3.3 gpp NR USER Plane introduction

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3GPP NR U-Plane Introduction
邱俊淵
工研院資通所
1

Agenda
• Work Plan of NR
• Radio Protocol Architecture
• SDAP (Service Data Adaptation Protocol)
• PDCP
• RLC
• MAC
2

Work Plan of NR
3
2016 2017 2018
Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
NSA = Non StandAlone
SA = StandAlone
5G study
5G NR Work Item 5G NR NSA
Completion
Stage 3 completion
for Non-Standalone 5G-NR
RAN
#74
RAN
#75
RAN
#78
RAN #80
(Rel-15 completion)
Further evolution5G NR SA
Completion
Stage 3 completion
for Standalone 5G-NR
NSA Option 3 family
ASN.1
Rel-15 ASN.1 for SA &
NSA

Non Standalone 5G-NR
• LTE eNB as a master node
• Data transport through LTE eNB and/or NR gNB via EPC
4
LTE eNB
PDCP
RLC NR RLCRLC
MAC
PDCP
gNB
NR PDCP
NR RLC
NR MAC
S1S1
MCG bearer Split bearer SCG bearer
Xx
Refer to TR 38.801 & TR 38.804

Other Scenarios of 5G-NR
5
CN-RAN deployment scenarios where
eNB connected to NextGen Core is a
master node
CN-RAN deployment scenarios where NR gNB is a master node
Refer to TR 38.804

Radio Protocol Architecture
6
gNB
PHY
UE
PHY
MAC
RLC
MAC
AMF
RLC
NAS NAS
RRC RRC
PDCP PDCP
User Plane Protocol Stack Control Plane Protocol Stack
Refer to TS 38.300

SDAP (Service Data Adaptation Protocol)
• The main services and functions of SDAP include:
• Mapping between a QoS flow and a data radio bearer
• Due to new QoS framework
• Marking QoS flow ID in both DL and UL packets
• For DL: due to reflective QoS
• For UL: due to new QoS framework
7

New QoS Framework
8
CN_UPANUE
Data packets from applications
“NAS” filters
(mapping packets
to QoS flows and apply marking)
Mapping flows
to DRBs
Packets marked with “QoS Flow ID”
PDU session
Packet filters classify
packets to SDFs
Application /Service Layer
AN Resources
Refer to TS 23.501

EPS Bearer Service Architecture
9Refer to TS 36.300

Reflective QoS
• In the uplink, the NG-RAN may control the mapping of QoS Flows to
DRB in two different ways:
• Reflective mapping:
• for each DRB, the UE monitors the QoS flow ID(s) of the downlink packets
and applies the same mapping in the uplink; that is, for a DRB, the UE
maps the uplink packets belonging to the QoS flows(s) corresponding to
the QoS flow ID(s) and PDU Session observed in the downlink packets for
that DRB. To enable this reflective mapping, the NG-RAN marks downlink
packets over Uu with QoS flow ID.
• Explicit Configuration:
• besides the reflective mapping, the NG-RAN may configure by RRC an
uplink “QoS Flow to DRB mapping”.
10

PDCP
• The main services and functions of the PDCP sublayer for the user plane include:
• Sequence Numbering
• Header compression and decompression: ROHC only
• Transfer of user data
• Reordering and duplicate detection (if in order delivery to layers above PDCP is required)
• PDCP PDU routing (in case of split bearers)
• Retransmission of PDCP SDUs
• Ciphering and deciphering
• PDCP SDU discard
• PDCP re-establishment and data recovery for RLC AM
• Duplication of PDCP PDUs
11

Out-of-Order Deciphering
• Drawback in LTE
• In-sequence delivery from RLC layer (i.e. reordering in RLC) might incur high
latency due to deciphering
• Enhancement in NR
• Complete PDCP PDUs can be delivered out-of-order from RLC to PDCP. RLC
delivers PDCP PDUs to PDCP after the PDU is reassembled
• PDCP reordering is always enabled if in sequence delivery to layers above
PDCP is needed (i.e. even in non-DC case)
• How does RLC Rx window operation work in NR?
• RLC Rx entity needs to keep track of each packet in the window to determine
if any of them has been completed and delivered to PDCP
12

Duplication of PDCP PDUs
• Motivation
• RLC retransmission (ARQ) is not assumed to be used for meeting the strict
user plane latency requirements of URLLC
• How to do?
• Duplication applies in case of multi-connectivity and carrier aggregation (CA).
• In case of CA, duplication to more than one logical channel is used for Carrier
Aggregation so that the duplicated PDCP PDUs are sent over different carriers.
• PDCP duplication solution for CA requires only one MAC entity.
• Logical channel mapping restrictions need to be introduced to handle
duplicates in within one MAC entity (CA).
13

