0590_500

ICS: 33.020
Key words: Digital cellular telecommunications system, Global System for Mobile communications (GSM)
GLOBAL SYSTEM FOR
(GSM 05.90 version 5.0.0)
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [email protected]
Tel.: +33 4 92 94 42 00 - Fax: +33 4 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1997. All rights reserved.

Page 2 ETR 357 (GSM 05.90 version 5.0.0): January 1997

Contents
Foreword .......................................................................................................................................................5
4 Laboratory results................................................................................................................................8 4.1 Hearing aids.........................................................................................................................8 4.2 Cardiac pace-makers...........................................................................................................9 4.3 Domestic equipment..........................................................................................................10
Annex B: GSM - Hearing aid interference modelling parameters ..........................................................30
Annex C: New digital transmission technologies - the EMC conundrum................................................33
Annex D: Potential GSM hazards on cardiac pacemakers.....................................................................37
Annex E: Summary document on GSM-TDMA interference..................................................................43
Annex F: Interference to hearing aids by the new digital mobile telephone system, Global System for Mobile (GSM) communications standard ..........................................................................51
Annex G: Studies on interference from GSM terminals to the fixed network telephone equipment.......68
History........................................................................................................................................................107
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Foreword
This ETSI Technical Report (ETR) has been produced by the Special Mobile Group (SMG) Technical Committee (TC) of the European Telecommunications Standards Institute (ETSI).
This ETR summarizes the work which has been conducted, mainly in the UK, to investigate the effect of wanted radio frequency transmissions from GSM Mobile Stations (MS) and Base Transceiver Stations (BTS) within the digital cellular telecommunications system on other equipment.
This ETR is an informative document resulting from SMG studies which are related to the digital cellular telecommunications system. This ETR is used to publish material which is of an informative nature, relating to the use or the application of ETSs and is not suitable for formal adoption as an ETS.
This ETR corresponds to GSM technical specification, GSM 05.90 version 5.0.0.
The specification from which this ETR has been derived was originally based on CEPT documentation, hence the presentation of this ETR may not be entirely in accordance with the ETSI/PNE rules.
Reference is made within this ETR to GSM Technical Specifications (GSM-TS) (see note).

Blank page
1 Scope
A considerable amount of work has been conducted, mainly in the UK, to investigate the effect of wanted radio frequency transmissions from GSM MS and BTS on other equipment. This report aims to summarize this work and to look at the implications for GSM. Since GSM EMC considerations extend outside the GSM arena, it is thought essential that GSM considers the implications of EMC and produces this report.
1.2 References
This ETR incorporates by dated and undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this ETR only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies.
[1] 89/336/EEC: "Council Directive on the approximation of the laws of the Member States relating to electromagnetic compatibility".
[2] EN 50082-1 (1992): "Electromagnetic compatibility - Generic immunity standard. Part 1: Residential, commercial and light industry".
[3] IEC 801-3, (1984): "Immunity to radiated, radio frequency, electromagnetic fields".
[4] GSM 01.04 (ETR 350): "Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms".
[5] DTI/RA: "A summarized report on measurement techniques used to investigate potential interference from new digital systems".
[6] INIRC (1988): "Guidelines on limits of exposure to radiofrequency electromagnetic fields in the frequency range 100 kHz to 300 GHz".
[7] NRPB (1989): "Guidance as to restrictions on exposures to time varying electromagnetic fields and the 1988 recommendations of the International Non-Ionizing Radiation Committee".
[8] IEEE C95.1 (1991): "IEEE standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 4 kHz to 300 GHz".
[9] Draft DIN VDE 0848 Part 2 (1991): "Safety in electromagnetic fields; protection of persons in the frequency range from 30 kHz to 300 GHz".
[10] CENELEC European prestandard ENV50166-2 (January 1995): "Human exposure to electromagnetic fields ,High Frequency (10 kHz to 300 GHz)".
2 Information available
A number of European organizations have conducted extensive investigations into GSM EMC. These investigations looked at the potential of a GSM transmission to interfere with a wide range of electrical apparatus. Having conducted both objective and subjective investigations, it was discovered that personal audio equipment (e.g. Walkmans) and hearing aids were most susceptible and most likely to be in close proximity to GSM apparatus.
Of these two types of apparatus, hearing aids were considered the greatest potential problem and thus a considerable amount of modelling work was conducted in order to assess the likely incidence of interference in various scenarios.

3 Cause of potential EMC interference
The source of GSM interference is the 100 % amplitude modulated RF envelope introduced by burst transmission necessary for Time Division multiple Access (TDMA). Audio apparatus having some non- linear component able to demodulate this Amplitude Modulation (AM) envelope will be subject to interference in the audio pass-band since the frame and burst rates for GSM are 220 Hz and 1,7 kHz.
Another source of interference is the DTX (Discontinuous Transmission) mode of operation in GSM. In the DTX mode there are two signal components with much lower frequencies than the normal GSM transmission: a component with a frequency of 2.1 Hz corresponding to the transmission of the 8 timeslots of the SID (Signal Descriptor) message block, and another with a frequency of 8,3 Hz corresponding to the repetition rate of SACCH.
4 Laboratory results
4.1 Hearing aids
Objective laboratory results from the United Kingdom, Department of Trade and Industry, Radiocommunications Agency (DTI/RA) [5] showed that a typical "behind the ear" hearing aid in normal (amplifying) mode was susceptible to peak GSM field intensities of;
- between 10 V/m and 17 V/m in order to produce the same audio power as speech, 0.5 m in front of the hearing aid; and
- between 5 V/m and 8.5 V/m to produce "audible, slightly annoying" interference.
It was noted that the group of hearing aids tested showed a 4 dB spread in susceptibility in the normal mode and a 13 dB spread in susceptibility in the inductive loop mode.
Subjective investigation conducted at BTRL with the hearing aid worn by the user showed that "audible, slightly annoying" interference was perceived when subject to a peak field intensity varying between 10 V/m and 4 V/m depending upon the orientation of the head. This was modelled by a peak field intensity of 10 V/m for a 270° arc and 4 V/m for the 90° arc not shielded by the head inferring an 8 dB attenuation provided by the head. This directional susceptibility corresponds to an average of 6.6 V/m and thus agrees with the DTI/RA objective results.
These results were subsequently used for modelling activities to assess the consequences of this susceptibility in various scenarios. It should be noted that the susceptibility without head attenuation used in the model (4 V/m) is somewhat worse than the DTI measurements (5 V/m - 8.5 V/m) and thus the modelling results will be very much worst case.
It was found that metallising the hearing aid case reduced the susceptibility with no head attenuation from 4 V/m to 12 V/m (10 dB).

Table 1. Field strength and safety distances for noticeable interference
Hearing aid type Field strength for noticeable interference Distance for noticeable interference
2 W MS 8 W MS
Behind the ear, microphone input
0.7 - 3.1 V/m 2.0 - 10 m 3.5 - 20 m
Behind the ear, telecoil input
0.4 - 4.9 V/m 1.5 - 20 m 2.5 - 40 m
In the ear 4.9 - 32.3 V/m 0.2 - 0.6 m 0.4 - 1.5 m
NOTE: The distances in table 1 can not be compared directly with those in table 2 because table 1 distances are approximate real-life distances whereas table 2 is based on theory.
In Denmark a study initiated by the Danish ministry of communications has been carried out recently. The results of the study are in a report "Interference to hearing aids caused by GSM mobile telephones". Following are the main conclusions of the report:
- so far there have not been many actual examples of interference but it must be foreseen that in 3 - 4 years there will be frequent reports of interference to hearing aids occasioned by GSM mobiles;
- it is anticipated that existing hearing aids will be replaced by new models with generally greater immunity to GSM signals; in any event, in 5 - 7 years the risk of interference should have diminished significantly;
- solutions to decrease the amount of interference based on GSM system will either have a highly limited effect (transmitter power regulation) or will be financially unfeasible (cell size optimization);
- solutions based on design changes to hearing aids will generally be possible and must offer immunity against signal strengths of up to 10 V/m; some hearing aids used today already satisfy requirements and future models will be able to be so constructed as to meet them too; designing a new hearing aid with the requisite level of immunity would increase prices approx. DKK 100 per unit, which is a 4 - 7 % increase to a current price of a hearing aid.
4.2 Cardiac pace-makers
Work was carried out by CSELT Italy to investigate the effects of GSM type burst structure on cardiac pace-makers (annex D). Unipolar and bipolar types from one manufacturer were tested. The results show that, although it was possible to interfere with pace-maker operation in free space, it was not possible, with the equipment power used, to interfere with operation when the pace-maker, leads and electrodes were placed in a phantom simulating realistic use in the human body. The equivalent maximum field strength used for this test would not normally be exceeded at further than 0.5 m away from any allowed GSM transmitter except the maximum power base station. For information the field strength required to defeat the pace-maker in free space was in excess of 40 V/m for the most sensitive class of pace-maker.

