1、 Rec. ITU-R BO.1696 1 RECOMMENDATION ITU-R BO.1696 Methodologies for determining the availability performance for digital multiprogramme broadcasting-satellite service systems, and their associated feeder links operating in the planned bands (Question ITU-R 3/6) (2005) Scope This Recommendation prop
2、oses methodologies for determining performance objectives for digital systems in the 11.7-12.7 GHz, and sets availability objectives for digital systems that are higher than those for analogue systems. Annex 1 to this Recommendation provides example implementations of the recommended methodologies,
3、as well as exact and approximate solutions. The ITU Radiocommunication Assembly, considering a) that digital multiprogramme systems are now in use in the broadcasting-satellite service (BSS); b) that the performance of digital multiprogramme systems is important to administrations implementing such
4、systems; c) that the system availability performance provides an important reference point for evaluating the relative performance of an administrations BSS assignment, should that assignment be implemented with a digital multiprogramme system; d) that the reception characteristics of a digital mult
5、iprogramme system are significantly different from the reception characteristics of an analogue FM system; e) that the existing Appendices 30 and 30A of the Radio Regulations performance objective of maintaining a C/N ratio equal to or better than 14 dB for 99% of the worst month is based on analogu
6、e FM transmission; f) that, because of these factors, it is desirable to develop an availability performance objective specifically for digital multiprogramme systems; g) that a methodology to determine availability performance for digital multiprogramme BSS systems must recognize the wide range of
7、threshold C/N ratios at which these various systems operate; h) that the development of a digital multiprogramme performance objective is not only useful for the planned BSS band, but also for other BSS bands, for example, the 17/21 GHz band, 2 Rec. ITU-R BO.1696 further considering a) that the perf
8、ormance of digital multiprogramme systems can be characterized by evaluating the system availability corresponding to the quasi-error-free (QEF) point1, which corresponds to high-picture quality reception, recognizing a) that although many operational digital multiprogramme BSS links have QEF link a
9、vailability better than 99.5% of the worst month (or about 99.86% of an average year for most rain zones), the required availability is determined by specific system performance objectives; b) that Recommendation ITU-R BO.1516 Digital multiprogramme television systems for use by satellites operating
10、 in the 11/12 GHz frequency range recommends, among other things, that one of the four transmission systems described in Annex 1 of that Recommendation be selected when implementing digital multiprogramme television services via satellite; c) that Recommendation ITU-R BO.1516 shows that the QEF C/N
11、ratio values for these systems is spread over a wide range of values, and that trade-offs among primary digital link parameters can be used to meet performance objectives, recommends 1 that administrations should use the methodologies provided in Annex 1 to this Recommendation to determine the syste
12、m availability performance for digital multiprogramme BSS systems, and their associated feeder links, operating in the planned bands; 2 that digital multiprogramme systems should provide, as guidance, QEF performance for at least X% of the worst month; 3 that when implementing digital multiprogramme
13、 systems, a target C/N value of (minimum C/N + Z) dB should be maintained within the service area or coverage area for at least X% of the worst month. As guidance, 99.5% can be taken for the default value of X. The values of the minimum C/N are defined in Table 1 (also described in Table 2 of Recomm
14、endation ITU-R BO.1516). The value Z is the additional degradation margin2. 1QEF generally refers to a BER of approximately one bit error per hour or per day. When a digital multi-programme system is operating at a BER equal to or better than the QEF point, picture quality becomes solely a function
15、of the video compression rates and algorithms in use, and not a function of the channel BER. When a digital multi-programme system is operating at a BER below or worse than QEF, then video quality becomes a function of both the video compression rates and algorithms, and the channel BER. 2The value
16、Z is the sum of Z1and Z2. In case of System C and System D in Table 1, additional margin Z1 is needed for hardware implementation and satellite transponder distortions. As guidance, a value of 1.8-2.3 dB, depending on the modulation used can be taken as the default value for Z1. Z2is the margin taki
17、ng into account interference from intra and interregional BSS satellites, uplink noise, and interference from other sources. The value of Z2needs to be determined for each specific case, taking into account the individual system operational and interference environment. Rec. ITU-R BO.16963TABLE 1 Mi
