ECC Recommedatio (14)02 Protectio of fixed moitorig statios agaist iterferece from earby or strog trasmitters Approved 07 February 2014
ECC/REC/(14)02 Page 2 INTRODUCTION The icreasig use of broadbad moitorig receivers ad the deploymet of cellular radio etworks require a more differetiated cosideratio of the situatio aroud a projected moitorig site. Thus, this Recommedatio specifies maximum field-stregth levels at moitorig statios to esure their iterferecefree operatio. Therefore this Recommedatio is i form ad cotet divided ito three mai sectios. The first sectio icludes a itroductio ad geeral cosideratios. The secod sectio cotais the determiatio of the maximum permissible field stregth, icludig techical aspects ad the calculatio process. The third sectio icludes typical techical parameters ad a example calculatio usig these.
ECC/REC/(14)02 Page 3 ECC RECOMMENDATION 14(02) ON PROTECTION OF FIXED MONITORING STATIONS AGAINST INTERFERENCE FROM NEARBY OR STRONG TRANSMITTERS The Europea Coferece of Postal ad Telecommuicatios Admiistratios, cosiderig a) that reliable ad ucorrupted spectrum moitorig iformatio forms a vital part i the spectrum maagemet process; b) that the power radiated from earby trasmitters may result i strog electromagetic fields at moitorig statios leadig to receiver desesitizatio ad blockig effects; c) that these effects i tur may produce false emissios which have to be avoided as far as possible; d) that the deploymet of cellular radio ad broadcastig statios makes it difficult to fid suitable locatios for a spectrum moitorig statio; e) that the received field stregth is a importat parameter to determie the suitability of a moitorig site; f) that differet frequecy rages require differet limitatios of the field stregth, g) that the ITU Hadbook o Spectrum Moitorig (Editio 2011) provides geeral ad specific cosideratios regardig the sitig of moitorig statios ad a site survey checklist; h) that Report ITU-R SM.2125 describes the measuremet procedures to determie the techical parameters of moitorig receivers ad moitorig systems, recommeds 1. that the method i Aex 1 is used for the calculatio of the maximum permissible field stregth to protect radio moitorig statios. Note: Please check the Office documetatio database http://www.ecodocdb.dk for the up to date positio o the implemetatio of this ad other ECC Recommedatios.
ECC/REC/(14)02 Page 4 ANNEX 1: CALCULATION OF THE MAXIMUM PERMISSIBLE FIELD STRENGTH TO PROTECT RADIO MONITORING STATIONS A1.1 INTRODUCTION Strog RF sigals may reduce the ability of a moitorig statio to receive weak sigals ad measure them correctly. The protectio of radio moitorig statios agaist strog RF sigals is of particular importace i view of the icreasig umber of atea sites for mobile ad other radio services. Sice moitorig statios are ofte located i urba areas ad exposed spots, it becomes more ad more difficult to idetify suitable ew sites ad to protect the existig oes. This Aex describes procedures ad calculatios for the establishmet of protectio zoes aroud radio moitorig statios. A1.2 GENERAL CONSIDERATIONS The specificatio of protectio criteria for radio moitorig statios primarily ivolves cosiderig techical aspects ad is based o the priciple that emissios from adjacet trasmittig statios may ot cause ay iterferece at the moitorig statios. Although pricipally there are various possible iterferig effects such as sidebad emissios, the most severe effect are 3 rd order itermodulatio products which may be geerated i a receiver resultig i fake emissios. This is therefore the oly effect cosidered i this Recommedatio. Give certai immuity agaist strog sigals, the occurrece of itermodulatio is directly depedet o the iput power ito the moitorig receiver. It would therefore be easiest to specify a maximum receiver iput power that surroudig trasmitters may create at the moitorig receiver as a protectio criteria. This approach, however, has the disadvatage that the resultig protectio distace would deped o the techical