H. A. Konber

An accurate model of worst case signal to interference ratio for frequency reuse cellular systems

In cellular networks, fractional frequency reuse (FFR) is an efficient inter-cell interference (ICI) mitigation scheme. Although many related research papers are published in this area. Formulas to handle this scheme in more accurate manner are still required. In this paper, closed-form formulas for worst case signal to interference ratio (SIR) in frequency reuse three, four, soft frequency reuse (SFR), and sectored FFR are derived. Also, an accurate closed-form formulas for inner radius for all these cases are driven based on worst SIR case taking into account the interference effect only and the impact of interference combined with path loss effect. Analytical models are validated using Long Term Evolution (LTE) simulator. Simulation results show that the proposed analytical models are in good agreement with those obtained through simulations and they are more accurate than previously published analytical treatments as they consider the practical scenarios.

Pileup recovery algorithms for digital gamma ray spectroscopy

This paper presents algorithms for overcoming a common problem of gamma ray spectroscopy, namely the peak pileup recovery problem. Three different approaches are studied and evaluated within a spectroscopy system. The algorithms are evaluated by the means of parameters error and fitting error calculations. The first approach is a direct search based on Nelder-Mead technique without any derivatives in order to find the local minimum points. A Gaussian shape in conjunction with the peak height and its position of each pulse are used to construct the pulse. So, the main pulse parameters such as peak amplitude, position and width can be determined. The second algorithm is based on the nonlinear least square method. In this paper another technique is tried. This technique which is proposed as third algorithm is based on a maximum peak search method combined with the first derivative method to determine peak position of each pulse. Comparison among these approaches is conducted in terms of parameters errors. The pulse parameters have been calculated and compared with the actual one. The second approach shows the best accuracy, for determining peak height and position, but the width parameter scored the highest error.

Analysis of Downlink sectored Frequency Reuse cellular systems combined with different beamforming techniques

Although Fractional Frequency Reuse (FFR) is a good solution for Inter-Cell Interference (ICI) problem, combined FFR and beamforming can be utilized for more improved cellular system performance. In this paper, we consider a hexagonal cellular network, where we derive the Downlink (DL) worst case Signal to Interference Ratio (SIR) closed form formula for three different beamforming techniques (horizontal, vertical, and 3D) combined with sectored FFR. Furthermore, the derived SIRs formulas are used to get Spectral Efficiency (SE) as well as channel capacity in terms of several parameters. Also, we derive an accurate closed form formula for inner radius based on the proposed analytical model including a correction factor. Simulation results show that the proposed analytical method is in good agreement with those obtained through simulations and more accurate than previously published analytical treatments. The same treatment can be applied for other FFR techniques.

Comparison studies of infrared photodetectors with a quantum-dot and a quantum-wire base

This paper mainly presents a theoretical analysis for the characteristics of quantum dot infrared photodetectors (QDIPs) and quantum wire infrared photodetectors (QRIPs). The paper introduces a unique mathematical model of solving Poisson’s equations with the usage of Lambert W functions for infrared detectors’ structures based on quantum effects. Even though QRIPs and QDIPs have been the subject of extensive researches and development during the past decade, it is still essential to implement theoretical models allowing to estimate the ultimate performance of those detectors such as photocurrent and its figure-of-merit detectivity vs. various parameter conditions such as applied voltage, number of quantum wire layers, quantum dot layers, lateral characteristic size, doping density, operation temperature, and structural parameters of the quantum dots (QDs), and quantum wires (QRs). A comparison is made between the computed results of the implemented models and fine agreements are observed. It is concluded from the obtained results that the total detectivity of QDIPs can be significantly lower than that in the QRIPs and main features of the QRIPs such as large gap between the induced photocurrent and dark current of QRIP which allows for overcoming the problems in the QDIPs. This confirms what is evaluated before in the literature. It is evident that by increasing the QD/QR absorption volume in QDIPs/QRIPs as well as by separating the dark current and photocurrents, the specific detectivity can be improved and consequently the devices can operate at higher temperatures. It is an interesting result and it may be benefit to the development of QDIP and QRIP for infrared sensing applications.