KR102547003B1 - Method and apparatus for random access in mobile communication system - Google Patents

Abstract

A random access method and apparatus in a mobile communication system are provided. The terminal obtains beam index information from the received synchronization signal block, and transmits a preamble message occupying a plurality of preamble resources including preamble resources corresponding to the beam index information to the base station. A random access resource includes a plurality of preamble resources, and the synchronization signal block is specific to one beam and corresponds to one preamble resource of the random access resources.

Description

Method and apparatus for random access in mobile communication system

The present invention relates to a random access method and apparatus in a mobile communication system.

As one of the next-generation communication technologies for processing rapidly increasing wireless data traffic, there is a beamforming technology. A beamforming-based mobile communication system uses a high frequency domain when transmitting a signal, and a base station and a terminal may perform beamforming to generate a large beamforming gain in a specific direction using a large number of antennas. In a beamforming-based mobile communication system, a beam sweeping operation is performed in which a signal is transmitted or a signal is received while changing a plurality of beams.

In a beamforming-based mobile communication system, a base station and a terminal operate several beams, and the base station transmits a reference signal for each beam so that the terminal can measure a channel state of each beam. For example, when the terminal informs the base station of the base station's optimal transmission beam index, the base station transmits data to the corresponding terminal using the optimal transmission beam.

On the other hand, in order to meet the growing demand for wireless data traffic after the commercialization of the 4G communication system, efforts are being made to develop an improved 5G communication system. In this next-generation communication system, a preamble format for random access is specified to support single-beam and multi-beam operations, and a preamble having the specified format is transmitted during a random access procedure.

However, in the next-generation communication system, a mechanism for informing a beam index is not defined. Therefore, when the base station does not know the beam correspondence, problems such as the terminal receiving multiple random access responses (RARs) occur, and the random access procedure becomes complicated.

An object to be solved by the present invention is to provide a method and apparatus for defining an association between a signal and a resource for random access in a mobile communication system using multiple beams and performing random access based thereon.

A method according to a feature of the present invention is a random access method in a multi-beam based mobile communication system, comprising: receiving, by a terminal, a synchronization signal block, and acquiring beam index information from the received synchronization signal block; and transmitting, by the terminal, a preamble message occupying a plurality of preamble resources including a preamble resource corresponding to the beam index information to a base station, wherein the random access resource includes a plurality of preamble resources, and the synchronization A signal block is specific to one beam and corresponds to one preamble resource of the random access resource.

The terminal may recognize a beam corresponding to the obtained beam index information as an optimal downlink transmission beam, and the step of transmitting the preamble message to the base station includes preamble resources corresponding to the beam index information and the beam index. The preamble message may be transmitted to the base station using a plurality of preamble resources including preamble resources located on left and right sides of the preamble resource corresponding to information.

Among the preamble resources through which the preamble message is transmitted, a beam specified for a preamble resource located in the middle may be recognized by the base station as an optimal downlink transmission beam for the terminal.

When beam grouping is performed, one burst including a plurality of synchronization signal blocks may correspond to one random access resource, and in the one burst, the synchronization signal blocks may correspond to different preamble resources in the random access resource. there is.

The obtaining of the beam index information may include: receiving, by the terminal, a plurality of synchronization signal blocks from the base station; selecting a synchronization signal block corresponding to a direction in which the terminal is located from among the plurality of received synchronization signal blocks; and obtaining beam index information by decoding the selected synchronization signal block.

The random access resource may include a plurality of preamble resources and one guard time (GT) resource, and in the step of transmitting the preamble message to the base station, an optimal beam recognized according to the beam index information If it is the first or last beam and the length of the preamble message is set, preamble resources are selected from the first preamble resource or the last preamble resource of the random access resource by the length of the preamble message, and the preamble message is generated using the selected preamble resources. can be sent

The method may include, after the step of transmitting the preamble message to the base station, the terminal receiving a RAR transmitted through a RAR resource selected through a random access response (RAR) selection process from the base station; Selecting one RAR from the plurality of RARs when the terminal receives a plurality of RARs; and recognizing, by the terminal, that the beam corresponding to the selected RAR is an optimal uplink reception beam.

The RAR resource may be specific to one beam, the RAR resource may correspond to one preamble resource of random access resources, and the step of selecting one RAR from the plurality of RARs may include When preamble messages each located in coverage and including a different preamble sequence are transmitted, one UE can select one RAR from among the plurality of RARs based on the preamble sequence used when transmitting the preamble message.

The RAR resource may be specific to one beam, the RAR resource may correspond to one preamble resource of random access resources, and the step of selecting one RAR from the plurality of RARs may include In the case of each being located in coverage and transmitting preamble messages including the same preamble sequence, one UE can select an RAR having the maximum received power from among the plurality of RARs.

The RAR selection process in the base station is performed based on a preamble message having the maximum received power among a plurality of preamble messages, and a beam corresponding to a preamble resource through which the preamble message having the maximum received power is transmitted is selected as an optimal beam. , RAR may be transmitted to the terminal through the RAR resource corresponding to the selected optimal beam.

A method according to another feature of the present invention is a random access method in a multi-beam based mobile communication system, comprising: transmitting, by a base station, synchronization signal blocks; Receiving, by the base station, a preamble message occupying a plurality of preamble resources from a terminal; and recognizing, by the base station, a beam specified in a synchronization signal block corresponding to a preamble resource through which the preamble message is transmitted as an optimal downlink transmission beam for the terminal, wherein the random access resource includes a plurality of preamble resource, the synchronization signal block is specific to one beam, and corresponds to one preamble resource of the random access resource.

