Control device, method, and program

Abstract

The control device executes: a first process for receiving, from each of the plurality of signal processing devices, information on the received power of a reference signal transmitted upstream and / or downstream between the user terminal and the access point; a second process for receiving, from each of a plurality of signal processing devices, information on a transfer function of a channel between a user terminal UE in charge of the signal processing device and the access point; and a third process in which, for each user terminal, an access point responsible for the user terminal is selected on the basis of the information of the received power received by the first process and the information of the transfer function received by the second process.

Description

Technical Field

[0001] The present invention relates to a control device, method and program for determining an access point cluster for each user terminal in an open wireless access network. Background Art

[0002] In existing cellular systems, there is a problem of poor communication quality at the cellular end because of interference of wireless signals between cells. Therefore, in Beyond 5G (5G, fifth-generation mobile communication system), CF-mMIMO (Cell-free massive MIMO) has attracted attention as a communication method that eliminates interference between cells and can achieve uniform user throughput. The signals sent and received by the dispersed APs (Access points) are processed together through the CPU (Central processing unit), and the wireless signals that are spatially multiplexed can be optimized for each terminal by collaboration between APs.

[0003] In CF-mMIMO, an estimated channel calculated based on a reference signal is used to remove interference from signals sent and received by an AP cluster. MMSE (Minimum Mean Square Error) and other methods are used in this interference removal process. As reference signals, DMRS (Demodulation Reference Signal) is used for uplink post-coding, and SRS (Sounding Reference Signal) is used for downlink pre-coding.

[0004] The RE (Resource Element) used in DMRS / SRS is allocated to each UE connected to the DU (distributed unit as CPU) according to the 3GPP (registered trademark) standard [Non-patent Document 4]. The RE area that can be used in DMRS / SRS is defined according to the 3GPP standard.

[0005] In order to reduce the amount of signal processing in the CPU, AP clustering technology has been proposed to select an AP group (AP cluster) for each user to transmit and receive data [Non-Patent Document 1]. By only processing the transmission and reception signals of the AP cluster for each user in a coordinated manner, the amount of signal processing in the CPU can be reduced.

[0006] Figure 1This is a diagram schematically showing the AP clustering technology as an existing method. For each UE (user terminal) #1 and #2, in UE #1, AP #2 to AP #4 are selected as the AP group and their signals are processed together by the CPU of site #1. In UE #2, AP #5 to AP #7 are selected as the AP group and their signals are processed together by the CPU of site #2.

[0007] Regarding the determination of a specific AP cluster, in order to select an appropriate AP cluster according to the user's movement, the RIC (RAN Intelligent Controller) specified in O-RAN (Open Radio Access Network) [Non-Patent Document 2] can be used to control the AP cluster. In addition, a method for selecting an AP based on SS-RSRP (SS (Synchronization Signal) - Reference Signal Received Power) as an existing IF (interface) is proposed in CF-mMIMO [Non-Patent Document 1], where the AP with the highest reference signal received power is the main AP, and the AP within the reference signal received power threshold of the main AP is the AP cluster of the UE.

[0008] Here, SS-RSRP is determined as a quality measurement value using a synchronization signal [Non-Patent Document 3], and the DU (distributed unit as a CPU) can grasp the received power in AP (RU) units.

[0009] Prior art literature

[0010] Non-patent literature

[0011] Non-patent document 1: E.Bjornson and L.Sanguinetti, "Scalable Cell-Free MassiveMIMO Systems," in IEEE Transactions on Communications, vol.68, no.7, pp.4247-4261, July 2020.

[0012] Non-patent document 2: O-RAN WG1, "Use Cases Detailed Specification", v06.00.02

[0013] Non-patent document 3: 3GPP TS28.552, "5G performance measurements", v16.1.0

[0014] Non-patent document 4: 3GPP TS38.211, "Physical channels and modulation" Summary of the invention

[0015] Problem that the invention aims to solve

[0016] However, in the AP clustering technology of the prior art, in order to select a cluster based on the reference signal received power, an AP cluster with high reference signal received power can be selected, but it does not consider selecting an AP cluster with low spatial correlation. Figure 1 When the spatial correlation of AP#2 to AP#4 selected by UE#1 is high, there is a risk that interference separation based on MIMO cannot be fully performed and high wireless quality cannot be ensured.

