阅读说明：本技术 在终端与基站之间建立连接的方法和装置 (Method and device for establishing connection between terminal and base station ) 是由 柳承甫 金东玟 全南烈 郑导泳 崔宝庚 于 2018-05-09 设计创作，主要内容包括：根据本公开的实施例,终端可以在到基站的RRC层连接期间存储从RA响应消息获得的时间校正值,从所述基站接收包括分配给所述终端的上行链路资源的上行链路资源分配消息,以及在到所述基站的所述RRC层连接被释放后并且当确定进行到所述基站的RRC层连接时,在尚未发送RA前导码消息时,基于所存储的时间校正值和所分配的上行链路资源来建立到所述基站的所述RRC层连接。(According to an embodiment of the present disclosure, a terminal may store a time correction value obtained from an RA response message during an RRC layer connection to a base station, receive an uplink resource allocation message including uplink resources allocated to the terminal from the base station, and establish the RRC layer connection to the base station based on the stored time correction value and the allocated uplink resources when an RA preamble message has not been transmitted after the RRC layer connection to the base station is released and when it is determined to proceed with the RRC layer connection to the base station.)

1. A Radio Resource Control (RRC) layer connection method in a terminal of a wireless communication system, the method comprising:

storing a timing advance value obtained based on a Random Access (RA) response message when an RRC layer connection with a base station is established;

Receiving, from the base station, an uplink resource allocation message indicating uplink resources allocated to the terminal after releasing the RRC layer connection with the base station; and

If it is determined that the RRC layer connection is to be made with the base station, establishing an RRC connection with the base station by transmitting an RRC layer connection request message based on the stored timing advance value and the allocated uplink resource when the RA preamble message has not been transmitted.

2. The method of claim 1, the method further comprising:

Receiving an RRC connection release message from the base station,

Wherein the RRC connection release message includes RACHless operation information.

3. The method of claim 1, the method further comprising:

Transmitting an RA preamble message to a base station of a target cell as a handover target while communicating with a base station of a source cell;

Storing a timing advance value included in the RA response message from the base station of the target cell;

Receiving an uplink resource allocation message including uplink resources allocated to the terminal from the base station of the target cell; and

If handover to the base station of the target cell is determined, establishing an RRC layer connection with the base station of the target cell by transmitting an RRC layer reconfiguration request message based on the stored timing advance value and the uplink resource allocated by the base station of the target cell when an RA preamble message has not been transmitted.

4. The method of claim 3, the method further comprising:

Receiving information of RACHless operation of the base station of the target cell from the base station of the source cell while communicating with the base station of the source cell,

Wherein the information of the RACHless operation is included in the RRC layer reconfiguration request message, and the handover to the base station of the target cell is determined based on satisfying a handover condition previously stored in the terminal and receiving an RRC connection reconfiguration message requesting the handover from the base station of the source cell to the base station of the target cell.

5. The method of claim 1, the method further comprising:

calculating a timing advance value of a target cell based on a timing advance value of a source cell, frame timing difference information between base stations, and time synchronization information between the base stations while the terminal communicates with the base station of the source cell, and storing the timing advance value of the target cell;

Receiving an uplink resource allocation message indicating uplink resources allocated to the terminal from a base station of the target cell; and

Based on determining to handover to the base station of the target cell, establishing an RRC layer connection with the base station of the target cell by sending an RRC layer reconfiguration request message using the stored timing advance value and the uplink resources allocated by the base station of the target cell when an RA preamble message has not been sent.

6. The method of claim 5, the method further comprising:

Receiving RACHless operation information of the base station of the target cell from the base station of the source cell while communicating with the base station of the source cell,

Wherein it is determined to perform handover to the base station of the target cell based on satisfying a handover condition stored in advance in the terminal and receiving an RRC connection reconfiguration message requesting handover from the source cell base station to the target cell base station.

7. A method of Radio Resource Control (RRC) layer connection in a base station of a wireless communication system, the method comprising:

Sending an RRC connection release message for releasing the RRC layer connection established with the terminal to the terminal, wherein the RRC connection release message comprises RACHless operation information;

Transmitting an uplink resource allocation message to the terminal after releasing the RRC layer connection established with the terminal, the uplink resource allocation message indicating uplink resources allocated to the terminal; and

Reconfiguring an RRC layer connection with the terminal, and transmitting an RRC connection configuration message to the terminal based on receiving an RRC connection request message when a Random Access (RA) preamble message has not been received from the terminal.

8. The method of claim 7, the method further comprising:

Receiving an RA preamble message including preemptive RACH access attempt information from the terminal;

Transmitting an RA response message including a timing advance value to the terminal in response to the RA preamble message;

Transmitting an uplink resource allocation message including uplink resources allocated to the terminal in response to the RA preamble message including the preemptive RACH access attempt information; and

Establishing an RRC layer connection with the terminal based on the RRC connection reestablishment request message or the RRC connection reconfiguration complete message received from the terminal,

Wherein the uplink resource allocation message including the uplink resource allocated to the terminal is periodically transmitted until the RRC connection re-establishment request message or the RRC connection reconfiguration complete message is received from the terminal.

9. A terminal for establishing an RRC layer connection with a base station, the terminal comprising:

A communication circuit configured to communicate with the base station;

a storage unit configured to store a timing advance value obtained from a Random Access (RA) response message when an RRC layer connection with the base station is established;

A controller configured to control the communication circuit to: receiving, from the base station, an uplink resource allocation message including uplink resources allocated to the terminal after releasing the RRC layer connection with the base station; and based on determining to make an RRC layer connection with the base station, establishing an RRC layer connection with the base station by transmitting an RRC layer connection request message using the stored timing advance value and the allocated uplink resource when an RA preamble message has not been transmitted.

10. The terminal of claim 9, wherein the controller is configured to control to detect RACHless operation information included in an RRC connection release message received by the communication circuit based on the RRC layer connection with the base station being released, and to control the communication circuit to receive an uplink resource allocation message periodically transmitted by the base station based on the RACHless operation information.

11. The terminal according to claim 9, wherein the storage unit is further configured to store a timing advance value included in an RA response message received from a base station of a target cell that is a handover target based on an RA preamble message transmitted to the base station of the target cell while the terminal is communicating with the base station of a source cell, and the controller is configured to control the communication circuit to: receiving an uplink resource allocation message indicating uplink resources allocated to the terminal from the base station of the target cell; and based on determining to handover to the base station of the target cell, establishing an RRC layer connection with the base station of the target cell by sending an RRC layer reconfiguration request message using the stored timing advance value and the uplink resource allocated by the base station of the target cell when no RA preamble message has been sent.

12. the terminal according to claim 11, wherein the controller is configured to control to receive RACHless operation information of the base station of the target cell from the base station of the source cell while communicating with the base station of the source cell, and

Wherein the RRC layer reconfiguration request message includes the RACHless operation information; and determining to perform handover to the base station of the target cell based on satisfying a handover condition stored in advance in the terminal and receiving an RRC connection reconfiguration message requesting handover from the base station of the source cell to the base station of the target cell.

13. The terminal according to claim 9, wherein the storage unit is configured to store a timing advance value of a source cell calculated based on a timing advance value of the source cell, frame timing difference information between base stations, and time synchronization information between the base stations when the terminal establishes an RRC layer connection with the base station, and the controller is configured to: after releasing the RRC layer connection established with the base station, control the communication circuitry to receive an uplink resource allocation message indicating uplink resources allocated to the terminal, based on the determination to establish the RRC layer connection with the base station, establishing an RRC layer connection by transmitting an RRC connection request message to the base station using the stored timing advance value and the allocated uplink resource when the RA preamble message has not been transmitted, receiving RACH-less operation information associated with the base station of the target cell from the base station of the source cell while the base station is in communication with the base station of the source cell, and said controller is configured to store said RACHless operation information in said memory, wherein the handover to the base station of the target cell is determined based on handover conditions stored in advance in the memory being satisfied.

14. a base station for establishing an RRC layer connection with a terminal, the base station comprising:

A communication circuit configured to communicate with the terminal; and

A controller configured to control the communication circuit to: sending an RRC connection release message for releasing the RRC layer connection established with the terminal to the terminal, wherein the RRC connection release message comprises RACHless operation information; after releasing the RRC layer connection established with the terminal, transmitting an uplink resource allocation message to the terminal, the uplink resource allocation message including uplink resources allocated to the terminal; and reconfiguring an RRC layer connection with the terminal to transmit an RRC connection configuration message to the terminal based on receiving an RRC connection request message from the terminal when a Random Access (RA) preamble message has not been received from the terminal.

