Control device, communication system, and communication method

Abstract

The present invention appropriately controls a beam in accordance with a change in a communication environment in beam management in communication with a moving terminal station.　This control device transmits, to the terminal station, a reference radio signal for measuring a reception state. Then, the control device receives a report of the reference radio signal measured by the terminal station. Furthermore, the control device controls a communication parameter in data communication with the terminal station in accordance with the frequency at which the report is received.

Description

Control device, communication system, and communication method

[0001] The present disclosure relates to a control device, a communication system, and a communication method.

[0002] In radio access networks for 5G and beyond, it is required to select and control an appropriate beam according to the location and reception conditions of a mobile terminal station. This control is also called beam management. In a radio access network, a beam management procedure for a base station to obtain an appropriate beam is, for example, as follows: A terminal station performs measurements using measurement resources and transmits a measurement report to a base station. After receiving this measurement report, the base station applies a more appropriate beam based on the measurement report.

[0003] “MIMO enhancements in Rel19”, RWS-230207 3GPP TSG RAN Rel 19 Workshop June 15-16, 2023 “Enhancements for Event-driven Beam Management”, R1-2400381 3GPP TSG RAN WG1 #116 February 26th - March 1st, 2024

[0004] However, with the above-mentioned conventional technology, the terminal station transmits measurement reports to the base station at fixed, predetermined intervals. The base station waits only during the intervals to acquire the measurement reports and control the beam. This makes it difficult to manage the beam in response to the speed of changes in the communication environment.

[0005] An aspect of the disclosed embodiment is to appropriately control beams in accordance with changes in the communication environment in beam management for communication with a moving terminal station.

[0006] One aspect of an embodiment of the disclosure is exemplified by a control device. The control device includes a controller. The controller transmits a reference radio signal to a terminal station for measuring a reception state. The control device then receives reports of the reference radio signal measured by the terminal station. Furthermore, the control device controls communication parameters in data communication with the terminal station according to the frequency at which the reports are received.

[0007] This control device can appropriately control beams in accordance with changes in the communication environment when managing beams in communication with a moving terminal station.

[0008] FIG. 1 is a diagram illustrating the use of beamforming in a mobile communication environment. FIG. 2 is a diagram illustrating a beam management procedure between a base station and a terminal station. FIG. 3 is a diagram illustrating a communication system of the first embodiment. FIG. 4 is a diagram illustrating another example of a communication system included in the first embodiment. FIG. 5 is a diagram illustrating a hardware configuration of a control device. FIG. 6 is a sequence diagram illustrating beam management processing of a comparative example. FIG. 7 is a sequence diagram illustrating beam management processing between the control device and a terminal station of the first embodiment. FIG. 8 is a diagram illustrating the relationship between a reporting period and a reporting frequency. FIG. 9 is a flowchart illustrating processing by the control device of the first embodiment. FIG. 10 is a flowchart illustrating processing by the control device of Modification 1. FIG. 11 is a flowchart illustrating processing by the control device of Modification 2. FIG. 12 is a sequence diagram illustrating setting of a time interval of a reporting slot group. FIG. 13 is a flowchart illustrating processing by the control device of Modification 3. FIG. 14 is a flowchart illustrating beam width expansion processing of the second embodiment.

[0009] Hereinafter, a control device 1, communication systems 100A and 100B, and a communication method according to an embodiment will be described with reference to the drawings (see FIGS. 3 and 4). The control device 1 transmits a reference radio signal (also called a reference signal) to a terminal station 4 (see FIGS. 3 and 4) for measuring a reception state at the terminal station 4. The control device 1 then receives a report of the reference radio signal measured by the terminal station 4. Furthermore, the control device 1 controls communication parameters in data communication with the terminal station 4 according to the frequency at which the report is received.

[0010] Here, the control device 1 may be built into the base station 2. Alternatively, the control device 1 may cooperate with the base station 2 through a communication carrier network called a core network. In either case, the control device 1 and the base station 2 constitute a control system and provide a wireless access network to the terminal station 4.

[0011] The communication parameter is, for example, the beam width of a radio signal transmitting user data. The communication parameter is, for example, the number of multiple measurement beams used by the terminal station 4 to determine the best reception beam and the best transmission beam transmitted from the base station 2. The communication parameter is, for example, the transmission interval of a reference radio signal transmitted by the base station 2 to allow the terminal station 4 to measure the reception status. A further communication parameter is, for example, the time interval of communication resources allocated to the terminal station 4 for transmitting a report. Therefore, the control device 1 can appropriately control communication parameters such as the beam width in accordance with changes in the communication environment, depending on the frequency at which the reports are received. That is, if the frequency at which the reports are received is equal to or greater than a first reference value, the control device 1 determines that the change in the communication environment is sudden or rapid. The control device 1 then expands the width of the beam used to transmit user data, increases the number of multiple measurement beams, shortens the transmission interval of the reference radio signal, and shortens the time interval of the communication resources. The control device 1 includes a controller that executes the above-described communication method.

[0012] First Embodiment Hereinafter, a control device 1, communication systems 100A and 100B, and a communication method according to a first embodiment will be described with reference to FIGS.

[0013] (Application Example) Application examples of the control device 1, communication systems 100A and 100B, and communication methods will be described with reference to Figures 1 and 2. Figure 1 is a diagram illustrating the use of beamforming in a mobile communication environment. Figure 1 illustrates a vehicle 50 traveling on a road R1. A terminal station 4 (referred to as UE) is mounted on the vehicle 50. UE is an abbreviation for User Equipment. The UE may be, for example, what is called an in-vehicle device.

[0014] In addition, for example, base stations 2-1 to 2-4 are deployed in the area in which the vehicle 50 travels. The base stations 2-1 to 2-4 are collectively referred to as base stations 2. Note that the number of base stations 2 is not limited to four.

[0015] The base stations 2 are connected to the control device 1 through a network N1. The network N1 includes a communication carrier network called a core network and public networks such as the Internet. The base stations 2 are equipped with antennas that can control the radiation pattern of the radio signals (electromagnetic waves) they transmit (see Figures 3 and 4). Using multiple antenna elements, the antenna elements can be controlled to have high gain (antenna gain) in a specific direction. The radiation pattern with directionality at this time is called a beam. The control device 1 can control the direction of the beam of each base station 2.

[0016] As described above, vehicle 50 travels on road R1. Terminal station 4 mounted on vehicle 50 moves on road R1 as vehicle 50 moves. Meanwhile, base station 2 transmits radio signals using beams that propagate in a specific direction. Therefore, in order to maintain good wireless communication between base station 2 and terminal station 4, it is desirable for base stations 2-1 to 2-4 to point the propagation direction of their beams toward the moving vehicle 50. Therefore, control device 1 controls the propagation direction of the beam depending on the position and reception conditions of moving terminal station 4. In FIG. 2, the controlled propagation direction of the beam is illustrated by a dotted arrow. This control is also called beam management.

[0017] 2 illustrates a beam management procedure between the base station 2 and the terminal station 4. The base station 2 has an antenna with an array of antenna elements, and is capable of scanning the transmission beam and reception beam by controlling the directivity (beam width and propagation direction) of the radio signals it transmits and receives.

[0018] On the other hand, the terminal station 4 has an antenna with multiple antenna elements arranged and can form multiple receiving beams (#U0 to #Uj) (see FIGS. 3 and 4). However, in this embodiment, the terminal station 4 is not limited to having an antenna with multiple antenna elements. The terminal station 4 may also have an antenna with a single antenna element.

[0019] As shown in Fig. 2, the beam management procedure includes three phases P1 to P3. In phase P1, the base station 2 sweeps a relatively wide transmission beam, for example, transmitting the transmission beam to the entire cell served by the base station 2. At this time, the terminal station 4 sweeps a relatively wide reception beam at the terminal station 4 and receives the transmission beams in multiple directions swept by the base station 2. The terminal station 4 then selects the best received signal (the best transmission beam measured at the best reception beam) from the transmission beams swept in multiple directions and reports this to the base station 2. This determines the initial transmission beam and reception beam.

