Method and device for random access in wireless communication system

Abstract

The present disclosure relates to a communication technology and a system thereof for combining IoT technology with a 5G communication system supporting a higher data transmission rate than a 4G system. The present disclosure can be applied to smart services (e.g., smart homes, smart buildings, smart cities, smart cars or connected cars, health care, digital education, retail business, security and safety related services, etc.) based on 5G communication technology and IoT related technology. According to the present disclosure, a method for a terminal in a wireless communication system includes: based on a plurality of synchronization signal blocks (SSBs) that have been transmitted by a base station, measuring a reference signal received power (RSRP) value corresponding to each SSB; based on the measured RSRP value and at least one RSRP threshold, identifying a coverage enhancement (CE) level of the terminal; and transmitting at least one random access preamble to the base station based on the identified CE level.

Description

Technical Field

[0001] The present disclosure relates to a cellular wireless communication system, and more particularly, to a method in which a terminal transmits a random access preamble code for random access to a base station. Background Art

[0002] Now that 4G communication systems are commercially available, efforts are being made to develop enhanced 5G communication systems or pre-5G communication systems in order to meet the increased demand for wireless data services. Therefore, 5G communication systems or pre-5G communication systems are referred to as super 4G network communication systems or post-LTE systems. In order to achieve high data transmission rates, 5G communication systems are being considered for implementation in millimeter wave bands (e.g., 60GHz bands). In order to mitigate any path loss of electronic waves in millimeter wave bands and increase the transmission distance of electronic waves, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technologies are being discussed for 5G communication systems. In addition, in order to enhance the network in the 5G communication system, innovative small cells, advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device communications (D2D), wireless backhaul, mobile networks, collaborative communications, coordinated multipoint (CoMP), and interference elimination technologies have been developed. In addition, hybrid frequency shift keying and quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) have been developed for 5G systems as advanced coding modulation (ACM) methods; and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet has undergone a transformation from a human-centered connected network in which humans generate and consume information to an Internet of Things (IoT) network that provides information to, receives and processes information from distributed constituent elements (such as things). Internet of Everything (IoE) technology, in which big data processing technology connected to a cloud server is combined with IoT technology, has emerged. In order to implement IoT, technical elements such as sensing technology, wired and wireless communication and network infrastructure, service interface technology, and security technology are required; therefore, today, research is being conducted on sensor networks, machine-to-machine (M2M), and machine-type communication (MTC) technologies for connection between things. In the IoT environment, intelligent Internet technology (IT) services can be provided that collect and analyze data generated in networked things to provide new value for human life. IoT can be applied to the fields of smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart home appliances, and high-tech medical services through the integration and complex connection between existing information technology (IT) and various industries.

[0004] Therefore, various attempts have been made to apply 5G communication systems to IoT networks. For example, 5G communication technologies such as sensor networks, machine-to-machine (M2M), and machine-type communications (MTC) have been implemented through beamforming, MIMO, and array antenna technologies. Cloud RAN as an application of the aforementioned big data processing technology can be an example of the fusion of 5G technology and IoT technology.

[0005] 5G communication systems are being developed to support various services such as enhanced mobile broadband (eMBB), massive machine type communication (mMTC), ultra-reliable low latency communication (URLLC), and in order to provide various services, base stations are required to broadcast configuration information to terminals that provide these services. In addition, terminals need to perform random access for various services. Summary of the invention

[0006] Technical issues

[0007] The present disclosure provides an effective random access method and device for various services in a mobile communication system.

[0008] Solution to the problem

[0009] According to the present disclosure, a method performed by a terminal in a wireless communication system includes: based on multiple synchronization signal blocks (SSBs) transmitted by a base station, measuring a reference signal received power (RSRP) value corresponding to each SSB; based on the measured RSRP value and at least one RSRP threshold, identifying a coverage enhancement (CE) level of the terminal; and transmitting one or more random access preamble codes to the base station based on the identified CE level.

[0010] According to the present disclosure, a terminal of a wireless communication system includes: a transceiver; and a controller, connected to the transceiver and configured to control: based on a synchronization signal block (SSB) transmitted by a base station, measuring a reference signal received power (RSRP) value corresponding to each SSB, identifying a coverage enhancement (CE) level of the terminal based on the measured RSRP value and at least one RSRP threshold, and transmitting one or more random access preamble codes to the base station based on the identified CE level.

[0011] According to the present disclosure, a method performed by a base station in a wireless communication system includes: transmitting multiple synchronization signal blocks (SSBs); receiving a random access preamble transmitted by a terminal; identifying, by the terminal, an index of the SSB selected as a basis for random access preamble transmission and a coverage enhancement (CE) level of the terminal based on the received random access preamble and the resource in which the random access preamble is received; and performing a random access process based on the identified index of the SSB and the CE level of the terminal.

[0012] According to the present disclosure, a base station in a wireless communication system includes: a transceiver; and a controller, connected to the transceiver and configured to control to: transmit multiple synchronization signal blocks (SSBs), receive a random access preamble transmitted by a terminal, identify an index of an SSB selected by the terminal as a basis for random access preamble transmission and a coverage enhancement (CE) level of the terminal based on the received random access preamble and the resource in which the random access preamble is received, and perform a random access process based on the identified index of the SSB and the CE level of the terminal.

[0013] Advantageous Effects of the Invention

[0014] The present disclosure provides an efficient random access method and apparatus in a mobile communication system, so that a terminal and / or a node desiring to transmit and receive an uplink signal can repeatedly transmit and receive a random access preamble to improve coverage and efficiently operate random access. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a diagram showing the basic structure of the time-frequency domain which is the radio resource domain of the 5G system.

[0016] Figure 2 is a diagram showing a time slot structure considered in a 5G system.

[0017] Figure 3 is a diagram showing a synchronization signal block considered in a 5G communication system.

[0018] Figure 4 is a diagram showing the transmission situation of a synchronization signal block in a frequency band of 6 GHz or lower considered in a 5G communication system.

[0019] Figure 5 is a diagram showing the transmission situation of a synchronization signal block in a frequency band of 6 GHz or higher considered in a 5G communication system.

[0020] Figure 6 It is a diagram showing the transmission of synchronization signal blocks according to subcarrier spacing within 5 ms.

[0021] Figure 7 is a message flow diagram illustrating a four-step random access procedure.

[0022] Figure 8 It is a diagram showing CE levels applicable to MTC terminals.

[0023] Fig. 9 is a flowchart illustrating a method of determining a CE level based on n SS-RSRPs having a maximum value among measured SS-RSRPs.

[0024] Fig.10 is a flowchart illustrating a method in which a terminal determines an initial CE level based on several thresholds and one threshold.

[0025] Fig.11 is a flowchart showing a process in which a terminal transmits a PRACH preamble code after determining an initial CE level by the above method.

[0026] Fig.12 is a flow chart showing a random access preamble transmission process of a terminal.

[0027] Fig.13 is a flowchart illustrating another random access preamble transmission process of a terminal.

[0028] Fig.14 is a diagram showing an example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to one SSB.

[0029] Fig.15 is a diagram showing another example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to one SSB.

[0030] Fig.16 is a diagram showing an example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to a plurality of SSBs.

[0031] Fig.17 is a diagram showing another example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to a plurality of SSBs.

[0032] Fig.18 is a block diagram of a terminal according to an embodiment of the present disclosure.

[0033] Fig.19 is a block diagram of a base station according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0035] When describing the embodiments, descriptions of technical contents that are well known in the technical field to which the present disclosure belongs and are not directly related to the present disclosure will be omitted. This is to convey the main points of the present disclosure more clearly by omitting unnecessary descriptions without obscuring the main points of the present disclosure.

[0036] For the same reason, some components are exaggerated, omitted or schematically shown in the drawings. In addition, the size of each component does not fully reflect the actual size. In each of the drawings, the same reference numerals represent the same or corresponding components.

[0037] With reference to the embodiments described in detail below in conjunction with the accompanying drawings, the advantages and features of the present disclosure and the methods for realizing them will become apparent. However, the present disclosure is not limited to the embodiments disclosed below, but can be implemented in various different forms, and only the current embodiments can make the present disclosure complete, and are provided to fully inform the scope of the present disclosure to those of ordinary skill in the art to which the present disclosure belongs, and the present disclosure is limited only by the scope of the claims. Throughout the specification, the same figure numerals refer to the same components. In addition, in the description of the present disclosure, when it is determined that the detailed description of the relevant functions or configurations may unnecessarily obscure the subject matter of the present disclosure, the detailed description thereof will be omitted. The terms described below are defined in view of the functions in the present disclosure, which may vary according to the intentions or habits of users and operators. Therefore, it should be defined based on the content throughout this specification.

[0038] In the following, the base station is a subject that performs resource allocation of the UE, and may be at least one of a gNode B, an eNode B, a nodeB, a base station (BS), a radio access unit, a base station controller, and a node on a network. The UE may include a user equipment (UE), a mobile station (MS), a cellular phone, a smart phone, a computer, or a multimedia system capable of performing a communication function. In the present disclosure, a downlink (DL) is a wireless transmission path for a signal transmitted from a base station to a UE, and an uplink (UL) is a wireless transmission path for a signal transmitted from a UE to a base station. In addition, in the following, although an LTE or LTE-A system may be described as an example, the embodiments of the present disclosure may be applied to other communication systems having similar technical backgrounds or channel types. For example, the embodiments of the present disclosure may be applied to 5G mobile communication technologies (5G, new radio, NR) developed after LTE-A, and the following 5G may be a concept including existing LTE, LTE-A, and other similar services. In addition, the present disclosure may be applied to other communication systems by some modifications within the scope that do not significantly deviate from the scope of the present disclosure, as determined by a person with skilled technical knowledge.

[0039] In this case, it should be understood that each block of the flowchart and the combination of the flowcharts can be executed by computer program instructions. Because these computer program instructions can be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, the instructions executed by the processor of the computer or other programmable data processing equipment generate a device for performing the functions described in the (multiple) flowchart blocks. Because these computer program instructions can be stored in a computer-usable or computer-readable memory, which can instruct the computer or other programmable data processing equipment to implement the functions in a specific manner, the instructions stored in the computer-usable or computer-readable memory can produce a product containing an instruction device for performing the functions described in the (multiple) flowchart blocks. Because the computer program instructions can be installed on a computer or other programmable data processing equipment, a series of operating steps are performed on the computer or other programmable data processing equipment to generate a computer-executed process; therefore, the instructions for executing the computer or other programmable data processing equipment can provide steps for performing the functions described in the (multiple) flowchart blocks.

[0040] In addition, each block can represent a module, a code segment or a code portion including one or more executable instructions for performing (multiple) specified logical functions. In addition, it should also be noted that in some alternative implementations, the functions listed in the block can occur out of order. For example, the two blocks shown in succession can actually be performed substantially simultaneously, or these blocks can sometimes be performed in reverse order according to the corresponding functions.

[0041] In this case, the term "-unit" used in this embodiment means a software or hardware component, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and the "-unit" performs certain roles. However, the "-unit" is not limited to software or hardware. The "-unit" can be configured to reside in an addressable storage medium, or can be configured to reproduce one or more processors. Therefore, as an example, the "-unit" includes components such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcodes, circuits, data, databases, data structures, tables, arrays and variables. The functions provided in the components and "-units" can be combined into a smaller number of components and "-units", or can be further separated into additional components and "-units". In addition, the components and "-units" can be implemented as one or more CPUs in a reproduction device or a secure multimedia card. In addition, in an embodiment, the "-unit" can include one or more processors.

[0042] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Hereinafter, embodiments of the present disclosure will describe mMTC services as examples of methods and devices proposed in embodiments of the present disclosure, but are not limited to each embodiment, and all or some combinations of one or more embodiments proposed in the present disclosure may be used for a random access method corresponding to another additional service and a method for repeatedly transmitting a random access channel preamble. Therefore, by determination by a person having skilled technical knowledge, the embodiments of the present disclosure may be applied with some modifications within the scope that does not significantly deviate from the scope of the present disclosure.

[0043] In addition, in the description of the present disclosure, when it is determined that the detailed description of the relevant function or configuration may unnecessarily obscure the main points of the present disclosure, its detailed description will be omitted. In addition, the terms described below are defined in consideration of the functions in the present disclosure, which may vary according to the intentions or habits of users and operators. Therefore, they should be defined based on the content throughout this specification.

[0044] Wireless communication systems have evolved from providing voice-oriented services in the early days to providing high-speed and high-quality packet data services (such as communication standards such as 3GPP's High Speed ​​Packet Access (HSPA), Long Term Evolution (LTE) or Evolved Universal Terrestrial Radio Access (E-UTRA), LTE-Advanced (LTE-A) and LTE-Pro, 3GPP2's High Speed ​​Packet Data (HRPD), Ultra Mobile Broadband (UMB) and IEEE802.16e). Broadband wireless communication systems have evolved from providing voice-oriented services in the early days to providing high-speed and high-quality packet data services (such as communication standards such as 3GPP's High Speed ​​Packet Access (HSPA), Long Term Evolution (LTE) or Evolved Universal Terrestrial Radio Access (E-UTRA), LTE-Advanced (LTE-A) and LTE-Pro, 3GPP2's High Speed ​​Packet Data (HRPD), Ultra Mobile Broadband (UMB) and IEEE802.16e).

