JP2011124733A - Radio communication system, radio base station, and communication control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system, a radio base station and a communication control method that suitably reduce interference. <P>SOLUTION: When the area of a small-cell PC1 is equal to or larger than a threshold, a large-output base station 100 considers that a radio terminal 300d increases interference to up communication between the large-output base station 100 and a radio terminal 300a, and selects a second interference control system. When the area of the small-cell PC1 is smaller than the threshold, on the other hand, the large-output base station 100 considers that a radio terminal 300 increases interference to up communication between a small-output base station 200 and the radio terminal 300d, and selects a first interference control system. Further, the large-output base station 100 reports the selected interference control system to the small-output base station 200. The small-output base station 200, on the other hand, performs communication control by the reported interference control system. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a radio communication system including a first radio base station and a second radio base station, a radio base station in the radio communication system, and a communication control method in the radio communication system.

  In 3GPP (3rd Generation Partnership Project), a standardization project for mobile communication systems, technical specifications for LTE (Long-Term Evolution) Release 8 are being developed as next-generation mobile communication systems, and commercial services are about to start. Furthermore, in parallel with the standardization of LTE Release 9 which is a function improvement version, the demand for the future evolution of LTE from 3GPP operators and the 4th generation mobile communication system defined by the International Telecommunications Union ( In order to meet the need to satisfy the IMT-Advanced capability, LTE-Advanced, an advanced LTE system, is being studied.

  In response to the ever increasing demand for wireless communication services, conventional macrocell systems that cover a large area with only a high-power base station (MeNB: Macro eNodeB) satisfy the required communication capacity and coverage. It becomes difficult. As a solution to this problem, the arrangement of a heterogeneous network in which a low-power base station is arranged in a conventional macro cell system is expected as a cost-effective technique. Therefore, it is very important that LTE-Advanced can efficiently support heterogeneous networks, and full-scale studies are about to start in 3GPP (for example, see Non-Patent Documents 1 and 2).

3GPP, RP-090665, Qualcomm, “Revised SID on LTE- Advanced,” May 2009. 3GPP, R1-092583, Nokia Siemens Networks, “Assumptions for LTE-Advanced Heterogeneous Deployment Studies,” Jun. 2009.

  From the viewpoint of frequency utilization efficiency in a heterogeneous network, a small cell (local cell) formed by a small output base station uses the same frequency band as a large cell (macro cell) formed by a large output base station. Placement is desired. However, in such a case, the interference situation becomes more complicated by overlapping the local cell with the macro cell. Further, in a heterogeneous network, the criterion for selecting a base station to which a wireless terminal is connected is greatly influenced by the throughput characteristics, and the interference state changes greatly accordingly. Therefore, in order to efficiently support a heterogeneous network in LTE-Advanced, it is necessary to solve an interference problem that is more complicated than that of a conventional macro cell system.

  Therefore, an object of the present invention is to provide a radio communication system, a radio base station, and a communication control method that can appropriately reduce interference.

  In order to solve the above-described problems, the present invention has the following features. A first feature of the present invention is a wireless communication system (wireless communication system 1) including a first wireless base station (high-power base station 100) and a second wireless base station (low-power base station 200). The first radio base station communicates between the first radio base station and the first radio terminal (radio terminal 300a), and the second radio base station and the second radio terminal (radio A selection unit (selection unit 111) for selecting one of the first and second interference control methods for controlling interference in communication with the terminal 300d), and the interference control method selected by the selection unit And a notification unit (used band determination unit 114, wired communication unit 106) for notifying the second radio base station of interference control information including information indicating the frequency band information to be subjected to interference control, Is the second radio base station the first radio base station? Based of the interference control information, and summarized in that a control unit for controlling communication between the second wireless terminal (used bandwidth determination unit 214, the scheduling unit 216).

  In such a radio communication system, the first radio base station selects one of the first and second interference control methods, notifies the second radio base station, and the second radio base station Then, communication control is performed using the notified interference control method. Therefore, it is possible to suppress interference with an appropriate interference control method according to the environment.

  A second feature of the present invention is that, in the first interference control method, the control unit suppresses interference with respect to a frequency band indicated by the interference control information from the first radio base station. Control communication with the second radio terminal, and in the second interference control method, the frequency band indicated by the interference control information from the first radio base station is taken into account, and The gist is to control communication with the second wireless terminal.

  A third feature of the present invention is that the selection unit is more likely to select the first interference control scheme as the second radio base station is closer to the first radio base station. To do.

  A fourth feature of the present invention is that, when there are a plurality of the second radio base stations, the selection unit selects one of the first and second interference control schemes for each second radio base station. The gist is to select.

  A fifth feature of the present invention is that a first cell (large cell MC1) is formed by the first radio base station, and a second cell smaller than the first cell by the second radio base station. (Small cell PC1) is formed, and the selection unit selects either the first interference control method or the second interference control method according to the size of the second cell.

  According to a sixth aspect of the present invention, the selection unit includes the maximum transmission power of the second radio base station and the second cell existing in the first cell formed by the first radio base station. The gist is to select one of the first and second interference control methods according to the number of radio base stations.

  A seventh feature of the present invention is that, in the first interference control method, the second radio base station and the second radio are used with respect to a frequency band used in an outer region in the first cell. An interference control method for suppressing an amount of interference caused by communication with a terminal, wherein the second interference control method includes the second wireless base station and the second wireless terminal among the first wireless terminals. An interference control scheme in which the second radio base station considers and uses a frequency band used by the first radio terminal that is considered to have an amount of interference given to communication with the first radio terminal equal to or greater than a predetermined value. The gist.

  An eighth feature of the present invention is a radio base station that constitutes a radio communication system together with another radio base station, wherein communication between the radio terminal and the other radio base station and the other radio terminal are performed. A selection unit that selects one of the first and second interference control methods for controlling interference in communication between the information, information indicating the interference control method selected by the selection unit, and a target of interference control And a notifying unit for notifying the other radio base station of interference control information including information on the frequency band to be obtained.

