Random access scheme for preventing unnecessary retransmission and user equipment for the same.

(54) Title: RANDOM ACCESS SCHEME TO AVOID UNNECESSARY RETRANSMISSION AND USER EQUIPMENT FOR THE SAME.

(54) Title: RANDOM ACCESS SCHEME FOR PREVENTING UNNECESSARY RETRANSMISSION AND USER EQUIPMENT FOR THE SAME.

(57) Summary

A random access scheme is described to avoid unnecessary retransmission and user equipment for it; if a contention resolution timer (CR) expires in contention resolution for a random procedure or if a physical uplink control channel (PDCCH) signal associated with the PDCCH signal does not match a terminal identifier , a hybrid automatic repeat request (HARQ) buffer for storing a medium access control packet data unit (MAC PDU) transmitted in the random access procedure is leveled so that unnecessary data retransmission can be avoided.

(57) Abstract

A random access scheme for preventing unnecessary retransmission and a user equipment for the same are disclosed. If a Contention Resolution (CR) timer expires in contention resolution during a random access procedure or if a Physical Downlink Control Channel (PDCCH) signal or a Physical Downlink Shared Channel (PDSCH) signal associated with the PDCCH signal does not match an identifier of a terminal, a Hybrid Automatic Repeat Request (HARQ) buffer for storing a Medium Access Control Packet Data Unit (MAC PDU) transmitted in the random access procedure is flushed such that unnecessary data retransmission can be prevented.

RANDOM ACCESS SCHEME TO AVOID UNNECESSARY RETRANSMISSION AND USER EQUIPMENT FOR THE SAME

TECHNICAL FIELD

The present invention relates to a random access scheme of user equipment in a mobile communication system and, more particularly, to a random access scheme to avoid unnecessary retransmission and user equipment for it.

BACKGROUND OF THE INVENTION

As an example of a mobile communication system for which the present invention can be applied, a long-term evolution third generation Partnership Project (3GPP LTE) communication system will be schematically described.

Figure 1 is a schematic diagram of an evolved universal mobile telecommunication system (EUMTS) network architecture as an example of the mobile communication system.

UMTS is an evolved version of existing UMTS and basic standardization of it is in progress under 3GPP. E-UMTS is also referred to as a Long Term Evolution (LTE) system.

The E-UMTS network can be broadly divided into an evolved UMTS terrestrial radio access network (E-UTRAN) 101 and a core network (CN) 102. The E-UTRAN 101 generally comprises a terminal (ie, a user equipment (UE) 103, a base station (i.e. eNode B or eNB) 104, an Access Portal (AG) 105 which is located at one end of the E-UMTS network and connects to one or more external networks. AG 105 can be divided into a part to process user traffic and a part to handle control traffic. At this point, an AG for processing new user traffic and an AG for processing control traffic can communicate with each other using a new interface.

An eNode B can have one or more cells. An interface for transmitting user traffic or control traffic can be used between Bs eNode. CN 102 can comprise AG 105, user registration nodes from other UEs 103, and the like. An interface can be used to distinguish E-UTRAN 101 and CN 102 from each other.

The various layers of the radio interface protocol between the terminal and the network can be divided into Layer 1 (L1), Layer 2 (L2) and Layer 3 (L3), based on the three lower layers of the standard Interconnection model of the open system (OSI) that is well known in the field of communication systems. Between these layers, layer 1 (L1), particularly the physical layer, provides an information transfer service using a physical channel, while a radio Resource Control (RRC) layer located at layer 3 (L3) It performs the function of controlling the radio resources between the terminal and the network. The RRC layer exchanges RRC messages between the terminal and the network. The RRC layer can be located at | be distributed on network nodes, such as eNode B 104, AG 105, and the like, or it may be located only on eNodeB 104 or AG 105.

Figures 2 and 3 show an architecture of a radio interface protocol between a terminal and a UTRAN according to the standard 3GPP radio access network.

The radio interface protocol shown in Figures 2 and 3 is horizontally composed of a physical layer, a data link layer, and a network layer, and is vertically composed of a user plane to transmit the data from the user and a control plane to transfer the control signaling. In detail, Figure 2 shows the layers of the radio protocol control plane and Figure 3 shows the layers of the radio protocol user plane. The protocol layers of Figures 2 and 3 can be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based on the lower three layers of the Open System Interconnection Standard (OSI) model. which are widely known in the field of communications systems.

Hereinafter, the particular layers of the radio protocol control plane of Figure 2 and the radio protocol user plane of Figure 3 will be described.

The physical layer (PHY) (Layer 1) provides an information transfer service to a higher layer using a physical channel. The PHY layer is connected to a Medium Access Control (MAC) layer located thereon via a transport channel, and data is transferred between the PHY layer and the MAC layer via the transport channel. At this time, the transfer channel is roughly divided into a dedicated transfer channel and a common transfer channel depending on whether a channel is shared or not. Additionally, the data is respectively transferred between different physical layers, particularly between the respective physical layers of the transmission side and the reception side by means of a physical channel using radio resources,

The various layers are located at layer 2. First, the Medium Access Control (MAC) layer maps multiple logical channels to various transfer channels and performs a logical channel multiplexing function to map various logical channels to one channel. transfer. The MAC layer is connected to a Radio Link Control (RLC) layer which is a top layer via the logical channel, and the logical channel can be roughly divided into a control channel to transmit information on the plane control and a traffic channel to transmit information on the user's plane, according to the type of information transmitted.

The RLC layer of the second substrate segments and concatenate the data received from an upper layer, controlling a data size so that it is suitable for a lower layer to transmit data at a radio interval. The RLC provides three modes, in particular, a transparent mode (TM), an unrecognized mode (UM), and a known mode (AM) to support the various QoSs requested by each radio bearer (RB). Especially for the reliable transmission of data through an automatic repeat request (ARQ).

