WO2013112009A1 - Apparatus and method for performing random access in wireless communication system - Google Patents

Abstract

The present invention relates to an apparatus and method for performing random access in a wireless communication system. The method for performing random access in the terminal of the present invention includes the steps of: transmitting a random access preamble to a base station in a sub-serving cell; starting a random access window; receiving a downlink control channel on which downlink control information including a new data indicator indicating that a new transmission or retransmission of a random access response message is mapped from the base station in the sub-serving cell; and determining whether the random access response message is received in the period of the random access window, and whether the random access response message is successfully received through a physical downlink common channel in the sub-serving cell.

Description

Apparatus and Method for Performing Random Access in Wireless Communication System

The present invention relates to wireless communication, and more particularly, to an apparatus and method for performing random access in a wireless communication system.

In a typical wireless communication system, even though the bandwidth between uplink and downlink is set differently, only one carrier is considered. In the 3rd Generation Partnership Project (3GPP) long term evolution (LTE), based on a single carrier, the number of carriers constituting uplink and downlink is one, and the bandwidth of the uplink and the downlink are generally symmetrical to each other. 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-component 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), timing alignment (timing alignment).

An object of the present invention is to provide an apparatus and method for performing random access in a wireless communication system.

Another technical problem of the present invention is to provide an apparatus and method for receiving a random access response message using a PDCCH received through a terminal specific search space of a secondary serving cell.

Another technical problem of the present invention is to provide an apparatus and method for performing a random access procedure accompanying HARQ.

Another technical problem of the present invention is to provide a method of determining whether a random access response message is successfully received based on a new data indicator and a random access window.

According to an aspect of the present invention, a method of performing random access by a terminal in a multi-component carrier system is provided. The method includes transmitting a random access preamble to a base station on a secondary serving cell, starting a random access window, and a new data indicator indicating new transmission or retransmission of a random access response message. receiving a physical downlink control channel to which downlink control information (DCI) including a new data indicator (NDI) is mapped from the base station on the secondary serving cell, and the random access response message Whether the random access response message is successfully received through the physical downlink common channel on the secondary serving cell based on whether the received data is received within a section of a random access window and whether the new data indicator indicates new transmission. Determining.

According to another aspect of the present invention, a terminal for performing random access in a multi-component carrier system is provided. The terminal receives a physical downlink control channel to which downlink control information (DCI) including a new data indicator (NDI) indicating new transmission or retransmission of a random access response message is mapped from the base station on the secondary serving cell A transmitter for transmitting a random access preamble to the base station on a secondary serving cell, an information analyzer for interpreting whether the new data indicator indicates new transmission, and generating the random access preamble, Starts a random access window (RA window) by transmitting an allocated random access preamble, and determines whether the random access response message is received within a section of the random access window and based on an analysis result of the information analyzer; Random to determine whether the response message is received successfully And a process processing unit.

Since only the UE-specific search space is defined in the secondary serving cell, the random access procedure is overcome. In addition, by using the parameters of the HARQ procedure that proceeds separately from the random access procedure to determine the success of the random access response message, it is possible to implement a random access procedure using a unique identifier of the terminal.

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

2 is a flowchart illustrating a random access procedure according to an embodiment of the present invention.

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

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

5 is an explanatory diagram illustrating a method of determining, by a terminal, a successful reception of a random access response message according to an embodiment of the present invention.

6 is an explanatory diagram illustrating a method of determining, by a terminal, a reception success of a random access response message according to another embodiment of the present invention.

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

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

9 is a block diagram illustrating a terminal and a base station according to an embodiment of the present invention.

Hereinafter, some embodiments will be described in detail with reference to the accompanying 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 addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

In addition, the present specification describes a wireless communication network, the operation performed in the wireless communication network is performed in the process of controlling the network and transmitting data in the system (for example, the base station) that is in charge of the wireless communication network, or the corresponding wireless Work may be done at the terminal coupled to the network.

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

Referring to FIG. 1, the wireless communication system 10 is widely deployed to provide various communication services such as voice and packet data. The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for specific cells 15a, 15b, and 15c. The cell can in turn be divided into a number of regions (called sectors).

The mobile station (MS) 12 may be fixed or mobile, and may include a user equipment (UE), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, and a PDA. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms. The base station 11 may be called in other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, an femto base station, a home nodeB, a relay, and the like. . The cell should be interpreted in a comprehensive sense of a part of the area covered by the base station 11 and encompasses various coverage areas such as megacells, macrocells, microcells, picocells and femtocells.

In the following, downlink means communication from the base station 11 to the terminal 12, and uplink means communication from the terminal 12 to the base station 11. In downlink, the transmitter may be part of the base station 11 and the receiver may be part of the terminal 12. In uplink, the transmitter may be part of the terminal 12 and the receiver may be part of the base station 11. There is no limitation on the multiple access scheme applied to the wireless communication system. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA For example, various multiple access schemes such as OFDM-CDMA may be used. The uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme that is transmitted using different times, or may use a frequency division duplex (FDD) scheme that is transmitted using different frequencies.

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 component carrier is defined by a bandwidth and a center frequency. Carrier aggregation is introduced to support increased throughput, to prevent cost increase due to the introduction of wideband radio frequency (RF) devices, and to ensure compatibility with existing systems. For example, if five component carriers are allocated as granularity in a carrier unit having a 20 MHz bandwidth, a bandwidth of up to 100 MHz may be supported.

Carrier aggregation may be divided into contiguous carrier aggregation between continuous component carriers in the frequency domain and non-contiguous carrier aggregation between discontinuous component carriers. The number of carriers aggregated between the downlink and the uplink may be set differently. The case where the number of downlink component carriers and the number of uplink component carriers are the same is called symmetric aggregation, and when the number is different, it is called asymmetric aggregation.