In the recognizing, a beam specified in a synchronization signal block corresponding to a preamble resource located in the middle among preamble resources through which the preamble message is transmitted may be recognized as an optimal downlink transmission beam for the terminal.

The preamble message includes a plurality of preamble resources including a preamble resource corresponding to the beam index information obtained by the terminal from the synchronization signal block and preamble resources located on left and right positions based on the preamble resource corresponding to the beam index information. can be transmitted using

The method may include, after the recognizing step, selecting, by the base station, an optimal uplink reception beam for the terminal through beam sweeping; and transmitting, by the base station, RAR through a random access response (RAR) resource corresponding to the selected beam, wherein the RAR resource may be specific to one beam, and the RAR resource may be random It may correspond to one preamble resource of access resources.

In the selecting of the optimum uplink reception beam, the optimum uplink reception beam may be selected based on maximum reception power.

A method according to another feature of the present invention is a random access method in a multi-beam based mobile communication system, wherein a terminal transmits a preamble message to a base station and then monitors resources using a resource window of a fixed length. step; Receiving, by the terminal, an RAR transmitted through a RAR resource selected through a random access response (RAR) selection process from the base station according to the monitoring; Selecting one RAR from the plurality of RARs when the terminal receives a plurality of RARs; And recognizing, by the terminal, that a beam corresponding to the selected RAR is an optimal uplink reception beam, wherein the random access resource includes a plurality of preamble resources, and the RAR resource is specific to one beam, , The RAR resource corresponds to one preamble resource of random access resources.

In the step of selecting one RAR from the plurality of RARs, when a plurality of terminals are located in different coverages and each transmits a preamble message including a different preamble sequence, one terminal selects a preamble message from among the plurality of RARs. One RAR can be selected based on the preamble sequence used in transmission.

In the step of selecting one RAR from the plurality of RARs, when a plurality of terminals are located in different coverages and each transmits a preamble message including the same preamble sequence, one terminal receives the maximum from among the plurality of RARs. RAR with power can be selected.

The method may include, before the monitoring step, receiving a synchronization signal block and obtaining beam index information from the received synchronization signal block; and transmitting the preamble message to a base station by using a plurality of preamble resources including preamble resources corresponding to the beam index information, wherein the synchronization signal block corresponds to one beam or one beam group. It may be specified and may correspond to one preamble resource of the random access resource.

Transmitting the preamble message to the base station may include using a plurality of preamble resources including a preamble resource corresponding to the beam index information and preamble resources located on left and right positions based on the preamble resource corresponding to the beam index information. , may transmit the preamble message to the base station.

According to an embodiment of the present invention, an association between a signal and a resource for random access in a mobile communication system using multiple beams, that is, an association between a synchronization signal block, a preamble resource, and a random access response (RAR) A relationship can be defined, and random access can be performed based on the relationship.

In particular, a structure of a preamble message having a fixed length is defined for practical implementation for a plurality of terminals, and beam-specific RAR transmission and reception is performed. Accordingly, load balancing of PRACH (Physical Random Access CHannel) and RAR resources for a plurality of terminals is performed.

In addition, by a two-step RAR selection process in the base station and the terminal, the terminal can identify one correct RAR from multiple RARs.

In addition, as resource allocation is performed in the RA procedure based on the association between signals and resources for random access, transmission and reception through efficient resources is performed, complexity is reduced, and latency is reduced. .

In addition, the PRACH detection process in the base station is simplified, and detection complexity is reduced.

In addition, the terminal may recognize whether there is a beam correspondence relationship with the base station and double check.

1 is a diagram illustrating a multi-beam communication direction.
2 is an exemplary diagram illustrating an SS burst set.
3 is an exemplary diagram illustrating an RA preamble format.
4 is a diagram showing the structure of a PRACH resource according to an embodiment of the present invention.
5 is a diagram illustrating an association between SS block resources and PRACH resources according to the first embodiment of the present invention.
6 is a flowchart illustrating a random access method according to the first embodiment of the present invention.
7 is a diagram illustrating an association between SS block resources and PRACH resources in the case of beam grouping according to the second embodiment of the present invention.
8 is a flowchart illustrating a random access method according to a second embodiment of the present invention.
9 is a diagram illustrating an association between PRACH resources and RAR resources in the case of beam grouping according to the third embodiment of the present invention.
10 is a diagram illustrating an example of multiple beam directions according to an embodiment of the present invention.
11 is an exemplary diagram showing the structure of PRACH resources occupied by three terminals according to an embodiment of the present invention.
12 is a flowchart illustrating a random access method according to a third embodiment of the present invention.
13 is a structural diagram of a base station according to an embodiment of the present invention.
14 is a structural diagram of a terminal according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Throughout the specification, a terminal includes user equipment (UE), mobile station (MS), mobile terminal (MT), advanced mobile station (AMS), and high reliability mobile station. (high reliability mobile station, HR-MS), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), machine type communication device, MTC device), etc., and may include all or some functions of UE, MS, MT, AMS, HR-MS, SS, PSS, AT, etc.

In addition, the base station (BS) includes a node B, an evolved node B (eNB), a gNB, an advanced base station (ABS), and a high reliability base station. HR-BS), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR)-BS, repeater serving as a base station (relay station, RS), relay node (RN) that serves as a base station, advanced relay station (ARS) that serves as a base station, and high reliability relay station that serves as a base station , HR-RS), small base stations [femto base station (femto BS), home node B (home node B, HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station (macro BS), micro base station ( micro BS), etc.], and may refer to all or part of the functions of NB, eNB, gNB, ABS, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc. may also include

Expressions written in the singular in this specification may be interpreted in the singular or plural unless an explicit expression such as “one” or “single” is used.

