Control device, control method, and program for improving communication efficiency of cell-free massive MIMO system composed of multiple antennas

Abstract

To improve communication efficiency in a cell-free massive MIMO system including a plurality of processing devices connected to one or more antennas.SOLUTION: A control device functioning as a RAN Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN) identifies a plurality of antennas expected to receive a signal with a predetermined power level or more based on the location where a terminal device is present when the signal is transmitted from the terminal device. Among O-RAN Distributed Units (O-DUs) connected to the plurality of antennas, the control device provides notification about setting information related to a pilot symbol transmitted by the terminal device to a first O-DU performing communication processing for the terminal device and to a second O-DU performing communication processing for other terminal devices subject to interference from the signal transmitted by the terminal device.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for improving communication efficiency in a cell-free massive MIMO system composed of a large number of antennas.

Background Art

[0002] A cell-free massive MIMO system in which a large number of antennas are arranged at high density and communication is performed with a terminal device using a part of the large number of antennas has been studied. In this cell-free massive MIMO system, by selecting the antennas used for each terminal device, a virtual cell is configured for each terminal device, and the terminal device generally exists at the center of its virtual cell. According to such a technique, the terminal device can obtain uniform communication quality regardless of its position.

[0003] In such a cell-free massive MIMO system, a processing device connected to the antennas forms a virtual cell for each terminal device by controlling those antennas. In such a system, since the number of antennas and terminal devices is extremely large, it is not easy to perform such control by a single processing device. For this reason, a plurality of processing devices each performing control of a part of the antennas are prepared, and it is assumed that the terminal device connects to one of the plurality of processing devices and performs communication. When such a configuration is used, if the terminal device exists at a position near the edge of the communicable area that can be communicated with by the antennas controlled by the connected processing device, another processing device that controls the antennas constituting the communicable area at that position may also be involved in the communication of the terminal device. For example, the other processing device may receive a signal transmitted from the terminal device and transfer it to the processing device to which the terminal device is connected, and the processing device may perform signal processing such as demodulation processing using the signal received by the antennas connected to its own device and the transferred signal (Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004] [Non-Patent Document 1] C. D’Andrea and E. G. Larsson, "User association in scalable cell-free massive MIMO systems", 2020 54th Asilomar Conference on Signals, Systems, and Computers, 2020 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] In the method described in Non-Patent Document 1, a signal received by an antenna under another processing device to which the terminal device is not connected is transferred to the processing device to which the terminal device is connected, but the influence on the communication of other terminal devices connected to that other processing device is not considered. For this reason, the communication of a terminal device connected to a certain processing device may interfere with other terminal devices connected to another processing device, and the efficiency of the entire system may deteriorate. [Means for Solving the Problems]

[0006] The present invention provides a technique for improving communication efficiency in a cell-free massive MIMO system including a plurality of processing devices connected to one or more antennas.

[0007] A control device according to one aspect of the present invention is a control device that functions as a RAN Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN), and based on the position where a terminal device exists, when a signal is transmitted from the terminal device, specific means for identifying a plurality of antennas expected to receive the signal with a predetermined power or more, and among the O-RAN Distributed Units (O-DUs) connected to the plurality of antennas, a first O-DU that executes communication processing for the terminal device and a second O-DU that executes communication processing for another terminal device that is interfered with by a signal transmitted from the terminal device, notification means for notifying setting information regarding pilot symbols transmitted by the terminal device The control device is a Non Real Time (Non-RT) RIC that performs long-term control, and further includes a notification means for notifying the O-DU or a Near Real Time (Near-RT) RIC that performs short-term control of the sequence length of the pilot symbol sequence used by the terminal device that executes communication processing in the O-DU, which is determined according to the density of terminal devices in the area where communication services are provided via the antenna connected to the O-DU. to do.

[0008] According to one aspect of the present invention The control device is a control device that functions as a RAN Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN). Based on the position where the terminal device exists, a specifying means for specifying a plurality of antennas that are expected to receive a signal from the terminal device at a predetermined power or more when the signal is transmitted, and among the O-RAN Distributed Units (O-DUs) connected to the plurality of antennas, a first O-DU that executes communication processing for the terminal device and a second O-DU that executes communication processing for another terminal device that is interfered with by the signal transmitted from the terminal device, and a notification means for notifying setting information regarding the pilot symbol transmitted by the terminal device. The control device is a Near Real Time (Near-RT) RIC that performs short-term control, and based on the positions of a plurality of terminal devices, when it is expected that signals transmitted by the plurality of terminal devices are received by a common antenna, the control device further includes a notification means for notifying the O-DU of the setting information that the plurality of terminal devices should use so that the plurality of terminal devices do not use the same setting information. .

Advantages of the Invention

[0009] According to the present invention, it is possible to improve communication efficiency in a cell-free massive MIMO system including a plurality of processing devices connected to one or more antennas.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are given the same reference numerals, and duplicate descriptions are omitted.

[0012] (Configuration of Wireless Communication System) FIG. 1 shows a configuration example of a wireless communication system according to this embodiment. This wireless communication system is a cell-free massive MIMO system configured to provide a wireless communication service to a terminal device (e.g., terminal devices 131 and 132) by geographically dispersing and arranging a large number of antennas (e.g., antennas 111 to 114 and antennas 121 to 124) and configuring a virtual cell using some of the antennas for each terminal device. In this embodiment, a large number of antennas are divided into a plurality of groups, each connected to a separate processing device, and the processing device controls the antenna weights, encodes and modulates the signals to be transmitted by the antennas, and demodulates and decodes the signals received by the antennas. Note that this processing device may be called, for example, a Central Processing Unit (CPU). A virtual CPU is set for each terminal device, and the virtual CPU can execute the communication processing of the corresponding terminal device. This virtual CPU may be called a vCPU. Also, the antenna may be, for example, the antenna itself having a function of capturing or radiating electromagnetic waves, or a communication device having a function of performing certain processing such as frequency conversion and amplification. Such an antenna may be called an access point (AP) in one example.