[0045] As a representative example of a broadband wireless communication system, the LTE system adopts an orthogonal frequency division multiplexing (OFDM) scheme in the downlink (DL) and a single carrier frequency division multiple access (SC-FDMA) scheme in the uplink. The uplink refers to a radio link in which a user equipment (UE) or a mobile station (MS) transmits data or a control signal to an eNode B (eNB) or a base station (BS), and the downlink refers to a radio link in which a base station transmits data or a control signal to a terminal. In addition, the above-mentioned multiple access method enables the data or control information of each user to be distinguished by allocating and operating the data or control information so that the time-frequency resources used to carry the data or control information of each user generally do not overlap with each other (i.e., establishing orthogonality).

[0046] As a communication system after LTE, the 5G communication system should support services that meet various needs at the same time so that the various needs of users and service providers can be freely reflected. Services considered for the 5G communication system include enhanced mobile broadband (eMBB), massive machine type communication (mMTC), ultra-reliable low latency communication (URLLC), etc.

[0047] eMBB is designed to provide a higher data transfer rate than that supported by existing LTE, LTE-A or LTE-Pro. For example, in a 5G communication system, from the perspective of a base station, eMBB should be able to provide a peak data rate of 20Gbps in the downlink and a peak data rate of 10Gbps in the uplink. In addition, the 5G communication system should provide an increased user-perceived UE data rate while providing the peak data rate. In order to meet such requirements, it may be necessary to improve various transmission and reception technologies, including more advanced multiple-input multiple-output (MIMO) transmission technology. In addition, the LTE system transmits signals using a transmission bandwidth of up to 20MHz in the 2GHz band, while the 5G communication system can meet the data transmission rate required by the 5G communication system by using a frequency bandwidth wider than 20MHz in the 3 to 6GHz or 6GHz or higher frequency bands.

[0048] Meanwhile, mMTC is considering supporting application services such as the Internet of Things (IoT) in 5G communication systems. In order to effectively provide the Internet of Things, mMTC requires access support for large-scale terminals within a cell, improved UE coverage, improved battery life, and reduced UE costs. Because the Internet of Things is attached to various sensors and various devices to provide communication functions, it should be able to support a large number of UEs within a cell (e.g., 1,000,000 UEs / square kilometer). In addition, due to the nature of the service, UEs supporting mMTC are likely to be located in shadow areas that cannot be covered by the cell, such as the basement of a building, so the UE requires wider coverage than other services provided by the 5G communication system. UEs supporting mMTC should be configured with low-cost UEs, and since it is difficult to frequently replace the batteries of the UEs, very long battery life, such as 10 to 15 years, is required.

[0049] Finally, URLLC is a cellular-based wireless communication service for mission-critical applications. For example, services for remote control of robots or machinery, industrial automation, unmanned aerial vehicles, telehealth, emergency alerts, etc. can be considered. Therefore, the communication provided by URLLC should provide very low latency and very high reliability. For example, services supporting URLLC should meet air interface latency of less than 0.5 milliseconds and should also meet 10 -5 Therefore, for services supporting URLLC, the 5G system should provide a smaller transmission time interval (TTI) than other services, and should simultaneously allocate wide resources in the frequency band to ensure the reliability of the communication link.

[0050] Three services, namely eMBB, URLLC and mMTC of a 5G communication system (hereinafter, interchangeable with a 5G system) can be multiplexed and transmitted in one system. In this case, in order to meet the different needs of each service, different transmission and reception technologies and transmission and reception parameters can be used between services.

[0051] Hereinafter, the frame structure of the 5G system will be described in more detail with reference to the accompanying drawings.

[0052] Figure 1 It is a diagram showing the basic structure of the time-frequency domain which is the radio resource domain of the 5G system.

[0053] exist Figure 1 In the figure, the horizontal axis represents the time domain and the vertical axis represents the frequency domain. The basic unit of resources in the time domain and the frequency domain is a resource element (RE) 101, and can be defined as an orthogonal frequency division multiplexing (OFDM) symbol (or discrete Fourier transform spread OFDM (DFT-s-OFDM) symbol) 102 on the time axis and a subcarrier 103 on the frequency axis. In the frequency domain, (For example, 12) consecutive REs may constitute a resource block (RB) 104. In addition, in the time domain, Consecutive OFDM symbols may constitute a subframe 110 .

[0054] Figure 2 is a diagram showing a time slot structure considered in a 5G system.

[0055] Figure 2 An example of the structure of a frame 200, a subframe 201, and a time slot 202 is shown. One frame 200 may be defined as 10 ms. One subframe 201 may be defined as 1 ms; therefore, one frame 200 may be configured with a total of 10 subframes 201. In addition, one time slot 202 and 203 may be defined as 14 OFDM symbols (i.e., the number of symbols per time slot). One subframe 201 may be configured with one or more time slots 202 and 203, and the number of time slots 202 and 203 of each subframe 201 may be different according to μ (204, 205), where μ is the configured value of the subcarrier spacing.

[0056] Figure 2 The example shows the time slot structure when μ = 0 (204) and μ = 1 (205) are used as subcarrier spacing configuration values. When μ = 0 (204), one subframe 201 can be configured with one time slot 202, and when μ = 1 (205), one subframe 201 can be configured with two time slots 203. That is, the number of time slots per subframe is The number of time slots per frame can vary according to the configured value μ of the subcarrier spacing. Can be changed. According to each subcarrier spacing configuration μ and It can be defined in Table 1.

[0057] [Table 1]

[0058]

[0059]

[0060] The 5G wireless communication system can transmit a synchronization signal block for initial access (which can be mixed with SSB, SS block, SS / PBCH block, etc.), and the synchronization signal block can be configured with a primary synchronization signal (PSS), a secondary synchronization signal (SSS) and a physical broadcast channel (PBCH). In the initial access step when the terminal first accesses the system, the terminal first obtains downlink time-frequency domain synchronization from the synchronization signal through cell search and obtains the cell ID. The synchronization signal includes PSS and SSS. The UE receives the PBCH for transmitting the master information block (MIB) from the base station, and obtains system information related to transmission and reception (such as system bandwidth or related control information), as well as basic parameter values. The terminal performs decoding on the PDCCH and PDSCH to obtain the system information block (SIB) based on the information. Thereafter, the UE exchanges identities with the base station through a random access step, and initially accesses the network through steps such as registration and authentication. In the following, the cell initial access operation process of the 5G wireless communication system will be described in more detail with reference to the accompanying drawings.

[0061] The synchronization signal is a signal that serves as a reference for cell search and is transmitted by applying a subcarrier spacing suitable for the channel environment (such as the phase noise of each frequency band). A 5G base station can transmit multiple synchronization signal blocks according to the number of analog beams to be operated. PSS and SSS can be mapped and transmitted through 12 RBs, and PBCH can be mapped and transmitted through 24 RBs. In the following, the structure of transmitting synchronization signals and PBCH in a 5G communication system will be described.

[0062] Figure 3 is a diagram showing a synchronization signal block considered in a 5G communication system.

[0063] according to Figure 3 , the synchronization signal block 300 includes PSS 301, SSS 303 and broadcast channel (PBCH) 302.

[0064] As shown in the figure, the synchronization signal block 300 is mapped to four OFDM symbols on the time axis. PSS301 and SSS 303 can be transmitted in 12 RBs 305 on the frequency axis and the first and third OFDM symbols on the time axis, respectively. In the 5G system, a total of 1008 different cell IDs can be defined, and PSS 301 can have 3 different values ​​and SSS 303 can have 336 different values ​​according to the physical layer ID of the cell. The UE can obtain one of the 1008 cell IDs using a combination of PSS 301 and SSS 303 through detection. This can be expressed by Equation 1.

[0065] [Equation 1]

[0066]

[0067] N (1) ID It can be estimated from SSS 303 and its value is between 0 and 335. (2) ID It can be estimated from PSS301 and its value is between 0 and 2. (1) ID and N (2) ID The combination of N as the cell ID is estimated cell ID The value of .

[0068] PBCH 302 may be transmitted in resources including 6 RBs 307 and 308 on both sides in addition to 12 RBs, and SSS 303 is transmitted in the second to fourth OFDM symbols of the SS block on the time axis and in 24 RBs 306 on the frequency axis. In PBCH 302, various system information referred to as MIB may be transmitted, and more specifically, MIB includes information as shown in Table 2, and PBCH payload and PBCH demodulation reference signal (DMRS) include the following additional information.

[0069] [Table 2]

[0070]

[0071] -Synchronization signal block information: The frequency domain offset of the synchronization signal block is indicated by 4 bits (ssb-SubcarrierOffset) in the MIB. The index of the synchronization signal block including the PBCH can be indirectly obtained by decoding the PBCH DMRS and the PBCH. More specifically, in a frequency band of 6 GHz or lower, the 3 bits obtained by decoding the PBCH DMRS indicate the synchronization signal block index, and in a frequency band of 6 GHz or greater, a total of 6 bits of 3 bits obtained by decoding the PBCH DMRS and 3 bits included in the PBCH payload obtained in the PBCH decoding indicate the synchronization signal block index including the PBCH. -Physical downlink control channel (PDCCH) information: The subcarrier spacing of the common downlink control channel is indicated by 1 bit (subCarrierSpacingCommon) in the MIB, and the time-frequency resource configuration information of the control resource set (CORESET) and the search space (SS) is indicated by 8 bits (pdcch-ConfigSIB1).

[0072] - System Frame Number (SFN): 6 bits (systemFrameNumber) in the MIB are used to indicate a part of the SFN. The least significant bits (LSBs) 4 bits of the SFN are included in the PBCH payload so that the terminal can obtain it indirectly through PBCH decoding.

[0073] Timing information in the radio frame: The terminal can use 1 bit (half frame) included in the above-mentioned synchronization signal block index and the PBCH payload obtained by PBCH decoding to indirectly identify whether the synchronization signal block has been transmitted in the first half frame or the second half frame of the radio frame.

[0074] Because the transmission bandwidths 12RB, 305 of PSS 301 and SSS 303 and the transmission bandwidth 24RB, 306 of PBCH 302 are different from each other, in the first OFDM symbol in which PSS 301 is transmitted within the transmission bandwidth of PBCH 302, when PSS 301 is transmitted, in addition to 12 RBs, there are 6 RBs 307 and 308 on both sides, and this area can be used to transmit other signals or can be empty.

[0075] All synchronization signal blocks can be transmitted using the same analog beam. That is, all PSS 301, SSS 303, and PBCH 302 can be transmitted using the same beam. Because the analog beam has the characteristic that it cannot be applied to the frequency axis separately, the same analog beam is applied to all frequency axis RBs within a specific OFDM symbol to which a specific analog beam is applied. That is, all four OFDM symbols in which PSS 301, SSS 303, and PBCH 302 are transmitted can be transmitted using the same analog beam.

[0076] Figure 4 401 is a diagram showing a transmission situation of a synchronization signal block in a frequency band of 6 GHz or lower considered in a 5G communication system. In a 5G communication system, in a frequency band of 6 GHz or lower, a subcarrier spacing (SCS) of 15 kHz (420) and a subcarrier spacing of 30 kHz (430, 440) can be used for synchronization signal block transmission. At a subcarrier spacing of 15 kHz, the synchronization signal block has one transmission situation (case #1) 401, and at a subcarrier spacing of 30 kHz, the synchronization signal block has two transmission situations (case #2 and case #3) 402 and 403.

[0077] In case #1 (401) where the subcarrier spacing is 15kHz (420), up to two synchronization signal blocks (404) can be transmitted within 1ms (or, when 1 slot is configured with 14 OFDM symbols, it corresponds to 1 slot length). Figure 4 The example of shows synchronization signal block #0 (407) and synchronization signal block #1 (408). In this case, synchronization signal block #0 (407) can be mapped to four consecutive symbols in the third OFDM symbol, and synchronization signal block #1 (408) can be mapped to four consecutive symbols in the ninth OFDM symbol.

[0078] Different analog beams can be applied to synchronization signal block #0 (407) and synchronization signal block #1 (408). Therefore, the same beam can be applied to all 3rd to 6th OFDM symbols to which synchronization signal block #0 (407) is mapped, and the same beam can be applied to all 9th ​​to 12th OFDM symbols to which synchronization signal block #1 (408) is mapped. In the 7th, 8th, 13th and 14th OFDM symbols to which the synchronization signal block is not mapped, which beam to use can be freely determined under the determination of the base station.

[0079] In case #2 (402) where the subcarrier spacing is 30kHz (430), up to two synchronization signal blocks (405) can be transmitted within 0.5ms (or when 1 time slot is configured with 14 OFDM symbols, it corresponds to 1 time slot length), and therefore, up to 4 synchronization signal blocks can be transmitted within 1ms (or when 1 time slot is configured with 14 OFDM symbols, it corresponds to 2 time slot lengths). Figure 4 The example shows a case where synchronization signal block #0 (409), synchronization signal block #1 (410), synchronization signal block #2 (411), and synchronization signal block #3 (412) are transmitted within 1 ms (i.e., two time slots). In this case, synchronization signal block #0 (409) and synchronization signal block #1 (410) can be mapped from the 5th OFDM symbol and the 9th OFDM symbol of the first time slot, respectively, and synchronization signal block #2 (411) and synchronization signal block #3 (412) can be mapped from the 3rd OFDM symbol and the 7th OFDM symbol of the second time slot, respectively.

[0080] Different analog beams can be applied to synchronization signal block #0 (409), synchronization signal block #1 (410), synchronization signal block #2 (411), and synchronization signal block #3 (412). Therefore, the same analog beam can be applied to each of the 5th to 8th OFDM symbols of the first time slot for transmitting synchronization signal block #0 (409), the 9th to 12th OFDM symbols of the first time slot for transmitting synchronization signal block #1 (410), the 3rd to 6th symbols of the second time slot for transmitting synchronization signal block #2 (411), and the 7th to 10th symbols of the second time slot for transmitting synchronization signal block #3 (412). In the OFDM symbols to which the synchronization signal block is not mapped, which beam to use can be freely determined by the base station.

