US 20100067495A1
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2010/0067495 A1
`Lee et al.
`(43) Pub. Date: Mar. 18, 2010
`
`
`(54) METHOD OF PERFORMING RANDOM
`ACCESS IN A WIRELESS COMMUNCATION
`SYSTEM
`
`(76)
`
`Inventors:
`
`Young Dae Lee, Anyang-si (KR);
`Sung Duck Chun, Anyang-si (KR);
`Sung Jun Park, Anyang-si (KR);
`Seung June Yi, Anyang-si (KR)
`
`Correspondence Address:
`MCKENNA LONG & ALDRIDGE LLP
`1900 K STREET, NW
`WASHINGTON, DC 20006 (US)
`
`(21) Appl. No.:
`
`12/312,172
`
`(22) PCT Filed:
`
`Oct. 30, 2007
`
`(86) PCT No.:
`
`PCT/KR2007/005384
`
`§ 371 (0(1),
`(2), (4) Date:
`
`Apr. 29, 2009
`
`Related US. Application Data
`
`(60) Provisional application No. 60/863,545, filed on Oct.
`30, 2006.
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 7, 2007
`
`(KR) .......................... 1020070012749
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`H043 7/216
`
`(2006.01)
`
`(52) U.S.Cl. ........................................................ 370/335
`
`(57)
`
`ABSTRACT
`
`A method of performing random access in a wireless com-
`munication system is disclosed. The method of performing
`random access in a user equipment of a wireless communi-
`cation system which uses multiple carriers includes transmit-
`ting a preamble for random access to a network, receiving a
`random access response message from the network in
`response to the preamble, transmitting a connection setup
`request message to the network, the connection setup request
`message requesting connection establishment with the net-
`work, and receiving a first message from the network, the first
`message including connection setup information and conten-
`tion resolution information in a random access procedure. If
`a user equipment identifier of the user equipment is included
`in the message, the user equipment determines that it has
`successfully performed random access and performs a next
`procedure in accordance with the connection setup informa-
`tion. If the user equipment identifier of the user equipment is
`not included in the message, the user equipment determines
`that it has failed in random access and transmits a random
`
`access preamble to the network again after the lapse of a
`predetermined time period.
`
` E—UTRAN _
`
`
`APPLE 1025
`
`APPLE 1025
`
`

`

`Patent Application Publication Mar. 18, 2010 Sheet 1 0f 6
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`US 2010/0067495 A1
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`
`
`

`

`Patent Application Publication Mar. 18, 2010 Sheet 2 of 6
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`US 2010/0067495 A1
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`‘ FIG. 2
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`Patent Application Publication Mar. 18, 2010 Sheet 3 0f 6
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`US 2010/0067495 A1
`
`FIG. 3A
`
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`

`

`Patent Application Publication Mar. 18, 2010 Sheet 4 0f 6
`
`US 2010/0067495 A1
`
`FIG. 3B
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`

`Patent Application Publication Mar. 18, 2010 Sheet 5 of 6
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`US 2010/0067495 A1
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`Patent Application Publication Mar. 18, 2010 Sheet 6 of 6
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`US 2010/0067495 A1
`
`FIG. 5
`
`
`Random access preamble
`-851
`
`
`
`
`
`Random access response
`
`RRC connection request
`
`
`
`RRC connectionsetup message and -'
`
`RRC contention resolution message
`
`FIG. 6
`
`
` Random access preamble
`
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`
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`S64
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`

