Sharif Digital Repository

In this paper we consider a single-cell downlink scenario where a multiple-antenna base station delivers contents to multiple cache-enabled user terminals. Based on the multicasting opportunities provided by the so-called Coded Caching technique, we investigate three delivery approaches. Our baseline scheme employs the coded caching technique on top of max-min fair multicasting. The second one consists of a joint design of Zero-Forcing (ZF) and coded caching, where the coded chunks are formed in the signal domain (complex field). The third scheme is similar to the second one with the difference that the coded chunks are formed in the data domain (finite field). We derive closed-form rate... 

We investigate the potentials of applying the coded caching paradigm in wireless networks. In order to do this, we investigate physical layer schemes for downlink transmission from a multiantenna transmitter to several cache-enabled users. As the baseline scheme, we consider employing coded caching on the top of max-min fair multicasting, which is shown to be far from optimal at high-SNR values. Our first proposed scheme, which is near-optimal in terms of DoF, is the natural extension of multiserver coded caching to Gaussian channels. As we demonstrate, its finite SNR performance is not satisfactory, and thus we propose a new scheme in which the linear combination of messages is implemented... 

The grain size of constrained groove pressed aluminum has been predicted through the genetic programming approach. “Sheet thickness,” “elongation,” “yield strength,” “ultimate tensile strength,” “total strain,” and “hardness,” along with “primary grain size” of the ultrafine-grained sheets were utilized as input parameters to obtain the ultimate grain size. A total number of 73 available data in the literature were gathered and randomly divided into 60 and 13 sets for algorithm training and testing, respectively. Among the presented models, the one with best performance utilized parameters of total strain, ultimate tensile strength, and primary grain size with 40 chromosomes, 10 head sizes,... 

The dynamic and static softening phenomena in Al-6Mg alloy were studied through interrupted two-stage hot compression test performed isothermally at 480°C and strain rate range of 0.001-0.1 s-1. The interruptions of 29 and 90 s were considered when the true strain reached 0.5. It was concluded that the effect of static softening on the flow stress was not highlighted by extending the interruption at a constant strain rate. Also, it was exhibited that softening rate highly enhanced with the strain rate decrement at a constant time. Moreover, the static and dynamic recrystallization was revealed as the dominant softening mechanisms at low and high strain rates, respectively  

In the present study, bainite fraction results of continuous cooling of high strength low alloy steels have been modeled by artificial neural networks. The artificial neural network models were constructed by 16 input parameters including chemical compositions (C, Mn, Nb, Mo, Ti, N, Cu, P, S, Si, Al, V), Nb in solution, austenitizing temperature, initial austenite grain size and cooling rate over the temperature range of the occurrence of phase transformations. The value for the output layer was the bainite fraction. According to the input parameters in feed-forward back-propagation algorithm, the constructed networks were trained, validated and tested. To make a decision on the completion... 

Post-uniform deformation energy of materials is defined as absorbed energy per unit area after necking. The energy is constant for a material type and its experienced specific processing history and also depends on its mechanical parameters as workhardening exponent, strain rate sensitivity, post-necking extension and inhomogeneity factor. Different methods such as single and multiple tensile testing had been proposed in the literature to calculate tearing energy, but the effect of post-necking extension had not been expressed explicitly. A new model by implementing uniform and failure elongations with the combination of Unwin theory is introduced. Based on the model, it was shown that... 

A duplex surface treatment on DIN 1.2210 steel has been developed involving nitriding and followed by chromium thermo-reactive deposition (TRD) techniques. The TRD process was performed in molten salt bath at 550, 625 and 700°C for 1-14h. The process formed a thickness up to 9.5μm of chromium carbonitride coatings on a hardened diffusion zone. Characterization of the coatings by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) indicates that the compact and dense coatings mainly consist of Cr(C,N) and Cr2(C,N) phase. All the growth processes of the chromium carbonitride obtained by TRD technique followed a parabolic kinetics. Activation energy (Q) for the... 

