KR101438238B1 - Method of performing random access procedure in wireless communication system - Google Patents

Abstract

A method for performing a random access procedure includes receiving information on a dedicated random access preamble, transmitting the dedicated random access preamble, and assigning a random access identifier corresponding to downlink radio resource allocation and the dedicated random access preamble. And receiving a random access response.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of performing random access in a wireless communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a method for transmitting or receiving data during a random access procedure in a wireless communication system.

A 3rd Generation Partnership Project (3GPP) mobile communication system based on WCDMA (Wideband Code Division Multiple Access) wireless access technology is widely deployed all over the world. HSDPA (High Speed Downlink Packet Access), which can be defined as the first evolutionary phase of WCDMA, provides the 3GPP with highly competitive wireless access technology in the mid-term future. However, since the requirements and expectations of users and operators are continuously increasing and wireless access technology is being developed, new technologies in 3GPP are required to be competitive in the future. Reduced cost per bit, increased service availability, the use of flexible frequency bands, simple structure and open interfaces, and proper power consumption of terminals are becoming a requirement.

In general, one base station is provided with one or more cells. A plurality of terminals may be located in one cell. Generally, a terminal performs a random access procedure to access a network. The purpose of the terminal performing the random access procedure to the network may be initial access, handover, scheduling request, timing alignment, and the like.

The random access procedure may be divided into a contention based random access procedure and a non-contention based random access procedure. The major difference between the contention based random access procedure and the non-contention based random access procedure is whether the random access preamble is dedicated to one UE. In the non-contention-based random access procedure, since the UE uses a dedicated random access preamble assigned only to itself, contention (or collision) with other UEs does not occur. Here, the contention means that two or more UEs attempt a random access procedure using the same random access preamble through the same resource. In the contention-based random access procedure, there is a possibility of contention because the UE uses randomly selected random access preamble.

As described above, when the random access procedure is started for various reasons, and is divided into a contention based random access procedure and a non-contention based random access procedure, if a random access response set to only one configuration is used, Can be achieved inefficiently.

For example, in a non-contention-based random access procedure, a UE can transmit uplink data using uplink radio resource allocation information included in a random access response. However, if the UE does not have any uplink data, the uplink radio resource allocation information is meaningless.

There is a need for a method that can more efficiently utilize radio resources in the random access procedure.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for performing a non-contention-based random access procedure for efficiently using radio resources in a wireless communication system.

Another aspect of the present invention is to provide a method for performing a non-contention-based random access procedure for reducing battery consumption of a terminal in a wireless communication system.

In one aspect, a method for performing a random access procedure in a wireless communication system includes receiving information on a dedicated random access preamble, transmitting the dedicated random access preamble, and assigning a downlink radio resource assignment and a dedicated random access preamble And receiving a random access response including a random access identifier corresponding to the random access identifier.

In another aspect, a method for performing a random access procedure in a wireless communication system includes receiving information about a dedicated random access preamble, transmitting the dedicated random access preamble, and transmitting the dedicated random access preamble, which is indicated by a physical downlink control channel (PDCCH) Receiving a random access response on a physical downlink shared channel (PDSCH), wherein the random access response includes a downlink radio resource assignment and a random access identifier corresponding to the dedicated random access preamble.

By using various types of random access responses, the efficiency of radio resources is increased. In addition, it is possible to receive downlink data over the PDSCH without receiving the PDCCH, thereby reducing battery consumption of the terminal and increasing the capacity of the cell.

1 is a block diagram illustrating a wireless communication system. This may be a network structure of an Evolved-Universal Mobile Telecommunications System (E-UMTS). The E-UMTS system may be referred to as an LTE (Long Term Evolution) system. Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and the like.

Referring to FIG. 1, an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) includes a base station (BS) 20 that provides a control plane and a user plane.

A user equipment (UE) 10 may be fixed or mobile and may be referred to as another term such as a mobile station (MS), a user terminal (UT), a subscriber station (SS) The base station 20 generally refers to a fixed station that communicates with the terminal 10 and may be referred to as another term such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point have. One base station 20 may have more than one cell. An interface for transmitting user traffic or control traffic may be used between the base stations 20. Hereinafter, downlink refers to communication from the base station 20 to the terminal 10, and uplink refers to communication from the terminal 10 to the base station 20.

