Measurements of protection ratios and overload thresholds for broadcast TV receivers

Transcription

1 Report ITU-R BT.2215 (5/211) Measurements of protecton ratos and overload thresholds for broadcast TV recevers BT Seres Broadcastng servce (televson)

2 Rep. ITU-R BT.2215 Foreord The role of the Radocommuncaton Sector s to ensure the ratonal, equtable, effcent and economcal use of the rado-frequency spectrum by all radocommuncaton servces, ncludng satellte servces, and carry out studes thout lmt of frequency range on the bass of hch Recommendatons are adopted. The regulatory and polcy functons of the Radocommuncaton Sector are performed by World and Regonal Radocommuncaton Conferences and Radocommuncaton Assembles supported by Study Groups. Polcy on Intellectual Property Rght (IPR) ITU-R polcy on IPR s descrbed n the Common Patent Polcy for ITU-T/ITU-R/ISO/IEC referenced n Annex 1 of Resoluton ITU-R 1. Forms to be used for the submsson of patent statements and lcensng declaratons by patent holders are avalable from here the Gudelnes for Implementaton of the Common Patent Polcy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent nformaton database can also be found. Seres of ITU-R Reports (Also avalable onlne at Seres BO BR BS BT F M P RA RS S SA SF SM Ttle Satellte delvery Recordng for producton, archval and play-out; flm for televson Broadcastng servce (sound) Broadcastng servce (televson) Fxed servce Moble, radodetermnaton, amateur and related satellte servces Radoave propagaton Rado astronomy Remote sensng systems Fxed-satellte servce Space applcatons and meteorology Frequency sharng and coordnaton beteen fxed-satellte and fxed servce systems Spectrum management Note: Ths ITU-R Report as approved n Englsh by the Study Group under the procedure detaled n Resoluton ITU-R 1. ITU 211 Electronc Publcaton Geneva, 211 All rghts reserved. No part of ths publcaton may be reproduced, by any means hatsoever, thout rtten permsson of ITU.

3 Rep. ITU-R BT REPORT ITU-R BT.2215 Measurements of protecton ratos and overload thresholds for broadcast TV recevers (211) TABLE OF CONTENTS Page 1 Executve summary Abbrevatons Useful defntons Rado frequency sgnal-to-nterference rato (C/I) Rado frequency protecton rato (PR) Recever (front-end) overloadng threshold Adjacent channel leakage poer rato Can tuners Slcon tuners References Broadcastng technology characterstcs Moble technology characterstcs Measurement methodology Example test set-up Wanted sgnal levels Frequency offsets beteen nterferng sgnal and anted sgnal Measurements n the presence of a tme varyng nterferng sgnal UMTS uplnk LTE donlnk LTE uplnk Interferer reference poer level Characterzaton of the nterferng sgnal Falure pont assessment methods Method for determnng protecton ratos and overloadng thresholds... 8

4 2 Rep. ITU-R BT.2215 Page 6 Conclusons and further ork requred Annex 1 DVB-T recever performance n the presence of nterferng sgnals from DVB-T, UMTS and LTE Executve summary Ths Report documents measurements of protecton rato (PR) and overloadng threshold (O th ) aganst nterference from other broadcasts or moble broadband servces n the 8 MHz band. The types of nterference used n the tests and the actual tests themselves vares th the dfferent broadcastng system and moble technologes used around the orld. The am of the Report s to establsh test procedures together th measurement results to assst n netork plannng and sharng studes for the co-exstence of TV broadcastng, th ether moble servces, or other servces and applcatons. The orgnal test detals and measurement data, together th nformaton on hch partcular Recommendaton and ts verson number as updated th ths data are contaned n the ndvdual annexes. 2 Abbrevatons BS Base staton O th Overloadng threshold PR Protecton rato TPC Transmt poer control UE User equpment the moble handset RB Resource block a unt of data transmsson n LTE, represented by a certan number of carrers n a uplnk or donlnk symbol n the frequency doman. FDMA Orthogonal frequency-dvson multplex access a mult-carrer modulaton system used for the LTE donlnk. SC-FDMA Sngle carrer frequency dvson multplex access a mult-carrer modulaton system used for the LTE uplnk. 3 Useful defntons 3.1 Rado frequency sgnal-to-nterference rato (C/I) It s the rato, generally expressed n db, of the poer of the anted sgnal to the total poer of nterferng sgnals and nose, evaluated at the recever nput (see Recommendaton ITU-R V.573).

