5G: Service Continuity in Heterogeneous Environments

Wireless Pers Commun (2011) 57:413–429DOI 10.1007/s11277-010-0077-6

5G: Service Continuity in Heterogeneous Environments

Josef Noll · Mohammad M. R. Chowdhury

Published online: 31 July 2010© Springer Science+Business Media, LLC. 2010

Abstract This paper introduces service continuity as the main driver for 5G systems.It addresses user- and service-aspects in recently opened LTE networks, and identifies thesystem challenges. The main challenges are related to radio coverage, especially for theprovision of high data rates for indoor users. The paper covers also network-, user- and ser-vice-authentication as well as user and society requirements. 5G is addressed as a systemof systems in order to provide service continuity. It addresses both technology challenges,user related issues and operator revenue. Collaborative radio and a system availability bea-con are discussed to cope with heterogeneity in 5G. As the SIM card has evolved towards athird-party offering for storage, authentication and payment, functionality of this future SIMis elaborated providing SIM-based service examples. The paper finally addresses serviceoptimization based on light-weight semantic reasoning.

Keywords Mobile · Wireless · 5G · Collaborative radio · Authentication · SIM card ·Semantics

1 Introduction

While mobile telephony serves more than 4.1 Billion people worldwide in 2009,1 represen-tation of the services is still performed using access technology terms. Naming follows theevolution from analogue to digital systems identified as generations. An examples of a 1Gsystem is the Nordic Mobile Telephony (NMT), examples of 2G are IS-95 and GSM, while

1 ITU Media kit, http://www.itu.int/newsroom/media-kit/story9.html.

J. Noll (B)Center for Wireless Innovation Norway, University of Oslo, Oslo, Norwaye-mail: [email protected]

M. M. R. ChowdhuryUniversity of Oslo/UNIK, Kjeller, Norwaye-mail: [email protected]

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414 J. Noll, M. M. R. Chowdhury

an example of 3G is wideband CDMA. The naming of technologies refers to the requirementsset by ITU-R.2

When wideband CDMA was developed discussions started on “what is the next gen-eration”. ITU-R continues the naming of 4G as the fourth generation of cellular wirelessstandards, called IMT Advanced. The IMT Advanced suggest target peak rates of 100 Mbit/sfor high mobility and up to approximately 1 Gbit/s for low mobility [1]. This naming conven-tion is followed by radio researchers, while system engineers pointed already back in 2000to systems covering multiple access scenarios [2].

Network operators such as Netcom3 have recognized the marketing value of the “4G”naming and opened in December 2010 the LTE “4G” network. Long Term Evolution (LTE)does not fully comply with the ITU-R recommendations for 4G, and is therefore regarded asa pre-4G standard.

The IT industry predicts that technology development will continue at the same speed astoday until at least 2025 [3], providing advanced access speed for mobile and wireless devices.Together with increases in antenna system technology such as MIMO the recommended 4Gaccess data rates might be achieved by advanced LTE systems.

The increase in access speed will enable new applications. Kellerer et al. pointed out thatfrom an operator’s point of view, a system beyond 3G (B3G) has to deal with various aspectslike user preferences, system requirements, network architecture, business model, security,and standardization [4]. Thus he moved away from radio access when talking about 4G and5G, and rather opens for a user- or service-centric view on the evolution of mobile systems.

Discussions in this paper take up the user-centric (I-centric) view as introduced by van derMeer et al. [5] and extend it by a service-centric aspect. In Sect. 2 the user perspectives of a5G system are discussed, and Sect. 3 deals with the challenges. These challenges will covertechnological aspects such as radio access and authentication, but will mainly focus on theservice aspects such as applications, device considerations, economics and society aspects.Section 4 will then provide details on the postulation of 5G as a system of systems, address-ing radio-on-demand, collaborative radio, the role of the SIM and service optimization. Theconclusions in Sect. 5 will summarize the findings and provide areas of future work.

2 User Perspective for 5G

This chapter describes the user- and service-perspective of 5G systems, as sketched in Fig. 1.Technology-wise it takes almost 10 years for a system to be developed, as indicated by thearrows left in the time-diagram. Mobile telephony was the first telecom communicationservice in the analog systems. One of the main reasons for introducing GSM was mobiletelephony service provision in European countries, including SMS and data services. 3Gwas introduced to provide roaming on a world-wide base, and compatible standards such asUMTS currently provide multimedia communication in the whole world.

