advanced multilayer handling

Nokia Siemens Networks GSM/EDGE BSS, rel. RG10(BSS), operating documentation, issue 06

Feature description

Advanced Multilayer Handling

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Issue 2-0Approval Date 27/02/2008 00:00:00

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Table of ContentsThis document has 15 pages.

Summary of Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1 Overview of Advanced Multilayer Handling . . . . . . . . . . . . . . . . . . . . . . . 6

2 Technical description of Advanced Multilayer Handling. . . . . . . . . . . . . . 8

3 Functionality of Advanced Multilayer Handling . . . . . . . . . . . . . . . . . . . . 93.1 BSC-initiated traffic reason handover . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 IUO load control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.3 Multilayer load control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4 User interface of Advanced Multilayer Handling . . . . . . . . . . . . . . . . . . 14

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List of FiguresFigure 1 Overview of the AMH concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Figure 2 BSC-initiated traffic reason handover . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Figure 3 BSC-initiated TRHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Figure 4 IUO load control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Figure 5 Multilayer load control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

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Advanced Multilayer Handling Summary of Changes

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Summary of ChangesChanges between document issues are cumulative. Therefore, the latest document issue contains all changes made to previous issues.

Changes between issues 1-0 and 2-0References have been updated.

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Overview of Advanced Multilayer Handling

1 Overview of Advanced Multilayer HandlingAdvanced Multilayer Handling (AMH) is used to redistribute traffic to the appropriate layer or frequency band according to the prevailing load of the network. Therefore, AMH can smooth out the traffic over the network. This procedure is also supported on an inter-BSC basis.

The AMH concept consists of three different features, which are all related to network load. The AMH features are:

• BSC-initiated traffic reason handover • IUO load control • Multilayer load control

BSC-initiated traffic reason handover provides you with both improved quality and capacity by distributing the traffic evenly over the network. By using BSC-initiated traffic reason handover, you can relieve the load of the congested cells and balance the load over the network by selecting the best mobile station (MS) and cell combination that is likely to survive and give good quality on the new cell. It is particularly useful in multi-band, microcellular, or multilayer (intelligent underlay-overlay) networks.

By using IUO load control, you can also direct traffic to use only the overlay network during low traffic periods, and consequently avoid additional handovers between two layers. Therefore, it is extremely efficient in multilayer networks.

With multilayer load control, you can prevent the use of the microcell layer during low traffic, and therefore keep the MSS only in the macro network, once they have camped on it.

To avoid additional handovers back to the heavy loaded cell, AMH has a particular interval system between the handover attempts. With the interval system the MSS cannot be directed back to the original heavy loaded cell before the interval timer has expired.

In general, by using AMH and by setting the AMH-related parameters, you can move the capacity between different layers according to the prevailing traffic.

Figure Overview of the AMH concept describes the AMH concept.

Figure 1 Overview of the AMH concept

GSM/micro

Intelligent underlay-overlay

Multilayerhandling

GSM/super

BSC-initiated trafficreason handover

Load

>80

<50

ATPM

0

-

TGT

60

-

IUO

-

Denied

microcellular layer

-

Denied

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Advanced Multilayer Handling Overview of Advanced Multilayer Handling

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Figure Overview of the AMH concept shows that if the load is over 80 %, AMH TRHO pbgt margin (ATPM) is 0 and TRHO guard time (TGT) is 60 s. If the load is under 50 %, access to IUO and microcellular layer is denied.

Advanced Multilayer Handling is an application software product in the BSC.

