LTE Capacity Management and Optimization
INTERNAL
LTE RF Capacity Management and
optimization
Huawei Technologies Co., Ltd.
All rights reserved
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Table of Contents
1 Overview .................................................................................................................................................... 4
2 PRB” Physical Resource Block”................................................................................................................... 5
2.1 Definition............................................................................................................................................. 5
2.2 Usage Increase by ............................................................................................................................... 5
2.3 Insufficiency ........................................................................................................................................ 5
2.4 Monitoring .......................................................................................................................................... 5
2.5 Root Cause Analysis/Solution ............................................................................................................. 6
Poor Channel Quality ............................................................................................................................ 6
Parameter Settings................................................................................................................................ 6
User Number ......................................................................................................................................... 7
2.6 Threshold for Expansion ..................................................................................................................... 7
2.7 OMSTAR Analysis ................................................................................................................................ 7
UL / DL Formulas ................................................................................................................................... 7
OMSTAR Threshold is ............................................................................................................................ 7
OMSTAR Analysis .................................................................................................................................. 8
3 PRACH” Physical random access channel”............................................................................................... 10
3.1 Definition........................................................................................................................................... 10
3.2 Usage Increase by ............................................................................................................................. 12
3.3 Insufficiency ...................................................................................................................................... 12
3.4 Monitoring ........................................................................................................................................ 13
3.5 Root Cause analysis/Solution ............................................................................................................ 14
3.6 Threshold for Expansion ................................................................................................................... 15
3.7 OMSTAR Analysis .............................................................................................................................. 15
PRACH Resource Usage Statistic ......................................................................................................... 15
Contention/non-Contention Preamble Resource Usage Distribution ................................................ 15
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The Cell List of Contention/non-Contention Preamble Resource Usage Over Threshold .................. 16
Contention/non-Contention Preamble Resource Usage (Daily)(Cell/Busy Hour)(Network/Busy Hour)
............................................................................................................................................................ 16
4 PDCCH” Physical downlink control channel” ........................................................................................... 17
4.1 Definition........................................................................................................................................... 17
4.2 Usage Increase by ............................................................................................................................. 18
4.3 Insufficiency ...................................................................................................................................... 18
4.4 Monitoring ........................................................................................................................................ 18
4.5 Root Cause Analysis/Solution ........................................................................................................... 19
Poor Channel Quality .......................................................................................................................... 19
Parameter Adjustment ....................................................................................................................... 19
4.6 Threshold for Expansion ................................................................................................................... 20
4.7 OMSTAR Analysis .............................................................................................................................. 20
Items outputted for OMSTAR ............................................................................................................. 20
OMSTAR Threshold ............................................................................................................................. 20
Whole Network PDCCH Usage ............................................................................................................ 20
CCE Usage Distribution ....................................................................................................................... 21
The Cell List of CCE Resource Usage Over Threshold ......................................................................... 21
CCE Usage(Daily) ................................................................................................................................. 21
CCE Usage(Cell/Busy Hour) ................................................................................................................. 21
CCE Usage(Network Busy Hour).......................................................................................................... 21
5 Profit from LTE RF Capacity management and optimization ................................................................... 23
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1
INTERNAL
Overview
With the rapid development of smart terminals and services the impact of capacity problems on KPIs
and User experience increased, therefore close monitoring for Key bottleneck of LTE resources is
required to ensure better KPIs and user experience.
Capacity monitoring can be implemented using the following two methods:


Daily monitoring for prediction: Counters are used to indicate the load or usage of various types
of resources on the LTE network. Thresholds for resource consumption are specified so that
preventive measures such as reconfiguration and expansion can be taken to prevent network
congestion when the consumption of a type of resource continually exceeds the threshold.
Problem-driven analysis: This method helps identify whether a problem indicated by counters is
caused by network congestion through in-depth analysis. With this method, problems can be
precisely located so that users can work out a proper network optimization and expansion
solution.
LTE Resources are
Cell
eNodeB
•PRB
•PRACH
•PDCCH
•Connected user license
•Paging resources
•Main-control-board CPU
•LTE baseband process unit (LBBP) CPU
•Transport resource groups
•Ethernet ports
This Document concentrate on LTE Cell Resources.
