand and one changes the total handover failure probability (P _{ns_adj)} has a total of handover failure probability (P _{ns_R)} If it is determined that a reduced more, the controlled beam width (RR _adj) and change the total handover failure probability (P _{ns_adj)} each current beam width (R) and the total handover failure probability (P _{ns_R} ) are updated, and the beamwidth (R) is additionally adjusted by the adjustment unit (R _adj ) in the previous adjustment direction (S15).

However, the initial When adjusting the beam width (RR _adj) to change the total handover failure probability according to the (P _{ns_adj)} is determined that is not lower than the total probability of handover failure (P _{ns_R),} i.e. to change the total handover failure probability (P _{ns_adj)} If this total handover failure probability (P _{ns_R} ) or more, it is adjusted by changing the adjustment direction with respect to the previous beam width (R). For example, if the previous beamwidth (RR _adj ) is decreased and adjusted, it is adjusted by increasing (R+R _{adj ) by a predetermined adjustment unit (R adj} ) with respect to the beamwidth (R) before the decrease (S17).

And by calculating the change total handover failure probability (P _{ns_adj)} according to the beam width (R + R _adj) the change control whether reduced as compared with the total handover failure probability (P _{ns_R)} calculated for the previous beam width (R) Status is determined (S18). Ten thousand and one changes the total handover failure probability (P _{ns_adj)} has a total of handover failure probability (P _{ns_R)} If it is determined that a reduced more, the controlled beam width (RR _adj) and change the total handover failure probability (P _{ns_adj)} each current beam width (R) and the total handover failure probability (P _{ns_R} ) are updated, and the beamwidth (R) is additionally adjusted by the adjustment unit (R _adj ) in the previous adjustment direction (S15).

On the other hand, if the additionally adjusted or changed modified total handover failure probability (P _{ns_adj} ) is equal to or greater than the total handover failure probability (P _{ns_R} ), the total handover failure probability (P _ns ) corresponding to the previously set beamwidth (R) It is determined whether the reference total handover failure probability (P _{ns_th} ) or less (S19). If the total handover failure probability (P _ns ) is greater than the reference total handover failure probability (P _{ns_th} ), the currently set beamwidth (R) cannot satisfy the QoS required by the system, so the call maintenance time (T _m ) It decreases (T _m -T _adj ) to a predetermined control unit (T _adj ) (S20). Then, based on the adjusted call holding time (T _m -T _{adj ), the total handover failure probability (P ns} ) according to the currently set beamwidth (R) is calculated again (S12). However, if the total handover failure probability (P _ns ) is less than or equal to the reference total handover failure probability (P _{ns_th} ), the currently set beamwidth (R) can satisfy the QoS required by the system, so the currently set beamwidth (R) is set to low orbit. It is determined by the beam width of the satellite, and the low orbit satellite forms a beam with the determined beam width (R) (S21).

The method according to the present invention may be implemented as a computer program stored in a medium for execution by a computer. Here, the computer-readable medium may be any available medium that can be accessed by a computer, and may include all computer storage media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, and read dedicated memory), RAM (Random Access Memory), CD (Compact Disk)-ROM, DVD (Digital Video Disk)-ROM, magnetic tape, floppy disk, optical data storage, and the like.

Although the present invention has been described with reference to the embodiment shown in the drawings, which is only exemplary, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom.

Accordingly, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims.

