evolium base station subsystem multilayer gsm network
TRANSCRIPT
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All rights reserved © 2005, Alcatel
Multilayer GSM Network Radio Optimization / B9
EVOLIUM Base Station Subsystem
Multilayer GSM Network Radio Optimization / B9
TRAINING MANUAL
3FL12033ABAAWBZZAEdition 01 - January 2006
Copyright © 2005 by Alcatel - All rights reservedPassing on and copying of this document, use and communication of its contents
not permitted without written authorization from Alcatel
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Legal Notice
Switch to notes view!Safety Warning
Both lethal and dangerous voltages are present within the equipment. Do not wear conductive jewelry while working
on the equipment. Always observe all safety precautions and do not work on the equipment alone.
Caution
The equipment used during this course is electrostatic sensitive. Please observe correct anti-static precautions.
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Users are not permitted to use these Marks without the prior consent of Alcatel or such third party owning the Mark.
The absence of a Mark identifier is not a representation that a particular product or service name is not a Mark.
Copyright
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other use or transmission of all or any part of this document is permitted without Alcatel’s written permission, and
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© 2005 Alcatel. All rights reserved.
Disclaimer
In no event will Alcatel be liable for any direct, indirect, special, incidental or consequential damages, including lost
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operation.
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Product Line EVOLIUM Base Station Subsystem
Course Title Multilayer GSM Network Radio Optimization / B8
Course Reference 3FL 12033 ABAA - AUE
Audience
Radio Network Engineers (operator or Alcatel staff) in charge of optimizing a hierarchical network.
Objectives
During the course, the trainee will be able to describe the specific radio algorithms in multi-layer networks in order to enhance the offered QoS.
By the end of the course, the participant will be able to:
- Describe the concepts and strategy of hierarchical networks.
- Describe the specific type of cells implemented in hierarchical networks.
- Describe the specific radio algorithms used in the Alcatel BSS in a hierarchical network.
- Propose default parameter values for the cells of a hierarchical network using these algorithms.
- Propose a list of specific indicators to monitor QoS and traffic in a hierarchical network.
Note: Radio Network Planning issues like micro site detection, site planning, frequency planning are not included.
Prerequisites
Training module “Introduction to GSM QoS and Traffic Load Monitoring” (3FL 10491 ABAA–AUE) and “Introduction to Radio Fine Tuning” (3FL 10493 ABAA–AUE) or equivalent level.
Training Methods
Theory / Practice.
Language
English, French
Duration
3 Days
Location
Alcatel University or Customer Premises.
Number of participants
Maximum 8
Course content
1 Multi-layer Network Architecture
• 1.1 Concepts and strategies
• 1.2 Cellular network architecture
• 1.3 Choosing a relevant architecture
• 1.4 Requirements
2 Algorithms and Associated Parameters
• 2.1 Introduction
• 2.2 Idle mode selection and reselection
• 2.3 Call setup
• 2.4 Handover strategies
• 2.5 Main standard handover algorithms
• 2.6 HO algorithms for multi-layer networks
• 2.7 Candidate cells evaluation
3 Creating a Multi-layer Network
• 3.1 Adding a micro cellular layer in an existing network for traffic and coverage increase
• 3.2 Adding hot spot microcells for traffic
• 3.3 Adding indoor microcells for coverage
• 3.4 Monitoring QoS in a multi-layer network
4 Case studies
• 4.1 Radar cell
• 4.2 Symmetric microcells at street corner
• 4.3 Asymmetric microcells at street corner
• 4.4 Indoor microcell within a monolayer network
• 4.5 Trilayer network: indoor cell within a multi-layer network
• 4.6 Indoor cell congestion
• 4.7 Transforming a microcell into an indoor cell
• 4.8 Picocells in skyscrapers
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Table of Contents [cont.]
Switch to notes view!
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1 MULTI-LAYER NETWORK ARCHITECTURE
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1 MULTI-LAYER NETWORK ARCHITECTURE
Session presentation
Objective: to be able to define relevant architectures for
multi-layer networks design
Program:
1.1 Concepts and strategies
1.2 Cellular network architecture
1.3 Choosing a relevant architecture
1.4 Requirements
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.1 Concepts and strategies
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Multi-layer network: a powerful solution for:
� Network capacity enhancement
• extra capacity provided by new cells / new TRXs
• specific radio algorithms send MSs to these new cells
� Coverage increase
• when introducing microcells (better indoor penetration, even for outdoor
microcells)
� While keeping a good QoS
• confined coverage for microcells, with less interference
• less congestion
1.1 Concepts and strategies
Introduction to multi-layer networks
Since B7:
� new HW capabilities with “Cell split” support
� enhancement of QoS monitoring capabilities with counters split per TRX
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Alcatel is providing multi-layer solutions
� Since R3.1: mini & microcells
� Improvements in B3.1 (smart speed discrimination)
� Improvements in B6.2 (external Directed Retry)
� Improvements in B7 (indoor layer introduction)
1.1 Concepts and strategies
Support of multi-layer features
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Multi-layer networks can be introduced as continuous layer or hotspots, for:
� Capacity increase
� Coverage increase
� Indoor solution
All types of mobiles can use both layers
1.1 Concepts and strategies
Network strategy
If the speed discrimination process is activated then Phase 2 MSs will be sent more or less quickly according to the
load of the umbrella cell.
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.2 Cellular network architecture
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Conventional
� Single cell
� Concentric cell
� Extended cell
� Multi-band cell
Hierarchical: introducing Upper and Lower cell layers
� Indoor cell
� Micro cell
� Mini cell
� Umbrella cell
1.2 Cellular network architecture
Cell environment
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One unique combination of the five parameters
� CELL_DIMENSION_TYPE: macro, micro
� CELL _LAYER_ TYPE : single, upper, lower, indoor
� CELL _PARTITION_ TYPE : normal, concentric
� CELL _RANGE: normal, extended inner, extended outer
� FREQUENCY_RANGE : PGSM(GSM900); DCS1800; EGSM;
DCS1900; PGSM-DCS1800; EGSM-DCS1800 and GSM 850
• based on BCCH frequency
1.2 Cellular network architecture
Cell profile
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1.2 Cellular network architecture
Mono-band Cell profiles
DCS1800 or DCS1900DCSNormalNormalIndoorMicroDCS indoor micro cell
PGSM or EGSMGSMNormalNormalIndoorMicroGSM indoor micro cell
DCS1800 or DCS1900DCSNormalConcentricUpperMacroDCS concentric umbrella
PGSM or EGSMGSMNormalConcentricUpperMacroGSM concentric umbrella
DCS1800 or DCS1900DCSNormalConcentricSingleMacroDCS concentric cell
PGSM or EGSMGSMNormalConcentricSingleMacroGSM concentric cell
DCS1800 or DCS1900DCSExtended-outerNormalSingleMacroDCS extended outer cell
PGSM or EGSMGSMExtended-outerNormalSingleMacroGSM extended outer cell
DCS1800 or DCS1900DCSExtended-innerNormalSingleMacroDCS extended inner cell
PGSM or EGSMGSMExtended-innerNormalSingleMacroGSM extended inner cell
DCS1800 or DCS1900DCSNormalNormalUpperMacroDCS umbrella cell
PGSM or EGSMGSMNormalNormalUpperMacroGSM umbrella cell
DCS1800 or DCS1900DCSNormalNormalLowerMacroDCS mini cell
PGSM or EGSMGSMNormalNormalLowerMacroGSM mini cell
DCS1800 or DCS1900DCSNormalNormalLowerMicroDCS micro cell
PGSM or EGSMGSMNormalNormalLowerMicroGSM micro cell
DCS1800 or DCS1900DCSNormalNormalSingleMacroDCS single cell
PGSM or EGSMGSMNormalNormalSingleMacroGSM single cell
Frequency rangeCell band
type
Cell
range
Cell partition
type
Cell layer
type
Cell dimension
type
Parameters
Cell Profile
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1.2 Cellular network architecture
Multi-band Cell profiles
PGSM-DCS1800 or
EGSM-DCS1800DCSNormalConcentricIndoorMicroDCS multiband indoor micro cell
PGSM-DCS1800 or
EGSM-DCS1800GSMNormalConcentricIndoorMicroGSM multiband indoor micro cell
PGSM-DCS1800 or
EGSM-DCS1800DCSNormalConcentricUpperMacroDCS multiband umbrella cell
PGSM-DCS1800 or
EGSM-DCS1800GSMNormalConcentricUpperMacroGSM multiband umbrella cell
PGSM-DCS1800 or
EGSM-DCS1800DCSNormalConcentricLowerMacroDCS multiband mini cell
PGSM-DCS1800 or
EGSM-DCS1800GSMNormalConcentricLowerMacroGSM multiband mini cell
PGSM-DCS1800 or
EGSM-DCS1800DCSNormalConcentricLowerMicroDCS multiband micro cell
PGSM-DCS1800 or
EGSM-DCS1800GSMNormalConcentricLowerMicroGSM multiband micro cell
PGSM-DCS1800 or
EGSM-DCS1800DCSNormalConcentricSingleMacroDCS multiband single cell
PGSM-DCS1800 or
EGSM-DCS1800GSMNormalConcentricSingleMacroGSM multiband single cell
Frequency rangeCell band typeCell
rangeCell partition typeCell layer typeCell dimension type
Parameters
Cell Profile
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1.2 Cellular network architecture
Cell profiles: example
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.3 Choosing a relevant architecture
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Multi-layer concept: 3 available layer types
� All these cells can be or not operating in the same band and defined as
concentric cells
1.3 Choosing a relevant architecture
Concept
mini
umbrella
micro
indoor
micro micro
umbrella
micro
indoor
single
mini
umbrellaUPPER
SINGLE
LOWER
INDOOR
3 layers are defined in the system, but more layers can be created by parameter tuning. For example, skyscrapers
specific configuration is made up of several consecutive layers designed with cells of the same “system” layer.
Indoor layer has been introduced in B7.
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Microcells configuration will depend on their position in the lower layer
� Microcell “classes” are introduced to deal with typical parameters settings
in each of these cases
1.3 Choosing a relevant architecture
Microcell classes
Indoor Microcell
Border Microcell
Inner MicrocellHotspot Microcell
Defining microcell classes is a very efficient way to set network parameters. It avoids defining a specific configuration
for each cell.
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.4 Requirements
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A multi-layer architecture can be built over all types of Hardware
� Since R3.1
� Microcell feature is NOT reserved to micro BTS!
Improvement in B6.2 with external Directed Retry
� From R3.1 to B4.1, since Directed Retry was only Internal:
• microcells had to be introduced within umbrella BSC
• OR microcells were barred (traffic allocation was done by handover from
umbrella cells)
� Since B6.2, External Directed Retry is available
• Microcells and Umbrella cells can belong to different BSCs
1.4 Requirements
Software & Hardware requirements
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
Session presentation
Objective: to be able to describe algorithms dedicated to
multi-layer networks management
Program:
2.1 Introduction
2.2 Idle mode selection and reselection
2.3 Call setup
2.4 Handover strategies
2.5 Main standard handover algorithms
2.6 Handover algorithms for multi-layer networks
2.7 Candidate cell evaluation
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.1 Introduction
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With the introduction of new feature and algorithms:
� Multi-layer
Designing, managing and monitoring complex networks is more difficult,
as all these features will interact
� An in-depth knowledge of all available algorithms is necessary to understand
all possibilities and difficulties. A relevant choice of architecture and
parameters settings will precede the introduction of a new layer in the existing
network
2.1 Introduction
Justification
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In all this document
� System parameters (can be set at the OMC-R level) will always be written in
BLUE BOLD FONT
� Variables (averages, internal system variables, etc.) will be typed in NORMAL
FONT
Light blue font highlights important points
2.1 Introduction
Typing conventions
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.2 Idle mode selection and reselection
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Adding a new layer is a powerful way of increasing network capacity if
the MS can be sent to the preferred cell
� In dedicated mode: see next sections
� But also in idle mode, so that the call is established directly in the preferred
cell
• Really increase capacity
• Maintain high QoS level, without creating extra HO
2.2 Idle mode selection and reselection
Strategy
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At startup (IMSI Attach), the MS is selecting cell with
� Defined priorities with CELL_BAR_QUALIFY
� Best C1 amongst highest priority cells (using CBQ)
Once “camped on” one cell (in idle mode)…
… The MS can decide to reselect another one if:
� C1 criterion is too low
� The MS cannot decode downlink messages
� The current cell is becoming forbidden (e.g. barred)
� The MS cannot access the cell
� there is a better cell, regarding C2 criterion
2.2 Idle mode selection and reselection
Selection and reselection principles
Note:
Cell selection (first selection) is performed using C1 criterion only (the chosen cell is the one with the best C1)
Reselection is done using the mechanisms referenced above.
e.g., the MS cannot access the cell.
It can be linked to SDCCH congestion, filtering of CHARQD due to TA greater than RACH_TA_FILTER, radio access
problem during the Radio Link Establishment phase.
� If SDCCH is to be seized for LU purpose, the MS will reselect on another cell.
� If SDCCH is seized for something else (e.g., MOC), the MS « may » reselect (this is up to the MS vendor
choice!!!). Some MSs do nothing. Call will never be possible. Some others do reselect. In that case, the user
has to reattempt his call (after the reselection, but before the MS is back to the original cell due to better C2,
etc. (done after 5 s, etc.)).