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PRB” Physical Resource Block”
2.1 Definition
Resource Block is the minimum unit for resource allocation used for data transmission in
physical layer, it consists of two dimensional domain:
 Time Domain: 1 Slot= 7 OFDM Symbol (normal CP).
 Frequency Domain: 12 Subcarriers.
RB number depend on the LTE system bandwidth as shown below
Channel bandwidth BWChannel
[MHz]
1
3
5
10
15
20
Sub-carriers Number
72
180
300
600
900
1200
RB Number
6
15
25
50
75
100
Resource Element (RE)
Smallest unit in PRB consist of two dimensional domain:
 Time Domain: 1 OFDM Symbol.
 Frequency Domain: 1 Subcarriers.
2.2 Usage Increase by
•
•
As Data traffic growth PRB Usage increase.
As PRB Usage reaches 100%, user perceived traffic will decrease.
Insufficiency
2.3 Insufficiency
Growing traffic leads to a continuous increase in PRB usage. When the PRB usage approaches to
100%, user-perceived rates will decrease as follow:
• New Users may fail to be admitted
• Admitted users experience is affected.
2.4 Monitoring
•
•
Downlink PRB usage = L.ChMeas.PRB.DL.Used.Avg/L.ChMeas.PRB.DL.Avail x 100%
L.ChMeas.PRB.DL.Used.Avg
= Average used DL PRBs
L.ChMeas.PRB.DL.Avail
= Available DL PRBs
Downlink user-perceived rate (Mbit/s) = L.Thrp.bits.DL/L.Thrp.Time.DL/1000
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L.Thrp.bits.DL = DL PDCP Layer Throughput
L.Thrp.Time.DL= duration for transmitting DL PDCP layer data
2.5 Root Cause Analysis/Solution
Factors affecting PRB usage:




Poor Channel Quality
Parameter Settings
User number
Traffic Model ”service requirement of each user”
PRB Limitation leads to prolong UE Scheduling delay  decreasing UE Data Rate.
Poor Channel Quality
Lead to low spectrum efficiency and increase PRB usage.
DL Spectrum Efficiency = L.Thrp.bits.DL/L.ChMeas.PRB.DL.Used.Avg/(report
Period*60)/180000 “bit/s/Hz”
if Less than 1bit/s/Hz  Optimize RF Quality
UL Spectrum Efficiency = L.Thrp.bits.UL/L.ChMeas.PRB.UL.Used.Avg/(report
Period*60)/180000 “bit/s/Hz”
if Less than 0.5bit/s/Hz  Optimize RF Quality
Parameter Settings
DL
RbgAllocStrategy=Adaptive
 If the number of required RBs is less than that of one RBG, RBs are allocated to
the scheduled UE as required, which is specified by resource allocation type 1.