The base stations 20 may be interconnected via an X2 interface. The base station 20 is connected to an EPC (Evolved Packet Core), more specifically, an MME (Mobility Management Entity) / S-GW (Serving Gateway) 30 via an S1 interface. The S1 interface supports many-to-many-relations between the base station 20 and the MME / SAE gateway 30.

2 is a block diagram illustrating a functional split between the E-UTRAN and the EPC. The hatched box represents the radio protocol layer and the white box represents the functional entity of the control plane.

Referring to FIG. 2, the base station performs the following functions. (1) radio resource management such as radio bearer control, radio admission control, connection mobility control, and dynamic resource allocation to a terminal, (RRM) function, (2) Internet Protocol (IP) header compression and encryption of user data streams, (3) routing of user plane data to the S-GW, (4) Scheduling and transmission, (5) scheduling and transmission of broadcast information, and (6) measurement and measurement reporting setup for mobility and scheduling.

The MME performs the following functions. (1) NAS (Non-Access Stratum) signaling, (2) NAS signaling security, (3) Idle mode UE reachability, (4) Tracking Area list management, , (5) Roaming, and (6) Authentication.

The S-GW performs the following functions. (1) mobiltiy anchoring, (2) lawful interception. The P-GW (PDN-Gateway) performs the following functions. (1) terminal IP (internet protocol) allocation, and (2) packet filtering.

3 is a block diagram showing elements of a terminal; The terminal 50 includes a processor 51, a memory 52, an RF unit 53, a display unit 54, and a user interface unit 55 . The processor 51 implements layers of the air interface protocol to provide a control plane and a user plane. The functions of the respective layers can be implemented through the processor 51. [ The memory 52 is connected to the processor 51 and stores a terminal driving system, an application, and general files. The display unit 54 displays various information of the terminal and can use well known elements such as a liquid crystal display (LCD) and an organic light emitting diode (OLED). The user interface unit 55 may be a combination of a well-known user interface such as a keypad or a touch screen. The RF unit 53 is connected to the processor to transmit and / or receive a radio signal.

The layers of the radio interface protocol between the terminal and the network are classified into L1 (first layer), L2 (first layer), and L2 (third layer) based on the lower three layers of the Open System Interconnection (Second layer), and L3 (third layer). The physical layer belonging to the first layer provides an information transfer service using a physical channel, and a radio resource control (RRC) layer located at the third layer Controls the radio resources between the UE and the network. To this end, the RRC layer exchanges RRC messages between the UE and the network.

4 is a block diagram illustrating a radio protocol architecture for a user plane. 5 is a block diagram illustrating a wireless protocol structure for a control plane. This represents the structure of the radio interface protocol between the UE and the E-UTRAN. The data plane is a protocol stack for transmitting user data, and the control plane is a protocol stack for transmitting control signals.

Referring to FIGS. 4 and 5, a physical layer (PHY) layer of the first layer provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to an upper layer MAC (Medium Access Control) layer through a transport channel, and data is transferred between the MAC layer and the physical layer through the transport channel. Data moves between physical layers between different physical layers, that is, between a transmitting side and a receiving physical layer.

The MAC layer of the second layer provides a service to a radio link control (RLC) layer, which is an upper layer, through a logical channel. The RLC layer of the second layer supports transmission of reliable data. There are three operation modes of the RLC layer according to the data transmission method, namely, a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM). The AM RLC provides a bi-directional data transmission service and supports retransmission when a RLC PDU (Protocol Data Unit) transmission fails.

The Packet Data Convergence Protocol (PDCP) layer of the second layer performs a header compression function to reduce the IP packet header size.

The third layer of Radio Resource Control (RRC) layer is defined only in the control plane. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of radio bearers (RBs). RB denotes a service provided by the second layer for data transmission between the UE and the E-UTRAN. If there is an RRC connection between the RRC of the UE and the RRC of the network, the UE is in the RRC Connected Mode, and if not, the UE is in the RRC Idle Mode.

The non-access stratum (NAS) layer located at the top of the RRC layer performs functions such as session management and mobility management.

6 shows a mapping between the DL logical channel and the DL transmission channel. 7 shows a mapping between the uplink logical channel and the uplink transport channel. These are 3GPP TS 36.300 V8.3.0 (2007-12) Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; You can refer to Section 6.1.3 of Stage 2 (Release 8).

