Lte coverage optimization analysis

LTE Coverage Optimization
Analysis

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ZTE Confidential Proprietary © 2016 ZTE CORPORATION. All rights reserved. III
Contents
1 COVERAGE PROBLEMS AND OPTIMIZATION SIGNIFICANCE ..................................... 1
1.1 CAUSES OF COVERAGE PROBLEMS.................................................................... 1
1.2 COVERAGE OPTIMIZATION CONTENTS ............................................................... 2
2 COVERAGE KPI DESCRIPTIONS AND ANALYSIS.......................................................... 3
2.1 RSRP DESCRIPTIONS ............................................................................................ 3
2.2 RS SINR DESCRIPTIONS........................................................................................ 4
2.3 RSRQ DESCRIPTIONS ............................................................................................ 4
2.4 COVERAGE OPTIMIZATION TOOLS....................................................................... 5
3 BASIC FLOW AND OPTIMIZATION PRINCIPLES OF COVERAGE OPTIMIZATION ....... 6
3.1 COVERAGE OPTIMIZATION FLOWCHART............................................................. 6
3.2 PREPARATIONS...................................................................................................... 8
3.2.1 COVERAGE OPTIMIZATION TARGET DETERMINATION ............................. 8
3.2.2 CLUSTER PARTITION .................................................................................... 9
3.2.3 ENODEB INFORMATION COLLECTION AND INFORMATION SHEET
FORMULATION............................................................................................. 10
3.2.4 ELECTRONIC MAP COLLECTION................................................................ 11
3.2.5 CHECK AND DEBUGGING OF COVERAGE OPTIMIZATION TOOLS.......... 11
3.2.6 SITE HEALTH CHECK .................................................................................. 12
3.2.7 PLANNING OF TESTING ROUTE................................................................. 12
4 DETERMINATION AND OPTIMIZATION METHODS FOR COMMON COVERAGE
PROBLEMS..................................................................................................................... 14
4.1 COMMON COVERAGE PROBLEM DETERMINATION .......................................... 14
4.1.1 DOWNLINK COVERAGE PROBLEM ANALYSIS .......................................... 14
4.1.2 UPLINK COVERAGE PROBLEM ANALYSIS ................................................ 17
4.1.3 UNBALANCED UPLINK AND DOWNLINK COVERAGE................................ 18
4.1.4 EXTERNAL INTERFERENCE PROBLEM ANALYSIS ................................... 18
4.1.5 HANDOVER PROBLEM ANALYSIS .............................................................. 19
4.1.6 ANALYSIS OF OTHER COVERAGE OPTIMIZATION PROBLEMS............... 20
4.2 COMMON COVERAGE OPTIMIZATION METHODS.............................................. 22
4.2.1 ANTENNA AND FEEDER OPTIMIZATION METHODS ................................. 22

ZTE Confidential Proprietary © 2016 ZTE CORPORATION. All rights reserved. IV
4.2.2 PARAMETER OPTIMIZATION ...................................................................... 24
A.1 ANTENNA DOWNTILT ANGLE FORMULA ............................................................ 25
A.2 DOWNTILT ANGLE CALCULATION METHODS .................................................... 27

ZTE Confidential Proprietary © 2016 ZTE CORPORATION. All rights reserved. V
Figures
Figure 2-1 Coverage Optimization Flow ....................................................................................... 7
Figure 2-2 Cluster Partition of a Project...................................................................................... 10
Figure 2-3 DT Route .................................................................................................................. 14
Tables
Table 2-1 Coverage Optimization Target Values (Reference KPIs) .............................................. 8
Table 3-1 Downlink Coverage Problems .................................................................................... 15

ZTE Confidential Proprietary © 2016 ZTE CORPORATION. All rights reserved. 1
1 Coverage Problems and Optimization
Significance
Good wireless coverage guarantees the quality and KPIs of a mobile communication
network. The FLTE network uses co-channel networking and hard handover, so
co-channel interference is great. Good coverage has a great significance for network
performance. This guide describes the workflow and cautions of LTE wireless
network coverage optimization.
1.1 Causes of Coverage Problems
There are six causes of wireless network coverage problems:
1. Wireless network planning is incorrect. Wireless network planning directly
determines the workload of subsequent coverage optimization and the optimal
performance that the network can have in the future. The correctness of wireless
network planning is determined by propagation model selection, propagation
model calibration, electronic maps, simulation parameter settings, and
simulation software, which avoid coverage problems caused by wireless
network planning and ensure that the network coverage requirements are met in
the planning phase.
2. The position of an actual eNodeB deviates from the planned position. Site
positions are planned through simulation to meet the coverage requirements. If
an actual eNodeB is not in the proper position, network coverage problems are
caused in the establishment phase.
3. The actual parameters and planning parameters are different. Because
installation is of poor quality, the actual antenna heights, azimuths, downtilt
angles, and antenna types are different from those planned, causing coverage
problems after the network is established, though the original plan meets
requirements. These problems can be solved through subsequent network
optimization, but the project cost is greatly increased.

