KR20120114171A - Method and apparatus for controlling random access in wireless communication system using carrier aggregation - Google Patents

Abstract

PURPOSE: A random access control method of a terminal and an apparatus thereof in a mobile communication system are provided to allow a terminal to efficiently control a random access process. CONSTITUTION: A transceiver(801) transceives a signal from a base station. A controller performs random access for a first cell or a second cell. The controller senses failure to the random access. The controller determines whether the sensed random access is about the first cell or the second cell. The controller determines whether to perform random access process according to whether to fail the random access to the first cell or the second cell. [Reference numerals] (801) Transceiver; (811) MAC random access implementation and management part; (821) RRC layer

Description

Efficient random access control method and apparatus for mobile communication system carrier integration operation {METHOD AND APPARATUS FOR CONTROLLING RANDOM ACCESS IN WIRELESS COMMUNICATION SYSTEM USING CARRIER AGGREGATION}

The present invention relates to a mobile communication system, and more particularly, to a method and apparatus for efficiently controlling random access in a mobile communication system using carrier aggregation.

In general, a mobile communication system has been developed for the purpose of providing communication while securing user mobility. Such a mobile communication system has reached a stage capable of providing high-speed data communication service as well as voice communication due to the rapid development of technology. Recently, 3GPP (3rd Generation Partnership Project) is working on the specification of Long Term Evolution (LTE) as one of the next generation mobile communication systems. LTE is a technology that implements high-speed packet-based communication with a transmission rate of up to 100 Mbps, which is higher than the data rate currently provided for commercialization in 2010. On the other hand, unlike a voice service, a data service can be allocated resources according to the amount of data to be transmitted and channel conditions. Therefore, in a wireless communication system such as a mobile communication system, a management such as allocating a transmission resource is performed in consideration of the amount of resources to be transmitted by the scheduler, channel conditions, and the amount of data. This is the same in LTE, one of the next generation mobile communication systems, and a scheduler located in a base station manages and allocates radio transmission resources. Recently, a discussion about an advanced LTE communication system (LTE-A: LTE-Advanced), which improves transmission speed by incorporating various new technologies into an LTE communication system, has been in full swing. Among the newly introduced technologies, there is a carrier aggregation technology (CA). In the carrier communication technology, only one carrier is used for downlink reception and uplink transmission between a user equipment (UE) and a base station in a conventional communication. The carrier carrier uses a subcarrier using a primary carrier and one or more subcarriers. It is a technique of increasing the data reception amount / reception rate or transmission amount / transmission rate by the number. In LTE, a cell configured as a primary carrier is called a PCell (Primary Cell, or a first cell, hereinafter same), and a cell configured as a subcarrier is called a SCell (Secondary Cell, or a second cell, hereinafter same). On the other hand, when the antenna positions for transmitting / receiving radios using the main carrier and the subcarrier are changed due to the introduction of repeaters and remote radio heads (RRH / Repeater), for example, the transmit / receive antennas of the main carrier are located in the base station. The transmit / receive antenna of the subcarrier may be located in the RRH), in which case the uplink timing for transmitting to a receiving antenna farther away according to the position of the terminal, and for transmitting to a receiving antenna of a closer position Uplink timing may be required. That is, a plurality of uplink timings may exist, and an efficient handling scheme for a random access operation for obtaining the plurality of uplink timings is required. The present invention defines an efficient handling scheme for a case where a random access for each uplink timing acquisition is problematic / failed when there are a plurality of uplink timings.

An object of the present invention is to provide a method and apparatus for efficiently controlling a random access procedure by a terminal in a mobile communication system, particularly in a telecommunication system using carrier aggregation.

In the present invention, in a carrier integration operation in which a plurality of uplink timings exist, when the random access procedure for acquiring each uplink timing is problematic / failure, whether the random access procedure is random access in the PCell or random access in the SCell. Therefore, we propose a separate random access problem / failure handling scheme. When random access is a problem / failure in the PCell, the random access problem / failure is notified from a medium access control (MAC) layer of a terminal detecting the problem / failure to a radio resource control (RRC) layer, and the RRC layer is connected to a base station. Performing an RRC Connection Re-establishment and the corresponding RRC Connection Reconfiguration to reset the connection and resetting the signaling radio bearer and the data radio bearer. Restart the Ciphering / Integrity protection check. On the other hand, if the random access is a problem / failure in the SCell, the random access that is being performed in the MAC layer of the terminal detecting the problem / failure is stopped. On the other hand, the random access problem / failure in the SCell is not known from the MAC layer to the RRC layer.

