I. Introduction
With the prosperity of wireless technology, the demands for practical applications around location-based service (LBS) [1] and the Internet of Things (IoT) are becoming more prevalent, such as smart manufacturing, homeland security, navigation, and personalized advertising. Among them, localization information has been essential and has drawn more attention nowadays. Especially for indoor wireless localization, which does not like outdoor scenarios having a mature solution such as the Global Positioning System (GPS), is still finding a solution to obtain accuracy, convenience, stability, and privacy. The performance of GPS in an indoor scenario is reduced due to degradation, shadow fading, and the multiple path effect. Therefore, Bluetooth, Zigbee, radio-frequency identification (RFID), ultra-wideband (UWB) with lower transmission range and more indoor applications are considered to be more proper and capable of estimating an accurate location of targets for indoor area. However, due to the low coverage range, a lot of infrastructures are needed before real-world implementation. Among the above reasons, wireless LAN (WLAN) is considered the most suitable solution. WLAN [2]–[4] has a higher error range than Bluetooth and UWB due to the greater coverage range; however, considering also its large coverage range and existing infrastructure prevalent for indoor areas as compensation, it is still a more acceptable solution.