alu loadbalancingsolution emcta v5.1

Alcatel-Lucent

End-To-End

Alcatel-Lucent solution for load balancing

between 2G, 3G, LTE and Wifi

JULY 2011

V5.1

E N D - T O - E N D L T E S O L U T I O N S � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

Load balancing solution between LTE, 2G, 3G.

Alcatel-Lucent Proprietary and Confidential © 2011 All Rights Reserved 2

CONTENTS

1 INTRODUCTION ................................................................................................ 5

2 STANDARDS PERSPECTIVE ................................................................................... 6

2.1 RADIO LOAD BALANCING ........................................................................................ 6

2.2 RADIO LOAD BALANCING IN 3GPP RELEASE 9 .................................................................... 8

3 ALCATEL-LUCENT SOLUTION FOR LOAD BALANCING ................................................... 9

3.1 THE EMCTA FUNCTION .......................................................................................10

3.1.1 Criteria used by eMCTA for the definition of the operator strategy for service allocation on

available carriers .............................................................................................11

3.1.2 Criteria used by eMCTA related to the UE context ..........................................13

3.2 LOAD BALANCING BY ADAPTING MOBILITY PARAMETERS ...........................................................14

3.3 TRAFFIC LOAD BALANCING BETWEEN RATS .....................................................................16

3.4 LOAD BALANCING ON THE WDCMA METRO CELL ...............................................................17

3.4.1 WCDMA Metro Cell Overload ....................................................................17

3.4.2 Reselection from WCMA to LTE and SIB 19 Support..........................................18

3.4.3 Load Measurements of the WCDMA Macro ....................................................18

3.4.4 Load Measurements of the WCDMA Metro ....................................................18

4 ALCATEL-LUCENT WLAN OFFLOAD SOLUTION ......................................................... 19

5 ALCATEL-LUCENT KEY DIFFERENTIATORS .............................................................. 20

6 CONCLUSION ................................................................................................. 21

7 ACRONYMS .................................................................................................... 22



LIST OF FIGURES

Figure 1: Load Indication ...................................................................................................... 7

Figure 2: Resource Status Reporting Initiation .............................................................................. 8

Figure 3: Load information exchange between RAT of different types ................................................. 9

Figure 4: The eMCTA function ................................................................................................ 10

Figure 5: Examples of eMCTA applications based on load, priority and services ...................................... 14

Figure 6: Load balancing by adapting handover parameters ............................................................. 15



History

Version Date Author Comment

V1.0 29/10/09 Philippe DAUCHY Document Creation

V2.0 18/11/09 Philippe DAUCHY Document Update



V5.1 31/07/11 Eric Wu

Philip Sapiano

Document Update



1 INTRODUCTION

LTE is being deployed in the areas where traffic demand justifies the investments. Such areas

are typically already served by 2G and 3G networks. Therefore the result will be a multilayer

network composed of both 2G, 3G and LTE layers, including traditional macro cells as well as

small cells (Metro Cells).

The challenge in a multilayer network is to intelligently distribute the load on the different

available layers to optimize the network resource usage while guaranteeing the quality of

service (QoS) of the different active connections and minimizing unnecessary redirections

between layers.

This is the task of a load balancing solution which aims at handling uneven distribution of the

traffic load over multiple cells. The purpose of load balancing is thus to influence the load

distribution in such a manner that radio resources remain highly utilized and the QoS of in-

progress sessions is maintained to the greatest extent possible and call dropping probabilities

are kept sufficiently small. Load balancing algorithms may result in handover or cell

reselection decisions with the purpose of redistributing traffic from highly loaded cells to

under-utilized cells.

Alcatel-Lucent believes that load balancing will play a key role in optimizing radio network

resources and will contribute to a high end user experience while retaining high revenue for

the service provider. Alcatel-Lucent is one of the top three leaders at the 3GPP

standardization body on load balancing related topics.

This document describes the Alcatel-Lucent load balancing solution for optimizing the system

capacity of a multilayer network composed of 2G, 3G and LTE cells. It is structured as follows:

o Section 2 presents the 3GPP mechanisms relevant for a load balancing solution.

o Section 3 presents the Alcatel-Lucent load balancing solution.

o Section 4 presents Alcatel-Lucent’s WLAN offload solution

o Section 5 presents the key differentiators of the Alcatel-Lucent load balancing

solution and

o Section 6 concludes the document.

Features related to the load balancing solution are listed in Section Error! Reference source

not found. “Annex”.



