Adaptivity in Mobile Devices

As mobile devices, e.g., smartphones, tablets, or notebooks, become more and more integrated into the everyday living of a person, mobile devices are exposed to continuous changes in their environmental context. This is especially the case for smartphones, because most people have their smartphone with them when they are mobile and change their location. Naturally, every device is differently constrained in its capabilities due to its mobility, production costs, and user-spe- cific requirements, e.g., lightweightness. Thus, it depends on the capabilities of a smartphone how the contextual environment may be exploited, e.g., a WLAN chip has to be integrated in the device to connect to a WLAN access point in the contextual environment. However, the capabilities of a smartphone may change over time, e.g., the battery is continuously drained at runtime or the device may be upgraded. An additional category, which influences the adaptation of a smart- phone, are the activities the user imposes on the device itself, i.e., the usage of the device. Every contextual category states certain requirements and together they restrict the possibilities in which a device is able to adapt itself.

As depicted in Figure 2.1, if the user sits at home, is reading an eBook, and the smartphone reaches a low battery threshold, the device has to find a suitable configuration within the highlighted plane that satisfies all contexts. Note that the contextual categorization location, device, activities is a matter of granularity. Therefore, additional contextual categories are imaginable, e.g., network, service, quality, or social context [PNS+00,RDN06].

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Figure 2.1:Adaptation Dimensions of Mobile Devices

Location. Depending on the contextual location, smartphones provide the means to access a large variety of available ubiquitous services. In recent years, the availability of these ubiquitous and mobile services have significantly in- creased due to the different form of connectivity provided by mobile devices, e.g., WLAN access points, cellular networks, or GPS navigation [Yan12]. To provide an optimum of service functionality smartphones have to exploit their surrounding environment, e.g., using a WLAN connection if an access point is available. Thus, a smartphone has to cope with the mobility of its user. Figure 2.2 depicts this problem. A user expects different functionality or services, i.e., goals, depending on the contextual situation of the smartphone.

Figure 2.2:Contextual Situations of a Mobile Devices

Example 2.1 (Impact of Mobility on a Smartphone).

Figure 2.2 depicts several contextual situations and in each situation the user expects different functionality or a different behavior. If the smartphone is con- nected to a desktop Personal Computer (PC) the smartphones becomes an external hard drive. An example for a very location sensitive situation is driving in a car, where the smartphone becomes a navigation device. Thus, the goal of a

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ament smartphone may change in different contextual situations. An example for a cost-optimization is the change of situation where the user is within the area of a WLAN access point, e.g., at home, or all communication is processed via a cellular network. Another requirement emerges if the user is in his office, where he has to be able to receive and send emails.

A mobility pattern of the user may be as follows on a working day: “home → car → office → car → home → couch → desktop PC”. However, such a mo- bility pattern on a weekend day will most likely be very different and include different contextual situations, e.g. going to a concert.

This example shows that mobile devices, and especially smartphones, are exposed to continuous changes of contextual situations. These situations occur based on certain mobility patterns of the individual user.

Device Capabilities. A smartphone is only able to access numerous ubiq- uitous services, which are provided by a certain environment according to its own capabilities. These capabilities are either static or change over the lifetime of the device. The Central Processing Unit (CPU) of a smartphone is an example for a static capability, whereas the battery load and available storage space are continuously changing at runtime.

Figure 2.3:Required Capabilities of a Smartphone at a Concert

Example 2.2 (Capabilities of a Smartphone).

According to Figure 2.2 a user wants to take pictures and probably publish them via a social network if he is on a concert. However, this is only possible if the smartphone is able to satisfy the requirements (i) the smartphone has a camera integrated to take a picture, (ii) the smartphone supports the avail- able communication standard, e.g., WLAN, GSM, or LTE, to share the pictures, (iii) there is enough storage space available to store the pictures, and (iv) the smartphone has sufficient energy resources available to execute the tasks.

User Activity. Independent of the external contextual environment of a smart- phone the user may request certain functionality or services on-demand. In this

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case, the smartphone has to respond accordingly and provide the functionality or service according to its capabilities and external ubiquitous services.

Example 2.3 (Usage Impact on a Smartphone).

If the user wants to do some on-line shopping, a connection to the Internet has to be established. However, depending on the contextual environment and local capabilities, a connection is establishable in different ways, e.g., via LTE or WLAN. Depending on the user preferences, the smartphone has to choose between the available connection types, e.g., if the user prefers a cheaper connection, the smartphone would choose WLAN instead of LTE.

Summarizing, independent from the mobility patterns of a user, the device is only able to adapt according to its capabilities. The expectations of a user, i.e. the requirements, depend on the environment and ubiquitous services or interfaces, which are provided. If there is a change in the context of the smartphone, the intentional goal of the smartphone may also change, e.g., the smartphone becomes an external hard drive if it is connected to a PC and it becomes a camera if the user is at a concert. Thus, to optimize the convenience of a user, smartphones have to change, i.e. adapt, themselves automatically to satisfy user-specific and context-specific requirements.

This overview shows that mobile devices, such as smartphones, are self-adap- tive software systems. The next section provides detailed insights into the overall adaptation process of SAS by describing key technical aspects and characteristics of these systems.