Huawei Concentric Cell Optimization

GSM BSS Concentric Cell Technical Clarification Secret

Product Name Security Level

GSM BSS For Internal Use Only

Product VersionTotal Page: 48

BSS 7.1

GSM BSS Concentric Cell Technical Clarification(For internal use only)

Prepared by WCDMA&GSM Network Performance Research Dept.

Date 2007-4-18

Reviewed by Date yyyy-mm-dd

Reviewed by Date yyyy-mm-dd

Approved by Date yyyy-mm-dd

Huawei Technologies Co, Ltd.All Rights Reserved

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Change History

Date Version

Description Author

2007-4-18 0.1 Initial draft completed Li Jing/62667

2007-4-26 0.7 Section 5 Network Optimization of the Concentric Cell is included and modified according to review comments.

Cheng Jun/50674Li Jing/62667

2007-7-12 0.7 Errors in the graphs of Section 4 are modified. Li Jing/62667

2007-8-17 0.7 Description errors are modified. Mao Minghui/51044

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Contents

1 Introduction to Concentric Cell.......................................................81.1 Overview............................................................................................................................................................81.2 Application of Concentric Cell..........................................................................................................................81.3 Features of Concentric Cell...............................................................................................................................9

1.3.1 Advantages................................................................................................................................................91.3.2 Disadvantages...........................................................................................................................................9

2 Channel Assignment and Handover Algorithms.............................102.1 Channel Assignment Technology of Concentric Cell......................................................................................10

2.1.1 Immediate Assignment...........................................................................................................................102.1.2 Assignment.............................................................................................................................................102.1.3 Intra-BSC Handover...............................................................................................................................102.1.4 Inter-BSC Handover...............................................................................................................................11

2.2 Handover Decision Algorithms........................................................................................................................112.2.1 Normal Concentric Cell Handover.........................................................................................................112.2.2 Enhanced Concentric Cell Handover.....................................................................................................142.2.3 Handover from a Concentric Cell to a Neighbor Cell............................................................................17

3 Application Scenarios of the Concentric Cell and Its Activation Strategy.........................................................................................19

3.1 Restriction........................................................................................................................................................193.2 Application Scenarios and Activation Strategy................................................................................................193.3 Problems Occurred in Activating the Concentric Cell and Solutions..............................................................21

4 Network Planning of Concentric Cells............................................224.1 Coverage Planning...........................................................................................................................................22

4.1.1 Populated Urban Areas...........................................................................................................................224.1.2 Common Urban Areas............................................................................................................................254.1.3 Suburbs...................................................................................................................................................274.1.4 Wide Coverage Areas.............................................................................................................................284.1.5 Conclusion..............................................................................................................................................29

4.2 Capacity Planning............................................................................................................................................294.2.1 Capacity Growth Due to Application of Concentric Cells.....................................................................294.2.2 Impact of Capacity on Coverage............................................................................................................30



4.3 Frequency Planning.........................................................................................................................................324.4 Impact of the Concentric Cell on Data Service Performance..........................................................................32

4.4.1 Timeslot Throughput Simulation in Common Urban Areas with a Coverage Radius of 600 m............324.4.2 Timeslot Throughput Simulation in Common Urban Areas with a Coverage Radius of 800 m............354.4.3 Timeslot Throughput Simulation in Suburbs with a Coverage Radius of 3190 m.................................384.4.4 Timeslot Throughput Simulation in Suburbs with a Coverage Radius of 4020 m.................................404.4.5 Conclusion..............................................................................................................................................41

5 Network Optimization of the Concentric Cell.................................425.1 Network Optimization Strategy for a Normal Concentric Cell.......................................................................425.2 Network optimization strategy for an enhanced concentric cell......................................................................42

6 Impact of Concentric Cell on Coverage Performance......................457 Impact of the Concentric Cell on Network Capacity........................468 Impact of the Concentric Cell on Network Quality..........................479 Impact of the Concentric Cell on KPI..............................................................48

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Tables

Table 2-1 Parameters related to the normal concentric cell handover...................................................................11

Table 2-1 Parameters related to the enhanced concentric cell handover...............................................................14

Table 3-1 Application scenarios of the concentric cell and its activation strategy................................................20

Table 4-1 Coverage budget in densely populated urban areas..............................................................................23

Table 4-1 Comparison of traffic among different site types..................................................................................30

Table 5-1 Network optimization parameters for a common concentric cell.........................................................42

Table 5-1 Network optimization parameters for an enhanced concentric cell......................................................43



Abstract and Acronyms

Key words: concentric cell technology, voice quality, capacity

Abstract: The document describes the impact of the concentric cell on the network capacity and quality.

Acronyms:

Acronyms Full Name

BSC Base Station Control

TCH Traffic Channel

BCCH Broadcast Control Channel

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GSM BSS Concentric Cell Technical ClarificationThis document describes the technology and application of the common concentric cell and enhanced concentric cell. As the COBCCH technology involves the allocation among different frequency bands and has its own features, this document does not address it in detail. Detailed information about the COBCCH technology can be found in the COBCCH Performance Technical Clarification.

1 Introduction to Concentric Cell

1.1 OverviewA concentric cell in the GSM network is divided into two layers: external layer and internal layer. The external layer is called the underlaid subcell and the internal layer the overlaid layer. Concentric cell technology is a technique concerning channel assignment and handover.

The underlaid subcell serves the area covered by a traditional cell and the overlaid subcell serves the area around the BTS. All the transceivers (TRXs) are divided into two groups: one group for the underlaid subcells and the other group for the overlaid subcells.

1.2 Application of Concentric CellWith the development of GSM network, the number of subscribers increases gradually, so the contradiction between short frequency resource and capacity demand is particularly obvious. In order to increase capacity, the technology of tight frequency reuse should be used to improve the frequency utilization. In a concentric cell, there are either two ways for connecting the feeder to the antenna or two types of TRXs with different transmit power, which enables an MS to switch from one TRX to another. The different ways for connecting the feeder to the antenna lead to different power loss on the path from the feeder to the antenna, or the different transmit power with the TRX will cause different transmit power for the TRXs serving a cell. Thus, the cell is physically divided different layers.

The concentric cell does not need the support of special signaling messages. All the call-related signaling procedures on the BSS side such as immediate assignment, immediate assignment, and handover support the concentric cell.

The static power varies between the TRXs within a cell due to the two causes described above. Some TRXs with higher transmit power on the Um interface serve the underlaid subcell of the concentric cell while the other TRXs with lower transmit power serve the overlaid subcell layer.

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In general, the BCCH frequency is configured for a TRX serving the underlaid subcell to ensure the coverage of the concentric cell, whereas the TRXs with lower transmit power serve the overlaid subcell to meet capacity requirements around the BTS site.

As the signal strength of the overlaid subcell and underlaid subcell cannot be determined by the signal strength of the underlaid subcell and overlaid subcell respectively, there is a demanding requirements for algorithm designing and the network planning and optimization.

