1、 Rec. ITU-R BT.1124-3 1 RECOMMENDATION ITU-R BT.1124-3 Reference signals for ghost cancelling in analogue television systems (Question ITU-R 55/11) (1994-1995-1998-2001) The ITU Radiocommunication Assembly, considering a) that a ghost cancelling system using a ghost cancelling reference (GCR) signal
2、 is one of the most effective countermeasures for ghost images in individual and collective antenna reception of television signals; b) that the system should be effective for cancelling multiple and long delayed ghost images as well as short delayed ghost images and it should be also effective for
3、leading ghosts and waveform equalization of video signals; c) that the GCR signals can be inserted into the lines in the vertical blanking intervals; d) that for each television system an appropriate GCR signal can be defined; e) that for each country the appropriate GCR signal can be used to suit t
4、he various propagation conditions and the types of transmission media; f) that the ghost canceller using the GCR signals can be manufactured at a reasonable cost; g) that the cost of ghost cancellers may be lower if there is widespread use of a common GCR signal, recommends 1 that the GCR signal sho
5、uld be a dedicated reference signal optimized for ghost cancelling; 2 that the GCR signal should allow the rapid determination of the channel response even under poor signal-to-noise conditions; 3 that the GCR signal must be able to provide a flat amplitude and flat group delay response versus frequ
6、ency over the entire passband of each system; 4 that the GCR signal should make efficient use of the vertical interval resources; 5 that for NTSC, PAL and SECAM television systems, a broadcaster wishing to integrate a GCR signal should use a GCR signal complying with the specifications given in Anne
7、x 1 for: GCR signal A, GCR signal B, GCR signal C; 6 that for new GCR applications for NTSC, PAL or SECAM, GCR signal C should preferable be used; 2 Rec. ITU-R BT.1124-3 7 that for advanced analogue television systems, a broadcaster wishing to integrate a GCR signal should use a GCR signal complying
8、 with the specifications given in Annex 2 for a MUSE system. ANNEX 1 GCR signal specifications for conventional TV systems 1 Introduction GCR Signal A for use with the NTSC system, was recommended by ITU-R in 1994 and has been used extensively in Japan since 1989. GCR Signal B was recommended by ITU
9、-R in 1994 and has been used extensively with the NTSC system in Korea since 1993. GCR Signal C for use with NTSC, PAL, and SECAM system is being adopted by broadcasters in many countries now introducing GCR signals. 1.1 GCR Signal A Requirements for the GCR signal relevant to the NTSC system are sp
10、ecified in Tables 1 to 4 and Figs. 1 to 3. TABLE 1 Specification of GCR waveform Value Remarks Amplitude 70 2 IRE units Difference between setup level and the centre point level of the GCR waveform Setup 0 2 IRE units Difference between blanking level and pedestal level of the active line. Differenc
11、e between line A and line B should be 0.5 IRE or less Width 160 1.0 sc(1)(44.7 0.28 s) Measured at 50% value of the GCR amplitude Start of GCR 60 1.5 sc(2)(16.76 0.42 s) GCR rising edge timing (50% point) with respect to leading edge of line sync Rising edge Integrated sin(x)/x See equation (1) Trai
12、ling edge 0.25 0.05 s (2T bar) Interval between 10% point and 90% point of the GCR amplitude (1)sc Subcarrier cycles (one colour subcarrier cycle: 1/3.579545 s). (2)Specified at the output point of the GCR signal generator. Not specified at the output point of the GCR inserter unless necessary. Rec.
