evolium base station subsystem multilayer gsm network

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

All rights reserved © 2005, AlcatelMultilayer GSM Network Radio Optimization / B9

2

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operation.

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


4

Table of Contents [cont.]

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5

1 MULTI-LAYER NETWORK ARCHITECTURE


6


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


7




8

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


Introduction to multi-layer networks

Since B7:

� new HW capabilities with “Cell split” support

� enhancement of QoS monitoring capabilities with counters split per TRX


9

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)


Support of multi-layer features


10

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


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.


11




12

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


Cell environment


13

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


Cell profile


14


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


15


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


16


Cell profiles: example


17




18

Multi-layer concept: 3 available layer types

� All these cells can be or not operating in the same band and defined as

concentric cells


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.


19

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


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.


20


1.4 Requirements


21

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


22

2 ALGORITHMS AND ASSOCIATED PARAMETERS


23



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


24


2.1 Introduction


25

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


26

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


27




28

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


Strategy


29

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


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.)).


30

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


Cell Selection with CBQ (1/3)


31

Example: highest priority set on microcell

� The MS will select the microcell (if available, C1>0), whatever the level of the

macrocell



2525microcell

CELL_BAR_QUALIFY = 0

2020

macrocell

CELL_BAR_QUALIFY = 1


32

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




33

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


C1 criterion (1/2)


34

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


C1 criteria (2/2)


35

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


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.


36

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


C2 parameters


37


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


38


2.3 Call setup


39

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


40

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


41

2.3 Call setup

Algorithms principles (1/3)

new

capacity

Traffic

increase

old

capacity


42

2.3 Call setup


new

capacity

Water Valve with filter:

Dual layer algorithms

Traffic

increase

old

capacity


43

2.3 Call setup


new

capacity

Water Pump:

Forced

Directed Retry

Traffic

increase

old

capacity


44

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


45

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


46

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


47

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


48

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


49

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


50

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


51

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


52




53

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


Objectives (1/2)


54

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


Objectives (2/2)


55

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


Handover algorithms


56


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


57

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


Handover causes (1/2)


58

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


Handover causes (2/2)


59

� 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


Handover causes priority


60




61

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


Emergency Intercell Handovers


62

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


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)


63

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




Handover Cause 3: UL Level

QUAL

LEV


64


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


65


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




66


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.


67

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


Emergency Intracell Handovers


68

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 ]




Handover Cause 15: UL Interference

THR_RXQUAL_CAUSE_15 and EN_CAUSE_15 are not parameters but variables defined just after.


69

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 [ no previous intracell handover for this connection

failed

or EN_INTRACELL_REPEATED = ENABLED ]




Handover Cause 16: DL Interference

THR_RXQUAL_CAUSE_16 and EN_CAUSE_16 are not parameters but variables defined after.


70


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).


71

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


Handover Cause 12: Power Budget (1/5)


72

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



The value of PBGT(n) is calculated every SACCH period for each neighboring cell n whose measures are kept in the

book-keeping list


73


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



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).


74


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.



HIGH LOW


75


� 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)



Annex 1

TCH_INFO_PERIOD = 5 s period used by the BSC to count the number of free TCH.


76

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


Cause 12: tuning of microcells parameters


77

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)



Micro 1Micro 2

Micro 3

PBGT HO between micro cells 1, 2


78

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.



BTS1

BTS2

Building

Interferer

fn

fn+1

Area of potential interferences: (C/I)adj < -

9dB


79

Transfer of fast MSs from lower or indoor layers to upper layer

� If EN_SPEED_DISC = ENABLED


Cause 12: speed discrimination in microcells (1/2)

Traffic Load = low Traffic Load ≠≠≠≠ low

HOHO HO HO

HO

MIN_CONNECT_TIME


80

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


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


81


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.


82


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.


83


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


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


84



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


85



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_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.


86


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


87

Is cause 12 triggered?


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


88




89

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)


Emergency handovers: introduction (1/2)


90

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


Emergency handovers: introduction (2/2)

in µ

umbrella

mini

umbrella

mini

single


91

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)


� If the MS is connected to the inner zone of a multi-band cell, the serving cell

is a candidate


Emergency Handovers specific to microcells


92

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


Cause 7: consecutive bad SACCH frames received in a microcell


93

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


Cause 17: too low level on the UL in a µcell compared to high thr.


94

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


Cause 18: too low level on the DL in a µcell compared to high thr.


