WO2004082169A1

WO2004082169A1 - Antenna transmission method and device for motor vehicles

Info

Publication number: WO2004082169A1
Application number: PCT/FR2004/000447
Authority: WO
Inventors: Olivier Seller
Original assignee: France Telecom
Priority date: 2003-03-07
Filing date: 2004-02-27
Publication date: 2004-09-23
Also published as: EP1602181A1; FR2852171A1

Abstract

The invention relates to an antenna transmission method and device for motor vehicles. The inventive device is intended to be fixed to a vehicle having a determined direction (4) of movement. According to the invention, at least one channel is formed, which corresponds to the transmission or reception of the signal and which is limited to an angular section (9j) associated with the path direction of the signal, of less than 360°. The channel is connected to a means which is used to apply a frequency correction thereto. The aforementioned frequency correction is dependent on the value of the speed at which the vehicle is moving in the direction (4) of movement and on an angular value included in the channel section (9j), such as to reduce the frequency offset of the channel owing to the Doppler effect acting on the signal.

Description

METHOD AND DEVICE FOR ANTENNA TRANSMISSION ON

MOTOR VEHICLE.

The invention relates to a transmission device intended to be fixed to a motor vehicle, as well as to a transmission method on a motor vehicle.

One field of application of the invention relates to communication between a fixed broadcasting center and a motor vehicle which moves in relation to the latter and on which a transmitting and / or receiving antenna is fixed.

The movement of the motor vehicle induces a Doppler effect during transmission or reception, which manifests itself in frequency spreading of the signal transmitted or received, due to an offset in frequency of each electromagnetic path transmitted or received. This frequency shift is troublesome for narrowband signals. Thus the Doppler effect is particularly penalizing for example for transmissions using a multi-carrier modulation of the OFDM type, in which the carriers have a low bandwidth, since it results in interference between carriers. More generally, the Doppler effect tends to scramble the transmitted or received signal.

The invention aims to obtain a transmission device remedying the drawbacks of the state of the art and making it possible to improve the transmission of signals during movement.

To this end, a first object of the invention is a transmission device intended to be fixed to a motor vehicle having a prescribed direction of instantaneous movement, the device comprising at least one antenna capable of transmitting or receiving a signal having at least one electromagnetic space propagation path and a channel forming means connected to said antenna, characterized in that the channel forming means and said antenna are such that at least one channel corresponding to the emission is formed or the reception of the signal, limited to at least one associated angular range of orientation of the electromagnetic path of the signal, the channel is connected to a means for applying a frequency correction to the channel, the frequency correction being controlled by correction control means and dependent on a value of the speed of movement of the motor vehicle in the direction of instantaneous movement and a prescribed angular value for said track, referred to the direction of travel instantaneous and included in the angular domain of the associated channel, so as to reduce the frequency offset of the channel, due to the Doppler effect acting on the electromagnetic path of the signal.

Thanks to the invention, the signal is corrected selectively as a function of the orientation of the path or paths in transmission or in reception and the speed of movement of the vehicle. Thus, the correction of the signal will be carried out each time the vehicle passes during its journey through the corresponding orientation. For each channel formed, the correction has an effect on the signal when the latter has one or more orientation paths included in the channel. It therefore dispenses with having to know at all times the orientation of the vehicle with respect to the electromagnetic path (s) of the received signal, or with respect to the electromagnetic path (s) between the vehicle and a recipient of the transmitted signal.

According to other features of the invention,

- the prescribed track angular value is the angle of the bisector of the associated track angular range with respect to the instantaneous direction of movement;

- or the prescribed angular value of the track is the angle formed by a pointing direction of the track, corresponding to a maximum of its radiation pattern and the direction of movement; - or the prescribed angular value of the track is the average angle θ _mj of the track, defined by

0 _mj = b ^2τ Eiiff. \ θ \. âθ _t where g _j (0) represents the radiation pattern of the channel;

- or the prescribed angular value of the track is the mean angle 0 _mj - of the track, defined by θ _mj ≈ arccos (jo ^27r _gj (0). cos (0). dθ), where arccos denotes the function arccosinus and g _j (0) represents the radiation pattern of the channel;

- the track frequency correction is proportional to the cosine of the track angular value and to the value of the speed of movement of the motor vehicle in the direction of instantaneous movement;

- the frequency correction Δf _j of the channel is given by: Δfj = -k _j . (v / c) .fo.cos (# _mj ), where θ _mj is the angular value of the channel, v is the value of the speed of movement of the motor vehicle in the instantaneous direction of movement, c is the speed of light, fo is the frequency of the carrier of the antenna signal, and k _j is a proportionality factor minimizing the mean absolute Doppler shift SDAM _j equal to SDAMj = (Je ⁺ "pj (f). | f | .df) / (j ≈ ⁺ -pj (f) .df), where p _j (f) is the Doppler spectrum of the channel;

- the frequency correction Δfj of the channel is given by: Δf _j = -k _j . (v / c) .f _o .cos (0 _mj ), where θ _mj is the angular value of the channel, v is the value of the speed of movement of the motor vehicle in the instantaneous direction of movement, c is the speed of light, fo is the frequency of the carrier of the antenna signal, and kj is a proportionality factor minimizing the moment SD _jj2 of order 2 of Doppler shift of the channel (7 _days ), equal to

