JP2015012333A - Base station device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform resource allocation corresponding to the amount of interference by sharing a change in inter-cell interference caused by power transmission control among base stations.SOLUTION: A base station device that communicates with one or more mobile stations by use of at least part of multiple sub-frames included in one communication frame acquires information on transmission power of the base station device and information on transmission power of at least one other base station device at each of the multiple sub-frames, and allocates resources for communication of the one or more mobile stations on the basis of the information on transmission power of the base station device and the information on transmission power of the at least one other base station device at each of the multiple sub-frames.

Description

  The present invention relates to an interference control technique in a wireless communication system.

  In mobile communication systems, “LTE (Long Term Evolution)”, which is one of the standards of 3GPP (Third Generation Partnership Project), has begun to spread (Non-patent Document 1). In recent years, in 3GPP, studies on LTE-Advanced, which has further enhanced LTE, are being conducted. Among them, aiming for rapid area development at low cost, as shown in Fig. 1, in addition to macro base stations, network configurations that use small and inexpensive small cell base stations such as pico base stations and femto base stations together Considered. In 3GPP, as an interference control technique when a macro base station and a small cell base station use the same frequency band in a network configuration as shown in FIG. 1, time division multiplexing (in which interference control is performed in units of subframes (SF)) ( TDM) type interference control has been studied (Non-Patent Document 2).

  FIG. 2 shows an overview of TDM interference control that has been conventionally studied. Each base station allocates resources to mobile stations in a cell that it develops in subframe units, and transmits signals using the allocated resources. Here, the macro base station has a larger transmission power than the small cell base station. For this reason, the signal transmitted from the macro base station can be a strong interference source for the mobile station communicating with the small cell base station. For this reason, when performing TDM type interference control, the macro base station restricts radio resource allocation (does not perform signal transmission) in order to reduce interference given to a mobile station in a small cell in a predetermined SF. Alternatively, control (interference control) such as restriction of signal transmission power is performed. FIG. 2 illustrates a state in which the macro base station suppresses signal transmission power in a subframe of SF set 1.

  The macro base station, for example, based on information obtained from a surrounding base station or a mobile station connected to its own station, an SF that does not perform interference control (SF set 0 in FIG. 2) and an SF that performs interference control (FIG. 2). And SF set 1) are set. Information obtained from surrounding base stations at this time is shown in FIG. This information includes, for example, each SF in the SF set 0 and SF set 1 in a predetermined number of SFs such as “ABS Pattern info” transmitted using the X2 line connecting the base stations. Information indicating to which one belongs is described (Non-Patent Document 3). Then, the macro base station does not allocate radio resources or restricts transmission power in the SF belonging to SF set 1. For example, according to FIG. 3, the macro base station performs interference control in the SF whose SF number is 1 or 4-6. The macro base station limits the transmission power or does not transmit a signal, thereby reducing the amount of interference with the mobile station in the small cell.

  Each base station executes at least one of acquiring information on the SF set pattern from the neighboring base station and transmitting the SF set pattern of the own station to the neighboring base station. Each base station allocates radio resources to mobile stations connected to the base station according to the SF set pattern. Note that the pattern of the SF set of the own station is generated based on the pattern of the SF set of the neighboring base station received from the neighboring base station, for example. Each base station, for example, assigns an SF for which interference control is performed in a macro cell to a mobile station located at a location distant from the mobile station among mobile stations connected to the mobile station. Is assigned an SF for which interference control is not performed in the macro cell. This makes it possible to allocate radio resources in consideration of interference that the mobile station receives from the neighboring base stations.

  When different frequency bands are used in the macro base station and the small cell base station, the macro base station does not interfere with the mobile station in the small cell. Therefore, only signals from other small cell base stations interfere with the mobile station in the small cell. In this case, there may be a plurality of small cell base stations that interfere with mobile stations in the small cell. Therefore, in this case, when performing TDM type interference control, the small cell base station controls radio resources based on different SF set patterns in cooperation with a plurality of small cell base stations existing in the vicinity. It will be. In this case, since a plurality of small cell base stations are the main interference sources, each small cell base station not only controls whether to allocate radio resources, but also controls transmission power in each SF. By doing so, the amount of interference can be adjusted, and finer interference control becomes possible. For this reason, a method of controlling transmission power in each small cell base station is being studied (Non-Patent Document 4).

