Microsoft PowerPoint - OEO106040 LTE eRAN6.0 Scheduling Feature ISSUE 1
Transcript of Microsoft PowerPoint - OEO106040 LTE eRAN6.0 Scheduling Feature ISSUE 1
LTE eRAN2.1 Scheduling Feature
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Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved.
LTE eRAN6.0 Scheduling Feature
Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Overview
2. Downlink Scheduling
3. Uplink Scheduling
4. Semi-Persistence Scheduling
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Scheduling Overview
Scheduling Function: Ensure high spectrum high spectral efficiency while providing the required.
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Scheduling Strategy
SchedulingStrategy
Effect Factor Scheduling PriorityApplication Scenario
Max C/I Channel qualityThe UE with better channel quality has a higher priority in scheduling.
To verify the maximum system throughput
RR NoneEach UE has equal opportunity to be scheduled.
To verify the upper limit of scheduling fairness
PFService rate and channel quality
The UE with a small ratio between the service rate and channel quality has a higher priority in scheduling.
To verify the system throughput and fairness
EPF
Service rate, channel quality, UE capability, and QoS requirement
Intergraded priority with service rate, UE category, QoS and CQI.
In operating networks
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Scheduling Scheme
• Period: 1ms (per TTI)
• Service application: all service
Dynamic scheduling
• Period: 20ms (Huawei eNodeB)
• Service application: Real time service, etc. VoIP
Semi-Persistent Scheduling
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QoS Class Index
QCI Type PriorityPacket Delay
Budget
Packet Error
RateService Example
1 GBR 2 100ms 10-2 Conversational Voice
2 GBR 4 150ms 10-3 Conversational Voice
3 GBR 3 50ms 10-3 Real time gaming
4 GBR 5 300ms 10-6 Real time video
5 Non GBR 1 100ms 10-6 IMS signaling
6 Non GBR 6 300ms 10-6 Video with buffer
7 Non GBR 7 100ms 10-3 Voice, Video, Interactive Gaming
8 Non GBR 8 300ms 10-6 Video, TCP (HTTP, E-mail, FTP etc)
9 Non GBR 9 300ms 10-6 Video, TCP (HTTP, E-mail, FTP etc)
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Scheduler Introduction
Scheduling in each TTI
Semi-persistent scheduling
Dynamic scheduling
Priority
calculation
MCS
selection
Resource
allocation
QoS management
Processing of measurement
quantities from PHY
Scheduling information
processing
UE capability
QoS (QCI/GBR/AMBR)
SINR (uplink)
CQI (downlink)
SR/BSR (uplink)
Buffer status(downlink)
PHR (uplink)
Tx power (downlink)
ACK/NACK
Virtual MIMO switch (uplink)
MIMO scheme (downlink)
ICIC strategyEdge frequency band
Center frequency band
RLC payload
MCS
Antenna and
resource mapping
Retransmission
control
Scheduler
The dashed line indicates the optional function.
Guarantee system
signaling sending
Ensure QoSrequirements
Take user differentiation and fairness into account
Maximize the system
throughput
Functions of MAC layer:
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Scheduling Execution
� DCI info for scheduling
� Resource allocation header: indicate allocation type
� Resource assignment block
� MCS (Modulation Coding Scheme)
� MIMO scheme
� NDI( New Data Indication)
� HARQ process number
DCI info (PDCCH)
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Contents
1. Overview
2. Downlink Scheduling
3. Uplink Scheduling
4. Semi-Persistence Scheduling
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Contents
2. Downlink Scheduling
2.1 Scheduling Priority Processing
2.2 MCS Selection & Resource Allocation
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DL Scheduler
DL Scheduler
Channel Quality
HARQ feedback
QoS parameters
UE Capability
Selected UE
RB number
MCS/MIMO
Every scheduling period
Priority calculation
MCS selection
Resource allocation
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Scheduling Priority of DL Scheduling
Obtain scheduling resource
Control message scheduling
Semi-persistent scheduling
Retransmission scheduling
Initial transmission in dynamic scheduling
End
Re
so
urc
e a
lloca
tion
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Control-Plane Data and IMS Signaling
� Common Control Messages
� Common control message regards to SIBs, paging and RA response
message.
� If the scheduling indication fails to be delivered due to insufficient
PDCCH resources , common control messages are not scheduled in the
current TTI.
� UE-Level Control Message or IMS Signaling
� SRB0 is delivered in the Contention Resolution message during the
random access process, has higher priority then SRB1/SRB2 and IMS
signaling
� During the DRX dormant period and measurement gap or when the UE
has urgent HARQ scheduling, SRB1 and SRB2 cannot be scheduled.
� The scheduling of IMS signaling is the same as that of SRB1 and SRB2
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HARQ Retransmission Scheduling
At least 8 TTI
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HARQ Retransmission Scheduling Exception� HARQ retransmissions cannot be performed for a UE in one of the
following states:
� The UE is in a measurement gap or enters a measurement gap
� The UE enters sleep time in DRX and the HARQ operating status
is discontinuous transmission
� The UE is non-synchronized to the eNodeB or a radio link failure
(RLF) occurs
� System information and IP Multimedia Subsystem (IMS) signaling
are already scheduled for the UE in the current TTI
� Semi-persistent scheduling is performed for the UE in the current
TTI.
