Network node, user equipment, and communication method

Abstract

A network node according to a first aspect manages a cell in a mobile communication system, and comprises: a transmission unit that transmits, by beamforming, a synchronization signal block used in a cell search performed by a user device; and a control unit that performs beam sweeping for switching a transmission beam direction of the synchronization signal block at predetermined time intervals. The control unit controls the transmission unit to simultaneously transmit N (N: an integer of 2 or more) synchronization signal blocks in a band of the cell at different frequencies.

Description

Technical Field

[0001] The present disclosure relates to a network node, a user apparatus, and a communication method for use in a mobile communication system.

Background Art

[0002] In the technical specifications for 5G (5th Generation) / NR (New Radio) of the 3rd Generation Partnership Project (3GPP (registered trademark, the same applies hereinafter)), radio waves in a higher frequency band are used for wireless communication compared with 4G (4th Generation) / LTE (Long Term Evolution). Since propagation loss increases in high frequency bands, beamforming that narrows the direction of radio wave transmission is used for wireless communication, and the propagation loss is compensated by beam gain.

[0003] A network node that manages a cell (for example, a base station) transmits a synchronization signal block (SSB: Synchronization Signal / Physical Broadcast Channel Block) used for cell search performed by a user apparatus by beamforming. The cell search is a procedure in which the user apparatus obtains time and frequency synchronization with a cell and detects the cell ID of the cell. The user apparatus performs cell search based on a primary synchronization signal, a secondary synchronization signal, and a demodulation reference signal (DMRS) for PBCH in the SSB.

[0004] Network nodes perform beam sweeping, which involves switching the transmission beam direction of SSB (also called the "beamforming pattern") at predetermined time intervals, in order to transmit SSB across the entire coverage area of ​​the cell. For example, a network node transmits an SS burst (also called an "SS burst set" or "synchronous signal burst") consisting of multiple SSBs arranged in the time direction at a period of 20 ms. Here, the network node transmits each SSB within the SS burst in a time-division multiplexed manner using beam sweeping, each with a different transmission beam direction. This ensures that even when transmitting SSB using beamforming, the SSB can be distributed across the entire coverage area of ​​the cell within the SS burst. Note that the SS burst is specified to be set within a predetermined time length (specifically, the time of a half frame).

[0005] As the frequency band increases, beamforming techniques that can create sharper beams are utilized, and therefore the number of SSBs within an SS burst tends to increase. For example, in FR (Frequency Range) 1, which corresponds to the Sub6 band, a maximum of 8 SSBs (i.e., a maximum of 8 SSB beamforming patterns) can be used within an SS burst, while in FR2, which corresponds to the millimeter-wave band, a maximum of 64 SSBs (i.e., a maximum of 64 SSB beamforming patterns) can be used within an SS burst. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP Technical Specification: 3GPP TS 38.300 V17.6.0 (2023-09) [Overview of the Initiative]

[0007] In 6G (6th Generation), the use of the subterahertz band (e.g., frequency range of 90 GHz to 300 GHz), which is a higher frequency band than the millimeter wave band, is being primarily considered. In the subterahertz band, it is expected that the number of SSBs within an SS burst will increase further. Therefore, there are concerns that the time required for network nodes to distribute SSBs throughout the entire cell, i.e., the time required for beam sweeping, will increase. Similarly, there are concerns that the time required for cell search performed by user equipment will also increase.

[0008] This disclosure provides a network node, user equipment, and communication method that can suppress the increase in the time required for beam sweeping and cell search, even when using higher frequency bands in a mobile communication system.

[0009] The network node according to the first embodiment is a network node that manages a cell in a mobile communication system, and comprises a transmitting unit that transmits synchronization signal blocks used for cell search performed by a user device by beamforming, and a control unit that performs beam sweeping to switch the transmission beam direction of the synchronization signal blocks at predetermined time intervals. The control unit controls the transmitting unit to transmit N (N: an integer of 2 or more) of the synchronization signal blocks simultaneously at different frequencies within the bandwidth of the cell.

[0010] A user device according to the second embodiment is a user device that performs wireless communication with a network node that manages a cell in a mobile communication system, and comprises a receiving unit that receives a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping, which switches the transmission beam direction at predetermined time intervals, is applied, and a control unit that performs cell search based on the synchronization signal block. The receiving unit receives at least one of N (N: an integer of 2 or more) of the synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell.

[0011] A third aspect of the communication method is a communication method used in a network node that manages a cell in a mobile communication system, comprising the steps of: transmitting a synchronization signal block used for cell search performed by a user device by beamforming; and performing beam sweeping to switch the transmission beam direction of the synchronization signal block at predetermined time intervals. The step of transmitting the synchronization signal block includes the step of simultaneously transmitting N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell.

[0012] A fourth aspect of the communication method is a communication method used in a user device that performs wireless communication with a network node that manages a cell in a mobile communication system, comprising the steps of: receiving a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping, which switches the transmission beam direction at predetermined time intervals, is applied; and performing a cell search based on the synchronization signal block. The step of receiving the synchronization signal block includes receiving at least one of N (N: an integer of 2 or more) of the synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. [Brief explanation of the drawing]

[0013] [Figure 1] This is a diagram showing an example configuration of a mobile communication system according to the embodiment. [Figure 2] This figure shows an example of the protocol stack configuration for a U-plane wireless interface that handles data. [Figure 3] This diagram shows an example of a protocol stack configuration for a C-plane wireless interface that handles signaling (control signals). [Figure 4] This diagram illustrates the overview of SSB, beam sweeping, and cell search according to the embodiment. [Figure 5] This diagram illustrates the overview of SSB, beam sweeping, and cell search according to the embodiment. [Figure 6]Figure is a diagram showing a configuration example of a base station (network node) according to an embodiment. [Figure 7] Figure is a diagram showing an example of beam sweeping. [Figure 8] Figure is a diagram for explaining a comparative example. [Figure 9] Figure is a diagram showing an example of an SSB transmission operation according to an embodiment. [Figure 10] Figure is a diagram showing an example of an SSB transmission operation according to an embodiment. [Figure 11] Figure is a diagram showing another example of an SSB transmission operation according to an embodiment. [Figure 12] Figure is a diagram for explaining OffsetToPointA and Kssb (ssb-SubcarrierOffset). [Figure 13] Figure is a diagram showing a configuration example of a UE (user apparatus) according to an embodiment. [Figure 14] Figure is a diagram showing an operation example of a base station (network node) according to an embodiment. [Figure 15] Figure is a diagram showing an operation example of a UE (user apparatus) according to an embodiment. [Mode for Carrying Out the Invention]

[0014] In the following, a mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0015] (1) System Configuration Example Figure 1 is a diagram showing a configuration example of a mobile communication system according to the present embodiment. The mobile communication system according to the present embodiment is a system compliant with the 3GPP standards. For example, the mobile communication system according to the present embodiment may be a 5th Generation (5G) system or a 6th Generation (6G) system.