2 STANDARDS PERSPECTIVE

3GPP standards applicable to the load balancing are listed in the table below:

Standard Specification Description

TS 23.401 General Packet Radio Service (GPRS) enhancements for Evolved Universal

Terrestrial Radio Access Network (E-UTRAN) access (Release 9)

TS 36.423 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 application

protocol (X2AP) (Release 9)

TR 36.902 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Self-configuring

and self-optimizing use cases and solutions (Release 9)

3GPP release 8 introduced several procedures allowing load balancing between network

elements of the LTE networks:

o Between eNodeB two procedures are defined to exchange cell load information:

“Load Indication” and “Resource Status Reporting Initiation”.

o Between eNodeB and MME the standard defines the mechanisms allowing to direct a

UE to an appropriate MME of a given MME pool area to achieve load balancing

between MMEs. This is achieved by setting a weight factor for each MME of the MME

pool area, such that the probability of the eNodeB selecting an MME is proportional to

its weight factor. The weight factor is typically set according to the capacity of an

MME node relative to other MME nodes.

o Load balancing between available SGWs can also be performed by the MME when

selecting a given SGW to serve the UE.

3GPP release 9 adds more sophisticated mechanisms to support load balancing in LTE

networks and between LTE and other RATs (e.g. GERAN, UTRAN). 3GPP release 10 will add

mechanisms for heterogeneous networks including small cells, such as enhanced inter-cell

interference coordination.

In this release this document focuses on radio load balancing and will not address MME or SGW

load balancing solutions.

2.1 Radio load balancing

As mentioned above, 3GPP introduces two procedures for exchanging load information

between eNodeB. They are described below.

Load Indication

The purpose of the load indication procedure is to transfer load and interference co-

ordination information between eNodeBs controlling intra-frequency neighboring cells. This is

needed to support the Inter-cell Interference Coordination function (ICIC) and enhanced ICIC

(eICIC).



Figure 1: Load Indication

The load indication may include the following parameters:

o UL Interference Overload Indication. It indicates the interference level experienced by

the indicated cell on all resource blocks per Physical Resource Block (PRB). The

receiving eNodeB may take such information into account when setting its scheduling

policy.

o UL High Interference Indication. It indicates, per PRB, the occurrence of high

interference sensitivity as seen from the sending eNodeB. The receiving eNodeB

should try to avoid scheduling cell edge UEs in its cells for the concerned PRBs.

o Relative Narrowband Tx Power (RNTP). It indicates, per PRB, whether downlink

transmission power is lower than the value indicated by the RNTP threshold. The

receiving eNodeB may take such information into account when setting its scheduling

policy.

Additionally, with 3GPP Release 10, the following may be included in the Load Indication

message:

o Invoke Indication set to " Almost Blank Subframe (ABS) Information." This indicates the

sending eNB would like the receiving eNB to initiate the Load Indication procedure.

o ABS Information. This indicates the subframes designated as almost blank subframes

by the sending eNB for the purpose of interference coordination. The receiving eNB

may take such information into consideration when scheduling UEs.

Resource Status Reporting Initiation

This procedure is used by an eNodeB to request the reporting of load measurements to

another eNodeB. Upon receipt, the eNodeB shall initiate the requested measurements

according to the parameters given in the request. The message indicates the type of

measurements the receiving eNodeB shall perform. The requested measurements may include:

o Radio Resource Status, which indicates the usage of the PRBs in downlink and uplink

(i.e. GBR, non-GBR and total).

o S1 Transport Network Layer Indicator, which indicates the status of the S1 transport

network load experienced by the cell (i.e. low load, medium load, high load,

overload).

o Hardware Load Indicator which indicates the status of the hardware load experienced

by the cell (i.e. low load, medium load, high load, overload).

o With 3GPP Release 10, Almost Blank Subframe Status may be included, which

indicates ABS pattern information.

eNodeB1 eNodeB2

Load Indication

eNodeB1 eNodeB2

Load Indication



Figure 2: Resource Status Reporting Initiation

The resource status information can be periodically exchanged between eNodeBs.

2.2 Radio load balancing in 3GPP release 9

With regards to load balancing two main tasks are under definition at the 3GPP in the release

9 scope:

o Mobility load balancing optimization

o Inter-eNB load information exchange

o Inter-RAT load information exchange.

