Near-field (NF) signal processing introduces a new epoch in communication and sensing realms, showcasing transformative potential, particularly in extremely large-scale (XL) aperture array (ELAA) systems compared to its far-field (FF) counterpart. The NF spherical wavefront, incorporating the distance/range parameter through amplitude variations and phase differences among antennas, enhances spatial sensing capabilities. Localization, often intertwined with angle estimation, emerges as a direct beneficiary of this phenomenon, commanding substantial research attention. Moreover, the NF effects on spatial channels in ELAA communications mandate the formulation of diverse NF channel estimation (CE) methods. In this vein, our study presents a tutorial review of NF CE and localization, encapsulating fundamental wavefront models and extended advanced scenarios. Recognizing their pivotal roles in integrated sensing and communication (ISAC) systems, we examine their similarities and explore NF-integrated CE and localization (NF-ICEL) at the signal processing level. Additionally, we analyze system-level NF-ICEL under three specific scenarios, comparing them with FF-ICEL and highlighting the unique abilities and potential uses of NF-ICEL in scatterer/environment sensing, high-mobility situations, and unsynchronized systems.
{"title":"Near-Field Channel Estimation and Localization: Recent developments, cooperative integration, and future directions","authors":"Songjie Yang;Hua Chen;Wei Liu;Xiao-Ping Zhang;Chau Yuen","doi":"10.1109/MSP.2024.3500791","DOIUrl":"https://doi.org/10.1109/MSP.2024.3500791","url":null,"abstract":"Near-field (NF) signal processing introduces a new epoch in communication and sensing realms, showcasing transformative potential, particularly in extremely large-scale (XL) aperture array (ELAA) systems compared to its far-field (FF) counterpart. The NF spherical wavefront, incorporating the distance/range parameter through amplitude variations and phase differences among antennas, enhances spatial sensing capabilities. Localization, often intertwined with angle estimation, emerges as a direct beneficiary of this phenomenon, commanding substantial research attention. Moreover, the NF effects on spatial channels in ELAA communications mandate the formulation of diverse NF channel estimation (CE) methods. In this vein, our study presents a tutorial review of NF CE and localization, encapsulating fundamental wavefront models and extended advanced scenarios. Recognizing their pivotal roles in integrated sensing and communication (ISAC) systems, we examine their similarities and explore NF-integrated CE and localization (NF-ICEL) at the signal processing level. Additionally, we analyze system-level NF-ICEL under three specific scenarios, comparing them with FF-ICEL and highlighting the unique abilities and potential uses of NF-ICEL in scatterer/environment sensing, high-mobility situations, and unsynchronized systems.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"60-73"},"PeriodicalIF":9.4,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-21DOI: 10.1109/MSP.2024.3486470
Amir Masoud Molaei;Shaoqing Hu;Vincent Fusco;Thomas Fromenteze;Rupesh Kumar;Muhammad Ali Babar Abbasi;Okan Yurduseven
Near-field (NF) microwave and millimeter-wave (mm-wave) imaging, extending into the terahertz (THz) frequency range, has seen remarkable advancements across diverse applications, particularly security screening. These technologies benefit from the unique properties of microwave, mm-wave, and THz (MMT) spectra, such as penetration, nonionizing radiation, material sensitivity and the capability to operate in all weather conditions. This article provides an overview of the evolution and current state of NF radar imaging, emphasizing the critical role of signal processing in overcoming challenges related to hardware complexity, long acquisition time, and image reconstruction quality. Advanced signal processing techniques—including Fourier-based algorithms, sparse imaging, low-rank matrix recovery, and deep learning—are highlighted for their contributions to enhancing image resolution and processing efficiency. The article also discusses recent innovations in antenna technologies, aperture configurations, and scanning methods that have significantly improved NF radar imaging capabilities. Future research directions are suggested to further advance the field, highlighting the importance of continued exploration and innovation in NF MMT imaging.