[0013] In one example, the wireless communication system of this embodiment is configured using an Open-Radio Access Network (O-RAN) for which standardization is underway to open up / intelligentize a Radio Access Network (RAN). In O-RAN, the intelligentization of the RAN is realized by controlling a plurality of O-DUs (E2 nodes) connected to a terminal device by a control device called a RAN Intelligent Controller (RIC). Note that O-DU is an abbreviation for O-RAN Distributed Unit, and here it corresponds to a processing device directly connected to an antenna. Here, it is assumed that antennas 111 to 114 are connected to O-DU 104, and antennas 121 to 124 are connected to O-DU 105. Note that these are just examples. Also, the RIC includes a Near-RT RIC 103 that generally performs short-cycle control in real time (RT), and a Non-RT RIC 102 that performs long-cycle control in non-real time. Note that the Non-RT RIC 102 is configured as part of Service Management and Orchestration (SMO 101).

[0014] The Non-RT RIC 102 performs long-term control such as RAN analysis and policy management. The Near-RT RIC 103 controls the O-DU according to the policy determined by the Non-RT RIC 102. An interface called an O1 interface is set between the Non-RT RIC 102 (SMO 101) and the O-DU, an A1 interface is set between the Non-RT RIC 102 and the Near-RT RIC 103, and an E2 interface is set between the Near-RT RIC 103 and the O-DU, respectively. Note that an interface (not shown) that allows direct communication between one O-DU and another O-DU may be provided.

[0015] In this embodiment, it is assumed that the terminal device 131 is located near the boundary between the area where communication is possible by the antennas 111 to 114 and the area where communication is possible by the antennas 121 to 122. In this case, when the terminal device 131 communicates, the antennas 111 to 114 and the antennas 121 to 122 can be utilized. For example, signals transmitted from the terminal device 131 are received by the antennas 111 to 114 and the antennas 121 to 122. Then, for example, when the O-DU 104 executes the communication processing of the terminal device 131, the signals received by the antennas 121 to 122 (for example, the IQ signals after being frequency-converted to baseband and sampled) can be transferred from the O-DU 105 to the O-DU 104. And the O-DU 104 can demodulate and decode the signals from the terminal device 131 using the signals received via the antennas 111 to 114 and the signals received via the antennas 121 to 122. Also, the data to be transmitted to the terminal device 131 is provided to the O-DU 104 and the O-DU 105 and is transmitted from the antennas 111 to 114 and the antennas 121 to 122 to the terminal device 131. Note that the signals transmitted from the antennas 121 to 122 can be generated by, for example, the O-DU 104. In this case, signals in the form transmitted from each of the antennas 121 to 122 are transferred from the O-DU 104 to the O-DU 105. And the O-DU 105 converts the received signals into the form of RF signals that can be sent out from the antennas and controls them to be output by each of the antennas 121 to 122. Thereby, when a terminal device exists in an area where communication is possible with a plurality of antennas connected to a plurality of O-DUs, communication services can be provided to the terminal device using the plurality of antennas connected to the plurality of O-DUs.

[0016] On the other hand, it is assumed that the terminal device 132 is located in the area where communication is possible with the antennas 122 to 124 connected to the O-DU 105. In this case, the communication of the terminal device 132 can be performed via the antennas 122 to 124. Note that it is assumed that the terminal device 132 does not exist within the communication range of the antennas connected to other O-DUs.

[0017] In this embodiment, for example, the Non-RT RIC 102 or the Near-RT RIC 103 determines an O-DU that executes communication processing related to these terminal devices according to the positions of the terminal devices 131 and 132. For example, the Non-RT RIC 102 or the Near-RT RIC 103 determines that the communication processing of the terminal device 131 is executed by the O-DU 104 and the communication processing of the communication device 132 is executed by the O-DU 105. Then, the Non-RT RIC 102 or the Near-RT RIC 103 can instruct the O-DU 104 to start up a vCPU for the communication processing of the terminal device 131 and instruct the O-DU 105 to start up a vCPU for the communication processing of the terminal device 132 according to the determination. Note that the Non-RT RIC 102 or the Near-RT RIC 103 identifies the antennas to be used for the communication of each terminal device and transmits an instruction to each O-DU so that processing according to the identification result is performed. For example, the Non-RT RIC 102 or the Near-RT RIC 103 can instruct the O-DU 105 to transfer the signals received by the antennas 121 to 122 for the communication of the terminal device 131 to the O-DU 104. Also, the Non-RT RIC 102 or the Near-RT RIC 103 can instruct the O-DU 104 to transmit the signals to be transmitted from the antennas 121 to 122 to the terminal device 131 to the O-DU 105. In this way, there is one O-DU that executes the communication processing of a certain terminal device, and that O-DU can execute the encoding and modulation processing and the demodulation and decoding processing for the communication of that terminal device in a lump. Note that in this embodiment, it can be expressed that the O-DU that executes the communication processing for the communication of a certain terminal device is determined, and the terminal device is in a state where the communication of the terminal device can be executed under the communication processing of that O-DU while the terminal device is connected to that O-DU. Here, it can be expressed that the terminal device 131 is connected to the O-DU 104 and the terminal device 132 is connected to the O-DU 105.

[0018] Note that the Non-RT RIC 102 may be configured to determine long-term policies, and the Near-RT RIC 103 may be configured to control the O-DUs according to the long-term policies. In this case, for example, the Non-RT RIC 102 may notify the Near-RT RIC 103 of the policies for the Near-RT RIC 103 to determine the O-DUs to which each terminal device should be connected. Then, the Near-RT RIC 103 may determine to which O-DU each terminal device should be connected (to which O-DU the vCPU for the communication processing of the terminal device should be started) according to the policies, and may control each O-DU based on the determined result. Further, the Near-RT RIC 103 may select the antennas to be used for the communication of each terminal device, and may control the O-DU to execute data transfer or the like according to the result of the selection.

