Communication terminals, programs, and wireless communication systems

Abstract

To improve communication quality of a communication terminal.SOLUTION: A communication terminal 3 includes: a terminal receiving unit 31 which receives quality measurement reference signals from a plurality of access points 2; a terminal control unit 34 which determines, when change in state of the communication terminal 3 is detected, one or more access points 2 for which a channel state is to be measured based on the quality measurement reference signals, out of the access points 2; and a terminal transmission unit 32 which transmits data, using a communication parameter determined based on the channel state measured based on the quality measurement reference signals transmitted from the determined one or more access points 2.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a communication terminal, a program, and a wireless communication system.

Background Art

[0002] Conventionally, a technique has been known in which a communication terminal (UE) performs data communication with a plurality of access points (APs). Patent Document 1 discloses a communication system in which a communication terminal can communicate with two access points. Non-Patent Document 1 discloses a Cell-Free Massive MIMO technique in which a plurality of access points form a dynamic cluster and the access points within the cluster communicate with a communication terminal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the wireless communication system disclosed in Non-Patent Document 1, the communication terminal communicates with multiple access points within a cluster corresponding to the communication terminal. The communication terminal periodically measures the channel state by measuring the characteristics of the CSI-RS (Channel State Information Reference Signal), which is a quality measurement reference signal transmitted from the access point, and adjusts the communication parameters based on the measurement results.

[0006] If the radio wave propagation environment around a communication terminal changes, unsuitable access points may arise. If communication parameters (e.g., modulation scheme or coding rate) are adjusted based on the results of measuring a quality measurement reference signal transmitted from an access point not used by the communication terminal, parameters unsuitable for communication between the communication terminal and the access point may be selected, potentially degrading communication quality.

[0007] Therefore, the present invention has been made in view of these points, and aims to improve the communication quality of communication terminals. [Means for solving the problem]

[0008] A first aspect of the present invention is a communication terminal that communicates with a communication control device via a plurality of access points, comprising: a receiving unit that receives quality measurement reference signals from the plurality of access points; a control unit that, when a change in the state of the communication terminal is detected, determines one or more of the plurality of access points to be used for measuring the channel state based on the quality measurement reference signals; and a transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signals transmitted from the one or more access points.

[0009] The communication terminal further includes a receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, and the control unit may select the one or more access points from the plurality of access points so as to satisfy the predetermined conditions.

[0010] The aforementioned predetermined condition may be that the power intensity of the quality measurement reference signal received by the communication terminal is equal to or greater than the intensity threshold.

[0011] The predetermined condition may also be that the difference between the power intensity of the quality measurement reference signal received by the communication terminal and the power intensity of the access point at which the power intensity of the quality measurement reference signal received by the communication terminal is maximum is greater than or equal to a predetermined threshold.

[0012] The aforementioned predetermined condition may also be that the number of the one or more access points whose channel state is to be measured based on the quality measurement reference signal is equal to or greater than a set threshold.

[0013] The control unit may, after determining the plurality of access points in the initial setup process based on the broadcast signal transmitted by the access point, determine one or more access points based on the predetermined conditions.

[0014] The control unit may, after determining one or more access points, determine one or more other access points if the predetermined conditions are no longer met due to a change in the state.

[0015] The control unit may select one or more access points that have relatively good quality communication channels with the communication terminal.

[0016] The control unit may determine the one or more access points based on the predetermined conditions included in the synchronization signal block (SSB) of the broadcast signal.

[0017] The transmitting unit transmits a reference signal, and the control unit may, after transmitting the reference signal, determine the one or more access points based on designation information that specifies the one or more access points, transmitted from a communication control device that has selected one or more access points based on the strength of the reference signal received by each of the plurality of access points.

[0018] A program according to a second aspect of the present invention causes a computer to function as a receiving unit that receives quality measurement reference signals from a plurality of access points; a control unit that, when a change in the state of the communication terminal is detected, determines one or more of the plurality of access points to be used for measuring the channel state based on the quality measurement reference signals; and a transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signals transmitted from the one or more access points.

[0019] A wireless communication system according to a third aspect of the present invention comprises a plurality of access points and a communication terminal that communicates with the plurality of access points, wherein each of the plurality of access points has a terminal-side transmitting unit that transmits a quality measurement reference signal and a terminal-side receiving unit that receives data from the communication terminal, and the communication terminal has a receiving unit that receives the quality measurement reference signal from the plurality of access points, a control unit that, when a change in the state of the communication terminal is detected, determines one or more of the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, and a transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from the one or more access points. [Effects of the Invention]

[0020] According to the present invention, the communication quality of communication terminals can be improved. [Brief explanation of the drawing]

[0021] [Figure 1] It is a diagram for explaining the outline of the wireless communication system S. [Figure 2] It is a diagram for explaining the outline of the wireless communication system S. [Figure 3] It is a diagram for explaining the outline of the wireless communication system S. [Figure 4] It is a diagram for explaining the outline of the wireless communication system S. [Figure 5] It is a diagram for explaining the switching process accompanying the change in the position of the communication terminal 3. [Figure 6] It is a diagram for explaining the switching process accompanying the change in the position of the communication terminal 3. [Figure 7] It is a diagram showing the concept of the switching process of the CSI measurement target in the wireless communication system S. [Figure 8] It is a diagram showing the configuration of the communication control device 1. [Figure 9] It is a diagram showing the configuration of the access point 2. [Figure 10] It is a diagram showing the configuration of the communication terminal 3. [Figure 11] It is a flowchart showing the processing flow in the communication terminal 3. [Figure 12] It is a sequence diagram showing the processing flow in the wireless communication system S.

