Begum Korunur Engiz

Performance analysis of pilot arrangement for OFDM systems over time varying frequency selective channels

In this study, the effect of pilot arrangement on OFDM system performance for different time and frequency selective fading channels is investigated. Pilot symbols are placed in rectangular 2-D pilot pattern in chosen intervals both in time and frequency domain, and corresponding system performances are given in terms of BER. The pilot symbols that give the lowest BER for different channel profiles are determined as the optimum pilot symbols, and the interval between these optimum pilot symbols are defined as the optimum pilot interval in time and frequency direction. Then the relationships between the optimum pilot intervals and channels coherence times and coherence bandwidths are evaluated. It is seen from the results the optimum pilot interval can be related best with coherence time and coherence bandwidth at 0.9 correlation. Therefore 2.5 pilot symbols per Bc,0.9 and 25 pilot symbols per Tc,0.9 can be used.

LONG-TERM ELECTROMAGNETIC FIELD MEASUREMENT AND ASSESSMENT FOR A SHOPPING MALL

As a result of the dense deployment of wireless devices and base stations, measuring and evaluating the electromagnetic (EM) exposure levels they emit have become important to human health especially if they exceed the limits defined in the standards. Base stations, Wi-Fi equipment and other electronic devices are used heavily, especially in densely crowded places like shopping centers. In this study, electric field strength (E) measurements were conducted at one of the largest shopping malls in Turkey. Broadband E measurements were performed using PMM 8053 EM field strength meter for 24 h a day for the duration of one week while frequency selective measurements were carried out with SRM-3006 EM field strength meter. It is concluded from the measurements that the mean measured total E in the band between 100 kHz and 3 GHz is 0.59 V/m while the maximum E is 7.88 V/m, which are both below the limit determined by International Commission on Non-Ionizing Radiation Protection. Evolutions show that E can increase by up to 55% during the daytime. Analyses demonstrate that 71.3% of total E is caused by UMTS2100, 16.3% is produced by GSM900, 6.2% by LTE, 3.5% by Wi-Fi, and 2.7% is generated by devices that use the remaining frequency bands. Based on the detailed statistical analysis of long-term E measurement results, it can be concluded that the measured E levels are not in normal distribution and that they are statistically different with respect to days. Furthermore, distribution of E can be best modeled with the non-parametric approach.

Performance evaluation of ANN based channel interpolation for OFDM system

In this study, the effect of three different techniques that used for interpolation on OFDM system with pilot based comb type channel estimation is investigated and results are given in terms of BER (Bit Error Rate). The estimation of channel at pilot subcarriers is done by LS (Least Square), and interpolation of channel at data subcarriers are obtained by low pass (LP) interpolation algorithm, ANFIS (Adaptive Network Based Fuzzy Inference Systems) and GRNN (Generalized Regression Neural Networks) artificial neural network (ANN) structures. The results show that there is a relationship between the number of used pilot bits and interpolation techniques performance. If the aim is to get high bandwidth efficiency over a given bandwidth LP algorithm should be used for interpolation, to get the lowest BER ANFIS or GRNN can be used.

Monitoring of RF/Microwave field strength at schools in a pilot district in Samsun/Turkey

As a result of the growing usage of wireless devices and a large number of WLANs installations at schools; determining the exposure levels to students and staff from these systems has become more crucial than before. Since microwave radio links are used to provide connection between wireless devices, proper assessment of exposure to microwave emissions must be carried out. For this reason, in this study electromagnetic radiation (EMR) measurements were conducted at 92 different schools in Ilkadim district twice in 2016 using PMM 8053 EMR meter. The changes in and statistical properties of electric field strengths (E) are determined on the basis of these measurements. The maximum Es (Emax) are 5.39 V/m and 3.04 V/m for each measurement while the maximum average Es (Eavg) are 2.22 and 2.25 V/m. Even though the measured E levels are below the limits that are determined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP); for providing a wide margin of protection and evaluating the health risks they may cause, regular control/measurement of exposed EMR levels is recommended.

MEASUREMENT AND EVALUATION OF ELECTRIC FIELD STRENGTH LEVELS IN PRIMARY AND SECONDARY SCHOOLS IN A PILOT REGION

In this study, in order to evaluate the exposed radiofrequency electromagnetic field (RF-EMF) levels, and to control their compliance with the limits determined by International Commission on Non-Ionizing Radiation Protection (ICNIRP), extensive short-term/band-selective and long-term RF-EMF measurements were conducted at 92 primary and secondary schools in the Ilkadım district of Samsun/Turkey. The measurements were performed once each in May, June, October and December in 2016, using the PMM-8053 EMF meter. It was seen from the measurement results that the maximum average electric field strength (Eavg) was recorded, 2.34 V/m, in October, when students were at school. It was concluded from the measurement results that the measured Eavg levels recorded at 92 schools were below the limits determined by ICNIRP. According to the band-selective measurement results performed using a Narda SRM-3006 EMF meter, the five main electric field strength (E) sources that had the most contribution in total E were LTE800, GSM900, GSM1800, UMTS2100 and WLAN services. With the use of these main E sources, an empirical model was then proposed that helps to determine the total E with 99.6% accuracy. It was also concluded from the long-term broadband measurement result that the number of active users affected the total E in the medium directly, and that the measured E levels were significantly higher in daytime than those of recorded in night-time. In the final stage of the study, all measurement results were transferred on scaled color maps. The use of these maps helped to determine and maintain control on the levels of RF-EMF exposure at schools using, or intending to install, such systems, and also to take measures for future precautions.

