Control device and control method thereof, processing device and processing method thereof, and program for improving communication efficiency of a cell-free massive MIMO system configured with multiple antennas

Abstract

To provide a control device, a processing device, methods, and programs that improve communication efficiency in a cell-free massive MIMO system.SOLUTION: One or more first antennas 122-124 are connected among a plurality of antennas expected to receive a signal from a first terminal device 132 like an O-DU 105 with a predetermined power level or more. Demodulation and decoding processing are performed. One or more second antennas 121-123 are connected, the second antennas included in a plurality of antennas 111-114 and 121-123 expected to receive a signal from a second terminal device 131 with the predetermined power level or more. An O-DU that does not perform demodulation and decoding processing for the second terminal device is caused to perform only transmission path estimation without performing communication processing. The O-DU is notified of information indicating the first antennas, and information indicating third antennas 122-123, which are transmission path estimation targets based on a pilot symbol received from the second terminal device, among the second antennas.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A cell-free massive MIMO system is being considered in which a large number of antennas are arranged at high density and some of the antennas are used to communicate with terminal devices. In this cell-free massive MIMO system, an antenna to be used is selected for each terminal device, and a cell is virtually formed for each terminal device, and the terminal device is generally located at the center of the virtual cell. With this technology, the terminal device can obtain uniform communication quality regardless of its location.

[0003] In such a cell-free massive MIMO system, a processing device connected to antennas controls the antennas to form a virtual cell for each terminal device. In such a system, the number of antennas and terminal devices is huge, so it is not easy to control them with one processing device. For this reason, it is assumed that multiple processing devices each controlling some of the antennas are prepared, and the terminal device connects to one of the multiple processing devices to communicate. When such a configuration is used, if the terminal device is located at a position near the edge of an area where communication is possible using an antenna controlled by the connected processing device, another processing device that controls an antenna that constitutes the communication area at that position may also be involved in the communication of the terminal device. For example, the other processing device receives a signal transmitted from the terminal device and transfers 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 antenna connected to the device itself and the transferred signal (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

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

[0005] In the method described in Non-Patent Document 1, a signal received by an antenna under a different processing device to which a terminal device is not connected is transferred to a processing device to which the terminal device is connected, but the influence on the communication of the other terminal device connected to the other processing device is not taken into consideration. Therefore, the communication of a terminal device connected to a certain processing device may interfere with the communication of the other terminal device connected to the other processing device, and the efficiency of the entire system may deteriorate. [Means for solving the problem]

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

[0007] A control device according to one embodiment 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 has an identification means for identifying, for each of a plurality of terminal devices, a plurality of antennas that are expected to receive a signal at a predetermined power or higher when the signal is transmitted from each of the plurality of terminal devices based on the locations of the plurality of terminal devices, and a notification means for notifying an O-RAN Distributed Unit (O-DU) that is connected to one or more first antennas included in the plurality of antennas for a first terminal device and performs demodulation and decoding processing for the first terminal device, and is connected to one or more second antennas included in the plurality of antennas for a second terminal device and does not perform demodulation and decoding processing for the second terminal device, of information indicating the first antenna and information indicating a third antenna among the second antennas that is to be subjected to transmission path estimation based on a pilot symbol received from the second terminal device.

[0008] A processing device according to one embodiment of the present invention is a processing device that functions as an O-RAN Distributed Unit (O-DU) of an Open-Radio Access Network (O-RAN) connected to a plurality of antennas for performing wireless communication with a terminal device, and has a receiving means for receiving information indicating a first antenna among the plurality of antennas that receives a signal transmitted by a first terminal device that is to perform signal demodulation and decoding processing, and information indicating a third antenna among second antennas that receives a signal transmitted by a second terminal device that is not to perform signal demodulation and decoding processing, and that is to perform transmission channel estimation based on a pilot symbol received from the second terminal device, an estimation means for performing transmission channel estimation between the third antenna and the second terminal device, and an execution means for executing communication processing for the first terminal device using the result of the transmission channel estimation. Effect 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] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2] FIG. 2 illustrates an example of a hardware configuration of the apparatus. [Diagram 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a control device. [Figure 4] FIG. 2 illustrates an example of a functional configuration of a processing device. [Diagram 5] FIG. 4 is a diagram illustrating an example of a flow of processing executed by the control device. [Figure 6] FIG. 2 is a diagram illustrating an example of a flow of processing executed by the processing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the 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 features described in the embodiments are essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. In addition, the same reference numbers are used for the same or similar configurations, and duplicated 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 wireless communication services to terminal devices (for example, terminal devices 131 and 132) by distributing a large number of antennas (for example, antennas 111 to 114 and antennas 121 to 124) geographically and configuring a virtual cell for each terminal device (for example, terminal device 131 and terminal device 132) using some of the antennas. In this embodiment, a large number of antennas are divided into a plurality of groups, each of which is connected to a separate processing device, and the processing device controls antenna weights, encodes and modulates signals to be transmitted by the antennas, and demodulates and decodes signals received by the antennas. 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 may execute communication processing for the corresponding terminal device. This virtual CPU may be called a vCPU. The antenna may be, for example, an antenna itself having a function of capturing electromagnetic waves or emitting electromagnetic waves, or a communication device having a function of executing certain processing such as frequency conversion and amplification. Such an antenna may be referred to as an access point (AP), in one example.