4.3 Domestic equipment
Tests carried out by various laboratories and collected together by the Radio Technology Laboratory (RTL) of the Radiocommunications Agency (annex E) show that for a limited number of devices under test the cassette decks, television receivers and portable radios/cassette players etc. are the most susceptible domestic equipment with the mean field intensities causing "visible/audible, but not annoying" interference being 2.9, 4.0, and 5.6 V/m, respectively. For example for 8 W MS the field strength of 4 V/m will be found at distances less than 5 m (worst case assuming 100 % efficiency and free space path loss) as can be seen in table 1.
This means that in practice, due to building attenuation etc., interference will not occur unless the transmitter and the victim equipment are in the same room. This is likely to occur if the GSM terminal is transportable (8 W output power for instance).
Studies on the GSM interference to the fixed network telephone equipment have been carried out in France, Norway, U.K. and Italy (annex G). All the studies highlight the fact that due to the lack of an international immunity standard to the fixed network telephone equipment the interference problem varies from country to country depending on the national immunity standards. The study carried out in France summarizes that no telephone analogue equipment or audio terminal can comply with a 10 V/m GSM type field strength, and half of the telephone sets tested did comply with the 3 V/m immunity level, both results derived with a selected performance criteria of -50 dBmop/600 Ohms in transmit direction and 50 dBA on receive direction. Regarding the maximum distances for potential interference the study gives the distances of 10 metres for 8 W GSM terminal and 5 metres for 2 W GSM terminal. The U.K. study tests the fixed network telephones and PBX equipment at 3 V/m and 10 V/m field strengths and concludes that in the U.K. the vast majority of telephones and telephone equipment is not susceptible at even 10 V/m. Hence, due to the immunity standard for fixed telephones the interference from GSM terminals is not considered as a major problem in U.K. In the Norwegian study it is summarized that with a 40 dB S/N ratio as a quality limit and with 10 W GSM transmitter 10 m away from a telephone, half of the telephones tested pass the test. Also, the study highlights the very large difference in the immunities of the fixed telephones, the immunities calculated in field strength being from 12.3 V/m to 0.6 V/m, with the same quality limit of 40 dB S/N ratio. The Italian study uses the same pass criteria as the French one and concludes that out of the tested fixed telephones, only an RF-shielded model and another with a very compact structure resulted complying with immunity requirements up to 6 V/m GSM field strength (that is 0.8 W GSM emission at 1 m distance), while some models did not even comply with 3 V/m (i.e. 0.8 W GSM emission at 2 m distance).
5 Modelling results
A wide range of scenarios were modelled (annexes A and B) to include the possible interference to hearing aid users from base stations, mobiles and handportables. Not surprisingly, by far the highest incidence of interference was caused in crowded urban environments where hearing aids and handportable transceivers are likely to be in closest proximity.
It was found that a hearing aid user would experience 3 seconds of interference every 8 minutes whilst walking on a London street and would be subject to a 2.4 % probability of interference whilst travelling on a commuter train for a GSM system occupying 2 x 25 MHz. Further results showed that with 1 % of the train passengers using GSM transmitters (0.1 % previously) and an average susceptibility of 4 V/m, the probability of interference was 5 %. These modelling results were based on a small sample of hearing aids with immunities in the region of 3 V/m. More recent measurements have shown that some hearing aids, in particular the in-the-ear aids, have immunities up to 30 V/m (see annex F). This would reduce these probabilities by a factor of 100.
It should be noted that the modelling work is based on free space path loses. The effect of, for example, people in a crowded train has not been measured, but in general it is expected that the presence of people or objects between the MS and the hearing aid will be to reduce the interference in most cases.
It should be noted that all the scenarios examined assumed the hearing aid was active all the time. Clearly, there will be instances where the user will switch off the aid when not required to communicate.

6 Solutions
The generic immunity standard, EN 50082-1, produced by CENELEC, calls for immunity to RF electromagnetic fields of 3 V/m. This work has shown that current hearing aids have immunities close to this proposed level and that a handportable GSM transmitter is likely to present a field strength greater than this at regular intervals in a crowded environment and thus cause interference to the hearing aid user (annex C). The actual field strength from a dipole, as calculated from IEC 801-3:1984, is shown in table 2 (the values are independent of frequency).
Table 2: Close proximity field strengths
Peak transmit GSM MS power Peak field strength (V/m)
power (Watts) class 1m 2m 5m
0.8 5 6.3 3.1 1.3
2 4 9.9 5.0 2.0
5 3 15.7 7.8 3.1 8 2 19.8 9.9 4.0
DCS 1 800 MS power class
0.25 2 3.5 1.8 0.7
1 1 7.0 3.5 1.4
A solution to this potential problem could be achieved by a combination of increased hearing aid immunity and constraints placed on the GSM system in urban environments.
Due to the likely peak field strengths that will be experienced from GSM transmitters in crowded urban areas, it is proposed that the immunity of future body worn apparatus, such as hearing aids, should be increased to 10 V/m since this has been found to significantly reduce the probability of GSM interference (this 10 V/m figure is derived from considerations of frequencies around 900 MHz and may not be applicable to frequencies significantly higher or lower than 900 MHz). Further to this, a number of simple constraints for urban GSM system design should be adhered to:-
- dynamic power control to be implemented at the MS such that only the minimum required transmit power is used at all times (BS interference was shown not to be a problem);
- urban cell sizes limited to reduce required transmit powers;
- discontinuous transmission (DTX) to be implemented where possible;
- GSM base site and mobile pay phone (e.g. on train) transmit antennas should not be located in close proximity to electrical apparatus likely to be susceptible to this type of interference.
It is assumed that DTX will provide a reduced interference potential although this has not been verified.
7 Non-ionizing radiation
Guideline levels for exposure to non-ionizing RF radiation have been published by many organizations including Non-Ionizing Radio Committee (INIRC), the UK National Radiological Protection Board (NRPB), the Institute of Electrical and Electronics Engineers (IEEE), German Electrotechnical Commission of DIN and VDE (DKE) and CENELEC. reference to these standards are given in reference [6] to [10].
8 Conclusion
Extensive research has highlighted a potential compatibility problem between GSM transmitters and body worn audio apparatus; in particular hearing aids. However, this research has been based on a limited sample of hearing aid types of fairly old design.

The studies made have shown that the immunity level of currently available hearing aids may not protect hearing aids very well from the interference of GSM phones. Also, it has been shown that increasing the immunity to 10 V/m, as found possible by simple hearing aid modification, will reduce the probability of interference considerably. More recent research has shown some modern hearing aids to have 10 times the immunity of the older designs (in V/m). This would reduce the interference probabilities by a factor of 100.
Concerning the domestic equipments it can be concluded that GSM transportable 8 W mobile stations are likely to cause problems to domestic equipment being used in a domestic environment.
Further, it is recommended that the user's data (like user's manual) of the mobile should include a warning of the possible interference effects of the GSM mobile to the other electronic equipments.
9 Other EMC reports
CEPT-SE report "Summary document on the interference to radio and non-radio devices from TDMA-type transmissions". The report from CEPT covers much of the work included in the GSM report and considers EMC susceptibility of a far greater range of products. The findings of the two reports are similar.
CEPT-SE report "Draft report from the ERC within CEPT on the impact from ISM emissions on mobile radio services operating in the 900 MHz band". This report studies the potential for interference on GSM and other terminal equipment operating in the 900 MHz band caused by ISM equipment (Industrial, Scientific and Medical). It shows that spurious emissions from ISM equipment can degrade mobile radio service coverage at considerable distances.

Annex A: A GSM interference model “
A GSM interference model.
Summarvo
This document attempts to forecast the likely extent of intcrfercncc to hearing aid
users fiwn
GSM
transmitters.
The assessment is made through modclling of the GSM cellular system in various
scenarios as the system matures fkom 1991 onwads. The potential intcrfczence in the
individual scenarios is combined to asses the actual interference perceived by through
modclling of ‘days in the life of hearing aid users.
The critical inputs to the model are the hearing aid immunities as determined during
extensive laboratory testing.
The report concludes that a hearing aid user will experience regular daily intcrfemncc
from GSM transmissions and this has been previously shown to be due to the TDMA name
of the system.
Qmmt i
Aa sump t i on a
Ce l Ch a r a c t e r iz a t io n
3.1) RF Link B udget
3.2) Minim um MS t ra nsmit POW=
3.3) Affet id a r ea
3.4) pectmmllocation
Scenarios
4.1.1) Vehicles a nd pedestr ia ns
4.1.2) Tra ins
4. 2. 2) H i gh s it e s
4J L3) B uildingCWWW
4.3) P or t a ble a n d t r a nspor t a bleMS
4.3.1) Railway Station
‘ A day in t h e life of’ Eoe iarios
5.1) Da ily commut erfi= omouta idaLondon
5.2) P er son w or kin g a n d d w ellin g in U m d on
5.3) R et ir ed per son
.
I h amaa i on
6.1) G S M C ust om er sw it h H ea r in g Aid a .
6. 1. 1) H a n d - P o rt a b les
u~
6.4) P oss ible v a r ia b les
Conc lus ions
u
I n t r oduc t i o n .
H a ving co plet ed ext ensive hea ring a id immunit y t est ing U . 5, 81 w it h
simula ta d G S M t ra nsmission, it w a s necessa ry t o a ssess t he likely impa ct of t he
la b or a t o ry r e su lt s on h ea r i ng a i d u ser s .
Th e k ey r es ul t s t a k en k m t h es e la b or a t o r yin v es t ig a t i on sw e re t h a t t h e h ea r i n g
a ids tes ted gave rise to ‘pemeptible’interkrance when subject to a f ield strengthof 4V/m
in some direct ions .
A t ypica l ur bsn cell is eh a ra ct a r izedusin g a n R F link bu dget a n d a n um ber of
necessary assumpt ions .The sa l ient assumpt ionsused in this paper are I ia ta din sect ion
2 wi th loca l assumpt ionsconta inedin individual scenar ios .
Having cha ra cterizedthe ca l l, individual
scenario’sw ithin the cell wherehea ring
a id users may comein conta ct wi th GS M tra nsmit terswerechosen.A conclus ionis drawn
horn the individualscenario’s which highlightsthoselikely to ha ve the highest incidence
of interference.
H a vin g a r rived a t a m odel cover in g sepa r a t e scen mio’s, it w a s n ecessa r y t o
com bin e t h ese t o bu ild a ‘d a y in t h e life of a h ea r in g a i d u ser . F ou r t y pica l ‘d a ys ’ w er e
ch os en -d il lu st r a t e t h e i nci den ce of in t er fer en ce w i t h r es pect t o t h e h ea r i ng a i d u ser .
S u bs eq u en t d is cu ss ion cover s G S M s ubs cr ibe w h o u se h ea r in g a i ds , pos sible
solut ions and other inter ferences to hear ing a ids .
I t w i ll b e n ot e d t h a t t h is d ocu m en t h a s b een com pil ed fiw n R @. 10, 11 a n d 12 w i t h
~
Aazmnmt i one .
A cen t ra l L on don ba s e s it e h a s a 2kr n r a diu s a n d a ba s e s ta t ion in pow er cla s s 4
(40W).
All cells a m oper a t in g a t 50 capacity .
Veh ic e m ou n t ed t r a n s ceiv er s h a v e pow e r con t r ol t o s us t a i n a t l ea s t 102 u plin k
B E R .
Transpor ta ble are in power class 2 (8W)a nd por ta blesin power class4 (2W)with
a n ten na s h a t ig OdB iga in .
Subscr ibersw i ll be evenly dis t r ibutedbetw een vehiclemounted tra nsceiver and
port a bles/tr a na port a bles.
P eople are evenly dis t r ibutedin the cel l.
Vehicle mountedt ra nsceivers a re loca tedon three concentricrings within the ceII
a n d a r e d is tr ibu t ed in t h e r a t io of t h eir d ist a n ce t l om t h e B S .
The r i&ber of hea ring a ids in t he U K is 1.5 miI Iion (D EWS est ima t e 1 t o 2
mill ion) i .e 2.5%of the UK popula t ion .

