The most familiar aspect of mobile computing technology is the hand phone. About two decades ago, a hand phone was bulky and was only used for voice communication. It was merely an extension of the fixed line telephony that allowed users to keep in touch with colleagues. Now the hand phone is not only used for voice communication, it is also used to send text and multimedia messages. Future mobile devices will not only enable Internet access, but will also support high-speed data services.
In addition to the hand phone, various types of mobile devices are now available, for example, personal digital assistants (PDAs) and pocket personal computers (PCs). Road warriors use mobile devices to access up-to-date information from the corporate database. A police officer at a crime scene may send a fingerprint picked up there for matching with data in a central database through a wireless network, hence leading to faster identification and arrest of potential suspects. The global positioning system (GPS) is used in search and rescue missions, for monitoring and preservation of wildlife, and for vehicle theft prevention. Though many of us are unaware of when mobile computing technology is being used, it has permeated all aspects of our lives.
What is mobile computing? Simply defined, it is the use of a wireless network infrastructure to provide anytime, anywhere communications and access to information. There are many aspects of mobile computing and, sometimes, different terms are used to refer to them. This chapter gives an overview of what mobile computing has to offer and how it improves the quality of our lives. Later chapters discuss the underlying wireless networks and technologies that make mobile computing applications possible.
Mobile Computing Applications
In 1991, Mark Weiser envisioned the next-generation computer technologies that "weave themselves into the fabric of everyday life until they are indistinguishable from it." He described a ubiquitous computing environment that enhances the environment by making many computers available throughout the physical realm, while making them effectively invisible to the user. Weiser pointed out that anthropological studies of work life showed that people primarily work in a world of shared situations and unexamined technological skills. Today's computer technology does not conform to this description because it remains the focus of attention instead of being a tool that disappears from users' awareness. Ubiquitous computing aims to make computers widely available throughout users' environments and effortless to use. In other words, users should be able to work with computing devices without having to acquire the technological skills to use them. Computers are integrated into their environments so that users are not even aware that they are using a computer to accomplish a task. Unlike the computer technology of today, users need not acquire specific skills to use computers because their use would be intuitive. The aim of ubiquitous computing is to create a new relationship between people and computers in which the computers are kept out of the way of users as they go about their lives.
Instead of computers that sit passively on desks, ubiquitous computers are aware of their surroundings and locations. They come in different sizes, each tailored to a specific task. At the Xerox Lab, Weiser and his colleagues developed a tab that is analogous to a Post-it® note, a pad that is analogous to a sheet of paper, and a board that is analogous to a yard-scale display. An office may contain hundreds of tabs, tens of pads, and one or two boards. These devices are not personal computers, but are a pervasive part of everyday life, with users often having many units in simultaneous operation. Unlike a laptop or a notebook, which is associated with a particular user, tabs and pads can be grabbed and used anywhere-they have no individualized identity and importance. You may have a few pads on your desk, each dedicated to a particular task in the same way that you spread papers on your desk.
An employee ID card is replaced by an active badge that is of the same size. It identifies itself to receivers placed throughout a building. It makes it possible to keep track of people and objects that it is attached to. Because an active badge is associated to a particular user, it can become a form of ID; for example, an electronic door to a restricted area would only open to authorized users. When I am not in my office, the system detects my current location and forwards phone calls there. When I walk into a lecture hall, the system detects my presence, checks the timetable, deduces that I am there for a WRES3405 lecture, and automatically downloads that day's lecture notes. When the system detects the presence of a team working on a particular project in a meeting room, it checks the room booking system to determine if there is a scheduled meeting. Confirming that it is indeed the case, it downloads and displays the previous minutes on the board. As the meeting progresses, team members may manipulate the board using a tetherless pen that need not touch the screen, but can operate from a few meters away. Using the pen, a team member may point to an object on the board, select it, and modify it.
Pervasive computing is a term that is synonymous with ubiquitous computing. Many interesting projects on pervasive computing are carried out at Carnegie-Mellon University. The Portable Help Desk (PHD) is an application developed under Project Aura that makes use of spatial (a user's relative and absolute position and orientation) and temporal (scheduled time of private and public events) awareness. PHD allows a user to determine the location of colleagues and information about them. It is equipped with the capability to display maps of surrounding areas, indicating resources and nearby people. It also notifies users of the availability of resources they may need, for example, a nearby printer or café. PHD is equipped with visual and audio interfaces, each of which provides support in different contexts; for example, a user who is walking is more likely to prefer an audio interface to interact with PHD.
An important requirement of the applications discussed so far is that for them to offer relevant information to the user (e.g., a café is about 100 m to your left), they need to be aware of their context. This is a very important aspect of mobile computing applications. To be useful, an application needs to be aware of its current environment. For example, if I am currently in Kuching and I request information about seafood restaurants, I expect the application to give me a list of seafood restaurants in Kuching, not Kuala Lumpur. For this reason, a tourist guide application must have context awareness embedded so that it can deliver information that is relevant to the users.