[0016] A mobile communication system includes a network (NW) 1 and a user apparatus (UE) 100. The UE 100 is a movable communication apparatus that performs radio communication with the NW 1. The UE 100 may be any apparatus used by a user, and may be, for example, a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC (Personal Computer), a communication module (including a communication card or a chipset), a sensor or an apparatus provided in a sensor, a vehicle or an apparatus provided in a vehicle (Vehicle UE), or a flying object or an apparatus provided in a flying object (Aerial UE).

[0017] The NW 1 includes a radio access network (RAN) 10 and a core network (CN) 20. When the mobile communication system is a 5th Generation System (5GS), the RAN 10 is referred to as NG-RAN (Next Generation Radio Access Network), and the CN 20 is referred to as 5GC (5G Core Network).

[0018] The RAN 10 includes a plurality of base stations 200 (in the illustrated example, base stations 200a to 200c). The base stations 200 are connected to each other via an inter-base station interface. The base station 200 is an example of a network node. The base station 200 may be composed of a CU (Central Unit) and a DU (Distributed Unit) (that is, functionally split), and the two units may be connected via a fronthaul interface. When the mobile communication system is a 5GS, the base station 200 is referred to as a gNB, the inter-base station interface is referred to as an Xn interface, and the fronthaul interface is referred to as an F1 interface.

[0019] Each base station 200 manages one or more cells. The base station 200 performs wireless communication with UE 100s that have established a connection with its own cell. Each base station 200 has radio resource management (RRM) functions, user data routing functions (also simply referred to as "data"), and measurement and control functions for mobility control and scheduling. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with the UE 100. One cell belongs to one carrier frequency. One cell may be associated with one downlink component carrier and one uplink component carrier. The bandwidth corresponding to one cell (system bandwidth) may be divided into multiple bandwidth parts (BWP).

[0020] CN20 includes CN equipment 300. CN equipment 300 may include a C-plane device corresponding to the control plane (C-plane) and a U-plane device corresponding to the user plane (U-plane). The C-plane device performs various mobility controls and paging for UE100. The C-plane device communicates with UE100 using NAS (Non-Access Stratum) signaling. The U-plane device controls data transfer. When the mobile communication system is 5GS, the C-plane device is called AMF (Access and Mobility Management Function), the U-plane device is called UPF (User Plane Function), and the interface between base station 200 and CN equipment 300 is called the NG interface.

[0021] Figure 2 shows an example of the protocol stack configuration for a U-plane radio interface that handles data.

[0022] A U-plane radio interface protocol, for example, includes a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0023] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the UE100's PHY layer and the base station 200's PHY layer via a physical channel. The UE100's PHY layer receives downlink control information (DCI) transmitted from the base station 200 over the physical downlink control channel (PDCCH). Specifically, the UE100 performs blind decoding of the PDCCH using a Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from the base station 200 has a CRC parity bit added, which is scrambled by the RNTI.

[0024] The MAC layer performs data priority control and retransmission processing using Hybrid ARQ (HARQ). Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of base station 200 via the transport channel. The MAC layer of base station 200 includes a scheduler. The scheduler determines the transport format for the uplink and downlink (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to UE100.

[0025] The RLC layer transmits data to the receiving RLC layer by utilizing the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of UE100 and the RLC layer of base station 200 via a logical channel.

[0026] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0027] The SDAP layer maps IP flows, which are the units for QoS control performed by CN20, to wireless bearers, which are the units for QoS control performed by AS (Access Stratum). Note that if CN30 performs QoS control at the same unit as RAN20 (i.e., QoS control is performed at the bearer level rather than the IP flow level, and a one-to-one mapping with wireless bearers is possible), the SRAP layer is not necessary.

[0028] Figure 3 shows an example of the protocol stack configuration for a C-plane wireless interface that handles signaling (control signals).

[0029] The protocol stack of the C-plane radio interface, for example, includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer instead of the SDAP layer shown in Figure 2.

[0030] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of base station 200. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. If there is a connection (RRC connection) between the RRC of UE100 and the RRC of base station 200, UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of UE100 and the RRC of base station 200, UE100 is in the RRC idle state. If the connection between the RRC of UE100 and the RRC of base station 200 is suspended, UE100 is in the RRC inactive state.

[0031] The NAS layer (also simply referred to as "NAS"), located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the NAS layer of the UE100 and the NAS layer of the CN device 300. The UE100 also has an application layer in addition to the wireless interface protocol. Furthermore, the layer below the NAS layer is called the AS layer (also simply referred to as "AS").

[0032] (2) Overview of SSB, beam sweeping, and cell search Figures 4 and 5 are diagrams illustrating the overview of SSB, beam sweeping, and cell search according to this embodiment.

[0033] As shown in Figure 4, in the frame structure used for 5G / NR wireless communication, one frame (wireless frame) is 10 ms in the time axis direction. Each frame is composed of 10 subframes, each 1 ms long. Each subframe is composed of a number of slots corresponding to the waveform configuration (also called "numerology"), such as the subcarrier spacing. Specifically, as the subcarrier spacing increases, the length of the slots in the time axis direction decreases. The number of symbols in one slot is 14 in the case of a normal CP (Cyclic Prefix). On the other hand, in the frequency axis direction, one resource block (RB) is composed of 12 subcarriers. Also, one resource element (RE) is composed of one symbol and one subcarrier.

