Digital homodyne demodulator and method for the synchronous demodulation of a plurality of multiplexed carriers

Abstract

The invention relates to a digital homodyne demodulator (28) for the synchronous demodulation of a plurality of multiplexed carriers, the demodulator (28) comprising a signal mixer module (30) provided with a plurality of mixers (32); a general digital oscillator configured to generate a shared general periodic synchronization signal (LOg[n]), the shared general periodic synchronization signal (LOg[n]) having a general frequency (fg); and a generator (34) of periodic demodulation signals, the generator (34) being configured to generate a plurality of local periodic demodulation signals (LOi[n]) on the basis of the shared general periodic synchronization signal (LOg[n]), each local periodic demodulation signal (LOi[n]) having a distinct frequency whose value is an integer multiple of the general frequency (fg).

Description

DESCRIPTION TITLE: Digital homodyne demodulator and synchronous demodulation method of a plurality of multiplexed carriers Technical field of the invention

[0001] The present invention relates to a digital homodyne demodulator and a method for the synchronous demodulation of a plurality of multiplexed carriers, implemented by such a digital homodyne demodulator. The invention also relates to a radio frequency signal receiver comprising such a digital homodyne demodulator, as well as a positioning system for at least one receiving mobile device, wherein the receiving mobile device is such a radio frequency signal receiver. The technical field of the invention is that of frequency demodulation (or demultiplexing) of a signal composed of a sum of multiplexed carriers, and in particular that of digital homodyne demodulation of such a signal, requiring precise phase synchronization. Prior art

[0002] A flexible and efficient solution for the real-time demodulation of a signal composed of a sum of multiple carriers is to implement a fully digital demodulation architecture. Demodulation involves recovering the phase and amplitude of the received signals. This operation is performed using a digital homodyne demodulator (receiver), which mixes the received incoming signal with local oscillators tuned to different expected frequencies, thus converting the resulting baseband output signals. The incoming digital signal is therefore composed of a sum of several carriers at stable and predefined frequencies, and the digital homodyne demodulator processes this signal and demodulates each frequency independently.For the purposes of this description, "carrier" means either a pure, unmodulated carrier wave (e.g., sinusoidal) or any waveform (e.g., sinusoidal) that is modulated by an input signal for the purpose of carrying information.

[0003] To achieve this, a typical digital homodyne demodulator uses several digital local oscillators and mixers, which operate in "digital local oscillator-mixer" pairs—that is, one "digital local oscillator-mixer" pair to demodulate each given received carrier. Each digital local oscillator generates a periodic local demodulation signal with a distinct frequency that corresponds to an expected demodulation frequency. The mixers are arranged in parallel to allow the parallel demodulation of multiple carriers, with each mixer associated with its respective digital local oscillator and configured to multiply the incoming digital signal with the periodic local demodulation signal generated by that local oscillator.

[0004] However, digital quantization of local oscillators introduces frequency shifts that affect each local digital oscillator differently. The frequency error caused by digital quantization, which accumulates over time, can typically be corrected using a phase-locked loop for each demodulated frequency. Nevertheless, independent frequency correction for each local digital oscillator is likely to lead to phase desynchronization between the different carriers. This is detrimental to the proper functioning of the system, especially when it is intended for applications requiring precise phase synchronization.Indeed, in applications where phase synchronization between frequencies is not critical, an automatic frequency control (AFC) mechanism can effectively mitigate frequency drift for each frequency. However, in applications requiring strict phase synchronization between carriers, a mutual automatic frequency control mechanism cannot fully compensate for the limitations imposed by the finite resolution of local oscillators.

[0005] The implementation of such frequency demultiplexing based on local digital oscillators is known in the prior art. As such, patent documents EP 0289401 A2 and US 4884265 A describe such known frequency demultiplexing solutions. The use of phase-locked loops to compensate for frequency offsets between the transmitter and receiver clocks (or to correct quantization errors) is also known, as evidenced, for example, by the article "Phase-synchronous chain of two multi-carrier lights spaced at 25GHz by cancelling micro-wave phase noise" (Akira Mizutori; Atsushi Kodama; Masafumi Koga; in "2011 International Topical Meeting on Microwave Photonics jointly held with the 2011 Asia-Pacific Microwave Photonics Conference").