 If the number of required RBs is greater than that of one RBG, the number of
allocated RBGs is rounded up and an integral number of RBGs are allocated to
the scheduled UE. Compared with RBG round-up, this mode prevents RB waste
when the number of required RBs is less than that of one RBG
UL
UlSchSwitch=PuschDtxSwitch-1
 During UL transmission if UE fail to detect UL GRANT or SR false alarm appear in
DRX state
 Enabled:UE will report(ACK/NACK/DTX) if the HARQ feedback state of one
uplink schedule is DTX, eNodeB will deliver UL GRANT again instead of starting
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HARQ retransmission. If the next HARQ feedback is still DTX, eNodeB will stop
the schedule triggered by this SR
Disabled:lead to the uplink retransmission repeatedly and waste the uplink
PUSCH resource and the uplink error code rate will increase obviously
User Number
 If average RRC_Connected User(L.Traffic.User.Avg) >300
Downlink user-perceived rate < a user-defined threshold (default value: 2 Mbit/s)
Resource Insufficiency cause the low Data Rate Consider Expansion
 Formula for Downlink user perceived rate:
Average DL Throughput for single User = (L.Thrp.bits.DLL.Thrp.bits.DL.LastTTI)/L.Thrp.Time.DL.RmvLastTTI*1000
2.6 Threshold for Expansion
•
•
Add carriers or eNodeBs if both of the following conditions are met:
Downlink PRB usage ≥ 70%
Downlink user-perceived rate < a user-defined threshold (default value: 2 Mbit/s)
2.7 OMSTAR Analysis
•
•
•
•
•
Whole Network PRB Analysis
PRB Resource Usage Distribution
Uplink/Downlink PRB Resource Usage Distribution(RRU)
The Cell List of Uplink/Downlink PRB Resource Usage Over Threshold
PRB Resource Usage(Daily)(Cell/Busy Hour)(Network/Busy Hour)
UL / DL Formulas
Uplink PRB resource usage = Average number of uplink PRBs scheduled in each second
(L.ChMeas.PRB.UL.Used.Avg+ L.ChMeas.PRB.PUCCH.Avg)/ Total number of uplink PRBs in a cell x
100%
Downlink PRB resource usage = Average number of downlink PRBs scheduled in each second
(L.ChMeas.PRB.DL.Used.Avg)/ Total number of downlink PRBs in a cell x 100%
OMSTAR Threshold is
OMSTAR threshold for Expansion is 70% PRB usage.
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OMSTAR Analysis
Whole Network PRB Analysis
Time
x
Whole Network
Average Number of
Uplink Used PRB per
Cell
Whole Network Average
Number of Downlink
Used PRB per Cell
Whole Network
Average Uplink PRB
Resource Usage per
Cell
Whole Network
Average Downlink PRB
Resource Usage per Cell
4.33
4.85
8.65%
9.71%
PRB Resource Usage Distribution
Uplink/Downlink PRB Resource Usage Distribution
Uplink/Do
Cell
Ratio(PDF)(N Ratio(CDF)(N
Cell
wnlink PRB Number(Ne
Ratio(PDF)(Ce Ratio(CDF)(Ce
etwork Busy etwork Busy Number(Cell
Resource twork Busy
ll/Busy Hour) ll/Busy Hour)
Hour)
Hour)
/Busy Hour)
Usage
Hour)
[0,10%)
217
83.78%
83.78%
206
79.54%
79.54%
[10%,20%)
31
11.97%
95.75%
43
16.60%
96.14%
[20%,30%)
7
2.70%
98.46%
8
3.09%
99.23%
[30%,40%)
3
1.16%
99.61%
1
0.39%
99.61%
[40%,50%)
1
0.39%
100.00%
1
0.39%
100.00%
[50%,60%)
0
0.00%
100.00%
0
0.00%
100.00%
[60%,70%)
0
0.00%
100.00%
0
0.00%
100.00%
[70%,80%)
0
0.00%
100.00%
0
0.00%
100.00%
[80%,90%)
0
0.00%
100.00%
0
0.00%
100.00%
[90%,100%]
0
0.00%
100.00%
0
0.00%
100.00%
The Cell List of Uplink/Downlink PRB Resource Usage over Threshold
The Cell List of Uplink/Downlink PRB Resource Usage Over Threshold
eNodeB
ID
eNodeB
Name
Cell
ID
Cell
Name
Time Uplink
PRB
Resource
Usage
Downlink
PRB
Resource
Usage
Average
Number
of Uplink
Used
PRB
Average
Number
of
Downlink
Used PRB
Average
number
of used
PRBs
over the
PUCCH
PRB Resource Usage (Daily) (Cell/Busy Hour) (Network/Busy Hour)
OMSTAR provide per Cell PRB usage and average number of used RBs and users for uplink and
downlink for :
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Average
number
of users
in a cell
LTE Capacity Management and Optimization



eNodeB
ID
INTERNAL
Daily format: Average per Day.
