EP3759837A1

EP3759837A1 - Method for emitting and receiving a radiofrequency signal in a satellite transmission system, corresponding emitter, characterisation receiver and computer program

Info

Publication number: EP3759837A1
Application number: EP19701373.3A
Authority: EP
Inventors: Olivier Rousset; Cyril Bernier
Original assignee: Teamcast
Current assignee: Enensys Technologies SA
Priority date: 2018-03-01
Filing date: 2019-01-29
Publication date: 2021-01-06
Also published as: US11115070B2; FR3078600B1; FR3078600A1; US20210044311A1; WO2019166168A1

Abstract

The invention concerns a method for receiving a radiofrequency signal, in a system comprising an emitter, a satellite and at least one characterisation receiver, implementing a characterisation phase of the satellite, comprising: transmitting (31) to said emitter, over a first transmission link, at least one emission command of at least one reference signal; receiving (34) said at least one reference signal, emitted by said emitter over a second transmission link via said satellite, termed the received signal; estimating (35) at least one distortion generated by the satellite, from said at least one reference signal; delivering at least one piece of information on compensation of the distortions affecting the received signal; and transmitting (36) to said emitter, over said first transmission link, said at least one piece of distortion compensation information.

Description

Processes for transmitting and receiving a radio frequency signal in a corresponding satellite transmission system, transmitter, characterization receiver and computer program.

1. Field of the invention

The field of the invention is that of satellite transmissions.

More precisely, the invention proposes an adaptive pre-correction technique, making it possible to compensate for at least part of the deformations related to the satellite transponder, in a satellite transmission system.

In particular, such a transmission system comprises a transmitter, a satellite and at least one receiver. At least one receiver of the system is a characterization receiver, making it possible to characterize the deformations related to the satellite transponder.

The invention finds applications in any satellite transmission system, and in particular in broadcasting networks according to the DVB-S, DVB-S2 or DVB-S2X standard (in English "Digital Video Broadcasting - Satellite", in French " digital television broadcasting - satellite "), or other existing or future standards.

In particular, the invention relates to single-carrier communications, implementing a single-carrier transmission by transponder, or multicarrier, implementing a multi-carrier transmission transponder, in point-to-point or point-to-multipoint connection.

For example, single-carrier communications may be used in broadcast-type applications, for head-end distribution, terrestrial transmitters, "live to home" receivers, etc., or in "broadband" type applications, for example of the "IP Trunking" type, "Mobile backhauling", etc.

Multicarrier communications can be used in broadcast-type applications DSNG (Digital Satellite News Gathering), broadband VSAT Telecommunications ", in French" terminal with very small opening "), etc.

2. Prior Art

As presented in particular in Appendix H.7 of the DVB-S2 standard "Digital Video Broadcasting (DVB); Second generation framing structure, channel coding and modulation Systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications; Part 1: DVB-S2 "- ETSI EN 302 307 v1.4.1 (201-07), and illustrated in FIG. 1, the satellite transponders are conventionally characterized by three elements:

a selective input filter IMUX 11, the central frequency of which varies according to the temperature;

a power amplifier 12, for example an traveling wave tube amplifier (TWTA); an OMUX output filter 13, which is generally less selective than the input filter IMUX 11, whose variations of the central frequency as a function of the temperature are small.

The deformations introduced by the IMUX input filter 11 and by the OMUX output filter 13 on the signal crossing the transponder are linear and characterized by amplitude and group time curves (in English "group-delay"). frequency function. Examples of curves illustrating the characteristics of the input and output filters, in terms of gain and group time, are provided in particular in Appendix H.7 of the above-mentioned DVB-S2 standard.

The deformations introduced by the power amplifier 12 on the signal crossing the transponder are non-linear and characterized by an AM / AM curve, representing an output power of the amplifier as a function of an input power, and a AM / PM curve, representing an output phase shift of the amplifier as a function of an input power. Examples of AM / AM and AM / PM curves illustrating the characteristics of the amplifier are also provided in Appendix H.7 of the aforementioned DVB-S2 standard.

Such deformations introduced by the satellite degrade the radiofrequency signal received by the receiver. There is therefore a need for a new transmission technique for characterizing and compensating for, or at least reducing, the deformations introduced by the satellite.

3. Presentation of the invention

In one embodiment, the invention proposes a method for receiving a radiofrequency signal, in a system comprising an emitter, a satellite and at least one receiver, including at least one characterization receiver, implementing a characterization phase. satellite comprising:

transmitting to the transmitter, on a first transmission link between the characterization receiver and the transmitter, at least one transmission command of at least one reference signal, receiving said at least one reference signal transmitted by the transmitter on a second transmission link between the transmitter and the characterization receiver via the satellite to be characterized, said received signal,

estimating at least one deformation generated by the satellite, from said at least one reference signal, delivering at least one compensation information of the deformations affecting the received signal,

transmitting to the transmitter, on said first transmission link, said at least one deformation compensation information.

The proposed solution, according to at least one embodiment, thus makes it possible to automatically determine, at the level of a characterization receiver, during a characterization phase, the characteristics of the satellite transponder in terms of linear and / or nonlinear deformations. . These characteristics are transmitted from the characterization receiver to the transmitter via a first transmission link, via a satellite (which may be the same as the satellite to be characterized or another satellite) or not, so that the transmitter transmits, during of an operating phase, a radio frequency useful signal pre-corrected. In particular, such a first transmission link implements a low-speed transmission, which can be implemented temporarily during the characterization phase.

In this way, the linear and / or nonlinear deformations introduced by the satellite transponder into the radio frequency signal received by the network receivers (receivers implementing the characterization or not), on the second transmission link via satellite, are less partially compensated.

