KR20090043434A - Method of performing random access procedure in wireless communication system - Google Patents

Abstract

A method of performing a random access process includes receiving information about a dedicated random access preamble, transmitting the dedicated random access preamble, and including a downlink radio resource allocation and a random access identifier corresponding to the dedicated random access preamble. Receiving a random access response.

Description

How to perform random access process in wireless communication system {METHOD OF PERFORMING RANDOM ACCESS PROCEDURE IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to wireless communication, and more particularly, to a method for transmitting or receiving data during a random access process in a wireless communication system.

3rd generation partnership project (3GPP) mobile communication systems based on wideband code division multiple access (WCDMA) wireless access technology are widely deployed around the world. High Speed Downlink Packet Access (HSDPA), which can be defined as the first evolution of WCDMA, provides 3GPP with a highly competitive wireless access technology in the mid-term future. However, as the demands and expectations of users and operators continue to increase and the development of wireless access technologies is in progress, new technological evolution in 3GPP is required to be competitive in the future. Reduced cost per bit, increased service availability, the use of flexible frequency bands, simple structure and open interface, and adequate power consumption of the terminal are demanding requirements.

In general, one or more cells are arranged in one base station. A plurality of terminals may be located in one cell. In general, a terminal undergoes a random access procedure to access a network. The purpose of the UE to perform a random access process to the network may be an initial access (initial access), handover (handover), radio resource request (Scheduling Request), timing synchronization (timing alignment).

The random access process may be divided into a contention based random access procedure and a non-contention based random access procedure. The biggest difference between the contention-based random access process and the non- contention-based random access process is whether a random access preamble is assigned to one UE. In the contention-free random access process, since the terminal uses a dedicated random access preamble designated only to the terminal, contention (or collision) with another terminal does not occur. Here, contention refers to two or more terminals attempting a random access procedure using the same random access preamble through the same resource. In the contention-based random access process, there is a possibility of contention because the terminal uses a randomly selected random access preamble.

As described above, the random access process is initiated for various reasons, and considering that the random access process is divided into a contention-based random access process and a contention-based random access process, if the random access response is set to only one configuration, the random access process is used. This can be done inefficiently.

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

There is a need for a method for more efficiently utilizing radio resources in a random access process.

An object of the present invention is to provide a method for performing a contention-based random access process that efficiently uses radio resources in a wireless communication system.

Another object of the present invention is to provide a method for performing a contention-based random access process to reduce battery consumption of a terminal in a wireless communication system.

In one aspect, a method of 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 assigning a downlink radio resource and the dedicated random access preamble And receiving a random access response that includes a random access identifier corresponding to.

In another aspect, a method of 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 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 allocation 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 improved. In addition, it is possible to receive downlink data through the PDSCH without receiving the PDCCH, thereby reducing the battery consumption of the terminal and increase 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 a Long Term Evolution (LTE) 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.

The UE 10 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, and the like. The base station 20 generally refers to a fixed station communicating with the terminal 10, and may be referred to as other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), and an access point. have. One or more cells may exist in one base station 20. An interface for transmitting user traffic or control traffic may be used between the base stations 20. Hereinafter, downlink means communication from the base station 20 to the terminal 10, and uplink means communication from the terminal 10 to the base station 20.

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

2 is a block diagram illustrating a functional split between an E-UTRAN and an 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 function. (1) Radio resource management such as radio bearer control, radio admission control, connection mobility control, and dynamic resource allocation to a terminal RRM), (2) Internet Protocol (IP) header compression and encryption of user data streams, (3) routing of user plane data to S-GW, and (4) paging messages. Scheduling and transmission, (5) scheduling and transmission of broadcast information, and (6) measurement and measurement report setup for mobility and scheduling.

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

S-GW performs the following functions. (1) mobility anchoring, (2) lawful interception. P-GW (P-Gateway) performs the following functions. (1) terminal IP (allocation) allocation (allocation), (2) packet filtering.