[0020] However, the receiving beam is swept when the terminal station 4 has an arrangement of multiple antenna elements and supports beamforming. Therefore, when the terminal station 4 does not support beamforming, reception is performed using a single relatively wide receiving beam or an omnidirectional antenna.

[0021] In phase P2, after the initial transmission beam and reception beam are determined, base station 2 sweeps a transmission beam narrower than in phase P1 and performs reception using the best reception beam determined in phase P1. That is, base station 2 refines the beam more than in phase P1 (for example, sweeps a beam narrower than in P1 within a narrower sweep range) and transmits a reference radio signal (reference signal) using the transmission beam. The range over which the transmission beam is swept in phase P2 is determined based on the best transmission beam selected in phase P1.

[0022] The terminal station 4 receives the narrower transmission beam transmitted from the base station 2 with a single fixed reception beam of the same width as in phase P1. The fixed reception beam is the reception beam determined to be the best in phase P1. The terminal station 4 then measures the received signal power of the reference signal from the multiple refined transmission beams and reports the transmission beam with the highest received signal power (the best transmission beam) to the base station 2. However, the terminal station 4 may also report to the base station 2 the transmission beam with the highest Signal to Interference plus Noise power Ratio (SINR) instead of the highest received signal power.

[0023] In Phase P3, the base station 2 locks the beam to the best transmission beam reported by the terminal station 4 in Phase P2. That is, the base station 2 repeatedly transmits the best transmission beam. The terminal station 4 sweeps the reception beam more precisely than in P2 and determines the best reception beam. As described above, the reception beam sweep is performed when the terminal station 4 supports beamforming. Furthermore, the best reception beam in Phase P3 is determined, for example, by measuring the received signal power of a reference radio signal (reference signal) received from multiple reception beams and determining the reception beam with the highest received signal power or the highest SINR.

[0024] Beam management is also performed when the terminal station 4 is connected to the control device 1 via the base station 2 and is in communication. That is, the terminal station 4 periodically receives reference signals from the base station 2 using multiple beams and measures the received signal power, SINR, etc. The terminal station 4 reports the reception status to the base station 2 or the control device 1 via the base station 2 based on the measured received signal power, SINR, etc. The base station 2 or the control device 1 resets (changes) the beam based on the report from the terminal station 4. For example, the base station 2 or the control device 1 selects a beam with higher received signal power or SINR, etc., instead of a transmission beam currently in use whose received signal power or SINR, etc. has deteriorated, and applies this beam to communication with the terminal station 4.

[0025] However, when the communication environment changes rapidly, a flexible and rapid beam management method is desired. In this embodiment, a control device 1, communication systems 100A (see FIG. 3) and 100B (see FIG. 4), and a communication method are exemplified, which appropriately control beams in accordance with changes in the communication environment in beam management for communication with a moving terminal station.

[0026] (System Configuration) Fig. 3 is a diagram illustrating a communication system 100A of this embodiment. The communication system 100A has a control device 1, a base station 2, and a terminal station 4. As described above, the control device 1 is a device on a core network to which the base station 2 is connected. However, the control device 1 can also be considered to be the core network itself, or a system included in the core network. The control device 1 controls the base station 2 and the terminal station 4, and provides communication services to the terminal station 4.

[0027] The base station 2 provides a wireless access network to the terminal station 4. An area where wireless communication is possible in the wireless access network is also called a cell. The base station 2 has an antenna capable of forming multiple beams (e.g., #B0 to #Bi, where i is an integer greater than or equal to 2), a radio 21 connected to these antennas, and a control circuit 22. The antenna forms transmission beams and reception beams with directional radiation patterns using the multiple beams (#B0 to #Bi). A station capable of transmitting and receiving radio waves is also called a Transmission and Reception Point (TRP). The base station 2 may have multiple TRPs capable of forming multiple beams (#B0 to #Bi).

[0028] The radio 21 includes a transceiver for transmitting radio signals and a receiver for receiving radio signals, and is connected to an antenna (forming beams #B0 to #Bi). The control circuit 22 includes, for example, a processor and a memory. The processor controls communication with the control device 1 and radio communication with the terminal station 4 using a computer program stored in the memory.

[0029] The terminal station 4 is also called a mobile station. The terminal station 4 connects to a wireless access network within the range of a cell provided by the base station 2. The terminal station 4 has an antenna (forming beams #U0 to #Uj), a radio 41 connected to the antenna, and a control circuit 42. The configurations of the radio 41 and the control circuit 42 are similar to the configurations of the radio 21 and the control circuit 22 of the base station 2. That is, the control circuit 42 has, for example, a processor and a memory. The processor controls wireless communication with the control device 1 and the base station 2 according to a computer program stored in the memory.

[0030] FIG. 4 is a diagram illustrating a communication system 100B, another example included in this embodiment. Compared to the communication system 100A of FIG. 3, the communication system 100B includes a central base station 2A and one or more distributed base stations 2B instead of the base station 2. When one or more distributed base stations 2B are individually distinguished, they are assigned sub-numbers such as distributed base stations 2B-1, ..., 2B-K. Here, the sub-number K is an integer indicating the number of distributed base stations. Each distributed base station 2B can transmit and receive radio waves using beams (#B0 to #Bi) instructed by the control device 1. Therefore, the beams that the terminal station 4 measures include not only beams transmitted from individual distributed base stations 2B (e.g., distributed base station 2B-1), but also beams transmitted from multiple distributed base stations 2B-1, ..., 2B-K, etc. In FIG. 4, distributed base stations 2B-1 and 2B-K are illustrated as examples. However, when the distributed base stations 2B-1, ..., 2B-K are collectively referred to, they are simply referred to as distributed base station 2B.

[0031] The central base station 2A has a control circuit 22A. Furthermore, the distributed base station 2B has a radio 21B. The control circuit 22A of the central base station 2A and the radio 21B of the distributed base station 2B are connected, for example, by an optical fiber C1 or a wireless network. There are no limitations on the topology of the optical fiber C1 connecting the central base station 2A and multiple distributed base stations 2B. For example, the topology of the optical fiber C1 may be a one-to-one connection between nodes, a network that branches with increasing distance from the central base station 2A, a star network, or a ring network. Furthermore, when the control circuit 22A of the central base station 2A and the radio 21B of the distributed base station 2B are connected by a wireless network, there are no limitations on the standard or protocol of the wireless network.

[0032] The control circuit 22A has a processor and a memory, similar to the control circuit 22 in Fig. 3. The processor controls communication with the control device 1 and wireless communication with the terminal stations 4 using a computer program in the memory. That is, the control circuit 22A controls wireless communication with the terminal stations 4 via the radios 21B of one or more distributed base stations 2B.

[0033] 3 and 4, the base station 2 and the distributed base station 2B use at least one of a plurality of antenna elements and a polarization plane to communicate with the terminal station 4 by Multiple-Input and Multiple-Output (MIMO). Note that the configuration of the terminal station 4 in FIG. 4 is the same as that in FIG. 3.

[0034] In this embodiment, the control device 1 is a device on a core network to which the base station 2 is connected. Alternatively, the control device 1 is the core network itself, or a system included in the core network. However, the control device 1 is not limited to such a device on a core network. For example, the control device 1 may be a device included in the base station 2. For example, the control device 1 may be a device provided in the base station 2 and communicating with the terminal station 4 via a radio 21.

[0035] FIG. 5 is a diagram illustrating an example of the hardware configuration of the control device 1. The control device 1 has a CPU 11, a main storage device 12, and external devices, and executes communication processing and information processing using a computer program. The CPU 11 is also called a processor. The CPU 11 is not limited to a single processor, and may have a multi-processor configuration. The CPU 11 may also include a graphics processing unit (GPU), a digital signal processor (DSP), etc. The CPU 11 may also cooperate with a hardware circuit such as a field programmable gate array (FPGA). Examples of external devices include an external storage device 13, an output device 14, an operation device 15, and a communication device 16.

