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Geneva June FT RD Joe Wiart
Personal Personal RF Exposure AssessmentRF Exposure Assessment
J. Wiart, A. Gati, E larcheveque and M.F Wong,FranceTelecom R&D
Geneva June FT RD Joe Wiart
OutlineOutline
• Specificity of the RF personal exposure assessment
• Personal dosimeter design description • Some measurements using PDM• Conclusion
Geneva June FT RD Joe Wiart
Personal dosimetryPersonal dosimetryStudies have been done to develop protocols and to assess the
compliance to limits at a given location. (e.g. COST 244 bis & COST 281 Short Term Mission; CENELEC & IEC. Working Group; EUREKA BASEXPO and French ADONIS project)
Base Station epidemiological studies require personal RF exposure assessment.
Public information needs also personal RF exposure assessment
The "in situ" measurement systems and protocol have been developed for compliance testing but they are not adapted.
A specific measurement system and approaches were needed
Geneva June FT RD Joe Wiart
traffic variation
0,00
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0,90
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0:00
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Heure
Traf
ic n
orm
alis
é au
max
imum
dB
meters
Anatomy of RF exposureAnatomy of RF exposureThe main parameters influencing the personal exposure are
- Location- Traffic, fading and power variation of signal- Frequency
- Polarization and direction of arrival of incident field
Prior to analyze what should be a personal dosimeter it is of interest to characterize the quantity to assess.
Geneva June FT RD Joe Wiart
Spectrum analysis of General Spectrum analysis of General Public exposurePublic exposure
Using compliance measurement protocols the spectrum of the General Pubic exposure has been analyzed .
Where General Public leaves and works the exposure is mainly linked to FM, TV, cellular network and wireless systems
Geneva June FT RD Joe Wiart
FrequencyFrequency bandsbands of interest for the of interest for the general public personal exposure general public personal exposure
assessment assessment
–FM
–TV
–GSM 900 Tx & Rx
–GSM1800 Tx & Rx
–UMTS Tx & Rx
–WIFI
In case of epi study or public information the exposure assessment can be limited to pre-determine service such as
Geneva June FT RD Joe Wiart
In RF domain the received power is In RF domain the received power is composed of many contributionscomposed of many contributions
At a given location a received signal is composed of many signals affected by reflections or
diffractions and coming from different sources. Therefore these contributions have different
amplitudes, phases and directions.
Locally a narrow band signal is affected by
spatial fading
This is a constraint for in situ exposure assessment but should be considered as an advantage for personal exposure assessment
∑= itotal EEρρ
Geneva June FT RD Joe Wiart
"in situ" measurements "in situ" measurements
Studies have been done* to analyze the accuracy of the mean value of the E field strength
- The fading law cannot be linked to the environment characteristic. The usual way to assess the uncertainty of the estimation versus the number of sample cannot be used.
- The uncertainty linked to the mean value estimation can be linked to a fading severity factor ( standard deviation/mean value).
- The distribution of the fading severity factor can be determine in area such as a town ( eg Paris). Therefore a mean uncertainty vs the number of sample can be estimated ( eg with 3 pt the mean uncertainty is 3 dB)
The minimum uncertainty of " in situ" exposure assessment is about 3 dB
The accuracy of any comparison of in situ exposure is there limited by such uncertainty.
* "Analysis of Electric Field Averaging for In Situ. Radiofrequency Exposure Assessment" Emmanuel Larchevêque, Christian Dale, Man-Faï Wong and Joe Wiart IEEE VT 2005
Geneva June FT RD Joe Wiart
Isotropy and multiIsotropy and multi--sources / multisources / multi--path RF propagationpath RF propagation
E
H
In a frequency band of interest the exposure is induced by
Different antennas
Waves coming from different directions
The isotropy can be seen as a mean isotropy.
