POSITIONING SYSTEM WITH EMISSIVE CABLE SEGMENTS

Abstract

The present invention relates to a positioning system (400) using a plurality of radiating cable segments. In addition to said cable segments (421, 422), the system comprises means (410) for generating a composite GNSS signal formed by a plurality of GNSS signals defined as those which would be received at points located at the ends of the various cable segments. In each segment, a first GNSS signal, corresponding to a first set of satellites visible in a first cone of visibility, travels through the segment in a forwards direction, and a second GNSS signal, corresponding to a second set of satellites in a cone of visibility, travels therethrough in the reverse direction, the frequencies of the first and second GNSS signals being equal to a reception frequency of a predetermined GNSS system. An RF interconnection housing (440) connecting consecutive first and second segments allows the GNSS signals to be demultiplexed from the composite GNSS signal it receives.

Description

[0001] RADIATING CABLE SEGMENT POSITIONING SYSTEM

[0002] Technical Field

[0003] The present invention generally relates to the field of indoor positioning systems or outdoor positioning systems when GPS signal reception conditions are degraded.

[0004] State of the prior art

[0005] The lack of GPS signals in indoor environments has led to the development of positioning systems specific to them. A large number of possible techniques have been used for this purpose. For example, it is known to deploy beacon networks in the environment in question, allowing a receiver to estimate its position by TDOA (Time Difference Of Arrival) or by triangulation from time of arrival, TOA (Time Of Arrival). It is also possible to use existing access points, for example a Wi-Fi network to determine the position of a terminal from fingerprints of power measurements (RSSI).

[0006] A positioning system based on radiating cables (leaky feeders) was proposed by the applicant in patent application FR3074921.

[0007] This positioning system allows any user with a GPS receiver to be able to locate themselves in an indoor environment such as a subway without having to suffer a service interruption when leaving or entering this environment.

[0008] Such a radiating cable positioning system is illustrated in Fig. 1 and its principle is recalled in relation to Fig. 2.

[0009] Said system, 100, comprises means 110 for generating first GNSS signals and second GNSS signals, a radiating cable 120, means 131 for injecting the first GNSS signals at a first end of the cable, and means 132 for injecting the second GNSS signals at a second end of the cable.

[0010] The generation means have access to a configuration file, Config_file, navigation data, Nav_data, data from a very low phase jitter clock, GPS_sync. The configuration file Config_file includes in particular: a visibility mask for each end of the cable, defined by an angular range in elevation [amax min ] and, where appropriate, in azimuth [flmax min ], the respective positions of the ends of the cable and its material characteristics (length, speed of propagation of electromagnetic waves within the cable, etc.).

[0011] The generation means 110 provide first GNSS signals and second GNSS signals. These first and second GNSS signals are generated locally by propagation simulation and not actual signals received from satellites.

[0012] The first GNSS signals are generated so that, at the instant they are injected at the first end of the cable, they are identical to those which would have been received at a first virtual end in open sky conditions, from a first set of satellites. The first set of satellites is chosen from those of the constellation(s) identified in the configuration file belonging to a first cone of visibility defined by an angular interval in elevation [amax min ] and an angular interval in azimuth [flmax min ], the angles being defined here from an axis directed from the second end towards the first end of the cable. The first set of satellites comprises at least one such satellite.

[0013] Similarly, the second GNSS signals generated are such that, at the instant they are injected at the second end of the cable, they are identical to those which would have been received at the position of a second virtual end, in open sky conditions, from a second set of satellites. The second set of satellites is chosen from those of the constellation identified in the configuration file belonging to a second cone of visibility defined by an angular interval in elevation [α min ,α max ] and an angular interval in azimuth [ ] angles being here defined from an axis oriented from the first to the second end of the cable. The second set of satellites comprises at least one such satellite.

[0014] The union of the first and second sets of satellites comprises at least four satellites, the two sets of satellites being disjoint.

[0015] The principle of operation is illustrated in Fig. 2 in the elevation plan.

[0016] The radiating cable, assumed to be rectilinear, is represented by the straight line segment [zlfî] where A and B are the ends of the cable. The first and second cones of visibility have been represented in C ± and C2, as well as a first satellite SV1 belonging to C ± and a second satellite SV2 belonging to the second cone of visibility. The distances separating the satellite SV1 (resp. SV2) from the ends A and B of the cable are noted and (resp. and ). Similarly, the elevation angles under which the satellite SV1 (resp. SV2) is seen from the ends A and B of the cable are noted (resp. and ). We have assumed here that a min .

[0017] A virtual end A' is defined located on a virtual extension of the cable, on the side of end A and at a distance A from the latter. Similarly, an end B' is defined located on a virtual extension of the cable, on the side of end B and at a distance A from the latter. The distance A is chosen such that being the apparent length of the cable, l, being its actual length, c being the speed of light in a vacuum and v being the speed of propagation of an electromagnetic wave in the cable.

