KR20130097586A - Apparatus and method for performing random access procedure in multiple component carrier system - Google Patents

Abstract

PURPOSE: An apparatus for performing random access procedure in a multiple component carrier system and a method thereof are provided to judge success of the random access procedure by referring to a random access valid reception section. CONSTITUTION: A receiving unit (1705) receives a physical downlink control channel instruction instructing to start random access procedure in a secondary serving cell configured in a terminal from a base station. A transmission unit (1720) transmits random access preamble to the base station in response to the physical downlink control channel instruction. A random access processing unit (1712) judges success of the random access procedure. The receiving unit receives a physical downlink shared channel (PDSCH) including a random access response message from the base station in response to the random access preamble. [Reference numerals] (1705,1760) Receiving unit; (1710) Terminal processor; (1711,1771) HARQ operation unit; (1712,1772) Random access processing unit; (1720,1755) Transmission unit; (1770) Base station processor; (AA) PDCCH order, PDCCH and PDSCH (including a random access and a response message); (BB) Random access preamble; (CC) ACK/NACK signal

Description

Apparatus and method for performing random access procedure in multi-component carrier system {APPARATUS AND METHOD FOR PERFORMING RANDOM ACCESS PROCEDURE IN MULTIPLE COMPONENT CARRIER SYSTEM}

The present invention relates to wireless communications, and more particularly, to an apparatus and method for performing a random access procedure in a multi-component carrier system.

In a typical wireless communication system, although a bandwidth between an uplink and a downlink is set to be different from each other, only one carrier is mainly considered. In the 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution), the number of carriers constituting the uplink and the downlink is 1 based on a single carrier, and the bandwidths of the UL and the DL are generally symmetrical to be. In this single carrier system, random access is performed using one carrier. However, with the recent introduction of multiple carrier systems, random access can be implemented through multiple component carriers.

The multi-carrier system refers to a wireless communication system capable of supporting carrier aggregation. Carrier aggregation is a technique for efficiently using fragmented small bands in order to combine physically non-continuous bands in the frequency domain and to have the same effect as using logically large bands.

In order to access the network, the UE goes through a random access process. 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 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), uplink timing alignment (uplink timing alignment).

An object of the present invention is to provide an apparatus and method for performing a random access procedure in a multi-component carrier system.

Another object of the present invention is to provide an apparatus and method for determining whether a random access procedure is successful based on a random access valid reception interval.

Another technical problem of the present invention is to provide an apparatus and method for determining whether a random access procedure succeeds by using a parameter of a HARQ procedure.

Another object of the present invention is to provide an apparatus and method for re-receiving a random access response message in a retransmission timer progress period of a discontinuous reception (DRX).

According to an aspect of the present invention, a method of performing a random access procedure by a terminal is provided. The method includes receiving a physical downlink control channel (PDCCH) indication from a base station indicating a start of a random access procedure in a secondary serving cell configured in a terminal, the physical downlink control channel Transmitting a random access preamble to the base station in response to the indication; and a physical downlink shared channel (PDSCH) including a random access response message in response to the random access preamble Receiving from, and determining whether the random access procedure is successful.

The determining of whether the random access procedure is successful may include: a hybrid automatic repeat request (HARQ) operation on the random access response message in a random access window section and the terminal in a discontinuous reception (DRX) mode; Determining a success of the random access procedure when the terminal receives and successfully decodes the physical downlink common channel in a random access valid time interval including a DRX retransmission timer progress period, which is a parameter used for It may include.

According to another aspect of the present invention, a terminal for performing a random access procedure is provided. The terminal receives a physical downlink control channel indication from the base station indicating the start of the random access procedure in the secondary serving cell configured in the terminal, the random access preamble (preamble) in response to the physical downlink control channel indication; A transmission unit for transmitting to the base station, and a random access processing unit for determining the success of the random access procedure.

The receiver may receive a physical downlink shared channel (PDSCH) including a random access response message from the base station in response to the random access preamble.

The random access processing unit may include a random access window period and a random access window period in which the terminal includes a progress period of a DRX retransmission timer which is a parameter used for HARQ operation for the random access response message in a discontinuous reception mode. When the terminal receives and successfully decodes the physical downlink shared channel, the terminal may determine success of the random access procedure.

Since the random access procedure is associated with the HARQ procedure, the DRX retransmission timer used in the HARQ procedure as well as the random access window may be used as a criterion for determining whether the random access procedure is successful. In addition, even if the random access procedure is already successful, system degradation such as resource waste and time delay caused by unnecessarily retransmitting the random access preamble can be prevented.

1 shows a wireless communication system to which the present invention is applied.
2 shows an example of a protocol structure for supporting multiple carriers to which the present invention is applied.
3 shows an example of a frame structure for multi-carrier operation to which the present invention is applied.
4 shows a linkage between a downlink component carrier and an uplink component carrier in a multi-carrier system to which the present invention is applied.
5 is a flowchart illustrating a procedure of obtaining a multi-time alignment value according to an example of the present invention.
6 is a flowchart illustrating a method of performing random access according to an embodiment of the present invention.
7 is a scenario illustrating a method of performing a random access procedure according to an embodiment of the present invention.
8 is a scenario for explaining a method of performing a random access procedure according to another example of the present invention.
FIG. 9 is an explanatory diagram illustrating a reference time point of success or failure of a random access procedure when transmitting the maximum number of RAP transmissions of a random access preamble according to an embodiment of the present invention.
10 is a block diagram illustrating a structure of a random access response message according to an embodiment of the present invention.
11 is a block diagram illustrating a structure of a random access response message according to another example of the present invention.
12 is an example of a MAC subheader applied to the present invention.
13 is an example of a MAC control element to which the present invention is applied.
14 is another example of a MAC control element to which the present invention is applied.
15 is a flowchart illustrating a method of performing a random access procedure by a terminal according to an embodiment of the present invention.
16 is a flowchart illustrating a method of performing a random access procedure by a base station according to an embodiment of the present invention.
17 is a block diagram illustrating a terminal and a base station performing a random access procedure according to an embodiment of the present invention.

Hereinafter, some embodiments will be described in detail with reference to exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

In addition, the present invention will be described with respect to a wireless communication network. The work performed in the wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) Work can be done at a terminal connected to the network.

1 shows a wireless communication system to which the present invention is applied.

Referring to FIG. 1, a wireless communication system 10 is widely deployed to provide various communication services such as voice, packet data, and the like. The wireless communication system 10 includes at least one base station 11 (BS). Each base station 11 provides communication services to specific cells (15a, 15b, 15c). The cell may again be divided into multiple regions (referred to as sectors).

A user equipment (UE) 12 may be fixed or mobile and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, (personal digital assistant), a wireless modem, a handheld device, and the like. The base station 11 may be called by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, a femto base station, a home node B, . The cell should be interpreted in a generic sense to indicate a partial area covered by the base station 11 and is meant to cover various coverage areas such as a megacell, a macro cell, a microcell, a picocell, and a femtocell.

Hereinafter, downlink refers to communication from the base station 11 to the terminal 12, and uplink refers to communication from the terminal 12 to the base station 11. In the downlink, the transmitter may be part of the base station 11, and the receiver may be part of the terminal 12. In the uplink, the transmitter may be part of the terminal 12, and the receiver may be part of the base station 11. There are no restrictions on multiple access schemes applied to wireless communication systems. (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA , OFDM-CDMA, and the like. A TDD (Time Division Duplex) scheme in which uplink and downlink transmissions are transmitted using different time periods, or an FDD (Frequency Division Duplex) scheme in which they are transmitted using different frequencies can be used.

Carrier aggregation (CA) supports a plurality of carriers, also referred to as spectrum aggregation or bandwidth aggregation. Individual unit carriers bound by carrier aggregation are called component carriers (CCs). Each element carrier is defined as the bandwidth and center frequency. Carrier aggregation is introduced to support increased throughput, prevent cost increases due to the introduction of wideband radio frequency (RF) devices, and ensure compatibility with existing systems. For example, if five elementary carriers are allocated as the granularity of a carrier unit having a bandwidth of 20 MHz, it can support a bandwidth of up to 100 MHz.

Carrier aggregation can be divided into contiguous carrier aggregation between successive element carriers in the frequency domain and non-contiguous carrier aggregation between discontinuous element carriers. The number of carriers aggregated between the downlink and the uplink may be set differently. The case where the number of downlink element carriers is equal to the number of uplink element carriers is referred to as symmetric aggregation and the case where the number of downlink element carriers is different is referred to as asymmetric aggregation.

The size (i.e. bandwidth) of the element carriers may be different. For example, if five element carriers are used for a 70 MHz band configuration, then 5 MHz element carrier (carrier # 0) + 20 MHz element carrier (carrier # 1) + 20 MHz element carrier (carrier # 2) + 20 MHz element carrier (carrier # 3) + 5 MHz element carrier (carrier # 4).

Hereinafter, a multi-carrier system refers to a system that supports carrier aggregation. In a multi-carrier system, adjacent carrier aggregation and / or non-adjacent carrier aggregation may be used, and either symmetric aggregation or asymmetric aggregation may be used.

2 shows an example of a protocol structure for supporting multiple carriers to which the present invention is applied.

Referring to FIG. 2, the common medium access control (MAC) entity 210 manages a physical layer 220 using a plurality of carriers. The MAC management message transmitted on a specific carrier may be applied to other carriers. That is, the MAC management message is a message capable of controlling other carriers including the specific carrier. The physical layer 220 may operate as a time division duplex (TDD) and / or a frequency division duplex (FDD).

There are several physical control channels used in the physical layer 220. The physical downlink control channel (PDCCH) informs the UE of resource allocation of a paging channel (PCH), a downlink shared channel (DL-SCH), and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry an uplink grant informing the UE of the resource allocation of the uplink transmission. A DL-SCH is mapped to a physical downlink shared channel (PDSCH). A physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. The physical hybrid ARQ indicator channel (PHICH) is a downlink channel, and carries an HARQ ACK / NACK signal, which is a response of an uplink transmission. Physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NACK signal, scheduling request and CQI for downlink transmission. A physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH). A physical random access channel (PRACH) carries a random access preamble.

3 shows an example of a frame structure for multi-carrier operation to which the present invention is applied.

Referring to FIG. 3, the frame consists of 10 subframes. The subframe includes a plurality of OFDM symbols. Each carrier may have its own control channel (eg, PDCCH). The multicarriers may or may not be adjacent to each other. The terminal may support one or more carriers according to its capabilities.

The element carrier may be divided into a primary component carrier (PCC) and a secondary component carrier (SCC). The terminal may use only one major carrier or use one or more sub-carrier with carrier. A terminal may be allocated a primary carrier and / or secondary carrier from a base station.

4 shows a linkage between a downlink component carrier and an uplink component carrier in a multi-carrier system to which the present invention is applied.

