Estudo de formas de onda e conceção de algoritmos para operação conjunta de sistemas de comunicação e radar

The focus of this thesis is the processing of signals and design of algorithms that can be used to enable radar functions in communications systems. Orthogonal frequency division multiplexing (OFDM) is a popular multicarrier modulation waveform in communication systems. As a wideband signal, OFDM improves resolution and enables spectral efficiency in radar systems, while also improving detection performance thanks to its inherent frequency diversity. This thesis aims to use multicarrier waveforms for radar systems, to enable the simultaneous operation of radar and communication functions on the same device. The thesis is divided in two parts. The first part, studies the adaptation and application of other multicarrier waveforms to radar functions. At the present time many studies have been carried out to jointly use the OFDM signal for communication and radar functions, but other waveforms have shown to be possible candidates for communication applications. Therefore, studies on the evaluation of the application of these same signals to radar functions are necessary. In this thesis, to demonstrate that other multicarrier waveforms can overcome the OFDM waveform in radar/communication (RadCom) systems, we propose the adaptation of the filter bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM) and universal filtering multicarrier (UFMC) waveforms for radar functions. These alternative waveforms were compared performance-wise regarding achievable target parameter estimation performance, amount of residual background noise in the radar image, impact of intersystem interference and flexibility of parameterization. In the second part of the thesis, signal processing techniques are explored to solve some of the limitations of the use of multicarrier waveforms for RadCom systems. Radar systems based on OFDM are promising candidates for future intelligent transport networks. Exploring the dual functionality enabled by OFDM, we presents cooperative methods for high-resolution delay-Doppler and direction-of-arrival estimation. High-resolution parameter estimation is an important requirement for automotive radar systems, especially in multi-target scenarios that require reliable target separation performance. By exploring the cooperation between vehicles, the studies presented in this thesis also enable the distributed tracking of targets. The result is a highly accurate multi-target tracking across the entire cooperative vehicle network, leading to improvements in transport reliability and safety.O foco desta tese é o processamento de sinais e desenvolvimento de algoritmos que podem ser utilizados para a habilitar a função de radar nos sistemas de comunicação. OFDM (Orthogonal Frequency Division Multiplexing) é uma forma de onda com modulação multi-portadora, popular em sistemas de comunicação. Para sistemas de radar, O OFDM melhora a resolução e fornece eficiência espectral, além disso sua diversidade de frequências melhora o desempenho na detecção do radar. Essa tese tem como objetivo utilizar formas de onda multi-portadoras para sistemas de radar, possibilitando a operação simultânea de funções de radar e de comunicação num mesmo dispositivo. A tese esta dividida em duas partes. Na primeira parte da tese são realizados estudos da adaptabilidade de outras formas de onda multi-portadora para funções de radar. Nos dias atuais, muitos estudos sobre o uso do sinal OFDM para funções de comunicação e radar vêm sendo realizados, no entanto, outras formas de onda mostram-se possíveis candidatas a aplicações em sistemas de comunicação, e assim, avaliações para funções de sistema de radar se tornam necessárias. Nesta tese, com a intenção de demonstrar que formas de onda multi-portadoras alternativas podem superar o OFDM nos sistemas de Radar/comunicação (RadCom), propomos a adaptação das seguintes formas de onda: FBMC (Filter Bank Multicarrier); GFDM (Generalized Frequency Division Multiplexing); e UFMC (Universal Filtering Multicarrier) para funções de radar. Também produzimos uma análise de desempenho dessas formas de onda sobre o aspecto da estimativa de parâmetros-alvo, ruído de fundo, interferência entre sistemas e parametrização do sistema. Na segunda parte da tese serão explorados técnicas de processamento de sinal de forma a solucionar algumas das limitações do uso de formas de ondas multi-portadora para sistemas RadCom. Os sistemas de radar baseados no OFDM são candidatos promissores para futuras redes de transporte inteligentes, porque combinam funções de estimativa de alvo com funções de rede de comunicação em um único sistema. Explorando a funcionalidade dupla habilitada pelo OFDM, nesta tese, apresentamos métodos cooperativos de alta resolução para estimar o posição, velocidade e direção dos alvos. A estimativa de parâmetros de alta resolução é um requisito importante para sistemas de radar automotivo, especialmente em cenários de múltiplos alvos que exigem melhor desempenho de separação de alvos. Ao explorar a cooperação entre veículos, os estudos apresentados nesta tese também permitem o rastreamento distribuído de alvos. O resultado é um rastreamento multi-alvo altamente preciso em toda a rede de veículos cooperativos, levando a melhorias na confiabilidade e segurança do transporte.Programa Doutoral em Telecomunicaçõe