[0018] The positioning system injects at the end A of the radiating cable the signals which would have been received at A' from the satellites belonging to the first cone of visibility C ± . Similarly, it injects at the end B of the radiating cable the signals which would have been received at B' from the satellites belonging to the second cone of visibility C2.

[0019] We can then show that a user equipped with a GNSS receiver located at a point M, will estimate the pseudo-distances separating him respectively from the satellites, SV1, SV2, by: [Math. 1]

[0020] [Math. 2] where = x- , x being the abscissa of M on the AB axis taking A as the origin and

[0021] 5 is the distance equivalent to the clock offset of the GNSS receiver.

[0022] From the pseudo-distances estimated for 4 satellites (belonging to the union of the two subsets of satellites mentioned above), the GNSS receiver can determine its position.

[0023] The radiating cable positioning system described above gives satisfactory results but its performance is limited by the cable length. Indeed, most common GNSS receivers have an input dynamic range of around 24dB, in other words the weakest received satellite signal cannot be more than 24dB weaker than the strongest satellite signal. However, the linear attenuation of GPS signals in a radiating cable is of the order of 3 to 20 dB / 100m. As a result, a radiating cable positioning system generally cannot work when the cable length exceeds a few hundred meters.

[0024] This constraint is illustrated in Fig. 3A: when the radiating cable 320 has a length greater than a critical length, the satellite signals simulated and injected at the first end A are attenuated by more than 24dB, when they reach the end . Similarly, the satellite signals simulated and injected at the second end B are attenuated by more than 24dB, when they reach the end A. In such a case, it is not possible for a GNSS receiver to estimate its position correctly at the ends of the cable because it cannot acquire the satellite signals coming from the end furthest from the receiver.

[0025] A known solution to remedy this situation is then to split the radiating cable into different segments of length less than the critical length and to inject simulated satellite signals at the respective ends of these segments, as illustrated in Fig. 3B. Each segment 321, 322 must then be considered as an independent radiating cable, requiring its own generation means, which is expensive, or a single generator 310 with several RF outputs (here 4) as shown, which does not allow scalability. Furthermore, in both cases, the number of coaxial cables (or optical fibers associated with optoelectronic converters) results in significant additional costs.

[0026] An object of the present invention is therefore to propose a positioning system with several radiating cable segments which does not have the aforementioned drawbacks, in particular to propose a system which is scalable and does not require the use of additional RF or optical links.

[0027] Patent applications CN113534196A and CN113534196A also describe positioning systems based on radiating cables and virtual GNSS signals.

[0028] Presentation of the invention

[0029] The present invention is defined by a system for positioning along a radiating cable, composed of at least a first segment and a second segment, said system comprising:

[0030] - means for generating a first composite GNSS signal formed from a plurality of GNSS signals defined as those which would be received in an open sky configuration by points located at the ends of the different segments of the cable, each segment being associated with a first GNSS signal which would be received from a first point at a proximal end of this segment from satellites belonging to a first cone of visibility, and a second GNSS signal which would be received from a second point at a distal end of this segment from satellites belonging to a second cone of visibility, said GNSS signals being frequency multiplexed to form said composite GNSS signal, said composite GNSS signal being injected at the proximal end of the first segment, the first GNSS signal associated with the first segment being at the reception frequency of a GNSS receiver, f GNSS ;

[0031] - an RF interconnection box connected between the first and second segments, intended to demultiplex the first composite GNSS signal by frequency shifting the different GNSS signals of the first composite signal and to provide, on the one hand, on a first output the second GNSS signal associated with the first segment at the frequency f GNSS , and to provide on the other hand, on a second output, a second composite GNSS signal in which the first and second GNSS signals associated with the first segment are eliminated, the second GNSS signal of the first segment being injected at the frequency f GNSS at the distal end of the first segment and said second composite GNSS signal being injected at the proximal end of the second segment;

[0032] - an RF termination box connected to the distal end of the second segment and intended to shift to the frequency f GNSS I esecond GNSS signal associated with the second segment, and inject it at the distal end of the second segment.

[0033] Advantageously, the GNSS signals of the first composite GNSS signal are located at frequencies f GNSS + where i is a relative integer.