[0019] In the above configuration, assume that the communication processing for the terminal device 131 is executed by the O-DU 104, and the communication processing for the terminal device 132 is executed by the O-DU 105. That is, in the O-DU 104, a vCPU for the terminal device 131 is started, and in the O-DU 105, a vCPU for the terminal device 131 is started. Here, as described above, the terminal device 131 communicates not only via the antennas 111 to 114 but also via the antennas 121 to 122. Even in this case, the processing for the communication of the terminal device 131 is performed by the vCPU started in the O-DU 104. That is, the signal transmitted by the terminal device 131 and received via the antennas 121 to 122 is not processed by the vCPU in the O-DU 105 and is directly transferred to the O-DU 104. Therefore, in the O-DU 105, the vCPU that performs the processing for the communication of the terminal device 132 cannot recognize the characteristics of the signal from the terminal device 131, and it is impossible to reduce the influence of interference from the signal from the terminal device 131 during demodulation and decoding of the signal from the terminal device 132. Here, for example, if the result of the transmission path estimation between the terminal device 131 and the antennas 121 to 122 performed in the vCPU of the O-DU 104 is notified to the O-DU 105, the vCPU of the O-DU 105 can reduce the influence of interference from the signal transmitted from the terminal device 131 using the transmission path estimation value. However, in this case, the amount of information that needs to be transmitted and received between the O-DU 104 and the O-DU 105 increases, and especially when there are a large number of terminal devices located near the boundary of the range controlled by a plurality of O-DUs such as the terminal device 131, it may put pressure on the capacity of the backhaul link. Also, the signal transmitted from the terminal device 131 may reach, for example, the antenna 123 that is not used for communication. However, since the O-DU 104 does not execute processing related to the antenna 123, it is impossible to reduce the influence of interference in the antenna 123.

[0020] In this embodiment, in view of such circumstances, in an O-DU connected to an antenna used for communication of a certain terminal device, even when the O-DU does not execute the communication process of the terminal device, a vCPU associated with the terminal device is set. Then, in the vCPU, for signals from the terminal device for which communication processing is not executed in the O-DU, processing for interference suppression such as transmission path estimation is executed, and the information obtained by the processing is provided to the vCPU set for communication by another terminal device using the same antenna as the terminal device. Then, the vCPU set for communication by another terminal device executes interference suppression control (for example, beam control) based on the provided information. For example, in O-DU 105, not only the vCPU for communication of the terminal device 132 that is the target of communication processing but also the vCPU associated with the terminal device 131 that is not the target of communication processing is set. Then, the vCPU associated with the terminal device 131 in O-DU 105 executes, for example, transmission path estimation between the antennas 121 to 123 and the terminal device 131, and provides the result of the transmission path estimation to the vCPU for communication of the terminal device 132. Note that the vCPU associated with the terminal device 131 in O-DU 105 is configured to execute only the processing (for example, transmission path estimation) necessary for interference suppression and not to participate in the communication of the terminal device 131 in one example. The vCPU for communication of the terminal device 132 can calculate the antenna weights in the antennas 122 to 124 according to, for example, the minimum mean square error (MMSE) norm based on this information, and reduce the interference caused by the signal from the terminal device 131.

[0021] For such processing, in this embodiment, information for enabling the above-described processing is provided from the Non-RT RIC 102 or the Near-RT RIC 103 to the O-DUs 104 and 105. For example, the pilot assignment information in each terminal device can be notified from the Non-RT RIC 102 or the Near-RT RIC 103 to the O-DUs 104 and 105. Note that the pilot assignment information can be information capable of specifying, for example, the frequency and time resource positions at which the terminal device 131 transmits pilot symbols and the pilot symbol sequence. Note that, for example, when the frequency and time resources at which pilot symbols are transmitted are fixed, the information indicating the positions of the frequency and time resources may not be included in the pilot assignment information. Also, for example, when the frequency and time resources at which pilot symbols are transmitted can be specified by the sequence length of the pilot symbol sequence, the information indicating the positions of the frequency and time resources may be implicitly notified by the sequence length. Also, when the positions of the frequency and time resources can be specified by other parameters, those parameters may be notified. Also, in addition to the pilot assignment information, information indicating the transmission power when the terminal device transmits pilot symbols may be provided. Note that when the transmission power of the pilot symbols is constant, the information on the transmission power may not be notified. Also, when the transmission power of the pilot symbols is determined by the category of the terminal device or the like, any information capable of specifying the transmission power of the category or the like may be notified. That is, the setting information regarding the pilot symbols for each terminal device can be provided to the O-DU that executes the communication processing of that terminal device and the O-DU that executes the communication processing of other terminal devices that are assumed to be affected by the signal transmitted from that terminal device. Thereby, for example, the O-DU 105 can acquire the pilot assignment information of the terminal device 131 and execute channel estimation between the terminal device 131 and each of the antennas 121 to 123 based on the signals received from the terminal device 131 at the antennas 121 to 123.Note that hereinafter, unless otherwise specified, the pilot allocation information may be read as the setting information regarding the pilot symbol.

