3GPP TS 36.321 V8.7.0 (2009-09)
`
`Technical Specification
`
`
`
`3rd Generation Partnership Project;
`Technical Specification Group Radio Access Network;
`Evolved Universal Terrestrial Radio Access (E-UTRA)
`Medium Access Control (MAC) protocol specification
`(Release 8)
`
`
`
`
`
`
`The present document has been developed within the 3rd Generation Partnership Project (3GPP TM) and may be further elaborated for the purposes of 3GPP.
`The present document has not been subject to any approval process by the 3GPP Organizational Partners and shall not be implemented.
`This Specification is provided for future development work within 3GPP only. The Organizational Partners accept no liability for any use of this Specification.
`Specifications and reports for implementation of the 3GPP TM system should be obtained via the 3GPP Organizational Partners' Publications Offices.
`
`
`
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`

`
`Keywords
`UMTS, radio
`
`
`
`
`
`3GPP
`
`Postal address
`
`
`3GPP support office address
`650 Route des Lucioles - Sophia Antipolis
`Valbonne - FRANCE
`Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16
`
`Internet
`http://www.3gpp.org
`
`Copyright Notification
`
`No part may be reproduced except as authorized by written permission.
`The copyright and the foregoing restriction extend to reproduction in all media.
`
`© 2009, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC).
`All rights reserved.
`
`UMTS™ is a Trade Mark of ETSI registered for the benefit of its members
`3GPP™ is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners
`LTE™ is a Trade Mark of ETSI currently being registered for the benefit of its Members and of the 3GPP Organizational Partners
`GSM® and the GSM logo are registered and owned by the GSM Association
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`TELEFONAKTIEBOLAGET LM ERICSSON AND
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`

`
`Contents
`Foreword............................................................................................................................................................. 5
`1
`Scope ........................................................................................................................................................ 6
`2
`References ................................................................................................................................................ 6
`3
`Definitions and abbreviations ................................................................................................................... 6
`3.1
`Definitions ......................................................................................................................................................... 6
`3.2
`Abbreviations ..................................................................................................................................................... 7
`4
`General ..................................................................................................................................................... 8
`4.1
`Introduction........................................................................................................................................................ 8
`4.2
`MAC architecture .............................................................................................................................................. 8
`4.2.1
`MAC Entities ............................................................................................................................................... 8
`4.3
`Services .............................................................................................................................................................. 9
`4.3.1
`Services provided to upper layers ................................................................................................................ 9
`4.3.2
`Services expected from physical layer ......................................................................................................... 9
`4.4
`Functions ........................................................................................................................................................... 9
`4.5
`Channel structure ............................................................................................................................................. 10
`4.5.1
`Transport Channels .................................................................................................................................... 10
`4.5.2
`Logical Channels ........................................................................................................................................ 10
`4.5.3
`Mapping of Transport Channels to Logical Channels ................................................................................ 11
`4.5.3.1
`Uplink mapping .................................................................................................................................... 11
`4.5.3.2
`Downlink mapping ............................................................................................................................... 11
`5
`MAC procedures .................................................................................................................................... 12
`5.1
`Random Access procedure ............................................................................................................................... 12
`5.1.1
`Random Access Procedure initialization .................................................................................................... 12
`5.1.2
`Random Access Resource selection ........................................................................................................... 13
`5.1.3
`Random Access Preamble transmission ..................................................................................................... 14
`5.1.4
`Random Access Response reception .......................................................................................................... 14
`5.1.5
`Contention Resolution ................................................................................................................................ 15
`5.1.6
`Completion of the Random Access procedure ........................................................................................... 16
`5.2
`Maintenance of Uplink Time Alignment ......................................................................................................... 17
`5.3
`DL-SCH data transfer ...................................................................................................................................... 17
`5.3.1
`DL Assignment reception ........................................................................................................................... 17
`5.3.2
`HARQ operation ........................................................................................................................................ 19
`5.3.2.1
`HARQ Entity ........................................................................................................................................ 19
`5.3.2.2
`HARQ process ...................................................................................................................................... 19
`5.3.3
`Disassembly and demultiplexing ................................................................................................................ 20
`5.4
`UL-SCH data transfer ...................................................................................................................................... 20
`5.4.1
`UL Grant reception .................................................................................................................................... 20
`5.4.2
