Full Leng h A icle
Me hodology o de e mining he h eshold dis ance o es ima ing he
main EM exposu e con ibu ion in WLAN
Ma a Fe nández
⇑
, Da id Gue a
Communica ions Enginee ing Depa men , Uni e si y o he Basque Coun y, 48013 Bilbao, Spain
a icle in o
A icle his o y:
Recei ed 26 Oc obe 2020
Re ised 19 Feb ua y 2021
Accep ed 1 May 2021
A ailable online 25 May 2021
Keywo ds:
Elec omagne ic exposu e
Elec omagne ic wa es
WiFi 5 GHz
WLAN
Wi eless Communica ions
abs ac
The loca ion o adia ion sou ces in wi eless ne wo ks is a key ac o o cha ac e ize hei con ibu ion o
elec omagne ic exposu e le els in o de o deploy u u e ne wo ks ha accoun o minimizing elec o-
magne ic ield le els. In ela ion o wi eless local a ea ne wo ks, conside ing ha mobile communica ion
de ices comply wi h he SAR (Speci ic Abso p ion Ra e) limi s imposed by he in e na ional s anda diza-
ion o ganiza ions o p ese ing human heal h, he in e es is nowadays ocused on he signal le els
coming om he WiFi access poin s. This pape p esen s a me hodology o de e mine he h eshold dis-
ance a which he ield s eng h le els om he AP a e negligible in compa ison wi h he adia ion gen-
e a ed by a use equipmen . The heo e ical concep s, which can be applied o o he echnologies, we e
implemen ed by means o simula ions and expe imen al measu emen s. Fo he simula ions, ac ual WiFi
an ennas we e modelled. Expe imen al measu emen s comple ed he esul s ob ained in simula ions,
esul ing in a g ea e numbe o eal si ua ions. Resul s showed ha he h eshold dis ance depends
on he WiFi s anda d employed by he de ices connec ed o he ne wo k.
Ó2021 Ka abuk Uni e si y. Publishing se ices by Else ie B.V. This is an open access a icle unde he CC
BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
1. In oduc ion
The massi e g ow h o mobile in e ne applica ions has aised
conce ns abou human exposu e due o WiFi signals, p esen in
mo e and mo e public and p i a e indoo en i onmen s. These sig-
nals a e de ined acco ding o a amily o s anda ds ha s emmed
om he ini ial IEEE 802.11, published in 1997 [1].
The good knowledge o elec omagne ic (EM) ield exposu e
le els, as well as in o ma ion ega ding he con ibu ion o each
adia ion sou ce o he o al exposu e, is essen ial o wo main
easons: gi e esponse o public conce n, and ensu e people’s p o-
ec ion agains hese emissions bu wi hou educing he echno-
logical bene i s because o o e ly es ic i e deploymen policies.
Thus, exposu e o adio equency ields is usually assessed in o de
o compa e measu ed signal le els wi h exposu e limi s. These lim-
i s a e exp essed in e ms o basic es ic ions and e e ence le els.
The e e ence le els a e employed o a p ac ical exposu e assess-
men , and hey can be ob ained in he a - ield egion o he adi-
a ion sou ces [2].
In WiFi ne wo ks, he e a e wo ypes o adia ion sou ces: he
Access Poin (AP) o ho spo and he Use Equipmen (UE). All o e
he wo ld, p io o he comme cializa ion phase, any model o
hese wo ypes o de ices has o pass ho ough Speci ic Abso p ion
Ra e (SAR) es s ha ensu e he ul illmen o he basic es ic ions
in he nea - ield egion [2], which is a egula use case o mos WiFi
UEs, bu no o APs. P ecisely, se e al dis ances om an AP should
be conside ed o assessing ac ual WiFi exposu e alues o he han
he wo s -case ones, and in o de o p ope ly assess he cumula i e
e ec o elec omagne ic adia ion coming om e e y WiFi ho -
spo wi hin he a ea o in e es . In addi ion, UEs may also p oduce
a - ield exposu e. This would be he case, o example, o a mobile
phone placed on a desk a a a - ield dis ance om he use , o o
he pe son si ing nex o a pe son who is using he phone o he
lap op. Finally, while a UE de ice can emain in s and-by mode,
hus ceasing i s con ibu ion o he EM exposu e, he egula ope -
a ion o an AP equi es he gene a ion o adio equency emissions,
disco e y beacons, ega dless o whe he a UE de ice is ope a ing
o no .
Fo all he p e ious easons, addi ional ield measu emen s a e
usually pe o med in he a - ield egion o he icini y o each AP
in o de o compa e measu ed signal le els wi h he e e ence
le els [3–7]. In his ega d, i was ound ha he ield s eng h
le els om APs a e gene ally highe han hose gene a ed by lap-
ops [8] o ha he exposu e in he 5 GHz WiFi band is nowadays
highe han in he 2.4 GHz equency band [9]. Fu he mo e, he
posi ion and cha ac e is ics o he ansmi e s we e ound impo -
h ps://doi.o g/10.1016/j.jes ch.2021.05.001
2215-0986/Ó2021 Ka abuk Uni e si y. Publishing se ices by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
⇑
Co esponding au ho .