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Other Initial Service Scheduling
Priority 2
Priority 1
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Other Initial Service Scheduling
Priority 2
Priority 1
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Priority of GBR Service Scheduling
� The priority of GBR service is determined by the following
formula:
� f(CQI): indicates the channel quality.
� f(delay): indicate packet delay budget which is specified in
3GPP
.
)()(Pr delayfCQIfiorityGBR ×=
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Priority of Non-GBR Service Scheduling� The priority of Non-GBR service is determined by the following
formula:
� eff: indicates the channel quality
� r: indicate historical service rate for the UE
� : indicates scheduling priorities corresponding to different
QCIs
� : indicates the service type weight. The service types are
bit torrent (BT) services and non-BT services
serviceQCIGBRnonr
effiority γγ ⋅⋅=
−Pr
QCIγ
serviceγ
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Contents
2. Downlink Scheduling
2.1 Scheduling Priority Processing
2.2 MCS Selection & Resource Allocation
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MCS Selection
� The eNodeB obtains the ITBS according to the adjusted
CQI.( eNodeB internal mapping )
� If frequency diversity scheduling is used, UE will adopt full band
CQI report
� If frequency selective scheduling is used, UE will adopt sub_band
CQI report
� If CQI adjustment is enabled, the eNodeB adjusts the CQI
reported by the UE and selects an MCS based on the adjusted
CQI, otherwise eNodeB use the original UE CQI report
� The eNodeB selects IMCS according to the mapping from ITBS to
IMCS. ( Specified in 3GPP)
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CQI Report Procedure
� Step 1: eNodeB configure CQI report mode with
periodic or aperiodic mode
� Step 2: If it aperiodic report, eNB send UE list to
UL scheduler for CQI report scheduling
� Step 3: The UL scheduler sends the UL grant to
UE in the aperiodic CQI user list
� Step 4: UE send CQI report to eNodeB
� If periodic CQI mode configuration, UE reports the
CQI on PUCCH as RRC configuration
� If aperiodic CQI mode configuration, UE reports the
CQI on PUSCH as UL grant.
UL UL
SchedulerScheduler
DL DL
schedulerscheduler
CQI Mode CQI Mode
ConfigurationConfiguration
UEUE
2
13
AA--CQICQI PP--CQICQI
1
4
eNB
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CQI Adjustment
� Why CQI adjustment
� The CQI report period is far greater than the scheduling period,
which leads to deviation between the CQI at the reported time
and CQI in scheduling.
� The reported CQI value depends on the UE measurement, and
it may not be very accurate sometimes.
� In order to maximize the system capacity, IBLER target other
than 10% may be more appropriate, then CQI adjustment is
required.
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CQI Adjustment Switch
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RB Calculation & Allocation
� RB calculation:
� The scheduler obtains the amount of data to be scheduled and the ITBS
and estimates the number of RBs to be scheduled based on the 3GPP
specification
� Based on estimate RB number and remaining power, eNodeB finally
decide the RB number
� RB allocation:
� If frequency diversity scheduling is used, eNodeB allocate all the RB from
lower end to the higher end of a frequency band based on full band CQI
report
� If frequency selective scheduling is used, eNodeB schedules the UEs to
frequency bands with the optimum channel quality. This brings frequency
selective gains.
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Frequency Selective Scheduling Scheme
� Required aperiod sub_band aperiod CQI report
� Calculate user’s priority in each sub-band with user queue
� Allocate the resource in each sub-band based on user
queue
1 RBG
UE1 10 9 8 13 6 5…612
12 8 6 6 5 8
…
1011
13 10 11 10 7 5…910
…
…
UE2
UEn
Sub-band1
Sub-band2
Sub-band n
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FSS VS FDS
FSS FDS
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Contents
1. Overview
2. Downlink Scheduling
3. Uplink Scheduling
4. Semi-Persistence Scheduling
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UL Scheduling Overview
� Scheduling on the uplink is more difficult than on the downlink
� Limited visibility of quantity of queued data per radio bearer
� Scheduler is unable to offer per-radio bearer grants
UL data
UL grant
(On PUCCH)
Scheduling Request
BSR & PHRPeriodic or
Event triggered
UE eNodeB
Scheduling among UEs
Logical Channel Prioritization &
Multiplexing
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UL Scheduler
UL Scheduler
SINR
HARQ feedback
QoS parameters
UE Capability
Selected UE
Bandwidthallocation
MCS/MIMO
Every scheduling period
Priority calculation
MCS selection
Resource allocation
PHR/BSR/SR
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UL Scheduling Procedure
� A basic function of UL
scheduling is to obtain PUSCH
resources. As the PUSCH,
PUCCH, and PRACH share the
UL bandwidth, the PUSCH
occupies the available UL
resources in addition to PUCCH
and PRACH resources.
