Sprint 4G
Sprint 4G LTE Troubleshooting and Optimization Guidelines
Document Version 2.0
4G National RF Engineering
The information contained in this document is proprietary and
confidential to Sprint and is intended solely for internal use by
Sprint employees. Any unauthorized distribution of this information
without the written consent of Sprint is strictly prohibited.
Revisions and Contributions
OrganizationName
Network EngineeringGreg OConnor
Network Engineering (Dir)Hui-Lin Chang
Network Engineering (Mgr)Rashmi Kumar
AuthorVersionDateE-mail Address
Geoff Lubeskie1.0November [email protected]
Geoff Lubeskie2.0January [email protected]
Table of Contents
1General41.1Purpose41.2Responsibility41.3Revision History42LTE
Optimization Process Flows52.1Site Level Optimization52.2Cluster
Level Optimization62.3Market level Optimization73RF
Conditions83.1RSRP83.2SINR84Cell Selection94.1Cell Selection
Process94.2Cell Selection Criteria94.3Cell
Reselection105Interference Control126LTE Handoff
Optimization136.1Active mode handover136.2Idle mode
handover167EUTRAN and CDMA2000 Handover168RAN
Parameters208.1Physical Cell Identity208.2Root Sequence Index
(RSI)20
LTE Troubleshooting / Optimization Guidelines1
Privileged & Confidential InformationThis information is
subject to Sprint policies regarding use and is the property of
Sprint and/or its relevant affiliates and may contain restricted,
confidential or privileged materials intended for the sole use of
the intended recipient. Any review, use, distribution or disclosure
is prohibited without authorization221. General
2.1 PurposeThe purpose of this document is to provide national
and local RF guidelines to troubleshoot and optimize Sprints 4G
Network. This document will be used by Sprint RF Engineering to
understand high level network performance metrics.
2.2 Responsibility
The 4G National RF Performance Engineering team is responsible
for updating, and monitoring the application of the guidelines
described in this document. Please contact the following, if there
are questions regarding these planning guidelines.
Geoff Lubeskie, National RF Planning and Engineering
(717-344-1869)[email protected]
Dusty Wyman (703-376-4463) Manager RF Planning and
[email protected]
Rashmi Kumar (703-433-4358) Manager RF Planning and
[email protected]
2.3 Revision History
DateVersionDocument OwnerComments
11/15/20131.0Geoff LubeskieOriginal document (1st Draft)
3 4 LTE Optimization Process Flows
LTE troubleshooting / optimization activities can be separated
into 3 distinct levels: Site Level Cluster Level Market Level
At the very start, eNBs are the foundation of all LTE Networks.
Contiguous groups of eNBs form clusters and groups of clusters make
up the markets.
Figure 1: Network Optimization Flowchart2.1 Site Level
Optimization
Single site verification, the first phase of network
optimization, involves function verification at each new site.
Single site verification aims to ensure that each site is properly
installed and that parameters are correctly configured according to
the Golden Image (GI). A link to the latest GI for all OEMS can be
found at the link below.
http://sprintcommunities.corp.sprint.com/sites/cops/4GRFPerformance/Parameter%20Management/Forms/AllItems.aspx?RootFolder=%2Fsites%2Fcops%2F4GRFPerformance%2FParameter%20Management%2FGolden%20Parameters%2FGolden%20Params
Key Performance Indicators (KPIs) ensure each site is performing
as it should be. At the very minimum the engineer should validate
and analyze the following metrics to ensure that the eNB is
performing as it should be. It should be mentioned that each OEM
has their own specific targets for each KPI and should be
referenced when analyzing the data.
Average & Peak download Throughput Average & Peak upload
Throughput Intra eNB handovers (between sectors) Inter eNB
handovers to first tier neighbors Connection setup time &
Connection success rate Latency Validate RSRP, CINR, Rx Power, and
Tx Power are as expected for the test location
2.2 Cluster Level Optimization
Contiguous coverage between eNBs within a cluster ensures
seamless mobility; therefore, this optimization activity is a major
factor in overall network accessibility and retainability.
As of the writing of this documentation there is no baseline of
the Sprint LTE network. It is imperative that when the OEMs submit
clusters for acceptance that the local RF teams are involved. Local
RF teams should create MapInfo files for each cluster, which show
areas for future optimization.