E-mail add ess: [email p o ec ed] (M. Fe nández).
Pee e iew unde esponsibili y o Ka abuk Uni e si y.
Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022) 10997
Con en s lis s a ailable a ScienceDi ec
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an ac o s ha a ec EM exposu e and should be conside ed a
he ne wo k planning s a egy o minimizing exposu e in u u e
ne wo ks [10].
Conside ing ha only measu emen s pe o med in he a - ield
egion can be compa ed wi h he elec ic ield e e ence le els [2],
he dis ance in he a - ield egion whe e he ield s eng h con i-
bu ion o a UE is signi ican ly highe han he one coming om an
AP is de ined in his wo k o WiFi applica ions in he 5 GHz e-
quency band. APs loca ed beyond ha e e ence dis ance will no
be a conce n in he analysis o human exposu e due o WiFi signals
wi hin he a ea o in e es , and he ul illmen o exposu e limi s
could be aken o g an ed as UEs comply wi h SAR limi s a sho e
dis ances.
Fu he mo e, he me hodology employed in his wo k can be
applied o o he echnologies and ne wo ks, such as In e ne o
Things (IoT) ne wo ks in wo king en i onmen s in which an indi-
idual can spend se e al hou s in close p oximi y o some adia-
ion sou ces and a om many o he s.
The emainde o he pape is o ganized as ollows. Sec ion 2
desc ibes he heo e ical concep s on which his wo k is based.
Using well-known p opaga ion exp essions, a sys em o equa ions
is p oposed o ob ain he dis ance a which he signal s eng h
le el gene a ed by he AP is much lowe han he signal ansmi -
ed by a UE. The desc ip ions o he simula ions and measu emen s
ca ied ou in his wo k a e p o ided in Sec ions 3 and 4, espec-
i ely. Resul s a e p esen ed in Sec ion 5 and he conclusions a e
summa ized in Sec ion 6.
2. Theo e ical calcula ion
In o de o calcula e he e e ence o h eshold dis ance, ha is,
he dis ance in he a - ield egion a which he powe s eng h
le el due o a UE is signi ican ly highe han he powe s eng h
gene a ed by an AP, wo scena ios ha e been de ined so ha each
ype o sou ce is cha ac e ized sepa a ely, as shown in Fig. 1(a) and
(b).
Le P
R1
and P
R2
deno e he powe alues measu ed by a ecei -
ing sys em when he wi eless signal is gene a ed only by he AP
and by he UE, espec i ely, bo h in he a - ield egion. As depic ed
in Fig. 1, hese powe le els a e ob ained when he AP and he UE
a e loca ed a dis ances o d
AP
and d
UE
om he ecei ing an enna,
espec i ely. The dis ance d
UE
does no ha e o ul ill any condi ion
o he han he a - ield egion condi ion. In his wo k i was con-
side ed ha he UE was placed a 20 cm om he use . This dis-
ance allows us o pe o m measu emen s in he a - ield egion
and, mo eo e , i is consis en wi h he de ini ion o po able
de ices, since hese de ices a e de ined as ansmi ing de ices
designed o be used so ha he adia ing s uc u es o he de ices
a e a mos 20 cm away om he body o he use [11]. Such a
maximum d
UE
will p o ide a wo s case scena io o he analysis
o his wo k, whe e he AP con ibu ion o EM exposu e is maxi-
mum wi h ega d o he UE’s. I is wo h highligh ing ha EM
exposu e due o po able de ices used in he nea - ield egion
mus be assessed by means o SAR alues ob ained by nume ical
calcula ions o labo a o y es s.
Fo a speci ic d
UE
, i is possible o de ine he h eshold dis ance
d
h
as he dis ance a which he powe le el ecei ed om he AP is
TH dB lowe han he powe le el gene a ed by he UE (Fig. 1(c)).
The calcula ion o he h eshold dis ance is pe o med in he a -
ield egion and i is based on he ee-space-p opaga ion F iis o -
mula which assumes one Line-o -Sigh (LoS) p opaga ion pa h.
This assump ion will be discussed in he measu emen s sec ion
o he pape .
Conside ing ha he AP ansmi s a powe le el o P(dBm) and
ha i is cha ac e ized by an an enna gain equal o G(dBi) in he
LoS di ec ion o he ecep ion an enna, hus being PþGðÞ
AP
he
EIRP o he AP, we can ob ain he ollowing sys em o equa ions
in loga i hmic uni s:
PþG
ðÞ
AP
L
FSAP
þG
R
¼P
R1
ð1Þ
PþGðÞ
AP
L
FS h
þG
R
¼P
R2
TH ð2Þ
whe e G
R
(dBi) is he gain o he ecei ing an enna, and L
FSAP
(dB) and
L
FS h
(dB) a e he ee space losses calcula ed a dis ances d
AP
(m) and
d
h
(m) om he AP (see Fig. 1).
