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The multiuser performance of two kinds of ultra-wideband (UWB) systems, namely, multi-carrier frequency-hopping-UWB and time-hopping-UWB, is evaluated. We derive the bit error rate of these systems in both AWGN and fading channels. Our numerical results show that the TH-UWB system always outperforms the MC-FH-UWB system with non-coherent detection. However, the MC-FH-UWB system with coherent detection presents a better performance than TH-UWB in a very few cases. Then, we use a practical low-rate convolutional error correcting code, which does not require any extra bandwidth further than that needed by the uncoded scheme, to improve the system performance. The results show that the coded... 

In this paper, we evaluate and compare the multiuser performance of the Fast Frequency-Hopping (FFH) and the MultiCarrier slow Frequency-Hopping (MC-FH) systems employing non-coherent detection for both uncoded and coded schemes in AWGN and slowly frequency-selective Rayleigh fading channels, based on Gaussian distribution assumption for the decision variable. Our numerical resulte indicate that with non-coherent detection, both systems show the same performance. However, the MC-FH system can be easily implemented using FFT algorithm. Furthermore with a slow hopping rate and high number of carriers, a coherent detection for the MC-FH system is feasible. Our results will indicate that the... 

In this paper, we present the bit error probability (BEP) of a relay network employing UWB links between its nodes. Since UWB systems can resolve many paths and are thus rich in multipath diversity, the use of the Rake diversity combining is very effective. However, because of the complexity, it is impractical in the scenarios with portable terminals or in the networks with multiple relays. Time-reversal technique, in which the transmitting nodes can do the pre-diversity filtering of UWB signal before transmission, is known as an approach to achieve the performance equivalent to the Rake combining without increasing the receiver complexity. The performance of such a network with simple... 

In this paper, the extension of cooperative communication to the context of TH-UWB is investigated. In particular, the average bit error probability (BEP) is provided for cooperative TH-UWB systems with decode-and-forward relaying protocol. In the considered relay network, UWB links among the nodes are modeled according to IEEE 802.15.4a standards. Our methodology is based on computing the Characteristic Function (CF) of the decision variable at the destination terminal. We use Gaussian quadrature numerical method to approximate the CF of interference component appeared in decision variable term. This technique permits to predict the system performance in different IEEE 802.15.4a defined... 

In this paper, we present the average bit error probability (BEP) of a decode-and-forward relay network employing UWB links, developed by IEEE 802.15.4a standards, between its nodes. Our methodology is based on computing the Characteristic Function (CF) of the decision variable at the destination terminal. Numerical results show that significant improvement in the BEP of impulse radio UWB system is obtained by adding a relay node. The analytical expressions are also validated by computer simulations which confirm the accuracy of the approximations used in obtaining the BEP  

A complete continuous adjoint formulation is presented here for the optimization of the turbulent flow entropy generation rate through a turbine cascade. The adjoint method allows one to have many design variables, but still afford to compute the objective function gradient. The new adjoint system can be applied to different structured and unstructured grids as well as mixed subsonic and supersonic flows. For turbulent flow simulation, the k-ω shear-stress transport turbulence model and Roe's flux function are used. To ensure all possible shape models, a mesh-point method is used for design parameters, and an implicit smoothing function is implemented to avoid the generation of non-smoothed... 

A cooperative space-frequency (SF) coded orthogonal frequency division multiplexing system is considered and its performance over quasi-static frequency-selective Rayleigh fading channels is evaluated. An expression for exact outage error probability is derived and its tight closed-form lower bound is presented. The tightness of the lower bound is demonstrated through Monte Carlo simulation. Asymptotic analysis indicates that the proposed protocol achieves full spatial and frequency diversities available in the cooperative communication system. The theoretical analysis of the proposed SF coded cooperation protocol is further confirmed by computer simulation using a previously introduced SF... 

We derive, evaluate, and discuss upper bounds on ergodic and outage capacities for a three-node relay network. The considered relay network has ultra-wideband (UWB) radio channels between the source, destination, and relay nodes. The derived bounds indicate that ergodic and outage capacities of the considered UWB-linked network increase up to 300% when a relay between the source and the destination is used. Furthermore, the bounds indicate that there is an optimum position for the relay node between the source and the destination, where ergodic capacity is maximized. Our numerical results shows that for the non-line-of-sight (NLOS) scenario, with the same signal to noise ratio on all links,... 

A gradient based optimization using the continuous adjoint method for inverse design of a turbine blade cascade is presented. The advantage of the adjoint method is that the objective function gradients can be evaluated by solving the adjoint equations with coefficients depending on the flow variables. This method is particularly suitable for aerodynamic design optimization for which the number of design variables is large. Bezier polynomials are used to parameterize suction side of the turbine blade. The numerical convective fluxes of both flow and adjoint equations are computed by using a Roe-type approximate Riemann solver. An approximate linearization is applied to simplify the... 

In this paper, the effect of turbine stage efficiency on fuel consumption of both gas turbines and aerial engines is assessed quantitatively. At the beginning of the gas generator optimization to decrease the fuel consumption, it is necessary to analyze the sensitivity of fuel consumption to its main components efficiencies. This will guide us which component is more important to be optimized. Here a zero-dimensional analysis has been done to determine the effect of turbine stage efficiency on the fuel consumption. Results of this analysis are evaluated in the context of thermodynamic cycle of a gas turbine generator and an aerial engine. As an example, it is shown that if the efficiency of... 

Traditionally, the frequency spectrum is licensed to users by government agencies in a fixed manner where the licensee has exclusive right to access the allocated band. However, with increasing demand for the spectrum and scarcity of vacant bands, a spectrum policy reform seems inevitable. Meanwhile, recent measurements suggest the possibility of sharing spectrum among different parties subject to interference-protection constraints. In order to enable access to an unused licensed spectrum, a secondary user has to monitor licensed bands and opportunistically transmit whenever no primary signal is detected. Spectrum-sharing between a primary licensee and a group of secondary users has been... 

Most researches on the application of the adjoint method in turbine blade design are concentrated on the aerodynamic shape optimization without considering the heat transfer to/from the blade material. In this study, the adjoint method is extended to the conjugate heat transfer problems in which the viscous flow field is coupled to heat transfer in the solid region. Introducing a new adjoint variable in the solid domain, a heat adjoint equation is derived which is coupled with the energy adjoint equation in the fluid zone at the fluid/solid interface. The detailed mathematical description associated with the derivation of the heat adjoint equation with corresponding boundary conditions are... 

We derive bounds on the expected capacity and outage capacity of a three-node relay network for UWB communications. We also provide a simple tight approximation for the derived upper bound on the capacity and then using this bound we obtain the outage probability of the network. Numerical results show that a significant improvement in the system capacity and outage probability is obtained by adding a relay node. Moreover, our theoretical results reveal that the diversity gain of a relay channel substantially increases by using UWB links instead of NB links. We also derive these bounds when we have a constraint on the total transmitted power of the source and the relay nodes. © 2009 IEEE  

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function...