[0006] The paper "Multi-Frequency Phase Difference of Arrival for precise localization in narrowband LPWA networks" (Florian Wolf; Vincent Berg; François Dehmas; Valérian Mannoni; Sébastien De Rivaz; in "ICC 2021 - IEEE International Conference on Communications") describes a system requiring phase synchronization between several demodulated carriers. However, a drawback of such a system is that it does not account for certain implementation limitations, such as the quantization error of local oscillators in time-of-flight calculations. This error occurs during the conversion of signals from the intermediate frequency to the baseband, an operation performed in the digital domain. Consequently, such a system, without an additional synchronization mechanism, is affected by frequency drift of the different carriers, induced by the quantization error of the local oscillator. Summary of the invention

[0007] The invention aims to remedy these defects. In particular, its objective is to provide a digital homodyne demodulator capable of demodulating in real time a digital signal composed of a sum of multiple carriers, while completely eliminating the frequency error for each carrier (caused by digital quantization) and offering precise phase synchronization between the different carriers.

[0008] To achieve this goal, the invention relates, according to a first aspect, to a digital homodyne demodulator for the synchronous demodulation of a plurality of multiplexed carriers, the demodulator being configured to receive at input a digital input signal composed of a sum of said plurality of multiplexed carriers and to provide at output a plurality of demodulated output signals, the demodulator comprising a signal mixer module equipped with a plurality of mixers, each mixer being configured to receive on a first input said digital input signal and on a second input a periodic local demodulation signal and being configured to provide on its output, from said digital input signal and said periodic local demodulation signal, one of said output signals obtained by multiplying the digital input signal and the periodic local demodulation signal,the digital homodyne demodulator further comprising a general digital oscillator configured to generate a shared general synchronization periodic signal, said shared general synchronization periodic signal having a general frequency and a general phase, the digital homodyne demodulator further comprising a demodulation periodic signal generator connected on one side to the output of the general digital oscillator and on the other side to the second input of each mixer, the demodulation periodic signal generator being configured to generate each of said demodulation periodic local signals from said shared general synchronization periodic signal, each demodulation periodic local signal having a distinct frequency whose value is an integer multiple of the general frequency, the output signals of the plurality of output signals being phase-synchronized,The periodic demodulation signal generator comprises a multiplier module connected to the output of the general digital oscillator and a direct digital synthesizer connected on one side to the output of the multiplier module and on the other side to the second input of each mixer, the multiplier module being configured to multiply the general phase by an integer multiple, the direct digital synthesizer being configured to generate each local periodic demodulation signal from a distinct phase value obtained by multiplying the general phase by an integer multiple.

[0009] Thanks to such a configuration, in which the digital homodyne demodulator comprises a general digital oscillator and a demodulation periodic signal generator configured to generate each local periodic demodulation signal from the shared general synchronization periodic signal, the quantization error for each carrier is eliminated and does not accumulate over time. Furthermore, synchronous compensation of frequency shifts is achieved by adjusting the frequency of the general digital oscillator. By relying on a single general synchronization source (namely the general digital oscillator), such a digital homodyne demodulator according to the invention thus makes it possible to maintain phase alignment between the carriers and to simplify the process of compensating for frequency drifts.Such a digital homodyne demodulator according to the invention therefore offers precise phase synchronization between the different carriers, and is particularly suited to applications requiring strict phase synchronization between carriers, such as, for example, communication systems based on frequency division multiplexing or geolocation systems based on multi-carrier phase measurements.

