JP6308898B2 - Base station control apparatus, radio communication network, and base station control method - Google Patents

Description

  The present invention relates to a base station control device, a radio communication network, and a base station control method.

  In LTE (Long Term Evolution) in 3GPP (Third Generation Partnership Project), user equipment (UE (user equipment)) feeds back channel quality information (CQI (Channel Quality Indicator)) to the base station (eNodeB). Based on the CQI, scheduling for each user terminal is performed. Furthermore, in LTE Release 11, a user terminal can feed back multiple types of CQI. The plurality of types of CQIs are CQIs obtained by quantizing different SINRs (signal power to noise interference power ratios) due to interference signals of different interference base stations.

  The base station, for the user terminal, combines a plurality of signal power measurement resources (CSI-RS resources) and interference signal power measurement resources (CSI-IM resource (CSI-interference measurement resource)) used for CQI calculation. Can be specified (Non-patent Document 1, Section 7.2, Section 7.2.5, Section 7.2.6). Each user terminal feeds back a plurality of types of CQIs, thereby enabling highly accurate control in cooperation with a plurality of base stations.

  In LTE Advanced, coordinated multi-point transmission (CoMP) between base stations for improving the throughput of downlink data transmission to user terminals is being studied. Various CoMPs have been devised, including DPS (Dynamic Point Selection) and DPB (Dynamic Point Blanking). Hereinafter, the base station may be referred to as a transmission point.

  In DPS, a plurality of transmission points share a downlink data signal destined for one user terminal, one transmission point transmits a data signal at a certain time, and another transmission point at another time. This is a technique for transmitting a data signal, and a transmission point (serving base station) that transmits a downlink data signal is periodically (one subframe (1 ms) cycle) selected from the plurality of transmission points. For example, a transmission point that is predicted to have higher throughput is selected based on a plurality of types of CQIs of the user terminal.

  DPB is a technique for reducing inter-cell interference by stopping (blanking) transmission of neighboring transmission points that are transmission sources of interference signals for data signals from transmission points that transmit data signals.

3GPP TS 36.213 V11.6.0 (2014-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); "Physical layer procedures" (Release 11), March 2014

  When implementing DPS, depending on the transmission point selection result, downlink traffic at the transmission point may or may not occur. When there is no downlink traffic, the transmission point does not interfere with user terminals served from other transmission points.

  However, at present, no method has been devised in DPS to select a serving base station using DPS information regarding other user terminals. That is, no method has been devised to appropriately select the serving base station according to the change in the interference situation accompanying the change in the traffic situation.

  Therefore, the present invention provides a base station control device, a radio communication network, and a base station control method that appropriately select a serving base station in accordance with a change in interference situation accompanying a change in traffic situation.

  A base station control apparatus according to the present invention is a base station control apparatus that controls a plurality of base stations that communicate wirelessly with a user terminal, wherein a serving base station that transmits a data signal to each user terminal is assigned to a channel related to the user terminal. Based on the quality information, a serving base station selection unit that periodically selects from among a plurality of base stations that share a downlink data signal to the user terminal, and other than the serving base station selected for each user terminal A base station transmission stop unit that stops downlink transmission of a non-transmission base station that is another base station, and a plurality of combinations of possible serving base station candidates for each user terminal are determined, and a non-transmission base station in each combination A serving base station candidate combination determining unit that determines the number of channel quality information for the user terminal for each of the combinations, A channel quality information selector for selecting one channel quality information reflecting the non-transmitting base station, and for each user terminal, for each of the combinations, for each user terminal, the serving base station A metric calculation unit that calculates a metric that is a criterion for selection, and the serving base station selection unit is configured to supply each user terminal based on a sum of the metrics for a plurality of user terminals for each of the combinations. A combination of serving base stations to be used for downlink data transmission is selected from the candidate combinations.

  A wireless communication network according to the present invention provides a plurality of base stations that wirelessly communicate with user terminals and a serving base station that transmits a data signal to each user terminal to the user terminals based on channel quality information related to the user terminals. A serving base station selecting unit that periodically selects among a plurality of base stations that share downlink data signals, and a non-transmitting base station that is a base station other than the serving base station selected for each user terminal Base station transmission stopping unit for stopping downlink transmission of the base station, and serving base station candidate combination determining unit for determining a plurality of possible serving base station candidates for each user terminal and determining a non-transmitting base station in each combination For each of the combinations, the non-transmission base station is reflected from among a plurality of channel quality information for each user terminal. A channel quality information selection unit that selects one channel quality information, and a metric that is a criterion for selection of a serving base station for each user terminal based on the selected channel quality information for each of the combinations The serving base station selection unit is used for downlink data transmission to each user terminal based on the sum of the metrics for a plurality of user terminals for each of the combinations. A combination of serving base stations to be selected is selected from the candidate combinations.

