1、 Rep. ITU-R M.2119 1 REPORT ITU-R M.2119 Sharing between aeronautical mobile telemetry systems for flight testing*and other systems operating in the 4 400-4 940 and 5 925-6 700 MHz bands (Question ITU-R 231/8) (2007) 1 Introduction This Report assesses frequency sharing between wideband aeronautical
2、 mobile telemetry (AMT) systems and other systems operating under primary allocations in the 5 925-6 700 MHz and 4 400-4 940 MHz bands. The Report is intended to address the technical and operational aspects of these sharing scenarios. These AMT systems are used to transmit supplementary data from a
3、ircraft to ground (aeronautical) stations in support of testing of aircraft at test ranges. Section 2 presents technical and operating parameters of AMT systems that are used in the analyses, which are presented in annexes and summarized in the sections below. Annex 1 addresses compatibility with FS
4、S space station receivers in the 5 925-6 700 MHz band; Annex 2 addresses compatibility with FSS earth station transmitters in the 5 925-6 700 MHz band and earth station receivers operating in the 4 500-4 800 MHz band under RR Appendix 30B; Annex 3 addresses sharing between AMT ground station receive
5、rs and FSS satellite transmitters in the 4 500-4 800 MHz band; Annex 4 addresses sharing between AMT and the radio astronomy service in the 4 825-4 835 MHz band; and Annex 5 addresses sharing between AMT and FS/MS systems in the 5 925-6 700 MHz and 4 400-4 940 MHz bands. 2 Parameters of AMT systems
6、2.1 General characteristics Table 1 provides representative values for parameters of AMT systems, which consist of aircraft transmitters and receiving ground stations that use high-gain antennas which track the aircraft. Link budgets encompassing these parameters show fade margins exceeding 13 dB, w
7、hich is necessary to maintain a reliable telemetry link and minimize signal dropouts due to nulls in the aircraft antenna pattern, obstruction by the aircraft fuselage, and multipath fading at the tracking receive station. The specified permissible levels of interference are based on interference-to
8、-noise power ratios (I/N) of 3 dB (long-term) and 0 dB (short-term. 2.2 AMT deployment scenario The assumed AMT deployment scenario consists of 17 representative test areas or flight zones shown in the map of Fig. 1. These zones indicate approximate airspace volumes within which test aircraft operat
9、e. Among all worldwide deployments, this deployment would yield the maximum potential AMT aggregate interference at the geostationary satellite orbit (GSO). For purposes of aeronautical safety, administrations authorize flight testing only in designated areas. *This Report addresses only flight appl
10、ications, and not other applications in these bands. 2 Rep. ITU-R M.2119 2.3 AMT frequency reuse For worst case analyses, no more than two co-frequency aircraft could operate in each of the four largest or most active test zones (DFRC, Utah, WSTF, and PAX in Fig. 1) where sufficient separation betwe
11、en co-channel aircraft is possible in order to avoid interference between aircraft. Self-interference among AMT systems is avoided by rigorous scheduling of AMT frequency usage by frequency managers. Only one aircraft would use a given frequency in the other test zones, for a worst-case total of 21
12、co-frequency aircraft transmitters. Although aircraft testing using AMT is conducted only several hours per day, all 21 co-frequency aircraft are assumed to be operating simultaneously in order to avoid underestimating aggregate interference. TABLE 1 Representative AMT system parameters Parameter Sy
13、mbol Value Aircraft antenna pattern Omni-directional Peak aircraft antenna gain (dBi) Gtmax3 Average aircraft antenna gain (dBi) Gtave4.8 Maximum aircraft e.i.r.p. density (dB(W/MHz) 2.2 Average aircraft e.i.r.p. density (dB(W/MHz) 10.0 Peak aircraft antenna input power density (dB(W/MHz) Pt5.2 Grou
14、nd receiver antenna aperture (m) 2 to 5 Ground receiver antenna pattern Rec. ITU-R F.1245 Ground receiver antenna height (m) 30 Ground antenna elevation angles (degrees) 0-20 Nominal permissible long-term interference at receiver antenna output (dBW/MHz to be exceeded for no more than 20% of the tim
15、e) 145.5 Nominal permissible short-term interference at receiver antenna output (dBW/MHz to be exceeded for no more than 0.4% of the time) 142.5 FIGURE 1 Map of assumed AMT test zones Rep. ITU-R M.2119 3 2.4 AMT aircraft antenna characteristics The AMT aircraft transmitter antenna gain (and e.i.r.p.