The size (ie, bandwidth) of component carriers may be different from each other. For example, assuming that 5 component carriers are used for the configuration of the 70 MHz band, a 5 MHz component carrier (carrier # 0) + 20 MHz component carrier (carrier # 1) + 20 MHz component carrier (carrier # 2) + 20 MHz component carrier (carrier # 3) + 5MHz component carrier (carrier # 4) may be configured.

Hereinafter, a multiple component carrier system refers to a system supporting carrier aggregation. Adjacent carrier aggregation and / or non-adjacent carrier aggregation may be used in a multi-component carrier system, and either symmetric aggregation or asymmetric aggregation may be used.

The component carrier may be divided into a primary component carrier (PCC) and a secondary component carrier (SCC) according to activation. The major carriers are always active carriers, and the subcarrier carriers are carriers that are activated / deactivated according to specific conditions. Activation refers to the transmission or reception of traffic data being made or in a ready state. Deactivation means that transmission or reception of traffic data is impossible, and measurement or transmission of minimum information is possible. The terminal may use only one major carrier, or may use one or more subcomponent carriers together with the major carrier. The terminal may be assigned a major carrier and / or sub-carrier carrier from the base station.

The primary serving cell refers to one serving cell that provides security input and NAS mobility information in an RRC connection or re-establishment state. According to the capabilities of the terminal, at least one cell may be configured to form a set of serving cells together with the main serving cell, wherein the at least one cell is called a secondary serving cell.

Therefore, the set of serving cells configured for one terminal 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 called a DL PCC, and the uplink component carrier corresponding to the main serving cell is called an UL PCC. In the downlink, the component carrier corresponding to the secondary serving cell is called a downlink sub-component carrier (DL SCC), and in the uplink, the component carrier corresponding to the secondary serving cell is called an uplink sub-component carrier (UL SCC). do. Only one DL CC may correspond to one serving cell, and a DL CC and a UL CC may correspond together.

Therefore, the communication between the terminal and the base station through the DL CC or the UL CC in the carrier system is a concept 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, transmitting a preamble by using a UL CC may be regarded as a concept equivalent to transmitting a preamble using a main serving cell or a secondary serving cell. In addition, the UE receiving the downlink information by using the DL CC, can be seen as a concept equivalent to receiving the downlink information by using the primary serving cell or secondary serving cell.

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

First, the primary serving cell is used for transmission of the PUCCH. On the other hand, the secondary serving cell may not transmit the PUCCH, but may transmit some control information 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 a specific condition. The specific condition may be a case where the activation / deactivation MAC control element message of the base station is received or the deactivation timer configured for each secondary serving cell in the terminal expires.

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. Or, do not define RLF for secondary serving cell. The radio link failure occurs when downlink performance is maintained below a threshold for a predetermined time or when a random access procedure through the main serving cell fails more than a threshold. If the random access procedure through the secondary serving cell fails more than the threshold number of times, only the corresponding random access procedure is terminated.

Fourth, the main serving cell may be changed by a security key change or a handover procedure accompanying a random access procedure. However, in the case of a content resolution (CR) message, only a downlink control channel (hereinafter referred to as 'PDCCH') indicating a CR should be transmitted through the main serving cell, and the CR information may be transmitted through the main serving cell or the secondary serving cell. It can be transmitted through.

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

Sixth, the main serving cell is always configured with a pair of DL PCC and UL PCC.

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 of a new secondary serving cell, RRC signaling may be used to transmit system information of a dedicated secondary serving cell.

Ninth, the main serving cell is a PDCCH (for example, downlink allocation information allocated to a UE-specific search space) configured to transmit control information only to a specific terminal in an area for transmitting control information. Or uplink grant information) and a PDCCH (for example, system information (for example, system information) allocated to a common search space configured for transmitting control information to all terminals in a cell or a plurality of terminals meeting specific conditions). SI), random access response (RAR), and transmit power control (TPC). On the other hand, the secondary serving cell may be set only a terminal-specific search space. That is, since the terminal cannot identify the common search space through the secondary serving cell, the terminal cannot receive control information transmitted only through the common search space and 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 configured when the special secondary serving cell is configured, or the base station may be allocated (configured) or released by RRC signaling (RRC reconfiguration message) when the base station is reconfigured for the secondary secondary cell. have.

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

In addition, the base station may configure one special secondary serving cell 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 secondary serving cell is because it is determined that CSS and PUCCH need not be set. For example, if it is determined that the contention-based random access procedure does not need to be performed in any secondary serving cell, or it is determined that the current capacity of the PUCCH of the primary serving cell is sufficient, it is not necessary to set the PUCCH for the additional secondary serving cell. Corresponding.

The technical spirit of the present invention with respect to the features of the primary serving cell and the secondary serving cell is not necessarily limited to the above description, which is merely an example and may include more examples.

In a wireless communication environment, a propagation delay occurs while a radio wave propagates at a transmitter and is transmitted from a receiver. Therefore, even if both transmitters and receivers know exactly the time when radio waves propagate in the transmitter, the time that a signal arrives at the receiver is affected by the transmission / reception period distance, the surrounding radio wave environment, and changes with time when the receiver moves. If the receiver does not know exactly when the signal transmitted by the transmitter is received, even if the signal reception fails or is received, the receiver receives the distorted signal and communication is impossible.

Therefore, in a wireless communication system, synchronization between a base station and a terminal must be made in advance in order to receive an information signal regardless of downlink and uplink. There are various types of synchronization, such as frame synchronization, information symbol synchronization, and sampling period synchronization. Sampling period synchronization is the most basic synchronization to be obtained in order to distinguish physical signals.

