Ray simulations for evaluating different methods used to locate mobiles in cities

Mobile location techniques for cellular environments are of current interest due to the great number of new value-added services that can be provided using location technology, as well as the Federal Communications Commission´s (FCC) requirement that all cellular service providers must be able to determine the location of a 911 caller with a radius of 100 m, 67% of the time (Federal Communications Commission CC Docket No. 94102, July 1996). Current mobile location technologies, such as the Global Positioning System (GPS), angle of arrival (AOA), uplink-time difference of arrival (UTDOA), and enhanced observation timed difference (EOTD) have difficulties in urban environments. The signature method uses a predetermined reference table of path gains between each of many possible mobile locations and several surrounding base stations. The path gain signatures contain information of the shadowing of the signals by the buildings surrounding the mobile. To the extent that this shadowing is unique to each mobile location, the shadowing information can serve to locate the mobile. This paper compares the time difference of arrival (TDOA) method and the path gain signature method to locate mobiles in a large urban environment.