Bioelectromagnetics 31:576^579 (2010)
Brief Communication Assessment of General Public Exposure to LTE and RF Sources Present in an Urban Environment Wout Joseph,* Leen Verloock, Francis Goeminne, Gu«nter Vermeeren, and Luc Martens Department of InformationTechnology, Ghent University/IBBT, Ghent, Belgium For the first time, in situ electromagnetic field exposure of the general public to fields from long term evolution (LTE) cellular base stations is assessed. Exposure contributions due to different radiofrequency (RF) sources are compared with LTE exposure at 30 locations in Stockholm, Sweden. Total exposures (0.2–2.6 V/m) satisfy the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference levels (from 28 V/m for frequency modulation (FM), up to 61 V/m for LTE) at all locations. LTE exposure levels up to 0.8 V/m were measured, and the average contribution of the LTE signal to the total RF exposure equals 4%. Bioelectromagnetics 31:576–579, 2010. 2010 Wiley-Liss, Inc. Key words: general public exposure; LTE; RF measurement
A priority in the research agenda of the World Health Organization (WHO) is to assess the typical range of exposures from emerging wireless network technologies. One of the newest wireless technologies is long term evolution (LTE). LTE is marketed as the fourth generation (4G) of radio technologies [3GPP, 2009]. Target values for the downlink peak data rates of LTE systems range from 10 Mbit/s up to 300 Mbit/s. In December 2009, the world’s first publicly available LTE service was started in Stockholm, Sweden. Procedures for measurements in the vicinity of Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) base stations have been developed by Neubauer et al. [2002], Joseph and Martens [2006], Olivier and Martens [2007] and Kim et al. [2008], and measurements in the neighborhood of Worldwide Interoperability for Microwave Access (WiMAX) base stations by Joseph et al. [2008a]. Foster [2007] investigated exposure of Wireless-Fidelity (Wi-Fi) access points. Exposures from TV and radio transmitters have been studied by Joseph and Martens [2006] and Sirav and Seyhan [2009]. Measurement campaigns of radiofrequency (RF) exposures using personal exposimeters and their results have been presented by Neubauer et al. [2007], Joseph et al. [2008b, 2010], Knafl et al. [2008], Ro¨o¨sli et al. [2008], Frei et al. [2009], and Viel et al. [2009]. Exposimeters are not suitable for accurate field assessment and current 4 2010 Wiley-Liss, Inc.
personal exposimeters cannot measure LTE, but one can use them to obtain an idea about exposure distributions. Thus, procedures for RF exposure measurements in the vicinity of base stations have already been developed and a standard has been written for the in situ measurement of electromagnetic field strength related to human exposure in the vicinity of base stations [CENELEC, 2008]. However, there are no assessments of exposure to electromagnetic fields of emerging wireless systems such as LTE. To our knowledge, this is the first time that in situ LTE base station exposure has been experimentally assessed in a real urban environment. The purpose of this study is to provide a range of typical LTE exposure values, compare the contribution with other sources, and check compliance with the International Commission on Non-Ionizing Radiation ————— — Grant sponsor: GSMA and WiMAX forum. *Correspondence to: Dr. Wout Joseph, Department of Information Technology, Ghent University/IBBT, Gaston Crommenlaan 8, B9050 Ghent, Belgium. E-mail:
[email protected] Received for review 7 April 2010; Accepted 28 May 2010 DOI 10.1002/bem.20594 Published online 6 July 2010 in Wiley Online Library (wileyonlinelibrary.com).
