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The utilization of use cases in the development of new communications standards and systems is taking on increasing importance. These use cases describe the interactions existing between the user and the system through a prototypical course of actions along with a possible set of alternative courses of action.

In the development and standardization of software radio systems, use cases can play a fundamental role in gathering user requirements. For instance, the European Union 5th

Framework Programme IST-TRUST project is already employing this methodology in order to drive more detailed UML modeling activities which are being used to represent the functionality and interactions of system modules. In this section, some simplified use cases are presented in order to show the reader some of the new possibilities that SDR will allow.

The SDR Forum, according to the functionality of the modules to be downloaded, has defined three different categories of ‘software download’:

† high-level communications and computing applications;

† download protocol entities for modification or changing of the bearer service;

† low-level signal processing algorithms for modification or changing of the communication physical layer processing.

These three categories can be mapped into their main enabled services and the three associated areas of interest for the operators. These areas are:

† advanced applications

† interoperability

† standard platform development

In the next paragraphs the main requirements of each area are discussed. The interoper-ability between standards will be considered first since this area includes many aspects that are also applicable to the other two areas.

6.4.1 Interoperability

Currently, world mobile communications consist of a mixed bunch of different 1G (AMPS, TACS, etc.) and 2G (GSM, IS-95, IS-136, PDC, etc.) cellular standards. Most of these standards are incompatible, so that roaming between them is not possible at all. The so-called 3G (IMT-2000) was hoped to be the solution to this serious problem. However, it failed in this goal and the reality is that at least three different cellular standards (UMTS, CDMA-2000, and UWC-136) may coexist.

Keeping in mind the radio access system evolution described above, it is clear that the ability to adapt the terminal to every existing standard is necessary to ‘survive’ in this multimode and multiband environment; whilst most users may not be global roamers, the main manufacturers, network operators, and service providers are global suppliers, and from their perspective the increasing proliferation of different standards and product variants is undesirable from an economic and logistical viewpoint. This is an important market driver for the interoperability offered by reconfigurable systems. This interoperability between standards generates a set of advantages for the different actors involved. These advantages include:

† Manufacturers will reduce costs and investment requirements because of enlarging the market (not a few technologies but just one technology platform will be able to deal with every radio access system).

† Users will profit from the enhanced roaming capabilities without changing their terminal.

Also it will be easy for them to select the most attractive network (considering costs, quality of service (QoS), offered applications, etc.) from the available set.

† Terminals will be able to incorporate new features dynamically as service technology continues to evolve. This fact makes reconfigurable terminals attractive both to the users and also to the operators, who may be able to reduce their current terminal subsidies.

† Radio transmission characteristics will be optimized according to the environment condi-tions and traffic demands as well as to the service or application desired, increasing the QoS and making a better use of the available resources.

† Operators will be able to reduce the current churn rate, achieving longer client fidelity.

† Operators will be able to improve continuously their QoS, following the modern business trends of Total Quality Management and Kaizen.

6.4.2 Standard Platform Development

This second kind of reconfiguration affects the lower layers of the protocol stack. Its aim is to improve the processes and operations performed by those layers in terms of quality, speed, cost, and functionality.

Normally, mobile terminals will be provided with a set of basic features. Whenever the user wants to upgrade these features, he will need to download a new software module to his terminal. Furthermore, such download may also be initiated by the network, if it needs to reconfigure some of the terminal features in order to ensure the communication will be completed properly (this will be shown in one of the particular use cases proposed later in this chapter).

Some examples of the downloadable software modules included in this category are:

† a new audio codec incorporating new features such as a higher compression rate;

† a new ciphering algorithm improving the system security;

† a new image compression algorithm with better quality and resolution levels.

These software modules will probably come from different sources. This implies that some validation procedures will have to be established by the operators in order to control the quality of these modules. A complete testing process will have to be completed before downloading these modules through the network.

The new capabilities provided by these downloadable modules can be used by the opera-tors as differentiating facopera-tors that allow them to secure important competitive advantages.

Users will add new features to their terminals as they are needed, potentially lengthening their life span. As it was said before, this will also benefit operators because they will be able to reduce the costs of their terminal subvention policy. (Of course, manufacturers will still strive to increase terminal sales, perhaps increasingly selling on the basis of style and fashion rather than technical functionality.)

The requirements for this software download category practically coincide with those of the reconfigurability use case. However, security and validation issues have an even greater importance here, because the software modules belonging to this category affect the lower layers of the protocol stack, i.e. the basis of the whole system. An apparently minor error at this level could be very harmful for the system and hence extreme precautions must be taken.

The fierce competition between network operators forces them to offer something different, something special and useful in order to increase their revenues and market share. Reconfi-guration offers the operators the opportunity to provide their users with higher capabilities improving the QoS. This fact can be used as a marketing tool in order to achieve some of the following goals:

† attracting new customers

† providing best customers with premium services

† decreasing churn rate

Therefore, standard platform development becomes an important marketing and value-creating tool that can significantly improve the quality of the services provided by a certain operator.

6.4.3 Advanced Applications

This last area of interest consists of downloadable software modules affecting the upper layers of the protocol stack (i.e. the application layer). Currently, the WAP technology (and also i-mode in Japan) is beginning to provide some of these services but in a limited way. Software radio technology will incorporate more powerful features and capabilities extending the possibilities of this kind of download. It will be possible to develop client-oriented services with customizable features. This will allow each user to enjoy services completely adapted to his/her own personal tastes and preferences.

Although the network operator is the most interested party in providing these services, this area will also be opened to external developers, service providers, and value added providers, which will compete with each other to maximize their market share. This variety of players implies the need for validation and testing procedures applicable to the different software modules (as was the case for the other two download categories).

The most interesting application areas that have been identified so far are listed below:

† mobile e-commerce

Of course all these applications will be multimedia, incorporating text, audio, still images, and video.

As was said before, some of these applications are already commercially available by means of the WAP technology. Nevertheless, their features and performance are still far away from their Internet counterparts because of the implicit limitations of WAP.

WAP applications currently find three main handicaps:

† Limited graphical capabilities.

† Interface restrictions, which make applications not always friendly to use.

† Poor interaction. Both client/server and JavaScript approaches are not fast enough and have very limited capabilities.

Terminal reconfigurability, combined with 3G devices and interfaces, will solve all these problems, improving application features dynamically as technology evolves.

Furthermore, these new services will result in an increase in client retention (reducing churn) and also will attract new customers. And of course, terminals will not be plain phones any more but multiservice and multifunction open devices.