Validation of a telecommunications satellite's payload based on a calculation of the power radiated ratio between the useful signal and intermodulation noise.

Abstract

The invention relates to a method (100) for controlling the performance, in terms of radiated noise power, of a telecommunications satellite payload based on a multibeam active antenna. The method notably includes the determination (105) of a spectral density of intermodulation noise power radiated to the ground by all the antenna sources from: the carrier allocation plan and the associated RF powers enabling the satellite to fulfill its telecommunications mission, the weighting coefficients of the beamforming array used to form the radio beams fulfilling the mission, the linearity characteristics of the amplifiers associated with the different antenna sources, and the radiation patterns of the different sources.The method allows us to determine (109) a radiated power ratio between useful signal and intermodulation noise ("radiated C / IM") for at least one carrier and for at least one geographical area of ​​interest. Figure for the abstract: Fig. 4.

Description

Title of the invention: Validation of the payload of a telecommunications satellite based on a calculation of the ratio of radiated power between useful signal and intermodulation noise. Field of the invention

[0001] The present invention relates to the field of performance control of the payload of a telecommunications satellite. More particularly, the invention relates to a method for validating the configuration of the payload of a telecommunications satellite based on an estimation of a radiated power ratio between useful signal and intermodulation noise ("radiated C / IM"). State of the art

[0002] Some telecommunications satellites are used for transmitting information to fixed receiving points; this is referred to as "fixed-satellite service" (FSS) or DTH broadcasting (English acronym for "Direct-To-Home," meaning "directly to the individual"). This is the case, for example, for broadcasting television programs or for international telephony.

[0003] Other telecommunications satellites are assigned to high-speed Internet connection services corresponding to HTS type missions (English acronym for "High-Throughput Satellite", "high-speed satellite" in French).

[0004] For the same amount of allocated radio spectrum, a satellite fulfilling an HTS mission provides significantly higher throughput than a satellite fulfilling an FSS mission. This significant increase in throughput for HTS missions is achieved by reusing frequency channels in tightly focused radio beams arranged to cover a geographical region of interest. The increase in throughput is also accompanied by increased coverage flexibility (beam variations over time).

[0005] Satellites fulfilling an HTS mission generally carry an active multibeam antenna. Such an antenna comprises a beamforming network (BFN) connected to a source array. Phase and amplitude weighting coefficients are associated respectively with the different sources and the different frequency channels in order to form the desired radio beams. Each source is associated with a suitable amplifier to amplify the signal to be emitted by the source.

[0006] The payload of a telecommunications satellite can be controlled and updated by a mission control center (MCC), particularly to respond to changes in an ongoing mission, or even to respond to a new mission that is significantly different from the ongoing mission.

[0007] To control the performance of the payload of a telecommunications satellite, it is necessary to control the radio link budget between the satellite and a receiving station located in a geographical area of ​​interest on the surface of the Earth.

[0008] The non-linearity of the amplifiers in the active multibeam antenna generates intermodulation noise. The ratio of radiated power between the useful signal and the intermodulation noise ("C / IM ratio") is an important element contributing to the calculation of the radio link budget of a communication between a satellite and a ground station.

[0009] However, there is currently no satisfactory solution for quickly calculating a C / IM ratio for a multibeam active antenna comprising a large number of sources (several dozen or even several hundred sources) and configured to form a large number of beams (several hundred or even several thousand beams).

[0010] The document "Calculation of third order intermodulation spectrum", YH LAU et al., describes a method for rapidly calculating the spectral density of intermodulation noise in a conducted (and not radiated) manner. Disclosure of the invention

[0011] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

[0012] To this end, and according to a first aspect, the present invention proposes a computer-implemented method for validating a payload configuration for a telecommunications satellite. The satellite is configured to transmit a signal with a multibeam active antenna comprising a beamforming array. The beamforming array is connected to a plurality of sources and adapted to simultaneously form several beams of interest serving geographical areas on the Earth's surface. The beamforming array is configured to receive, for each beam of interest to be formed, an input signal comprising one or more frequency channels with respective power levels, and to transmit to each source a linear combination of the input signals weighted by weighting coefficients, each source being connected to an amplifier.The method includes for each amplifier: - a determination of a "normalized mask" of intermodulation noise power spectral density from the frequency channels composing the input signals and the respective power levels of said frequency channels, . - a determination of an operating point corresponding to an output power of the amplifier, the operating point being determined according to the power levels of the frequency channels of the input signals, and according to the weighting coefficients associated with said amplifier, - a determination of the total intermodulation noise power as a function of the operating point and linearity characteristics of the amplifier, - a determination of an "absolute mask" of spectral density of intermodulation noise power by weighting the normalized mask with the total intermodulation noise power.

