Underwater wireless optical communication (UWOC) enables high-speed links in water for the optical Internet of Underwater Things (O-IoUT) networks. O-IoUT provides various marine applications, including ocean exploration, environmental monitoring, and underwater navigation. O-IoUT typically utilizes light-emitting diodes (LEDs) and different laser diodes (LDs) such as green/blue lasers to achieve efficient data communication in the underwater environment. The high-speed optical communication is limited up to a few tens of meters due to underwater channel impairments and misalignment between the transmitter (Tx) and the receiver (Rx). UWOC provides high-speed communications only in the line of sight conditions, and a small misalignment between the Tx and the Rx can degrade the system performance. In an attempt to understand and minimize this misalignment issue, we investigate how received power in a UWOC system depends on the transmitted beam’s divergence angle. Simulation results are provided to show the effectiveness of the study by comparing the plane, Gaussian, and spherical beams. Monte Carlo simulations are utilized to determine the maximum allowable lateral offset between Tx and Rx for a given Tx divergence angle. The results provide an overview and design-based trade-off between different parameters such as lateral offset, the power received, and bandwidth of the channel. The proposed method improves not only the maximum allowed link-span but also the bandwidth of the channel for a given transmission distance.

The cyclical nature and high investment costs of the wind and photovoltaic renewable energy sources are the two critical issues seeking attention for the use of such systems in backup or isolated applications. This paper aims to present the experimental and economic analysis of a wind–photovoltaic-based hybrid direct current microgrid (DCMG) system for backup power and off-grid isolated power generation system for emergency purposes. The two distributed generating units comprising photovoltaic panels and wind generator were designed and developed for the experimental study. A lead-acid battery is also added as an energy storage system to enhance the system supply. The electric load of this system comprise of 42 DC light emitting diode (LED) lamps of 12 Watt each and a 25 Watt DC fan. The charge controller provides the control and protection features for the designed system. The complete system design and fabrication of this system have been undertaken at Mehran University of Engineering & Technology (MUET, Jamshoro, Pakistan). The compatibility of the designed system has been analysed by comparing the Levelized Cost of Energy (LCOE) with a conventional gasoline generator system of the same capacity. The capital, running and lifetime costs of DCMG are found to be 1.29, 0.15 and 0.29 times those of the gasoline generator, respectively. Moreover, it is found that per unit cost of gasoline generator is $0.3 (i.e., PKR 31.4) which is almost 3.4 times higher than that of the hybrid DCMG system. The performance and cost evaluation of the designed system indicate its broad potential to be adopted for commercialisation to meet backup power and off-grid power requirements. This study concludes that proposed DCMG system is a not only low cost, but also a pollution-free alternative option compared to the existing traditional small gasoline generator system.

Futuristic requirements of mobile communication systems ask for discovering new possibilities and dimensions to enable ultrafast and reliable communication. This work relates to the advancements in jointly decoded iterative multimedia communication systems for the H.264 source standard. The beneficial technique of Over-Complete Mapping (OCM) is utilized for introducing redundancy in the highly compressed source encoded video streams. Differential Space–Time Spreading (DSTS) is invoked along with Rate-3/4 Recursive Systematic Convolutional (RSC) as intermediate encoder in the proposed three-stage setup. More specifically, the RSC encoder is beneficial in attaining the iterative gain as it divides the decoder into two parts. The DSTS is invoked with the Sphere Packing (SP) modulation which is highly desirable for the non-coherent detection schemes without requiring any information from the channel. The proposed system comprises of three main components, namely OCM, Rate-3/4 RSC and SP modules, thus we call this as three-stage system. The iterative decoding enhances the Bit-Error Rate (BER) and Peak Signal-to-Noise Ratio (PSNR) performances of the joint source-channel systems. Furthermore, to expeditiously predict the convergence pattern of the proposed three-stage iteratively decoded systems, EXtrinsic Information Transfer (EXIT) chart analysis is performed. Moreover, the effect of variations in the minimum Hamming distance ( $${d}_{H,min}$$ d H , m i n ) is observed for the proposed three-stage system. The $${{DSTS}-{SP}-{RSC}-{OCM}}_{[5 15]}$$ DSTS - SP - RSC - OCM [ 515 ] having $${d}_{H,min}=6$$ d H , m i n = 6 exhibits a gain of 20 dB against the benchmarker $${{DSTS}-{SP}-{RSC}-{OCM}}_{[2 6]}^{*}$$ DSTS - SP - RSC - OCM [ 26 ] ∗ with $${d}_{H,min}=1$$ d H , m i n = 1 at the PSNR degradation point of 1 dB over a correlated Rayleigh fading channel.

This paper proposes a novel efficient multistage algorithm to extract source speech signals from a noisy convolutive mixture. The proposed approach comprises two stages named Blind Source Separation (BSS) and de-noising. A hybrid source prior model separates the source signals from the noisy reverberant mixture in the BSS stage. Moreover, we model the low- and high-energy components by generalized multivariate Gaussian and super-Gaussian models, respectively. We use Minimum Mean Square Error (MMSE) to reduce noise in the noisy convolutive mixture signal in the de-noising stage. Furthermore, the two proposed models investigate the performance gain. In the first model, the speech signal is separated from the observed noisy convolutive mixture in the BSS stage, followed by suppression of noise in the estimated source signals in the de-noising module. In the second approach, the noise is reduced using the MMSE filtering technique in the received noisy convolutive mixture at the de-noising stage, followed by separation of source signals from the de-noised reverberant mixture at the BSS stage. We evaluate the performance of the proposed scheme in terms of signal-to-distortion ratio (SDR) with respect to other well-known multistage BSS methods. The results show the superior performance of the proposed algorithm over the other state-of-the-art methods.

A novel low-profile and miniaturized patch antenna on a substrate material of high dielectric constant has been designed, fabricated and tested in an indigenous laboratory. It is highly important to reduce the size of patch antenna as it limits the reduction of the sizes of the devices using this antenna. A number of techniques have been given for the size reduction of patch such as DGS (Defected Ground Structure), use of fractals and the use of metamaterials but in this paper the technique of high permittivity substrate has been implemented. The substrate as well as this conventional antenna has been prepared locally in Pakistan. A ceramic material of chemical composition {(Sr0.5Pb0.25Ca0.25)-Tio3-3Bi2O3.TiO2} having a high dielectric constant has beenused in the substrate of the antenna. The fabricated prototype was investigated experimentally for important parameters using Vector Network analyzer. The total measure of the antenna is 20.5x26.5x1.5 mm3. The antenna presented a large bandwidth of 186 MHz (1070-1256 MHz)in L-Band with a Return Loss of 21.10 dB at resonance. The VSWR (Voltage Standing Wave Ratio) remained under the standard value of 2 in the whole operating range. The proposed antenna may be employed in GPS (Global Positioning System) devices, Amateur Radio, Terrestrial Mobile Communication, Aeronautical and Maritime Mobile and other Military and Low Earth Orbit Satellite Communications.