Control device, wireless communication system, and program

Abstract

Provided is a control device that determines a remedial carrier and a tilt angle therefor, the remedial carrier remedying the communication of a fault area that occurs in the event of failure of the antenna of a wireless base station thereof. The control device comprises: a fault area consolidation unit that aggregates a plurality of adjacent fault areas, and generates a single consolidated fault area; a remedial carrier selecting unit that selects a plurality of remedial carriers for the consolidated fault area; and a tilt angle determining unit that simultaneously optimizes a plurality of tilt angles in the plurality of remedial carriers.

Description

Technical Field

[0001] The present invention relates to a technique for relieving an area where communication has become impossible due to a failure of a radio base station in a mobile communication network.

Background Art

[0002] When a radio base station fails due to a natural disaster or the like, a communication failure occurs in the area covered by the base station. Since high availability is required for wireless communication, recovery within a short time of about several minutes is required.

[0003] On the other hand, a technique has been studied to recover from a failure by changing the depression angle (tilt angle) of a beam (carrier) in a specific frequency band in an antenna of a base station around an area where a failure has occurred (failure area) to cover (relieve) the failure area (for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the prior art for the relief of the affected area, when the affected area caused by the failure of the radio base station cannot be fully covered, when prompt relief for the affected area cannot be provided, or even if it can be fully covered, there is a possibility that the communication quality may deteriorate. That is, there is a problem in the prior art that the affected area caused by the failure of the radio base station may not be appropriately relieved.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a technology that enables appropriate relief of an affected area caused by the failure of a radio base station.

Means for Solving the Problem

[0007] According to the disclosed technology, there is provided a control device that determines a relief carrier for relieving communication in an affected area that occurs when an antenna of a radio base station fails and its tilt angle, an affected area aggregating unit that aggregates a plurality of adjacent affected areas to generate a single aggregated affected area, a relief carrier selecting unit that selects a plurality of relief carriers for the aggregated affected area, a tilt angle determining unit that simultaneously optimizes a plurality of tilt angles in the plurality of relief carriers, and includes a control device.

Effect of the Invention

[0008] According to the disclosed technology, there is provided a technology that enables appropriate relief of an affected area caused by the failure of a radio base station.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention (these embodiments) will be described with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the following embodiments.

[0011] (Definition of Terms) First, the definitions of "antenna, carrier" and "area mesh" used in this specification will be described.

[0012] (1) Antenna, Carrier The base station is composed of a plurality of antennas, and each antenna is responsible for communication coverage in a specific direction. An antenna is composed of a plurality of carriers, and each carrier in a certain antenna is responsible for communication coverage of an area in a specific frequency band in the same direction. At this time, a tilt angle is set for each carrier, and if the angles are different, the coverage areas are also different.

[0013] Since there is a case where only some antennas of the base station fail, in this embodiment, instead of considering a failure at the base station level, a failure at the antenna level is considered.

[0014] (2) Area Mesh The area mesh is "a division of an area into meshes of approximately the same size based on latitude and longitude" defined by the Ministry of Internal Affairs and Communications (currently the Ministry of Public Management, Home Affairs, Posts and Telecommunications). In this embodiment, the area is considered in mesh units.

[0015] There are multiple regional meshes in the regional mesh, each having a different mesh granularity, that is, a different area per mesh. For example, there are 1 / 2 regional meshes (with a side length of approximately 500 m) and 1 / 8 regional meshes (with a side length of approximately 125 m).

[0016] The coarser the regional mesh, the less computational effort required to calculate the coverage area, and the shorter the time required to estimate the coverage area. The granularity of the regional mesh can be determined in advance by, for example, the operator of the radio base station control device 100 in the present embodiment.

[0017] (Regarding the problem) Here, the prior art and its problems will be described in detail. In the following description, the content disclosed in Non-Patent Document 1 is well-known, but the content of the description of its problems is not well-known.

[0018] (1) Prior art and its problem 1 As an existing method, Non-Patent Document 1 discloses a method for covering a failure area caused by a base station failure or the like. In this method, one carrier (relief carrier) for relief is selected from the base stations around the failure area, and the tilt angle of the carrier is changed so as to cover the failure area.