[0013] The method comprises, for each source: - a determination of a "radiated mask" of intermodulation noise power spectral density from the absolute mask of intermodulation noise power spectral density of the amplifier to which the source is connected, and from a radiation pattern of the source.

[0014] The method further comprises: - a determination of a "total radiated mask" of spectral density of power of intermodulation noise by a power summation of the radiated masks of the different sources.

[0015] For at least one frequency channel of interest, and for at least one geographical area of ​​interest: - a determination of the radiated power of intermodulation noise by integrating, over a sub-band of frequencies corresponding to said frequency channel, the total radiated mask of spectral density of intermodulation noise power for the geographical area of ​​interest, - a determination, for the frequency channel of interest, of an equivalent isotropic power radiated by the multibeam active antenna, - a determination of a "C / IM radiated" ratio between the equivalent isotropic radiated power and the intermodulation noise radiated power, - a verification of a predetermined criterion based on the "C / IM radiated" ratio thus determined.

[0016] The method according to the invention thus provides a rapid and efficient method for an analytical evaluation of the performance of the ratio of radiated power between the useful signal and intermodulation noise. A telecommunications satellite payload configuration can thus be validated as meeting a set of specifications. Several configurations can advantageously be tested and compared to select the configuration that best meets a need.

[0017] The proposed solution advantageously allows for the calculation of radiated performance on the ground per carrier, taking into account: - the carrier plane of the telecommunications mission under consideration (the frequency channels composing the input signals of the beamforming network), - the weights used by the active antenna beamforming array (the weighting coefficients associated with the different frequency channels and the different sources), - the linearity characteristics of the amplifiers associated respectively with the different sources of the active antenna, and - the radiation patterns of the different sources of the active antenna.

[0018] The method according to the invention is applicable to any type of multi-beam active antenna. It may be a transmitting antenna or a receiving antenna. The antenna may include one or more beamforming arrays of the analog or digital type. It may also be an antenna with or without a reflector. The active antenna may have several reflectors and / or several source arrays. The amplifiers associated with the different sources may be of the SSPA (Solid State Power Amplifier) ​​type or based on tubes.

[0019] Advantageously, the execution time of the method remains very short and is little impacted by the number of frequency channels, the number of sources and the number of beams formed.

[0020] The method according to the invention can be applied to tools for designing, parameterizing or validating the configuration of the payload of a telecommunications satellite, or to tools for modeling the performance of the payload of a telecommunications satellite.

[0021] The method can be implemented for satellites evolving on different types of orbit: geostationary orbit (“Geostationary Orbit” or GEO in English), medium Earth Orbit (MEO) type, low Earth Orbit (LEO) type, Molnia orbit, etc.

[0022] In particular embodiments, the invention may further comprise one or more of the following features, taken individually or in all technically possible combinations.

[0023] In particular embodiments, the normalized intermodulation noise power spectral density mask is common to all amplifiers.

[0024] In particular embodiments, the normalized spectral density mask of intermodulation noise power is determined for an amplifier as a function of the weighting coefficients associated with said amplifier.

[0025] In particular embodiments, the determination of the standardized mask intermodulation noise power spectral density involves a calculation of third-order intermodulation products generated by the frequency channels of the input signals.

[0026] In particular embodiments, the determination of the normalized spectral density mask of intermodulation noise power further involves a calculation of odd-order intermodulation products strictly greater than three generated by the frequency channels of the input signals.

[0027] In particular embodiments, the determination of the normalized spectral density mask of intermodulation noise power involves the application of a correction value intended to compensate for intermodulation products of order strictly greater than three not taken into account.

[0028] In particular embodiments, the determination of the normalized intermodulation noise power spectral density mask involves a normalization calculation based on the result of an integration, over a frequency band, of the intermodulation noise power spectral density.

[0029] In particular embodiments, the determination of the normalized intermodulation noise power spectral density mask involves a normalization calculation based on the result of an integration, over a frequency band, of the intermodulation noise power spectral density for power values ​​within a predetermined range of values.

[0030] In particular embodiments, the method further includes applying a correction value to the "radiated C / IM" ratio. The correction value is determined based on a reuse factor for the frequency channels used to form the beams of interest.

[0031] In particular embodiments, the frequency band is one of the W, Q, V, Ka, Ku, L, S, C bands.

[0032] According to a second aspect, the present invention relates to a computer program product comprising instructions which, when executed by a computer, lead the computer to implement the steps of a method for validating a configuration of a payload of a telecommunications satellite according to any one of the preceding implementation modes.

