Node localization in wireless sensor networks (WSNs) is one of the most important primary requisite that needs to be resolved efficiently as it plays a significant role in many applications namely environmental monitoring, routing and target tracking which is location dependent. Localization is defined as finding the physical co-ordinates of a group of sensor nodes. Localization is classified as an unconstrained optimization problem. Localization protocols are broadly classified as range-based and range-free protocols. The range based protocols employ distance or angle estimation techniques, hardware. The range-free techniques depend on