  A base station control method according to the present invention is a base station control method for controlling a plurality of base stations that wirelessly communicate with user terminals, wherein a serving base station that transmits a data signal to each user terminal is assigned to a channel related to the user terminal. Based on the quality information, periodically selecting from a plurality of base stations sharing the downlink data signal to the user terminal, and other base stations other than the serving base station selected for each user terminal Stopping downlink transmission of non-transmitting base stations, determining a plurality of possible serving base station candidates for each user terminal, determining non-transmitting base stations in each combination, and the combination For each of these, one channel quality information reflecting the non-transmission base station is selected from a plurality of channel quality information for each user terminal. And, for each of the combinations, calculating a metric that is a criterion for selection of a serving base station for each user terminal based on the selected channel quality information, the serving base station comprising: Selecting a combination of serving base stations to be used for downlink data transmission to each user terminal from the candidate combination based on a sum of the metrics for a plurality of user terminals for each of the combinations Comprising selecting.

  In the present invention, for each combination of serving base station candidates for transmitting data signals to user terminals, one channel quality reflecting a non-transmitting base station from among a plurality of channel quality information for each user terminal. Information is selected. Then, based on the selected channel quality information, a combination of serving base stations to be used for downlink data transmission to each user terminal is selected. Therefore, it is possible to appropriately select a transmission point (serving base station) to be used for transmission of a downlink data signal in accordance with a change in interference situation accompanying a change in traffic situation.

It is the schematic which shows the radio | wireless communication network which concerns on embodiment of this invention. It is a figure for demonstrating a CSI-RS resource and a CSI-IM resource. It is a table | surface which shows a CSI process. It is a figure for demonstrating DPS and DPB. It is a figure which shows the several CQI calculated with one user terminal. It is a figure which shows CQI for every subband in case a data signal is transmitted from a different base station about one user terminal. It is a figure for demonstrating DPS and DPB implemented by three base stations. It is a figure for demonstrating the change of CQI which should be used for DPB according to the change of the interference condition accompanying the change of the traffic condition accompanying implementation of DPS. It is a figure which shows the bias | inclination of the number of user terminals connected to a base station. It is a figure which shows CQI for every subband in case the data signal is transmitted from a different base station about one user terminal in the condition of FIG. It is a block diagram which shows the structure of the base station control apparatus which concerns on embodiment of this invention. It is a flowchart which shows the base station control method which concerns on embodiment of this invention. It is a table | surface which shows the non-transmission base station assumed in each combination of several possible serving base station candidates with respect to each user terminal determined in the base station control method. It is a figure which shows several CQI calculated in each user terminal. FIG. 7 is a table showing selected CQIs for each of the serving base station candidate combinations. FIG. It is a figure which shows the log | history of the serving base station of one user terminal. It is a figure which shows the subband used in the past for transmission of the data signal in the base station. It is a figure which shows the subband used in the past for transmission of a data signal in the other base station. It is a table | surface which shows the prediction metric in case each subband is allocated to the user terminal in one base station estimated with the deformation | transformation of embodiment.

Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the wireless communication network according to the present invention includes a base station control device 10 and a plurality of base stations (transmission points) TP1, TP2, TP3. The base stations TP1, TP2, TP3 communicate wirelessly with the user terminals UE1, UE2. Communication between the base station and the user terminal conforms to, for example, LTE Advanced. The base station controller 10 communicates with the base stations TP1, TP2, TP3 and controls these base stations TP1, TP2, TP3.

  FIG. 2 shows communication resources transmitted by the two base stations TP1 and TP2. In FIG. 2, each square is a communication resource defined by time and frequency. Black resources are used for transmission of CSI-RS (channel state information reference signal), gray resources are used for transmission of PDSCH (physical downlink shared channel) data signals, and white resources are not transmitted (for downlink transmission). Not used).

  In FIG. 2, the resources in the second and third columns (second and third time points from the left) in the first row (first frequency point from the top) are not used for the downlink transmission of the base station TP1, Used for PDSCH from the base station TP2. Therefore, the user terminal served from the base station TP1 can estimate the power of an interference signal from a base station other than the base station TP1 (for example, the base station TP2) using these resources. These resources are called CSI-IM resources # 1.

  The resources in the second and third columns of the second row (second frequency point from the top) are allocated to the CSI-RS from the base station TP1, and are not used for downlink transmission of the base station TP2. Therefore, the user terminal served from the base station TP1 can estimate the power of the signal from the base station TP1 using these resources. These resources are called CSI-RS resources # 1.

  The resources in the second and third columns of the third row are not used for downlink transmission of the base station TP1, but are allocated to the CSI-RS from the base station TP2. Therefore, the user terminal served from the base station TP2 can estimate the power of the signal from the base station TP2 using these resources. These resources are called CSI-RS resources # 2.

  The resources in the second and third columns of the fourth row are used for PDSCH from the base station TP1, and are not used for downlink transmission of the base station TP2. Therefore, the user terminal served from the base station TP2 can estimate the power of an interference signal from a base station other than the base station TP2 (for example, the base station TP1) using these resources. These resources are called CSI-IM resources # 2.

  The resources in the second and third columns of the fifth row are not used for downlink transmission of the base station TP1, and are not used for downlink transmission of the base station TP2. Therefore, the user terminal served from the base station TP1 or the base station TP2 can estimate the power of interference signals from base stations other than the base stations TP1 and TP2 (for example, the base station TP3) using these resources. it can. These resources are called CSI-IM resources # 3.