Nomencla u e
EIRP E ec i e Iso opic Radia ed Powe
GRGain o he ecei ing an enna
dAP Dis ance be ween he AP and he ecei e
dUE Dis ance be ween he UE and he ecei e
d h Th eshold dis ance
LFS F ee space loss
TH Th eshold
PR1Recei ed powe in downlink ansmissions
PR2Recei ed powe in uplink ansmissions
Abb e ia ions
AP Access Poin
UE Use Equipmen
EM Elec omagne ic
SAR Speci ic Abso p ion Ra e
BW Bandwid h
SWT Sweep ime
RBW Resolu ion bandwid h
VBW Video bandwid h
CIR Channel impulse esponse
LoS Line o Sigh
Fig. 1. Scena ios o calcula ing he h eshold dis ance: (a) AP cha ac e iza ion, (b)
UE cha ac e iza ion, (c) es ima ion o d
h
.
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022)10997
2
L
FSAP
¼20log 4
p
d
AP
k
ð3Þ
L
FS h
¼20log 4
p
d
h
k
ð4Þ
The h eshold dis ance can be assessed by sub ac ing Eq. (2)
om Eq. (1):
d
h
¼d
AP
10
PR1PR2þTH
20
ð5Þ
I is wo h no ing ha in his wo k a h eshold le el TH =10dB
was selec ed o ensu ing a one-o de -o -magni ude di e ence o
he UE con ibu ion o e he AP con ibu ion o he EM exposu e.
Howe e , a mo e es ic i e h eshold le el could be selec ed wi h-
ou any change o addi ional di icul y o he p ocedu e in o de o
conside he powe o he UE signi ican ly highe han ha o he
AP.
3. Simula ions
The cha ac e iza ion o he adia ion sou ces, i.e. he UE and he
AP, was i s pe o med by means o simula ions. To his end, he
comme cial h ee-dimensional elec omagne ic simula ion so -
wa e CST S udio was employed. The AP an enna was designed ol-
lowing he design o [12], since i has he cha ac e is ics o a
s anda d AP: he adia ion pa e n is omnidi ec ional, he an enna
can wo k simul aneously in he 2.4 and 5 GHz equency bands and
i can be easily i in o he casing o an AP. I consis s o a 2.4 GHz
monopole and a 5 GHz dipole an enna, made o coppe and p in ed
on a 0.8 mm- hick dielec ic subs a e. The 5 GHz an enna, which
is he one o in e es in his wo k, consis s o wo sub-dipoles
p in ed on bo h sides o he subs a e wi h a 4 mm g ound p in ed
on he op laye . The inal design o his an enna is shown in Fig. 2
(a), and mo e de ails o he 2.4 GHz an enna can be ound in [12].
Rega ding he UE, a sma phone om he CST Lib a y was
selec ed, which con ains he RF sys ems equi ed o cellula and
WiFi applica ions, as well as s anda d phone componen s such as
a came a, ba e y, cha ging connec o o a sc een. The elec onics
o he phone no ela ed o he RF sys ems a e designed as solid
me als and i is co e ed by a plas ic housing. The inne side o
he sma phone can be seen in Fig. 2(b). I has wo PIFA an ennas
o WiFi applica ions, which we e modi ied and op imized o wo k
in he WiFi channels o in e es (5.49–5.57 GHz), since hese we e
he ope a ing equencies o he communica ion link du ing he
expe imen al measu emen s (explained in he nex sec ion). The
dimensions o he PIFA an ennas a e such op imiza ion a e also
gi en in Fig. 2(b). Table 1 shows he gain, he S11 ampli ude and
he adia ion e iciency ob ained in simula ions o bo h an ennas
a 5.51 GHz (in he case o he UE, he an enna was inside he
sma phone).
The simula ed adia ion pa e ns o he AP and UE an ennas can
be obse ed in Fig. 3. In bo h cases, he adia ion pa e ns a e
omnidi ec ional in he ho izon al plane and in he case o he AP,
he adia ion pa e n is simila o he ypical pa e n o a e ical
hal -wa e dipole an enna. The adia ion pa e n o he UE is in lu-
enced by he o he componen s o he phone a ound i .
4. Expe imen al measu emen s
4.1. Measu emen se -up
Expe imen al measu emen s we e pe o med o ob ain he
powe s eng h le els gene a ed by APs and UEs in a labo a o y
o he Uni e si y o he Basque Coun y (Spain), whe e a Cisco Ai -
one 1702I-E-K9 access poin p o ides access o he Edu oam WiFi
ne wo k deployed in he p emises o he Facul y [13]. This AP
wo ks unde he s anda ds 802.11a/g/n/ac and p o ides a maxi-
mum ansmi ed powe o 22 dBm in he 5 GHz WiFi band. The
ho izon ally omnidi ec ional AP an enna has a gain equal o 4
dBi. Du ing he measu emen s, his AP was wo king a equencies
be ween 5.49 and 5.57 GHz, which co espond o a channel band-
wid h (BW) o 80 MHz.
