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VISIONS AND CHALLENGES OF MOBILE COMPUTING

MOBILITY VISIONS There have been many vision papers in computer science that include aspects of mobile computing. The following four papers have had the most significant impact on the research community. The first two topics below, ubiquitous and pervasive computing, were initially distinct terms deriving from research programs at Xerox PARC and IBM, respectively. However, over time they have evolved to include an expanded set of ideas, and now the research community considers them to be synonymous. These programs make the case for the benefits and opportunity that embedded computing can bring to work practices via wireless coordination. The third topic, autonomous computing, argues that we need self-managed computer systems to handle complexity; a problem that has become particularly acute now that billions of mobile devices are in use throughout the world. And the fourth topic, sentient computing, argues for designing computer systems that are capable of monitoring and responding to real-time data sensed from the physical world.

MOBILITY CHALLENGES

The following two articles provide a summary of the research challenges in mobile computing in 1995, and then later in 2011, almost 15 years apart, in a fast changing field. Reading these two articles together will provide a perspective view of mobile computing achievements and the remaining open issues in this exciting field:

CONTEXT-AWARE COMPUTING

Context-aware computing enables a computer to modify its behavior based on its local context such as location, time of day, who is nearby, and state of motion. As a result, computer applications can provide an improved user experience by customizing their behavior to better support a user task. This kind of adaptation is particularly useful when designing mobile applications that will be placed in continuously changing contexts. There are two key components required for creating context-awareness: first, the ability to capture a wide-variety of sensor data (both hardware sensors and software sensors); and second, to infer activities based on that data. The following articles provide an overview of the research in this area:

MOBILE AD HOC NETWORKS

Mobile routing in the context of ad-hoc networks has received lots of attention from the research community. Below, we include a few representative articles in this area, such as the key original ones that defined a new ad-hoc protocol, and a survey that compares them. We also provide a reference for the theoretic analysis of the capacity of such a network, and an article that examines the critical model required to make a simulation accurate. An excellent quite comprehensive list of ad hoc routing protocols along with their references can also be found on Wikipedia at the link included:

SENSOR NETWORKS

With the advent of small form-factor devices capable of sensing, processing, and communication, it became possible to conceive of large numbers of small battery-operated wirelessly-connected sensor nodes, which could enable more fine-grain observation of physical phenomena, and man-made structures, than previously possible. An important challenge in networked sensing is managing the energy cost of communication This challenge inspired a whole field devoted to exploring energy-aware network architectures and algorithms, as well as novel applications of sensor networks.

VEHICULAR NETWORKS

Vehicular networks have emerged from the strong desire to communicate on the move. Car manufacturers all over the world are developing industry standards and prototypes for vehicular networks. The design of vehicular networks involves theoretical, network, system, and security issues.

DEPLOYMENTS AND USER TRIALS

In this section we single out projects that capture results, perform user evaluations, and record experiences from real-world deployments and user trials. These projects are notable for the design considerations that need to be taken into account for use in the real world, making them more complicated than if deployed in a lab environment or as a theoretical study. As such, these articles inform researchers about real issues that should be taken into account when designing a system for everyday use.

WIRELESS AND MOBILE TECHNOLOGIES

SHORT RANGE WIRELESS: RFID, NFC, BLUETOOTH, BANs, and PANs Wireless technologies that only operate over a short range have many applications for mobile computing. "Short range" implies they need to be proximate to respond. An example is Radio Frequency IDentification (RFID), which is designed to identify an object or person in front of a reader, perhaps for access control or inventory management. For these purposes, the proximity constraint is necessary for the information that is determined to have value by a reader (e.g., detecting RFID badges 1m away is useful for access control to a door, but detecting badges 500m away is not). Near-Field Communication (NFC) is a standard that is a subset of RFID technology with added features to allow both reader-to-tag communication and reader-to-reader communication. As a result, it can also be used to facilitate high-bandwidth wireless connections between laptop and mobile computers by sharing a secret channel key across a proximate link (e.g., physically secure). Once the key has been transferred securely, it can be used to set up an additional Bluetooth, or WiFi radio channel. The Bluetooth radio standard was developed by the Bluetooth SIG to enable a short-range Personal Area Network (PAN) that can wirelessly connect all of a person's computing devices (e.g., laptop to phone, mouse, PDA, GPS). This standard has also been adopted by cellular handset developers to support hands-free operation; this is now a requirement in many countries for using cell phones while driving. Another use of short-range radio has been to wirelessly connect medical sensors (placed on the human body) to a small wearable computing hub that can buffer data and then communicate it to a remote hospital server using cellular radio technology. Often, Bluetooth, or Zigbee, is used for the proximate link, but near-field communication has also been adapted for this purpose. Such a network is called a Body Area Network (BAN) or Body Sensor Network (BSN).

WIRELESS LOCAL AREA NETWORK (WLAN) TECHNOLOGY

Wireless LANs are one of the most widely used network technologies. However, understanding its performance and predicting its behavior under various conditions pose significant research challenges. These challenges motivate researchers to develop models to predict behavior under different usage scenarios, design techniques to optimize WLAN performance, diagnose problems when things go wrong, and measure/analyze how well WLANs work in reality. (See also the section on measurement, below.)

