Compensation of Physical Impairments in Multi-Carrier Communications

Among various multi-carrier transmission techniques, orthogonal frequency-division multiplexing (OFDM) is currently a popular choice in many wireless communication systems. This is mainly due to its numerous advantages, including resistance to multi-path distortions by using the cyclic prefix (CP) and a simple one-tap channel equalization, and efficient implementations based on the fast Fourier and inverse Fourier transforms. However, OFDM also has disadvantages which limit its use in some applications. First, the high out-of-band (OOB) emission in OFDM due to the inherent rectangular shaping filters poses a challenge for opportunistic and dynamic spectrum access where multiple users are sharing a limited transmission bandwidth. Second, a strict orthogonal synchronization between sub-carriers makes OFDM less attractive in low-power communication systems. Furthermore, the use of the CP in OFDM reduces the spectral efficiency and thus it may not be suitable for short-packet and low-latency transmission applications. Generalized frequency division multiplexing (GFDM) and circular filter-bank multi-carrier offset quadrature amplitude modulation (CFBMC-OQAM) have recently been considered as alternatives to OFDM for the air interface of wireless communication systems because they can overcome certain disadvantages in OFDM. Specifically, these two systems offer a flexibility in choosing the shaping filters so that the high OOB emission in OFDM can be avoided. Moreover, the strict orthogonality requirement in OFDM is relaxed in GFDM and CFBMC-OQAM which are, respectively, non-orthogonal and real-field orthogonal systems. Although a CP is also used in these two systems, the CP is added for a block of many symbols instead of only one symbol as in OFDM, which, therefore, improves the spectral efficiency. Given that the performance of a wireless communication system is affected by various physical impairments such as phase noise (PN), in-phase and quadrature (IQ) imbalance and imperfect channel estimation, this thesis proposes a number of novel signal processing algorithms to compensate for physical impairments in multi-carrier communication systems, including OFDM, GFDM and CFBMC-OQAM. The first part of the thesis examines the use of OFDM in full-duplex (FD) communication under the presence of PN, IQ imbalance and nonlinearities. FD communication is a promising technique since it can potentially double the spectral efficiency of the conventional half-duplex (HD) technique. However, the main challenge in implementing an FD wireless device is to cope with the self-interference (SI) imposed by the device's own transmission. The implementation of SI cancellation (SIC) faces many technical issues due to the physical impairments. In this part of research, an iterative algorithm is proposed in which the SI cancellation and detection of the desired signal benefit from each other. Specifically, in each iteration, the SI cancellation performs a widely linear estimation of the SI channel and compensates for the physical impairments to improve the detection performance of the desired signal. The detected desired signal is in turn removed from the received signal to improve SI channel estimation and SI cancellation in the next iteration. Results obtained show that the proposed algorithm significantly outperforms existing algorithms in SI cancellation and detection of the desired signal. In the next part of the thesis, the impact of PN and its compensation for CFBMC-OQAM systems are considered. The sources of performance degradation are first quantified. Then, a two-stage PN compensation algorithm is proposed. In the first stage, the channel frequency response and PN are estimated based on the transmission of a preamble, which is designed to minimize the channel mean squared error (MSE). In the second stage the PN compensation is performed using the estimate obtained from the first stage together with the transmitted pilot symbols. Simulation results obtained under practical scenarios show that the proposed algorithm effectively estimates the channel frequency response and compensates for the PN. The proposed algorithm is also shown to outperform an existing algorithm that implements iterative PN compensation when the PN impact is high. As a further development from the second part, the third part of the thesis considers the impacts of both PN and IQ imbalance and proposes a unified two-stage compensation algorithm for a general multi-carrier system, which can include OFDM, GFDM and CFBMC-OQAM. Specifically, in the first stage, the channel impulse response and IQ imbalance parameters are first estimated based on the transmission of a preamble. Given the estimates obtained from the first stage, in the second stage the IQ imbalance and PN are compensated in that order based on the pilot symbols for the rest of data transmission blocks. The preamble is designed such that the estimation of IQ imbalance does not depend on the channel and PN estimation errors. The proposed algorithm is then further extended to a multiple-input multiple-output (MIMO) system. For such a MIMO system, the preamble design is generalized so that the multiple IQ imbalances as well as channel impulse responses can be effectively estimated based on a single preamble block. Simulation results are presented and discussed in a variety of scenarios to show the effectiveness of the proposed algorithm

Analysis of reproductive traits and laying egg rhythm of maize weevil sitophilus zeamais (motschulsky)

The maize weevil, Sitophilus zeamais (Motschulsky), is a serious pest affecting a wide range of cereal crops, such as maize, rice, beans and other stored dried grains. As a S. zeamais female can keep laying eggs for a long time throughout its life after chewing its way into the grains, most development stages of the maize weevil, such as eggs, larvae and pupae, can always be found in stored maize grains. Our experiment with S.  zeamais on long grain rice showed that 10 days after eclosion and mating, maize weevil females started laying eggs for a period of 145 days. On average, a S.  zeamais female laid 38.67 eggs, of which, up to 62.81% were laid in the first 7–8 weeks (with the remaining 37.19% in the latter half of the 145 day period), and 55.07%  were laid within day 55–95. The egg laying pattern of S. zeamais was modeled using cubic polynomials, which described the maximum percentages of eggs laid at day 15, 35, 75, 95 and 105.  