The ecei ing sys em was composed o a spec um analyze
An i su MS2690A and an omnidi ec ional an enna wi h 3-dBi gain
(model VERT2450 om E us Resea ch) app op ia e o equencies
be ween 4.9 and 5.9 GHz. The con igu a ion o he analyze is
shown in Table 2, and i is based on [14]. I is widely known ha ,
when measu ing WiFi signals, he con igu a ion o he measu e-
men equipmen can ha e signi ican in luence on he esul s due
o he na u e o WiFi signals, which a e ansmi ed in he o m
o pulses o sho du a ion [15]. Howe e , as he expe imen al es s
o his wo k we e made when gene a ing high da a a ic, he
in luence o he measu emen equipmen was educed, as demon-
s a ed in [16]. Finally, a lap op unning au oma ion so wa e was
employed o he collec ion and con enien s o age o he mea-
su ed da a.
Fi e di e en sma phones we e used as UEs. The main cha ac-
e is ics o he sma phones conside ed in his s udy a e summa-
ized in Table 3. As shown, all he UEs we e using he 802.11ac
s anda d du ing he measu emen s and occupying he 80 MHz o
he channel, excep he UE 1 ha was employing he 802.11n s an-
da d and he e o e using a BW o 40 MHz. The maximum EIRP
le els speci ied in he sma phone guides o he equency band
5470–5725 MHz a e also gi en in he able.
Fig. 2. An ennas designs (dimensions in mm): (a) Top and bo om iews o he AP
an enna, (b) sma phone and side (le ) and op ( igh ) iews o he PIFA an enna.
Table 1
Pa ame e s o he designed an ennas a 5.51 GHz.
An enna Gain S11 ampli ude Rad. e iciency
AP 1.66 dBi 23.12 dB 82%
UE 5.65 dBi 21.19 dB 96%
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022) 10997
3
4.2. Access poin cha ac e iza ion
In his scena io, he signal le els coming exclusi ely om he
AP we e measu ed. Fi s al all, he ee space p opaga ion condi ion
o he WiFi signals was e i ied by calcula ing he channel impulse
esponse (CIR) o he p opaga ion pa h. To his end, a ne wo k ana-
lyze , a Keysigh ENA E5071C, was employed along wi h wo
an ennas: he same an enna used o ecep ion in he es s and a
monopole an enna wi h oughly he same di ec i i y cha ac e is-
ics o he AP an enna. This analyze was calib a ed wi h he wo
connec ion cables in he in e al be ween 5570 and 5650 MHz,
as his was a non-occupied 80-MHz channel adjacen o he one
unde es . In o de o exac ly eplica e he p opaga ion pa h unde
analysis, he monopole an enna was loca ed in lieu o he ho spo
while he ecep ion an enna was le on he holde o he measu e-
men scena io. Values o he S21 pa ame e we e measu ed o
ob aining he CIR g aph ollowing he p ocedu e desc ibed in
[18]. This g aph e i ied he ee space p opaga ion condi ion, since
he signal le el co esponding o he LoS pa h was 18 dB highe
han he one co esponding o nex signi ican delayed pa h.
Once he ee space p opaga ion condi ion was e i ied, he
ecei e an enna was placed a di e en dis ances om he AP
be ween 2 and 3 m (in o de o ge se e al alues o P
R1
and d
AP
),
Fig. 3. Simula ed adia ion pa e ns in bo h ho izon al (le ) and e ical ( igh ) planes (a) o he AP, and (b) o he UE.
Table 2
Con igu a ion o he spec um analyze .
Pa ame e Value
Cen e F equency 5530 MHz
Span 80 MHz
De ec o RMS
Sweep ime (SWT) 5 ms
Resolu ion bandwid h (RBW) 1 MHz
Video bandwid h (VBW) 3 MHz
T ace Mode Clea /W i e
Table 3
Cha ac e is ics o he sma phones in he equency band o in e es .
Sma phone S anda d (5 GHz) Max EIRP (dBm) Occupied BW (MHz)
UE 1 802.11a/n 20 40
UE 2 802.11a/n/ac 23 80
UE 3 802.11a/n/ac 24 80
UE 4 802.11a/n/ac 30 80
UE 5 802.11a/n/ac 30
a
80
a
The speci ic powe limi was no ound, bu in he use manual i is speci ied
ha he maximum powe is less han he highes limi alue speci ied in he ela ed
Ha monized S anda d, which is 30 dBm o he co esponding equency band [17].
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022)10997
4
while he UE was a leas 10 m away om he ecei e . This way,
acco ding o ancilla y measu emen s, he ield s eng h coming
om he UE was a leas 25 dB lowe han he one o he ho spo .
Bo h con ibu ions occupied he same RF channel, so hey we e
dis inguished by changing om downloading o uploading a ic.
In o de o ge he highes powe le el ecei ed om he AP, a la ge
ile was downloaded om a local se e . Measu emen du a ion
was equal o 3 min (sho e han ile download) and a leas 3 mea-
su emen s pe posi ion we e pe o med in o de o ensu e epea a-
bili y o he esul s.
