1、228 Rec. ITU-R S.671-3 RECOMMENDATION ITU-R S.67 1-3 NECESSARY PROTECTION RATIOS FOR NARROW-BAND SINGLE CHANNEL-PER-CARRIER TRANSMISSIONS INTERFERED WITH BY ANALOGUE TELEVISION CARRIERS (Question ITU-R 50/4) (1990-1992-1993-1994) The ITU Radiocommunication Assembly, considering that narrow-band SCPC
2、 carriers are sensitive to the interference caused by analogue television carriers, 4 especially when such TV carriers are only modulated with energy dispersal signais at the television frame rate; b) closely spaced satellites; c) unique to this class of signals; d) that interference from FM-TV into
3、 SCPC transmissions is generally a determining factor in the coordination of that the calculation methods required for determining the level of permissible interference in such cases are that the uniqueness of this situation is recognized in Appendix 4 of the Radio Regulations, recommends 1. for the
4、 purposes of calculating the permissible levels of interference between analogue television and narrow- band SCPC carriers, the protection ratio of SCPC carriers interfered with by analogue TV carriers modulated only by energy dispersal at the TV frame rate, be calculated from the following: I. z fo
5、r 64 kbi/s SCPC, without forward error correction (FEC); CII = C/N + 6.4 + 3 log 6 - 8 log (AO) dB 1.2 for companded frequency modulation (CFM) SCPC; C/Z = 13.5 + 2 log 6 - 3 log (i/lO) dB where: CU: ratio of the interfered with SCPC carrier power to the total carrier power of the interfering disper
6、sed TV signal operating carrier-to-noise power ratio of the SCPC carrier which corresponds to a BER of 1 x 10-6 ratio of the occupied bandwidth of the SCPC carrier to the TV peak-to-peak deviation due to dispersal the total allocated pre-demodulation interference power in the SCPC bandwidth, consist
7、ing of the interference power contributed by the TV carrier as well as the noise-like interference coming from other interfering carriers (see Annex l), expressed as a percentage of the total pre-demodulation noise power (10 I i I 25); C/N: 6: 1: 2. Note 1 - The interference criteria in 0 1.1 and 1.
8、2 are applicable for interfering TV signals using frame rate energy dispersal only. that the following Notes should be regarded as part of the Recommendation: Note 2 - The formulae in 5 1.1 and 1.2 are correct on the assumption that the interference determined by the relative power value i is caused
9、 by a TV carrier I and noise-like interference IN, for a ratio INII = 2.5 and for a power spectral density of the noise-like interference of -62 dBc/Hz. ITU-R RECMN*S* 671-3 94 4855212 0523505 T28 Rec. ITU-R S.671-3 229 Note 3 - To protect 64 kbit/s SCPC carriers having FEC coding at rates between 1
10、12 and 718 using soft decision Viterbi decoding, the following expression may be used: C/Z = C/N + 9.4 + 3.5 log6 - 6log(i/10) dB This interference criterion is valid for interfering FM-TV signals modulated only by a dispersal signal. Note 4 - Significant additional protection for narrow-band SCPC c
11、arriers can be obtained if they are appropriately offset in frequency from the centre frequency of the TV carrier. This applies, in different degrees, both when the TV carrier is modulated with live programme material and otherwise and in such cases the effect of power spectral density of FM-TV carr
12、iers should be taken into account for determining the interference at frequencies outside the energy dispersal bandwidth. Note 5 - Further study is needed to determine the level of additional protection which can be realized when the TV carrier is modulated with live programme material or otherwise.