[0034] The RF interconnection box may comprise a first demultiplexer (including an RF divider for dividing the first composite signal between a first channel and a second channel, the first channel comprising: a first mixer for mixing the composite signal thus divided with a first translation frequency (f1) so that the second GNSS signal of the first segment is translated to an intermediate frequency (1F0); a first bandpass filter having a first bandwidth (BP1 around said intermediate frequency for selecting the second GNSS signal of the first segment thus translated; and a second mixer for mixing the second GNSS signal of the first segment thus selected with a first reference frequency so as to transpose the latter to the fGNSS- frequency

[0035] The second channel may comprise a third mixer for mixing the divided composite signal with a second translation frequency ( f2) so that a second composite GNSS signal is translated to the intermediate frequency ( IF0); a second bandpass filter having a second bandwidth ( BP2) around said intermediate frequency for selecting the second composite GNSS signal; and a fourth mixer for mixing the second composite GNSS signal with a second reference frequency ( ) so as to transpose the latter to the frequency f GNSS .

[0036] The first channel may further comprise a third bandpass filter for filtering the second GNSS signal of the first segment and the second channel also comprises a fourth bandpass filter for filtering the second composite GNSS signal.

[0037] The RF interconnect box may further include a duplexer having its common port connected to the distal end of the first segment, its output port connected to the input of the RF splitter, and its input port connected to the output of the second mixer of the first path.

[0038] The RF interconnection box may further comprise, between the output port of the duplexer and the input of the RF divider, a common bandpass filter having the bandwidth of the first composite signal in series with an amplifier, the gain of the amplifier being chosen to compensate for the attenuation of the composite GNSS signal in the first segment. According to an alternative embodiment, the radiating cable is composed of a plurality N of segments, the RF termination box then comprising: a first mixer at an Nth translation frequency (f N) so that the second GNSS signal of the Nth segment is translated to an intermediate frequency (IF0), a first bandpass filter having a first bandwidth (BP l ) around said intermediate frequency to select the second GNSS signal of the Nth segment thus translated, and a second mixer to mix the second GNSS signal of the Nth segment thus selected with an Nth reference frequency ( ) so as to transpose the latter to the frequency f GNSS .

[0039] The RF termination box may then further comprise a duplexer whose common port is connected to the distal end of the Nth segment, the output port is connected to the input of the first mixer and the input port is connected to the output of the second mixer.

[0040] The RF termination box may further comprise, between the output port of the duplexer and the input of the RF divider, a second bandpass filter, having the bandwidth of the last composite signal associated with the Nth segment, said last segment, followed by an amplifier, the gain of the amplifier being chosen to compensate for the attenuation of the last composite GNSS signal in the last segment.

[0041] The means for generating the composite GNSS signal can also generate in this signal at least two synchronization signals having a frequency difference of Sf, each synchronization signal being obtained by modulating a continuous wave with a pseudo-random spectral spreading sequence, said random sequence being chosen to be identical for all of the synchronization signals.

[0042] The center frequencies of the synchronization signals are advantageously located in areas of reliable spectral density of the first composite GNSS signal. The RF interconnect box and the RF termination box may each comprise a clock signal generation circuit comprising a mixer for multiplying the composite signal with itself, a low-pass or band-pass filter so as to isolate from the mixture a component at the frequency Sf.

[0043] Brief description of the figures

[0044] Other characteristics and advantages of the invention will appear on reading a preferred embodiment of the invention, made with reference to the attached figures among which:

[0045] [Fig. 1] schematically represents a positioning system along a radiating cable known from the state of the art;

[0046] [Fig. 2] schematically represents the operating principle of the positioning system illustrated in Fig. 1;

[0047] [Fig. 3A] illustrates a constraint on a radiating cable positioning system known from the state of the art;

[0048] [Fig. 3B] represents a solution allowing this constraint to be released;

[0049] [Fig. 4] schematically represents a positioning system using 2 segments of radiating cable according to a first exemplary embodiment of the invention;

[0050] [Fig. 5A]

[0051] [Fig. 5B]

[0052] [Fig. 5C] schematically represent an RF interconnection device and an RF termination device of Fig. 4, as well as the signals present at different points of these devices;

[0053] [Fig. 6A]

[0054] [Fig. 6B]

[0055] [Fig. 6C] schematically represent a positioning system using 4 radiating cable segments according to different exemplary embodiments of the invention;

[0056] [Fig. 7] schematically represents an RF interconnection device of Fig. 6C;

[0057] [Fig. 8] schematically represents the spectrum of a composite signal injected into a radiating cable comprising GNSS signals and synchronization signals;

[0058] [Fig. 9] schematically represents a circuit for generating a frequency transposition signal from the composite signal of Fig. 8.

[0059] Description of the embodiments

[0060] We will consider in the following a radiating cable positioning system as presented in the introductory part.

[0061] A leaky feeder cable is understood to mean a coaxial cable whose outer conductor has slots or openings at regular intervals to allow radial emission along its entire length. Similarly, any waveguide, with slots or openings, with a large extension along its longitudinal axis and allowing radial emission along this axis may be used.

[0062] The radiating cable can be linear or have curved sections.

