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

Propagation modelling of C band directional UAV ground control links

Unmanned Aerial Vehicles (UAVs), commonly known as drones, have been widely used in specific military applications since the last century. In the recent years, technological developments regarding main aspects of these vehicles such as batteries, electronics and lightweight materials, have made UAVs more feasible to commercial applications. One of the most remarkable fields where the drones are being applied is for telecommunication applications. Several studies propose systems where the UAVs are used as communication relays. These systems, known as Drone Small Cells (DSCs), act as aerial base stations to support communication networks in high demand situations or when the current ground infrastructures have been damaged. The work done in this Thesis belongs to a project whose main goal is to implement a DSC system. The system proposed in this project will provide a wireless access point to the clients using a communication relay mounted in an aerial vehicle. The link that connects the terminals of the clients to the UAV is performed with a simple connection that uses omnidirectional antennas. However, the most critical part of this design, is the link between the UAV and the ground station which will connect the system to the backbone network. This link will use antennas with high directivity in order to deploy the aerial access point at longer distances. In this way, this Master Thesis focuses on the characterization of the link channel with more complexity. This Master Thesis has developed a propagation model intended for air-to-ground communication links. The path loss between a ground station and a UAV can be analysed by means of the implemented propagation model. The measurement equipment has been set and calibrated in advance in order to present the desired path loss information. Based on empirical data obtained in three different LOS scenarios, a comparison is proposed to some well-known state of art models. However, none of the analysed models describes the path loss properly for this type of environment. Therefore, a new propagation model has been developed by a linear approach which considers a correction factor according to the UAV's height. As the model is based on a set of empirical measurements, it can only be applied in environments with a certain of features. These characteristics are a distance range between 0 and 600 m, a drone antenna height between 7 and 35 m and a carrier frequency of 5580 MHz. The performance and accuracy of the proposed model have been analysed considering a fourth set of measurements deployed with a different drone antenna height

Propagation modelling of C band directional UAV ground control links

Unmanned Aerial Vehicles (UAVs), commonly known as drones, have been widely used in specific military applications since the last century. In the recent years, technological developments regarding main aspects of these vehicles such as batteries, electronics and lightweight materials, have made UAVs more feasible to commercial applications. One of the most remarkable fields where the drones are being applied is for telecommunication applications. Several studies propose systems where the UAVs are used as communication relays. These systems, known as Drone Small Cells (DSCs), act as aerial base stations to support communication networks in high demand situations or when the current ground infrastructures have been damaged. The work done in this Thesis belongs to a project whose main goal is to implement a DSC system. The system proposed in this project will provide a wireless access point to the clients using a communication relay mounted in an aerial vehicle. The link that connects the terminals of the clients to the UAV is performed with a simple connection that uses omnidirectional antennas. However, the most critical part of this design, is the link between the UAV and the ground station which will connect the system to the backbone network. This link will use antennas with high directivity in order to deploy the aerial access point at longer distances. In this way, this Master Thesis focuses on the characterization of the link channel with more complexity. This Master Thesis has developed a propagation model intended for air-to-ground communication links. The path loss between a ground station and a UAV can be analysed by means of the implemented propagation model. The measurement equipment has been set and calibrated in advance in order to present the desired path loss information. Based on empirical data obtained in three different LOS scenarios, a comparison is proposed to some well-known state of art models. However, none of the analysed models describes the path loss properly for this type of environment. Therefore, a new propagation model has been developed by a linear approach which considers a correction factor according to the UAV's height. As the model is based on a set of empirical measurements, it can only be applied in environments with a certain of features. These characteristics are a distance range between 0 and 600 m, a drone antenna height between 7 and 35 m and a carrier frequency of 5580 MHz. The performance and accuracy of the proposed model have been analysed considering a fourth set of measurements deployed with a different drone antenna height

Joint MIMO Communications and Sensing with Hybrid Beamforming Architecture and OFDM Waveform Optimization

