05 a rrm ul dl scheduler

1 © Nokia Siemens Networks RA41218EN10GLA1
Presentation / Author / Date
UL & DL Scheduler
(from LTE Radio Parameters RL20)

Index
•DL Scheduler
•UL Scheduler

DL Scheduler Overview
• LTE downlink scheduler is channel aware and assigns resources in a
proportional fair manner.
• Resource allocation is done in time domain as well as frequency domain.
• Specific priority shall be granted to Signaling Data and to HARQ
retransmission.
• In RL20 supports service differentiation (QCI profiles)
•The Number of UEs simultaneously scheduled per TTI can be limited.
• There is a max number of UE’s that can be scheduled per TTI based on
the Bandwidth employed
• Scope of the Packet Scheduler is cell level

DL Scheduler
• One downlink scheduler per cell,
separate schedulers for downlink and
uplink
• Distributed transmission (with PDCCH
format 1C) used for common channels
• Distributed transmission (with PDCCH
format 1A) used for Random Access
Message 4
• Localised transmission (PDCCH format
1/2/2A) used for data and signalling
bearers
• For DL Resource Allocation following
Allocation Types are implemented:
• Allocation Type 0 and 2
DCI
Format
Meaning DL Resource
Allocation
0 Scheduling of PUSCH N/A
1 Scheduling of one PDSCH
codeword
Type 0 or 1
1A Compact scheduling of one
PDSCH codeword or RA
procedure initiated by PDCCH
Type 2
1B Compact scheduling of one
PDSCH codeword with precoding
information
Type 2
1C Very compact scheduling of one
PDSCH codeword. Used for
Common Channels.
Type 2 (but
only distributed
VRBs)
1D Compact scheduling of one
PDSCH codeword with precoding
and power offset information
Type 2
2 Scheduling PDSCH to UEs
configured in closed-loop spatial
multiplexing mode
Type 0 or 1
2A Scheduling PDSCH to UEs
configured in open loop spatial
multiplexing mode
Type 0 or 1
3 and 3A Transmission of TPC commands N/A

DL Scheduler
• Resource allocation of type 0 used for data
and signalling bearers, i.e. PRBs can be only
allocated with granularity of a Resource Block
Group (size depends on bandwidth, 3 for
10Mhz for example)
• Resource type allocation 0 best fits data
centric applications
• Usage of resource allocation type 0 allows
(near) maximum bit rate
• Channel Aware scheduling
• Only dynamic scheduling supported in RL20,
(semi) persistent scheduling in later release
• DCI Formats: 1, 2, 2A
• Resource allocation type 2 is used for DCI
Formats 1A, 1B, 1C, 1D
• Used for common channels
DL Resource
Allocation
Meaning
Type 0 Bitmap of Resource Block Groups,
covering whole BW
Type 1 Bitmap of Resource Blocks,
covering one Resource Block
Group Subset
Type 2 Contiguously allocated localized
virtual resource blocks or
distributed virtual resource blocks
*Type 1 for voice-like
applications – not in RL10
Possible to allocate with
the granularity of 1 PRB

DL Scheduler
• DL Scheduler is a proportional fair scheduler in which:
• Each UE is guaranteed a minBitrateDl
• SRB data and HARQ retransmissions will always have priority over new
transmissions. Priority for SRB and HARQ retransmissions is set via:
prioHarqDl, prioSrbDl
• HARQ retransmissions use the same MCS/ rate matching/ number of
PRBs but may use different PRBs
• Flat power allocation, i.e., all PRBs are sent with the same transmission
power; this means, the scheduler does not evaluate any power control
information in RL20
• Duration of PRB/MCS allocation is one TTI (1ms)
• Number of RB’s allocated from scheduler can be limited by UE
capabilities, AMBR (RL20), parameters or data in buffer.
*AMBR = Aggregate Maximum Bit Rate
minBitrateDl
LNCEL; 5..500kbps; 5kbps;
30Kbps
prioHarqDl
LNCEL; 1..1000; 1; 1000
prioSrbDl
LNCEL; 1..1000; 1; 10