CELLULAR TECHNOLOGIES

Although largely developed in the communication's industry, cellular networks are a key component of any mobile system that requires metropolitan- or national-scale connectivity. Analog (1G) was the base technology of the first cell phones. The first digital systems were called 2nd generation (2G), primarily GSM & Cellular Data Packet Data (CDPD), which operated with low bandwidth (9.6kbps). They were of limited value for mobile computing compared to what was available over a wireless LAN at that time (10Mbps). However, as the various standards have progressed from 2G to 2.5G (GPRS at 48Kbps), to 3G, which provides 384Kbps moving and 2Mbps stationary, and now 4G (long-term evolution (LTE), with the eventual goal of 100Mbps for mobile operation and 1Gbps for stationary), these data rates are now comparable to those available on today's WLANs. Thus, mobile applications that had only been imagined in the early days of mobile systems will soon be possible almost anywhere. The following references provide an overview of cellular technology developments, along with their strengths and weaknesses:

LOCALIZATION

Localization, is the ability of a mobile or stationary device to ascertain its own position; this is a crucial capability for ubiquitous computing as well as mobile and wireless systems. It enables context-aware applications on handheld and portable devices, and is also critical metadata that provides context for data gathered by wireless devices. Location is easily obtained outdoors using GPS, although this may incur a significant energy cost. Work in this area has explored indoor localization systems, or methods to localize nodes and objects when GPS may be unavailable or too expensive to use.

TIME SYNCHRONIZATION

For some classes of wireless networks, especially sensor networks, data acquisition can be improved by placing synchronized clocks at every node in the network. Often, time synchronization is achieved by explicit message exchanges to communication clock offsets between neighboring nodes, and then algorithmically adjusting those offsets over time to compensate for clock drifts. The following articles describe important additional time synchronization techniques in some detail.

MOBILE HCI—TEXT INPUT WHILE MOBILE

One of the HCI challenges for mobile computing is providing users with the ability to have an effective mobile user experience while using a small handheld computer such as a smart phone. The scope of this topic is very large, but here we limit it to mobile input, and provide a set of references that cover the research behind stylus and soft keyboard solutions for text input on a mobile handset (smart phone or PDA):

LOW-POWER OPERATION

One of the constraints that distinguishes mobile systems from desktop, or server, systems is their reliance on battery technology. This means that energy is limited for a mobile computer, and needs to be used sparingly. As a result, low-power operation has always been a core research area for mobile computing and encompasses the design of hardware, wireless protocols, architecture, operating systems, and user interaction mechanisms. As the world has become more concerned about total energy usage and the green movement has gained momentum, many of the techniques developed for mobile computing are now also being applied to desktop and server systems in order to save energy in both the home and corporate environments. The following articles provide some insight into the creative ways the energy footprint of mobile systems has been reduced by redesigning applications, languages, and devices and by building hybrid wireless technologies and employing energy-scavenging techniques.

SECURITY AND PRIVACY

Security and privacy pose unique challenges in mobile computing, because device mobility and personalized usage make it possible to infer personal information from the system's location, or usage patterns. In this section we highlight a few of the many interesting articles in this field, providing examples of security attacks that highlight some of the risks. This article provides an overview of privacy challenges in mobile and ubiquitous computing.

MOBILE DATA ACCESS WHILE INTERMITTENTLY DISCONNECTED

This section includes research that spans disconnected operation, weak connectivity, and conflict resolution. Note this is different from delay tolerant networks (DTNs), as, in this scenario, computers are sometimes directly plugged into a high-bandwidth network connections, but in other situations a computer may intermittently have no connection at all. The articles below describe how mobile systems can usefully continue their work despite these varying conditions:

MOBILE ROUTING: MESH NETWORKS AND MOBILE IP

Wireless mesh networks are becoming a new attractive communication paradigm. Many cities have deployed, or are planning to deploy, them to provide Internet access to homes and businesses. In order to compete with wire-line access technology, routing in wireless mesh network should provide high throughput and reliable performance. This goal has inspired lots of research into developing effective routing protocols for wireless mesh networks. We also include an article on routing using Mobile IP that is representative of the key ideas described in several articles on this subject.

MEASUREMENT AND PROFILING

Mobile measurement and profiling is a topic of growing importance in the mobile community because significant insights can be obtained by performing measurements at various network locations and on various platforms. This provides visibility into mobile user behavior, mobile traffic characteristics, and mobile application operation. Measurement and profiling research efforts can be roughly categorized on the basis of the vantage point and objectives. Tools deployed on end-hosts, or mobile devices, offer direct insight into user-perceived performance and energy efficiency. Measurement studies based on data collected inside the network can provide aggregate resource usage as well as global traffic patterns. Beyond studies done for 802.11 wireless networks, there is also growing interest in investigating cellular data networks.

VIRTUAL MACHINES IN SUPPORT OF MOBILITY

For many years, virtual machines have been used in data centers to move services between sets of physical machines to provide processor load balancing, while at the same time ensuring secure isolation between services running on the same machine. However, in recent years research has shown the benefit of using virtual machines to support mobile computing. The idea is that a computation can be migrated from a local computer to a remote computer while the user travels between them, thus removing the need to actually carry a computer. Alternatively, computation can be moved from a powerful desktop computer to a mobile smart phone, and then back to a desktop, thus providing seamless access to the same computation environment on the best available hardware at hand. The following articles present various systems that exploit this idea.

Resources

KEY CONFERENCES

In addition, conferences such as ACM CHI and UIST have mobile computing sessions; 
see ACM SIGCHI (CHI is the premier conference) at www.sigchi.org; see ACM UISTwww.uist.org.

PERIODICALS AND JOURNALS

BOOKS

Mobility-aware Networking

Mobile sensing

for Smartphones", MobiSys 2010, PDF

Participatory Sensing

Application", MobiSys 2010, PDF

Situation recognition

Mobility Profiling

Behavior Profiling

Context-aware Intelligence

Security

Network Security

Location Privacy

Privacy

Health

Traffic Monitoring / Vehicular Apps

ETC

PDF

Collaborative Applications