  A ninth feature of the present invention is a radio base station that constitutes a radio communication system together with another radio base station, the communication between the radio base station and the radio terminal from the other radio base station, , Information indicating one of the first and second interference control methods for controlling interference in communication between the other radio base station and another radio terminal, and a frequency band to be subjected to interference control And a control unit that controls communication with the wireless terminal based on interference control information including the above information.

  A tenth feature of the present invention is a communication control method in a radio communication system comprising a first radio base station and a second radio base station, wherein the first radio base station is the first radio base station. Of first and second interference control methods for controlling interference between a communication between a station and a first wireless terminal and a communication between the second wireless base station and the second wireless terminal And selecting interference control information including information indicating the selected interference control method and information on a frequency band to be subjected to interference control, in the second radio base station. Notifying to a base station, and controlling the communication with the second radio terminal based on the interference control information from the first radio base station, the second radio base station; It is a summary to provide.

  According to the characteristics of the present invention, it is possible to appropriately reduce interference.

1 is an overall schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. It is a block diagram which shows the structure of the high output base station and small output base station which concern on embodiment of this invention. It is a figure which shows an example of the frequency band used in the high output base station and the small output base station in the case of the 1st interference control system which concerns on embodiment of this invention. It is a figure which shows an example of the frequency band used in the high output base station and the small output base station in the case of the 2nd interference control system which concerns on embodiment of this invention. It is a flowchart which shows the operation example of the selection of the interference control system which concerns on embodiment of this invention. It is a flowchart which shows the operation example in the case of the 1st interference control system in the high output base station which concerns on embodiment of this invention. It is a flowchart which shows the operation example of cancellation | release of the 1st interference control system in the high output base station which concerns on embodiment of this invention. It is a flowchart which shows the operation example in the case of the 2nd interference control system in the high output base station which concerns on embodiment of this invention. It is a flowchart which shows the operation example of the small output base station which concerns on embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. Specifically, (1) the configuration of the wireless communication system, (2) the operation of the wireless communication system, (3) the operation and effect, and (4) other embodiments will be described. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Configuration of Radio Communication System (1.1) Overall Schematic Configuration of Radio Communication System FIG. 1 is an overall schematic configuration diagram of a radio communication system 1 according to an embodiment of the present invention. The wireless communication system 1 has, for example, a configuration based on LTE Release 9 which is a 3.9th generation (3.9G) mobile phone system and LTE-Advanced which is positioned as a 4th generation (4G) mobile phone system.

  As shown in FIG. 1, the wireless communication system 1 includes a high-power base station (for example, a macro cell base station) 100 that forms a large cell (for example, a macro cell) MC1. The large cell MC1 indicates a range in which a wireless terminal can connect to the high-power base station 100, and the radius is, for example, about several hundreds [m].

  In addition, the wireless communication system 1 includes a low-power base station (for example, a picocell base station) 200 installed outdoors and in the large cell MC1. The small output base station 200 has a smaller transmission output (transmission power) than the large output base station 100, and forms a small cell (for example, a pico cell) PC1. The small cell PC1 indicates a range in which the wireless terminal can connect to the small output base station 200, and the radius is, for example, about several tens [m].

  The high-power base station 100 is installed at a location based on a station design that considers inter-cell interference. On the other hand, the small output base station 200 is configured to be small enough to be installed at an arbitrary location. The small output base station 200 is installed for the purpose of distributing the traffic of the large output base station 100 and covering the dead zone in the large cell MC1. The high-power base station 100 and the small-power base station 200 are connected to the core network 500 via a dedicated line.

  Wireless terminals 300a, 300b and 300c in the large cell MC1 are connected to the high output base station 100, and a wireless terminal 300d in the small cell PC1 is connected to the small output base station 200.

(1.2) Configuration of High Output Base Station and Low Output Base Station FIG. 2 is a block diagram showing the configuration of the high output base station 100 and the low output base station 200 according to the embodiment of the present invention.

  As illustrated in FIG. 2, the high-power base station 100 includes a control unit 102, a wireless communication unit 104, and a wired communication unit 106. On the other hand, the small output base station 200 includes a control unit 202, a wireless communication unit 204, and a wired communication unit 206.

  The control unit 102 in the high-power base station 100 is configured using, for example, a CPU, and controls various functions provided in the high-power base station 100.

  The radio communication unit 104 is configured using, for example, a radio frequency (RF) circuit, a baseband (BB) circuit, or the like, and transmits radio signals to and from the radio terminals 300a, 300b, and 300c via the antenna units 105a and 105b. Send and receive. Further, the wireless communication unit 104 performs encoding and modulation of transmission signals for the wireless terminals 300a, 300b, and 300c, and demodulation and decoding of reception signals from the wireless terminals 300a, 300b, and 300c. The wireless communication unit 104 acquires data and measurement information (terminal measurement information) in the wireless terminals 300a, 300b, and 300c by demodulating received signals from the wireless terminals 300a, 300b, and 300c. The terminal measurement information is received power density (high output received power density) measured at the wireless terminals 300a, 300b, and 300c when the wireless terminals 300a, 300b, and 300c receive a wireless signal from the high output base station 100. And when the wireless terminals 300a, 300b and 300c receive a wireless signal from the small output base station 200, the received power density (small output received power density) measured in the wireless terminals 300a, 300b and 300c, And identification information (base station identification information) of the low-power base station 200.

  Further, the radio communication unit 104 is configured to use an uplink channel (large cell uplink channel) from the radio terminals 300a, 300b, and 300c toward the high-power base station 100 based on a reference signal that is a received signal from the radio terminals 300a, 300b, and 300c. Measure the channel state of

  The wired communication unit 106 transmits and receives various types of information to and from the wired communication unit 206 in the small output base station 200 via the X2 interface set in the core network 500.

