MobiSys 2004: Second International Conference on Mobile Systems, Applications, and Services, June, 2004, Boston, USA
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       June 7th, Monday
 
       08:00 a.m. onwards   -   Continental Breakfast
       09:00 a.m. - 09:15 a.m.   Opening Remarks and Awards
       09:15 a.m. - 10:30 a.m.   Keynote Address
       Human Needs and Mobile Technologies: Small, fast, and fun
       Ben Shneiderman, University of Maryland

  The central thesis of "Leonardo's Laptop" (MIT Press, 2002) is that designers who are sensitive to human needs are more likely to make the breakthroughs that yield new technologies successes. Therefore, a theory of mobile devices would focus on compact devices that support human relationships, provide salient information, and enable creative expression. The foundations are not only the megahertz of connectivity, but also the usability and universality of interfaces. Demonstrations include digital photo applications, personal info, healthcare, and e-commerce.

       10:30 a.m. - 11:00 a.m.   Break
       11:00 a.m. - 12:30 p.m.   Energy Conservation for Mobile Devices
      Session Chair: Carla Ellis, Duke University
  • NWSLite: A Light-Weight Prediction Utility for Mobile Devices
    Selim Gurun, Chandra Krintz, and Rich Wolski, University of California, Santa Barbara
  • Computation off-loading, i.e., remote execution, has been shown to be effective for extending the computational power and battery life of resource-restricted devices, e.g., hand-held, wearable, and pervasive computers. Remote execution systems must predict the cost of executing both locally and remotely to determine when off-loading will be most beneficial. These costs however, are dependent upon the execution behavior of the task being considered and the highly-variable performance of the underlying resources, e.g., CPU (local and remote), bandwidth, and network latency. As such, remote execution systems must employ sophisticated, prediction techniques that accurately guide computation off-loading. Moreover, these techniques must be efficient, i.e., they cannot consume significant resources, e.g., energy, execution time, etc., since they are performed on the mobile device.

    In this paper, we present NWSLite, a computationally efficient, highly accurate prediction utility for mobile devices. NWSLite is an extension to the Network Weather Service (NWS), a dynamic forecasting toolkit for adaptive scheduling of high-performance Computational Grid applications. We significantly scaled down the NWS to reduce its resource consumption yet still achieve accuracy that exceeds that of extant remote execution prediction methods. We empirically analyze and compare both the prediction accuracy and the cost of NWSLite and a number of different forecasting methods from existing remote execution systems. We evaluate the efficacy of the different methods using a wide range of mobile applications and resources.
     

  • uSleep: A Technique for Reducing Energy Consumption in Handheld Devices
    Lawrence S. Brakmo, HP Labs; Deborah A. Wallach, Google; Marc A. Viredaz, Hp Labs
  • Energy management has become one of the great challenges in portable computing. This is the result of the increasing energy requirements of modern portable devices without a corresponding increase in battery technology. uSleep (pronounced micro-sleep) is an energy reduction technique for handheld devices that is most effective when the handheld is mostly idle, such as when the user is reading a document or looking at a web page. When idle, rather than using the processor's idle mode, uSleep tries to put the processor in sleep mode for short periods (less than one second) without affecting the user's experience. To enhance the perception that the system is on, an image is maintained on the display and activity is resumed as a result of external events such as touchscreen and button activity. We have implemented uSleep on a prototype pocket computer, where it has reduced energy consumption by up to 60%.
     

  • Ghosts in the Machine: Interfaces for Better Power Management
    Manish Anand, Edmund B. Nightingale, and Jason Flinn, University of Michigan
  • We observe that the modularity of current power management algorithms often leads to poor results. We propose two new interfaces that pierce the abstraction barrier that inhibits device power management. First, an OS power manager allows applications to query the current power mode of I/O devices to evaluate the performance and energy cost of alternative strategies for reading and writing data. Second, we allow applications to disclose ghost hints that enable better power management in the presence of multiple devices. Adaptive applications issue ghost hints to device power managers when they are forced to use a poor I/O path because a device is not in an ideal power mode; such hints allow devices to implement proactive power management strategies that do not depend upon passive load observation. Using these new interfaces, we implement a middleware layer that supports adaptive disk cache management. On an iPAQ handheld running Linux, our cache manager reduces interactive response time for a Web browser by 27 and decreases total energy usage by 9. For a mail reader, the cache manager decreases response time by 42 and energy use by 5.

