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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.
Trade Marks
Alcatel and MainStreet are trademarks of Alcatel.
All other trademarks, service marks and logos (Marks) are the property of their respective holders including Alcatel.
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
This document contains information that is proprietary to Alcatel and may be used for training purposes only. No
other use or transmission of all or any part of this document is permitted without Alcatels written permission, and
must include all copyright and other proprietary notices. No other use or transmission of all or any part of its contents
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Alcatel, The Alcatel logo, MainStreet and Newbridge are registered trademarks of Alcatel.
All other trademarks are the property of their respective owners. Alcatel assumes no responsibility for the accuracy of
the information presented, which is subject to change without notice.
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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Please refer to technical practices supplied by Alcatel for current information concerning Alcatel equipment and its
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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 ABAAAUE) and Introduction to Radio Fine Tuning (3FL 10493 ABAAAUE) 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 cell compared to a high threshold cause 18 : too low level on the downlink in a cell 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
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CAUSE 3: too low level on the uplink
AV_RXQUAL_UL_HO
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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
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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
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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
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 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 cell 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 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 cell 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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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 shouldnt 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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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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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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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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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 pe