SD _{j> 2} = (L - ^∞ _Pj (f). | F | ² .df) / (^ ^{+ ∞} _Pj (f) .df), where p _j (f) is the Doppler spectrum of the channel;

- or the frequency correction Δf _j of track is given by: Δfj = - (v / c) .fo.cos (0 _raj ), where θ _mj is the angular value of track, v is the value of the speed of movement of the motor vehicle in the instantaneous direction of travel, c is the speed of light, f ₀ is the frequency of the carrier of the antenna signal; - A track angular domain includes the direction of instantaneous movement;

- At least one track angular domain comprises the direction of instantaneous movement in one direction and another track angular domain comprises the direction of instantaneous movement in the opposite direction; - the track is symmetrical with respect to the direction of instantaneous movement;

the channel forming means and said antenna are such that at least two channels are formed corresponding to the transmission or reception of the signal, limited to at least two different angular domains associated with the orientation of the electromagnetic path of the signal, less than 360 °, and the frequency correction means of the channels are connected to means for combining the corrected channels to output a frequency corrected reception signal or the frequency correction means of the channels are connected to decombination means of an input signal to be transmitted to form accesses to be corrected in frequency by the frequency correction means to form said corrected channels, which supply emission signals to said antenna via the channel forming means;

the combination means or the decombination means comprise channel phase shifting means and / or channel amplitude correction means; - or the combination means or the decombination means are free of channel phase shifting means and channel amplitude correction means;

- The transmission device includes for each channel an antem directive and a link without phase shift to the directive antenna as a means of channel formation;

- the device for transmitting a plurality of N antennas spaced from each other at least along the direction of instantaneous movement, the channel forming means being connected to the plurality of antennas and forming signals V _j of M channels for 1 <i ≤M in the angular domain of associated channel by linear combination of the signals A] of antennas, for 1 ≤l ≤N, according to the formula V _j = ∑ι _{= 1} os, ι Ai, where 0!;, ] = exp (2J7τdj _; ι IX), j is the pure imaginary unit, λ is the wavelength and the value d is the path difference, taken between one chosen antenna and the other antennas, a plane wave making a target angle γ, of track equal to the prescribed angular value θ _{m \} of track i with the direction of movement;

- The antennas are equidistant and aligned parallel to the direction of movement; - the antennas are omnidirectional;

- three omnidirectional antennas separated by λ / 3 are provided, the means for forming channels forming from the three antennas three channels, whose signals Vi, V ₂ , V are given by

V ₁ = A ₁ + e ^{, 'φ} .A ₂ + e ^{]' 2φ} .A ₃

V ₂ = Aι + A ₂ + A ₃

V ₃ = Aι + e- ^jφ .A ₂ + e- ^2jφ .A ₃ where Ai, A ₂ , A ₃ are the signals of the antennas and = 2τβ. - The three channels having the signals Vi, V ₂ , V respectively receive from the correction application means, respectively, channel frequency corrections of -k.fj, 0 and + kf _<. d, where f _d = (v / c) .f ₀ v is the value of the speed of movement of the motor vehicle in the direction of instantaneous movement, c is the speed of light, f ₀ is the frequency of the carrier of the antenna signal, and k is a proportionality factor equal to 0.85;

- a number M of tracks, greater than or equal to 2, are formed by the track forming means, and the angular value θ _m [prescribed track, referred to the direction of instantaneous movement, is a target angle j _\ of track taking the values γ, = (il). 7r / (Ml) for 1 <i <M and ₀ = 0. - the transmission device comprises means for determining the instantaneous value of the speed of movement of the motor vehicle according to the direction of instantaneous movement;

A second object of the invention is a transmission method on a motor vehicle having a prescribed direction of instantaneous movement and on which is fixed at least one antenna capable of transmitting or receiving a signal having at least one electromagnetic propagation path in the space in which at least one channel is formed from or for said antenna, characterized in that said formed channel corresponds to the emission or reception of the signal, limited to at least one associated angular range of electromagnetic path orientation of the signal, a frequency correction for said channel is calculated for said channel depending on the value of the speed of movement of the motor vehicle in the direction of instantaneous movement and of an angular value prescribed for said channel, related to the direction of instantaneous movement and included in the associated angular range of the channel, and the frequency correction is applied to said channel whole, so as to reduce the frequency offset of said channel, due to the Doppler effect acting on the electromagnetic path of the signal.

The invention will be better understood in the light of the description which follows, given solely by way of nonlimiting example with reference to the appended drawings in which:

FIG. 1 is a schematic top view of a motor vehicle fitted with a device according to the invention, FIG. 2 shows a channel training module of the device according to the invention, in the case where it is inserted in a reception chain,

FIG. 3 is a schematic view of the angular domains of the tracks of the device according to the invention,

FIG. 4 schematically shows the formation of corrected channels of the device according to the invention,

FIG. 5 schematically shows another possibility of implementing the formation of corrected channels of the device according to the invention,

FIG. 6 schematically shows a channel correction control module of the device according to the invention,

FIG. 7 is a schematic top view of a motor vehicle fitted with a device according to the invention in an embodiment with three antennas,

FIG. 8 schematically shows the embodiment of the device according to FIG. 7,

FIG. 9 shows a radiation diagram of the channels formed according to FIG. 8, and

FIG. 10 shows the conventional Doppler spectrum of an antenna and the Doppler spectrum of the device according to FIGS. 8 and 9.

