1、 Rec. ITU-R S.1325-3 1 RECOMMENDATION ITU-R S.1325-3 Simulation methodologies for determining statistics of short-term interference between co-frequency, codirectional non-geostationary-satellite orbit fixed-satellite service systems in circular orbits and other non-geostationary fixed-satellite ser
2、vice systems in circular orbits or geostationary-satellite orbit fixed-satellite service networks (Questions ITU-R 206/4 and ITU-R 231/4) (1997-2000-2001-2003) The ITU Radiocommunication Assembly, considering a) that emissions from the earth stations as well as from the space station of a satellite
3、network (GSO FSS; non-GSO FSS; non-GSO mobile-satellite service (MSS) feeder links) in the FSS may result in interference to another such network when both networks operate in the same bands; b) that it is desirable to have a common methodology of simulation for assessing interference between system
4、s that have co-frequency, codirectional feeder links when one of the systems is non-GSO; c) that it is possible to make some simplifying assumptions for these systems; d) that the simplifications in considering c) should not adversely affect the output results; e) that it would be desirable to have
5、a common set of input parameters for each of the two communication systems; f) that it is necessary for the methodology to consider the type of fade compensation to counteract signal fading such as adaptive power control; g) that the methodology should have the ability to accurately calculate the ti
6、me dependence of a single interference event in order to more accurately assess the impact on the interfered system; h) that the vast majority of the non-GSO FSS systems are in circular orbits; j) that information on the numbers and precise locations of earth stations is usually unavailable from ITU
7、 sources, recommends 1 that the methodology given in Annex 1 may be used to obtain cumulative probability statistics for assessing short-term interference between systems that have co-frequency, codirectional links with one system employing a non-GSO MSS feeder link or non-GSO FSS system; 2 that the
8、 output should be evaluated against an agreed set of common output statistics; 2 Rec. ITU-R S.1325-3 3 that the methodology given in Annex 2 may be used to compute the aggregate total interference produced by a non-GSO system into a GSO satellite network and may be used to calculate the cumulative d
9、ensity function of the equivalent power flux-density (epfd) for a given antenna diameter of the GSO earth station or the epfd of the non-GSO system in the uplink direction; 4 that the methodology given in Annex 2 may be used to compute the epfd produced by a non-GSO system into an operational GSO ea
10、rth station to assess compliance with additional operational limits contained in Article 22 of the Radio Regulations (RR); 5 that the following Notes should be regarded as part of this Recommendation. NOTE 1 Short-term interference refers to cumulative probability distribution of those bit error rat
11、ios (or C/N values) that are calculated for 1% of the time or less. NOTE 2 The methodology of Annex 1 also can be used to evaluate the time dependent nature of the interference during a single near in-line event. NOTE 3 Annex 2 provides a methodology for computing the epfdand epfdof a non-GSO system
12、. Annex 3 provides approaches to relate the methodology of Annex 1 to compute epfdand epfdof a non-GSO system. NOTE 4 It should be assumed that the noise is thermal in nature and is referenced to the total system noise power including the antenna thermal noise at the input to the demodulator. NOTE 5
13、 There is need to develop a methodology for characterizing and calculating the long-term interference between non-GSO FSS systems and GSO FSS networks. NOTE 6 Annex 3 is the description and example of computational methodology. NOTE 7 Annex 4 provides a list of subjects for continuing work on this R
14、ecommendation. NOTE 8 Software meeting Recommendation ITU-R S.1503 would be used by the Radiocommunication Bureau to validate compliance with epfd limits in Article 22 of the RR. NOTE 9 The Annexes to this Recommendation apply to non-GSO systems having circular orbit. Annex 1 Methodology for determi
15、ning statistics of short-term interference between co-frequency, codirectional non-GSO FSS systems in circular orbits and other non-GSO FSS systems in circular orbits or GSO FSS networks 1 Method and simulation approach description The framework for this methodology is to model the satellite systems
16、 in their orbits and allow each space station and earth station to track their respective aimpoints while taking into account the Earths rotation. A simulation of this framework is sampled over a period of time at a relatively fine rate. At each sample the range gain product is computed. The raw dat
