5G RAN2.0 Scheduling
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Copyright © 2018 Huawei Technologies Co., Ltd. All rights reserved.
Preface

To improve spectral efficiency, the New Radio (NR) system
uses shared channels for transmission and time-frequency
resources are dynamically allocated among UEs. The
resource allocation mode (such as modulation scheme, and
allocation priority) directly affects user perception and
network performance.
Copyright © 2018 Huawei Technologies Co., Ltd. All rights reserved.
Page 2
Objectives

Upon completion of this course, you will be able to:

Have a basic knowledge of the Scheduling feature.

List the scheduling algorithms of Huawei gNodeB.

Describe basic and enhanced uplink/downlink scheduling.

Describe scheduling methods for typical services.
Copyright © 2018 Huawei Technologies Co., Ltd. All rights reserved.
Page 3
Contents
1. Technical Principles
2. Downlink Scheduling
3. Uplink Scheduling
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Page 4
Introduction
• Scheduling enables the gNodeB to allocate PDSCH or PUSCH resources (time
domain, frequency domain, or spatial domain resources) to UEs for transmitting
system information or user data. The resource allocation must comply with the
frame structure configuration and use a scheduling basic unit.
• Key factors
 Frame structure configuration
Upper layer
 Basic scheduling unit
 Scheduler (MAC entity)
 Execution
Downlink scheduler
• The figure on the right illustrates
downlink scheduling.
Cell
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MAC layer
Frame Structure Configuration
Example: TDD, 30-kHz subcarrier, uplink/downlink subframe
assignment = 1:4

Three slot formats: downlink-specific slot, uplink-specific
slot, and slot with flexible configuration
One radio frame (10 ms), containing 20 slots (0.5 ms per slot)
D
D
D
S
U
D
D
D
S
U
D
D
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D
S
U
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D
D
D
S
U
Basic Scheduling Unit: PRB
Slot
D
S
U
D
D
D
S
…
1 slot D GAP U
D
U
D
D
GAP U
1 slot, 14 OFDM symbols
PRB
PRB
…
…
PRB
PRB
Band
(GHz)
Mode
Subcarrier Bandwidth
(KHz)
(MHz)
RB
Count
1.8
FDD
15
20
106
3.5
TDD
30
100
273
28/39
TDD
120
100
66
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12 subcarriers
PRB
PRB
Implementation

Scheduling is implemented by schedulers (MAC entities),
which are located at the UE and the gNodeB separately in
the NR system.
RRC
PDCP
PDCP
RLC
RLC
Layer 3
Layer 2
Logical channel
MAC
MAC
PHY
PHY
UE
gNB
Transport channel
Physical channel
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Layer 1
MAC Entity
Upper layer
PCCH
BCCH
CCCH
DCCH
DTCH
MAC control
Logical channel priority (uplink)
Multiplexing/Demultiplexing
Random access control
HARQ
PCH
BCH
DL-SCH
UL-SCH
RACH
Lower layer
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Control
Execution
CQI/RI/PMI
PDCCH (DCI)
PDSCH&PUSCH

Basic process:

The UE measures user-level CSI-RI SINR and reports channel quality
information such as CQI/RI/PMI to the gNodeB.

Based on the reported channel quality and UE capability, the gNodeB selects
a proper MCS and transmits data on the PDSCH/PUSCH.

The UE obtains the uplink/downlink resource allocation information from the
DCI carried over the PDCCH.
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CQI

CQI indicates the channel quality. The CQI reported by the
UE to the gNodeB is obtained after quantification on the
SINR obtained from pilot measurement. In 5G RAN1.0, the
reported CQI is measured on full bandwidth and used for:

MCS and TBS selection
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PDCCH&PDSCH
Example: 30-kHz subcarrier, D slot
Example: 30-kHz subcarrier, S slot
One slot = 0.5 ms
One slot = 0.5 ms
PDCCH
PDSCH
PDCCH
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PDSCH
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GP
SRS
PDSCH Resource Allocation
Power
Sequential allocation
UE1
UE2
20 MHz RBG size 4 as an example
UE3
…
Frequency
Start RB
System bandwidth
Total RB Count
RBG Size
1-36
2
37-72
4
73-144
8
145-273
16
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Page 13
Contents
1. Technical Principles
2. Downlink Scheduling
3. Uplink Scheduling
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Page 14
Terms

Modulation and coding scheme (MCS)

Represents a particular combination of a modulation scheme and a channel
code rate. Layer 2 determines the MCS for each UE to be scheduled.

