نشریه مهندسی مخابرات جنوب
پیاپی 48 (تابستان 1402)

The paper proposes a novel iterative channel estimation technique for multipath fading channels in Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing(MIMO-OFDM)systems with Gaussian noise and impulse noise. MIMO-OFDM systems can be beneficial if the estimated channel quality is assured at the receiver. The paper also proposes an auxiliary pilot for channel re-estimation based on some reliably retrieved data symbols. In subsequent iterations, adding new auxiliary pilots improves channel estimation accuracy. The correlation between the data channel coefficients and the original pilots is used to select reliable data. Since iterative channel estimation is time-consuming, using a channel estimator with a low processing time and computational complexity is imperative. An easy-to-implement baseline least squares(LS)method is used in the proposed estimator. According to the simulation results, the proposed iterative channel estimation technique improves MIMO-OFDM performance by increasing the number of pilots in subsequent iterations compared to the conventional channel estimation techniques.

This paper comprehensively investigates how the control voltage settles in Voltage Controlled Oscillators (VCO) by considering all non-ideal factors in phase lock loop circuits. Also, the different structures of the phase detector and their effect on the locking speed of the phase-locking loop circuit, the control voltage ripple and the locking frequency range will be compared. Three phase locked loop circuits with XOR detector, RS-FF detector and dynamic phase detector were investigated in this paper. The simulations were performed on 0.18 µm-CMOS technology with a 1.8V power supply. The simulation results show that the operating range of the phase-locked loop circuit including dynamic phase detector with charge pump circuit has less ripple for the non-ideal effects compared to the phase-locked loop circuit including XOR phase detector and the phase-locked loop circuit including RS-FF phase detector. of the phase-locked loop circuit including dynamic phase detector is designed using 180nm CMOS technology and the simulation results show that for a supply voltage of 1.8V, frequency range is 0.284-3.33GHz, power consumption is 2.86mW and phase noise is -118.8dBc/Hz.

Homing missiles are classified as Surface-to-air missiles. These missiles are used for air targets like airplane or helicopter combat. To counteract these missiles, fighter aircrafts use pseudo targets to deviate the course of the missiles. These pseudo targets in the form of Flyer Decoys, Jamming or Clutter are effective means to disable such missiles. In early versions of guidance systems, missiles turn-off their guidance systems temporarily. This can help in limited situations. However, in this paper an advanced guidance system based on Extended Kalman Filters is proposed. It is shown that using the estimated values of the variables from Kalman Filter, can modify the course of missile fight leading to the target. Due to the bearing-only nature of the system, it shown that initial conditions are very important in the estimation process. To reduce the effect of initial conditions, a set of Extended Kalman Filter is introduced. Simulation results are provided to show the effectiveness of the proposed methodology.

In this paper, an attempt is made to design an antenna to be used in different radar and telecommunication applications. Paying attention to antenna radiation is on the agenda And studies have been done on antenna radiation as well as their radiation pattern.Considering that the feature of the pattern with the vane feature is used in antennas with radar applications, it is also used in various telecommunication applications. In this article, an attempt has been made to increase the antenna's fan beam properties The designed antenna has two radiation elements And in the 3.5 GHz frequency band, it consists of a two-layer structure. The radiation elements are placed in the upper layer and the feeding network is located in the lower layer. The built dual antenna has an impedance bandwidth of 3.8-3.4 GHz.The maximum gain Hz is 6/76 dBi and the half power beam width is 44˚ and 104˚ in H- and E- planes.respectively which shows that this is fan beam antenna. The overall dimensions of the antenna are 105 × 32/3 ×3/708 mm square. The provided antenna is recommended for use in radar systems and 5G systems in the 3/5 GHz frequency band. According to the laboratory test of this antenna, it can be said that the theoretical and practicical results are in good agreement...

The capability of a neuro-fuzzy control approach for frequency fluctuation damping in an isolated hybrid microgrid (IHMG) system (DEG/WTG /PV/FC/ESSs) is investigated in this paper. Due to the intermittent behavior of renewable energy sources (RESs) like wind turbines and photovoltaic arrays and the time-varying nature of demands, frequency fluctuation is more likely, specifically in the grid-connected mode. Model parametric uncertainties as well as load changes, wind power, and solar irradiation variations are the main uncertainty sources of the IHMG system. In the suggested approach, a neuro-fuzzy output feedback controller with three inputs that are inspired by PID control is designed considering the power balance between demands and generations, by optimizing fuzzy membership functions’ locations. The proposed controller is compared with two popular other methods on the investigated IHMG system in terms of time-domain characteristics. The outcome illustrates remarkable merit compared to the state-of-the-art methods in the presence of simultaneous disturbances and the model parametric uncertainties.

Today, one of the most important issues in mobile communication systems is having a long battery life. Therefore, the problem of power consumption appears as one of the challenges in the field of designing high frequency circuits. In a high-frequency receiver, due to the placement of the low-noise amplifier in the first stage of the receiver, this amplifier is very important to determine the linearity and noise in the entire receiver. In this paper, a low noise amplifier has been designed for the GPS standard. Compared to previous works, the noise of the amplifier has been reduced somehow, and its power consumption has reached its minimum value. The working method is that in common source amplifiers, their source base is connected with an inductor, which results in improving circuit noise. But the used inductor occupies the surface of the chip. Therefore, in this article, the existence of the inductor in wire-bond is used, and the noise of the amplifier is reduced, and the occupied area of the chip is not increased. Gain, NF, input impedance of the proposed amplifier have been calculated in the best case and the worst case in the corners of FF and SS, and it can be seen that in this article, compared to the previous works, very favorable results have been obtained.