HyperAudio and HIPS are handheld electronic museum guides that adapt their behavior to that of a visitor. A visitor to a museum is given a handheld device equipped with headphones. As the visitor approaches an exhibit, the system dynamically composes a presentation of the object in sight. When the system detects that a visitor pauses in front of a display, it presents information about it. The information is presented in the form of audio recording, a relevant image, and a set of links for obtaining more information about it. The system obtains an estimate of the distance between the visitor and the display and adapts the way the information is presented. For example, if it detects that the visitor is standing right in front of the display, the audio message would say, "this item is. . . ." If the visitor is a distance away, it may attract his attention to it by saying, "the display in front of you . . ." or "the display to your left is. . . ." The system deduces that the visitor is very interested in the display if he or she pauses in front of it for more than a certain period of time and proceeds to present more detailed information about it. As the visitor moves away to view another display, the system detects the distance between the current display and the next one and starts to download the presentation for the next display.
Another class of information that makes use of wireless technology is wearable computing, which involves integrating computers into our clothes to perform certain functions, for example, monitor the wearer's heartbeat and blood pressure. There are many practical and useful applications of wearable computing. Guide dogs and canes are very useful in assisting visually impaired people to avoid obstacles and negotiate changes in ground level, such as steps. However, they are not helpful in avoiding higher obstacles such as street signs and tree branches. This difficulty may be overcome with the use of a wearable headset consisting of a laptop, a video camera with infrared (IR) light emitting diodes mounted on one side of an eyeglass frame, and a scanning fiber display and optics mounted in a tube. The software comprises a machine vision program that identifies potential collision objects,
a program that controls the display, and a graphical user interface (GUI) to help set parameters for the embedded processors and generate bright warning icons.
A more recent technology is a wireless sensor network (WSN). In a WSN, sensors are placed at strategic locations to monitor certain aspects of the environment. For example, biologists may use it for habitat monitoring to study behavioral patterns of a species. The use of sensor networks assists ecologists to accurately measure the degree of micro-environmental variance that organisms experience. Data collected by scientists regarding population dynamics and habitat needs is important in conservation biology, landscape monitoring and management, and species-recovery efforts. Sensor nodes are also used to monitor personnel and mobile assets; for example, an alarm is triggered when a printer is detected leaving an office area without authorization. One application of this technology is in agriculture, where sensors are used to monitor environmental conditions that may affect the crop. Early detection and alert of a change in temperature, for example, would help farmers to take precautionary steps to protect their crops.
Another novel invention using wireless technology is the virtual fence. Cowboys on horsebacks herding cattle might one day become a feature of a bygone era as the introduction of virtual fences allows ranchers to herd their cattle from the comfort of their homes. The virtual fence is downloaded to the cows by transmitting GPS coordinates to head collars worn by the cows. The dynamic virtual fences are moved along desired trajectories. The collars are equipped with a wireless fidelity (Wi-Fi) networking card, a Zaurus PDA, an eTrex GPS unit, and a loudspeaker that transmits occurring sounds (e.g., roaring tigers, barking dogs) when a cow strays from the intended path. This multidisciplinary project, the brain child of a biologist, is made possible in collaboration with computer scientists.
Sensor technology can potentially play an important role in search and rescue operations by first responders (i.e., emergency personnel), such as firefighters, paramedics, and police, who arrive at the scene immediately after an event (e.g., a fire, an earthquake, a building collapse) occurs. Firefighters wear tags to allow easy tracking of their movements to coordinate search and rescue operations more effectively. The firefighters can be informed if a particular section of a building is found to be unstable and is about to collapse, and they are directed to evacuate it immediately. A wireless vital sign monitor is attached to victims found trapped so that their condition can be monitored to ensure that they receive the appropriate medical attention as soon as they are rescued. This noninvasive sensor monitors vital signs such as heart rate, oxygen saturation, and serum chemistry measurements.
The vital sign monitor helps the paramedic team determine which victims' conditions are more critical so that they can prioritize medical attention to more severely injured victims. The application and architecture required to support this emergency response application is being developed under the CodeBlue project at Harvard University.
Wireless technology is also used in healthcare. The Arrhythmia Monitoring System (AMS) is a medical telemetry (telemedicine) system that makes use of wireless technology to monitor patients suffering from arrhythmia (Liszka et al. 2004). Among the complications that arise from arrhythmia are the loss of regular heartbeat and subsequent loss of function and rapid heartbeats. AMS provides a means for healthcare professionals to continuously monitor a patient's electrical cardiac rhythms remotely even though the patient is not at the hospital. This technology allows patients to be in the comfort of their homes without jeopardizing their health. It is also useful for monitoring the heart functions of astronauts who are more susceptible to cardiac dysrhythmias when in space.
The system architecture consists of a wearable server, a central server, and a call center. The wearable server is a small communications device worn by the patient that collects the patient's electrocardiogram ([ECG], i.e., the heart muscles' electrical activity). The data is collected using wires attached to skin-contact biosensors. The wearable server receives analog signals from the sensors and converts them into digital signals. Data is collected every 4 ms and requires a minimum baud rate of 22.5 kbps to transmit over a wireless link to the central server.
