Base station device, communication system, beam search method and program

Abstract

Provided is a base station device comprising: a candidate beam determination unit that, for each terminal device that is a transmission destination, determines a candidate beam that is a candidate for a beam of a pilot signal to be transmitted; a beam ID assignment unit that assigns a different beam ID to each candidate beam of the same terminal device and further assigns the beam IDs among the candidate beams of the different terminal devices 3 such that the combination of candidate beams assigned with the same beam ID is maximized; and a pilot signal generation unit that, for each candidate beam assigned with the same beam ID, generates a pilot signal to be transmitted in the same time domain or the same frequency domain.

Description

[Technical Field]

[0001] The present invention relates to a base station device, a communication system, a beam search method, and a program. [Background technology]

[0002] In high-frequency bands such as the millimeter wave band and the terahertz band, free space propagation loss is greater than in low-frequency bands such as the microwave band, so beamforming technology, which forms beams that concentrate power in a specific direction, must be used to compensate for this (see, for example, Non-Patent Document 1). Beamforming can be performed in a fixed manner in advance, such as when the wireless stations are installed, in point-to-point (PP) communications, where the combination of wireless stations that communicate is always fixed, and the relative positions of the wireless stations and the propagation environment around the wireless stations do not change. However, in point-to-multipoint (P-MP) communications, which accommodate multiple wireless stations, or in cases where at least one of the wireless stations moves, fixed beamforming cannot be performed, and adaptive beamforming is required, which adaptively controls the beam formation direction in accordance with the position of the wireless station that needs to communicate among the multiple wireless stations, the movement of the wireless station, and changes in the propagation environment around the wireless station.

[0003] Adaptive beamforming, which does not require a mechanical drive unit, typically uses multiple antenna elements and adjusts the phase relationship of the radio waves radiated between the elements. However, to properly adjust the phase relationship, it is necessary to understand the phase relationship between each antenna element at both the transmitting and receiving wireless stations and then derive the appropriate phase relationship. For this reason, adaptive beamforming transmits known signals using multiple discretely pre-defined candidate beams, and selects the candidate beam that is determined to be most suitable for communication. This candidate beam selection method is specified and implemented in wireless communication systems that have recently been put into practical use, such as 3GPP (registered trademark) 5G (5th Generation) and IEEE802.11ad / ay (see, for example, Non-Patent Documents 1, 2, and 3). This method is used to search for a beam to use for communication.

[0004] Methods for searching for beams for multiple terminal devices include time-division and transmitting signals from each candidate beam using a single beam, and frequency-division for each terminal device and transmitting signals with different frequencies using multiple beams for each candidate beam. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] “5G Multi-Antenna Technology,” NTT DOCOMO Technical Journal, Vol. 23, No. 4, pp. 4039, January 2016. [Non-patent document 2] Kazuaki Takeda et al., "Status of Study on Physical Layer Elemental Technologies and High Frequency Band Utilization in 5G," NTT DOCOMO Technical Journal, Vol. 25, No. 3, pp. 23-32, October 2017 [Non-patent document 3] Koji Takinami et al., "Standardization Trends and Elemental Technologies of Millimeter-Wave Wireless LAN Systems," IEICE Communications Society Magazine, No. 38, Autumn Issue, pp. 100-106, 2016 [Non-patent document 4] M. Giordani, M. Polese, A. Roy, D. Castor and M. Zorzi, "A Tutorial on Beam Management for 3GPP NR at mmWave Frequencies," in IEEE Communications Surveys & Tutorials, vol. 21, no. 1, pp. 173-196, Firstquarter 2019, doi: 10.1109 / COMST.2018.2869411. [Non-Patent Document 5] P. Zhou et al., "IEEE 802.11ay-Based mmWave WLANs: Design Challenges and Solutions," in IEEE Communications Surveys & Tutorials, vol. 20, no. 3, pp. 1654-1681, thirdquarter 2018, doi: 10.1109 / COMST.2018.2816920. Summary of the Invention [Problem to be solved by the invention]

[0006] However, the time division method has the drawback that the time resources increase in proportion to the number of terminal devices. The frequency division method also has the drawback that the frequency resources increase in proportion to the number of terminal devices. The increase in time resources may result in, for example, a failure to complete beam search within a predetermined time when performing periodic beam search, making data transmission difficult. The increase in frequency resources may also limit the frequency resources available to other communication devices.

