ETSI TS 136 321 V8.12.0 (2012-03)

LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification (3GPP TS 36.321 version 8.12.0 Release 8)

RTS/TSGR-0236321v8c0

General Information

• Status: Published
• Publication Date: 25-Mar-2012
• Technical Committee: 3GPP RAN 2 - Radio layer 2 specification and Radio layer 3 RR specification
• Current Stage: 12 - Completion
• Due Date: 30-Mar-2012
• Completion Date: 26-Mar-2012

Standards Content (Sample)

Technical Specification
LTE;
Evolved Universal Terrestrial Radio Access (E-UTRA);
Medium Access Control (MAC) protocol specification
(3GPP TS 36.321 version 8.12.0 Release 8)

3GPP TS 36.321 version 8.12.0 Release 8 1 ETSI TS 136 321 V8.12.0 (2012-03)

Reference
RTS/TSGR-0236321v8c0
Keywords
LTE
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ETSI
3GPP TS 36.321 version 8.12.0 Release 8 2 ETSI TS 136 321 V8.12.0 (2012-03)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
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Foreword
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
http://webapp.etsi.org/key/queryform.asp.
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Contents
Intellectual Property Rights . 2
Foreword . 2
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
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5.10 Semi-Persistent Scheduling . 29
5.10.1 Downlink . 30
5.10.2 Uplink . 30
5.11 Handling of unknown, unforeseen and erroneous protocol data . 30
6 Protocol Data Units, formats and parameters . 31
6.1 Protocol Data Units . 31
6.1.1 General . 31
6.1.2 MAC PDU (DL-SCH and UL-SCH except transparent MAC and Random Access Response) . 31
6.1.3 MAC Control Elements . 32
6.1.3.1 Buffer Status Report MAC Control Elements . 32
6.1.3.2 C-RNTI MAC Control Element . 34
6.1.3.3 DRX Command MAC Control Element . 34
6.1.3.4 UE Contention Resolution Identity MAC Control Element . 34
6.1.3.5 Timing Advance Command MAC Control Element . 34
6.1.3.6 Power Headroom MAC Control Element . 35
6.1.4 MAC PDU (transparent MAC) . 35
6.1.5 MAC PDU (Random Access Response) . 35
6.2 Formats and parameters . 36
6.2.1 MAC header for DL-SCH and UL-SCH. 36
6.2.2 MAC header for Random Access Response . 37
6.2.3 MAC payload for Random Access Response . 38
7 Variables and constants . 38
7.1 RNTI values . 38
7.2 Backoff Parameter values . 39
7.3 PRACH Mask Index values. 40
7.4 Subframe_Offset values . 40
7.5 TTI_BUNDLE_SIZE value. 40
7.6 DELTA_PREAMBLE values . 40
7.7 HARQ RTT Timer . 41
Annex A (normative): Handling of measurement gaps . 42
Annex B (normative): Contention resolution for RACH access . 43
Annex C (informative): Change history . 44
History . 48

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Foreword
rd
This Technical Specification has been produced by the 3 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.
2 References
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] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TR 36.213: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer
Procedures".
[3] 3GPP TS 36.322: 'Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control
(RLC) protocol specification'.
[4] 3GPP TS 36.323: 'Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data
Convergence Protocol (PDCP) Specification'.
[5] 3GPP TS 36.212: 'Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and
channel coding'.
[6] 3GPP TS 36.214: 'Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer;
Measurements'.
[7] 3GPP TS 36.211: 'Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and
Modulation'.
[8] 3GPP TS 36.331: 'Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
Control (RRC); Protocol specification'.
[9] 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
3.1 Definitions
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).
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.
3.2 Abbreviations
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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C-RNTI  Cell RNTI
CQI  Channel Quality Indicator
E-UTRA  Evolved UMTS Terrestrial Radio Access
E-UTRAN  Evolved UMTS Terrestrial Radio Access Network
MAC  Medium Access Control
LCG  Logical Channel Group
PHR  Power Headroom Report
PMI  Precoding Matrix Index
P-RNTI  Paging RNTI
RA-RNTI  Random Access RNTI
RI  Rank Indicator
RNTI  Radio Network Temporary Identifier
SI-RNTI  System Information RNTI
SR  Scheduling Request
SRS  Sounding Reference Symbols
TB  Transport Block
TPC-PUCCH-RNTI Transmit Power Control-Physical Uplink Control Channel-RNTI
TPC-PUSCH-RNTI Transmit Power Control-Physical Uplink Shared Channel-RNTI