Embodiments for Carrying Out the Invention

[0022] [Outline of Wireless Communication System S] Figures 1 to 4 are diagrams illustrating the overview of the wireless communication system S. The wireless communication system S comprises a communication control device 1, a plurality of access points 2, and a plurality of communication terminals 3. The wireless communication system S is a mobile communication system that enables communication terminals 3 to communicate with other communication terminals 3 via a network. The wireless communication system S is a system that enables data communication of communication terminals 3 without configuring a fixed cell, by having communication terminals 3 send and receive data with the plurality of access points 2, and the plurality of access points 2 send and receive data with the communication control device 1.

[0023] The communication control device 1 is a computer managed by the operator of the mobile communication system. The communication control device 1 transmits and receives data with multiple access points 2 and also communicates with other devices via the network.

[0024] The communication terminal 3 is a mobile information terminal, such as a smartphone, tablet, personal computer, or IoT (Internet of Things) device. The communication terminal 3 uses multiple access points 2 as antenna ports to send and receive data to and from the communication control device 1 via the multiple access points 2. When the communication terminal 3 establishes wireless communication links with the multiple access points 2, a cluster including the multiple access points 2 is formed.

[0025] Multiple access points 2 are configured to communicate with the communication control device 1 and the communication terminal 3. The multiple access points 2 are connected to the communication control device 1 via a wired connection, for example, but may also be connected to the communication control device 1 wirelessly.

[0026] Access point 2 functions as an antenna port when communication terminal 3 communicates with communication control device 1. By using multiple access points 2 included in the formed cluster as multiple antenna ports, communication terminal 3 constructs a distributed antenna system.

[0027] Each of the multiple access points 2 stores its own primary preamble data and transmits primary preamble sequence information when establishing a wireless communication link with the communication terminal 3. The primary preamble sequence information is information that allows the communication terminal 3 to identify the primary preamble data, and may be the primary preamble data itself, or it may be information that uniquely identifies the primary preamble data. Access point 2 notifies the terminal of the preamble sequence information using, for example, SS / PBCH (Synchronization Signal / Physical Broadcast Channel), which is an example of a broadcast signal.

[0028] Access point 2 stores the primary preamble data of other nearby access points 2 as its secondary preamble data. Access point 2 also stores the primary preamble data of other access points 2 notified by, for example, communication control device 1, as secondary preamble data.

[0029] Access point 2 determines whether the terminal preamble data transmitted by communication terminal 3 corresponds to either the main preamble data or the sub-preamble data, and switches the subsequent processing depending on whether the terminal preamble data corresponds to the main preamble data or the sub-preamble data.

[0030] The following outlines the initial setup process (RRC Configuration) of the wireless communication system S, referring to Figures 1 to 4. Figures 1 to 4 show four access points 2 and one communication terminal 3, but the number of access points 2 and communication terminals 3 is arbitrary.

[0031] In Figure 1, "P:1" displayed below access point 2-1 indicates that access point 2-1 stores preamble data 1 (hereinafter sometimes referred to as "PR1") as its primary preamble data. "S:2,3,4" indicates that access point 2-1 stores preamble data 2, 3, and 4 (hereinafter sometimes referred to as "PR2", "PR3", and "PR4", respectively) as secondary preamble data, which are the primary preamble data of the neighboring access points 2-2, 2-3, and 2-4.

[0032] The "P:2" displayed below access point 2-2 indicates that access point 2-2 stores PR2 as its primary preamble system. "S:1,3,4" indicates that access point 2-2 stores PR1, PR3, and PR4, which are the primary preamble data of its neighboring access points 2-1, 2-3, and 2-4, as secondary preamble data.

[0033] As shown in Figure 1, first, when no cluster is formed, multiple access points 2 transmit broadcast signals containing preamble sequence information corresponding to the stored main preamble data. Specifically, access points 2-1 to 2-4 each transmit broadcast signals containing PR1 to PR4. Communication terminal 3 receives these broadcast signals.

[0034] The communication terminal 3 selects the access point 2 that transmitted the broadcast signal that satisfies predetermined initial setting conditions from among the received broadcast signals. The initial setting conditions are, for example, the highest received signal level, but the initial setting conditions are not limited to this and may be a combination of multiple conditions. In this example, the broadcast signal containing PR2 has the highest received signal level, and the communication terminal 3 selects access point 2-2.

[0035] In this case, as shown in Figure 2, the communication terminal 3 transmits a signal containing PR2 as terminal preamble data in order to establish a wireless communication link with access point 2-2. Terminal preamble data is the preamble data included in the data transmitted by the communication terminal 3. The wireless communication link establishment process is, for example, a 4-step RACH (Random Access Channel) process, and the communication terminal 3 transmits a Msg 1 signal containing PR2 as Msg 1 in the 4-step RACH process. The Msg 1 signal contains the UE-ID, which is terminal identification information for identifying the communication terminal 3.

[0036] Multiple access points 2 receive a signal containing PR2 and compare it with the main preamble data and sub-preamble data stored in their own memory. If the received PR2 corresponds to either the main preamble data or sub-preamble data stored in their own memory, access point 2 transmits the UE-ID contained in the received Msg 1 signal and reception timing data indicating the timing at which the Msg 1 signal was received to the communication control device 1.