In this paper, we analyze the cooperative diversity of amplify-and-forward half-duplex relay networks under longterm power constraints. The system model we consider consists of one transmit-receive pair and an arbitrary number of relays. This paper analyzes bit error rate and network diversity for two different power distribution scenarios in network. Using the derived network error probability, the distributed signal to noise ratio for network is introduced  

Caching has been widely considered an efficient way of reducing and balancing the growing traffic in communications networks in recent years. The cache network of interest consists of one content server connected via a shared link to a number of caching nodes, also known as a single bottleneck caching network. In this paper, for the first time, the stochastic requests traffic model in such networks is considered and a performance analysis is provided based on such a realistic assumption. In addition, we introduce new comprehensive performance metrics, which simultaneously take into account, the cache hit probability, load on the bottleneck link, and requests arrival rates. The main... 

Energy consumption is a main issue of concern in wireless networks. Energy minimization increases the time that networks' nodes work properly without recharging or substituting batteries. Another criterion for network performance is data transmission rate which is usually quantified by a network utility function. There exists an inherent tradeoff between these criteria and enhancing one of them can deteriorate the other one. In this paper, we consider both Network Utility Maximization (NUM) and energy minimization in a bi-criterion optimization problem. The problem is formulated for Random Access (RA) Medium Access Control (MAC) for ad-hoc networks. First, we optimize performance of the MAC... 

In this paper, we consider the problem of optimum selection of quality-of-service (QoS) classes in underworking between the networks in a next-generation-network (NGN) environment. After introducing the delay-cost and loss-cost characteristics, we discuss the time-invariant (TI) and time-variant (TV) scenarios. For the TI case, we show that under nearly lossless transmission condition, each network can make its own optimization regardless of other networks. For the TV case, we present sufficient conditions under which the optimum QoS class of each network can be considered fixed with respect to time without considerable degradation in the optimization target. Therefore, under the conditions... 

Hidden-terminal is one of the main problems in ad hoc wireless networks. In addition, there are scenarios where the desired destination is located in the range of other transmitters, so that the efforts on setting up communication with this terminal will fail due to collisions that may occur between transmitted control frames and undesired received control and data frames. This phenomenon becomes a bottleneck when most of data transmissions experience packet fragmentation. In such scenarios, the desired destination becomes unreachable during the data transfer of neighboring nodes. Using the same PHY of IEEE 802.11 and making slight modifications in its MAC, a new medium access control scheme... 

Adaptive scheduling schemes which consider channel conditions are examples of cross-layer design in wireless networks. Research work which has been done on optimizing the performance of scheduling systems have shown that in each time slot it is better to transmit to the users with the best channel condition. In order to realize such schemes, most of earlier works have considered perfect feedback channels to send Channel State Information (CSI) to the scheduler. However, in practical systems there are some sources of imperfectness in feedback channels such as delay and quantization error. In this paper, we consider the effect of CSI delay on the performance of such systems. A new delay-aware... 

The article was originally published with the splitting of the corresponding author name into two author names. The original article has been corrected. © The Author(s), under exclusive licence to Springer Nature B.V. 2022  

In this paper, by making slight modifications in protocol stack of wireless access points, the proposed CICADA scheme aims at isolating problems related to wireless section of a TCP connection from its wired portion, using IP spoofing and Virtual Protocol Stack scheme. As the simulation results for an 802.11 based system show, the proposed scheme improves the overall network throughput while reducing the mean and variance of end-to-end delay for voice and video flows due to smarter bandwidth allocation to elastic and real-time traffic. In addition, the proposed scheme uses a centralized NAT structure that prevents undesired disconnections during handovers and achieves a smaller handoff delay... 

In this paper, by making slight modifications in protocol stack of wireless access points, the proposed CICADA scheme aims at isolating problems related to wireless section of a transmission control protocol (TCP) connection from its wired portion, using IP spoofing and virtual protocol stack scheme. As the simulation results for an 802.11 based system show, the proposed scheme improves the overall network throughput for both DCF and PCF scenarios, while reducing the mean and variance of end-to-end delay for voice and video flows due to smarter bandwidth allocation to elastic and real-time traffic. In addition, the proposed scheme uses a centralized network address translation (NAT)... 

Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising applications due to their unique characteristics in which composite nature is combined with graded structure. Different architectures of Al6061/SiCp composite laminates were fabricated by successive hot roll-bonding. For FGAMCs, two composite layers as outer strips and a layer of Al1050 as interlayer were applied. To investigate laminate toughness, the quasi-static three-point bending test was conducted in the crack divider orientation. Genetic programming as a soft computing technique was implemented to find mathematical correlations between architectural parameters and experimentally obtained...