In the figures, it is assumed that the transmission device according to the invention is used for receiving signals from the outside. Of course, the transmission device according to the invention can also be used to transmit signals to the outside.

The transmission device comprises one or more antennas li, 1 ₂ , ..., 1 _N for transmitting and / or receiving electromagnetic signals, assumed below for reception of these and generally designated by the number 1. The transmission device comprises suitable means for mounting the antenna (s) 1 on a motor vehicle 2 for fixing them thereon, so that the antenna (s) 1 are immobilized relative to the reference frame of the vehicle 2. The motor vehicle 2 is for example a road passenger car with four wheels 3 running on the ground. Motor vehicle 2 could also be part of a train.

The motor vehicle 2 has a prescribed direction 4 of instantaneous displacement, hereinafter called direction of displacement, which is the direction of its instantaneous speed vector relative to the terrestrial frame of reference and its direction going from its rear part to its front part in one direction. Steps. Each signal transmitted or received by the antennas 1 can have an electromagnetic path of propagation in space, or several electromagnetic paths of propagation in space due to the different reflections undergone on obstacles and / or on the ground. The same information system can also come from several transmitters, as in the case of single frequency networks SFN (Single Frequency Network). The electromagnetic, for example radio, paths transmitted or received by the antenna (s) 1 and the radiation patterns are identified in a horizontal plane containing the direction 4 of displacement by an angle θ relative to the latter.

The antennas li, 1 ₂ , ..., 1 _N are respectively connected to the accesses 5ι, 5 ₂ , ..., 5N of a module 6 for forming channels 7 \, 7 ₂ , ..., 7 _M , WHERE M is less than or equal to N, the channels being also called beams.

According to a first embodiment, the antennas li, 1 ₂ , ..., 1 _N are directional, that is to say each have a radiation diagram having at least a maximum respectively in a determined direction 8ι, 8, ..., 8 _N , different for each antenna l _ls 1 ₂ , ...., 1N, compared to the direction 4 of movement. In this case, M is equal to N and each channel 7 _j (1 ≤j ≤M) is respectively connected to the access 5 _j (1 ≤j ≤N) of the antennas l _ls 1 ₂ , ..., 1N by a single link, without linear combination with the other accesses 5j, where i §, as shown by the broken lines in Figure 2.

In a second embodiment, each channel 7 _j (1 ≤j ≤M) is a linear combination of some of the ports or all of the ports 5ι, 5 ₂ , ..., 5N of the antennas l _l5 1 ₂ , .. ., 1 _N , carried out by module 6, module 5 then being of the beam forming type by calculation (FFC). In this case, the antennas li, 1 ₂ , ..., 1 _N are not necessarily directional and can be omnidirectional.

The beamforming module 5 is arranged so that the channels 7ι 7 _2, _.... 7M formed each correspond to a directional channel radiation diagram in the sense defined above. In addition, each channel radiation diagram has at least a maximum power respectively in a determined direction 8ι, 8 ₂ , ..., 8 _M pointing, different for each channel 7ι, 7 ₂ , ..., 7 _M relative to direction 4 of movement. Each channel 7ι, 7 ₂ , ..., 7 _M is further limited to an angular domain 9ι, 9 ₂ , ..., 9 _M of electromagnetic path orientation with respect to direction 4 of movement. The areas 9ι, 9 ₂ , ..., 9 _M respectively contain the directions 8 _ls 8, ..., 8M pointing and are each less than 360 °. Channels 7 _\ , 7 ₂ , ..., 7 _M are for example each formed by a main radiation lobe, the part of which is located within 3 dB of the maximum power of the lobe is delimited by the associated angular domain 9ι, 92, ..., 9 _M - Each channel 7ι, 7 ₂ , ..., 7 can also include an angular domain 9 _ls 9 ₂ , ..., 9 _M composed of two symmetrical portions with respect to the direction 4 of displacement as shown in FIG. 3 for each of the angular domains 9 ₂ , 9 ₃ and 9 _j , a main radiation lobe being located in each portion. For example, the angular domains 9ι, 9 ₂ , ..., 9 _M are slightly disjointed, meet to cover together 360 ° as shown in the figures

3 and 9, or may overlap slightly. The maximum power of each angular range 9 _\ , 9, ..., 9 _M can be constant or different from one direction of lane pointing to another.

For example, the M channels 7 _ls 7 ₂ , ..., 7 _{M are formed} using N sensors, not shown, connected to the ports 5, 5 ₂ , ..., 5 _N of the antennas. A target angle 7ι, 72, ..., 7 _M of track is chosen for each track 7_, 7 ₂ , ..., 7 _M. These target angles γi, 7 ₂ , - • -, 7 _M of channel take for example the values γ, = (il) .7r / (Ml), for 1 ≤i ≤M and γ ₀ = 0.

