{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,2]],"date-time":"2026-04-02T05:03:30Z","timestamp":1775106210581,"version":"3.50.1"},"reference-count":118,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2023,4,7]],"date-time":"2023-04-07T00:00:00Z","timestamp":1680825600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"CNPq"},{"name":"CAPES"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>High data rate coverage, security, and energy efficiency will play a key role in the continued performance scaling of next-generation mobile systems. Dense, small mobile cells based on a novel network architecture are part of the answer. Motivated by the recent mounting interest in free-space optical (FSO) technologies, this paper addresses a novel mobile fronthaul network architecture based on FSO, spread spectrum codes, and graphene modulators for the creation of dense small cells. The network uses an energy-efficient graphene modulator to send data bits to be coded with spread codes for achieving higher security before their transmission to remote units via high-speed FSO transmitters. Analytical results show the new fronthaul mobile network can accommodate up to 32 remote antennas under error-free transmissions with forward error correction. Furthermore, the modulator is optimized to provide maximum efficiency in terms of energy consumption per bit. The optimization procedure is carried out by optimizing both the amount of graphene used on the ring resonator and the modulator\u2019s design. The optimized graphene modulator is used in the new fronthaul network and requires as low as 4.6 fJ\/bit while enabling high-speed performance up to 42.6 GHz and remarkably using one-quarter of graphene only.<\/jats:p>","DOI":"10.3390\/s23083791","type":"journal-article","created":{"date-parts":[[2023,4,7]],"date-time":"2023-04-07T04:04:16Z","timestamp":1680840256000},"page":"3791","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["Beyond 5G Fronthaul Based on FSO Using Spread Spectrum Codes and Graphene Modulators"],"prefix":"10.3390","volume":"23","author":[{"given":"Daniel","family":"Neves","sequence":"first","affiliation":[{"name":"Electrical Engineering Department, Federal University of Ceara, Fortaleza 60020-181, Brazil"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Anderson","family":"Sanches","sequence":"additional","affiliation":[{"name":"Engineering, Modeling & Applied Social Sciences Center, Federal University of ABC, Santo Andre 09210-580, Brazil"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Rafael","family":"Nobrega","sequence":"additional","affiliation":[{"name":"Engineering, Modeling & Applied Social Sciences Center, Federal University of ABC, Santo Andre 09210-580, Brazil"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hichem","family":"Mrabet","sequence":"additional","affiliation":[{"name":"SERCOM Laboratory, Tunisia Polytechnic School, Carthage University, Carthage 1054, Tunisia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Iyad","family":"Dayoub","sequence":"additional","affiliation":[{"name":"Universite Polytechnique Hauts-de-France, Universite Lille, and INSA Hauts-de-France, 59313 Valenciennes, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kohei","family":"Ohno","sequence":"additional","affiliation":[{"name":"School of Interdisciplinary Mathematical Sciences, Meiji University, Tokyo 101-8301, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9641-5520","authenticated-orcid":false,"given":"Shyqyri","family":"Haxha","sequence":"additional","affiliation":[{"name":"Department of Electronic Engineering, Royal Holloway, University of London, London WC1B 5DN, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3176-8069","authenticated-orcid":false,"given":"Ivan","family":"Glesk","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, University of Strathclyde, Glasgow G1 1XJ, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4381-5109","authenticated-orcid":false,"given":"Antonio","family":"Jurado-Navas","sequence":"additional","affiliation":[{"name":"Communications and Signal Processing Laboratory, Telecommunication Research Institute, University of Malaga, 29010 Malaga, Spain"},{"name":"Department of Communications Engineering, University of Malaga, 29010 Malaga, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Thiago","family":"Raddo","sequence":"additional","affiliation":[{"name":"Engineering, Modeling & Applied Social Sciences Center, Federal University of ABC, Santo Andre 09210-580, Brazil"},{"name":"Department of Communications Engineering, University of Malaga, 29010 Malaga, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,4,7]]},"reference":[{"key":"ref_1","unstructured":"Carson, S., and Davies, S. 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