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 of receiving, from each of the plurality of signal processing devices, information of resource elements allocated from a reference signal transmitted from a user terminal in charge of the signal processing device; 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 reception power received by the first process and the information of the resource element 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 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.

[0004] Figure 1 This is a diagram schematically showing the AP clustering technology as an existing method. As shown in Example EX1, 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, and 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.

[0005] 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.

[0006] 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.

[0007] Prior art literature

[0008] Non-patent literature

[0009] 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.

[0010] Non-patent document 2: O-RAN WG1, "Use Cases Detailed Specification", v06.00.02

[0011] Non-patent document 3: 3GPP TS28.552, "5G performance measurements", v16.1.0

[0012] Non-patent document 4: 3GPP TS38.211, "Physical channels and modulation" Summary of the invention

[0013] Problem that the invention aims to solve

[0014] However, in the AP clustering technology of the prior art, interference of reference signals may sometimes occur.

[0015] That is, in CF-mMIMO, the estimated channel calculated based on the reference signal is used to remove interference from the signal received and sent by the AP cluster. As the reference signal, DMRS (Demodulation Reference Signal) is used for uplink post-coding, and SRS (Sounding Reference Signal) is used for downlink pre-coding.

[0016] 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 resource element area that can be used in DMRS / SRS is specified in the 3GPP standard and has an upper limit. Therefore, sometimes due to congestion, reference signal interference occurs between UEs using the same resource elements and the channel estimation accuracy deteriorates. In the case of low channel estimation accuracy, there is a risk that interference removal processing using MMSE (Minimum Mean Square Error) and the like will not fully function, resulting in reduced wireless quality.

[0017] Figure 1 Example EX2 is an example in which interference of the reference signal occurs relative to the situation in Example EX1. Although interference removal is performed in CPU#1, REs of the reference signal overlap between UE#1 and #2, for example, interference occurs in AP#4.

[0018] Means used to solve problems

[0019] In view of the above problems in the prior art, the present invention provides a technology for selecting an AP cluster while avoiding interference of reference signals.

[0020] A control device involved in one embodiment of the present invention is a control device in a radio access network of O-RAN (Open Radio Access Network) specifications, 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 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 transmitted between the user terminal and the access point via uplink and / or downlink is received from each of the plurality of signal processing devices; a second processing, in which information on resource elements allocated in a reference signal transmitted from the user terminal for which the signal processing device is responsible is received from each of the plurality of signal processing devices; and a third processing, in which an access point responsible for each user terminal is selected based on the received power information received through the first processing and the resource element information received through the second processing.

[0021] Effects of the Invention

[0022] According to the present invention, by using information of resource elements, it is possible to select an AP cluster while avoiding interference of reference signals.

[0023] 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

[0024] 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.

[0025] Figure 1 It is a diagram schematically showing the existing method and its problems.

[0026] Figure 2 This is a block diagram showing a configuration example of a wireless access network according to an embodiment.

[0027] Figure 3 This is a block diagram showing a configuration example of a communication control system according to one embodiment.

[0028] Figure 4 This is a step diagram of the present embodiment related to the uplink.

[0029] Figure 5 This is a step diagram of the present embodiment related to downlink. DETAILED DESCRIPTION

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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".

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 allocation information of DMRS / SRS resources to each UE as reference signals used in each of the uplink and downlink, the 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 MU-MIMO-related performance measurements, 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 no DMRS / SRS-related information is specified.).

[0045] Therefore, according to the existing method, RIC cannot determine the AP with high interference caused by the duplication of DMRS / SRS resources between UEs, and RIC selects an AP with high SS-RSRP but low channel estimation accuracy due to DMRS / SRS interference as the AP cluster. As a result, in APs with low channel estimation accuracy and large errors between the actual channel and the estimated channel, interference separation based on MIMO may not fully function and high wireless quality may not be ensured.

[0046] 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.

[0047] (1) For uplink, DMRS resource allocation information

[0048] (2) For downlink, SRS resource allocation information

[0049] 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 3Each 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.

[0050] Furthermore, in the following description, Near-RT RIC is abbreviated as RIC.

[0051] 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).

[0052] (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.

[0053] (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.

[0054] Alternatively, the method of this embodiment may be used to continuously implement the content of re-forming the AP cluster.

[0055] The following is about Figure 4 The steps of the implementation method related to the upstream are described.

[0056] In step S10, each UE sends a reference signal for measuring SS-RSPR to the corresponding AP (UE of the AP cluster determined by the UE), and the AP measures the received power of SS-RSRP. In step S11, each AP sends information on the SS-RSPR measured for each UE to the CPU.

[0057] 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.