Target angles can take other values but check

The sensors can be on a straight line, for example horizontal, or not be aligned. If they are on a straight line, it can be parallel to the direction

4 or not.

The signal V, of the channel 7j for 1 ≤i ≤M is a linear combination of the signals Ai present on the accesses 5ι of the antennas for 1 ≤l ≤N, according to the formula V _j = ∑ι ₌ ι ^N o., Ι .Aι. where 04, ₁ ⁼ exp (2J7idi, ι / λ), j is the pure imaginary unit and the value d ^ is the path difference, taken between the one chosen li of the antennas and the other antennas 1 ₂ , .. ., 1N, of a plane wave making the target angle γ; of track with direction 4 of movement.

The radiation pattern g _\ (θ) of each channel 7j for 1 ≤i ≤M, results from a linear combination of the radiation pattern g _\ (θ) present on the access 5ι of the antennas for 1 ≤l ≤N, according to the formula _gi (0) = l Ei- .. "Q4, ι a (0) |

The value dy is the path difference of a plane wave whose direction of propagation makes an angle γ, with direction 4 of displacement. For equidistant antennas in direction 4 of displacement, the spacing between two consecutive antennas is equal to d and the antenna l _\ is located at the front, we have di, ι = cos (7i) .d. ( ll), or i ≤l ≤M. Each channel 7ι, 7 ₂ , ..., 7M is connected to a module 10ι, 10 ₂ , ..., 10 _M of channel correction. Each module 10ι, 10 ₂ , ..., 10 _M of channel correction corrects respectively by an offset Δf _ls Δf ₂ , ..., ΔfM in frequency the channel 7ι, 7 _2. _.... 7 _M to which it is connected, so that the frequency offset of channel 7_, 7 _2. _.... 7 _M due to the Doppler effect acting on the electromagnetic path of the signal from the antenna (s) li, 1 ₂ , ..., 1 _N is reduced. Each correction Δfi, Δf ₂ , ..., Δf _M in frequency depends respectively on the channel 7ι, 7 ₂ , ..., 7 _M. On reception, the modules 10ι, 10 ₂ , ..., 10 _M of channel correction include output ports 17_, 17 ₂ , ..., 17 _M of channel corrected by the offset Δfi, Δf ₂ , ... , Δf in frequency compared to channels 7 _\ , 7, ..., 7 _M not corrected. Conversely, in transmission, the modules 10 _1} 10, ..., 10M of channel correction comprise channels 7 \, 7, ..., 7 _M , which supply the antenna li, 1 with transmission signals. ₂ , ..., 1N and which are corrected by the offset Δfi, Δf ₂ , ..., Δf _M in frequency with respect to the input ports 17 _. , 17 ₂ , ..., 17 _M of track.

In FIGS. 4 and 5, a control access l li, 11 ₂ , ..., 11 _M , generally designated by the number 11, is provided on each module 10 _ls 10 ₂ , ..., 10 _M channel correction to apply a frequency shift signal Δfi, Δf, ..., Δf to it. The correction signals Δfi, Δf ₂ , ..., FM in frequency are generated respectively by modules 12 _l5 12, ..., 12M of correction control, similar to that shown in detail in FIG. 6 and designated by generally by the number 12.

In FIG. 6, each correction control module 12 comprises:

a first input 13 of a positive value v of the speed of movement of the vehicle 2 in the direction 4 of movement,

a second input 14 of a carrier frequency f ₀ of the useful signal to be transmitted or received by the antennas 1,

a third entry 15 with an angular value θ _{m \} , β ^ a, ..., Θ „ _M associated with a channel and generally designated by θ _m , and

- a fourth entry 16 with a multiplier coefficient.

The value v of the speed of movement of the vehicle 2 along the direction of movement 4 is obtained by a determination or a measurement carried out in real time on the vehicle 2, for example using the speedometer present on its dashboard or knowledge of successive positions of the vehicle obtained by a GPS system, and / or by a blind estimator and / or by a digital signal from pilots using the signal emitted by a source distant from the vehicle and the signal received by an antenna other than or formed by the above-mentioned antennas 1.

The carrier frequency fo is a constant prescribed in the transmission device in the case where the latter comprises a single carrier. In the case of a device comprising several carriers, such as a device of the OFDM type, the frequency correction Δf may be different for each carrier for the same channel. In general, the frequency correction Δf can be narrowband and the correction modules 10 can be provided in various stages of the reception or transmission chain and be produced by analog or digital circuits.

The angular value θ _{m \} , ^ a, ..., # _mM of channel depends on channel 7ι, 7 ₂ , ..., 7 respectively associated with the module 12 _ls 12, ..., 12 _M of correction command . The angular value θ _{m \} , θπa, - - -, #mM of track is related to direction 4 of movement and corresponds to a direction included in the angular range 9ι, 9 ₂ , ..., 9 _M deviates.

The channel angular value θ _m] - is equal to the target channel angle γ ₃ for 1 ≤j ≤M.