[0033] According to a third aspect, the present invention relates to a computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to implement the steps of a method for validating a configuration of a telecommunications satellite payload according to any one of the preceding embodiments. Figures

[0034] The invention will be better understood upon reading the following description, given by way of non-limiting example, and made with reference to the following figures:

[0035] [Fig-1] a schematic representation of a telecommunications system by satellite,

[0036] [Fig.2] a schematic representation of a multibeam active antenna of a telecommunications satellite,

[0037] [Fig.3] a schematic representation of a computer configured to put into implements a method according to the invention to validate the payload configuration of a telecommunications satellite,

[0038] [Fig.4] a schematic representation of the main stages of a first mode of implementation of the method according to the invention,

[0039] [Fig. 5] a schematic representation of the main steps of a second mode implementation of the method according to the invention.

[0040] In these figures, identical reference numerals from one figure to another designate identical or analogous elements. For clarity, the elements shown are not necessarily to the same scale, unless otherwise stated.

[0041] Detailed description of an embodiment of the invention

[0042] Figure 1 schematically represents a satellite telecommunications system. As illustrated in Figure 1, the system comprises at least one telecommunications satellite 30 in orbit around the Earth 50. In the example considered, the mission of the telecommunications satellite 30 corresponds to a high-speed Internet connection service (HTS type service). This example is limited to cases where the satellite 30 is in a geostationary orbit (GEO type orbit). However, following other examples, it is not precluded to consider a non-geostationary Earth orbit, such as a low-altitude orbit (LEO type orbit) or a medium-altitude orbit (MEO type orbit).

[0043] Conventionally, the telecommunications satellite 30 can enable data exchange between two gateway stations 40 via radio communication links 41 established respectively between each gateway station 40 and the telecommunications satellite 30. In another example, the telecommunications satellite 30 can enable data exchange between a user 42 and a gateway station 40 via, on the one hand, a radio communication link 41 established between the satellite 30 and the user 42, and on the other hand, a radio communication link 43 established between the satellite 30 and the gateway station 40. In yet another example, the telecommunications satellite 30 can enable data exchange between two users 42 via radio communication links 43 established respectively between each user 42 and the telecommunications satellite 30.

[0044] Each radio communication link 41, 43 can support a downlink direction (downlink in Anglo-Saxon literature) for the transmission of data by satellite 30 and / or an uplink (uplink in Anglo-Saxon literature) for the reception of data by satellite 30.

[0045] The transmissions and / or receptions on the radio communication links 41, 43 take place for example in one or more frequency bands among the W, Q, V, Ka, Ku, L, S, C, etc. bands.

[0046] In the example considered and illustrated in [Fig.1], the telecommunications satellite 30 is controlled by a mission control center 17 located on the ground, on the surface of the Earth 50. The mission control center 17 allows in particular to update the payload of the telecommunications satellite 30 to respond to possible changes in the mission in progress, or even to respond to a new mission significantly different from the mission in progress.

[0047] Conventionally, the payload of the telecommunications satellite 30 can be configured remotely by sending commands through radio signals transmitted over a control link 16 established between the telecommunications satellite 30 and the mission control center 17.

[0048] As illustrated in [Fig.1], the mission control center 17 includes an antenna 15 for communicating with the telecommunications satellite 30 on the control link 16.

[0049] The mission control center 17 also includes a computer 10 configured to implement a method for validating the payload of the telecommunications satellite 30. It is indeed useful to be able to monitor the performance of the telecommunications satellite 30's payload in terms of the radio link budget between the satellite 30 and a receiving station (corresponding, for example, to a gateway station 40 or a user 42) located in a geographical area of ​​interest on the Earth's surface 50. More specifically, it is useful to be able to evaluate, for a given carrier and for a given geographical area of ​​interest, a radiated power ratio between the useful signal and the intermodulation noise ("C / IM ratio"). The C / IM ratio is indeed an important element in the radio link budget of a communication established between a satellite and a ground receiving station.

[0050] To meet the needs of its HTS mission, particularly in terms of bandwidth flexibility and geographical coverage, the telecommunications satellite 30 carries an active multibeam antenna 20.

[0051] Figure 2 schematically represents such an active multibeam antenna 20. The antenna 20 includes, in particular, a beamforming array 25 connected to an array 23 of sources 24. The method according to the invention is particularly well suited to cases where the number of sources 24 is large, for example, at least fifty (M > 50), or even at least one hundred (M > 100). Nothing would prevent However, the invention can be applied to cases where the number of sources is less important. In the example considered, the network 23 of sources comprises two hundred sources 24 (M = 200).

[0052] In the example considered and illustrated in [Fig. 2], the antenna 20 also includes a reflector 22. The array 23 of sources 24 is, for example, positioned at the focal point of the reflector 22 (AFR type antenna, acronym for "Array Fed Reflector"). According to another example, the array 23 of sources 24 is offset from a focal point of the reflector 22 (DAFR type antenna, acronym for "Defocused Array Fed Reflector"). However, there is nothing to preclude the use of an antenna 20 without a reflector (DRA type antenna, acronym for "Direct Radiating Array"), or an antenna with several reflectors. Nor would there be anything to prevent the use of an antenna 20 with several reflectors.