15. The base station of claim 14, wherein the controller is configured to control the communication circuitry to: receiving an RA preamble message including preemptive RACH access attempt information from the terminal; transmitting an RA response message including a timing advance value to the terminal in response to the RA preamble message; transmitting an uplink resource allocation message indicating uplink resources allocated to the terminal in response to an RA preamble message including the preemptive RACH access attempt information; establishing an RRC layer connection with the terminal based on receiving an RRC connection re-establishment request message or an RRC connection reconfiguration complete message from the terminal,

wherein the uplink resource allocation message indicating the uplink resource allocated to the terminal is periodically transmitted until the RRC connection re-establishment request message or the RRC connection reconfiguration complete message is received from the terminal.

Technical Field

The present disclosure relates to a terminal, a base station, and a control method thereof for reducing a delay when establishing an RRC layer connection between the terminal and the base station.

Background

In order to meet the increasing demand for wireless data services since the deployment of 4G communication systems, efforts have been made to develop improved 5G or quasi-5G communication systems. Therefore, the 5G or quasi-5G communication system is also referred to as a "super 4G network" or a "post-LTE system".

the telecommunications industry organization, including the International Telecommunications Union (ITU) and the 3 rd generation partnership project (3GPP), proposes three main use cases for 5G communication systems: enhanced mobile broadband (eMBB), ultra-reliable low latency communication (URLLC), and large-scale machine type communication (mtc).

It is being considered to implement a 5G communication system in a high frequency (millimeter wave) band (for example, 60GHz band) in order to achieve a higher data rate. In order to reduce path loss of radio waves and increase transmission distance, beamforming, massive Multiple Input Multiple Output (MIMO), full-dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large antenna technology are discussed for the 5G communication system.

In addition, in the 5G communication system, development of improvement of a system network is performed based on advanced small cells, cloud Radio Access Network (RAN), ultra dense network, device-to-device (D2D) communication, wireless backhaul, mobile network, cooperative communication, coordinated multipoint (CoMP), reception side interference cancellation, and the like.

In 5G systems, hybrid FSK and QAM modulation (FQAM) and Sliding Window Superposition Coding (SWSC) have been developed as Advanced Coding Modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and Sparse Code Multiple Access (SCMA) as advanced access techniques.

in a 5G communication system, a Random Access Channel (RACH) procedure is defined for a terminal to communicate with a base station through a network.

In the RACH procedure, the terminal may perform a Radio Resource Control (RRC) layer connection establishment procedure with the base station. Through the RRC connection layer connection, the terminal can control logical channels, transport channels, and physical channels related to radio bearer establishment, re-establishment, and release operations of the base station or the network.

Disclosure of Invention

technical problem

the terminal must perform a RACH procedure to access a certain network.

for example, if the terminal receives a Random Access (RA) response message in reply to an RA preamble message transmitted to the base station according to the RACH procedure, the terminal may perform an RRC layer connection procedure with the base station.

In this case, the initial RACH procedure of transmitting the RA preamble message and receiving the RA response message may generate a delay before the RRC layer connection.

For example, each time the terminal performs an idle to active (IdleToActive) state transition procedure or a handover procedure, the initial RACH procedure delay has to be increased.

The present disclosure provides methods and apparatus for reducing latency before an RRC layer connection between a terminal and a base station.

The present disclosure provides a method and apparatus for quickly establishing a connection between a terminal and a base station.

The object of the present disclosure is not limited to the above object, and other objects not described herein will be clearly understood by those skilled in the art from the following description.

Means for solving the problems

According to an embodiment of the present disclosure, a Radio Resource Control (RRC) layer connection method for a terminal to establish an RRC layer connection with a base station in a wireless communication system includes: the method includes storing a timing advance value obtained from a Random Access (RA) response message when establishing an RRC layer connection with the base station, receiving an uplink resource allocation message indicating uplink resources allocated to the terminal from the base station after releasing the RRC connection with the base station, and establishing an RRC connection with the base station by transmitting an RRC layer connection request message using the stored timing advance value and the allocated uplink resources when an RA preamble message has not been transmitted based on a decision to be RRC layer connected with the base station.

According to an embodiment of the present disclosure, a Radio Resource Control (RRC) layer connection method in which a base station establishes an RRC layer connection with a terminal in a wireless communication system includes: transmitting an RRC connection release message for releasing an RRC layer connection established with the terminal to the terminal, the RRC connection release message including RACHless (non-RACH) operation information; transmitting an uplink resource allocation message to the terminal after releasing the RRC layer connection established with the terminal, the uplink resource allocation message indicating uplink resources allocated to the terminal; and reconfiguring an RRC layer connection with the terminal, and transmitting an RRC connection configuration message to the terminal based on receiving an RRC connection request message from the terminal in case that a Random Access (RA) preamble message is not received from the terminal.

According to an embodiment of the present disclosure, a Radio Resource Control (RRC) layer connection method for a terminal to establish an RRC layer connection with a base station in a wireless communication system includes: transmitting an RA preamble message to a base station of a target cell as a handover target in handover of a terminal while communicating with a base station of a source cell; storing a timing advance value included in an RA response message when the RA response message is received from the base station of the target cell; receiving an uplink resource allocation message indicating uplink resources allocated to the terminal from the base station of the target cell; based on determining handover to the base station of the target cell, establishing an RRC layer connection with the base station of the target cell by sending an RRC layer reconfiguration request message using the stored timing advance value and the uplink resources allocated by the base station of the target cell when an RA preamble message has not been sent.

According to an embodiment of the present disclosure, a Radio Resource Control (RRC) layer connection method in which a terminal establishes an RRC layer connection with a base station in a wireless communication system includes: when the terminal communicates with a base station of a source cell, calculating a timing advance value of a target cell based on the timing advance value of the source cell, frame timing difference information between base stations and time synchronization information between the base stations; receiving an uplink resource allocation message indicating uplink resources allocated to the terminal from a base station of the target cell; and based on determining handover to the base station of the target cell, establishing an RRC layer connection with the base station of the target cell by sending an RRC layer reconfiguration request message using the stored timing advance value and the uplink resources allocated by the base station of the target cell when an RA preamble message has not been sent.

According to an embodiment of the present disclosure, a Radio Resource Control (RRC) layer connection method in which a base station establishes an RRC layer connection with a terminal in a wireless communication system includes: receiving an RA preamble message including preemptive RACH access attempt information from the terminal; transmitting an RA response message including a timing advance value to the terminal in response to the RA preamble message; transmitting an uplink resource allocation message indicating uplink resources allocated to the terminal in response to the RA preamble message including the preemptive RACH access attempt information; and establishing an RRC layer connection with the terminal based on an RRC connection re-establishment request message or an RRC connection reconfiguration complete message received from the terminal, wherein the uplink resource allocation message indicating the uplink resource allocated to the terminal is periodically transmitted before the RRC connection re-establishment request message or the RRC connection reconfiguration complete message is received from the terminal.

According to an embodiment of the present disclosure, a terminal for establishing an RRC layer connection with a base station includes: communication circuitry configured to communicate with the base station; a storage unit configured to store a timing advance value obtained from a Random Access (RA) response message at the establishment of an RRC layer connection with the base station; and a controller configured to: after releasing the RRC layer connection with the base station, control the communication circuitry to receive an uplink resource allocation message from the base station indicating uplink resources allocated to the terminal, and based on a decision to make an RRC layer connection with the base station, establish an RRC connection with the base station by transmitting an RRC layer connection request message using the stored timing advance value and the allocated uplink resources when no RA preamble message has been transmitted.

According to an embodiment of the present disclosure, a terminal for establishing an RRC layer connection with a base station includes: a communication circuit configured to communicate with the base station; a storage unit configured to store a timing advance value calculated based on a timing advance value of a source cell, frame timing difference information between base stations; and a controller configured to control the communication circuit to receive, after releasing the RRC layer connection with the base station, an uplink resource allocation message indicating an uplink resource allocated to the terminal from the base station, and to establish an RRC connection with the base station by transmitting an RRC layer connection request message using the stored timing advance value and the allocated uplink resource when an RA preamble message has not been transmitted based on a decision to make an RRC layer connection with the base station.