[0022] Note that the allocation of pilots to be used by each terminal device may be determined by the Non-RT RIC 102 or the Near-RT RIC 103. Also, as described above, the Non-RT RIC 102 or the Near-RT RIC 103 determines the antennas to be used for the communication of each terminal device. Therefore, the Non-RT RIC 102 and the Near-RT RIC 103 can identify not only the O-DU that executes the communication process of each terminal device, but also the O-DU connected to the antenna used for the communication of that terminal device, and for one or more of those O-DUs, the pilot symbol sequence, frequency, and time resources allocated to that terminal device can be notified. Note that the allocation of pilots to be used by each terminal device may be determined by the O-DU that executes the communication process of that terminal device. In this case, the information indicating the allocation is notified to the Near-RT RIC 103 or the Non-RT RIC 102, and can be notified from the Near-RT RIC 103 or the Non-RT RIC 102 to other O-DUs to which the antennas used for the communication of that terminal device are connected. Note that, for example, the Non-RT RIC 102 or the Near-RT RIC 103 determines candidates for the allocation of pilots available in each O-DU, and each O-DU may select the allocation of pilots to be actually used by the terminal device for which the communication process is to be executed from among those candidates. According to this, for a plurality of O-DUs corresponding to adjacent areas, by making the allocation candidates different from each other, it is possible to prevent the terminal devices connected to adjacent O-DUs from using the same pilot allocation, and to prevent deterioration in the accuracy of channel estimation.

[0023] As described above, in the pilot assignment, different sequences can be set for each terminal device. However, as the number of terminal devices increases, the number of sequences becomes insufficient, and in some cases, two or more terminal devices may use the same sequence. Therefore, the Non-RT RIC 102 or the Near-RT RIC 103 can determine, for example, that in a situation where the number of terminal devices staying within a certain area increases, the sequence length of the pilot symbol sequence to be used by the terminal devices located in that certain area should be increased. By increasing the sequence length of the pilot symbol sequence, a large number of candidate orthogonal sequences that can be used as the pilot symbol sequence can be prepared, and it becomes possible to perform channel estimation based on signals from each terminal device with high accuracy. On the other hand, the Non-RT RIC 102 or the Near-RT RIC 103 can, for example, shorten the sequence length of the pilot symbol sequence in a situation where the number of terminal devices staying within a certain area decreases. According to this, the amount of frequency and time resources required to transmit the pilot symbol sequence can be reduced, and the frequency and time resources available for transmitting and receiving user data can be increased. In one example, the Non-RT RIC 102 or the Near-RT RIC 103 can identify the density of terminal devices for each area under each O-DU, refer to a table in which the relationship between the density and the sequence length of the pilot symbol sequence is predefined, or input the value indicating the density as an argument to a predetermined function, thereby determining the sequence length of the pilot symbol sequence to be used in the terminal devices under each O-DU. Then, the Non-RT RIC 102 or the Near-RT RIC 103 can notify the O-DU of the policy information indicating that the sequence length of the pilot symbol sequence should be increased.

[0024] In one example, Non-RT RIC 102 identifies areas where the density of terminal devices is expected to increase over a long period based on information such as the history and events of the number of terminal devices in each area. Then, as a long-term policy for that area, Non-RT RIC 102 may determine to increase the sequence length of the pilot symbol sequence. Also, Non-RT RIC 102 identifies areas where the density of terminal devices is expected to decrease over a long period, and as a long-term policy for that area, may determine to shorten the sequence length of the pilot symbol sequence. For example, Non-RT RIC 102 identifies the number of terminal devices in each area where communication services are provided via each antenna as the density, determines the sequence length according to the density, and generates policy information including information that can identify the determined sequence length. In one example, the number of terminal devices (density) is identified for each of a plurality of antennas as described above, and the sequence length may be determined according to the largest number among the numbers of terminal devices corresponding to each of the plurality of antennas. Note that the sequence length can be applied, for example, in an area where communication services can be provided by the antenna with the largest number of corresponding terminal devices and in other areas that at least partially overlap with that area. Then, Non-RT RIC 102 may notify this policy information to at least one of Near-RT RIC 103 and O-DU. Note that this policy information may indicate the sequence length to be used, or may indicate that the currently used sequence length should be extended or shortened.

[0025] When this policy information is notified to Near-RT RIC 103, Near-RT RIC 103 determines the sequence length of the pilot symbol sequence to be used by each terminal device under the control of each O-DU based on the policy information, generates short-term policy information, and notifies this policy information to each O-DU. Note that this short-term policy information may also include information indicating the sequence length of the pilot symbol sequence, or information indicating that the sequence length should be extended or shortened.

[0026] The O-DU can receive long-term policy information from the Non-RT RIC 102 or short-term policy information from the Near-RT RIC 103, and allocate a pilot symbol sequence with a sequence length specified by the policy information to subordinate terminal devices. Note that the pilot symbol sequence to be allocated to each terminal device may be determined by the Non-RT RIC 102 or the Near-RT RIC 103. Also, the Non-RT RIC 102 or the Near-RT RIC 103 may determine candidates for sequences that can be used in each O-DU among the pilot symbol sequences with the determined sequence length, and notify the O-DU of information indicating the candidates. Then, the O-DU can select a pilot symbol sequence from among the candidates and allocate it to each connected terminal device. In this case, the O-DU can notify other O-DUs of information regarding the pilot symbols allocated to each terminal device (sequence and resources of the frequency and time to be used) via the Near-RT RIC 103.

[0027] Note that when the terminal device moves, it is possible to assume that signals transmitted by terminal devices using the same pilot symbol sequence reach the same antenna on the network side. Therefore, for example, Near-RT RIC 103 can monitor the positions of each terminal device and perform different pilot assignments for terminal devices existing in the range corresponding to each antenna of each O-DU. For example, Near-RT RIC 103 can update the pilot assignment so that the pilot symbol sequence assigned to the terminal devices existing in the range corresponding to each antenna and the frequency and time resources used for transmitting the pilot symbols do not match. Then, when Near-RT RIC 103 updates the pilot assignment for a certain terminal device, it notifies the O-DU connected to the antenna corresponding to the position of that terminal device of the updated assignment. Note that the antenna corresponding to the position of the terminal device here refers to an antenna that may receive the signal at a power level equal to or higher than a predetermined level when the signal is transmitted from that terminal device, and is not limited to the antenna actually used for communication with the terminal device. That is, as described above, information indicating the pilot assignment is notified not only to the O-DU that starts the vCPU that executes the communication processing of the terminal device, but also to all O-DUs that should start the vCPU that performs processing for interference suppression. In this way, by performing pilot assignment for terminal devices existing over a wide area by Near-RT RIC 103, even if the terminal device moves, multiple terminal devices do not use the same pilot assignment for the same antenna, and deterioration of transmission path estimation accuracy can be prevented.