More specifically, in a wireless communication system in which the first cell and the at least one second cell of the present invention are integrated and used, the random access control method of the terminal may include performing random access to the first cell or the second cell; Detecting a failure for the random access, determining whether the failure detected random access is for the first cell or for the second cell, and random access for the first cell or the second cell And determining whether to continue the random access procedure according to the failure.

In addition, in a wireless communication system in which a first cell and at least one second cell of the present invention are integrated and used, a terminal performing random access to a base station includes a transceiver for transmitting and receiving a signal to and from the base station, and the first cell or the first cell. Perform a random access to two cells, detect a failure for the random access, determine whether the failed detected random access is for the first cell or for the second cell, and determines the first cell or And a controller configured to determine whether to continue the random access procedure according to whether a random access to a second cell has failed.

According to an embodiment of the present invention, when there is a plurality of uplink timings, when random access for each uplink timing acquisition is problematic / failed, the random access procedure can be efficiently handled.

Fig. Illustrating one embodiment of a 3GPP system architecture.
Fig. Illustrating one embodiment of a radio protocol architecture of a 3GPP system.
3. Illustrating one embodiment of carrier integration.
Figure 4. Figure 1 illustrates one embodiment for the need and role of an uplink timing sync procedure.
Figure 5. Illustrates one embodiment for a scenario in which multiple uplink timings are required in carrier integration.
Figure 6. Random Access Problem / Failure Handling Scheme in Proposed Carrier Integration Operation A flowchart illustrating one embodiment.
Figure 7. 6 is a flowchart illustrating one embodiment of a terminal operation flowchart for the embodiment.
Figure 8. 6 is a block diagram showing one embodiment of a device block diagram of a terminal according to the embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in the drawings, the same components are denoted by the same reference symbols as possible. Further, the detailed description of well-known functions and constructions that may obscure the gist of the present invention will be omitted.

1 is a diagram illustrating an embodiment of a 3GPP LTE system structure, which is an embodiment system to which the present invention is applied.

The radio access network of the LTE mobile communication system is a next-generation base station (hereinafter referred to as Evolved Node B, ENB or Node B) 105, 110, 115, and 120, 125 Mobility Management Entity (MME) and 130 Serving Gateway (S-GW). It is composed of

The user equipment (hereinafter referred to as UE) 135 connects to an external network through the ENB and S-GW. The ENBs 105 to 120 correspond to existing Node Bs of the UMTS system.

The ENB is connected to the UE 135 by a radio channel and performs a more complicated role than the existing Node B. In LTE, all user traffic, including real-time services such as Voice over IP (VoIP) over the Internet protocol, is serviced through a shared channel, which requires a device that collects the UE's context information and schedules it. 105-120).

One ENB typically controls multiple cells. In order to realize a transmission rate of up to 100 Mbps, LTE uses Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology in a bandwidth of up to 20 MHz. In addition, an adaptive modulation & coding (AMC) scheme that determines a modulation scheme and a channel coding rate according to the channel state of the terminal is applied.

S-GW is a device that provides a data bearer, and generates or removes a data bearer under the control of the MME. MME MME is a device that is responsible for various control functions are connected to a plurality of base stations.

2 is a diagram illustrating an embodiment of a radio protocol structure in an LTE system to which the present invention is applied.

Referring to FIG. 2, the wireless protocol of the LTE system is PDCP (Packet Data Convergence Protocol 205, 240), RRC (Radio Resource Control 208, 238), RLC (Radio Link Control 210, 235), MAC (Medium) at the terminal and ENB, respectively. Access Control 215, 230), PHY (Physical 2210, 225).

PDCP is responsible for IP header compression / restore, ciphering and integrity protection checks over wireless protocols. The RRC defines the transmission of control information messages and related actions / procedures of upper layers for radio resource handling.

RLC reconfigures the PDCP Packet Data Unit (PDU) to the appropriate size.

The MAC is connected to several RLC layer devices configured in one terminal and performs an operation of multiplexing the RLC PDUs to the MAC PDU and demultiplexing the RLC PDUs from the MAC PDU.