A mobile communication system (wireless communication system) according to an embodiment of the present invention can be applied to various wireless communication networks. For example, the mobile communication system may be applied to a wireless communication network based on current radio access technology (RAT) or a 5G and later wireless communication network. 3GPP is developing a new RAT-based 5G standard that meets IMT-2020 requirements, and this new RAT is called NR (New Radio). In an embodiment of the present invention, a NR-based mobile communication system is taken as an example for convenience of description, but the embodiment of the present invention is not limited thereto and can be applied to various mobile communication systems.

One of the characteristics that NR differs from existing 3GPP systems such as Code Division Multiple Access (CDMA) or LTE is that it utilizes a wide range of frequency bands to increase transmission capacity. Waveform technologies for NR include Orthogonal Frequency Division Multiplexing (OFDM), Filtered OFDM (Filtered OFDM), Generalized Frequency Division Multiplexing (GFDM), Filter Bank Multi-Carrier (FBMC), and Universal Filtered Multi-Carrier (UFMC). ) are being discussed as candidate technologies. In the embodiment of the present invention, CP (Cyclic Prefix) based OFDM (CP-OFDM) is taken as an example as a waveform technology for convenience of explanation, but the embodiment of the present invention is not limited thereto and may use various waveform technologies. Meanwhile, the CP-OFDM technology may include CP-OFDM or spread spectrum OFDM (eg, DFT-spread OFDM) technology to which windowing and/or filtering is applied.

The frequency band of the NR system, for example, 700 MHz to 100 GHz, is a low frequency band (eg, ~ 6 GHz), a high frequency band (eg, 3 to 40 GHz), and a very high frequency band (eg, 30 to 100 GHz) It is divided into three areas of , and different OFDM parameters can be applied to each frequency band. OFDM parameters include subcarrier spacing, CP length, and OFDM symbol length, and may further include system bandwidth, sampling rate, FFT (Fast Fourier Transform) size, and the like.

Hereinafter, a random access method and apparatus according to an embodiment of the present invention will be described.

1 is a diagram illustrating a multi-beam communication direction.

As shown in FIG. 1, in a multi-beam communication environment, beams used in a base station are grouped, and each beam group may include N beams.

In order to detect an optimal transmission beam in such a multi-beam communication environment, beam sweeping is performed on transmission beams in various possible directions. Beam sweeping is performed based on analog beamforming, and accordingly, a synchronization signal (SS) burst set is designed to include multiple SS bursts in the time domain.

2 is an exemplary diagram illustrating an SS burst set.

As shown in FIG. 2, one SS burst set includes one or more SS bursts, and one SS burst includes at least one SS block. The structure shown in FIG. 2 may be regarded as an SS structure suitable for single-beam or multi-beam operation.

One SS burst may correspond to one beam group, and in one SS burst, SS blocks may be successively positioned to correspond to different beams within one beam group.

On the other hand, in the case of PRACH (Physical Random Access CHannel), which is a set of time-frequency resources or resource elements carrying a random access signal, a random access (RA) preamble for supporting single-beam and multi-beam operations The format is the same as in FIG. 3 .

3 is an exemplary diagram illustrating an RA preamble format.

As shown in FIG. 3, one RA preamble format includes Y RA preambles and a guard time (GT). One RA preamble includes a Cyclic Prefix (CP) and a preamble sequence. CP is used to cover time delay due to beam sweeping as well as multipath delay compensation. The preamble sequence includes one or Z symbols (aka Random Access CHannel (RACH) OFDM symbols). Here, Y and X represent positive integers. Y may be related to the number of transmitter (Tx) beams and receiver (Rx) beams in the base station. The Tx beam may also be referred to as a "transmit beam" and the Rx beam may be referred to as a "receive beam".

A base station uses multiple RA preambles for Rx beam sweeping. During an RA procedure, the UE transmits a message using one RA preamble format. A message using the RA preamble format may be named a preamble message or Msg.1.

The structure of the PRACH used in the NR system is suitable for single-beam and multi-beam operation, and is preferably designed to be suitable for both cases with and without beam correspondence.

When the beam correspondence relationship does not exist at the base station side, beam index information must be transmitted through information transmission and reception during initial access. However, in the case of a next-generation mobile communication system such as an NR system, a mechanism for notifying a beam index during initial access has not yet been defined.

In an embodiment of the present invention, an association between an SS block, a PRACH resource, and an RAR (RA response) is defined, and random access is performed based on the association.

PRACH resources represent time-frequency resources or resource elements (REs) allocated to PRACH. The expression of transmitting the PRACH is used in the same sense as transmitting a random access signal on or through the PRACH. A PRACH resource may also be referred to as a "random access resource".

Here, for convenience of explanation, it is assumed that, for example, the Tx beam and the Rx beam have the same direction (or pattern) in the base station. If the terminal does not acquire beam correspondence information, the base station performs Rx beam sweeping to find an optimal beam for a specific terminal, which is for beam calibration.

4 is a diagram showing the structure of a PRACH resource according to an embodiment of the present invention.

As shown in FIG. 4, a PRACH resource according to an embodiment of the present invention includes a plurality of RA preamble resources and a GT resource. Basically, when it is assumed that there are a total of N beams without beam grouping, the PRACH resource may have a structure as shown in FIG. 4(a). In order to perform Rx beam sweeping in the base station, as shown in (a) of FIG. 4, at least N RA preamble resources are required in PRACH.