According to an embodiment of the present disclosure, a base station for establishing an RRC layer connection with a terminal includes: a communication circuit configured to communicate with the terminal; and a controller configured to control the communication circuit to: sending an RRC connection release message for releasing the RRC layer connection established with the terminal to the terminal, wherein the RRC connection release message comprises RACHless operation information; transmitting an uplink resource allocation message to the terminal after releasing the RRC layer connection established with the terminal, the uplink resource allocation message indicating uplink resources allocated to the terminal; and reconfiguring an RRC layer connection with the terminal to transmit an RRC connection configuration message to the terminal based on receiving an RRC connection request message from the terminal when a Random Access (RA) preamble message has not been received from the terminal.

According to an embodiment of the present disclosure, a terminal for establishing an RRC layer connection with a base station includes: a communication circuit configured to communicate with the base station; a storage unit configured to: storing a timing advance value of a target cell obtained from a Random Access (RA) response message transmitted by a base station of the target cell in response to an RA preamble message transmitted to the base station of the target cell that is a handover target, when the terminal communicates with the base station of a source cell; and a controller configured to control the communication circuit to: receiving an uplink resource allocation message from the base station of the target cell indicating uplink resources allocated to the terminal, and transmitting an RRC layer reconfiguration request message to a target base station of the target cell using the stored timing advance value and the uplink resources allocated by the base station of the target cell to establish an RRC layer connection, when an RA preamble message has not been transmitted, based on a handover decision of the base station to the target cell.

According to an embodiment of the present disclosure, a terminal for establishing an RRC layer connection with a base station includes: a communication circuit configured to communicate with the base station; a storage unit configured to store a timing advance value of the calculation target cell based on a timing advance value of a source cell, frame timing difference information between base stations, and time synchronization information between the base stations when the terminal communicates with a base station of the source cell; and a controller configured to control the communication circuitry to receive an uplink resource allocation message from a base station of the target cell indicating uplink resources allocated to the terminal; and based on a handover decision of the base station to the target cell, sending an RRC layer reconfiguration request message to the base station of the target cell using the stored timing advance value and the uplink resources allocated by the base station of the target cell to establish an RRC layer connection when no RA preamble message has been sent.

According to the embodiment of the disclosure, the base station for establishing the foreign RRC layer connection with the terminal comprises: a communication circuit configured to communicate with the terminal; and a controller configured to control the communication circuit to: receiving an RA preamble message including preemptive RACH access attempt information from the terminal; transmitting an RA response message including a timing advance value to the terminal in response to the RA preamble message; receiving RACHless indication information including RACHless operation information from the terminal; transmitting an uplink resource allocation message indicating uplink resources allocated to the terminal in response to an RA preamble message including the preemptive RACH access attempt information; establishing an RRC layer connection with the terminal upon receiving an RRC connection reestablishment request message or an RRC connection reconfiguration complete message from the terminal.

The invention has the advantages of

The disclosed embodiments are advantageous in significantly reducing the latency of RRC connection between a terminal and a base station by omitting an initial RACH procedure, even when the terminal performs an idle to active (idle active) state transition procedure or when the terminal or the base station performs a handover procedure.

that is, the time delay of the RRC layer connection between the terminal and the base station can be significantly reduced by omitting the initial RACH procedure as follows: so that the terminal obtains the timing advance value and the base station sends the uplink resource allocation message in advance.

Omitting the initial RACH procedure can significantly reduce the latency of the RRC layer connection between the terminal and the base station, especially when the beam mapping information is transmitted together with the RA preamble causing a certain degree of time delay in a beam-based communication mode operating in a high frequency band.

Other effects may be explicitly or implicitly disclosed in the description of the embodiments of the present disclosure. That is, in the following description of the embodiments of the present disclosure, various effects expected from the present disclosure will become clear.

drawings

Fig. 1 is a signal flow diagram illustrating a RACH procedure between a base station and a UE;

Fig. 2 is a view illustrating a sync symbol index for transmitting strongest sync beam information in a RACH procedure according to an embodiment;

fig. 3-5 are signal flow diagrams illustrating a process for reducing latency of an RRC layer connection between a terminal and a base station according to an embodiment of the present disclosure;

Fig. 6 is a flowchart illustrating a procedure in which a UE obtains a TA value from a candidate target cell and updates the TA value according to an embodiment of the present disclosure;

Fig. 7a, 7b, 8a to 8d, and 9 are views illustrating message syntax defined for reducing connection latency between a UE and a base station according to an embodiment of the present disclosure;

Fig. 10 is a block diagram illustrating a configuration of a UE according to an embodiment of the present disclosure;

Fig. 11 is a block diagram showing a configuration of a base station according to an embodiment of the present disclosure;

Fig. 12 to 14 are flowcharts illustrating a procedure in which a terminal establishes an RRC layer connection with a base station according to an embodiment of the present disclosure; and

fig. 15 to 17 are flowcharts illustrating a procedure in which a base station establishes an RRC layer connection with a terminal according to an embodiment of the present disclosure.

Detailed Description

the operational principle of the present disclosure will be described in detail with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to the same or like parts. A detailed description of known functions and configurations incorporated herein may be omitted to avoid obscuring the subject matter of the present disclosure. Further, the following terms are defined in consideration of functions in the present disclosure, and they may be changed according to intention and use of a user or an operator, and the like. Therefore, terms should be defined based on the entire contents of the present specification.

As used herein, the singular forms also are intended to include the plural forms as well, unless the context clearly indicates otherwise.

As used herein, terms such as "first" and "second," etc., are used to describe various components. It will be apparent, however, that these components should not be limited by these terms. These terms are only used to distinguish one component from another component. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element. The expression "and/or" is to be taken as a specific disclosure of each and any combination of the enumerated items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms also are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," if used in this specification, specify the presence of stated features, integers, steps, operations, components, elements, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, elements, and/or groups thereof.

The phrases "associated with," and "associated therewith," and derivatives thereof, may mean including, contained within, interconnected with, containing, contained within, connected to or with … …, coupled to or with … …, in communication with … …, cooperating with … …, interleaved, juxtaposed, adjacent, constrained or having, having the characteristics of something, and the like.

When it is described that one element is "connected to" or "coupled to" another element (functionally or communicatively) it may be meant to include not only the case of "directly connecting" but also the case of "indirectly connecting" by interposing another device therebetween.

Unless otherwise defined herein, all terms (including technical and scientific terms) used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Before proceeding with the following detailed description of the present disclosure, it may be advantageous to set forth definitions of certain words and phrases used throughout this specification: it should be noted, however, that the words and phrases are not limited to the exemplary interpretation herein.

The term "base station" denotes an entity that communicates with the terminals and may be referred to interchangeably as a BS, NodeB (NB), evolved NodeB (enb), Access Point (AP), fixed station, Base Transceiver System (BTS), macro enb (menb), and secondary enb (senb).

The term "user equipment (or communication terminal)" denotes an entity communicating with a base station or another terminal, and may be interchangeably referred to as a node, a UE, a Mobile Station (MS), a Mobile Equipment (ME), a device, a User Terminal (UT), a mobile subscriber station (MSs), a Subscriber Station (SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), a Machine Type Communication (MTC) device, a machine-to-machine (M2M) device, a device-to-device (D2D) device, and a terminal.

fig. 1 is a signal flow diagram illustrating a RACH procedure between a base station and a UE.

referring to fig. 1, a UE 101 may select a Physical Random Access Channel (PRACH) resource for transmitting an RA preamble message based on system information received from a base station 102. In step 111, the UE 101 may transmit an RA preamble, randomly selected from a set of RA preambles, on the selected PRACH channel resources to the base station 102.

here, the RACH signal transmitted from the UE 101 to the base station 102 may be referred to as "message 1(Msg 1)".

next, if the base station 102 receives the RA preamble message on the PRACH channel resource, the base station may transmit an RA response message to the UE 101 in response to the RA preamble signal in step 113. In this case, the RA response signal may include a Timing Advance (TA) value for uplink synchronization of the UE 101, an uplink resource and a temporary UE identifier (temporary C-RNTI) allocated for scheduling transmission, and the like.

Here, the RA response signal transmitted from the base station 120 to the UE 101 in step 113 in response to the message 1(Msg 1) transmitted in step 111 may be referred to as "message 2(Msg 2)".

