Control device, method performed by control device, and program

Abstract

To contribute to reduction of both inter-subset interference and intra-subset interference when using a partial weight generation method.SOLUTION: A control device determines that a second wireless terminal needs to belong to a same wireless terminal subset as at least one first wireless terminal in order to allocate time and frequency resources for spatial multiplexed transmission to the second wireless terminal when an interference level between the second wireless terminal and at least one of one or more first wireless terminals is estimated to be at a second level greater than a first level and smaller than a third level. On the other hand, the control device determines that the second wireless terminal is not allowed to belong to any wireless terminal subset and the second wireless terminal is excluded from the spatial multiplexed transmission on the time and frequency resources when the interference level between the second wireless terminal and at least one of one or more first wireless terminals is estimated to be at a third level greater than the second level.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to wireless communication systems, and more particularly to spatial multiplexing transmission between a base station and multiple wireless terminals using the same time and frequency resources. [Background technology]

[0002] Massive multiple-input multiple-output (MIMO) is a physical layer technology used in 3rd Generation Partnership Project (3GPP®) Fifth Generation (5G) systems. In Massive MIMO (mMIMO) technology, a Radio Access Network (RAN) base station (i.e., gNB in ​​5G systems) uses an antenna array with multiple antennas. The antenna array is used for digital beamforming, especially for multi-user MIMO (MU-MIMO) to spatially multiplex multiple wireless terminals (i.e., User Equipments (UEs)) on the same time and frequency resources. The spatially distributed antenna arrays may be located within one cell served by the base station.

[0003] Distributed MIMO is one of the important technologies for Beyond 5G or Sixth Generation (6G). The basic idea of ​​distributed MIMO is to distribute multiple radio devices, each equipped with one or more antennas, over a wide area in order to provide services to multiple wireless terminals distributed over a wide area (see, for example, Non-Patent Documents 1 and 2). Each of the distributed radio devices is connected to a control device that handles digital baseband signal processing via a transmission path. The control device that handles digital baseband signal processing is called, for example, a baseband unit, a digital unit, a distributed unit (Distributed Unit (DU)), a central processing unit (CPU), or an edge cloud processor. Distributed MIMO is also called cell-free Massive MIMO or a distributed antenna system (DAS). Each distributed radio device is also called a transmission and reception point (TRP), a radio unit (RU), a remote radio head, or an access point (AP).

[0004] Distributed MIMO supports MU-MIMO transmission, similar to existing centralized MIMO. MU-MIMO base stations can eliminate interference between wireless terminals by digitally combining signals using precoding weights and postcoding weights during downlink transmission and uplink reception, respectively. Postcoding weights are also called combining weights, receiving combining weights, receiving weights, spatial filtering weights, etc. Hereinafter, precoding weights and postcoding weights are collectively referred to as weights.

[0005] Non-Patent Document 2 proposes a method for reducing the amount of computation for weight calculation in a distributed MU-MIMO system. In the method proposed in Non-Patent Document 2, a control device forms a subset (or cluster) of wireless terminals selected from a plurality of wireless terminals in a service area provided by a plurality of wireless devices of a base station. The control device further selects a subset (or cluster) of antennas serving the formed subset of wireless terminals from a plurality of antennas of the plurality of wireless devices. Hereinafter, a combination of a subset of the selected wireless terminals (hereinafter referred to as a communication wireless terminal subset) and a subset of antennas serving these selected wireless terminals (hereinafter referred to as an antenna subset) is called a subsystem. A communication wireless terminal subset includes one or more wireless terminals that perform subset-based MIMO transmission on the same time and frequency resources with a corresponding antenna subset. The base station or its control device generates zero forcing (ZF) or minimum mean squared error (MMSE) weights for each subsystem. This reduces the amount of computation required for inverse matrix calculation in weight generation. The base station or its control device may further select a wireless terminal (hereinafter referred to as an interfering wireless terminal) to be considered as an interference source when calculating the weight for each subsystem. In this case, one subsystem is a combination of a communication wireless terminal subset, an antenna subset, and a subset of interfering wireless terminals (hereinafter referred to as an interfering wireless terminal subset). In the following, as described in Non-Patent Document 2, a method in which the base station calculates weights on a subsystem basis is called a partial or local weight generation method. On the other hand, a method in which the base station or its control device calculates weights by collectively considering all of the multiple antennas connected to the control device and all of the wireless terminals served by these multiple antennas is called a global weight generation method.

[0006] The partial weight generation method reduces the amount of calculation required for inverse matrix calculation in weight generation, but causes degradation of communication quality due to interference between wireless terminals compared to the full weight generation method. This interference between wireless terminals is divided into intra-subset interference and inter-subset interference. Intra-subset interference is interference between wireless terminals belonging to the same communication wireless terminal subset that remains after interference removal by the partial weight generation method. Inter-subset interference is interference from other wireless terminal subsets that are not taken into account by the partial weight generation method to wireless terminals belonging to the communication wireless terminal subset. When the partial weight generation method is used, the degradation of characteristics due to inter-subset interference is significant.

[0007] Non-Patent Document 2 proposes a radio resource allocation method for reducing inter-subset interference. The method proposed in Non-Patent Document 2 defines an interference offset distance and classifies or divides multiple wireless terminal subsets (or clusters) based on the interference offset distance. In the terminology of Non-Patent Document 2, the multiple wireless terminal subsets are divided into multiple "layers". The method proposed in Non-Patent Document 2 gives each layer a transmission opportunity (or time resource) in a predetermined order to mitigate inter-subset interference at the expense of time scheduling loss.

[0008] Specifically, the method proposed in Non-Patent Document 2 arranges a plurality of wireless terminal subsets in which the distance between the cluster centroids is equal to or greater than a predefined interference offset distance in a first layer. Furthermore, the method can arrange a plurality of other wireless terminal subsets in which the distance to any of the wireless terminal subsets belonging to the first layer is less than the interference offset distance and the distance between each other is equal to or greater than the interference offset distance in a second layer. The interference offset distance is defined, for example, as a multiple of the average distance between two neighboring wireless terminal subsets. Then, the method allocates frequency resources for spatial multiplexing to the first and second layers in a time-division manner in turn. In other words, spatial multiplexing using the same time and frequency resources is performed on a layer-by-layer basis, and different layers do not share the same frequency and time resources for spatial multiplexing.

[0009] On the other hand, Patent Document 1 points out that, depending on the combination of wireless terminals (UEs) spatially multiplexed for MU-MIMO transmission, even if a precoding weight is multiplied to a transmission signal, nulls are not sufficiently directed between the wireless terminals, and the characteristics are significantly deteriorated, and therefore it is preferable to appropriately determine the combination of wireless terminals to be multiplexed. Patent Document 1 discloses a method for determining a wireless terminal group that receives MU-MIMO transmission on the same time and frequency resources from among multiple wireless terminals. Specifically, this method calculates a Signal to Interference and Noise Ratio (SINR) for each wireless terminal based on the inner product of a received power vector of a first wireless terminal that has already been determined to belong to the wireless terminal group and a received power vector of a second wireless terminal that is a candidate to be newly added to the wireless terminal group, and further calculates a metric indicating the throughput when the second wireless terminal is newly added to the wireless terminal group using the calculated SINR. Then, the method determines whether the metric increases compared to before the second wireless terminal is added, and if the metric increases, determines to add the second wireless terminal to the wireless terminal group.

[0010] Hereinafter, unless otherwise specified, the term "subset of wireless terminals" or "wireless terminal subset" as used in this specification means a communicating wireless terminal subset, or a subset defined as the union of the communicating wireless terminal subset and the interfering wireless terminal subset. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2018-061152 A [Non-patent literature]

[0012] [Non-Patent Document 1] E. Bjornson and L. Sanguinetti, "Scalable Cell-Free Massive MIMO Systems," IEEE Transactions on Communications, vol. 68, no. 7, pp. 4247-4261, July 2020 [Non-Patent Document 2] R. Takahashi, H. Matsuo and F. Adachi, "Scalable and Reconfigurable Distributed MU-MIMO System," 2022 IEEE 95th Vehicular Technology Conference: (VTC2022-Spring), Helsinki, Finland, 2022, pp. 1-5 Summary of the Invention [Problem to be solved by the invention]

[0013] The method described in Non-Patent Document 2, that is, a method of dividing a plurality of wireless terminal subsets into a plurality of layers based on the interference offset distance and allocating frequency resources for spatial multiplexing transmission sequentially to each layer in a time-division manner, can reduce inter-subset interference by placing wireless terminal subsets whose distance from each other is closer than the interference offset distance into different layers. However, the method described in Non-Patent Document 2 may not be able to sufficiently reduce intra-subset interference. Since intra-subset interference is residual interference after interference elimination using the partial weight generation method, this tends to have relatively less adverse effects compared to inter-subset interference. However, in the partial weight generation method, the number of antennas used for interference elimination for each subset is smaller than in the total weight generation method, and therefore it is possible that intra-subset interference is not sufficiently eliminated. The remaining intra-subset interference may cause a decrease in communication quality, similar to inter-subset interference.

