Novel techniques for location-cloaked applications

Location cloaking has been shown to be cost-effective in mitigating location privacy and safety risks. This strategy, however, has significant impact on the applications that rely on location information. They may suffer efficiency loss; some may not even work with reduced location resolution. This research investigates two problems. 1) How to process location-cloaked queries. Processing such queries incurs significant more workload for both server and client. While the server needs to retrieve more query results and transmit them to the client, the client downloading these results wastes its battery power because most of them are useless. To address these problems, we propose a suite of novel techniques including query decomposition, scheduling, and personalized air indexing. These techniques are integrated into a single unified platform that is capable of handling various types of queries. 2) How a node V can verify whether or not another node P indeed locates in a cloaking region it claims. This problem is challenging due to the fact that the process of location verification may allow V to refine P\u27s location within the region. We identify two types of attacks, transmission coverage attack and distance bounding attack. In the former, V refines a cloaking region by adjusting its transmission range to partially overlap with the region, whereas in the latter, by measuring the round trip time of its communication with P. We present two corresponding counter strategies, and built on top of them, propose a novel technique that allows P to participate in location verification while providing a certain level of guarantee that its cloaking region will not be refined during the process

Managing continuous k-nearest neighbor queries in mobile peer-to-peer networks

A continuous k nearest neighbor (CKNN) query retrieves the set of k mobile nodes that are nearest to a query point, and provides real-time updates whenever this set of nodes changes. A CKNN query can be either stationary or mobile, depending on the mobility of its query point. Efficient processing of CKNN queries is essential to many applications, yet most existing techniques assume a centralized system, where one or more central servers are used for query management. In this thesis, we assume a fully distributed mobile peer-to-peer system, where mobile nodes are the only computing devices, and present a unified platform for efficient processing of both stationary and mobile CKNN queries. For each query, our technique computes a set of safe boundaries and lets mobile nodes monitor their movement with respect to these boundaries. We show that the result of a query does not change unless a node crosses over a safe boundary. As such, our technique requires a query to be re-evaluated only when there is a crossing event, thus minimizing the cost of query evaluation. For performance study, we model the communication cost incurred in query processing with a detailed mathematical analysis and verify its accuracy using simulation. Our extensive study shows that the proposed technique is able to provide real-time and accurate query results with a reasonable cost

An Efficient Probabilistic Algorithm to Detect Periodic Patterns in Spatio-Temporal Datasets

Author Contributions: Conceptualization, C.G.-S.; methodology, C.G.-S.; software, C.G.-S.; validation, C.G.-S., P.G. and M.A.P.; formal analysis, C.G.-S.; investigation, C.G.-S., P.G. and M.A.P.; data curation, C.G.-S.; writing—original draft preparation, C.G.-S., P.G. and M.A.P.; writing—review and editing, M.A.P.; funding acquisition, C.G.-S. and M.A.P. All authors have read and agreed to the published version of the manuscript.Peer reviewe

A model for a collaborative recommender system for multimedia learning material

Abstract. In a cluster of many servers containing heterogeneous multimedia learning material and serving users with different backgrounds (e.g. language, interests, previous knowledge, hardware and connectivity) it may be difficult for the learners to find a piece of material which fit their needs. This is the case of the COLDEX project. Recommender systems have been used to help people sift through all the available information to find that most valuable to them. We propose a recommender system, which suggest multimedia learning material based on the learner's background preferences as well as the available hardware and software that he/she has.

Efficiently Finding Cyclical Patterns on Twitter Considering the Inherent Spatio-temporal Attributes of Data

Social networks such as Twitter provide thousands of terabytes per day, which can be exploited to find relevant information. This relevant information is used to promote marketing strategies, analyze current political issues, and track market trends, to name a few examples. One instance of relevant information is finding cyclic behavior patterns (i.e., patterns that frequently repeat themselves over time) in the population. Because trending topics on Twitter change rapidly, efficient algorithms are required, especially when considering location and time (i.e., the specific location and time) during broadcasts. This article presents an efficient algorithm based on association rules to find cyclical patterns on Twitter, considering the inherent spatio-temporal attributes of data. Using a Hash Table enhances the efficiency of this algorithm, called HashCycle. Notably, HashCycle does not use minimum support and can detect patterns in a single run over a sequence. The processing times of HashCycle were compared to the Apriori (which is a well-known and widely used on diverse platforms) and Projection-based Partial Periodic Patterns (PPA) algorithms (which is one of the most efficient algorithms in terms of processing times). Empirical results from two spatio-temporal databases (a synthetic data set and one based on Twitter) show that HashCycle has more efficient processing times than two state-of-the-art algorithms: Apriori and PPA

