SpectrumManagement and Telecommunications
The followingIndustry Canada employees helped perform the measurement work described in thisdocument.
Joe Doria, P.Eng.
Senior EMC/EMI and BioelectromagneticsEngineer
Vicky Lai, P.Eng.
Regional Engineer –Operations
Regional Engineer -Operations
Hughes Nappert, P.Eng.
TelecommunicationsTest and Measurement Technologist
Enquiries related to this reportmay be sent to the following address:
Engineering, Planning andStandards Branch
300 Slater Street
Ottawa, Ontario K1A 0C8
- Executive Summary
- 1.0 Introduction
- 2.0 Materials and Methods
- 3.0 Measurement Results
- 4.0 Discussion
- 5.0 Conclusion
- Annex A – Wi-Fi Standards, Spectral Allocations and Emissions
- Annex B – Near-Field and Far-Field Zones
- Annex C – Uncertainty due to Measurement Equipment
- Annex D – Health Canada's Safety Code 6 Limits for Uncontrolled Environment
- Annex E – Detailed Measurement Results
Radiocommunication, including the technicalaspects related to broadcasting, falls under the responsibility of Industry Canada, which has the power to establish standards, rules, policies and procedures. Underthis authority, the Department has adopted Health Canada's Safety Code 6 (SC6) guidelinefor the purpose of protecting the general public from radio frequency(RF) overexposure.
As part of its ongoing monitoring ofwireless devices for compliance with regulatory specifications, Industry Canada conducted an extensive series of tests to measure RF exposure from the use of Wi-Fidevices in a simulated classroom setting. This study, performed in late 2011,confirms that the level of RF exposure is considerably below the SC6 limits foruncontrolled environments. The wireless devices that were studied operate athigher power than most Wi-Fi devices currently available in Canada.
The measurements were based on 24 laptopsand two wireless access points, or routers, used in a situation designed as aworst-case scenario, which involved downloads of a very large file, such as a videofile, as well as the use of interactive applications among several computers,as would be found in a school setting.
Measurements were taken at several pointsin the room and at various distances from the Wi-Fi access points, including thosewhere higher levels of RF exposure are typically reported. All measurements ofRF exposure were well below the SC6 limits for uncontrolled environments.
Many consumers, businesses, and public andprivate institutions (such as schools, hospitals and libraries) install Wi-Fi accesspoints on their premises. These Wi-Fi access points typically consist of one ormore low-power transmitters installed at ceiling level or on tabletops, which areused by individuals to gain Internet access through standard Wi-Fi-enableddevices, such as laptops. To address the recent public concerns related to theproliferation of Wi-Fi technology, Industry Canada staff performed measurementsof radio frequency (RF) field measurements in an Industry Canada boardroomlocated in Aurora, Ontario. The boardroom contained two Wi-Fi access points and24 Wi-Fi-enabled devices (laptops). The goal of this study was to obtain measurementsof the levels of aggregated RF exposure from multiple Wi-Fi access pointsand Wi-Fi-enabled devices in an indoor environment.
Health Canada's Safety Code 6 (SC6) specifies maximum exposure limits for RF fields in uncontrolledand controlled environments.1
Industry Canada has adopted Health Canada's guideline for the purpose of protecting the general public from RFoverexposure. All installations and apparatus must comply with the SC6 limitsfor uncontrolled environments. Themaximum exposure limit of SC6 is expressed in terms of field strength (voltsper metre, or V/m, and amperes per metre, or A/m) or power density (watts persquare metre, or W/m2). This document presents the results moresimply as percentage of SC6 limits for uncontrolled environments.
In accordance with the requirements for spatial and time averaging set forth by Industry Canada, the RF exposure level was measured at 0.19% of the SC6 limits (515 times below the limit).This value includes the measurement equipment uncertainty. In this scenario, thetwo Wi-Fi access points were operational with the 24 Wi-Fi-enabled devicesdownloading a large file simultaneously. This measurement was carried out atthe location found to exhibit the highest RF exposure level during the initialscanning of the boardroom.
For these measurements, the Wi-Fi accesspoint 1 (AP1) was in a test mode that forced it to transmit continuously, whilethe Wi-Fi access point 2 (AP2) was in normal communication with all 24 laptops,which were all in downloading mode. With one of the Wi-Fi access points set totransmit continuously while test software was used, the measured RF levels werehigher than they would be for the same device in normal operating mode.