[0058] In step S13, as additional collection information in this embodiment as described above in the overview, the CPU sends DMRS resource allocation information to the RIC via the E2 interface. That is, for all UEs managed by the CPU, the resource (frequency band in RB (resource block)) allocation information of the DMRS reference signal is sent to the RIC. (In addition, for UEs in Figure 4 The cluster that has been formed before the process starts, because the CPU grasps the resource allocation information of the DMRS reference signal, it can send it to the RIC in order to form the information again. ).

[0059] 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.

[0060] 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.

[0061] On the other hand, in this embodiment, as described above, in cluster selection based on SS-RSPR information, by requiring restrictions on resource allocation information using DMRS received in step S13, APs that may interfere can be excluded from selection. Specifically, by the following processes 1 and 2, APs that may interfere can be removed.

[0062] (Process 1) In order to understand the interference state of the reference signal, the SIR (Signal Power to Interference Power Ratio) of the UE-AP group between each UE to which the same resource is allocated is calculated as follows.

[0063] The reference signal SIR=S / I.

[0064] Here, S is the value received through step S12 as the reference signal reception power between UE_k (k is the identifier of the UE and k=1, 2, ..., etc.) and AP_i (i is the identifier of the AP and i=1, 2, ..., etc.), and I is the total value of the reference signal reception power from all UE_k' (k'≠k) using the same resources of UE_k (the DMRS signal in the same frequency band is equivalent to the same resources and is independent of the object AP) other UE_k' (k'≠k) other than the UE_k itself.

[0065] (Process 2) AP_i whose calculated signal-to-interference ratio is below the threshold is restricted in cluster selection so as not to be included in the AP cluster of UE_k. (If the signal-to-interference ratio is greater than the threshold, this restriction is not required.)

[0066] In step S14, as described above, an AP cluster is formed again to avoid APs with low channel estimation accuracy. In step S16, the AP cluster can be updated to the re-formed AP cluster to prevent the channel estimation accuracy from decreasing after the next step S17 and improve the wireless quality.

[0067] 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.

[0068] The following is about Figure 5 The steps of the downlink-related implementation method are described.

[0069] 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.

[0070] 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.

[0071] In step S33, as the additional collection information in this embodiment as described above in the overview, the CPU sends the SRS resource allocation information to the RIC via the E2 interface. That is, for all UEs managed by the CPU, the SRS resource (frequency band in RB (resource block)) allocation information is sent to the RIC. (In addition, for Figure 5 Before the process starts and the cluster is formed, since the CPU has grasped the resource allocation information of the DMRS reference signal, it can send it to the RIC in order to form the information again. ).

[0072] 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.

[0073] 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.

[0074] On the other hand, in this embodiment, further, in the cluster selection based on the SS-RSPR information as described above, it is possible to impose a restriction on the resource allocation information using the SRS received in step S33 so that the AP that may cause interference is not selected. Figure 4 Similarly, in step S14, in step S14, the DMRS information is used as the information of the uplink situation. Conversely, in step S34, the SRS information is used as the information of the downlink situation, and the reference signal SIR=S / I calculation and threshold judgment based on the processing 1 and 2 are performed.

[0075] In step S34, as described above, an AP cluster is formed again to avoid APs with low channel estimation accuracy. In step S36, the AP cluster is updated to the re-formed AP cluster, which can prevent the channel estimation accuracy from decreasing after the next step S37 and improve the wireless quality.

[0076] 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.

[0077] According to the above-mentioned embodiment, it is possible to select an AP cluster while avoiding interference of reference signals. Various supplementary examples, alternative examples, additional examples, etc. are described below.

[0078] <About providing the hardware configuration and the present embodiment as a program>

[0079] 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.

[0080] 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."

[0081] This application claims priority based on Japanese patent application No. 2022-159226 filed on October 3, 2022, and all the contents described 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 on resource elements allocated in a reference signal transmitted from a user terminal 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 on the received power received through the first process and the information on the resource elements 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 in such a manner that reception power becomes larger and duplication of resource elements in the plurality of signal processing devices is avoided.

4. The control device according to claim 1, wherein: In the third process, for one or more second user terminals whose resource elements are the same as the resource elements between the first user terminal and the first access point, a signal power to interference power ratio is calculated by dividing the received power between the first user terminal and the first access point by the sum of the received powers corresponding to the same resource elements in the one or more second user terminals, and the first access point determined to have a small signal power to interference power ratio is removed from the access points selected for the first user.

5. 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 performs 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 on resource elements allocated in a reference signal sent from a user terminal for which the signal processing device is responsible is received from each of the plurality of signal processing devices; as well as The third step is to select an access point responsible for each user terminal based on the information of the received power received in the first step and the information of the resource element received in the second step.

6. 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 on resource elements allocated in a reference signal transmitted from a user terminal 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 on the received power received through the first process and the information on the resource elements received through the second process.

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