3 is a block diagram illustrating 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 is implemented with layers of the air interface protocol to provide a control plane and a user plane. The functions of each layer may be implemented through the processor 51. The memory 52 is connected to the processor 51 to store a terminal driving system, an application, and a general file. The display unit 54 displays various information of the terminal, and may use well-known elements such as liquid crystal display (LCD) and organic light emitting diodes (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 a processor and transmits and / or receives a radio signal.

Layers of the radio interface protocol between the terminal and the network are based on the lower three layers of the Open System Interconnection (OSI) model, which is well known in communication systems. (Second layer) and L3 (third layer). Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel, and is a radio resource control (RRC) layer located in the third layer. The role of controlling the radio resources between the terminal 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 radio protocol structure for a control plane. This shows the structure of the air interface protocol between the terminal and the E-UTRAN. The data plane is a protocol stack for user data transmission, and the control plane is a protocol stack for control signal transmission.

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

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

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

The radio resource control (RRC) layer of the third layer is defined only in the control plane. The RRC layer is responsible for controlling logical channels, transport channels, and physical channels in connection with configuration, re-configuration, and release of radio bearers (RBs). RB means a service provided by the second layer for data transmission between the UE and the E-UTRAN. If there is an RRC connection (RRC Connection) between the RRC of the terminal and the RRC of the network, the terminal is in the RRC Connected Mode, otherwise it is in the RRC Idle Mode.

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

6 shows a mapping between a downlink logical channel and a downlink transport channel. 7 shows mapping between an uplink logical channel and an uplink transport channel. These include 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; See section 6.1.3 of Stage 2 (Release 8).

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

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

The control channel is used for transmission of control plane information. BCCH is a downlink channel for broadcasting system control information. PCCH is a downlink channel that transmits paging information and is used when the network does not know the location of the terminal. CCCH is a channel for transmitting control information between the terminal and the network, and is used when the terminal does not have an RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used to transmit multimedia broadcast multicast service (MBMS) control information, and is used for terminals receiving MBMS. DCCH is a point-to-point one-way channel for transmitting dedicated control information between the terminal and the network, and is used by a terminal having an RRC connection.

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

Transport channels are classified according to how and with what characteristics data is transmitted over the air interface. The BCH has a predefined transmission format that is broadcast and fixed in the entire cell area. DL-SCH supports hybrid automatic repeat request (HARQ). Support for dynamic link adaptation by changing modulation, coding and transmission power, possibility of broadcast, possibility of beamforming, support for dynamic / semi-static resource allocation, and support for discontinuous reception (DRX) to save terminal power 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 and MBMS Single Frequency Network (MBSFN) support.

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

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

8 and 9, in downlink, BCH is mapped to a physical broadcast channel (PBCH), MCH is mapped to a physical multicast channel (PMCH), and PCH and DL-SCH are mapped to a physical downlink shared channel (PDSCH). do. PBCH carries the BCH transport block, PMCH carries the MCH, and PDSCH carries the DL-SCH and PCH. In 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 of resource allocation of the PCH and DL-SCH and HARQ information related to the DL_SCH. The PDCCH may carry an uplink scheduling grant informing the UE of resource allocation of uplink transmission. The 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 a HARQ ACK / NAK signal in response to uplink transmission. Physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request, and CQI for downlink transmission.

10 shows the structure of a radio frame.

Referring to FIG. 10, a radio frame consists of 10 subframes, and one subframe consists of two slots. The time it takes for one subframe to be transmitted is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms.

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

11 is an exemplary diagram 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. Here, one downlink slot includes 7 OFDM symbols and one resource block includes 12 subcarriers in a frequency domain, but is not limited thereto.

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

12 shows a structure of a subframe.

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

13 shows an example of data transmission and reception.

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

The base station determines the PDCCH format according to the control information to send to the terminal, 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 purpose of the PDCCH. If the PDCCH is for a specific terminal, a unique identifier of the terminal, for example, a C-RNTI (Cell-RNTI) may be masked to the CRC. Or, if the PDCCH for paging information, a paging indication identifier, for example, Paging Indication-RNTI (PI-RNTI) may be masked to the CRC. If the PDCCH for the system information, the system information identifier, SI-RNTI (system inforamtion-RNTI) may be masked to the CRC. A random access-RNTI (RA-RNTI) may be masked to the CRC to indicate a random access response that is a response to the transmission of the random access preamble of the UE.