Start
End
Downlink Scheduling:
Step 1: Scheduling of common channels
(SIBs, paging and Random Access) to PDSCH
using Virtual Resource Blocks with distributed
transmission
Step 2: Evaluation of resources available for
dynamic allocation on PDSCH
1. Reserve PRB groups (RBGs) needed for
common physical channels
2. Reserve PRB groups (RBGs) needed for
PBCH and Syncronisation signals
• Note that these partly used RBGs
may be used for user data in later
releases
Step 3: Evaluating which users can be
scheduled:
1. UE has data buffered in the eNodeB?
2. UE has valid CQI available?
3. Is UE in inactive DRX/DTX mode?
4. Is UE in measurement Gap?
Step 4: Time domain scheduling:
Calculates Scheduling metric according to a fair
throughput criterion and select X best users for
frequency domain scheduling
The scheduling metric is given by parameters
for certain traffic types, like SRB data and HARQ
retransmission
Step 5: Frequency domain scheduling:
Allocate the selected X users to PRBs
UEs will be scheduled to PRBs where they
experience the best channel quality
Step 6: Allocated PDCCHs to CCEs
Combined step for Downlink and Uplink after
both scheduling decisions available for the TTI

Step 1
Scheduling of common channel data:
• Evaluate the amount of physical resources for transmission of BCCH
SIBs, Paging and Random Access data
• Physical resources are scheduled from DL Packet Scheduler together with
user plane data from cell users
• Parameter LNCEL: dlsUsePartPrb parameter specifies whether dynamic
scheduling with localized transmission is used for:
– physical resource blocks to transmit synchronization signals
– physical resource blocks to transmit synchronization signals and PBCH
STEP 1
dlUsePartPrb
LNCEL; not used (0), PRBs with PSS
or SSS used (1), PRBs with PSS or
SSS and PBCH used (2); PRBs with
PSS or SSS and PBCH used (2)

Step 2 Resource Evaluation, UL + DL
UL DL
PUSCH PDSCH
step 1.1
step 1.2 disregard PRBs permanently assigned to
- PUCCH
- PRACH
disregard resources needed for
- synchronization signals (primary and
secondary)
- physical broadcast channel (PBCH)
- (cell-specific) reference signals
- L1/L2 control signaling (PDCCH, PCFICH,
PHICH)
- …
step 1.3 Evaluation and virtual reservation of resources
required for RAP message 3 (needed for FD
scheduling)
- list of free PRBs - list of free PRBs
- list of free RBGs (resource block groups)
(RBG is free if all its PRBs are free)
ICIC defines per cell the set of resources usable for data transmission
ICIC not RL10 => all PRBs usable for allocation to UEs
evaluation of resources available for dynamic scheduling on
target
final
result
list of resources available for dynamic allocation
eNB calculates the availalable resources for data transmission –
evaluate all resources being used for common cannels like BCCH, paging and RA.
Do not count any resources which can not be allocated anyway (e.g. DL synch)
*ICIC = intercell interference cancellation, RAP = random access procedure, FD = frequency division
STEP 2

Step 2 Resource Evaluation, DL
• Main input to calculate the required resources for common channel transmission are
parameters to control coding overhead for common channel transmission
• System Information BCCH LNCEL: maxCrSibDl
• Paging LNCEL: maxCrPgDl
• Random Access message 2 LNCEL: maxCrRaDl
• Random Access message 4 LNCEL: maxCrRa4Dl
STEP 2
maxCrRaDL
Max. Code rate for random access
mesage 2 – RA response
LNCEL; 0.05…0.5; 0.01; 0.12
maxCrRa4DL
Max. Code rate for random access
mesage 4 – SRB0 message
LNCEL; 0.05…0.5; 0.01; 0.12
maxCrSibDL
Max. Code rate for BCCH
LNCEL; 0.05…0.5; 0.01; 0.12
maxCrPgDL
Max. Code rate for Paging
LNCEL; 0.05…0.5; 0.01; 0.12