6 and 7, a paging control channel (PCCH) is mapped to a paging channel (PCH) in a downlink, a BCCH (Broadcast Control Channel) is mapped to a broadcast channel (BCH) or a downlink shared channel do. A Common Control Channel (CCCH), a Dedicated Control Channel (DCCH), a Dedicated Traffic Channel (DTCH), a Multicast Control Channel (MCCH), and a Multicast Traffic Channel (MTCH) are mapped to a DL-SCH. MCCH and MTCH are also mapped to MCH (Multicast Channel). In the uplink, the CCCH, DCCH and DTCH are mapped to UL-SCH (uplink shared channel).

Each logical channel type is defined according to what kind of information is transmitted. There are two types of logical channels: control channel and traffic channel.

The control channel is used for transmission of control plane information. The BCCH is a downlink channel for broadcasting system control information. The PCCH is a downlink channel for transmitting paging information, and is used when the network does not know the location of the terminal. The CCCH is a channel for transmitting control information between the UE and the network, and is used when the UE does not have an RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used for transmitting MBMS control information, and is used for terminals receiving MBMS. The DCCH is a point-to-point unidirectional channel for transmitting dedicated control information between the UE and the network, and is used by the UE having the RRC connection.

The traffic channel is used for transmission of user plane information. The DTCH is a point-to-point channel for transmitting user information, and exists in both the uplink and the downlink. The MTCH is a point-to-multipoint downlink channel for the transmission of traffic data and is used for terminals receiving MBMS.

The transport channel is classified according to how the data is transmitted through the air interface. The BCH is broadcast in the entire cell area and has a fixed predefined transmission format. DL-SCH supports hybrid automatic repeat request (HARQ). Support for dynamic link adaptation due to modulation, coding and transmission power changes, possibility of broadcasting, possibility of beamforming, support for dynamic / semi-static resource allocation, support for discontinuous reception (DRX) And MBMS transmission support. PCH is characterized by DRX support for terminal power saving, and broadcast to the entire cell area. The MCH is characterized by broadcast to the entire cell area and support for MBMS Single Frequency Network (MBSFN).

The uplink transport channel includes a UL-SCH and a random access channel (RACH). The UL-SCH is characterized by support for dynamic link adaptation that changes transmit power and modulation and coding, HARQ support, and support for dynamic and semi-static resource allocation. The RACH is characterized by limited control information and a risk of collision.

8 shows a mapping between a downlink transport channel and a downlink physical channel. 9 shows a mapping between an uplink transport channel and an uplink physical channel.

8 and 9, the BCH is mapped to a physical broadcast channel (PBCH), the MCH is mapped to a physical multicast channel (PMCH), the PCH and the DL-SCH are mapped to a physical downlink shared channel (PDSCH) do. The PBCH carries the BCH transport block, the PMCH carries the MCH, and the PDSCH carry the DL-SCH and PCH. In the uplink, the UL-SCH is mapped to a physical uplink shared channel (PUSCH), and the RACH is mapped to a physical random access channel (PRACH). The PRACH carries a random access preamble.

There are several physical control channels used in the physical layer. The physical downlink control channel (PDCCH) informs the UE about the resource allocation of the PCH and the DL-SCH and the HARQ information associated with the DL_SCH. The PDCCH may carry an uplink scheduling grant informing the UE of the resource allocation of the uplink transmission. A physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. PHICH (Physical Hybrid ARQ Indicator Channel) carries HARQ ACK / NAK signal in response to uplink transmission. A physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request and CQI for downlink transmission.

10 shows a structure of a radio frame.

Referring to FIG. 10, a radio frame is composed of 10 subframes, and one subframe is composed of two slots. The time taken for one subframe to be transmitted is referred to as a transmission time interval (TTI). For example, the length of one subframe may be 1 ms and the length of one slot may be 0.5 ms.

The structure of the radio frame is merely an example, and the number of subframes included in a radio frame, the number of slots included in a subframe, and the number of OFDM symbols included in a slot can be variously changed.

11 is an exemplary view illustrating a resource grid for one downlink slot.

Referring to FIG. 11, a downlink slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain. Herein, one downlink slot includes 7 OFDM symbols, and one resource block includes 12 subcarriers in the frequency domain, but the present invention is not limited thereto.

