Multi-Radio Infrastructure for 4G

◆ Multi-Radio Infrastructure for 4GRolf Sigle, Oliver Blume, Lutz Ewe, and Wieslawa Wajda

Future multi-radio infrastructure for the fourth generation (4G) will combineexisting radio network technologies into a common communication system.For such an infrastructure, we propose a multi-radio management (MRM)that enables optimized access selection and handover control for mobileusers and increases the overall efficiency of network resources. This paperpresents the MRM concept by its functional architecture, its main andsupporting functions, the migration of the 3rd Generation PartnershipProject (3GPP) system architecture evolution, and last but not least, resultsfrom a demonstrator and simulations. MRM comprises multi-radio resourcemanagement (MRRM) and multi-radio mobility management (MRMM),which are tightly coupled to corresponding legacy subsystems through anabstraction and adaptation layer (AAL). In this way, MRM interworks withdifferent radio access technologies (RATs) and extends their legacy functionswith multi-radio control and sophisticated management based on genericmechanisms and virtualized interfaces. MRM is scalable due to thedistribution of MRM across network nodes, and future RATs can be addedseamlessly due to the AAL concept. © 2009 Alcatel-Lucent.

Bell Labs Technical Journal 13(4), 257–276 (2009) © 2009 Alcatel-Lucent. Published by Wiley Periodicals, Inc.Published online in Wiley InterScience (www.interscience.wiley.com) • DOI: 10.1002/bltj.20348

IntroductionToday, many different radio access technologies

(RATs) such as Global System for Mobile Communica-

tions* (GSM*), Universal Mobile Telecommunications

System (UMTS), code division multiple access 2000

(CDMA2000), or Worldwide Interoperability for

Microwave Access (WiMAX) [22] coexist in parallel—

quite often in an overlaying deployment by the same

operator. These operators demand network solutions

that provide their subscribers with ubiquitous mobile

services in overlay cells, hotspots, indoor-coverage, and

added cells with newly introduced wireless technolo-

gies. The benefit from an interworking of those differ-

ent technologies is constrained, however, by the fact

that inter-RAT handovers of ongoing services are inade-

quately supported today. An interworking between

3rd Generation Partnership Project (3GPP*) RATs, i.e.,

GSM/General Packet Radio Service (GPRS), UMTS, and

the upcoming Long Term Evolution (LTE), is currently

being standardized [5, 7, 8], but inter-RAT mobility with

selected non-3GPP technologies (CDMA2000 and

WiMAX) is only envisaged for the latest LTE technol-

ogy [6]. The interworking between different non-3GPP

technologies is even more limited. Furthermore, these

developed or prepared solutions only deal with the

interworking between two considered technologies at

a time. Some standardization bodies, such as the

Institute of Electrical and Electronics Engineers (IEEE)

with standard draft 802.21 [26], started to address the

problem of a general interworking solution. This paper

presents a multi-radio management concept developed

Panel 1. Abbreviations, Acronyms, and Terms

3GPP—3rd Generation Partnership Project3GPP2—3rd Generation Partnership Project 24G—Fourth generationAAL—Abstraction and adaptation layerANDSF—Access network discovery and

selection functionAP—Access pointBMBF—German Federal Ministry of Research

and EducationBSC—Base station controllerCDMA2000—Code division multiple access

2000CMM—Communication and module managerCN—Core networkCODEC—Coder decoderCQI—Channel quality indicatorDAD—Duplicate address detectionDHCP—Dynamic Host Configuration ProtocolDL—DownlinkeNodeB—Evolved node BePDG—Enhanced packet data gatewayEU—European UnionFMIP—Fast Mobile IPFTP—File Transfer ProtocolGSM—Global System for Mobile

CommunicationsGPRS—General packet radio serviceHSDPA—High speed downlink packet accessHTTP—Hypertext Transfer ProtocolIEEE—Institute of Electrical and Electronics

EngineersIMS—IP Multimedia SubsystemIP—Internet ProtocolIPsec—Internet Protocol securityIPv4—Internet Protocol version 4IPv6—Internet Protocol version 6L2—Layer 2L3—Layer 3LLC—Link layer controlLTE—Long Term EvolutionMIP—Mobile IPMIPv4—MIP version 4

MIPv6—MIP version 6MRM—Multi-radio managementMRM-HAM—MRM heterogeneous access

managementMRMM—Multi-radio mobility managementMRM-NET—MRM radio access networkMRM-TE—MRM terminal entityMRRM—Multi-radio resource managementmsec—MillisecondO&M—Operations and maintenanceOFDM—Orthogonal frequency division

multiplexingOFDMA—Orthogonal frequency division

multiple accessPMIP—Proxy Mobile IPQoS—Quality of serviceRAN—Radio access networkRAS—Radio access selectionRAT—Radio access technologyRel—ReleaseRF—Radio frequencyRNC—Radio network controllerRRC—Radio resource controlRSSI—Received signal strength indicatorRTP—Real Time Transport ProtocolSAE—System architecture evolutionScaleNet—Scalable, Efficient and Flexible

NetworksSINR—Signal-to-interference-plus-noise ratioSIP—Session Initiation ProtocolTDMA—Time division multiple accessUE—User equipmentUL—UplinkUMTS—Universal Mobile Telecommunications

SystemWAG—Wireless access gatewayWIGWAM—Wireless Gigabit with Advanced

Multimedia SupportWiMAX—Worldwide Interoperability for

Microwave AccessWLAN—Wireless local area network

258 Bell Labs Technical Journal DOI: 10.1002/bltj

in Alcatel-Lucent Bell Labs in the framework of coop-

erative national and international projects, such as the

European Union’s (EU’s) Ambient Networks [12–14,

28] project, and the German Federal Ministry of

Research and Education’s (BMBF’s) Scalable, Efficient

and Flexible Networks (ScaleNet) [16] and Wireless

Gigabit with Advanced Multimedia Support (WIG-

WAM) projects [15, 17, 18].

DOI: 10.1002/bltj Bell Labs Technical Journal 259

MRM OverviewToday’s multi-radio interworking approach,

which specifies individual solutions between two indi-

vidual RATs, leads to increasing complexity when

additional technologies are envisaged for interwork-

ing. As an alternative, we propose the creation of a

generic management mechanism for all inter-RAT rele-

vant tasks between any considered radio access tech-

nologies. This solution minimizes the impact on

existing radio technologies, reduces the efforts for

standardization and implementation, and improves

time-to-market for operator deployment.

The multi-radio management (MRM) concept

presented in this paper envisions such a framework

for the integration of multiple RATs in an operator

network. MRM aims to provide the multi-radio infra-

structure with:

• Flexibility for operators to deploy different RATs

in their network,

• Full mobility support between RATs to allow

selection of the most appropriate RAT at any time,

• A common resource management platform

enabling the operator to optimize network usage

and revenue, and

• Minimized requirements for user equipment (UE).

