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`R2-084156
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`3GPP TSG-RAN WG2 #63
`August 18th – 22nd 2008
`Jeju Island, Korea
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`Agenda item:
`6.1.1.4
`Source:
`Qualcomm Europe
`Title:
`NDI and Message 3
`Document for: Discussion, Decision
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`Introduction
`1.
`The agreed in principle CR [1] is capturing the handling of NDI for the UL grant corresponding to message 3 by stating
`that:
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`1.
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`the HARQ entity shall request a new transmission in response to a grant in random access response
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`2. when determining if NDI has been incremented compared to the value in the previous transmission UE shall
`ignore NDI received in all uplink grants on PDCCH for its Temporary C-RNTI
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`3. uplink grant to Temporary C-RNTI trigger retransmissions.
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`2. Discussion
`Points 1 and 2 seem to have an undesirable side effect for the HARQ process interrupted by a Message3 transmission
`as illustrated with the scenario below:
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`1. UL HARQ process #A has data “blah” in the buffer for a transmission
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`2. A random access response is received containing a grant for Message3, to be transmitted by UL HARQ
`process #A
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`3. Message 3 overwrites “blah” and is transmitted
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`4. A PDCCH for the UE’s C-RNTI for an UL grant where NDI is the same as the NDI associated with step 1) is
`received. What happened? UE lost contention; eNB never saw that UE’s message 3; eNB thinks it can ask for
`“blah”. Or eNB takes some time to decode MAC UE ID control element in Message 3 and happens to resume
`UL retransmission for HARQ process #A at this time.
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`5. What should UE do:
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`a. Retransmit Message3
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`1. makes no sense: retransmissions of Message3 happen only with Temporary C-RNTI
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`2. eNB is expecting a retransmission of “blah” since it schedules UE on C-RNTI
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`b. Retransmit “blah”
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`SAMSUNG 1008-0001
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`2
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`1.
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`impossible: “blah” was overwritten by Message 3 in UE’s buffers
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`c. Perform a new transmission
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`6. What will eNB do when receiving
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`a. Retransmission of Message3
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`1. eNB will attempt to combine “blah” with “Message 3” and fail
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`2. eNB may try to decode “Message3” alone and will get useless information
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`b. Retransmission of “blah”
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`1.
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`this cannot happen because “blah” was overwritten by Message3
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`c. A new transmission
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`1. eNB will combine “blah” with “new message” and fail
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`2. under some conditions, eNB may try to decode “new message” alone and succeed
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`7. What behaviour does the current state of specification (after RAN2#62bis) CRs dictate?
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`a. RACH is still ongoing, there is a Message3 in Message3 buffer so should retransmit Message3
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`b. But most likely size of TB for Message3 and grant on C-RNTI do not match
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`c. MAC PDU to retransmit does not fit in provided TB: Undefined UE behaviour?
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`Of all options above, we note that the only option that give eNB a chance to cleanly handle this case is option c).
`Therefore we propose:
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`Proposal 1: The first use of an HARQ process following its use for a message 3 transmission, in response to a
`grant on C-RNTI or SPS-C-RNTI always starts a new transmission (irrespective of NDI).
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`In addition, we note that the Message3 buffer is populated when a Random Access Response is received. Therefore
`the MAC PDU in Message3 buffer only fits in a TB of the appropriate size. If a grant to C-RNTI with NDI flipped
`is received in the middle of RACH, UE should not send the Message3 on that grant, even if RACH is ongoing.
`Therefore we propose:
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`Proposal 2: HARQ should obtain the MAC PDU to transmit from the [Message3] buffer only in response to
`UL grant in a Random Access Response.
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`On a more editorial note we also propose:
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`Proposal 3: Use terminology “grant received on the PDCCH for the UE’s x-RNTI” in 5.4.2.1 for consistency
`with text in 5.4.1
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`Proposal 4: add missing “Semi-Persistent Scheduling C-RNTI” in 5.4.1 (an old oversight)
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`3. Conclusion
`We propose to agree to the changes implementing proposals 1/2/3/4 as illustrated in the Annex. Changes compared to
`the CR [1] are highlighted for easier tracking.
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`SAMSUNG 1008-0002
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`3
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`4. References
`[1]
`R2-083723 NDI and Msg3, LGE CR approved in principle at RAN2#62bis
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`SAMSUNG 1008-0003
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`4
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` Annex [changes to R2-083723]
`5.4 UL-SCH data transfer
`Editor’s note: Current text applies to, at least, FDD.