Hybrid automatic repeat request (HARQ) feedback

Indicates whether data has been correctly transmitted or retransmitted. It can
be acknowledgment (ACK) or negative acknowledgment (NACK).

Carrier bandwidth part (BWP)

Indicates a combination of contiguous RBs. The BWP of UEs is generally
smaller than the gNodeB system bandwidth. UEs can be scheduled over the
same BWP at the same time.
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Processing by the Scheduler
Processing physicallayer measurement
information
Scheduler
Scheduling in each TTI
Data
-Downlink data buffer status
-HARQ feedback status
Processing scheduling
information
Dynamic scheduling
MCS & Rank for
scheduled UEs
Priority calculation
PRB and TBS
allocation for
scheduled UEs
MCS selection
Rank for
scheduled UEs
Resource allocation
Inputs
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Outputs
Page 16
Downlink Scheduling – Inputs
HARQ feedback
• Whether retransmission or initial
transmission is required
Downlink buffer status
• Used for calculating the required
resources
else
gNodeB model and UE capability，etc
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Downlink Scheduling – Process
Data and
scheduling type
UE and priority
MCS
selection
PDSCH
allocation
DMRS
allocation
end
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Page 18
Control-Plane Scheduling

Control-plane information includes:

Common control information: remaining minimum system
information (RMSI) and Paging and random access response (RAR)


Dedicated control information: SRB0, SRB1, SRB2，and SRB3
User-plane information
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Page 19
Downlink HARQ Retransmission
Scheduling Process
Start
No
Are there UEs qualified for
HARQ retransmissions?
Yes
The gNodeB selects a UE requiring an HARQ
retransmission
No
No
Is the number of consecutive
failed HARQ retransmissions
smaller than the upper limit?
Yes
Are there remaining downlink
resources?
Yes
End
The gNodeB allocates resources for the HARQ
retransmission.
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Priorities of UEs with Initial
Transmissions

Huawei gNodeB supports the proportion fairness (EPF)
algorithm.
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PDSCH Resource Allocation Type0

Several continuous RBs form an RB group (RBG), and RBs to
be used are indicated in the unit of RBG.

The number of RBs that an RB group has is determined by the
downlink bandwidth.
Number of Downlink PRBs
RBG Size
1 to 36
2
37 to 72
4
73 to 144
8
145 to 273
16
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Page 22
PDSCH Resource Allocation Type0

Take 34 downlink RBs for example. The RBG size is 2 and the 34
RBs can be divided into 17 RBGs (34/2). If 18 RBs are scheduled
for a UE, which are mapped to RBGs 2, 3, 4, 5, 8, 10, 11, 13, and
17. The bitmap of this example is as follows:
34 RBs
RBG
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17
Bitmap
(0/1)
0
1
1
1
1
0
0
1
0
1
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1
0
Page 23
1
0
0
0
1
Questions

What is the basic process of downlink scheduling?

What advantages and disadvantages does the PF scheduling
algorithm present?
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Page 24
Downlink Scheduling-Related
Parameters
PDSCH
IBLER target
value
The PDSCH IBLER target value can be
configured to ensure network performance for
cell-center, near-of-center, and cell-edge UEs
in different commercial network scenarios.
Parameters
PDCCH
IBLER target
value
AMC step
adjustment
switch
The PDCCH IBLER target value can be configured to ensure
network performance for cell-center, near-of-center, and celledge UEs in different commercial network scenarios.
The AMC adjustment step can be adjusted so that
fast IBLER convergence can be allowed to improve
throughput.
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Downlink Interference Randomizationbased Scheduling

The resource allocation start location of each cell is different from its neighbor
clls to get a smaller interference.
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Page 26
Contents
1. Technical Principles
2. Downlink Scheduling
3. Uplink Scheduling
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Page 27
Terms

PHR


BSR


A power headroom report (PHR) indicates the difference
between the maximum allowed TX power and the used TX
power in the uplink. UEs send PHRs to the gNodeB
periodically or in event-triggered mode.
The buffer status report (BSR) indicates the amount of to-besent data in the uplink buffer of a UE.
SR