Measurementswere also conducted at one location with the laptops in different uploading ordownloading modes, or both, to determine the variations in RF exposure levels. Forthese measurements, the laptops were connected to Wi-Fi AP2, operating at 2437MHz. The highest average RF level obtained from among four different uploadingand/or downloading configurations occurred when a single laptop was indownloading mode, as opposed to numerous laptops in uploading mode, downloadingmode, or both.
At 20 cm from the Wi-Fi access points, themaximum instantaneous RF exposure levels obtained for Wi-Fi AP1 and Wi-Fi AP2 were10.59% and 7.73% of the SC6 limits, respectively. For a typical scenario inwhich a person is located at several metres from the access point andsurrounded by other users, the RF exposure level will be thousands of timesbelow the SC6 limits.
Industry Canada found that the aggregatedRF exposure levels are well below the SC6 limits at this indoor location. Inaddition, the Wi-Fi access points selected for this study were operating athigher power compared with most of the Wi-Fi devices currently available on theCanadian market. Therefore, the results of this study are likely higher than wouldtypically be observed in equivalent setups in public and private environments.
Wi-Fi is a trademark of the Wi-Fi Alliance. Manufacturers may use the term "Wi-Fi" to brand certified products that belong to a class of wireless local area network (WLAN) devices based on IEEE 802.11 standards. Because of the close relationship with its underlying standards, the term "Wi-Fi" is often used as a synonym for IEEE 802.11 technology (see Annex A).
Under Industry Canada's regulations, Wi-Fi devicesare licence-exempt if they meet the technical certification requirements of bothRSS-210, Licence-exempt Radio Apparatus (All Frequency Bands): Category IEquipment,4which includes specifications for power levels, and RSS-102, RadioFrequency (RF) Exposure Compliance of Radiocommunication Apparatus (AllFrequency Bands),5 which includes Health Canada's Safety Code 6 (SC6)6 limits for RF exposure (seeAnnex D of this document). An RF exposure evaluation7 must be performed on Wi-Fiaccess points.8As part of the certification requirements outlined in RSS-102, a specificabsorption rate (SAR) evaluation9must be performed on Wi-Fi-enabled devices, such as laptops that containthe Wi-Fi client cards. Under the requirements of RSS-102, the manufacturer isalso responsible for providing proper instruction to users of wireless devicesand for informing users of any usage restrictions to ensure compliance with theSC6 limits.
In Canada, Wi-Fi systems may operate at 2400-2483.5 MHz (RSS-210, Annex 8),5150-5350 MHz (RSS-210, Annex 9), 5470-5825 MHz (RSS-210, Annex 9) and5725-5875 MHz (RSS-210, Annex 8), using either 20- or 40-MHz channels. Wi-Fidevices may operate at different power levels, depending on the band andoperating characteristics. Based on the technical requirements of RSS-210, themaximum conducted power (into the antenna) and maximum equivalent isotropicallyradiated power (e.i.r.p.) must not exceed 1 watt and 4 watts, respectively.However, the majority of Wi-Fi devices currently on the Canadian market operateat lower power (e.g. <1 W e.i.r.p.).
Many consumers, businesses, and public andprivate institutions install Wi-Fi access points on their premises. These accesspoints typically consist of one or more low-power transmitters installed atceiling level or on tabletops, which are used by individuals to gain Internetaccess through standard Wi-Fi-enabled-devices, such as laptops.
Given the recent public concerns related tothe proliferation of Wi-Fi technology, the goal of this case study was toobtain RF exposure levels from multiple access points and Wi-Fi-enabled devicesin an indoor environment, and to assess compliance with the SC6 limits. However,the testing of all possible configurations under which these devices aredeployed would not be possible. Therefore, specific scenarios were tested todetermine the levels of aggregated RF exposure within an indoor environment.
Table 1 lists the equipment for RFmeasurement that was used during the Wi-Fi measurement case study, includingthe equipment used during the laboratory testing for radiated emission levels.
|Equipment/auxiliary devices||Model||Manufacturer||Serial No.||Calibration date||Calibration due date|
|Selective Radiation Meter||SRM 3006||Narda||D0154||2011-01-31||2013-01-31|
|RF-Cable SRM, 9 kHz to 6 GHz, N 50 ohm, 5 m||3602/02||Narda||AA-0096||2011-01-28||2013-01-28|
|Three-Axis E-field Antenna, 50 MHz to 3 GHz||3501/02||Narda||H-0350||2011-02-28||2013-02-28|
|Three-Axis E-field Antenna, 420 MHz to 6 GHz||3502/01||Narda||B-0137||2011-01-28||2013-01-28|
|Spectrum Analyzer||FSL||Rohde & Schwarz||101098||2011-02-01||2012-02-01|
|RF Chamber Cable||NA||Huber & Suhner||236469 001||2011-10-17||2012-10-17|
|RF Cable||RD-162||Huber & Suhner||121-42673 001||2011-03-30||2012-03-30|
|RF Cable||RD-101||Huber & Suhner||160561 001||2011-02-01||2012-02-01|
Auxiliary devices, such as non-metallic tripod, measuring tape, digital camera and masking tape, were also used duringthe study.