       12:30 p.m. - 02:00 p.m.   Lunch - sponsored by IBM
       02:00 p.m. - 03:30 p.m.   Mobile Applications
      Session Chair: Brian Noble, University of Michigan
  • Metadata Creation System for Mobile Images
    Risto Sarvas, Helsinki Institute for Information Technology (HIIT); Erick Herrarte, Anita Wilhelm, and Marc Davis, School of Information Management and Systems, UC Berkeley
  • The amount of personal digital media is increasing, and managing it has become a pressing problem. Effective management of media content is not possible without content-related metadata. In this paper we describe a content metadata creation process for images taken with a mobile phone. The design goals were to automate the creation of image content metadata by leveraging automatically available contextual metadata on the mobile phone, to use similarity processing algorithms for re-using shared metadata and images on a remote server, and to interact with the mobile phone user during image capture to confirm and augment the system supplied metadata. We built a prototype system to evaluate the designed metadata creation process. The main findings were that the creation process could be implemented with current technology, and it facilitated the creation of semantic metadata at the time of image capture. However, the limited bandwidth and unpredictability of the GPRS network significantly hindered the users’ experience. Also, the usability of the mobile phone was considered problematic.
     

  • Bluetooth and WAP Push Based Location-Aware Mobile Advertising System
    Lauri Aalto, University of Oulu; Nicklas Göthlin, University of Linköping; Jani Korhonen, and Timo Ojala, University of Oulu
  • Advertising on mobile devices has large potential due to the very personal and intimate nature of the devices and high targeting possibilities. We introduce a novel B-MAD system for delivering permission-based location-aware mobile advertisements to mobile phones using Bluetooth positioning and Wireless Application Protocol (WAP) Push. We present a thorough quantitative evaluation of the system in a laboratory environment and qualitative user evaluation in form of a field trial in the real environment of use. Experimental results show that the system provides a viable solution for realizing permission-based mobile advertising.
     

  • Impromptu: Managing Networked Audio Applications for Mobile Users
    Chris Schmandt, Kwan Hong Lee, Jang Kim, and Mark Ackerman, MIT Media Laboratory
  • This paper describes the software architecture of Impromptu, a mobile IP-based audio computing platform, with an associated set of network-based applications and services. Impromptu merges the communication properties and universal mobility of the telephone with the multi-tasking and open protocol world of the handheld PC. Its supporting architecture handles multiple streaming audio applications, provides speech services for consistent audio user interfaces across applications, and enables user management of these varied applications running simultaneously.

       03:30 p.m. - 04:00 p.m.   Break
       04:00 p.m. - 05:00 p.m.   Communication over Wireless LANs
      Session Chair: Victor Bahl, Microsoft Research
  • Improving the Latency of 802.11 hand-offs using Neighbor Graphs
    Minho Shin, Arunesh Mishra, and William A. Arbaugh, University of Maryland
  • The 802.11 IEEE Standard has enabled low cost and effective wireless LAN services (WLAN). With the sales and deployment of WLAN based networks exploding, many people believe that they will become the fourth generation cellular system (4G) or a major portion of it. However, the small cell size of WLAN networks creates frequent hand-offs for mobile users. If the latency of these hand-offs is high, as previous studies have shown, then the users of synchronous multimedia applications such as voice over IP (VoIP) will experience excessive jitter. The dominating factor in WLAN hand-offs has been shown to be the discovery of the candidate set of next access points. In this paper, we describe the use of a novel and efficient discovery method using neighbor graphs and overlap graphs. Our method reduces the total number probed channels as well as the total time spent waiting on each channel. Our implementation results show that this approach reduces the overall probe time significantly when compared to other approaches. Furthermore, simulation results show that the effectiveness of our method improves as the number of non-overlapping channels increases, such as in the 5 GHz band used by the IEEE 802.11a standard.
     

