Publications
In Press
Article
Multimedia Systems
This paper presents a RESTful Web service platform for building mixed reality applications for both Web browsers and mobile clients. Having a common service backend makes creating applications fast, simple, and open to 3rd parties. The paper presents two mixed reality applications that have been built on the platform. It summarizes requirements for a mixed reality platform and defines a mixed reality domain model that the platform and applications share. In addition, it describes how the clients can use the REST interface to perform operations on user-generated content, as well as access real life commercial geo-content such as street view panoramas and building models.
Article
Pervasive Computing
Nokia Research Center’s Multimedia Technologies Laboratory in Santa Monica, CA is exploring how to design engaging, entertaining, and exciting novel experiences using interactive pervasive technologies. This exploration is exemplified by their creation of a socially-activated gaming experience built upon a custom platform of a multitude of interactive pervasive technologies. The results of a series of user tests of the game are discussed and techniques for overcoming challenges associated with the design of interactive applications for pervasive platforms are highlighted as potentially generalizable design insights
Article
Personal and Ubiquitous Computing
In this paper, we investigate the relation-
ship between automatically extracted behavioral char-
acteristics derived from rich smartphone data and self-
reported Big-Five personality traits (Extraversion, Agree-
ableness, Conscientiousness, Emotional Stability and
Openness to Experience). Our data stems from smart-
phones of 117 Nokia N95 smartphone users, collected
over a continuous period of 17 months in Switzerland.
From the analysis, we show that several aggregated fea-
tures obtained from smartphone usage data can be in-
dicators of the Big-Five traits. Next, we describe a ma-
chine learning method to detect the personality trait of
a user based on smartphone usage. Finally, we study the
bene ts of using gender-speci c models for this task.
Apart from a psychological viewpoint, this study facil-
itates further research on the automated classi cation
and usage of personality traits for personalizing services
on smartphones.
Article
Nano Letters
<p>We report the first successful application of an ordered bicontinuous double-gyroid vanadium pentoxide network in an electrochromic supercapacitor. The freestanding vanadia network was fabricated by electrodeposition into a voided block copolymer template that had self-assembled into the double-gyroid morphology. The highly ordered structure with 11.0-nm-wide struts and a high specific surface to bulk volume ratio of 161.4 /µm is ideal for fast and efficient lithium ion intercalation/extraction and faradaic surface reactions, which are essential for high energy and high power density electrochemical energy storage devices. Supercapacitors made from such gyroid-structured vanadia electrodes exhibit a high specific capacitance of 155 F/g and show a strong electrochromic color change from green/gray to yellow, indicating the capacitor's charge condition. The nanostructuring approach, and utilizing an electrode material which has intrinsic electrochemical color-change properties, are concepts that can be readily extended to other electrochromic intercalation compounds.</p>
In Proceedings
ACM Conference of Computer Supported Cooperative Work
ACM
In Proceedings
Proceedings of the ACM SIGCHI Conference on Human Factors in Computing Systems
ACM
Article
IEEE Transactions on Parallel and Distributed Systems
In Proceedings
ACM SIGCHI Conference on Human Factors in Computing Systems
ACM
2012
Article
ACM Transactions on Intelligent Systems and Technology (ACM-TIST)
With the prevalence of smart mobile devices with multiple sensors, the commercial application of intelligent
context-aware services becomes more and more attractive. However, limited by the battery capacity, the
energy efficiency of context-sensing is the bottleneck for the success of context-aware applications. Though
several previous studies for energy efficient context-sensing have been reported, none of them can be applied
to multiple types of high energy consuming sensors. Moreover, applying machine learning technologies to
energy efficient context-sensing is under-explored too. In this paper, we propose to leverage machine learn-
ing technologies for improving the energy efficiency of multiple high energy consuming context sensors by
trading-off the sensing accuracy. To be specific, we try to infer the status of high energy consuming sen-
sors according to the outputs of software based sensors and the physical sensors that are necessary to work
all the time for supporting the basic functions of mobile devices. If the inference indicates the high energy
consuming sensor is in a stable status, we avoid the unnecessary invocation and instead use the latest in-
voked value as the estimation. The experimental results on real data sets show that the energy efficiency of
GPS sensing and audio level sensing are significantly improved by the proposed approach while the sensing
accuracy is over 90%.
Article
Journal of Visual Communication and Image Representation
We propose a patch-based image compression framework inspired by the inpainting techniques. The repeated patterns in one image are exploited for compression in a non-parametric manner, i.e., directly sampling image patches and encoding the similarity between them. We show how this idea leads to an assisted inpainting method, and how the inpainting method can be integrated into a patch-based image compression framework in a rate-distortion (R-D) optimal fashion. Two specific techniques - assisted inpainting for decoding, and R-D optimization for encoding by mode selection or image analysis - are presented in this paper. Experimental results show that compared with standard H.264 intra coding, our system (1) achieves up to 0.85 dB gain when optimized for objective quality and (2) saves as much as 25% bit-rate at similar subjective quality levels.