2.1 System and Service Aspects

Systems beyond 3G, as introduced by the Eurescom P1145 project, were supposed to providepersonalized wireless broadband access [6]. Currently access systems such as LTE provide

2 ITU-R, http://www.itu.int/ITU-R/.3 4G launch Dec 2010, http://accelerati.blogspot.com/2009/06/netcom-with-worlds-first-4g-connection.html.

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5G: Service Continuity in Heterogeneous Environments 415

Mobile telephony

Mobile telephony, SMS, FAX, Data

Multimedia communication

Personalised broadband wireless services

2000

Seamless heterogeneity

2020

5G?

1G:

1970 1980 1990 2010

3G:

2G:

B3G:

Fig. 1 Generations of mobile communications—a user perspective on services

wireless broadband with a typical user bit-rate of 10–20 Mbit/s, but will on the longer runsuffer from reduced user satisfaction when being indoor. Further details on these radio topicsare provided in Sect. 3.1.

Mobile broadband is the fastest growing access technology. The total number of mobilebroadband subscribers in key European markets will rise from about 22 million at the end of2009 to over 43 million in 2011.4 As compared to traditional mobile telephony, only about2% of this mobile traffic comes from mobile phones. The dominating part comes from Note-books with inbuilt or USB-modems.5 These customers expect a similar service experienceas known from the fixed network, including other types of services.

The main changes in user expectations towards 5G systems are:

Handsets: The traditional handsets are extended by other form factors such as notebooks,mobile TVs, music players and video recorders.

Applications and operating systems: While more and more applications are web-centric,the total variety of application types is just increasing, covering all types of applets andwidgets as well as specific streaming and gaming applications. A variety of operatingsystems has to be supported such as OS X, Android, S60, and Linux.

Security: Solutions for access authentications such as EAP-SIM, -AKA, Diameter andpassword-based need to be supported, as well as session encryptions and various end-to-end application encryptions. Users will expect that these security mechanisms workseamless even in a handover situation.

Network Technologies: From a network technology point of view not only mobile tech-nologies such as GSM, UMTS and LTE++ need to be supported, but also extensions ofwireless systems such as 802.11 and 802.16. Communication between devices throughe.g. wireless USB will need support, as well as M2M communication towards sensors.

4 http://www.gsmworld.com/newsroom/press-releases/2010/4549.htm.5 Vegard Kjenner, NetCom, Norwegian UMTS Forum, Feb 2010, http://umts.no/index.aspx?pid=30&docid=63.

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All this communication is happening in a wide range of frequencies, spanning from the “dig-ital dividend” bands below 850 MHz towards 5.8 GHz bands for high-speed wireless. Ourexpectation is that context-independent service continuity in heterogeneous environments isthe main challenge for 5G systems.

2.2 Context-Independent Service Continuity

The service continuity refers to the continuity of the same service session without any disrup-tion or with least possible interruption. Users want uninterrupted service experience thoughdue to mobility there are frequent changes of locations, networks, and devices. Thus servicecontinuity should have the goal of being context-independent. Nowadays a user expects acontinuous good quality video streaming though he moves from outdoor to indoor.

Users change to locations which may offer better networks and devices. Due to thedynamic nature of ubiquitous environments continuous service access is one of the mainfactors restricting the deployment of services [7]. This requires continuous monitoring ofsurroundings and a proactive handover scheme, both limiting the time of operation of themobile device. A mobile agent based platform or middleware as suggested in [8,9] mayaddress aspects of service continuity across networks, but complexities involved for derivingthe decisions may hinder real-time service deliveries.

With the advent of mobile devices the service continuity also needs to be ensured acrossheterogeneous devices. A change of location may provide the user with higher processingcapabilities or lower the cost of service usage. For example, a user moving from outdoor toindoor may want to transfer his video streaming from the mobile phone towards a pad-readerwithout or with least possible interruption. Jorstad et. al [10] introduced a service continuitylayer responsible for managing the service continuity. Realizing service continuity acrossheterogeneous devices does not only require information relevant to application layers butalso needs to know about the network resources because the devices may not be connectedto the same network.

