{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T02:55:31Z","timestamp":1760237731718,"version":"build-2065373602"},"reference-count":36,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2020,6,16]],"date-time":"2020-06-16T00:00:00Z","timestamp":1592265600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>This paper investigates the achievable per-user degrees-of-freedom (DoF) in multi-cloud based sectored hexagonal cellular networks (M-CRAN) at uplink. The network consists of N base stations (BS) and     K \u2264 N     base band unit pools (BBUP), which function as independent cloud centers. The communication between BSs and BBUPs occurs by means of finite-capacity fronthaul links of capacities      C F  =  \u03bc F  \u00b7  1 2  log  ( 1 + P )      with P denoting transmit power. In the system model, BBUPs have limited processing capacity      C BBU  =  \u03bc BBU  \u00b7  1 2  log  ( 1 + P )     . We propose two different achievability schemes based on dividing the network into non-interfering parallelogram and hexagonal clusters, respectively. The minimum number of users in a cluster is determined by the ratio of BBUPs to BSs,     r = K \/ N    . Both of the parallelogram and hexagonal schemes are based on practically implementable beamforming and adapt the way of forming clusters to the sectorization of the cells. Proposed coding schemes improve the sum-rate over naive approaches that ignore cell sectorization, both at finite signal-to-noise ratio (SNR) and in the high-SNR limit. We derive a lower bound on per-user DoF which is a function of     \u03bc BBU    ,     \u03bc F    , and r. We show that cut-set bound are attained for several cases, the achievability gap between lower and cut-set bounds decreases with the inverse of BBUP-BS ratio     1 r     for      \u03bc F  \u2264 2 M     irrespective of     \u03bc BBU    , and that per-user DoF achieved through hexagonal clustering can not exceed the per-user DoF of parallelogram clustering for any value of     \u03bc BBU     and r as long as      \u03bc F  \u2264 2 M    . Since the achievability gap decreases with inverse of the BBUP-BS ratio for small and moderate fronthaul capacities, the cut-set bound is almost achieved even for small cluster sizes for this range of fronthaul capacities. For higher fronthaul capacities, the achievability gap is not always tight but decreases with processing capacity. However, the cut-set bound, e.g., at      5 M  6    , can be achieved with a moderate clustering size.<\/jats:p>","DOI":"10.3390\/e22060668","type":"journal-article","created":{"date-parts":[[2020,6,16]],"date-time":"2020-06-16T13:20:43Z","timestamp":1592313643000},"page":"668","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Degrees-Of-Freedom in Multi-Cloud Based Sectored Cellular Networks"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3368-8465","authenticated-orcid":false,"given":"Samet","family":"Gelincik","sequence":"first","affiliation":[{"name":"Institut National des Sciences Appliqu\u00e9es de Rennes, Universit\u00e9 de Rennes, 20 Avenue des Buttes de Coesmes, 35708 Rennes, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ghaya","family":"Rekaya-Ben Othman","sequence":"additional","affiliation":[{"name":"Laboratoire Traitement et Communication de l\u2019Information (LTCI), Telecom Paris, Institut Polytechnique de Paris, 91120 Palaiseau, France"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,6,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"3768","DOI":"10.1109\/TWC.2016.2528245","article-title":"Analytical tractability of hexagonal network model with random user location","volume":"15","author":"Nasri","year":"2016","journal-title":"IEEE Trans. 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