The explosive growth in social network content suggests that the largest "sensor network" yet might be human. Extending the participatory sensing model, this paper explores the prospect of utilizing social networks as sensor networks, which gives rise to an interesting reliable sensing problem. In this problem, individuals are represented by sensors (data sources) who occasionally make observations about the physical world. These observations may be true or false, and hence are viewed as binary claims. The reliable sensing problem is to determine the correctness of reported observations. From a networked sensing standpoint, what makes this sensing problem formulation different is that, in the case of human participants, not only is the reliability of sources usually unknown but also the original data provenance may be uncertain. Individuals may report observations made by others as their own. The contribution of this paper lies in developing a model that considers the impact of such information sharing on the analytical foundations of reliable sensing, and embed it into a tool called Apollo that uses Twitter as a "sensor network" for observing events in the physical world. Evaluation, using Twitter-based case-studies, shows good correspondence between observations deemed correct by Apollo and ground truth.

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Using humans as sensors: an estimation-theoretic perspective

Increasingly, human beings are sensors engaging directly with the mobile Internet. Individuals can now share real-time experiences at an unprecedented scale. Social Sensing: Building Reliable Systems on Unreliable Data looks at recent advances in the emerging field of social sensing, emphasizing the key problem faced by application designers: how to extract reliable information from data collected from largely unknown and possibly unreliable sources. The book explains how a myriad of societal applications can be derived from this massive amount of data collected and shared by average individuals. The title offers theoretical foundations to support emerging data-driven cyber-physical applications and touches on key issues such as privacy. The authors present solutions based on recent research and novel ideas that leverage techniques from cyber-physical systems, sensor networks, machine learning, data mining, and information fusion. Offers a unique interdisciplinary perspective bridging social networks, big data, cyber-physical systems, and reliability Presents novel theoretical foundations for assured social sensing and modeling humans as sensors Includes case studies and application examples based on real data sets Supplemental material includes sample datasets and fact-finding software that implements the main algorithms described in the book

Social Sensing: Building Reliable Systems on Unreliable Data

With the proliferation of e-commerce, e-wallet, and e-health smartphone applications, the need for trusted mobile applications is greater than ever. Unlike their desktop counterparts, many mobile applications rely heavily on sensor inputs. As a result, trust often requires authenticity and integrity of sensor readings. For example, applications may need trusted readings from sensors such as a GPS, camera, or microphone. Recent research has started to recognize the need for "trusted sensors", yet providing the right programming abstractions and system support for building mobile trusted applications is an open problem.This paper proposes two software abstractions for offering trusted sensors to mobile applications. We present the design and implementation of these abstractions on both x86 and ARM platforms. We implement a trusted GPS sensor on both platforms, and we provide a privacy control for trusted location using differential privacy. Our evaluation shows that implementing these abstractions comes with moderate overhead on both x86 and ARM platforms. We find these software abstractions to be versatile and practical - using them we implement one novel enterprise mobile application.

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Software abstractions for trusted sensors

Trust management and reputation systems in mobile participatory sensing applications

Mobile crowd sensing enables a broad range of novel applications by leveraging mobile devices and smartphone users worldwide. While this paradigm is immensely useful, it involves the collection of detailed information from sensors and their carriers (i.e. participants) during task management processes including participant recruitment and task distribution. Such information might compromise participant privacy in various regards by identification or disclosure of sensitive attributes -- thereby increasing vulnerability and subsequently reducing participation. In this survey, we identify different task management approaches in mobile crowd sensing, and assess the threats to participant privacy when personal information is disclosed. We also outline how privacy mechanisms are utilized in existing sensing applications to protect the participants against these threats. Finally, we discuss continuing challenges facing participant privacy-preserving approaches during task management.

Participant Privacy in Mobile Crowd Sensing Task Management: A Survey of Methods and Challenges

As more services have come to rely on sensor data such as audio and photos collected by mobile phone users, verifying the authenticity of this data has become critical for service correctness. At the same time, clients require the flexibility to tradeoff the fidelity of the data they contribute for resource efficiency or privacy. This paper describes YouProve, a partnership between a mobile device's trusted hardware and software that allows untrusted client applications to directly control the fidelity of data they upload and services to verify that the meaning of source data is preserved. The key to our approach is trusted analysis of derived data, which generates statements comparing the content of a derived data item to its source. Experiments with a prototype implementation for Android demonstrate that YouProve is feasible. Our photo analyzer is over 99% accurate at identifying regions changed only through meaning-preserving modifications such as cropping, compression, and scaling. Our audio analyzer is similarly accurate at detecting which sub-clips of a source audio clip are present in a derived version, even in the face of compression, normalization, splicing, and other modifications. Finally, performance and power costs are reasonable, with analyzers having little noticeable effect on interactive applications and CPU-intensive analysis completing asynchronously in under 70 seconds for 5-minute audio clips and under 30 seconds for 5-megapixel photos.

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Daniel Sharkey

Papers

YouProve: authenticity and fidelity in mobile sensing