3 System Aspects of 5G

This section will address the challenges for mobile communications in a 5G system. In Sect. 1we postulated that the ITU-R requirements for 4G systems might be met by advanced LTE. Auser- and service-centric view as introduced in Sect. 2 and concludes with the statement of aa context-independent service continuity. Our postulation is that only collaborative radio cansatisfy these requirements, which will be further outlined by discussing the main componentsof 5G systems.

3.1 Radio and Wave Propagation

Claude E. Shannon defined the capacity C of a system as being proportional to thebandwidth B

C = Blog2

(1 + P

N0 B

), (1)

with B the bandwidth of the carrier, P the signal power and N0 the noise level of the system.For a given bandwidth B, the maximum range Rmax is a log-function of the signal to noiseratio

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Table 1 Cellular technologies for urban scenario

Frequency Cellulartechnology

Allocatedfrequency(MHz)

Number ofoperators

Bandwidth/operator(MHz)

AvailableLTEbandwidth(MHz)

900 GSM, LTE 30 2 15 5

1,800 HSPA, LTE 65 4 10, 15, 20 10

2,100 LTE 45 3 15 15

2,600 LTE 50 3 15, 20 20

Fig. 2 Simulation of relative capacity in an outdoor to indoor scenario

Rmax = log2

(1 + P

N0

). (2)

Propagation attenuation (free space loss) is proportional to the carrier frequency, thuscarriers such as WiFi have shorter ranges than GSM, but provide higher throughput. Theseindications support the usage of specific access networks for applications, e.g. broadcast forvideo, WiFi for email and ftp services, GSM for short messages, UMTS for voice and mobileservices, and LTE for high-bandwidth services. The experienced increase in air capacity isdue to increased bandwidth B of the communication channel, from BGSM = 200 kHz inGSM to BUMTS = 3.8 MHz in UMTS, and B802.11 = 25 MHz for 802.11b and BLTE =5, . . . , 20 MHz for different operational modes of LTE.

Equations 1 and 2 are valid for free space propagation. We computed the capacity increaseof typical LTE systems at different mobile frequencies, both for free space and for indoorusage with a single concrete wall between the transmitter and the receiver. In order to simplifythe calculations we assume that the SNR of LTE 900 MHz system having 5 MHz bandwidthis 10 dB. To derive the indoor communication capacity, the attenuation of a concrete wall atthe specific carrier frequency has been taken into consideration.

Table 1 presents our assumption for a typical distribution of cellular technologies in anurban scenario citing available bandwidth for LTE at each frequency spectrum.

Figure 2 shows the result of the capacity calculation of LTE systems at different frequen-cies compared to LTE 900 system. The calculations suggest that higher frequencies provide

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Fig. 3 Radio coverage simulation of the inner Oslo area as a function of transmit power

less capacity to indoor users despite the increase of bandwidth. As a result, providing highcapacity services such as video streaming to indoor users from an outdoor base station is achallenging task for a network operator, especially for frequencies higher than 2 GHz.

Radio coverage simulations for 1,800 MHz as shown in Fig. 3 for the inner Oslo areawere performed by H. Dommarsnes from Telenor. The simulations provide an estimation ofindoor signal strengths, being 10–20 dB lower than the equivalent outdoor coverage. To copewith the additional path loss suggests to provide higher Tx power, indicated the Tx = 35 dBmlevel in Fig. 3. However such an over-provisioning will decrease the overall network capacitydue to interference.

Mobile operators have to cope with this radio dilemma, suggesting to use “as much band-width” as possible at low frequencies to provide high-capacity indoor service. Bandwidth inthese lower bands is limited, only 24 MHz are available in the 900 MHz frequency range forstandard GSM operation (see Table 1). Assuming a minimum of two operators in this bandwill limit the capabilities to provide LTE to 10 MHz bandwidth.

Another access challenge for mobile operators is the service selection of users. Offeringhigh-capacity networks will shift the service usage towards streaming instead of download-ing content. Typical examples are music streaming, e.g. Spotify and video streaming fromWeb-TV or YouTube. However, the higher capacity demand does not increase the willingnessto pay. Customers pay for mobility, i.e. having access independent of location, but not forhigh-bandwidth services.

The outdoor to indoor challenge limits effectively the capacity that can be provided inmobile networks, as further outlined in Sect. 4.1.