In order to determine the characteristics of the satellite transponder in terms of linear and / or non-linear deformations, the characterization receiver sends the transmitter at least one transmission command of at least one reference signal. Such a reference signal is for example transmitted from the transmitter to the characterization receiver, on the second transmission link via the satellite, in a frame of the physical layer usually used for stuffing or rate adaptation, such as the "Dummy PLFRAME" frame of the DVB-S2 / S2X standard. In this way, the reference signal does not disturb receivers other than the characterization receiver (s).

In another embodiment, the invention relates to a corresponding characterization receptor.

The reception technique according to the invention can therefore be implemented in various ways, in particular in hardware form and / or in software form. In another embodiment, the invention proposes a corresponding transmission method, implementing a satellite characterization phase comprising:

receiving at least one transmission command of at least one reference signal, from said characterization receiver, on a first transmission link between the characterization receiver and the transmitter,

transmitting said at least one reference signal to the characterization receiver on a second transmission link between the transmitter and the characterization receiver via the satellite,

receiving at least one deformation compensation information affecting the signal received by the characterization receiver, from the characterization receiver, on the first transmission link.

Such a method, implemented at a transmitter, is in particular intended to receive at least one transmission command of at least one reference signal and at least one compensation information of the deformations obtained by the reception process of a radio frequency signal described above.

In another embodiment, the invention relates to a corresponding transmitter.

The technique for transmitting a radio frequency signal according to the invention can therefore be implemented in various ways, in particular in hardware form and / or in software form.

For example, at least one step of the transmission or reception technique according to one embodiment of the invention can be implemented:

on a reprogrammable calculation machine (a computer, a processor for example DSP (in English "Digital Signal Processor"), a microcontroller, etc.) executing a program comprising a sequence of instructions,

on a dedicated computing machine (for example a set of logic gates such as an FPGA (English Field Programmable Gate Array) or an ASIC (in English "Application-Specific Integrated Circuit"), or any other hardware module).

In particular, the computer program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other desirable form.

Accordingly, an embodiment of the invention also aims to protect one or more computer programs having instructions adapted to the implementation of the transmission or reception methods as described above when this or these programs are executed by a processor, as well as at least one computer-readable information carrier having instructions from at least one computer program as mentioned above.

An embodiment of the invention also relates to a system comprising an emitter, a satellite and at least one characterization receiver as described above.

4. List of figures

Other features and advantages of the invention will appear more clearly on reading the following description of a particular embodiment, given as a simple illustrative and nonlimiting example, and the appended drawings, among which:

Figure 1, described in relation to the prior art, illustrates the payload of a satellite transponder;

FIG. 2 illustrates an example of a transmission system according to one embodiment of the invention;

FIG. 3 illustrates the main steps implemented for the characterization phase according to one embodiment of the invention;

Figures 4 and 5 show architecture examples for the estimation of linear deformations introduced by the satellite transponder;

Figures 6 and 7 show architecture examples for estimating nonlinear deformations introduced by the satellite transponder;

FIG. 8 illustrates an exemplary transmission chain according to one embodiment of the invention;

FIGS. 9A to 9B illustrate the constellations associated with a reference signal according to one embodiment of the invention;

Figures 10 and 11 respectively show the simplified structure of a characterization receiver and a transmitter according to one embodiment of the invention.

5. Description of embodiments of the invention

5.1 General principle

The invention is placed in the context of satellite transmissions.

Figure 2 illustrates an example of a transmission system in which the invention can be implemented. Such a system comprises a transmitter 21, implementing for example a modulator according to the DVB-S2 standard, DVB-S2X, or another existing or future standard, a satellite 22, and at least one receiver. At least one receiver of the system is a receiver of Characterization 23. The system may also include other receivers not implementing the characterization, known as conventional receivers, in particular individual receivers (also called satellite terminals).

In the context of a point-to-multipoint link, several characterization receivers can be used and distributed over a territory, in order to improve the estimation of the transmission channel.

Two transmission links are defined between the transmitter 21 and the characterization receiver 23:

a first transmission link between the characterization receiver 23 and the transmitter 21, via a satellite or not, used in particular to parameterize the transmitter, implementing for example a low-speed transmission, which can be temporary during the characterization phase , and

a second transmission link between the transmitter 21 and the characterization receiver 23, passing through the satellite 22, used to transmit the DVB-S / S2 / S2X signal for example, implementing for example a radio frequency transmission type "broadcast Or broadband broadband.

For example, the bit rate on the first link is of the order of a few kilobits per second, and the bit rate on the second link is of the order of a few hundred megabits per second. More generally, the bit rate on the first link is less than the bit rate on the second link.

The general principle of the invention is based on the implementation of a phase of characterization of the satellite, during which the characteristics of the satellite transponder, in terms of deformation, are determined, thanks to the emission, on the second link transmission via the satellite, at least one known reference signal of the characterization receiver, and the transmission, on the first transmission link, of these characteristics to the transmitter.

In this way, the transmitter can transmit on the second transmission link passing through the satellite, during an operating phase, a useful radio frequency signal pre-corrected to take into account the characteristics of the satellite transponder (in particular linear and non-linear introduced by the satellite), which a priori makes it possible to improve the reception of the useful signal for all the receivers of the network (receiver (s) of characterization and / or receiver (s) classical (s)).

In other words, the characterization receiver 23 can receive radiofrequency signals transmitted by the transmitter 21 via the transponder 22, ie on the second link of FIG. transmission, for example of the DVB-S / S2 / S2X type. In an advantageous embodiment, but not mandatory, such a characterization receiver has a reception antenna of good quality (for example a large parabola, a universal professional LNB head "Low Noise Block-converter") so as to increase the level of the received signal with respect to the reception noise, as well as to limit the phase noise. It is thus possible to obtain a better characterization of the deformations introduced by the transponder.

