FR3118324A1 - Method for generating beams of a radio communication antenna array and corresponding device - Google Patents

Abstract

Method for generating beams from a network of radio communication antennas and corresponding device The invention relates to a method for generating beams of a radio communication antenna network, a beam corresponding to a subdivision of a beam grid of the radio communication antenna network consisting of a given number of subdivisions, the method comprising the following steps: - determining an angular aperture of at least one beam of said beam grid as a function of a probability density of the presence of a user terminal to be served in the corresponding subdivision of said beam grid beams, - determination, as a function of the angular aperture of said at least one beam of said beam grid, of modulation coefficients of a signal in amplitude and phase, - modulation of at least one signal processed by an antenna of the network of radio communication antennas by means of said amplitude and phase modulation coefficients. FIGURE 5

Description

Method for generating beams of a radio communication antenna array and corresponding device

Field of the invention

The field of the invention is that of radio communication antenna networks. More particularly, the invention relates to a method for modifying the beamwidth of radio communication antenna arrays.

Prior art and its disadvantages

The new mobile communication standards, such as the 5G standard, or fifth generation of standards for mobile telephony, propose to use new radio frequency bands such as the millimeter frequency band which extends from 30 to 300 GHz.

The use of this millimetric frequency band makes it possible to meet the growing need for data exchange, which is at the heart of the issues that the 5G standard seeks to solve.

However, the millimeter frequency band has some disadvantages compared to historical frequency bands, such as higher free-space propagation losses, as well as higher penetration losses. The use of radio communication antenna arrays makes it possible to compensate for propagation losses in free space thanks to the implementation of energy focusing techniques.

A classic technique consists in controlling the transmission or reception of a network of radio communication antennas by means of an amplitude and/or phase modulation law applied to the signals (known as electric as opposed to the radio signal transmitted by an antenna) processed by the various constituent antennas of the network of radio communication antennas in order to focus the energy of the associated radio signal in a desired direction. Such a technique is commonly referred to as beamforming or beam formation in French. A particularity of this technique is that the aperture of the beam formed is inversely proportional to the size of the antenna array used for forming the beams. Thus, the larger the radio communication antenna array, the narrower the beam and the greater the radiation gain in the direction of this beam. This characteristic can be a drawback when the direction favorable to the establishment of a communication link between, for example, a base station and a mobile terminal is not precisely known or when significant sectoral and stochastic attenuations occur.

Indeed, this increases the access time to the base station because many beams must be tested to cover the same area of a cell served by the base station in order to identify the appropriate beam. There is therefore a need for a technique for generating beams of a network of radio communication antennas that does not have all or part of the aforementioned drawbacks, in particular during procedures for establishing a communication link between a base station and a mobile terminal.

The invention meets this need by proposing a method for generating beams of a network of radio communication antennas, a beam corresponding to a subdivision of a grid of beams of the network of radio communication antennas consisting of a given number of subdivisions, the method comprising the following steps:
- determination of an angular aperture of at least one beam of said beam grid as a function of a probability density of presence, in the corresponding subdivision of said beam grid, of a user terminal to be served,
- determination, as a function of the angular aperture of said at least one beam of said beam grid, of modulation coefficients of a signal in amplitude and in phase,
- modulation of at least one signal feeding an antenna of the network of radio communication antennas by means of said amplitude and phase modulation coefficients.

Determining the angular aperture of the beams of the beam grid as a function of a probability density of the presence of a user terminal, such as for example a mobile terminal, makes it possible to adapt the radiation gain in the direction of each beam of the beam grid as needed. More specifically, the aperture of the beams of the beam grid is determined according to a probability density characterizing the angular position of the user terminal in a spherical coordinate frame centered on the antenna array. By playing on the angular opening of the beams of the beam grid, it is possible to ensure the same probability of selection of the different beams.

Indeed, it is advantageous to have beams with a low angular aperture and a large radiation gain to target an area where the probability density of the presence of a user terminal is high and beams with a larger angular aperture and a low radiation gain to cover an area where the probability density of the presence of a user terminal is low, since this makes it possible to best serve the user terminals.

