Journal of Exposure Science and Environmental Epidemiology (2015) 25, 80–83 © 2015 Nature America, Inc. All rights reserved 1559-0631/15
www.nature.com/jes
ORIGINAL ARTICLE
Mobile telephones: A comparison of radiated power between 3G VoIP calls and 3G VoCS calls Dragan Jovanovic1, Guillaume Bragard1, Dominique Picard2 and Sébastien Chauvin1 The purpose of this study is to assess the mean RF power radiated by mobile telephones during voice calls in 3G VoIP (Voice over Internet Protocol) using an application well known to mobile Internet users, and to compare it with the mean power radiated during voice calls in 3G VoCS (Voice over Circuit Switch) on a traditional network. Knowing that the specific absorption rate (SAR) is proportional to the mean radiated power, the user's exposure could be clearly identified at the same time. Three 3G (High Speed Packet Access) smartphones from three different manufacturers, all dual-band for GSM (900 MHz, 1800 MHz) and dual-band for UMTS (900 MHz, 1950 MHz), were used between 28 July and 04 August 2011 in Paris (France) to make 220 two-minute calls on a mobile telephone network with national coverage. The places where the calls were made were selected in such a way as to describe the whole range of usage situations of the mobile telephone. The measuring equipment, called “SYRPOM”, recorded the radiation power levels and the frequency bands used during the calls with a sampling rate of 20,000 per second. In the framework of this study, the mean normalised power radiated by a telephone in 3G VoIP calls was evaluated at 0.75% maximum power of the smartphone, compared with 0.22% in 3G VoCS calls. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR. Journal of Exposure Science and Environmental Epidemiology (2015) 25, 80–83; doi:10.1038/jes.2014.74; published online 5 November 2014
INTRODUCTION The arrival of 3G networks has enabled considerable advances in mobile communication services, allowing them to progress from just a few kbps in 2G to several dozen Mbps in 3G/HSPA (High Speed Packet Access). Like their forerunners, 3G networks offer voice calls in VoCS mode (Voice over Circuit Switch). The 3G VoCS is characterised by “circuit routing” in the core network and by the use of a dedicated radio channel called R99 (Release 99). It is increasingly frequent for the 3G networks to route voice calls in VoIP mode (Voice over Internet Protocol), the use of which has become widespread due to numerous mobile applications. The 3G VoIP is characterised by “packet routing” in the core network and by the use of a shared radio channel (HSPA) initially meant for the data service (with a speed clearly superior to R99). Research studies have been carried out over recent years to measure the radio-frequency power radiated by 2G and/or 3G mobile telephones in order to assess the real exposure of users.1–12 Radiated power, which can vary in a dynamic range of 70 dB, is the parameter that has the greatest influence on exposure. For voice calls in 3G, the modes studied so far are VoCS on R99, and VoIP calls embedded in other uses such as web-browsing, downloading, so on.7,10 All mobile telephones commercialised in the European market must respect the specific absorption rate (SAR) limit of 2 W/kg averaged over 10 g of tissue (1.6 W/kg over 1 g for the United States). As the SAR is proportional to the radiated power, measuring this radiated power provides an assessment of the reduction of the SAR, and hence the exposure associated with this parameter. The purpose of this study is to compare, in real usage situations, the power radiated by a mobile telephone in 3G
VoIP (HSPA) voice calls to that radiated in 3G VoCS (R99) voice calls, in order to evaluate the different user exposure levels. We are presenting, successively, the results on the mean power values detailed by places, then globally and then finally, the results regarding the highest power encountered during each individual call. MATERIALS AND METHODS The device used for measuring the RF power (Pe) radiated by the telephone is called “SYRPOM”. A view of the system as a whole is shown in Figure 1. It comprises a probe consisting of a resistor-loaded dipole, processing electronics and a micro-computer which controls the system, processes and records the data and displays the results. The processing electronics consist, essentially, of an amplitude-sensitive receiver which detects and records the three European frequency bands, that is, GSM900 and UMTS900 (880–915 MHz), DCS1800 (1710–1785 MHz) and UMTS2100 (1920–1980 MHz). This frequency selectivity enables identification of the frequency band in which the transmission takes place. The links between the different parts of the SYRPOM are hardwired, thus avoiding the pick up of unwanted radio-frequency radiation. The probe is placed behind the telephone close to the aerial. It is electro-magnetically coupled to the telephone’s aerial; this coupling is constant over time. Thus, the output power of the probe is proportional to the radiation power of the telephone. The probe interferes very little with the signal radiated by the telephone and its presence does not modify the latter's operation.11 Following a first version developed to study the radiation from GSM mobile telephones, a new version of the SYRPOM has been devised for 3G telephony. The study of a telephone in 3G mode requires a prior calibration phase to be carried out in the laboratory on the mobile driven by a base station emulator, to determine the reception level of the
1 Direction Fréquences et Protection (Frequencies and Protection Division), Bouygues Telecom, Issy-les-Moulineaux, France and 2Département Electromagnétisme (Electromagnetics Department), DRE, Supélec, Gif-sur-Yvette, France. Correspondence: D Jovanovic, Direction Fréquences et Protection (Frequencies and Protection Division), Bouygues Telecom, 82 rue Henry Farman, 92130 Issy-les-Moulineaux, France. Tel.: +331 394 53067. Fax: +331 392 66468. E-mail: [email protected] Received 17 March 2014; revised 1 September 2014; accepted 3 September 2014; published online 5 November 2014
Radiated power: 3G VoIP vs VoCS Jovanovic et al
81
Figure 1.
