A comprehensive approach for opportunistic navigation with fifth-generation (5G) cellular signals that exploits the downlink channel is developed. The structure of possible 5G reference signals that ...can be exploited is presented. Then, a software-defined receiver (SDR) to extract navigation observables from cellular 5G signals is proposed. The statistics of the code phase error in a multipath-free environment and in the presence of multipath are derived, which are subsequently used to analyze the statistics of the position estimation error with different simulated channel models. Finally, experimental results are conducted to evaluate the ranging performance of the proposed SDR with real 5G signals. After removing the effect of the clock bias and drift from the estimated pseudorange, the ranging error standard deviation is shown to be 1.19 m.
A receiver structure is proposed to jointly estimate the time-of-arrival (TOA) and azimuth and elevation angles of direction-of-arrival (DOA) from received cellular long-term evolution (LTE) signals. ...In the proposed receiver, a matrix pencil (MP) algorithm is used in the acquisition stage to obtain a coarse estimate of the TOA and DOA. Then, a tracking loop is proposed to refine the estimates and jointly track the TOA and DOA changes. The performance of the acquisition and tracking stages are evaluated in the presence of noise and multipath. Simulation results are provided to validate the analytical results. The Cramér-Rao lower bounds (CRLBs) of the TOA and DOA estimates are derived to compare the performance of the proposed acquisition and tracking approaches with the best-case performance. It is shown that the proposed approach has lower complexity compared to the MP algorithm. Finally, experimental results are provided with real LTE signals, showing a reduction of 93%, 57%, and 31% in the standard deviation of TOA, azimuth, and elevation angles' estimation errors, respectively, using the proposed receiver compared to the MP algorithm.
This letter shows the first acquisition, Doppler tracking, and positioning results with Starlink's low Earth orbit satellite signals. A generalized-likelihood-ratio-based test is proposed to acquire ...Starlink's downlink signals. A Kalman-filter-based algorithm for tracking the Doppler frequency from the unknown Starlink signals is developed. Experimental results show Doppler tracking of six Starlink satellites, achieving a horizontal positioning error of 10 m.
Mitigating multipath of cellular long‐term evolution (LTE) signals for robust positioning in urban environments is considered. A computationally efficient receiver, which uses a phase‐locked loop ...(PLL)–aided delay‐locked loop (DLL) to track the received LTE signals, is presented. The PLL‐aided DLL uses orthogonal frequency division multiplexing (OFDM)–based discriminator functions to estimate and track the time‐of‐arrival. The code phase and carrier phase performances in an additive white Gaussian noise (AWGN) channel are evaluated numerically. The effects of multipath on the code phase and carrier phase are analyzed, demonstrating robust multipath mitigation for high transmission LTE bandwidths. The average of the DLL discriminator functions over multiple LTE symbols is presented to reduce the pseudorange error. The proposed receiver is evaluated on a ground vehicle in an urban environment. Experimental results show a root mean square error (RMSE) of 3.17 m, a standard deviation of 1.06 m, and a maximum error of 6.58 m between the proposed LTE receiver and the GPS navigation solution over a 1.44 km trajectory. The accuracy of the obtained pseudoranges with the proposed receiver is compared against two algorithms: estimation of signal parameters by rotational invariance techniques (ESPRIT) and EKAT (ESPRIT and Kalman filter).
A framework that could achieve submeter-level unmanned aerial vehicle (UAV) horizontal navigation in multipath-free environments with cellular carrier phase measurements is developed. This framework ...exploits the “loose” synchronization between cellular base transceiver station (BTS) clocks. It is shown through extensive experimental data that the beat frequency stability of cellular BTSs approaches that of atomic standards and that the clock deviations can be realized as a stable autoregressive moving average model. This BTS clock model is referred to as loose network synchronization. A rule-of-thumb is established for clustering the clock deviations to minimize the position estimation error, while significantly reducing the computational complexity. The presented models allow the UAV to achieve sustained carrier phase-based meter- to submeter-accurate navigation. To demonstrate the efficacy of the developed framework, this article presents three UAV flight experiments in Southern California, USA, utilizing signals from different cellular providers transmitting at different frequencies. The three experiments took place in open, semiurban environments with nearly multipath-free, line-of-sight (LOS) conditions, in which the UAV traveled 1.72, 3.07, and 0.61 km, achieving a horizontal position root mean squared error of 36.61, 88.58, and 89.33 cm, respectively, with respect to the UAV’s on-board navigation system.