[0053] The beamforming array 25 can be “adaptive”, that is to say that the beams formed by the beamforming array 25 can vary over time.

[0054] The beamforming grating 25 can be analog or digital. An analog beamforming grating processes analog signals (electrical or microwave), for example with discrete electronic circuits such as attenuators, phase shifters, or time-delay circuits. A digital beamforming grating, on the other hand, processes digital signals.

[0055] The beamforming network 25 can be of any type known to a person skilled in the art, including phase shifter type or true time delay type.

[0056] In the following description, we consider the case where the antenna 20 is a transmitting antenna using an analog adaptive beamforming array 25 of the phase-shifter type.

[0057] As illustrated in [Fig. 2], the beamforming array 25 receives as input a plurality of input signals, each comprising one or more frequency channels with respective power levels. In the example considered and illustrated in [Fig. 2], M input signals are considered. Each input signal corresponds to a beam of interest to be formed. There may be several hundred, or even several thousand, beams to be formed simultaneously. The method according to the invention is particularly well suited to cases where the number of beams to be generated is large, for example, at least five hundred (L > 500), or at least one thousand (L > 1000). However, nothing would prevent the invention from being applied to cases where the number of The beam size would be less significant. As a purely illustrative example, we consider the case where there are two thousand beams to be formed (L = 2000). These input signals correspond, for example, to a carrier plane defined by a telecommunications satellite operator. Each carrier corresponds to a frequency channel occupying a sub-band Af of a frequency band AF. The frequency band AF corresponds, for example, to the Ka band, which extends between 27.5 and 31 GHz for transmit communications. The sub-band Af occupied by a frequency channel has, for example, a bandwidth of 10 MHz. Each frequency channel is associated with a predetermined power level. A beam can be formed by one or more carriers (one or more frequency channels per input signal). It should be noted that the same frequency channel can be used for different beams (the same frequency channel can be present in different input signals).

[0058] The power levels (conducted RF power) of the frequency channels in the input signals can be determined from EIRP (Equivalent Isotropically Radiated Power) specifications provided by the operator. These specifications provide the minimum EIRP level that the antenna must provide for each frequency channel. EIRP is a combination of the antenna directivity and the conducted RF power. The antenna directivity is known from the radiation patterns of the sources 24 and the weighting coefficients used by the beamforming array 25 (see below). The conducted RF power required to meet the specifications can therefore be deduced from this.

[0059] Conventionally, the beamforming network 25 is configured to apply phase and amplitude weighting coefficients to the different sources 24 and the different frequency channels in order to form the desired radio beams to serve geographical areas of interest on the Earth's surface 50.

[0060] In other words, the beamforming array 25 is configured to transmit to each source 24 a linear combination of input signals weighted by phase and amplitude weighting coefficients in order to form the desired radio beams. The weighting coefficients allow the position and shape of each of the beams to be formed to be modulated.

[0061] For this purpose, the beamforming network 25 may include, in a known manner, duplicator circuits, phase shifters and attenuators allowing an amplitude and phase weighting coefficient to be applied to each frequency channel for each source 24 of the network 23.

[0062] It should be noted that at any given time, not all the sources 24 of the network 23 are necessarily used to form the desired beams. If this is the case, it is sufficient to take into account the sources 24 that are actually used.

[0063] Each source 24 is connected to an amplifier. This could be, for example, an amplifier SSPA-type amplifier or a tube-based amplifier. In the example considered, an amplifier is associated with one and only one source 24 (a one-to-one correspondence between the amplifiers and the sources 24). However, nothing would prevent us from considering the case where the same amplifier is associated with several sources 24.

[0064] An amplifier associated with a source 24 has the role of amplifying the power of the signal transmitted to the source 24 by the beamforming network 25 before the radio emission of said signal by the source 24. An amplifier therefore receives at input the linear combination of the weighted input signals intended for the source 24 to which (or to the sources 24 to which) the amplifier is associated.

[0065] An amplifier generally exhibits non-linear characteristics when the expected output power level is high. The more output power the amplifier must deliver, the more non-linear it is, and the more intermodulation products it will generate.

[0066] Intermodulation products resulting from amplifier non-linearity impact the link budget of a communication established between the telecommunications satellite 30 and a ground receiving station. This impact can be evaluated by calculating a ratio between the useful signal and the intermodulation noise ("C / IM ratio") at the level of the signal radiated to the ground in a geographical area of ​​interest (geographic area served by a radio beam emitted by the active multibeam antenna 20). This radiated C / IM ratio can notably be calculated for a given carrier (i.e., for a particular frequency channel).

