In order to understand the challenges that are related to the usability of a mobile phone, we need to understand the main mobile phone design areas that have impact on the user experience. The main areas are industrial design, hardware platform, mechanical concept, software platform, and user interface style. There are also many other design areas, such as localisation, that are left out of this review.
4.2.1 Industrial design
"The customer grabs the most attractive product, whatever that means to him or her… Products are no longer bought on the basis of functional values (Pulkkinen 1997, 146)."
Industrial design has tremendous impact on the product success. For example, watches or scissors are often sold based on the design and not on the functions. A mobile phone is identified and differentiated by its industrial design. Each new mobile phone design is somehow different from earlier designs.
"The sizes of mobile handsets are decreasing continuously. New models are lighter, more flat and shorter. The small size and simple-looking face of a mobile phone have been for a long time the main challenges for industrial designers. Though the sizes of the devices have shrunk, the design principles and portability solutions have changed amazingly little (Keinonen 2000). "
According to Frank Nuovo, Nokia's chief designer, a mobile phone design "gives faces to a company, globally" (Helsingin Sanomat 2001). Nuovo compares a phone to fashion statement, such as watch or sunglasses. Nokia mobile phones are identified by the their continuity. The essential factors are big display, lack of external antenna, round shapes and ellipse around the display (Figure 4.1).
Figure 4.1. Nokia Mobile phone industrial designs. Nokia 5510 and Nokia 6210.
A good design has potential to create global identifiable icons. For example, Nokia 2110 design has been used globally as a symbol of a mobile phone in different contexts. In the same way, in some countries, for example China, the common noun for a mobile phone is "nokia".
Technically, industrial design defines the overall dimensions of the product and the main factors for mechanical design.
4.2.2 Mechanical design
Mechanical product design is a detailed implementation of industrial design. Mechanical design initially defines the physical product implementation, such as materials, dimensions and positions of product components. Hence, industrial design together with mechanical design provides the key ergonomic design decisions. Mobile phone manufacturers have tried several mechanical basic concepts. Some concept variables are listed in the following:
- orientation: Horizontal vs. landscape product (Figure 4.1)
- covers: No cover, clamshell, flip, slide (keypad cover) (Figure 4.2)
- keypad: ITU-T phone keypad, QWERTY keypad, touch/pen keypad (Figure 4.2) - display: different sizes, 1 vs. 2 displays (Nokia 9210), display colours/no colours - softkeys (key label in the display, but physical button under the display): 1-4 - call management keys: Send/End keys vs. uni-key (Figure 4.4)
- navigation tool:
- no navigation tool, 2-way scroll (Nokia 7110), 4-way scroll (Nokia 7650)
- 2 navigation keys (up/down), 4 keys (up/down/left/right), joystick (analogue or digital), navi-wheel (Sony), roller (Nokia)
- internal vs. external antenna
- detachable parts: battery, SIM card, memory card, flip-on covers - carrying concept: Hand-held, wearable (wrist phone, headset)
- need for hands in operation: no hands (vice control, one hand, two hands)
Examples of mobile phones industrial and mechanical designs from different manufacturers are presented in Figure 4.2.
Figure 4.2. Mechanical product designs. Nokia 9210 (clamshell), Samsung wristphone, Benefon Esc. Ericsson R380 (flip phone).
Innovative products are often presenting new ideas for user interaction, such as, new navigation tool concept, special display size or shape, experimental keyboard layout, moving components (flip covers, hinged camera), and built-in sensors. Each new interaction concept is a challenge for the product development (implementation risks) and user acceptance (usability, utility).
Industrial and mechanical designs form the physical interface between user and the phone.
Underneath mechanics there is hardware that enables both mechanical and software functionality. The main mechanical components of a basic mobile phone user interface are displayed in Figure 4.3:
Keyboard, text input keys
N avigation tool
Covers Softkeys
Microphone, earpiece
Battery
Power switch
Call management keys
Display
SIM card
holder Connectors
Figure 4.3. Mechanical components in a mobile phone user interface (Nokia 8310).
4.2.3 Hardware
Hardware defines main performance issues, such as display capabilities, battery consumption (together with SW), memory capacity and processor efficiency. Mobile phone hardware is highly and tightly integrated entity, typically without readiness for modifications such as extending or upgrading. In some phones it is possible to extend the memory capacity with
special memory cards, for example Nokia 9210. The capability to optimise the size, compactness and functions is critical, due to continuous and competitive attempts to make the mobile phones smaller. Hardware enables certain software performance. Hence, software functionality is dependent on hardware.
4.2.4 Software
Telephone development started as hardware-focused engineering. However, the importance of software and SW based functions is continuously increasing. It is no longer possible to develop a mobile phone, especially a smart phone, without extensive software engineering. Mobile phone manufacturers have entered the software industry.
Practically, software platform defines what software functionality it is possible to implement and what is not with reasonable effort, and the software architecture defines how flexible the platform is, especially with complex products and rapidly changing technologies (Hofmeister et al. 2001, xxiii). For example, multitasking is not implementable with one SW platform, or activities requiring high processing capability will not run smoothly with another platform.