The central server is located close to the patient. Its functions are data compression, location awareness utilizing GPS, and rudimentary arrhythmia detection. It serves as a wireless gateway to a long-distance cellular network. Data is routed via the call center that is manned 24/7, by healthcare professionals who monitor the ECG signals and respond to alerts. The system transmits an alert automatically if it detects that the patient is about to have or is having an arrhythmia attack. A patient can press a button on the wearable server to send a non-critical alert to the call center if the heart flutters or other unusual feeling occurs. There is also a panic button that a patient can press to send a critical alert for help so that an emergency response team can be rushed to the most recent GPS location.
The GPS location service is a critical part of the system as it is imperative that an emergency response team is dispatched in the quickest time possible. A patient's location is tracked using a GPS transceiver equipped with a 1.55 GHz GPS antenna and a 2.4 GHz Bluetooth antenna. The location information is sent to the receiver every 10 s and acquires a minimum of three GSP satellite signals. A patient's location can be accurately tracked within 10 m.
Another category of mobile applications that is gaining popularity is mobile commerce or m-commerce, which is likely to become an important application of this technology. M-commerce application can be classified into ten types:
- Mobile financial application (business-to-customer [B2C] and business-to-business [B2B]): The mobile device is used as a powerful financial medium.
- Mobile advertising (B2C): It turns the wireless infrastructure and devices into a powerful marketing medium.
- Mobile inventory management (B2C and B2B) or product locating and shopping (B2C and B2B): It is an attempt to reduce the amount of inventory needed by managing in-house and on-the-move inventory. It also includes applications that help to locate products and services that are needed.
- Proactive service management (B2C and B2B): It attempts to locate products and services that are needed.
- Wireless reengineering (B2C and B2B): It focuses on improving the quality of business services using mobile devices and wireless infrastructure.
- Mobile auction or reverse auction (B2C and B2B): It allows users to buy or sell certain items using multicast support of wireless infrastructure.
- Mobile entertainment services and games (B2C): It provides entertainment services to users on a per-event or subscription basis.
- Mobile office (B2C): It provides the complete office environment to mobile users anywhere, anytime.
- Mobile distance education (B2C): It extends distance or virtual education support for mobile uses everywhere.
- Wireless data center (B2C and B2B): It supports large amounts of stored data to be made available to mobile users for making "intelligent" decisions.
The mobile computing applications discussed so far provide a glimpse of what mobile computing technology has to offer. The applications are used in many different fields and may perform generic functions or be tailored to specific needs. The next section gives an overview the evolution of wireless networks that have made these applications possible.
Evolution of Wireless Networks and Services
The first generation (1G) wireless network was analog. The first in North America was advanced mobile phone system (AMPS), which was based on frequency division multiple access. A total of 1664 channels were available in the 824 to 849 MHz and 869 to 894 MHz band, providing 832 downlink (DL) and 832 uplink (UL) channels. AMPS, widely used in North America, supports frequency reuse. The underlying network is a cellular network where a geographical region is divided into cells. A base station (BS) at the center of the cell transmits signals to and from users within the cell.
The second generation (2G) systems onward are digital. Digital systems make possible an array of new services such as caller ID. The Global System for Mobile Communications (GSM) is a popular 2G system. GSM offers a data rate of 9.6 to 14.4 kbps. It supports international roaming, which means users may have access to wireless services even when traveling abroad. The most popular service offered by GSM is the Short Message Service (SMS), which allows users to send text messages up to 160 characters long.
2.5G systems support more than just voice communications. In addition to text messaging, 2.5G systems offer a data rate on the order of 100 kbps to support various data technologies, such as Internet access. Most 2.5G systems implement packet switching. The 2.5G systems help provide seamless transition technology between 2G and third generation (3G) systems. The following are 2.5G systems:
High-Speed Circuit-Switched Data (HSCSD): Even though most 2.5G systems implement packet switching, HSCSD continues support for circuit-switched data. It offers a data rate of 115 kbps and is designed to enhance GSM networks. The access technology used is time division multiple access (TDMA). It provides support for Web browsing and file transfers.
General Packet Radio Service (GPRS): GPRS offers a data rate of 168 kbps. It enhances the performance and transmission speeds of GSM. GPRS provides always-on connectivity, which means users do not have to reconnect to the network for each transmission. Because there is a maximum of eight slots to transmit calls on one device, it allows more than one transmission at one time; for example, a voice call and an incoming text message can be handled simultaneously.
Enhanced Data Rates for GSM Evolution (EDGE): EDGE works in conjunction with GPRS and TDMA over GSM networks. Its offered data rate is 384 kbps. EDGE supports data communications while voice communications are supported using the technology on existing networks.
Third-generation (3G) wireless systems are designed to support high bit rate telecommunications. 3G systems are designed to meet the requirements of multimedia applications and Internet services. The bit rate offered ranges from 144 kbps for full mobility applications, 384 kbps for limited mobility applications in macro- and microcellular environments, and 2 Mbps for low-mobility applications in micro- and picocellular environments. A very useful service provided by 3G systems is an emergency service with the ability to identify a user's location within 125 m 67% of time. Figure 1.1 shows the evolution of wireless standards.