`

`US 2010/0067495 A1
`
`Mar. 18, 2010
`
`METHOD OF PERFORMING RANDOM
`ACCESS IN A WIRELESS COMMUNCATION
`SYSTEM
`
`TECHNICAL FIELD
`
`[0001] The present invention relates to a wireless commu-
`nication system, and more particularly, to a method of per-
`forming random access in a wireless communication system.
`
`BACKGROUND ART
`
`In a wideband code division multiple access
`[0002]
`(WCDMA) system according to asynchronous mobile com-
`munication system standard (3GPP: 3rd Generation Partner-
`ship Project), examples of a downlink transmission channel
`which transmits data from a network (UTRAN: UMTS Ter-
`restrial Radio Access Network) to a user equipment include a
`broadcast channel (BCH) which transmits system informa-
`tion and a downlink shared channel (DL-SCH) which trans-
`mits user traffic or control messages. Trafiic or control mes-
`sages of downlink multicast or broadcast service (MBMS:
`Multimedia Broadcasting and Multicast Service) may be
`transmitted through the DL-SCH or a separate multicast
`channel (MCH). Meanwhile, examples of an uplink transmis-
`sion channel which transmits data from a user equipment to a
`network include a random access channel (RACH) which
`transmits initial control message and an uplink shared chan-
`nel (UL-SCH) which transmits user traffic or control mes-
`sages.
`[0003] Hereinafter, the RACH in the WCDMA system will
`be described. The RACH is used to transmit data of short
`
`length to an uplink, and some RRC messages such as RRC
`connection request message, cell update message, and URA
`update message can be transmitted through the RACH. Fur-
`thermore, a common control channel (CCCH), a dedicated
`control channel (DCCH), or a dedicated trafiic channel
`(DTCH), which is one of logical channels, can be mapped
`with the RACH which is one of transmission channels. Fur-
`thermore, the RACH which is one oftransmission channels is
`again mapped with a physical
`random access channel
`(PRACH) which is one of physical channels.
`[0004]
`If a medium access control (MAC) layer of a user
`equipment commands a physical layer of the user equipment
`to perform PRACH transmission, the physical layer of the
`user equipment selects one access slot and one signature and
`transmits PRACH preamble to the uplink depending on the
`selected result. The preamble is transmitted for an access slot
`period oflength of l .33 ms, and one signature among 16 kinds
`of signatures is selected and transmitted for a first certain
`length of the access slot.
`[0005]
`Ifthe user equipment transmits the preamble, a base
`station transmits a response signal through an acquisition
`indicator channel (AICH) which is a downlink physical chan-
`nel. The AICH transmitted in response to the preamble trans-
`mits the signature selected by the preamble for a first certain
`time period of an access slot corresponding to the access slot
`to which the preamble is transmitted. At this time, the base
`station transmits acknowledgement (ACK) or non-acknowl-
`edgement (NACK) through the signature transmitted from
`the AICH. If the user equipment receives ACK, the user
`equipment transmits a message part of 10 ms or 20 ms by
`using an orthogonal variable spreading factor (OVSF) code
`corresponding to the transmitted signature. If the user equip-
`ment receives NACK, the MAC of the UE again commands
`
`the physical layer of the user equipment to perform the
`PRACH transmission after a proper time period. Meanwhile,
`if the user equipment does not receive the AICH correspond-
`ing to the transmitted preamble, the user equipment transmits
`a new preamble at a power higher than that of the previous
`preamble by one level after a given access slot.
`[0006] Hereinafter, examples where the user equipment
`transmits messages by using the RACH in the WCDMA
`system will be described.
`[0007]
`In case of the first example, the user equipment
`which is in an idle mode transmits an initial control message
`to a network through the RACH. Generally, the user equip-
`ment uses the RACH when the user equipment temporally
`synchronizes with the network and when the user equipment
`desires to acquire radio resources to transmit data to an
`uplink. For example, if the user equipment is powered on and
`first accesses a new cell, the user equipment generally syn-
`chronizes with a downlink and receives system information in
`a cell where the user equipment desires to access. After
`receiving system information, the user equipment transmits
`an access request message for RRC connection. However,
`since the user equipment is not synchronized with the net-
`work temporally and does not yet acquire radio resource of
`the uplink, the user equipment uses the RACH. In other
`words, the user equipment requests the network to provide
`radio resources for transmission of a connection request mes-
`sage, through the RACH. The base station which has been
`requested to provide corresponding radio resources allocates
`proper radio resources to the user equipment so that the user
`equipment can transmit RRC connection request message.
`Then, the user equipment can transmit the RRC connection
`request message to the network through the radio resources.
`[0008]
`In case ofthe second example, in a state that the user
`equipment is connected with the network in a type of RRC,
`the user equipment which is in an RRC connected mode uses
`the RACH. In this case, the user equipment is allocated with
`radio resources in accordance with radio resource scheduling
`of the network, and transmits data to the network through the
`allocated radio resources. However, if data to be transmitted
`do not remain in a buffer ofthe user equipment any longer, the
`network will not allocate radio resources of the uplink any
`longer. This is because that allocating radio resources of the
`uplink to the user equipment having no data to be transmitted
`is inefficient.
`
`[0009] The buffer status ofthe user equipment is reported to
`the network periodically or whenever a specific event occurs.
`If new data occur in the buffer of the user equipment having
`no radio resources, since there are no radio resources of the
`uplink allocated to the user equipment, the user equipment
`uses the RACH. In other words, the user equipment requests
`the network to provide radio resources required for data trans-
`mission, through the RACH.
`[0010] The RACH is an uplink common channel and is a
`channel available for all user equipments which desires to try
`initial access to the network. Accordingly, if two or more user
`equipments use the RACH simultaneously, collision may
`occur. If collision occurs due to the two or more user equip-
`ments, the network should select one of the user equipments
`to perform a normal procedure, and should perform next
`procedures for the other user equipments after resolving a
`problem caused by the collision. In this case, it is necessary to
`define a procedure of avoiding delay in procedures after ran-
`
`

