Time Difference Of Arrival System Research Articles

High-Precision Time Difference of Arrival Estimation Method Based on Phase Measurement

In unmanned aerial vehicle (UAV)-based time difference of arrival (TDOA) positioning technique, baselines are limited due to communication constraints. In this case, the accuracy is highly sensitive to the TDOA measurements’ error. This article primarily addresses the problem of short-baseline high-precision time synchronization and TDOA measurement. We conducted a detailed analysis of error models in TDOA systems, considering both the time and phase measurement. We utilize the frequency division wireless phase synchronization technique in TDOA systems. Building upon this synchronization scheme, we propose a novel time delay estimation method that relies on phase measurements based on the integer least squares method. The performance of this method is demonstrated through Monte Carlo simulations and outdoor experiments. The standard deviations of synchronization and TDOA measurements in experiments are 1.12 ps and 1.66 ps, respectively. Furthermore, the circular error probable (CEP) accuracy is improved from 0.33%R to 0.02%R, offering support for the practical application of distributed short-baseline high-precision passive location techniques.

High-Precision Joint TDOA and FDOA Location System

Passive location based on TDOA (time difference of arrival) and FDOA (frequency difference of arrival) is the mainstream method for target localization. This paper proposes a fast time–frequency difference positioning method to address issues such as low accuracy, large computational resource utilization, and limited suitability for real-time signal processing in the conventional CAF (cross-ambiguity function)-based approach, aiming to complete the processing of the target radiation source to obtain the target parameters within a short timeframe. In the mixing product operation step of the CAF, a frequency-domain approach replaces the time-domain convolution operation in PW-ZFFT (pre-weighted Zoom-FFT) to reduce the computational load of the CAF. Additionally, a quadratic surface fitting method is used to enhance the accuracy of TDOA and FDOA. The localization solution is obtained using Newton’s method, which can provide more accurate results compared to analytical methods. Next, a signal processing platform is designed with FPGA (field-programmable gate array) and multi-core DSP (digital signal processor), and works by dividing and mapping the algorithm functional modules according to the hardware’s characteristics. We analyze the architectural advantages of multi-core DSP and design methods to improve program performance, such as EDMA transfer optimization, inline function optimization, and cache optimization. Finally, this paper constructs simulation tests in typical positioning scenarios and compares them to hardware measurement results, thus confirming the correctness and real-time capability of the program.

Reconfigurable Intelligent Surface-Aided Emitter Localization

Localization of radio-frequency (RF) transmitters using time difference of arrival (TDOA)-based methods is one of the conventional passive techniques that admits noncooperative source position finding, but suffers from challenging requirements such as precise intersensor synchronization and high-throughput transmission data links. A tradeoff governing the TDOA systems is in the sensor placement configuration. The more distance the sensors are placed, the more accurate localization is carried out, while the cost for the synchronization and data link increases, at the same time. In this work, a novel reconfigurable intelligent surface (RIS)-aided localization system is proposed that enjoys precise location accuracy while reducing the required expenses. The study reveals that the new setup, utilizing the beam-scanning property of the RIS sensors, improves the localization algorithm and outperforms the conventional approach. Also, comparisons with Cramér Rao lower bound (CRLB) are provided, which confirms the efficiency of the proposed method. Several numerical examples indicate the effectiveness of the proposed method, especially in a low signal-to-noise ratio (SNR) regime.

The Complete Analytical Solution of the TDOA Localization Method

This article is focused on the analytical solution of a TDOA (Time Difference of Arrival) localization method, including analysis of accuracy and unambiguity of a target position estimation in 2D space. The method is processed under two conditions - sufficiently determined localization system and an overdetermined localization system. It is assumed that the TDOA localization system operates in a LOS (Line of Sight) situation and several time-synchronized sensors are placed arbitrarily across the area. The main contribution of the article is the complete description of the TDOA localization method in analytical form only. It means, this paper shows a geometric representation and an analytical solution of the TDOA localization technique model. In addition, analyses of unambiguity and solvability of the method algorithm are presented, together with accuracy analysis of this TDOA technique in analytical form. Finally, the description of this TDOA method is extended to an overdetermined TDOA system. This makes it possible to determine and subsequently optimize its computational complexity, for example increase its computational speed. It seems that such a description of the TDOA localization technique creates a simple and effective tool for technological implementation of this method into military localization systems.

Location Performance Test and Evaluation for Tri-Station Time Difference of Arrival System

Location Performance Test and Evaluation for Tri-Station Time Difference of Arrival System

Multi-link channel simulation based on propagation graph theory and application in performance evaluation of TDOA positioning system

In order to solve the problems of high measurement cost and many uncontrollable interference factors in the accuracy evaluation of time difference of arrival (TDOA) localization method by measurement, a method of evaluating the accuracy of a TDOA localization system based on multi-link channel propagation graph theory is proposed. In this paper, we use the propagation graph theory to generate different channel impulse responses, and ultilize software-defined radio devices to generate channel-distorted radio frequency signals as inputs to multiple TDOA sensors and construct a novel TDOA localization evaluation method. In order to verify the accuracy of the TDOA technology effectively, we simulate the method in 4 typical scenarios. It is the first time that a complex scenario is simulated using multi-channel radio frequency signal to test the localization accuracy of the TDOA system. The simulation result shows that when the signal bandwidth is not smaller than 200 kHz, the multi-link localization system based on graph modeling shows good and stable performance. Moreover, graph modeling method with diffraction model embedded enhances the accuracy of performance simulation for the TDOA system, particularly in the non-line-of-sight scenarios.

