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Mobile Computing, IEEE Transactions on

Issue 7 • Date July 2006

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Displaying Results 1 - 18 of 18
  • [Front cover]

    Page(s): c1
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  • [Inside front cover]

    Page(s): c2
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  • Efficient OVSF code assignment and reassignment strategies in UMTS

    Page(s): 769 - 783
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5312 KB) |  | HTML iconHTML  

    This paper presents an integrated solution for code management, assignment, and reassignment problems in UMTS. We propose a new architecture for code management and, based upon this new architecture, a code assignment strategy, referred to as "crowded-group first strategy". Our system architecture and code assignment strategy represent significant improvements both in the time complexity and the maintenance complexity. Moreover, the code blocking probability of the crowded-group first strategy is competitive to that of the other strategies. In this paper, we also propose a new code reassignment strategy, called the "crowded-branch first strategy". The main objective of this reassignment strategy is to reduce reassigned call probability with low computation overhead and extend this strategy for the general case. In order to systematically analyze the performances of the code assignment strategy, we implement a simulator to analyze the code selection behavior and code blocking probability of each strategy. Moreover, we propose some new performance metrics, named "weighted code blocking", "reassigned call probability", and "ratio of actual code reassignments", in order to precisely measure the performance obtained by different strategies. From the simulation results, we show that our proposed strategies efficiently utilize the OVSF codes with low computation overhead. View full abstract»

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  • Discovering the architecture of geo-located web services for next generation mobile networks

    Page(s): 784 - 798
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    As many geo-located Web services will be deployed in the future, mobile clients will be interested in locating a specific application server based on requirements such as proximity, service cost per location area, bandwidth, and server utilization rates. This paper presents a middleware system called GLWSA (Geo-Located Web Services Architecture) that aims to satisfy these requirements in addition to providing a thematic factorization of common location functions in order to locate mobile clients. The GLWSA supports a set of GLWSMs (Geo-Located Web Services Manager) distributed over the mobile network. It defines protocols to discover and inform a Supplier Application Server (SAS) to migrate the service execution (from a specific client) to the nearest SAS based on the client's location. This architecture is suitable to assist mobile clients to discover the geo-located Web services and to maintain the service execution closest to their location. View full abstract»

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  • GRACE-1: cross-layer adaptation for multimedia quality and battery energy

    Page(s): 799 - 815
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4344 KB) |  | HTML iconHTML  

    Mobile devices primarily processing multimedia data need to support multimedia quality with limited battery energy. To address this challenging problem, researchers have introduced adaptation into multiple system layers, ranging from hardware to applications. Given these adaptive layers, a new challenge is how to coordinate them to fully exploit the adaptation benefits. This paper presents a novel cross-layer adaptation framework, called GRACE-1, that coordinates the adaptation of the CPU hardware, OS scheduling, and multimedia quality based on users' preferences. To balance the benefits and overhead of cross-layer adaptation, GRACE-1 takes a hierarchical approach: It globally adapts all three layers to large system changes, such as application entry or exit, and internally adapts individual layers to small changes in the processed multimedia data. We have implemented GRACE-1 on an HIP laptop with the adaptive Athlon CPU, Linux-based OS, and video codecs. Our experimental results show that, compared to schemes that adapt only some layers or adapt only to large changes, GRACE-1 reduces the laptop's energy consumption up to 31.4 percent while providing better or the same video quality. View full abstract»

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  • PowerNap: an efficient power management scheme for mobile devices

    Page(s): 816 - 828
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1744 KB) |  | HTML iconHTML  

    We present PowerNap, an OS power management scheme, which can significantly improve the battery life of mobile devices. The key feature of PowerNap is the skipping of the periodic system timer ticks associated with the operating system. On an idle device, this modification increases the time between successive timer interrupts and enables us to put the processor/system into a more efficient low power state. This saves the energy consumed by workless timer interrupts and the excess energy consumed by the processor in less efficient low power states. PowerNap is tightly integrated with the kernel and is designed for optimal control of the latency and energy associated with transitioning in and out of the low power states. We describe an implementation of PowerNap and its impact on system software. Experiments with IBM's WatchPad verify the ability of PowerNap to extend battery life. An analytical model that quantifies the ability of the scheme to reduce power is also presented. The model is in good agreement with experimental results. We apply the model to small form-factor devices which use processors that have a PowerDown state. In such devices, PowerNap may extend battery life by more than 42 percent for small processor workloads and for background power levels below 10 mW. View full abstract»

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  • Performance impact of interlayer dependence in infrastructure WLANs

    Page(s): 829 - 845
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4664 KB) |  | HTML iconHTML  