&
W c ha ra ct e r iz a t ion
S.1 ) RF lin k bu dge t .
This budget is based on G SM Recommendat ion03.30.
R x R F i npu t s en s it i vi t y =
N F (d B ) + E t /N o (d B ) + W - kT @B S for 102 B E R (dB m )
Where
t h er m a l n oiee, k T = -1 4 d B m /H z @ 290K
W (bitrate)= 1 0 lo g 2 7 0 .8 3 3 k bit / s
NF (noise f igure)= 8dB
E &o = 8dB
Th er ef or e, R x R F in pu t s en s it i vi t y@ B S = -104d B m .
Ieotropicpower= RXs en sit iv it y + I n t er fer en cem a r gin + C a b le 10S S- bt en n a G a in
Where
a n ten na ga in = 12d B i
,
’
Allowing for Iognormel 5d B) and Rayleighfa ding (lOdB) margins gives
M in im u m s ig n a l l ev el f or 102 B E R = -94d B m .
3 2 ) Min im um MS t ran a rn it p ower s
Th e r eq u ir ed pow e r t o b e r a d i a t ed f kom a m ob il e st a t ion t o m a i n t a i n a 102 u plin k
B E R m a y b e f bu n d a f t er ch a r a c t er iz a t i onof t h e p rop a g a t i on pa t h l ees .
A t y pica l cen t r a l L on don c ell is 2k Kn n r a d iu s a n d h a s a B S loca t e d 2 m a b ov e t h e
r oof of a t a l l b uild in g . Th is b uil din g w ill b e loca t e d i n a d en s e u rb a n en vir on m en t a n d of
s im ila r h eig h t t a it s s ur r ou n din gs (@m ). As su m in g a r eceiv e a n t en n a h eig h t of 2m a n d
a f keq u en cy of 900M H z , t he pa t h l os s m a y b e f ou n d f rom eq u a t i on 3. 25 in R ef 17
~ t i = 69. 55+ 26. 1610g - 13.8210g& - A(h J + (44. 9-6.5510gh J log ~ ~ (d B )
w h er e f - ik eq u en cyin M H z (900)
& - t r a n s m it a n t e n na h ei gh t (62M )
&-dia tmca &om B S inkm
a nd km eq ua t ion 3.27 in Ref7
A(k )” : 3. 2(l og (ll .75 h J ~ -4. 97 (d B )
L - r eceiv e a n t en n a h eig ht (2m )
These equat ions thus s impli fi to
L@= 121 + 3310g~ t i (m)

ETR 357 (GSM 5.90 version 5.0.0): January 1997
S u ch a ca l l m a y t h us b e ch a r a ct er iz ed by a lk m in t er cept o f 121d B a n d a pa t h l s s
of s lops Y=3.3.Hence the
minimum t a n@t pow er needed - t he MS t o ma int a in a
104 B E R w i ll b e
121. 94 = 27d B m @ lk m (500m W )
.27+ 331 gl.5= 32.8dBm @ l.lkn (1.9W)
27+ 3310g2= 36.9dBm @ 2km (4.9W)
a ll pow er s q u ot ed bein g E R P a t MS .
Eq uat ion for interfering dista nce, &,
S. 3 ? 2
E 4%~~
E = f ield strength
Ther efor e, ~ ~ = G 302P ,
H ow e ver , s in ce p a t h los s ca l cu la t i on leads to E R P ‘:&m t he m obile st a t ion t hen t he
a n ten na ga in t er m, G , is r edu nda n t. i .e G = 1.
I t w a s fou ncl d ur in g in t er fer en ce t es ts lJ t E &5],t h a t a realistic hearing aid
suscept ib il itywas 4 V/m for a 90 degreea rc and 10V/m fbr the remaining270 degreesas
shown in Fig.lo
Fig.1
Let interference radius at 4 V/m b e & a n d a t 10 V /m d 10 h en
P, = P i
di~ = 30 P , = 0 .3 P i
a s sh ow n in F ig .1
100
& = 3z4d,7
= 0.71 P t a s s how n in F ig .1
Therefore, &= Al+ &
3.4) spectrum allocation
The GS M system will probablyopera t ewi th 3 base s itesper clus ter and therefore,
even if sectorizat ionis employe&the entirespectrum allocat ion wil l be used repeatedly
by gr oups of t hese ba se sit es. I t h a s been a ssu med t h a t ea ch ba se sit e ( B S ) cover s a
cimlla r m a of ra dius 2kln.
The GS M system will begin in 1991wi th an ini t ia l duplex spectrum al loca t ion of
5MHz per opera t or above the current TACS bands .This a l lows252001sHz carr iers and
t hus 25/3= 8 tiers per B S a nd 8 x 8 t ime s lot s = 64 physid bek per B S w
operator.
Assu min g t h a t t h er e w ill be n o m or e t h a n 8 of t hese t im e slot s u na v a ila ble f or
t r a f liq t h en 56 ph y si ca l ch a n n els r e ma i n g iv in g a m a x im u m of 112 s u bs cr ib er s .
As the G SM systemmatures, thecurrentTACS allocat ionwillbe gradua llyha nded
over until G SM occupiesthe entire25MHzcellular a lloca tion.Ea chopera torwillt herefore
ha ve 12.5MHzor62200kHz carriersa ndt hus620= 21 carriersper base si te.Thisnumber
of ca r r ier s a l low s 21x 8= 168 ph y sica l ch a n nels a n d t h us 160 a v a ila b le for t r a ffic per
opera t or and 3 2 0 in t o t al.
5 ) Ove ra ll p robabilit y.
I t w a s fou nd t h a t a g ood a ppr oxim a t ion to even d ist r ibu tion o f MS ’s cou ld be
a t t a in ed by a ssum in g t he t ra n sm it t er s w er e loca t ed on t hr ee con cen tr ic r in gs a n d
d is t r ib ut e din t h e r a t i o f t h eir d is t a n ce fm m t h e B S . Tw o r in gs p rov ed t o b e i na ccu r a t e
w i t h fou r g iv in g li t t le ch a n g e in t h e r es ul t ob t a in ed w i t h t h r ee.
Using a 10MHz al loca t ion and f id l cel l capac ity g ives the fol lowing resul t :
l12x~= 25 MS @ lkm
43
The aflbctedarea a r ou n d ea c h t r a n s m it t e r f iv m eq u a t i on 1 is :
2.18 x 0.5 = l.lm z
2.18X 1.9= 4.1m 2
2.18 x 4.9 = 10. 7m 2
G i vin g a t ot a l a . fE ect eda r ea fr om M S’s of 25x1.1 + 37x4.1 + 5ox1O .7= 714. 2m *.
As su min g t h e B S is pow er cla s s 4 4 0W) t hen , fiw m eq ua t ion 1 t hem w ill be a ibr th er
a f fect e d a r ea of 87. 2m za m n m dt h e B S g iv in g a t ot a l of 801. 4m 2.
S in ce t he a m a of t he 2km cell is YC (2000Y 1.26x107m Zh en t he per cen ta ge
@ect ed a r ea is
~o,” o oo649b
Substitutingfigures fo r a fu lly loa d ed 25M H z s ys t em y ield s a t ot a l a f fect ed a m a
of 2123.4m2or 0 . 017 .
As yet , however , we have no informat ion concerning the f iwquencya nd dura t ion
of this interference.
Ve h ic le m o un t ed MS.
Vehicles a nd pedestr ians.
A m obile on t he edge of t he 2km cell h a s been sh ow n t o be t ra n sm it t in g4.9W
r ise t o a n a i lk ct ed a r e of 10.7m2and hence a mean interference ra dius of 1.8m.
Assumingthe separa t ionbetweenpedestr ia nson the pavementa nd vehicleson the
r oa d is 4m , t h e h ea r in g a id u ser w ill n ot exper ien ce in t er fer en ce h t h e t r a nsm it t er .
Eveni f the a id is or ienta t edwi th maximumsuscept ibi li ty towa rds the road , the car would
st ill h a ve t o be closer t h a n 3m t o c a u s e i n t e r k e n c e .
It is uniihel thut inteqkmce will be pemeived ~m vehide8 on the road whilst
walking on the pavement.
4.1.2 Tr a in s.
I f it is a ssumed t ha t t here is a IOdB a t tenuat ion into a carriage fkom a r d
m ou nt ed a n t en na , t hen a G S M pa y ph on e on t h e t r a in in pow er cla s s 1 (20W) w i ll h a ve
a n a f fkct ed ra d iu s in t h e t r a in eq u iv a len t t o t h a t fr om a 2W t r a n sm it t er .
Aeeumingthetrawdt tar
k loca t a d in t he cen t re o f t h e t r a in , i t is fou nd t h a t 1. 2M
or 1.2% of t he t ra in w ill be a fE ect edfkom eq ua t ion 1. Assum in g people a r e even ly
dis t r ibutedon the tra in then the probabil ity of perceiving inte t ierence is 0.012.
I t sh ou ld be n ot ed t h a t in vest ig a t ion h a s sh ow n t h a t pem on a l t a pe pla y er s a r e
eq u a l ly a s s us cept i bl et o AM t r a n s mis si on a n d t h er e is l ik el y t o b e a h ig h d en s it y of such
equipmenton commuter tra ins.

