Iranian Journal of Electrical and Electronic Engineering
Volume:9 Issue: 1, Mar 2013

In the down link scenario of code division multiple access (CDMA) systems, multi user detectors (MUDs) such as linear de-correlating detector (LDDs) provide satisfactory symbol error rates (SERs) at the expense of much increased complexity, they require all active users’ spreading sequences, which is impractical from privacy point of view. To overcome this impracticality, a simple matched filter receiver is considered in this paper, which requires no knowledge of co-users’ spreading sequences. However, this simple receiver degrades the SER due to multiple access interference (MAI). To overcome this SER degradation, a zero force (ZF) pre-coder is employed in the transmitter traditionally. Moreover, a composite of CDMA signals has a large peak to average power ratio (PAPR), which causes nonlinear distortion (NLD) at the output of the base station high power amplifier (HPA). This also results in degrading the SER. We analyze the down link scenario of CDMA system to derive an equation for the SER of system with ZF-pre-coder plus HPA in the transmitter and matched filter in the receiver over two cases: additive white Gaussian noise (AWGN) and AWGN plus flat fading channels. Theoretical analysis and numerical results show that the ZF pre-coder increases the total degradation of the link significantly compared with that of the LDD. So, as a solution, rather than using ZF pre-coder, we propose a new method which is called extended joint channel estimation method, it is based on joint estimation of channel gains and LDD operator by the mobile station (MS). In that base station (BS) transmits the row k of LDD operator to the MS k. Simulation results show that the SER of this new proposed method is matched to that of LDD in AWGN channel when the number of pilot symbol repetition is equal to 8. Moreover, this method has the two added advantages of no need for providing the spreading sequences of all co-users and meeting a satisfactory total degradation. Furthermore, our analysis shows that loss in spectral efficiency due to transmitting the pilot symbols in the proposed method is negligible for the practical values of traffic variations.

The effects of aberration on the Bit-Error-Rate (BER) and reliability of free- space optical (FSO) communication links are investigated. Based on aberrated divergent rectangular partially coherent flat-topped beam formula on the receiver plane and considering the atmosphere losses due to absorption and scattering, numerical values for Power In Bucket (PIB), Signal to Noise Ratio (SNR) and BER are calculated. Using above mentioned values, the effects of source parameters on link reliability is described. The results are illustrated by graphs obtained by calculation and simulation.

This paper presents a general formulation to investigate the scattering from Multilayer Lossy Inhomogeneous Metamaterial Planar Structure (MLIMPS) with arbitrary number of layers and polarization. First, the dominating differential equation of transverse components of electromagnetic fields in each layers derived. Considering the general form of solution of the differential equations and the boundary conditions of the problem; a set of linear equations is obtained. By solving these equations, the electromagnetic fields in all layers and reflection and transmission coefficients are calculated. This method is applied in an interesting example for two bi-layered structures with inhomogeneous conventional material and metamaterial profile for constitutive parameters. Results which are presented in example are useful for constructing general duality between conventional material and metamaterials.

This paper presents a new variable step-size normalized subband adaptive filter (VSS-NSAF) algorithm. The proposed algorithm uses the prior knowledge of the system impulse response statistics and the optimal step-size vector is obtained by minimizing the mean-square deviation(MSD). In comparison with NSAF, the VSS-NSAF algorithm has faster convergence speed and lower MSD. To reduce the computational complexity of VSSNSAF, the VSS selective partial update NSAF (VSS-SPU-NSAF) is proposed where the filter coefficients are partially updated in each subband at every iteration. We demonstrated the good performance of the proposed algorithms in convergence speed and steady-state MSD for a system identification set-up.

Strategic bidding in joint energy and spinning reserve markets is a challenging task from the viewpoint of generation companies (GenCos). In this paper, the interaction between energy and spinning reserve markets is modeled considering a joint probability density function for the prices of these markets. Considering pay-as-bid pricing mechanism, the bidding problem is formulated and solved as a classic optimization problem. The results show that the contribution of a GenCo in each market strongly depends on its production cost and its level of risk-aversion. Furthermore, if reserve bid acceptance is considered subjected to winning in the energy market, it can affect the strategic bidding behavior.

Insulator strings with several material and profiles are very common in overhead transmission lines. However, the electric field and voltage distribution of insulator string is uneven which may easily lead to corona, insulators’ surface deterioration and even flashover. So the calculation of the electric field and voltage distribution along them is a very important factor in the operation time. Besides, no remarkable endeavor regarding insulator material and profile and their impacts upon the electric field and voltage distribution has been made so far. In this paper several 230-kV insulator strings with different porcelain and glass units were simulated using 3-D FEM based software, and their electric fields and voltage distributions were calculated and compared together, to investigate the effect of insulator types on these quantities. Tower and conductors were included in all simulations and also the effect of corona ring on voltage and electric field distribution over insulator strings with different insulator types was investigated. Reported results show the dependency of voltage distribution to insulator material and profile.

This paper presents modeling and control of a hybrid distributed energy sources including photovoltaic (PV), fuel cell (FC) and battery energy storage (BES) in a microgrid which provides both real and reactive power to support an unbalanced utility grid. The overall configuration of the microgrid including dynamic models for the PV, FC, BES and its power electronic interfacing are briefly described. Then controller design methodologies for the power conditioning units to control the power flow from the hybrid power plant to the unbalanced utility grid are presented. In order to distribute the power between power sources, the neuro-fuzzy power controller has been developed. Simulation results are presented to demonstrate the effectiveness and capability of proposed control strategy.