Each element on the resource grid is called a resource element, and one resource block contains 12 × 7 resource elements. The number N ^DL of resource blocks included in the downlink slot is dependent on the downlink transmission bandwidth set in the cell.

12 shows the structure of a subframe.

Referring to FIG. 12, a subframe includes two consecutive slots. The maximum 3 OFDM symbols preceding the first slot in the subframe are the control regions to which the PDCCH is allocated and the remaining OFDM symbols are the user regions to which the PDSCH is allocated. The PCFICH carries information about the number of OFDM symbols used in the transmission of the PDCCHs in the subframe.

13 is an exemplary diagram showing data transmission and reception.

Referring to FIG. 13, a base station transmits general user data on a physical channel PDSCH mapped to a transport channel DL-SCH. The PDCCH is information on downlink radio resource allocation information, that is, data on the PDSCH is transmitted to a terminal (one or a plurality of terminals), and also includes information on how the terminals should receive and decode the PDSCH.

The base station determines the PDCCH format according to the control information to be transmitted to the UE, and attaches a CRC (Cyclic Redundancy Check) to the control information. The CRC is masked with a unique identifier (referred to as RNTI (Radio Network Temporary Identifier)) according to the owner or use of the PDCCH. If the PDCCH is for a particular UE, the unique identifier of the UE, e.g., C-RNTI (Cell-RNTI), may be masked in the CRC. Alternatively, if it is a PDCCH for paging information, a paging indication identifier, for example a paging indication-RNTI (PI-RNTI), may be masked in the CRC. If the PDCCH is for system information, the system information identifier, SI-RNTI (system infor- mation-RNTI), may be masked in the CRC. A random access-RNTI (RA-RNTI) may be masked in the CRC to indicate a random access response that is a response to the transmission of the UE's random access preamble.

For example, the PDCCH is CRC masked with a C-RNTI of A, and transmission format information (for example, a transport block size, modulation and coding scheme, etc.) is transmitted through a radio resource (for example, ) Is transmitted in a specific sub-frame including information on data being transmitted in a specific sub-frame. The UEs in the cell monitor the PDCCH using their C-RNTI. Upon receiving the PDCCH addressed by its C-RNTI A in the subframe, the UE receives the PDSCH through the B radio resource and the C format information in the PDCCH.

The random access procedure will be described below.

First, the terminal can perform a random access procedure to the base station in the following cases.

(1) When the UE does not have an RRC connection with the base station and performs initial access

(2) When the terminal first accesses the target cell in the handover process

(3) When requested by a base station command

(4) When uplink data is generated in a situation where the time synchronization of the uplink does not match or the uplink radio resource is not allocated

(4) In case of radio link failure or handover failure recovery process

The random access procedure may be divided into a contention based random access procedure and a non-contention based random access procedure. The major difference between the contention-based random access procedure and the non-contention-based random access procedure is whether the random access preamble is dedicated to one UE. In the non-contention-based random access procedure, since the UE uses a dedicated random access preamble assigned only to itself, contention (or collision) with other UEs does not occur. Here, the contention means that two or more UEs attempt a random access procedure using the same random access preamble through the same resource. In the contention-based random access procedure, there is a possibility of contention because the UE uses randomly selected random access preamble. The non-contention-based random access procedure can be used only when a random access cause is requested by a handover process or a command of a base station.

14 is a flowchart illustrating a contention based random access procedure.

Referring to FIG. 14, in step S110, the UE randomly selects one random access preamble from the random access preamble set and transmits the selected random access preamble to the base station through the PRACH resource. The information on the configuration of the random access preamble set can be obtained from the base station through a part of system information or a handover command message.

In step S120, the terminal attempts to receive its random access response in the random access response reception window. A random access response reception window can be indicated through a part of the system information or a handover command message, and is a window for monitoring a random access response. In more detail, the random access response is transmitted in the form of a MAC PDU, and the MAC PDU is delivered to the PDSCH, which is a physical channel. The reception information of the PDSCH is acquired through the PDCCH, which is a control channel. The PDCCH carries information of the terminal to receive the PDSCH, radio resource allocation information of the PDSCH, and transmission format of the PDSCH. The UE first monitors the PDCCH in a subframe belonging to the random access response reception window and receives a random access response on the PDSCH indicated by the PDCCH when the PDCCH is successfully received.