  Each base station provides a plurality of signal power measurement resources (CSI-RS resource) and interference signal power measurement resources (CSI-IM resource (CSI-IM resource)) used for CQI calculation to user terminals served by the base station. It is possible to specify a CSI process that is a combination of interference measurement resource)). FIG. 3 is a table showing a CSI process that the base station can designate to the user terminal. In CSI process # 1, the user terminal served from base station TP1 estimates the power of the desired signal from base station TP1 using CSI-RS resources # 1, and uses CSI-IM resources # 1. The power of an interference signal from a base station (for example, base station TP2) other than the base station TP1 is estimated. And a user terminal calculates SINR from a desired signal and an interference signal, and feeds back CQI which quantized the SINR to a serving base station. In CSI process # 2, the user terminal served from base station TP1 estimates the power of the desired signal from base station TP1 using CSI-RS resources # 1, and uses CSI-IM resources # 3. The power of interference signals from base stations other than the base stations TP1 and TP2 is estimated. Then, the user terminal calculates another SINR from the desired signal and the interference signal, and feeds back the CQI obtained by quantizing the SINR to the serving base station.

  In CSI process # 3, the user terminal served from base station TP2 estimates the power of the desired signal from base station TP2 using CSI-RS resources # 2, and uses CSI-IM resources # 2. The power of an interference signal from a base station (for example, base station TP1) other than the base station TP2 is estimated. And a user terminal calculates SINR from a desired signal and an interference signal, and feeds back CQI which quantized the SINR to a serving base station. In CSI process # 4, the user terminal served from base station TP2 estimates the power of the desired signal from base station TP2 using CSI-RS resources # 2, and uses CSI-IM resources # 3. The power of interference signals from base stations other than the base stations TP1 and TP2 is estimated. Then, the user terminal calculates another SINR from the desired signal and the interference signal, and feeds back the CQI obtained by quantizing the SINR to the serving base station.

  By specifying a plurality of CSI processes for one user terminal, the user terminal can obtain a plurality of types of CQIs and feed them back. For example, if CSI process # 1 and CSI process # 3 are specified for one user terminal, the user terminal can use the CQI based on the desired signal from the base station TP1 and the interference signal from the base station TP2, and the base station TP2 The CQI based on the desired signal from the base station TP1 and the interference signal from the base station TP1 is fed back. When each user terminal feeds back a plurality of types of CQIs, the plurality of base stations share, for example, their CQIs, and high-precision control (for example, DPS and DPB) in cooperation with the plurality of base stations is possible.

  FIG. 4 is a diagram for explaining DPS and DPB. In DPS, a plurality of transmission points (for example, base stations TP1 and TP2) share a downlink data signal destined for one user terminal (for example, user terminal UE1). The transmission point (serving base station) transmitting the downlink data signal is periodically transmitted from these multiple transmission points (the serving base station). 1 subframe (1 ms) period). For example, a transmission point that is predicted to have higher transmission throughput is selected based on a plurality of types of CQIs of the user terminal. DPB is a technique for reducing inter-cell interference by stopping (blanking) transmission of neighboring transmission points that are transmission sources of interference signals for data signals from transmission points that transmit data signals. For example, if the downlink transmission from the base station TP2 is blanked in the state shown in the figure, the user terminal UE1 can receive the desired signal from the base station TP1 with high accuracy. DPS and DPB may be implemented separately or in combination.

  One method of DPS will be described with reference to FIGS. 5 and 6. FIG. 5 shows a plurality of types of CQI calculated by the user terminal UE1. In a situation where two base stations TP1 and TP2 can be serving base stations of the user terminal UE1 and no other base station exists, four types of CQI are assumed. When one of the base stations TP1 and TP2 is a serving base station (serving cell), the other is an interfering base station (interfering cell) that transmits a downlink signal that causes interference, or a blanking base station that does not transmit a downlink signal ( Blanking cell).

  Each user terminal calculates a plurality of types of CQI for each subband of a frequency band used for downlink transmission. The upper graph of FIG. 6 shows the CQI (ie, CQI1) in each subband when the base station TP1 is a serving base station and the base station TP2 is an interfering base station, and the lower graph shows the serving of the base station TP2 The CQI (ie, CQI3) in each subband when the base station TP1 is an interference base station is shown.

  Based on these CQIs of the user terminals, the base station control apparatus 10 estimates or calculates the transmission throughput when it is assumed that each base station transmits downlink data to the user terminals using all subbands. Then, the base station having the higher estimated transmission throughput is selected or determined as the serving base station of the user terminal. Such selection of the serving base station is performed in one subframe cycle.

  However, when DPS is performed, downlink traffic of a certain base station may be generated or lost depending on the transmission point selection result. When there is no downlink traffic, the base station does not interfere with user terminals served from other base stations. For example, in the network shown in FIG. 7, it is assumed that the serving base station of the user terminal UE1 is changed from the base station TP2 to the base station TP1 by DPS. In this case, if there is no other user terminal that the base station TP2 serves, the base station TP2 does not interfere with the user terminal UE2. When the serving base station candidates of the user terminal UE2 are the base stations TP2 and TP3, in the selection of the serving base station for the user terminal UE2 in the DPS, the CQI # 1 to CQI # 4 of the UE2 shown in FIG. If CQI # 3 (base station TP3 is a serving base station and base station TP2 is an interfering base station) is used, base station TP2 is actually a blanking base station rather than an interfering base station. A serving base station for the user terminal UE2 is selected based on the appropriate CQI. In this case, CQI # 4 (base station TP3 is a serving base station and base station TP2 is a blanking base station) should be used instead of CQI # 3, and CQI # 1 (base station TP2 is The serving base station should be selected by comparing the throughput obtained at the serving base station and the base station TP3 as an interference base station) with the throughput obtained at CQI # 4.