[0063] We will assume that the radiating cable is split into several distinct segments of equal or distinct lengths, the length of each segment being chosen to be less than a critical length. By critical length, we mean a length such that the attenuation of a GNSS signal in a segment of this length corresponds to the maximum permissible power difference (in dB) between GNSS signals allowing their simultaneous acquisition by a GNSS receiver. Generally speaking, by GNSS (Global Navigation Satellite System) signals, we mean here any type of satellite signal allowing positioning, whatever the system considered (GPS, Galileo, GLONASS, Beidou, etc.)

[0064] Fig. 4 schematically represents a positioning system using 2 radiating cable segments according to a first exemplary embodiment of the invention.

[0065] The first radiating cable segment, 421, is connected to the common output of a diplexer, 430, receiving on the one hand, in a first band, GNSS signals generated by simulation from the generator 410, and on the other hand, in second bands, mobile communication signals intended for the different users, from the communication module 415. Thus, advantageously, a single signal output is necessary for the 2 segments 421 and 422. The diplexer 430 can be produced from an RF divider powered by the outputs and thus providing at its input a combination of the GNSS signals and the mobile communication signals.

[0066] The GNSS signals are represented here at 4 distinct frequencies separated from each other by a step δf of 10 MHz: 1565.42 MHz, 1575.42 MHz, 1585.42 MHz and

[0067] 1595.42 MHz. It is clear to those skilled in the art that other frequencies may be used, for example 1575.42 MHz, 1585.42 MHz, 1595.42 MHz and

[0068] 1605.42 MHz.

[0069] Only the frequency f GNSS (here fGNSS = 1575.42 MHz, L1 frequency of a GPS system) can be used by user receivers, the other frequencies not being taken into account in the tracking algorithm by such a receiver. These other frequencies are simply intended to transport the GNSS signals in the radiating cable. In general, these frequencies can take values ​​f GNSS where i is a relative integer. In certain cases, this constraint may be waived, the frequencies used for transport then having any offset compared to the frequency f GNSS .

[0070] In the illustrated example (diagram A), only the signal s2 at frequency f GNss, transmitted on the forward propagation path in the cable segment 421 can be used by a receiver to determine its position. It is worth noting (diagram B) the effect of attenuation after propagation in the cable. The RF interconnect box, 440, returns, as explained later, the signal S1 transposed to the frequency f GNSS in the first segment, 421 (diagram C). Thus, for a user, everything happens as if the signal s2 was injected at the first end, called the proximal end of segment 421, and the signal SL was injected at its second end, called the distal end. The RF interconnect box further injects into the second segment 422 the remaining GNSS signals, namely those which were not transmitted at the frequency f GNSS , in the first segment, 421, or s3,s4., are injected at the proximal end of the second segment.

[0071] The signal is transmitted at the frequency f GNSS sur Ie forward propagation path in the second segment, 422. We note the attenuation of the signals s3, s4 after having propagated in the second segment. The RF termination box, 450, returns the signal s4 transposed to the frequency f GNSS in segment 421 (diagram F). Thus, for a user's receiver, everything happens as if the signal S3 were injected at the proximal end of the second segment 422 and the signal S4 were injected at its distal end.

[0072] According to a variant not shown in this figure, the signal s4 can be transmitted at the frequency f GNSS sur I e propagation path in the second segment, 422, and, in this case, the RF termination box, 450, returns the signal s3transposed to the frequency f GNSS in the segment, 421.

[0073] Furthermore, the RF interconnect box 440 as well as the RF termination box, 450, can be directly powered via the radiating cable segments 421, 422. The detail of the RF interconnect box of Fig. 4 has been shown schematically in Fig. 5A.

[0074] The housing comprises a first RF port, 500, intended to be connected to the first radiating cable segment, 421, and a second RF port, 590 intended to be connected to the second radiating cable segment, 422. More generally, the RF ports 500 and 590 may be connected respectively to the distal end and the proximal end of two consecutive segments, the proximal or distal character being determined by reference to the GNSS signal generator.

[0075] The number N of generated GNSS signals is equal to twice the number of segments ( N = 4 ).

[0076] The RF port 500, called common port, is connected to a duplexer 510, the composite GNSS signal, formed by the signals . . , received on this port, being filtered by a bandpass filter, 520, whose bandwidth, BP , corresponds to the band of GNSS signals, then amplified by an amplifier, 530.

[0077] The gain of the amplifier 530 is advantageously chosen so as to compensate for the attenuation in the first radiating cable segment, 421. The spectrum of the composite GNSS signal at the output of the amplifier 530 is illustrated in diagram A of Fig. 5B: we note that the spectrum of the signal s2 is here centered on the frequency f GNSS > in other words that the signal s2 was at the frequency f GNSS during its propagation in the first segment.