Referring to FIG. 4, the downlink component carriers D1, D2, and D3 are aggregated in the downlink, and the uplink component carriers U1, U2, and U3 are aggregated in the uplink. Where Di is the index of the downlink component carrier and Ui is the index of the uplink component carrier (i = 1, 2, 3). At least one downlink element carrier is a dominant carrier and the remainder is a subordinate element carrier. Similarly, at least one uplink component carrier is a dominant carrier and the remainder is a subindent carrier. For example, D1, U1 are the dominant carriers, and D2, U2, D3, U3 are the subelement carriers.

In the FDD system, the downlink component carrier and the uplink component carrier are configured to be 1: 1. For example, D1 is connected to U1, D2 is U2, and D3 is U1 1: 1. The UE establishes a connection between the downlink component carriers and the uplink component carriers through the system information transmitted by the logical channel BCCH or the terminal dedicated RRC message transmitted by the DCCH. Each connection setting may be cell specific or UE specific.

4 illustrates only a 1: 1 connection setup between the downlink component carrier and the uplink component carrier, but it is needless to say that a 1: n or n: 1 connection setup can also be established. The index of the element carrier does not match the order of the element carriers or the position of the frequency band of the corresponding element carrier.

A primary serving cell is a serving cell that provides security input and NAS mobility information in an RRC establishment or re-establishment state. Depending on the capabilities of the terminal, at least one cell may be configured to form a set of serving cells together with a main serving cell, said at least one cell being referred to as a secondary serving cell.

Therefore, the set of serving cells set for one UE may consist of only one main serving cell, or may consist of one main serving cell and at least one secondary serving cell.

The downlink component carrier corresponding to the main serving cell is referred to as a downlink principal carrier (DL PCC), and the uplink component carrier corresponding to the main serving cell is referred to as an uplink principal carrier (UL PCC). In the downlink, the element carrier corresponding to the secondary serving cell is referred to as a downlink sub-element carrier (DL SCC), and in the uplink, an elementary carrier corresponding to the secondary serving cell is referred to as an uplink sub-element carrier (UL SCC) do. Only one DL serving carrier may correspond to one serving cell, and DL CC and UL CC may correspond to each other.

Therefore, the communication between the terminal and the base station in the carrier system is performed through the DL CC or the UL CC, which is equivalent to the communication between the terminal and the base station through the serving cell. For example, in the method of performing random access according to the present invention, a UE transmits a preamble using UL CC is equivalent to transmitting a preamble using a main serving cell or a secondary serving cell. In addition, receiving a downlink information using a DL CC by a UE can be regarded as equivalent to receiving downlink information using a main serving cell or a secondary serving cell.

On the other hand, the main serving cell and the secondary serving cell have the following characteristics.

First, the main serving cell is used for transmission of the PUCCH. On the other hand, the secondary serving cell can not transmit the PUCCH but may transmit some of the information in the PUCCH through the PUSCH.

Second, the main serving cell is always activated, while the secondary serving cell is a carrier that is activated / deactivated according to certain conditions. The specific condition may be a case where an activation / deactivation indicator of the base station is received or an inactivation timer in the terminal expires. Activation means that the transmission or reception of traffic data is performed or is in a ready state. Deactivation means that transmission or reception of traffic data is impossible and measurement or transmission / reception of minimum information is possible.

Third, when the primary serving cell experiences RLF, RRC reconnection is triggered, but when the secondary serving cell experiences RLF, RRC reconnection is not triggered. The radio link failure occurs when the downlink performance is maintained below the threshold for a predetermined time or when the RACH fails more than the threshold number of times.

Fourth, the main serving cell may be changed by a security key change or a handover procedure accompanied by the RACH procedure. However, in the case of a contention resolution (CR) message, only the PDCCH indicating the contention resolution message should be transmitted through the main serving cell, and the contention resolution message may be transmitted through the main serving cell or the secondary serving cell.

Fifth, NAS (non-access stratum) information is received through the main serving cell.

Sixth, the main serving cell always consists of DL PCC and UL PCC in pairs.

Seventh, a different CC may be set as a primary serving cell for each terminal.

Eighth, procedures such as reconfiguration, adding, and removal of the secondary serving cell may be performed by the radio resource control (RRC) layer. In addition to the new secondary serving cell, RRC signaling may be used to transmit the system information of the dedicated secondary serving cell.

Ninth, the main serving cell transmits PDCCH (e.g., downlink allocation information) assigned to a UE-specific search space set for transmitting control information for a specific UE in a region for transmitting control information Or PDCCH (e.g., system information (e.g., uplink information) allocated to a common search space set for transmitting control information to all terminals in the cell or to a plurality of terminals conforming to a specific condition, SI), a random access response (RAR), and transmit power control (TPC). On the other hand, only the UE-specific search space can be set as the serving cell. That is, since the UE can not confirm the common search space through the secondary serving cell, it can not receive the control information transmitted only through the common search space and the data information indicated by the control information.

Among the secondary serving cells, a secondary serving cell in which a common search space (CSS) can be defined may be defined, and the secondary serving cell is referred to as a special secondary serving cell (special SCell). The special secondary serving cell is always configured as a scheduling cell during cross carrier scheduling. In addition, the PUCCH configured in the PCell may be defined for the special secondary serving cell.

The PUCCH for the special secondary serving cell may be fixedly set in the special secondary serving cell configuration or the base station may be allocated (configured) or released by RRC signaling (RRC reconfiguration message) upon reconfiguration for that secondary serving cell have.

The PUCCH for the special-purpose serving cell includes ACK / NACK information or CQI (channel quality information) of the secondary serving cells existing in the sTAG, and as mentioned above, can be configured through RRC signaling by the base station have.

In addition, the base station may configure a special secondary serving cell of one of a plurality of secondary serving cells in the sTAG, or may not configure a special secondary serving cell. The reason for not configuring the special-purpose serving cell is that CSS and PUCCH need not be set. For example, if the contention-based random access procedure does not need to proceed in any serving cell, or if it is determined that the capacity of the current serving cell's PUCCH is sufficient and the PUCCH for the additional serving cell is not needed .

The technical idea of the present invention regarding the characteristics of the main serving cell and the secondary serving cell is not necessarily limited to the above description, but is merely an example and may include more examples.

In a wireless communication environment, a propagation delay is propagated while a transmitter propagates and propagates in a receiver. Therefore, even if the transmitter and the receiver both know the time at which the radio wave is propagated correctly, the arrival time of the signal to the receiver is influenced by the transmission / reception period distance and the surrounding propagation environment. If the receiver does not know exactly when the signal transmitted by the transmitter is received, it will receive the distorted signal even if it fails to receive or receive the signal.

Therefore, in the wireless communication system, synchronization between the base station and the terminal must be predetermined in order to receive the information signal regardless of the downlink / uplink. Types of synchronization include frame synchronization, information symbol synchronization, and sampling period synchronization. Sampling period synchronization is the most basic motivation to distinguish physical signals.

The downlink synchronization acquisition is performed in the UE based on the signal of the base station. The base station transmits a mutually agreed specific signal for facilitating downlink synchronization acquisition at the terminal. The terminal must be able to accurately identify the time at which a particular signal sent from the base station is transmitted. In case of downlink, since one base station simultaneously transmits the same synchronization signal to a plurality of terminals, each of the terminals can acquire synchronization independently of each other.

In case of uplink, the base station receives signals transmitted from a plurality of terminals. When the distance between each terminal and the base station is different, signals received by each base station have different transmission delay times. When uplink information is transmitted on the basis of the acquired downlink synchronization, Is received at the corresponding base station. In this case, the base station can not acquire synchronization based on any one of the terminals. Therefore, uplink synchronization acquisition requires a procedure different from downlink.

A random access procedure is performed to obtain uplink synchronization, and the terminal acquires uplink synchronization based on a timing alignment value transmitted from the base station during the random access procedure. The time alignment value may be referred to as a timing advance value in that it has a value to advance the uplink time.

When uplink synchronization is obtained, the terminal starts a time alignment timer. When the time alignment timer is in operation, the terminal and the base station are in a state of uplink synchronization with each other. If the time alignment timer expires or does not operate, the UE and the base station report that they are not synchronized with each other, and the UE does not perform uplink transmission other than the transmission of the random access preamble.

Meanwhile, in a multi-carrier system, one terminal communicates with a base station via a plurality of element carriers or a plurality of serving cells. If all the signals of the plurality of serving cells set in the UE have the same time delay, the UE can acquire uplink synchronization for all the serving cells with only one time alignment value. On the other hand, if the signals of the plurality of serving cells have different time delays, a different time alignment value is required for each serving cell. That is, multiple timing alignment values are required. If the UE performs random access to each serving cell in order to obtain multi-time alignment values, overhead occurs in the limited uplink resources, and the complexity of the random access may increase. A timing alignment group (TAG) is defined to reduce this overhead and complexity.

The time alignment group is a group including serving cell (s) using the same time alignment value and the same timing reference among the serving cells configured with the UL CC. Each time alignment group includes at least one serving cell configured with a UL CC, and information on the serving cell mapped to each time alignment group is referred to as time alignment group configuration information (hereinafter referred to as 'TAG configuration information'). The mapping to the time alignment group may be reconfigured by the serving base station and transmitted to the terminal by RRC signaling.

The time alignment group is a group including at least one serving cell, and the same time alignment value and the same timing reference are applied to the serving cells in the time alignment group. For example, when the first serving cell and the second serving cell belong to the same time alignment group TAG1, the same time alignment value TA1 is applied to the first serving cell and the second serving cell. On the other hand, when the first serving cell and the second serving cell belong to different time alignment groups TAG1 and TAG2, different time alignment values TA1 and TA2 are applied to the first serving cell and the second serving cell, respectively. The time alignment group may include a main serving cell, may include at least one secondary serving cell, and may include a primary serving cell and at least one secondary serving cell.

The time alignment group is determined by the serving base station constituting the serving cell, the initial group configuration and group reorganization is transmitted to the terminal through the RRC signaling.

The main serving cell does not change the TAG. Also, the terminal must be able to support at least two TAGs when multi-time alignment values are needed. For example, it should be able to support pTAG (primary TAG) including main serving cell and TAG separated by sTAG (secondary TAG) without main serving cell. Here, there is always only one pTAG, and sTAG can exist at least one if multiple time alignment values are needed. The maximum number of TAGs may be set to two or four. Also, pTAG always has a value of TAG ID = 0.

The serving base station and the terminal may proceed as follows to obtain and maintain a time alignment (TA) value for each time alignment group.

1. The TA value acquisition and maintenance of pTAG always proceed through the main serving cell. In addition, the timing reference as a reference of downlink synchronization for calculating the TA value of the pTAG is always the DL CC in the main serving cell.