The UE 101 may compensate the timing of transmitting data on the uplink channel based on the TA value included in the RA response signal, thereby achieving synchronization of the call connection with the base station 102. The UE 101 may receive and store the temporary UE identifier transmitted by the base station 102. In step 115, the UE 101 may send a scheduled transmission message to the base station 102 by using the TA value and the temporary UE identifier received from the base station 102 and the uplink resource allocated by the base station 102. The scheduling transmission message may include a UE identifier (C-RNTI, S-TMSI, or random Id). The UE 101 may establish an RRC layer connection with the base station 102 based on the allocated uplink resources.

Herein, the scheduled transmission message sent from the UE 101 to the base station 102 in step 115 in response to the message 2(Msg 2) sent in step 113 may be referred to as message 3(Msg 3) or a different terminology used in embodiments of the present disclosure.

Next, at step 117, the base station 102 may send a contention resolution message to the UE 101 to avoid collisions between UEs 101, the contention resolution message including the identifier received from the UE 101.

After receiving the contention resolution message, the UE 101 may determine whether the UE identifier included in the contention resolution message matches a value that the UE has transmitted. If the identifiers match, the UE 101 can continue the process; if the identifiers do not match, the UE 101 can resume the RACH procedure.

Meanwhile, the UE 101 may perform an RRC connection procedure corresponding to message 3 using the allocated uplink resource.

The RRC connection procedure may be a procedure for establishing a logical connection at an RRC layer between the UE 101 and the base station 102.

In this case, establishing the RRC layer connection between the UE 101 and the base station can include establishing a logical connection at the RRC layer between the UE 101 and a network (e.g., a cell or E-UTRAN) covered by the base station 102. In the following description, for convenience of explanation, it is assumed that establishing RRC layer connection includes the following two cases: including establishing logical connections at the RRC layer between the UE 101 and the network covered by the base station 102 (e.g., a cell or E-UTRAN) and not between the UE 101 and the network covered by the base station 102 (e.g., a cell or E-UTRAN).

the state when the RRC layer connection is established between the UE 101 and the base station 102 may be referred to as an RRC activated state; the state when the RRC layer connection between the UE 101 and the base station 102 is released may be referred to as an RRC idle state. The process of transitioning the UE 101 from the RRC idle state to the RRC active state may be referred to as an idle to active (IdleToActive) process.

in the case where the UE 101 performs the IdleToActive procedure or the handover procedure, it may be necessary to perform the RACH procedure described above.

In this case, the initial RACH procedure between the UE 101 and the base station 102 may cause a delay of the connection. The initial RACH procedure may include: transmitting a random access preamble message from the UE 101 to the base station 102; and transmitting a random access response message from the base station 102 to the UE 101. Referring to fig. 1, the time delay may be as much as the time it takes to complete steps 111 and 113.

In view of the beamforming-based access in the 5G communication system, the connection latency may be further increased since the UE must perform a RACH procedure for each beam to transmit the strongest synchronization beam information to the base station. This is described with reference to fig. 2.

Fig. 2 is a view illustrating a sync symbol index for transmitting strongest synchronization beam information in a RACH procedure according to an embodiment.

Referring to fig. 2, assume that base station 102 has 112 beams. It is also assumed that two xPRACH subframes are allocated per radio frame and 5 beam indexes are mapped per xPRACH subframe. Whereas the base station 102 may form 112 beams, the UE 101 may transmit the RA preamble at the position where the strongest synchronization beam is indexed. If the base station receives the RA preamble at the indexed beam position, the base station may obtain synchronization beam information based thereon and transmit an RA response message to the UE on the corresponding beam. Assume that the 100 th beam is the strongest of the 112 beams available between the UE 101 and the base station 102. In this case, the UE 101 may perform the RACH procedure at the beam position of the 100 th index in the RACH subframe. This causes the UE 101 to perform a RACH procedure in the radio frame indexed by the 11 th System Frame Number (SFN)201 according to the synchronization symbol index.

This means that the RACH latency 202 is about 100ms assuming a 10ms spanned radio frame.

In this regard, in case of performing the IdleToActive procedure or the handover procedure, it may be considered to omit at least a part of the RACH procedure to reduce the RACH latency. Of course, it should be ensured that omitting at least a portion of the RACH procedure does not interrupt communication.

Fig. 3 is a signal flow diagram illustrating a method for reducing latency of an RRC layer connection between a UE301 and a base station 302 in case of an IdleToActive procedure of the UE301 according to an embodiment of the present disclosure.

In fig. 3, UE301 may be in communication after synchronization with a base station covering a source cell is achieved based on a TA value with the source cell.

In this case, the base station 302 may transmit an RRC connection release message to the UE301 in step 311 to transition the UE301 from the connected state to the RRC idle state. For example, the RRC connection release message may include a RACHless operation information list (rachlessnfolist) indicating that at least a portion or all of the RACH procedure is to be abandoned.

The format and insertion location of RACHless operation information included in the RRC connection release message will be described in detail later with reference to the accompanying drawings.

Upon receiving the RRC connection release message, the UE301 may transition to an idle state.

Upon receiving the RRC connection release message, the UE301 may also store the TA value of the target cell or the base station 302, which has been obtained through the RACH procedure for establishing the RRC layer connection with the base station 302, in step 313.

After transmitting the RRC connection release message, the base station 302 may periodically allocate uplink resources (UL grant) to the UE301 to which the RRC connection release message has been transmitted and transmit the uplink resource allocation message to the UE301 in step 315.

Thereafter, an RRC layer connection may be requested. For example, in step 317, the UE301 may make an RRC connection determination (e.g., a call attempt by the user to determine an RRC connection) or receive a paging message (e.g., a paging message triggered by a call placed by the other party). That is, the IdleToActive procedure of transitioning from the RRC idle state to the RRC active state may be triggered.

in this case, the UE301 may omit at least part or all of the RACH procedure and establish an RRC layer connection with the base station 302 by using the TA value stored in step 313 and a resource previously allocated by the base station 302. Here, the at least one part omitted in the RACH procedure may include at least one of: a procedure of transmitting an RA preamble message from the UE 302 to the base station 302, a procedure of transmitting an RA response message from the base station 302 to the UE301, or a procedure of transmitting a contention resolution message from the base station 302 to the UE 301. Here, omitting at least a portion of the RACH procedure may include omitting all RACH procedures.

In detail, if the IdleToActive procedure is triggered, the UE301 may transmit an RRC connection request message corresponding to message 3 to the base station 302 by using a pre-stored TA value and pre-allocated uplink resources in step 319. At this time, information on the beam of the base station 302 measured by the UE301 may also be transmitted. Upon receiving the RRC connection request message from the UE301, the base station 302 may communicate with the UE301 using a corresponding beam based on the beam information received from the UE 301. After receiving the RRC connection request message corresponding to message 3, the base station 302 may stop periodically transmitting an uplink resource allocation (UL grant) message to the UE301 according to the proposed RACHless operation.

In step 321, the base station 302 may transmit an RRC connection setup message to the UE301 in response to the RRC connection request message.

Upon receiving the RRC connection setup message, the UE301 may transition to an RRC active state. Next, in step 323, the UE301 may send an RRC connection setup complete message to the base station 302 to confirm that the RRC connection is successfully established.

fig. 4 is a signal flow diagram illustrating a method for reducing delay of an RRC layer connection between UE 401 and base station 402 in the event of a handover by UE 401 according to a UE-based handover procedure.

Although not shown in fig. 4, upon establishing an RRC connection between UE 401 and base station 402 covering the source cell, base station 402 covering the source cell may send a measurement configuration message for handover to UE 401. The measurement configuration message may include information indicating a cell on which UE 401 performs measurements. Although not shown in fig. 4, the source cell base station 402 may transmit an RRC connection reconfiguration (RRCConnectionReconfiguration) message including information on whether the source cell and the neighbor base station are time-synchronized (time-based synchronization) to the UE 401 in advance. Such information may be transmitted, for example, during an initial access procedure with the source cell base station 402.

If UE 401 receives the measurement configuration message, the UE may measure the signal quality (e.g., signal strength and signal-to-interference ratio, etc.) of the cell indicated in the measurement configuration message. Thereafter, in step 411, the UE 401 may transmit a measurement report message including information on the measured signal quality to the source cell base station 402.

If there is a candidate handover target cell for the UE 401, the source cell base station 402 may request RACHless operation information (RACHlessinfo) from the candidate cell, and the candidate cell may transmit RACHless operation information to the source cell. A detailed description thereof will be made with reference to the accompanying drawings.

