Signal Design and Analysis for Time Delay Estimation with Application to Satellite Positioning

Positioning accuracy in satellite navigation systems depends on time-delay estimation (TDE) between satellite transmitted codes and local receiver replicas. This thesis explores the fundamental limits of TDE accuracy of spread spectrum (SS) signals making use of estimation theory and signal synchronization tools, which makes the proposed analysis suitable for both navigation and communication systems and independent from receiver configurations. In particular, this contribution derives some criteria to improve positioning accuracy in the additive white Gaussian noise (multipath-free) scenario, focusing on the (satellite) transmitter side of a SS system. Four different solutions, based on the minimization of the variance of the TDE, are presented by means of signal design. The first method speculates on the shaping of the pulse format of a linearly modulated Direct Sequence (DS)-SS signal. A pulse loss parameter useful for comparing performance of different pulse signals in a dedicated receiver bandwidth is thus defined. The second approach still considers DS-SS linearly modulated signals, proposing a joint shaping pulse-spreading code optimization. A design criterion to derive an optimal spreading waveform is thus derived both theoretically and numerically. A set of non-binary band-limited (NBBL) spreading waveforms that further improve the TDE accuracy while maintaining good properties of code acquisition and interference management are thus obtained. The third solution encompasses the design of SS-Continuous Phase Modulation (SS-CPM) that allows good TDE performance while guaranteing a constant complex envelope of the signal, thus showing high robustness to non-linear distortions introduced by non-linear HPA. Finally, as fourth approach, we show how a multicarrier signal can be formatted to obtain maximum estimation accuracy. Capitalizing on this, we also demonstrate that the inherent flexibility about power and frequency allocation possessed by such signal is expedient to the achievement of a cognitive localization system that adapts to the changing situation of availability and interference of a wideband radio channel. Performance of the proposed solutions for future GNSS systems is compared with that of existing DS-SS signals for current satellite positioning systems. Performance of some schemes is evaluated as signal options to be used in the C-band portion envisioned for GNSS evolutions. Possible countermeasures to the effects of multipath propagation are also discussed.