properties of the moitorig receiver ad atea which is ot kow to the operator of a earby trasmitter or it is equal for all moitorig sites. I additio, it would oly provide protectio for the curret moitorig equipmet. Should this be chaged i the future (e. g. by istallig ateas differet gai), the protectio criteria would chage leadig to a differet protectio zoe. Beside techical aspects, moetary ad maagemet aspects are also of high importace. I order to reduce the admiistrative expeses a ucomplicated ad efficiet cotrol process eeds to be established. A ucomplicated process will be more acceptable to the trasmitter operators. For these reasos uiform protectio criteria shall apply idepedet of the locatio of the moitorig statios ad their techical specificatios (directio fider or rotatable atea, type of receiver, atea gai). This leads to the approach to defie a particular field stregth that must ot be exceeded as the protectio criterio. This is also the most trasparet approach to other parties ivolved because the field stregth that a trasmitter produces at the locatio of the moitorig statio ca easily be calculated or measured. The fact whether the maximum field stregth actually does produce iterferece at the moitorig receiver, however, depeds o the followig parameters: immuity of the receiver agaist strog sigals; sesitivity of the receiver; exteral oise level; atea gai; atteuatio of the RF cable betwee atea ad receiver; badwidth ad frequecy of the disturbig sigal(s). As these parameters may vary i a wide rage, a certai defied maximum field stregth does ot guaratee iterferece-free operatio of the moitorig statio uder all possible combiatios of them. For example, a very sesitive receiver i combiatio a high-gai atea would result i a maximum field stregth beig so low that o suitable moitorig site could be foud i the whole coutry.
ECC/REC/(14)02 Page 5 The followig procedure provides a geeral method to calculate the maximum permissible field stregth. The resultig value for this field stregth the depeds o the selectio of reasoable ad typical values for the above parameters. A1.3 DETERMINATION OF THE MAXIMUM PERMISSIBLE FIELD STRENGTH The calculatio of the maximum agreeable field stregth icludes: the immuity (3rd order) of the receiver agaist strog sigals; the sesitivity of the receiver; the badwidth ad frequecy of the disturbig sigal(s); the gai of the atea; the level of exteral oise. A1.3.1 Immuity of the receiver agaist strog sigals The level of 3rd order itermodulatio products are geerally calculated from the iput power ad the 3 rd order itercept poit of the moitorig receiver. The most critical combiatio is the itermodulatio of three sigals of the same power. Accordig to Recommedatio ITU-R SM.1134-1, Table 2, the power of the itermodulatio product ca be calculated the formula for IM3(1;1;1) (three sigal case). P IM 3 3PS 2PIP3 6 db (1) PIM3: power of the 3rd order itermodulatio product IM3(1;1;1) i dbm; PS: power of each sigle sigal ivolved i the itermodulatio i dbm; PIP3: 3rd order itercept poit (IP3) of the receiver i dbm. The value of PIP3 ca be take from the receiver specificatio sheet. It is the power of the iput sigals at the poit where the level of the 3 rd order itermodulatio product is equal to the iput level of the strog sigals cotributig to this itermodulatio. A1.3.2 Receiver sesitivity A weak sigal ca be detected a receiver whe its level exceeds the iteral oise of the receiver. This is the idicated level whe o atea is coected ad the receiver is operated i its most sesitive mode (e. g. o iput atteuatio). The root-mea-square (r.m.s.) value of the iteral oise of a receiver is geerally calculated by f : k : p ( f 1) kt0b ( f 1) p R oise factor of the receiver; Boltzma s costat; B (2) t 0 : referece temperature take as 290 K; B : oise badwidth of the receiver; p kt 0 : available thermal oise power (W) i 1 Hz badwidth. The sesitivity of a receiver is characterised i data sheets oise figure NF. Thus equatio (2) ca be writte as the followig.