[0013] In one example, the wireless communication system of the present embodiment is configured using an Open-Radio Access Network (O-RAN) that is being standardized to open up and make the Radio Access Network (RAN) intelligent. In the O-RAN, a control device called a RAN Intelligent Controller (RIC) controls a plurality of O-DUs (E2 nodes) connected to terminal devices, thereby realizing the intelligentization of the RAN. Note that O-DU is an abbreviation of O-RAN Distributed Unit, and corresponds to a processing device directly connected to an antenna. Here, it is assumed that antennas 111 to 114 are connected to the O-DU 104, and antennas 121 to 124 are connected to the O-DU 105. Note that these are only examples, and the RIC includes a Near-RT RIC 103 that performs short-cycle control in approximately 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 a part of a 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. An interface (not shown) that allows direct communication between the O-DU and another O-DU may be provided. In this embodiment, the terminal device 131 is assumed to be present, for example, at a position near the boundary between an area where communication is possible by the antennas 111 to 114 and an area where communication is possible by the antennas 121 to 122. In this case, the antennas 111 to 114 and the antennas 121 to 122 may be utilized during communication of the terminal device 131. For example, a signal transmitted from the terminal device 131 is received by the antennas 111 to 114 and the antennas 121 to 122. Then, for example, when the O-DU 104 executes communication processing of the terminal device 131, a signal received by the antennas 121 to 122 (for example, an IQ signal after being frequency-converted to baseband and sampled) may be transferred from the O-DU 105 to the O-DU 104. Then, the O-DU 104 may demodulate and decode the signal from the terminal device 131 using the signal received via the antennas 111 to 114 and the signal received via the antennas 121 to 122. Furthermore, data to be transmitted to the terminal device 131 is provided to the O-DU 104 and O-DU 105, and is transmitted to the terminal device 131 from the antennas 111 to 114 and the antennas 121 to 122. The signals transmitted from the antennas 121 to 122 may be generated by, for example, the O-DU 104. In this case, signals in a format transmitted from each of the antennas 121 to 122 are transferred from the O-DU 104 to the O-DU 105. The O-DU 105 then converts the received signal into an RF signal format that can be sent from the antenna, and controls the signal to be output from each of the antennas 121 to 122. In this way, when a terminal device is present in an area where communication with multiple antennas connected to multiple O-DUs is possible, a communication service can be provided to the terminal device using the multiple antennas connected to the multiple O-DUs.

[0015] On the other hand, it is assumed that the terminal device 132 exists within a communication range of 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. It is assumed that the terminal device 132 does not exist within the communication range of the antennas connected to another O-DU.

[0016] In this embodiment, for example, the Non-RT RIC 102 or Near-RT RIC 103 determines an O-DU that executes communication processing related to the terminal device 131 and the terminal device 132 according to the positions of these terminal devices. For example, the Non-RT RIC 102 or Near-RT RIC 103 determines that the communication processing of the terminal device 131 is executed by the O-DU 104, and that the communication processing of the communication device 132 is executed by the O-DU 105. Then, according to the determination, the Non-RT RIC 102 or Near-RT RIC 103 may 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. The Non-RT RIC 102 or Near-RT RIC 103 identifies an antenna to be used for 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 may instruct the O-DU 105 to transfer signals received by the antennas 121 to 122 to the O-DU 104 for communication with the terminal device 131. The Non-RT RIC 102 or the Near-RT RIC 103 may also instruct the O-DU 104 to transmit 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 performs communication processing for a certain terminal device, and the O-DU may collectively perform encoding and modulation processing, and demodulation and decoding processing for communication with the terminal device. Note that in this embodiment, a state in which an O-DU that performs communication processing for communication with a certain terminal device is determined and communication with the terminal device can be performed under the communication processing of the O-DU may be expressed as the terminal device being connected to the O-DU. Here, it can be expressed that the terminal equipment 131 is connected to the O-DU 104 , and the terminal equipment 132 is connected to the O-DU 105 .

[0017] The Non-RT RIC 102 may be configured to determine a long-term policy, and the Near-RT RIC 103 may be configured to control the O-DU according to the long-term policy. In this case, for example, the Non-RT RIC 102 may notify the Near-RT RIC 103 of a policy for the Near-RT RIC 103 to determine an O-DU to which each terminal device should be connected. The Near-RT RIC 103 may then determine which O-DU each terminal device should be connected to (which O-DU should start up the vCPU for the communication processing of the terminal device) according to the policy, and control each O-DU based on the determined result. The Near-RT RIC 103 may also select an antenna to be used for communication of each terminal device, and control the O-DU to perform data transfer, etc., according to the result of the selection.

