A Comparison of Radiolocation Methods for Mobile Terminals by Distance Measurements

Popular methods to locate wireless terminals use measurements of Received Signal Strength (RSS), Time of Arrival (ToA), and Time Difference of Arrival (TDoA). RSS has low cost and experiments for small scale networks show that it provides good accuracy. With large scale networks, experiments show that ToA/TDoA has better accuracy than RSS. This paper derives Cramer-Rao bounds for the RSS, ToA, and TDoA estimators and calculates limits on accuracy. These limits are used to demonstrate analytically the reason for the results at different size scales and can be used to identify when the cheaper RSS location method can be utilized.