[0081] In case #3 (403) where the subcarrier spacing is 30kHz (440), up to two synchronization signal blocks (406) can be transmitted within 0.5ms (or when 1 time slot is configured with 14 OFDM symbols, it corresponds to 1 time slot length), and therefore, up to 4 synchronization signal blocks can be transmitted within 1ms (or, when 1 time slot is configured with 14 OFDM symbols, it corresponds to 2 time slot lengths). Figure 4The example shows that synchronization signal block #0 (413), synchronization signal block #1 (414), synchronization signal block #2 (415) and synchronization signal block #3 (416) are transmitted in 1 ms (i.e., two time slots). In this case, synchronization signal block #0 (413) and synchronization signal block #1 (414) can be mapped from the 3rd OFDM symbol and the 9th OFDM symbol of the first time slot, respectively, and synchronization signal block #2 (415) and synchronization signal block #3 (416) can be mapped from the 3rd OFDM symbol and the 9th OFDM symbol of the second time slot, respectively.

[0082] Different analog beams can be used for synchronization signal block #0 (413), synchronization signal block #1 (414), synchronization signal block #2 (415) and synchronization signal block #3 (416), respectively. As described above, the same analog beam can be used in all four OFDM symbols for transmitting each synchronization signal block, and which beam to use in the OFDM symbol to which the synchronization signal block is not mapped can be freely determined by the base station.

[0083] Figure 5 1 is a diagram showing the transmission of a synchronization signal block in a frequency band of 6 GHz or higher considered in a 5G communication system. In a 5G communication system, in a frequency band of 6 GHz or higher, a subcarrier spacing of 120 kHz (530) and a subcarrier spacing of 240 kHz (540) may be used for synchronization signal block transmission.

[0084] In case #4 (510) where the subcarrier spacing is 120kHz (530), up to 4 synchronization signal blocks can be transmitted within 0.25ms (501) (or, when 1 time slot is configured with 14 OFDM symbols, it corresponds to 2 time slot lengths). Figure 5 The example of FIG. 1 shows a case where synchronization signal block #0 (503), synchronization signal block #1 (504), synchronization signal block #2 (505), and synchronization signal block #3 (506) are transmitted in 0.25 ms (i.e., two time slots). In this case, synchronization signal block #0 (503) and synchronization signal block #1 (504) can be mapped from the 5th OFDM symbol and the 9th OFDM symbol of the first time slot, respectively, and synchronization signal block #2 (505) and synchronization signal block #3 (506) can be mapped from the 3rd OFDM symbol and the 7th OFDM symbol of the second time slot, respectively.

[0085] As described above, a different analog beam can be used for each of synchronization signal block #0 (503), synchronization signal block #1 (504), synchronization signal block #2 (505), and synchronization signal block #3 (506). The same analog beam can be used in all four OFDM symbols of each synchronization signal block, and which beam will be used for the OFDM symbol to which the synchronization signal block is not mapped can be freely determined by the base station.

[0086] In case #5 (520) where the subcarrier spacing is 240kHz (540), up to 8 synchronization signal blocks can be transmitted within a time of 0.25ms (502) (or when 1 time slot is configured with 14 OFDM symbols, it corresponds to the length of 4 time slots). Figure 5 The example shows a case where synchronization signal block #0 (507), synchronization signal block #1 (508), synchronization signal block #2 (509), synchronization signal block #3 (510), synchronization signal block #4 (511), synchronization signal block #5 (512), synchronization signal block #6 (513) and synchronization signal block #7 (514) are transmitted in 0.25ms (i.e., 4 time slots). In this case, synchronization signal block #0 (507) and synchronization signal block #1 (508) can be mapped from the ninth OFDM symbol and the thirteenth OFDM symbol of the first time slot, respectively, synchronization signal block #2 (509) and synchronization signal block #3 (510) can be mapped from the third OFDM symbol and the seventh OFDM symbol of the second time slot, respectively, synchronization signal block #4 (511), synchronization signal block #5 (512) and synchronization signal block #6 (513) can be mapped from the fifth OFDM symbol, the ninth OFDM symbol and the thirteenth OFDM symbol of the third time slot, respectively, and synchronization signal block #7 (514) can be mapped from the third OFDM symbol of the fourth time slot.

[0087] As described above, different analog beams can be used for each of synchronization signal block #0 (507), synchronization signal block #1 (508), synchronization signal block #2 (509), synchronization signal block #3 (510), synchronization signal block #4 (511), synchronization signal block #5 (512), synchronization signal block #6 (513), and synchronization signal block #7 (514). The same analog beam can be used in all four OFDM symbols for transmitting each synchronization signal block, and in the OFDM symbol to which the synchronization signal block is not mapped, which beam to use can be freely determined by the base station.

[0088] Figure 6 6. It is a diagram showing the transmission of synchronization signal blocks according to subcarrier spacing within 5 ms. In the 5G communication system, the synchronization signal blocks are periodically transmitted in units of 5 ms (corresponding to 5 subframes or half frames).

[0089] In frequency bands of 3 GHz or lower, up to four synchronization signal blocks may be transmitted in a 5 ms (610) period. In frequency bands of 3 GHz or higher and 6 GHz or lower, up to 8 synchronization signal blocks may be transmitted. In frequency bands of 6 GHz or higher, up to 64 synchronization signal blocks may be transmitted. As described above, at 6 GHz or lower, subcarrier spacings of 15 kHz and 30 kHz may be used.

[0090] exist Figure 6 In the example, because Figure 4 Since case #1 (401) of the configuration having a time slot with a subcarrier spacing of 15 kHz can be mapped to the first time slot and the second time slot in the frequency band of 3 GHz or less, up to four synchronization signal blocks 621 can be transmitted, and since case #1 (401) can be mapped to the first, second, third, and fourth time slots in the frequency bands of 3 GHz or more and 6 GHz or less, up to 8 synchronization signal blocks 622 can be transmitted. Figure 4 Case #2 (402) or case #3 (403) in which two time slots are configured with a subcarrier spacing of 30kHz can be mapped starting from the first time slot in a frequency band of 3 GHz or lower, so up to 4 synchronization signal blocks 631 and 641 can be transmitted, and because case #2 (402) or case #3 (403) can be mapped starting from the first and third time slots in frequency bands of 3 GHz or higher and 6 GHz or lower, up to 8 synchronization signal blocks 632 and 642 can be transmitted.

[0091] At frequencies of 6 GHz or higher, subcarrier spacings of 120 kHz and 240 kHz may be used. Figure 6 In the example, because Figure 5 Case #4 (510) of a configuration with two time slots and a subcarrier spacing of 120kHz can be mapped starting from the 1st, 3rd, 5th, 7th, 11th, 13th, 15th, 17th, 21st, 23rd, 25th, 27th, 31st, 33rd, 35th and 37th time slots in a frequency band of 6GHz or higher, so up to 64 synchronization signal blocks 651 can be transmitted. Figure 6 In the example, because Figure 5 Case #5 (520) configured with 4 time slots and a subcarrier spacing of 240kHz can be mapped starting from the 1st, 5th, 9th, 13th, 21st, 25th, 29th and 33rd time slots in the 6GHz or higher frequency band, so up to 64 synchronization signal blocks 661 can be transmitted.

[0092] The UE can decode the PDCCH and PDSCH based on the system information included in the received MIB, and then obtain the SIB. The SIB includes at least one of the uplink cell bandwidth, random access parameters, paging parameters, and parameters related to uplink power control. The UE can form a radio link with the network through a random access process based on the system information obtained in the cell search process of the cell and synchronization with the network. For random access, a contention-based or non-contention method can be used. In the initial access step of the cell, when the UE performs cell selection and reselection, the contention-based access method can be used for purposes such as moving from the RRC_IDLE state to the RRC_CONNECTED state. In the case of switching, or in the case of position measurement, when downlink data arrives, non-contention random access can be used to reconfigure uplink synchronization.

[0093] In the following, reference will be made to Figure 7 The 4-step RACH process is described in detail. Figure 7 is a message flow diagram showing the four-step random access process. Figure 7 , in the first step 701 of the random access process, the UE transmits a random access preamble (or message 1) to the base station. Therefore, the base station measures the transmission delay value between the terminal and the base station and performs uplink synchronization. In this case, the UE transmits a random access preamble arbitrarily selected from the random access preamble set given in advance by the system information. The initial transmission power of the random access preamble is determined based on the path loss between the base station and the UE measured by the UE. In addition, the terminal determines the transmission beam direction (or transmission beam or beams) of the random access preamble based on the synchronization signal (or SSB) received from the base station, and transmits the random access preamble by applying the determined transmission beam direction.

[0094] In a second step 702, the base station transmits a response (random access response, RAR or message 2) to the detected random access attempt to the UE. The base station transmits an uplink transmission timing control command to the UE by measuring the transmission delay value from the random access preamble received in the first step. In addition, the base station transmits the uplink resources and power control commands to be used by the UE as scheduling information. The scheduling information may include control information about the uplink transmission beam of the terminal. The RAR is transmitted through the PDSCH and includes the following information.

[0095] - Random access preamble sequence index detected by the network (or base station)

[0096] -TC-RNTI (Temporary Cell Radio Network Temporary Identifier)

[0097] - Uplink Scheduling Grant

[0098] -Timing advance value

[0099] If in the second step 702, the terminal does not receive the RAR as the scheduling information on the message 3 from the base station within a predetermined time, the first step 701 is performed again. When the first step is performed again, the UE increases the transmission power of the random access preamble by a predetermined step size and transmits the random access preamble (this is called power ramping), thereby increasing the random access preamble reception probability of the base station.

[0100] In a third step 703, the terminal transmits uplink data (scheduled transmission or message 3) including its terminal identifier to the base station through a physical uplink shared channel (PUSCH) using the uplink resources allocated in the second step 702. The transmission timing of the uplink data channel for transmitting message 3 follows the uplink transmission timing control command received from the base station in the second step 702. In addition, the transmission power of the uplink data channel for transmitting message 3 is determined taking into account the power control command received from the base station in the second step 702 and the power boost value of the random access preamble. The uplink data channel for transmitting message 3 is the first uplink data signal transmitted by the UE to the base station after the UE transmits the random access preamble.

[0101] Finally, when the base station determines in the fourth step 704 that the terminal has performed random access without conflicting with other UEs, the base station transmits data (contention resolution message or message 4) including an identifier of the terminal that has transmitted uplink data in the third step 703 to the corresponding UE. When the UE receives a signal transmitted by the base station from the base station in the fourth step 704, the UE determines that the random access is successful. The UE transmits a HARQ-ACK / NACK indicating whether message 4 has been successfully received to the base station through a physical uplink control channel (PUCCH).

[0102] When the base station fails to receive a data signal from the UE because the data transmitted by the UE collides with the data of another UE in the third step 703, the base station does not perform any further data transmission to the UE. Therefore, when the UE does not receive data transmitted from the base station within a predetermined period of time in the fourth step 704, the UE determines that the random access procedure has failed and starts again from the first step 701.

[0103] As described above, in the first step 701 of the random access procedure, the UE may transmit a random access preamble on the PRACH. Each cell has 64 available preamble sequences, and depending on the transmission type, 4 long preamble formats and 9 short preamble formats may be used. The UE generates 64 preamble sequences using the root sequence index and cyclic shift value signaled as system information, and randomly selects a sequence and uses it as a preamble.

[0104] The network can use SIB or high-level signaling to inform the terminal which time-frequency resources can be used for PRACH. The frequency resource indicates the starting RB point of the transmission to the UE, and the number of RBs used is determined according to the preamble format and the applied subcarrier spacing. The time resource can notify the preconfigured PRACH configuration period, the starting symbol and the subframe index including the PRACH opportunity (which can be mixed with the opportunity) through the PRACH configuration index (0 to 255), as well as the number of PRACH opportunities in the time slot, as shown in Table 3. Through the PRACH configuration index, the random access configuration information included in the SIB, and the index of the SSB selected by the UE, the terminal can identify the time and frequency resources for transmitting the random access preamble, and transmit the selected sequence as a preamble to the base station.

[0105] [Table 3]

[0106]

[0107] In the conventional LTE communication system, LTE-MTC (machine type communication) technology has been developed to support application services such as the Internet of Things (IoT). LTE-MTC is an IoT-specific access technology that takes into account key requirements such as low-power design, low-cost equipment supply, low construction cost, stable coverage, and large-scale UE access implementation. In the LTE-MTC technology, by introducing a power saving mode and reducing the transmission speed and transmission bandwidth compared to LTE services, a long battery life of the UE can be guaranteed based on a low-power design. In addition, because the transmission speed and transmission bandwidth are greatly reduced, the complexity of the communication modem is greatly reduced, so that a low-cost UE can be implemented. In addition, a single antenna technology can be applied instead of MIMO technology to minimize power consumption. In addition, because the existing LTE network can be used as is, existing LTE services and LTE-MTC services can be supported simultaneously without additional investment.