[0014] The method described in Patent Document 1 may be usable to reduce intra-subset interference in the method described in Non-Patent Document 2. However, Patent Document 1 does not assume the partial weight generation method described in Non-Patent Document 2. Therefore, it is not fully clear how to combine the technique of Patent Document 1 with the method of Non-Patent Document 2 that uses the partial weight generation method.

[0015] One of the objectives that the embodiments disclosed in this specification aim to achieve is to provide an apparatus, a method, and a program that contribute to reducing both inter-subset interference and intra-subset interference when using a partial weight generation method. It should be noted that this objective is only one of the objectives that the embodiments disclosed in this specification aim to achieve. Other objectives or problems and novel features will be apparent from the description of this specification or the accompanying drawings. [Means for solving the problem]

[0016] In a first aspect, the control device is configured to determine a plurality of wireless terminal subsets that perform spatial multiplexing transmission on the same time and frequency resources as a base station device equipped with a plurality of antennas. Each wireless terminal subset includes one or more wireless terminals that perform subset-based MIMO transmission on the time and frequency resources with a corresponding base station antenna subset selected from the plurality of antennas. More specifically, when an interference level between a second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree, the control device determines that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset. On the other hand, when the interference level between the second radio terminal and at least one of the one or more first radio terminals is estimated to be a second degree greater than the first degree and less than a third degree, the control device determines that the second radio terminal needs to belong to the same radio terminal subset as the at least one first radio terminal in order to allocate the time and frequency resources to the second radio terminal for the spatial multiplexing. Also, when the interference level between the second radio terminal and at least one of the one or more first radio terminals is estimated to be the third degree greater than the first degree and the second degree, the control device determines that the second radio terminal is not permitted to belong to any radio terminal subset and is excluded from the spatial multiplexing on the time and frequency resources.

[0017] In a second aspect, a method performed by a control device includes determining a plurality of wireless terminal subsets that perform spatial multiplexing transmission on the same time and frequency resources as a base station device equipped with a plurality of antennas, each wireless terminal subset including one or more wireless terminals that perform subset-based MIMO transmission on the time and frequency resources with a corresponding base station antenna subset selected from the plurality of antennas. The determining includes the following steps: (a) determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset when an interference level between the second wireless terminal and each of one or more first wireless terminals that have been previously determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be of a first degree; (b) when an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing; and (c) if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree, determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and that the second wireless terminal is excluded from the spatial multiplexing on the time and frequency resources.

[0018] In a third aspect, a program includes a set of instructions (software code) for causing a computer to carry out the method according to the second aspect above when the program is loaded into the computer. Effect of the Invention

[0019] According to the above-mentioned aspects, it is possible to provide an apparatus, a method, and a program that contribute to reducing both inter-subset interference and intra-subset interference when using the partial weight generation method. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 illustrates an example configuration of a wireless communication system related to one or more embodiments. [Diagram 2]FIG. 2 illustrates an example of a configuration of a wireless terminal related to one or more embodiments. [Diagram 3] FIG. 2 illustrates an example of a configuration of a control device related to one or more embodiments. [Figure 4] FIG. 1 illustrates an example of a configuration of a wireless device related to one or more embodiments. [Diagram 5] FIG. 2 is a diagram illustrating an example of a configuration of a radio signal processing unit related to one or more embodiments. [Figure 6] 5 is a flow chart illustrating an example of the operation of a controller in accordance with one or more embodiments. [Figure 7] FIG. 2 illustrates an example of a configuration of a scheduling unit related to one or more embodiments. [Figure 8] FIG. 2 conceptually illustrates an example of an indicator representing an interference level, in accordance with one or more embodiments. [Figure 9A] FIG. 4 conceptually illustrates an example operation of an index calculation unit, in accordance with one or more embodiments. [Figure 9B] FIG. 4 conceptually illustrates an example operation of an index calculation unit, in accordance with one or more embodiments. [Figure 10] 10A and 10B conceptually illustrate example operations of a condition setting unit, in accordance with one or more embodiments. [Figure 11A] 11 is a flow chart illustrating an example of an allocation determiner process, which may be relevant to one or more embodiments. [Figure 11B] 11 is a flow chart illustrating an example of an allocation determiner process, which may be relevant to one or more embodiments. [Figure 11C] 11 is a flow chart illustrating an example of an allocation determiner process, which may be relevant to one or more embodiments. [Figure 12] FIG. 2 conceptually illustrates an example of an indicator representing an interference level, in accordance with one or more embodiments. [Figure 13] FIG. 2 conceptually illustrates an example of an indicator representing an interference level, in accordance with one or more embodiments. [Figure 14]FIG. 2 conceptually illustrates an example of an indicator representing an interference level, in accordance with one or more embodiments. [Figure 15] 11 is a flow chart illustrating an example of a process of a condition setting unit, which may be related to one or more embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In the following, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and duplicated descriptions will be omitted as necessary for clarity of explanation.

[0022] Each of the embodiments described below may be used alone, or two or more of the embodiments may be appropriately combined. These embodiments may have different novel features. Therefore, these embodiments may contribute to achieving different objectives or solving different problems, and may contribute to achieving different effects.

[0023] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but to one or more other embodiments. As can be understood by those skilled in the art, various features or steps described with reference to any one drawing may be combined with features or steps shown in one or more other drawings to create an embodiment not explicitly shown or described, for example. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0024] As used herein, depending on the context, "if" may be interpreted to mean "when," "while," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be interpreted to have the same meaning, depending on the context.

[0025] [Wireless communication system configuration] First, the configuration and operation of a plurality of elements common to a plurality of embodiments will be described. FIG. 1 illustrates a configuration example of a wireless communication system 1 related to a plurality of embodiments. The wireless communication system 1 may be, for example and not limited to, a system conforming to the technical specifications of 3GPP, or may be a device conforming to the technical specifications of 5G. Each element (network function) illustrated in FIG. 1 may be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0026] 1, the wireless communication system 1 includes a plurality of wireless terminals 10 and a base station device 20. The wireless communication system 1 may include three or more wireless terminals 10. When describing matters common to a plurality of wireless terminals 10, reference will be made to one wireless terminal 10 unless otherwise specified.

[0027] The base station device 20 includes a control device 21 and one or more radio devices 22. The base station device 20 may be, for example, a base station or a base station element of a RAN. The base station device 20 may be called a base station, a radio station, a RAN node, or an access point, or other terms. Assuming a Beyond 5G or 6G system, the base station device 20 may be an enhanced gNB, or a DU and one or more radio units (RUs) in the enhanced gNB.

[0028] The wireless terminal 10 may be, for example, a mobile terminal such as a smartphone, a mobile phone, or a tablet, or a sensing device. The wireless terminal 10 may be a relay device having a function of relaying signals of other wireless terminals. The wireless terminal 10 may be called a mobile terminal, a mobile station, a UE, or other terms such as a wireless transmit receive unit (WTRU). Some or all of the multiple wireless terminals 10 are spatially multiplexed on the same time and frequency resources for transmission to or reception from the base station device 20. Each wireless terminal 10 may have one or more transmission or reception layers.

[0029] [Base station equipment configuration] As described above, the base station device 20 includes a control device 21 and one or more radio devices 22. The base station device 20 may include only one radio device 22, or three or more radio devices. When describing matters common to multiple radio devices 22, reference will be made to one radio device 22 unless otherwise specified.

[0030] The control device 21 may be responsible for digital baseband signal processing and scheduling. The control device 21 may be called, for example, a baseband unit, a digital unit, a distributed unit (DU), a CPU, or an edge cloud processor. If a Beyond 5G or 6G system is assumed, the control device 21 may host the Radio Link Control (RLC) layer and the Medium Access Control (MAC) layer of the enhanced gNB, and may host a part or all of the physical (Physical (PHY)) layer of the enhanced gNB. If the control device 21 hosts a part of the PHY layer, i.e., the high PHY layer, the remaining signal processing of the PHY layer, i.e., the low PHY layer, is located in the radio device 22. The control device 21 may include a function of the Central Unit (CU) of the enhanced gNB, or may include a function of the RAN Intelligent Controller (RIC). The RIC may be a Near-Real-Time (Near-RT) RIC or a Non-RT RIC, or both, conforming to the Open RAN (O-RAN) technical specifications. Some or all of the functions of the control device 21 may be implemented on a virtualized or cloud platform as a virtualized, containerized, or cloudified network function.

