NEI_LTE1235_ready_02.pdf

1 © Nokia Solutions and Networks 2014
Optimization of PRACH/RACH power
LTE1235
For internal use
Network Engineering Information
• Tomasz Tymiński
• 07-12-2015
Please always check the latest version of the NEI slides!

LTE1235 Optimization of PRACH/RACH power
Table of contents
Simulation, Lab
and Field Findings
Introduction
Motivation and Feature
Overview
Inter –
dependencies
Interdependencies with
other features and
functions
Benefits and
Gains
Simulation, Lab and
Field Findings
Deployment
Aspects
Activation,
Configuration Examples,
Fault Mgmt, Trial Area
Performance
Aspects
Counters and KPIs,
Feature Impact Analysis
and Verification
For internal use
Configuration
Management
Parameters and
Parameterization
Scenarios

Introduction
Table of contents
For internal use

Disclaimer
For internal use
It is recommended to have a basic understanding of
PRACH management before going through this material.

Introduction
Random Access Procedure – Initial Access (example: contention based)
For internal use
Random Access Procedure is used:
- to get access to the services (C-RNTI),
- to align timing advance,
- followed by synchronisation, etc.
Before sending Preamble UE must synchronise
and must know where/what/how to transmit.
These informations are provided by MIB and SIB2.
eNodeB
UE
Synchronisation, Information Blocks
Random Access Preamble
Random Access Response
Scheduled Transmission
Contention Resolution
Random Access Procedure
RACH
RRC Connection Establishment
SIBs are broadcasted by eNB
SIB1
SIB2
SIB7
SIB6 SIB8
MIB
SIB3
SIB5

Introduction
System Information Broadcast
Master Information Block
System Information Block Type 1
reading
reading
allows the UE to read
allows the UE to read
Parameters essential for a UE’s
initial access to the network
Information about
scheduling of other SIBs
SIB2:
PRACH/RACH
configuration

Introduction
SIB2 – Common and Shared channel configuration
contains radio resource configuration
information that is common for all UEs.
Without SIB2 UE is not able to initiate
ATTACH procedure.
Barring factor
Barring time
Barring for special AC
t300
t301
t310
n310
t311
n311
RACH , BCCH, PCCH,
PRACH, PDSCH, PUSCH,
PUCCH, SRS UL,
UL power control
Parameters
UL carrier freq
UL bandwidth
Access class
barring
information
UE Timers and
constants
Frequency info Radio resource
configuration
SIB2 transmission is
mandatory in each cell
Preamble Initial Received
Target Power

Introduction
Random Access Procedure – power ramping scheme
For internal use
Power ramping is used if Random Access
procedure cannot be finished successfully in
initial step and if UE is not already using full
power.
With the each retransmission Preamble
power is increased by power increment
step (prachPwrRamp).
When the maximum number of
retransmissions is reached (preambTxMx)
and Random Access procedure is still not
succesfull, radio link failure can be detected.
eNodeB
UE
Random Access Preamble
RACH
ulpcIniPrePwr
raRespWinSize

Introduction
Preamble Initial Received Target Power
For internal use
Preamble Initial Received Target Power:
ulpcIniPrePwr (LNCEL) is the parameter
indicating Random Access preamble
signal level targeted at eNodeB side.
This parameter is used to calculate UE
output power for sending preamble
during the Random Access procedure:
Preamble Initial Received Target Power principle
 
Pathloss
Power
Target
Received
Preamble
,
min max 
 P
PPRACH
where:
PPRACH – power used by UE to send preamble
Pmax – UE maximum output power
UE
eNodeB
PL = Pathloss

Introduction
LTE1235 principle
For internal use
The idea behind LTE1235 feature is to adapt
PRACH/RACH power in the network autonomously
based on real network feedback to overcome the
interference in the cell.
With this feature enabled the Preamble Initial
Received Target Power is set just high enough to
allow UEs to access the cell with one preamble
transmission while keeping the RACH interference
generated to a minimum.
The feature optimizes PRACH power to ensure that:
• power is as low as possible for low interference,
• power is high enough to avoid unnecessary
retransmissions.
PRACH
power INTERFERENCE
RETRANSMISSION
Principle of PRACH target power
Target
Power
SUCCESS

Introduction
LTE1235 general procedure
For internal use
Optimization of PRACH/RACH power algorithm:
1) Received Interference Power (RIP) measurements are
collected by eNodeB.
2) PRACH power update (increase or decrease) is triggered if the
average RIP value changes by more than a configurable delta
(ulpcRachTgtPwrDelta) .
3) The PRACH power value is set an offset above the average RIP
value (ulpcRachPwrRipOffset).
4) SIB2 update is sent when RACH preamble power settings are
changed.
5) SIB update rate is monitored to check if SIB update rate is
being exceeded (sibUpdateRateThreshold). Principle of PRACH target power
time
RIP
Preamble
Initial
Received
Target
Power
BEFORE
update
AFTER
update
offset
delta
target
value