[0108] In this case, in order not to have any impact on UEs supported by existing LTE services, the base station indicates that the cell transmitting the PBCH also supports the LTE-MTC service by including additional information in the remaining bits of the MIB included in the PBCH of the existing LTE service, and further indirectly indicates the resource location of the system information block (system information block type 1-bandwidth reduction, SIB1-BR) for transmitting the LTE-MTC service. As a result, the UE or node supported by the LTE-MTC service can determine whether the cell found by the cell search is a cell supporting the LTE-MTC service, and if the cell found by the cell search is a cell supporting the LTE-MTC service, the UE or node can obtain the location of the resources capable of receiving the corresponding system information block. In addition, the UE supported by the existing LTE service can receive support for the LTE service without additional operations or new operations for the existing operations.

[0109] The UE supporting LTE-MTC service (hereinafter referred to as MTC UE) performs a random access process based on various system information received. In addition, in the first step, the MTC terminal determines the coverage enhancement level (CE level) before transmitting the random access preamble to the base station (hereinafter, the physical random access channel (PRACH), the PRACH preamble and the preamble can be mixed). As described in the LTE-MTC service, the MTC UE can repeatedly transmit the random access preamble multiple times so that the terminals at the edge of the cell can also successfully perform random access in order to increase coverage. However, because the UE at the center of the cell does not need to repeatedly transmit the random access preamble, multiple CE levels can be configured, and the number of repetitions of the random access preamble applied to each MTC UE, the time resources, frequency resources and sequence resources of the preamble can be configured differently.

[0110] Will refer to Figure 8 Describe in detail how the terminal determines the CE level. Figure 8801) is a diagram showing CE levels applicable to MTC UEs. The UE first measures the reference signal received power (RSRP) based on the received cell-specific reference signal (CRS). The CE level is determined by comparing the CRS-RSRP value measured by the UE with a preconfigured RSRP threshold. For example, if the measured CRS-RSRP value exceeds RSRP threshold 1 (810), the UE transmits a preamble in a PRACH resource allocated to CE level 0 (801). If the measured CRS-RSRP value is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the UE transmits a preamble in a PRACH resource allocated to CE level 1 (802). In the same manner as described above, the terminal can determine that it corresponds to CE levels 2 (803) and 3 (804), and transmit the preamble in the PRACH resource corresponding to the determined CE level. In this case, as the CE level increases, the coverage of successful random access can be increased by increasing the number of preamble repetitions.

[0111] Even in 5G communication systems, mMTC services are being considered to support application services such as the Internet of Things (IoT). In mMTC services, in order to effectively provide the Internet of Things, it is necessary to support large-scale terminal access within a cell, improve UE coverage, improve battery life, and reduce terminal costs. Specifically, in order to improve UE coverage, a random access procedure in which the UE first transmits should be successfully performed.

[0112] Therefore, the present disclosure provides a random access method for improving the coverage of base stations and UEs in 5G mobile communication services and mMTC services. In addition, the present disclosure provides a method for repeatedly transmitting a random access preamble to improve coverage.

[0113] In the following, the present disclosure proposes a random access method and device for improving coverage in mMTC services, but the main points of the present disclosure are not limited to mMTC, and can be applied to services that require access support for large-scale terminals within a cell or services for providing IoT services, UE coverage improvement, battery time improvement and UE cost reduction, and can also be applied to random access methods and devices for services that can be provided in another 5G system (e.g., URLLC).

[0114] <First Embodiment>

[0115] The first embodiment of the present disclosure relates to a method in which a base station configures transmission configurations and resources for transmitting a random access preamble differently, and in which a UE determines and transmits resources and configurations for transmitting a random access preamble by itself. Through the random access transmission method described in this embodiment, when the UE changes the resources and the number of repetitions for transmitting a preamble according to the channel state of the UE and the base station, the UE can effectively perform a random access procedure.

[0116] Specifically, when considering the resources and transmission configuration configured to the UE for transmitting a random access preamble, as in the existing 5G communication system, all terminals should use the same resources and transmission configuration to transmit the preamble, regardless of the channel state of the UE and the base station. When the base station determines the random access preamble resources and transmission configuration for the UE located at the edge of the cell, the base station should configure the UE to transmit the preamble with a very high number of repetitions in a very large resource so that random access is successful. However, in this case, in the case of a UE located at the center of the cell and having a good channel state between the UE and the base station, even if the terminal can successfully perform the preamble transmission with only one preamble transmission in a very small resource, the UE may inefficiently have to perform up to hundreds of preamble transmissions instead of one transmission.

[0117] In the opposite case, when the base station configures the UE to transmit the preamble with very small resources and a small number of repetitions, the UE at the edge of the cell cannot successfully perform the random access process according to the configuration. Therefore, as with the random access method for the above-mentioned LTE-MTC service, a method is proposed in which the base station configures several CE levels, and in which the UE determines the CE level by itself and transmits a random access preamble. Specifically, when multiple CE levels are configured for the mMTC service, if the initial CE level is configured based on the RSRP calculated by only one CRS in LTE-MTC, the present disclosure proposes a method for configuring the initial CE level based on multiple RSRPs calculated by multiple SSBs.

[0118] The following method can be considered as a method for the UE to determine the initial CE level in the mMTC service.

[0119] [Method 1]

[0120] The base station may enable the terminal to determine the CE level based on a threshold. In this case, as the initial CE level is determined, when the UE attempts to use the configuration of the corresponding CE level for random access, but the random access fails, the terminal may increase the CE level from the initial CE level to the next CE level (CE level upgrade) after meeting certain conditions, and attempt to use the configuration of the increased CE level for random access to increase the probability of receiving the random access preamble code of the base station. The specific method of increasing the CE level follows the method described in the second embodiment.

[0121] The UE can compare multiple measured SS-RSRPs (secondary synchronization RSRPs) with a threshold (which can be the same as the threshold configured to determine the SSB that can be selected as the basis for preamble transmission when the terminal transmits a preamble in an existing 5G mobile communication system) to determine the CE level, thereby determining the initial CE level with little additional overhead (or no additional overhead) of high-layer signaling.

[0122] In this case, the following method may be considered as a method in which the UE determines a CE level based on one threshold through a plurality of measured Secondary Synchronization RSRPs (SS-RSRPs).

[0123] [Method 1-1]

[0124] The UE can calculate the number of SSBs with SS-RSRP greater than the configured threshold and determine the CE level based on the number. Specifically, the UE can know the location of the SSB actually transmitted by the base station based on the received SIB information, thereby measuring the SS-RSRP of each SSB based on multiple SSBs. After the measurement, the UE can calculate the number of SSBs with SS-RSRP greater than the configured threshold and determine the CE level based on the number.

[0125] As described above, in a 5G communication system, a base station may transmit each SSB through other transmission beams, and even in random access preamble transmission, the UE uses a beam and PRACH resource corresponding to one of several SSBs selected (which may mean a time and / or frequency resource in which the PRACH may be transmitted) to select and transmit the preamble. When the UE fails to transmit the preamble in a resource corresponding to a selected SSB, in order to obtain gain (diversity gain) through diversity, the UE may select another SSB with different beams and resources. Therefore, the fact that the number of SSBs that the UE can select from that exceeds a threshold is several means that the UE can obtain diversity gain by changing the SSB corresponding to the CE level. In addition, in the repeated random access preamble transmission method corresponding to multiple SSBs proposed in the fourth embodiment, since the number of SSBs may be related to the number of repetitions, the number of SSBs whose SS-RSRP values ​​exceed a threshold may be an important reference for selecting a CE level.

[0126] For example, if the number of SSBs whose SS-RSRP values ​​exceed a threshold value is 4 or more, the UE may determine the initial CE level as CE level 0, if the number of SSBs whose SS-RSRP values ​​exceed a threshold value is between 3 and 2, the terminal may determine the initial CE level as CE level 1, if the number of SSBs whose SS-RSRP values ​​exceed a threshold value is 1, the UE may determine the initial CE level as CE level 2, and if the number of SSBs whose SS-RSRP values ​​exceed a threshold value is 0, the UE may determine the initial CE level as CE level 3. In this case, the number of reference SSBs for determining the CE level may be configured to the UE through higher layer signaling.

[0127] [Method 1-2]

[0128] The UE can calculate the ratio of SSBs in which the SS-RSRP is greater than the configured threshold, and determine the CE level based on the ratio. Specifically, the UE can know the position of the SSB actually transmitted by the base station based on the received SIB information, thereby measuring the SS-RSRP of each SSB based on multiple SSBs. The UE can calculate the ratio of SSBs in which the measured SS-RSRP is greater than the configured threshold, and determine the CE level based on the ratio.

[0129] Specifically, the SIB information received by the UE includes the SIB information actually transmitted by the base station. Thus, the UE can know the total number of SSBs that the base station has transmitted, and calculate the ratio of SSBs whose corresponding SS-RSRP is greater than the configured threshold. This method can have the same effect as method 1-1, and the UE can determine the initial CE level by the ratio of the number of SSBs actually transmitted rather than the absolute number of SSBs. The fact that the number of SSBs that the terminal can select that exceeds a threshold is several means that diversity gain can be obtained by changing the SSBs in the corresponding CE level. In addition, in the repeated random access preamble transmission method corresponding to multiple SSBs proposed in the fourth embodiment, because the number of SSBs may be related to the number of repetitions, the ratio of SSBs whose SS-RSRP values ​​exceed a threshold may be an important reference for selecting the CE level.

[0130] For example, if the number of SSBs in which the SS-RSRP value exceeds a threshold value is 75% or more based on the number of actually transmitted SSBs, the UE may determine the initial CE level as CE level 0, and if the number of SSBs in which the SS-RSRP value exceeds a threshold value is between 75% and 50%, the UE may determine the initial CE level as CE level 1, if the number of SSBs in which the SS-RSRP value exceeds a threshold value is between 50% and 25%, the UE may determine the initial CE level as CE level 2, and if the number of SSBs in which the SS-RSRP value exceeds a threshold value is less than 25%, the UE may determine the initial CE level as CE level 3. In this case, the reference SSB ratio for determining the CE level may be configured to the UE through higher layer signaling.

[0131] [Method 2]

[0132] The base station may enable the UE to determine the CE level using several thresholds. In this case, as the initial CE level is determined, when the UE has attempted to use the configuration of the corresponding CE level for random access, but the random access fails, after meeting certain conditions, the UE may increase the CE level from the initial CE level to the next CE level (CE level upgrade), and attempt to use the configuration of the increased CE level for random access to increase the probability of receiving the random access preamble of the base station. The specific method for increasing the CE level follows the method described in the second embodiment. When the UE determines the CE level based on several thresholds (one of the several thresholds may be the same as the threshold configured for determining the SSB that can be selected as the basis for preamble transmission when the UE transmits a preamble in an existing 5G mobile communication system) through multiple measured SS-RSRPs, the UE can effectively determine the initial CE level through precise reference.

[0133] In this case, the following method may be considered as a method in which the UE determines the CE level based on several thresholds through a plurality of measured Secondary Synchronization RSRPs (SS-RSRPs).

[0134] [Method 2-1]

[0135] The UE determines the CE level based on all measured SS-RSRP. Specifically, the UE can know the location of the SSB actually transmitted by the base station based on the received SIB information, thereby measuring the SS-RSRP of each SSB based on multiple SSBs. After the measurement, the UE can determine the CE level based on all measured SS-RSRP. In this case, the following method can be considered as a method for determining the CE level based on all measured SS-RSRP.

[0136] [Method 2-1-1]

[0137] The UE may compare the maximum value of all measured SS-RSRP values ​​with multiple thresholds to determine the initial CE level. The initial CE level is determined by the maximum value of all measured SS-RSRPs. When transmitting or repeatedly transmitting a preamble corresponding to an SSB, the UE may transmit the random access preamble using the minimum resources (and / or number of repetitions) in the lowest CE level. That is, by using a small amount of PRACH resources for preamble transmission, the UE can effectively use radio resources.

[0138] For example, if the maximum value of all measured SS-RSRP is greater than RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the maximum value of all measured SS-RSRP is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the UE may determine the initial CE level to be CE level 1, if the maximum value of all measured SS-RSRP is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the maximum value of all measured SS-RSRP is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0139] [Method 2-1-2]

[0140] The UE may compare the minimum value among all measured SS-RSRP values ​​with a plurality of thresholds to determine an initial CE level. By determining the initial UE level by the minimum value among all measured SS-RSRPs, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails (this includes, for example, a case where the UE does not receive an RAR within a certain time after transmitting the preamble), even if the UE changes the SSB serving as the basis for preamble transmission to another SSB among all measured SSBs (i.e., even if the beam used to transmit the preamble is changed), the preamble may be transmitted at a CE level that satisfies the reference for stable preamble transmission. In this case, even when the UE repeatedly transmits preambles corresponding to a plurality of SSBs, all measured SSBs satisfy the reference; therefore, even if the terminal selects a plurality of some SSBs to repeatedly transmit the preamble, a CE level that satisfies the reference may be selected.

[0141] For example, if the minimum value among all measured SS-RSRP is greater than RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the minimum value among all measured SS-RSRP is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the UE may determine the initial CE level to be CE level 1, if the minimum value among all measured SS-RSRP is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the minimum value among all measured SS-RSRP is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0142] [Method 2-1-3]

[0143] The UE may compare the average of all measured SS-RSRP values ​​with multiple thresholds to determine an initial CE level. By determining the initial CE level by the average of all measured SS-RSRPs, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB serving as the basis for preamble transmission to another SSB among n SSBs (i.e., even if the beam used for preamble transmission is changed), the preamble may be transmitted at a CE level that satisfies the reference for stable preamble transmission on average. Here, n may be the number of all SSBs for which SS-RSRP is measured, or the number of SSBs whose SS-RSRP value is greater than or equal to the average of all measured SS-RSRPs. Even when the UE repeatedly transmits preambles corresponding to multiple SSBs, the n SSBs satisfy the reference on average; therefore, when multiple appropriate SSBs are selected for repeated transmission, a valid CE level may be selected.

