Control device, method and program

Abstract

To provide a control device that can select an AP cluster while avoiding interference of a reference signal.SOLUTION: The control device executes: first processing S12 for receiving information on received electric power of reference signals that are transmitted upward and / or downward between a user terminal UE and an access point AP, from each of a plurality of signal processors CPU; second processing S13 for receiving information on resource elements allocated to the reference signals from the user terminal UE which the signal processing devices CPU take charge of, from each of the plurality of signal processors CPU; and third processing S14 for selecting an access point AP which takes charge of the user terminal UE for each user terminal TE, on the basis of the information on the received electric power received in the first processing and information on the resource elements received in the second processing.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Conventional cellular systems have had the issue of degraded communication quality at the cell edge due to interference between wireless signals between cells. Therefore, in Beyond 5G (5G, fifth-generation mobile communication systems), CF-mMIMO (Cell-free massive MIMO) is attracting attention as a communication method that can eliminate interference between cells and equalize user throughput. By processing signals sent and received by distributed access points (APs) in a central processing unit (CPU), APs can work together to optimize the spatially multiplexed wireless signals for each terminal.

[0003] In order to reduce the amount of signal processing in the CPU, AP clustering technology has been proposed, which selects a group of APs (AP clusters) that transmit and receive data for each user [Non-Patent Document 1]. By processing only the transmitted and received signals of the AP clusters for each user in a coordinated manner, the amount of signal processing in the CPU can be reduced.

[0004] Figure 1 is a diagram that schematically illustrates the AP clustering technology, which is an existing method. As shown in example EX1, for each UE (user equipment) #1 and #2, AP #2 to AP #4 are selected as the AP group for UE #1, and their signals are collectively processed by the CPU at site #1, and AP #5 to AP #7 are selected as the AP group for UE #2, and their signals are collectively processed by the CPU at site #2.

[0005] Regarding the specific determination of the AP cluster, in order to select an appropriate AP cluster according to the user's movement, the AP cluster can be controlled using the RIC (RAN Intelligent Controller) defined in O-RAN (Open Radio Access Network) [Non-Patent Document 2] [Patent Document 1]. Also, in CF-mMIMO, a method of selecting an AP based on SS-RSRP (SS (synchronization signal) - reference signal received power), which is an existing IF (interface), has been proposed as an AP cluster selection method [Non-Patent Document 1]. The AP with the highest RSRP is designated as the master AP, and the AP within a threshold of the RSRP of the master AP is designated as the AP cluster for the UE.

[0006] Here, SS-RSRP is defined as a quality measurement value using a synchronization signal [Non-Patent Document 3], and allows a DU (distributed unit that is a CPU) to grasp the received power for each AP (RU). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Application No. 2021-195443 [Non-patent literature]

[0008] [Non-Patent Document 1] E. Bjornson and L. Sanguinetti, "Scalable Cell-Free Massive MIMO Systems," in IEEE Transactions on Communications, vol. 68, no. 7, pp. 4247-4261, July 2020. [Non-patent document 2] O-RAN WG1, "Use Cases Detailed Specification", v06.00.02 [Non-patent document 3] 3GPP(R) TS28.552, "5G performance measurements", v16.1.0 [Non-patent document 4] 3GPP(registered trademark) TS38.211, "Physical channels and modulation" Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the conventional AP clustering technique, interference of reference signals may occur.

[0010] In other words, CF-mMIMO uses an estimated channel calculated from a reference signal to remove interference from signals transmitted and received by an AP cluster. As reference signals, DMRS (Demodulation Reference Signal) is used for uplink postcoding, and SRS (Sounding Reference Signal) is used for downlink precoding.

[0011] In the 3GPP (registered trademark) standard [Non-Patent Document 4], REs (Resource Elements) used in DMRS / SRS are allocated to each UE connected by a DU (Distributed Unit, which is a CPU). The RE region available for DMRS / SRS is specified in the 3GPP (registered trademark) standard and has an upper limit. Therefore, depending on the congestion situation, interference of reference signals may occur between UEs using the same RE, leading to deterioration of channel estimation accuracy. If the channel estimation accuracy is low, interference cancellation processing using MMSE (Minimum Mean Square Error) or the like may not function sufficiently, and wireless quality may deteriorate.