[0037] A received PR2 corresponds to either the main preamble data or the sub-preamble data stored by the access point 2 if it can determine that the received PR2 was created based on either the main preamble data or the sub-preamble data stored by the access point 2, for example, if the received PR2 matches either the main preamble data or the sub-preamble data. If the received PR2 does not correspond to either the main preamble data or the sub-preamble data stored by the access point 2, the access point 2 terminates processing without transmitting the UE-ID and received timing data to the communication control device 1.

[0038] In the example shown in Figure 2, access point 2-2, whose PR2 in the Msg 1 signal corresponds to its main preamble data, and access points 2-1, 2-3, and 2-4, whose PR2 in the Msg 1 signal corresponds to their sub-preamble data, transmit UE-IDs to the communication control device 1. Multiple access points 2 transmit the UE-IDs between the time they receive terminal preamble data from the communication terminal 3 and the completion of the 4-step RACH process between access point 2-2 and the communication terminal 3.

[0039] Multiple access points 2 may, for example, send a UE-ID at the time when they expect the access point 2-2 selected by the communication terminal 3 to complete the 4-step RACH process. Multiple access points 2 may also send a UE-ID while access point 2-2 is performing the 4-step RACH process, or they may monitor the data being sent and received during the 4-step RACH process and send a UE-ID when the 4-step RACH process is completed.

[0040] Access point 2-2, having received its main preamble data PR2 from communication terminal 3, establishes a wireless communication link between access point 2-2 and communication terminal 3 by exchanging messages from Msg 2 onward in the 4-step RACH process. Once the 4-step RACH process is complete, access point 2-2 notifies communication control device 1 that the wireless communication link has been established. Access points 2-1, 2-3, and 2-4 recognize that the wireless communication link between access point 2-2 and communication terminal 3 has been established by observing the 4-step RACH process performed between access point 2-2 and communication terminal 3.

[0041] Next, as shown in Figure 4, the communication control device 1 creates scheduling information to notify each of the three access points 2, including access point 2-2 and access points 2-1 and 2-3, which received the UE-ID from the communication terminal 3 at approximately the same time as access point 2-2, in order to send and receive data with the communication terminal 3. The scheduling information includes the frequency and time (slot) to be assigned to each access point 2, as well as the precoding coefficients used for the download link. The communication control device 1 notifies access points 2-1, 2-2, 2-3, and 2-4 of the scheduling information. Access point 2-2 transmits the notified scheduling information to the communication terminal 3. As a result, an initial cluster consisting of access points 2-1, 2-2, 2-3, and 2-4 is formed.

[0042] From this point onward, communication terminal 3 initiates data communication based on scheduling information. Specifically, it transmits data at frequencies and times when access points 2-1, 2-2, 2-3, and 2-4 can receive data, and receives data at frequencies and times when access points 2-1, 2-2, 2-3, and 2-4 transmit data.

[0043] The communication control device 1 or the communication terminal 3 may determine a plurality of access points 2 that constitute the initial cluster, which are multiple access points 2 whose received power of the broadcast signal received by the communication terminal 3 from the access point 2 is equal to or greater than a threshold, or a predetermined number of multiple access points 2 in descending order of received power of the broadcast signal. Alternatively, the access points 2 may be determined based on the access point 2 with the highest received power of the broadcast signal, with the difference being within a threshold.

[0044] However, since there is an upper limit to the transmission power of communication terminal 3, if the distance between communication terminal 3 and access point 2 increases, or if the radio wave environment of communication terminal 3 deteriorates, the signal transmitted by communication terminal 3 may not reach access point 2. As a result, a situation may arise where communication terminal 3 does not use some of the access points 2 among the multiple access points 2 in the cluster.

[0045] In this situation, if communication terminal 3 measures the power of the CSI-RS (Channel State Information Reference Signal), which is a quality measurement reference signal transmitted from access point 2 that is not used by communication terminal 3, the result of the CSI-RS measurement (hereinafter referred to as "CSI measurement") will not accurately represent the state of the communication channel between communication terminal 3 and access point 2 that is used by communication terminal 3. As a result, there is a risk that communication parameters such as the coding rate or modulation scheme, which are determined based on the results of the CSI measurement, will not be set appropriately.

[0046] Therefore, it is desirable that the communication terminal 3 does not measure the power of the CSI-RS transmitted from access points 2 that are not being used. This also leads to a reduction in the power consumption of the communication terminal 3. Thus, it is necessary for the communication terminal 3 to switch which access point 2 is the target of CSI measurement depending on the status of the communication terminal 3 and the multiple access points 2.

[0047] Figures 5 and 6 illustrate the switching process associated with changes in the location of the communication terminal 3. Figure 5(a) shows the positional relationship between multiple access points 2 and the communication terminal 3. Figure 5(b) shows the received power intensity at the communication terminal 3 of the broadcast signal, including preamble data, transmitted by each of the multiple access points 2.

[0048] In the state shown in Figure 5(a), the distance between communication terminal 3 and access points 2-2 and 2-3 is smaller than the distance between communication terminal 3 and access points 2-1 and 2-4. Therefore, as shown in Figure 5(b), the received power at access points 2-2 and 2-3 is greater than the received power at access points 2-1 and 2-4. If communication terminal 3 is to measure two access points 2, then in this case, access points 2-2 and 2-3 form cluster CL1, and although they are included in cluster CL1, access points 2-2 and 2-3 are the targets of CSI measurement.