Mobility load balancing optimization

The mobility load balancing optimization aims at optimizing the cell reselection and handover

parameters in order to cope with the unequal traffic load and to minimize the number of

handovers and redirections needed to achieve the load balancing. Self-optimization of intra-

LTE and inter-RAT mobility parameters to the current load in the cell and in the adjacent cells

can improve the system capacity compared to static and non-optimized cell reselection and

handovers parameters.

Inter-eNB load information exchange

Based on X2 protocol (Resource status update procedure), 3GPP recommendations allow an

eNB to report to a target eNB its eUTRAN cell load information for downlink and uplink. This

enables a load criteria to be included in the target cell selection process for inter-eNB

mobility management.

Inter-RAT load information exchange

The RAN Information Management (RIM) protocol allows the request and transfer of RAN

system information (e.g. UTRAN system information) between two RAN nodes via the core

network. This approach is depicted in Figure 3.

For legacy systems load information is provided by the handover procedure.

eNodeB1 eNodeB2

Resource Status Request

Resource Status Response

eNodeB1 eNodeB2

Resource Status Request

Resource Status Response



Figure 3: Load information exchange between RAT of different types

3 ALCATEL-LUCENT SOLUTION FOR LOAD BALANCING

In any wireless system the radio resources are expensive and scarce. Thus optimizing radio

resources is critical to any wireless telecom network. Due to cost reasons, LTE introduction

will be done progressively. The first LTE deployments will probably be in dense urban areas

where the capacity demand is important. In those areas LTE will not be the unique wireless

access technology. Indeed, LTE will come in addition to already available 2G and 3G coverage.

Optimizing the global usage of all available wireless resources at any given location becomes a

key topic for a mobile network operator. Indeed, thanks to this optimization new users can be

supported by the whole wireless system or additional connections can be supported leading to

revenue increase for the mobile network operator.

Alcatel-Lucent’s approach for optimizing all available radio resources (i.e. 2G, 3G and LTE as

well as macro / small cell) is based on several components:

o The “enhanced Multi-Carrier Traffic Allocation” (eMCTA) which aims at distributing

traffic intelligently between the different carriers in a multi carrier deployment

during call admission control or mobility procedures. The eMCTA function is an

evolution of a function already deployed in WCDMA networks. This function is a key

differentiator of the Alcatel-Lucent solution.

o The self-optimizing approach for adjusting mobility parameters dynamically to

balance the load between cells.

o A strategy for moving UEs between layers when load reaches a dangerous level and

redirections need to be done. The two pillars of the load balancing solution are the

eMCTA and the self-optimizing approach. However in cases where this is not

sufficient, a strategy for moving UEs between layers will be triggered.

o Additionally, Alcatel-Lucent is studying a mechanism for moving UEs between LTE

macro and LTE small cells to implement in conjunction with enhanced inter-cell

interference coordination (eICIC). This would enable optimal utilization of macro and

small cell eNBs in the network.

Iu

Core Network

S1

UTRAN L

TERNC eNodeB

MMESGSNS3/Gn

RIM signalling

Iu

Core Network

S1

UTRAN L

TERNCRNC eNodeBeNodeB

MMESGSNS3/Gn

RIM signalling



This section starts with a description of the eMCTA function. Then the self-optimizing

approach for adjusting mobility parameters is described. To conclude the strategy for moving

UEs between layers is explained.

3.1 The eMCTA function

The eMCTA function aims at allocating traffic intelligently across multiple carriers during call

admission and mobility procedures. It applies to mobility management for both intra-LTE and inter-

RAT cases: Intra-LTE inter-frequency; LTE to GERAN; LTE to WCDMA; LTE to CDMA (TBC).

Two types of criteria can be used by the eMCTA function to take its decision:

o Criteria used for the definition of the operator strategy for service allocation on

available carriers

o Criteria related to the UE context as defined in 3GPP TS 36.413.

As depicted in Figure 4 the eMCTA will be triggered on specific events and will take decision

regarding the cells to be used to handle the new request. To take its decision the eMCTA uses

cell load information and the operator defined policy describing the traffic allocation to the

different carriers.

Figure 4: The eMCTA function

In the following figure, the eMCTA framework is further explained. During the outgoing

mobility procedures in RRC connected mode, eMCTA process enables the eNB to take the

input ‘Neighbor RAT/Carrier List’; applies filters; provides the output ‘Candidate

RAT/Carrier Sorted List’ as depicted in the following figure. eMCTA provides the most suited

RAT/Carriers candidates towards which radio measurements are configured while other

mobility features launch the most suited mobility procedure upon the corresponding

measurement event.

