ALTERNATING BIDIRECTIONAL RADIO LINK SYSTEM WITH SUBCARDHOLDER MODULATION.

Abstract

L'invention concerne un système de liaison hertzienne bidirectionnelle alternée à modulation de sous-porteuse. Le système comporte des premiers moyens émetteursrécepteurs 1 et des deuxièmes moyens émetteurs-récepteurs 2. Pour la transmission de messages, les moyens émetteurs-récepteurs 1 émettent une onde hyperfréquence continue vers les moyens émetteurs-récepteurs 2, lesquels réfléchissent l'onde électromagnétique précitée vers les moyens émetteurs-récepteurs 1 en effectuant une modulation de sous-porteuse à fréquence intermédiaire au moyen d'un modulateur 52110, 5211. La détection du système d'onde stationnaire créée du fait de l'émission de l'onde électromagnétique et de la réflexion de celle-ci vers les moyens émetteurs-récepteurs 1 est effectuée au moyen de deux diodes de détection 5161, 5162 décalées d'un multiple impair de quarts de longueur d'onde dans la direction de propagation de l'onde électromagnétique dans le guide d'onde d'alimentation de l'antenne 515 des premiers moyens émetteurs récepteurs 1. Un traitement logique 514 permet de restituer le signal de modulation binaire constitutif du message transmis par les moyens émetteurs-récepteurs 2. Application à l'échange de messages bidirectionnels entre un ou plusieurs véhicules et un point fixe ou lui-même mobile.