[0012] Example EX2 in Figure 1 is an example in which reference signal interference occurs in the situation of example EX1.Although interference cancellation is performed in CPU #1, the RE of the reference signal overlaps between UE #1 and #2, and interference occurs, for example, at AP #4.

[0013] In view of the above-described problems with the conventional technology, an object of the present invention is to provide a control device, a method, and a program that can select an AP cluster while avoiding interference of reference signals. [Means for solving the problem]

[0014] To achieve the above object, the present invention provides a control device in a radio access network conforming to O-RAN (Open Radio Access Network) specifications, which includes user terminals, access points that transmit and receive radio signals to and from the user terminals, signal processing devices that perform signal processing for the access points, and a control device, the control device performing the following steps: a first process of receiving, from each of the plurality of signal processing devices, information on received power of reference signals transmitted in uplink and / or downlink between the user terminals and the access points, a second process of receiving, from each of the plurality of signal processing devices, information on resource elements allocated to reference signals from the user terminals served by that signal processing device, and a third process of selecting, for each user terminal, an access point that serves that user terminal based on the received power information received in the first process and the resource element information received in the second process. The present invention also provides a method and a program corresponding to the control device. [Effects of the Invention]

[0015] According to the present invention, by using information on resource elements, it is possible to select an AP cluster while avoiding interference of reference signals. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram schematically illustrating an existing method and its problems. [Figure 2]FIG. 1 is a block diagram illustrating an example of the configuration of a radio access network according to an embodiment. [Figure 3] 1 is a block diagram illustrating an example of the configuration of a communication control system according to an embodiment. [Figure 4] FIG. 10 is a diagram showing the procedure of the present embodiment for uplink. [Figure 5] FIG. 10 is a diagram showing a procedure for downlink according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] 2 is a block diagram showing an example of the configuration of a radio access network according to an embodiment, to which the O-RAN specification is applied.

[0018] In RAN1, a plurality of access points (AP) 2 (AP#1, AP#2, ...) are distributed. From the plurality of APs 2 distributed in RAN1, an AP cluster (a group of access points) is formed that transmits and receives radio signals to each user equipment (UE). In the example of FIG. 2, for example, an AP cluster is formed from two APs 2 (AP#1, AP#2) for UE#1. Similarly, AP clusters are formed for other UEs such as UE#2, depending on the UE.

[0019] Note that the example in Figure 2 is an example of a specific AP cluster formed for each UE at a specific time (moment), and as UEs and the like move over time, the AP cluster group formed by RAN1 of this embodiment will also change dynamically from moment to moment.

[0020] Each AP2 in an AP cluster of a certain UE transmits and receives wireless signals to and from the UE using its own antenna 3. For example, two AP2s (AP#1, AP#2) in the access point group of UE#1 transmit and receive wireless signals to and from UE#1 using their respective antennas 3.

[0021] Each AP cluster is communicatively connected to the O-DU (Distributed Unit) 6 that it is responsible for. The O-DU 6 performs signal processing for the AP cluster that it is responsible for. In the example of Fig. 2, for example, O-DU #1 performs signal processing for the AP cluster (AP #4, AP #5, AP #6) of UE #3. Other O-DUs such as #2 similarly perform signal processing for the AP cluster that they are responsible for.

[0022] The signal processing related to the access point group executed by the O-DU6 is, for example, signal processing such as SU-MIMO (Single User MIMO) and MU-MIMO (Multi-User MIMO).