Enhanced MCTA

function

Neighbour LTE cells

load information

Neighbour 2G, 3G cells

load information

EventCell to be

used

Operator policy

Enhanced MCTA

function

Neighbour LTE cells

load information

Neighbour 2G, 3G cells

load information

EventCell to be

used

Operator policy



Figure 5: The eMCTA Framework

The main events that can trigger the eMCTA function are:

o A Call Admission Control failure during a new radio access bearer establishment.

o A mobility procedure.

o A new service request.

The result can be a potential redirection or handover of the UE to another layer depending on

load conditions, service type and operator policy.

The eMCTA function is located in each eNodeB. Because the LTE small cell uses the same

software as the LTE macro eNodeB, the eMCTA function is fully supported on the LTE small

cell. Standard 3GPP procedures are used to “redirect” the UE to other layers (3G or other

LTE carriers). If the 3G network is also provided by Alcatel-Lucent then a consistent load

balancing policy can be defined on the two networks.

3.1.1 Criteria used by eMCTA for the definition of the operator

strategy for service allocation on available carriers

The criteria used for the definition of the operator strategy for service allocation on available

carriers are:

o Carrier Priority

o Requested Service type

o Cell Load of current and best target cells on other carriers,

These criteria are defined at the eUTRAN network management system level.

3.1.1.1 Carrier priority and Requested service type

In order to allow different service-based allocation strategies, the carrier priorities are

defined per service type. When the eMCTA function is invoked, the algorithm tries to redirect

the call to the highest priority carrier for the requested service type. If priorities are equal,

then the carrier with the lowest load is selected preferentially. Depending on the rules

configured by the operator the carrier selection can be always done or can be done only if a

given load threshold has been reached in the serving cell.



The following table presents an example of a possible configuration in which:

o When available, LTE is preferred whatever the service

o UTRAN is preferred as a second choice

o GERAN is used as a third choice only.

LTE UTRAN GERAN

VoIP 0 (highest) 1 N/A

Video 0 (highest) 1 2 (lowest)

Best Effort 0 (highest) 1 2 (lowest)

For LTE, service types are based on QoS Class Id (QCI) range defined in 3GPP. They are listed

in the table below (table 6.1.7 “Standardized QCI characteristics” extracted from TS 23.203).

The service-table provides one priority (value 0/highest-7/lowest) per service-type per

RAT/Carrier (Up to 16). The service-table is the unique entry make the sorting of the

candidate RAT/Carrier list.To be noted that multi-service calls (e.g. audio and video

conferencing) are handled according to the highest service type component.

QCI Resource

Type

Service Type

1

GBR

Conversational Voice

2 Conversational Video (Live Streaming)

3 Real Time Gaming

4 Non-Conversational Video (Buffered Streaming)

5

Non-GBR

IMS signalling

6 Video (Buffered Streaming) TCP-based

7 Voice, video (Live Streaming), Interactive gaming

8 Typically used for default bearer

9

Cell Load of current and best target cells on other carriers A load-based criterion is defined

for the originating cell and for the best target cells. Today it is foreseen that load of a cell



will be defined by the concept of “cell colour” (as already the case in 3G). Three colours will

probably be defined to reflect the cell load; green, yellow and red.

When the serving cell radio resource is congested or in a heavily loaded condition, eMCTA will

trigger mobility behavior to neighbor cells.

The target cell load criterion is a new eMCTA filter. It applies when eMCTA is triggered upon

bad radio conditions, Alarm, preventive load control and reactive load control. A target cell

may have several load information (several IE on X2 and S1). The target load criteria applying

to neighboring cell located on the serving eNB will be based on load information with X2

format.

Based on 3GPP Rel9 definition:

RIM doesn’t allow exchanging load information between two eNB which may not have

an X2 interface.

Load information exchanged over X2 may only be done in a periodic mode. Multi cell

reporting may apply. Max period value is 10 sec.

Load information exchange over S1 may only be done in mono reporting mode. Mono

cell reporting applies.

3GPP doesn’t define event mode on S1 and X2 in order to refresh load information state.

In the originating cell, the load level is used to define the level of load above which the

eMCTA function is triggered. The originating cell eMCTA can be always triggered (i.e. cell is

green) or can be triggered only if the cell becomes loaded (i.e. cell is yellow) or congested

(i.e. cell is red).

In the target cell, the load level is used to avoid redirection to an overloaded cell.