Introduction
LTE1235 procedure constraints
For internal use
3) The PRACH power value is set an offset above the
average RIP value (ulpcRachPwrRipOffset).
• The RACH power levels specified by LTE1235 must be
compliant with TS 36.331 (RRC spec):
preambleInitialReceivedTargetPower ENUMERATED
{dBm-120, dBm-118, dBm-116, dBm-114,
dBm-112, dBm-110, dBm-108, dBm-106,
dBm-104, dBm-102, dBm-100, dBm-98,
dBm-96, dBm-94, dBm-92, dBm-90}
PRACH power allowed values
Preamble Initial Received
Target Power
…
-90dBm
-92dBm
-94dBm
-120dBm
-118dBm
-116dBm

Introduction
LTE1235 procedure constraints
For internal use
5) SIB update rate is monitored to check if SIB update
rate is being exceeded.
• There is a limit of 31 SIB updates per 3 hours (3GPP
36.331). SIB update rate threshold is controlled by a
dedicated parameter: sibUpdateRateThreshold (LNBTS).
• When the SIB update rate is exceeded only critical SIB
updates are allowed - this applies to all features that
make SIB changes.
- For LTE1235 RACH preamble power up SIB changes
are defined as critical and will be made regardless of
the SIB update rate.
PRACH
power
Principle of SIB2 critical updates
t0 t0 +3h
1 2 3 4 31 32
DECLINED

Introduction
LTE1235 procedure monitoring
For internal use
Collection of PRACH/RACH statistics algorithm:
1) eNodeB selects the UE randomly (details in backup).
2) The RACH data is retrieved from the selected UE.
3) eNodeB determines if the UE had sufficient power to send the
RACH preamble at the power level specified by Preamble Initial
Received Target Power (ulpcIniPrePwr).
4) Respective RACH counters are updated depending if UE was
power limited or not (RACH Preamble Attempts/Collisions).
UE1
UE2
UEn
SIB2
PRE
PRE
PRE
LTE1235 principle
Results from the statistics loop can be used to tune the power optimization loop.

Introduction
PRACH power setting methods
Before
• PRACH/RACH power is fixed in a cell
• If conditions within cell change then fixed RACH power can lead
to high interference or preamble retransmissions
After
• PRACH/RACH power is adapted autonomously
• Power is low enough to limit the interference
• Power is high enough to avoid premble retransmissions
• Power limited UEs are statisticaly monitored
For internal use
PRACH
power
time
PRACH
power
time

Introduction
Dependency Table (LTE1235)
FDD LTE RL release eNodeB NetAct
Release/version FDD-LTE 16 - 16.2
TDD LTE RL release eNodeB NetAct
Release/version TD-LTE 16 - 16.2
Flexi Zone Micro
(FZM/FZP)
RL release eNodeB NetAct
Release/version FDD-LTE16/TDD-LTE16 FLF16/TLF16 16.2
HW & IOT HW requirements MME SAE GW UE Specified by 3GPP
- - - - Rel. 9 -
For internal use
Flexi Zone Controller (FZC) RL release eNodeB NetAct
Release/version FDD-LTE16/TDD-LTE16 FLC16/TLC16 16.2
BSW/ASW ASW
Sales information
Release information - macro
Release information – micro/pico/controller
Release information – general

Interdependencies
Table of contents
For internal use

does not depend on other features.
Interdependencies
prerequisites
For internal use

Benefits and Gains
Table of contents
For internal use

• With the feature enabled the network is able to automatically adapt PRACH
power to changing PRACH interference conditions (ex. due to
increase/decrease of traffic).
• The feature ensures that as the interference goes down the RACH power will
be decreased so that the UE preamble transmissions will not cause unnecessary
interference in adjoining cells.
• With the feature enabled, there is no need to manually tune the ulpcIniPrePwr
parameter to achieve the optimal preamble power setting per cell.
• With the feature enabled PRACH interference into neighboring cells are
minimised.
Benefits and Gains
For internal use