[0023] O-DU#1 is provided in a central site 4 and is connected to a core network CNW. O-DU#2 is provided in an edge site #1_5 (here, an underscore is used as a separator to distinguish between identification number #1 and reference number 5, and the same applies hereinafter), and is connected to the core network CNW via the central site 4. A MEC (Multi-access Edge Computing) server 7 is provided in the edge site #1_5. O-DU#3 is provided in edge site #2_5. A MEC server 7 is provided in the edge site #2_5.

[0024] The communication control system 10 is connected to each of the sites 4 and 5 for communication. The communication control system 10 controls each O-DU 6. The communication control system 10 provides the O-DU 6 with information for forming an AP cluster corresponding to the UE. Based on the information provided by the communication control system 10, the O-DU 6 forms an AP cluster corresponding to the UE it is responsible for.

[0025] 3 is a block diagram showing an example of the configuration of a communication control system 10 according to an embodiment. The communication control system 10 includes a "Non-RT RIC (Non-real-time RAN Intelligent Controller)" 11 and a "Near-RT RIC (Near-real-time RAN Intelligent Controller)" 12. The "Non-RT RIC" 11 is realized using a Service and Management Orchestration (SMO) framework.

[0026] The "Non-RT RIC" 11 and the "Near-RT RIC" 12 collect information such as KPIs (Key Performance Indicators) from the O-DU 6 via the O1 interface. The O1 interface is defined in the O-RAN (Non-Patent Document 2) specifications. Parameters that can be collected by the O1 interface correspond to those defined in the Non-Patent Document 3. For example, these parameters include "DL PRB usage," "UL PRB usage," "Average DL UE throughput," "Average UL UE throughput," and "Number of PDU Sessions requested."

[0027] The "Non-RT RIC" 11 analyzes the information collected from the O-DU 6 and changes the settings of the "Near-RT RIC" 12 based on the analysis results. Here, the "Non-RT RIC" 11 provides the setting change information to the "Near-RT RIC" 12 via the A1 interface. The A1 interface is defined in the O-RAN specifications.

[0028] The "Near-RT RIC" 12 analyzes the information collected from the O-DU6 and changes the settings of the O-DU6 based on the analysis results. Here, the "Near-RT RIC" 12 provides the setting change information to the O-DU6 via the E2 interface. The E2 interface is defined in the O-RAN specifications.

[0029] As shown in Figure 3, in terms of functional configuration, the "Non-RT RIC" 11 constitutes the first control device, the "Near-RT RIC" 12 constitutes the second control device, and the O-DU 6 constitutes the signal processing device.

[0030] A cluster selection method for realizing interference cancellation according to this embodiment will be described below. The outline of this embodiment is as follows, and adds information to be collected within the framework of existing methods.

[0031] That is, the cluster selection using the existing methods of Non-Patent Documents 1 and 3 has the following problem. Specifically, although the information collected from the DU to the RIC for cluster selection includes power information such as SS-RSRP, the information does not include allocation information for each UE of DMRS / SRS resources, which are reference signals used in uplink and downlink, respectively, and therefore the RIC is unable to grasp this information. (That is, in the existing methods, Performance Measurements information specified in 3GPP (registered trademark) 28.552 [Non-Patent Document 3] can be collected over the E2 / O1 interface. 3GPP (registered trademark) 28.552 specifies scheduling statistical information such as "Scheduled PUSCH / PDSCH RBs per layer of MU-MIMO" and power information such as SS-RSRP as MU-MIMO-related Performance Measurements, but does not specify DMRS / SRS-related information.)

[0032] For this reason, with existing methods, the RIC is unable to identify APs with high interference caused by overlapping DMRS / SRS resources between UEs, and the RIC may end up selecting APs with high SS-RSRP but low channel estimation accuracy due to DMRS / SRS interference as an AP cluster.As a result, for APs with low channel estimation accuracy and large errors between the actual channel and the estimated channel, MIMO interference separation does not function sufficiently, and there is a risk that high wireless quality cannot be ensured.