For example, the PDCCH is masked with a C-RNTI named A, and the transmission type information (e.g., a transport block size, modulation and coding scheme, etc.) is transmitted through a radio resource (e.g., a frequency position) called B. Let's assume that the information is transmitted in a specific sub-frame including information about the data being transmitted in). In-cell terminals monitor the PDCCH using their C-RNTI. When 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 transmission type information in the PDCCH.

The random access procedure will be described below.

First, the UE may perform a random access procedure to the base station in the following cases.

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

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

(3) When requested by the command of the base station

(4) When uplink data occurs when uplink time synchronization is not correct or when uplink radio resources are not allocated.

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

The random access process may be divided into a contention based random access procedure and a non-contention based random access procedure. The biggest difference between the contention-based random access process and the non- contention-based random access process is whether a random access preamble is assigned to one UE. In the contention-free random access process, since the terminal uses a dedicated random access preamble designated only to the terminal, contention (or collision) with another terminal does not occur. Here, contention refers to two or more terminals attempting a random access procedure using the same random access preamble through the same resource. In the contention-based random access process, there is a possibility of contention because the terminal uses a randomly selected random access preamble. The non-contention based random access procedure may be used only when requested by a handover procedure or a command of a base station among the random access reasons described above.

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 a PRACH resource. Information on the configuration of the random access preamble set may be obtained from a 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 within the random access response reception window. The random access response reception window may be indicated through a part of the system information or a handover command message, and refers to 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 transmitted on a PDSCH, which is a physical channel. The reception information of the PDSCH is obtained through a PDCCH which is a control channel. The PDCCH carries information of a terminal to receive the PDSCH, radio resource allocation information of the PDSCH, a transmission format of the PDSCH, and the like. The UE first monitors the PDCCH in a subframe belonging to the random access response reception window, and upon successful reception of the PDCCH, receives the random access response on the PDSCH indicated by the PDCCH.

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

In step S130, the terminal applies the time synchronization value, and transmits a scheduled message including a random access identifier to the base station by using the uplink radio resource allocation information. As the time synchronization value is applied, the UE starts or restarts a time alignment timer. If the time synchronization timer was previously running and restarts the time synchronization timer, start the time synchronization timer if the time synchronization timer was not previously running.

The random access identifier is used by the base station to identify a terminal performing a random access process. The random access identifier can be obtained in two ways. The first method uses the cell identifier as the random access identifier if the terminal already has a valid cell identifier (eg, C-RNTI) allocated in the corresponding cell before the random access procedure. In the second method, if the terminal has not been assigned a valid cell identifier before the random access procedure, the terminal uses its own unique identifier (SAE Temporary Mobile Station Identifier (S-TMSI) or higher layer identifier) as the random access identifier. The terminal starts a contention resolution timer according to the transmission of 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 terminal.

Contention in a contention-based random access process occurs because the number of possible random access preambles is finite. Since the UE cannot assign a unique random access preamble to all UEs in the cell, the UE randomly selects and transmits one random access preamble from the random access preamble set. Accordingly, two or more terminals may select and transmit the same random access preamble through the same PRACH resource. This is the case where contention has occurred. The base station receiving the random access preamble transmits a random access response to the random access preamble without knowing whether there is contention. However, since contention has occurred, two or more terminals receive the same random access response, and the terminals each transmit a scheduled message based on the information included in the random access response. This means that two or more terminals transmit different scheduled messages through uplink radio resource allocation information included in the random access response. At this time, transmission of the scheduled message all fails, or only the scheduled message of the specific terminal is successfully received by the base station according to the location or transmission power of the terminals. When the scheduled message is successfully received at the base station, the base station transmits a contention resolution message using the random access identifier included in the scheduled message. Upon receiving its random access identifier, the UE may know that contention resolution is successful. In the contention-based random access process, contention resolution may be performed so that the UE knows whether contention fails or succeeds.

