In recent years, the 5G network has been deployed more and more densely. The signal coverage area is increasing, and in many countries, it allows the use of the new radio (NR) in most large cities. This makes it possible to use 5G network signals for telecommunication and remote sensing purposes. This article describes the opportunities and limitations of using 5G signals for radars. The waveform characteristics of the 5G network were tested and compared, range analyses were made, and the possibilities of detecting targets using impulse signals sent for various purposes in the network were examined. The article presents measurable properties of 5G signals that allow one to detect targets. Also, possibilities of exploiting 5G signalling for radar applications are provided. Moreover, the main limitations of using 5G waveforms and the general 5G architecture for radar purposes are discussed. Finally, a preliminary concept validation is shown with experimental results of car detection using 5G network-based passive radar.

This paper presents an approach for joint radar sensing and communications based on the OTFS (Orthogonal Time Frequency Space) modulation, applied to a moving target detection during regular digital wireless transmission. Most communication systems estimate and correct channel influence using specially designed reference signals or pilots. Pilots are usually known to the receiver before the transmission, and the receiver estimates the channel impulse response (CIR) by analyzing the input (pilots) and output of the channel. Because of the Doppler effect, the movement of reflection sources (or targets in radar terminology) in multi-path channels causes oscillations of CIR coefficients. Based on the frequency analysis of time-varying CIR, one can extract the distances and velocities of moving targets when data is transmitted through the wireless channel. This paper describes the application of OTFS with random pilots using both simulations and real-life field tests. It is shown that applied time-varying CIR estimation based on random pilot signals overcomes the OTFS with zero padding during vehicle velocity estimation in very noisy conditions. The proposed OTFS-based sensing method with the CIR-based channel estimation and vehicle detection is experimentally compared with the cross-ambiguity function (CAF) approach commonly used in radars. A thorough analysis shows that the proposed CIR-based approach outperforms the classical CAF-based radar processing in terms of target detection. Finally, the proposed integrated sensing and communication concept, including bit transmission, is experimentally verified.

This paper presents the first successful drone detection results using a 5G network as a source of illumination in a passive radar system. Furthermore, a novel adaptive strategy for signal integration is shown. The proposed approach is based on the Rényi entropy. It allows one to select time frames with a densely allocated downlink channel both in the time and frequency domains. The resource allocation is strongly related to a network load and has a crucial influence on 5G-based passive radar range resolution and detection capabilities. The proposed technique was validated using simulated and real-life signals, confirming the possibility of detecting unmanned aerial vehicles (UAVs) in 5G-network-based passive radars. Moreover, the proposed methodology can be directly used in passive radar systems where the illuminating signal duration and bandwidth are content-dependent, and the radar resolution may vary significantly.

In this paper, the possibilities of using the signal of 5G cellular networks for passive radar are investigated. In contrast to the traditional approach, i.e. the passive coherent location (PCL), in which the cross-ambiguity function (CAF) between the transmitted and received signal is calculated, in the presented method, known from the automotive industry, the channel frequency response (CFR) is first estimated, then the channel impulse response (CIR) is computed and spectrally analyzed to obtain a range-velocity map. It is shown that CFR/CIR-based 5G radar, known as an OFDM-based radar, outperforms CAF-based 5G radar in some aspects, e.g. ease of implementation and lower complexity, while maintaining comparable measurement accuracy. In this paper, CFR/CIR is estimated using standard 5G channel state information reference signals (CSI-RS) or some additional radar-on-demand (RoD) OFDM symbols that could be offered by mobile network operators as an extra paid service. Different time and frequency densities of RoD OFDM symbols are tested. The results are compared with the application of CAF and 5G positioning reference-like signals (PRS). The paper shows that even rare CSI-RS pilots can make a low-cost radar device from a 5G receiver. It is demonstrated that slightly irregular sampling of the CIR taps, caused by using cyclic prefixes of different lengths in 5G, does not lead to major velocity estimation errors.

In recent years, radar sensing technology has witnessed significant expansion, transitioning from its traditional military applications to various domains. Consequently, this proliferation has led to the emergence of numerous research topics that require exploration. Of these topics, Joint Communication and Sensing (JCAS) is of particular interest. Many scientific papers devoted to this topic have recently been published. However, JCAS is a very wide concept and still immature. It requires intensive study, going beyond theory and simulations, and overcoming a wide variety of practical challenges, not limited to technological type. One specific approach to JCAS is to extend the functionality of a communication system to have sensing capability. This work focuses on such a promising trend related to 5G mobile telephony (with the possibility of applying it in the coming 6G standard). This work summarizes the current state of the art of research in the field of 5G-based JCAS and spreads the vision of the maturation of this technology. Special attention is paid to the fusion of active and passive 5G-based sensing. Future challenges are highlighted and suggestions for the 6G standardization are included.

The fifth-generation (5G) standard has been rapidly gaining popularity as its deployment expands worldwide. With the increasing availability of 5G services, the potential for leveraging its signals for radar applications continues to grow. However, in today's densely occupied spectrum, both radar and communication systems face significant limitations in terms of bandwidth and power. This article introduces the concept and experimental results of a joint communication and sensing (JCAS) system utilizing 5G signals for both active and passive target detection as well as data transmission. A software-defined radio (SDR) was employed as a base station and an active radar node, while a second device emulated a user terminal capable of receiving, demodulating, and decoding the signal, and passively detecting nearby targets. The proposed methodology successfully detected the target and, despite involving only two nodes, precisely estimated its location.