[0017] Means used to solve problems

[0018] In view of the above problems in the prior art, the present invention provides a technology capable of selecting an AP cluster as APs with low spatial correlation.

[0019] A control device involved in one embodiment of the present invention is a control device in a wireless access network of O-RAN (Open Radio Access Network) specifications, which includes a user terminal, an access point for transmitting and receiving wireless signals to and from the user terminal, multiple signal processing devices for performing signal processing on the access point, and a control device, wherein the control device performs the following processing: a first processing, in which information on the received power of a reference signal sent between the user terminal and the access point via uplink and / or downlink is received from each of the multiple signal processing devices; a second processing, in which information on a transfer function of a channel between the user terminal and the access point for which the signal processing device is responsible is received from each of the multiple signal processing devices; and a third processing, in which an access point responsible for each user terminal is selected based on the information on the received power received through the first processing and the information on the transfer function received through the second processing.

[0020] Effects of the Invention

[0021] According to the present invention, by using information of the transfer function, it is possible to select an AP cluster as APs with low spatial correlation.

[0022] Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In addition, in the accompanying drawings, the same or similar components are denoted by the same reference numerals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are incorporated in and constitute a part of the specification, illustrate embodiments of the present invention, and together with the description, serve to explain the principles of the present invention.

[0024] Figure 1 It is a diagram schematically showing a conventional method.

[0025] Figure 2 This is a block diagram showing a configuration example of a wireless access network according to an embodiment.

[0026] Figure 3 This is a block diagram showing a configuration example of a communication control system according to one embodiment.

[0027] Figure 4 This is a step diagram of the present embodiment related to the uplink.

[0028] Figure 5 This is a step diagram of the present embodiment related to downlink. DETAILED DESCRIPTION

[0029] Figure 2 This is a block diagram showing a configuration example of a wireless access network according to an embodiment. Figure 2 The radio access network (RAN) 1 shown is adapted to the O-RAN specification.

[0030] In RAN1, multiple access points (AP) 2 (AP#1, AP#2, ...) are dispersedly arranged. From the multiple AP2 dispersedly arranged in RAN1, an AP cluster (access point group) is formed to transmit and receive wireless signals to each user terminal (UE). Figure 2 In the example, for example, for UE#1, two AP2s (AP#1, AP#2) form an AP cluster. For other UEs such as UE#2, AP clusters corresponding to each UE are also formed in the same manner.

[0031] also, Figure 2 The example is an example of a specific AP cluster formed for each UE at a specific time (moment). As UEs move over time, the AP cluster group formed by RAN1 of this embodiment also changes dynamically from moment to moment.

[0032] Each AP2 of an AP cluster of a certain UE transmits and receives wireless signals with the UE via its own antenna 3. For example, two AP2 (AP#1, AP#2) of an access point group of UE#1 transmit and receive wireless signals with UE#1 via their own antennas 3.

[0033] Each AP cluster is connected to its own O-DU (distributed unit) 6 for communication. The O-DU 6 performs signal processing related to the AP cluster it is responsible for. Figure 2 In the example, for example, O-DU#1 performs signal processing related to the AP cluster (AP#4, AP#5, AP#6) of UE#3. The other O-DU#2 and others also perform signal processing related to the AP clusters they are responsible for.

[0034] The signal processing related to the access point group performed by the O-DU 6 is, for example, SU-MIMO (Single User MIMO) and MU-MIMO (Multi-User MIMO) signal processing.