[0036] The CPU 11 executes a computer program executable in the main memory device 12 to provide processing for the control device 1. The main memory device 12 stores the computer program executed by the CPU 11, data processed by the CPU 11, etc. The main memory device 12 may be, for example, a dynamic random access memory (DRAM), a static random access memory (SRAM), a read-only memory (ROM), etc. Furthermore, the external storage device 13 is used as a storage area supporting the main memory device 12 and stores the computer program executed by the CPU 11, data processed by the CPU 11, etc. The external storage device 13 may be, for example, a hard disk drive, a solid state drive (SSD), etc. Furthermore, a drive device for a removable storage medium may be connected to the control device 1. The removable storage medium may be, for example, a Blu-ray disc, a digital versatile disc (DVD), a compact disc (CD), a flash memory card, etc.

[0037] The output device 14 is, for example, a display device such as a liquid crystal display or an electroluminescence panel. However, the output device 14 may also include a speaker or other device that outputs sound. The operation device 15 is, for example, a touch panel with a touch sensor superimposed on a display. The communication device 16 communicates with the base station 2 and an external network such as the Internet via, for example, optical fiber. The communication device 16 is, for example, a gateway connected to the base station 2 and a gateway that communicates with an external network such as the Internet. The communication device 16 may be a single device or a combination of multiple devices.

[0038] (Processing Procedure of Comparative Example) Fig. 6 is a sequence diagram illustrating a beam management process of a comparative example. In the comparative example, beam management between a control device 301 and a terminal station 304 is illustrated. However, in Fig. 6, at least a part of the processing of the control device 301 may be executed by a base station that provides a cell to the terminal station 304.

[0039] As explained in Fig. 2, beam management is performed even when the terminal station 4 is in communication connected to the control device 1 via the base station 2. That is, the terminal station 4 in Fig. 2 periodically receives reference signals from multiple beams from the base station 2 (TRP) and measures the received signal power or SINR, etc. The terminal station 4 reports the reception status to the base station 2 or the control device 1 via the base station 2 based on the measured received signal power or SINR, etc. The base station 2 or the control device 1 resets, changes, or controls the beam based on the report from the terminal station 4. An example of beam management processing according to a comparative example is given below.

[0040] In this process, the control device 301 sets a beam (S301). By setting the beam, for example, the width (directivity) of the transmission beam and the reception beam at the base station, the angular range over which the transmission beam and the reception beam are swept, the number of times the sweep is repeated, the period for repeating the sweep, etc. are determined. Then, the control device 301 notifies the terminal station 304 of information about the set beam and a communication resource slot (also called a reporting slot) for the terminal station 304 to report the reception status (S302).

[0041] Then, the terminal station 304 applies the beam information received from the control device 301 to its own processing (S303). That is, the terminal station 304 prepares to receive a reference signal from the control device 301. More specifically, the terminal station 304 sets its own receiving beam.

[0042] Next, the control device 301 transmits a data transmission radio signal for transmitting user data on a data transmission beam via the base station (TRP). The data transmission radio signal includes a slot for user data and a slot for a reference radio signal. The control device 301 also allocates a radio signal for beam reception status evaluation to multiple beams, sweeps the beams, and transmits the beams via the base station (TRP) (S304). That is, the beams of the radio signals transmitted from the base station 302 include a beam for transmitting user data and multiple measurement beams transmitted in multiple directions for beam management.

[0043] At least a part of the processing of S304 may be executed by the base station. Then, the terminal station 304 receives radio signals for beam reception status evaluation transmitted by the beam for data transmission, and measures, for example, the received signal power, SINR, etc. of each beam. The terminal station 304 also receives radio signals for beam reception status evaluation assigned to multiple beams, and measures, for example, the received signal power, SINR, etc. of each beam. Then, the terminal station 304 reports the reception status based on the measurement results (S305, S306).

[0044] The control device 301 or the base station then determines whether a beam change is necessary based on the reception status reported by the terminal station 304 (S307). If a beam change is necessary, the processing from S312 onward is executed. On the other hand, if a beam change is not necessary, the control device 301 or the base station continues processing without changing the beam. That is, the control device 301 or the base station transmits a radio signal for data transmission. The control device 301 or the base station also allocates a radio signal for beam reception status evaluation to multiple beams, sweeps the beams, and transmits the signal again (S308). The terminal station 304 then receives the radio signal for beam reception status evaluation and measures, for example, the received signal power, SINR, etc. of each beam. The terminal station 304 then reports the reception status based on the measurement results (S309, S310).

[0045] Then, the control device 301 or the base station determines whether or not a beam change is necessary based on the reception status reported from the terminal station 4 (S311). If a beam change is not necessary, the processing from S308 onwards is executed. On the other hand, if a beam change is necessary, the control device 301 or the base station sets a beam (S312). The processing of S312 is the same as the processing of S301.

[0046] Here, the comparative example has the following problem. That is, the terminal station 304 reports the reception status of the downlink signal for the assigned beam to the control device 301 at a predetermined interval. However, because the reports are made at a fixed interval, it is not possible to update the beam pattern in accordance with the speed of changes in the communication environment. If the interval is made shorter, the overhead will increase. That is, even if there is a sudden change in the communication situation (such as in a high-speed moving environment), the control device 301 or the base station will have to wait for the assigned reporting timing. As a result, there is a possibility that the communication line will be interrupted.

[0047] 7 to 9, processing procedures performed by the control device 1, the base station 2, and the terminal station 4 according to this embodiment are illustrated. In this embodiment, a method is illustrated in which the terminal station 4 determines whether it is necessary to report the reception status and whether it is necessary to change the beam in response to the possibility of deterioration in the reception status. In this embodiment, the terminal station 4 notifies the control device 1 of a request to report the reception status or change the beam when it determines that it is necessary.

[0048] 6, the control device 1 or the base station 2 determines whether or not a beam change is necessary based on the reception status reported from the terminal station 4. In this embodiment, the control device 1 or the base station 2 further controls communication parameters according to the frequency of receiving reports from the terminal station 4. Here, the communication parameters also include parameters related to beam change.

[0049] The control device 1, for example, adjusts the width of a beam of a data wireless signal for transmitting user data to the terminal station 4. The beam of the data wireless signal is an example of a first beam. The control device 1 also adjusts the number of measurement beams transmitted in multiple directions from the base station to manage the direction of the beam at the terminal station 4 and have the terminal station 4 report the reception status. The measurement beam is an example of a second beam.

[0050] More specifically, for example, when the frequency of reports from the terminal station 4 is equal to or greater than a first reference value, the control device 1 widens the beam width of the data wireless signal for transmitting user data by a predetermined width. Furthermore, when the frequency of reports is less than a second reference value that is smaller than the first reference value, the control device 1 narrows the beam width of the data wireless signal by a predetermined width. Furthermore, for example, when the frequency of reports from the terminal station 4 is equal to or greater than the first reference value, the control device 1 increases the number of beams used for measurement by a predetermined number. Furthermore, when the frequency of reports is less than a second reference value that is smaller than the first reference value, the control device 1 reduces the number of beams used for measurement by a predetermined number. In other words, if the report interval becomes shorter, the control device 1 widens the beam width transmitted from the base station 2 or increases the number of beams used for measurement.

[0051] 7 is a sequence diagram illustrating a beam management process between the control device 1 and the terminal station 4 according to this embodiment. Note that, although this embodiment illustrates a beam management process between the control device 1 and the terminal station 4, at least a part of the process of the control device 1 may be executed by the base station 2.

[0052] Of the processes in Fig. 7, the processes from S1 to S4 are the same as S301 to S304 in Fig. 6. That is, the control device 1 transmits a beam of a data radio signal for data transmission via the base station 2 or base station 2. Furthermore, the control device 1 transmits a reference radio signal (reference signal) in the data radio signal for data transmission via the base station 2 or base station 2 (S4). Here, the reference radio signal is, for example, a reference signal (CSI-RS) used for estimating Channel State Information (CSI) necessary for data communication. The reference signal such as CSI-RS is transmitted by the beam of the radio signal for data transmission at slot intervals set by the control device 1 or base station 2. The reference signal is an example of a reference radio signal.