The physical layer (PHY) performs channel coding and modulation on higher layer data, makes an OFDM symbol, transmits it to a radio channel, or demodulates, decodes, and channel-decodes an OFDM symbol received through the radio channel to a higher layer.

3 is a diagram illustrating an embodiment of carrier aggregation in a terminal.

In one base station, multiple carriers are generally transmitted and received over several frequency bands. For example, when a carrier 315 having a center frequency of f1 and a carrier having a center frequency of f3 310 are transmitted from a base station 305, one terminal uses data from one of the two carriers. Received.

However, a terminal having a carrier aggregation capability may receive data from several carriers at the same time. The base station 305 may increase the data reception rate of the terminal 330 by allocating more carriers to the terminal 330 having the carrier aggregation capability according to the situation. The above is described in terms of transmitting a carrier in a base station, and the same is true in terms of receiving a carrier in a base station. Conventionally, although one terminal transmits data using one carrier among a plurality of carriers, a terminal having carrier aggregation capability may increase data transmission rate by simultaneously transmitting data using multiple carriers.

In the conventional sense, when one forward carrier and one backward carrier transmitted and received by one base station constitute one cell, carrier aggregation may be understood as a terminal transmitting and receiving data through multiple cells at the same time. . Through this, the maximum transmission rate is increased in proportion to the number of carriers integrated.

In the following description of the present invention, the terminal receiving data through an arbitrary forward carrier or transmitting data through an arbitrary backward carrier includes a control channel provided by a cell corresponding to a center frequency and a frequency band that characterize the carrier; It has the same meaning as transmitting and receiving data using the data channel. In addition, embodiments of the present invention will be described assuming an LTE system for convenience of description, but the present invention can be applied to various wireless communication systems supporting carrier aggregation.

FIG. 4 is a diagram illustrating an embodiment of a necessity and a role of an uplink timing sink procedure in a 3GPP LTE system using an OFDM multiplexing scheme.

UE1 (hereinafter referred to as terminal 1) indicates a terminal located near to the ENB, and UE2 (hereinafter referred to as terminal 2) refers to a terminal far from the ENB. The first propagation delay time T_pro1 represents a propagation delay time in radio transmission to the terminal 1, and the second propagation delay time T_pro2 is radio wave in radio transmission to the terminal 2 Delay time.

Since terminal 1 is located closer to ENB than terminal 2, it has a relatively small propagation delay time (T_pro1 shows 0.333us and T_pro2 shows 3.33us in FIG. 4).

The initial uplink timing of the terminal 1 and the terminal 2 in one cell of the ENB does not match the uplink timing of the terminals in the cell detected by the ENB. 401 indicates an uplink transmission timing for a specific OFDM symbol of the terminal 1 and 403 indicates an uplink transmission timing for the OFDM symbol of the terminal 2.

Considering the propagation delay time of the uplink transmission of the terminal 1 and the terminal 2, the reception timing in the ENB for receiving the uplink OFDM symbol is equal to 407 and 409. That is, the uplink transmission of the 401 terminal 1 is received by the ENB at the timing of 407 with a short propagation delay time, and the uplink transmission of the 403 terminal 2 is received by the ENB at the timing of 409 with a relatively long propagation delay time. 405 represents a reference reception timing of the ENB. Since 407 and 409 are still uplink timing synchronization with respect to the terminal 1 and the terminal 2, the reference timing 405 at which ENB receives and decodes the OFDM symbol and the timing 407 for receiving the OFDM symbol from the terminal 1 and the terminal. 409, timing of receiving an OFDM symbol from two, is different. Therefore, since the uplink OFDM symbols transmitted from the terminal 1 and the terminal 2 do not have orthogonality with the uplink OFDM symbol received at the 405 reference reception timing, the uplink OFDM symbols act as interferences with each other and the ENBs cause the respective OFDM symbols due to the interference. There is a problem that cannot be successfully decoded.

The uplink timing sync procedure is a process of matching the uplink symbol reception timings of the terminal 1, the terminal 2, and the E-NB equally. When the uplink timing sink procedure is finished, the E-NB performs uplink OFDM as shown in 411, 413, and 415. The timing of receiving and decoding symbols is set.