1.3 Features of Concentric Cell1.3.1 Advantages

Using the concentric cell has the following advantages:

Improvement on system performanceThe concentric cell decreases the transmit power of the TRXs serving the overlaid subcell and reduces the radio interference for the adjacent cells. Thus, the tight frequency reuse technology can be applied to the overlaid subcell.

Increase on system capacity− The main BCCH and SDCCH, which are generally configured in the underlaid

subcell, are fully used because they are shared by the underlaid subcell and overlaid subcell. Thus, the number of TCHs and the capacity of the site are increased.

− The tight frequency reuse technology can be used to increase system capacity.

1.3.2 DisadvantagesUsing the concentric cell has the following disadvantages:

1. The concentric cell technology only applies to specific scenarios. Enabling the concentric cell feature in some unsuitable areas will affect network counters, as shown in section 3.3.

2. The adjustment of network parameters is difficult. The parameters of the concentric cells vary with the application scenarios and must be set and adjusted separately based on actual situations to reach optimal performance. These parameters should be adjusted with the changing of the network environment.



2 Channel Assignment and Handover Algorithms

2.1 Channel Assignment Technology of Concentric Cell2.1.1 Immediate Assignment

To ensure fast call connection within a concentric cell, you are advised to use the TRXs serving the underlaid subcell to assign the channels in the immediate assignment procedure.

2.1.2 AssignmentThe assignment of channels in the overlaid subcell or underlaid subcell is determined by the Assign Optimum Layer and Assign-Optimum-Level Threshold parameters. The concentric cell assigns a channel based on the RX level and TA threshold. The handover between two concentric cells is supported.

The ways for assigning the TCH in the concentric cell are as follows:

1. The system decides the TCH assignment based on the measurement report from the SDCCH and chooses the serving layer that is assigned first.

After System Optimization is configured for the Assign Optimum Layer, the current SDCCH level can be estimated (inserted/ filtered) based on the uplink measurement result in the previous SDCCH measurement report. Then, the RX level on the SDCCH is compared against the Assign Optimum-Level Threshold, and the TA against the TA Threshold of Assignment Preference to determine where the TCH should be used, from the underlaid subcell or from the overlaid subcell. For example, if the RX level on the SDCCH is equal to or greater than the Assign Optimum-Level Threshold and the TA is smaller than the TA Threshold of Assignment Preference, a TCH in the overlaid subcell is assigned to the MS. Otherwise, a TCH in the underlaid subcell is assigned for the MS to ensure successful assignment.

2. A TCH in the underlaid subcell is preferred.3. A TCH in the overlaid subcell is preferred.4. No priority.

2.1.3 Intra-BSC HandoverYou can set the Pref. Subcell in HO of Intra-BSC parameter to specify an underlaid or overlaid channel during intra-BSC handover.

The ways for handling the intra-BSC handover in the concentric cell are as follows:



1. System Optimization: This method provides the concentric cell with a BCCH measurement value of the target cell in the intra-BSC Handover Request message. This enables the concentric cell to compare the RX level of the BCCH with the RX_LEV Thrsh. to select the optimum layer, without regard to the RX_LEV Hysteresis.

2. Overlaid Subcell: A TCH in the overlaid subcell is preferred.3. Underlaid Subcell: A TCH in the underlaid subcell is preferred.4. No Priority: A TCH is assigned with normal channel assignment algorithms.

2.1.4 Inter-BSC HandoverYou can set the Incoming-to-BSC HO Optimum Layer parameter to specify an underlaid subcell or overlaid subcell during inter-BSC handover. The inter-cell handover usually occurs on the edge of cells, the Underlaid Subcell is thus configured for the Incoming-to-BSC HO Optimum Layer parameter by default. As the target cell cannot determine the signal strength of the MS receiving the BCCH signal while assigning the TCH, the inter-BSC handover does not support System Optimization.

Pay attention to the following points:

1. The BCCH TRX must be configured in the underlaid subcell.2. The SDCCH is configured in the underlaid subcell.3. If the RX_LEV Thrsh. and RX_LEV Hysteresis are set to 63 and 63 or the TA Thrsh.

or TA Hysteresis are set to 63 and 63 respectively, the handover between the overlaid and underlaid subcells are forbidden.

4. Perform data configuration of the dual-timeslot TRXs in accordance with concentric cell features.

2.2 Handover Decision AlgorithmsThe concentric cell handover is classified into normal concentric cell handover and enhanced concentric cell handover.

2.2.1 Normal Concentric Cell HandoverThis section describes the handover algorithms concerning the normal concentric cell.

Table 2-1 lists the parameters related to the normal concentric cell handover.

Table 2-1 Parameters related to the normal concentric cell handover

Parameter Description Remarks

UO Signal Strength Difference

The signal strength difference between the overlaid and underlaid subcells affects the MS receiving the signals within the concentric cell. This parameter is used to compensate the signal strength between the overlaid and underlaid subcells. The value of the parameter is the sum of the power difference between UO power amplifiers, insertion loss difference between combiners, path loss difference between antennas, and path loss difference over different frequencies. This value is measured at the site. Multiple-point measurements should be performed when different antennas are used for the overlaid and underlaid subcells.

This value is invalid when the Enhanced Concentric Cell Allowed parameter is selected.



Parameter Description Remarks

RX_LEV Thrsh. This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells. When the Enhanced Concentric Cell Allowed parameter is not selected, the coverage of the overlaid and underlaid subcells is determined by the RX_LEV Thrsh., RX_LEV Hysteresis, RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.


RX_LEV Hysteresis

This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells. When the Enhanced Concentric Cell Allowed parameter is not selected, the coverage of the overlaid and underlaid subcells is determined by the RX_LEV Thrsh., RX_LEV Hysteresis, RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.


RX_QUAL Thrsh.

This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells. When the Enhanced Concentric Cell Allowed parameter is not selected, the coverage of the overlaid and underlaid subcells is determined by the RX_LEV Thrsh., RX_LEV Hysteresis, RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.

This parameter applies to both enhanced concentric cell and normal concentric cell.

TA Thrsh. This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells. When the Enhanced Concentric Cell Allowed parameter is not selected, the coverage of the overlaid and underlaid subcells is determined by the RX_LEV Thrsh., RX_LEV Hysteresis, RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.

This parameter applies to both enhanced concentric cell and normal concentric cell. Its value must be smaller than the TA Emergency Handover Threshold.

TA Hysteresis This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells. When the Enhanced Concentric Cell Allowed parameter is not selected, the coverage of the overlaid and underlaid subcells is determined by the RX_LEV Thrsh., RX_LEV Hysteresis, RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.


The coverage of the overlaid and underlaid subcells is determined by the five parameters, namely, RX_LEV Thrsh., RX_LEV Hysteresis, RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.

The coverage of the overlaid subcell is presented as follows:RX level RX_LEV Thrsh. + RX_LEV Hysteresis, TA < TA Thrsh. - TA Hysteresis, and RX quality < RX_QUAL Thrsh.