[0053] Furthermore, the base station 2 or the control device 1 via the base station 2 sweeps and transmits a plurality of measurement beams (S4). The measurement beams include, for example, reference signals and Synchronization Signals (SS) / Physical Broadcast Channel (PBCH) Blocks (SSB). The measurement beams are transmitted in radio frames at a period (for example, the transmission period of SSB) set by the control device 1 or the base station 2. The terminal station 4 receives the measurement beams and measures their intensities to manage the beam directions.

[0054] The processing of S4 is an example of transmitting a reference radio signal for measuring the reception state to the terminal station 4. The reference radio signal includes a reference signal (also called a first reference signal) transmitted by a beam for data transmission. The beam for data transmission is an example of a first beam. The reference radio signal also includes a reference signal (also called a second reference signal) transmitted by multiple beams for measurement. The multiple beams for measurement are an example of a second beam.

[0055] Terminal station 4 then receives the reference radio signals transmitted by the data transmission beams and measures, for example, the received signal power, SINR, etc. of each beam. Terminal station 4 then determines whether or not a reception status report is required. Similarly, terminal station 4 receives the reference radio signals transmitted by the measurement beams and measures, for example, the received signal power, SINR, etc. of each beam.

[0056] Similarly, the terminal station 4 determines whether a reception status report is necessary. For example, if the received signal power, SINR, etc. of each beam have deteriorated below a reference value, the terminal station 4 determines that a reception status report is "necessary." Also, if the received signal power, SINR, etc. of each beam are stable within a predetermined range, the terminal station 4 determines that a reception status report is "unnecessary."

[0057] In this example, the terminal station 4 determines that a report is "necessary" (S5). Therefore, the terminal station 4 notifies the control device 1 of a report of the reception status to the base station 2 or via the base station 2 (S6). The report of the reception status includes measurement results of beams for CSI estimation or measurement, etc.

[0058] Then, the base station 2 or the control device 1 receives the reception status report via the base station 2 and calculates the reception frequency of the reception status report. In this case, it is assumed that the report frequency is equal to or greater than the first reference value in S6. Then, the control device 1 or the base station 2 sets the beam so as to widen the beam width for transmitting the data signal by a predetermined width (S7).

[0059] By widening the beam width, the received signal strength at the terminal station 4 decreases, but reception over a wider area becomes possible. Therefore, a wide beam width is desirable when the reception conditions change rapidly. Then, the base station 2 or the control device 1 notifies the terminal station 4 via the base station 2 of information about the set beam and the communication resource slot for the terminal station 4 to report the reception conditions (S8).

[0060] Then, the terminal station 4 applies the beam information received from the base station 2 or the control device 1 via the base station 2 to its own processing (S9). Next, the base station 2 or the control device 1 transmits a radio signal for data transmission using the widened beam set in S7 via the base station 2 or the control device 1 via the base station 2. In addition, the control device 1 sweeps and transmits multiple beams for measurement via the base station 2 or the base station 2 (S10).

[0061] Then, similar to S5, the terminal station 4 receives the reference radio signal using the data transmission beam and measures, for example, the received signal power, SINR, etc. The terminal station 4 also receives the reference radio signal using the measurement beam and measures, for example, the received signal power, SINR, etc. of each beam. The terminal station 4 then determines whether a reception status report is necessary. In this example, the terminal station 4 determines that a report is "necessary" (S11). Therefore, the terminal station 4 notifies the control device 1 of the reception status report to the base station 2 or via the base station 2 (S12).

[0062] In this embodiment, the control device 1 or the base station 2 repeats the above process (S14 to S16). If the terminal station 4 determines that a reception status report is "unnecessary" (S17), the terminal station 4 does not report the reception status to the base station 2 or the control device 1 via the base station 2.

[0063] 8 is a diagram illustrating the relationship between the reporting period Tt and the reporting frequency. In FIG. 8, the horizontal axis represents time. Reporting slot groups SLk (K=1, 2, ...) are arranged on the time axis. The time interval between the reporting slot group SLk and the next slot group SLk+1 is the reporting period Tt. Therefore, when the terminal station 4 most frequently reports the reception status to the base station 2 or to the control device 1 via the base station 2, it can report in the reporting period Tt.

[0064] In this embodiment, the frequency of reporting the reception status is determined by the number of actual reports in a period (INTk (k is an integer equal to or greater than 1)) of a predetermined number of reporting periods Tt. In the example of FIG. 8 , the period INTk is illustrated as three times the reporting period Tt (Nrep). However, Nrep is an integer equal to or greater than 1, and the period INTk is not limited to three times the reporting period Tt.

[0065] Furthermore, among the reporting slot group SLk, the slots filled in black ("Reported") exemplify slots for which a report has been made. In the example of FIG. 8 , in period INT1, two slot groups include "Reported" slots. That is, in this example, in period INT1, the terminal station 4 notifies the control device 1 of two reports via the base station 2 or the base station 2. That is, the number of reports in period INT1 is two (frequency is 2). Similarly, the number of reports in periods INT2 and INT3 is also two (frequency is 2). In this embodiment, for example, if the number of reports in period INTk is equal to or greater than a first reference value, the control device 1 widens the beam width for data signal transmission by a predetermined width. The first reference value is, for example, the number of reports in period INTk is two. The number of reports in period INTk can be said to be the frequency of reports. The first reference value is a reference value for determining whether the frequency of reports is high.

[0066] On the other hand, the number of reports during periods INT4 and INT5 is 0. In this embodiment, for example, if the number of reports during period INTk is less than a second reference value that is smaller than the first reference value, the control device 1 narrows the beam width of the data wireless signal by a predetermined width. The second reference value is a reference value for determining that the frequency of reports is low. The second reference value is, for example, 1.

[0067] Fig. 9 is a flowchart illustrating the processing of the control device 1 of this embodiment. However, at least a part of the processing of Fig. 9 may be executed by the base station 2. The control device 1 executes the processing of Fig. 9 at a reporting period Tt, which is the arrangement interval of the reporting slot group SLk.

[0068] In this process, the control device 1 acquires a signal in the reporting slot group SLk in the uplink wireless signal transmitted from the terminal station 4 (S101). The control device 1 also records the number of times the reporting slot group SLk has been received, i.e., the number of times the reporting period Tt has elapsed (S102). However, the control device 1 may also accumulate the time (reporting period Tt) that has elapsed since the previous process.

[0069] Next, the control device 1 determines whether there is a report in the reporting slot group SLk (S103). If there is a report in the reporting slot group SLk, the control device 1 updates and records the number of reports (S104). On the other hand, if there is no report in the reporting slot group, the control device 1 proceeds to S105 without updating the number of reports.

[0070] Then, the control device 1 calculates the reporting frequency (S105). That is, the control device 1 determines the number of reports in the period INTk as the reporting frequency based on the number of times (or elapsed time) the reporting period Tt recorded in S102 and the number of reports recorded in S104. In Fig. 8, for example, the period INTk is the third case of the reporting period Tt. In this way, if it is determined in S103 that a report has been made, the calculated reporting frequency increases, and if it is determined in S103 that a report has not been made, the calculated reporting frequency decreases.

[0071] Next, the control device 1 compares the reporting frequency with a first reference value (S106). If the reporting frequency is equal to or greater than the first reference value, the control device 1 determines whether or not it is possible to expand the beam width of the data wireless signal (S107). If it is possible to expand the beam width of the data wireless signal, the control device 1 instructs the base station 2 to expand the beam width of the data wireless signal by a certain allowable width (S108). The beam width of the data wireless signal is an example of a communication parameter, and the beam of the data wireless signal is an example of a first beam. In other words, the processing of S108 is an example of an expansion process that expands the width of the first beam within the range of the allowable width. The allowable width can be calculated, for example, from the desired received signal strength gamma in the modulation and coding scheme (MCS) (see FIG. 14).

[0072] A case in which the determination in S107 indicates that the beam width of the data wireless signal cannot be expanded is a case in which expanding the beam width would cause the beam width to exceed the maximum beam width. The maximum beam width may be empirically determined as a desirable value in, for example, communication systems 100A, 100B including control device 1, base station 2, and terminal station 4. Therefore, a case in which the determination in S107 indicates that the beam width of the data wireless signal cannot be expanded is a case in which expanding the beam width would cause the width of the first beam to reach the maximum allowable limit.

