User interfaces for mobile phones: New UI challenges and solutions for small mobile communication devices Dr. Ulrich Leiner, Dr. Pia Honold Siemens AG - Information and Communication Mobile, Munich, Germany ulrich.leiner@siemens.com, pia.honold@siemens.com Abstract User- and operator-requirements for mobile devices have multiplied and diversified during recent years. User interface designers have to find solutions for the multifunctional all-round device as well as for the fancy fashion phone. The paper describes trends and demands of the current market; resulting challenges for the user interface designers and user-interface solutions, which are illustrated by examples of latest products. Key words: Handheld devices, user interface design, mobile phones, smart phones, hardware design, miniaturization, user interface design process 1 Introduction Worldwide over a billion humans use mobile phones as ubiquitous devices helping them to manage their every-day life. The wide range of users, their difference in pre-experiences and expectations as well as the variety of usage situations provide challenges for the user interface design. An ever-growing multitude of functions has to be communicated to and mastered by a diversity of users in a clear, concise and easy to learn way. Nevertheless it seems that just because of the overwhelming abundance of functionality and services, more and more customers base their buying decisions mostly on fun and fashion factors like design, form, size and entertainment-value. For the hardware design this has for example resulted in a new diversity of interaction elements drifting from the standard 3x4 number keypad to solutions which offer more design freedom. Contrary to PC-based systems that offer mainly standardized input and output elements (mouse, keyboard, display) a standardization process for mobile devices seems not (yet) to be finalized. In this situation a best balance between usability and design has to be developed. To deal with user interface challenges like this, the business division Information and Communication Mobile of Siemens AG built up the Competence Center User Interfaces already eight years ago. A multi-disciplinary team of interaction designers, psychologists, engineers and visual designers is dedicated to the creation of highly usable communication devices. In the following we want to illustrate how we react to market tendencies and which
most recent innovative user interface solutions we have achieved and discuss their pros and cons. Figure 1: Some of Siemens most current mobile phones: Diversity and consistency in keypad and screen design are an ongoing challange. 2 User guidance for different levels of experience As stated in the introduction, the group of mobile phone users can be described as extremely divers: There are communication addicted power users of text-messaging and multi-media applications, business users with the need for excellent personal information management and synchronization with other tools and there are lots of users, which need the mobile for just one task: making calls. This wide range offers a challenging task for the user interface designer: How can we create a user interface in a way so that all kind of user types feel comfortable, find the function they are heading for easily and can use the device quickly and error-free? 2.1 One answer does not fit all needs Studies and usability test results showed that such inhomogeneous and diverging user needs cannot be satisfied by just one standard way, one possibility to use a function or to complete a task. Based on this well-proven assumption, we offer different UI-solutions for most relevant phone-features. In this way we will match different user models and strategies, depending on the expertise of the user. Simply stated, there are three categories of expertise: Novices, which have only little pre-experience with our devices: For this group of users, a step-by-step guidance to and through the function has proven to be the best solution. Each step should not offer too many information entities or choices. Ideally, each step offers help functionality in addition. Standard-users, with heavy experience in basic phone functionality: For this group, beside a clear guidance also the speed of using a function is important. Efficiency becomes more and more a criterion for their judgement of satisfying usability.
Power users, which are well experienced and technology centered. They are ready to learn short cuts and configure the device to their specific needs; efficiency is their main focus, complexity is accepted or even appreciated, if it helps to speed up. 2.2 Examples To make these categories, which may sound a little bit theoretical, more comprehensive, we want to match them to existing UI-solutions of Siemens mobile phones: Example #1: Navigate to functionality through the application menu. The novice user wills see only one item per time, scroll stepwise to the next, select and proceed scrolling, till the destination is reached. In addition a highly logical menu structure shall support his navigation. The standard solution may use the same up-/down-navigation, but add left right navigation and show the entries in a grid-view. Using number keys as shortcuts for the direct selection of entries excels the user as a clearly advanced one. Power-users typically will configure their soft and hard keys to access the most often used functions directly or even use voice commands to have a one step access as well. Example #2: A further example for this experience-level UI-design shall be given in the messaging domain. Sending an SMS means for the novice user a stepwise walk through Options Send Select enter the recipients number and go. A strictly stepwise procedure, following one and only one logic can clearly be observed. A standard user will notice, that he can abbreviate the sending by using the send key, thus saving a click, but accepting a change in flow logic. Experienced user might have found out, that predefining a recipient profile for up to 5 frequently contacted partners is possible. Using these profiles through a send via - options skips the step of number selection, thus reducing the task to not more than 4 clicks. 3 Form follows fashion Mobile phones have become more and more fashion accessories, and are affected by rapidly changing trends. Requirements for device design are no longer triggered by functionality, but by brand and trends. To lead this trend Siemens introduced in spring 2003 a new brand Xelibri targeting especially this young fashion segment. 3.1 Less functionality opens up new design spaces Xelibri phones offer two new requirements for the UI-design, which only at first glance seem to be independent of each other. Simplification and reduction of functionality: From Bluetooth to Cell broadcast -we reevaluated every function and removed or at least simplified most of them, including a slimming of the main menu. Assuming that most of the users actually only make use of a handful of functions the phone offers, we concentrated on simplicity over functionality. Hereby, this new brand is clearly not targeted on customers with the mind set get most functions for a given price, but on fashion victims. In parallel, also the hardware got reduced to the maximum. For all devices the send and end-key was removed, and their functionality was shifted to the situation-dependent soft keys.