AN EMPIRICAL STUDY: THE IMPACT OF THE NUMBER OF USERS ON ELECTRIC FIELD STRENGTH OF WIRELESS COMMUNICATIONS

As a result of the drastic increase in the number of mobile device users, there is considerable public debate about possible health hazards especially due to base stations and Wi-Fi access points. For this reason, in this study the effects of the number of users in a base station and wireless fidelity (Wi-Fi) access point on electric field strength (E) levels were investigated using real-time measurements. Two-stage E measurements were performed on Ondokuz Mayıs Universitys (OMU) Kurupelit Campus with a PMM-8053 and SRM-3006 electromagnetic field (EMF) meter. In the first stage, 24-h measurements were performed with PMM-8053 at the location where the maximum E was measured and from which the busiest times of the day were then determined. The relationship among band selective E values was assessed using the number of users per minute provided by three cellular system operators for the location. Upper and lower bounds of E according to the number of users were calculated, and then an empirical model that helps calculate the E of medium with 86% accuracy was proposed. In the second stage, the effect of the number of users in a Wi-Fi access point on E level was investigated. For this purpose, the measurement environment was set as including one Wi-Fi access point with needed measurement devices. The number of users was increased as per user per minute. The number of users was validated with the data obtained from OMU IT Department. Using the measurement result, a model with a 96% accuracy between the E value in the environment and the number of users accessing the Wi-Fi system is proposed. With the use of these models, E level in the medium can be determined without using any EMF meters, thus precautions can be taken to stay within regulatory limits.

What is adverse effect of wireless local area network, using 2.45 GHz, on the reproductive system?

Abstract Aim: To investigate the inflammatory effect and testicular damage on rats exposed to low level of electromagnetic fields (EMF) at 2.45u2009GHz microwave radiation. Methods: Twenty two Wistar rats were divided into two groups. Group 1 was the control group and not exposed to EMF. Group 2 was exposed to low level EMF (average E-field 3.68u2009±u20090.36 V/m, whole body average SAR, 0.0233 W/kg, in 10u2009g tissue) at 2.45u2009GHz for 1u2009hour/day for 30 consecutive days. At the end of the study, interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-32 (IL-32), C-reactive protein (CRP) were measured in rat serum and IL-6, IL-10, IL-32 were measured in rat testis tissue. Furthermore, testicular tissues were evaluated histopathologically in terms of spermatogenesis and coagulation necrosis. Results: Serum IL-6 and CRP levels were found to be significantly different in the study group compared to the control group (pu2009<u2009.05), but no significant difference was found in serum IL-10, IL-32 levels and testis tissue IL-6, IL-10, IL-32 levels compared to the control group (pu2009>u2009.05). On the other hand, histopathological evaluation of testicular tissue revealed a significant difference in necrosis and spermatogenesis when compared with the control group (pu2009<u2009.05). Conclusions: It may be concluded that low level EMF at 2.45u2009GHz increases inflammation and testicular damage and negative impact on male reproductive system function.

Distribution fitting for long term electric field strength measurements

As a result of the enormous increase in usage of wireless systems; electromagnetic radiation (EMR) sources in residential areas as well as the exposed EMR levels has increased significantly. Therefore this study aims to determine the exposed E levels and characterize the electromagnetic environment on the basis of long term (24 hours) E measurements conducted at five different home environments. The measurements were collected using PMM 8053 EMR meter in band from 100 kHz to 3 GHz, and the electric field strength (E) was recorded. The measurement results show that the E originating from the base stations change significantly within a day, and the highest E is 6.21 V/m and the highest mean E is 3.59 V/m. Analysis of 24 hour measurements so as to division of a day into four equal parts show that afternoon and evening E levels are comparatively higher than those recorded during morning and night. Morning E level increases by 80.61% compared to night. At the end of the study to characterize the measured E levels with a distribution; fitting methods are applied to measured data. Since a Weibull distribution yield the lowest NRMSE; appears to be a candidate for a representation of the distribution of the measured E levels.

Determination of the sources of electric field strength in a medium by artificial neural network

This study aims to determine total electric field strength (E) levels and its main sources in Samsun city center. To reach this goal extensive E and band selective E measurements were performed using Narda SRM 3006. The measurements were collected on the busiest streets of Samsun city during a journey of more than two hours on a vehicle moving with a certain velocity. On the basis of over 700 measurements E and E sources within the band were determined. It is seen from the results that the main sources of E were the base stations that operates at GSM900, GSM1800 and UMTS frequency bands. Because of difficulties encountered in band selective measurements (need for specific and expensive meters); a model that helps to obtain the three band selective Es in terms of E was proposed, and its performance was improved by using multilayer perceptron (MLP) artificial neural network system. With the use of this model; E levels of the three main sources can be determined from E in the environment up to 95% accuracy.

Investigating the effect of number of users on signal strength level and throughput for Wi-Fi system

In this study, the effect of the number of users in a Wi-Fi access point on signal strength and throughput is investigated. For this purpose, measurement environment was set as including one Wi-Fi access point, needed measurement devices and 70 users. The number of users was increased as per user/per second. Each user was asked to download the same 300 MB data file from the certain WEB page. In the meanwhile, the signal strength was measured using android based “Wi-Fi Analyzer” application and the data traffic on the Wi-Fi modem was tracked. The changes in Wi-Fi channel usage and channels signal strengths depending on the increment in the number of users were investigated. The number of users and throughput rates were validated with the data obtained from Ondokuz Mayis University IT Department. It is seen from the results that the signal strength may vary between ‘80 dBm and ‘46 dBm depending on the number of users. The sudden changes have occurred in throughput rates as a result of the number of users connected to the access point at the same time. It is also determined from the measurement results that the maximum throughput is 20.26 Mbps while the mean is 10.07 Mbps, and the maximum allowable number of users is 64.