  The control unit 102 includes a selection unit 111, a small interference cell detection unit 112, a specification unit 113, a use band determination unit 114, and a scheduling unit 116.

  On the other hand, the control unit 202 in the small output base station 200 is configured using, for example, a CPU, and controls various functions provided in the small output base station 200.

  The wireless communication unit 204 is configured using, for example, a radio frequency (RF) circuit, a baseband (BB) circuit, or the like, and transmits and receives a wireless signal to and from the wireless terminal 300d via the antenna units 205a and 205b. Do. In addition, the wireless communication unit 204 performs encoding and modulation of a transmission signal for the wireless terminal 300d and demodulation and decoding of a reception signal from the wireless terminal 300d. The wireless communication unit 204 acquires data and measurement information (terminal measurement information) in the wireless terminal 300d by demodulating a reception signal from the wireless terminal 300d.

  Further, the radio communication unit 204 measures the channel state of the uplink channel (small cell uplink channel) from the radio terminal 300d toward the small output base station 200 based on a reference signal that is a received signal from the radio terminal 300d.

  The wired communication unit 206 transmits and receives various types of information to and from the wired communication unit 106 in the high-power base station 100 via the X2 interface set in the core network 500.

  The control unit 202 includes a use band determination unit 214 and a scheduling unit 216.

  Hereinafter, detailed processing of the high-power base station 100 and the small-power base station 200 will be described.

  First, detailed processing of the high-power base station 100 will be described. The selection unit 111 performs communication between the high-power base station 100 and the wireless terminals 300a, 300b, and 300c connected to the high-power base station 100, and communication between the small-power base station 200 and the wireless terminal 300d. One of the first interference control method and the second interference control method for controlling interference is selected.

  Here, the first interference control scheme is an interference control that suppresses the amount of interference caused by communication between the low-power base station 200 and the radio terminal 300d with respect to the frequency band used in the outer region MC1OUT in the large cell MC1. It is a method. Specifically, the first interference control method is a frequency band used in the inner area (cell center area) MC1IN in the large cell MC1 and a frequency band used in the outer area (cell edge area) MC1OUT in the large cell MC1. In contrast, the frequency band used in the small cell PC1 is the same as the frequency band used in the inner region MC1IN in the large cell MC1.

  On the other hand, the second interference control method is used by wireless terminals among the wireless terminals 300a, 300b, and 300c, in which the amount of interference given to communication between the low-power base station 200 and the wireless terminal 300d is considered to be a predetermined value or more This is an interference control method used by the low-power base station 200 in consideration of the frequency band to be used. Specifically, in the second interference control method, among the wireless terminals 300a, 300b, and 300c connected to the high output base station 100, the low output base station 200 and the wireless terminal 300d connected to the small output base station 200 are connected. This is an interference control method in which a frequency band used by a wireless terminal that is considered to have an interference amount that is greater than or equal to a predetermined value is different from a frequency band used by the wireless terminal 300d.

  Specifically, the selection unit 111 acquires the transmission power density of the small output base station 200. For example, the selection unit 111 can acquire the transmission power density of the small output base station 200 from the small output base station 200 via the X2 interface and the wired communication unit 106. Furthermore, the selection unit 111 estimates the area of the small cell PC1 based on the acquired transmission power density of the small output base station 200. The area of the small cell PC1 increases as the transmission power density of the small output base station 200 increases.

  Next, the selection unit 111 acquires the position of the high-power base station 100 and the position of the small-power base station 200, and calculates the distance between the high-power base station 100 and the small-power base station 200. Furthermore, the selection unit 111 sets the threshold value such that the threshold value regarding the area increases as the calculated distance increases. Further, the selection unit 111 determines whether or not the area of the small cell PC1 is equal to or larger than a threshold value.

  When the area of the small cell PC1 is equal to or larger than the threshold, the selection unit 111 selects the first interference control method. On the other hand, when the area of the small cell PC1 is less than the threshold, the selection unit 111 selects the second interference control method.

  In addition, the selection unit 111 acquires the maximum transmission power of the low-power base station 200, and when the transmission power is less than the threshold, selects the first interference control method, and the transmission power is greater than or equal to the threshold. Alternatively, the second interference control method may be selected. Alternatively, when there are a plurality of small output base stations 200 in the large cell MC1, the selection unit 111 acquires the number of small output base stations 200 present in the large cell MC1, and the small output base station 200 The first interference control method may be selected when the number of is less than the threshold value, and the second interference control method may be selected when the number of small-power base stations 200 is equal to or greater than the threshold value.

  When the selection unit 111 selects the first interference control method, the selection unit 111 outputs a notification to that effect to the small interference cell detection unit 112. On the other hand, when selecting the second interference control method, the selection unit 111 outputs a notification to that effect to the specifying unit 113.

  Hereinafter, details of the processing of the high-power base station 100 in the case of the first interference control method will be described. When receiving the notification from the selection unit 111, the interference small cell detection unit 112 inputs the terminal measurement information received by the wireless communication unit 104. Furthermore, when the small output received power included in the terminal measurement information is greater than or equal to a predetermined value, the interference small cell detection unit 112 is formed by the small output base station 200 specified by the base station identification information included in the terminal measurement information. The small cell PC1 to be determined is an interference source in the large cell uplink channel.

  When the small cell PC1 that is an interference source is specified by the interference small cell detection unit 112, the use band determining unit 114 changes the frequency band used in the cell edge region and the frequency band used in the cell center band. decide.

  Specifically, the use band determining unit 114 divides all frequency bands (system bands) usable in the wireless communication system 1 into a first frequency band and a second frequency band. Further, as shown in FIG. 3, the use band determining unit 114 determines the first frequency band as a frequency band (cell center band) used in the cell center region MC1IN. Furthermore, the use band determining unit 114 determines the second frequency band as a frequency band (cell edge band) used in the cell edge region MC1OUT.