[0019] This is repeated until the failure area is sufficiently covered or all the carriers of the nearby base stations are used. When multiple base stations fail simultaneously, relief is performed in order for each failure area associated with each failure.

[0020] At this time, the relief carrier must be selected from carriers other than those that have been used for relief so far. Therefore, in the technology disclosed in Non-Patent Document 1, especially in the case where "multiple base stations fail simultaneously in an area where there are few base stations (peripheral stations) such as in a local area", there is a high possibility that there will be insufficient relief carriers for the failure areas to be relieved later, resulting in failure areas that cannot be fully covered.

[0021] (2) Prior art and its problem 2 As described above, in the technology disclosed in Non-Patent Document 1, for a plurality of failure areas, relief is performed in order for each failure area. Further, for one failure area, one relief carrier is selected at a time, and the tilt angle is calculated.

[0022] Therefore, the time required for all control calculations increases according to the number of failed base stations, and it may not be possible to provide prompt relief for a plurality of failure areas.

[0023] (3) Conventional Technology and Its Problems 3 As described above, in the technology disclosed in Non-Patent Document 1, for a failure area, one relief carrier is selected and the tilt angle is calculated one by one. At this time, only the coverage of the failure area is targeted, and the overlap with the coverage area of the relief carriers that have already been selected is not considered.

[0024] Therefore, even if sufficient coverage is achieved, there is a possibility that radio interference will be large and the communication quality will deteriorate.

[0025] (Features (Highlights) of the Technology According to the Embodiment) In the technology according to the present embodiment, in order to solve the above problems, a radio base station control device described later controls the tilt angles of surrounding base stations for the purpose of covering failure areas associated with base station failures and the like. The technology according to the present embodiment can solve the above-described problems by particularly having the following features (highlights). Note that the highlights described below are the highlights in the technology of the embodiment, and it is not essential to include all the highlights as the invention.

[0026] <Highlight 1> When a plurality of base stations fail and the failure areas associated with each of them are adjacent, they are treated as a single failure area, and a relief carrier and a tilt angle are calculated for this.

[0027] <Highlight 2> Relief carriers are prepared in advance for a failure area, their tilt angles are simultaneously optimized, and a combination of tilt angles that can obtain a high coverage rate is adopted.

[0028] <Point 3> Not only set the objective function in the simultaneous optimization of the tilt angle as the "coverage rate of the obstacle area", but also add the "size of the coverage area of the rescue carrier" as a penalty term.

[0029] (Effect of the technology according to the embodiment) The technology according to the present embodiment having the above-described points has the following effects.

[0030] <Effect 1> By Point 1, the problem that "the candidates for rescue carriers for the obstacle area are insufficient" described in Problem 1 can be alleviated. As a result, when multiple base station failures occur in an area with few surrounding stations, the coverage rate can be improved compared to the existing method.

[0031] <Effect 2> By Point 1, the calculation time of the control does not increase according to the number of failed base stations, thereby solving Problem 2 and enabling prompt rescue even when the number of failed base stations is large.

[0032] <Effect 3> By Point 2, by simultaneously optimizing the tilt angles of multiple rescue carriers, the coverage accuracy can be improved compared to the conventional method of sequentially changing the tilt angle for each rescue carrier.

[0033] <Effect 4> By Point 3, it is possible to prevent each rescue carrier from inadvertently expanding the coverage area, and the overlap of the coverage areas between the rescue carriers is reduced. As a result, the radio wave interference between the rescue carriers described in Problem 3 can be suppressed more than the conventional method, and an improvement in communication quality can be expected.

[0034] (Overall configuration of the system) FIG. 1 shows an example of the overall configuration of the wireless communication system according to the embodiment of the present invention. As shown in FIG. 1, the system according to the present embodiment includes a configuration in which a plurality of radio base stations 10 and a radio base station control device 100 are connected to a network 200. The network 200 is, for example, a network including a mobile core network. Communication terminals exist under each radio base station, and each communication terminal communicates wirelessly with the radio base station.