A packet data convergence protocol (PDCP) layer located in the second layer was used to efficiently transmit IP packets, such as IPv4 or IPv6, over a radio interval with relatively narrow bandwidth. For this purpose, the PDCP layer reduces the size of an IP packet header, which is relatively larger in size and includes unnecessary control information, in particular, it performs a function called header compression. Consequently, only the necessary information can be included in the data header part for transmission, so that it increases a transmission efficiency of a radio interval. In the LTE system, the PDCP layer also performs a security function. The security feature includes an encryption feature to prevent third-party data monitoring, and an integrity protection feature to prevent tampering with third-party data.

A radio resource control layer (RRC) located in a higher portion of the third layer is defined in the control plane. The RRC layer handles logical channels, transport channels, and physical channels for configuration, reconfiguration, and release of radio bearers. At this point, a radio bearer (RB) denotes a logical path provided by the first and second layers of radio protocols for data transfer between the terminal and the UTRAN. Generally, the RB configuration indicates a procedure to regulate the radio protocol layers and channel characteristics necessary to provide a specific service, and to configure the specific parameters and methods of operation. The RB is divided into RB (SRB) signaling and RB (DRB) data. The SRB is used as a path through which it is transmitted

I an RRC message on a C plane, while the DRB is used as a path through which user data is transmitted on a U plane.

Downlink transport channels to transmit data from a network to a terminal, may include a broadcast channel (BCH) to transmit system information and a shared downlink channel (SCH) to transmit other user traffic or message messages. control. Traffic or control messages from a downlink multicast or broadcast service may be transmitted either via a downlink SCH, or via a

I separate downlink (MCH). Additionally, the uplink transport channels to transmit data from a terminal to a network may include a random access channel (RACH) to transmit an initial control message and an uplink shared channel (SCH) to transmit the information of traffic or control messages.

Downlink physical channels for transmitting information transferred to the downlink transport channel by means of a radio interval between a network and a terminal may include a physical broadcast channel (PBCH) for transmitting BCH information, a broadcast channel physical multiple (PMCH) to transmit MCH information, a physical downlink shared channel (PDSCH) to transmit PCH information and downlink SCH information, and a physical downlink control channel (PDCCH) (also called an L1 / L2 control channel) to transmit the control information sent from the first and second layers, such as the downlink radio resource allocation information or uplink (Programming granted DL / UL) or the like. The physical uplink channels to transmit the information transferred to an uplink transport channel by means of a radio interval between a network and a terminal can include a shared physical uplink channel (PUSCH) to transmit link information SCH upstream, a physical random access channel (PRACH) to transmit RACH information, and a physical uplink control channel (PUCCH) to transmit the control information sent from the first and second layers, such as HARQ ACK or NACK, schedule request (SR), channel quality indicator (CQI) report and the like.

The HARQ operation performed on the LTE system based on the above description will now be described.

Figure 4 is a diagram showing a HARQ operation performed on the LTE system.

In Figure 4, a description will be provided in an uplink state in which, a UE is a transmit side, a base station i (eNode B or eNB) is a receive side, and the HARQ feedback information is it receives from the base station, although it can still be applied to downlink transmission.

First, the eNB may transmit uplink scheduling information, i.e., uplink granted (UL granted), via a physical downlink control channel (PDCCH), in order to allow the UE to transmit data using the HARQ schema (S401). The granted UL may include a UE identifier (eg C-RNTI, semi-persistent C-RNTI schedule), a location of an assigned radio resource (a resource block allocation), a transmission parameter such as an index modulation / coding, a redundancy version and the like, a new data indicator (NDI), etc.

The UE can verify the issued UL information itself by monitoring a PDCCH at each transmission time interval (TTI). In the case of discovering the granted UL information sent to itself, the UE can transmit data (data 1 in Figure 4) via the physical uplink shared channel (PUSCH) according to the received granted UL information (S402 ). In this case, the transmitted data can be transmitted using a MAC protocol data unit (PDU).

As described above, after the UE has performed the uplink transmission via the PUSCH, the UÉ waits for the reception of the HARQ feedback information via the physical hybrid ARQ indicator channel (PHICH) from the eNB. If HARQ NACK for data 1 is transmitted from the eNB (S403), the UE again transmits the data 1 in a newly transmitted TTI of data 1 (S404). Conversely, if HARQ ACK is received from the eNB (not shown), the UE stops the HARQ retransmission of data 1.

Each time the UE performs a data transmission using the HARQ scheme, the UE takes a count of the number of transmissions (CURRENT_TX_NB). If the transmission number reaches a maximum transmission number (CURRENT_TX_NB) set by a higher layer, the UE discards the MAC PDU stored in a HARQ buffer.

If the HARQ ACK for the data 1 retransmitted in step S404 from the UE is received (S405) and if a granted UL is received via the PDCCH (S406), the UE can determine whether the data to be transmitted this time is a Initially transmitted MAC PUDs or if retransmitting a previous MAC PDU use a new data indicator field (NDI) received through the PDCCH. In this case, the NDI field is a 1 bit field. The NDI field is alternated as 0-> 1-> 0-> 1-> ... every time a MAC is transmitted

PDU. For retransmission, the NDI field is set to a value equal to that of the initial transmission. In particular, the UE can determine whether to retransmit the MAC PDU by comparing the NDI field with a previously transmitted value.

In the case of FIG. 4, as a value of NDI = 0 in step S401 is alternated to NDI = 1 in step S406, the UE recognizes that the corresponding transmission is a new transmission. The UE can transmit data 2 via PUSCH (S407).

In the meantime, a procedure will now be described, to a UE, that performs random access for an eNB.

First, the UE can perform a random access procedure in the following cases:

- when the UE makes the initial access because there is no RRC connection to the eNB,

- when the UE initially accesses a target cell in a handover procedure,

- when the random access procedure is requested by a command from a base station,

- when there is an uplink data transmission in a situation where the uplink time synchronization is not aligned or where a specific radio resource used to request radio resources is not allocated, and

- when a recovery procedure is performed in the case of a radio link failure or handover failure.