Factors influencing the occurrence of labour accidents in Vietnamese residential construction projects

There was a sharp increase in the annual injury rate and the annual death rate per 100,000 employees in the Vietnam construction industry (VCI) from 2000 to 2006. This study aimed to identify and analyze factors affecting the occurrence of labour accidents (OLA) in residential construction projects. A survey questionnaire was used to collect data from construction practitioners. The results show that labour accidents in the VCI resulted from factors related to unqualified construction resources, unsafe human behaviour and poor management. The results can be used to gain insight into the OLA in order to deal with high labour accident rate and to develop safety programs in Vietnam as well as in other developing countries

Miliutine A acid, a new cyclofarnesane sesquiterpene from the stems of <i>Miliusa velutina</i>

Six compounds were isolated from the ethyl acetate extract of the stems of Miliusa velutina, including miliutine A acid (1), a new cyclofarnesane sesquiterpenoid; miliutine B methyl ester (2), a cyclofarnesane sesquiterpenoid which was determined the absolute configuration for the first time and four known phenol derivatives (3–6). NMR spectroscopic and mass spectrometry were used for identifying relative configurations. The assignments of the absolute configurations were determined based on Electronic Circular Dichroism (ECD) and NOESY spectra analysis. All six compounds were screened for their in vitro cytotoxic activities against HepG2 cell line using the SRB assay and they showed weak or none activities.</p

Synthesis and Photocatalytic Activity for Toluene Removal of CDs/TiO2 - Zeolite Y

Hydrothermally synthesized carbon nanodots (CDs) were impregnated on TiO2. The product (CDs/TiO2) was mechanically mixed with zeolite Y for application in toluene photocatalytic oxidation reaction under UV radiation. Material properties of the samples were investigated by different methods. Toluene vapor was chosen as a typical volatile organic compound to investigate the performance of CDs/TiO2 – zeolite Y photocatalyst when these technological parameters were changed: toluene concentration, gas flow rate, humidity and UV light intensity. In each reaction, only one parameter was changed and the remaining conditions were fixed. The toluene concentrations at the beginning and the end of each reaction were analyzed with the use of gas chromatography (GC). The results of different reaction conditions show the trends for toluene treatment of the CDs/TiO2 – zeolite Y catalyst, thereby providing specific explanations for these trends. The experiments also show that toluene removal is highest when the toluene concentration in the inlet gas is 314 ppmv, the flow rate is 3 L/h, the humidity is 60%, and the catalyst (CDs/TiO2 – zeolite Y composite with 70% zeolite in weight) is illuminated by 4 UV lamps. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Preparation, Characterization, and Antibacterial Activity of Silver Nanoparticle-Decorated Ordered Mesoporous Carbon

In this study, Ordered Mesoporous Carbon (OMC) was prepared using resol as a carbon precursor and F127 as a soft template. Small-angle X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) images, and nitrogen adsorption and desorption isotherms revealed that OMC possessed ordered hexagonal mesostructures (p6m) with an ordered pore size of 3.2nm, a high specific surface area (SBET) of 539m2/g, and a large total pore volume (Vtotal) of 0.44cm3/g. Subsequently, silver nanoparticles synthesized from an aqueous AgNO3 solution using glucose as a reducing agent and starch as a stabilizing agent were decorated on OMC, producing Ag/OMC. XRD analysis revealed that the composite contained silver crystals. In addition, the content and size of silver nanoparticles in Ag/OMC were 0.71wt% (AAS) and around 25-50nm (TEM), respectively. Due to the surface cover of silver nanoparticles, SBET and Vtotal of Ag/OMC slightly decreased to 417m2/g and 0.38cm3/g, respectively. Both agar and broth dilution techniques were used to evaluate the antibacterial activity of the material against Staphylococcus aureus. Ag/OMC with a Minimum Inhibitory Concentration (MIC) of 25.0μg/mL is a potential candidate for use against Staphylococcus aureus

Enhancement of photocatalytic activity of TIO2 for gaseous toluene removal by simple mechanical mixing with modified zeolite

A zeolite Y was modified by the microwave-assisted method (MWA) for generating mesopores and was mechanically mixed with TiO2 for photocatalytic application. The external surface area, which is represented to the mesopore, was significantly increased about 5 to 10 times in the modified zeolites compared to the parent zeolite. The catalysts were used to catalyze the gas phase photodegradation of toluene, a volatile organic compound (VOC). The photocatalytic activity and stability of the catalyst were improved when the mesoporous zeolite was presented. The mechanical mixture contained 30 wt%. TiO2 and 70 wt%. mesoporous zeolite showed the highest toluene removal efficiency