With the increase of services that need accurate location of the user, new techniques that cooperate with the Global Navigation Satellite System (GNSS) are necessary. Toward this objective, this thesis presents our research work about the estimation of the time of arrival (TOA) and of the angle of arrival (AOA) exploiting modern cellular signals. In particular, we focus on the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard, and in particular uplink and downlink reference signals are exploited to this purposes. The current release of the 3GPP LTE specification supports a UTDOA localization technique based on the Sounding Reference Signal (SRS). In real environments, however, user equipments (UE) are rarely set up to transmit this particular signal.
The main original contribution of this thesis consists in a new TOA estimation method based on uplink transmission. In particular, we explore the possibility of performing radio localization exploiting the uplink Demodulation Reference Signal (DM-RS), which is always sent by UEs during data transmission. Real uplink transmissions are modeled in simulations and the performance of known algorithms like SAGE and IAA-APES are evaluated for TOA estimation. A new method to estimate the initial conditions of the SAGE algorithm is proposed and the estimation performance in uplink scenarios is evaluated. The analysis revealed that the proposed method outperforms the non-coherent initial conditions estimation proposed in the literature, when uplink transmission are used. Then, the benefits of our proposal are evaluated and the feasibility of TOA estimation exploiting the DM-RS is demonstrated by means of experiments using real DM-RS signals generated by an LTE module.
A second original contribution is given by AOA estimation. In particular, the independence of AOA estimation with respect to uplink and downlink transmission is verified. According to this result, the performance of IAA-APES and SAGE in real-world AOA experiments is evaluated in the downlink scenarios. Based on the overall results, we conclude that the proposed radio localization method, exploiting the uplink Demodulation Reference Signal (DM-RS), can be extended also to joint TOA, AOA using SAGE, for hybrid localization techniques. We can also conclude that the proposed method can be easily extended to downlink transmission exploiting the cell specific reference signal (CRS).