  Therefore, the base station control apparatus 10 according to this embodiment appropriately selects the serving base station according to the change in the interference situation accompanying the change in the traffic situation.

  Also, as described above, the transmission throughput estimated on the assumption that each base station transmits downlink data to one user terminal using all subbands is the sub-rate actually allocated to the user terminal at the base station. May differ from transmission throughput when using bands. This is because when a plurality of user terminals are connected to one base station, all subbands are not allocated to one user terminal. Furthermore, as shown in FIG. 9, when the number of user terminals connected to a certain base station and the number of user terminals connected to other base stations are significantly different, the subbands allocated to the user terminals The number varies greatly depending on the base station. For example, in the situation shown in FIG. 9, if the user terminal UE1 is connected to the base station TP2, no other user terminals are connected to the base station TP2, so as shown in FIG. While subbands are assigned to the user terminal UE1, even if the user terminal UE1 is connected to the base station TP1, since many user terminals are connected to the base station TP1, only a few subbands of the base station TP1 are used by the user. It is not assigned to the terminal UE1. If transmission throughput is estimated on the assumption that each base station transmits downlink data to one user terminal using all subbands, a base station with low transmission throughput may actually be selected as a serving base station. is there.

  Therefore, the base station control apparatus 10 according to this embodiment estimates a subband to be used for data transmission to the user terminal, and appropriately selects a serving base station based on the estimation.

  As shown in FIG. 11, the base station control device 10 includes a base station communication unit 12, a controller 14, and a storage device 15. The controller 14 includes a serving base station selection unit 16, a base station transmission stop unit 18, a serving base station candidate combination determination unit 20, a channel quality information selection unit 22, and a metric calculation unit 24. The metric calculation unit 24 includes a subband estimation unit 26, an individual metric determination unit 28, and a total metric calculation unit 30.

  The base station communication unit 12 is a communication interface for the base station control device 10 to communicate with other elements in the network, for example, the base stations TP1, TP2, TP3.

  The controller 14 is, for example, a CPU (central processing unit). The internal elements of the controller 14 are functional blocks that are executed when the controller 14 executes a computer program stored in the storage device 15 and functions according to the computer program. The function of the controller 14 will be described below.

  The serving base station selection unit 16 is an element for executing DPS. Specifically, the serving base station selection unit 16 uses a plurality of serving base stations that transmit data signals to each user terminal to share downlink data signals to the user terminal based on the CQI related to the user terminal. Periodically select from serving base station candidates. The serving base station selection unit 16 controls each base station based on the selection result.

  The base station transmission stop unit 18 is an element for determining a non-transmission base station (blanking base station) based on the DPS result. Specifically, the base station transmission stop unit 18 sends a blanking base station to stop downlink transmission of a blanking base station that is a base station other than the serving base station selected for each user terminal. Command. The function of the other elements of the controller 14 will be described in the following flowchart description.

  FIG. 12 is a flowchart showing the base station control method according to this embodiment. This method is executed by the function of the controller 14 in accordance with the above computer program. In the following description, it is assumed that there are three serving base station candidates (base stations TP1, TP2, TP3) for the three user terminals UE1, UE2, UE3. However, the present invention is applied when there are more serving base station candidates for more user terminals.

  In step S1, the serving base station candidate combination determining unit 20 of the controller 14 determines a plurality of possible serving base station TP1, TP2, and TP3 combinations for each user terminal UE1, UE2, UE3, and assumes in each combination Determine the blanking base station to be used. FIG. 13 shows the determination result. For example, in combination number 1, for user terminals UE1, UE2, UE3, the serving base station candidate is base station TP1, and the blanking base stations are necessarily base stations TP2, TP3. In combination number 4, for the user terminals UE1, UE2 and UE3, the serving base station candidates are base stations TP1, TP2 and TP3, respectively, and there is necessarily no blanking base station. In the combination number 8, the serving base station candidate for the user terminals UE1 and UE2 is the base station TP2, the serving base station candidate for the user terminal UE3 is the base station TP3, and the blanking base station is necessarily a base station Station TP1.

  In step S2, the channel quality information selection unit 22 of the controller 14 selects the combination number N = 1. That is, the combination of the serving base station candidate with the combination number 1 and the blanking base station is selected. In step S3, the channel quality information selection unit 22 selects one channel quality information CQI from among a plurality of types of CQI for each of the user terminals UE1, UE2, UE3 with respect to the combination of the combination number N.

  FIG. 14 shows a plurality of types of CQIs calculated by each of the user terminals UE1, UE2, UE3. For example, for any user terminal, CQI # 1 is CQI when base station TP1 is a serving base station and base stations TP2 and TP3 are interfering base stations, and for user terminal UE1, CQI # 2 is base station TP1. Is the CQI when base station TP2 is a blanking base station and TP3 is an interfering base station. Since there are three serving base station candidates, each user terminal can theoretically calculate 12 types of CQI. However, considering the processing burden on the user terminal, the number of CQI types calculated by one user terminal is limited to 4 in the LTE specification (3GPP TS 36.213 V11.6.0, Section 7.2. 1). Therefore, the illustrated CQI is the maximum number of types of CQI calculated in each user terminal. The type of CQI calculated by the user terminal is instructed to the user terminal by the designation of the CSI process of the base station in the previous stage.