17、a is a time history of the interference level versus time. It can be shown that if power control is not used on either system Rec. ITU-R S.1325-3 3 then the range gain product (defined in equation (2) can be directly related to the interference level. The raw data can be evaluated to compute the per
18、 cent of time that the range gain product for all interference paths is above a certain level. The interference geometry is shown in Fig. 1, and the interference paths considered are those below: 1325-0112Space station(Constellation 2)Space station(Constellation 1)Wanted signal pathsInterference sig
19、nal pathsFIGURE 1Interference geometryTo compute the interference to noise ratio, I0/N0, the following equation can be used: 2212221004)()(114114)()(irtptxtpirttxtRGGLTkBWPLTkRGGBWPNI=(1) where: Pt: available transmit power (W) BWtx: transmit bandwidth (Hz) Gt(1) : transmit gain (relative intensity)
20、 (numerical ratio) Gr(2) : receiver gain (relative intensity) (numerical ratio) 1: off bore-sight angle of the transmitter in the direction of the receiver (degrees) 2: off bore-sight angle of the receiver in the direction of the transmitter (degrees) Space station (Constellation 1) Earth station (C
21、onstellation 1) Space station (Constellation 2) None Uplink1 Uplink2Downlink2 Downlink1Earth station (Constellation 2) Downlink1 Downlink2Uplink2 Uplink1None 4 Rec. ITU-R S.1325-3 : wavelength of transmitter (m) Ri: length of the interfering path (m) k : Boltzmanns constant (1.38 1023W/(Hz K) T : no
22、ise temperature (K) Lp: polarization isolation factor (numerical ratio 1). If there is no range compensating power control on the links between the space station and the earth station, the only elements of equation (1) that are dependent variables for the time varying simulation are the receiver gai
23、n angle, the transmitter gain angle and the range between transmitter and receiver. To compute I0/N0the range gain product can be multiplied by the constant: ptxtLTkBWP 1142For example the range gain product for space station 1 downlink into earth station 2 downlink is computed as (Fig. 1): 2214)()(
24、irtRGG (2) For interference assessment from satellite networks with multiple ground terminals, the interference from all of the ground terminals (for the uplink case) or from all of the space stations (for the downlink case) must be combined to determine the total interference. The interference data
25、 can be combined at each simulation time step during the simulation, or by combining the data from a set of individual simulations. In either case the receive satellite antenna discrimination in the direction of each earth terminal must be considered when calculating the total uplink interference, e
26、pfd, and the receive earth station antenna discrimination in the direction of each non-GSO space station must be considered when calculating the total downlink interference epfd. The epfd is defined as the sum of the power flux-densities produced at a receive station of the interfered system, on the
27、 Earths surface or in an orbit, as appropriate, by all the transmit stations within the interfering system, taking into account the off-axis discrimination of a reference receiving antenna assumed to be pointing in its nominal direction. = maxaiririitNiiPGGRGepfd)(4)(10log10221110/10(2a) where: Na:
28、number of transmit stations in the interfering satellite system that are visible from the receive station of the interfered satellite system, considered on the Earths surface or in an orbit as appropriate i : the index of the transmit station considered in the interfering satellite system Pi: RF pow
29、er at the input of the antenna of the transmit station, considered in the non-GSO satellite system (dBW) Rec. ITU-R S.1325-3 5 )(1itG : transmit antenna gain of the station considered in the non-GSO satellite system in the direction of the receive station (relative intensity, numerical ratio) )(2irG
30、 : receive antenna gain of the receive station in the direction of the i-th transmit station considered in the non-GSO satellite system (relative intensity, numerical ratio) maxrG : maximum gain of the receive station antenna (numerical ratio) 1: off bore-sight angle of the transmit station consider
31、ed in the non-GSO satellite system in the direction of the receive station 2: off bore-sight angle of the receive station in the direction of the i-th transmit station considered in the non-GSO satellite system Ri: distance between the transmit station considered in the non-GSO satellite system and
32、the receive station (m). In terms of I0/N0, epfd can be expressed as: (W/BW)Hz),(dB(W/(m)(4)(10222110/irritiiepfdPepfdGGRGPmaxii=(2b) )W(Hz),(dB(W/(m)(4)(10222110/iiiitirrittxtepfdPepfdGGRGBWPmax=(2c) =iprrpittxtepfdLTkGGLTkRGBWPmaxiii114)(1144)(102222110/(2d) where epfd is in dB(W/(m2 Hz), itPis in
33、 W, and BWtxis the transmit bandwidth in Hz. Substituting I0/N0(equation (1): =iprepfdLTkGNImaxi1141020010/(2e) so: =iprLTkGNIepfdmaxi114log10200(2f) )()( HzmW/dBlog106.2284log10log102200+=priLTGNIepfdmaxi(2g) 6 Rec. ITU-R S.1325-3 2 Simulation assumptions 2.1 Orbit model The orbit model to simulate