The scheduling request carries 1-bit information that a UE
sends to the gNodeB over the uplink channel to request
uplink resources for data transmission.
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Uplink Scheduling Resource – PUSCH
Front-loaded RS
Short PUCCH
Long PUCCH
Additional RS
PRACH
1 RB/12 subcarriers
273 RBs (30 kHz@100 MHz)
PUSCH
1 subframe/14 symbols
Uplink subframe
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Uplink Scheduling Process
UE
gNodeB
Scheduling Request (PUCCH)
BSR & PHR (PUSCH)
Uplink scheduling
command (PDCCH)
Schedule based
on the logical
channel group
Schedule based on
each logical channel Uplink data (PUSCH)
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Uplink Scheduler
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Uplink Scheduling – Inputs
HARQACKs/NACKs
• Whether retransmission or initial transmission is required
SINR
• Uplink channel conditions obtained from the sounding
reference signal (SRS) and demodulation reference
signal (DMRS) measurement
PHR
• Power status of a UE
BSR
• Amount of to-be-sent data in the uplink buffer of a UE
SR
• 1-bit information that a UE sends to the gNodeB over the
uplink channel to request uplink resources for data
transmission
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Uplink Scheduling – Priority
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Uplink HARQ Retransmission
Scheduling

Uplink scheduling for retransmissions uses asynchronous adaptive
retransmission. In HARQ retransmissions, the MCS can be adaptively
selected and differ from the MCS for initial transmissions. A HARQ
retransmission and an initial transmission use the same TBS.

If the gNodeB replies with an ACK to a packet sent by a UE on the PUSCH,
the UE does not transmit the packet again.

If the reply is NACK, retransmission scheduling is triggered for this packet.

In asynchronous adaptive retransmission, a DCI must be delivered to instruct
the UE to perform retransmissions.

After the number of uplink HARQ transmissions reaches the maximum
number of 5, uplink HARQ retransmission stops.
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Page 34
Control-Plane Scheduling

Control-plane data includes uplink SRBs and the DRBs
that carry IMS signaling.

The gNodeB often uses a small MCS index and fixed RB
resources for control information to ensure correct
reception.
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Page 35
Uplink Scheduling for Initial
Transmissions

Initial transmissions in uplink scheduling include to-be-scheduled
UE selection, scheduling resource acquisition, MCS selection,
and RB allocation (the number and positions of allocated RBs).
To-be-scheduled UE
selection
Scheduling resource
acquisition
RB selection
MCS selection
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To-Be-Scheduled UE Selection

The uplink scheduler selects the target UEs with initial
transmissions based on the scheduling priorities.

EPF is supported in the uplink:
𝑒𝑓𝑓 𝐴𝑙𝑝ℎ𝑎
𝑝𝑟𝑖𝑜𝑟𝑖𝑡𝑦 =
𝑟
• eff: uplink channel quality obtained from the SINR of gNodeBmeasured SRS
• Alpha: uplink capacity factor that has the same function as the
downlink capacity factor
• r: historical rate of a UE
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RB Allocation

The uplink scheduler determines the RB resources
required by a UE in a TTI based on the buffer status
(BSR), power headroom status, and hardware limitations.
UE power
headroom
gNodeB
hardware
limitations
UE buffer
status
Number of
RBs
required
by the UE
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Page 38
PUSCH Waveforms

5G PUSCHs support two waveforms: CP-OFDM and DFT-SOFDM.

CP-OFDM is characterized by flexible resource allocation and high
frequency diversity gain thanks to the use of discontinuous
frequency-domain resources. However, it causes high peak-toaverage power ratio (PAPR).

DFT-S-OFDM ensures low PAPR and high transmit power, with the
PAPR approximately close to that of a single carrier. However, it
requires continuous frequency-domain resources.

Huawei products support adaptive switching between the two
waveforms.
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PUSCH RB Allocation

Uplink scheduling uses frequency selective scheduling or frequency diversity
scheduling to allocate uplink resources.