`HARQ operation ........................................................................................................................................ 21
`5.4.2.1
`HARQ entity ......................................................................................................................................... 21
`5.4.2.2
`HARQ process ...................................................................................................................................... 22
`5.4.3
`Multiplexing and assembly ........................................................................................................................ 24
`5.4.3.1
`Logical channel prioritization ............................................................................................................... 24
`5.4.3.2
`Multiplexing of MAC Control Elements and MAC SDUs ................................................................... 25
`5.4.4
`Scheduling Request .................................................................................................................................... 25
`5.4.5
`Buffer Status Reporting .............................................................................................................................. 25
`5.4.6
`Power Headroom Reporting ....................................................................................................................... 26
`5.5
`PCH reception .................................................................................................................................................. 27
`5.6
`BCH reception ................................................................................................................................................. 27
`5.7
`Discontinuous Reception (DRX) ..................................................................................................................... 27
`5.8
`MAC reconfiguration ....................................................................................................................................... 29
`5.9
`MAC Reset ...................................................................................................................................................... 29
`5.10
`Semi-Persistent Scheduling ............................................................................................................................. 29
`5.10.1
`Downlink .................................................................................................................................................... 30
`5.10.2
`Uplink......................................................................................................................................................... 30
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`Handling of unknown, unforeseen and erroneous protocol data ...................................................................... 30
`5.11
`Protocol Data Units, formats and parameters ......................................................................................... 30
`6
`Protocol Data Units .......................................................................................................................................... 30
`6.1
`General ....................................................................................................................................................... 30
`6.1.1
`MAC PDU (DL-SCH and UL-SCH except transparent MAC and Random Access Response) ................ 31
`6.1.2
`MAC Control Elements .............................................................................................................................. 32
`6.1.3
`Buffer Status Report MAC Control Elements ...................................................................................... 32
`6.1.3.1
`C-RNTI MAC Control Element ........................................................................................................... 33
`6.1.3.2
`DRX Command MAC Control Element ............................................................................................... 34
`6.1.3.3
`UE Contention Resolution Identity MAC Control Element ................................................................. 34
`6.1.3.4
`Timing Advance Command MAC Control Element ............................................................................ 34
`6.1.3.5
`Power Headroom MAC Control Element ............................................................................................. 34
`6.1.3.6
`MAC PDU (transparent MAC) .................................................................................................................. 35
`6.1.4
`MAC PDU (Random Access Response) .................................................................................................... 35
`6.1.5
`Formats and parameters ................................................................................................................................... 36
`6.2
`MAC header for DL-SCH and UL-SCH .................................................................................................... 36
`6.2.1
`MAC header for Random Access Response .............................................................................................. 37
`6.2.2
`MAC payload for Random Access Response ............................................................................................ 38
`6.2.3
`Variables and constants .......................................................................................................................... 38
`7
`RNTI values ..................................................................................................................................................... 38
`7.1
`Backoff Parameter values ................................................................................................................................ 39
`7.2
`PRACH Mask Index values ............................................................................................................................. 40
`7.3
`Subframe_Offset values ................................................................................................................................... 40
`7.4
`TTI_BUNDLE_SIZE value ............................................................................................................................. 40
`7.5
`DELTA_PREAMBLE values .......................................................................................................................... 40
`7.6
`HARQ RTT Timer ........................................................................................................................................... 41
`7.7
`Handling of measurement gaps .................................................................... 42
`Annex A (normative):
`Contention resolution for RACH access ...................................................... 43
`Annex B (informative):
`Change history ............................................................................................... 44
`Annex C (informative):
`
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`
`Foreword
`This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
`
`The contents of the present document are subject to continuing work within the TSG and may change following formal
`TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
`identifying change of release date and an increase in version number as follows:
`
`Version x.y.z
`
`where:
`
`x
`
`the first digit:
`
`1 presented to TSG for information;
`
`2 presented to TSG for approval;
`
`3 or greater indicates TSG approved document under change control.
`
`y
`
`the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
`updates, etc.
`
`z
`
`the third digit is incremented when editorial only changes have been incorporated in the document.
`
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`
`1 Scope
`The present document specifies the E-UTRA MAC protocol.