5 is a diagram illustrating an association relationship between SS blocks and PRACH resources according to the first embodiment of the present invention.

In the first embodiment of the present invention, as shown in FIG. 5, one SS block may correspond to one RA preamble resource in PRACH resources. The SS block includes a primary SS (PSS), a secondary SS (SSS), and a physical broadcast channel (PBCH).

6 is a flowchart illustrating a random access method according to the first embodiment of the present invention.

As described above, in a state where one SS block has an association relationship corresponding to one RA preamble resource in a PRACH resource, as shown in the accompanying FIG. 6, the base station 1 has a plurality of downlink (DL) ) transmits SS blocks through the Tx beam (S100), and during initial access, the terminal 2 first detects the SS block (S110). Since the base station 1 transmits SS blocks through a plurality of downlink (DL) Tx beams, a terminal located in a specific direction can receive an SS block corresponding to its own direction. That is, the SS block transmitted by the base station is beam-specific. Also, the same SS block may be transmitted over multiple beams, and the SS block is beam group specific. The SS block carries DL beam index information of the base station.

The terminal 2 detects the SS block corresponding to its own direction and obtains DL beam index information of the base station based on this (S120). For example, when the terminal 2 receives the m-th SS block, the terminal 2 can obtain DL beam index information of the base station, that is, m, after decoding the m-th SS block. Here, m represents the DL beam index of the base station.

The terminal 2 recognizes that the beam corresponding to the acquired DL beam index m is the optimal beam, and reports information on the optimal beam, that is, the optimal DL Tx beam index m, to the base station during a subsequent RA procedure. Since the base station does not hold a beam correspondence relationship, the terminal 2 has one preamble format including a plurality of preambles for Rx beam sweeping in the base station through uplink (UL), that is, a preamble message ( Send Msg.1).

Here, it is assumed that the Tx multi-beam direction is the same as the Rx multi-beam direction in the base station.

The terminal 2 transmits a preamble message (Msg.1) occupying PRACH resources around the m-th RA preamble resource corresponding to the optimal DL beam for Rx beam calibration in the base station (S130). For example, based on the optimal DL Tx beam index m, a preamble message (Msg. 1) occupying the m-1 th RA preamble resource, the m th RA preamble resource, and the m + 1 th RA preamble resource in the PRACH resource is transmitted. do.

After receiving such a preamble message (Msg. 1) (S140), the base station 1 selects three RA preamble resources around the m-th RA preamble resource, so that the optimal DL Tx beam for the terminal 2 is m It can be recognized that it is the th beam (S150). That is, based on the m-1 th RA preamble resource in which the preamble message (Msg. 1) is transmitted, the m th RA preamble resource, and the m+1 th RA preamble resource, the m th beam corresponding to the m th RA preamble resource located in the middle It is recognized that this is the optimal DL Tx beam for the terminal 2.

7 is a diagram illustrating an association between SS block resources and PRACH resources in the case of beam grouping according to the second embodiment of the present invention.

As shown in the attached FIG. 7, in the second embodiment of the present invention, an association relationship between RA preamble resources of an SS burst set and a PRACH resource set is defined according to beam grouping. An SS burst set includes a number of SS bursts, and each SS burst includes sequentially located SS blocks. A PRACH resource set consists of a plurality of PRACH resources, and each PRACH resource may have a structure as shown in FIG. 4(a). Each SS burst corresponds to one PRACH resource. In one SS burst, SS blocks correspond to different RA preamble resources within one PRACH resource.

In the second embodiment of the present invention, the method according to the first embodiment of the present invention described above, that is, the mechanism without beam grouping may be equally applied.

8 is a flowchart illustrating a random access method according to a second embodiment of the present invention.

8, the base station 1 transmits SS blocks through a plurality of DL Tx beams (S200), and during initial access, first, the terminal 2 detects the SS blocks (S210). The SS block carries DL beam index information of the base station, where the DL beam index information is a beam group index that is a group index for one PRACH resource and a beam corresponding to an RA preamble resource index in the PRACH resource according to beam grouping. contains the index

The terminal 2 receives the SS block corresponding to the direction in which it is located, and acquires DL beam index information of the base station by decoding the SS block (S220). For example, when the terminal 2 receives the m-th SS block, the terminal 2 can obtain DL beam index information of the base station, that is, m and k, after decoding the m-th SS block. Here, m is the DL beam index of the base station, and k represents the index of the beam group including the corresponding beam index.

The terminal 2 recognizes that the beam corresponding to the acquired DL beam index information (m, k) is the optimal beam, and information on the optimal beam in the subsequent RA procedure, that is, the optimal DL Tx beam index information (m, k) can be reported to the base station. Here, it is assumed that the Tx multi-beam direction is the same as the Rx multi-beam direction in the base station.

The terminal 2 transmits a preamble message (Msg.1) occupying preamble resources around the m-th RA preamble resource of the k group corresponding to the optimal DL beam for Rx beam calibration in the base station (S230). For example, based on m and k, which are optimal DL Tx beam index information, a preamble format that occupies the m−1 th RA preamble resource, the m th RA preamble resource, and the m+1 th RA preamble resource in the k th PRACH resource group A preamble message (Msg. 1) is transmitted using

After the base station 1 receives this message (Msg. 1) (S240), by selecting three RA preamble resources around the m-th preamble resource in the k-th PRACH resource, optimal DL Tx for the terminal 2 It can be recognized that the beam corresponds to the m-th RA preamble resource in the k-th PRACH resource (S250).