402) Bases .
4.2.1) L ow s it es .
I f it is a ssum ed t h a t t he B S is ~wer class 4 (40W), t h en t h e a f kct ed a r ea w i ll b e
942m2
&am
equat ion 1.
As su m in g p eop le a r e ev en ly d is t r ib u t ed w i t h in t h e cell, t h en t h e p rob a b il it y of a
hearing aid user experiencinginterferencewil l be
9 4 2 = 7 .5X l&
1.26x107
s in ce t h e a r ea of 2k m r a d iu s cell is 12.6k m2.
The probability of intetienmce j oma base site whilst walking on the pavement is
negligible. This is fiwther reduced since BS’Swill be sited on top of uildings and not at
ground level.
4. 2. 2/ H i zh S i t es .
Many (MM BS will be located on t op of t a l l b uild in g s w h i ch m a y b e of fice b lock s
con t a i n in g a h ig h d en s it y of pe op le.
hbgt iet i~ io ~ ofa ~ doffi~ ~ ~ ~ ~ x 15x15 mw it ha B S
a n ten na m ou nt ed 10M a bove t he t op floor t hen r a dia t ion a t a n gles gre at e r t h an 6 0
d eg rees f rom t h e m a in lob e w ill pen et r a t e t h e b uild in g a s su min g t h e a n t en n a h a s n ot
been t ilt ed t o m o@ cover a ge.
Th e v er t ica l r a d ia t i on pa t t e rn f kom a t y pica l s ect or iz ed B S a n t in n a s how s t h a t
r a d ia t i on a t 60 d eg rees o r g rea t e r t im t h e m a i n lob e ia s uppr es sed by 20d B t o S O dBa n d
t h u s, a s s u mi ng a n a t t e n u a t ion of 10d B lR ef .6] in t o t h e b uil din g a n d a f ur t h er 5d B f rom
t h e r oof (n o w i nd ow s ) g iv es a m in im um a t t en ua t i onof 35d B .
Assuming the transmi t ter is in power class 1 (320W)55dBm, then the ana logous
scenar io is a 55435= 20dBm (1OOMW)ransmiss ioninto &es space. This equat8s to an
int erference ra dius of 0.26m a t 60 degrees born t he ma in lobe a nd O.&m (65dB
at tenuat ion)ver t ica l ly downw ards f rom equat ion 1.
It is themfom u likeiy thut hearing aid users in an ome block directly underneath
a (2SM BS will experience any interfmnce even if they w at the top of the building and
the BS is in power cltis 1.
4 .2 .3 ) B uilding coveraze.
A typkal a t t e nu a t ion in t o a b uild in g is 10d B [R ef .6] a n d t h us t h e in t er fer en ce
.
~ * a n .cmensit e. I t fbllow s t ha t anY b uik lb w w i t h in a 1. 7m r a d iu s f kom t h e
B S w ill h a ve su&ie& field st ren gt h in sid e t h ~ bu i d i~ t o
h ea r in g a i d u ser s.
rise to
interfienmce in a@acent buildings.
Po rt a ble s a n d Tr an a po rt a ble s.
Rai lwav Sta t ion .
give *e
to interferenceto
Por table
G S M

maximum power of 2W. This gives ~ t o a n t i ct ed a ma of 4.4m9 per t ra nsmit t er ,
a s s u min g n o a n t e n n a g a in a t t h e por t a b le; f kom eq u a t i on 1.
Ta king t he a rea of a pla t form a s IOOm x 10m = 1000rn*a nd t he number of
pla t for ms a s 10 t h en t h e t ot a l s ta t ion a r ea is 10,000m *.I f ea ch t r a in h a s 10 ca r ria g es
ca rrying 100 people, a nd a t ra in a rrives a t ea ch pla t form during t he rush hour
s im ult a n eou sly t hen N M()x 10 = 10J M Opeople w ill be in t h e s ta t ion a t a n y on e t im e
le a d in g t o 1 p er s on p er m 2.
The populat ionof greater Londonis roughly 7 mill ion in an a rea of 15801Rn2hich
is assumedto riset o roughIy 10mill ion, &un tra . i%clow ana lysis ,during working hours.
As su min gt h e s t a t ion is loca t e d in a 2k m r a d iu s ca l l of a m a 12.6k m2a n d t h a t t h e
popula t ionof London is evenly dis t r ibutedin the 1580km*wi th in Grea ter hmdon, then
Ioxl@ X 12.6 = 80,000
people will be in t h e cell.
S ince therea re 10,000people in the s ta t ion dur ing rush hour (1/8th of the tota l ),
a s s um in g t h e cell is 50%l oa d e d a n d t h a t 50%of ca lls w ill be fkom hand por tab les then
28x l/8 = 3.5 ca lls w ill be a ct iv e in t h e s ta t ion a t a n y on e t im e d ur in g r u sh h ou r w it h a
10MHZallocation
S in ce ea ch t r a n sm it t er h a s a n a f %ct ed a r ea of 4.4r n 2a r ou nd it t h en a t ot a l a r ea
of 3.5 x 4.4 = 15.4m 2( 0.154%) of
the
st a tion a rea w ill be a ffbct a d. Th em is t hus a
pr ob a bilit y of 0.00154 t h a t a h ea r in g a i d u ser w i ll b e in a n a 6@ed a m a a s su min g cla s s
4 porta bletra nsceivers .
When the system @y occu pies 25M H z , t h e n u m ber of ca l ls or ig in a t i n g i n t h e
s t a t i on iiw m h a n d por t a b les r is es t o 80 x l/8 = 10, t h e a f I b ct e da r e a t o 10 x 4. 4 = 44m 2a n d
thus the probabil ityr i ses to 0.0044.
Theprobability of interference~m a handportable tmnsceiver in a milwaystatwn
is 0.00154 with a 10MHz allocation and 0.W44 with 25MHz.
I t h a s been fou nd t h a t t h er e a r e 80,000 p eople in a 2k m r a diu s cell t hu s w it h a
50%loa d ed cell a n d a 10MH z a lloca t ion , 28 of t h es e ( 1 in 2800 ) w ill be u sin g a G S M
h a n d por t a b le .A t y p ica l of fice h a s 1 per s on in l(h n a a n d h en ce w i t h a 10 s t or ey b uild in g
wi th 100 people per f loor there wi ll be 10 0people in 10,000m2.
Since 1in 2800peoplewi l lbe us ing a GS M transmit ter ,0.36people in the building
w i ll b e r a d ia t i n g 2W (cla s s 4) g iv in g a t ot a l a f f ect e d a r e a of 1. 6m *f kom e q u a t ion 1. Th is
eq u a t e s t o 0. 016%of t h e of fice a r e a a n d h en ce a pr ob a b il it y of in t er fer en ce of 0. 00016
assumingeven distr ibutionof workers.
Wit h a 25M H z a l loca t i on , 1 in 1000p eop le w i ll b e u sin g a G S M h a n d p or t a b le a n d
thus the tota l f iected area wi ll be 4.4m2ikomequat ion 1 and the inter ferenceprobabil ity
r is es t a O J I U WL
Thepmbabiiity of interjknce jhm hand portable tmnsceivers in an o Ze bkch k
0.00016 with 10MHz allocated and 0.00044 with 25MHz
- 4.3.3] Street
As su min g t h e pa v em en t s of cen t r a l L on don a r e 3m in w i dt h a n d a r e loca t e d on
bot h sides of t he roa d t hen, know ing t here a re 17.5 km of roa d per km2, w e ha ve a
pa v em en t a r ea of 17.5xl@ x 2 x 3 = 100, 000m 2n U s m 2.As su min g t h er e i s 1 per son per
5m 2t h en t h er e w i ll b e 20, 000 pe op le o n t h e p a v em en t s i n lk n a 2.

will be 28 actively transmitting ha nd porta blesdistr ibutedbetween 20,000 p eopl e ( 1 in
714 ).
S in ce t he pa v em en t is 3m in w id th t hen t her e w ill be 1 per son ever y 1.6m a n d
h en ce 1 h a n d por t a b le ev er y 1.6x 714= l143m . As su m in g t h e t r a n sm it t er is s t a t ion a r y
a n d t h e h ea r i ng a i d u ser is w a lk in g a t 3k m /h (0. 83m /s ),
then
it w ill t a ke 23 m in ut es t o
w a lk b et w e en t r a n s m it t e rs .
Wh en t h e s y st e m occu pies 25M H z , t h er e w i ll b e 1 in 250 p eop le w i t h a n a ct i vel y
t r a n s m it t i n gh a n d por t a b le a n d t h u s on e t r a n s m it t e rev er y 400m . At 3k m /h i t w i ll t a k e
8 mi lllt to -k bCtWW Xitransmitters.
If the transmitters in power class 4 (2W) thent heinter fimnce radiuswi ll be 1.2m
fr om eq ua t ion 1, a n d t h us t h e su bject w ill h a ve t o w a lk fbr 2.4m w h ilst exper ien cin g
inter ference .At Win/h this wi ll t a ke 2.9 seoonds .
The@re, a hearing aid ueer walhing along a Lm&n street duringpeak time will
experience 2.9 seconds of inte~emnce j omhand portable tmnsceivers every 23 minutes
with 10MHz allocated and evay 8 minutes with 25MHz.
4.3.4) Train.
Sin ce i t h a s be an sh ow n t ha t t her e a r e 8 0 ,0 0 0p eo ple in a 2 km r ad iu s c e ll a n d
a s s um i n g 5 0 of t h e 112 ch a n n el ca p a cit y w ill b e t a k e n u p by h a n d por t a bles t h en 1 in
2800 people w ill ca my por t a ble tra nsceivers. .1
As su m in g t h e t r a i n is ca r r y in g w or ker s t o L &d on , t h en r ou g hly 0. 36 p eopl e w i ll
b e u sin g a G S M h a n d por t a ble. I f t h is is a cla s s 4 (2W) t r a n s mit t er t hen t h e in t er fer in g
r a diu s w ill be 1.2m a n d h en ce, a s su min g t h e t r a ns mit t eris n ot a t t h e en d of t h e t r a in ,
a 0.36 x 2.4 = 0.9m lengt h of t he t ra in ( 0.9% ) w ill be a ffect ed. Ass ming a n even
distr ibution of peopie, the probabili tyof interferenceis 0.009.
With a 25MHz allocat ion, the penetration rises to 1 t r a n sm i t t e ri n 1 0 0 0peopleand
thus
2.4 of the train will be
a f kt ed a n d t h e pr ob a bilit yr is es t o .024.
Aga in t her e a r e likely t o be a la r ge n um ber of per son a l t a pe pla y em on such a
t r a i n w h i ch h a v e b een f ou n d t o b e eq u a l ly a s s u sce pt i ble t o in t er fer en ce.
Thepmbability of inte emnce fim a hand portable transceiver on a train is 0.009
with 10MHz alkmzted and 0.024 with 25MHz.
n
‘A Day in t h e life of s c e n ar im
5 .1 ) Da ily com m u t er fr om ou t sid e I.a n dom
Th is d a y in t h e life of a h ea r in g a id u ser is m a d e u p of t h e f ollow in g s cen a rios
Tr a vel f om h om e ( m ra l ) t o r a ilw a y s ta t ion a n d r et ur n
2 x 15m in s = 30m in s
[email protected] za injOuma y t Ahmdon 2xlhr = 2hrs
Time spent lea ving a nd w a it ing for t ra in 2x15mins= 30inins
Tube journey 2x15mins= 30mins
Time spent in office 8hrs
The tra vel conducted in t h e r ur a l a re a a nd on t he t ube maybe ignored since them will
be no interference.
Wh en t r a v elin g on t h e t r a in , in t er fer en ce ma y b e ca u s ed b y a pa y ph on e on t h e t r a in or