The random access response includes a time alignment (TA) value for uplink synchronization of the UE, uplink radio resource allocation information, a random access preamble identifier (RAPID) for identifying UEs performing random access, And temporary C-RNTI (Cell-Radio Network Temporary Identity). The random access preamble identifier is used to identify the received random access preamble.

In step S130, the UE applies the time synchronization value and transmits a scheduled message including the random access identifier to the base station using the uplink radio resource allocation information. Upon applying the time synchronization value, the terminal starts or restarts a time alignment timer. If the time synchronization timer has been previously activated and the time synchronization timer is restarted, the time synchronization timer is started if the time synchronization timer has not been previously activated.

The random access identifier is used to distinguish a terminal from which a base station performs a random access procedure. The random access identifier can be obtained in two ways. The first method uses the cell identifier as the random access identifier if the UE has a valid cell identifier (for example, C-RNTI) already allocated in the cell before the random access procedure. The second method uses a unique identifier (S-TMSI (Temporary Mobile Station Identifier) or upper layer identifier (S-TMSI)) as the random access identifier if the UE has not been assigned a valid cell identifier before the random access procedure. The UE starts a contention resolution timer as it transmits the scheduled message.

In step S140, after receiving the scheduled message, the base station transmits a contention resolution message including the random access identifier to the UE.

Contention in the contention-based random access procedure occurs because the number of possible random access preambles is finite. Since a unique random access preamble can not be assigned to all UEs in a cell, the UE selects and transmits random access preamble randomly among the random access preamble sets. Accordingly, two or more UEs can select and transmit the same random access preamble through the same PRACH resource. This is the case where contention occurs. The base station that has received the random access preamble transmits a random access response for the random access preamble without knowing whether or not there is contention. However, since a contention has occurred, two or more UEs receive the same random access response, and the UEs each transmit a scheduled message based on the information included in the random access response. This means that two or more UEs transmit different scheduled messages through the uplink radio resource allocation information included in the random access response. At this time, the transmission of the scheduled message fails, or the base station successfully receives only the scheduled message of the specific UE according to the location or transmission power of the UEs. If the base station successfully receives the scheduled message, the base station transmits the contention resolution message using the random access identifier included in the scheduled message. The UE receiving the random access identifier of its own can know that the contention resolution is successful. In a contention-based random access procedure, contention resolution is a method in which a UE can determine whether a contention has failed or succeeded.

Contention resolution timer is used for conflict resolution. The contention resolution timer is started after receiving the random access response. The contention resolution timer may be started when the UE transmits a scheduled message. When the contention resolution timer expires, it determines that the contention resolution is not successful and starts a new random access procedure. Upon receiving a contention resolution message containing its own random access identifier, the contention resolution timer is stopped and determines that the contention resolution is successful. If the UE has a unique cell identifier such as C-RNTI before the random access procedure, the UE transmits a scheduled message including its cell identifier to the base station and then starts a contention resolution timer. When the PDCCH addressed by its cell identifier is received before the contention resolution timer expires, the UE determines that it has succeeded in the contention and ends the random access procedure normally. Alternatively, if the terminal does not have a C-RNTI, the upper layer identifier may be used as the random access identifier. The UE transmits a scheduling message including an upper layer identifier, and then starts a contention resolution timer. If the contention resolution message including its upper identifier is received on the DL-SCH before the contention resolution timer expires, the terminal determines that the random access procedure is successful. The contention resolution message is received using the PDCCH indicated by the temporary C-RNTI. However, if the contention resolution message including its own random access identifier is not received on the DL-SCH until the contention resolution timer expires, the terminal determines that the contention failed.

15 is a flowchart illustrating a non-contention based random access procedure.

Referring to FIG. 15, in step S210, a UE is allocated a dedicated random access preamble from a base station. For a non-contention-based random access procedure, it is necessary to allocate a dedicated random access preamble from the base station that is not likely to collide. The dedicated random access preamble may be included in the handover command message or transmitted on the PDCCH. If the random access procedure is performed during the handover procedure, the UE can obtain a dedicated random access preamble from the handover command message. If the random access procedure is performed at the request of the base station, the UE can acquire a dedicated random access preamble through the PDCCH.

In step S220, the UE transmits a dedicated random access preamble to the base station through the PRACH resource.