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Cell selection, use of CELL_BAR_QUALIFY:
� set on a per cell basis
� broadcast on the BCCH
� 2 possible values:
• 0 = normal priority (default value)
• 1 = lower priority
� The MS selects the suitable (C1 > 0) cell with the highest C1 belonging to the
list of highest priority
2.2 Idle mode selection and reselection
Cell Selection with CBQ (1/3)
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Example: highest priority set on microcell
� The MS will select the microcell (if available, C1>0), whatever the level of the
macrocell
2.2 Idle mode selection and reselection
Cell Selection with CBQ (2/3)
2525microcell
CELL_BAR_QUALIFY = 0
2020
macrocell
CELL_BAR_QUALIFY = 1
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WARNING: usage of CELL_BAR_QUALIFY:
� interacts with CELL_BAR_ACCESS
• A cell with low priority (CELL_BAR_QUALIFY = 1) cannot be barred
• Some MSs will be able to access it, whatever the value of CELL_BAR_ACCESS
2.2 Idle mode selection and reselection
Cell Selection with CBQ (3/3)
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C1
� ensures that, if a call was attempted, it would be done with a sufficient
downlink and uplink received level
� based on 2 parameters, broadcast on the BCCH
• RXLEV_ACCESS_MIN [dBm]
- Minimum level to access the cell- Default value (for Evolium): -103 dBm
• MS_TXPWR_MAX_CCH [dBm]
- Maximum level for MS emitting- Default value: 33 dBm
2.2 Idle mode selection and reselection
C1 criterion (1/2)
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C1
� evaluated every 5 s (minimum)
� C1 = A - MAX(0,B) > 0
� A = RxLev - RXLEV_ACCESS_MIN
• assess that the MS received level is sufficient
� B = MS_TXPWR_MAX_CCH - P
• P maximum power of MS
• assess that the BTS received level will be sufficient
• if MS_TXPWR_MAX_CCH < P
2.2 Idle mode selection and reselection
C1 criteria (2/2)
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C2� If CELL_RESELECT_PARAM_IND= not present THEN C2=C1 else
• C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET (T)
(if PENALTY_TIME ≠ 31)
- if T > PENALTY_TIME, TEMPORARY_OFFSET(T) = 0
- used to avoid locating on “transient cell”
- CELL_RESELECT_OFFSET used to favor a cell among other (e.g. micro-cell vs.
umbrella, once T > PENALTY_TIME)
• Or C2 = C1 - CELL_RESELECT_OFFSET
(if PENALTY_TIME = 31)
- CELL_RESELECT_OFFSET used to handicap some cells among others
� One reselection criterion is comparison with C2
• C2neighboring > C2current if cells belong to the same LA
• C2neighboring > C2current+CELL_RESELECT_HYSTERESIS if cells from
different LA
2.2 Idle mode selection and reselection
C2 criterion
The use of a second formula (Penalty_time = 31) is restricted to very special cases, as we do not like to penalize a
cell. If a cell is parametered with PT=31, it will be penalized compared to ALL its neighboring cells. To penalize a cell
compared to one neighboring cell, one should better boost the neighboring cell (using first formula).
The first formula is very useful to favor an indoor cell or a microcell.
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CELL_RESELECT_PARAM_IND� C2 parameters are broadcast if = 1 (default)
� otherwise C2 = C1
PENALTY_TIME
� 0 to 31, =20s + 20s step, default value = 0
� From 0=20s to 30=620 s, plus 31: infinite penalty
CELL_RESELECT_OFFSET
� 0 to 63, 2 dB step, default value = 0
� From 0 dB to 126 dB
TEMPORARY_OFFSET
� 0 to 7, 10 dB step, default value = 0
� From 0 dB to 60 dB, plus 7: infinite dB
2.2 Idle mode selection and reselection
C2 parameters
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2.2 Idle mode selection and reselection
Application
MINIMINI
MINI 900
CELL_RESELECT_OFFSET = 20
dB
TEMPORARY_OFFSET = 0 dB
PENALTY_TIME = 0 (20 s)UMBUMB
UMBRELLA 900
CELL_RESELECT_OFFSET = 0 dB
TEMPORARY_OFFSET = 0 dB
PENALTY_TIME = 0 (20 s)
C2(MINI) = C1(MINI) + 20
C2(900) = C1(900)
=> the reselection of the mini cell is favored
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.3 Call setup
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Call setup is to be made on the cell selected in idle mode
� Priorities have been defined with idle mode parameters
� MSs are sent to the preferred cell
• Lower layers
What is the risk??
2.3 Call setup
Principles
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The risk is to have congestion in the preferred cell!
� Old cells (old layer capacity) are unloaded…
� … as all MSs are sent to new cells
This phenomenon is amplified by handovers behavior
� Dual layer algorithms are based on CAPTURE mechanisms
• Send the MS in the preferred cell as soon as it is OK…
• … Without comparing serving and preferred cells…
• … to reach the maximum capacity increase
• See handover parts for details
2.3 Call setup
Congestion in the preferred cell
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2.3 Call setup
Algorithms principles (1/3)
new
capacity
Traffic
increase
old
capacity
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2.3 Call setup
Algorithms principles (2/3)
new
capacity
Water Valve with filter:
Dual layer algorithms
Traffic
increase
old
capacity
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2.3 Call setup
Algorithms principles (3/3)
new
capacity
Water Pump:
Forced
Directed Retry
Traffic
increase
old
capacity
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A Directed Retry:
� Is an SDCCH to TCH intercell handover
� Is triggered during a call setup procedure
If the serving cell is completely congested, the MS is allocated an
SDCCH
If no TCH is available, the MS is queued
� Under certain conditions, the MS obtains a TCH in another cell
SDCCH-TCH handover on:
� better condition or emergency causes = Directed Retry
� cause 20 = Forced Directed Retry
Internal and External Directed Retries are possible (since B6.2)
2.3 Call setup
Directed Retry principles
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Directed Retry
� Set on a per cell basis with parameter EN_DR
� Same behavior as TCH HO
� Intercell handover causes are checked (i.e. all HO causes except 10, 11 and
13 (concentric cells) and causes 15 and 16 (intracell HO))
� candidate cell evaluation process: same as for TCH HO
2.3 Call setup
Directed Retry
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CAUSE 20: Forced Directed Retry
AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)
And EN_FORCED_DR = ENABLED
� EN_FORCED_DR value is only relevant if EN_DR = true
� AV_RXLEV_NCELL_DR(n) is calculated with the A_PBGT_DR window
� if less than A_PBGT_DR samples are available, the average value is
calculated with the available samples and the averaging window is filled in
with -110 dBm
2.3 Call setup
Forced Directed Retry: cause 20
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Pre-ranking� using PREF_LAYER, PRIORITY(0,n), frequency band
Filtering process� AV_RXLEV_NCELL_DR(n) > RXLEVmin(n) + max(0,MS_TXPWR_MAX(n) - P)
� Number of free TCHs t(n) > FREElevel_DR(n)
The remaining cells are sorted according to their PBGT_DR(n) (averaging window A_PBGT_DR)
� PBGT_DR(n) = AV_RXLEV_NCELL_DR(n) - AV_RXLEV_PBGT_DR
- (BS_TXPWR_MAX - BS_TXPWR)
- (MS_TXPWR_MAX(n) - MS_TXPWR_MAX)
2.3 Call setup
FDR: Candidate cell evaluation
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L_RXLEV_NCELL_DR(n): level required in the neighboring cell n
� The parameter considered is the one set in the neighboring cell
� The default value depends on the network architecture
� See the next slide
Freelevel_DR(n): number of free TCH channels required in the
neighboring cell n
� The parameter considered is the one set in the neighboring cell
� Default value = 0 to 4 TCHs (linked to the nb of TRXs)
A_PBGT_DR: average window
� Default value = 4 SACCHs
2.3 Call setup
FDR: parameters
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DR on usual HO alarms does not create any radio problems as mobiles
remain within the service area of the new serving cell
Forced DR can introduce severe interference problems because MSs
are outside the cell normal service area
� Forced directed retry between one
micro cell and its umbrella macro cell
• OK: same service area
• Simple parameters settings
� Forced directed retry between 2
micro or macro cells
• according to the frequency plan
2.3 Call setup
Managing DR parameters
Umbrella cell
microcell
FDRcapture
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Thanks to idle mode parameters,� Access to one « preferred cell »…
• Micro / Indoor layer: layer with very good QoS
� …For a better capacity increase and to avoid QoS degradation that may be
induced by an increase in HO attempts
Prevention of congestion in the “preferred cell”� Forced Directed Retry to the “old” cells
Prevention of congestion in the “old” cells� MSs are sent in idle mode to the “preferred cell”
� HO strategy favoring the “preferred cell” in dedicated mode
2.3 Call setup
Access strategy
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2.3 Call Setup
Exercise
Time allowed:
10 minutes
A dual layer network is considered
� Umbrella cells 900
� Micro cells 900
Set FDR parameters to avoid interference and allow
a powerful TCH resource usage
Umbrella cells
microcells
FDRcapture
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.4 Handover strategies
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Maximizing capacity
� Intelligent MS sharing between available resources
• Avoid congestion of historical band (for old MS)
• Consider traffic conditions of all layers
• Consider MS speed for layer discrimination
� Keep mobiles in the same layer as long as possible
2.4 Handover strategies
Objectives (1/2)
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Assuring good quality communications and avoiding call drops
� Send MS towards the layer that will provide the best QoS
� Minimize the number of HO between cells for good speech Quality
• Fast moving mobiles are handled by the macrocell layer
� Identify a best target for emergency handovers cases
�The tuning of the parameters will result in trade-offs
2.4 Handover strategies
Objectives (2/2)
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Next parts will detail available HO causes for multi-layer network
management
� Mainly, HO performed between cells of the same layer are the same as for
standard networks
� New handover causes are mandatory to manage HO between cells of
• Different layers
2.4 Handover strategies
Handover algorithms
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2.4 Handover strategies
Functional Entities
Radio
Link
Measurements
Active
Channel
Pre-processing
Assignment of HO functions in the ALCATEL BSS
BTS BSC
HO DetectionHO Candidate
Cell Evaluation
HO
management
MSC
HO
protocol
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HO causes for standard networks
� cause 2 : too low quality on the uplink
� cause 3 : too low level on the uplink
� cause 4 : too low quality on the downlink
� cause 5 : too low level on the downlink
� cause 6 : too large distance between the MS and the BTS
� cause 15 : high interference on the uplink (intra-cell HO)
� cause 16 : high interference on the downlink (intra-cell HO)
� cause 26 : AMR channel adaptation HO (HR to FR)
� cause 12 : power budget evaluation
� cause 23 : traffic
� cause 27 : AMR channel adaptation HO (FR to HR)
� cause 28 : Fast traffic HO
� cause 29 : TFO HO
� cause 20 : FDR
2.4 Handover strategies
Handover causes (1/2)
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HO causes for multi-layer networks
� cause 7 : consecutive bad SACCH frames received in a microcell
� cause 17 : too low level on the uplink in a microcell compared to a high
threshold
� cause 18 : too low level on the downlink in a microcell compared to a high
threshold
� cause 14 : high level in the neighboring cell of a lower or indoor layer for
slow mobile
� cause 24 : general capture
2.4 Handover strategies
Handover causes (2/2)
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� cause 7 : consecutive bad SACCH frames received in a microcell� cause 17 : too low level on the uplink in a µcell compared to a high threshold� cause 18 : too low level on the downlink in a µcell compared to a high threshold� cause 2 : too low quality on the uplink � cause 3 : too low level on the uplink � cause 4 : too low quality on the downlink � cause 5 : too low level on the downlink � cause 6 : too large distance between the MS and the BTS� cause 10 : too low level on the uplink in the inner zone� cause 11 : too low level on the downlink the in inner zone� cause 26 : AMR channel adaptation HO (HR to FR)� cause 15 : high interference on the uplink (intra-cell HO)� cause 16 : high interference on the downlink (intra-cell HO)� cause 21 : high level in the neighboring cell in the preferred band
cause 14 : high level in neighboring cell of a lower or an indoor layer cell for slow mobile
cause 24 : general capturecause 12 : power budget evaluationcause 23 : traffic
� cause 13 : too high level on the uplink and downlink in the outer zone� cause 27 : AMR channel adaptation HO (FR to HR)� cause 20 : Forced Directed Retry DR� cause 28 : Fast traffic HO
2.4 Handover strategies
Handover causes priority
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.5 Main standard handover algorithms
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Emergency intercell handovers
� cause 2 : too low quality on the uplink
� cause 3 : too low level on the uplink
� cause 4 : too low quality on the downlink
� cause 5 : too low level on the downlink
� cause 6 : too large distance between the MS and the BTS
May be triggered
� From any cell type / band / layer / zone
� Towards any cell except the serving one
2.5 Main standard handover algorithms
Emergency Intercell Handovers
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CAUSE 2: too low quality on the uplink
AV_RXQUAL_UL_HO > L_RXQUAL_UL_H + OFFSET_RXQUAL_FH
and AV_RXLEV_UL_HO <= RXLEV_UL_IH
and MS_TXPWR = min (P, MS_TXPWR_MAX)
and EN_RXQUAL_UL= ENABLED
� Size of window for averaging quality: A_QUAL_HO
� Size of window for averaging level: A_LEV_HO
2.5 Main standard handover algorithms
Handover Cause 2: UL Quality
QUAL
LEV
Quality and Level causes (2, 3, 4, 5, 15, 16)
The aim of these causes is to keep the call going when the radio link is degrading otherwise the radio link failure
might be detected and the call released. These causes wait generally for the power control process to increase the
BTS and MS power to their maximum values, except for the causes specific to microcellular environment.
Handover on "too low level" is used to avoid situations where the interference level is low, while the attenuation is
quite high. These conditions may appear for example in big city streets which ENABLED a line of sight propagation
from the BTS antenna. There is in this case a risk of abrupt quality degradation, if the MS moves away from the line
of sight street.
In case of simultaneous low-level and low-quality signals, an intercell handover is requested.
Level
Quality
-110 -47
7
0
PC
L_RXQUALxx_H
L_RXLEV_xx_H RXLEV_xx_IH
xx = UL or DL
Qual pb (2 / 4)
Levpb
(3 /5)
Int pb (15 / 16)
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CAUSE 3: too low level on the uplink
AV_RXQUAL_UL_HO <= L_RXQUAL_UL_H + OFFSET_RXQUAL_FH
and AV_RXLEV_UL_HO < L_RXLEV_UL_H
and MS_TXPWR = min (P, MS_TXPWR_MAX)
and EN_RXLEV_UL= ENABLED
� Size of window for averaging quality: A_QUAL_HO
� Size of window for averaging level: A_LEV_HO
2.5 Main standard handover algorithms
Handover Cause 3: UL Level
QUAL
LEV
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2.5 Main standard handover algorithms
Handover Cause 4: DL Quality
CAUSE 4: too low quality on the downlink
AV_RXQUAL_DL_HO > L_RXQUAL_DL_H + OFFSET_RXQUAL_FH
and AV_RXLEV_DL_HO <= RXLEV_DL_IH
and BS_TXPWR = BS_TXPWR_MAX
and EN_RXQUAL_DL = ENABLED
� Size of window for average quality: A_QUAL_HO
� Size of window for average level: A_LEV_HO
QUAL
LEV
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2.5 Main standard handover algorithms
Handover Cause 5: DL Level
QUAL
LEV
CAUSE 5: too low level on the downlink
AV_RXQUAL_UL_HO <= L_RXQUAL_DL_H + OFFSET_RXQUAL_FH
and AV_RXLEV_UL_HO < L_RXLEV_DL_H
and BS_TXPWR = BS_TXPWR_MAX
and EN_RXLEV_DL= ENABLED
� Size of window for averaging quality: A_QUAL_HO
� Size of window for averaging level: A_LEV_HO
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2.5 Main standard handover algorithms
Handover Cause 6: Distance
CAUSE 6 : Too long distance
AV_RANGE_HO > U_TIME_ADVANCE
and EN_DIST_HO = ENABLED
� Size of window for distance average: A_RANGE_HO
This cause is used when a dominant cell provides a lot of scattered coverages inside other cells, due to propagation
conditions of the operational network. These spurious coverages is the probable production of a high level of co-
channel interference.