[0018] In the above configuration, it is assumed that communication processing for the terminal device 131 is executed by the O-DU 104, and communication processing for the terminal device 132 is executed by the O-DU 105. That is, it is assumed that a vCPU for the terminal device 131 is started in the O-DU 104, and a vCPU for the terminal device 131 is started in the O-DU 105. Here, as described above, the terminal device 131 performs communication via not only the antennas 111 to 114 but also the antennas 121 to 122. Even in this case, it is the vCPU started in the O-DU 104 that performs processing for communication of the terminal device 131. That is, signals transmitted by the terminal device 131 and received via the antennas 121 to 122 are not processed by the vCPU in the O-DU 105, but are transferred directly to the O-DU 104. For this reason, in the O-DU105, the vCPU that performs processing for communication with the terminal device 132 cannot recognize the characteristics of the signal from the terminal device 131, and cannot reduce the influence of interference due to the signal from the terminal device 131 when demodulating and decoding the signal from the terminal device 132. Here, for example, 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-DU104 is notified to the O-DU105, and the vCPU of the O-DU105 can reduce the influence of interference due to 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-DU104 and the O-DU105 increases, and the capacity of the backhaul link may be strained, especially when there are many terminal devices such as the terminal device 131 that are located near the boundary of the range under the control of multiple O-DUs. In addition, a signal transmitted from terminal device 131 may reach, for example, antenna 123 that is not used for communication, but since O-DU 104 does not perform processing related to antenna 123, it is not possible to reduce the effects of interference at antenna 123.

[0019] In this embodiment, in consideration of such circumstances, in an O-DU connected to an antenna used for communication of a certain terminal device, even if the O-DU does not execute communication processing of the terminal device, a vCPU associated with the terminal device is set. Then, the vCPU executes processing for interference suppression such as transmission path estimation for a signal from a terminal device for which communication processing is not executed in the O-DU, and provides information obtained by the processing to a vCPU set for communication by another terminal device using the same antenna as the terminal device. Then, the vCPU set for communication by the other terminal device executes interference suppression control (e.g., beam control) based on the provided information. For example, in the O-DU 105, not only a vCPU for communication of the terminal device 132 that is the target for executing communication processing, but also a vCPU associated with the terminal device 131 that is not the target for executing communication processing is set. Then, the vCPU associated with the terminal device 131 in the 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 a vCPU for communication of the terminal device 132. In addition, in one example, the vCPU associated with the terminal device 131 in the O-DU 105 is configured to execute only processing (e.g., transmission path estimation) necessary for suppressing interference, and not to be involved in the communication of the terminal device 131. The vCPU for the communication of the terminal device 132 can calculate antenna weights for the antennas 122 to 124 based on this information, for example, according to a minimum mean square error (MMSE) criterion, and reduce interference due to signals from the terminal device 131.

[0020] For such processing, in this embodiment, information for enabling the above-mentioned processing to be executed is provided from the Non-RT RIC 102 or the Near-RT RIC 103 to the O-DU 104 and the O-DU 105. For example, pilot allocation information in each terminal device can be notified from the Non-RT RIC 102 or the Near-RT RIC 103 to the O-DU 104 and the O-DU 105. Note that the pilot allocation information can be, for example, information that can identify the positions of the frequency and time resources 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 the pilot symbols are transmitted are fixed, information indicating the positions of the frequency and time resources may not be included in the pilot allocation information. Also, for example, when the frequency and time resources at which the pilot symbols are transmitted can be identified by the sequence length of the pilot symbol sequence, 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 identified by other parameters, the parameters may be notified. In addition to the pilot allocation information, information indicating the transmission power when the terminal device transmits the pilot symbol may be provided. Note that, when the transmission power of the pilot symbol is constant, the information on the transmission power may not be notified. When the transmission power of the pilot symbol is determined by the category of the terminal device or the like, any information capable of identifying the transmission power of the category or the like may be notified. That is, setting information on the pilot symbol for each terminal device may be provided to the O-DU that executes the communication process of the terminal device and the O-DU that executes the communication process of another terminal device that is expected to be interfered with by the signal transmitted from the terminal device. This allows, for example, the O-DU 105 to acquire the pilot allocation information of the terminal device 131 and to execute the transmission path estimation between the terminal device 131 and each of the antennas 121 to 123 based on the signal received from the terminal device 131 at the antennas 121 to 123.In the following description, unless otherwise specified, pilot allocation information may be read as setting information regarding pilot symbols.

[0021] 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. As described above, the Non-RT RIC 102 or the Near-RT RIC 103 determines the antenna to be used for the communication of each terminal device. For this reason, the Non-RT RIC 102 or the Near-RT RIC 103 can specify 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 the terminal device, and the pilot symbol sequence and the frequency and time resources allocated to the terminal device may be notified to one or more O-DUs. The allocation of pilots to be used by each terminal device may be determined by the O-DU that executes the communication process of the terminal device. In this case, information indicating the allocation may be notified to the Near-RT RIC 103 or the Non-RT RIC 102, and may be notified from the Near-RT RIC 103 or the Non-RT RIC 102 to another O-DU to which the antenna used for the communication of the terminal device is connected. For example, the Non-RT RIC 102 or the Near-RT RIC 103 may determine candidates for pilot allocation available in each O-DU, and each O-DU may select pilot allocation to be actually used by a terminal device that executes communication processing from among the candidates. In this way, by making the candidates to be allocated differently for a plurality of O-DUs corresponding to adjacent areas, it is possible to prevent terminal devices connected to adjacent O-DUs from using the same pilot allocation, and to prevent deterioration in the accuracy of transmission channel estimation.