Description

The present invention relates to an improvement of a bidirectional alternating radio link system in accordance with the main patent application no. 87 17219 filed on December 10, 1987 in the name of the Applicant. In the aforementioned main patent application, the alternating bidirectional radio link system comprises first and second transceiver means ensuring bidirectional communication by transmitting an electromagnetic signal. The first transceiver means include means for transmitting a continuous electromagnetic wave to the second transceiver means, means for modulating the amplitude of the continuous electromagnetic wave, means for controlling and commanding the modulation means, and means for receiving the electromagnetic signal transmitted by the second transceiver means.The second transmitter-receiver means include means for receiving the continuous electromagnetic wave emitted by the first transmitter-receiver means, means for reflecting the continuous electromagnetic wave emitted by the first transmitter-receiver means to generate a reflected electromagnetic wave, means for modulating the amplitude of the reflected continuous electromagnetic wave to generate the electromagnetic signal transmitted by the second transmitter-receiver means, and means for controlling and commanding the modulation means and the receiving means. In order to ensure better detection of transmitted electromagnetic signals, in the aforementioned device a system for moving the short-circuit plane in the antenna feed waveguide can be provided at the level of the reflectors of the second transmitter-receiver means, this movement ensuring a corresponding movement of the maxima and minima of the voltage of the standing waves generated by the emission of electromagnetic waves and their reflection between the first and second transmitter-receiver means and a correction of the amplitude level of the detected signal. This correction system, while satisfactory during experimentation, proved sensitive to the environment of the first and second transceiver units. In particular, when using these two-way radio link systems with motor vehicles, as described in the main patent application, the second transceiver units, which are essentially highly sophisticated carriers, are supported by the vehicle's infrastructure. This infrastructure can then cause glare from the electromagnetic wave emitted by the first transceiver units by reflecting it, which, in most cases, leads to malfunction of the entire system. The present invention aims to remedy the aforementioned drawback that may arise in the application under consideration. In accordance with the object of the present invention, the aforementioned correction system is eliminated and the amplitude modulation means of the second transmitter-receiver means are provided with means for generating an intermediate frequency subcarrier wave, the subcarrier wave being transmitted as a modulation signal of the electromagnetic signal transmitted by the second transmitter-receiver means to the first transmitter-receiver means during the values ​​of the bits constituting the link messages, the zero or one values ​​of the aforementioned bits corresponding to an absence of transmitted electromagnetic signal and subcarrier.The first transmitter-receiver means then include receiver means comprising, on the one hand, means for detecting standing waves generated by the emission of the continuous electromagnetic wave and by the reception of the electromagnetic signal transmitted by the second transmitter-receiver means, these detection means delivering a detected signal and, on the other hand, means for demodulating the detected signal to restore the modulation signal of the reflected electromagnetic wave to generate the electromagnetic signal transmitted by the second transmitter-receiver means to the first transmitter-receiver means. The system according to the invention is then usable for the two-way radio link of motor vehicles, regardless of the importance of the infrastructure of the latter. A more detailed description of a particularly advantageous embodiment of the system that is the subject of the invention will be given below in connection with the accompanying figures in which Figure 1 represents, in parts a) and b), a synoptic diagram of the second and first transmitter-receiver means. Figure 2, in its parts A to E, represents signal timing diagrams at the corresponding test points A to E of Figure 1, relative to the first and second transmitter-receiver means, Figure 3 represents in its part a) a perspective view of the microwave part of the first transmitter-receiver means 1, and in its part b) a cross-sectional view along a longitudinal plane of symmetry containing the longitudinal axis A of the feed waveguide of the antenna of the transmitter-receiver means 1. A very detailed description of the system which is the subject of the invention will be given in connection with Figure 1 in its parts a) and b). Throughout the figures, references identical to those used in the main patent application designate the same elements. According to Figure 1 at point A) thereof, the amplitude modulation means 23 of the second transmitter-receiver means 2 include means for generating a subcarrier wave at an intermediate frequency IF. The means for generating the intermediate frequency subcarrier wave may consist, as shown in the aforementioned figure, of a modulator 52110 and a diode 5211, the diode 5211 being, for example, connected in parallel to the feed waveguide of the antenna 5210 of the second transceiver means 2. According to an advantageous aspect of the system of the invention, the subcarrier wave may be emitted by the modulator 52110 at a frequency of a few hundred kHz and, preferably, equal to 400 kHz. The subcarrier wave is transmitted as a modulation signal of the electromagnetic wave transmitted by the second transceiver means 2 to the first transceiver means 1.Preferably, and as will be described in detail later in the description, the link messages between the transmitter-receiver means 1 and the transmitter-receiver means 2 are binary messages, the subcarrier wave being transmitted in bursts with the carrier wave during the values ​​of the bits of the aforementioned link messages, the zero or one values ​​of the bits of these same messages corresponding, for example, to an absence of transmitted electromagnetic wave and subcarrier. Furthermore, and analogously to the system and the second transmitter-receiver means described in the main patent application, the