3GPP TS 36.201, “Evolved Universal Terrestrial Radio Access (E-UTRA); LTE physical layer; General description”, V11.1.0, December 2012 Satoshi Konishi et al., “Performance Evaluation of Downlink in Pet Station Mixed HetNet Applying TDM Type Interference Control Technique”, IEICE General Conference, B-5-73, March 2011 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”, V11.1.0, December 2012. NTT DOCOMO INC. "Scenario and Candidate Technologies for Small Cell Enhancement", R1-130402, January 28-February 1, 2013.

  However, conventionally, it is assumed that the same frequency band is used in the macro base station and the small cell base station, and information on the SF set shared between the base stations is based on whether or not radio resources are allocated. It was targeted. For this reason, there has been a problem that fine changes in inter-cell interference caused by transmission power control cannot be shared between base stations, and resource allocation according to the amount of interference cannot be performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to share changes in inter-cell interference caused by transmission power control between base stations and perform resource allocation according to the amount of interference. To do.

  To achieve the above object, a base station apparatus according to the present invention communicates with one or more mobile stations using at least a part of a plurality of subframes included in one communication frame. The acquisition means for acquiring the transmission power information of the base station apparatus and the transmission power information of at least one other base station apparatus in each of the plurality of subframes, and the plurality of subframes Allocating resources for communication of the one or more mobile stations based on the transmission power information of the base station device and the transmission power information of at least one other base station device And assigning means.

  According to the present invention, it is possible to share a change in inter-cell interference caused by transmission power control between base stations and perform resource allocation according to the amount of interference.

The figure which shows the structural example of the radio | wireless communications system containing a macrocell and a small cell. The figure which shows the example of the state of the communication control of each base station in the case of performing TDM type | mold interference control between a macrocell and a small cell. The figure which shows schematically the information of the pattern of SF set transmitted / received between base stations in the case of performing the conventional TDM type | mold interference control. The block diagram which shows the structural example of a base station apparatus. The 1st example of the pattern information of SF set exchanged between base station apparatuses. The figure which shows a response | compatibility with SF set identifier and transmission power. The 2nd example of the pattern information of SF set exchanged between base station apparatuses.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  In the following, it is assumed downlink communication in which a mobile station apparatus receives a signal transmitted from a base station apparatus by radio. Here, for the sake of simplicity, the case where one mobile station apparatus receives a signal transmitted from one base station apparatus will be described. However, the present invention relates to two or more mobile station apparatuses that receive this signal. Can be applied even in the presence of, and its generality is not lost.

  FIG. 4 shows a configuration example of the base station apparatus 100. For example, as illustrated in FIG. 4, the base station apparatus 100 includes a transmission power information acquisition unit 101, a transmission power information transmission unit 102, a resource allocation unit 103, a communication unit 104, and a quality information acquisition unit 105. FIG. 4 shows a functional unit that executes the processing according to the present embodiment, and the base station device 100 separately includes functions included in a normal base station device.

  The transmission power information acquisition unit 101 stores information for specifying transmission power of at least one other base station apparatus, for example, a base station apparatus of an adjacent cell, in each of a plurality of subframes (SF) included in one communication frame. get. Note that information specifying transmission power is acquired from base station apparatuses of all adjacent cells, for example. Also, the information specifying the transmission power may be acquired from a base station apparatus that can be interfered by a mobile station connected to the base station apparatus 100, for example, other than the base station apparatus in the adjacent cell. Also, the transmission power information acquisition unit 101 may acquire this information by receiving it directly from at least one other base station apparatus, for example, via the X2 interface, You may acquire from an apparatus.

  Here, the information for specifying the transmission power is, for example, information for specifying the magnitude of the transmission power used when transmitting a signal to the mobile station in each base station apparatus. Also, the transmission power information acquisition unit 101 acquires information for specifying the transmission power in each of a plurality of subframes of the base station device 100 itself, for example, from a memory (not shown). Thereby, the base station apparatus 100 can grasp the relationship between the transmission power of the own station and the acquired transmission power of at least one other base station apparatus.