[0022] As described above, in the allocation of pilots, different sequences may be set for each terminal device. However, when the number of terminal devices increases, the number of sequences may become insufficient, and in some cases, two or more terminal devices may use the same sequence. For this reason, the Non-RT RIC 102 or Near-RT RIC 103 may determine that the sequence length of the pilot symbol sequence to be used by the terminal device located in a certain area should be increased, for example, in a situation where the number of terminal devices staying in the certain area increases. By increasing the sequence length of the pilot symbol sequence, it is possible to prepare many candidates for mutually orthogonal sequences that can be used as pilot symbol sequences, and it is possible to perform transmission channel estimation based on signals from each terminal device with high accuracy. On the other hand, the Non-RT RIC 102 or Near-RT RIC 103 may shorten the sequence length of the pilot symbol sequence, for example, in a situation where the number of terminal devices staying in the certain area decreases. This makes it possible to reduce the amount of frequency and time resources required to transmit the pilot symbol sequence, and to increase the frequency and time resources available for transmitting and receiving user data. In one example, the Non-RT RIC 102 or Near-RT RIC 103 may determine the density of terminal devices for each area under each O-DU, and may determine the sequence length of a pilot symbol sequence to be used in terminal devices under each O-DU by referring to a table in which the relationship between the density and the sequence length of a pilot symbol sequence is predefined, or by inputting a value indicating the density into a predetermined function as an argument.The Non-RT RIC 102 or Near-RT RIC 103 may then notify the O-DU of policy information indicating that the sequence length of the pilot symbol sequence should be increased.

[0023] In one example, the Non-RT RIC 102 identifies an area where the density of terminal devices is expected to increase in a long-term cycle based on information such as the history of the number of terminal devices for each area and events. The Non-RT RIC 102 may then determine to lengthen the sequence length of the pilot symbol sequence as a long-term policy for that area. The Non-RT RIC 102 may also identify an area where the density of terminal devices is expected to decrease in a long-term cycle, and may determine to shorten the sequence length of the pilot symbol sequence as a long-term policy for that area. For example, the Non-RT RIC 102 may identify the number of terminal devices in each area where communication services are provided via each antenna as the density, determine a sequence length according to the density, and generate policy information including information that can identify the determined sequence length. In one example, the number (density) of terminal devices may be identified for each of a plurality of antennas as described above, and the sequence length may be determined according to the largest number of terminal devices corresponding to each of the plurality of antennas. The sequence length may be applied, for example, to an area in which communication services can be provided by the antenna with the largest number of corresponding terminal devices, and to another area that at least partially overlaps with the area.The Non-RT RIC 102 may notify at least one of the Near-RT RIC 103 and the O-DU of this policy information.The policy information may indicate the sequence length to be used, or may indicate that the currently used sequence length should be extended or shortened.

[0024] When this policy information is notified to the Near-RT RIC 103, the 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 each O-DU of the policy information. 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.

[0025] The O-DU may receive long-term policy information from the Non-RT RIC 102 or short-term policy information from the Near-RT RIC 103, and assign pilot symbol sequences of a sequence length specified by the policy information to terminal devices under its control. The pilot symbol sequences to be assigned to each terminal device may be determined by the Non-RT RIC 102 or the Near-RT RIC 103. The Non-RT RIC 102 or the Near-RT RIC 103 may also determine candidates for sequences that can be used in each O-DU from among the pilot symbol sequences of the determined sequence length, and notify the O-DU of information indicating the candidates. The O-DU may then select a pilot symbol sequence from the candidates and assign it to each terminal device currently connected. In this case, the O-DU may notify other O-DUs of information (sequences and frequency and time resources to be used) related to the pilot symbols assigned to each terminal device via the Near-RT RIC 103.

[0026] In addition, it may be assumed that, due to the movement of the terminal device, signals transmitted by the terminal device using the same pilot symbol sequence may reach the same antenna on the network side. For this reason, for example, the Near-RT RIC 103 may monitor the position of each terminal device and allocate different pilots to the terminal device present in the range corresponding to each antenna of each O-DU. For example, the Near-RT RIC 103 may update the pilot allocation so that the pilot symbol sequence allocated to the terminal device present in the range corresponding to each antenna and the frequency and time resources used for transmitting the pilot symbols do not match. Then, when the Near-RT RIC 103 updates the pilot allocation for a certain terminal device, it notifies the O-DU connected to the antenna corresponding to the position of the terminal device of the updated allocation. In addition, the antenna corresponding to the position of the terminal device here refers to an antenna that may receive a signal with power equal to or higher than a predetermined level when the signal is transmitted from the terminal device, and is not limited to an antenna actually used for communication with the terminal device. That is, as described above, information indicating pilot allocation is notified not only to the O-DU that starts up the vCPU that executes the communication processing of the terminal device, but also to all O-DUs that should start up the vCPU that performs processing for interference suppression. In this way, the Near-RT RIC 103 allocates pilots to terminal devices that exist in a wide area, so that even if the terminal device moves, multiple terminal devices do not use a common pilot allocation for the same antenna, and deterioration of the transmission path estimation accuracy can be prevented.