Geneva June FT RD Joe Wiart
Direction of arrival of in situ Direction of arrival of in situ contributionscontributions
The direction of arrival is important since they should have an impact on the design ( isotropy) of any "in situ" measurement system
The angles of arrival *(between waves and the horizontal) of contributions are mainly comprise between +40° and -30°
The polarization is mainly vertical (+-20°) in rural area and 40° (+-15°) in urban area
* "Angular Power Distribution and Mean Effective Gain of Mobile Antenna in Different Propagation Environments", K. Kalliola, K. Sulonen, H.Laitinen, O. Kivekäs, J. Krogerus, and P. Vainikainen, IEEE Sept. 2002.
Geneva June FT RD Joe Wiart
Traffic and Time variations of RF Traffic and Time variations of RF exposure: Experimental approachesexposure: Experimental approaches
0 2 4 6 8 10 12 14 16 18 20 220.8
0.9
1
1.1
1.2
1.3
1.4
1.5time variation of FM services normalized to the mean value
FM/M
ean
valu
e
Hours0 2 4 6 8 10 12 14 16 18 20 22
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5time variation of GSM1800 services normalized to the mean value
GS
M18
00/M
ean
valu
e
Hours0 2 4 6 8 10 12 14 16 18 20 22
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5time variation of FM services normalized to the mean value
FM/M
ean
valu
e
Hours0 2 4 6 8 10 12 14 16 18 20 22
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5time variation of GSM1800 services normalized to the mean value
GS
M18
00/M
ean
valu
e
Hours
With GSM cellular
The ratio day / night is limited
night
Afternoon morning
With FM
There is no traffic
Geneva June FT RD Joe Wiart
Theoretical analysis of cellular Theoretical analysis of cellular network traffic influence network traffic influence
The probability to have a saturated network is usually less than 2%
The probability to have all TRX emitted at the same time at fullpower during a significant time is also very small
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1,200:
00
2:30
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7:30
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0
15:0
0
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0
20:0
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22:3
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Time (hours)
perc
enta
ge o
f the
max
imum Traffic
Oupout power with4 TRXOupout power with6 TRXOupout power with8 TRX
Geneva June FT RD Joe Wiart
Spatial DistributionSpatial Distribution
There is a real influence of the location
Geneva June FT RD Joe Wiart
Personal dosimeter design and Personal dosimeter design and exposure characteristics exposure characteristics
The dosimeter has to take advantage of the RF human exposure specificity
– The main variations are linked to the location• Assess the personal exposure = assess the exposure where
the person is sleeping, working, walking….» Mean value?» Exposure distribution?
– The main Frequency of interest are those of FM, TV and wireless
– The main D.o.A are +40° -30° with vertical or Cross polar polarizations
Geneva June FT RD Joe Wiart
The Personal DosimeterThe Personal Dosimeter
Geneva June FT RD Joe Wiart
PPersonalersonal Dosimeter requirementsDosimeter requirements
From previous analysis the objectives of PDM are:
- Record over 24 h the RF exposure coming from main wireless systems and broadcast.
- Avoid interference with the person activity- Have a dynamic of 40 dB and a range [0.05v/m
5 v/m]
with reasonable cost to design and built it
Geneva June FT RD Joe Wiart
Basic Basic technicaltechnical requirementrequirement• Isotropy has to take into account the D.o.A and
polarization of incident wave:– The electronic and power supply ( that will perturb
the isotropy) have to be located to minimize the X-Y isotropy
– The isotropy has be estimated in a statistic way
• Put on a table and the PDM shall be able to perform isotropic measurement of wave having DoA in the X-Y plane
• The PDM has to detect between 0.05 V/m and 5 V/m (@900MHz between ~ ICNIRP/1.000.000: and ICNIRP/100 )
• The PDM has to assess the exposure in FM, TV, GSM and UMTS + TETRA and Wifi
• The PDM has to be able to separate what is coming from handset and what is coming from base station
Z
XY
Geneva June FT RD Joe Wiart