The characterization receiver 23 can also exchange information with the transmitter 21 on the first transmission link, for example through an Ethernet / IP type interface. Of course, a communication protocol other than the IP protocol can be used. Indeed, the transmitter 21 and the characterization receiver 23 are generally not on the same geographical site, and may be spaced several hundred kilometers apart. With the first transmission link, the characterization receiver 23 can manage the characterization phase by, for example, asking the transmitter 21 to transmit a reference signal, to reduce or increase the transmission power, and so on. Once the characterization phase is complete, the characterization receiver 23 can provide the transmitter 21 with the parameters necessary for precorrecting the transponder, always on the first transmission link. Then, the communication between the characterization receiver and the transmitter can be interrupted. In other words, the characterization receiver can be turned off, or go into standby mode, once the characterization phase is performed. The characterization receiver can therefore function only punctually.

In relation to FIG. 3, the main steps implemented by a characterization receiver and an emitter according to one embodiment of the invention are presented for the characterization of the deformations introduced by the satellite transponder.

By taking up the transmission system illustrated in FIG. 2, the characterization receiver 23 transmits (31) to the transmitter 21, on the first low speed transmission link, at least one transmission command of at least one reference signal. .

Optionally, said at least one transmission command (or another transmission command) also carries at least one transmission power information of said at least one reference signal. In particular, the transmission power of a first reference signal, used to estimate the linear deformations introduced by the satellite, can be decreased during the characterization phase, in order to avoid being disturbed by the saturations of the satellite. amplifier, then increased during the operation phase. In other words, the characterization receiver 23 requests the transmitter 21, in particular the modulator of the transmitter 21, to transmit at least one reference signal, possibly by reducing the transmission power in order to avoid that the reference signal is disturbed by the saturation of the satellite amplifier.

According to yet another embodiment, the transmission control (or another transmission command) also carries at least one transmission time indicator of said at least one reference signal. Such an indicator is used in particular to indicate whether a reference signal, used to estimate the deformations introduced by the satellite, must be emitted by the transmitter, and at what frequency (for example punctually or regularly).

The transmitter 21 receives (32) said at least one transmission command of at least one reference signal coming from the characterization receiver 23.

The transmitter 21 then transmits (33) said at least one reference signal on the second transmission link passing through the satellite 22. For example, such a reference signal is transmitted in a physical layer frame usually used for the stuffing or transmission. rate adaptation, such as the "Dummy PLFrame" frame according to the DVB-S2 standard.

The characterization receiver 23 receives (34) said at least one reference signal emitted by the transmitter on the second transmission link passing through the satellite 22, said received signal.

The characterization receiver estimates (35) at least one deformation generated by the satellite, from said at least one reference signal, delivering at least one deformation compensation information affecting the received signal. Such an estimate uses, for example:

the estimate 351 of at least one deformation generated by the input filter and / or the satellite output filter (defL), from a reference signal from said at least one reference signal, said first signal reference, delivering at least one compensation information of the linear deformations affecting the received signal,

the estimate 352 of at least one deformation generated by the amplifier of the satellite defNL, from a reference signal among said at least one reference signal, said second reference signal, delivering at least one compensation information of the non-linear deformations affecting the received signal.

The characterization receiver 23 transmits (36) to the transmitter 21, on the first transmission link, said at least one deformation compensation information.

Such a transmission 36 implements for example: the transmission 361 of said at least one compensation information of the linear deformations, and

the transmission 362 of said at least one compensation information of nonlinear deformations.

For example, said at least one linear strain compensation information comprises a set of complex coefficients representing a precorrection filter of a modulator of the transmitter 21, or a curve representing the response of the precorrection filter in the frequency domain, in amplitude and in phase (group time).

Said at least one non-linear strain compensation information comprises at least one curve, or polynomial representative of said curve, of an AM / AM curve representing an amplifier output power as a function of the input power and a AM / PM curve representing an output phase shift of the amplifier as a function of the input power. Optionally, it also comprises at least one curve, or a polynomial representative of said curve, representing the memory effect of the amplifier, i.e. at least one curve related to the memory effect on the transmission signal.

The transmitter 21 receives (37) therefore at least one compensation information of the deformations affecting the signal received by the characterization receiver, from the characterization receiver 23, on the first transmission link.

Such a reception 37 implements, for example:

the reception 371 of at least one compensation information of the linear deformations generated by the input filter and / or the output filter of the satellite,

the reception 372 of at least one compensation information of the non-linear deformations generated by the amplifier of the satellite.

Note that the estimates of the linear deformations 351 and the nonlinear deformations 352 can be implemented during the same step, on the basis of the same reference signal. In this case, we consider a single reference signal, which may possibly be issued several times. Alternatively, estimates of linear deformations 351 and nonlinear deformations 352 may be implemented in two distinct steps, implemented simultaneously or one after the other, regardless of the order.

Likewise, the transmissions (or receptions) of at least one compensation information of the linear deformations 361 (respectively 371) and the nonlinear deformations 362 (respectively 372) can be implemented during the same step or in two separate stages, implemented simultaneously or one after the other, regardless of the order. In addition, it is noted that the transmission (or reception) of at least one compensation information of the linear deformations 361 (respectively 371) can be implemented after the estimation of the linear deformations 351, but before the estimation of the nonlinear deformations 352.

As a variant, the transmission (or reception) of at least one compensation information of the nonlinear deformations 362 (or 372) can be implemented after the estimation of the nonlinear deformations 352, but before the estimation of the deformations. linear 351.