This cause is different from the others as it is more preventive. It does not make use of the propagation conditions of
a call. It just does not allow an MS to talk to a BTS if it is too far away.
It may happen for example that some peculiar propagation conditions exist at one point in time that provide
exceptional quality and level although the serving BTS is far and another is closer and should be the one the mobile
should be connected to if the conditions were normal.
It may then happen that these exceptional conditions suddenly drop and the link is lost, which would not have
happened if the mobile had been connected to the closest cell. For these reasons also, this cause does not wait for
the power control to react.
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Emergency intracell handovers
� cause 15 : high interference on the uplink (intra-cell HO)
� cause 16 : high interference on the downlink (intra-cell HO)
May be triggered
� From any cell type / band / layer / zone
� Towards the same cell
2.5 Main standard handover algorithms
Emergency Intracell Handovers
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CAUSE 15: High interference on the uplink
� Intra-cell HO
AV_RXQUAL_UL_HO > THR_RXQUAL_CAUSE_15 +
OFFSET_RXQUAL_FH
and AV_RXLEV_UL_HO > RXLEV_UL_IH
and EN_CAUSE_15 = ENABLED
and [ no previous intracell handover for this connection
failed
or EN_INTRACELL_REPEATED = ENABLED ]
� Size of window for averaging quality: A_QUAL_HO
� Size of window for averaging level: A_LEV_HO
2.5 Main standard handover algorithms
Handover Cause 15: UL Interference
THR_RXQUAL_CAUSE_15 and EN_CAUSE_15 are not parameters but variables defined just after.
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CAUSE 16: High interference on the downlink
� Intra-cell HO
AV_RXQUAL_DL_HO > THR_RXQUAL_CAUSE_16 +
OFFSET_RXQUAL_FH
and AV_RXLEV_DL_HO > RXLEV_DL_IH
and EN_CAUSE_16 = ENABLED
and [ no previous intracell handover for this connection
failed
or EN_INTRACELL_REPEATED = ENABLED ]
� Size of window for averaging quality: A_QUAL_HO
� Size of window for averaging level: A_LEV_HO
2.5 Main standard handover algorithms
Handover Cause 16: DL Interference
THR_RXQUAL_CAUSE_16 and EN_CAUSE_16 are not parameters but variables defined after.
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2.5 Main standard handover algorithms
New parameters for causes 15 & 16
CAUSE 15 and CAUSE 16:
� THR_RXQUAL_CAUSE_15 (or 16) and EN_CAUSE_15 (or 16) are specific
to HOP
� THR_RXQUAL_CAUSE_15 (or 16) =
• L_RXQUAL_XX_H for a non AMR call (same threshold as CAUSE 2 or CAUSE 4)
• L_RXQUAL_XX_H_AMR for an AMR call
� EN_ CAUSE _15 (or 16) =
• EN_INTRA_XX for a non-AMR call
• EN_INTRA_XX_AMR for an AMR call
XX = UL or DL
For a non AMR call, the thresholds used are identical to the ones used for CAUSE 2 and CAUSE 4.
In this case and if EN_INTRACELL_REPEATED = DISABLED, when a HO CAUSE 15 (or 16) fails, it can be modified
as UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).
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CAUSE 12: Power budget
� “Normal” handover type, no matter of emergency
� Checked between
• Cells of the same layer only
• Specific case of Fast MSs: after detection of cause 12 in the lower or indoor layer,
they can execute cause 12 HO towards the upper layer
• Cells may be of different cell_band_type, depending on parameter
EN_MULTIBAND_PBGT_HO
• if EN_MULTIBAND_PBGT_HO = DISABLED and if the MS is located in the inner
zone of a multi-band cell, it can only go to another multi-band cell
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (1/5)
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CAUSE 12:
� Based on Power budget equation
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)
- PING_PONG_MARGIN(n, call_ref)
� Size of window for level averaging: A_PBGT_HO
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (2/5)
The value of PBGT(n) is calculated every SACCH period for each neighboring cell n whose measures are kept in the
book-keeping list
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CAUSE 12: Power budget
if EN_TRAFFIC_HO(0,n)=ENABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
+ max(0, DELTA_HO_MARGIN(0,n))
else PBGT(n) > HO _MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
� Size of window for level averaging: A_PBGT_HO
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (3/5)
Cause 12 HO is correlated with cause 23 HO. This is why there are two equations according to the activation of
cause 23 HO (EN_TRAFFIC_HO).
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CAUSE 12: Power budget
DELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of the
serving cell and the neighboring cell n (Traffic_load(n)) in the following way:
If Traffic_load(0) = high and Traffic_load(n) = low,DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_MARGIN
If Traffic_load(0) = low and Traffic_load(n) = high,DELTA_HO_MARGIN(0,n) = + DELTA_INC_HO_MARGIN
Else DELTA_HO_MARGIN(0,n) = 0
Philosophy
This mechanism aims at penalizing cause 12 detection when the traffic in
the serving cell is low and is high in the cell n.
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (4/5)
HIGH LOW
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CAUSE 12: Power budget
� Traffic_load() is managed for every cell of a BSC
� Traffic_load() can have three values:
• HIGH: cell is loaded
• LOW: cell is unloaded
• INDEFINITE: cell load is neither loaded nor unloaded, or unknown
� The traffic_load() value is modified according to the long term traffic evaluation algorithm using the following parameters:
• A_TRAFFIC_LOAD, N_TRAFFIC_LOAD, HIGH_TRAFFIC_LOAD,
IND_TRAFFIC_LOAD, LOW_TRAFFIC_LOAD: can be modified per cell
• TCH_INFO_PERIOD: cannot be modified (5 s)
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (5/5)
Annex 1
TCH_INFO_PERIOD = 5 s period used by the BSC to count the number of free TCH.
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HO_MARGIN(0,n)
� A high value is usually used to avoid ping-pong HO in urban environment
where signal strength varies rapidly due to fading
• Default value: site dependent (but 10 dB observed for dense urban microcellular
area)
• To be optimized: can be reduced to 5dB and even 0 dB when applying an anti ping-
pong mechanism
A_PBGT_HO
� To find a compromise with HO_MARGIN(0,n)
• Default value: 8 SACCHs for urban microcells, 6 for dense urban
2.5 Main standard handover algorithms
Cause 12: tuning of microcells parameters
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HO_MARGIN(0,n) optimization
� Not triggering too many HOs (ping-
pong)
� Not triggering HO to a « bad »
target cell (for example, the
perpendicular cell at a crossroads)
� Not favoring emergency HO (towards the
umbrella cell) with respect to power budget HO
between 2 micro cells (for example when turning
at a street corner)
2.5 Main standard handover algorithms
Cause 12: tuning of microcells parameters
Micro 1Micro 2
Micro 3
PBGT HO between micro cells 1, 2
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HO_MARGIN(0,n) optimization
� A high value of HO_MARGIN(0,n)
will delay the HO, thus it may
create interference problems in
case of adjacent frequencies
between 2 neighboring microcells
� If HO_MARGIN(0,n) is reduced
(5dB or 0 dB), it allows adjacent
frequencies between neighboring
microcells, BUT the average
window should be increased to
reduce ping-pong HO risks or the
anti ping-pong mechanism should
be applied.
2.5 Main standard handover algorithms
Cause 12: tuning of microcells parameters
BTS1
BTS2
Building
Interferer
fn
fn+1
Area of potential interferences: (C/I)adj < -
9dB
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Transfer of fast MSs from lower or indoor layers to upper layer
� If EN_SPEED_DISC = ENABLED
2.5 Main standard handover algorithms
Cause 12: speed discrimination in microcells (1/2)
Traffic Load = low Traffic Load ≠≠≠≠ low
HOHO HO HO
HO
MIN_CONNECT_TIME
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Speed discrimination process in micro cells:
� speed estimation based on the connection time in the cell
� speed is estimated from the last handover from another microcell
� if this connect time is below MIN_CONNECT_TIME, MS_SPEED is set to
FAST. Consequently the MS will be sent to an unloaded umbrella cell.
• C_DWELL is a counter measuring the number of SACCH periods of monitoring
serving micro cell
• if the call has been established after an intra-BSC handover from another micro cell
then C_DWELL is compared to the threshold 2*MIN_CONNECT_TIME in order to
determine MS speed
• if C_DWELL < 2*MIN_CONNECT_TIME then MS_SPEED is set to FAST
• MIN_CONNECT_TIME is not modified according to the load of the micro or
umbrella cells
2.5 Main standard handover algorithms
Cause 12: speed discrimination in microcells (2/2)
Initialization of C_DWELL in serving micro cells
� after call setup or incoming inter-cell handover
� C_DWELL = 0
� after intra-cell handover
� C_DWELL is unchanged
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2.5 Main standard handover algorithms
Handover Cause 23: Traffic (1/2)
CAUSE 23: Traffic Handover
� The aim of this cause is to speed HO detection when
• The serving cell is loaded
• The target cell is unloaded
� When traffic distribution is taken into account for handover detection,
this cause reacts in the opposite way of cause 12, to maintain an
equivalent ping-pong static hysteresis
Checked between
� Cells of the same layer only
� If EN_MULTIBAND_PBGT_HO = disabled
• Cells of the same cell_band_type only
• if the MS is located in the inner zone of a multi-band cell, it can only go to
another multi-band cell
� Else any other cells whatever their cell_band_type
HIGH LOW
In some multi-band networks, the radio coverage is ensured by DCS cells in one geographical area and by GSM cells
in another geographical area. As these cells form a multi-band and mono-layer network, the capture handovers
between cells of different bands will be inefficient to regulate the CS traffic load in the serving cell neighboringhood.
The solution consists in allowing intra-layer traffic handovers (Cause 23) based on a power budget evaluation
between cells of different bands.
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2.5 Main standard handover algorithms
Handover Cause 23: Traffic (2/2)
CAUSE 23: Traffic Handover
DELTA_HO_MARGIN(0,n) < 0 dB
and PBGT(n)>HO_MARGIN(0,n)+OFFSET_HO_MARGIN_INNER
+ DELTA_HO_MARGIN(0,n)
and EN_TRAFFIC_HO(0,n) = ENABLED
�Size of window for level average: A_PBGT_HO
The principle of this handover is to reduce the size of the serving cell when it is high loaded relatively to a low loaded
cell.
When the mobile moves away from the BTS, the power budget will increase and a better cell handover will be
triggered earlier.
It is recommended to inhibit Traffic handover towards 1 TRX cells. These cells do not have enough resources to
receive incoming handovers due to congestion of neighboring cells. Moreover because of the great variation of traffic
in the 1 TRX cells, traffic load is never considered as low.
This cause is inhibited for handover from SDCCH to SDCCH.
Cause 23 is checked over all the neighboring cells belonging to the same layer. It means that it is checked between
cells whose CELL_LAYER_TYPE is single or upper, between cells whose CELL_LAYER_TYPE is lower, and
between cells whose CELL_LAYER_TYPE is indoor.
In addition to the condition on the cell layer type, the cell frequency band condition for checking Cause 23 is as
follows whether or not the MS is in the inner zone of a multi-band cell:
� a) The MS is not in the inner zone of a multi-band cell
• If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 must not be checked between cells
which use different frequency bands (i.e cells having different CELL_BAND_TYPE).
• If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the
neighboring cells without any cell frequency band restriction.
� b) The MS is in the inner zone of a multi-band cell
• If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 is checked over all the neighboring
cell multi-band cells (FREQUENCY_RANGE= PGSM-DCS1800 or EGSM-DCS1800) which belong to the
same BSC as the serving cell.
• If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the
neighboring cells without any cell frequency band restriction.
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2.5 Main standard handover algorithms
Handover Cause 28: Fast Traffic HO (1/3)
CAUSE 28: Fast Traffic Handover� Push out of a cell a mobile in dedicated mode to allow a queued request
to be served in the serving cell
May be triggered� From any non concentric cell OR concentric outer zone
� Towards any cell except the serving one
HO
New call attempt Most appropriate MS
to be pushed out
Congested cell
New call attempt
HO
Most appropriate MS
to be pushed out
Upper Layer Cell
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2.5 Main standard handover algorithms
Handover Cause 28: Fast Traffic HO (2/3)
CAUSE 28: Fast Traffic Handover
� Cause 28 is only checked if the channel of the candidate MS can support the
channel rate (HR or FR) required by the queued request:
� HO is triggered when a request is queued at the top of the queue
FR (whatever the TRX
type)FR
HR
or
FR on dual rate TRX
HR
Candidate MSQueued Request
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2.5 Main standard handover algorithms
Handover Cause 28: Fast Traffic HO (3/3)
CAUSE 28: Fast Traffic Handover equation
AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) +
max (0, [MS_TXPWR_MAX(n) - P])
and t(n) > FREELEVEL_DR(n)
and EN_CAUSE_28 = ENABLED
and EN_FAST_TRAFFIC_HO = ENABLED
�Size of window for averaging level: A_PBGT_DR
�Same thresholds and window as Cause 20 (FDR)
�EN_CAUSE_28 is an internal HOP process variable, ENABLED when a
request is queued
HO cause 28 process:
� If EN_FAST_TRAFFIC_HO = enabled, when an assignment request (or external emergency HO request) is
queued, the RAM process sends to the HOP process a Fast Traffic HO request which contains the queued
request reference and its channel rate.
� Then, HO cause 28 becomes checkable (EN_CAUSE_28=enabled).
� Once an HO alarm for cause 28 is triggered, the flag EN_CAUSE_28 is set to “disabled” so as not to perform
more than one handover. In the same time, the HOP process gets back to the RAM process a Fast Traffic HO
Acknowledge which contains the queued request reference and the reference of the MS that can perform HO.
� If several answers are sent to the RAM process, only the first one corresponding to the queued request is
taken into account.
� The RAM process checks if the request is still queued. If it is so, RAM asks HOP to start HO for this mobile;
otherwise the process is stopped.
� Once the HOP process receives this message, the first two conditions of Cause 28 (good enough level,
enough free resources in the target cell) are checked one more time. If the conditions are fulfilled, the HOP
process sends an alarm to the HOM entity and the timer T_FILTER is started; otherwise the process is
stopped.