In the LTE system, there are two procedures for selecting a random access preamble: one is a contention based on the random access procedure in which the UE randomly selects a preamble within a specific group for use, another is a non-contention based random access procedure in which the UÉ uses a random access preamble assigned only to a specific UE by the eNB. Non-contention based on the random access procedure can be used, as described above, only in the handover procedure or when requested by the eNB command.

Meanwhile, a procedure in which a UE performs random access for a specific eNB may include steps of (1) in the UE, transmitting a random access preamble for the eNB (hereinafter referred to as a transmission step of "first message (message 1)", (2) receiving a random access response from the eNB corresponding to the transmitted random access preamble (hereinafter referred to as a "second message (message 2)" reception step , (3) transmit an uplink message using the information received by the random access response message (hereinafter as a "third message (message 3)" transmission step, and (4) receive a corresponding message I sent the eNB to the uplink message (hereinafter referred to as a "fourth message (message 4)" reception step.

Figure 5 shows an operating procedure between a UE and an eNB in ​​a contention-based random access procedure.

(1) First message transmission (Message 1)

First, a UE can randomly select a random access preamble from a group of random access preambles indicated through system information or a handover command, it can select PRACH resources with the ability to transmit the random access preamble, and can subsequently transmit the selected random access preamble (step 501).

(2) Second message reception (Message 2)

After transmitting the random access preamble in step S501, the UE may attempt to receive a response with respect to its random access preamble within a random access response receive window indicated by the system information or command. handover by the eNB (Step S502). More specifically, the random access response information is transmitted as a MAC PDU, and the MAC PDU can be transferred via the Physical Downlink Shared Channel (PDSCH). Additionally, the physical downlink control channel (PDCCH) can be monitored, so that the terminal adequately receives the information transferred through the PDSCH. That is, the PDCCH may include information about a UE that should receive the PDSCH, frequency and time information of the PDSCH radio resources, a form of PDSCH transfer, and the like. At this point, if the PDCCH has been successfully received, the UE can suitably receive the random access response transmitted via the PDSCH in accordance with the PDCCH information. The random access response may include a random access preamble identifier (ID) (for example, the random accessp preamble identifier (RAPID)), an ascending access resource indicating the granted UL, a temporary C-RNTI, a time advance command (TAC), and the like.

At this point, the random access preamble identifier is included in the random access response in order to notify UEs what information such as the granted UL, temporary C-RNTI and TAC, might be valid because a random access response may include random access response information for one or more UEs. At this point, it was assumed that the random access preamble identifier can be identical to the random access preamble selected by the UE in step 502. Accordingly, the UE can receive the granted UL, temporary C-RNTI, and TAC .

(3) Transmission and third message (Message 3) i

If the UE has received the valid random access response for the UE itself, the UE can process each information included in the random access response. That is, the UE applies the TAC and stores the temporary C-RNTl. Additionally, the data to be transmitted can be stored in a message buffer 3 corresponding to the reception of the valid random access response.

Additionally, the UE uses the received granted UL so that it transmits data (i.e. message 3) to the eNB (step S503). Message 3 must be included in the UE identifier. This is because, in contention based on the random access procedure, the eNB cannot determine which UEs are performing the random access procedure * although later the UEs must be identifier by contention resolution.

At this point, two different schemes can be provided to include the UE identifier. A first scheme is to transmit the cell identifier UE through an uplink transmission signal that corresponds to the granted UL if the UE has already received the valid cell identifier assigned in a corresponding cell prior to the random access procedure. In contrast, the second scheme is to transmit the unique identifier of the UE (eg S-TMSI or Random ID) if the UE has not received a valid cell identifier prior to the random access procedure. In general, the unique identifier is longer than the cell identifier. If the UE has transmitted the data corresponding to the granted UL, the UE starts a contention resolution timer (CR) '.

(4) Receiving fourth message (Message 4)

After transmitting the data with its identifier through the granted UL included in the random access response, the UE waits for an indication (command) from the eNB for contention resolution. That is, the UE tries to receive the PDCCH so that it receives a specific message (step 504). At this point, there are two schemes for receiving the PDCCH. As described above, if the UE identifier included in message 3 transmitted in correspondence with the granted UL is the cell identifier, the UE attempts to receive the PDCCH using its own cell identifier. If the UE identifier included in message 3 transmitted in correspondence with the granted UL is its unique identifier, the UE attempts to receive the PDCCH using the temporary C-RNTI included in the random access response. After which, for the above, if the PDCCH is received through its cell identifier before the contention resolution timer expires, the UE determines that the random access procedure has been performed successfully (normally) , thus completing the random access procedure. For the latter, if the PDCCH is received through the temporary cell identifier before the contention resolution timer expires, the UE verifies the data transferred by the PDSCH indicating the

PDCCH. If the unique identifier of the UE is included in the data, the UE determines that the random access procedure has been performed successfully (normally), thereby completing the random access procedure.

In the meantime, if the contention resolution procedure through the transmission of message 3 and the reception of message 4 has not been performed successfully, the UE may select another random access preamble so that it restarts the random access procedure . For this purpose, the UE can receive message 2 from the eNB, configure message 3 for the contention resolution procedure, and transmit message 3 to the eNB. The HARQ procedure used for transmission of message 3 in the HARQ system, which was described with reference to Figure 4, may be different from the HARQ procedure for transmission of message 3 in the above random access attempt. In this case, there may be a problem in which the MAC PDU stored in the HARQ buffer corresponding to the HARQ procedure above can be unnecessarily retransmitted. The present inventors provide a technology to recognize and solve the above problem.

BRIEF DESCRIPTION OF THE INVENTION

Accordingly, the present invention is directed to a random access scheme to avoid unnecessary data retransmission and user equipment therefor which substantially obviates one or more

I problems that are due to the limitations and disadvantages of the related technique i.

An objective of the present invention is to provide a random access scheme to avoid unnecessary data retransmission and user equipment therefor.