A second aspect of radio is related to the complexity of the radio interface in the handset.Figure 4 provides simulation results for high-speed download packet access (HSDPA) ascompared to the Shannon limit [11].

As can be seen from the High Speed Data Packet Access (HSDPA) link adaptation curve,there is still some 10–20% improvement possible to provide higher data rates. Such advancesare the goal of the HSPA+ developments. Similar evaluations for LTE were performed byMogensen et. al [12] and are presented in Fig. 5. Both system simulations and link results

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Fig. 4 Capacity of UMTS HSDPA as compared to the Shannon bounds [11]

Fig. 5 Capacity of LTE as compared to Shannon [12]

have practically reached the Shannon limit. A further development of the radio interface hasonly minimum room for advances in data rates, especially taking into account the naturalvariation of the radio channel and the outdoor to indoor dilemma.

3.2 Authentication

Authentication is formally spoken the process of verifying the authenticity of the claims madeby a subject. In telecommunication authentication is used to verify user devices towards thenetwork and the network towards the user devices. The former also requires that a user isauthenticated towards his device. Authentication is only a part of the overall security frame-work of a telecommunication network with the SIM card being the digital representation ofthe user.

EAP protocols (e.g. EAP-SIM and EAP-AKA) are used for authentication in 2G and3G. EAP can be exclusively used for tunneled authentication where authentication isachieved through encrypted tunnel between the client and authentication server. But such

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authentication methods can be subject to active and passive attacks revealing for exampleIMSI in EAP-AKA. The protocol should have provision for mutual authentication to pre-vent such attacks. This has been included in 4G networks, but heterogeneity with seamlessinteroperability has not been achieved yet. From an authentication point of view the seamlessinterworking is critical because each network follows different authentication mechanisms.Thus seamless but secure authentication will be a crucial challenge in 5G networks.

3.3 Form Factors of Devices

A mobile phone is an always-on device evolving towards an always-on computing device.The currently hand-held small form factor device turns into an embedded computing devicerequiring pervasive wireless connectivity.

In order to deal with everyday tasks on the Web, it needs to provide a reasonable screenwith good resolution, powerful processing unit, memory, keyboard, speaker and other exten-sions. It will have integrated capabilities such as digital signal processing or high definitionaudio and video.

The first and the foremost challenge is to ensure adequate power supply to all these sophis-ticated units. Longer battery life, heat dissipation, and power management are some of thecritical issues for these small form factor but high performance devices. In the network side,equipments such as base stations are also getting smaller (e.g. mini BTS, femtocell). Smallform factors here brings advantages such as low energy requirements, low heat dissipation,convenient relocation and easy installation.

3.4 User and Society

A constantly changing environment creates demands for a good understanding of user needsand preferences. The user’s contextual information may tailor the services to be delivered.The user should have full control on the decision and disclosure process. From a privacypoint of view, it is very important for the user to decide which information can be disclosedto the provider. A user-centric control of information is crucial already today, but is absolutelyessential for a upcoming SIM with multiple identity storage capabilities.

One of the results of a multi-identity on the SIM might result in a bandwidth brokeringsystem, where users can select the economically best connectivity for the selected application.

An item of increased concern is the total energy consumption of mobile networks. Cur-rent network optimization is done towards coverage and data rates, not towards minimumenergy consumption or minimum total radiation. Even though there is very little indicationof electromagnetic impact from mobile networks on human beings, regulators might decidethat the overall electromagnetic radiation has to be minimized. Such a decision would needanother optimization of the radio interface. And it would also force mobile and fixed networkoperators to work together.

4 Evolution Towards Collaborative Radio Systems

The previous section has provided challenges for 5G systems, pointing out the radio dilemmabeing of fundamental importance for service delivery to indoor users. This section outlinesa strategy, suggesting collaborative radio systems to provide a good Quality of Experience(QoE) for indoor users. The section first indicates that LTE is already seen as an incorporationof a collaborative system, adding instead of replacing new access technologies. Collaboration

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Table 2 Requirements for 5G, a collaborative mobile system

Generation Frequency Radio Authentication Devices Applications

1G 450, 900 MHz Analog Credential Handset Voice

2Ga 900, 1,800 MHz TDMA SIM, EAP-SIM Handset “1G” & SMS (data)

3Ga 2,100 MHz(1,800 MHz)

WD-CDMA USIM, ISIM,EAP-AKA

“2G” & modem “2G” & multimedia

B3G/4G 450–2,700 MHz OFDMA,SC-FDMA

UMTS-AKA &FutureSIMb

“3G” & inbuilt “3G” & broadband

5G 450–5,800 MHz Collaborativeradio

Servicecontinuity“B3G” &Diameter++

“B3G” & mobileTV, others

Service continuity

a Description of 2G and 3G are based on European standardsb Further details on future SIM are found in Sect. 4.3

between existing 2G and 3G systems will dominate the rollout, supporting our postulationfor an application—and context-specific radio interface.

