As wireless technology begins to utilize physically larger arrays and/or higher frequencies, the transmitter and receiver will reside in each other’s radiative near field. This fact gives rise to unusual propagation phenomena, such as spherical wavefronts and beam focusing, creating the impression that new spatial dimensions—called degrees of freedom (DOF)—can be exploited in the near field. However, this is a fallacy because the theoretically maximum DOF are already achievable in the far field. This article sheds light on these issues by providing a tutorial on spatial frequencies, which are the fundamental components of wireless channels, and by explaining their role in characterizing the DOF in the near and far fields. In particular, we demonstrate how a single propagation path utilizes one spatial frequency in the far field and an interval of spatial frequencies in the near field. We explain how the array geometry determines the number of distinguishable spatial frequency bins and, thereby, the spatial DOF. We also describe how to model near-field multipath channels and their spatial correlation matrices. Finally, we discuss the research challenges and future directions in this field.
{"title":"Spatial Frequencies and Degrees of Freedom: Their roles in near-field communications","authors":"Alva Kosasih;Özlem Tuğfe Demir;Nikolaos Kolomvakis;Emil Björnson","doi":"10.1109/MSP.2024.3511922","DOIUrl":"https://doi.org/10.1109/MSP.2024.3511922","url":null,"abstract":"As wireless technology begins to utilize physically larger arrays and/or higher frequencies, the transmitter and receiver will reside in each other’s radiative near field. This fact gives rise to unusual propagation phenomena, such as spherical wavefronts and beam focusing, creating the impression that new spatial dimensions—called <italic>degrees of freedom</i> (<italic>DOF</i>)—can be exploited in the near field. However, this is a fallacy because the theoretically maximum DOF are already achievable in the far field. This article sheds light on these issues by providing a tutorial on spatial frequencies, which are the fundamental components of wireless channels, and by explaining their role in characterizing the DOF in the near and far fields. In particular, we demonstrate how a single propagation path utilizes one spatial frequency in the far field and an interval of spatial frequencies in the near field. We explain how the array geometry determines the number of distinguishable spatial frequency bins and, thereby, the spatial DOF. We also describe how to model near-field multipath channels and their spatial correlation matrices. Finally, we discuss the research challenges and future directions in this field.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"33-44"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667327","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.2025.3540344
Tülay Adali
{"title":"Looking Back on My First Year as Editor-in-Chief and Reflecting on the Challenges Ahead","authors":"Tülay Adali","doi":"10.1109/MSP.2025.3540344","DOIUrl":"https://doi.org/10.1109/MSP.2025.3540344","url":null,"abstract":"","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"3-5"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10934751","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667249","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.2025.3531083
Ahmet M. Elbir;Ana Isabel Pèrez-Neira;Henry Arguello;Martin Haardt;Moeness G. Amin;Tie Jun Cui
{"title":"Special Issue on Near-Field Signal Processing: Communications, Sensing, and Imaging","authors":"Ahmet M. Elbir;Ana Isabel Pèrez-Neira;Henry Arguello;Martin Haardt;Moeness G. Amin;Tie Jun Cui","doi":"10.1109/MSP.2025.3531083","DOIUrl":"https://doi.org/10.1109/MSP.2025.3531083","url":null,"abstract":"","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"16-18"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10934775","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667551","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.2025.3539918
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提供从业人员和研究人员感兴趣的社会信息，包括新闻、评论或技术说明。
{"title":"2025 IEEE SPS President-Elect Special Election","authors":"","doi":"10.1109/MSP.2025.3539918","DOIUrl":"https://doi.org/10.1109/MSP.2025.3539918","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":"9-11"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10934797","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667333","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}
The signal processing community is currently witnessing a growing interest in near-field signal processing, driven by the trend toward the use of large-aperture arrays with high spatial resolution in the fields of communication, localization, sensing, imaging, and so on. From the perspective of localization and sensing, this trend breaks the basic far-field assumptions that have dominated the array signal processing research in the past, presenting new challenges and promising opportunities.
{"title":"Near-Field Localization and Sensing With Large-Aperture Arrays: From signal modeling to processing","authors":"Zhaolin Wang;Parisa Ramezani;Yuanwei Liu;Emil Björnson","doi":"10.1109/MSP.2024.3486471","DOIUrl":"https://doi.org/10.1109/MSP.2024.3486471","url":null,"abstract":"The signal processing community is currently witnessing a growing interest in near-field signal processing, driven by the trend toward the use of large-aperture arrays with high spatial resolution in the fields of communication, localization, sensing, imaging, and so on. From the perspective of localization and sensing, this trend breaks the basic far-field assumptions that have dominated the array signal processing research in the past, presenting new challenges and promising opportunities.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"74-87"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667331","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.2025.3533996
Kostas Plataniotis
{"title":"IEEE Signal Processing Society: State of the Society","authors":"Kostas Plataniotis","doi":"10.1109/MSP.2025.3533996","DOIUrl":"https://doi.org/10.1109/MSP.2025.3533996","url":null,"abstract":"","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"42 1","pages":"6-8"},"PeriodicalIF":9.4,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10934793","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143667366","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}
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