4 General
4.1 Introduction
The objective is to describe the MAC architecture and the MAC entity from a functional point of view.
4.2 MAC architecture
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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Figure 4.2.1.1: MAC structure overview, UE side

4.3 Services
4.3.1 Services provided to upper layers
This clause describes the different services provided by MAC sublayer to upper layers.
- data transfer
- radio resource allocation
4.3.2 Services expected from physical layer
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.
4.4 Functions
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.
Table 4.4-1: MAC function location and link direction association.
MAC function UE eNB Downlink Uplink
Mapping between logical channels and transport channels X X X
X X X
Multiplexing X  X
X X
Demultiplexing X X
X X
Error correction through HARQ X X X
X X X
Transport Format Selection X X X
Priority handling between UEs X X X
Priority handling between logical channels of one UE X X X
Logical Channel prioritisation X  X
Scheduling information reporting X  X

4.5 Channel structure
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.
4.5.1 Transport Channels
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
4.5.2 Logical Channels
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.
4.5.3.1 Uplink mapping
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
Uplink
Transport channels
RACH UL-SCH
Figure 4.5.3.1-1
Table 4.5.3.1-1: Uplink channel mapping.
Transport channel UL-SCH RACH
Logical channel
CCCH X
DCCH X
DTCH X
4.5.3.2 Downlink mapping
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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Figure 4.5.3.2-1
Table 4.5.3.2-1: Downlink channel mapping.
Transport channel BCH PCH DL-SCH
Logical channel
BCCH X X
PCCH X
CCCH  X
DCCH  X
DTCH  X
5 MAC procedures
5.1 Random Access procedure
5.1.1 Random Access Procedure initialization
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, P [10], and the offset between the preamble and
CMAX
Msg3, deltaPreambleMsg3, that are required for selecting one of the two groups of Random Access Preambles.
- the RA response window size ra-ResponseWindowSize.
- the power-ramping factor powerRampingStep.
- the maximum number of preamble transmission preambleTransMax.
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- the initial preamble power preambleInitialReceivedTargetPower.
- the preamble format based offset DELTA_PREAMBLE (see subclause 7.6).
- the maximum number of Msg3 HARQ transmissions maxHARQ-Msg3Tx.
- the Contention Resolution Timer mac-ContentionResolutionTimer.
NOTE: The above parameters may be updated from upper layers before each Random Access procedure is
initiated.
The Random Access procedure shall be performed as follows:
- Flush the Msg3 buffer;
- set the PREAMBLE_TRANSMISSION_COUNTER to 1;
- set the backoff parameter value in the UE to 0 ms;
- proceed to the selection of the Random Access Resource (see subclause 5.1.2).
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.
5.1.2 Random Access Resource selection
The Random Access Resource selection procedure shall be performed as follows:
- If ra-PreambleIndex (Random Access Preamble) and ra-PRACH-MaskIndex (PRACH Mask Index) have been
explicitly signalled and ra-PreambleIndex is not 000000:
- the Random Access Preamble and the PRACH Mask Index are those explicitly signalled.
- else the Random Access Preamble shall be selected by the UE as follows:
- If Msg3 has not yet been transmitted, the UE shall:
- 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 P – preambleInitialReceivedTargetPower –
CMAX
deltaPreambleMsg3 – messagePowerOffsetGroupB, then:
- select the Random Access Preambles group B;
- else:
- select the Random Access Preambles group A.
- else, if Msg3 is being retransmitted, the UE shall:
- select the same group of Random Access Preambles as was used for the preamble transmission attempt
corresponding to the first transmission of Msg3.
- 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;
- set PRACH Mask Index to 0.
- 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);
- if the transmission mode is TDD and the PRACH Mask Index is equal to zero:
- if ra-PreambleIndex was explicitly signalled and it was not 000000 (i.e., not selected by MAC):
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- randomly select, with equal probability, one PRACH from the PRACHs available in the determined
subframe.
- else:
- randomly select, with equal probability, one PRACH from the PRACHs available in the determined
subframe and the next two consecutive subframes.