`

`US 2010/0067495 A1
`
`Mar. 18, 2010
`
`dom access for the selected user equipment and resolving the
`problem caused by collision for the other user equipments.
`
`DISCLOSURE OF THE INVENTION
`
`[0011] Accordingly, the present invention is directed to a
`method of performing random access in a wireless commu-
`nication system, which substantially obviates one or more
`problems due to limitations and disadvantages of the related
`art.
`
`[0012] An object of the present invention is to provide a
`method of performing random access in a wireless commu-
`nication system, in which random access is provided to avoid
`unnecessary delay in the wireless communication system.
`[0013] Another object ofthe present invention is to provide
`a method ofperforming random access in a wireless commu-
`nication system, in which radio resources are efficiently used
`in the wireless communication system.
`[0014]
`To achieve these objects and other advantages and in
`accordance with the purpose of the invention, as embodied
`and broadly described herein, a method of performing ran-
`dom access in a user equipment of a wireless communication
`system which uses multiple carriers comprises transmitting a
`preamble for random access to a network, receiving a random
`access response message from the network in response to the
`preamble, transmitting a connection setup request message to
`the network, the connection setup request message requesting
`connection establishment with the network, and receiving a
`first message from the network, the first message including
`connection setup information and contention resolution
`information in a random access procedure. If a user equip-
`ment identifier of the user equipment is included in the mes-
`sage, the user equipment realizes that it has succeeded in
`random access and performs a next procedure in accordance
`with the connection setup information. If the user equipment
`identifier of the user equipment is not included in the mes-
`sage, the user equipment realizes that it has failed in random
`access and transmits a random access preamble to the net-
`work again after the lapse of a predetermined time period.
`[0015]
`In another aspect of the present invention, a method
`of performing random access in a user equipment of a wire-
`less communication system which uses multiple carriers
`comprises transmitting a preamble for random access to a
`network in a state that the user equipment is connected with
`the network, receiving a random access response message
`from the network in response to the preamble, the random
`access response message including a temporary user equip-
`ment identifier of the user equipment, requesting the network
`to allocate uplink resources, and receiving at least one of a
`resource grant message and a contention resolution message
`from the network by using the temporary user equipment
`identifier and a private user equipment identifier of the user
`equipment.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates a network structure of an E-UMTS
`[0016]
`(Evolved-Universal Mobile Telecommunications System);
`[0017]
`FIG. 2 is a schematic view illustrating an E-UTRAN
`(Evolved Universal Terrestrial Radio Access Network);
`[0018]
`FIG. 3A and FIG. 3B illustrate a structure of a radio
`interface protocol between a user equipment (UE) and E-UT-
`RAN, in which FIG. 3A is a schematic view of a control plane
`protocol and FIG. 3B is a schematic view of a user plane
`protocol;
`
`FIG. 4 illustrates an example of a structure of physi-
`[0019]
`cal channels used in an E-UMTS system;
`[0020]
`FIG. 5 is a flow chart
`illustrating a procedure
`according to one embodiment of the present invention; and
`[0021]
`FIG. 6 is a flow chart
`illustrating a procedure
`according to another embodiment of the present invention.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`[0022] Hereinafter, structures, operations, and other fea-
`tures of the present invention will be understood readily by
`the preferred embodiments ofthe present invention, examples
`of which are illustrated in the accompanying drawings.
`Embodiments described later are examples in which techni-
`cal features of the present invention are applied to E-UMTS
`(Evolved Universal Mobile Telecommunications System).
`[0023]
`FIG.
`1
`illustrates
`a network structure of an
`E-UMTS. An E-UMTS is a system evolving from the con-
`ventional WCDMA UMTS and its basic standardization is
`
`currently handled by the 3GPP (3rd Generation Partnership
`Project). The E-UMTS can also be called an LTE (Long Term
`Evolution) system. Release 7 and Release 8 of 3GPP techni-
`cal specifications (3rd Generation Partnership Project; Tech-
`nical Specification Group Radio Access Network) can be
`referred to obtain detailed information about the UMTS and
`E-UMTS.
`
`[0024] Referring to FIG. 1, an E-UTRAN includes base
`stations (hereinafter, referred to as ‘eNode B’ or ‘eNB’),
`wherein respective eNBs are connected with each other
`through X2 interface. Also, each of eNBs is connected with a
`user equipment (UE) through a radio interface and connected
`with EPC (Evolved Packet Core) through Si interface. The
`EPC includes a mobility management entity/system architec-
`ture evolution (MME/SAE) gateway.
`[0025] Layers of a radio interface protocol between a UE
`and a network can be classified into a first layer L1, a second
`layer L2 and a third layer L3 based on three lower layers of
`OSI (open system interconnection) standard model widely
`known in communication systems. A physical layer belong-
`ing to the first layer L1 provides an information transfer
`service using a physical channel. A radio resource control
`(hereinafter, abbreviated as ‘RRC’) located at the third layer
`plays a role in controlling radio resources between the UE and
`the network. For this, the RRC layer enables RRC messages
`to be exchanged between the UE and the network. The RRC
`layer can be distributively located at network nodes including
`Node B, an AG and the like or at either the Node B or the AG.
`[0026]
`FIG. 2 is a schematic view illustrating an E-UTRAN
`(UMTS terrestrial radio access network). In FIG. 2, a hatch-
`ing part represents functional entities of a user plane and a
`non-hatching part represents functional entities of a control
`plane.
`FIG. 3A and FIG. 3B illustrate a structure of a radio
`[0027]
`interface protocol between the user equipment (UE) and the
`E-UTRAN, in which FIG. 3A is a schematic view of a control
`plane protocol and FIG. 3B is a schematic view ofa userplane
`protocol. Referring to FIG. 3A and FIG. 3B, a radio interface
`protocol vertically includes a physical layer, a data link layer,
`and a network layer and horizontally includes a user plane for
`data information transfer and a control plane for signaling
`transfer. The protocol layers in FIG. 3A and FIG. 3B can be
`classified into L1 (first layer), L2 (secondlayer), and L3 (third
`
`