[0031] The wireless device 22 may be located at a position distant from the control device 21. A plurality of wireless devices 22 may be located geographically distributed. That is, the base station device 20 may support distributed MIMO. Distributed MIMO supports MU-MIMO transmission in which communication is performed with a plurality of wireless terminals 10 that are spatially multiplexed on the same time and frequency resources, similar to the existing centralized MIMO.

[0032] The control device 21 is connected to the radio device 22 via a transmission path 23, and communicates with one or more radio terminals 10 via the radio device 22. The transmission path 23 may be an optical fiber, a metal cable, or a radio propagation path. For example, the Radio over Fiber (RoF) technology, the Common Public Radio Interface (CPRI) technology, or the Enhanced CPRI (eCPRI) technology may be applied to the transmission path 23.

[0033] [Wireless terminal configuration] FIG. 2 shows an example of the configuration of the wireless terminal 10. The wireless terminal 10 includes a wireless communication unit 101, a storage unit 102, and a processing unit 103. The wireless communication unit 101 is an element that performs wireless communication with the wireless device 22. For example, the wireless communication unit 101 includes an antenna and a Radio Frequency (RF) circuit. The storage unit 102 includes a volatile memory and a non-volatile memory. The volatile memory may include, for example, a Random Access Memory (RAM). The non-volatile memory may include, for example, one or more of a Read Only Memory (ROM), a Hard Disk Drive (HDD), and a Solid State Drive (SSD). The non-volatile memory stores program codes (instructions) for implementing various functions of the wireless terminal 10. The processing unit 103 includes one or more processors. The one or more processors may include, for example, one or more of a Central Processing Unit (CPU), a Micro Processing Unit (MPU), a Field Programmable Gate Array (FPGA), and an Application Specific Integrated Circuit (ASIC). The processing unit 103 executes program codes stored in the storage unit 102 to realize various functions of the wireless terminal 10.

[0034] [Control device configuration] FIG. 3 shows an example of the configuration of the control device 21. The control device 21 includes a transmission line interface (IF) 211, a storage unit 212, and a processing unit 213. The transmission line IF 211 includes an interface that communicates with the wireless device 22 via the transmission line 23. The storage unit 212 includes a volatile memory and a non-volatile memory. The volatile memory may include, for example, a RAM. The non-volatile memory may include, for example, one or more of a ROM, a HDD, and an SSD. The non-volatile memory stores program codes (instructions) for realizing various functions of the control device 21. The processing unit 213 includes one or more processors. The one or more processors may include, for example, one or more of a CPU, an MPU, an FPGA, and an ASIC. The processing unit 213 realizes various functions of the control device 21 by executing the program codes stored in the storage unit 212.

[0035] The processing unit 213 has a wireless signal processing unit 214 as a functional block. The wireless signal processing unit 214 performs transmission processing and reception processing of wireless signals. The processing unit 213 may further include components other than the above-mentioned functional blocks. That is, the processing unit 213 can execute operations other than those of the above-mentioned functional blocks. Note that the wireless device 22 may have part of the functions of the wireless signal processing unit 214. In another example, another device physically separated from the control device 21 may have part of the functions of the wireless signal processing unit 214. A detailed configuration of the wireless signal processing unit 214 will be described later.

[0036] [Wireless device configuration] FIG. 4 shows an example of the configuration of the wireless device 22. The wireless device 22 includes a transmission path IF 221, a storage unit 222, a processing unit 223, and a wireless communication unit 224. The transmission path IF 221 is an interface for communicating with the control device 21 via the transmission path 23. The storage unit 222 includes a volatile memory and a non-volatile memory. The volatile memory may include, for example, a RAM. The non-volatile memory may include, for example, one or more of a ROM, a HDD, and an SSD. The non-volatile memory stores program codes (instructions) for realizing various functions of the wireless device 22. The processing unit 223 includes one or more processors. The one or more processors may include, for example, one or more of a CPU, an MPU, an FPGA, and an ASIC. The processing unit 223 realizes various functions of the wireless device 22 by executing the program codes stored in the storage unit 222. The processing unit 223 performs a process of converting a baseband signal or an intermediate frequency signal into a radio frequency signal, and a process of converting a radio frequency signal into a baseband signal or an intermediate frequency signal. In another example, the control device 21 may perform these processes.

[0037] The wireless communication unit 224 is an element that performs wireless communication with the wireless terminal 10. For example, the wireless communication unit 224 includes an antenna and an RF circuit. The wireless communication unit 224 transmits a radio frequency signal to the wireless terminal 10 during downlink communication, and receives a radio frequency signal from the wireless terminal 10 during uplink communication. The wireless communication unit 224 includes one or more antenna elements. When the wireless communication unit 224 includes multiple antenna elements, the wireless communication unit 224 may have a full digital configuration in which each antenna element is connected to a respective RF circuit, or may have a subarray configuration in which subarrays formed of multiple antenna elements share one RF circuit. When the wireless communication unit 224 has a subarray configuration, each subarray may perform analog beamforming. The baseband side port of the RF circuit is regarded as an equivalent antenna in the baseband domain, and is hereinafter referred to as an antenna.

[0038] [Configuration of the radio signal processing section] 5 shows an example of the configuration of the radio signal processing unit 214 in the control device 21. The radio signal processing unit 214 includes a transmission signal processing unit 310, a reception signal processing unit 320, and a scheduling unit 330. The transmission signal processing unit 310 generates a signal to be transmitted to the radio terminal 10. The transmission signal processing unit 310 transmits the generated signal to the radio device 22 via the transmission path IF 211. When generating a signal to be transmitted to the radio terminal 10, the transmission signal processing unit 310 may digitally combine the signal using a precoding weight. In addition, the transmission signal processing unit 310 may use a partial weight generation method for weight calculation.

[0039] The reception signal processing unit 320 receives a signal received by the wireless device 22 via the transmission path IF 221. When processing the signal received by the wireless device 22, the reception signal processing unit 320 may digitally combine the signal using a post-coding weight. The reception signal processing unit 320 may also use a partial weight generation method for weight calculation. The reception signal processing unit 320 measures channel information between the wireless device 22 and the wireless terminal 10 using a reference signal received via the transmission path IF 221, and transmits the channel information to the scheduling unit 330. The reference signal may be, for example, one or both of a Sounding Reference Signal (SRS) and a Demodulation Reference Signal (DMRS).

[0040] The scheduling unit 330 allocates radio resources used for communication with the wireless terminal 10. In other words, the scheduling unit 330 allocates radio resources to multiple wireless terminals 10. For example, the radio resources may include antennas, beams, frequencies, and time. In addition, when a partial weight generation method is applied, the scheduling unit 330 may determine a subsystem.

[0041] Specifically, the scheduling unit 330 estimates the interference level or degree between the multiple wireless terminals 10 based on the channel information received from the reception signal processing unit 320. The scheduling unit 330 may calculate an index representing the interference level between the multiple wireless terminals 10 based on the channel information received from the reception signal processing unit 320. Hereinafter, these indexes are referred to as interference level indexes. Each of the interference level indexes may be an index representing the level or degree of interference between two wireless terminals 10, that is, a wireless terminal pair. Alternatively, each of the interference level indexes may be an index representing the level or degree of interference between one wireless terminal 10 and a group of wireless terminals. Next, the scheduling unit 330 uses the estimated interference level or the calculated interference level index to determine a wireless terminal subset to which each wireless terminal 10 can belong, and determines whether or not to allocate wireless resources to each wireless terminal 10. Then, the scheduling unit 330 transmits information on the wireless terminal subset to which each wireless terminal 10 can belong and the result of the wireless resource allocation to the transmission signal processing unit 310 and the reception signal processing unit 320.

[0042] <First embodiment> A configuration example of the wireless communication system according to this embodiment is similar to the example described with reference to Figs. 1 to 5. This embodiment provides details of selection of wireless terminals 10 to which the same time and frequency resources are assigned for spatial multiplexing transmission in downlink or uplink. The spatial multiplexing transmission may be downlink transmission or uplink transmission, or both. The spatial multiplexing transmission may also be referred to as spatial multiplexing communication. In this embodiment, the scheduling unit 330 selects a subset of wireless terminals that share or are assigned the same time and frequency resources for spatial multiplexing communication, and determines one or more wireless terminals 10 to be excluded from spatial multiplexing communication in the time and frequency resources.