[0144] For example, if the average value of n SS-RSRPs is greater than RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the average value of n SS-RSRPs is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the UE may determine the initial CE level to be CE level 1, if the average value of n SS-RSRPs is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the average value of n SS-RSRPs is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0145] [Method 2-1-4]

[0146] The terminal can identify the CE level corresponding to the SS-RSRP value of all measured SSBs based on multiple thresholds, and select the CE level that occupies the largest proportion as the initial CE level. By determining that all measured SS-RSRPs include the most CE levels as the initial CE level, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB that is the basis for preamble transmission to another SSB among all measured SSBs (that is, even if the beam applied to the preamble transmission is changed), the preamble can be transmitted according to the CE level with the largest SSB ratio. Even when the UE repeatedly transmits preambles corresponding to multiple SSBs, the SSB corresponding to a specific CE level occupies the largest proportion among all measured SSBs; therefore, when selecting multiple appropriate SSBs for repeated transmission of preambles, an effective CE level can be selected.

[0147] For example, among all the measured 7 SS-RSRP values, if the value greater than RSRP threshold 1 (810) is 2, if the value less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820) is 3, if the value less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830) is 1, and if the value less than RSRP threshold 3 (830) is 1, the terminal can determine the initial CE level as CE level 1 including the largest SS-RSRP value.

[0148] [Method 2-2]

[0149] The terminal determines the CE level based on n largest SS-RSRPs among the measured SS-RSRPs. Fig. 9 is a flowchart showing a method of determining a CE level based on n SS-RSRPs having a maximum value among measured SS-RSRPs. Fig. 9, the UE can know the position of the SSB actually transmitted by the base station based on the received SIB information, thereby measuring each SS-RSRP based on multiple SSBs (step 901). After the measurement, the UE can determine the CE level based on the n largest SS-RSRPs among the measured SS-RSRPs (step 902). Here, n can be a pre-configured value or a value configured by the SIB (n can be explicitly indicated by the SIB, or can be related to the number of related repeated transmissions that can be indicated by the SIB or the number of SSBs actually transmitted for repeated transmissions of preambles corresponding to multiple SSBs (see the fourth embodiment)). In this case, the following method can be considered as a method for determining the CE level based on the n largest SS-RSRPs. Through the method described below, the UE selects the CE level based on n SS-RSRPs (step 903). Each step described in the accompanying drawings does not necessarily have to be performed in the order described, and the order of performing each step can be changed or omitted.

[0150] [Method 2-2-1]

[0151] The UE may compare the minimum value among the n selected SS-RSRP values ​​with a plurality of thresholds to determine an initial CE level. By determining the initial CE level by the minimum value among the n selected SS-RSRP values, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB serving as the basis for preamble transmission to another SSB among the n SSBs (i.e., even if the beam used for preamble transmission is changed), the preamble may be transmitted at a CE level that satisfies the reference for stable preamble transmission. Even when the UE repeatedly transmits preambles corresponding to multiple SSBs, all n SSBs satisfy the reference; therefore, even if multiple SSBs are selected for repeated transmission, a CE level that satisfies the reference may be selected.

[0152] For example, if the minimum value among the n SS-RSRPs is greater than the RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the minimum value among the n SS-RSRPs is less than the RSRP threshold 1 (810) and greater than the RSRP threshold 2 (820), the UE may determine the initial CE level to be CE level 1, if the minimum value among the n SS-RSRPs is less than the RSRP threshold 2 (820) and greater than the RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the minimum value among the n SS-RSRPs is less than the RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0153] [Method 2-2-2]

[0154] The UE may compare an average value of n selected SS-RSRP values ​​with a plurality of thresholds to determine an initial CE level. By determining the initial CE level by the average value of n selected SS-RSRPs, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB serving as the basis for preamble transmission to another SSB among n SSBs (i.e., even if the beam used for preamble transmission is changed), the preamble may be transmitted at a CE level that satisfies the reference for stable preamble transmission on average. Even when the UE repeatedly transmits preambles corresponding to a plurality of SSBs, the n SSBs satisfy the reference on average; therefore, when a plurality of appropriate SSBs are selected for repeated transmission, an effective CE level may be selected.

[0155] For example, if the average value of n SS-RSRPs is greater than RSRP threshold 1 (810), the terminal may determine the initial CE level to be 0. If the average value of n SS-RSRPs is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the terminal may determine the initial CE level to be CE level 1, if the average value of n SS-RSRPs is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the average value of n SS-RSRPs is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0156] [Method 2-2-3]

[0157] The terminal can identify the CE levels corresponding to n selected SS-RSRP values ​​based on multiple thresholds, and select the CE level that occupies the largest proportion as the initial CE level. By determining that the n selected SS-RSRPs include the most CE levels as the initial CE level, when the UE transmits or repeatedly transmits a preamble corresponding to a CE level, but random access fails, even if the UE changes the SSB that is the basis for the preamble transmission to another SSB among the n SSBs (that is, even if the beam applied to the preamble transmission is changed), the preamble can be transmitted according to the CE level with the maximum SSB ratio. Even when the UE repeatedly transmits preambles corresponding to multiple SSBs, the SSB corresponding to a specific CE level has the largest ratio among the n SSBs; therefore, when multiple appropriate SSBs are selected for repeated transmission, an effective CE level can be selected.

[0158] For example, among the seven SS-RSRP values, if the value greater than RSRP threshold 1 (810) is 2, if the value less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820) is 3, if the value less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830) is 1, and if the value less than RSRP threshold 3 (830) is 1, the UE can determine the initial CE level as CE level 1 including the largest SS-RSRP value.

[0159] [Method 3]

[0160] The base station can enable the terminal to determine the CE level using several thresholds and one threshold. In this case, when the initial CE level is determined, when the UE has attempted to use the configuration of the corresponding CE level for random access, but the random access fails, after meeting certain conditions, the UE can increase the CE level from the initial CE level to the next CE level (CE level upgrade), and attempt to use the configuration of the increased CE level for random access to increase the probability of receiving the random access preamble code of the base station. The specific method of increasing the CE level follows the method described in the second embodiment.

[0161] Fig.10 is a flow chart showing a method in which a UE determines an initial CE level based on several thresholds and a threshold. Fig.10 , the UE can know the position of the SSB actually transmitted by the base station based on the received SIB information, thereby measuring the SS-RSRP of each SSB based on multiple SSBs (step 1001). The UE first selects a SS-RSRP greater than a threshold of one of the multiple measured SS-RSRPs (this may be the same as the threshold configured to determine the SSB that can be selected as the basis for preamble transmission when the UE transmits a preamble in an existing 5G mobile communication system) (step 1002). The UE identifies the number of SS-RSRP values ​​greater than a threshold (step 1003). If one or more SS-RSRPs exceed the threshold, the UE may compare the selected SS-RSRP with several thresholds (which may be the same as the threshold configured for the existing 5G mobile communication system) to determine the CE level (step 1004). Each step described in the accompanying drawings does not necessarily have to be performed in the order described, and the order of performing each step may be changed or omitted.

[0162] If no SS-RSRP exceeds the threshold, the UE can compare several thresholds (which can be the same as the thresholds configured for the existing 5G mobile communication system) based on all measured SS-RSRP to determine the CE level (step 1005). In this case, the UE can determine the initial CE level through the above method 2-1.

[0163] By the above method, the UE can effectively determine the initial CE level by accurate reference. In this case, the following method can be considered as Fig.10 In step 1004 of the above method, a plurality of SS-RSRPs measured by the UE are compared with several thresholds to determine the CE level.

[0164] [Method 3-1]

[0165] The UE may compare the maximum value among the selected SS-RSRP values ​​with multiple thresholds to determine the initial CE level. By determining the initial CE level by the maximum value among the selected SS-RSRP, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, the UE may transmit the random access preamble using the minimum resources (or / and number of repetitions) in the lowest CE level. That is, by using a small amount of PRACH resources for preamble transmission, the terminal can effectively use radio resources.

[0166] For example, if the maximum value among the selected SS-RSRP is greater than RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the maximum value among the selected SS-RSRP is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the UE may determine the initial CE level to be CE level 1, if the maximum value among the selected SS-RSRP is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the maximum value among the selected SS-RSRP is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0167] [Method 3-2]

[0168] The UE may compare the minimum value among the selected SS-RSRP values ​​with a plurality of thresholds to determine an initial CE level. By determining the initial CE level by the minimum value among the selected SS-RSRP, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB serving as the basis for preamble transmission to another SSB among the selected SSBs (i.e., even if the beam used for preamble transmission is changed), the preamble may be transmitted at a CE level that satisfies the reference for stable preamble transmission. In this case, even when the UE repeatedly transmits preambles corresponding to a plurality of SSBs, all selected SSBs satisfy the reference; therefore, even if a plurality of SSBs are selected for repeated transmission, a CE level that satisfies the reference may be selected.

[0169] For example, if the minimum value among the selected SS-RSRP is greater than RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the minimum value among the selected SS-RSRP is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the UE may determine the initial CE level to be CE level 1, if the minimum value among the selected SS-RSRP is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the minimum value among the selected SS-RSRP is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0170] [Method 3-3]

[0171] The UE may compare the average of the selected SS-RSRP values ​​with a plurality of thresholds to determine an initial CE level. By determining the initial CE level by the average of the n selected SS-RSRPs, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB serving as the basis for preamble transmission to another SSB among the selected SSBs (i.e., even if the beam used for preamble transmission is changed), the preamble may be transmitted at a CE level that satisfies the reference for stable preamble transmission on average. Even when the UE repeatedly transmits preambles corresponding to a plurality of SSBs, the selected SSBs satisfy the reference on average; therefore, when a plurality of appropriate SSBs are selected for repeated transmission, an effective CE level may be selected.

[0172] For example, if the average value of the selected SS-RSRP is greater than RSRP threshold 1 (810), the UE may determine the initial CE level to be 0. If the average value of the selected SS-RSRP is less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820), the terminal may determine the initial CE level to be CE level 1, if the average value of the selected SS-RSRP is less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 2, and if the average value of the selected SS-RSRP is less than RSRP threshold 3 (830), the UE may determine the initial CE level to be CE level 3.

[0173] [Method 3-4]

[0174] The UE can identify the CE level corresponding to each selected SS-RSRP value based on multiple thresholds, and select the CE level that occupies the largest proportion as the initial CE level. By determining the CE level including the most selected SS-RSRP as the initial CE level, when the UE transmits or repeatedly transmits a preamble corresponding to one SSB, but random access fails, even if the UE changes the SSB that is the basis for the preamble transmission to another SSB among the selected SSBs (that is, even if the beam applied to the preamble transmission is changed), the preamble can be transmitted according to the CE level with the largest SSB ratio. Even when the terminal repeatedly transmits preambles corresponding to multiple SSBs, the SSB corresponding to a specific CE level occupies the largest proportion among the selected SSBs; therefore, when multiple appropriate SSBs are selected for repeated transmission, an effective CE level can be selected.

[0175] For example, among 7 SS-RSRP values ​​exceeding one RSRP threshold, if the value greater than RSRP threshold 1 (810) is 2, if the value less than RSRP threshold 1 (810) and greater than RSRP threshold 2 (820) is 3, if the value less than RSRP threshold 2 (820) and greater than RSRP threshold 3 (830) is 1, and if the value less than RSRP threshold 3 (830) is 1, the UE can determine the initial CE level as CE level 1 including the most SS-RSRP value.

[0176] When the initial CE level is determined by the above method, the UE transmits a random access preamble based on configuration information related to the corresponding CE level included in a system information block (SIB). The corresponding CE level related information may include one or more of the following information.

[0177] -PRACH configuration index (preamble format, subframe index, number of PRACH slots included in a subframe, number of PRACH opportunities in one PRACH slot, number of OFDM symbols of a PRACH opportunity, and start symbol index)

[0178] -Number of repetitions of the random access preamble

[0179] - Random access preamble repetition starts in slot / subframe

[0180] - Maximum number of preamble transmission attempts

[0181] - Whether frequency hopping can be applied to preamble transmission

[0182] - Number of PDCCH repetitions of RAR (this can be understood as the number of repetitions of downlink control information (DCI) used to schedule RAR)

[0183] - Time / frequency resources for RAR's CORESET

[0184] -Configure search area for RAR

[0185] The base station can estimate the PRACH timing at which the UE will transmit a random access preamble based on the CE level related information. When the random access preamble is received at a specific PRACH timing, the base station can identify the index of the SSB that is the basis for the random access preamble transmission of the terminal based on the PRACH timing, and identify the CE level determined by the UE taking into account the CE level related information. Taking into account the identified CE level on the PDCCH, the base station can transmit downlink control information (DCI) for transmitting the RAR, and the configuration information related to each CE level can be applied to the downlink control information transmission.

[0186] Fig.11 is a flowchart showing a process in which a UE transmits a PRACH preamble code after determining an initial CE level through the above method.

[0187] Specifically, after determining the initial CE level (step 1101), the UE obtains one or more pieces of information among the configured information according to the determined CE level (step 1102). In the case where the repetition of the preamble is not configured based on the configured information (e.g., PRACH configuration index, repetition start time slot and / or subframe of the PRACH preamble, frequency hopping of the preamble), the UE calculates the position of the PRACH opportunity at which the corresponding PRACH preamble can be transmitted (step 1103). The UE randomly selects the timing for transmitting the preamble among the calculated PRACH preamble timings (step 1104). Finally, the UE repeats the transmission of the PRACH preamble according to the configured repetition transmission unit (configuration unit in the information or pre-configured fixed unit) at the selected timing (and the timing determined based on the selected timing) (step 1105). Alternatively, when repeated transmission is not configured, step 1105 can be omitted. Each step described in the accompanying drawings does not necessarily have to be performed in the described order, and the order of performing each step can be changed or omitted.

