Ionut Constandache

SurroundSense: mobile phone localization via ambience fingerprinting

A growing number of mobile computing applications are centered around the users location. The notion of location is broad, ranging from physical coordinates (latitude/longitude) to logical labels (like Starbucks, McDonalds). While extensive research has been performed in physical localization, there have been few attempts in recognizing logical locations. This paper argues that the increasing number of sensors on mobile phones presents new opportunities for logical localization. We postulate that ambient sound, light, and color in a place convey a photo-acoustic signature that can be sensed by the phones camera and microphone. In-built accelerometers in some phones may also be useful in inferring broad classes of user-motion, often dictated by the nature of the place. By combining these optical, acoustic, and motion attributes, it may be feasible to construct an identifiable fingerprint for logical localization. Hence, users in adjacent stores can be separated logically, even when their physical positions are extremely close. We propose SurroundSense, a mobile phone based system that explores logical localization via ambience fingerprinting. Evaluation results from 51 different stores show that SurroundSense can achieve an average accuracy of 87% when all sensing modalities are employed. We believe this is an encouraging result, opening new possibilities in indoor localization.

Towards Mobile Phone Localization without War-Driving

This paper identifies the possibility of using electronic compasses and accelerometers in mobile phones, as a simple and scalable method of localization without war-driving. The idea is not fundamentally different from ship or air navigation systems, known for centuries. Nonetheless, directly applying the idea to human-scale environments is non-trivial. Noisy phone sensors and complicated human movements present practical research challenges. We cope with these challenges by recording a persons walking patterns, and matching it against possible path signatures generated from a local electronic map. Electronic maps enable greater coverage, while eliminating the reliance on WiFi infrastructure and expensive war-driving. Measurements on Nokia phones and evaluation with real users confirm the anticipated benefits. Results show a location accuracy of less than 11m in regions where todays localization services are unsatisfactory or unavailable.

EnLoc: Energy-Efficient Localization for Mobile Phones

A growing number of mobile phone applications utilize physical location to express the context of information. Most of these location-based applications assume GPS capabilities. Unfortunately, GPS incurs an unacceptable energy cost that can reduce the phones battery life to less than nine hours. Alternate localization technologies, based on WiFi or GSM, improve battery life at the expense of localization accuracy. This paper quantifies this important tradeoff that underlies a range of emerging services. Driven by measurements from Nokia N95 phones, we develop an energy-efficient localization framework called EnLoc. The framework characterizes the optimal localization accuracy for a given energy budget, and develops prediction- based heuristics for real-time use. Evaluation on traces from real users demonstrates the possibility of achieving good localization accuracy for a realistic energy budget.

Using mobile phones to write in air

Numerous sensors in modern mobile phones enable a range of people-centric applications. This paper envisions a system called PhonePoint Pen that uses the in-built accelerometer in mobile phones to recognize human writing. By holding the phone like a pen, a user should be able to write short messages or draw simple diagrams in the air. The acceleration due to hand gestures can be translated into geometric strokes, and recognized as characters. We prototype the PhonePoint Pen on the Nokia N95 platform, and evaluate it through real users. Results show that English characters can be identified with an average accuracy of 91.9%, if the users conform to a few reasonable constraints. Future work is focused on refining the prototype, with the goal of offering a new user-experience that complements keyboards and touch-screens.

PhonePoint pen: using mobile phones to write in air

The ability to note down small pieces of information, quickly and ubiquitously, can be useful. This paper proposes a system called PhonePoint Pen that uses the in-built accelerometer in mobile phones to recognize human writing. By holding the phone like a pen, an user should be able to write short messages or even draw simple diagrams in air. The acceleration due to hand gestures can be converted into an image, and sent to the users Internet email address for future reference. We motivate the utility of such a system through simple use-cases and applications, and present the design and implementation challenges towards a functional prototype. Our early results show that the PhonePoint Pen is feasible if the user is restricted to a few simple constraints.

