SIST EN 301 210 V1.1.1:2003

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digitalna videoradiodifuzija (DVB) – Struktura okvirov, kodiranje kanalov in modulacija za satelitsko novinarstvo (DSNG) in druge prispevne aplikacije prek satelitovDigital Video Broadcasting (DVB); Framing structure, channel coding and modulation for Digital Satellite News Gathering (DSNG) and other contribution applications by satellite33.170Televizijska in radijska difuzijaTelevision and radio broadcasting33.060.30Radiorelejni in fiksni satelitski komunikacijski sistemiRadio relay and fixed satellite communications systemsICS:Ta slovenski standard je istoveten z:EN 301 210 Version 1.1.1SIST EN 301 210 V1.1.1:2003en01-december-2003SIST EN 301 210 V1.1.1:2003SLOVENSKI
STANDARD
EN 301 210 V1.1.1 (1999-03)European Standard (Telecommunications series)Digital Video Broadcasting (DVB);Framing structure, channel coding and modulationfor Digital Satellite News Gathering (DSNG)and other contribution applications by satelliteEBUUEREuropean Broadcasting UnionUnion Européenne de Radio-TélévisionSIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)2ReferenceDEN/JTC-DVB-73 (b7c00ico.PDF)Keywordsbroadcasting, digital, DVB, SNG, TV, videoETSIPostal addressF-06921 Sophia Antipolis Cedex - FRANCEOffice address650 Route des Lucioles - Sophia AntipolisValbonne - FRANCETel.: +33 4 92 94 42 00
Fax: +33 4 93 65 47 16Siret N° 348 623 562 00017 - NAF 742 CAssociation à but non lucratif enregistrée à laSous-Préfecture de Grasse (06) N° 7803/88Internetsecretariat@etsi.frIndividual copies of this ETSI deliverablecan be downloaded fromhttp://www.etsi.orgIf you find errors in the present document, send yourcomment to: editor@etsi.frCopyright NotificationNo 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 1999.© European Broadcasting Union 1999.All rights reserved.SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)3ContentsIntellectual Property Rights.4Foreword.41Scope.52References.63Symbols and abbreviations.73.1Symbols.73.2Abbreviations.74Transmission system.84.1System definition.84.2Adaptation to satellite transponder characteristics.94.3Interfacing.94.4Channel coding for QPSK modes.94.4.1Transport multiplex adaptation and randomization for energy dispersal.104.4.2Outer coding (RS), interleaving and framing.104.4.3Inner coding (convolutional).104.5Bit mapping, baseband shaping and modulation for QPSK modes.114.5.1Bit mapping to QPSK constellation.114.5.2Baseband shaping and quadrature modulation.124.6Channel coding for the optional 8PSK and 16QAM modes.124.6.1Transport multiplex adaptation and randomization for energy dispersal (8PSK and 16QAM modes).124.6.2Outer coding (RS), interleaving and framing (8PSK and 16QAM modes).124.6.3Inner coding ("pragmatic" trellis coding type) (8PSK and 16QAM modes).124.7Bit mapping, baseband shaping and modulation for the optional 8PSK and 16QAM modes.154.7.1Bit mapping to constellations (8PSK and 16QAM modes).154.7.1.1Inner coding and constellation for 8PSK 2/3 (2CBPS).164.7.1.2Inner coding and constellation for 8PSK 5/6 and 8/9 (1CBPS).174.7.1.3Inner coding and constellation for 16QAM 3/4 and 7/8 (2CBPS).184.7.2Baseband shaping and modulation (8PSK and 16QAM modes).205Error performance requirements.21Annex A (normative):Signal spectrum at the modulator output.22Annex B (normative):Transmission setups for interoperability tests and emergencysituations.24Annex C (normative):Implementation of the "optional" modes.25Annex D (normative):SI implementation for DSNG and other contribution applications.26Annex E (informative):Examples of possible use of the System.28Bibliography.31History.32SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)4Intellectual Property RightsIPRs essential or potentially essential to the present document may have been declared to ETSI. The informationpertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be foundin SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respectof ETSI standards", which is available free of charge from the ETSI Secretariat. Latest updates are available on theETSI Web server (http://www.etsi.org/ipr).Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guaranteecan be given as to the existence of other IPRs not referenced in SR 000 314 (or the updates on the ETSI Web server)which are, or may be, or may become, essential to the present document.ForewordThis European Standard (Telecommunications series) has been produced by the Joint Technical Committee Broadcast ofthe European Broadcasting Union (EBU), Comité Européen de Normalisation ELECtrotechnique (CENELEC) and theEuropean Telecommunications Standards Institute (ETSI).The work was based on the studies carried out by the European DVB Project under the auspices of the Ad Hoc Groupon DSNG of the DVB Technical Module. This joint group of industry, operators and broadcasters provided thenecessary information on all relevant technical matters (see bibliography).NOTE:The EBU/ETSI JTC Broadcast was established in 1990 to co-ordinate the drafting of standards in thespecific field of broadcasting and related fields. Since 1995 the JTC Broadcast became a tripartite bodyby including in the Memorandum of Understanding also CENELEC, which is responsible for thestandardization of radio and television receivers. The EBU is a professional association of broadcastingorganizations whose work includes the co-ordination of its members' activities in the technical, legal,programme-making and programme-exchange domains. The EBU has active members in about 60countries in the European broadcasting area; its headquarters is in Geneva.European Broadcasting UnionCH-1218 GRAND SACONNEX (Geneva)SwitzerlandTel:+41 22 717 21 11Fax:+41 22 717 24 81Digital Video Broadcasting (DVB) ProjectFounded in September 1993, the DVB Project is a marked-led consortium of public and private sector organizations inthe television industry. Its aim is to establish the framework for the introduction of MPEG-2 based digital televisionservices. Now comprising over 200 organizations from more than 25 countries around the world, DVB fostersmarked-led systems, which meet the real needs, and economic circumstances, of the consumer electronics and thebroadcast industry.National transposition datesDate of adoption of this EN:5 February 1999Date of latest announcement of this EN (doa):31 May 1999Date of latest publication of new National Standardor endorsement of this EN (dop/e):30 November 1999Date of withdrawal of any conflicting National Standard (dow):30 November 1999SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)51ScopeThe present document describes the modulation and channel coding system (denoted the "System" for the purposes ofthe present document) for Digital Satellite News Gathering (DSNG) and other contribution applications by satellite.According to ITU-R Recommendation SNG.770-1 [12], SNG is defined as "Temporary and occasional transmissionwith short notice of television or sound for broadcasting purposes, using highly portable or transportable uplink earthstations.". The equipment should be capable of uplinking the video programme (or programmes) with its associatedsound or sound programme signals. Optionally it should be capable of providing two-way co-ordination(communication) circuits and data transmission according to EN 301 222 [6]. The equipment should be capable of beingset up and operated by a crew of no more than two people within a reasonably short time. Limited receiving capabilityshould be available in the uplink terminal to assist in pointing the antenna and to monitor the transmitted signal, wherepossible.Digital television contribution applications by satellite consist of point-to-point or point-to-multipoint transmissions,connecting fixed or transportable uplink and receiving stations, not intended to be received by the general public.Although these applications often transmit a single TV service, the Transport Stream multiplex flexibility also allowsmulti-programme TV services with associated sound, including commentary sound channels and data services; in thiscase multiple service components are Time Division Multiplexed (TDM) on a single digital carrier.Maximum commonality with EN 300 421 [3] is maintained, such as Transport Stream multiplexing [1], scrambling forenergy dispersal, concatenated