MRM does not aim to be a replacement but

instead an extension of existing heterogeneous radio

access deployments, and thus creates an overlay per-

forming the integration of different RATs. Figure 1shows the functional separation of MRM into multi-

radio resource management (MRRM), which is inter-

working with technology-specific radio resource

management, and multi-radio mobility management

(MRMM), which is in charge of the interworking

between existing technology-specific mobility man-

agement and the Internet Protocol (IP)-based mobil-

ity towards non-3GPP air interfaces. An intermediate

abstraction and adaptation layer (AAL) performs the

interworking of these generic MRM procedures with

the “legacy” RAT functions, hiding the RAT-specific

mechanisms and control functions from the MRM.

Furthermore, it provides a translation of RAT-specific

parameters into generalized parameters that are han-

dled by the MRM. Thus, the management of the

multi-radio infrastructure for fourth generation (4G)

is decoupled from the evolution of air interfaces

defined by different standardization bodies.

MRM FunctionsThe new MRM functionality enables the man-

agement of multiple radio technologies in future 4G

networks. In the following sections, the different com-

ponents and functions of the MRM are described in

detail.

MRM Main TasksMulti-radio management can be separated into

four main tasks which constitute the MRM function-

ality on top of the RAT-specific procedures:

• Collection and provisioning of neighborhood informa-

tion. The MRM collects and provides information

on the network topology.

• Radio access advertisement. The MRM informs idle

mobile terminals about available neighbor cells

of the technology in use and of other RATs.

• Radio access selection. The MRM provides mobile

terminals in connected mode with measurement

Abstraction

Radio equipment/modem

MRM

RAT control

MRMM MRRM

MRM—Multi-radio managementMRMM—Multi-radio mobility managementMRRM—Multi-radio resource managementRAT—Radio access technology

Figure 1.MRM concept for integration of different accesstechnologies by abstraction of the RAT-specificfunctions and parameters.


configuration and triggers handovers. This

process, denoted as RAS, takes all available radio

technologies into consideration and regards qual-

ity of service (QoS) requirements for the ongo-

ing service, as well as the radio resource usage in

the serving and in candidate technologies.

• Mobility management. The MRM controls the hand-

over sequences that are applied during a change

of the serving RAT.

The primary tasks listed above are supported by

supplemental tasks which, for instance, handle the

configuration, monitoring, and reporting of measure-

ments. In subsequent sections, the MRM tasks will be

considered in detail.

Neighborhood information collection and provisioning.Although the distribution of information about neigh-

boring cells of the same network/technology is already

a part of each 3GPP radio access technology, there is no

mechanism that covers this information distribution at

the inter-RAT level. In order to perform multi-radio

management, comprehensive knowledge about the

present state of all overlapping RANs is indispensable.

This task is achieved by informing the MRM about the

registration and de-registration of cells and their respec-

tive properties. The MRM collects the data, calculates

neighborhood relations from coverage information, and

provides the result as neighborhood information

together with RAT-specific access information.

MRM supplies the managed RANs with informa-

tion about adjacent cells of different RATs which is

used as input for the advertisement and measurement

configuration functions. This enables the terminal to

scan efficiently for pilot channels of neighboring cells,

minimizing battery consumption.

Advertisement. A terminal in idle mode has no

active connection to the network. Hence, the initial

access selection in idle mode must be performed by

the terminal itself. The advertisement process supplies

a terminal with neighborhood information, allowing

it to scan other frequencies and to make an access

selection autonomously. This advertisement can be

done using one of two alternative mechanisms: 1) a

broadcast in RAT-specific system broadcast channels,

or 2) a request/response mechanism between the ter-

minal and the MRM entity in the network.

A generic mechanism is proposed to avoid stan-

dardization issues regarding changes to the system

broadcast for different RATs. Instead, the radio access

information of advertised cells is sent on a broadcast

channel as a container list where the RAT-specific

neighbor cell information is included transparently.

Each container is equipped with a RAT-indicating tag

for identification by the decoding terminal. The bene-

fit of such a generic cell broadcast list is an intrinsic

extensibility to further RATs, since a decoding termi-

nal does not have to have knowledge about the con-

tainer content of unsupported technologies.

Additional measurement parameters or assistance

data that parameterizes the access selection algorithm

in the terminal may be distributed by the advertise-

ment as well, according to the operator deployment

and user subscription model.

Radio access selection. Generally, radio access

selection denotes the process of choosing for a termi-

nal the most appropriate access technology and cell

within a heterogeneous network for a requested ser-

vice at a given location, in terms of configured opera-

tor and user criteria.

RAS is a challenging task as the suitability of dif-

ferent radio technologies varies by service. For mov-

ing users, detection of entering or exiting broadband

hotspot coverage has to be performed fast and effi-

ciently. However, inter-technology handover at

hotspot detection is not always the most reasonable

alternative [9]. Real time services may not be sup-

ported by a wireless local area network (WLAN) [21]

hotspot or fast moving mobile terminals may reside

within a hotspot for only a small duration of time.

Next to the provisioning of best connectivity to

the user, access selection also offers operators the

potential of optimizing network usage and maximiz-

ing revenue. It is known that an inefficient service

distribution between the different access systems leads

to overload on some access systems, even if resources

in alternative access systems are still available.

Moreover, depending on the link performance and

the service type, the resource costs of different access

technologies may differ, leading to a potential for

overall resource usage optimization and hence a

capacity increase.


The RAS function comprises the access selection

in idle mode (including initial access selection), and

access selection in connected mode.

During the switch-on procedure, the terminal scans

for radio networks and selects a cell of a certain RAT on

the basis of a stored RAT preference list. The terminal

will stay in idle mode if no service is requested. Because

a terminal in idle mode has no active connection to

the network, the access selection in idle mode must

take place in the terminal itself using the neighborhood

information and assistance data received via network

advertisement as mentioned above.

After the terminal requests a service, any further

RAS will be performed in the access network since it

can apply network status information and policies in

addition to the measurements received from the ter-

minal to assess the most suitable radio access.

Additionally, the network receives threshold-based

triggers and events indicating relevant changes in the

system that require making a new RAS decision. Those

events include detection of a hotspot, dropping of a

session, or crossing of link performance/load threshold.

The algorithms applied for the RAS decision make

use of various parameters such as cell load and capac-

ity, candidate link characteristics, user and operator

preferences, and radio efficiency of different services,

which are obtained from different sources in RANs,

the terminal, and by operations and maintenance

(O&M) or policy databases.

The application of a sophisticated RAS algorithm

is decisive for MRM operation. Load balancing RAS

algorithms focus mainly on the resource usage in each

RAT in an effort to exploit all available resources. The

utility maximization based RAS algorithm [10]

designed in this work additionally takes into account

the resource costs of each RAT, based on service qual-

ity and link performance. This leads to a further

increase of system throughput, compared to load bal-

ancing RAS algorithms. Moreover, the approach has

low signaling needs even for decentralized operation,

while being auto adapting and operator tuneable

(throughput-fairness trade-off).

Heterogeneous mobility management. When a RAS

decision is made that changes the serving technology,

the handover will involve a change of the radio interface

and a change of the IP connectivity. The execution of

such an IP layer handover is the task of MRMM.

