1、 Rep. ITU-R SF.2046 1 REPORT ITU-R SF.2046 Determination of the interference potential, and its possible reduction by mitigation techniques, between earth stations in the fixed-satellite service operating with non-geostationary satellites and stations in the fixed service in the 18/19 GHz band (Ques
2、tions ITU-R 237/4 and ITU-R 206/9) (2004) 1 Introduction Frequency bands have been allocated and identified for use by GSO and non-GSO FSS systems in bands shared on a primary basis with the FS. WRC-95/97 adopted a different set of provisions through No. 5.523A of the Radio Regulations (RR) to the n
3、on-GSO FSS utilizing the bands 18.8-19.3 GHz and 28.6-29.1 GHz from those provisions for non-GSO FSS utilizing bands outside these bands. This Report addresses only the 18.8-19.3 GHz band, which is referred to throughout as the 18/19 GHz band. Sharing between the FSS and the FS should also take into
4、 consideration the impact of the proposed high-density deployment of both services, which requires special attention to the required separation distances. Such restrictions could impair the use of both services in the same areas, however, the sharing situation could be improved by the use of mitigat
5、ion techniques. 2 Interference from an FS transmitter into a non-GSO FSS satellite earth station The progressing deployment of FS stations or FSS earth stations may affect the future expansion of either service in the same frequency band. Accordingly, the FS station deployment patterns and the FSS e
6、arth station deployment patterns required for the introduction and growth of viable services have a major impact on the planning of band sharing. Studies to date are limited to the considered interference from FS transmitters into the LEOSAT-1 non-GSO FSS earth stations operating in the 18.8-19.3 GH
7、z band. 2.1 Interference criteria and methodology The interference calculations were performed by several administrations using FS parameters obtained from their administration databases. Deterministic studies assume line-of-sight (LoS) transmission and were based on the use of a free-space loss plu
8、s atmospheric absorption propagation model. Some studies also took into account diffraction due to terrain and man-made obstacles. 2 Rep. ITU-R SF.2046 The interference level into the earth station was calculated for each FS transmitter in the database and for all azimuths around each of these trans
9、mitters. The resulting exclusion zones were then superimposed graphically on maps of some major metropolitan areas. In all cases the minimum earth station antenna gain (backlobe) was used and the calculations were not dependent on anomalous propagation conditions, therefore, a long-term I/N criterio
10、n corresponding to 6% to 10% of the thermal noise level was used. This criterion may require further study to take into account the effects of multiple FS transmitters simultaneously interfering into an non-GSO FSS user terminal receive bandwidth. In the case of LEOSAT-1, this would be the full 500
11、MHz receive bandwidth. When the non-GSO FSS user terminal receive bandwidth is reduced, the probability of having multiple FS transmitters interfering simultaneously is reduced. Statistical studies evaluate, based on certain assumptions, the interfering power spectral density levels suffered by FSS
12、receivers distributing these terminals in the satellite spot-beam with respect to assumed penetration rates in the different ground clutter classes. During the interference calculation procedure the FSS terminal location is selected randomly out of the predefined locations according to the penetrati
13、on scenario with the following assumptions: the assigned frequency channel in the FSS downlink is randomly selected inside the FS frequency band with a bandwidth according to a randomly selected transmission capacity by combining the frequency channels for the FSS terminal under consideration (altho
14、ugh this study assumes varying bandwidth such studies should be based on 500 MHz in the case of LEOSAT-1); the satellite responsible for communication with the FSS cell/spot-beam under consideration is determined by the criterion of the shortest distance; the antenna of the FSS terminal is placed on
15、 top of the buildings or above the vegetation. The received power level from the serving satellite is calculated according to the elevation angle and the propagation conditions concerned. All FS transmitters within a distance of 60 km to the FSS receiver are selected in the affected frequency band.