The angular value

θ _πM of track is for example the angle of the bisector of the angular domain 9 _l5 9 ₂ , ..., 9 _M with respect to the direction 4 of displacement.

As a variant, the angular value 0 _ml , # „ _£ , ..., Θ _ΠM of track is the angle formed by the direction 8ι, 8 ₂ , ..., 8M pointing and the direction 4 of movement.

In another variant, the angular value θ _{m \} , θ _π a, ..., # _mM of track is the mean angle θ _mj of the track, defined by

where 1 ≤j ≤M and g _j (0) represents the radiation pattern of channel 7 _j .

In another variant, the angular value θ _{m \} , 0 _m2 , ..., # _m of track is the average angle θ _mj of the track, defined by θ _mi = arccos (jo ^27r g _j (0) .cos (0). Dθ), where 1 ≤j ≤M, arccos denotes the function arccosinus and g _j (#) represents the radiation diagram for channel 7 _j .

The correction signals Δfi, Δf ₂ , ..., Δf _M in frequency generated respectively by the modules 12ι, 12, ..., 12 _M of correction command depend on the values applied to their first, second, third and fourth inputs 13, 14, 15 and 16. The frequency correction Δfi, Δf ₂ , ..., M of the channel is proportional to the cosine of the angular value 0 _ml , 0π_. _. ..., Θ „ _M of track and at the value of the speed v of movement of the antenna (s) 1 _1} 1 ₂ , ..., 1N in the direction 4 of instantaneous movement of the vehicle 2. The frequency correction Δf _1} Δf ₂ , ..., Δf _M of channel is given by:

Δfj = -kj. (V / c) .fo.cos (0 _mj ), where 1 ≤j ≤M, c is the speed of light, and k _j is a proportionality factor minimizing the mean absolute Doppler shift SDAM or moment of order 1 of the Doppler shift of channel 7j, equal to

SDAM _j = (^ ^{+ ∞} _Pj (f). | F | .df) / ( ^≈ _j φ.df), where p _j (f) is the Doppler spectrum of channel 7 _j , f is the frequency and | | denotes the absolute value. As a variant, the proportionality factor k _j can be calculated as minimizing the second order moment of the Doppler shift of the channel 7 _j , equal to SDj, ₂ = (\ _-0 o ⁺⁰ ° P _j (f). f | ² .df) / (| _-∞ ⁺⁰ ° P _j (f) .df), or as jointly minimizing SDAMj and SD _{j, 2} .

The Doppler spectrum p _j (f) is for example calculated beforehand according to the following approximate numerical method.

In another variant, the factor k _j of proportionality is chosen equal to one, for all channels 7 _j , where 1 ≤j ≤M.

The radiation diagram g _j (0) of each channel 7j is divided into L equal angular sectors related to the direction 4 of movement and going from 0 to 360 °. For each angular sector h, where 1 ≤h ≤L, the bisector angle is equal to ft ⁼ 27ih / L + τr / L and the mean Doppler shift in frequency, related to the Doppler frequency f _d = fo.v / c, is worth cos (/ 3 _h ) when L tends to infinity. Assuming that the electromagnetic paths arrive uniformly from all directions, the average power received by each channel 7 _j or antenna 1, in the sector h is g _j (5 _h ) / L when L tends to infinity.

The Doppler spectrum p _j (f) of channel 7 _j is calculated as the histogram of the values {cos (/? _H )} ι _{≤ h} ≤ _L on the abscissa with associated numbers {gj (/ 3 _h ) / L } ι ≤h ≤L, î ≤j ≤ _M -

The Doppler P spectrum _j.or (f) of channel 7 _j corrected by the frequency offset Δfj on the accesses 17ι, 17 ₂ , ..., 17M of channel is calculated as being the histogram of the values {cos (-h) - Δζ} ι ≤h ≤ _L , I ≤j ≤ _M on the abscissa with associated numbers {g _j (0h) / L} i ≤h ≤L, I ≤j ≤ M-

The overall Doppler spectrum of the corrected or uncorrected channels is equal to the sum of the individual Doppler spectra P _jCOr (f) or p _j (f) of these.

On reception, the channels corrected on the accesses 17ι, 172, • • •, 1 M are then combined into a reception signal corrected on the access 18 then serving as output. The recombination of 17ι access, 172, _.... 17 _M is carried out for example by an adder module 19 receiving on its inputs the accesses 17 _ls 17 ₂ , • • -, 7 _M in FIG. 4. Or the recombination of the accesses 17ι, 17 ₂ , • • •, 17 _M is carried out for example by an adder 20 receiving on its inputs the accesses 17ι, 17 ₂ , • • -, 17 _M phase-shifted individually by phase-shifters or phase correctors 21 _l5 21 ₂ , ..., 21 _M in FIG. 5, in the case of a combination of antenna diversity, for example, for an identical gain combination (Equal Gain Combining, EGC). Or the recombination of the accesses 17ι, 17 ₂ , ..., 17M is carried out for example by an adder 20 receiving on its inputs the accesses 17ι, 17 ₂ , ..., 17 _M individually phase-shifted by phase and phase correctors amplitude 21 _1} 21 ₂ , ..., 21M in FIG. 5, in the case of a combination with diversity of antennas, for example, for a combination with maximum ratio (MRC, Maximum Ratio Combining). In the case of a combination with diversity, the recombination can also be carried out by frequency sub-bands, that is to say in the case of a transmission of the OFDM type, carrier by carrier.