Note: the first two conditions of cause 28 are tested twice in order to be sure that the candidate cells are still valid
when the « cause 28 start HO » message is received from the RAM process.
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2.5 Main standard handover algorithms
Exercise (1/2)
Detection of cause 12
� Parameters settings
• No Power Control DL, no anti ping-pong
• EN_PBGT_HO = enabled
• EN_TRAFFIC_HO(0,n) = disabled
• HO_MARGIN(0,n) = 5 dB
• RXLEV_LIMIT_PBGT_HO = -47 dBm
� In each case, determine if cause 12 is detected or not
Time allowed:
15 minutes
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Is cause 12 triggered?
2.5 Main standard handover algorithms
Exercise (2/2)
9009001800900Band
FastFastSlowIndMS speed
Cause 12 ?
PBGT ?
-80 dBm-65 dBm- 65 dBm-80 dBmRx_Lev(n)
HIGHLOWLOWINDTraffic(n)
MicroUmbrellaUmbrellaSingleType
Target
-90 dBm-90 dBm- 90 dBm-85 dBmRx_Lev(0)
NoYesYesNoEN_SPEED_DISC
900900900900Band
MiniMicroMicroSingleType
Source
Case 4Case 3Case 2Case 1Inputs
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.6 Handover algorithms for multi-layer networks
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An MS is located in a lower or an indoor layer of a hierarchical network
A problem is detected on the radio link between the MS and the BTS,
this problem is reported with an alarm cause:
� Identical to standard networks
• cause UL or DL quality (cause 2 and 4)
• cause UL or DL Level - Low threshold (cause 3 and 5)
• cause Distance (cause 6)
� Specific to microcells or indoor cells
• cause UL or DL for Microcell - High threshold (cause 17 and 18)
• cause consecutive bad SACCH frames (cause 7)
2.6 Handover algorithms for multi-layer networks
Emergency handovers: introduction (1/2)
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An MS is located in a micro or an indoor cell
� During an emergency HO, the MS is directed preferably towards an upper or
a single cell
An MS is located in a mini cell
� During an emergency HO, the MS is directed preferably towards neighboring
mini cells
2.6 Handover algorithms for multi-layer networks
Emergency handovers: introduction (2/2)
in µ
umbrella
mini
umbrella
mini
single
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Emergency handovers specific to microcells
� cause 7 : consecutive bad SACCH frames received in a microcell
� cause 17 : too low level on the uplink in a microcell compared to a high
threshold
� cause 18 : too low level on the downlink in a microcell compared to a high
threshold
May be triggered
� From microcells only (cell_dimension_type = micro)
• Outdoor microcell (micro layer)
• Indoor microcell (indoor layer)
� Towards any cell except the serving one
� If the MS is connected to the inner zone of a multi-band cell, the serving cell
is a candidate
2.6 Handover algorithms for multi-layer networks
Emergency Handovers specific to microcells
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CAUSE 7: consecutive bad SACCH frames received in a microcell
Last N_BAD_SACCH frames received are not correct
and EN_MCHO_RESCUE = ENABLED
� N_BAD_SACCH
• Default value: 4 SACCHs
• Rule:
N_BAD_SACCH > RADIOLINK_TIMEOUT_BS - N_BSTXPWR_M
• to be sure that Radio Link Recovery in the microcell will be triggered before trying to
make a handover towards the umbrella
• RADIOLINK_TIMEOUT_BS = 18 SACCH
N_BSTPWR_M = 15 SACCH
2.6 Handover algorithms for multi-layer networks
Cause 7: consecutive bad SACCH frames received in a microcell
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CAUSE 17: too low level on the UL in a microcell compared to a high
threshold
AV_RXLEV_UL_MCHO(i) <= U_RXLEV_UL_MCHO
and AV_RXLEV_UL_MCHO(i-1) > U_RXLEV_UL_MCHO
and EN_MCHO_H_UL = ENABLED
� Averaging window: A_LEV_MCHO
2.6 Handover algorithms for multi-layer networks
Cause 17: too low level on the UL in a µcell compared to high thr.
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CAUSE 18: too low level on the DL in a microcell compared to a high
threshold
AV_RXLEV_DL_MCHO(i) <= U_RXLEV_DL_MCHO
and AV_RXLEV_DL_MCHO(i-1) > U_RXLEV_DL_MCHO
and EN_MCHO_H_DL = ENABLED
� Averaging window: A_LEV_MCHO
2.6 Handover algorithms for multi-layer networks
Cause 18: too low level on the DL in a µcell compared to high thr.
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High threshold (U_RXLEV_XX_MCHO)
� the HO is triggered when the signal drops under the threshold
� the corresponding HO causes consist in comparing, at 2 successive SACCH periods, the
DL and UL levels in the serving microcell with a high threshold
• Beginning a call under the threshold does not trigger an HO
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (1/4)
ii-1
t
AV_RXLEV_XX_MCHO
High
Threshold
HO alarm
ii-1
t
AV_RXLEV_XX_MCHO
High
Threshold
no HO alarm
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96
High threshold (U_RXLEV_XX_MCHO)
� With high value, mobiles will be sent too early to the macro layer
� With low value, mobiles turning at a street corner will be maintained in the
microcell layer during a longer period
• In theory, there is risk of call drop
• In practice, with appropriate parameters,
- A PBGT HO should be triggered before (speed < 40 km/h)
- Low Threshold for safety
� Problems of indoor mobiles with a signal strength level close to the high
threshold that should be kept as long as possible in the micro-layer
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (2/4)
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U_RXLEV_XX_MCHO compared to L_RXLEV_XX_H
� typical gap taken: 2dB
� for DL:
• L_RXLEV_DL_H = -93 dBm
• U_RXLEV_DL_MCHO = -91 dBm
� for UL:
• L_RXLEV_UL_H = -95 (M2M), -98 (M4M), -102 (Evolium) dBm
• U_RXLEV_UL_MCHO = -93 (M2M), -96 (M4M), -100 (Evolium) dBm
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (3/4)
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A_LEV_MCHO
� The averaging window size shouldn’t be too small in order to:
• avoid triggering too easily an HO on fading and overloading needlessly the macrocell
• favor as much as possible between 2 micro cells PBGT HO
� Typical value: 10 SACCHs
• The high threshold is used to modelize a slow decrease of the signal level at microcell
border
• Really urgent handovers will be triggered using the Low Threshold (cause 3 & 5) with a
short averaging window size
A_LEV_HO
� Default value: 6 SACCHs for urban micro cells, 4 for dense urban ones
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (4/4)
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer
for slow mobiles
� “historical” capture handover
• Introduced in R3
• Improved in B4 (enhanced speed disc.)
• Improved in B4.1 (dual band MS support)
• Improved in B7 (indoor & anti ping-pong)
� May be triggered
• From upper layer cells
• Towards lower or indoor layer cells
• From lower layer cells
• Towards indoor layer cells
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (1/4)
mini
umbrella
micro
indoor
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer for slow mobiles
� in order to keep dual band MSs in the preferred band, cause 14 is not checked in the following cases, when EN_BI-BAND_MS(n) = DISABLED
� The same scheme can be drawn between lower and indoor layers
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (2/4)
CELL_BAND_TYPE = Preferred_band
CELL_LAYER_TYPE =
upper
CELL_LAYER_TYPE =
lower or indoor
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE = CELL_BAND_TYPE(0)
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE ≠ Preferred_band
CELL_BAND_TYPE = Preferred_bandCELL_BAND_TYPE <> Preferred_band
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer for
slow mobiles
� If cell_layer_type (0) = upper
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED = SLOW
and EN_MCHO_NCELL = ENABLED
� Averaging window: A_PBGT_HO
� Anti ping-pong: not checked if T_INHIBIT_CPT is running
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (3/4)
mini
umbrella
micro indoor
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer for
slow mobiles
� If cell_layer_type (0) = lower
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED ≠≠≠≠ FAST
and EN_MCHO_NCELL = ENABLED
� Averaging window: A_PBGT_HO
� Anti ping-pong: not checked if T_INHIBIT_CPT is running
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (4/4)
mini micro
indoor
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Speed discrimination objectives
� maximize capacity (maximum traffic in microcells)
� while optimizing quality (minimize the number of handovers)
� Smart speed discrimination:
• The higher the load in the umbrella cell, the higher the speed of MSs can be before
being directed to microcells
- to maximize capacity
- to maximize quality (avoid multiple handovers) when the load is low
� Fast moving mobiles are directed to umbrella cells
• a fast moving MS connected to a microcell or an indoor cell is directed to an
unloaded umbrella cell (see previous part)
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (1/6)
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Interlayer HO based on speed discrimination
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (2/6)
Lower layer
Upper layer
Indoor layer
Cause12MS_speed = FAST
Cause12MS_speed = FAST
Cause14MS_speed = SLOW
Or INDEFINITE
Cause14MS_speed = SLOW
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105
Speed discrimination process in umbrella cells
� speed estimation based on the dwell time in the neighboring micro cells
� if this dwell time exceeds MIN_DWELL_TIME, the MS is slow and is sent to the microcell
• C_DWELL(n) is a counter measuring the number of SACCH periods of monitoring
neighboring cell n over the threshold L_RXLEV_CPT_HO(0,n)
• C_DWELL(n) is compared to the threshold 2*MIN_DWELL_TIME in order to
determine MS speed
- MIN_DWELL_TIME is a variable linked to the load of the serving umbrella cell)
• if for one neighboring cell n, C_DWELL(n) >= 2*MIN_DWELL_TIME then
MS_SPEED is set to SLOW
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (3/6)
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106
Initialization of C_DWELL(n) in serving umbrella cells:
� for all neighboring cells n of a lower layer
• if EN_SPEED_DISC = ENABLED
- C_DWELL(n) = 0
• else if EN_SPEED_DISC = DISABLED
- C_DWELL(n) = (MIN_DWELL_TIME - L_MIN_DWELL_TIME)*2
� Consequences
• if EN_SPEED_DISC = DISABLED
MSs will handover to the lower layer after L_MIN_DWELL_TIME seconds
• if EN_SPEED_DISC = ENABLED
MSs will have to receive sufficient level from a lower layer cell during
MIN_DWELL_TIME seconds before leaving the upper layer
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (4/6)
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107
Example with default values
� Initial values
• MIN_DWELL_TIME = H_MIN_DWELL_TIME = 20s
• L_MIN_DWELL_TIME = 8s
• C_DWELL(n) = (MIN_DWELL_TIME - L_MIN_DWELL_TIME)*2
• C_DWELL(n) = ( 2 - 8 )*2
• C_DWELL(n) = 12*2s
� Algorithm
• MS is deemed as slow if C_DWELL(n) > MIN_DWELL_TIME
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (5/6)
0 2 4 6 8 10 12 14 16 18 20 22
: EN_SPEED_DISC = Disable
: EN_SPEED_DISC = Enable
INDEFINITE or FAST SLOW
Maximum time to reach
MIN_DWELL_TIME
=
L_MIN_DWELL_TIME
C_DWELL MIN_DWELL_TIMEC_DWELL
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Traffic regulation through the variation of MIN_DWELL_TIME
� Parameters: L_MIN_DWELL_TIME, DWELL_TIME_STEP,
H_MIN_DWELL_TIME, H_LOAD_OBJ, L_LOAD_OBJ
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (6/6)
100 %
Load in the
umbrella Cell
H_LOAD_OBJ
L_LOAD_OBJ
L_MIN_DWELL_TIME
10 seconds
DWELL_TIME_STEP
5 seconds
H_MIN_DWELL_TIME
40 seconds
end: low traffic
start: low traffic
Regulation of
traffic peak
Default values
dependent on
the number of
TRXs
Default values: 8 seconds 2 seconds 20 seconds
MIN_DWELL_TIME
The initial value of MIN_DWELL_TIME is the H_MIN_DWELL_TIME parameter value.
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CAUSE 24: general capture
� new capture handover
• Introduced in B6.2
• Improved in B7 (anti ping-pong)
� May be triggered
• From all cells
• Towards any cell except the serving one
• Can be used to capture traffic by any cell, whatever its type, band, etc.
2.6 Handover algorithms for multi-layer networks
Cause 24: general capture (1/3)
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CAUSE 24: general capture
� in order to keep dual band MS in the preferred band, cause 24 is not checked
in the following cases, when EN_BI-BAND_MS(n) = DISABLED
2.6 Handover algorithms for multi-layer networks
Cause 24: general capture (2/3)
CELL_BAND_TYPE = Preferred_band
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE = CELL_BAND_TYPE(0)
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE ≠ Preferred_band
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CAUSE 24: general capture
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) +
max (0, [MS_TXPWR_MAX(n) - P])
and Traffic_load(0) = CAPTURE_TRAFFIC_CONDITION
and Traffic_load(n) ≠≠≠≠ HIGH
and EN_GENERAL_CAPTURE_HO = ENABLED
� Size of window for averaging level: A_PBGT_HO
� CAPTURE_TRAFFIC_CONDITION can take 3 values: ANY_LOAD
(default), HIGH, NOT_LOW
� Anti ping-pong: not checked if T_INHIBIT_CPT is running
2.6 Handover algorithms for multi-layer networks
Cause 24: general capture (3/3)
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Use of cause 21 or 14?
� Considering the following network
� Which cause has to be used for capture? 14 or 21?
� Highlight one complexity linked to causes 14 and
21 interworking when using traffic discrimination
2.6 Handover algorithms for multi-layer networks
Exercises (1/3)
900
mini1800
Time allowed:
5 minutes
CAUSE 21: high level in the neighboring cell in the preferred band
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) +
max (0, [MS_TXPWR_MAX(n) - P])
and Traffic_load(0) = MULTI-BAND_TRAFFIC_CONDITION
and Traffic_load(n) ≠≠≠≠ HIGH
and EN_PREFERRED_BAND_HO = ENABLED
� Size of window for average level: A_PBGT_HO
� MULTI-BAND_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default), HIGH, NOT_LOW
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2.6 Handover algorithms for multi-layer networks
Exercises (2/3)
Inputs Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7 Case 8
Type Single Umbrella Umbrella Umbrella Multiband Multiband Micro Mini
Band 900 900 900 1800 900+1800 900+1800 900 900
Zone --- --- --- --- Outer Inner --- ---
Speed_disc Yes Yes No No No No Yes Yes
Rx_Lev(0) -84 dBm -60 dBm -90 dBm -90 dBm -90 dBm -90 dBm -60 dBm -90 dBm
Source
MS Speed Slow Slow Slow Slow Slow Slow Indefinite Fast
Type Micro Micro Mini Mini Mini Mini Indoor Indoor
Band 900 900 1800 900 1800 1800 900 1800
RxLev(n) -84 dBm -80 dBm -80 dBm -80 dBm -80 dBm -80 dBm -70 dBm -80 dBm
Target
EN_BI-BAND_MS Enable Enable Disable Disable Disable Disable Enable Disable
? Cause 14 ?