4.3. Use equipmen cha ac e iza ion
To measu e he WiFi signals ha we e coming om he UE in
his scena io, he ecei ing an enna was placed a a dis ance o
20 cm om i , in o de o ensu e a - ield egion condi ions
(3k< 17 cm) [19]. On he o he hand, he AP was loca ed a leas
10 m a away om he ecep ion an enna, so ha he ield
s eng h le el coming om he UE was 25 dB highe han he
one ecei ed om he ho spo , acco ding o he esul s o ancilla y
measu emen s. The ecep ion an enna was ixed o a piece o oam
a ached o he able wi h adhesi e ape, as can be obse ed in
Fig. 4. The UE was ixed on a ipod and, be o e collec ing da a, i
was placed in an o ien a ion ha ensu ed he highes ield s eng h
le el a he ecei ing an enna. In his case, uplink a ic was gen-
e a ed by he UE, uploading a la ge ile o a local se e . Measu e-
men du a ion was also equal o 3 min o ensu e da a a ic du ing
he whole measu emen , and a leas 2 measu emen s pe UE we e
pe o med in o de o ge se e al alues o P
R2
o he calcula ions.
4.4. Assessmen o he in luence o nea by APs in he 5 GHz equency
band
As explained in subsec ion 4.1, he measu emen s we e aken
inside a labo a o y o he Uni e si y o he Basque Coun y, which
has one AP ins alled inside. Howe e , wi hin he Uni e si y, se e al
APs we e wo king in he icini y. These APs can wo k a di e en
channels co esponding o equencies anging om 5.17 GHz o
5.71 GHz, and can au oma ically adjus he channel acco ding o
he signals de ec ed in he su oundings, in o de o selec an
unused channel. Pa icula ly, measu emen s we e pe o med on
he 4 h loo o he Uni e si y and he e we e 11 APs wo king on
his loo . Expe imen al measu emen s we e pe o med in he
whole 5 GHz equency band o analyze he e ec o o he APs
on he calcula ed h eshold dis ance.
A ex ac o he loo plan o he measu emen en i onmen is
p esen ed in Fig. 5, whe e he closes AP co esponds o he ans-
mi e o he labo a o y in which he expe imen s we e pe o med
(i.e. he same AP as he one de ailed in subsec ion 4.1). As shown,
he e is ano he access poin (i.e. AP 2), which was one o he clos-
es APs om he AP o in e es . In his case, he signal powe le els
we e eco ded a di e en dis ances be ween he ed poin in Fig. 5
and he AP o he labo a o y (Closes AP). This ed poin was si u-
a ed a 6.5 m om he AP o he labo a o y. As shown, as he ecei-
e was mo ed away om he AP o in e es , i was placed close o
AP 2. As can be obse ed, each access poin was loca ed in a di e -
en labo a o y o he Uni e si y, sepa a ed by a conc e e wall. The
esul s p esen ed in his wo k will analyze he con ibu ion o
hese di e en APs o he o al powe le els gene a ed in he
5 GHz equency band.
4.5. Assessmen o he in luence o mul ipa h e ec s
The heo e ical calcula ion o Sec ion 2 was based on ee space
p opaga ion condi ions. Ne e heless, e en unde LoS condi ions,
some imes mul ipa h e ec s can be signi ican . When mul ipa h
p opaga ion exis s, he powe le el ecei ed om non-LoS pa hs
is usually lowe han he le el ecei ed in ee space p opaga ion
due o he a enua ion su e ed by he signals when hey collide
wi h walls o o he objec s. Howe e , some imes he o al ene gy
ecei ed a a poin is highe han he ene gy o he LoS componen
due o he addi ion o mul ipa h componen s. This las case is o
in e es in his wo k since i he powe le el ecei ed om he
AP inc eases, he calcula ed h eshold dis ance would also
inc ease.
In o de o e alua e he e ec o mul ipa h componen s on he
calcula ed h eshold dis ance, a model p oposed by he IEEE ask
Fig. 4. Measu emen scena io o cha ac e izing he WiFi signals ansmi ed by an
UE. Fig. 5. Floo plan o he measu emen en i onmen .
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022) 10997
5
g oup on 802.11n channel models was employed [20]. In pa icu-
la , he Model B om [20] was used since i ep esen s a ypical
channel o la ge open space and o ice en i onmen s. Table 4 p o-
ides he alues o he ap delays and co esponding powe le els
o one clus e . These aps we e employed o calcula e he o al
powe le el ecei ed when also mul ipa h componen s a e p esen ,
conside ing ha he LoS componen , he i s one, is he signal
ecei ed unde ee space condi ions.