Depending on the capabilities of the terminal and of the

source and target RANs, a variety of mobility protocols

may be available, e.g., MIP version 4 (MIPv4) [31], MIP

version 6 (MIPv6) [27], Proxy Mobile IP (PMIP) [19],

or Fast Mobile IP (FMIP) [29]. Furthermore, different

handover sequences can be selected: If the mobile device

is capable of sustaining multiple radio connections simul-

taneously, the current user plane connectivity may be

retained until the new connectivity is ready (make-

before-break) instead of disrupting the current radio link

(break-before-make).

When MRRM indicates an RAS event, MRMM

selects the proper handover protocol from the availa-

ble protocols. The MRMM handles the IP mecha-

nisms, while the MRRM is charged with assignment

of radio resources. For initial attachment, as shown in

Figure 2, MRRM attaches the radio link before ini-

tialization of IP. For a handover, MRMM requests

attachment and detachment of the radio links during

the selected handover sequence. As an example,

Figure 2 shows the sequence for a make-before-break

handover.

For both connection establishment and handover

execution, the MRMM must interact with IP kernel

functions for the selection of a valid IP locator on the

new interface, and with the Mobile IP protocol for a

“binding update” of the IP address known as a “care of

address” at the terminal’s home agent. The IP

kernel performs the IP address configuration with

Stateless Address Autoconfiguration, Dynamic Host

Configuration Protocol (DHCP), and Duplicate

Address Detection (DAD). In addition, the handover

event may result in a change of QoS which is reported

to the session layer for coder decoder (CODEC) adap-

tation, i.e., MRM interacts with Session Initiation

Protocol (SIP) and IP Multimedia Subsystem (IMS) to

benefit from the increased bandwidth after handover

into a hotspot or to change to a transmission CODEC

with lower bandwidth before handover to a large

overlay cell. Thus, it can be seen that for a smooth

handover execution, MRMM and MRRM are closely

cooperating and are performing cross layer synchro-

nization between layer 2 (L2), layer 3 (L3), and even


the application layer, to minimize packet loss and hand-

over latency.

Using neighborhood information and configura-

tion of multi-radio measurements for candidate and

serving link access selection, decisions can be made

proactively before radio connectivity is lost. This

enables further optimization of handover perfor-

mance: some time-consuming parts of the handover

sequence may be performed proactively before the

actual handover event. In this case, the handover

sequence is separated into three phases.

1. The pre-registration phase comprises authentication

and authorization. Advantageously, for single-

radio terminals these steps are supported by the

serving access network with a transparent con-

tainer over the current radio link [6], so that pre-

registration and preparation can start even before

reaching coverage area of the target system. The

preregistration state does not consume resources

and can be sustained for a long time.

2. The handover preparation phase can include radio

resource preparation (e.g., obtaining a descrip-

tion of the target radio channel or UMTS

downlink (DL) scrambling code), as well as IP-

connectivity preparation (IP address assignment).

Handover preparation is performed on a timelier

basis than preregistration, and may have a

restricted lifetime. If there is no assurance that

the ensuing handover will be executed shortly

or at all, then critical resources, like codes, time

slots, or memory for context transfer shall not

yet be reserved.

3. During handover execution the final steps are taken.

This phase involves context transfer, resource

assignment and data forwarding mechanisms in

the access network.

A variety of triggering events can cause the three

phases to be executed. They can be executed consecu-

tively or repeatedly on demand, as coverage of target

cells becomes available or unavailable. Simulation

To abstraction:attach newradio link

MRMM MRRM

HOexecution

Locator

HO protocol select

To session manager:HO occurred, new QoS

Locator select

LinkAttach

LinkDetach

HO finalized

To MIPv6:binding update

To abstraction:detach oldradio link

MRRMLocator selection MRMM

IPConnectionrequest

Locator

LocatorSelect

IP initialization

To abstraction:attach radio link

IPConnectionavailable

To MIPv6:binding update

IP protocol select

HO protocol exec.

exec.—ExecutionHO—HandoverIP—Internet ProtocolMIPv6—Mobile IP version 6

MRM—Multi-radio managementMRMM—Multi-radio mobility managementMRRM—Multi-radio resource managementQoS—Quality of service

(a) Connection establishment (b) Make-before-break handover

Locator selection

Figure 2.Signaling for initial attachment and handover.


results show that proactive preparation of the most

attractive target cell can significantly increase the

probability of seamless execution of the handover [9].

Thus, using MRM with proactive RAS and a separa-

tion of handover phases reduces the need for cell

overlap at network planning, and can thereby reduce

deployment costs.

MRM measurements. Up-to-date information is

essential to enable well-informed MRM decisions.

This information includes the current state of the

radio access networks and the current state of the radio

links of the mobile terminals served within these

networks.

Measurements of link performance include both

the quality of established links, and the signal strength

and quality of candidate links of multiple technologies

(inter-RAT measurements). The measurement tasks

comprise:

• Determination of potential candidate cells of a

neighboring RAT,

• Setting of thresholds and measurement periods,

• Configuration and initiation of the measure-

ments,

• Measurement result monitoring including filter-

ing, averaging, and threshold supervision, and

• Measurement reporting according to configured

events.

The reported measurements are used on the net-

work side for decisions about establishing and chang-

ing of radio access, and collected for statistics and

predictions in RAS algorithms. The mobile-based

MRM measurements above are also used in the ter-

minal for RAS in idle mode mobility.

In addition to measurements of radio link quality,

MRM is in charge of determining up-to-date system

load states, since the load is considered for RAS strat-

egy. For this purpose, resource measurements are per-

formed by the radio access network nodes. Analogous

to the link measurements, the MRM either makes use

of existing resource measurement procedures in the

considered RAT, or it supplies the functionality by

itself. Resource measurements performed in the net-

work nodes, e.g., cell load measurements, are

reported to the serving MRM component according to

the configured reporting events, such as load thresh-

olds exceeded in a cell.

For both radio link measurements and network

resource measurements, the abstraction and adapta-

tion mechanisms described below provide independ-

ence of MRM functionality from the controlled radio

technology.

Distribution of MRM FunctionalityModern wireless networks distinguish between

entities such as the mobile terminal, the radio access

network, and the core network (CN), which in turn

consist of a number of hierarchical nodes, such as the

base station, the radio network controller (RNC), and

the mobility and session controller. Likewise, MRM

functionality is distributed over those nodes and over

particular access technologies.

MRM functionality is distributed to:

• The MRM terminal entity (MRM-TE) subsystem,

• The MRM radio access network (MRM-NET) sub-

system, and

• MRM heterogeneous access management (MRM-

HAM).

The MRM-TE subsystem handles access selection

in idle state, measurement reporting, configuration

of routing towards the selected air interface, and

finally, the interface to terminal-based IP mobility

(e.g., Mobile IPv4/6) for handover support between

3GPP and non-3GPP air interfaces.

The main task of the MRM-NET subsystem is to trig-

ger the access selection, based on terminal and network

measurements in cooperation with MRM-HAM. Other

functions include triggering the radio access bearer setup

and release, configuring inter-RAT measurements, and

also advertising and discovering accesses (in coopera-

tion with HAM). The MRM-NET has an interface func-

tion toward 3GPP resource and mobility management in

RAN controllers to trigger handover between 3GPP air

interfaces. MRM-NET decisions are based on static con-

figuration or dynamic policies loaded from MRM-HAM.

