1、CCIR RECMN*735-L 93 4855212 0520880 564 W Rec. ITU-R S.735-1 51 SECTION 4D: FREQUENCY SHARING BETWEEN NETWORKS OF THE FIXED-SATELLITE SERVICE - EFFICIENT USE OF THE SPECTRUM AND GEOSTATIONARY-SATELLITE ORBIT 4D1: Permissible levels of interference RECOMMENDATION ITU-R S.735-1* MAXIMUM PERMISSIBLE LE
2、VELS OF INTERFERENCE IN A GEOSTATIONARY-SATELLITE NETWORK FOR AN HRDP WHEN FORMING PART OF THE ISDN IN THE F,XEDSATELLITE SERVICE CAUSED BY OTHER NETWORKS OF THIS SERVICE BELOW 15 GHz (Question ITU-R 50/4 (1990)* (1992- 1993) The ITU Radiocommunication Assembly, conside ring a) that emissions from t
3、he earth stations as well as from the space station of a geostationary-satellite network in the fixed-satellite service (FSS) may result in interference to another such network when both networks operate in the same bands; b) that it is desirable that the interference in networks in the FSS caused b
4、y transmitters of different networks in that service should be such, as to give a reasonable orbit utilization; c) that the system designer should control the overall performance of a network and be entitled to provide a quality of service that meets ITU recommended performance criteria which are ex
5、pressed in terms of a bit error ratio (BER); d) e) aggregate interference a network must be able to tolerate from emissions of all other networks; 0 network should be expected to tolerate from any one other network; 9 fraction of the total noise that would give rise to a bit error ratio, as set out
6、in Recommendation ITU-R S.614*; h) that the levels of interference between geostationary-satellite networks in the FSS below 10 GHz are not expected to exhibit a large variation with time, and under these conditions it is preferable to define the permissible interference limit as a fraction of the p
7、re-demodulator noise power, as this allows multiple interference entries to be superimposed on each other on the basis of RF power addition; j) that in frequency bands between 10 and 15 GHz where very high propagation attenuation may occur for short periods of time, it may be desirable for systems t
8、o make use of some form of fade compensation to counteract signal fading; k) that interference between networks in the FSS may exhibit a non-uniform spectral disuibution containing narrow-bandwidth peaks and that narrow-bandwidth chers are more sensitive to this type of interference, that it is nece
9、ssary to protect a network of the FSS from interference by other such networks; that to allow an operator to exercise control over the quality of service there needs to be a limit on the that to limit the aggregate interference from all other networks, there needs to be a limit on the interference a
10、 that it is desirable that the increase in interference from other satellite networks should be a controlled * * Former CCIR Question 5014. * Former CCIR Recommendation 614. New version of CCIR Recommendation 735 CCIR RECMN*735-1 93 W 4855212 0520881 4T0 52 Rec. NU-R S.735-1 recommends 1. that a geo
11、stationary network in the FSS operating in the frequency bands below 15 GHz should be designed and operated in such a manner that in any satellite hypothetical reference digitai path which forms part of a 64 kbit/s ISDN connection the provisions of 9 1 of Recommendation ITU-R S.614* can be met when
12、the aggregate interfering power from the earth and space station emissions of all other networks operating in the same frequency band or bands, assuming clear-sky conditions on the interference paths, does not exceed at the input to the demodulator: 1.1 25% of the total system noise power under clea
13、r-sky conditions when the network does not practice frequency re-use; 1.2 20% of the total system noise power under clear-sky conditions when the network does practice frequency re-use; 2. that for a geostationary network in the FSS as mentioned in 9 1, the inter-network interference caused by the e
14、arth and space station emissions of any one other network operating in the same frequency band or bands should be limited to 6% of the total system noise power under clear-sky conditions; 3. that the maximum level of interference noise power caused to that network should be calculated on the basis o
15、f the following values for the receiving earth station antenna gain, in a direction at an angle cp (in degrees) referred to the main beam direction: G = 32 - 2510gcp dBi for 1“ I cp 48“ G = -10 dBi for 48“ I cp I 180“ 4. Note I - For the calculation of the limits quoted in Q 1.1, 1.2 and 2 it should
16、 be assumed that the total system noise power at the input to the demodulator is of thermal nature and includes all inter-system noise contributions as well as interference noise from other systems. For interference not of a thermal nature the permissible level of interference into a digital carrier
17、 should be based upon the degradation of the long-term performance objective as given in Annex 1 to Recommen- dation ITU-R S.614*. Note 2 - For this interference calculation, as applied to satellite networks operating in a fading environment, it should be assumed that the carrier power level is redu
18、ced, until the system performance coincides with the above BER and percentage of month (see Annex 1 for clarification). Nute 3 - It is assumed in this Recommendation that the interference from other satellite networks is of a continuous nature at frequencies below 10 GHz: further study is required w
19、ith respect to cases where interference is not of a continuous nature above 10 GHz. Note 4 - When interference is characterized by a non-uniform spectral disuibution there may be cases where, for design purposes, a greater interference allocation of total system noise may be made to narrow-bandwidth