Figure 2: Mapinfo file created by local RF showing areas for
future optimization
A cluster drive route must be carefully designed to cover each
sector of all sites so that all major highways, roads, Sprint
stores and major customer locations are covered. Analysis of the
drive data will show areas for potential optimization changes to
improve the overall user experience. All changes made during the
optimization phase should be documented for future reference and
possibly shared with other markets as a means of best practice.
A major challenge that the engineer will face is the fact that
the 4G and 3G networks are using the same antenna. At this time,
voice is still the number one revenue source for Sprint; therefore,
optimization efforts on the 4G sites should not negatively impact
the underlying 3G network.
As in Site level optimization at the very minimum the engineer
should verify the following KPIs during Cluster Optimization
Average & Peak download Throughput Average & Peak upload
Throughput Intra eNB handovers (between sectors) Inter eNB
handovers to first tier neighbors Connection setup time &
Connection success rate Latency Validate RSRP, CINR, Rx Power, and
Tx Power are as expected for the test location
2.3 Market level Optimization
Similar to cluster level optimization, multiple subsets are
looked at as a whole. Here, several clusters should be evaluated
and analyzed as a whole to verify that mobility and proper
networking exists. The on-going evolution of the network due to the
addition of new macro, micro, Pico and in-building sites requires
that the engineer continuously look at optimizing the network to
meet the demands of capacity, and customer expectations.
3 RF Conditions3.1 RSRP
Reference signal received power (RSRP), is determined for a
considered cell as the linear average over the power contributions
(in [W]) of the resource elements that carry cell-specific
reference signals within the considered measurement frequency
bandwidth.
Note: Different from GSM or TD-SCDMA systems, TD-LTE systems
have multiple subcarriers multiplexed. Therefore, the measured
pilot signal strength is the RSRP of a single subcarrier (15 kHz)
not the total bandwidth power of the frequency.
If receiver diversity is in use by the UE, the reported value
shall not be lower than the corresponding RSRP of any of the
individual diversity branches
The RSRPs near a cell, in the middle of a cell, and at the edge
of a cell are determined based on the distribution of signals on
the entire network. Generally, the RSRP near a cell is -85 dBm, the
RSRP in the middle of a cell is -95 dBm, and the RSRP at the edge
of a cell is -105 dBm.
3.2 SINR
The SINR is not specifically defined in 3GPP specifications. A
common formula is as follows: SINR = S/(I + N)
S: indicates the power of measured usable signals. Reference
signals (RS) and physical downlink shared channels (PDSCHs) are
mainly involved.
I: indicates the power of measured signals or channel
interference signals from other cells in the current system and
from inter-RAT cells. N: indicates background noise, which is
related to measurement bandwidths and receiver noise coefficients.4
Cell Selection
The cell selection process and cell selection criteria as per
3GPP standard 36.304 are: 4.1 Cell Selection Process
The UE shall use one of the following two cell selection
procedures:
1. Initial Cell SelectionThis procedure requires no prior
knowledge of which RF channels are E-UTRA carriers. The UE shall
scan all RF channels in the E-UTRA bands according to its
capabilities to find a suitable cell. On each carrier frequency,
the UE need only search for the strongest cell. Once a suitable
cell is found this cell shall be selected.
2. Stored Information Cell SelectionThis procedure requires
stored information of carrier frequencies and optionally also
information on cell parameters, from previously received
measurement control information elements or from previously
detected cells. Once the UE has found a suitable cell the UE shall
select it. If no suitable cell is found the Initial Cell Selection
procedure shall be started.
NOTE: Priorities between different RAT or frequencies provided
to the UE by system information or dedicated signaling are not used
in the cell selection process.
4.2 Cell Selection Criteria
The cell selection criterion S is fulfilled when:Srxlev >
0Where:Srxlev = Qrxlevmeas (Qrxlevmin Qrxlevminoffset)
-PcompensationWhere:The signaled value QrxlevminOffset is only
applied when a cell is evaluated for cell selection as a result of
a periodic search for a higher priority PLMN while camped normally
in a VPLMN [5]. During this periodic search for higher priority
PLMN the UE may check the S criteria of a cell using parameter
values stored from a different cell of this higher priority
PLMN.Srxlev Cell Selection RX level value (dB)Qrxlevmeas Measured
cell RX level value (RSRP).Qrxlevmin Minimum required RX level in
thecell (dBm)Qrxlevminoffset Offset to the signalled Qrxlevmin
taken into account in the Srxlevevaluation as a result of a
periodic search for a higher priority PLMNwhile camped normally in
a VPLMN [5]Pcompensation [FFS]
4.3 Cell Reselection
Cell reselection parameters are broadcast in system information
and are read from the serving cell as follows:
Qoffsets,nThis specifies the offset between the two cells.