13、 Note 6 - Annex 1 contains methods for performing the calculations which utilize the protection ratios in 9 1 and the results of measurements in support of both Note 7 - Further study is needed to develop appropriate interference criteria for interfering FM-TV carriers with a line rate energy disper
14、sal or a composite line rate and frame rate dispersal. 1 and 2. ANNEX 1 Calculation of protection ratio for FM-TV interference into singe-channel-per-carrier transmissions in networks of the fixed-satellite service 1. Interference in uncoded 8-bit PCM 4-phase PSK singe-channel-per-carrier transmissi
15、ons One of the most common carriers in use is 8-bit PCM 4-phase PSK (QPSK) SCPC at 64 kbit/s and the establishment of an interference criterion is based on the following considerations. Monitoring of TV transmissions in the INTELSAT system indicates that TV carriers are modulated by video signals or
16、 test patterns most of the time and that for only very short periods the TV carriers are modulated by energy dispersal signals (EDS) alone. These periods are of the order of 0.6% of the total transmission time. The average length of such periods is about 5 min. The longest continuous such period was
17、 found to be about 18 min. Thus, the probability of simultaneous occurrences of two or more such interferers is very small. Additional measurements are needed to examine the validity of these statistical results in other satellite systems. To establish a criterion to be used for protecting the uncod
18、ed SCPC/QPSK (64 kbit/s) transmissions, one TV carrier modulated with EDS alone is assumed to be present all of the time (one such entry representing time addition of all such interfering signals from different satellites). This type of interference is assumed to coexist with other noise-like interf
19、erers. Therefore, the total pre-demodulation interference noise allowed by Recommendation ITU-R S.523 should be divided between these two dissimilar types of interference. A model has been developed to derive the apportionment of the total allowed interference between the two types of interferers. T
20、he model assumes a contribution coming from an energy dispersal modulated TV carrier and a noise-like contribution which is equal to 2.5 times the single entry interference. The noise-like single entry interference is assumed to originate from a modulated carrier, whose spectral density (power in a
21、bandwidth of 1 Hz relative to the total carrier power) in the proximity of the carrier frequency is -62 dBc/Hz. This value is appropriate for representing a high density FM carrier or a modulated TV carrier. ITU-R RECMN*S. 673-3 74 m 4855232 052350b 9b4 m 230 Rec. ITU-R S.671-3 The following laborat
22、ory measurements were made. The SCPC transmission was operated at different carrier- to-noise ratio values above CIN = 14.6 dB (& IN0 = 12.3 dB) which corresponds to BER = 10-6. Then, the energy dispersal modulated TV interferer was added and the value of the carrier-to-interferer carrier power was
23、recorded which restored the BER to lop6. The results are presented in Fig. 1 for different peak-to-peak energy dispersal signal deviations. In the same figure, the relationship between the noise-like interference CI1 (for both single entry and total noise-like interference) and degradation is shown.
24、 FIGURE 1 C/I vs degradation of C/N ratio 22 21 20 19 18 17 16 15 14 13 8 12 II 10 9 8 7 6 5 O 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Degradation to C/1v (dB) Single entry 2.5 times single entry DO1 . - ITU-R RECMN*S- 673-3 74 4855212 O523507 8TO W Rec. ITU-R S.671-3 231 Using Fig. 1, b
25、y equating the total degradation caused by the TV (EDS modulated only) interference and noise-like interference with the criterion defined in Recommendation ITU-R S.523, the protection ratios for uncoded SCPC/QPSK (64 kbit/s) were determined, as shown in Fig. 2. FIGURE 2 Protection criteria or: 18 1
26、7 16 15 14 13 12 11 10 0.01 0.02 0.05 o. 1 6 SCPC bandwidth 6= peak-to-peak deviation by EDS of interfering TV canier These results can be approximated by the equation: where : CI1 : C/N : 6: i: c/z = 21 + 3 log6 + Slog(lO/i) C/I = C/N + 6.4 + 3 log 6 - 8 log (i/lO) dB dB ratio of the SCPC carrier p
27、ower to the total carrier power of the interfering dispersed TV signal operating carrier-to-noise ratio which corresponds to BER = 10 (SCPC occupied bandwidth)/(TV peak-to-peak deviation by EDS) the total allocated pre-demodulation interference power in the SCPC bandwidth, consisting of the interfer
28、ence power contributed by the TV carrier as well as the noise-like interference coming from other interfering carriers (see Annex l), expressed as a percentage of the total pre-demodulation noise power (10 5 i 5 25). ITU-R RECMNUS. 671-3 94 m 4855212 0523508 737 m Transmission parameter INTELSAT, EU
29、TELSAT Information rate (IR) (kbitis) 64 Overhead bits (OH) 16/15 Composite rate (CR) (kbitis) 68.27 FEC code rate (C) 112 Transmission rate (TR) (kbis) (CWC) Nyquist bandwidth (0.5 TR) 136.5 68 k 5.4 5.4 Composite rate EdNo() (dB) for i BER I GIN() (dB) for 10-6 BER 232 Rec. ITU-R S.671-3 I 2. Inte
30、rference in 8-bit PCM 4-phase PSK single-channel-per-crier transmissions with FEC coding Measurements have been carried out on two 64 kbis SCPC/QPSK systems with rate 1/2 FEC coding, i.e. EUTELSAT SMS carriers and INTELSAT Business Service IBS carriers. The signal parameters are listed in Table 1 an
31、d are in accordance with the specification of these systems. TABLE i Encoded QPSK transmission parameters (I) The values for EdNO and CIN relate to the actual demodulator performance of the equipment used in the measurements. The measurements resulted in curves of C/Z versus degradation for BER valu