error protection strategy based on Reed-Solomon coding, convolutional interleaving andinner convolutional coding. The baseline System compatibly includes (as a subset) all the transmission formats specifiedby EN 300 421 [3], based on Quaternary Phase Shift Keying (QPSK) modulation and is suitable for DSNG services aswell as for other contribution applications by satellite. Nevertheless, other optional (annex C explains the meaning of"optional" within the present document) transmission modes are added, using Eight Phase Shift Keying (8PSK)modulation and Sixteen Quadrature Amplitude Modulation (16QAM), in order to fulfil specific applicationrequirements. These optional modes can be very efficient in certain contribution applications by satellite.The following warnings should be taken into account while using the high spectrum efficiency modes, 8PSK and16QAM:·they require higher transmitted EIRPs and/or receiving antenna diameters, because of their intrinsic sensitivity tonoise and interferences;·they are more sensitive to linear and non-linear distortions; in particular 16QAM cannot be used on transpondersdriven near saturation;·they are more sensitive to phase noise, especially at low symbol rates; therefore high quality frequency convertersshould be used (see annex E);·the System modulation/coding schemes are not rotationally-invariant, so that "cycle-slips" and "phase snaps" inthe chain can produce service interruptions; therefore frequency conversions and demodulation carrier recoverysystems should be designed to avoid cycle-slips and phase snaps.The System is suitable for use on different satellite transponder bandwidths, either in single carrier per transponder or inmultiple carriers per transponder (Frequency Division Multiplex, FDM) configuration. Annex E gives examples ofpossible use of the System.The present document:-gives a general description of the System;-specifies the digitally modulated signal in order to allow compatibility between pieces of equipment developedby different manufacturers. This is achieved by describing in detail the signal processing principles at themodulator side, while the processing at the receive side is left open to different implementation solutions.However, it is necessary in the present document to refer to certain aspects of reception;-identifies the global performance requirements and features of the System, in order to meet the service qualitytargets.SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)62ReferencesThe following documents contain provisions which, through reference in this text, constitute provisions of the presentdocument.· References are either specific (identified by date of publication, edition number, version number, etc.) ornon-specific.· For a specific reference, subsequent revisions do not apply.· For a non-specific reference, subsequent revisions do apply.· A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the samenumber.[1]ISO/IEC 13818-1: "Information technology; Generic coding of moving pictures and associatedaudio information: Systems".[2]ISO/IEC 13818-2: "Information technology; Generic coding of moving pictures and associatedaudio information: Video".[3]EN 300 421: "Digital Video Broadcasting (DVB); Framing structure, channel coding andmodulation for 11/12 GHz satellite services".[4]EN 50083-9: "Cabled distribution systems for television, sound and interactive multimedia signals;Part 9: Interfaces for CATV/SMATV headends and similar professional equipment forDVB/MPEG-2 transport streams".[5]ETR 154: "Digital Video Broadcasting (DVB); Implementation guidelines for the use of MPEG-2Systems, Video and Audio in satellite, cable and terrestrial broadcasting applications".[6]EN 301 222: "Digital Video Broadcasting (DVB); Co-ordination channels associated with DigitalSatellite News Gathering (DSNG)".[7]Void.[8]EN 300 468: "Digital Video Broadcasting (DVB); Specification for Service Information (SI) inDVB systems".[9]ETS 300 327: "Satellite Earth Stations and Systems (SES); Satellite News Gathering (SNG)Transportable Earth Stations (TES) (13-14/11-12 GHz)".