Such a solution makes it possible to distribute the energy radiated by a network of radio communication antennas between the various beams in a useful and reasoned manner in order to improve the conditions for establishing a communication between a mobile terminal and a base station. .

Finally, such a solution responds in an adaptable manner to the latency time/signal-to-noise ratio or SNR (signal-to-noise ratio) compromise. In the case where the number of beams used is sufficient to avoid using enlargement techniques, the gain on transmission is maximum. However, the greater the number of beams, the greater the access time since the beams are time multiplexed. The present solution therefore offers a compromise between the latency time linked to the access to the cell and the signal-to-noise ratio SNR.

According to a feature of the method for generating beams, the latter further comprises a distribution of the constituent subdivisions of said grid of beams according to a geometry of an area to be covered by the network of radio communication antennas. More particularly, the geometry of an area to be covered by the radio communication antenna array is a function of a position and an orientation of the radio communication antenna array in an environment where the communication antenna array radio is located.

The division of the beam grid is adapted to the shape and orientation of the area to be covered by the antenna array as perceived by the antenna array. This shape depends on the position and orientation of the antenna array with respect to the area to be covered.

Thus, the beams generated by the antenna array are oriented so that radiation reaches all the points of the area to be covered by the antenna array, thus allowing a user terminal to be served wherever it is in this area to cover.

According to another feature of the method for generating beams, the number of constituent subdivisions of the beam grid is determined as a function of a value of a signal-to-noise ratio of the radio signals emitted by the antenna array and of a latency time to serve said user terminal.

This makes it possible to ensure that each beam has a radiation gain adapted to the need by finding a compromise between a value of a signal-to-noise ratio and a value of a latency time for access to a cell served by a station. base comprising the antenna array considered. Indeed, it is possible to evaluate the gain associated with each direction of the spherical coordinate frame centered on the antenna array as a function of the number of beams used and also the latency time to serve said user terminal since the cell access signals are transmitted on OFDM symbols well specified in the texts standards relating to the fifth generation of radio communication currently being specified.

Finally, according to a last feature of the method for generating beams, the modulation coefficients of a signal in amplitude and in phase are obtained by applying a Fourier transformation to the radiation emitted by at least one network of radio communication antennas .

The invention also relates to a device configured to generate beams, a beam corresponding to a subdivision of a grid of beams of a network of radio communication antennae consisting of a given number of subdivisions, the device comprising means for :
- determining an angular aperture of at least one beam of said beam grid as a function of a probability density of presence of a user terminal to be served in the corresponding subdivision of said beam grid,
- determining, as a function of the angular aperture of said at least one beam of said beam grid, modulation coefficients of a signal in amplitude and in phase,
- Interfacing with means for modulating at least one signal supplying an antenna of the network of radio communication antennas by means of said amplitude and phase modulation coefficients.

Another subject of the invention is a network of radio communication antennas suitable for interfacing with at least one device configured to generate beams, a beam corresponding to a subdivision of a grid of beams of the network of communication antennas radio consisting of a given number of subdivisions, the antenna array comprising means for:

- modulating at least one signal to supply an antenna of the network of radio communication antennas by means of amplitude and phase modulation coefficients determined by the device.

The invention finally relates to a computer program product comprising program code instructions for the implementation of a method as described previously, when it is executed by a processor.

The invention also relates to a recording medium readable by a computer on which is recorded a computer program comprising program code instructions for the execution of the steps of the method according to the invention as described above.

Such recording medium can be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or else a magnetic recording means, for example a USB key or a hard disk.

On the other hand, such a recording medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means, so that the program computer it contains is executable remotely. The program according to the invention can in particular be downloaded onto a network, for example the Internet network.

Alternatively, the recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method which is the subject of the aforementioned invention.

List of Figures

Other aims, characteristics and advantages of the invention will appear more clearly on reading the following description, given by way of a simple illustrative example, and not limiting, in relation to the figures, among which:

: this figure represents the steps of a method for generating at least one beam of an array of radio communication antennas according to one embodiment of the invention,

: this figure represents an antenna array in position in its environment,

: this figure represents the rotation performed in order to move from a global reference to a spherical reference centered on the antenna array,

: this figure represents the possible positions of a user equipment in a spherical frame centered on the antenna array,

: this figure represents a gain provided by the antenna array RA for each beam,

: this figure represents a distribution of a radiation gain as a function of the nature of the splitting, uniform or not, of the beam grid,

: this figure represents a grid of beams cut in a uniform way,

: this figure represents a device capable of implementing the method for generating beams,

: this figure represents the device of the connected to a phase modulator and an amplitude modulator of an antenna of the antenna array.