[0027] The Non-RT RIC 102 or the Near-RT RIC 103 may notify each O-DU of information indicating that the transmission channel estimation for each terminal device should be performed based on the pilot symbol received through which antenna. For example, in the state as shown in FIG. 1, the Non-RT RIC 102 or the Near-RT RIC 103 may notify the O-DU 105 that the transmission channel estimation for the terminal device 131 should be performed using the pilot symbol received through the antennas 122 to 123. The antenna 121 may receive a signal from the terminal device 131 at a sufficiently strong power level, but since it does not affect the communication of the terminal device 132, it may be determined that the transmission channel estimation does not need to be performed. In this way, information indicating that the transmission channel estimation should be performed limited to an antenna that may cause a non-negligible level of interference with the communication of the terminal device 132 may be notified to the O-DU 105. According to this, for example, the O-DU 105 may not perform the transmission channel estimation for the terminal device 131 for the antennas 121 and 124. Therefore, by not performing transmission path estimation for signals received via antenna 124 in a range where the communication of terminal device 131 is not affected or the effect is sufficiently minor, consumption of calculation resources in O-DU 105 can be suppressed.

[0028] (Device configuration) Next, the configuration of the control device (at least one of Non-RT RIC 102 and Near-RT RIC 103) and the processing device (O-DU) will be described. FIG. 2 shows an example of the hardware configuration of these control devices and processing devices. Note that Non-RT RIC 102 and Near-RT RIC 103 may be realized as a logical configuration, or the functions of these RICs may be implemented in one control device. Also, the functions of the RIC may be implemented in a distributed manner by multiple devices. Also, with regard to the processing device, the functions of the O-DU may be implemented as a single device, or the functions of the O-DU may be implemented in a distributed manner by using multiple devices.

[0029] In one example, the control device and the processing device have 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, a computer-readable program for realizing each function of each device as described above, which is recorded in, for example, the ROM 202, the RAM 203, or the storage device 204, is executed by the processor 201. 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 communicates with other devices by controlling the communication circuit 205 by the processor 201, for example. In FIG. 2, the control device and the processing device are shown in a schematic diagram having one communication circuit 205, but are not limited thereto.

[0030] FIG. 3 shows an example of the functional configuration of a control device functioning 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, by a processor 201 of the control device executing a program stored in a ROM 202, a RAM 203, and a storage device 204. The control device may have hardware corresponding to at least one of the functions described below. FIG. 3 selectively shows functional units particularly related to this embodiment among the functions of the control device, and the control device naturally has functions that a RIC generally has. The control device includes, as its functions, for example, a used antenna identification unit 301, an interference range identification unit 302, an estimation target determination unit 303, a pilot setting determination unit 304, and an information notification unit 305.

[0031] The use antenna identifying unit 301 identifies, for each terminal device, which antenna should be used among the antennas that are arranged in a large number in a planar manner and connected to any of the O-DUs when providing a communication service to the terminal device. The interference range identifying unit 302 identifies, for each terminal device, an antenna that is expected to cause a signal transmitted by the terminal device to interfere with communication of other terminal devices at a sufficient power level. For example, the interference range identifying unit 302 identifies a group of antennas that are expected to receive a signal transmitted from the terminal device at a predetermined power level or higher when the signal is transmitted from the terminal device based on the location of the terminal device. Then, the use antenna identifying unit 301 can identify, from the group of antennas, an antenna that is arranged near the location of the terminal device or an antenna that is expected to have good wireless quality in communication with the terminal device, as an antenna to be used for communication with the terminal device.

[0032] The use antenna specifying unit 301 may, for example, specify an O-DU to which an antenna used for communication of a certain terminal device is connected, and determine an O-DU to which the most antennas used for the communication are connected as an O-DU that performs communication processing including demodulation and decoding of signals for the terminal device. The use antenna specifying unit 301 may also select an O-DU that performs communication processing of a certain terminal device, for example, according to the load state of one or more O-DUs to which antennas used for communication of the certain terminal device are respectively connected. Then, the control device may, for example, notify the O-DU that performs the communication processing of the terminal device via the information notifying unit 305, of identification information of the terminal device that is the target of the communication processing, and information on other O-DUs to which antennas used for communication of the terminal device are connected. The control device may also notify other O-DUs to which antennas used for communication of the terminal device are connected of information that specifies which antenna is used for communication of the terminal device, and information that specifies the O-DU that performs communication processing of the terminal device.

[0033] The used antenna identifying unit 301 and the interference range identifying unit 302 identify an antenna for each terminal device. For example, in FIG. 1, the interference range identifying unit 302 identifies antennas 111-114 and antennas 121-123 as antennas that are expected to receive a signal at a predetermined power or higher when the signal is transmitted from the terminal device 131 based on the location where the terminal device 131 exists. Also, the interference range identifying unit 302 identifies antennas 122-124 as antennas that are expected to receive a signal at a predetermined power or higher when the signal is transmitted from the terminal device 132 based on the location where the terminal device 132 exists. The used antenna identifying unit 301 may identify antennas 111-114 and antennas 121-122 as antennas used for communication of the terminal device 131 out of the identified antenna group, and may identify antennas 122-124 as antennas used for communication of the terminal device 132.