Time allowed:
5 minutes
Detection of cause 14
� EN_MCHO_NCELL(0) = ENABLED
� L_RXLEV_CPT_HO(0,n) = -85 dBm
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2.6 Handover algorithms for multi-layer networks
Exercises (3/3)
Time allowed:
5 minutes
Speed discrimination
� What is the role of parameter EN_SPEED_DISC?
� If EN_SPEED_DISC is disabled, can fast MSs be
directed toward microcells?
� What is the difference between EN_SPEED_DISC =
DISABLED and EN_SPEED_DISC = ENABLED when
L_LOAD_OBJ = 0% and H_LOAD_OBJ = 100%?
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
2.7 Candidate cell evaluation
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116
As soon as an intercell HO alarm has been detected
HO Detection sends to Candidate Cell Evaluation
� the HO cause value
� the preferred layer for the target cell indicated by the variable PREF_LAYER (it
depends on the cell network architecture and on the operator strategy)
� the list of potential candidates (it depends on type of handover cause)
2.7 Candidate cell evaluation
From HO Detection to Candidate Cell Evaluation
Candidate
Cell
Evaluation
Handover
Detection
Raw cell list
cell 1: cause C1
cell 2: cause C2
cell 3: cause C3
…
Max 32 cells
PREF_LAYER
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Standard cell environment
� CELL_LAYER_TYPE = SINGLE
• Better condition HO cause
• Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the
serving cell
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (2/4)
upper + singlePREF_LAYE
R
subset of cells verifying the HO
causesRaw cell list
upper + singlePREF_LAYE
R
all neighboring cells*Raw cell list
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Hierarchical cell environment
� CELL_LAYER_TYPE = UPPER
• Better condition HO cause
• Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the
serving cell
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (2/4)
nonePREF_LAYE
R
subset of cells verifying the HO
causesRaw cell list
upper + singlePREF_LAYE
R
all neighboring cells*Raw cell list
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� CELL_LAYER_TYPE = LOWER or INDOOR
• Better condition HO cause
• Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the serving cell
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (3/4)
noneLower + indoorUpper + SinglePREF_LAYER
All neighboring cells* except
umbrella cells which do not
verify AV_Rxlev_Ncell(n) >
OUTDOOR_UMB_LEV(0,n)
All neighboring cells* except
umbrella cells which do not
verify AV_Rxlev_Ncell(n) >
OUTDOOR_UMB_LEV(0,n)
All neighboring cells* except
umbrella cells which do not
verify AV_Rxlev_Ncell(n) >
OUTDOOR_UMB_LEV(0,n)
Raw cell list
EN_RESCUE_UM = indefiniteEN_RESCUE_UM =
DISABLED
EN_RESCUE_UM =
ENABLED
noneUpperPREF_LAYER
Subset of cells verifying the
HO causes
Subset of cells verifying the HO
causes plus all neighboring
umbrella cells with
Traffic_Load(n) = LOW
Raw cell list
MS_SPEED <> FAST or
HO Cause <> 12
MS_SPEED = FAST and
There is a cell in the list
because of cause 12
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Emergency handovers from lower or indoor layers
� behavior depends on EN_RESCUE_UM
� Normal parameter settings for minicells
• EN_RESCUE_UM = DISABLED
• thus PREF_LAYER = lower
• Emergency handovers are preferably sent to neighboring minicells
� Normal parameter settings for microcells
• EN_RESCUE_UM = ENABLED
• thus PREF_LAYER = upper + single
• Emergency handovers are preferably sent to umbrella cells or neighboring
macrocells
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (4/4)
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MEASUREMENT PREPROCESSING
according
• A_LEV_HO
• A_QUAL_HO
• A_PBGT_HO
• A_RANGE_HO
Performed every SACCH
Measurement result
HO_DETECTION
cause 2: uplink quality
cause 3: uplink level
cause 4: downlink quality
cause 5: downlink level
cause 6: distance
cause 12: power budget
Performed every SACCH
Preprocess measurement
Raw cell list
cell 1: cause C2
cell 2: cause C2
cell 3: cause C2
cell 4: cause C2
cell 5: cause C2
cell 6: cause C2
cell 7: cause C2
cell 8: cause C2
…
Max 32 cells
max EverySACCH
HO CANDIDATE CELLS EVALUATION
Priority (0,n) = 0
cell 2: cause C2
cell 3: cause C3
cell 4: cause C4
Priority (0,n) = 1
cell 1: cause C1
Priority (0,n) = 2
Priority (0,n) = 3
cell 5: cause C5
cell 6: cause C6
cell 7: cause C7
cell 8: cause C8
PRE-RANKING
PBGT_FILTERING
HO_MARGIN_XX(0,n)
Priority (0,n) = 0
cell 2: cause C2
cell 3: cause C3
cell 4: cause C4
Priority (0,n) = 1
-----------------------
Priority (0,n) = 2
Priority (0,n) = 3
----------------------
cell 6: cause C6
-----------------------
cell 8: cause C8
CELLS EVALUATION PROCESS
Order or Grade
Grade
Priority (0,n) = 0
cell 4
cell 2
Priority (0,n) = 1
Priority (0,n) = 2
Priority (0,n) = 3
cell 8
Order
Priority (0,n) = 0
cell 4
cell 3
cell 2
Priority (0,n) = 1
Priority (0,n) = 2
Priority (0,n) = 3
cell 8
2.7 Candidate cell evaluation
Evaluation process
The HO candidate evaluation process is run after all intercell handover alarms.
In case of intra-cell handover alarm (HO causes 10, 11, 13, 15, 16), the candidate cell evaluation process is skipped:
the target cell is the serving cell.
The handover detection gives as indication the raw cell list (built from the book-keeping list) and the preferred layer
for the handover.In case of emergency handover alarms or cause 20 alarm, the cell evaluation will order the cells
given in the raw list, putting in the first position the cells belonging to the preferred layer, having the highest priority (if
EN_PRIORITY_ORDERING=ENABLED) and/or having the same frequency band type as the serving cell. In case of
an intercell handover alarm, if the serving cell belongs to the raw cell list (emergency handover from the DCS 1800
inner zone of a multi-band cell), this cell is put at the end of the candidate cell list with the MS zone indication
OUTER.
In case of better condition handover alarms (except cause 20), the cell evaluation will order the cells given in the raw
list, putting in the first position the cells belonging to the preferred layer and having the highest priority (if
EN_PRIORITY_ORDERING=ENABLED).
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2.7 Candidate cell evaluation
Pre-ranking in standard networks
with PRIORITY(0,n) settings, the operator can
� for each couple of cells
� tag the target cell with a defined priority (from 0 = max to 5 = min)
� this definition has a higher priority than usual order/grade ranking
especially useful for multi band/hierarchical architectures
� a simple way to force a target cell whatever its RxLev and PBGT
� nevertheless it can be skipped over by filtering processes
� low interest for standard networks
Serving cell
Candidate cell 1: RxLev: - 70 dBm, pbgt: + 10 dB
Candidate cell 2: Rxlev: - 90 dBm, PBGT: + 5dB
P0
P1
PRIORITY(0,n) can take 6 different values since B7, to take into account new indoor layers.
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In hierarchical or multi-band networks, pre-ranking is used
� For emergency handovers + Forced Directed Retry
• Cell_layer_type: single, upper, lower, indoor
• PRIORITY(0,n): 0 to 5
• Cell_band_type: GSM or DCS
� For better condition handovers
• Cell_layer_type: single, upper, lower, indoor
• PRIORITY(0,n): 0 to 5
� PRIORITY(0,n) are taken into account only if EN_PRIORITY_ORDERING is
set to enabled on the serving cell
2.7 Candidate cell evaluation
Pre-ranking in complex networks (1/3)
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Pre-ranking in case of emergency HO, plus cause 20 and 28 :
2.7 Candidate cell evaluation
Pre-ranking in complex networks (2/3)
Cell_layer_type = Pref_layer
Cell_layer_type ≠ Pref_layer
List of candidate cells n
Cell_band_type = serving cell
Cell_band_type ≠ serving cell
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
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Pre-ranking in case of better condition HO:
2.7 Candidate cell evaluation
Pre-ranking in complex networks (3/3)
Cell_layer_type = Pref_layer
Cell_layer_type ≠ Pref_layer
List of candidate cells n
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
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2.7 Candidate cell evaluation
PBGT Filtering
PBGT filtering: process introduced since B5
� optional, activated through the flag EN_PBGT_FILTERING
� filter out cells from the target list
� inhibited for better conditions handovers
� based on power budget
� Mandatory for multi-band networks
PBGT(n) > HO_MARGIN_XX (0,n) + OFFSET_HO_MARGIN_INNER
• HO_MARGIN_XX (0,n) = HO_MARGIN_QUAL (0,n) for causes 2, 4, 7
• HO_MARGIN_XX (0,n) = HO_MARGIN_LEV (0,n) for causes 3, 5, 17, 18, 28
• HO_MARGIN_XX (0,n) = HO_MARGIN_DIST (0,n) for cause 6
• OFFSET_HO_MARGIN_INNER is only applied when the MS is in the inner zone of a concentric or multi band cell
• The average window is A_PBGT_HO
The filtering process allows to filter out cells from the target list before sending them to the ORDER or GRADE
evaluation process.
It can be enabled/disabled on-line on a per cell basis from the OMC-R with the flag EN_PBGT_FILTERING.
The candidate cells are filtered on their power budget in relation to a handover margin threshold based on the
handover cause.
Note: the average window used for this process is A_PBGT_HO (even for emergency handovers, where handover
alarm could have been raised through A_LEV_HO or A_QUAL_HO samples).
Warning: HO_MARGIN_xx (LEV, DIST or QUAL) has nothing to do with a handover margin value, specific for certain
handover causes (anyway, these handovers cause only tackle source cell and are not looking at level of targets for
handover detection).
HO_MARGIN is used for handover detection (cause 12 or 23).
HO_MARGIN_xx are used for candidate cell evaluation.
Thus, there is no having HO_MARGIN = HO_MARGIN_xx! Let us see three examples:
1) If HO_MARGIN_xx = HO_MARGIN = 5 dB
In that case, when an emergency handover is triggered (level, quality, distance, etc.), all neighboring cells are
filtered regarding their PBGT compared to 5 dB! By the way, if a cell that is not greater than the serving one +
5 dB will be filtered out: this handover, detected as an emergency case, is in fact a better cell one.
2) If HO_MARGIN_xx is very small (for example, -30 dB), risk of ping-pong handovers.
For example, all cells have L_RXLEV_DL_H = -97dBm. If Lev(cell1)=-98dBm, HO can be triggered to cell2 with
level -99dBm (-99>-98-30), and then, as -99<-97, HO is triggered back to cell1: ping-pong of emergency HO.
3) HO_MARGIN_xx can be used to simulate PBGT HO (for example, usage of distance HO to simulate 900-1800
PBGT HO before it was existing). HO_MARGIN_DIST is very small (e.g., 2 on 1800). Thus, a Distance HO
alarm is raised very early. If HO_MARGIN_DIST (1800,900)= 8 dB, no HO will be in fact triggered before the
level of the 900 neighboring cell is greater than the one of 1800 + 8 dB: this distance HO is in fact a PBGT HO
between bands.
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ORDER cell evaluation process, if CELL_EV = ORDER
Cell "n" is ranked among others according to the best ORDER:
If EN_LOAD_ORDER = ENABLED and cell n is internal to the BSC
ORDER (n) = PBGT(n) + LINK_FACTOR(0,n) + FREEfactor(n) - FREEfactor(0) -HO_MARGIN_XX(0,n)
� LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell
� FREEfactor are TCH traffic based bonus/penalty to rank cells
If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
ORDER (n) = PBGT(n) + LINK_FACTOR(0,n) - HO_MARGIN_XX(0,n)
Cell "n" is kept if:
� AV_RXLEV_NCELL (n) > RXLEVmin (n) + max [0;(MS_TXPWR_MAX(n)-P)]
2.7 Candidate cell evaluation
ORDER evaluation
Two types of cell evaluation algorithms can be used: ORDER and GRADE.
ORDER and GRADE are two different methods of cell ranking. They both consist in giving a mark or ’figure of merit’
to each candidate cell.
The basic differences between ORDER and GRADE are that:
� with ORDER:
• The candidate cell evaluation process interacts with the handover detection by use of cause dependent
handover margins.
• The candidate cell evaluation process takes into account the number of free TCH in the candidate cells.
� with GRADE,:
• The candidate cell evaluation process does not interact with the handover detection.
• The candidate cell evaluation process takes into account the relative load of traffic channels in the
candidate cells.
The type of cell evaluation is chosen by the operator on a (serving) cell basis and is provided to the BSC with the
parameter CELL_EV
For any handover cause, the first cell in the list is taken as the target cell, i.e. the cell with the highest value of
ORDER(n). The cells do not need to fulfil any other condition.
If no cell fulfils the condition and the serving cell does not belong to the target cell list, the target cell list is empty and
no further action is carried out.
Note: the A_PBGT_HO average window is used for this process.
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2.7 Candidate cell evaluation
GRADE Evaluation
GRADE cell evaluation process, if CELL_EV = GRADE
Cell "n" is ranked among other according to the best GRADE:
If EN_LOAD_ORDER = ENABLED and cell n is internal to the BSC
GRADE (n) = PBGT(n) + LINK_FACTOR(0,n) + LOADfactor(n)
� LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell
� LOADfactor(n) is a weighting factor that takes into account the relative load of traffic channels in a cell
If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
GRADE (n) = PBGT(n) + LINK_FACTOR(0,n)
Cell "n" is kept if:
� AV_RXLEV_NCELL (n) > RXLEVmin(n) + max [0;(MS_TXPWR_MAX(n)-P)]
LINKfactor(0,n) is a parameter set by OMC command for each cell(n).
LINKfactor(n1,n2) allows the operator to handicap or to favor the cell n1 with respect to its neighboring cell n2. In
particular, it can be used to disadvantage an external cell when an internal cell is also a possible candidate.
For any handover cause the first cell in the list is taken as the target cell, i.e. the cell with the highest value of
GRADE(n). If no cell fulfils the condition and the serving cell does not belong to the target cell list, the target cell list is
empty and no further action is carried out.
Note: the A_PBGT_HO average window is used for this process.