20、 carriers by the system designer. One model developed to address this is presented in detail in Annex 2, Note 5 - For networks using 8 bit PCM encoded telephony see Recommendation ITU-R S.523*. Note 6 - In some cases it may be necessary to limit the single entry interference value to less than the v
21、alue quoted in Q 2 above in order that the total value recommended in 5 1 may not be exceeded. In other cases, particularly in congested arcs of the geostationary-satellite orbit, administrations may agree bilaterally to use higher single entry interference values than those quoted in 9 2 above, but
22、 any interference noise power in excess of the value recommended in Q 2 should be disregarded in calculating whether the total value recommended in 9 1 is exceeded. Note 7 - There is an urgent need for study of the acceptability of an increase in the maximum total interference noise values recommend
23、ed in 9 1. that the following Notes should be regarded as part of this Recommendation: * Former CCIR Recommendations 614 and 523. CCIR RECMN*735-3 93 4855232 0520882 337 Rec. U-R S.735-1 53 Note 8 - Although this Recommendation bas an upper frequency limit of 15 GHz, in the frequency range from 10 t
24、o 15 GHz short-term propagation data are not available uniformly throughout the world and there is a continuing need to examine such data to confirm an appropriate interference allowance to meet Q 1.2 and 1.3 of Recommen- dation ITU-R S.614*. Note 9 - There is a need for urgent study to be given to
25、the interference noise allowances appropriate to systems operating at frequencies above 15 GHz. Note 10 - The interference criteria of this Recommendation apply only to the transmission of digital services that fall under the provisions of Recommendation ITU-T G.821* and Recommendation ITU-R S.614*.
26、 Further study by radiocommunication Study Group 4 is required regarding the performance objectives and appropriate interference criteria for other than 64 kbit/s digital transmissions within an ISDN connection as information on the performance requirements for such services becomes available to it.
27、 Note I I - The principles of this Recommendation may also be applied to digital-satellite networks providing long-term performance objectives different from those in Recommendation ITU-R S.614*. This is a subject for further study. Note 12 - Special attention may have to be given to digital carrier
28、s with narrow bandwidths when they are being interfered with by analogue TV transmissions. For such cases with artificial energy dispersal at the frame rate the protection ratios given in Recommendation ITU-R S.671” apply. This is a subject for further study. Note I3 - Attention should also be drawn
29、 to the interference from TDMA systems when, due to burst overlapping at the transponder input of an interfered-with system, the BER is increased relative to that of a synchronous burst allocation. Note 14 - In order to promote orbit efficiency, satellite networks operating in heavy rain environment
30、s are encouraged to use some form of fade compensation. Note 15 - This Recommendation is closely related to Recommendation ITU-R S.614*, a fact that needs to be considered in any future revisions to either of these two Recommendations. Note 16 - Annexes 1 and 2 provide information on the permissible
31、 level of interference into an ISDN satellite digital path. ANNEX 1 Considerations on the permissible level of interference into an ISDN satellite digital path The development of a Recommendation on the permissible level of interference into an ISDN satellite digital path is essential if satellite n
32、etworks are to have some basis on which to undertake coordination, or for system designers to include some margin for interference in their link calculations. It was noted in the preparation of this Recommendation that there were two ways of interpreting the noise level referred to in Recommendation
33、 ITU-R S.523* which is dealing with maximum permissible levels of interference in an FSS 8 bit PCM telephony system. The expression used in 8 1.1 of Recommendation ITU-R S.523* is: “the interference power level should not exceed 25% of the total noise power level at the input to the demodulator whic
34、h would give rise to a bit error ratio of 1 x 10-6”. * * Former CCIIT Recommendation G.821. Former CCIR Recommendations 614,671 and 523. CCIR RECMN*735-3 93 4855232 0520883 273 54 Rec. ITU-R S.735-1 The point discussed was the total noise power level to be applied in the Recommendation when the oper
35、ating carrier level is higher than that which corresponds to BER of 10-6. One way is to reduce the carrier level as shown in Fig. la so that BER becomes 10-6. The other way is to increase the noise as shown in Fig. Ib to the level with which BER of 10-6 is obtained. Through the discussions in recent
36、 meetings, it was agreed that the former interpretation was appropriate. FIGURE la Interpretation based on reduction of signal power power FIGURE lb Interpretation based on increase of noise power I 1 Signal noise d12 I I In the preparation of this Recommendation there was further discussion on the
37、need to base the permissible interference on the ISDN performance objectives (Recommendation ITU-R S.614*), or to base the interference on an IIN ratio. The following sections summarize the discussions that led to the development of this Recommendation. ZIN method In the agreed interpretation, i.e.