3.1.2 Criteria used by eMCTA related to the UE context

During the network attachment procedure the MME may provide additional information on the

UE to the eUTRAN. This additional information may include:

o UE Radio Capability /Network Capability

o S1AP CS Fallback Indicator IE, which indicates that fallback to CS domain needs to

be done for voice call.

o SRVCC Operation Possible, which indicates that both the UE and MME are SRVCC-

capable.

o S1AP Handover Restriction List IE, , which may contain roaming, area or access

restrictions.

o S1AP Subscriber Profile ID for RAT/Frequency priority IE

o S1AP UE History Information IE



The MME may also include the UE History Information IE in each handover request, which

contains information about cells that a UE has been served by in active state prior to the

target cell and in particular the duration of the time the UE stayed in the cell in seconds.

Those criteria can be used to direct the UE to the most appropriate RAT:

o A voice centric UE with voice solution based on CS fallback and 2G/3G/LTE

capabilities could be forced to camp on the 2G or most probably 3G layer when in

idle mode. As in CS fallback a redirection to the CS domain needs to be done to

establish a call (both incoming and terminating) this will allow speeding up the call

establishment. Thus increasing the subscriber’s experience. The UE will be directed

to the LTE layer at a data session establishment. A refinement of this is to redirect

the UE to the LTE layer only after a threshold of volume of data exchanged has been

reached.

o The UE history information will be used to redirect fast moving UEs to an umbrella

cell to avoid successive handovers.

The Figure 5 provides examples of eMCTA applications based on load, priority and services.

Figure 5: Examples of eMCTA applications based on load, priority and services

3.2 Load balancing by adapting mobility parameters

In a mobile network parameters used for managing handovers are critical parameters. Indeed

values and thresholds used for handling handovers directly impact the handover success rate.

And in turn the handover success rate directly impacts the quality of experience perceived by

the end-user. Traditionally, those parameters are statically configured to get the best

handover success rate. The traditional approach is not dynamic and system load is not taken

Load based service segmentation

LTE cell

3G cell

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Sequential Loading

Load F1 first

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Load Balancing

Overloaded

cell

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Non loaded cell

3G cell

LTE cell

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Voice CS fallback centric UE

If LTE cell load > threshold thenNew best-effort

connection on 3G

Move voice CS

fallback centric UE to

3G

Load based service segmentation

LTE cell

3G cell

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Load F1 first

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Load Balancing

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Non loaded cell

3G cell

LTE cell

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Voice CS fallback centric UE

If LTE cell load > threshold thenNew best-effort

connection on 3G

Move voice CS

fallback centric UE to

3G



into account. The decentralized self-optimizing approach for adjusting mobility parameters

aims at dynamically adjusting mobility parameters to balance the load between cells in order

to optimize the system resource usage. When the load is equally distributed within the

system, the use of the default value is the best compromise. However when load starts to

become dangerously unbalanced between cells, adjusting handover parameters is a way to

effectively achieve load balancing by moving traffic from one cell to another. This approach is

depicted (simplified view) in Figure 6 with two cells. While the simplified representation

shows two cells of similar size, it should be noted that these could also be a macro cell and a

small cell.

Figure 6: Load balancing by adapting handover parameters

It is clear that the adjustments of the mobility parameters will be triggered only if there is a

need to balance the load. This means that the algorithm will be triggered only if a given load

threshold has been reached. In addition the algorithm will use neighbor cells load information

in order to avoid creating overload situations in neighbor cells or increasing the handover

failure rate.

Alcatel-Lucent will implement the 3GPP defined decentralized self-optimizing approach for

adjusting mobility parameters. The standard approach is based on the direct use of

information from the UE to optimize the mobility parameters. The Alcatel-Lucent solution will

go a step further by exploiting the rich geometric information via proprietary intelligent

algorithms.

The geometric approach

The geometric approach nicely complements the self-optimizing approach. Indeed, the quality

of the self optimization is greatly impacted by the initial values of the mobility parameters.