sources is
= 0.012+ 0. 009 + 1.08x104
P ti = 0.012 + 0.024 + 2.88xl@
= 0. 036 f or 25 M H z
Assumingthe average d ur a t ion of a ca ll is 2m in a a n d s in ce t h e t im e s pen t on t h e t r a in
is 2 h ou rs , t h en
Tota l inter ferencedura t ion = 120x 0.021= 2.5 mine
Number of ca l s = 2.5 = 1.26 ca lls
2
‘.Nm ebet w een ca I Is = 120 95 min e
1.26
SubstitutingP-l = 0. 036 g iv es a cor r es pon d in g t im e b et w e en ca l ls f or a 25M H z s y st e m
of 56 minutes .
U w ill b e n ot ed t h a t if t h e pr ob a bili~ ofin t er fem n m fiw r nt h e pa y ph on e a n d t h e
ha nd porta bletra nsceiverare sepa ra ted,the timebetw eenexposuret o interferencefor the
d ur a tion of a ca ll is 167 m in ut es d ue t o t he pa y ph on e, 222 m in ut es d ue t o t he h a nd
por t a b le w i t h 10M H z a l loca t e d a n d 83 m in u t es d u e t o t h e h a n d p or t a b le w i t h 25M H z.
Whilst on the train interference wiU be experienced for 2mhs evtvy 95mins for a 10MHz
system and evew 56 minz fbr a 25MHz system.
Wh ils t in t be r a ilwa y s t a t i on , t h e probabil ity of incidence of in ter ference is 0.00154(
10MHz) or 0.0044 ( 25M H z ). As uming 30 minutes ( 1800s ) are spent in the ra i lway
s t a t ion a n d a ca l l l a s t s for 2m in s, t h en
Tota l interferencedura t ion = 1800x 0.00154= 2.8seconds
Number of ca lls = 2.8 = 0.02 ca lls
m
a
Subst i tut inga probabili tyof 0.0044givesa correspondingtimebetw een cal ls for a 25MHz
sys tem of 7.6 hours .
Whilst in a milwa.. - interfikrenceLuillbeexperiencedfor 2 reins eve~ 22 hours /br
10MHz and eve~ 7.6hours for 25MHz.
I t ha s been s@wn in section 4.3.3 that a 2.9 second burst of inteflenmce wiff be heard eve~
- 23 minutes jbr 10MHz and eve~ 8 minutes for 25MHz.
D u r in g t h e 8 h ou r s in t h e of fice, t h e pr ob a b ili t y of in t er fer en ce is 0.00016 with 10MHz
and 0.00044w i th 25MHz.Assuming 2 minuteca l l dura t ion then
Tot a l in t er fer en ce d ur a t i on = 8 x 60x 60x 0. 00016= 4.6s econ d s
Number of ca lls = 4.6 = 0.038 calls

120
Time b et w een ca lls = 8 = 208 h oiw s
0~ 8
S u bs t it u t in g a pr ob a bilit y of 0.00044 g iv es a cor res pon din g t im e b et w een ca l ls f or a
.25MHzSySteM of 75 hours.
Whilst in the ofiee, inteqfmmce will be heard for 2 minut s eve~ 208 hours /br a 10 MHz
system and evay 75 hours fir a 25MHz system.
Ovendl conclusion of *ce aria S.10
The incidence’s of interference wil l be as fol lows:
10MHZ.
1 x 2 minutes at the station every 1. months
1 x 3 s econ d b ur st ev er y d a y whilst walking on the
s t r e e t
1 x 2 minutes every month in the @ice
?
2 x 2 minutesevery day on the train
1 x 2 m in ut es a t t h e s t a t ion ev er y 2 weeks
4 x 3 s econ d b ur s t ev er y d a y w h i ls t w a l k in g cm t h e s t r eet
lx2m in u t es ev er y 9d a y s in t h eof fice
M) Pe r son workinga nd dwe llin g in Lon don .
.
Wa l k &om h om e t o t u be s t a t i on
2x15mins= 30rnins
No interference
Walk *m t u be s t a t i on t o of fice
2x15mins= 30mins
Tot a l t im e o n s t reet = 60 m in e
‘lYmespent in office
8 h ou r s
OvemU conclusion of scenario 63.
U s in g t h e r ea s on in g in 5.1, the incidence of inter ferencewiI Ibe as foI Iows .
10MHZ.
— .+
3 x 3 s econ d b ur s t ev er y d a y w h i ls t w a l k in g on t h e s t r ee
1 x 2 m in ut es ever y m on t h in t h e offke
25MHZ.

1 x 2 minutes every 9 d a ys in t h e office
5.3) Re t ir ed p er aom
Whilst t h e r et i red p er s on is d w ell in gin a r u ra l a r a a , t h e incidence of interfbnmce wil l be
n eg lig ible. H ow ever , i f t h a t per son spen ds a d a y s hoppin g in L on don , t he d a y m a y be
char acterizedas f~ows.
Tr a vel fkom h om e ( r ur a l ) t o r a ilw a y s t a t ion a n d r et u rn
No Merf&w ence
R et u rn t r a in jou rn ey b L on don
2xlhr
=2hrs
Tim e s pen t lea v in g a n d w a i t i ng f or t r a i n
2x15mins= 30mins
No interference
3 h ou rs s hoppin g of w h ich 1 h ou r is s pen t in t h e s t reet
1 h ou r
Overall conckwn of 8cenario 5.3
Using the reasoningin 5.1, the incidenceof inter ferencewi l l be as fol lows .
10MHZ.
lx2minut es ont he t ra in
U nlikely incidence of int dersnce a t st a tion ‘”
3 x 3 s econ d bu rs t w h ils t w a l kin g on t h e s t reet
25MHZ.
2x2m in ut es on t het r a in
Unlikely incidence of interferencea t sta t ion
7 x 3 s econ d b u rs t w h ils t w a l kin g on t h e s t reet
5.4) Mo t orwa y t r a ffio jam
I t h a s b een s how n ~ f.10] t h a t a h ea r in g a i d u ser d riv in g a v eh icle o n a m ot om va y ,
w it h t h e a id or ien t a t ed such t h a t m a xim um su scept ibilit y is t ow a r ds t he t r a fE c, w ill
exper ienceinter feren~ i f the adjacentvehicle is radia t inga (XM tra nsmit power of more
t h a n 2W.
I t wa s found tha t the probabil ityof the adjacentvehiclehaving a GS M transceiver
w a s 0. 05 a n d t h a t if t h e t r a f lic h a d a r el a t iv e speed of 5 m ph in t er fer en ce w ou ld b e h ea r d
f or 2 s econ d s ev er y 4 m in ut i s.
6 .1 ) GSM cu s t om er s wit h h ea r in g a id s .
- 6.1.1) H a ndP or ta bles.
E qua t ion 1 st a tes t ha t &= 2.18 P , a nd hence d2m m= 2.18 P ,
K

P t = 0.252 = 90mW
0.7
or , t h e m a x im u m t r a n s m it pow e r f mm a h a n d -por t a b le t r a n sm it t e r h el d t o t h e u n a id ed
ea r is less t h a n 90M W t o pr even t in t er fer en ce t o t h e h ea r in g a i d on t h e ot h er ea r .
I fit is a ssum ed t ha t minimum suscept ib il ity is in the direct ion of the tra nsml
t er
( i.e t h rou gh t h e h ea d ) t h a n t h is pow er m a y r is e t o 210m W. S i nce G S M h a n d por t a ble’s
in pow er cla s s 5 w i ll b e r a d ia t i ng 800M W, a h ea r in g a i d u ser w ill be u na b le t o u se s uch
a t r a n s cei ver w h en n ot u n der pow e r con t r ol .
mm
nmmtables.
Tr a n spor t a ble t r a n sceiver s w ill be in pow er cla s s 2 en d w ill hence ra dia t e a
ma ximumpower of8W with an interferencera dius of 2.4m &om equation 1. ‘I%eopera tor
of s uch a t r a n s cei ver w i ll ob viou sly b e w i t h in t h is r a d iu s a n d h en ce in t er fer en ce w ill b e
perceived by a he*g ~ d -r w hi~ t a @ iS bet ig ma de. I t is P msible tha t t he subject
cou ld or ien t a t e h im self w it h r es pect t o t h e a n t en na t o elim in a t e t h e in t er fkr en ca a n d
m a k e a ca l l pos sib le.
6.1.3) Mobiles.
A in ves t ig a t i on M . 9] h a s s how n t h a t a h ea r i ng a id ed d r iv er of a v eh icle is lik ely
t o b e a b le t o u se a GSM mobile t ra nsmit terprwided the antennais mountedin thecentre
of a ontinuousmetal l icroof . Other ant ennaposit iom or a non-metal l icsun-roofmay lea d
to unaccepta blyhigh f ie ld s t rength ins ide the vehicle.
62) dUtiOIML
I t w a s n ot ed du rin g in &fbr en ce t es tin g, t h a t t h e 100%AM in t rod uced b y t h e
TD MA s tr uct u re of G S M w a s t h e ca u se of t h e in t er kr en ce a n d t h a t con t in uou s G MS K
h a d n o effect . Th e in t er &r en ce &m t h e ba s e s it e cou ld t h er efb re b e elim in a t ed by t ill
loa ding a t a ll t imes i.e a ll t ime slot s a ct ive a ll t he t ime a nd const ant a mplit ude
transmiss ion .However th is drama t ica l ly increasesC A fm the fbl lowingreasons :
.
i i) Discont inuoustransmission (DTX) at the BS wouldbe impossibleleadingto a two fold
degra dat ionin spectra l eff iciency since one way speech is interspersedw ith roughly 50
of silence.
i ii )Adapt ivepower control a t the B S wouldbe imposs ib lesince this wouldbe requiredon
individual-t imeslots leading to am pli tudemodula t ionof the carrier .
I t s hou ld b e n ot ed t h a t a n y t hin g l es s t h a n 100%loa d in g WWr es ult in a s im ila r
audiospectrumperceived by the subject as havingonly one t imeslot ac t ive.This is to say
t h a t t h e a u d io s pect r um d em od ula t e d &om a on e t im e s lot a ct iv e B S w ill b e t h e s a m e a s
t h a t fr om on e w it h on e t im e s lot in a ct ive.
The base s ite scenar ios presentedin this documenta re based on the results of the
in t er fer en ce s t u die a t B TR L i. e on e ca m i er a c t iv e. H ow e ver , a G S M b a s e s it e w i ll h a v e
8 ca r r ier s per cell w h en occu py in g 5M H z per oper a t or a n d u t ilk in g a t h ree cell r epea t
pa t t a r m .S in ce TD MA fk a mes on s epa r a t e ca r r ier s w ill b e s yn ch ron bed a t t h e B S , t h e