Downlink synchronization acquisition is performed in the terminal based on the signal of the base station. The base station transmits a specific signal mutually promised to facilitate downlink synchronization acquisition in the terminal. The terminal should be able to accurately discern the time when the specific signal transmitted from the base station is transmitted. In the case of downlink, since one base station simultaneously transmits the same synchronization signal to a plurality of terminals, the terminals can independently acquire synchronization.

In the 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, the signals received by each base station has a different transmission delay time, and when the uplink information is transmitted based on the downlink synchronization obtained respectively, the information of each terminal is different time Is received at the base station. In this case, the base station cannot obtain synchronization based on any one terminal. Therefore, uplink sync acquisition requires a different procedure 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. 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-component carrier system, one terminal communicates with a base station through a plurality of component carriers or a plurality of serving cells. If the signals of the plurality of serving cells configured in the terminal all have the same time delay, the terminal may 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, different time alignment values are required for each serving cell. That is, multiple timing alignment values are required. If the UE performs random access for each serving cell in order to obtain multi-time alignment values, overhead may be generated for limited uplink resources, and complexity of random access may increase. To reduce this overhead and complexity, a timing alignment group (TAG) is defined.

The time alignment group is a group including at least one serving cell, and the same time alignment value is 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 TA ₁ 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 TA ₁ and TA ₂ 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 base station, 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. In addition, the terminal should be able to support at least two TAG when a multi-time forward value is required. For example, it should be possible to support TAGs divided into pTAGs (primary TAGs) including the primary serving cell and sTAGs (secondary TAGs) not including the primary serving cell. Here, only one pTAG may exist at any time, and at least one sTAG may exist if a multi-time forward value is required.

The serving base station and the terminal may proceed as follows to obtain and maintain a time advance (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, a timing reference as a reference of downlink synchronization for calculating a TA value of pTAG is always a downlink CC in a main serving cell.

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

3. The timing reference for the sTAG is an uplink CC and a system information block 2 (SIB2) linked downlink CC of the secondary serving cell that transmitted the random access preamble in the most recent RA procedure. 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 downlink CC configured based on information in the SIB1 of the secondary serving cell and the uplink CC configured based on the information in the SIB2.

4. Each TAG has one timing reference and one time 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 downlinks and uplinks. 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. In addition, the configuration of the PUCCH and type 0 (periodic) SRS of all serving cells is released.

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

A. Stop SRS transmission on the uplink CC of secondary serving cells in the sTAG.

B. Disable Type 0 (cyclic) SRS configuration. Type 1 (aperiodic) SRS configuration is maintained.

C. Maintain configuration information for CSI reporting.

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.

8. If the last secondary serving cell in the sTAG is removed, that is, no secondary serving cell in the sTAG is configured, 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 the PDCCH order for the activated secondary serving cell. It may proceed in the form of a contention free random access procedure or contention random access procedure.

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. The path loss reference of the pTAG may be a main serving cell or a secondary serving cell in the pTAG, and the base station may set differently through RRC signaling for each serving cell in the pTAG.

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

2 is a flowchart illustrating a random access procedure according to an embodiment of the present invention. This is a contention free random access procedure.

Referring to FIG. 2, the base station selects one of the reserved random access preambles previously reserved for the non-contention based random access procedure among all available random access preambles, and the index and available time / of the selected random access preamble / The preamble assignment information including the frequency resource information is transmitted to the terminal (S500). The UE needs to be allocated a dedicated random access preamble with no possibility of collision from the base station for a non-contention based random access procedure.

As an example, when the random access procedure is performed during the handover procedure, the UE may obtain a dedicated random access preamble from the handover command message. As another example, when the random access procedure is performed by a request of the base station (PDCCH order), the UE 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 설정됨 Table 1 Carrier 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. -under- 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.

TABLE 2 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 time domain, first PRACH resource index in subframe 12 All odd PRACH opportunities in time domain, first PRACH resource index in subframe All odd PRACH opportunities in 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

The terminal transmits the allocated dedicated random access preamble to the base station (S505). 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, it is assumed that the time alignment groups configured in the terminal are TAG1 and TAG2, and TAG1 = first serving cell, second serving cell, third serving cell, TAG2 = fourth serving cell, and 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. Unlike the above embodiment, if the time alignment group configuration information does not include information related to the representative serving cell, the base station transmits a preamble through a random access procedure indicator such as a PDCCH order (order) and SIB2 connection establishment ( linked) A DL CC is defined as a DL CC as a timing reference, and a serving cell including the timing reference DL CC is defined as a timing reference serving cell.

The random access procedure may proceed after the representative serving cell is activated. In addition, the random access procedure for the secondary serving cell may be initiated by the PDCCH order (order) transmitted by the base station.

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.

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 UE proceeds with a random access procedure for the secondary serving cell according to the PDCCH order of the base station, the UE already has a unique identifier of the UE in the main serving cell, for example, a 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 sets a value of a new data indicator (NDI) (S510). The new data indicator is a parameter used to perform 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 (S515). 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 비트 TABLE 3 Resource 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 3, 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 DCI is mapped to information bits of a total of 44 bits in length, 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 terminal adds a cyclic redundancy check (CRC) parity bit to the generated DCI (S520), and scrambles the added CRC as its own C-RNTI (S525). 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 let the CRC parity bits be 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. for k = 0, 1, 2, ...., A-1, c _k = b _k, and for k = A, A + 1, A + 2, ..., A + 15 c _k = (b _k + x _{RNTI, kA} ) mod 2.