[0010] Furthermore, the presence in the demodulation periodic signal generator of a multiplier module and a direct digital synthesizer configured in this way eliminates the generation of harmonics associated with physical signal mixing and frequency multiplication by injection. More precisely, since the generation of periodic demodulation signals is purely digital in the demodulator according to the invention, there is no physical signal mixing or frequency multiplication by injection, and the demodulator according to the invention does not create harmonics through the generation process itself. This advantageously avoids the complex management of unwanted harmonics related, for example, to destructive interference, such harmonics being generated in prior art injection systems configured to inject out-of-phase physical signals into a clock multiplier.When the digital homodyne demodulator is implemented within a programmable logic circuit, such as a field-programmable gate array (FPGA), the direct digital synthesizer includes a lookup table that stores samples of a sine wave. The phases generated by multiplying the overall phase by integers represent the instantaneous phases of the sine waves, which serve as input to the synthesizer. The lookup table provides the phase-to-amplitude conversion that produces each local periodic demodulation signal.

[0011] In another variant, the digital homodyne demodulator further includes a plurality of filter modules, the number of filter modules being equal to the number of mixers, each filter module being connected to the output of one of the mixers. This makes it possible to suppress noise and interference from adjacent carriers, thus ensuring a clear separation between the demodulated signals.

[0012] Preferably, each filtering module is an infinite impulse response filter.

[0013] According to a second aspect, the invention relates to a radio frequency signal receiver, comprising a radio frequency signal receiving antenna, an analog signal processing module, an analog-to-digital converter, and a digital homodyne demodulator for the synchronous demodulation of a plurality of multiplexed carriers, the analog signal processing module being connected between the radio frequency signal receiving antenna and the analog-to-digital converter, the analog-to-digital converter being connected between the analog signal processing module and the digital homodyne demodulator, the digital homodyne demodulator being as described above, the radio frequency signal suitable for reception by the antenna corresponding to said digital input signal composed of a sum of said plurality of multiplexed carriers.

[0014] According to a third aspect, the invention relates to a positioning system for at least one receiving mobile, the system comprising, in addition to the mobile, at least two fixed transmitting bases, each transmitting base being configured to emit radio frequency signals, the transmitting bases being synchronized with each other to emit their respective signals, the receiving mobile being configured to receive and process said radio frequency signals and to deduce its position by calculating the time-of-flight difference(s) between the receiving mobile and the transmitting bases, the receiving mobile comprising means for storing position data of the fixed transmitting bases, means for measuring the phases of radio frequency signals, and calculation means connected to the measurement means and the storage means, each transmitting base being configured to emit a sum of at least two unmodulated pure carrier signals of distinct frequencies,Each pure carrier signal is in the form of a sustained, unmodulated wave, preferably sinusoidal; the receiving mobile device is a radio frequency signal receiver as described above.

[0015] According to one variant, radio frequency signal phase measurement means are means for measuring, for each given signal frequency and for each respective transmitting base, the phase of the signal consisting of the different signals originating from said base and exhibiting said frequency. According to this variant, the digital homodyne demodulator as described above constitutes such phase measurement means.

[0016] According to a fourth aspect, the invention relates to a method, implemented by a digital homodyne demodulator, for the synchronous demodulation of a plurality of multiplexed carriers, the demodulator comprising a signal mixer module equipped with a plurality of mixers, the digital homodyne demodulator further comprising a general digital oscillator and a generator of periodic demodulation signals, with a signal at the output of the general digital oscillator and at an input of each mixer, the general digital oscillator generating a shared general synchronization periodic signal, said shared general synchronization periodic signal having a general frequency and a general phase,the periodic demodulation signal generator comprising a multiphaser module connected to the output of the general digital oscillator and a direct digital synthesizer connected on one side to the output of the multiphaser module and on the other side to the second input of each mixer, and the method comprising the following steps: • a reception on its input, by the digital homodyne demodulator, of a digital input signal composed of a sum of said plurality of multiplexed carriers, each mixer receiving said digital input signal on a first input; • a multiplication, by the multiplier modulus, of the general phase of the periodic general synchronization signal shared by an integer multiple; • a generation, by the periodic demodulation signal generator, from said shared general synchronization periodic signal, of several local periodic demodulation signals, each local periodic demodulation signal being generated by the direct digital synthesizer from a distinct phase value obtained by multiplying the general phase by an integer multiple, each local periodic demodulation signal being supplied on a second input of a respective mixer and having a distinct frequency whose value is an integer multiple of the general frequency; • a supply on its output, by each mixer, from said digital input signal and one of said periodic local demodulation signals, of an output signal from among a plurality of demodulated output signals supplied at the output of the homodyne digital demodulator, said output signal being obtained by multiplying the digital input signal and the corresponding periodic local demodulation signal, the output signals of said plurality of output signals being synchronized in phase. Brief description of the figures