32、es 10“ . The protection criterion which has been developed is based on measurements using two different interference models. One model is the same as described in Q 1 for uncoded QPSK transmission. The model divides the total allowed interference between two types of interferers: one TV carrier modu
33、lated only with an energy dispersal signal (EDS), and other carriers modulated by noise-like signals. In the model, the apportionment of the total allowed interference is determined from the different interference effects of the two types of interferers. The spectral density of -62 dBc/Hz is used to
34、 derive the noise-like interference. The other model considered an interference scenario in which total interference is equivalent to 20% of the pre-modulation noise, shared equally between noise-like interference and a single TV carrier modulated by an energy dispersal signal. The energy dispersed
35、carrier is, therefore, assumed to represent 10% of the total pre-demodulation noise, hence leading to an equivalent thermal noise increase of 0.5 dB (referred to as “CIN degradation”). The tests involved the measurement of the increase in mean BER caused by the introduction of the interferer for a g
36、iven constant value of the CIN ratio (carrier-to-thermal noise power ratio), set to give a BER of 1 x 1 in the absence of interference (5.4 dB for 64 kbit/s carriers). The measured increase in mean BER was converted into an equivalent thermal noise increase using the back-to-back modem noise perform
37、ance curve. The measurements thus provide a relationship between the C/I (ratio of the SCPC carrier power to the total carrier power of the interfering TV signal) and the degradation of the C/N in the SCPC channel caused by the presence of the TV interference as single scfurce interference (modulate
38、d by EDS only). Results using the two above-mentioned models agree well and lead to the following single entry interference criterion which can be used for intersystem coordination purposes: C/i = C/N + 9.4 -t 3.5 log 6 - 6 log (i/lO) dB (2) where: CIN : carrier-to-noise ratio which corresponds to a
39、 BER of 1 x i: total allowed interference power in the carrier bandwidth expressed as a percentage of the total pre-demodulation noise power (i0 I i I 25, as defined in Recommendation ITU-R S.523). - ITU-R RECMN*S- 671-3 94 W 4855232 0523509 673 Rec. ITU-R S.671-3 233 3. Interference in FM-SCPC tran
40、smissions using syllabic companding Based on the assumption used in 5 1, protection criteria have been developed for SCPC-CFM using two distinct bases for the criteria: - impulse noise counts above a threshold of -21 dBmO, and - subjective evaluations. The modem employed was designed to operate in t
41、he INTELSAT system in accordance with INTELSAT performance specifications for its VISTA service. The carrier-to-noise density C/NO at the normal operating point is 54.2 dB(Hz) which corresponds to a CIN of 10.2 dB. The threshold of this equipment is approximately a CINO of 50.2 dB(Hz). The nominal I
42、F noise bandwidth is 25 kHz with the deviation established such that for a O dBmO test tone at 1 kHz the corresponding r.m.s. deviation is 5.1 kHz. The pre-emphasis cross-over frequency is at 1 kHz. The companding is 2: 1 syllabic according to ITU-T Recommendation G.162 with an unaffected level of O
43、 dBmO. For the impulse count measurements, a threshold value of -21 dBmO was used in accordance with ITU-T Recommendation M.1020. The test instrument used for the impulse counts employed a 1 kHz tone at the transmit side which was removed by a notch filter at the receive side. The level of this tone
44、 was -10 dBmO. Degradations to the CIN, for this tone level and with the compander on, for the case of 6 impulses per 15 min, were measured as a function of the CI1 ratios. These results are shown in Fig. 3 where Cil versus the degradation to the CIN is shown for the four values of energy dispersal
45、peak-to-peak deviations. The calculated noise-like interference curve is shown in Fig. 4 from which the protection criterion is derived. CIZ = 13.5 + 210g6 - 3 lg(i/lO) dB (3) where 6 and i are as defined above. In the same way, subjective assessments of the degradation to the SCPC-CFM channel were
46、made with a criterion based upon one audible “pop” per minute. The characteristic interference on the EDS at or near the nominal 54.2 dB(Hz) operating point is observed in the form of impulsive noise or “pops”. These results are shown in Fig. 5. The resulting criteria are of the form CII = 13 + 2 lo
47、g 6 - 3 log (i/lO) dB (4) as shown in Fig. 6 and are slightly lower than those based on impulse counts. Comparing equations (3) and (4), it is concluded that the criterion of equation (3) should be used as a single criterion for SCPC-CFM for both impulse count and subjective impairments, and graphic
48、ally shown in Fig. 4. 234 14 13 12 11 10 8 9 8 7 6 ITU-R RECMNxS. 673-3 74 4855232 052L5LO 375 M Rec. ITU-R S.671-3 FIGURE 3 CZ vs degradation in C/N for a SCPC-CFM modem based upon impulse noise counts (a constant impulse count criterion of six counts exceeding a threshold of -21 dBmO in a 15 min i
49、nterval was used) I l l I I I O 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Degradation in CXV (dB) A: C/&“, (carrier to single entry noise-like interference ratio) B: C/I,l (carrier to noise-like interference ratio) - 0.5 MHz - 1MHz 2MHz 4 MHz FIGURE 4 C/I vs duty cycle based upon impulse noise count for a SCPC-CFM modem U1 = 133 + 2 log 6 - 3 log (i/ 7 1 L - i= 10% i= 15% - i=20% i = 25% 2 5 1 o-* 1 o- Duty cycle, 6 SCPC bandwidth 6=- _ peak-to-peak deviation by EDS of interfering TV carrier Rec. RU-R S.671-3 235 FIGURE 5 C/I vs degradation