In an embodiment of the present invention, the terminal may not need to feed back m (intra-group beam index) and k (beam group index). SS blocks can be transmitted simultaneously and in parallel over multiple beams. In this case, the terminal can only feed back the beam index in group k, and since the base station can generally know the direction of the terminal based on the direction of the UL Rx beam of the terminal, the base station can recognize both m and k. .

Meanwhile, due to reasons such as UE mobility or SS block detection error, there is a possibility that the optimal UL Rx beam for the UE is determined to be other than the m-th beam. After UL Rx beam sweeping, the base station may recognize that the optimal UL Rx beam for the UE is the m-1 th beam. In this case, the base station may feed back optimal UL Rx beam information to the terminal so that the terminal completes beam calibration and resets the beam correspondence relationship of the base station. Beam index feedback may be implemented using an association between RACH resources and RAR according to an embodiment of the present invention.

The length of the RA preamble format used by the UE to transmit the preamble message (Msg.1) may be a variable value, for example, a value of "3" may be used. As several RA preamble resources around the RA preamble resources corresponding to the optimal DL Tx beam of the UE are used, some tolerance for Tx/Rx beam correspondence error can be given. If the length of the RA preamble format is "3" and several RA preamble resources around resources corresponding to the optimal DL Tx beam of the UE are selected, the PRACH resource structure may be as shown in (b) of FIG. A PRACH resource structure as shown in (b) of FIG. 4 is used in consideration of resource occupation for the first beam and the Nth beam. That is, when the optimal DL Tx beam of the UE is the first beam or the last beam, since the Nth beam (last beam) is physically adjacent to the first beam, the UE uses the first 3 RA preamble resources or the last 3 RA preamble resources An occupied preamble message (Msg.1) is transmitted. Based on this, the PRACH resource structure can be configured as shown in (c) of FIG. 4 to be suitable for the length of the variable RA preamble format.

9 is a diagram illustrating an association between PRACH resources and RAR resources according to a third embodiment of the present invention.

As shown in FIG. 9, in the third embodiment of the present invention, a one-to-one mapping relationship as shown in FIG. 9 may be used to feed back UR Rx beam index information between a terminal and a base station.

In the third embodiment of the present invention, RAR resources are mapped one-to-one with PRACH resources. That is, as shown in FIG. 9, an RAR resource through which one RAR is transmitted may correspond to one RA preamble resource in a PRACH resource. In other words, RAR is beam specific.

10 is a diagram illustrating an example of multiple beam directions according to an embodiment of the present invention.

For example, as in FIG. 10, it is assumed that there are three terminals located in different beam coverages. Regardless of the beam correspondence in the base station, the three terminals may use different RA preamble resources to transmit the preamble message (Msg.1). Here, it is assumed that the length of the RA preamble format is "3" and the PRACH resources occupied by 3 UEs are as shown in FIG.

11 is an exemplary diagram showing the structure of PRACH resources occupied by three terminals according to an embodiment of the present invention.

As illustrated in FIG. 11, UEs UE1, UE2, and UE3 occupy RA preamble resources of a fixed length (eg, 3) in PRACH resources.

And, for example, the optimal DL Tx beam for UE1 is beam i-1, the optimal DL Tx beam for UE2 is beam i, and the optimal DL Tx beam for UE3 is The DL Tx beam of may be beam (i+1). However, since beam sweeping at the base station is essential for Rx beam calibration, the optimal UL Rx beam for these UEs (UE1 to UE3) may be different from their optimal DL Tx beam.

When receiving three RA preamble messages from the UEs UE1 to UE3, since the UE1 is located in an area where beams i-1 and beam i overlap, the base station receives the i-1th and a preamble message (Msg.1) from the UE (UE1) is detected on the i-th RA preamble resources. In addition, since the terminal UE2 is located in an area where three beams (i−1, i, and i+1) overlap, the base station transmits the UE on the i−1th, ith and i+1th RA preamble resources Detect the preamble message (Msg.1) from (UE2). In addition, since the terminal UE3 is located in an area where beam i and beam i+1 overlap, the base station receives a preamble message from the terminal UE3 on the i-th and i+1-th RA preamble resources ( Msg.1) is detected.

In an embodiment of the present invention, a two-step RAR selection process is performed as follows so that the base station can transmit one RAR for each terminal and the terminal can receive one RAR.

In the first RAR selection process, beam specific RAR selection is performed by the base station.

The base station selects a beam index based on the maximum received power and transmits RAR using a resource corresponding to the selected beam index. That is, the base station can receive a plurality of preamble messages from the terminals, and the base station selects a UL Rx beam index based on the preamble message having the maximum received power. In the RA preamble resource corresponding to the selected UL Rx beam index, one RAR is transmitted through the corresponding RAR resource.

In the second RAR selection process, beam-specific RAR selection is performed by the UE.

The UE may receive multiple RARs. When a plurality of RARs correspond to different preamble sequences, the UE immediately identifies an accurate RAR for the preamble message transmitted by the UE based on the preamble sequence used by the UE. When multiple RARs correspond to the same preamble sequence, the UE selects one RAR from among the multiple RARs based on maximum received power.

In an embodiment of the present invention, maximum received power is used as a condition for RAR selection, but the present invention is not limited thereto.

A specific two-step RAR selection process will be described using an example.

The base station selects the i-1th beam as the optimal UL Rx beam for the terminal UE1 through beam sweeping and selects the i-th beam as the optimal UL Rx beam for the terminal UE2 and UE3 Let's assume. In this case, the base station can select the optimal UL Rx beam for the terminal based on the maximum received power.