SYRPOM measurement system.
SYRPOM corresponding to a radiation at maximum power (Pmax) of each band. The SYRPOM therefore can calculate the mean normalised radiated power (Pe/Pmax; hereinafter MNRP) of the UMTS frames, which it identifies by discarding the GSM frames, if any. The SYRPOM has a dynamic range of around 80 dB (i.e., a factor of 1:100,000,000 in power), making it easy to measure the complete set of levels encountered in 3 G.13 The SYRPOM is independent from the network and from the mobile telephone, which is not so when using other systems, for example, systems based on analysis of data provided by a network supervisor software,2,3,8,10 or using test mobile telephones1 or software-modified telephones.4–6,9 The system carries out the tests on a real user; it is lightweight and portable, so tests can be carried out in all possible situations, in particular in the case of a user on foot. This would be impossible, for example, with a SYNEHA2 type system.12 Bearing in mind the principle, it is compatible with all mobile telephones, whatever their type (Figure 2). A measuring campaign was carried out. In order to simulate genuine usage situations, real voice calls were made to a voice server (telephone line with automatic answering). The telephone, equipped with a SIM card issued by a French operator and associated with a general public mobile telephone plan, provided access to the 3G network and, if unavailable, to the 2G network. The telephone was hand-held by the technician close to his head. For reasons of repeatability and comfort of the technician, a medium-speed speech (recorded on the PC) was played back over a small speaker close to the mobile telephone's microphone throughout the call. The mobile telephone was also charged regularly and its good performance was also checked. The places where the readings were taken were selected in such a way as to cover the whole range of usage situations of the mobile telephone: Offices, cafes/restaurants, public spaces (parks, railway stations and tourist venues), shops, on the street and in cars. Thus, the technician’s position depended on these kinds of use: Sitting; walking quickly or slowly, travelling in a vehicle. All the readings were taken in Paris (France) or its surroundings between 08:00 and 20:00 hours. The calls lasted 2 min and took place between 28 July and 04 August 2011. Three 3G smartphones (HSPA) from three different manufacturers (available in the European market since 2010), two-band for GSM900 and DCS1800 and two-band for UMTS900 and UMTS2100, were used successively without pause, and with no delay between the 3G VoCS call and the 3G VoIP call of each telephone. Kühn et al.12 meanwhile, have shown that the mean radiated power of a 3G telephone in an urban area varied slightly from one telephony operator to another (2.7 dB peak-to-peak between three different operators). Our study will therefore be focused on the network of a single operator as is the case of most studies. Our study will consider, successively, the following three points: ●
●
●
To study the effect of places on the MNRP, the latter is calculated for each call, along with the ratios between the MNRPs in 3G VoCS and in 3G VoIP. Statistics are drawn up on the full set of MNRP values. They consist of assessing the average MNRP, the SD, the median and the 90th percentile. Some of the results are compared with those obtained by Gati et al.7 and Persson et al.10 Finally, we study the highest power attained for each call, as well as the length of time during which the power exceeded 50% of maximum power.
© 2015 Nature America, Inc.
Figure 2.
Table 1.
SYRPOM measurement system in real conditions.
List of places and number of readings.
Places indoor
No. meas
Places outdoor
No. meas
Office
10
18
Cafe, restaurant Commercial centre Railway station Total indoor
26 20
Outdoor (parking, courtyard, etc.) Park Street
54 46
18 74
Total outdoor
118
Places in-car
No. meas
Transport 28 (car)
Total in-car
28
On a total of 135 couples of calls (3G VoCS and 3G VoIP), we have excluded those which lasted o50% of the time in 3G: this leaves us with a total of 110 couples.