Article
Applied Physics Letters
We have observed multimode transport and high ON/OFF ratio in silicon nanochain devices.
Silicon nanochains grown by thermal evaporation of SiO solid sources consisted of chains of
silicon nanocrystals ~10 nm in diameter, separated by SiO2 regions. The devices were fabricated
using electron beam lithography on SiO2 thermally grown on silicon substrate. These devices
exhibited high ON/OFF current ratio up to 104. The inverse subthreshold slope as small as
500 mV/decade was observed in these devices. Therefore, we believe silicon nanochains hold
great potential to be used in field effect transistors.
Conference
21st International World Wide Web Conference
ACM Press
Third-party applications (apps) drive the attractiveness of web and mobile application platforms. Many of these platforms adopt a decentralized control strategy, relying on explicit user consent for granting permissions that the apps request. Users have to rely primarily on community ratings as the signals to identify the potentially harmful and inappropriate apps even though community ratings typically reflect opinions about perceived functionality or performance rather than about risks. With the arrival of HTML5 web apps, such user-consent permission systems will become more widespread. We study the effectiveness of user-consent permission systems through a large scale data collection of Facebook apps, Chrome extensions and Android apps. Our analysis confirms that the current forms of community ratings used in app markets today are not reliable indicators of privacy risks of an app. We find some evidence indicating attempts to mislead or entice users into granting permissions: free applications and applications with mature content request more permissions than is typical; 'look-alike' applications which have names similar to popular applications also request more permissions than is typical. We also find that across all three platforms popular applications request more permissions than average.
In Book
Handbook of Visual Display Technology
The transmissive and transflective LCDs are essentially stacks of optical films. Aside from the electro-optic function of the LC material itself, the viewing characteristics of the display are determined by the optical properties of these films. This chapter concentrates on the light management in mobile LCDs starting with light sources and light guide plates, and subsequently the role of individual film layers in light management is described.
In Proceedings
IEEE International Symposium on Information Theory
The connectivity graph of wireless networks, under many models as well as in practice, may contain unidirectional links. The simplifying assumption that such links are useless is often made, mainly because most wireless protocols use per-hop acknowledgments. However, two-way communication between a pair of nodes can be established as soon as there exists paths in both directions between them. Therefore, instead of discarding unidirectional links, one might be interested in studying the strongly connected components of the connectivity graph.
<br>
In this paper, we look at the percolation phenomenon in some directed random geometric graphs that can be used to model wireless networks. We show that among the nodes that can be reached from the origin, a non-zero fraction can also reach the origin. In other words, the percolation threshold for strong connectivity is equal to the threshold for one-way connectivity.
Article
Special Issue of the Elsevier’s Journal of Systems and Software on “Mobile Applications: Status and Trends”
Mobile devices are increasingly being used to store and manage users' personal information, as well as to access popular third-party context-based services. Very often, these applications need to determine common availabilities among a set of user schedules, in order to allow colleagues, business partners and people to meet. The privacy of the scheduling operation is paramount to the success of such applications, as often users do not want to share their personal schedule details with other users or third-parties. In this paper, we propose practical and privacy-preserving solutions for mobile devices to the server-based scheduling problem. Our three novel algorithms take advantage of the homomorphic properties of well-known cryptosystems in order to privately and efficiently compute common user availabilities. We also formally outline the privacy requirements in such scheduling applications and we implement our solutions on real mobile devices. The experimental measurements and analytical results show that the proposed solutions not only satisfy the privacy properties but also fare better, in regard to computation and communication efficiency, compared to other well-known solutions. Finally, we assess the utility and expectations, in terms of privacy and usability, of the proposed solutions by means of a targeted survey and user-study of mobile-phone users.
Article
Distributed and Parallel Databases
Many applications of wireless sensor networks monitor the physical world and report events of interest. To facilitate event detection in these applications, in this paper we propose a pattern-based event detection approach and integrate the approach into an in-network sensor query processing framework. Different from existing threshold-based event detection, we abstract events into patterns in sensory data and convert the problem of event detection into a pattern matching problem.We focus
on applying single-node temporal patterns, and define the general patterns as well as five types of basic patterns for event specification. Considering the limited storage on sensor nodes, we design an on-node cache manager to maintain the historical data required for pattern matching and develop event-driven processing techniques for queries in our framework. We have conducted experiments using patterns for events that are extracted from real-world datasets. The results demonstrate the effectiveness and efficiency of our approach.
Conference
CSCW
ACM Press
In Northern rural China, many people own a mobile phone without ever having purchased it: they received it as a gift from better off relatives, usually their migrant children. Drawing from ethnographic field work in three Chinese villages, we describe practices of mobile phone gifting and the social relations that underlie them, as well as the consequences of the circulation of mobile phones, from the change of use that happens when they move from an urban environment to the countryside, to the possibilities that they open up or close out for rural users. We conclude with implications for technology design that emphasize the situated nature of these experiences and thoughtful approaches to the design of ‘traveling’ mobiles.