Step 3 Pre-scheduling
• check all active UEs -> the result will be candidate set 1 (CS1) of UEs
– UE must not have “Out-of-Sync” status
 => radio link not synchronized
– UE must not be in measurement gap
 purpose: handovers
 no transmission/reception of data possible during measurement gaps
– UE must have data in Tx buffer for DRBs or SRB
 data availability on DRB(s) also basis for activity detection:
 2 timers (UL and DL) started after each scheduling event
 if both expired the UE is released (“RRC connected” -> “RRC idle”)
– UE radio channel quality feedback availability (see next slide)
STEP 3
inactivityTimer
Inactivity for UL & DL
LNCEL; 10..65535s; 1s ; 300s

Step 3 Pre-scheduling
• UE can be candidate for downlink scheduling:
– If CQI values are available and up-to-date
– If default CQI is used – O&M Parameter LNCEL: dlamcCqiDef
– Whenever no up-to-date CQI values are available on per-TTI basis, it shall be
possible to use the latest available CQI for a configurable period of time as
determined by parameter LNBTS: dlamcTHistCqi
– If available CQI is older than LNCEL: dlamcTHistCqi: default CQI value used
•NSN’s DL scheduler implementation is based on the UE radio channel quality
feedback (CQI)
• The availability of valid CQI values ensures reliable channel quality estimates, and
thus optimum scheduling for the relevant UE.
STEP 3
dlamcEnable
Enable Adaptive Modulation and
Coding in DL
LNCEL; true, false ; true
dlamcCqiDef
Default CQI used when no
updated CQI available
LNCEL; 0..15; 1; 2

Step 4 DL Time Domain Scheduling
• For all candidate UEs a TD scheduling metric is calculated
• priority per UE i:
• service term C1,i(t)
– static value depending on the service scheduled for the UE
– target: cluster UEs according to services and prioritise services against each other
• throughput term C2,i(t)
– “equal throughput criterion using minimum bit rate”
– based on data volume which was transferred via the DRB(s) in the past
– SRB doesn’t matter
– target: fairness
• final result: Candidate Set 2 = a number of UEs (maxNumUe) of CS1 with highest Ci(t)
(t)
C
(t)
C
(t)
C i
2,
i
1,
i 









otherwise
0
i
UE
for
sion
retransmis
HARQ
pending
has
UE
(HARQ)
prio
i
for UE
ission
for transm
available
data
SRB
DL
indicates
report
status
buffer
(SRB)
prio
)
( DL
DL
,
_
1 t
C i
DL
0
,
,
,
,
,
_
2
)
(
_
_
_
)
(


j
j
i
DL
j
i
j
i
DL
t
R
DL
RATE
BIT
MIN
t
C
STEP 4
minBitrateDl
LNCEL; 5..500kbps; 5kbps;
30Kbps
CS1= candidate set 1 from step 3

Step 4 DL Time Domain Scheduling
• Service criteria metric C1 is determined whether data in eNB buffers
is:
• Data re-transmission from active HARQ process
• Data from signaling connection (SRB data)
• Data re-transmission from HARQ process: LNBTS: prioHarqDl
• Data in DRB and SRB buffer: LNBTS: prioSrbDl
Value of prioHarqDl >> prioSrbDl – HARQ has higher priority than SRB transmission
STEP 4
prioHarqDl
LNCEL; 1..1000; 1; 1000
prioSrbDl
LNCEL; 1..1000; 1; 10

• per DRB j:
• Throughput term C2,i,j(t): DRB j served by UE i in TTI t (RLT: only 1 DRB per UE)
• MIN_BIT_RATEi,j
– minimum bit rate to be granted by scheduler, O&M parameter: LNCEL: minBitrateDl
– reference and target value for denominator => prefers high data rate services
• mean throughput rate
– Ri,j(t-1): throughput of DRB j of UE i in TTI t-1
– T: averaging period (weighting factor, no dimension)
– initialization: MIN_BIT_RATEi,j
Step 4 DL TD scheduling, Throughput term C2,i(t)
0
j
j
i,
j
i,
j
i,
2,
(t)
R
TE
MIN_BIT_RA
(t)
C