[0049] Figure 6(a) shows that the communication terminal 3 has moved from the state shown in Figure 5(a), and the distance between the communication terminal 3 and access points 2-1 and 2-4 is smaller than the distance between the communication terminal 3 and access points 2-2 and 2-3. Therefore, as shown in Figure 6(b), the received power at access points 2-1 and 2-4 is greater than the received power at access points 2-2 and 2-3. In this case, access points 2-1 and 2-4 form cluster CL2, and access points 2-1 and 2-4 included in cluster CL2 become the targets of CSI measurement.

[0050] Figure 7 is a diagram illustrating the concept of the switching process for CSI measurement targets in the wireless communication system S. Each of the multiple squares containing numbers in Figure 7 represents an access point 2. Figure 7(a) shows that when the RRC Configuration is completed and the communication terminal 3 is connected to the communication control device 1, access points 2-1 to 2-6 are selected as multiple access points 2 that constitute the initial cluster shown by the dashed line. The initial cluster contains more access points 2 than or equal to the number of clusters composed of one or more access points 2 that are the targets of CSI measurement.

[0051] Figure 7(b) shows that at time T=1, access points 2-3 to 2-6 were selected by communication terminal 3 for CSI measurement, and cluster CL(1), shown by the dashed line, was formed. Figure 7(c) shows that at time T=2, access points 2-2 to 2-5 were selected by communication terminal 3 for CSI measurement, and cluster CL(2) was formed. Subsequently, the cluster changes over time, and at time T=10, cluster CL(10), composed of access points 2-1 to 2-4, is formed.

[0052] Subsequently, when RRC Configuration is performed again, access points 2-2 to 2-7 are selected as the targets for communication terminal 3. From this point onward, until further RRC Configuration is performed, the cluster that communication terminal 3 targets for CSI measurement will switch depending on the status of communication terminal 3, as shown in Figures 7(b) to 7(d). The configuration and operation of the communication control device 1, access point 2, and communication terminal 3 will be described in detail below.

[0053] [Configuration of Communication Control Device 1] Figure 8 shows the configuration of the communication control device 1. The communication control device 1 includes an information receiving unit 11, an information transmitting unit 12, a storage unit 13, and a device control unit 14.

[0054] The information receiving unit 11 receives various types of information from multiple access points 2. For example, the information receiving unit 11 receives UE-IDs received from communication terminals 3 that are the communication targets of the multiple access points 2.

[0055] The information transmission unit 12 transmits various types of information to multiple access points 2. For example, the information transmission unit 12 transmits scheduling information created by the device control unit 14 to multiple access points 2.

[0056] The storage unit 13 has storage media such as ROM (Read Only Memory), RAM (Random Access Memory), and SSD (Solid State Drive). The storage unit 13 stores programs executed by the device control unit 14. The storage unit 13 also stores scheduling information corresponding to each of the multiple access points 2.

[0057] The device control unit 14, for example, has a CPU (Central Processing Unit) and realizes various functions performed by the communication control device 1 by executing programs stored in the memory unit 13. The device control unit 14 functions, for example, as an information creation unit that creates scheduling information in response to the information receiving unit 11 receiving UE-IDs from each of the multiple access points 2.

[0058] [Configuration of Access Point 2] Figure 9 shows the configuration of access point 2. Access point 2 includes a terminal-side communication unit 21, a network-side communication unit 22 (hereinafter referred to as "NW-side communication unit 22"), a storage unit 23, and a control unit 24.

[0059] The terminal-side communication unit 21 includes a device that performs communication processing for sending and receiving data with the communication terminal 3, and has a terminal-side transmitting unit 211 and a terminal-side receiving unit 212. The terminal-side transmitting unit 211 and the terminal-side receiving unit 212 operate based on the control of the control unit 24.

[0060] The terminal-side transmitting unit 211 transmits an SS / PBCH signal, which is a broadcast signal containing main preamble sequence information corresponding to the main preamble data stored in the storage unit 23, when a wireless communication link has not been established with the communication terminal 3. The broadcast signal also includes condition information indicating predetermined conditions used by the communication terminal 3 to determine a plurality of access points 2 for which CSI measurement will be performed. The predetermined conditions may be, for example, that the power intensity of the CSI-RS received by the communication terminal 3 is equal to or greater than a strength threshold. The predetermined conditions may also be that the number of access points 2 for which CSI measurement will be performed is equal to or greater than a set threshold. The predetermined conditions may also be that the difference between the power intensity of the quality measurement reference signal received by the communication terminal 3 and the power intensity of the access point 2 where the power intensity of the quality measurement reference signal received by the communication terminal 3 is maximum is equal to or greater than a predetermined threshold.

[0061] The terminal-side receiving unit 212 receives various data from the communication terminal 3. For example, the terminal-side receiving unit 212 receives terminal preamble data and the UE-ID of the communication terminal 3 from the communication terminal 3. When the access point 2 performs a 4-step RACH process with the communication terminal 3, the terminal-side receiving unit 212 receives the Msg 1 signal transmitted by the communication terminal 3. After the wireless communication link with the communication terminal 3 is established, the terminal-side receiving unit 212 receives the data transmitted by the communication terminal 3 to the communication control device 1 and notifies the control unit 24 of the received data.