The coverage of the underlaid subcell is presented as follows:RX level RX_LEV Thrsh. - RX_LEV Hysteresis or TA TA Thrsh. + TA Hysteresis or and RX quality RX_QUAL Thrsh.

There is a "blank" area between the two formulas described above.That is, RX_LEV Thrsh. - RX_LEV Hysteresis RX level RX_LEV Thrsh. + RX_LEV Hysteresis, and TA Thrsh. - TA Hysteresis TA < TA Thrsh. + TA Hysteresis.This area, called the Hysteresis area of the concentric cell, is used to prevent the ping-pong handover.



When TA Thrsh. is set to 63 and TA Hysteresis to 0, the boundary of the overlaid subcell is determined by the RX_LEV Thrsh. and RX_QUAL Thrsh. When RX_LEV Thrsh. is set to 63 and RX_LEV Hysteresis to 0, the boundary of the overlaid subcell is determined by the TA Thrsh. and RX_QUAL Thrsh.

Handover from Overlaid Subcell to Underlaid SubcellDuring the normal concentric cell handover, the MS occupying an overlaid subcell TCH can be handed over to the underlaid subcell or to a neighbor cell. The triggering conditions are as follows (OL to UL HO Allowed):

Actual DL RX level + UO Signal Strength Difference < RX_LEV Thrsh. - RX_LEV Hysteresis - power control compensationThis is controlled by the RX_LEV for UO HO Allowed parameter.

DL RX quality > RX_QUAL Thrsh.This is controlled by the RX_QUAL for UO HO Allowed parameter.

Current TA value > TA Thrsh. + TA HysteresisThis is controlled by the TA Pref. of Imme-Assign Allowed parameter.

When any of the previous conditions is met, the handover from the overlaid subcell to the underlaid subcell is triggered.If the handover from the overlaid subcell to the underlaid subcell fails, there is a handover penalty. A predefined timer determines the penalty time.

The principle for selecting a target cell is as follows:If the original TCH occupied by an MS belongs to the overlaid subcell, the MS is handed over to a cell with highest priority by performance. In case that this cell is the serving cell (concentric cell), the MS is then handed over to the underlaid subcell.

The underlaid subcell level is an approximate value, which is the difference between the overlaid subcell level and the UO Signal Strength Difference.

Handover from Underlaid Subcell to Overlaid SubcellDuring the normal concentric cell handover, the MS occupying an underlaid TCH can only be handed over to the overlaid subcell. The triggering conditions are as follows (UL to OL HO Allowed):

Actual DL RX level RX_LEV Thrsh. + RX_LEV Hysteresis - power control compensationThis is controlled by the RX_LEV for UO HO Allowed parameter.

DL RX quality < RX_QUAL Thrsh.This is controlled by the RX_QUAL for UO HO Allowed parameter.

Current TA value < TA Thrsh. - TA Hysteresis

When all the previous conditions are met, the handover from the underlaid subcell to the overlaid subcell is triggered.If the handover from the underlaid subcell to the overlaid subcell fails, there is a handover penalty. A predefined timer determines the penalty time.

The principle for selecting a target cell is as follows:If the original TCH occupied by an MS belongs to the underlaid subcell, the MS can only be handed over to the overlaid subcell.



2.2.2 Enhanced Concentric Cell HandoverThis section describes the handover algorithms concerning the enhanced concentric cell. The main difference between the enhanced concentric cell handover and the normal concentric cell handover is as follows:

In the enhanced concentric cell, an MS occupying an overlaid channel can monitor the signal strength of the BCCH. However, in the normal concentric cell, the MS handed from the overlaid channel to the underlaid channel cannot obtain the signal strength of the underlaid subcell.

Table 2-1 lists the parameters related to the enhanced concentric cell handover.

Table 2-1 Parameters related to the enhanced concentric cell handover

Parameter

Description Remarks

OL to UL HO Received Level Thrsh.

This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells in the enhanced concentric cell. When the Enhanced Concentric Cell Allowed is selected, the coverage of the overlaid and underlaid subcells is determined by the OL to UL HO Received Level Thrsh., UL to OL HO Received Level Thrsh., RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.

This parameter only applies to the enhanced concentric cell.

UL to OL HO Received Level Thrsh.


This parameter only applies to the enhanced concentric cell.

RX_QUAL Thrsh.



TA Thrsh. This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells in the enhanced concentric cell. When the Enhanced Concentric Cell Allowed is selected, the coverage of the overlaid and underlaid subcells is determined by the OL to UL HO Received Level Thrsh., UL to OL HO Received Level Thrsh., RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.

This parameter applies to both enhanced concentric cell and normal concentric cell. Its value must be smaller than the TA Emergency Handover Threshold.

TA Hysteresis This parameter is one of the parameters that determine the coverage of the overlaid and underlaid subcells in the enhanced concentric cell. When the Enhanced Concentric Cell Allowed is selected, the coverage of the overlaid and underlaid subcells is determined by the OL to UL HO Received Level Thrsh., UL to OL HO Received Level Thrsh., RX_QUAL Thrsh., TA Thrsh., and TA Hysteresis.




Traffic Thrsh. of Underlaid Subcell

The MS is handed from the underlaid subcell to the overlaid subcell only when the traffic in the underlaid subcell is higher than the value of the Traffic Thrsh. of Underlaid Subcell. This is caused by the fact that the signal quality in the underlaid subcell is better than that in the overlaid subcell. If the UL to OL Traffic HO Allowed parameter is not selected, the MS is handed from an underlaid subcell to an overlaid subcell without regard to the traffic in the underlaid subcell.

This value is valid when the UL to OL Traffic HO Allowed parameter is selected.

Underlaid Subcell HO Step Period (s)

Many calls may initiate handover requests from the underlaid subcell to the overlaid subcell at the same time. In this case, the calls with lower level might be handled first. This does not comply with the concept of handing over the calls with optimal RX level first. Therefore, the hierarchy handover algorithm is adopted to hand the calls with higher RX level from the underlaid subcell to the overlaid subcell. This period is equal to the Underlaid Subcell HO Step Level, the decreasing level in the handover belt.

This value is valid when the Enhanced Concentric Cell Allowed parameter is selected.

Underlaid Subcell HO Step Level

During the handover from the underlaid subcell to the overlaid subcell, the calls are hierarchically handled from level 63 to 0. This enables the calls with better RX level to be handed over to the overlaid subcell first. Its value defines the step in which the handover belt is decreased.


Penalty Time of UL to OL HO (s)

This parameter specifies the time during which a call having handed from an overlaid subcell to an underlaid subcell is not allowed to be handed over to the overlaid to avoid the ping-pong handover between the overlaid and underlaid subcells. If the Penalty Time of UL to OL HO (s) is set to 0, the penalty mechanism is not enabled.