[10]ETS 300 673 (1997): "Radio Equipment and Systems (RES); ElectroMagnetic Compatibility(EMC) standard for 4/6 GHz and 11/12/14 GHz Very Small Aperture Terminal (VSAT) equipmentand 11/12/13/14 GHz Satellite News Gathering (SNG) Transportable Earth Station (TES)equipment".[11]TBR 30: "Satellite Earth Stations and Systems (SES); Satellite News Gathering (SNG)Transportable Earth Stations (TES) operating in the 11-12/13-14 GHz frequency bands".[12]ITU-R Recommendation SNG.770-1: "Uniform operational procedures for Satellite NewsGathering (SNG)".SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)73Symbols and abbreviations3.1SymbolsFor the purposes of the present document, the following symbols apply:aRoll-off factorC/NCarrier-to-noise ratiodfreeConvolutional code free distanceEb/N0Ratio between the energy per useful bit and twice the noise power spectral densityfNNyquist frequencyG1,G2Convolutional code generatorsIInterleaving depth [bytes]I, QIn-phase, Quadrature phase components of the modulated signaljBranch index of the interleaverKConvolutional code constraint lengthmnumber of transmitted bits per constellation symbolMConvolutional interleaver branch depth for j = 1, M = N/INError protected frame length (bytes)RsSymbol rate corresponding to the bilateral Nyquist bandwidth of the modulated signalRuUseful bit rate after MPEG-2 [1] transport multiplexer, referred to the 188 byte formatTNumber of bytes which can be corrected in RS error protected packetTsSymbol periodX,YDi-bit stream after rate 1/2 convolutional coding3.2AbbreviationsFor the purposes of the present document, the following abbreviations apply:16QAMSixteen Quadrature Amplitude Modulation1CBPS1 Coded Bit Per Symbol2CBPS2 Coded Bits Per Symbol8PSKEight Phase Shift KeyingAWGNAdditive White Gaussian NoiseBERBit Error RatioBSBandwidth of the frequency Slot allocated to a serviceBWBandwidth (at -3 dB) of the transponderCBPSCoded Bits Per SymbolDSNGDigital Satellite News GatheringFDM Frequency Division MultiplexFEC Forward Error CorrectionHEXHexadecimal notationIFIntermediate FrequencyIRDIntegrated Receiver DecoderMCPCMultiple Channels Per Carrier transmissionMPEGMoving Pictures Experts GroupMUXMultiplexOBOOutput Back OffOCTOctal notationPPuncturingPDHPlesiochronous Digital HierarchyPSKPhase Shift KeyingQEFQuasi-Error-FreeQPSKQuaternary PSKRFRadio FrequencyRSReed-SolomonSCPCSingle Channel Per Carrier transmissionSIService InformationSIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)8SMATVSatellite Master Antenna TelevisionSNGSatellite News GatheringTCMTrellis Coded ModulationTDMTime Division MultiplexTSDTTransport Stream Descriptor TableTVTelevision4Transmission system4.1System definitionThe System is defined as the functional block of equipment performing the adaptation of the baseband TV signals, fromthe output of the MPEG-2 transport multiplexer (see ISO/IEC 13818-1 [1]), to the satellite channel characteristics. TheSystem is designed to support source coding as defined in [1], [2], [5].The System transmission frame is synchronous with the MPEG-2 multiplex transport packets (see [1]).The System shall use QPSK modulation, and optionally (annex C explains the meaning of "optional") 8PSK and16QAM modulations, and the concatenation of convolutional and RS codes. For 8PSK and 16QAM, "pragmatic" trelliscoding shall be applied, optimizing the error protection of the convolutional code defined in EN 300 421 [3]. Theconvolutional code is able to be configured flexibly, allowing the optimization of the system performance for a givensatellite transponder bandwidth (see annex E).Digital television transmissions via satellite can be affected by power limitations, therefore ruggedness against noise andinterference has been one of the design objectives of the System. On the other hand, when larger power margins areavailable, spectrum efficiency can be increased to reduce the cost of the space segment. Therefore the System offersmany transmission modes (inner coding and modulations), giving different trade-offs between power and spectrumefficiency. For some specific contribution applications, some modes (QPSK and 8PSK) thanks to their quasi-constantenvelope, are appropriate for operation with saturated