In Book
Handbook of Visual Display Technology
Springer-SBM
Energy savings and device efficiency aspects have become increasingly important in mobile device design. Displays are responsible for a large portion of modern mobile multimedia device power consumption, and thus, traditional power management methods often rely on shutting off the display for inactive periods. Since the multimedia consumption is becoming the prominent use case for a mobile device, this logic does not apply for power savings any more. The focus needs to shift to making the device itself more power-efficient. This Chapter describes some of the power management principles for modern mobile multimedia displays.
In Book
Handbook of Visual Display Technology
Springer-SBM
Displays can be found in many handheld electronic products, especially those that rely on visual communication and multimedia. These are features that ever more often also appear among the variety that today’s mobile phones offer. The mobile phone market can be thought of as the model market of display-centric handheld electronic devices. This Chapter describes shortly the history of the display in a mobile phone, discusses the mobile display requirements, and summarizes the technology alternatives for mobile device displays. Finally, a short outline of the Section is given.
In Book
Handbook of Visual Display Technology
Springer-SBM
Besides transmissive and transflective displays, especially organic light-emitting devices (OLEDs) are present on the mobile display market. Of these, mobile display aspects of OLEDs are introduced in this Chapter. In addition to these main display technologies, there are many others that attempt to gain a presence on the mobile device application area. Some of these, such as Field Sequential Color (FSC) displays, Electrowetting Displays (EWDs), Micro-ElectroMechanical (MEMS) displays, and Autostereoscopic Displays are discussed. Finally, as a special case, Electrophoretic Displays (EPIDs) are described, as applied to Electronic Book Reader (EBR) displays.
In Book
Handbook of Visual Display Technology
Springer-SBM
An introduction to transflective displays for mobile devices is given, and the transflective display structure is discussed, with regard to optimization of the display to mobile devices. Ways to improve the viewing angle of transflective displays are described. Finally, some aspects of integrating touch capability to transflective displays are given.
Article
Service Oriented Computing and Applications (SOCA)
<p>With more and more personal data being collected and stored by service providers, there is an increasing need to ensure that their usage is compliant with privacy regulations and user preferences. We consider the specific scenario where promised usage is specified as metric temporal logic policies, and these policies can be verified against the database usage logs. Given the vast amount of data being collected, scalability is very important. In this work, we show how such usage monitoring can be performed in a distributed fashion for an expressive subset of policies. Experimental results are given for a real-life use case to show the genericness and scalability of the results.</p>
Conference
CHI EA '12 - Proceedings of the 2012 ACM annual conference extended abstracts on Human Factors in Computing Systems
ACM Press
<p>We present a touch and proximity based method for binding a group of mobile devices into an ecosystem for collaborative interactions. We aim to provide a seamless user experience by integrating the binding method with the application start-up flow. Our method also determines the order of the devices, allowing implementation of spatial interactions.</p>
Article
Journal of Electronic Imaging
<p>We examined the image quality, image clarity, and viewing comfort of 2-D images rendered on an autostereoscopic display. Opinions on daily use of the content was gathered. Two different stereo displays were used in the experiments—a lenticular lens stereo display employing fixed 3-D stereo and a display with a switchable lenticular lens structure. Images were rendered on the displays with three different rendering schemes. Photos of natural scenes, artificial content, and content containing textual elements were used as the test stimuli. When images with natural scenes or artificial content were categorized into clusters according to the amount of details, significant differences in image quality, image clarity, and viewing comfort scores were observed. When two of the schemes were compared using the images containing textual elements, a significant difference in the viewing comfort and a significant increase in perceived stereoscopic depth impression were found with one of the schemes. Furthermore, image quality and viewing comfort were better with the 2-D display mode than with the 3-D mode. The use of the 2-D text content in the 3-D display mode seemed to be acceptable in general, but for longer term and repeated use, improvements in text quality should be considered. The results indicate that an increase in detail levels may decrease the evaluated image quality, clarity, and viewing comfort. Moreover, for all experimental conditions, better image quality, increased image clarity, and a more comfortable viewing experience had a positive influence on decisions of daily use.</p>
Article
PHYSICA SCRIPTA
<p>We discuss some aspects of how graphene could be used in mainstream electronic devices.<br />
The main focus is on signal processing applications in high-volume, industrially manufactured<br />
battery-powered devices, e.g. mobile phones and laptop computers, but we will also discuss<br />
applicability to other components like interconnects, wireless communication antennae and<br />
camera sensors, as well as novel types of signal processing devices, based on the unique<br />
physical properties of graphene.</p>
Conference
International Conference on Signal Processing and Communications
IEEE