[0035] O-DU#1 is set at the central site 4 and connected to the core network CNW. O-DU#2 is set at the edge site #1_5 (here, an underscore is used as a boundary to distinguish between the identification number #1 and the reference figure mark 5, and the same applies below), and is connected to the core network CNW via the central site 4. A MEC (Multi-access Edge Computing) server 7 is set at the edge site #1_5. O-DU#3 is set at the edge site #2_5. A MEC server 7 is set at the edge site #2_5.

[0036] The communication control system 10 is connected to each station 4, 5 for communication. The communication control system 10 controls each O-DU 6. The communication control system 10 provides information for forming an AP cluster corresponding to the UE to the O-DU 6. The O-DU 6 forms an AP cluster corresponding to the UE for which it is responsible based on the information provided from the communication control system 10.

[0037] Figure 3 1 is a block diagram showing a configuration example of a communication control system 10 according to an embodiment. The communication control system 10 includes a "Non-RT RIC (Non-real-time Radio Access Network Intelligent Controller)" 11 and a "Near-RT RIC (Near-real-time Radio Access Network Intelligent Controller)" 12. The "Non-RT RIC" 11 is implemented using a SMO (Service and Management Orchestration) framework.

[0038] The "Non-RT RIC" 11 and the "Near-RT RIC" 12 collect information such as KPI (Key Performance Indicator) from the O-DU 6 via the O1 interface. The O1 interface is specified by the O-RAN (the aforementioned non-patent document 2) specification. The parameters that can be collected through the O1 interface correspond to the parameters specified in the aforementioned non-patent document 3. For example, they are parameters such as "download physical resource block utilization", "upload physical resource block utilization", "average download user throughput", "average upload user throughput", and "number of requested PDU sessions".

[0039] The "Non-RT RIC" 11 analyzes the information collected from the O-DU 6 and changes the settings for the "Near-RT RIC" 12 based on the analysis results. Here, the "Non-RT RIC" 11 provides the "Near-RT RIC" 12 with the setting change information via the A1 interface. The A1 interface is defined by the O-RAN specification.

[0040] The "Near-RT RIC" 12 analyzes the information collected from the O-DU 6 and changes the settings for the O-DU 6 based on the analysis result. Here, the "Near-RT RIC" 12 provides the O-DU 6 with the setting change information via the E2 interface. The E2 interface is defined by the open radio access network standard.

[0041] In addition, if Figure 3 As shown therein, as a functional structure, "Non-RT RIC" 11 constitutes a first control device, "Near-RT RIC" 12 constitutes a second control device, and O-DU 6 constitutes a signal processing device.

[0042] The following is a description of a cluster selection method for implementing interference removal according to the present embodiment. The present embodiment is summarized as follows, and it supplements the information collected within the framework of the existing method.

[0043] That is, the following problems exist in cluster selection based on the existing methods of non-patent document 1 and non-patent document 3. Specifically, since the information collected from DU to RIC for cluster selection includes power information such as SS-RSRP, but does not include phase information between AP-UE, this information cannot be grasped in RIC. (That is, in the existing method, the Performance Measurements information specified by 3GPP 28.552 [non-patent document 3] can be collected through the E2 / O1 interface. According to 3GPP 28.552, as a performance measurement related to MU-MIMO, scheduling statistical information such as "Scheduled PUSCH / PDSCH RBs for each layer of MU-MIMO" and power information such as SS-RSRP are specified, but the phase information between AP-UE is not specified.).

[0044] Therefore, according to the existing method, RIC cannot calculate the uplink correlation and downlink correlation between APs, and RIC selects APs with high SS-RSRP and high AP correlation as AP clusters. As a result, there is a risk that interference separation based on multiple input and multiple output cannot fully function in APs with high spatial correlation, and high wireless quality cannot be ensured.

[0045] Based on the above problem, in this embodiment, the resource allocation information of the following two reference signals is added to the data collection interface (E2 / O1 interface of O-RAN) from DU to RIC for uplink and downlink respectively, and the control of forming AP cluster is performed based on this information. In addition, as a result, it can be considered that the AP clusters formed in uplink and downlink are often the same, and there may be a case where the AP clusters formed in uplink and downlink are different.