[0062] The NW-side communication unit 22 includes a device that performs communication processing for sending and receiving data with the communication control device 1, and has a network-side transmission unit 221 (hereinafter referred to as "NW-side transmission unit 221") and a network-side reception unit 222 (hereinafter referred to as "NW-side reception unit 222"). The NW-side transmission unit 221 and the NW-side reception unit 222 operate based on the control of the control unit 24.

[0063] The NW-side transmitting unit 221 transmits the UE-ID of the communication terminal 3 and time data indicating the time the terminal preamble data was received to the communication control device 1 when the terminal preamble data received from the communication terminal 3 corresponds to either the main preamble data or the sub-preamble data stored in the storage unit 23.

[0064] The NW-side transmitting unit 221 may send notification data to the communication control device 1 indicating that it has received terminal preamble data corresponding to the main preamble data when the terminal preamble data received from the communication terminal 3 corresponds to the main preamble data. The NW-side transmitting unit 221 may also send notification data to the communication control device 1 indicating that it has received terminal preamble data corresponding to the sub-preamble data when the terminal preamble data received from the communication terminal 3 corresponds to the sub-preamble data. After the wireless communication link between the access point 2 and the communication terminal 3 is established, the NW-side transmitting unit 221 transmits the data to be sent to the communication control device 1.

[0065] The NW-side receiving unit 222 receives data transmitted from the communication control device 1. For example, the NW-side receiving unit 222 receives scheduling information from the communication control device 1 that specifies the timing and frequency for transmitting data to the communication terminal 3. The NW-side receiving unit 222 notifies the control unit 24 of the received scheduling information. The NW-side receiving unit 222 may also store the received scheduling information in the storage unit 23.

[0066] The storage unit 23 has storage media such as ROM (Read Only Memory), RAM (Random Access Memory), and SSD (Solid State Drive). The storage unit 23 stores the program executed by the control unit 24. The storage unit 23 also stores the main preamble data assigned to access point 2 and the sub-preamble data assigned to other access point 2. Furthermore, the storage unit 23 stores various types of data used by access point 2 to relay data transmitted and received between the communication control device 1 and the communication terminal 3.

[0067] The control unit 24 includes, for example, a CPU (Central Processing Unit). The control unit 24 executes a program stored in the memory unit 23 to establish a wireless communication link with the communication terminal 3 and performs various processes to relay data transmitted and received between the communication control device 1 and the communication terminal 3.

[0068] The control unit 24 controls the operation of the terminal-side transmitter 211, the terminal-side receiver 212, the network-side transmitter 221, and the network-side receiver 222. For example, the control unit 24 notifies the terminal-side transmitter 211 of the main preamble data stored in the storage unit 23 and controls the terminal-side transmitter 211 to transmit a notification signal including the main preamble data. The control unit 24 also controls the network-side transmitter 221 to transmit a UE-ID to the communication control device 1 when the terminal preamble data received from the communication terminal 3 corresponds to either the main preamble data or the sub-preamble data stored in the storage unit 23.

[0069] When the terminal preamble data received from the communication terminal 3 corresponds to the main preamble data or sub-preamble data stored in the storage unit 23, the control unit 24 stores the UE-ID, which is terminal identification information for identifying the communication terminal 3, in the storage unit 23.

[0070] The control unit 24 controls the terminal-side transmitting unit 211 to execute the process of establishing a wireless communication link with the communication terminal 3 when the terminal preamble data received from the communication terminal 3 corresponds to the main preamble data stored in the storage unit 23. The control unit 24 controls the terminal-side receiving unit 212 to receive data transmitted and received while the other access point 2 is performing the process of establishing a wireless communication link with the communication terminal 3 when the terminal preamble data received from the communication terminal 3 corresponds to the sub-preamble data stored in the storage unit 23.

[0071] The control unit 24 controls the terminal-side transmitting unit 211 to transmit data to the communication terminal 3 based on the scheduling information received by the NW-side receiving unit 222 from the communication control device 1. The control unit 24 controls the terminal-side receiving unit 212 to receive data from the communication terminal 3 based on the scheduling information. For example, if the UE-ID included in the scheduling information corresponds to a UE-ID stored in the storage unit 23, the control unit 24 controls the terminal-side transmitting unit 211 and the terminal-side receiving unit 212 to send and receive data to and from the communication terminal 3 based on the frequency and time included in the scheduling information.

[0072] [Configuration of communication terminal 3] Figure 10 shows the configuration of the communication terminal 3. The communication terminal 3 includes a terminal receiving unit 31, a terminal transmitting unit 32, a storage unit 33, and a terminal control unit 34.

[0073] The terminal receiver 31 receives various types of information from multiple access points 2. The terminal receiver 31 receives CSI-RS, which is a reference signal for quality measurement, from each of the multiple access points 2. The terminal receiver 31 receives main preamble sequence information assigned to each of the multiple access points 2.

[0074] Furthermore, the terminal receiving unit 31 receives condition information from the communication control device 1 via the multiple access points 2, which indicates predetermined conditions for determining one or more access points 2 to be used for CSI measurement. The terminal receiving unit 31 receives the condition information, for example, through a synchronization signal block (SSB) included in the broadcast signal transmitted by the multiple access points 2.

