Direct position estimation from wavefront curvature with single antenna array

In this paper we investigate the possibility to perform direct positioning by retrieving information from the wavefront curvature. Despite such an approach has been considered in the past at microwave and acoustic frequencies using extremely large antennas, it is of interest to investigate its potential exploitation at mm-wave with practical size antennas in the context of next 5G systems. Thus, here we first consider a dedicated model to gather the source position information from the wavefront curvature for different array architectures, i.e., traditional and lens-based arrays, and successively we derive the maximum likelihood estimator to investigate the attainable performance. Results, obtained for different number of antennas, i.e., for different array apertures, confirm the possibility to achieve interesting positioning performance using a single antenna array with limited dimensions

Near and Far Field Model Mismatch: Implications on 6G Communications, Localization, and Sensing

The upcoming 6G technology is expected to operate in near-field (NF) radiating conditions thanks to high-frequency and electrically large antenna arrays. While several studies have already addressed this possibility, it is worth noting that NF models introduce heightened complexity, the justification for which is not always evident in terms of performance improvements. Therefore, this paper delves into the implications of the disparity between NF and far-field (FF) models concerning communication, localization, and sensing systems. Such disparity might lead to a degradation of performance metrics like localization accuracy, sensing reliability, and communication efficiency. Through an exploration of the effects arising from the mismatches between NF and FF models, this study seeks to illuminate the challenges confronting system designers and offer valuable insights into the balance between model accuracy, which typically requires a high complexity and achievable performance. To substantiate our perspective, we also incorporate a numerical performance assessment confirming the repercussions of the mismatch between NF and FF models.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Exact Conditional and Unconditional Cram\`er-Rao Bounds for Near Field Localization

This paper considers the Cram\`er-Rao lower Bound (CRB) for the source localization problem in the near field. More specifically, we use the exact expression of the delay parameter for the CRB derivation and show how this exact CRB can be significantly different from the one given in the literature and based on an approximate time delay expression (usually considered in the Fresnel region). This CRB derivation is then generalized by considering the exact expression of the received power profile (i.e., variable gain case) which, to our best knowledge, has been ignored in the literature. Finally, we exploit the CRB expression to introduce the new concept of Near Field Localization (NFL) region for a target localization performance associated to the application at hand. We illustrate the usefulness of the proposed CRB derivation and its developments as well as the NFL region concept through numerical simulations in different scenarios

Determining the Position and Orientation of In-body Medical Instruments Using Near-Field Magnetic Field Mapping

There is a increasing demand for localizing medical implants in-body, such as wireless capsule endoscope (WCE) and Nasogastric tube (NGT). Some studies have been conducted to solve this issue using either permanent magnets, static current sources or RF fields. The permanent magnet fails due to low power, and static current source requires relatively high power source. The RF field source requires high frequencies to get enough precision, which undergoes high attenuation in the body. At low frequency, when the distance between the source and the receiver array is shorter than the wavelength, the far field assumption fails for localization methods. Therefore, we propose a novel method of mapping the magnetic field vector in the near field region, with which wavelength independent localization is done. We did extensive MATLAB and CST Microwave simulations followed by practical experiments. The proposed method has achieved localization accuracy of less than 1 cm in Y-Z plane, 2 cm in depth (in X-axis) and the maximum orientation error remained 10° in 3-D

