CONTENTS

Introduction
DECT/GSM dual mode terminals
UMTS migration aspects of DECT/GSM integration
UMTS multimode terminals

1 Introduction

During the recent years, growth of new telecommunication services have been more rapid than ever. Provision of mobility and personal services are keywords in the elaboration of these scenarios. A combination of two, or more, systems are one of the most likely concepts to realise the 3rd generation of systems for Personal Communication. In Europe, DECT, GSM and ISDN have been identified as the focal points for the work on migration into the 3rd generation, UMTS. One extremely powerful combination in this concept is to attach DECT radio access systems to the GSM network. By integrating DECT and GSM, operators could increase the capacity of their networks in traffic dense areas, increase the service quality and extend the GSM service penetration into environments which are not suited for the GSM radio interface. With DECT and GSM terminal functionalities integrated into the same handset, the user will experience the advantage of carrying only one terminal instead of two but he will also be provided with a personal communication terminal that enables optimised cost, quality and service performance in addition to continuous reachability.

This paper addresses the aspects of DECT/GSM dual mode terminals that are identified as relevant for UMTS scenarios, i.e. multi mode terminals operating in multi network environments.

2 DECT/GSM dual mode terminals

Within ETSIs joint DECT/GSM subproject, dual mode terminals for DECT and GSM have been studied with the purpose of identifying how the existing DECT and GSM TBRs can be applied for type approval of DECT/GSM dual mode terminals. Especially the essential requirements on waste of radio spectrum and harming of networks have been addressed. (GSM meaning here GSM900 as well as DCS1800.)

Several different types of dual mode configurations have been identified: Terminals that can only work in one mode at the time and that change mode manually or automatically. The automatic attachment in one mode can be initiated when coverage for the other is lost or it can be initiated when the terminal after continuous scanning identifies a prefered coverage for the other mode. Dual mode terminals with two subscriptions can possibly be registered in both modes - on different networks - simultaneously although they can only be in active traffic in one mode at the time. More advanced dual mode terminals could maybe be in active traffic in both modes at the same time, e.g. speech call on GSM and data call on DECT or receiving a SMS on GSM while having an active speech call on DECT.

Other important aspects of dual mode terminals are related to the number of subscriptions in the terminal, the access profyle that the DECT part is compliant to and the services that supports the dual mode terminal user. If the DECT part of the dual mode terminal is compliant to the DECT/GSM InterWorking Profyle, only one subscription has to be supported - the GSM subscription. The terminal could then be used for increasing the network capacity in dense traffic areas, the link quality in indoor environments and the service level (e.g. higher data rates over DECT). If the DECT part is compliant to the Generic Access Profyle (or the CTM or ISDN Access Profyles) the terminal must support at least two subscriptions - one for DECT and one GSM subscription. This terminal could be supported by a one number service by an operator (i.e. one personal number connection the GSM number and the DECT number) that delivers incoming calls to the networks and terminal mode where the dual mode terminal is registered. It could, though, be used also for the purpose of reducing the number of terminals that the user needs to carry around. If it could be registered, and listen for incoming calls, on both modes at the same time it would make the user available on his two regular phone numbers just a two terminals would.

Important problems to solve by regulations is that the dual mode terminals do not overload networks with excessive signalling due the automatic switching of networks. It must also be guaranteed that the dual mode terminal does not decrease the reachability for the user due to missing of pagings in one mode when it is scanning the other mode for alternative networks.

3 UMTS migration aspects of DECT/GSM integration

In the Global Multimedia Mobility report [PAC EG5], the conceptual model of network architectures is divided into four domains:

• Application Services Domain (service nodes)
• Core Transport Network Domain (IN + e.g. GSM NSS, N- & B-ISDN, IP-based)
• Access Network Domain (e.g. GSM BSS, DECT, UMTS GRAN + fixed accesses)
• Terminal Equipment Domain (single and multi mode terminals)

Each entity within a domain is considered to be connected to several entities in other domains, see figure 1.

In the same way as the new UMTS radio interface and the UMTS Generic Radio Access Networks is intended for connection to several core networks and delivery a variety of services and applications, the DECT access network will be used in a similar way. DECT interworking to GSM, ISDN and data networks is already specified. In relation to the study on a 2 Mbit/s radio for DECT, the feasibility of interworking to B-ISDN, ISDN Primary Rate and other 2 Mbit/s interfaces will be studied. The DECT 2 Mbit/s radio would have to be clearly evaluated with respect to the UMTS radio interface so that they can be optimised for use in certain environments and an optimum access tollbox is created for the operators.

The standardisation of DECT/GSM integration and DECT/ISDN interworking is believed to be an important step on the way to realise the UMTS migration scenario. Many of the general problems related to interworking between core networks and access networks and the operation of multi mode terminals in multi network environments has already been addressed in the DECT/GSM standards.

4 UMTS multimode terminals

The UMTS scenario of figure 1 would cover ordinary single mode GSM and DECT terminals, GPRS terminals as well as speech and data terminals working only on the new UMTS radio interface. Since these radio networks are complementary, multi mode terminals capable of operating on two or more of the radio interfaces should be considered in order to be able to manage provision of a 'complete' set of services over the limited radio medium. It is expected that a lot can be learned from the DECT/GSM dual mode terminals when evaluting the requirements on different combinations.

Some things may, though, differ for the UMTS multimode terminals. Most likely, they will use subscriptions that integrate a variety of features although relayed via different access providers. The requirements on the different radio systems in the multi mode terminal are to support a as uniform set of services as possible. While the DECT/GSM dual mode terminal development initially has some degree of freedom for the manufacturers to construct their dual mode terminals by just combining two existing single mode terminals into the same casing, the UMTS multi mode terminal will from the beginning have stronger requirements imposed on it. The DECT/GSM dual mode terminal with the DECT part compliant to the DECT/GSM InterWorking Profyle is likely to be able to fullfill these requirements.