4. The wireless environment in the coverage area is changed. One change is that
the wireless environment is changed in the network establishment procedure
and buildings are added or reduced, and this causes weak coverage or
overshoot coverage. The other change is that overshoot coverage occurs or
there is no dominant cell because of street effect and the reflection of the water
surface. To solve these problems, you can control the azimuths and downtilt
angles of antennas to avoid street effect and reduce the signal propagation
distance.
5. New coverage requirements are added. Network coverage is changed because
wider coverage is required, new eNodeBs are added, or eNodeBs are relocated.
6. With network development, users and services are increased. As a result,
network load is increased, network coverage is affected, and a cell may bear too
many users. Therefore, the network needs to be optimized as required to
improve network coverage and make the load of each cell reasonable.
During network establishment, you should take measures to improve network
coverage according to the above contents.
1.2 Coverage Optimization Contents
The main coverage optimization contents are as follows:
Downlink coverage optimization eliminates four problems of the network: coverage
holes, weak coverage, overshoot coverage, and no dominant cell. Coverage holes
can be regarded as a weak coverage problem, and overshoot coverage and no
dominant cell can be regarded as cross coverage problems. Therefore, coverage
optimization mainly includes weak coverage elimination and cross coverage
optimization.
In addition, uplink coverage problems, unbalanced uplink and downlink coverage,
interference, and handover problems must also be considered.
The coverage optimization target refers to the standard set according to the actual
network establishment to solve the above problems.

2 Coverage KPI Descriptions and Analysis
For FDD LTE, KPIs such as RSRP, RS SINR, and RSRQ are provided in drive
testing data to measure downlink coverage. SINR and RSRP are widely used, and
RSRQ is rarely used (it was found that RSRQ submitted by some terminals was
incorrect).
2.1 RSRP Descriptions
In 3GPP 36.214, Reference Signal Received Power (RSRP) is defined as the linear
average over the power contributions of the resource elements that carry cell-specific
reference signals within the considered measurement frequency bandwidth. The
measurement reference point on the UE is the antenna connector. This KPI is
measured when the UE is in the following status: RRC_IDLE intra-frequency,
RRC_IDLE inter-frequency, RRC_CONNECTED intra-frequency, and
RRC_CONNECTED inter-frequency.
Definition
Reference signal received power (RSRP), is defined 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.
For RSRP determination the cell-specific reference signals R0 according TS
36.211 [3] shall be used. If the UE can reliably detect that R1 is available it
may use R1 in addition to R0 to determine RSRP.
The reference pointfor the RSRP shall be the antenna connector of the UE.
If receiver diversity is used by the UE, the reported value shall not be lower
than the corresponding RSRP ofany of the individual diversity branches.
Applicable
to
RRC_IDLE intra-frequency
RRC_IDLE inter-frequency
RRC_CONNECTED intra-frequency
RRC_CONNECTED inter-frequency
To set RSRP on a road (antennas are placed outside the car), you should take the
shadow fading margin and penetration loss into account. The shadow fading margin
is taken into account to guarantee the wireless connection rate when shadows are
fading, and the penetration loss is taken into account to provide services for users in
buildings.

2.2 RS SINR Descriptions
RS SINR refers to the signal-to-interference-plus-noise ratio. The SINR is for
available signal power, so the SINR is equal to the Carrier-to-Noise-and-Interference
Ratio (CINR).
Besides the inter-eNodeB distance and parameters, the RS SINR is also related to
network load. Heavy network load determines a low RS SINR. If the PCI mode 3
values of a neighbor cell and the service cell are different, their RS does not overlap
in the frequency domain and does not affect each other when there is no load. When
the load of a neighbor cell is changed, the frequency domain of the RS of the local
cell may be the same as the RE position of the service channel of the neighbor cell,
and the RS SINR of the service cell is affected by the service channel of the neighbor
cell and reduced.
2.3 RSRQ Descriptions
In 3GPP 36.214, Reference Signal Received Quality (RSRQ) is defined as the ratio
N × RSRP / (E - UTRA carrier RSSI), where N is the number of RBs of the E-UTRA
carrier RSSI measurement bandwidth. E-UTRA Carrier Received Signal Strength
Indicator (RSSI), comprises the linear average of the total received power 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, and thermal noise.

Definition
Reference Signal Received Quality (RSRQ) is defined as the ratio N × RSRP /
(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 setofresource 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,and thermal noise.
The reference pointfor the RSRQ shall be the antenna connector of the UE.
If receiver diversity is used by the UE, the reported value shall not be lower than
the corresponding RSRQof any of the individual diversity branches.
Applicable
for
RRC_CONNECTED intra-frequency
RRC_CONNECTED inter-frequency
From the above definition, RSRQ is related to not only the RE power bearing RS but
also the RE power bearing user data and the interference from neighbor cells.
Therefore, RSRQ is changed with network load and interference. Heavier network
load and greater interference determine a smaller RSRQ value.
2.4 Coverage Optimization Tools
Coverage optimization tools are divided into coverage testing tools and analysis
tools.
Coverage testing tools include CNT, CXT, and other testing software. When
connecting a testing tool to a testing UE to perform the coverage test, note that:
1. Possible relationships with neighbor cells must be added before drive testing.
2. The test must be performed after the UE is connected. You can customize an
automatic and repeated download task through the testing software.
Coverage analysis tools include CAN, CXA, and other compatible analysis software.