95

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


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


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




97

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




98

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




99

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


Cause 14: high level in a lower or an indoor layer for slow MSs (1/4)

mini

umbrella

micro

indoor


100

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



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)


CELL_BAND_TYPE ≠ Preferred_band

CELL_BAND_TYPE = Preferred_bandCELL_BAND_TYPE <> Preferred_band


101

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



mini

umbrella

micro indoor


102

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




mini micro

indoor


103

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)


Cause 14: speed discrimination (1/6)


104

Interlayer HO based on speed discrimination



Lower layer

Upper layer

Indoor layer

Cause12MS_speed = FAST

Cause12MS_speed = FAST

Cause14MS_speed = SLOW

Or INDEFINITE

Cause14MS_speed = SLOW


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




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




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



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


108

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



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.


109

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.


Cause 24: general capture (1/3)


110


� 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



CELL_BAND_TYPE = Preferred_band


CELL_BAND_TYPE = CELL_BAND_TYPE(0)


CELL_BAND_TYPE ≠ Preferred_band


111


AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) +


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





112

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


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) +


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


113


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


114


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%?


115




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)


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


117

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


Raw Cell List and PREF_LAYER (2/4)

upper + singlePREF_LAYE

R

subset of cells verifying the HO

causesRaw cell list


R

all neighboring cells*Raw cell list


118

Hierarchical cell environment

� CELL_LAYER_TYPE = UPPER



* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the

serving cell



nonePREF_LAYE

R

subset of cells verifying the HO

causesRaw cell list


R

all neighboring cells*Raw cell list


119

� CELL_LAYER_TYPE = LOWER or INDOOR



* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the serving cell



noneLower + indoorUpper + SinglePREF_LAYER

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


120

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




121

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


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).


122


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.


123

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


Pre-ranking in complex networks (1/3)


124

Pre-ranking in case of emergency HO, plus cause 20 and 28 :



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


125

Pre-ranking in case of better condition HO:



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


126


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.


127

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)]


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.


128


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.


129


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


130


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.


131


Exercise (3/4)

-82 dBm

Disabled

1800

Single

-75 dBm

Disabled

900

micro

-85 dBm

Disabled

1800

micro

900900900Band

SlowMS speed

Best Target ?


EnabledEnabledDisabledEN_BI-BAND_MS

IndoorUmbrellaSingleType

Possible

Target

-76 dBmRx_Lev(0)

YesEN_SPEED_DISC

900Band

UmbrellaType

Source

Time allowed:

5 minutes




� PRORITY(0,n) = 1

� LINK_FACTOR(0,n) = 0 dB



RXLEVmin= -100 dBm.


132


Exercise (4/4)

-82 dBm

Disabled

1800

Single

-75 dBm

Disabled

900

micro

-85 dBm

Disabled

1800

micro

900900900Band

SlowMS speed

Best Target ?


EnabledEnabledDisabledEN_BI-BAND_MS

IndoorUmbrellaSingleType

Possible

Target

-68 dBmRx_Lev(0)

NoEN_SPEED_DISC

900Band

microType

Source

Time allowed:

5 minutes




� PRORITY(0,n) = 1, LINK_FACTOR(0,n) = 0 dB

� EN_RESCUE_UM = Enabled



RXLEVmin= -100 dBm.


133

3 CREATING A MULTI-LAYER NETWORK


134



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


135




136

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.


Introduction (1/3)


137


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.


138

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


Introduction (3/3)


139

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):


Architecture

umbrella

micro micro micro

umbrella

micro

singleUPPER

SINGLE

LOWER


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)


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).


141

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


Microcell classes

Indoor Microcell

Border Microcell

Inner Microcell


142

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


Inner microcell class

Inner Microcell


143

Causes 12 and 14


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_SPEED_DISC = ENABLED

A_PBGT_HO = 6

Cause 14


L_RXLEV_CPT_HO(umb, micro)

= -85 dBm

Cause 12 / 23


HO_MARGIN(umb, umb) = 5 dB

DELTA_INC_HO_MARGIN = 2 dB

DELTA_DEC_HO_MARGIN = 2 dB

Cause 12


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).


144

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


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.


145

Use Level, Quality causes


Inner microcell: emergency handovers

Umbrella

Pref_layer = upper + single

Inner Microcell



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).


146


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



HO_MARGIN_LEV(umb,umb)= 0 dB

HO_MARGIN_QUAL(umb,umb)= -1 dB

HO_MARGIN_DIST(umb,umb)= 0 dB


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


HO_MARGIN_LEV(umb,micro)= 0 dB

HO_MARGIN_QUAL(umb,micro)= -1 dB

HO_MARGIN_DIST(umb,micro)= 0 dB


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.


147


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.