18、nimum C/N for QEF operation (dB) (quoted from Table 2 of Recommendation ITU-R BO.1516) Modulation and coding System A System B System C System D Modulation modes supported individually and on the same carrier QPSK QPSK QPSK 8-PSK, QPSK, and BPSK Performance requirement C/N (dB) C/N for QEF(1)C/N for
19、 QEF(2)C/N for QEF(3)C/N for QEF(4)Modes Inner code BPSK Conv. 1/2 Not used Not used No 0.2 5/11 Not used Not used 2.8/3.0 Not used 1/2 4.1 3.8 3.3/3.5 3.2 3/5 No Not used 4.5/4.7 Not used 2/3 5.8 5 5.1/5.3 4.9 3/4 6.8 Not used 6.0/6.2 5.9 4/5 Not used Not used 6.6/6.8 Not used 5/6 7.8 Not used 7.0/
20、7.2 6.8 6/7 Not used 7.6 Not used Not used QPSK Conv. 7/8 8.4 Not used 7.7/7.9 7.4 8-PSK Trellis Not used Not used Not used 8.4 (1)At a BER round(X-Y)/0.1 should be sufficient where round(x) is the next integer greater than x. Step 5: Define M equally spaced values in the interval 10X/10 dw, 10Y/10
21、and denote them as w(n) where for n = M j + 1 we get w(M j + 1) = 10Y/10 ( j 1)*dw; dw = (10Y/10 10/10)/ (M 2) and j = 1, , M. The array w(n) defines the values of +cinover which the uplink and downlink PDFs will be defined. Step 6: For j = 1 to M if w( j) 10Yu/10set Pu( j) = 0; else, calculate Apu(
22、pu) required to achieve C/(N + I)u = 10 log w( j); calculate puassociated with this Apuusing Recommendation ITU-R P.618-8; set Pu( j) = pu/100; end. End-for-loop. At the end of this step, we have the array Pu( j) defining the CDF for the ucin +values of interest (i.e. w( j). Step 7: Repeat step (5)
23、to find Pd( j) given C/(N + I)d, Xdand Yd. At the end of this step, we have the array Pd( j) defining the CDF for the dcin +values of interest (i.e. w( j). Step 8: Denote the PDF of ucin +as fu() and of dcin +as fd() defined by: MjjPjPjwcinjfuuuu2,3,.,)()1()1(Prob)1( = += MjjPjPjwcinjfdddd2,3,.,)()1
24、()1(Prob)1( = += 18 Rec. ITU-R BO.1696 Step 9: Define k = m + j 1, then z(k) = w(m) + w( j) for m, j = 1, , M 1 and thus k = 1, 2, , 2*M 3. Step 10: Apply the convolution of the individual PDFs as follows: =113*2.,1)()()(MjduMkjkfjfkzf Note that if n is not in the interval 1, M 1, then fu(n) = 0 and
25、 fd(n) = 0. Step 11: The PDF of the overall aggregate C/(N + I) is then given by: Prob(C/(N + I) = 10 log z(k) = f (z(k) Step 12: The system availability Pswhich is the probability of the overall aggregate C/(N + I) being greater than a threshold (Z) is given by: =LkskzfP1)( where L is such that 10
26、log z(L) Z and 10 log z(L + 1) Z. 2 Approximated system availability The following algorithm describes one possible approach to implementing the approximation methodology described in 2.3.3 of Annex 1 to determine an upper bound and an approximated lower bound of the overall system availability Ps.
27、2.1 Upper bound The approach consists of first solving dp and then ,up assuming that when the link of interest is rain faded, the other link is not. For solving ,dp the target C/(N + I)drequired to meet the QEF threshold C/(N + I) for clear-sky uplink is determined, from which is derived an upper bo
28、und on the downlink propagation loss with which the system can close the downlink. An iterative algorithm then determines the increase in receiver noise temperature as a function of system unavailability and downlink propagation loss, converging to a solution for the overall system unavailability wh
29、ich, when applied to both clear-sky uplink and rain faded downlink, meets the QEF threshold C/(N + I). For solving ,up a first estimate of overall system unavailability psis calculated assuming an ideal downlink, i.e. no rain, cloud or scintillation fading. up is then iteratively recalculated assumi
30、ng the previous psto determine the cloud and scintillation fading effect on the C/(N + I)dwhich impacts on .up This iteration eventually converges to a final solution for psand .up As mentioned in the previous section, the propagation models in Recommendation ITU-R P.618-8 for cloud, rain and scinti
31、llation fading are only valid over a combined range of exceedance ( puor pd) of 0.01% to 5%, the lower bound being imposed by the scintillation fading model. In the following procedure, this range is extended down to 0.001% by assuming that the scintillation fading at 0.01% is maintained for lower p
32、ercentages. Rec. ITU-R BO.1696 19 2.1.1 dp calculation The following algorithm implements the calculation of .dp Step 1: Using equations (1) to (4), calculate the target C/(N + I)dat which the overall C/(N + I) = QEF threshold C/(N + I), assuming clear-sky uplink (Apu= 0; UPC = 0). Step 2: Set pd= 0
33、.001% and calculate Apdand dT. Step 3: Calculate the lowest C/(N + I)dusing the above Apdand dT values. Step 4: If the lowest C/(N + I)dis above the target C/(N + I)d, then set dp = pd= 0 and skip the remaining Steps. Step 5: Calculate Apdto meet the target C/(N + I)dassuming dT = 0. Step 6: Using R