In step S230, the UE receives a random access response corresponding to the dedicated random access preamble. Contrary to the contention-based random access procedure, in the non-contention-based random access procedure, it is determined that the random access procedure has been normally performed by receiving the random access response, and the random access procedure is terminated.

Hereinafter, time alignment for uplink synchronization will be described. In the wireless communication system, it is important to synchronize the time synchronization between the terminal and the base station in order to minimize interference between users.

The random access procedure is one of the methods for uplink time synchronization. The BS measures the time synchronization value through the random access preamble transmitted by the MS and provides the time synchronization value to the MS through the random access response. The UE receiving the random access response applies the time synchronization value and starts a time alignment timer. During the operation of the time synchronization timer, the time synchronization between the terminal and the base station is maintained. If the time synchronization timer expires or does not operate, the time synchronization between the terminal and the base station is not maintained. If a contention occurs in the contention-based random access procedure and the contention fails, the UE can stop the time synchronization timer. If the time synchronization timer expires or does not operate, the UE can not perform any uplink transmission other than the transmission of the random access preamble.

16 shows a MAC PDU structure for a random access response. The MAC PDU includes a MAC header and a MAC payload. The MAC payload includes at least one MAC random access response (RAR). The MAC header includes at least one MAC subheader, and the MAC subheader is divided into a RAPID MAC subheader and a BI (backoff indicator) MAC subheader. Each RAPID MAC subheader corresponds to one MAC RAR.

17 shows a RAPID MAC subheader. The E (extents) field is a flag indicating whether another field exists in the MAC header. The T (type) field is a flag indicating whether the MAC subheader includes RAPID or BI. The RAPID field is used to distinguish the transmitted random access preamble.

18 shows the BI MAC subheader. The E (extents) field is a flag indicating whether another field exists in the MAC header. The T (type) field is a flag indicating whether the MAC subheader includes RAPID or BI. The R (reserved) field indicates a reserved bit. The BI field is used to identify when to attempt the next random access according to the overload state in the cell.

19 shows MAC RAR. MAC RAR contains information about the response to each random access preamble. The TA (time alignment) field indicates the necessary adjustment for the uplink transmission timing used for timing synchronization. The UL Grant field indicates the resource used for the uplink. The temporary C-RNTI indicates a temporary identifier used by the terminal during random access.

According to the random access response configured as described above, the temporary C-RNTI and the uplink radio resource allocation are always included in the random access response. However, the random access procedure is initiated for various reasons, and the configuration of the random access response may be inefficient, considering that it is divided into contention based and non-contention based.

For example, in a non-contention-based random access procedure, the UE transmits uplink data using uplink radio resource allocation information included in the random access response, except when requested by an instruction of the base station. Generally, in order for a UE to transmit uplink data to a Node B, an uplink radio resource must be allocated through a PDCCH. However, since an uplink radio resource allocation is included in a random access response transmitted through a PDSCH in a random access procedure, Lt; RTI ID = 0.0 > PDCCH < / RTI >

However, uplink radio resource allocation in the random access response may be unnecessary in the non-contention based random access procedure by the instruction of the base station. The base station requests a non-contention-based random access procedure to the UE as follows. There may be a state in which uplink time synchronization between the UE and the BS is inconsistent. At this time, it is assumed that downlink data to be transmitted to the mobile station is generated by the base station. If the downlink data is transmitted using HARQ, the UE must transmit HARQ feedback (i.e., HARQ ACK / NACK signal) indicating the reception result of the downlink data to the base station. However, if the UE does not have uplink time synchronization with the BS, the uplink transmission is prohibited to prevent interference with other UEs. Therefore, even if the UE receives the downlink data, the UE can not transmit HARQ feedback. That is, in the above situation, the base station first requests the terminal to perform a random access procedure. Also, the base station may instruct the UE to allocate a dedicated random access preamble and perform a non-contention-based random access procedure.

If the non-contention-based random access procedure is performed at the request of the base station, the UE may not have uplink data to be transmitted using the uplink radio resource allocation included in the dummy access response. In this case, uplink radio resource allocation is unnecessary. In addition, the base station must inform the UE of a downlink radio resource allocation through an additional PDCCH for transmission of downlink data on the DL-SCH. At this time, in the configuration of the random access response shown in FIG. 19, radio resources are wasted due to the transmission of unnecessary uplink radio resource allocation, and a problem of requiring additional PDCCH transmission in addition to the random access response for downlink data transmission Lt; / RTI >

20 shows a data transmission method according to an embodiment of the present invention.

