Handover

Issue 05 (2010-11-30) Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd.

Handover Feature Parameter Description

Copyright Huawei Technologies Co., Ltd. 2010. All rights reserved.

No part of this document may be reproduced or transmitted in any form or by any means without prior written consent of Huawei Technologies Co., Ltd.

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and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.

All other trademarks and trade names mentioned in this document are the property of their respective holders.

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The information in this document is subject to change without notice. Every effort has been made in the preparation of this document to ensure accuracy of the contents, but all statements, information, and recommendations in this document do not constitute the warranty of any kind, express or implied.

BSS Handover Contents

Issue 05 (2010-11-30) Huawei Proprietary and Confidential Copyright Huawei Technologies Co.,

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Contents 1 Introduction ................................................................................................................................ 1-1

1.1 Scope ............................................................................................................................................ 1-1 1.2 Intended Audience ........................................................................................................................ 1-1 1.3 Change History .............................................................................................................................. 1-1

2 Overview ..................................................................................................................................... 2-1

3 Technical Description .............................................................................................................. 3-1 3.1 Measurement Report Processing .................................................................................................. 3-1 3.2 Handover Preprocessing ............................................................................................................... 3-2 3.3 Handover Decision Based on Handover Algorithm I ..................................................................... 3-5

3.3.1 Quick Handover .................................................................................................................... 3-5 3.3.2 TA Handover ......................................................................................................................... 3-7 3.3.3 BQ Handover ........................................................................................................................ 3-8 3.3.4 Rapid Level Drop Handover ................................................................................................. 3-9 3.3.5 Interference Handover .......................................................................................................... 3-9 3.3.6 Handover Due to No Downlink Measurement Report ........................................................ 3-10 3.3.7 Enhanced Dual-Band Network Handover ...........................................................................3-11 3.3.8 Load Handover ................................................................................................................... 3-14 3.3.9 Edge Handover ................................................................................................................... 3-16 3.3.10 Fast-Moving Micro Cell Handover .................................................................................... 3-17 3.3.11 Inter-Layer Handover ........................................................................................................ 3-19 3.3.12 PBGT Handover ............................................................................................................... 3-20 3.3.13 AMR Handover ................................................................................................................. 3-21 3.3.14 SDCCH Handover ............................................................................................................ 3-22 3.3.15 Other Handovers .............................................................................................................. 3-23

3.4 Handover Decision Based on Handover Algorithm II .................................................................. 3-23 3.4.1 Quick Handover .................................................................................................................. 3-25 3.4.2 TA Handover ....................................................................................................................... 3-26 3.4.3 BQ Handover ...................................................................................................................... 3-27 3.4.4 Interference Handover ........................................................................................................ 3-28 3.4.5 Handover Due to No Downlink Measurement Report ........................................................ 3-29 3.4.6 Enhanced Dual-Band Network Handover .......................................................................... 3-30 3.4.7 Load Handover ................................................................................................................... 3-32 3.4.8 Edge Handover ................................................................................................................... 3-32 3.4.9 Fast-Moving Micro Cell Handover ...................................................................................... 3-33 3.4.10 Better Cell Handover ........................................................................................................ 3-35 3.4.11 Handover Between a Full-Rate TCH and a Half-Rate TCH ............................................. 3-37 3.4.12 SDCCH Handover ............................................................................................................ 3-38 3.4.13 Other Handovers .............................................................................................................. 3-39

Contents BSS

Handover

ii Huawei Proprietary and Confidential Copyright Huawei Technologies Co.,

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4 Parameters ................................................................................................................................. 4-1

5 Counters ...................................................................................................................................... 5-1

6 Glossary ...................................................................................................................................... 6-1

7 Reference Documents ............................................................................................................. 7-1

BSS Handover 1 Introduction


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1 Introduction 1.1 Scope This document describes the overall procedure of Huawei handover algorithms and the specific handover decisions.

1.2 Intended Audience It is assumed that users of this document are familiar with GSM basics and have a working knowledge of GSM telecommunication.

This document is intended for:

z Personnel working on Huawei GSM products or systems z System operators who need a general understanding of this feature

1.3 Change History The change history provides information on the changes in different document versions.

There are two types of changes, which are defined as follows:

z Feature change Feature change refers to the change in the Handover feature of a specific product version.

z Editorial change Editorial change refers to the change in wording or the addition of the information that was not described in the earlier version.

Document Issues The document issues are as follows:

z 05 (2010-11-30) z 04 (2010-08-06) z 03 (2010-01-20) z 02 (2009-09-30) z 01 (2009-06-30)

05 (2010-11-30) This is the fifth commercial release of GBSS9.0.

Compared with issue 04 (2010-08-06) of GBSS9.0, issue 05 (2010-11-30) of GBSS9.0 incorporates the changes described in the following table.

1 Introduction BSS

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Change Type Change Description Parameter Change

Feature change

A description of AMR Handover is optimized. A description of Edge Handoveris optimized. A description of Inter-Layer Handover is optimized. A description of PBGT Handover is optimized. A description of Better Cell Handover is optimized.

The parameters added are as follows: z Enhanced Outgoing Cell Handover

Allowed z Enhanced Outgoing Cell Handover

Offset z Neighboring Cell Penalty Switch z Penalty Stop Level Threshold z Penalty Timer Length Level Penalty Value on Neighboring Cell

Editorial change

None. None.

04 (2010-08-06) This is the fourth commercial release of GBSS9.0.



Feature change

A description of 16-bit queuing is added in 3.2 Handover Preprocessing. A description of negative handover is added in section 3.4.10 Better Cell Handover.

The parameters changed are as follows: Cell Priority Co-BSC/MSC Adj K Bias RSCP Offset Ec/No Offset

Editorial change

None. None.

03 (2010-01-20) This is the third commercial release of GBSS9.0.


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Feature change

A description of 3.3.14 SDCCH Handover (Huawei handover algorithm I) and 3.4.12 SDCCH Handover (Huawei handover algorithm II) is added. The value range of Inter-cell HO Hysteresis in 3.3.9 Edge Handover (Huawei handover algorithm I), 3.4.8 Edge Handover (Huawei handover algorithm II), 3.3.3 BQ Handover(Huawei handover algorithm I), 3.4.3 BQ Handover (Huawei handover algorithm II), and 3.4.5 Handover Due to No Downlink Measurement Report (Huawei handover algorithm II) is changed.

The parameter changed is as follows:Inter-cell HO Hysteresis

Editorial change

The triggering conditions of better cell handover in 3.4.10 Better Cell Handover are changed.

None.

02 (2009-09-30) This is the second commercial release of GBSS9.0.

Compared with issue 01 (2009-06-30) of GBSS9.0, the following changes are incorporated:


Feature change

In 3.3.9 Edge Handover (handover algorithm I) and 3.4.8 Edge Handover (handover algorithm II), the parameters Edge HO Watch 0.5s Time, Edge HO Valid 0.5s Time, Edge HO AdjCell Watch 0.5s Time, and Edge HO AdjCell Valid 0.5s Time are changed.

The parameters are changed as follows: Handover algorithm I Edge HO Watch Time Handover algorithm II Edge HO Watch Time Handover algorithm I Edge HO Valid Time Handover algorithm II Edge HO Valid Time Edge HO AdjCell Watch Time Edge HO AdjCell Valid Time

Editorial change

The structure of the document isoptimized.

None.

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01 (2009-06-30) This is the first commercial release of GBSS9.0.



Feature change

The description of handover direction forecast during the target cell selection is added in 3.3.1 Quick Handover.

The parameters added are as follows: z Handover Direction Forecast

Enable z Chain Neighbour Cell Type z Handover Direction Forecast

Statistic Times z Handover Direction Forecast Last

Times

Editorial change

None. None.

BSS Handover 2 Overview


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2 Overview The GSM network comprises multiple cells with continuous coverage. The handover technique is introduced into the GSM system to enable the users who are in motion to continue with the current call without interruption, thus optimizing the network performance.