Collaboration in such a system of systems is of fundamental importance, and should besupported through an indication of available radio interfaces through a system beacon (seeSect. 4.2) as well as seamless authentication (see Sect. 4.3). Handling authentication, provid-ing security and protecting private data is the challenge addressed in this section, where wesuggest that these aspects can be handled in upcoming SIM cards. The last Sect. 4.4 deals withservice integration and optimization, focussing on semantic technologies for context-awareand personalized service provisioning.

4.1 Application Specific Radio Interface

Having to provide high data rates in indoor environments is a challenge which to our under-standing can only be solved by an application specific radio interface. Current technologiessuch as 3G and LTE move towards this approach, providing operations in the frequency range450–2,700 MHz. Table 2 summarizes these trends, indicating in gray areas of collaboration.

Application specific radio concerns the selection of radio interfaces on demand. Thefollowing are the drivers to introduce the notion of radio on demand:

1. Reducing the number of active radio interfaces will minimize the interferences and thusimproves the performance of the network.

2. There are concerns regarding the health effects of radio frequency and microwaveradiations. Reducing the number of active radios also contributes in lowering such healthhazards.

3. Cost of service provisioning varies with technology, e.g. voice over 3G is cheaper toproduce than voice over 2G.

4. Different types of services require different communication bandwidth. For example, alow bandwidth network is enough for voice communication. For such services, switch-ing the device to low energy radio may still satisfy the requirements but consumes lessenergy. In 4G we can have data-only LTE service where the device will only connect to2G/3G circuit-switched network during voice communication.

Collaborative radio can be an instance of radio on demand and an extension of the mobilenetwork. To explain collaborative radio, we need to introduce a scenario which is illustratedin Fig. 6. Numbers in this scenario were provided by Telenor in the Norwegian UMTS forum

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(a)

(b)

Fig. 6 (a) Cell capacity and user bit-rate with low usage and (b) high usage with indoor consumers

meeting in 2010 [13]. Let us assume a mobile cell with a cell capacity of 10 Mbit/s. Userswill only experience this data rate close to the center of the cell. Moving further to the edge ofthe cell will reduce the user data rate to 0.5 Mbit/s (Fig. 6a). If the traffic in the cell increasesthe overall cell capacity will be reduced to 2.5 Mbit/s, and users at the edge of the cell mightonly experience 0.05 Mbit/s.

Let us assume that mobile users require high data rates indoor. Penetration losses throughthe building walls will have a similar effect as moving towards the edge of the network (seesimulations in Fig. 3). Both cell capacity, here: 2.5 Mbit/s and user data rate will be reduced(Fig. 6b).

Providing indoor coverage reduces the cell capacity of the mobile operator, in the givenexample to 1/4 of the original cell data rate. Customers will experience a reduced user band-width. For an operator this scenario might lead to reduced customer satisfaction as well asreduced revenue.

A collaborative radio with handover to an indoor operator will provide the end user withhigh data rates and release network load of the mobile operator by enhancing the overallavailable cell capacity. Such a collaborative scenario demands a service-handover of theconnection to an indoor operator. In a collaborative business model both mobile and indoor

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Fig. 7 The collaborativebusiness model in NFC, creatinga Trusted Service Manager(adopted from [14])

operators have agreements to share the revenue. The handover happened because a demandis created either from the current operator or from the user himself. The following reasonsprompt the mobile operator to perform a handover:

– reduced cell capacity,– reduced customer satisfaction, and– declined revenue.

From the user side, the demand is created as the user experiences much lower data rates whenmoving to an indoor location.