    Widespread deployment of infrastructure WLANs has made Wi-Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end-to-end performance, past research has focused on MAC protocol enhancement, analysis, and simulation-based performance evaluation without sufficient consideration for modeling inaccuracies stemming from interlayer dependencies, including physical layer diversity, that significantly impact performance. We take a fresh look at IEEE 802.11 WLANs and using experiment, simulation, and analysis demonstrate its surprisingly agile performance traits. Our findings are two-fold. First, contention-based MAC throughput degrades gracefully under congested conditions, enabled by physical layer channel diversity that reduces the effective level of MAC contention. In contrast, fairness degrades and jitter increases significantly at a critical offered load. This duality obviates the need for link layer flow control for throughput improvement. Second, TCP-over-WLAN achieves high throughput commensurate with that of wireline TCP under saturated conditions, challenging the widely held perception that TCP throughput fares poorly over WLANs when subject to heavy contention. We show that TCP-over-WLAN prowess is facilitated by the self-regulating actions of DCF and TCP feedback control that jointly drive the shared channel at an effective load of two to three wireless stations, even when the number of active stations is large. We show that the mitigating influence of TCP extends to unfairness and adverse impact of dynamic rate shifting under multiple access contention. We use experimentation and simulation in a complementary fashion, pointing out performance characteristics where they agree and differ. View full abstract»

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  • Energy-efficient graphical user interface design

    Page(s): 846 - 859
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2728 KB) |  | HTML iconHTML  

    Mobile computers, such as cell phones and personal digital assistants (PDAs), have dramatically increased in sophistication. At the same time, the desire of consumers for portability limits batters size. As a result, many researchers have targeted hardware and software energy optimization. However, most of these techniques focus on compute-intensive applications rather than interactive applications, which are dominant in mobile computers. These systems frequently use graphical user interfaces (GUIs) to handle human-computer interaction. This paper is the first to explore how GUIs can be designed to improve system energy efficiency. We investigate how GUI design approaches should be changed to improve system. Energy efficiency and provide specific suggestions to mobile computer designers to enable them to develop more energy-efficient systems. We demonstrate that energy-efficient GUI (E2GUI) design techniques can improve the average system energy of three benchmarks (text-viewer, personnel viewer, and calculator) by 26.9, 45.2, and 16.4 percent, respectively. Average performance is simultaneously improved by 23.7, 34.6, and 19.3 percent, respectively. View full abstract»

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  • A general framework to construct stationary mobility models for the simulation of mobile networks

    Page(s): 860 - 871
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1968 KB) |  | HTML iconHTML  

    Simulation has become an indispensable tool in the design and evaluation of mobile systems. By using mobility models that describe constituent movement, one can explore large systems, producing repeatable results for comparison between alternatives. In this paper, we show that a large class of mobility models - including all those in which nodal speed and distance or destination are chosen independently - have a transient period in which the average node speed decreases until converging to some long-term average. This speed decay provides an unsound basis for simulation studies that collect results averaged over time, complicating the experimental process. In this paper, we derive a general framework for describing this decay and apply it to a number of cases. Furthermore, this framework allows us to transform a given mobility model into a stationary one by initializing the simulation using the steady-state speed distribution and using the original speed distribution subsequently. This transformation completely eliminates the transient period and the decay in average node speed and, thus, provides sound models for the simulation of mobile systems. View full abstract»

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  • A traffic-aware scheduling for bluetooth scatternets

    Page(s): 872 - 883
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1752 KB) |  | HTML iconHTML  

    Bluetooth is a low cost, low power, short-range radio technology used for wireless personal area networks (PANS). Bluetooth scatternet is a set of piconets interconnected via bridge devices. Good interpiconet schedulings are necessary for bridge devices to switch among piconets they participate in. This paper proposes an interpiconet scheduling algorithm named "Traffic-Aware Scatternet Scheduling" (TASS), for bridges in Bluetooth scatternets. According to masters' traffic information, TASS can adaptively switch the bridge to high traffic load masters, and increase the usage of the bridge. In addition, TASS can reduce the number of failed "unsniffs" and the overhead of "bridge switch wastes" to further increase overall system performance. Simulation results show that TASS outperforms existing interpiconet scheduling in both network throughput and adaptability for various traffic loads. View full abstract»

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  • Improved genetic algorithm for channel allocation with channel borrowing in mobile computing

    Page(s): 884 - 892
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1656 KB) |  | HTML iconHTML  

    This paper exploits the potential of the Genetic Algorithm to solve the cellular resource allocation problem. When a blocked host is to be allocated to a borrowable channel, a crucial decision is which neighboring cell to choose to borrow a channel. It is an optimization problem and the genetic algorithm is efficiently applied to handle this. The Genetic Algorithm, for this particular problem, is improved by introducing a new genetic operator, named pluck, that incorporates a problem-specific knowledge in population generation and leads to a better channel utilization by reducing the average blocked hosts. The pluck operator makes the crucial decision of when and which cell to borrow with the future consideration that the borrowing should not lead the network to chaos. It makes a channel borrowing decision that minimizes the number of blocked hosts and improves the long-term performance of the network. Efficacy of the proposed method has been evaluated by experimentation. View full abstract»