[0028] Note that the Non-RT RIC 102 or Near-RT RIC 103 can notify each O-DU of information indicating through which antenna the transmission path estimation for each terminal device should be performed based on the pilot symbols received. For example, in a state as shown in FIG. 1, the Non-RT RIC 102 or Near-RT RIC 103 can notify the O-DU 105 that the transmission path estimation for the terminal device 131 should be performed using the pilot symbols received via the antennas 122 to 123. Note that although the antenna 121 can receive signals from the terminal device 131 at a sufficiently strong power level and does not affect the communication of the terminal device 132, it can be determined that there is no need to perform transmission path estimation. In this way, information indicating that transmission path estimation should be performed can be notified to the O-DU 105, limited to antennas that may cause non-negligible interference to the communication of the terminal device 132. According to this, for example, the O-DU 105 can refrain from performing transmission path estimation for the antennas 121 and 124 for the terminal device 131. Therefore, by not performing transmission path estimation for signals received via the antenna 124 where the influence on the communication of the terminal device 131 does not occur or the influence is sufficiently minor, the consumption of computing resources in the O-DU 105 can be suppressed.

[0029] (Device Configuration) Subsequently, the configurations of the control device (at least one of the Non-RT RIC 102 and Near-RT RIC 103) and the processing device (O-DU) will be described. FIG. 2 shows a hardware configuration example of these control device and processing device. Note that the Non-RT RIC 102 and Near-RT RIC 103 may be realized as a logical configuration, and the functions as these RICs may be implemented in one control device. Also, the functions of the RIC may be implemented distributively by a plurality of devices. Also, regarding the processing device, the function of the O-DU may be implemented as a single device, or the function of the O-DU may be implemented distributively using a plurality of devices.

[0030] In one example, the control device and the processing device include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. In the control device and the processing device, for example, a computer-readable program that realizes each function of each device as described above and is recorded in any one of the ROM 202, the RAM 203, and the storage device 204 is executed by the processor 201. Note that the processor 201 may be replaced by one or more processors such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a DSP (Digital Signal Processor). The control device and the processing device control the communication circuit 205 by, for example, the processor 201 to perform communication with other devices. Note that FIG. 2 shows a schematic diagram in which the control device and the processing device have one communication circuit 205, but the present invention is not limited to this.

[0031] FIG. 3 shows a functional configuration example of a control device that functions as a RIC (at least one of Non-RT RIC 102 and Near-RT RIC 103). The functions shown in FIG. 3 are realized, for example, when the processor 201 of the control device executes programs stored in the ROM 202, the RAM 203, and the storage device 204. Note that the control device may have hardware corresponding to at least any one of the functions described later. Note that FIG. 3 selectively shows functional parts particularly related to the present embodiment among the functions of the control device, and the control device naturally has the functions generally possessed by the RIC. As its functions, the control device includes, for example, a used antenna specifying unit 301, an interference range specifying unit 302, an estimation target determining unit 303, a pilot setting determining unit 304, and an information notifying unit 305.

[0032] The used antenna specifying unit 301 specifies, for each terminal device, which antenna among the antennas that are arranged in large quantities in a planar manner and connected to any one of the O-DUs should be used when providing a communication service to the terminal device. The interference range specifying unit 302 specifies, for each terminal device, the antennas that are expected to interfere with the communication of other terminal devices at a sufficient power level with the signal transmitted by the terminal device. For example, the interference range specifying unit 302 specifies, based on the position where the terminal device exists, a group of antennas that are expected to receive the signal at a predetermined power or higher when a signal is transmitted from the terminal device. Then, the used antenna specifying unit 301 can specify, from among the group of antennas, for example, an antenna arranged close to the position of the terminal device or an antenna that is expected to have good radio quality in the communication with the terminal device as the antenna to be used for the communication of the terminal device.

[0033] Note that the used antenna specifying unit 301 can specify, for example, the O-DU to which the antenna used for the communication of a certain terminal device is connected, and determine the O-DU to which the most antennas used for the communication are connected as the O-DU that executes communication processing including demodulation and decoding processing of the signal for the terminal device. Also, the used antenna specifying unit 301 can select, for example, the O-DU that executes the communication processing of the terminal device according to the load states of one or more O-DUs to which the antennas used for the communication of a certain terminal device are respectively connected. Then, the control device can notify, for example, the O-DU that executes the communication processing, via the information notification unit 305, of the identification information of the terminal device that is the target of the communication processing and information regarding other O-DUs to which the antennas used for the communication of the terminal device are connected. Also, the control device can notify other O-DUs to which the antennas used for the communication of the terminal device are connected of information specifying which antenna is used for the communication of the terminal device and information specifying the O-DU that executes the communication processing of the terminal device.

[0034] Note that the used antenna identification unit 301 and the interference range identification unit 302 identify the antenna for each terminal device. For example, in FIG. 1, based on the position where the terminal device 131 exists, when a signal is transmitted from the terminal device 131, the interference range identification unit 302 identifies antennas 111 to 114 and antennas 121 to 123 as an antenna group that is expected to receive the signal with a power equal to or higher than a predetermined power. Further, based on the position where the terminal device 132 exists, when a signal is transmitted from the terminal device 132, the interference range identification unit 302 identifies antennas 122 to 124 as an antenna group that is expected to receive the signal with a power equal to or higher than a predetermined power. The used antenna identification unit 301 can identify antennas 111 to 114 and antennas 121 to 122 as the antennas used for the communication of the terminal device 131, and can identify antennas 122 to 124 as the antennas used for the communication of the terminal device 132, from among the identified antenna groups.