  In step S3, the channel quality information selection unit 22 relates to the combination of the combination number N, one channel quality information reflecting a blanking base station from among a plurality of types of CQI for each user terminal UE1, UE2, UE3. Select CQI. For example, in the combination of the serving base station candidate with the combination number 1 and the blanking base station, as shown in FIG. 13, the serving base station candidate is the base station TP1 for the user terminals UE1, UE2, and UE3. The base stations are base stations TP2 and TP3, and there are no interfering base stations. The channel quality information selection unit 22 searches for the CQI reflecting the combination closest to the combination of the combination number 1 from the four CQI # 1 to CQI # 4 of the user terminal UE1. Since there is no CQI in which the base station TP3 is a blanking base station among the four CQIs # 1 to CQI # 4 of the user terminal UE1, the channel quality information selection unit 22 uses the CQI # 2 closest to the combination of the combination number 1 (The base station TP1 is the serving base station, the base station TP2 is the blanking base station, and the base station TP3 is the interference base station) is selected as the CQI of the user terminal UE1 in the combination of the combination number 1.

  The channel quality information selection unit 22 searches for the CQI reflecting the combination closest to the combination of the combination number 1 from the four CQI # 1 to CQI # 4 of the user terminal UE2. In the four CQI # 1 to CQI # 4 of the user terminal UE1, CQI # 3 matches the combination of combination number 1 (base station TP1 is serving base station, base station TP2 is blanking base station, base station TP3 Is a blanking base station). Therefore, the channel quality information selection unit 22 selects CQI # 3 of the user terminal UE2 as the CQI of the user terminal UE2 in the combination of the combination number 1.

  The channel quality information selection unit 22 searches for the CQI reflecting the combination closest to the combination of the combination number 1 from the four CQI # 1 to CQI # 4 of the user terminal UE3. Since there is no CQI in which the base station TP2 is a blanking base station among the four CQIs # 1 to CQI # 4 of the user terminal UE3, the channel quality information selection unit 22 has the CQI # 2 closest to the combination of the combination number 1 (The base station TP1 is the serving base station, the base station TP2 is the interference base station, and the base station TP3 is the blanking base station) is selected as the CQI of the user terminal UE3 in the combination of the combination number 1.

  In the flowchart of FIG. 12, the completion of metric calculation is checked in all combinations of serving base station candidates and blanking base stations in steps S5 and S6. FIG. 15 is a table showing the CQI selected by the channel quality information selection unit 22 for each user terminal UE1, UE2, UE3 for each combination.

  In step S4, the metric calculation unit 24 of the controller 14 selects a serving base station for each user terminal UE1, UE2, UE3 based on the CQI selected by the channel quality information selection unit 22 for the combination of the combination number N. Calculate the metric that is the criterion for. In this embodiment, the metric calculation unit 24 estimates a subband to be used for downlink data transmission to each user terminal UE1, UE2, UE3 for each of a plurality of serving base station candidates. Then, an individual metric for each subband is calculated, and a total metric that is the sum of the individual metrics is calculated for each serving base station candidate of each user terminal.

  First, the subband estimation unit 26 of the metric calculation unit 24 uses, for each of a plurality of serving base station candidates of each user terminal UE1, UE2, UE3, a subband to be used for downlink data transmission to the user terminal. Is estimated. In this embodiment, for each serving base station candidate of each user terminal, the subband estimation unit 26 finally transmits the subband used for downlink data transmission to the user terminal to the user terminal. Estimated as a subband to be used for downlink data transmission.

  FIG. 16 is a chart showing the history of the serving base station of the user terminal UE1. The last time the base station TP1 was the serving base station for the user terminal UE1 was the previous serving base station selection. FIG. 17 shows subband allocation for downlink data transmission of the base station TP1 at that time. Regarding the user terminal UE1, the last time the base station TP2 was the serving base station was the selection of the serving base station four times before. FIG. 18 shows subband allocation for downlink data transmission of the base station TP2 at that time.

  For the combination of combination numbers 1 to 4 where the serving base station candidate of the user terminal UE1 is the base station TP1 (see FIG. 13), the subband estimation unit 26 selects the user terminal in the previous serving base station selection. The subbands used for downlink data transmission to UE1 (specifically, subbands # 3 and # 6) are used for downlink data transmission from base station TP1 to user terminal UE1. Estimate as a power subband. This is because when the base station TP1 is determined as the serving base station of the user terminal UE1 this time, the subband assigned to the user terminal UE1 by the base station TP1 in the previous selection of the serving base station is transmitted to the user terminal UE1. This is because it is highly likely to be used for downlink data transmission.