2. To obtain the initial uplink time alignment value for the sTAG, the RA procedure initialized by the base station must be used.

3. The timing reference for the sTAG is the UL CC of the secondary serving cell that transmitted the random access preamble in the most recent RA procedure and the DL CC linked to the system information block 2 (SIB2). Here, SIB2 is one of system information blocks transmitted through a broadcasting channel, and the SIB2 information is transmitted from the base station to the terminal through an RRC reconfiguration procedure when configuring the corresponding secondary serving cell. Uplink center frequency information is included in SIB2 and downlink center frequency information is included in SIB1. Therefore, the SIB2 connection setup means a connection setup between the DL CC configured based on the information in the SIB1 of the secondary serving cell and the UL CC configured based on the information in the SIB2.

4. Each TAG has one timing reference and one timing alignment timer (TAT), and each TAT can be configured with a different timer expiration value. The TAT starts or restarts immediately after acquiring the time alignment value from the serving base station to determine whether the time alignment value obtained and applied by each time alignment group is valid.

5. If the TTAG of the pTAG has expired, the TAT of all TAGs including the pTAG expires. The terminal initializes (flush) HARQ buffers of all serving cells. It also clears the resource allocation configuration for all downlink and uplink. For example, if the periodic resource allocation is configured without control information transmitted for resource allocation for downlink / uplink such as PDCCH, such as semi-persistent scheduling (SPS), the SPS configuration is initialized. do. Also, the configuration of PUCCH and Type 0 (periodic) SRS of all serving cells is released.

6. If the TAT of the sTAG has expired, proceed as follows.

A. Stop SRS transmission through UL CC of sTAG internal serving cells.

B. Type 0 (periodic) Unconfigure SRS. Type 1 (aperiodic) SRS configuration is maintained.

C. Maintain configuration information for CSI reports.

D. Flush HARQ buffers for the uplink of secondary serving cells in sTAG.

7. Even if all secondary serving cells in the sTAG are deactivated, the terminal does not stop the TAT of the corresponding sTAG. Even when all secondary serving cells in the sTAG are deactivated as in operation 7, the terminal does not stop the TAT of the corresponding sTAG. This means that the validity of the TA value of the sTAG can be guaranteed through the TAT even when all secondary serving cells in the sTAG are inactive and no SRS for tracking uplink synchronization is maintained for a certain time.

8. If the last secondary serving cell in the sTAG is removed, ie no serving cell is configured in the sTAG, the TAT in that sTAG is stopped.

9. The random access procedure for the secondary serving cell may be performed by the base station transmitting a PDCCH order for the activated secondary serving cell. In addition, it proceeds only through a contention-free random access procedure. Therefore, the random access preamble information included in the PDCCH indication should be indicated by information other than '000000'.

10. The PDCCH for RAR transmission may be transmitted through a serving cell other than the secondary serving cell that transmitted the random access preamble.

11. When the number of retransmissions of the random access preamble of the secondary serving cell reaches the maximum allowed number of retransmissions: A. The MAC layer does not inform the RRC layer that the random access has failed. Therefore, it does not trigger the RLF. B. The terminal does not inform the base station that the random access of the secondary serving cell has failed.

12. The path attenuation reference of the pTAG may be a primary serving cell or a secondary serving cell within a pTAG, and the base station may set differently for each serving cell within the pTAG through RRC signaling.

13. The path loss reference of the uplink CCs of each serving cell in the sTAG is each an SIB2 configured downlink CC.

5 is a flowchart illustrating a procedure of obtaining a multi-time alignment value according to an example of the present invention.

Referring to FIG. 5, the terminal and the base station perform an RRC connection establishment procedure for the base station through the selected cell (S500). The selected cell becomes the main serving cell.

The base station performs an RRC connection reconfiguration procedure for additionally configuring at least one secondary serving cell to the terminal (S505). The addition of the secondary serving cell may be performed when it is necessary to allocate to the terminal of more radio resources, for example, by the request of the terminal or the request of the network or the self-determination of the base station.

The base station configures a time alignment group for the serving cell added to the terminal (S510). The TAG setting between the serving cells may be cell-specific depending on the carrier aggregation state. For example, if a serving cell of a specific frequency band is always provided through an FSR or a remote radio head (RRH), the serving cell of the specific frequency band and the base station directly for all terminals in the serving area of the base station. Served serving cells are configured to belong to different TAGs. I) If the base station determines that the same time alignment value as the main serving cell can be applied to the added secondary serving cell, the added secondary serving cell is set to the same TAG as the primary serving cell. In this case, the transmission operation of the TAG configuration information as in step S515 may not be performed. In this case, when the terminal receives the activation indicator and uplink scheduling information for the added secondary serving cell without receiving the TAG configuration information, the terminal considers the added secondary serving cell to be set to the same TAG as the main serving cell.

Ii) If the base station determines that the same time alignment value as the main serving cell cannot be applied to the added secondary serving cell, the base station configures an sTAG including the added secondary serving cell. Each TAG is given a TAG ID for identifying the TAG. However, the base station may selectively assign a TAG ID for the sTAG. As an example, when the base station determines that the sTAG including the added secondary serving cell is a different TAG from previously configured TAGs, the base station acquires a TAG ID for the sTAG before acquiring uplink synchronization through a random access procedure. Can be given. As another example, when the base station determines that the added secondary serving cell may be included in an existing TAG or cannot determine which TAG is included, the base station before acquiring uplink synchronization through a random access procedure The TAG ID for the sTAG may not be assigned. Therefore, in this case, the base station transmits TAG configuration information to the terminal if necessary after the terminal acquires uplink synchronization, and the terminal may acquire the TAG ID of the corresponding sTAG.

The base station transmits the TAG configuration information to the terminal (S515). The TAG configuration information may be in a format including TAG ID information for each secondary serving cell. In more detail, the uplink configuration information of each secondary serving cell may include TAG ID information. Alternatively, the TAG configuration information may be a format for mapping a serving cell index (ServCellIndex) allocated to each serving cell or a secondary serving cell index (ScellIndex) allocated only to secondary serving cells. For example, pTAG = {ServCellIndex = '1', '2'}, sTAG1 = {ServCellIndex = '3', '4'}. Since the main serving cell always has TAG ID = 0, there is no configuration information. In addition, if there is no TAG ID information among the secondary serving cells, the secondary serving cells may mean that the serving cell in the pTAG.

The TAG configuration information may further include representative serving cell information in each TAG. The representative serving cell is a serving cell capable of performing a random access procedure for maintaining and configuring uplink synchronization in each TAG. Unlike the above embodiment, if the TAG configuration information does not include a representative serving cell, the terminal may select a representative serving cell in each TAG by itself. For example, the serving cell indicating the most recent random access procedure among the serving cells indicating the random access procedure may be selected as the representative serving cell. Alternatively, the base station may select a serving cell including parameters for a random access procedure as a representative serving cell when configuring a secondary serving cell. If there are a plurality of serving cells that meet the condition of being the representative serving cell or the representative serving cell is deactivated, the secondary serving cell having the lowest secondary serving cell index may be set as the representative serving cell.

If the base station intends to schedule a specific secondary serving cell, the base station transmits an activation indicator for activating the specific secondary serving cell to the terminal (S520).

If the terminal does not secure uplink synchronization in a specific sTAG, the terminal should obtain a time alignment value to be adjusted for the specific sTAG. This may be expressed through a random access procedure indicated by the base station.

The random access procedure for the active secondary serving cell in the sTAG may be initiated by a PDCCH indication sent by the base station. A secondary serving cell capable of receiving a PDCCH indication may be limited to a secondary serving cell including a timing reference specified in the sTAG, or may be any secondary serving cell configured for RACH.

The base station controls so that the terminal does not simultaneously perform two or more random access procedures. Simultaneous progress of the random access procedure includes a case where two or more random access procedures are synchronized and progress simultaneously, and a case where the random access procedure is concurrently progressed for some time when the random access procedure proceeds. For example, when the UE proceeds with the random access procedure through the main serving cell, the random access procedure starts through the secondary serving cell while the UE waits for the random access response message (receives a PDCCH order).

The base station is enough information to map a specific secondary serving cell to a specific TAG even using the existing network information and / or assistant information (eg location information, RSRP, RSRQ, etc.) received from the terminal If not obtained, the secondary serving cell required for time alignment grouping (sTAG information) is set to another sTAG and the uplink time alignment value is obtained through a random access procedure.

The random access procedure of step S525 may be performed by, for example, the procedure of FIG. 6.

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

Referring to FIG. 6, the base station transmits a PDCCH order for initiating a random access procedure for the secondary serving cell configured in the terminal to the terminal (S600). The random access procedure may be contention based or may be contention based.

For example, in the case of a non-contention based random access procedure, the base station selects one of pre-reserved dedicated random access preambles among all available random access preambles, and the index and the available time / frequency of the selected random access preamble. RA preamble assignment including resource information is transmitted to the UE through a PDCCH indication. This is because the UE must be allocated a dedicated random access preamble with no possibility of collision for the non-contention based random access procedure from the base station.

For example, when the random access procedure is performed during the handover procedure, the terminal may obtain a dedicated random access preamble from the handover command message. Or, for example, when a random access procedure is performed by a request of a base station (PDCCH order), the terminal may obtain a dedicated random access preamble through PDCCH, that is, physical layer signaling. In this case, the physical layer signaling is downlink control information (DCI) format 1A and may include fields shown in Table 1 below.

bits. 모든 비트들이 1로 설정됨
- 프리앰블 인덱스(Preamble Index) - 6 bits
- PRACH 마스크 인덱스(Mask Index) - 4 bits
- 하나의 PDSCH 부호어의 간이 스케줄링 할당을 위한 포맷 1A의 모든 남은 비트들이 0으로 설정됨Carrier indicator field (CIF)-0 or 3 bits.
-Flag to identify format 0 / 1A-1 bit (format 0 if 0, format 1A if 1)
If the Format 1A CRC is scrambled by the C-RNTI and the remaining fields are set as follows, Format 1A is used for the random access procedure initiated by the PDCCH order.
-bottom-
Localized / Distributed VRB allocation flag-1 bit. Set to 0
Resource block allocation

bits. All bits are set to 1
Preamble Index-6 bits
PRACH Mask Index-4 bits
All remaining bits of format 1A for simple scheduling allocation of one PDSCH codeword are set to 0.

Referring to Table 1, the preamble index is an index indicating a preamble selected from among dedicated random access preambles reserved for the contention-free random access procedure, and the PRACH mask index is available time / frequency resource information. The available time / frequency resource information is indicated again according to a frequency division duplex (FDD) system and a time division duplex (TDD) system, as shown in Table 2 below.