MRM-HAM is mainly responsible for RAS and

support of network advertisement and network neigh-

borhood information collection and provisioning. The

RAS decision is based on link performance, service

requirements, operator policies, terminal capabilities,

and user profiles. Moreover, it utilizes network status

information collected from all of the involved RATs, as

well as statistical and prediction information.


The distribution of MRM components in the ter-

minal, radio network, and core network and their

links to other functions is shown in Figure 3. In

this layered model, MRM operates on top of the

technology-specific radio management layer functions

and interacts with higher layer functions such as the

session and mobility management, as well as with

application layer functions. Different solutions are

envisaged for the communication between MRM

components over the respective air interfaces,

depending on whether a 3GPP or non-3GPP technol-

ogy is considered. We discuss this issue in the next

section.

Figure 4 illustrates the information flow between

the MRM-TE, the MRM-NET, and the MRM-HAM.

Once the cell and network information has been col-

lected from all RANs, the MRM-HAM processes it and

provides neighborhood information to the MRM-NET,

which in turn advertises available RATs to the MRM-

TE. Based on this information, the MRM-TE carries

out candidate link performance measurements and

performs initial access selection.

The distributed MRM measurement function in

MRM-HAM and the MRM-NET is responsible for

measurement configuration. MRM-HAM requests the

MRM-NET for cell load/cell capacity measurement.

User planeL3/RNL

Air

inte

rfac

e

Sessionlayer

MRM layer

Abstractionand

adaptationlayer

RAT andtransport

layer

Applicationlayer

E2E—End-to-endIP—Internet ProtocolL3—Layer 3MAP—Mobility anchor pointMM—Mobility managementMRM—Multi-radio managementMRM-HAM—MRM heterogeneous access managementMRM-NET—MRM radio access network

MRM-TE—MRM terminal entityPCRF—Policy and charging rules functionRAT—Radio access technologyRNL—Radio network layerRRM—Radio resource managementSIP—Session Initiation ProtocolSM—Session managementTNL—Transport network layer

Terminal

Application,E2E-SM

MRM-TE

SM/MM

Radio access network

RRM

User planeRNL/TNL

MRM-NET

Evolved packet core

User planeTNL/including MAP

MRM-HAM

SM/MM/PCRF

E2E-SM(SIP Proxy)

IP network

Application,E2E-SM

User planeTNL/including MAP

Generic

RAT specific

RRMRRM

User planeL3/RNL

Generic

RAT specific

Transport of user dataLegacy control interfaces

MRM control interfacesMRM signaling

Figure 3.Location of MRM entities in a mobile network layer model.


The MRM-NET performs, collects, and analyzes the

measurements of the RAN, and reports them to

MRM-HAM.

The MRM-NET configures link performance

measurements for active and candidate RATs to the

terminal. The terminal, in connected mode, collects,

generalizes, preprocesses, and reports the measure-

ments to the MRM-NET.

Once the RAS triggering function of the MRM-

NET has detected the need for a new access selection

decision, the MRM-NET sends an RAS request to the

MRM-HAM, which calculates the metrics for the suita-

bility of available access alternatives. MRM-HAM

then returns this result to the MRM-NET. If client-

based Mobile IP is used as the handover protocol,

the MRM-NET finally instructs the MRM-TE accordingly

for handover execution.

Abstraction and AdaptationMRM is designed as a generic concept operating

with any kind of radio access technology, which can dif-

fer significantly in design and capabilities. The parame-

ters of radio access networks for different RATs are not

directly comparable, and mechanisms and procedures

differ as well. Therefore, an abstraction and adaptation

layer is proposed, hiding the RAT-specific properties

from the generic MRM. The main functions of this layer

are the translation of generic MRM procedures into

RAT-specific procedures and the mapping of RAT-

specific parameters to generic values and vice versa.

MRM-TE MRM-NETMRM-HAM

MRM—Multi-radio managementMRM-HAM—MRM heterogeneous access managementMRM-NET—MRM radio access network

MRM-TE—MRM terminal entityUE—User equipment

Access advertisement

Radio access selectionin idle mode

Radio access selectiontriggering in connected

mode

Radio access selectiondecision in connected mode

HandoverdecisionHandover

execution

Access advice

Handover initiation

Access selection

Measurement abstraction

Measurement monitoring

Downlink performancemeasurement configuration for

UE in connected mode

Measurement reporting

Measurement reporting

Cell load/capacitymeasurements

Resource usagemeasurement configuration

Link performancemeasurements

Measurement collection

Measurement abstraction

Measurement monitoring

Link performancemeasurements in idle mode

Neighborhood information provisioning

Neighborhood information collection

Measurement collection

Figure 4.Information flow between the functions of the MRM entities.


The advantage of these abstraction and adapta-

tion functions becomes particularly visible when new

radio technologies are integrated into existing sys-

tems. In this case, the MRM as well as the AAL for

existing RATs remain unchanged, while only the

adaptation and abstraction functions for the new RAT

must be defined.

Parameter Abstraction. Parameter abstraction

denotes the transformation of RAT-specific quantities

to a common denominator so that they become com-

parable by generic MRM algorithms for measurement

evaluation, access selection triggering, and access

selection decision. Before this abstraction takes place,

RAT specific processing can be performed by support-

ing functions such as parameter collection, frequency

domain filtering, averaging, threshold supervision

including hysteresis, and timeouts.

The reverse translation of generalized quantities into

RAT-specific values is required, too. This applies

especially to generic measurement where thresholds

have to be configured, and as a consequence, RAT-

specific measurements must be requested.

The main parameters to be evaluated by MRM

are link performance and access resource usage.

Link performance abstraction. The link perfor-

mance describes at what level of efficiency a link can

fulfil the users’ service requirements. This applies to

both an active link and alternative candidate links.

The abstracted link quality is derived from access-

specific measured quantities such as the:

• Received signal strength indicator (RSSI),

• Signal-to-interference-plus-noise ratio (SINR),

and

• Channel quality indicator (CQI).

A variety of access-specific measures have to be

used for different access technologies. The abstract-

ing functions map the RAT-specific quantities on

abstracted, generalized dimensions. A mapping

function can also consider implementation-specific

variations. For example, simple or complex receivers

of the same access technology achieve different levels of

link performance in terms of data rate for the same

received signal strength.

In order to evaluate the link performance and to

decide if a considered session can be served by an

available RAT, we propose using parameters similar

to the main application QoS requirement, i.e., the link

data rate. Further parameters, such as the required

residual error rate or the maximum delay, serve as

input for the abstraction function. Additionally, they

are used as constraints, which may rule out some of

the candidate links, e.g., if a service such as gaming

requires short packet transfer delays, then a RAT with

high transfer delays like GSM/GPRS cannot be used

for this service.

Only the downlink performance of candidate

links can be estimated. The QoS that each provides

may differ from the estimated link performance based

on terminal measurements. Resource management

in the network may apply additional constraints, such

as change of transmission power or available codes,

which results in a different provided QoS. These con-

straints have to be taken into account by MRM for a

final evaluation.