3 Basic Flow and Optimization Principles of
Coverage Optimization
3.1 Coverage Optimization Flowchart
Coverage optimization is started once all eNodeBs are established and tested in the
planned area. Coverage optimization can be started when 80% of the eNodeBs in a
cluster are tested.
The coverage optimization phase involves preparations, data collection, problem
analysis, and adjustment implementation, see Error! Not a valid bookmark
self-reference.. According to the optimization target of the project team and the
actual situation, data collection, problem analysis, and optimization adjustment shall
be repeated until the network meets the target optimization KPIs of the project team.

Figure 3-1 Coverage Optimization Flow
Start
Preparations
1. Coverage optimization target
determination
2. Cluster partition
3. eNodeB information collection
4. Electronic map collection
5. Check and debugging of coverage
optimization tools
6. Site health check
7. Planning of the testing route
Data Collection
1. Front-end DT test
2. Indoor system test
3. Configuration data collection
4. NMS UDT data collection
Do testing indicators meet the
requirements?
Problem Analysis
1. Coverage problem analysis
2. Handover problem analysis
3. Interference problem
analysis
4. Others
Adjustment
Implementation
Complete the optimization
report and end.
Yes
No
In the test preparation phase, the target optimization KPIs must be determined
according to the contract, clusters must be assigned properly, the testing route must
be determined together with the operator, and necessary tools and materials for
coverage optimization must be ready to ensure that coverage optimization can be
implemented successfully.
In the data collection phase, DT and the indoor test are performed to collect UE data,
integrating with the call tracking data and configuration data on the located faulty
eNodeB, to get ready for the subsequent problem analysis phase.
Through data analysis, problems in the network can be found and adjustment
measures can be provided. After adjustment is finished, perform test data collection

again. If the test result does not meet the target KPIs, perform problem analysis and
adjustment again until all the KPIs are met.
After coverage optimization, the updated eNodeB information sheet containing
downtilt angles and azimuths must be output.
3.2 Preparations
This section corresponds to the first step in the above flowchart. Because many
preparations need to be done in this step and they directly affect the quality and
results of subsequent phases, this step is described separately.
3.2.1 Coverage Optimization Target Determination
The key point of coverage optimization is to solve the problems of weak coverage, no
dominant cell, and handover. However, in the actual project operation, operators'
requirements for, definitions of, and attention to KPIs are different. Therefore, the
coverage optimization target must meet the coverage and handover KPIs in the
contract (for a commercial eNodeB) or planning report (for a trial eNodeB), and KPIs
must be defined according to the contract. KPIs must be defined in the following
format: The ratio of the sampling eNodeBs where the XX (such as RSRP, SINR, and
CINR) KPI is larger than the reference value XX to the total sampling eNodeBs is
higher than X%, or is determined by the XX project team.
Through coverage optimization, the network must meet the KPIs in Table 2-1. (This
table is for reference only. Coverage assessment KPIs and KPI thresholds must be
determined together with the customer as required. It is not recommended to use the
coverage rate as an assessment KPI. The connection rate, dropped-call rate, and
rate can be used as assessment KPIs.)
Table 3-1 Coverage Optimization Target Values (Reference KPIs)
KPI Requirement Criteria
Coverage rate
Both the following two requirements must be
met:
RSRP > –105 dBm
-

SINR > 0 dB
Connection rate RRC connection rate -
FTP upload and downloadAverage throughput -
3.2.2 Cluster Partition
For the eNodeBs in a group or cluster, coverage optimization must be implemented
for them at the same time. Only in this way, the interference from co-channel
neighbor cells is taken into account during optimization. Before an eNodeB is
adjusted, the effect on adjacent eNodeBs must be analyzed in advance to prevent
them from being impacted.
Cluster partition must be determined together with the customer. During cluster
partition, the following factors must be considered:
1. According to experience, the number of clusters must be determined as
required, and a cluster can contain 15 to 25 eNodeBs.
2. You can refer to the cluster partition that the operator uses for the existing
networks.
3. Terrain factors: Different terrain has different effects on signal propagation.
Mountains hinder signal propagation and are natural borders for cluster partition.
Rivers can lead to wider radio signal propagation and have different effects on
cluster partition. For a narrow river, the mutual effects of both riversides on
signals must be considered. If transport conditions permit, eNodeBs along the
riversides should be allocated to the same cluster. For a wide river, the mutual
effects of the upstream and downstream of the river must be considered.
Because transport conditions are not good in this case, eNodeBs must be
allocated according to the river as required.
4. Clusters in a honeycomb structure are more used than strips of clusters.
5. The principle to partition clusters in administrative areas is: When the network to
be optimized covers multiple administrative areas, partitioning clusters
according to the administrative areas is a method that the customer will accept.
6. Workload of drive testing: When partitioning clusters, you must ensure that the
drive testing of each cluster can be finished within a day. It is better if drive
testing can be finished within four hours. Error! Not a valid bookmark

