JP2014110465A - Femto-cell base station, output control method and output control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a substantially constant handover zone, irrespective of the number of mobile units located in a femto-cell.SOLUTION: A femto-cell base station 10 includes: a radio communication unit 11 for output a transmission radio wave for communicating with a mobile unit 20; a storage unit 13 for retaining statistical information 14 indicative of a statistical variation trend related to the varied number of mobile units 20 located in a femto-cell 30 which is a coverage area of the transmission radio wave; and a control unit 12 for controlling transmission radio wave output to obtain a substantially constant handover zone of the mobile unit 20 on the basis of the statistical information 14.

Description

  The present invention relates to a femtocell base station that controls output of a transmission radio wave, and an output control method and output control program thereof.

  Macro base stations that make up public mobile phone networks use macro cells with a cell radius of several hundreds of meters to several tens of kilometers as the coverage area, but in the boundary area between macro cells or in the back or underground of buildings where radio waves are difficult to reach As a result, the radio wave intensity becomes weak, and a place where communication is difficult occurs. In order to ensure communication in such places where communication is difficult, femtocell base stations having a coverage area of a femtocell having a cell radius of about several tens of meters are being operated. For example, Japanese Patent Application Laid-Open No. 2011-082692 is cited as a patent document referring to a method for realizing handover of a mobile device between a macro cell and a femto cell in a mobile communication network in which macro base stations and femto cell base stations are mixed. It has been known.

JP 2011-082692 A

  Since the femtocell base station outputs a weaker transmission radio wave than the macro base station, a phenomenon occurs in which the cell edge fluctuates in accordance with the number of mobile stations that change fluidly. This phenomenon will be described with reference to FIG. In the figure, reference numeral 50 indicates a conventional femtocell base station, reference numeral 20 indicates a mobile device, reference numeral 30 indicates a femtocell, and reference numeral 31 indicates a cell edge. Although the transmission output of the femtocell base station 50 in FIG. 5A and FIG. 5B is the same, the number of mobile stations 20 in FIG. 5A is larger than that in FIG. 5B. . As the number of mobile stations 20 located in the femtocell 30 increases, the range of the femtocell 30 is narrowed due to an increase in intra-cell interference accompanying an increase in the number of simultaneous communications of the femtocell base station 50, and as a result The cell edge 31 varies. Such a tendency is noticeable when the transmission output of the femtocell base station 50 approaches the upper limit.

  It has been found that there is a certain regularity in the variation tendency of the number of mobile devices 20 located in the femtocell 30. For example, when the femtocell base station 50 is installed in an office, the number of mobile devices 20 is increased during the day, and the number of mobile devices 20 is decreased at night. When the femtocell base station 50 is installed in a restaurant, the number of mobile stations 20 increases after noon or at night. Periodic fluctuations in the number of mobile stations 20 located in the femtocell 30 cause periodic fluctuations in the cell edge 31.

  Such cell edge fluctuations cause instability of the handover zone of the mobile device. This point will be described with reference to FIG. The horizontal axis of the graph in the figure indicates the distance (L) from the femtocell base station, and the vertical time axis indicates the ratio of energy per desired wave chip to in-band received power density (Ec / No). If the Ec / No of the femtocell is lower than the threshold value TH2, the mobile station located in the femtocell is disconnected, and handover from the femtocell to the macro cell becomes difficult. For this reason, if the mobile station located in the femtocell continues for a certain period of time when the Ec / No of the femtocell falls below the threshold value TH1, it hands over to a macro cell that shows Ec / No with better communication quality. In this specification, the handover zone indicates a range in which Ec / No of a femtocell is greater than or equal to TH2 and less than or equal to TH1.

  Here, reference numeral 81 denotes the handover of the mobile station when the Ec / No of the femtocell is attenuated as indicated by the graph indicated by reference numeral 61 and the Ec / No of the macro cell is attenuated as indicated by the graph indicated by reference numeral 71. Indicates the zone. Similarly, reference numeral 82 denotes a handover of the mobile station when the Ec / No of the femtocell is attenuated as indicated by the graph indicated by reference numeral 62 and the Ec / No of the macro cell is attenuated as indicated by the graph indicated by reference numeral 72. Indicates the zone. When the number of mobile stations located in the femtocell increases, the attenuation of Ec / No increases, and for example, a transition from a graph indicated by reference numeral 61 to a graph indicated by reference numeral 62 is made. Accordingly, the handover zone of the mobile device transitions from the point indicated by reference numeral 81 to the point indicated by reference numeral 82. Reference numeral 90 indicates the amount of change in the handover zone, and this change is related to the change in the cell edge. If the handover zone fluctuates in this way, the mobile device may fail to perform handover.