Further, even if a software platform is ideal for multitasking and PDA tasks, it may be unsuitable or inefficient for cellular processing tasks, such as digital signal processing (DSP).
Mobile phone software is embedded software or system. This means that the software is integrated to other product components, such as specific hardware interfaces. Mobile phone software platforms can be grouped as follows:
- manufacturer specific (proprietary) platforms. These platforms are typically designed and evolved for the very specific needs of a company and they are not open for software developers. These platforms are optimised for and efficient in a specific hardware platform.
These SW platforms require very specialised company-internal know-how and SW tools that are difficult to buy from outside.
- open software platforms. These platforms for mobile devices are developed for enabling open (3rd party) software development. Examples of these platforms are Symbian (www.symbian.com), Windows CE, Stinger (www.microsoft.com), and Geos (www.geoworks.com). These platforms may not be optimal for a specific company or hardware platform but they open better possibilities to outsource software development, know-how or find SW development tools. Symbian platform is an example of SW development where the actual SW engineering is done by partners, subcontractors, or even competitors.
Symbian (2001) lists principles of mobile phone software capability requirements. These principles may seem obvious but they are radically different to the current desktop applications:
- call handling and management of personal data must be possible anywhere anytime (user expectation)
- serious power management. The device needs to be responsive in all situations, and cannot afford to go through a boot sequence when it is turned on. It must always be able to raise alarms or handle incoming calls. It must provide many hours of operation on a single charge or set of batteries.
- at a very basic level the OS shouldn't be too resource hungry. It should support low-power CPUs with limited amounts of memory.
- at a deeper technical level, expensive operations such as context-switching should be minimised: it is better to implement most of the multitasking through event-driven messaging rather than with multithreading.
- code reuse should be maximised. This is a goal often stated but rarely achieved.
- the allocation and use of resources has to be tightly controlled. This can best be done on a system-wide basis using servers to control system resources.
- reliability is a major issue for mass-market devices. Data loss in a personal mobile device causes a loss of trust between the user and the device: a WID must be at least as resilient as paper diaries and agendas.
- the kernel should be small: much of the functionality conventionally handled by device drivers should be handled, instead, by system servers, running without special privilege.
- an effective memory management system is needed to prevent memory leaks. For systems that are never completely shut down and cannot be rebooted, keeping an accurate track of resources is what makes the difference between peak performance at all times and slow degradation to partial or total lack of usability.
- sound consumer design is necessary.
- applications should take advantage of the uniqueness of the WID.
- they should be designed both for current usability and for future developments in wireless technology.
- consistency of style is paramount. If a function is too difficult to use, then it cannot justify either the time it took to develop or the space it takes in the device.
Software platform functions and UI style are often dependent on each other. The selection of software platform, for example Symbian platform, may define principles of the UI style for a product, or the selection of UI style may guide the company in selecting the software platform, for example Microsoft CE.
4.2.5 UI style
A user interface style is a design framework describing interaction style and objects, including appearance (look) and behaviour (feel) (Hix and Hartson 1993). In the world of desktop computers UI style refers to the software UI (display). For a mobile phone, user interface style defines both the display and the required keys and buttons in the device. In mobile world, there is no single ruling UI style as there is in the world of personal computers. Instead, mobile phone manufacturers are maintaining and developing brand specific UI styles. Even inside one UI style there can be hundreds of rules and guides for the UI design. For example, (in a non-published study) over 800 UI design rules and guidelines for PC environment were identified. In addition, some manufacturers have several different UI styles. Some examples of Nokia UI styles are shown below (Figure 4.4).
Figure 4.4. Nokia 7110 (left) has two softkeys and a “roller” for UI navigation. Call handling keys are green and red buttons. Nokia 3110 (right) has one softkey and up/down arrows for
navigation. No special keys for call handling.
Mobile phone displays are small, with display area of few square centimetres. The evolution is driving to maximise the portion of screen size in the phone face, colorize the display,
simultaneously decreasing the whole product size. Several phone manufacturers have already gone below the challenging 100g weight. In current products on the market (December 2001) the interaction is mainly based on physical keys and buttons instead of touch-input systems.
There are signs of emerging competition in using the UI style as competing issue, and pressures to provide a de-facto UI style in order to enable open software development for mobile phones.
Symbian is providing UI platforms for different product categories and Microsoft is on the way to develop mobile phone user interface style (known as “Stinger9”).
Changing from one UI style to another is difficult for the user due to the challenge of learning new way to perform familiar tasks. Currently, the diversity of UI styles leads to the situation where the user has to learn new ways to perform tasks, i.e. adapt to the particular UI style when she replaces old product to a newer one. This is an important issue, because replacement customers are a major group in the consumer markets. During 2001 about 70% (Gartner 2001) of the mobile phones were sold to persons that already have one. At 2002 the replacement market of mobile phones is larger than the share of new customers.