16、The resulting interference power density level is evaluated by aggregation of the signals of all FS transmitters considered. The C/I ratio at the FSS receiver is calculated by comparing the interference power level with the received power level from the serving satellite. The interference level can
17、also be referred to the receiver noise level, N. These interference levels are compared with a reference interference level of 145 dB(W/MHz) (i.e. 10 dB I/N). The cumulative distributions of the C/I ratios for standard propagation conditions (losses exceeded for less than 20% of time) as well as for
18、 rainy conditions (worst case: 0.001% of time) on the space-to-Earth path have been derived. 2.2 Possible application of a convolution process for assessing interference One study presented a possible method for assessing interference from FS transmitters into non-GSO FSS earth station receivers, ba
19、sed on an application of a methodology similar to that of Recommendation ITU-R S.1323. The method accommodates the time-varying nature of the interference by convolving the probability density functions (pdf) of the rain degradation and the interference degradation, obtained through computer simulat
20、ion, to generate the total degradation pdf. Rep. ITU-R SF.2046 3 3 Potential interference from point-to-point FS transmitters into non-GSO FSS earth station receivers without mitigation techniques 3.1 Interference without mitigation techniques 3.1.1 Deterministic studies FS transmitters impose regio
21、ns around themselves in which reliable operation of non-GSO user terminals may be precluded due to excessive interference. These blocked regions are referred to as “exclusion zones”. A single point-to-point FS transmitter will (under clear sky, clear terrain conditions) impose a circular exclusion z
22、one in the area immediately surrounding it (off-axis directions) and a elliptical exclusion zone extending a long distance along its on-axis direction of transmission. 3.1.1.1 Results using free-space loss calculations and no blockage Figure 1 presents an example exclusion zone calculated using the
23、parameters of a typical point-to-point FS transmitter with a 0.6 m parabolic dish. The boundary is based on a single-source, conservative long-term interference criterion of 6% of the non-GSO user terminal system noise (i.e. I/N = 12.2 dB) under clear sky, clear terrain conditions. Non-GSO user term
24、inals would need to be kept outside of this contour in order to guarantee that interference levels from the FS transmitter would be acceptably low. It can be observed in the expanded view in Fig. 2 that the diameter of the exclusion zone around the terminal can be nearly 1 km and the length of the e
25、xclusion zone in the direction of transmission can be well over 45 km. However, this distance and the affected area would be reduced using a more appropriate long-term interference criterion of 10%. Rap 2046-015 5 152535455521012FIGURE 1Example exclusion zone for LEOSAT-1 standard terminals createdb
26、y one typical FS transmitter using a 0.6 m diameter antenna(assuming 6% interference criterion unter free space loss propagation condition)1.50.50.51.5On-axis distance (km)Cross-axisdistance(km)FS transmitter0.6 m dish56.1 km24 Rep. ITU-R SF.2046 Rap 2046-020111 0 1FIGURE 2Expanded view of Fig. 10.8
27、0.60.40.20.20.40.60.8FS transmitter0.5 0.5Cross-axisdistance(km)On-axis distance (km)A study analysed the effects of interference from FS transmitters in Canada into a receiving non-GSO FSS earth station in the 18.8-19.3 GHz band. The calculations were performed using a database of FS parameters obt
28、ained from the Canadian licensing database and the resulting exclusion zones were then superimposed graphically on maps of some major metropolitan areas in Canada. The results of the deterministic interference calculations showed that the exclusion zone caused by the FS transmitters would be very lo
29、ng in the main direction of transmission, on the order of 40 to 80 km typically, but would be small in other directions well away from the FS main beam. In all cases, it was found that there was a significant area in each city where the non-GSO FSS terminal siting would be very difficult or perhaps
30、even impossible. In fact, calculating the area of the exclusion zone within a 40-km diameter circle, representative of the metropolitan sites, indicated that areas of 35%, 48% and 47% would be unavailable for non-GSO FSS terminals in the three cases studied, in the absence of some blocking. Another
31、study analysed the interference that could be generated by typical FS transmitters into non-GSO FSS user terminals where they operate co-frequency and in close proximity, in the 18.8-19.3 GHz band. This analysis calculated these exclusion zones using the actual characteristics of the FS transmitters
32、 contained in a database of FS transmitters from Argentina. Figure 3 shows the computed exclusion zones corresponding to each potentially interfering FS transmitter in the Buenos Aires urban region (assuming clear sky, flat and clear terrain conditions). The size variation between some exclusion zon