- else:
- determine a PRACH within the determined subframe in accordance with the requirements of the PRACH
Mask Index.
- proceed to the transmission of the Random Access Preamble (see subclause 5.1.3).
5.1.3 Random Access Preamble transmission
The random-access procedure shall be performed as follows:
- set PREAMBLE_RECEIVED_TARGET_POWER to preambleInitialReceivedTargetPower +
DELTA_PREAMBLE + (PREAMBLE_TRANSMISSION_COUNTER – 1) * powerRampingStep;
- instruct the physical layer to transmit a preamble using the selected PRACH, corresponding RA-RNTI, preamble
index and PREAMBLE_RECEIVED_TARGET_POWER.
5.1.4 Random Access Response reception
Once the Random Access Preamble is transmitted and regardless of the possible occurrence of a measurement gap, the
UE shall monitor the PDCCH for Random Access Response(s) identified by the RA-RNTI defined below, in the RA
Response window which starts at the subframe that contains the end of the preamble transmission [7] plus three
subframes and has length ra-ResponseWindowSize subframes. The RA-RNTI associated with the PRACH in which the
Random Access Preamble is transmitted, is computed as:
RA-RNTI= 1 + t_id+10*f_id
Where t_id is the index of the first subframe of the specified PRACH (0≤ t_id <10), and f_id is the index of the
specified PRACH within that subframe, in ascending order of frequency domain (0≤ f_id< 6). The UE may stop
monitoring for Random Access Response(s) after successful reception of a Random Access Response containing
Random Access Preamble identifiers that matches the transmitted Random Access Preamble.
- If a downlink assignment for this TTI has been received on the PDCCH for the RA-RNTI and the received TB is
successfully decoded, the UE shall regardless of the possible occurrence of a measurement gap:
- if the Random Access Response contains a Backoff Indicator subheader:
- set the backoff parameter value in the UE as indicated by the BI field of the Backoff Indicator subheader
and Table 7.2-1.
- else, set the backoff parameter value in the UE to 0 ms.
- if the Random Access Response contains a Random Access Preamble identifier corresponding to the
transmitted Random Access Preamble (see subclause 5.1.3), the UE shall:
- consider this Random Access Response reception successful;
- process the received Timing Advance Command (see subclause 5.2);
- indicate the preambleInitialReceivedTargetPower and the amount of power ramping applied to the latest
preamble transmission to lower layers (i.e., (PREAMBLE_TRANSMISSION_COUNTER – 1) *
powerRampingStep);
- process the received UL grant value and indicate it to the lower layers;
- if ra-PreambleIndex was explicitly signalled and it was not 000000 (i.e., not selected by MAC):
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- consider the Random Access procedure successfully completed.
- else, if the Random Access Preamble was selected by UE MAC:
- set the Temporary C-RNTI to the value received in the Random Access Response message no later
than at the time of the first transmission corresponding to the UL grant provided in the Random
Access Response message;
- if this is the first successfully received Random Access Response within this Random Access
procedure:
- if the transmission is not being made for the CCCH logical channel, indicate to the Multiplexing
and assembly entity to include a C-RNTI MAC control element in the subsequent uplink
transmission;
- obtain the MAC PDU to transmit from the "Multiplexing and assembly" entity and store it in the
Msg3 buffer.
NOTE: When an uplink transmission is required, e.g., for contention resolution, the eNB should not provide a
grant smaller than 56 bits in the Random Access Response.
NOTE: If within a Random Access procedure, an uplink grant provided in the Random Access Response for the
same group of Random Access Preambles has a different size than the first uplink grant allocated during
that Random Access procedure, the UE behavior is not defined.
If no Random Access Response is received within the RA Response window, or if none of all received Random Access
Responses contains a Random Access Preamble identifier corresponding to the transmitted Random Access Preamble,
the Random Access Response reception is considered not successful and the UE shall:
- increment PREAMBLE_TRANSMISSION_COUNTER by 1;
- If PREAMBLE_TRANSMISSION_COUNTER = preambleTransMax + 1:
- indicate a Random Access problem to upper layers.
- if in this Random Access procedure, the Random Access Preamble was selected by MAC:
- based on the backoff parameter in the UE, select a random backoff time according to a uniform distribution