self-reference. shows the cluster partition of a project. JB03 and JB04 are
dense urban areas. JB01 is a highway area. JB02, JB05, JB06, and JB07 are
common urban areas. JB08 is a suburb. Each cluster contains 18 to 22
eNodeBs.
Figure 3-2 Cluster Partition of a Project
3.2.3 eNodeB Information Collection and Information Sheet Formulation
After network planning is finished and before coverage optimization is started, you
must obtain the detailed information about the eNodeBs in the network to be
optimized, including the eNodeB information sheet. This sheet contains longitudes
and latitudes of eNodeBs (cells), azimuths and downtilt angles (mechanical and
electrical downtilt angles) of antennas, PCIs, and cell IDs. The eNodeB information
sheet is a prerequisite for you to optimize the network. With this sheet, you can know
the information about all the eNodeBs in the network to be optimized, and take
precautions against possible problems. You can effectively perform the network
optimization test only after obtaining the eNodeB information sheet.
eNodeB information includes:
1. eNodeB planning information: eNodeB names, numbers, and types.
2. Wireless parameter planning information: cell IDs, PCIs, eNodeB IDs, and
TACs.

3. Onsite engineering survey information: longitudes and latitudes of eNodeBs,
and heights, azimuths, downtilt angles (mechanical and electrical downtilt
angles), and types of antennas.
4. Other information that must be paid attention to on site: shelters and adjustable
antennas and feeders. These can be added or deleted as required.
After coverage optimization is started, antennas and feeders of eNodeBs are
adjusted or even relocated and cut over as required. In this case, the eNodeB
information sheet must be updated in a timely manner.
3.2.4 Electronic Map Collection
Before coverage optimization, you must obtain electronic maps involved in the
network optimization. An electronic map refers to a visible map in TAB format, saving
geomorphology and city information and used on computers. Electronic maps play
an important role in network optimization. In addition, Google Earth is a common tool
for network optimization.
Because the formulation of electronic maps is greatly limited and electronic maps
cannot be updated in a timely manner, the existing electronic map may different from
the actual situation. You must obtain an updated paper map to correctly know the
information about the desired area, including roads and buildings. The map can be
easily bought in the local area.
3.2.5 Check and Debugging of Coverage Optimization Tools
Before coverage optimization, it is necessary to check the software tools for
coverage optimization. ZTE uses CNT (CXT), CAN (CXA), and CNO, of which the
versions must be checked to ensure that they are updated. You can know whether
the software is updated through your department platform. All patches must be
installed in a timely manner, and software licenses or dongles must be checked to
see whether they can be used. If they are unavailable or will expire soon, update
them immediately.

3.2.6 Site Health Check
Before network-wide optimization, the alarm information and troubleshooting
progress of all related eNodeBs must be obtained to find coverage problems that
cannot be solved through network optimization. The required information includes:
1. eNodeB alarm (affecting wireless performance) sheet containing alarms of the
day and historical alarms
2. Main and diversity RSSI statistics of each cell every day
3. eNodeB commissioning sheet (containing incremental information)
4. Tracking table of standing wave ratios, transmission, and eNodeB interruption
processing information, and the processing plan for the next day (in special
cases, you need to perform onsite survey on eNodeBs)
3.2.7 Planning of Testing Route
DT is the most common method to obtain network data during coverage optimization.
Therefore, the selection of the testing route directly affects the KPIs and optimization
target of DT. Before drive testing, you should determine the drive testing acceptance
route with the customer first. If the customer already has a preset route, the preset
route must be considered during the design of the testing route. If the coverage
requirements of the customer's preset testing route cannot be met because of
objective factors, such as network layout, you should explain the situation to the
customer in a timely manner.
The testing route must pass all commissioned eNodeBs in the planned area. In
addition, testing routes must include main streets, important places, and VIPs/VICs.
Main roads and highways in the testing area must also be included in testing routes.
The local driving habits must be considered in the design of the testing route. To
correctly compare performance changes, it is recommended to use the same route in
drive testing. If possible, it is necessary to perform a two-way test on the route.
Before determining the testing route, you should take the actual situation into
consideration, such as one-way streets and left turn restrictions. You can fully
communicate with a local driver or drive to determine the route, and then
communicate with the customer to determine it.

The eNodeB commissioning ratio in the area is an important factor affecting the
design of the testing route. For example, in cluster optimization, if the eNodeB
commissioning ratio is lower than 80%, the testing route must be designed to avoid
the target coverage areas of uncommissioned eNodeBs. In this way, continuous
coverage can be ensured for the testing route. In practice, drive testing data includes
the abnormal data of areas with coverage holes, and the abnormal data directly
affects the test result of coverage and service performance. The abnormal data must
be filtered out when you process and analyze drive testing data.
The testing route must be saved in tab format of MapInfo so that the same testing
route can be used in the subsequent optimization verification test. In addition, the
testing route must also be saved in the format of Google Earth so that the test result
can be analyzed through Google Earth.
The method to work out the route through Mapinfo is: Create a layer on the
map and mark the start point and end point of the test, and use lines with arrows to
indicate the test route, see Figure 3-3 DT Route
. Note that the figure is only an example. When designing a route for cluster coverage
optimization, you may need to take a two-way route into consideration.
In addition, you can export the drive testing data collected through CNT as a route
map in the format of MapInfo. During the test, use CNT to load the data so that you
can use the original testing route.

