Sharif Digital Repository

Exploiting Compressive Sensing (CS) in MIMO radars, we can remove the need of the high rate A/D converters and send much less samples to the fusion center. In distributed MIMO radars, the received signal can be modeled as a block sparse signal in a basis. Thus, block CS methods can be used instead of classical CS ones to achieve more accurate target parameter estimation. In this paper a new method of energy allocation to the transmitters is proposed to improve the performance of the block CS-based distributed MIMO radars. This method is based on the minimization of an upper bound of the sensing matrix block-coherence. Simulation results show a significant increase in the accuracy of multiple... 

Multiple-input multiple-output (MIMO) radars offer higher resolution, better target detection, and more accurate target parameter estimation. Due to the sparsity of the targets in space-velocity domain, we can exploit Compressive Sensing (CS) to improve the performance of MIMO radars when the sampling rate is much less than the Nyquist rate. In distributed MIMO radars, block CS methods can be used instead of classical CS ones for more performance improvement, because the received signal in this group of MIMO radars is a block sparse signal in a basis. In this paper, two new methods are proposed to improve the performance of the block CS-based distributed MIMO radars. The first one is a new... 

A multistage decoder for the internally convolutionally coded fibre-optic time-hopping code division multiple access system recently introduced is considered. In this system, the decoder consists of several stages. The first stage is implemented using one of the single-user decoders introduced. The following stages are maximum likelihood (ML) decoders each of which use the decisions made by the previous stage. The performance of the proposed decoder is evaluated by a Monte Carlo simulation. Numerical results show that a multistage decoder with only two stages greatly outperforms the single-stage decoder with negligible increase in complexity. The authors also derive the Chernoff bound for... 

In this paper, we study two important transmission strategies in full-duplex two-way relaying in the presence of channel estimation errors. In analog network coding (ANC), the relay transmits the combined signals that were received from both sources, with the aim of achieving better spectral efficiency. However, due to imperfect channel-state information (CSI), sources cannot perfectly cancel their own data in the relayed signal. We derive an achievable information rate for ANC in imperfect-CSI conditions and show how the ANC performance can significantly be degraded as a result. Moreover, we derive cut-set bounds with channel estimation errors for traditional routing (TR), in which time... 

We consider an internally coded time-hopping coherent ultrashort light pulse code division multiple access scheme (TH-CULP CDMA) and analyze its performance in the fiber-optic communication systems. This system combines the TH and CULP CDMA techniques and exploits the advantages of both. In our method, each bit time interval is divided into Ns frames, and the spectral phase-coded pulse is transmitted in one of these frames. Two exclusive PN sequences are assigned to each user. One is added to a superorthogonal convolutional encoder output to select the transmission frame, and the other is used to encode the phase of the ultrashort pulse in the spectral domain. We evaluate the bit error rate... 

The internally coded time-hopping coherent ultra-short light pulse code division multiple access (CULP CDMA) scheme (recently introduced) with an optical amplifier is described and its performance in fibre-optic communication systems is analysed. In accordance with the important role of optical amplifiers in optical communication systems, a preamplifier at the input of the receiver is used in order to compensate the losses because of the spectral encoder, spectral decoder and optical fibre path. The authors evaluate the bit error rate of the system considering the effects of the multiple access interference, noise because of the optical amplifier and thermal noise using saddle point... 

In this study, the authors optimise the outage probability of amplify and forward incremental relaying (IR) scheme using two different power allocation methods in the presence of channel estimation errors. The authors find the outage probability of IR scheme and minimise it subject to traditional power (TP) constraint in which the sum of nodes' powers is fixed and outage-dependent power (ODP) constraint which is compatible with the physical concept of IR and takes into account the quality of the direct path in the optimisation problem. The authors provide closed-form expressions to allocate power to pilot and data symbols of both the source and the relay. Although, their analysis uses high... 

This paper studies the statistical properties of the signal-to-noise ratio (SNR) of the dual-hop relaying link in a cooperative wireless communication system in the presence of channel estimation errors for fixed-gain (FG) and variable-gain (VG) relays. The SNR expression is derived and three different analytical approaches with different simplifying assumptions are proposed to obtain the probability distribution function of the SNR and the outage probability in each mode. All but one approach result in closed-form expressions for the outage probability. The simplest approach in each mode has been used to find an optimum power allocation scheme for pilot and data symbols transmission at the... 

In this study, the authors optimise the outage probability of amplify and forward incremental relaying (IR) scheme using two different power allocation methods in the presence of channel estimation errors. The authors find the outage probability of IR scheme and minimise it subject to traditional power (TP) constraint in which the sum of nodes' powers is fixed and outage-dependent power (ODP) constraint which is compatible with the physical concept of IR and takes into account the quality of the direct path in the optimisation problem. The authors provide closed-form expressions to allocate power to pilot and data symbols of both the source and the relay. Although, their analysis uses high... 

This paper studies the statistical properties of the signal-to-noise ratio (SNR) of the dual-hop relaying link in a cooperative wireless communication system in the presence of channel estimation errors for fixed-gain (FG) and variable-gain (VG) relays. The SNR expression is derived and three different analytical approaches with different simplifying assumptions are proposed to obtain the probability distribution function of the SNR and the outage probability in each mode. All but one approach result in closed-form expressions for the outage probability. The simplest approach in each mode has been used to find an optimum power allocation scheme for pilot and data symbols transmission at the... 