`

`US 2010/0067495 Al
`
`Mar. 18, 2010
`
`layer) based on three lower layers of the open system inter-
`connection (OSI) standard model widely known in the com-
`munications systems.
`[0028] The physical layer as the first layer provides infor-
`mation transfer service to an upper layer using physical chan-
`nels. The physical layer (PHY) is connected to a medium
`access control (hereinafter, abbreviated as ‘MAC’) layer
`above the physical layer via transport channels. Data are
`transferred between the medium access control layer and the
`physical layer via the transport channels. Moreover, data are
`transferred between different physical layers, and more par-
`ticularly, between one physical layer of a transmitting side
`and the other physical layer of a receiving side via the physi-
`cal channels. The physical channel of the E-UMTS is modu-
`lated according to an orthogonal frequency division multi-
`plexing (OFDM) scheme, and time and frequency are used as
`radio resources.
`
`[0029] The medium access control (hereinafter, abbrevi-
`ated as ‘MAC’) layer ofthe second layer provides a service to
`a radio link control (hereinafter, abbreviated as ‘RLC’) layer
`above the MAC layer via logical channels. The RLC layer of
`the second layer supports reliable data transfer. In order to
`effectively transmit IP packets (e.g., IPv4 or IPv6) within a
`radio-communication period having a narrow bandwidth, a
`PDCP layer of the second layer (L2) performs header com-
`pression to reduce the size of a relatively-large IP packet
`header containing unnecessary control information.
`[0030] A radio resource control (hereinafter, abbreviated as
`‘RRC’) layer located on a lowest part of the third layer is
`defined in the control plane only and is associated with con-
`figuration, reconfiguration and release ofradio bearers (here-
`inafter, abbreviated as ‘RBs’) to be in charge of controlling
`the logical, transport and physical channels. In this case, the
`RB means a service provided by the second layer for the data
`transfer between the UE and the UTRAN.
`
`[0031] As downlink transport channels carrying data from
`the network to UEs, there are provided a broadcast channel
`(BCH) carrying system information, a paging channel (PCH)
`carrying paging message, and a downlink shared channel
`(SCH) carrying user traffic or control messages. The traffic or
`control messages ofa downlink multicast or broadcast service
`can be transmitted via the downlink SCH or an additional
`
`downlink multicast channel (MCH). Meanwhile, as uplink
`transport channels carrying data from UEs to the network,
`there are provided a random access channel (RACH) carrying
`an initial control message and an uplink shared channel (UL-
`SCH) carrying user traffic or control message. As logical
`channels located above the transport channels and mapped
`with the transport channels, there are provided a broadcast
`channel (BCCH), a paging control channel (PCCH), a com-
`mon control channel (CCCH), a multicast control channel
`(MCCH), and a multicast traffic channel (MTCH).
`[0032]
`In the E-UMTS system, an OFDM is used on the
`downlink and a single carrier frequency division multiple
`access (SC-FDMA) on the uplink. The OFDM scheme using
`multiple carriers allocates resources by unit of multiple sub-
`carriers including a group of carriers and utilizes an orthogo-
`nal frequency division multiple access (OFDMA) as an
`access scheme.
`
`[0033] A physical layer of an OFDM or OFDMA scheme
`divides active carriers into a plurality of groups and transmits
`respective groups to different receiving sides. Radio resource
`allocated to each UE which is defined by a time-frequency