AFDM vs OTFS: A Comparative Study of Promising Waveforms for ISAC in Doubly-Dispersive Channels

This white paper aims to briefly describe a proposed article that will provide a thorough comparative study of waveforms designed to exploit the features of doubly-dispersive channels arising in heterogeneous high-mobility scenarios as expected in the beyond fifth generation (B5G) and sixth generation (6G), in relation to their suitability to integrated sensing and communications (ISAC) systems. In particular, the full article will compare the well-established delay-Doppler domain-based orthognal time frequency space (OTFS) and the recently proposed chirp domain-based affine frequency division multiplexing (AFDM) waveforms. Both these waveforms are designed based on a full delay- Doppler representation of the time variant (TV) multipath channel, yielding not only robustness and orthogonality of information symbols in high-mobility scenarios, but also a beneficial implication for environment target detection through the inherent capability of estimating the path delay and Doppler shifts, which are standard radar parameters. These modulation schemes are distinct candidates for ISAC in B5G/6G systems, such that a thorough study of their advantages, shortcomings, implications to signal processing, and performance of communication and sensing functions are well in order. In light of the above, a sample of the intended contribution (Special Issue paper) is provided below

Sensing with OFDM Waveform at mmWave Band based on Micro-Doppler Analysis

Joint communication and sensing (JCAS) technology has been regarded as one of the innovations in the 6G network. With the channel modeling proposed by the 3rd Generation Partnership Project (3GPP) TR 38.901, this paper investigates the sensing capability using the millimeter-wave (mmWave) band with an orthogonal frequency division multiplexing (OFDM) waveform. Based on micro-Doppler (MD) analysis, we present two case studies, i.e., fan speed detection and human activity recognition, to demonstrate the target modeling with micro-motions, backscattering signal construction, and MD signature extraction using an OFDM waveform at 28 GHz. Simulated signatures demonstrate distinct fan rotation or human motion, and waveform parameters that affect the MD signature extraction are analyzed. Simulation results draw the validity of the proposed modeling and simulation methods, which also aim to facilitate the generation of data sets for various JCAS applications

Codificação de bloco espaço-tempo na habilitação de sistemas MIMO-OFDM

The available bandwidth in the radio frequency spectrum is decreasing due to the growing number of applications and users. Therefore, in order to ensure a sustainable evolution in this area it is crucial to develop strategies to optimize the spectrum usage. Joining RADAR and communication functionalities in a single terminal represents exactly this same strategy. As such, the two functionalities, which usually compete for the same radio resources, can coexist through a cooperative relation in which they can thrive and cease to introduce interferences in between them. In this dissertation, the integration of both systems is achieved through the use of OFDM as the common waveform. Through the space time/frequency block codes, namely the Tarokh coding it is possible to introduce spatial diversity and orthogonality to the system, therefore increasing the system’s robustness and allowing to use the virtual antenna concept, which enables improved RADAR resolution and detection. In order to evaluate the system’s performance, a simulation platform was developed. In these simulations we start by firstly considering RADAR detection for single and multiple antenna systems and then integrate the radar and communication functionalities. We have verified the good performance levels of the proposed system, which thanks to its low complexity can be an interesting RadCom approach for future wireless systems.A largura de banda disponível no espectro de radio frequência enfrenta uma diminuição face ao crescente número de aplicações e utilizadores. Assim, por forma a assegurar uma evolução sustentável neste campo é fulcral desenvolver estratégias que otimizem o uso do espectro. A junção das funcionalidades RADAR e comunicação num só terminal faz parte dessa estratégia. Desta forma, duas funcionalidades usualmente concorrentes pelos mesmos recursos radio, podem coexistir em cooperação, sem interferência entre ambos. Nesta dissertação a integração dos dois sistemas é conseguida através do uso do OFDM como forma de onda comum. Através de códigos desenhados no espaço-tempo/frequência, nomeadamente a codificação de Tarokh, foi possível introduzir diversidade espacial e ortogonalidade no sistema, aumentando assim a sua robustez e permitindo o uso do conceito de antenas virtuais, que por sua vez possibilitam uma melhoria na resolução e deteção do RADAR. De forma a avaliar o desempenho do sistema desenvolveu-se uma plataforma de simulação. Nesta plataforma começou-se por considerar a deteção RADAR para sistemas com uma e múltiplas antenas, onde posteriormente se integraram as funcionalidades de comunicação. Os resultados obtidos mostraram um excelente desempenho do sistema, que devido à sua baixa complexidade, pode ser um sistema RadCom interessante para os futuros sistemas sem fios.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Joint radar and communication application for traffic safety system