[0046] (1) For the uplink, use the transfer function information estimated by DMRS

[0047] (2) For downlink, use the transfer function information estimated by SRS

[0048] Figure 4 is a step diagram of this embodiment related to the above (1) uplink, Figure 5 is a step diagram of this embodiment related to the above-mentioned (2) downlink. Figure 4 as well as Figure 5 In the example, UE, AP, CPU, and Near-RT RIC appear as action subjects. These are respectively related to the above Figure 2 as well as Figure 3 Each of UE#1, #2, ..., etc., each of AP2, any one of O-DU6, and "Near-RT RIC" 12 correspond to each other. Since the difference is obvious, the reference numerals are omitted, such as Figure 4 , 5 As shown in the figure, they are called UE, AP, CPU, and Near-RT RIC.

[0049] Furthermore, in the following description, Near-RT RIC is abbreviated as RIC.

[0050] In addition, Figure 4 as well as Figure 5 Before the step starts, an AP cluster is pre-formed. Figure 4 as well as Figure 5 As a method of pre-forming an AP cluster, for example, the method of the aforementioned patent document 1 may be followed, such as the following (a) and (b).

[0051] (a) Access point group information (information of access point cluster for each UE) indicating the configuration of an access point group for transmitting and receiving wireless signals to and from each UE from among a plurality of dispersedly arranged APs is transmitted from the RIC to the CPU.

[0052] (b) The CPU receives the AP group information sent from the RIC, and based on the received AP group information, performs signal processing related to the AP (channel estimation based on interference removal, etc.), thereby forming an AP cluster for each UE.

[0053] Alternatively, the method of this embodiment may be used to continuously implement the content of re-forming the AP cluster.

[0054] The following is about Figure 4 The steps of the implementation method related to the upstream are described.

[0055] In step S10, each UE sends a reference signal for measuring SS-RSRP to the corresponding AP (UE of the AP cluster determined by the UE), and the AP measures the received power of SS-RSPR. In step S11, each AP sends information on the SS-RSPR measured for each UE to the CPU.

[0056] In step S12, the CPU sends SS-RSPR information (SS-RSPR information of all APs and all UEs that the CPU is responsible for) to the RIC via the E2 interface.

[0057] In step S13, as the supplementary collection information in this embodiment as described above in the overview, the CPU sends "estimated channel information using DMRS of each UE-AP" to the RIC via the E2 interface. Here, the CPU estimates the estimated channel information as information of the transfer function h (channel matrix h) of the channel between each UE-AP in the formed cluster using the information of the SS-RSPR received in step S12, and thus can send the estimated channel information in step S13.

[0058] In step S14, the CPU uses the information received in steps S12 and S13 to select an AP cluster to be formed for each UE. In step S15, the CPU sends the information of the selected AP cluster to the CPU via the E2 interface. In step S16, the AP cluster is updated in the CPU using the selected and sent AP cluster, and instructions are sent to each AP and each UE to form the updated AP cluster.

[0059] The cluster selection in step S14 can be selected by using the SS-RSPR information received in step S12. For example, as in the existing method of the aforementioned non-patent document 1, the AP with the highest reference signal receiving power is selected as the main AP, and the APs within the reference signal receiving power threshold of the main AP are the AP clusters of the UE.

[0060] On the other hand, in this embodiment, as described above, in cluster selection based on SS-RSPR information, the estimated channel information received in step S13 is also used to prevent APs that may cause interference from being selected. Specifically, the following processes 1 and 2 can remove APs that may cause interference.

[0061] (Processing 1) Based on the information of the transfer function h, for each UE, an expected SINR value is calculated using an AP cluster in which the number of APs is increased or decreased from the existing AP cluster.

[0062] (Process 2) Determine whether the wireless quality required by each UE is met, and adjust the AP cluster to ensure the wireless quality within the limitation of computer resources. Figure 1 For example, it is determined whether the wireless quality required by UE#1 and UE#2 is met, and the AP clusters of UE#1 and UE#2 are adjusted to ensure the wireless quality within the limitations of the computing resources of CPU#1 and CPU#2, which are computers responsible for UE#1 and UE#2 respectively, resulting in the re-formation of the cluster.