Dilution of Precision in Three Dimensional Angle-of-Arrival Positioning Systems

Dilution of precision (DOP) for time-of-arrival (TOA) or time-difference-of-arrival (TDOA) positioning systems has been thoroughly investigated. This is not the case for angle-of-arrival (AOA) positioning systems, especially three dimensional AOA systems. However, the recent increase in deployment of antenna arrays and multipath mitigation techniques make AOA systems more attractive. In this paper, the DOPs for position systems using range measurements are reviewed and an expression for 3D AOA DOP is derived. The average values of DOPs for different deployments of base station geometries are examined. It is found that for a 3D AOA system, unlike TOA or TDOA systems, vertical DOP (VDOP) is generally smaller than horizontal DOP (HDOP), and the best VDOP can be achieved when the base stations are at the same height as the user. Moving the base stations away from the plane of the user may decrease the HDOP and Geometric DOP (GDOP) slightly, but it also increases the VDOP. For applications that the height of the user changes frequently, the base stations should be deployed with height close to half the height of the area of interest.

Semidefinite Programming for NLOS Error Mitigation in TDOA Localization

Non-line-of-sight (NLOS) error mitigation for the time-of-arrival (TOA) localization has been extensively studied, but these methods cannot be directly applied for the time-difference-of-arrival (TDOA) systems. Recent work has applied convex optimization for NLOS error mitigation in TDOA systems. Issues remain unsolved with this technique include the convex hull problem, reference-anchor selection problem, and difficulties dealing with a wide range of NLOS-caused ranging errors. This letter proposes a new technique to transform a TDOA model into a TOA model and develops a semidefinite programming method with new constraints for effective NLOS error mitigation in TDOA systems. Major advantages of this method include: 1) it resolves the issues such as convex hull and reference-anchor selection issues that existing schemes are facing; 2) it does not require any a priori information about NLOS links or NLOS error statistics; and 3) it achieves a better performance than existing convex optimization schemes, which is verified in both simulation and real experiments.

Simulation of Discrete Source of Relative Signal Time Delays Measurement Errors in Multiposition Passive TDOA System

We present the software realization of the discrete source of errors which can be applied while simulating the procedures for the signal detection and the determination of radio source coordinates in multiposition passive time difference of arrival systems. We introduce and validate the probabilistic models of errors occurring during signal time delays measurements performed by such systems.

A Three-Dimensional Position Architecture Using Digital TDE Receiver and Cylindrical Array Antenna

The robust three-dimensional position architecture is proposed in the paper, where the hybrid time difference of arrival(TDOA) and direction of arrival (DOA) position system was designed to backup the four-station TDOA positionsystem. The digital time delay estimation (TDE) receiver is used for TDOA measurement and the cylindrical arrayantenna is used for DOA measurement. The general formula of linear phase compensation for cylindrical arrayantenna in horizontal plane is derived. The detection probability of the TDE receiver and the circular error probability(CEP) of the position systems over Rayleigh fading channel were numerically computed in three-dimensional space.Simulations indicate that the position accuracy of the four-station TDOA position system is degraded but the locationfunction can be retained by the hybrid TDOA and DOA position system when any one of four-stations is out of work.

Performance evaluation of TDOA system based on maximum likelihood location estimation in cellular systems

With the spreading use of cellular phones in recent years, there has been an increasing demand for various services based on location information. The location-dependent information to be used in location estimation can be the TOA (time of arrival), TDOA (time difference of arrival), signal strength, and AOA (angle of arrival). In third-generation cellular phones, whose widespread use is expected, the communications data rate will be increased. The chip resolution will also be improved, making it possible to measure the signal arrival time with higher accuracy. Consequently, this paper presents an evaluation and discussion of the location estimation performance of a TDOA system. An exponential distribution is assumed for the signal delay profile, and the location estimation algorithm is formulated on the basis of maximum likelihood estimation. Then the accuracy of location estimation is compared by simulation for maximum likelihood estimation in the TDOA system and the existing method. The accuracy of location estimation by maximum likelihood is also evaluated for various environments. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 47–54, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20155

An ionospheric error model for time difference of arrival applications

The geolocation accuracy of satellite‐borne time difference of arrival systems is limited by the uncompensated differential delay experienced by each pair of satellite‐to‐ground paths. We have measured the ionospheric component of this differential delay using two‐frequency GPS receivers at seven ground sites; one in the high‐latitude region, four at midlatitudes, and two in the equatorial region. The measurements were expressed as differential total electron content (ΔTEC) so that they could be used at frequencies other than the 1.6 and 1.2 GHz GPS values and be readily compared with ionospheric models. Three models were used to account for the measured ΔTEC values: a climatological model (RIBG) and two modified versions of Jet Propulsion Laboratory's GIM model (a postanalysis and a near‐real‐time implementation using a subset of reporting stations). All three models reduced the ΔTEC differences significantly. The postanalysis GIM model performed better than the other two in the tails of the residual error distribution, but there was no clear difference among the three in about 75% of the cases. However, when the data were binned according to local time and angle between the two rays, both GIM models were more accurate than RIBG between about 0600 and 1900 LT at angles greater than about 50°.