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  • Random walk for self-stabilizing group communication in ad hoc networks

    Page(s): 893 - 905
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    We introduce a self-stabilizing group communication system for ad hoc networks. The system design is based on a mobile agent, collecting and distributing information, during a random walk. Three possible settings for modeling the location of the mobile nodes (processors) in the ad hoc network are presented: slow location change, complete random change, and neighbors with probability. The group membership algorithm is based on a mobile agent collecting and distributing information. The new techniques support group membership and multicast, and also support resource allocation. View full abstract»

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  • Performance enhancement of multirate IEEE 802.11 WLANs with geographically scattered stations

    Page(s): 906 - 919
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    In today's IEEE 802.11 Wireless LANs (WLANs), e.g., the popular IEEE 802.11 b, stations support multiple transmission rates, and use them adaptively depending on the underlying channel condition via link adaptation. It has been known that when some stations use low transmission rates due to bad channel conditions, the performance of the stations using high rates is heavily degraded, and this phenomenon is often referred to as performance anomaly. In this paper, we model the WLAN incorporating stations with multiple transmission rates in order to demonstrate the performance anomaly analytically. Note that all the previously proposed models of the IEEE 802.11 assume a single transmission rate. We also develop possible remedies to improve the performance. Our solution is basically to control the access parameters such as the initial backoff window, the frame size, and the maximum backoff stage, depending on the employed transmission rate. Throughout simulations, we demonstrate that our analytical model is accurate, and the proposed mechanism can indeed provide the remedies to the performance anomaly by increasing the aggregate throughput up to six times. View full abstract»

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  • PEDAMACS: power efficient and delay aware medium access protocol for sensor networks

    Page(s): 920 - 930
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    PEDAMACS is a Time Division Multiple Access (TDMA) scheme that extends the common single hop TDMA to a multihop sensor network, using a high-powered access point to synchronize the nodes and to schedule their transmissions and receptions. The protocol first enables the access point to gather topology (connectivity) information. A scheduling algorithm then determines when each node should transmit and receive data, and the access point announces the transmission schedule to the other nodes. The performance of PEDAMACS is compared to existing protocols based on simulations in TOSSIM, a simulation environment for TinyOS, the operating system for the Berkeley sensor nodes. For the traffic application we consider, the PEDAMACS network provides a lifetime of several years compared to several months and days based on random access schemes with and without sleep cycles, respectively, making sensor network technology economically viable. View full abstract»

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  • Real-time processing of range-monitoring queries in heterogeneous mobile databases

    Page(s): 931 - 942
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1960 KB) |  | HTML iconHTML  

    Unlike conventional range queries, a range-monitoring query is a continuous query. It requires retrieving mobile objects inside a user-defined region and providing continuous updates as the objects move into and out of the region. In this paper, we present an efficient technique for real-time processing of such queries. In our approach, each mobile object is associated with a resident domain, and when an object moves, it monitors its spatial relationship with its resident domain and the monitoring areas inside it. An object reports its location to the server when it crosses over some query boundary or moves out of its resident domain. In the first case, the server updates the affected query results accordingly, while in the second case, the server determines a new resident domain for the object. This distributive approach achieves an accurate and real-time monitoring effect with minimal mobile communication and server processing costs. Our approach also allows a mobile object to negotiate a resident domain based on its computing capability. By having a larger resident domain, a more capable object has less of a chance of moving out of it and having to request a new one. As a result, both communication and server processing costs are reduced. Our comprehensive performance study shows that the proposed technique can be highly scalable in supporting location-based services in a wireless environment that consists of a large number of mobile devices. View full abstract»

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  • A comment on "The critical transmitting range for connectivity in sparse wireless ad hoc networks"

    Page(s): 943 - 944
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    In a previous paper P. Santi and D. Blough (see ibid., vol.2, no.1, p.25-39, Jan.-Mar. 2003) presented a number of results concerning the asymptotic connectivity of wireless ad hoc networks. This comment includes fixes to several of that paper's results. View full abstract»

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  • TMC Information for authors

    Page(s): c3
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    Freely Available from IEEE
  • [Back cover]

    Page(s): c4
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Aims & Scope

Mobile Computing, as proposed in this Transactions, focuses on the key technical issues related to (a) architectures, (b) support services, (c) algorithm/protocol design and analysis, (d) mobile environments, (e) mobile communication systems, (f) applications, and (g) emerging technologies.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Prasant Mohapatra
Interim Vice-Provost and CIO
Professor, Dept. Computer Science
University of California, Davis, USA
pmohapatra@ucdavis.edu