[0017] Other features and advantages of the invention will become apparent from the detailed description below and the accompanying figures, in which:

[0018] [Fig. 1] is a functional diagram of a prior art digital homodyne demodulator;

[0019] [Fig. 2] is a functional diagram of a radio frequency signal receiver comprising a digital homodyne demodulator according to the invention;

[0020] [Fig. 3] is a detailed functional diagram of the digital homodyne demodulator in Figure 2; and

[0021] [Fig. 4] is a flowchart of the steps of a synchronous demodulation process of a plurality of multiplexed carriers, implemented by the digital homodyne demodulator of figure 3. Detailed description of the invention

[0022] Figure 1 illustrates a conventional prior art digital homodyne demodulator 10, which receives an incoming digital signal s[n] consisting of a sum of N multiplexed carriers. The digital homodyne demodulator 10 comprises N digital local oscillators (not shown in Figure 1 for clarity), and a signal mixer module 12 equipped with N mixers 14. Each digital local oscillator generates a periodic demodulation local signal LOi[n], with 1 < i < N. Each periodic demodulation local signal LOi[n] has a distinct frequency fi that corresponds to an expected demodulation frequency. As shown in Figure 1, the digital local oscillators and mixers 14 operate in pairs, namely one "digital local oscillator - mixer 14" pair to demodulate each given received carrier.The N mixers 14 are arranged in parallel to allow the parallel demodulation of the N carriers, each mixer 14 being associated with a respective digital local oscillator and configured to multiply the incoming digital signal s[n] with the periodic local demodulation signal LOi[n] generated by that local oscillator. This multiplication performed by each mixer 14 is adjusted to the sampling frequency of an analog-to-digital converter (not shown) located upstream of the homodyne digital demodulator 10.

[0023] A digital accumulator (not shown) typically generates the phase of each LOi[n] periodic local demodulation signal independently of each other. From these phases, a direct digital synthesizer (not shown) generates the LOi[n] signals. To do this, the direct digital synthesizer typically reads samples of a sinusoidal wavefunction stored in a lookup table. The phase of each of the LOi[n] periodic local demodulation signals, for each sampling instant of the analog-to-digital converter, is determined via the following equation (1):

[0024] [Math.Eq(l)] 4> f [n] = 4>i[n — 1] + Ad>t

[0025] Or :

[0026] [Math.Eq(2)]f. A4> = 2 LOres .—^— + 6; fcAN

[0027] Here, LOres represents the resolution of the digital phase accumulator, fi is the carrier frequency to be demodulated, fcAN is the sampling frequency of the analog-to-digital converter and Ci is a digital quantization error (which accumulates over time).

[0028] A significant limitation of this prior art architecture, as illustrated in Figure 1, arises from the resolution of the digital accumulator step size Acf>, which adds a quantization error determined by LOres. This limitation introduces a time-varying frequency gap, which affects each local digital oscillator (and therefore each demodulated frequency) differently.

[0029] The digital homodyne demodulator 10 also includes N filter modules 16, each filter module 16 being connected to the output of one of the mixers 14. Preferably, each filter module 16 is an infinite impulse response filter. Each resulting signal Ci[k], supplied at the output of a respective filter module 16, is then a filtered signal and corresponds to a demodulated signal supplied at the output of the digital homodyne demodulator 10.