Configuration
Management
Table of contents
For internal use

Definition of terms and rules for parameter classification*
* - purpose: categories of parameters have been defined to simplify network parameterization. Parameterization effort shall be focused mainly on parameters included in basic
category. Categorization is reflected in a ‘view’ definition in NetAct CM Editor (released in RL60) i.e. parameters will be displayed according to the category: either in the ‘Basic
parameters’ view or the ‘Advanced parameters’ view.
Configuration Management
The ‘Basic Parameters’ category contains
primary parameters which should be considered
during cell deployment and must be adjusted to
a particular scenario:
• Network Element (NE) identifiers
• Planning parameters, e.g. neighbour definitions, frequency,
scrambling codes, PCI, RA preambles
• Parameters that are the outcome from dimensioning, i.e. basic
parameters defining amount of resources
• Basic parameters activating basic functionalities, e.g. power
control, admission control, handovers
• Parameters defining operators’ strategy, e.g. traffic steering,
thresholds for power control, handovers, cell reselections, basic
parameters defining feature behaviour
The ‘Advanced Parameters’ category contains
the parameters for network optimisation and
fine tuning:
• Decent network performance should be achieved without tuning
these parameters
• Universal defaults ensuring decent network performance need
to be defined for all parameters of this category. If this is not
possible for a given parameter it must be put to the ‘Basic
Parameters’ category
• Parameters requiring detailed system knowledge and broad
experience unless rules for the ‘Basic Parameters’ category are
violated
• All parameters (even without defaults, e.g. optional structures)
related to advanced and very complex features
For internal use

New parameters
Abbreviated name Full name PKDB link
LNCEL: actUlpcRachPwrCtrl
Activate RACH preamble power
control
For internal use

New parameters
LNBTS: sibUpdateRateThreshold SIB update rate threshold
LNBTS: ulpcRachPwrRipOffset
RACH preamble interference power
offset
LNBTS: ulpcRachTgtPwrDelta RACH preamble target power delta
For internal use

Related parameters
LNCEL: ulpcIniPrePwr
Preamble initial received target
power
For internal use

Deployment
Aspects
Network graphic boxes Network element boxes
Table of contents
For internal use

LTE1235 feature activation:
• Set cell-level feature activation flag actUlpcRachPwrCtrl to ’true’.
• Set the optimization parameters on eNB-level in order to support a dynamic adjustment of
the preamble power:
- ulpcRachTgtPwrDelta (default=3dB): to define the delta between newly calculated
preamble power and current preamble power required to change RACH preamble power
- ulpcRachPwrRipOffset (default=10dB): to define the dB offset that is applied to the RIP
average when calculating the new RACH preamble power value
- sibUpdateRateThreshold (default=25): to define a threshold for the SIB update rate. If
this threshold is exceeded, non-critical SIB updates will be blocked.
Deployment Aspects
For internal use

Deployment Aspects
For internal use
STEP1:
set activation flag on a
LNCEL level for each and
every cell the feature
needs to be active
Using Site Manager – refer to backup.

Deployment Aspects
For internal use
STEP2:
set PRACH delta/offset
on a LNBTS level – the
same values apply for all
cells

Deployment Aspects
For internal use
STEP3:
set SIB update rate
threshold if required

Performance
Aspects
Table of contents
For internal use

Performance Aspects
New counters/KPIs
Feature LTE1235 introduces 6 new counters and new KPIs
Counter name Description
RACH_ONE_PREAMBLE_SUCC
(M8005C340)
#LTE Power and Quality UL
This measurement provides the total number of sampled UEs that satisfies the
following conditions:
- UE is a "non-power limited" UE.
- with RACH "contentionDetected" IE equal to "false"
- with RACH success after one preamble transmission
Trigger event: This counter will be updated for the sampled UE when the value of
the IE field is "numberOfPreamblesSent = 1" in the "UEInformationReport".
Granularity: 500ms
KPI: LTE_5820a The KPI indicates the total number of sampled UEs that fulfill the above
mentioned conditions.

Performance Aspects
New counters/KPIs
RACH_RETX_PREAMBLE_SUCC
(M8005C341)
- UE is a "non-power limited" UE.
- with RACH success after more than one transmission of the preamble
the IE field is "numberOfPreamblesSent > 1" in the "UEInformationReport".
Granularity: 500ms

Performance Aspects
New counters/KPIs
RACH_ALL_ONE_PREAMBLE_SUC
C
(M8005C342)
- UE is either a "non-power limited" or a "power limited" UE.
- with RACH success after one preamble transmission
the IE field is "numberOfPreamblesSent = 1" in the "UEInformationReport".
Granularity: 500ms

Performance Aspects
New counters/KPIs
RACH_ALL_RETX_PREAMBLE_SU
CC
(M8005C343)
- UE is either a "non-power limited" or a "power limited" UE
- with RACH success after more than one transmission of the preamble
the IE field is "numberOfPreamblesSent > 1" in the "UEInformationReport".
Granularity: 500ms

Performance Aspects
New counters/KPIs
RACH_PREAMBLE_COLLISIONS
(M8005C344)
This measurement provides the total number of sampled UEs (both non-power
limited and power limited UEs) that experienced preamble contention.
the IE field is "contentionDetected = true" in the "UEInformationReport", which
indicates that UEs experience a preamble contention.
Granularity: 500ms

Performance Aspects
New counters/KPIs
RACH_TARGET_PREAMBLE_PWR
(M8005C345)
This measurement provides the value of RACH initial preamble target power at
the end of each statistics interval.
Trigger event: This counter will be updated every second and at the end of the
measurement interval, this counter provides the last value, which is equal to the
SIB2 "preambleInitialReceivedTargetPower".
Granularity: 1 sec
KPI: LTE_5831a The KPI indicates the value of RACH initial preamble target power at the end of
each measurement period interval (the last value).