13、 ITU-R BT.1124-3 3 xxhxxAtftd)()(sin1)(= (1) where A is a normalizing factor (A = f (), = 2 4.177447 106, and h(x) is a window function to give the signal spectrum as shown in Fig. 4, such as raised cosine having the half amplitude width of 10.5 s. 1124-0104070060 2002 TFIGURE 1GCR waveform for line
14、 Asin xx160 sc61.4616.7644.7 sIREunits227.5 sc63.56 s1124-0200407063.56 sIREunitsFIGURE 2Zero-pedestal waveform for line B4 Rec. ITU-R BT.1124-3 1124-03000.51.00.150.90.951.051.14.1774471.0 3.58 4.09 4.16 4.194.26RelativeamplitudeNominal valueUpper toleranceLower toleranceFrequency (MHz)FIGURE 3Freq
15、uency spectrum for reference pulse GCR signalThe characteristics are applied to the differential or one-sample difference of the GCR signal. TABLE 2 GCR insertion line TABLE 3 Signal on the line immediately preceding the GCR line Insertion line numbers 18 and 281 Field numbers 1 2 3 4 5 6 7 8 x1x2x3
16、x4x1x2x3x4x1, x2, x3and x4should not contain time varying information. Rec. ITU-R BT.1124-3 5 TABLE 4 GCR transmission sequence 1.2 GCR signal B Requirements for the GRC signal relevant to the 525-line NTSC and 625-line PAL systems are specified in Tables 5 to 8 and Figs. 4 and 5. TABLE 5 Ternary se
17、quence of length 366 Field number 1 2 3 4 5 6 7 8 Waveform Line A Line B Line A Line B Line B Line A Line B Line A 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1
18、 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0
19、 0 0 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 6 Rec. ITU-R BT.1124-3 TABLE 6 Specifications of GCR
20、waveform TABLE 7a Transmission sequence of NTSC GCR signal TABLE 7b Transmission sequence of PAL GCR signal* 625-line Television system 525-line B, G D, K GCR signal frequency limit 4.18 MHz 5.0 MHz 6.0 MHz(1)Pedestal height 30 IRE units 300 mV Start of pedestal(2)8.75 s 10.5 s Finish of pedestal(2)
21、61.9 s 62.5 s Start of GCR(2)11.5 s 12.2 s Duration of GCR 25.6 s 20.6 s Lowest level of GCR 10 IRE units 0 mV Highest level of GCR +70 IRE units 600 mV Clock frequency(3)4 3.58 MHz 4 4.43 MHz (1)The 6 MHz option is not compatible with transmission of NICAM digital sound using a 5.85 MHz carrier. (2
22、)The start and finish times are defined at the half-amplitude points. (3)This refers to the use of a clock at four times the colour subcarrier frequency of NTSC or PAL, as appropriate. Field number 1 2 3 4 GCR signal polarity + + Field number 2 4 6 8 GCR signal polarity + + * There is no absolute re
23、lationship between the polarity of the GCR transmission sequence and the eight-field sequence of PAL. Rec. ITU-R BT.1124-3 7 TABLE 8 The frequency values in Fig. 4 1124-04f1 f2 f3 f4 f500.51.0RelativeamplitudeFrequencyFIGURE 4Frequency characteristic of the lowpass filter625-line TV system frequency
24、 525-line B, G D, K f1 (MHz) 1.00 1.00 1.00 f2 (MHz) 3.58 4.43 4.43 f3 (MHz) 4.09 4.80 5.80 f4 (MHz) 4.18 5.00 6.00 f5 (MHz) 4.25 5.20 6.20 8 Rec. ITU-R BT.1124-3 1124-05a4020020406080IREunitsFIGURE 5aPositive GCR signal for 525-line systems1124-05b4020020406080IREunitsFIGURE 5bNegative GCR signal f
25、or 525-line systemsRec. ITU-R BT.1124-3 9 1124-05c10006005004003002001002003000 200 400 600 800 1 000 1 200 1 400FIGURE 5cPositive GCR signal for 625-line systems (5 MHz)Sample numberAmplitude (mV)1124-05d10006005004003002001002003000 200 400 600 800 1 000 1 200 1 400FIGURE 5dNegative GCR signal for
26、 625-line systems (5 MHz)Sample numberAmplitude (mV)10 Rec. ITU-R BT.1124-3 1124-05e10006005004003002001002003000 200 400 600 800 1 000 1 200 1 400FIGURE 5ePositive GCR signal for 625-line systems (6 MHz)Sample numberAmplitude (mV)1124-05f10006005004003002001002003000 200 400 600 800 1 000 1 200 1 4