[0007] The invention according to this embodiment can suppress an increase in time and frequency resources in beam search. [Means for solving the problem]

[0008] One aspect of the present invention is a base station device comprising: a candidate beam determination unit that determines, for each terminal device to which the signal is being transmitted, a candidate beam that is a candidate for the beam of a pilot signal to be transmitted; a beam ID assignment unit that assigns different beam IDs to the candidate beams of the same terminal device and further assigns beam IDs to candidate beams between different terminal devices 3 so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned; and a pilot signal generation unit that generates, for each candidate beam to which the same beam ID is assigned, a pilot signal to be transmitted in the same time domain or the same frequency domain.

[0009] One aspect of the present invention is a beam search method having a candidate beam determination step of determining, for each terminal device to which the signal is being transmitted, a candidate beam that is a candidate for the beam of the pilot signal to be transmitted; a beam ID assignment step of assigning different beam IDs to the candidate beams of the same terminal device and further assigning beam IDs to candidate beams between different terminal devices 3 so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned; and a pilot signal generation step of generating, for each candidate beam to which the same beam ID is assigned, a pilot signal to be transmitted in the same time domain or the same frequency domain. [Effects of the Invention]

[0010] The base station apparatus, communication system, and beam search method of the present invention can suppress an increase in time and frequency resources in beam search. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating an example of the configuration of a communication system 1 according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a base station device 2 according to the first embodiment. [Figure 3] A figure showing examples of candidate beams. [Figure 4] A figure showing an example of a beam ID assigned to a candidate beam. [Figure 5] 2 is a diagram showing an example of the relationship between the time and frequency of a pilot signal transmitted from an antenna 21. FIG. [Figure 6] FIG. 2 is a diagram illustrating an example of the configuration of a terminal device 3 according to the first embodiment. [Figure 7] FIG. 2 is a sequence diagram showing the operation of the communication system 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] (First embodiment) 1 is a diagram showing an example of the configuration of a communication system 1 according to the first embodiment. The communication system 1 includes one base station device 2 and multiple terminal devices 3 (for example, three terminal devices 3-1, 3-2, and 3-3). The base station device 2 and the terminal devices 3 communicate with each other.

[0013] 2 is a diagram showing an example of the configuration of a base station device 2 according to the first embodiment. The base station device 2 includes an antenna 21, a signal conversion unit 22, a transmission unit 24, and a reception unit 26. In the base station device 2, the signal conversion unit 22 converts a signal generated by the transmission unit 24 into an analog signal, and the antenna 21 transmits the analog signal. The signal conversion unit 22 also converts the analog signal received via the antenna 21 into a digital signal, and the reception unit 26 processes the digital signal.

[0014] The transmitter 24 includes a candidate beam determiner 241 , a beam ID assigner 242 , and a pilot signal generator 243 .

[0015] The candidate beam determination unit 241 determines, for each terminal device 3, a candidate beam that is a candidate for the beam of the pilot signal to be transmitted. For example, of the wide beams searched using wide beams with a wide beam width, the wide beam with the best reception sensitivity for each terminal device 3 is selected and a beam with a finer range is determined as the candidate beam for that terminal device 3. For example, the vicinity of the beam used by the base station device 2 when transmitting a signal to each terminal device 3 is determined as the candidate beam for that terminal device 3. The former method is used, for example, when the base station device 2 and the terminal device 3 have not previously communicated, and the latter method is used, for example, when the base station device 2 and the terminal device 3 are already communicating.

[0016] Furthermore, the candidate beam determination unit 241 may select several beams for each terminal device 3 from a plurality of predetermined beams.

[0017] Furthermore, the number of candidate beams may be different for each terminal device 3.

[0018] 3 is a diagram showing examples of candidate beams. The candidate beam determination unit 241 determines candidate beams 41-1 to 41-5 for the terminal device 3-1, determines candidate beams 42-1 to 42-4 for the terminal device 3-2, and determines candidate beams 43-1 to 43-4 for the terminal device 3-3.