After the first RAR selection process in the base station, the base station transmits RAR feedback using RAR resources corresponding to RA preamble resources of PRACH resources based on the association between PRACH resources and RAR resources (see FIG. 9). Specifically, based on the optimal UL Rx beam index, the base station uses the i-1 th RAR resource corresponding to the i-1 th RA preamble resource to feedback transmit the RAR for the UE1, and the i th RA preamble resource A combined RAR (combined RAR) for the terminal UE2 and the terminal UE3 is feedback-transmitted using the i-th RAR resource corresponding to . In transmitting the combined RAR in the same resource, a method used in an existing mobile communication system (eg, a long term evolution (LTE) system) may be used.

Since different terminals transmit the preamble message (Msg.1) using different RA preamble resources, each terminal will monitor the RAR window. The RAR window covers the duration of a plurality of RAR resources corresponding to the used RA preamble resource, and may have a fixed length. For example, based on FIG. 11, UE1 monitors a RAR window that covers RAR resources (i-2, i-1, i), and UE2 monitors RAR resources (i-1, i). The RAR window covering i, i+1) is monitored, and the UE3 monitors the RAR window covering RAR resources (i, i+1, i+2). The UE1 receives the RAR from the i-1 th RAR resource and receives the combined RAR from the i th RAR resource. UE1 and UE2 receive RAR from the i-1th RAR resource and RAR combined from the i-th RAR resource, and UE3 receives RAR combined from the i-th RAR resource.

If all three terminals transmit the preamble message (Msg.1) using different preamble sequences, the terminals receive multiple RARs. In an embodiment of the present invention, through the second RAR selection process in the terminal, even if the terminal receives multiple RARs, it can select an accurate RAR corresponding to itself based on the preamble sequence used by the terminal from multiple RARs.

The UE1 may immediately recognize the RAR in the ith RAR resource as an accurate RAR based on the preamble sequence used by the UE1. Similarly, when the UE2 receives the RAR from the i-1th RAR resource and the combined RAR from the ith RAR resource, the UE2 determines that the combined RAR of the ith RAR resource is the correct RAR. can be recognized as being The UE3 may also recognize that the combined RAR of the ith RAR resource is the correct RAR.

Here, all terminals can know the optimal UL Rx beam in the base station based on the relation between the PRACH resource and the RAR resource according to the embodiment of the present invention. That is, it can be seen that the i-1th beam is the optimal UL Rx beam in the base station for the terminal UE1, and the i-th beam is the optimal UL Rx beam in the base station for the terminals UE2 and UE3.

If all three terminals transmit the message (Msg.1) using the same preamble sequence, the second RAR selection process performed at the terminal side may be performed based on a different criterion. For example, the UE may select one RAR from among multiple RARs based on the maximum RAR received power. Since there is a possibility that only the RAR transmitted in the correct beam arrives at the terminal with the maximum received power, the RAR can be selected based on the maximum RAR received power.

When the UE1 receives the RAR from the i-1 th RAR resource and the combined RAR from the i-th RAR resource, the RAR of the i-1 th RAR resource is possibly higher in power than the combined RAR of the i-1 th RAR resource. are likely to have Therefore, the UE1 may recognize the RAR of the i-1 th RAR resource having the maximum RAR reception power as an accurate RAR. Even in the case of the terminals UE2 and UE3, the combined RAR of the ith RAR resource having a comparable received power level is received, so that the correct RAR for the terminals UE2 and UE3 can be recognized.

12 is a flowchart illustrating a random access method according to a third embodiment of the present invention.

The base station 1 listens to a preamble message (Msg.1) from one or more potential terminals within coverage (S300), and when receiving a plurality of preamble messages from one terminal, the maximum received power Based on this, the optimal UL Rx beam for the UE is selected (S310, S320). That is, a beam corresponding to an RA preamble resource through which a preamble message having the maximum received power is transmitted is selected as an optimal UL Rx beam.

The base station 1 transmits RAR feedback using RAR resources corresponding to RA preamble resources of PRACH resources based on the optimal UL Rx beam selected based on the association between PRACH resources and RAR resources (see FIG. 9) ( S330). When one preamble message is received from one UE, a beam corresponding to an RA preamble resource through which the received preamble message is transmitted is selected as an optimal UL Rx beam.

The terminal 2 monitors the RAR window and receives the RAR from the base station (S340). When one RAR is received, the received RAR is selected (S350).

When multiple RARs are received (S360), if the UEs transmit preamble messages using different preamble sequences (S370), the UE 2 selects one RAR from the received multiple RARs based on the transmitted preamble sequences. Do (S380).

When multiple RARs are received, if the UEs transmit preamble messages using the same preamble sequence (S370), the UE 2 selects the RAR having the maximum received power from the multiple RARs (S390).

In these embodiments of the present invention, all terminals can know the optimal UL Rx beam in the base station based on the resource association relationship according to the embodiment of the present invention. That is, for the terminal UE1, the i-1 th beam corresponding to the selected RAR is the optimal UL Rx beam in the base station, and for the terminals UE2 and UE3, the i th beam corresponding to the selected RAR is the optimal UL Rx beam in the base station. It can be seen that the UL Rx beam of

Based on the association between the SS block, the RA preamble resource, and the beam specific RAR according to an embodiment of the present invention, the terminal may identify whether there is a beam correspondence relationship between the base station and double check. For example, if the terminal recognizes that the optimal DL Tx beam index (which can be known by SS block detection) is the same as the optimal UL Rx beam index (which can be known by RAR resource index detection), the base station's beam It can be seen that there is a corresponding relationship. When information on whether or not there is a beam correspondence between base stations is not broadcast, the terminal can know the beam correspondence between base stations through the method described above.