During a handover, the MS and BTS in service measure the conditions of uplink and downlink radio links respectively, record the measurement results into measurement reports (MRs), and then send the MRs to the BSC. The BSC determines whether to trigger a handover based on the MRs and the actual conditions of the radio network.

Huawei handover algorithms (handover algorithm I and handover algorithm II) involve measurement and MR reporting, MR processing, handover decision, and handover execution.

Huawei handover algorithms apply to the handovers on TCHs as well as the handovers on SDCCHs.

You can determine the handover algorithm used in a cell through Current HO Control Algorithm.

Figure 2-1 shows the procedure for performing Huawei handover algorithms (including handover algorithm I and handover algorithm II).

Figure 2-1 Procedure for performing Huawei handover algorithms

Handover Decision Based on Handover Algorithm I Figure 2-2 shows the procedure of handover decision based on handover algorithm I.

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Figure 2-2 Procedure of handover decision based on handover algorithm I

In handover algorithm I, five types of handover decisions are defined:

z Quick handover (including quick Power BudGet Handover (PBGT) handover and frequency offset handover). Good and stable services can be provided when the voice quality deteriorates during the fast movement of an MS. Quick handover is mainly applicable in the railway scenario.



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z Emergency handover. Emergency handover can ensure the call continuity when the radio condition severely deteriorates. Theoretically, the emergency handover has a bigger deviation than other handovers in terms of the selection of the target cell. In a normal cell, frequent emergency handovers should be avoided.

z Enhanced dual-band network handover. In an enhanced dual-band network, the resources in the overlaid DCS1800 cell and underlaid GSM900 cell can be shared during the assignment and handover procedures. That is, the calls in the high-traffic GSM900 cell can be handed over to the low-traffic DCS1800 cell to balance traffic.

z Load handover. Load handover enables the system load to be balanced among multiple cells so that the system performance can be ensured.

z Normal handover. Normal handover ensures good services when an MS is moving.

Figure 2-3 shows the handovers provided in Figure 2-2 and their priorities in handover algorithm I.

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Figure 2-3 Handover decisions based on handover algorithm I

Handover Decision Based on Handover Algorithm II Figure 2-4 shows the procedure of handover decision based on handover algorithm II.



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Figure 2-4 Procedure of handover decision based on handover algorithm II

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In handover algorithm II, three types of handover decisions are defined, as shown in Figure 2-5.

Figure 2-5 Handover decisions based on handover algorithm II

Handover Execution BTS power lift for handover function determines whether the BTS of the serving cell transmits signals at the maximum power during a handover. The BSC maximizes the transmit power of the BTS before sending a handover command to the MS. The BSC does not adjust the BTS power during the handover to ensure the success of the handover.

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3 Technical Description 3.1 Measurement Report Processing Measurement report processing involves measurement report interpolation and filtering.

NE Selection for Measurement Report Processing The processing can be performed either on the BSC side or on the BTS side.

z If MR.Preprocessing is set to No, then the processing is performed on the BSC side. z If MR.Preprocessing is set to Yes, then the processing is performed on the BTS side. By setting the

parameters Transfer Original MR, Transfer BTS/MS Power Class, and Sent Freq.of preprocessed MR, you can specify the contents of the MRs to be provided and the period during which the MRs are provided. This decreases the signaling traffic on the Abis interface and the traffic volume processed by the BSC.

Data Selection for Measurement Report The MR can be classified into enhanced MR and normal MR. The parameter Measurement Report Type determines the type to be used.

In the MR, the TCH measurement of the serving cell is classified into FULL SET and SUB SET.

Measurement Report Interpolation The neighboring cell indexes are found on the basis of the BCCH frequencies and BSICs provided by the MS. Then, the uplink and downlink measurement results are obtained from the measurement reports.

z If measurement reports are issued continuously, they are directly added to the measurement report list.

z If measurement reports are not issued continuously and the number of lost measurement reports is smaller than the value of Allowed MR Number Lost, the system performs operations as follows: For the serving cell, the handover algorithm I performs the linear interpolation for the MRs. The lowest values are applied to the interpolation of MRs by the handover algorithm II according to the protocols; that is, level 0 (-110 dBm) and quality 7 are applied in the interpolation.

For the neighboring cell, the lowest value is applied to the lost level value according to the protocols; that is, level 0 (-110 dBm) is applied in the interpolation.

If no MR is reported because the RX level in the neighboring cell is too low, level 0 (-110 dBm) is applied in the interpolation. z If measurement reports are not issued continuously and the number of lost measurement reports is

greater than the value of Allowed MR Number Lost, the previous measurement reports are discarded. When new measurement reports are issued, calculation is done again.

Measurement Report Filtering Filtering is performed on measurement reports obtained continuously from the measurement report list. Averaging is performed on uplink/downlink RX level, uplink/downlink RX quality, Timing Advance(TA), Radio Quality Indication(RQI), BTS power, 2G neighboring cell level, and the Common PIlot CHannel(CPICH ), Received Signal Code Power(RSCP), and Ec/No of neighboring 3G cell. The averaging minimizes the effect on the result of handover decision due to sudden changes in the measurement values.

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Power control compensation needs to be performed for the downlink RX level of the serving cell by the handover algorithm II. If you compare the RX level of the serving cell after the power control with that of all BCCH TRXs of the neighboring cell, there is no mapping between them. In situations where the cells overlap severely, the handover is easily triggered, thus causing the ping-pong handover. After the power control compensation is performed, the RX level of the serving cell can reflect the coverage condition of the BCCH TRX of the serving cell. The power control compensation of the serving cell is performed after the interpolation processing and before the filtering processing. In general, the compensation of power control is calculated by adding the downlink RX level of the serving cell and twice the current downlink transmit Power Level of the BTS.

The number of consecutive measurement reports required for filtering are determined by the measurement object and channel type. See Table 3-1 for details.

Table 3-1 Parameters related to the number of measurement reports

Measurement Object Channel TypeParameter

Receive level of the serving cell

SDCCH Filter Length for SDCCH Level

TCH Filter Length for TCH Level

Quality of the serving cell

SDCCH Filter Length for SDCCH Qual.

TCH Filter Length for TCH Qual

TA of the serving cell

TCH Filter Length for TA

SDCCH TA filter length for SDCCH level

Receive level of the neighboring cell

BCCH Filter Length for Ncell RX_LEV

SDCCH NCell filter length for SDCCH level

Power of the BTS in the serving cell

TCH Filter Length for TCH Level

RQI TCH Filter Length for TCH Qual

If consecutive measurement reports are insufficient, the filtering fails. The handover decision is not performed.

3.2 Handover Preprocessing Handover Penalty According to the neighboring cell information in the measurement report and the parameters, the system performs handover preprocessing and adjusts the priorities of the neighboring cells.

The handover penalty is performed after successful fast-moving micro cell handover, TA handover, BQ handover, fast-moving micro cell handover, OL subcell to UL subcell handover within an enhanced concentric cell, and after the handover failures.

In handover algorithm II, in addition to the situations mentioned above, the handover penalty is also performed after successful or failed load handover and interference handover.



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In handover decision procedure of handover algorithm II, the handover penalty is performed after the network characteristics adjustment and before the emergency handover decision. z After the quick handover, TA handover, Bad Quality (BQ) handover, or load handover (in handover

algorithm II) is successfully performed, the penalty level is subtracted from the actual RX level of the original cell during the penalty period. Table 3-2 lists the parameters related to handover penalty.