[0035] Hereinafter, the configuration and operation of the radio base station control device 100 according to the present embodiment will be described in detail.

[0036] (Example of the configuration of the radio base station control device 100) FIG. 2 shows a configuration diagram of the radio base station control device 100 according to the embodiment of the present invention. As shown in FIG. 2, the radio base station control device 100 includes an input reception unit 110, a data processing unit 120, and a radio base station control unit 130.

[0037] Further, as shown in FIG. 2, the data processing unit 120 includes a relief priority determination unit 121, a relief carrier selection unit 122, a failure area aggregation unit 123, and a tilt angle determination unit 123. The radio base station control unit 130 includes a reception unit 131 and a transmission unit 132.

[0038] Note that the radio base station control device 100 may be physically one device or may be a system composed of a plurality of physical devices. For example, “input reception unit 110 + data processing unit 120” may be composed of one device, and the radio base station control unit 130 may be composed of one device. Note that “input reception unit 110 + data processing unit 120” or “data processing unit 120” may be referred to as a control device. The functional outlines of the respective units are as follows.

[0039] <Radio base station control unit 130> The reception unit 131 and the transmission unit 132 of the radio base station control unit 130 can each communicate with the radio base station. The reception unit 131 receives information from the radio base station, and the transmission unit 132 transmits information to the radio base station.

[0040] <Input Reception Unit 110> The input reception unit 110 receives "information about each radio base station", "information about the antennas (failed antennas) that have failed within the failed station", and "important area information" from the radio base station control unit 130.

[0041] The "information about each radio base station" includes, for example, the following information.

[0042] · The positions (latitude, longitude), heights, and azimuths of all carriers installed in the radio base station · The vertical and horizontal beam widths of the beams of each carrier · The tilt angles set for each carrier · Information about adjacent stations In this embodiment, a radio base station located within a distance of n (km) from a certain radio base station (target radio base station (for example, the failed station)) and that is not a failed station is defined as an adjacent station of the target radio base station.

[0043] The "information about the antennas (failed antennas) that have failed within the failed station" includes, for example, the following information. Note that the "area" below is defined as a set of regional meshes. Also, the "area covered by the failed antenna" is defined as the affected area.

[0044] · The presence or absence of important facilities in the area covered by the failed antenna · The area covered by the failed antenna · The number of active users communicating with the failed antenna · The total traffic volume processed by the failed antenna The "important area information" is as follows.

[0045] · The regional meshes including important facilities and the set of regional meshes specified in advance by the operator are defined as important areas. Information is managed as important area information by embedding flag information indicating important areas in these meshes in advance.

[0046] <Affected Area Aggregation Unit 123> The failure area aggregation unit 123 receives information from the input reception unit 110 and generates a failure area obtained by aggregating adjacent failure areas into one failure area. One failure area obtained by aggregating a plurality of failure areas may be referred to as an aggregated failure area.

[0047] <Salvage priority determination unit 121> The salvage priority determination unit 121 receives information from the input reception unit 110 and the failure area aggregation unit 121 and determines the salvage priority of the failure area. The salvage priority is defined based on the nature of the failure area. Salvage is considered one by one from the failure area with the highest salvage priority.

[0048] <Salvage carrier selection unit 122> The salvage carrier selection unit 122 selects a salvage carrier from the base stations around the failure area to be salvaged.

[0049] <Tilt angle determination unit 124> The tilt angle determination unit 124 determines a tilt angle for the salvage carrier selected by the salvage carrier selection unit 122 such that a high coverage rate is obtained for the failure area and the overlap between the coverage areas of the salvage carriers is small. Specific operations will be described later.

[0050] The tilt angle determination unit 124 transmits the determined tilt angle to the radio base station control unit 130 to change the tilt angle of the salvage carrier in the radio base station.

[0051] (Operation of the radio base station control device 100) Hereinafter, an operation example of the radio base station control device 100 having the above configuration will be described in detail according to the procedure of the flowchart in FIG. 3.