5. Resul s and discussion
5.1. Simula ions
I is wo h highligh ing ha al hough Table 3 epo s he max-
imum EIRP le els ha he employed UEs can ansmi , he UE usu-
ally ansmi s lowe powe le els. In his ega d, he lis p esen ed
in [21] shows, among o he s, he esul s o ansmi powe capabil-
i ies by many de ices when using WiFi a 5 GHz. The maximum
ansmi ed powe by he sma phones o ha s udy ook alues
be ween 14 and 30 dBm. Fu he mo e, as WiFi signals a e ans-
mi ed in he o m o pulses, he mean powe le el ansmi ed
o a speci ic pe iod o ime will be signi ican ly lowe e en in high
a ic condi ions [16]. Fo his eason, simula ions we e pe o med
o UE ansmi ed powe le els anging om 10 o 30 dBm, while
he AP was ansmi ing 22 dBm. Fig. 6 shows he h eshold dis-
ance d
h
es ima ed using Eq. (5) om he da a ob ained in simula-
ions, when he UE was placed a 20 cm om he ecei e , his is, in
he case in which he UE would be a 20 cm om he use . As
shown he highes d
h
was 1.92 m. Thus, acco ding o he simula-
ions esul s, being a a dis ance highe han 1.92 m om he AP
would ensu e ha he signals gene a ed by he AP a e negligible
compa ed o he signals ansmi ed by a UE loca ed a 20 cm o
close o he body.
5.2. Measu emen s
Fo calcula ing he h eshold dis ance, he 90 h pe cen ile (P90)
o he measu ed da a was employed, since i is conside ed an
app op ia e s a is ic o ep esen ing he WiFi exposu e a ia ions
[14].Table 5 epo s he measu ed le els a equencies be ween
5.49 GHz and 5.57 GHz (i.e. conside ing only he closes AP), when
he AP was gene a ing da a a di e en dis ances om he ecei e ,
and when he UEs we e ansmi ing WiFi signals a 20 cm om
he ecei e .
Fig. 7 shows he calcula ed d
h
o he di e en UEs. The black
e o ba s ep esen he di e ences in he esul s due o he di e -
en alues o P
R1
and d
AP
(as expec ed, in simula ions d
h
ook he
same alue o di e en d
AP
). As shown, he highes d
h
was
ob ained o UE 1, which makes sense since his UE only employed
40 MHz o ans e da a, while he o’ he UEs employed he
80 MHz bandwid h o he WiFi channel, so he signal powe le el
ecei ed o hese UEs was highe han o he UE 1 (see Table 5).
Fo he o he UEs, d
h
ook alues om 1.64 o 2.16 m, which
means ha being a a dis ance highe han 2.16 m om an AP
ensu es ha he EM adia ion coming om he AP is negligible in
compa ison o he adia ion om hese UEs (using 802.11ac s an-
da d) placed a 20 cm o close o he use . Rega ding emissions
om APs, wo main pa ame e s mus be conside ed, namely, ans-
mi ed powe and dis ance. Hence, o a speci ic da a a ic and a
speci ic AP wi h a speci ic ansmi ed powe , i was ound ha he
dis ance be ween he AP and he measu ing poin was he only
pa ame e ha in luenced he esul s unde ee space p opaga ion
condi ions (see sec ion 5.4 o mul ipa h channel e ec s). How-
e e , i da a a ic is lowe han he one conside ed in his s udy
(in which he highes a ic was conside ed o AP and UEs), mea-
su ed emissions would be educed o he same dis ance. An exam-
ple o exposu e le els gene a ed by an AP o di e en a ic
condi ions can be obse ed in [16].
Table 4
Values o he ap delays and powe le els o he selec ed model [20].
Tap index 1 2 3 4 5
Delay (ns) 0 10 20 30 40
Powe (dB) 0 5.4 10.8 16.2 21.7
Fig. 6. Th eshold dis ances ob ained in simula ions o di e en maximum
ansmi ed powe le els by he UE (when d_UE = 20 cm).
Table 5
Measu ed powe le els when gene a ing a ic om he AP o om he UEs.
Pa ame e P90 (dBm)
P
R1
(d
AP
= 2.2 m) 46.10
P
R1
(d
AP
= 2.9 m) 49.04
P
R2
UE 1 43.21
P
R2
UE 2 34.09
P
R2
UE 3 35.95
P
R2
UE 4 34.48
P
R2
UE 5 34.29
Fig. 7. Th eshold dis ances ob ained om he expe imen al measu emen s.
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022)10997
6
Compa ing he esul s ob ained by means o simula ions and
measu emen s, he e a e se e al easons o ob aining sho e dis-
ances when using simula ed da a han when employing measu ed
da a. Fi s o all, simula ions we e ca ied ou o a con inuous sig-
nal. Howe e , WiFi signals a e ansmi ed in he o m o bu s s. As
measu emen s can accoun o hose pe iods o ime in which he
signal is no being ansmi ed, measu ed powe le els a e lowe .
Mo eo e , al hough he maximum ansmi ed powe le els spec-
i ied in he sma phone guides we e used o simula ions, i is
p obable ha he UE employs lowe powe le els in a eal si ua-
ion. Finally, an example o a UE an enna was selec ed o unning
he simula ions, which esul ed in an an enna gain equal o 5.65
dBi. Bu he employed UE can use a di e en ype o an enna wi h
di e en an enna gain.
In iew o hese esul s, one c ucial conside a ion mus be
made. Al hough i may seem ha highe powe UEs allow lowe
h eshold dis ances o APs, i mus be clea ly s a ed ha his allow-
ance e e s o and only o assessmen pu poses. F om he sa e y
poin o iew, he si ua ions wi h lowe h eshold dis ances a e
o be a oided by all means.