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TTI Bundling Scheduling
� Benefit
� It increases the UL cell edge user throughput and improve UL
coverage.
� There is more than 3db gain for uplink coverage
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TTI Bundling Functionality
� A TTI bundle permanently consists of four TTIs. The same
data is transmitted during the four TTIs
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Synchronized UL Retransmission
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UL Dynamic Scheduling for Initial Transmissions
� UL dynamic scheduling for initial transmission perform three
operations:
� Selects UEs for UL scheduling
� Determines MCSs to be used
� Determines the number and positions of RBs to be allocated
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UL MCS Selection
� The process of determining MCSs for UL scheduling consists of
three parts: SINR adjustment, initial MCS selection, and MCS
adjustment
SINR adjustment
IBLER
measurement
DRS
measurement
IBLER target
Adjusted
SINR
Initial MCS selection
Whether message 3
is transmitted on UL
MCS adjustment
SRS
transmission
UCI
transmission
UE
capability
Final MCS
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SINR Adjustment
� Why SINR adjustment
� Due to fading effect, SINR measurement can not reflect the
actual channel quality
� SIRN adjustment is used to make the actual IBLER is
converged to the target IBLER
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Initial MCS Selection & Adjustment
� On uplink, initial MCS selection is an internal decision by eNodeB
according to adjusted SINR
� MCS should be adjusted due to the following scenarios :
� To ensure the initial access performance, Huawei eNodeB uses a
fixed low-order MCS to transmit message 3
� If uplink data is conflict with UCI and SRS transmission, it will
cause higher IBLER, so the MCS should be adjusted
� If UCI(CQI/PMI/RI) is transmitted on PUSCH, it will use lower
MCS to ensure the performance based on a offset. In most of
scenario, the default offset can be used, and when the radio
environment is extreme bad, we can also adjust it manually.
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Determine Number of RB
� The following info are required to determine number of RB
� Buffer report from UE
� Power headroom report from UE
� QoS satisfaction rate
� Maximum number of RBs supported by a single carrier
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UL QoS Management
� The scheduler use EFP to ensure the QoS for each service, show as
below:
� The UL scheduler ensures the PELR and PDB as well as the service rate
for GBR services
� The UL scheduler uses a best effort policy for non-GBR services and
ensures only the minimum GBR specified by the UlMinGbr parameter
� If GBR and non-GBR services run simultaneously, GBR services take
precedence over non-GBR services
� eNodeB scheduler and UE scheduler are involved together on UL
scheduling, eNodeB scheduler decide the total resource for each UE
and UE scheduler decide the priority of each logic channel
scheduling.
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Token Bucket Rate Control in eNB
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Service Priority in UE Scheduler
� The differentiation between services with different QCIs is
achieved by setting the logical channel priority and
prioritized bit rate
Logical Channel Type PRB Configuration Priority
QCI 1 8 kbyte/s Not configurable
QCI 2 to QCI 4 Configurable Not configurable
QCI 5 8kbyte/s Not configurable
QCI 6 to QCI 9 Configurable Configurable
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Pre-Allocation Scheduling
Pre-Allocation Non Pre-Allocation
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Contents
1. Overview
2. Downlink Scheduling
3. Uplink Scheduling
4. Semi-Persistence Scheduling
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VoIP Service Status
� Transient state: A newly set up service is unstable
� Talk spurt: User is in normal conversation
� Silent period: User pauses during the conversation. In this
state, a silence insertion descriptor (SID) frame is
transmitted every 160 ms.
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Scheduling Scheme
� VoIP initial, transient and silent period: Adopt dynamic scheduling
� Talk spurt: Normally use semi-persistence scheduling except the following scenarios:
� High speed scenario
� UE has the other EPS bear more beside VoIP
� The cell bandwidth is 1.4 MHz
� UEs request emergency calls
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Semi-Persistence Scheduling
� In semi-persistent scheduling mode, the VoIP service
quality can be better ensured because the transmitted DL
data has a priority that is second only to that of common
control information.
� MCS selection: It is the very similar as dynamic scheduling,
but the maximum MCS IMCS can only be 15, If the derived
IMCS is greater than 15, the eNodeB takes IMCS as 15.
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Resource Limitation
� In order to avoid too much resource occupation by semi-
persistent scheduling, we can set a threshold to limit semi-
persistent service. If the total PRB used by semi- persistent
service is more than threshold in a TTI, then eNB stop the
scheduling for the other semi-persistent service and also it
stops the admission for this service
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Reference: Parameter description (1/5)
� For detail, please refer to the notes.
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Reference: Parameter description (2/5)
� For detail, please refer to the notes.
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Reference: Parameter description (3/5)
� For detail, please refer to the notes.
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Reference: Parameter description (4/5)
� For detail, please refer to the notes.
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Reference: Parameter description (5/5)
� For detail, please refer to the notes.
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