When a cell supports the enhanced concentric cell feature, the coverage of the overlaid and underlaid subcells is determined by the following ways:

The coverage of the overlaid subcell is presented as follows:RX level UL to OL HO Received Level Thrsh., and TA < (TA Thrsh. - TA Hysteresis), and RX quality < RX_QUAL Thrsh.

The coverage of the underlaid subcell is presented as follows:RX level < OL to UL HO Received Level Thrsh., or TA (TA Thrsh. + TA Hysteresis), or RX quality RX_QUAL Thrsh.

There is a "blank" area between the two formulas described above.That is, OL to UL HO Received Level Thrsh. RX quality < UL to OL HO Received Level Thrsh., and (TA Thrsh. - TA Hysteresis) TA < (TA Thrsh. + TA Hysteresis) This area, called the Hysteresis area of the concentric cell, is used to prevent the ping-pong handover.

Handover from Overlaid Subcell to Underlaid SubcellDuring the enhanced concentric cell handover, the MS occupying an overlaid subcell TCH can be handed over to the underlaid subcell or to a neighbor cell. The triggering conditions are as follows (OL to UL HO Allowed):

DL RX level < OL to UL HO Received Level Thrsh. This is controlled by the RX_LEV for Concentric Cell HO Allowed parameter.

DL RX quality RX_QUAL Thrsh.



This is controlled by the RX_QUAL for Concentric Cell HO Allowed parameter. TA > TA Thrsh. + TA Hysteresis

This is controlled by the TA Pref. of Imme-Assign Allowed parameter.

When any of the previous conditions is met, the handover from the overlaid subcell to the underlaid subcell is triggered.If the handover from the overlaid subcell to the underlaid subcell fails, there is a handover penalty. A predefined timer determines the penalty time.

The principle for selecting a target cell is as follows:If the original TCH occupied by an MS belongs to the overlaid subcell, the MS is handed over to a cell with highest priority by performance. In case that this cell is the serving cell (concentric cell), the MS is then handed over to the underlaid subcell.

Handover from Underlaid Subcell to Overlaid SubcellDuring the enhanced concentric cell handover, the MS occupying an underlaid TCH can only be handed over to the overlaid subcell. The triggering conditions are as follows (UL to OL HO Allowed):

DL RX level UL to OL HO Received Level Thrsh.This is controlled by the RX_LEV for Concentric Cell HO Allowed parameter.

DL RX quality < RX_QUAL Thrsh.This is controlled by the RX_QUAL for Concentric Cell HO Allowed parameter.

TA < TA Thrsh. - TA HysteresisThis is controlled by the TA Pref. of Imme-Assign Allowed parameter.

Traffic of the underlaid subcell > Traffic Thrsh. of Underlaid SubcellThis is controlled by the UL to OL Traffic HO Allowed parameter.

When all the previous conditions are met, the handover from the underlaid subcell to the overlaid subcell is triggered.If the handover from the underlaid subcell to the overlaid subcell fails, there is a handover penalty. A predefined timer determines the penalty time.

The principle for selecting a target cell is as follows:If the original TCH occupied by an MS belongs to the underlaid subcell, the MS can only be handed over to the overlaid subcell.

2.2.3 Handover from a Concentric Cell to a Neighbor CellHandover from a Normal Concentric Cell to a Neighbor Cell

When the MS is located in the overlaid subcell, the principle for selecting a neighbor cell is as follows:Use the RX level of the overlaid subcell + UO Signal Strength Difference to participate in Huawei M and K rules. In addition, use actual RX level of the overlaid subcell + UO Signal Strength Difference to participate in all handover decisions.

When the MS is located in the underlaid subcell, the principle for selecting a neighbor cell is as follows:



Use the actual RX level of the underlaid subcell to participate in Huawei M and K rules. In addition, use actual RX level of the underlaid subcell to participate in all handover decisions.

Handover from an Enhanced Concentric Cell to a Neighbor Cell When the MS is located in the overlaid subcell, the principle for selecting a neighbor cell

is as follows:− When non-PBGT handover algorithms are selected, use the RX level of the overlaid

subcell to participate in the M rule, the actual RX level of the underlaid subcell in the K rule, and the actual RX level of the overlaid subcell in the handover decision.

− When the PBGT handover algorithm is selected, use the actual RX level of the overlaid subcell to participate in the M rule, the actual RX level of the underlaid subcell in the K rule, and the actual RX level of the underlaid subcell in the handover decision.

When the MS is located in the underlaid subcell, the principle for selecting a neighbor cell is as follows:Use the actual RX level of the underlaid subcell to participate in the M rule, the actual level of the underlaid in the K rule, and the actual RX level of the underlaid subcell in all handover decisions.



3 Application Scenarios of the Concentric Cell and Its Activation

Strategy

This chapter describes the networking features of the concentric cell technology, specifies its application scenarios, and highlights some common problems and troubleshooting strategies.

3.1 RestrictionThe principles for designing the concentric cell strategy are as follows:

1. Allocate the TRXs in the overlaid and underlaid subcells reasonably based on their traffic distribution. Otherwise, the TRXs in fully loaded underlaid subcells might be congested in busy hours. This affects the KPIs, such as TCH Seizure Success Ratio.

2. Do not implement the concentric cells with more than two layers.3. Configure the BCCH in the underlaid subcell.4. The concentric cell does not support the frequency hopping between the underlaid

subcell and the overlaid subcell. The frequency hopping within the underlaid subcell or overlaid subcell is supported.

The principles for technical clarification are as follows:



At present, Huawei concentric cell (excluding COBCCH cell) solution only supports configuring the BCCH in the underlaid subcell.

For the versions before GBSS 7.0, it is recommended to configure the PDCHs in the underlaid subcell. If the PDCHs are configured in the overlaid subcell, the PCU might assign an overlaid PDCH for an underlaid MS as the PCU cannot decide whether the PDCH is in the overlaid subcell or in the underlaid subcell. In this case, the packet service assignment might fail. The GBSS 7.0 and later releases support configuring the PDCHs in the underlaid subcell. Matched BSC and PCU versions are required.

3.2 Application Scenarios and Activation Strategy

The concentric cell feature is usually applied in the following scenarios:

1. Scenario with short inter-site distance, tight frequency reuse, high traffic, and strong intra-network interferenceIn this scenario, decrease the transmit power of the TRXs used for tight frequency reuse purpose, and then activate the concentric cell feature. This solution not only decreases the intra-network interference but also increases the system capacity with the tight frequency reuse of the overlaid frequencies.

2. Inconsistency of the transmit power at the RF port within a cell due to the differences of transmit power and combination modes of the TRXsIn this case, configure the TRXs in the overlaid and underlaid subcells reasonably based on the traffic distribution within the concentric cell.

Table 3-1 describes the different application scenarios of the concentric cell and its activation strategy.

Table 3-1 Application scenarios of the concentric cell and its activation strategy

Scenario

Description

Suggestion Scenario Analysis and Operations

Advantages

1 The 900M sites are placed 1.5 km apart or the 1800M sites are 1 km apart. The transmit power difference at the RF port is within 2 dB.