Table 3-2 Parameters related to handover penalty

Handover Parameter

Quick handover Quick Handover Punish Time Quick Handover Punish Value

TA Handover Penalty Level after TA HO Penalty Time after TA HO

BQ Handover Penalty Level after BQ HO Penalty Time after BQ HO

Load handover (handover algorithm II)

Penalty Time on Load HO Penalty Value on Load HO

z After the fast-moving micro cell handover is successfully performed, penalty is performed on all the neighboring cells of the micro cell. Related parameters are Penalty on Fast Moving HO and Penalty Time on Fast Moving HO.

z If an MS fails to initiate an intra-cell AMR TCHF to TCHH handover, it cannot initiate another intra-cell AMR TCHF to TCHH handover within Penalty Time after AMR TCHF-H HO Fail.

z In handover algorithm II, after the interference handover is initiated, this handover is not allowed to be initiated again within Penalty Time on Interfere HO regardless of whether the handover is successful or not.

z After the OL subcell to UL subcell handover within an enhanced concentric cell is successful, the handover from UL subcell to OL subcell is not allowed within Penalty Time of UtoO HO.

z After the OL cell to UL cell handover in the enhanced dual-band network is successful, the handover from UL cell to OL cell is not allowed within Inter UL/OL Subcells HO Penalty Time.

z After the handover fails, different penalties are performed on the target cell based on the causes: If the handover to a neighboring 2G or 3G cell fails, the actual RX level of the target cell is subtracted by Penalty Level after HO Fail for neighboring cell ranking during the penalty.

Based on the handover failure cause, the penalty time could be UmPenaltyTimer, RscPenaltyTimer, or CfgPenaltyTimer.

If the OL subcell to UL subcell handover within a concentric cell fails, the handover from OL subcell to UL subcell is not allowed within Penalty Time after OtoU HO Fail.

If the UL subcell to OL subcell handover within a concentric cell fails, the handover from UL subcell to OL subcell is not allowed within Penalty Time after UtoO HO Fail.


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Basic Ranking Basic ranking is performed after handover penalty to generate a candidate cell list in descending order taking the following information into account: RX levels of the serving cell and neighboring cells carried in the MRs, hysteresis, usage of TCHs in the neighboring cells, and so on.

z In the case of non-directed retry, if an MS in an external BSC cell occupies an SDCCH and Inter-BSC SDCCH HO ALLowed is set to No, then this cell should be removed from the candidate cell list. In other words, the handover to this external BSC cell is prohibited.

z If a neighboring 2G cell and the serving cell are controlled by the same BSC and the TCH usage of the neighboring cell is 100%, then the neighboring cell should be removed from the candidate cell list; that is, the handover to this neighboring cell is prohibited.

z If the downlink RX level of a neighboring 2G cell is lower than the sum of Min DL Level on Candidate Cell and Min Access Level Offset, then the neighboring cell should be removed from the candidate cell list; that is, the handover to this neighboring cell is prohibited.

z If the uplink RX level of a neighboring 2G cell is lower than the sum of Min UL Level on Candidate Cell and Min Access Level Offset, then the neighboring cell should be removed from the candidate cell list; that is, the handover to this neighboring cell is prohibited.

z If a neighboring 3G cell is an FDD cell, the cell is processed according to FDD REP QUANT: If FDD REP QUANT is set to Ec/N0, and the Ec/N0 of a neighboring cell is lower than Min Ec/No threshold, the neighboring cell should be removed from the candidate cell list; that is, the handover to this neighboring cell is prohibited.

If FDD REP QUANT is set to RSCP, and the RSCP of a neighboring cell is lower than Min RSCP threshold, the neighboring cell should be removed from the candidate cell list; that is, the handover to this neighboring cell is prohibited.

z If a neighboring 3G cell is a TDD cell and the RSCP after penalty is lower than the Min RSCP threshold, the neighboring cell should be removed from the candidate cell list; that is, the handover to this neighboring cell is prohibited.

z Calculate the difference between the downlink RX level of the neighboring cells and the downlink RX level of the serving cell. Based on the difference, rank the neighboring cells in descending order.

Network Characteristics Adjustment Network characteristics adjustment is a process in which the position of each cell in the candidate cell list is determined based on the related network information. Network characteristics adjustment provides the final candidate cell list for handover decision.

After the network characteristics adjustment, the final candidate cell list (including neighboring cells and serving cell) is generated. The candidate cells are ranked in descending order by priority. Then, the handover decision procedure starts.

In handover algorithm II, the emergency handover decision is made after the network characteristics adjustment.

After the emergency handover decision, Penalty Value on Load HO is subtracted from the level of the original cell within Penalty Time on Load HO if the load handover is successful. The level of the target cell changes after the penalty of load handover; then, the network characteristics needs to be readjusted.

In handover algorithm I, all related factors are adjusted in network characteristics adjustment phase; in handover algorithm II, some of the factors are adjusted before the emergency handover decision procedure is initiated.



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Forced Handover If the forced handover is triggered, the subsequent handover decisions are not performed.

The purpose of the forced handover is as follows:

z If no TCH is available in the serving cell during the MS access process, the directed retry procedure is performed when Directed Retry is set to Yes.

z When BTS maintenance is performed, the MSs under control of the related BTS should be handed over to the cells controlled by a functional BTS to ensure that no call drop occurs during BTS maintenance.

The forced handover is classified into these four types:

z Outgoing cell handover (direct retry) z Outgoing BTS handover z Outgoing BSC handover z Specified target cell list handover

3.3 Handover Decision Based on Handover Algorithm I According to the emergency condition of an MS in the network, the handover decision based on handover algorithm I is made in the following order: quick handover, emergency handover, enhanced dual-band network handover, load handover, and normal handover.

Handover decision based on handover algorithm I involves the following procedures:

z Determining whether the serving cell meets the triggering conditions z Selecting corresponding candidate cells

In handover algorithm I, Inter-rat HO Preference specifies whether a neighboring 2G cell or a neighboring 3G cell is preferred.

z When Inter-rat HO Preference is set to Preference for 2G Cell: A neighboring 2G cell is preferred. If the candidate cell list contains suitable neighboring 3G cells but no suitable neighboring 2G cells, a neighboring 3G cell is selected.

z When Inter-rat HO Preference is set to Preference for 3G Cell: A neighboring 3G cell is preferred. If the candidate cell list contains suitable neighboring 2G cells but no suitable neighboring 3G cells, a neighboring 2G cell is selected.

z When Inter-rat HO Preference is set to Preference for 2G Cell: If the RX level of a candidate 2G cell is lower than or equal to HO Preference Threshold for 2G Cell, a neighboring 3G cell is preferred.

If the triggering conditions of emergency handover are met and there is at least one candidate cell, then the emergency handover timer Min Interval for Emerg. HO is started. Another emergency handover decision can be performed only when Min Interval for Emerg. HO times out.

3.3.1 Quick Handover Quick handover aims to increase the handover success rate of an MS moving at a high speed and to ensure the call continuity and low call drop rate. Quick handover applies to the scenario where an MS moves fast along an urban backbone road, a selected route, or a high-speed railroad.

Quick Handover Types Quick handover consists of frequency offset handover and quick PBGT handover.


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z Frequency offset handover Whether the MS is moving away from the serving cell is determined based on the frequency offset information provided by an MS moving at a high speed. Frequency offset handover decision is made according to the uplink/downlink RX level of the serving cell and the path loss of neighboring cells.

z Quick PBGT handover Quick PBGT handover decision is made according to the path loss of neighboring cells.

For quick handover, the handover response speed is enhanced by:

z Accurately calculating the moving speed of the MS z Derestricting the interval between handover decisions z Reducing the number of measurement reports for the handover decision z Introducing the filtering

Quick Handover Preparation The preparation for quick handover involves the following aspects:

z Frequency offset is decoded from the measurement report. Frequency offset of the MS is obtained from the uplink measurement report that the BTS sends to the BSC.

z filtering is performed on the measurement report.

Triggering Conditions During handover decision, it is first determined whether the triggering conditions of frequency offset handover are met. When the BTS cannot send the frequency offset information or the reported frequency offset information is invalid, quick PBGT handover is triggered, provided that other conditions of frequency offset handover are met.

If Quick Handover Enable is set to Yes, the triggering conditions of quick handover are as follows:

z The MS is moving away from the serving cell (the frequency offset in the measurement result is a negative value) and the moving speed of the MS is greater than Quick Move Speed Threshold.

z The filtered uplink level of the serving cell is lower than Quick Handover Up Trigger Level. z The compensated downlink level of the serving cell is lower than Quick Handover Down Trigger

Level. z The path loss of configured chain neighboring cells is lower than the specified threshold of the path

loss of the serving cell. In other words, PBGT(n) is greater than or equal to 0.