Figure 3-3 DT Route
4 Determination and Optimization Methods
for Common Coverage Problems
Coverage problem analysis is the key point and basis of cluster optimization and
focuses on signal distribution. The coverage problem analysis procedure involves
downlink dominant cell coverage analysis, uplink coverage analysis, analysis of
unbalanced uplink and downlink coverage, interference analysis, handover analysis,
and analysis of other coverage optimization problems.
4.1 Common Coverage Problem Determination
4.1.1 Downlink Coverage Problem Analysis
Downlink coverage problem analysis refers to the analysis of RSRP and SINR
obtained through DT. For possible downlink coverage problems, refer to the following
table.

Table 4-1 Downlink Coverage Problems
Problem Description
No coverage or
weak coverage
If no PCI signals or weak PCI signals of cells are detected through drive
testing data, it means that a site does not transmit power or antennas are
blocked during the test. Check eNodeB alarms and onsite antennas.
Overshoot
coverage
If the signals of a cell are widely distributed, and neighbor cells in one or
two circles around the cell all receive its signals, it means that the cell
overshoots coverage, and the area may become an area with no dominant
cell. Overshoot coverage may be caused by improper eNodeB heights or
downtilt angles of antennas. The cell with overshoot coverage interferes in
neighbor cells and reduces the capacity. To solve the overshoot coverage
problem, you can increase the downtilt angles of antennas or lower
antennas. During the troubleshooting, note that coverage holes cannot be
caused.
Area with no
dominantcell
This area refers to an area where there is no dominant cell or the dominant
cell is changed too frequently. In an area with no dominant cell, handover is
performed frequently, system efficiency is reduced, and the dropped-call
rate is increased.
By adjusting the downtilt angles and direction angles of antennas, you can
enhance the coverage of a cell (or near cell) with strong signals and
weaken the coverage of a cell (or far cell) with weak signals. In this way,
the problem ofthe area with no dominantcell can be solved.
4.1.1.1 Weak Coverage
If the RSRP of a area is lower than –105 dBm after being tested by antennas in a car,
the area is defined as an area with weak coverage.
To solve the weak coverage problem, you can use the following methods:
(1) Adjust the direction angles or downtilt angles of antennas, increase antenna
heights, use a high gain antenna, and enhance RS power to optimize
coverage.
(2) If there are a large number of users in a weak area or the coverage of the
area is wide, add eNodeBs or adjust surrounding eNodeBs.
(3) For weak coverage caused by hollows or hillsides, add eNodeBs or RRUs to
expand coverage. For coverage holes in elevator shafts, tunnels,

underground garages, basements, and tall buildings, add RRUs, indoor
distribution systems, leaky cables, and directional antennas.
Note that once you solve the weak coverage problem of an area by adjusting
antennas, check whether there are new areas with weak coverage. If you cannot
solve the weak coverage problem of an area by adjusting antennas, add eNodeBs in
the area.
4.1.1.2 Overshoot Coverage
Overshoot coverage means that the coverage areas of some eNodeBs exceed
the planned areas, and discontinuous dominant areas are formed in the
coverage areas of other eNodeBs.
To solve the overshoot coverage problem, you can use the following methods:
(1) Reduce downtilt angles of antennas.
(2) Adjust direction angles of antennas.
(3) Lower antennas.
(4) Change antennas. Use a low gain antenna instead or replace the
mechanical downtilt antenna with an electrical downtilt antenna.
Replace the wide lobe beam antenna with a narrow lobe antenna.
(5) Reduce the power of the cell with overshoot coverage.
(4) If overshoot coverage is caused because an eNodeB is too high and
other methods do not work, consider adjusting network topology and
relocate the eNodeB.
4.1.1.3 No Dominant Cell
An area with no dominant cell means that there is no obvious dominant cell or the
dominant cell is changed frequently in the area. In this area, handover is performed
frequently, system efficiency is reduced, and the dropped-call rate in increased.
An area meeting the following conditions is an area with no dominant cell:

(1) There are three or more cells of which RSRP is higher than –100 dBm
(RSRP is –95 dBm when antennas are placed outside the car).
(2) RSRP of the cell with the strongest signals - RSRP of the cell with the second
strongest signals < 6 dB.
For an area with no dominant cell, perform the following operations:
(1) Determine the dominant cell in the area first according to distances.
(2) Check whether the signal strength of the dominant cell is higher than –95
dBm. If not, adjust the downtilt angles, direction angles, and power of the
antennas of the cell.
(3) After the dominant cell is determined, adjust antennas, feeders, and
parameters to suppress the signal coverage of other cells.
(4) Adjust the handover parameters such as CIO of the cell to affect terminal
handover. You can reduce the handovers with far neighbor cells or increase
the handovers with near cells. Note that this adjustment is not recommended
because it cannot improve the SINR of coverage. It is recommended to use
the above three methods. This method can be used to optimize network
performance only when the problem of no dominant cell cannot be solved.
4.1.2 Uplink Coverage Problem Analysis
Uplink coverage problem analysis refers to the analysis of UE Tx Power obtained
through DT.
If UE Tx Power is higher than the threshold, the uplink coverage problem may exist.
Mark the areas with uplink coverage holes, and check whether there are RSRP
coverage holes. There are uplink and downlink weak coverage problems, solve the
downlink coverage problem first and then solve the uplink coverage problem. If there
is only the uplink weak coverage problem, you can eliminate uplink interference,
adjust the direction angles and downtilt angles of antennas, and add tower mounted
amplifiers to solve the problem.
In practice, UE transmit power is rarely noted. During the uplink rate test, the UE
keeps operating at a high rate and the transmit power is very high. Therefore, the