5 Rep. ITU-R BT The poer of the anted sgnal s measured n a banddth equal to the anted sgnal banddth, hle the total poer of nterferng sgnal and nose s measured n a banddth equal to the nterferng sgnal banddth. 3.2 Rado frequency protecton rato (PR) It s the mnmum value of the sgnal-to-nterference rato requred to obtan a specfed recepton qualty under specfed condtons at the recever nput (note that ths dffers from the defnton n Recommendaton ITU-R V.573). In ths Report, the specfed recepton qualty and the specfed condtons have been defned separately by each entty that has undertaken measurements. Usually, PR s specfed as a functon of the frequency offset beteen the anted and nterferng sgnals over a de frequency range. In ths Report, PR specfed n ths ay s referred to as PR curve. PR curves sho the ablty of a recever to dscrmnate aganst nterferng sgnals on frequences dfferng from that of the anted sgnal. 3.3 Recever (front-end) overloadng threshold Overloadng threshold (O th ) s the nterferng sgnal level expressed n dbm, above hch the recever begns to lose ts ablty to dscrmnate aganst nterferng sgnals at frequences dfferng from that of the anted sgnal (.e., the onset of strong non-lnear behavour). Therefore, above the overloadng threshold the recever ll behave n a non-lnear ay, but does not necessarly fal mmedately dependng on the recever and nterference characterstcs. 3.4 Adjacent channel leakage poer rato Adjacent channel leakage poer rato (ACLR) s the rato of the fltered mean poer centred on the assgned channel frequency to the fltered mean poer centred on an adjacent channel frequency. The requrements shall apply hatever the type of transmtter consdered (sngle carrer or mult-carrer). It apples for all transmsson modes foreseen by the manufacturer's specfcaton. For a mult-carrer base staton (BS), the requrement apples for the adjacent channel frequences belo the loest carrer frequency transmtted by the BS and above the hghest carrer frequency transmtted by the BS for each supported mult-carrer transmsson confguraton. The requrement apples durng the transmtter ON perod. 3.5 Can tuners Can tuners are classcal superheterodyne tuners housed n a metal enclosure contanng dscrete components. Classcally, there are fxed and tunable crcuts made up from dscrete nductors and transstors usually th varactor dode frequency control. The metal enclosure should mnmze RF nterference and elmnate crosstalk and stray radaton. 3.6 Slcon tuners Slcon tuners are IC-based tuners ntegratng all tuner crcutry nto a small package drectly to be ftted onto man boards. The tuned crcuts may be completely absent or can be ntegrated onto the slcon. The slcon chp may be protected from external electromagnetc nterference by a metallc cover. Slcon tuners have dfferent characterstcs to can tuners and ther performance can be better and orse at some frequency offsets compared to can tuners. Ths technology s stll developng.

6 4 Rep. ITU-R BT References 4.1 Broadcastng technology characterstcs The follong references explan the characterstcs of the dfferent broadcast systems ncludng transmtter spectrum masks. DVB-T system characterstcs: Recommendaton ITU-R BT.136, ETSI EN DVB-T2 system characterstcs: Recommendaton ITU-R BT.1877, ETSI EN ISDB-T system characterstcs: Recommendaton ITU-R BT.136, ARIB STD-B31 ATSC system characterstcs: Recommendaton ITU-R BT.136, ATSC A/53 DTMB system characterstcs: Recommendaton ITU-R BT.136, GB Moble technology characterstcs The follong references explan the characterstcs of the dfferent moble broadband systems. UMTS system characterstcs: ETSI TS , ETSI TS LTE system characterstcs: ETSI TS , ETSI TS Measurement methodology 5.1 Example test set-up An example basc test setup for protecton rato and overloadng threshold measurements s depcted n Fg. 1. FIGURE 1 Spectrum analyzer Isolator Wanted sgnal path DVB-T sgnal generator MPEG-2/4 vdeo source Impedance matchng (5 Ω/75Ω) DVB-T recever Combner Varable attenuator Adjustable band-pass flter Interferng sgnal path Interferng sgnal generator Observer Report BT