<p>We analyze the spectral zero-crossing rate (SZCR) properties of transient signals and show that SZCR contains accurate localization information about the transient. For a train of pulses containing transient events, the SZCR computed on a sliding window basis is useful in locating the impulse locations accurately. We present the properties of SZCR on standard stylized signal models and then show how it may be used to estimate the epochs in speech signals. We also present comparisons with some state-of-the-art techniques that are based on the group-delay function. Experiments on real speech show that the proposed SZCR technique is comparable to, and in some cases better than group-delay-based epoch detectors. In the presence of noise, a comparison with the zero-frequency filtering technique (ZFF) and Dynamic programming projected Phase-Slope Algorithm (DYPSA) showed that performance of the SZCR technique is comparable to that of DYPSA and marginally inferior to that of ZFF. For low SNRs, SZCR technique is slightly better than DYPSA but poorer than ZFF. For highpass-filtered speech, the identification rates of SZCR are slightly better than those of DYPSA, whereas ZFF performance suffers drastically.<br />
The standard deviation in the localization estimates of SZCR is<br />
marginally inferior to that of DYPSA</p>
Conference
CHI '12 - Proceedings of the 2012 ACM annual conference on Human Factors in Computing Systems
ACM Press
<p>User experience (UX) research on pervasive technologies faces considerable challenges regarding today's mobile context-sensitive applications: evaluative field studies lack control, whereas lab studies miss the interaction with a dynamic context. This dilemma has inspired researchers to use virtual environments (VEs) to acquire control while offering the user a rich contextual experience. Although promising, these studies are mainly concerned with usability and the technical realization of their setup. Furthermore, previous setups leave room for improvement regarding the user's immersive experience. This paper contributes to this line of research by presenting a UX case study on mobile advertising with a novel CAVE-smartphone interface. We conducted two experiments in which we evaluated the intrusiveness of a mobile location-based advertising app in a virtual supermarket. The results confirm our hypothesis that context-congruent ads lessen the experienced intrusiveness thereby demonstrating that our setup is capable of generating preliminary meaningful results with regards to UX. Furthermore, we share insights in conducting these studies.</p>
Article
Proceedings of the IEEE
<p>Thin-film electronics in its myriad forms has underpinned much of the technological innovation in the fields of displays, sensors, and energy conversion over the past four decades. This technology also forms the basis of flexible electronics. Here we review the current status of flexible electronics and attempt to predict the future promise of these pervading technologies in healthcare, environmental monitoring, displays and human–machine interactivity, energy conversion, management and storage, and communication and wireless networks.</p>
Article
International Journal of Pervasive Computing and Communications
<p>The recent advances in the field of ubiquitous and mobile technologies have resulted in the proliferation of mobile context-aware applications that can utilize mobile devices to monitor, detect and adapt to the changes of the surrounding environment automatically. Previous research has indicated that a context data management system is an integral part for the realization of context awareness. However, as compared to static context entities, mobile entities have special properties, such as frequent changes in the surrounding environment and intermittent network connection, which provide a need for specialized modeling and management strategies for mobile entities. Motivated by this, we propose a new modeling strategy along with additional functionalities to model and manage the contexts of mobile entities. We highlight two main contributions in this paper: firstly, we define the concept of "Mobile Space" to model mobile entities and design mechanisms to manage the different contexts associated with a specific mobile space. Secondly, we propose the design of a framework incorporating two services "Availability Updating Service" and "Application Callback Service" to handle the issue of inherent intermittent network connection for each mobile space. A prototype based on the proposed concepts and mechanisms has been developed and experiments were conducted to verify the workability of this framework.</p>
Proceedings
International Conference on Mobile Web Information Systems
Elsevier Science
<p>The many sensors embedded in phones nowadays provide advanced sensing capabilities that make it possible to capture<br />
real-time information about the user and his surroundings. There are already examples of apps that use this information to provide highly useful and contextual services to the users. However, users are still reluctant to share their personal data with service providers due to their privacy implications (if misused).<br />
In this work, we provide protocols that allow users to store their sensor data on third party (untrusted) cloud servers. The data is stored in encrypted form (so protected from the cloud providers) with access only to service providers explicitly pre-approved by the users. The protocols simultaneously also ensure that the data accessed by service providers is in fact ‘current’ and consistent. This is achieved by integrating transactional and cryptographic primitives, such as atomic uploads, optimistic concurrency control, proxy re-encryption and homomorphic encryption, among others. Finally, experimental results are given to illustrate the practical feasibility and scalability of the proposed protocols.</p>
Article
Self-optimization of random access channel in 3rd Generation Partnership Project Long Term Evolution
Wireless Communications and Mobile Computing
<p>The long term evolution (LTE) is being designed to enhance third generation radio access technologies, and it represents a major step towards high-performance mobile data networks that are fully optimized for packet-switched connections. In an initial access, the LTE user equipment executes the random access (RA) procedure while searching for serving base station and initiating services. For a good cell coverage to be obtained, feasible uplink data rate and low delays in, for example, call setup, the optimal random access channel (RACH) performance is essential. Although manual tuning of procedures can be very costly, it is important to design self-organizing network (SON) algorithms that optimize procedures such as RA. In this paper, a mathematical framework for the RACH modeling in LTE technology is presented on the basis of probability theory and statistics. A self-optimization algorithm for RACH preamble sequence allocation and preamble split is then examined using the deduced mathematical framework and system-level simulations. Performance analysis is semi-analytical: First, RACH performance results are produced using analytical model, and second, outputs are fed into a dynamic LTE network simulator. Results show that the proposed optimization approach clearly improves uplink performance and ensures a certain success rate at the first RA attempt so that shorter handover durations and call setup delays can be achieved.</p>