  • DOMINO: A System to Detect Greedy Behavior in IEEE 802.11 Hotspots
    Maxim Raya, Jean-Pierre Hubaux, and Imad Aad, EPFL
  • The proliferation of hotspots based on IEEE 802.11 wireless LANs brings the promise of seamless Internet access from a large number of public locations. However, as the number of users soars, so does the risk of possible misbehavior; to protect themselves, wireless ISPs already make use of a number of security mechanisms, and require mobile stations to authenticate themselves at the Access Points (APs). However, IEEE 802.11 works properly only if the stations also respect the MAC protocol. We show in this paper that a greedy user can substantially increase his share of bandwidth, at the expense of the other users, by slightly modifying the driver of his network adapter. We explain how easily this can be performed, in particular with the new generation of adapters. We then present DOMINO (System for Detection Of greedy behavior in the MAC layer of IEEE 802.11 public NetwOrks), a piece of software to be installed in the Access Point. DOMINO can detect and identify greedy stations, without requiring any modification of the standard protocol at the AP and without revealing its own presence. We illustrate these concepts by simulation results and by the description of our prototype.

       06:00 p.m. - 08:00 p.m.   Poster/Video/Demo and Reception - sponsored by Intel
       08:00 p.m. - 09:00 p.m.   Intel reception continues
       June 8th, Tuesday
 
       08:00 a.m. onwards   -   Continental Breakfast
       09:00 a.m. - 09:15 a.m.   Opening Remarks and Awards
       09:15 a.m. - 10:30 a.m.   Keynote Address
       Talking Phones: a cultural reading of mobile technologies
       Genevieve Bell, Intel Research

  In June of 2002, Malaysian newsstands carried the latest issue of "Mobile Stuff" -- a magazine geared toward Malaysia's growing population of mobile phone subscribers. On the cover, two young Malay men in clothing that suggests more LA hood and less KL suburbs, hold out their mobile phones to the camera beneath the banner headline "Real Men Uses SMS." Six months later, billboards in Shanghai carried the image of a woman'' shapely calves and ankles, bound with black patent leather ankle straps; positioned beneath one strap is her mobile phone. Using ethnographic and cultural data from her recent fieldwork in Asia, Bell will explore some of the ways in which mobile technologies are shifting function and form. Beyond their utility as a technology of information exchange, mobile phones specifically and mobile technologies more broadly, appear to have inserted themselves into the cultural fabric of societies across the world. In so doing, while the underlying technologies might not have changed per se, the applications, usage models and indeed, understandings of the objects have undergone radical shifts and re-purposings.

       10:30 a.m. - 11:00 a.m.   Break
       11:00 a.m. - 12:30 p.m.   Wireless Sensor Networks
      Session Chair: Hari Balakrisnan, MIT
  • Hood: A Neighborhood Abstraction for Sensor Networks
    Kamin Whitehouse, Cory Sharp, David Culler, and Eric Brewer, University of California, Berkeley
  • This paper proposes a neighborhood programming abstraction for sensor networks, wherein a node can identify a subset of nodes around it by a variety of criteria and share state with those nodes. This abstraction allows developers to design distributed algorithms in terms of the neighborhood abstraction itself, instead of decomposing them into component parts such as messaging protocols, data caches, and neighbor lists. In those applications that are already neighborhood-based, this abstraction is shown to facilitate good application design and to reduce algorithmic complexity, inter-component coupling, and total lines of code. The abstraction as defined here has been successfully used to implement several complex applications and is shown to capture the essence of many more existing distributed sensor network algorithms.
     

  • Intelligent Fluid Infrastructure for Embedded Networking
    Aman Kansal, Arun A Somasundara, David Jea, Mani B Srivastava, and Deborah Estrin, University of California, Los Angeles
  • Computer networks have historically considered support for mobile devices as an extra overhead to be borne by the system. Recently however, researchers have proposed methods by which the network can take advantage of mobile components. We exploit mobility to develop a fluid infrastructure: mobile components are deliberately built into the system infrastructure for enabling specific functionality that is very hard to achieve using other methods. Built-in intelligence helps our system adapt to run time dynamics when pursuing pre-defined performance objectives. Our approach yields significant advantages for energy constrained systems, sparsely deployed networks, delay tolerant networks, and in security sensitive situations. We first show why our approach is advantageous in terms of network lifetime and data fidelity. Second, we present adaptive algorithms that are used to control mobility. Third, we design the communication protocol supporting a fluid infrastructure and long sleep durations on energy-constrained devices. Our algorithms are not based on abstract radio range models or idealized unobstructed environments but founded on real world behavior of wireless devices. We implement a prototype system in which infrastructure components move autonomously to carry out important networking tasks. The prototype is used to validate and evaluate our suggested mobility control methods.
     