The triggering conditions of quick handover are as follows:

z If the last three conditions are met simultaneously, the decision is made as follows: If the first condition is met, a frequency offset handover is performed. If the first condition is not met, a quick PBGT handover is performed.

z If all the last three conditions are not met, quick handover is not triggered.

Target Cell Selection The target cell must be a chain neighboring cell of the serving cell. The target cell can be obtained through the setting of Chain Neighbor Cell. If Handover Direction Forecast Enable is set to Yes, a neighboring cell in the moving direction of the MS is selected preferentially.

To forecast the moving direction of the MS, the direction of a chain neighboring cell (A or B) compared with the serving cell is specified by Chain Neighbour Cell Type. If the number of times that the MS is



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handed over to neighboring cells in the same direction (B for example) is greater than or equal to Handover Direction Forecast Last Times when the handover time reaches Handover Direction Forecast Statistic Times, then the MS is inferred to be moving towards the B direction. Subsequently, the MS is preferentially handed over to the neighboring cell whose Chain Neighbour Cell Type is B.

Limitations The limitations on quick handover are as follows:

z The serving cell cannot be selected as the target cell. z The candidate cells for quick handover must be chain neighboring cells of the serving cell. Each cell

can be configured with a maximum of three chain neighboring cells. z After a quick handover is successful, the penalty is performed on the original cell during the penalty

time to prevent an immediate handover back to the original cell. The penalty time and penalty value are specified by Quick Handover Punish Time and Quick Handover Punish Value respectively.

3.3.2 TA Handover TA handover is a type of emergency handover. The TA handover decision is made according to the TA value reported by the MS.

The TA value of a normal cell ranges from 0 to 63 and that of an extended cell ranges from 0 to 229. The TA can be stepped up or down in steps of 553.5 m. The TA value of 63 corresponds to a distance of 35 km.

Triggering Conditions TA handover is triggered when the following conditions are met:

z TA HO Allowed is set to Yes. z Filtered TA value in the measurement report provided by the MS is greater than or equal to TA

Threshold.

The TA handover can be triggered only when the preceding two conditions are met simultaneously.

From the perspective of the triggering conditions of TA handover, TA can be regarded as a limitation to the size of a cell.

Target Cell Selection The target cell should have the highest priority in the candidate cell list after handover preprocessing. In addition, the target cell should meet the following conditions:

z The serving cell cannot be selected as the target cell. z If TA Threshold of a co-site neighboring cell is lower than or equal to the TA Threshold of the serving

cell, a handover to the neighboring cell is prohibited.

If the triggering conditions of TA handover are met but the candidate 2G cells are not suitable, the following operations are performed:

z If a neighboring 3G cell is available, if Inter-RAT Out BSC Handover Enable is set to Yes, and if the MS supports the 2G/3G inter-RAT handover, the 2G/3G inter-RAT handover is performed.

z If no neighboring 3G cell is available, if Inter-RAT Out BSC Handover Enable is set to No, or if the MS does not support the 2G/3G inter-RAT handover, the decision on whether to initiate another type of emergency handover is made.


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Limitations After the TA handover is successful, the penalty is performed on the original cell. During Penalty Time after TA HO, Penalty Level after TA HO is subtracted from the level of the original cell to prevent an immediate handover back to the original cell.

3.3.3 BQ Handover BQ handover is a type of emergency handover in which the system makes the decision based on the uplink/downlink RX quality on the Um interface.

The RX quality is measured in bit error rate (BER). The BSC measures the quality of a radio link based on the quality class in the measurement report. The probable cause of an increase in BER is that the signal power is too low or the channel interference increases.

Triggering Conditions If BQ HO Allowed is set to Yes, the triggering conditions of BQ handover are as follows:

z The uplink RX quality is greater than or equal to the uplink RX quality threshold of the serving cell. z The downlink RX quality is greater than or equal to the downlink RX quality threshold of the serving

cell.

The BQ handover is triggered when either of the preceding conditions is met.

The parameters for specifying the uplink and downlink RX quality thresholds are as follows:

z For non-AMR calls, the parameter for specifying the uplink RX quality threshold is UL Qual. Threshold and the parameter for specifying the downlink RX quality threshold is DL Qual. Threshold.

z For AMR FR calls, the parameter for specifying the uplink RX quality threshold is UL Qual. Limit for AMR FR and the parameter for specifying the downlink RX quality threshold is DL Qual. Limit for AMR FR.

z For AMR HR calls, the parameter for specifying the uplink RX quality threshold is UL Qual. Limit for AMR HR and the parameter for specifying the downlink RX quality threshold is DL Qual. Limit for AMR HR.


z If the target cell is a neighboring cell, the RX level of the target cell must meet the following condition: Filtered downlink RX level of the target cell > Filtered downlink RX level of the serving cell + (Inter-cell HO Hysteresis of the serving cell configured for the neighboring cell - 64) - (BQ HO Margin - 64)

In handover algorithm I, if there is only one cell in the candidate cell list and the cell is a neighboring cell, then the preceding condition need not be met. z In handover algorithm I, if there is no neighboring cell, Intracell HO Allowed is set to Yes, and the

serving cell is not in the intra-cell handover penalty state, then the MS is handed over to the serving cell. A channel with different frequency band, different frequency, different TRX, or different timeslot is preferred (priority: different frequency band > different frequency > different TRX > different timeslot).

If the triggering conditions of BQ handover are met but the candidate 2G cells are not suitable, the following operations are performed:




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Limitations After the BQ handover is successful, the penalty is performed on the original cell. During Penalty Time after BQ HO, Penalty Level after BQ HO is subtracted from the level of the original cell to prevent an immediate handover back to the original cell.

3.3.4 Rapid Level Drop Handover Rapid level drop handover is a type of emergency handover.

In edge handover and PBGT handover, the mean value filtering and P/N decision methods are not responsive to short-period rapid level drop. Therefore, to solve the rapid level drop problem, the finite impact response filtering can be performed on the original RX level. This filtering method is responsive to the rapid level drop based on the drop slope of the original RX level.

Triggering Conditions If Rx_Level_Drop HO Allowed is set to Yes, the triggering conditions of rapid level drop handover are as follows:

z Filtered uplink level < Edge HO UL RX_LEV Threshold z A1 x C(nt) + A2 x C(nt - t) + A3 x C(nt - 2t) + + A8 x C(nt - 7t) < B

Here, A1 indicates Filter Parameter A1, A2 indicates Filter Parameter A2, A3 indicates Filter Parameter A3, A4 indicates Filter Parameter A4, A5 indicates Filter Parameter A5, A6 indicates Filter Parameter A6, A7 indicates Filter Parameter A7, and A8 indicates Filter Parameter A8. B indicates Filter Parameter B.


z The target cell has a higher priority than the serving cell. z The serving cell cannot be selected as the target cell.

If the triggering conditions of rapid level drop handover are met but the candidate 2G cells are not suitable, the following operations are performed:



3.3.5 Interference Handover In handover algorithm I, interference handover is a type of emergency handover.

Interference handover helps protect the interfered calls and reduce the network interference. It is applicable to scenarios with interference.


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In handover algorithm I, the difference between interference handover and BQ handover is that in BQ handover the bad quality resulting from both coverage and interference is checked. In interference handover, the bad quality resulting from coverage is not checked.

Triggering Conditions If Interference HO Allowed is set to Yes, the triggering conditions of interference handover are as follows:

z The filtered value of uplink RX quality is greater than or equal to the specified RX quality threshold at the current uplink RX level.

z The filtered value of downlink RX quality is greater than or equal to the specified RX quality threshold at the current downlink RX level.

The interference handover is triggered if either of the previous conditions is met.