The concept of “smart” cars or intelligent vehicles is presented as one of the most promising solutions to reduce the high mortality rate that occurs on the world’s roads nowadays. Besides, the recent publication of standards as the European Standard for Intelligent Transportation System (ITS) or the international standard IEEE 802.11p confirm the importance of the future vehicle-to-vehicle or vehicle-to-infrastructure networks, which can diminish gridlocks or aid the driver with information about the road status or the weather forecast in order to prevent accidents, for instance. The main drawbacks of such intelligent network regarding the accident prevention lie in the presence of obstructing objects on the road or cars that do not implement this V2V system. Therefore, a radar application based on the used waveform for the V2V communication can be suitable as a direct method to avoid collisions. The aim of this thesis consists in the verification of the viability of a radar application in a V2V scenario. Thus, a thorough evaluation of the implemented V2V propagation channel has been performed so as to determine the main constraint factors, such as the power fading, Non Wide Sense Stationary Uncorrelated Scattering (NWSSUS) or the Doppler frequency, that can affect at detection and location application. From the conclusions obtained based on the characterization of a V2V channel, a radar algorithm has been designed as well as a tracking system. The design of the proposed radar algorithm is based on power peak detection that the estimated channel impulse response presents based on the reflected power originated by possible targets. The trilateration method is used for the location of these targets in the azimuth plane; thus, a Multiple Input Multiple Output system is required. In order to carry out this viability study, a MIMO structure 4x4 using OFDM with PSK or QAM as the modulation and over a real V2V propagation channel has been simulated. The Geometric Stochastic Channel Model (GSCM) is considered, since it contains most of the relevant channel-specific features; in particular it models the Non Wide Sense Stationary Uncorrelated Scattering (NWSSUS) behavior typical for such channels. Furthermore, the IEEE 802.11p standard has been implemented so as to simulate a scenario as close to reality as possible. The results obtained conclude with a positive result for the implemented scenarios. It is important to highlight that the extrapolation of this algorithm to other environments can lead to improvements or deteriorations of the probability of detection. However, the most valuable part of the thesis is the conclusion obtained for a radar implementation in a V2V scenario. The thesis is organized into 5 chapters. The first chapter provides an introduction, the second chapter explains the V2V implemented system, the third chapter contains the characterization of the V2V propagation channel, the forth chapter explains the radar and tracking system, while the fifth chapter presents the results of the proposed radar algorithm. Furthermore, at the end of the thesis some conclusions and future work are detailed

Weniger ist mehr: Fusion von Radar- und Kommunikationssystemen

Radar und Kommunikation sind fur die Verkehrssicherheit sehr nutzliche Hilfsmittel. Es wird ein Projekt vorgestellt, in welchem die Fusion der beiden Systeme untersucht wird. Anhand von verwandten Forschungsprojekten wird gezeigt, wie durch Ausnutzen von Synergieeffekten die einzelnen Komponenten sogar verbessert werden können