Azimuthally periodic and radially quasi-periodic Bessel-correlated fields

We introduce a class of partially coherent sources, which are capable of producing beams with radially quasi-periodic and azimuthally fully periodic intensity profiles. The physical properties of the source, as well as the propagation of the intensity distribution and the complex degree of spatial coherence of the ensuing beams are investigated and interpreted. It is shown that the shape and symmetry of the intensity and the degree of spatial coherence are generally adjustable and modulated by the parameters related to the beam source. Moreover, the periodic changes of intensity arise from the discontinuity of the phase. The results provide a method for synthesizing fields with peculiar periodic intensity distributions in polar coordinates.publishedVersionPeer reviewe

RF self-interference canceller prototype for 100-W full-duplex operation at 225-400 MHz

Military applications require more and different characteristics from in-band full-duplex radio technology than what the research prototypes developed for civil/commercial applications can offer. While the challenge of cancelling the strong transmit-receive coupling, i.e., self-interference (SI), in a full-duplex radio has been largely resolved at higher ultra high frequency (UHF) bands for low-power transmission, tactical communication and electronic warfare applications require major research efforts toward supporting lower military-relevant frequencies and significantly higher transmission power levels. In this paper, we present a prototype of a radio-frequency SI cancellation circuit for the lower UHF band at 225-400 MHz and transmit power of up to 100-200 W. The experimental results demonstrate that the canceller can suppress SI by 40-50 dB depending on the operation frequency within the band. It is targeted for the military application of simultaneous full-duplex jamming and interception of communications, where we can estimate that a 5-W signal-of-interest could be intercepted from 10 km away when simultaneously jamming with 100 W power.publishedVersionPeer reviewe

Design of RF Self-interference Cancellation Circuit for 100-W Full-Duplex Radio at 225-400 MHz

The full-duplex (FD) technology enables future military radios to simultaneously transmit and receive (STAR) on the same and adjacent frequencies. This enhances spectral efficiency and makes simultaneous integrated tactical communications and electronic warfare operations possible as opposed to the current time- or frequency-division radios used in military applications. The main challenge in implementing full-duplex radios is the strong self-interference (SI) between the transmitter and the receiver requiring solutions how to cancel the coupling, which has been largely resolved at higher ultra high frequency (UHF) bands for low power transmission. This paper presents a radio-frequency SI cancellation circuit suitable especially for very high-power military applications at military-relevant lower UHF band (225-400 MHz). The circuit couples power from the transmitter and tunes the phase and amplitude of the signal to destructively combine with the received SI, and thus isolates the receiver and transmitter. The paper introduces a concept consisting of a 90° vector modulator and switchable delay lines for a low-loss and high-power-handling cancellation circuit that enables operation with very-high transmit powers of even up to 1 kW.acceptedVersionPeer reviewe

Full-Duplex OFDM Radar With LTE and 5G NR Waveforms: Challenges, Solutions, and Measurements

This paper studies the processing principles, implementation challenges, and performance of OFDM-based radars, with particular focus on the fourth-generation Long-Term Evolution (LTE) and fifth-generation (5G) New Radio (NR) mobile networks' base stations and their utilization for radar/sensing purposes. First, we address the problem stemming from the unused subcarriers within the LTE and NR transmit signal passbands, and their impact on frequency-domain radar processing. Particularly, we formulate and adopt a computationally efficient interpolation approach to mitigate the effects of such empty subcarriers in the radar processing. We evaluate the target detection and the corresponding range and velocity estimation performance through computer simulations, and show that high-quality target detection as well as high-precision range and velocity estimation can be achieved. Especially 5G NR waveforms, through their impressive channel bandwidths and configurable subcarrier spacing, are shown to provide very good radar/sensing performance. Then, a fundamental implementation challenge of transmitter-receiver (TX-RX) isolation in OFDM radars is addressed, with specific emphasis on shared-antenna cases, where the TX-RX isolation challenges are the largest. It is confirmed that from the OFDM radar processing perspective, limited TX-RX isolation is primarily a concern in detection of static targets while moving targets are inherently more robust to transmitter self-interference. Properly tailored analog/RF and digital self-interference cancellation solutions for OFDM radars are also described and implemented, and shown through RF measurements to be key technical ingredients for practical deployments, particularly from static and slowly moving targets' point of view.Comment: Paper accepted by IEEE Transactions on Microwave Theory and Technique

Partially coherent beam generation with metasurfaces

An optical system for the generation of partially coherent beams with genuine cross-spectral density functions from spatially modulated globally incoherent sources is presented. The spatial intensity modulation of the incoherent source is achieved by quasi-planar metasurfaces based on spatial-frequency modulation of binary Bragg surface-relief diffraction gratings. Two types of beams are demonstrated experimentally: (i) azimuthally periodic, radially quasi-periodic beams and (ii) rotationally symmetric Bessel-correlated beams with annular far-zone radiation patterns.Peer reviewe

Millimeter-wave Mobile Sensing and Environment Mapping: Models, Algorithms and Validation

Integrating efficient connectivity, positioning and sensing functionalities into 5G New Radio (NR) and beyond mobile cellular systems is one timely research paradigm, especially at mm-wave and sub-THz bands. In this article, we address the radio-based sensing and environment mapping prospect with specific emphasis on the user equipment (UE) side. We first describe an efficient l1-regularized least-squares (LS) approach to obtain sparse range--angle charts at individual measurement or sensing locations. For the subsequent environment mapping, we then introduce a novel state model for mapping diffuse and specular scattering, which allows efficient tracking of individual scatterers over time using interacting multiple model (IMM) extended Kalman filter and smoother. We provide extensive numerical indoor mapping results at the 28~GHz band deploying OFDM-based 5G NR uplink waveform with 400~MHz channel bandwidth, covering both accurate ray-tracing based as well as actual RF measurement results. The results illustrate the superiority of the dynamic tracking-based solutions, compared to static reference methods, while overall demonstrate the excellent prospects of radio-based mobile environment sensing and mapping in future mm-wave networks

Spectral scale transformations of nonstationary optical fields

The notions of cross-spectral purity and spectral invariance of light impose specific structures for the field coherence. Such concepts were originally introduced for stationary light and recently extended to nonstationary fields. In this work, we establish general conditions for transforming scalar, pulsed, isodiffracting light beams produced, for instance, in usual spherical-mirror laser resonators, to nonstationary secondary sources that exhibit cross-spectral purity or spectral invariance. Further, we introduce hybrid refractive-diffractive imaging systems which perform the desired transformation accurately over a wide spectral range irrespective of the spatial coherence of the incident isodiffracting beam.publishedVersionPeer reviewe

Known-Interference Cancellation in Cooperative Jamming : Experimental Evaluation and Benchmark Algorithm Performance

Physical layer security is a sought-after concept to complement the established upper layer security techniques in wireless communications. An appealing approach to achieve physical layer security is to use cooperative jamming with interference that is known to and suppressible by the legitimate receiver but unknown to, and hence not suppressible by, the eavesdropper. Suppressing known interference (KI), however, is challenging due to the numerous unknowns, including carrier and sampling frequency offsets, that impact its reception. This letter presents a measurement campaign that captures this challenge and then demonstrates the feasibility of solving that challenge by cancelling the KI using the frequency offsets least mean squares (FO-LMS) algorithm. Results show that KI suppression directly improves processing the signal-of-interest and that cooperative jamming effectively provides security at the physical layer.Peer reviewe