[0075] The terminal transmission unit 32 transmits various information to multiple access points 2. For example, the terminal transmission unit 32 transmits terminal preamble data corresponding to one of the multiple main preamble data received by the terminal reception unit 31 using RACH (Random Access Channel). Specifically, for example, the terminal transmission unit 32 transmits terminal preamble data corresponding to the main preamble data received from an access point 2 selected by the terminal control unit 34 from among the multiple access points 2. The terminal preamble data may be data that matches the main preamble data, or it may be data created by converting the main preamble data based on predetermined conversion rules.

[0076] Furthermore, the terminal transmission unit 32 transmits data using communication parameters determined based on the channel status measured based on the CSI-RS transmitted from one or more access points 2. For example, the terminal transmission unit 32 transmits a CS report showing channel quality indicators such as RI (Rank Indicator), PMI (Precoding Matrix Indicator), and CQI (Channel Quality Indicator) based on the CSI measurement results notified by the terminal control unit 34, and transmits data using communication parameters (e.g., precoding matrix, rank, modulation scheme, and coding rate) determined by the communication control device 1 based on the transmitted channel quality indicators.

[0077] The memory unit 33 has storage media such as ROM and RAM. The memory unit 33 stores the program executed by the terminal control unit 34. The memory unit 33 also stores the UE-ID.

[0078] The terminal control unit 34, for example, has a CPU and implements various functions performed by the communication terminal 3 by executing programs stored in the memory unit 33. For example, in the initial setup process, the terminal control unit 34 determines the multiple access points 2 that constitute the initial cluster based on the received power of the broadcast signals received by the terminal receiving unit 31 from each of the multiple access points 2.

[0079] Specifically, in order to determine the initial cluster using the procedure described with reference to Figures 1 to 4, the terminal control unit 34 first selects one access point 2 based on the received power of the broadcast signal received by the terminal receiving unit 31. The terminal control unit 34 creates terminal preamble data corresponding to the main preamble sequence information received from the selected access point 2 and has the terminal transmitting unit 32 transmit the created terminal preamble data. Subsequently, the terminal control unit 34 determines multiple access points 2 that constitute the initial cluster based on scheduling information transmitted from the communication control device 1 via the access point 2.

[0080] After determining multiple access points 2 in the initial setup process, the control unit 34 determines one or more access points 2 to be subject to CSI measurement based on predetermined conditions. That is, the terminal control unit 34 selects one or more access points 2 from multiple access points 2 that constitute the initial cluster so as to satisfy predetermined conditions indicated by the condition information included in the synchronization signal block of the broadcast signal transmitted by the access point 2. As described above, the predetermined conditions are the condition that the power intensity of the quality measurement reference signal received by the communication terminal is equal to or greater than the intensity threshold, or the condition that the number of access points 2 to be subject to CSI measurement (i.e., the number of access points 2 included in the cluster to be measured) is equal to or greater than the set number threshold. The predetermined conditions may also be that the difference in the power intensity of the quality measurement reference signal received by the communication terminal 3 with respect to the power intensity of the access point 2 where the power intensity of the quality measurement reference signal received by the communication terminal 3 is maximum is equal to or greater than the predetermined threshold.

[0081] The terminal control unit 34 performs channel state measurement (i.e., CSI measurement) based on the CSI-RS received by the terminal receiving unit 31 from one or more access points 2 included in the selected cluster. For example, the terminal control unit 34 identifies the state of the radio waves that the communication terminal 3 is receiving from one or more access points 2 by at least one of the following: CSI reference signal received power (CSI-RSRP), CSI received signal strength indicator (CSI-RSSI), or CSI reference signal received quality (CSI-RSRQ). The terminal control unit 34 causes the terminal transmitting unit 32 to transmit channel quality indicators such as RI, PMI, and CQI identified by the CSI measurement.

[0082] However, if CSI measurements are performed based on CSI-RS transmitted from access point 2 with poor channel conditions, the problem may arise that appropriate communication parameters cannot be determined, as described above. Therefore, the terminal control unit 34 selects one or more access points with relatively good communication channel quality with respect to the communication terminal 3 as the access point 2 to be measured for CSI. The terminal control unit 34 may also select one or more access points 2 that have relatively good communication channel quality with respect to the communication terminal 3 and that meet predetermined conditions.

[0083] The terminal control unit 34 monitors the state of the communication terminal 3, and when it detects a change in state, it determines one or more access points 2 to be used for CSI measurement from among a plurality of access points corresponding to predetermined conditions. After determining one or more access points 2, the terminal control unit 34 may determine one or more other access points 2 if the predetermined conditions are no longer met due to a change in state. A change in state may be, for example, a change in the radio wave propagation environment around the communication terminal 3, or a change in the number of other communication terminals 3 communicating simultaneously in the vicinity, as identified by interference measurement by the communication terminal 3. A change in state may also be a change in the position of the communication terminal 3.

[0084] [Processing flow in communication terminal 3] Figure 11 is a flowchart showing the processing flow in communication terminal 3. The flowchart shown in Figure 11 starts from the point when communication terminal 3 performs initial setup processing (e.g., RRC Configuration).

[0085] The terminal control unit 34 determines multiple access points 2 that constitute the initial cluster by following the procedure described, for example, with reference to Figures 1 to 4 (S1). The terminal control unit 34 may determine the multiple access points 2 itself, or it may determine the multiple access points 2 based on information transmitted from the communication control device 1.

[0086] Next, the terminal control unit 34 measures, for example, the received power of the signal received by the terminal receiving unit 31 from the access point 2 (S2), and based on the measurement results, determines a cluster including one or more access points 2 that will be subject to CSI measurement (S3).