faulty area is difficult to find even if the values are formulated in a curve chart or a
geographical distribution map.
If there is uplink interference from the outside world, you can find it through the uplink
RSSI statistics and frequency spectrum scanning result of the cell.
4.1.3 Unbalanced Uplink and Downlink Coverage
Unbalance uplink and downlink coverage means that in the target coverage area,
downlink coverage is good while uplink coverage is limited (the transmit power of the
UE reaches the highest power but cannot meet the uplink BLER requirement), or
downlink coverage is limited (the transmit power of the dedicated downlink channel
code reaches the highest power but cannot meet the downlink BLER requirement).
Unbalanced uplink and downlink coverage can easily cause call loss, and the
common phenomenon is that uplink coverage is limited.
To solve the unbalanced uplink and downlink coverage problem, you can use the
following methods:
1. For unbalanced uplink and downlink coverage caused by uplink interference,
monitor the RSSI statistics and frequency spectrum scanning of the cell to
determine whether there is interference.
2. If uplink coverage is limited but there is no interference, add uplink diversities
(4R) and tower mounted amplifiers to expand uplink coverage.
4.1.4 External Interference Problem Analysis
Interference problem analysis includes uplink interference problem analysis and
downlink interference problem analysis. If there is interference, the cell capacity is
affected. If interference is great, call loss and access failures are caused.
1. Downlink interference analysis
Locate the problem by analyzing the SINR received by the scanner in DT.
If RSRP coverage is good but the SINR is lower than the threshold, the downlink
interference problem exists. Mark the areas where the SINR is degraded, and check
the downlink RSRP coverage of the areas. If the downlink RSRP coverage is poor, it
means that a coverage problem exists and must be solved through coverage

problem analysis. If RSRP is good but the SINR is low, the downlink interference
problem is determined. Analyze the interference cause and solve the problem.
2. Uplink interference problem
Determine the uplink interference problem by checking the noise floor of each cell. If
the noise floor of a cell is high but there is no corresponding heavy traffic, it means
that the uplink interference problem exists. Analyze the interference cause and solve
the problem.
4.1.5 Handover Problem Analysis
The cluster optimization phase involves handover parameter optimization and
neighbor cell optimization.
1. Handover parameter optimization.
2. Neighbor cell optimization focuses on missed neighbor cells. Missed neighbor
cells may cause call loss during handover. You can provide neighbor cell
addition, deletion, and reservation suggestions for each cell according to drive
testing data analysis software and statistics analysis.
3. It is recommended to enable the ANR function in SON and set the threshold for
deleting incorrect neighbor cells.
A handover problem may occur when the handover area size is not proper or the
signal strength in the handover area changes. If the handover area is too small and
the car speed is too high, there is not enough time to complete the handover
procedure and handover fails. If the handover area is too large, too many system
resources may be occupied. In addition, if the signal strength in the handover area is
changed frequently, handover is performed frequency and ping-pong effect is
caused. As a result, too many system resources are occupied and the dropped-call
rate is increased.
To solve the handover problem, you must control the position and size of the
handover area and ensure that the signal strength related to handover is changed
stably. The position and size of the handover area must be taken into consideration
during planning. The position and size should be adjusted during optimization
according to the actual environment, and determined according to the average
duration of a handover and the general car speed in the area. Prevent the handover
area from being in a corner, because additional propagation loss can be caused,

signals can be attenuated quickly, and the size of the handover area can be reduced.
If corners cannot be avoided, ensure that signals at the corners are strong enough.
Do not set the handover area at a crossroads, in a region with heavy traffic, or in a
VIP service zone.
You can adjust the direction angles and downtilt angles of antennas to change the
location and signal distribution of the handover area. If the handover area is too
small, you can reduce the downtilt angles and direction angles of antennas to solve
the problem. If signals are changed frequently in the handover areas, consider
adjusting the downtilt angles and direction angles of antennas to ensure that the
signal strength in each cell is changed stably.
4.1.6 Analysis of Other Coverage Optimization Problems
1. Feeder connection problem
According the coverage test result of an eNodeB to check whether the coverage
signals of the cell are the same as those of the planned cell. Determine whether there
are feeders connected incorrectly.
When the RRU is not mounted on the tower, the antenna of each of the three cells of
the direction eNodeB 2T2R has two feeders. On the eNodeB, the feeders are
connected to jumpers and access the eNodeB cabinet. The connection may have
faults. The two feeders of an antenna may be connected to any one or two cells, so
the signals from the antennas of three cells may be from any one or two cells of the
eNodeB. If the RRU is mounted to the tower, cells may be misconnected. For
example, cell A is connected to cell B, and cell B is connected to cell A.
During optimization, the coverage signals of cells must be checked eNodeB by
eNodeB according to the coverage test result to see whether they are consistent with
the planned coverage cells. The strongest signals detected by an antenna are from
the cell corresponding to the antenna. If strong signals of other cells are detected,
check whether feeders are not connected properly.
If feeders are not connected properly, contact device engineers to check feeder
connections.
2. Antenna and environment problems
According to the network-wide coverage test result, check whether there are
overshoot coverage signals and whether there are coverage signals obviously