interference level when correspondingtime slots ar e act ive
6=6) Other interferences.
The two hear inga id users who took par t in the or igina l suscept ibi li ty t es t ing were
given a quest ionnaireconcerning
current levels of interibrence.
I t wa s determinedtha t one subjectusedhis hear inga idonly once or twice a month
w h er e t h e ot h er u sed h is for t h e m qjor i~ of t h e w or kin g d a y. Th e t im es w h en t h e a id s
w ou ld d efit ely b e u sed w er e in t h e office, a t m eet in gs a n d d ur in g lect u rw .
B oth subjectsvery ra rely pemeiveda nyinterferenceto their aids with one recal l ing
only ever hear ing a single burst lasting for several minutes. The second subject recalled
h ea r in g bu rst s la s tin g a secon d or so ver y in t keq uen t ly a nd iden t ified t he sou rce a s
fluorescent lights.
6.4) P ossible va ria bl~
The scopeof this model is seen to be smal land dominat edby assumpt ions .There
follow s a lis t of va r ia b les t h a t m a y s ig nifica n t ly a f fect t h e con clu sion s d ra w n fk om t h e
model.
i)
ii)
iii)
iv )
v)
vi )
vii)
viii)
ix)
Th e h ea r in g a id u ser m a y sw it ch t h e a id off for per iod s of t h e d a y w h en ver ba l
communicat ionis not essential .
Hear inga id users may ident i&the sourceof the inter ferenceand learn to posit ion
t hemselves aw a y * t his source.
The scenar ios only apply to G reat erLondon.
Th er e t e nd s t o b e a n a t u r a l e xclu si on z on e a r o un d a per s on u sin g a h a n d por t a b le
t r a n s ceiv er w h ich w i ll r ed uce t h e a r e a in w h ich a h ea r i ng a i d ed ped es t r ia n m a y
be a nd hence reduce the probabili tyof interference.
D is con t in u ou s t r a n s mis sion a t t h e M S w i ll pr od uce b rea k s in t r a n s m is sion w i ll
change the wa y in which inter ferenceis perceived.
.
N ot a l l t r a in s w ill h a ve a pu blic p a y ph on e a n d t h os e t h a t d o w i ll h a ve t h e ph on e
loca t ed between carr iages i .e wheret here are no passengers .
Th e h ea r in g a i ded popu la t i on w ill be b ia s ed t ow a r d s r et ir ed people w h o d o n o
commuteinto the ci ty .
D u e t o t h e n a t u re o f t h e ca l cu la t i on ,t h e n um ber of expos ur es t o in t er fiin ce a r e
a v er a g e fig ur es . Th e s t a n d a r d d ev ia t i ona w a y t i m t h is m ea n is li kely t o b e l a r ge.
Th e ‘l&d por ta ble on a t ra in ’figur es m a ybe si~ ca n tly r educed if t he h ea r in g
a id is n ot oca t ed i n t h e cen tr e of t he t r a in a n d if a sign ifica n t a t t en ua t ion of t h e

n
i)
ii)
iii)
iv )
v)
vi )
vii)
viii)
ix)
x)
xi )
u a i on s .
Th e s c ena r i o sp r e s en t e d in t h i s do cumen ts ugge s tthat the maximum incidence of
G S M i nt er fb mn ce w i ll b e 5 m h a n d or t a b le a n d t r a n s por t a b le t r a n sm v
em S ince
this appsuatusis carr ied by the public in to areas of high popula t ion
concentration.
There is a lso a s ignif icant probabil ity of in ter ferencefkom a publicpay phoneon
a com m ut er t r a i n .
I t a ppea rs t ha t a hea ring a id user will be una ble t o use a G SM port able or
transportabletransca
‘v er in a n y pow er cla s s.
I t islikely t ha ta hea ring a iduger w ill bea blet o usea vehicle mount ed
t r a n s ceiv er pr ov id ed t h e a n t e nn a is m ou n t ed i n t h e cen t r e of t h e m of
Sincei t has been found tha t inter ferencemaybe perceivedinikaquent lyt im other
s ou rces , t h en it is G S M in t er fer en ce per ceived d a ily t h a t g iv es r is e t o t h e m os t
concern.
O f t h e fou r ‘d a y in t h e life of
s cen a r ios ch os en t h e d a i ly com m ut er t o L a &n f rom
a r u ra l a r e a is m os t lik ely b ex per ien ce r eg ula r i n t a r kr en ce w i t h a d a i ly expos ur e
fm t he dur a tion of a ca ll (2m in s) w hilst on t he t ra in a n d a 9 secon d da ily bur st
w h i ls t w a lk in g on t h e s t r eet ev en w i t h t h e in it i a l 10M H z a l loca t i on .
Th is r is es t o t w o d a ily expos ur es fa a cd l d ur a t ion a n d fou r 8 s em m dd a ily b ur st s
when the al loca t ion reaches 25MHz.
The scena rio of t he London w orker dw elling in t he a t y highlight a sma ller
eXP OSIUWo inter ference.-t opera t ingwi th a 10MHzal loca t ion , three3 second
b ur s t s w i ll b e ex per ien ced on t h e s t r eet ev e~ d a y r is in g t o s ev en d a i ly b ur s t s w i t h
system mat ur ity .
Th e r et i red per s on is fh r m or e l ik ely t o b e w e a r in g a h ea r i ng a i d b ut l es s lik ely t o
b e in t h e cit y . I f s pen din g a d a y s hoppin g in t h e s t y, t h e expos ur e t o in t dbm n ce
w ill be high dur ing t ha t da y w it h a burst for a ca ll dura t ion dur ing t he t ra in
journey and thwe 3 second bumta whi ls t wa lkingbetw eenshops .This r ises to two
expos ur es f or a ca l l d ur a t i on a n d s ev en 3 s econ d b u r st s w i t h s y st em m a t u r it y .
Wh ils t in a v eh icle in a m ot om v a yt r a f fic ja m moving a t 5m ph , a h ea r in g a i d u ser
wi ll exper iencebura ta of inter ference las t ing z seconds every 4 minutes .
I t ca a b a seen t h a t giva n t h e cu men t im mu nit y of N HS h ea r in g a id s t o 900MH z
G SM E MI, a person w ea ring such a n a id a nd req uiring t o use it dur ing t he
w or kin g / t r a v elin g d a y w i ll exper ien ce r eg ula r d a ily in t er fer en ce a s t h e G S M
system mat uree.
I f t h e in cid en ce of in t er fer en ce is d eem ed u na ccept a b le, a greater h ea r i ng a i d
immunity a t 900MHz wil l be required to reducethe incidence of G SM interference,
s in ce t h er e a p pea r s t o b e n o pr a ct i ca l m od if ica t i ont o t h e G S M s t m ct u r e t h a t w i ll
achieve this .
Page 29
Refe rences .
Centra l S ta t i s t ica l OfEce- ‘Annual abs t rac to f s ta t i s t ics 1987’
H M SO N o. 123
Central Statistical Office - ‘&giOIl&drends 1985’
HMso
C C I R - ‘VH F and UHF propaga t ioncumes for land mobile services’
CC IR Rec.529 Rep.567-3
G S M recommendations 03.30 and 05.05
Short J M - ‘An invest igat ioninto the eft ’ectsof RF interference on
h ea r i ng a i d u ser s’
W8f89
I E E G r ou p E l l - P r opa g a t ion kt or s a n d in t efler en ce m od ellin g f or m ob ile r a d io
systems’ IE E Colloquium,Digest No. 1988/123
HolbecheR J - ‘Land mobilera dio systems’ IEE Telecomms ser ies 14
P eter P eregrinus 1985
t
Ta t tersa ll P R - ‘D om est ic eq uipm ent suscept ibilit y t o G S M m obile ra dio
transmission’
X3W89
S hort J M - ‘An investigation to determine the penetration of 900MHz RF into
vehicles’ 23/lW89
Mu a da y P J - ‘G S M E MC scen a rio model - M ot oxw a y t dE c ja m ’ 9/f80
S h or t J M - ‘G S M I n t er fer en ce S cen a r ios ’
3W11/89
S h or t J M -’Ad a y in t h elif e of a h ea r i ng ei du se 9n /90
Munda y P J - Correspondenceof 31/1/90and 12/12/89
.