Use a contention resolution timer to resolve contention. The contention resolution timer is started after receiving the random access response. The contention resolution timer may be started when the terminal transmits the scheduled message. When the contention resolution timer expires, it is determined that contention resolution is not successful, and a new random access procedure is started. Upon receiving a contention resolution message that includes its random access identifier, the contention resolution timer stops and determines that contention resolution is successful. If the terminal already has a unique cell identifier such as C-RNTI before the random access procedure, the terminal transmits a scheduled message including its cell identifier to the base station and then starts a contention resolution timer. If the PDCCH addressed by its cell identifier is received before the contention resolution timer expires, the UE determines that the contention has succeeded in contention and ends the random access process normally. Or, if the terminal does not have a C-RNTI can use the upper layer identifier as a random access identifier. After transmitting the scheduling message including the higher layer identifier, the terminal starts a contention resolution timer. If the contention resolution message including its higher 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 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, the terminal is allocated a dedicated random access preamble from the base station. For the contention-free random access procedure, it is necessary to allocate a dedicated random access preamble from the base station without collision. The dedicated random access preamble may be included in the handover command message or transmitted on the PDCCH. When the random access procedure is performed during the handover procedure, the UE may obtain a dedicated random access preamble from the handover command message. When the random access procedure is performed at the request of the base station, the terminal may obtain a dedicated random access preamble through the PDCCH.

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

In step S230, the terminal receives a random access response corresponding to the dedicated random access preamble. Compared to the contention-based random access process, by receiving a random access response in the contention-free random access process, it is determined that the random access process is normally performed, and ends the random access process.

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

The random access procedure is one of methods for time synchronization of uplink. The base station measures the time synchronization value through the random access preamble transmitted by the terminal, and provides the time synchronization value to the terminal through the random access response. The terminal receiving the random access response applies the time synchronization value and starts a time alignment timer. It is assumed that time synchronization between the terminal and the base station is maintained during the operation of the time synchronization timer, and that time synchronization between the terminal and the base station is not maintained when the time synchronization timer expires or does not operate. When contention occurs in a contention-based random access process, and when contention fails, the terminal may stop the time synchronization timer. If the time synchronization timer expires or does not operate, the UE cannot 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, which is divided into a RAPID MAC subheader and a backoff indicator (BI) MAC subheader. Each RAPID MAC subheader corresponds to one MAC RAR.

17 illustrates a RAPID MAC subheader. The E (extentsion) field is a flag indicating whether other fields exist 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 illustrates a BI MAC subheader. The E (extentsion) field is a flag indicating whether other fields exist in the MAC header. The T (type) field is a flag indicating whether the MAC subheader includes RAPID or BI. The R (reserved) field represents a reserved bit. The BI field is used to identify when the next random access will be attempted according to the overloaded state in the cell.

19 shows MAC RAR. The MAC RAR contains information about the response to each random access preamble. The TA (time alignment) field indicates an adjustment necessary for uplink transmission timing used for timing synchronization. The UL Grant field indicates a resource used for 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 uplink radio resource allocation are always included in the random access response. However, the random access process is initiated for various reasons, and considering that the contention is divided into contention-based and contention-based, the configuration of the random access response may be inefficient.

For example, in a non-contention-based random access process, except for the case where requested by the command of the base station, the terminal transmits uplink data using uplink radio resource allocation information included in the random access response. In general, in order to transmit the uplink data to the base station, the UE needs to be allocated an uplink radio resource through a PDCCH. No additional PDCCH reception is necessary for the transmission of the message.