[0030] Figure 2 illustrates a radio frequency signal receiver 20, comprising a radio frequency signal receiving antenna 22, an analog signal processing module 24, an analog-to-digital converter 26, and a digital homodyne demodulator 28 according to the invention. The analog signal processing module 24 is connected between the radio frequency signal receiving antenna 22 and the analog-to-digital converter 26, and is configured to perform one or more signal processing operations such as signal amplification, filtering, and / or attenuation. The analog-to-digital converter 26 is connected between the analog signal processing module 24 and the digital homodyne demodulator 28. The antenna 22 receives a radio frequency signal S(t) which is composed of a sum of N multiplexed carriers.The analog-to-digital converter 26 provides the digital homodyne demodulator 28 with a corresponding incoming digital signal s[n], which is composed of a sum of N multiplexed carriers. The digital homodyne demodulator 28 is capable of performing synchronous demodulation of the N multiplexed carriers, as will be detailed later.

[0031] As shown in Figure 3, the digital homodyne demodulator 28 comprises a signal mixer module 30 equipped with N mixers 32. The digital homodyne demodulator 28 also includes a general digital oscillator (not shown in Figure 3 for clarity) and a demodulation periodic signal generator 34. In other words, unlike the prior art digital homodyne demodulator 10 (shown in Figure 1), the digital homodyne demodulator 28 according to the invention comprises, instead of N local digital oscillators, a single general digital oscillator and the demodulation periodic signal generator 34. Preferably, as illustrated in Figure 3, the demodulation periodic signal generator 34 comprises a multiphaser module 36 and a direct digital synthesizer 38.The digital homodyne demodulator 28 is typically implemented within a microcontroller or within a programmable logic circuit, such as for example a field-programmable gate array (FPGA), such elements not being represented in the figures for reasons of clarity.

[0032] Each mixer 32 is configured to receive on a first input the incoming digital signal s[n],

[0033] The general digital oscillator generates a shared periodic general synchronization signal LO g [n], This shared periodic general synchronization signal LO g [n] has a general frequency f g and a general phase E> g [n], The shared general synchronization periodic signal LO g[n] is typically a sinusoidal signal, although this is not imitative within the scope of the present invention. According to a particular embodiment of the invention, the shared general synchronization periodic signal LO g [n] is expressed by means of the following equation 3:

[0034] [Math.Eq(3)] LO^[n] = cos 2nf g n)

[0035] The demodulation periodic signal generator 34 is connected on one side to the output of the general digital oscillator and on the other side to a second input of each mixer 32. The demodulation periodic signal generator 34 is configured to generate N local periodic demodulation signals LOi[n] (with 1 < i < N) from the shared general synchronization periodic signal LO g[n] In the particular embodiment shown in Figure 3, in which the demodulation periodic signal generator 34 comprises a multiphaser module 36 and a direct digital synthesizer 38, the multiphaser module 36 is connected to the output of the general digital oscillator, and the direct digital synthesizer 38 is connected on one side to the output of the multiphaser module 36 and on the other side to the second input of each mixer 32. The multiphaser module 36 is configured to multiply the general phase g [n] of the shared general synchronization periodic signal LO g [n] by an integer multiple. Such a multiplication may or may not be incremental. The direct digital synthesizer 38 is configured to generate each LOi[n] periodic local demodulation signal from a distinct phase value i[n] obtained by multiplication of the general phase g [n] by an integer multiple.

[0036] Each local periodic demodulation signal LOi[n] then has a distinct frequency £ whose value is an integer multiple of the general frequency f g , and is expressed via the following equation (4):

[0037] [Math.Eq(4)] fi = ^i- fg

[0038] where Ni is an integer.