Of course, according to the embodiment considered, only the linear deformations, or only the nonlinear deformations, can be estimated by the characterization receiver 23 and transmitted to the transmitter 21.

On receipt of the compensation information of the linear deformations 371 and / or nonlinear 372, the transmitter 21 can load this information into the corresponding module of its modulator (linear strain precorrection module or precorrection module of the nonlinear deformations, as detailed below).

The transmitter 21 and the characterization receiver 23 then enter an operating phase, during which the transmitter 21 can transmit a useful signal, precorrected from said at least one deformation compensation information, to the receivers. of the network, comprising at least the characterization receiver 23, via the satellite 22.

The operating phase continues as long as the characterization receiver 23 does not send to the transmission control transmitter 21 at least one reference signal. The characterization phase is again implemented when the transmitter 21 receives a transmission command of at least one reference signal.

5.2 Example of characterization of linear deformations

An example of implementation of the estimate 351 of at least one deformation generated by the input filter IMUX and / or the output filter OMUX of the satellite (defL) is presented below, from a first reference signal. For example, such an estimate implements an adaptive equalization of the received signal. Several iterations can therefore be implemented to estimate the linear deformations introduced by the satellite. Such an equalization makes it possible in particular to determine the characteristics of a precorrection filter implemented in a module for precorrecting the linear deformations of the transmitter 21.

Indeed, the linear deformations related to the IMUX input and / or OMUX output filters of the transponder can be corrected by a finite impulse response filter implemented. in the modulator of the transmitter 21, for example after the shaping filter (for example of the Nyquist filter type). According to an advantageous embodiment, such a precorrection filter has complex coefficients, in order to correct both the amplitude and the phase (and therefore the group time). For example, the coefficients of such a precorrection filter can be obtained by copying the coefficients of the adaptive equalizer implemented in the characterization receiver 23, once the signal is equalized. According to at least one embodiment, it is therefore sought to implement a powerful and stable equalizer.

In the following, with reference to FIGS. 4 and 5, different equalization techniques for estimating linear deformations are presented.

With reference to FIGS. 4 and 5, there are:

U (n) the first reference signal emitted by the transmitter (transmitted following reception of the transmission command of at least one reference signal coming from the characterization receiver),

U '(n) the first reference signal generated in the characterization receiver,

V (n) the output signal of the satellite transponder 41, 51, V (n) = U (ri) * H (n), with H corresponding to the time response of the transponder 41, 51,

Y (ri) = V (ri) + b (ri) the signal received by the characterization receiver, with b (ri) corresponding to the Gaussian reception noise

X (n) the output signal of the adaptive equalizer 42, 52, X (n) = W (n) * Y (ri), with W (n) corresponding to the coefficients of the adaptive equalizer 42, 52,

E (n) the error signal, E (ri) = U '(ri) - X (n).

If the correction is ideal, then the output signal of the adaptive equalizer X (n) is equal to the first reference signal emitted by the transmitter U (n), since the transponder / equalizer assembly is transparent (the goal being to minimize the distortions of the original signal at the output of the equalizer).

These techniques for estimating linear deformations are based on a first reference signal known to the characterization receiver and transmitted by the transmitter upon receipt of a transmission command of at least one reference signal coming from the receiver of characterization. In particular, such a first reference signal can be transmitted in a physical layer frame conventionally used for stuffing or rate adaptation, such as the "Dummy PLFRAME" frame according to the DVB-S2 / S2X standard. Thus the other receivers of the network are not disturbed by the reference signal. They remain hooked on the signal coming from the transmitter even if they do not need to demodulate this reference signal. According to a first example, illustrated in FIG. 4, the equalization implements an LMS ("Least Mean Square") type algorithm, also called a stochastic gradient algorithm.

In this case, the coefficients of the adaptive equalizer are obtained from the following recursive algorithm:

W (n + 1) = W (n) + mE (n). Y ^* (n)

with m corresponding to the adaptation step.

Note that the larger this adaptation step, the faster the algorithm converges. However, the residual noise may be larger. For example, we choose m = 0.005.

To facilitate convergence, the initial conditions chosen are, for example:

W _N / ₂ = 1 for N corresponding to the length of the equalizer 42,

Wi = 0 otherwise.

The LMS algorithm offers a good compromise in terms of computing complexity, stability, and convergence time.

An alternative to the LMS algorithm is NLMS, that is, the standard version of the LMS algorithm.

According to a second example, also illustrated in FIG. 4, the equalization implements an RLS ("Recursive Least Squares") algorithm, also called a recursive least squares algorithm.

The principle of the RLS algorithm is the same as that of the LMS algorithm. However, the calculation of the coefficients is based on a matrix calculation depending on the length of the equalizer 42, i.e., the length of the precorrection filter.

W (n + 1) = W (n) + K (n). In)

with: K (n) = P (ri). Y (n) / (J + Y ^T (n), P (n), Y (n))

P (n + 1) = ¹ P (n) - Z ^-1 K (n) Y ^T (n). P (n)

with l corresponding to the forgetting parameter, less than 1.

In this case, the smaller this forgetting parameter, the faster the algorithm converges. However, the residual noise may be larger. For example, we choose l = 0.996.

According to a third example, illustrated in FIG. 5, the equalization implements an equalization in the frequency domain FDE (Frequency Domain Equalizer). The objective of this algorithm is to find the amplitude and phase response of the precorrection filter in the frequency domain. For this, the reference signal U '(n) generated in the characterization receiver is transposed into frequency by means of a time / frequency transformation of FFT 53 type. The signal X (n) at the output of the adaptive equalizer 52 is also transposed into frequency by means of a time / frequency transformation of the FFT 54 type. It is then divided by a reference frequency mask 55, obtained from the reference signal U '(n) transposed into frequency, in order to estimate the frequency deformations . The estimated frequency distortions are then transposed in the time domain, thanks to a frequency / time transformation of IFFT type 53, so as to find the coefficients W (n) of the adaptive equalizer 52, and consequently the coefficients of the precorrection filter. .