[0067] Figures 4 and 5 illustrate the main steps of two embodiments of a method 100 for controlling the payload configuration of a telecommunications satellite 30. Method 100 according to the invention calculates a radiated C / IM ratio for at least one carrier and for at least one geographical area of ​​interest. Method 100 then verifies a predetermined criterion based on the calculated radiated C / IM ratio.

[0068] In the example considered, this method is implemented by a computer 10 in the mission control center 17. In other words, in the example considered, this method is used during an operational phase of the telecommunications satellite 30. It should be noted, however, that this method could also be used during upstream phases, for example during a design or sizing phase of the payload of the telecommunications satellite 30.

[0069] Figure 3 schematically represents a computer 10 configured to implement method 100 according to the invention for validating the payload configuration of a telecommunications satellite 30. As illustrated in Figure 3, the computer 10 comprises at least one processor 11 and at least one memory 12. The memory 12 stores code instructions from a computer program 13 which, when they are executed by the processor 11, configures the processor 11 to implement method 100 according to the invention. The computer 10 may also include a user interface 14 (also known as an HMI, short for "Human-Machine Interface") to receive optional input parameters. Alternatively or in addition, the computer 10 may also be connected to another machine configured to provide all or part of the input parameters.

[0070] As illustrated in Figures 3 and 4, Method 100 takes various parameters as input. A first set of parameters corresponds to the power levels of the frequency channels composing the input signals. This corresponds to a frequency plan allocated for the mission assigned to the telecommunications satellite 30. This frequency plan is, for example, provided by an operator of the telecommunications system described with reference to [Fig. 1]. The frequency plan indicates the RF conducted power level of each frequency channel contained in the input signals.

[0071] A second set of parameters corresponds to the weighting coefficients associated with the different frequency channels and the different sources 24. These weighting coefficients include, in particular, amplitude weights applied by the beamforming array 25 to the different frequency channels for each source 24. These weights correspond to a particular configuration of the beamforming array 25 of the antenna 20 to form radio beams enabling it to fulfill the mission of the telecommunications satellite 30 at a given time. In this application, the expression "the weighting coefficients associated with an amplifier" should be understood as "the weighting coefficients associated with a source 24 (or the sources 24 to which) the amplifier is associated."

[0072] A third set of parameters corresponds to the linearity characteristics of the amplifiers associated with the different sources 24. The linearity characteristics of an amplifier are, for example, defined by a curve describing a noise power ratio (NPR) as a function of the amplifier's output power (operating point, or OBO for output back-off). This curve, NPR = f(OBO), is, for example, provided by the amplifier manufacturer. The OBO corresponds to an output power relative to the amplifier's saturation point.

[0073] A fourth set of parameters corresponds to the radiation patterns of the different sources 24 of the antenna 20. Each radiation pattern is a representation of the distribution in three-dimensional space of a quantity representative of the power radiated by a source 24.

[0074] As illustrated in Figures 3 and 4, the method 100 includes a step 101 of determining a "normalized mask" of power spectral density (PSD) of intermodulation (IM) noise from the power levels of the frequency channels composing the input signals.

[0075] The power spectral density of the noise generated by the intermodulation products of the frequency channels contained in the frequency plane can be calculated analytically as described in the document "Calculation of third order intermodulation spectrum", YH LAU et al., ELECTRONICIS LETTERS, October 1st, 1990, Vol. 26, No. 21. This method makes it possible to calculate the power spectral density of the intermodulation products by convolving the power spectrum of the signal present at the input of an amplifier.

[0076] It is possible to consider only third-order intermodulation products (those that dominate the power spectrum of the intermodulation noise). Third-order intermodulation products include triple products (of the type + ff formed from three distinct frequency channels centered respectively on the frequencies , and f^), and double products (of the type Mf - f Y formed from two distinct frequency channels centered respectively on the frequencies etfk). The power of a triple product is 6 dB stronger than that of a double product.

[0077] The power spectral density of the noise generated by the third-order intermodulation products can then be written in the form: [°°78i = 4 ws(y) * ws(jy ws( - / ) 100791 -{(£","(7) 100801

[0081] In this expression, the operator * corresponds to a convolution operation. N corresponds to the number of different frequency channels contained in the input signals. The term wi corresponds to the power spectrum of a frequency channel of index i. For example, it is considered to take the form of a square wave centered at frequency i and with bandwidth Af. The amplitude of the square wave corresponds to the power level assigned to the frequency channel (different power levels are assigned to the different frequency channels, depending on the frequency plane considered). We then have - f) and - f - f )• term IV y( f ) corresponds to the spectrum input signal power:

[0082] Convolutions involving the power spectrum of the input signal (IVv) can be calculated using FFT (Fast Fourier Transform) routines. applying frequency channels individually (w0 can be obtained numerically or analytically.