16、) in the direction of the receiving ground station fluctuates as a result of multipath and blockage effects of the aircraft fuselage. The aircraft antenna gain statistics were based on the Rayleigh model specified in Recommendation ITU-R M.1459, which yields 3 dBi peak gain, 1.5 dBi gain exceeded fo
17、r 1% of the time, and 6 dBi gain for 50% of the time (average). It should be noted that the average aircraft antenna gain of 4.8 dBi in Table 1 was found by calculating the expected value of gain using the Rayleigh-like probability density function in Recommendation ITU-R M.1459 (thus the average ga
18、in and e.i.r.p. density is 3 (4.8) = 7.8 dB below the peak value rather than 9 dB using the 6 dBi/50% statistic). The antennas typically are of slot or blade (dipole) type. Installation locations of these temporary AMT antennas typically are on the underside of the aircraft so as to direct the radia
19、tion toward the ground during level flight. These temporary installations for testing are constrained by load-bearing aircraft structural features, such as stringers that cannot be cut; thus, the antenna locations cannot be freely optimized to achieve the best possible AMT transmission performance.
20、2.5 AMT e.i.r.p. and modulation The total average power out of the telemetry transmitter, Pt, typically is 10W. It is common in test installations for a single transmitter to simultaneously feed two or more antennas on the aircraft fuselage. For example, a power split of 90%/10% is typical in which
21、90% of the total transmitter power is fed to an antenna on the bottom of the aircraft (since most of the time it is the one in view of the ground station) and 10% to an antenna on the top of the aircraft. Although the peak e.i.r.p. density in any direction (2.2 dB(W/MHz) is based on use of a single
22、antenna with 3 dBi peak gain, the power splitting and two-antenna arrangement could theoretically produce the same peak e.i.r.p. in directions emanating from underside of the aircraft fuselage. Wideband AMT systems are expected to operate at data rates upwards of 20 Mbit/s. The assumed peak e.i.r.p.
23、 is based on the highest power density associated with the modulation and coding techniques used in narrowband aircraft telemetry systems at frequencies below 3 GHz. Other modulation and coding choices tend to have more uniform spectral power density distributions such that the assumed 10 W AMT tran
24、smitter would produce a lower peak e.i.r.p. density. 3 Sharing between AMT and space station receivers in the 5 925-6 700 MHz band AMT transmitters operate well below the power limits specified in Article 21 of the Radio Regulations (RR) for terrestrial stations in frequency bands shared with space
25、services (Earth-to-space) above 1 GHz. FSS operators must take into account these regulatory provisions when designing their systems. The analyses in Annex 1 show that interference from AMT is below permissible levels specified in Recommendation ITU-R S.1432. Specifically, aggregate interference fro
26、m AMT causes an increase in equivalent uplink noise temperature Ts/Tsof no more than 2.7% in existing and planned FSS systems and Ts/Tsis no more than 4.9% in more vulnerable, hypothetical FSS systems (assumed to have a very high uniform G/T of +7 dB/K over the satellite coverage area). These calcul
27、ated values are conservative because they are based on the maximum expected number of co-frequency aircraft in the satellite uplink beam (21 aircraft), each aircraft simultaneously radiating its peak instantaneous e.i.r.p. towards the satellite, and no polarization discrimination or atmospheric loss
28、es. Under these assumptions, the interference averaged over existing and planned FSS systems is Ts/Ts= 1.1%. Substitution of the average aircraft e.i.r.p. (10.0 dB(W/MHz) for the peak level and application of the central limit theorem of statistics yields an average aggregate Ts/Tslevel of 0.2% (ave
29、raged over existing and planned FSS systems). 4 Rep. ITU-R M.2119 4 Sharing between AMT and FSS earth stations in the 5 925-6 700 and 4 500-4 800 MHz bands Studies in Annex 2 compare the coordination distances calculated in accordance with the methodology of RR Appendix 7 to the actual required sepa
30、ration distances based on conservative yet possible operational scenarios for AMT. While coordination distances are large, the separation distances required to prevent interference are shown to be smaller. 5 Sharing between AMT and FSS space stations in the 4 500-4 800 MHz band Annex 3 evaluates pot
31、ential interference to AMT ground stations from FSS satellite downlink transmissions in the 4 500-4 800 MHz band. This analysis shows that FSS downlink transmissions will not exceed permissible levels of interference to AMT ground stations except when the AMT receiver antenna is pointed in the direc
32、tion of the satellite (main beam coupling). Although the random probability of such interference may be acceptably low for wideband AMT, this pointing situation can be avoided via selection of AMT ground station sites that would prevent or minimize pointing of the AMT antenna toward the GSO. 6 Shari