[0034] Base station 200, which manages the cell, transmits SSB (SS / PBCH block) used for cell search performed by UE100. Each SSB consists of four symbols in the time axis direction and 240 consecutive subcarriers (i.e., 20 RBs) in the frequency axis direction. These subcarriers are numbered in ascending order from 0 to 239 within the SSB, from low frequency to high frequency. The lowest frequency subcarrier in the SSB is also called subcarrier 0. Note that PSS and SSS each consist of one symbol and 127 subcarriers. PBCH consists of three symbols and 240 subcarriers.

[0035] Each SSB includes a synchronization signal (SS) and a physical broadcast channel (PBCH). The SS includes a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). The PSS and SSS are used for synchronization at least in the time axis direction. The combination of each signal sequence of the PSS and SSS indicates the cell ID (PCI: Physical Cell ID) of the source cell. The PBCH includes a master information block (MIB) and a demodulation reference signal (DMRS). The MIB contains parameters for decoding the system information block type 1 (SIB1). The DMRS is the reference signal for decoding the PBCH. Note that SIB1 is also called RMSI (Remaining Minimum System Information). An SSB associated with SIB1 (RMSI) is called a cell-defined SSB (CD-SSB). Hereafter, SSB refers to CD-SSB.

[0036] SSB is continuously placed in the time direction at a specific frequency within the cell's bandwidth. Specifically, under the current 3GPP technical specifications, SSB is placed at a single frequency predetermined by the base station 200, and SSB is repeatedly transmitted in the time axis direction. The position of the SSB on the frequency axis can be communicated from the base station 200 to the UE100 via RRC signaling.

[0037] Base station 200 periodically transmits SS bursts (also called "SS burst sets" or "synchronous signal bursts") consisting of multiple SSBs arranged in time. The transmission period of the SS burst can be selected from 5 [ms], 10 [ms], 20 [ms], 40 [ms], 80 [ms], and 160 [ms], but 20 [ms] is the most common. The maximum number of SSBs in a single SS burst, i.e., the maximum number of consecutive SSBs, is 8 for FR1, which corresponds to the Sub6 band, and 64 for FR2, which corresponds to the millimeter wave band. In the example in Figure 4, the transmission period of the SS burst is 20 [ms], and the number of SSBs in the SS burst is 8. Note that SS bursts are specified to be set within the time of a half frame (5 [ms]). The time positions in which SSBs can be placed within a half frame are determined according to the subcarrier interval. On the other hand, the transmission period of the SS burst (i.e., the periodicity of the half-frames in which SSB is transmitted) is set by NW1 (base station 200).

[0038] In the example in Figure 4, all SSBs within an SS burst are shown being transmitted, but base station 200 is not necessarily required to transmit all SSBs within an SS burst. Base station 200 can selectively transmit only some of the SSBs within an SS burst, depending on the requirements of NW1. Furthermore, base station 200 can notify UE100 via RRC signaling which SSBs are transmitted and which are not within the SS burst. Specifically, this transmission pattern is notified to UE100 by an RRC information element (IE) called ssb-PositionInBurst.

[0039] The base station 200 assigns an SSB Index, which is an identifier for each SSB within an SS burst. In the example in Figure 4, "#1" through "#8" represent the SSB Index. This number is reset to 1 in the next SS burst. The SSB Index may also be a unique number that starts from 0 and increases by 1 each time. If the SSB Index starts from 0, it is reset to 0 in the next SS burst. The base station 200 notifies the UE 100 of the SSB Index in the PBCH within the SSB. Upon receiving the SSB, the UE 100 can identify the SSB Index of the received SSB based on the PBCH within the SSB.

[0040] As shown in Figure 5, the base station 200 performs beam sweeping, which switches the transmission beam direction of the SSB (also called the "beamforming pattern (BF pattern)") at predetermined time intervals within the duration of each SS burst (SS burst period) in order to transmit the SSB to the entire coverage area of ​​the cell. In other words, the base station 200 time-division transmits each SSB within the SS burst with a different transmission beam direction by beam sweeping. Therefore, within a half frame, different SSBs are transmitted in different spatial directions (i.e., different transmission beam directions) so as to span the coverage area of ​​the cell. This makes it possible to spread the SSB across the entire coverage area of ​​the cell (cell coverage) within an SS burst, even when transmitting SSB using beamforming.

[0041] UE100 performs a cell search based on SSBs (specifically, PSS, SSS, and DMRS within the SSB). Cell search is a procedure in which UE100 obtains time and frequency synchronization with a cell and detects the cell ID of that cell. UE100 performs a scan (cell search) of SSBs against a synchronization raster, which is the location on the frequency axis where SSBs may be placed. UE100 measures the reception quality of each received SSB and identifies the appropriate beam by identifying the SSB Index of SSBs whose reception quality satisfies predetermined conditions. Here, reception quality may be RSRP (Reference Signal Received Power) in the SSB. The predetermined condition may be that the reception quality exceeds a threshold. The predetermined condition may also be that the SSB has the highest reception quality among those received within a predetermined period (e.g., SS burst period). In the example in Figure 5, since SSB#2 has the highest reception quality, UE100 can identify SSB#2 as the SSB whose reception quality satisfies the predetermined conditions.

[0042] UE100 performs random access (RA) for initial access to NW1 (base station 200). Specifically, UE100 transmits an RA preamble to base station 200 in order to perform RA. There are as many RA occasions as there are transmit beams on base station 200 (i.e., the number of SSBs in an SS burst), which are the timings in which an RA preamble can be transmitted. UE100 transmits an RA preamble to base station 200 at the RA occasion corresponding to an SSB (SSB Index) whose received quality meets predetermined conditions. Upon receiving the RA preamble, base station 200 can determine the preferred transmit beam for UE100 (i.e., the direction in which UE100 is located) based on the correspondence between the beam (SSB Index) and the RA occasion.

[0043] Furthermore, RA occasions are notified to the UE100 in the system information provided by the base station 200. Specifically, the base station 200 notifies the UE100 of the time and frequency resources for the RA occasion. There is a one-to-one relationship between SSB and RA occasions. When the base station 200 directs its transmit beam in a certain direction, it receives the SSB during the corresponding RA occasion using a receive beam directed in the same direction as the transmit beam.