27、00FIGURE 5fNegative GCR signal for 625-line systems (6 MHz)Sample numberAmplitude (mV)Rec. ITU-R BT.1124-3 11 1.3 GCR signal C Requirements for the GCR signal are described below. Specific parameters for 525- and 625-line NTSC, PAL and SECAM television systems (see Note 1) are set out in Table 9. NO
28、TE 1 Correct operation of the motion adaptive colour plus (MACP) process used by the PALplus system relies on the fact that points separated by 312 lines within a frame have a precise phase relationship. In order to avoid disturbing this relationship, any changes to the equalization of the signal ap
29、plied by a ghost canceller located in either the transmission or reception chain should preferably be made during the period of lines 624 to 22. The GCR signal is placed on a single line in the vertical blanking interval, on one line per field in 525-line systems, and on one line per frame (two fiel
30、ds) in 625-line systems. The GCR signal has a flat spectrum and high energy up to the frequency f1 and has low energy beyond the frequency f2. The values of f1 and f2 are shown in Table 9. Figure 6 shows the spectrum of the GCR signal. The normalized GCR signal as a function of time is shown in Fig.
31、 7. In 525-line systems, the GCR signal is placed on line 19 (and the corresponding line in the following field). In 625-line systems, the GCR signal is preferably placed on line 318, with the preceding line 317 containing no time-varying information. For both 625- and 525-line systems the line imme
32、diately preceding the GCR line should preferably not contain time varying information to avoid constraining the performance of ghost cancellers. To provide efficient cancellation of 625-(525)-line systems requiring post ghost cancellation ranges greater than approximately 38 (31) s, at least the fol
33、lowing line should preferably not contain any time-varying information (e.g. if line 318 (19 and 282) is used for the GCR then line 319 (20 and 283) should not contain time varying information. The GCR has nominally constant amplitude within the band of interest, and is placed on a pedestal of heigh
34、t V1. The rise and fall times of the pedestal are nominally 4 T, and the start and finish times to the half amplitude points, with respect to the leading edge of the horizontal sync are T1 and T2 respectively. The values of V1, T1 and T2 are given in Table 9. The GCR signal has a duration of T3 (mea
35、sured at 1% of the maximum value) and begins at time T4 after the leading edge of horizontal sync. The first peak (positive or negative) is T5 after the leading edge of horizontal sync. The GCR varies from V2 to V3. Note that the pedestal V1 is the mean of these extreme values. The values of T3, T4,
36、 T5, V2 and V3 are given in Table 9. Waveforms of the GCR signal on the pedestal are shown in Figs. 8 and 9 represent line A and line B respectively. Line A and line B have the same pedestal height V1, but the GCR polarity is inverted from line A to line B. 12 Rec. ITU-R BT.1124-3 TABLE 9 Television
37、 system 525-line 625-line f1 GCR signal frequency limit 4.1 MHz 5.0 MHz(1)6.0 MHz f2 GCR signal frequency stop limit 4.3 MHz 5.2 MHz 6.2 MHz V1 Pedestal height 30 IRE units 350 mV T1 Start of pedestal 9.5 s 10.5 s T2 Finish of pedestal 58.5 s 62.5 s T3 Duration of GCR 35.5 s 23.2 s 22.32 s T4 Start