Design of the Personal dosimeter Design of the Personal dosimeter
www.antennessa.com
www.francetelecom.com
In 2001 FT RD and In 2001 FT RD and AntennessaAntennessa decided to decided to Combine their efforts to design and built a Combine their efforts to design and built a personal dosimeterpersonal dosimeter
Geneva June FT RD Joe Wiart
DosimeterDosimeter PrinciplePrinciple
RF board
Power supply
CA
LC
UL
AT
OR
storage
MEASUREMENT
antenna
supe
rvis
or
+ post processing to take into account the type of signal ( e.g pulse in case of handset)
Geneva June FT RD Joe Wiart
Anatomy of the PDM Anatomy of the PDM
RF analysis
Patent: EP-03300264.3
SUPERVISEUR/TRAITEMENT
USB
Analog to Digital
Converter
data storage
TV3FM
TV4&5GSM Tx
GSM Rx
DCS TxDCS Rx
UMTS TxUMTS Rx
Vbatterie
(temperature
power supply
real time clock
RF board power supply
RF board control
RF board
user’s interface
Numerical processing
Antenna(s)
Patent EP-04300371.4
Geneva June FT RD Joe Wiart
Capability of present dosimeterCapability of present dosimeter
Sample from 3 to 255 seconds
Up to 7000 records able to be down loaded in txt as well as Excel format
Few days of autonomy
HMI to help users
Geneva June FT RD Joe Wiart
TechnicalTechnical characteristicscharacteristicsIsotropyIsotropy
• Isotropy • Isotropy X-Y
- Vertical and horizontal fields • Vertical dosimeter
• In other configuration the isotropy is perturbed by the presence of the electronic and power supply but these configuration are not really relevant for the configuration.
• Rejection– In major cases up to -38 dB except special cases:
– Filter design is complex and a rejection should be limited in specific case such as DCS limit band (DCS Rx on UMTS Tx limit bands)
Z
XY
+- 2 dB at 95%
Geneva June FT RD Joe Wiart
Manage Manage thethe Influence Influence ofof thethe body body throughthrough a a statisticalstatistical approachapproach
ϕθϕθϕθϕθ ddpGfEPi
iPWreceived ),(),(),,(∑ ∫∫=
On a table
-50-40
-30-20
-10
01
2
3
4
5
6
7
89
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-50
-40
-30
-20
-10
01
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3
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6
7
89
10
11
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15
16
Body worn
CalibrationFactor 1
CalibrationFactor 2
In each frequency band of interest the total exposure is the sum of different sources and reflections therefore the exposure is often coming from everywhere……
The main question is the calibration: in situ and using comparisons with reference method
Geneva June FT RD Joe Wiart
Example of result: record over 10hExample of result: record over 10h
@ 900 MHz @ 1800 MHz
Geneva June FT RD Joe Wiart
Influence of samplingInfluence of sampling
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
3
3.5
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4.5
5
Time (Hour)
Ele
ctric
fiel
d (V
/m)
Field induced by down link GSM 900 MHz
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
10
20
30
40
50
60
70
80
Exposure (V/m)
Per
cent
age
Exposure distribution with a sample of 5s
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
10
20
30
40
50
60
70
80
Exposure (V/m)
Per
cent
age
Exposure distribution with a sampling of 15s
Non frequent events are affected by the sampling. This frequent events correspond to high exposure during very short time (e.g exposure above 5V/m for one measurement over 7000).
Geneva June FT RD Joe Wiart
Importance of the log bookImportance of the log bookExposure induced by GSM 900 down
0
1
2
3
4
5
0 500 1000 1500
x 3s (300=15min)
V/m GSMrx
Exposure induced by GSM down
0,01
0,1
1
10
0 500 1000 1500
x 3s (300=15min)
V/m GSMrx
Exposure induced by GSM 1800 Down
00,20,40,60,8
11,2
0 300 600 900 1200 1500
x 3s (300=15min)
V/m DCSRx
Linear representation and logarithmic representation
In this case the dosimeter was put close to the body and put on a table every 15 min…
Exposure induced by GSM 1800 Down
0,01
0,1
1
10
0 300 600 900 1200 1500
x 3s (300=15min)
V/m DCSRx
Geneva June FT RD Joe Wiart
ThanksThanks
http://perso.rd.francetelecom.fr/joe.wiart/
"Il faut de l'imagination pour se "Il faut de l'imagination pour se représenter la réalité" représenter la réalité"
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