Referring to FIG. 20, in step S410, the UE is allocated a dedicated random access preamble from the BS. The base station transmits a dedicated random access preamble onto the PDCCH to request the UE to perform the random access procedure. That is, in order to transmit downlink data to a UE not maintaining uplink time synchronization, the Node B first requests the UE to perform a random access procedure. The request is transmitted on the CRC masked PDCCH with the cell identifier (i.e., C-RNTI) of the UE. The PDCCH may carry information about a dedicated random access preamble. Accordingly, the UE can perform a non-contention-based random access procedure.

In step S420, the UE transmits the dedicated random access preamble to the base station.

In step S430, the base station transmits a random access response to the terminal in response to the dedicated random access preamble. The random access response is transmitted to the UE through the PDSCH indicated in the PDCCH, which is CRC-masked with the RA-RNTI. The random access response includes downlink radio resource allocation.

In step S440, according to downlink radio resource allocation in the random access response, the UE receives downlink data on the PDSCH without receiving a separate PDCCH.

In step S450, if the decoding of the downlink data fails, the UE transmits an HARQ NACK signal for the downlink data to the base station. Information on the transmission of the HARQ feedback (HARQ ACK / NACK signal) may be included in a part of the system information, a handover command message, or a random access response, so that the base station can inform the terminal.

In step S460, according to the HARQ NACK signal, the UE receives downlink data retransmitted on a PDSCH indicated by a CRC masked PDCCH with its C-RNTI.

In the random access procedure, a random access response includes a downlink radio resource assignment. Since the UE can directly receive the downlink data on the PDSCH through the downlink radio resource allocation, it is unnecessary to monitor the PDCCH and thus the battery consumption of the UE can be reduced. Particularly, in a non-contention-based random access procedure performed by an instruction of a base station, if the UE does not have uplink data to be transmitted, unnecessary uplink radio resource allocation can be prevented from being transmitted through a random access response.

21 shows a MAC RAR structure according to an embodiment of the present invention.

Referring to FIG. 21, the MAC RAR includes a TA field and a DL Grant field. The TA field includes an uplink time synchronization value. The DL Grant field indicates downlink radio resource allocation and includes various allocation information such as a modulation and coding scheme, a transmit power control command, a CQI request, a resource allocation, HARQ feedback transmission information, . ≪ / RTI >

At least one MAC RAR structure exists for the random access response, and the UE can determine the MAC RAR structure to be received according to the type of the random access preamble used and the random access procedure generation condition. For example, if the random access procedure is requested by the command of the base station and the random access procedure is a non-contention-based random access procedure, the terminal determines that the random access response transmitted to it is to be transmitted to the MAC RAR structure of FIG. In the other random access procedure, the UE determines that a random access response is to be transmitted in the MAC RAR structure of FIG.

When receiving a random access response including a DL Grant field, the UE receives downlink data on the PDSCH directly without attempting to receive another PDCCH according to the downlink radio resource allocation information included in the DL Grant field. Accordingly, the UE does not need to attempt to monitor the PDCCH from the reception of the random access response to the reception of the downlink data on the PDSCH, so that the UE can perform Discontinuous Reception (DRX) and reduce battery consumption.

If the downlink data is transmitted in the HARQ scheme, the UE must transmit HARQ feedback to the Node B. Generally, when the downlink data is received by the HARQ scheme, a method of transmitting HARQ feedback by the UE is as follows. As described above, the reception of the downlink data can be divided into the reception of the PDCCH and the reception of the PDSCH accordingly. And transmits HARQ positive feedback (referred to as HARQ ACK signal) or HARQ negative feedback (referred to as HARQ NACK signal) according to the decoding result of data transmitted on the PDSCH. In addition, information for transmitting the HARQ feedback is associated with the PDCCH associated with the PDSCH for the downlink data. That is, the UE determines frequency / time information for HARQ feedback transmission of the PDSCH associated with the PDCCH according to time / frequency information of the PDCCH.