In transmission, the module 19 decomposes the signal to be transmitted by the antennas li, 1 ₂ , ..., 1 _N , which is present on the access 18 then serving as input, in said accesses 17ι, 17 ₂ , .. ., 17 _M , possibly with a phase shift caused by phase shifters or phase correctors 21 _ls 21, ..., 21 -

The transmission device is described below with reference to the example of Figure 7, showing three antennas li, 1 ₂ , 1 ₃ omnidirectional fixed to the vehicle 2, aligned rectilinear in the direction 4 of movement and spaced one of the other by a distance d equal to one third of the wavelength λ, for the case where N = M = 3.

In FIG. 8, the antennas li, 1, 1 ₃ are connected respectively to the accesses 5, 5, 5 ₃ of the module 6 for forming channels 7, 7, ₂ , 7 ₃ by means of OFDM demodulators numbered 22, 22, 22 ₃ .

The signals Vi, V ₂ , V ₃ of the channels 7ι, 7 ₂ , 7 ₃ are the following:

Vι = Aι + e ^iΦ .A ₂ + e ^{) '2φ} .A ₃

V ₂ = Aι + A ₂ + A ₃ V ₃ = A ₁ + e- ^jφ .A ₂ + e ^2jφ .A ₃

Where Ai, A ₂ , A ₃ are the access signals 5ι, 5 ₂ , 5 ₃

The radiation diagrams of the signals Vi, V ₂ , V ₃ are represented in FIG. 9, Vi being the signal of the path forward in the angular range 9ι, for which 0 _m ι = 0, V ₂ being the signal of the channel to the sides in the angular domain 9 ₂ , for which β ^ a - ττ / 2 and V ₃ being the signal of the channel back in the angular domain 9 ₃ for which 0 _m3 = relative to the direction 4 of displacement .

The front channel Vi receives a frequency correction Δf = -kf _d of the modules 10ι, 12 _l5 the side channel V ₂ receives a zero frequency correction of the modules 10 ₂ , 12 ₂ , and the rear channel V ₃ receives a correction in frequency Δf = + kf _d of modules 10 ₃ , 12 ₃ .

The coefficient k is taken equal to 0.85 in order to minimize the mean absolute Doppler shift SDAM, which is equal to 0.26 after recombination. f _d .

The corrected channels 17ι, 17 ₂ , 17 ₃ are recombined by an MRC system 23 to obtain the corrected reception signal 18.

The example of FIGS. 8 to 10 also applies in the case of three antennas occupying the same position on the vehicle but but having directivities towards the front, towards the sides and towards the rear according to the radiation diagrams of the signals Vi, V ₂ , V ₃ in Figure 9.

FIG. 10 shows in dashed lines the classic Doppler spectrum, known as the Jakes type, of an omnidirectional antenna in the absence of correction, given by the equation

H _d (δf) = B. [l- (δf / fd) ² r ^1/2 where δf is the Doppler shift on the abscissa, B is a constant and the normalized Doppler frequency is equal to δf / f.

The Doppler spectrum of the corrected reception signal 18 according to FIG. 8 is shown in solid lines in FIG. 10. It can be seen that the Doppler spectrum of the corrected signal is much more concentrated around the vertical axis δf = 0 of zero Doppler shift than the classical spectrum is not corrected and goes through zero values, almost zero and in any case very limited in δf = ± f _d compared to the classical spectrum, which is infinite at these points, which means that the power of the corrected signal undergoes a lower frequency spreading than in the conventional case. Thus, in this embodiment, the corrected signal has a much narrower band after having undergone the Doppler effect than is the uncorrected signal of the conventional spectrum. Consequently, this embodiment of the transmission device gives the possibility of applying a much greater frequency excursion to the useful signal and makes it possible to reduce the overlapping of spectrum between carriers. In addition, the spectral spread of the signal due to the Doppler effect is reduced in the corrected signal. The mean absolute Doppler shift SDAM of the classical spectrum Hd (f) is equal to 0.64.f _d . Therefore, the average absolute Doppler shift is reduced by more than 59% in this embodiment. It follows the possibility in this embodiment of more than doubling the maximum displacement speed, if the frequency spread due to the Doppler effect is the limiting factor of the transmission in this embodiment.

Claims

1. Transmission device intended to be fixed to a motor vehicle having a prescribed direction (4) of instantaneous displacement, the device comprising at least one antenna (lj) capable of transmitting or receiving a signal having at least one electromagnetic propagation path in the space and a means (6) for forming a channel connected to said antenna (1;), characterized in that the means (6) for forming a channel and said antenna (1 are such that it is formed at least one channel (7j) corresponding to the emission or reception of the signal, limited to at least one associated angular range (9j) of orientation of the electromagnetic path of the signal, the channel ( _7d ) is connected to a means ( _10d ) to apply a frequency correction (Δf _j ) to the channel (7 _j ), the frequency conection (Δf _j ) being controlled by means (12 _j ) of correction control and dependent on a value of the speed (v) of movement of the motor vehicle following the direct ion (4) of instantaneous displacement and of an angular value (0 _mj ) prescribed for said channel (7 _d ), related to the direction (4) of instantaneous displacement and included in the angular domain (9 _d ) of associated channel, so as to reduce the frequency offset of the channel (7 _d ), due to the Doppler effect acting on the electromagnetic path of the signal.