Related topics in Advanced Multilayer Handling

• Technical description of Advanced Multilayer Handling • Functionality of Advanced Multilayer Handling • User Interface of Advanced Multilayer Handling

Related topics in BSC/TCSM documentation

• Test and activate • Radio network performance

• BSS8123: Advanced Multilayer Handling • Activating and Testing BSS8123: Advanced Multilayer Handling

• Reference • Commands

• MML commands • EE - Base Station Controller Parameter Handling in BSC • EH - Handover Control Parameter Handling • EQ - Base Transceiver Station Handling in BSC

• Counters/Performance indicators • Call control measurements (CS)

• 1 Traffic Measurement • 4 Handover Measurement • 51 BSC Level Clear Code (PM) Measurement

• Parameters • BSS Radio Network Parameter Dictionary

• Descriptions • Feature descriptions

• Radio network performance • Dual Band Network Operation • Intelligent Underlay-Overlay

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Technical description of Advanced Multilayer Handling

2 Technical description of Advanced Multilayer HandlingInterworkingDirect Access to Desired Layer/Band

AMH multilayer load control has lower priority than Direct Access to Desired Layer/Band (DADL/B). For more information on DADL/B, see Direct Access to Desired Layer/Band under Feature descriptions/Radio network performance in the PDF view.

GSM-WCDMA Inter-System Handover

When deciding on an initiation of a BSC-initiated traffic reason handover (TRHO), both the completed BSC-initiated TRHOs and the load decrease of the serving cell because of an inter-system handover (ISHO) are taken into consideration. Correspondingly, when deciding on an initiation of an ISHO, both the completed ISHOs and the load decrease of the serving cell because of a BSC-initiated TRHO are taken into consider-ation.

Both of the above conditions are valid, when a new BSC-initiated TRHO, or ISHO are evaluated after either a previous BSC-initiated TRHO or ISHO, but before a new load information report has been received. For more information on GSM-WCDMA Inter-System Handover, see GSM-WCDMA Interworking under Feature descriptions/Radio network performance in the PDF view.

HSCSD

The BSC-initiated TRHO is only made for single-slot connections. The HSCSD cell load upper limit (HCU) parameter should be set to a greater value than the AMH upper load threshold (AUT) parameter. Consequently, unnecessary down-grades are avoided and radio resources are used efficiently. For more information on HSCSD, see HSCSD and 14.4 kbit/s Data Services in BSC under Feature descrip-tions/Data in the PDF view.

RestrictionsMSC Controlled Traffic Reason Handover

It is not recommended that you use MSC controlled TRHO and BSC-initiated TRHO in the same cell at the same time.

Queueing

Queueing is not used with BSC-initiated traffic reason handover.

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Advanced Multilayer Handling Functionality of Advanced Multilayer Handling

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3 Functionality of Advanced Multilayer Handling

3.1 BSC-initiated traffic reason handoverYou can smooth out the overall traffic load of the network by using the BSC-initiated traffic reason handover (TRHO). BSC-initiated TRHO directs the traffic to the appropri-ate cell according to the prevailing load of the network and consequently smooths out the traffic over the network. The traffic is redistributed from the congested regular layer to other cells. The best MS and cell combination that is likely to survive and provide good quality on the new cell is selected.

The figure BSC-initiated traffic reason handover shows the process leading to a BSC-initiated TRHO.

g Do not use BSC-initiated traffic reason handover at the same time and in the same cell as the existing MSC-controlled traffic reason handover.

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Functionality of Advanced Multilayer Handling

Figure 2 BSC-initiated traffic reason handover

BSC-initiated traffic reason handover is based on the traffic load situation of the serving cell. The load of the serving cell is calculated by dividing the number of busy TCH channels by the number of working TCH channels. If the traffic load of the serving cell exceeds the parameter AMH upper load threshold (AUT), the parameter AMH TRHO pbgt margin (ATPM) is used for all adjacent cells in the power budget equation instead of the existing HO margin pbgt (PMRG).

The basic evaluation algorithm calculated according to radio link properties is based on the following strategy and order:

1. AV_RXLEV_NCELL(n)>TRHO_TARGET_LEVEL(n)+Max(0,(MS_TXPWR_MAX_CELL(n)-P))

Target cell evaluation:

AND

where

Order of preference of target cells

Interval between handovers and handover attempts:

AV_RXLEV_NCELL(n) > TrhoTargetLevel(n) + Max(0,Pa)

PBGT (n) > AmhTrhoMarginPBGT AND PBGT (n) <HOMarginPBGT

P = maximum power of MS

IF

AmhTrho PbgtMargin = from -24 to 24 dBm

PRIORITY (n) =HoPriorityLevel(n) - HoLoadFactor(n)

HoLoadFactor value is taken into

If the percentage of free channels in the

channel for BSC initiated traffic reason handover is allocated.