RESULTS The MNRP was assessed for the voice calls in 3G VoCS and 3G VoIP taking place together in different places (Table 1). Table 2 presents the MNRP values and the 3G VoCS/3G VoIP MNRP ratios for these calls. They are divided into three categories: indoor, outdoor and in-car. It is observed that in 3G VoCS the MNRP values range from 0.01% to 0.71% and in 3G VoIP from 0.04% to 2.57%. The 3G VoCS/ 3G VoIP MNRP ratio is always negative and its value is limited to the interval from − 2.5 dB to − 7.9 dB, except for offices (dedicated network with microcells to ensure good coverage) for which the MNRPs are particularly weak with a ratio of − 13.1 dB. It is also observed that the average indoor MNRPs are around five times higher (+7 dB) than the average outdoor MNRPs, whether in 3G Journal of Exposure Science and Environmental Epidemiology (2015), 80 – 83
Radiated power: 3G VoIP vs VoCS Jovanovic et al
82 Table 2.
MNRP by places for 3G VoCS and 3G VoIP. Number of readings
Office Café, restaurant Commercial centre Railway station Total indoor Outdoor (parking, courtyard, etc.) Park Street Total outdoor Total in-car
Table 3.
3G VoCS 3G VoIP (%) (%)
3G VoCS/3G VoIP MNRP ratio (dB)
10 26 20 18 74 18
0.01 0.67 0.71 0.01 0.43 0.23
0.13 2.57 2.19 0.04 1.52 1.39
− 13.1 − 5.8 − 4.9 − 6.2 − 5.5 − 7.9
54 46 118 28
0.06 0.05 0.08 0.20
0.13 0.10 0.31 0.52
− 3.6 − 2.5 − 5.8 −4.1
Figure 3. Distribution function for normalised uplink output power (MNRP) for 3G VoCS and 3G VoIP (dB).
MNRP for 3G VoCS and 3G VoIP in an urban environment.
Average SD Median 90th percentile
3G VoCS (%)
3G VoIP (%)
0.22 0.75 0.02 0.43
0.75 2.53 0.07 1.87
VoCS or in 3G VoIP calls. The average Indoor and Outdoor 3G VoCS/3G VoIP MNRP ratios are very close. The average in-car MNRPs are somewhere between the indoor and outdoor ones, irrespective of whether the calls are in 3G VoCS or in 3G VoIP. In Table 3, the average MNRP, the SD, the median and the 90th percentile are shown for these calls. Globally, the MNRP in a 3G VoCS call is 0.22%, whereas the MNRP in a 3G VoIP call is 0.75%. This gives an average ratio of − 5.3 dB between a 3G VoIP call and a 3G VoCS call. On a linear scale, this corresponds to a ratio of 1:3.4. It is to be noted that only 10% of all the calls made had an MNRP higher than 0.43% and 1.87% in 3G VoCS and 3G VoIP, respectively. Figure 3 shows the distribution function of the 220 readings. It is observed that 94% to 98% of the MNRPs are between − 50 and − 10 dB referred to Pmax. Shown in Figure 4 is the cumulative distribution function of 3G VoCS and 3G VoIP voice calls. It is to be noted that the value on the far right corresponds to Pmax (0 dB). It is observed that for 10% of the voice calls the highest power level is below − 45 dB (referred to Pmax) and, at the other end of the scale, that 10% of the voice calls have power levels exceeding − 24 dB (referred to Pmax). Shown in Figure 5 is the cumulative distribution function for the highest normalised power reached in each call. It is to be noted that the value on the far right corresponds to Pmax (0 dB). It is observed that 84.5% of 3G VoCS calls and 69% of 3G VoIP calls never reach the maximum power (Pmax) of the smartphone. It is also to be noted that 10% of these calls never exceed − 28 dB referred to Pmax in 3G VoCS, and − 22 dB in 3G VoIP. Among the 110 3G VoCS and the 110 3G VoIP calls lasting 2 min each, the radiated power exceeds on average 50% of maximum power (i.e. Pmax/2) only during 40 ms and 231 ms, respectively, which is a very short time. The results show a global trend, leading us to assert, first of all, that the mean power in a 3G VoIP call is very low, and second, that it is slightly higher than in a 3G VoCS call. In order to verify whether the trend is statistic or systematic, the 3G VoCS/3G VoIP MNRP ratio was assessed for each couple. Figure 6 shows the CDF of the ratio. Journal of Exposure Science and Environmental Epidemiology (2015), 80 – 83
Figure 4. Cumulative distribution function for normalised uplink output power (MNRP) for 3G VoCS and 3G VoIP (dB).
Figure 5. Cumulative distribution function for the highest normalised power reached in each call (dB).
It is noticed that 92% of the couples show a ratio of o 0 dB between the 3G VoCS calls and the 3G VoIP calls, as indicated in Figure 6. Among the nine couples that show a ratio of over 0 dB, five correspond to readings taken in a car. In these conditions, the 3G VoCS and 3G VoIP calls did not occur in the same place, which produces unreliable results. Only the remaining four cases appear to correspond to a real inversion, which is very few. DISCUSSION With regard to the analysis by places, it is observed that the weakest MNRP was found in the railway stations (three stations covered by microcells), with extremely low values of o0.04%. This is followed by the “street” with a value of o 0.1%, evidencing the good coverage by the operator due to a high number of base stations. In indoor, the highest values are found in cafés/ restaurants where coverage is assured by the base stations outside. The in-car MNRPs are somewhere between the indoor and outdoor ones, irrespective of whether the calls are in 3G VoCS © 2015 Nature America, Inc.