[0083] The "normalized mask" of intermodulation noise spectral density can then be determined by normalizing the result with respect to the noise power total intermodulation noise power over the AF frequency band. The total intermodulation noise power is obtained by integrating the spectral density of intermodulation noise power over the AF frequency band.

[0084] According to another example, the result W1M(f) can be normalized with respect to the aggregate intermodulation noise power over the AF frequency band for power values ​​within a predetermined range of values ​​(for example, for power values ​​between a lower threshold, for example -10 dB, and a maximum power value).

[0085] Other methods for normalizing the spectral density of intermodulation noise could be considered (for example, normalization with respect to a maximum power value rather than with respect to an aggregate power value). The choice of a normalization method is only one variant of the invention.

[0086] It should be noted that it is also possible to consider intermodulation products of odd order greater than three (for example, intermodulation products of order five or seven). These intermodulation products can be calculated by an analytical method similar to that described above for third-order intermodulation products. Considering intermodulation products of odd order greater than three allows for greater accuracy in determining the normalized spectral density mask of intermodulation noise. However, this involves a greater number of calculations and consequently an increase in the time required to perform method 10 according to the invention.

[0087] Instead of precisely calculating the intermodulation products of odd order greater than three, it is possible to apply a correction value to the intermodulation noise spectral density to compensate for the products intermodulation not taken into account.

[0088] This correction value can, for example, be estimated by simulation by comparing, for several examples, the spectral density of intermodulation noise calculated taking into account third- and fifth-order intermodulation products (or even third-, fifth-, and seventh-order intermodulation products) with the spectral density of intermodulation noise calculated taking into account only third-order intermodulation products. The correction value can then be determined based on an average difference observed between the spectral densities thus calculated.

[0089] In the implementation described with reference to [Fig. 4], the normalized intermodulation noise power spectral density mask is the same for all amplifiers. In other words, to calculate the normalized intermodulation noise power spectral density mask of an amplifier, the set of all frequency channels present in the input signals is considered, and the weighting coefficients are not taken into account. Theoretically, this should not be the case because the frequency channels at the amplifier's input and the power levels of said frequency channels are not the same from one amplifier to another (because the weighting coefficients associated with the different frequency channels are not the same from one amplifier to another).

[0090] Experience shows, however, that this approximation is acceptable because the error introduced in the calculation of the C / IM ratio with this assumption remains relatively small. This approximation is all the more valid as the number of sources 24 is large (the power is averaged over all the sources).

[0091] However, it is also possible to avoid this approximation and to take into account, for each amplifier, the weighting coefficients associated with the different frequency channels in the calculation of the normalized intermodulation noise power spectral density mask. This is what is proposed by the embodiment described with reference to [Fig. 4]. In this case, a different normalized mask is calculated for each amplifier. This embodiment increases the accuracy of the calculated C / IM ratio, but it requires a greater number of calculations and therefore a longer execution time.

[0092] The following steps of method 100 according to the invention (steps 102 to 110) are identical for the two embodiments described respectively in figures 4 and 5.

[0093] Method 100 includes a step 102 for determining, for each amplifier, an operating point of the amplifier. This is determined from the respective power levels of the frequency channels of the input signals, and from the weighting coefficients associated respectively with said amplifier (i.e., the weighting coefficients associated with the source 24 to which said amplifier is connected). The operating point corresponds to the aggregate power at the output of the amplifier over the entire considered AF frequency band.

[0094] At the output of step 102, we therefore know the operating point (i.e. the output power) of each amplifier.

[0095] Method 100 then includes a step 103 of determining, for each amplifier, a total intermodulation noise power as a function of the operating point and as a function of the linearity characteristics of the amplifier.

[0096] As previously stated, the linearity characteristics of the amplifier For example, the linearity characteristics of the amplifier are defined by an NPR = f(OBO) curve provided by the amplifier manufacturer. However, it is also possible to obtain the amplifier's linearity characteristics using simulation methods. This simulation can be implemented by modeling the amplifier with a Shimbo model. The amplifier's linearity characteristics can then be defined by a curve of the type C / IM = f(OBO).

[0097] At the output of step 103, the power level at which each amplifier contributes to the intermodulation noise is known, but the spectral distribution of the intermodulation products is not known (the intermodulation products are not uniformly distributed in terms of power). The spectral distribution of the intermodulation products is, however, indicated by the normalized mask determined in step 101.

[0098] Method 100 includes a step 104 for determining, for each amplifier, an "absolute mask" of intermodulation noise power spectral density by weighting the normalized mask (determined in step 101) with the total intermodulation noise power (determined in step 103). An "absolute mask" of intermodulation noise power spectral density is thus determined for each amplifier.

[0099] Thus, at the output of step 104, for each amplifier, we obtain a power spectral density mask of intermodulation noise which is representative of both the spectral distribution and the power levels of the intermodulation products specific to the amplifier.

