1、 Rec. ITU-R F.1766 1 RECOMMENDATION ITU-R F.1766Methodology to determine the probability of a radio astronomy observatory receiving interference based on calculated exclusion zones to protect against interference from point-to-multipoint high-density applications in the fixed service operating in ba
2、nds around 43 GHz (2006) Scope This Recommendation provides a methodology which may be used to derive exclusion zones around radio astronomy sites for transmitting point-to-multipoint (P-MP) high density applications in the fixed service (HDFS) which may be used by administrations in national and bi
3、lateral discussions as method to protect radio astronomy sites from potential interference from P-MP HDFS stations. The ITU Radiocommunication Assembly, considering a) that the frequency band 42.5-43.5 GHz is used or is planned to be used for continuum observations; b) that the frequency bands 42.77
4、-42.87 GHz, 43.07-43.17 GHz, and 43.37-43.47 GHz are used by radio astronomers to observe the spectral lines of silicon monoxide; c) that these observations can be made from a single antenna or from a network of antennas using very long baseline array (VLBI) techniques; d) that these observations em
5、ploy very high-gain antennas and very low-noise amplifiers to receive extremely weak cosmic radio emissions over which astronomers have no control; e) that point-to-multipoint (P-MP) high density applications in the fixed service (HDFS) could involve the deployment of a large numbers of terminals, f
6、or which individual coordination would not be feasible; f) that administrations wishing to protect a Radio Astronomy (RAS) site from potential interference from P-MP HDFS stations may consider the use of an exclusion zone around the RAS site in their national and bilateral discussions; g) that the d
7、etermination of size of the exclusion zone could be improved by considering the topology and demographic data around RAS sites, recognizing 1 that the frequency band 42.5-43.5 GHz is allocated to the radio astronomy service (RAS) on a primary basis worldwide; 2 that No. 5.149 of the Radio Regulation
8、s (RR) states that “in making assignments to stations of other services to which the bands 42.5-43.5 GHz, 42.77-42.87 GHz, 43.07-43.17 GHz, 43.37-43.47 GHz are allocated, administrations are urged to take all practicable steps to protect the radio astronomy service from harmful interference”; This R
9、ecommendation should be brought to the attention of Radiocommunication Study Group 7. 2 Rec. ITU-R F.1766 3 that the band 42.5-43.5 GHz is also allocated to the fixed service (FS) on a primary basis; 4 that RR No. 5.547 notes that the band 42.5-43.5 GHz is available for high density applications in
10、the fixed service, and that administrations should take this into account when considering regulatory provisions in relation to this band, noting a) that Resolution 79 (WRC-2000) calls for ITU-R “to conduct studies on the coordination distance between radio astronomy stations operating in the 42.5-4
11、3.5 GHz band and P-MP HDFS stations with a view to developing ITU-R Recommendations”; b) that Recommendation ITU-R F.1765 describes a methodology to calculate the aggregate equivalent isotropically radiated power (a.e.i.r.p.) from stations of the P-MP HDFS operating in bands around 43 GHz, recommend
12、s 1 that Annex 1 may be used to determine the probability of an RAS observation receiving interference from the deployment of P-MP HDFS outside a specified exclusion zone (EZ) based upon a.e.i.r.p. distributions; 2 that Annex 2 may be used to determine the EZ around the RAS site, defined by a propag
13、ation loss from the RAS site, outside of which stations of the P-MP HDFS may be deployed without likelihood of causing unacceptable interference into the RAS, using the methodology in Annex 1 to calculate probability of interference. Annex 1 Methodology to determine the probability of an RAS observa
14、tion receiving interference from the deployment of P-MP HDFS outside a specified EZ based upon a.e.i.r.p. distributions 1 Introduction In order to be in a position to offer the RAS the required level of protection, it is necessary to be able to predict interference levels at a RAS site from potentia
15、l deployments of P-MP HDFS stations. This interference level will depend upon the characteristics assumed for each service and the terrain and clutter around the RAS site. A number of the input parameters are not available as a numerical constant, but vary according to a distribution. For example th
16、e propagation loss between two points depends upon a number of parameters including the percentage of time. The methodology described in this Annex is based upon Monte Carlo techniques, whereby these input distributions are convolved using an interference equation to produce a distribution of interf