The base station transmits the scrambled PDCCH and the PDSCH to which the random access response message is mapped to the terminal (S530). 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 random access response message is transmitted to the terminal through the PDSCH indicated by the PDCCH scrambled with the C-RNTI of the terminal. 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 of Table 3. 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. Since the common search space is not defined in the secondary serving cell and only the UE-specific search space is defined, the terminal may receive 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.

The random access response message may include a timing advance command (TAC) field. The base station measures a relative change in the current uplink time relative to the reference time based on the random access preamble received from the terminal, and reflects the measured value in a timing advance command field (TACF). The measured change in the uplink time may be an integer multiple of the sampling time T _s , for example 16T _s . The time advance command field indicates a time alignment value for equally adjusting the uplink time of all the serving cells in the time alignment group. The time alignment value can be given by a specific index.

Here, the reference time may be determined differently for each downlink and uplink by the base station. The reference time may be, for example, the transmission reference time point of the downlink signal transmitted by the base station and the reception reference time point of the uplink signal expected by the base station. In general, the downlink transmission reference time of each serving cell may vary within 0 μs to 1.3 μs.

The DCI of Table 3 may be transmitted through a lower layer control channel defined as EPDCCH (Extended PDCCH). EPDCCH consists of a resource block (RB) pair. Here, the RB pair may be defined as an RB for each of two slots constituting one subframe, and may be defined as a pair when each RB is configured as one pair. Here, each RB constituting the RB pair may not be configured with slots having the same time. In addition, it may be composed of RBs existing in the same frequency band or may be composed of RBs existing in different frequency bands.

The terminal determines whether a random access response message (RAR) has been successfully received (S535). The following conditions i) and ii) must be met for successful reception of a random access response message. i) A random access response message will be received during a given RA window period. The receiving of the random access response message may include receiving a PDCCH scrambled with C-RNTI using a C-RNTI in a terminal-specific search space of a secondary serving cell, and receiving the PDCCH scrambled with the C-RNTI. Receiving a PDSCH indicated by the step, and confirming that a random access response message including a time alignment value for the terminal exists in the received PDSCH. Receiving the PDCCH scrambled with the C-RNTI, the UE searches for the PDCCH in the UE-specific search space of the secondary serving cell, performs channel decoding, descrambling with the C-RNTI, CRC Removing the parity bit.

ii) the transmission of the random access response message is new. The terminal may determine whether the random access response message is new by using the new data indicator. The new data indicator is included in the DCI of the PDCCH scrambled with C-RNTI. If the new data indicator is initially transmitted for the random access response message, or if the value of the new data indicator is toggled compared to the previous value, the terminal considers the random access response message to be new. Otherwise, the terminal assumes that the random access response message has been resent.

For example, if the terminal receives the random access response message within the random access window interval and the random access response message is due to new transmission, the terminal is considered to have successfully received the random access response message. On the other hand, if the terminal does not receive the random access response message within the random access window interval, or if the random access response message is retransmission, the terminal is considered to have failed to receive the random access response message. In this case, the terminal ignores the received random access response message and transmits a new random access preamble to the base station.

Meanwhile, the terminal transmits an ACK / NACK signal indicating the success or failure of decoding of the PDSCH itself to which the random access response message is mapped, to the base station. This is performed separately from the progress of the random access procedure. Since the random access response message is indicated by the PDCCH scrambled with the C-RNTI, and the random access response message itself is also downlink data, the HARQ procedure can be equally applied. Accordingly, the UE transmits an ACK signal when the decoding of the PDSCH to which the random access response message is mapped is successful, and transmits an NACK signal when decoding of the PDSCH to which the random access response message is mapped is failed. Successful decoding of the PDSCH to which the random access response message is mapped is different from successful reception of the random access response message. Successful reception of the random access response message is defined in terms of the success of the random access procedure rather than HARQ, and the conditions of i) and ii) must be satisfied.

When the random access response message is successfully received, the UE checks the time advance command field in the random access response message and adjusts an uplink time for the corresponding secondary serving cell by a time alignment value according to the time advance command (S540). . The uplink time TA adjusted by the time alignment value may be calculated by Equation 1 below.

Equation 1

Here, N _TA is a time alignment value, which is variably controlled by a time advance command of a base station, and N _{TA offset} is a value fixed by a frame structure. T _s is the sampling period. In this case, when the time alignment value N _TA is positive, it indicates adjusting to advance the uplink time, and when it is negative, it adjusts to delaying the uplink time.

Let N _{TA be} the maximum value. For example, when the TAC field is defined as 11 bits, M may be defined as 2047. Here, the maximum value of the time alignment value defined by K bits is not always fixed to (2 ^K -1). That is, the maximum value of the time alignment value defined by K bits may be one of 2 ^K-1 to (2 ^K- 1) values. For example, the maximum value of the time alignment value defined by 11 bits may be 1282, which is one of values in the range of 1024 to 2047.

On the other hand, the time alignment value (N _TA) are is adjusted from N _TA value (N _TA-old) are set to the new N _TA value (N _TA-new) by an index value, the new N _TA value is obtained as equation (2) Can be done.

Equation 2

Referring to Equation 2, T _i is an index value, and 0, 1, 2, ..., 63.

Alternatively, the time alignment value N _TA may be determined as a difference value with respect to the time alignment value of the TAG included in the main serving cell as shown in Equation 3.

