A Joint TOA and DOA Approach for Opportunistic Navigation with Beamformed 5G Signals
Shaghayegh Shahcheraghi and Zak (Zaher) M. Kassas, The Ohio State University
Over the past decade, the tremendous potential of signals of opportunity (SOPs) as a promising candidate for navigation has been unveiled [1]. SOPs include cellular [2–5], low Earth orbit (LEO) satellite signals [6], FM radio [7], and digital television [8]. Among the aforementioned SOPs, the most accurate navigation results have been demonstrated with cellular signals [9]. Cellular signals have attracted a lot of attention due to their desirable characteristics, such as abundance, geometric and spectral diversity, and large bandwidth. The recent research has shown the potential of cellular SOP for providing a meter-level accuracy for ground vehicle navigation [10] and sub-meter-level accuracy for unmanned aerial vehicles (UAV) navigation [11].
Different techniques have been studied for cellular-based navigation. Using time-of-arrival (TOA) estimates from fifth-generation (5G) signals, experimental results showed meter-level navigation accuracy [12]. The direction-of-departure (DOD) and user equipment (UE)’s position were estimated using multiple base stations in [13], resulting in sub-meter-level position accuracy. A positioning method was proposed in [14], where the direction-of-arrival (DOA) and TOA of the received signal were used to localize a UE. In [15], estimation of signal parameters via rotational invariant techniques (ESPRIT) was used to estimate the DOA and DOD of the signal. In [16], a long-term evolution (LTE)-based receiver was proposed, where DOA and TOA were jointly tracked to navigate the UE.
In the recent research, most of the DOA-based positioning methods and beamforming have focused on mmWave signals, characterized by highly directive beams [17–19]. However, since signal propagation at sub-6 GHz differs from that at mmWave, alternative methods are needed to be applied to 5G signals operating at frequencies below 6 GHz. Another category of DOA-based research explored in the literature is network-based methods, where all processing occurs on the network side using uplink signals [20, 21]. In [22], TOA and azimuth DOA of received sub-6 GHz 5G signals were estimated at the user, beamforming was implemented, and joint TOA and azimuth DOA were exploited to localize a stationary receiver.
In [22], we introduced a new algorithm for joint azimuth and elevation DOA estimation of downlink 5G signals, where the DOA was estimated through delay-Doppler processing. Using the estimated DOA, beamforming was implemented. Additionally, experimental results were presented to assess the performance of the proposed receiver in both stationary and moving scenarios, showing a carrier-to-noise-ratio (C/N0) improvement of 7 dB in the stationary scenario and about 6 dB in the moving scenario, compared to a non-beamformed 5G framework. The stationary receiver was localized with a final 2D error of 10.6 m using beamformed 5G signals. In the mobile scenario, the framework achieved a position root mean-squared error (RMSE) of 5.4 m, showing a reduction of 2.7 m in RMSE compared to a non-beamformed 5G framework [22].
In [22], joint TOA and DOA were leveraged for localizing a stationary receiver, while TOA alone was used for navigating a moving ground vehicle. In this paper, we will extend this approach by utilizing both TOA and DOA for the navigation of the moving vehicle, investigating the impact of adding DOA on navigation accuracy. Specifically, using a custom antenna array, we design a receiver for estimating DOA from downlink 5G signals, followed by an analysis of the DOA estimation accuracy. Additionally, we explore how the structure of the antenna array influences beamforming and DOA estimation. Finally, we assess how incorporating DOA alongside TOA affects the overall navigation performance.
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