[0033] In consideration of the above problem, in this embodiment, resource allocation information for the following two reference signals for uplink and downlink is added to the data collection IF (E2 / O1 interface of O-RAN) from the DU to the RIC, and control for forming AP clusters is performed based on this information. Note that while it is considered that the AP clusters formed as a result will often be the same for uplink and downlink, there may also be cases where the AP clusters formed for uplink and downlink are different. (1) DMRS resource allocation information for uplink (2) Downstream: SRS resource allocation information

[0034] Fig. 4 is a procedure diagram of this embodiment relating to the above (1) uplink, and Fig. 5 is a procedure diagram of this embodiment relating to the above (2) downlink. Note that in Figs. 4 and 5, the UE, AP, CPU, and Near-RT RIC appear as the operating entities. These correspond to each of the UEs #1, #2, ..., etc., each AP 2, any one of the O-DUs 6, and the "Near-RT RIC" 12 in Figs. 2 and 3 described above, but since the distinction is clear, the reference numerals will be omitted and these will be referred to as the UE, AP, CPU, and Near-RT RIC as shown in Figs. 4 and 5.

[0035] Furthermore, in the following description, Near-RT RIC will be abbreviated as RIC.

[0036] Note that an AP cluster is formed in advance before the procedures of Figures 4 and 5 are started, and the AP cluster can be re-formed by the procedures of Figures 4 and 5. A method for forming an AP cluster in advance may be, for example, in accordance with the method of Patent Document 1 cited above, as shown in the following (a) and (b). (a) Access point group information (AP cluster information for each UE) indicating the configuration of the AP group that transmits and receives wireless signals for each UE from multiple APs that are distributed in a distributed manner is sent from the RIC to the CPU. (b) The CPU receives the access point group information transmitted from the RIC, and performs signal processing related to the access points (such as channel estimation by interference removal) based on the received access point group information, forming an AP cluster for each UE.

[0037] Alternatively, the AP cluster may be re-formed continuously using the method of this embodiment.

[0038] Each step of the embodiment relating to the upstream in FIG. 4 will be described below.

[0039] In step S10, each UE transmits a reference signal for SS-RSRP measurement to a corresponding AP (a UE in an AP cluster already determined for the UE), and the AP measures the received power of SS-RSPR. In step S11, each AP transmits information on the SS-RSPR measured for each UE to the CPU.

[0040] In step S12, the CPU transmits SS-RSPR information (SS-RSPR information of all APs and all UEs managed by the CPU) to the RIC via the E2 interface.

[0041] In step S13, as described above in the overview, the CPU transmits DMRS resource allocation information to the RIC via the E2 interface as additional information to be collected in this embodiment. That is, the CPU transmits DMRS reference signal resource (frequency bands in RBs (resource blocks)) allocation information for all UEs that it is responsible for and manages to the RIC. (Note that for clusters that have already been formed before the start of the flow in FIG. 4, the CPU knows this DMRS reference signal resource allocation information, and can transmit this information to the RIC for re-formation.)

[0042] In step S14, the CPU selects an AP cluster to be formed for each UE using the information received in steps S12 and S13. In step S15, the CPU transmits information about the selected AP cluster to the CPU via the E2 interface. In step S16, the CPU updates the AP cluster using the selected and transmitted AP cluster, and transmits an instruction to each AP and each UE to form the updated AP cluster.

[0043] The cluster selection in step S14 may be performed 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 RSRP may be selected as the master AP, and the AP within a threshold value of the RSRP of the master AP may be selected as the AP cluster for the UE.

[0044] On the other hand, in this embodiment, as described above, in the cluster selection based on the SS-RSPR information, by imposing a constraint using the DMRS resource allocation information received in step S13, it is possible to prevent the selection of APs that may cause interference. Specifically, by the following processes 1 and 2, it is possible to exclude APs that may cause interference.