[0044] In mobile communication system 1, beam sweeping and cell search are performed in this manner. Here, beamforming is used, which can form sharper beams as the frequency band increases. In 6G, the use of the subterahertz band (for example, the frequency range of 90 GHz to 300 GHz) is mainly being considered, but in the subterahertz band, it is expected that the number of SSBs in an SS burst will increase further. Therefore, there is a concern that the time required for base station 200 to spread SSBs throughout the entire cell, i.e., the time required for beam sweeping, will increase. Similarly, there is a concern that the time required for cell search performed by UE 100 will also increase.

[0045] (3) Example of base station configuration Figure 6 shows an example configuration of a base station 200 (network node) according to this embodiment. The base station 200 according to this embodiment may be configured to perform wireless communication in the subterahertz band.

[0046] The base station 200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and a network communication unit 240. The transmitting unit 210 and the receiving unit 220 constitute a wireless communication unit 250 that performs wireless communication with the UE 100.

[0047] The transmitting unit 210 performs various types of transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna. The receiving unit 220 performs various types of receptions under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 230.

[0048] At high frequencies, to compensate for propagation loss, the wireless communication unit 250 needs to perform beamforming, which narrows the direction in which radio waves are transmitted by giving the antenna directionality. To control the antenna directionality, in the case of digital beamforming, it is necessary to have the same number of antenna weights in the digital domain as the number of antenna elements. These antenna weights are weights for controlling amplitude and phase. However, controlling in the digital domain results in a large digital circuit. For this reason, it is common practice to use a phase shifter, which is an antenna weight that can control only the phase in the analog domain. The antenna weight in the digital domain is realized in the frequency domain when using the OFDM modulation method, i.e., before the inverse fast Fourier transform (IFFT) during transmission. During reception, it is realized after the fast fourier transform (FFT). Therefore, if the antenna weight in the digital domain is realized in the frequency domain, the beam can be directed in different directions using resources at different frequencies, even at the same time. On the other hand, antenna weights realized in the analog domain are always controlled in the time domain, so at the same time, the beam can only be directed in the same direction across all frequency domains. Furthermore, typically, a single antenna panel cannot form beams in different directions using different frequencies at the same time. However, by using two antenna panels, beams in different directions can be formed even at the same time. Therefore, in this embodiment, the wireless communication unit 250 may have N (N: an integer of 2 or more) antenna panels.

[0049] The control unit 230 performs various control and processing operations at the base station 200. The operation of the base station 200 described above and below may be controlled by the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing operations.

[0050] The NW communication unit 240 is connected to an adjacent base station via an inter-base station interface. The NW communication unit 240 is also connected to the CN device 300 via a base station-CN interface.

[0051] The base station 200 configured in this way manages cells in the mobile communication system. The transmitting unit 210 transmits SSB, which is used for cell search performed by the UE 100, by beamforming. The control unit 230 performs beam sweeping, which switches the transmission beam direction (i.e., BF pattern) of the SSB at predetermined time intervals. Figure 7 shows an example of beam sweeping. The base station 200 holds multiple BF patterns. The base station 200 transmits SSB sequentially while switching BF patterns. In the example in Figure 7, during the SS burst period within a half frame, the base station 200 transmits SSB#1 with a certain BF pattern, and then transmits SSB#2 with a different BF pattern. For example, the base station 200 transmits SSB#1 with a BF pattern 30° to the left as viewed from the base station 200, and then transmits SSB#2 with a BF pattern 10° to the left as viewed from the base station 200. In this way, the BF patterns and SSBs are transmitted in a one-to-one correspondence. Furthermore, the positions in which SSBs can be positioned along the time axis within the SS burst period may be determined according to the subcarrier interval. In other words, the predetermined time interval for switching the BF pattern may be determined according to the subcarrier interval.

[0052] In this embodiment, the control unit 230 controls the transmitter unit 210 to simultaneously transmit N SSBs (N: an integer of 2 or more) at different frequencies within the bandwidth of the cell (itself cell). In particular, the control unit 230 controls the transmitter unit 210 to simultaneously transmit N SSBs at different frequencies and in different transmission beam directions (different BF patterns) within the bandwidth of the cell. In the subterahertz band, the number of SSBs in an SS burst is expected to increase further, but by simultaneously transmitting N SSBs (N: an integer of 2 or more) at different frequencies (i.e., N frequencies) within the bandwidth of the self cell, the time required for beam sweeping can be reduced to 1 / N compared to transmitting an SSB at a single frequency within the bandwidth of the self cell.

[0053] Here, as a comparative example, let's consider the case where multiple SSB signals are transmitted at the same frequency. Figure 8 is a diagram illustrating this comparative example. In the comparative example shown in Figure 8, the aim is to complete beam sweeping faster by simultaneously applying multiple BF patterns to one SSB signal within the cell's bandwidth. However, when signals (in this case, SSBs) of the same time and frequency are transmitted using multiple BF patterns, the BF patterns interfere with each other in complex ways, resulting in a distorted beam that differs from the originally designed BF pattern, leading to unexpected beam sweeping.

[0054] In contrast, the base station 200 according to this embodiment can suppress interference between BF patterns by multiplexing different SSBs using frequency division by simultaneously transmitting N SSBs at different frequencies (N frequencies) within the bandwidth of its own cell. Therefore, beam sweeping using the originally designed BF pattern is possible. Figure 9 shows an example of the SSB transmission operation according to this embodiment. In the following, an example where N=2 will be mainly described, but N may be an integer of 3 or more. In the example shown in Figure 9, first, the base station 200 transmits SSB#1 with the first BF pattern and transmits SSB#33 with the second BF pattern which is spatially continuous with the first BF pattern. Here, the transmission frequency of SSB#1 and the transmission frequency of SSB#33 are different from each other. Next, the base station 200 transmits SSB#2 with the third BF pattern which is spatially continuous with the second BF pattern and transmits SSB#34 with the fourth BF pattern which is spatially continuous with the third BF pattern. Here, the transmission frequencies for SSB#2 and SSB#34 are different. Specifically, the transmission frequency for SSB#2 is the same as that of SSB#1, and the transmission frequency for SSB#34 is the same as that of SSB#33.

