Cetin Kurnaz

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.

Investigating MC-CDMA system performance using measurement-based channel models

This paper investigates the performance of the downlink in Multi Carrier CDMA (MC-CDMA) systems using a channel model from in-the-field propagation measurements. Results are presented also for channel models having non-exponentially decaying profiles. Channel coherence bandwidth (Bc) is incorporated within the analysis in order to demonstrate the effect of channel frequency selectivity on system performance. The effect of transmission bandwidth, number of users and number of sub-carriers on system performance is analyzed. Our simulation results show that Bc values for correlation coefficients of 0.75 or 0.9 can be used to represent the channel properties to investigate the required number of subcarriers. The level of multiple access interference is also shown to be related to the Bc value for correlation coefficient of 0.5. Performance was analyzed for transmission bandwidths of 20 MHz and 40 MHz. Our results show that for some channels, performance is improved by using narrower transmission bandwidth and by selecting the band of transmission within the available band.

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.

Performance evaluation of dual carrier HSDPA in indoor environment

3GPP aims to respond the increasing demands of higher data rate dual carrier HSDPA (DC-HSDPA) with Release 8. DC-HSDPA system allows up to 42 Mbps data rates by using 10 MHz bandwidth. DC-HSDPA system performance varies depending on wireless channel quality and number of users. In this study DC-HSDPA system performance is evaluated for different number of users by using TEMS program. Performance assessment is determined in the average download data speeds. It is seen from the results users requests can effect air interface and the data rate. It is determined that with the increase of the number of users, the power of interference also increases, consequently channel quality indicator and by using low modulation index schemes the average data rate decrease.

MC-CDMA System Performance for Different Frequency Selective Channels

Multi-carrier CDMA (MC-CDMA) is a promising multiple access scheme for the fourth generation mobile radio systems which aim to support services with wide range of data rates up to 100 Mbps. MC-CDMA exploits frequency diversity by transmitting chips of a bit over multiple subcarriers, making the communication system more robust to diverse frequency selective fading of the outdoor environment. Up to now, performance of multicarrier systems has been investigated mainly for indoor environment that is characterised by small delay spreads and low mobile speeds. We investigated performance of MC-CDMA system for outdoor environment. MMSEC combining technique was used. The results show that the system parameters, like Pn code length (i.e., number of subcarriers) and size of S-P conversion, can be varied in order to provide optimal system performance. Furthermore, in the case of no movement, an increase in the spectral efficiency can be attained by selecting the frequency band in a hybrid FDMA/MC-CDMA system depending on the frequency selectivity and the data rate.

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.

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.