AnnexB:
1
interference.
Attenuationproduced by wearer’s h ead : VP t o ~ dB
GSM Power ~Vdm

1 ot her
Averagecalllast8Z dn
21?GsMEPu
1* ---
3%
10%
4V/m
5%
14*
40%
lZV/m.
0.5
1.5*
5*
1
Averageoallalast2 *UteS
Annex C:
IJEW DIGITAL TRANSMISSION TECHNOLOGIES - THE EMC CONUNDRUM
1 INTRODUCTION
personal mobility.
growth in the use of cordless telephones and cellular radios
has been spectacular.
where frequency spectrum is similarly in demand, has required
the development of new technologies.
TECENOLOGXES
selected ‘time division multiple access’
(TDMA) technologies
The
analogue, techniques are still used extensively but are slowly
being replaced by digital TDMA systems, which offer both
improved performance and spectral efficiency, particularly in
large ‘public systemsl.
In a TDMA system the
‘channel’ used by an individual
represents one time slot from say 10, allocated to that user
normally at a sub-audio rate, for example, 200Hz.
The resultant effect is that a burst of RF is transmitted at
that sub-audio rate, in the example above the RF burst would
last for 5 msec and be repeated every 50 msec. The
m= RF
burst would contain the transmitted information at a rate
10 times faster than the basic rate to provide a continuous
transmission for the user.
The RF signal described above is amplitude modulated (AM), in
this case at 200Hz, this AM is in addition to the modulation
contained within the RF burst itself. Tests to date have
shown that many radicrand non-radio (particularly audio
products) are susceptible to an RF signal with t ese
characteristics.
equipment also means that the transmitter will be physically
much closer to potentially susceptible equipment.
4 EMC DIRECTIVE AND LEGISL74TIVEPROVISION
The Community’s EMC Directive requires that all
electrical/electroni equipment neither emit nor radiate
unwanted RF signals, and not be susceptible to other (wantedl
RF signals, ie legitimate radio transmissions.
Legitimate radio transmissions are licensed in the UK by the
Radiocommunications Agency of DTI, under the ‘Wireless
Telegraphy’ Acts. The licence provision includes the
frequency,

equipment approved to definitive standards of performance.
The EMC Directive will come into force on 1 January 1992; it
offers the power to control,
from that date, equipment ‘placed
on the market’ and will require compliance with essential
immunity’ standards.
is also supported by a Community Directive, should become
operational at a similar date.
The WT Act licence offers the
potential to control the power levels of GSM equipment.
s
The ‘generic’ immunity standard being set by CENELEC has been
currently agreed to be set at ‘3 volts per metre~
The immunity standard necessary to avoid interference from a
GSM equ pment will need to be in the range ‘IO volts per
metre~ to ~20 volts per metrel if the current power levels o
GSM equipments are to be maintained. IIIt is, of course,
subject to the distance between the &M transmitter and the
target device being defined.
related’ or
provides the conundrum.
6
DISCUSSION
Scant regard, has in the past been paid to the design of
equipment with realistic immunity standards - particularly in
the domestic market.
legislative framework to correct this deficiency.
The
pitched at a level that most equipment designs already meet
and thus provides little or no real improvement.
A more
The adoption of TDMA technology, with its inherent advantages
is more intrusive, in EMC terms, than previous FDMA
technologies.
such as”
being in close proximity to the new digital radio telephones.
It could.-beargued that th AM component of the TDMA
transmission is also Iunwantedl and hence covered by the EMC
Directive; this view is not shared b the spectrum managers,
where it seen as a legitimate and efficient transmission.
The spectrum manager has the option of defining the maximum
radiated power,
standards.
7
CONCLUSION
non-radio equipments, coupled with a limitation of radiated
power from, particularly hand held TDMA transmitters, will be
essential to avoid unwanted EMC problems.
The attached Annex
o J WHEATON
ANNEx
1 metre;
standard level.
at 10 volts per metre minimum:
sectorial immunity standards for body worn audio
equipments be set at 15 volts per metre minimum;
sectorial immunity standards for any ‘safety
co scious’ system be set at 25 volts per metre
minimum. t
radiated power to:
vehicle mounted equipment, where the antenna is at a
minimum height of 1.5m, located at least 0.75m from
th vehicle~s outline - 5 watt peak power.
. “
Annex D:
Source: CSELT (Italy)
Operation
1
= Pacemaker
Cardiac pacemakers
hcan disease in order to stimulate artificially the beat of the heart.
1,
Demand types sense w en the heart beat is abnormal and make necessary
corrections. Most pacemakers in use arc of the demand type.
A simplified block diagram of a demand type pacemaker is shown in fig. 1. The
circuit and the power supply (a solid state battery) arc sealed in a titanium
package to redu e
the
electromagnetic
shielding.
The circuit is implanted in the abdomen of the pati nt while the pacing lead
carncs the pulses directly to the hcmt.
The pacing lead is a
catheter introduced through veins and has the double
function of exciting the cardiac activity and detecting the spontaneous signals.
In fact when the detector reveals the natural heart beat (which is an electric
pulse with pea to peak ampIitudc near to 5 mV) turns off the pulse generator
(which give out peak to peak pulse of approximately 5 V). So cting the
pacemaker
unnecessary
s imulations. There rc two different kinds of pacing leads: unipolar and bipolar,
bipolar leads arc less sensitive to the external interferences but they are ICS
sensitive to the cardiac signal too.
Single channel and multichannel dcviccs (i.e. with a stimulation irtrd dwecrim in
more than a single hcan point) arc available according to the patient needs. In a
large part of the pacemakers the physician can program the parameters of the
implanted generator
(e.g. amplitude, frequency, sensitivity) using a radio
int crface cent rolled by a computer. Moreover the radio interface allows the
physician to get the operating parameters of the stimulator using some clcmctry
measurement functions built in into the device.
2
exposure to an electromagnetic field
may:
a ) Introduce cuments from the leads into th heart causing fibrillation or locai
heating:
b ) Induce voltages in the lead that damage the pulse generatoc
c ) Induce voltages in the lead that the pacemaker confuses with the intrinsic
heart signal and turn off the pulse generator. -
Additionally implantable pulse generators incorporat reed switches which are
used for controlling the battery charge and may be ctivated by strong
magnetics fields.
T& safety f implantablc pacemakers and their protection against EMI (E1ectro
Magnetic Interference) is the subject of the CENELEC European Standard 5600].
A draft amendment prepared by the Technical Committee 62 [1] suggests both the
maximum ratings of interference
pacemakers should comply.
Surely clauses a) and b) do not concern the GSM system because the power of a
direct radiation excited in the lead wh ch can damage the hcan or the pulse
generator is very much higher than the power of the GSM fixed or mobile
equipments. Moreover the transmission frequencies of the GSM system arc so
high that the by-pass capacitor which protects the pacemaker input filtrates
enough the residua) components. For instance it has been verified t at AM radio
broadcast transmissions using very high power.’ (kilowatts or megawatts) can
introduce a strong hazard.
instead. clause c) has needed some investigations because an interfering signal
with low frequency components approximating the heart beat could cause
potential hazards even if their power is relatively low.
In caac of GSM signals, while the normal burst transmission has a repetition rate
of 216 Hz nd risks cannot rise (consider that a 50 Hz component is already
strongly filtered by the post-detector filter of the pacemaker detector input), the
particular case of DTX (Discontinuous Transmission) mode had to be carefully
investigated.
In fact DTX mode has signal components t frequencies much ower than in the
case of normal C3SM transmissions (see fig. 2): there is a sub-component with
repetition rate of ?.08 Hz,
which corresponds to the transmission of t e 8
timesiots of the SID (Silence Descriptor) message block frame and another
low frequency component rcprescntcd by the SACC14 repetition rate (8.33 Hz).
The amplitude nd duty cycle (one timcslot out of 26) of this component are much
lower than those of the previous one.
Since electrical signals with periodicity
below 6-8 Hz inhibit the pulse generator while interfering signals with
penodicity above 6-8 Hz will reven the paccmakcr operation into the so called
asynchronous
it Waa” fW&Wtcaad-
importance to identi y possible danger thresholds,
In fact, if the power excited by these signals in an active
enough, the pulse generator could bc turned off and the
h art failure
been conducted both with unipolar and bipolar

An arbitrary waveform generator jointly with an RF generator simulated the
900 MHz DTX transmission. The signal was amplified by a power amplifier.
Pacemakers were placed in a phantom,
an imitali.on of the human body filled
with physiological solution (water and NaCl whose concentration corres onded
to a specific conductivity of 0.5 S/m al 20”C room lcmpcraturc) according to the
-standard values.
The phantom was a Plexiglas cylinder 1.7 m ta[l, with diameter of 0.3 m. The
pacing lead was placed in 8 loop similar to the one really done in the human
chest and his distance from the plexiglas wail was not larger than 1 cm. An
oscilloscope con-ted to two steeJ plates plunged into the soiution was used to
detect the regular operation of the generators.
Experiments were conducted in a controlled (anechoic) environment with the
im of measuring the field strength next to the phantom chest by an isotropic
detector atvoiding any unwanted component.
The measurement results show that no risk of hazards exists aminst Pacemakers
from GSM quiprncnt.
In fact it has been verified that it is necessary
(corresponding to 8 W transmit peak power
istance) for inhibiting an unipolar pacemaker
air with the pacing lead loaded with a 500
interface.
of- a GSM equipment at 0.S m
when the device is leaved in the
ohm resistor simulating the tissue
On the other hand, when the device was put into the physiological solution, it was
not poasibie to inhibit his regular operation even with electric fields of 200 V/m
(corrcaponding to 208 W transmit peak power at 0.5 m distance).
For bipolar pacemakers the results are even more reassuring: with the device in
the opeu air the electrical field could inhibit the pub generator only if it was
above 75 V/m (corresponding to transmit peak power of 28 W at 0.5 m
distance). Obviously no inhibitions have been dete ted with the Dacemaker
plunged - into the solution. “
bipolar pacemakers manufactured by SORIN have demonstrated
hazard exists.
(1989)
pr EN 50 061
[2] “immunity to disturbance of cardiac pacemakers in RF fields of powerful
radio transmitters”,

Annex E:
PROJKT : 60
L

Comlmtms
ETR 357 ( SM 05.90 version 5.0.0) January 1997
In the course of a meeting to disouss the potential interference
[1] problems as ociated with the introduction of GSM and other
transmission systems eqloying IZIMAtechniques, Mr Williams of
the Radio Technology Laboratory was
tasked with producing a
..
summary document covering all o the work carried out to date.
The minutes of that meeting are reproduced in ann x 5, it should
be not ed t ha t the chairman stated that the summary report should
aim to concern itself with the direct breakthrough problem only,
and ILQ&the TV image problem which ay affect the UK only.
[z] Interference to TV,
equipment, including personal stereo equipment and hearing aids.
.,
.