148

Causes 12 and 14


Border microcell: better condition handovers

Umbrella





H_MIN_DWELL_TIME = 16s

Border Microcell



A_PBGT_HO = 6

Cause 14



= -83 dBm

Cause 12 / 23





Cause 12





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.


149



Border microcell: emergency handovers

Umbrella


Border Microcell


EN_MCHO_H_DL = ENABLED


A_QUAL_HO = 4

A_LEV_HO = 4


U_RXLEV_DL_MCHO = -92 dBm

A_LEV_MCHO = 10





A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.


150

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


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.


151

Causes 12 and 14


Indoor microcell: better condition handovers

Umbrella






Indoor Microcell



A_PBGT_HO = 6

Cause 14



= -85 dBm

or -75 dBm if jamming

Cause 12 / 23





Cause 12





L_RXLEV_CPT_HO tuning is closely linked to real radio propagation and cell coverage. Values given on this slide

are just examples.


152



Indoor microcell: emergency handovers

Umbrella


Indoor Microcell




A_QUAL_HO = 4

A_LEV_HO = 4



A_LEV_MCHO = 10





A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.


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


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


154


3.2 Adding hot spot microcell for traffic


155

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


156

Causes 12 and 14


Hotspot microcell: better condition handovers

Umbrella






Hotspot Microcell

Cause 14



= -85 dBm

Cause 12 / 23








157



Hotspot microcell: emergency handovers

Umbrella


Hotspot Microcell




A_QUAL_HO = 4

A_LEV_HO = 4



A_LEV_MCHO = 10





158




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)


Hotspot indoor microcell

See session 4 Case studies for more details.


160




161

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


Indicators monitoring


162

4 CASE STUDIES


163

4 CASE STUDIES


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


164

4 CASE STUDIES

4.1 Radar Cell


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


166

4 CASE STUDIES



167

Define relevant parameter settings to obtain good QoS in the microcell

layer for

� symmetric microcells at a street corner


Cell B

Cell Ad

d


168

4 CASE STUDIES



169

Define relevant parameter settings to obtain good QoS in the microcell

layer for

� Asymmetric microcells at a street corner

• 1 < x < 2.5


Cell B

Cell Ax.d

d


170

4 CASE STUDIES



171

An indoor microcell is introduced within a monolayer network, for a new

coverage

� Define parameter settings for both idle and connected mode


Indoor Microcell


172

4 CASE STUDIES



173

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



174

4 CASE STUDIES



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



176

4 CASE STUDIES



177

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



178

4 CASE STUDIES



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



180

END SESSION


181

5 APPENDIX


182

Appendix

Content:

5.1 Load & Traffic evaluation

5.2 Extended cell overview

5.3 Exercises & Case Studies Solutions


183

5 APPENDIX



184


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


185


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


186



FREEfactor determination:

� FREElevel in absolute number of TCHs

� FREEfactor in dB

FREEfactor_5FREELevel_4< t

FREEfactor_4FREELevel_3< t <= FREElevel_4



FREEfactor_1t <= FREElevel_1

Nb free TCHNb free TCH


187



LOADfactor determination:

� LOADlevel in %

� LOADfactor in dB

LOADfactor_5LOADLevel_4< t

LOADfactor_4LOADLevel_3< t <= LOADlevel_4



LOADfactor_1t <= LOADlevel_1

LOADfactort = (1 - Nb free TCH/Total Nb TCH) x 100


188

example: cells with 4 TRXs (28 TCHs)



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


189


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


190


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

∑ −


191


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


192



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


193



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


194

Example with N_TRAFFIC_LOAD = 3



Back

Cause 12


195

5 APPENDIX



196



Program:

5.2.1 Presentation

5.2.2 Radio Link Establishment

5.2.3 Handover

5.2.4 Parameters setting


197

One BTS (G3 or G4): 2 cells

� INNER cell: range from 0 to 35 km

� OUTER cell: range from 33 to 70 km


5.2.1 Presentation - General

The extended cell has up to 4 TRX in the inner cell and up to 4 TRX in the outer cell.


198


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.


199

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)


5.2.1 Presentation - RF Interference


200


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.


201

If TA < 60


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.


202


5.2.2 Radio Link Establishment - MS located in the overlap zone (1/2)


203


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.


204

CAUSE 6 : Too long distance

AV_RANGE_HO > U_TIME_ADVANCE

and EN_DIST_HO = ENABLE

U_TIME_ADVANCE = 62

EN_PBGT_FILTERING = Disable


5.2.3 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.


205

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


5.2.3 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.


206

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


5.2.3 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.


207

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


5.2.4 Parameters Setting


208

End of Module

evolium base station subsystem multilayer gsm network

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