[0055] Figure 10 shows an example of SSB transmission operation according to this embodiment. The transmitting unit 210 of the base station 200 according to this embodiment transmits a first SSB group at a first frequency within the cell bandwidth and a second SSB group at a second frequency within the cell bandwidth during a periodically occurring SS burst period. In the example shown in Figure 10, the first SSB group consists of SSB#1 to SSB#32, and the second SSB group consists of SSB#33 to SSB#64. Therefore, a total of 64 SSBs are transmitted within one SS burst period. By transmitting two SSB groups in parallel at two frequencies, the time required for SSB transmission can be reduced by half compared to transmitting 64 SSBs at one frequency.

[0056] In this embodiment, the control unit 230 of the base station 200 controls beam sweeping so that, within each SS burst period, the first SSB group covers a first portion of the cell's coverage area, and the second SSB group covers a second portion of the same coverage area. In other words, the control unit 230 makes the area covered by the first SSB group and the area covered by the second SSB group different within the cell's coverage area. This enables efficient beam sweeping.

[0057] In the example shown in Figure 10, the control unit 230 assigns an SSB Index to each SSB such that the SSB Index of the first SSB group (SSB#1 to SSB#32) does not overlap with the SSB Index of the second SSB group. This makes it possible to uniquely identify SSBs within the SS burst period by their SSB Index. "#1" to "#64" represent the SSB Index, but the SSB Index may also be a unique number that starts from 0 and increases by 1 over time. This number is reset to 0 in the next SS burst. The base station 200 notifies the UE 100 of the SSB Index using the PBCH in the SSB. The UE 100, upon receiving the SSB, can identify the SSB Index of the received SSB based on the PBCH in the received SSB.

[0058] The control unit 230 may assign different frequency indices (ssb-freqIdx) to the SSBs of the first SSB group and the SSBs of the second SSB group. The ssb-freqIdx may be a unique number that starts from 0 and increases by 1 from the low frequency side to the high frequency side. The base station 200 may notify the UE 100 of the ssb-freqIdx in the PBCH of the SSB. Upon receiving the SSB, the UE 100 can determine the ssb-freqIdx of the received SSB (i.e., the frequency from the lowest) based on the PBCH in the received SSB.

[0059] Alternatively, the control unit 230 may assign identifiers to the SSBs such that the identifiers of the SSBs in the first SSB group and the identifiers of the SSBs in the second SSB group overlap at least partially. In this case, the control unit 230 assigns different frequency indices (ssb-freqIdx) to the SSBs in the first SSB group and the SSBs in the second SSB group. Figure 11 shows another example of the SSB transmission operation according to this embodiment. In the example shown in Figure 11, the first SSB group consists of SSB#1 to SSB#32 with ssb-freqIdx=0, and the second SSB group consists of SSB#1 to SSB#32 with ssb-freqIdx=1. In other words, the SSB Index is common to both the first and second SSB groups. The base station 200 notifies the UE 100 of the SSB Index and ssb-freqIdx in the PBCH during the SSB. Upon receiving an SSB, UE100 can identify the SSB Index and ssb-freqIdx of the received SSB based on the PBCH in the received SSB.

[0060] The transmitting unit 210 of the base station 200 according to this embodiment transmits N configuration information items indicating the parameters of N SSBs to be transmitted simultaneously at different frequencies. For example, the control unit 230 generates N configuration information items, and the transmitting unit 210 transmits the N configuration information items to the UE 100 in the form of a PBCH (MIB), SIB, or RRC message (e.g., an RRC Reconfiguration message).

[0061] Each of the N configuration pieces may be at least one of the following 1) to 3) (configuration parameter):

[0062] 1) OffsetToPointA OffsetToPointA, as shown in Figure 12, is information that indicates the frequency offset between the lowest-frequency subcarrier (subcarrier 0) of the corresponding SSB and the reference point (referred to as "PointA") on the resource block grid, on a per-resource block basis. PointA indicates the position on the reference frequency axis.

[0063] The base station 200 may notify (set) the UE 100 of N OffsetToPointA in the SIB1. For example, the base station 200 may include in the SIB1 broadcast in its own cell each of the N SSBs that are transmitted simultaneously on different frequencies within that cell the OffsetToPointA of.

[0064] SIB1 includes FrequencyInfoDL-SIB, which is an IE that provides basic parameters for the downlink carrier and transmission on the downlink carrier. In this embodiment, FrequencyInfoDL-SIB may include N OffsetToPointA. In FrequencyInfoDL-SIB, each of the N OffsetToPointA may be associated with an ssb-freqIdx. For example, the N OffsetToPointA may be provided in list form, and the order of the OffsetToPointA in the list (i.e., the position of the entry) may indicate an ssb-freqIdx. Alternatively, FrequencyInfoDL-SIB may include N sets of OffsetToPointA and ssb-freqIdx.

[0065] 2) Kssb(ssb-SubcarrierOffset) Kssb(ssb-SubcarrierOffset), as shown in Figure 12, is information that indicates the frequency offset in subcarrier units between the lowest frequency subcarrier (subcarrier 0) of the corresponding SSB and the low-frequency boundary of the resource block to which that subcarrier (subcarrier 0) belongs. Therefore, UE100 can determine the reference point (PointA) of the resource block grid by subtracting the sum of Kssb(ssb-SubcarrierOffset) and OffsetToPointA from subcarrier 0.

[0066] Base station 200 may notify (configure) UE100 of N Kssb(ssb-SubcarrierOffset) values. For example, base station 200 may include in the MIB broadcast within its cell the Kssb(ssb-SubcarrierOffset) values ​​for each of the N SSBs that are transmitted simultaneously on different frequencies within that cell.

[0067] Thus, in this embodiment, the MIB may contain N OffsetToPointA. In the MIB, each of the N Kssb(ssb-SubcarrierOffset) may be associated with an ssb-freqIdx. For example, the N Kssb(ssb-SubcarrierOffset) may be provided in list format, and the order of the Kssb(ssb-SubcarrierOffset) in the list (i.e., the position of the entry) may indicate the ssb-freqIdx. Alternatively, the MIB may contain N sets of Kssb(ssb-SubcarrierOffset) and ssb-freqIdx.

[0068] 3) absoluteFrequencySSB absoluteFrequencySSB is information (ARFCN: Absolute Radio-Frequency Channel Number) indicating the frequency of the corresponding SSB. The frequency indicated by absoluteFrequencySSB may also be at the position of resource element RE=#0 in the SSB resource block RB#10.