PRACH
Mask index PRACH (FDD) allowed PRACH (TDD) allowed 0 all all One PRACH resource index 0 PRACH resource index 0 2 PRACH resource index1 PRACH resource index1 3 PRACH resource index2 PRACH resource index2 4 PRACH resource index 3 PRACH resource index 3 5 PRACH resource index 4 PRACH resource index 4 6 PRACH resource index 5 PRACH resource index 5 7 PRACH resource index 6 Reserved 8 PRACH resource index7 Reserved 9 PRACH resource index8 Reserved 10 PRACH resource index9 Reserved 11 All even PRACH opportunities in the time domain, first PRACH resource index in the subframe All even PRACH opportunities in the time domain,
First PRACH Resource Index in Subframe 12 All odd PRACH opportunities in the time domain,
First PRACH Resource Index in Subframe All odd PRACH opportunities in the time domain,
First PRACH Resource Index in Subframe 13 Reserved First PRACH Resource Index in Subframe 14 Reserved Second PRACH Resource Index in Subframe 15 Reserved Third PRACH Resource Index in Subframe

As another example, in the case of a contention-based random access procedure, the base station sets the preamble index in the preamble allocation information to '000000' and transmits it to the terminal. The UE randomly selects one of the contention-based random access preambles and sets the PRACH mask index value to '0' and then proceeds to the contention-based procedure. In addition, the preamble allocation information may be transmitted to the terminal through a message of a higher layer such as RRC (for example, mobility control information (MCI) in a handover command).

The terminal transmits the random access preamble to the base station (S605). The random access preamble may be transmitted through the representative serving cell. The representative serving cell is a serving cell selected to transmit a random access preamble in a time alignment group configured in the terminal. The representative serving cell may be selected for each time alignment group. In addition, the UE may transmit a random access preamble on a representative serving cell in any one time alignment group among a plurality of time alignment groups, or may transmit a random access preamble on each representative serving cell in two or more time alignment groups. . For example, suppose that the time alignment groups configured in the terminal are TAG1 and TAG2, and TAG1 = {first serving cell, second serving cell, third serving cell}, and TAG2 = {fourth serving cell, fifth serving cell}. . If the representative serving cell of TAG1 is the second serving cell and the representative serving cell of TAG2 is the fifth serving cell, the terminal transmits the allocated dedicated random access preamble to the base station through the second serving cell or the fifth serving cell.

The representative serving cell may be called a special SCell, a reference SCell, or a timing reference serving cell. If the TAG configuration information does not include information related to the representative serving cell, the UL CC to which the preamble is transmitted and the DL CC linked to the SIB2 are defined as timing reference DL CCs based on the PDCCH indication of the base station. A serving cell including the timing reference DL CC is defined as a timing reference serving cell. If only the time alignment value (hereinafter, the representative time alignment value) regarding the representative serving cell is obtained, the terminal may use the representative time alignment value as the time alignment value of another serving cell. This is because the same time alignment value is applied to the serving cells belonging to the same time alignment group. By blocking unnecessary random access procedures in a specific serving cell, duplication, complexity, and overhead of the random access procedure can be reduced.

When the base station successfully receives the random access preamble, the base station may determine which terminal transmits the random access preamble through which serving cell based on the received random access preamble and time / frequency resources. In particular, when the terminal initiates a random access procedure for the secondary serving cell according to the PDCCH indication of the base station, the terminal already has a unique identifier of the terminal in the main serving cell, for example, C-RNTI (Cell-Radio Network Temporary Identifier) Is secured. Accordingly, the base station may use the C-RNTI of the terminal as needed, and may transmit downlink information to the terminal using the C-RNTI. For example, the downlink information includes a random access response message that is a response to the reception of the random access preamble.

The base station transmits the PDCCH scrambled to the C-RNTI of the terminal and the PDSCH to which the random access response message is mapped (S610). Downlink control information (DCI) is mapped to the PDCCH. DCI includes HARQ information. The HARQ information includes a new data indicator (NDI) and a transport block (TB) size. For downlink shared channel (DL-SCH) transmission, HARQ information includes a HARQ process ID. On the other hand, for transmission of the UL common channel (UL-SCH), HARQ information includes a redundancy version (RV).

The random access response message may be mapped to the PDSCH alone, or may be multiplexed with other data in a single MAC PDU and mapped to the PDSCH. The PDSCH to which the random access response message is mapped is indicated by the PDCCH scrambled with C-RNTI. The random access response message may be transmitted on the secondary serving cell. The resource used for transmission of the PDSCH to which the random access response message is mapped is indicated by the resource block allocation field in the DCI. The random access response message may be transmitted through a scheduling cell for the secondary serving cell.

The common search space is allocated a PDCCH scrambled by random access (RA) -RNTI. However, since the common search space is not defined in the secondary serving cell and only the UE-specific search space is defined, the terminal receives the PDCCH scrambled by the RA-RNTI and the random access response message indicated by the PDCCH on the secondary serving cell. Can not. Accordingly, in order to receive a random access response message in the secondary serving cell, the terminal has no choice but to use the terminal-specific search space. Since the PDCCH scrambled by the C-RNTI is allocated in the UE-specific search space, the base station indicates the PDSCH for the random access response message as the PDCCH scrambled by the C-RNTI.

Since the PDCCH is scrambled with the C-RNTI and transmitted, the HARQ entity of the terminal may perform a HARQ process for a random access response message. Therefore, when the UE monitors the PDCCH and the PDCCH indicates downlink transmission, the UE starts a HARQ round trip time (RTT) timer (S615).

The HARQ RTT timer specifies the minimum number of subframes before the downlink retransmission expected by the UE. For example, for an FDD system, the HARQ RTT timer is set to 8 subframes. On the other hand, in the TDD system, the HARQ RTT timer is set to k + 4 subframes, where k is defined as the interval between the downlink transmission and the transmission of the HARQ feedback. HARQ RTT timer is defined for each downlink HARQ process. During the HARQ RTT timer, the UE determines that there is no retransmission of downlink data for the corresponding HARQ process. Therefore, the terminal does not proceed with the reception operation for the HARQ process. For example, if the UE does not receive any downlink data other than the HARQ process and the corresponding subframe is not included in the active time, the UE does not have to maintain a state for receiving the PDCCH.

If the UE does not detect the PDCCH itself, HARQ RTT timer can not be started. Meanwhile, if the UE succeeds in receiving the PDSCH to which the random access response message is mapped, the UE may transmit an ACK signal corresponding thereto. In addition, when the terminal fails to receive the PDSCH to which the random access response message is mapped, the terminal may transmit a corresponding NACK signal to the base station. The ACK / NACK signal may be transmitted after four subframes from the subframe in which the PDSCH is received. The channel on which the ACK / NACK signal is transmitted may be a PUCCH of the main serving cell. Alternatively, the channel through which the ACK / NACK signal is transmitted may be a PUSCH of a primary serving cell or a secondary serving cell.

The base station may retransmit the random access response message to the terminal at a predetermined timing after receiving the ACK / NACK signal from the terminal. The transmission of the random access response message in step S610 may be a new transmission in response to step S605, or may be retransmission by the HARQ process.

Even when the transmission of the random access response message is retransmission, the transmission of the random access response message is valid. Therefore, in determining successful reception of the random access response message, the terminal may consider a time delay caused by retransmission. The terminal determines whether the random access procedure is successful within the RA valid reception duration (S620). The random access validity interval refers to a period in which the UE monitors the PDCCH of the secondary serving cell identified by the C-RNTI while allocating resources of the PDSCH to which the random access response message is mapped. The random access validity interval starts after a predetermined number of subframes (for example, three subframes) from a subframe including an end of the random access preamble.

As one example, the random access validity interval includes an active time defined in a discontinuous receiving operation. This is because, when the UE performs a discontinuous reception (DRX) operation, the subframe must belong to an active time in order for the UE to monitor the PDCCH of the subframe. A time for which a UE performing a discontinuous reception operation monitors a PDCCH in a PDCCH subframe is called an active time.

As another example, the random access validity interval may include a random access window (RA window) interval. The random access window period may be, for example, one of 2ms to 10ms. Alternatively, the random access window period may be set to a value of 10 ms or more. The random access window interval is maintained at the active time. Therefore, the UE can receive the PDCCH scrambled with all C-RNTI.

As another example, the random access validity interval may include a DRX retransmission timer progress period. The DRX retransmission timer is a period for monitoring reception of data retransmitted in the HARQ process. The setting of the DRX retransmission timer is defined by the MAC-MainConfig message of the RRC layer. The MAC-MainConfig message includes a drx-RetransmissionTimer field that sets the length of the DRX retransmission timer. For example, the field drx-RetransmissionTimer may be set to any one of {psf1, psf2, psf4, psf6, psf8, psf16, psf24, psf33}, where psf1 means one PDCCH subframe. For example, in a TDD system, an uplink subframe cannot be counted as a PDCCH subframe because a PDCCH cannot exist. This is because the DRX retransmission timer counts only PDCCH subframes. Therefore, there are two PDCCH subframes during the five subframes of UL, UL, UL, DL, and DL.

If data corresponding to the HARQ process is not successfully decoded after the HARQ RTT timer starts and the HARQ RTT timer expires, the DRX retransmission timer corresponding to the HARQ process starts. Here, the data corresponding to the HARQ process may be a transport block to which a random access response message is mapped. The subframe in which the HARQ RTT timer expires and the subframe in which the DRX retransmission timer starts may be the same or different. In this case, there is no PDCCH for the downlink resource allocation received for the subframe in which the HARQ RTT timer expires, or even if it is not for the corresponding HARQ process. On the other hand, the different cases may be different cases when the UE determines that data decoding for the subframe in which the HARQ RTT timer has expired has failed. That is, when data for the corresponding HARQ process is received but the final decoding fails.

The end of the random access valid reception section is the same as the end of the DRX retransmission timer. Since the DRX retransmission timer progress period ends when data corresponding to the HARQ process is received again, the random access valid reception period also ends at this time. And the HARQ RTT timer expired starts again from this point.

As another example, the random access validity interval may include a random access window interval and a discontinuous reception (DRX) retransmission timer progress period. 6 illustrates that the random access valid reception section includes a random access window section and a DRX retransmission timer progress section. The DRX retransmission timer specifies the maximum number of consecutive PDCCH subframe (s) for immediate downlink retransmission expected by the UE.

Discontinuous reception is configured by the RRC layer, and controls the PDCCH monitoring for the C-RNTI of the terminal (for). For example, if the UE is in an RRC connected mode and discontinuous reception is configured, the UE may discontinuously monitor the PDCCH using a discontinuous reception operation. The RRC layer may control the discontinuous receiving operation by configuring a timer related to the discontinuous receiving operation.

As another example, the random access validity interval may be defined as a random access time alignment command timer starting based on a start point of the random access window interval. The driving time of the timer may be fixedly set to a parameter set by the base station for the secondary serving cell. The driving time of the timer may be a parameter commonly applied to all terminals in a cell through system information, and different parameter values may be applied to each terminal or to each secondary serving cell through RRC signaling.

