Channel Modelling and Estimation in Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing Wireless Communication Systems

In wireless communications, the demands for high data rates, enhanced mobility, improved coverage, and link reliability have enormously increased in recent years and are expected to further increase in the near future. To meet these requirements, new concepts and technologies are needed. Theoretical studies have shown that using multiple antennas at the transmitter and receiver, known as multiple-input multipleoutput (MIMO) technology, can dramatically increase the capacity, coverage, and link reliability of a communication system. Orthogonal frequency-division multiplexing (OFDM) is an attractive technique for high data rates transmission over frequency-selective fading channels, due to its capability in combating the intersymbol interference (ISI). The combination of MIMO and OFDM results in a powerful technique that incorporates the advantages of both MIMO and OFDM, and is a strong candidate for fourth generation (4G) wireless communication systems. In this thesis, two issues related to realizing practical mobile MIMO OFDM communication systems are addressed. The first issue is about MIMO channel modeling and effect of realistic channels on the theoretical capacity. For this target, a geometrically-based three-dimensional (3-D) scattering MIMO channel model is developed. The correlation expressions are derived and analytically evaluated. The impact of spatial correlation on MIMO channel capacity is investigated under different antenna array configurations, angular energy distributions, and parameters. Analytical and numerical results have shown that the elevation angle has considerable effect on the spatial correlation and consequently on the MIMO channel capacity for the case when the antenna array of the mobile station (MS) is vertically oriented. This has led to a conclusion that 3-D scattering MIMO channel modeling is necessary for accurate prediction of MIMO system performance. The second issue addressed in this thesis is the channel estimation in MIMO OFDM systems. New time-domain (TD) adaptive estimation methods based on recursive least squares (RLS) and normalized least-mean squares (NLMS) algorithms are proposed. These estimators are then extended to blindly track the time-variations of the channel in the decision-directed (DD) mode. Simulation results have shown that TD adaptive channel estimation and tracking in MIMO OFDM systems is very effective in slow to moderate time-varying fading channels. It was observed that the performance of the DD RLS-based estimator always outperform that of the DD NLMS estimator at low mobility and low SNR. In contrast, it was found that the DD NLMS estimator gives better tracking performance at moderate mobility and higher SNR. However, as the training rate is reduced, comparable performance with both estimators is obtained at high SNR. Finally, it has been shown that channel estimation in TD is more accurate with less complexity compared to its counterpart in frequency-domain (FD)

MIMO OFDM channel estimation based on RLS algorithm: the time- versus frequency-domain implementations

In this paper, exponentially-weighted recursive least squared (EW-RLS) channel estimation for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is investigated. Channel estimation in time-domain (TD) as well as frequency-domain (FD) is investigated through exploiting preambles and pilot symbols inserted in TD and FD, respectively. The channel is assumed to be slowly time-varying frequency-selective, constant during one OFDM symbol but changing from symbol to symbol. Simulation results show that the TD EW-RLS estimator has better estimation performance in terms of the mean-squares error (MSE) and bit-error rate (BER), compared to FD EW-RLS estimation approach. The computational complexity is significantly reduced by recursively updating the channel estimates and by applying the matrix inversion lemma

Time-domain adaptive channel estimation for OFDM-based WLAN with multiple-antennas

In this paper, an adaptive time-domain (TD) channel estimation scheme, based on recursive least squares (RLS) algorithm, is proposed for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) based wireless local area networks (WLANs). The estimator is then extended to perform decision-directed (DD) channel tracking during data transmission. The channel is assumed to be constant during one OFDM symbol but evolves in time according to the first-order Markov process. Different training rates at different Doppler frequencies were investigated. Simulation results show that the proposed estimation scheme has excellent performance measured in terms of the mean squares error (MSE) and the bit error rate (BER), provided that the forgetting factor of the RLS algorithm is optimally selected

Diversité inter-organisationnelle et internationale dans les processus d'innovation : une étude exploratoire dans le secteur des énergies renouvelables

National audienceLa transition énergétique est un des enjeux majeurs de notre époque. Parmi les entreprises engagées dans la transition, certaines collaborent avec des organisations différentes en vue de produire et d'implémenter des technologies innovantes. Cette communication pose la question de savoir dans quelle mesure la diversité au niveau international et interculturel, mais aussi au niveau des types d'organisations, contribue à l'innovation soutenable dans le secteur des énergies renouvelables. Dans une logique exploratoire et qualitative, nous étudions neuf cas de collaborations internationales et inter-organisationnelles qui ont mené à des innovations soutenables. Comment ces collaborations entre des acteurs différents, entre entreprises et organisations à but non lucratif, ont-elles pu engendrer de l'innovation ? Ce papier contribue à une meilleure compréhension des contextes et conditions de collaborations internationales réussies entre entreprises et organisations à but non lucratif