This article presents a framework for opportunistic unmanned aerial vehicle (UAV) navigation by exploiting carrier phase measurements from ambient cellular signals of opportunity. In the proposed ...framework, the cellular base transceiver stations (BTSs) are not assumed to be synchronous. A complete framework that employs an extended Kalman filter (EKF) is presented, including filter initialization and process and measurement noise covariance selection. The EKF estimates the position and velocity of the UAV, as well as the differences between the UAV-mounted receiver and each of the BTSs' clock bias and clock drift. The observability of the estimation framework is analyzed, and the boundedness of the EKF's errors is studied. It is shown that the system is observable given a class of vehicle and receiver clock dynamics. A lower bound for the EKF estimation error covariance is derived, and it is shown that the covariance remains bounded. Monte Carlo simulations are conducted to study the effect of the number of BTSs, the initial UAV speed, and the receiver's oscillator quality, on the estimation performance. Two sets of experimental results are presented demonstrating UAVs navigating exclusively with cellular carrier phase measurements via the developed framework, achieving a total position root-mean-squared error of 2.94 and 5.99 m for UAV trajectories of 2.6 and 2.9 km, respectively.
A receiver autonomous integrity monitoring (RAIM) framework for ground vehicle navigation using ambient cellular signals of opportunity (SOPs) and an inertial measurement unit (IMU) is developed. The ...proposed framework accounts for two types of errors that compromise the integrity of the navigation solution: (i) multipath and (ii) unmodeled biases in the cellular pseudorange measurements due to line-of-sight (LOS) signal blockage and high signal attenuation. This paper, first, characterizes the multipath in a cellular-based navigation framework. Next, a fault detection and exclusion technique for a cellular-based navigation framework is developed. Simulation and experimental results with real long-term evolution (LTE) signals are presented evaluating the efficacy of the proposed RAIM-based fault detection and exclusion technique on a ground vehicle navigating in a deep urban environment in the absence of global navigation satellite system (GNSS) signals. The experimental results on a ground vehicle traversing 825 m in an urban environment show that the proposed RAIM-based measurement exclusion technique reduces the position root mean-squared error (RMSE) by 66%.
The fundamental tracking performance in radio navigation is characterized, leading to optimal receiver design considerations. First, a generalized beacon model is proposed and its sufficient, salient ...parameters are defined. Second, closed-form approximations of the delay, Doppler, Doppler stretch, and Doppler rate ambiguity functions (AFs) and a generalized coherent integration efficiency model are proposed. Third, design considerations and optimal coherent processing interval (CPI) length selection are presented, based on the complete navigation framework, entailing the: (i) beacon's parameters, (ii) channel dynamics between the transmitter and receiver, (iii) employed clocks by the transmitter and receiver, (iv) search space adopted in the acquisition stage, and (v) dynamical model's order employed in the tracking stage. Fourth, the acquisition and tracking stages of the navigation receiver architecture are discussed. Fifth, three sets of experimental results are presented validating the proposed closed-form approximation of the Doppler stretch and Doppler rate AFs and demonstrating the performance of a receiver tuned by the proposed design considerations in acquiring, tracking, and localization, namely: (i) aircraft tracking of terrestrial 4G signals, (ii) stationary receiver tracking of Starlink low Earth orbit (LEO) signals, and (iii) stationary receiver localization with Starlink and OneWeb LEO signals. For the Starlink and OneWeb receiver localization experiment, the receiver was capable of tracking the Doppler and carrier phase of 5 Starlink and 3 OneWeb LEO satellites. Starting from an initial estimate 50 km away from its true position, the receiver converged to a final two-dimensional (2D) position error of 30.3 m.
This letter unveils the unknown structure of Starlink low Earth orbit (LEO) satellites' orthogonal frequency division multiplexing (OFDM)-like reference signals (RSs). The spectrum of Starlink's ...dowlink signals is presented, and the frame length is estimated. A blind receiver is proposed, which acquires via a sequential generalized likelihood ratio test multiple satellites, estimates their RSs and respective Doppler, and tracks their carrier and code phases. Experimental results are presented showing six tracked Starlink LEO satellites, three of which transmitted pure tones, while the other transmitted OFDM-like signals. The achieved horizontal positioning error with the six satellites was 6.5 m.
A navigation framework with carrier phase differential measurements from megaconstellation low Earth orbit (LEO) satellite signals is developed. The measurement errors due to ephemeris errors and ...ionospheric and tropospheric delays are derived and the statistics of the dilution of precision is characterized. Moreover, the joint probability density function of the megaconstellation LEO satellites' azimuth and elevation angles is derived to 1) enable performance characterization of navigation frameworks with LEO satellites in a computationally efficient way and 2) facilitate parameter design, namely, the differential baseline, to meet desired performance requirements. The Starlink constellation is used as a specific LEO megaconstellation example to demonstrate the developed carrier phase differential LEO (CD-LEO) navigation framework. Simulation results are presented demonstrating the efficacy of the proposed CD-LEO framework for an unmanned aerial vehicle (UAV) navigating for 15.1 km in 300 s, while using signals from 44 Starlink satellites, achieving a 3-D position root mean squared error (RMSE) of 2.2 m and a 2-D RMSE of 32.4 cm. Experimental results are presented showing UAV navigating for 2.28 km in 2 min over Aliso Viejo, CA, USA, using exclusively signals from only two Orbcomm LEO satellites, achieving an unprecedented position RMSE of 14.8 m.
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