The parameters for specifying the uplink and downlink RX quality thresholds are as follows:

z For non-AMR FR calls, the parameter for specifying the RX quality threshold is Interfere HO Qual. Thresh n for Non-AMR FR, where 1 n 12.

z For AMR FR calls, the parameters for specifying the RX quality threshold are Interfere HO Qual. Thresh n for Non-AMR FR (1 n 12) and Interfere HO Qual. Thresh Offset for AMR FR. If n = 1, the RX quality threshold is Interfere HO Qual. Thresh 1 for Non-AMR FR. If 2 n 12, the RX quality threshold is Interfere HO Qual. Thresh n for Non-AMR FR + Interfere HO Qual. Thresh Offset for AMR FR.

Target Cell Selection In handover algorithm I, the target cell should have the highest priority in the candidate cell list. In addition, the target cell should meet the following conditions:

z If Intracell HO Allowed is set to Yes and the intra-cell handover penalty timer expires, the serving cell can be selected as the target cell.

When a number of consecutive intra-cell handovers occur, Forbidden time after MAX Times is triggered and the intra-cell handover is prohibited in the corresponding period. z If the filtered level of a neighboring cell after handover penalty Inter-layer HO Threshold of the

neighboring cell + Adjacent Cell Inter-layer HO Hysteresis - 64, this neighboring cell can serve as the target cell.

If the triggering conditions of interference handover are met but the candidate 2G cells are not suitable, the following operations need to be performed:



3.3.6 Handover Due to No Downlink Measurement Report Handover due to no downlink measurement report is performed on the basis of the uplink quality. The purpose is to ensure the call continuity and minimize the possibility of call drops.



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Handover due to no downlink measurement report is generally caused by adverse radio environment on the uplink. In this case, the requirements of the filtering algorithm cannot be met, so other handover decisions cannot be performed.

Triggering Conditions In handover algorithm I, the triggering conditions of handover due to no downlink measurement report are as follows:

z No Dl Mr.HO Allowed is set to Yes. z There is no downlink information in the measurement report of the call. z The filtered value of uplink quality is greater than or equal to No Dl Mr.Ul Qual HO Limit. z The number of lost downlink MRs is smaller than Cons.No Dl Mr.HO Allowed Limit. z For TCH, the number of saved MRs with uplink quality value is greater than Filter Length for TCH

Qual; for SDCCH, the number of saved MRs with uplink quality value is greater than Filter Length for SDCCH Qual..

When all the previous conditions are met, the handover due to no downlink measurement report is triggered.

Target Cell Selection In handover algorithm I, the conditions for selecting the target cell are as follows:

z The ranked neighboring cells recorded in the last complete measurement report are saved as candidate cells.

z Preferably a neighboring cell is selected as the target cell. z If no neighboring cell is available, the serving cell is selected as the target cell.

3.3.7 Enhanced Dual-Band Network Handover Enhanced dual-band network handover is performed based on the traffic volume of the overlaid and underlaid cells and based on the receive level.

Enhanced dual-band network handover is classified into the following types:

z Handover due to high load in the underlaid cell z Handover due to low load in the underlaid cell z Handover due to MS movement to the border of the overlaid cell

Triggering Conditions of Handover Due to High Load in the Underlaid Cell The triggering conditions of the handover due to high load in the underlaid cell are as follows:

z The two cells are in the enhanced dual-band network and Load HO Allowed is set to Yes. z The MS supports the frequency band on which the overlaid cell operates. z The handover due to high load in the underlaid cell is performed only on TCHs. z The load in the underlaid cell is higher than or equal to UL Subcell General Overload Threshold. z The load in the overlaid cell is lower than Inner Cell Serious OverLoad Thred. z The system traffic volume is lower than or equal to Subcell HO Allowed Flow Control Level. z The current call is within the handover margin and the receive level is greater than or equal to

Incoming OL Subcell HO Level TH.


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When all the preceding conditions are met, the handover due to high load in the underlaid cell is triggered.

If the load of the underlaid subcell in the cell is higher than or equal to UL Subcell Serious Overload Threshold, then the handover margin is adjusted in a period of UL Subcell Load Hierarchical HO Periods subtracted by MOD Step LEN of UL Load HO Period. The step length for handover margin adjustment is specified by Step Length of UL Subcell Load HO.

Triggering Conditions of Handover Due to Low Load in the Underlaid Cell The triggering conditions of the handover due to low load in the underlaid cell are as follows:

z The load in the underlaid cell is lower than UL Subcell Lower Load Threshold. z The system traffic volume is lower than or equal to Subcell HO Allowed Flow Control Level. z The current call is within the handover margin and the receive level is greater than or equal to

Outgoing OL Subcell HO Level TH.

When all the preceding conditions are met, the handover due to low load in the underlaid cell is triggered.

If the load of the underlaid subcell is lower than UL Subcell Lower Load Threshold for a specified period, then the handover margin is adjusted in a period of OL Subcell Load Diversity HO Period. The step length for handover margin adjustment is specified by Step Length of OL Subcell Load HO.

Triggering Conditions of Handover Due to MS Movement to the Border of the Overlaid Cell The triggering conditions of the handover due to MS movement to the border of the overlaid cell are as follows:

z SS(s) < Thdouter z SS(u) - SS(n) < ATCB_THRD - ATCB_HYST

Here, SS(s): specifies the filtering compensated downlink RX level in the serving cell. Thdouter: specifies Outgoing OL Subcell HO Level TH. SS(u): specifies the downlink level (power compensation is performed on the downlink level based on the measurement) of the underlaid cell where the call is originated. If the SS(u) value cannot be obtained, you can infer that the decision of enhanced dual-band network handover is not performed and the decision condition is met by default.

SS(n): The best neighboring cell is the one whose measured BCCH level is the highest among neighboring cells. SS(n) is the signal level of the best neighboring cell that operates on the same frequency band, locates at the same layer, and has the same priority as the underlaid cell but is not co-sited with the underlaid cell. If such a neighboring cell is not available, the value of SS(n) is -110 dBm.

ATCB_THRD: specifies Distance Between Boundaries of Subcells. ATCB_HYST: specifies Distance Hysteresis Between Boundaries. Handover due to MS movement to the border of the overlaid cell is triggered if either of the preceding conditions is met.



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z In the adapter distance to cell border(ATCB) handover algorithm, the border between the overlaid and underlaid cells is

determined according to the signal strength of the serving cell and that of neighboring cells. If SS(s) = SS(n), the system considers that the MS is located at the border of the underlaid cell. If SS(s) - SS(n) > ATCB_THRD, the system considers that the MS is located in the coverage area of the overlaid cell. The coverage area of the overlaid cell is determined according to different networking and coverage conditions of the existing network. In addition, the overlaid cell of the serving cells and the overlaid cell of the neighboring cells will not overlap regardless of the distance between BTSs.

z The handover margin specifies the range of signal level. In the case of overlaid/underlaid load handover on the enhanced dual-band network, the MSs whose downlink levels are within the handover margin are handed over level by level.

Target Cell Selection The requirements for target cell selection in the enhanced dual-band network are as follows:

z For the handover due to high load in the underlaid cell, the MS must be handed over to the overlaid cell.

z For the handover due to low load in the underlaid cell, the MS must be handed over to the underlaid cell.

z For the handover due to MS movement to the border of the overlaid cell, the MS is handed over to the neighboring cell that ranks first among neighboring cells. The MS should not be handed over to the cell that ranks after the serving cell. Generally, the target cell is the underlaid cell. The target cell can also be another neighboring cell.

Limitations The limitations on the handover due to high load in the underlaid cell are as follows:

z If the cell where the call is located is on an enhanced dual-band network, Cell Inner/Extra Property is set to Extra(Extra).

z The Load HO Allowed parameter should be set. z The maximum range of the handover margin is from 63 to Incoming OL Subcell HO Level TH. The

MS with the highest receive level is handed over first.

The limitations on the handover due to low load in the underlaid cell are as follows:

z If the cell where the call is located is on the enhanced dual-band network, Cell Inner/Extra Property is set to Inner(Inner).

z The Load HO of OL Subcell to UL Subcell parameter should be set. z The maximum range of the handover margin is from 63 to Outgoing OL Subcell HO Level TH. The

MS with the lowest receive level is handed over first.