Diversité inter-organisationnelle et internationale dans les processus d'innovation : une étude exploratoire dans le secteur des énergies renouvelables

National audienceLa transition énergétique est un des enjeux majeurs de notre époque. Parmi les entreprises engagées dans la transition, certaines collaborent avec des organisations différentes en vue de produire et d'implémenter des technologies innovantes. Cette communication pose la question de savoir dans quelle mesure la diversité au niveau international et interculturel, mais aussi au niveau des types d'organisations, contribue à l'innovation soutenable dans le secteur des énergies renouvelables. Dans une logique exploratoire et qualitative, nous étudions neuf cas de collaborations internationales et inter-organisationnelles qui ont mené à des innovations soutenables. Comment ces collaborations entre des acteurs différents, entre entreprises et organisations à but non lucratif, ont-elles pu engendrer de l'innovation ? Ce papier contribue à une meilleure compréhension des contextes et conditions de collaborations internationales réussies entre entreprises et organisations à but non lucratif

Ternary Bi2S3/MoS2/TiO2 with double Z-scheme configuration as high performance photocatalyst

Due to unique electron transport properties, nanostructured catalysts with certain morphology, such as nanotube, nanosheet and nanorods, have shown outstanding photocatalytic performance. Herein, preparation of ternary photocatalytic architecture is demonstrated using a facile microwave-assisted hydrothermal method. The as-prepared ternary photocatalyst (denoted as Bi2S3/MoS2/TiO2) comprises bismuth sulfide (Bi2S3) nanorods, molybdenum sulfide (MoS2) nanosheets, and titanium dioxide (TiO2) nanotubes. The photocatalytic performance of the as-prepared nanocomposite is evaluated by monitoring water splitting and dye degradation. The results show that the Bi2S3/MoS2/TiO2 exhibits stable and highly efficient photocatalytic hydrogen production under visible light, and photocatalytic degradation of methylene blue (MB) under sunlight. The photocatalytic performance of Bi2S3/MoS2/TiO2 is much better than that of TiO2, MoS2, or Bi2S3. The improved performance is correlated to the high surface area and the formation of the double Z-scheme heterostructure, which together render abundant catalytic sites and efficient charge separation with strong redox capability. Additionally, X-ray photoelectron spectroscopy and electron spin resonance spectroscopies, combined with reactive species trapping experiments, confirm that the surface charge transport in Bi2S3/MoS2/TiO2 occurs through the double Z-scheme approach. This work paves the way for designing more photocatalytic systems with double Z-scheme for high efficiency and wide practical applications

A review on zeolite imidazole frameworks: synthesis, properties, and applications

Zeolitic imidazolate frameworks (ZIFs) consist of transition metal ions (Zinc or Cobalt) and imidazolate (Im) linkers in tetrahedral coordination surrounded by nitrogen atoms from the five-membered imidazole ring serving as a bridging linker, i.e. a link connecting the metal centres in the three-dimensional framework. The crystal structures of ZIFs share the same topologies as those that can be found in aluminosilicate zeolites. ZIFs have advantages over zeolites such that the hybrid framework structures are expected to have more flexibility in surface modification. Due to their interesting properties such as high porosity, high surface area, exceptional thermal and chemical stability, ZIFs are very attractive materials with potential applications including gas sorption, gas separation, and catalysis. Over a decade tremendous work has been carried out to develop ZIFs in synthesis and its various applications. In this review, we have briefly composed the different methods for the synthesis of ZIFs such as solvent-based and solvent-free methods. In addition, its thermal and chemical properties and potential applications in the field of adsorption, separation, catalysis, sensing, and drug delivery have been summarized

Smart Fortified PHBV-CS Biopolymer with ZnO-Ag Nanocomposites for Enhanced Shelf Life of Food Packaging

