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UID:20260522T064230EDT-7379Vxam1l@132.216.98.100
DTSTAMP:20260522T104230Z
DESCRIPTION: \n\nAbstract\n\nCell-free massive MIMO (m-MIMO) has been desig
 nated as a key enabling technology for beyond the fifth generation (B5G) a
 nd the sixth generation (6G) of wireless communication networks. It is ess
 entially a distributed heterogeneous network in which a large number of ac
 cess points (APs)\, scattered over a geographical area and coordinated by 
 a central processing unit (CPU)\, serve multiple users without being bound
 ed by cells. Cell-free m-MIMO\, as a state-of-the-art technology\, offers 
 several advantages\, including: high spectral efficiency (SE)\, large-scal
 e diversity gain\, and avoiding the need for frequent handovers.\n\nNevert
 heless\, the practical deployment of cell-free m-MIMO poses several signal
  processing challenges at the physical layer. For instance\, the total pow
 er consumption for the communication links can reach such a high level as 
 to defeat the SE gains. As a distributed network\, cell-free m-MIMO suffer
 s potentially from physical security issues\, especially the pilot spoofin
 g attack\, which is launched by an eavesdropper (Eve) to overhear an inten
 ded user. Finally\, the quality of certain channel parameters\, required f
 or signal processing tasks at the CPU can be severely affected due to the 
 use of low-resolution quantizers on the backhaul links between the APs and
  the CPU.\n\nIn this thesis\, we respectively address and propose novel so
 lutions to the above issues in three parts. Specifically\, we commence wit
 h the problem of downlink power allocation in a cell-free m-MIMO system un
 der SE constraints for the users. The power allocation is formulated as an
  optimization problem where the aim is to maximize the sum SE as the objec
 tive function\, while limiting the transmission power of APs and imposing 
 lower and upper bounds on the achievable SEs of different users. While the
  problem is non-convex\, an efficient solution approach is developed throu
 gh the use of bounding and relaxation techniques. Interestingly\, it revea
 ls that each user is allocated a fraction of available power proportional 
 to its required data rate\, which in turn\, leads to a significant reducti
 on in total power consumption. Besides\, the quality of service can be enh
 anced for users who require high SE but are located at the periphery of th
 e network coverage area.\n\nIn the second part of the thesis\, we propose 
 two novel methods based on the log-likelihood ratio test (LLRT)\, one in a
  centralized and the other in a decentralized fashion\, to cope with the p
 roblem of pilot spoofing attack in a cell-free m-MIMO system. The methods 
 take advantage of a special protocol in which the legitimate users switch 
 to an off-mode irregularly\, without significantly affecting the spectral 
 efficiency of the data transmission. The protocol is applicable to environ
 ments with low to moderate mobility but can be extended to high mobility t
 hrough a simple rearrangement of available pilot sequences among users. Th
 e detection performances of the proposed methods are mathematically analyz
 ed and their validity is confirmed via simulations. Moreover\, the propose
 d methods significantly outperform benchmark approaches from the recent li
 terature in terms of detection and false alarm probabilities\, while requi
 ring low fronthaul overhead.\n\nIn the last part of the thesis\, we consid
 er the problem direction of arrival (DoA) estimation in cell-free m-MIMO a
 nd propose a new method based on cutting-edge deep neural network (DNN) te
 chnology. To train the DNN\, a special feature set is proposed as obtained
  from the first superdiagonal entries of the spatial correlation matrix. T
 his selection of features makes it possible to employ a DNN with only a fe
 w low-dimensional layers\, which considerably speeds up training and proce
 ssing. The proposed method offers a high resolution and a significant redu
 ction in terms of processing time compared to the established approaches i
 n the literature.\n
DTSTART:20221107T163000Z
DTEND:20221107T183000Z
LOCATION:\, Room 603\, McConnell Engineering Building\, CA\, QC\, Montreal\
 , H3A 0E9\, 3480 rue University
SUMMARY:PhD defence of Seyyed Saleh Hosseini - Studies in Cell-Free Massive
 -MIMO: Green Power Allocation\, Physical Security\, and DoA Estimation
URL:/ece/channels/event/phd-defence-seyyed-saleh-hosse
 ini-studies-cell-free-massive-mimo-green-power-allocation-physical-343191
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