`
`References
`2
`The following documents contain provisions which, through reference in this text, constitute provisions of the present
`document.
`
`• References are either specific (identified by date of publication, edition number, version number, etc.) or
`non-specific.
`
`• For a specific reference, subsequent revisions do not apply.
`
`• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
`a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
`Release as the present document.
`
`[1]
`
`[2]
`
`[3]
`
`[4]
`
`[5]
`
`[6]
`
`[7]
`
`[8]
`
`[9]
`
`3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
`
`3GPP TR 36.213: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer
`Procedures".
`
`3GPP TS 36.322: “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control
`(RLC) protocol specification”.
`
`3GPP TS 36.323: “Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data
`Convergence Protocol (PDCP) Specification”.
`
`3GPP TS 36.212: “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and
`channel coding”.
`
`3GPP TS 36.214: “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer;
`Measurements”.
`
`3GPP TS 36.211: “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels
`and Modulation”.
`
`3GPP TS 36.331: “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
`Control (RRC); Protocol specification”.
`
`3GPP TS 36.133: "Evolved Universal Terrestrial Radio Access (E-UTRA); Requirements for
`support of radio resource management".
`
`[10]
`
`3GPP TS 36.101: "Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE)
`radio transmission and reception".
`
`3
`
`Definitions and abbreviations
`
`Definitions
`3.1
`For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A
`term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
`
`Active Time: Time related to DRX operation, as defined in subclause 5.7, during which the UE monitors the PDCCH
`in PDCCH-subframes.
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`mac-ContentionResolutionTimer: Specifies the number of consecutive subframe(s) during which the UE shall monitor
`the PDCCH after Msg3 is transmitted.
`
`DRX Cycle: Specifies the periodic repetition of the On Duration followed by a possible period of inactivity (see figure
`3.1-1 below).
`
`On Duration
`
`Opportunity for DRX
`
`UE shall monitor
`PDCCH
`
`DRX Cycle
`
`Figure 3.1-1: DRX Cycle
`
`
`
`drx-InactivityTimer: Specifies the number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH
`indicating an initial UL or DL user data transmission for this UE.
`
`drx-RetransmissionTimer: Specifies the maximum number of consecutive PDCCH-subframe(s) for as soon as a DL
`retransmission is expected by the UE.
`
`drxShortCycleTimer: Specifies the number of consecutive subframe(s) the UE shall follow the Short DRX cycle.
`
`drxStartOffset: Specifies the subframe where the DRX Cycle starts.
`
`HARQ information: HARQ information consists of New Data Indicator (NDI), Transport Block (TB) size. For DL-
`SCH transmissions the HARQ information also includes HARQ process ID. For UL-SCH transmission the HARQ info
`also includes Redundancy Version (RV). In case of spatial multiplexing on DL-SCH the HARQ information comprises
`a set of NDI and TB size for each transport block.
`
`HARQ RTT Timer: This parameter specifies the minimum amount of subframe(s) before a DL HARQ retransmission
`is expected by the UE.
`
`Msg3: Message transmitted on UL-SCH containing a C-RNTI MAC CE or CCCH SDU, submitted from upper layer
`and associated with the UE Contention Resolution Identity, as part of a random access procedure.
`
`onDurationTimer: Specifies the number of consecutive PDCCH-subframe(s) at the beginning of a DRX Cycle.
`
`PDCCH-subframe: For FDD UE operation, this represents any subframe; for TDD, only downlink subframes and
`subframes including DwPTS.
`
`PRACH Resource Index: The index of a PRACH within a system frame [7]
`
`ra-PRACH-MaskIndex: Defines in which PRACHs within a system frame the UE can transmit a Random Access
`Preamble (see subclause 7.3).
`
`RA-RNTI: The Random Access RNTI is used on the PDCCH when Random Access Response messages are
`transmitted. It unambiguously identifies which time-frequency resource was utilized by the UE to transmit the Random
`Access preamble.
`
`NOTE: A timer is running once it is started, until it is stopped or until it expires; otherwise it is not running. A
`timer can be started if it is not running or restarted if it is running. A Timer is always started or restarted
`from its initial value.
`
`Abbreviations
`3.2
`For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
`abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
`TR 21.905 [1].