2. Transmission device according to claim 1, characterized in that the prescribed angular value (0 _mj ) of channel is the angle of the bisector of the angular domain (9 _j ) of associated channel with respect to the direction (4) of instant move.

3. Transmission device according to claim 1, characterized in that the prescribed angular value (0 _m j) of track is the angle formed by a direction (8j) of pointing of the track (7j), corresponding to a maximum of its radiation diagram (g _j (0)) and the direction (4) of movement.

4. Transmission device according to claim 1, characterized in that the prescribed angular value (0 _m j) of track is the mean angle 0 _mj of the track (7j), defined by mj = jo ^{2, r} gj (0 ). | 0 | . d0, where gj (0) represents the radiation pattern of the channel (7 _j ).

5. Transmission device according to claim 1, characterized in that the prescribed angular value (0 _m j) of track is the mean angle 0 _m j of the track (7j), defined by

0 _mj = arccos (jo ^{2? R} j (0) • cos (0). D0), where arccos denotes the function arccosine and g _j (0) represents the radiation pattern of the channel (7 _j ).

6. Transmission device according to any one of the preceding claims, characterized in that the frequency correction (Δf _j ) of the channel is proportional to the cosine of the angular value (0 _mj ) of the channel and to the value (v) of the speed of movement of the motor vehicle in the direction (4) of instantaneous movement.

7. Transmission device according to claim 6, characterized in that the frequency correction Δfj of the channel is given by:

Δf _j = -k _j . (V / c) .f _o .cos (0 _mj ), where 0 _mj is the track angular value, v is the value of the speed of movement of the motor vehicle in the direction (4) instantaneous displacement, c is the speed of light, fo is the frequency of the carrier of the antenna signal, and k _j is a proportionality factor minimizing the mean absolute Doppler shift SDAM _j equal to

SDAM _j = ( _∞ ⁺⁰⁰ _Pj (f). | F | .df) / (i _∞ ^{+ ∞} p _j (f) .âf), where p _j (f) is the Doppler spectrum of the channel (7 _j ) .

8. Transmission device according to claim 6 or 7, characterized in that the frequency correction Δf _j of the channel is given by:

Δζ = -k _j . (V / c) .f _o .cos (0 _mj ), where 0 _m j is the track angular value, v is the value of the speed of movement of the motor vehicle in the direction (4) instantaneous displacement, c is the speed of light, fo is the frequency of the carrier of the antenna signal, and k _j is a proportionality factor minimizing the moment SD _j , ₂ of order 2 of the Doppler shift of the channel (7 _d ), equal to

SD _jj2 ≈ (o ⁺⁰ ° pj (f). | F | ² .df) / (c ^{+ ra} pj (f) .df), where pj (f) is the Doppler spectrum of the channel (7j).

9. Transmission device according to claim 6, characterized in that the frequency correction Δf _j of the channel is given by:

Δf _j = - (v / c) .f _o .cos (0 _mj ), where 0 _mj is the angular value of the track, v is the value of the speed of movement of the motor vehicle in the direction (4) of instantaneous movement , c is the speed of light, fo is the frequency of the carrier of the antenna signal.

10. Transmission device according to any one of the preceding claims, characterized in that an angular domain (9 _j ) of track comprises the direction (4) of instantaneous movement.

11. Transmission device according to any one of the preceding claims, characterized in that at least one angular domain (9ι) of track comprises the direction (4) of instantaneous movement in one direction and another angular domain (9 ₃ ) track comprises the direction (4) of instantaneous movement in the opposite direction.

12. Transmission device according to any one of the preceding claims, characterized in that the track (7 _j ) is symmetrical with respect to the direction (4) of instantaneous movement.

13. Transmission device according to any one of the preceding claims, characterized in that the channel forming means (6) and said antenna (l _ls 1 ₂ , ..., 1N) are such that it is formed at at least two channels (7ι, 7 ₂ , ..., 7 _M ) corresponding to the transmission or reception of the signal, limited to at least two angular domains (9ι, 9 ₂ , ..., 9 _M ) associated with different orientation of the electromagnetic path of the signal, less than 360 °, and the means (10ι, 10 ₂ , ..., 10 _M ) for frequency correction of the channels are connected to means (19; 20, 21) for combining the channels corrected (17ι, 17 ₂ , ..., 17 _M ) to provide as output a frequency corrected reception signal (18) or the means (10ι, 10 ₂ , ..., 10 _M ) for frequency correction of the channels are connected to means (19; 20, 21) for decombination of an input signal (18) to be transmitted to form accesses (17) to be corrected in frequency by the correcting means (10 _j ) frequency ion to form said corrected channels (7ι, 7, ..., 7 _M ), which supply emission signals to said antenna (li, 1 ₂ , .. ,, lκ) by means (6) track training.