{"title":"Advanced Near-Field Radar Imaging Approaches in Security: An overview on signal processing challenges, opportunities, and future directions","authors":"Amir Masoud Molaei;Shaoqing Hu;Vincent Fusco;Thomas Fromenteze;Rupesh Kumar;Muhammad Ali Babar Abbasi;Okan Yurduseven","doi":"10.1109/MSP.2024.3486470","DOIUrl":"https://doi.org/10.1109/MSP.2024.3486470","url":null,"abstract":"Near-field (NF) microwave and millimeter-wave (mm-wave) imaging, extending into the terahertz (THz) frequency range, has seen remarkable advancements across diverse applications, particularly security screening. These technologies benefit from the unique properties of microwave, mm-wave, and THz (MMT) spectra, such as penetration, nonionizing radiation, material sensitivity and the capability to operate in all weather conditions. This article provides an overview of the evolution and current state of NF radar imaging, emphasizing the critical role of signal processing in overcoming challenges related to hardware complexity, long acquisition time, and image reconstruction quality. Advanced signal processing techniques—including Fourier-based algorithms, sparse imaging, low-rank matrix recovery, and deep learning—are highlighted for their contributions to enhancing image resolution and processing efficiency. The article also discusses recent innovations in antenna technologies, aperture configurations, and scanning methods that have significantly improved NF radar imaging capabilities. Future research directions are suggested to further advance the field, highlighting the importance of continued exploration and innovation in NF MMT imaging.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"126-146"},"PeriodicalIF":9.4,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-21DOI: 10.1109/MSP.2024.3508474
Asmaa Abdallah;Ahmed Hussain;Abdulkadir Celik;Ahmed M. Eltawil
As sixth-generation (6G) wireless networks approach, leveraging the millimeter-wave (mmWave) and terahertz (THz) bands’ abundant spectrum becomes crucial, promising ultrahigh data rates and enabling immersive communication experiences. This transformation, characterized by the integration of ultramassive multi-in multi-out (UM-MIMO) systems, facilitates significant increases in throughput and capacity by utilizing densely packed antenna arrays. The resulting shift from traditional far-field communication, with its planar wavefronts, to near-field communication, where spherical wavefronts predominate, necessitates a reevaluation of conventional beamforming and channel estimation methods. Effective codebooks, based on the spherical wavefront phenomenon, are vital for both channel estimation and beam focusing, providing predefined sets of beam steering vectors or codewords needed to efficiently probe the channel and direct the beams toward desired directions. This article explores the development of polar-domain codebooks tailored for these near-field conditions. We reveal the exact boundaries of near-field communication, design polar codebooks based on our sparsity analysis findings, and demonstrate their efficacy in channel estimation and beam training without relying on user range information. These codebooks significantly reduce dimensionality, offering a practical solution to the challenges of minimal pilot overhead. Through two case studies, one on channel estimation and the other on beam training using the defined polar-domain codebooks, we illustrate the potential of these methodologies to enhance system performance and spectral efficiency in near-field wireless systems.
{"title":"Exploring Frontiers of Polar-Domain Codebooks for Near-Field Channel Estimation and Beam Training: A comprehensive analysis, case studies, and implications for 6G","authors":"Asmaa Abdallah;Ahmed Hussain;Abdulkadir Celik;Ahmed M. Eltawil","doi":"10.1109/MSP.2024.3508474","DOIUrl":"https://doi.org/10.1109/MSP.2024.3508474","url":null,"abstract":"As sixth-generation (6G) wireless networks approach, leveraging the millimeter-wave (mmWave) and terahertz (THz) bands’ abundant spectrum becomes crucial, promising ultrahigh data rates and enabling immersive communication experiences. This transformation, characterized by the integration of ultramassive multi-in multi-out (UM-MIMO) systems, facilitates significant increases in throughput and capacity by utilizing densely packed antenna arrays. The resulting shift from traditional far-field communication, with its planar wavefronts, to near-field communication, where spherical wavefronts predominate, necessitates a reevaluation of conventional beamforming and channel estimation methods. Effective codebooks, based on the spherical wavefront phenomenon, are vital for both channel estimation and beam focusing, providing predefined sets of beam steering vectors or codewords needed to efficiently probe the channel and direct the beams toward desired directions. This article explores the development of polar-domain codebooks tailored for these near-field conditions. We reveal the exact boundaries of near-field communication, design polar codebooks based on our sparsity analysis findings, and demonstrate their efficacy in channel estimation and beam training without relying on user range information. These codebooks significantly reduce dimensionality, offering a practical solution to the challenges of minimal pilot overhead. Through two case studies, one on channel estimation and the other on beam training using the defined polar-domain codebooks, we illustrate the potential of these methodologies to enhance system performance and spectral efficiency in near-field wireless systems.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"45-59"},"PeriodicalIF":9.4,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667556","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Terahertz (THz) band communications is envisioned as a key technology for future wireless standards. Advances in hardware design, channel models, and signal processing have all contributed significantly to advancing the field. Practical THz wireless has been demonstrated in high data-rate backhaul links. However, the next great leap for adopting THz-band frequencies in widespread communication systems must cover a massive canyon. Such communication systems must operate in the massive near field of the high-gain devices that are required to overcome the very high spreading losses of THz frequencies while providing all the promises of very high data rates and sensing resolution. Recent years have seen progress toward near-field THz, with investigations centered around the physical layer, combining both wave and communication theory to provide meaningful solutions to the challenges of THz signal propagation in the near field. In this article, an in-depth look is presented on the aspect of near-field THz. The aspect of signal propagation is first explained from a symbiosis of array and wave theory, following which it is conclusively shown how canonical beamforming is decimated in the near field. It is further explained why THz wireless must necessarily be near field, at least in some cases. Then, a vision of beamshaping is presented in which wavefront engineering is presented to address the design of new beams, specifically beamfocusing, Bessel beams, and Airy beams, which each offer distinct attractive advantages in creating THz links. Issues related to their generation and reception and issues involving narrowband limitations are presented. Finally, the article ends by discussing some of the more promising and upcoming applications of these beams as well as the exciting challenges and opportunities in this new and intriguing research area.