In the uplink timing sync procedure, the ENB transmits timing advance (Timing Advance) information to the terminals, and provides information on how much uplink transmission should be performed by adjusting timing relative to the reception downlink. Inform. TA information is transmitted through a random access response (hereinafter referred to as RAR) for a random access preamble transmitted by the terminal in the random access process or a timing advance command MAC control element (hereinafter referred to as TAC MAC CE). It may be transmitted through).

FIG. 5 is a diagram illustrating an embodiment of a scenario in which a plurality of uplink timings is required in carrier integration.

The Remote Radio Head (RRH) 503 using the F2 frequency band 507 is distributed around the macro base station 501 using the F1 frequency band 505. If the terminal uses both the macro base station and the remote radio at the same time (ie, the terminal is located near the remote radio, the carrier integrates the F1 and F2 frequency bands for uplink transmission) and the downlink with the remote radio. Uplink transmission has a short propagation delay time, while downlink and uplink transmissions with a macro base station have a relatively long propagation delay time, so the uplink transmission timing to the remote radio equipment is the uplink transmission timing to the macro base station. And wrong.

That is, in the carrier aggregation scenario, a plurality of uplink transmission timings are required. Accordingly, in order to match the initial uplink transmission timing, a random access procedure is performed to the remote wireless equipment by F2 to randomize the uplink transmission timing to a macro base station to F1. The access procedure must be performed to match each uplink transmission timing. In other words, if there are a plurality of uplink transmission timings in carrier integration, a random access procedure for matching the uplink transmission timing is required for the plurality of cells (the random access procedure for the plurality of cells needs to be performed at the same timing). none).

In the present invention, a group for carriers having the same uplink timing is referred to as a timing advance group (TAG). For example, if three SCells A, B, and C are integrated in a PCell, PCell and SCell A have the same uplink timing, and SCell B and SCell C have the same uplink timing, then PCell and SCell A are assigned to TAG # 0. SCell B and SCell C may belong to TAG # 1.

Hereinafter, TAG # 0 including the PCell may be referred to as PTAG (Primary TAG) and TAG # 1 not including the PCell as STAG. The PCell refers to the serving cell of the primary carrier and is usually the one that initially established the RRC connection, established the RRC connection, established the RRC connection, or was the target of a handover (HO). It is a cell. The present invention proposes a method for efficiently handling a random access problem / failure that may occur when a random access procedure is performed on a plurality of cells described above.

FIG. 6 is a flowchart illustrating an embodiment of a handling scheme for a random access problem / failure in the carrier aggregation operation proposed in the present invention.

The terminal 601 determines that the base station establishes carrier aggregation in the terminal while the terminal 601 is connected to the base station 611 only by the PCell 613 (621). 603 shows an RRC protocol layer in the terminal, 606 shows a MAC protocol layer in the terminal, and 609 shows a PHY protocol layer in the terminal. When the base station determines a carrier aggregation setting for the terminal, the base station transmits an RRC layer message to signal configuration information on the SCell 616 to be added for the carrier integration, and adds the SCell to the carrier aggregation target cell (631). At this time, the information on the uplink transmission timing of the SCell is informed to the terminal using information such as STAG id.

If the terminal is not currently maintaining the uplink timing for the STAG id, the SCell requires a new uplink transmission timing. As an example of the RRC layer message, an RRC connection reconfiguration procedure may be used.

The base station then activates the added SCell as needed for the carrier integration (633). An MAC activation control message may be used as an example of the activation indication message for the SCell.

In the present invention, it is assumed that the activated SCell needs a new uplink transmission timing that is different from the uplink transmission timing (the uplink transmission timing for the 613 PCell in FIG. 6) that the terminal maintains. The base station instructs to perform a random access procedure for the SCell to obtain uplink transmission timing information for the SCell (636). As an example of the command message, a PDCCH order message may be used. The PHY layer 609 notifies the MAC layer of the random access procedure execution command (639), and the MAC layer selects a random access preamble to transmit and notifies the PHY layer (641). The PHY layer transmits the random access preamble to the base station. (642).

If the terminal does not receive a response message for the transmitted random access preamble from the base station, the terminal (re) transmits the random access preamble (645, 646, 648, 649). If the number of the (re) transmitted random access preambles exceeds a predetermined threshold value, it is determined that there is a problem and / or failure for random access in the MAC layer (651).

