IWO-based Synthesis of Log-Periodic Dipole Array

The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. Due to its better performance in comparison to other well-known optimization methods, IWO has been chosen to solve many complex non-linear problems in telecommunications and electromagnetics. In the present study, the IWO is applied to optimize the geometry of a realistic log-periodic dipole array (LPDA) that operates in the frequency range 800-3300 MHz and therefore is suitable for signal reception from several RF services. The optimization is applied under specific requirements, concerning the standing wave ratio, the forward gain, the gain flatness and the side lobe level, over a wide frequency range. The optimization variables are the lengths and the radii of the dipoles, the distances between them, and the characteristic impedance of the transmission line that connects the dipoles. The optimized LPDA seems to be superior compared to the antenna derived from the practical design procedure

Optimal Wideband LPDA Design for Efficient Multimedia Content Delivery over Emerging Mobile Computing Systems

An optimal synthesis of a wideband Log-Periodic Dipole Array (LPDA) is introduced in the present study. The LPDA optimization is performed under several requirements concerning the standing wave ratio, the forward gain, the gain flatness, the front-to-back ratio and the side lobe level, over a wide frequency range. The LPDA geometry that complies with the above requirements is suitable for efficient multimedia content delivery. The optimization process is accomplished by applying a recently introduced method called Invasive Weed Optimization (IWO). The method has already been compared to other evolutionary methods and has shown superiority in solving complex non-linear problems in telecommunications and electromagnetics. In the present study, the IWO method has been chosen to optimize an LPDA for operation in the frequency range 800-3300 MHz. Due to its excellent performance, the LPDA can effectively be used for multimedia content reception over future mobile computing systems

Evaluation of prediction accuracy for the Longley-Rice model in the FM and TV bands

Accurate geographical coverage predictions maps for FM and TV are needed for channel and frequency allocations and in order to avoid unwanted interferences. The Longley-Rice model has been used for this purpose over the last four decades and still being used almost exclusively by the FCC in the United States. In this work a comparison is presented between the relative accuracy of this model in the VHF-FM and UHF-TV frequency bands. Simulations were made with accurate and up to date input data (antenna height, location, gain, transmit power, etc.) for the FM-TV stations provided by the ERT S.A. public broadcaster in the region of Thessaloniki – Greece. Finally, the calculated – simulated results were confronted to field measurements using a Rohde & Schwarz FSH3 portable spectrum analyzer and high precision calibrated biconical and log-periodic antennas, and the errors between predictions and measurements were statistically analyzed in the two frequency bands. It has been found in this study that the Longley-Rice model, in general, overestimates field-strength values, but this overestimation is much higher in the VHF – FM radio band (88-108 MHz) than in the UHF-TV band (470-790 MHz)

Comparative study of Radio Mobile and ICS Telecom propagation prediction models for DVB-T

In this paper, a comparative study between the results of a measurement campaign conducted in northern Greece and simulations performed with Radio Mobile and ICS Telecom radio planning tools is performed. The DVB-T coverage of a transmitting station located near the city of Thessaloniki is estimated using three empirical propagation models (NTIA-ITS Longley Rice, ITU-R P.1546 and Okumura-Hata-Davidson) and one deterministic model (ITU-R 525/526). The best results in terms of minimum average error and standard deviation are obtained using the deterministic model and the NTIA-ITS Longley Rice empirical model. In order to improve the results, the tuning options available in the ICS Telecom software are used on the Okumura-Hata-Davidson model, leading to a significant increase in accuracy

An Empirical Study of Link Quality Assessment in Wireless Sensor Networks applicable to Transmission Power Control Protocols

Transmission Power Control (TPC) protocols are poised for wide spread adoption in Wireless Sensor Networks (WSNs) to address energy constraints. Identifying the optimum transmission power is a significant challenge due to the complex and dynamic nature of the wireless transmission medium and this has resulted in several previous TPC protocols reporting poor reliability and energy efficiency in certain scenarios. In line with current studies, this study presents an empirical characterisation of the transmission medium in typical WSN environments. Through this, the sources of link quality degradation are identified and extensive empirical evidence of their effects are presented. The results highlight that low power wireless links are significantly affected by spatio-temporal factors with the severity of these factors being heavily dependent on environment

Comparison of Evolutionary Optimization Algorithms for FM-TV Broadcasting Antenna Array Null Filling

Broadcasting antenna array null filling is a very challenging problem for antenna design optimization. This paper compares five antenna design optimization algorithms (Differential Evolution, Particle Swarm, Taguchi, Invasive Weed, Adaptive Invasive Weed) as solutions to the antenna array null filling problem. The algorithms compared are evolutionary algorithms which use mechanisms inspired by biological evolution, such as reproduction, mutation, recombination, and selection. The focus of the comparison is given to the algorithm with the best results, nevertheless, it becomes obvious that the algorithm which produces the best fitness (Invasive Weed Optimization) requires very substantial computational resources due to its random search nature

An empirical investigation on the correlation between solar cell cracks and hotspots

In recent years, solar cell cracks have been a topic of interest to industry because of their impact on performance deterioration. Therefore, in this work, we investigate the correlation of four crack modes and their effects on the temperature of the solar cell, well known as hotspot. We divided the crack modes to crack free (mode 1), micro-crack (mode 2), shaded area (mode 3), and breakdown (mode 4). Using a dataset of 12 different solar cell samples, we have found that there are no hotspots detected for a solar cell affected by modes 1 or 2. However, we discovered that the solar cell is likely to have hotspots if affected by crack mode 3 or 4, with an expected increase in the temperature from 25∘C to 100∘C. Additionally, we have noticed that an increase in the shading ratio in solar cells can cause severe hotspots. For this reason, we observed that the worst-case scenario for a hotspot to develop is at shading ratios of 40% to 60%, with an identified increase in the cell temperature from 25∘C to 105∘C

Approximating Shading Ratio Using the Total-Sky Imaging System: An Application for Photovoltaic Systems

In recent years, a determined shading ratio of photovoltaic (PV) systems has been broadly reviewed and explained. Observing the shading ratio of PV systems allows us to navigate for PV faults and helps to recognize possible degradation mechanisms. Therefore, this work introduces a novel approximation shading ratio technique using an all-sky imaging system. The proposed solution has the following structure: (i) we determined four all-sky imagers for a region of 25 km2, (ii) computed the cloud images using our new proposed model, called color-adjusted (CA), (iii) computed the shading ratio, and (iv) estimated the global horizontal irradiance (GHI) and consequently, obtained the predicted output power of the PV system. The estimation of the GHI was empirically compared with captured data from two different weather stations; we found that the average accuracy of the proposed technique was within a maximum ±12.7% error rate. In addition, the PV output power approximation accuracy was as high as 97.5% when the shading was zero and reduced to the lowest value of 83% when overcasting conditions affected the examined PV system

Visible Light Communication Based On Offset Pulse Position Modulation (Offset-PPM) Using High Power LED

In this paper, the performance of a visible light communication (VLC) system based on offset pulse position modulation (Offset-PPM) has been demonstrated using a commercial high power white single LED (30 W) and the new coding scheme. Data at a speed of 11 Mbps has been successfully transmitted over a distance of 1 m with zero bit error rate (BER), and 18 Mbps with 1.15 × 10^-6 of BER through the simplest transceiver circuits