1、Rec. ITU-R BS.706-2 1RECOMMENDATION ITU-R BS.706-2DATA SYSTEM IN MONOPHONIC AM SOUND BROADCASTING (AMDS)(Question ITU-R 60/10)(l990-1992-1998)Rec. ITU-R BS.706-2The ITU Radiocommunication Assembly,consideringa) the growing interest for a data transmission system for AM broadcasting and its applicati
2、ons;b) that it is desirable to have one system applicable to all AM broadcasting bands and that the future introductionof SSB in HF and of synchronous detection should be taken into account;c) that existing systems cannot be implemented on single-sideband (SSB) transmission in band 7 (HF);d) that ce
3、rtain applications of an AM data transmission system could correspond to similar features in the FMradio data system (RDS), as defined in Recommendation ITU-R BS.643, taking account of the lower bit rate available;e) that the design of such a system should take into account the mass production of re
4、ceivers;f) that data signals can be added to existing AM broadcast transmissions in such a way that they are inaudible,thus achieving good compatibility with reception of the normal monophonic sound programme signals,recommends1 that a system for data transmission in AM broadcasting (AMDS) should fu
5、lfil the requirements listed inAnnex 1;2 that since a system is not available for SSB in band 7 (HF) and for AM-Stereo in band 6 (MF) a system fordata transmission in AM-DSB broadcasting bands 5 (LF), 6 (MF) and 7 (HF) shall fulfil the requirements listed inAnnex 1 and shall comply with the minimum
6、specification listed in Annex 2.NOTE 1 Information regarding operational or projected systems is given in Annex 3.ANNEX 1Requirements for an AM radio-data transmission system1 Compatibility aspects1.1 Compatibility with the main programmeThe supplementary data system must be compatible with the main
7、 audio programme under all operational conditionsincluding: transmitters operated with energy-saving carrier-control techniques; synchronized networks of transmitters;2 Rec. ITU-R BS.706-2 SSB transmissions (if the introduction of an AM data system in HF broadcasting is feasible); transmitters which
8、 are used as a high stability frequency reference; mobile reception and, where necessary, reception with a stereophonic AM receiver in band 6 (MF).1.2 Compatibility with other programmes in co- or adjacent channelsThe protection ratios used in planning should not be affected, i.e. no additional inte
9、rference should be caused to theaudio programme signal by the data signals.2 Reliability of data receptionThe area in which the data signal can be reliably received, should be at least as large as that where the main programmeservice for ground- and sky-wave propagation conditions is provided.3 Appl
10、icationsBecause of the low data-rate which is expected to be available in an AM radio-data system, it may not be feasible tosupport simultaneously more than a few of the applications listed below.It is expected that a large part of the data-transmission capacity will usually be used for features rel
11、ated to automatic orassisted tuning functions. These features are therefore labelled “primary“. Other applications are labelled “secondary”and may be introduced to meet the needs of individual broadcasters. Note that although similar terms are used, thesefeatures may not correspond exactly with thos
12、e used in RDS (see Recommendation ITU-R BS.643).Primary Programme Identification (PI) code including: unique country code for each ITU country; unique language code. List of Alternative Frequencies (AFs). Programme Service (PS) name: this comprises at least four alpha-numeric characters and is inten
13、ded for display. Scheduling information (SI). Traffic Programme (TP) identification and Traffic Announcement (TA) identification.Secondary (examples) Differential GPS data (dGPS) Clock-Time (CT) and date (UTC and MJD) Programme Item Number (PIN) Decoder Identification code (DI) (e.g. stereo) Program
14、me Type code (PTY) Transparent Data Channel (TDC) In-House (IH) applications Traffic Message Channel (TMC) Radio Paging (RP).Rec. ITU-R BS.706-2 3ANNEX 2Specification of a data system for use in monophonic AM sound-broadcastingFrequency bands: LF, MF and HFMethod of modulation: phase modulation of t
15、he main carrierMaximum phase deviation: depending on bit rate according to Fig. 1Data format for bit rates below 100 bit/s: depending on applicationData format for bit rates 100 bit/s: according to Annex 40706-0110 50 100 200 3000153045Br(bit/s)DjDj : maximum peak phase deviationDj =210Br(bit/s)(deg