[0034] The estimation target determination unit 303 determines, for each terminal device identified by the interference range determination unit 302, an O-DU for which transmission channel estimation should be performed without performing communication processing for the terminal device and an antenna connected to that O-DU, based on an antenna expected to interfere with communication of other terminal devices. For example, for the terminal device 131, antennas 111-114 and antennas 121-123 exist as antennas that may interfere with communication of other terminal devices, and when the O-DU 104 performs communication processing for the terminal device 131, the estimation target determination unit 303 may determine that, among the O-DUs that do not perform communication processing for the terminal device 131, the O-DU 105 to which the antennas 121-123 that may cause interference are connected, performs transmission channel estimation. In addition, the estimation target determination unit 303 may determine, for example, all of the antennas 121-123 that may cause interference among the antennas connected to the O-DU 105, as targets for transmission channel estimation between the terminal device 131. That is, in one example, for a certain terminal device, among O-DUs connected to an antenna that may cause interference due to a signal transmitted from the terminal device, it is determined that an O-DU that does not perform communication processing should perform transmission channel estimation, and all antennas connected to the O-DU that may cause interference may be targets of transmission channel estimation between the terminal device. Note that this is just one example, and for example, among antennas 121-124 connected to the O-DU 105, only antennas 122-124 used for communication of the terminal device 132 that is the target of communication processing in the O-DU 105 may be targets of transmission channel estimation for the terminal device 131. In this case, since it is antennas 121-123 that may cause interference due to a signal transmitted from the terminal device 131, only antennas 122-123 included in both the antennas 121-123 and the antennas 122-124 used for communication of the terminal device 132 may be targets of transmission channel estimation for the terminal device 131. In this case, for an O-DU that does not perform communication processing for any terminal device, transmission channel estimation may not be performed.

[0035] In general, it is determined that an O-DU such as the O-DU 105, which is connected to one or more first antennas (antennas 122-124) among a plurality of antennas expected to receive a signal from a first terminal device (terminal device 132) at a predetermined power or more, performs demodulation and decoding processing for the first terminal device, and is connected to one or more second antennas (antennas 121-123) included in a plurality of antennas (antennas 111-114 and antennas 121-123) expected to receive a signal from a second terminal device (terminal device 131) at a predetermined power or more, does not perform demodulation and decoding processing for the second terminal device, performs only transmission path estimation without performing communication processing as described above. Information indicating the first antenna for the first terminal device identified by the used antenna identification unit 301 is notified to such an O-DU. Also, the O-DU is notified of information indicating a third antenna (for example, antennas 122 to 123) to be subjected to transmission path estimation among the second antennas identified by the interference range identification unit 302 for the second terminal device that is not the target of the communication process. The notification of these pieces of information is performed, for example, via the information notification unit 305. The O-DU 105 may also be notified of information on a fourth antenna to be used for communication of the second terminal device identified by the used antenna identification unit 301. The fourth antenna to be 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 predetermined power or more. For example, the O-DU 105 in FIG. 1 is notified of information on the antennas 121 to 122 to be used for communication of the terminal device 131, which is a part of the antennas 121 to 123 expected to receive a signal from the terminal device 131 at a predetermined power or more. Based on the notification, the O-DU 105 transfers the signals received by the antennas 121 to 122 to the O-DU that executes communication processing for the terminal device 131.In addition, a signal received from a 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) is not transferred to the O-DU that performs communication processing for the second terminal device.

[0036] The pilot setting determination unit 304 determines setting information related to pilot symbols to be used for transmission channel estimation in each terminal device. As described above, the setting information related to the pilot symbols includes information capable of identifying a pilot symbol sequence to be transmitted in each terminal device. In one example, the information capable of identifying a pilot symbol sequence may be the pilot symbol sequence itself, or may be a value indicating any of the indexes pre-assigned to each of the pilot symbol sequence candidates. The setting information related to the pilot symbols may include information capable of identifying a frequency and time resource to be used when the pilot symbol is transmitted. The information capable of identifying the frequency and time resource may be information directly specifying the frequency and time resource, or may be information such as an index for specifying which of a plurality of frequency and time resource allocation patterns should be used. The setting information related to the pilot symbols may include information capable of identifying a transmission power when transmitting the pilot symbol.

[0037] In addition, when the control device has the function of the Non-RT RIC 102, the pilot setting determination unit 304 may identify the number (density) of terminal devices in an area in which communication services can be provided via each of a plurality of antennas connected to any one of the O-DUs, 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 so 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. In addition, the sequence length may be determined by a calculation using a function with information indicating the density of the terminal devices as an argument, or the sequence length may be determined by referring to a table that specifies the relationship between the density of the terminal devices and the sequence length, for example. The control device may notify the determined sequence length to the device functioning as the Near-RT RIC 103 or each O-DU via the information notification unit 305.

[0038] In addition, when the control device has the function of Near-RT RIC 103, for example, when signals transmitted by a plurality of terminal devices are expected to be received by a common antenna based on the positions of the plurality of terminal devices, the pilot setting determination unit 304 may determine setting information to be used by each terminal device so that the plurality of terminal devices do not use setting information of the same pilot symbol. In particular, the pilot setting determination unit 304 may determine setting information to be used by 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 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.

[0039] The information notification unit 305 notifies the O-DU or other control devices (for example, a control device functioning 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-mentioned functional units. Note that 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, information notification to other control devices functioning as Near-RT RIC can be performed via the A1 interface.

