Sharif Digital Repository

In this study, a new two-way relaying scheme based on compute-and-forward (CMF) framework and relay selection strategies is proposed, which provides a higher throughput than the conventional two-way relaying schemes. Two cases of relays with or without feedback transmission capability are considered. An upper bound on the computation rate of each relay is derived, and based on that, a lower bound on the outage probability of the system is presented assuming block Rayleigh fading channels. Numerical results show that while the average sum rate of the system without feedback, named as max-CMF (M-CMF), reaches the derived upper bound only in low SNRs, that of the system with feedback, named as... 

This paper develops a stochastic geometry-based approach for the modeling, analysis, and optimization of wireless cloud caching networks comprised of multiple-antenna radio units (RUs) inside clouds with coordinated multi-point transmissions and guard zones. We consider Poisson cluster processes to model RUs and users, and the probabilistic content placement to cache files in RUs. Accordingly, we study the exact hit probability for a user of interest for two strategies; closest selection, where the user is served by the closest RU that has its requested file, and best power selection, where the serving RU having the requested file provides the maximum instantaneous received power at the... 

In this paper, we propose a new transmission scheme, called integer forcing-and-forward (IFF), for communications among multipair multiple-antenna users in which each pair exchanges their messages with the help of a single multiple-antenna relay in the multiple-access and broadcast phases. The proposed scheme utilizes integer forcing linear receiver (IFLR) at the relay, which uses equations, i.e., linear integer combinations of messages, to harness intrapair interference. Accordingly, we propose the design of a mean square error (MSE)-based transceiver, including precoder and projection matrices for the relay and users, assuming that perfect channel state information (CSI) is available. In... 

This paper develops a stochastic geometry-based approach for the modeling and analysis of finite millimeter wave (mmWave) wireless networks where a random number of transmitters and receivers are randomly located inside a finite region. We consider a selection strategy to serve a reference receiver by the transmitter providing the maximum average received power among all transmitters. In our system model, we employ the unique features of mmWave communications such as directional transmit and receive beamforming and different channels for line-of-sight (LOS) and non-line-of-sight (NLOS) links. Accordingly, deploying a blockage process suitable for mmWave networks, we study the coverage... 

In this letter, we introduce a decentralized compute-and-forward (DCMF) protocol to solve the rank failure problem in compute-and-forward (CMF) ad hoc multi-user multi-relay networks without a central coordinator. In sufficiently strong inter-relay links, we show that the DCMF scheme can reach the same achievable rate as in the successive centralized CMF (SCCMF), which is a modified version of the previously introduced centralized CMF in using our proposed successive method for a fair comparison. We evaluate the outage probability and rate of the proposed strategy, and compare the results with those of the conventional CMF and decode-and-forward, and the SCCMF  

In this paper, we propose a scheme referred to as integer-forcing message recovering (IFMR) to enable receivers to recover their desirable messages in interference channels. Compared to the state-of-the-art integer-forcing linear receiver (IFLR), our proposed IFMR approach needs to decode considerably less number of messages. In our method, each receiver recovers independent linear integer combinations of the desirable messages each from two independent equations. We propose an efficient polynomial-time algorithm to sequentially find the equations and integer combinations with maximum rates and analyze its complexity. We evaluate the performance of our scheme and compare the results with the... 

This paper develops a stochastic geometry-based approach for the modeling and analysis of single- and multi-cluster wireless networks. We first define finite homogeneous Poisson point processes to model the number and locations of the transmitters in a confined region as a single-cluster wireless network. We study the coverage probability for a reference receiver for two strategies; closest-selection, where the receiver is served by the closest transmitter among all transmitters, and uniform-selection, where the serving transmitter is selected randomly with uniform distribution. Second, using Matern cluster processes, we extend our model and analysis to multi-cluster wireless networks. Here,... 

This paper develops a tractable modeling and analysis framework for finite cellular wireless networks using stochastic geometry. Defining finite homogeneous Poisson point processes to model the number and locations of access points in a confined region, we study the coverage probability for an arbitrarily-located reference user that is served by the closest access point. The distance distribution and the Laplace transform (LT) of the interference are derived. We also derive a closed-form lower bound on the LT of the interference. Our analyses reveal that a higher path loss exponent improves the coverage probability and that there is a location where the coverage probability is maximized. ©... 

In this paper, we consider a relay-assisted uplink non-orthogonal multiple access (NOMA) system where two radio frequency (RF) users are grouped for simultaneous transmission, over each resource block, to an intermediate relay which forwards the amplified version of the users' aggregated signals in the presence of multiuser interference to a relatively far destination. In order to cope with the users' ever-increasing desire for higher data rates, a high-throughput free-space optics (FSO) link is employed as the relay-destination backhaul link. Dynamic-order decoding is employed at the destination to determine the priority of the users based on their instantaneous channel state information... 