Resource abstraction. A resource-aware MRM also

needs a resource abstraction model of the access

technologies’ resource structures. This information

includes the critical resources available, their geo-

graphical and node-dependent distribution, as well as

bearer-dependent resource demands.

The critical resources differ depending on the

medium access technology, e.g., time division multi-

ple access (TDMA), code division multiple access

(CDMA), or orthogonal frequency division multiple

access (OFDMA). In TDMA-based systems such as

GSM, the number of time slots is a limiting factor,

while for CDMA-based systems such as UMTS, the

channelization codes and quantity of power used

describe the current resource usage. Hence, the

resource usage descriptive parameters differ in nature

and number for a considered technology.

For each of these parameters, an abstracted usage

value (e.g., given as a percentage) is defined. For its cal-

culation, the MRM has to distinguish between resources

for guaranteed bit-rate traffic and for best-effort traffic,

since assigned resources of the former cannot be freed

to serve another request. Hence, two resource levels

indicating both types of traffic are required.

Moreover, depending on the current service mix

and user distribution a certain amount of extra

resources may be necessary to maintain ongoing ser-

vices, since resource usage may change due to a change


in channel quality or due to handover. Hence, a third

resource level is defined to indicate the maximum

amount of resources which may be assigned in a cell.

Procedure MappingThe key design principle of the MRM in general

and abstraction and adaptation in particular is the

reuse of existing functions and procedures. This is

especially important in a 3GPP network environment

where specific interworking solutions between some

RATs have already been defined and will be reused

instead of being replaced by MRM.

Figure 5 shows a model of the abstraction and

adaptation layer. Requests from the MRM are for-

warded by the communication and module manager

(CMM) to the procedure mapping of the relevant

RAT, which translates the generic request in RAT-

specific procedures. This may also require parameter

abstraction as discussed above. In the opposite direc-

tion, triggers and measurement reports that are

received from the RAT are translated into generic

answers and forwarded by the CMM to the MRM.

Depending on the capabilities of the underlying

RATs, requests for remote information (e.g., measure-

ments in the terminal) may either be processed locally

by existing RAT-specific procedures or are forwarded

via MRM signaling to the remote side. There, the

CMM sends the request to the corresponding local

“procedure mapping and parameter abstraction” mod-

ule. The response to a request follows the reverse path.

The CMM plays a key role in routing requests and

answers between the MRM and the corresponding

procedure mapping and parameter abstraction mod-

ules and between remote sites. The routing table can

be configured during the registration of the RAT-

specific modules using a “default route” through the

MRM signaling module for remote requests, and

thereby also provides a location abstraction, i.e., the

MRM does not need to know whether its request is

answered locally or by a remote service.

“Transport adaptation” provides message trans-

port for MRM signaling on layer 2 or layer 3. The

mechanism that actually is applied depends on the

specific radio access technology. For 3GPP technolo-

gies, existing message transport mechanisms are

reused, such as the radio resource control (RRC)

direct transfer mechanism of UMTS or the corre-

sponding mechanism on the link layer control (LLC)

level for GSM/GPRS. For non-3GPP technologies, IP-

based transport mechanisms are applied, providing

MRM signaling to connected mobile terminals.

Besides the transport issue, access to MRM-related

radio resource parameters also has to be adapted sepa-

rately for each interworking RAT considered. Again,

for 3GPP technologies, reuse of existing radio resource

control mechanisms can be applied, such as the com-

mon measurements and dedicated measurements

available for UMTS systems. For non-3GPP technolo-

gies, a utilization of standard enhancements is envis-

aged. The IEEE has passed enhancements to WLAN

standards such as 802.11k [23] and 802.11u [25],

which provide measurements on both link layer level

and neighbor cell information provisioning.

Furthermore, the IEEE passed the 802.16g stan-

dard amendment to the WiMAX system [24].

Utilization of these additional management plane pro-

cedures and services allows for neighbor information

provisioning, intra-RAT measurements, and the sup-

ply of handover primitives.

Finally, the IEEE is preparing a cross-technology

standard—IEEE 802.21—to address inter-RAT inter-

working through a media-independent handover

Adaptation/abstraction

Proceduremapping/parameterabstraction


Communication and module manager

MRMSignalingProtocol

Transportadaptation

MRM

RAT 1 RAT 2

MRM—Multi-radio managementRAT—Radio access technology

Figure 5.Model of the adaptation and abstraction layer.


signaling framework [26]. Its functionality covers much

of the MRM communication and adaptation demands,

however, access selection, parameter abstraction, and

handover control are neither defined nor intended,

which prevents 802.21 from offering a complete solu-

tion for multi-radio management. Moreover, adequate

support for 802.21 is still imponderable for radio tech-

nologies other than those of IEEE.

MRM CommunicationThe principle of using either RAT-specific com-

munication mechanisms or generic MRM procedures

is presented in Figure 6, which shows MRM signaling

between a terminal and an access network in a 3GPP

UMTS network.

Network-side information and services like inter-

RAT measurements for GSM/GPRS and LTE can be

requested via the network-side procedure mapping

and parameter abstraction function. Other informa-

tion, such as measurements of the link performance of

non-3GPP candidate cells, is requested via MRM sig-

naling. It is envisaged to transport signaling messages

using the existing RRC direct transfer mechanism. A

similar situation arises if a terminal is served by a non-

3GPP network, but with somewhat different mapping

to RAT-specific procedures and MRM message


MRM-TE MRM-NET

3GPPL1/L2

Messagetransport

Messagetransport

Signaling

Radio bearer

RRMRAC/RRC

3GPP†

modem

RRMRAC/RRC



Non3GPPmodem

Non3GPPdriver

RRCdirecttransfer

RRCdirect

transfer

TCP/IP

MRM-HAM

TCP/IP


Transportadaptation

Communication and module managerMRM communication

manager

RRC Protocol RRC Protocol

Generic elements

UMTS-adaptation/abstraction

Non3GPP-adaptation/abstraction

MRM scope

Logical interfaces Physical interfaces

UMTS-specific

Non3GPP-specific

Adaptation

3GPP—3rd Generation Partnership ProjectIP—Internet ProtocolL1—Layer 1L2—Layer 2MRM—Multi-radio managementMRM-HAM—MRM heterogeneous access managementMRM-NET—MRM radio access network

MRM-TE—MRM terminal entityRAC—Radio access controllerRRC—Radio resource controlRRM—Radio resource managementTCP—Transmission Control ProtocolUMTS—Universal Mobile Telecommunications System

†Trademark of the European Telecommunications Standards Institute.

Communication and module manager




Transportadaptation

Transportadaptation

Transportadaptation



Operator IP network

Figure 6.MRM signaling between terminal and 3GPP UMTS access network.


transport. Examples of the mapping of MRM proce-

dures onto RAT-specific procedures in a 3GPP system

are discussed below.

In Figure 7, the MRM-NET uses a generic LOAD

REQUEST message to obtain cell load information. The

abstraction and adaptation function interprets this

request and maps it onto RAT-specific procedures (DL

TxPOWER REQUEST, UL NOISE REQUEST and DL

DELAY REQUEST) that request measurements accord-

ingly from the corresponding RNC, which then pro-

vides the input for the load abstraction. For illustration

purposes each measurement is requested using a sepa-

rate procedure, while a combined request may be sent

to the RNC by implementation. The RNC either already

holds the measurement values or it must request meas-

urements from the respective node B. The measure-

ment values are transferred to the abstraction function

which translates the UMTS-specific values into generic

resource usage and reports the result to the MRM-NET.