[0069] For example, when base station 200 configures a secondary cell (SCell) on UE 100, it notifies (configures) UE 100 of N absoluteFrequencySSBs for that secondary cell using an RRC Reconfiguration message. Thus, in this embodiment, the RRC Reconfiguration message may contain N absoluteFrequencySSBs. In the RRC Reconfiguration message, each of the N absoluteFrequencySSBs may be associated with an ssb-freqIdx. For example, the N absoluteFrequencySSBs may be provided in list format, and the order of the absoluteFrequencySSBs in the list (i.e., the position of the entry) may indicate the ssb-freqIdx. Alternatively, the RRC Reconfiguration message may contain N sets of absoluteFrequencySSBs and ssb-freqIdx.

[0070] (4) Example of user device configuration Figure 13 shows an example configuration of UE100 (user device) according to this embodiment. UE100 according to this embodiment may be configured to perform wireless communication in the subterahertz band.

[0071] The UE100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit 140 that performs wireless communication with the base station 200.

[0072] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130. The transmitting unit 120 performs various types of transmission under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmitted signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0073] The control unit 130 performs various controls and processes in the UE100. The operation of the UE100 described above and below may also be controlled by the control unit 230. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processes.

[0074] The UE100 configured in this way performs wireless communication with a base station 200 that manages a cell in a mobile communication system. The receiving unit 110 receives SSBs transmitted from the base station 200 by beamforming and to which beam sweeping, which switches the transmission beam direction at predetermined time intervals, is applied. In this embodiment, the receiving unit 110 receives at least one of N SSBs transmitted simultaneously at different frequencies within the cell's bandwidth. The control unit 130 performs a cell search based on the SSBs received by the receiving unit 110.

[0075] In this embodiment, the receiver 110 receives at least one of N SSBs that are transmitted simultaneously at different frequencies and in different transmission beam directions (different BF patterns) within the cell's bandwidth. In addition, during periodically occurring SS burst periods, the receiver 110 receives a first group of SSBs at a first frequency within the cell's bandwidth and a second group of SSBs at a second frequency within the cell's bandwidth.

[0076] Furthermore, in this embodiment, the receiving unit 110 receives N configuration information from the base station 200, which indicates the parameters of N SSBs transmitted simultaneously at different frequencies. Here, each of the N configuration information may be OffsetToPointA, i.e., information indicating the frequency offset between the lowest frequency subcarrier of the corresponding SSB and the reference point of the resource block grid on a resource block basis. Each of the N configuration information may be Kssb(ssb-SubcarrierOffset), i.e., information indicating the frequency offset between the lowest frequency subcarrier of the corresponding SSB and the low-frequency boundary of the resource block to which the subcarrier belongs on a subcarrier basis. Each of the N configuration information may be absoluteFrequencySSB, i.e., information indicating the frequency of the corresponding SSB.

[0077] (5) System operation example Figure 14 shows an example of the operation of the base station 200 (network node) according to this embodiment.

[0078] In step S11, base station 200 transmits SSB used for cell search performed by UE100 by beamforming. Base station 200 simultaneously transmits N SSBs within its own cell's bandwidth at different frequencies and with different BF patterns.

[0079] In step S12, the base station 200 checks whether the SS burst period (i.e., beam sweeping) has ended. Specifically, the base station 200 checks whether all SSB transmissions that were to be transmitted during the current SS burst period have been completed.

[0080] If the SS burst period has not ended (step S12: NO), in step S13, the base station 200 switches the transmission beam directions (BF patterns) of the N SSBs and returns to step S11.

[0081] If the SS burst period ends (step S12: YES), in step S14, the base station 200 checks whether the next SS burst period has started. If the next SS burst period has started (step S14: YES), the base station 200 returns to step S11 and simultaneously transmits N SSBs within its own cell's bandwidth at different frequencies and with different BF patterns.

[0082] Figure 15 shows an example of the operation of the UE100 (user device) according to this embodiment.

[0083] In step S21, UE100 receives an SSB transmitted from base station 200 by beamforming and to which beam sweeping is applied, which switches the transmission beam direction at predetermined time intervals. UE100 receives at least one of N SSBs transmitted simultaneously at different frequencies within the cell's bandwidth.

[0084] In step S22, UE100 performs a cell search based on the received SSB. Specifically, UE100 obtains time and frequency synchronization with the cell and detects the cell ID of that cell.

[0085] In step S23, UE100 measures the received SSB reception quality (e.g., RSRP).

[0086] In step S24, UE100 determines whether an SSB with reception quality that satisfies predetermined conditions has been identified. If no SSB with reception quality that satisfies predetermined conditions has been identified (step S24: NO), UE100 returns to step S21.

[0087] On the other hand, if an SSB with reception quality that meets the predetermined conditions is identified (step S24: YES), in step S25, an RA preamble is transmitted in the RA occasion associated with the identified SSB.

[0088] (6) Other embodiments Each of the above-described operation flows can be performed not only independently, but also in combination of two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow. It is not necessary to execute all steps in each flow; only some steps may be executed.

[0089] In the above embodiment, an example was described in which the base station is an NR base station (gNB), but the base station may also be an LTE base station (eNB) or a 6G base station. Furthermore, the base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of an IAB node. Additionally, UE100 may be an MT (Mobile Termination) of an IAB node.

[0090] Furthermore, the term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). Additionally, a network node may consist of a combination of at least a part of the core network device and at least a part of a base station.

[0091] A program may be provided that causes a computer to execute each process performed by the UE100 or base station 200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM. Alternatively, the circuits that execute each process performed by the UE100 or base station 200 may be integrated, and at least a part of the UE100 or base station 200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0092] The functions realized by UE100 or base station 200 (network node) may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to realize the described functions. A processor, including transistors and other circuits, is considered circuitry or processing circuitry. A processor may be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, and means are hardware programmed to realize or perform the described functions. Such hardware may be any hardware disclosed herein, or any hardware known to be programmed to realize or perform the described functions. If such hardware is a processor that is considered to be of the type of circuitry, such circuitry, means, or unit is a combination of hardware and software used to constitute such hardware and / or processor.