However, the uplink radio resource allocation in the random access response may be unnecessary in the non-contention based random access process by the command of the base station. The base station requests the terminal for a contention-free random access procedure as follows. There may be a state in which uplink time synchronization is not correct between the terminal and the base station. In this case, it is assumed that the downlink data to be transmitted to the base station is generated. If the downlink data is transmitted using HARQ, the terminal should transmit a HARQ feedback (ie, HARQ ACK / NACK signal) indicating the reception result of the downlink data to the base station. However, if the terminal does not match uplink time synchronization with the base station, uplink transmission is prohibited in order to prevent interference with other terminals. Thus, even when receiving the downlink data, the terminal cannot transmit HARQ feedback. That is, in the above situation, the base station first requests the terminal to perform a random access procedure. In addition, the base station may allocate a dedicated random access preamble to the terminal to instruct a non-contention based random access procedure to be performed.

If a non-contention based random access procedure is performed at the request of the base station, there may be no uplink data to be transmitted to the terminal using uplink radio resource allocation included in the dumb access response. In this case, uplink radio resource allocation is unnecessary. In addition, the base station should inform the UE of downlink radio resource allocation through an additional PDCCH for transmission of downlink data on the DL-SCH. At this time, the configuration of the random access response shown in FIG. 19 causes waste of radio resources due to unnecessary uplink radio resource allocation and also requires additional PDCCH transmission in addition to the random access response to transmit downlink data. This happens.

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

Referring to FIG. 20, in step S410, a terminal is allocated a dedicated random access preamble from a base station. The base station transmits a dedicated random access preamble on the PDCCH to request the terminal to perform a random access procedure. That is, in order to transmit downlink data to a terminal whose uplink time synchronization is not maintained, the base station first requests the terminal to perform a random access procedure. The request is transmitted on a CRC masked PDCCH with a cell identifier (ie, C-RNTI) of the terminal. The PDCCH may carry information about a dedicated random access preamble. Accordingly, the terminal may perform a contention-free random access procedure.

In step S420, the terminal 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 on the PDCCH masked with the CR-RNTI RA-RNTI. The random access response includes downlink radio resource allocation.

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

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

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

In the random access process, the downlink radio resource allocation is included in the random access response. Since the terminal can directly receive the downlink data on the PDSCH through the downlink radio resource allocation, monitoring of the PDCCH is unnecessary, thereby reducing battery consumption of the terminal. In particular, in the non-contention-based random access process performed by the base station command, if there is no uplink data to be transmitted by the terminal, it is possible to prevent the unnecessary uplink radio resource allocation to be transmitted through the random access response.

21 illustrates 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 sync value. The DL Grant field indicates a downlink radio resource allocation, and various allocation information such as a modulation and coding scheme, a transmit power control command, a CQI request, a resource allocation, and HARQ feedback transmission information It may include.

One or more MAC RAR structures exist for the random access response, and the UE may determine the MAC RAR structure to be received by the UE according to the type of random access preamble used by the UE and a condition for generating a random access process. For example, if a random access process is requested by a command of the base station and the contention-free random access process is performed, the terminal determines that the random access response transmitted to the UE is transmitted in the MAC RAR structure of FIG. 21. In addition, in the other random access process, the UE determines that the random access response will be transmitted in the MAC RAR structure of FIG. 19.

When the UE receives the random access response including the DL Grant field, the UE directly receives downlink data on the PDSCH without attempting to receive a separate 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 receiving a random access response to receiving downlink data on the PDSCH, thereby performing DRX (Discontinuous Reception) and reducing battery consumption.

If downlink data is transmitted in the HARQ scheme, the terminal should transmit the HARQ feedback to the base station. In general, when the downlink data is received in the HARQ scheme, a method of transmitting HARQ feedback by the UE is as follows. As described above, the reception of downlink data may be divided into reception of PDCCH and reception of PDSCH. According to the decoding result of the data transmitted to the PDSCH, HARQ positive feedback (called HARQ ACK signal) or HARQ negative feedback (called HARQ NACK signal) is transmitted. In addition, the information for transmitting the HARQ feedback is related to 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 the time / frequency information of the PDCCH.