Equation 3

Referring to Equation 3, N _{TA-TAG (Sn)} is a time alignment value for a time alignment group having an index value of n without including a main serving cell (PCell), and N _{TA-TAG (p)} is a main serving. A time alignment value for a time alignment group including a cell (PCell). T _in T _i is the value for the time alignment of the group index value n. If the maximum value of the time alignment value is M, it may be defined as (M-1) / 2 instead of the constant value 31. For example, if the TAC field is 11 bits, the maximum value of the time alignment value is 2047. In this case, the constant value 31 may be replaced with the value (2047-1) / 2 = 1023. However, the maximum value of the time alignment value defined by K bits is not always fixed to (2 ^K -1). That is, the maximum value of the time alignment value defined by K bits may be one of 2 ^K-1 to 2 ^K- 1 values. For example, the maximum value of the time alignment value defined by 11 bits may be 1282, which is one of values in the range of 1024 to 2047.

When the UE first receives the time alignment value for the serving cell, since there is no target value to prepare, the time alignment value NTA may be determined as shown in Equation 4. Where the constant value 31 is replaced with zero.

Equation 4

As another example, when the propagation delay time of the downlink transmission is the same as the propagation delay time of the uplink transmission, the terminal may adjust the uplink time for all serving cells using the propagation delay time of the downlink transmission.

If there is a time advance command and / or a time alignment group index for a plurality of time alignment groups in the random access response message, the UE transmits an uplink time for the serving cell (s) of each time alignment group to the corresponding time advance command. Adjust by time alignment value accordingly.

2 shows a process of adjusting uplink time based on a contention-free random access procedure. However, the technical idea of FIG. 2 may be equally applied to a contention-based random access procedure. According to the contention-based random access procedure, step S500 is not performed. In addition, in step S505, the terminal does not use the dedicated random access preamble. Instead, the UE randomly selects one preamble signature from the random access preamble signature set and transmits a random access preamble according to the selected preamble signature to the base station through the secondary serving cell using the PRACH resource. In addition, when the contention-based random access procedure is followed, the BS may additionally transmit a contention resolution message indicating that the random access is successfully terminated to the UE. This is to inform that random access is successfully terminated because contention-based transmission of random access preambles may collide when contention-based.

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

Referring to FIG. 3, the random access response message may be configured in the format of the MAC PDU 600. MAC PDU 600 is contained within a single transport block.

The MAC PDU 600 includes a MAC header 610, at least one MAC control element (CE), 620-1, ..., 620-n, and at least one MAC SDU (Service Data Unit). , 630-1,..., 630-m) and padding 640.

MAC control elements 620-1, ..., 620-n are control messages generated by the MAC layer.

The MAC header 610 includes at least one subheader 610-1, 610-2, 610-3, 610-4,..., 610-k, each subheader 610-k. 1, 610-2, 610-3, 610-4, ..., 610-k correspond to one MAC SDU or one MAC control element or padding 640. The order of subheaders 610-1, 610-2, 610-3, 610-4,..., 610-k is the corresponding MAC SDUs 630-1, 630 in the MAC PDU 600. m), MAC control elements 620-1, ..., 620-n) or padding 640 in the same order.

Each subheader 610-1, 610-2, 610-3, 610-4,..., 610-k includes 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 620-1, ..., 620-n or padding 640, and subheaders containing six fields are MAC SDUs 630. Subheader corresponding to -1, ..., 630-m).

The Logical Channel ID (LCID) field may identify a logical channel corresponding to the MAC SDUs 630-1,..., 630-m, or may include a MAC control element 620,. An identification field for identifying the type of padding, and each subheader 610-1, 610-2, 610-3, 610-4, ..., 610-k has an octet structure. The LCID field may be 5 bits.

For example, the LCID field indicates whether the MAC control elements 620-1, ..., 620-n are MAC control elements for indicating activation / deactivation of the serving cell as shown in Table 4, 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.

Table 4 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 4, 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.

On the other hand, when a plurality of serving cells are configured in the terminal, when the time advance command is given to the plurality of serving cells, the LCID field may be given as shown in Table 5.

Table 5 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 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 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 6.

Table 6 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 6, 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.

Padding 640 is a predetermined number of bits added to make the size of MAC PDU 600 constant. The MAC control elements 620-1,..., 620-n, the MAC SDUs 630-1,..., 630-m and the padding 640 together are also referred to as MAC payloads.

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

Referring to FIG. 4, the random access response message may be configured in the format of the RAR MAC PDU 700. The RAR MAC PDU 700 includes a MAC header 710, at least one MAC RAR field 715-1,..., 715-n, and padding 740.

The MAC header 710 includes at least one subheader 705-1, 705-2,..., 705-n, each subheader 705-1, 705-2,... .705-n corresponds to each MAC RAR field 715-1,..., 715-n. The order of subheaders 705-1, 705-2, ..., 705-n is the corresponding MAC RAR fields 715-1, 715-2, ..., 715- in RAR MAC PDU 700. n) may be arranged in the same order.

Meanwhile, the MAC header 710 may further include a backoff indicator (BI) subheader 701. The backoff indicator (BI) subheader 701 includes a backoff indicator. The MAC RAR field corresponding to the backoff indicator subheader 701 is not present in the RAR MAC PDU 700. However, the backoff indicator subheader 701 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 701 may be included in the RAR MAC PDU 700 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 701 that increases the backoff parameter value. It can be included in the RAR MAC PDU 700 and transmitted.

The backoff indicator subheader 701 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 705-1, 705-2, ..., 705-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.

5 is an explanatory diagram illustrating a method of determining, by a terminal, a successful reception of a random access response message according to an embodiment of the present invention. This is a case where the terminal succeeds in receiving a random access response message.

Referring to FIG. 5, a terminal receives a random access start indicator indicating a start of a random access procedure from a base station in a specific serving cell. The random access start indicator is also called a PDCCH order. The terminal transmits the random access preamble to the base station through the PRACH in subframe # 0 where the random access preamble can be transmitted based on the PRACH configuration information for the specific serving cell. This can be applied to both contention-based random access procedures or non- contention-based random access procedures.

