1、 Rec. ITU-R BS.1194-2 1 RECOMMENDATION ITU-R BS.1194-2 SYSTEMS FOR MULTIPLEXING FREQUENCY MODULATION (FM) SOUND BROADCASTING WITH A SUB-CARRIER DATA CHANNEL HAVING A RELATIVELY LARGE TRANSMISSION CAPACITY FOR STATIONARY AND MOBILE RECEPTION (Question ITU-R 71/10) (1995-1998) Rec. ITU-R BS.1194-2 The
2、 ITU Radiocommunication Assembly, considering a) that many countries use the Radio Data System (RDS) according to Recommendation ITU-R BS.643; b) that although RDS is able to accommodate many of the data services required, the data capacity is nevertheless limited; c) that it is a fundamental requir
3、ement that compatibility be achieved between FM stereophonic services including RDS and any new additional sub-carrier system; d) that a much larger data capacity may be needed for some applications; e) that sub-carrier data radio channel systems can provide a much larger capacity compared to RDS an
4、d are capable of meeting the requirement stated in c) as regards protection ratios and interference levels; f) that high speed data systems have already been put into operation; g) that the diversity of applications as described in ITU-R BS.1350 precludes the suitability of a single system for all a
5、pplications, recommends 1 that one of the following 3 systems be used for multiplexing frequency modulation (FM) sound broadcasting with a sub-carrier data channel having a relatively large transmission capacity for stationary and mobile reception: the Data Radio Channel (DARC) System, as specified
6、in Annex 1, which is best suited for its high level of compatibility with the main broadcast audio channel and for Intelligent Transportation Services; or the High Speed Data System (HSDS) as specified in Annex 2, which is best suited for its minimum duty cycle for power savings and for paging servi
7、ces; or the Sub-carrier Transmission Information Channel (STIC) system as specified in Annex 3, which is best suited for its long message reliability in multipath and for Intelligent Transportation Services particularly when a high level of audio processing is used on the main broadcast audio channe
8、l. NOTE 1 Recommendation ITU-R BS.1350 specifying the system requirements will assist broadcasters in evaluating how to meet their service requirements with the available high speed data systems. NOTE 2 A comparison of systems is provided in Appendix 1. Appendix 2 provides test results for 3 systems
9、, tested side-by-side by an independent body in the United States. 2 Rec. ITU-R BS.1194-2 ANNEX 1 System description: System A, Data Radio Channel (DARC) The DARC system provides a highly acceptable balance of throughput, robustness and occupied bandwidth to support multiple applications of a standa
10、rdized data sub-carrier. The system is designed to minimize the effects of multipath and fading on the channel in both stationary and mobile environments. Three dimensional error correction/detection provides virtually error-free data reception on all types of receiver. Some multiplexed applications
11、 that DARC supports are: receiver displayed information in the form of multiple page text and graphics including, but not limited to, audio program information, news, sport, weather, navigational data and travel information; computer database refreshing and file transfer; portable paging/messaging a
12、nd conditional access (receiver addressability); DGPS correction data for portable and mobile receivers. DARCs Level-controlled Minimum Shift Keying (LMSK) modulation method allows easy, inexpensive receiver implementation. The DARC FM sub-carrier specifications are a matter of ETSI Standard ETS 300
13、 751. 1 Modulation characteristics (physical layer) 1.1 Sub-carrier frequency The sub-carrier frequency is 76 kHz locked in phase to the fourth harmonic and, in the case of stereophonic services, is of pilot tone. The frequency tolerance shall be within 76 kHz 7.6 Hz (0.01%) and the phase difference
14、 shall not exceed 5 for the phase of pilot tone. 1.2 Method of modulation LMSK modulation is used with a spectrum shaping according to Figure 1. LMSK is a form of MSK in which the amplitude is controlled by stereo sound signals of left minus right. A frequency of 76 kHz + 4 kHz is used when the inpu
15、t data is 1 and 76 kHz 4 kHz is used when the input data is 0. 1.3 Bit rate The bit rate is 16 kbit/s 1.6 bit/s. 1.4 Sub-carrier level The sub-carrier level is varied depending on the level of the stereo L-R signals (see Figure 2). If the deviation of the main FM carrier when modulated by the stereo
16、 L-R signals is less than 2.5%, the sub-carrier is deviated by 4% (3 kHz) of the main FM carrier. If the deviation of the main FM carrier when modulated by the stereo L-R signals is more than 5%, the sub-carrier is deviated by up to 10% (7.5 kHz) of the main carrier. Between these limits the deviati
17、on has a linear relation. Rec. ITU-R BS.1194-2 3 1194-01 80 60 40 2002050 60 70 80 90 10056 58 64 88 94 970.5 0.5FIGURE 1Spectrum-shaping filterBaseband frequency (kHz)Relativeamplitude(dB)Lower boundUpper bound1194-020510012345678FIGURE 2Sub-carrier deviationInjectionlevel(%)Deviation of left-right