QoffsetfrequencyFrequency specific offset for equal priority
E-UTRAN frequencies.
QhystThis specifies the hysteresis value for ranking
criteria.
QrxlevminThis specifies the minimum required Rx level in the
cell in dBm.
TreselectionRATThis specifies the cell reselection timer value.
For each target RAT a specific value for the cell reselection timer
isdefined, which is applicable when evaluating reselection within
E-UTRAN or towards other RAT (i.e. TreselectionRATfor E-UTRAN is
TreselectionEUTRAN, for UTRAN TreselectionUTRAN for GERAN
TreselectionGERAN, forTreselectionCDMA_HRPD, and for
TreselectionCDMA_1xRTT).Note: TreselectionRAT is not sent on system
information, but used in reselection rules by the UE for each
RAT.
TreselectionEUTRANThis specifies the cell reselection timer
value TreselectionRAT forE-UTRAN
TreselectionUTRANThis specifies the cell reselection timer value
TreselectionRAT for UTRAN
TreselectionGERANThis specifies the cell reselection timer value
TreselectionRAT for GERAN
TreselectionCDMA_HRPDThis specifies the cell reselection timer
value TreselectionRAT for CDMA HRPD
TreselectionCDMA_1xRTTThis specifies the cell reselection timer
value TreselectionRAT for CDMA 1xRTT
Threshx, highThis specifies the threshold used by the UE when
reselecting towards the higher priority frequencyX than
currentlyserving frequency. Each frequency of E-UTRAN and UTRAN,
each band of GERAN, each band class of CDMA2000HRPD and CDMA2000
1xRTT will have a specific threshold.
Threshx, lowThis specifies the threshold used in reselection
towards frequencyX priority from a higher priority frequency.
Eachfrequency of E-UTRAN and UTRAN, each band of GERAN, each band
class of CDMA2000 HRPD and CDMA20001xRTT will have a specific
threshold.
Threshserving, lowThis specifies the threshold for serving
frequency used in reselection evaluation towards lower priority
E-UTRANfrequency or RAT.
SintrasearchThis specifies the threshold (in dB) for intra
frequency measurements.
SnonintrasearchThis specifies the threshold (in dB) for EUTRAN
inter-frequency and inter-RAT measurements.
TCRmaxThis specifies the duration for evaluating allowed amount
of cell reselection(s).
NCR_MThis specifies the maximum number of cell reselections to
enter medium mobility state.
NCR_HThis specifies the maximum number of cell reselections to
enter high mobility state.
TCRmaxHystThis specifies the additional time period before the
UE can enter normal-mobility.
5 Interference Control
Downlink (DL) inter cell interference which reduces the signal
quality is a major factor contributing to degraded service. It
usually impacts cell-edge users which lack good quality RF signal
due to the presence of multiple serving sectors of similar signal
strength. DL inter-cell interference scenario can also be observed
in dense urban areas where multipath factor can results in strong
signals from various sectors in one geographic region. DL
interference if not corrected can lead to poor throughput
performance on both downlink and uplink. Therefore an improved DL
coverage in terms of both signal strength and quality provides
better user experience.
Indicators such as low Signal to noise ratio (SINR), low scale
Channel quality indicator (CQI), Transmission mode (transmit
diversity), low Reference Signal Received Quality (RSRQ) and high
Block error rate (BLER) are common indicators of DL interference.
Low SINR and low CQI reports result in lower and more robust
modulation scheme for data transmission. The first step in
optimization efforts is to improve the coverage and quality of
existing serving cells resulting in good quality of service
(QoS).
RSRQ is defined in TS 36.214 as:
Reference Signal Received Quality (RSRQ) is defined as the ratio
NRSRP/(E-UTRA carrier RSSI), where N is the number of RBs of the
E-UTRA carrier RSSI measurement bandwidth. The measurements in the
numerator and denominator shall be made over the same set of
resource blocks.