Radiated power: 3G VoIP vs VoCS Jovanovic et al
83
Figure 6. Cumulative distribution function for VoCS/VoIP uplink output power ratio for the 110 couples (dB).
or in 3G VoIP. In terms of the 3G VoCS/3G VoIP MNRP ratio, the weakest ratio is observed in streets and parks. The ratio inside offices is the only one that really differs from other places. This is probably due to the fact that the two offices studied have a dedicated indoor coverage by microcells, so these are not representative of such places. It is likely that in offices without indoor coverage the ratio would be closer to that found in cafés/ restaurants. Finally, the average ratios for indoor, outdoor and incar are more or less the same. With regard to the global statistic analysis, taken as a whole, the MNRPs of telephones during 3G VoCS and 3G VoIP calls are of the same magnitude, that is, very weak, and on average, o 0.75% of Pmax. In UMTS technology, the theoretic maximum power (Pmax) is 24 dBm (250 mW), which allows transforming the MNRPs into absolute power values in order to compare them with the results of other studies. Upon using telephones on a 3G network at 2100 MHz in Paris (France) and its suburbs, linked to a computer running specific software, Gati et al.7 determined the mean power radiated by the telephone. For a 3G VoCS call, their study determined that the mean power in an urban environment is 0.2 mW outdoors and 1.7 mW indoors, which is identical to the results obtained with the SYRPOM (0.2 mW and 1.07 mW). Likewise, Gati et al.7 concluded there is a gap of 6 dB in mean radiated power between the most commonly used data service and the voice service, which is also in accordance with our results (5.3 dB). Finally, Persson et al.10 gathered up during 1 week the output powers of 3G telephones recorded by six different Radio Network Controllers on the TeliaSonera network. Readings were collected from a total of 800,000 hours of voice calls and different data services. The mean power observed for 3G VoCS in urban environments was 0.4 mW, close to the results of our own measuring campaign (0.55 mW), as were the median and the 90th percentile. Likewise, Persson et al.10 found the mean power during a data transfer to be between 1.3 and 1.7 mW, which is also in line with our results (1.9 mW). A ratio of 5–6 dB was observed between a voice call and a data transfer, matching our own results (5.3 dB). In the framework of these readings, only 10% of all the calls made, gave off an output power of more than 1.1 mW in VoCS and 4.7 mW in 3G VoIP. CONCLUSION Numerous readings were taken in a wide range of situations and places, allowing us to obtain a reliable statistic assessment of the
© 2015 Nature America, Inc.
mean radiated power of the telephone in 3G. In this study, intended to compare 3G VoIP and 3G VoCS voice calls made with the telephone held against the ear, the mean radiated power during 3G VoCS calls was assessed at 0.55 mW (i.e., ~ 0.22% Pmax) and the mean radiated power during 3G VoIP calls was assessed at 1.9 mW (i.e., ~ 0.75% Pmax). In 3G, there is on average a ratio of 1:3 between the mean radiated power in VoIP and that in VoCS, in a global sense, but likewise in a nearly systematic way irrespective of the place where the calls occur. Using the entire dynamic range, along with very efficient power control, the 3G technology makes it possible to achieve extremely weak radiated power levels. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR. A complementary study on LTE (4G) technology is currently being drawn up. CONFLICT OF INTEREST The authors declare no conflict of interest.
ACKNOWLEDGEMENTS This research is sponsored by Bouygues Telecom.