Monitoring includes an operation of detecting a PDCCH by blind decoding in a PDCCH subframe. The PDCCH subframe refers to a subframe including the PDCCH. Alternatively, the PDCCH subframe for a relay node refers to a subframe including an R-PDCCH. For example, in an FDD system, the PDCCH subframe may be any subframe. On the other hand, in a TDD system, a PDCCH subframe means a subframe including a downlink subframe and a DwPTS.

The terminal determines whether the random access procedure is successful (S615). Common requirements for the success of the random access procedure include: i) the UE receives the PDSCH within the random access validity interval, ii) the UE succeeds in decoding the PDSCH, and iii) the random access response message is mapped to the PDSCH. will be. Therefore, determining the success of the random access procedure requires ii) time t1 for determining requirements and iii) time t2 for determining requirements. The required time t1 and t2 are values determined according to the hardware structure of each terminal. Here, t1 = 1 ms or 2 ms or 3 ms, t2 = 1 ms or 2 ms, or 3 ms. iii) Determination of requirements confirms that the MAC protocol data unit (PDU) containing the random access response message is mapped to the PDSCH, or that a random access response (RAR) MAC control element (CE) is assigned to the PDSCH. This includes checking that it is mapped.

Meanwhile, in determining the success of the random access procedure, special requirements may be added to the common requirements.

As an example of the special requirement, the UE may specify that the NDI indicates 'new transmission' in the HARQ information identified by the PDCCH scrambled with the C-RNTI within the random access window period. When the PDSCH indicated by the received PDCCH is successfully received and decoded through the HARQ process, the UE considers that the random access procedure is successful. At this time, the random access valid reception section includes a random access window. Otherwise, the terminal assumes that the random access procedure has failed. For example, when the UE receives a PDCCH indicating 'new transmission' outside the random access window period.

As another example of the special requirement, it may be a special requirement that the UE re-receives and successfully decodes the PDSCH retransmitted through the HARQ process within the DRX retransmission timer progress period. Otherwise, the terminal assumes that the random access procedure has failed. For example, the random access response message received by the UE through the HARQ process is not successfully decoded and the DRX retransmission timer expires.

When the random access procedure succeeds because the common requirement is satisfied or the common requirement and the special requirement are satisfied, the terminal applies the time alignment value included in the random access response message to adjust the uplink time of the secondary serving cell. The terminal also drives a timing alignment timer (TAT).

The UE may retransmit the random access preamble when the random access procedure is still unsuccessful even in the subframe scheduled as the retransmission timing of the random access preamble. On the other hand, if a random access response message is received in one of the random access window section and the DRX retransmission timer progress section, it is considered as success of the random access procedure. Therefore, retransmission of the random access preamble is unnecessary. For example, if the terminal does not receive the random access response message in the random access window, retransmission of the random access preamble is triggered.

The terminal retransmits or does not retransmit the random access preamble according to the following various conditions.

i) When the subframe scheduled as retransmission timing is before the DRX retransmission timer progress period: The UE retransmits the random access preamble.

ii) When a subframe scheduled for retransmission timing is within a DRX retransmission timer progress period: If a time point at which the UE receives a random access response message is ahead of a subframe scheduled for retransmission timing, the terminal does not retransmit the random access preamble. If the time point at which the UE receives the random access response message is later than the subframe scheduled as the retransmission timing, the UE may retransmit the random access preamble.

iii) When the subframe scheduled as the retransmission timing is after the DRX retransmission timer progress interval: If the UE receives the random access response message in the DRX retransmission timer progress interval, the UE may need to retransmit the random access preamble because the random access procedure is successful. none. This is because, if the random access procedure succeeds, the UE acquires a time alignment value for the secondary serving cell. Therefore, even if retransmission of the random access preamble is triggered, the terminal ignores or cancels the retransmission of the random access preamble.

As such, the random access window is used as a reference for retransmission of the random access preamble, and the HARQ procedure is used as a reference for transmitting and receiving a random access response message. When transmitting or receiving the random access response message using the HARQ procedure, the success or failure of the random access procedure will be described in more detail as follows.

7 is a scenario illustrating a method of performing a random access procedure according to an embodiment of the present invention. This is an example of a random access procedure succeeding.

Referring to FIG. 7, the UE performs a non-contention based random access procedure in a specific random access preamble sequence (eg, 62) and subframe 0 through a corresponding secondary serving cell based on a PDCCH indication received from a base station. do. Accordingly, the UE maps the 62 random access preamble (RAP) sequence to the PRACH in the first subframe 0 after a predetermined time elapses after receiving the PDCCH indication and transmits it to the base station. The predetermined time may be 6 ms.

The UE starts the random access window after subframe n from the subframe in which the random access preamble is transmitted. Where n may be 3. The random access window period may be, for example, one of 2ms to 10ms. Alternatively, the random access window period may be set to a value of 10 ms or more. 7 shows an example in which a random access window section is set to 5 ms. The random access window interval is maintained at the active time. Therefore, the UE can receive the PDCCH scrambled with all C-RNTI.

By the HARQ process P1, the base station responds to the random access preamble, and the PDCCH1 scrambled with the C-RNTI for the terminal, and the PDSCH1 indicated by the PDCCH1 and including the random access response message from the subframe 4 to the terminal. send. When the terminal receives the PDCCH1 or PDSCH1, the HARQ process P1 drives the HARQ RTT timer. 7 shows an example in which a length of a HARQ RTT timer is set to eight subframes.

The random access window is included in the random access validity period. In order for the random access procedure to succeed in this interval, the common and special requirements must be satisfied. That is, when the terminal succeeds in decoding the PDSCH1, the PDSCH1 includes a random access response message (common requirement), and the new data indicator included in the DCI of the PDCCH1 indicates 'new transmission' (special requirement), the terminal is random The access procedure can be successful. However, in the scenario of FIG. 7, the UE fails to decode PDSCH1 in subframe 7 after three subframes have passed. Therefore, the terminal transmits a NACK signal to the base station in subframe # 8.

Next, it is assumed that the UE receives another downlink data in the random access window interval in the scenario of FIG. 7 by the HARQ process P2. That is, the UE receives the PDCCH2 scrambled with the C-RNTI for the UE in subframe 7 and the PDSCH2 indicated by the PDCCH2 from the base station. Since the HARQ RTT timer is already running, the terminal does not drive a separate HARQ RTT timer.

The random access window is included in the random access validity period. Therefore, if the UE succeeds in decoding the PDSCH2 and the PDSCH2 includes the random access response message, the UE may succeed in the random access procedure. In the scenario of FIG. 7, the UE successfully decodes PDSCH2 and transmits an ACK signal in subframe 1 of the next radio frame. However, since PDSCH2 does not include a random access response message, the random access procedure cannot be successful. The time taken for the MAC layer of the UE to recognize that the random access procedure has failed is t1 + t2. For example, the time t1 taken to determine whether the decoding of PDCCH2 and PDSCH2 succeeds is 3ms. In addition, the time t2 for transmitting the information included in PDSCH2 to the MAC layer and confirming the random access response message in the MAC layer is 3ms. Therefore, the UE recognizes the failure of the random access procedure in subframe 3 after 3ms + 3ms = 6ms (or 6 subframes) elapsed from subframe 7 receiving the PDCCH2 / PDSCH2.

Since the UE does not receive the random access response message until the random access window period ends, retransmission of the random access preamble is triggered in subframe 3, which is finally confirmed. Retransmission of the random access preamble is scheduled to occur in the first subframe 0 coming next.

Returning to the HARQ process P1, the base station receiving the NACK signal for PDSCH1 should retransmit the random access response message to the terminal. If the random access response message is successfully retransmitted within the random access validity time period, the terminal regards the random access procedure as successful. The random access validity time period includes an active time for the terminal to effectively receive a random access response message, and in particular, may include a random access window period and a DRX retransmission timer progress period. Since the random access window period has already elapsed, the UE next needs to determine whether the random access procedure succeeds within the DRX retransmission timer progress period.

For the random access procedure to succeed within the DRX retransmission timer progress interval, the common requirements must be met. That is, if the terminal succeeds in decoding the PDSCH1 and the PDSCH1 includes the random access response message, the terminal may succeed in the random access procedure. As in the random access window period, the new data indicator included in the DCI of PDCCH1 does not need to indicate 'new transmission'.

In subframe 3, the DRX retransmission timer is driven for retransmission of PDCCH1 / PDSCH1. The DRX retransmission timer is run when the HARQ RTT timer expires. When the data is retransmitted and the terminal successfully decodes the data, the terminal stops the DRX retransmission timer and drives the HARQ RTT timer again. When the base station retransmits PDCCH1 and PDSCH1 in subframe 4 and the terminal succeeds in decoding PDSCH1, the terminal transmits an ACK signal to the base station in subframe 8. In addition, the MAC layer of the UE may confirm that the random access response message is included in PDSCH1 in subframe 0 that follows. That is, the terminal considers the random access procedure to be successful. The time it takes is also t1 + t2. The terminal applies a time alignment value indicated by the random access response message to the sTAG to which the secondary serving cell belongs, and drives a time alignment timer (TAT).

However, in the next subframe # 0, the retransmission of the random access preamble is scheduled. Since the time alignment timer is already driven, the terminal ignores or cancels the retransmission of the random access preamble. This is because the UE does not need to retransmit the random access preamble since the random access procedure is successful. Although retransmission of the random access preamble is triggered due to non-receipt of the random access response message in the random access window, if it is determined that the random access procedure is successful, the retransmission of the random access preamble does not proceed.

If the time point at which retransmission of the random access preamble is scheduled is before the time alignment timer is driven, the retransmission of the random access preamble may proceed. The terminal may ignore or discard the random access response message for the retransmitted random access preamble, or may be used to update the time alignment value. This is a problem of the implementation of the terminal.

Since the random access procedure is associated with the HARQ procedure, the DRX retransmission timer used in the HARQ procedure as well as the random access window may be used as a criterion for determining whether the random access procedure is successful. In addition, even if the random access procedure is already successful, system degradation such as resource waste and time delay caused by unnecessarily retransmitting the random access preamble can be prevented.

8 is a scenario for explaining a method of performing a random access procedure according to another example of the present invention. This is an example where the random access procedure fails.

Referring to FIG. 8, the UE performs a non-contention based random access procedure in a specific random access preamble sequence (eg, 62) and subframe 0 through a corresponding secondary serving cell based on the PDCCH indication received from the base station. do. Accordingly, the UE maps the 62 random access preamble (RAP) sequence to the PRACH in the first subframe 0 after a predetermined time elapses after receiving the PDCCH indication and transmits it to the base station. The predetermined time may be 6 ms.