110: QoS setting unit 120: beam width control unit
130: failure probability calculation unit 140: call holding time control unit
150: beam width determiner

Claims (16)

a beam width adjusting unit for increasing or decreasing the currently set beam width in a predetermined adjustment unit;
Calculate the total handover failure probability for each of the current beamwidth and the increased or decreased adjusted beamwidth in a predetermined manner, and the change failure probability, which is the total handover failure probability for the adjusted beamwidth, and the total handover failure probability for the current beamwidth The failure probability is compared, and if the change failure probability is less than the failure probability, the adjusted beamwidth is updated to the current beamwidth and the beamwidth adjustment is requested to the beamwidth adjuster. If the failure probability is greater than the failure probability, the failure probability corresponding to the last updated beamwidth a failure probability calculator that outputs;
If the failure probability output from the failure probability calculation unit is greater than a predetermined reference total handover failure probability, the predetermined call holding time is reduced by a predetermined adjustment unit, and the reduced call maintenance time is transmitted to the failure probability calculation unit to fail. a call holding time control unit for recalculating the probability; and
and a beamwidth determiner configured to determine the last updated beamwidth as the beamwidth of the low-orbit satellite communication system when the call holding time controller determines that the failure probability is smaller than the reference total handover failure probability. The method of claim 1, wherein the failure probability calculator
When the change failure probability for the adjusted beamwidth is reduced than the failure probability for the current beamwidth, the adjusted beamwidth is updated to the current beamwidth, and the beamwidth controller requests additional adjustment in the adjustment direction for the beamwidth,
If it is more than the failure probability, it requests to change the adjustment direction for the beam width to the beam width adjustment unit,
A low orbit satellite beamwidth adjusting device for outputting a failure probability corresponding to the last updated beamwidth if the failure probability for the beamwidth applied through additional adjustment or change adjustment is greater than or equal to the failure probability for the updated current beamwidth. The method of claim 2, wherein the failure probability calculator
A low orbit satellite beamwidth adjusting device that requests a change to increase the beamwidth if the updated beamwidth is the updated beamwidth by decreasing the last updated beamwidth, and requests a change so that the beamwidth is increased if the last updated beamwidth is increased and adjusted and updated. The method of claim 2, wherein the failure probability calculator
Equation for the probability of failure (P _{ns ) for the beam width (R)}

(Here, P _b1 represents the blocking probability of a new call attempt within the cell, and P _drop is the probability that the maintained call is disconnected due to a handover failure.)
A low-orbit satellite beamwidth adjuster that calculates according to 5. The system of claim 4, wherein the low orbit satellite communication system is
According to a fixed channel allocation (FCA) method in which a channel is allocated to each of a plurality of cells in advance, and a queuing handover (QH) method in which a handover queue is allocated to each cell to process a handover call. A low-orbit satellite beamwidth modulator that provides telecommunications services. The method of claim 5, wherein the low orbit satellite communication system is
A handover queue allocated to each cell according to the QH technique is an infinite queue, and M/M/S (M: Poission arrival process / M: service time exponentially distributed / S: number of channels assigned per cell) A low-orbit satellite beamwidth control device to which a queuing model is applied. The method of claim 6, wherein the failure probability calculator
Equation for the _{probability (P drop} ) of the maintained call being disconnected due to failure of handover

(Here, P _h1 and P _h2 represent the probability that a handover request will be made in the source cell, which is the cell in which a new call is made, and the transition cell, which is the cell in which the mobile subscriber moves while the call is maintained, and P _b2 is the handover request when the mobile subscriber moves between cells. It indicates the probability of over failure.)
A low-orbit satellite beamwidth adjuster that calculates according to The method of claim 7, wherein the failure probability calculator
Equation for blocking probability (P _{b1 ) for a new call attempt}

(Where S is the number of channels allocated to each cell, n is the number of mobile subscribers in the cell, and λ _h and λ are the handover and new call arrival rates, respectively. And μ is the average call completion rate, μ _w is the call incomplete rate calculated as the reciprocal of the predetermined maximum waiting time (t _w max) (μ _w = 1/t _{w max).}
Calculated according to the equation, the _{handover failure probability (P b2} ) when the mobile subscriber moves between cells