weaker than the expected signals. For cells with these problems, check whether the
direction angles, downtilt angles, and heights of antennas match the design, and
whether the isolation meets the design requirements. In addition, check whether
antennas are blocked on the main lobe direction, and whether guyed masts are
vertical.
If the actual direction angles and downtilt angles of antennas do not match the
design, the main reason is that the engineering team does not completely follow the
work flow according to diagrams and planned data. In addition, devices, for example,
the compass, may have errors. The direction angle error of 5° is acceptance. The
downtilt angle error larger than 2° has a great impact on coverage.
During optimization, you may find that there are obvious blocks in the main lobe
direction of antennas. As a result, coverage holes are caused. To solve this problem,
you can adjust the direction angles of antennas. If the actual downtilt angles of
antennas do not match the design, the reason is that the guyed masts of antennas
are not vertical, or downtilt angles are not measured properly.
An easy method to measure downtilt angles is to use the antenna-attached scale
papers provided by the antenna manufacturer. You should attach scale papers to
antennas first, and then adjust them with a ruler. Note that before using this
command, ensure that the guyed masts or supports of antennas are vertically
installed on the ground so that the downtilt angles of antennas can be measured
properly. For antennas installed on towers or antennas of which guyed masts are
mounted to walls, ensure that their guyed masts are vertical to the ground. Another
method to measure downtilt angles properly is to use a bubble level directly.
The above problems can be found through the measurement of special tools. Once a
problem is found, contact the engineering team to solve it. If there are blocks or
guyed masts cannot be vertical to the ground, you can adjust the direction angles
and downtilt angles of antennas. If the downtilt angles of antennas are reduced,
overshoot coverage can be easily caused and interference can be easily increased. If
downtilt angles are increased, coverage holes can be easily caused, and too large
downtilt angles can cause beam distortion and create new interference. Therefore,
the downtilt angles of antennas must be adjusted properly to ensure network
performance.
Direction angle adjustment can solve the problems of a large scale of weak
coverage, and downtilt angle adjustment can solve coverage distance problems. The

prerequisite to ensure engineering quality is that the engineering team followings the
work flow strictly. The verification check performed by device engineers after
installation is also important.
3. eNodeB hardware problem
Another thing that you should pay attention to during coverage optimization is that
you must ensure the transmit power of an eNodeB is sent properly from the RF end
to the antenna.
The standing wave ratio is an important indicator. Before optimization, ensure that
the standing wave ratio of LTE working frequency of each cell is lower than 1.5.
Device engineers measure the standing wave ratio by using a standing wave ratio
tester before devices are installed, or the standing wave ratio is measured in batches
on the back end. For unqualified antenna and feeder systems, they must be modified
in a timely manner.
4.2 Common Coverage Optimization Methods
Coverage optimization principles:
Principle 1: Optimize RSRP first and then the RS SINR.
Principle 2: The two key tasks of coverage optimization are weak coverage
elimination and cross coverage reduction.
Principle 3: Optimize areas with weak coverage and overshoot coverage first, and
then optimize areas with no dominant cell.
Principle 4: Perform adjustment in the following order: downtilt angles and direction
angles of antennas, RS transmit power, antenna heights, eNodeB reallocation, and
eNodeB addition.
4.2.1 Antenna and Feeder Optimization Methods
1. Adjust direction angles of antennas.
Direction angles of antennas are adjusted to change the coverage areas of cells.
When the direction angles are adjusted by 5° or 10°, there are not big changes.
Therefore, direction angles are generally adjusted by more than 10° at 5° intervals.

To set and calculate downtilt angles of antennas properly, refer to “Antenna Downtilt
Angle Formula” and “For insufficient coverage or for sectors for the dominant
coverage in the areas with no dominant cell, only ensure that there is no overshoot
coverage after optimization. Antenna downtilt angles can be smaller than those
calculated through formula 1 or even smaller than those calculated through formula
2.
”.
2. Adjust downtilt angles of antennas.
Downtilt angles of antennas are adjusted to change the coverage radius of cells. The
mechanical downtilt angles of antennas are generally adjusted by 0° to 10°. In
practice, note that downtilt angles cannot be too large. Otherwise, forward
transmitted waveforms may be distorted. Many existing antennas support electrical
downtilt, so you can adjust the electrical downtilt angles of antennas remotely first.
3. Adjust antenna heights.
This adjustment is mainly for high and low eNodeBs. If an eNodeB is in a too high or
low place, serious overshoot coverage or insufficient coverage is caused. If the
coverage problems cannot be solved after the downtilt angles and direction angles of
antennas are adjusted and mechanical downtilt antennas are replaced with remote
electrical tilt antennas, you can adjust antenna heights or relocate the eNodeB.
4. Adjust antenna positions.
5. Modify antenna and feeder connections (if the connections are incorrect).
6. Replace antennas.
Antenna model adjustment means to replace omni antennas with directional
antennas, or replace 90° antennas with 65° antennas, or replace mechanical downtilt
antennas with fixed electrical downtilt antennas or remote electrical tilt antennas.
Determine the replace as required.
7. Adjust accessories such as tower mounted amplifiers, power dividers, and
feeders.
Two recommendations for antenna and feeder coverage optimization:
1. Before adjusting antennas and feeders, carry out a survey on the related
eNodeBs and provide reasonable coverage optimization suggestions.