[0087] Subsequently, the terminal control unit 34 measures the received power of signals received from one or more access points 2 included in the determined cluster (S4). Based on the measured received power, the terminal control unit 34 determines whether or not the state of the communication terminal 3 has changed (S5). If the terminal control unit 34 determines that the state of the communication terminal 3 has not changed (NO in S5), it periodically measures the received power without changing the cluster targeted for CSI measurement (S4).

[0088] When the terminal control unit 34 determines that the state of the communication terminal 3 has changed (YES in S5), it determines whether or not it is necessary to change the cluster to be measured for CSI (S6). The terminal control unit 34 determines that a change in the cluster is necessary if, for example, a predetermined condition notified by the communication control device 1 via the access point 2 is no longer met (YES in S6), and determines that a change in the cluster is not necessary if the predetermined condition is met, and returns the process to S4 (NO in S6).

[0089] If the terminal control unit 34 determines that a cluster change is necessary (YES in S6), it changes the cluster by re-selecting one or more access points 2 that meet predetermined conditions from among multiple access points 2 (S7). After that, the terminal control unit 34 determines whether or not a reset initial setup process is necessary (S8). If a reset initial setup is not necessary (NO in S8), the terminal control unit 34 determines whether or not an operation to terminate communication has been performed (S9). If communication is to continue (NO in S9), it repeats the processes from S4 to S9. If the terminal control unit 34 determines that a reset initial setup is necessary (YES in S8), it returns to the process in S1 and resets the initial cluster.

[0090] [Processing flow in wireless communication system S] Figure 12 is a sequence diagram showing the processing flow in the wireless communication system S. In Figure 12, "CPU" represents the communication control device 1, "AP" represents the access point 2, and "UE" represents the communication terminal 3. The processing shown in Figure 11 starts from a state where the communication terminal 3 is not connected to the access point 2.

[0091] The communication terminal 3 performs the initial setup process (RRC Configuration) according to the procedure shown in Figures 1 to 4, and determines the initial cluster including access points 2-1, 2-2, 2-3, and 2-4. Subsequently, based on predetermined conditions notified by the communication control device 1, it determines the cluster including one or more access points 2 to be measured for CSI. In the example shown in Figure 12, the communication terminal 3 has selected access points 2-1, 2-2, and 2-3 as targets for CSI measurement.

[0092] Communication terminal 3 measures the channel status based on the CSI-RS received from access points 2-1, 2-2, and 2-3, and sends a CSI report showing the measurement results to the communication control device 1. Subsequently, when communication terminal 3 detects a change in its state, it changes the cluster targeted for CSI measurement. In the example shown in Figure 12, the cluster targeted for CSI measurement has been changed to the cluster consisting of access points 2-1, 2-2, and 2-4. After changing the cluster, communication terminal 3 measures the channel status based on the CSI-RS received from access points 2-1, 2-2, and 2-4, and sends a CSI report showing the measurement results to the communication control device 1.

[0093] [Differentiation] In the above description, an example was given in which the terminal control unit 34 selects one or more access points 2 to be targeted for CSI measurement in order to satisfy predetermined conditions notified by the communication control device 1. However, the method by which the terminal control unit 34 determines one or more access points 2 is not limited to this. The terminal control unit 34 may receive a designation from the communication control device 1 of one or more access points 2 to be targeted for CSI measurement and perform CSI measurement based on the CSI-RS received from the designated one or more access points 2.

[0094] In this case, the terminal transmission unit 32 periodically transmits a Sounding Reference Signal (SRS), and the access point 2 measures the strength of the received reference signal and notifies the communication control device 1 of the measurement result. Based on the measurement results received from multiple access points 2, the communication control device 1 determines one or more access points 2 to be used for CSI measurement by the communication terminal 3, and transmits information specifying the determined one or more access points 2 to the communication terminal 3.

[0095] For example, when the communication control device 1 detects a change in the state of the communication terminal 3 due to a change in the strength of a reference signal measured by an access point 2, it selects one or more access points 2 with relatively high measured reference signal strengths. The selection information is notified, for example, via the downlink control channel (PDCCH: Physical Downlink Control Channel).

[0096] After transmitting a reference signal, the control unit 34 of the communication terminal 3 determines one or more access points 2 based on the designation information transmitted from the communication control device 1, which has selected one or more access points 2 based on the strength of the reference signal received by each of the multiple access points 2. With the wireless communication system S configured in this way, the processing load on the communication terminal 3 is reduced, and thus the power consumption of the communication terminal 3 can be reduced.

[0097] In the above explanation, we have provided an example where the communication terminal 3 establishes a wireless communication link with only one of the multiple access points 2. However, the procedure for enabling the communication terminal 3 to communicate with multiple access points 2 is arbitrary. For example, the communication terminal 3 may perform the process of establishing a wireless communication link with each of the multiple access points 2.

[0098] [Effects of Wireless Communication System S] As explained above, in the wireless communication system S, when a change in the state of the communication terminal 3 is detected, the communication terminal 3 determines one or more access points 2 from among multiple access points 2 to be used for CSI measurement, and transmits state information indicating the channel state, measured based on the CSI-RS transmitted from the determined one or more access points 2, to the communication control device 1. By operating in this manner, communication parameters such as the precoding matrix, rank, modulation scheme, or coding rate are determined based on the CSI-RS measurement results transmitted from the access points 2 used by the communication terminal 3, rather than the CSI-RS measurement results transmitted from access points 2 not used by the communication terminal 3. As a result, the communication quality of the communication terminal 3 is improved.