Power budget handovers back to the original heavy

GUARD_TIME =TrhoGuardTime

EnablePowerBudgetHO = Yes

HoPeriodPBGT - interval between the power budget

threshold comparisons

AND

PBGT(n) = (B - AV_RXLEV_DL_HO -(BsTxPwrMax - BS_TXPWR)) - (A - AV_RXLEV_NCELL(n))

where B = MsTxPwrMaxGSM(BTS) if serving cell is GSM 900 or GSM 850B = MsTxPwrMaxGSM1x00(BTS) if serving cell isGSM 1800 or GSM 1900

A = MsTxPwrMaxGSM(ADJ)(n) if adjacent cell is GSM 900 or GSM 850A = MsTxPwrMaxGSM1x00(ADJ)(n) if adjacent cell isGSM 1800 or GSM 1900

Pa = (MsTxPwrMaxGSM(ADJ)(n) - P) if adjacent cell is GSM 900 or GSM 850

Pa = (MsTxPwrMaxGSM1x00(ADJ)(n) - P)

loaded cell are not allowed during the guard time

if adjacent cell is GSM 1800 or GSM 1900

account when BTSLoadThreshold is exceeded.

target cell is below AmhMaxLoadOfTgtCell,

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2. PBGT(n)>AmhTrhoMarginPBGT AND PBGT(n)<HOMarginPBGT

For more information on the basic evaluation algorithms, see RF Power Control and Handover Algorithm.

If the power budget (PBGT) value is between AMH TRHO pbgt margin and HO margin pbgt, a handover is triggered because of BSC-initiated Traffic Reason Han-dover. If the PBGT value exceeds the parameter HO margin pbgt, a handover is trig-gered because of power budget handover. The range of the parameter AMH TRHO pbgt margin is from -24 to 24 dBm and of the parameter HO margin pbgt from -24 to 63 dB.

For the BSC-initiated traffic reason handover to be triggered, power budget handover has to be enabled. BSC-initiated traffic reason handover uses the same periods as the normal power budget handover. BSC-initiated traffic reason handover has lower priority than the normal power budget handover.

☞ Pay attention to the following:

• Queuing is not used with BSC-initiated traffic reason handover. • To make an external BSC-initiated traffic reason handover successful, the

parameter CauseFieldInHandoverRequestSupported must have the value YES in the BSSAP version profile of the MSC. The value must be YES so that HO guard timers are used and queuing is not used.

• BSC-initiated traffic reason handover is made only for single-slot connections. The parameter HSCSD cell load upper limit (HCU) should be set to a greater value than the parameter AMH upper load threshold. Then unnec-essary downgrades are avoided and radio resources are used efficiently.

• TRHO guard time (TGT) applies only to power budget handovers.

Figure 3 BSC-initiated TRHO

Note that only calls from the regular layer can be redirected because of the traffic reason handover.

3.2 IUO load controlAMH can be applied with Intelligent Underlay-Overlay (IUO) to avoid congestion on the overlay layer, thereby providing more trunking gain.

IUO is applied into the network to increase capacity. On the other hand, when the capacity needs are not so high, IUO is still performing many handovers. Therefore, the quality of the network can be improved by avoiding additional handovers between differ-ent frequency layers.

BSC-initiated trafficreason handover

+0 db +4 db +6 db

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Functionality of Advanced Multilayer Handling

Figure 4 IUO load control

You can use AMH to prevent the use of IUO during very low traffic, and therefore keep the MSS only in the overlay network. The solution is based on the traffic load of the serving cell. If the traffic load of the serving cell does not exceed AMH lower load threshold (ALT) the IUO handover and the Direct Access to Super-reuse TRX are not allowed. If the traffic load of the serving cell exceeds AMH lower load threshold (ALT), the Intelligent Underlay-Overlay handover and Direct Access to Super-reuse TRX are allowed again. The function is controlled by the parameter AMH traffic control IUO (ATCI).