  Furthermore, the use band determination unit 114 includes information (flag) indicating that the first interference control method is used and information indicating the determined cell center band (cell center band information) in the terminal measurement information. The base station identification information of the small output base station 200 is added to generate interference control information and output to the wired communication unit 106.

  The wired communication unit 106 transmits the interference control information to the small output base station 200 corresponding to the base station identification information included in the interference control information via the X2 interface. In LTE, HII (High Interference Indication) can be exchanged between base stations via an X2 interface. Accordingly, the wired communication unit 106 can transmit the interference control information in the HII.

  On the other hand, when the small output base station 200 that is an interference source is not specified by the interference small cell detection unit 112, the use band determination unit 114 sets the system band to a frequency band (large band) that can be used in the entire area of the large cell MC1. Cell band).

  In addition, after the first frequency band is determined as the frequency band used in the cell center region MC1IN and the second frequency band is determined as the frequency band used in the cell edge region MC1OUT by the use band determining unit 114. When the connection between the small output base station 200 and the wireless terminal 300d is released, the wired communication unit 106 receives information indicating that the connection between the small output base station 200 and the wireless terminal 300d from the core network 500 is released ( Get disconnect information). The connection release information is transmitted from the small output base station 200 or another communication device (not shown). This connection release information includes base station identification information of the low-power base station 200 that has released the connection with the wireless terminal 300d. When the connection release information is input, the use band determining unit 114 determines the system band as the large cell band.

  Based on the terminal measurement information and the channel state from the radio communication unit 104 and the frequency band determined by the use band determination unit 114, the scheduling unit 116 provides the radio terminals 300a, 300b, and 300c as radio resources. Allocate resource blocks.

  Specifically, the use band determination unit 114 determines the first frequency band as the frequency band used in the cell center region MC1IN, and the second frequency band as the frequency band used in the cell edge region MC1OUT. The scheduling unit 116 allocates a resource block of the first frequency band to the wireless terminal (wireless terminal 300b in FIG. 1) in the cell center region MC1IN, and the wireless terminal (wireless in FIG. 1) in the cell edge region MC1OUT. Terminal blocks 300a and 300c) are allocated resource blocks in the second frequency band.

  Here, the radio communication unit 104 measures the reception power of radio signals from the radio terminals 300a, 300b, and 300c, thereby reducing the propagation loss of the uplink channel from the radio terminals 300a, 300b, and 300c to the high-power base station 100. It can be measured. The scheduling unit 116 calculates the distances from the radio terminals 300a, 300b, and 300c to the high-power base station 100 based on the propagation loss, and based on the distances, the radio terminals 300a, 300b, and 300c are within the cell center region MC1IN. Or in the cell edge region MC1OUT.

  Further, when the system band is determined as a frequency band to be used in the large cell MC1 by the use band determining unit 114, the scheduling unit 116 applies to the radio terminals 300a, 300b, and 300c in the large cell MC1. Allocate resource blocks for system bandwidth.

  Hereinafter, details of the processing of the high-power base station 100 in the case of the second interference control method will be described. Upon receiving the notification from the selection unit 111, the specifying unit 113 among the wireless terminals 300a, 300b, and 300c connected to the high-power base station 100, the wireless terminal connected to the small-power base station 200 and the small-power base station 200 A radio terminal in which the amount of interference (hereinafter referred to as “interference given to the small cell PC1”) given to the uplink communication with 300d is considered to be equal to or greater than the first predetermined value is specified.

  Specifically, the specifying unit 113 acquires the transmission power density of the wireless terminals 300 a, 300 b, and 300 c assumed in advance and the transmission power density of the small output base station 200. The transmission power densities of the wireless terminals 300a, 300b, and 300c are stored in a storage unit (not shown) in the high-power base station 100, for example. Further, the specifying unit 113 can acquire the transmission power density of the small output base station 200 from the small output base station 200 via, for example, the X2 interface and the wired communication unit 106. Next, the specifying unit 113 acquires the small output received power density included in the terminal measurement information from the wireless terminals 300a, 300b, and 300c.

  Next, the specifying unit 113 sets a propagation loss (small output propagation loss) that is a difference between the corresponding small output received power density and the transmission power density of the small output base station 200 for each of the wireless terminals 300a, 300b, and 300c. calculate. Further, the specifying unit 113 selects a wireless terminal having a transmission power density equal to or higher than the second predetermined value and a corresponding small output propagation loss less than the third predetermined value among the wireless terminals 300a, 300b, and 300c. The interference amount given to the small cell PC1 is specified as a wireless terminal that is considered to be greater than or equal to the first predetermined value.

  Note that the identifying unit 113 may identify a wireless terminal whose distance from the low-power base station 200 is a predetermined length or more among the wireless terminals 300a, 300b, and 300c as a strong interference large cell terminal. In this case, the specifying unit 113 acquires the positions of the wireless terminals 300a, 300b, and 300c and the position of the small output base station 200, and based on these positions, the wireless terminals 300a, 300b, and 300c, and the small output base station The distance to 200 is calculated.

  Further, the identifying unit 113 has the amount of interference given to the small cell PC1 among the radio terminals 300a, 300b, and 300c is equal to or greater than a first predetermined value and the distance from the small output base station 200 is equal to or greater than a predetermined length. May be specified as a strong interference large cell terminal.

  In the following description, the radio terminal 300a is a strong interference large cell terminal, and the radio terminals 300b and 300c are considered to be radio terminals (weak interference large cells) in which the amount of interference given to the small cell PC1 is less than a first predetermined value. Terminal).

  When the wireless terminal 300a that is a strong interference large cell terminal is identified, the use band determination unit 114 determines the frequency band used by the wireless terminal 300a that is a strong interference large cell terminal and the wireless terminal that is a weak interference large cell terminal. The frequency band used by 300b and 300c is determined differently.