Geometric information means all aspects that govern how RF is perceived by the UEs in

Cell coverage

Threshold for HO to

neighbor cell

AA

A

A

A

A

A

AA

A

A

B

B

B

B

B

B

Load = 95%

Load = 40%

A

A

A

AA

A

A

A

A

A

AA

A

A

B

B

B

B

B

B

Load = 75%

Load = 60%

A

A

A

After HO parameters

adjustment

Threshold

modified

Cell coverage

Threshold for HO to

neighbor cell

AA

A

A

A

A

A

AA

A

A

B

B

B

B

B

B

Load = 95%

Load = 40%

A

A

A

AA

A

A

A

A

A

AA

A

A

B

B

B

B

B

B

Load = 75%

Load = 60%

A

A

A

After HO parameters

adjustment

Threshold

modified



different geometrical locations. Therefore, the term geometry involves location information

of eNodeBs, antenna height and azimuth and frequency band. Alcatel-Lucent has developed an

extensive set of algorithms that addresses local geometrical challenges while exploiting local

opportunities to prescribe good initial parameter values based on geometry information. This

means that the decentralized self-optimizing approach for adjusting mobility parameters will

start off with an already good initial set of values to provide improved performance. Alcatel-

Lucent sees these geometric algorithms as a strong differentiator for any type of deployment.

Inter RAT context

It should be noted that the approach described above aiming at adapting dynamically the

mobility parameters could be extended to an inter RAT context. The approach will aim at

dynamically updating in a consistent manner the 3G and LTE mobility parameters to move UEs

between the 3G and the LTE layer when needed. However, supporting such an approach is

subject to standardization.

3.3 Traffic load balancing between RATs

As mentioned in the previous sections the Alcatel-Lucent load balancing solution is composed

of several components aiming at balancing the traffic between carriers. In most cases the use

of both the eMCTA function and the dynamic adjustments of mobility parameters will be

enough to balance the load between available carriers.

However in cases where this is not sufficient, a strategy for moving UEs between layers will be

triggered to solve dangerous unbalanced situations.

The general strategy is:

1. To support both intra-LTE and inter-RAT load balancing.

2. When an inter-RAT load balancing is needed to select first the UEs with best-

effort connections before UEs with QoS sensitive connections.

Intra-LTE load balancing

This will be achieved by triggering the self-optimizing approach for adjusting mobility

parameters described in section 3.2.

For intra-frequency LTE cells the inter-cell interference coordination (ICIC) function is a

powerful technique to improve the performances at cell edge. Indeed, in case of intra-

frequency LTE cells as the radio signal conditions are rather difficult at the border region

between two cells (i.e. reuse-1 and no scrambling gain) it is anticipated that the margin for

the variation of the handover threshold between two cells without impacting the handover

failure rate will be rather small. In this context ICIC is a technique that can improve the intra-

frequency intra-LTE load balancing by a more efficient usage of the radio resources between

involved cells. The load itself is not moved away from heavily loaded cells but resources are

conceptually moved into the heavily loaded cells by managing interference on physical

resource blocks.



Traffic load balancing for active UEs

When an inter-RAT load balancing is needed QoS will be taken into account to select the UEs

to be moved to the other RATs. UEs with QoS sensitive applications that need the enhanced

LTE capabilities will be kept on the LTE coverage. UEs with best-effort connections will be

moved to the other RATs (i.e. 3G).

Traffic balancing at network attachment

When the carrier to which the UE is trying to attach is loaded (configurable parameter) the

new network attachment request can be redirected to a less loaded available carrier. The

carrier selection is based on the UE measurements.

Traffic balancing of idle mode UEs

When a carrier becomes highly loaded it can be beneficial to move UEs in idle mode to

another cell. The main advantage is of course to minimize the need to perform unnecessary

handovers on service request from UE in idle mode. This can be achieved by automatically

adapting the SIB3 cell reselection parameters based on the serving cell load.

If a cell is truly overloaded and wishes no idle UEs to camp on it, it could indicate to all UEs

that the cell is barred for any camping. This can be done by setting the cellBarred field in the

SIB1 to be “barred” and setting intraFrequencyReselection field to be “allowed”. In that case,

no idle mode UE will try to camp on the cell. Instead, idle UE will look for other suitable cells

for camping. Besides complete barring, there are others means to encourage idle UEs to camp

on other less-loaded cells:

o Encourage more UEs to perform intra-frequency measurements by increasing the value

of QrxLevMin broadcast in SIB1 and SIB3.

o Encourage more UEs to camp on other sectors by reducing Qhyst in SIB3 and/or

Qoffset in SIB4.

The eNodeB can utilize above means to deviate the idle UEs camping behavior.

3.4 Load Balancing on the WDCMA Metro Cell

3.4.1 WCDMA Metro Cell Overload

The following strategies may be performed with overload on the WCDMA Metro :

1) RRC Redirection to an inter-frequency 3G or 2G Macro using the RRC connection reject

mechanism.