The UE starts a random access window after subframe 3 from the subframe in which the random access preamble is transmitted.

By the HARQ process P1, the base station responds to the random access preamble, and the PDCCH1 scrambled with the C-RNTI for the terminal, and the PDSCH1 indicated by the PDCCH1 and including the random access response message from the subframe 4 to the terminal. send. When the terminal receives the PDCCH1 or PDSCH1, the HARQ process P1 drives the HARQ RTT timer. 8 shows an example in which a length of a HARQ RTT timer is set to eight subframes.

The random access window is included in the random access validity period. In order for the random access procedure to succeed in this interval, the common and special requirements must be satisfied. That is, when the terminal succeeds in decoding the PDSCH1, the PDSCH1 includes a random access response message (common requirement), and the new data indicator included in the DCI of the PDCCH1 indicates 'new transmission' (special requirement), the terminal is random The access procedure can be successful. However, in the scenario of FIG. 8, the UE confirms failure of decoding of PDSCH1 in subframe # 7 after three subframes have passed. Therefore, the terminal transmits a NACK signal to the base station in subframe # 8.

Since the UE does not receive the random access response message until the random access window period ends after the decoding of the PDSCH1 fails, retransmission of the random access preamble is triggered. The random access response failure may be finally confirmed in subframe 7 at which the random access window ends. This is because the decoding of PDSCH1 fails, and therefore it is not possible to separately determine whether the random access response message is included in the MAC layer. Retransmission of the random access preamble is scheduled to occur in the first subframe 0 coming next.

The retransmission time point of the random access preamble is subframe 0 and the DRX retransmission timer driving time point is subframe 3. That is, the retransmission time of the random access preamble is earlier than the DRX retransmission timer driving time. Accordingly, the terminal does not determine the success of the random access procedure in the DRX retransmission timer progress section and immediately retransmits the random access preamble to the base station.

The UE may not retransmit the random access preamble indefinitely, and may transmit only the preset maximum RAP transmission number M. FIG. When the UE transmits the M-th random access preamble, a reference time for determining the success or failure of the random access procedure should be defined.

As an example, the reference time point may be an end time point of the random access window. In this case, if the random access procedure is unsuccessful for the M-th transmitted random access preamble until the end of the random access window, the random access procedure is regarded as a failure.

As another example, the reference time point may be a DRX retransmission timer expiration time. In this case, if the random access procedure does not succeed for the Mth random access preamble transmitted until the DRX retransmission timer expires, the random access procedure is regarded as a failure.

FIG. 9 is an explanatory diagram illustrating a reference time point of success or failure of a random access procedure when transmitting the maximum number of RAP transmissions of a random access preamble according to an embodiment of the present invention.

Referring to FIG. 9, the UE transmits the same random access preamble in the secondary serving cell for the Mth. The UE starts a random access window after subframe 3 from the subframe in which the M-th random access preamble is transmitted. By the HARQ process P1, the base station responds to the random access preamble, and the PDCCH1 scrambled with the C-RNTI for the terminal, and the PDSCH1 indicated by the PDCCH1 and including the random access response message from the subframe 4 to the terminal. send. When the terminal receives the PDCCH1 or PDSCH1, the HARQ process P1 drives the HARQ RTT timer.

If the UE fails to receive or decode PDCCH1 and PDSCH1 in subframe 4, the UE transmits a NACK signal for PDSCH1 to the base station in subframe 8. When the HARQ RTT timer expires, the DRX retransmission timer runs. The base station retransmits the PDCCH1 / PDSCH1 in the next 4 subframes. If the decoding for PDSCH1 succeeds, the UE transmits an ACK signal for PDSCH1 to the base station in subframe # 8.

In such a scenario, whether the random access procedure succeeds or fails may vary from baseline. For example, when the reference time point is the end time of the random access window, if the decoding failure of PDSCH1 is confirmed in subframe # 7, the UE regards the failure of the random access procedure in the corresponding secondary serving cell. On the other hand, when the reference time is the DRX retransmission timer expiration time, since the UE succeeds in decoding the PDSCH1 and the random access response message is included in the PDSCH1 before the DRX retransmission timer expires, the terminal considers the success of the random access procedure. When the reference time point is when the DRX retransmission timer expires, the retransmission of the random access response message is different from the case where the reference time point is the end point of the random access window.

Hereinafter, the structure of the random access response message will be described in detail. The random access response message may be included in the MAC PDU. And MAC PDU is included in a single transport block. The transport block may be defined as a variable number of bits based on downlink resource allocation in a single subframe.

10 is a block diagram illustrating a structure of a random access response message according to an embodiment of the present invention.

Referring to FIG. 10, the random access response message may be configured in the format of the MAC PDU 1000. The MAC PDU 1000 includes a MAC header 1010, at least one MAC control element (CE), 1020-1,... 1010-n, and at least one MAC SDU (Service Data Unit). , 1030-1, ..., 1030m) and padding 1040.

MAC control elements 1020-1, ..., 1020-n are control messages generated by the MAC layer.

The MAC header 1010 includes at least one sub-header 1010-1, 1010-2, 1010-3, 1010-4, ..., 1010-k, each subheader 1010-k. 1, 1010-2, 1010-3, 1010-4, ..., 1010-k correspond to one MAC SDU or one MAC control element or padding 1040. The order of the subheaders 1010-1, 1010-2, 1010-3, 1010-4, ..., 1010-k is the corresponding MAC SDUs 1030-1, ... 1030 in the MAC PDU 1000. m), MAC control elements 1020-1, ..., 1020-n or padding 1040 in the same order.

Each subheader 1010-1, 1010-2, 1010-3, 1010-4, ..., 1010-k contains four fields, such as R, R, E, LCID, or R, R, E It can contain six fields: LCID, F, L. Subheaders containing four fields are subheaders corresponding to MAC control elements 1020-1, ..., 1020-n or padding 1040, and subheaders containing six fields are MAC SDUs 1030. Subheader corresponding to -1, ..., 1030-m).

The Logical Channel ID (LCID) field may identify a logical channel corresponding to the MAC SDUs 1030-1,..., 1010-m, or MAC control elements 1020,. An identification field for identifying the type of padding, and each subheader 1010-1, 1010-2, 1010-3, 1010-4, ..., 1010-k has an octet structure. The LCID field may be 5 bits.

For example, as shown in Table 3, the LCID field indicates whether the MAC control elements 1020-1, ..., 1020-n are MAC control elements for indicating activation / deactivation of the serving cell or contention for contention resolution between terminals. Contention Resolution Identity Identifies whether it is a MAC control element or a MAC control element for time advance commands. The MAC control element for the time forward command is the MAC control element used for time alignment in random access.

LCID Index LCID value 00000 CCCH 00001-01010 Logical channel identifier 01011-11010 Reserved 11011 Activation / deactivation 11100 UE contention resolution identifier 11101 Time Forward Command (TAC) 11110 DRX command 11111 padding

Referring to Table 3, if the value of the LCID field is 11101, the corresponding MAC control element is a MAC control element for the time forward command. In this case, the MAC control element for the time advance command may be 8 bits as one octet structure, and the number of bits used in the time advance command field TACF may be 6 bits. The remaining two bits are reserved bits.

Meanwhile, when a time advance command is given to a plurality of serving cells because a plurality of serving cells are configured in a terminal, an LCID field may be given as shown in Table 4.

LCID Index LCID value 00000 CCCH 00001-01010 Logical channel identifier 01011-11001 Reserved 11010 Extended Timing Advance Command 11011 Activation / deactivation 11100 UE contention resolution identifier 11101 Time Forward Command (TAC) 11110 DRX command

Referring to Table 4, if the value of the LCID field is 11010, the corresponding MAC control element is a MAC control element for time advance commands for the plurality of serving cells. In this case, the MAC control element for the time advance command is, for example, six octets and has a total of 48 bits, and the number of bits used in the time advance command field (TACF) may be 11 bits. The remaining bits are used as reserved bits, uplink grants or as temporary C-RNTIs.

Meanwhile, the LCID field may identify that the MAC control elements 620-1,..., 620-n are MAC control elements for the random access response as shown in Table 5.

LCID Index LCID value 00000 CCCH 00001-01010 Logical channel identifier 01011-11001 Reserved 11010 Random access response for secondary serving cell 11011 Activation / deactivation 11100 UE contention resolution identifier 11101 Time Forward Command (TAC) 11110 DRX command 11111 padding

Referring to Table 5, if the value of the LCID field is 11010, the corresponding MAC control element is a MAC control element for the random access response of the secondary serving cell. In this case, the MAC control element for the random access response is, for example, p octets, and includes only 11-bit time forward command field (TACF), or in addition to the time forward command field, a backoff indicator field and an uplink grant. (uplink grant) may be included.

11 is a block diagram illustrating a structure of a random access response message according to another example of the present invention.

Referring to FIG. 11, the random access response message may be configured in the format of the RAR MAC PDU 1100. The RAR MAC PDU 1100 includes a MAC header 1110, at least one MAC RAR field 1115-1,..., 1151-n, and padding 1140.

The MAC header 1110 includes at least one subheader 1105-1, 1105-2,..., 1105-n, and each subheader 1105-1, 1105-2,. n) corresponds to each MAC RAR field 1115-1, ..., 1151-n. The order of the subheaders 1105-1, 1105-2,..., 1105-n is the corresponding MAC RAR fields 1115-1, 1115-2,..., 1115- in RAR MAC PDU 1100. n) may be arranged in the same order.

Meanwhile, the MAC header 1110 may further include a backoff indicator (BI) subheader 1101. The backoff indicator (BI) subheader 1101 includes a backoff indicator. The MAC RAR field corresponding to the backoff indicator subheader 1101 is not present in the RAR MAC PDU 1100. However, the backoff indicator subheader 1101 is a parameter that is commonly applied to all terminals that receive the random access response message. If the UE has never received the backoff indicator, the backoff parameter becomes '0ms' as an initial value or a default value.

The backoff indicator subheader 1101 may be included in the RAR MAC PDU 1100 only when the base station needs to change the backoff parameter for the corresponding serving cell. For example, when the random access preamble transmission through the serving cell is more than a predetermined level or when the base station continuously fails to receive the random access preamble, the base station uses a backoff indicator subheader 1101 to increase the backoff parameter value. It can be included in the RAR MAC PDU 1100 and transmitted.

The backoff indicator subheader 1101 may include five fields, such as E, T, R, R, and BI. Here, the E field is a field indicating whether the corresponding subheader is the last subheader or not. The T field is a field indicating whether the corresponding subheader is a subheader including a random access preamble ID (RAPID) or a backoff indicator subheader. In addition, the R field indicates a reserved bit. The BI field is defined with 4 bits. The BI field value indicates one of 16 index values as shown in Table 5 below.