33、ng between AMT and radio astronomy observatories in the 4 825-4 835 MHz band Annex 4 assesses potential interference to radio astronomy receivers from AMT aircraft transmitters in the 4 825-4 835 MHz band. This study shows that, in general, careful frequency planning/coordination is needed to preven
34、t interference in co-frequency sharing situations where radio astronomy receivers are located within the radio horizon of the AMT aircraft (450 km). In such cases, time sharing may be feasible insofar as radio astronomy observations and flight testing are not continuous operations. 7 Sharing between
35、 AMT and the fixed and mobile service in the 4 400-4 940 MHz and 5 925-6 700 MHz bands Annex 5 evaluates potential interference between AMT systems and systems in the fixed and mobile services (FS/MS). The MS systems are transportable (these and AMT systems are the only kinds of MS systems in the 4
36、GHz and 6 GHz bands for which parameters were available for analysis). Permissible levels of interference to FS/MS stations are not exceeded when the distance along the main-beam axis from the FS/MS receiver to the AMT area of operation is larger than 450 km or when the main-beam axis of the FS/MS a
37、ntenna is separated from the aircraft flight zone by 12 km or more. Further study would be needed (e.g. during bilateral coordination) to determine whether significantly smaller distance separations could result for actual co-frequency sharing situations. While it might be possible to operate AMT ai
38、rcraft closer to a FS/MS receiver, this may require restrictions on the AMT system. These restrictions could include, for instance, frequency separation between AMT and FS/MS signals, limits on the region of aircraft operation, or the limits on the altitude range of operation. Because of the intensi
39、ve use of the 4 GHz and 6 GHz bands by the FS, substantial frequency spectrum may not be available for AMT use in some flight test zones. The number of FS systems is generally growing throughout the world, e.g. by as much as 25% per year at 6 GHz in the territory of one administration. It remains to
40、 be seen, perhaps by AMT coordination trials, how much spectrum could be coordinated for AMT use in the 4 GHz and 6 GHz bands, particularly at test ranges where the FS/MS frequency usage is intense. Rep. ITU-R M.2119 5 Separation distances are needed between FS/MS transmitters and AMT ground station
41、 receivers using the same frequencies in order to keep interference below permissible levels. In the worst hypothetical case, assuming that both the FS and AMT antennas are constantly pointed at each other, several hundred km of separation would be required (i.e. up to 425 km) for compliance with th
42、e short-term permissible level of interference. When this pointing condition is completely avoided, e.g. via selection of the AMT ground receiver site, distance separations of the order of 1-20 km enable co-frequency sharing. 8 Conclusions Potential interference between typical wideband AMT systems
43、and FSS space stations using the bands around 6 GHz is below permissible levels under assumptions provided in 2 above. Additionally interference to AMT ground stations would be within acceptable levels as described in 2 at 4 GHz assuming that the AMT systems are designed and deployed to prevent AMT
44、ground station antenna pointing at the GSO FSS satellites. However, the combined effects of all the local frequency sharing situations with FS/MS stations, radioastronomy observatories, and FSS earth stations may severely limit availability of spectrum resources for introduction and operation of AMT
45、 systems in the 4 400-4 940 MHz and 5 925-6 700 MHz bands. This is especially true for flight test zones that are located in areas where the bands are intensively used by systems in other services. Annex 1 Potential aeronautical mobile telemetry (AMT) for flight testing interference to GSO satellite
46、s in the fixed-satellite service (FSS) (E-S) in the 5 925-6 700 MHz candidate band 1 Introduction The 5 925-6 425 MHz portion of the band is heavily used by the FSS (Earth-to-space). This Annex evaluates potential interference from AMT aircraft transmitters into FSS satellite receivers. Note that po
47、tential AMT interference into FSS satellite receivers is an aggregate interference problem since all aircraft transmitters in the satellite field-of-view (FOV) will contribute to the total interference at the satellite. Thus, these analyses below consider all aircraft transmitters in worst-case AMT
48、deployment situation described in 2 of the main text. 6 Rep. ITU-R M.2119 2 Methodology and assumptions 2.1 FSS satellite characteristics Recommendation ITU-R S.1432 apportions 27% of the total FSS system noise plus interference power to aggregate interference and 6% of the total FSS system noise pl
49、us interference power to interference from other co-primary services. Working Party 4A suggested that this 6% noise allowance should be further subdivided among AMT and other allocated services. The 6% noise apportionment for interference corresponds to a 8.2% increase in FSS equivalent satellite receive noise temperature, Ts/Ts(100 6%/(100-27%). Accordingly, this analysis determines aggregate Ts/Tslevels that can be compared to the permissible levels of interference specified in Recommendation ITU-R S.1432. These calculations were performed for two