The limitations on the handover due to MS movement to the border of the overlaid cell are as follows:

z If the cell where the call is located is on the enhanced dual-band network, Cell Inner/Extra Property is set to Inner(Inner).

Impact of the Enhanced Dual-Band Network Handover on the Existing Algorithm The impact of the enhanced dual-band network handover on the existing algorithm is as follows:

z On the enhanced dual-band network, the MS should not be handed over to a cell in the same underlaid/overlaid cell group when the load handovers between the overlaid cell and the underlaid cell (specified by Load HO Allowed and Load HO of OL Subcell to UL Subcell) are allowed. This is to prevent a load handover of a normal cell from colliding with a load handover between the overlaid cell and the underlaid cell on the network.


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z The PBGT handover algorithm may cause inter-cell handover; thus, the MS should not be handed over to the cell in the same group in the case of PBGT handover between cells on the enhanced dual-band network.

3.3.8 Load Handover In the network, some cells carry heavy load whereas the overlapping upper-layer cells and the neighboring cells may carry light load. To balance the load of these cells, the load handover is required.

In a load handover procedure, some load in heavy-load cells is switched to light-load cells. Meanwhile, the load in neighboring cells is not switched to heavy-load cells.

Load handover can be performed between cells at different layers. Figure 3-1 shows the details.

For details about the inter-RAT load handover, see the 2G/3G Interoperability Feature Parameter Description.

Figure 3-1 Load handover between cells

To perform load sharing, increase Edge HO DL RX_LEV Threshold so that the load at the border of a cell is switched to a neighboring cell with light load.

Whether a cell carries heavy load or light load is determined by the traffic volume in the cell, that is whether the traffic volume (generally TCH usage) in the cell exceeds the preset threshold.

z If the traffic volume in a cell is greater than Load HO Threshold, you can infer that the load in this cell is heavy. The load handover algorithm needs to be enabled.

z If the traffic volume in a cell is lower than Load handover Load Accept Threshold, you can infer that the load in this cell is light and the cell can receive load from the heavy-load cells.

Load handover may lead to many handovers. Therefore, the load of the system CPU should be considered before load handover is performed. In other words, the system traffic volume should be taken into account. In addition, to prevent too many MSs from being handed over at a time, load handover is performed step by step. In other words, the edge handover threshold is increased on the basis of Load HO Step Level (CLS_Ramp) and Load HO Step Period (CLS_Period). When the increase in the edge handover threshold equals Load HO Bandwidth (CLS_Offset), the edge handover threshold is not increased any more. See Figure 3-2 for details.



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Figure 3-2 Load handover

Triggering Conditions If Load Handover Support is set to Yes, the triggering conditions of load handover are as follows:

z The CPU usage of the system is less than or equal to System Flux Threshold for Load HO. z The current load of the serving cell is greater than or equal to Load HO Threshold.

Target Cell Selection The conditions for selecting the target cell are as follows:

z Filtered RX level after handover penalty Inter-layer HO Threshold + Adjacent Cell Inter-layer HO Hysteresis - 64

z The serving cell cannot be selected as the target cell. z If the target cell and the serving cell are in the same BSC, a load handover is performed when the

current load of the target cell is lower than Load handover Load Accept Threshold. z If the target cell and the serving cell are not in the same BSC, a load handover is performed when the

load of the target cell is lower than Load handover Load Accept Threshold and Inter BSC Load Information Allowed is set to Yes.

Examples The system assigns MSs to different load handover margins based on the downlink RX level. The load handover algorithm is used to hand over the MSs out of a cell step by step.

1. The MSs in load handover margin 1 are handed over to the neighboring cells. Load handover margin 1 specifies the area where the downlink level ranges from Edge HO DL RX_LEV Threshold to the sum of Edge HO DL RX_LEV Threshold and Load HO Step Level.

2. After a Load HO Step Period elapses, the MSs in load handover margin 2 are handed over to the neighboring cells. The load handover margin 2 specifies the area where the downlink level ranges from Edge HO DL RX_LEV Threshold to the sum of Edge HO DL RX_LEV Threshold and (2 x Load HO Step Level).

3. The load handover stops when the traffic volume in the cell is less than or equal to Load HO Threshold.

The load handover is performed step by step to prevent call drops caused by a sudden increase in CPU load or the congestion in the target cell.


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3.3.9 Edge Handover Edge handover is performed on the basis of receive level.

To trigger an edge handover, the receive level of the target cell should be at least one hysteresis value (specified by Inter-cell HO Hysteresis - 64) greater than the receive level of the serving cell.

Triggering Conditions If Edge HO Allowed is set to Yes, the triggering conditions of edge handover are as follows:

z Either of the following conditions is met. The filtered downlink RX level of the serving cell is lower than Edge HO DL RX_LEV Threshold. The filtered uplink RX level of the serving cell is lower than Edge HO UL RX_LEV Threshold.

z RX level of the neighboring cell > RX level of the serving cell + Inter-cell HO Hysteresis - 64

An edge handover is triggered when the P/N criterion is met, that is, when the previous conditions are met for Handover Algorithm I Edge HO Valid Time within Handover Algorithm I Edge HO Watch Time. The parameters used for P/N criterion judgment must be configured for the neighboring cells. In different radio conditions, these parameters should be configured differently for the neighboring cells to ensure that an optimal target cell is selected during handover.

When both Edge HO Allowed and Enhanced Outgoing Cell Handover Allowed are set to YES(Yes),

z The condition for triggering uplink edge handover is as follows: SS_ULs_f



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Figure 3-3 Edge handover

Target Cell Selection The target cell should have the highest priority among the candidate cells. In addition, it should meet the following conditions:

z The serving cell cannot be selected as the target cell. z After cells are ranked, the target cell must have a higher priority than the serving cell.

A cell becomes the target cell if the previous conditions are met for Edge HO AdjCell Valid Time within Edge HO AdjCell Watch Time.

If the triggering conditions of edge handover are met but the candidate 2G cells are not suitable, the following operations are performed:


z If no neighboring 3G cell is available, if Inter-RAT Out BSC Handover Enable is set to No, or if the MS does not support the 2G/3G inter-RAT handover, the decision on whether to initiate another type of handover is made.

3.3.10 Fast-Moving Micro Cell Handover Fast-moving micro cell handover is performed from a micro cell to a macro cell according to the relative speed of an MS so that the number of handovers can be minimized.

Fast-moving micro cell handover applies to the following scenarios:

z If an MS is moving fast in a micro cell, it is handed over to a macro cell. z To prevent an MS that is moving fast in a macro cell from entering a micro cell, time penalty is

performed on the micro cell so that the fast-moving MS camps on the macro cell.

Figure 3-4 shows the fast-moving micro cell handover.


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Figure 3-4 Fast-moving micro cell handover

Triggering Conditions If MS Fast Moving HO Allowed is set to Yes, the handover decision procedure of fast-moving micro cell handover is as follows:

1. When the triggering conditions of edge handover or PBGT handover are met, the fast-moving micro cell handover decision is started.

2. When the period during which the MS camps on the serving cell is shorter than MS Fast-moving Time Threshold, the number of cells through which the fast-moving MS passes is incremented by one.

The cell counted by the system must locate at a layer lower than layer 4. In other words, it must be a non-Umbrella cell.

3. When the number of cells that the MS passes in fast movement reaches MS Fast-moving Watch Cells, the fast-moving micro cell handover is triggered if the number of cells that the MS passes in fast movement counted by the system is greater than or equal to MS Fast-moving Valid Cells.

Target Cell Selection In handover algorithm I, the target cell should have the highest priority among the candidate cells. In addition, the target cell should meet the following conditions:

z The target cell must be at layer 4, that is, Umbrella cell. z Filtered RX level of the target cell Inter-layer HO Threshold + Adjacent Cell Inter-layer HO

Hysteresis - 64

Limitations After the fast-moving micro cell handover is successful, the penalty is performed on all the neighboring micro cells. During Penalty Time on Fast Moving HO, Penalty on Fast Moving HO is subtracted from the RX level of every neighboring micro cell.