[0019] The beam ID assignment unit 242 assigns beam IDs to candidate beams. The beam ID assignment unit 242 assigns different beam IDs to candidate beams of the same terminal device 3. Furthermore, the beam ID assignment unit 242 assigns beam IDs to candidate beams between different terminal devices 3 so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned. For example, in the example shown in FIG. 3, the beam ID assignment unit 242 assigns beam IDs #1 to 5 to candidate beams 41-1 to 5, assigns beam IDs #1 to 4 to candidate beams 42-1 to 4, and assigns beam IDs #1 to 4 to candidate beams 43-1 to 4. In this way, the beam ID assignment unit 242 assigns different beam IDs to candidate beams of the same terminal device 3 and assigns beam IDs to candidate beams between different terminal devices 3 so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned, which is four (#1 to #4). First, the beam ID assignment unit 242 determines the number of beam IDs. The number of beam IDs is the maximum number of candidate beams for each terminal device 3. Then, the beam ID assignment unit 242 assigns beam IDs to each candidate beam for each terminal device 3 in order starting from #1.

[0020] Furthermore, when candidate beams overlap between terminal devices 3, the beam ID assignment unit 242 may assign the same beam ID to the overlapping candidate beams. Candidate beams overlap when, for example, the angular difference between the centers of two beams is less than a predetermined angle. When the candidate beam determination unit 241 selects several beams from a plurality of predetermined beams for each terminal device 3, the same beam ID is assigned when the same candidate beam is selected between terminal devices 3.

[0021] In the example shown in Figure 3, candidate beam 41-4 and candidate beam 42-1 overlap, and candidate beam 41-5 and candidate beam 42-2 overlap. In this case, the beam ID assignment unit 242 may assign the same beam ID to candidate beam 41-4 and candidate beam 42-1, and the same beam ID to candidate beam 41-5 and candidate beam 42-2. Figure 4 is a diagram showing an example of beam IDs assigned to candidate beams. Candidate beam 41-4 and candidate beam 42-1 may be assigned the same beam ID, #1, and candidate beam 41-5 and candidate beam 42-2 may be assigned the same beam ID, #2.

[0022] The pilot signal generation unit 243 generates a pilot signal to be transmitted in the same time domain or the same frequency domain for each candidate beam assigned the same beam ID. The pilot signal generation unit 243 may generate pilot signals to be transmitted simultaneously for each candidate beam assigned the same beam ID, or may generate pilot signals to be transmitted at the same frequency. When generating pilot signals to be transmitted in the same time domain or simultaneously from candidate beams assigned the same beam ID, the pilot signal generation unit 243 may generate pilot signals to be transmitted in different frequency domains or frequencies for each candidate beam assigned a different beam ID, and transmit pilot signals generated based on candidate beams assigned different beam IDs in the same time domain or simultaneously. Furthermore, when generating pilot signals to be transmitted in the same frequency domain or frequency from candidate beams assigned the same beam ID, the pilot signal generation unit 243 may generate pilot signals to be transmitted in different time domains or at different timings for each candidate beam assigned a different beam ID, and transmit pilot signals generated based on candidate beams assigned different beam IDs in the same frequency or frequency domain.

[0023] In addition, although the case where the pilot signal generating unit 243 divides the pilot signal into either the time domain or the frequency domain as many times as the number of different beam IDs and transmits it has been explained, it is also possible to use both division of the time domain and division of the frequency domain and transmit the pilot signal by dividing it into any time-frequency resources as many times as the number of different beam IDs.

[0024] When the same beam ID is assigned to overlapping candidate beams, the pilot signal generation unit 243 does not need to generate a pilot signal for each candidate beam, but may generate a single pilot signal collectively. When the same beam ID is assigned to overlapping candidate beams, for example, the pilot signal generation unit 243 may generate a pilot signal using one of the overlapping candidate beams, a beam pointing in a direction between the overlapping candidate beams, or a beam combining the multiple candidate beams. The pilot signal generation unit 243 outputs the generated pilot signal to the signal conversion unit 22. The pilot signal generation unit 243 generates multiple pilot signals and controls the direction of the beam in which the pilot signals are transmitted from the antenna 21 by using a beamforming technique that controls the phase of the generated pilot signals. The signal conversion unit 22 converts the pilot signal input from the pilot signal generation unit 243 from a digital signal to an analog signal. The converted analog pilot signal is transmitted to the terminal device 3 via the antenna 21. The antenna 21 transmits a pilot signal by beaming in a specific direction via, for example, a plurality of antennas (antennas 21-1, 21-2, and 21-3).