  Therefore, an object of the present invention is to make the handover zone substantially constant regardless of the number of mobile stations.

  In order to solve the above-described problems, a femtocell base station according to the present invention includes a wireless communication unit that outputs a transmission radio wave for communication with a mobile device, and the number of mobile devices located within the coverage area of the transmission radio wave. A storage unit that holds statistical information indicating a statistical variation tendency related to increase / decrease, and a control unit that controls the output of transmission radio waves so that the handover zone of the mobile device becomes substantially constant based on the statistical information. Since the number of mobile stations located can be predicted from the statistical information, the output of the transmission radio wave can be controlled based on the statistical information so that the handover zone of the mobile apparatus becomes substantially constant.

  The statistical information may be, for example, information indicating that the number of mobile stations existing in the coverage area periodically increases or decreases with 24 hours as a unit, or the number of mobile stations present in the coverage area is predetermined. Information indicating that the number of period days (for example, one week, one month, one year, etc.) is periodically increased or decreased as a unit may be used.

  For example, the control unit may further control the output of the transmission radio wave so that the handover zone becomes substantially constant by further adding an evaluation index of communication between the mobile device and the wireless communication unit. Thereby, the success rate of a handover can be increased. The control unit may control the output of the transmission radio wave so that the handover zone becomes substantially constant after weighting and evaluating the statistical information and the evaluation index.

  The storage unit may further hold a handover parameter that defines a condition for determining whether or not the handover of the mobile device is appropriate. The femtocell base station may further include correction means for feedback correcting the handover parameter based on the evaluation index so that the mobile device can perform handover in the handover zone. Such handover parameter feedback correction can increase the success rate of handover.

  The statistical information is statistical information indicating a statistical fluctuation tendency regarding the increase / decrease in the number of mobile stations located in the coverage area of other femtocell base stations installed in an environment similar to the installation environment of the femtocell base stations. May be used as default setting information. When the environment where the femtocell base station is installed is similar, it has been found that the statistical information tends to be similar.

  According to the present invention, since the number of mobile stations can be predicted from statistical information indicating a statistical fluctuation tendency regarding the increase or decrease of the number of mobile stations located in the coverage area of the transmission radio wave, the mobile station moves based on the statistical information. The output of the transmission radio wave can be controlled so that the handover zone of the machine becomes substantially constant.

It is a block diagram which shows the function structure of the femtocell base station concerning this embodiment. It is a graph which shows an example of the statistical information concerning this embodiment. It is a graph which shows an example of the statistical information concerning this embodiment. It is a flowchart which shows the flow of a process of the transmission output control of the femtocell base station concerning this embodiment. It is explanatory drawing which shows the mode of the fluctuation | variation of the cell edge concerning the conventional femtocell base station. It is explanatory drawing which shows the mode of the fluctuation | variation of the handover zone concerning the conventional femtocell base station.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a functional configuration of a femtocell base station 10 according to the present embodiment. The femtocell base station 10 includes a wireless communication unit 11 that outputs a transmission radio wave for communication with the mobile device 20, a storage unit 13 that holds statistical information 14 and a handover parameter 15, and a mobile device based on the statistical information 14. And a control unit 12 that controls the output of the transmission radio wave so that the 20 handover zones are substantially constant. The wireless communication unit 11 includes a circuit board including a high-frequency circuit and a baseband circuit for performing communication using a predetermined communication method (for example, code division multiple access method). The control unit 12 includes a circuit chip such as a CPU. The storage unit 13 includes a storage resource such as a memory. The statistical information 14 is information indicating a statistical fluctuation tendency related to an increase or decrease in the number of mobile devices 20 located in the femtocell 30 that is a coverage area of a transmission radio wave. The handover parameter 15 is a parameter that defines conditions for determining whether or not the handover of the mobile device 20 is appropriate. The mobile device 20 is, for example, a high function mobile phone such as a smartphone.

