Bader Alhasson

PAPR Distribution Analysis of OFDM signals with Partial Transmit Sequence

Third Generation Partnership Project (3GPP) LTE has adopted OFDMA as the uplink multiple access scheme. One of the major drawbacks is the high PAPR. Not only is the performance of PAPR with PTS technique influenced by the number of subblocks and the phase vector but also by the subblock partitioning. The Partial Transmit Sequence (PTS) technique suffers from the search complexity of finding the optimum set of phase vectors. We propose a suboptimal combination algorithm that reduces the search complexity. The number of commutations in the suboptimal combination algorithm is much lower than the required by the original PTS technique. In this paper, we propose a suboptimal combination algorithm to reduce the searching complexity of finding the optimum set of vectors to minimize PAPR. The performance of PAPR utilizing the PTS technique improves by the use of the proposed suboptimal combination algorithm.

The challenge of scheduling user transmissions on the downlink of a long-term evolution (LTE) cellular communication system

Wideband code division multiple access (WCDMA) is currently being extended into high-speed downlink access (HSDPA) and high-speed uplink packet access (HSUPA). The continuing research of next generation communication proposed by 3GPP is named long term evolution (LTE). The main goal of LTE Release is to offer high peak downlink and uplink rates by the use of Orthogonal Frequency-Division Multiple Access (OFDMA) that attributes a very flexible multi-user bandwidth, high spectral efficiency and scalable bandwidth. The benefit of LTE is the fact that it offers higher data rates in both uplink and downlink and enhances the services for the terminals. A notable fact is that several WiMAX projects have been reoriented toward Long Term Evolution (LTE), mainly aimed at increasing performance. In this paper the challenge of scheduling user transmissions on the downlink of LTE cellular communication system is discussed. Various results show that the system performance improves with increasing correlation among OFDMA subcarriers.

Simulation of OFDM Technique for wireless communication systems

Orthogonal Frequency Division Multiplex (OFDM) is a modulation technique to transmit the baseband Radio signals over Fiber (RoF). Combining OFDM modulation technique and radio over fiber technology will improve future wireless communication. This technique can be implemented using laser and photodetector as optical modulator and demodulator. OFDM uses multiple sub-carriers to transmit low data rate streams in parallel, by using Quadrature Amplitude Modulation (QAM) or Phase Shift Keying (PSK). In this paper we will compare power spectrum signal and signal constellation of transmitted and received signals in RoF using Matlab and OptiSystem simulation software.

LTE-advanced MIMO uplink for mobile system

By increasing multimedia communications, mobile communications are expected to reliably support high data rate transmissions. To provide higher peak rate at a better system efficiency, which is necessary to support broadband data services over Wireless links, we need to employ long term evolution Advanced (LTE-A) Multiple-input multiple-output MIMO uplink. The outline of this paper is to investigate and discuss the Long Term Evolution (LTE) for broadband wireless technologies and to discuss its functionality. We explore how LTE uses the inter-technology mobility to support a variety of access technology. This paper investigates the channel capacity and bit error rate of MIMO-OFDM system. In addition, it introduces various MIMO technologies employed in LTE and provide a brief overview on the MIMO technologies currently discussed in the LTE-Advanced forum.

Dispersion and nonlinear effects in OFDM-RoF system

The radio-over-fiber (RoF) network has been a proven technology to be the best candidate for the wireless-access technology, and the orthogonal frequency division multiplexing (OFDM) technique has been established as the core technology in the physical layer of next generation wireless communication system, as a result OFDM-RoF has drawn attentions worldwide and raised many new research topics recently. At the present time, the trend of information industry is towards mobile, wireless, digital and broadband. The next generation network (NGN) has motivated researchers to study higher-speed wider-band multimedia communication to transmit (voice, data, and all sorts of media such as video) at a higher speed. The NGN would offer services that would necessitate broadband networks with bandwidth higher than 2Mbit/s per radio channel. Many new services emerged, such as Internet Protocol TV (IPTV), High Definition TV (HDTV), mobile multimedia and video stream media. Both speed and capacity have been the key objectives in transmission. In the meantime, the demand for transmission bandwidth increased at a very quick pace. The coming of 4G and 5G era will provide faster data transmission and higher bit rate and bandwidth. Taking advantages of both optical communication and wireless communication, OFDM Radio over Fiber (OFDM-RoF) system is characterized by its high speed, large capacity and high spectral efficiency. However, up to the present there are some problems to be solved, such as dispersion and nonlinearity effects. In this paper we will study the dispersion and nonlinearity effects and their elimination in OFDM-radio-over-fiber system.