Near-field acoustic source localization based on beam space processing

The passive sonar systems estimate the target position using the radiated noise from ship such as machinery noise, cavitation noise, etc. In passive localization problem, various approaches have been investigated such as time difference of arrival (TDoA), the triangulation method and focused beamforming. However, when multiple targets exist, it can create problems with localization based on TDoA. It is difficult to obtain an accurate cross-correlation when other interference signals are present at the same time. Focused beamforming estimates the positions by measuring the spatial spectrum. Unlike localization based on TDoA and triangulation, this method has no classification problems. In this thesis, a focused array algorithm is proposed to reduce the computational complexity. The focused MVDR(minimum variance distortionless response) and MUSIC(multiple signal classification) algorithm is typically used to estimate location. It has high spatial resolution but it also has a high computational complexity. The main complexity load of the focused MVDR algorithm is in inverse matrix. And for the focused MUSIC algorithm it is in eigen-decomposition. The computational complexity of those depends on the dimensions of the correlation matrix. To reduce computational complexity, the dimensions of the correlation matrix using beam-space transformation are reduced. The beam-space signals are transformed from the originally received signal using the fact that the far-field beamformers have different direction. Simulation results are presented to evaluate the performance of the proposed method compared to the previous method. The computational complexity of the proposed method is lower than that of the previous focused beamforming, but it has a similar range resolution|수동형 소나는 선박의 기계 소음, 캐비테이션 소음 등의 방사 소음을 이용하여 표적의 위치를 추정한다. 수동형 위치 추정에는 도달 시간차, 삼각기법, 초점 빔 형성기 등을 이용한 다양한 연구가 있어 왔다. 그 중, 도달 시간차와 삼각기법 기반의 위치 추정은 수신된 신호들 사이의 상호 상관을 이용하여 추정한다. 이때 다수의 표적이 존재 한다면 관심 있는 표적 신호 이외의 표적 신호는 간섭 신호가 된다. 이 경우, 상호 상관을 이용하여 정확한 위치 정보를 구할 수 없게 된다. 또한 추정된 상호 상관 중 관심 표적 신호와 비 관심 표적 신호의 도달 시간차를 분류해야 한다. 초점 빔 형성기는 공간 스팩트럼을 추정하여 표적의 위치 추정을 하는 방법이다. 이때 초점 빔 형성기는 도달 시간차 및 삼각 기법과 같은 분류 문제가 발생하지 않는다. 본 학위 논문에서는 초점 빔 형성 알고리즘의 계산량을 줄이는 방법을 제안한다. 초점 MVDR(minimum variance distortionless response) 빔 형성과 MUSIC(multiple signal classification) 방법은 대표적인 위치 추정 알고리즘이다. 초점 MVDR 빔 형성과 MUSIC 방법은 높은 공간 분해능을 가지고 있으며, 많은 계산량을 가진다. 초점 MVDR 빔 형성 알고리즘에서 역행렬은 많은 계산량을 가지고, 초점 MUSIC 방법은 고유치 분해 과정이 많은 계산량을 가진다. 역행렬과 고유치 분해는 상관 행렬의 계산량은 행렬의 크기에 따라 달라지며, 계산량을 줄이기 위해 상관 행렬의 크기를 빔 영역으로 변환하여 줄인다. 이때 빔 영역 변환은 다른 방향으로 지향하는 원 거리 빔 형성기를 이용한다. 본 학위 논문에서 모의실험을 통해 제안된 방법을 비교 분석을 수행하였다. 제안된 방법은 기존의 방법보다 적은 계산량을 가지고 있으며 비슷한 위치 추정 성능을 가진다.List of Tables iii List of Figures iv Abstract v 제 1 장 서론 1 제 2 장 근접장 표적 거리 추정 2.1 근접장 신호 모델 4 2.2 도달 시간차 추정 기반 방법 5 2.3 초점 지연-합 빔 형성 7 2.4 초점 MVDR 빔 형성 10 2.5 초점 MUSIC 방법 11 제 3 장 빔 영역 근접장 표적 거리 추정 3.1 문제점 14 3.2 빔 영역 초점 MVDR 빔 형성 15 3.3 빔 영역 초점 MUSIC 방법 19 3.4 계산량 비교 22 제 4 장 모의실험 및 결과 분석 4.1 단일 표적 위치 추정 성능 24 4.2 근접 표적 위치 추정 성능 28 제 5 장 결론 33 참고문헌 35Maste

Integrated Sensing and Communications with Joint Beam Squint and Beam Split for Massive MIMO

Integrated sensing and communications (ISAC) has attracted tremendous attention for the future 6G wireless communication systems. To improve the transmission rates and sensing accuracy, massive multi-input multi-output (MIMO) technique is leveraged with large transmission bandwidth. However, the growing size of transmission bandwidth and antenna array results in the beam squint effect, which hampers the communications. Moreover, the time overhead of the traditional sensing algorithm is prohibitive for practical systems. In this paper, instead of alleviating the wideband beam squint effect, we take advantage of joint beam squint and beam split effect and propose a novel user directions sensing method integrated with massive MIMO orthogonal frequency division multiplexing (OFDM) systems. Specifically, with the beam squint effect, the BS utilizes the true-time-delay (TTD) lines to steer the beams of different OFDM subcarriers towards different directions simultaneously. The users feedback the subcarrier frequency with the maximum array gain to the BS. Then, the BS calculates the direction based on the subcarrier frequency feedback. Futhermore, the beam split effect introduced by enlarging the inter-antenna spacing is exploited to expand the sensing range. The proposed sensing method operates over frequency-domain, and the intended sensing range is covered by all the subcarriers simultaneously, which reduces the time overhead of the conventional sensing significantly. Simulation results have demonstrated the effectiveness as well as the superior performance of the proposed ISAC scheme.Comment: 13 pages, 11 figures, submitted to IEEE journa

Localization and tracking of electronic devices with their unintended emissions

The precise localization and tracking of electronic devices via their unintended emissions has a broad range of commercial and security applications. Active stimulation of the receivers of such devices with a known signal generates very low power unintended emissions. This dissertation presents localization and tracking of multiple devices using both simulation and experimental data in the form of five papers. First the localization of multiple emitting devices through active stimulation under multipath fading with a Smooth MUSIC based scheme in the near field region is presented. Spatial smoothing helps to separate the correlated sources and the multipath fading and results confirm improved accuracy. A cost effective near-field localization method is proposed next to locate multiple correlated unintended emitting devices under colored noise conditions using two well separated antenna arrays since colored noise in the environment degrades the subspace-based localization techniques. Subsequently, in order to track moving sources, a near-field scheme by using array output is introduced to monitor direction of arrival (DOA) and the distance between the antenna array and the moving source. The array output, which is a nonlinear function of DOA and distance information, is employed in the Extended Kalman Filter (EKF). In order to show the near- and far-field effect on estimation accuracy, computer simulation results are included for localization and tracking techniques. Finally, an L-shaped array is constructed and a suite of schemes are introduced for localization and tracking of such devices in the three-dimensional environment. Experimental results for localization and tracking of unintended emissions from single and multiple devices in the near-field environment of an antenna array are demonstrated --Abstract, page iv