If downlink data is received through downlink radio resource allocation in the random access response, it may be difficult to transmit HARQ feedback in the HARQ scheme. There is no PDCCH and the transmission information of HARQ feedback can not be known. Therefore, the proposed random access response may include HARQ feedback transmission information. The HARQ feedback transmission information may be included in the random access response as part of the DL Grant field. Alternatively, the base station can inform the UE of the HARQ feedback transmission information through a part of system information, a handover command message, or another signaling. In addition, the HARQ feedback transmission information may be indexed to inform the UE. For example, if the index information is composed of 3 bits, it is possible to inform the UE of frequency and time information for HARQ feedback transmission mapped to indexes 0 to 7 in advance.

After receiving the random access response including the downlink radio resource allocation, the UE receives the downlink data on the PDSCH according to the downlink radio resource allocation. If decoding of the downlink data fails, the UE transmits an HARQ NACK signal to the Node B according to the HARQ feedback transmission information included in the random access response. After that, the UE attempts to monitor the PDCCH using its cell identifier to receive the retransmission of the downlink data.

Alternatively, after receiving the random access response including the downlink radio resource allocation, the UE may not transmit the HARQ feedback regardless of the decoding result even if it receives the downlink data on the PDSCH according to the downlink radio resource allocation .

The UE can be switched to the DRX state after receiving the random access response including the downlink radio resource allocation. The UE can maintain the DRX state before receiving the corresponding PDSCH according to the downlink radio resource allocation, and can be switched from the subframe in which the PDSCH is transmitted to the continuous reception state. In addition, if the downlink data is not normally received in the subframe, the UE may transmit the HARQ feedback to the Node B and switch to the DRX state again. Upon switching to the DRX state, the terminal may initiate a RTT (Round Trip Time) timer. If the RRC timer expires, the terminal can be switched back to the continuous reception state again. Preferably, the value of the RRT timer can inform the UE through the RRC message such as a part of system information, a radio bearer setup, and a handover command.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

1 is a block diagram illustrating a wireless communication system.

2 is a block diagram showing functional division between E-UTRAN and EPC.

3 is a block diagram showing elements of a terminal;

4 is a block diagram illustrating a wireless protocol structure for a user plane.

5 is a block diagram illustrating a wireless protocol structure for a control plane.

6 shows a mapping between the DL logical channel and the DL transmission channel.

7 shows a mapping between the uplink logical channel and the uplink transport channel.

8 shows a mapping between a downlink transport channel and a downlink physical channel.

9 shows a mapping between an uplink transport channel and an uplink physical channel.

10 shows a structure of a radio frame.

11 is an exemplary view illustrating a resource grid for one downlink slot.

12 shows the structure of a subframe.

13 is an exemplary diagram showing data transmission and reception.

14 is a flowchart illustrating a contention based random access procedure.

15 is a flowchart illustrating a non-contention based random access procedure.

16 shows a MAC PDU structure for a random access response.

17 shows a RAPID MAC subheader.

18 shows the BI MAC subheader.

19 shows MAC RAR.

20 shows a data transmission method according to an embodiment of the present invention.

21 shows a MAC RAR structure according to an embodiment of the present invention.

Claims (15)

A method for performing a random access procedure by a user equipment (UE) in a wireless communication system, Receiving information on a dedicated random access preamble through a physical downlink control channel (PDCCH); Transmitting the dedicated random access preamble; Receiving a random access response including a downlink radio resource assignment and a random access preamble identifier corresponding to the dedicated random access preamble through a physical downlink shared channel (PDSCH) indicated by the PDCCH with CRC masked with a unique identifier; ; And And receiving downlink data on the PDSCH without monitoring an additional PDCCH using the downlink radio resource allocation. delete 2. The method of claim 1, wherein the downlink radio resource allocation includes information on resource allocation configured to receive the downlink data and hybrid automatic repeat request (HARQ) feedback transmission for the downlink data. How to. 4. The method of claim 3, further comprising transmitting HARQ feedback for the downlink data using information on the HARQ feedback transmission. The method of claim 1, further comprising transmitting HARQ feedback for the downlink data using information received from the system information. The method of claim 1, further comprising transmitting HARQ feedback for the downlink data using information received from a handover command message. 2. The method of claim 1, wherein a time correction timer enabling uplink transmission during operation expires before receiving information about the dedicated random access preamble. delete delete delete delete delete delete delete delete

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