For example, the coefficients of the adaptive equalizer are obtained from the following recursive algorithm:

W (n + 1) = W (n) + a. In )

with a corresponding to a forgetting parameter used to suppress Gaussian noise.

The equalization techniques presented above, which can be implemented for the estimation 351 of at least one deformation generated by the input filter and / or the output filter of the satellite, make it possible to directly obtain the complex coefficients precorrection filter. Alternatively, it is possible to obtain at the output of the equalizer a curve representing the response of the precorrection filter or other information representative of the precorrection filter.

The linear strain compensation information or information affecting the received signal thus obtained can then be transmitted to the linear strain precorrection module (pre-correction filter) of the transmitter.

5.3 Example of characterization of nonlinear deformations

An example of implementation of the estimate 352 of at least one deformation generated by the satellite amplifier (defNL) from a second reference signal is presented below. For example, such an estimate implements a modeling of the amplifier from the second reference signal. Such a modeling makes it possible in particular to determine the AM / AM and AM / PM curves characterizing the amplifier, in particular the tube amplifiers, and consequently, the distortion or deformation to be made to the constellation of symbols in the modulator in view of these curves. . For example, the document "DVB-S2 Modem Algorithms Design and Performance over Typical Satellite Channels" (E. Casini et al., INTERNATIONAL JOURNAL OF SATELLITE COMMU NICATIONS AN DN ETWORKING 2004; 22: 281-318) proposes a technique for pre-compensation of nonlinear deformations.

Thus, the nonlinear deformations related to the power amplifier of the satellite transponder can be pre-corrected by deformation of the constellation in the modulator of the transmitter, before the shaping filter.

If one considers a traveling-wave tube amplifier, there is no memory effect on the target frequency band. On the other hand, the modulation filter of the modulator as well as the IMUX input and OMUX output filters of the satellite transponder bring a memory effect. According to at least one embodiment, the invention makes it possible to parameterize the algorithms used for estimating non-linear deformations, so as to be able to characterize the transponders with or without memory effect.

In the following, with reference to FIGS. 6 and 7, various techniques for estimating nonlinear deformations are presented.

We notice :

U (n) the second reference signal emitted by the transmitter (transmitted following reception of the transmission command of at least one reference signal coming from the characterization receiver),

U '(n) the second reference signal generated in the characterization receiver, V (n) the output signal of the satellite transponder 61, 71, V (n) = U (ri) * H (n), with corresponding H the time response of the transponder 61, 71,

Y (n) the signal received by the characterization receiver, Y (ri) = V (ri) + b (n), with b (n) corresponding to the Gaussian reception noise.

For example, such techniques are based on a mathematical model modeling the behavior of the amplifier to be pre-corrected, here a polynomial model with a memory effect, and on an iterative algorithm that estimates the polynomial coefficients of the polynomial model:

where: k G. K corresponds to the order of the polynomial (for example equal to 5, or more generally of the order of 3 to 7), and

l G L is the depth of the memory effect (if 1 = 0, there is no memory effect).

These techniques for estimating nonlinear deformations are based on a second reference signal known to the characterization receiver and transmitted by the transmitter on reception. a command for transmitting at least one reference signal from the characterization receiver. In particular, such a second reference signal can be transmitted in a physical layer frame conventionally used for stuffing or rate adaptation, such as the "Dummy PLFRAME" frame according to the DVB-S2 / S2X standard, modified to have a factor of peak adapted to the modulation in progress, without however disturbing the synchronization of the network receivers other than the characterization receiver (s).

Such a modified frame can be inserted into the modulator before the shaping filter. The modulated data associated with this modified frame, and therefore with the second reference signal, deformed by the transponder amplifier and the noise, are received by the characterization receiver, demodulated through the shaping filter, and compared to the second one. known reference signal of the characterization receiver. Thus, the characterization receiver compares the emitted modified "Dummy PLFRAME" frame with a modified "Dummy PLFRAME" frame known to the characterization receiver.

According to a first example illustrated in FIG. 6, implementing a nonlinear deformation characterization algorithm based on the trend curve, the samples of the second reference signal are classified by increasing amplitude value (corresponding to the input power AMi of the amplifier), with the corresponding samples of the received signal, in the classification block 62. This gives a set of points (Us, Ys) illustrating the power of the received signal as a function of the power of the transmitted signal. A polynomial interpolation is implemented in the interpolation block 63. Thus AM / AM and AM / PM graphs are obtained. Then, in block 64, the polynomial coefficients of the curves closest to the points of the AM / AM and AM / PM graphs are determined. The output power values AMo and PM0 of the amplifier are output as a function of the input power AMi.

One advantage of such an algorithm based on the trend curve is that the calculation time is short.

According to a second example illustrated in FIG. 7, implementing a nonlinear strain characterization algorithm based on the Volterra model, an NL 72 iterative algorithm is used, in order to estimate in block 73 the coefficients of the polynomial of the polynomial model. The output power values AMo and PM0 of the amplifier are output as a function of the input power AMi.

For example, the calculation of the polynomial coefficients is based on the article "A Generalized Memory Polynomial Model for Digital Predistorsion of RF Power Amplifier" (IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 54, NO. 10, 10 / 2006J.