7 Rep. ITU-R BT It s necessary to nsert an adjustable band-pass flter beteen the nterferng sgnal generator and the combner. The objectve of ths flter s to elmnate the nose generated by the nterferng sgnal generator and adjust the nterferng sgnal to the correct nterference transmsson mask and adjacent channel leakage rato (ACLR) values. In fact, most of the RF sgnal generators have a de frequency range (from several hundred of khz to several GHz) prohbtng the use of an nternal adjustable RF channel flter over ther hole frequency range. Consequently, dependng on the generated sgnal level, a non-neglgble deband nose may be observed at the generator output. The hgher the generated nterferng sgnal level, the hgher the nose level. The reducton of the undesred deband nose by flterng at the output of nterferng sgnal generator s shon n Fg. 2. If ths nose s not reduced by flterng, t s mpossble to measure the actual protecton ratos of the recever under test. Ths s due to the deband nose generated by the nterferng sgnal generator, fallng nto the anted sgnal channel, hch cannot be reduced by the recever flter. In ths partcular case, the recever loses ts ablty to dscrmnate aganst nterferng sgnals on frequences dfferng from that t s tuned to. Ths phenomenon s shon n Fg. 3. It s also advsable to nsert an solator beteen the combner and the DVB-T sgnal generator to keep the poer from the nterferng sgnal generator returnng to the DVB-T sgnal generator output. FIGURE 2 The beneft of band-pass flterng at the nterferng sgnal generator output psd (dbm/1 khz) Frequency (MHz) Useful DVB- T sgnal Useful DVB- T sgnal + unfltered nterferng sgnal Useful DVB- T sgnal + fltered nterferng sgnal Report BT

8 6 Rep. ITU-R BT.2215 FIGURE 3 The beneft of band-pass flterng at the output of the nterferng sgnal generator (anted sgnal level = Rx senstvty +1 db) CI / (db) Frequency offset n MHz (f-f) Measurements conducted thout flter Measurements conducted th a flter Report BT Wanted sgnal levels Protecton ratos and overloadng thresholds of a recever are derved from ts C(I) curves (see 5.11). The measurements should be carred out by usng dfferent anted sgnal levels to cover the range from eakest to strongest sgnals. The follong anted sgnal levels are advsed as a possble range: recever senstvty +5, +1, +2, +3, +4, +5, +6, +7 and +8 db. Ths range could be extended f the overloadng threshold of the recever s not reached. At lo anted sgnal levels the protecton rato lmt s usually reached before the overloadng threshold. Therefore t s necessary to use hgher anted sgnal levels to reach the onset of overload. 5.3 Frequency offsets beteen nterferng sgnal and anted sgnal It s usual to use the follong frequency offsets:, ±N, ±(N+BW I ), ±(N+2 BW I ), ±(N+3 BW I ), ±(N+4 BW I ),.. and 9 BW W (mage channel). Where: N = (BW W + BW I )/2 BW W : anted sgnal banddth BW I : nterferng sgnal banddth Hoever, regonal specfc frequency offsets could also be used, and smaller steps here more detaled nvestgaton s requred.

9 Rep. ITU-R BT Measurements n the presence of a tme varyng nterferng sgnal An mportant dfference beteen exstng nterference by other broadcast sgnals, and moble sgnals s that n many cases the moble sgnal poer can exhbt sgnfcant tme varaton hch can degrade the PR and O th performance of some DTT recevers due to nterferng th automatc gan control (AGC) and channel estmaton algorthms. It s mportant to test aganst such types of nterference. Tme varaton occurs n (at least) the follong crcumstances: 5.5 UMTS uplnk The UE can use transmt poer control (TPC) to mprove performance n moble recepton condtons here the channel can be rapdly changng. The effect of ths s for the UE to vary ts transmt poer rapdly over tme n response to feedback messages from the BS. 5.6 LTE donlnk The Base staton output poer can vary over tme f only some resource blocks (RB) are used n each OFDMA symbol, or f some OFDMA symbols are completely empty. Ths tends to happen hen the BS traffc loadng s zero or at lo levels. Consequently, n the presence of a BS nterferng sgnal, t s recommended to carry out the measurements th dfferent netork traffc loadngs of %, 5% and 1%. 5.7 LTE uplnk The uplnk sgnal can vary consderably n both the tme and frequency domans dependng upon the traffc loadng requred. In the frequency doman the number of RBs allocated for each SC-FDMA symbol can vary rapdly. In the tme doman, there can be long perods here the UE does not transmt at all, leadng to an rregular pulse lke poer profle. Consequently, n the presence of a UE nterferng sgnal, t s recommended to carry out the measurements th dfferent data rates on the uplnk. The modes should nclude both fully loaded contnuous operaton and tme dvson multplexed.e. pulsed operaton. 5.8 Interferer reference poer level Sgnal level varaton can be from level reductons or tme dvson occupancy. In order to be able to see the degradatons caused by tme varaton n the nterferng sgnal, t s necessary to set the approprate rms poer or poer spectral densty (psd) of the actve portons of the tme varyng nterference sgnal relatve to the rms poer or psd of the nterferer th a 1% traffc loadng (tme nvarant poer condton). 5.9 Characterzaton of the nterferng sgnal Protecton ratos and overloadng thresholds of a recever strongly depend on the frequency and tme doman characterstcs of the nterferng sgnal used n the measurements. Therefore, t s necessary to record the poer spectral densty (psd), the adjacent channel leakage poer rato (ACLR) as ell as the ampltude as functon of tme of the nterferng sgnal. These peces of nformaton allo comparsons of dfferent measurement results from dfferent measurement campagns.