Figure 8 demonstrates a signaling flow of a ter-

minal currently served by UMTS and the MRM-NET

that is requesting LTE candidate link measurements.

By using neighborhood information received from

MRM-HAM, the MRM-NET sends a generic LINK

MEASUREMENT REQUEST to the AAL located in the

UMTS RNC, which in turn triggers a UMTS RRC

measurement configuration. The requested measure-

ment results are returned to the AAL on the network

side which translates them into a generic value of a

link data rate, and forwards the information to the

MRM-NET.

As indicated above, for other candidate measure-

ments which are not directly supported by UMTS

(e.g., WLAN measurements) the AAL on the network

side forwards the generic measurement request to the

AAL on the terminal side which translates this request

to local RAT-specific procedures (e.g., as provided by

802.11k standard extensions).

Adaptation andabstraction

NET

RESOURCE USAGEMEASUREMENT REQUEST

DL TxPOWER REQUEST(NBAP) CONFIGURE

MEASUREMENT REQUEST

MEASUREMENT REPORTDL TxPOWER

DL TxPOWER INDICATION

UL NOISE RISE REQUEST

…

DL DELAY REQUEST

DL DELAY INDICATION RESOURCE USAGEINDICATION

UL NOISE INDICATION

MRM-NETNode B RNCRRC/RAC

…

DL—DownlinkMRM—Multi-radio managementNBAP—Node B application partNET—Network

RAC—Radio access controllerRNC—Radio network controllerRRC—Radio resource controlUL—Uplink

Figure 7.Signaling flow obtaining resource usage information.


Migration Towards the MRM Concept: A 3GPPApproach

MRM, as represented by its functions and com-

ponents, has to be distributed among the radio access

and core network infrastructure to obtain the

intended inter-RAT mobility. The 3GPP is concerned

with a system architecture evolution (SAE) [8] intro-

ducing the interworking of different RATs. Since this

is the most advanced approach to a multi-radio archi-

tecture, the MRM concept aims to match to that

approach. Figure 9 shows a distribution of MRM as it

would be integrated in the SAE architecture.

The MRM-TE and the MRM-NET components

operate in close cooperation with technology-specific

radio resource management. Since the MRM-TE com-

ponent handles MRM terminal-side operations, it

must be linked to the corresponding radio resource

and mobility control as implemented technology-

specifically in the terminal. The MRM-NET compo-

nent in turn is placed as close as possible to the

network-side radio resource management controller.

For trusted domains such as a 3GPP or 3GPP2 net-

works, this would be within the corresponding radio

network controller, i.e., the RNC, base station con-

troller (BSC), or evolved node B (eNodeB). For

untrusted domains, however, the MRM-NET should

be located in the closest trusted network node within

that untrusted domain. Since the MRM signaling takes

place at the IP-level in these non-3GPP networks,

communication with the terminal-side MRM is

secured through application of Internet Protocol secu-

rity (IPsec) tunnelling. In the case of an interworking

WLAN, the MRM-NET component would therefore

be placed in the corresponding enhanced packet data

MRM-TE MRM-NET MRM-HAMTerminal Node B RNC

MRM: NEIGHBOUR CELL INFORMATION REQUESTRetrieve cell

informationon accessible RATs:

Adaptation andabstraction

NET

MRM: NEIGHBOUR CELLINFORMATION RESPONSE

LINK MEASUREMENT REQUEST (setup)

MEASUREMENTCOMMAND

(SNR, path loss)

LINK MEASUREMENTREPORT (data rate)

MEASUREMENTREPORT

(SNR, path loss)

LINK MEASUREMENTREPORT (data rate)

Can be a trigger for a potentialchange of RAT

MEASUREMENTREPORT

(SNR, path loss)

LTE—Long Term EvolutionMRM—Multi-radio managementMRM-HAM—MRM heterogeneous access managementMRM-NET—MRM radio access networkMRM-TE—MRM terminal entityNET—Network

RAT—Radio access technologyRNC—Radio network controllerRRC—Radio resource controlSNR—Signal-to-noise ratioUMTS—Universal Mobile Telecommunications System

(repeatedly)

~ ~ ~ ~ ~ ~ ~

RRC: MEASUREMENT REPORT

RRC: MEASUREMENT REPORT

RRC: MEASUREMENT CONTROL(setup)

Figure 8.Signaling flow obtaining LTE candidate link measurements for a terminal currently served by UMTS.


the same radio network controller. As a result, any

signaling between both components would be node-

internal, thus avoiding additional signaling load on

external links and reducing delay times. However, in

this case, configuration information and the accumu-

lating up-to-date load information have to be exchanged

between neighboring MRM-HAM entities, causing addi-

tional signaling traffic. In a centralised scenario, as

shown in Figure 9, the MRM-HAM resides outside the

RAN of any technology, i.e., within the core network.

gateway (ePDG) node, but not in the wireless

access gateway (WAG) or the access point (AP), since

these nodes are parts of the untrusted domain.

There is no similarly obvious placement for the

MRM-HAM component within the network, since

the MRM-HAM is focused on radio resources yet func-

tions on top of managed radio technologies. Two alter-

native placements can be considered, each having

different benefits. In a collocated scenario the MRM-

HAM is placed near the MRM-NET component within

Figure 9.Example of the mapping of MRM functions onto the 3GPP architecture.

GERAN

GbBTS BSC

Abis

Rx�

Iu

S7

SGSN

GPRS core

S3S6

UTRAN

RNCNode B

PCRFS4

MME

HSSIur

SGi

X2

E-UTRAN

S11

SAE servinggateway

SAE PDNgateway

S1-MMES5/8

MRM-HAM

X2ePDGWi

eNodeB

eNodeB

Evolved packet coreS1-U

MRM-NET

S2a S2beNodeB

3GPP—3rd Generation Partnership ProjectASN—Access service networkBSC—Base station controllerBTS—Base transceiver stationEDGE—Enhanced data rates for GSM evolutioneNodeB—Evolved node Be-PDG—Enhanced packet data gatewayE-UTRAN—Evolved UTRANGERAN—GSM EDGE radio access networkGPRS—General packet radio serviceGSM††—Global System for Mobile Communications††

HSS—Home subscriber serverIMS—IP Multimedia SubsystemIP—Internet Protocol

MME—Mobility management entityMRM—Multi-radio managementMRM-HAM—MRM heterogeneous access managementMRM-NET—MRM radio access networkMRM-TE—MRM terminal entityMRRM—Multi-radio resource managementPCRF—Policy charging rules functionPDN—Packet data networkSAE—System architecture evolutionSGSN—Serving GPRS support nodeUMTS—Universal Mobile Telecommunications SystemUTRAN—UMTS terrestrial radio access networkWiMAX—Worldwide Interoperability for Microwave AccessWLAN—Wireless local area network

†Trademark of the European Telecommunications Standards Institute.††Registered trademarks of the GSM Association.