3.2 Example The product Xelibri 3 abandoned the number keypad completely; a four-way navigation key is the only interaction element, as figure 2 shows. In addition to this, a sophisticated voicecontrol function (speaker-independent entry of numbers) has been realized. Figure 2: Xelibri 3 without number key But entering numbers and even text messages is still possible via this navigation key. For this, a completely new concept of character selection in two steps was invented, tested and implemented. With up/down a group of letters, with right/left a specific letter is selected and inserted after a time-out (see figure 3). Figure 3: Text input with Xelibri 3 Usability tests indicated that this method is not an equivalent for text-input via a standard keypad, but that it is easy to understand and has high acceptability for entering short text messages. Therefore we assess this minimalist text method entry as a successful trade-off between miniaturization and usability.
4 Small is beautiful isn t it? The question of size is a critical one. This applies not only for devices with basic functionality but as well for smart phones, packed with features and memory. Still their physical size is a main criterion for ubiquitous availability. Multimedia-functions and services like taking snapshots or videos, multi-media messaging and WAP-browsing are demanding a display, which is reasonably large to support them. The resulting challenge is: How can we integrate a large display in a small device? 4.1 User Interface Challenge The effort of integrating a large display in a small device sometimes results in proposals that save device-size at the cost of other elements, e.g. key-size. But while miniaturization is in principle unlimited from the technological side, this is not true for human beings! Obviously the flexibility of the human body is not unlimited. The mission of user interface designers herein is to cooperate with industrial designers and hardware construction engineers to strive for the best and most usable solution. 4.2 Design Alternatives Till now, the following design alternatives meet the challenge to balance small form factors and large display sizes: - Clamshell design (e.g. Samsung SGH-V200) - Slider design (e.g. Siemens SL 55, Nokia 7650) - Mono-block design with 2x6 egde-keyboard (e.g. Siemens SX1) 4.3 Example For the SX1 our team has been confronted with exactly the question described above: A multiplicity of number- and function-keys needed to be accommodated on the device s faceplate. A total change in mind-set and complete rearrangement of the keypad resulted in an overall device size of only 80% compared to similar device with 3x4 standard keypad solution (see figure 4). Figure 4: Miniaturization through 2x6 number keypad of Siemens SX1
4.4 User s Feedback to 2x6 keypad Usability test results made clear that users need some time to learn and automate the input of numbers and text. Two-hand operation was clearly favored. Nevertheless the reasonable size of the number-keys made it easy to press the keys which was appreciated by most test-users. After several repetitions of a standard text, the input speed converged to the one observed for traditional keyboards. 4.5 2x6 keypad opens up new UI-opportunities Furthermore the new hardware design offered new possibilities of interaction. In selected applications edge-placed number-keys are used as soft-keys. The radio application can be taken as an example. Like in a car-radio, short press on a key selects a station, press and hold stores the currently broadcasting station. The stations are visualized on the display, and the user does not have to memorize them. Figure 5 shows this visual coherence of number keys and screen content. Figure 5: Radio-application in Siemens SX1, making use of number keys as soft keys 5 Conclusions In recent years mobile phones have developed towards fun and fashion devices on the one hand and towards multifunctional, sophisticated information and communication products on the other. The task of user interface designers in this area is to understand and represent the requirements of the end-users and thereby to help product managers and marketing specialists in the realization of their product vision. The creation of an optimal user experience whether this experience is more fashion or function oriented is the overall aim.