The Narda SRM 3006 Selective Radiation Meterwas set in the Safety Evaluation mode. It displayed the RF exposure levels as apercentage of the SC6 limits. Between 50 and 70 sweeps10 of approximately 1.2 secondper sweep were performed at each measurement location (except when a time-averagingperiod of 6 minutes was applied).
The Wi-Fi access points and Wi-Fi-enabledlaptops used during this case study can be found in Table 2 and Table 3,respectively.
Wi-Fi access point 1 (AP1) was set totransmit continuously11through the use of the test-mode software. The continuous transmission wasselected to provide a worst-case exposure from this Wi-Fi access point. Theoperating center frequency was set at 5180 MHz (Channel 36). AP1 was installed onthe ceiling with the antenna located at approximately 2.05 metres from thefloor (see Figure 1). The antenna panel used had a directional gain of 7.5 dBi.
Figure 1 – Setup of Wi-Fi access point 1 (5180 MHz) near the ceiling
For Wi-Fi access point 2 (AP2), the devicewas transmitting normally at a center frequency of 2437 MHz (Channel 6). Testsoftware was not available for AP2. Therefore, measurements were not performedin continuous mode for this access point. AP2 was installed on top of a computerdesktop tower at approximately 1.1 metres from the floor (see Figure 2).
Figure 2 – Setup of Wi-Fi access point 2 (2437 MHz) at 1.1 metresfrom the floor
The AP1 and AP2 were each set for a conductedpower level of 24 dBm (251 mW). AP1 had an e.i.r.p. of 30.3 dBm (1.1 W), and AP2had an e.i.r.p. of 33.7 dBm (2.3 W).12
These two access points were specificallychosen because they had slightly higher e.i.r.p. values than most Wi-Fi accesspoints currently on the Canadian market. With Wi-Fi AP1 set to transmitcontinuously, the measured RF levels are higher than when the same device is innormal operating mode.13Therefore, the results of this study are likely higher than would typically beobserved in equivalent setups in public and private environments.
|Access point No.||Wi-Fi band available||IC certification No.||Model|
|1||2/5 GHz||4675A-AP134135||Aruba AP-134|
|2||2/5 GHz||3839A-E3200||Cisco E3200|
|Laptop No.||Wi-Fi band available||IC certification No.||Model|
|1||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|2||2/5 GHz||248H-DPA3489W||Toshiba Tecra S4|
|3||2/5 GHz||248H-DPA3795W||Toshiba Tecra S11|
|4||2 GHz||248H-DPA3362W||Toshiba Portégé M200|
|5||2 GHz||248H-DPA3272W||Toshiba Tecra S1|
|6||2 GHz||248H-DPA3362W||Toshiba Tecra S1|
|7||2 GHz||248H-DPA3272W||Toshiba Tecra S1|
|8||2/5 GHz||248H-DPA3538W||Toshiba Tecra S9|
|9||2/5 GHz||248H-DPA3489W||Toshiba Portégé M700/M710|
|10||2/5 GHz||248H-DPA3489W||Toshiba Portégé M700/M710|
|11||2/5 GHz||248H-DPA3489W||Toshiba Portégé M700/M710|
|12||2/5 GHz||248H-DPA3489W||Toshiba Portégé M700/M710|
|13||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|14||2/5 GHz||248H-DPA3538W||Toshiba Tecra A9|
|15||2/5 GHz||248H-DPA3538W||Toshiba Tecra A9|
|16||2/5 GHz||248H-DPA3538W||Toshiba Tecra A9|
|17||2/5 GHz||248H-DPA3538W||Toshiba Tecra A9|
|18||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|19||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|20||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|21||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|22||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|23||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
|24||2/5 GHz||248H-DPA3375W||Toshiba Tecra S2|
The program NetStumbler14 was installed on a laptop to identifythe Wi-Fi access points in the area. The software provided information on thesignal strength of each Wi-Fi access point. On November 8, 2011, NetStumblerdetected four additional access points. These Wi-Fi access points had signalstrengths that were 45-51 dB lower than the two Wi-Fi access points beingtested. On November 9, 2011, NetStumbler detected seven additionalWi-Fi access points. These Wi-Fi access points had signal strengths that were 33-65dB lower than AP1 and AP2. These additional Wi-Fi access points were alloperating in the 2.4 GHz band.