In this paper, we present a novel power allocation scheme for amplify and forward incremental relaying (IR) systems with the aim to minimize the overall outage probability at the destination. In our problem formulation, we take into account the outage-dependent activation of the relay when writing the power constraint. We provide a simple closed-form solution to the IR power allocation problem that is based on high signal-to-noise (SNR) approximation of the outage probability assuming maximum ratio combining (MRC) at the destination. We investigate the effectiveness of the proposed solution by comparing the achieved outage probabilities with those obtained through global numerical search. We... 

In this paper, we study two important transmission strategies in full-duplex two-way relaying in the presence of channel estimation errors. In analog network coding (ANC), the relay transmits the combined signals that were received from both sources, with the aim of achieving better spectral efficiency. However, due to imperfect channel-state information (CSI), sources cannot perfectly cancel their own data in the relayed signal. We derive an achievable information rate for ANC in imperfect-CSI conditions and show how the ANC performance can significantly be degraded as a result. Moreover, we derive cut-set bounds with channel estimation errors for traditional routing (TR), in which time... 

This paper studies the statistical properties of the signal-to-noise ratio (SNR) of the relay link in a cooperative wireless communication system with fixed gain relay in presence of channel estimation error. The SNR expression is derived and three different analytic approaches with different approximate assumptions are used to obtain the probability distribution function of the SNR and outage probability of the relay link. The first approach is the most accurate one in many cases, however it does not have a closed-form expression. The other two approaches result in closed-form expressions for the outage probability. Therefore, the third approach has been used to find a sub-optimum power... 

In the context of sustainable clean hydrogen production pathways, photovoltaic-electrolyzer systems are one of the most promising alternatives for acquiring hydrogen from renewable energy sources. In fact, determining the optimal set of design and operating variables are always a key issue while coupling directly renewable electricity sources to PEM electrolyzers. Few previous studies have attempted to find the optimal size and operational condition of directly coupled photovoltaic-electrolyzer (PV/El) systems in order to maximize the hydrogen production or to minimize energy transfer loss between photovoltaic devices and the electrolyzer. Nevertheless an easy and efficient approach still... 

Ground improvement techniques are inevitable for weak soils that cannot endure the design load imposed by superstructures. Deep mixing technique (DMT) as one of these methods is promising and effective when a deep soil layer with low bearing capacity is encountered. Such deposits are quite common in the South-west of Iran where the studied site is located. In order to validate the influence of DMT on the enhancement of strength, both in-situ and laboratory tests were conducted. Afterwards, a parametric study was carried out to investigate the influence of key factors including cement content, water–cement ratio, curing time and plasticity index (PI) on the performance of DMT. In summary, a... 

Ground improvement techniques are inevitable for weak soils that cannot endure the design load imposed by superstructures. Deep mixing technique (DMT) as one of these methods is promising and effective when a deep soil layer with low bearing capacity is encountered. Such deposits are quite common in the South-west of Iran where the studied site is located. In order to validate the influence of DMT on the enhancement of strength, both in-situ and laboratory tests were conducted. Afterwards, a parametric study was carried out to investigate the influence of key factors including cement content, water–cement ratio, curing time and plasticity index (PI) on the performance of DMT. In summary, a... 

This article proposes a scheme for balancing the voltage of series-connected insulated gate bipolar transistors (IGBTs), which is also very effective under short-circuit conditions. An optimized clamp-mode snubber is proposed, including an active-driver to balance the currents of the IGBTs during short-circuit, which in turn allows for a considerable reduction of the snubber capacitance. The approach is proven to be effective under short-circuit conditions by a maximum of 55 V voltage increment and a negligible difference in the current values. The effectiveness of the proposed approach is demonstrated through simulations in PSPICE software and experimental tests performed at 2 kV. ©... 

This research aimed at finding the factors with more impact on the bioleaching of a spent hydrocracking catalyst by thermophilic acidophilic archaea called Acidianus brierleyi and determining the optimal condition in order to reach the maximum metals recovery. Initially, four more significant factors affecting the bioleaching efficiency including pH, pulp density, inoculation and elemental sulfur concentration, were screened and identified among ten key factors using Plackett-Burman factorial design. Next, a central composite design was applied to obtain the optimum conditions for achieving the maximum efficiency of the bioleaching process. pH 1.6, pulp density 0.6% (w/v), inoculation 4%... 

Purpose - The purpose of this paper is to devise a new approach to synthesize closed-loop feedback guidance law for online thrust- insensitive optimal trajectory generation utilizing neural networks. Design/methodology/approach - The proposed methodology utilizes an open- loop variational formulation that initially determines optimal launch/ ascent trajectories for various scenarios of known uncertainties in the thrust profile of typical solid propellant engines. These open-loop optimized trajectories will then provide the knowledge base needed for the subsequent training of a neural network. The trained network could eventually produce thrust-insensitive closed-loop optimal guidance laws...