  • Impact of Radio Irregularity on Wireless Sensor Networks
    Gang Zhou, Tian He, Sudha Krishnamurthy, and John A. Stankovic, University of Virginia
  • In this paper, we investigate the impact of radio irregularity on the communication performance in wireless sensor networks. Radio irregularity is a common phenomenon which arises from multiple factors, such as variance in RF sending power and different path losses depending on the direction of propagation. From our experiments, we discover that the variance in received signal strength is largely random; however, it exhibits a continuous change with incremental changes in direction. With empirical data obtained from the MICA2 platform, we establish a radio model for simulation, called the Radio Irregularity Model (RIM). This model is the first to bridge the discrepancy between spherical radio models used by simulators and the physical reality of radio signals. With this model, we are able to analyze the impact of radio irregularity on some of the well-known MAC and routing protocols. Our results show that radio irregularity has a significant impact on routing protocols, but a relatively small impact on MAC protocols. Finally, we propose six solutions to deal with radio irregularity. We evaluate two of them in detail. The results obtained from both the simulation and a running testbed demonstrate that our solutions greatly improve communication performance in the presence of radio irregularity.

       12:30 p.m. - 02:00 p.m.   lunch - sponsored by Docomo and HP
       02:00 p.m. - 03:30 p.m.   Mobile Data Management
      Session Chair: Eyal De Lara, University of Toronto
  • Middleware Support for Reconciling Client Updates and Data Transcoding
    Thomas Phan, George Zorpas, and Rajive Bagrodia, University of California at Los Angeles
  • In mobile Internet applications, data can be transcoded, updated, and transferred across heterogenous clients. The problem then arises where updates made in the context of an initial transcoding results in content too stringently transcoded for subsequent clients, thereby causing loss of semantic value. We solve this problem by suggesting that the updates themselves can be transformed so that they can be applied directly to the original data instead of to the transcoded data; this approach allows the data to preserve as much semantic value as possible across all heterogeneous clients without unnecessary transcoding artifacts. We define reconciliation rules that can govern the interaction between client updates and transcoding, demonstrate a complete middleware architecture that supports our methodology, and provide two case studies using content-transferring applications. We show that our resulting middleware system executes our reconciliation approach with acceptable latency (under 5 seconds for 200 kbytes of layered content), good scalability, and well-organised modularity.
     

  • Exponential Index: A Parameterized Distributed Indexing Scheme for Data on Air
    Jianliang Xu, Hong Kong Baptist University; Wang-Chien Lee, Penn State University; Xueyan Tang, Nanyang Technological University, Singapore
  • Wireless data broadcast has received a lot of attention from industries and academia in recent years. Access efficiency and energy conservation are two critical performance concerns in a wireless data broadcast environment. To improve the efficiency of energy consumption on mobile devices, traditional disk-based indexing techniques such as B+-tree have been extended to index broadcast data on a wireless channel. However, existing designs are mostly based on centralized tree structures. Most of these indexing techniques are not flexible in the sense that the trade-off between access efficiency and energy conservation is not adjustable based on application specific requirements. We propose in this paper a novel parameterized index, called the exponential index, which can be tuned to optimize the access latency with the tuning time bounded by a given limit, and vice versa. The proposed index is very efficient because it facilitates replication naturally by sharing links in multiple search trees and thus minimizes storage overhead. Experimental results show that the exponential index not only achieves better performance than the state-of-the-art indexes but also enables great flexibility in trade-offs between access latency and tuning time.
     