10 8 Rep. ITU-R BT Falure pont assessment methods Intal studes of the protecton ratos for the DVB-T system ere based on a target BER of measured beteen the nner and outer codes, before Reed-Solomon decodng. For the case of a nose-lke nterferer, ths has been taken to correspond to a quas-error-free (QEF) pcture qualty th the BER < at the nput of the MPEG-2 demultplexer. For domestc recevers t may not be possble to measure the BER and therefore a ne method called the SFP (Subjectve falure pont) method has been proposed n Recommendaton ITU-R BT.1368 for protecton rato measurements n a unfed manner. The qualty crteron for protecton rato measurements s to fnd a lmt for a just error-free pcture at the TV screen. The RF protecton rato for the anted DVB-T sgnal s a value of anted-to-unanted sgnal rato at the recever nput, determned by the SFP method, and rounded to the next hgher nteger value. The SFP method corresponds to the pcture qualty here no more than one error s vsble n the pcture for an average observaton tme of 2 s. The adjustment of the anted and unanted sgnal levels for the SFP method s to be carred out n small steps, usually n steps of.1 db. For a nose-lke nterferer the dfference n a value of anted-to-unanted sgnal rato beteen the QEF method th a BER of and the SFP method s less than 1 db. It s proposed that the SFP method should be adopted for assessment of all DTTB systems. (For the dgtal system ISDB-T ths method ll be studed n Japan.) 5.11 Method for determnng protecton ratos and overloadng thresholds It should be stressed that the protecton ratos are generally consdered and used as ndependent of the anted sgnal level. That s C(I) s supposed to be a lnear functon th unty slope (a straght lne th unty slope). The protecton rato of the recever s obtaned by subtractng I from C(I) at any ponts on ths lne and can be used for all anted sgnal levels. Hoever, the measurement results sho that n most cases the protecton ratos of deband TV recevers vary as a functon of the anted sgnal level. Consequently, C(I) s not a straght lne th unty slope th some varaton th the nterferng sgnal strength. Nevertheless, for nterferng sgnals belo the overloadng threshold such C(I) curves can alays be approxmated by a straght lne th unty slope th an acceptable error. Ths method has been used n ths report for determnng the PR of DTT recevers. The method used for determnng protecton ratos and overloadng thresholds s composed of to steps: 1. The measured C(I) curve s approxmated by a straght lne th unty slope hch represents the deal lnear behavour of the recever front-end (constant PR case). The protecton rato of the recever s obtaned by subtractng I from C(I) at any ponts on ths lne. The protecton rato obtaned can be used for all anted sgnal levels. 2. A strong devaton of the measured C(I) curve from the straght lne th unty slope ndcates here the nterferng sgnal reaches the overloadng threshold;.e., the onset of strong non-lnear behavour. The devated segment of C(I) curve s approxmated by a lne vertcal to I-axs (constant I case). The value of I at the pont of ntersecton beteen the straght lne th unty slope and the lne vertcal to I-axs s consdered to be the recever overloadng threshold (I = O th ).

11 Rep. ITU-R BT Ths to steps procedure s depcted n Fg. 4. FIGURE 4 Determnaton of the recever protecton rato and overloadng threshold from ts C(I) curve; PR = 46 db, Oth = 2 dbm f- f = 16 MHz Measured C(I) Constant PR case Oth Report BT In some cases the approxmaton of a measured C(I) curve by a straght lne th unty slope and a lne vertcal to I-axs may seem not to be very straght forard, but t s alays possble to do t th an acceptable approxmaton error that should be n favour of the vctm recever. Examples of approxmatons are shon n Fgs 5 to 12. These examples use a anted sgnal level range startng at 7 dbm, but loer levels are possble dependng upon the senstvty of the recever mode beng tested.