No need to activate the concentric cell feature.

As the inter-site distance is short and the transmit power difference at the RF port is small, the TRXs with lower transmit power at the RF port can cover the entire cell. To minimize operation and maintenance flexibility, there is no need to activate the concentric cell feature.

-



Scenario

Description

Suggestion Scenario Analysis and Operations

Advantages

2 The transmit power difference at the RF port is greater than 2 dB.

Activate the concentric cell feature. As the transmit power difference at the RF port is large, the concentric cell feature should be activated. You should configure the underlaid/overlaid handover level thresholds reasonably based on the transmit power difference.

The traffic in the underlaid/overlaid subcells is allocated reasonably and the deterioration of relevant KPIs due to the coverage failure of the TRXs with lower transmit power at the RF port is prevented.

3 Scenario with short inter-site distance, tight frequency reuse, high traffic, and strong intra-network interference

Activate the concentric cell feature. Reduce the transmit power of the TRXs used for tight frequency reuse purpose to reduce intra-network interference. Configure the underlaid/overlaid handover level thresholds reasonably based on the transmit power difference.

The intra-network interference is reduced and the relevant KPIs are increased.

4 Other scenarios

Decide the implementation based on the actual situations by referring to 4 "Network Planning of Concentric Cells."

Decide the implementation by taking full consideration of the inter-site distance, transmit power difference at the RF port, frequency reuse, traffic load, and interference situations.

-

3.3 Problems Occurred in Activating the Concentric Cell and Solutions

In the concentric cell implementation, the TRXs with different coverage capabilities are managed within a cell. To avoid the decrease of the concentric cell KPIs, network planners



should prevent the congestion of the TRXs serving the underlaid subcell. In the Concentric Cell HO Data tab page, the Assign Optimum Layer is set to System Optimization by default at present. This means that the calls are handled by the overlaid and underlaid subcells based on their coverage. The congestion of the underlaid subcell causes call drops and affects the KPIs such as Success Rate of Inter-Cell Handover and TCH Assignment Success Rate.

The probable problems you might encounter in implementing the concentric cell and their solutions are as follows:

Congested underlaid subcell and idle overlaid subcell1. Adjust the handover parameters to have the overlaid subcell share the traffic of the

underlaid subcell. You can increase the logical coverage of the overlaid subcell and its traffic handling capability by decreasing the RX_LEV Thrsh. for the normal concentric cell or the UL to OL HO Received Level Thrsh. for the enhanced concentric cell. Note that the adjusted logical coverage of the overlaid subcell does not exceed its physical coverage. Otherwise, the handover failures from the underlaid subcell to the overlaid subcell increase.

2. Enable the Direct Retry and Load Sharing features.3. Allocate some underlaid PDCHs in the overlaid subcell.

The versions before GBSS 7.0 do not support the configuration of the PDCHs in the overlaid subcell. The GBSS 7.0 and later versions support the configuration of the PDCHs in the overlaid subcell.

4. Add TRXs in the underlaid subcell.5. Enable the half-rate scheme of the underlaid subcell.6. Decrease the transmit power of the underlaid TRXs to reduce the coverage of the current

cell and have the neighbor cell share its traffic. Strong interference and poor call quality in the underlaid subcell

The underlaid subcell with strong interference is always accompanied by higher interference band, poor voice quality, and high call drops. You can adjust the parameters concerning the concentric cell to minimize the interference.

1. Clear the RX_QUAL for Concentric Cell HO Allowed parameter; otherwise, the calls in the underlaid subcell, which has high RX level but low RX quality (caused by interference), cannot be handed over to the overlaid subcell.

2. Increase the logical coverage of the overlaid subcell by decreasing the level thresholds of the overlaid and underlaid subcells to have the overlaid subcell share more traffic.



4 Network Planning of Concentric Cells

4.1 Coverage Planning4.1.1 Populated Urban AreasCoverage Radius of Overlaid and Underlaid Subcells in Densely Populated Urban Areas

Table 4-1 describes the coverage budget in densely populated urban areas using Huawei link budget tool.

Table 4-1 Coverage budget in densely populated urban areas

Link Budget

Densely Populated Urban Area

Uplink Downlink

Cell configuration 3-sector

Environment application Outdoor

Use of TMA No

BTS type BTS3012

Maximum TX power (dBm) 33 47.8

Combination loss (dB) 0 4.5

Feeder loss (TX) (dB) 0 2.471

Body loss (TX) (dB) - -

Antenna gain (TX) (dBi) 0 15

EiRP (dBm) 33 55.829

Antenna gain (RX) (dBi) 15 0

Antenna diversity gain (RX) (dBi) 2.5 0

Feeder loss (RX) (dB) 2.471 0

Body loss (RX) (dB) 3



Link Budget

Receive sensitivity (dBm) –112.5 –104

Improvement of receive sensitivity after using the TMA (dB)

0

Minimum RX level requirement (dB) –93.529 –70

Penetration loss (dB) 0

Standard flow fading deviation (dB) 10

Area coverage rate 0.95

Boundary coverage rate 0.876

Slow fading margin (dB) 11.591

Fast fading margin (dB) 3

Interference margin (dB) 1

Maximum path loss allowed (dB) 114.94 114.24

MS antenna height (m) 1.5

BTS antenna height (m) 25

Frequency band (MHz) 900

Propagation model Okumuru-Hata

Cell radius (km) 0.445 0.425

Path loss allowed for link balancing (dB) 114.24

Cell radius allowed for link balancing (km)

0.425

BTS coverage area (km2) 0.35

Target coverage area (km2) 200

Number of BTSs 568

Measurement results

Populated Urban Area

Cell radius (km) Number of BTSs

2008 0.43 568

Transmit power at the RF port for the underlaid subcell: 47.78 (TRX power) – 4.5 (combination loss) = 43.28 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 430 m (outdoor coverage rate: 95%).

Transmit power at the RF port for the overlaid subcell: 47.78 (TRX power) – 8 (combination loss) = 39.78 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 340 m (outdoor coverage rate: 95%).



In densely populated urban areas, the coverage radius of the BTS is usually smaller than 300 m. The continuous coverage is available in the overlaid subcell. Thus, the 8 dB combination loss will not affect the coverage in this scenario.

There is no restriction on the hardware to implement the concentric cell in this scenario. You can manually configure the concentric cell to implement the tight frequency reuse solution and increase the BTS capacity.

This concentric cell configuration not only guarantees the tight frequency reuse in the overlaid subcell, but also achieves the trunk gain listed in the Erl B table.