The advantages, objectives and additional features of the present invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from examination of the following or may be learned from practice. of the present invention. The objects and other advantages of the present invention can be achieved and achieved by the structure particularly pointed out in the written description and claims therein as well as the accompanying drawings.

To achieve these objectives and other advantages and in accordance with the purpose of the present invention, as represented and broadly described in the present description, a method of realizing random access to a base station through a terminal includes transmitting a preamble of random access to the base station; receiving, from the base station in response to the random access preamble, a random access response message including uplink granted information: and storing a Medium Access Control Packet Data Unit (MAC PDU) including uplink data and up terminal identifier in a message buffer 3 (Msg3) in response to the uplink granted information; copying the MAC PDU stored in the Msg3 buffer to a first hybrid automatic repeat request (HARQ) buffer associated with a first HARQ procedure; transmitting the MAC PDU stored in the first HARQ buffer to the base station using the first HARQ procedure; starting or starting a containment resolution (CR) timer again; receiving, from the base station, a physical downlink control channel (PDCCH) signal; and cleaning the first buffer HARQ, if the received PDCCH signal or a physical downlink shared channel signal (PDSCH) associated with the received PDCCH signal does not match the terminal identifier or if the CR timer expires.

A containment resolution may be considered by the terminal to be unsuccessful if the received PDCCH signal or a physical downlink shared channel signal (PDSCH) associated with the received PDCCH signal does not match the terminal identifier or if the CR timer expires .

The terminal may stop a timing alignment timer (TAT), when the terminal considers the containment resolution to be unsuccessful. The terminal can clear the first HARQ buffer, when the TAT expires or stops.

The terminal identifier may be one of a terminal Cellular Radio Network Temporary Identifier (C-RNTI) of the terminal or a contention resolution identity UE of the terminal.

The terminal may consider the contention resolution unsuccessful when the terminal has transmitted the MAC PDU including the terminal's CRNTI and the received PDCCH signal is not directed to the terminal's C-RNTI. Alternatively, the terminal may consider the contention resolution as unsuccessful, when the terminal has transmitted the MAC PDÜ including the terminal's contention resolution identity UE and the PDSCH signal associated with the received PDCCH signal does not match the resolution identity UE containment terminal.

The method may further include transmitting the selected random access preamble back to the base station in accordance with the contention resolution failure, receiving a random access response message including a Timing Alignment Command (TAC) from the base station , starting or starting a Timing Alignment Stopwatch (TAT) according to the receipt of the TAC; copying the MAC PDU stored in the Msg3 buffer to a second HARQ buffer associated with a second HARQ procedure, and transmitting the MAC PDU stored in the second HARQ buffer to the base station using the second HARQ procedure, and the In accordance with the present embodiment, the MAC PDU stored in the first HARQ buffer may not transmit even when the TAT is started or started again.

In another aspect of the present invention, a terminal includes a physical layer module that includes a transmission module configured to transmit a random access preamble to a base station, and a receive module configured to receive a random access response message. including the uplink information provided from the base station; and a medium access control layer (MAC) module including a multiplexing and assembly entity configured to configure a medium access control packet data unit (MAC PDU) including the uplink data and a terminal identifier according to the uplink information provided received by the receiving module, a message buffer 3 (Msg3) configured to store the MAC PDU configured by multiplexing and assembly entity according to the reception of the random access response message, a plurality of hybrid automatic repeat request (HARQ) procedure modules ) and a plurality of HARQ buffers associated with the plurality of HARQ procedure modules, and a HARQ entity configured for control operations of the plurality of HARQ procedure modules, wherein the MAC layer module copies the MAC PDU stored in the Msg3 buffer to a first HARQ buffer associated with a first HARQ procedure of according to the receipt of the random access response message by the receiving module, controlling the MAC PDU stored in the first HARQ buffer to be transmitted to the base station using the first HARQ procedure, and starting or starting a contention resolution timer (CR) again when transmitting the MAC PDU stored in the first HARQ buffer , and where, if the reception of a physical downlink control channel (PDCCH) signal from the base station is reported from the physical layer module, is the MAC layer module determines whether the PDCCH or a physical downlink shared channel signal (PDSCH) associated with the PDCCH signal matches the terminal identifier or whether the CR timer expires, and cleans the first HARQ buffer if The PDCCH signal or the PDSCH signal associated with the PDCCH signal does not match the terminal identifier or if the CR timer expires.

A contention resolution may be considered by the MAC layer module as unsuccessful if the received PDCCH signal or the PDSCH signal associated with the received PDCCH signal does not match the terminal identifier or if the CR timer expires.

The MAC layer module can stop a timing alignment timer (TAT), when the terminal considers the contention resolution to be unsuccessful. The MAC layer module can clean the first HARQ buffer, when the TAT expires or stops.

The terminal identifier may be one of the terminal's cellular radio network temporary identifier (C-RNTI) or a terminal UE containment resolution identity. The MAC layer module may consider the contention resolution as unsuccessful, when the terminal has transmitted the MAC PDU including the C-RNTI of the terminal and the received PDCCH signal is not directed to the C-RNTI of the terminal.

The contention resolution may be considered by the MAC layer module as unsuccessful, when the terminal has transmitted the MAC PDU including the contention resolution identity UE from the terminal to the PDSCH associated with the received PDCCH signal does not match the resolution resolution identity of UE containment of the terminal.

In accordance with the present invention, it is possible to avoid retransmitting unnecessary data during a random access procedure or after completing the random access procedure.