2.1 Domestic
proved to be the most susceptible domestic equipments with mean
immunities of 4.0 and 5.6V/mreepectively. _nua recg$
~J these ew~-ts ‘ould ‘nly suf~er
er
interference from a 20 W GSM mobile a t dist a nces o less than
about 8 metres (worse case ass@n9 100* effici~cl’ d free
space path loss).
~is means that in practice, due to building attenuation etc.,
interference will not occur unless the transmitter and victim
equipment are very close, and within the same room.
2.2 liearingAids.
ilmnunityof 4.1 v/m.
cassetteplayers etc.) outside the domestic environmentis likely
to prwe more problematic since the interfering GSM transmission
is unlikely to be under the control of the user of the victim
eguipment.
Work conducted by the RTL and Racal Research Ltd. suggests that
the ixnunity of small behind the ear hearing aids canbe improved
at reasonable cost (by -t 10 m) by applying co ductivePaint
to the inside of the hearing aids plastic case. This would reduce
the interferi g range of a 5 W portable GSM t ansceiverto about
0.5 metres which is considered acceptable.
2.3 Eighu requenoy Systems, DECT, DCS1800 etc.
ds ~rw~re su~ to 1900 MlkkhWA
This has
obvious implications

3. Xnrmunity Data.
this summaq document;
Partl, XJ181 Part2.
Netherlands Pm (hoofddirectieteleconnnun
3.2 Normalisation of Data.
The above laboratories presented their findings in a variety of
forms. Introducing this summary report it was necessary to unify
the various abs ract results and findings, by calculation and
extrapolation,
acceptabilityfor GSM interferencesince it falls halfway between
the impaiment that is considered acceptable, by the CCIR, for
continuous interference (CCIR grade 4 , and that which is only
considered acceptable for a v ry small percentage of the time
(CCIR grade 3).
The approximate field intensitiesthat would result in CCIR grade
3 or 4 impairments can be obtained by adding or subtracting 5 dB
audio impairment respectively (sincea 1 dB change in the field
intensity results in approximately a 2 dB change in the udio
impairment (square law), multiplying or dividing the grade 3.5
field intensity by 1.33 will produce the approximate grade 3 and
4 field intensities respectively).
A description of the impairment associated with each of the
standard CCIR impairment grades is given in Annex 1.
3.3 Analysis of the IIata.
The original laboratories
intensity for grade 3.5 impairment is given in Annex 2.
The Mean and StandardDeviation of the extrapolateddata is given
in Annex 3,

4 Obaaz=atians
4.1 Earlier work at the RTL has shown that th magnitude of AM
or pulse [2] interference is related to the peak envelope power
f the transmission. i.e.
A victim equipment demonstrating
immunity to 3 V/m (carrier)with lkHz, 80% emplitude modulation,
.
This is supported by the recent tests
aids by
[2] 1:24< duty ~cl@ <24:1
4.2 The recent tests conducted by RFI shows that the majority of
the hearing aids tested (the smaller ones) were more susceptible
at 1900 MKz han at 900 MHz (the mean izxzunitywas 7 dB w rse).
l’hisfinding has obvious inqlications regarding the introduction
of DECT etc., and is supported by some (limited) earlier work
conducted by the RTIJ (KJ132a).
4.3 Inteationallybhmkforreportwdimmminatedoutdle theAgi?rIcy.
cmclus*oa8•
which various equipments would suffer visible/audible, but not
annoying interference (approximatelyCCIR grade 3.5) are listed
below.
Telephones
Computers
>7.8
From the above generalisation it can be seen that the most
susceptible equipments are hearing aids, television receive=t
cassette decks end portableradios/cassetteplayers etc. ~
~f these ‘Ould only “Uffer
interference from a 20 W mobile at distances of less than about
8 metres (worsecas assuming 100% efficiency and ree space path
loss).
This means that in pract ce, due to building attenuation
etc., interference will not occur unless the transmitter and
victim equipment are very close, and within the same room.
It can therefore be concluded that GSM interference is unlikely
to cause any serious problems to domestic equipment, being used
in a domestic environment.
portable cassette players etc.
environment is more likely. ~rlier work conductedby the RTL and
Racal Research Ltd. suggests that the immunity of small behind
the ear hearing aids canbe improved at reasonable cost (byabout
10 dB) by applying conductivepaint to the inside of the hearing
aids plastic case.
5 W portable GSM t about
0.5 metres which is considered
acceptable.
[41 Although it was requested that this sununaryreport should aim
to concern itself with the c im ?ct_~
poblemonlyr =&
not the TV image problem which may affect the U only,
following background information is included for completeness.
-
potentially quite problematic because, for some of the higher
Band V channels, this response falls within the bands allocated
to TACS and GSM. However, interferencevia this mechanism is no
worse for GSM (or other ‘IWA systa) t- it is for ~l~e
systems e.g. TACS. As no cases of TV image interference from TAC S
have been recordedduring several years of operation,major image
interference problems from GSM are not anticipated.

5.2 The following pertinent information has been extracted from
RET’s test report RFI\TR2\2494;
5.2.1 h-iC XZIUJUUity~.
The draft generic immunity standard (prm 50082-1) requires the
BUT to be tested at 3 V/m fmm27 MEz to 500 MHz, but since there
is no requirement to modulate the field it is unlikely that any
hearing aid equipme=t would fail this test.
The final version will almost certainly require that two further
tests listed in the informative annex to be carried out:
Electromagnetic field at a severity level of 3 V/m 80*
&itude modulated with 1 kSiztone swept from 80 MHz to 1 GHz.
2. electromagnetic field at a severity level of 3 V/m pu se
modulated with a 100 Hz square wave at a frequency of 1.89 GHz.
5.2.2 Field Strength Produced by Porteblo Transcdvers.
WfimhumQWwe Wikluhe Qm,ezic a~
RFI have calculated
how closely the user of a piece of hearing aid eguipment may
approach a portable transceiver before the level of unwanted
interference
table;
symtm
RFI state that;
These f gures only provide a rough guide as they make no
allowance for the type of modulation employed or for the
disturbance of the electromagnetic field caused by the person
using the hearing aid.
The values calculated above would suggest that users of hearing
aid equipment are likeIy to experience ~interferenoe frcxBGSM.
mobiles in close
systems themselves.
.ETR 357 (GSM 05.90 version 5.0.0): January 1997
Annex F: Interference to hearing aids by the new digital mobile telephone
system, Global System for Mobile (GSM) communications standard
.
Global systam for Mobil- (GSM
Communications Standard
ABSTRACT :‘
interference caused to hearing aids by mobile telephones using
the new “Global system
considerable interference to users of hearing a ds.
known at present if hearing aids can be de igned to be
completely immune from this interference.
This report has been
written to alert all hearing aid users and those concerned with
.
. .

Ta.bloof Contants
Interference to Hearing Aids
Hearing Aids
to Hearing Aids
with Interference
Transmission
3
Test set-up
1
1
1
2
2
3
4
4
5
5
5
6
7
8
9
10
11
12
13
1
Introduction
The new mobile telephone system, using the ‘Global System for
Mobile” (GSM) communications standard, is due for introduction in
April this year.
radio frequencies (RF) in the 900 MHZ region.
The ortable hand
commonly
NAL
was
checking if the system interferes with hearing aids.
Telecom was
digital telephones.
a series of measurements designed to establish the nature and
extent of interference to hearing aids.
The following is a report of these measurements, together with
some recommendations.
first approached NAL
through Mr. Eric Burwood and visited NAL on 18th and 19th
February, 1993 when it was establishe that interference may be a
problem.
Subsequently, measurements were carried out on 4th and
5th March 1993 to quantify the extent of the interference likely
to be experienced by hearing aid users.
Dr. Joyner and Mike Wood
of Telecom Research Laboratories Electromagnetic Compatibility
Section set up the equipment o generate the radio frequency
field to simulate the telephone emissions and also provided
Tables 3 and 4 of field strengths emitted by the GSM mobile
telephones.
Strange of National Acoustic Laboratories carried out the hearing
aid measurements.
890 and 915 MHz,
The modulation produces
A number of
GSM mobile telephones for use within Australia.
These include a
2 watt hand held unit and an 8 watt transportable unit.
When due
account is taken of the pulsed nature of the transmissions, the
corresponding average power
respective y.
The peak RF field strengths close to the antenna of the mobile
telephone can be quite high.
At 10 cm from an SW transportable
unit a peak RF field of 70-80 V/m has been measured.
The GSM system is a pulsed system with a higher peak power than
the present analog mobile telephone system.
This makes the G W

system much more likely to cause
interference into electronic
equipment which is apparent y not affected by analog RF fields.
Obviously the potential for interference depends on the number of
GSM mobile telephones in use in the community and this is
unlikely to be very high in the next few years.
4 Xnterfarenoe to Xearing Aid*
Interference
depending on the details of its design.
Considerable concern is
felt by the European Hearing Instrument Manufacturers Association
as the new system is being implemented in all European countries.
The Australian Telecommunications Authority, Austel is embarking
on an investigation into
of
wireless personal communications.
The interference from one transmitter is heard in the hearing aid
as a constant, distinctive buzzing sound while the telephone is
transmitting nearby.
Figure 1 shows a typical frequency spectrum
of the output of a hearing aid with interference, which occurs
across the useable range from 200 to over 5000 Hz.
Hearing aids rom all manufacturers will be similarly prone to
this interference.
to the Interfering RF signal
a ~:
with the peak RF field strength, so that useful predictions
could be made about the effect on hearing aids in proximity
to these telephone transmitters.
This was done by:-
i Measuring the output of the aids subjected to varying RF
field strengths, and
of known intensity.
bMWM:”
i
ii
The hearing aids were placed in a known variable RF field
generated by the system provided by Telecom shown in
Figure 2
of the hearing aid was
measured in a 2 cc coupler with a B&K 2120 FreWencY
An lyser set for wide band with a 100 Hz high pass filter
~w=

mic~ophone
output was then measured under a suitable range of field
strengths, including that which produced an output 10 dB
above-the noise floor.
large metallic objects which
alter the field strength
order to obtain reasonably
accurate field strength at the aid, the 2 cc coupler and
microphone were moved away rom th vicinity of the aid.
A 460 mm length of 2 mm
diameter Tygon tubing was
This
This change of
reduced significantly. The peak RF field strengths were
measured using the apparatus shown in Fi ure 2. The
output of the generator was varied with its attenuator in
order to adjust the RF field incident on the hearing aid
under test.
ii On rotating the aids in the RF field the received
interference changed. However, for the purpose of this
investigation, it was decided that the orientation which
produced the most interference in the ma ority of aids
would be used,
extensive
obtained.
iii
normal acoustic termination and also with the extra
tubi g using a NAL 8500 system whose calibration was
chec ed with a B&X calibrator.
This shows that the
aids were operating correctly.
recorded with and without
interference for subsequent subjective evaluation.
ii Recordings were made of the outpu of some of the hearing
aids with test speech passages of known average SPL with
and without interference to ascertain what may be deemed a
suitable threshold for characterizing the effect of
interference. It was confirmed that a useful ‘annoyance”
threshold.is the RF field strength that causes an output
10 dB above the noise floor of the hearing aid, i.e. the
output without interference and when the microphone was
blocked to ambient sound.
e.g. when the interference was increased to 20 dB above
the noise floor,
though the accompanying speech was still intelligible.
iii It is intended to prepare-a cass

0590_500

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