[0100] The method 100 then includes a step of determining 105, for each source 24, a "radiated mask" of intermodulation noise power spectral density by weighting the absolute mask (determined in step 104) of the amplifier to which the source is connected by the radiation pattern of the source 24.

[0101] Step 105 thus makes it possible to add the spatial dimension, via the radiation pattern. The "radiated mask" thus makes it possible to determine, at a given point on the Earth's surface, for each source 24, a spectral power density of intermodulation noise radiated at that point.

[0102] The method 100 then includes a step of determining 106 a "total radiated mask" of intermodulation noise power spectral density by a power summation of the radiated masks of intermodulation noise power spectral density of the different sources 24. The total radiated mask makes it possible to determine at a given point at the level of the earth's surface, for all the sources 24, a radiated intermodulation noise power spectral density at that point.

[0103] The use of the power sum of radiated masks relies on a simplification that assumes the intermodulation noise between the different sources is uncorrelated, which is not theoretically the case. However, experience shows that this simplification is acceptable because the error introduced in the calculation of the C / IM ratio with this assumption remains relatively small compared to results provided by theoretically exact models. This simplification reduces computation time, allowing for a model of performance in terms of radiated C / IM in a limited time. It should be noted that the higher the number of intermodulation products, the more the intermodulation noise between the different sources is uncorrelated. Method 100 according to the invention is therefore particularly well-suited to antennas capable of forming a large number of beams simultaneously.

[0104] Optionally, a correction value may be applied to the calculated C / IM ratio to account for the error introduced by the approximation related to the power summation of the radiated masks. This correction value may, in particular, be determined based on a frequency channel reuse factor for forming the various desired radio beams. For example, it may be an average reuse rate (corresponding to the average of the reuse rates of the different frequency channels). It has been observed that the higher the average reuse rate, the higher the correction value should be applied to the calculated C / IM ratio to compensate for the approximation related to the power summation of the radiated masks.In another example, the reuse factor can correspond to a difference between the maximum and minimum reuse rates among the different frequency channels. It has been observed that the greater this difference (i.e., the more heterogeneous the reuse rate is for the frequency channels), the higher the correction value should be applied to the calculated C / IM ratio to compensate for the approximation related to the power summation of the radiated masks.

[0105] We then consider a particular frequency channel and a particular geographical area of ​​interest (area served by a beam), and we seek to determine the C / IM ratio radiated in this geographical area of ​​interest for the frequency channel in question. For example, we determine the C / IM ratio radiated at a point corresponding to the center of the geographical area. Alternatively, it is possible to determine a C / IM ratio radiated at several points in the geographical area of ​​interest (for example, according to a grid of the geographical area of ​​interest).

[0106] To this end, the method 100 includes a step 107 for determining the intermodulation noise radiated power for the geographical area of ​​interest and for the frequency channel considered. This determination step 107 is implemented in work by an integration, on the sub-band of frequencies Af corresponding to said frequency channel, of the total radiated mask of spectral density of power of intermodulation noise for the geographical area of ​​interest considered.

[0107] Method 100 then includes a step 108 for determining, for the frequency channel considered, an equivalent isotropic power radiated by the active multibeam antenna 20 (EIRP of the carrier corresponding to the frequency channel). This EIRP can be calculated from the RF power in the carrier's conduit and from the radiation patterns and weighting coefficients.

[0108] Method 100 then includes a step 109 for determining, for the geographical area of ​​interest and for the frequency channel considered, a "C / IM radiated" ratio between the equivalent isotropic radiated power (determined in step 108) and the intermodulation noise radiated power (determined in step 107).

[0109] Finally, method 100 includes a verification step 110 of a predetermined criterion based on the "radiated C / IM" ratio thus determined. This step validates the configuration of the telecommunications satellite's payload 30 in terms of radiated C / IM performance. For example, it is possible to raise an alert (e.g., via the user interface 14) if the radiated C / IM is below a predefined threshold. Such provisions make it possible to verify whether it is necessary to take measures to modify the configuration of the telecommunications satellite's payload 30 so that it can perform its mission effectively. As another example, it is possible to define a Cumulative Distribution Function (CDF) of a radiated C / IM ratio over the entire AF frequency band considered and for the entire coverage area considered.For example, for a point in the coverage area, it is possible to determine which carrier illuminates it and calculate the radiated C / IM ratio for that carrier at the point in question. If the point is illuminated by several carriers, it is possible to calculate an average value, or a worst-case value, for the radiated C / IM ratio at that point. Such a repair function allows, for example, determining what percentage of the coverage area has a radiated C / IM ratio greater than or equal to a predefined threshold.

