Positioning in a Multipath Channel Using OFDM Signals With Carrier Phase Tracking

Abstract

In developing a high accuracy terrestrial radio navigation system, as a complement to a global navigation satellite system (GNSS), it is recognized that the performance of time delay estimation is proportional to, and thereby limited by, the signal bandwidth. Given a possibly narrow signal bandwidth, the central carrier phase can, alternatively, provide a better distance accuracy, though the central carrier phase cycle ambiguity should be resolved. In practice, the carrier phase may be perturbed by multipath. In this paper, considering an orthogonal frequency division multiplexing (OFDM) signal, we propose a twostep carrier phase estimation method to reduce the error introduced by multipath. First, the propagation delay of the LoS path is coarsely determined, then the carrier phase is estimated using the earlier determined coarse time delays. Furthermore, a positioning model only based on carrier phase estimates is presented in this paper. The proposed technique is evaluated by statistical analyses and a simulated OFDM-based terrestrial positioning system in different roadway multipath environments. The results show that the impact of multipath on carrier phase estimation can be largely mitigated, so that the carrier phase can be used for precise positioning. In addition, fixing the integer carrier phase cycle ambiguities can significantly reduce the time for the position solution to converge to high precision. INDEX TERMS Multipath channels, OFDM, phase estimation, radio navigation, multipath mitigation, phase ambiguity. HAN DUN received the B.Sc. degree in communication engineering and the M.Sc. degree in communication and information engineering from Shanghai University, China, in 2013 and 2016, respectively. He is currently pursuing the Ph.D. degree with the

Terrestrial Precise Positioning System Using Carrier Phase from Burst Signals and Optically Distributed Time and Frequency Reference

“…Thus, one can first estimate the time delayτ , construct the design matrix A(τ ), and then estimate the complex gain, from which the carrier phase of the LoS path can be computed for positioning [16].…”

“…The time delay and the carrier phase are the most common observables for positioning. They can be jointly estimated from the ranging signal through maximum likelihood (ML) estimation in a stepwise manner [16,17]. Compared with the propagation time delay, the carrier phase is much more spectrum efficient in providing an equivalent ranging precision, because of the short wavelength of the central carrier.…”

Design of Sparse Multiband Signal for Precise Positioning With Joint Low-Complexity Time Delay and Carrier Phase Estimation

“…To avoid rank deficiencies in the positioning model, which will be introduced in the next subsection, the carrier phase should be continuously tracked and the carrier phase estimates have to be compensated for changes of the phase cycle due to movement of the receiver, referred to as phase unwrapping, so that only the initial carrier phase integer cycle ambiguity remains as an unknown parameter in the measurements. Readers are referred to [43] for more details. As long as a phase jump can be properly identified and a series of carrier phase estimate can be correctly unwrapped (i.e., no cycle-slips occur), we can use the carrier phase to compute position solutions.…”

Optimal Parameter Design of Continuous Phase Modulation for Future GNSS Signals

“…Subsequent innovations for GNSS signal design have mainly focused on spectrum-efficient modulations, particularly such as square root-raised cosine (SRRC) [9], prolate spheroidal wave functions (PSWF) [13], [14], complex carrier modulation [15], orthogonal frequency division multiplexing (OFDM) [16], [17], and filtered multitoned (FMT) modulation [18]. Although abovementioned modulations preserve spectral compactness well, their envelopes are not constant intrinsically, resulting in the nonlinear signal distortion at the high power amplifier (HPA) output if not considering peak to average power ratio (PAPR) reduction or constant-envelope multiplexing technique [19].…”