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asynchronous-system
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Asynchronous downlink massive MIMO networks: A stochastic geometry approach
, Article IEEE Transactions on Wireless Communications ; Volume 19, Issue 1 , 2020 , Pages 579-594 ; Azimi Abarghouyi, S. M ; Makki, B ; Nasiri Kenari, M ; Svensson, T ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
Massive multiple-input multiple-output (M-MIMO) is recognized as a promising technology for the next generation of wireless networks because of its potential to increase the spectral efficiency. In initial studies of M-MIMO, the system has been considered to be perfectly synchronized throughout the entire cells. However, perfect synchronization may be hard to attain in practice. Therefore, we study a M-MIMO system whose cells are not synchronous to each other, while transmissions in a cell are still synchronous. We analyze an asynchronous downlink M-MIMO system in terms of the coverage probability and the ergodic rate by means of the stochastic geometry tool. For comparison, we also obtain...
Detection in Code Division Multiple Access Systems
, Ph.D. Dissertation Sharif University of Technology ; Marvasti, Farokh (Supervisor)
Abstract
In this thesis, detection problem in CDMA systems in overloaded regim is investigated. To thid end, both wireless and optical CDMA systems are considered. In overloaded CDMA systems, if the spreading matrix is invertible and channel is ideal and noiseless, then in the receiver the information of users can be detected without any error. Previusely, it was proven that for limited information symbols space, there are some matrices which are invertible or detecting. However, optimal receiver in these systems is comlex and infeasible. The only case that the optimal receiver can be implemented in a fesible way, is when the spreading matrix is constructed using kronecker technique. Therefore, in...
Resource Allocation in mmWave Massive MIMO Transmission in the Presence of Neighboring Cells Interference
, M.Sc. Thesis Sharif University of Technology ; Nasiri Kenari, Masoumeh (Supervisor)
Abstract
In Massive multiple input multiple output (MIMO) systems, due to utilizing a large antenna array in each base station, each user’s channel is orthogonal to one another. These systems have some valuable advantages such as the reduction of energy needed for transmission and significant improvement in spectral efficiency, which makes them be suitable for the next generation of wireless communication systems. In this thesis a massive MIMO working is considered on TDD mode, for wich the channel estimation is done in the base station using the pilot sequences recieved from users. At the beginning of each coherence block, users send their pilot sequences and the rest of the times is allocated to...
Non-uniform sampling based on an adaptive level-crossing scheme
, Article IET Signal Processing ; Volume 9, Issue 6 , 2015 , Pages 484-490 ; 17519675 (ISSN) ; Kafashan, M. M ; Ghassemian, M ; Marvasti, F ; Sharif University of Technology
Institution of Engineering and Technology
2015
Abstract
Level-crossing (LC) analog-to-digital (A/D) converters can efficiently sample certain classes of signals. An LC A/D converter is a real-time asynchronous system, which encodes the information of an analog signal into a sequence of nonuniformly spaced time instants. In particular, this class of A/D converters uses an asynchronous data conversion approach, which is a power efficient technique. In this study, the authors propose adaptive and multi-level adaptive LC sampling models as alternatives to conventional LC schemes and apply an iterative algorithm to improve the reconstruction quality of LC A/D converters. This simulation results show that multi-level adaptive LC outperforms...
Vulnerability analysis of networks to detect multiphase attacks using the actor-based language Rebeca
, Article Computers and Electrical Engineering ; Volume 36, Issue 5 , 2010 , Pages 874-885 ; 00457906 (ISSN) ; Makarem, M. S ; Sirjani, M ; Jalili, R ; Movaghar, A ; Sharif University of Technology
2010
Abstract
Increasing use of networks and their complexity make the task of security analysis more and more complicated. Accordingly, automatic verification approaches have received more attention recently. In this paper, we investigate applying of an actor-based language based on reactive objects for analyzing a network environment communicating via Transport Protocol Layer (TCP). The formal foundation of the language and available tools for model checking provide us with formal verification support. Having the model of a typical network including client and server, we show how an attacker may combine simple attacks to construct a complex multiphase attack. We use Rebeca language to model the network...