  The transmission power information transmission unit 102 notifies information specifying the transmission power of the base station apparatus 100 itself in each of the plurality of subframes to at least one other base station apparatus such as a base station apparatus of an adjacent cell. This information may also be notified directly to other base station devices via the X2 interface, or by notifying other devices that manage this information and accessing the devices by other base station devices. The other base station apparatus may be notified.

  Here, an example of information specifying transmission power is shown in FIG. In the example of FIG. 5, the information specifying transmission power includes a value (SF set identifier) specifying transmission power for each of a plurality of subframes. Here, one SF set identifier corresponds to one transmission power as shown in FIG. In the example of FIG. 6, when the SF set identifier is 0, the transmission power is 5 dBm, when the SF set identifier is 1, the transmission power is 10 dBm, when the SF set identifier is 2, the transmission power is 15 dBm, and the SF set identifier. When 3 is 3, the transmission power is 20 dBm. Based on this, for example, when the base station apparatus 100 acquires the information of FIG. 5 as transmission power information of another base station apparatus, the other base station apparatus transmits a signal at 5 dBm in the subframe of subframe number 0. It can be specified to transmit. Note that the information specifying the transmission power acquired by the base station apparatus 100 may be only the SF set identifier portion in FIG. 5 and may not be acquired for the subframe number portion. That is, it may be determined in advance in which position of the acquired information the SF set identifier information corresponding to which subframe number is included, and the subframe number is specified in the acquired information. There is no need for a bit field to be prepared.

  Here, for example, if it is determined that the SF set identifier is expressed by 4 bits, the base station apparatus can specify the SF set identifier for each SF by reading the acquired information every 4 bits. it can. On the other hand, for example, when the SF set identifier has only four values, each SF set identifier can be originally expressed by 2 bits. For this reason, in this method, the amount of information signaled may be larger than the originally required amount.

  On the other hand, the minimum number of bits for expressing each SF set identifier can be specified by notifying the number of value patterns that the SF set identifier can take. For this reason, the information specifying the transmission power may include the number of value patterns that can be taken by the SF set identifier. For example, in the example of FIG. 5, the SF set identifier can take four values from 0 to 3. For this reason, the information specifying transmission power may include, for example, “4”, which is the number of patterns that the SF set identifier can take. Thereby, the base station apparatus can specify the number of bits used to express each SF set identifier, and as a result, the amount of information signaled can be reduced. In addition, instead of information on the number of SF set identifier patterns, information on the number of bits used to express one SF set identifier may be included in the information specifying the transmission power.

  Further, as shown in FIG. 7, the information for specifying the transmission power may be information indicating in which subframe the transmission power becomes the transmission power specified by the value for each value for specifying the transmission power. Good. The SF sets 0 to 3 in FIG. 7 correspond to the SF set identifiers 0 to 3 of the transmission power in FIG. 6, for example. The information in FIG. 7 indicates in which subframe the transmission power specified by each SF set is used. That is, for example, in FIG. 7, the transmission power specified by SF set 0 (5 dBm in the example of FIG. 6) is used in subframes with subframe numbers 0 and 39. Similarly, the transmission power specified by SF set 1 (10 dBm in the example of FIG. 6) is used in subframes of subframe numbers 1, 2, 5, and 6. For the transmission power specified by SF sets 2 and 3 (15 dBm and 20 dBm in the example of FIG. 6), the subframe to be used is similarly specified. As a result, the information in FIG. 7 represents the same information as the information in FIG.

  In FIG. 7, information on the number of SF set patterns (“number of SF sets” in FIG. 7) is given, but this may not be necessary. In this case, for example, bit fields corresponding to the SF set 15 may be prepared, and all bits may be set to 0 for an SF set that is not used. On the other hand, by providing information on the number of SF set patterns, it is not necessary to exchange information on unused SF sets between base station apparatuses. As a result, the amount of signaling can be reduced.