34、 the space stations in their orbits is for circular orbits only accounting for precession of the line of nodes in the equatorial plane due to asphericity of the Earth. 2.1.1 Discussion The orbit model represents satellite motion in a geocentric inertial coordinate frame shown in Fig. 2. The origin o
35、f this inertial frame is at the centre of the Earth. The x-axis points to the first point in the constellation Aries (i.e., vernal equinox), the z-axis is the mean rotation axis of the Earth, and the y-axis is determined as the cross product of the unit vectors in the z and x direction, i.e. xzyrrr=
36、 . The orbital model is based on Newtons equation of motion for a satellite orbiting a perfectly spherical Earth in a circle. The characteristics of this motion that make it easy to model is that the satellite orbital radius and velocity are constant. These parameters are connected by Newtons second
37、 law. The equation of motion is: 22rmMGrvmsvesv= (3) where: msv: mass of the space station v : constant velocity of the space station G : Newtonian gravitational constant (6.673 1011N m2/kg2) r : radius of orbit Me: mass of the Earth (5.974 1024kg). 1325-02yzIEOrbit planeEquator planeCentre of the E
38、arthx, (vernal equinox)FIGURE 2Representation of Keplerian orbital elementsNodeRec. ITU-R S.1325-3 7 Equation (3) can be written in the form: rRRMGrMGveeee222= (4) where Reis the radius of a perfectly spherical Earth (6 378 km). Since at the surface of the Earth: 2eeRmMGgm = (5) where g is the accel
39、eration due to gravity at the surface of the Earth is: 22s/m 806.9=eeRMGg (6) we find that (4) can be written as: rRgve22= (7) or: rgRve= (8) The period of the orbit, T, is given by the expression: grRvrTe322 = (9) These equations completely describe the dynamics of circular orbit motion about a per
40、fectly spherical Earth. The description of this motion in the geocentric coordinate system shown in Fig. 2 is based on specifying the satellite position using the Keplerian orbital parameters. These variables are defined as: : the right ascension of the ascending node (RAAN) of the orbit. The angle
41、as measured from the x-axis in the equatorial plane (x-y plane). I : the inclination of the orbit. The angle as measured from the equatorial plane to the orbital plane of the space station. E : the argument of latitude (true anomaly). The angle as measured from the line of nodes to the radius vector
42、 at the position of the space vehicle. It should be noted that the true anomaly is a function of the angular position of the space station at time t0and the angular velocity of the space station. It can be expressed as: tEE +=0(10) where: E0: angular position of the space station at time t0(rad) : a
43、ngular velocity of the space station (rad/s) = v/r. 8 Rec. ITU-R S.1325-3 To account for orbital precession the RAAN of the orbit is also a function of the RAAN at time t0and the orbital precession rate. It can be expressed as: tr+=0(11) where: 0: RAAN of the space station at time t0(rad) r: orbital
44、 precession rate of the space station (rad/s). 422)cos(23rrRIJer= (12) where: : Earth attraction constant (3.986 105km3/s2) J2: second harmonic Earth potential constant (1 082.6 106). The representation of the space station position in terms of the geocentric inertial coordinate system is: +=EIEIEEI
45、Erzyxsinsinsincoscoscossinsincossincoscos(13) The representation of the space station velocity in terms of the geocentric inertial coordinate system, ignoring the relatively long-term variation in , is: +=EIEIEEIErtztytxcossinosccoscossinsinosccossinsincosd/dd/dd/d(14) 2.1.2 Perturbations For GSO sa
46、tellites: The orbit inclination of the satellite The slight inclination of the satellite orbit may occur for satellites that have been in orbit for a period of time. A deviation generally takes place, with a limit in the deviation not to be exceeded. The deviation of the antenna beam from its nomina
47、l pointing direction The following factors contribute to the total variation on the area on the surface of the Earth illuminated by the satellite beam: variations on satellite station-keeping; variations caused by the pointing tolerances, which become more significant for coverage areas with low ang
48、les of elevation; effect of yaw error, which increases as the beam ellipse lengthens. The effect of these possible variations should be assessed on a case-by-case basis, since their total effect on the area covered will vary with the geometry of the satellite beam, and it would not be reasonable to
49、indicate a single value of shift on the area covered for all situations. For non-GSO satellites, the exact longitude precession rate would be affected by a slight drift due to longitudinal station-keeping errors. This effect should be modelled and integrated in the simulations. Rec. ITU-R S.1325-3 9 2.2 Conside