  • Mimic: Raw Activity Shipping for File Synchronization in Mobile File Systems
    Tae-Young Chang, Aravind Velayutham, and Raghupathy Sivakumar, Georgia Institute of Technology
  • In this paper, we consider the problem of file synchronization when a mobile host shares files with a backbone file server in a network file system. Previous schemes proposed to improve upon the transfer overheads of full file transfer based synchronization approaches are based on the diff or dirty block approach. In such schemes, file system blocks that have either been changed, or newly introduced, with respect to the old copy at the server are identified and selectively transferred. However, we show that for most common applications, the magnitude of changes in the file's structure predominantly lacks any correlation to the magnitude of changes actually made to its contents, chiefly due to application specific storage semantics. For such applications, diff based schemes effectively reduce to a full file transfer approach. In this context, we motivate the need for an approach that can incur transfer overheads proportional to the magnitude of user level changes, but at the same time remains application unaware. We then propose an application independent approach that relies on transferring user activity records to the server, where the new file is recreated through a playback of the user activity on the old copy of the file. The proposed approach relies on a combination of schemes including user activity to file mapping, intelligent recording, fast playback, and file verification to perform the synchronization efficiently. Finally, we identify conditions under which diff based approaches do perform better than the proposed approach, but show that detection of such conditions is straightforward thus enabling both schemes to be used in tandem with a mobile file system for bandwidth-efficient file synchronization.

       03:30 p.m. - 04:00 p.m.   Break
       04:00 p.m. - 05:00 p.m.   Support for Location
      Session Chair: Gaetano Borriello, University of Washington
  • An Architecture for Privacy-Sensitive Ubiquitous Computing
    Jason I. Hong, University of California at Berkeley; James A. Landay, University of Washington
  • Privacy is the most often-cited criticism of ubiquitous computing, and may be the greatest barrier to its long-term success. However, developers currently have little guidance or programming support in creating useful and usable interactions that are effective in helping end-users manage their privacy. To address this problem, we present Context Fabric, an infrastructure for facilitating the development of privacy-sensitive ubiquitous computing applications. The requirements for Context Fabric were gathered through an analysis of end-user needs and application developer needs for privacy. Context Fabric provides basic support for building ubiquitous computing applications, providing several customizable privacy mechanisms as well as a framework for extending privacy functionality. These mechanisms facilitate the creation of three basic interaction patterns for privacy-sensitive applications: optimistic, pessimistic, and mixed-initiative. Combined, these features allow application developers and end-users to support a spectrum of trust levels and privacy needs.
     

  • Tracking Moving Devices with the Cricket Location System
    Adam Smith, Hari Balakrishnan, Michel Goraczko, and Nissanka B. Priyantha, MIT
  • We study the problem of tracking a moving device under two indoor location architectures: an active mobile architecture and a passive mobile architecture. In the former, the infrastructure has receivers at known locations, which estimate distances to a mobile device based on an active transmission from the device. In the latter, the infrastructure has active beacons that periodically transmit signals to a passively listening mobile device, which in turn estimates distances to the beacons. Because the active mobile architecture receives simultaneous distance estimates at multiple receivers from the mobile device, it is likely to perform better tracking than the passive mobile system in which the device obtains only one distance estimate at a time and may have moved between successive estimates. However, an passive mobile system scales better with the number of mobile devices and puts users in control of whether their whereabouts are tracked.

    We answer the following question: How do the two architectures compare in tracking performance? We find that the active mobile architecture performs better at tracking, but that the passive mobile architecture has acceptable performance; moreover, we devise a hybrid approach that preserves the benefits of the passive mobile architecture while simultaneously providing the same performance as an active mobile system, suggesting a viable practical solution to the three goals of scalability, privacy, and tracking agility.

       05:00 p.m. - 06:30 p.m.   Panel Session: RFID
      Moderator & panel chair: Steven Shafer, Microsoft Research

  Radio Frequency ID (RFID) tags are small, single-purpose mobile computers that report their ID number, and sometimes other information such as memory contents or sensor measurements, over a strict tag-to-reader radio protocol. RFID protocols emphasize rapid reporting by scores or hundreds of tags to a single reader. Developments over the last 5 years have made it possible for RFID to augment or even challenge bar codes for manufacturing, shipping, and retail applications. With tag costs expected to drop to 5 cents each, we may one day be living in a world with a tag in almost everything made by humans. How is this happening? What are the obstacles and issues? The RFID Panel will explore the subject from diverse points of view in this panel session.