There are five formats of the random access preamble as shown in Table 7.

TABLE 7 Preamble format T _CP T _SEQ 0 3168T _S 24576T _S One 21024T _S 24576T _S 2 6240T _S 2,24576, T _S 3 21024T _S 2,24576, T _S 4 448T _S 4096T _S

Referring to Table 7, T _CP is a parameter representing a section of a cyclic prefix (CP) of a PRACH symbol, T _SEQ is a parameter representing a sequence section, and T _S represents a sampling time. According to each format, the number of subframes occupied by the PRACH may be variably defined. For example, in the preamble format 0, the sum of the CP and the sequence is smaller than that of the subframe, and the maximum cell size (two times the radius) that can consider propagation delay is the smallest. In contrast, in the preamble formats 1, 2, and 3, the sum of the CP and the sequence is one or more subframes. In the preamble format 1 or the format 2, two occupied subframes of the PRACH, and in the preamble format 3, three occupied subframes of the PRACH.

The UE starts a random access window for checking whether a random access response message is received in subframe # 3 plus 3 from subframe # 0 through which the random access preamble is transmitted. The random access window period is defined as a total of five subframes from subframe # 3 to subframe # 7. Of course, this is an example, and the length of the random access window interval may be smaller or larger than five subframes. For example, the random access window interval is a parameter determined by the base station and a cell specific parameter. Generally it has a length of 3ms to 10ms.

The UE receives the PDCCH scrambled with the C-RNTI and receives the PDSCH indicated by the PDCCH. The terminal then checks whether a random access response message exists in the data of the received PDSCH. This is called the processing time for P1. The random access response message may have a MAC PDU structure as shown in FIG. 3.

The terminal determines whether the random access response message has been successfully received. To this end, the terminal i) confirms whether the random access response message was received during the random access window period, and ii) confirms that the random access response message was received by the new transmission from the value of the new data indicator in the DCI mapped to the PDCCH. do. If all of the conditions i) and ii) are satisfied, the terminal is considered to have successfully received the random access response message. Here, in addition to the processing section for the P1, an additional processing section for determining whether there is a random access response message for the random access preamble transmitted by the UE through the secondary serving cell in the MAC PDU may be required. Therefore, the processing interval required to confirm whether the random access response message is received during the random access window interval may be larger than the processing interval for P1. For example, a total of 6 ms processing interval may be required by adding 3 ms of processing interval for P1 and 3 ms for checking whether a random access response message is present in the MAC layer.

Meanwhile, the terminal transmits an ACK signal indicating that the PDSCH has been successfully received to the base station in subframe # 9, which is a time point determined by the HARQ rule.

6 is an explanatory diagram illustrating a method of determining, by a terminal, a reception success of a random access response message according to another embodiment of the present invention. This is a case where the terminal fails to receive the random access response message.

Referring to FIG. 6, a terminal receives a random access start indicator indicating a start of a random access procedure from a base station in a specific serving cell. The terminal transmits the random access preamble P1 to the base station through the PRACH in subframe # 0 where the random access preamble can be transmitted based on the PRACH configuration information about the specific serving cell. This can be applied to both contention-based random access procedures or non- contention-based random access procedures.

The UE starts a random access window for confirming whether a random access response message is received in subframe # 3 plus 3 from subframe # 0 through which the random access preamble P1 is transmitted. The random access window period is defined as a total of five subframes from subframe # 3 to subframe # 7.

The base station receives the P1, checks the C-RNTI of the terminal from the P1, and transmits the PDCCH1 scrambled with the C-RNTI and the PDSCH1 mapped with the random access response message to the terminal in subframe # 4. In this case, the new data indicator in the DCI mapped to PDCCH1 indicates that the random access response message is a new transmission.

In connection with performing HARQ, the UE receives the PDCCH1 scrambled with the C-RNTI and fails to decode the PDSCH2 indicated by the PDCCH1. Accordingly, the terminal transmits the NACK signal to the base station in subframe # 8, which is a time point determined by the HARQ rule.

Here, in order to determine successful reception of the random access response message, i) check whether a random access response message has been received during the random access window period, and ii) the random access response message is new from the value of the new data indicator in the DCI mapped to the PDCCH. Confirm that it was received by transmission. As a result of the check, the UE fails to decode the PDSCH and cannot know whether the PDSCH includes a random access response message. Therefore, since the condition of i) is not satisfied, the terminal is considered to have failed in receiving the random access response message.

If the reception success condition of the random access response message is not satisfied during the random access window period, the terminal transmits the random access preamble again based on the end time of the random access window. For example, the UE transmits the random access preamble P2 in subframe # 10. When the previous random access preamble is transmitted in subframe n, the UE should transmit the random access preamble in subframe n + k (k ≧ 6) in which the first PRACH resource is a valid subframe. If the PDSCH decoding is successful, the timing at which the UE confirms that the random access response message does not exist may be after an additional processing period for determining whether the random access response message exists. That is, the success or failure of the random access response message reception may be determined 6 ms after the total random access response message reception processing interval from the most recent subframe in which the PDSCH decoding in the random access window succeeds. In this case, the terminal retransmits the random access preamble based on the timing of determining whether the random access response message has been successfully received or not, rather than the type of random access window.

For example, if the decoding of the PDSCH indicating that the NDI is new data is successful in the last random access window subframe, a random access response message is received 6 ms later (subframe # 13) at the end of the random access window (subframe # 7). Since the UE can recognize the failure, the UE cannot transmit the random access preamble P2 in subframe # 10. Therefore, after that, the first PRACH resource is transmitted in # 20, which is a valid subframe.