For more information on IUO, see Intelligent Underlay-Overlay under Feature descrip-tions/Radio network performance in the PDF view.

3.3 Multilayer load controlAs the number of network layers increases, the number of handovers between the layers also increase. When the traffic is low, that is, at night, extra capacity is not needed and the underlay capacity is not necessarily needed either. Therefore, an adequate capacity can be achieved by using only the overlay network.

On the other hand, most of the traffic at night occurs outside, particularly from fast moving vehicles. Furthermore, fast moving mobiles (FMMS) in the microcell network generate many handovers with a relatively high speed. Therefore, it is more reasonable to keep the traffic in the overlay network instead of the underlay network to provide better quality to end users.

AMH can be used to prevent the use of the microcell layer during low traffic and there-fore to keep the MSS only in the macro network, once they have camped on it.

Figure 5 Multilayer load control

GSM/macro

GSM/micro

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If the traffic load of the serving cell decreases under the predefined threshold AMH lower load threshold (ALT), the FMMS, MS Speed Detection, DADL/B, and Umbrella handovers are not allowed to the lower layer cells. The function is controlled by the parameter AMH traffic control MCN (ATCM).

Note that the access to microcells cannot be prevented, but C2 reselection can be used to keep the fast moving mobiles in the overlay network during idle mode.

For more information, see Dual Band Network Operation under Feature descrip-tions/Radio network performance in the PDF view.

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User interface of Advanced Multilayer Handling

4 User interface of Advanced Multilayer HandlingMMLs and ParametersThe following parameters are controlled by means of the Base Station Controller Param-eter Handling in BSC (EE command group):

• AMH upper load threshold (AUT)

• AMH lower load threshold (ALT)

• AMH max load of target cell (AML) • TRHO guard time (TGT)

☞ The above-mentioned parameters can also be configured on BTS level with the Base Transceiver Station Handling in BSC commands (EQ command group). Note that if you have set a value for the BTS level parameters, the BTS level parameters take preference over the BSC level parameters.

The following parameters are controlled by means of the Handover Control Parameter Handling (EH command group):

• AMH TRHO pbgt margin (ATPM) • AMH traffic control MCN (ATCM)

• AMH traffic control IUO (ATCI)

For more information on parameters, see BSS Radio Network Parameter Dictionary under Reference/Parameters in the PDF view.

InterfacesThe BSC-controlled TRHO is mapped to the 'better cell' cause on the A interface.

There are no effects to either the Abis interface or the Radio interface.

Measurements and CountersTraffic Measurement

• 001167 TCH REQUEST FOR A BSC CONTROLLED TRHO PROCEDURE • 001168 SUCC TCH SEIZ FOR A BSC CONTROLLED TRHO • 001169 REJ TCH SEIZ FOR A BSC CONTROLLED TRHO DUE LACK OF

RESOURCES

Handover Measurement

• 004035 CAUSE HO STARTED BY TRAFFIC REASON

BSC Level Clear Code (PM) Measurement

• 051078 EXT IN BSC TRHO • 051140 INTER BSC TRHO • 051145 EXT OUT BSC TRHO

For more information on the measurements and counters, see:

• 1 Traffic Measurement under Reference/Counters/performance indicators/Call control measurements (CS)

• 4 Handover Measurement under Reference/Counters/performance indicators/Call control measurements (CS)

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Advanced Multilayer Handling User interface of Advanced Multilayer Handling

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• 51 BSC Level Clear Code (PM) Measurement under Reference/Counters/perfor-mance indicators/Call control measurements (CS)

AlarmsAdvanced Multilayer Handling involves no alarms.

advanced multilayer handling

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