 

       07:00 p.m. - 09:00 p.m.   banquet dinner - sponsored by Microsoft
       June 9th, Wednesday
 
       08:00 a.m. onwards   -   Continental Breakfast
       09:00 a.m. - 09:15 a.m.   Opening Remarks and Awards
       09:00 a.m. - 10:30 a.m.   Exploiting Path Diversity in Mobile Systems
      Session Chair: Roy Want, Intel Research
  • Divert: Fine-grained Path Selection for Wireless LANs
    Allen Miu, Godfrey Tan, and Hari Balakrishnan, MIT CSAIL; John Apostolopoulos, HP Labs
  • The performance of Wireless Local Area Networks (WLANs) often suffers from link-layer frame losses caused by noise, interference, multipath, attenuation, and user mobility. We observe that frame losses often occur in bursts and that three of the five main causes of frame losses--multipath, attenuation, mobility--depends on the transmission path traversed between an access point (AP) and a client station.

    In a typical WLAN deployment, different transmission paths to a client exist in places where overlapping coverage is provided by a set of neighboring APs. Using experimental measurements and analysis on a 802.11b testbed, we show that fine-grained path selection among a set of neighboring APs can significantly reduce path-dependent losses in WLANs. We design and implement a WLAN distribution system called Divert, which supports fine-grained path selection for downlink communications, on an 802.11b testbed. Divert reduces frame losses without consuming any extra bandwidth in the wireless medium. Our experimental results show that Divert can reduce frame loss rates in realistic scenarios by as much as 26% compared to a fixed-path scheme that uses the best available transmitter.
     

  • MAR: A Commuter Router Infrastructure for the Mobile Internet
    Pablo Rodriguez, Microsoft Research Cambridge; Rajiv Chakravorty, Julian Chesterfield, and Ian Pratt, Cambridge University; Suman Banerjee, University of Wisconsin-Madison
  • We introduce MAR, a commuter mobile access router infrastructure that exploits wireless diversity (e.g. channel diversity, network diversity, and technology diversity) to provide improved data performance for wireless data users. Our system design stems from the observation that rather than choosing a single wireless service provider (e.g. Sprint, AT&T, BT, Vodafone), a single technology (e.g. GPRS, UMTS, CDMA, 802.11), or a single wireless channel, users can obtain significant benefits by using the multiplicity of choices available. MAR is a wireless multi-homed device that can be placed in moving vehicles (e.g. car, bus, train) to enable high-speed data access. MAR dynamically instantiates new channels based on traffic demand, aggregates the bandwidth and dynamically shifts load from poor quality to better quality channels. MAR, thus, provides a faster, more stable, and reliable communication channel to mobile users. We have implemented and tested the MAR system in our testbed which spans the networks of three different cellular providers. Through our experiments we have performed a detailed evaluation to quantify the benefits of MAR for different protocols and applications. For example, even in highly mobile environments, MAR, on average, improves the end-user experience of web-browsing and streaming applications by a factor of 2.8 and 4.4 respectively. Our results show that significant benefits can be obtained by exploiting the diversity in coverage offered by many cellular operators, different technology networks (e.g. GPRS, CDMA), and diverse wireless channels.
     

  • A Mechanism for Host Mobility Management supporting Application Awareness
    A.J.H. Peddemors, H. Zandbelt, and M.S. Bargh, Telematica Instituut
  • Many approaches exist today that address the issues that arise when a mobile node changes its point(s) of attachment to the Internet. Mobile IP takes care of host mobility at the IP layer; others at the transport layer (Mobile SCTP) or at the application layer (SIP with re-invite). In practice, most of these approaches rely on functionality residing on the mobile host that scans, detects and activates the networks available through one or more network interfaces. The mechanism proposed in this paper takes into account that multiple of these approaches may be applied at the same time. It provides the applications on the mobile host with information about the state of the lower-layer mobility management protocols (such as Mobile IP) as well as the state and characteristics of the available network resources. Applications may consecutively adapt their behavior depending on this mobility process information and thus accommodate to the changed network connectivity conditions, possibly in an application specific manner. In this paper, we present the architecture of our mobility management mechanism. We also describe the implementation of our prototype and the results of experiments with the mechanism, thereby addressing the complexities of an integrated application-aware mobility management system.