[0052] <s1> In S1, the input reception unit 110 receives, as information necessary for relief, the input of failure area information and important area information from the radio base station control unit 130. The information received by the input reception unit 110 is passed to the failure area aggregation unit 123 and the relief priority determination unit 121.

[0053] <s2> In S2, the failure area aggregation unit 123 combines adjacent failure areas into one. That is, the failure area aggregation unit 123 redefines, for each failure area, the adjacent areas as a single failure area. An upper limit may be set for the number of areas to be combined and the size of the areas.

[0054] At this time, the failure area aggregation unit 123 also aggregates the number of active users in communication and the total traffic volume being processed, and aggregates the information into one failure area.

[0055] <S3, S4> When there are multiple failure areas that have undergone the processing in S2, the radio base station control device 100 performs relief one by one from the failure area with the highest relief priority.

[0056] Therefore, in S3, the relief priority determination unit 121 checks whether there is an unrelieved failure area. If not, the process ends. If there is an unrelieved failure area, the process proceeds to S4. The relief priority determination unit 121 determines the relief priority of each unrelieved failure area, and selects one failure area with the highest relief priority among the unrelieved failure areas.

[0057] The method by which the relief priority determination unit 121 determines the relief priority of each failure area is not limited to a specific method. For example, it can be determined based on indicators corresponding to the urgency of communication establishment, such as "presence or absence of important facilities in the failure area", "size of important areas within the failure area", "size of the failure area", "number of active users communicating with the failed antenna associated with the failure area", "total traffic volume processed by the failed antenna associated with the failure area", etc. Specific indicators may be determined as appropriate by the system operator.

[0058] For example, when the relief priority determination unit 121 determines the relief priority based on the "number of active users communicating with the failed antenna", the higher the number of active users, the higher the relief priority is set. Note that the relief priority determination unit 121 may determine the relief priority using any one of "the presence or absence of important facilities in the affected area", "the size of important areas within the affected area", "the size of the affected area", "the number of active users communicating with the failed antenna associated with the affected area", and "the total traffic volume processed by the failed antenna associated with the affected area", or may determine it using any plurality of them.

[0059] <s5> In S5, the relief carrier selection unit 122 selects a relief carrier for the failed area targeted for relief. Here, a plurality of carriers are selected from base stations around the failed area and used as relief carriers. Specifically, it is as follows.

[0060] The relief carrier selection unit 122 first calculates the centroid of the failed area. Then, m base stations are selected in ascending order of proximity to this centroid, and one carrier with the lowest frequency band at each base station is selected from each base station, and these are used as relief carriers.

[0061] For example, assume that in ascending order of proximity to the centroid of the failed area, there are base station 1, base station 2, and base station 3, and the relief carrier of base station 1 is carrier 1, the relief carrier of base station 2 is relief carrier 2, and the relief carrier of base station 3 is relief carrier 3. In this case, first, for relief carrier 1, S6 to S8 are executed. If the determination in S8 is No, then for relief carrier 1 and relief carrier 2, S6 to S8 are executed. If the determination in S8 is Yes, relief is executed at the tilt angles determined for each of relief carrier 1 and relief carrier 2. Note that such processing is an example. For example, S6 to S8 may be executed for a plurality of relief carriers from the beginning.

[0062] In this embodiment, based on the property that the lower the frequency band, the less the attenuation of radio waves due to distance, carriers in the lower frequency band with a prospect of covering a wider area up to a farther distance are preferentially selected as relief carriers. Additionally, if the traffic load situation for each carrier can be obtained, the carrier with the lowest load may be selected as the relief carrier.

[0063] Regarding the base stations from which the relief carriers are selected, they may be limited to the adjacent stations of the failed antenna in the failed area. In this case, if the number l of adjacent stations satisfies l < m, relief carriers are selected from all adjacent stations.

[0064] <s6> In S6, the tilt angle determination unit 124 estimates the radio wave propagation range for each combination of the relief carrier and the tilt angle. Since the estimation of these radio wave propagation ranges can be calculated independently for each combination, parallel calculation is possible. This makes it possible to speed up the calculation in S6.