In step 413, source cell base station 402 may send a handover request message to target cell base station 403 for handover of UE 401. Here, the handover request message transmitted from the source cell base station 402 to the target cell base station 403 may include a RACHless operation request (rachlessforrequest). This may include information requesting omission of at least a portion or all of the RACH procedure in the case of handover of UE 401 to target cell base station 403.

If the target cell base station 430 receives the handover request message in step 413, it may send a handover request acknowledge message to the source cell base station 402 in step 415. The target cell base station 403 may include RACHless operation information (RACHlessinfo) in the handover request confirm message if the target cell base station 403 can omit at least a part or all of the RACH procedure. The target cell base station 403 may transmit RACHless operation information (rachlessnfo) in the handover request Ack message in response to the RACH-less operation request (RachlessinfoRequest) included in the handover request message transmitted by the source cell base station 402 in step 413.

In step 417, the source cell base station 402 may transmit an RRC connection reconfiguration (RRCConnectionReconfiguration) message including candidate cell information to the UE 401. In this case, the RRC connection reconfiguration message may include RACHless operation information (RACHlessinfo) and mobility control information (mobility control info) indicating candidate cells supporting the RACHless operation. The mobility control information (mobility control info) may include access information of the target cell base station 403. The format of RACHless operation information included in the RRC connection reconfiguration message will be described later with reference to the drawings.

After receiving the RRC connection reconfiguration message, the UE 401 may transmit an RRC connection reconfiguration complete (rrcconnectionreconfiguration complete) message to the base station 402 in step 419 to provide notification that the RRC connection reconfiguration has been successfully completed.

If desired, UE 401 may perform a RACH procedure, for example, if it detects that source cell base station 402 and target cell base station 403 are not time synchronized. UE 401 may, if desired, preemptively perform at least a portion of RACH procedure 420 with handover target cell base station 403 before triggering the handover.

In step 421, UE 401 may send an RA preamble message to candidate handover target cell base station 403. That is, UE 401 may preemptively perform at least a portion of a RACH procedure with at least one candidate cell base station that is a handover target. For example, when UE 401 is communicating with source cell base station 402, UE 401 may perform at least a portion of a RACH procedure with a base station of a candidate cell.

If the target cell base station 403 receives the RA preamble message, it may transmit an RA response message including the TA value to the UE 401 in step 423.

If the UE 401 receives the RA response message, it may generate a RACHless operation indication message for notifying the target cell base station 403 of the preemptive RACH attempt thereto) in step 425 and transmit the RACHless operation indication message to the target cell base station 403. In step 431, UE 401 may obtain the TA value included in the RA response message received in step 423 of target cell base station 403.

Meanwhile, if the UE 401 detects that the source cell base station 402 and the target cell base station 403 are time synchronized, it may obtain a TA value of the target cell based on the TA value of the source cell and a timing difference value between the source cell base station 402 and the target cell base station 403 and store the obtained TA value in step 431, omitting the RACH procedure, i.e., steps 421 to 425.

If the target cell base station 403 receives a message indicating that at least a part of the RACH procedure is omitted from the UE 401 obtaining the TA value, it may allocate uplink resources to the UE 401 and periodically transmit an uplink resource allocation message to the UE 401 in step 435.

During this procedure, UE 401 may transmit user data to source cell base station 402 or receive user data from source cell base station 402 in step 433.

In this case, UE 401 may make a handover decision in step 441. That is, handover of the communication service from the source cell base station 402 to the target cell base station 403 may be triggered. For example, if the UE 401 is a fixed Customer Premises Equipment (CPE) that is rarely moving, a handover may occur when a beam formed in one direction is blocked by an obstacle.

In this case, the UE 401 may omit at least part of the RACH procedure and establish an RRC layer connection with the target cell base station 403 by using the stored TA value and the uplink resource previously allocated by the target cell base station 403.

In detail, in step 442, the UE 401 may transmit an RRC connection reestablishment request message corresponding to message 3 to the target cell base station 403. At this time, the base station beam information measured by the UE 401 may be transmitted together with a message so that the target cell base station 403 can communicate with the UE 401 using a beam based on the corresponding beam information. After receiving the RRC connection re-establishment request message corresponding to message 3, the target cell base station 403 may stop periodically transmitting an uplink resource allocation (UL grant) message for RACH-less operation.

Upon receiving the RRC connection re-establishment request message, the target cell base station 403 accepts the RRC connection re-establishment and transmits an RRC connection re-establishment message to the UE 401 at step S443.

After receiving the RRC connection re-establishment message, UE 401 may send an RRC connection re-establishment complete message to the target cell base station at step 444 to provide notification of completion of the RRC connection re-establishment procedure.

Meanwhile, if the UE 401 receives an RRC connection reconfiguration (RRCConnectionReconfiguration) message from the target cell base station 435 in step 445, the UE 401 may transmit an RRC connection reconfiguration complete (RRCConnectionReconfiguration complete) message to the target cell base station 403 in response to the RRC connection reconfiguration message in step 446.

The above-described operations of steps 441 through 446 may constitute the switching process 440.

Thereafter, in step 450, UE 401 may transmit user data to target cell base station 403 or receive user data from target cell base station 403.

Fig. 5 is a signal flow diagram illustrating a method for reducing the delay of the RRC layer connection between a UE501 and a base station 502 in case of a network controlled handover procedure.

as described above, if desired, the UE501 may preemptively obtain the TA value of the target cell base station 503 and store the TA value through at least a portion of the RACH procedure, for example, if it detects that the source cell base station 502 and the target cell base station 503 are not time synchronized. Steps 511 to 515 by which the UE501 obtains the TA value may correspond to steps 421 to 425 of fig. 4.

In step 515, in order to notify the target cell base station 503 of the preemptive RACH attempt according to the RACH-less operation, the UE501 may generate a RACHless indication (RACHless indication) message and transmit the message to the target cell base station 503. The RACHless indication (RACHless indication) message may include information indicating that at least a portion of RACH operations may be subsequently omitted for handover of the UE501 to the target cell base station 530.

The target cell base station 503 may send RACH-less indication (RACHless indication) information to the source cell base station 502 in step 517, so that the source cell base station 502 then uses this information when selecting a target cell for handover of the UE through RACHless operation.

As described above, steps 511 to 517 may be performed in a case where the source cell base station 502 and the target cell base station 503 are not time-synchronized. Steps 511 to 517, in which the target cell base station sends RACHless indication (RACHless indication) information to the source cell base station 502, may be operations for preemptively implementing synchronization between the target cell base station 503 and the UE 501. In step 521, the UE501 stores the TA value received from the target cell base station 503 in step 513.

If the UE501 detects that the source cell base station 502 and the target cell base station 503 are time synchronized, it may obtain a TA value of the target cell based on the TA value of the source cell and a timing difference between the source cell base station 502 and the target cell base station 503 in step 521. And stores the obtained TA value, omitting the RACH procedure, steps 511 to 515.

in step 523, the UE501 may transmit a measurement report message including signal quality measurement information to the source base station 502.

In this case, the source cell base station 502 may make a handover decision of the UE501 in step 531.

In step 532, the source cell base station 502 may transmit a handover request message including a RACH-less operation request (rachlessnfaway request) to the target cell base station 503 as a candidate cell. In step 533, the target cell base station 503 as the candidate cell may transmit a handover request confirm message including RACHless operation information (Rachlessinfo) to the source cell base station 502 as a response.

In step 534, the source cell base station 502 may transmit an RRC connection reconfiguration (RRCConnectionReconfiguration) message including RACHless operation information (rachlessnfo) including information on candidate cells available for RACHless operation to the UE 501. The RRC connection reconfiguration message may include mobility control information associated with information regarding accessing the target cell base station 502 (e.g., the frequency and channel of the target cell).

After receiving the RACHless operation request (rachlessfonreqeust) message from the source cell base station 502, the target cell base station 503 may allocate uplink resources associated with the RACH-less operation request (rachlessfonrequest) to the UE and transmit an uplink resource allocation (UL grant) message to the UE501 in step 536.

If the UE501 receives the RRC connection reconfiguration message, it may transmit an RRC connection reconfiguration complete message corresponding to message 3 to the target cell base station 503 in step 535 to confirm that the RRC connection is successfully established using the TA value and pre-allocated uplink resources stored in step 521, omitting the RACH procedure with the target cell base station 503. In this case, base station beam information measured by the UE may be transmitted so that the target cell base station 503 communicates with the UE501 using a beam based on the beam information.