[0073] If the beam width of the data wireless signal cannot be expanded, the control device 1 instructs the terminal station 4 to use a mode in which reporting is performed every reporting period Tt (S109). In the mode in which reporting is performed every reporting period Tt, the terminal station 4 does not determine whether a report is necessary based on the reception status, but instead always notifies the control device 1 of a report every reporting period Tt. This mode is called the full-period reporting mode. In the full-period reporting mode, the terminal station 4 notifies the control device 1 of all reception status reports, or via the base station 2, regardless of the measurement results. Furthermore, in the full-period reporting mode, the control device 1 transmits the data wireless signal with the maximum beam width.

[0074] On the other hand, if the determination in S106 is that the reporting frequency is less than the first reference value, the control device 1 compares the reporting frequency with a second reference value that is less than the first reference value (S110).If the reporting frequency is less than the second reference value, the control device 1 determines whether reporting is currently in a full-cycle reporting mode (S111).

[0075] If the reporting mode is currently set to the full cycle reporting mode, the control device 1 instructs the terminal station 4 to report in a mode that determines whether a report is necessary depending on the reception status (S112). The mode that determines whether a report is necessary depending on the reception status is called a report necessity determination mode. Note that if the reporting mode is not currently set to the full cycle reporting mode, the control device 1 proceeds to S113.

[0076] The control device 1 then determines whether it is possible to reduce the beam width of the data wireless signal (S113). The determination in S113 that the beam width of the data wireless signal cannot be reduced means that reducing the beam width would result in the beam width being less than the minimum beam width. The minimum beam width is the limit of the beam width determined by the physical arrangement of the antenna elements.

[0077] However, in S113, the control device 1 may determine whether the beam width of the data wireless signal has reached an appropriate value. The appropriate value of the beam width is a beam width that is desirable when the radio wave propagation environment is stable, and is determined, for example, experimentally or empirically. In other words, if the beam width is at the appropriate value, the control device 1 may execute processing that indicates that there is no need to further narrow the beam width.

[0078] If it is possible to reduce the beam width of the data wireless signal, the control device 1 instructs the base station 2 to reduce the beam width by a predetermined width (S114), and the control device 1 then ends the beam setting process.

[0079] (Modification 1) Fig. 10 is a flowchart illustrating the processing of the control device 1 in Modification 1. However, at least a part of the processing of Fig. 10 may be executed by the base station 2. The control device 1 or the base station 2 executes the processing of Fig. 10 at a reporting period Tt, which is the arrangement interval of the reporting slot group SLk. The control device 1 or the base station 2 may execute the processing of Fig. 10 in addition to the processing of Fig. 9. Furthermore, the control device 1 or the base station 2 may execute the processing of Fig. 10 instead of the processing of Fig. 9. In the processing of Fig. 9, the width of the beam of the data wireless signal is changed depending on the reporting frequency. In the processing of Fig. 10, the number of multiple beams for measurement is changed depending on the reporting frequency.

[0080] In Figure 10, the processes from S101 to S106 are the same as those in Figure 9. If the determination in S106 in Figure 10 shows that the reporting frequency is equal to or greater than the first reference value, the control device 1 determines whether it is possible to increase the number of measurement beams (S107A). If it is possible to increase the number of measurement beams, the control device 1 instructs the base station 2 to increase the number of measurement beams by a predetermined number (S108A). The number of measurement beams is an example of a communication parameter. The process in S108A is also an example of a process of increasing the number of second beams by a predetermined number. Here, the predetermined number may be a communication parameter set in the control device 1.

[0081] A case in which the determination in S107A indicates that the number of measurement beams cannot be increased is a case in which increasing the number of measurement beams would cause the number of beams to exceed the maximum value. The maximum number of measurement beams may be determined as the maximum number of beams that can be managed or processed in the communication systems 100A and 100B including the control device 1, the base station 2, and the terminal station 4, for example. Therefore, a case in which the determination in S107A indicates that the number of measurement beams cannot be increased is a case in which increasing the number of measurement beams by a predetermined number would cause the number of second beams to reach the maximum number of beams.

[0082] If the number of multiple beams for measurement cannot be increased, the control device 1 instructs the terminal station 4 to use a mode in which reporting is performed in every reporting cycle Tt (full cycle reporting mode) (S109). The processing in S109 is the same as in Fig. 9. In the full cycle reporting mode, the control device 1 transmits multiple beams for measurement via the base station 2 with the maximum number of beams.

[0083] On the other hand, if the determination in S106 indicates that the reporting frequency is less than the first reference value, the control device 1 executes the processes of S110, S111, and S112. These processes are the same as those in FIG. 9 . Then, the control device 1 determines whether or not it is possible to reduce the number of multiple beams for measurement (S113A). The minimum value of the number of multiple beams for measurement may be determined as the desired minimum number of beams in the communication systems 100A and 100B including the control device 1, the base station 2, and the terminal station 4, for example. The desired number of beams may be 1 or an integer equal to or greater than 1.

[0084] Therefore, if reducing the number of multiple beams for measurement would result in the number of beams being less than the minimum number of beams, it is determined that the number of multiple beams for measurement cannot be reduced. If it is possible to reduce the number of multiple beams for measurement, the control device 1 instructs the base station 2 to reduce the number of multiple beams for measurement by a predetermined number (S114A).

[0085] (Modification 2) Fig. 11 is a flowchart illustrating the processing of the control device 1 in Modification 2. However, at least a part of the processing of Fig. 11 may be executed by the base station 2. The control device 1 or the base station 2 may execute the processing of Fig. 11 together with at least one of the processing of Fig. 9 and the processing of Fig. 10. Furthermore, the control device 1 or the base station 2 may execute the processing of Fig. 11 instead of the processing of Figs. 9 and 10. In the processing of Fig. 9, the beam width of the data wireless signal is changed in accordance with the reporting frequency. In the processing of Fig. 10, the number of multiple beams for measurement is changed in accordance with the reporting frequency. In the processing of Fig. 11, the transmission interval of the reference wireless signal for measuring the reception status of the beam is changed in accordance with the reporting frequency.

[0086] Here, the transmission interval of the reference radio signal for measuring the reception status of the beam is, first, the arrangement interval of slots including a reference signal (CSI-RS, etc.) in a data radio signal that transmits user data. Also, the transmission interval of the reference radio signal for measuring the reception status of the beam is, second, the arrangement interval of frames including slots of the reference radio signal in multiple beams for measurement. Hereinafter, this second modification will be described assuming that the transmission interval of the reference radio signal for measuring the reception status of the beam is the above-mentioned first or second case.

[0087] 11 , the processes from S101 to S106 are the same as those in FIGS. 9 and 10 . If the determination in S106 in FIG. 11 indicates that the reporting frequency is equal to or greater than the first reference value, the control device 1 determines whether or not it is possible to shorten the transmission interval of the reference radio signal (S107B). If it is possible to shorten the transmission interval of the reference radio signal, the control device 1 instructs the base station 2 to shorten the transmission interval of the reference radio signal by a predetermined value (S108B). The transmission interval of the reference radio signal is an example of a communication parameter. The process in S108B is an example of a process of shortening the transmission interval for transmitting the reference radio signal by a first predetermined time. The predetermined value is an example of the first predetermined time. The predetermined value in S108B may be a parameter set in the control device 1.

[0088] A case in which the determination in S107B indicates that the transmission interval of the reference radio signal cannot be shortened is, for example, a case in which the reference radio signal has already been allocated to all slots in one frame of the data radio signal that transmits user data. Therefore, a case in which the determination in S107B indicates that the transmission interval of the reference radio signal cannot be shortened can be said to be a case in which shortening the transmission interval of the reference radio signal by a predetermined value results in the transmission interval for transmitting the reference signal becoming the minimum interval.