[0065] The relief carrier has a settable range of tilt angles. In the present embodiment, within the settable range, the tilt angle is changed at a granularity of a predetermined angle unit such as 0.5° units or 1.0° units. The tilt angles prepared for each predetermined angle unit within the settable range are referred to as "each tilt angle". Then, the radio wave propagation range is estimated independently for all combinations of each relief carrier and "each tilt angle".

[0066] For example, when the settable range of the tilt angle of a certain relief carrier is 1° to 15° and the predetermined angle unit is 1°, for that relief carrier, the radio wave propagation range is estimated by the method described later for each of the 15 tilt angles of {1°, 2°,...... 14°, 15°}.

[0067] Generally, the exact radio wave propagation range is calculated in three dimensions of latitude, longitude, and altitude. However, in order to achieve the rapidity of relief, it is necessary to estimate the radio wave propagation range in a shorter time. Therefore, in the present embodiment, only the range covered by radio waves at a height of 1.5 m above the ground is considered as the radio wave propagation range. Here, a communication terminal held by a user is assumed, and 1.5 m above the ground is used as an example, but other heights other than 1.5 m may also be used.

[0068] As a result, since the radio wave propagation range is not estimated three-dimensionally, the accuracy of the estimation result decreases, but it is expected that the performance will improve from the viewpoint of the calculation speed.

[0069] In addition, the tilt angle determination unit 124 according to the present embodiment calculates the radio wave propagation range using a geometric approximation by a sector.

[0070] To accurately determine the radio wave propagation range, it is common to estimate the field strength at each point and use the estimation results. However, as described above, in order to prioritize the speed of relief, it is necessary to estimate the radio wave propagation range in a shorter time. Therefore, in this embodiment, considering the property that "the propagation loss of radio waves increases with distance", it is assumed that radio waves reach an equal distance throughout the entire range of the beam width, and under this assumption, the radio wave propagation range is calculated using a geometric approximation by a sector. The specific calculation method is as follows.

[0071] Here, the position of the relief carrier is (latitude lat, longitude lon), the height of the carrier is h, the center azimuth of the carrier is az center and the tilt angle of the carrier is x, and the vertical and horizontal beam widths (°) of the beam of the carrier are α and β, respectively. Note that the height h of the carrier is the height from 1.5 m above the ground.

[0072] Also, regarding the settable range of the tilt angle x, the minimum value is x min , and the maximum value is x max .

[0073] At this time, the range of the angle of the beam of the carrier in the vertical direction is [v min , v max . v min , v max are obtained by the following formulas respectively.

[0074] v min = max{x - α / 2, x min}}, v max = min{x + α / 2, x max} Let the radii of the two sectors used for the approximation of the radio wave propagation range be d min , d max , then they are obtained by the following formulas respectively.

[0075] d min = h / tan(v max ), d max = h / tan(v min ) d obtained by the above formula min , d max is shown in Figure 4 as shown.

[0076] Let the starting azimuth angles of the above two sectors be az start , and the ending azimuth angles be az end . Then, they can be obtained by the following formula.

[0077] az start = az center + β / 2, az end = az center - β / 2 As described above, the starting azimuth angles and ending azimuth angles of the two sectors are the same. However, the definition domains of az start , az end are set as 0 ≤ az start , az end < 360°. When the calculated values of az start , az end are outside the definition domain, the remainder with 360 as the modulus is used.

[0078] A sector with the center at the point (lat, lon), radius d min , central angle az start - az end , and facing the azimuth from az start to az end is defined as Sector A. Similarly, a sector with the center at the point (lat, lon), radius d max , central angle az start - az end , and facing the azimuth from az start to az end is defined as Sector B.

[0079] The tilt angle determination unit 124 obtains Sector A and Sector B by the above calculation, and among the areas included in Sector B, the areas not included in Sector A are used as the estimation result of the radio wave propagation range. When Sector A and Sector B are shown, they are as shown in Figure 5. Figure 5 shows the two sectors as seen from above.

[0080] The tilt angle determination unit 124 performs the above calculations for each relief carrier and each tilt angle to estimate the radio wave propagation range.