[0043] FIG. 6 shows an example of a process performed by the scheduling unit 330. In the example of FIG. 6, the "one or more first wireless terminals" are one or more wireless terminals 10 that have already been determined by the scheduling unit 330 to share the same time and frequency resources for spatial multiplexing transmission. It has been determined that the one or more first wireless terminals can belong to one wireless terminal subset, or can be divided into two or more wireless terminal subsets. Each wireless terminal subset includes one or more wireless terminals 10 that perform subset-based spatial multiplexing transmission or MIMO transmission (or MIMO communication) on the downlink or uplink with a corresponding antenna subset of the base station device 20 on the same time and frequency resources. Each wireless terminal subset is a unit in which calculation of precoding or postcoding weights is performed on a subsystem-by-subsystem basis using a partial weight generation method. The precoding or postcoding weights of each wireless terminal subset can be calculated using a common interference cancellation matrix. In other words, a common interference cancellation matrix is ​​applied to the wireless terminal subsets in one subsystem. The interference cancellation matrix refers to the inverse matrix part in the calculation formula of the ZF weights or the MMSE weights.

[0044] On the other hand, in the example of Fig. 6, the "second wireless terminal" is a candidate wireless terminal 10 to be newly added to the "one or more first wireless terminals". That is, the process of Fig. 6 determines whether the new second wireless terminal is permitted to share the same time and frequency resources for spatial multiplexing communication with one or more already determined first wireless terminals. If it is determined that the second wireless terminal can share resources with one or more first wireless terminals, the process of Fig. 6 further determines a wireless terminal subset to which the second wireless terminal can belong.

[0045] In step 601, the scheduling unit 330 estimates an interference level or degree between each of one or more first wireless terminals that have already been determined to share the same time and frequency resources for spatial multiplexing transmission and the second wireless terminal. As already described, the scheduling unit 330 may obtain or calculate one or more interference level indicators representing the degree of interference between the second wireless terminal and one or more first wireless terminals based on channel information received from the reception signal processing unit 320. Each of these interference level indicators may represent the degree of interference between each of the one or more first wireless terminals and the second wireless terminal, that is, the wireless terminal pair. Alternatively, each of these interference level indicators may be an indicator representing the degree of interference between each of a plurality of wireless terminal groups to which one or more wireless terminals belong and the second wireless terminal. More specifically, each of these interference level indicators may represent the degree of interference between each of one or more wireless terminal subsets to which one or more first wireless terminals belong or can belong and the second wireless terminal.

[0046] In step 602, it is estimated that the interference level between the second wireless terminal and each of the one or more first wireless terminals is a first degree. In this case, the scheduling unit 330 determines that the time and frequency resources can be assigned to the second wireless terminal and that the second wireless terminal can belong to any wireless terminal subset. The second wireless terminal may be grouped into any of the one or more wireless terminal subsets to which the one or more first wireless terminals belong or can belong. Alternatively, the second wireless terminal may be assigned to a new wireless terminal subset other than the wireless terminal subset to which the one or more first wireless terminals belong or can belong. This allows the second wireless terminal to share the same time and frequency resources with the one or more wireless terminals estimated to have relatively small interference.

[0047] In step 603, it is estimated that the interference level between the second wireless terminal and at least one of the one or more first wireless terminals is a second degree, which is greater than the first degree and less than the third degree. In this case, the scheduling unit 330 determines that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal estimated to have the second degree of interference with the second wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for spatial multiplexing communication. As a result, the second wireless terminal is grouped into the same wireless terminal subset as the at least one first wireless terminal estimated to have a certain degree of interference, and the intra-subset interference can be reduced using a partial weight generation method.

[0048] In step 604, it is estimated that the interference level between the second wireless terminal and at least one of the one or more first wireless terminals is a third degree greater than the second degree. In this case, the scheduling unit 330 determines that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from spatial multiplexing on the time and frequency resources. This ensures that the second wireless terminal does not share the same time and frequency resources as one or more wireless terminals estimated to have relatively strong interference. More specifically, according to step 604, the second wireless terminal estimated to have large interference with one or more first wireless terminals and therefore not sufficient intra-subset interference elimination by the partial weight generation method can be excluded from spatial multiplexing using the same time and frequency resources as the one or more first wireless terminals.

[0049] The scheduling unit 330 repeats the process of FIG. 6 for multiple second wireless terminals, i.e., wireless terminals for which it has not yet been determined whether the target time and frequency resources can be shared with other wireless terminals (i.e., one or more first wireless terminals).

[0050] According to the operation or process described with reference to Fig. 6, the base station device 20, the control device 21, or the scheduling unit 330 can generate multiple wireless terminal subsets to be used in the partial weight generation method based on the determination results of steps 602 and 603. On the other hand, the base station device 20, the control device 21, or the scheduling unit 330 can exclude wireless terminals for which it is estimated that the removal of intra-subset interference by the partial weight generation method is not sufficient, from spatial multiplexing transmission in the target time and frequency resources, based on the determination result of step 604. This contributes to reducing both inter-subset interference and intra-subset interference when using the partial weight generation method.

[0051] <Second embodiment> A configuration example of a wireless communication system according to this embodiment is similar to the example described with reference to Figures 1 to 5. This embodiment provides details of the selection of wireless terminals 10 that share the same time and frequency resources for spatial multiplexing transmission, described in the first embodiment.

[0052] [Configuration of the scheduling section] 7 shows an example of the configuration of the scheduling unit 330. The scheduling unit 330 includes an index calculation unit 331 and an allocation determination unit 332. The index calculation unit 331 receives channel information between the radio device 22 and the radio terminal 10 from the received signal processing unit 320, and calculates an interference level index between the multiple radio terminals 10 based on the received channel information. The index calculation unit 331 transmits the calculated interference level index to the allocation determination unit 332 or the storage unit 212.

[0053] The allocation determination unit 332 receives one or more interference level indicators from the indicator calculation unit 331 or the storage unit 212. The allocation determination unit 332 includes a condition setting unit 333. The condition setting unit 333 sets a first condition, a second condition, and a third condition related to the interference level indicator. The first condition represents or corresponds to a case where the interference between the two wireless terminals estimated from the interference level indicator is relatively small. The first condition represents or corresponds to a case where the interference between the two wireless terminals estimated from the interference level indicator is relatively small (for example, a first degree). The second condition represents or corresponds to a case where the interference between the two wireless terminals estimated from the interference level indicator is medium (for example, a second degree larger than the first degree). The third condition represents or corresponds to a case where the interference between the two wireless terminals estimated from the interference level indicator is relatively large (for example, a third degree larger than the second degree).

[0054] The allocation determination unit 332 determines whether each wireless terminal 10 can share the same time and frequency resources with other wireless terminals 10 for spatial multiplexing transmission based on the received one or more interference level indicators and the set first, second, and third conditions. Furthermore, the allocation determination unit 332 determines a wireless terminal subset to which each wireless terminal 10 permitted to share the wireless resources belongs or can belong.

[0055] Specifically, if the interference level indicator between two wireless terminals satisfies a first condition, the assignment determination unit 332 determines that the partial weight generation method is not necessary to remove the interference between these two wireless terminals. In other words, the assignment determination unit 332 allows these two wireless terminals to belong to different wireless terminal subsets. This operation corresponds to step 602 in FIG. 6.

[0056] If the interference level indicator between the two wireless terminals satisfies the second condition, the assignment determination unit 332 determines that a partial weight generation method is necessary to eliminate the interference between these two wireless terminals. In other words, the assignment determination unit 332 determines that these two wireless terminals need to belong to the same wireless terminal subset. This operation corresponds to step 603 in FIG. 6.

[0057] On the other hand, if the interference level indicator between the two wireless terminals satisfies the third condition, the assignment determination unit 332 determines that the interference between these two wireless terminals is not sufficiently eliminated by the partial weight generation method. In other words, the assignment determination unit 332 determines that these two wireless terminals are not allowed to share the same time and frequency resources. This operation corresponds to step 604 in FIG. 6.

[0058] [Example of interference level indicator] 8 conceptually illustrates an example of an interference level index calculated in the index calculation unit 331. As a first example, the interference level index may be a channel spatial correlation of each wireless terminal 10, which can be calculated from a channel coefficient or a channel power between each wireless terminal 10 and multiple antennas of one or more wireless devices 22. The index calculation unit 331 calculates an interference level index r based on the spatial correlation between two wireless terminals #i and #j. i,j may be calculated using the following formula, which corresponds to the case where channel coefficients between each wireless terminal 10 and multiple antennas of one or more wireless devices 22 are used:

number

[0059] If the channel power is used instead of the channel coefficients to determine the interference level indicator, the channel vector h i and h j Each element of the above formula may be replaced with a channel power. The channel power may be a squared value of a channel coefficient estimated from an SRS or a DMRS. Alternatively, the channel power may be calculated using a received power of a downlink reference signal (e.g., Reference Signal Received Power (RSRP)) reported from a wireless terminal.