[0188] The above method can be applied to determine the initial CE level in the random access process of the supplementary uplink (SUL). In addition, the above method is not limited to the method for determining the initial CE level in the random access process corresponding to the mMTC service, and can be applied to determine the initial CE level in the random access process for new services other than mMTC. In addition, the above method is not limited to the method for determining the initial CE level in the random access process based on the SS-RSRP value, and the RSRP value measured based on a signal different from the SS-RSRP value or a measurement value different from RSRP can be used to determine the initial CE level in the random access process.

[0189] Furthermore, the above-mentioned methods are not mutually exclusive, and a combination of one or more of the proposed methods may be used to solve the problem.

[0190] <Second Embodiment>

[0191] The second embodiment describes the process of the terminal in the case where the preamble transmission fails when the UE has transmitted the random access preamble in the corresponding resource after determining the initial CE level. Specifically, after determining the initial CE level according to the first embodiment, the UE transmits the random access preamble in the corresponding resource, and waits for the RAR transmitted by the base station within the configured time after the transmission of the preamble. If the RAR is not received from the base station within the predetermined time, the UE assumes that the base station has failed to receive the preamble and attempts to transmit the preamble again. In this case, in order to successfully transmit the preamble, the terminal can increase the CE level and transmit the corresponding resources and the corresponding preamble.

[0192] The following process can be considered as a process for the UE to increase the CE level.

[0193] [Method 1]

[0194] When the number of transmissions of the preamble exceeds the configured maximum number of transmissions of the preamble, the UE may increase the CE level and transmit the preamble.

[0195] Fig.12 is a flow chart showing a random access preamble transmission process of a terminal. Fig.12 , the UE transmits a RACH preamble (step 1201). The UE determines whether the random access preamble has been successfully transmitted based on whether the RAR transmitted by the base station is received within the configured time after the preamble is transmitted (step 1202). If the UE receives the RAR within the configured time, the UE determines that the random access preamble has been successfully transmitted and prepares to transmit message 3 (step 1208).

[0196] If the UE does not receive the RAR within the configured time, the UE assumes that the base station has not received the preamble, and compares the maximum number of transmissions of the preamble configured by the SIB with the number of times the preamble has been actually transmitted (step 1203). If the number of times the UE has actually transmitted the preamble is less than the maximum number of transmissions, the UE selects an SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) (step 1204). In this case, the UE determines whether the selected SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the terminal) is the same as the previously selected SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) (step 1205). If the same SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) as the one selected for the previous preamble transmission (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) is selected, the UE can increase the transmission power of the random access preamble by a predetermined step size and transmit the random access preamble (step 1206), thereby increasing the random access preamble reception probability of the base station.

[0197] If an SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) different from the one selected for the previous preamble transmission is selected, the UE transmits the corresponding preamble in the resources corresponding to the selected SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) (step 1201). In this way, conflicts caused by multiple UEs transmitting preambles in the same resources can be avoided.

[0198] If in step 1203, the number of times the UE has actually transmitted the preamble exceeds the maximum number of transmissions, the UE may increase the CE level and transmit the corresponding preamble in the resources corresponding to the increased CE level (step 1207). Each step described in the drawings does not necessarily have to be performed in the order described, and the order of performing each step may be changed or omitted.

[0199] For example, the SSB combination specified above can be configured as follows.

[0200] - SSBs whose SS-RSRP exceeds an RSRP threshold based on an RSRP threshold may be configured as a single combination. (The RSRP threshold may be the same as the threshold configured for configuring the initial CE level in the first embodiment, or may be one of the multiple thresholds if there are multiple thresholds)

[0201] - n SSBs with the highest SS-RSRP may be configured as a single combination.

[0202] The base station may configure a combination of pre-configured SSBs for the UE.

[0203] [Method 2]

[0204] When the number of transmissions of the preamble exceeds the configured maximum number of transmissions of the preamble, the UE selects a combination of SSBs or multiple other SSBs to transmit the random access preamble. If there is no combination of SSBs or multiple SSBs to select, the UE can increase the CE level and transmit the preamble.

[0205] Fig.13 is a flowchart showing another random access preamble transmission process of a UE. Fig.13 , the UE transmits a RACH preamble (step 1301). The terminal determines whether the random access preamble has been successfully transmitted based on whether a RAR transmitted by the base station is received within a configured time after the preamble is transmitted (step 1302). When the RAR is received within the configured time, the UE determines that the random access preamble has been successfully transmitted and prepares to transmit message 3 (step 1310).

[0206] If the UE does not receive the RAR within the configured time, the UE assumes that the base station has not received the preamble, and compares the maximum number of transmissions of the preamble configured by the SIB with the number of times the preamble has been actually transmitted (step 1303). If the number of times the UE has actually transmitted the preamble is less than the maximum number of transmissions, the UE selects an SSB (or multiple SSBs) from a plurality of selected SSBs or a combination of SSBs (step 1304). The UE determines whether the selected SSB (or one of the multiple SSBs or a combination of SSBs configured by the base station to the UE) is the same as the previously selected SSB (or one of the multiple SSBs or a combination of SSBs configured by the base station to the UE) (step 1305). In this case, if the same SSB (or one of the multiple SSBs or a combination of SSBs configured by the base station to the UE) as the one selected for the previous preamble transmission (or one of the multiple SSBs or a combination of SSBs configured by the base station to the UE) is selected, the UE increases the transmission power of the random access preamble by a predetermined step size and transmits the random access preamble (step 1306), thereby increasing the random access preamble reception probability of the base station.

[0207] If an SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) different from the one selected for the previous preamble transmission is selected, the UE transmits the corresponding preamble in the resources corresponding to the selected SSB (or one of multiple SSBs or a combination of SSBs configured by the base station to the UE) (step 1301). In this way, conflicts caused by multiple UEs transmitting in the same resources can be avoided.

[0208] If the number of times the UE has actually transmitted the preamble exceeds the maximum number of transmissions in step 1303, the UE determines whether there is an SSB combination (or multiple SSBs) different from the currently selected SSB combination (or multiple SSBs) among the SSB combinations corresponding to the currently applied CE level (step 1307). If there is another selectable SSB combination (or multiple SSBs), the terminal can change the SSB combination and transmit the corresponding preamble in the resources corresponding to the SSB combination (step 1308). If there is no other SSB combination (or multiple SSBs) selectable by the UE, the terminal can increase the UE level and transmit the corresponding preamble in the resources corresponding to the increased UE level (step 1309). Each step described in the drawings does not necessarily have to be performed in the order described, and the order of performing each step can be changed or omitted.

[0209] The above method is not limited to the case where the preamble transmission fails when the random access preamble is transmitted in the corresponding resource after the initial CE level is determined in the mMTC service, and can be applied to new services other than mMTC.

[0210] The above methods are not mutually exclusive, and a combination of one or more methods proposed above may be used to solve the problem.

[0211] <Third Embodiment>

[0212] The third embodiment describes a method for repeatedly transmitting a random access preamble corresponding to one SSB. Specifically, in the current 5G communication system, in order to transmit a random access preamble, the terminal first selects an SSB and transmits the preamble at a PRACH opportunity corresponding to the selected SSB.

[0213] As mentioned above, because coverage improvement is an important factor in mMTC services, the probability of random access success can be increased by repeated transmission so that the random access preamble can be successfully transmitted. In this case, the base station should configure the exact location of the resources for the repeated transmission of the preamble. When the terminal and the base station transmit or receive the preamble at different resource locations, it may not be possible to gain from the repeated transmission, and there may even be losses. Specifically, in the transmission of the random access preamble, the base station does not configure the accurate resource location to the UE, but the terminal selects one from the resource locations that can transmit the preamble and transmits the preamble. Therefore, in the following, a method is proposed for the UE and the base station to calculate the resource location for repeated transmission of the random access preamble.

[0214] Specifically, the terminal can calculate a resource (which can be a starting point among resources capable of transmitting a preamble) based on an existing configuration to transmit the preamble as many times as the number of times the preamble is repeatedly transmitted from the starting resource. Specifically, in a 5G mobile communication service, a resource position of a random access preamble corresponding to each SSB is determined according to an SSB selected by a UE, and hereinafter, a method for calculating a resource position for repeated transmission of a preamble based on a resource position is proposed.

[0215] In the mMTC service, the following method may be considered as a method in which a UE and a base station calculate a resource location for repeatedly transmitting a random access preamble corresponding to one SSB.

[0216] [Method 1]

[0217] The UE can continuously and repeatedly transmit the random access preamble code at the PRACH opportunity corresponding to the SSB selected by the UE. Specifically, the UE and the base station can identify the index of the resource that can transmit the preamble code based on the existing configuration. The UE can know the SSB information actually transmitted by the base station based on the received SIB information, and calculate the position of the PRACH opportunity where the preamble code corresponding to each SSB can be transmitted according to Table 3 and the SIB configuration. When the number of PRACH opportunities corresponding to all actually transmitted SSBs is N (this can be the number of PRACH opportunities configured for a specific period), the UE starts the index of the first PRACH opportunity from 0, and configures the index of the last PRACH opportunity where the preamble code can be transmitted within the specific period to N-1.

[0218] Here, the specific period may be explicitly configured through the SIB, may be indirectly calculated, or may follow a pre-configured time. The above-mentioned specific period may be, for example, a period in which the pattern between the PRACH opportunity and the SSB does not change, an association period (which is a multiple {1, 2, 4, 8, 16} interval of the minimum PRACH configuration period in which the PRACH opportunities corresponding to all actually transmitted SSBs are mapped at least once, and for example, when the value of the association period is n, the specific period is n times larger than the PRACH configuration period), a PRACH configuration period (x system frame periods in Table 3), and a period configured by the base station to the UE through the SIB.

[0219] When the terminal is in N SSB Select the i-th SSB from the actual transmitted SSBs SSB When there are multiple SSBs, the first opportunity position of the preamble code can be repeated n start It can be expressed by equation 2.

[0220] [Equation 2]

[0221] For j=0, 1, 2, ... and iSSB =0, ..., N SSB -1

[0222] Indicates the number of repetitions of the configured random access preamble. represents the period (i.e., n) of resources that can repeatedly transmit the preamble code corresponding to one SSB start With the ability to transmit The period of opportunity for a specific SSB preamble. For example, when 4 and SSB 1 is selected (i SSB When n start Occurs at every opportunity where a preamble corresponding to 4 SSB 1s can be transmitted). N SSB Indicates the number of SSBs actually transmitted by the base station.

[0223] When the terminal calculates the initial timing corresponding to the selected SSB, the terminal may repeatedly transmit the preamble code at consecutive timings corresponding to the selected SSB starting from the initial timing, and the number of repetitions is the configured number of repeated transmissions.

[0224] Fig.14 is a diagram showing an example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to one SSB. Fig.14 An example of the transmission resource location of the random access preamble corresponding to each SSB is shown. When the SCS of the 5G mobile communication system is configured to 30kHz and the PRACH configuration index of Table 3 is configured to 104, the transmission resource of the preamble exists in all frames 1401, and in subframes 1402 with indexes 1, 4, and 7 in each frame, there are transmission resources for the preamble. Each subframe is configured with two time slots including 14 symbols, and there are a total of 6 PRACH opportunities in each time slot 1403. Each PRACH opportunity 1404 is configured with two symbols. These configurations follow Table 4.

[0225] [Table 4]

[0226]

[0227] In this case, assuming that the base station transmits 4 SSBs (in this case, the NSSB is 4), the transmission resource position of the random access preamble code corresponding to each SSB can be sequentially configured (1405) in the order of, for example, frequency resources and time resources. For example, the PRACH opportunity corresponding to SSB index 0 is n=0 (1410), the PRACH opportunity corresponding to SSB index 1 is n=1 (1411), these two PRACH opportunities are located at symbols 0 and 1, and use different frequency resources, the PRACH opportunity corresponding to SSB index 2 is n=2 (1412), and the PRACH opportunity corresponding to SSB index 3 is n=3 (1413), these two PRACH opportunities are located at symbols 2 and 3, and use different frequency resources.

[0228] In this case, the terminal may perform repeated transmission of the random access preamble in consecutive resources corresponding to each SSB. For example, when the number of repeated transmissions is is configured as 2 and the period When configured as 4, based on equation 2, the first opportunity for repeating the transmission of the preamble corresponding to SSB index 1 can be calculated as n start =9, 25, 41, .... When UE is in n start = 9, the UE may perform repetitive transmission of the preamble at PRACH opportunities 9 and 13 (1406). Similarly, when the UE starts repetitive transmission of the preamble corresponding to SSB index 1 at PRACH opportunity 25, the UE may perform repetitive transmission of the preamble at PRACH opportunities 25 and 29 (1407).

[0229] [Method 2]

[0230] The UE may repeatedly transmit the random access preamble at a specific interval in the PRACH opportunity corresponding to the SSB selected by the UE. Specifically, the UE and the base station may compile the resource index capable of transmitting the preamble based on the existing configuration. The UE may know the SIB information actually transmitted by the base station based on the received SIB information, and calculate the PRACH transmission point position at which the preamble corresponding to each SSB may be transmitted according to Table 3 and the SIB configuration. When the number of PRACH opportunities corresponding to all actually transmitted SSBs is N (this may be the number of PRACH opportunities configured for a specific period), the UE may start the index of the first PRACH opportunity from 0, and configure the index of the last PRACH opportunity in which the preamble may be transmitted within the specific period to N-1. Here, the specific period may be explicitly configured through the SIB, may be indirectly calculated, or may follow a preconfigured time. The specific details follow the above method 1.

