1. A method for determining accuracy of an estimated location of a target device in a wireless system, said method comprising the steps of: determining a location probability density function of said target device based on a location probability model; calculating an uncertainty at a current estimated location and a possible maximum uncertainty based on radio signals received by said target device according to said location probability density function; and calculating a confidence index of said current estimated location based on said uncertainty and said maximum uncertainty; wherein said confidence index of said current estimated location determines the accuracy of said current estimated location with higher confidence index representing higher accuracy.