REFERENCES 1 Wiart J, Dale C, Bosisio AV, Le Cornec A. Analysis of the influence of the power control and discontinuous transmission on RF exposure with GSM mobile phones. IEEE Trans Electromagn Compat 2000: 62: 376–385. 2 Lönn S, Forssen U, Vecchia P, Ahlbom A, Feychting M. Output power levels from mobile phones in different geographical areas; implications for exposure assessment. Occup Environ Med 2004: 61: 769–772. 3 Hillert L, Ahlbom A, Neasham D, Feychting M, Jarüp L, Navin R et al. Call-related factors influencing output power from mobile phones. J Expo Anal Environ Epidemiol 2006; 16: 507–514. 4 Morrissey JJ. Radio frequency exposure in mobile phones users: Implications for exposure assessment in epidemiological studies. Radiat Prot Dosimetry 2007: 123: 490–497. 5 Erdreich LS, Van Kerkove MD, Scrafford C, Barraj L, McNeely M, Shum M et al. Factors that influence RF power output of GSM mobile phones. Radiat Research 2007: 168: 253–261. 6 Vrijheid M, Mann S, Vecchia P, Wiart J, Taki M, Ardoino L et al. Determinants of mobile phone output power in a multinational study: implications for exposure assessment. Occup Environ Med 2009: 66: 664–671. 7 Gati A, Hadjem A, Wong M-F, Wiart J. Exposure induced by WCDMA mobiles phones in operating networks. IEEE Trans Wireless Commun 2009: 8: 5723–5727. 8 Gati A, Conil E, Wong M, Wiart J. Duality between uplink local and downlink whole-body exposures in operating networks. IEEE Trans Electromagn Compat 2010: 52: 829–836. 9 Kelsh MA, Shum M, Sheppard AR, McNeely M, Kuster N, Lau E et al. Measured radiofrequency exposure during various mobile-phone use scenarios. Journal of Exp Science and Environ Epidemio 2011: 21: 343–354. 10 Persson T, Törnevik C, Larsson L-E, Lovén J. Output power distributions of terminals in a 3G mobile communication network. Bioelectromagnetics 2012: 33: 320–325. 11 Picard D, Fouquet L, Chauvin S. Assessment of real exposure to gsm mobile telephones using the syrpom. Radiat Prot Dosimetry 2013: 157: 22–35. 12 Kühn S, Kuster N. Field Evaluation of the Human exposure from multiband, multisystem mobile phones. IEEE Trans Electromagn Compat 2013: 55: 275–287. 13 Picard D, Jovanovic D, Fouquet L, Chauvin S. A new high performances sarmeter [poster]. BEMS 2012.
Journal of Exposure Science and Environmental Epidemiology (2015), 80 – 83
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ORIGINAL ARTICLE
Mobile telephones: A comparison of radiated power between 3G VoIP calls and 3G VoCS calls Dragan Jovanovic1, Guillaume Bragard1, Dominique Picard2 and Sébastien Chauvin1 The purpose of this study is to assess the mean RF power radiated by mobile telephones during voice calls in 3G VoIP (Voice over Internet Protocol) using an application well known to mobile Internet users, and to compare it with the mean power radiated during voice calls in 3G VoCS (Voice over Circuit Switch) on a traditional network. Knowing that the specific absorption rate (SAR) is proportional to the mean radiated power, the user's exposure could be clearly identified at the same time. Three 3G (High Speed Packet Access) smartphones from three different manufacturers, all dual-band for GSM (900 MHz, 1800 MHz) and dual-band for UMTS (900 MHz, 1950 MHz), were used between 28 July and 04 August 2011 in Paris (France) to make 220 two-minute calls on a mobile telephone network with national coverage. The places where the calls were made were selected in such a way as to describe the whole range of usage situations of the mobile telephone. The measuring equipment, called “SYRPOM”, recorded the radiation power levels and the frequency bands used during the calls with a sampling rate of 20,000 per second. In the framework of this study, the mean normalised power radiated by a telephone in 3G VoIP calls was evaluated at 0.75% maximum power of the smartphone, compared with 0.22% in 3G VoCS calls. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR. Journal of Exposure Science and Environmental Epidemiology (2015) 25, 80–83; doi:10.1038/jes.2014.74; published online 5 November 2014
INTRODUCTION The arrival of 3G networks has enabled considerable advances in mobile communication services, allowing them to progress from just a few kbps in 2G to several dozen Mbps in 3G/HSPA (High Speed Packet Access). Like their forerunners, 3G networks offer voice calls in VoCS mode (Voice over Circuit Switch). The 3G VoCS is characterised by “circuit routing” in the core network and by the use of a dedicated radio channel called R99 (Release 99). It is increasingly frequent for the 3G networks to route voice calls in VoIP mode (Voice over Internet Protocol), the use of which has become widespread due to numerous mobile applications. The 3G VoIP is characterised by “packet routing” in the core network and by the use of a shared radio channel (HSPA) initially meant for the data service (with a speed clearly superior to R99). Research studies have been carried out over recent years to measure the radio-frequency power radiated by 2G and/or 3G mobile telephones in order to assess the real exposure of users.1–12 Radiated power, which can vary in a dynamic range of 70 dB, is the parameter that has the greatest influence on exposure. For voice calls in 3G, the modes studied so far are VoCS on R99, and VoIP calls embedded in other uses such as web-browsing, downloading, so on.7,10 All mobile telephones commercialised in the European market must respect the specific absorption rate (SAR) limit of 2 W/kg averaged over 10 g of tissue (1.6 W/kg over 1 g for the United States). As the SAR is proportional to the radiated power, measuring this radiated power provides an assessment of the reduction of the SAR, and hence the exposure associated with this parameter. The purpose of this study is to compare, in real usage situations, the power radiated by a mobile telephone in 3G