It should be understood that both the above general description i

As the following detailed description of the present invention are exemplary and explanatory and are intended to provide a further explanation of the present invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the present invention and are incorporated in and formed by this application, illustrate embodiment (s) of the invention and, in conjunction with the description, serve to explain the principle of the invention. . In the drawings:

Figure 1 is a schematic diagram of an evolved universal mobile telecommunication system network architecture (E23

UMTS) as an example of a mobile communication system;

Figures 2 and 3 are diagrams showing the radio interface protocol architectures between a user equipment (UE) and a UMTS terrestrial radio access network (UTRAN) based on the radio access network standard of the 3rd generation collaboration project (3GPP);

Figure 4 is a diagram showing a HARQ operation performed on the LTE system;

Figure 5 is a diagram illustrating an UE and eNB operating procedure in contention based on the random access procedure;

Figure 6 is a diagram illustrating the case where a UE performs unintended HARQ retransmission, which is recognized by the present inventors;

Fig. 7 is a diagram illustrating an operation of a UE, which performs a random access procedure according to a first embodiment of the present invention;

Fig. 8 is a diagram illustrating an operation of a UE, which performs a random access procedure in accordance with a second embodiment of the present invention;

FIG. 9 is a diagram illustrating an operation of a UE, which performs a random access procedure in accordance with a third embodiment of the present invention;

Figure 10 is a diagram illustrating a procedure in it.

I which, a UE performs a random access procedure with respect to up

I eNB according to an embodiment of the present invention;

Fig. 11 is a diagram showing the configuration of a UE processor in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, the examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be understood that the detailed description that will be described together with the i

Accompanying drawings are intended to describe the example embodiments of the present invention, and are not intended to describe a single embodiment through which the present invention is to be performed. Hereinafter, the detailed description includes detailed questions to provide a complete understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be accomplished without the detailed issues. For example, although the following detailed description is made under the assumption that a mobile communication system is the 3GPP LTE system, it may apply to other prescribed mobile communication systems excluding the unique items of the 3GPP LTE.

In some cases, well-known structures and devices are omitted in order to avoid obscuring the concepts of the present invention, and the important functions of the structures and devices are shown in block diagram form. The same reference numbers will be used throughout the drawings to refer to the same or similar parts.

In the following description, a terminal was assumed to be a generic term for a mobile device or a fixed user end device, such as user equipment (UE), a mobile station (MS), and the like. Additionally, it was assumed that a base station is a generic name for any node at a network endpoint, which communicates with a terminal, such as Node B, eNode B, and the like.

As described above, the present invention provides a random access scheme to avoid unnecessary retransmission of data in a random access procedure and a User Equipment (UE) therefor. First, an uplink stopwatch alignment maintenance scheme and a contention resolution procedure for the random access procedure will be described in detail.

The description of the uplink stopwatch alignment maintenance in an LTE system will be provided. In the LTE system based on Orthogonal Frequency Division Multiplexing (OFDM) technology, there is the possibility of interference between UEs during communication between the UE and the eNB. In order to minimize interference between UEs, it is important that the eNB handle or manipulate the UE transmission timing. More particularly, the UE may be present in a random area within a cell, and this implies that a

The travel time of the data from the UE to the eNB can be varied based on a location in the UE. Particularly, if a UE tries to transmit data on one edge of the cell, the data transmission time of this specific UE will be much longer than the data transmission time of a UE located in a center of the cell. In contrast, if a UE is located in the center of the cell, the data transmission time of this specific terminal will be much shorter than the data transmission time of a UE located on the edge of the cell. The eNB must handle or manipulate all data or signals, which are transmitted by the UEs within the cell, within the time limit in order to avoid interference between the UEs. In particular, the eNB must adjust or manage a timing of transmission of the UEs according to the location condition of the UE, and such adjustment may be termed timing alignment maintenance.

One of the methods to maintain the timing alignment is a random access procedure. Particularly, during the random access procedure, the eNB receives a random access preamble transmitted from the UE, and the eNB can calculate a time alignment value (Sinc) using the received random access preamble. The calculated time alignment value can be notified to the UE by a random access response, and the UE can update the data transmission timer based on the calculated time alignment value.

In another method, the eNB may receive a sound reference symbol (SRS) transmitted from the UE on a periodic or random basis, calculate the time alignment value (Sinc) based on the SRS, and notify the UE of the alignment value of time. The terminal can then update the data transmission timing.

As described above, the eNB can measure the transmission timing of the UE through a random access preamble or SRS, and can notify the UE of an adjustable timing value. As described above, the time alignment value (Sinc), transmitted from the eNB to the UE can be called a time advance command (hereinafter referred to as "TAC"). The TAC can be processed at a Media Access Control (MAC) layer. Because the UE does not have a fixed location, the transmission timing is frequently changed based on a location of the UE and / or a movement speed of the UE. In consideration of this point, if the

UE receives the TAC from the eNB, it was assumed that the TAC is not valid for an infinite duration although it is only valid for a certain duration. A time alignment timer (TAT) is used to indicate or represent the determined duration. As such, the TAT is initiated when the UE receives the TAC from the eNB. The UE was assumed to be time synchronized with the eNB only during the TAT operation. The TAT value is transmitted to the UE through a radio resource control signal (RRC) such system information (SI) or a reconfiguration of the radio bearer. Additionally, if the UE receives a new TAC from the eNB during a TAT operation, the TAT is started again. Additionally, when the TAT has expired or is not running, the UE determines that the UE is not time synchronized with the eNB and does not transmit any other uplink data or control signal, except for the random access preamble.

Hereinafter, the contention resolution method of the random access procedure will be described in detail.

The reason contention occurs in the random access procedure is because the number of random access preambles is finite. That is, because the eNB cannot apply the unique random access preambles of all UEs to the UEs, each of the UEs randomly selects one of the common random access preambles and transmits the selected random access preamble. . Therefore, two or more UEs can select and transmit the same random access preamble using the same PRACH resources. In this case, the eNB determines that the received random access preamble is transmitted from a UE.

For this purpose, the eNB transmits a random access response to the UE and waits for a UE to receive the random access response. However, as described above, because contention may occur, two or more UEs receive a random access response and accordingly perform the respective operations in accordance with the receipt of the random access response. That is, the two or more UEs transmit I different data by means of the same radio resources using a granted UL included in the random access response.

