A mobile phone user interface is an integrated entity that is built from several hardware and software interaction components (example in Figure 5.2). These technical factors and details define the familiarity, look and feel, and usability of a mobile phone.
Keyboard, text input keys
Navigation tool
One-hand operating Ergonomics,
balance, touch and feeling
Softkeys
Familiarity Interruption
Audio, voices
Battery replacement
User support: Manuals
& Documentation, Web support, On-line help
Accessories Power on/off
Call management keys
Services (Operators, service providers)
Applications Display,
interaction, icons, indicators
Handling the SIM card.
Figure 5.2. Factors affecting to usability in a mobile phone.
5.2.1 Mobile phone user interface and external interface
We can divide these interaction components to the three different categories: User Interface, External Interface and Service Interface (Table 5.1).
The User Interface category includes input and output devices and techniques, industrial and mechanical design and application (software) factors. User support elements, accessories, PC connectivity and downloadable software form the External Interface of a mobile phone. External interface is the interface that helps to use the device but is not physically part of it. Though it is important part of the overall usability, it is too often omitted in usability engineering. Service Interface is provided by the wireless network, as described in Section 5.2.2.
Interface Category Components
1. User interface
Input tools (functionality, industrial and mechanical design)
Navigation tool, Softkeys, Keypad/
keyboard, Special keys (Power, Call management, Voice)
Display Icons, Indicators, Language,. Familiarity, Localisation
Audio, Voices Ringing tones, Quality, Interruption Ergonomics Touch and feeling . Slide, one-hand
operating. Balance, Weight, Size Detachable parts SIM card, Battery, Snap-on cover Communication method Radio link, Bluetooth, Infrared, Cable Applications Fun, Utility, Usability
2. External interface
User Support Local help, Manuals, Documentation Accessories Charger. Hands-free sets, Loopset, External
keyboard
Supporting software PC software, Downloadable applications 3. Service
Interface Services Availability, Utility, Interoperability Table 5.1. Interaction elements and factors that affect to mobile phone product usability Input tool of a mobile phone is typically a keypad. Sometimes voice input is possible for phone operation. Voice is the primary information and communication channel in basic phones. Data communication is increasingly important channel for smart phones and wireless information devices. Mobile phone interface is operated with special control tools, such as navigation and call management keys. Output is given as audio (speaker) and as display activity (icons, indicators). The industrial and mechanical design define whether the phone is pocketable, user can use it with one hand and has a nice touch, if the SIM card and battery handling are easy, and if the buttons are easy to press.
Mobile phone manufacturers are developing and maintaining brand specific UI styles. This means, that usability is also affected by such factors as, for example, familiarity and consistency of terminology between products.
5.2.2 Mobile phone Service Interface
In order to understand some characteristics of mobile phone use, we need to separate user interface from service. Service interface is users’ view of an available operator or service provider's service through the phone UI. Service interface enables access to existing cellular infrastructure, such as basic voice communication, and services provided through the infrastructure, such as the Internet. For example, WAP browser is part of the user interface, but a WAP service belongs to the service interface. Due to mobile phone interaction and UI design conventions it is sometimes difficult and confusing for the user to understand which part of the service is phone functionality and which belongs to the service.
The next figure (5.3) provides an example. In Internet browsers, such as Netscape, there is always user-defined function “Home” available in the menu (Figure 5.4). “Home” takes the user always to the same place making it context independent. There is similar function in some WAP browsers, for example in Nokia 7110 where the exact Internet address (URL) of "Home" item in Service options list depends on the currently used service, i.e. it is context dependent. Other options (Bookmarks, Select, Use number) are provided by the phone UI and they have always the same meaning, i.e. they are context independent. In addition to that, due to the underlying WML protocol, the service provider can define whether Home option is available at all. The users are not able to guess or know where in the user interface or in the service they are taken when option “Home” is selected.
Figure 5.3. Mobile phone as service interface (Nokia 7110). Notice the double “Select”.
Figure 5.4. “Home” in Internet browser.
In cellular networks, services have initially been voice communication, voice mailbox, text messaging and simple data services provided by the network operators. Cellular networks and terminals are evolving to the direction where IP (Internet protocol) networks and cellular networks are converging, and the same services are available in both environments. For example, banking services are available in Internet with WWW browsers, and the same services can be used with a mobile phone either with voice interface or via WAP browser. Convergence will also create new services that are based, for example, on multimedia messaging, positioning technologies, or remote control capabilities. The key factors in the service interface are cost, quality, availability, utility and interoperability of the services.
Mobile services are not yet mature. Many current (WAP and text messaging) services are difficult or slow to use, or to take into use. Services are not usable. This was reported by Finnish consumer service department (Kuluttajavirasto 2001) in a market review about 491 mobile services. A special problem is that consumers are often billed even in the case when the connection fails or is interrupted.
5.2.3 Structuring mobile phone interfaces
The three mobile phone interfaces can be organised to a hierarchical system (Figure 5.5).
4. Accessories
3. Phone UI 2. Services
1. Network, infrastructure
Is dependent External interface
User interface Service interface Figure 5.5. Interface hierarchy
Each interface in Figure 5.5 is dependent on underlying layers. For example, Services can't be accessed without network structure, Phone UI is not useful without Services, and Accessories are not functioning without a phone. In several usability tests I have observed that user problems are most often related to the highest level in the hierarchy. For example, in normal phone use the problems in network connection or failures in service use are often blamed to be phone UI issues, or if user has problems with headset, the specific accessory is blamed for problems.
5.2.4 Operators and service providers
The user experiences a usability of a mobile phone in specific context of use by using the phone through an available operator service (cellular network) in order to connect a service (or person) that provides the content. The experienced usability is an outcome of these all.
The network operator, that provides the basic connectivity, forms the communication platform for a mobile phone. Depending on the network quality and accessible services the user is able to perform his tasks. There are situations when the user is not able to use his phone temporarily or permanently. To manage network dependent problems the phone needs functionality to inform the user about the status of the network and about the available services. In some cases, a service may not be automatically available for the user. For example, voice mail is a network function that typically needs to be activated or purchased in addition to the basic service.
A service provider provides a specific service for the user. For example, Internet access is sometimes provided by some other organisation than the network operator. Especially in the case of Internet based services, such as WAP and email, Internet access may require configuration in the phone as well as agreement with the service provider (in order to be able to bill the user).
5.2.5 Feedback and feedthrough
Mobile phones enable communication between user and different types of terminals via cellular networks. The physical distance between the two ends can't be predicted or seen in the phone
user interface. The communication quality is dependent on the prevailing capabilities of terminals and network systems. Dix et al. (2000) noted that feedback (seeing the results of one's own actions) and feedthrough (seeing the effect of other user's actions) are essential for interactive mobile systems. Communication delays and failed connections are more usual than in wired communication.
Feedback is a user interface issue that often can be analyzed and improved as part of product development. Feedthrough is a service interface issue that can't be fully analyzed or improved as part of product design, because it is dependent on the network latency and bandwidth. Mobility brings yet more issues, such as small screens and restricted input devices. Slow feedback and feedthrough problems are familiar for mobile phone users. Improving feedback and feedthrough related problems is an identified and strong driver in the development of mobile terminals and cellular network technologies.