Modeling and Simulation of Plasmonic Surfaces

Plasmons are simply density waves of electrons, shaped when light hits the surface of a metal under particular conditions. These waves are produced at optical frequencies, very small and rapid waves; as a result they can in theory encode plenty of information. Surface Plasmon resonance (SPR) has become a significant optical tool for identifying a selection of specific binding interactions such as DNA. In this paper we will show the results of simulation for the angular excitation spectra of surface Plasmon for various metal and oxide thicknesses. In addition, we will illustrate multiple angles surface Plasmon resonance data for different wavelengths.

Effects of structural parameters in metallic nano slit arrays

Nano slit arrays perforated on thin metallic film are the basic structure of metallic nano-optic lenses, which resemble the shape of the conventional glass lens, and can be applied to beam manipulation, such as beam reflecting/deflecting or focusing. It has been proven that optical transmission is feasible through metallic nano slit arrays, making new nano technology applications possible. In conventional dielectric lenses, the edge effect-the very strong diffraction of the transmitted beam that take place at the lens edges restricts the possibility of sizing down the conventional optics components to a sub-wavelength range. This is due to the fact that the size of the lens is an important determinant of focusing beam to the nano scale. In this paper we present the metallic nano lenses and study their optical transmission properties. These lenses do not suffer from the edge effect mentioned above. The phase of each nanoslit element can be managed by changing the material of the metal film and/or the structural parameters of the lens. In our simulation work, we examine the transmission performance of metallic nano slit arrays by the method of finite-difference time-domain (FDTD). We use various metals such as copper, silver, aluminum and titanium as the material of the thin films. We also investigate various structural parameters such as slit number, width and thickness, to show their influence on the optical transmission performance. By adjusting the material and/or structural parameters of the Nano slit arrays, the desired transmission performance can be realized.

Plasmonic excitation for high-efficiency photovoltaics

Photovoltaic absorbers ought to be optically thick to allow almost total light absorption and photocarrier current collection. They are typically semiconductors with a thickness more than the optical absorption length. When the absorber layer thickness is reduced significantly, then the quality of the absorber material could considerably increase by allowing resourceful photocarrier collection across tiny distances in structures such as quantum wells or quantum dots. For absorber layers with fine surface passivation, the capability to reduce the solar cell base thickness by means of plasmonic design improves carrier collection. The objective of this paper is to show how plasmonics could be exploited to our benefit in high efficiency photovoltaics.

Nanoscale materials for sensing and detection based on surface plasmon excitation

In this paper we present the effect of gold, silver and oxide thicknesses on the sensitivity of Surface Plasmon Resonance (SPR). SPR sensor with enhanced sensitivities can be realized based on gold/silver films. Surface Plasmons (SP) are electromagnetic waves that transmit along the interference between a metal and a dielectric film, and the electromagnetic wave of the surface plasmons is coupled to oscillations of free electrons in the metal. SPR has attracted interest in many applications such as solar cells, chemical and biological sensing. The potential sensor application by using gold/silver nanocrystal enhanced SPR phenomenon. Sensitivity is a significant parameter to assess the sensors performance. Essentially, sensitivity is determined by the force of light and matter interaction.

Characterizations of multi-segment DFB laser

Tunable semiconductor laser has various applications including Wavelength Division Multiplexing (WDM), Frequency Division Multiplexing (FDM), optical switching in Local Area Networks (LAN) and Chemical Sensing, or Spectroscopy. There are different approaches for tunable semiconductor lasers. Large wavelength tuning range is required for communication applications, such as WDM. Whereas a frequency modulation (FM) requires small but fast frequency shifts. Two-Segment laser is one of the methods to realize continuous optical tuning. The device consists of two coupled cavities having a series of well-defined modes. The modes are equally spaced within a cavity but the mode spacing between the two cavities is slightly different. Characterization results of such lasers are very important. In this paper we will present the characterization results of two segment InGaAs/InP distributed feed back (DFB) tunable lasers.