[0045] (Process 1) In order to grasp the interference state of the reference signal, the SIR (Signal to Interference Ratio) for each UE-AP pair between UEs to which the same resources are allocated is calculated as follows. Reference signal SIR=S / I

[0046] Here, S is the value received in step S12 as the RSRP between UE_k (k is the UE identifier, k=1, 2, ..., etc.) and AP_i (i is the AP identifier, i=1, 2, ..., etc.), and I is the sum of the RSRPs from all UE_k's other than the UE_k itself (k' ≠ k) that use the same resources as UE_k (DMRS signals in the same frequency band correspond to the same resources, regardless of the target AP).

[0047] (Process 2) A cluster selection constraint is imposed so that AP_i whose calculated SIR is equal to or less than a threshold is not included in the AP cluster of UE_k. (If the SIR is greater than the threshold, this constraint is not imposed.)

[0048] In step S14, as described above, an AP cluster is re-formed to avoid APs with low channel estimation accuracy, and in step S16 the AP cluster is updated to the re-formed one, thereby preventing a decrease in channel estimation accuracy in subsequent steps S17 and onwards and improving wireless quality.

[0049] In step S17, under the re-formed AP cluster, each UE transmits a signal containing DMRS and data for each RB to the corresponding AP, in step S18 each AP demodulates the DMRS signal and data and transmits the results to the CPU, in step S19 channel estimation is performed using the results, in step S20 weights for the channel estimation results (channel matrix that estimates the characteristics of the transmission path from the transmitting UE to the receiving AP) are generated, and in step S21 post-coding processing is performed, ending the flow of Figure 4.

[0050] Each step of the embodiment relating to the downstream of FIG. 5 will be described below.

[0051] In step S30, each AP transmits a reference signal for SS-RSRP measurement to a corresponding UE (a UE belonging to an AP cluster already determined by the AP), and the UE measures the received power of the SS-RSPR and returns the measurement result to the AP. In step S31, each AP transmits information on the SS-RSPR measured for each UE to the CPU.

[0052] In step S32, the CPU transmits SS-RSPR information (SS-RSPR information of all APs and all UEs managed by the CPU) to the RIC via the E2 interface.

[0053] In step S33, as described above in the overview, the CPU transmits SRS resource allocation information to the RIC via the E2 interface as additional information to be collected in this embodiment. That is, for all UEs managed by the CPU, resource allocation information (frequency bands in RBs (resource blocks)) for SRS reference signals is transmitted to the RIC. (Note that for clusters already formed before the start of the flow in FIG. 5, the CPU already knows the resource allocation information for the DMRS reference signals, and can transmit this information to the RIC for re-formation.)

[0054] In step S34, the CPU selects an AP cluster to be formed for each UE using the information received in steps S32 and S33. In step S35, the CPU transmits information about the selected AP cluster to the CPU via the E2 interface. In step S36, the CPU updates the AP cluster with the selected and transmitted AP cluster, and transmits an instruction to each AP and each UE to form the updated AP cluster.

[0055] The cluster selection in step S34 may be performed using the SS-RSPR information received in step S32. For example, as in the existing method of the aforementioned non-patent document 1, the AP with the highest RSRP may be selected as the master AP, and the AP within a threshold value from the RSRP of the master AP may be selected as the AP cluster for the UE.

[0056] On the other hand, in the present embodiment, as described above, in the cluster selection based on the information on the SS-RSPR, by imposing a constraint using the resource allocation information of the SRS received in step S33, it is possible to prevent the selection of an AP that may cause interference. Specifically, this is the same as step S14 in Fig. 4, but while step S14 uses the information on the DMRS as the information for the uplink, step S34 uses the information on the SRS as the information for the downlink, and the calculation of the reference signal SIR = S / I and the threshold determination by the above processes 1 and 2 may be performed.

[0057] In step S34, as described above, an AP cluster is re-formed to avoid APs with low channel estimation accuracy, and in step S36 the AP cluster is updated to the re-formed one, thereby preventing a decrease in channel estimation accuracy in subsequent steps S37 and onwards and improving wireless quality.