CA case
14Refer to R2-1702032

RLC
• The main services and functions of the RLC sublayer depend on the
transmission mode and include:
• Transfer of upper layer PDUs
• Sequence numbering independent of the one in PDCP
• Error Correction through ARQ
• Segmentation and re-segmentation
• Reassembly of SDU
• RLC SDU discard
• RLC re-establishment
(note: no concatenation and no reordering)
15

No Concatenation
• Motivation
• Extreme latency requirement in 5G
• For URLLC the target for user plane latency should be 0.5ms for UL, and 0.5ms for DL.
• For eMBB, the target for user plane latency should be 4ms for UL, and 4ms for DL.
• RAN1 intends to reduce the delay from the end of the reception of the DCI (UL grant) to
the beginning of the transmission of the corresponding UL transport block to 1-2 OFDM
symbol durations
16
e.g. 1 ms
TDLUL TULDL
DL
ULULULULUL ULULULUL ULULUL

• Drawback in LTE
• In order to perform TB filling, RLC and MAC PDUs are generated after reception of UL grant
17

• Removing RLC concatenation enables the pre-processing procedure of both
RLC and MAC layer
18Refer to TS 38.300

MAC
• The main services and functions of the MAC sublayer include:
• Mapping between logical channels and transport channels
• Multiplexing/demultiplexing of MAC SDUs belonging to one or different
logical channels into/from transport blocks (TB) delivered to/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 by means of logical
channel prioritisation
• Padding
19

New MAC PDU Format
• Drawback in LTE
• The LTE MAC PDU format does not facilitate MAC/PHY parallel processing
20Refer to TS 36.321

• MAC subheaders are placed immediately in front of the corresponding MAC
SDUs, MAC CEs, or padding. The possibility to parse the MAC PDU from the
back is not precluded.
• UL MAC CE(s) is placed after all the MAC SDUs. For DL the placement will be
deterministic (i.e. it should not be up to the network to decide). FFS if we
have the same behaviour for both or for DL the MAC CE is placed at the front
21Refer to R2-1703511

LCP Enhancement
• Motivation
• Multiple numerologies/TTI durations are supported and different numerologies/TTI durations
may be suitable for different kind of traffic
• A single logical channel can be mapped to one or more numerology/TTI duration.
• For the purpose of LCP, the MAC entity learns the TTI duration/numerology from the PHY
layer. FFS on the details of how it is signalled
• This can be done explicitly (i.e. some field in the DCI) or
• implicitly (e.g. the TTI duration of the UL transmission is the same as the DL transmission of the UL
grant)
• LCP takes into account the mapping of logical channel to one or more numerology/TTI
duration. Details of LCP will be discussed in the WI phase
• Priority, PBR concept is used in NR as a baseline.
• Logical channel priority is configured per UE as a baseline. FFS is anything needs to be done to
treat logical channels differently
22

SR/BSR Enhancement
• Motivation
• The SR should at least distinguish the “numerology/TTI type” of the logical channel that
triggered the SR
• Like the SR, also the design of the BSR is impacted by the multi-numerology/TTI duration
configuration supported in NR
• How SR enhancement is done is FFS
• Multiple-bit SR or
• Single-bit SR with multiple SR configurations
• The existing LTE BSR framework is used as baseline for NR BSR framework. Further
enhancements at least related to numerologies and granularity and can be further discussed
• Numerologies: Extend the number of LCGs to link a LCG to a specific numerology
• Granularity: increasing the number of bits in the BS field, increasing the number of LCGs, reporting
BSR per logical channel
23

HARQ Enhancement
• Motivation
• Performance degradation of HARQ due to large transport block size
• Code Block Group (CBG)-based transmission with single/multi-bit HARQ-ACK feedback is
supported (FFS: two alternatives to form CBG)
• The UE is semi-statically configured by RRC signaling to enable CBG-based retransmission.
• The above semi-static configuration to enable CBG-based retransmission is separate for DL
and UL.
24Refer to R1-1705401

• Asynchronous and adaptive UL HARQ is supported at least for eMBB
• Flexible timing
• Timing between DL assignment and corresponding DL data transmission is indicated by a field in
the DCI from a set of values
• Timing between UL assignment and corresponding UL data transmission is indicated by a field in
• Timing between DL data reception and corresponding acknowledgement is indicated by a field in
• The set of values is configured by higher layer
• NR UE supports a set of minimum HARQ processing time
• Delay between DL data reception timing to the corresponding HARQ-ACK transmission
timing
• Delay between UL grant reception timing to the corresponding UL data transmission timing
• NR UE is required to indicate its capability of minimum HARQ processing time to gNB
25

Thanks
ccy@itri.org.tw
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3.3 gpp NR USER Plane introduction

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