The BI field may be applied when the terminal determines that the random access procedure is not successful. For example, when the terminal fails to receive the random access response message when the terminal proceeds with the random access procedure later, including the current random access procedure, the terminal increases the number of random access procedure retries by one. If the increased number of random access procedure retries is less than or equal to the maximum number of retries set by the base station, the terminal may retry the random access procedure. In this case, when the UE receives the BI field and the backoff parameter value is not 0, the UE selects one of the value between the backoff parameter value and 0 based on the uniform probability distribution function.

The terminal delays the start or restart of the random access procedure by the selected value. For example, when the BI field value is '1000', this corresponds to a value of 8, so the backoff parameter value is 160ms according to Table 5 below. Therefore, the terminal selects one of the values within 0 to 160ms with the same probability. If the terminal selects 83ms, the terminal delays restart of the random access procedure for 83ms when it determines that the random access has failed, and restarts the random access procedure in the fastest subframe where the random access procedure is possible after 83ms.

The RAPID is information for confirming whether or not the RAR MAC PDU for the random access preamble transmitted by the corresponding terminal among the random access preambles transmitted through the same time / frequency resource by the multiple terminals. The subheaders 1105-1, 1105-2, ..., 1105-n including the RAPID may include three fields, E, T, and RAPID. Here, the E field is a field indicating whether the corresponding subheader is the last subheader or not. The T field is a field indicating whether the corresponding subheader is a subheader including a RAPID or a backoff indicator subheader. The RAPID field is defined by 6 bits and represents information about a random access preamble allocated by the base station or a random access preamble selected by the terminal.

12 is an example of a MAC subheader applied to the present invention.

12, Embodiment 1 is a MAC subheader to which the LCID according to Table 3 is applied, and Embodiment 1 is a MAC subheader to which the LCID according to Table 5 is applied.

13 is an example of a MAC control element to which the present invention is applied.

Referring to FIG. 13, Embodiments 1 to 3 are all MAC control elements having an octet structure (8 bits). Embodiments 1 and 2 are MAC control elements having one octet. Example 3 is a MAC control element consisting of two octets.

In Embodiment 1, the MAC control element includes a 2-bit TAG index and a 6-bit time advance command (TAC) field. The time advance command field indicates a time alignment value. In Embodiment 2, the MAC control element includes an R field of 1 bit, a G field of 1 bit, and a time forward command field of 6 bits. In Embodiment 3, the MAC control element includes a 5-bit R field and a 11-bit time advance command field.

14 is another example of a MAC control element to which the present invention is applied.

Referring to FIG. 14, Embodiment 1 and Embodiment 2 are both MAC control elements having an octet structure (8 bits), Embodiment 1 is a MAC control element consisting of two octets, and Embodiment 2 is composed of three octets. Configured MAC control element. In Embodiment 1, the MAC control element includes a 3-bit R field, a 1-bit TAG index field, and an 11-bit time advance command field. Of course, a format in which the TAG index field is 1 bit and the R field has 4 bits is also possible. Alternatively, a 3-bit serving cell index or secondary serving index may be included instead of the TAG index field. The MAC control element of Embodiment 1 may be indicated by the LCID field according to Table 3 or Table 5.

In Embodiment 2, the MAC control element includes a 1-bit R field, an 11-bit time forward command field, and a 20-bit UL grant. The R bit may be set and used as a flag bit indicating whether an uplink grant is included in a MAC control element. If the MAC control element does not include an uplink grant, four bits of Oct 2 are set to R bits and the length of the entire MAC control element is 16 bits. The MAC control element of Embodiment 2 may be indicated by the LCID field according to Table 5.

15 is a flowchart illustrating a method of performing a random access procedure by a terminal according to an embodiment of the present invention.

Referring to FIG. 15, the terminal receives a PDCCH indication from the base station indicating the start of a random access procedure for a secondary serving cell configured in the terminal (S1500).

The terminal transmits the random access preamble to the base station (S1505).

The terminal receives the PDCCH scrambled with the C-RNTI and the PDSCH to which the random access response message is mapped (S1510). Downlink control information (DCI) is mapped to the PDCCH. DCI includes HARQ information. HARQ information includes a new data indicator (NDI), a transport block (TB) size. For downlink shared channel (DL-SCH) transmission, HARQ information includes a HARQ process ID. On the other hand, for the transmission of the UL common channel (UL-SCH), HARQ information includes a repetitive version (RV). In this case, the UE may drive the HARQ RTT timer by receiving the PDSCH.

The terminal determines whether the random access procedure succeeds within the random access valid time period. The random access validity time period basically includes a random access window and may include a DRX retransmission timer progress period when retransmitting the random access response message. Accordingly, when the UE determines whether the random access procedure succeeds in the random access validity time period, success / failure determination of the random access procedure in the random access window and success / failure determination of the random access procedure in the DRX retransmission timer are determined. It may include.

First, the terminal primarily determines whether the random access (RA) procedure is successful in the random access window (S1515). In the random access window, the UE successfully decodes the PDCCH scrambled with C-RNTI, a new data indicator indicates 'new transmission' to the DCI of the PDCCH, and successfully receives and decodes the PDSCH indicated by the PDCCH. If it is satisfied that the PDSCH includes a random access response message, the terminal considers the success of the random access procedure. If any one of these is not satisfied, the terminal considers the failure of the random access procedure.

If the random access procedure succeeds, the UE transmits an ACK signal indicating successful decoding of the PDSCH to the base station (S1540). Then, the terminal adjusts the uplink time of the secondary serving cell based on the time alignment value included in the random access response message (S1545).

If the random access procedure fails, the UE triggers retransmission of the random access preamble (RAP). If the random access procedure fails because the decoding of the PDSCH fails, the terminal transmits a NACK signal related to the PDSCH to the base station by the corresponding HARQ process (S1520). If the HARQ RTT timer expires, the terminal may drive the DRX retransmission timer. In this case, the UE may monitor the PDCCH and receive and decode the retransmitted data.

Next, the UE secondarily determines whether the random access (RA) procedure is successful in the DRX retransmission timer (S1525). If the UE successfully decodes the PDCCH scrambled with the C-RNTI during the progress of the DRX retransmission timer, successfully receives and decodes the PDSCH indicated by the PDCCH, and the PDSCH includes a random access response message, The terminal considers the success of the random access procedure. If any one of these is not satisfied, the terminal considers the failure of the random access procedure. Here, the random access response message may be retransmitted.

If the random access procedure succeeds in step S1525, the UE transmits an ACK signal indicating successful decoding of the PDSCH to the base station and based on the time alignment value in the random access response message, the uplink time of the secondary serving cell. Adjust (S1530). At this time, the terminal drives a time alignment timer (TAT).

On the other hand, if the time alignment timer is already in progress in the subframe in which the random access preamble is to be retransmitted, the UE may cancel retransmission of the random access preamble (S1535).

In step S1525, if the random access procedure fails, the terminal retransmits the random access preamble to the base station in a predetermined subframe (S1550).

16 is a flowchart illustrating a method of performing a random access procedure by a base station according to an embodiment of the present invention.

Referring to FIG. 16, the base station transmits a PDCCH indication indicating the start of a random access procedure for a secondary serving cell configured in the terminal to the terminal (S1600).

The base station receives a random access preamble from the terminal in response to the PDCCH indication (S1605). When the base station successfully receives the random access preamble, the base station may determine which terminal transmits the random access preamble through which serving cell based on the received random access preamble and time / frequency resources. In particular, when the terminal initiates a random access procedure for the secondary serving cell according to the PDCCH indication of the base station, the terminal already has a unique identifier of the terminal in the main serving cell, for example, C-RNTI (Cell-Radio Network Temporary Identifier) Is secured. Accordingly, the base station may use the C-RNTI of the terminal as needed, and may transmit downlink information to the terminal using the C-RNTI. For example, the downlink information includes a random access response message that is a response to the reception of the random access preamble.

The base station generates a DCI (S1610). The process of generating the DCI may include setting a value of a new data indicator, generating a DCI including HARQ information, adding a cyclic redundancy check (CRC) parity bit to the DCI, and Scramble the added CRC as a unique C-RNTI of the UE. These steps are described in detail as follows.

First, the base station sets a value of the new data indicator. The new data indicator is a parameter used for performing HARQ and indicates whether a transport block (TB) for a terminal is first transmitted or retransmitted. Here, the transport block includes a random access response message. A transport block may be defined as a variable number of bits based on downlink resource allocation in a single subframe. The new data indicator may be transmitted in a subframe period. The new data indicator may correspond to the transport block either 1: 1 or 1: 2 (in case of spatial multiplexing). The new data indicator is, for example, 1 bit, and its value may or may not be toggled every subframe period.

As an example, when the value of the new data indicator is compared with the previous value, the toggle means that the corresponding transport block is new transmission. For example, when the base station transmits the random access response message to the terminal for the first time, the base station sets to toggle the new data indicator corresponding to the random access response message.

As another example, when the value of the new data indicator is not toggled when compared to the previous value, it means that the corresponding transport block is retransmitted in the HARQ process. For example, when the base station retransmits the random access response message to the terminal, the base station sets not to toggle the value of the new data indicator corresponding to the random access response message.

As another example, when a new data indicator corresponding to a transport block is first transmitted to the terminal (that is, there is no previous new data indicator corresponding to the transport block), the terminal transmits the transmission block for the corresponding transport block regardless of the toggle. It is determined that this is a new transmission. For example, when the base station first transmits a random access response message to the terminal, the base station sets the first new data indicator corresponding to the random access response message.

The base station generates a DCI including the new data indicator. DCI including the new data indicator may be defined as shown in the following table.