[0089] If the transmission interval of the reference radio signal cannot be shortened, the control device 1 instructs the terminal station 4 to use a mode in which reporting is performed in every reporting period Tt (full-period reporting mode) (S109). The processing of S109 is the same as that shown in Fig. 9. In the full-period reporting mode, the control device 1 instructs the base station 2 to maintain the state in which the reference radio signal is allocated to every slot and transmitted.

[0090] On the other hand, if the determination in S106 indicates that the reporting frequency is less than the first reference value, the control device 1 executes the processes of S110, S111, and S112. These processes are similar to those in FIGS. 9 and 10 . The control device 1 then determines whether or not it is possible to extend the transmission interval of the reference radio signal (S113B). The maximum value of the transmission interval of the reference radio signal may be determined as a desirable limit of the transmission interval of the reference radio signal in, for example, the communication systems 100A and 100B including the control device 1, the base station 2, and the terminal station 4. For example, the desirable limit of the transmission interval of the reference radio signal is an interval in which at least one slot of the reference radio signal is allocated within one frame for a data radio signal beam (first beam). Furthermore, for example, the desirable limit of the transmission interval of the reference radio signal is a frame interval including a slot of the reference radio signal for multiple measurement beams (second beams).

[0091] Therefore, if extending the transmission interval of the reference radio signal would cause the arrangement interval of slots containing the reference radio signal to exceed the maximum value, it is determined that the transmission interval of the reference radio signal cannot be extended. If it is possible to extend the transmission interval of the reference radio signal, the control device 1 instructs the base station 2 to extend the transmission interval (slot interval) of the reference radio signal (S114B).

[0092] (Modification 3) The beam setting process of Modification 3 is described with reference to FIGS. 12 and 13 . The control device 1 or the base station 2 may execute the process of Modification 3 together with at least one of the processes of FIGS. 9 to 11 . Furthermore, the control device 1 or the base station 2 may execute the process of Modification 3 instead of the processes of FIGS. 9 to 11 . In the process of FIG. 9 , the beam width of the data wireless signal is changed in accordance with the reporting frequency. In the process of FIG. 10 , the number of multiple measurement beams is changed in accordance with the reporting frequency. In the process of FIG. 11 , the transmission interval of the reference wireless signal for measuring the reception status of the beam is changed in accordance with the reporting frequency. In the process of Modification 3, the time interval Tt of the reporting slot group SLk (see FIG. 8 ), which is a communication resource allocated to the terminal station 4 for transmitting a report, is changed in accordance with the reporting frequency. The time interval Tt of the reporting slot group SLk (see FIG. 8 ) coincides with the reporting period Tt (see FIG. 8 ) in the full-cycle reporting mode. As described above, the full-cycle reporting mode is a mode in which the terminal station 4 reports the reception status without determining whether or not a report is necessary in accordance with the reception status. Therefore, the time interval Tt is also called the reporting period Tt.

[0093] Fig. 12 is a sequence diagram illustrating the setting of the time interval Tt of the reporting slot group SLk (see Fig. 8). The processing (S31 to S47) in Fig. 12 is similar to the beam management processing (S1 to S17) in Fig. 7. However, in Fig. 12, the control device 1 sets or changes the reporting period Tt, which is the time interval of the reporting slot group SLk, in accordance with the reporting frequency in addition to the beam setting processing (S31, S37, S42).

[0094] On the other hand, the terminal station 4 determines whether or not a report of the reception status is required (S5, S11, S17), and if a report is required, reports the reception status using a group of reporting slots SLk arranged at set time intervals Tt, Tt+1, Tt+2, etc. (S36, S42).

[0095] FIG. 13 is a flowchart illustrating the processing of the control device 1 according to Modification 3. However, at least a portion of the processing of FIG. 11 may be executed by the base station 2. In FIG. 13, the processing from S101 to S106 is the same as that of FIGS. 9 to 11. If the determination in S106 of FIG. 13 indicates that the reporting frequency is equal to or greater than the first reference value, the control device 1 determines whether the reporting period Tt can be shortened (S107C). ​​If the reporting period Tt can be shortened, the control device 1 instructs the base station 2 to shorten the reporting period Tt by a predetermined value (S108C). The reporting period Tt is an example of a communication parameter. The processing in S108C is an example of a processing for shortening the time interval of communication resources by a second predetermined time. The reporting slot group SLk (see FIG. 8) is an example of a communication resource. This predetermined value is an example of a second predetermined time. The predetermined value in S108C may be a parameter set in the control device 1.

[0096] A case in which the determination in S107C indicates that the reporting period Tt cannot be shortened is, for example, when the reporting period Tt is shortened and the proportion of the reporting slot group SLk in the frame exceeds a certain limit. Such a limit can be set as an empirical value or a design value. Therefore, a case in which the determination in S107C indicates that the reporting period Tt cannot be shortened is when shortening the reporting period Tt causes the time interval of communication resources to become the minimum time.

[0097] If the reporting period Tt cannot be shortened, the control device 1 instructs the terminal station 4 to use a mode in which reporting is performed in every reporting period Tt (reporting mode in every period) (S109). The processing in S109 is the same as in Fig. 9. The control device 1 also instructs the base station 2 to maintain the shortest reporting period Tt.

[0098] On the other hand, if the determination in S106 indicates that the reporting frequency is less than the first reference value, the control device 1 executes the processes of S110, S111, and S112. These processes are similar to those in FIGS. 9, 10, and 11. The control device 1 then determines whether the reporting period Tt can be extended (S113C). The maximum value of the reporting period Tt may be determined as the desired limit of the reporting period Tt in the communication systems 100A and 100B including the control device 1, the base station 2, and the terminal station 4, for example. If the reporting period Tt can be extended, the control device 1 instructs the base station 2 to extend the reporting period Tt by a predetermined time (S114C). The control device 1 then terminates the process of setting the reporting period Tt. The process of S114C is an example of a process of extending the time interval of a communication resource by a predetermined time.

[0099] (Effects of the Embodiment) As described above, the control device 1 transmits a reference radio signal (reference signal) for measuring the reception status to the terminal station 4. Then, the control device 1 receives a report of the reference radio signal measured by the terminal station 4. Here, the terminal station 4 decides whether or not to notify the control device 1 of a report of the reception status based on the measurement result of the reference radio signal. Then, if it is decided to notify, the terminal station 4 notifies the control device 1 of the report via the base station 2 or the base station 2. Then, the control device 1 controls communication parameters in data communication with the terminal station 4 according to the frequency at which the report is received. Therefore, the control device 1 can detect the speed of change in the communication environment according to the frequency at which the report is received in addition to the content of the report from the terminal station 4, and can appropriately control the beam in accordance with this change.

[0100] The reference radio signals include a first reference signal transmitted in a data radio signal beam (first beam) for transmitting user data to the terminal station 4, and a second reference signal transmitted in multiple measurement beams (second beams) directed in multiple directions. Therefore, the control device 1 can appropriately set communication parameters related to the reference radio signals of both the data radio signal beam and the multiple measurement beams.

[0101] In controlling communication parameters, the control device 1 adjusts at least one of the width of the beam (first beam) of the data wireless signal, the number of multiple beams for measurement (second beams), the transmission interval for transmitting the reference wireless signal, and the time interval of the group of report slots SLk (communication resources) allocated for transmitting reports by the terminal station 4. Therefore, the control device 1 can appropriately set the width of the beam of the data wireless signal and the number of multiple beams for measurement in accordance with changes in the communication environment. Furthermore, the control device 1 can allocate communication resources such as the slots of the reference wireless signal and the group of report slots SLk to the base station 2, the terminal station 4, etc. in accordance with changes in the communication environment.

[0102] When the reporting frequency is equal to or greater than a first reference value, the control device 1 executes an expansion process to expand the width of the beam of the data wireless signal (first beam) within an allowable width range and a process to increase the number of multiple beams for measurement (second beams) by a predetermined number. Thus, the control device 1 can appropriately set the width of the beam of the data wireless signal and the number of multiple beams for measurement in accordance with changes in the communication environment.