Note: an example summarizing all steps of candidate cell evaluation, in case of a multi-band network, can be given
here: MS on a 1800 cell, 3 possible neighboring cells (1*900 + 2*1800). P(1800,900)=1 and P(1800,1800)=0. All
HO_MARGIN_xx = 0 dB. PBGT:
� PBGT (900) = +5 (second cell seen in the book-keeping list)
� PBGT (1800_1) = -2 (first cell seen in the book-keeping list)
� PBGT (1800_2) = +2 (third cell seen in the book-keeping list)
Cell (1800_2) is chosen.
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2.7 Candidate cell evaluation
Exercise (1/4)
Time allowed:
5 minutes
A hierarchical network is considered (umbrella +
micro cells)
� A slow moving MS starts a call in lower layer
� After a while, this MS becomes a fast moving MS (for
example, a car starting at traffic light) and
EN_SPEED_DISC is ENABLED
• Explain the exact process that will send the MS towards the
umbrella layer
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2.7 Candidate cell evaluation
Exercise (2/4)
1800900900Band
SlowMS speed
Best Target ?
-84 dBm-80 dBm-74 dBmRx_Lev(n)
DisabledEnabledDisabledEN_BI-BAND_MS
SingleUmbrellaSingleType
Possible
Target
-82 dBmRx_Lev(0)
YesEN_SPEED_DISC
1800Band
SingleType
Source
Time allowed:
5 minutes
Which is the best target cell ?
� Emergency qual ho triggered in serving cell
� HO_MARGIN_QUAL(0,n) = -2 dB
� PRORITY(0,n) = 1
� LINK_FACTOR(0,n) = 0 dB
EN_LOAD_ORDER = Disabled.
EN_PBGT_FILTERING = Enabled.
RXLEVmin= -100 dBm.
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2.7 Candidate cell evaluation
Exercise (3/4)
-82 dBm
Disabled
1800
Single
-75 dBm
Disabled
900
micro
-85 dBm
Disabled
1800
micro
900900900Band
SlowMS speed
Best Target ?
-80 dBm-80 dBm-74 dBmRx_Lev(n)
EnabledEnabledDisabledEN_BI-BAND_MS
IndoorUmbrellaSingleType
Possible
Target
-76 dBmRx_Lev(0)
YesEN_SPEED_DISC
900Band
UmbrellaType
Source
Time allowed:
5 minutes
Which is the best target cell ?
� Emergency qual ho triggered in serving cell
� HO_MARGIN_QUAL(0,n) = -2 dB
� PRORITY(0,n) = 1
� LINK_FACTOR(0,n) = 0 dB
EN_LOAD_ORDER = Disabled.
EN_PBGT_FILTERING = Enabled.
RXLEVmin= -100 dBm.
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2.7 Candidate cell evaluation
Exercise (4/4)
-82 dBm
Disabled
1800
Single
-75 dBm
Disabled
900
micro
-85 dBm
Disabled
1800
micro
900900900Band
SlowMS speed
Best Target ?
-80 dBm-80 dBm-84 dBmRx_Lev(n)
EnabledEnabledDisabledEN_BI-BAND_MS
IndoorUmbrellaSingleType
Possible
Target
-68 dBmRx_Lev(0)
NoEN_SPEED_DISC
900Band
microType
Source
Time allowed:
5 minutes
Which is the best target cell ?
� Emergency qual ho triggered in serving cell
� HO_MARGIN_QUAL(0,n) = -2 dB
� PRORITY(0,n) = 1, LINK_FACTOR(0,n) = 0 dB
� EN_RESCUE_UM = Enabled
EN_LOAD_ORDER = Disabled.
EN_PBGT_FILTERING = Enabled.
RXLEVmin= -100 dBm.
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3 CREATING A MULTI-LAYER NETWORK
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3 CREATING A MULTI-LAYER NETWORK
Session presentation
Objective: to be able to define relevant parameters settings
to introduce a new layer in an existing network
Program:
3.1 Adding a microcellular layer for traffic and coverage increase
3.2 Adding hot spot microcells for traffic
3.3 Adding indoor microcells for coverage
3.4 Monitoring QoS in a multi-layer network
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3 CREATING A MULTI-LAYER NETWORK
3.1 Adding a microcellular layer for traffic and coverage increase
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Introducing a microcell layer in an existing network allows
� Capacity improvement
• new TRXs introduced in the network
• With easier frequency planning due to microcells confined coverage
� Coverage improvement
• Good indoor penetration due to microcells position
- Field trials show that coverage of shops in microcell area is 20dB better after microcell
introduction
• Specific microcells to handle indoor traffic area
- Airports, stations, shopping malls, etc.
3.1 Adding a microcellular layer for traffic and coverage increase
Introduction (1/3)
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3.1 Adding a microcellular layer for traffic and coverage increase
Introduction (2/3)
70.5
31.4
19.2
71
71.6 72.5
76.8
72.3
29.1
17.9
71.1 78
95.9 95.1 98.4 94.6100.7
41.736.4
94.398.4
117.9114 116.9
54.7
42.9
116.1112.5
118.5
121.6
121.6
60
45.9
115.1
124.5
70.6
68.6
0
20
40
60
80
100
120
1408/9
9/9
10/9
11/9
12/9
13/9
14/9
15/9
16/9
17/9
18/9
19/9
20/9
21/9
22/9
23/9
24/9
25/9
26/9
27/9
28/9
29/9
30/9
Macrocells Microcells
Microlayer commercial opening Field Example: Busy Hour Traffic
• 20% of new traffic generation
• 50% of old macro traffic is handled by microcells
This example corresponds to the following network design:
� Lower layer: 16 micro cells (37 TRXs)
• 11 outdoor micro cells with 2 TRXs
• 1 outdoor micro cell with 3 TRXs
• 2 indoor micro cells (pico cells) with 2 TRXs
• 2 indoor micro cells (pico cells) with 4 TRXs
� Upper layer: 12 macro cells
• umbrella macro cells are concentric (but not multi-band)
• 4 belong to the same BSS as the micro cells
• 8 belong to another BSS
All micro cells were declared as micro and not as indoor.
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Keep a good QoS
� Avoid call drops on microcells
• specific emergency HO towards umbrella rescue cells
� Avoid unnecessary handovers
• to ensure good QoS and speech quality
• The idle mode is favoring microcells to avoid subsequent capture
• fast MSs are kept in the umbrella layer
3.1 Adding a microcellular layer for traffic and coverage increase
Introduction (3/3)
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Capture towards microcells, emergency towards umbrella
� Capture HO is used to send slow MSs to the overlaid layer
• Capture HO (cause 14):
• PBGT HO (cause 12):
• Emergency HO (Level or Quality):
3.1 Adding a microcellular layer for traffic and coverage increase
Architecture
umbrella
micro micro micro
umbrella
micro
singleUPPER
SINGLE
LOWER
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140
DR and FDR are ENABLED
� An FDR (cause 20) is triggered when the average level of a neighboring cell is higher
than L_RXLEV_NCELL_DR(n)
3.1 Adding a microcellular layer for traffic and coverage increase
Call Setup
Umbrella
EN_DR = ENABLED
EN_FORCED_DR = DISABLED
L_RXLEV_NCELL_DR(n) = -97
dBm
FREElevel_DR(n) = 0
Micro
EN_RESCUE_UM = ENABLED
EN_DR = ENABLED
EN_FORCED_DR = ENABLED
L_RXLEV_NCELL_DR(n) = -47 dBm
FREElevel_DR(n) = 0
DR & FDR
PRIORITY(micro, umb) = 1
DR only
PRIORITY(umb, umb) = 1
DR only
PRIORITY(umb, micro) = 0
DR & FDR
PRIORITY(micro, micro) = 1
The Setting of PRIORITY(0,n) is very important as network behavior will not be driven by Pref_layer which is equal to
"none" in this case.
But setting L_RXLEV_NCELL_DR(n) to -47 dBm in the micro cells inhibits the incoming FDR to them. Therefore
Priority(0,n) can be kept to the same value everywhere.
Priority(umb,micro) is set to 0 for Better Cell purpose (see the next pages).
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Parameter settings will depend on the microcells position in the lower
layer
� Microcell “classes” are introduced to deal with typical parameters settings
in each of these cases
3.1 Adding a microcellular layer for traffic and coverage increase
Microcell classes
Indoor Microcell
Border Microcell
Inner Microcell
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Definition
� A microcell surrounded by other microcells in a dense environment
Rules
� The MS is comfortably installed in the microcell area. Calls have to be handled by
a micro layer, which is a “traffic-catcher”
• Fast handover from the umbrella to micro cell
• If the MS is already on call in the micro-layer, it must stay on it
- the handover that may be triggered will be a PBGT handover
3.1 Adding a microcellular layer for traffic and coverage increase
Inner microcell class
Inner Microcell
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Causes 12 and 14
3.1 Adding a microcellular layer for traffic and coverage increase
Inner microcell: better condition handovers
Umbrella
EN_PBGT_HO = ENABLED
EN_MCHO_NCELL = ENABLED
EN_SPEED_DISC = DISABLED
L_MIN_DWELL_TIME = 6s
Inner Microcell
EN_PBGT_HO = ENABLED
EN_SPEED_DISC = ENABLED
A_PBGT_HO = 6
Cause 14
PRIORITY(umb, micro) = 0
L_RXLEV_CPT_HO(umb, micro)
= -85 dBm
Cause 12 / 23
PRIORITY(umb, umb) = 1
HO_MARGIN(umb, umb) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12
PRIORITY(micro, micro) = 1
HO_MARGIN(micro, micro) =?
No better condition HO from a micro
to an umbrella cell (different layers)
A capture towards a microcell is triggered after L_MIN_DWELL_TIME. A low value is chosen, as we consider an
inner microcell.
In an umbrella 900 cell, a capture to a micro cell is preferred to a PBGT HO to a neighboring 900 cell using
Priority(0,n).
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HO_MARGIN(micro,micro) and A_PBGT_HO(micro)
tuning� Avoid making too many handovers
• No HO is triggered to the perpendicular cell at a crossroads if the MS is
not turning at a street corner
� favor a PBGT HO to a micro cell and not an emergency HO towards
an umbrella cell
• When turning at a street corner, a PBGT HO has to be triggered towards
the perpendicular microcell before any emergency alarm detection
� Thus
• Reduce A_PBGT_HO
• Increase HO_MARGIN and
tune it regarding the respective
microcell positions
3.1 Adding a microcellular layer for traffic and coverage increase
Inner microcell: tuning of cause 12 parameters
Micro 1Micro 2
Micro 3
PBGT HO between micro cells 1, 2
HO_MARGIN tuning will be detailed in section 4: case studies.
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Use Level, Quality causes
3.1 Adding a microcellular layer for traffic and coverage increase
Inner microcell: emergency handovers
Umbrella
Pref_layer = upper + single
Inner Microcell
EN_RESCUE_UM = ENABLED
Pref_layer = upper + single
A_QUAL_HO = 4
A_LEV_HO = 4
L_RXLEV_DL_H = -97 dBm
PRIORITY(umb,micro) = 0
PRIORITY(umb,umb) = 1
PRIORITY(micro,micro) = 1
PRIORITY(micro,umb) = 1
EN_RESCUE_UM is set to ENABLED for an emergency handovers behavior (send MSs towards the upper layer).
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3.1 Adding a microcellular layer for traffic and coverage increase
Inner microcell: candidate cells evaluation process
Umbrella
EN_PRIORITY_ORDERING = ENABLED
EN_PBGT_FILTERING = ENABLED
CELL_EV = GRADE
Inner Microcell
EN_PRIORITY_ORDERING = ENABLED
EN_PBGT_FILTERING = ENABLED
CELL_EV = ORDER
EN_RESCUE_UM = ENABLED
PRIORITY(umb,umb) = 1
HO_MARGIN_LEV(umb,umb)= 0 dB
HO_MARGIN_QUAL(umb,umb)= -1 dB
HO_MARGIN_DIST(umb,umb)= 0 dB
PRIORITY(micro,umb) = 1
HO_MARGIN_LEV(micro,umb)= -127 dB
HO_MARGIN_QUAL(micro,umb)= -127 dB
HO_MARGIN_DIST(micro,umb)= -127 dB
OUTDOOR_UMB_LEV(micro,umb)=
-100 dBm
PRIORITY(umb,micro) = 0
HO_MARGIN_LEV(umb,micro)= 0 dB
HO_MARGIN_QUAL(umb,micro)= -1 dB
HO_MARGIN_DIST(umb,micro)= 0 dB
PRIORITY(micro,micro) = 1
HO_MARGIN_LEV(micro,micro)= 0 dB
HO_MARGIN_QUAL(micro,micro)= -1 dB
HO_MARGIN_DIST(micro,micro)= 0 dB
The upper layer is a rescue layer for microcells: thus, all HO_MARGIN_XX(micro,umb) are set to -127 dB.
OUTDOOR_UMB_LEV is set to -100 dBm: all umbrella cells with a received level lower than -100 dBm will be filtered
out at candidate cell evaluation.
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3.1 Adding a microcellular layer for traffic and coverage increase
Border microcell class
Definition
� A microcell bordering the microcell area
� Hybrid situation between the inner microcell and the hotspot microcell
Rules
� Prevent MSs having a tangential trajectory from being captured by the
microcell layer. Deal with microcell zone exit. A border microcell is a
“traffic-selector”.
• Selective capture HO (cause 14) from the umbrella to the micro cell
• Avoid keeping MSs exiting the
microcell area in the microlayer:
trigger a high threshold handover
(causes 17&18)
towards the upper layer
Border Microcell
The upper layer is a rescue layer for microcells: thus, all HO_MARGIN_XX(micro,umb) are set to -127 dB.
OUTDOOR_UMB_LEV is set to -100 dBm: all umbrella cells with a received level lower than -100 dBm will be filtered
out at candidate cell evaluation.
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Causes 12 and 14
3.1 Adding a microcellular layer for traffic and coverage increase
Border microcell: better condition handovers
Umbrella
EN_PBGT_HO = ENABLED
EN_MCHO_NCELL = ENABLED
EN_SPEED_DISC = ENABLED
L_MIN_DWELL_TIME = 8s
H_MIN_DWELL_TIME = 16s
Border Microcell
EN_PBGT_HO = ENABLED
EN_SPEED_DISC = ENABLED
A_PBGT_HO = 6
Cause 14
PRIORITY(umb, micro) = 0
L_RXLEV_CPT_HO(umb, micro)
= -83 dBm
Cause 12 / 23
PRIORITY(umb, umb) = 1
HO_MARGIN(umb, umb) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12
PRIORITY(micro, micro) = 1
HO_MARGIN(micro, micro) =?