[0231] When UE is in NSSB Select the i-th SSB from the actual transmitted SSBs SSB When there are multiple SSBs, the first opportunity position of the preamble code can be repeated n start It can be expressed by equation 3.

[0232] [Equation 3]

[0233] For j = 0, 1, 2, ...

[0234] And i SSB =0,...N SSB -1

[0235] Indicates the number of repetitions of the configured random access preamble. represents the period (i.e., n) of resources that can repeatedly transmit the preamble code corresponding to one SSB start With the ability to transmit The period of opportunity for a specific SSB preamble. For example, when 4 and SSB 1 is selected (i SSB When n start Occurs at every opportunity where a preamble corresponding to 4 SSB 1s can be transmitted). N SSB Indicates the number of SSBs actually transmitted by the base station.

[0236] Referring to Equation 3, when the UE selects SSB, it determines the index i SSB , and based on the configured and The interval between repeated transmissions can be configured as The terminal can randomly select from 0 to A value (the value is k) among the values ​​of , to randomly select the first timing of the preamble code. The UE can calculate the initial timing corresponding to the selected SSB according to the selected value, and start from the initial timing at intervals of The preamble is transmitted repeatedly at a timing corresponding to the selected SSB, the number of repetitions being the same as the configured number of repetitions. In this way, the probability of collision of preamble transmissions between UEs can be reduced, which may occur when multiple UEs simultaneously perform random access in mMTC services. Specifically, when the preamble is transmitted repeatedly, collisions are likely to occur during multiple repetitions; therefore, reducing the probability of collisions between UEs may be important.

[0237] Fig.15 is a diagram showing another example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to one SSB. Fig.15An example of the transmission resource location of the random access preamble corresponding to each SSB is shown. When the SCS applied to the 5G mobile communication system is 30kHz and the PRACH configuration index of Table 3 is configured as 104, the transmission resource of the preamble exists in all frames 1501, and in subframes 1502 with indexes 1, 4, and 7 in each frame, there are transmission resources for the preamble. Two time slots are configured for each subframe, and there are a total of six PRACH opportunities in each time slot 1503. Each PRACH opportunity 1504 is configured with two symbols. These configurations follow Table 4.

[0238] In this case, assume that the base station transmits 4 SSBs (in this case, N SSB 4), the transmission resource position of the random access preamble code corresponding to each SSB can be sequentially configured in the order of, for example, frequency resources and time resources (1505). This configuration is similar to Fig.14 In this case, the UE may perform repeated transmission of the random access preamble in consecutive resources corresponding to each SSB. For example, when the number of repeated transmissions is is configured as 2 and the period When k is configured as 4 and the UE selects k=1, based on equation 3, the repeatable transmission start position of the preamble corresponding to SSB index 1 can be calculated as n start =13, 29, 45, ..... When UE is in n start = 13 when repeating the preamble transmission (after skipping PRACH opportunity index 17 according to the interval between opportunities calculated above ), the UE may perform repeated transmission of the preamble at PRACH opportunities 13 and 21 (1507).

[0239] According to method 1 or 2, since the base station can know the index of the SSB actually transmitted, the base station can estimate the multiple PRACH opportunities determined according to method 1 or 2 at which the preamble can be repeatedly transmitted based on the SSB index. Thereafter, the base station can receive the preamble transmitted by the UE, and identify the preambles transmitted and received by the UE at multiple estimated PRACH opportunities as the preambles transmitted repeatedly. The base station can identify the SSB index based on the UE's preamble transmission based on the received multiple preambles and the PRACH opportunity at which the preamble is transmitted, and transmit the downlink control information of the scheduling RAR, thereby performing a random access procedure.

[0240] According to the above method, the mMTC UE can repeatedly transmit the preamble corresponding to one SSB during random access to improve coverage. Coverage improvement is one of the main goals of mMTC services. According to the above method, since coverage can be increased according to repeated transmission of the preamble, mMTC service support can be effectively performed.

[0241] The above method is not limited to the repeated transmission method of the random access preamble code corresponding to one SSB in the mMTC service, and can be applied to new services other than mMTC.

[0242] <Example 3-1>

[0243] In the repeated random access preamble transmission method described in the third embodiment, when the number of repetitions of the random access preamble configured by the base station is configured to be greater than the number of PRACH transmission points corresponding to each SSB during a specific period that can transmit the preamble corresponding to a specific SSB, the repeated transmission of the preamble can be performed in the following method.

[0244] [Method 1]

[0245] When the number of repeated transmissions of the random access preamble code configured by the base station to the terminal is greater than the number of PRACH opportunities corresponding to each SSB during a specific period that can transmit the preamble code corresponding to the specific SSB, the specific period known in advance by the base station and the UE can be gradually increased by multiples of 2 until the number of PRACH opportunities corresponding to each SSB that can transmit the preamble code corresponding to the specific SSB is greater than the number of repeated transmissions. In this case, the base station can directly configure the multiples applied to the specific period to the UE, but because the base station and the UE can each identify the PRACH opportunity, it may not be necessary for the base station to notify the UE that the multiples of the specific period should be increased.

[0246] [Method 2]

[0247] When the number of repeated random access preamble transmissions configured by the base station to the terminal is greater than the number of PRACH opportunities corresponding to each SSB during a specific period during which the preamble corresponding to the specific SSB can be transmitted, the UE can repeat the transmission of the preamble as many times as the number of PRACH opportunities corresponding to each SSB during which the preamble can be transmitted. That is, the preamble may not be repeatedly transmitted as many times as the configured number of repeated transmissions. When the above-mentioned specific period or the number of repeated preamble transmissions is not configured at the same time (for example, when the specific period is configured by MIB and the number of repeated preamble transmissions is configured by SIB), the UE can receive the number of repeated transmissions of the preamble by the above method.

[0248] The above methods are not mutually exclusive, and a combination of one or more methods proposed above may be used to solve the problem.

[0249] <Fourth Embodiment>

[0250] In the fourth embodiment, a method for repeatedly transmitting a random access preamble corresponding to multiple SSBs is described. Specifically, in order for the UE to repeatedly transmit a random access preamble corresponding to multiple SSBs, the base station may first configure one or more sets including at least one of the SSBs actually transmitted. When the UE repeatedly transmits the preamble, if the UE and the base station do not transmit and receive in mutually agreed resources, it is impossible to obtain a gain from the repeated transmission. Therefore, in the case of transmitting a random access preamble corresponding to multiple SSBs, because the base station does not know how many SSBs the UE has selected and transmitted, by pre-configuring the set, the UE transmits the preamble corresponding to the SSB included in the specific set; therefore, the UE and the base station can transmit the preamble in mutually agreed resources.

[0251] That is, when transmitting a random access preamble corresponding to one SSB, if the terminal selects an SSB, the terminal can select a set of SSBs when simultaneously transmitting random access preambles corresponding to multiple SSBs. After the terminal selects a set of SSBs, the UE transmits a random access preamble corresponding to the SSB included in the set. In the following, a method is proposed for a UE and a base station to calculate the location of resources for repeated transmission of a random access preamble. Specifically, according to the present disclosure, the UE can calculate a resource (which may be a starting point among resources that can transmit a preamble) based on an existing configuration to transmit the number of times the preamble is repeatedly transmitted from the starting resource. Specifically, in a 5G mobile communication service, the resource location of the random access preamble corresponding to each SSB is determined according to the SSB selected by the terminal, and in the following, a method is proposed for calculating the resource location for repeated transmission of a preamble based on the resource location.

[0252] For example, the multiple SSBs constituting the above-mentioned set can be configured as follows.

[0253] - The SS-RSRP of the SSB can be configured as the SSB that exceeds the threshold based on an RSRP threshold. (This can be the same as the threshold configured for configuring the initial CE level in the first embodiment, or it can be a threshold when there are multiple thresholds.)

[0254] -Multiple SSBs can be configured as n SSBs with the highest SS-RSRP.

[0255] -The base station can configure multiple pre-configured SSBs for the UE.

[0256] In the mMTC service, the following method may be considered as a method in which a UE and a base station calculate resource locations for repeatedly transmitting a random access preamble corresponding to a plurality of SSBs.

[0257] [Method 1]

[0258] The terminal can continuously and repeatedly transmit the random access preamble code at the PRACH opportunity corresponding to the SSB included in the set selected by the UE. Specifically, the UE and the base station can identify the index of the resource capable of transmitting the preamble code based on the existing configuration. The UE can know the SIB information actually transmitted by the base station based on the received SIB information, and calculate the position of the PRACH opportunity at which the preamble code corresponding to each SSB can be transmitted according to Table 3 and the SIB configuration. If the number of PRACH opportunities corresponding to all actually transmitted SSBs is N (this can be the number of PRACH opportunities configured for a specific period), the terminal can start the index of the first PRACH opportunity from 0, and configure the index of the last PRACH opportunity at which the preamble code can be transmitted within the specific period to N-1. Here, the specific period can be explicitly configured by the SIB, can be indirectly calculated, or can follow a preconfigured time. An example of a specific period can follow the third embodiment.

[0259] When the terminal selects the set of the lth SSB, it can be based on the The i-th SSB with the lowest index among the SSB SSB is used to repeat the transmission of the first opportunity position n of the preamble start It can be expressed by equation 4.

[0260] [Equation 4]

[0261] For j = 0, 1, 2, ...

[0262] And i SSB =0, ..., N SSB -1

[0263] Indicates the number of repetitions of the configured random access preamble. Indicates the period of time during which the resources corresponding to the preamble code of one SSB can be repeatedly transmitted. SSB Indicates the number of SSBs actually transmitted by the base station.

[0264] The terminal may calculate an initial timing corresponding to the SSB included in the selected set, and repeatedly transmit the preamble code at consecutive timings corresponding to all included SSBs starting from the initial timing, the number of repetitions being the same as the number of configured repetition transmissions.

[0265] Fig.16 is a diagram showing an example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to a plurality of SSBs. Fig.16An example of the transmission resource location of the random access preamble corresponding to each SSB is shown. When the SCS of the 5G mobile communication system is 30kHz and the PRACH configuration index of Table 3 is configured as 104, the transmission resource of the preamble exists in all frames 1601, and in each frame, in subframes 1602 with indexes 1, 4, and 7, there are transmission resources for the preamble. Two time slots are configured for each subframe, and there are a total of six PRACH opportunities in each time slot 1603. Each PRACH opportunity 1604 is configured with two symbols.

[0266] In this case, assume that the base station transmits 4 SSBs (in this case, N SSB 4), the transmission resource position of the random access preamble code corresponding to each SSB can be sequentially configured in the order of, for example, frequency resources and time resources (1605). This configuration is similar to Fig.14 In this case, the UE may perform repeated transmission of the random access preamble in consecutive resources corresponding to multiple SSBs. For example, when the number of repeated transmissions is is configured as 4 (which is the sum of 2 repetitions of SSB1 and 2 repetitions of SSB 3) and the period When configured as 4, if the terminal selects a set including SSB indexes 1 and 3 and the number of SSBs included in the set is is 2, then based on equation 4, the initial timing at which the corresponding preamble can be repeatedly transmitted can be calculated as n start =9, 25, 41, .... When UE is in n start =9, the UE may repeatedly transmit (1606) the preamble corresponding to SSB indices 1 and 3 at PRACH opportunity indices 9, 11, 13, and 15. Similarly, when the UE starts to repeat preamble transmission at PRACH opportunity index 25, the UE may repeatedly transmit (1607) the preamble corresponding to SSB indices 1 and 3 at PRACH opportunity indices 25, 27, 29, and 31.

[0267] [Method 2]

[0268] The UE can repeatedly transmit the random access preamble at a specific interval in the PRACH opportunity corresponding to the SSB included in the set selected by the terminal. Specifically, the UE and the base station can compile the resource index capable of transmitting the preamble based on the existing configuration. The UE can know the SIB information actually transmitted by the base station based on the received SIB information, and calculate the position of the PRACH opportunity at which the preamble corresponding to each SSB can be transmitted according to Table 3 and the SIB configuration. When the number of PRACH opportunities corresponding to all actually transmitted SSBs is N (this can be the number of PRACH opportunities configured for a specific period), the UE can start the index of the first PRACH opportunity from 0, and configure the index of the last PRACH opportunity at which the preamble can be transmitted in the specific period to N-1. Here, the specific period can be explicitly configured through the SIB, can be indirectly calculated, or can follow a preconfigured time. The specific details follow the third embodiment.

[0269] When the UE selects the set of the lth SSB, it may be based on the The i-th SSB with the lowest index among the SSB SSB is used to repeat the transmission of the first opportunity position n of the preamble start It can be expressed by Equation 5.

[0270] [Equation 5]

[0271] For j = 0, 1, 2, ...

[0272] and And i SSB =0, ..., N SSB -1

[0273] Indicates the number of repetitions of the configured random access preamble. Indicates the period of time during which the resources corresponding to the preamble code of one SSB can be repeatedly transmitted. SSB Indicates the number of SSBs actually transmitted by the base station.