17、erence against probability that these levels of interference are exceeded. This approach allows comparison against RAS thresholds defined in Recommendation ITU-R RA.769, which are defined in terms of an interference threshold (mean power over observation) and probability of an observation being inte
18、rfered. Rec. ITU-R F.1766 3 The calculation requires three stages: 1 definition of RAS model; 2 definition of P-MP HDFS model; 3 calculation of interference. Each of these stages are described in the sections below. 2 RAS model 2.1 Interference threshold The basis of the RAS model is the protection
19、criteria for radioastronomical measurements described in Recommendation ITU-R RA.769. In order to protect radio astronomy it is necessary that there be a (100 x)% probability that an observation is interference free. An observation is interference free if the mean interfering power over the integrat
20、ion period T is less than the levels specified in Annex 1 of Recommendation ITU-R RA.769. A value of T = 2 000 s is typically used within this Recommendation and other analysis of sharing with the RAS. This integration period also determines the sensitivity of the receiver, and hence the threshold o
21、r mean interference level. These vary depending upon the type of observation, whether continuum or spectral line observation. The continuum observations are more sensitive than those for spectral lines, and so require a lower threshold. Operation of a telescope as part of a VLBI system results in hi
22、gher thresholds due to the low correlation of sources of interference. The values in Table 1 of Recommendation ITU-R RA.769 specify mean interference thresholds in terms of spectral power flux-density, based upon an assumed receiver gain of 0 dBi. This corresponds to an antenna with side lobes as gi
23、ven in Recommendation ITU-R SA.509 at an off-axis angle of 19. In order to be able to model RAS telescopes at lower elevation angles and to include other gain patterns for the telescope, it is necessary to define the threshold in terms of interference at the receiver, i.e. using PHas defined in equa
24、tion (4) of that Recommendation. As noted above there must be an (100 x)% probability that an observation is interference free, i.e. that this threshold is not exceeded. Recommendation ITU-R RA.1513 identifies that for a single network, in this case for a P-MP HDFS deployment, a value of x = 2% shou
25、ld be used. 2.2 Location The location of the RAS antenna is defined by its latitude, longitude and height above local terrain. 2.3 Gain pattern The RAS antenna should be modelled by a suitable gain pattern, such as that specified in Recommendations ITU-R S.1238 or ITU-R RA.1630, or, where available,
26、 measured data. As noted above the interference threshold is based upon mean interference over an observation period, typically 2 000 s. Assuming that the propagation environment and P-MP HDFS deployment is constant over that period, then the mean interference will be that calculated using the mean
27、gain over the observation. The mean gain of an RAS telescope can be determined by: locating a number of test points (e.g. every 3) on the horizon around the test RAS site; set the RAS antenna to the gain pattern selected as described above; 4 Rec. ITU-R F.1766 set the antenna elevation to the minimu
28、m for observations at this site (e.g. 5) and azimuth = 0; increase the antenna elevation at a rate equal to the Earths rotation for 2 000 s; determine the mean gain at each test point over this period. Note that the averaging should be in linear units rather than dBi, even if the resulting table may
29、 be presented in dBi. The table of (mean gain over 2 000 s), (angle from RAS azimuth) can be used to represent the mean gain pattern of the RAS antenna towards the horizon over an observation. 2.4 Summary The input parameters required to define the RAS in the model are summarized in Table 1. TABLE 1
30、 RAS model parameters Input Source Interference threshold Mean interference over 2 000 s observation period calculated from Recommendation ITU-R RA.769 for the relevant observation type Acceptable probability of observation receiving interference From a P-MP HDFS network, 2% from Recommendation ITU-
31、R RA.1513 RAS latitude From RAS site location RAS longitude From RAS site location RAS antenna height above terrain From RAS site location Mean gain over observation Table of (mean gain over 2 000 s), (angle from RAS azimuth), calculated using the algorithm described above 3 P-MP HDFS model 3.1 a.e.