Then, the transmission of the data in all the two or more UEs may fail or the eNB may only receive the data from a specific UE according to the locations or the transmission powers of the UEs. For the latter, because two or more UEs determine that their data transmission is successful, the eNB could notify the UEs, which fail to contain information about the failure. That is, the notification of the information about the failure or success of the containment, is called containment resolution.

The containment resolution method includes two methods: one is a method of using a containment resolution (CR) timer and the other is a method of transmitting a UE identifier, which successfully performs data transmission to the UEs.

The above method is used when the UE has its unique cell identifier (C-RNTI) before the random access procedure. That is, the UE, which already has the cell identifier, transmits data including its cellular identifier with the eNB according to the random access response and operates the timer CR. Then, when the UE receives the PDCCH information included in its cellular identifier before the timer CR expires, the UE determines that the UE itself is successful in contention and normally completes the random access procedure. In contrast, if the UE does not receive the PDCCH including its cell identifier before the CR timer expires, the UE determines that the UE itself fails contention and performs the random access procedure again or reports a higher layer of the failure .

The last method of contention resolution methods, i.e. the method of transmitting the UE identifier, which successfully performs data transmission, is used when the UE does not have its unique cell identifier prior to the random access. That is, if the UE does not have its cell identifier, an identifier (for example,

S-TMSI or Random ID) higher than the cell identifier is included in the data, so that it is transmitted according to the granted UL included in the random access response, and the UE operates the timer CR. If the data including its top identifier is transmitted by means of a DL-SCH before the timer CR expires, the UE determines that the random access procedure is successful. In contrast, if the data including its top identifier is not transmitted via the DL-SCH before the CR timer expires, the UE determines that the random access procedure fails.

The case where data is unnecessarily retransmitted during the random access procedure or after the random access procedure will be described in detail and the cause thereof will be defined.

Figure 6 is a diagram illustrating the case where the UE performs unintentional HARQ retransmission, which is recognized by present inventors Iqs.

Step 1: The UE may transmit a random access preamble to the eNB in ​​order to perform contention based on the random access procedure.

Step 2: The eNB may transmit a random access response in the UE in response to the random access preamble.

Step 3: The UE can apply a TAC included in the random access response so that a TAT begins. Additionally, the UE can generate a MAC PDU in accordance with the uplink scheduling information included in the random access response and store the MAC PDU in a Message 3 buffer (Msg3).

I

The UE can then search the MAC PDU from the Msg3 buffer, store the MAC PDU in a HARQ buffer associated with a specific HARQ procedure (a HARQ procedure x, in the present embodiment) of a plurality of HARQ procedures, and transmit the MAC PDU stored in the HARQ buffer for the eNB at a transmission time point of the HARQ procedure.

Step 4: The random access procedure is determined to fail due to a specific condition as described above. The UE then stops the TAT operation. The UE may then transmit a random access preamble to the eNB and perform the subsequent necessary operation, in order to retry the random access procedure.

Step 5: The UE may transmit the random access preamble and receive a random access response from the eNB, in order to retry the random access procedure. In this case, the UE may apply a TAC included in the random access response so that a TAT is started again. Additionally, the UE can search for the MAC PDU from the Msg3 buffer and store the MAC PDU in a HARQ buffer associated with a specific HARQ procedure (a HARQ procedure and, in the present embodiment) of the plurality of HARQ procedures and prepare the transmission of the MAC PDU at a transmission time point of the HARQ procedure.

Step 6: during the operation of the UE TAT, the UE determines that an uplink time is synchronized, determines whether a MAC PDU is present in the HARQ buffers corresponding to the respective transmission time points corresponding to the plurality of HARQ procedures (more particularly, eight HARQ procedures on the LTE system), and transmits or transmits the MAC PDU again at a corresponding transmission time point if the MAC PDU is stored in a corresponding HARQ buffer. Consequently, if the MAC PDU is still stored in the HARQ buffer (HARQ x buffer) associated with the HARQ x procedures in Step 6 and the UE TAT is operated, the MAC PDU stored in the HARQ x buffer is transmitted again at the transmission time point which corresponds to the HARQ x procedures, independent of the transmission of the MAC PDU stored in the HARQ buffer (HARQ and) associated with the HARQ and procedures. However, the retransmission of the MAC PDU stored in the HARQ x buffer corresponding to an unintended retransmission.

Because the HARQ procedure used when the UÉ starts the random access procedure again in the example associated with Figure 6, may be different from a HARQ procedure using in a previous random access procedure, the retransmission of unnecessary data may occur as previously described. Therefore, the embodiment of the present invention, in order to avoid the unintentional data retransmission situations described above, in which the random access procedure is started again and verified and a HARQ buffer used in the previous transmission is cleaned in the subsequent procedures, which will be performed in the respective situations, thus avoiding unnecessary retransmission.

Hereinafter, the cases of application of the method in accordance with the present modality to the respective situations will be described.

First modality

Fig. 7 is a diagram illustrating an operation of a UE, which performs a random access procedure in accordance with a first embodiment of the present invention.

The UE may transmit a random access preamble to an eNB in ​​order to perform the random access procedure (S701). In response to the transmission of the random access preamble, the eNB may transmit a random access response message to the UE (S702). The random access response message may include the UL granted for transmission of Message 3 by the UE.

If the UE has a cell identifier (C-RNTI) determined with respect to the eNB in ​​this state, the UE can configure a MAC PDU that includes the UE's cellular identifier (C-RNTI) and transmits the MAC PDU to the eNB as the Message 3 in order to carry out the containment resolution procedure. The UE MAC PDU is configured by multiplexing an assembly entity from a MAC stratum, it is stored in the Msg3 buffer, and it is stored in a buffer

HARQ of a specific HARQ procedure for transmitting Message 3 again.

The UE, which transmits Message 3, using specific HARQ procedures can start a CR timer (S704). In the present embodiment, it was reported that the UE receives a PDCCH signal from the eNB before the timer CR (S705) expires. When the UE receives the PDCCH, and more particularly, if the physical layer of the UÉ informs the MAC layer of the reception of the PDCCH, the UE according to the present modality determines if the PDCCH signal is received using the cell identifier (C -RNTI) transmitted by UE Message 3.