ECC/REC/(14)02 Page 6 NF = 10 log (f) : receiver oise figure i db R NF 10 p ( 10 1) p B (3) Writte i dbm the r.m.s. value of the receiver s iteral oise becomes: NF 10 P ( dbm) 10log(10 1) 10log( B ) 174( dbm) R - 174 dbm: available thermal oise power at room temperature i 1 Hz badwidth (4) Usually the measuremet badwidth of a receiver is about equal to its oise badwidth. I additio, oise figures (NF) of typical moitorig receivers have values of 10 db or larger. Takig this i accout, the formula of the r.m.s. value of the receiver s iteral oise becomes less complex: P ( dbm) P NF 10log( B) R (5) P : available thermal oise power at room temperature i 1 Hz badwidth ( 174 dbm); B : measuremet badwidth i Hz. The value of the oise figure ca be take from the receiver specificatio sheet. The parameter P R is also kow as displayed average oise level (DANL). A1.3.3 Receiver badwidth Wheever specifyig levels of RF sigals, the referece badwidth used to measure this level also has to be specified. Without further iformatio, the maximum field stregth to protect a moitorig statio would ormally be measured i the total badwidth of the respective sigal. A1.3.4 Atea gai To covert measured iput levels ito field stregth it is importat to kow the properties of the atea. The atea gai is coected to the atea factor accordig to G i 20log( f ) k 30dB Gi: atea gai i the directio of the mai beam i dbi; f: frequecy i MHz; k: atea factor i db/m. (6) The atea factor may be used to calculate the field stregth from the voltage at the atea coector accordig to E U k (7) E: electrical field stregth i dbµv/m;
ECC/REC/(14)02 Page 7 U : voltage at the atea output i dbµv. The values for the atea factor ad/or atea gai ca be take from the atea specificatio sheet. For 50 Ohm systems, RF power ad RF voltage are coected through So that P[ dbm] U[ dbµv ] 107dB E[ dbµv / m] P[ dbm] 20log( f [ MHz]) Gi[ db] 77dB (8) (9) A1.3.5 Exteral oise Exteral oise i this cotext is the level of all uwated emissios, whether ma-made or atural, that the moitorig receiver gets from the atea. For frequecies above about 30 MHz, the mai compoet is ma-made oise (MMN). However, the level of the MMN is i most cases lower tha the receiver oise level, especially i rural areas ad ca therefore be eglected i the calculatio process. For frequecies below 30 MHz, however, the sesitivity of the moitorig setup is determied by the exteral oise rather tha the receiver oise. The actual level of the exteral oise is strogly depedat o the locatio of the moitorig statio ad eve o the time of day. Furthermore the sky wave propagatio of sigals below 30 MHz usually results i the strogest sigals received beig foreig AM broadcast statios. Although the receptio level of these statios may be so high that moitorig performace is cosiderably decreased, the moitorig admiistratio has o legal ifluece o the presece of these sigals. Moreover, they are preset at ay possible moitorig locatio. Therefore it seems ot sesible to calculate protectio field stregths for frequecies below 30 MHz. The followig calculatio is valid oly for frequecies above 30 MHz where exteral oise is ot domiat. A1.3.6 Calculatio process For the calculatio of the power of the 3rd order itermodulatio product IM3 we presume the case that a total umber of three sigals of equal power ad badwidth iteract i the receiver s iput circuit. I this case, the badwidth of a itermodulatio product from three sigals is three times the sigal badwidth Bs. However, it is ot easy to determie the badwidth of a itermodulatio product whe real sigals iteract (e.g. DVB-T or LTE). Usually these spectrums have o sigificat miimums ad maximums. Thus, it is possible to presume, out makig great error that the shape of the spectrum of this itermodulatio product is rectagular, i which case the badwidth calculatio above also applies for this situatio. The part of the power PIM3 of the itermodulatio product measured i the badwidth B ca be calculated by Usig formula (1) this term becomes P dbm) P IM 3 ( IM 3 B 10log 3BS (10) P B ( dbm) 3PS 2PIP3 6dB 10log 3PS 2PIP3 3B S 6dB 10 log( B) 10 log(3b IM 3 S ) (11) Iterferece due to IM products begi to be visible whe the level PIM3 exceeds the receiver oise floor:
