关键词：无线传感器网络；传感器；节点位置；先验知识网络
摘 要：In wireless sensor networks, sensors are often deployed without a priori knowledge of their locations or sensor node locations can change during the lifetime of a network. However, location information is essential for a variety of reasons. Sensors monitor phenomena in the physical world and given the location of the sensors, it is then possible to estimate the location of the observed phenomenon. For example, chemical and humidity sensors deployed on a farm can provide information about soil moisture, crop health, and animal movement if the sensor locations are known. Accurate location information is also needed for various sensor network management tasks such as routing based on geographic information, object tracking, and providing location-aware services. Frequently, sensor node localization is performed using ranging techniques, where the distances between a sensor device and several known reference points are determined to derive the position of a sensor. However, the cost and limitations of the hardware needed for range-based localization schemes often make them poor choices for WSNs. Therefore, a variety of localization protocols have been proposed that attempt to avoid the use of ranging techniques with the goal to provide more cost-effective and simpler alternatives. These range-free localization techniques estimate a node's position using either neighborhood information, hop counts from well-known anchor points, or information derived from the area a node is believed to reside in. This chapter introduces the basic concepts of range-free localization, surveys a variety of state-of-the-art localization techniques, compares qualitatively the characteristics of these protocols, and discusses current research directions in range-free localization.