If the UE transmitting Message 3 including the UE's cell identifier (C-RNTI) does not receive the PDCCH corresponding to its cell identifier, the UE may consider the contention resolution procedure unsuccessful and perform the operations subsequent deal with the failure of the containment resolution procedure.

For example, the UE, which considers the contention resolution procedure to be unsuccessful, may (1) increment a random access preamble transmission counter (PREAMBLE_TRANSMISSION_COUNTER) by 1 and (2) determine whether the transmission counter value The preamble reaches a maximum preamble transmission number (preambleTransMx + 1). (3) If the preamble transmission counter value reaches the maximum preamble transmission number, a problem of the random access procedure can be reported to a higher layer. (4) If the preamble transmission counter value does not reach the maximum preamble transmission number, the UE may apply a grant parameter such that it delays a subsequent random access preamble transmission time point and performs a procedure selecting a new random access preamble.

Meanwhile, the UE according to the present mode is configured to perform an operation to clear a HARQ buffer of a specific HARQ procedure used for transmission of Message 3 prior to operation in accordance with failure of the containment resolution procedure . By clearing the HARQ buffer in the operation in which the UE considers the contention resolution procedure to be unsuccessful, the unnecessary retransmission described with respect to Figure 6 can be avoided.

Second modality

Fig. 8 is a diagram illustrating an operation of a UE performing a random access procedure in accordance with a second embodiment of the present invention.

The operations for, in the UE, which transmits a random access preamble to an eNB in ​​order to perform the random access procedure (S801), and receive a corresponding random access response message (S802) are ¡ equal to those of the first modality.

It was assumed that the UE according to the present embodiment does not have a cell identifier (C-RNTI) determined with respect to the eNB in ​​this state. In this case, the UE may include its unique identifier (eg, S-TMSI or a random ID) in a MAC PDU and transmit the MAC PDU when Message 3 is transmitted. The unique identifier of the UE used

I for the content resolution procedure can be called “EU contention resolution identity”.

It was assumed that the UE in accordance with the present mode configures the MAC PDU including the S-TMSI and transmits the MAC PDU to the eNB (S803). The UE MAC PDU is also configured by multiplexing and the MAC layer assembly entity was stored in an Msg3 buffer, and was stored in a HARQ buffer of a specific HARQ procedure used for transmission of Message 3 again .

The UE, which transmits Message 3 using the HARQ procedure, can start a CR timer (S804). In the present embodiment, it was assumed that the UE receives a PDCCH signal from the eNB before the CR timer (S805) expires. When the UE receives the PDCCH, the UE according to the present mode can determine if the PDCCH signal is received using the cell identifier (C-RNTI) used for the current random access procedure.

If the received PDCCH is not received using the UE temporary cell identifier or the UE S-TMSI is not included in the PDSCH received via the radio area corresponding to the PDCH, the UE may consider the contention resolution procedure as unsuccessful and performs subsequent operations in accordance with the failure of the containment resolution procedure.

The UE according to the present modality can perform the operation according to the failure of the containment resolution procedure, which is described in the first modality. Additionally, the UE according to the present embodiment is configured to perform an operation to clear a HARQ buffer of a specific HARQ procedure for the transmission of Message 3 prior to the operation in accordance with the failure of the contention resolution procedure. By clearing the HARQ buffer in the operation in which the UE considers the contention resolution procedure to be unsuccessful, the unnecessary retransmission described with respect to Figure 6 can be avoided.

Third modality

FIG. 9 is a diagram illustrating an operation of a UE, which performs a random access procedure in accordance with a third embodiment of the present invention.

The operations for, in the UE, transmitting a random access preamble for an eNB in ​​order to perform the random access procedure (S901), and receive a corresponding random access response message (S902) are equal to those of the first modality.

In the present embodiment, the UE may include both a cellular identifier (C-RNTI) and a contention resolution identity UE (eg, S-TMSI) in a MAC PDU transmitted via Message 3 and transmitting the MAC PDU ( S903).

When the UE transmits message 3, the UE can start a CR timer (S904). In the present embodiment, if Message 4 corresponding to the UE's message 3 transmission is not received from the eNB before the contention resolution timer (S905) expires, the UE may consider the contention resolution procedure as unsuccessful and performs subsequent operations in accordance with the failure of the containment resolution procedure. At this point, the UE agreed with the present mode is configured to perform an operation to clear a HARQ buffer of a specific HARQ procedure used for transmission of Message 3 prior to the operation in accordance with the failure of the troubleshooting procedure. containment. By clearing the HARQ buffer in the operation in which the UE considers the contention resolution procedure to be unsuccessful, the unnecessary retransmission described with respect to Figure 6 can be avoided.

The first to third modalities described with reference to Figures 7 to 9 may be associated with the case where the UE considers the containment resolution procedure as unsuccessful.

If the UE considers the contention resolution procedure to be unsuccessful, the HARQ buffer used for the above random access procedure is limited as an example of the subsequent operation, so that the MAC PDU retransmission unnecessary for the random access operation The additional HARQ operation is avoided and cleared.

In the meantime, the TAT indicating the uplink synchronization status of the UE according to another embodiment of the present invention will be described.

As described above, when the UE receives a TAC from the eNB, the UE can apply the TAC and start or start the TAT again. The UE may be uplink synchronized with the eNB such that it transmits an uplink signal to the eNB only during the operation of the TAT. If the TAT expires, the UE can clear all HARQ buffers and notify an RRC layer of the release of a PUCCH and an SRS. Additionally, all downlink assignment information and granted UL information can be erased.

In another embodiment of the present invention, in addition to the case where the TAT expires, even when the TAT has stopped, the HARQ buffer is cleared. More particularly, the UE is configured to stop the TAT if the contention resolution procedure is considered to fail as described above with respect to Figures 7a

9. Therefore, in addition to the case where the EU TAT expires, if the

TAT is stopped, the HARQ buffer that corresponds to stopping the TAT is cleared so that unnecessary retransmission of uplink data from the subsequent procedure can be avoided.