[0058] In step S37, each UE transmits an SRS signal to the corresponding AP under the re-formed AP cluster, and in step S38, each AP transmits the received power of the SRS signal to the CPU, and in step S39, the CPU uses the result to perform channel estimation, and in step S40, it generates a weight (a channel matrix that estimates the characteristics of the transmission path from the transmitting UE to the receiving AP) of the channel estimation result, and in step S41, the CPU performs precoding processing, and in step S42, the CPU transmits DL data (the weight obtained by the precoding processing) to the AP, and in step S43, the AP further transmits the received DL data to the UE, thereby completing the flow of Figure 5.

[0059] As described above, according to the embodiments of the present invention, it is possible to select an AP cluster while avoiding interference of reference signals. Various supplementary examples, alternative examples, additional examples, etc. will be described below.

[0060] <About the hardware configuration and providing this embodiment as a program> Each function of the communication control system 10 is realized by the communication control system 10 including computer hardware such as a CPU and memory, and the CPU executing a computer program stored in the memory. The communication control system 10 may be configured using a general-purpose computer device, or may be configured as a dedicated hardware device. For example, the communication control system 10 may be configured using a server computer connected to a communication network. Each function of the communication control system 10 may be realized by cloud computing. The communication control system 10 may be realized by a single computer, or may be realized by distributing the functions of the communication control system 10 across multiple computers.

[0061] The communication control system 10 of this embodiment can contribute to the development of infrastructure for information and communication technology, thereby contributing to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "Develop resilient infrastructure, promote sustainable industrialization, and foster innovation." [Explanation of symbols]

[0062] 10...Communication control system, 11...Non-RT RIC (first control device), 12...Near-RT RIC (second control device), 6...O-DU (signal processing device)

Claims

1. A control device in a radio access network conforming to O-RAN (Open Radio Access Network) specifications, the control device including: a user terminal; an access point that transmits and receives radio signals between the user terminal; a signal processing device that performs signal processing for the access point; and a control device, a first process of receiving, from each of the plurality of signal processing devices, information on received power of a reference signal transmitted in uplink and / or downlink between a user terminal and an access point; a second process of receiving, from each of the plurality of signal processing devices, information on resource elements allocated to reference signals from user terminals served by the signal processing devices; and a third process of selecting, for each user terminal, an access point that will serve that user terminal based on the received power information received in the first process and the resource element information received in the second process.

2. The control device is realized using a NearRT RIC (Near-Real Time RAN Intelligent Controller), and the signal processing device is realized using an O-DU (O-RAN Distributed Unit), The control device according to claim 1, wherein the reception of the second process is performed using an interface between a "NearRT RIC" and an O-DU.

3. The control device according to claim 1 , wherein in the third process, the selection is made so as to increase received power and to avoid overlapping of resource elements in a plurality of signal processing devices.

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

5. A method executed by a control device in a radio access network conforming to O-RAN (Open Radio Access Network) specifications, the method comprising: a user terminal; an access point that transmits and receives radio signals to and from the user terminal; a signal processing device that performs signal processing for the access point; and a control device, a first step of receiving, from each of the plurality of signal processing devices, information on received power of a reference signal transmitted in uplink and / or downlink between a user terminal and an access point; a second step of receiving, from each of the plurality of signal processing devices, information on resource elements allocated to reference signals from user terminals served by the signal processing devices; and a third step of selecting, for each user terminal, an access point that will serve that user terminal based on the received power information received in the first step and the resource element information 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 O-RAN (Open Radio Access Network) specifications, the program comprising: a user terminal; an access point that transmits and receives radio signals between the user terminal; a signal processing device that performs signal processing on the access point; and a control device, a first process of receiving, from each of the plurality of signal processing devices, information on received power of a reference signal transmitted in uplink and / or downlink between a user terminal and an access point; a second process of receiving, from each of the plurality of signal processing devices, information on resource elements allocated to reference signals from user terminals served by the signal processing devices; and a third process of selecting, for each user terminal, an access point that will serve that user terminal based on the received power information received in the first process and the resource element information received in the second process.

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