[0078] The amplified composite GNSS signal is then supplied to an RF divider, 540.

[0079] On a first branch at the output of the RF divider, the signal is mixed, by means of a mixer 551, at a first translation frequency to bring the signal an intermediate frequency, IF Q (here — δf).

[0080] The intermediate frequency can be chosen equal to a multiple of Sf. According to an example of realization 8f = 10MHz and IF Q = 70MHz. The intermediate frequency signal thus obtained is filtered using a bandpass filter, 561, with narrow bandwidth, BP lt centered on the IF frequency Q , to select the signal s 1; as shown in the Bi diagram of Fig. 5B. The signal at the output of the filter 561 is then mixed with a first reference frequency, to bring the signal at frequency f GNSS• The signal thus mixed is filtered by means of the band-pass filter, 581, of bandwidth, BP, before being returned to the duplexer to be injected at the distal end of the first cable segment. As can be seen in diagram Ci of Fig. 5B, the signal at the output of the filter 581 now only includes the signal s 1; centered on the frequency f GNSS - This signal propagates in the first cable segment in the return direction.

[0081] On a second branch at the output of the RF divider, the signal is mixed, by means of a mixer 552, at a second translation frequency f2 to center the spectrum of all the signals s3, ..., s N at the intermediate frequency IF Q . The intermediate frequency signal thus obtained is filtered by means of a band-pass filter 562, the bandwidth of which, BP2, makes it possible to select all the remaining signals s3, . . . , s N, as shown in diagram B? of Fig. 5B.

[0082] The output signal of the 562 filter is then mixed with a second reference frequency2 re ^ in the mixer 572, then filtered by means of the bandpass filter, 582, of bandwidth, BP, before being injected into the second cable segment. As can be seen in diagram C2 of Fig. 5B, the second composite signal at the output of the filter 582 now only includes the GNSS signals s3, s4, . . . , s N , the signal then being centered on the frequency f GNSS • The second composite signal propagates in the second cable segment, in the forward direction.

[0083] According to a variant not shown, mentioned above in relation to Fig. 4, the second reference frequency of the mixer 572 can be chosen so that the signal s4 is centered on the frequency f GNSS- The second composite signal at the output of filter 582 comprises the same GNSS signals as above but shifted by - δf . It will be noted that, in this variant, the shape of the second composite signal is similar to that of the first composite signal and consequently, the chaining of the cable segments can be iterated while keeping the same principle of bandpass filtering at the intermediate frequency then transposition to the frequency f GNSS -

[0084] Other variants of the RF interconnection box may still be envisaged by those skilled in the art without departing from the scope of the present invention. For example, the bandpass filter 520 and the amplifier 530 may be placed on each of the channels. In addition, amplifiers may be provided on each of the channels so as to compensate for the attenuation in the RF divider and the bandpass filters 561, 581, resp. 562, 582.

[0085] The detail of the RF termination box of Fig. 4 has been shown schematically in Fig. 5C.

[0086] The RF termination box is connected to the distal end of the last radiating cable segment from the GNSS signal generator. When the positioning system structure is tree-like as shown below, an RF termination box is provided at each leaf of the tree.

[0087] The RF termination box includes an RF port, 500, for connection to the cable segment in question. The RF port 500 is connected to a duplexer 510, the composite GNSS signal, formed here by the signals s N-lt s N(e.g. s3, s4 in the example of Fig. 4) received on this port, is filtered by the bandpass filter 520, of bandwidth BP, then supplied to the amplifier 530. The gain of the amplifier is again advantageously chosen so as to compensate for the attenuation in the radiating cable segment, 422. The spectrum of the composite signal is illustrated in diagram A, the spectrum of the signal s N-± being centered on the frequency f GNSS . We thus understand that the signal s N-± was at frequency f GNSS during its propagation to go into segment 422. Without loss of generality, we will assume here that TV = 4 and give the general case in parentheses). The second amplified composite signal is then mixed in the mixer 550 with a third translation frequency / 3 (more generally with an Nth translation frequency f N ) to bring the signal s4 (more generally the signal s w) at the intermediate frequency IF Q The output signal of the mixer 550 is then filtered by the bandpass filter 560, with a bandwidth BP ± centered on / F0 to select the last remaining GNSS signal, in this case the s4 signal. The signal filtered by the filter 560 is then mixed, in the mixer 570, with a third reference frequency, (more generally to transpose the signal \4 to the frequency f GNSS .

[0088] The signal s4(s w ) thus transposed in frequency is filtered by means of the bandpass filter, 580, of bandwidth, BP. This signal is supplied to the duplexer 510 which injects it at the distal end of the second segment, so that it propagates there in the return direction.