38、decreasing carrier level as Fig. la, the total noise power level corresponds to the operational noise level, and this level does not change whatever the carrier level may be. Since the noise level to be applied to the Recommendation is constant irrespective of the carrier level, there is no longer a
39、 need to refer to the BER value in the Recommendation. Thus, the majority favoured a proposal to describe the permissible interference level simply in terms of the total noise without referring to the BER in the new Recommendation for the 64 kbit/s ISDN application as well as in Recommendation ITU-R
40、 S.523*. It should be noted that this method does not preclude the use of CII in a coordination. When it is convenient to use the CII, the lowest permissible CII value can be calculated by taking the ratio of the operational carrier level C to the permissible interference I derived from the total sy
41、stem noise. In this case the permissible CII value depends upon the carrier level of the interfered-with system. However, the absolute value of the maximum permissible level of the interfering carrier is not affected by the carrier level of the interfered-with system. * Former CCIR Recommendations 6
42、14 and 523. CCIR RECMN*735-3 93 4855232 0520884 10T Rec. ITU-R S.735-1 55 BER method On the other hand, the retention of the BER in an interference Recommendation was required, since all interference cannot be assumed to be treated as Gaussian noise. For these exceptions to the interference being tr
43、eated as Gaussian noise, the BER performance should be used in the calculations of interference. This is particularly true if it is found that in many other cases the effect of the interference is more severe than Gaussian noise. Examples of such exception are: TV into SCK, TV into intermediate data
44、 rate carrier, high capacity FM telephony with energy dispersal into sensitive carriers, and TDMA into digitai system when TDMA bursts overlap in time at the interfered-with satellite. Further it was not believed that the various types of interference, including the effects of FEC and the effects of
45、 various frequency offset between carriers, bave been thoroughly explored at this time. Finally it was felt that the conservative approach of including BER performance should be retained in an annex with the understanding that this interference Recommendation was based on the assumption that the int
46、erference was noise-like in nature. ANNEX 2 Interference allocation model for narrow-band carriers 1. exposed high-power density interference peaks than wider bandwidth carriers. Satellite carriers of bandwidth less than 12.5 MHz which provide 64 kbit/s connections are more affected by In these case
47、s an additional allowance for interference can be futed for design purpose as follows: - in the case of carriers with bandwidth of less than 2.5 MHz up to 20% can be added to the percentages of total system noise given in recommends 1.1, 1.2 and 2; in the case of carriers with bandwidth between 2.5
48、MHz and 12.5 MHz up to X% can be added to the percentages of total system noise in recommends 1.1, 1.2 and 2. - The value of X% decreases linearly between 20% and 0% as a function of the bandwidth. These allowances fixed in a bandwidth dependent manner are based on the interference model explained i
49、n the following section. These allowances can be adopted by satellite operators in designing their systems. 2. Model for the allocation of interference A Co-frequency FM-TV carrier with energy dispersal (ED) is the worst interfering signal for narrow-band carriers. Figure 2 shows the results of a series of measurements. The curves give the amount of thermal noise which would cause the same BER degradation produced by the interfering signals. Curves in Fig. 2, which are rather insensitive of the BER in the interfered channel, are normalized with O dB level arbitrarily fixed as