5.3. In luence o nea by APs in he 5 GHz equency band
Fig. 8 shows he ecei ed signal ace a e 6 min o a max-hold
measu emen in he 5 GHz WiFi band, when placing he ecei e a
3 m om he closes AP (see Fig. 8(a)) and when he ecei e was a
5 m om ha AP (see Fig. 8(b)). These measu emen s we e aken
in no mal wo king condi ions. Thus, he e we e di e en UE con-
nec ed o he di e en APs o he uni e si y, including he closes
AP. Mo eo e , o aking hese measu emen s, LoS condi ions
be ween he closes AP and he ecei e we e ensu ed, bu in his
case he ee space p opaga ion condi ion was no checked in o de
o conside he whole mul ipa h wo king en i onmen .
Al hough in he 2.4 GHz equency band signals ansmi ed by
o he APs we e no iceable in he measu emen s when he ecei -
ing an enna was placed a 3 m om he AP o in e es , a 5 GHz,
as shown in he igu e, signals coming om o he APs could no
be dis inguished om ha posi ion. This di e ence can be
explained because o he sho e wa eleng h and highe a enua-
ion a highe equencies. Howe e , a 5 m om he AP o in e es ,
some powe le el ansmi ed by o he AP can be obse ed in he
lowe channels o he 5 GHz WiFi band. To accoun o he con i-
bu ion o his second AP, addi ional measu emen s wi h a du a ion
equal o 6 min we e pe o med a a dis ance o 5 m:
– Fi s se : 3 measu emen s we e pe o med in he equency
ange o he closes AP (be ween 5.49 and 5.57 GHz).
– Second se : One measu emen o he ecei e noise le el was
aken in he 5 GHz WiFi band, excep in he equency ange
om 5.49 o 5.57 GHz.
– Thi d se : 3 measu emen s we e ca ied ou conside ing he
whole 5 GHz WiFi band.
Recei ed powe le els om he i s and second se s we e
added and his esul ed in powe le els simila o hose eco ded
in he hi d se , being he signals coming om he o he AP he e-
o e negligible. Table 6 p o ides he 50 h and 90 h pe cen iles o
he esul s ob ained in hese se s o measu emen s.
Rega dless o he e ec o signals coming om o he APs a 5 m
om he AP o in e es , his dis ance is highe han he calcula ed
h eshold dis ances, so in any case, addi ional measu emen s
should be pe o med a such dis ances om he AP i in o ma ion
abou adia ion sou ces is equi ed.
5.4. In luence o mul ipa h e ec s
Recei ed signal powe le els we e calcula ed conside ing he
mul ipa h channel model o he signals gene a ed by he AP when
he ecei e was placed be ween 2.2 and 2.9 m om i . F om hese
alues, he h eshold dis ances we e calcula ed ollowing he same
p ocedu e as he one applied in subsec ion 5.2. Fo he UEs, he
ecei ed powe le els o Table 5 we e employed.
Fig. 9 shows he esul s o he new h eshold dis ances ob ained
o mul ipa h channels ( ed columns). Fo compa ison pu poses,
he alues o hese h eshold dis ances a e gi en oge he wi h
Fig. 8. Powe le els ecei ed a di e en dis ances om he closes AP: (a) a 3 m,
and (b) a 5 m.
Table 6
Measu ed powe le els a 5 m om he closes AP.
Pe cen ile Channel measu emen s + band
noise (dBm)
WiFi band measu emen s
(dBm)
P50 51.82 51.69
P90 51.14 51.55
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022) 10997
7
he p e iously calcula ed h eshold dis ances unde ee space con-
di ions (blue columns). The black e o ba s ep esen he di e -
ences in he esul s due o he di e en alues o powe le els
measu ed a di e en dis ances om he AP. As can be obse ed,
calcula ed h eshold dis ances in mul ipa h en i onmen s ook
alues be ween 5.55 m and 5.92 m o UE 1 and be ween 1.94 m
and 2.57 m o he es o he UEs. Again, he di e ences in he
ob ained esul s be ween UE 1 and he o he UEs is due o he WiFi
s anda d employed by he UEs. Du ing hese measu emen s, he
UE 1 was employing he 802.11n s anda d and he e o e using a
BW o 40 MHz, while he o he UEs we e employing he
802.11ac s anda d and 80 MHz bandwid h.
Finally, Table 7 shows a compa ison o he h eshold dis ances
ob ained om simula ions and expe imen al measu emen s aken
unde ee space p opaga ion condi ions. The able shows he
h eshold dis ances ob ained o UE ansmi ed powe s anging
om 10 o 16 dBm in he simula ions, which be e i he expe i-
men al se up.
6. Conclusions
The con ibu ion each o he EM sou ces o he o al exposu e in
wi eless ne wo ks is an essen ial pa ame e o cha ac e izing EM
exposu e and de elop ne wo k deploymen s ha minimize EM
ield le els. This manusc ip p esen s a me hodology o de e min-
ing he dis ance a which he EM ield le els ansmi ed by an AP
can be negligible in compa ison wi h hose ansmi ed by a UE in
o de o simpli y he assessmen o he o al exposu e. This can
also gi e in o ma ion abou he posi ions in which measu emen s
should be aken in u u e measu emen campaigns.