[0089] Alternatively, according to the second variant mentioned above if the signal s4(s w ) was at frequency f GNSSduring its forward propagation in segment 422, the third translation frequency would be chosen so as to bring the signal s3 (more generally the signal s N-1 ) at the intermediate frequency IF Q . The bandpass filter 560 would then select the signal s3(s N-1 ) with bandwidth BP1 and mixer 570 would use the same third reference frequency, to transpose the signal s3 to the frequency f GNSS •

[0090] Finally, other variants of the RF termination box may be envisaged by those skilled in the art without departing from the scope of the present invention. Thus, for example, an additional amplifier may be provided before injection into the input port of the duplexer, so as to compensate for the attenuation undergone by the signal in the bandpass filters 560 and

[0091] 580. Fig. 6A schematically represents a positioning system using 4 radiating cable segments according to a first exemplary embodiment of the invention.

[0092] This exemplary embodiment is a 4-segment extension of the embodiment of Fig. 4, with elements 610, 615, 630 having the same functions as elements 410, 415, 430, respectively. RF interconnect boxes 641, 642, 643 also have the same function as RF interconnect box 440, the structure of which is shown in Fig. 5A. Finally, RF termination box 650 has the same function as RF termination box 450, the structure of which was shown in Fig. 5C.

[0093] Unlike the embodiment of Fig. 4, the GNSS signal generator here provides 8 signals s1, s2, ..., s7, s8.

[0094] In this embodiment, the signals s1, s2 are emitted at the frequency fûNss P ar I efirst segment (respectively in the return and forward propagation directions), and, if we adopt the aforementioned variant, the signals s3, s4 are emitted at this same frequency by the second segment (respectively in the return and forward propagation directions),..., and finally the signals s7, s8 are emitted at the frequency fûNss P ar I e last segment (respectively in the return and forward propagation directions).

[0095] Fig. 6B schematically represents a positioning system using 4 radiating cable segments according to a second exemplary embodiment of the invention.

[0096] This embodiment differs from the first in that it comprises two 2-segment positioning systems, of the type illustrated in Fig. 4, mounted head to tail. The first positioning system consists of the elements designated 610-650 and the second consists of the elements designated 610'- 650'. Elements 610 to 650, on the one hand, and 610' to 650', on the other hand, are identical to elements 410 to 450 of Fig. 4. Thus, the GNSS generator 610', like the generator 610, generates 4 GNSS signals S1', s2', s3,.S4, the signals being emitted at the frequency f GNSSBy the first segment 621' (respectively in the return and forward propagation direction) and the signals s^,s^ being emitted at this same frequency by the second segment (respectively in the forward and return direction; and vice versa in the case of the aforementioned variant). The communication signals 660 can be transmitted between the RF termination boxes 650 and 650', so as to ensure their availability along the 4 segments.

[0097] Fig. 6C schematically represents a positioning system using 4 radiating cable segments according to a third exemplary embodiment of the invention.

[0098] Elements 610, 615, 630 are identical to those bearing the same references in Fig. 6A.

[0099] The third embodiment differs from the first in that its configuration is no longer linear but tree-like. It uses a multiple RF interconnection box with the 4 radiating cable segments. Other configurations, in particular mixed linear / tree-like configurations, may be envisaged by those skilled in the art without departing from the scope of the present invention.

[0100] In the illustrated case, each of the leaves of the tree is equipped with an RF termination box, namely boxes 651, 652, 653.

[0101] Fig. 7 schematically represents the multiple interconnect RF box of Fig. 6C.

[0102] This interconnection box comprises, like that shown in Fig. 5A, a duplexer 710, a first bandpass filter, 720-1, a first amplifier 730-1, as well as a first demultiplexer 745-1, having respectively the same functions as the duplexer 510, the bandpass filter 520, the amplifier 530 and the demultiplexer 545 of Fig. 5A. However, unlike the interconnection box of Fig. 5A, the multiple interconnection box comprises a second demultiplexer 745-2 and a third multiplexer 745-3 in series.

[0103] The first demultiplexer 745-1 translates the spectrum of the composite GNSS signal so as to center the signal s3 on the reception frequency f GNSS > and provides respectively on its first output the signal s 1; reinjected into segment 621, and on its second output a second composite signal formed from signals s3—s8, this second composite signal being injected into segment 623.

[0104] The second demultiplexer 745-2 translates the spectrum so as to center the signal s5 on f GNSS and to provide as output a third composite signal formed from the signals s5—s8, this third composite signal being injected into the segment 624.

[0105] Finally, the third demultiplexer 745-3 translates the spectrum so as to center the signal s7 on f GNSS and to provide as output a fourth composite signal formed from the signals s7—s8, this fourth composite signal being injected into the segment 622.