Collaborative business models are known from network infrastructure sharing, wheremultiple operators use the same infrastructure. Collaborative business has also been intro-duced in mobile service provisioning, i.e. Near Field Communication (NFC)6 for paymentand access. Fig. 7 outlines the collaborative business, where mobile operators and banks haveintroduced a Trusted Service Manager (TSM) [14]. A similar business model is proposed forcustomer-owned access infrastructure and will overcome the radio dilemma, with increasedrevenue for operators and enhanced QoE of the customer.

4.2 System Availability Beacon (SAB)

While a collaborative business model between the operator and the customer will solve theradio dilemma in indoor communications, it will not ease the access network selection. Thechallenge for multi-network terminals is how to select an appropriate network, without theneed of scanning through all available frequencies and standards. In GSM the network avail-ability is signaled through the Broadcast Control CHannel (BCCH), which provides bothavailability as well as network quality parameters such as Mobile Network Code (MNC),Location Area Code (LAC), Routing Area Code (RAC) and BCCH Allocation (BA) list.

Assuming co-existence of n generations (e.g. 2G, 3G and 4G systems) in m frequencybands (e.g. 450, 800, 900, 1800, 2100 and 2700 MHz) requires a n × m availability checks.For the selected example this means 18 checks of broadcast control channels, not includingany potential channels of wireless networks.

In order to overcome this cumbersome search we suggest a common system availabilitybeacon—SAB, providing a common pilot channel for all infrastructure-based wireless sys-tems in the “digital dividend” spectrum. Such a SAB signal should be only available in thecoverage area of the network, thus a statistical model for frequency scaling is suggested. TheSAB signal shall further include system information such as capacity, QoS parameters andnetwork authentication information to ease the handover to this system.

6 NFC Forum, http://www.nfc-forum.org.

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The European E3 project7 suggests in a paper by Tian and Feng [15] a Cognitive PilotChannel (CPC) to send necessary network information to the terminals. The projects suggestsusing a public downlink channel to deliver the networks information in order to assist thenetwork selection for reconfigurable terminals. The CPC is the combinational application ofan out-of-band and in-band signal, where the out-band CPC is used to transmit vital infor-mation such as operators information, and the in-band CPC transmits detailed informationabout the network.

As most of the frequency bands are already regulated, this paper suggests to standardizea pilot channel in the “digital dividend” band from 790 to 862 MHz. This band is reservedfor future mobile broadband applications by the European Union and other regions, but asof May 2010 no spectrum has been licensed yet. Thus a part of this band could be reservedfor a system available beacon.

Having introduced access issues like indoor radio access and access availability, theseamless access to services and service optimization are remaining challenges for servicecontinuity in 5G systems.

4.3 Seamless Authentication

Seamless access to heterogeneous wireless networks needs to make the physical changetransparent to the mobile users and thus preserve the ongoing connection in application level.During the vertical handover, an authentication process is performed to ensure the securityof the mobile terminal. As the authentication procedures are different in wireless networks,the associated delay can be an important factor in quality of service of many application.For example, in 3G-WLAN handover the authentication process can take up to hundreds ofmilliseconds which is not acceptable in delay-sensitive applications such as video streaming,VoIP or interactive gaming [16]. 3GPP provided a specific security architecture (3GPP TS33.234 [17]) for 3G-WLAN interworking which is based on the EAP-AKA authenticationprocedure. But the authentication overhead is high due to double execution of the EAP-AKAprotocol. Researchers proposed modified security architectures in 3G-WLAN interworkingreducing such overheads but those may compromise security [18]. A simultaneous networkconnection as suggested in [19] reduces switching time without reducing security.

A short overview over authentication protocols used for 3G and LTE shows already thevariety of protocols being used to allow seamless service access. The Diameter protocolhas been adopted as primary signaling protocol in the IP Multimedia Subsystem (IMS) forAAA and mobility management. It is a protocol for AAA (Authentication, Authorizationand Accounting) which is a successor of RADIUS.

Authentication and key agreement in LTE are based on UMTS AKA, providing strongmutual authentication. Because of the extended key hierarchy in LTE, the intra-LTE hand-overs are fast. The interoperability with non-3GPP networks is based on EAP-AKA. However,the latency due to the key management and mutual authentication can be significant. Effi-cient interworking between UMTS AKA and EAP-AKA can be achieved by avoiding thesignaling with the home domain which may serve 3GPPs seamlessness requirement [20].