ECC/REC/(14)02 Page 8 PIM 3 P R. (12) The critical poit where this situatio occurs ca be calculated usig formulas (5) ad (11) as follows: 3PS 2PIP3 6dB 10log( B) 10log(3BS ) NF 10log( B) 174dBm (13) P S 2PIP3 NF 10log( BS ) 10log(3) 6dB 174dB 3 (14) P 2PIP3 NF 10 log( B ) 3 S S 58. 4 dbm. (15) Assumig o cosiderable cable atteuatio betwee atea ad receiver, the field stregth correspodig to PS ca be calculated usig formula (9) as follows: E max ( dbµv / m) 2P IP3 ( dbm) NF( db) 10log BS ( Hz) 20log f ( MHz) Gi ( db) 18.6dB 3 (16) A1.3.7 Iterferece effect of a larger umber of statios Formula (16) already reveals the maximum permissible field stregth of every sigle disturbig trasmitter that maybe ivolved i a possible itermodulatio product. If more tha three trasmitters are received this maximum field stregth, the oly effect will be that additioal itermodulatio products will show up at differet frequecies, but the level of each of the itermodulatio products will ot rise. Therefore additioal adaptio of the maximum permissible field stregth values is ot ecessary. A1.4 TYPICAL PARAMETER VALUES To get a umerical value for the maximum permissible field stregth from formula (16), realistic values for the parameters receiver oise figure, 3rd order itercept poit, referece badwidth ad atea gai have to be chose. This sectio provides guidace o how to select these values. A1.4.1 Receiver oise figure Noise figures of moitorig receivers ad spectrum aalysers are ofte i the rage betwee 7 ad 24 db. The overall oise figure of the measuremet setup may be improved eve dow to 1 db by usig exteral low oise amplifiers (LNA), but for a fixed moitorig statio, this is ot a typical cofiguratio. Assumig built-i preamplifiers, a typical oise figure aroud 10 db is suggested to be used whe calculatig the maximum permissible field stregth i the cotext of this Recommedatio. A1.4.2 IP3 IP3 levels of moitorig receivers ad spectrum aalysers are ofte i the rage betwee +10 ad +30 dbm. A value of +15 dbm may be regarded as typical although special digital widebad receivers o preselectio at all ad poor dyamic rage may have lower IP3 levels. A1.4.3 Sigal badwidth Whe measurig weak sigals, the highest S/N would be achieved whe usig the arrowest possible measuremet badwidth because this would result i the lowest possible DANL. This, however, is oly true for umodulated carriers. Whe measurig digital sigals, for example, arrower measuremet badwidths
ECC/REC/(14)02 Page 9 do ot icrease the sigal-to-oise ratio (S/N) ad hece would ot icrease measuremet sesitivity. Also the IM products iterferig a measuremet are ot umodulated carriers. They have a badwidth eve wider tha the strog sigals ivolved, so that their iterferece potetial does ot icrease whe usig a measuremet badwidth that is arrower tha the sigal badwidth. It is therefore recommeded to specify a typical sigal badwidth i the respective frequecy bad whe calculatig the maximum field stregth to protect the moitorig statio. The followig Table 1 specifies the badwidths of typical sigals i various frequecy bads. It should be oted that these are the badwidths of the sigals that are used for level measuremets ad for the calculatios. They may ot always coicide commo chael spacig. Table 1: Badwidths of typical sigals i differet frequecy bads Frequecy bad Systems operatig i the bad likely Sigal badwidth to produce high receivig levels 30-890 MHz Narrowbad FM 12.5 khz (Note 1) 87.6-108 MHz FM broadcastig 12.5 khz (Note 2) 470-790 MHz Televisio Broadcastig (DVB-T) 7.6 MHz (Note 3) 390-1990 MHz GSM 250 khz (Note 3) 780 MHz - 2.7 GHz 3G/4G mobile phoe systems (e.g. UMTS, LTE 5MHz) 780 MHz 2.7 GHz LTE 1.4 MHz LTE 10 MHz LTE 20 MHz, RLAN 5 MHz (Note 3) 1.4 MHz (Note 3) 10 MHz (Note 3) 20 MHz (Note 3) Note 1: As all aalogue FM modulated sigals, the actual RF