[0093] The phrases “based on” and “depending on / in response to” used in this disclosure do not mean “based solely on” or “depending solely on” unless otherwise specified. “Based on” means both “based solely on” and “at least partially on.” Similarly, “depending on” means both “at least partially on” and “at least partially on.” The terms “include,” “comprise,” and variations thereof do not mean that only the listed items are included; they mean that only the listed items may be included, or that additional items may be included in addition to the listed items. Furthermore, the term “or” used in this disclosure is not intended to mean exclusive OR. Additionally, any reference to elements using designations such as “first,” “second,” etc., used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Therefore, references to the first and second elements do not imply that only two elements may be adopted therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated by the context that they are not.

[0094] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the gist of the invention. Furthermore, each embodiment, each operation example, or each process can be combined as appropriate, within the bounds of consistency.

[0095] (7) Note The features of the above-described embodiment are noted below.

[0096] (Note 1) A network node that manages cells in a mobile communication system, A transmitting unit that transmits a synchronization signal block used for cell search performed by the user device by beamforming, The system includes a control unit that performs beam sweeping, which switches the transmission beam direction of the synchronization signal block at predetermined time intervals, The control unit controls the transmission unit to simultaneously transmit N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell. Network node.

[0097] (Note 2) The control unit controls the transmitting unit to simultaneously transmit N of the synchronization signal blocks within the cell's bandwidth at different frequencies and in different transmission beam directions. The network node described in Appendix 1.

[0098] (Note 3) The transmitting unit transmits a first set of synchronization signal blocks at a first frequency within the cell's bandwidth and a second set of synchronization signal blocks at a second frequency within the cell's bandwidth during a periodically occurring synchronization signal burst period. The network node described in Appendix 1 or 2.

[0099] (Note 4) The control unit controls the beam sweeping during the synchronization signal burst period such that the first synchronization signal block group covers a first portion of the coverage area of ​​the cell and the second synchronization signal block group covers a second portion of the coverage area. The network node described in Appendix 3.

[0100] (Note 5) The control unit assigns identifiers to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group do not overlap. The network node described in Appendix 3.

[0101] (Note 6) The control unit assigns identifiers to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group overlap at least partially, and assigns different frequency indices to the synchronization signal blocks in the first synchronization signal block group and the synchronization signal blocks in the second synchronization signal block group. The network node described in Appendix 3.

[0102] (Note 7) The transmitting unit transmits N pieces of setting information indicating the parameters of N synchronization signal blocks that are transmitted simultaneously at different frequencies. A network node as described in any of the appendices 1 through 6.

[0103] (Note 8) Each of the N setting pieces of information indicates, on a per-resource-block basis, the frequency offset between the lowest-frequency subcarrier of the corresponding synchronization signal block and the reference point of the resource block grid. The network node described in Appendix 7.

[0104] (Note 9) Each of the N setting pieces of information indicates, on a subcarrier basis, the frequency offset between the lowest-frequency subcarrier of the corresponding synchronization signal block and the low-frequency boundary of the resource block to which that subcarrier belongs. The network node described in Appendix 7.

[0105] (Note 10) Each of the N setting pieces is information indicating the frequency of the corresponding synchronization signal block. The network node described in Appendix 7.

[0106] (Note 11) A user device that performs wireless communication with a network node that manages a cell in a mobile communication system, A receiving unit that receives a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping is applied, which switches the direction of the transmitted beam at predetermined time intervals, The system includes a control unit that performs a cell search based on the aforementioned synchronization signal block, The receiving unit receives at least one of the N (N: an integer of 2 or more) synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. User device.

[0107] (Note 12) The receiving unit receives at least one of the N synchronization signal blocks that are transmitted simultaneously within the cell's bandwidth at different frequencies and in different transmission beam directions. User device as described in Appendix 11.

[0108] (Note 13) The receiving unit receives a first set of synchronization signal blocks at a first frequency within the cell's bandwidth and a second set of synchronization signal blocks at a second frequency within the cell's bandwidth during a periodically occurring synchronization signal burst period. User device as described in Appendix 12.

[0109] (Note 14) Identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group do not overlap. User device as described in Appendix 13.

[0110] (Note 15) Identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group overlap at least partially. The synchronization signal blocks of the first synchronization signal block group and the synchronization signal blocks of the second synchronization signal block group are assigned different frequency identifiers. User device as described in Appendix 13.

[0111] (Note 16) The receiving unit receives N pieces of configuration information from the network node that indicate the parameters of N synchronization signal blocks transmitted simultaneously at different frequencies. A user device as described in any of the appendices 11 to 15.

[0112] (Note 17) Each of the N setting pieces of information indicates, on a per-resource-block basis, the frequency offset between the lowest-frequency subcarrier of the corresponding synchronization signal block and the reference point of the resource block grid. User equipment as described in Appendix 16.

[0113] (Note 18) Each of the N setting pieces of information indicates, on a subcarrier basis, the frequency offset between the lowest-frequency subcarrier of the corresponding synchronization signal block and the low-frequency boundary of the resource block to which that subcarrier belongs. User equipment as described in Appendix 16.

[0114] (Note 19) Each of the N setting pieces is information indicating the frequency of the corresponding synchronization signal block. User equipment as described in Appendix 16.

[0115] (Note 20) A communication method used in a network node that manages cells in a mobile communication system, The steps include transmitting a synchronization signal block used for cell search performed by the user device by beamforming, The step includes performing beam sweeping, which switches the transmission beam direction of the synchronization signal block at predetermined time intervals. The step of transmitting the synchronization signal block includes the step of simultaneously transmitting N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell. Communication method.

[0116] (Note 21) A communication method used in a user device that performs wireless communication with a network node that manages a cell in a mobile communication system, The steps include receiving a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping is applied, which switches the direction of the transmitted beam at predetermined time intervals, The step includes performing a cell search based on the aforementioned synchronization signal block, The step of receiving the synchronization signal block includes receiving at least one of the N (N: an integer of 2 or more) synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. Communication method. [Explanation of symbols]

[0117] 1: Network 10: RAN 20 :CN 100 :UE 110: Receiving unit 120: Transmitter 130: Control Unit 140: Wireless Communication Department 200:Base station 210: Transmitter 220: Receiving unit 230: Control Unit 240: NW Communications Department 250: Wireless Communication Department 300:CN device

Claims

1. A network node that manages cells in a mobile communication system, A transmitting unit that transmits a synchronization signal block used for cell search performed by the user device by beamforming, The system includes a control unit that performs beam sweeping, which switches the transmission beam direction of the synchronization signal block at predetermined time intervals, The control unit controls the transmission unit to simultaneously transmit N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell. The transmitting unit transmits a first set of synchronization signal blocks at a first frequency within the cell's bandwidth and a second set of synchronization signal blocks at a second frequency within the cell's bandwidth during a periodically occurring synchronization signal burst period. The control unit assigns identifiers to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group do not overlap. Network node.