Frequency selective scheduling: The uplink scheduler sets a sliding window for each UE
based on the number of RBs required by the UE. During frequency selective scheduling,
the uplink scheduler slides the window in sequence in the frequency domain and selects
the resource combination with the maximum expected gain in the window to allocate
resources to the UE. The SINR in the window is used to calculate the expected gain of
the sliding window during uplink frequency selective scheduling.
Frequency diversity scheduling: The uplink scheduler allocates RBs to each UE in
sequence based on the number of RBs required by the UE in uplink frequency diversity
scheduling.
Frequency selective scheduling yields gains by leveraging differences in channel quality
or interference. However, it may result in frequency band fragments and inefficient use of
RBs. In addition, frequency selective scheduling is complicated and results in high
processing overheads. The gNodeB in the NR system adaptively enables or disables
uplink frequency selective scheduling based on the number of synchronized UEs in a
cell. When uplink frequency selective scheduling is disabled, frequency diversity
scheduling is performed.
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PUSCH Discontinuous RB Allocation

If the allocated RB resources in an uplink slot cause frequency band fragments,
the gNodeB allocates inconsecutive RB resources for to-be-scheduled UEs.

When selecting the uplink RB location of each UE, the gNodeB searches for the
RB segment that meets the requirements and can deliver the highest spectral
efficiency.
Frequency
band
UE 2
UE 2
RBs required
for UE 3
...UE 3
Consecutive resource allocation
UE 1
UE 3
Frequency
band
...UE 3
UE 2
Inconsecutive resource allocation
UE 1
Inconsecutive resource allocation: Inconsecutive RB
segments are allocated to the to-be-scheduled UEs.
Gain: Increase the cell capacity by 5%.
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Uplink Interference Randomizationbased Scheduling
 Baseline (without this function enabled)
RB resources are allocated for cells from the low frequency band, resulting in a high RB collision rate and strong co-channel interference.
 Interference Randomization-based Scheduling
The RB resources allocated to each cell are staggered, the RB collision rate is low, and the intra-frequency interference is small.
Resource
search
direction
Resource
search
direction
Scheduling RBs
Cell 1
Cell 1
Start
location
Cell 0
Cell 2
Mode 6: PCI%6=
0
1
Mode 3: PCI%3=
0
Cell 0
2
Cell 2
3
4
1
Mode 2: PCI%2=
Mode 3
RbUtil-based mode 3to-mode 6 switching
5
2
0
Low frequency
RbUtil-based mode 6to-mode 3 switching
Mode 6
Start
location
1
High frequency
Resource search direction
RbUtil-based mode 3RbUtil-based mode 2to-mode 2 switching
to-baseline switching
Mode 2
RbUtil-based mode 2to-mode 3 switching
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Baseline
RbUtil-based baselineto-mode 2 switching
Page 42
MCS Selection for Uplink Scheduling

Involve three steps: SINR adjustment, initial MCS selection, and
MCS adjustment, as illustrated in the following figure:
Uplink IBLER adaptation
During MCS selection, the uplink scheduler
can adaptively select the IBLER target based
on the average value and variance of SINRs.
This improves UE throughput.
Initial uplink SINR adjustment
The initial uplink SINR adjustment value can
be configured using a parameter. The default
value is -4 dB.
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Page 43
Uplink Scheduling Enhancement:
Preallocation

After the gNodeB schedules resources for UEs with data
transmission, it initiates uplink scheduling for UEs if uplink
resources are sufficient. This is called preallocation.

Benefits: Shorten the UE scheduling delay.

A UE is in a preallocation queue when the following
conditions are met:

The UE is not scheduled within the current TTI.

The UE meets the minimum interval between preallocations.

The UE has a preallocation weight greater than 0.
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Page 44
Uplink Scheduling-Related Parameters
Adaptive
Uplink
Waveform
If this switch is turned on, the gNodeB selects
transmitting signal waveform for UEs and
instructs UEs to change waveforms according
to the radio environment.
If this switch is turned off, the gNodeB instructs
UEs to use the CP-OFDM waveform.
Parameters
Uplink IBLER
Adaptation
Switch
Initial Uplink
SINR
Adjustment
If this switch is turned on, the IBLER target value is
adaptively selected based on UE's uplink SINR mean value
and variance.
If this switch is turned off, the uplink IBLER target value is
fixed at 10%.
This parameter specifies the initial value of uplink SINR
adjustment. It is -4 dB by default.
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Page 45
Questions

What is the basic process of uplink scheduling? What factors
can have an impact on uplink scheduling?

How do we determine the number of RBs during uplink
scheduling?
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Page 46
Thank you
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