latter comprise an amplifier 5212 whose function is analogous to the amplifier 212 described in the main patent application, as well as control and command means 524 whose function is analogous to the control and command means 24 of the second transmitter-receiver means 2 described in the main patent application.It is worth noting for the record that the control and command means 524 may consist of a system for modifying the transmitted code, a code storage system, and a code generator system. Furthermore, a VMOS-type switch 5215 is controlled by the amplifier system 5212; this switch allows control of the code generator and ultimately of the modulator 52110, for example. The operation of the second set of transceiver means 2 will not be described in further detail with regard to the code generation process and thus the link messages, as this process is similar to the operating mode already described in the main patent application for the same assemblies. In accordance with the object of the invention, as shown in part b) of figure 1, the receiving means of the first transmitter-receiver means 1 advantageously comprise means 516 for detecting standing waves generated by the emission of the continuous electromagnetic wave and by the reception of the electromagnetic signal transmitted by the second transmitter-receiver means 2. Of course, these standing waves are generated between the transmit-receive antenna 515 of the first transmitter-receiver means 1 and the transmit-receive antenna 5210 of the second transmitter-receiver means 2. The detection means 516 deliver a detected signal. In addition, the first transmitter-receiver means 1 include means 514 demodulators of the detected signal to restore the modulation signal of the reflected electromagnetic wave to generate the electromagnetic signal transmitted by the second transmitter-receiver means to the first transmitter-receiver means 1. Preferably, as advantageously shown in part b) of Figure 1, the aforementioned standing wave detection means 516 comprise two detection diodes 5161 and 5162, these diodes being arranged in the feed waveguide of the transmit-receive antenna 515 of the first transmit-receive means. These diodes are preferably arranged orthogonally to the polarization direction of the electric field of the electromagnetic wave and are separated, along the propagation direction of the aforementioned electromagnetic wave, by an odd multiple of quarter-wavelengths from the electromagnetic wave propagating in the aforementioned waveguide. As further shown in Figure 1, part b), the detected signal demodulators 514 comprise, for each detection diode 5161, 5162, amplifier means 5141A and 5152A, which amplify the detected signal and deliver an amplified detected signal. The demodulators 514 also comprise trigger means 5141D and 5142D, respectively. These threshold trigger means shape the amplified detected signal. As noted in Figure 1, part b, an amplifier and a threshold trigger, associated with each diode, form a first and second detection channel, 5141 and 5142, respectively. Each detection channel delivers a detection logic signal. Furthermore, as also shown in Figure 1 at point b), the demodulating means 514 of the detected signal include a circuit 5143 for processing the elimination of the subcarrier and restoring the modulation signal of the reflected electromagnetic wave to generate the electromagnetic signal transmitted by the second transmitter-receiver means 2 to the first transmitter-receiver means 1. The previously mentioned processing circuit 5143 includes, in an advantageous embodiment, an OR logic gate receiving, at a first and second input respectively, the detection logic signal delivered by the first and second detection channels 5141 and 5142 respectively. The OR logic gate outputs a resulting detection logic signal. The processing circuit 5143 also includes a monostable circuit receiving the resulting detection logic signal. The duration of the metastable state of the aforementioned monostable circuit is much greater than the subcarrier period. The aforementioned monostable circuit thus allows for the replication of the modulation signal of the reflected electromagnetic wave to generate the electromagnetic signal transmitted by the second transmitter-receiver means 2. It will be understood that the transmission operation of the first transmitter-receiver means 1 to the second transmitter-receiver means 2 is substantially analogous to the transmission operation of the system described in the main patent application. The same applies to the reception operation of the aforementioned electromagnetic wave by the second transmitter-receiver means and, in particular, of the standby amplifier 5512 and the control circuits 524 that generate the message or code in question. On the other hand, the operation of the message generated by the second transmitter-receiver means 2 and the operation of the reception of these same messages by the first transmitter-receiver means I in their configuration as represented in Figure 1 at point a) and b) thereof will be described in detail in connection with Figure 2. In the aforementioned Figure 2, at point A, the transmission signal present at test point A of Figure 1 in part a) is represented. As a non-limiting example, when a bit of a transmitted binary message has a value of 1, no microwave or subcarrier wave is emitted; the incident wave is simply reflected by the transmitting antenna 5210. Conversely, when a bit has a value of zero, the intermediate frequency modulator 5210 is activated and an intermediate frequency modulation wave IF is generated, which then modulates the electromagnetic wave reflected by the transmitting antenna 5210 and together with it constitutes the electromagnetic signal transmitted by the second transmitter-receiver means.It should be noted, however, that for clarity in Figure 2, the reflected microwave electromagnetic wave is not shown, although it is present regardless of whether the bits zero or one are in the transmitted message. The electromagnetic signal shown at point A in Figure 2, transmitted to the first transmitter-receiver means 1, then induces a standing wave system in the space between the transmitting antennas 5210 and 515 of the second transmitter-receiver means 2 and the first transmitter-receiver means 1, respectively. This standing wave system is shown, for example, at test point B in Figure 1 in part b) of that figure relating to the transmitter-receiver means 1.It should be noted in particular that, with regard to point B in