An interest of an algorithm based on the Volterra model is to be able to take into account the memory effects. Indeed, such an algorithm offers the possibility of identifying the AM / AM and AM / PM curves as well as the parameters of the memory effect.

The nonlinear strain characterization techniques presented above, which can be used for the estimation 352 of at least one deformation generated by the satellite amplifier, make it possible to directly obtain the coefficients of the polynomials describing the curves AM / AM and AM / PM. Alternatively, it is possible to obtain the AM / AM and AM / PM curves or other information representative of these curves.

The nonlinear deformation compensation information or information affecting the received signal thus obtained can then be transmitted to the module for precorrecting the non-linear deformations of the transmitter.

5.4 Example of a transmission chain

An exemplary implementation of the invention in a transmission system according to the DVB-S2 standard is described below. It is recalled that this is a simple example and that the invention finds applications in any satellite transmission system, regardless of the standard considered.

FIG. 8 illustrates the main blocks of a transmission chain according to the DVB-S2 standard according to a particular embodiment of the invention. Such a transmission chain comprises a transmitter 81, a satellite transponder 82, and a characterization receiver 83.

The transmitter 81 complies with the DVB-S2 standard as described in the aforementioned document ETSI EN 302 307-1 VI.4.1. It includes the modules needed to build the physical layer of a DVB-S2 link. The transmitter comprises, for example, a stream matching module 811, an FEC coding module 812, and a modulator 813. The modulator 813 comprises a mapping module 8131, a framing module 8132 "PL Framing", a nonlinear strain precorrection module 8133, a modulation module 8134, and a precorrection module for linear deformations 8135.

In particular, the "PL Framing" framing module 8132 generates "PLFRAME" frames comprising a "PLHEADER" header and a useful part. This module can in particular insert stuffing or rate adaptation frames, called "Dummy PLFRAME", between the useful frames, before scrambling at the level of the physical layer ("scrambling").

The modulation module 8134 generates a radio frequency signal DVB-S2 intended to be transmitted to the characterization receiver via the satellite.

Apart from the precorrection modules of the 8133 and linear 8135 nonlinear deformations, the other modules are conventional and in particular described in the aforementioned standard.

The satellite transponder 82 comprises for example an IMUX input filter, an HPA power amplifier, an OM UX output filter. For example, the satellite transponder operates in Ku band and has a bandwidth of 36MHz.

The characterization receiver 83 comprises a radiofrequency signal receiving module 831, a demodulator 832, a DVB decoding module S2 833 and a DVB adaptation module S2 834.

The receiving module 831 notably implements an analog-digital conversion of the received radio frequency signal, and makes it possible to synchronize with the received signal.

The demodulator 832 comprises a linear deformation estimation module 8321 (for example an equalizer), a symbol rate synchronization module 8322, a frame synchronization module 8323, a descrambling module 8324, a deformation estimation module. non-linear 8325 (characterization of non-linear deformations) and a demapping module 8326.

Apart from the 8321 and non-linear 8325 linear strain estimation modules, the other modules are conventional.

As illustrated in FIG. 8, the characterization elements thus comprise:

on the one hand a linear strain precorrection module 8135, for example taking the form of a precorrection filter, at the output of the transmitter 81, and an estimation module for the linear deformations 8321, taking for example the form of an equalizer, at the input of the characterization receiver 83;

on the other hand a non-linear strain precorrection module 8133, for example implementing a deformation of the symbol constellations, upstream of the shaping filter in the transmitter 81, and a nonlinear deformation estimation module 8325, downstream of the shaping filter in the characterization receiver 83.

The linear strain estimation module 8321 estimates at least one linear strain generated by the input filter and / or the output filter of the satellite 82, from a first reference signal, and delivers at least one piece of information. compensation of the linear deformations affecting the received signal (for example of the type of the precorrection filter), transmitted to the linear strain precorrection module 8135. The nonlinear strain estimation module 8325 estimates at least one nonlinear deformation generated by the satellite amplifier 82, from a second reference signal, and delivers at least one compensation information for the nonlinear deformations affecting the received signal (for example of type coefficients of the polynomial model modeling the behavior of the amplifier), transmitted to the precorrection module of the nonlinear deformations 8133.

For example, the first reference signal is transmitted from the transmitter to the characterization receiver via the satellite in a conventional "Dummy PLFRAME" frame according to the DVB-S2 standard, comprising a PLHeader header and 36 unmodulated carrier slots (I = 1 / V2, Q = 1 / V2). To do this, the characterization receiver 83 transmits beforehand to the transmitter 81, on the first transmission link, a transmission command of at least one conventional "Dummy PLFRAM E" frame. The characterization receiver 83 thus knows the first reference signal.

The second reference signal may be transmitted in a proprietary "Dummy PLFRAME" type frame, i.e. having the same "PLHeader" header and the same length as a conventional "Dummy PLFRAME" frame. Such a modified "Dummy PLFRAME" frame comprises a header "PLHeader" and a plurality of slots ("slots") each comprising a set of symbols forming the second reference signal. In this way, conventional receivers (i.e. other than characterization receivers) are not disturbed by the reception of this proprietary frame. In particular, the set of symbols comprises the symbols of a constellation associated with a modulation, with different power levels (i.e. amplitude) assigned to each symbol.

To do this, the characterization receiver 83 transmits beforehand to the transmitter 81, on the first transmission link, a transmission command of at least one modified "Dummy PLFRAME" frame. In particular, the characterization receiver 83 transmits to the transmitter 81 the contents of the "Dummy PLFRAME" frame, i.e. the IQ samples, which the modulator must insert in the DVB-S2 stream. The characterization receiver 83 thus knows the second reference signal. The "Framing" 8132 framing module can then insert the modified "Dummy PLFRAME" frame between the useful frames, according to the chosen insertion frequency.