Thymus vulgaris leaf extract was used as a stabilizer and reducing agent in the green, facile, and biomimetic hydrothermal decomposition reaction for the fabrication of zinc oxide silver nanocomposites (ZnO-Ag NCs). The nanocomposite (NC) as an active agent was integrated into poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-chitosan (PHBV-CS) in a highly precise ratio of solvent mixture by ultrasonication without the aid of any coupling agent to fabricate the novel degradable biopolymer (BP) nanocomposite via solvent casting method to enhance the mechanical properties and antimicrobial activity and with the lowest immigration rate to improve the shelf life of poultry items. The ZnO-Ag NCs as a nanoactive agent in the food packaging preserved food safety by controlling its spoilage. The morphology, physical, mechanical, barrier, antibacterial, and migration properties of the nanocrystals were assessed via several characterization methods to show the enhancement of the prepared polymer in various aspects of properties. The NCs BP were used for potential sensory evaluation of chicken breast refrigerated over a period of 15 days. The data demonstrated that these bio-based nanocomposites show great antimicrobial activity that offers perspectives for the replacement of traditional petrochemical-based polymers currently used for food packaging of poultry items

Synthesis of heterostructured Bi2O3–CeO2–ZnO photocatalyst with enhanced sunlight photocatalytic activity

The development of heterostructured semiconductor photocatalysts makes a noteworthy advancement in environmental purification technology. In this work, a novel heterostructured Bi2O3−CeO2−ZnO, fabricated by a combination of microwave-assisted hydrothermal and thermal decomposition methods, showed an enhanced photocatalytic activity for Rhodamine B (RhB) degradation under sunlight, as compared to pristine ZnO, Bi2O3, CeO2, and commercial Degussa TiO2-P25. The obtained products were thoroughly characterized by various techniques including X- ray powder diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), elemental color mapping, energy-dispersive X-ray spectroscopy (EDAX), Raman spectrometry, Fourier transform infrared (FT-IR) spectroscopy, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and photoluminescence (PL) spectroscopy. PXRD analysis reveals that the heterostructure has the monoclinic lattice phase of α-Bi2O3, the cubic phase of CeO2 and the hexagonal wurtzite phase of ZnO. FE-SEM images show that Bi2O3−CeO2−ZnO has an ordered mixture of nanorod and nanochain structures. EDAX, elemental color mapping, Raman and FT-IR analyses confirm the successful formation of the heterostructured Bi2O3−CeO2−ZnO. The UV–Vis DRS results demonstrate that Bi2O3−CeO2−ZnO exhibits wide visible-light photoabsorption in 400–780nm range. Moreover, the reduction in PL intensity of the heterostructured Bi2O3−CeO2−ZnO, when compared to the pristine Bi2O3, CeO2, and ZnO, indicates enhanced charge separation. The study on the mechanism displayed that the improved photocatalytic activity of Bi2O3−CeO2−ZnO could be attributed to (1) the efficient separation of photoinduced electrons and holes of the photocatalysts, caused by the vectorial transfer of electrons and holes among ZnO, CeO2 and Bi2O3, and (2) the wide visible-light photoabsorption range. This study introduces a new class of promising sunlight-driven photocatalysts

Transient Liquid Phase Bonding of Ti-6Al-4V and Mg-AZ31 Alloys Using Zn Coatings

Ti-6Al-4V and Mg-AZ31 were bonded together using the Transient Liquid Phase Bonding Process (TLP) after coating both surfaces with zinc. The zinc coatings were applied using the screen printing process of zinc paste. Successful bonds were obtained in a vacuum furnace at 500 °C and under a uniaxial pressure of 1 MPa using high frequency induction heat sintering furnace (HFIHS). Various bonding times were selected and all gave solid joints. The bonds were successfully achieved at 5, 10, 15, 20, 25, and 30 min. The energy dispersive spectroscopy (EDS) line scan confirmed the diffusion of Zn in both sides but with more diffusion in the Mg side. Diffusion of Mg into the joint region was detected with significant amounts at bonds made for 20 min and above, which indicate that the isothermal solidification was achieved. In addition, Ti and Al from the base alloys were diffused into the joint region. Based on microstructural analysis, the joint mechanism was attributed to the formation of solidified mixture of Mg and Zn at the joint region with a presence of diffused Ti and Al. This conclusion was also supported by structural analysis of the fractured surfaces as well as the analysis across the joint region. The fractured surfaces were analyzed and it was concluded that the fractures occurred within the joint region where ductile fractures were observed. The strength of the joint was evaluated by shear test and found that the maximum shear strength achieved was 30.5 MPa for the bond made at 20 min