Since the base station receives the NACK signal from the terminal, the base station retransmits the random access response message transmitted in subframe # 4 in subframe # 12. At this time, the new data indicator of the PDCCH2 indicates retransmission (ReTx). In determining whether the random access response message is successfully received, since both i) requirements and ii) requirements are not satisfied, the terminal ignores the retransmitted random access response message.

On the other hand, the base station transmits the PDSCH3 indicated by the PDCCH3 and PDCCH3 scrambled with the C-RNTI for the P2 to the UE in subframe # 15. In determining whether the random access response message is successfully received, the subframe # 15 belongs to the random access window section, and the new data indicator indicates new transmission, thereby satisfying both i) and ii) requirements. Accordingly, the terminal determines that the random access response message is successfully received.

7 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. 7, the terminal receives preamble allocation information from the base station (S1000). The terminal selects a dedicated random access preamble based on the preamble allocation information and transmits the selected dedicated random access preamble to the base station on the secondary serving cell (S1005).

The terminal starts the random access window (S1010), and determines whether the reception of the random access response message (RAR) is successful (S1015). Successful reception of the random access response message must satisfy the following two requirements. i) a requirement to receive the PDCCH scrambled with the C-RNTI of the UE and the PDSCH indicated by the PDCCH within the random access window interval, and ii) a requirement for the new data indicator in the PDCCH to indicate new transmission.

If both of the above requirements are satisfied, the terminal is considered to have successfully received the random access response message. The terminal analyzes the time advance command field in the random access response message to obtain a time alignment value, and aligns the uplink times of all serving cells in the time alignment group including the corresponding secondary serving cell based on the obtained time alignment value. (S1020). The terminal transmits an ACK signal to the base station according to the HARQ procedure (S1025).

On the other hand, if either of the two requirements are not satisfied, the terminal is considered to have failed in receiving the random access response message. Therefore, the terminal transmits a new random access preamble to the base station at a predetermined time point (S1030). And, the terminal transmits the ACK / NACK signal to the base station according to the HARQ procedure (S1025).

8 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. 8, the base station transmits preamble allocation information to the terminal (S1100). The base station receives the dedicated random access preamble from the terminal on the secondary serving cell (S1105). The base station sets the value of the new data indicator (NDI) corresponding to the random access response message to either new transmission or retransmission (S1110). The base station generates a DCI including the new data indicator (S1115). The base station adds the CRC parity bit to the generated DCI (S1120), and scrambles the CRC parity bit with a unique C-RNTI of the terminal (S1125).

The base station transmits the PDCCH to which the DCI scrambled with the C-RNTI is mapped and the PDSCH indicated by the PDCCH and to which the random access response message is mapped (S1130). The random access response message includes a time forward command field, and the time forward command field indicates a time alignment value that is information about an uplink time to be adjusted in the secondary serving cell.

The base station receives an ACK / NACK signal from the terminal indicating the successful reception of the PDSCH (S1135).

9 is a block diagram illustrating a terminal and a base station according to an embodiment of the present invention.

Referring to FIG. 9, the terminal 1200 includes a receiver 1205, a terminal processor 1210, and a transmitter 1220. The terminal processor 1210 includes an information analyzer 1211 and a random access processor 1212.

The receiver 1205 receives, from the base station 1250, preamble allocation information, a PDCCH scrambled with C-RNTI, and a PDSCH indicated by the PDCCH and mapped with a random access response message. The DCI including the new data indicator is mapped to the PDCCH scrambled with C-RNTI. PDSCH is received on the secondary serving cell.

The information analyzing unit 1211 interprets the indications of the fields included in the DCI. For example, the information analysis unit 1211 determines whether the new data indicator means new transmission of the random access response message or retransmission of the random access response message. The information analyzing unit 1211 then transmits the determination result regarding the new transmission or retransmission of the random access response message to the random access processing unit 1212.

The random access processor 1212 starts a random access window after a predetermined time or subframe has elapsed from the time when the transmitter 1220 transmits the random access preamble. The receiver 1205 determines whether the time when the random access response message is received falls within the random access window section. Based on the determination result of the information analyzing unit 1211 and the determination result regarding the reception time of the random access response message, the random access processing unit 1212 determines whether the random access response message has been successfully received.

For example, when the determination result of the information analysis unit 1211 indicates new transmission of the random access response message, and the random access response message is received within the random access window section, the random access processing unit 1212 receives the random access response. The message is considered to have been successfully received. On the other hand, when the determination result of the information analysis unit 1211 indicates retransmission of the random access response message, or if the random access response message is not received within the random access window interval, the random access processing unit 1212 determines that the random access response message is successful. As not received.

On the other hand, upon successful reception of the random access response message, the information analyzer 1211 analyzes the time advance command field in the random access response message to obtain a time alignment value. The random access processor 1212 sorts the uplink times in all serving cells in the time alignment group including the corresponding secondary serving cell based on the obtained time alignment value.

On the contrary, if the random access response message fails to be received, the random access processor 1212 generates a new random access preamble at the predetermined time point and sends it to the transmitter 1220, and the transmitter 1220 transmits the new random access preamble to the base station ( 1250).

The transmitter 1220 transmits the random access preamble to the base station 1250. In addition, the transmitter 1220 transmits an ACK / NACK signal indicating whether the PDSCH to which the random access response message is mapped is successfully received to the base station 1250 using the HARQ procedure.

The base station 1250 includes a transmitter 1255, a receiver 1260, and a base station processor 1270. The base station processor 1270 includes an information generating unit 1271 and a random access processing unit 1272.