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`5.4.1 UL Grant reception
`When the UE has a C-RNTI, Semi-Persistent Scheduling C-RNTI, or Temporary C-RNTI, the UE shall for each TTI:
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`-
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`if an uplink grant for this TTI has been received on the PDCCH for the UE’s C-RNTI, Semi-Persistent
`Scheduling C-RNTI or Temporary C-RNTI; or
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`Formatted: Highlight
`Formatted: Highlight
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`-
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`if an uplink grant for this TTI has been received in a Random Access Response:
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`-
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`indicate a valid uplink grant and the associated HARQ information to the HARQ entity for this TTI.
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`- else, if an uplink grant for this TTI has been configured:
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`-
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`indicate an uplink grant, valid for new transmission, and the associated HARQ information to the HARQ
`entity for this TTI.
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`NOTE: The period of configured uplink grants is expressed in TTIs.
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`NOTE:
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`If the UE receives both a grant for its RA-RNTI and a grant for its C-RNTI, the UE may choose to
`continue with either the grant for its RA-RNTI or the grant for its C-RNTI.
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`5.4.2 HARQ operation
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`HARQ entity
`5.4.2.1
`There is one HARQ entity at the UE. A number of parallel HARQ processes are used in the UE to support the HARQ
`entity, allowing transmissions to take place continuously while waiting for the feedback on the successful or
`unsuccessful reception of previous transmissions.
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`At a given TTI, if an uplink grant is indicated for the TTI, the HARQ entity identifies the HARQ process for which a
`transmission should take place. It also routes the receiver feedback (ACK/NACK information), MCS and resource,
`relayed by the physical layer, to the appropriate HARQ process.
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`If TTI bundling is configured, the parameter TTI_BUNDLE_SIZE provides the number of TTIs of a TTI bundle. If a
`transmission is indicated for the TTI, the HARQ entity identifies the HARQ process for which a transmission should
`take place. The next TTI_BUNDLE_SIZE uplink TTIs are subsequently used for transmissions for the identified
`HARQ process. HARQ retransmissions within a bundle shall be performed without waiting for feedback from previous
`transmissions according to TTI_BUNDLE_SIZE. The UE expects feedback only for the last transmission of a bundle.
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`For transmission of an uplink message containing the C-RNTI MAC control element or an uplink message including a
`CCCH SDU during Random Access (see section 5.1.5) TTI bundling does not apply.
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`The number of HARQ processes is equal to [X] [FFS]. Each process is associated with a number from 0 to [X-1].
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`At the given TTI, the HARQ entity shall:
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`if an uplink grant indicating that the NDI has been incremented compared to the value in the previous
`transmission of this HARQ process is indicated for this TTI; or
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`if an uplink grant for this is the very first transmission offor this HARQ process (i.e. a new transmission takes
`place for this HARQ process) is indicated for this TTI; or
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`if an uplink grant received in a Random Access Response is indicated for this TTI; or
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`if the last use of this HARQ process was for transmission of a MAC PDU from the [Message3] buffer and an
`uplink grant on the PDCCH for the UE’s C-RNTI or Semi-Persistent Scheduling C-RNTI is indicated
`for this TTI::
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`SAMSUNG 1008-0004
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`5
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`if there is an ongoing Random Access procedure and there is a MAC PDU in the [Message3] buffer and the
`uplink grant is received in a Random Access Response:
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`Formatted: Highlight
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`- obtain the MAC PDU to transmit from the [Message3] buffer.
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`- else, if the "uplink prioritisation" entity indicates the need for a new transmission:
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`- obtain the MAC PDU to transmit from the "Multiplexing and assembly" entity;
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`-
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`instruct the HARQ process corresponding to this TTI to trigger a new transmission using the identified
`parameters.
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`- else:
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`flush the HARQ buffer.
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`- else:
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`, if an uplink grant, indicating that the NDI is identical to the value in the previous transmission of this
`HARQ process (i.e. a retransmission takes place for this HARQ process), is indicated for this TTI; or
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`Formatted: Indent: Left: 0.39"
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`-
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`if an uplink grant on the PDCCH for the UE’s addressed to a Temporary C-RNTI is indicated for this TTI:
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`Formatted: Highlight
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`instruct the HARQ process to generate an adaptive retransmission.
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`Formatted: Indent: First line: 0"
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`- else, if the HARQ buffer of the HARQ process corresponding to this TTI is not empty:
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`-
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`instruct the HARQ process to generate a non-adaptive retransmission.
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`When determining if NDI has been incremented compared to the value in the previous transmission UE shall ignore
`NDI received in all uplink grants on PDCCH for its Temporary C-RNTI.
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`Formatted: Normal
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`NOTE: A retransmission triggered by the HARQ entity should be cancelled by the corresponding HARQ process
`if it collides with a measurement gap or if a non-adaptive retransmission is not allowed.
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`SAMSUNG 1008-0005