`
`BSR
`
` Buffer Status Report
`
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` Cell RNTI
`C-RNTI
` Channel Quality Indicator
`CQI
` Evolved UMTS Terrestrial Radio Access
`E-UTRA
` Evolved UMTS Terrestrial Radio Access Network
`E-UTRAN
` Medium Access Control
`MAC
` Logical Channel Group
`LCG
`
`Power Headroom Report
`PHR
`
`Precoding Matrix Index
`PMI
`
`Paging RNTI
`P-RNTI
` Random Access RNTI
`RA-RNTI
` Rank Indicator
`RI
` Radio Network Temporary Identifier
`RNTI
`
`System Information RNTI
`SI-RNTI
`
`Scheduling Request
`SR
`
`Sounding Reference Symbols
`SRS
` Transport Block
`TB
`TPC-PUCCH-RNTI Transmit Power Control-Physical Uplink Control Channel-RNTI
`TPC-PUSCH-RNTI Transmit Power Control-Physical Uplink Shared Channel-RNTI
`
`General
`
` 4
`
`
`
`Introduction
`4.1
`The objective is to describe the MAC architecture and the MAC entity from a functional point of view.
`
`MAC architecture
`4.2
`The description in this sub clause is a model and does not specify or restrict implementations.
`
`RRC is in control of configuration of MAC.
`
`4.2.1 MAC Entities
`E-UTRA defines two MAC entities; one in the UE and one in the E-UTRAN. These MAC entities handle the following
`transport channels:
`
`- Broadcast Channel (BCH);
`
`- Downlink Shared Channel (DL-SCH);
`
`- Paging Channel (PCH);
`
`- Uplink Shared Channel (UL-SCH);
`
`- Random Access Channel(s) (RACH).
`
`The exact functions performed by the MAC entities are different in the UE from those performed in the E-UTRAN.
`
`Figure 4.2.1.1 illustrates one possible structure for the UE side MAC entity, and it should not restrict implementation.
`
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`PCCH
`
`BCCH
`
`CCCH
`
`Upper layers
`DCCH
`
`DTCH
`
`MAC-control
`
`Logical Channel Prioritization (UL only)
`
`(De-) Multiplexing
`
`Control
`
`HARQ
`
`Random
`Access Control
`
`PCH
`
`BCH
`
`DL-SCH
`
`UL-SCH
`Lower layer
`
`RACH
`
`Figure 4.2.1.1: MAC structure overview, UE side
`
`
`
`
`
`4.3
`
`Services
`
`Services provided to upper layers
`4.3.1
`This clause describes the different services provided by MAC sublayer to upper layers.
`
`- data transfer
`
`-
`
`radio resource allocation
`
`Services expected from physical layer
`4.3.2
`The physical layer provides the following services to MAC:
`
`- data transfer services;
`
`-
`
`-
`
`signalling of HARQ feedback;
`
`signalling of Scheduling Request;
`
`- measurements (e.g. Channel Quality Indication (CQI)).
`
`The access to the data transfer services is through the use of transport channels. The characteristics of a transport
`channel are defined by its transport format (or format set), specifying the physical layer processing to be applied to the
`transport channel in question, such as channel coding and interleaving, and any service-specific rate matching as
`needed.
`
`Functions
`4.4
`The following functions are supported by MAC sublayer:
`
`- mapping between logical channels and transport channels;
`
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`- multiplexing of MAC SDUs from one or different logical channels onto transport blocks (TB) to be delivered to
`the physical layer on transport channels;
`
`- demultiplexing of MAC SDUs from one or different logical channels from transport blocks (TB) delivered from
`the physical layer on transport channels;
`
`-
`
`scheduling information reporting;
`
`- error correction through HARQ;
`
`- priority handling between UEs by means of dynamic scheduling;
`
`- priority handling between logical channels of one UE;
`
`- Logical Channel prioritisation;
`
`-
`
`transport format selection.
`
`The location of the different functions and their relevance for uplink and downlink respectively is illustrated in Table
`4.4-1.
`
`Multiplexing
`
`Demultiplexing
`
`Table 4.4-1: MAC function location and link direction association.