[0060] When the wireless terminal 10 has multiple antennas, the index calculation unit 331 may calculate the interference level index in the following manner. In one example, the index calculation unit 331 may calculate the interference level index using a channel vector or a channel power vector between one antenna arbitrarily selected from the multiple antennas of the wireless terminal 10 and each of the multiple antennas of some or all of the one or more wireless devices 22 connected to the control device 21.

[0061] In another example, the index calculation unit 331 may use a channel vector or a channel power vector that is a concatenation of channel vectors or channel power vectors between each of multiple antennas possessed by some or all of one or more radio devices 22 and each of some or all of the multiple antennas of the wireless terminal 10.

[0062] In another example, the index calculation unit 331 may calculate channel power vectors between each of multiple antennas possessed by some or all of one or more wireless devices 22 and each of some or all of multiple antennas of the wireless terminal 10, and calculate the interference level index using the sum or average of these channel power vectors.

[0063] In another example, the index calculation unit 331 may use an equivalent channel vector or an equivalent channel power vector between the wireless terminal 10 and multiple antennas possessed by some or all of one or more wireless devices 22 when signals transmitted or received by some or all of the multiple antennas of the wireless terminal 10 are combined with a specific weight.

[0064] [Example of the operation of the index calculation unit] An operation example of the index calculation unit 331 will be described with respect to the case where the interference level index is the above-mentioned first example. The index calculation unit 331 calculates the interference level index for all possible pairs from some or all of the multiple wireless terminals 10. All of the multiple wireless terminals 10 may be all wireless terminals 10 located within the service area of ​​the base station device 20. Some of the multiple wireless terminals 10 may be one or more wireless terminals 10 located within the service area of ​​the base station device 20 and waiting for allocation of wireless resources. FIGS. 9A and 9B are conceptual diagrams showing an operation example of the index calculation unit 331. FIG. 9A shows an example of calculating 12 types of interference level indexes for four wireless terminals #1 to #4. In the example of FIG. 9B, the index calculation unit 331 calculates the interference level index r between the wireless terminal #1 and each of the wireless terminals #2 to #4. 1,2 , r 1,3 , and r 1,4 Calculate.

[0065] The index calculation unit 331 may calculate an interference level index every time the allocation determination unit 332 determines whether or not to allocate radio resources to each wireless terminal 10 and a wireless terminal subset to which each wireless terminal 10 can belong. Alternatively, the interference level index calculated by the index calculation unit 331 may be reused in multiple determinations in the allocation determination unit 332.

[0066] [Example of condition setting section operation] An operation example of the condition setting unit 333 will be described with respect to the case where the interference level indicator is the above-mentioned first example. Fig. 10 is a conceptual diagram showing an operation example of the condition setting unit 333. The condition setting unit 333 determines the first, second, and third conditions as described above. In the example of Fig. 10, the interference level indicator r i,j Similarly, a first threshold value for the interference level indicator r is used to define the boundary between the second and third conditions. i,j A second threshold for the interference level index r is used. i,j Depending on the nature or definition of the interference level indicator r, the magnitude relationship between the first and second thresholds may be reversed. i,j If is defined as an index that increases with an increase in interference (e.g., proportional to the interference level), the magnitude relationship between the first and second thresholds is as shown in the example of FIG. 10. In contrast, the interference level index r i,j If is defined as an index that decreases as interference increases (eg, inversely proportional to the interference level), the magnitude relationship between the first and second thresholds becomes the opposite of that in FIG.

[0067] Interference level indicator r between wireless terminal #i and wireless terminal #j i,j If the value of is less than the first threshold, the condition setting unit 333 (or the allocation determination unit 332) determines that the interference level between the wireless terminal #i and the wireless terminal #j satisfies the first condition. In other words, the condition setting unit 333 (or the allocation determination unit 332) estimates that the interference level between the wireless terminal #i and the wireless terminal #j is of the first degree.

[0068] Interference level indicator r between wireless terminal #i and wireless terminal #j i,j If the value of is greater than the first threshold and less than the second threshold, the condition setting unit 333 (or the allocation determination unit 332) determines that the interference level between the wireless terminal #i and the wireless terminal #j satisfies the second condition. In other words, the condition setting unit 333 (or the allocation determination unit 332) estimates that the interference level between the wireless terminal #i and the wireless terminal #j is of the second degree.

[0069] Interference level indicator r between wireless terminal #i and wireless terminal #j i,j If the value of exceeds the second threshold, the condition setting unit 333 (or the allocation determination unit 332) determines that the interference level between the wireless terminal #i and the wireless terminal #j satisfies the third condition. In other words, the condition setting unit 333 (or the allocation determination unit 332) estimates that the interference level between the wireless terminal #i and the wireless terminal #j is of the third degree.

[0070] The definitions of the first, second, and third conditions described with reference to FIG. 10 are merely examples, and are not limited thereto. For example, the first, second, and third conditions can be defined using one threshold (e.g., zero) and one scaling or offset parameter. In this case, the condition setting unit 333 (or the allocation determination unit 332) determines the interference level indicator r i,j The first condition can be determined based on whether the interference level indicator r i,j The value of may be adjusted using a scaling or offset parameter, and the fulfillment of the second or third condition may be determined based on whether the adjusted value exceeds the same threshold (eg, zero).

[0071] [Example of operation of the allocation decision unit] 11A, 11B, and 11C show an example of processing performed by the allocation determination unit 332 to determine multiple wireless terminals 10 to which the same radio resources for spatial multiplexing transmission, i.e., time and frequency resources, are assigned. In step 1101, one or more interference level indicators indicating the degree of interference between wireless terminals are obtained. In step 1102, the allocation determination unit 332 sets first, second, and third conditions in the condition setting unit 333.

[0072] In step 1103, the allocation determination unit 332 selects one allocation target wireless terminal (i.e., a second wireless terminal) from among the allocation candidate wireless terminals of the wireless resource. The allocation determination unit 332 may randomly select one of the multiple allocation candidate wireless terminals. Alternatively, the allocation determination unit 332 may select the allocation target wireless terminal based on a specific metric calculated from channel information and resource allocation status of each allocation candidate wireless terminal. The allocation determination unit 332 may select the allocation target wireless terminal based on a known scheduling metric.

[0073] In step 1104, the allocation determination unit 332 arbitrarily selects one wireless terminal as a comparison target wireless terminal from among one or more wireless terminals (i.e., one or more first wireless terminals) that have already been determined to be able to allocate wireless resources in previous processing (Figures 11A to 11C).

[0074] In step 1105, the allocation determination unit 332 checks whether the interference level indicator between the allocation target wireless terminal and the comparison target wireless terminal satisfies the first, second, or third condition. If the interference level indicator satisfies the first condition (left branch in step 1105), the allocation determination unit 332 does not place any restriction on the wireless terminal subset to which the allocation target wireless terminal belongs or can belong (step 1106). If the interference level indicator satisfies the second condition (center branch in step 1105), the allocation determination unit 332 determines that the allocation target wireless terminal can belong only to the same wireless terminal subset as the comparison target wireless terminal (step 1107). If the interference level indicator satisfies the third condition (right branch in 1105), the allocation determination unit 332 determines that the allocation target wireless terminal cannot belong to any wireless terminal subset, and does not allocate the wireless resource to the allocation target wireless terminal.

[0075] If the interference level indicator satisfies the first or second condition, the allocation determination unit 332 proceeds to step 1108. In step 1108, the allocation determination unit 332 checks whether the selected wireless terminal to be compared is the last wireless terminal to be compared. If this is not the last wireless terminal to be compared (No in step 1108), the allocation determination unit 332 returns to step 1104 to select the next wireless terminal to be compared. On the other hand, if this is the last wireless terminal to be compared (Yes in step 1108), in step 1109, the allocation determination unit 332 checks whether there is a wireless terminal subset to which the allocation target wireless terminal can belong. The allocation determination unit 332 may perform the check or determination in step 1109 as follows.

[0076] In one example, the interference level indicators between the assignment target wireless terminal and all the comparison target wireless terminals satisfy a first condition. In this case, the assignment determination unit 332 determines that the assignment target wireless terminal can belong to any wireless terminal subset, and therefore there is a wireless terminal subset to which the assignment target wireless terminal can belong.

[0077] In another example, an interference level indicator between the allocation target wireless terminal and at least one comparison target wireless terminal satisfies a second condition, and an interference level indicator between the allocation target wireless terminal and the remaining comparison target wireless terminals satisfies a first condition. In this case, the allocation determination unit 332 determines that the allocation target wireless terminal can belong to the same wireless terminal subset as the comparison target wireless terminal that satisfies the second condition, and therefore there is a wireless terminal subset to which the allocation target wireless terminal can belong.