  The subband estimation unit 26, for the combination of the combination number 5-8 (see FIG. 13) in which the serving base station candidate of the user terminal UE1 is the base station TP2 (see FIG. 13), the user terminal in the selection of the serving base station four times before The subbands (specifically, subbands # 2, # 3, # 4, and # 7) used for downlink data transmission from the base station TP2 to the UE1 are transmitted to the user terminal UE1. Estimate as a subband to be used for data transmission. This is because when the base station TP2 is determined as the serving base station of the user terminal UE1 this time, the subband assigned to the user terminal UE1 by the base station TP2 in the selection of the serving base station four times before is transmitted to the user terminal UE1. This is because it is highly likely to be used for downlink data transmission.

The individual metric determination unit 28 of the metric calculation unit 24 determines the individual metric of the subband estimated by the subband estimation unit 26 for each serving base station candidate of each user terminal. For example, if the serving base station candidate is a base station TP1, user terminal UE1 individual metrics can be expressed by _{f UE1 (TP1, subband # 3} ). If the serving base station candidate is a base station TP2, the user terminal UE1 separate metric for subband # 2 is expressed by _{f UE1 (TP2, subband # 2} ).

  f is a function for deriving an individual metric from the CQI of the user terminal in each subband. As described above, each user terminal calculates a plurality of types of CQIs for each subband (see FIG. 6). Since the type of CQI is selected in step S3, the individual metric determination unit 28 calculates the individual metric using the function f from the CQI of that type in each subband estimated by the subband estimation unit 26. . The individual metric may be an instantaneous transmission throughput, a ratio of the instantaneous transmission throughput to a past average transmission throughput to which the concept of proportional fairness is applied, or another metric.

The total metric calculation unit 30 of the metric calculation unit 24 calculates a total metric that is the sum of the individual metrics for each serving base station candidate of each user terminal. For example, when the serving base station candidate is the base station TP1, the total metric TM _UE1 (TP1) of the user terminal UE1 can be expressed by the following equation if subbands # 3 and # 6 are used as described above. .
TM _UE1 (TP1) = f _UE1 (TP1, subband # 3) + f _UE1 (TP1, subband # 6)

When the serving base station candidate is the base station TP2, the total metric TM _UE1 (TP2) of the user terminal UE1 is as follows if the subbands # 2, # 3, # 4, and # 7 are used as described above. It can be expressed as
TM _UE1 (TP2)
_{= F UE1 (TP2, subband #} 2) + f UE1 (TP2, subband # 3) + f UE1 (TP2, subband # 4) + f UE1 (TP2, subband # 7)

  In step S5, the controller 14 determines whether or not the total metric of each user terminal UE1, UE2, UE3 has been calculated for all combinations of serving base station candidates and blanking base stations. If this determination is negative, the controller 14 increments N in step S6, and the process returns to step S3. If this determination is affirmative, in step S7, the serving base station selection unit 16 sums the total metrics of the plurality of user terminals UE1, UE2, UE3 for each combination of the serving base station candidate and the blanking base station. Calculate

  In step S8, the serving base station selection unit 16 selects a serving base station combination to be used for downlink data transmission to each user terminal UE1, UE2, UE3 based on the sum of the total metrics. Select from a combination of candidates. For example, the serving base station selection unit 16 may determine a combination having the maximum total metric as a combination of serving base stations to be used. In step S8, a blanking base station is also determined. For example, if the combination of the combination number 2 is selected, the blanking base station is the base station TP2 (FIG. 13), and if the combination of the combination number 6 is selected, there is no blanking base station.

  In step S9, the controller 14 executes scheduling. Specifically, it is determined which user terminal is allocated to which frequency resource of the serving base station determined in step S8. In scheduling, the base station transmission stop unit 18 instructs the non-transmission base station to stop the downlink transmission of the transmission point that is the transmission source of the interference signal. That is, in scheduling, DPB may be executed.

  As described above, in this embodiment, for each combination of serving base station candidates that transmit a data signal to a user terminal, a non-transmission base station is reflected from a plurality of types of CQIs for each user terminal. One CQI is selected (step S3). Then, based on the selected CQI, a combination of serving base stations to be used for downlink data transmission to each user terminal is selected. Therefore, it is possible to appropriately select a transmission point (serving base station) to be used for transmission of a downlink data signal in accordance with a change in interference situation accompanying a change in traffic situation. That is, the problem described above with reference to FIGS. 7 and 8 is solved.

  Further, in this embodiment, for each of a plurality of serving base station candidates of each user terminal, a subband to be used for downlink data transmission to the user terminal is estimated, and the estimated subband is Based on this, a total metric is calculated (step S4). Therefore, the serving base station can be selected more appropriately based on the subband approximate to the subband actually allocated. That is, the problem described above with reference to FIGS. 9 and 10 is solved.

  Further, the subband estimation unit 26 of the base station control apparatus 10 finally sends the subband used for downlink data transmission to the user terminal to each user terminal. As a subband to be used for downlink data transmission. Therefore, it is possible to estimate a subband to be used for downlink data transmission to the user terminal easily and with high accuracy.

  Next, a modification of this embodiment will be described. In this modification, the base station control method shown in the flowchart of FIG. 12 is executed as in the above embodiment. However, the details of step S4 are different from the above embodiment. In step S4, the metric calculation unit 24 of the controller 14 relates to the combination of the combination number N, based on the CQI selected by the channel quality information selection unit 22 in each of the plurality of serving base station candidates, for each user terminal UE1, UE2 , UE3 calculates a metric that is a criterion for selection of the serving base station. In this modification, the metric calculation unit 24 compares, for each user terminal UE1, UE2, UE3, a subband to be used for downlink data transmission to the user terminal with a prediction metric of another user terminal. Estimate and compute the metric sum for the estimated subbands.