For example, in the context of the DVB-S2 standard, the modified "Dummy PLFRAME" frame includes a "PLHeader" header and 36 slots each comprising 90 symbols of a modulation, QPSK for example, the power of each symbol varying around a nominal power. For example, the 36 intervals carry the symbols defined by the couples (/, Q) such that / = a / V 2, Q = a / V 2, with a varying between 0.5 and 2.

In this case, the characterization receiver 83 transmits to the transmitter 81 the samples IQ such that I = a / V2, Q = a / V2, with a varying between 0.5 and 2, that the modulator must insert into the stream. DVB-S2.

According to a first example, the characterization receiver 83 always transmits the same frame of samples IQ, with a fixed. As a variant, the characterization receiver 83 transmits to the transmitter 81 a frame of IQ samples adapted during the iterations, in order to refine the characterization.

It should be noted that the use of physical layer frames ("dummy frames") for the transmission of the reference signal or signals makes it possible in particular to ensure continuity of service.

As a variant, it is possible to modify the header of the physical layer of stuffing frames for the transmission of the reference signal or signals.

FIGS. 9A to 9B illustrate the constellation associated with the "Dummy PLFRAME" frame modified for QPSK modulation. Of course, other modulations, and thus other constellations, can be used, varying the power (i.e. the amplitude) of the symbols of the constellation.

In particular, FIG. 9A illustrates the constellation at the output of the modulator. It can be seen in this figure that the four symbols of the QPSK are emitted with a difference in power levels, varying between a minimum power parameter Pmin and a maximum power parameter Pmax. According to the example illustrated in FIG. 9A, Pmin is equal to -9 dB and P max is equal to +5 dB. These values Pmin and Pmax depend, for example, on the IBO (in English "Input Back Off"), the input power with respect to the compression point of the amplifierj supplied by the user.

FIG. 9B illustrates the constellation deformed by an amplifier without memory effect, at the output of the amplifier.

Thus, according to a particular embodiment, three different types of commands are defined at the level of the characterization receiver 83, transmitted to the transmitter 81 on the first transmission link:

at least one control command, comprising a transmission command of the reference signal or signals, for starting the characterization phase, updating the precorrections, stopping the transmission of the reference signal;

at least one compensation information for linear deformations, for example in the form of a linear precorrection file based on the coefficients of a complex filter;

at least one compensation information for non-linear deformations, for example in the form of a file comprising tables for non-linear precorrections.

In particular, the control commands comprise two commands defined for both the transmitter and the characterization receiver, in order to insert at least one specific frame ("Dummy PLFrame" modified) between the useful frames:

Validation of the insertion of the specific frame:

o 0: no insertion,

o 1: punctual insertion,

o 2: regular insertion according to the time limit below;

Insertion delay in steps of 1ms (varies from 1 to 60000)

In addition, the characterization receiver provides the transmitter with the content of the specific frame that the modulator must insert in the radiofrequency signal passing over the satellite transmission path (DVB-S2 stream for example).

For example, the characterization receiver provides the transmitter with a file comprising the IQ samples to be inserted directly into a physical layer type of padding frame (for example of the modified Dummy PLFrame type), before the nonlinear precorrections and the filter of formatting.

Said at least one compensation information of the linear deformations is for example transmitted in the form of a file comprising the coefficients to be used in the filter, composed of two columns: a column containing the real part of the coefficients and a column containing the imaginary part coefficients.

Said at least one compensation information for non-linear deformations is for example transmitted in the form of a file comprising tables to be used for the non-linear precorrections, including the AM / AM and AM / PM curves in the form of a polynomial.

5.5 Devices

Finally, with reference to FIGS. 10 and 11, the simplified structure of a characterization receiver and a transmitter according to one embodiment of the invention is presented.

As illustrated in FIG. 10, a characterization receiver according to one embodiment of the invention comprises a memory 101 (comprising, for example, a buffer memory) and a processing unit 102 (equipped for example with at least one processor, FPGA, or DSP), driven or pre-programmed by an application or a computer program 103 implementing the method of receiving a transmitted radio frequency signal via a satellite according to one embodiment of the invention.

At initialization, the code instructions of the computer program 103 are for example loaded into a RAM before being executed by the processing unit 102. The processing unit 102 implements the steps of the method of reception described above, according to the instructions of the computer program 103, to characterize the linear and / or non-linear deformations of the satellite transponder.

To do this, according to one embodiment, the processing unit 102 is configured to:

transmitting to the transmitter, on a first transmission link, at least one transmission command of at least one reference signal,

receiving the reference signal (s) transmitted by the transmitter on a second transmission link via the satellite, said signal received,

estimating at least one deformation generated by the satellite, from the reference signal or signals, delivering at least one compensation information of the linear and / or non-linear deformations affecting the received signal,

transmitting to the transmitter, on the first transmission link, said at least one compensation information for linear and / or non-linear deformations.

As illustrated in FIG. 11, a transmitter according to a particular embodiment of the invention comprises a memory 111 (comprising, for example, a buffer memory) and a processing unit 112 (equipped for example with at least one processor, FPGA, or DSP), driven or pre-programmed by an application or a computer program 113 implementing the transmission method according to one embodiment of the invention.

At initialization, the code instructions of the computer program 113 are for example loaded into a RAM memory before being executed by the processing unit 112. The processing unit 112 receives as input a transmission command at least one reference signal. The processing unit 112 implements the steps of the transmission method described above, according to the instructions of the computer program 113, to compensate at least in part the linear and / or non-linear deformations introduced by the satellite transponder.

