At present, although there are many communication modes that are unsuitable for the central anonymous servers, current location privacy preserving schemes mainly adopt the central server mode [42, 43].
(1) When the user requests the location query service, all the query contents, location information, and parameters needed to be set are sent to the central anonymous servers.
(2) After receiving the query information sent by users, according to certain rules, the central anonymous servers will generate an anonymous user set which meets the requirements, figure out the number of subanonymity regions, and then partition them; a few scattered subanonymity regions are yielded.
(3) The LBS server handles the query information sent by the central anonymous servers and returns the query results.
(4) After the refinement process, the central anonymous servers return the corresponding results to the users.
The anonymous server receives the request from the user, generates the anonymous sets, and sends the information ((X, Y, R), ([zid.sub.1], [Cont.sub.1]), ..., ([zid.sub.k], [Cont.sub.k])) to the location service server, where (X, Y, R) is the anonymous area and [zid.sub.i] is the ith anonymous identifier of the user and [Cont.sub.i] represents the content of the ith request from the user, i = 1 ~ k.
The location service server receives the requests of the user and returns the processed results ([zid.sub.1], [result.sub.1], ..., ([zid.sub.k], [result.sub.k]) to the anonymous server, and the anonymous server sends the transformed ID result to the user.
When the location anonymous server has received the request from the user, it searches the location indexes in B-tree and inserts the location information into the request queue.
The performance of the anonymous server is directly affected by the number of the request queues on the anonymous server.
We used a multicore computer to simulate the anonymous server and the PC computers to simulate the users to request concurrently the location services.
Do be wary if the person asks for your name, e-mail address (if you're on an anonymous server
), phone number, place of work, photo all in the initial letter or two.
We know that the user, the anonymous server
, and LBSPs share the space division based on quad-tree.