2) It could be possible to redirect a LTE capable UE to the LTE Metro, although care would

need to be taken here that the UE is not on the WCDMA layer due to congestion on the LTE

layer.

3) When the WCDMA Metro cell gets to the maximum number of users either pre-emption of

existing calls through RRC connection release or handing off active calls to macro are

possible.

The redirection case will be blind, but the scope is a whole 3G Frequency or 2G RAT, so as

long as the UE can find any suitable cell on the target layer, the redirection will succeed.



The handover case can make use of mobile assisted measurements to guide the handover.

4) Service based handover - it is possible to dedicate the Metro Cell to data only to take the

highest resource consuming users (PS Data) onto the Metro cell, and leave lower resource

consuming services such a voice on the Macro.

In an isolated Metro cell it can be possible to shrink coverage as the cell starts to get to full

load to avoid attracting too many UEs.

In a mesh scenario, any coverage reduction to avoid overload should take into account the

necessary coverage overlap between small cells to avoid making coverage holes. Whitepaper

B3_5 provides further details on this.

3.4.2 Reselection from WCMA to LTE and SIB 19 Support

Generally a UE will be expected to camp and reselect directly on the LTE Metro layer.

However, in the case that the UE is on the WCDMA metro cell e.g. redirected to the WCDMA

metro from the LTE Metro, or in the case where the footprints are different, SIB 19 broadcast

allows the UE to reselect to the LTE Metro layer.

In the case that the LTE Metro layer is overloaded, it is possible to prevent reselection to that

cell from the WCDMA Metro Cell by indicating that it is blacklisted in the system information

broadcast.

3.4.3 Load Measurements of the WCDMA Macro

The loading of the WCDMA macro cell could be used to determine the optimal layer to

handover to or redirect to from the Metro Cell. It is not simple to get the information

transferred between the two technologies due to the following considerations :

1) The RAN Information Management (RIM) could be used to pass load information using the

SON Transfer RIM application through the Core Network. However, 48.018, section 8c.6.4

limits this procedure to inter-RAT exchange. This means that intra-system load information

sharing through the CN is against the current versions of 3GPP standards.

In addition, any information transfer through the CN would involve CN loading, and rapid

updates for many cells could be intensive for both the RNC and the CN.

2) The 3GPP standard allows cell load information to be passed through an Iur link. The Iur

link would require a new interface from the Metro Gateway to the RNC.

If such an interface were developed, the RNC would need to expect many more common

measurements than normally supported. The Metro Gateway would need to act as a

concentrator for the measurements and request one set of measurements to pass to the

relevant Metro Cells which see the Macro cells as neighbours.

3.4.4 Load Measurements of the WCDMA Metro

The mechanisms for the WCDMA Macro to determine WCDMA Metro load are the same as for

the WCDMA Metro to determine WCDMA Macro load, but with the additional considerations :

If there is PSC reuse on the Metro Cell, the Macro will not know which cell is applicable to a

UE being handed over from the Macro to the Metro, and makes the load information

ambiguous (See Incoming HO Whitepaper).



It is therefore doubtful whether the WCDMA macro could make good use of such load

measurements.

4 ALCATEL-LUCENT WLAN OFFLOAD SOLUTION

The Alcatel-Lucent solution for load balancing with WiFi is provided using the Access Network

Discovery and Selection Function (ANDSF). This provides a 3GPP standardized mechanism to

aid the UE in access network discover and selection. Operator provided information, includes:

� Inter-system mobility policy (pre-IFOM UEs) - provides guidance according to access

technology, network ID, etc.

� Access network discovery information – provides list of access networks in the

vicinity of the UE, including access technologies, frequencies, & validity conditions

(eg: location)

� Inter-System Routing Policy – per-flow or per-APN polices for routing packet flows

for UEs that are capable of routing IP traffic simultaneously over multiple radio

access interfaces. It is also used to support Non-seamless WLAN offload.

ANDSF function is defined in 3GPP 23.402. ANDSF supplies the UE with information for

discovering and selecting appropriate access networks according to service provider policies.

It implements a new standardized interface (S14) between a network server and the UE.

Different phases are currently planned:

� Phase 1 provides the basic functionality on the server and UE ANDSF functionality.

It includes support for the S14 interface, security mechanisms as required by 3GPP

33.402, and server provisioned inter-system mobility and network discovery policies.

UE Access is via 3GPP.

� Phase 2 adds inter-working with the Network Assisted WLAN off-load feature to

provide real-time intelligence to assist with network selection decisions.