  Specifically, the use band determination unit 114 uses all frequency bands (system bands) that can be used in the radio communication system 1 by the radio terminal 300a, which is a strong interference large cell terminal, as shown in FIG. Frequency band (large cell strong interference band) and a frequency band (large cell weak interference band) used by the radio terminals 300b and 300c which are weak interference large cell terminals. Here, in view of the fact that the strong interference large cell terminal is one of the wireless terminals 300a and the weak interference large cell terminal is two of the wireless terminals 300b and 300c, the use band determining unit 114 is for large cell strong interference. The bandwidth is divided so that the bandwidth of the band and the bandwidth of the large cell weak interference band are 1: 2.

  Further, the use band determining unit 114 includes the determined large cell strong interference band information (large cell strong interference band information) included in the terminal measurement information from the radio terminal 300a which is a strong interference large cell terminal. The base station identification information of the small output base station 200 is added to generate interference control information, which is output to the wired communication unit 106.

  The wired communication unit 106 transmits the interference control information to the small output base station 200 corresponding to the base station identification information included in the interference control information via the X2 interface. Here, the wired communication unit 106 can transmit the HII including the interference control information.

  On the other hand, when the strong interference large cell terminal is not specified by the specifying unit 113, the use band determining unit 114 determines the system band as a frequency band (large cell band) that can be used in the large cell MC1.

  The scheduling unit 116 allocates a resource block as a radio resource to the radio terminal based on the terminal measurement information and the channel state from the radio communication unit 104 and the frequency band determined by the use band determination unit 114.

  Specifically, when the large band strong interference band and the large cell weak interference band are determined by the use band determining unit 114, the scheduling unit 116 determines that the radio terminal 300a that is a strong interference large cell terminal On the other hand, resource blocks in the large cell strong interference band are allocated, and resource blocks in the large cell weak interference band are allocated to the radio terminals 300b and 300c which are weak interference large cell terminals.

  In addition, when the system band is determined as the frequency band used in the large cell MC1 by the use band determining unit 114, the scheduling unit 116 transmits the resource of the system band to the radio terminals 300a, 300b, and 300c. Allocate a block.

  Next, detailed processing of the small output base station 200 will be described.

  The wired communication unit 206 receives the interference control information from the wired communication unit 106 in the high-power base station 100 and outputs it to the control unit 202.

  The use band determining unit 214 in the control unit 202 determines whether or not the input interference control information includes information (bits) indicating the first interference control method.

  When the interference control information includes information (bits) indicating the first interference control method, interference control is performed using the first interference control method. That is, the used band determining unit 214 acquires cell center band information included in the interference control information. Next, as shown in FIG. 3, the use band determining unit 214 converts the cell center band indicated by the cell center band information into usable bands (available for small cells) of the radio terminal 300 d connected to the small output base station 200. Band).

  The scheduling unit 216 allocates a resource block as a radio resource to the radio terminal based on the terminal measurement information and the channel state from the radio communication unit 204 and the frequency band determined by the use band determination unit 214. Specifically, when the cell center band is determined as the small cell usable band by the use band determining unit 214, the scheduling unit 216 uses the small cell use for the radio terminal in the small cell PC1. Allocate resource blocks of possible bandwidth.

  On the other hand, when the interference control information does not include information (bits) indicating the first interference control method, interference control is performed using the second interference control method. That is, the used band determining unit 214 acquires large cell strong interference band information included in the interference control information. Next, the used band determining unit 214 determines a frequency band other than the large cell strong interference band as the usable band (small cell usable band) of the radio terminal 300d connected to the small output base station 200. Here, the frequency band other than the large cell strong interference band means the large cell weak interference band, and as shown in FIG. 4, the small cell usable band coincides with the large cell weak interference band. .

  The scheduling unit 216 allocates a resource block as a radio resource to the radio terminal based on the terminal measurement information and the channel state from the radio communication unit 204 and the frequency band determined by the use band determination unit 214. Specifically, when the frequency band other than the large cell strong interference band is determined as the small cell usable band by the use band determining unit 214, the scheduling unit 216 determines that the radio terminal 300d in the small cell PC1 On the other hand, resource blocks in frequency bands other than the large cell strong interference band are allocated. When the use band determining unit 214 determines that the system band is the small cell usable band, the scheduling unit 216 allocates a resource block of the system band to the radio terminal 300d in the small cell PC1. .

(2) Operation of Radio Communication System Next, the operation of the radio communication system 1 will be described. FIG. 5 is a flowchart showing an operation example of selecting an interference control scheme in the high-power base station 100 according to the embodiment of the present invention.

  In step S11, the high power base station 100 detects the area of the small cell PC1. In step S12, the high power base station 100 determines whether or not the area of the small cell PC1 is equal to or greater than a threshold value. When the area of the small cell PC1 is equal to or larger than the threshold value, the high power base station 100 selects the first interference control method in Step S13. On the other hand, when the area of the small cell PC1 is less than the threshold value, the high-power base station 100 selects the second interference control method in Step S14.

  FIG. 6 is a flowchart illustrating an operation example in the case of the first interference control method in the high-power base station 100.

  In step S101, the high-power base station 100 is configured by the small-power base station 200, which is an interference source, based on the small-power received power included in the terminal measurement information from the wireless terminals 300a, 300b, and 300c. It is determined whether or not PC1 is detected.

  When the small cell PC1 that is an interference source is not detected, in step S102, the high-power base station 100 determines the system band as a frequency band (large cell band) that can be used in the entire area of the large cell MC1. . On the other hand, when the small cell PC1 that is the interference source is detected, in step S103, the high-power base station 100 determines that the cell edge band used in the cell edge area MC1OUT and the cell center band used in the cell center area MC1IN. The cell edge band and the cell center band are determined differently.

  In step S104, the high-power base station 100 receives interference control information including information indicating the first interference control scheme and information indicating the determined cell center band (cell center band information) as a small output base station. Transmit to station 200.