[0078] In yet another example, a plurality of interference level indicators between the allocation target wireless terminal and each of a plurality of comparison target wireless terminals satisfy the second condition, and an interference level indicator between the remaining comparison target wireless terminals satisfies the first condition. In this case, if all of the plurality of comparison target wireless terminals that meet the second condition can belong to the same wireless terminal subset, the allocation determination unit 332 determines that the allocation target wireless terminal can belong to the same wireless terminal subset as all of the wireless terminals that meet the second condition, and therefore a wireless terminal subset to which the allocation target wireless terminal can belong exists. Otherwise, that is, if the allocation target wireless terminal and all of the wireless terminals that meet the second condition cannot belong to the same wireless terminal subset, the allocation determination unit 332 determines that there is no wireless terminal to which the allocation target wireless terminal can belong, and excludes the allocation target wireless terminal from spatial multiplexing transmission in the wireless resource.

[0079] If there is a wireless terminal subset to which the allocation target wireless terminal can belong (Yes in step 1109), the allocation determination unit 332 proceeds to step 1110. In step 1110, the allocation determination unit 332 determines one or more wireless terminal subsets to which the allocation target wireless terminal can belong, and determines the allocation of the wireless resources to the allocation target wireless terminal.

[0080] In step 1111, the allocation determination unit 332 determines whether or not a termination condition is satisfied. For example, the termination condition may be that the number of assignment target wireless terminals for which determination has been completed reaches a predetermined number, or that determination has been completed for all assignment candidate wireless terminals. If the termination condition is satisfied (Yes in step 1111), the allocation determination unit 332 terminates the process. If the termination condition is not satisfied (No in step 1111), the allocation determination unit 332 returns to step 1103 to make a determination on the next assignment target wireless terminal.

[0081] 11A, 11B, and 11C, the assignment determination unit 332 identifies a wireless terminal subset to which the assignment target wireless terminal can belong, but does not determine the wireless terminal subset to which the assignment target wireless terminal actually belongs. After the processes of FIG. 11A, 11B, and 11C, the assignment determination unit 332 or the scheduling unit 330 may determine the wireless terminal subset to which the assignment target wireless terminal belongs.

[0082] 11A, 11B, and 11C, the subset to which the assignment target wireless terminal belongs has already been determined and cannot be changed. In this case, if one or more wireless terminal subsets to which the assignment target wireless terminal can belong determined in step 1110 include the already determined wireless terminal subset, the assignment determination unit 332 or the scheduling unit 330 may determine the assignment of the wireless resource to the assignment target wireless terminal. Otherwise, the assignment determination unit 332 or the scheduling unit 330 may exclude the assignment target wireless terminal from spatial multiplexing transmission in the wireless resource.

[0083] According to the operation or processing described in this embodiment, the base station device 20, the control device 21, or the scheduling unit 330 can generate multiple wireless terminal subsets to be used in the partial weight generation method from multiple wireless terminals that satisfy the first or second condition. On the other hand, the base station device 20, the control device 21, or the scheduling unit 330 can exclude wireless terminals that satisfy the third condition, that is, wireless terminals for which it is estimated that the removal of intra-subset interference by the partial weight generation method is not sufficient, from spatial multiplexing transmission in the target time and frequency resource. This contributes to reducing both inter-subset interference and intra-subset interference when using the partial weight generation method.

[0084] Furthermore, by appropriately setting the first, second, and third conditions (e.g., the first and second thresholds) in the condition setting unit 333, the base station device 20, the control device 21, or the scheduling unit 330 can suppress intra-subset interference and inter-subset interference to different degrees, respectively. This contributes to achieving an optimal trade-off between interference suppression and spatial multiplexing rate.

[0085] <Third embodiment> A configuration example of the wireless communication system according to this embodiment is similar to the example described with reference to Figures 1 to 5 and 7. This embodiment provides a specific example or a modified example of the interference level indicator described in the first and second embodiments.

[0086] The interference level index calculated in the index calculation unit 331 may be a second example shown below. The index calculation unit 331 may calculate the interference level index as a ratio (difference in the case of a decibel scale) between a channel power in a main connection link of a wireless terminal and a channel power in an interference link of another wireless terminal that causes interference to the wireless terminal.

[0087] The main connection link is a link between an antenna or beam of the base station device 20 that is mainly used when the wireless terminal communicates with the wireless terminal. The mainly used antenna or beam may be a part or all of the antennas or beams used when actually communicating with the wireless terminal. For example, the main connection link may be a link between the wireless terminal and an antenna or beam of one wireless device 22 that gives the maximum channel power among the multiple wireless devices 22 for the wireless terminal of interest. In another example, the main connection link may be a link between the wireless terminal and antennas or beams of the multiple wireless devices 22 selected by an arbitrary criterion.

[0088] An interference link is a link of another wireless terminal that causes interference to the communication of the wireless terminal under consideration. For example, in the case of an uplink, the channel power of the interference link may be the channel power of the uplink signal of the other wireless terminal received by the antenna or beam of the main connection link of the wireless terminal under consideration. In the case of a downlink, the channel power of the interference link may be the channel power of the downlink signal of the other wireless terminal transmitted from the main connection antenna or beam of the other wireless terminal received by the wireless terminal under consideration.

[0089] The channel power may be a squared value of a channel coefficient estimated from the SRS, the DMRS, etc. Alternatively, the channel power may be calculated using the received power of a downlink reference signal (e.g., RSRP) reported from the wireless terminal.

[0090] The index calculation unit 331 calculates an interference level index r between the wireless terminal #i and the wireless terminal #j. i,j is calculated according to the following formula:

number

[0091] This modification can reduce the amount of calculation required for calculating the interference level indicator, compared with the case where the interference level indicator is calculated based on the inner product of the channel vector or the channel power vector between the wireless terminal and the wireless device. In addition, this modification requires only the channel power of the wireless terminal's main connection link and the channel power of the interference link from another wireless terminal to the wireless terminal to calculate the interference level indicator. Therefore, this makes it easier to obtain channel information, compared with the case where the interference level indicator is calculated based on the inner product of the channel vector or the channel power vector between the wireless terminal and the wireless device.

[0092] <Fourth embodiment> A configuration example of the wireless communication system according to this embodiment is similar to the example described with reference to Figures 1 to 5 and 7. This embodiment provides a specific example or a modified example of the interference level indicator described in the first and second embodiments.

[0093] The interference level index calculated in the index calculation unit 331 may be a third example shown below. The index calculation unit 331 obtains the product (sum in the case of a decibel scale) of the maximum interference to noise power ratio (INR) caused by the assignment target wireless terminal to one or more wireless terminals determined to be assigned wireless resources and the maximum interference to noise power ratio caused by one or more wireless terminals determined to be assigned wireless resources to the assignment target wireless terminal. Then, the index calculation unit 331 calculates the interference level index by subtracting the product (sum in the case of a decibel scale) of the maximum given INR and the maximum received INR from the signal to noise power ratio (SNR) of the channel in the main connection link of the assignment target wireless terminal.

[0094] The index calculation unit 331 calculates an interference level index r between the assignment target wireless terminal #i and the comparison target wireless terminal #j. i,j is calculated according to the following formula:

number

[0095] In this modification, the amount of calculation required for calculating the interference level index can be reduced compared to the case where the interference level index is calculated based on the inner product of the channel vector or the channel power vector between the wireless terminal and the wireless device. In addition, in this modification, the interference-to-noise power ratio that the assignment target wireless terminal gives to the comparison target wireless terminal and the interference-to-noise power ratio that the comparison target wireless terminal causes to the assignment target wireless terminal can be considered at the same time.

[0096] <Fifth embodiment> A configuration example of the wireless communication system according to this embodiment is similar to the example described with reference to Figures 1 to 5 and 7. This embodiment provides a specific example or a modified example of the interference level indicator described in the first and second embodiments.

[0097] As already explained, the index calculation unit 331 may calculate an interference level index that indicates the degree of interference between a wireless terminal and a group of wireless terminals. Fig. 14 is a conceptual diagram of the calculation of an interference level index in this modification. In the example of Fig. 14, the index calculation unit 331 calculates the interference level index r between the wireless terminal #6 and each of the wireless terminal subsets #1, #2, and #3. 6,1 , r 6,2 , and r 6,3 For example, the index calculation unit 331 calculates the interference level index r 6,1 is calculated according to the following formula:

number

[0098] The index calculation unit 331 may calculate the interference level index between the wireless terminal and the wireless terminal subset as an interference level index based on a Treating Interference as Noise (TIN) condition. 6,1 may be calculated according to the following formula:

number

[0099] Sixth embodiment A configuration example of a wireless communication system according to this embodiment is similar to the example described with reference to Fig. 1 to Fig. 5 and Fig. 7. This embodiment provides a specific example of a method for determining or adjusting the boundary between the first and second degrees of interference level and the boundary between the second and third degrees of interference level, described in the first embodiment. Alternatively, this embodiment provides a specific example of a method for setting or adjusting the first, second, and third conditions related to the interference level index, described in the second embodiment.