[0063] When the wireless quality required by the UE for the service is insufficient, an AP that is not included in the AP cluster and has the highest RSRP is added to the AP cluster. When the quality is excessive (for example, more than +5dB), the AP with the lowest RSRP is removed from the AP cluster. All UEs perform the same process and process 1 is executed again. Repeating the process from 1 to 2 a certain number of times can provide the UE with sufficient quality.

[0064] In step S14, as described above, an AP cluster is formed again to avoid APs with high spatial correlation, and in step S16, the AP cluster is updated to the re-formed AP cluster, which can improve the wireless quality after the next step S17.

[0065] In step S17, based on the re-formed AP cluster, a signal storing DMRS and data for each resource block is sent from each UE to the corresponding AP. In step S18, each AP sends the result of demodulating the DMRS and data to the CPU. In step S19, the result is used to perform channel estimation. In step S20, a weight of the channel estimation result is generated (a channel matrix formed by estimating the characteristics of the transmission path from the UE on the transmitting side to the AP on the receiving side). In step S21, post-coding processing is performed to end. Figure 4 process.

[0066] The following is about Figure 5 The steps of the downlink-related implementation method are described.

[0067] In step S30, each AP sends a reference signal for measuring SS-RSRP to the corresponding UE (the UE belonging to the AP cluster determined by the AP), measures the received power of SS-RSPR in the UE, and replies the measurement result to the AP. In step S31, each AP sends the information of SS-RSPR measured for each UE to the CPU.

[0068] In step S32, the CPU sends SS-RSPR information (SS-RSPR information of all APs and all UEs that the CPU is responsible for) to the RIC via the E2 interface.

[0069] In step S33, as the supplementary collection information in the present embodiment as described above in the overview, the CPU sends "estimated channel information using the SRS of each UE-AP" to the RIC via the E2 interface. Here, similarly to step S13 in the uplink case, in step S33, the CPU also estimates the estimated channel information as information of the transfer function h (channel matrix h) of the channel between each UE-AP using the information of the SS-RSPR received in step S32 in the already formed cluster, and therefore the estimated channel information can be sent in step S33.

[0070] In step S34, the CPU selects an AP cluster to be formed for each UE by using the information received in steps S32 and S33. In step S35, the CPU sends the information of the selected AP cluster to the CPU via the E2 interface. In step S36, the AP cluster is updated in the CPU by the selected and sent AP cluster, and instructions are sent to each AP and each UE to form the updated AP cluster.

[0071] The cluster selection in step S34 can choose to use the SS-RSPR information received through step S32, or it can also be like the existing method of the aforementioned non-patent document 1, where the AP with the highest reference signal receiving power is used as the main AP, and the APs within the reference signal receiving power threshold of the main AP are the AP clusters of the UE.

[0072] On the other hand, in this embodiment, as described above, in cluster selection based on SS-RSPR information, the channel estimation information received in step S33 is used to prevent the selection of APs with high spatial correlation. Figure 4 Similarly to step S14, in step S14, the DMRS information is used as the information in the case of the uplink. On the contrary, in step S34, the SRS information is used as the information in the case of the downlink to perform the above-mentioned processes 1 and 2.

[0073] In step S34, as described above, an AP cluster is formed again to avoid APs with high spatial correlation, and in step S36, the AP cluster is updated to the re-formed AP cluster, thereby preventing the channel estimation accuracy from being reduced after the next step S37 and improving the wireless quality.

[0074] In step S37, based on the re-formed AP cluster, an SRS signal is sent from each UE to the corresponding AP. In step S38, each AP sends the received power of the SRS signal to the CPU. In step S39, the CPU uses the result to perform channel estimation. In step S40, a weight of the channel estimation result is generated (a channel matrix formed by estimating the characteristics of the transmission path from the UE on the transmitting side to the AP on the receiving side). In step S41, the CPU performs precoding processing. In step S42, the CPU sends download data to the AP (the weight obtained by the precoding processing). In step S43, the AP further sends the received download data to the UE, and the process ends. Figure 5 process.