[0039] Each local periodic demodulation signal LOi[n] can then be expressed as a function of the general frequency f g of the shared general synchronization periodic signal LO g [n], via the following equation (5):

[0040] [Math.Eq(5)] LOt [n] = cos(2nNif g )

[0041] When the digital homodyne demodulator 28 is implemented within a programmable logic circuit, such as a programmable FPGA pre-diffused integrated circuit, the general digital oscillator typically includes a phase accumulator incremented proportionally to the general frequency f g (this component is not shown in the figures). The phase obtained at each sampling instant n of the analog-to-digital converter 26 is multiplied, in parallel by several multipliers 36, by the constants Ni, so that N phases are generated for each sample. Then, several lookup tables storing samples of a sinusoidal wave (direct digital synthesizer 38) perform the phase-amplitude conversion, thus producing the local signals LOi[n],

[0042] The digital homodyne demodulator 28 also includes N filter modules 40, each filter module 40 being connected to the output of one of the mixers 32. Preferably, each filter module 40 is an infinite impulse response filter. Each resulting signal Ci[k], supplied at the output of a respective filter module 40, is then a filtered signal and corresponds to a demodulated signal supplied at the output of the digital homodyne demodulator 28. In an alternative not shown, each of the N filter modules 40 can be replaced by any other signal processing module.

[0043] Such an architecture of the digital homodyne demodulator 28 according to the invention advantageously ensures that the resulting N output signals Ci[k] are synchronized with each other in phase (and in a stable manner over time), thus completely eliminating the frequency error for each carrier (caused by digital quantization).

[0044] A particularly advantageous application of the digital homodyne demodulator 28 according to the invention, and of the radio frequency signal receiver 20 comprising such a demodulator 28, will now be described. This application relates to a positioning system for at least one receiving mobile, the receiving mobile in this case being the radio frequency signal receiver 20; the positioning system as a whole is not shown in the figures for reasons of clarity.

[0045] The positioning system comprises, in addition to the receiver 20, at least two fixed transmitting bases. The receiver 20 is configured to receive and process radio frequency signals from the fixed transmitting bases and to deduce its position by calculating the time-of-flight difference(s) between the receiver 20 and the transmitting bases. This differential time-of-flight calculation avoids any time synchronization constraints between the receiver 20 and the transmitting bases. The receiver 20 includes storage means configured to store position data from the fixed transmitting bases. The storage means typically consist of memory, typically non-volatile memory. The receiver 20 further includes means for measuring the phases of radio frequency signals, which in this case consist of the digital homodyne demodulator 28 according to the invention.The receiver 20 also includes computing means connected to the measurement and storage means. The computing means typically consist of a processing unit, for example, one or more processors, or integrated within an electronic chip. By way of non-limiting examples, the receiver 20 typically consists of a chip or an electronic card, for example, integrated into a portable device; or a mobile communication device such as a mobile phone.

[0046] Each transmitting base station is typically a radio frequency signal transmission antenna. The transmitting bases of the positioning system are synchronized with each other to transmit their respective signals. By "synchronized with each other," we mean that the phase difference between the signals emitted by the different transmitting bases is constant, in order to prevent signal drift and thus avoid distorting the measurement performed by the receiver 20 for its positioning. Each transmitting base station is configured to transmit a sum of at least two unmodulated pure carrier signals of distinct frequencies. Each pure carrier signal is in the form of an unmodulated continuous wave, preferably sinusoidal. In a preferred embodiment, each unmodulated pure carrier signal is a pure sinusoidal signal, and each fixed transmitting base station is configured to transmit a sum of N unmodulated sinusoidal signals of distinct frequencies.The means for measuring the phases of radio frequency signals (consisting of the digital homodyne demodulator 28) are then means for measuring, for each given signal frequency and for each respective transmitting base, the phase of the signal consisting of the different signals from that base and presenting said frequency.