Fig. 6 is a flowchart illustrating a procedure in which a UE obtains a TA value from a candidate target cell and updates the TA value according to an embodiment of the present disclosure.

In step 601, if the UE detects that it needs to obtain the TA value of the candidate cell, it may receive an RRC connection reconfiguration (RRCConnectionReconfiguration) message in advance from the source cell base station, the message including information on whether the source cell is time-synchronized with the neighbor base station. This information may be received, for example, during an initial connection with the source cell.

If it is determined in step 603 that the source cell base station and the target cell base station are time-synchronized, the UE may measure a subframe timing difference (SFN and subframe timing difference (SSTD)) between the source cell base station and the target cell base station in step 611.

In step 613, the UE may calculate a TA value of the target cell base station by using the TA value and the SSTD value of the source cell. In step 615, the UE stores the TA value calculated for the target cell base station and maintains the TA value while the target cell base station or the source cell base station is active. In step 617, the UE may determine whether the TA value and/or the SSTD value of the source cell base station has changed. If it is determined that the TA value and/or the SSTD value of the source cell base station is changed, the UE performs the operation of step 613 again using the changed value to recalculate the TA value of the target cell base station. The UE may maintain the TA value of the candidate target cell base station if it is determined that the TA value and/or SSTD value of the source cell has not changed.

If it is determined that the source cell base station and the target cell base station are not time synchronized, the UE may perform a preemptive RACH procedure with the target cell in step 621. In step 623, the UE obtains the TA value of the current target cell base station. In step 625, the UE may measure an SSTD value between the source cell base station and the target cell base station. In step 627, the UE may calculate a time difference between the source cell base station and the target cell base station.

In step 629, the UE may maintain the time difference values of the candidate target cell base stations when the candidate target cell base stations or the source cell base station are valid. Thereafter, the UE may determine whether the TA value and/or the SSTD value for the source cell base station is changed in step 631. If it is determined that the TA value and/or SSTD value of the source cell base station is changed, the UE may recalculate the TA value of the candidate target cell base station in step 633. After the UE recalculates the TA values of the candidate target cell base stations, the procedure may return to step 629. The UE may maintain the TA value of the candidate target cell base station if it is determined that the TA value and/or SSTD value of the source cell base station has not changed.

Hereinafter, a method for calculating a TA value of a candidate target cell base station in a case where a source cell base station and a target cell base station are not time synchronized and a method for calculating a TA value of a candidate target cell in a case where the source cell base station and the target cell base station are time synchronized are described with reference to equations.

the TA value between the source cell base station (source 5G node-B) and the UE may be denoted by TASource. The UE may periodically update the TA value of the source cell base station to obtain a source value.

the TA value between the candidate target cell base station (target 5G node-B) and the UE may be denoted by TATarget.

The SFN of the source cell base station measured by the UE may be represented by SFNsource, the SFN of the target cell base station measured by the UE may be represented by SFNtarget, and the SFN offset between the source cell base station and the target cell (target 5G node-B) may be represented as SFNsWhich is set to range from radio frame 0 to radio frame 1023.

The radio frame start time of the source cell measured by the UE is represented by a tradioframeboundummy source, the radio frame start time of the target cell measured by the UE may be represented by a tradioframeboundummy target, and the radio frame boundary offset between the source cell base station and the target cell base station may be represented as a radio frame boundary offsetRanging from subframe-25 to subframe 24. The subframe start time of the source cell base station measured by the UE may be represented by TSubframeBoundarySource, the subframe start time of the target cell base station measured by the UE may be represented by tsubfodiofamenboundarytarget, and the subframe boundary offset between the source cell base station and the target cell base station may be represented as tsubfameboundarytarget

The transmission time offset between the source cell base station and the target cell base station may be represented by tifffset.

The unit time Ts may be set to 1/(2048 × 15000) ═ 1/30720000 seconds, and TA ═ 16 × Ts. The radio frame time period may be denoted by tradiofrme.

Equation 1 is established using the above parameters.

[ EQUATION 1 ]

As described above, in the case where the base station of the source cell and the base station of the target cell are time-synchronized, i.e., TI_offsetTATarget may be calculated by equation 2, 0.

[ EQUATION 2 ]

Even if the TASource value and/or SSTD value is changed, TATarget can be recalculated by equation 2 using these values.

In the case where the source cell base station and the target cell base station are not time synchronized, i.e. TI_offsetAnd if not equal to 0, the UE acquires through a preemptive RACH process with the target cell base stationAnd then based onCalculating TI_offset。

TI can be calculated from equation 3_offset。

[ EQUATION 3 ]

In obtaining TI_offsetAfter that, TATarget may be calculated by equation 4.

[ EQUATION 4 ]

As described above, it is possible to use the information obtained by the preemptive RACG procedure with the target cell base stationCalculated TI_offsetTo calculate TATarget.

If the TASource value and the SSTD value are changed thereafter, TATarget can be calculated by equation 4 using the changed values.

fig. 7a, 7b, 8a to 8d, and 9 are views illustrating message syntax defined for reducing connection latency between a UE and a base station.

Although the messages shown in fig. 7a, 7b, 8 a-8 d, and 9 include information elements having specific names and placed at specific locations, these names and locations are merely exemplary and may be changed to preferred names for the same or similar purposes as the normalization process proceeds.

The information elements included in the messages included in fig. 7a, 7b, 8a to 8d, and 9 may be added to a reserved field of a message used in the existing standard or replace the existing information elements so as to be transmitted to the respective entities or to transmit the information elements by using separate information.

The message syntax of fig. 7a may correspond to the RRC connection release message sent from the base station 302 to the UE301 in step 311 of fig. 3.

The RRC connection release message may include a RACHless operation information list (rachlessnfolist) 701 as information indicating that the base station 302 supports omitting at least a part of the RACH procedure. This information may include a continuous SEQUENCE (SEQUENCE)703 of RACHless operation information (RACHlessinfo). A detailed item of RACHless operation information (RACHlessinfo) is specified in the SEQUENCE (SEQUENCE) 720.

The message syntax of fig. 7b may correspond to an RRC connection reconfiguration (RRCConnectionReconfiguration) message transmitted from the source cell base station 402 to the UE 401 in step 417 of fig. 4.

In case of performing handover according to a network controller handover procedure, RACHless operation information (RACHlessinfo)710 indicating that the candidate target cell base station supports omission of the RACH procedure may be included in mobility control info of the RRC connection reconfiguration message. In the case of performing handover according to the UE-based handover procedure, a RACHless operation information list (rachlessnfoistlist) 715 indicating that the candidate target cell base station supports omission of the RACH procedure may be included in the candidatecelllnfolist of the RRC connection reconfiguration message. The RACHless operation information 710 may include the following detailed information 720.

(1) Time synchronization information between a source cell and a candidate target cell

(2) C-RNTI ID information for use in candidate target cells

(3) Starting subframe information of UL grant of candidate target cell

(4) UL grant period information for candidate target cells

(5) UL grant termination timer for candidate target cell

The message syntax of fig. 8a may correspond to a RACHless indication (RACHless indication) message transmitted from the UE to the target cell base station in step 425 of fig. 4 and step 515 of fig. 5, and may include RACH-less indication (RACHless indication) syntax 810.

The RACHless Indication (RACHless Indication) message may be used for the purpose of requesting the base station to start uplink resources for the UE, or for the purpose of notifying the target cell base station and the source cell base station that the UE obtains a TA value in advance.

The message syntax of fig. 8b to 8d is an RRC connection request message corresponding to message 3, which is transmitted from the UE to the base station using pre-allocated uplink resources. The message syntax of fig. 8b to 8d includes base station beam information 820, 821, 830, 831, 840, and 841 measured by the UE for the base station to use for communication with the UE using the beam.

The message syntax of fig. 9 may correspond to a UE capability information message transmitted from the UE to the base station as an RRC message.

The UE capability information message may include a feature group indicator (featuregroupiditors) information element 901 that defines features to be implemented at the UE.

In this case, the feature group indicator information element 901 may include a flag that may be used to indicate whether the UE supports omitting at least a portion of the RACH procedure as proposed in the present disclosure.

Fig. 10 is a block diagram illustrating a configuration of a UE according to an embodiment of the present disclosure.

The UE 1100 of fig. 10 may correspond to the UE 101 in fig. 1, the UE301 in fig. 3, the UE 401 in fig. 4, and the UE501 in fig. 5.