E-UTRA Carrier Received Signal Strength Indicator (RSSI),
comprises the linear average of the total received power (in [W])
observed only in OFDM symbols containing reference symbols for
antenna port 0, in the measurement bandwidth, over N number of
resource blocks by the UE from all sources, including co-channel
serving and non-serving cells, adjacent channel interference,
thermal noise etc.
The reference point for the RSRQ shall be the antenna connector
of the UE.
If receiver diversity is in use by the UE, the reported value
shall not be lower than the corresponding RSRQ of any of the
individual diversity branches.
Other than general optimization practices to control
interference, LTE also offers features such as Inter cell
Interference Coordination (ICIC) technique which dynamically
controls interference based on UEs CQI reports.
Downlink ICIC (DL-ICIC) enhances cell-edge UE performance by
adjusting the power for UE based on reported channel condition.
Cell center users get different power allocation based on UEs
feedback.
Average CQI Threshold metric is used to differentiate cell edge
and cell center users. DL power control mechanism uses the channel
estimation to adjust the Pa parameter which leads to: If the user
is estimated to be in cell center condition, UE specific DL power
related parameter Pa is lowered, which results in power reduction
of data subcarriers for that UE and further decreases interference
to neighboring cells
If UE is estimated to be in cell center condition, Pa is
increased and hence data subcarriers power is increased to maintain
edge UEs quality
6 LTE Handoff Optimization
Handover success rate is another important KPI focused on in
optimization process. Having a good success rate indicates that
sites in network connect to each and user can enjoy uninterrupted
access to network in mobility scenarios. The impact of LTE handover
performance depends on what type of applications users are running
at their end. For example, poor handover performance or high
handover latency have low impact on applications such as file
transfer where a small interruption can be tolerable whereas bad
handover performance may have severe impact on VOIP applications
where a handover drop results in voice call drop.
6.1 Active mode handover
Active mode handover can be of three different types:
1. Intra/Inter Frequency Handover between cells using sane or
different center frequencies 2. Intra/Inter eNB Handover between
cells of the same or different site 3. S1/X2 based Handover
involving MME interaction or directly between two eNBs using X2
links
UE can be configured in connected state to report several
different types of measurements based on event types as explained
below.
Event A1 Serving becomes better than a threshold Used to
deactivate Gap Measurements
Event A2 Serving becomes worse than a threshold Used to activate
Gap Measurements
Event A3 Neighbor becomes offset better than the Serving Used to
trigger Intra-FA Handoff
Event A4 Neighbor becomes better than a threshold Used for
ANR
Next section discusses the configuration related to Event A3
which is used to facilitate Intra-FA LTE handover.
In active mode measurements are performed only when Serving Cell
RSRP falls below a configurable threshold (Smeasure) The A3 event
parameters for Active mode measurement are transmitted via RRC
Connection Reconfiguration Message The parameter a3offsetdefines
the (neighbor + offset > serving) criteria. Additionally, there
is a cell individual offset that can be configured per neighbor
(Ind_offset). This criterion must be satisfied over a configurable
period of time for the measurement report to be done
(TimeToTrigger). The measurement criteria can be based on RSRP or
RSRQ and is configurable (TriggerQuantity). The measurement report
can be configured to report RSRP/RSRQ or both (ReportQuantity).
Periodic reports can be generated after the Event criteria are met
based on a configurable parameter (reportInterval). Number of
reports generated based on the event is controlled using a
configurable parameter (reportAmount)
6.2 Idle mode handover
Idle mode handover or cell reselection is the process used by UE
and network to monitor UEs location without it requiring radio
resources. In Idle mode, UE remains attached at MME level but
remains RRC idle unless it requires RRC resources (for e.g. To
perform TAU or Paging procedures)
Maintaining most current and updated neighbor list on the eNBs
is critical to facilitate successful handover. Neighbor list must
be updated frequently to accommodate addition of new sites and
sectors in the network.
Condition where multiple handovers are recorded within a very
short period between same two cells in stationary or mobile
scenario is known as Ping-Pong. Ping-Pong condition affects the end
user as more processing time results in poor user experience. This
situation arises when both source and target sectors meet the
handover thresholds and are equivalent in signal strength.