  Note that the transmission power specified by the SF set identifier as shown in FIG. 6 may be variable. That is, for example, the SF set identifier “1” may correspond to a transmission power of 10 dBm, for example, as shown in FIG. 6 in a certain frame, and may correspond to, for example, 8 dBm in another frame. In this case, the transmission power information acquisition unit 101 may acquire transmission power information specified by the SF set identifier in addition to the information shown in FIG. 5 or FIG. At this time, a plurality of correspondence tables between SF set identifiers and transmission power may be defined in the system, and the plurality of correspondence tables may be stored in each base station apparatus. In this case, for example, the transmission power information acquisition unit 101 acquires an identifier for specifying the correspondence table, and selects a correspondence table corresponding to the identifier from a plurality of correspondence tables stored in a memory (not illustrated). Thus, the transmission power information specified by the SF set identifier is specified. Thereby, it becomes possible to reduce the amount of signaling compared with the case where all the information of a correspondence table is signaled.

  Note that the correspondence between the SF set identifier and the transmission power may be determined for each base station. Further, the number of SF set identifiers may be variable. That is, according to the situation, the number of SF set identifiers may be increased when finer transmission power control is required, and the number of SF set identifiers may be decreased when coarse transmission power control is sufficient.

  For example, the resource allocation unit 103 is connected to the base station apparatus 100 based on information identifying transmission power of other base station apparatuses and information identifying transmission power of the base station apparatus 100 itself. Allocating radio resources for communication of mobile stations. For example, if there is a subframe in which the transmission power of another adjacent base station apparatus is sufficiently low and the transmission power of the base station apparatus 100 is sufficiently high, the subframe is allocated to the mobile station. Thereby, for example, it is possible to allocate a subframe considered to have the best radio quality for mobile station communication.

  The communication unit 104 transmits data to one or more mobile stations according to the radio resource allocated by the resource allocation unit 103. Also, data is received from one or more mobile stations. Note that the received data may include radio quality information measured by at least one subframe by one or more mobile stations. In this case, the wireless quality information is input to the quality information acquisition unit 105. The quality information acquisition unit 105 extracts radio quality information measured by one or more mobile stations from the input data and inputs it to the resource allocation unit 103. In addition, when the resource allocation unit 103 does not use the wireless quality information, the quality information acquisition unit 105 may be omitted.

  The resource allocating unit 103, based on the information on the radio quality measured in at least one subframe by one or more mobile stations acquired by the quality information acquiring unit 105, in addition to the information specifying the transmission power The radio resource can be assigned to. Specifically, the resource allocation unit 103 can specify the transmission power of the base station device 100 itself and the transmission power used by other base station devices in, for example, adjacent cells, in a certain subframe. For example, it is assumed that the transmission powers of the base station device 100 itself and other adjacent base station devices are both 10 dBm. In order to simplify the description, it is assumed that there is one other base station apparatus to be considered. At this time, it is assumed that the quality information acquisition unit 105 receives and acquires information (for example, SINR: Signal to Interference and Noise Ratio) regarding the amount of interference measured in one or more mobile stations. For example, assume that the SINR notified by one of the mobile stations is 3 dB. In this case, the resource allocating unit 103, for example, in a subframe in which the transmission power of the base station device 100 is 15 dBm and the transmission power of the other base station device is 10 dBm, the radio quality of the signal that the mobile station will receive ( SINR) can be estimated to be about 8 dB. This is because the desired signal power increases by 5 dB while the interference power does not change.

  Similarly, the resource allocation unit 103 can estimate the radio quality of a signal that will be received by the mobile station in another subframe. Also, for other mobile stations, the radio quality of signals that the mobile station will receive in all subframes is determined from the radio quality information in a subframe notified from the other mobile stations. Can be estimated. In addition, in order to estimate the radio quality, information on the measurement results of the radio quality a plurality of times may be acquired from one mobile station.

  The resource allocation unit 103 determines resource allocation to each mobile station according to the estimated radio quality. For example, in each subframe, it is determined to transmit data in the subframe to at least one of the mobile stations with the highest radio quality or the mobile station having the radio quality equal to or higher than a predetermined value. For example, regarding a mobile station in which data to be transmitted exists, data is transmitted to the mobile station in a subframe where the radio quality at the mobile station is the best.

  In addition, when the resource allocation unit 103 can estimate the received power in the mobile station of the signal from each of the plurality of base station devices from the information on the radio quality measured by the mobile station acquired by the quality information acquisition unit 105, Resources may be allocated based on the estimated value.