Figure 2, the x-axis is graduated in distance, unlike the other points A, C to F in the same figure, for which the x-axis is graduated in time, the y-axis of all the timing diagrams being graduated in amplitude. However, for reasons of pure convenience, the time-domain timing diagram of the intermediate frequency (IF) subcarrier is also represented at point B in Figure 2 within the standing wave node and antinode system, it being understood that this representation cannot, however, be made with respect to the x-axis graduated in distance from point B in this figure. Conventionally, the distance between a node and an antinode of the standing wave system is equal to one-quarter of the wavelength of the microwave propagating in the interconnect waveguide of the transmit-receive antenna.The corresponding signals, taken from diodes 5161 and 5162 respectively, are shown at point C in Figure 2 at points a) and b) thereof. Due to the offset of the position of the aforementioned diodes along the direction of propagation of the electromagnetic wave in the waveguide and the phenomenon of standing waves present in the waveguide, there is always a relative maximum or minimum of electric field on each diode, depending on the position of the aforementioned diodes with respect to a node or antinode of the standing wave system established in the waveguide.The relative maxima and minima are represented in points a) and b), and it will be understood that, regardless of the established standing wave system, which depends in particular on the distance between the transmitting and receiving antennas of the first and second transmitter-receivers 1 and 2, the aforementioned relative maxima and minima present at either diode constitute the previously mentioned detection signal. It will also be understood that the intermediate frequency signal of the subcarrier present at one diode is slightly out of phase with the subcarrier signal present at the other diode, but this phase shift does not affect the overall signal.The signals represented at test point C at points a) and b) are respectively received by amplifiers 5141A and 5142A, which deliver amplified signals to threshold triggers 5141D and 5142D, the aforementioned threshold triggers ensuring a reshaping of the amplitude modulation of the subcarrier, as represented at point B of Figure 2 at points 1) and 2) thereof, these points corresponding to test points D1 and. D2 of figure 1 part b). The 5143 subcarrier removal processing circuit then receives the signals shown at point D in 1) and 2) of Figure 2, and the OR gate, regardless of the relative amplitude of the signals shown in D1 or D2, then outputs a resulting logic detection signal shown at point E of Figure 2, which corresponds to test point E of Figure 1, part b) thereof. The monostable receiving the aforementioned signal, due to the much longer duration of its metastable state than the period of the intermediate frequency signal, is then held in its position during the presence of the intermediate frequency signal IF. The repetition of the metastable state of the aforementioned monostable thus allows the values ​​of the bits of the transmitted message to be copied according to the signal shown at point A of Figure 2, and the value of the following bit to be zero or one, in the absence of a subcarrier or intermediate frequency signal IF.The aforementioned monostable thus makes it possible to eliminate the aforementioned subcarrier by ensuring a copy of the binary state of the modulation signal constituting the message transmitted by the second means transmitter-receiver 2. In Figure 1, part b) thereof, a microwave emission source constituting the emission source of the transmitting means constituting the first transmitter-receiver means 1 has been further represented by 511. Similarly, a modulator allowing the amplitude modulation of the electromagnetic wave emitted by the first transmitter-receiver means 1 has been represented by 512. In a conventional manner, the transmitter comprising the aforementioned source 511 of the first transmitter-receiver means 1 can be constituted by a resonant cavity whose active element is, for example, a diode Gunn. The oscillation frequency, as already mentioned in the main patent application for generating the emission microwave wave, is 9.9 CHz and the radiated power is less than 10 mW. In addition, the detection diodes 5161 and 5162 can be made up of Schottky diodes. A more detailed description of the microwave part of the first transmitter-receiver means 1 will be given in connection with Figure 3. The aforementioned figure shows the transmitting / receiving antenna, which, in an advantageous but non-limiting embodiment, consists of a parabolic reflector and a waveguide feeding a transmitting dipole. The antenna 515 thus constituted is fed by a rectangular LW waveguide, as shown in point a) of Figure 3. The detection diodes 5161 and 5162 are arranged, as shown in point a) of Figure 3, in the vicinity of the walls of the LW waveguide perpendicular to the electric field of the emitted or received electromagnetic wave. At point b) of this same figure 3, we have shown in cross-section the waveguide GO equipped in the vicinity of its walls with the detection diodes 5161 and 5162. The diodes are orthogonal to the electric field E and are spaced along the direction of propagation B of the guided electromagnetic wave by an odd multiple of quarters of wavelength of the latter.The arrangement of the aforementioned diodes in the vicinity of the walls of the waveguide, the diodes being further arranged on either side of the longitudinal axis A of the aforementioned waveguide, makes it possible not to affect the configuration of the standing wave system created between the transmit-receive antenna 515 of the first transmit-receive means and the transmit-receive antenna 5210 of the second transmit-receive means 2. While still allowing one or the other diode to be maintained at a relative maximum of voltage or signal with respect to the other, regardless of the distance of the transmit-receive means 1 with respect to the transmit-receive means 2 or regardless of the variation thereof. A high-performance, alternating bidirectional radio link system has been described, suitable for use in challenging environmental conditions, particularly for exchanging messages between one or more motor vehicles and a fixed or moving point. Naturally, the message exchange protocols previously described in the main patent application can be used to implement the system of the present invention.