VoIP (HSPA) voice calls to that radiated in 3G VoCS (R99) voice calls, in order to evaluate the different user exposure levels. We are presenting, successively, the results on the mean power values detailed by places, then globally and then finally, the results regarding the highest power encountered during each individual call. MATERIALS AND METHODS The device used for measuring the RF power (Pe) radiated by the telephone is called “SYRPOM”. A view of the system as a whole is shown in Figure 1. It comprises a probe consisting of a resistor-loaded dipole, processing electronics and a micro-computer which controls the system, processes and records the data and displays the results. The processing electronics consist, essentially, of an amplitude-sensitive receiver which detects and records the three European frequency bands, that is, GSM900 and UMTS900 (880–915 MHz), DCS1800 (1710–1785 MHz) and UMTS2100 (1920–1980 MHz). This frequency selectivity enables identification of the frequency band in which the transmission takes place. The links between the different parts of the SYRPOM are hardwired, thus avoiding the pick up of unwanted radio-frequency radiation. The probe is placed behind the telephone close to the aerial. It is electro-magnetically coupled to the telephone’s aerial; this coupling is constant over time. Thus, the output power of the probe is proportional to the radiation power of the telephone. The probe interferes very little with the signal radiated by the telephone and its presence does not modify the latter's operation.11 Following a first version developed to study the radiation from GSM mobile telephones, a new version of the SYRPOM has been devised for 3G telephony. The study of a telephone in 3G mode requires a prior calibration phase to be carried out in the laboratory on the mobile driven by a base station emulator, to determine the reception level of the
1 Direction Fréquences et Protection (Frequencies and Protection Division), Bouygues Telecom, Issy-les-Moulineaux, France and 2Département Electromagnétisme (Electromagnetics Department), DRE, Supélec, Gif-sur-Yvette, France. Correspondence: D Jovanovic, Direction Fréquences et Protection (Frequencies and Protection Division), Bouygues Telecom, 82 rue Henry Farman, 92130 Issy-les-Moulineaux, France. Tel.: +331 394 53067. Fax: +331 392 66468. E-mail: [email protected] Received 17 March 2014; revised 1 September 2014; accepted 3 September 2014; published online 5 November 2014
Radiated power: 3G VoIP vs VoCS Jovanovic et al
81
Figure 1.
SYRPOM measurement system.
SYRPOM corresponding to a radiation at maximum power (Pmax) of each band. The SYRPOM therefore can calculate the mean normalised radiated power (Pe/Pmax; hereinafter MNRP) of the UMTS frames, which it identifies by discarding the GSM frames, if any. The SYRPOM has a dynamic range of around 80 dB (i.e., a factor of 1:100,000,000 in power), making it easy to measure the complete set of levels encountered in 3 G.13 The SYRPOM is independent from the network and from the mobile telephone, which is not so when using other systems, for example, systems based on analysis of data provided by a network supervisor software,2,3,8,10 or using test mobile telephones1 or software-modified telephones.4–6,9 The system carries out the tests on a real user; it is lightweight and portable, so tests can be carried out in all possible situations, in particular in the case of a user on foot. This would be impossible, for example, with a SYNEHA2 type system.12 Bearing in mind the principle, it is compatible with all mobile telephones, whatever their type (Figure 2). A measuring campaign was carried out. In order to simulate genuine usage situations, real voice calls were made to a voice server (telephone line with automatic answering). The telephone, equipped with a SIM card issued by a French operator and associated with a general public mobile telephone plan, provided access to the 3G network and, if unavailable, to the 2G network. The telephone was hand-held by the technician close to his head. For reasons of repeatability and comfort of the technician, a medium-speed speech (recorded on the PC) was played back over a small speaker close to the mobile telephone's microphone throughout the call. The mobile telephone was also charged regularly and its good performance was also checked. The places where the readings were taken were selected in such a way as to cover the whole range of usage situations of the mobile telephone: Offices, cafes/restaurants, public spaces (parks, railway stations and tourist venues), shops, on the street and in cars. Thus, the technician’s position depended on these kinds of use: Sitting; walking quickly or slowly, travelling in a vehicle. All the readings were taken in Paris (France) or its surroundings between 08:00 and 20:00 hours. The calls lasted 2 min and took place between 28 July and 04 August 2011. Three 3G smartphones (HSPA) from three different manufacturers (available in the European market since 2010), two-band for GSM900 and DCS1800 and two-band for UMTS900 and UMTS2100, were used successively without pause, and with no delay between the 3G VoCS call and the 3G VoIP call of each telephone. Kühn et al.12 meanwhile, have shown that the mean radiated power of a 3G telephone in an urban area varied slightly from one telephony operator to another (2.7 dB peak-to-peak between three different operators). Our study will therefore be focused on the network of a single operator as is the case of most studies. Our study will consider, successively, the following three points: ●
●
●
To study the effect of places on the MNRP, the latter is calculated for each call, along with the ratios between the MNRPs in 3G VoCS and in 3G VoIP. Statistics are drawn up on the full set of MNRP values. They consist of assessing the average MNRP, the SD, the median and the 90th percentile. Some of the results are compared with those obtained by Gati et al.7 and Persson et al.10 Finally, we study the highest power attained for each call, as well as the length of time during which the power exceeded 50% of maximum power.