Level Distribution Under for Different Combination Loss1. The emulation conditions are as follows: Antenna height: 25 m Antenna type: 14 dBi, 65 deg, o title, 900 MHz Combination loss: 4.5 dB and 8 dB Propagation model: Okumura-Hata (populated urban areas) BTS coverage radius: 300 m Cell edge design level: –70 dBm Area coverage rate: 95% Map: Ha Erbin2. The emulation result for the coverage radius smaller than 300 m is as follows:

Under different combination losses, both the coverage of the overlaid subcell and that of the underlaid subcell meet the edge design level. In large combination loss situations, the area with greater level is smaller than that with smaller level.

4.1.2 Common Urban AreasCoverage Radius of Overlaid and Underlaid Subcells in Common Urban Areas

Transmit power at the RF port for the underlaid subcell: 47.78 (TRX power) – 4.5 (combination loss) = 43.28 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 800 m (outdoor coverage rate: 95%).



Transmit power at the RF port for the overlaid subcell: 47.78 (TRX power) – 8 (combination loss) = 39.78 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 630m (outdoor coverage rate: 95%).

Level Distribution for Different Combination Loss1. The emulation conditions are as follows: Antenna height: 30 m Antenna type: 14 dBi, 65 deg, o title, 900 MHz Combination loss: 4.5 dB and 8 dB Propagation model: Okumura-Hata (common urban areas) BTS coverage radius: 600 m Cell edge design level: –75 dBm Area coverage rate: 95% Map: Ha Erbin2. The emulation result for the coverage radius of 600 m is as follows:

In common urban areas, the coverage radius of the concentric cell is generally less than 600 m. Under different combination losses, both the coverage of the overlaid subcell and that of the underlaid subcell meet the edge design level.

3. The emulation result for the coverage radius of 800 m is as follows:



When 800 m of coverage radius is planned for the underlaid subcell, there will be 30% of the overlaid subcell that does not meet the coverage requirements.

4.1.3 SuburbsCoverage Radius of Overlaid and Underlaid Subcells in Suburbs

Transmit power at the RF port for the underlaid subcell: 47.78 (TRX power) – 4.5 (combination loss) = 43.28 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 4,020 m (outdoor coverage rate: 95%).

Transmit power at the RF port for the overlaid subcell: 47.78 (TRX power) – 8 (combination loss) = 39.78 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 3,190 m (outdoor coverage rate: 95%).

Level Distribution for Different Combination Loss1. The emulation conditions are as follows: Antenna height: 35 m Antenna type: 17 dBi, 65 deg, o title, 900 MHz Combination loss: 4.5 dB and 8 dB Propagation model: Okumura-Hata (suburbs) BTS coverage radius: 3190 m Cell edge design level: –85 dBm Area coverage rate: 95% Map: none2. The emulation result for the coverage radius of 3190 m is as follows:



The BTS edge level is designed as –85 dBm in suburbs. When the coverage radius of the concentric cell is 3,190 m, the overlaid subcell can be fully covered.

3. The emulation result for the coverage radius of 4020 m is as follows:

The BTS edge level is designed as –85 dBm in suburbs. When 4,020 m of coverage radius is planned for the underlaid subcell, there will be 40% of the overlaid subcell that does not meet the coverage requirements.



4.1.4 Wide Coverage AreasCoverage Radius of Overlaid and Underlaid Subcells in Wide Coverage Areas

Transmit power at the RF port for the underlaid subcell: 47.78 (TRX power) – 4.5 (combination loss) = 43.28 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 29.65 km (the coverage target is that the MS has a sensitivity of –104 dBm).

Transmit power at the RF port for the overlaid subcell: 47.78 (TRX power) -8 (combination loss) = 39.78 (transmit power at the RF port). The coverage radius calculated by the link budget tool is 23.4 km (the coverage target is that the MS has a sensitivity of –104 dBm).

Advantages of the Application of Concentric Cells in Wide Coverage Areas

Wide coverage is generally applied in deserts, oasis, or islands where one BTS can meet the coverage requirements. The traffic near the BTS is high and that far away from the BTS is low. The site planning should meet the capacity requirements near the BTS, as well as its wide coverage requirements.

The link budget result calculated above shows that the coverage radius of an overlaid subcell is larger than required. In this case, the overlaid subcell can be planned to meet the coverage requirements near the BTS. In addition, you can decrease the transmit power in the overlaid subcell to reduce the coverage area of the overlaid subcell. This not only meets the capacity requirements of the overlaid subcell, but also guarantees the wide coverage requirements of the underlaid subcell.

You can always change the transmit power in the overlaid subcell to adjust the overlaid and underlaid coverage, regardless of whether there is signal combination or not. This not only meets the capacity and coverage requirements, but also saves the BTS power consumption.

4.1.5 ConclusionIn all the scenarios described above, the coverage of the populated urban areas is not affected by combination loss, and the overlaid subcell can meet all the coverage requirements. In common urban areas and suburbs however, the concentric cell has to be applied to meet the coverage requirements due to the hardware restriction of the combiner. The previous emulation shows that the trunk effect of the voice service capacity, in the Erl B table, is reduced due to the coverage difference between the overlaid and underlaid subcells.



4.2 Capacity Planning4.2.1 Capacity Growth Due to Application of Concentric CellsCoverage Difference Existed Between Overlaid and Underlaid Subcells

If the overlaid subcell does not support continuous coverage, apply tight frequency reuse solution for the overlaid subcell to improve its capacity.

Example 1: There are 48 frequencies available.

When the concentric cell is not applied, the largest BTS configuration is S4/4/4 under 43 frequency reuse pattern. Each cell is configured with 29 TCHs, carrying the traffic of 21.03 Erl when the congestion rate is 2%.

When the concentric cell is applied, the BCCHs adopt the 43 pattern and the TCHs the 43 pattern. The largest BTS configuration is S2+3/2+3/2+3.One BCCH and three SDCCHs are configured in the overlaid subcell. There are 12 TCHs configured in the underlaid subcell and 24 TCHs in the overlaid subcell. The overall traffic in the concentric cell is 23. 245 (6.615+16.63) Erl. The maximum traffic described above is calculated in ideal situation where the congestion caused by the restriction in the underlaid subcell capacity is ignored.

Example 2: There are 48 frequencies available.

When the concentric cell is applied, the BCCHs and the TCHs in the overlaid subcell adopt the 43 pattern, and the other TCHs adopts the 13 pattern. The largest BTS configuration is S2+4/2+4/2+4.

As with the previous example, there are 12 TCHs configured in the underlaid subcell. The TCHs in the overlaid subcell, however, are increased to 32. The overall traffic in the concentric cell is 30.345 (6.615+32.73) Erl.

No Coverage Difference Between Overlaid and Underlaid SubcellsWhen there is no coverage difference between the overlaid and underlaid subcells, the trunk gain listed in the Erl B table will increase the cell capacity.

Table 4-1 compares the traffic among different site types.