If the problem with the random access is a random access problem / failure for the SCell (651), the MAC stops the random access procedure for the SCell and no longer (re) transmits the random access preamble (653).

In step 661, the base station again instructs the PDCCH order to perform a random access procedure for the SCell. This time, the random access procedure for the SCell is completed successfully to obtain the TA information for the SCell uplink transmission timing Assume that is obtained. Since the uplink timing of the SCell is obtained, uplink scheduling is possible not only for the PCell but also for the SCell, and uplink transmission may occur due to the uplink scheduling (663).

The base station then instructs this time to perform a random access procedure for the PCell (671). The PHY layer 609 notifies the MAC layer of the command to perform the random access procedure (673), and if the MAC layer selects a random access preamble to transmit and notifies the PHY layer (674), the PHY layer transmits the random access preamble to the base station. (675).

If the terminal does not receive a response message for the transmitted random access preamble from the base station, the terminal (re) transmits the random access preamble (676, 677, 678, 679). If the number of the (re) transmitted random access preambles exceeds a predetermined threshold, it is determined that there is a problem / failure for random access in the MAC layer (681).

If the problem with the random access is a random access problem / failure for the PCell (681), the MAC notifies the RRC layer 603 that there is a problem / failure with the random access and the RRC layer receiving the notification is connected to the RRC connection. Perform the procedure to reset the (691).

Although not shown in FIG. 6, the RRC layer that is notified of a random access problem / failure waits a little longer until a specific timer in the RRC layer expires instead of immediately performing a procedure for resetting the RRC connection. If not successful, then the procedure to reset the RRC connection may be performed. As an example of the procedure for resetting the RRC connection, an RRC connection reestablishment and an RRC connection reconfiguration procedure thereafter may be used.

The procedure for resetting the RRC connection is to reset the signaling radio bearer and the data radio bearer assuming that the link between the terminal and the base station is broken, and to restart the security (referring to security, encryption and integrity check operations) on the radio interface. .

In addition, in case of a random access problem / failure for the PCell, the random access procedure may continue until the RRC layer instructs the MAC layer to stop the random access procedure. That is, the random access preamble may be continuously (re) transmitted even after the random access problem / failure detection until there is a stop condition or an indication in the RRC layer. As an example of the random access stop condition of the RRC layer, the start of the RRC connection reestablishment procedure, the change of the PCell, or the termination of a specific timer of the RRC layer may be used. In conclusion, in FIG. 6, when a random access problem / failure occurs, a separate handling scheme is discriminated according to whether the random access is performed in the PCell or the random access in the SCell. In the present invention, it is assumed that the random access to the PCell will be more important, but a handling scheme opposite to that of FIG. 6 is also applicable (the random access problem / failure handling scheme and the random access problem to the SCell of FIG. Swapping of handling methods in case of failure is also applicable).

Although not shown in FIG. 6, as another embodiment, when the random access is a problem / failure in the PCell or when the random access is a problem / failure in the SCell, the MAC layer is an RRC layer. It may be known. In this case, however, when the RRC layer announces the random access problem / failure to the RRC layer, which cell has the random access problem / failure or which TAG has the random access problem / failure? The additional information should be informed, and the RRC layer receiving the information performs the RRC connection resetting procedure when the random access of the PCell is a problem / failure. Or, it may signal that random access has a problem / failure in a cell included in a certain STAG.

The base station receiving the information may perform an operation such as re-commanding random access, releasing a cell having a random / failed random access, or changing configuration information of cells for carrier integration.

7 is a flow chart illustrating one embodiment of a terminal operation flow diagram for the FIG. 6 embodiment.

In 701, the MAC layer detects a problem / failure of a random access procedure. An embodiment of problem / failure detection of the random access procedure may determine that there is a problem / failure in random access when the number of (re) transmitted random access preambles exceeds a predetermined threshold. When a problem / failure of a random access procedure is detected, it is determined whether the random access problem / failure is a problem / failure for random access of the PCell or a random access problem / failure for the SCell (711). If random access to the SCell is a problem / failure, the MAC layer stops / terminates the random access procedure (721).

On the contrary, if the random access to the PCell is a problem / failure, the MAC layer may announce the random access problem / failure to the RRC layer while the random access procedure may be continuously performed (731).