[0025] FIG. 5 is a diagram showing an example of the time-frequency relationship of pilot signals transmitted from antenna 21. Pilot signals are transmitted in the same frequency domain for each beam ID in a time-division manner. The direction in which pilot signals are transmitted may depend on whether candidate beams overlap. For example, a pilot signal generated based on a candidate beam assigned beam ID #1 may have two directions because candidate beams 41-4 and 42-1 overlap. A pilot signal generated based on a candidate beam assigned beam ID #3 has three directions because there are no overlapping candidate beams.

[0026] In the example shown in Figure 5, pilot signals are time-divided and transmitted in the same frequency domain for each beam ID, but this is not limited to this.For example, pilot signals may be frequency-divided and transmitted in the same time domain for each beam ID, or pilot signals may be transmitted using a combination of time division and frequency division.

[0027] The pilot signal transmitted from the base station device 2 may or may not include beam ID information. For example, the pilot signal generation unit 243 may generate a pilot signal including beam ID information based on the beam ID assignment by the beam ID assignment unit 242, and output the generated pilot signal to the signal conversion unit 22. Note that if the pilot signal does not include beam ID information, the base station device 2 notifies the timing of signal transmission by each candidate beam, for example, by transmitting in advance information on the timing of starting signal transmission and the time interval for switching between candidate beams.

[0028] In the case of a method for generating a pilot signal including beam ID information, signals from beams in multiple directions at the same time frequency are transmitted to the terminal device 3, which may result in multipath interference. However, because the same pilot signal including the same beam ID information is transmitted in multiple directions at the same time frequency, degradation of signal quality due to multipath interference can be avoided by a method for compensating for multipath interference used in ordinary wireless communication systems. In order to compensate for multipath interference, the time difference between reception of signals from different beams transmitted from the base station device 2 must be shorter than the allowable delay time difference for multipath interference. In other words, the time difference between reception of multiple identical pilot signals transmitted at the same time frequency by the terminal device 3 must be shorter than the allowable delay time difference for multipath interference. Note that in the case of a method for generating a pilot signal that does not include beam ID information, the terminal device 3 does not need to extract beam ID information from the pilot signal, so the base station device 2 does not need to transmit the same pilot signal including the same beam ID information, and may transmit different pilot signals.

[0029] Hereinafter, the receiver 26 will be described in detail later, followed by a description of the configuration of the terminal device 3. Fig. 6 is a diagram showing an example configuration of the terminal device 3 according to the first embodiment. The terminal device 3 includes an antenna 31, a signal converter 32, a receiver 34, and a feedback signal generator 36. The receiver 34 includes a signal processor 341, a reception quality measurer 342, and a candidate beam selector 343.

[0030] The antenna 31 receives a pilot signal transmitted from the base station device 2. The signal conversion unit 32 converts the pilot signal received by the antenna 31 from an analog signal to a digital signal. The signal processing unit 341 processes the pilot signal. For example, the signal processing unit 341 processes the pilot signal to obtain a beam ID included in the pilot signal.

[0031] If the pilot signal does not include beam ID information, the beam ID cannot be acquired from the pilot signal, and therefore the receiver 34 acquires the transmission timing and the like in advance from the base station device 2. For example, the receiver 34 acquires the timing at which each candidate beam is transmitted by acquiring information on the timing at which the signal transmission starts and the time interval for switching between candidate beams, and can estimate the beam ID corresponding to the received pilot signal.

[0032] The reception quality measurement unit 342 measures the reception quality of the pilot signal. The candidate beam selection unit 343 selects a candidate beam to be used based on the reception quality of the pilot signal. The candidate beam selection unit 343 selects, for example, a candidate beam corresponding to the pilot signal with the best reception quality as the candidate beam to be used.

[0033] The feedback signal generation unit 36 ​​generates a feedback signal to be transmitted to the base station device 2. The feedback signal includes information about the candidate beam to be used selected by the candidate beam to be used selection unit 343. The feedback signal generation unit 36 ​​outputs the feedback signal to the signal conversion unit 32.

[0034] The feedback signal is converted into an analog signal by a signal converter 32 and transmitted from an antenna 31 .

[0035] 2, the following describes the receiver 26 of the base station device 2. The receiver 26 includes a feedback signal processor 261 and a used beam setting unit 262.