32、i.r.p. distribution(s) A wide range of services, architectures and characteristics could be employed by P-MP HDFS systems. To support regulation of this band, reference models can be defined, with characteristics such as maximum cell size, e.i.r.p., antenna heights, etc. From these reference models
33、it is possible to derive distributions of aggregate e.i.r.p. (a.e.i.r.p.) that define the probability that the a.e.i.r.p. within an area, or building block (BB) is no more than a certain value. The algorithm to derive these a.e.i.r.p. distributions is described in Recommendation ITU-R F.1765 Methodo
34、logy for determining the aggregate equivalent isotropically radiated power from point-to-point high-density applications in the fixed service operating in bands above 30 GHz. The a.e.i.r.p. encapsulates the characteristics of all transmitters within the BB, including aspects such as power control, g
35、ain patterns, aggregation, and clutter. The deployment of P-MP HDFS terminals will vary between BBs: however a large number of BBs are likely to produce a range of a.e.i.r.p.s as defined by the distribution. A scenario could be based upon widespread deployment of a single P-MP HDFS reference model,
36、in which case the input would be a single a.e.i.r.p. distribution. However, more complex deployments could involve different types of P-MP HDFS reference models, in which case there would have to be multiple a.e.i.r.p. distributions. Rec. ITU-R F.1766 5 3.2 Transmitter height The transmitter height
37、will be the maximum that could be used for each reference model, and so is associated with the a.e.i.r.p. distribution. 3.3 Deployment area The deployment area (DA) represents those locations where there could be P-MP HDFS transmitters and is typically between: the exclusion zone (EZ) around the RAS
38、 site within which P-MP HDFS deployment is not permitted. This could be in the form of a distance from RAS site, D, or locations for which the propagation loss using a model such as Recommendation ITU-R P.452 is at greater than a specified value, i.e. L452 X dB; the maximum distance Dmaxafter which
39、additional deployment would bring a negligible increase in the interference level calculated and therefore need not be considered. EZs based upon distance are circles centred upon the RAS site. EZs based upon propagation loss can be polygon(s). The maximum distance to consider will vary depending up
40、on the size of the EZ. For example with an EZ defined by D = 50 km, it is not necessary to consider deployment of P-MP HDFS stations beyond Dmax= 110 km. The value of Dmaxcan be determine by continuing to add further interfering stations until the increase in interference level is negligible. If the
41、 DA is a narrow ring around the RAS site then it is likely that Dmaxshould be increased. Within the DA an array of test points should be located at regular intervals, each representing one BB. The area used to derive the a.e.i.r.p. determines the separation distance between test points. The DA could
42、 contain a uniform distribution of BBs, all representing the same P-MP HDFS reference model or there could be locations with different types of service, architecture, etc., represented by different a.e.i.r.p. distributions. The DA could also include areas with no P-MP HDFS deployment. The a.e.i.r.p.
43、 distribution could represent either in-band or out-of-band (OoB) emissions from P-MP HDFS transmitters. In the case of OoB analysis there could be an attenuation of signal with respect to in-band transmission, AOoB. Annex 2 to this Recommendation specifies various approaches and algorithms to defin
44、e a DA. 3.4 Summary The input parameters required to define the P-MP HDFS in the model are summarized in Table 2. 6 Rec. ITU-R F.1766 TABLE 2 P-MP HDFS model parameters Input Source a.e.i.r.p. distribution(s) Calculated using algorithm in Recommendation ITU-R F.1765 Transmitter height As defined for
45、 each reference model, i.e. could vary between a.e.i.r.p. distribution Deployment area A set of test points between the EZ and the maximum distance to consider, Dmax. Each test point is associated with a transmitter height and a.e.i.r.p. distribution If required, AOoBIf required, an attenuation betw
46、een in-band and OoB operation. For in-band analysis this field can be set to zero 4 Interference calculation The Monte Carlo methodology consists of calculating the mean aggregate interference for a series of samples. It consists of the convolution of three varying inputs, the P-MP HDFS deployment,
47、the propagation environment, and the azimuth of the RAS observation. This convolution is shown in Fig. 1. FIGURE 1 Monte Carlo approach to calculate aggregate interference For each sample the mean aggregate interference I is calculated using: OoBiRASjijiAazjGjpLpAEIRPI +=),(),()(452,(1) where: i: i-
48、th sample number j: j-th building block AEIRP(pi,j): aggregate e.i.r.p. for probability pi,jpi,j: probability for i-th sample for j-th building block Rec. ITU-R F.1766 7 L452(pi, j): Recommendation ITU-R P.452 loss for probability pifrom j-th building block pi: probability to use in ITU-R P.452 for
49、i-th sample GRAS(j, azi): RAS receive mean gain over observation towards j-th building block for RAS pointing angle aziAOoB: attenuation between in-band and OoB emissions. In the case of in-band analysis this field can be ignored or set to zero. Note that L452is assumed to be a positive number representing a loss. The antenna heights of P-MP HDFS transmitter and RAS receiver are used with the Recommendation ITU-R P.452. propagation model to determine the loss as required. Based upon equation (1), the probability of an observation receiving interference can be