Table 4-1 Comparison of traffic among different site types

Site Type Number of TCHs Traffic

S4/4/4 29 21.03

S2+3/2+3/2+3 12+24 23.245

S5/5/5 36 27.33

S2+4/2+4/2+4 12+32 30.345

S6/6/6 44 34.68



4.2.2 Impact of Capacity on CoverageThe main drawback of Huawei concentric cell solution at present is that the capacity of the underlaid subcell is relatively small; thus, the underlaid subcell is prone to congestion. This prevents the full use of the concentric cell feature. The following describes the application of the concentric cell in S2+3 and S2+4 scenarios, combined with Huawei equipment and networking experience.

Populated Urban AreasWith the link budget result calculated from section 2.1, the coverage radius of the underlaid subcell is 430 m and that of the overlaid subcell is 340 m. In actual networks, the coverage radius of a cell is generally smaller than 300 m in populated urban areas. In such scenarios, the restriction of combination loss on the concentric cell is not involved. Plan the coverage of the overlaid and underlaid subcells reasonably by referring to section 4.2.2.2. This concentric cell configuration not only guarantees the tight frequency reuse in the overlaid subcell, but also achieves the trunk gain listed in the Erl B table. This concentric cell is equal to a common cell using new channel allocation algorithms.

Common Urban AreasBased on the link budget result obtained from 2.2 "Handover Decision Algorithms," suppose the maximum radius of the underlaid is 800 m and that of the overlaid is 630 m.

S2+3 pattern (60 W TRX used)− Configuration in the underlaid subcell: 1 BCCH, 3 SDCCHs, and 12 TCHs− Configuration in the overlaid subcell: 24 TCHs− Suppose the traffic is evenly distributed.− Traffic in the overlaid subcell: 16.63 Erl− Traffic in the underlaid subcell: 6.615 Erl− To avoid congestion in the underlaid subcell, plan its coverage radius based on its

capacity.− Suppose that the coverage radius of the underlaid subcell is R and that of the overlaid

subcell is r. The coverage radius of the underlaid subcell can extend x meters. The traffic of the underlaid subcell is BR and that of the overlaid subcell is Br.Thus, Br*x*x + 2r*Br*x - BR*r*r = 0

Thus, x = 115 mThe coverage radius of the underlaid subcell is R, where R = r + x = 745 m.

S2+4 pattern (60 W TRX used)− Configuration in the underlaid subcell: 1 BCCH, 3 SDCCHs, and 12 TCHs− Configuration in the overlaid subcell: 32 TCHs− Suppose the traffic is evenly distributed.− Traffic in the overlaid subcell: 23.73 Erl− Traffic in the underlaid subcell: 6.615 ErlThus, x = 111 mThe coverage radius of the underlaid subcell is R, where R = r + x = 741 m.



SuburbsBased on the link budget result obtained from 2.2 "Handover Decision Algorithms," suppose the maximum radius of the underlaid is 4020 m and that of the overlaid is 3190 m.

S2+3 pattern (60 W TRX used)− Configuration in the underlaid subcell: 1 BCCH, 3 SDCCHs, 12 TCHs− Configuration in the overlaid subcell: 24 TCHs− Suppose the traffic is evenly distributed.− Traffic in the overlaid subcell: 16.63 Erl− Traffic in the underlaid subcell: 6.615 ErlThus, x = 581 mThe coverage radius of the underlaid subcell is R, where R = r + x = 3771 m.

S2+4 pattern (60 W TRX used)− Configuration in the underlaid subcell: 1 BCCH, 3 SDCCHs, 12 TCHs− Configuration in the overlaid subcell: 32 TCHs− Suppose the traffic is evenly distributed.− Traffic in the overlaid subcell: 23.73 Erl− Traffic in the underlaid subcell: 6.615 ErlThus, x = 417 mThe coverage radius of the underlaid subcell is R, where R = r + x = 3607 m.

ConclusionTo avoid traffic congestion and performance decrease of the underlaid subcell due to its capacity restriction, it is not recommended to use the maximum coverage radius calculated from the link budget. In other words, you should plan the coverage radius of the underlaid subcell based on the traffic configuration of the overlaid and underlaid subcells.

The versions before GBSS 7.0 do not support the configuration of the PDCHs in the overlaid subcell. The traffic handling capabilities of the underlaid subcell decrease after you configure PDCHs in the underlaid subcell. To avoid underlaid congestion in this case, you should further decrease its coverage. The GBSS 7.0 and later versions support the configuration of the PDCHs in the overlaid subcell. You should design the coverage radius of the underlaid subcell based on the channel configuration of the overlaid and underlaid subcells.

4.3 Frequency PlanningIn general concentric cell scenarios, the coverage between the overlaid and underlaid subcells is different. The co-frequency distance for the overlaid subcell is relatively long; thus, apply tight frequency reuse for the overlaid subcell and less tight frequency reuse for the underlaid subcell. In this way, the underlaid subcell can share the highly interfered edge traffic and improve the cell capacity.



4.4 Impact of the Concentric Cell on Data Service Performance4.4.1 Timeslot Throughput Simulation in Common Urban Areas with a Coverage Radius of 600 m43 Reuse (with 18 dB Indoor Loss)

The emulated urban areas are the real scenarios in Ha Erbin. The impact of indoor coverage uses the actual clutter in Ha Erbin as the emulation input. In actual emulation settings, the penetration loss for the building in common urban areas is set to 18 dB.

The following figure shows the emulation in outdoor application.



33 Reuse (with 18 dB Indoor Loss)






Conclusion The scenario described above involves continuous overlaid coverage. In the 43 reuse pattern, the intra-network interference is relatively small. The coding

schemes used indoors are determined by receiving level. The timeslot throughput in the overlaid subcell is lower than that of the underlaid subcell due to their loss difference. In outdoor application however, there is no penetration loss involved, and the receiving level requirements in both overlaid and underlaid subcells are met. The coding schemes are determined by C/I value. Therefore, the timeslot throughput between the overlaid and underlaid subcells is distributed evenly in outdoor application.

The 33 and 13 reuse patterns experience greater interference than the 43 pattern. The indoor coding schemes are determined by both receiving level and C/I value. Thus, the signal loss has litter impact on the coding schemes used indoors. The coding schemes used outdoors are determined by C/I value, similar to the 43 pattern.

4.4.2 Timeslot Throughput Simulation in Common Urban Areas with a Coverage Radius of 800 m43 Reuse (with 18 dB Indoor Loss)



Conclusion The scenario described above involves continuous coverage in the underlaid subcell. Compared with the overlaid continuous coverage scenarios with 8 dB combination loss,

the underlaid continuous coverage for indoor application is difficult. The uncovered area however, is small.

Compared to the overlaid continuous coverage scenarios, the coverage of this scenario is increased, accompanied with increased propagation loss. The impact of the combination loss on the data service performance is increased.

The coding schemes for indoor application is generally determined by the receiving level under different frequency reuse patterns, with no regard to the 18 dB penetration loss. With the application of frequency reuse, the intra-network interference increases, whereas the impact of the receiving level on timeslot throughput decreases.

The high receiving level in outdoor coverage is not the leading factor to determine the coding schemes. In this case, the coding schemes are determined by C/I value.