0
j
j
i,
2,
i
2, (t)
C
(t)
C
(t)
R j
i,
1)
(t
R
T
1
1
1)
(t
R
T
1
(t)
R j
i,
j
i,
j
i, 










current TTI
preceding TTI
mean
throughput
used for TD
scheduling in
current TTI
throughput
served in
preceding TTI
T = LNBTS: dlsTputAvgT
*“equal throughput
criterion using
minimum bit rate”
STEP 4
minBitrateDl
LNCEL; 5..500; 5kbps;
30Kbps

• After calculation of time-domain metric for all UEs candidates
for scheduling all UEs are listed in decreasing order
• Operator configurable parameter LNCEL: maxNumUeDl
can limit maximum number of UEs for frequency domain
scheduling
Step 4 DL TD scheduling
1 UE 7
2 UE 4
3 UE 5
4 UE 1
5 UE 6
6 UE 2
7 UE 3
8 UE 8
Time Domain Metric Calculation
maxNumUeDl
(default = 10)
STEP 4
maxNumUeDl
Max. Simultaneous UEs
in DL per TTI
LNCEL; 1...20; 1; 7
maxNumUeDl
Depending on dlChBw
the values are limited as
follows:
5.0 MHz => 1...7
10.0 MHz => 1...10
20.0 MHz => 1...20

Downlink Frequency Domain Scheduler
Channel aware scheduling
• Based on CQI feedback
• ~40% frequency diversity gain (when there
are multiple simultaneous users)
• Requires sub-band CQI reporting
Two algorithms
• DL Scheduler FD Algorithm parameter, dlsFdAlg
1. Time-to-Average (TTA) (dlsFdAlg=0)
• Only CQI information for current TTI is
considered
• Fair scheduling in ever TTI (same amount of
FD resources for each terminal selected by
TD scheduler)
• No support for QCI weights
2. Proportional fair (PF) (dlsFdAlg=1)
• Considers scheduling history
• Proportional fair per TTI
• Support different QCI weights
Frequency
Resource block
Transmit on those sub-carriers
that are not faded
Carrier bandwidth
STEP 5

• Required PF scheduling to be activated (dlsFdAlg=1)
• The QCI-specific relative scheduling weights are associated with each non-GBR bearer
• Scheduling Weight (schedulWeight) parameter defines the weight for each QCI.
• QCI used for the default radio bearer is defined in the QoS parameters in the core network.
QCI scheduling weights
STEP 5

– check limits
 UE capabilities of UE i: NTx,i shall not exceed maxBitrateDl
 UE category of UE i
• [3GPP-36.306], DL Shared Data Channel (DL-SCH)
 available amount of data for UE i
 AMBR for UE i
• rate capping enabled (rcEnableDl) => allocation over several TTIs limited by
UE AMBR
• UE-AMBR limits the aggregate bit rate per UE (all non-GBR bearers)
 Restriction for DL PRB assignment (redBwEnDl, redBwMaxRbDl)
– if 1 limit reached: stop resource allocation and remove UE i from CS2 (column i of
M)
– if multiple limits reached: chose lowest MCS level (and smallest TBS)
• stop conditions for resource allocation loop
– resources exhausted (number k of RBGs available for allocation reached
– no UEs with 1st Tx left in CS2
Step 5. FD scheduling, DL,
Resource allocation for UEs with 1st Tx only
STEP 5
maxBitrateDl
LNCEL; 50..300000 kbps;
50kbps; 170000Kbps
redBwEnDl
Enable DL PRB restriction per UE
LNCEL; false; false
redBwMaxRBDl
Max. UE specific PRB assignment
per TTI
LNCEL; 1…100; 25PRBs

PDCCH Scheduling
• PDCCH carries DCI (Downlink Control Information) to inform UE
– about UL and DL Resource Block allocation for user data transmission
• After UL and DL scheduling list was generated by UL and DL scheduler,
this algorithm selects UEs for UL and DL physical resource block allocation
• Share between UL and DL can be set with parameter LNCEL:
pdcchUlDlBal
• ZIG-ZAG is not used anymore (trial approach)
– only if entries have same priority level
• UE specific search space can be limited by LNCEL: PDCCHAlpha
– [0,5 .. 2], step 0,05, default = 0,8 (PDCCH UE search space capacity
is multiplied with this parameter)
pdcchUlDlBal
PDCCH allocation balance constant between UL and DL. The
PDCCH UE-specific search space capacity is divided into UL
and DL based on the parameter before dynamic schedulings
LNCEL; 0…0.9; 0.05; 0.5