between 0 and the Backoff Parameter Value;
- delay the subsequent Random Access transmission by the backoff time;
- proceed to the selection of a Random Access Resource (see subclause 5.1.2).
5.1.5 Contention Resolution
Contention Resolution is based on either C-RNTI on PDCCH or UE Contention Resolution Identity on DL-SCH.
Once Msg3 is transmitted, the UE shall:
- start mac-ContentionResolutionTimer and restart mac-ContentionResolutionTimer at each HARQ
retransmission;
- regardless of the possible occurrence of a measurement gap, monitor the PDCCH until mac-
ContentionResolutionTimer expires or is stopped;
- if notification of a reception of a PDCCH transmission is received from lower layers, the UE shall:
- if the C-RNTI MAC control element was included in Msg3:
- if the Random Access procedure was initiated by the MAC sublayer itself and the PDCCH transmission is
addressed to the C-RNTI and contains an UL grant for a new transmission; or
- if the Random Access procedure was initiated by a PDCCH order and the PDCCH transmission is
addressed to the C-RNTI:
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- consider this Contention Resolution successful;
- stop mac-ContentionResolutionTimer;
- discard the Temporary C-RNTI;
- consider this Random Access procedure successfully completed.
- else if the CCCH SDU was included in Msg3 and the PDCCH transmission is addressed to its Temporary C-
RNTI:
- if the MAC PDU is successfully decoded:
- stop mac-ContentionResolutionTimer;
- if the MAC PDU contains a UE Contention Resolution Identity MAC control element; and
- if the UE Contention Resolution Identity included in the MAC control element matches the CCCH
SDU transmitted in Msg3:
- consider this Contention Resolution successful and finish the disassembly and demultiplexing of
the MAC PDU;
- set the C-RNTI to the value of the Temporary C-RNTI;
- discard the Temporary C-RNTI;
- consider this Random Access procedure successfully completed.
- else
- discard the Temporary C-RNTI;
- consider this Contention Resolution not successful and discard the successfully decoded MAC
PDU.
- if mac-ContentionResolutionTimer expires:
- discard the Temporary C-RNTI;
- consider the Contention Resolution not successful.
- if the Contention Resolution is considered not successful the UE shall:
- flush the HARQ buffer used for transmission of the MAC PDU in the Msg3 buffer;
- increment PREAMBLE_TRANSMISSION_COUNTER by 1;
- If PREAMBLE_TRANSMISSION_COUNTER = preambleTransMax + 1:
- indicate a Random Access problem to upper layers.
- based on the backoff parameter in the UE, select a random backoff time according to a uniform distribution
between 0 and the Backoff Parameter Value;
- delay the subsequent Random Access transmission by the backoff time;
- proceed to the selection of a Random Access Resource (see subclause 5.1.2).
5.1.6 Completion of the Random Access procedure
At successful completion of the Random Access procedure, the UE shall:
- discard explicitly signalled ra-PreambleIndex and ra-PRACH-MaskIndex, if any;
- flush the HARQ buffer used for transmission of the MAC PDU in the Msg3 buffer.
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5.2 Maintenance of Uplink Time Alignment
The UE has a configurable timer timeAlignmentTimer which is used to control how long the UE is considered uplink
time aligned [8].
The UE shall:
- when a Timing Advance Command MAC control element is received:
- apply the Timing Advance Command;
- start or restart timeAlignmentTimer.
- when a Timing Advance Command is received in a Random Access Response message:
- if the Random Access Preamble was not selected by UE MAC:
- apply the Timing Advance Command;
- start or restart timeAlignmentTimer.
- else, if the timeAlignmentTimer is not running:
- apply the Timing Advance Command;
- start timeAlignmentTimer;
- when the contention resolution is considered not successful as described in subclause 5.1.5, stop
timeAlignmentTimer.
- else:
- ignore the received Timing Advance Command.
- when timeAlignmentTimer expires:
- flush all HARQ buffers;
- notify RRC to release PUCCH/SRS;
- clear any configured downlink assignments and uplink grants.
5.3 DL-SCH data transfer
5.3.1 DL Assignment reception
Downlink assignments transmitted on the PDCCH indicate if there is a transmission on the DL-SCH for a particular UE
and provide the relevant HARQ information.
When the UE has a C-RNTI, Semi-Persistent Scheduling C-RNTI, or Temporary C-RNTI, the UE shall for each TTI
during which it monitors PDCCH:
- if a downlink assignment for this TTI has been received on the PDCCH for the UE"s C-RNT
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