  After the system band is determined as the large cell band in step S102, or in step S103, the cell edge band used in the cell edge area MC1OUT and the cell center band used in the cell center area MC1IN are different. After the determination, in step S105, the high-power base station 100 performs a scheduling process for allocating resource blocks to the radio terminals 300a, 300b, and 300c.

  FIG. 7 is a flowchart illustrating an operation example in the case of canceling the first interference control method in the high-power base station 100. The operation in the flowchart shown in FIG. 7 is performed when the operation in step S103 of the flowchart shown in FIG. 6 is performed.

  In step S201, the high-power base station 100 determines whether or not the connection between the low-power base station 200 and the wireless terminal 300d is released. When the connection is released, in step S202, the high power base station 100 determines the system band as the large cell band.

  FIG. 8 is a flowchart showing an operation example in the case of the second interference control method in the high-power base station 100.

  In step S301, the high-power base station 100 determines whether or not a strong-interference large cell terminal has been identified from the wireless terminals 300a, 300b, and 300c connected to the high-power base station 100.

  When the strong interference large cell terminal is not specified, the high power base station 100 determines the system band as the large cell band in step S302.

  On the other hand, when the strong interference large cell terminal is identified, in step S303, the high output base station 100 determines that the frequency band used by the strong interference large cell terminal (wireless terminal 300a in FIG. 1) and the weak interference large cell terminal are the same. The frequency band used by the wireless terminals 300b and 300c in FIG. 1 is determined differently.

  In step S304, the high power base station 100 performs interference control including information indicating the second interference control method and information indicating the determined large cell strong interference band (large cell strong interference band information). Information is transmitted to the low-power base station 200.

  When the system band is determined as the large cell band in step S302, in step S305, the high power base station 100 allocates system band resource blocks to the connected wireless terminals 300a, 300b, and 300c. . On the other hand, when the frequency band used by the radio terminal 300a that is a strong interference large cell terminal and the frequency band used by the radio terminals 300b and 300c that are weak interference large cell terminals are determined in step S303. In step S305, the high-power base station 100 allocates a resource block of a large cell strong interference band to the radio terminal 300a that is a strong interference large cell terminal, and the radio terminal 300b that is a weak interference large cell terminal. For 300c, a resource block in the large cell weak interference band is allocated.

  FIG. 9 is a flowchart showing an operation example in the low-power base station 200.

  In step S <b> 401, the small output base station 200 receives the interference control information from the large output base station 100. In step S402, the small power base station 200 determines whether or not the interference control information includes information (bits) indicating the first interference control method.

  When the interference control information includes information (bits) indicating the first interference control method, in step S403, the low-power base station 200 acquires cell center band information in the interference control information.

  In step S404, the small output base station 200 determines that the cell center band is a frequency band (small cell usable band) used in the small cell PC1. Thereafter, in step S407, the small output base station 200 performs a scheduling process for allocating resource blocks in the small cell usable band to the radio terminal 300d.

  On the other hand, when the interference control information does not include information (bits) indicating that the first interference control method is used, in step S405, the small power base station 200 performs the large cell strong interference included in the interference control information. Obtain bandwidth information.

  In step S406, the small power base station 200 determines, for example, a frequency band other than the large cell strong interference band as the small cell usable band. Thereafter, in step S407, the small output base station 200 performs a scheduling process for allocating resource blocks in the small cell usable band to the radio terminal 300d.

(3) Operation / Effect In the wireless communication system 1 according to the present embodiment, the high-power base station 100 selects one of the first interference control method and the second interference control method. Specifically, when the area of the small cell PC1 is equal to or larger than the threshold value, the high-power base station 100 causes the radio terminal 300d to interfere with uplink communication between the high-power base station 100 and the radio terminal 300a. The first interference control method is selected on the assumption that it becomes larger. On the other hand, when the area of the small cell PC1 is less than the threshold value, the high-power base station 100 regards that the interference that the wireless terminal 300 gives to the uplink communication between the small-power base station 200 and the wireless terminal 300d increases. Then, the second interference control method is selected. Further, the high-power base station 100 notifies the low-power base station 200 of the selected interference control method. On the other hand, the low-power base station 200 performs communication control using the notified interference control method. Therefore, it is possible to suppress interference with an appropriate interference control method according to the environment.

  In the present embodiment, the low-power base station 200 uses the frequency band indicated by the cell center band information in the interference control information from the high-power base station 100 for the radio terminal 300d in the first interference control method. Let On the other hand, in the second interference control method, the small output base station 200 transmits all frequency bands including the frequency band indicated by the large cell strong interference band information in the interference control information from the large output base station 100 to the wireless terminal. 300d is determined as an available frequency band. In this case, the low-power base station 200 determines a frequency band that can be used by the radio terminal 300d in consideration of the large-cell strong interference band information. Therefore, the second interference control method has a higher degree of freedom regarding frequency selection than the first interference control method.

  Further, the high power base station 100 increases the threshold used for comparison with the area of the small cell PC1 as the distance between the high power base station 100 and the small power base station 200 is longer. As a result, the shorter the distance between the high-power base station 100 and the small-power base station 200, in other words, the higher the possibility that interference will occur, the higher the power of the first base station 100, the higher the first interference. The possibility of selecting a control method is increased, and appropriate interference suppression is possible.

  In the case of the first interference control method, communication between the high-power base station 100 and the radio terminal 300a that exists in the cell edge region MC1OUT and is connected to the high-power base station 100 Interference is prevented by communication with the wireless terminal 300d connected to the small output base station 200. Moreover, as a result of the fact that part of the total frequency band that can be used in the wireless communication system becomes a frequency band dedicated to small cells as in the conventional case, the frequency band that can be used by the high-power base station does not become small, and the large output The base station 100 can use all frequency bands usable in the radio communication system 1 by using the cell center band for the cell center area MC1IN and using the cell edge band for the cell edge area MC1OUT. For this reason, deterioration of the throughput of the radio terminal 300a connected to the high-power base station 100 is prevented.

