Positioning Limits for UMTS Mobiles in Delay & Angular Dispersive Channels

The conventional methods for wireless positioning are based on the estimation of direction-of-arrival (DOA), time-of-arrival (TOA) or time-difference-of-arrival (TDOA), once multiple timing or angles of arrival are measured at a convenient number of base stations (BS). The use of smart antennas (both in diversity or beamforming configurations) offers increased potentialities in the task of locating a user equipment (UE) since better estimation of delays is obtained, and AOAs may be determined. In those cases where both TOA and AOA are reliably estimated, positioning may be obtained with a lower variance than using a single measure. However, the accuracy is mainly limited by the wild conditions of the propagation channel and the multiple access schemes. In particular, the delay-angular-Doppler spreads, the SINR, the multipath, the number of possible averages, etc. limit seriously the expectations aroused by the increased UMTS bandwitdh.