3GPP TSG-RAN WG2 Meeting #Ad-hoc1801
`Vancouver, Canada, 22th – 26th January 2018
`
`R2-1800041
` Resubmission of R2-1712214
`
`Agenda Item:
`
`10.4.1.6.5
`
`Source:
`
`Title:
`
`ASUSTeK
`
`Discussion on On-demand system information request in NR
`
`Document for: Discussion and Decision
`
`1.
`
`INTRODUCTION
`
`Agreements
`1
`Only progress on the two agreed approaches for delivering on-demand system information (via
`dedicated signalling to RRC_CONNECTED UEs; via SI-Message broadcast to RRC_IDLE and
`RRC_INACTIVE UEs) and refrain from introducing additional solution variants.
`Agreements for Msg3 based SI request method:
`1. UE determines successful Msg3 based on reception of Msg4
`FFS Details of the Msg4 content used to confirm successful Msg3. To be discussed initially CP.
`2. Preamble(s) for SI request using Msg3 based Method are not reserved.
`3. RRC signaling is used for SI request in Msg3.
`FFS: RRC signaling how to indicate the requested SI/SIB details left to ASN.1 work.
`4. Temporary C-RNTI received in Msg2 is used for Msg4 reception
`
`In this contribution, we discuss Msg3 based System information request and system information request for
`RRC_CONNECTED UE.
`
`2. DISCUSSION
`Based on current agreement, the possible steps for Msg3 based system information request are shown in
`Figure 1.
`
`UE
`
`I
`
`I
`Preamble
`( No reserved RACH resource)
`
`I
`
`gNB
`
`I
`
`Msg2
`(TC-RNTI, UL grant, TA)
`
`Msg3 ( SI request )
`
`Msg4 (resolve contention)
`
`~
`
`~
`
`~ .
`
`~
`
`~
`
`Ex.1012
`APPLE INC. / Page 1 of 3
`
`

`

`
`
`
`
`Figure .1 Msg3 based system information request procedure
`
`When a UE in RRC_IDLE/in RRC_INACTIVE wants to request system information, the UE will need to
`check whether the system information is associated with special PRACH. If not, the UE will transmit a SI
`request through the Msg3 in a random access procedure. Moreover, the system information request
`message should be transmitted through SRB0 (i.e. CCCH message) due to the UE’s state. And the system
`information request will need to include UE identity for resolving the contention. Moreover, the UE has no
`need to set the Temporary C-RNTI as C-RNTI in such case. On the other hand, it is reasonable for UE in
`RRC_CONNECTED state to reuse the system information request message in Msg3 based SI request.
`
`Proposal 1: For Msg3 based SI request, a UE in RRC_IDLE/RRC_INACTIVE transmits a system
`information request message containing a UE identity through SRB0.
`
`Proposal 2: The system information request message in Msg3 based SI request method will also be
`used by UE in RRC_CONNECTED mode.
`
`In general, if UE wants to transmit a RRC message, the UE may either use received uplink grant or need to
`derive uplink resource through SR procedure or random access procedure. When the UE uses a dedicated
`uplink grant for transmitting the system information request message, the gNB will forward system
`information to the UE through DL assignment addressed to the UE’s C-RNTI. In such case, it is obvious
`that the system information request has no need to include an UE identity.
`
`Observation 1: A UE in RRC_CONNECTED mode has no need to include a UE identity into the
`system information request message when the UE uses a dedicated uplink grant to
`transmit the system information request message.
`
`Regarding SR case, if the UE could trigger a SR for the system information request, then the UE will
`receives a dedicated uplink grant for transmitting the system information request message. And the gNB
`will forward system information to the UE through DL assignment addressed to the UE’s C-RNTI. And the
`system information request also has no need to include an UE identity in this case. However, it is not clear
`whether the SR will be triggered if the system information request is transmitted through CCCH. There is
`no association between the CCCH and SR configuration.
`
`On the other hand, regarding RA case, the UE in RRC_CONNECTED will perform a random access
`procedure
`similar
`to
`the Msg3 based SI
`request method performed by
`the UE
`in
`RRC_IDLE/RRC_INACTIVE. One main difference would be the UE in RRC_CONNECTED already has
`C-RNTI. In such case, since the UE transmits the system information request message through SRB0
`(CCCH), the C-RNTI MAC CE would not be included based on LTE RA design (Baseline). It will force
`UE in RRC_CONNECTED state to resolve contention based on other identity included in the system
`information request message. And it also makes condition for whether to include UE identity into system
`information message more complex. Here are
`two possible options proposed
`for UE
`in
`RRC_CONNECTED to decide the contents in system information request message.
`
`Option 1: A UE in RRC_CONNECTED transmits the system information request message
`through SRB1 (DCCH). And no UE identity will be included into system information request
`message.
`
`Option 2: A UE in RRC_CONNECTED decides whether to include UE identity (e.g. S-TMSI or
`C-RNTI) into system information request message based on whether the UE has PUCCH
`resource configured for CCCH.
`
`Ex.1012
`APPLE INC. / Page 2 of 3
`
`

`

`
`
`
`
`In most of cases, the two options could avoid UE including UE identity in SR forwarding case, while allow
`UE to include UE identity for RA forwarding case. In option 1, the UE identity will be included as C-RNTI
`MAC CE for RA forwarding case. In option 2, the UE identity will be included as information element for
`RA forwarding case. Comparing the two options, the option 1 will have less specification impact and can
`solve the concern mentioned in SR case at the same time. We prefer to use Option 1 for handling contents
`of system information request message transmitted by UE in RRC_CONNECTED.
`
`Proposal 3: A UE in RRC_CONNECTED transmits a system information request message
`containing no UE identity through SRB1.
`
`3. CONCLUSION
`
`In this contribution, we propose the following:
`
`Proposal 1: For Msg3 based SI request, a UE in RRC_IDLE/RRC_INACTIVE transmits a system
`information request message containing a UE identity through SRB0.
`
`Proposal 2: The system information request message in Msg3 based SI request method will also be
`used by UE in RRC_CONNECTED mode.
`
`Proposal 3: A UE in RRC_CONNECTED transmits a system information request message
`containing no UE identity through SRB1.
`
`4. REFERENCE
`
`[1] RAN2 98 Chairman’s note
`[2] RAN2 Adhoc2 Chairman’s note
`
`
`Ex.1012
`APPLE INC. / Page 3 of 3
`
`