A low-orbit satellite beamwidth adjuster that calculates according to A method for adjusting a beam width of a beam width adjusting device for a low orbit satellite communication system, the method comprising:
setting a reference total handover failure probability as a required QoS;
increasing or decreasing the currently set beamwidth by a predetermined adjustment unit;
calculating a total handover failure probability for each of the current beamwidth and the increased or decreased beamwidth in a predetermined manner;
By comparing the change failure probability, which is the total handover failure probability for the adjusted beamwidth, with the failure probability, which is the total handover failure probability for the current beamwidth, if the change failure probability is less than the failure probability, the adjusted beamwidth is updated to the current beamwidth. repeatedly calculating the failure probability by further adjusting the beam width;
If the failure probability is greater than or equal to the failure probability, the failure probability corresponding to the last updated beamwidth is compared with the reference total handover failure probability, and the predetermined call holding time is adjusted in a predetermined adjustment unit according to the comparison result to recalculate the failure probability. to readjust the beam width; and
and determining a last updated beamwidth as a beamwidth of a low-orbit satellite communication system when the failure probability is less than the reference total handover failure probability. The method of claim 9, wherein the repeatedly calculating the failure probability comprises:
If the change failure probability for the adjusted beamwidth is reduced than the failure probability for the current beamwidth, updating the adjusted beamwidth to the current beamwidth and further adjusting the beamwidth in the adjustment direction in the step of determining the beamwidth; and
and if the failure probability is greater than or equal to the failure probability, adjusting the beam width by changing the adjustment direction. 11. The method of claim 10, wherein the step of re-adjusting the beam width comprises:
comparing the failure probability corresponding to the last updated beamwidth with the reference total handover failure probability when the failure probability for the beamwidth applied through additional adjustment or change adjustment is equal to or greater than the failure probability for the updated current beamwidth;
if the failure probability is greater than the reference total handover failure probability, reducing a predetermined call holding time by a predetermined adjustment unit; and
A method for adjusting a beamwidth of a low-orbit satellite, comprising the step of re-calculating a failure probability based on the reduced call holding time to readjust the beamwidth. The method of claim 11, wherein the failure probability (P _ns ) is
formula

(Here, P _b1 represents the blocking probability of a new call attempt within the cell, and P _drop is the probability that the maintained call is disconnected due to a handover failure.)
A low-orbit satellite beamwidth adjustment method calculated according to 13. The system of claim 12, wherein the low orbit satellite communication system is
According to a fixed channel allocation (FCA) method in which a channel is allocated to each of a plurality of cells in advance, and a queuing handover (QH) method in which a handover queue is allocated to each cell to process a handover call. A method of adjusting the beamwidth of a low-orbit satellite for providing a communication service. 14. The method of claim 13, wherein the low orbit satellite communication system is
A handover queue allocated to each cell according to the QH technique is an infinite queue, and M/M/S (M: Poission arrival process / M: service time exponentially distributed / S: number of channels assigned per cell) A low-orbit satellite beamwidth adjustment method to which the queuing model is applied. 15. The method of claim 14, wherein the probability that the maintained call is dropped because the handover fails (P _drop ) is

(Here, P _h1 and P _h2 represent the probability that a handover request will be made in the source cell, which is the cell in which a new call is made, and the transition cell, which is the cell in which the mobile subscriber moves while the call is maintained, and P _b2 is the handover request when the mobile subscriber moves between cells. It indicates the probability of over failure.)
A low-orbit satellite beamwidth adjustment method calculated according to 16. The method of claim 15, wherein the blocking probability (P _b1 ) for the new call attempt is
formula

(Where S is the number of channels allocated to each cell, n is the number of mobile subscribers in the cell, and λ _h and λ are the handover and new call arrival rates, respectively. And μ is the average call completion rate, μ _w is the call incomplete rate calculated as the reciprocal of the predetermined maximum waiting time (t _w max) (μ _w = 1/t _{w max).}
is calculated according to
_{The handover failure probability (P b2} ) when the mobile subscriber moves between cells is
formula

A low-orbit satellite beamwidth adjustment method calculated according to

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