[0100] The scheduling unit 330 may set a first boundary between the first and second degrees of interference levels and a second boundary between the second and third degrees of interference levels based on an interference level index representing the degree of interference between wireless terminals. Similarly, the condition setting unit 333 may dynamically set the first, second, and third conditions based on the interference level index. For example, consider a case where the first, second, and third conditions are determined or defined by first and second thresholds for the interference level index as shown in FIG. 10. In this case, the condition setting unit 333 may determine the first and second thresholds using an average value of the interference level index between multiple wireless terminals and first and second scaling parameters. In this modification, the condition setting unit 333 may calculate the first threshold Th1 and the second threshold Th2 by the following formula:

number

number

[0101] The average value of the interference level index between a plurality of wireless terminals may be, for example, an average of interference level indexes of possible wireless terminal pairs of all wireless terminals located within the service area of ​​the base station device 20. As another example, the average value of the interference level index between a plurality of wireless terminals may be an average of interference level indexes between one or more wireless terminals located within the service area of ​​the base station device 20 and waiting for allocation of wireless resources and each of the other wireless terminals.

[0102] In this modification, the first, second, and third degrees of the interference level or the first, second, and third conditions related to the interference level index can be determined or adjusted in accordance with the state of the communication path between the radio device 22 and the radio terminal 10. This makes it possible to appropriately set conditions for determining multiple radio terminals 10 to which the same time and frequency resources are assigned and for determining a radio terminal subset, following fluctuations in the communication path due to fluctuations in the positions and number of radio terminals communicating with the base station device 20.

[0103] Seventh embodiment A configuration example of a wireless communication system according to this embodiment is similar to the example described with reference to Fig. 1 to Fig. 5 and Fig. 7. This embodiment provides a specific example of a method for determining or adjusting the boundary between the first and second degrees of interference level and the boundary between the second and third degrees of interference level, described in the first embodiment. Alternatively, this embodiment provides a specific example of a method for setting or adjusting the first, second, and third conditions related to the interference level index, described in the second embodiment.

[0104] The scheduling unit 330 may change or adjust one or both of the first boundary between the first degree and the second degree of the interference level and the second boundary between the second degree and the third degree of the interference level according to the total number of wireless terminals determined to be able to belong to any wireless terminal subset for spatial multiplexing. For example, if the total number of wireless terminals determined to be able to belong to any wireless terminal subset for spatial multiplexing falls below a reference value, the scheduling unit 330 may update one or both of the first boundary value and the second boundary value to be larger than the current value. In other words, the scheduling unit 330 may adjust one or both of the first boundary value and the second boundary value so that more wireless terminals can share the same time and frequency resources.

[0105] After this update, the scheduling unit 330 may redo the process of determining whether or not to allocate radio resources to each wireless terminal 10 and the process of determining the wireless terminal subset to which each wireless terminal 10 can belong (for example, the process in FIG. 6). The scheduling unit 330 may gradually change or adjust one or both of the first and second boundaries until the total number of wireless terminals determined to be able to belong to any wireless terminal subset for spatial multiplexing transmission exceeds a reference value.

[0106] Similarly, the condition setting unit 333 may change or adjust at least one of the first, second, and third conditions according to the number of wireless terminals determined to be able to belong to a plurality of wireless terminal subsets for spatial multiplexing. For example, consider a case where the first, second, and third conditions are determined or defined by first and second thresholds for the interference level indicator as shown in FIG. 10. In this case, if the total number of wireless terminals determined to be able to belong to any wireless terminal subset for spatial multiplexing falls below a reference value, the condition setting unit 333 may update one or both of the first threshold and the second threshold to be larger than the current value. Note that, if the interference level indicator is defined as an indicator that decreases with an increase in interference (e.g., inversely proportional to the interference level), the condition setting unit 333 may update one or both of the first threshold and the second threshold to be smaller than the current value. The condition setting unit 333 may gradually change or adjust one or both of the first and second thresholds until the total number of wireless terminals determined to be able to belong to any of the wireless terminal subsets for spatial multiplexing transmission exceeds a reference value.

[0107] Fig. 15 shows an example of processing in the scheduling unit 330. In step 1501, the condition setting unit 333 sets or resets at least one of the first, second, and third conditions. In step 1502, the allocation determination unit 332 performs processing to determine whether or not radio resources can be allocated to each wireless terminal 10 and to which wireless terminal subset each wireless terminal 10 can belong. This processing may be similar to the example described with reference to Fig. 6 or the examples described with reference to Figs. 11A to 11C, for example.

[0108] In step 1503, the allocation determination unit 332 determines whether the radio resource efficiency exceeds a reference value. In other words, the allocation determination unit 332 determines whether the total number of radio terminals determined to be able to belong to any of the radio terminal subsets for spatial multiplexing transmission exceeds a reference value. If the radio resource efficiency exceeds the reference value (Yes in step 1503), the allocation determination unit 332 ends the process. If the radio resource efficiency is below the reference value (No in step 1503), the allocation determination unit 332 returns to step 1401. The condition setting unit 333 resets at least one of the first, second, and third conditions to be relaxed so that more radio terminals can share the same time and frequency resources to perform spatial multiplexing transmission.

[0109] In the specific example described in this embodiment, the scheduler 330 can adjust the first, second, and third degrees of the interference level or the first, second, and third conditions related to the interference level indicator so that the radio resource efficiency exceeds the reference value. This contributes to preventing the radio resource efficiency from being excessively reduced. In other words, this can contribute to achieving radio resource allocation that exceeds the target radio resource efficiency while reducing intra-subset and inter-subset interference.

[0110] <Eighth embodiment> An example of the configuration of the wireless communication system according to this embodiment is similar to the example described with reference to FIGS. 1 to 5 and 7.

[0111] The process performed by the scheduling unit 330 or the allocation determination unit 332 in the above-described embodiment, specifically, a part or all of the process of determining whether or not to allocate radio resources to each wireless terminal 10 and the wireless terminal subset to which each wireless terminal 10 can belong, may be performed by inference using a trained Machine Learning (ML) model. Training of the ML model may be performed by the control device 21 or by other network elements, for example, Near-RT RIC or Non-RT RIC. The control device 21, the scheduling unit 330, or the allocation determination unit 332 may operate as an ML model inference host, and other network elements such as Near-RT RIC or Non-RT RIC may operate as an ML model training host.

[0112] In one implementation, the control device 21, the scheduling unit 330, or the allocation determination unit 332 may use identifiers of multiple wireless terminals 10 and interference level indicators between multiple wireless terminals 10 as input data to a trained ML model. The trained ML model may output, as an inference result, identifiers of wireless terminals 10 that are assigned to the same time and frequency resources and a grouping of these identifiers into one or more wireless terminal subsets. The inference result by the trained ML model may be similar to the results of steps 602, 603, and 604 in FIG. 6. In other words, the ML model may be trained to be able to output inference results similar to the results of steps 602, 603, and 604 in FIG. 6.

[0113] <Ninth embodiment> A configuration example of the wireless communication system according to this embodiment is similar to the example described with reference to Figs. 1 to 5 and 7. The processing of the scheduling unit 330 described in the above embodiment may be realized by the processing unit 213 of the control device 21 executing one or more programs. The program includes a set of instructions (or software code) for causing the computer to perform one or more functions of the wireless terminal 10 when the program is loaded into the computer. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium may include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray (registered trademark) disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, the transitory computer-readable medium or communication medium may include electrical, optical, acoustic, or other forms of propagated signals.

[0114] The above-described embodiment is merely an example of the application of the technical idea obtained by the inventor of the present invention. In other words, the technical idea is not limited to the above-described embodiment, and various modifications are possible.

[0115] For example, some or all of the above embodiments may be described as, but are not limited to, the following appendices. Some or all of the elements (e.g., configurations and functions) described in appendices directed to devices (e.g., control devices) may naturally be described as appendices directed to methods and programs. For example, some or all of the elements described in appendices 2-13 dependent on appendices 1 may also be described as appendices dependent on appendices 14 and 15 due to the same dependency relationship as appendices 2-13. Some or all of the elements described in any appendice may be applied to various hardware, software, recording means for recording software, systems, and methods.