Performance Aspects
New KPIs
KPI name Description
Number of power limited UEs
with RACH success within 1st
preamble
LTE_5824a
The KPI indicates the total number of sampled UEs that fulfill the following
conditions: UE is power limited, IE "contentionDetected" is equal to "false", IE
"numberOfPreamblesSent" is equal to "1" in the "UEInformationReport:".
Number of power limited UEs
with RACH success for preamble
re-transmission
LTE_5825a
The KPI indicates the total number of sampled UEs that fulfill the following
conditions: UE is power limited, IE "contentionDetected" is equal to "false", IE
"numberOfPreamblesSent" is greater than "1" in the "UEInformationReport:".
LTE_5824a =
sum(RACH_ALL_ONE_PREAMBLE_SUCC) -
sum(RACH_ONE_PREAMBLE_SUCC)
LTE_5825a =
sum(RACH_ALL_RETX_PREAMBLE_SUCC) -
sum(RACH_RETX_PREAMBLE_SUCC)

Performance Aspects
New KPIs
Preamble re-transmission ratio
for power limited UEs
LTE_5828a
The KPI indicates ratio of preamble retransmission for power limited UEs to all
transmissions and retransmissions for total number of UEs.
Preamble re-transmission ratio
for non-power limited UEs
LTE_5830a
The KPI indicates ratio of preamble retransmission for non-power limited UEs to
all transmissions and retransmissions for total number of UEs.
LTE_5828a =
sum(RACH_ALL_RETX_PREAMBLE_SUCC) –
sum(RACH_ALL_ONE_PREAMBLE_SUCC) +
sum(RACH_ALL_RETX_PREAMBLE_SUCC)
×100%
LTE_5830a =
×100%

Performance Aspects
New KPIs
Preamble transmission ratio
within 1st preamble for power
limited UEs
LTE_5827a
The KPI indicates ratio of preamble transmission within 1st preamble for power
limited UEs to all transmissions and retransmissions for total number of UEs.
Preamble transmission ratio
within 1st preamble for non-
power limited UEs
LTE_5829a
The KPI indicates ratio of preamble transmission within 1st preamble for non-
power limited UEs to all transmissions and retransmissions for total number of
UEs.
LTE_5827a =
sum(RACH_ALL_ONE_PREAMBLE_SUCC) –
×100%
LTE_5829a =
×100%

Performance Aspects
New KPIs
Total UE RACH preamble
contention collision ratio
LTE_5832a
The KPI indicates the contention collision ratio of all UEs during RACH procedure
to the total number of UEs for all successful RACH transmissions.
Total UE RACH preamble
contention-free ratio
LTE_5833a
The KPI indicates the contention-free ratio of all UEs during RACH procedure to
the total number of UEs for all successful RACH transmissions.
LTE_5832a =
sum(RACH_PREAMBLE_COLLISIONS)
×100%
LTE_5833a =
sum(RACH_PREAMBLE_COLLISIONS)
×100%
(1 - )

For internal use

Backup
For internal use

Backup
LTE1235 procedure monitoring – random UE selection
For internal use
1) eNodeB selects the UE randomly.
UE1
UE2
UEn
SIB2
PRE
PRE
PRE
LTE1235 principle
One single UE is selected each 500ms.
The following conditions must be fullfilled:
· Fixed 500ms timer is running and during current sampling interval no
connection for rach reporting was selected yet,
· UE is capable of sending rach-Report,
· UE is establishing in the cell connection either for:
· new RRC Connection Request following by Initial Context Setup;
· incoming X2/S1 HO;
· intra eNB inter cell HO;
· intra cell HO;
· The eNodeB doesn't process for this UE any RRC Measurement Report for
Event A3/A5/B2/A4 or Event A2 for RRC Connection release with redirect.
If all above conditions are fullfilled, the eNodeB shall start UE Information
procedure sending the message RRC UEInformationRequest to the UE to
request the UE to send the rach-Report.
Back to introduction.

Backup
For internal use
STEP1:
set activation flag on a
LNCEL level for each and
every cell the feature
needs to be active

Backup
For internal use
STEP2:
create ’Optimize RACH
Power’ object under LNBTS

Backup
For internal use
STEP3:
set PRACH delta/offset
on a LNBTS level – the
same values apply for all
cells

Backup
For internal use
STEP4:
set SIB update rate
threshold if required

NEI_LTE1235_ready_02.pdf

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