  Further, in the case of the second interference control method, the low-power base station 200 is a radio connected to the small-power base station 200 when it is appropriate to perform control in consideration of interference given to the small cell PC1 by the radio terminal 300a. The frequency band that can be used by the terminal 300d is determined to be a frequency band other than the large cell strong interference band, and scheduling is performed. Therefore, the low-power base station 200 can perform control for suppressing interference.

(4) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above-described embodiment, in the case of the first interference control scheme, the interference small cell detection unit 112 in the control unit 102 of the high output base station 100 is based on the small output power in the terminal measurement information from the radio terminal 300a. It was determined whether or not the small cell PC1 formed by the small output base station 200 is an interference source in the large cell uplink channel.

  However, as described below, it may be determined whether or not the small cell PC1 is an interference source in the large cell uplink channel. That is, the small interference cell detection unit 112 inputs information (interference source information) of the small output base station 200 installed in the MC 1 from the core network 500 received by the wired communication unit 106. The interference source information is transmitted from the small output base station 200 or another communication device (not shown). The interference source information includes information indicating that the small output base station 200 is installed in the MC 1 and the small output base station 200. The identification information of the output base station 200 is included. Further, the interference small cell detection unit 112 determines that the small cell PC1 formed by the small output base station 200 specified by the identification information included in the interference source information is an interference source in the large cell uplink channel.

  Further, in the above-described embodiment, in the case of the second interference control method, the small-power base station 200 has a large cell strength when it is appropriate to perform control in consideration of interference given to the small cell PC1 by the radio terminal 300a. A frequency band other than the interference band is determined as a frequency band that can be used by the radio terminal 300d connected to the small output base station 200. However, the frequency band that can be used by the wireless terminal 300d connected to the small output base station 200 may be determined by other methods.

  Specifically, when it is appropriate to perform control in consideration of interference, the use band determining unit 214 determines whether the wireless terminal 300d connected to the small output base station 200 exists in the inner region in the small cell PC1, or Determine if it exists in the outer area. Here, the use band determining unit 214 calculates a propagation loss that is a difference between a transmission power density of the wireless terminal 300d that is assumed in advance and a reception power density of the wireless signal from the wireless terminal 300d in the low-output base station 200. To do. Next, when the calculated propagation loss is less than the fifth predetermined value, the use band determining unit 214 determines that the wireless terminal 300d exists in the inner region in the small cell PC1, and the calculated propagation loss is the first. When the value is equal to or greater than a predetermined value of 1, it is determined that the wireless terminal 300d exists in the outer area in the small cell PC1.

  Furthermore, when the radio terminal 300d exists in the inner area in the small cell PC1, the use band determining unit 214 determines the large cell strong interference band as a frequency band that can be used by the radio terminal 300d. On the other hand, when the radio terminal 300d exists in the inner area in the small cell PC1, the use band determining unit 214 determines the large cell strong interference band as a frequency band that the radio terminal 300d cannot use.

  When the radio terminal 300d exists in the inner area in the small cell PC1, the interference given by the radio terminal 300a to the small output base station 200 and the radio terminal 300d is between the small output base station 200 and the radio terminal 300d. The impact on the communication is considered to be small. For this reason, as described above, when the wireless terminal 300d exists in the inner region in the small cell PC1, the large cell strong interference band is determined as a frequency band that can be used by the wireless terminal 300d. Efficient use is possible.

  Further, when the large cell strong interference band is determined as a frequency band that can be used by the radio terminal 300d existing in the inner area of the small cell PC1, the use band determining unit 214 further determines the transmission power density of the radio terminal 300d. You may make it perform control to raise. In this case, the use band determining unit 214 transmits instruction information indicating an instruction to increase the transmission power density to the wireless terminal 300d via the wireless communication unit 204 and the antennas 205a and 205b.

  Alternatively, when the large cell strong interference band is determined as a frequency band that can be used by the wireless terminal 300d existing in the inner area of the small cell PC1, and the transmission power of the wireless terminal 300d reaches the maximum value. In other words, the use band determining unit 214 performs control to cause the radio terminal 300d to use radio resources in the large cell strong interference band. In this case, the use band determining unit 214 receives the transmission power of the wireless terminal 300d via the antennas 205a and 205b and the wireless communication unit 204, and determines whether or not the transmission power of the wireless terminal 300d is less than the maximum value. To do. Next, when the transmission power of the wireless terminal 300d is equal to or less than the maximum value, the used band determining unit 214 determines a radio resource in the large cell strong interference band as an allocation target of the wireless terminal 300d. Furthermore, the use band determining unit 214 transmits the determined radio resource information to the radio terminal 300d via the radio communication unit 204 and the antennas 205a and 205b.

  Further, in the second interference control method, when the use band determining unit 214 enables the large cell strong interference band, the wireless terminal 300d performs communication using the large cell strong interference band. The transmission power density may be made larger than the reference value.

  Further, in the above-described embodiment, the case where one small-power base station 200 is installed in the large cell MC1 has been described. However, when one small-power base station 200 is installed in the large cell MC1, Similarly, the present invention can be applied.

  Specifically, when there are a plurality of small output base stations 200, the selection unit 111 in the control unit 102 of the large output base station 100 performs the first interference control method and the second interference for each small output base station 200. Select one of the interference control methods. The scheduling unit 116 selects a frequency to be used for the wireless terminals 300a, 300b, and 300c. Here, the scheduling unit 116 selects a frequency to be used for the radio terminals 300a, 300b, and 300c at predetermined time intervals according to the channel state at that time.

  In this case, the frequency used for the radio terminals 300a, 300b, and 300c is a radio terminal that exists in the outer area MC1OUT of the large cell MC1 for the small-power base station 200 to which the first interference control method is applied. Means a frequency that may be used, and may cause strong interference to communication between the low-power base station 200 and the radio terminal 300d for the low-power base station 200 to which the second interference control method is applied. Means a certain frequency.