In this article, we consider a multiple-input multiple-output (MIMO) transceiver performing joint communications and sensing (JCAS) using fifth-generation New Radio (5G NR) standard-compliant orthogonal frequency-division multiplexing (OFDM) waveforms. Communication links are maintained with users having multiple spatial data streams over frequency-selective non-line-of-sight channels while simultaneously transmitting separate spatial data streams to different sensing directions, where a portion of the communication data streams’ power is reallocated to the sensing data streams. The received reflections from the environment due to all transmit (TX) streams are used to obtain range–velocity and range–angle maps. Through optimizing the TX precoding and receive combining, inter-user, intra-user, and radar–communications interference are also canceled. In addition, streams transmitted in the sensing directions are optimized to minimize the lower bounds of direction-of-arrival and delay estimates jointly, and the solution is analytically derived. The simulation results illustrate that the JCAS system can reliably perform target detection while minimizing lower bounds compared with a communications-only scenario. Further, the detection probability and estimation errors of sensing can be improved while also controlling the communications capacity of the OFDM waveform, thereby indicating the need to appropriately choose the optimization parameters to obtain an optimal trade-off.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

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

Beamformer Design and Optimization for Joint Communication and Full-Duplex Sensing at mm-Waves

In this article, we study the joint communication and sensing (JCAS) paradigm in the context of millimeter-wave (mm-wave) mobile communication networks. We specifically address the JCAS challenges stemming from the full-duplex operation in monostatic orthogonal frequency-division multiplexing (OFDM) radars and from the co-existence of multiple simultaneous beams for communications and sensing purposes. To this end, we first formulate and solve beamforming optimization problems for hybrid beamforming based multiuser multiple-input and multiple-output JCAS systems. The cost function to be maximized is the beamformed power at the sensing direction while constraining the beamformed power at the communications directions, suppressing interuser interference and cancelling full-duplexing related self-interference (SI). We then also propose new transmitter and receiver beamforming solutions for purely analog beamforming based JCAS systems that maximize the beamforming gain at the sensing direction while controlling the beamformed power at the communications direction(s), cancelling the SI as well as eliminating the potential reflection from the communication direction and optimizing the combined radar pattern (CRP). Both closed-form and numerical optimization based formulations are provided. We analyze and evaluate the performance through extensive numerical experiments, and show that substantial gains and benefits in terms of radar transmit gain, CRP, and SI suppression can be achieved with the proposed beamforming methods.publishedVersionPeer 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. Also the related measurement selection and data association problems are addressed. 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.publishedVersionPeer reviewe

OFDM Waveform Optimization for Joint Communications and Sensing

The proliferation of mobile devices has resulted in the frequencies of operation of communication systems to coincide with those of the radar systems, causing mutual interference. To minimize the level of interference, a novel approach is to combine both systems in a single platform. This presentation considers a joint radar and communication system, where the radar transmitter and receiver as well as the communication transmitter are the same device while the communication receiver is at some distance. The same waveform is used for both systems and it is optimized such that it maximizes the performance of both systems.publishedVersio

Design of Phased Array Architectures for Full-Duplex Joint Communications and Sensing

The short wavelength of millimeter-waves in fifth-generation (5G) mobile communications enables the implementation of multi-element antenna arrays in relatively small space, e.g., in user devices and small base stations. Joint communication and sensing (JCAS) is a scheme which utilizes the beamsteering capabilities of the multi-element antenna arrays for simultaneously maintaining a communication link and sensing the surroundings with a radar beam and receiving it with the same device. The simultaneous transmission and reception requires a beam weighting algorithm which cancels the self-interference while at the same time maintaining the integrity of both beams. In this paper, the performance of different linear patch antenna array architectures is studied in terms of self-interference cancellation performance and obtained maximum gain in the beamsteering range. A mirror-beam problem in the self-interference cancellation algorithm for parallel arrays is studied and novel coupling randomization is introduced for the arrays to prevent the forming of the mirror beams.acceptedVersionPeer reviewe