16、rees)FIGURE 1Dependence of the permitted phase deviation value Dj on the transmission bit rate (Br)4 Rec. ITU-R BS.706-2ANNEX 3Information on operational and projected AM data systems (AMDS)Table 1 gives information on AMDS systems as applied in different countries.TABLE 1Application of AMDS systems
17、Characteristics United Kingdom France Germany Operating frequency band Possible frequency bands Phase deviation Bit rate Data coding Data structure Achieved bit error ratio(normal conditions) ApplicationIn operation sinceReferenceLFLF, MF22.525 bit/sBi-phaseBlocks of 50 bits with32 usefulCoded weath
18、er informationElectricity supply switching1985LFLF, MF, HF28.540 bit/sNRZBlocks of 50 bits with32 usefulTime information1986French national standardNFC 90-002LF, MF, HFLF, MF, HF15200 bit/sNRZBlocks of 47 bits with 36useful 10-3for LF and MF(50% time)Automatic or assisted tuningTraffic informationFi
19、eld tests since 1988Rec. ITU-R BS.706-250706-02A CB12 V5 V12 V5 VDj, j (t)m, A(t)Dj, j (t)Dj, j (t)m, A(t)SoundmodulationamplifierPhasemodula-tionDj (t)Signalprepa-rationPowersupplyCrystalgeneratorandseparatorstagesAmplifierandseparatorstagesPowerpreamplifierand driveramplifierOutputcircuitModulated
20、powerstagegeneratorMasterData signal (TTL level)Sound signal(normalizedlevel)Data signal (TTL level)Limitingand phasedemodu-lationRegene-rationstagesLocaloscillatorRFpre-selectorstagesIF amplifierMixerSounddemodulatorSoundamplifierIFseparatoramplifiersound signalAM sound broadcasting transmitter AM
21、sound broadcasting receiverA: additional module (phase modulator)B: additional module (output decoupling unit)C: additional module (frequency demodulator and data signal regenerator)FIGURE 2Basic circuit diagram of a monophonic AM sound broadcasting system (AMDS)for supplementary data transmissionTr
22、ansmissionpathPowersupply6 Rec. ITU-R BS.706-2ANNEX 4*1 Baseband coding1.1 Structure of baseband coding1.2 Features of data transmission1.3 Error protection1.4 Block and Group synchronization2 Data format2.1 Definitions relating to the data transmission2.2 Programme identification2.2.1 PI code2.2.2
23、BI code3 Group types3.1 Usage of Groups3.2 Group sequences4 Description of Groups4.1 Group type 0/Basic tuning and switching information BTI4.2 Group type 1/Radiotext RT4.3 Group type 2/Alternative frequencies AF4.4 Group type 3/Traffic message channel TMC4.5 Group type 4/In-house applications IH4.6
24、 Group type 5/Transparent Data Channel TDC4.7 Group type 6/Scheduling information SI4.7.1 Coding of START and END4.8 Group type 7/Scheduling information supplementary SIS4.8.1 Information addressed by the usage code UCI4.8.2 Coding of latitude and longitude4.9 Group type 8/Additional tuning informat
25、ion ATI4.9.1 Information addressed by the usage code UC24.10 Group type 9/differential GPS-data dGPS4.11 Group type 10/TIME information UTC5 Glossary of terms6 Index of Tables7 Index of Figures8 Index of Formulas_*Editors Note - The text of Annex 4 is new.Rec. ITU-R BS.706-2 71 Baseband coding1.1 St
26、ructure of baseband codingFigure 3 shows the structure of the baseband coding. The largest element within the structure is called a Group. OneGroup consists of 2 Blocks with 47 bits each. Each Block contains one information word (36 bits) and one check word(11 bits). To distinguish the Blocks of a G
27、roup and to improve the Block synchronization, each Block is superimposedby an offset word (11 bits, modulo-2 addition).Group = 94 bitsBlock 1 Block 2Block = 47 bitsInformation word Check wordInformation word = 36 bitsm35 m34 m01 m00Check word (+ offset word) = 11 bitsc10 c09 c01 c00FIGURE 3Baseband
28、 coding structure1.2 Features of data transmissionFor all information words, check words, binary numbers or addresses, the most significant bit will be transmitted first(Figure 4). The order assigned to the binary number or address bit transmitted last is 20.The transmission of data is fully synchro
29、nized, i.e. there are no gaps between Groups and Blocks.8 Rec. ITU-R BS.706-2GroupBlock 1will be transmitted before Block 2Block 2GTPI orBIMSBcode Check wordGT Check wordGrouptype code4 Bits 16 BitsInfor-mation16 Bits+ Offsetword A11 BitsGroup typecode4 BitsInformation32 Bits+ Offsetword B11 BitsGro
30、up type code (GT)a3 a2 a1 a0most significant bitwill be transmitted firstleast significant bitFIGURE 4Data format and addressingTABLE 2Data elementsData element Note ChapterCheck word Error detection, error correction,Block and Group synchronization2.1 - 2.4PI code Programme identification code 3.2.
