{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,6]],"date-time":"2026-02-06T02:56:51Z","timestamp":1770346611302,"version":"3.49.0"},"reference-count":41,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2021,5,13]],"date-time":"2021-05-13T00:00:00Z","timestamp":1620864000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We address the accuracy of wideband direct position estimation of a radio transmitter via a distributed antenna array in 5G cellular systems. Our derivations are based only on the presence of spatially coherent line-of-sight (LoS) signal components, which is a realistic assumption in small cells, especially in the mmWave range. The system model considers collocated time and phase synchronized receiving front-ends with antennas distributed in 3D space at known locations and connected to the front-ends via calibrated coaxial cables or analog radio-frequency-over-fiber links. Furthermore, the signal model assumes spherical wavefronts. We derive the Cram\u00e9r-Rao bounds (CRBs) for two implementations of the system: with (a) known signals and (b) random Gaussian signals. The results show how the bounds depend on the carrier frequency, number of samples used for estimation, and signal-to-noise ratios. They also show that increasing the number of antennas (such as in massive MIMO systems) considerably improves the accuracy and lowers the signal-to-noise threshold for localization even for non-cooperative transmitters. Finally, our derivations show that the square roots of the bounds are two to three orders of magnitude below the carrier wavelength for realistic system parameters.<\/jats:p>","DOI":"10.3390\/s21103401","type":"journal-article","created":{"date-parts":[[2021,5,14]],"date-time":"2021-05-14T03:28:36Z","timestamp":1620962916000},"page":"3401","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Performance Limits of Direct Wideband Coherent 3D Localization in Distributed Massive MIMO Systems"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2784-1494","authenticated-orcid":false,"given":"Nenad","family":"Vukmirovi\u0107","sequence":"first","affiliation":[{"name":"School of Electrical Engineering, University of Belgrade, 11120 Belgrade, Serbia"},{"name":"Innovation Center of the School of Electrical Engineering, University of Belgrade, 11120 Belgrade, Serbia"}]},{"given":"Miljko","family":"Eri\u0107","sequence":"additional","affiliation":[{"name":"School of Electrical Engineering, University of Belgrade, 11120 Belgrade, Serbia"},{"name":"Vlatacom Institute, 11070 Belgrade, Serbia"}]},{"given":"Petar M.","family":"Djuri\u0107","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, Stony Brook University, New York, NY 11794, USA"}]}],"member":"1968","published-online":{"date-parts":[[2021,5,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2475","DOI":"10.1109\/TSP.2017.2666779","article-title":"Direct localization for massive MIMO","volume":"65","author":"Garcia","year":"2017","journal-title":"IEEE Trans. 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