Proceedings
9th IEEE Workshop on Managing Ubiquitous Communications and Services
IEEE CS
<p>The ever increasing popularity of apps stems from their ability to provide highly customized services for the user.<br />
The flip side is that to provide such customized services, apps need access to very sensitive personal user information. This has led to a lot of rogue apps that e.g. pass personal information to 3rd party Ad servers in the background. Studies have shown that current app vetting processes which are mainly restricted to install time verification mechanisms are incapable of detecting and preventing such attacks. We argue that the missing fundamental aspect here is the inability to capture and control runtime characteristics of apps, e.g. we need to know not only the list of sensors that need to be accessed by an app but also their frequency of access. This leads to the need for an expressive policy language that in addition to the list of sensors, also allows specifying when, where and how frequently can they be accessed.<br />
An expressive policy language has the disadvantage of making the task of an average user more difficult in setting and analyzing the consequences of his privacy settings. Further, privacy polices evolve over time. Over time, users are likely to change their privacy settings, as a response to a recently discovered vulnerability, or to be able to install that “much desired” app, etc. Such a policy change affects both already installed (may no longer be compliant) and previously rejected apps (may be compliant now).<br />
In this paper, we propose an integrated privacy add-on that (i) compares the apps profiles vs. user’s privacy settings, outlining the points of conflict as well as the different ways in which they can be resolved. And (ii) provides efficient change management with respect to any changes in user privacy settings.</p>
Article
Conduction Bottleneck in Silicon Nanochain Single Electron Transistors Operating at Room Temperature
Japanese Journal of Applied Physics
<p>Single electron transistors are fabricated on single Si nanochains, synthesised by thermal evaporation of SiO solid sources. The nanochains consist of one-dimensional arrays of ~10nm Si nanocrystals, separated by SiO2 regions. At 300 K, strong Coulomb staircases are seen in the drain–source current–voltage (Ids–Vds) characteristics, and single-electron oscillations are seen in the drain–source current–gate voltage (Ids–Vgs) characteristics. From 300–20 K, a large increase in the Coulomb blockade region is observed. The characteristics are explained using single-electron Monte Carlo simulation, where an inhomogeneous multiple tunnel junction represents a nanochain. Any reduction in capacitance at a nanocrystal well within the nanochain creates a conduction "bottleneck", suppressing current at low voltage and improving the Coulomb staircase. The single-electron charging energy at such an island can be very high, ~20kBT at 300 K.</p>
In Proceedings
CHI 2012 Extend Abstracts
ACM
<p>Recently the text input community has seen a flurry of research attempting to refine the methods by which input technologies are rigorously evaluated. Specifically, researchers have investigated the validity of the phrases that study participants input when engaged in transcription typing tasks. The phrase set published by MacKenzie and Soukoreff has become the de facto standard for text entry evaluations since its publication. New phrase sets have recently emerged that attempt to address limitations of MacKenzie and Soukoreff’s phrase set. In this paper, we present a preliminary investigation of whether the choice of phrase sets has an impact on potential typing performance by analyzing several different phrase sets using existing typing data from mini-qwerty keyboards.</p>
Conference
Workshop on Positioning, Navigation, and Communication
<p>Personal location discovery and navigation within buildings has become an important research topic in the last years. One method to determine one’s current position based on mobile-devices is to compare the set of available WiFi access points (APs), i.e. the fingerprint of a given space, to a previously collected database. In this context, this paper addresses the inherent problem of such systems that this fingerprint database needs to be established beforehand. Thus, situations can occur where a building is only partially represented in the database and localization can only be provided in a subset of the spaces of the building. This problem occurs especially in crowd-sourcing (organic) approaches where users consecutively contribute location-binds. In these situations an additional system is needed to provide localization. We present a first study on the fusion of pedestrian dead reckoning (PDR) from inertial sensors with position estimates from a WiFi localization system. We outline a possible design of particle filter and analyze its behavior on experimental data. We conclude that the outlined method can help to improve WiFi localization and is especially useful within crowd-sourcing environments.</p>
Conference
To Appear in 45th AES Conference on Time-Frequency Applications
Audio Engineering Society
<p>Our ability to localize sounds is based on the relative time and level differences between the wavefronts arriving at the two ears. These parameters are measured as interaural time difference (ITD) and interaural level difference (ILD), respectively. ITD is the dominant cue at low frequencies and ILD is more important at high frequencies. ITD is of the order of less than a millisecond and is difficult to estimate based on sampled data. We consider the problem of ITD estimation and show that the ITD manifests as a change in the zero-crossing rate (ZCR) of the head related transfer functions (HRTFs). As a result, it becomes possible to estimate the ITD precisely by comparing the ZCRs of the left and right HRTFs. Our experimental results indicate that zero-crossings of the HRTFs alone (which are devoid of amplitude information) contain sufficient information to estimate ITD as reliably as the state-of-the-art techniques.</p>