In he p oposed me hodology, he h eshold dis ances we e cal-
cula ed o a speci ic dis ance o he UE. In his wo k he h eshold
dis ance was de e mined by means o a igo ous me hodology
assuming he wo s case scena io, ha is, ull ac i i y o he WiFi
ne wo k, 90 h pe cen iles, and a dis ance o 20 cm be ween he
UE and he ecep ion poin . This dis ance allows us o pe o m
measu emen s in he a ield egion and, i can ep esen scena ios
in which a sma phone is placed on a desk a 20 cm om he use ,
o scena ios in which he exposu e is due o he UE o ano he pe -
son. Mo eo e , i is consis en wi h he de ini ion o po able
de ices, since hese de ices a e de ined as ansmi ing de ices
designed o be used so ha he adia ing s uc u es o he de ices
a e wi hin 20 cm o he body o he use [11]. Thus, in he selec ed
condi ions he esul s p o ide he la ges h eshold dis ance when
he own use o he pe son nex o him/he is exposed o adia ion
coming om he UE. Howe e , o people who a e a g ea e dis-
ances om he exposu e sou ce, he h eshold dis ances would
be longe . This way, unde ee space p opaga ion condi ions,
h eshold dis ances anging om 1.64 m and 4.99 m we e ob ained
o he cases o ho spo s ansmi ing 160 mW wi h bandwid hs o
80 MHz and 40 MHz, espec i ely. This dis ances can inc ease in
mul ipa h en i onmen s as demons a ed in Sec ion 5.4, whe e a
maximum h eshold dis ance o 5.92 m was ob ained. In all he
cases, i he UE was placed close o he human body, he h eshold
dis ance would be lowe . This conclusion may lead o a misconcep-
ion ha needs o be cla i ied. The esul s poin ou ha he highe
he UE powe is, he lowe h eshold dis ance o he AP is allowed.
Howe e , ega ding sa e y as he main scope o his ype o
esea ch, such h eshold si ua ions cha ac e ized by maximum
powe UEs and minimum dis ances o APs should be a oided by
all means. Tha is, he highe he h eshold dis ance is, he be e
he exposu e scena io will be.
Expe imen al esul s showed ha he h eshold dis ance
depends on he bandwid h employed by he communica ion link,
which is ela ed o he WiFi s anda d employed by he AP and
UE. Fu he mo e, measu emen s in he whole 5 GHz WiFi band
we e ca ied ou in a uni e si y en i onmen and i was p o ed
ha WiFi signals coming om u he APs ha e lowe in luence
han a 2.4 GHz due o he highe a enua ions su e ed a highe
equencies. Finally, he h eshold dis ances we e also calcula ed
in mul ipa h en i onmen s.
The p oposed me hodology ensu es ha WiFi APs will no be a
ma e o conce n i he use is loca ed a la ge dis ances han he
h eshold dis ance. On he con a y, measu emen s o he adia ion
coming om he ho spo would be needed a sho e dis ances, in
o de o check he compliance wi h he e e ence le els.
Finally, he du a ion o signal ansmission may be o g ea
in e es when assessing EMF exposu e, especially in places whe e
people spend many hou s such as schools, uni e si ies o o ices.
In his ega d, WiFi exposu e le els a 2.4 GHz we e e alua ed by
means o 24-hou measu emen s in a uni e si y en i onmen in
[14]. As can be obse ed in Fig. 4 o [14], WiFi signals ansmission
inc eased in wo king days compa ed o weekends. Bu e en du ing
wo king hou s, WiFi ac i i y and he e o e AP and UE ansmis-
sions a ies om one loca ion o ano he inside he same building.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing inan-
cial in e es s o pe sonal ela ionships ha could ha e appea ed
o in luence he wo k epo ed in his pape .
Acknowledgmen s
This wo k was suppo ed in pa by he Uni e si y o he Basque
Coun y UPV/EHU unde Pos doc o al G an ESPDOC19/43, by he
Fig. 9. Th eshold dis ances ob ained in ee space p opaga ion condi ions and in
mul ipa h channel models.
Table 7
Compa ison o h eshold dis ances ob ained by means o simula ions and expe imen al measu emen s unde ee space p opaga ion condi ions.
Simula ions UE Powe (dBm) 16 12 10
Th eshold dis ance (m) 0.96 1.53 1.92
Measu emen s UE UE 1 UE 2 UE 3 UE 4 UE 5
Mean h eshold dis ance (m) 1.69 1.73 1.77 2.10 4.84
M. Fe nández and D. Gue a Enginee ing Science and Technology, an In e na ional Jou nal 25 (2022)10997
8
Spanish Minis y unde G an RTI2018–099162-B-I00 (MCIU/AEI/
FEDER, UE), and by he Basque Go e nmen unde G an IT1234-
19.
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