Assessment of LTE Exposure
Protection (ICNRIP) guidelines for general public exposure [ICNIRP, 1998]. A commercial LTE network is deployed in the urban environment of Stockholm. Two LTE channels are present: at the frequency of 2660 MHz with a channel bandwidth of 10 MHz and at the frequency of 2630 MHz with a channel bandwidth of 20 MHz. RF electromagnetic field measurements in the band 80 MHz to 6 GHz were performed at 30 different locations with a spectrum analyzer (noted as narrowband measurements). In order to compare base station exposure of different sources, these measurement locations were randomly selected and spread throughout Stockholm; 27 outdoor locations and 3 indoor locations were selected. The measurement setup consisted of tri-axial TS-EMF isotropic antennas (Rohde and Schwarz, Zaventem, Belgium; dynamic range 1 mV/m to 100 V/m for a frequency range of 80 MHz to 3 GHz, and 2.5 mV/m to 200 V/m for a frequency range of 2–6 GHz) in combination with a spectrum analyzer (FSL6, Rohde and Schwarz; frequency range 9 kHz to 6 GHz). The measurement uncertainty for the electric field is 3 dB (29% to 41%) for the considered setup [CENELEC, 2008]. This uncertainty represents the expanded uncertainty evaluated using a confidence interval of 95% (thus estimated at twice the level of the standard deviation, corresponding in the case of a normal distribution to a confidence level of 95%). Current wireless RF sources are mainly operating in the frequency range of 80 MHz to 6 GHz. After allocating the present signals by a spectral survey, these signals were measured in greater detail. The narrowband measurements were executed during the daytime on weekdays. This setup for narrowband measurements is used here because it enables the most accurate assessment of in situ exposure from various sources [CENELEC, 2008]. Exposure to amplitude modulation (AM) signals (below 10 MHz) is not considered here because this concerns different biological effects [ICNIRP, 1998]. If the spectrum analyzer settings are discussed in literature, rarely are all parameters (and certainly not the sweep time) discussed, or they are only vaguely specified. These settings have a major influence on the measurement results and it is very important to specify them [Verloock et al., 2010]. To determine the optimal settings to check compliance of LTE signals with the ICNIRP guidelines, the method of Verloock et al. [2010] is used. After investigations, we obtained the following optimal settings to perform exposure assessment of LTE: a root-mean-square (rms) detector, with a resolution bandwidth (RBW) of 1 MHz, sweep time (SWT) of 20 s, and an appropriate selection of the
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frequency span, for example, 50 MHz. These settings have been determined by laboratory and in situ testing. The settings used for the other RF signals are available in CENELEC [2008], Joseph et al. [2008a], and Verloock et al. [2010]. Table 1 lists the variation of the electric-field strength (V/m) for the RF signals present at the 30 random locations, the average electric field strength (Eavg), the exposure ratio (defined as the ratio between the maximal measured field value for the considered signal over 30 locations and the corresponding ICNIRP reference level for the electric fields; thus ratios smaller than 1 satisfy the ICNIRP guidelines), and the average (APD) and maximal (MPD) power density contribution of each signal to the total power density value (in %) are defined as follows, for X ¼ APD or MPD: Ssignal;i X¼ u 100½% i¼1;...;30 Stot;i with u(. . .) representing a function where Ssignal,i (W/m2) is the power density of an RF signal (e.g., FM, GSM, LTE, etc.) at a location i (i ¼ 1, . . ., 30), and Stot,i is the total power density for all signals at the considered measurement location i. All measured electric field values in Stockholm satisfy the ICNIRP guidelines [ICNIRP, 1998]. The maximal total field value equals 2.6 V/m (Table 1); this is 17 times below the ICNIRP guidelines. The exposure ratio varies between 0.002 and 0.051 for the different RF signals (20–500 times below the ICNIRP guidelines for electric fields). The average of the total values for all locations equals 1.11 V/m. The highest electric field value was measured for the GSM900 signal (2.1 V/m). The highest value for Eavg is also due to the GSM900 signal and equals 0.7 V/m (Table 1). The maximal measured field value for the LTE signal was 0.8 V/m (about 80 times below the ICNIRP reference levels for electric fields). The ranges of exposures for the various sources are comparable to related literature [Joseph and Martens, 2006; Neubauer et al., 2007; Ro¨ o¨ sli et al., 2008; Frei et al., 2009]. Figure 1a shows the LTE exposures and total field values for the 30 measurement locations. The error bars in Figure 1a are calculated from the uncertainties of the experimental values. LTE exposures range from 0.02 to 0.8 V/m (except at location 23, where LTE exposure was below the sensitivity of the measurement equipment). The exposure ratios for LTE range from 0.0004 to 0.012 at the locations where LTE is measured. The mean LTE exposure equals 0.2 V/m (Table 1). Figure 1b shows the power density contribution of each signal (%) at the different measurement locations. At all positions (except location 6, which was in the Bioelectromagnetics
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TABLE 1. Electric-Field Strengths (V/m) for LTE and Different RF Signals at the Different Locations, the Exposure Ratio, and the Average (APD) and Maximal (MPD) Power Density Contribution
RF signal FM T-DAB TETRA PMR Analogue TV—DVB-T GSM900 GSM1800 DECT UMTS-HSPA Wi-Fi LTE WiMAX Total all signals
Frequency band (MHz)
Variation of E over 30 measurement locations (V/m)
ICNIRP reference level (V/m)
Eavg (V/m)
Exposure ratioa
APDb (%)
MPDc (%)
100 220 390 146–174, 406–470 174–223, 470–830 900 1800 1880 2100 2400 2600 3500 —