[0081] <s7> In S7, the tilt angle determination unit 124 calculates the tilt angle of the relief carrier. Specifically, for each relief carrier selected in S5, the tilt angle determination unit 124 calculates a combination of tilt angles that covers the obstacle area and minimizes the overlap of area coverage between the relief carriers.

[0082] Here, an objective function with the tilt angle of each relief carrier as an input is defined, and the combination of tilt angles that gives the best objective function value is adopted as the calculation result. The objective function is defined by combining the "coverage rate of the obstacle area", the "coverage rate of the important area (if there is an important area)", and the "coverage area size of the relief carrier". The obstacle area coverage rate, the important area coverage rate, and the coverage area size of the relief carrier are calculated using the estimated results of the radio wave propagation range corresponding to each carrier and tilt angle calculated in S6.

[0083] However, as a constraint, an upper limit is set for the number of meshes in the regional area (described later) with respect to the coverage area of each carrier, and the tilt angle is obtained within a range not exceeding this limit.

[0084] Hereinafter, after explaining the calculation methods of the obstacle area coverage rate, the important area coverage rate, and the coverage area size of the relief carrier, the calculation method of the combination of tilt angles will be explained.

[0085] <Calculation Method of Obstacle Area Coverage Rate> First, the calculation method of the obstacle area coverage rate will be explained.

[0086] Here, the radio wave propagation range calculated in S6 is defined as the coverage area. Also, the area originally covered by the relief carrier is defined as the foot area. Regarding the foot area, it is also possible to obtain it as base station information, or the tilt angle determination unit 124 may estimate the foot area using the radio wave propagation range estimation method described above. The area combining the obstacle area and the foot area is defined as the relief target obstacle area.

[0087] The tilt angle determination unit 124 compares the coverage area with the disaster area to be relieved, calculates the ratio of the coverage area included in the disaster area to be relieved, and defines this as the disaster area coverage rate. The coverage rate is calculated using the number of meshes in the regional mesh.

[0088] If the area included in the coverage area and also in the disaster area to be relieved is defined as the relievable disaster area, when using the regional mesh as described above, the tilt angle determination unit 124 calculates the disaster area coverage rate using the following formula.

[0089] (Disaster area coverage rate) = (Number of meshes in the relievable disaster area) / (Number of meshes in the disaster area to be relieved) <Calculation method of important area coverage rate> Next, the calculation method of the coverage area size of the relief carrier will be described.

[0090] When there is an important area in the disaster area, the area combining the important area and the foot area is defined as the important area to be relieved.

[0091] The tilt angle determination unit 124 compares the coverage area with the important area to be relieved, calculates the ratio of the coverage area included in the important area to be relieved, and defines this as the important area coverage rate.

[0092] That is, if the area included in the coverage area and also in the important area to be relieved is defined as the relievable important area, the tilt angle determination unit 124 calculates the important area coverage rate using the following formula.

[0093] (Important area coverage rate) = (Number of meshes in the relievable important area) / (Number of meshes in the important area to be relieved) <Calculation method of the coverage area size of the relief carrier> Next, the calculation method of the coverage area size of the relief carrier will be described. The tilt angle determination unit 124 calculates the coverage area size of each carrier as the ratio of the calculated number of meshes in the coverage area to the upper limit of the number of meshes in the coverage area as follows.

[0094] (Coverage area size of the carrier) = ((Number of meshes in the coverage area)) / ((Upper limit of the number of meshes in the coverage area)) The tilt angle determination unit 124 calculates this value for each rescue carrier, uses the average value as the (coverage area size of the rescue carrier), and uses it as a penalty term for the objective function. This can prevent each rescue carrier from inadvertently expanding the coverage area for improving the coverage rate, and can suppress the overlap of the coverage areas among the rescue carriers.

[0095] <Calculation method of tilt angle> Next, the calculation method of the tilt angle will be described. First, the objective function is defined as follows.

[0096] (Objective function) = α (Important area coverage rate) + β (Obstacle area coverage rate) - γ (Coverage area size of the rescue carrier).