`region on a two-dimensional sphere comprises continuous
`
`sub-carriers. A time-frequency region in the OFDM or
`OFDMA scheme is a rectangular form sectioned by time and
`sub-carrier coordinates. In other words, one time-frequency
`region could be a rectangular form sectioned by at least one
`symbol on a time axis and sub-carriers on a frequency axis.
`Such a time-frequency region can be allocated to an uplink for
`a specific UE, or an eNB can transmit the time-frequency
`region to a specific UE in a downlink. In order to define such
`a time-frequency region on the two-dimensional sphere, the
`number of OFDM symbols and the number of continuous
`sub-carriers starting from a point having an offset from a
`reference point should be given.
`[0034] The E-UMTS which is currently being discussed
`uses 10 ms radio frame comprising 20 sub-frames. Namely, a
`sub-frame has a length of 0.5 ms. A resource block comprises
`one sub-frame and twelve sub-carriers, each of which is 15
`kHz. One sub-frame comprises a plurality of OFDM symbols
`and a part (for example, first symbol) of the plurality of
`OFDM symbols can be used for transmission of L1/L2 con-
`trol information.
`
`FIG. 4 is a diagram illustrating a structure of physi-
`[0035]
`cal channels used in the E-UMTS. In FIG. 4, a sub-frame
`comprises an L1/L2 control information transmission region
`(the hatching part) and a data transmission region (the non-
`hatching part).
`illustrating a procedure
`[0036]
`FIG. 5 is a flow chart
`according to one embodiment of the present invention. In the
`embodiment of FIG. 5,
`technical features of the present
`invention are applied to a procedure of initial random access
`of a user equipment which is in an idle mode.
`[0037] Referring to FIG. 5, the user equipment transmits a
`random access preamble to a base station eNB [$51]. In other
`words, the user equipment selects a specific signature among
`a plurality of signatures through one access slot and transmits
`the selected signature to the base station. At this time, the
`random access preamble may include uplink message infor-
`mation or channel measurement information so that the base
`
`station may perform resource allocation for uplink message
`transmission. In this case, if at least two user equipments
`simultaneously perform uplink transmission of random
`access preambles by using same radio resources such as same
`signatures, collision may occur.
`[0038] The base station transmits a random access response
`message to the user equipment in response to the random
`access preamble [SS2]. The random access response message
`includes the signature transmitted from the user equipment,
`grant or rejection information ofthe random access preamble
`transmission, a temporary cell radio network temporary iden-
`tifier (Temporary C-RNTI) allocated to the user equipment,
`and control information related to transmission of the RRC
`
`connection request message, etc. The control information
`related to transmission of the RRC connection request mes-
`sage includes radio resource allocation information, a mes-
`sage size, and radio parameters (modulation and coding infor-
`mation and hybrid ARQ information) for transmission of the
`RRC connection request message.
`[0039] The base station transmits signaling information for
`receiving the random access response message to the user
`equipment through L1/L2 control channel. The signaling
`information includes a random access radio network tempo-
`rary identifier (RA-RNTI) indicating transmission of the ran-
`dom access response message and transmission parameters
`related to transmission of the random access response mes-
`sage. Since the RA-RNTI is previously forwarded from the
`
`