Novel techniques for location-cloaked applications

Location cloaking has been shown to be cost-effective in mitigating location privacy and safety risks. This strategy, however, has significant impact on the applications that rely on location information. They may suffer efficiency loss; some may not even work with reduced location resolution. This research investigates two problems. 1) How to process location-cloaked queries. Processing such queries incurs significant more workload for both server and client. While the server needs to retrieve more query results and transmit them to the client, the client downloading these results wastes its battery power because most of them are useless. To address these problems, we propose a suite of novel techniques including query decomposition, scheduling, and personalized air indexing. These techniques are integrated into a single unified platform that is capable of handling various types of queries. 2) How a node V can verify whether or not another node P indeed locates in a cloaking region it claims. This problem is challenging due to the fact that the process of location verification may allow V to refine P's location within the region. We identify two types of attacks, transmission coverage attack and distance bounding attack. In the former, V refines a cloaking region by adjusting its transmission range to partially overlap with the region, whereas in the latter, by measuring the round trip time of its communication with P. We present two corresponding counter strategies, and built on top of them, propose a novel technique that allows P to participate in location verification while providing a certain level of guarantee that its cloaking region will not be refined during the process.</p

Managing continuous k-nearest neighbor queries in mobile peer-to-peer networks

A continuous k nearest neighbor (CKNN) query retrieves the set of k mobile nodes that are nearest to a query point, and provides real-time updates whenever this set of nodes changes. A CKNN query can be either stationary or mobile, depending on the mobility of its query point. Efficient processing of CKNN queries is essential to many applications, yet most existing techniques assume a centralized system, where one or more central servers are used for query management. In this thesis, we assume a fully distributed mobile peer-to-peer system, where mobile nodes are the only computing devices, and present a unified platform for efficient processing of both stationary and mobile CKNN queries. For each query, our technique computes a set of safe boundaries and lets mobile nodes monitor their movement with respect to these boundaries. We show that the result of a query does not change unless a node crosses over a safe boundary. As such, our technique requires a query to be re-evaluated only when there is a crossing event, thus minimizing the cost of query evaluation. For performance study, we model the communication cost incurred in query processing with a detailed mathematical analysis and verify its accuracy using simulation. Our extensive study shows that the proposed technique is able to provide real-time and accurate query results with a reasonable cost.</p

Efficiently Finding Cyclical Patterns on Twitter Considering the Inherent Spatio-temporal Attributes of Data

Social networks such as Twitter provide thousands of terabytes per day, which can be exploited to find relevant information. This relevant information is used to promote marketing strategies, analyze current political issues, and track market trends, to name a few examples. One instance of relevant information is finding cyclic behavior patterns (i.e., patterns that frequently repeat themselves over time) in the population. Because trending topics on Twitter change rapidly, efficient algorithms are required, especially when considering location and time (i.e., the specific location and time) during broadcasts. This article presents an efficient algorithm based on association rules to find cyclical patterns on Twitter, considering the inherent spatio-temporal attributes of data. Using a Hash Table enhances the efficiency of this algorithm, called HashCycle. Notably, HashCycle does not use minimum support and can detect patterns in a single run over a sequence. The processing times of HashCycle were compared to the Apriori (which is a well-known and widely used on diverse platforms) and Projection-based Partial Periodic Patterns (PPA) algorithms (which is one of the most efficient algorithms in terms of processing times). Empirical results from two spatio-temporal databases (a synthetic data set and one based on Twitter) show that HashCycle has more efficient processing times than two state-of-the-art algorithms: Apriori and PPA

Batching Location Cloaking Techniques for Location Privacy and Safety Protection

Location-based services (LBSs) have become a profitable market because they offer real-time and local information to their users. Although several benefits are obtained from the usage of LBSs, they have opened up many privacy and safety challenges because a user needs to release his/her location. To tackle these challenges, many location-cloaking techniques have been proposed. Even though these solutions are effective in protecting either location privacy or location safety, they do not provide unified protection. Furthermore, most of them do not address the potential bottleneck in the anonymity server as a high demand of location and safety protection is requested. Finally, they do not take into account the potential impact of processing a large amount of location-cloaked queries. This paper deals with the efficient construction of location-cloaking areas for many users, who have both privacy and safety requirements. To achieve this goal, the construction of location-cloaking areas is carried out in batches. The LBSs’ batch processing takes advantage of users who are close to each other and who have similar requirements. Two batching techniques to build cloaking regions are analyzed using simulations. Empirical results show our techniques are able to balance the anonymizer workload, quality of location privacy and safety protection, and LBS workload