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Location-based Service (LBS) becomes increasingly important for wireless and mobile networks. In current LBS schemes, Service Providers (SPs) require users report their accurate locations, which can be illegally used by adversaries to infer sensitive information of users. Privacy disclosure raises serious concerns and limits the application of LBS. Previous solutions either rely on pre-installed centralized intermediary or assume cooperative users. Other distributed solutions, lacking of user obligation, only provide relatively poor anonymity. In this study, we propose a new solution of pseudonym change, which works for non-cooperative users and in the absence of intermediary. The basic idea behind our solution is ad-hoc anonymity. The proposed solution allows users to decide whether or not participating according to their own wills. In addition, artificially generated dummies mix up all the users who have participated in pseudonym changes at different times. Theoretical analysis demonstrates that asynchronous pseudonym change and dummy participation notably enhance privacy protection. We implement our solution on a real-world dataset of mobile phone users, which is collected at Boston, MA, and by the Reality Mining, MIT. The simulation results show that our approach significantly outperforms existing solutions.