Meanwhile, in accordance with the previously described embodiments of the present invention, the random access operation of the UE is performed as follows.

FIG. 10 is a diagram illustrating a procedure in which a UE performs a random access procedure with respect to an eNB in ​​accordance with an embodiment of the present invention.

Step 1: The UE may transmit a random access preamble to the eNB in ​​order to perform contention based on the random access procedure.

Step 2: The eNB may transmit a random access response message to the EU.

Step 3: The UE can apply a TAC included in the random access response so that it starts or starts a TAT again. Additionally, the UE may generate a MAC PDU in accordance with the uplink scheduling information included in the random access response and store the MAC PDU in a Message 3 buffer (Msg3). The UE can then fetch the MAC PDU from the Msg3 buffer, store the MAC PDU in an associated HARQ buffer (a HARQ buffer associated with a HARQ x procedure, in the present mode) again, and transmit the

MAC PDU stored in HARQ buffer for the eNB at a transmission time point of the HARQ procedure. Additionally, the containment resolution timer can be started.

Step 4: if the CR timer expires, if the UE has not received the PDCCH addressed to the cell identifier of the UE after transmitting Message 3 that includes the cellular identifier (C-RNTI) or if the cell identifier (C-RNTI) is not assigned to the UE, the UE includes a superior identifier (S-TMSI or a random ID) in a message according to the uplink scheduling information included in the random access response and transmits the message, and the same information as the top identifier is not included in PDSCH data corresponding to a PDCCH indicated and transmitted by the eNB, the UE may determine that the contention resolution procedure, which is currently performed, fails and, more particularly, the containment resolution procedure procedure fails. The UE according to the present embodiment is configured to discard the data stored in the HARQ buffer of the UE if the contention resolution procedure is considered to fail.

Additionally, the UE may transmit a random access preamble to the eNB and receive a random access response from the eNB, in order to retry the random access procedure.

Step 5: The UE can apply a TAC included in the random access response, such that a TAT is started again. Additionally, the UE can fetch the MAC PDU from memory

I buffer Msg3 and store the MAC PDU in an associated HARQ buffer (a HARQ buffer associated with a HARQ procedure and, in the present embodiment) and prepare for transmission of the MAC PDU at a transmission time point of the HARQ procedure.

As described above, in the LTE system, if the data is stored in a HARQ buffer at the transmission time points corresponding to a plurality of HARQ procedures, the HARQ operation is configured to retransmit the data to the eNB. In the present embodiment, because the MAC PDU stored in the HARQ x procedure is cleared in Step 4, unnecessary data retransmission is not performed at the transmission time point corresponding to the HARQ procedures.

Hereinafter, the configuration of a UE according to an embodiment of the present invention will be described.

In a mobile communication system, the UE may include a signal input module, a display module, an antenna, a signal processor, and the like. Among these modules, the configuration of the UE processor to perform a random access operation in accordance with an embodiment of the present invention will be described.

Fig. 11 is a diagram showing the configuration of a UE processor in accordance with an embodiment of the present invention.

As shown in Figure 11, the UE processor may have a layer structure shown in Figures 2 and 3. Among these layers, the physical layer module 1110 and the MAC layer mode will be described.

1120 in accordance with the present modality.

UE physical layer module 1110 in accordance with the present embodiment may include a transmit (Tx) 1111 module configured to transmit a Random Access (RA) preamble to an eNB and a receive (Rx) 1112 module configured to receive a Random Access Response (RAR) message including the UL information given from the eNB. Additionally, the UE's MAC layer 1120 module according to the present embodiment may include multiplexing and the assembly entity 1121 configured to configure a MAC PDU including the uplink data and the UE identifier according to the received UL information received by the Rx 1112 module, a Msg3 1122 buffer configured to store a MAC PDU configured by multiplexing and assembly entity 1121 according to the reception of the RAR message, a plurality of HARQ 1124 procedure modules, a plurality of HARQ 1125 buffers, respectively, corresponding to the plurality of HARQ procedure modules, and a HARQ 1123 entity to control the operations of the plurality of HARQ 1124 procedure modules.

More particularly, the MAC layer 1120 module can be configured to copy the MAC PDU stored in the buffer memory

Msg3 1122 in a first HARQ 1125 buffer corresponding to a first HARQ 1124 procedure module of the plurality of HARQ procedure modules according to the reception of the RAR message. Additionally, the MAC 1120 layer module can control the MAC PDU stored in the first HARQ 1125 buffer to be transmitted to the eNB via the Tx 1111 module using the first HARQ 1124 procedure module. When the MAC PDU stored in the first HARQ 1125 buffer is transmitted, the MAC layer module 1120 can be configured to start or start the CR timer again.

Meanwhile, if the physical layer module 1110 reports receipt of the PDCCH from the eNB, the MAC layer module 1120 can determine whether the PDCCH signal or the PDSCH signal associated with the PDCCH signal is directed to the UE identifier or whether the CR timer has expired. If the PDCCH or PDSCH associated with the DCCH is not directed to the UE identifier or if the CR timer has expired, the UE MAC layer module 1120 according to the present embodiment is configured to clear the first HARQ 1125 buffer.

If the MAC layer 1120 module considers the contention resolution procedure unsuccessful, the MAC layer 1120 module stops the TAT. More particularly, if the TAT expires or is stopped, the MAC layer module can be configured to clear the MAC PDU stored in the first HARQ 1125 buffer.

Although the present invention is described with respect to a signal transmission or reception technology and user equipment therefor applied to a 3GPP LTE system, the present invention can be applied to various mobile communication systems having similar procedures in addition to 3GPP LTE system.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Accordingly, the present invention is intended to encompass the modifications and variations of the present invention as long as they are within the scope of the appended claims and their equivalents.