Ping-Pong can occur in both strong and weak conditions. A3 offset,
S-measure, Hysteresis and Cell individual offset are some
parameters which can be tweaked to reduce Ping-Pong rate.
7 EUTRAN and CDMA2000 Handover
EUTRAN and CDMA2000 handover can be useful when both networks
are overlaid on same geographical region. A user traveling out of
LTE coverage area can hand down to HRPD while maintaining the same
data session and uninterrupted data transfer. This feature is
helpful in cases where a new LTE network is deployed on a matured
CDMA2000 network and UE can rely on underlying network whenever it
goes out of coverage on LTE
Implementation of Neighbor list for underlying CDMA network is
needed to facilitate EUTRAN to CDMA2000 handover. On LTE side,
appropriate neighboring sectors with PN and channel information are
populated. Right HRPD neighbors can be selected based statistics
such as Handover matrix (HOM) data of CDMA network. Optimization
drive test can also give useful information in defining missing or
appropriate neighbors for EUTRAN to CDMA2000 interworking.
Below table explains Parameters and Events used on EUTRAN to
CDMA2000 interworking:
MessageIEParameterDescription
RRC Connection ReconfigurationB2 Eventb2Threshold1RsrpRSRP
threshold1 used for triggering the EUTRA measurement report for
CDMA2000 HRPD Event B2.
b2Threshold1RsrqRSRQ threshold1 used for triggering the EUTRA
measurement report for CDMA2000 HRPD Event B2.
RRC Connection Reconfigurationb2Threshold2Cdma2000CDMA2000
threshold 2 used for triggering the inter-RAT CDMA2000 measurement
report for CDMA2000 HRPD Event B2.
qOffsetFreq
hysteresisB2Hysteresis applied to entry and leave condition of
CDMA2000 HRPD Event B2.
timeToTriggerB2timeToTrigger value for CDMA2000 HRPD Event B2.
The timeToTrigger value is the period of time that must be met for
the UE to trigger a measurement report.
reportIntervalB2The reporting interval of a measurement report
for CDMA2000 HRPD Event B2.
reportAmountB2The number of measurement reports for CDMA2000
HRPD Event B2.
maxReportCellsB2The maximum number of cells included in a
measurement report for CDMA2000 HRPD Event B2.
triggerQuantityB2Quantity that triggers the Event B2 measurement
The trigger can be set for either RSRP or RSRQ and is only
applicable on threshold 1.
RRC Connection ReconfigurationA2 Eventa2ThresholdRsrpA2 event is
triggered when source becomes worse than the configured RSRP
threshold (Refer to standard 36.133 for RSRP Report mapping)
a2ThresholdRsrqPrimary RSRQ threshold value for eventA2. Used
only when triggerQuantityA2Prim is set to RSRQ.
reportIntervalA2Determines the reporting interval of a
measurement report for Event
triggerQuantityA2A1 event is triggered when source becomes worse
than the configured RSRQ threshold (Refer to standard 36.133 for
RSRQ Report Mapping.
hysteresisA2Hysteresis applied to entry and leave conditions of
Event A2
timeToTriggerA2The timeToTrigger value is the period of time
that must be met for the UE to trigger a measurement report for
Event A2
reportAmountA2The number of reports for periodical reporting for
the primary eventA2 measurement .Value 0 means that reports are
sent as long as the event is fulfilled. Primary and secondary
measurement parameters refer to the option to use different
settings for two simultaneous measurements for eventA2.
maxReportCellsA2The maximum number of cells included in a
measurement report for Event A2.
reportQuantityA2Determines whether the Measurement report for A2
event includes both RSRP and RSRQ information or the only RSRP or
RSRQ as configured by the Trigger event above.
filterCoefficientEUtraRsrp
Filtering coefficient used by the UE to filter RSRP measurements
before event evaluation The measurement filter averages a number of
measurement report values to filter out the impact of large scale
fast fading.
filterCoefficientEUtraRsrq
Filtering coefficient used by the UE to filter RSRQ measurements
before event evaluation The measurement filter averages a number of
measurement report values to filter out the impact of large scale
fast fading.