In addition, based on the correlation between the SS block, the RA preamble resource, and the beam-specific RAR according to an embodiment of the present invention, a case of incorrectly detecting system information can be known. For example, although beam correspondence information is transmitted to the terminals, some terminals may detect erroneous information. In this case, the terminal can double-check the beam correspondence relationship of the base station based on the association relationship according to the embodiment of the present invention, and the terminal reconfigures the beam correspondence relationship of the base station based on the method according to the embodiment of the present invention. can do.

In embodiments of the present invention, the SS block may carry DL beam index information of the base station, and the terminal detects the SS block corresponding to its own direction and obtains the DL beam index information of the base station based on the detected SS block. .

If there is only an SSB (SS block) index and beam index information is not clearly included in the SSB, the UE may detect the SSB index and feed back the detected SSB index to the base station through preamble resources used for Msg.1 transmission. there is. Since the base station knows which beam or beam group was used to transmit this particular SS block, the base station can know the beam index of the optimal DL Tx beam for the terminal.

In addition, when both the SSB index and the beam index information are clearly included in the SSB content, the terminal can detect the SS block and know the SSB index and the beam index information. The UE feeds back not only the SSB index but also the beam index (or one of them) to send Msg. 1 Optimum DL Tx beam information may be reported to the base station through preamble resources used for transmission.

In this way, the terminal can detect the SSB index with or without the additional beam index by detecting the SS block. Obtaining beam index information from the SS block in an embodiment of the present invention may include the two cases described above.

In an embodiment of the present invention, the beam index may be one beam index, and may be a beam group index when the same SS block is simultaneously transmitted through a beam group (multiple beams). In this case, the beam group may be regarded as equivalent to a wide single beam.

Also, when the same SS block is transmitted through multiple beams, the SS block is specific to the beam group. In this case, the terminal can find an optimal DL Tx beam group (DL wider beam) instead of a specific accurate (or narrow) beam. Also, in this case, DL beam calibration is not completely completed, and a procedure for finding an accurate DL Tx beam for the UE may be additionally performed.

13 is a structural diagram of a base station according to an embodiment of the present invention.

As shown in FIG. 13, the base station 1 according to an embodiment of the present invention includes a processor 110, a memory 120, and a transceiver 130. The processor 110 may be configured to implement the methods described above based on FIGS. 1 to 12 .

The memory 120 is connected to the processor 110 and stores various information related to the operation of the processor 110 . The memory 120 may store instructions to be executed by the processor 110 or may load and temporarily store instructions from a storage device (not shown). The processor 110 may execute instructions stored or loaded in the memory 120 . The processor 110 and the memory 120 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus.

The transceiver 130 is configured to transmit and receive signals, for example, to receive an RA preamble message and to transmit an RAR.

14 is a structural diagram of a terminal according to an embodiment of the present invention.

As shown in the accompanying FIG. 14 , the terminal 2 according to an embodiment of the present invention includes a processor 210, a memory 220, and a transceiver 230.

The processor 210 may be configured to implement the methods described above based on FIGS. 1 to 12 .

The memory 220 is connected to the processor 210 and stores various information related to the operation of the processor 210 . The memory 220 may store instructions to be executed by the processor 210 or may load and temporarily store instructions from a storage device (not shown).

The processor 210 may execute instructions stored or loaded in the memory 220 . The processor 210 and the memory 220 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus.

The transceiver 230 is configured to transmit and receive signals, for example, transmit an RA preamble message and receive an RAR.

Embodiments of the present invention are not implemented only through the devices and/or methods described above, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiments of the present invention, a recording medium on which the program is recorded, and the like. Also, this implementation can be easily implemented by an expert in the art to which the present invention belongs based on the description of the above-described embodiment.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of operators using the basic concept of the present invention defined in the following claims are also included in the scope of the present invention. that fall within the scope of the right.

Claims (20)