12 1 Rep. ITU-R BT.2215 FIGURE 5 A ell approxmated C(I) curve; PR = 12 db; overloadng threshold s not reached f- f = 8 MHz Measured C(I) Constant PR case Oth Report BT FIGURE 6 A ell approxmated C(I) curve; PR = 53 db; O th = 1 dbm f- f = 24 MHz Measured C(I) Constant PR case Oth Report BT

13 Rep. ITU-R BT FIGURE 7 Some dffcultes to determne the overloadng threshold; PR = 39dB; Oth = 6 dbm f- f = 8 MHz Measured C(I) Constant PR case Oth Report BT FIGURE 8 A ell approxmated C(I) curve; PR = 61 db; Oth = 4 dbm f- f = 56 MHz Measured C(I) Constant PR case Oth Report BT In the follong example the recever appears to behave n a non lnear fashon hen the nterferng sgnal level reaches 21 dbm, but s qute lnear for hgher nterferng sgnal levels up to 3 dbm.

14 12 Rep. ITU-R BT.2215 FIGURE 9 A ell approxmated C(I) curve; PR = 39 db; Oth = 4 dbm f- f = 36.5 MHz Measured C(I) Constant PR case Oth Report BT In the follong example the O th s reached at an nterferng sgnal level of 24 dbm. Hoever, the measured C(I) curve shos that an ncrease of the anted sgnal level by about 3 db allos the recever to behave lnearly once agan but th a reduced PR ( 16 db nstead of 48 db). FIGURE 1 C(I) th recovery after an ncrease of 4 db of the anted sgnal level; PR = 47,5 db, O th = 24 dbm f- f = 72 MHz Measured C(I) Constant PR case Oth Report BT

15 Rep. ITU-R BT In the follong examples the O th s reached before the PR havng been reached. In such cases the PR s obtaned by subtractng I from C(I) at the loest ntersecton pont beteen the straght lne th unty slope representng the constant PR case and the lne vertcal to I-axs representng the constant I case. FIGURE 11 C(I) early reached overloadng threshold; PR = 62 db, O th = 8 dbm f- f = 32 MHz Measured C(I) Constant PR case Oth Report BT FIGURE 12 Early reached overloadng threshold; PR = 39 db, O th = 29dBm f- f = 64 MHz Measured C(I) Constant PR case Oth Report BT

16 14 Rep. ITU-R BT Conclusons and further ork requred The results ncluded n the annexes to ths report are beng used to mprove and update Recommendaton ITU-R BT They are also an opportunty to stmulate ne areas of nvestgaton for example the effects of tme varaton n nterferng sgnals. Other Recommendatons could also be consdered as canddates for the materal as requred and a note added hen requred. Where relevant the materal n the annexes has a note ndcatng the verson of Recommendaton ITU-R BT.1368 hch s amended, or another Recommendaton here relevant. It s recommended that any future updates to ths report add materal together th smlar notes of any partcular verson of a recommendaton hch reled on ths nformaton. Addtonal results of recever measurement tests are alays elcome and are n some cases urgently needed for all the other major TV broadcastng standards such as DVB-T2, ISDB-T, ATSC, DTMB, so that the approprate sectons of Recommendaton ITU-R BT.1368 can be flled th sutable PR and O th data for assstance n netork plannng actvtes. Ideas for future contrbutons are hghlghted n the annexes of ths report.

17 Rep. ITU-R BT Annexes Annex 1 DVB-T recever performance n the presence of nterferng sgnals from DVB-T, UMTS and LTE A.1.1.doc Measurements of protecton ratos and overload thresholds for DVB-T recevers under nterference from DVB-T n other channels (Doc. 6/352) * Ths nformaton as used n the generaton of Recommendaton ITU-R BT Embedded-from 6A-364.doc A.1.2.doc Measurements of protecton rato and overload threshold for DVB-T recevers under nterference from UMT n other channels (Doc. 6/352)* Ths nformaton as used n the generaton of Recommendaton ITU-R BT Embedded-from 6A-529.doc A.1.3.doc Measurements of protecton ratos and overload thresholds for DVB-T recevers under nterference from LTE n other channels (Doc. 6/352)* Ths nformaton as used n the generaton of Recommendaton ITU-R BT Embedded-from 6A-365.doc Embedded-from 6A-526.doc Embedded from 398.docx * To be updated accordngly follong the approval of Document 6/352, hch s a revson of Recommendaton ITU-R BT