If downlink data is received through the downlink radio resource allocation in the random access response, it may be difficult to transmit the HARQ feedback through the HARQ scheme as described above. This is because transmission information of HARQ feedback is not known because there is no PDCCH. 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 HARQ feedback transmission information may be informed by the base station to the terminal through a part of system information, a handover command message, or separate signaling. In addition, the HARQ feedback transmission information may be informed to the terminal by indexing. For example, assuming that the index information consists of 3 bits, the terminal may inform the terminal in advance of frequency and time information for transmitting HARQ feedback mapped to the indices of 0 to 7.

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

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

The terminal may be switched to the DRX state after receiving the random access response including the downlink radio resource allocation. The UE may maintain a DRX state until a corresponding PDSCH is received according to the downlink radio resource allocation, and may be switched to a continuous reception state in a subframe in which the PDSCH is transmitted. In addition, when the downlink data is not normally received in the subframe, the terminal may transmit the HARQ feedback to the base station and may be switched back to the DRX state. When switched to the DRX state, the terminal may start a round trip time (RTT) timer. When the RRC timer expires, the terminal may be switched back to the continuous reception state. Preferably, the value of the RRT timer, the base station can inform the terminal through the RRC message such as part of the system information, radio bearer setup and handover command.

The invention can be implemented in hardware, software or a combination thereof. In hardware implementation, an application specific integrated circuit (ASIC), a digital signal processing (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, and a microprocessor are designed to perform the above functions. , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. 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.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

1 is a block diagram illustrating a wireless communication system.

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

3 is a block diagram illustrating elements of a terminal.

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

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

6 shows a mapping between a downlink logical channel and a downlink transport channel.

7 shows mapping between an uplink logical channel and an uplink transport channel.

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

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

10 shows the structure of a radio frame.

11 shows an example of a resource grid for one downlink slot.

12 shows a structure of a subframe.

13 shows an example of 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 illustrates a RAPID MAC subheader.

18 illustrates a BI MAC subheader.

19 shows MAC RAR.

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

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

Claims (15)

In the method for performing a random access process in a wireless communication system, Receiving information regarding a dedicated random access preamble; Transmitting the dedicated random access preamble; And And receiving a random access response comprising a downlink radio resource allocation and a random access identifier corresponding to the dedicated random access preamble. 2. The method of claim 1, further comprising receiving downlink data using the downlink radio resource allocation. The method of claim 2, wherein the downlink radio resource allocation includes information on resource allocation for receiving the downlink data and transmission of a hybrid automatic repeat request (HARQ) feedback for the downlink data. . 4. The method of claim 3, further comprising transmitting HARQ feedback for the downlink data using the information on the HARQ feedback transmission. 2. The method of claim 1, further comprising transmitting HARQ feedback for the downlink data using information received from system information. 2. 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 that enables uplink transmission while in operation expires before receiving information about the dedicated random access preamble. 2. The method of claim 1, wherein the random access response further comprises a time correction value for adjusting uplink time correction. The method of claim 1, wherein the random access response is a MAC protocol data unit (PDU) including a medium access control (MAC) header and at least one random access response (MAR), the MAC header corresponding to the MAC RAR And a MAC subheader including the random access identifier, wherein the MAC RAR comprises the downlink radio resource allocation. In the method for performing a random access process in a wireless communication system, Receiving information regarding a dedicated random access preamble; Transmitting the dedicated random access preamble; And Receiving a random access response on a physical downlink shared channel (PDSCH) indicated by a physical downlink control channel (PDCCH), And wherein the random access response includes a downlink radio resource allocation and a random access identifier corresponding to the dedicated random access preamble. The method of claim 10, wherein the PDCCH is indicated by a random access-radio network temporary identifier (RA-RNTI). 11. The method of claim 10, wherein the information about the dedicated random access preamble is received on a PDCCH indicated by a C-RNTI. 12. The method of claim 10, further comprising receiving downlink data on a PDSCH indicated by the downlink radio resource allocation. The method of claim 13, wherein the downlink radio resource allocation includes information on resource allocation for receiving the downlink data and HARQ feedback transmission for the downlink data. 15. The method of claim 14, further comprising transmitting HARQ feedback for the downlink data using the information on the HARQ feedback transmission.

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