© 2015 Nature America, Inc.
Figure 2.
Table 1.
SYRPOM measurement system in real conditions.
List of places and number of readings.
Places indoor
No. meas
Places outdoor
No. meas
Office
10
18
Cafe, restaurant Commercial centre Railway station Total indoor
26 20
Outdoor (parking, courtyard, etc.) Park Street
54 46
18 74
Total outdoor
118
Places in-car
No. meas
Transport 28 (car)
Total in-car
28
On a total of 135 couples of calls (3G VoCS and 3G VoIP), we have excluded those which lasted o50% of the time in 3G: this leaves us with a total of 110 couples.
RESULTS The MNRP was assessed for the voice calls in 3G VoCS and 3G VoIP taking place together in different places (Table 1). Table 2 presents the MNRP values and the 3G VoCS/3G VoIP MNRP ratios for these calls. They are divided into three categories: indoor, outdoor and in-car. It is observed that in 3G VoCS the MNRP values range from 0.01% to 0.71% and in 3G VoIP from 0.04% to 2.57%. The 3G VoCS/ 3G VoIP MNRP ratio is always negative and its value is limited to the interval from − 2.5 dB to − 7.9 dB, except for offices (dedicated network with microcells to ensure good coverage) for which the MNRPs are particularly weak with a ratio of − 13.1 dB. It is also observed that the average indoor MNRPs are around five times higher (+7 dB) than the average outdoor MNRPs, whether in 3G Journal of Exposure Science and Environmental Epidemiology (2015), 80 – 83
Radiated power: 3G VoIP vs VoCS Jovanovic et al
82 Table 2.
MNRP by places for 3G VoCS and 3G VoIP. Number of readings
Office Café, restaurant Commercial centre Railway station Total indoor Outdoor (parking, courtyard, etc.) Park Street Total outdoor Total in-car
Table 3.
3G VoCS 3G VoIP (%) (%)
3G VoCS/3G VoIP MNRP ratio (dB)
10 26 20 18 74 18
0.01 0.67 0.71 0.01 0.43 0.23
0.13 2.57 2.19 0.04 1.52 1.39
− 13.1 − 5.8 − 4.9 − 6.2 − 5.5 − 7.9
54 46 118 28
0.06 0.05 0.08 0.20
0.13 0.10 0.31 0.52
− 3.6 − 2.5 − 5.8 −4.1
Figure 3. Distribution function for normalised uplink output power (MNRP) for 3G VoCS and 3G VoIP (dB).
MNRP for 3G VoCS and 3G VoIP in an urban environment.
Average SD Median 90th percentile
3G VoCS (%)
3G VoIP (%)
0.22 0.75 0.02 0.43
0.75 2.53 0.07 1.87
VoCS or in 3G VoIP calls. The average Indoor and Outdoor 3G VoCS/3G VoIP MNRP ratios are very close. The average in-car MNRPs are somewhere between the indoor and outdoor ones, irrespective of whether the calls are in 3G VoCS or in 3G VoIP. In Table 3, the average MNRP, the SD, the median and the 90th percentile are shown for these calls. Globally, the MNRP in a 3G VoCS call is 0.22%, whereas the MNRP in a 3G VoIP call is 0.75%. This gives an average ratio of − 5.3 dB between a 3G VoIP call and a 3G VoCS call. On a linear scale, this corresponds to a ratio of 1:3.4. It is to be noted that only 10% of all the calls made had an MNRP higher than 0.43% and 1.87% in 3G VoCS and 3G VoIP, respectively. Figure 3 shows the distribution function of the 220 readings. It is observed that 94% to 98% of the MNRPs are between − 50 and − 10 dB referred to Pmax. Shown in Figure 4 is the cumulative distribution function of 3G VoCS and 3G VoIP voice calls. It is to be noted that the value on the far right corresponds to Pmax (0 dB). It is observed that for 10% of the voice calls the highest power level is below − 45 dB (referred to Pmax) and, at the other end of the scale, that 10% of the voice calls have power levels exceeding − 24 dB (referred to Pmax). Shown in Figure 5 is the cumulative distribution function for the highest normalised power reached in each call. It is to be noted that the value on the far right corresponds to Pmax (0 dB). It is observed that 84.5% of 3G VoCS calls and 69% of 3G VoIP calls never reach the maximum power (Pmax) of the smartphone. It is also to be noted that 10% of these calls never exceed − 28 dB referred to Pmax in 3G VoCS, and − 22 dB in 3G VoIP. Among the 110 3G VoCS and the 110 3G VoIP calls lasting 2 min each, the radiated power exceeds on average 50% of maximum power (i.e. Pmax/2) only during 40 ms and 231 ms, respectively, which is a very short time. The results show a global trend, leading us to assert, first of all, that the mean power in a 3G VoIP call is very low, and second, that it is slightly higher than in a 3G VoCS call. In order to verify whether the trend is statistic or systematic, the 3G VoCS/3G VoIP MNRP ratio was assessed for each couple. Figure 6 shows the CDF of the ratio. Journal of Exposure Science and Environmental Epidemiology (2015), 80 – 83
Figure 4. Cumulative distribution function for normalised uplink output power (MNRP) for 3G VoCS and 3G VoIP (dB).