No better condition HO from a micro
to an umbrella cell (different layers)
A capture towards a microcell is triggered after MIN_DWELL_TIME which will vary from H_MIN_DWELL_TIME down
to L_MIN_DWELL_TIME if the umbrella 900 cell is loaded. MIN_DWELL_TIME is increased to prevent tangential
MSs from being captured by the border microcell.
L_RXLEV_CPT_HO is increased.
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Use Level, Quality causes
3.1 Adding a microcellular layer for traffic and coverage increase
Border microcell: emergency handovers
Umbrella
Pref_layer = upper + single
Border Microcell
EN_RESCUE_UM = ENABLED
EN_MCHO_H_DL = ENABLED
Pref_layer = upper + single
A_QUAL_HO = 4
A_LEV_HO = 4
L_RXLEV_DL_H = -97 dBm
U_RXLEV_DL_MCHO = -92 dBm
A_LEV_MCHO = 10
PRIORITY(umb,micro) = 0
PRIORITY(umb,umb) = 1
PRIORITY(micro,micro) = 1
PRIORITY(micro,umb) = 1
A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.
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Definition
� An indoor area located within the micro cell area
� This indoor cell aims at absorbing traffic in a strategic building
Rules
� Absorb indoor traffic, and only indoor traffic
• An MS nearby the building door but still outside should camp on the outdoor
cell
• An indoor MS handled by the indoor
micro cell should be handed over to
the outdoor cell when exiting the building
• A special attention has to be paid to
high floor cases, where there might be
jamming from outdoor macro cells
3.1 Adding a microcellular layer for traffic and coverage increase
Indoor microcell class
Indoor Microcell
Another type of indoor microcell can be defined:
� Indoor microcell for coverage, when the indoor cell is a hotspot and the indoor coverage from the macro layer
is not good. This chapter does not deal with this case. See the next slides for detailed parameter settings of
indoor microcell for coverage.
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Causes 12 and 14
3.1 Adding a microcellular layer for traffic and coverage increase
Indoor microcell: better condition handovers
Umbrella
EN_PBGT_HO = ENABLED
EN_MCHO_NCELL = ENABLED
EN_SPEED_DISC = ENABLED
L_MIN_DWELL_TIME = 8s
H_MIN_DWELL_TIME = 16s
Indoor Microcell
EN_PBGT_HO = ENABLED
EN_SPEED_DISC = ENABLED
A_PBGT_HO = 6
Cause 14
PRIORITY(umb, micro) = 0
L_RXLEV_CPT_HO(umb, micro)
= -85 dBm
or -75 dBm if jamming
Cause 12 / 23
PRIORITY(umb, umb) = 1
HO_MARGIN(umb, umb) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12
PRIORITY(micro, micro) = 1
HO_MARGIN(micro, micro) =?
No better condition HO from a micro
to an umbrella cell (different layers)
L_RXLEV_CPT_HO tuning is closely linked to real radio propagation and cell coverage. Values given on this slide
are just examples.
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Use Level, Quality causes
3.1 Adding a microcellular layer for traffic and coverage increase
Indoor microcell: emergency handovers
Umbrella
Pref_layer = upper + single
Indoor Microcell
EN_RESCUE_UM = ENABLED
EN_MCHO_H_DL = ENABLED
Pref_layer = upper + single
A_QUAL_HO = 4
A_LEV_HO = 4
L_RXLEV_DL_H = -93 dBm
U_RXLEV_DL_MCHO = -91 dBm
A_LEV_MCHO = 10
PRIORITY(umb,micro) = 0
PRIORITY(umb,umb) = 1
PRIORITY(micro,micro) = 1
PRIORITY(micro,umb) = 1
A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.
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153
In high floors, the level from surrounding umbrella cells is very high
One solution
� Provide a very high level in the indoor area
� Increase L_RXLEV_CPT_HO from -85 to -75 dBm
� … but it will reduce the service area
3.1 Adding a microcellular layer for traffic and coverage increase
Indoor microcell: high floors case
Indoor Microcell
-110
-100
-90
-80
-70
-60
-50
-40
-30
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
03DIM2
03SPK1
03DIAO
03CEN2
03CAR3
03ATH
03DKR0->03DKM
FLOOR
LEVEL (dBm)
Indoor microcell
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3 CREATING A MULTI-LAYER NETWORK
3.2 Adding hot spot microcell for traffic
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Definition
� A microcell totally isolated from any other microcell
Rules
� Should act as a real “motionless traffic-catcher”
• capture HO (cause 14) only triggered if the MS is not moving
• No better cell handover is expected. An emergency HO has to be triggered
very quickly
3.2 Adding hotspot microcells for traffic
Hotspot microcell class
Hotspot Microcell
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156
Causes 12 and 14
3.2 Adding hotspot microcells for traffic
Hotspot microcell: better condition handovers
Umbrella
EN_PBGT_HO = ENABLED
EN_MCHO_NCELL = ENABLED
EN_SPEED_DISC = ENABLED
L_MIN_DWELL_TIME = 10s
H_MIN_DWELL_TIME = 16s
Hotspot Microcell
Cause 14
PRIORITY(umb, micro) = 0
L_RXLEV_CPT_HO(umb, micro)
= -85 dBm
Cause 12 / 23
PRIORITY(umb, umb) = 0
HO_MARGIN(umb, umb) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
No better condition HO from a micro
to an umbrella cell (different layers)
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Use Level, Quality causes
3.2 Adding hotspot microcells for traffic
Hotspot microcell: emergency handovers
Umbrella
Pref_layer = upper + single
Hotspot Microcell
EN_RESCUE_UM = ENABLED
EN_MCHO_H_DL = ENABLED
Pref_layer = upper + single
A_QUAL_HO = 4
A_LEV_HO = 4
L_RXLEV_DL_H = -93 dBm
U_RXLEV_DL_MCHO = -90 dBm
A_LEV_MCHO = 10
PRIORITY(umb,micro) = 0
PRIORITY(umb,umb) = 0
PRIORITY(micro,umb) = 0
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3 CREATING A MULTI-LAYER NETWORK
3.3 Adding indoor microcells for coverage
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159
Definition
� An indoor microcell introduced to provide a building with coverage
Rules
� As for indoor microcell, it should absorb indoor traffic, and only indoor
traffic
• An MS nearby the building door but still outside should camp on the outdoor
cell
• An indoor MS handled by the indoor microcell should be handed over to the
outdoor cell when exiting the building
� But also, a fast handover has to be made towards the indoor cell to avoid
call drop (no coverage is provided by the outdoor cell)
• This indoor microcell should behave like a “macrocell”
• Cause 14 has to be triggered very quickly
• Indoor layer is a good solution (capture of IND and SLOW MS)
3.3 Adding indoor microcells for coverage
Hotspot indoor microcell
See session 4 Case studies for more details.
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3 CREATING A MULTI-LAYER NETWORK
3.4 Monitoring QoS in a multi-layer network
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QoS indicators in each layer
� To identify specific problems (interference, coverage, etc.)
• CDR, CSSR, SDCCH congestion, etc.
• Split of HO causes
• HO incoming / outgoing efficiency
• Nb of HOs per call (for speech quality)
• FDR success rate
� Traffic in each layer
• Distribution micro / macro
• Average RTCH duration
• Congestion (and queueing efficiency)
• FDR usage (internal / external)
� Traffic flows
• HO per couple of cells (PMC type 180)
• In case of problem, use ODMC type 26 and 27 for detailed incoming and outgoing
behaviors
3.4 Monitoring QoS in a multi-layer network
Indicators monitoring
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4 CASE STUDIES
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4 CASE STUDIES
Session presentation
Objective: to be able to define relevant parameter settings for the
following field cases
Program:
4.1 Radar cell
4.2 Symmetric microcells at a street corner
4.3 Asymmetric microcells at a street corner
4.4 Indoor microcell within a monolayer network
4.5 Trilayer network: indoor cell within a multi-layer network
4.6 Indoor cell congestion
4.7 Transforming a microcell into an indoor cell
4.8 Picocells in skyscrapers
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4 CASE STUDIES
4.1 Radar Cell
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165
A radar cell is covering an industrial zone
� Find relevant parameter settings to favor IZ cells in idle and connected mode
• Propose 2 architectures
4.1 Radar Cell
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4 CASE STUDIES
4.2 Symmetric microcells at a street corner
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167
Define relevant parameter settings to obtain good QoS in the microcell
layer for
� symmetric microcells at a street corner
4.2 Symmetric microcells at a street corner
Cell B
Cell Ad
d
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4 CASE STUDIES
4.3 Asymmetric microcells at a street corner
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169
Define relevant parameter settings to obtain good QoS in the microcell
layer for
� Asymmetric microcells at a street corner
• 1 < x < 2.5
4.3 Asymmetric microcells at a street corner
Cell B
Cell Ax.d
d
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4 CASE STUDIES
4.4 Indoor microcell within a monolayer network
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171
An indoor microcell is introduced within a monolayer network, for a new
coverage
� Define parameter settings for both idle and connected mode
4.4 Indoor microcell within a monolayer network
Indoor Microcell
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4 CASE STUDIES
4.5 Trilayer network: indoor cell within a multi-layer network
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An indoor microcell is introduced within a multi-layer network (macro +
micro cells), for capacity & coverage increase
� So called « trilayer » network
� Define parameter settings for both idle and connected mode
4.5 Trilayer network: indoor cell within a multi-layer network
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4 CASE STUDIES
4.6 Indoor cell congestion
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175
An indoor microcell has been introduced within a multi-layer network
(macro + micro), based on the previous exercise recommendations
When an indoor microcell is congested, the FDR may not be working as
some MSs can be covered only by this cell
� Define parameter settings to find a good solution in case of indoor cell
congestion
4.6 Indoor cell congestion
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4 CASE STUDIES
4.7 Transforming a microcell into an indoor cell
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Within a multi-layer network, a microcell has been designed in the
micro-layer, with parameters of the microcell class
One may want to configure this cell in the « indoor » layer
� Propose parameter settings
4.7 Transforming a microcell into an indoor cell
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4 CASE STUDIES
4.8 Picocells in skyscrapers
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179
Skyscrapers may need several picocells to achieve a sufficient
coverage while avoiding interference (sufficient received level from the
serving cell)
� Define parameters settings to deal with this configuration
4.8 Picocells in skyscrapers
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END SESSION
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5 APPENDIX
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Appendix
Content:
5.1 Load & Traffic evaluation
5.2 Extended cell overview
5.3 Exercises & Case Studies Solutions
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5 APPENDIX
5.1 Load & Traffic evaluation
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5.1 Load & Traffic evaluation
Cell TCH radio resource evaluation usage
Power budget Handover
Traffic Handover
Multiband capture Handover
General capture Handover
N_TRAFFIC_LOAD x A_TRAFFIC_LOAD x
TCH_INFO_PERIODlong term
Speed discrimination for hierarchical network
Full Rate / Half Rate channel allocationLOAD_EV_PERIOD x TCH_INFO_PERIOD
medium
term
FREEfactors
LOADfactorsTCH_INFO_PERIODshort term
UsagePeriodLoad
evaluation
Back
Cause 12
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5.1 Load & Traffic evaluation
Short term evaluation (1/4)
LOADfactors and FREEfactors are determined from Nb free TCH samples every TCH_INFO_PERIOD seconds (short term evaluation)
LOADlevels are boundaries of load intervals associating a LOADfactor(db) to a Nb free TCH sample
FREElevels are boundaries of Nb free TCH intervals associating a FREEfactor (db) to a Nb free TCH sample
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5.1 Load & Traffic evaluation
Short term evaluation (2/4)
FREEfactor determination:
� FREElevel in absolute number of TCHs
� FREEfactor in dB
FREEfactor_5FREELevel_4< t
FREEfactor_4FREELevel_3< t <= FREElevel_4
FREEfactor_3FREELevel_2< t <= FREElevel_3
FREEfactor_2FREELevel_1< t <= FREElevel_2
FREEfactor_1t <= FREElevel_1
Nb free TCHNb free TCH
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5.1 Load & Traffic evaluation
Short term evaluation (3/4)
LOADfactor determination:
� LOADlevel in %
� LOADfactor in dB
LOADfactor_5LOADLevel_4< t
LOADfactor_4LOADLevel_3< t <= LOADlevel_4
LOADfactor_3LOADLevel_2< t <= LOADlevel_3
LOADfactor_2LOADLevel_1< t <= LOADlevel_2
LOADfactor_1t <= LOADlevel_1
LOADfactort = (1 - Nb free TCH/Total Nb TCH) x 100
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example: cells with 4 TRXs (28 TCHs)
5.1 Load & Traffic evaluation
Short term evaluation (4/4)
Nb free TCH = 4
Load = 85,7%
Cell 0�
FREEfactor(0) = -8 dBm
LOADfactor(0) = -15 dBm
Nb free TCH = 20
Load = 28,6%
Cell n
FREEfactor(n) = +7 dBm
LOADfactor(n) = 0 dBm
�
• in ORDER(n): + FREEfactor(n) - FREEfactor(0) = +7 - (-8) = +15 dB
• in GRADE(n): + LOADfactor(n) = +0 = 0 dB
in evaluation of cell n for outgoing HO from cell 0 :
HO?
