Atef M. Ghuniem

Planar Transmission Line Medium With Negative Refractive Index Based on Complementary Omega-Like Structure

A new planar left-handed transmission line medium based on complementary omega-like structure (COLS) is proposed. A microstrip implementation of the structure is demonstrated. By etching COLS in the ground plane just below the strip, a band over which the refractive index is negative has been found. Numerical simulation of the scattering (S) parameters for the proposed structure is presented. Simulated dispersion characteristic is also shown. The structure under study has been fabricated and very good agreement has been found between measured and simulated frequency responses.

Analysis of end coupling between microstrip line and cylindrical dielectric resonator using the FDTD method

In this paper, the analysis of end coupling between microstrip line and cylindrical dielectric resonator in a microwave integrated-circuit (MIC) environment is presented. The analysis is performed using the finite-difference time-domain (FDTD) method. The perfectly matched layer (PML) boundary condition has been used as a means to truncate FDTD lattice. Numerical results of the insertion loss characteristic are obtained. The effect of the distance between the end of the microstrip line and the dielectric resonator on the loaded quality factor, as well as the coupling coefficient between them is studied.

Pilot hopping in massive MIMO systems: Spectral efficiency analysis and achievable rates

In this paper, we analyze the performance of multi-cell least-square (LS) channel estimation using pilot sequence hopping and pilot reuse strategy for pilot decontamination. We obtain achievable rates in uplink synchronous system in L-cell system using LS channel estimation and zero forcing (ZF) detection. Polynomial expansion approximation is performed to obtain a closed form bound of the asymptotic sum-rate. We show that pilot hopping can achieve significant spectral efficiency gain compared to the conventional non-hopping schemes. Moreover, the number of antennas can be also greatly reduced when using the pilot hopping. However, the achieved gains depend on the pilot reuse factor β. It is shown that this gain is not monotonic function of β in some cases and therefore brings to attention that a careful cell planning is required when applying pilot hopping.

Sensing-Throughput tradeoff with primary user traffic and cooperative sensing in cognitive radio

In cognitive radio (CR), changing the primary users status diminishes the achievable throughput for secondary user. Traffic of primary user is inversely proportional to throughput of secondary user. Increasing sensing time increases the primary user protection, but has a negative effect on the throughput of secondary user. Solving the dilemma of sensing-throughput tradeoff is to find the optimal sensing time to achieve the maximum throughput. Cooperative spectrum sensing is used as a solution. Enhancement of the achievable throughput can be done by using cooperative spectrum sensing instead of local spectrum sensing. Moreover, optimal spectrum sensing time is increased.

Hybrid constant modulus array

The hybrid implementation of the multistage constant modulus CM array is designed for separating correlated signals. The canceller weights in the cascade structure provide estimates of the direction vectors of the captured signals. These estimates are then used in a parallel implementation of the linearly constraint CM (LCCM) array leading to the hybrid structure. In this paper, the hybrid implementation is extended to a three stage case for separating three correlated signals. The three correlated signals are of equal power and randomly generated. Mean Square Error (MSE) learning curves indicate that the proposed hybrid LCCM algorithm converges faster and has lower MSE than the conventional cascade implementation.

Spatial correlation function of the sky wave for use in space diversity reception

Fading is a serious problem in HF communication. It is caused primarily by the random irregularities in the refractive index of the ionosphere. One of the successful solutions to this problem is the space diversity reception. In this work the spatial correlation function of the received signal fluctuations is derived using geometric optics and single scattering approximations. Then the correlation function is used to calculate the required distance between the two receiving antennas to obtain uncorrelated signals. The results provide the base for the optimum design of the space diversity system.