18、stereo sound (%)2 Frame structure (data link) 2.1 General features The largest element of the structure is called a “frame” and consists normally of 78 336 bits in total, organized as 190 information blocks of 288 bits each and 82 parity blocks of 288 bits each. An information block comprises a Bloc
19、k Identification Code (BIC) of 16 bits, information of 176 bits, a Cyclic Redundancy Check (CRC) of 14 bits and parity of 82 bits. 4 Rec. ITU-R BS.1194-2 A parity block comprises a BIC of 16 bits and parity of 272 bits. There are four different types of BIC (see Table 1) to generate block synchroniz
20、ation and frame synchronization. There are three methods to organize data, methods A and B, which both use product coding (272,190) (272,190) and method C that uses only block code (272,190). All three methods are identified and distinguished by the sequence of BICs. TABLE 1 Block Identification Cod
21、e (BIC) 2.2 Method A This method limits the transmission delay on the transmitter side. In method A the frame (called Frame A) consists normally of 190 information blocks followed by 82 parity blocks (see Figure 3) but, for services with strong demand for real-time transmission it is possible to ins
22、ert 12 additional information blocks (block coded only) among the parity blocks in the product coded frame. 1194-03CRCFIGURE 3Frame according to method A, without insertion of real-time blocksBIC3BIC2BIC1BIC460blocks70blocks82blocks60blocksInformationInformationInformationHorizontalparityVertical pa
23、rityThe 12 inserted blocks are not a part of the product coded frame. They are placed at fixed positions, four blocks at a time at three positions (see Figure 4). The first four blocks are placed after 20 parity blocks, the next four after another 21 parity blocks and the last four blocks after anot
24、her 21 parity blocks. The BIC for the inserted blocks is BIC2. The receiver extracts such blocks and decodes them immediately. BIC1 0001 0011 0101 1110 BIC2 0111 0100 1010 0110 BIC3 1010 0111 1001 0001 BIC4 1100 1000 0111 0101 Rec. ITU-R BS.1194-2 5 1194-04CRCCRCCRCCRCVertical parityFIGURE 4Frame ac
25、cording to method A, with static insertion of real-time blocks60blocks70blocks60blocks82+12blocksInformationInformationInformationHorizontalparityBIC2 ParityReal time information blocksBIC2 ParityReal time information blocksBIC2 ParityReal time information blocksBIC4BIC4Vertical parityBIC4Vertical p
26、arityBIC4Vertical parityBIC3BIC2BIC12.3 Method B To allow an almost uniform transmission during the whole frame (called Frame B), the parity blocks are interleaved with the information blocks (see Figure 5). This method causes a delay (about 5 s) on the transmitter side. 2.4 Method C Method C compri
27、ses only information blocks of 288 bits. BIC3 is used within this method. This method is intended for services with a strong demand for real-time transmission, but at a lower level of error protection, e.g. for real-time services, stationary reception or repetitive information. 2.5 Error correction
28、code A product code (272,190) (272,190) is used for the frame in methods A and B to enable the receiver/decoder to detect and correct errors which occur in reception. A block code (272,190) is used for method C. The (272,190) code is a shortened majority logic decodable difference set cyclic code. T
29、he generator polynomial for the (272,190) code is given by: g(x) = x82+ x77+ x76+ x71+ x67+ x66+ x56+ x52+ x48+ x40+ x36+ x34+ x24+ x22+ x18+ x10+ x4+ 1 2.6 Error detection 14 bits of CRC are used to enable the receiver/decoder to detect errors. From the 176 information bits, a CRC is calculated usi
30、ng the generator polynomial: g(x) = x14+ x11 + x2 + 1 6 Rec. ITU-R BS.1194-2 2.7 Scrambling To avoid restrictions on the data input format and to spread the modulation spectrum, data should be scrambled by the Pseudo-Noise (PN) sequence specified by: g(x) = x9+ x4+ 1 1194-05CRCCRCCRCCRCCRCCRCCRCCRCC
31、RCCRCCRCCRCCRCCRCCRCCRCCRCCRCCRCCRCFIGURE 5Frame according to method B, with block interleaving13blocks123blocks123blocks13blocksInformation 1Information 2Information 12Information 13Information 14Information 15Parity 1Information 16Information 17Parity 2Information 95Information 96Parity 41Informat
32、ion 97Information 98Information 108Information 109Information 110Information 111Parity 42Information 112Information 113Parity 43Information 189Information 190Parity 82BIC1BIC1BIC1BIC1BIC3BIC3BIC4BIC3BIC3BIC4BIC3BIC3BIC4BIC2BIC2BIC2BIC2BIC3BIC3BIC4BIC3BIC3BIC4BIC3BIC3BIC4ParityParityParityParity1194-
33、06CRCFIGURE 6Frame according to method C, block code onlyBIC3 ParityInformationRec. ITU-R BS.1194-2 7 3 Operational characteristics of the Data Radio Channel (DARC) 3.1 Transmission characteristics 3.1.1 Laboratory transmission tests Laboratory transmission experiments of Bit Error Rate (BER) charac