[0099] Furthermore, this invention will make it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0100] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of its gist. For example, all or part of the apparatus can be configured by functionally or physically distributing and integrating in any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combinations are combined with the effects of the original embodiments. [Explanation of Symbols]

[0101] 1. Communication control device 2 access points 3. Communication terminals 11 Information Receiving Unit 12 Information Transmission Section 13 Storage section 14. Device Control Unit 21 Terminal-side communication unit 22 Network-side communication unit 23 Memory section 24 Control Unit 31 Terminal receiving unit 32 Terminal transmission unit 33 Storage section 34 Terminal Control Unit 211 Terminal-side transmitting unit 212 Terminal-side receiving unit 221 Network-side transmitting unit 222 Network-side receiving unit

Claims

1. A communication terminal that communicates with a communication control device via multiple access points, A receiving unit that receives quality measurement reference signals from the aforementioned multiple access points, When a change in the state of the communication terminal is detected, a control unit determines one or more access points from among the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, A transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from one or more access points, A receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, It has, The control unit determines the plurality of access points in an initial setup process based on the broadcast signal transmitted by the access point, and then determines one or more access points by selecting one or more access points from the plurality of access points in such a way that the predetermined conditions are met.

2. A communication terminal that communicates with a communication control device via multiple access points, A receiving unit that receives quality measurement reference signals from the aforementioned multiple access points, When a change in the state of the communication terminal is detected, a control unit determines one or more access points from among the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, A transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from one or more access points, A receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, It has, The control unit is a communication terminal that determines one or more access points by selecting one or more access points from the plurality of access points in such a way as to satisfy the predetermined conditions included in the synchronization signal block (SSB) of the broadcast signal transmitted by the plurality of access points.

3. The predetermined condition is that the power intensity of the quality measurement reference signal received by the communication terminal is equal to or greater than the intensity threshold. A communication terminal according to claim 1 or 2.

4. The predetermined condition is that the difference between the power intensity of the quality measurement reference signal received by the communication terminal and the power intensity of the access point at which the power intensity of the quality measurement reference signal received by the communication terminal is maximum is greater than or equal to a predetermined threshold. A communication terminal according to claim 1 or 2.

5. The predetermined condition is that the number of access points, one or more, that are the target of measuring the channel state based on the quality measurement reference signal is equal to or greater than a set threshold. A communication terminal according to claim 1 or 2.

6. The control unit, after determining one or more access points, determines one or more other access points if the predetermined conditions are no longer met due to a change in state. The communication terminal according to claim 1.

7. The processor of the communication terminal A receiving unit that receives quality measurement reference signals from multiple access points, When a change in the state of the communication terminal is detected, a control unit determines one or more access points from among the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, A transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from one or more access points, A receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, To make it function as, A program for determining one or more access points by selecting one or more access points from the plurality of access points in an initial setup process based on a broadcast signal transmitted by the access point, after the control unit has determined the plurality of access points in an initial setup process based on the broadcast signal transmitted by the access point.

8. The processor of the communication terminal A receiving unit that receives quality measurement reference signals from multiple access points, When a change in the state of the communication terminal is detected, a control unit determines one or more access points from among the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, A transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from one or more access points, A receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, To make it function as, A program for the control unit to determine one or more access points by selecting one or more access points from the plurality of access points in such a way that they satisfy the predetermined conditions included in the synchronization signal block (SSB) of the broadcast signal transmitted by the plurality of access points.

9. The system comprises multiple access points and a communication terminal that communicates with the multiple access points, Each of the aforementioned multiple access points is A terminal-side transmitting unit that transmits a reference signal for quality measurement, The data is received from the aforementioned communication terminal and the terminal-side receiving unit is configured as follows: It has, The aforementioned communication terminal is A receiving unit that receives the quality measurement reference signal from the plurality of access points, When a change in the state of the communication terminal is detected, a control unit determines one or more access points from among the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, A transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from one or more access points, A receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, It has, A wireless communication system in which the control unit determines the plurality of access points in an initial setup process based on a broadcast signal transmitted by the access point, and then determines the one or more access points by selecting one or more access points from the plurality of access points in such a way that the predetermined conditions are met.

10. The system comprises multiple access points and a communication terminal that communicates with the multiple access points, Each of the aforementioned multiple access points is A terminal-side transmitting unit that transmits a reference signal for quality measurement, The data is received from the aforementioned communication terminal and the terminal-side receiving unit is configured as follows: It has, The aforementioned communication terminal is A receiving unit that receives the quality measurement reference signal from the plurality of access points, When a change in the state of the communication terminal is detected, a control unit determines one or more access points from among the plurality of access points to be used to measure the channel state based on the quality measurement reference signal, A transmitting unit that transmits data using communication parameters determined based on the channel state measured based on the quality measurement reference signal transmitted from one or more access points, A receiving unit that receives predetermined conditions for determining the one or more access points from a communication control device, It has, The control unit determines one or more access points by selecting one or more access points from the plurality of access points so as to satisfy the predetermined conditions included in the synchronization signal block (SSB) of the broadcast signal transmitted by the plurality of access points, thereby determining the one or more access points.

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