  For the small-power base station 200 to which the first interference control method is applied, the use band determination unit 114 exists in the outer region MC1OUT of the large cell MC1 among the frequencies used by the radio terminals 300a, 300b, and 300c. Information on the frequency used by the wireless terminal is included in the interference control information and transmitted. The use band determination unit 214 in the control unit 202 of the small output base station 200 determines a frequency other than the frequency used by the radio terminal existing in the outer area MC1OUT of the large cell MC1 as the frequency used by the radio terminal 200d.

  On the other hand, for the small-power base station 200 to which the second interference control method is applied, the use band determining unit 114 has the small-power base station 200 and the wireless terminal out of the frequencies used by the wireless terminals 300a, 300b, and 300c. Information on a frequency that gives strong interference to communication with 300d is transmitted as interference control information. The use band determination unit 214 in the control unit 202 of the low-power base station 200, when the control considering interference is appropriate, other than the frequency that gives strong interference to the communication between the low-power base station 200 and the radio terminal 300d Is determined as the frequency used by the wireless terminal 200d.

  In the above-described embodiment, a case has been described in which the high power base station 100 is a macro cell base station that forms a macro cell, and the small power base station 200 is a pico cell base station that forms a pico cell. The station 100 and the low-power base station 200 are not limited to these. For example, when the high-power base station 100 is a macro cell base station that forms a macro cell, the small-power base station 200 can be a base station that forms a micro cell or a femto cell. When the high-power base station 100 is a microcell base station that forms a microcell, the small-power base station 200 can be a base station that forms a picocell or a femto. Furthermore, when the high-power base station 100 is a picocell base station that forms a picocell, the small-power base station 200 can be a base station that forms a femto. Furthermore, the present invention can be applied to any wireless communication system including at least two wireless base stations.

  In the above-described embodiment, the wireless communication system 10 has a configuration based on LTE Release 9 or LTE-Advanced, but may have a configuration based on other communication standards.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  INDUSTRIAL APPLICABILITY The radio communication system, radio base station, and communication control method of the present invention can appropriately reduce interference and are useful as a radio communication system or the like.

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 100 ... High output base station, 102 ... Control part, 104 ... Wireless communication part, 105a, 105b ... Antenna part, 106 ... Wired communication part, 111 ... Selection part, 112 ... Interference small cell detection part, DESCRIPTION OF SYMBOLS 113 ... Identification part, 114 ... Use band determination part, 116 ... Scheduling part, 200 ... Small output base station, 202 ... Control part, 204 ... Wireless communication part, 205a, 205b ... Antenna part, 214 ... Use band determination part, 216 ... Scheduling unit, 300a, 300b, 300c, 300d ... Wireless terminal

Claims (10)

A wireless communication system comprising a first wireless base station and a second wireless base station,
The first radio base station is
First and second for controlling interference in communication between the first radio base station and the first radio terminal and communication between the second radio base station and the second radio terminal A selection unit for selecting one of the two interference control methods;
A notification unit for notifying the second radio base station of interference control information including information indicating the interference control method selected by the selection unit and information on a frequency band to be subjected to interference control;
With
The second radio base station is
A radio | wireless communications system provided with the control part which controls communication with a said 2nd radio | wireless terminal based on the said interference control information from a said 1st radio base station.   In the first interference control method, the control unit is connected to the second radio terminal so as to suppress interference in the frequency band indicated by the interference control information from the first radio base station. In the second interference control method, in consideration of the frequency band indicated by the interference control information from the first radio base station, communication with the second radio terminal is performed. The wireless communication system according to claim 1, which controls communication.   3. The radio communication system according to claim 2, wherein the selection unit is more likely to select the first interference control method as the second radio base station is closer to the first radio base station.   The said selection part selects either the said 1st and 2nd interference control system for every said 2nd radio base station, when there are two or more said 2nd radio base stations. The radio | wireless communications system in any one. A first cell is formed by the first radio base station, and a second cell smaller than the first cell is formed by the second radio base station;
5. The radio communication system according to claim 1, wherein the selection unit selects one of the first and second interference control schemes according to a size of the second cell.   The selection unit depends on the maximum transmission power of the second radio base station and the number of the second radio base stations present in the first cell formed by the first radio base station. 6. The wireless communication system according to claim 1, wherein one of the first and second interference control methods is selected. The first interference control method is an interference provided by communication between the second radio base station and the second radio terminal with respect to a frequency band used in an outer region in the first cell. It is an interference control method that suppresses the amount,
In the second interference control method, the amount of interference given to communication between the second radio base station and the second radio terminal among the first radio terminals is considered to be a predetermined value or more. The radio communication system according to claim 5 or 6, wherein the second radio base station considers a frequency band used by the first radio terminal and uses it. A radio base station that constitutes a radio communication system with other radio base stations,
A selection unit that selects one of the first and second interference control methods for controlling interference between the communication with the wireless terminal and the communication between the other wireless base station and the other wireless terminal. When,
A notification unit for notifying the other radio base station of interference control information including information indicating the interference control method selected by the selection unit and information on a frequency band to be subjected to interference control;
A wireless base station comprising: A radio base station that constitutes a radio communication system with other radio base stations,
A first and a second for controlling interference between the other radio base station and the communication between the own radio base station and the radio terminal and between the other radio base station and the other radio terminal. A radio comprising a control unit for controlling communication with the radio terminal based on interference control information including information indicating any one of the second interference control methods and information on a frequency band to be subjected to interference control base station. A communication control method in a radio communication system including a first radio base station and a second radio base station,
The first radio base station interferes with communication between the first radio base station and the first radio terminal and communication between the second radio base station and the second radio terminal. Selecting one of the first and second interference control schemes for controlling
The first radio base station notifying the second radio base station of interference control information including information indicating the selected interference control method and information on a frequency band to be subjected to interference control;
The second radio base station controlling communication with the second radio terminal based on the interference control information from the first radio base station;
A communication control method comprising:

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