  For example, when the mobile station can detect from which base station apparatus and at what power the interference signal is received, the quality information acquisition unit 105 acquires the information, so that other base stations in each subframe The amount of interference from each of the devices can be estimated. For example, if the interference power when another base station apparatus transmits a signal at 10 dBm in a certain subframe is known, the amount of interference in the subframe in which the other base station apparatus transmits a signal at 15 dBm is It can be estimated that it will increase by 5 dB. In this way, the amount of interference can be specified. Similarly, when the received power of the signal from the base station apparatus 100 in a certain subframe can be identified, the received power of the signal from the base station apparatus 100 in each subframe is determined based on the result. Can be estimated. Thereby, since the desired signal power and the interference signal power in each subframe can be estimated, it is possible to estimate the radio quality of the signal received by the mobile station in each subframe. In this case, the resource allocation unit 103 can perform resource allocation according to the radio quality for each mobile station, and thus can perform finer interference control.

  The interference amount estimated here is a relative interference amount with respect to a signal transmitted by the base station device 100 as described above, or a relative interference amount with respect to a signal transmitted by another base station device. Also good. That is, for example, when signals from the first other base station apparatus and the second other base station apparatus have the same transmission power, the signal power from the first other base station apparatus is 3 dB larger. It may be information such as received. In this case, the resource allocation unit 103 uses a subframe in which the transmission power of the first base station device is lower than that of the second base station device, and the transmission power of the second base station device is lower than that of the first base station device. It may be assigned with priority over subframes that are as small as the same.

  Further, the quality information acquisition unit 105 can also roughly estimate the amount of interference in the mobile station from each of the other base station devices, for example, from the radio quality measured by the mobile station in a plurality of subframes. For example, when the first other base station apparatus and the second other base station apparatus transmit signals at 10 dBm, the first other base station apparatus is 15 dBm, and the second other base station apparatus Let us consider a case where the radio quality measured by the mobile station does not substantially change when the signal is transmitted at 10 dBm. In this case, it can be estimated that the amount of interference received from the first other base station device is sufficiently lower than the amount of interference received from the second other base station device. If the amount of interference received from the first other base station device is not sufficiently lower than the amount of interference received from the second other base station device, when the transmission power of the first other base station device increases by 5 dB, This is because the overall interference amount changes significantly and the radio quality also changes significantly. In this case, quality information acquisition section 105 notifies resource allocation section 103 that the amount of interference from the first other base station apparatus is sufficiently lower than the amount of interference from the second other base station apparatus. Then, for example, the resource allocation unit 103 does not pay attention to the transmission power of the first other base station device, but uses the transmission power of the second other base station device and the transmission power of the base station device 100 itself. Based on this, resource allocation is determined. In this way, even when the mobile station cannot identify the received power of signals from a plurality of base station devices, the quality information acquisition unit 105 is relatively concerned about the amount of interference from each of the other base station devices. The size can be roughly specified. Since the resource allocation unit 103 can identify an interference source having a sufficiently low amount of interference, it is possible to perform interference control by paying attention only to the transmission power of the interference source that affects radio quality. . Since the amount of interference from each base station apparatus differs for each mobile station, it is possible to perform more detailed interference control by specifying a base station apparatus that is susceptible to interference for each mobile station.

  As described above, in this embodiment, it becomes possible to notify each other's transmission power between base station apparatuses, and appropriate resource allocation is performed in consideration of interference received by mobile stations from other base station apparatuses. It becomes possible. Further, by using the wireless quality measurement result by the mobile station, the base station apparatus can perform more detailed resource allocation, and can perform fine interference control.

  Note that the transmission power pattern for each subframe in each base station apparatus may be changed for each frame or for a predetermined number of frames. Further, this pattern may be changed when a predetermined trigger occurs. For example, when there are many low-quality radio values measured by a plurality of mobile stations, the pattern is changed so as to increase the number of subframes with high transmission power. Similarly, when it is considered that the mobile station is concentrated at the cell edge according to the result of positioning performed by the mobile station, the pattern is changed so as to increase the number of subframes with high transmission power. On the other hand, if the radio quality measured by the mobile station is good, or if the mobile station is considered to be concentrated near the base station, the pattern may be changed to reduce the number of subframes with high transmission power. Good.