Cell/Busy Hour
Network Busy Hour
eNodeB
Name
Cell
ID
Cell
Name
Time Uplink
PRB
Resource
Usage
Downlink
PRB
Resource
Usage
Average
Number
of Uplink
Used
PRB
Average
Number
of
Downlink
Used PRB
Average
number
of used
PRBs
over the
PUCCH
DL / UL Spectral Efficiency
OMSTAR Formula
-DL Spectrum Efficiency(bps/Hz) = L.Thrp.bits.DL/L.Thrp.Time.Cell.DL/(L.ChMeas.PRB.DL.Used.Avg *
(BAND*10^6/L.ChMeas.PRB.DL.Avail))
-UL Spectrum Efficiency (bps/Hz) = L.Thrp.bits.UL/L.Thrp.Time.Cell.UL/(L.ChMeas.PRB.UL.Used.Avg *
(BAND*10^6/L.ChMeas.PRB.PUSCH.Avg))
For Low Spectral Efficiency
DL (1bPs/Hz):
Check if MCS <10 or CQI<6  RF Issues  otherwise Check MIMO Setting
UL (0.5 bps/HZ)
Check if MCS<10 or SINR<5  RF Issues
Downlink/Uplink Spectral Efficiency (Daily) (Cell/BH) (Network/BH)
eNodeB
ID
eNodeB
ID
eNodeB
Name
eNodeB
Name
Cell
ID
Cell
ID
Cell
Name
Downlink Spectral Efficiency
Time Downlink
Downlink
Traffic
Bits for
Volume for PDCP
PDCP
SDUs
SDUs(Gb)
Average
Number of
used
Downlink
PRBs
Uplink Spectral Efficiency(Cell/Busy Hour)
Cell
Time Uplink
Uplink Bits Number
Name
Traffic
for PDCP
of Used
Volume for SDUs(Gb)
Uplink
PDCP
PRBs
SDUs(Gb)
Downlink Spectral
Efficiency(bps/Hz)
Uplink Spectral
Efficiency(bps/Hz)
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Average
number
of users
in a cell
LTE Capacity Management and Optimization
3
INTERNAL
PRACH” Physical random access channel”
3.1 Definition
1.
2.
3.
4.
5.
6.
Random access is performed in the following scenarios:
Initial RRC connection setup to switch from the RRC_IDLE state to the RRC_CONNECTED state, a
UE initiates random access.
RRC connection reestablishment When a radio link failure (RLF) occurs, the UE needs to
reestablish an RRC connection. In this scenario, the UE initiates random access.
Handover During a handover, a UE initiates random access in the target cell.
Downlink data arrival when an eNodeB needs to send downlink data to a UE in the
RRC_CONNECTED state and finds that the UE is out of uplink synchronization, the eNodeB
instructs the UE to initiate random access.
Uplink data arrival When a UE in the RRC_CONNECTED state needs to send uplink data to an
eNodeB and finds that it is out of uplink synchronization, the UE initiates random access.
LCS When a location service (LCS) is required, the eNodeB initiates random access.
Random Access message
is as shown below consist of
CP
Sequence
 CP ”Cyclic prefix”
 preamble sequence
TCP
TSEQ
Guard Period
 Guard period
Preamble
Since Random Access message is first message sent from UE side and the TA “Time advance” is
not known yet, so guard period is used to ensure message arrival is within the TS.
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random access preamble formats
There is five Random Access preamble formats used as below depending on cell radius from parameter
Cell.CellRadius
Define the Cell preamble format in parameter: Cell.PreambleFmt
Preamble
Format
Allocated
Subframes
TSEQ
(µs)
TCP
(Ts)
TCP (µs)
TGT
(µs)
Max. Delay
Spread (µs)
Cell Radius (km)
0
1
800
3168
103.125
96.875
5.208
R < 14.531
1
2
800
21024
684.375
515.625
16.666
29.5 < R < 77.344
2
2
1600
6240
203.125
196.875
5.208
14.5 < R < 29.531
3
3
1600
21024
684.375
715.625
16.666
77.3 < R < 102.65
4 (TDD)
Special
Frame
133.3
448
14.6
9.417
16.666
R < 1.41
Subframe 1ms
Subframe 1ms
Format 3
Format 2
Format 1
6
PRB
Format 0
CP
Zadoff Chu Sequence
Random access is categorized into:
 Contention-based random access
Random access preambles are generated by UEs, and conflicts may exist among these
preambles. The eNodeB uses a contention resolution mechanism to handle such a conflict.