[0036] The feedback signal is received by the antenna 21 of the base station device 2 and converted into a digital signal by the signal conversion unit 22. The feedback signal processing unit 261 processes the feedback signal and obtains information about the candidate beam to be used.

[0037] The used beam setting unit 262 sets a beam to be used based on information about the candidate beam to be used, which is included in the feedback signal. By receiving the feedback signal from each terminal device 3, the base station device 2 sets a beam to be used when communicating with each terminal device 3. Thereafter, the base station device 2 communicates with each terminal device 3 by transmitting a signal to each terminal device 3 using the set beam.

[0038] 7 is a sequence diagram showing the operation of the communication system 1. First, the candidate beam determination unit 241 of the base station device 2 determines a candidate beam for each terminal device 3 (step S201). Then, the beam ID assignment unit 242 assigns a beam ID to the candidate beam (step S202). Here, the beam ID assignment unit 242 assigns different beam IDs to candidate beams for the same terminal device 3, and also assigns beam IDs to candidate beams between different terminal devices 3 so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned. The beam ID assignment unit 242 may assign the same beam ID when candidate beams overlap between terminal devices 3. Then, the pilot signal generation unit 243 generates a pilot signal, which is converted into an analog signal by the signal conversion unit 22 and transmitted from the antenna 21 to the terminal device 3 (step S203). The order in which pilot signals are transmitted is based on the beam ID. For example, antenna 21 first transmits a pilot signal on a candidate beam with beam ID #1 (step S203-1), then transmits a pilot signal on a candidate beam with beam ID #2 (step S203-2), and so on until it transmits pilot signals on all candidate beams.

[0039] The terminal device 3 receives a pilot signal via the antenna 31 (step S301), and the signal conversion unit 32 converts the pilot signal from an analog signal to a digital signal. The signal processing unit 341 processes the pilot signal and acquires information about the beam ID (step S302). If the received signal is an unmodulated wave signal that does not contain information about the beam ID, the receiving unit 34 acquires the timing at which each candidate beam is transmitted, for example, by acquiring the timing at which the signal transmission starts and the time interval at which the candidate beams are switched, and estimates the beam ID corresponding to the unmodulated wave signal. The reception quality measurement unit 342 measures the reception quality of the received signal (step S303). The terminal device 3 performs the operations of steps S301 to S303 every time it receives a pilot signal. For example, when terminal device 3-1 receives a pilot signal transmitted by a candidate beam with beam ID #1, it performs the operations from step S301-1 to step S303-1, and when it receives a pilot signal transmitted by a candidate beam with beam ID #2, it performs the operations from step S301-2 to step S303-2, and performs the operations for all pilot signals thereafter. Similar operations are performed in other terminal devices 3 to measure the reception quality of all transmitted pilot signals.

[0040] The candidate beam to be used selection unit 343 selects a candidate beam to be used based on the reception quality (step S304). Thereafter, the feedback signal generation unit 36 ​​generates a feedback signal including information on the candidate beam to be used, and the signal conversion unit 32 converts the generated signal into an analog signal, which is then transmitted from the antenna 31 (step S305). The antenna 21 of the base station device 2 receives the feedback signal (step S204), the signal conversion unit converts the feedback signal from an analog signal to a digital signal, and the feedback signal processing unit 261 processes the feedback signal to obtain information on the candidate beam to be used (step S205). The beam to be used setting unit 262 sets a beam to be used for each terminal device 3 based on the information on the candidate beam to be used (step S206).

[0041] The base station device 2 assigns beam IDs to candidate beams so that different beam IDs are assigned to candidate beams for the same terminal device 3, and the same beam ID is assigned the maximum number of times to candidate beams between terminal devices 3. In addition, for each candidate beam to which the same beam ID is assigned, a pilot signal transmitted in the same time domain or the same frequency domain is generated. This makes it possible to suppress an increase in time and frequency resources due to an increase in the number of terminal devices 3.

[0042] Furthermore, the base station device 2 can assign the same beam ID to overlapping candidate beams and transmit pilot signals as a single candidate beam. For example, in the case of candidate beams 41-4 and 42-1, which are overlapping candidate beams in FIG. 5 showing time frequencies, one pilot signal is transmitted based on the two candidate beams, rather than transmitting a pilot signal for each terminal device 3 using the two candidate beams. This saves resources for transmitting one pilot signal from time T1 to T2, and can save resources for transmitting one pilot signal from time T2 to T3. As described above, the communication system 1 according to this embodiment can save resources for transmitting signals when the base station device 2 selects a beam to use for communication.