  The pattern change timing may be different for each base station apparatus. In this case, the base station apparatus changes the pattern so as to increase the communication opportunities of the mobile stations connected to the own station, for example, according to the amount of interference from other base station apparatuses. Thereby, the base station apparatus can perform interference control with a high degree of freedom. Each time the pattern is changed, the other base station apparatus in the vicinity is notified of the changed pattern. Alternatively, a control device that collectively controls pattern changes may be prepared, and a plurality of base station devices may simultaneously change the pattern in accordance with instructions from the device. Note that this control device may be one of a plurality of base station devices. In this way, by changing the transmission power pattern in a centralized manner, when one base station device increases the transmission power, the amount of interference with mobile stations connected to other base station devices increases, and the other It is possible to prevent control divergence such as the base station apparatus increasing the transmission power.

  The example of the TDM interference control technique according to the present embodiment has been described above, but the present technique is not limited to the above example. For example, the above-described technique can be applied not only to LTE but also to other methods. Further, the present invention can be applied not only to a cellular radio communication system but also to other radio communication systems capable of performing interference control between similar base stations. Further, for convenience, the functional configuration of the base station apparatus 100 is illustrated as in FIG. 4, but each block in FIG. 4 may be combined into two blocks, or one block is divided into two. Also good. Each function may be executed by dedicated hardware, or may be realized as a software program executed by general-purpose hardware such as a CPU. It is also possible to realize part of it with software and the rest with dedicated hardware.

Claims (8)

A base station apparatus that communicates with one or more mobile stations using at least some of a plurality of subframes included in one communication frame,
Obtaining means for obtaining information on transmission power of the base station apparatus and information on transmission power of at least one other base station apparatus in each of the plurality of subframes;
Based on the transmission power information of the base station apparatus and the transmission power information of at least one other base station apparatus in each of the plurality of subframes, for communication of the one or more mobile stations An allocation means for allocating resources;
A base station apparatus comprising: Receiving means for receiving, from the one or more mobile stations, information on the amount of interference measured by the one or more mobile stations in at least one subframe;
The one or more movements in at least one of the plurality of subframes based on transmission power information of the at least one other base station apparatus in each of the plurality of subframes and information on the interference amount Estimating means for estimating the amount of interference received by the station;
Further comprising
The allocating means communicates with the one or more mobile stations based on the interference amount and transmission power information of the base station apparatus in at least one of the plurality of subframes for which the interference amount is estimated. Allocate resources for
The base station apparatus according to claim 1. The information on the transmission power of the at least one other base station apparatus includes a value specifying the transmission power of the at least one other base station apparatus for each of the plurality of subframes.
The base station apparatus according to claim 1 or 2, characterized in that The transmission power information of the at least one other base station apparatus is a transmission in which the transmission power of the at least one other base station apparatus is specified by the value in which subframe for each value specifying the transmission power. Including information indicating whether it will be power,
The base station apparatus according to any one of claims 1 and 2. The transmission power information of the at least one other base station apparatus further includes information on the number of patterns that a value specifying the transmission power can take.
The base station apparatus according to claim 3 or 4, characterized by the above. The acquisition means further acquires information on transmission power specified by the value,
The base station apparatus according to claim 3, wherein the base station apparatus is a base station apparatus. A notification means for notifying the at least one other base station apparatus of transmission power information of the base station apparatus in each of the plurality of subframes;
The base station apparatus according to claim 1, wherein the base station apparatus is a base station apparatus. A control method for a base station apparatus that performs communication with at least a part of a plurality of subframes included in one communication frame with one or more mobile stations,
An acquisition step in which the acquisition unit acquires the transmission power information of the base station apparatus and the transmission power information of at least one other base station apparatus in each of the plurality of subframes;
An allocating unit is configured to transmit the one or more mobile stations based on the transmission power information of the base station apparatus and the transmission power information of at least one other base station apparatus in each of the plurality of subframes. An allocation process for allocating resources for communication;
A control method characterized by comprising:

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