[0035] The interference target determination unit 303 determines, for each terminal device specified by the interference range specification unit 302, an O-DU that should perform transmission path estimation without performing communication processing for that terminal device and an antenna connected to that O-DU, based on the antennas that are expected to interfere with the communication of other terminal devices. For example, for terminal device 131, antennas 111 to 114 and antennas 121 to 123 are present as antennas that may interfere with the communication of other terminal devices. When O-DU 104 executes the communication processing of terminal device 131, the interference target determination unit 303 may determine to cause O-DU 105, to which antennas 121 to 123 that may cause interference are connected, among the O-DUs that do not perform the communication processing of terminal device 131, to perform transmission path estimation. Further, the interference target determination unit 303 may determine, for example, all of the antennas 121 to 123 that may cause interference among the antennas connected to O-DU 105 as the target of transmission path estimation between the antennas and terminal device 131. That is, in one example, for a certain terminal device, among the O-DUs to which antennas that may be interfered by the signal transmitted by that terminal device are connected, an O-DU that does not perform communication processing is determined to execute transmission path estimation, and all of the antennas that may cause interference among the antennas connected to that O-DU may be the target of transmission path estimation between the antennas and the terminal device. Note that this is just an example. For example, among antennas 121 to 124 connected to O-DU 105, only antennas 122 to 124 used for the communication of terminal device 132, which is the target of communication processing in that O-DU 105, may be the target of transmission path estimation for terminal device 131. In this case, since the signal transmitted from terminal device 131 may interfere with antennas 121 to 123, only antennas 122 to 123, which are also included in antennas 122 to 124 used for the communication of terminal device 132, among these antennas 121 to 123 may be the target of transmission path estimation for terminal device 131. Note that in this case, for an O-DU that does not perform communication processing for any terminal device, transmission path estimation may not be performed.

[0036] Generally, for an O-DU that is connected to one or more first antennas (antennas 122 to 124) among a plurality of antennas expected to receive a signal from a first terminal device (terminal device 132) such as O-DU105 at a power equal to or higher than a predetermined power, executes demodulation and decoding processes for the first terminal device, and is not connected to one or more second antennas (antennas 121 to 123) included in a plurality of antennas (antennas 111 to 114 and antennas 121 to 123) expected to receive a signal from a second terminal device (terminal device 131) at a power equal to or higher than a predetermined power and does not execute demodulation and decoding processes for the second terminal device, it is determined to perform only transmission path estimation without performing the above-described communication process. Such an O-DU is notified of information indicating the first antenna for the first terminal device specified by the used antenna specifying unit 301. Further, such an O-DU is notified of information indicating a third antenna (for example, antennas 122 to 123) that is the target for performing transmission path estimation among the second antennas specified by the interference range specifying unit 302 with respect to the second terminal device that is not the target of the communication process. Note that the notification of these pieces of information is performed, for example, via the information notification unit 305. Note that for O-DU105, information on a fourth antenna used for communication of the second terminal device specified by the used antenna specifying unit 301 may also be notified. Note that the fourth antenna used for communication of the second terminal device is at least a part of one or more second antennas included in a plurality of antennas expected to receive a signal from the second terminal device at a power equal to or higher than a predetermined power. For example, for O-DU105 in FIG. 1, information on antennas 121 to 122 used for communication of terminal device 131 is notified, and this is a part of antennas 121 to 123 expected to receive a signal from terminal device 131 at a power equal to or higher than a predetermined power. O-DU105 transfers the signal received by antennas 121 to 122 to an O-DU that executes communication processing for terminal device 131 based on the notification.Note that, for a signal received from the second terminal device (terminal device 131) by a fifth antenna (for example, antenna 123) among the second antennas (antennas 121 to 123) that does not belong to the fourth antenna (antennas 121 to 122), the signal is not transferred to the O-DU that executes the communication process of the second terminal device.

[0037] The pilot setting determination unit 304 determines setting information regarding pilot symbols to be used for channel estimation in each terminal device. As described above, the setting information regarding the pilot symbols includes information that can identify the pilot symbol sequence to be transmitted in each terminal device. In one example, the information that can identify the pilot symbol sequence may be the pilot symbol sequence itself, or a value indicating any one of the indexes previously assigned to each candidate of the pilot symbol sequence. Further, the setting information regarding the pilot symbols may include information that can identify the frequency and time resources used when the pilot symbols are transmitted. The information that can identify the frequency and time resources may be information that directly designates the frequency and time resources, or information such as an index for designating which of the allocation patterns of a plurality of frequency and time resources should be used. Further, the setting information regarding the pilot symbols may include information that can identify the transmission power when transmitting the pilot symbols.

[0038] In addition, when the control device has the function of the Non-RT RIC 102, the pilot setting determination unit 304 may specify the number (density) of terminal devices in an area where communication services can be provided via each of a plurality of antennas connected to any O-DU, and determine the sequence length of the pilot symbol sequence according to the number. For example, the sequence length of the pilot symbol sequence may be set such that the higher the density of the terminal devices, the longer the sequence length, and the lower the density of the terminal devices, the shorter the sequence length. Note that the sequence length may be determined by an operation using a function with information indicating the density of the terminal devices as an argument, or for example, the sequence length may be determined by referring to a table defining the relationship between the density of the terminal devices and the sequence length. The control device may notify the device functioning as the Near-RT RIC 103 or each O-DU of the determined sequence length via the information notification unit 305.