badwidth depeds o the audio sigal. The badwidth 12.5 khz has bee chose because it is assumed that this is the miimum measuremet badwidth used at moitorig statios i these frequecy bads. Note 2 FM broadcastig emissios i the frequecy rage 87.6 to 108 MHz have a much larger maximum badwidth tha 12.5 khz. However, i the modulatio pauses the full eergy of the sigal (ad hece the full power of the itermodulatio products) would also fall completely iside the suggested badwidth of 12.5 khz which is more critical i this cotext. Note 3: For digital systems that have a costat badwidth, the referece badwidth chose is the rouded occupied (99%) badwidth of the sigals. This badwidth may ot always coicide chael spacig. For example, GSM has a chael spacig of 200 khz but the occupied badwidth is about 250 khz. This Table cotais oly examples, thus ot all sigals that have a comparable importace like LTE 3 MHz, LTE 15 MHz, CDMA 2000 or TETRA 25 khz are metioed. A1.4.4 Atea parameters A tued dipole atea has a gai of 2.15 dbi. May moitorig ateas are omidirectioal ad have o higher gai. Also the ateas used i directio fiders may usually be regarded as havig gai of dipoles. However, may moitorig statios are also equipped directioal ateas. The gai of these ateas would i tur decrease the permissible field stregth. Nevertheless it is recommeded to assume a dipole atea i the calculatio of maximum permissible field stregth for the followig reasos: cosiderig directive ateas would lead to a permissible field stregth depedig o the moitorig equipmet which was iteded to be avoided (see sectio 1.2) for the beefit of trasparet, uiform field stregth limits; itermodulatio products as cosidered here always ivolve at least two strog sigals. Calculatig the gai of a directive atea i its mai beam assumes that all strog sigals are received from the same directio which is ot always realistic ad overestimates the iterferece potetial; possible iterferece due to icreased sigal level directive ateas would oly be effective i a certai directio while i all other directios the field stregth ad hece iterferece potetial is eve lower tha omidirectioal ateas.
ECC/REC/(14)02 Page 10 It should be oted that the use of high gai directioal ateas may result i iterferig effects i certai directios due to field stregth levels higher tha calculated whe assumig omidirectioal ateas. If these effects caot be tolerated, bad stop filters or atteuators may be iserted to prevet icorrect measuremets. A1.5 EXAMPLE CALCULATION USING TYPICAL VALUES This sectio provides a calculatio example usig the typical parameter values suggested i sectio 1.4. Lookig at formula (16) ad cosiderig the differet referece badwidths, it is obvious that the resultig maximum field stregth will be frequecy-depedat. For the GSM frequecy rage aroud 950 MHz, for example, formula (16) yields E max [ dbµv / m] 107.3dBµV / m 2 *15dBm 10dB 10 log(250,000hz) 20 log(950mhz) 2.15dB 18.6dB 3 The followig graph illustrates the resultig maximum field stregths to protect a moitorig statio whe usig the typical parameters suggested i sectio 1.4. 130 dbµv/m 120 dbµv/m 110 dbµv/m Max. field stregth 100 dbµv/m 90 dbµv/m 80 dbµv/m Narrowbad FM, FM Broadcastig Televisio Broadcastig (DVB-T) GSM 3G/4G (UMTS, LTE5MHz) LTE 1.4 MHz LTE 10 MHz LTE 20 MHz, RLAN 70 dbµv/m 10 MHz 100 MHz 1000 MHz 10000 MHz Frequecy Figure 1: Maximum permissible field stregths whe usig typical parameter values It should be oted that the field stregths give i this sectio are oly valid for the recommeded typical parameter values. If moitorig service uses equipmet parameters cosiderably divergig from those suggested i sectio 1.4, idividual field stregth curves have to be calculated usig formula (16).
ECC/REC/(14)02 Page 11 ANNEX 2: LIST OF REFERENCE This aex cotais the list of relevat referece documets. [1] Report ITU-R SM.2125: Parameters of ad measuremet procedures o H/V/UHF moitorig receivers ad statios [2] Recommedatio ITU-R SM.1134-1: Itermodulatio iterferece calculatios i the lad-mobile service