satellite power amplifiers, in single carrier per transponderconfiguration. All the modes (including 16QAM) are appropriate for operation in quasi-linear satellite channels, inmulti-carrier Frequency Division Multiplex (FDM) type applications.The following processes shall be applied to the data stream (see figure 1):·transport multiplex adaptation and randomization for energy dispersal (according to EN 300 421 [3]);·outer coding (i.e. Reed-Solomon) (according to EN 300 421 [3]);·convolutional interleaving (according to EN 300 421 [3]);·inner coding:-punctured convolutional coding (according to EN 300 421 [3]);-"pragmatic" trellis coding associated with 8PSK and 16QAM (optional);·bit mapping into constellations:-QPSK (according to EN 300 421 [3]);-8PSK (optional);-16QAM (optional);·squared-root raised-cosine baseband shaping:-roll-off factor a = 0,35 according to EN 300 421 [3] for QPSK, 8PSK and 16QAM;-additional optional roll-off factor a = 0,25 (for the optional modulations 8PSK and 16QAM);·quadrature modulation (according to EN 300 421 [3]).SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)9Audio Data MUX 1 2 n MPEG-2 Source Coding and Multiplexing Coders Video MUX Programme Transport MUX Adaptation & Energy Dispersal Satellite Channel Adapter Outer Coder RS (204,188)Inter- leaver (I=12) Convolutional Inner Coder to the RF Satellite Channel Baseband Shaping Quadrature Modulator Mapping Constellation Bit Into type QPSK 8PSK (optional) 16QAM (optional) According to EN 300 421 According to EN 300 421 for QPSK a = 0,35(see note)NOTE:a = 0,25 for 8PSK and 16QAM (additional and optional).Figure 1: Functional block diagram of the SystemIf the received signal is above C/N and C/I threshold, the Forward Error Correction (FEC) technique adopted in theSystem is designed to provide a "Quasi Error Free" (QEF) quality target. The QEF means less than one uncorrectederror-event per transmission hour, corresponding to Bit Error Ratio (BER) = 10-10 to 10-11 at the input of the MPEG-2demultiplexer.4.2Adaptation to satellite transponder characteristicsThe symbol rate shall be matched to given transponder characteristics, and, in the case of multiple carriers pertransponder (FDM), to the adopted frequency plan. Examples of possible use of the System are given in annex E.4.3InterfacingThe System, as defined in the present document, shall be delimited by the following interfaces given in table 1.Table 1: System interfacesLocationInterfaceInterface typeConnectionTransmit stationInputMPEG-2 [1], [2], [4] transport multiplex (note 1)from MPEG-2 multiplexerOutput70/140 MHz IF, L-band IF, RFto RF devicesReceive installationOutputMPEG-2 transport multiplex [1], [2], [4] (note 1)to MPEG-2 demultiplexerInput70/140 MHz IF, L-band IFfrom RF devicesNOTE 1:For interoperability reasons, the Asynchronous Serial Interface (ASI) with 188 bytes format, data burstmode (bytes regularly spread over time) is recommended.NOTE 2:The 70 MHz IF may imply limitation on the maximum symbol rate.4.4Channel coding for QPSK modesThe information on QPSK modulation summarized here is only partial. Refer to EN 300 421 [3] for the completespecification.SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)104.4.1Transport multiplex adaptation and randomization for energydispersalThis processing shall be in accordance with EN 300 421 [3], as summarized in the following.The System input stream shall be organized in fixed length packets, following the MPEG-2 transport multiplexer (seeISO/IEC 13818-1 [1]). The total packet length of the MPEG-2 transport Multiplex (MUX) packet is 188 bytes. Thisincludes 1 sync-word byte (i.e. 47HEX). In order to comply with ITU Radio Regulations and to ensure adequate binarytransitions, the data of the input MPEG-2 multiplex shall be randomized. To provide an initialization signal for thedescrambler, the MPEG-2 sync byte of the first transport packet in a group of eight packets is bit-wise inverted from47HEX to B8HEX. This process is referred to as the "Transport Multiplex Adaptation".4.4.2Outer coding (RS), interleaving and framingThis processing shall be in accordance with EN 300 421 [3], as summarized in the