14. Transmission device according to claim 13, characterized in that the means (19; 20, 21) of combination or the means (19; 20, 21) of decombination include means (211, 21, ..., 21 _M ) for channel phase shifting and / or means (21 ₁ , 21 ₂ , ..., 21 _M ) for channel amplitude correction.

15. Transmission device according to claim 13, characterized in that the means (19; 20, 21) of combination or the means (19; 20, 21) of decombination are free of means (211, 21 ₂ , ... , 21 _M ) of channel phase shift and of means (211, 21 ₂ , ..., 21 _M ) of channel amplitude correction.

16. Transmission device according to any one of the preceding claims, characterized in that it comprises for each channel (7ι, 72 7 _M ) a directive antenna (L, 1 ₂ ,. .., 1N) and a link without phase shift at the directive antenna as a means (6) of channel formation.

17. Transmission device according to any one of claims 1 to 15, characterized in that it comprises a plurality of N antennas (li, 1 ₂ , ..., 1 _N ) spaced from each other at least along from the direction (4) of instantaneous movement, the means (6) for forming a track being connected to the plurality of antennas (l _ls 1, ..., 1 _N ) and forming signals V _j of M tracks (7_ , 7 ₂ , ..., 7 _M ) for l ≤i ≤M in the angular domain (9ι, 9 ₂ , ..., 9 _M ) of associated channel by linear combination of the signals Ai of antennas, for 1 ≤ l ≤N, according to the formula V _j = ∑ι _{= 1} ^N 05 _{, 1} Ai, where 04, ₁ = exp (2J7rdi, ι IX), j is the pure imaginary unit, λ is the wavelength and the value d;, ι is the path difference, taken between the chosen one (li) of the antennas and the other antennas (1 ₂ , ..., 1 _N ), of a plane wave making a target angle γ; of track equal to the prescribed angular value 0 _m j of track i with the direction (4) of movement.

18. Transmission device according to claim 17, characterized in that the antennas (h, I2, ..., 1 _N ) are equidistant and aligned parallel to the direction (4) of movement.

19. Transmission device according to any one of claims 17 and 18, characterized in that the antennas (li, I ₂ , ..., 1N) are omnidirectional.

20. Transmission device according to Claims 18 and 19, characterized in that three omnidirectional antennas (li, I ₂ , 1 ₃ ) separated by λ 3 are provided, the means (6) for forming channels forming from the three antennas (1 ₁ , 1 ₂ , 1 ₃ ) three channels (7ι, 7, 7 ₃ ), whose signals Vi, V ₂ , V ₃ are given by

V ₂ = Ai + A ₂ + A ₃

V ₃ = Aι + e- ^jφ .A ₂ + e- ^2jφ .A ₃ where Ai, A ₂ , A ₃ are the antenna signals (li, I ₂ , 1 ₃ ) and Φ = 2 ^ / 3.

21. Transmission device according to claim 20, characterized in that the three channels (7ι, 7, 73) having respectively the signals Vi, V ₂ , V3 receive means (10ι _, 10 ₂ , IO ₃ ) for applying correction respectively of the channel frequency corrections of -k.fd, 0 and + kf _d d, where f _d = (v / c) .f ₀ v is the value of the speed of movement of the motor vehicle in the direction (4 ) instantaneous displacement, c is the speed of light, fo is the frequency of the carrier of the antenna signal, and k is a proportionality factor equal to 0.85.

22. A transmission device according to any one of the preceding claims, characterized in that a M number of channels _(7., 7 _2, ... 7 _M) greater than or equal to 2, are formed by means (6) of track formation, and the prescribed angular value 0 _m j of track, referred to the direction (4) of instantaneous displacement, is a target angle 7 of track taking the values 7 = (il) .7r / (Ml ) for 1 ≤i ≤M and 7 ₀ = 0.

23. Transmission device according to any one of the preceding claims, characterized in that it comprises means for determining the instantaneous value of the speed (v) of movement of the motor vehicle in the direction (4) of instantaneous movement.

24. Transmission method on a motor vehicle having a prescribed direction (4) of instantaneous movement and on which is fixed at least one antenna (1;) capable of transmitting or receiving a signal having at least one electromagnetic propagation path in the space, in which at least one channel (7 _j ) is formed from or for said antenna (lj), characterized in that said channel (7 _j ) formed corresponds to the emission or reception of the signal, limited to at minus an angular range (9 _j ) associated with the electromagnetic path orientation of the signal, for said channel (7 _j ) a frequency correction (Δf _j ) of path dependent on the value of the speed of movement of the vehicle is calculated automobile according to the direction (4) of instantaneous movement and of an angular value (0 _mj ) prescribed for said track (7 _d ), related to the direction (4) of instantaneous movement and included in the angular range (9 _d ) of associated channel, and is applied to said path (7d) the frequency correction (.DELTA.f _j), so as to reduce the offset frequentiel of said path (7 _j), due to the Doppler effect acting on the electromagnetic signal path.