비트들이 자원할당을 제공함
- 자원할당타입1
- 이 필드의

비트들이 이 자원할당타입에 특정한 헤더로서 사용되며, 선택된 자원블록 서브셋을 지시함.
- 1비트는 자원할당 스팬(span)의 쉬프트(shift)를 지시함
-

비트들이 자원할당을 제공함. 영기서, P의 값은 하향링크 자원의 개수에 의존함.
- 변조 및 코딩 방식/중복버젼(redundancy version) - 5 비트
- HARQ 프로세스 번호 - 3비트(FDD), 4비트(TDD)
- 신규 데이터 지시자(New data indicator) - 1 비트
- 반복 버전 - 2비트
- 스케줄링된 PUCCH를 위한 TPC 명령 -2비트
- 요소 반송파의 인덱스를 지시하는 반송파 지시자(carrier indicator: CI) - 3비트
- 하향링크 할당 인덱스(downlink assignment index: DAI) : 이 필드는 TDD에서 모든 상향링크-하향링크 설정(configurations)에 대해 존재함. - 2 비트Resource allocation header (resource allocation type 0 / type 1)-1 bit. If the downlink bandwidth is less than or equal to 10PRB, no resource allocation header is present and resource allocation type 0 is assumed.
Resource Block Assignment Field
Resource allocation type 0
-

Bits provide resource allocation
Resource allocation type 1
-For this field

Bits are used as headers specific to this resource allocation type, indicating the selected resource block subset.
1 bit indicates the shift of resource allocation span
-

Bits provide resource allocation. In value, the value of P depends on the number of downlink resources.
Modulation and coding scheme / redundancy version 5 bits
HARQ process number-3 bits (FDD), 4 bits (TDD)
New data indicator-1 bit
-Repeated version-2 bits
TPC command for scheduled PUCCH-2 bits
A carrier indicator (CI) indicating the index of the component carrier-3 bits
Downlink assignment index (DAI): This field is present for all uplink-downlink configurations in the TDD. -2 bits

Referring to Table 6, DCI is format 1, and resource allocation header, resource block allocation field, modulation and coding scheme / duplicate version, HARQ process number, new data indicator, repetitive version, TPC command, carrier indicator, downlink allocation index It includes. Each field of the DCI is sequentially mapped to _A information bits a ₀ to a _{A -1} . For example, if the DCI is mapped to a total of 44 bits of information bits, each DCI field is sequentially mapped to a ₀ to a ₄₃ . DCI formats 0, 1A, 3, and 3A may all have the same payload size. DCI may be called PDCCH payload.

The base station adds a cyclic repetition check (CRC) parity bit to the generated DCI, and scrambles the added CRC with its own C-RNTI. Scrambled may also be called masking. The PDCCH to which the CRC scrambled with DCI and C-RNTI is mapped is called PDCCH scambled with C-RNTI. The specific process of scrambling is as follows. Let the payloads of the PDCCH be a ₀ , a ₁ , a ₂ , ..., a _{A -1} and the CRC parity bits are p ₀ , p ₁ , p ₂ , ..., p _{L -1} . As a result of the calculation, the CRC parity bits are converted into the sequences b ₀ , b ₁ , b ₂ ,..., B _{B −1} , where B = A + L. If k = 0, 1, 2, ...., A-1, c _k = b _k, and if k = A, A + 1, A + 2, ..., A + 15 c _k = (b _k + x _{RNTI , kA} ) mod 2.

The base station transmits the PDSCH indicated by the PDCCH and the PDCCH to which the DCI is mapped (S1615). The PDCCH is scrambled with the C-RNTI for the UE.

When the base station receives the NACK signal for the PDSCH, the base station retransmits the PDCCH including the PDCCH and the random access response message to the terminal (S1620).

17 is a block diagram illustrating a terminal and a base station performing a random access procedure according to an embodiment of the present invention.

Referring to FIG. 17, the terminal 1700 includes a receiver 1705, a terminal processor 1710, and a transmitter 1720. The terminal processor 1710 includes a HARQ performer 1711 and a random access processor 1712.

The receiving unit 1705 receives a PDCCH indication from the base station 1750 indicating the start of a random access procedure for the secondary serving cell configured in the terminal 1700. In addition, the reception unit 1705 receives the PDCCH scrambled with the C-RNTI and the PDSCH to which the random access response message is mapped from the base station 1750. The receiver 1705 monitors the PDCCH using the C-RNTI of the terminal 1700, descrambles the DCI, and extracts the DCI. Downlink control information (DCI) is mapped to the PDCCH. DCI includes HARQ information. HARQ information includes a new data indicator (NDI), a transport block (TB) size. For downlink shared channel (DL-SCH) transmission, HARQ information includes a HARQ process ID. On the other hand, for the transmission of the UL common channel (UL-SCH), HARQ information includes a repetitive version (RV).

When the receiver 1705 receives the PDSCH, the HARQ performer 1711 drives a HARQ RTT timer. When the receiver 1705 successfully decodes the PDSCH, the HARQ performer 1711 generates an ACK signal indicating successful decoding of the PDSCH, and the transmitter 1720 transmits the generated ACK signal to the base station 1750. . If the receiver 1705 does not successfully decode the PDSCH, the HARQ performer 1711 generates a NACK signal indicating that the PDSCH has failed to be decoded by the HARQ process, and the transmitter 1720 transmits the generated NACK signal to the base station. 1750).

The random access processing unit 1712 determines whether the random access procedure succeeds within the random access valid time period. The random access validity time period basically includes a random access window and may include a DRX retransmission timer progress period when retransmitting the random access response message. Therefore, the random access processing unit 1712 determines whether the random access procedure succeeds in the random access valid time interval is determined by the success / failure determination of the random access procedure in the random access window and the random access procedure in the DRX retransmission timer. It may include a success / failure determination.

First, the random access processor 1712 primarily determines whether a random access (RA) procedure is successful in the random access window. In the random access window, the receiver 1705 successfully decodes the PDCCH scrambled with the C-RNTI, a new data indicator indicates 'new transmission' to the DCI of the PDCCH, and the receiver 1705 uses the PDCCH. If the PDSCH is successfully received and decoded, and the PDSCH is satisfied to include a random access response message, the random access processing unit 1712 determines that the random access procedure is successful. If any of these are not satisfied, the random access processing unit 1712 determines that the random access procedure has failed.

If the random access procedure succeeds, the random access processor 1712 adjusts the uplink time of the secondary serving cell based on the time alignment value included in the random access response message. If the random access procedure fails, the random access processing unit 1712 triggers retransmission of the random access preamble (RAP). If the HARQ RTT timer expires, the terminal may drive the DRX retransmission timer. In this case, the UE may monitor the PDCCH and receive and decode the retransmitted data.

The random access processor 1712 secondarily determines whether the random access (RA) procedure is successful in the DRX retransmission timer. During the progress of the DRX retransmission timer, the receiver 1705 successfully decodes the PDCCH scrambled with the C-RNTI, the receiver 1705 successfully receives and decodes the PDSCH indicated by the PDCCH, and the PDSCH receives a random access response. If it is satisfied that the message is included, the random access processing unit 1712 determines that the random access procedure is successful. If any of these are not satisfied, the random access processing unit 1712 determines that the random access procedure has failed. Here, the random access response message may be retransmitted.

If the random access procedure succeeds, the random access processor 1712 adjusts the uplink time of the secondary serving cell based on the time alignment value in the random access response message. The random access processing unit 1712 drives the time alignment timer TAT.

On the other hand, if the time alignment timer is already in progress in the subframe where the random access preamble is to be retransmitted, the random access processor 1712 may cancel the retransmission of the random access preamble. If the random access procedure fails, the random access processing unit 1712 regenerates the random access preamble and controls the regenerated random access preamble to transmit the random access preamble in a predetermined subframe.

The base station 1750 includes a transmitter 1755, a receiver 1760, and a base station processor 1770. The base station processor 1770 includes a HARQ execution unit 1775 and a random access processing unit 1772.

The transmitter 1755 is a PDCCH instruction indicating the start of a random access procedure for a secondary serving cell configured in the terminal 1700, a PDCCH scrambled with a C-RNTI for the terminal 1700, and scrambled with the C-RNTI. The PDSCH indicated by the PDCCH and including the random access response message is transmitted to the terminal 1700.

The reception unit 1760 receives the random access preamble from the terminal 1700 in response to the PDCCH indication. The receiver 1760 receives an ACK / NACK signal from the terminal 1700 in response to the PDSCH transmission.

The HARQ execution unit 1775 generates a DCI including HARQ information. The process of generating the DCI includes setting a value of a new data indicator, generating a DCI including HARQ information, adding a cyclic repetition check (CRC) parity bit to the DCI, and adding the added CRC to the UE. Scrambled with one C-RNTI.

The random access processing unit 1772 sets parameters necessary for a random access procedure such as a PRACH mask index assigned to the terminal, and upon successful reception of the random access preamble, generates a random access response message and sends the random access response message to the HARQ performing unit 1775. The HARQ performer 1775 generates a MAC PDU including the random access response message, maps the generated MAC PDU to the PDSCH, and sends the transmitted MAC address 1755. The transmitter 1755 transmits the PDSCH to the terminal 1700.

If the receiver 1760 receives the NACK signal for the PDSCH, the HARQ performer 1711 controls retransmission of data mapped to the PDSCH.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (10)

In the method of performing a random access procedure by the terminal,
Receiving a physical downlink control channel (PDCCH) indication from the base station to indicate the start of a random access procedure in a secondary serving cell configured in the terminal;
Transmitting a random access preamble to the base station in response to the physical downlink control channel indication;
Receiving a physical downlink shared channel (PDSCH) including a random access response message from the base station in response to the random access preamble; And
Determining whether the random access procedure is successful;
Determining whether the random access procedure is successful,
A random access window section and a DRX retransmission timer progress period which is a parameter used for a hybrid automatic repeat request (HARQ) operation on the random access response message in a discontinuous reception (DRX) mode. And performing a random access procedure in a random access validity time period including determining the success of the random access procedure when the terminal receives and successfully decodes the physical downlink shared channel. Way. The method of claim 1, wherein the success of the random access procedure is determined.
And performing an uplink time of the secondary serving cell by using a timing alignment value for the secondary serving cell included in the random access response message. Way. 3. The method of claim 2,
And driving a timing alignment timer (TAT) indicating that the time alignment value is valid. The method of claim 1, wherein the physical downlink control channel is scrambled by a cell-temporary network identifier (C-RNTI) identifying the terminal. Way. The method of claim 1,
If the terminal has not successfully decoded the physical downlink shared channel, further comprising transmitting a NACK signal for the physical downlink shared channel to the base station. In a terminal performing a random access procedure,
Receiving unit for receiving a physical downlink control channel indication from the base station to indicate the start of the random access procedure in the secondary serving cell configured in the terminal;
A transmitter for transmitting a random access preamble to the base station in response to the physical downlink control channel indication; And
Including a random access processing unit for determining the success of the random access procedure,
The receiver receives a physical downlink shared channel (PDSCH) including a random access response message from the base station in response to the random access preamble,
The random access processing unit may include a random access window section and a random access window section including a progress period of a DRX retransmission timer which is a parameter used for HARQ operation for the random access response message in a discontinuous reception mode, And when the terminal receives and successfully decodes the physical downlink shared channel, determining that the random access procedure is successful. The method of claim 6, wherein if the success of the random access procedure is confirmed,
The random access processing unit, characterized in that further comprising adjusting the uplink time of the secondary serving cell using the time alignment value for the secondary serving cell included in the random access response message. The method of claim 7, wherein the random access processing unit,
And operating a time alignment timer indicating that the time alignment value is valid. The method of claim 6, wherein the receiving unit,
And descramble the physical downlink control channel using a cell temporary network identifier identifying the terminal. The method of claim 6, wherein when the receiver does not successfully decode the physical downlink common channel,
And a HARQ performer for generating a NACK signal for the physical downlink shared channel.

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