[0274] Referring to Equation 5, when the terminal selects an SSB set, it determines the minimum index i included in the set. SSB , and based on the configured and The interval between repeated transmissions can be configured as UE can randomly select a value from 0 to The UE can calculate the initial timing corresponding to the selected SSB set and start from the initial timing at intervals of The preamble is repeatedly transmitted at the timing corresponding to the SSB included in the selected set, the number of repetitions being as many as the number of configured repetition transmissions.

[0275] By this method, the probability of collision between terminals that may occur when multiple UEs simultaneously perform random access in mMTC services can be reduced. Specifically, when a preamble is repeatedly transmitted, a collision is likely to occur during multiple repeated transmissions; therefore, it may be important to reduce the probability of collision between UEs.

[0276] Fig.17 is a diagram showing another example of a method of calculating a repeatable transmission start position of a random access preamble corresponding to a plurality of SSBs. Fig.17 An example of the transmission resource location of the random access preamble corresponding to each SSB is shown. When the SCS applied to the 5G mobile communication system is 30kHz and the PRACH configuration index of Table 3 is configured as 104, the transmission resource of the preamble exists in all frames 1701, and in each frame, in subframes 1702 with indexes 1, 4, and 7, there are transmission resources for the preamble. Two time slots are configured for each subframe, and there are a total of six PRACH opportunities in each time slot 1703. Each PRACH opportunity 1704 is configured with two symbols. These configurations follow Table 4.

[0277] In this case, assuming that the base station transmits 4 SSBs, the transmission resource position of the random access preamble code corresponding to each SSB can be sequentially configured in the order of, for example, frequency resources and time resources (1705). This configuration is similar to Fig.14 In this case, the UE may perform repeated transmission of the random access preamble in consecutive resources corresponding to each SSB. For example, when the number of repeated transmissions is is configured as 4, period When k is configured as 4 and the UE selects k=1, if the UE selects a set including SSB indexes 1 and 3, based on equation 5, the reproducible transmission start position of the corresponding preamble code can be calculated as n start =13, 29, 45, .... When UE is in n start = 13, the terminal may perform repeated transmission of the preamble (1707) at PRACH opportunities 13 and 15 and 21 and 23 (after skipping the opportunities of indexes 17 and 19 according to the interval 8 between opportunities of the same SSB index calculated above). In this case, the preamble corresponding to SSB1 is transmitted at PRACH opportunities 13 and 21, and the preamble corresponding to SSB 3 is transmitted at PRACH opportunities 15 and 23.

[0278] In this embodiment and the third embodiment, when repeated random access preamble transmission is configured, if the number of repeated random access preamble transmissions configured by the base station is greater than the number of PRACH opportunities during which the preamble corresponding to a specific SSB can be transmitted during a specific period, the description of embodiment 3-1 can be applied.

[0279] According to method 1 or 2, since the base station can know the index of one or more SSBs constituting the set of SSBs that the UE can select, the base station can estimate the multiple PRACH opportunities at which the preamble determined according to method 1 or 2 can be repeatedly transmitted based on the one or more SSB indexes. Thereafter, the base station can receive the preamble transmitted by the terminal, and identify the preambles transmitted and received by the UE at multiple estimated PRACH opportunities as the preambles transmitted repeatedly. The base station can identify the SSB index for the UE-based preamble transmission based on the received multiple preambles and the PRACH opportunity for transmitting the preamble, and transmit the downlink control information for the scheduling RAR, thereby performing a random access process.

[0280] According to the above method, by simultaneously and repeatedly transmitting preamble codes corresponding to multiple SSBs in random access, the mMTC UE can improve coverage. Coverage improvement is one of the main goals of mMTC services. According to the above method, by allowing more preamble codes to be repeatedly transmitted within a specific time period, coverage can be improved; therefore, mMTC services can be effectively supported.

[0281] In the above method, the repeated transmission method of the random access preamble code corresponding to multiple SSBs in the mMTC service is not limited to the above example and can be applied to new services other than mMTC.

[0282] The above methods are not mutually exclusive, and a combination of one or more methods proposed above may be used to solve the problem.

[0283] Fig.18 is a block diagram of a terminal according to an embodiment of the present disclosure.

[0284] refer to Fig.18 , the terminal 1800 may include a transceiver 1810, a controller 1820, and a storage unit 1830. According to the effective system information block transmission and reception method in the 5G communication system corresponding to the above-mentioned embodiment, the transceiver 1810, the controller 1820, and the storage unit 1830 of the terminal 1800 can operate. However, the components of the UE 1800 according to the embodiment are not limited to the above-mentioned examples. According to another embodiment, the UE 1800 may include more or fewer components than the aforementioned components. In addition, in certain cases, the transceiver 1810, the controller 1820, and the storage unit 1830 may be implemented in the form of a single chip.

[0285] According to another embodiment, the transceiver 1810 may include a transmitter and a receiver. The transceiver 1810 may transmit signals to and receive signals from a base station. The signal may include control information and data. To this end, the transceiver 1810 may include an RF transmitter for up-converting and amplifying the frequency of the transmitted signal, and an RF receiver for low-noise amplifying the received signal and down-converting its frequency. In addition, the transceiver 1810 may receive a signal through a wireless channel, output the signal to the controller 1820, and transmit the signal output from the controller 1820 through the wireless channel.

[0286] The controller 1820 may control a series of processes in which the UE 1800 may operate according to the above-mentioned embodiments of the present disclosure. For example, according to an embodiment of the present disclosure, the controller 1820 may control the random access preamble transmission method differently, i.e., a resource and transmission configuration method for transmitting a random access preamble corresponding to an mMTC service, a method for determining a random access preamble transmission resource and a configuration of a UE corresponding thereto, a method for repeatedly transmitting a random access preamble corresponding to one SSB, and a method for repeatedly transmitting a random access preamble corresponding to multiple SSBs.

[0287] The storage unit 1830 may store control information or data such as a random access preamble transmission resource configuration included in a signal obtained from the UE 1800 , and has an area for storing data required for control by the controller 1820 and data generated when controlled by the controller 1820 .

[0288] Fig.19 is a block diagram of a base station according to an embodiment.

[0289] refer to Fig.19, the base station 1900 may include a transceiver 1910, a controller 1920, and a storage unit 1930. According to the effective random access preamble transmission method in the 5G communication system corresponding to the above-mentioned embodiment, the transceiver 1910, the controller 1920, and the storage unit 1930 of the base station 1900 may operate. However, the components of the base station 1900 according to the embodiment are not limited to the above-mentioned examples. According to another embodiment, the base station 1900 may include more or less components than the above-mentioned components. In addition, in certain cases, the transceiver 1910, the controller 1920, and the storage unit 1930 may be implemented in the form of a single chip. According to another embodiment, the transceiver 1910 may include a transmitter and a receiver. The transceiver 1910 may transmit a signal to a terminal and receive a signal from a terminal. The signal may include control information and data. To this end, the transceiver 1910 may include an RF transmitter for up-converting and amplifying the frequency of the transmitted signal, and an RF receiver for low-noise amplifying the received signal and down-converting its frequency. In addition, the transceiver 1910 may receive a signal through a wireless channel, output the signal to the controller 1920 , and transmit a signal output from the controller 1920 through the wireless channel.

[0290] The controller 1920 may control a series of processes so that the base station 1900 may operate according to the above-mentioned embodiments of the present disclosure. For example, according to an embodiment of the present disclosure, the controller 1920 may control the random access preamble transmission method differently, i.e., a resource and transmission configuration method for transmitting a random access preamble corresponding to an mMTC service, a method for determining a random access preamble transmission resource and a configuration of a terminal corresponding thereto, a method for repeatedly transmitting a random access preamble corresponding to one SSB, and a method for repeatedly transmitting a random access preamble corresponding to multiple SSBs.

[0291] The storage unit 1930 can store control information and data, such as the random access preamble code transmission resource configuration determined by the base station 1900 and the control information and data received from the UE, and has an area for storing data required for the control of the controller 1920 and data generated when controlled by the controller 1920.

[0292] The embodiments of the present disclosure disclosed in this specification and the accompanying drawings only present specific examples in order to easily explain the technical content of the present disclosure and help understand the present disclosure, and are not intended to limit the scope of the present disclosure. That is, it is obvious to a person skilled in the art that the present disclosure belongs to that other modifications based on the technical spirit of the present disclosure can be implemented. In addition, each of the above embodiments can be combined with each other for operation as needed.

Claims

1. A method performed by a user equipment UE in a wireless communication system, the method comprising: Based on a plurality of synchronization signal blocks SSB transmitted by the base station, measuring a reference signal received power RSRP value corresponding to each SSB; identifying a coverage enhancement CE level of the UE based on the measured RSRP value and at least one RSRP threshold; as well as sending one or more random access preambles to the base station based on the identified CE level, Wherein, in the case of using multiple RSRP thresholds, the CE level of the UE is identified based on the multiple RSRP thresholds and n maximum RSRP values ​​among the measured RSRP values, and Wherein, n is configured by the system information block SIB.

2. The method according to claim 1, wherein: The at least one RSRP threshold is sent through a system information block SIB sent by the base station, or is predetermined.

3. The method according to claim 1, wherein: When the number of the at least one RSRP threshold is one, the CE level is identified based on the number of measured RSRP values ​​exceeding the one RSRP threshold, or based on a ratio of the number of measured RSRP values ​​to the number of measured RSRP values ​​exceeding the one RSRP threshold.

4. The method according to claim 1, wherein: Sending one or more random access preambles includes: selecting at least one SSB as a basis for preamble transmission; and identifying one or more opportunities to send the random access preamble based on at least one of an index of the at least one SSB or the identified CE level, The one or more random access preamble codes are sent at the identified one or more occasions.

5. The method according to claim 4, in, One or more opportunities for sending the random access preamble are identified based on a first opportunity among a plurality of opportunities, the first opportunity being identified based on a minimum SSB index among the indexes of the at least one SSB, and The one or more opportunities for sending the random access preamble code include the first opportunity and one of a opportunity continuous with the first opportunity or a opportunity after a specific interval from the first opportunity.

6. The method according to claim 1, in, In case of using multiple RSRP thresholds, the CE level of the UE is identified by comparing the minimum value of the n maximum RSRP values ​​with the multiple RSRP thresholds, or comparing the average value of the n maximum RSRP values ​​with the multiple RSRP thresholds.

7. A user equipment UE (1800) in a wireless communication system, the UE comprising: Transceiver (1810); and A controller (1820), connected to the transceiver, and configured to: Based on a plurality of synchronization signal blocks SSB transmitted by the base station, a reference signal received power RSRP value corresponding to each SSB is measured, identifying a coverage enhancement CE level of the UE based on the measured RSRP value and at least one RSRP threshold, and sending one or more random access preambles to the base station based on the identified CE level, Wherein, in the case of using multiple RSRP thresholds, the CE level of the UE is identified based on the multiple RSRP thresholds and n maximum RSRP values ​​among the measured RSRP values, and Wherein, n is configured by the system information block SIB.

8. The UE according to claim 7, wherein: The at least one RSRP threshold is sent through a system information block SIB sent by the base station, or is predetermined.

9. The UE according to claim 7, wherein: When the number of the at least one RSRP threshold is one, the CE level is identified based on the number of measured RSRP values ​​exceeding the one RSRP threshold, or based on a ratio of the number of measured RSRP values ​​to the number of measured RSRP values ​​exceeding the one RSRP threshold.

10. The UE according to claim 7, wherein: In case of using multiple RSRP thresholds, the CE level is identified by comparing a minimum value of the n maximum RSRP values ​​with the multiple RSRP thresholds, or comparing an average value of the n maximum RSRP values ​​with the multiple RSRP thresholds.

11. The UE according to claim 7, wherein: The controller is further configured to select at least one SSB as a basis for sending the preamble, and identify one or more opportunities for sending the random access preamble based on at least one of an index of the at least one SSB or an identified CE level, and The one or more random access preambles are sent at the identified one or more occasions.

12. The UE according to claim 11, wherein: One or more occasions for sending the random access preamble code are identified based on a first occasion among multiple occasions, and the first occasion is identified based on a minimum SSB index among the index of the at least one SSB.

13. The UE according to claim 12, wherein: The one or more timings at which the random access preamble is transmitted include the first timing and one of a timing continuous with the first timing or a timing after a specific interval from the first timing.

14. A method performed by a base station in a wireless communication system, the method comprising: Sending a plurality of synchronization signal blocks SSB to a user equipment UE; receiving a random access preamble from the UE; identifying, based on a received random access preamble and a resource in which the random access preamble is received, a coverage enhancement CE level of the UE and an index of an SSB selected as a basis for transmission of the random access preamble; as well as performing a random access procedure based on the identified index of the SSB and the CE level of the UE, The CE level of the UE is based on a plurality of reference signal received power (RSRP) thresholds and n maximum RSRP values ​​among a plurality of RSRP values ​​corresponding to each of the plurality of SSBs, and Wherein, n is configured by the system information block SIB.

15. A base station (1900) in a wireless communication system, the base station comprising: Transceiver (1910); and A controller (1920), connected to the transceiver, and configured to: Sending a plurality of synchronization signal blocks SSB to a user equipment UE, receiving a random access preamble from the UE, identifying, based on a received random access preamble and a resource in which the random access preamble is received, an index of an SSB selected as a basis for transmission of a random access preamble and a coverage enhancement CE level of the UE, and performing a random access procedure based on the identified index of the SSB and the CE level of the UE, The CE level of the UE is based on a plurality of reference signal received power (RSRP) thresholds and n maximum RSRP values ​​among a plurality of RSRP values ​​corresponding to each of the plurality of SSBs, and Wherein, n is configured by the system information block SIB.

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