RRC Connection Reconfiguration
A1 Event
a1ThresholdRsrp
A1 event is triggered when source becomes better than the
configured RSRP threshold ( Actual Threshold= Parameter -140,
36.133 standards) dBm
a1ThresholdRsrqA1 event is triggered when source becomes better
than the configured RSRQ threshold (Refer to 36.133 standard for
RSRP Report mapping)
triggerQuantityA1Determines whether Event A1 is triggered based
on RSRP or RSRQ criteria.
reportQuantityA1Determines whether the Measurement report for A1
event includes both RSRP and RSRQ information or the only RSRP or
RSRQ as configured by the Trigger event above.
maxReportCellsA1The maximum number of cells included in a
measurement report for Event A1.
hysteresisA1Hysteresis applied to entry and leave conditions of
Event A1.
timeToTriggerA1The timeToTrigger value is the period of time
that must be met for the UE to trigger a measurement report for
Event A1
reportIntervalA1Determines the reporting interval of a
measurement report for Event A1
reportAmountA1Determines the number of measurement reports UE
needs to send when Event A1 criteria is met
SIB8systemTimeInfotimieAndPahseSynchCritical
CellReselection Parameters CDMA 2000
bandClassIdentifies the CDMA-eHRPD frequency band class in which
the carrier frequency can be found
cellReselectionPriorityReselection priority of the cell in the
eNB. The range is 0-7, where 0 indicates low, and 7 high in
priority.
threshXHighThreshXHigh of CDMA2000 HRPD band class DB.
threshXLowThreshXLow of CDMA2000 HRPD band class DB.
tReselectionSfUsageHRPDWhether to use tReselectionSfUsageHRPD of
HRPD reselection information that is sent down to SIB8.
tReselectionSfUsageHRPD determines whether to apply a scaling
factor for HRPD cell reselection.
tReselectionHRPDTReselctionHRPD included in the HRPD Reselection
information sent to SIB8. The default is 0, and can be changed by
the operator.
tReselectionSfHighHRPDValue by which parameter
tReselectionCdmaHrpd is multiplied if the UE is in a high mobility
state as defined in 3GPP TS 36.304
tReselectionSfMediumHRPDTReselectionSfMediumHRPD included in the
HRPD Reselection information sent to SIB8.
searchWindowSizeThe size of the search window in the eNB.
8 RAN Parameters
8.1 Physical Cell IdentityPCI is derived from two physical layer
signals Primary Synchronization Signal (PSS) and Secondary
synchronization signal (SSS). There are 504 unique PCIs. The
physical-layer cell identities are grouped into 168 unique
physical-layer cell-identity groups, each group containing three
unique identities. The grouping is such that each physical-layer
cell identity is part of one and only one physical-layer
cell-identity group. A physical-layer cell identity is thus
uniquely defined by a number in the range of 0 to 167, representing
the physical-layer cell-identity group, and a number in the range
of 0 to 2, representing the physical-layer identity within the
physical-layer cell-identity group.(2) ID (1) ID cell ID 3N N N (1)
ID N (2) ID N
Each cells Reference signal transmits a pseudo random sequence
corresponding to assigned PCI. And channel quality measurements are
also made on reference signals. Thus, an optimized allocation of
PCIs is needed to avoid problems in cell recognition or cell
search. During PCI planning, one needs to avoid same PCI and PSS on
neighboring cell. This eliminates confusion in cell search and also
reduces interference which can occur due to PSS or reference signal
collision.
8.2 Root Sequence Index (RSI)
The Preambles used in RACH procedure are derived from Root
Sequence. Preambles are obtained by cyclic shifts of root sequence
which are based on Zadoff-Chu sequence. There are 838 Root
Sequences available. There are 64 preambles available per cell and
UE randomly selects one preamble to perform random access
procedure. If number of preambles per root sequence is less than 64
Preambles, continue deriving Preambles with next Root Sequence unit
64 preambles are obtained.Thus, unique assignment of Root sequence
is recommended between neighboring cells. The Below tables
describes Ncs to Zero Correlation zone configuration mapping and
LSM parameter for configuring RSI and Zero correlation zone
configuration parameter.
9 References
https://Systems.samsungwireless.comNetwork Vision >
Publications > Sprint > 4G RAN > Manuals 430 LTE eNB
Maintenance Troubleshooting Manual410 MMBS Operational Manual819
LTE Optimization Guidelines
LTE standard documents: 3GPP TS 36 series
LTE optimization guidelines Huawei Technologies
LTE Optimization Guidelines Anritsu