[0039] In addition, when the control device has the function of the Near-RT RIC 103, for example, when it is predicted that signals transmitted by a plurality of terminal devices will be received by a common antenna based on the positions of the plurality of terminal devices, the pilot setting determination unit 304 may determine the setting information to be used by each terminal device so that the plurality of terminal devices do not use the same pilot symbol setting information. In particular, the pilot setting determination unit 304 may determine the setting information used in each terminal device so that the plurality of terminal devices do not transmit the same pilot symbol sequence using the same frequency and time resources. The control device may notify the O-DU that executes the communication processing of each terminal device of the setting information determined in this way, and cause the O-DU to notify each terminal device of the setting information.

[0040] The information notification unit 305 notifies the O-DU or another control device (for example, a control device that functions as a Near-RT RIC when the control device is a Non-RT RIC) of the information determined or set by each of the above-described functional units. Note that the information notification to the O-DU is performed using the O1 interface when the control device is a Non-RT RIC, and is performed using the E2 interface when the control device is a Near-RT RIC. Also, when the control device is a Non-RT RIC, the information notification to another control device that functions as a Near-RT RIC can be performed via the A1 interface.

[0041] FIG. 4 shows a functional configuration example of a processing device that functions as an O-DU. The functions shown in FIG. 4 are realized, for example, when a processor 201 of the processing device executes programs stored in a ROM 202, a RAM 203, and a storage device 204. Note that the processing device may have hardware corresponding to at least any of the functions described later. Note that FIG. 4 selectively shows functional units particularly relevant to the present embodiment among the functions of the processing device, and the processing device naturally has functions generally possessed by an O-DU. The processing device includes, as its functions, for example, an information reception unit 401, an estimation processing unit 402, a communication processing unit 403, and a received signal transfer unit 404.

[0042] The information receiving unit 401 receives the information notified by the control device as described above. For example, when it is expected that a signal transmitted by a certain terminal device is received at a power equal to or higher than a predetermined power at an antenna connected to the processing device, the information receiving unit 401 receives the information associating the terminal device with the antenna. For example, the information receiving unit 401 of the O-DU 105 can receive the information associating the terminal device 131 not subject to communication processing with the antennas 121 to 123, and the information associating the terminal device 132 subject to communication processing with the antennas 122 to 124. Note that for the terminal device 131, when it is determined by the control device that only the antennas 122 to 123 are the targets of transmission path estimation, the information receiving unit 401 of the O-DU 105 can receive the information associating the antennas 122 to 123 with the terminal device 131. Further, the information receiving unit 401 can receive the setting information of the pilot symbol used when each terminal device transmits a pilot symbol. For example, the information receiving unit 401 of the O-DU 105 receives the setting information of the pilot symbols of the terminal device 131 and the terminal device 132. Note that for the terminal device 132 which is the target of communication processing, the O-DU 105 can notify the terminal device 132 of the setting information of the pilot symbol received by the information receiving unit 401 and instruct the terminal device 132 to transmit the pilot symbol according to the setting information. On the other hand, for the terminal device 131 which is not the target of communication processing, the O-DU 105 does not notify the received setting information to the terminal device 131. This is because the setting information is notified to the terminal device 131 from the O-DU 104 that executes the communication processing of the terminal device 131.

[0043] Based on the information received by the information receiving unit 401, the transmission path estimation unit 402 receives pilot symbols from a terminal device that is the target of transmission path estimation (but not the target of communication processing) at the antenna that is the target of transmission path estimation, and performs transmission path estimation based on the result of the reception. The communication processing unit 403 uses the result of the transmission path estimation to perform interference suppression control, for example, based on the MMSE criterion, on the signal received from the terminal device that is the target of communication processing, and performs reception processing including demodulation and decoding processing of the signal after interference suppression. The received signal transfer unit 404 transfers the signal received at the antenna used for the communication of the terminal device that is not the target of communication processing, for example, to the O-DU that performs the communication processing of that terminal device.

[0044] (Flow of processing) Subsequently, an example of the flow of processing executed by the control device and the processing device will be described. Since the details of the processing executed by each device are as described above, hereinafter, only an overview of the processing executed by each device will be given.

[0045] FIG. 5 is a diagram showing an example of a process flow executed by a control device. The control device identifies, for example, for each of a plurality of terminal devices, an antenna that is expected to receive a signal at a power equal to or higher than a predetermined power when a signal is transmitted from each terminal device. Then, in one example, the control device can determine an O-DU that executes communication processing for each terminal device based on the identified antenna. Then, for a certain O-DU, the control device identifies, as an antenna for communication processing, an antenna that is expected to receive a signal at a power equal to or higher than a predetermined power when a terminal device that is the target of communication processing transmits a signal, and identifies, as an antenna for transmission path estimation, an antenna that is expected to receive a signal at a power equal to or higher than a predetermined power when a terminal device that is not the target of communication processing transmits a signal (S501). Then, the control device notifies each O-DU of the antenna for communication processing and the antenna for transmission path estimation of that O-DU (S502). Note that information associating the antenna for communication processing with the terminal device for communication processing and information associating the antenna for transmission path estimation with the terminal device for transmission path estimation are notified to each O-DU. Further, the control device notifies each O-DU of setting information regarding pilot symbols used in the terminal device that is the target of communication processing and the terminal device that is the target of transmission path estimation in that O-DU (S503). Note that the control device can update the setting information of the pilot symbols to be used by each terminal device, for example, periodically or when it is determined that interference may occur between the pilot symbols of a plurality of terminal devices.

[0046] FIG. 6 is a diagram showing an example of the flow of processing executed by the processing device. The processing device receives, for example, information specifying the antenna for communication processing and the antenna for transmission path estimation in the processing device itself, which is transmitted from the control device in S502 (S601). Further, the processing device receives setting information regarding the pilot symbols of the terminal device for communication processing and the terminal device for transmission path estimation (S602). Note that the processing device may perform the setting process regarding the pilot symbols for the terminal device for communication processing by itself. In that case, in S602, only the setting information regarding the pilot symbols of the terminal device for transmission path estimation can be received. Then, based on the information received in S601 and S602, the processing device measures the pilot symbols from the terminal device for transmission path estimation at the antenna for transmission path estimation and executes transmission path estimation (S603). Then, the processing device executes communication processing including demodulation and decoding processing of the signal from the terminal device for communication processing using the result of the transmission path estimation (S604).