  First, the subband estimation unit 26 of the metric calculation unit 24 uses the above-described function f for deriving an individual metric from the CQI of the user terminal in each subband to calculate prediction metrics in all available subbands. presume. FIG. 19 shows an example of a prediction metric of the base station TP1 corresponding to the combination of the combination number 1 estimated in this way (the serving base station candidate is the base station TP1 for the user terminals UE1, UE2, UE3). It is a table. For example, the prediction metric when the subband # 1 is allocated to the user terminal UE1 is 1, and the prediction metric when the subband # 4 is allocated to the user terminal UE2 is 2.

  The subband estimation unit 26 of the metric calculation unit 24 sets the best prediction metric among the prediction metrics of a plurality of user terminals estimated for each subband for each serving base station candidate of each user terminal UE1, UE2, UE3. A corresponding user terminal is estimated as a user terminal used for downlink data transmission in the subband. Then, according to this estimation, the subband estimation unit 26 estimates a subband to be used for downlink data transmission to each user terminal. For example, in the example shown in FIG. 19, the subband estimation unit 26 estimates that subband # 3 should be used for user terminal UE1 having the best prediction metric 4, and subbands # 2 and # 5 are the best. The subbands # 1, # 4, # 6, and # 7 are estimated to be used for the user terminal UE3 having the best prediction metric. Thus, the subband estimation unit 26 uses subband # 3 as the subband to be used for the user terminal UE1, and subbands # 2 and # 5 as the subband to be used for the user terminal UE2. The subbands to be used for UE3 are determined to be subbands # 1, # 4, # 6, and # 7.

  The individual metric determination unit 28 of the metric calculation unit 24 determines the individual metric of the subband estimated by the subband estimation unit 26 for each serving base station candidate of each user terminal. Specifically, the prediction metric corresponding to the subband estimated by the subband estimation unit 26 for each user terminal is determined as the individual metric of the subband estimated by the subband estimation unit 26 of the user terminal. . For example, in the example illustrated in FIG. 19, the individual metric determination unit 28 determines the prediction metric 4 of subband # 3 estimated for the user terminal UE1 as the individual metric of the user terminal UE1. The individual metric determination unit 28 determines the prediction metric 3 of subband # 2 and the prediction metric 4 of subband # 5 estimated for the user terminal UE2 as the individual metrics of the user terminal UE2. The individual metric determination unit 28 predicts the prediction metric 4 of subband # 1, the prediction metric 3 of subband # 4, the prediction metric 3 of subband # 6, and the prediction metric 4 of subband 7 estimated for the user terminal UE3. Is determined as the individual metric of the user terminal UE2.

The total metric calculation unit 30 of the metric calculation unit 24 calculates a total metric that is the sum of the individual metrics determined by the individual metric determination unit 28 for each serving base station candidate of each user terminal. For example, in the example shown in FIG. 20, the total metric TM _UE1 (TP1) of the user terminal UE1 is 4, the total metric TM _UE2 (TP1) of the user terminal UE2 is 3 + 4 = 7, and the total metric TM of the user terminal UE3. _UE3 (TP1) is 4 + 3 + 3 + 4 = 14. In this modification, the prediction metric once estimated from the CQI is used to estimate the subband to be used, thereby easily and accurately used for downlink data transmission to the user terminal. Power subbands can be estimated and metrics can be calculated with high accuracy.

  In the above-described embodiments and modifications, the base station control device 10 may be a macro cell base station that can wirelessly communicate with user terminals. The base stations TP1, TP2, and TP3 may be small cell base stations (for example, pico cell base stations) having a transmission power smaller than that of the macro cell base station. That is, the wireless communication network may be a heterogeneous network in which cell areas of base stations having different transmission powers are overlaid.

  In the above-described embodiment and modification, all the steps of the base station control method shown in the flowchart of FIG. However, some steps may be performed at each of the base stations TP1, TP2, TP3. For example, the scheduling (step S9) may be executed in each of the base stations TP1, TP2, TP3.

  In the above-described embodiments and modifications, each function executed by the CPU may be executed by hardware instead of the CPU. For example, programmable functions such as FPGA (Field Programmable Gate Array) and DSP (Digital Signal Processor) are possible. It may be executed by a logic device.

  In the above embodiments and variations, the metric calculation estimates the subbands to be used for downlink data transmission, but each base station uses all subbands to downlink its user terminal. You may calculate the metric when assuming data transmission. That is, it is not essential in the present invention to solve the problem described above with reference to FIGS.

TP1, TP2, TP3 base station, UE1, UE2, UE3 user terminal, 10 base station control device, 12 base station communication unit, 14 controller, 15 storage device, 16 serving base station selection unit, 18 base station transmission stop unit, 20 Serving base station candidate combination determination unit, 22 channel quality information selection unit, 24 metric calculation unit, 26 subband estimation unit, 28 individual metric determination unit, 30 total metric calculation unit.