� Phase 3 adds support for per-APN and per-flow policies to support MAPCON and

IFOM. This includes S14 support for Untrusted Non-3GPP Access via secure tunnels

to the EPC. Interworking with Intelligent Presence is provided for service provider

policy driven guidance of network connections on a per-application basis.

ALU Network Assisted WLAN off-load provides network intelligence to ANDSF so better

decisions may be made in selecting the network priorities communicated to the UE. For 3GPP

R8, Network Assisted WLAN off-load formulates the inter-system mobility policy by

incorporating information from several sources, including the UE, network probes, the

HSS/SPR, provisioned operator policy and subscriber preferences. Factors that may be

considered in assessing network priorities include, expected performance on WLAN APs, UE

mobility, subscriber subscription level, access to operator services and current subscriber data

usage. This allows tailoring of the mobility policy to maximize the QoE for individual

subscribers while taking into account the impact those subscriber have on the mobility

network.

For 3GPP R8, Network Assisted WLAN off-load provides a prioritized list that can be

communicated using the standard ANDSF S14 interface. In addition ALU provides enhanced

functions available with an extended S14 interface supported with partner ANDSF clients. The

enhancements provide:



1. Communication of Wifi Access Point performance information to an ALU Reputation

Database. The information in the database is used to determine whether UEs will

receive better service on WiFi or the mobility network.

2. Dynamic queries that allow for relative QoE assessment between Wifi and the mobility

network, taking into account mobility network congestion and expected Wifi access

point performance. Prior to attaching to an access point based on Inter-system

mobility policy received via the standard S14 interface, the UE sends an additional

query containing the results of WLAN scan. This information, combined with

information received from the Reputation Database, and mobility network congestion

information, is used to select the best access option, which is then communicated to

the UE.

5 ALCATEL-LUCENT KEY DIFFERENTIATORS

The Alcatel-Lucent load balancing solution key differentiators are:

1. The eMCTA feature. This feature aims at intelligently distributing the load between

the different layers in a multi layers deployment. This feature is an evolution of a

feature already available in 3G. The eMCTA function provides the operator with a

flexible approach for defining its strategy in terms of carrier priority and service

allocation on available carriers. The benefits are a higher success rate in case of

alarm or call admission control failure and a better load balancing between LTE, 3G

and 2G carriers. This feature can also be utilized in a Heterogeneous Network

(HetNET) when operator starts to include small cells into the wireless network.

2. Alcatel-Lucent will go further than what will be defined in the 3GPP standard release

10 for self-optimization of mobility parameters by exploiting the rich geometric

information via proprietary intelligent algorithms. This approach will allow prescribing

good initial parameter values based on geometry information. The decentralized self-

optimizing approach for adjusting mobility parameters will start off with an already

good initial set of values to provide improved performances.

3. 3GPPdefine ANDSF provides a standardized mechanism to communicate network

policies and node discovery information associated with WLAN access. Alcatel-

Lucent’s offering enhances the standardized Network<->UE communication channel

provided by ANDSF with Network Assisted WLAN off-load. Network Assisted WLAN

off-load adds network intelligence to the network selection decision process, changing

the dynamic for network selection from one that involves a binary interaction

between a subscriber and their device, to a three way decision process that exploits

network intelligence. The goal of the process is always pick the best connection for

the device, taking into account service provider policies, network congestion, Wifi AP

performance, UE mobility, data usage patterns, subscribed services and other factors

known to the network.



6 CONCLUSION

LTE will be deployed in areas already covered by 2G and 3G networks. The result will be a

multilayer network composed of both 2G, 3G and LTE layers, and even small cells, as well as

WiFi. Balancing the load between all available layers will be an important feature to optimize

the system capacity. Alcatel-Lucent load balancing solution is composed of several

components described in this document. Those components aim at intelligently distributing

the load between available carriers and offering the operator the tools to fully define its load

sharing strategy to better address its needs.



7 ACRONYMS

Acronym Expansion

e-UTRAN Evolved UTRAN

eMCTA Enhanced Multi-Carrier Traffic Allocation

GBR Guaranteed Bit Rate

ICIC Inter-Cell Interference Coordination

LTE Long Term Evolution

MME Mobility Management Entity

PRB Physical Resource Block

QCI QoS Class Id

QoS Quality of Service

RAT Radio Access Technology

RIM RAN Information Management

SIB System Information Block

SRVCC Single Radio Voice Call Continuity

UE User Equipment

alu loadbalancingsolution emcta v5.1

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