To do this, according to one embodiment, the processing unit 112 is configured to: receiving at least one transmission command of at least one reference signal, from the characterization receiver, on a first transmission link, transmitting the reference signal or signals to the characterization receiver, on a second link transmission via the satellite,

receiving at least one compensation information of the deformations affecting the signal received by the characterization receiver, from the characterization receiver, on the first transmission link.

Claims

A method for receiving a radiofrequency signal in a system comprising an emitter (21), a satellite (22) and at least one characterization receiver (23),

said method implementing a satellite characterization phase comprising:

transmitting (31) to said transmitter, on a first transmission link between said characterization receiver and said transmitter, at least one transmission command of at least one reference signal,

receiving (34) said at least one reference signal transmitted by said transmitter on a second transmission link between said transmitter and said characterization receiver via said satellite, said received signal,

estimating (35) at least one deformation generated by the satellite, from said at least one reference signal, delivering at least one compensation information of the deformations affecting the received signal,

transmitting (36) to said transmitter on said first transmission link said at least one deformation compensation information.

2. Reception method according to claim 1, characterized in that said estimate (35) implements:

estimating (351) at least one deformation generated by the input filter and / or the output filter of the satellite, from a reference signal among said at least one reference signal, said first signal of reference, delivering at least one compensation information of the linear deformations affecting the received signal,

estimating (352) at least one deformation generated by the satellite amplifier, from a reference signal from said at least one reference signal, said second reference signal, delivering at least one compensation information non-linear deformations affecting the received signal,

and in that said transmission (36) of said at least one deformation compensation information implements:

transmitting (361) said at least one compensation information of the linear deformations, and

transmitting (362) said at least one compensation information for non-linear deformations.

3. Reception method according to claim 2, characterized in that said at least one compensation information of the linear deformations comprises a set of coefficients. complexes representing a precorrection filter of a modulator of said emitter, or a curve representing the amplitude and phase response of said precorrection filter in the frequency domain.

4. Reception method according to any one of claims 2 and 3, characterized in that said at least one compensation information of the nonlinear deformations comprises at least one curve, or a polynomial representative of said curve, among a curve AM / AM representing an output power of the amplifier as a function of the input power, an AM / PM curve representing an output phase shift of the amplifier as a function of the input power, and a curve representing the memory effect of the amplifier.

5. Reception method according to any one of claims 2 to 4, characterized in that said second reference signal is said first reference signal.

A method for transmitting a radiofrequency signal in a system comprising an emitter (21), a satellite (22) and at least one characterization receiver (23),

said method implementing a satellite characterization phase comprising:

receiving (32) at least one transmission command of at least one reference signal, from said characterization receiver, on a first transmission link between said characterization receiver and said transmitter,

transmitting (33) said at least one reference signal, to said characterization receiver, on a second transmission link between said transmitter and said characterization receiver via said satellite,

receiving (37) at least one deformation compensation information affecting the signal received by the characterization receiver, from said characterization receiver, on said first transmission link.

7. Transmission method according to claim 6, characterized in that said reception (37) of at least one deformation compensation information implements:

receiving (371) at least one compensation information of the linear deformations generated by the input filter and / or the output filter of the satellite,

receiving (372) at least one compensation information of the non-linear deformations generated by the satellite amplifier.

8. Transmission process according to any one of claims 6 and 7, characterized in that it comprises an operating phase comprising:

precorrecting a useful signal, from said at least one deformation compensation information.

9. A reception or transmission method according to any one of claims 1 to 8, characterized in that said reference signal is transmitted in a physical layer padding frame.

Receiving or transmitting method according to any one of Claims 1 to 9, characterized in that the said reference signal is transmitted in a "Dummy PLFRAME" type frame according to the DVB-S2 or DVB-S2X standard.

Receiving or transmitting method according to claim 10, characterized in that said "Dummy PLFRAME" type frame comprises a "PLHeader" header and a plurality of intervals each comprising a set of symbols forming said reference signal, and in that said set of symbols comprises the symbols of a modulation with different power levels.

12. The receiving or transmitting method according to any one of claims 1 to 11, characterized in that said at least one transmission command also carries at least one transmission time indicator of said at least one reference signal.

Receiving or transmitting method according to any one of claims 1 to 12, characterized in that said at least one deformation compensation information and / or said transmission command of at least one reference signal are transmitted from said characterization receiver to said transmitter over an IP link.

14. A method of receiving or transmitting according to any one of claims 1 to 13, characterized in that the transmission on the first transmission link has a lower rate than the transmission on the second transmission link.

15. A receiver for characterizing a radiofrequency signal, comprising at least one processor operatively coupled to a memory, and configured to:

transmitting to a transmitter, on a first transmission link between said characterization receiver and said transmitter, at least one transmission command of at least one reference signal,

receiving said at least one reference signal transmitted by said transmitter on a second transmission link between said transmitter and said characterization receiver via a satellite, said received signal,

estimating at least one deformation generated by said satellite, from said at least one reference signal, delivering at least one compensation information of the deformations affecting the received signal, transmitting to said transmitter, on said first transmission link, said at least one deformation compensation information.

16. Transmitter of a radiofrequency signal comprising at least one processor operatively coupled to a memory, and configured to:

receiving at least one transmission command of at least one reference signal, coming from a characterization receiver, on a first transmission link between said characterization receiver and said transmitter,

transmitting said at least one reference signal, to said characterization receiver, on a second transmission link between said transmitter and said characterization receiver via a satellite,

receiving at least one compensation information of the deformations affecting the signal received by the characterization receiver, from said characterization receiver, on said first transmission link.

17. Computer program comprising instructions for implementing a method according to any one of claims 1 to 14 when the program is executed by a processor.