Though seamless authentication is a critical issue in the operation of heterogeneous net-works, it can be solved through the combination of existing authentication methods. Keysused in the cryptographic algorithms and security in key management is an important issue.But the security solution should not add undue delay and thus impede the mobility and hetero-geneity of the devices. Secure but fast key management is necessary in interworking between

7 E3 (End-to-End Efficiency) Project, http://www.ict-e3.eu/.

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Fig. 8 Capabilities of anupcoming SIM with USB andNFC interfaces

networks. This paper suggest to handle key management through the SIM card, which hasevolved to become a standardised element in all mobile communications.

Lately SIM-card standardization has succeeded in letting the SIM card become a UniversalIntegrated Circuit Card (UICC) card, including both communication and service provision-ing capabilities. Figure 8 provides an overview over the new functionality, which can besummarized as follows:

– Increased communication capabilities through USB and NFC interfaces,– Compatibility to advanced applications through adopting JavaCard specifications,– Applications support on the UICC including finance, transactions, physical and logical

access, and– Third-party offerings for storage, authentication and payment.

Communicating capabilities have been improved from the 9.6 kbit/s rate of current cardsto around 8–12 Mbit/s using the USB protocol. This is actually one of the driving factorsfor the development of higher bandwidth protocols in the SIM, such as the SCWS andthe implementation of native TCP/IP. Besides the advances in the physical communication,recent releases from SIM card producers such as Samsung and SanDisk have managed todeploy smart cards with powerful 32-bit processors and more than 1GB of memory. Suchan enhanced SIM card will have the capability to handle multiple-operator accounts, andprovide sufficient authentication security for operations in collaborative radio systems.

There are several examples of applications and projects using the SIM card as a trustedelement. Some examples are digital rights management (DRM), mobile-banking, one-timepassword (OTP) solutions, biometric verification, and unified authentication. Some of theseapplications make use of the Near-Field Communication (NFC) capabilities of the SIM asstandardised in [21,22].

The current potential of the SIM towards a local identity manager is further discussed in[23]. This identity management is especially improved with the new hardware changes inthe SIM, and it has triggered the specification of an Identity Management (IdM) frameworkby GSMA [24]. This IdM framework is capable of handling authentication protocols neces-sary for a seamless authentication in collaborative networks. Vilarinho et. al [25] provide anexample of evidence-based trust modeling based on a mobile device. The work suggests that

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the SIM might become a harmonized infrastructure for secure network and service access,as well as protecting the privacy of the users.

The following section addresses service integration and optimization and identifies therole of semantic technologies for mobile service provisioning.

4.4 Service Integration and Optimization

Service integration has two different aspects: network service integration and integration offunctionalities or services. Integration of indoor and outdoor network run by different oper-ators is beneficial not only from a business point of view but also from service continuityaspects.

An example of service integration is voice and data services in LTE. Several optionsare defined: Data-only LTE and Voice over LTE Generic Access (VoLGA). VoLGA is acombination of circuit-switched and packet switched approach supporting voice and datasimultaneously. Voice can be carried over LTE through VoIP. Unfortunately there is no singlemethod in LTE for integrating data, voice and SMS services.

This rather simple example receives a much higher degree of complexity when integrat-ing personalized and context-aware services to a mobile device. A user wants to prioritizerelevant information and services depending on situation, mood, interests, preferences andindividual privacy setting. Economy can also drive userb́ds interest for services for exam-ple user may prefer VoIP than GSM call when connected to a WiFi network. Contextualinformation is getting increasingly important when users are traceable in a wireless net-work. Visibility and location-aware service offerings may depend on context appropriatesecurity measures. For example, an automatic encryption can be turned on while deliveringsensitive information. Limited battery life is a main driver behind the device optimizationwhere devices can sense the context and use the optimum capability for applications. From aservice point of view, service requirements can trigger best-suited applications and appro-priate network parameters.

Most of these aspects require a multi-parameter optimization. Currently, the process ofreaching optimum values are rule-based. This approach is too difficult to manage and main-tain. The goal of a 5G system is to achieve an automatic optimization, e.g. through reasoningbased on semantic technologies. Current semantics and automated reasoning have too muchoverhead and are not applicable to mobile devices with limited battery and CPU capacity.Light-weight semantics and event-based reasoning may address these problems. An exampleof such a light-weight semantic is the adding of machine readable tags to social informationin web pages.