A new approach for attaining numerical solution to sinusoidal steady-state Maxwell's equations is developed. This approach is based on Yee's method, and can be applied on unstructured grids. A problem is solved by the method and the results show good agreement with the available analytical solution. This method can be improved to be applicable for general unsteady problems. © 2018 Sharif University of Technology. All rights reserved  

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... 

The free vibration analysis of rotating axially functionally graded nanobeams under an in-plane nonlinear thermal loading is provided for the first time in this paper. The formulations are based on Timoshenko beam theory through Hamilton’s principle. The small-scale effect has been considered using the nonlocal Eringen’s elasticity theory. Then, the governing equations are solved by generalized differential quadrature method. It is supposed that the thermal distribution is considered as nonlinear, material properties are temperature dependent, and the power-law form is the basis of the variation of the material properties through the axial of beam. Free vibration frequencies obtained are... 

The original version of this article unfortunately contained a mistake. The affiliation 3 was incorrect. The correct affiliation 3 is: Department of Mechanical Engineering, Payame Noor University (PNU), P. O. Box 19395-3697, Tehran, Iran. © 2016, Indian Society of Haematology & Transfusion Medicine  

Demand-side management (DSM) and the integration of the energy hub concept as a main part of future energy networks play an essential role in the process of improving the efficiency and reliability of the power grids. In this paper, we consider a smart multi-carrier energy system in which users are equipped with energy storage and conversion devices (i.e., an energy hub). Users intend to reduce their energy payment by shifting energy consumption to off-peak hours and switching between different energy carriers. This system enables both users with shiftable loads and must-run loads to be active in a DSM program. We apply game theory to formulate the energy consumption and conversion for a... 

To limit the peak power consumption of a cluster, a centralized power capping system typically assigns power caps to the individual servers, which are then enforced using local capping controllers. Consequently, the performance and throughput of the servers are affected, and the runtime of jobs is extended as a result. We observe that servers in big data processing clusters often execute big data applications that have different tolerance for approximate results. To mitigate the impact of power capping, we propose a new power-Capping aware resource manager for Approximate Big data processing (CAB) that takes into consideration the minimum Quality-of-Result (QoR) of the jobs. We use... 

The effect of graphene (G) and graphene oxide (GO), used as the nanofiller in polymer nanocomposites (NC), on the structural and dynamic properties of polymer chains, has been studied by means of molecular dynamics (MD) simulations. Two polymers, i.e., poly(propylene) and poly(vinyl alcohol), are employed as matrices to cover a wider range of polymer–filler interactions. The local structural properties, e.g., density profile, average Rg, and end-to-end distance as well as dynamic properties, e.g., estimated translational and orientational relaxation times, of polymer chains are studied. In addition, the interaction energies are estimated between polymers and nanofillers for different hybrid... 

The findings of cantilever beam bending tests conducted on a series of full-scale glass fibre-reinforced polymer (GFRP) and steel-reinforced concrete utility poles are presented. The poles were reinforced by (i) longitudinal steel bars and steel stirrups (ii) longitudinal GFRP bars and steel stirrups, and (iii) longitudinal GFRP bars and GFRP stirrups. Crack initiation and propagation as well as load carrying capacity and free end deflections of GFRP reinforced poles were obtained and compared with their counterpart steel reinforced poles. Based on the results all longitudinal GFRP reinforced poles have shown higher load-carrying capacity than that of steel reinforced poles, while due to the... 

The vibration analysis of rotating, functionally graded Timoshenko nano-beams under an in-plane nonlinear thermal loading is studied for the first time. The formulation is based on Eringen's nonlocal elasticity theory. Hamilton's principle is used for the derivation of the equations. The governing equations are solved by the differential quadrature method. The nano-beam is under axial load due to the rotation and thermal effects, and the boundary conditions are considered as cantilever and propped cantilever. The thermal distribution is considered to be nonlinear and material properties are temperature-dependent and are changing continuously through the thickness according to the power-law... 

The feasibility of a mesophilic anaerobic treatment of an alcohol distillery wastewater (beet molasses stillage) was studied in a 1300 I Upflow Anaerobic Sludge Blanket (UASB) reactor for a period of 180 days. The system was seeded with 600 L of mesophilic anaerobic sludge harvested from the bottom of a dairy anaerobic lagoon. Nutrients were added to acidified effluent and after adjusting the pH in an equalization tank, the system was fed with a diluted effluent containing COD in the range of 1000-11000 mg/L at 30°C. Initially, the system had an OLR of 1 kg COD m-3 d-1 and upflow velocity was maintained at 0.6 m/h (HRT= 6 h) throughout the study. A gradual increase in OLR, through increased...