[0047] The operation of the digital homodyne demodulator 28 according to the invention will now be described. More specifically, a synchronous demodulation method for a plurality of multiplexed carriers, implemented by this digital homodyne demodulator 28, will now be described with reference to Figure 4. The general digital oscillator generates the shared periodic general synchronization signal LO g [n], which has the general frequency f g and the general phase E> g [n],

[0048] The process includes an initial step 100 during which the digital homodyne demodulator 28 receives at its input a digital input signal s[n] composed of a sum of N multiplexed carriers. Following this initial step 100, each mixer 32 receives at a first input this digital input signal s[n],

[0049] The process includes a subsequent step 110 in which the demodulation periodic signal generator 34 generates N local periodic demodulation signals LOi[n] (with 1 < i < N), from the shared general synchronization periodic signal LO g [n], Each local periodic demodulation signal LOi[n] thus generated is supplied to a second input of a respective mixer 32 and has a distinct frequency L whose value is an integer multiple of the general frequency f g More specifically, in the particular rearrangement example of Figure 3, in which the periodic demodulation signal generator 34 comprises a multiplier module 36 and a direct digital synthesizer 38, the multiplier module 36 multiplies the general phase g [n] of the shared general synchronization periodic signal LO g [n] by an integer multiple. Such a multiplication may or may not be incremental. The direct digital synthesizer 38, on the other hand, generates each periodic local demodulation signal LOi[n] from a distinct phase value i[n] obtained by multiplication of the general phase g [n] by an integer multiple.

[0050] The process includes a subsequent step 120 in which each mixer 32 provides a signal on its output, from the digital input signal s[n] and one of the periodic local demodulation signals LOi[n]. This output signal is obtained by multiplying the digital input signal s[n] and the corresponding periodic local demodulation signal LOi[n].

[0051] Preferably, the process finally includes a further step 130 in which each filtering module 40 filters the signal received at its input and provides at its output a resulting signal Ci[k] which corresponds to a demodulated signal provided at the output of the digital homodyne demodulator 28. The demodulated output signals Ci[k] are then synchronized in phase.

Claims

DEMANDS:

1. Homodyne demodulator (28) for the synchronous demodulation of a plurality of multiplexed carriers, the demodulator (28) being configured to receive as input an input signal (s[n]) composed of a sum of said plurality of multiplexed carriers and to provide as output a plurality of demodulated output signals (Ci[k]), the demodulator (28) comprising a signal mixer module (30) equipped with a plurality of mixers (32), each mixer (32) being configured to receive on a first input said input signal (s[n]) and on a second input a periodic local demodulation signal (LOi[n]) and being configured to provide on its output, from said input signal (s[n]) and said periodic local demodulation signal (LOi[n]), one of said output signals (Ci[k]) obtained by multiplying the input signal and the periodic local demodulation signal,the homodyne demodulator (28) further comprising a general oscillator configured to generate a shared general synchronization periodic signal (LO, g [n]), said shared general synchronization periodic signal (LO g [n]) exhibiting a general frequency (f g ) and a general phase ( g [n]), the homodyne demodulator (28) further comprising a demodulation periodic signal generator (34) connected on one side to the output of the general oscillator and on the other side to the second input of each mixer (32), the demodulation periodic signal generator (34) being configured to generate each of said local periodic demodulation signals (LOi[n]) from said shared general synchronization periodic signal (LO g [n]), each local periodic demodulation signal (LOi[n]) having a distinct frequency whose value is an integer multiple of the general frequency (f g ), the output signals (Ci[k]) of the plurality of output signals being phase-synchronized, characterized in that the demodulator is a homodyne digital demodulator (28) configured to receive as input a digital input signal (s[n]) composed of a sum of said plurality of multiplexed carriers; in that the oscillator is a general digital oscillator; and in that the generator (34) of periodic demodulation signals comprises a multiplier module (36) connected to the output of the general digital oscillator and a direct digital synthesizer (38) connected on the one hand to the output of the multiplier module (36) and on the other hand to the second input of each mixer (32), the multiplier module (36) being configured to multiply the general phase ( g [n]) by an integer multiple, the direct digital synthesizer (38) being configured to generate each periodic local demodulation signal (LOi[n]) from a distinct phase value obtained by multiplying the overall phase ( g [n]) by an integer multiple.

2. Digital homodyne demodulator (28) according to claim 1, characterized in that it further comprises a plurality of filter modules (40), the number of filter modules (40) being equal to the number of mixers (32), each filter module (40) being connected to the output of one of the mixers (32).

