A Survey on Fundamental Limits of Integrated Sensing and Communication

The integrated sensing and communication (ISAC), in which the sensing and communication share the same frequency band and hardware, has emerged as a key technology in future wireless systems due to two main reasons. First, many important application scenarios in fifth generation (5G) and beyond, such as autonomous vehicles, Wi-Fi sensing and extended reality, requires both high-performance sensing and wireless communications. Second, with millimeter wave and massive multiple-input multiple-output (MIMO) technologies widely employed in 5G and beyond, the future communication signals tend to have high-resolution in both time and angular domain, opening up the possibility for ISAC. As such, ISAC has attracted tremendous research interest and attentions in both academia and industry. Early works on ISAC have been focused on the design, analysis and optimization of practical ISAC technologies for various ISAC systems. While this line of works are necessary, it is equally important to study the fundamental limits of ISAC in order to understand the gap between the current state-of-the-art technologies and the performance limits, and provide useful insights and guidance for the development of better ISAC technologies that can approach the performance limits. In this paper, we aim to provide a comprehensive survey for the current research progress on the fundamental limits of ISAC. Particularly, we first propose a systematic classification method for both traditional radio sensing (such as radar sensing and wireless localization) and ISAC so that they can be naturally incorporated into a unified framework. Then we summarize the major performance metrics and bounds used in sensing, communications and ISAC, respectively. After that, we present the current research progresses on fundamental limits of each class of the traditional sensing and ISAC systems. Finally, the open problems and future research directions are discussed

Study of GSM based passive radar system

Study and access the feasibility and suitability of using the GSM downlink signal from the GSM base station transmitter as the transmissions of opportunity. It also describes the research and development of a totally independent low-cost experimental GSM based passive radar system in Nanyang Technological University.Master of Engineerin

Traitement du signal pour le radar aéroporté passif : suppression d’interférences et techniques STAP adaptées à des émissions d’opportunité

The novel concept for the airborne passive radar is to have multiple passive receiving arrays covering a 4 steradian angle around the platform which makes use of the ground-based stationary transmitter as the illuminator of opportunity. This challenging passive radar configuration would well find application for localized covert surveillance on an airborne platform such as an unmanned aerial vehicle, helicopter, etc. For the airborne passive radar, during moving target detections, it encounters the effects of strong interfering signal returns against the weak target returns where this severe interfering environment is usually characterized by the high levels of direct path and clutter against the thermal noise background. Due to the continuous wave, random and aperiodic nature of the passive signal and given the strong direct path and clutter signals, their random range sidelobes couplings into further range cells will seriously exacerbate the background interference, making target detections a big challenge. Moreover, owing to the platform motion, the clutter received by the airborne passive radar is not only extended in both range and angle, it is also spread over a region in Doppler frequency which further complicates the problem.This research work is focused on identifying and analyzing the critical issues faced by the airborne passive radar on moving target detections and to develop effective signal processing schemes for improved performance. As a first step, it is important to accurately derive the model for the received passive signals and consequently, efficient signal processing schemes can be studied to mitigate and to improve detections performance. The signal processing schemes for the airborne passive radar can be segregated into a two-step interference cancellation process where the direct path and strong clutter coupling components (and their corresponding random range sidelobes) present in the received signal at each antenna element can first be effectively suppressed by the adaptive interference cancellation algorithm prior to matched filter processing. Further cancellation on the residual random range sidelobes couplings and on the spatial-Doppler dependent clutter can be achieved using reduced-dimension STAP. Trials based on the ground-based moving passive radar experiments are conducted as the final part of this research work to validate and evaluate the signal processing schemes which is a major progress towards implementing an operational airborne passive radar.Le concept de radar passif aéroporté repose sur l’utilisation de plusieurs antennes réseau, disposées sur une plateforme en vue de couvrir un angle solide large de détection, en s’appuyant sur l’utilisation de signaux d’opportunité provenant d’émetteurs au sol. La détection aéroportée à partir de signaux d’opportunité est intéressante, notamment pour assurer l’autoprotection d’un avion ou d’un hélicoptère ; en revanche elle constitue un défi technique notamment en raison du niveau des signaux interférents, en provenance de l’émetteur et des trajets multiples indirects (le fouillis), bien supérieur au niveau de signal utile diffusé par la cible à détecter. D’autres effets, tels que la structure arbitraire des signaux (forme d’onde non-radar) et sa conséquence sur les lobes secondaires en distance, contribuent à la complexité du traitement à mettre en œuvre.Le point de départ des recherches se situe à l’intersection des techniques de radar passif (utilisant la corrélation entre un signal de référence non connu a priori et les signaux diffus renvoyés par l’environnement) et les techniques de type STAP (Space Time Adaptive Processing) utilisées pour la détection des cibles mobiles par les radars aéroportés conventionnels. Dans ce contexte, les travaux de thèse permettent d’étendre d’une part la caractérisation et la qualification des signaux « radar passif » à une configuration aéroportée, d’autre part les techniques STAP à une configuration bistatique et à des signaux de forme arbitraire et non structurés comme des signaux radar. Les recherches mettent en évidence l’importance primordiale du trajet direct et des premiers échos de fouillis qui parasitent la caractérisation spatio-temporelle des échos reçus dans la case distance de la cible sous test. La caractéristique du fouillis, habituellement tracée dans le plan Doppler-angle, se trouve affectée par ces interférences qu’il faut éliminer au préalable. Pour cela, un premier filtre à réponse finie est mis en œuvre sur chaque capteur, puis le traitement STAP est appliqué à l’ensemble du réseau d’antennes.Les traitements proposés sont simulés et les performances en détection sont analysées. Une expérimentation est conduite, à l’aide d’un réseau de 4 antennes mobiles au sol. Les conditions sont réunies pour collecter des signaux de fouillis étalés en Doppler et analyser l’effet d’une forme d’onde non-radar. Les traitements d’élimination des interférences sont mis en œuvre et ainsi qualifiés expérimentalement

