Localization in Wireless Sensor Networks: A Survey
  Localization is widely used in Wireless Sensor Networks (WSNs) to identify the current location of the sensor odes. A WSN consist of thousands of nodes that make the installation of GPS on each sensor node expensive and moreover GPS may not provide exact localization results in an indoor environment. Manually configuring location reference on each sensor node is also not possible for dense network. This gives rise to a problem where the sensor nodes must identify its current location without using any special hardware like GPS and without the help of manual configuration. In this paper we review the localization techniques used by wireless sensor nodes to identify their current location. 
Jeril Kuriakose, Sandeep Joshi and V.I. George
cs.NI