[0075] According to the above-described embodiment, it is possible to select an AP cluster so that the spatial correlation becomes low. Various supplementary examples, alternative examples, additional examples, etc. are described below.

[0076] <About providing the hardware configuration and the present embodiment as a program>

[0077] Each function of the communication control system 10 is realized by providing the communication control system 10 with computer hardware such as a CPU and a memory and the CPU executing a computer program stored in the memory. In addition, the communication control system 10 can be configured using a general-purpose computer device, or it can also be configured as a dedicated hardware device. For example, the communication control system 10 can also be configured using a server computer connected to a communication network. In addition, each function of the communication control system 10 can also be realized by cloud computing. In addition, the communication control system 10 can be realized by a single computer, or the functions of the communication control system 10 can be dispersed across multiple computers.

[0078] The communication control system 10 of this embodiment can contribute to the improvement of information and communication technology infrastructure, thereby contributing to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations: "Building resilient infrastructure, promoting sustainable industrialization, and expanding innovation."

[0079] This application claims priority based on Japanese patent application No. 2022-159227 filed on October 3, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. A control device, comprising a user terminal, an access point for transmitting and receiving wireless signals to and from the user terminal, a plurality of signal processing devices for performing signal processing for the access point, and a control device in a radio access network conforming to the O-RAN (Open Radio Access Network) standard, wherein: The control device performs the following processing: a first process, in which information on received power of a reference signal transmitted via uplink and / or downlink between a user terminal and an access point is received from each of the plurality of signal processing devices; a second process, in which information of a transfer function of a channel between a user terminal and an access point for which the signal processing device is responsible is received from each of the plurality of signal processing devices; as well as A third process, in which an access point responsible for each user terminal is selected based on the information of the received power received through the first process and the information of the transfer function received through the second process.

2. The control device according to claim 1, wherein: The control device is implemented using a Near-RT RIC (Near Real-Time Radio Access Network Intelligent Controller), and each of the plurality of signal processing devices is implemented using an O-DU (Open Radio Access Network Distributed Unit). The reception of the second process is implemented using the interface between the Near-RT RIC and the O-DU.

3. The control device according to claim 1, wherein: In the third process, the selection is performed so that the received power becomes larger and the spatial correlation among the plurality of access points becomes lower.

4. A method, which is performed by a control device in a radio access network of O-RAN (Open Radio Access Network) standards, comprising a user terminal, an access point for transmitting and receiving radio signals to and from the user terminal, a plurality of signal processing devices for performing signal processing for the access point, and a control device, wherein: The method comprises the following steps: A first step, in which information on received power of a reference signal transmitted between a user terminal and an access point via uplink and / or downlink is received from each of the plurality of signal processing devices; A second step, in which information of a transfer function of a channel between a user terminal and an access point that the signal processing device is responsible for is received from each of the plurality of signal processing devices; as well as A third step, in which an access point responsible for each user terminal is selected based on the information of the received power received in the first step and the information of the transfer function received in the second step.

5. A program that causes a computer to function as a control device in a radio access network conforming to the O-RAN (Open Radio Access Network) standard, including a user terminal, an access point for transmitting and receiving radio signals to and from the user terminal, a plurality of signal processing devices for performing signal processing for the access point, and a control device, wherein: The program causes the computer to execute the following processing: a first process, in which information on received power of a reference signal transmitted via uplink and / or downlink between a user terminal and an access point is received from each of the plurality of signal processing devices; a second process, in which information of a transfer function of a channel between a user terminal and an access point for which the signal processing device is responsible is received from each of the plurality of signal processing devices; as well as A third process, in which an access point responsible for each user terminal is selected based on the information of the received power received through the first process and the information of the transfer function received through the second process.

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