Claims

DEMANDS 1. A bidirectional alternating radio link system according to any one of claims 1 to 14 or 18, 19 of the main patent, characterized in that said amplitude modulation means (23) of the second (2) transceiver means comprise means for generating an intermediate frequency subcarrier wave, said subcarrier wave being transmitted as a modulation signal of the electromagnetic wave transmitted by the second (2) transceiver means to the first transceiver means during the values ​​of the bits constituting the link messages, the values ​​zero or one of said bits corresponding to an absence of transmitted electromagnetic wave and subcarrier, said receiver means of the first (1) transceiver means comprising - means (516) for detecting standing waves generated by the emission of the continuous electromagnetic wave and by the reception of the electromagnetic signal transmitted by the second (2) means transceivers, said detection means delivering a signal detected, - means (514) demodulators of said detected signal to restore the modulation signal of the reflected electromagnetic wave for generate said electromagnetic signal transmitted by the second (2) transmitting and receiving means towards the first transmitting means receptors (1).

2. System according to claim 1, characterized in that said standing wave detection means (516) comprise: two detection diodes (5161, 5162) arranged in the feed waveguide (90) of the transmit-receive antenna (515), said diodes arranged orthogonally to the polarization direction of the electric field of said electromagnetic wave being separated, along the propagation direction thereof, by an odd multiple of quarters of wavelength of said electromagnetic wave.

3. System according to claim 2, characterized in that said detection diodes (5161, 5162) are arranged in the vicinity of the walls of the waveguide orthogonal to the electric field of the emitted and / or received electromagnetic wave.

4. System according to claim 3, characterized in that said diodes (5161, 5162) are arranged on either side of the longitudinal axis of the feed waveguide of the transmit-receive antenna.

5. A system according to any one of claims 2 to 4, characterized in that said demodulating means (514) for said detected signal comprise, for each detection diode (5161, 5162), amplifier means (5141A, 5142A) for amplifying the signal detected, and delivering an amplified detected signal - threshold triggering means (5141D, 5142D) allowing to perform a shaping of the detected amplified signal, an amplifier and a threshold trigger associated with each diode forming a first and a second detection channel (5141, 5142), each detection channel delivering a logic detection signal, - a subcarrier removal processing circuit (5143) and restoration of the modulation signal of the reflected electromagnetic wave to generate the electromagnetic signal transmitted by the second (2) transmitting-receiving means to the first transmitting means receptors (1).

6. System according to claim 5, characterized in that said processing circuit (5143) comprises - an OR logic gate receiving on a first respectively second input the detection logic signal delivered by the first respectively second detection channel, and delivering a logic signal resulting detection, - a monostable type circuit receiving said detection logic signal resulting in the duration of the metastable state of said monostable circuit being much longer than the duration of the period of said sub-carrier, said monostable allowing to perform a copy of the modulation signal of the reflected electromagnetic wave to generate the electromagnetic signal transmitted by the second (2) means transmitter-receivers.