The measurements were performed on November8-9, 2011, in an Industry Canada office located in Aurora, Ontario (see Figure 3).The temperature within the boardroom was approximately 20oC with lowhumidity.
Figure3 – Aerial view of the measurement location in Aurora, Ontario
The measurement locations within theboardroom are represented in Figure 4, and a photo of the boardroom setup ispresented in Figure 5.
Figure 4 – Schematic of Wi-Fi measurement locations
Figure 5 – Boardroom setup
The measurement methodology was based onIndustry Canada's GL-01, Guidelines for the Measurement of Radio FrequencyFields at Frequencies from 3 kHz to 300 GHz,15
This case study did not include an assessmentof near-field exposure, which requires a laboratory test setup to determine compliancewith the SAR limits outlined in RSS-102. SAR evaluations of Wi-Fi-enableddevices such as laptop computers are conducted as part of the technicalrequirements for certification by independent laboratories, so this assessmentwould already have been performed.
Table 4 and Table 5 present details of the testcases related to the ambient fields and to the Wi-Fi devices in operation,respectively.
|Test case no.||Frequency range||Measurement location||Tri-axis antenna height||Total measurement/scan time||Wi-Fi access points|
|1a||50 MHz to 6 GHz||At each preselected locationa||1.75 m||~1 min||Off|
|2a||50 MHz to 6 GHz||At one location (P11)||1.25 mb||~1 min||Off|
|3a||50 MHz to 6 GHz||At one location (P11)||1.25 m||6 min||Off|
|4a||50 MHz to 6 GHz||At one location (P11)||Nine-point matrix representing a cross-section of the human bodyc||12 sec at each point||Off|
a See Figure 4 for preselected measurement locations.
b The height of 1.25 metres is approximately the height of a person inthe sitting position.
c The nine-point matrix is described in Health Canada's Technical Guide for Interpretation and Compliance Assessment of Health Canada'sRadiofrequency Exposure Guidelines (http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/radio_guide-lignes_direct-eng.php).
|Test case No.||Frequency range||Measurement location||Tri-axis antenna height||Total measurement/ scan time||Wi-Fi-enabled devices||Wi-Fi access points|
|1b||2.4 to 5.825 GHz||At each preselected location||1.75 m||~1 min||All laptops in downloading modea||On|
|2b||2.4 to 5.825 GHz||At each preselected location||1.25 m||~1 min||All laptops in downloading mode||On|
|3b||2.4 to 5.825 GHz||At location with highest RF level from results of 1b and 2b (location P5)||Nine-point matrix representing a cross-section of the human body||6 min for each pointb||All laptops in downloading mode||On|
|4b||2400 to 2483.5 MHz||At 50 cm from location P7, closer to location P8||1.25 m||6 min||8 laptops in uploading mode;c |
16 laptops off
|5b||2400 to 2483.5 MHz||At 50 cm from location P7, closer to location P8||1.25 m||6 min||8 laptops in uploading mode; 16 laptops in downloading mode||On|
|6b||2400 to 2483.5 MHz||At 50 cm from location P7, closer to location P8||1.25 m||6 min||1 laptop in uploading mode; 23 laptops off||On|
|7b||2400 to 2483.5 MHz||At 50 cm from location P7, closer to location P8||1.25 m||6 min||1 laptop in downloading mode; 23 laptops off||On|
|8b||5150 to 5350 MHz||20 cm from AP1||NA||~1 min||All laptops in downloading mode||On|
|9b||2400 to 2483.5 MHz||20 cm from AP2||NA||~1 min||All laptops in downloading mode||On|
a Downloading mode: Wi-Fi-enabled devices are receiving data from aremote network location (from a host server via a Wi-Fi access point).
b For each point in the nine-point matrix, ameasurement of 6 minutes is performed to provide the RF level based on spatialand time averaging.
c Uploading mode: Wi-Fi-enabled devices are sending data to a remotenetwork location (to a host server via a Wi-Fi access point).