感謝資訊科技的進步，在這樣一個行動服務發展迅速的時代，人們可以在任何的時間和地點得到他們想要的行動服務，其中基於位置的服務是一種需要使用者的地理位置來產生相應結果的服務，隨著存取該服務次數的增加，私人軌跡信息安全的威脅越來越高，一旦使用者的軌跡被揭露或是使用者動向被識別成功，它將置使用者的人身安全於危險之中。因此，為了保護使用者私人的軌跡隱私，相關的技術便油然而生，其中K匿名和區域混淆是保護使用者位置信息的最新技術，但他們都有著致命的缺點，無法應用於現實層面。

在本論文中。我們指出以往的研究工作中被忽視的問題，並提供有效的解決方案。當群集內的使用者們過度集中時，群集內使用者的移動軌跡與該群集中心的移動軌跡相似，故攻擊者便能容易的推斷出使用者的移動軌跡導致使用者的軌跡隱私被揭露。此外，我們提出克服該弱點的解決方案，透過最大化最小群集中的最小使用者距離，使群集內使用者不要過於集中，降低與群集移動軌跡的相似性，使移動方向不易被識別。同時，在文末通過與其他研究工作之結果進行比較，以證明我們提出的方法能有效確保位置及軌跡的安全性。

Thanks for the progress of science and technology, in such an era that mobile technology develops rapidly. People could frequently get the services what they want at any given time or place. Location based service is a kind of service that requires user's geographical location to generate the corresponding results. With the increasing of access times, the threat of personal information security gets higher and higher. For the location based services, once the trajectory has been revealed or identified, it will place personal safety at risk. In order to preserve trajectory privacy, the related technology arises spontaneously. K-anonymity and area obfuscation are the state of the art strategies of protecting location infomation. Both of them have fatal shortcoming which cannot be applied in real world.
In this paper. We point out the neglected problem in present solutions and provide effective solutions. When users tend to center in a cluster which is composed by several users, the trajectory of user is similar to the trajectory of cluster center, it may be inferred by the attacker, causing the user's privacy to be exposed. Furthermore, we propose solutions which overcome the weaknesses. By maximizing the minimum user distance in minimum cluster, hides trajectory so that the moving direction of user will not be identified. By comparing with other schemes, the performance shows that the strategy we proposed ensures the location and trajectory security.

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