Cell Layer and Cell Priority With Huawei multiband handover algorithm, a proper traffic volume distribution can be realized among multiple frequency bands.

Huawei multiband handover algorithm divides cells into four layers, with 16 priorities at each layer. The Layer of the cell parameter specifies at which layer a cell is located. This algorithm is applicable to complex networking scenarios. Figure 3-5 shows the cell layers.



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Figure 3-5 Cell layers

In Huawei multiband handover algorithm, a GSM network covering a certain area is divided into four layers, which are:

z Layer 4: Umbrella cell. The umbrella cells are generally GSM900 cells having the wide coverage feature. It also implements fast MS connection.

z Layer 3: Macro cell. The macro cells are generally GSM900 cells, which are commonly used in current GSM system and serve majority of subscribers.

z Layer 2: Micro cell. The micro cells are generally DCS1800 cells having the small coverage feature. They enable capacity expansion.

z Layer 1: Pico cell. The pico cells are generally DCS1800 cells, which are used in hot spots and blind spots.

The cell at the lower layer has a higher priority.

Cell Priority controls handover between cells at the same layer. Each layer has 16 priorities, numbered 1-16 respectively. A high value indicates a low priority. If the cells at the same layer have different priorities, a cell with a lower priority value has a higher priority. Cell Priority along with Layer of the cell determines the priority of a cell. The priority affects the sequence of neighboring cells for handover.

3.3.11 Inter-Layer Handover Inter-layer handover is a type of normal handover. It is used to enable the cells at low layers to absorb traffic volume.

To balance the traffic volume flexibly and to meet the requirements of different network topologies, the GSM network is divided into several layers. See 3.3.10 Fast-Moving Micro Cell Handover for details.

Triggering Conditions If Level HO Allowed is set to Yes, the triggering conditions of inter-layer handover are as follows:

z The layer at which the target cell is located has a higher priority than the layer at which the serving cell is located.

z Filtered downlink RX level of the target cell Inter-layer HO Threshold + Adjacent Cell Inter-layer HO Hysteresis - 64


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z After cells are ranked, the target cell must have a higher priority than the serving cell.

The inter-layer handover is triggered when the P/N criterion is met, that is, the previous conditions are met for Layer HO Valid Time within Layer HO Watch Time. The parameters used for P/N criterion judgment must be configured for the neighboring cells. In different radio conditions, these parameters should be configured differently for the neighboring cells to ensure that an optimal target cell is selected during handover.

When the Neighboring Cell Penalty Switch is set to ON(ON), a timer is started when the inter-layer handover conditions (including the conditions for making handover decisions and the P/N criterion) are met, and no handover towards the neighboring cell is triggered this time. Within the Penalty Timer Length, the neighboring cell level after filtering is punished. That is, within the penalty timer length, the neighboring cell level used by the system is equal to the original filtered level minus Level Penalty Value on Neighboring Cell. The Penalty Stop Level Threshold is used for stopping the penalty timer. The penalty timer is stopped if the following formula is or the bad quality handover conditions are met (The level conditions are checked after filtering. If the neighboring cell level after filtering is lower than the Penalty Stop Level Threshold, the penalty timer for the neighboring cell is stopped. The bad quality handover conditions are checked when making bad quality handover decisions. If the uplink or downlink bad quality handover conditions are met, the penalty timers that are started for all the neighboring cells of the serving cell are stopped.). The penalty timer can be started only once, and it cannot be restarted when it expires or the conditions for stopping the penalty timer are met.

SS_DLs_f PBGT_HO_MARGIN



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Here, RXLEV_DL: indicates the filtered downlink RX level of the serving cell. MS_TXPWR_MAX: indicates the maximum allowed transmit power of an MS in the serving cell. MS_TXPWR_MAX (n): indicates the maximum allowed transmit power of an MS in neighboring cell n.

RxLev_NCELL (n): indicates the downlink receive level in neighboring cell n. PWR_DIFF: indicates the difference between the maximum downlink transmit power in the serving cell due to power control and the actual downlink transmit power in the serving cell.

P: indicates the maximum transmit power of an MS. PBGT_HO_MARGIN: indicates PBGT HO Threshold minus 64.

The PBGT handover can be triggered only when all the previous conditions are met.

When the Neighboring Cell Penalty Switch is set to YES(Yes), a timer is started when the PBGT handover conditions (including the conditions for making handover decisions and the P/N criterion) are met, and no handover towards the neighboring cell is triggered this time. Within the Penalty Timer Length, the neighboring cell level after filtering is punished. That is, within the penalty timer length, the neighboring cell level used by the system is equal to the original filtered level minus Level Penalty Value on Neighboring Cell. The Penalty Stop Level Threshold is used for stopping the penalty timer. The penalty timer is stopped if the following formula is or the bad quality handover conditions are met (The level conditions are checked after filtering. If the neighboring cell level after filtering is lower than the Penalty Stop Level Threshold, the penalty timer for the neighboring cell is stopped. The bad quality handover conditions are checked when making bad quality handover decisions. If the uplink or downlink bad quality handover conditions are met, the penalty timers that are started for all the neighboring cells of the serving cell are stopped.). The penalty timer can be started only once, and it cannot be restarted when it expires or the conditions for stopping the penalty timer are met.

SS_DLs_f


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The conversion formula between RQI and C/I is RQI = 2 x C/I.

Triggering Conditions of AMR TCHF-TCHH Handover The triggering conditions of AMR TCHF-TCHH handover are as follows:

z Intracell F-H HO Allowed is set to Yes. z The target call is an AMR call. z The half-rate function must be enabled in the cell where the call is initiated. z The full-rate speech version 3 and half-rate speech version 3 must be supported by the cell where the

call is initiated. z The type of channel specified by the MSC during a call can be changed during a handover. z For AMR FR calls, when the parameter AMR TCH/H Prior Allowed is set to ON(On), TCHF-to-TCHH

handover is triggered only when the cell load is greater than the value of the parameter AMR TCH/H Prior Cell Load Threshold and the proportion of AMR HR users is smaller than the value of the parameter Ratio of AMR-HR.

z For AMR FR calls, when the parameter AMR TCH/H Prior Allowed is set to OFF(Off), TCHF-to-TCHH handover is triggered only the proportion of AMR HR users is smaller than the value of the parameter Ratio of AMR-HR.

z The call occupies the full-rate TCH. The RQI is greater than F2H HO Threshold .

For an AMR FR call, the AMR TCHF-TCHH handover can be performed if the preceding conditions are met for Intracell F-H HO Last Time within Intracell F-H HO Stat Time.

Triggering Conditions of AMR TCHH-TCHF Handover The triggering conditions of AMR TCHH-TCHF handover are as follows:

z Intracell F-H HO Allowed is set to Yes. z The target call is an AMR call. z The half-rate function must be enabled in the cell where the call is initiated. z The full-rate speech version 3 and half-rate speech version 3 must be supported by the cell where the

call is initiated. z The type of channel specified by the MSC during a call can be changed during a handover. z The call occupies the half-rate TCH. The RQI is smaller than H2F HO Threshold.

For an AMR HR call, the AMR TCHH-TCHF handover can be performed if the preceding conditions are met for Intracell F-H HO Last Time within Intracell F-H HO Stat Time.

Target Cell Selection The AMR handover is an intra-cell handover. Therefore, only the serving cell can be selected as the target cell.

3.3.14 SDCCH Handover SDCCH handover is a process in which the MS is handed over from an SDCCH to another SDCCH in an immediate assignment. SDCCH handover helps improve the access success rate of the MSs on the edge of the network, thus improving the network QoS.

The principle of SDCCH handover is the same as that of TCH handover. Regarding procedure, an SDCCH handover involves measurement and MR reporting, MR processing, handover decision, and handover execution.



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Whether an SDCCH handover can be performed is controlled by the SDCCH HO Allowed parameter. If an inter-BSC SDCCH handover is required, both SDCCH HO Allowed and Inter-BSC SDCCH HO ALLowed should be set to YES(Yes).