Contention-based random access are divided into group A and group B:
o The UE selects group A when it transmits a small Msg3. This selection indicates that radio
channel quality is poor.
o The UE selects group B when it transmits a large Msg3. This selection indicates that radio
channel quality is good.
 Non-contention-based random access
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Random access preambles are allocated by the eNodeB, and each preamble is dedicated to only
one UE. Therefore, there is no preamble conflict.
Non-contention-based access is used when there are available dedicated preambles. However,
contention-based access is used when dedicated preambles are exhausted.
Each Cell has 64 preambles which used for both contention and non- contention preambles assigned
using below parameters:
RACHCFG.RandomPreambleRatio:
Indicates the proportion of the number of random preambles in a cell to the number of
preambles in the cell.
RACHCFG.RaPreambleGrpARatio
Indicates the proportion of the number of group A random preambles in a cell to the number of
random preambles in the cell.
Number of random preamble sequences = 4 x rounddown (total number of preamble sequences in a cell
x RandomPreambleRatio value/4)
Number of random preamble sequences in group A = 4 x roundup (total number of preamble sequences
x RaPreambleGrpARatio value/4)
3.2 Usage Increase by
o
o
o
o
Access requests (initial- UL/DL Data).
Handover times.
LCS
RRC connection reestablishment.
3.3 Insufficiency
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Preamble Usage in Random Access
Contention
Based
Number> N in Second
Non-Contention Based
Conflict
Probability <1%
 access delay increase.
Number >100
 Use Contention Preamble 
increase access/HO delay.
Where N is
Bandwidth
PRACH resource adjustment algorithm
N
15-->20
5-->10
5-->10
X
NO
Yes
100
50
100
3.4 Monitoring
Contention Preamble Usage
•(L.RA.GrpA.Att + L.RA.GrpB.Att)/3600/N x 100%
Non-Contention Preamble Usage
•L.RA.Dedicate.Att/3600/100 x 100%
where
o L.RA.GrpA.Att indicates the number of times that random preambles in group A are received.
o L.RA.GrpB.Att indicates the number of times that random preambles in group B are received.
o L.RA.Dedicate.Att indicates the number of times that dedicated preambles are received.
o The value of N varies as follows:
− If the system bandwidth is 15 MHz or 20 MHz, N is 100.
− If the system bandwidth is 5 MHz or 10 MHz and the PRACH resource adjustment algorithm is
disabled, N is 50.
− If the system bandwidth is 5 MHz or 10 MHz and the PRACH resource adjustment algorithm is enabled,
N is 100.
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To check whether the PRACH resource adjustment algorithm is enabled, run the LST CELLALGOSWITCH
command to query the value of the RachAlgoSwitch.
3.5 Root Cause analysis/Solution
Enable Random Access Backoff
The RACH does not interfere with other uplink channels in LTE. Generally, the probability of RACH
conflicts is low.
If excessive UEs are admitted on a PRACH, however, preamble conflicts may occur, and some UEs may
fail to access the network. To solve this problem, random access backoff is introduced to control the
time for preamble retransmission by UEs.
If random access backoff is enabled, the eNodeB notifies a UE of a backoff value in the random access
response message. When the UE needs to retransmit a preamble, it randomly selects a value (from 0 to
the received backoff value) as its backoff time. The UE can retransmit the preamble only after the
backoff time ends.
Random access backoff is not performed in the following two scenarios:
o Initial preamble transmission
o Preamble retransmission in non-contention-based random access
When to use?
If the random preamble usage reaches or exceeds 75% for three days by default in a week,
enable the adaptive backoff function
MOD CELLALGOSWITCH: LocalCellId=x, RachAlgoSwitch=BackOffSwitch-1;
PRACH resource adjustment algorithm
In case of Preambles are insufficient PRACH resource adjustment algorithm acts as follow:
 If dedicated preambles are in surplus and random preambles are insufficient, the
eNodeB reduces the number of dedicated preambles.
 If dedicated preambles are insufficient, the eNodeB increases the number of dedicated
preambles.