MRM-TE

MRM-NET

MRM-NET

MRM-NET

IMS/non-IMS PDN

(e.g., Internet)

MRM-NET

MRM-NET

Trusted non-3GPP†

IP access, e.g.,WiMAX

ASNMRM-NET

Untrusted non-3GPPIP access, e.g., WLAN


Here, communication to the served MRM-NET enti-

ties takes place on wired links between different

network nodes. Since the focus of a considered MRM-

HAM entity is spread across several neighboring RANs

of different technologies, less configuration and load

information has to be exchanged with other neighbor-

ing MRM-HAM entities focusing on different adjacent

RANs in this scenario.

The first steps towards an MRM architecture have

been taken with the 3GPP LTE/SAE Release (Rel.) 8

standardization. However, only a terminal based solu-

tions has been defined, supported by a standardized

access network discovery and selection function

(ANDSF) [8]. Compliant with this approach, the

ANDSF is to be extended towards an MRM-HAM com-

ponent with network control of the terminal’s RAS,

leading to a so-called “policy based terminal triggered

ANDSF decided access selection” [2–4]. This solution

combines advantages of network-based decisions with

terminal-based decisions, where terminal decisions

reflect policies distributed by the network. The solution

is characterized by a significant accuracy of handover

decisions and a low amount of signaling traffic between

processing network nodes. This distribution of the opera-

tional effort between the UE and the ANDSF considers

all relevant information without increased signaling

effort, because decision steps are prepared and calcu-

lated at the origin of the information.

This extended ANDSF collects information about

RANs; provides the terminal with policies, neighbor-

hood information, and further assistance data; and

carries out access selection decisions based on infor-

mation received from the terminal, RANs, and from

other databases. The terminal provides measure-

ments, conducts measurement evaluation, and trig-

gers access selection based on link measurements and

configurable thresholds. As a result, the terminal

either receives a handover command and initiates

handover execution, or requests new assistance data

from ANDSF.

This approach was presented to 3GPP and

received support [2–4]. Due to imminent finalization

of 3GPP Rel. 8, however, it was deferred to 3GPP Rel.

9. An aspect of the MRM concept that proposes a

generic framework for the signaling and handling of

UE capability information, promising a simplification

in the treatment of RAT-specific capability informa-

tion, has been adopted by 3GPP [1].

Proof of Concept by DemonstratorIn order to validate the MRM concept, a demon-

strator [14, 18] has been set up comprising two dif-

ferent radio access networks and a dual-radio mobile

terminal. Generic MRM instances are integrated in

the terminal, the core network, and the access net-

works of each RAT. The demonstrator supports the

Internet Protocol version 6 (IPv6) mobility protocol

[27] during ongoing services of different QoS classes:

file transfer via File Transfer Protocol (FTP), Web

browsing via Hypertext Transfer Protocol (HTTP),

video streaming via Real Time Transport Protocol

(RTP) and video calls via SIP/IMS. MRM interfaces

are specified and implemented between the MRM

instances based on the Diameter protocol, an inter-

face for cross-layer interaction to the MIP kernel func-

tions [20] of the terminal, and an interface to the

AAL. The latter has been implemented for an Alcatel-

Lucent 3GPP high speed downlink packet access

(HSDPA) base station (NodeB) as an overlay cell and

an orthogonal frequency division multiplexing

(OFDM) 802.11a-based hotspot. Real radio signal

strength measurements are acquired. The movement

of the dual-radio UE is emulated through changes to

link performance induced by a radio frequency (RF)

attenuator at the OFDM antenna. Compatibility

between Internet Protocol version 4 (IPv4) and IPv6

devices is achieved by IP tunnelling mechanisms. The

demonstrator setup for the distributed MRM scenario

is shown in Figure 10.

The feasibility of the MRM concept and the scala-

bility by MRM distribution were verified successfully.

The MRM-NET triggers handover decisions in a central

or co-located MRM-HAM based on abstracted radio

link measurements, radio bearer type, preferences and

cell load. MRMM instructs the UE to perform a MIPv6

handover between the two heterogeneous RATs. The

trigger levels, decision algorithm, and the number of

active radio interfaces during handover (make-before-

break versus break-before-make) can be configured.

The resulting handover performance is determined by

user-perceived service interruption and by measure-

ments of packet loss and transmission time.


The usage of MRM neighborhood information has

been shown to decrease OFDM scanning time from

about half a minute to only a few seconds for a full

scan. But this alone cannot prevent the interruption of

running services during MIP handover. Demonstrator

experiments reveal that proactive measurements and

a timely triggered handover preparation (make-

before-break) are essential for seamless handover. For

a completely lossless handover, optimized MIP imple-

mentations are required, since a binding update can

overtake packets on the fly by as much as 80 mil-

liseconds (msec) between the OFDM and the UMTS

uplink of our demonstrator. This finding resulted in a

proposal for the optimization of make-before-break

handover in PMIP. [11, 30].

ConclusionFourth generation wireless networks will consist of

multiple radio technologies requiring intelligent inter-

working solutions. The multi-radio management

concept presented here is one necessary step towards

a pervasive and effective integration of current and

future access technologies.

MRM handles the differences between hetero-

geneous access technologies in a unified way by

abstraction from RAT-specific parameters and adaptation

OFDM access networkOFDM RAN IPv4 domain

UMTS/HSDPA access network

Core networkIPv6 domain

SignalionOFDM access point

IPv4

IPv6

MIPv6home agent

IPv4

IPv6

MRM-NET

MRM-HAM

SignalionOFDM station

MRM-TE

OFDMcontrol

OFDMcontrol Access

router

Qualcommmobile

IPv6 Core domain SIP@Alice

Accessrouter

UMTS/HSDPAcontrol

HSDPA—High speed downlink packet accessIP—Internet ProtocolIPv4—Internet Protocol version 4IPv6—Internet Protocol version 6IMS—IP Multimedia SubsystemMIPv6—Mobile IP version 6MRM—Multi-radio management

Node B

IPv4

Laptop

MRM-HAM—MRM heterogeneous access managementMRM-NET—MRM radio access networkMRM-TE—MRM terminal entityOFDM—Orthogonal frequency division multiplexingRAN—Radio access networkSIP—Session Initiation ProtocolUMTS—Universal Mobile Telecommunications System

UMTS RAN IPv4 domain

Applicationserver

IMS SIP@ Bob

User terminalTerminal IPv4 domain

MRM-NET

MRM-HAM

UMTS/HSDPAcontrol

Figure 10.Setup of the MRM demonstrator with HSDPA and OFDM access networks and a dual-radio terminal.


to RAT-specific functionality in an adaptation and

abstraction layer. The proposed general approach

reuses existing protocols where available and com-

plements them with generic MRM protocols where

necessary. This leads to a significant reduction of stan-

dardization and implementation efforts compared to

bilateral interworking solutions between each pair of

radio access technologies.

The MRM functions and architecture, as well as a

possible integration of MRM into the 3GPP SAE archi-

tecture were discussed in detail. The key functionality

of MRM is a network-based radio access selection

mechanism that considers radio link performance,

resource usage, and user and operator preferences.