  FIG. 2 is a graph showing an example of the statistical information 14. In this example, the number of areas in the mobile device 20 tends to increase or decrease periodically with 24 hours as a unit. The horizontal axis of the graph in the figure shows the passage of time (from 0 o'clock to 24 o'clock), and the vertical axis shows the number of people in the area. The code | symbol 41 is a graph which shows the fluctuation tendency of the number of area | regions when the femtocell base station 10 is installed in the office for 24 hours, and the code | symbol 42 is the case where the femtocell base station 10 is installed in the restaurant It is a graph which shows the fluctuation tendency of 24 hours of the number of located areas. In the office, as shown in the graph 41, the number of in-zones starts to increase from 0 at the start time and then changes to a substantially constant value, and then decreases from the end time to 0. In the restaurant, as shown in the graph 42, the number of in-zones starts to increase from 0 at the opening time, once reaches a peak after noon, decreases at around 15:00, and then increases again at around 18:00. start. In this way, although there are some differences in the fluctuations of the number of locations with the passage of time according to the difference in the installation environment of the femtocell base station 10, all of them periodically change with 24 hours as a unit. Therefore, the feasible cell base station 10 installed in a specific environment is measured and analyzed over a predetermined number of days (for example, several days) with respect to a statistical fluctuation tendency regarding the increase / decrease in the number of mobile stations 20 in the service area. Thus, the statistical information 14 can be obtained. The femtocell base station 10 can predict the number of mobile stations 20 at a certain time with sufficient accuracy by referring to the statistical information 14 thus obtained.

  FIG. 3 is a graph showing another example of the statistical information 14, and in this example, shows a case where the number of mobile stations 20 tends to increase or decrease periodically with one week as a unit. The horizontal axis of the graph in the figure shows the passage of time (Monday to Sunday), and the vertical axis shows the number of mobile stations 20 in the service area. The code | symbol 43 is a graph which shows the fluctuation tendency of the number of area | regions for one week when the femtocell base station 10 is installed in the office, and the code | symbol 44 is the case where the femtocell base station 10 is installed in the restaurant. It is a graph which shows the fluctuation tendency of the number of area | regions for one week. In the office, as shown in the graph 43, a similar increase / decrease change in the number of areas is seen on each weekday from Monday to Friday, while almost no increase / decrease change in the number of areas is seen from Saturday to Sunday. In the restaurant, as shown in the graph 44, similar increase / decrease fluctuations in the number of areas are observed on each day from Monday to Sunday. In this way, although there are some differences in the fluctuations of the number of areas with the passage of time according to the difference in the installation environment of the femtocell base station 10, all of them periodically change with one week as one unit. Since the same is true, measurement and analysis of a statistical fluctuation tendency regarding increase / decrease in the number of mobile stations 20 in a certain environment over a predetermined number of days (for example, several weeks) for a femtocell base station 10 installed in a specific environment. Thus, the statistical information 14 can be obtained. By referring to the statistical information 14 thus obtained, the femtocell base station 10 can predict the number of mobile stations 20 on a certain day with sufficient practical accuracy.

  In addition, for the same environment, there is a statistical information 14 obtained by combining the fluctuation tendency of the number of areas obtained with 24 hours as one unit and the fluctuation tendency of the number of areas obtained with one week as one unit. The number of mobile stations 20 at a certain day of the week can be predicted. For example, by combining the above-described graphs 41 and 43, the number of mobile stations 20 at a certain time on a certain day of the week in a certain office environment can be predicted. Moreover, it is good also considering one month or one year as one unit instead of one week.

  FIG. 4 is a flowchart showing a process flow of the transmission output control of the femtocell base station 10. When paying attention to the fact that the handover zone fluctuates in accordance with the fluctuation of the number of areas in which the mobile device 20 is located, the femtocell base station 10 predicts the number of areas that fluctuate from moment to moment from the statistical information 14, and It is desirable to control the output of the transmission radio wave so that the handover zone becomes substantially constant. For example, when an increase in the number of serving areas is predicted, the output of the transmission radio wave is increased, and when a decrease in the number of serving areas is predicted, the output of the transmitting radio wave is decreased. In addition to the statistical information 14, the femtocell base station 10 further considers an evaluation index for communication between the mobile device 20 and the femtocell base station 10, so that the handover radio wave can be kept substantially constant. The output may be controlled. As one of the evaluation indexes, KPI (key performance indicator) is known, and handover parameters can be feedback-corrected based on the evaluation indexes to increase the success rate of handover. Examples of the handover parameters include thresholds TH1 and TH2 and handover determination time (time for determining whether handover is appropriate or not when Ec / No falls below threshold TH1) as shown in FIG. it can. Examples of the KPI include information such as the success rate of handover, the Ec / No of the femtocell base station 10, and the distance from the femtocell base station 10 to the mobile device 20. For example, the mobile device 20 may transmit the KPI to the femtocell base station 10 via the uplink channel when in the standby state.

