{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T02:12:07Z","timestamp":1760148727642,"version":"build-2065373602"},"reference-count":30,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2023,6,2]],"date-time":"2023-06-02T00:00:00Z","timestamp":1685664000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["62271155"],"award-info":[{"award-number":["62271155"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Cell-free massive multiple-input multiple-output (MIMO) is a promising technology for the Internet of Things (IoT) because it can increase connectivity and provide considerable energy efficiency (EE) and spectral efficiency (SE). However, pilot contamination caused by pilot reuse severely limits the performance of the system. In this paper, we propose a left-null-space-based massive access method that can significantly reduce interference among users. The proposed method includes three stages: initial orthogonal access, left-null-space-based opportunistic access and data detection of all accessed users. The simulation results show that the proposed method can achieve much higher spectral efficiency than the existing massive access methods.<\/jats:p>","DOI":"10.3390\/s23115285","type":"journal-article","created":{"date-parts":[[2023,6,2]],"date-time":"2023-06-02T02:41:35Z","timestamp":1685673695000},"page":"5285","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["A Left-Null-Space-Based Massive Access Method for Cell-Free Massive MIMO IoT Systems"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2189-152X","authenticated-orcid":false,"given":"Yang","family":"Wang","sequence":"first","affiliation":[{"name":"Department of Communication Science and Engineering, Fudan University, Shanghai 200082, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8081-8512","authenticated-orcid":false,"given":"Die","family":"Hu","sequence":"additional","affiliation":[{"name":"Department of Communication Science and Engineering, Fudan University, Shanghai 200082, China"}]}],"member":"1968","published-online":{"date-parts":[[2023,6,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2347","DOI":"10.1109\/COMST.2015.2444095","article-title":"Internet of Things: A Survey on Enabling Technologies, Protocols, and Applications","volume":"17","author":"Guizani","year":"2015","journal-title":"IEEE Commun. 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