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Mobile computing platforms combining small, lightweight, low-power devices with wireless network connectivity enable the performance of familiar tasks in new environments and create opportunities for novel interactions. Since mobility imposes significant cognitive and ergonomic constraints affecting device and application usability, ease of use is central to devices in the fully mobile wirelessly connected (FMWC) world. In this paper, we consider mobility as an attribute both of the computer and the user. We explain the differences between transportable and fully mobile devices, and we contrast applications that are essentially FMWC applications, those that can be adapted to the FMWC context, and those that are unsuitable for it. We discuss the unique challenges to usability for mobile users and devices and their interaction, and we point out the increasingly critical role of usability in the mobile environment.
Mobile devices supported by wireless connectivity can dramatically change the ways in which people interact with computers. On the one hand, tasks that have been traditionally undertaken in a fixed setting, such as an office, can be performed in arbitrary locations (at least in theory.) On the other hand, many types of field work that had not been previously assisted by computers can benefit from instantly available computational and informational resources. Furthermore, the connected mobile world opens up numerous possibilities beyond the realm of work--expanding our leisure, entertainment, and informal communication activities. The field of mobile wireless computing is continuing to develop rapidly, not only in the range of mobile devices (for example, personal digital assistants [PDAs], mobile phones, and wearable computers), but also in the range of available communication technologies (for example, the Wireless Applications Protocol [WAP], Bluetooth (**) wireless technology, and IEEE 802.11 wireless standards).
Attempts to understand the design and usability implications of the connected mobile world started more than a decade ago. These included the construction of taxonomies of mobile computers (1) as well as identification of some broad issues in mobile user interfaces. (2) At first, the intrinsic constraints of mobile devices were identified with technological limitations, such as poor computational resources (compared with static computers), limited energy sources, and less reliable network connections. (3) Later, various aspects of human interaction with mobile computers came under scrutiny, including ergonomic constraints, (4) properties of ubiquitous access, (5) and collaboration in mobile environments. (6) In the last few years, particularly intensive debates have focused on the problems of input and output mechanisms for mobile devices.
It is now clear that the goal of "anytime, anywhere, anyhow access for anybody" (7) presents more challenges to its inventors and designers than had been originally anticipated. While many existing technological restrictions may be only a few steps away from being resolved, a large number of environmental constraints and some limitations on the human side will remain. For a mobile solution to be successful, everyone involved in the development of various components must focus on the total user experience in general, and on usability in particular. This calls for technical specialists to attend meticulously to the impact of mobility on usability, and for usability experts to be well informed about one of the fastest growing segments of the human-computer-interaction (HCI) domain.
This paper presents a detailed analysis of the field of mobile wireless computing. Most contemporary mobile devices feature wireless connectivity. Typically, mobile is used as an attribute of a computing device; it implies that a device can be easily transported to a location where the user wants to interact with it. However, mobility in its usual sense conveys nothing about the user and the type of interaction. In this paper, we consider mobility an attribute of both the user and the device; we classify an interaction as mobile if both the user and the device can relocate during the interaction. Only those devices that support mobile interactions are fully mobile; devices that can be moved to a different location but require the user to remain stationary during the interaction are no more than transportable. To distinguish the specific case of fully mobile computing combined with wireless connectivity, we introduce the concept of fully mobile wirelessly connected (FMWC) computing, and apply it to devices, applications, and contexts of use. On the usability side, we see some critical differences between stationary interactions, where user movement is restrained, and mobile interactions, where various degrees of body movement are allowed, particularly, walking. Placing the interaction into a freely moving context, we face a whole new world of environmental and cognitive challenges that affect usability of devices and applications. Within applications that can be considered for FMWC devices, we distinguish three types: essentially FMWC applications, applications adapted for the FMWC context, and applications that are unsuitable for it. We describe the salient characteristics of each type and their impact on application usability.
The paper is written for both the technical and broad HCI communities. Both groups can benefit from the analysis of the FMWC field (see the section "Defining the space of mobile wireless computing") that examines various classes of mobile devices and the three types of FMWC application. The section "Contexts and interactions in the FMWC world" also targets both reader audiences and describes two major types of mobile interaction context: the mobile office context and the field context. The following section, on implications for technical and HCI communities, emphasizes the importance of User-Centered Design (UCD) for creating easy-to-use FMWC products. Essential usability implications of the FMWC world that need particular attention from hardware and software engineers are then presented, followed by a discussion targeted for the HCI community focusing on methodological issues of UCD in the FMWC environment.
Defining the space of mobile wireless computing
The following section describes the spectrum of FMWC devices and how these devices, the applications that run on them, and interactions with them can be characterized.
Mobile, pervasive, ubiquitous or wireless? As in any new area of technology, the terminology of mobile wireless computing is still unsettled. Every now and then, the term mobile wireless computing is used in conjunction or interchangeably with ubiquitous or pervasive computing. Ubiquitous computing, first introduced at Xerox PARC (Palo Alto Research Center) in 1988, is "the method of enhancing computer use by making many computers available throughout the physical environment, but making them effectively invisible to the user." (8) Some attributes of ubiquitous computing, such as instant availability to the user, may be similar to those of mobile computing, but the two are not synonymous. While the notion of a computer being with the user at all times is essential for mobile computing, ubiquitous computing emphasizes the invisibility of the computing environment; that is, the notion of computers being widely available and inconspicuous. Pervasive computing aims to "manage information and reduce complexity for a mobile workforce and a mobile society." (9) Pervasive computing emphasizes the networking capabilities of computers and, as IBM's Pervasive Computing initiative defines the term, is about "everything [being] wireless, mobile, and voice." (9)
Most often, however, computers that feature network connectivity on the move are described simply as mobile or wireless computers (the term portable is also occasionally used.) Although common, each definition captures only part of the meaning of mobile connectivity. Not all mobile devices are enabled as wireless, and not all wireless devices are mobile. Figure 1 gives a more accurate view of the mobile and wireless categories. As a generic term for mobile wireless computing, pervasive computing seems most appropriate. However, for the purpose of evaluating usability of mobile wireless products, this definition is imprecise, as we shall see in the following sections.
[FIGURE 1 OMITTED]
Device mobility and modes of interaction. From the usability point of view, it is not the qualities of a computing device that are paramount, but the qualities of the interaction between the user and the device. A continuum of existing personal computers, of varying degrees of mobility, is shown in Figure 2, and this figure assists us in analyzing how the degree of device mobility determines possible interaction modes. Figure 2 presents the five major types of personal computers in existence today, with degree of device mobility increasing from left to …