[0097] α, β, and γ are parameters for weighting each item and are set in advance. For example, if the priority at the time of rescue is "maximizing the coverage rate of the important area", "maximizing the coverage rate of the obstacle area (excluding the important area)", and "minimizing the overlap of the coverage areas", then α > β > γ (e.g., α = 10, β = 5, γ = 1) may be used.

[0098] Next, the tilt angle determination unit 124 maximizes the objective function using the particle swarm optimization method (Non-Patent Document 2). Particle swarm optimization is a metaheuristic method for obtaining an approximate solution to a combinatorial optimization problem. A plurality of candidate solutions to the optimization problem called particles are prepared, and each particle is updated while sharing the objective function values of each other among the particles. Note that using the particle swarm optimization method for maximizing the objective function is just an example.

[0099] Here, "the combination of the tilt angles of all the rescue carriers" corresponds to one particle. Let the i-th particle be x i and the tilt angle of the j-th rescue carrier in x i be θ ij Assume (1 < j < m), then x i = [θ i1 , θ i2 ,..., θ im .

[0100] In the particle swarm optimization method, each particle x i is updated according to the following formula.

[0101] Update formula for particles: x i (t + 1) = x i (t) + v i (t + 1) Update formula for the update velocity of particles: v i (t + 1) = wv i (t + 1) + c1r1(x i p (t) - x i (t)) + c2r2(x g (t) - x i (t)) However, the meanings of each symbol (variable, etc.) are as follows.

[0102] x i (t): The particle at update count t v i (t): The velocity of the particle at update count t x i p (t): The best solution of particle i up to update count t x g (t): The best solution of all particles up to update count t w, c1, and c2 are coefficients, and r is a random number.

[0103] The update ends when the objective function value no longer increases or when the pre-set number of updates is reached. The particle with the maximum objective function value among all particles obtained by the above updates is adopted as the solution.

[0104] In addition to the above processing, when giving top priority to covering important areas, a particle with the maximum coverage rate of important areas among the obtained particles may be adopted.

[0105] In the above example, an objective function is used with the aim of optimizing to maximize the objective function value, but this is just an example. An objective function with the aim of optimizing to minimize the objective function value may also be used.

[0106] <S8, S9> In S8, the tilt angle determination unit 124 makes an end determination of the relief by determining whether the calculation result satisfies the end condition of the relief.

[0107] The end condition of the relief is, for example, "satisfying P% or more of the important area coverage rate of the obstacle area and Q% or more of the obstacle area coverage rate by the control of the relief station and tilt angle so far" or "(the number of relief carriers) = (the number of adjacent stations l)".

[0108] Note that (the number of relief carriers) = (the number of adjacent stations l) corresponds to the judgment that the number of relief carriers cannot be increased any further.

[0109] If the end condition of S8 is satisfied, the relief of the obstacle area currently being relieved is terminated, and the process proceeds to S9, where information on "each relief carrier and tilt angle" is transmitted to the radio base station control unit 130. Then, the process returns to S3.

[0110] If the condition is not satisfied in S8, the number of relief carriers is increased by one, the process returns to S5, and the tilt angles of all the relief carriers are recalculated.

[0111] (Hardware configuration example) The radio base station control device (or control device) in the present embodiment can be realized, for example, by causing a computer to execute a program describing the processing contents described in the present embodiment. Note that this "computer" may be a physical machine or a virtual machine on the cloud. When using a virtual machine, the "hardware" described here is virtual hardware.

[0112] The above program can be recorded on a computer-readable recording medium (such as a portable memory), saved, and distributed. It is also possible to provide the above program through a network such as the Internet or e-mail.

[0113] FIG. 6 is a diagram showing an example of the hardware configuration of the above computer. The computer in FIG. 6 includes a drive device 1000, an auxiliary storage device 1002, a memory device 1003, a CPU 1004, an interface device 1005, a display device 1006, an input device 1007, an output device 1008, etc., which are mutually connected by a bus BS.

[0114] A program for realizing the processing on the computer is provided by a recording medium 1001 such as a CD-ROM or a memory card, for example. When the recording medium 1001 storing the program is set in the drive device 1000, the program is installed from the recording medium 1001 via the drive device 1000 into the auxiliary storage device 1002. However, the program does not necessarily have to be installed from the recording medium 1001, and it may be downloaded from another computer via a network. The auxiliary storage device 1002 stores the installed program and also stores necessary files, data, etc.