  When receiving the KPI transmitted from the mobile device 20 via the uplink channel (Step 401), the control unit 12 evaluates the handover parameter (Step 402) and corrects the parameter so that the handover can be performed in the handover zone. Perform (step 403). Then, the control unit 12 controls the output of the transmission radio wave so that the handover zone becomes substantially constant based on the statistical information 14 or in addition to the statistical information 14 in consideration of the KPI (step 404). When controlling the transmission output in consideration of the KPI in addition to the statistical information 14, the control unit 12 performs the weighting evaluation of the statistical information 14 and the KPI, and transmits the handover zone so that the handover zone becomes substantially constant. The output of radio waves may be controlled. The storage unit 13 stores an output control program for causing the control unit 12 to execute the output control method of steps 401 to 404, and the control unit 12 is configured to interpret and execute the output control program. Yes.

  If the environment in which the femtocell base station 10 is installed is similar, the statistical information 14 also tends to be similar, so the statistical information 14 is an environment similar to the installation environment of the femtocell base station 10. Statistical information indicating a statistical fluctuation tendency regarding the increase or decrease of the number of mobile stations located in the femtocell that is the coverage area of another femtocell base station installed in the femtocell may be used as default setting information.

  According to the present embodiment, since the number of mobile stations 20 can be predicted from the statistical information 14, the output of the transmission radio wave is controlled based on the statistical information 14 so that the handover zone of the mobile station 20 becomes substantially constant. be able to. For example, in the case where the femtocell base station 10 is installed indoors and the radio wave of the outdoor macrocell base station is slightly penetrating the indoors, when the door installed indoors closes, Since radio waves from the penetrating macro base station rapidly decrease, it is desirable to make the handover zone constant so that the handover is completed indoors as much as possible. In addition to the statistical information 14, by further adding an evaluation index for communication between the mobile device 20 and the wireless communication unit 11, the output of the transmission radio wave is controlled so that the handover zone becomes substantially constant. The success rate of the handover of the machine 20 can be increased.

DESCRIPTION OF SYMBOLS 10 ... Femtocell base station 11 ... Wireless communication part 12 ... Control part 13 ... Memory | storage part 14 ... Statistical information 15 ... Handover parameter 20 ... Mobile station 30 ... Femtocell (coverage area)
31 ... Cell edge 81, 82 ... Handover zone

Claims (8)

A wireless communication unit that outputs a transmission radio wave for communicating with the mobile device;
A storage unit that holds statistical information indicating a statistical variation tendency related to an increase or decrease in the number of mobile stations located in the coverage area of the transmission radio wave;
A control unit that controls the output of the transmission radio wave so that a handover zone of the mobile device becomes substantially constant based on the statistical information;
A femtocell base station comprising: The femtocell base station according to claim 1,
The femtocell base station, wherein the statistical information is information indicating that the number of the mobile stations located in the coverage area periodically increases or decreases with 24 hours as a unit or with a predetermined period of days as a unit. The femtocell base station according to claim 1 or 2,
The control unit further considers an evaluation index of communication between the mobile device and the wireless communication unit, and controls the output of the transmission radio wave so that the handover zone becomes substantially constant. Bureau. A femtocell base station according to claim 3,
The said control part is a femtocell base station which controls the output of the said transmission radio wave so that the said handover zone may become substantially constant after weighting evaluation of the said statistical information and the said evaluation parameter | index, respectively. A femtocell base station according to claim 3 or claim 4,
The storage unit further holds a handover parameter that defines a condition for determining whether or not handover of the mobile device is appropriate.
The femtocell base station further includes correction means for feedback correcting the handover parameter based on the evaluation index so that the mobile device can perform handover in the handover zone. The femtocell base station according to any one of claims 1 to 5,
The statistical information indicates a statistical fluctuation tendency related to an increase or decrease in the number of mobile stations located in the coverage area of another femtocell base station installed in an environment similar to the installation environment of the femtocell base station. A femtocell base station that uses statistical information as default setting information. An output control method for controlling the output of a transmission radio wave of a femtocell base station,
The output of the transmission radio wave is set so that the handover zone of the mobile station is substantially constant based on statistical information indicating a statistical fluctuation tendency regarding the increase or decrease of the number of mobile stations located in the coverage area of the transmission radio wave. Output control method to control.   An output control program for causing a femtocell base station to execute the output control method according to claim 7.

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