Claims (9)

A base station control apparatus that controls a plurality of base stations that communicate wirelessly with a user terminal,
A serving base station that transmits a data signal to each user terminal is periodically selected from a plurality of base stations that share downlink data signals to the user terminal based on channel quality information about the user terminal. A serving base station selector,
A base station transmission stop unit that stops downlink transmission of a non-transmission base station that is a base station other than the serving base station selected for each user terminal;
A plurality of combinations of possible serving base station candidates for each user terminal, and a serving base station candidate combination determining unit that determines non-transmitting base stations in each combination;
For each of the combinations, a channel quality information selection unit that selects one channel quality information reflecting the non-transmission base station from a plurality of channel quality information for each user terminal;
A metric calculator for calculating a metric for selection of a serving base station for each user terminal based on the selected channel quality information for each of the combinations;
The serving base station selection unit selects a combination of serving base stations to be used for downlink data transmission to each user terminal based on a sum of the metrics for a plurality of user terminals for each of the combinations. A base station control device selected from a combination of The metric calculator is
For each of a plurality of serving base station candidates of each user terminal, a subband estimation unit that estimates a subband to be used for downlink data transmission to the user terminal,
An individual metric determination unit that determines an individual metric of the subband estimated by the subband estimation unit for each serving base station candidate of each user terminal;
The base station control apparatus according to claim 1, further comprising: a total metric calculation unit that calculates the metric that is the sum of the individual metrics for each serving base station candidate of each user terminal. For each serving base station candidate of each user terminal, the subband estimation unit finally uses the subband used for downlink data transmission to the user terminal for downlink data transmission to the user terminal. Estimated as the subband to be used,
The base station control apparatus according to claim 2, wherein the dedicated metric calculation unit determines a dedicated metric of the subband estimated by the subband estimation unit based on the channel quality information. The subband estimation unit estimates prediction metrics in all available subbands for each serving base station candidate of each user terminal based on the channel quality information, and sets the best prediction metric for each subband. Estimating a corresponding user terminal as a user terminal used for downlink data transmission in the subband, and in accordance with this estimation, estimating a subband to be used for downlink data transmission to each user terminal;
The said individual metric determination part determines the said prediction metric corresponding to the said subband estimated by the said subband estimation part with respect to each user terminal as an individual metric of the user terminal. The base station control apparatus described in 1. A plurality of base stations that wirelessly communicate with user terminals;
A serving base station that transmits a data signal to each user terminal is periodically selected from a plurality of base stations that share downlink data signals to the user terminal based on channel quality information about the user terminal. A serving base station selector,
A base station transmission stop unit that stops downlink transmission of a non-transmission base station that is a base station other than the serving base station selected for each user terminal;
A plurality of combinations of possible serving base station candidates for each user terminal, and a serving base station candidate combination determining unit that determines non-transmitting base stations in each combination;
For each of the combinations, a channel quality information selection unit that selects one channel quality information reflecting the non-transmission base station from a plurality of channel quality information for each user terminal;
A metric calculator for calculating a metric for selection of a serving base station for each user terminal based on the selected channel quality information for each of the combinations;
The serving base station selection unit selects a combination of serving base stations to be used for downlink data transmission to each user terminal based on a sum of the metrics for a plurality of user terminals for each of the combinations. A wireless communication network characterized by being selected from a combination of: A base station control method for controlling a plurality of base stations that wirelessly communicate with user terminals,
A serving base station that transmits a data signal to each user terminal is periodically selected from a plurality of base stations that share downlink data signals to the user terminal based on channel quality information about the user terminal. And
Stopping downlink transmission of non-transmitting base stations that are other base stations other than the serving base station selected for each user terminal;
Determining a plurality of possible serving base station candidates for each user terminal and determining a non-transmitting base station in each combination;
For each of the combinations, selecting one channel quality information reflecting the non-transmitting base station from among a plurality of channel quality information for each user terminal;
For each of the combinations, for each user terminal based on selected channel quality information, calculating a metric that is a criterion for selection of a serving base station;
Selecting the serving base station determines a combination of serving base stations to be used for downlink data transmission to each user terminal based on a sum of the metrics for a plurality of user terminals for each of the combinations. A base station control method comprising selecting from a combination of candidates. Computing the metric is
For each of a plurality of serving base station candidates for each user terminal, estimating a subband to be used for downlink data transmission to that user terminal;
Determining an estimated individual metric of the subband for each serving base station candidate for each user terminal;
The base station control method according to claim 6, further comprising: calculating the metric that is the sum of the individual metrics for each serving base station candidate of each user terminal. Estimating the subband means that, for each serving base station candidate of each user terminal, finally, the subband used for downlink data transmission to the user terminal is determined as downlink data to the user terminal. Estimating as a subband to be used for transmission,
The base station control method according to claim 7, wherein calculating the dedicated metric is determining an estimated individual metric of the subband based on the channel quality information. Estimating the subbands is to estimate prediction metrics for all available subbands for each serving base station candidate for each user terminal based on the channel quality information and to obtain the best prediction for each subband. A user terminal corresponding to the metric is estimated as a user terminal used for downlink data transmission in the subband, and a subband to be used for downlink data transmission to each user terminal is estimated according to this estimation. That is,
Determining the individual metric is determining the prediction metric corresponding to the subband estimated to be used for each user terminal as an individual metric of the user terminal; The base station control method according to claim 7.

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