[0115] When an instruction to start the program is given, the memory device 1003 reads out and stores the program from the auxiliary storage device 1002. The CPU 1004 realizes the functions related to the radio base station control device 100 (control device) according to the program stored in the memory device 1003. The interface device 1005 is used as an interface for connecting to a network. The display device 1006 displays a GUI (Graphical User Interface) etc. by the program. The input device 1007 is composed of a keyboard, a mouse, buttons, or a touch panel, etc., and is used to input various operation instructions. The output device 1008 outputs the calculation result.

[0116] (Appendix) This specification describes at least a control device, a wireless communication system, and a program described in each of the following sections. (Section 1) A control device that determines a relief carrier for relieving communication in a failure area that occurs when an antenna of a radio base station fails and its tilt angle, A failure area aggregation unit that aggregates a plurality of adjacent failure areas to generate a single aggregated failure area, A relief carrier selection unit that selects a plurality of relief carriers for the aggregated failure area, A tilt angle determination unit that simultaneously optimizes a plurality of tilt angles in the plurality of relief carriers, A control device comprising: (Section 2) The relief carrier selection unit selects, as a relief carrier, the carrier with the lowest frequency in each base station selected in ascending order from the center of gravity of the aggregated failure area. The control device according to Item 1. (Section 3) The tilt angle determination unit performs the optimization using an objective function that includes the coverage area size of the relief carrier as a penalty term. The control device according to Item 1 or Item 2. (Section 4) The tilt angle determination unit performs the optimization using the objective function that includes the failure area coverage rate for the aggregated failure area, the important area coverage rate for important areas in the aggregated failure area, and the coverage area size of the relief carrier. The control device according to Item 3. (Section 5) The control device according to any one of Items 1 to 4, and a radio base station that performs communication using the relief carrier and tilt angle determined by the control device. A wireless communication system comprising: (Section 6) A program for causing a computer to function as each part in the control device according to any one of Items 1 to 4.

[0117] As described above, although the present embodiment has been explained, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Signs

[0118] 10 Radio Base Station 100 Radio Base Station Control Device 110 Input Reception Unit 120 Data Processing Unit 121 Relief Priority Determination Unit 122 Relief Carrier Selection Unit 123 Failure Area Aggregation Unit 124 Tilt Angle Determination Unit 130 Radio Base Station Control Unit 131 Receiver 132 Transmitter 1000 Drive Device 1001 Recording Medium 1002 Auxiliary Storage Device 1003 Memory Device 1004 CPU 1005 Interface Device 1006 Display Device 1007 Input Device 1008 Output Device

Claims

1. A control device for determining a relief carrier for relieving communication in a failure area that occurs when an antenna of a wireless base station fails and its tilt angle, comprising: A failure area aggregation unit that aggregates a plurality of adjacent failure areas to generate a single aggregated failure area; A relief carrier selection unit that selects a plurality of relief carriers for the aggregated failure area; A tilt angle determination unit that simultaneously optimizes a plurality of tilt angles in the plurality of relief carriers; A control device comprising the above.

2. The relief carrier selection unit selects, as a relief carrier, the carrier with the lowest frequency in each base station selected in ascending order from the center of gravity of the aggregated failure area. The control device according to claim 1.

3. The tilt angle determination unit performs the optimization using an objective function that includes the coverage area size of the relief carrier as a penalty term. The control device according to claim 1 or 2.

4. The tilt angle determination unit performs the optimization using the objective function that includes the failure area coverage rate for the aggregated failure area, the important area coverage rate for important areas in the aggregated failure area, and the coverage area size of the relief carrier. The control device according to claim 3.

5. The control device according to any one of claims 1 to 4, and a wireless base station that performs communication using the relief carrier and tilt angle determined by the control device. A wireless communication system comprising the above.

6. A program for causing a computer to function as each part in the control device according to any one of claims 1 to 4.

Images