In fig. 10, UE 1100 includes a controller 1110, communication circuitry 1120, and a memory unit 1130.

The communication circuit 1120 may include a Radio Frequency (RF) processor 1021 and a baseband processor 1022.

The RF processor 1021 performs functions for transmitting/receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processor 1021 up-converts a baseband signal from the baseband processor 1022 to generate an RF band signal that can be transmitted through an antenna, and down-converts an RF signal received by the antenna to generate a baseband signal. The RF processor 1021 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC). Although a single antenna is shown in fig. 10, the UE 1000 may be equipped with multiple antennas. The RF processor 1021 may include a plurality of RF chains. The RF processor 1021 may perform beamforming. To form a beam, the RF processor 1021 may adjust the phase and magnitude of signals transmitted/received through a plurality of antennas or antenna elements. The RF processor may also perform MIMO operations to receive multiple layers. The RF processor 1021 may appropriately configure a plurality of antennas or antenna elements under the control of the controller to perform receive beam scanning and adjust the receive direction and width to match the transmit beam.

The baseband processor 1022 is responsible for converting between baseband signals and bit strings according to the physical layer protocol of the system. For example, the baseband processor 1022 performs coding and modulation on a transmission bit string to generate complex symbols in a data transmission mode. The baseband processor 1022 also performs demodulation and decoding on the baseband signal from the RF processor 1021 to recover the received bit string in the data reception mode. For the case of an Orthogonal Frequency Division Multiplexing (OFDM) system, the baseband processor 1022 performs coding and modulation on a transmission bit string to generate complex symbols, maps the complex symbols to subcarriers, performs fast inverse fourier transform (IFFT) on the subcarriers, and inserts a Cyclic Prefix (CP) to generate an OFDM symbol in a data transmission mode. The baseband processor 1022 divides the baseband signal from the RF processor 1021 into OFDM symbols, restores the signal mapped to subcarriers by Fast Fourier Transform (FFT), and performs demodulation and decoding to restore a bit string in a data reception mode.

As described above, the baseband processor 1022 and the RF processor 1021 are responsible for transmitting and receiving signals. Accordingly, the baseband processor 1022 and the RF processor 1021 may be referred to as communication circuits 1020, transmitters, receivers, and transceivers. The baseband processor 1022 and the RF processor 1021 may each include a plurality of communication modules for supporting different radio access technologies. The baseband processor 1022 and the RF processor 1021 may each include a plurality of communication modules for processing signals of different frequency bands. Examples of radio access technologies include LTE networks and RR networks. Examples of different frequency bands may include the ultra high frequency (SHF) band (e.g., 2.5GHz and 5GHz) and the millimeter wave (mmWave) band (e.g., 60 GHz).

the storage unit (or memory) 1030 stores basic programs for the operation of the terminal, application programs, and data such as configuration information. The storage unit 1030 provides stored data in response to a request from the controller 1010. For example, the storage unit 1030 may store a TA value obtained through the preemptive RACH procedure for a next RACH procedure proposed in the present disclosure. The storage unit 1030 may also store a TA value of the target cell calculated based on the TA value of the source cell and the frame timing difference information and time synchronization information between the base stations. The storage unit 1030 may be implemented with a single memory or a plurality of memory devices. In the following description, the term "memory cell" includes two cases.

A controller (or processor) 1010 controls overall operation of the UE 1000. For example, the controller 1010 may transmit/receive signals through the communication circuit 1020. The controller 1010 also writes data to the memory unit 1030 and reads data from the memory unit 1030. To accomplish this, the controller 1010 may include at least one processor. For example, the controller 1010 may include a Communication Processor (CP) for controlling communication and an Application Processor (AP) for controlling a higher layer such as an application program.

According to various embodiments, if the RRC layer connection established between the UE 1000 and the base station is released, the storage unit 1030 may store a TA value obtained through a RACH procedure for establishing the RRC layer connection. Controller 1010 can control communications circuitry 1020 to receive an uplink resource allocation message from a base station indicating uplink resources allocated to UE 1000 after releasing the RRC layer connection. If it is determined that the RRC layer connection is re-established between the UE 1000 and the base station, the controller 1010 may establish the RRC layer connection with the base station based on the pre-stored TA value and the allocated uplink resource, thereby omitting at least a portion of the RACH procedure.

In this case, the controller 1010 may control the communication circuit 1020 to receive a message including information indicating that the base station omits at least a part of the RACH procedure.

Here, information indicating that the base station omits at least a part of the RACH procedure may be included in the RRC connection release message transmitted from the base station to the UE 1000.

according to various embodiments, when communicating with a source cell base station, a UE may store TA values obtained through at least a portion of a RACH procedure with a handover target cell base station in the storage unit 1030. The controller 101 may control the communication circuitry 1020 to receive an uplink resource allocation message from the target cell base station indicating uplink resources allocated to the UE 1000. The controller 1010 can establish an RRC layer connection with a target cell base station based on the pre-stored TA value and the allocated uplink resource.

In the case where the UE 1000 makes a handover decision, the controller 1010 may establish an RRC layer connection with the target cell base station based on a pre-stored TA value and the allocated uplink resource.

In the case where the source cell base station makes a handover decision for the UE 1000, the uplink resource allocation message may be an uplink resource allocation message transmitted based on an uplink resource allocation request message transmitted from the source cell base station to the target cell base station.

controller 1010 may control communications circuitry 1020 to transmit a message indicating omission of at least a portion of a RACH procedure based on the stored TA value. In the case of receiving an uplink resource allocation message from the target cell base station, controller 1010 may control communications circuitry 1020 to receive an uplink resource allocation message (indicating uplink resources allocated to UE 1000) from the target cell base station based on the message indicating omission of at least a portion of the RACH procedure.

Controller 1010 may control communications circuitry 1020 to receive a message from a target cell base station including information indicating that the target cell base station omits at least a portion of a RACH procedure. Here, information indicating that the target cell base station omits at least a part of the RACH procedure may be included in the RRC connection reconfiguration message transmitted from the source cell base station to the UE 1000.

In addition to the above-described operations, the controller 1010 may also perform a control operation that will be described later with reference to the flowchart and a control operation described with reference to fig. 1 to 6.

Fig. 11 is a block diagram showing a configuration of a base station according to an embodiment of the present disclosure.

Base station 1100 of fig. 11 may correspond to base station 102 in fig. 1, base station 302 in fig. 3, base stations 402 and 403 in fig. 4, and base stations 502 and 503 in fig. 5.

In fig. 11, base station 1100 includes a controller 1110, communication circuitry 1120, and backhaul communication circuitry 1130.

The communication circuitry 1120 includes an RF processor 1121 and a baseband processor 1122.

The RF processor 1121 performs functions for transmitting/receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processor 1121 up-converts a baseband signal from the baseband processor 1122 to generate an RF band signal that can be transmitted through an antenna, and down-converts an RF signal received by the antenna to generate a baseband signal. The RF processor 1121 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC. Although a single antenna is shown in fig. 10, the base station 1100 may be equipped with multiple antennas. The RF processor 1121 may include a plurality of RF chains. The RF processor 1121 may perform beamforming. In order to form a beam, the RF processor 1121 may adjust the phase and magnitude of signals transmitted/received through a plurality of antennas or antenna elements. The RF processor may transmit one or more layers to perform downlink MIMO operations.

The baseband processor 1122 is responsible for converting between baseband signals and bit strings according to the physical layer protocol of the system. For example, the baseband processor 1122 performs coding and modulation on a transmission bit string to generate complex symbols in a data transmission mode. The baseband processor 1122 also performs demodulation and decoding on the baseband signal from the RF processor 1121 to recover a received bit string in a data reception mode. For the case of employing the OFDM scheme, the baseband processor 1122 performs coding and modulation on a transmission bit string to generate complex symbols, maps the complex symbols to subcarriers, performs IFFT on the subcarriers, and inserts a CP to generate OFDM symbols in a data transmission mode. The baseband processor 1122 divides the baseband signal from the RF processor 1121 into OFDM symbols, restores the signals mapped to the subcarriers through FFT, and performs demodulation and decoding to restore a bit string in a data reception mode. The baseband processor 1122 and the RF processor 1121 transmit and receive signals as described above. Thus, the baseband processor 1122 and the RF processor 1121 may be referred to as communication circuitry 1120, a transmitter, a receiver, a transceiver, or wireless communication circuitry.

backhaul communication circuit 1130 provides an interface for communicating with other network nodes. That is, the backhaul communication circuit 1130 may provide an interface for communicating with advanced nodes and an interface for communicating with neighboring base stations.