`MAC function
`UE
`eNB
`Downlink
`Mapping between logical channels and transport channels
`X
`
`X
`
`X
`X
`X
`
`
`
`X
`X
`X
`
`X
`
`X
`
`X
`
`X
`
`X
`X
`
`X
`X
`
`X
`X
`
`X
`X
`X
`
`
`X
`
`
`
`Error correction through HARQ
`
`Transport Format Selection
`Priority handling between UEs
`Priority handling between logical channels of one UE
`Logical Channel prioritisation
`Scheduling information reporting
`
`Uplink
`X
`X
`X
`
`
`X
`X
`X
`X
`X
`X
`X
`X
`
`
`
`Channel structure
`4.5
`The MAC sublayer operates on the channels defined below; transport channels are SAPs between MAC and Layer 1,
`logical channels are SAPs between MAC and RLC.
`
`Transport Channels
`4.5.1
`The transport channels used by MAC are described in Table 4.5.1-1 below.
`
`Table 4.5.1-1: Transport channels used by MAC
`Transport channel name
`Acronym
`Downlink
`Uplink
`Broadcast Channel
`BCH
`X
`
`Downlink Shared Channel
`DL-SCH
`X
`
`Paging Channel
`PCH
`X
`
`Uplink Shared Channel
`UL-SCH
`
`X
`Random Access Channel
`RACH
`
`X
`
`
`
`Logical Channels
`4.5.2
`The MAC layer provides data transfer services on logical channels. A set of logical channel types is defined for
`different kinds of data transfer services as offered by MAC.
`
`Each logical channel type is defined by what type of information is transferred.
`
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`MAC provides the control and traffic channels listed in Table 4.5.2-1 below.
`
`Table 4.5.2-1: Logical channels provided by MAC.
`Logical channel name
`Acronym
`Control channel
`Traffic channel
`Broadcast Control Channel
`BCCH
`X
`
`Paging Control Channel
`PCCH
`X
`
`Common Control Channel
`CCCH
`X
`
`Dedicated Control Channel
`DCCH
`X
`
`Dedicated Traffic Channel
`DTCH
`
`X
`
`
`
`4.5.3 Mapping of Transport Channels to Logical Channels
`The mapping of logical channels on transport channels depends on the multiplexing that is configured by RRC.
`
`Uplink mapping
`4.5.3.1
`The MAC entity is responsible for mapping logical channels for the uplink onto uplink transport channels. The uplink
`logical channels can be mapped as described in Figure 4.5.3.1-1 and Table 4.5.3.1-1.
`
`CCCH
`
`DCCH
`
`DTCH
`
`Uplink
`Logical channels
`
`RACH
`
`UL-SCH
`
`Uplink
`Transport channels
`
`
`
`Figure 4.5.3.1-1
`
`Table 4.5.3.1-1: Uplink channel mapping.
`Transport channel
`UL-SCH
`
`Logical channel
`CCCH
`DCCH
`DTCH
`
`X
`X
`X
`
`RACH
`
`
`
`
`
`
`
`Downlink mapping
`4.5.3.2
`The MAC entity is responsible for mapping the downlink logical channels to downlink transport channels. The
`downlink logical channels can be mapped as described in Figure 4.5.3.2-1 and Table 4.5.3.2-1.
`
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`PCCH
`
`BCCH
`
`CCCH
`
`DCCH
`
`DTCH
`
`Downlink
`Logical channels
`
`PCH
`
`BCH
`
`DL-SCH
`
`Figure 4.5.3.2-1
`
`Downlink
`Transport channels
`
`
`
`Table 4.5.3.2-1: Downlink channel mapping.
`Transport channel
`BCH
`PCH
`
`Logical channel
`BCCH
`PCCH
`CCCH
`DCCH
`DTCH
`
`
`X
`
`
`
`
`X
`
`
`
`
`
`DL-SCH
`
`X
`
`X
`X
`X
`
`MAC procedures
`
` 5
`
`
`
`5.1
`
`Random Access procedure
`
`Random Access Procedure initialization
`5.1.1
`The Random Access procedure described in this subclause is initiated by a PDCCH order or by the MAC sublayer
`itself. If a UE receives a PDCCH transmission consistent with a PDCCH order [5] masked with its C-RNTI, it shall
`initiate a Random Access procedure. The PDCCH order or RRC optionally indicate ra-PreambleIndex and ra-PRACH-
`MaskIndex.