[0040] Fig. 4 shows an example of the functional configuration of a processing device functioning as an O-DU. The functions shown in Fig. 4 are realized, for example, by the processor 201 of the processing device executing a program stored in the ROM 202, the RAM 203, and the storage device 204. The processing device may have hardware corresponding to at least any of the functions described below. Fig. 4 selectively shows functional units particularly related to this embodiment among the functions of the processing device, and the processing device naturally has functions that an O-DU generally has. The processing device is configured to include, for example, an information receiving unit 401, an estimation processing unit 402, a communication processing unit 403, and a received signal forwarding unit 404 as its functions.

[0041] The information receiving unit 401 receives information notified by the control device as described above. For example, when a signal transmitted by a certain terminal device is expected to be 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 information associating the terminal device with the antenna. For example, the information receiving unit 401 of the O-DU 105 may receive information associating the terminal device 131, which is not a target of communication processing, with the antennas 121 to 123, and information associating the terminal device 132, which is a target of communication processing, with the antennas 122 to 124. Note that, for the terminal device 131, when the control device determines that the targets of transmission path estimation are only the antennas 122 to 123, the information receiving unit 401 of the O-DU 105 may receive information associating the antennas 122 to 123 with the terminal device 131. Also, the information receiving unit 401 may receive setting information of pilot symbols used when transmitting pilot symbols in each terminal device. For example, the information receiving unit 401 of the O-DU 105 receives setting information of pilot symbols of the terminal devices 131 and 132. For the terminal device 132 that is the target of communication processing, the O-DU 105 may notify the terminal device 132 of the setting information of the pilot symbols received by the information receiving unit 401 and instruct the terminal device 132 to transmit pilot symbols according to the setting information. On the other hand, for the terminal device 131 that is not the target of communication processing, the O-DU 105 does not notify the terminal device 131 of the received setting information. This is because the terminal device 131 is notified of the setting information from the O-DU 104 that executes the communication processing of the terminal device 131.

[0042] The estimation processing unit 402 receives pilot symbols from a terminal device that is the target of the transmission path estimation (not the target of the communication processing) at an antenna that is the target of the transmission path estimation based on the information received by the information receiving unit 401, 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 based on, for example, the MMSE standard for a signal received from a terminal device that is the target of the communication processing, and performs reception processing including demodulation and decoding processing of the signal after interference suppression. The received signal forwarding unit 404 forwards, for example, a signal received at an antenna used for communication of a terminal device that is not the target of the communication processing to an O-DU that performs communication processing of the terminal device.

[0043] (Processing flow) Next, an example of the flow of the process executed by the control device and the processing device will be described. Note that since the details of the process executed by each device are as described above, the process executed by each device will be merely outlined below.

[0044] FIG. 5 is a diagram showing an example of the flow of processing executed by the control device. For example, for each of a plurality of terminal devices, the control device identifies an antenna that is expected to receive a signal at a power equal to or greater than a predetermined power when the signal is transmitted from each terminal device. In one example, the control device may determine an O-DU that performs communication processing for each terminal device based on the identified antenna. For a certain O-DU, the control device identifies an antenna that is expected to receive a signal at a power equal to or greater than a predetermined power when the terminal device that is the target of the communication processing transmits a signal as an antenna to be targeted for communication processing, and identifies an antenna that is expected to receive a signal at a power equal to or greater than a predetermined power when the terminal device that is not the target of the communication processing transmits a signal as an antenna to be targeted for transmission path estimation (S501). Then, the control device notifies each O-DU of the antenna that is the target of the communication processing of the O-DU and the antenna that is the target of the transmission path estimation (S502). Note that information associating the antenna that is the target of the communication processing with the terminal device of the communication processing and information associating the antenna that is the target of the transmission path estimation with the terminal device that is the target of the transmission path estimation are notified to each O-DU. The control device also notifies each O-DU of setting information on pilot symbols used in the terminal device that is the target of communication processing in the O-DU and the terminal device that is the target of transmission path estimation (S503). Note that the control device can update the setting information on pilot symbols to be used by each terminal device, for example, periodically or when it is determined that interference may occur between pilot symbols of multiple terminal devices.

[0045] FIG. 6 is a diagram showing an example of the flow of processing executed by the processing device. The processing device receives information for identifying the antenna to be the target of communication processing in the processing device itself and the antenna to be the target of transmission channel estimation, which is transmitted from the control device in S502, for example (S601). The processing device also receives setting information on the pilot symbols of the terminal device to be the target of communication processing and the terminal device to be the target of transmission channel estimation (S602). The processing device may itself perform setting processing on the pilot symbols for the terminal device to be the target of communication processing, and in that case, in S602, the processing device may only receive setting information on the pilot symbols of the terminal device to be the target of transmission channel estimation. Then, based on the information received in S601 and S602, the processing device measures the pilot symbols from the terminal device to be the target of transmission channel estimation at the antenna to be the target of transmission channel estimation, and executes transmission channel estimation (S603). Then, the processing device executes communication processing including demodulation and decoding of the signal from the terminal device to be the target of communication processing using the result of the transmission channel estimation (S604).