-15 dB80% < t
-10 dB50% < t <= 80%
0 dB25% < t <= 50%
+5 dB10% < t <= 25%
+10 dBt <= 10%
LOADfactorLoad = (1-Nb free TCH/Total TCH)x 100
+10 dB21 < t
+7 dB15 < t <= 21
0 dB8 < t <= 15
- 8 dB3 < t <= 8
- 16 dBt <= 3
FREEfactorNb free TCH
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5.1 Load & Traffic evaluation
Medium term evaluation (1/2)
Medium term measurement of the load of a cell
� corresponds to function AV_LOAD(cell)
� a new sample of the “Nb free TCHs” in the cell is available every
TCH_INFO_PERIOD seconds
� AV_LOAD() is a non-sliding window load average from Nb free TCH samples
updated every LOAD_EV_PERIOD x TCH_INFO_PERIOD s
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5.1 Load & Traffic evaluation
Medium term evaluation (2/2)
AV_LOAD(cell n) calculated from N Nb free TCH samples available during LOAD_EV_PERIOD x TCH_INFO_PERIOD s
100*)(n) TCHTot Nb
(n) TCH free Nb1(
Nsamples
1 = AV_LOAD(n)
Nsamples
1 = i
∑ −
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5.1 Load & Traffic evaluation
Long term evaluation (1/4)
Long term measurement of the load of a cell
� corresponds to function Traffic_load(cell)
� Traffic_load() value is determined from a number N_TRAFFIC_LOAD of
consecutive non-sliding window load averages AV_TRAFFIC_LOAD
calculated from Nb free TCH samples updated every A_TRAFFIC_LOAD x
TCH_INFO_PERIOD s
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5.1 Load & Traffic evaluation
Long term evaluation (2/4)
3 possible values for Traffic_load(): high, low, indefinite
initialization: Traffic_load() = indefinite
Traffic_load() becomes :
� high if the last N_TRAFFIC_LOAD consecutive AV_TRAFFIC_LOAD load averages are all greater than the HIGH_TRAFFIC_LOAD threshold
� low if the last N_TRAFFIC_LOAD consecutive AV_TRAFFIC_LOAD load averages are all lower than the LOW_TRAFFIC_LOAD threshold
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5.1 Load & Traffic evaluation
Long term evaluation (3/4)
Traffic_load() becomes indefinite if:
� Traffic_load() was high and the last AV_TRAFFIC_LOAD load average is
lower than LOW_TRAFFIC_LOAD (or IND_TRAFFIC_LOAD if not 0%)
� Traffic_load() was low and the last AV_TRAFFIC_LOAD load average is
greater than HIGH_TRAFFIC_LOAD (or IND_TRAFFIC_LOAD if not 0%)
Traffic_load(n) is always equal to indefinite if cell n is external to the
BSC
HIGH_TRAFFIC_LOAD ≥ IND_TRAFFIC_LOAD ≥ LOW_TRAFFIC_LOAD
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Example with N_TRAFFIC_LOAD = 3
5.1 Load & Traffic evaluation
Long term evaluation (4/4)
Back
Cause 12
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5 APPENDIX
5.2 Extended cell overview
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5.2 Extended cell overview
Session presentation
Program:
5.2.1 Presentation
5.2.2 Radio Link Establishment
5.2.3 Handover
5.2.4 Parameters setting
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One BTS (G3 or G4): 2 cells
� INNER cell: range from 0 to 35 km
� OUTER cell: range from 33 to 70 km
5.2 Extended cell overview
5.2.1 Presentation - General
The extended cell has up to 4 TRX in the inner cell and up to 4 TRX in the outer cell.
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5.2 Extended cell overview
5.2.1 Presentation - Synchronisation
OUTER cellINNER cell
Freq BCCH OUTER <> Freq BCCH INNER
� MS reports measurements on both cells
for the handover algorithms
BSICINNER = BSICOUTER
� INNER cell can decode the RACH
received on OUTER BCCH frequency
INNER cell always BARRED
� MS always camps on OUTER cell
At the border of the two cells, an overlapping area allows to provide a continuous coverage. When the MS moves
from one cell to the other, a handover is triggered in the overlap zone. Two BCCH channels are needed (one for the
inner cell, one for the outer cell), so that the MS reports measurements on both cells for the handover algorithms.
The TRXs of the inner cell and of the outer cell are synchronised, but the reception of the outer cell is delayed by
60bits period to account for the propagation delay.
In the inner cell, the MS can receive the BCCH inner frequency as wells as the outer BCCH frequency. To avoid to
manage RACH reception on two different frequencies in the inner cell, the MS is forced to access the inner cell on the
outer BCCH frequency. For this purpose, the RACH reception (BCCH TRX) of the inner cell is tuned to the outer
BCCH frequency, and the inner cell is barred1. So on time slot 0 of the inner cell, transmission is done on the inner
cell BCCH frequency, and reception is done on outer BCCH frequency.
The chosen implementation allows to make use of all timeslots2 of the TDMA frame and to use the combined
configuration for the CCCH channel.
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UL interference on TS0 of the INNER cell if
� Access burst received in the INNER cell (on frequency BCCH OUTER)
AND
� Call on TS7 of the OUTER cell
Then, TS7 of the OUTER cell is always set to IDLE (never used)
5.2 Extended cell overview
5.2.1 Presentation - RF Interference
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5.2 Extended cell overview
5.2.2 Radio Link Establishment - MS located in the outer cell area
The inner cell is always barred, so the MS cannot camp on the inner cell, even if located in the inner cell range. In the whole
extended cell coverage, the MS has a good reception of the outer cell BCCH, so the MS will always be camping in the outer cell,
whether in the inner cell or outer cell range.
For this reason, a special radio and link establishment procedure is used to cope with this behaviour .
It consists of receiving the CHANNEL REQUEST messages on outer BCCH frequency, and allocating the SDCCH channel
according to the MS estimated position. The IMMEDIATE ASSIGNMENT COMMAND for an SDCCH is sent on the outer cell
BCCH frequencies, but the SDCCH may be allocated in either inner or outer cell, depending on the MS position.
(1) The MS camping on the outer cell sends an access burst on the RACH on outer cell BCCH frequency. These bursts will be
received successfully in the inner cell by the BCCH TRE. In the outer cell, the access burst arrives too early and cannot be
decoded.
(2) The inner cell BCCH TRE sends a CHANNEL REQUIRED message to the BSC containing the random reference sent by the
mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3) The TCU controlling this TRE allocates an SDCCH subchannel to the transaction in the inner cell and asks the BTS to activate
this subchannel.
(4) The BTS activates the requested channel and sends back and acknowledgement, once this is done.
(5) The TCU sends the IMMEDIATE ASSIGNMENT COMMAND (which provides the description of the allocated SDCCH) to the
BCCH TRE of the inner cell.
The TCU controlling the inner cell BCCH sends a copy of the message to the TCU handling the BCCH of the
outer cell. This is done if and only if the timing advance IE included in the CHANNEL REQUIRED is smaller than 60, thus
indicating that the MS is strictly in the inner cell (in order to avoid that the MS receives two Immediate Assignment messages
when located in the overlap zone).
The TCU controlling the outer cell BCCH forwards the IMMEDIATE ASSIGNMENT COMMAND to the outer cell
BCCH TRE.
(6) The IMMEDIATE ASSIGNMENT message is sent over the air to the MS on the AGCH of the outer cell.
(6') The IMMEDIATE ASSIGNMENT message sent by the inner cell is lost, because the MS listens to the outer cell frequency.
(7) The mobile switches its transceiver to the SDCCH allocated in the inner cell and sends repeatedly an SABM frame to establish
the layer 2 connection with the BTS.
(8) The BTS acknowledges the establishment of the LapDm link to the MS with a UA frame sent on the SDCCH allocated to the
MS.
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If TA < 60
5.2 Extended cell overview
5.2.2 Radio Link Establishment - MS located in the inner cell area
The TCU sends the IMMEDIATE ASSIGNMENT COMMAND (which provides the description of the allocated
SDCCH ) to the BCCH TRE of the inner cell.
The TCU controlling the inner cell BCCH sends a copy of the message to the TCU handling the BCCH of the outer
cell. This is done if and only if the timing advance IE included in the CHANNEL REQUIRED is smaller than 60, thus
indicating that the MS is strictly in the inner cell (in order to avoid that the MS receives two Immediate Assignment
messages when located in the overlap zone).
The TCU controlling the outer cell BCCH forwards the IMMEDIATE ASSIGNMENT COMMAND to the outer cell
BCCH TRE.
(1) The MS in the outer cell sends an access burst on the RACH of the outer cell. This burst is successfully received
by the outer cell BCCH TRE. In the inner cell, the access burst arrives too late to be successfully decoded.
(2) The outer cell BCCH TRE sends a CHANNEL REQUIRED message to the BSC containing the random reference
sent by the mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3) The TCU controlling this TRE allocates an SDCCH subchannel in the outer cell to the transaction and asks the
BTS to activate this subchannel.
(4) The BTS activates the requested channel and sends back an acknowledgement, once this is done.
(5) The TCU then sends the description of the channel in the IMMEDIATE ASSIGNMENT COMMAND to the outer
cell BCCH TRE.
(6) The IMMEDIATE ASSIGNMENT message is sent over the air to the MS on the AGCH of the outer cell.
(7) The mobile switches its transceiver to the required channel and sends repeatedly an SABM frame to establish the
layer 2 connection with the BTS.
(8) The BTS acknowledges the establishment of the LAPDm link to the MS with a UA frame sent on the SDCCH
allocated to the MS.
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5.2 Extended cell overview
5.2.2 Radio Link Establishment - MS located in the overlap zone (1/2)
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5.2 Extended cell overview
5.2.2 Radio Link Establishment - MS located in the overlap zone (2/2)
(1a&b) The MS camping on the outer cell sends an access burst on the RACH. This burst is correctly received by the inner cell BCCH TRE and
outer cell BCCH TRE.
(2a&b) The inner cell and outer cell BCCH TRE send a CHANNEL REQUIRED message to the BSC containing the random reference sent by the
mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3a&b) Both TCUs controlling the TREs having BCCH allocate an SDCCH subchannel to the transaction and ask the BTS to activate this
subchannel.
(4a&b) The BTS activates the requested channels and sends back an acknowledgement for each, once this is done.
(5b) The TCU controlling the outer cell, sends the IMMEDIATE ASSIGNMENT COMMAND with SDCCH description in the outer cell to the outer
cell BCCH TRE.
(5a&c)The TCU controlling the inner cell sends in the IMMEDIATE ASSIGNMENT COMMAND with SDCCH description in the inner cell. Two
cases are possible:
� Access Delay IE > 59 the inner cell TCU will not send a copy of the IMMEDIATE ASSIGNMENT command to the outer cell TCU. This is
the desired behaviour.
� Access Delay in [58,59] range, the inner cell TCU sends a copy of the IMMEDIATE ASSIGNMENT command to the outer cell TCU. This
is not the desired behaviour (corresponds to inner cell scenario). This is due to the fact that the BSC definition of the overlap zone does
not match the exact BTS overlap area (negative values of TOA in the outer cell up to –2, are clipped to 0).
(6b) The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in outer cell, is sent to the MS on the outer cell BCCH
frequency. In most cases this message should be received by the MS (except if 6c is received first)
(6a) The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in inner cell is lost on the inner cell air interface, because the
MS does not listen to that frequency. The unused SDCCH will be released by the BSC when the supervising timer expires6.
(6c) Access Delay in [58,59] range: The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in inner cell is sent on the BCCH
frequency of the outer cell. In most cases, the MS should have received message (6b) before and has already switched to the SDCCH in the
outer cell, and so this message is lost. It is however possible, in case the message (6b) is delayed in the inner cell, that the message (6c) is
received earlier by the MS. In this case establishment will occur on the SDCCH allocated in the inner cell (not drawn).
(7b) The mobile receives the IMMEDIATE ASSIGNEMENT describing the SDCCH allocation in outer cell on the BCCH outer cell frequency. It
then switches to the designated channel and sends repeatedly an SABM frame to establish the layer 2 connection with the BTS in the outer cell.
If the message (6c) is received before (6b), then the establishment will occur in the inner cell.
(8b) The BTS acknowledges the establishment of the LapDm link to the MS with a UA frame sent on the SDCCH allocated to the MS.
(9) The unused SDCCH is released in the inner cell (double SDCCH allocation). If message 6c arrives first, then the unused SDCCH release will
occur in the outer cell.
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CAUSE 6 : Too long distance
AV_RANGE_HO > U_TIME_ADVANCE
and EN_DIST_HO = ENABLE
U_TIME_ADVANCE = 62
EN_PBGT_FILTERING = Disable
5.2 Extended cell overview
5.2.3 Handover - from the INNER cell to the OUTER cell
In the extended cell , the handover procedure is purely controlled by settings of the handover detection parameters.
Two special causes allow handover from the inner cell to the outer cell and handover from the outer cell to the inner
cell. There is no change in the BSC handover algorithm either for handover preparation or execution.
From the inner cell to the outer cell , the handover alarm is only triggered by the handover cause “too long MS-BS
distance”. When this cause is triggered the extended outer cell is always a candidate cell.
However the operator setting of the handover parameters must insure that this cause is only triggered when the
distance from the serving inner cell BTS is greater than the limit of the overlap zone (TA > 62) by setting
U_TIME_ADVANCE to 62.
In order to avoid the extended outer cell to be filtered by the filtering process the flag EN_PBGT_FILTERING must be
set to DISABLE.
The candidate cell evaluation process is recommended to be the GRADE mode.
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CAUSE 22 : Too short distance
AV_RANGE_HO < L_TIME_ADVANCE
L_TIME_ADVANCE = 0
EN_PBGT_FILTERING = Disable
Cause 22 is only checked if
� Cell_range(serving) = extended_outer
5.2 Extended cell overview
5.2.3 Handover - from the OUTER cell to the INNER cell
In the same way, from the outer cell to the inner cell , the handover alarm is only triggered by the handover cause
“too short MS-BS distance”. When this cause is triggered the extended inner cell is always a candidate cell.
However the operator setting of the handover parameters must insure that this cause is only triggered when the
timing advance applied by the mobile reaches 0, this is achieved by setting L_TIME_ADVANCE to 0.
In order to avoid the extended inner cell to be filtered by the filtering process the flag EN_PBGT_FILTERING must be
set to DISABLE.
The candidate cell evaluation process is recommended to be the GRADE mode.
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All the standard HO causes can be used
� Emergency HO causes 2, 3, 4, 5
� Better condition HO causes 12, 23, 24
The OUTER or INNER cell is always present in the Candidate CellEvaluation
5.2 Extended cell overview
5.2.3 Handover - from the OUTER or INNER cell towards an other cell
The setting of the handover parameter does not prevent any handover cause to trigger an alarm for a handover
towards a third cell.
It is possible to use exactly the same rules and parameters for handover towards a third cell as in the macro cellular
normal cases.
The synchronous handover does not work between the inner and the outer cell.
In order to avoid call terminations due to directed retry into the inner or outer cell with an incorrect distance range it is
recommended to disable the forced directed retry towards the inner and the outer cell. For this purpose, the
parameter FREELEVEL_DR(n) is set to the maximum value (255) for the inner and the outer cell.
� But the Normal DR can be activated.
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The Inner Cell shall always be BARRED
If combined CCCH/SDCCH is used in the inner extended cell, then the same
configuration is required in outer extended cell, and vice-versa (ie same in both
cells)
BSICINNER = BSICOUTER
The TS 7 of BCCH TRX of outer cell must be set to IDLE
The INNER cell and OUTER cell must belong to the same location area
Synchronous handover must be disabled.
U_TIME_ADVANCE = 62
L_TIME_ADVANCE = 0
EN_PBGT_FILTERING = DISABLE.
CELL_EV = “Grade”
FREELEVEL_DR(n) = 255 (this is done automatically, at configuration time)
INNER cell and OUTER cell must be neighbour, handover relationship must exist
in both directions
5.2 Extended cell overview
5.2.4 Parameters Setting
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End of Module