For seamless inter-technology handovers, MRM syn-

chronizes IP mobility protocols with link and session

layer procedures. This approach provides the follow-

ing benefits for multi-radio infrastructure for 4G:

• Flexibility for operators to deploy in their net-

work the RATs best suited to provide their sub-

scribers with mobile services in each location (city,

rural, or on the road),

• Common resource and mobility management,

offering the operator the potential to optimize

network usage and revenue by selecting the most

efficient RAT for each service,

• Scalable generic algorithms for network assisted

inter-RAT access selection, tunable according to

the operator’s strategy (e.g., to maximize resource

usage, capacity, user satisfaction, fairness, and rev-

enue), and

• Minimizing measurement requirements on UEs

by utilizing network status knowledge for neigh-

borhood indications and measurement configu-

ration.

The improvement of network performance by

multi-radio access selection algorithms has been vali-

dated in multi-cell multi-RAT system simulations.

The feasibility of the MRM concept and the distributed

MRM architecture have been proven by network simu-

lations investigating signaling and processing efforts.

Additionally, simulations have shown that proactive

preparation of the most attractive target cell can sig-

nificantly increase the probability of seamless execu-

tion of the handover. Finally, the MRM concept has

been realized and validated in an MRM demonstrator

offering optimized network-based access selection and

seamless inter-technology IP-based mobility between

a cellular UMTS/HSDPA network and a WLAN

hotspot during ongoing multi-media sessions.

This MRM concept is proposed as a basis for stan-

dardization and realization of fourth generation wire-

less networks.

AcknowledgementsThe authors would like to acknowledge the con-

tribution of the following former and present mem-

bers of the Multi-Radio Management team and

cooperating partners: Anton Ambrosy, Ulrich Barth,

Harald Eckhardt, Dirk Hofmann, Ingo Karla, Edgar

Kühn, Ingmar Blau, and Christian Müller.

This work has been partly funded by the

European Commission within the Sixth Research

Framework Program Ambient Networks project

and the German Federal Ministry of Research and

Education projects ScaleNet and WIGWAM.

*Trademarks3GPP is a trademark of the European Telecommunications

Standards Institute.GSM and Global System for Mobile Communications are

registered trademarks of the GSM Association.

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[20] Helsinki University of Technology, Laboratory forTheoretical Computer Science (TCS), “MobileIPv6 Implementation for Linux, MIPL,” GO-CoreProject, June 2004, �http://go.cs.hut.fi/�.

[21] Institute of Electrical and ElectronicsEngineers, “Local and Metropolitan AreaNetworks—Specific Requirements—Part 11:Wireless LAN Medium Access Control (MAC)and Physical Layer (PHY) Specifications,”ANSI/IEEE 802.11, 1999 Ed. (R2003),Reaffirmed June 2003.

[22] Institute of Electrical and Electronics Engineers,“Draft IEEE Standard for Local and MetropolitanArea Networks—Part 16: Air Interface for Fixedand Mobile Broadband Wireless AccessSystems—Amendment for Physical and MediumAccess Control Layers for Combined Fixed andMobile Operation in Licensed Bands,” IEEEP802.16e/D5a, Dec. 2004.

[23] Institute of Electrical and ElectronicsEngineers, “Draft Standard for Local andMetropolitan Area Networks—SpecificRequirements—Part 11: Wireless LAN MediumAccess Control (MAC) and Physical Layer(PHY) Specifications—Amendment: RadioResource Management of Wireless LANs,”IEEE P802.11k/D7.0, Jan. 2007.


[24] Institute of Electrical and Electronics Engineers,“Draft IEEE Standard for Local andMetropolitan Area Networks—Part 16: AirInterface for Fixed and Mobile BroadbandWireless Access Systems—Management PlaneProcedures and Services,” IEEE P802.16g/D5a,Apr. 2007.

[25] Institute of Electrical and Electronics Engineers,“Draft Standard for Local and MetropolitanArea Networks—Specific Requirements—Part11: Wireless LAN Medium Access Control(MAC) and Physical Layer (PHY)Specifications—Amendment: Enhancements forInterworking with External Networks,” IEEEP802.11u/D1.0, May 2007.

[26] Institute of Electrical and Electronics Engineers,“Draft Standard for Local and MetropolitanArea Networks: Media Independent HandoverServices,” IEEE P802.21/D8.1, Feb. 2008.

[27] D. Johnson, C. Perkins, and J. Arkko, “MobilitySupport in IPv6,” IETF RFC 3775, June 2004,�http://www.ietf.org/rfc/rfc3775.txt�.

[28] F. Kalleitner and J. Eisl (eds.), “MobilitySupport: System Specification, Implementationand Evaluation,” Ambient Networks Phase 2,Project IST-2004-027662, Deliverable D20,European Union 6th Framework Program (FP6)IST-2004-2.4.5, Dec. 2007, �http://www.ambient-networks.org/deliverables.html�.

[29] R. Koodli (ed.), “Mobile IPv6 Fast Handovers,”IETF RFC 5268, June 2008, �http://www.ietf.org/rfc/rfc5268.txt�.

[30] M. Liebsch, A. Muhanna, O. Blume, “TransientBinding for Proxy Mobile IPv6,” IETF InternetDraft, MIPSHOP Working Group, October 24,2008, �http://tools.ietf.org/ id/draft-ietf-mipshop-transient-bce-pmipv6-00.txt�

[31] C. Perkins (ed.), “IP Mobility Support for IPv4,”IETF RFC 3344, Aug. 2002, �http://www.ietf.org/rfc/rfc3344.txt�.

(Manuscript approved August 2008)

ROLF SIGLE is team manger in the Radio SystemOptimization department within the BellLabs Wireless Access Domain in Stuttgart,Germany. He received a diploma degree inelectrical engineering from the Universityof Stuttgart. He is responsible for the Multi-

Radio Infrastructure for 4G project. His researchinterests are radio access network architecture, radioresource management, and system performanceoptimization.

OLIVER BLUME is a research engineer in the RadioSystem Optimization department within theBell Labs Wireless Access Domain inStuttgart, Germany. He holds a degree inphysics from the University of Hamburg,Germany, and a Dr.-Ing. degree in

integrated optical amplifiers from the TechnicalUniversity of Hamburg-Harburg. Dr. Blume’s currentresearch interests are in wireless communications, radio research management, and IP mobility protocols.

LUTZ EWE is a member of technical staff in the RadioSystem Optimization department within theBell Labs Wireless Access Domain inStuttgart, Germany. He received a diplomain physics at the University of Giessen, and adoctoral degree in micro system technology

at the University of Duisburg, Germany. Dr. Ewe’scurrent research focus includes collaboration ofheterogeneous radio access technologies and selfoptimization strategies in radio access systems.

WIESLAWA WAJDA is a research engineer in the RadioSystem Optimization department within theBell Labs Wireless Access Domain inStuttgart, Germany. She received a degreein electrical engineering from the TechnicalUniversity Wroclaw, Poland. Her research

interests are focused on system architectures andtelecommunication system concepts. ◆

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Multi-Radio Infrastructure for 4G