34、teristics against random noise and multipath fading were conducted. Figure 7 shows BER characteristics in relation to receiver input voltage. It can be seen from the figure that error correction eliminates bit errors where the receiver input voltage is 16 dBV or above. 1194-0715 20 25101252525252521
35、02103104105106Before error correctionAfter error correctionReceiver input voltage (dBV)FIGURE 7Bit error characteristics for random noiseBERFigure 8 indicates BER characteristics under fading distortion. Without error correction, the error rate does not fall below about 7.104even if the receiver inp
36、ut voltage is increased. The use of error correction will enable the BER to be kept to an adequately low level for input voltages above 27 dBV. 3.1.2 Field transmission tests Figure 9 shows the correct reception time rates for mobile reception. When a page is made up of one packet, a time rate of 90
37、% or more can be secured by using DARC Frame C shown in Figure 6. When a page is formed with 250 packets (8 500 bytes), DARC Frames A and B would ensure a correct reception time rate of about 85%. 8 Rec. ITU-R BS.1194-2 1194-0820 30 40 50101251021031042525Before error correctionAfter error correctio
38、nFIGURE 8Bit error characteristics for fading distortionBERReceiver input voltage (dBV)Fading frequency:Multipath D/U:Delay time:3.3 Hz10 dB5 s1194-0902040608010011021025 2 5 2FIGURE 9Effect of error correction code in the FM service areaCorrect receptiontimerate(%)Number of packets per one pageNo c
39、odingFrame CFrames A and BRec. ITU-R BS.1194-2 9 3.2 Compatibility with stereo sound broadcasting 3.2.1 Questionnaire survey Compatibility with stereo sound broadcasting is important in deciding the multiplexing level of multiplex signals. A mail questionnaire survey of more than 2 000 people was co
40、nducted by changing the multiplexing level of the LMSK signals which were experimentally multiplexed with the stereo sound signals. Speech and piano music were used as stereo sound signals. Table 2 shows the results of the survey in terms of the percentage of receivers out of the total number of ans
41、wers, which showed a quality impairment of two grades as a function of six multiplexing levels. TABLE 2 The number and percentage of impaired receivers as a function of the multiplexing level The questionnaire survey has shown that the ratio of deteriorated receivers could be controlled at below 0.5
42、% if the minimum multiplexing level of the LMSK was below 4%. 3.2.2 Subjective assessment of sound quality The test procedure was based on Recommendation ITU-R BS.562. Three types of programme material were used, namely piano music, pop music and female speech. Slightly more than 100 people more or
43、less experts on sound quality, responded by listening to the test transmission in their homes and reporting their assessment on a special form. Figure 10 gives the main results. The assessment for eight different sub-carrier parameter combinations is shown for the three types of programme material t
44、ogether. Results for three decay values along with the sub-carrier level control characteristic finally chosen are shown. The outcome of the consistency test cases (without sub-carrier) is shown for comparison as well as the results for constant sub-carrier levels 3 and 7.5 kHz. The test has shown t
45、hat a sub-carrier frequency of 76 kHz and LMSK with the sub-carrier level controlled to give a main carrier deviation varying between 3-7.5 kHz and with a decay time of 5 ms gives the best result. The mean assessment grade is 4.96 on the five-grade impairment scale and the system is therefore consid
46、ered to be compatible with the FM stereophonic sound-broadcasting system at VHF. LMSK minimum multiplexing level (%) No. Of receivers Ratio (%) 2 7 0.31 3 7 0.31 4 10 0.44 5 14 0.61 6.5 18 0.78 10 27 1.18 10 Rec. ITU-R BS.1194-2 1194-105543210 0.5 1.5 2.5 3.5 4.54.934.964.914.84.944.984.95FIGURE 10T
47、est results from subjective assessment of sound qualitySubjective assessment of sound qualityFive-grade impairment scaleStandard deviationMeanSubcarriermodulationAssessment consistency 3Assessment consistency 2Assessment consistency 1L-MSK: Fix 3 kHzL-MSK: Fix 7.5 kHzL-MSK: 3-7.5 kHzdecay 25 msL-MSK
48、: 3-7.5 kHzdecay 5 msL-MSK: 3-7.5 kHzdecay 1 ms3.2.3 Multipath distortion The above compatibility tests have not assessed the effects of multipath propagation. It is to be expected that such conditions may cause some interference to the main programme signal, as well as, perhaps, the RDS signal if t
49、his is transmitted simultaneously. In such circumstances, however, the received programme signal is also expected to be impaired by multipath distortion. In this section, compatibility tests of the DARC signal with the main programme under the conditions of multipath propagation are described. Inter-modulation between a DARC signal and the pilot tone of 19 kHz causes interference within the audio frequency band. Figure 11 indicates the audio signal-to-noise (S/N) ratio for various sub-carrier frequencies in which the bit rate of 16 kbit/
