中文摘要：

移动用户经常会发出基于目前位置的最近邻查询.通常移动终端（用户）向不可信的位置服务器发送查询请求,请求中包含移动终端的位置信息,因而导致位置隐私的泄露.给移动用户提供位置服务的同时,保护移动用户的位置隐私也至关重要,而这种需求在公路网络应用中尤为明显.根据公路网络的结构特点,提出了隐匿环和隐匿树这两种子图结构.利用隐匿环和隐匿树模糊移动用户在公路网络中的位置信息,可以有效地保护位置隐私.文中提出了一种新的位置隐私保护方法——隐匿环与森林（CCF）,即利用宽度优先搜索在图中寻找满足一定要求的环和森林.对于包含单行线的公路网络,CCF依然能够保护移动用户的位置隐私.在基于真实与模拟数据集的实验测试中,CCF方法显示了其在保护位置隐私方面的有效性以及在提供服务质量方面的高效性.

英文摘要：

Mobile users often issue the nearest neighbor query based on their current locations.Generally,a mobile terminal（user） sends the query including his location information to an untrusted location-based server and leads to his location privacy is leaked.So,it is important to protect mobile user＇s location privacy while providing location-based service,especially in a road network application.According to the structural characteristics of the road network,two cloaking subgraph structures,cloaking cycle and cloaking tree,are proposed.They blur the user＇s location information and protect the user＇s location privacy effectively.Furthermore,a novel location privacy preserving approach,called cloaking cycle and forest（CCF for short）,is proposed.CCF finds cycles and forest that satisfy certain conditions using breadth-first search in graph.When the road network contains one-way streets,CCF can still protect the mobile user＇s location privacy.In an experimental test based on real and simulated datasets,the effectiveness on protecting location privacy and efficiency on providing service quality of CCF are given.