Energy-Efficient Localization via Personal Mobility Profiling

Location based services are on the rise, many of which assume GPS based localization. Unfortunately, GPS incurs an unacceptable energy cost that can reduce the phone’s battery life to less than ten hours. Alternate localization technology, based on WiFi or GSM, improve battery life at the expense of localization accuracy. This paper quantifies this important tradeoff that underlies a wide range of emerging applications. To address this tradeoff, we show that humans can be profiled based on their mobility patterns, and such profiles can be effective for location prediction. Prediction reduces the energy consumption due to continuous localization. Driven by measurements from Nokia N95 phones, we develop an energy-efficient localization framework called EnLoc. Evaluation on real user traces demonstrates the possibility of achieving good localization accuracy for a realistic energy budget.

Creating a room connectivity graph of a building from per-room sensor units

Sensor and actuator networks are often installed in buildings for energy-related applications such as lighting and climate control. Such systems require metadata about the deployed hardware (e.g. which room each is in, what the function of each room is) in order to operate effectively. In this paper we present methods to automatically determine such metadata, in particular the room connectivity graph (i.e., which rooms share a doorway/interior window). Crucially, our method works with just one sensor unit per room, does not require special placement of any of the sensors, and can therefore work on data from existing widely-deployed applications (such as burglar alarms). We apply this method to a 30-day data set from single per-room sensor units deployed in two residential homes in the United Kingdom. Room connectivity is determined based on: spillover of artificial light between rooms; occupancy detections due to movement between rooms; and a fusion of the two. The fusion of both techniques is shown to work better than either technique alone, with a 93% true positive rate and 0.5% false positive rate (aggregate across both houses), and a convergence time of under a week.

Secure control of portable images in a virtual computing utility

A virtual computing utility hosts guest virtual machines on server provider sites. Each VM is an instantiation of some image or virtual appliance, which might be supplied by the VM owner or a third-party image provider. This paper addresses the problem of establishing a secure channel between a VM and an automated controller running on behalf of the VMs authorized owner. A secure channel is an essential toehold for post-install actions by the controller to adapt the VM to its local environment, join it to an application service, and/or monitor and control its execution. A simple and practical solution is to modify an image for a particular site or owner, e.g., by pre-installing keys or tokens onto the image. That approach compromises the portability of images, and could interfere with image sharing, use of new operating systems on image appliances, or endorsement of standard images by image providers. This paper presents an alternative solution that preserves the portability of images. The solution employs a standard keymaster service on the images. The keymaster and controller conduct a one-round binding protocol for mutual authentication and key exchange, seeded by secure tokens passed from the utility boot authority. The binding protocol relies only on security mechanisms at the transport layer and above, so it is suitable for use with remote controllers.

Policy-Driven Negotiation for Authorization in the Grid

In many grid services deployments, the clients and servers reside in different administrative domains. Hence, there is a requirement both to discover each others authorization policy, in order to be able to present the right assertions that allow access, and to reveal as little as possible of the access policy details to unauthorized parties. This paper describes a mechanism where the client and servers are semantically annotated with policies that protect their resources. These annotations specify both constraints and capabilities that are used during a negotiation to reason about and communicate the need to see certain credentials from the other party and to determine whether requested credentials can be obtained and revealed. The result of the negotiation is a state where both parties have satisfied their policy constraints for a subsequent interaction or where such interaction is disallowed by either or both. Furthermore, we present an implementation of a prototype, based on the PEERTRUST policy language, and a reasoning engine that is integrated in the Web services runtime component of the globus toolkit. The negotiation process is facilitated through the implementation of WSRF-compliant service interfaces for protocol message exchanges.

Daredevil: indoor location using sound

A variety of techniques have been used by prior work on the problem of smartphone location. In this paper, we propose a novel approach using sound source localization (SSL) with microphone arrays to determine where in a room a smartphone is located. In our system called Daredevil, smartphones emit sound at particular times and frequencies, which are received by microphone arrays. Using SSL that we modified for our purposes, we can calculate the angle between the center of each microphone array and the phone, and thereby triangulate the phones position. In this early work, we demonstrate the feasibility of our approach and present initial results. Daredevil can locate smartphones in a room with an average precision of 3.19 feet. We identify a number of challenges in realizing the system in large deployments, and we hope this work will benefit researchers who pursue such techniques.