PDCCH scheduling
• TOTAL_INPUT_LIST_DL_
AMC may be composed
based on different joint list
creation techniques
however as mentioned on
the previous slide, Prio-
oriented solution has been
chosen for RL10
• ZIG-ZAG solution is valid
only in case of entries with
the same priorities
High
priority
High
priority
High
priority
Low
priority
Low
priority
Low
priority
Downlink
list
Uplink
list
Joint
list
“ZIG-ZAG approach”
Joint list
Common
signalling (CSS),
Msg4
Highest
priority
Lowest
priority
Prio-oriented approach
UL HARQ
Dedicated
signalling (USS)
Scheduling
requests
Other DL/UL

PDCCH scheduling
Structured Parameter: 15 single parameters – not configurable
pdcchUlDlPrio
PDCCH LA priorities
LNCEL; 0…99; 1; -
Parameter is vendor specific

Index
•DL Scheduler
•UL Scheduler

Uplink Scheduler
•Uplink Packet Scheduling has the responsible for allocating PUSCH
resources (PRBs) to UEs in time domain and frequency domain
•In uplink (unlike downlink) only contiguous allocation of PRBs to a UE
possible
•One uplink scheduler per cell, separate schedulers for downlink and
uplink
•Always Channel Unaware, channel aware in later release
•There is no MIMO support in the UL-Scheduler

Uplink scheduler – General Framework
• HARQ - Due to synchronous
HARQ operation in uplink,
users with pending HARQ
retransmissions shall always
be scheduled
• Buffer status report - Users
should be scheduled
depending on the amount of
data in their buffer
• Power headroom report
• Uplink scheduler
– Time domain scheduling
– Frequency domain
scheduling
 Channel unaware scheduler
Buffer status
reports (from UE)
Packet
Scheduler
Link Adaptation
AMC
QoS
parameters
UL grant
on PDCCH
PHY
MAC
Power
Control
OLLA
SINR measurements
BLER
measurements
Offset
Demodulation
reference
symbols
Sounding
reference
symbols
Power headroom
reports (from UE)
Fast ATB
Slow
ATB
ATB = Adaptive Transmission Bandwidth

Start
End
Uplink Scheduler:
Step 1: Evaluate the available physical
resources for PUSCH
PRBs used for PUCCH and PRACH are not
used for PUSCH
Step 2: Reserve resources needed for
Random Access message 3
Random Access messages 3 are allocated when
PRACH preambles are reserved and this step is
needed to disable those already allocated
resources from dynamic scheduling
Step 3: Evaluating which users can be
scheduled:
UE has data buffered / pending HARQ retrans /
has send scheduling request?
UE has UL channel synchronised?
Is UE in inactive DRX/DTX mode?
Is UE in measurement Gap?
Step 4: Time domain scheduling:
Calculates Scheduling metric according to a fair
throughput criterion and select X best users for
frequency domain scheduling
The scheduling metric is given by parameters for
certain traffic types, like SRB data, HARQ
retransmission and Scheduling Request
Step 5: Frequency domain scheduling:
Allocate the selected X users to PRBs
UEs will be scheduled randomly on PRBs, see
next slide

UL Time Domain Scheduling
• priority per UE i:
• service term C1,i(t)
– static value depending on the service scheduled for the UE
– target: cluster UEs according to services and prioritise services against each other
• throughput term C2,i(t)
– “equal throughput criterion using minimum bit rate”
– based on data volume which was transferred via
the DRB(s) in the past
– SRB doesn’t matter
– target: fairness
• final result: Candidate Set for FD scheduling = a number of UEs (maxNumUe) of CS1 with
highest Ci(t)