[0103] Alternatively, when the reporting frequency is equal to or greater than a first reference value, the control device 1 executes at least one of a process of shortening the transmission interval for transmitting a reference radio signal (reference signal) by a first predetermined time and a process of shortening the time interval of the reporting slot group SLk (communication resource) by a second predetermined time. Thus, the control device 1 can allocate communication resources such as slots of the reference radio signal and the reporting slot group SLk to the base station 2, the terminal station 4, etc. in accordance with changes in the communication environment.

[0104] The control device 1 instructs the terminal station 4 to use the full-cycle reporting mode when the width of the beam (first beam) of the data radio signal reaches the maximum allowable limit. The control device 1 also instructs the terminal station 4 to use the full-cycle reporting mode when the number of multiple measurement beams (second beams) reaches the maximum. The control device 1 also instructs the terminal station 4 to use the full-cycle reporting mode when the transmission interval for transmitting the reference radio signal (reference signal) reaches the minimum interval. The control device 1 also instructs the terminal station 4 to use the full-cycle reporting mode when the time interval between reporting slot groups SLk (communication resources) reaches the minimum time. In the full-cycle reporting mode, the terminal station 4 notifies the base station 2 or the control device 1 via the base station 2 of all reports on the reception status of the reference radio signal, regardless of the measurement results. Therefore, when the communication parameters are not within an adjustable range, the control device 1 can receive reports from the terminal station 4 as frequently as possible.

[0105] When the reporting frequency is less than a second reference value that is smaller than the first reference value, the control device 1 adjusts the communication parameters in the opposite direction to the above. That is, the control device 1 executes a process of narrowing the width of the beam (first beam) of the data wireless signal by a predetermined width, or a process of reducing the number of multiple measurement beams (second beams) by a predetermined number. Alternatively, the control device 1 executes a process of extending the transmission interval for transmitting the reference wireless signal (reference signal) by a predetermined interval, or a process of extending the time interval of the reporting slot group SLk (communication resource) by a predetermined time. When the reporting frequency is low, the control device 1 determines that the communication environment is stable and can return the beams to a normal state. Furthermore, the control device 1 can suppress unnecessary allocation of resources such as the reference wireless signal or the reporting slots.

[0106] Second Embodiment A communication parameter setting process according to a second embodiment will be described below with reference to FIG. 14. In the first embodiment, the control device 1 sets communication parameters for data communication, such as the beam width, based on the frequency of reports of reception status from the terminal stations 4 (e.g., S108 in FIG. 9). However, the control device 1 is not limited to this process. For example, the control device 1 may set communication parameters for data communication by reflecting the content of the reports of reception status in addition to the frequency of reports of reception status.

[0107] 14 is a flowchart illustrating the beam width expansion process of this embodiment, which can be considered as an example of details of S108 in FIG.

[0108] Here, it is assumed that there are N types of measurement beams that terminal station 4 is to measure. The received signal strength for the nth beam contained in the kth report from the terminal station is G(k, n). It is assumed that the k-1th report R(k-1) and the kth report R(k) from terminal station 4 are given as follows. It is also assumed that the beam numbers 1 to N are the same as the order in which the beams are sorted in azimuth order.

[0109] R(k-1) = {G(k-1,1),..., G(k-1,N)}; R(k) = {G(k,1),..., G(k,N)}; Here, R(k-1) is the report immediately before R(k) or the report immediately before R(k). The maximum values ​​of the received signal strength in each report are defined as G(k-1,max) and G(k,max). Also, the beam numbers that give the maximum values ​​in each report are defined as n(k-1,max) and n(k,max). Then, the difference between the maximum values ​​of the received signal strength in the kth report and the k-1th report is defined as DG(k). Here, the two vertical bars "|" indicate absolute values.

[0110] DG(k) = |G(k, max) - G(k-1, max)|; Also, let Dn(k) be the difference between the beam numbers that give the maximum received signal strength in the kth report and the k-1th report.

[0111] Dn(k) = |n(k, max) - n(k-1, max)|; The desired received signal strength in the modulation and coding scheme (MCS) used in downlink data communication is denoted by gamma. Furthermore, the gain loss when one beam covers the beam width covered by m adjacent beams, i.e., when the current beam is expanded to m beams (m is a number equal to or greater than 1), is denoted by L(m).

[0112] In the process of FIG. 14, the control device 1 first determines whether G(k,max)-DG(k) is less than gamma (S201). G(k,max)-DG(k) is the maximum received signal strength G(k,max) fluctuated by the difference DG(k) between the maximum received signal strengths (a margin is included). This value G(k,max)-DG(k) can be considered an estimate of the received signal strength calculated by varying the maximum received signal strength G(k,max) in the latest report R(k) from the terminal station 4 by the difference DG(k), which is the fluctuation value of the received signal strength. If this value G(k,max)-DG(k) is equal to or greater than the desired received signal strength gamma in the MCS (NO in S201), the received signal strength is sufficient even considering the fluctuation of the difference DG(k). Therefore, the control device 1 does not change the beam width (S206).

[0113] On the other hand, if the determination in S201 is NO, the control device 1 then sets the largest m among the m's that make G(k,max)-DG(k)-gamma-L(m) greater than 0 as mmax. Furthermore, if there is no m that makes G(k,max)-DG(k)-gamma-L(m) greater than 0, the control device 1 sets mmax = 0 (S202). An m that makes G(k,max)-DG(k)-gamma-L(m) greater than 0 can be considered an example of information that specifies the allowable width for widening the width of the first beam. Furthermore, m or its maximum value mmax can be considered an example of a calculated value of a predetermined number in the process of increasing the number of second beams by a predetermined number.

[0114] Here, G(k,max)-DG(k)-gamma is the difference between the estimated value of the received signal strength taking into account the margin of the difference value DG(k) and the desired received signal strength gamma in the MCS. Meanwhile, L(m) is the gain loss when the beam width is expanded to m adjacent beams. Therefore, if G(k,max)-DG(k)-gamma-L(m) is 0 or less, there is a risk that the received signal strength will not reach the desired received signal strength gamma in the MCS when the beam width is expanded.

[0115] Therefore, the control device 1 determines whether mmax is a value other than 0 (S203). If mmax is 0 (NO in S203), the control device 1 determines that there is no point in expanding the beam width. Therefore, the control device 1 does not change the beam width (S206). If mmax is 0, this is an example of a case where the received signal strength does not reach the predetermined standard by expanding the width of the first beam within the allowable width range.

[0116] Next, the control device 1 determines whether the difference Dn(k) between the beam numbers that provide the maximum received signal strength between the kth report and the k-1th report is less than mmax (S204). If the difference Dn(k) is greater than mmax (NO in S204), even if the control device 1 expands the beam width to the maximum allowable value mmax, it will not be able to cover the change in beam number. Therefore, the control device 1 does not change the beam width (S206). Here, if the difference Dn(k) between the beam numbers that provide the maximum received signal strength is greater than mmax, this is an example of a case where the direction of the beam n(k, max) with the maximum received signal strength among the second beams directed in multiple directions fluctuates more than the range specified by the allowable width between the latest report R(k) and the immediately previous report R(k-1).

[0117] On the other hand, if the difference Dn(k) is smaller than mmax, the control device 1 expands the width of the beam to m (S205), where m is a real number ranging from 1 to mmax.

[0118] (Effects of Second Embodiment) As described above, according to this embodiment, the control device 1 can set communication parameters by reflecting not only the report frequency from the terminal station 4 but also the report content of the reception status from the terminal station 4. Note that in Fig. 14, as an example of the processing of S108 in Fig. 9, the control device 1 determines whether to change the beam width based on the report content of the reception status.

[0119] More specifically, the control device 1 obtains an estimate of the next received signal strength G(k+1,max) by varying the maximum received signal strength G(k,max) in the latest report R(k) from the terminal station 4 by a difference value DG(k), which is a fluctuation value of the received signal strength. Then, in the expansion process of widening the width of the beam (first beam) of the data wireless signal within the allowable width range, if the estimated value of the received signal strength reaches a predetermined standard (gamma) (NO in S201), the control device 1 maintains the width of the beam (first beam) of the data wireless signal. Therefore, the control device 1 can set the beam width to an appropriate value based on the report content from the terminal station 4 and suppress unnecessary changes to communication parameters.