Event-based reasoning can populate the decision results in advance and they are disclosedfor interpretation only when results are queried. An example of such a light-weight imple-mentation was performed in the ITEA-WellCom project,8 where user vicinity to a set-top boxwas used to trigger the event-based reasoning [26]. The resulting rule-set is then populated tothe set-top box to perform content-matching of user preferences with the electronic serviceguide (ESG).

While this scenario addressed user preferences and content match, the more generic 5Gsystem needs to provide personalized and context-aware services.

8 ITEA WellCom project, http://itea-wellcom.org.

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5 Conclusions and Future Work

This paper introduces a user- and service-perspective on the “generation”-term used in thedevelopments of mobile systems. While technological parameters are defined by ITU-R,the mobile customers have set their own requirements. In the first available “4G” networksonly about 2% of the traffic originates from mobile phones, the majority comes from mobilecomputers. Only 20–30% of mobile broadband services are generated outdoor, service usageis predominantly indoor and follows the trends from fixed broadband access, with a highamount of bandwidth-intensive applications such as streaming. Expectations for 5G systemssee the need for integration of heterogeneity in handsets, applications, operating systems,security and network technologies.

The main driver for system aspects in 5G is the radio dilemma, showing that an outdoorto indoor operation will decrease the cell capacity of the mobile cell to less than 30% of acell with limited traffic. Likewise will the user data rate inside a building drop, leading toreduced customer satisfaction and reduced revenue of the mobile operator.

The paper suggests collaborative radio for 5G systems, where users provide their ownhome network. Users in such a heterogeneous environment ask for service continuity, requir-ing trust-based relationships between the mobile and the fixed networks. Such a collaborativebusiness model was lately introduced for Near-Field Communication (NFC), and will pro-vide both increased user data rates for customers and increased revenues for operators. Thepaper further suggests a common system availability beacon—SAB, providing a commonpilot channel for all infrastructure-based wireless systems in the “digital dividend” spectrum.Such a SAB will include coverage, capacity and system information and ease the handoverto other systems. Further research is recommended for seamless authentication, required forservice continuity.

As the SIM card has evolved to a “system within a system”, the SIM might become theharmonized infrastructure for secure network and service access, carrying user- and 3rd-party information. Users require service offers tailored towards their specific situation. Suchservice optimization is based on user-, context-, device- and service-aspects. As reasoningbased on semantic technologies is too resource intensive, the paper suggests light-weightsemantics through event-based reasoning and rule execution.

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Author Biographies

Josef Noll is professor at the University of Oslo in the area of MobileServices. His group ConnectedLife concentrates on the working areasmobile-based trust and authentication, personalised and context-awareservice provisioning, and service continuation in 5G systems. He is alsoChief Technologist in Movation, Norway’s open innovation companyfor mobile services. He is co-founder and steering board member of theCenter for Wireless Innovation Norway and Mobile Monday Norway,the Norway section of the worldwide community for nerds and profes-sionals in mobile services.Previously he was Senior Advisor at Telenor R&I in the Products andMarkets group, and project leader of Eurescom’s ‘Broadband servicesin the Intelligent Home’ and use-case leader in the EU FP6 ‘Adap-tive Services Grid (ASG)’ projects, and has initiated a.o. the EU’s 6thFP ePerSpace and several Eurescom projects. In 2008 he received theIARIA fellow award. He is editorial board member of four Interna-tional Journals, as well as reviewer and evaluator for several nationaland European projects and programs.

Mohammad M. R. Chowdhury received the Ph.D. degree from theDepartment of Informatics, University of Oslo in 2009. He received theM.Sc. degree in Telecommunication Engineering from Helsinki Uni-versity of Technology (HUT). His current research interests includenext generation networks and services, access control, identity manage-ment, personalized service access, and Internet of Things.He is currently working as postdoctoral fellow at UNIK-UniversityGraduate Center, Kjeller, Norway. He was involved in research pro-jects funded by the Norwegian Research Council and the EuropeanUnion. Dr. Chowdhury has published more than 30 scientific articlesin journals, books and international academic conferences. He contrib-uted in several international conferences as technical program commit-tee member, session chair and reviewer. Dr. Chowdhury is a memberof IEEE Communication Society.

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5G: Service Continuity in Heterogeneous Environments

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