Uplink versus Downlink wirless mobile positioning in UMTS cellular radio systems

A performance comparison between radio location positioning (LP) in Wide band Code Division Multiple Access (WCDMA), more precisely in UMTS FDD cellular phones, using the Uplink (UL) and Downlink (DL) scenarios, is carried out. The radio location algorithm using the Time Difference Of Arrival (TDOA) is applied, where the TDOA is the difference between two TOA estimated at two base stations. We propose a practical algorithm to obtain high precision PL under high level interference. It consists in a matched filter followed by high resolution MUltiple SIgnal Classification (MUSIC) algorithm to estimate with a high resolution the TOA. indeed, in practice near-far resistant detection algorithms are not easy to implement directly on the received data due to the large spreading factors. The power-up and Idle Slot (IS) techniques together with Interference cancellation algorithms are used to combat the near-far problem. Simulations were carried out in the same observation conditions for UL and DL scenarios. The results show an enhancement in the LP using MUSIC algorithm after matched filtering besides, a better performance in the DL scenario.

1 Introduction

Radio location is a growing practice in cellular mobile phone systems because of its vast useful applications like: localizing the traffic by the operators, emergency interventions, billing tariffs depending on the mobile position and discouraging criminal activities using the cellular systems. Techniques of radio location were developed for the GSM cellular phone and are now standardized. However, these standards are not applicable to the wide band CDMA cellular systems since it uses a different air interface technology. Studies on the radio LP of cellular phones in the IS-95 CDMA systems have been performed [1] [2]. But this system is also different from the Universal Mobile Telecommunications System (UMTS) wide band CDMA standards. Few studies were carried out on the radio LP in UMTS systems [3] [4].