`

`US 2010/0067495 A1
`
`Mar. 18, 2010
`
`user equipment to the base station through system informa-
`tion, etc., the user equipment acquires the signaling informa-
`tion through the L1/L2 control channel by using the RA-
`RNTI and receives the random access response message by
`using the acquired signaling information.
`[0040]
`Ifthe signature transmitted from the user equipment
`and grant information for signature transmission are included
`in the random access response message, the user equipment
`transmits the RRC connection request message to the base
`station [S53]. At this time, the user equipment transmits the
`RRC connection request message to the base station by using
`the uplink radio resource allocation information, the message
`size, and the radio parameters, which are included in the
`random access response message. The RRC connection
`request message includes a user equipment identifier for iden-
`tifying the user equipment. Examples of the user equipment
`identifier include wideband UE identifiers such as an inter-
`
`national mobile subscriber identity (IMSI) or a temporary
`mobile subscriber identity (TMSI).
`[0041]
`Ifthe signature transmitted from the user equipment
`and the rejection information of the signature transmission
`are included in the random access response message, or if the
`signature transmitted from the user equipment is not included
`in the random access response message, the user equipment
`retransmits the random access preamble after a certain time
`without transmitting the RRC connection request message.
`[0042]
`If the RRC connection request message is received
`from the user equipment, the RRC layer of the base station
`transmits the RRC connection setup message or the RRC
`contention resolution message to the user equipment. Prefer-
`ably,
`the RRC layer transmits one RRC message which
`includes the RRC connection setup message and the RRC
`contention resolution message. For another example, after
`transmitting the RRC connection setup message to the user
`equipment, the base station can transmit the RRC contention
`resolution message.
`[0043]
`If one RRC message which including the RRC con-
`nection setup message and the RRC contention resolution
`message is transmitted, padding included in the message can
`be reduced, whereby the radio resources can be used effi-
`ciently. The RRC message includes user equipment identifier
`of a user equipment which has succeeded in random access.
`Preferably, the user equipment identifier is a user equipment
`identifier included in the RRC connection request message,
`for example, IMSI and TMSI.
`[0044]
`If a plurality of user equipments collide with one
`another during a transmission procedure ofthe random access
`preamble or the RRC connection setup message, only one
`user equipment which has successfully performed random
`access is operated in accordance with the RRC connection
`setup message. In this case, the success ofthe user equipment
`which has succeeded in the random access means that the
`
`random access preamble transmitted from the user equipment
`has been successfully received by the base station and then
`the RRC connection request has been successfully per-
`formed.
`
`[0045] As described above, the RRC connection setup mes-
`sage included in the RRC message includes the wideband
`user equipment identifier such as IMSI and TMSI of the user
`equipment which has succeeded in the random access. The
`user equipment receives control
`information required to
`receive the RRC message through the L1/L2 control channel
`by using its temporary C-RNTI. For example, the user equip-
`ment can identify whether a specific channel of the L1/L2
`
`control channel is transmitted to itself in accordance with the
`
`result of cyclic redundancy code (CRC) test of the specific
`channel by using the temporary C-RNTI. For another
`example, the user equipment receives a message indicated by
`the temporary C-RNTI if the temporary C-RNTI is received
`through the L1/L2 control channel. If the specific channel is
`transmitted to the user equipment,
`the user equipment
`receives the RRC message transmitted to a downlink channel