`
`Before the procedure can be initiated, the following information is assumed to be available [8]:
`
`-
`
`-
`
`the available set of PRACH resources for the transmission of the Random Access Preamble, prach-ConfigIndex.
`
`the groups of Random Access Preambles and the set of available Random Access Preambles in each group:
`
` The preambles that are contained in Random Access Preambles group A and Random Access Preambles group B
`are calculated from the parameters numberOfRA-Preambles and sizeOfRA-PreamblesGroupA:
`
`
`
`-
`
`-
`
`-
`
`-
`
`If sizeOfRA-PreamblesGroupA is equal to numberOfRA-Preambles then there is no Random Access Preambles
`group B. The preambles in Random Access Preamble group A are the preambles 0 to sizeOfRA-
`PreamblesGroupA – 1 and, if it exists, the preambles in Random Access Preamble group B are the preambles
`sizeOfRA-PreamblesGroupA to numberOfRA-Preambles – 1 from the set of 64 preambles as defined in [7].
`
`if Random Access Preambles group B exists, the thresholds, messagePowerOffsetGroupB and
`messageSizeGroupA, the configured UE transmitted power, PCMAX [10], and the offset between the preamble and
`Msg3, deltaPreambleMsg3, that are required for selecting one of the two groups of Random Access Preambles.
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`the RA response window size ra-ResponseWindowSize.
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`the power-ramping factor powerRampingStep.
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`the maximum number of preamble transmission preambleTransMax.
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`the initial preamble power preambleInitialReceivedTargetPower.
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`the preamble format based offset DELTA_PREAMBLE (see subclause 7.6).
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`the maximum number of Msg3 HARQ transmissions maxHARQ-Msg3Tx.
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`the Contention Resolution Timer mac-ContentionResolutionTimer.
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`NOTE: The above parameters may be updated from upper layers before each Random Access procedure is
`initiated.
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`The Random Access procedure shall be performed as follows:
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`- Flush the Msg3 buffer;
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`-
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`-
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`set the PREAMBLE_TRANSMISSION_COUNTER to 1;
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`set the backoff parameter value in the UE to 0 ms;
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`- proceed to the selection of the Random Access Resource (see subclause 5.1.2).
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`NOTE: There is only one Random Access procedure ongoing at any point in time. If the UE receives a request for
`a new Random Access procedure while another is already ongoing, it is up to UE implementation whether
`to continue with the ongoing procedure or start with the new procedure.
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`Random Access Resource selection
`5.1.2
`The Random Access Resource selection procedure shall be performed as follows:
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`-
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`If ra-PreambleIndex (Random Access Preamble) and ra-PRACH-MaskIndex (PRACH Mask Index) have been
`explicitly signalled and ra-PreambleIndex is not 000000:
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`-
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`the Random Access Preamble and the PRACH Mask Index are those explicitly signalled.
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`- else the Random Access Preamble shall be selected by the UE as follows:
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`-
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`If Msg3 has not yet been transmitted, the UE shall:
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`-
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`if Random Access Preambles group B exists and if the potential message size (data available for
`transmission plus MAC header and, where required, MAC control elements) is greater than
`messageSizeGroupA and if the pathloss is less than PCMAX – preambleInitialReceivedTargetPower –
`deltaPreambleMsg3 – messagePowerOffsetGroupB, then:
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`-
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`select the Random Access Preambles group B;
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`- else:
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`-
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`select the Random Access Preambles group A.
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`- else, if Msg3 is being retransmitted, the UE shall:
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`-
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`select the same group of Random Access Preambles as was used for the preamble transmission attempt
`corresponding to the first transmission of Msg3.
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`-
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`randomly select a Random Access Preamble within the selected group. The random function shall be such
`that each of the allowed selections can be chosen with equal probability;
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`-
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`set PRACH Mask Index to 0.
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`- determine the next available subframe containing PRACH permitted by the restrictions given by the prach-
`ConfigIndex, the PRACH Mask Index (see subclause 7.3) and physical layer timing requirements [2] (a UE may
`take into account the possible occurrence of measurement gaps when determining the next available PRACH
`subframe);
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`-
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`if the transmission mode is TDD and the PRACH Mask Index is equ