33、es is due to the differences in FS characteristics found in the database, such as transmitter power and antenna size. A circular region with a 40 km diameter was used as the reference area. In the high FS density urban region, 65% of the area would result in FSS terminals not meeting their performan
34、ce objectives and would potentially be excluded from LEOSAT-1 service in the band 18.8-19.3 GHz. Rep. ITU-R SF.2046 5 Rap 2046-03Buenos AireskmFIGURE 3Potential FSS earth station exclusion area in the Buenos Aires urban region due to 18.8-19.3 GHz FS terminal locations:composite exclusion zone 65% i
35、n reference 40 km circleThe conclusion of this study is that, assuming free-space propagation and no blockage, deployment of FS stations in the band 18.8-19.3 GHz could significantly constrain the placement of non-GSO FSS user terminals. This is particularly true for areas that have a high density o
36、f FS stations. As FS deployment density increases, the placement of non-GSO FSS user terminals becomes more constrained. 3.1.1.2 Results using topographical data and building blockage environment When topographical databases are used in the calculation of the exclusion zones, the area covered by exc
37、lusion zones can be significantly reduced. Table 1 compares the cases of two simulations where the exclusion zones correspond to areas where the long-term criterion (I/N = 10 dB) is not fulfilled and where: Case 1: the propagation model assumes that there are no terrain or man-made obstacles within
38、the LoS around each FS and is based on the use of free space loss and atmospheric absorption. Case 2: the propagation model takes into account propagation loss and diffraction over terrain as well as man-made obstacles, using a topographical database (the non-GSO FSS receivers are placed 1 m above t
39、he building roofs). 6 Rep. ITU-R SF.2046 The studies have been made with a radio planning software which includes digital terrain modelling and ground occupancy layers (buildings, population, .) and calculates the areas where the interference level into the ground stations receivers exceeds 97 dBm (
40、10 dB below the receive system noise) from any of the fixed links. The fixed links that have been taken into account in this study are those transmitting in the band 18.8-19.3 GHz and located in a square area of 14 km 14 km around Paris (23 links). 3.1.2 Statistical studies Two statistical studies h
41、ave been carried out. 3.1.2.1 First statistical study Statistical interference simulations between actual and planned FS links and non-GSO FSS user terminals at 18/19 GHz (LEO-SAT-1 system) in a 118 118 km square centred on Paris have been carried out. The principle of the methodology used was to cr
42、eate, on a studied area, a hypothetical FSS user terminals network by a random deployment and then to calculate, for each user terminal, the aggregate interference from the existing FS microwave links in this area. The FSS user terminals were implemented on the studied area according to penetration
43、ratios (random stations/km2) associated with each ground clutter class. The C/I required was assumed to be 20 dB. This active satellite is chosen, at the beginning of the simulation, as the one with the higher elevation (closer satellite) and is kept as long as its elevation is higher than the minim
44、um (40 for LEOSAT-1). The interference simulations consist of interference calculations (C/I) for each user terminal, taking into account: the constellation geometry (elevation and azimuth); the Earth-to-space propagation conditions, according to Recommendation ITU-R P.618 (for this purpose, the rai
45、n attenuation and the scintillation attenuation are associated to a random percentage to provide, for each calculation, the space-to-Earth attenuation); the propagation loss according to Recommendation ITU-R P.452 (visibility, diffraction, tropospheric scattering, including all statistical factors);
46、 the characteristics of the microwave links (power, azimuth, antenna, ) and of the user terminal (receiver characteristics, antenna, ). Each C/I calculation is called a “sample” and, at the end of the simulation, the results are presented as a graph representing the C/I distribution. TABLE 1 Compari
47、son of exclusion areas with and without blockage Simulation Percentage of exclusion zone relatively to the global area (14 km 14 km centred on Paris) Case 1 (without taking into account any terrain or man-made obstacles) 20.6 Case 2 (taking into account terrain and man-made obstacles) 5.2 Rep. ITU-R
48、 SF.2046 7 Table 2 gives the results for a simulation with FSS terminal distribution in the dense urban zone. It was noted that a higher percentage of blocking would be indicated if this study were to take into account the 500 MHz downlink receiver bandwidth which is the normal bandwidth for LEOSAT-
49、1. 3.1.2.2 Second statistical study A particular study addressed the sharing between FS and FSS applications in the 18/19 GHz band taking into account heavy deployment of FS stations in a geographical area. The methodology applied differs from that of the previous study in that it includes the use of terrain and the use of the most common parameters and characteristics for the radio systems deployed in the 18/19 GHz band in the United Kingdom. 3.1.2.2.1 Approach The study investigated the effects that FS links and receiving earth stations will have on each o