3. Digital homodyne demodulator (28) according to the preceding claim, characterized in that each filtering module (40) is an infinite impulse response filter.

4. Radio frequency signal receiver (20), comprising a radio frequency signal receiving antenna (22), an analog signal processing module (24), an analog-to-digital converter (26), and a digital homodyne demodulator (28) for the synchronous demodulation of a plurality of multiplexed carriers, the analog signal processing module (24) being connected between the radio frequency signal receiving antenna (20) and the analog-to-digital converter (26), the analog-to-digital converter (26) being connected between the analog signal processing module (24) and the digital homodyne demodulator (28), characterized in that the digital homodyne demodulator (28) conforms to any one of the preceding claims,The radio frequency signal (S(t)) capable of being received by the antenna (22) corresponding to said digital input signal (s[n]) composed of a sum of said plurality of multiplexed carriers.

5. Positioning system for at least one receiving mobile, the system comprising, in addition to the mobile, at least two fixed transmitting bases, each transmitting base being configured to emit radio frequency signals, the transmitting bases being synchronized with each other to emit their respective signals, the receiving mobile being configured to receive and process said radio frequency signals and to deduce its position by calculating the time-of-flight difference(s) between the receiving mobile and the transmitting bases, the receiving mobile comprising means for storing position data of the fixed transmitting bases, means for measuring the phases of radio frequency signals, and computing means connected to the measurement means and the storage means,each transmitting base being configured to emit a sum of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated sustained wave, preferably sinusoidal; characterized in that the receiving mobile is a radio frequency signal receiver (20) conforming to the preceding claim.

6. A method, implemented by a homodyne demodulator (28), for the synchronous demodulation of a plurality of multiplexed carriers, the demodulator (28) comprising a signal mixer module (30) equipped with a plurality of mixers (32), the homodyne demodulator (28) further comprising a general oscillator and a generator (34) of periodic demodulation signals connected on the one hand to the output of the general oscillator and on the other hand to an input of each mixer (32), the general oscillator generating a shared periodic general synchronization signal (LO g [n]), said shared general synchronization periodic signal (LO g [n]) exhibiting a general frequency (f g ) and a general phase ( g [n]), characterized in that the demodulator is a homodyne digital demodulator (28); in that the oscillator is a general digital oscillator; in that the generator (34) of periodic demodulation signals comprises a multiplier module (36) connected to the output of the general digital oscillator and a direct digital synthesizer (38) connected on one side to the output of the multiplier module (36) and on the other side to the second input of each mixer (32); and in that the method comprises the following steps: • a reception (100) at its input, by the digital homodyne demodulator (28), of a digital input signal (s[n]) composed of a sum of said plurality of multiplexed carriers, each mixer (32) receiving said digital input signal (s[n]) at a first input; • a multiplication (110), by the multiphcator module (36), of the general phase ( g [n]) of the shared general synchronization periodic signal LO g [n] by an integer multiple; • a generation (110), by the generator (34) of periodic demodulation signals, from said shared general synchronization periodic signal (LO g [n]), of several periodic local demodulation signals (LOi[n]), each periodic local demodulation signal (LOi[n]) being generated by the direct digital synthesizer (38) from a distinct phase value obtained by multiplying the overall phase ( g [n]) by an integer multiple, each local periodic demodulation signal (LOi[n]) being supplied on a second input of a respective mixer (32) and having a distinct frequency whose value is an integer multiple of the general frequency (f g ) ; • a supply (120) on its output, by each mixer (32), from said digital input signal (s[n]) and one of said periodic local demodulation signals (LOi[n]), of an output signal (Ci[k]) from among a plurality of demodulated output signals supplied at the output of the digital homodyne demodulator (28), said output signal (Ci[k]) being obtained by multiplying the digital input signal (s[n]) and the corresponding periodic local demodulation signal (LOi[n]), the output signals (Ci[k]) of said plurality of output signals being synchronized in phase.

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