[0046] The above-mentioned process is an example, and the process flow as shown in FIG. 5 and FIG. 6 does not necessarily have to be performed. For example, the O-DU may perform transmission channel estimation for all connected antennas for each terminal device that is not the processing target. In this case, for example, the antenna to be the target of the transmission channel estimation may not be specified, and the processes of S501, S502, and S601 may be omitted. On the other hand, the processes of S501, S502, and S601 are performed, so that the antennas to be the target of the transmission channel estimation are limited, and the calculation resources of the O-DU can be saved. In addition, the O-DU may perform transmission channel estimation using setting information related to all possible pilot symbols. In this case, the O-DU does not need to know setting information related to the pilot symbols used in each terminal device, for example, and therefore the processes of S503 and S602 can be omitted. In contrast, the processes of S503 and S602 are performed, so that the transmission channel estimation can be performed using limited setting information, and therefore the calculation resources of the O-DU can be saved.

[0047] As described above, in a cell-free massive MIMO system including multiple processing devices connected to one or more antennas, the processing device can suppress interference from terminal devices that are the targets of communication processing in other processing devices, and can perform communication of the terminal devices that are the targets of communication processing in the processing device itself with high efficiency. This makes it possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0048] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. A control device that functions as a RAN Intelligent Controller (RIC) of an Open-Radio Access Network (O-RAN), a specifying means for specifying, for each of a plurality of terminal devices, a plurality of antennas that are expected to receive a signal with a predetermined power or more when the signal is transmitted from each of the plurality of terminal devices, based on the locations of the plurality of terminal devices; A notification means for notifying an O-RAN Distributed Unit (O-DU) that is connected to one or more first antennas included in the plurality of antennas for a first terminal device and executes demodulation and decoding processing for the first terminal device, and that is connected to one or more second antennas included in the plurality of antennas for a second terminal device and does not execute demodulation and decoding processing for the second terminal device, of information indicating the first antenna and information indicating a third antenna among the second antennas that is to be a target for performing transmission path estimation based on a pilot symbol received from the second terminal device; A control device comprising:

2. The control device according to claim 1 , wherein the third antenna is included in both the first antenna and the second antenna.

3. The second antenna includes a fourth antenna used to receive a signal that is demodulated and decoded by another O-DU of the second terminal device; A signal received from the second terminal device via the fourth antenna is transferred from the O-DU to the other O-DU.

3. The control device according to claim 1 or 2.

4. The third antenna includes a fifth antenna through which a signal that is not subject to demodulation and decoding processing of the second terminal device by the other O-DU is received; A signal received from the second terminal device via the fifth antenna is not forwarded from the O-DU to the other O-DU; 4. The control device according to claim 3.

5. A processing device that functions as an O-RAN Distributed Unit (O-DU) of an Open-Radio Access Network (O-RAN) connected to a plurality of antennas for wireless communication with a terminal device, a receiving means for receiving information indicating a first antenna, among the plurality of antennas, that receives a signal transmitted by a first terminal device that is to be subjected to signal demodulation and decoding processing, and information indicating a third antenna, among second antennas that receives a signal transmitted by a second terminal device that is not to be subjected to signal demodulation and decoding processing, that is to be subjected to transmission path estimation based on a pilot symbol received from the second terminal device; an estimation means for performing a transmission path estimation between the third antenna and the second terminal device; an execution means for executing a communication process for the first terminal device using a result of the transmission channel estimation; A processing device comprising:

6. The processing device according to claim 5 , wherein the third antenna is included in both the first antenna and the second antenna.

7. The second antenna includes a fourth antenna used to receive a signal that is demodulated and decoded by another O-DU of the second terminal device; Further comprising a forwarding means for forwarding a signal received from the second terminal device via the fourth antenna to the other O-DU.

7. The processing apparatus according to claim 5 or 6.

8. The third antenna includes a fifth antenna through which a signal that is not subject to demodulation and decoding processing of the second terminal device by the other O-DU is received; A signal received from the second terminal device via the fifth antenna is not forwarded to the other O-DU; 8. The processing device according to claim 7.

9. 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, for each of a plurality of terminal devices, a plurality of antennas that are expected to receive a signal with a predetermined power or more when the signal is transmitted from each of the plurality of terminal devices, based on locations where the plurality of terminal devices are present; Notifying an O-RAN Distributed Unit (O-DU) that is connected to one or more first antennas included in the plurality of antennas for a first terminal device and performs demodulation and decoding processing for the first terminal device, and that is connected to one or more second antennas included in the plurality of antennas for a second terminal device and does not perform demodulation and decoding processing for the second terminal device, of information indicating the first antenna and information indicating a third antenna, among the second antennas, that is to be a target for performing transmission path estimation based on a pilot symbol received from the second terminal device; A control method comprising the steps of:

10. A processing method executed by a processing device functioning as an O-RAN Distributed Unit (O-DU) of an Open-Radio Access Network (O-RAN) connected to a plurality of antennas for wireless communication with a terminal device, comprising: receiving information indicating a first antenna among the plurality of antennas, which receives a signal transmitted by a first terminal device that is to perform signal demodulation and decoding processing, and information indicating a third antenna among second antennas, which receives a signal transmitted by a second terminal device that is not to perform signal demodulation and decoding processing, which is to perform transmission path estimation based on a pilot symbol received from the second terminal device; performing a transmission channel estimation between the third antenna and the second terminal device; executing a communication process for the first terminal device using a result of the transmission channel estimation; A processing method comprising the steps of:

11. A program for causing a computer to function as the control device according to any one of claims 1 to 4.

12. A program for causing a computer to function as the processing device according to any one of claims 5 to 8.

Images