38、of GCR 12.0 s 12.2 s 12.6 s T5 First peak of GCR 16.7 s 15.8 s 15.7 s V2 Lowest level of GCR 10 IRE units 0 mV V3 Highest level of GCR +70 IRE units 700 mV GCR polarity: Line A Normal Normal Line B Inverted Inverted GCR transmission sequence(2): Field 1 Line A (3)Field 2 Line B Line A Field 3 Line A
39、 (3)Field 4 Line B Line B Field 5 Line B (3)Field 6 Line A Line A Field 7 Line B (3)Field 8 Line A Line A (1)For 625-line television system N, described in Recommendation ITU-R BT.470, the available vision bandwidth (4.2 MHz), is less than the bandwidth of the 625-line GCR (5.0 MHz). It is suggested
40、 that for television system N, the GCR signal for bandwidth 5 MHz described in this Recommendation for 625-line signals be used, but the band limited to the available vision bandwidth. (2)There is no absolute relationship between the polarity of the GCR transmission sequence and the eight-field sequ
41、ence of PAL. (3)The use of a field mode GCR signal for 625-line systems, in conjunction with appropriate receiving equipment might offer improved performance in the case of moving ghost signals. Further studies need to be conducted to investigate this possibility. Rec. ITU-R BT.1124-3 13 Numerical v
42、alues of the reference signal as a function of time can be calculated from equation (2): +=de)()(sinj)(cosde)()(sinj)(cos2)(j022j022ttWbbWbbAtf(2) W() is the window function (3): dtede21)(cos2121)(jj11tcctctW+= (3) where the constants: A, b, , c and 1are given in Table 10. Alternative formulae for d
43、efinition of this signal in real and in spectral spaces are presented in Appendix 1. They may be used for calculation numerical values of the reference signal instead of equations (2), (3) with the same result. They are presented for better understanding of the nature of GCR signal C. More detailed
44、information on possibilities of this signal is published in Report ITU-R BT.2018. Parameters for GCR formulae are given in Table 10. TABLE 10 Parameters for GCR formulae NTSC (Normalized)(1)525-lines 625-lines (5 MHz) 625-lines (6 MHz) Units A 9 3.592 1070.30358 1062.7 106V b 110 0.53656 10120.2829
45、10120.23 1012s2/rad 4.3/7.16 2 4.3 1062 5.5 1062 6.25 106rad/s c /49 0.917998 1060.9121 1060.9121 106rad/s 14.15/7.16 2 4.15 1062 5.0 1062 6.0 106rad/s (1)NTSC parameters normalized to 4 3.579545 MHz to 1 Hz and 1 V p-p. 14 Rec. ITU-R BT.1124-3 1124-06a0123456701FIGURE 6aMagnitude of the spectrum of
46、 the GCR signal for 525-line systemsFrequency (MHz)Magnitude0.20.40.60.81.21124-06b0123456701FIGURE 6bMagnitude of the spectrum of the GCR signal for 625-line systems (5 MHz)Frequency (MHz)0.20.40.60.81.2MagnitudeRec. ITU-R BT.1124-3 15 1124-06c0123456701FIGURE 6cMagnitude of the spectrum of the GCR
47、 signal for 625-line systems (6 MHz)Frequency (MHz)0.20.40.60.81.2Magnitude1124-0700 10203040506070FIGURE 7An example of a GCR signal as a function of time for 525-line systemsTime (s)Amplitude (normalized) (V) 0.4 0.3 0.2 0.10.10.20.30.40.50.6 0.6 0.516 Rec. ITU-R BT.1124-3 1124-08a020406010 30 50
48、70 50050100FIGURE 8aGCR signal line A for 525-line systemsTime (s)Amplitude (IRE units)1124-08b01002003005006007008009001 0004001 1000 1020304050607FIGURE 8bGCR signal line A for 625-line systems (5 MHz)Time (s)Amplitude (mV)Rec. ITU-R BT.1124-3 17 1124-08c3000350700200100100200300400500600010 203040506070FIGURE 8cGCR signal line A for 625-line systems (6 MHz)Time (s)Amplitude (mV)12.2 15.8 35.41124-09a020406010 30 50 7050050100FIGURE 9aGCR signal line B for 525-line systemsTime (s)Amplitude (IRE units)18 Rec. ITU-R BT.1124-3 1124-09b010020030050060070080