[0110] The foregoing description clearly illustrates that, through its various features and their advantages, the present invention achieves the stated objectives. In particular, the proposed solution makes it possible to calculate a radiated C / IM ratio within a limited time, notably to allow its use during operational phases, while ensuring a sufficient level of accuracy. The complexity of evaluating the C / IM ratio is linked to the large number of carriers and beams required to carry out the mission of the telecommunications satellite 30. The proposed method is therefore particularly This method is particularly well-suited for evaluating the C / IM ratio in complex payload cases (where other prior art calculation methods are too time-consuming). The proposed method uses a comprehensive and analytical approach that eliminates numerous unit calculations, thus keeping execution time to a minimum.

Claims

Claims

1. Method (100) implemented by a computer (10) for validating a configuration of a payload of a telecommunications satellite (30), said satellite (30) being configured to transmit a signal with an active multi-beam antenna (20) comprising a beam-forming network (25), the beam-forming network (25) being connected to a plurality of sources (24) and adapted to simultaneously form several beams of interest serving geographical areas on the surface of the Earth, the beam-forming network (25) being configured to receive as input, for each beam of interest to be formed, an input signal comprising one or more frequency channels with respective power levels, and to transmit to each source (24) a linear combination of the input signals weighted by weighting coefficients, each source (24) being connected to an amplifier, the method (100) comprises for each amplifier: - a determination (101) of a "normalized mask" of intermodulation noise power spectral density from the frequency channels composing the input signals and the respective power levels of said frequency channels, - a determination (102) of an operating point corresponding to an output power of the amplifier, the operating point being determined as a function of the power levels of the frequency channels of the input signals, and as a function of the weighting coefficients associated with said amplifier, - a determination (103) of a total intermodulation noise power as a function of the operating point and linearity characteristics of the amplifier, - a determination (104) of an “absolute mask” of intermodulation noise power spectral density by weighting the normalized mask with the total intermodulation noise power, the method (100) comprises for each source (24): - a determination (105) of a “radiated mask” of intermodulation noise power spectral density from the absolute intermodulation noise power spectral density mask of the amplifier to which the source (24) is connected, and from a radiation pattern of the source, the method (100) further comprises: - a determination (106) of a "total radiated mask" of intermodulation noise power spectral density by a power summation of the radiated masks of the different sources (24), for at least one frequency channel of interest, and for at least one geographical area of interest: - a determination (107) of an intermodulation noise radiated power by an integration, over a frequency sub-band corresponding to said frequency channel, of the total radiated mask of intermodulation noise power spectral density for the geographical area of interest, - a determination (108), for the frequency channel of interest, of an equivalent isotropic power radiated by the multi-beam active antenna (20),- a determination (109) of a “radiated C / IM” ratio between the equivalent radiated isotropic power and the radiated intermodulation noise power, - a verification (110) of a predetermined criterion as a function of the “radiated C / IM” ratio thus determined.,

2. The method (100) of claim 1 wherein the normalized intermodulation noise power spectral density mask is common to all amplifiers.

3. The method (100) of claim 1 wherein the normalized intermodulation noise power spectral density mask is determined for an amplifier based on weighting coefficients associated with said amplifier.

4. A method (100) according to any one of claims 1 to 3 wherein determining (101) the normalized intermodulation noise power spectral density mask comprises calculating third-order intermodulation products generated by the frequency channels of the input signals.

5. Method (100) according to claim 4 in which the determination (101) of the normalized intermodulation noise power spectral density mask further comprises a calculation of intermodulation products of odd order strictly greater than three generated by the frequency channels of the input signals.

6. Method (100) according to claim 4 in which the determination (101) of the normalized intermodulation noise power spectral density mask comprises an application of a correction value aimed at compensating for intermodulation products of order strictly higher than three not taken into account.

7. Method (100) according to any one of claims 1 to 6 in which the determination (101) of the normalized intermodulation noise power spectral density mask comprises a normalization calculation as a function of the result of an integration, over a frequency band, of the intermodulation noise power spectral density.

8. Method (100) according to any one of claims 1 to 6 wherein the determination (101) of the normalized intermodulation noise power spectral density mask comprises a normalization calculation as a function of the result of an integration, over a frequency band, of the intermodulation noise power spectral density for power values included in a predetermined range of values.

9. Method (100) according to any one of claims 1 to 8 comprising an application of a correction value to the “radiated C / IM” ratio, the correction value being determined as a function of a reuse factor of the frequency channels to form the beams of interest.

10. A method (100) according to any one of claims 8 or 9 wherein the frequency band is one of the bands W, Q, V, Ka, Ku, L, S, C.

11. A computer program product (13) comprising instructions which, when executed by a computer (10), cause the latter to implement the steps of the method (100) according to any one of claims 1 to 10.

12. A computer-readable recording medium (12) comprising ins- instructions which, when executed by a computer, cause the computer to implement the steps of the method (100) according to any one of claims 1 to 10.