Space–time interference analysis and suppression for airborne passive radar using transmissions of opportunity

International audienceThis study presents the space-time snapshot models for the interfering passive signals received by the airborne passive radar which uses a ground-based stationary non-cooperative transmitter. The random range sidelobes couplings of the direct path and of the strong clutter signals into further range cells are major concerns in moving target detection performance. The least squares-based adaptive interference cancellation technique is proposed to efficiently suppress the direct path, strong clutter and Doppler-shifted strong clutter signals present at each antenna element prior to matched filter processing. In mitigating the interfering signals, their corresponding random range sidelobes will also be suppressed by the same amount. Ground-based moving passive radar trials were conducted to validate and ascertain the effectiveness of the proposed adaptive interference cancellation algorithm

Signal processing for airborne passive radar

International audienceThe airborne passive radar signal processing for moving target detections can be segregated into a two-step interference cancellation process where the random range sidelobes couplings of the direct path and of the strong clutter are to be first suppressed. Further cancellation of the residual sidelobes couplings and on the spatial-Doppler dependent clutter is then achieved using reduced-dimension space-time adaptive processing. Ground-based moving passive radar experimental trials are conducted which validated the proposed signal processing schemes

Random Range Sidelobes analysis and Suppression in Airborne Passive Radar

International audienceThe severe interference environment in an airborne passive radar is usually characterized by the high levels of direct path and clutter signals against the thermal noise background. Owing to the properties of the passive signal, the random range sidelobes of the direct path and of the strong clutter will exhibit significant couplings into further range cells. The random range sidelobes of the strong clutter may cause moving target detections to be random range sidelobes limited. An adaptive interference cancellation technique is proposed to suppress these interfering signals received at each antenna element. Simulations showed that the algorithm is effective in suppressing the undesirable direct path and strong clutter signals which in turn reduces their corresponding random range sidelobes coupling effects that manifest into further range cells, lowering the overall pedestal in the ambiguity function and spatial-Doppler power spectrum

Applications of Passive Surveillance Radar System using Cell Phone Base Station Illuminators

International audienceThe networks of cell phone base stations not only provide continuous service for mobile communications users but also offer abundant illuminator resources for passive surveillance radar systems. This extensively explores the potential applications of passive surveillance radar using cell phone base station signals for various scenarios such as ground traffic monitoring, coastal and air surveillance, and through-the-wall motion detections. These promising experimental results demonstrated that such systems can be an attractive, low-cost alternative solution for various applications and prospectively as a complement to traditional active radar systems

Moving Target Localization Using Dual-Frequency CW Radar for Urban Sensing Applications

International audienceThe dual-frequency continuous wave radar measures the target range by comparing the signal phases of two single-tone frequencies. Unfortunately, in practical measurements, the range estimation result suffers significantly from direct-path coupling and return signals from other unwanted scatterers. It is also not applicable when multiple targets exist simultaneously. This paper adopts a simple but effective approach that takes the phases of target signals in Doppler domain for comparison. Thus, the range of the moving target can be estimated without the influences of direct-path coupling and other unwanted return signals. Benefiting from the coherent Doppler integration, the range estimation accuracy in noisy environment is improved. Moreover, the adopted technique is also applicable for multiple moving targets if their Doppler frequencies are separable in the Doppler domain

Target Detection Performance Analysis for Airborne Passive Bistatic Radar

International audienceFor a ground-based/airborne passive bistatic radar, its performance is dependent on the geometrical configuration and the passive transmit signal attributes. Theoretical power budget and ambiguity function analysis using a ground-based non-cooperative transmitter of opportunity with a passive bistatic radar being airborne but stationary (airship, etc.) had shown that target detection performance is limited by the strong direct path coupling signal. In comparison, the bistatic ground clutter power is significantly lower and even more so for noise power. For the passive radar to perform satisfactorily, sufficient attenuation must be provided for the direct path and strong ground clutter signals, corresponding to increasing the height of the target peak on the ambiguity function pedestal. In addition, performance could also be improved by increasing the time-bandwidth product (assuming no target migration issues), which lowers the pedestal of the ambiguity function of the strong direct path interfering signal

Signal Analysis of Airborne Passive Radar using Transmissions of Opportunity

International audienceThe composite space-time snapshot signal for the airborne passive radar using transmissions of opportunity is presented. Power budget simulations based on a three-dimensional bistatic airborne passive radar geometry with typical parameters illustrate the power spectra and eigenspectra of the interference scenario and highlight the undesirable random range sidelobes coupling of the direct path and strong clutter signals. These effects drastically increase the significant eigenvalues of the interference covariance matrix, and thus inhibit target detection performances