[0116] (Appendix 1) A means for determining a subset of a plurality of wireless terminals that perform spatial multiplexing transmission using the same time and frequency resources as a base station device having a plurality of antennas, each wireless terminal subset includes one or more wireless terminals that perform subset-based multiple-input multiple-output (MIMO) transmission on the time and frequency resources between a corresponding base station antenna subset selected from the plurality of antennas; The determining means includes: determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset if an interference level between the second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing transmission; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree, determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from the spatial multiplexing on the time and frequency resources; It is adapted to Control device. (Appendix 2) and a means for adjusting one or both of a first boundary between the first degree and the second degree and a second boundary between the second degree and the third degree according to a number of wireless terminals determined to be able to belong to the plurality of wireless terminal subsets for the spatial multiplexing transmission. 2. The control device according to claim 1. (Appendix 3) said adjusting means being adapted to increase said first boundary value or said second boundary value, or both, compared to a current value if said number of wireless terminals falls below a reference value. 3. The control device according to claim 2. (Appendix 4) the determining means is adapted to determine whether the interference level is estimated to be of the first, second or third degree based on an indicator representing a degree of interference between each of the one or more first wireless terminals and the second wireless terminal; 4. The control device according to claim 1, wherein the control device is a (Appendix 5) and means for setting a first boundary between the first degree and the second degree and a second boundary between the second degree and the third degree based on the index. 5. The control device according to claim 4. (Appendix 6) the determining means is adapted to calculate an indicator representing a degree of interference between the second wireless terminal and each of one or more wireless terminal subsets to which the one or more first wireless terminals belong or can belong, and to determine whether the interference level is estimated to be of the first, second or third degree based on the indicator; 4. The control device according to claim 1, wherein the control device is a (Appendix 7) The method further includes setting a first boundary between the first degree and the second degree and a second boundary between the second degree and the third degree based on the index. 7. The control device according to claim 6. (Appendix 8) and calculating the indicator based on channel information between each first wireless terminal and some or all of the plurality of antennas, and channel information between the second wireless terminal and some or all of the plurality of antennas. 6. The control device according to claim 4 or 5. (Appendix 9) The method further includes: calculating the index based on an inner product of a channel vector or a channel power vector between each first wireless terminal and some or all of the plurality of antennas and a channel vector or a channel power vector between the second wireless terminal and some or all of the plurality of antennas; 6. The control device according to claim 4 or 5. (Appendix 10) The method further includes: calculating the index based on a difference or ratio between the received power of the second wireless terminal and the received power of each of the first wireless terminals; 6. The control device according to claim 4 or 5. (Appendix 11) The method further comprises: calculating means for calculating the index based on a value obtained by subtracting a product of a maximum interference-to-noise power ratio caused by the second wireless terminal to each first wireless terminal and a received interference-to-noise power ratio caused by each first wireless terminal to the second wireless terminal from a signal-to-noise power ratio of the second wireless terminal; 6. The control device according to claim 4 or 5. (Appendix 12) and means for computing precoding or postcoding weights for each of the plurality of subsets of wireless terminals using a partial weight generation method. 12. The control device according to any one of claims 1 to 11. (Appendix 13) means for calculating precoding or postcoding weights for each of the plurality of wireless terminal subsets using an interference cancellation matrix for each wireless terminal subset; 12. The control device according to any one of claims 1 to 11. (Appendix 14) said adjusting means being adapted to increase the value of said first boundary by increasing a threshold for an indicator defined to increase in response to an increase in interference between each of said one or more first wireless terminals and said second wireless terminal; 4. The control device according to claim 3. (Appendix 15) said adjusting means being adapted to increase the value of said first boundary by decreasing a threshold for an indicator defined to decrease in response to an increase in interference between each of said one or more first wireless terminals and said second wireless terminal; 4. The control device according to claim 3. (Appendix 16) determining a subset of a plurality of wireless terminals that perform spatial multiplexing transmission using the same time and frequency resources as a base station device having a plurality of antennas; each wireless terminal subset includes one or more wireless terminals that perform subset-based multiple-input multiple-output (MIMO) transmission on the time and frequency resources between a corresponding base station antenna subset selected from the plurality of antennas; The determining step comprises: determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset if an interference level between the second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing transmission; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree, determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from the spatial multiplexing on the time and frequency resources; Prepare for this. A method performed by a control device. (Appendix 17) A program for causing a computer to carry out a method, The method includes determining a subset of multiple wireless terminals that perform spatial multiplexing transmission in the same time and frequency resources as a base station device having multiple antennas; each wireless terminal subset includes one or more wireless terminals that perform subset-based multiple-input multiple-output (MIMO) transmission on the time and frequency resources between a corresponding base station antenna subset selected from the plurality of antennas; The determining step comprises: determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset if an interference level between the second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing transmission; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree, determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from the spatial multiplexing on the time and frequency resources; Prepare for this. program. [Explanation of symbols]

[0117] 10 Wireless terminals 20 Base station equipment 21 Control device 22 Radio equipment 23 Transmission Line 101 Wireless Communication Department 102 Storage section 103 Processing section 211 Transmission IF 212 Storage section 213 Processing section 214 Radio signal processing unit 221 Transmission IF 222 Storage section 223 Processing section 224 Wireless Communication Department 310 Transmission signal processing section 320 Receiving signal processing section 330 Scheduling Department 331 Indicator calculation section 332 Allocation Judgment Unit 333 Condition Setting Section

Claims

1. A means for determining a subset of a plurality of wireless terminals that perform spatial multiplexing transmission using the same time and frequency resources as a base station device having a plurality of antennas, each wireless terminal subset includes one or more wireless terminals that perform subset-based multiple-input multiple-output (MIMO) transmission on the time and frequency resources between a corresponding base station antenna subset selected from the plurality of antennas; The determining means includes: determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset if an interference level between the second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing transmission; determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from the spatial multiplexing on the time and frequency resources if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree; It is adapted to Control device.

2. and adjusting one or both of a first boundary between the first degree and the second degree and a second boundary between the second degree and the third degree according to a number of wireless terminals determined to be able to belong to the plurality of wireless terminal subsets for the spatial multiplexing transmission. The control device according to claim 1 .

3. said adjusting means being adapted to increase said first boundary value or said second boundary value, or both, compared to a current value if the number of said wireless terminals falls below a reference value. The control device according to claim 2.

4. the determining means is adapted to determine whether the interference level is estimated to be of the first, second or third degree based on an indicator representing a degree of interference between each of the one or more first wireless terminals and the second wireless terminal; The control device according to any one of claims 1 to 3.

5. and means for setting a first boundary between the first degree and the second degree and a second boundary between the second degree and the third degree based on the index. The control device according to claim 4.

6. the determining means is adapted to calculate an indicator representing a degree of interference between the second wireless terminal and each of one or more wireless terminal subsets to which the one or more first wireless terminals belong or can belong, and to determine whether the interference level is estimated to be of the first, second or third degree based on the indicator; The control device according to any one of claims 1 to 3.

7. and means for setting a first boundary between the first degree and the second degree and a second boundary between the second degree and the third degree based on the index. The control device according to claim 6.

8. and means for calculating the index based on channel information between each first wireless terminal and some or all of the plurality of antennas, and channel information between the second wireless terminal and some or all of the plurality of antennas. The control device according to claim 4.

9. determining a subset of a plurality of wireless terminals that perform spatial multiplexing transmission using the same time and frequency resources as a base station device having a plurality of antennas; each wireless terminal subset includes one or more wireless terminals that perform subset-based multiple-input multiple-output (MIMO) transmission on the time and frequency resources between a corresponding base station antenna subset selected from the plurality of antennas; The determining step comprises: determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset if an interference level between the second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing transmission; determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from the spatial multiplexing on the time and frequency resources if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree; Prepare for this. A method performed by a control device.

10. A program for causing a computer to carry out a method, The method includes determining a subset of multiple wireless terminals that perform spatial multiplexing transmission in the same time and frequency resources as a base station device having multiple antennas; each wireless terminal subset includes one or more wireless terminals that perform subset-based multiple-input multiple-output (MIMO) transmission on the time and frequency resources between a corresponding base station antenna subset selected from the plurality of antennas; The determining step comprises: determining that the second wireless terminal can be assigned the time and frequency resources and that the second wireless terminal can belong to any wireless terminal subset if an interference level between the second wireless terminal and each of one or more first wireless terminals that have already been determined to share the time and frequency resources for the spatial multiplexing transmission is estimated to be a first degree; if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a second degree greater than the first degree and less than a third degree, determining that the second wireless terminal needs to belong to the same wireless terminal subset as the at least one first wireless terminal in order to allocate the time and frequency resources to the second wireless terminal for the spatial multiplexing transmission; determining that the second wireless terminal is not permitted to belong to any wireless terminal subset and is excluded from the spatial multiplexing on the time and frequency resources if an interference level between the second wireless terminal and at least one of the one or more first wireless terminals is estimated to be a third degree greater than the first degree and the second degree; Prepare for this. program.

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