(1) If you cannot carry out a survey on site, you can view historical site survey
reports and pictures.
(2) If you are also a planning engineer, it is important for you to know the
environment and provide reasonable coverage optimization suggestions.
2. If conditions permit, you can perform adjustment and analysis at the same time
to reduce workload.
(1) With the cooperation of engineering personnel, try two to three
adjustments and perform onsite tests, analysis, and comparison to
determine the optimal adjustment plan.
(2) This helps you gather coverage adjustment experience.
4.2.2 Parameter Optimization
4.2.2.1 Neighbor and PCI Adjustment
Improper neighbor cell planning may result in poor receiving signal quality, handover
failure, and call loss, and can affect network performance. During PCI planning, note
that the PCI mode 3 values of any two adjacent sectors of an eNodeB must be
different.
4.2.2.2 Handover Parameter Optimization
Improper handover thresholds may result in the early or late handover of terminals to
neighbor cells. Therefore, you need to check whether handover parameters need to
be adjusted according to the actual drive testing result.
4.2.2.3 Power Parameter Optimization
During optimization, the downlink power parameters that need to be modified include
RS, maximum cell power, Pa, and Pb. The following is only a brief description.
4.2.2.4 RS Setting
1. Cell-specific Reference Signals Power (RS) indicates the power (absolute value)
of cell reference signals. Cell reference signals search for cells, estimate

downlink channels, detect channels, and directly affect cell coverage. This
parameter is notified to UEs in SIB2 broadcast mode, and is constant in
downlink system bandwidth and all subframes except when the SIB2 message
is updated (for example, RS is enhanced).
2. Range: (–60…50) Step: 0. 1, unit: dBm.
3. Description: Downlink channel power is set on the basis of reference signal
power. Therefore, the setting and change of reference signal power affect
downlink power. Too high RSRP causes areas with no dominant cell and
inter-cell interference. Too low RSRP causes cell selection or reselection failure
and data channel demodulation failure.
4.2.2.5 Cell Transmit Power Settings
1. Cell Transmit Power indicates the maximum transmission power of a cell of the
eNodeB, and is required to be lower than or equal to the rated power of the
RRU.
2. Range: 0–50, Step:0. 1, unit: dBm.
3. Description: depends on network planning and expected coverage and
determines the maximum transmission power of the cell. This parameter
ensures valid coverage and avoids overshoot coverage. This parameter
indicates the total transmission power of the multiple antennas of a cell. 43 dBm
corresponds to 20 W, and 46 dBm corresponds to 40 W.
A.1 Antenna Downtilt Angle Formula
Antenna downtilt formula 1:
Θ = atan (2H / L ) * 360 / (2 *  ) +  / 2 - e_γ
Antenna downtilt formula 2:
θ = atan (H / L ) * 360 / (2 *  ) - e_γ
where θ indicates the initial mechanical downtilt angle of the antenna, H indicates the
valid height of the eNodeB, L indicates the distance between the antenna to the

eNodeB cell in the positive direction,  indicates the vertical field angle, and e_γ
indicates the electrical downtilt angle.
Descriptions of the formulas:
1. Formula 1 is used for eNodeBs in dense urban areas to most antenna power
can cover the coverage and reduce interference to neighbor cells. When setting
the initial downtilt angle of an antenna, you should make the half power point on
the main lobe of the antenna aim at the coverage edge (defined as L+L/2). It is
not recommended to use this formula to plan the initial downtilt of the antenna.
Otherwise, the initial downtilt angle may be too large and cause network
coverage problems. This formula is mainly used as a reference for optimization.
2. Formula 2 is a general formula mainly used for suburbs, villages, roads, and
seas to make coverage wide, reduce the initial downtilt angle, and make the
maximum gaining point of the main lobe of the antenna aim at the position in the
position direction of the eNodeB.
3. In actual wireless network optimization, the optimization setting of the antenna
downtilt angle depends on the analysis of drive testing data.
 According to the SINR coverage diagram of each PCI, the coverage of each
sector can be determined. For sectors with overshoot coverage, you can
consider increasing the downtilt angles of antennas according to formula 1.
Because downtilt angle settings are related to the environment, coverage
optimization requires great experience.
 For sectors with serious overshoot coverage, antennal downtilt angles set
during optimization may be much larger than those calculated through formula
1.

 For insufficient coverage or for sectors for the dominant coverage in the areas
with no dominant cell, only ensure that there is no overshoot coverage after
optimization. Antenna downtilt angles can be smaller than those calculated
through formula 1 or even smaller than those calculated through formula 2.
A.2 Downtilt Angle Calculation Methods
You can determine whether a downtilt angle is proper in the following ways:
1. Obtain the theoretical proper downtilt angle through simulation.
2. Determine whether the downtilt angle is proper according to drive testing data.

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