[0106] It will be understood that unlike the 545 demultiplexer, the 745-2 and 745-3 demultiplexers only include one output, corresponding to that of the first branch of the 545 demultiplexer.

[0107] Generally, demultiplexers provide frequency changes of GNSS signals within composite signals, typically by means of a frequency shift. Since the GNSS signals are regularly spaced by a gap Sf in the spectrum of the composite GNSS signal, and the intermediate frequency is advantageously chosen to be equal to a multiple of this gap, the different translation frequencies f_...f N as well as the different reference frequencies f™ f -- -f™ fcan be generated from a clock signal at the frequency Sf. In other words, this clock signal can serve as a basic signal from which the translation and reference frequencies are generated programmatically. A first approach could be to transmit the clock signal with the GNSS signals from one segment to the other. However, if this frequency is radiated by the cable segments, authorization to transmit at this frequency and radio certification may be necessary. This frequency may also be prohibited because it is already used for other purposes by other user equipment and could therefore disrupt the user's operation by interference. Finally, the signals propagating in the outward and return directions, intended for the GNSS receiver, must be perfectly at the same frequency f GNSS -

[0108] According to an advantageous embodiment of the invention, the clock signal is generated in each interconnection box by mixing at least two so-called synchronization signals. These synchronization signals are obtained by modulating two continuous waves, separated by a gap Sf, by a common frequency spreading sequence of low frequency compared to that of the C / A codes, in other words that of the pseudo-random sequences (PRN) used in the GNSS signals.

[0109] Fig. 8 schematically represents the spectrum of a composite GNSS signal injected into a radiating cable, this signal including both GNSS signals (here two GPS signals) and synchronization signals.

[0110] The GNSS signals were represented at 810 and 820 and the synchronization signals were represented at 830 and 840. The frequency difference between the GNSS signals is equal to that between the synchronization signals (here Sf = 10MHz). It is noted that the spectral spread of the synchronization signals is much less than that of the GNSS signals. The use of spectrally spread synchronization signals reduces the level of interference in the environment. The synchronization signals can be placed arbitrarily in unoccupied areas of the spectrum. Advantageously, the synchronization signals can be located far from the central frequency f G Nss, in holes in the spectral density of the GNSS signal (zeros of the cardinal sine). This precaution improves the signal-to-noise ratio of both the GNSS signals and the clock signal.

[0111] The clock signal Clk can be obtained by multiplying the synchronization signals together, for example the synchronization signals 830 and 840, as explained below.

[0112] Fig. 9 schematically represents a circuit for generating a clock signal from the composite signal shown in Fig. 8.

[0113] The generation circuit receives the aforementioned composite signal, comprising the GNSS signals and the synchronization signals. This composite signal is filtered by a first bandpass filter 910 (isolating the band of the GNSS signals, for example a filter centered on the L1 frequency in the case of a GPS system) so as to improve the signal-to-noise ratio in the processing chain.

[0114] The composite signal thus filtered is then amplified in an automatic gain control (AGC) amplifier, 920, divided into 2 by a power divider, 930, and then multiplied with itself in a mixer 940 (or a component with a non-linear characteristic). Since the synchronization signals are modulated by means of the same pseudo-random sequence, the product of two such signals centered on two frequencies and = fsync + δf gives, on the one hand, a continuous wave at the (beat) frequency Af and, on the other hand, a continuous wave at the frequency + Sf , the latter being eliminated here by a second band-pass filter, 950, centered on Sf . Indeed, the multiplication of a pseudo-random sequence (expressed in BPSK form) with itself gives a constant value. The output signal of the second bandpass filter is then amplified in amplifier 960 and then, if necessary, injected into a phase-locked loop 970 to reduce jitter.The output signal of the clock generation circuit is a stable continuous wave at frequency Sf which can be used as a basic signal to generate the frequencies supplied to the various mixers as described previously.

Claims

DEMANDS 1. A positioning system along a radiating cable, composed of at least a first segment (421) and a second segment (422), said system comprising: means for generating (410) a first composite GNSS signal formed from a plurality of GNSS signals defined as those that would be received in an open-sky configuration by points located at the ends of the different segments of the cable, each segment being associated with a first GNSS signal that would be received from a first point at a proximal end of that segment from satellites belonging to a first cone of visibility, and a second GNSS signal that would be received from a second point at a distal end of that segment from satellites belonging to a second cone of visibility, said GNSS signals being frequency multiplexed to form said composite GNSS signal, said composite GNSS signal being injected at the proximal end of the first segment,the first GNSS signal associated with the first segment being at the reception frequency of a GNSS receiver, f, GNSS ; an RF interconnection box (440) connected between the first and second segments, intended to demultiplex the first composite GNSS signal by frequency-shifting the different GNSS signals of the first composite signal and to provide, on the one hand, on a first output, the second GNSS signal associated with the first segment at the frequency f GNSS and to provide, on the other hand, on a second output, a second composite GNSS signal in which the first and second GNSS signals associated with the first segment are eliminated, the second GNSS signal of the first segment being injected at frequency f GNSS at the distal end of the first segment and said second composite GNSS signal being injected at the proximal end of the second segment; an RF termination box (450) connected to the distal end of the second segment and intended to shift at the frequency f GNSSI e second GNSS signal associated with the second segment, and to inject it at the distal end of the second segment.