{"title":"Near-Field Terahertz Communications for 6G and Beyond: From concepts to realizations","authors":"Arjun Singh;Vitaly Petrov;Priyangshu Sen;Josep Miquel Jornet","doi":"10.1109/MSP.2024.3496395","DOIUrl":"https://doi.org/10.1109/MSP.2024.3496395","url":null,"abstract":"Terahertz (THz) band communications is envisioned as a key technology for future wireless standards. Advances in hardware design, channel models, and signal processing have all contributed significantly to advancing the field. Practical THz wireless has been demonstrated in high data-rate backhaul links. However, the next great leap for adopting THz-band frequencies in widespread communication systems must cover a massive canyon. Such communication systems must operate in the massive near field of the high-gain devices that are required to overcome the very high spreading losses of THz frequencies while providing all the promises of very high data rates and sensing resolution. Recent years have seen progress toward near-field THz, with investigations centered around the physical layer, combining both wave and communication theory to provide meaningful solutions to the challenges of THz signal propagation in the near field. In this article, an in-depth look is presented on the aspect of near-field THz. The aspect of signal propagation is first explained from a symbiosis of array and wave theory, following which it is conclusively shown how canonical beamforming is decimated in the near field. It is further explained why THz wireless must necessarily be near field, at least in some cases. Then, a vision of beamshaping is presented in which wavefront engineering is presented to address the design of new beams, specifically beamfocusing, Bessel beams, and Airy beams, which each offer distinct attractive advantages in creating THz links. Issues related to their generation and reception and issues involving narrowband limitations are presented. Finally, the article ends by discussing some of the more promising and upcoming applications of these beams as well as the exciting challenges and opportunities in this new and intriguing research area.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"106-125"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-20DOI: 10.1109/MSP.2025.3531196
Provides society information that may include news, reviews or technical notes that should be of interest to practitioners and researchers.
{"title":"Chapter of the Year and New IEEE Fellows","authors":"","doi":"10.1109/MSP.2025.3531196","DOIUrl":"https://doi.org/10.1109/MSP.2025.3531196","url":null,"abstract":"Provides society information that may include news, reviews or technical notes that should be of interest to practitioners and researchers.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"12-14"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10934795","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Integrated sensing and communications (ISAC) is a promising technology in solving the exacerbated spectrum congestion problem. Future developments of ISAC are expected to provide high-data-rate communications and high-resolution sensing, which demand a large frequency bandwidth and a large-scale (XL) antenna array. This has a two-fold consequence. The electromagnetic (EM) properties change from far-field uniform planar wave (UPW) to near-field uniform spherical wave (USW) propagation, and the waveform must now follow the wideband signal model in lieu of the commonly assumed narrow-band signal structure. The consideration of near-field wideband ISAC has recently prompted a reevaluation of the design techniques, including channel modeling and parameter estimation as well as precoding technologies. In this article, we review the principles of near-field wideband sensing and communications and describe the progress made in devising suitable precoding techniques. Various approaches to ISAC system design, including fully digital and hybrid analog‒digital precoders, are discussed along with their respective benefits and limitations. The efficacy of the design is judged by the achievable accuracy in target range and angular direction estimates, the power focusing, and the communication quality of service (QoS). We provide at the end a perspective on possible future research and trends in this area.