In Proceedings
IEEE 13th International Conference on Mobile Data Management
<p>Most current mobile devices are able to determine their location, which has become part of the contextual information available to applications. However, in many cases, the exact position of the device in terms of longitude and latitude is not necessary. On the contrary, applications might benefit more from a discrete context variable that indicates the "place" in which the device currently is. To realize this, the continuous device's trajectory needs to be clustered into discrete locations.<br />
Besides, the device's location is often not measured directly, but rather inferred from other measurements, such as the list of available WiFi access points. Since similar WiFi measurements lead to similar estimates of the position, it appears that the conversion into geographical coordinates is an unnecessary step in the identification of places. In this paper, we describe a density-based clustering approach that allows to learn significant places directly from a set of raw WiFi measurements. We show that this purely WiFi-based method significantly outperforms previous WiFi-based approaches and compares with some GPS-based methods.</p>
Article
Journal of Photonics for Energy
<p>Modern mobile communication devices have user interfaces that are dominated by high-quality displays. Increased multimedia use imposes high demands on the design of display modules, as the content available for mobile use becomes visually richer. Especially the power dissipation of the display can limit the amount of time available for multimedia consumption and interaction. In the mobile liquid-crystal display (LCD), the energy efficiency is determined by the backlight design. State-of-the-art backlights direct white light through a display subpixel array, with high uniformity and up to 90 % efficiency in white light output. Therefore, it is difficult to obtain system-level energy savings by improving the backlight design alone. Diffractive backlights have recently been proposed to reduce the power dissipation of the display module, and slanted grating arrays are among the enabling optical features that allow for reduction in power dissipation beyond what is available in the state of the art. By the use of diffractive grating arrays, the required primary color (red, green, or blue) is directed through the LCD subpixel array with geometrical registration, instead of flooding the whole LCD with white light and filtering the primary colors through the subpixel color filter array. This paper presents a study on grating structures based on slanted grating arrays fabricated in high refractive index materials. The grating design principles and grating outcoupling results are provided, and an outline of a new embedded system design is given. Emphasis is on grating array design aspects for future energy-efficient display system design. The results show that savings in power consumption can be expected with advanced display system design based on embedded slanted grating array backlight light guide plates.</p>
Conference
TEI 2012: 6th International Conference on Tangible, Embedded and Embodied Interaction
ACM Press
<p>Location-based services are increasingly popular, and the Earth has become covered with geotagged data. To assess a novel approach to access this information, we conducted a field trial of a mobile mixed reality application called MAA, which operates on a mobile phone. MAA displays a view through the Earth and geospatial content in the direction to which the user is pointing the device. In this paper, we report the results of the two-week long field trial of MAA. We found that the embodied usage of MAA is experienced as engaging and surprising, but may also be cumbersome in some usage situations. Virtual viewing of locations around the planet was considered pleasant. MAA was often shown to friends, and was used for watching visual materials and searching for information about cities. MAA was found to be a promising platform for many kinds of location-based content, especially for real-time events and local information.</p>
Article
Journal of the Society for Information Display
<p>Liquid-crystal-display backlight units have developed in their conventional configuration into very efficient and uniform components that allow the display to present a high-quality image to the user. Developing the backlight unit itself further faces a challenge of diminishing returns to the investment in innovation. A system-level redesign is required for the entire display module, and diffractive alternatives to the backlight design can allow a more-energy-efficient design for the display. This review concentrates on small-to-medium displays because diffractive backlight studies have also centered in this class of displays. The state of the art of backlight design is summarized and the motivation for energy-efficient system design is outlined. The theoretical basis of diffractive backlights is given, and key research studies in the area of diffractive backlights are reviewed. Finally, a discussion on the performance and future outlook of diffractive backlights completes the paper.</p>
Conference
CSCW 2012
ACM
<p>Group buying is a business model where people with the same merchandize interests form a group and conduct the purchase together to achieve a discount. Third-party proxy websites negotiate with merchants for appealing deals and then provide them to end customers. We call it online group buying. Besides, there exists local group buying where the joiners, the initiator, and sometimes even the merchants are in the same local community. Such locality induces some interesting characteristics in group buying, which remain largely unexplored in the research community. This study attempts to reveal users’ behaviors in group buying within the local context. We developed a mobile service called “HappyGo” that supports local group buying. We conducted a trial involving more than 300 users from a company office. From our findings, we believe that local group buying complements online group buying by creating a “local” economic circle while also providing users with social benefits.</p>