The transmitter 1255 maps the DCI scrambled by the C-RNTI generated by the information generator 1271 to the PDCCH and transmits the DCI to the terminal 1200. The transmitter 1255 maps the random access response message generated by the random access processor 1272 to the PDSCH and transmits the random access response message to the terminal 1200. In addition, the transmitter 1255 transmits the preamble allocation information to the terminal 1200.

The receiver 1260 receives a random access preamble from the terminal 1200 on the secondary serving cell. In addition, the receiver 1260 receives an ACK / NACK signal from the terminal 1200 indicating whether the PDSCH to which the random access response message is mapped is successfully received using the HARQ procedure.

The information generator 1271 sets the value of the new data indicator (NDI) corresponding to the random access response message to either new transmission or retransmission. The information generator 1271 generates a DCI including the new data indicator. The information generator 1271 adds a CRC parity bit to the generated DCI, scrambles the CRC parity bit with a unique C-RNTI of the terminal 1200, and sends the CRC parity bit to the transmitter 1255.

The random access processor 1272 measures an uplink time based on a random access preamble received on the secondary serving cell and calculates a time alignment value. In addition, the random access processing unit 1272 generates a random access response message including a time advance command field indicating a time alignment value, and sends the random access response message to the transmission unit 1255.

When the ACK / NACK signal received by the receiver 1260 is a NACK signal, the random access processor 1272 regenerates a random access response message and sends it to the transmitter 1255. At this time, the information generating unit 1271 sets the new data indicator to 'new transmission'.

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 changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited thereto. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (18)

A method for performing random access by a terminal in a multi-component carrier system, Transmitting a random access preamble to the base station on a secondary serving cell; Starting a random access window (RA window); On the secondary serving cell, a physical downlink control channel to which downlink control information (DCI) is mapped, including a new data indicator (NDI) indicating new transmission or retransmission of a random access response message, is mapped. Receiving from the base station; And Based on whether the random access response message is received within the interval of the random access window and whether the new data indicator indicates new transmission, the random access response message is a physical downlink shared channel on the secondary serving cell And determining whether the reception is successful via the random access. The method of claim 1, The random access response message includes a timing advance command (TAC) field indicating a time alignment value for adjusting an uplink time in the secondary serving cell. The method of claim 2, If it is determined that the random access response message is successfully received, adjusting the uplink time in the secondary serving cell by using the time alignment value. The method of claim 1, And the physical downlink control channel is scrambled with a cell-radio network temporary identifier (C-RNTI) which is a unique identifier of the terminal. The method of claim 1, The random access response message is a method of performing a random access, characterized in that the protocol data unit (PDU) generated in the medium access control (MAC) layer of the base station. The method of claim 1, Receiving preamble allocation information from the base station including preamble index and time / frequency resource information; The random access preamble is transmitted based on the preamble index and the time / frequency resource information. A terminal for performing random access in a multi-component carrier system, A receiving unit receiving a physical downlink control channel to which downlink control information (DCI) including a new data indicator (NDI) indicating new transmission or retransmission of a random access response message is mapped, from the base station on a secondary serving cell; A transmitter for transmitting a random access preamble to the base station on a secondary serving cell; An information analyzer for analyzing whether the new data indicator indicates new transmission; And Generate the random access preamble, start a random access window (RA window) by transmitting the allocated random access preamble, and interpret the information and whether the random access response message is received within the interval of the random access window And a random access processing unit for determining whether the random access response message is successfully received based on a negative analysis result. The method of claim 7, wherein The receiving unit receives preamble allocation information including a preamble index and time / frequency resource information from the base station, The random access processor generates the random access preamble based on the preamble index and the time / frequency resource information. The transmitter is characterized in that for transmitting the random access preamble based on the preamble index and time / frequency resource information. The method of claim 8, The random access response message, characterized in that it comprises a time advance command (TAC) field indicating a time alignment value for adjusting the uplink time in the secondary serving cell. The method of claim 9, If it is determined that the random access response message is successfully received, The random access processing unit, characterized in that for adjusting the uplink time in the secondary serving cell using the time alignment value. The method of claim 8, Wherein the physical downlink control channel is scrambled with a Cell-Wireless Network Temporary Identifier (C-RNTI) which is a unique identifier of the terminal. The method of claim 8, The random access response message is a terminal, characterized in that the protocol data unit (PDU) generated in the medium access control (MAC) layer of the base station. A method of performing random access by a base station in a multi-component carrier system, Receiving a random access preamble from a terminal on a secondary serving cell; Starting a random access window (RA window); And On the secondary serving cell, a physical downlink control channel to which downlink control information (DCI) is mapped, including a new data indicator (NDI) indicating new transmission or retransmission of a random access response message, is mapped. Including the step of transmitting to the terminal, Whether the random access response message is successfully transmitted through the physical downlink shared channel on the secondary serving cell is determined whether the random access response message is received within the interval of the random access window and whether the new data indicator indicates a new transmission. Characterized in that it is determined based on whether or not to indicate. The method of claim 13, The random access response message includes a timing advance command (TAC) field indicating a time alignment value for adjusting an uplink time in the secondary serving cell. The method of claim 14, If it is determined that the random access response message is successfully transmitted, And the terminal adjusts an uplink time in the secondary serving cell using the time alignment value. The method of claim 13, And the physical downlink control channel is scrambled with a cell-radio network temporary identifier (C-RNTI) which is a unique identifier of the terminal. The method of claim 13, The random access response message is a method of performing a random access, characterized in that the protocol data unit (PDU) generated in the medium access control (MAC) layer of the base station. The method of claim 13, Transmitting preamble allocation information including a preamble index and time / frequency resource information to the terminal; The random access preamble is transmitted based on the preamble index and the time / frequency resource information.

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