       10:30 a.m. - 11:00 a.m.   Break
       11:00 a.m. - 12:30 p.m.   Wide-area Monitoring of Mobile Objects
      Session Chair: Mary Baker, HP Labs
  • Electronic Shepherd - a Low-Cost, Low-Bandwidth, Wireless Network System
    Bjorn Thorstensen, Tore Syversen, Tron Walseth, and Trond-Are Bjornvold, Telenor R&D, Tromso, Norway
  • This paper reports a new novel low-cost, wireless communication network system, called the Electronic Shepherd (ES). The system is innovative in the way that it supports flock behavior, meaning that a flock leader monitors the state of the other elements in the flock using low-cost radio communication equipment. The paper addresses both details of the terminal devices and communication protocols, as well as testing of the system in a real environment. The ES system was originally made to address special needs for sheep and reindeer farmers who were seeking a system to keep track of their animals during the grazing season. The system, including GPS receivers, UHF radio communication transceivers and GPRS modems, contributes a new approach for low-cost networking and service implementation, not only for the purpose of animal tracking, but also for other applications where objects are to be monitored at a low cost.
     

  • Implementing Software on Resource-Constrained Mobile Sensors: Experiences with Impala and ZebraNet
    Ting Liu, Christopher M. Sadler, Pei Zhang, and Margaret Martonosi, Princeton University
  • ZebraNet is a mobile, wireless sensor network in which nodes move throughout an environment working to gather and process information about their surroundings [10]. As in many sensor or wireless systems, nodes have critical resource constraints such as processing speed, memory size, and energy supply; they also face special hardware issues such as sensing device sample time, data storage/access restrictions, and wireless transceiver capabilities. This paper discusses and evaluates ZebraNet's system design decisions in the face of a range of real-world constraints.

    Impala -- ZebraNet's middleware layer -- serves as a lightweight operating system, but also has been designed to encourage application modularity, simplicity, adaptivity, and repairability. Impala is now implemented on ZebraNet hardware nodes, which include a 16-bit microcontroller, a low-power GPS unit, a 900MHz radio, and 4Mbits of non-volatile FLASH memory. This paper discusses Impala's operation scheduling and event handling model, and explains how system constraints and goals led to the interface designs we chose between the application, middleware, and firmware layers. We also describe Impala's network interface which unifies media access control and transport control into an efficient network protocol. With the minimum overhead in communication, buffering, and processing, it supports a range of message models, all inspired by and tailored to ZebraNet's application needs. By discussing design tradeoffs in the context of a real hardware system and a real sensor network application, this paper's design choices and performance measurements offer some concrete experiences with software systems issues for the mobile sensor design space. More generally, we feel that these experiences can guide design choices in a range of related systems.
     

  • Energy-Efficient Surveillance System Using Wireless Sensor Networks
    Tian He, Sudha Krishnamurthy, John A. Stankovic, Tarek Abdelzaher, Liqian Luo, Radu Stoleru, Ting Yan, and Lin Gu, University of Virginia; Jonathan Hui and Bruce Krogh, Carnegie-Mellon University
  • The focus of surveillance missions is to acquire and verify information about enemy capabilities and positions of hostile targets. Such missions often involve a high element of risk for human personnel and require a high degree of stealthiness. Hence, the ability to deploy unmanned surveillance missions, by using wireless sensor networks, is of great practical importance for the military. Because of the energy constraints of sensor devices, such systems necessitate an energy-aware design to ensure the longevity of surveillance missions. Solutions proposed recently for this type of system show promising results through simulations. However, the simplified assumptions they make about the system in the simulator often do not hold well in practice and energy consumption is narrowly accounted for within a single protocol. In this paper, we describe the design and implementation of a running system for energy-efficient surveillance. The system allows a group of cooperating sensor devices to detect and track the positions of moving vehicles in an energy-efficient and stealthy manner. We can trade off energy-awareness and surveillance performance by adaptively adjusting the sensitivity of the system. We evaluate the performance on a network of 70 MICA2 motes equipped with dual-axis magnetometers. Our results show that our surveillance strategy is adaptable and achieves a significant extension of network lifetime. Finally, we share lessons learned in building such a complete running system.

       12:30 p.m. -   Conference ends.