The handover decision algorithm for SDCCH handover is different from that for TCH handover in the following ways:

z The algorithms for the following handovers support SDCCH handover: quick handover, TA handover, BQ handover, rapid level drop handover, interference handover, handover due to no downlink measurement report, edge handover, and fast-moving micro cell handover

z The algorithms for the following handovers do not support SDCCH handover: enhanced dual-band network handover, load handover, inter-layer handover, PBGT handover, AMR handover, better 3G cell handover, concentric cell handover, and tight BCCH handover

3.3.15 Other Handovers Other handovers here refer to better 3G cell handover and tight BCCH handover.

Better 3G Cell Handover See 2G/3G Interoperability Feature Parameter Description.

Tight BCCH Handover See BCCH Dense Frequency Multiplexing Feature Parameter Description.

3.4 Handover Decision Based on Handover Algorithm II Handover decision based on handover algorithm II is made in the following order: forced handover, emergency handover, intra-cell handover, and inter-cell handover.

Handover decision based on handover algorithm II involves the following procedures:

z Determining whether the serving cell meets the triggering conditions z Selecting corresponding candidate cell list for each handover type z Performing the comprehensive decision and determining the candidate neighboring cells

The procedure for performing comprehensive decision based on handover results and determining the candidate neighboring cells is as follows:

1. The BSC selects a handover type with the highest priority from all the handovers that can be performed on each neighboring cell.

The handover priority is as follows: Forced handover, emergency handover, and interference handover have a high priority. Figure 3-6 shows the details.


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Figure 3-6 Handovers with high priority

Quick handover is classified into frequency offset handover and quick PBGT handover. Frequency offset handover has a higher priority than quick PBGT handover.

Intra-cell handover (excluding interference handover) and inter-cell handover have a normal priority. Figure 3-7 shows the details.

AMR handover has the same priority as TCHF-TCHH handover.

Figure 3-7 Handovers with normal priority

2. The BSC ranks the candidate cells according to the network characteristics adjustment algorithm and then generates the final candidate cell list. Every neighboring cell in the candidate cell list has its own handover decision. Neighboring 2G cells and neighboring 3G cells are ranked separately.



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3. In handover algorithm II, Inter-rat HO Preference specifies whether a neighboring 2G or a neighboring 3G cell is preferred.

When Inter-rat HO Preference is set to Preference for 2G Cell: A neighboring 2G cell is preferred. If the candidate cell list contains suitable neighboring 3G cells but no suitable neighboring 2G cells, a neighboring 3G cell is selected.

When Inter-rat HO Preference is set to Preference for 3G Cell: A neighboring 3G cell is preferred. If the candidate cell list contains suitable neighboring 2G cells but no suitable neighboring 3G cells, a neighboring 2G cell is selected.

When Inter-rat HO Preference is set to Preference for 2G Cell By Threshold: If the RX level of a candidate 2G cell is lower than or equal to HO Preference Threshold for 2G Cell, a neighboring 3G cell is preferred.

When a neighboring 3G cell is preferred among the candidate cells, the priority of 3G better cell handover is the lowest.

If the triggering conditions of emergency handover are met and there is at least one candidate cell, then the emergency handover timer Min Interval for Emerg. HO is started. Another emergency handover decision can be performed only when Min Interval for Emerg. HO times out.

3.4.1 Quick Handover Quick handover aims to increase the handover success rate of an MS moving at a high speed and to ensure the call continuity and low call drop rate. Quick handover applies to the scenario where an MS moves fast along an urban backbone road, a selected route, or a high-speed railroad.

Quick Handover Types Quick handover consists of frequency offset handover and quick PBGT handover.

z Frequency offset handover Whether the MS is moving away from the serving cell is determined based on the frequency offset information provided by an MS moving at a high speed. Frequency offset handover decision is made according to the uplink/downlink RX level of the serving cell and the path loss of neighboring cells.

z Quick PBGT handover Quick PBGT handover decision is made according to the path loss of neighboring cells.

For quick handover, the handover response speed is enhanced by:

z Accurately calculating the moving speed of the MS z Derestricting the interval between handover decisions z Reducing the number of measurement reports for the handover decision z Introducing the filtering

Quick Handover Preparation The preparation for quick handover involves the following aspects:

z Frequency offset is decoded from the measurement report. Frequency offset of the MS is obtained from the uplink measurement report that the BTS sends to the BSC.

z filtering is performed on the measurement report.


Handover


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Triggering Conditions During handover decision, it is first determined whether the triggering conditions of frequency offset handover are met. When the BTS cannot send the frequency offset information or the reported frequency offset information is invalid, quick PBGT handover is triggered, provided that other conditions of frequency offset handover are met.

If Quick Handover Enable is set to Yes, the triggering conditions of quick handover are as follows:

z The MS is moving away from the serving cell (the frequency offset in the measurement result is a negative value) and the moving speed of the MS is greater than Quick Move Speed Threshold.

z The filtered uplink level of the serving cell is lower than Quick Handover Up Trigger Level. z The compensated downlink level of the serving cell is lower than Quick Handover Down Trigger

Level. z The path loss of configured chain neighboring cells is lower than the specified threshold of the path

loss of the serving cell. In other words, PBGT(n) is greater than or equal to 0.

The triggering conditions of quick handover are as follows:

z If the last three conditions are met simultaneously, the decision is made as follows: If the first condition is met, a frequency offset handover is performed. If the first condition is not met, a quick PBGT handover is performed.

z If all the last three conditions are not met, quick handover is not triggered.

Target Cell Selection The target cell must be a chain neighboring cell of the serving cell. The target cell can be obtained through the setting of Chain Neighbor Cell. If Handover Direction Forecast Enable is set to Yes, a neighboring cell in the moving direction of the MS is selected preferentially.

To forecast the moving direction of the MS, the direction of a chain neighboring cell (A or B) compared with the serving cell is specified by Chain Neighbour Cell Type. If the number of times that the MS is handed over to neighboring cells in the same direction (B for example) is greater than or equal to Handover Direction Forecast Last Times when the handover time reaches Handover Direction Forecast Statistic Times, then the MS is inferred to be moving towards the B direction. Subsequently, the MS is preferentially handed over to the neighboring cell whose Chain Neighbour Cell Type is B.

Limitations The limitations on quick handover are as follows:

z The serving cell cannot be selected as the target cell. z The candidate cells for quick handover must be chain neighboring cells of the serving cell. Each cell

can be configured with a maximum of three chain neighboring cells. z After a quick handover is successful, the penalty is performed on the original cell during the penalty

time to prevent an immediate handover back to the original cell. The penalty time and penalty value are specified by Quick Handover Punish Time and Quick Handover Punish Value respectively.

3.4.2 TA Handover TA handover is a type of emergency handover. The TA handover decision is made according to the TA value reported by the MS.

The TA value of a normal cell ranges from 0 to 63 and that of an extended cell ranges from 0 to 229. The TA can be stepped up or down in steps of 553.5 m. The TA value of 63 corresponds to a distance of 35 km.



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Triggering Conditions TA handover is triggered when the following conditions are met:

z TA HO Allowed is set to Yes. z Filtered TA value in the measurement report provided by the MS is greater than or equal to TA

Threshold.

The TA handover can be triggered only when the preceding two conditions are met simultaneously.

From the perspective of the triggering conditions of TA handover, TA can be regarded as a limitation to the size of a cell.

Target Cell Selection The target cell should have the highest priority in the candidate cell list after handover preprocessing. In addition, the target cell should meet the following limitations:

z The serving cell cannot be selected as the target cell. z If TA Threshold of a co-site neighboring cell is lower than or equal to the TA Threshold of the serving

cell, a handover to the neighboring cell is prohibited. z In handover algorithm II, a cell becomes the target cell for TA handover if the previous conditions are

met for TA HO Valid Time within TA HO Watch Time.

If the triggering conditions of TA handover are met but the candidate 2G cells are not suitable, the following operations are performed:

z If a neighboring 3G cell is available, if Inter-RAT Out BSC Han

Handover

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handover preprocessing

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