0
j
j
i,
2_UL,
i
1_UL,
i
_UL, (t)
C
(t)
C
(t)
C












otherwise
0
UE
of
buffer
ssion
in transmi
available
are
data
SRB
that
indicates
report
status
buffer
if
(SRB)
prio
1
set
candidate
in
is
Request
Scheduling
if
(SR)
prio
UE
of
proc.
HARQ
for the
occured
retransm.
of
number
the
represents
n
for UE
performed
be
to
needs
ion
retranmiss
HARQ
if
(HARQ)
prio
n x
(t)
C
i
UL
UL
i
i
UL
i
1_UL,
0
j
j
i,
_UL,
j
i,
j
i,
2_UL,
(t)
R
TE_UL
MIN_BIT_RA
(t)
C


maxNumUeUl
5.0 MHz => 1...7
10.0 MHz => 1...10
20.0 MHz => 1...20
LNCEL; 1...20; 1; 7
tPeriodicBsr
Time period of the periodic Buffer
Status Report for the reporting of the
UE transmission buffer utilization.
5ms (0), 10ms (1), 16ms (2), 20ms (3),
32ms (4), 40ms (5), 64ms (6), 80ms (7),
128ms (8), 160ms (9), 320ms (10),
640ms (11), 1280ms (12), 2560ms (13),
infinity (14) ; 20 ms(3)

Uplink Frequency Domain Scheduler
• In uplink (unlike downlink) only contiguous
allocation of PRBs to a UE possible (see
picture on the right)
• Random allocation of PRBs to UEs (blind
frequency hopping), Channel unaware
frequency scheduling does not require
channel sounding
• Uplink Channel Aware Scheduler not
supported in RL20
DOWNLINK
UE1
UE2
SINR
UPLINK
UE1
UE2
SINR

Uplink Frequency Domain Scheduler
Two algorithms for UL FD scheduling in RL20:
• UL Scheduler FD Type (ulsFdPrbAssignAlg) parameter
1. Round Robin scheduler (ulsFdPrbAssignAlg=0)
• Weighted round robin. Weights are defined in used QCI.
• Assigns the physical resources equally fair to the UEs selected by the
TD scheduler until the PRBs are sufficient for the service or the
physical resources of the cell are exhaust
2. Exhaustive scheduler (ulsFdPrbAssignAlg=1)
• Assigns in the priority sequence defined by the TD scheduler as many
physical resources as possible to the UEs until the number of PRBs
are sufficient for the service or the resources of the cell are exhaust

UL Scheduler: Latency Improvement (1/3)
•This feature allows for a faster allocation of UL resources for a UE who no
longer has data in the buffer to send and has no on going Scheduling
Request
•The latency improvement feature can be enabled/disabled by the parameter
ilReactionTimerUL.
•When a UE has reported no more data in the buffer and there are available
PRB’s, the UL scheduler will schedule dummy grants for these UE ‘s
•This way the UE’s are given a chance to transmit in the UL if they suddenly
have data in the buffer during a period of time ilReactionTimerUL.
(0..20000 ms, step 100 ms, default = 1500 ms)
ilReactionTimerUl
LNCEL; 0…2000; 100; 1500 ms
(not modifiable)

•The UEs which may be potentially taken into account for the improved
latency feature shall be those that:
– have no pending Random Access Procedure
– be synchronised in UL
– not be in DRX/DTX active mode
– have no HARQ retransmission
– not be interrupted by a measurement gap
– have no ongoing Scheduling Request
– have no data in the transmission buffer (SRB and DRB)
– but sent data on a dummy grant during the configurable period of time
(ilReactionTimerUL).
ilReactionTimerUl
LNCEL; 0…2000; 100; 1500 ms
(not modifiable)

•The UEs have to utilize the dummy grants for the transmission of data
packets during a specifiable period of time
•When the UE doesn’t utilize the dummy grant during the specified period of
time the UE won’t be longer taken into account for the assignment
•When scheduling resources for these UE’s the channel unaware scheduler
shall take into account for each UE the predefined data volume required
specified by the parameter ilMinDatVolUL (not configurable).
(0..4000 bits, step 80 bits, default = 560 bit)
•Deduced from the volume the number of required PRBs shall be calculated
by means of the UE-specific MCS which is provided by the LA and the
outcome of the calculation shall be sent with a so-called ‘dummy grant’ to the
UE.

05 a rrm ul dl scheduler

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05 a rrm ul dl scheduler