A storage unit (or memory 1140) stores data such as basic programs, application programs, and configuration information for the operation of base station 1100. In particular, the storage unit 1140 may store information on bearers allocated to the accessed UE and measurement results reported by the accessed UE. The storage unit 1140 may also store information such as criteria for determining whether to enable or disable multi-connectivity for the UE. The storage unit 1140 may provide the stored data in response to a request from the controller 1110. The storage unit 1140 may also store information on the synchronization state with the neighboring base stations. The storage unit may further store information indicating that a part or all of RA procedures of the UE are omitted and related control information. The storage unit 1140 may also store information required for the operation described with reference to fig. 1 to 6 and/or related control information, and information required for the operation to be described later and/or related control information.

A controller (or processor) 1010 controls the overall operation of base station 1100. For example, the controller 1110 transmits/receives signals through the baseband processor 1122 and the RF processor 1121 or through the backhaul communication circuit 1130. The controller 1110 writes data to the memory unit 1140 and reads data from the memory unit 1030. To accomplish this, the controller 1110 may include at least one processor. The controller 1110 may also control an operation of omitting a part or all of the RA procedure of the UE as well as the operations described with reference to fig. 1 to 6 and the operations described later.

Fig. 12 is a flowchart illustrating a method of a UE establishing an RRC layer connection with a base station according to an embodiment of the present disclosure.

In step 1201, the UE may store the TA value obtained from the RA response message while establishing the RRC layer connection with the base station.

In step 1203, the UE may release the RRC layer connection and receive an uplink resource allocation message indicating uplink resources allocated to the UE. For example, the UE may periodically receive an uplink resource allocation message from the base station.

In step 1205, the UE may again determine whether to establish an RRC layer connection with the base station.

If it is determined to establish the RRC layer connection with the base station again, the UE may establish the RRC layer connection with the base station based on the TA value obtained in the previous RRC layer connection procedure and the allocated uplink resource when the RA preamble message has not been transmitted in step 1207.

Fig. 13 is a flowchart illustrating a method of a UE establishing an RRC layer connection with a base station according to another embodiment of the present disclosure.

In step 1301, the UE may transmit an RA preamble message to the handover target cell base station while communicating with the source cell base station. For example, if the UE receives a message from the source cell base station including information indicating omission of at least a portion of a RACH procedure with the target cell base station, the UE may transmit an RA preamble message to the target cell base station.

In step 1303, the UE may store a TA value obtained from an RA response message transmitted by the target cell base station in response to the RA preamble message.

In case that the base station is time synchronized, the UE may calculate and store a TA value based on the TASource and SSTD, omitting (omitting) steps 1301 and 1303.

in step 1305, the UE may receive an uplink resource allocation message indicating uplink resources allocated to the UE by the target cell base station from the target cell base station.

in this case, the UE may transmit a message indicating omission of at least a portion of the RACH procedure to the target cell base station based on the stored TA value. The UE may receive an uplink resource allocation message from the target cell base station in response to the message indicating that at least a portion of the RACH procedure is omitted.

In this case, the UE may determine whether to handover to the target cell base station in step 1307.

If it is determined to perform handover, the UE may establish an RRC layer connection with the target cell base station based on the stored TA value and the uplink resource allocated by the target cell base station when the RA preamble message has not been transmitted in step 1309.

Fig. 14 is a flowchart illustrating a method of a UE establishing an RRC layer connection with a base station according to another embodiment of the present disclosure.

In step 1401, the UE may transmit an RA preamble message to a handover target cell base station while communicating with a source cell base station. For example, if the UE receives a message from the source cell base station including information indicating omission of at least a portion of a RACH procedure with the target cell base station, the UE may transmit an RA preamble message to the target cell base station.

In step 1403, the UE may store the TA value obtained from the RA response message transmitted by the target cell base station in response to the RA preamble message.

In case the base station is time synchronized, the UE may calculate and store a TA value based on the TASource and SSTD, omitting (omitting) steps 1401 and 1403.

If a handover is determined from the source cell base station to the target cell base station, the UE may receive an uplink resource allocation message indicating uplink resources allocated to the UE from the target cell base station in step 1405.

In step 1407, the UE may establish an RRC layer connection with the target cell base station based on the stored TA value and the uplink resource allocated by the target cell base station when the RA preamble message has not been transmitted.

Fig. 15 is a flowchart illustrating a method of a base station establishing an RRC layer connection with a UE according to an embodiment of the present disclosure.

In case that the RRC layer connection established with the UE is released, the base station may transmit a message including information indicating that the base station omits at least a part of the RACH procedure to the UE in step 1501.

In step 1503, the base station may release the RRC layer connection established with the UE and transmit an uplink resource allocation message indicating uplink resources allocated to the UE.

In step 1505, the base station may establish an RRC layer connection with the UE based on the allocated uplink resource when the RA preamble message has not been received after receiving the RRC connection request message from the UE.

Fig. 16 is a flowchart illustrating a method of a base station establishing an RRC layer connection with a UE according to another embodiment of the present disclosure.

In step 1601, a base station may receive an RA preamble message from a UE communicating with a source cell base station.

In step 1603, the base station may transmit an RA response message including the TA value to the UE in response to the RA preamble message.

In step 1605, the base station may receive a message from the UE indicating omission of at least a portion of the RACH procedure based on the TA value stored at the UE.

in step 1607, the base station may transmit an uplink resource allocation message indicating uplink resources allocated to the UE in response to the message indicating omission of at least a portion of the RACH procedure.

In case that the base station is time-synchronized, the base station may omit steps 1601 to 1605, and the UE may calculate a TA value using TASource and SSTD and store the calculated TA value. In this case, the base station may transmit an uplink resource allocation message indicating uplink resources allocated to the UE without receiving any message.

In step 1690, when the UE determines to handover to the target cell base station, the base station may establish an RRC layer connection with the UE upon receiving an RRC connection reestablishment request message on the allocated uplink resources.

Fig. 17 is a flowchart illustrating a method of a base station establishing an RRC layer connection with a UE according to another embodiment of the present disclosure.

In step 1701, the base station may receive an RA preamble message from a UE communicating with a source cell base station.

In step 1703, the base station may transmit an RA response message including a TA value to the UE in response to the RA preamble message.

In case the base station is time synchronized, the base station may omit (skip) step 1701 and step 1703, and the UE may calculate a TA value using the TASource and SSTD and store the calculated TA value. In this case, the base station may transmit an uplink resource allocation message indicating uplink resources allocated to the UE without receiving any message.

When the source cell base station makes a handover decision for the UE to the target cell base station, the base station may receive an uplink resource allocation request message from the source cell base station requesting uplink resources allocated to the UE in step 1705.

In step 1707, the base station may transmit an uplink resource allocation message indicating uplink resources allocated to the UE in response to the uplink resource allocation request message.

In step 1709, the base station may establish an RRC layer connection with the UE upon receiving an RRC connection reconfiguration complete message on the allocated uplink resources

The disclosed embodiments may be implemented in the form of an S/W program comprising instructions stored in a computer-readable storage medium.

Examples of computers that can be used in accordance with the disclosed embodiments include the UE and base stations present in the disclosed embodiments as devices capable of invoking instructions from a storage medium and executing the instructions to perform operations.

The computer readable storage medium may be a non-transitory storage medium. As used herein, the expression "non-transitory" is used to indicate that the storage medium does not include a signal and is tangible, regardless of whether data is semi-permanently or temporarily stored in the storage medium.

the method according to the disclosed embodiments may be provided in the form of a computer program product. The computer program product may enable transactions between buyers and sellers.

The computer program product may include a software product and a computer-readable storage medium including the software product. For example, the computer program product may include a product that is distributed online in the form of a software program (e.g., a downloadable application) or distributed through an electronic Store (e.g., Google Play Store or App Store) by the manufacturer of the terminal and the base station. In the case of online distribution, at least part of the software program may be temporarily stored or generated in a storage medium. In this case, at least a portion of the computer program product may be temporarily stored or immediately generated in a storage medium such as a memory of a manufacturer's server, application store server, or relay server.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a wireless communication system in which a UE establishes a radio resource control layer connection with a base station.