Article
Chemical Communications
<p>Graphite was electrochemically exfoliated in mixtures of room temperature ionic liquids and deionized water containing lithium<br />
salts to produce functionalized graphenes and such an electrochemical exfoliation technique can be directly used in making<br />
primary battery electrodes with significantly enhanced specific energy capacity.</p>
Article
Particuology
<p>Graphene-based materials are intriguing from the perspective of fundamental science and technology<br />
because they are non-toxic, chemically and thermally tolerant, and mechanically robust. Graphene<br />
exhibits superior electrical conductivity, high surface area and a broad electrochemical window that may<br />
be particularly advantageous for their applications in energy storage devices. In addition, graphene can be<br />
prepared in the form of a colloidal suspension with adjustable solubility and thus is suitable for printing<br />
applications and offers both transparency and good conductivity at the same time. In this review, applications<br />
of graphene in solar cells, batteries, supercapacitors and fuel cells are summarized with the latest<br />
developments. Furthermore, graphene as a conductive ink for printed electronics is also discussed.</p>
Conference
The Language Resources and Evaluation Conference, LREC
<p>Global communication of information and interaction<br />
is witnessing very rapid changes due to a number of<br />
technological advances. The growth rate of mobile<br />
communication has increased manifold and subsequently<br />
demand for speech and text data in this area has increased.<br />
This paper describes the method and experiences of text<br />
and speech data collection in mobile communication in<br />
Hindi and Indian English. The primary data collection is<br />
done in the form of large number of messages as part of<br />
Personal communication among natives of Hindi language<br />
and Indian speakers of English. The goal of the current<br />
project is to use large databases of Hindi and Indian<br />
English text and speech collection for development of<br />
language and acoustics models which can be further used<br />
for training Automatic speech recognition, synthesis or<br />
translation systems for Hindi in mobile communication<br />
situations. One of the interesting characteristics of mobile<br />
communication through Short Message Service (SMS)<br />
is the use of multiple languages in one message text.<br />
This type of database is ideal for language identification<br />
purpose.<br />
To gather the versatility of mobile communication<br />
among Hindi Speaking population of different age groups,<br />
12 domains have been identified for collection of text<br />
corpus. The text obtained in raw form i.e. one used in<br />
mobile communication generally based on slangs and<br />
unconventional grammar were cleaned based on language<br />
grammar rule and then was tagged and expanded to explain<br />
context specific meaning of the words. Texts of 1163<br />
participants from Hindi speaking regions and 1405 English<br />
users from India were taken for creating 13 prompt sheets.<br />
Each prompt sheet consists of 630 phonetically rich<br />
sentences made to capture all phoneme of the language.<br />
Software was developed for the creation of phonetically<br />
rich sentences. Each prompt sheet was recorded by at<br />
least 7 users simultaneously by three channels. Several<br />
dialectal variation of the language have been tried to<br />
capture by dividing the whole Hindi speaking region<br />
in 5 dialects and selecting speakers representing them.<br />
Recording of 100 speakers (male and female) belonging to<br />
different age groups from different dialects were selected<br />
to capture the impact of age, gender and dialect. The<br />
Paper also covers the observation of recording through 3 channels. The recorded utterances and the analysis of<br />
collected message helped us to analyze the traits of English<br />
in Indian context.The work is also a step forward in the<br />
direction of development of standards for mobile text and<br />
speech data collection for Indian languages.</p>
Conference
ACM SIGCHI Conference on Human Factors in Computer Systems (CHI ’12)
05/2012
<p>Digital memorabilia, such as video remixes, can increase the value of attending music events. Remixes can be made using video clips recorded by attendees during the event; however, producing them is a laborious task. In this paper we study the prospects of automatic video remixing and present the results of a study on users’ perceptions and attitudes towards collaborative automatic mobile video production.The three findings are as follows: People assess automatic video remix memorabilia as fairly equal to amateur- made manual ones, even if the manually-created video remixes are better in overall quality; as a remixing actor, a computer can be perceived to be more trustworthy than a human remixer; and, the quality of the video remix and the publication forum of the remix outcome plays a significant role when people are deciding whether or not they need public acknowledgement for their contribution. We conclude by discussing the design implications for collaborative automatic mobile video production.</p>
In Proceedings
16th International ITG Workshop on Smart Antennas (WSA)
IEEE (Xplore)
<p>Current interest is centered on non-orthogonal resource sharing between device-to-device (D2D) and cellular user<br />
equipments (C-UEs) that share the same frequency band, which then requires careful interference management techniques to avoid degrading the quality-of-service of the C-UEs. This work proposes an improved paradigm named device-to-multidevice (D2MD) communications, where a transmitting device communicates simultaneously with multiple receiving devices in an energy-efficient manner, and the underlay communication is augmented with the use of multiple transmit and receive antennas. Due to the difficulty of acquiring channel state information (CSI) of the C-UEs, we also present an enhanced D2MD scheme that does not require explicit feedback of CSI matrices from the C-UEs and/or D2MD receivers. Numerical simulations are presented to verify the efficacy of D2MD underlay transmission under a variety of CSI assumptions.</p>
Article
Applied Physics Letters