[0120] Furthermore, in this expansion process, the control device 1 widens the width of the data wireless signal beam (first beam) within the allowable range, and maintains the width of the first beam if the received signal strength does not reach a predetermined standard (NO in S203). Therefore, the control device 1 can adjust the beam width to an appropriate value based on the report from the terminal station 4.

[0121] Furthermore, in this extension process, the control device 1 calculates the fluctuation range of the direction of the beam with the maximum received signal strength between the latest report R(k) from the terminal station 4 and the previous report R(k-1) immediately before the latest report. If the beam direction fluctuates by more than the range specified by the tolerance range (NO in S204), the width of the beam of the data wireless signal (first beam) is maintained. If changing the beam width would provide little benefit, the control device 1 does not change the beam width. This allows the control device 1 to suppress unnecessary control of communication parameters.

[0122] Other Embodiments The above-described embodiment is merely an example, and the present disclosure may be modified as appropriate without departing from the spirit and scope of the present disclosure. Furthermore, the processes and means described in the present disclosure may be freely combined and implemented as long as no technical contradiction occurs.

[0123] Furthermore, a process described as being performed by one device may be shared and executed by multiple devices. Alternatively, a process described as being performed by different devices may be executed by one device. The hardware configuration (server configuration) by which each function is realized in each of the terminal station 4, the control device 1, and the base station 2, or in the communication systems 100A and 100B, can be flexibly changed.

[0124] The present disclosure can also be realized by supplying a computer program that implements the functions described in the above embodiments to a computer, and having one or more processors in the computer read and execute the program. Such a computer program may be provided to the computer on a non-transitory computer-readable storage medium connectable to the computer's system bus or via a network. Non-transitory computer-readable storage media include any type of medium suitable for storing electronic instructions, such as any type of disk, including magnetic disks (e.g., floppy disks, hard disk drives (HDDs), etc.), optical disks (e.g., CD-ROMs, DVDs, Blu-ray disks), read-only memory (ROM), random access memory (RAM), EPROM, EEPROM, magnetic cards, flash memory, or optical cards.

[0125] REFERENCE SIGNS LIST 1 control device 2 base station 2A central base station 2B distributed base station 4 terminal station 11 CPU 12 main memory device 13 external memory device 16 communication device 21, 21B, 41 radio device 22, 22A, 42 control circuit 50 vehicle

Claims

1. A control device comprising a controller that performs the following operations: transmitting a reference radio signal to a terminal station for measuring the reception state; receiving reports of the reference radio signal measured by the terminal station; and controlling communication parameters in data communication with the terminal station according to the frequency at which the reports are received.

2. The control device according to claim 1, wherein the reference radio signals include a first reference signal transmitted in a first beam for transmitting user data to the terminal station and a second reference signal transmitted in a second beam directed in multiple directions.

3. The control device according to claim 2, wherein the controller, in controlling the communication parameters, adjusts at least one of the width of the first beam, the number of the second beams, the transmission interval for transmitting the reference radio signal, and the time interval of the communication resource allocated to the terminal station for transmitting the report.

4. The control device described in claim 3, wherein when the frequency is equal to or greater than a first reference value, the controller executes at least one of the following processes: an expansion process for widening the width of the first beam within an allowable width range; a process for increasing the number of the second beams by a predetermined number; a process for shortening the transmission interval for transmitting the reference radio signal by a first predetermined time; and a process for shortening the time interval of the communication resource by a second predetermined time.

5. The control device according to claim 4, wherein the terminal station determines whether or not to notify the control device of the report based on the measurement results of the reference radio signal, and is capable of notifying the report if it is determined to notify, and the controller instructs the terminal station to notify all of the reports regardless of the measurement results when the width of the first beam reaches the maximum allowable limit, when the number of second beams reaches the maximum number, when the transmission interval for transmitting the reference radio signal reaches the minimum interval, or when the time interval for the communication resource reaches the minimum time.

6. The control device described in claim 4, wherein the controller performs at least one of the following processes when the frequency is less than a second reference value that is smaller than the first reference value: narrowing the width of the first beam by a predetermined width; reducing the number of the second beams by a predetermined number; extending the transmission interval for transmitting the reference radio signal by a predetermined interval; and extending the time interval of the communication resource by a predetermined time.

7. A control device as described in claim 4, wherein the controller maintains the width of the first beam if, during the extension process, the estimated value of the received signal strength calculated by varying the maximum received signal strength in the latest report from the terminal station by the fluctuation value of the received signal strength reaches a predetermined standard.

8. A control device as described in claim 4, wherein the controller, in the expansion process, widens the width of the first beam within the range of the allowable width, and maintains the width of the first beam if the received signal strength does not reach a predetermined standard.

9. A control device as described in claim 4, wherein the controller maintains the width of the first beam if, during the extension process, the direction of the beam with the greatest received signal strength among the second beams directed in multiple directions fluctuates more than the range specified by the tolerance width between the latest report from the terminal station and the previous report immediately prior to the latest report.

10. A communication system comprising: a control device having a controller that performs the following operations: transmitting a reference radio signal to a terminal station for measuring a reception state; receiving a report of the reference radio signal measured by the terminal station; and controlling communication parameters in data communication with the terminal station according to the frequency at which the report is received; and the terminal station.

11. A communication method comprising: transmitting a reference radio signal to a terminal station for measuring a reception state; receiving a report of the reference radio signal measured by the terminal station; and controlling communication parameters in data communication with the terminal station according to the frequency at which the report is received.

12. The communication method according to claim 11, wherein the reference radio signals include a first reference signal transmitted in a first beam for transmitting user data to the terminal station and a second reference signal transmitted in a second beam directed in multiple directions.

13. The communication method of claim 12, wherein controlling the communication parameters adjusts at least one of the width of the first beam, the number of the second beams, the transmission interval for transmitting the reference radio signal, and the time interval of the communication resource allocated to the terminal station for transmitting the report.

14. A communication method as described in claim 13, wherein, when the frequency is equal to or greater than a first reference value, at least one of the following processes is executed: an expansion process for widening the width of the first beam within an allowable width range; a process for increasing the number of the second beams by a predetermined number; a process for shortening the transmission interval for transmitting the reference radio signal by a first predetermined time; and a process for shortening the time interval of the communication resource by a second predetermined time.

15. The communication method according to claim 14, wherein the terminal station determines whether or not to notify the control device of the report based on the measurement results of the reference radio signal, and is capable of notifying the control device of the report if it is determined that the report should be notified, and includes instructing the terminal station to notify all of the reports regardless of the measurement results when the width of the first beam reaches the maximum allowable limit, when the number of second beams reaches the maximum number, when the transmission interval for transmitting the reference radio signal reaches the minimum interval, or when the time interval for the communication resource reaches the minimum time.

16. A communication method according to claim 14, wherein, when the frequency is less than a second reference value that is smaller than the first reference value, at least one of the following processes is executed: narrowing the width of the first beam by a predetermined width; reducing the number of second beams by a predetermined number; extending the transmission interval for transmitting the reference radio signal by a predetermined interval; and extending the time interval of the communication resource by a predetermined time.

17. A communication method as described in claim 14, wherein in the extension process, if the estimated value of the received signal strength calculated by varying the maximum received signal strength in the latest report from the terminal station by the fluctuation value of the received signal strength reaches a predetermined standard, the width of the first beam is maintained.

18. A communication method according to claim 14, wherein in the expansion process, if the received signal strength does not reach a predetermined standard by expanding the width of the first beam within the range of the allowable width, the width of the first beam is maintained.

19. A communication method as described in claim 14, wherein, in the extension process, if the direction of the beam with the greatest received signal strength among the second beams directed in multiple directions fluctuates by more than the range specified by the tolerance width between the latest report from the terminal station and the previous report immediately prior to the latest report, the width of the first beam is maintained.

20. The communication method according to claim 12, wherein at least one of the first beam and the second beam includes a beam formed by beams transmitted from a plurality of distributed base stations.

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