`of a data region, for example, a downlink shared channel
`(DL-SCH) by using control information transmitted through
`the specific channel.
`[0046]
`If the wideband user equipment identifier transmit-
`ted through the RRC connection request message is included
`in the RRC connection setup message, the user equipment
`realizes that it has succeeded in the random access and rec-
`
`ognizes the RRC connection setup message as its message. At
`this time, the user equipment uses the temporary user equip-
`ment identifier (temporary C-RNTI) as a private C-RNTI for
`performing communication with a network later.
`[0047]
`If the wideband user equipment identifier transmit-
`ted through the RRC connection request message is not
`included in the RRC message, the user equipment realizes
`that it has failed in the random access. Also, if the RRC
`message which includes the wideband user equipment iden-
`tifier is not received for a certain time period, the user equip-
`ment realizes that it has failed in the random access. At this
`
`time, the user equipment can start a random access procedure
`again by retransmitting the random access preamble to the
`base station after a certain time period.
`[0048] The aforementioned embodiments of the present
`invention can be applied to a random access procedure for
`initial access performed after radio link failure or handover.
`[0049]
`FIG. 6 is a flow chart
`illustrating a procedure
`according to another embodiment of the present invention. In
`the embodiment of FIG. 6, technical features of the present
`invention are applied to a random access procedure of a user
`equipment which is in an RRC connected mode. For example,
`if radio resources for data to be transmitted to the base station
`
`are not allocated to the user equipment, the user equipment
`can transmit data through the random access procedure
`through the RACH. The embodiments described hereinafter
`can be applied to the case where the base station is not uplink-
`synchronized with the user equipment even though it has
`downlink data to be transmitted to the user equipment which
`is in the RRC connected mode.
`
`[0050] Referring to FIG. 6, the user equipment transmits a
`random access preamble to the base station eNB [S61], and
`receives a random access response message from the base
`station in response to the random access preamble [S62].
`Since the steps S61 and S61 are the same as S51 and S52 of
`FIG. 5, their detailed description will be omitted.
`[0051]
`Ifthe signature transmitted from the user equipment
`and grant information for signature transmission are included
`in the random access response message, the user equipment
`transmits a MAC scheduling request message to the base
`station [S63]. At this time, the user equipment transmits the
`MAC scheduling request message to the base station by using
`the uplink radio resource allocation information, the message
`size, and the radio parameters, which are included in the
`random access response message. Preferably,
`the MAC
`scheduling request message includes a wideband user equip-
`ment identifier for identifying the user equipment. Examples
`of the user equipment identifier include wideband UE iden-
`tifiers such as international mobile subscriber identity (IMSI)
`
`

`

`US 2010/0067495 A1
`
`Mar. 18, 2010
`
`identity (TMSI). The
`temporary mobile subscriber
`or
`embodiment of FIG. 6 is different from that of FIG. 5 in that
`
`scheduling request and contention resolution procedures are
`performed by the MAC layer.
`[0052]
`Ifthe signature transmitted from the user equipment
`and the rejection information of the signature transmission
`are included in the random access response message, or if the
`signature transmitted from the user equipment is not included
`in the random access response message, the user equipment
`retransmits the random access preamble after a certain time
`without transmitting the MAC scheduling request message.
`[0053]
`If the MAC scheduling request message is received
`from the user equipment, the MAC layer of the base station
`transmits a resource grant message and MAC contention
`r