[0043] Other Embodiments One embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes and the like are possible within the scope that does not deviate from the gist of the present invention.

[0044] Even if the communication system 1 is configured to have one terminal device 3 and multiple base station devices 2, as in this embodiment, the terminal device 3 determines a candidate beam for each base station device 2, assigns a beam ID to the candidate beam for the base station device 2, and generates a pilot signal, thereby suppressing the increase in time and frequency resources.

[0045] The pilot signal can be interpreted as a reference signal, a control signal, control information, or a control channel. The beam ID can be notified not only by the pilot signal but also by the reference signal, the control signal, the control information, or the control channel.

[0046] The beam ID may be information related to the beam. The beam ID may be notified to the terminal device 3 by using the resource ID of a reference signal generated based on a candidate beam to which the same beam ID is assigned.

[0047] The transmitter 24 includes a candidate beam determiner 241, a beam ID assigner 242, and a pilot signal generator 243. The receiver 26 includes a feedback signal processor 261 and a used beam setting unit 262. The receiver 34 includes a signal processor 341, a reception quality measurer 342, and a used candidate beam selector 343. These components and the feedback signal generator 36 are realized, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by a combination of software and hardware. The program may be stored in advance in a storage device (a storage device with a non-transitory storage medium) such as an HDD (Hard Disk Drive) or flash memory, or may be stored in a removable storage medium (a non-transitory storage medium) such as a DVD or CD-ROM, and installed by inserting the storage medium into a drive device. [Explanation of symbols]

[0048] REFERENCE SIGNS LIST 1 communication system, 2 base station device, 3 terminal device, 21 antenna, 22 signal conversion unit, 24 transmission unit, 241 candidate beam determination unit, 242 beam ID assignment unit, 243 pilot signal generation unit, 26 reception unit, 261 feedback signal processing unit, 262 used beam setting unit, 31 antenna, 32 signal conversion unit, 34 reception unit, 341 signal processing unit, 342 reception quality measurement unit, 343 used candidate beam selection unit, 36 feedback signal generation unit

Claims

1. a candidate beam determination unit that determines a candidate beam that is a candidate for a beam of a pilot signal to be transmitted for each terminal device that is a transmission destination; A beam ID assignment unit that assigns different beam IDs to the candidate beams of the same terminal device and further assigns beam IDs to candidate beams between different terminal devices so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned; a pilot signal generating unit that generates a pilot signal to be transmitted in the same time domain or the same frequency domain for each candidate beam to which the same beam ID is assigned; A base station device comprising:

2. The beam ID assignment unit When the candidate beams overlap between the terminal devices, assigning the same beam ID to the overlapping candidate beams. The base station device according to claim 1 .

3. The pilot signal generation unit generates a pilot signal including a corresponding beam ID. The base station device according to claim 1 or 2.

4. a difference in time at which a plurality of pilot signals transmitted in the same time domain are received by the terminal device is smaller than a time difference in allowable delay of multipath interference in the pilot signals; The base station device according to claim 1 or 2.

5. The base station device according to claim 1; a plurality of terminal devices; Equipped with The terminal device a reception quality measurement unit for measuring the reception quality of a pilot signal; a candidate beam selection unit for selecting a candidate beam to be used based on the reception quality and a correspondence between a pilot signal and a beam ID of the candidate beam; a feedback signal generator for generating a feedback signal including information on a candidate beam to be used; Equipped with Communication system.

6. a candidate beam determination step of determining a candidate beam, which is a candidate for a beam of a pilot signal to be transmitted, for each terminal device to which the signal is transmitted; A beam ID assignment step of assigning different beam IDs to the candidate beams of the same terminal device, and further assigning beam IDs to candidate beams between different terminal devices so as to maximize the number of combinations of candidate beams to which the same beam ID is assigned; a pilot signal generation step of generating a pilot signal to be transmitted in the same time domain or the same frequency domain for each candidate beam to which the same beam ID is assigned; A beam search method having:

7. A program that causes a computer to operate as the base station device according to claim 1.

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