31、1BI code Broadcast identification code 3.2.2GT Group type 4Information is defined by the Group type code 5.1 - 5.11X unused capacity 5.1 - 5.11Rec. ITU-R BS.706-2 91.3 Error protectionIn order to enable the receiver/decoder to detect and correct transmission errors, each Block is assigned a check wo
32、rd(11 bits). This check wordc(x) (c10, c09, . , c00 shown in Figure 3) is the sum total (modulo 2) of: the remainder obtained after multiplication of the 36-bit information word m(x) by x11and a following division(modulo 2) by the generator polynomial g(x), and an 11-bit binary sequence d(x), called
33、 offset word such that:c(x) d(x)m(x) xg(x)mod g(x)11=+(1)whereby the generator polynomial (degree 11) may be described by the following formula:g(x) = x11+ x8+ x6+ 1 (2)Different offset words A and B are used for each Block of a Group.The 11-bit binary sequence for the offset words A and B are shown
34、 in the table below:TABLE 3Offset wordsThe error protection code offers the following features: detects all single and double errors in a Block; detects any single burst spanning 10 bits or less; detects about 99.90% of bursts spanning 11 bits; and about 99.95% of all longer bursts.The code is an op
35、timal burst error correcting code and is capable of correcting any single burst of span 5 bits or less.Depending on the number of errors within a Block or within the content of a Block the receiver/decoder may utilizeeither the error detection mode or the error correction mode or both of them.The pr
36、obability of unrecognized errors depends on the number of errors which are corrected. Field trials have shown thatno more than 2 errors in a Block should be corrected.Offset Offset word d(x)d10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0A 01011010101B 1011010101110 Rec. ITU-R BS.706-21.4 Block and Group synchroni
37、zationThe beginning and end of a data Block as well as the beginning and end of a Group may be detected in thereceiver/decoder by using the two offset words A and B. These offset words destroy the cyclic property of the basic codeso that in the modified code, cyclic shifts of code words do not give
38、rise to other code words. By means of this methodthe Block synchronization becomes reliable.2 Data format2.1 Definitions relating to the data transmissionThere is no specific repetition cycle fixed for the various types of Groups (see 4), i.e. a large degree of flexibility isprovided. This allows th
39、e user to create combinations of different types of information, which comply with hisrequirements.The selected data format comprises 5 Group types which are still unused and therefore provides a sufficient degree ofadaptability for future applications.In order to ensure efficient utilization of the
40、 AM data channel, the number of different types of information is minimizedwithin a given Group. Thereby the user will not be forced to waste data capacity by the transmission of unusedinformation.The first 4 bits of each Block are assigned to the Group type code (Figure 5) specifying the applicatio
41、n of the Group. Bythis process each Block of a Group can be decoded within the receiver/decoder without reference to the other Block.Thus the access time for data which are transmitted in several Blocks is reduced during interference.2.2 Programme identificationThe programme identification is a code
42、 which enables the receiver to distinguish between country of origin, programmearea, language and the identification of the programme itself.The code is not intended for direct display. It is assigned to each individual broadcast programme to identify transmittersradiating the same sound programme.
43、By this code the mobile receiver/decoder is enabled to search automatically for analternative frequency in case of bad reception of the just received frequency. In cases of stationary reception andespecially in the HF bands the listener may start search tuning for transmissions originated in a speci
44、fic country with adesired language.Except for Group type 5 (Transparent Data Channel) the programme identification is always included in the first Blockof each Group (see Figure 5). Depending on the service two different codes for the programme identification areavailable. These are the BI code and
45、the PI code.2.2.1 PI codeThe usage of the PI code is equivalent to RDS. For reasons of compatibility with RDS, transmissions that areimplemented on LF and/or MF and also on VHF/FM Band II, have to be identified with the PI code. This is necessaryfor automatic search tuning on all bands and moreover
46、to support cross-border functions especially for the TMC service(Traffic Message Channel).Rec. ITU-R BS.706-2 11TABLE 4PI structureExtended country codes (ECC) may optionally be transmitted to render the country identification in bits 1 to 4 of the PIcode unique. The extended country code consists o
47、f eight bits and is coded according to RDS-Standards.2.2.2 BI codeThe BI code (Broadcast identification) should be used to facilitate maximum flexibility with respect to tuning andsearching for a particular HF transmission. An eight-bit extension (bits 17 to 24) allows identification of up to 32broa
48、dcasters (organization number has to be agreed nationally) and up to 8 different simultaneous programmes from asingle broadcaster (programme marker).TABLE 5BI structureNOTES: Use of PI vs. BI code:a) For reasons of compatibility with RDS, those programmes that are implemented on LF and/or MF and VHF
49、/FMBand II, have to be identified with PI-code. The use of the ECC code will be optional.b) All other applications can use BI code instead of the PI code.c) For HF, the BI code should be used to facilitate maximum flexibility with respect to tuning and searching for aparticular transmission.d) The usage of BI or PI code is signalled by the codeflag CF.e) A short designation of the respective country could be derived from the Country identification or ECC to beshown on the receiver display. 2-Letter ISO 3166 codes are recomm
