BLE for Indoor Positioning

Bluetooth Low Energy uses 40 channels on the 2.4 GHz band. Three of those channels are used for advertising messages. The received signal strength (RSS) of these channels from multiple BLE devices are used to determine relative distance and location. Transmission power for BLE devices can be set from 0 dBm to -40 dBm and the advertising rate can be configured up to 50 Hz. Typically, transmission power is set to less than -16 dBm and the advertising rate to less than 10 Hz, for the purpose of energy conservation. Zhuang 2016
Several proposed and/or existing solutions for indoor positioning require costly infrastructure and deliver a wide range of accuracy. WiFi is restricted by environment, power supply and mobile device support, while RFID is requires specialized equipment. Many technologies have limited accuracy due to fluctuating signal strength Wang 2016Bluetooth Low Energy (BLE), also known as Bluetooth Smart, provides a low-cost, reasonably accurate, and zero infrastructure solution to this problem with the following advantages.
Several algorithms have been proposed for calculating location with varying degrees of accuracy. These algorithms encompass several methods and produce a wide range of accuracy. The following sections look at these in detail, do a qualitative comparison, and recommend the best method for producing  the most accurate results.