34、ecommendation ITU-R P.618, determine the downlink unavailability pdassociated with Apd. Step 7: Calculate dT associated with pd. Step 8: Recalculate Apdto meet the target C/(N + I)dgiven the above dT. Step 9: Repeat Steps 6 to 8 until the recalculated Apdconverges within an acceptable error (delta)
35、at which point ddpp = has been solved for the scenario of clear-sky uplink and rain faded downlink. 2.1.2 up and pscalculation As discussed above, uplink cloud and scintillation fading can be ignored for this calculation. Hence Au= Aru. Step 1: Using equations (1) to (4), calculate Aruat which the o
36、verall C/(N + I) = QEF threshold C/(N + I), assuming: no rain fading on the downlink (Ard= Acd= Asd= 0), and maximum uplink power control (UPC = UPCmax) if applicable. This initial value of Arurepresents an upper bound on the uplink rain attenuation with which the system can close the link. Step 2:
37、Using Recommendation ITU-R P.618, determine the uplink unavailability puassociated with Aru. This represents a lower bound on unavailability. Step 3: Calculate the overall unavailability psusing equation (5) with up = puand dp calculated in 2.1 above. Step 4: Set pdto a fraction of psat the first it
38、eration or augment pdby this fractional amount thereafter. The fraction is related to the accuracy required. As an example, set the fraction to be ten times smaller than the accuracy sought. Keeping in mind that the procedure is valid for exceedance percentages above 0.001%, then the step size canno
39、t be less than 0.001%. 20 Rec. ITU-R BO.1696 Step 5: Calculate Apdand C/(N + I)dfor pdand without downlink rain attenuation (Ard= 0) i.e. including only gas absorption, cloud and scintillation fading. Step 6: Recalculate Aruat which the overall C/(N + I) = QEF threshold C/(N + I) given C/(N + I)dfro
40、m Step 5. Step 7: Using Recommendation ITU-R P.618, determine the new uplink unavailability pugiven Aru. Step 8: Recalculate psusing uupp = and dp calculated in 2.1 above. Step 9: Repeat Steps 4 to 8 until the recalculated psconverges within an acceptable error (i.e. changes by less than this accept
41、able error with subsequent iterations). 2.2 Approximated lower bound The following algorithm implements a methodology described in 2.3.3.2 of Annex 1 to determine an approximate lower bound of the overall system availability Ps. Step 1: Using equations (1), (3) and (4), calculate the target C/(N + I
42、)dat which the overall C/(N + I) = QEF threshold C/(N + I), assuming a constant C/(N + I)uwell above QEF. Step 2: Set pd= 0.001% and calculate Apdand dT. Step 3: Calculate the lowest C/(N + I)dusing the above Apdand dT values. Step 4: If the lowest C/(N + I)dis above the target C/(N + I)d, then set
43、pd= 0 and skip the remaining steps to step 10. Step 5: Calculate Apdto meet the target C/(N + I)dassuming dT = 0. Step 6: Using Recommendation ITU-R P.618, determine the downlink unavailability pdassociated with Apd. Step 7: Calculate dT associated with pd. Step 8: Recalculate Apdto meet the target
44、C/(N + I)dgiven the above dT. Step 9: Repeat Steps 6 to 8 until the recalculated Apdconverges within an acceptable error (delta). Step 10: The overall system availability Ps= 100 pd. Rec. ITU-R BO.1696 21 Appendix 2 to Annex 1 Additional information on digital BSS multi-programme availability in the
45、 12 GHz bands 1 Impact of current propagation data on the availability of digital BSS systems This section addresses current propagation data as well as their impact on the availability of digital BSS links. An analysis was conducted to determine the effect of the propagation data contained in Recom
46、mendations ITU-R P.618 and ITU-R P.8373on the availability of digital BSS carriers transmitted to cities in Regions 1, 2 and 3. A major difference with the previous propagation data is the use of continuous curves for rainfall rates based on measured data at actual sites as opposed to rainfall rates
47、 based on a discrete number of rain climatic zones. When conducting the analysis, the following formula was used: (C/N)p= (C/N)cs Apwhere: (C/N)p: carrier-to-noise level exceeded for p% of the time (C/N)cs: clear-sky carrier-to-noise level Ap: attenuation level not exceeded for p% of the time P : pe
48、rcentage of time used to specify the target availability. In the case of Regions 1 and 3, digital BSS links with characteristics given in Table 6 were assumed to be transmitted to over 600 major cities from orbital locations as per the Regions 1 and 3 Plan. The orbital location associated with trans
49、missions to each city was chosen to be that of the corresponding administrations Plan assignment. It was assumed that, for Region 2, digital BSS carriers with characteristics given in Table 7 were transmitted to 158 cities. The rainfall rates derived for each of the carriers are plotted in Figs. 4-7. These Figures indicate rainfall rates between 1 mm/h and 159.44 mm/h. The C/N ratio exceeded for various time percentages varying from 99.9
