Lte coverage optimization analysis

LTE Coverage Optimization Analysis

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Intended Audience: LTE network optimization engineers



Contents1 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............................................................32.1 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........63.1 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..........................................................................................................................144.1 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



4.2.2 PARAMETER OPTIMIZATION.........................................................................24

A.1 ANTENNA DOWNTILT ANGLE FORMULA...............................................................25

A.2 DOWNTILT ANGLE CALCULATION METHODS.......................................................27



FiguresFigure 2-1 Coverage Optimization Flow...........................................................................................7

Figure 2-2 Cluster Partition of a Project..........................................................................................10

Figure 2-3 DT Route.......................................................................................................................14

TablesTable 2-1 Coverage Optimization Target Values (Reference KPIs).................................................8

Table 3-1 Downlink Coverage Problems........................................................................................15


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 point for 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 of any 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 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, and thermal noise.

The reference point for 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 RSRQ of 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 The coverage optimization phase

involves preparations, data collection, problem analysis, and adjustment

implementation, see The coverage optimization phase involves preparations, data

collection, problem analysis, and adjustment implementation, see The coverage

optimization phase involves preparations, data collection, problem analysis, and

adjustment implementation, see The coverage optimization phase involves

preparations, data collection, problem analysis, and adjustment implementation, see

The coverage optimization phase involves preparations, data collection, problem

analysis, and adjustment implementation, see The coverage optimization phase

involves preparations, data collection, problem analysis, and adjustment

implementation, see The coverage optimization phase involves preparations, data

collection, problem analysis, and adjustment implementation, see The coverage

optimization phase involves preparations, data collection, problem analysis, and

adjustment implementation, see Figure 2-1. 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. . According to the optimization target of the

project team and the actual situation, data collection, problem analysis, and
























optimization KPIs of the project team.


Figure 2-1 Coverage Optimization Flow

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 2-1 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. 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. 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. 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. 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. 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. 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. Figure

2-2 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.

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. 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. 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. 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. 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. 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 2-2 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 digital

map and mark the start point and end point of the test, and use lines with arrows to

indicate the test route, see Figure 2-3 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 2-3 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 3-2 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

dominant cell

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 of the area with no dominant cell 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 * p ) + b / 2 - e_γ

Antenna downtilt formula 2:

θ = atan (H / L ) * 360 / (2 * p ) - 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, b 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 MethodsYou 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.


Engineering

Lte coverage optimization analysis