4.4.3 Timeslot Throughput Simulation in Suburbs with a Coverage Radius of 3190 m43 Frequency Reuse



33 Frequency Reuse

13 Frequency Reuse

Conclusion As there is no example scenario in this coverage radius, a 12 dB of penetration loss is

added while addressing the indoor coverage. In the 43 and 33 frequency reuse patterns, the receiving level can meet all the outdoor

coverage. Different combination loss has no impact on the distribution of timeslot throughput.

As the intra-network interference increases, the impact of the indoor level on timeslot throughput decreases.

The intra-network interference in 11 frequency reuse pattern is large and coverage level has less impact on the timeslot throughput than the C/I value does. Thus, the ultimate coding schemes are determined by C/I value.



4.4.4 Timeslot Throughput Simulation in Suburbs with a Coverage Radius of 4020 m43 Frequency Reuse

33 Frequency Reuse



13 Frequency Reuse

Conclusion In scenarios covered by underlaid subcells, 4.5 dB or 8 dB of combination loss has no

impact on outdoor timeslot throughput. In indoor application, continuous coverage for data services can be achieved with 4.5 dB

combination loss. The service performance with tight frequency reuse is nearly equivalent to that of the outdoor application though the service performance with less tight frequency reuse is worse than that of the outdoor application.

In indoor application, continuous coverage for data service cannot be achieved with 8 dB combination loss. There are also uncovered areas compared with that of the underlaid subcell.

4.4.5 ConclusionAs the coding schemes are subject to receiving level and C/I value, the impact of combination loss on data services varies with the frequency reuse pattern. To conclude, the outdoor coding schemes are determined by interference when the intra-network interference is high, and the combination loss has litter impact on data services. When the intra-network interference is low, the combination loss nearly has no impact on outdoor data services whether the concentric cell is planned by underlaid subcell or overlaid subcell. For indoor application, receiving level is the leading factor to determine the coding schemes with the increase of penetration loss and the decrease of indoor level. Therefore, high combination loss has a great impact on indoor data services.

When the concentric cell is applied due to combination loss restriction, the data service in the overlaid subcell deteriorates, compared with the normal cell. The impact degree depends on the frequency and coverage planning. Even there is no combination loss restriction, the data service in the overlaid subcell still deteriorates as the tight frequency reuse scheme is applied for the overlaid subcell.



5 Network Optimization of the Concentric Cell

5.1 Network Optimization Strategy for a Normal Concentric Cell

Table 5-1 lists the network optimization parameters for a normal concentric cell.

Table 5-1 Network optimization parameters for a common concentric cell

Parameter Configuration Suggestions

UO Signal Strength Difference

Set this parameter based on the site measurement or the transmit power difference at the RF port between the overlaid and underlaid subcells.

RX_LEV Thrsh. Generally, its value is equal to the edge handover level threshold subtracted by the UO Signal Strength Difference. You should adjust this value based on the actual terrain and traffic distribution.

RX_LEV Hysteresis The default value is 3. Increase this value if the overlaid-underlaid handover is busy or decrease this value if the overlaid-underlaid handover is difficult.

RX_QUAL Thrsh. Generally, you are advised to disable the quality threshold decision by clearing the RX_QUAL for Concentric Cell HO Allowed feature. Enable the quality threshold decision only when you are sure that the underlaid interference is smaller than the overlaid interference.

TA Thrsh. As it is not precise and flexible to use TA to determine the overlaid/underlaid boundary, you are advised to set the parameter to its maximum value to disable its function.

TA Hysteresis The default value is 0.

5.2 Network optimization strategy for an enhanced concentric cell

Table 5-1 lists the network optimization parameters for an enhanced concentric cell.



Table 5-1 Network optimization parameters for an enhanced concentric cell

Parameter Configuration Suggestions

OL to UL HO Received Level Thrsh.

Generally, its value is equal to the edge handover level threshold subtracted by the UO Signal Strength Difference. You should adjust this value based on the actual terrain and traffic distribution.

UL to OL HO Received Level Thrsh.

Generally, this value is greater than that of the OL to UL HO Received Level Thrsh. You should adjust this value based on the actual terrain and traffic distribution.

RX_QUAL Thrsh.

Generally, you are advised to disable the quality threshold decision by clearing the RX_QUAL for Concentric Cell HO Allowed feature. Enable the quality threshold decision only when you are sure that the underlaid interference is smaller than the overlaid interference.

TA Thrsh. As it is not precise and flexible to use TA to determine the overlaid/underlaid boundary, you are advised to set the parameter to its maximum value to disable its function.

TA Hysteresis The default value is 0.

Traffic Thrsh. of Underlaid Subcell

Set this parameter based on the number of TRXs configured in the overlaid/underlaid subcells and the traffic distribution. If there are many TCHs in the underlaid subcell, set the parameter to a big value; otherwise, set the parameter to a small value.

Underlaid Subcell HO Step Period (s)

Set this parameter based on the actual traffic load in the overlaid/underlaid subcells. Setting a small value increases the handover speed, but increases the system load, which may lead to unnecessary load handover.

Underlaid Subcell HO Step Level

Set this parameter based on the actual traffic load in the overlaid/underlaid subcells. Setting a small value increases the handover speed, but increases the system load, which may lead to unnecessary load handover.

Penalty Time of UL to OL HO (s)

Set this parameter based on the actual traffic load in the overlaid/underlaid subcells. Setting a big value reduces the load handovers, but may lead to underlaid congestion.



6 Impact of Concentric Cell on Coverage Performance

Concentric cell technology uses the underlaid subcell to guarantee coverage; thus, the coverage performance between the concentric cell and normal cell is the same.



7 Impact of the Concentric Cell on Network Capacity

Concentric cell improves the network capacity through its application of tight frequency reuse in the overlaid subcell. For example, the frequency bandwidth of a common cell is 3.6 MHz and the frequency reuse pattern is 43. After the concentric cell is applied, the frequency reuse pattern is 33 in the overlaid subcell and 43 in the underlaid subcell, and the frequency bandwidth of the underlaid subcell is 1 MHz and that of the overlaid subcell is 2.6 MHz. Therefore, the system capacity after using the concentric cell is ((1 + 2.6 (4 3)/(3 3 ))/3.6 -1 ) 100%=24%.



8 Impact of the Concentric Cell on Network Quality

The concentric cell improves the network quality through the transmit power decrease in the overlaid subcell. This enables the MSs near the BTS to use the overlaid frequencies, and thus reduces intra-network interference and improves network quality. The network operating experience shows that using concentric cell can improve the network quality by 30% to 40%.



9 Impact of the Concentric Cell on KPI

The application of concentric cell varies with scenarios. The KPIs of a normally activated concentric cell are nearly the same with those of a common cell. Applying concentric cell in unqualified areas affects the KPIs such as TCH Assignment Success Rate and Success Rate of Inter-Cell Handover.


Huawei Concentric Cell Optimization

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