2. A positioning system along a radiating cable according to claim 1, characterized in that the GNSS signals of the first composite GNSS signal are located at frequencies f GNSS + where i is an integer.

3. A positioning system along a radiating cable according to claim 2, characterized in that the RF interconnection housing comprises a first demultiplexer (545) including an RF divider (540) for dividing the first composite signal between a first channel and a second channel, the first channel comprising: a first mixer (551) for mixing the composite signal thus divided with a first translation frequency (f) such that the second GNSS signal of the first segment is translated to an intermediate frequency (IF0); a first bandpass filter (561) having a first bandwidth (BP) around said intermediate frequency for selecting the second GNSS signal of the first segment thus translated; and a second mixer (571) for mixing the second GNSS signal of the first segment thus selected with a first reference frequency. so as to transpose the latter to the frequency f GNSS - 4. A positioning system along a radiating cable according to claim 3, characterized in that the second channel comprises a third mixer (552) for mixing the split composite signal with a second translation frequency (θ2) such that a second composite GNSS signal is translated at the intermediate frequency (7F0); a second bandpass filter (562) having a second bandwidth (5F2) around said intermediate frequency for selecting the second composite GNSS signal; and a fourth mixer (572) for mixing the second composite GNSS signal with a second reference frequency so as to transpose the latter to the frequency f GNSS .

5. Positioning system along a radiating cable according to claim 3 or 4, characterized in that the first channel further comprises a third bandpass filter (581) for filtering the second GNSS signal of the first segment and that the second channel also comprises a fourth bandpass filter (582) for filtering the second composite GNSS signal.

6. Positioning system along a radiating cable according to any one of claims 3 to 5, characterized in that the RF interconnect housing further comprises a duplexer (510) whose common port (500) is connected to the distal end of the first segment, the output port is connected to the input of the RF divider (540) and the input port is connected to the output of the second mixer (571) of the first channel.

7. Positioning system along a radiating cable according to claim 6, characterized in that the RF interconnect housing further comprises, between the output port of the duplexer and the input of the RF divider, a common bandpass filter (520) having the bandwidth of the first composite signal in series with an amplifier (530), the gain of the amplifier being chosen to compensate for the attenuation of the composite GNSS signal in the first segment.

8. A positioning system along a radiating cable according to claim 2, said radiating cable being composed of a plurality N of segments, characterized in that the RF termination box comprises: a first mixer (550) at an Nth translation frequency (f N ) so that the second GNSS signal of the Nth segment is translated to an intermediate frequency (IF0), a first bandpass filter (560) having a first bandwidth (BP) around said intermediate frequency to select the second GNSS signal of the Nth segment thus translated, and a second mixer (570) to mix the second GNSS signal of the Nth segment thus selected with an Nth reference frequency so as to transpose the latter to the frequency f GNSS - 9. Positioning system along a radiating cable according to claim 8, characterized in that the RF termination box further comprises a duplexer (510) whose common port (500) is connected to the distal end of the Nth segment, the output port is connected to the input of the first mixer (550) and the input port is connected to the output of the second mixer (570).

10. Positioning system along a radiating cable according to claim 9, characterized in that the RF termination box further comprises, between the output port of the duplexer and the input of the RF divider, a second bandpass filter (520), having the bandwidth of the last composite signal associated with the Nth segment, called the last segment, followed by an amplifier (530), the gain of the amplifier being chosen to compensate for the attenuation of the last composite GNSS signal in the last segment.

11. Positioning system along a radiating cable according to claim 2, characterized in that the means for generating the composite GNSS signal also generate in this signal at least two synchronization signals having a frequency difference of Sf, each synchronization signal being obtained by modulating a continuous wave with a pseudo-random spectral spreading sequence, said random sequence being chosen to be identical for all the synchronization signals.

12. Positioning system along a radiating cable according to claim 11, characterized in that the center frequencies of the synchronization signals are located in areas of reliable spectral density of the first composite GNSS signal.

13. Positioning system along a radiating cable according to claim 11 or 12, characterized in that the RF interconnection box and the RF termination box each comprise a clock signal generation circuit comprising a mixer (940) for multiplying the composite signal with itself, a low-pass or band-pass filter (950) so as to isolate from the mix a component at the frequency Sf.