2. The control unit controls the transmitting unit to simultaneously transmit N of the synchronization signal blocks within the cell's bandwidth at different frequencies and in different transmission beam directions. The network node according to claim 1.

3. The control unit controls the beam sweeping during the synchronization signal burst period such that the first synchronization signal block group covers a first portion of the coverage area of ​​the cell and the second synchronization signal block group covers a second portion of the coverage area. The network node according to claim 1.

4. A network node that manages cells in a mobile communication system, A transmitting unit that transmits a synchronization signal block used for cell search performed by the user device by beamforming, The system includes a control unit that performs beam sweeping, which switches the transmission beam direction of the synchronization signal block at predetermined time intervals, The control unit controls the transmission unit to simultaneously transmit N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell. The transmitting unit transmits a first set of synchronization signal blocks at a first frequency within the cell's bandwidth and a second set of synchronization signal blocks at a second frequency within the cell's bandwidth during a periodically occurring synchronization signal burst period. The control unit assigns identifiers to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group overlap at least partially, and assigns different frequency indices to the synchronization signal blocks in the first synchronization signal block group and the synchronization signal blocks in the second synchronization signal block group. Network node.

5. A user device that performs wireless communication with a network node that manages a cell in a mobile communication system, A receiving unit that receives a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping is applied, which switches the direction of the transmitted beam at predetermined time intervals, The system includes a control unit that performs a cell search based on the aforementioned synchronization signal block, The receiving unit receives at least one of the N (N: an integer of 2 or more) synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. The receiving unit receives a first set of synchronization signal blocks at a first frequency within the cell's bandwidth during a periodically occurring synchronization signal burst period, and receives a second set of synchronization signal blocks at a second frequency within the cell's bandwidth. Identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group do not overlap. User device.

6. The receiving unit receives at least one of the N synchronization signal blocks that are transmitted simultaneously within the cell's bandwidth at different frequencies and in different transmission beam directions. The user device according to claim 5.

7. A user device that performs wireless communication with a network node that manages a cell in a mobile communication system, A receiving unit that receives a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping is applied, which switches the direction of the transmitted beam at predetermined time intervals, The system includes a control unit that performs a cell search based on the aforementioned synchronization signal block, The receiving unit receives at least one of the N (N: an integer of 2 or more) synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. The receiving unit receives a first set of synchronization signal blocks at a first frequency within the cell's bandwidth during a periodically occurring synchronization signal burst period, and receives a second set of synchronization signal blocks at a second frequency within the cell's bandwidth. Identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group overlap at least partially. The synchronization signal blocks of the first synchronization signal block group and the synchronization signal blocks of the second synchronization signal block group are assigned different frequency identifiers. User device.

8. A communication method used in a network node that manages cells in a mobile communication system, A transmission step in which a synchronization signal block used for cell search performed by the user device is transmitted by beamforming, The control step includes performing beam sweeping, which switches the transmission beam direction of the synchronization signal block at predetermined time intervals. The transmission step includes the step of simultaneously transmitting N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell. In the transmission step, during the periodically occurring synchronization signal burst period, a first synchronization signal block group is transmitted at a first frequency within the cell's bandwidth, and a second synchronization signal block group is transmitted at a second frequency within the cell's bandwidth. In the control step, identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group do not overlap. Communication method.

9. A communication method used in a network node that manages cells in a mobile communication system, A transmission step in which a synchronization signal block used for cell search performed by the user device is transmitted by beamforming, The control step includes performing beam sweeping, which switches the transmission beam direction of the synchronization signal block at predetermined time intervals. The transmission step includes the step of simultaneously transmitting N (N: an integer of 2 or more) of the synchronization signal blocks at different frequencies within the bandwidth of the cell. In the transmission step, during the periodically occurring synchronization signal burst period, a first synchronization signal block group is transmitted at a first frequency within the cell's bandwidth, and a second synchronization signal block group is transmitted at a second frequency within the cell's bandwidth. In the control step, identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group overlap at least partially, and different frequency indices are assigned to the synchronization signal blocks in the first synchronization signal block group and the synchronization signal blocks in the second synchronization signal block group. Communication method.

10. A communication method used in a user device that performs wireless communication with a network node that manages a cell in a mobile communication system, A receiving step of receiving a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping is applied, which switches the transmission beam direction at predetermined time intervals, The step includes performing a cell search based on the aforementioned synchronization signal block, The receiving step includes receiving at least one of the N (N: an integer of 2 or more) synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. In the receiving step, during the periodically occurring synchronization signal burst period, a first synchronization signal block group is received at a first frequency within the cell's bandwidth, and a second synchronization signal block group is received at a second frequency within the cell's bandwidth. Identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group do not overlap. Communication method.

11. A communication method used in a user device that performs wireless communication with a network node that manages a cell in a mobile communication system, A receiving step of receiving a synchronization signal block transmitted from the network node by beamforming and to which beam sweeping is applied, which switches the transmission beam direction at predetermined time intervals, The step includes performing a cell search based on the aforementioned synchronization signal block, The receiving step includes receiving at least one of the N (N: an integer of 2 or more) synchronization signal blocks that are transmitted simultaneously at different frequencies within the bandwidth of the cell. In the receiving step, during the periodically occurring synchronization signal burst period, a first synchronization signal block group is received at a first frequency within the cell's bandwidth, and a second synchronization signal block group is received at a second frequency within the cell's bandwidth. Identifiers are assigned to the synchronization signal blocks such that the identifiers of the synchronization signal blocks in the first synchronization signal block group and the identifiers of the synchronization signal blocks in the second synchronization signal block group overlap at least partially. The synchronization signal blocks of the first synchronization signal block group and the synchronization signal blocks of the second synchronization signal block group are assigned different frequency identifiers. Communication method.

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