<p>Close-packed monolayers of 20 nm Au nanoparticles are self-assembled at hexane/water interfaces<br />
and transferred to elastic substrates. Stretching the resulting nanoparticle mats provides active and<br />
reversible tuning of their plasmonic properties, with a clear polarization dependance. Both uniaxial<br />
and biaxial strains induce strong blue shifts in the plasmonic resonances. This matches theoretical<br />
simulations and indicates that plasmonic coupling at nanometer scale distances is responsible for<br />
the observed spectral tuning. Such stretch-tunable metal nanoparticle mats can be exploited for the<br />
development of optical devices, such as flexible colour filters and molecular sensors.</p>
In Book
LTE Self-Organising Networks (SON): Network Management Automation for Operational Efficiency
Wiley
<p>Cellular networks are very large and extremely complicated systems. For systems of this size and complexity it is not uncommon for faults to occur. Faults can appear at several functional areas of a complex cellular network, however, the most critical domain from a fault management viewpoint is the Radio Access Network (RAN). Every base station is responsible to serve a dedicated space of the coverage area with little, if any, redundancy. If one of these network elements is not capable to fulfil its responsibilities due to the presence of a fault, there will be no other entity to offer service until the fault is rectified. During the resulting period of degraded performance, users are not experiencing services with acceptable availability, reliability or quality-of-service, which may cause serious revenue loss for the operator.</p>
<p>The problem for the network operator is, first of all, that there is huge number of network elements (i.e. base stations) each of which can go into a state of degradation. Such degradations manifest themselves in variations of several KPIs and raised alarms which are not easily mapped to a specific cause. These facts imply that considerable manual workload is required to manage this part of the system, because troubleshooting engineers need to permanently analyse performance data. ‘Manual work’ often also means that the degradation time period mentioned above can be significant.</p>
Article
IEEE Transactions on Magnetics
<p>An internal quad-band printed monopole antenna for oval-shaped mobile phone is presented. The antenna occupies a compact area of the upper part of the oval-shaped ground plane. The printed monopole antenna has two branches, which generate two resonant bands centered at around 888 and 1820 MHz. The achieved bandwidth covers GSM850 (824–894 MHz), GSM900 (880–960 MHz), DCS1800 (1710–1880 MHz), and PCS1900 (1850–1990 MHz) bands. Details of the proposed antenna design and results are presented and discussed; and good agreement is obtained between the simulated and measured results.<br />
</p>
In Book
LTE Self-Organising Networks (SON): Network Management Automation for Operational Efficiency
Wiley
<p>After having configured the network appropriately as described in the previous chapter, further optimisation steps are necessary during the operation of the network. One reason for this need is the fact that the environment may change, such as:</p>
<ul>
<li>Propagation conditions, for example, new buildings or streets, falling leaves in autumn.</li>
<li>Traffic behaviour, for example, new traffic concentrations.</li>
<li>Deployment, for example, the insertion of new base stations.</li>
</ul>
<p>As a consequence, previously configured parameters will become suboptimal. Adaptation of the parameters in order to track those changes can obviously improve the performance of the network. Another reason for further optimisation steps is the fact that measurements from the operating network under realistic load conditions provide a much more accurate picture of the reality compared with the assumptions which the initial configuration was based on. In many cases, the measurements will reveal problems which could not have been predicted from the initial assumptions on propagation or traffic. Thus, even without the aforementioned environmental changes, the configured parameters should be checked and potentially updated during the operation. The expression ‘self-optimisation’ summarises mechanisms which optimise parameters during operation, in particular based on measurements from the network. The demarcation towards ‘self-configuration’ is not always unique, that is, Dynamic Radio Configuration functions like Automatic Neighbour Relation (ANR) are executed during the initial self-configuration phase and then re-executed (when required) as a self-optimising function in the operational phase. The third SON area, ‘self-healing’ will be treated in the next chapter. In this book, the following features are categorised as ‘self-optimisation’ and discussed in detail in this chapter:</p>
<ul>
<li><i>Mobility Robustness Optimisation </i>guarantees proper mobility for the users, that is, proper handovers and re-selection between cells of the same, but also of a different RAT.</li>
<li><i>Mobility Load Balancing </i>and <i>Traffic Steering </i>try to optimally distribute traffic over the cells in particular due to load condition, but also due to other properties such as velocity, QoS or energy consumption. Obviously there is significant interaction with mobility robustness optimisation which is addressed explicitly.</li>
<li><i>Energy Saving </i>has gained more and more interest in the past. Savings are achieved on both network and UE side, for example, through switching off inactive network nodes or, for example, reducing transmit power.</li>
<li><i>Coverage and Capacity Optimisation</i> continuously adapts in particular antenna tilts and transmit powers to maximise coverage, but also to optimise capacity through minimising interference between the cells.</li>
<li><i>RACH Optimisation </i>finds the best trade-off between performance of the random access and the resources which have to be sacrificed for it.</li>
<li>Finally there are parameters for radio resource management which need adaptive configuration. Many of those parameters can be optimised based on local information inside the eNB and thus are not treated here, for example, configuration of control channels. Others have a clear SON character and will be discussed in detail, namely optimisation of parameters for power control and inter-cell interference coordination.</li>
</ul>