The RRC layer, which is informed of the random access problem / failure information from the MAC, performs an RRC connection reconfiguration procedure and instructs the MAC to abort / end the random access procedure when a specific condition is satisfied (741).

As an example of the specific condition, a start of an RRC connection reestablishment procedure, a change of a PCell, or an end of a specific timer of an RRC layer may be used. Although not shown in FIG. 7, the RRC layer that is notified of a random access problem / failure waits a little longer until a specific timer in the RRC layer expires instead of immediately performing a procedure for resetting the RRC connection. If not successful, then the procedure to reset the RRC connection may be performed. If instructed to abort / terminate the random access procedure from the RRC, the MAC abort / terminate if the random access procedure was still running.

8 is a block diagram illustrating an embodiment of a terminal device block diagram for the FIG. 6 embodiment.

The terminal communicates with the base station through the transceiver 801.

The RRC layer 821 generates an RRC control message and transmits it to a base station through a transceiver, or receives an RRC control message received through a transceiver, decrypts it, and performs a related procedure based on the received information. In addition, when the RRC layer receives information on a problem / detection of a random access procedure from the MAC layer, the RRC layer performs a related procedure and may instruct the MAC layer to stop / end the random access procedure.

When the MAC random access performing and managing unit 811 is instructed to perform a random access procedure for a specific cell from a base station through a transceiver, or is instructed to start performing a random access procedure from an RRC inside a terminal, or a random access procedure is triggered from a MAC, the corresponding random access is performed. When the procedure is performed and a problem / failure is detected in the random access procedure, the random access procedure is automatically stopped or terminated or a random access procedure problem / failure is notified to the RRC layer.

On the other hand, although not shown in the terminal device block diagram of Figure 8, it should be noted that all the above process can be performed under the control of the controller.

In this case, the controller performs random access on the first cell or the second cell and detects a failure for the random access. The control beam determines whether the failure-detected random access is for the first cell or the second cell, and continues the random access procedure according to whether the random access to the first cell or the second cell fails. Determine whether or not.

Specifically, the controller controls to perform a radio resource control (RRC) connection reestablishment procedure when detecting a random access failure for the first cell. In this case, the control unit according to an embodiment of the present invention may drive a timer when detecting a random access failure for the first cell and perform the RRC connection resetting procedure upon the random access failure until the timer is completed.

 On the other hand, upon detecting a random access failure for the second cell, the controller controls to stop performing the random access procedure.

Claims (10)

A random access control method of a terminal in a wireless communication system in which a first cell and at least one second cell are integrated and used,
Performing random access to the first cell or the second cell;
Detecting a failure for the random access;
Determining whether the failed detected random access is for the first cell or for the second cell; And
And determining whether to continue the random access procedure according to whether the random access to the first cell or the second cell has failed. The method of claim 1, wherein the determining step,
The random access control method for random access to the first cell, further comprising the step of performing a radio resource control (RRC) connection resetting procedure. The method of claim 2, wherein the determining step,
Driving a timer upon detection of a random access failure for the first cell; And
And performing the RRC connection reestablishment procedure when the random access fails before completion of the timer driving. The method of claim 1, wherein the determining step,
And stopping the execution of the random access procedure when detecting a random access failure for the second cell. The method of claim 1, wherein the determining step,
And determining that the random access has failed when transmitting the random access preamble to the base station more than a predetermined number of times. A terminal for performing random access to a base station in a wireless communication system in which a first cell and at least one second cell are integrated and used,
Transmitting and receiving unit for transmitting and receiving a signal with the base station; And
Perform a random access to the first cell or a second cell, detect a failure for the random access, determine whether the failed detected random access is for the first cell or for the second cell, and And a controller configured to determine whether to continue the random access procedure according to whether the random access to the first cell or the second cell has failed. 7. The apparatus of claim 6,
And detecting a radio resource control (RRC) connection reestablishment procedure when detecting a random access failure for the first cell. 8. The apparatus of claim 7,
And a timer is driven when the random access failure is detected for the first cell and the RRC connection resetting procedure is performed when the random access fails until the timer is completed. 7. The apparatus of claim 6,
When the random access failure is detected for the second cell, the terminal characterized in that the control to stop performing the random access procedure. 7. The apparatus of claim 6,
And transmitting the random access preamble to the base station more than a predetermined number of times, determining that the random access has failed.

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