Whether dedicated preambles are insufficient is measured based on the dedicated preamble
allocation failure rate, which is equal to one minus the ratio of the number of UEs that are
allocated dedicated preambles to the number of UEs that apply for dedicated preambles.
MaksIdxSwitch: Indicates the switch used to control reuse of dedicated preambles between UEs.
If the switch is on, the eNodeB enables reuse of dedicated preambles among UEs based on the
MaskIndex parameter. If the switch is off, the eNodeB allocates a dedicated preamble to only
one UE at a time.
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When to use?
If the dedicated preamble usage reaches or exceeds 75% for X days (three days by default) in a
week, enable the PRACH resource adjustment algorithm and reuse of dedicated preambles
between UEs by running the following command:
MOD CELLALGOSWITCH: LocalCellId=x,RachAlgoSwitch= RachAdjSwitch1,RachAlgoSwitch=MaksIdxSwitch-1;
This helps reduce the probability of UEs initiating contention-based random access in the case of
dedicated preamble insufficiency and therefore helps reduce the access delay
3.6 Threshold for Expansion
If above actions implemented and the resource usage is still >75% add eNodeB or split Cell
3.7 OMSTAR Analysis
PRACH Resource Usage Statistic
Time
Contention Preamble Resource Usage
Non-Contention Preamble Resource Usage
0.14%
0.00%
x
Contention/non-Contention Preamble Resource Usage Distribution
Pream
ble
Resour
ce
Usage
[0,10%)
Cell
Number(N
etwork
Busy
Hour)
3
Ratio(PDF)(
Network
Busy Hour)
Ratio(CDF)(
Network
Busy Hour)
100.00%
100.00%
[10%,2
0%)
[20%,3
0%)
[30%,4
0%)
[40%,5
0%)
[50%,6
0%)
[60%,7
0%)
[70%,8
0%)
[80%,9
0%)
[90%,1
00%]
0
0.00%
0
Cell
Number(Ce
ll/Busy
Hour)
Ratio(PDF)(C
ell/Busy
Hour)
Ratio(CDF)(C
ell/Busy
Hour)
3
100.00%
100.00%
100.00%
0
0.00%
100.00%
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
0
0.00%
100.00%
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The Cell List of Contention/non-Contention Preamble Resource Usage Over Threshold
Contention/non-Contention Preamble Resource Usage (Daily)(Cell/Busy
Hour)(Network/Busy Hour)
The Cell List of Contention Preamble Resource Usage Over Threshold
Contention
eNodeB eNodeB Cell Cell
Preamble
Time
Resource
ID
Name ID Name
Usage
Average
number of Contention Preamble
users in a Received(Group A)
cell
Contention
Preamble
Received(Group B)
The Cell List of Non-Contention Preamble Resource Usage Over Threshold
NonContention
eNodeB eNodeB Cell Cell
Time Preamble
ID
Name ID Name
Resource
Usage
Average Non-Contention
Non-Contention
number of Preamble
Preamble
users in a Received(Recovery
Received(HO)
cell
Uplink Synchronization)
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4
INTERNAL
PDCCH” Physical downlink control
channel”
4.1 Definition
The PDCCH/EPDCCH carries the following types of DCI:
Downlink grant
This DCI includes the PDSCH resource indicator, modulation and coding scheme (MCS),
HARQ process number information, and PUCCH power control commands. This DCI has
multiple formats, such as formats 1, 1A, 1B, 1C, 1D, 2, and 2A.
Uplink grant
This DCI includes the PUSCH resource indicator, MCS, and PUSCH power control
commands. This DCI has only format 0.
Power control command
This DCI is a group of PUSCH power control commands for a UE, which supplement
PUSCH and PUCCH power control commands in an uplink grant. This DCI has formats 3
and 3A.