{"title":"Wideband Near-Field Integrated Sensing and Communications: A hybrid precoding perspective","authors":"Xiangrong Wang;Weitong Zhai;Xianghua Wang;Moeness Amin;Abdelhak Zoubir","doi":"10.1109/MSP.2024.3496396","DOIUrl":"https://doi.org/10.1109/MSP.2024.3496396","url":null,"abstract":"Integrated sensing and communications (ISAC) is a promising technology in solving the exacerbated spectrum congestion problem. Future developments of ISAC are expected to provide high-data-rate communications and high-resolution sensing, which demand a large frequency bandwidth and a large-scale (XL) antenna array. This has a two-fold consequence. The electromagnetic (EM) properties change from far-field uniform planar wave (UPW) to near-field uniform spherical wave (USW) propagation, and the waveform must now follow the wideband signal model in lieu of the commonly assumed narrow-band signal structure. The consideration of near-field wideband ISAC has recently prompted a reevaluation of the design techniques, including channel modeling and parameter estimation as well as precoding technologies. In this article, we review the principles of near-field wideband sensing and communications and describe the progress made in devising suitable precoding techniques. Various approaches to ISAC system design, including fully digital and hybrid analog‒digital precoders, are discussed along with their respective benefits and limitations. The efficacy of the design is judged by the achievable accuracy in target range and angular direction estimates, the power focusing, and the communication quality of service (QoS). We provide at the end a perspective on possible future research and trends in this area.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"88-105"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667332","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-20DOI: 10.1109/MSP.2025.3546042
{"title":"SPS Social Media","authors":"","doi":"10.1109/MSP.2025.3546042","DOIUrl":"https://doi.org/10.1109/MSP.2025.3546042","url":null,"abstract":"","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"8-8"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10934777","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-20DOI: 10.1109/MSP.2025.3527199
Ahmet M. Elbir;Özlem Tuğfe Demir;Kumar Vijay Mishra;Symeon Chatzinotas;Martin Haardt
After nearly a century of specialized applications in optics, remote sensing, and acoustics, the near-field (NF) electromagnetic (EM) propagation zone is experiencing a resurgence in research interest. This renewed attention is fueled by the emergence of promising applications in various fields, such as wireless communications, holography, medical imaging, and quantum-inspired systems. Signal processing within NF sensing and wireless communications environments entails addressing issues related to extended scatterers, range-dependent beampatterns, spherical wavefronts, mutual coupling effects, and the presence of both reactive and radiative fields. Recent investigations have focused on these aspects in the context of extremely large arrays and wide bandwidths, giving rise to novel challenges in channel estimation, beamforming, beam training, sensing, and localization. While NF optics has a longstanding history, advancements in NF phase retrieval (PR) techniques and their applications have lately garnered significant research attention. Similarly, utilizing NF localization with acoustic arrays represents a contemporary extension of established principles in NF acoustic array signal processing. This article aims to provide an overview of state-of-the-art signal processing techniques within the NF domain, offering a comprehensive perspective on recent advances in diverse applications.
{"title":"Near-Field Signal Processing: Unleashing the power of proximity","authors":"Ahmet M. Elbir;Özlem Tuğfe Demir;Kumar Vijay Mishra;Symeon Chatzinotas;Martin Haardt","doi":"10.1109/MSP.2025.3527199","DOIUrl":"https://doi.org/10.1109/MSP.2025.3527199","url":null,"abstract":"After nearly a century of specialized applications in optics, remote sensing, and acoustics, the near-field (NF) electromagnetic (EM) propagation zone is experiencing a resurgence in research interest. This renewed attention is fueled by the emergence of promising applications in various fields, such as wireless communications, holography, medical imaging, and quantum-inspired systems. Signal processing within NF sensing and wireless communications environments entails addressing issues related to extended scatterers, range-dependent beampatterns, spherical wavefronts, mutual coupling effects, and the presence of both reactive and radiative fields. Recent investigations have focused on these aspects in the context of extremely large arrays and wide bandwidths, giving rise to novel challenges in channel estimation, beamforming, beam training, sensing, and localization. While NF optics has a longstanding history, advancements in NF phase retrieval (PR) techniques and their applications have lately garnered significant research attention. Similarly, utilizing NF localization with acoustic arrays represents a contemporary extension of established principles in NF acoustic array signal processing. This article aims to provide an overview of state-of-the-art signal processing techniques within the NF domain, offering a comprehensive perspective on recent advances in diverse applications.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"20-32"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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