Figure 5. Cumulative distribution function for the highest normalised power reached in each call (dB).
It is noticed that 92% of the couples show a ratio of o 0 dB between the 3G VoCS calls and the 3G VoIP calls, as indicated in Figure 6. Among the nine couples that show a ratio of over 0 dB, five correspond to readings taken in a car. In these conditions, the 3G VoCS and 3G VoIP calls did not occur in the same place, which produces unreliable results. Only the remaining four cases appear to correspond to a real inversion, which is very few. DISCUSSION With regard to the analysis by places, it is observed that the weakest MNRP was found in the railway stations (three stations covered by microcells), with extremely low values of o0.04%. This is followed by the “street” with a value of o 0.1%, evidencing the good coverage by the operator due to a high number of base stations. In indoor, the highest values are found in cafés/ restaurants where coverage is assured by the base stations outside. The in-car MNRPs are somewhere between the indoor and outdoor ones, irrespective of whether the calls are in 3G VoCS © 2015 Nature America, Inc.
Radiated power: 3G VoIP vs VoCS Jovanovic et al
83
Figure 6. Cumulative distribution function for VoCS/VoIP uplink output power ratio for the 110 couples (dB).
or in 3G VoIP. In terms of the 3G VoCS/3G VoIP MNRP ratio, the weakest ratio is observed in streets and parks. The ratio inside offices is the only one that really differs from other places. This is probably due to the fact that the two offices studied have a dedicated indoor coverage by microcells, so these are not representative of such places. It is likely that in offices without indoor coverage the ratio would be closer to that found in cafés/ restaurants. Finally, the average ratios for indoor, outdoor and incar are more or less the same. With regard to the global statistic analysis, taken as a whole, the MNRPs of telephones during 3G VoCS and 3G VoIP calls are of the same magnitude, that is, very weak, and on average, o 0.75% of Pmax. In UMTS technology, the theoretic maximum power (Pmax) is 24 dBm (250 mW), which allows transforming the MNRPs into absolute power values in order to compare them with the results of other studies. Upon using telephones on a 3G network at 2100 MHz in Paris (France) and its suburbs, linked to a computer running specific software, Gati et al.7 determined the mean power radiated by the telephone. For a 3G VoCS call, their study determined that the mean power in an urban environment is 0.2 mW outdoors and 1.7 mW indoors, which is identical to the results obtained with the SYRPOM (0.2 mW and 1.07 mW). Likewise, Gati et al.7 concluded there is a gap of 6 dB in mean radiated power between the most commonly used data service and the voice service, which is also in accordance with our results (5.3 dB). Finally, Persson et al.10 gathered up during 1 week the output powers of 3G telephones recorded by six different Radio Network Controllers on the TeliaSonera network. Readings were collected from a total of 800,000 hours of voice calls and different data services. The mean power observed for 3G VoCS in urban environments was 0.4 mW, close to the results of our own measuring campaign (0.55 mW), as were the median and the 90th percentile. Likewise, Persson et al.10 found the mean power during a data transfer to be between 1.3 and 1.7 mW, which is also in line with our results (1.9 mW). A ratio of 5–6 dB was observed between a voice call and a data transfer, matching our own results (5.3 dB). In the framework of these readings, only 10% of all the calls made, gave off an output power of more than 1.1 mW in VoCS and 4.7 mW in 3G VoIP. CONCLUSION Numerous readings were taken in a wide range of situations and places, allowing us to obtain a reliable statistic assessment of the
© 2015 Nature America, Inc.
mean radiated power of the telephone in 3G. In this study, intended to compare 3G VoIP and 3G VoCS voice calls made with the telephone held against the ear, the mean radiated power during 3G VoCS calls was assessed at 0.55 mW (i.e., ~ 0.22% Pmax) and the mean radiated power during 3G VoIP calls was assessed at 1.9 mW (i.e., ~ 0.75% Pmax). In 3G, there is on average a ratio of 1:3 between the mean radiated power in VoIP and that in VoCS, in a global sense, but likewise in a nearly systematic way irrespective of the place where the calls occur. Using the entire dynamic range, along with very efficient power control, the 3G technology makes it possible to achieve extremely weak radiated power levels. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR. A complementary study on LTE (4G) technology is currently being drawn up. CONFLICT OF INTEREST The authors declare no conflict of interest.
ACKNOWLEDGEMENTS This research is sponsored by Bouygues Telecom.
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Journal of Exposure Science and Environmental Epidemiology (2015), 80 – 83
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