[0047] Note that the above processing is an example, and the processing flows such as those in FIGS. 5 and 6 do not necessarily have to be performed. For example, the O-DU may execute transmission path estimation at all of the antennas to which each terminal device that is not a processing target is connected. In this case, for example, the specification of the antenna for transmission path estimation may not be performed, and the processes of S501, S502, and S601 may be omitted. On the other hand, since the antenna to be subjected to transmission path estimation is limited by performing the processes of S501, S502, and S601, the arithmetic resources of the O-DU can be saved. Further, the O-DU may execute transmission path estimation using the setting information regarding all possible pilot symbols. In this case, for example, since the O-DU does not need to know the setting information regarding the pilot symbols used in each terminal device, the processes of S503 and S602 can be omitted. On the contrary, since transmission path estimation can be executed using limited setting information by performing the processes of S503 and S602, the arithmetic resources of the O-DU can be saved.

[0048] As described above, in a cell-free massive MIMO system including a plurality of processing devices connected to one or more antennas, the processing device can suppress interference from a terminal device that is the target of communication processing in another processing device and efficiently perform communication with the terminal device that is the target of communication processing in its own device. Therefore, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0049] The invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. A control device that functions as a Radio Access Network Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN), identifying means for identifying a plurality of antennas that are expected to receive a signal from a terminal device at a predetermined power or more when the signal is transmitted from the terminal device based on the location where the terminal device exists; notification means for notifying setting information regarding pilot symbols transmitted by the terminal device to a first O-DU that executes communication processing for the terminal device and a second O-DU that executes communication processing for another terminal device that is interfered with by a signal transmitted from the terminal device, among the O-RAN Distributed Units (O-DUs) connected to the plurality of antennas; having; the control device is a Non Real Time (Non-RT) RIC that performs long-term control, further having notification means for notifying the O-DU or a Near Real Time (Near-RT) RIC that performs short-term control of the sequence length of a pilot symbol sequence used by a terminal device for which the O-DU executes communication processing, determined according to the density of terminal devices in an area where a communication service is provided via an antenna connected to the O-DU, a control device characterized by this.

2. A control device that functions as a Radio Access Network Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN), identifying means for identifying a plurality of antennas that are expected to receive a signal from a terminal device at a predetermined power or more when the signal is transmitted from the terminal device based on the location where the terminal device exists; notification means for notifying setting information regarding pilot symbols transmitted by the terminal device to a first O-DU that executes communication processing for the terminal device and a second O-DU that executes communication processing for another terminal device that is interfered with by a signal transmitted from the terminal device, among the O-RAN Distributed Units (O-DUs) connected to the plurality of antennas; having; the control device is a Near Real Time (Near-RT) RIC that performs short-term control, When it is expected that signals transmitted by a plurality of terminal devices are received by a common antenna based on the positions of the plurality of terminal devices, the control device further includes notification means for notifying the O-DU of the setting information to be used by the plurality of terminal devices so that the plurality of terminal devices do not use the same setting information.

3. The control device according to claim 1 or 2, wherein the setting information includes information capable of specifying a pilot symbol sequence transmitted by the terminal device.

4. The control device according to claim 3, wherein the setting information includes information capable of specifying frequency and time resources used when the pilot symbol sequence is transmitted by the terminal device.

5. The control device according to claim 3 or 4, wherein the setting information includes information capable of specifying transmission power when the terminal device transmits the pilot symbol sequence.

6. A control method executed by a control device functioning as a RAN Intelligent Controller (RIC) of Open-Radio Access Network (O-RAN), identifying a plurality of antennas that are expected to receive a signal from the terminal device at a predetermined power or more when the signal is transmitted from the terminal device based on the position where the terminal device exists; notifying setting information regarding a pilot symbol transmitted by the terminal device to a first O-DU that executes communication processing for the terminal device and a second O-DU that executes communication processing for another terminal device that is interfered with by the signal transmitted from the terminal device, among the O-RAN Distributed Units (O-DUs) connected to the plurality of antennas; having the control device is a Non Real Time (Non-RT) RIC that performs long-term control; The control method further includes notifying the O-DU or a Near Real Time (Near-RT) RIC that performs short-term control of the sequence length of a pilot symbol sequence used by a terminal device for which the O-DU executes communication processing, which is determined according to the density of terminal devices in an area where a communication service is provided via an antenna connected to the O-DU. A control method executed by a control device functioning as a RAN Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN), comprising: identifying a plurality of antennas that are expected to receive a signal from a terminal device at a power equal to or higher than a predetermined power when the signal is transmitted from the terminal device, based on the location where the terminal device is present; notifying setting information regarding a pilot symbol transmitted by the terminal device to a first O-DU that executes communication processing for the terminal device and a second O-DU that executes communication processing for another terminal device that is interfered with by the signal transmitted from the terminal device, among the O-RAN Distributed Units (O-DUs) connected to the plurality of antennas; having; the control device is a Near Real Time (Near-RT) RIC that performs short-cycle control; the control method further comprises notifying the O-DU of the setting information to be used by the plurality of terminal devices so that the plurality of terminal devices do not use the same setting information when signals transmitted by the plurality of terminal devices are expected to be received by a common antenna, based on the locations of the plurality of terminal devices. A control method characterized by this. Claim 8 A program for causing a computer to function as the control device according to Claim 1. Claim 9 A program for causing a computer to function as the control device according to Claim 2.

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