PDCCH defined in following terms
REG – Resource element group
which is smallest defined unit and includes 4 subcarriers/resource elements
CCE – Control channel element
1CCE=9 REGs, that means there are a total of 9×4=36 subcarriers and since all the
control channels are mapped using QPSK/BPSK which basically can map 2 bits per
subcarrier, we can accommodate 72 control channel bits per CCE
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LTE Capacity Management and Optimization
INTERNAL
PDCCH aggregation Level
LTE support 4 Aggregation Levels 1,2,4,8 CCEs to map a PDCCH DCI
Higher PDCCH aggregation level higher probability for the UE to successfully decode the DCI
4.2 Usage Increase by
In each radio frame, CCEs must be allocated to uplink and downlink UEs to be scheduled and
common control signaling .
 So higher number UEs to be scheduled  increase the PDCCH Usage.
 Poor channel quality  higher CCE aggregation level higher PDCCH Usage.
4.3 Insufficiency
Uplink and downlink scheduling delays are prolonged, and user experience is affected.
4.4 Monitoring
CCE usage = (L.ChMeas.CCE.CommUsed + L.ChMeas.CCE.ULUsed +
L.ChMeas.CCE.DLUsed)/L.ChMeas.CCE.Avail x 100%
Where
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



INTERNAL
L.ChMeas.CCE.Comm Used indicates the number of PDCCH CCEs used for common signaling.
L.ChMeas.CCE.ULUsed indicates the number of PDCCH CCEs used for uplink scheduling.
L.ChMeas.CCE.DLUsed indicates the number of PDCCH CCEs used for downlink scheduling.
L.ChMeas.CCE.Avail indicates the number of available CCEs.
4.5 Root Cause Analysis/Solution
Poor Channel Quality
If Dynamic CCE Aggregation Level is enabled
Generally in Poor Channel Quality area the CCE aggregation level increases to ensure correct
PDCCH decoding, therefore CCE aggregation level incensement reflect poor radio conditions
CCE Aggregation level =
L.ChMeas.PDCCH.AggLvl1Num ∗1+L.ChMeas.PDCCH.AggLvl2Num ∗2+L.ChMeas.PDCCH.AggLvl4Num ∗4+L.ChMeas.PDCCH.AggLvl8Num ∗8
L.ChMeas.PDCCH.AggLvl1Num +L.ChMeas.PDCCH.AggLvl2Num +L.ChMeas.PDCCH.AggLvl4Num +L.ChMeas.PDCCH.AggLvl8Num
If CCE Average aggregation Level >= 4  optimize Radio Conditions
Parameter Adjustment
PDCCH Symbol Adaptation ( PdcchSymNumSwitch)
OFF: Symbols reserved for PDCCH are fixed regardless of current usage
ON :based on the CCE usage assign PDCCH symbols, Initial PDCCH symbols= InitPdcchSymNum
ECfiAdaptionON: based on CCE usage , PRB Usage, Power Usage  assign the PDCCH Symbols,
Initial PDCCH symbols= InitPdcchSymNum
PDCCH Aggregation Level (AggLvlSelStrageForDualCW)
eNodeB dynamically select appropriate aggregation Level based on:
• CQI reported from User  SINR DL.
• DCI Format used , demodulation threshold for coding rates used.
STRATEGYBASEDONCAPACITY: Tends to select lower aggregation level  increase capacity
 increase BLER
STRATEGYBASEDONCOVERAGE: Tends to Select higher aggregation Level demodulation
improved  decrease capacity.
Maximum PDCCH Code Rate (PdcchMaxCodeRate)
If PDCCH Code Rate exceed this value eNodeB increases the PDCCH Aggregation Level
• High Value: lower PDCCH Aggregation Value  improve Capacity  decrease Coverage
• Lower Value: higher PDCCH Aggregation Value  lower Capacity  increase Coverage
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LTE Capacity Management and Optimization
INTERNAL
PDCCH and PDSCH Resource Balance Scheduling
At Heavy Traffic and majority of UEs with small volume services, limited number of UEs can be
scheduled due to PDCCH UEs limitations  PDSCH resources are not fully utilized, and the downlink
throughput is low.
To solve this problem, DL scheduling is now optimized to
• A threshold for the number of UEs (UeNumThdInPdcchPdschBal )in a cell is introduced
to determine whether traffic is heavy.
