Context Sharing In Inter-Smart Spaces

Pervasive Computing enables access to information anywhere,anytime,and makes the computing disappear.A smart space is a local Pervasive Computing environment,in which context-aware computing plays an important role in bringing intelligent interaction to users.With the development and spread of Pervasive Computing technology,research and application of smart space has extended from individual-smart-space stage to inter-smart-space stage.This extension demonstrates "pervasiveness" of Pervasive Computing,i.e.people can enjoy computing services in any smart spaces. Context-aware computing is still important in the inter-smart -space stage.However, in this stage,context sharing faces several theoretic and technical difficulties,such as semantic translation of context between smart spaces,inter-smart-space privacy protection and timely provision of massive contexts.In this dissertation,the author's researches focus on privacy protection and timely context processing in inter-smart-space context sharing scenarios.The specific issues and contributions include:(1) Firstly,it studies the state of the arts on "smart space","inter-smart space" and "context-aware computing",and proposed a context-sharing infrastructure in the inter-smart-space scenarios.Privacy and timeliness problems are briefly discussed with respect to this infrastructure.(2) Research on privacy protection in the inter-smart-space scenarios.Using location context,a typical and most widely used context,as the research object,it focuses on the users' location privacy protection in untrusted smart spaces.The two classical k-anonymity algorithm in Location-Based Service(LBS),i.e.,Clique Cloaking and Non-Clique Cloaking,provide good privacy protection only for snapshot queries but not for continuous ones.A continuous query-issuing model is proposed,which incorporates a query issuing interval model and a consecutive queries relationship model.Under this model,an attacking algorithm is devised against the k-anonymity algorithm.It is arguedthat the cardinality of anonymity-set is not a good anonymity measurement under such attacking and an entropy-based anonymity measurement AD is proposed.Experiments demonstrate that the attacking algorithms have high success rate in identifying query senders when the consecutive queries have strong relationship,and that AD is better anonymity measurement than the cardinality of anonymity-set.(3) Research on the timeliness of context dissemination in the inter-smart-space scenarios.Caching is an effective way to reduce context access overhead and improve application availability when disconnections occur.The reasoning-oriented COntext cache Replacement Algorithm(CORA) is proposed in this dissertation,which adopts context state space as a general model for diverse context reasoning methods.And based on this model,it computes the estimated access probability and invalidation time of low-level contexts to get their caching values for replacement.Simulations demonstrate that CORA gets higher hit rate than conventional replacement algorithm for high data update rate(versus access rate) in pervasive computing scenarios.(4) Research on the timeliness of context reasoning in the inter-smart-space scenarios.Considering the fact that reasoning results remain fresh within a period of time,it introduces the concept of reasoning result reuse efficiency and its computation method.Then a Freshness-aware Real-time Scheduling Algorithm(FRSA) is proposed to promote the system throughput when the reasoner is overloaded,which schedules reasoning jobs according to their result reuse efficiencies and deadlines.A heuristic algorithm of real-time scheduling is also proposed to reduce the computing complexity of value function-based real-time scheduling.The simulation demonstrates that when the reasoner is heavily overloaded,the throughput of FRSA is 10%to 30%better than those of classic scheduling algorithms,i.e.,SJF,EDF,LSF and FCFS.