As a random access method in a multi-beam based mobile communication system,
Receiving, by a terminal, a synchronization signal block, and acquiring beam index information from the received synchronization signal block;
Checking, by the terminal, a first preamble resource corresponding to the beam index information;
Checking, by the terminal, a second preamble resource located before the first preamble resource in the time domain;
Checking, by the terminal, a third preamble resource located after the first preamble resource in the time domain; and
Transmitting a preamble message to a base station using the first preamble resource, the second preamble resource, and the third preamble resource
including,
The random access resource includes the first preamble resource, the second preamble resource, and the third preamble resource, the synchronization signal block is specific to one beam, and the synchronization signal block is one included in the random access resource. Corresponding to the first preamble resource, which is a preamble resource of, random access method. According to claim 1,
The terminal recognizes the beam corresponding to the obtained beam index information as an optimal downlink transmission beam,
random access method. According to claim 1,
A beam specified for the first preamble resource located in the middle among the first preamble resource, the second preamble resource, and the third preamble resource through which the preamble message is transmitted is optimized by the base station for the terminal. A random access method, perceived as a link transmit beam. According to claim 1,
When beam grouping is performed, one burst including a plurality of synchronization signal blocks corresponds to one random access resource, and in the one burst, the plurality of synchronization signal blocks correspond to different preamble resources in the random access resource. , random access method. According to claim 1,
Obtaining the beam index information
receiving, by the terminal, a plurality of synchronization signal blocks from the base station;
selecting a synchronization signal block corresponding to a direction in which the terminal is located from among the received plurality of synchronization signal blocks; and
Decoding the selected synchronization signal block to obtain beam index information
Including, random access method. According to claim 1,
The random access resource includes a plurality of preamble resources and one guard time (GT) resource,
In the step of transmitting the preamble message to the base station, when the optimal beam recognized according to the beam index information is the first or the last beam and the length of the preamble message is set, the random access resource is equal to the length of the preamble message. A random access method comprising: selecting preamble resources from a first preamble resource or a last preamble resource, and transmitting the preamble message using the selected preamble resources. According to claim 1,
After transmitting the preamble message to the base station,
Receiving, by the terminal, a RAR transmitted through a RAR resource selected through a random access response (RAR) selection process from the base station;
Selecting one RAR from the plurality of RARs when the terminal receives a plurality of RARs; and
Recognizing, by the terminal, that the beam corresponding to the selected RAR is an optimal uplink reception beam
Further comprising, random access method. According to claim 7,
The RAR resource is specific to one beam, the RAR resource corresponds to one preamble resource of the random access resource,
The step of selecting one RAR from the plurality of RARs,
When a plurality of terminals are located in different coverages and each transmits a preamble message including a different preamble sequence, one terminal selects one RAR from among the plurality of RARs based on the preamble sequence used when transmitting the preamble message. random access method. According to claim 7,
The RAR resource is specific to one beam, the RAR resource corresponds to one preamble resource of the random access resource,
The step of selecting one RAR from the plurality of RARs,
When a plurality of terminals are located in different coverages and each transmits a preamble message including the same preamble sequence, one terminal selects an RAR having the maximum received power from among the plurality of RARs. Random access method. According to claim 7,
The RAR selection process in the base station is performed based on a preamble message having the maximum received power among a plurality of preamble messages, and a beam corresponding to a preamble resource through which the preamble message having the maximum received power is transmitted is selected as an optimal beam. , RAR is transmitted to the terminal through the RAR resource corresponding to the selected optimal beam. As a random access method in a multi-beam based mobile communication system,
transmitting, by a base station, synchronization signal blocks;
The base station receives a preamble message from a terminal in a first preamble resource, a second preamble resource located before the first preamble resource in the time domain, and a third preamble resource located after the first preamble resource in the time domain step; and
The base station selects a beam specified for a synchronization signal block corresponding to the first preamble resource among the first preamble resource, the second preamble resource, and the third preamble resource in which the preamble message is received, as an optimum for the terminal. Recognizing as a downlink transmission beam of
Including,
The random access resource includes the first preamble resource, the second preamble resource, and the third preamble resource, the synchronization signal block is specific to one beam, and the synchronization signal block is one included in the random access resource. Corresponding to the first preamble resource, which is a preamble resource of, random access method. According to claim 11,
The recognizing may include selecting a beam specified for the synchronization signal block corresponding to the first preamble resource located in the middle among the first preamble resource, the second preamble resource, and the third preamble resource in which the preamble message is received. , which is recognized as an optimal downlink transmission beam for the terminal, a random access method. According to claim 11,
The preamble message includes the first preamble resource corresponding to the beam index information obtained by the terminal from the synchronization signal block, the second preamble resource located before the first preamble resource, and the first preamble resource located after the first preamble resource. A random access method transmitted using a third preamble resource. According to claim 11,
After the step of recognizing,
selecting, by the base station, an optimal uplink reception beam for the terminal through beam sweeping; and
Transmitting, by the base station, a RAR through a random access response (RAR) resource corresponding to the selected beam
Including more,
The RAR resource is specific to one beam, and the RAR resource corresponds to one preamble resource of random access resources. According to claim 14,
Wherein the selecting of the optimal uplink reception beam selects the optimal uplink reception beam based on maximum received power. As a random access method in a multi-beam based mobile communication system,
Monitoring, by a terminal, a resource using a resource window of a fixed length after transmitting a preamble message to the base station;
Receiving, by the terminal, an RAR transmitted through a RAR resource selected through a random access response (RAR) selection process from the base station according to the monitoring;
Selecting one RAR from the plurality of RARs when the terminal receives a plurality of RARs; and
Recognizing, by the terminal, that the beam corresponding to the selected RAR is an optimal uplink reception beam
Including,
The random access resource includes a plurality of preamble resources, the RAR resource is specific to one beam, and the RAR resource corresponds to one preamble resource of random access resources. According to claim 16,
The step of selecting one RAR from the plurality of RARs,
When a plurality of terminals are located in different coverages and each transmits a preamble message including a different preamble sequence, one terminal selects one RAR from among the plurality of RARs based on the preamble sequence used when transmitting the preamble message. random access method. According to claim 16,
The step of selecting one RAR from the plurality of RARs,
When a plurality of terminals are located in different coverages and each transmits a preamble message including the same preamble sequence, one terminal selects an RAR having the maximum received power from among the plurality of RARs. Random access method. According to claim 16,
Prior to the monitoring step,
Receiving a synchronization signal block and obtaining beam index information from the received synchronization signal block; and
Transmitting the preamble message to a base station using a plurality of preamble resources including a preamble resource corresponding to the beam index information
Including more,
The synchronization signal block is specific to one beam or one beam group and corresponds to one preamble resource of the random access resources. According to claim 19,
The transmitting of the preamble message to the base station may include a plurality of preamble resources including a preamble resource corresponding to the beam index information and preamble resources located before and after the preamble resource corresponding to the beam index information in the time domain. Random access method for transmitting the preamble message to the base station by using.

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