• If traffic is heavy, the downlink scheduler randomly selects a UE with large-volume
services( DataThdInPdcchPdschBal) and reserves PDCCH resources for the UE.
When scheduling the last UE, the scheduler allocates PDSCH resources to the selected UE.
4.6 Threshold for Expansion
Add carriers or eNodeBs if after previous Actions CCE Usage > 60%
4.7 OMSTAR Analysis
Items outputted for OMSTAR
• Whole Network PDCCH Usage
• CCE Usage Distribution
• The Cell List of CCE Resource Usage Over Threshold
• CCE Usage(Daily)
• CCE Usage(Cell/Busy Hour)
• CCE Usage(Network Busy Hour)
OMSTAR Formula for CCE Usage is
CCE usage = (Number of CCEs used by common signaling + Number of CCEs used for uplink scheduling +
Number of CCEs used by downlink scheduling)/3600/1000/Total number of CCEs supported by a cell x
100%
OMSTAR Threshold
OMSTAR CCE Usage Threshold is 80%
Whole Network PDCCH Usage
Whole Network PDCCH Usage
Time CCE
Usage
Number of PDCCH Number of PDCCH
CCEs used by
CCEs used by
common DCI
Uplink DCI
Number of PDCCH
CCEs used by
Downlink DCI
Number of
available PDCCH
CCEs
x
0
750750160
14894086494
10.85%
865975601
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INTERNAL
CCE Usage Distribution
• Result calculated for Network Busy Hour and Cell Busy Hour
• For Each CCE Usage Percentage  How many Cells/ PDF Ratio/ CDF Ratio
CCE Usage Distribution
Cell
Number Ratio(PDF)(Net
CCE Usage
(Networ work Busy
k Busy
Hour)
Hour)
Ratio(CDF)(Net
work Busy
Hour)
Cell
Number(Cell/
Busy Hour)
Ratio(PDF)(C
ell/Busy
Hour)
Ratio(CDF)(C
ell/Busy
Hour)
[0,10%)
172
65.65%
65.65%
141
53.82%
53.82%
[10%,20%)
54
20.61%
86.26%
82
31.30%
85.11%
[20%,30%)
19
7.25%
93.51%
23
8.78%
93.89%
[30%,40%)
11
4.20%
97.71%
9
3.44%
97.33%
[40%,50%)
4
1.53%
99.24%
3
1.15%
98.47%
[50%,60%)
0
0.00%
99.24%
3
1.15%
99.62%
[60%,70%)
2
0.76%
100.00%
1
0.38%
100.00%
[70%,80%)
0
0.00%
100.00%
0
0.00%
100.00%
[80%,90%)
0
0.00%
100.00%
0
0.00%
100.00%
[90%,100%]
0
0.00%
100.00%
0
0.00%
100.00%
The Cell List of CCE Resource Usage Over Threshold
• List of Cells that has high CCE Usage and breakdown for the high usage reason:
• Common DCI
• UL DCI
• DL DCI
The Cell List of CCE Resource Usage Over Threshold
Time eNodeB
Name
Cell
Name
CCE
Usage
Number of
PDCCH CCEs
used by
common DCI
Number of
PDCCH CCEs
used by
Uplink DCI
Number of
PDCCH CCEs
used by
Downlink DCI
Number of
available
PDCCH CCEs
CCE Usage(Daily)
CCE Usage(Cell/Busy Hour)
CCE Usage(Network Busy Hour)
All has the same below format, only difference on the time of getting the data
CCE Usage(Daily) (Cell/Busy Hour) (Network Busy Hour)
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LTE Capacity Management and Optimization
Time eNodeB
Name
Cell
Name
CCE
Usage
Number of
PDCCH CCEs
used by
common DCI
Number of
PDCCH CCEs
used by
Uplink DCI
Number of
PDCCH CCEs
used by
Downlink DCI
INTERNAL
Number of
available
PDCCH CCEs
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INTERNAL
5
Profit from LTE RF Capacity
management and optimization
By monitoring and managing and optimizing LTE Capacity you can:





Avoid Access Failure
Improve UE Experience
Decrease Handover Delay
Decrease Uplink and downlink scheduling delays.
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