following.Reed-Solomon RS (204,188, T = 8) shortened code, from the original RS(255,239, T = 8) code, shall be applied to eachrandomized transport packet (188 bytes) to generate an error protected packet. Reed-Solomon coding shall also beapplied to the packet sync byte, either non-inverted (i.e. 47HEX) or inverted (i.e. B8HEX).Convolutional interleaving with depth I = 12 shall be applied to the error protected packets. This results in aninterleaved frame, composed of overlapping error protected packets and delimited by inverted or non-invertedMPEG-2 [1] sync bytes (preserving the periodicity of 204 bytes).4.4.3Inner coding (convolutional)Processing of the convolutional encoder shall be in accordance with EN 300 421 [3], as summarized in the following.The System shall allow for a range of punctured convolutional codes, based on a rate 1/2 mother convolutional codewith constraint length K = 7 corresponding to 64 trellis states (figure 2). This will allow selection of the mostappropriate level of error correction for a given service or data rate. The System shall allow convolutional coding withcode rates of 1/2, 2/3, 3/4, 5/6 and 7/8.1-bitdelayserialbit-stream1-bitdelayY output (133 octal)1-bitdelay1-bitdelay1-bitdelay1-bitdelayModulo-2 adderModulo-2 adderX output (171 octal)inputFigure 2: Convolutional code of rate 1/2The punctured convolutional code shall be used as given in table 2, according to EN 300 421 [3].NOTE:At the receiver, each of the code rates and puncturing configurations is in a position to be tried until lockis acquired. Phase ambiguity in the demodulator is able to be resolved by decoding the MPEG-2 [1] syncbyte delimiting the interleaved frame. Automatic receiver synchronization is an important feature inDSNG applications, to simplify and accelerate the satellite connection setup.SIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)11Table 2: Punctured code definitionOriginal codeCode rates1/22/33/45/67/8KG1(X)G2(Y)PdfreePdfreePdfreePdfreePdfree7171OCT133OCTX: 1Y: 1C1 = X1C2 = Y110X : 1 0Y : 1 1C1 = X1 Y2 Y3C2 = Y1 X3 Y46X: 1 0 1Y: 1 1 0C1 = X1 Y2C2 = Y1 X35X: 1 0 1 0 1Y: 1 1 0 1 0C1 = X1 Y2 Y4C2 = Y1 X3 X54X: 1 0 0 0 1 0 1Y: 1 1 1 1 0 1 0C1 = X1 Y2 Y4 Y6C2 = Y1 Y3 X5 X73NOTE:1 = transmitted bit0 = non transmitted bit4.5Bit mapping, baseband shaping and modulation for QPSKmodes4.5.1Bit mapping to QPSK constellationFor QPSK, inner coding and mapping into constellation shall be in accordance with EN 300 421 [3], as summarized inthe following.The serial input stream (see figures 2 and 3) shall be directly fed into the convolutional encoder. The outputs C1 and C2of the punctured convolutional encoder shall be directly sent to the QPSK mapper.serialbit-streamXYIQPuncturingEncoderConvolutionalbit mappingconstellationto QPSKC1C2m=2
bits per symbolrate k/n convolutional codeBasebandshapingQuadratureModulationFigure 3: Inner coding principle for QPSKThe System shall employ conventional Gray-coded QPSK modulation with absolute mapping (no differential coding).Bit mapping in the QPSK constellation shall follow figure 4. If the normalization factor 1/Ö2 is applied to the I and Qcomponents, the corresponding average energy per symbol becomes equal to 1.C1=0QIC1=0C1=111C2=0C2=1C1=1C2=0C2=1Figure 4: Bit mapping into QPSK constellationSIST EN 301 210 V1.1.1:2003

ETSIEN 301 210 V1.1.1 (1999-03)124.5.2Baseband shaping and quadrature modulationPrior to modulation, the I and Q signals (mathematically represented by a succession of Dirac delta functions, multipliedby the amplitudes I and Q, spaced by the symbol duration Ts = 1/Rs) shall be square root raised cosine filtered. Theroll-off factor shall be a = 0,35.The baseband square root raised cosine filter shall have a theoretical function defined by the following expression:1)(=fH for ()ffN<-1a HfsinfNfNf()=+éëêêùûúúìíïîïüýïþï-1212212pa for ()()fffNN11-££+aaHf()=0 for ()ffN>+1a,where:fTRNss==122 is the Nyquist frequency and a is the roll-off factor.A template for the signal spectrum at the modulator output is given in annex A.4.6Channel coding for the optional 8PSK and 16QAM modesSome details on QP
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