Successive Self-Interference Cancellation in a Low-Complexity WCP-OFDM Radar Receiver

In this paper, we consider a multicarrier waveform to perform simultaneously data transmission and radar sensing. On the radar receiver side, a state-of-the-art symbol-based algorithm generates a range-Doppler map affected by a self-interference phenomenon, potentially leading to target masking issues. Herein, we propose a successive interference cancellation procedure to enhance the radar performance while keeping a low-complexity implementation. We show that a very low reconstruction error is obtained in various scenarios. We also investigate the robustness of the proposed algorithm since it is subject to error propagation

Clairvoyant Clutter Mitigation in a Symbol-Based OFDM Radar Receiver

This paper investigates clutter rejection techniques in an OFDM symbol-based radar receiver. Two rejection filters that assume known the clutter covariance matrix are proposed. These aim at mitigating not only the clutter main peak but also its noise-like pedestal that leads to target masking issues. Performance is assessed with synthetic data on filters outputs and in terms of signal-to-clutter-plus-noise-ratio. Results show that the proposed methods succeed, to some extent, in uncovering exo-clutter targets. Rejecting clutter within the symbol-based architecture (instead of prior to) is advantageous for slowly-moving targets

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

Target Sidelobes Removal via Sparse Recovery in the Subband Domain of an OFDM RadCom System

In this paper, the problem of target masking induced by sidelobes arising in an OFDM RadCom System is considered. To fully exploit the waveform structure and address practical scenarios, we propose to deal with the sidelobes in the subband domain via sparse recovery. Accordingly, we design a sparsifying dictionary modeling at the same time the target's peak and pedestal. Results on synthetic data show that our approach allows one to remove not only the target random sidelobes but also range ambiguities arising when all subbands are not active

Comparison of Correlation-Based OFDM Radar Receivers

Various correlation-based receivers have been proposed in passive bistatic and active monostatic radar exploiting information-bearing orthogonal frequency-division multiplexing (OFDM) transmissions, but too little has been dedicated to establishing their relations and advantages over each other. Accordingly, this paper provides an analytical comparison of the most commonly encountered filters, along with a performance analysis regarding three criteria: computational complexity, signal-to-interference-plus-noise-ratio and resilience to ground clutter. The last two especially assess the possible detrimental effects of the random sidelobes (or pedestal) induced by the data symbols in the range-Doppler map. Although simulations show that none of the filters performs unanimously better, the ones employing circular correlations globally evidence attractive results

Wideband Self-Interference Cancellation Using Multi-Tap Filter in Radar Front End

The largest hurdle in full duplex wireless systems is the self-interference introduced by the transmitted signal into the received signal. In multi antenna systems this interference is caused by the direct coupling between the transmitting and receiving antennas. In systems where the transmitter and receiver uses the same antenna the interference is caused by inadequate isolation between the transmitter and receiver front-ends. In most systems the transmitted power is orders of magnitude higher than the received signal power. This causes the interference to saturate the receiver and can damage the receiver. One way of reducing this interference is to include a filter in the microwave front-end. This filter uses the transmitted signal to generate an inverse of the interference and adds it to the receiver signal path. In this thesis a multi-tap self-interference cancellation filter is designed, optimized and fabricated. The filter parameters are optimized using the basin-hopping algorithm combined with the Nelder-Mead downhill simplex algorithm. The filter is a multi-tap filter, where each tap contains phase shift, attenuation and delay elements. The filter is experimentally verified to reduce the self interference by 10.45 dB over a frequency band from 1GHz to 3GHz

A Miniaturized Low Power Millimeter Wave RFID tag for Spatial Localization and Detection

The work outlined in this thesis investigates the applicability of millimeter wave semi-passive backscatter nodes for use in the spatial localization and tracking of objects at short distances. A miniaturized semi-passive ultra-low power energy autonomous RFID tag operating in the 24 GHz ISM frequency band is developed. The spatial localization of the RFID tags is enabled by the use of a Frequency Modulated Continuous Wave (FMCW) Radar as the reader. The radar is used to resolve the modulated backscatter returned by the RFID tags when interrogated by a Continuous Wave from the reader.M.S

Analysis and Design of Joint Communication and Sensing for Wireless Cellular Networks

Joint communication and sensing (JCAS) has emerged as an important piece of technology that will radically change ordinary wireless communication and radar systems. This research area, which has significantly grown over the last decade, aims to develop integrated systems that can provide both communication and sensing/radar functionalities simultaneously. The convergence of both systems into the same joint platform facilitates a more efficient use of the hardware and spectrum resources, enabling new civilian and professional applications. This thesis focuses on the integration of JCAS functionalities into mobile cellular networks, such as fifth-generation new radio (5G NR) and sixth generation (6G) communication systems, which are developing toward higher frequency ranges at millimeter-wave (mm-wave) bands, coming with wider bandwidths, and have massive antenna arrays, providing a great framework to develop sensing functionalities. By implementing JCAS, the different nodes of the cellular network, such as the base station and user equipment, can sense and reconstruct their surroundings. However, the JCAS operation yields multiple design challenges that need to be addressed. To this end, this thesis aims to develop novel algorithms in two relevant research areas that comprise self-interference (SI) cancellation and beamforming optimization techniques for JCAS systems. This work analyzes the potential sensing performance of mobile cellular networks, proposing a joint framework and identifying the main radar processing techniques to support JCAS. The fundamental SI challenge stemming from the simultaneous operation of the transmitter and receiver is investigated, and different JCAS cancellation techniques are proposed. The performance and feasibility of the proposed JCAS system is evaluated through simulation and measurement experiments at different frequency bands and scenarios, identifying mm-wave frequencies as the key enabler for future JCAS systems. Alternative antenna architectures and beamforming methods for mm-wave JCAS platforms are proposed by considering both communication and sensing requirements. Specifically, this thesis proposes novel beamforming methods that provide multiple beams, supporting efficient beamformed communications while an additional beam senses the environment simultaneously. In addition, the proposed beam-forming algorithms address the SI challenge by implementing an efficient spatial suppression scheme to suppress the direct transmitter–receiver coupling

Air Traffic Management Abbreviation Compendium

As in all fields of work, an unmanageable number of abbreviations are used today in aviation for terms, definitions, commands, standards and technical descriptions. This applies in general to the areas of aeronautical communication, navigation and surveillance, cockpit and air traffic control working positions, passenger and cargo transport, and all other areas of flight planning, organization and guidance. In addition, many abbreviations are used more than once or have different meanings in different languages. In order to obtain an overview of the most common abbreviations used in air traffic management, organizations like EUROCONTROL, FAA, DWD and DLR have published lists of abbreviations in the past, which have also been enclosed in this document. In addition, abbreviations from some larger international projects related to aviation have been included to provide users with a directory as complete as possible. This means that the second edition of the Air Traffic Management Abbreviation Compendium includes now around 16,500 abbreviations and acronyms from the field of aviation