Location monitoring is an important issue for real time management of mobile object positions. Significant research efforts have been dedic ated to techniques for efficient processing of spatial continuous queries on moving objects in a centralized location monitoring system. Surprisingly, very few have promoted a distributed approach to real-time location monitoring. MobiEyes is a distribute d real-time location monitoring system in a mobile environment and provides a distributed and scalable solution to processing continuously moving queries on moving objects. Mobieyes utilizes the computational power at mobile objects, leading to significan t savings in terms of server load and messaging cost when compared to solutions relying on central processing of location information at the server.

A moving query over moving objects (MQ for short) is a spatial continuous moving query over locations of moving objects. An MQ defines a spatia l region bound to a specific moving object and a filter which is a boolean predicate on object properties. The result of an MQ consists of objects that are inside the area covered by the query's spatial region and satisfy the query filter.

MQs are continuous queries, in the sense that the results of queries continuously change as time progresses. We refer to the object to which an MQ is bounded, the focal object of that query. The set of objects that are subject to be included in a query's result are called target objects of the MQ. Note that the spatial region of an MQ also moves as the focal object of the MQ moves. There are many examples of moving queries over moving objects in real life. For instance, the query MQ1: "Give me the number of friendly units within 5 miles radius around me during next 2 hours" can be submitted by a soldier equipped with mobile devices marching in the field, or a moving t ank in a military setting. The query MQ2: "Give me the positions of those customers who are looking for taxi and are within 5 miles (of my location at each instance of time or at an interval of every minute) during the next 20 minutes" can be po sted by a taxi driver marching on the road. The focal object of MQ1 is the solider marching in the field or a moving tank. The focal object of MQ2 is the taxi driver on the road.
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Most of the existing approaches for processing spatial queries on moving objects are not scalable, due to their inherent assumption that location monitoring and communication s of mobile objects are controlled by a central server. Namely, mobile objects report their position changes to the server whenever their position information changes, and the server determines which moving objects should be included in which moving queri es at each instance of time or at a given time interval. For mobile applications that need to handle a large and growing number of moving objects, the centralized approaches can suffer from dramatic performance degradation in terms of server load and netw ork bandwidth.

MobiEyes ships some part of the query processing down to the moving objects, and the server mainly acts as a mediator between moving objects. This significantly reduces the l oad on the server side and also results in savings on the communication between moving objects and the server. There are three main motivations for promoting a distributed approach for evaluation of MQs in a mobile setup:

  1. Shipping some of the MQ processing to the moving object side can be seen as a mechanism for moving computation close to places where the data is produced. Such techniques are especially bene ficial when there are a large and growing number of mobile moving objects and MQs are not uniformly distributed over these moving objects.
  2. The computational capabilities of mobile objects can be utilized in a distributed solution, which not only decreases the load on the server and the communication cost between the mobile obje cts and the server, but also increases the scalability of the system.
  3. The distributed solution allows us to restrict the area that covers the objects that need to be aware of a query’s state (position change of the query's focal object), since it is onl y the objects in close proximity to the query that need to be aware of this information. The communication asymmetry inherent in mobile communications makes it efficient to convey information regarding a query's state to appropriate set of moving objects.

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