Detailed Description of Embodiments of the Invention

The general principle of the invention is based on the determination of the angular aperture of the beams of the beam grid as a function of a probability density of the presence of a user terminal, such as for example a mobile terminal, which makes it possible to adapt the radiation gain in the direction of each beam of the beam grid to the needs. More specifically, the aperture of the beams of the beam grid is determined according to a probability density characterizing the angular position of the user terminal in a spherical coordinate frame centered on the antenna array. By playing on the angular opening of the beams of the beam grid, it is possible to ensure the same probability of selection of the different beams.

Indeed, it is advantageous to have beams with a low angular aperture and a high radiation gain in an area where the probability density of the presence of a user terminal is high and beams with a larger angular aperture and a low radiation gain in an area where the presence probability density of a user terminal is low, since this makes it possible to best serve the user terminals.

We now present, in relation to the the steps of the method for generating at least one beam of an array of radio communication antennas.

The first step E1 of the method for generating beams consists in defining the position of the antenna array RA in a global frame RG. Such a global reference RG is a Cartesian reference. For example, the RA antenna array shown in is positioned in the global reference RG such that . orientation of the antenna array RA relative to the global reference RG is also determined. In the example shown in Figure 2, the antenna array RA is oriented such that Such an orientation is shown in by the axes .

During a step E2, a presence probability density law characterizing a position of the user equipment UE to be served in an area ZC to be covered by the antenna array RA is determined in the global reference RG.

When, as on the , the area ZC to be covered by the antenna array RA corresponds to a room such as for example a storage space where the movements of robots equipped with user equipment UE are constrained and where the tasks performed are known, such a law of presence probability density is obtained in a simple way. When a user equipment item is located outside and/or performs unconstrained movements, such a presence probability density law can be more complex to determine.

In the rest of the document, it is considered that the position of the user equipment UE is random along the x and y axes of the global frame, but constant along the z axis of this same general frame RG. In other words, in this example embodiment, the user equipment UE moves at a given height with ).

Two independent random variables are then introduced And , characterizing a position of the user equipment UE to be served in the global reference RG, defined such that And , these two intervals defining the limit coordinates of the part of the zone ZC to be covered by the antenna array RA in which the user equipment UE moves. The variables And are respectively associated with the following functions And representing a probability density of presence of the user equipment UE in the reference RG such that:

.

The variable with is also introduced.

During a step E3, a position of the user equipment UE expressed in a frame RRA centered on the antenna array RA is obtained by performing a translation then a rotation:

(1)

Or , And are random variables characterizing a position of the user equipment UE to be served in the Cartesian frame RRA associated with the antenna array RA, and where is the rotation matrix expressed as:

(2)

In a step E4, a position of the user equipment UE is expressed in an RSRA coordinate system in spherical coordinates . Such a reference RSRA in spherical coordinates is centered on the antenna array RA. In such an RSRA frame in spherical coordinates, the position of the user equipment UE then given by:

(3)

Or , And are random variables defining the position of the user equipment UE in the RSRA frame of reference in spherical coordinates associated with the antenna array RA.

On the , the spherical coordinates of the user equipment UE are represented for 1,000,000 possible positions with the assumption And, . In this example, the random variables And previously defined follow laws , , presence probability density uniforms in the Cartesian frame RG:

(4)

(5)

Or And in the chosen example.

On the , it can be seen that the area ZC to be covered by the antenna array RA is cut out by means of a grid G consisting of a plurality of SDnbbeam subdivisions. The grid G is a grid of beams of the antenna array RA. Each subdivision SDnbbeam of the grid G corresponds to a beam of the antenna array RA.

Knowing the number nb _beam of subdivisions of the grid G and therefore the number of beams that the antenna array RA must generate, one determines, during a step E5, the distribution of the subdivisions SD _nbbeam constituting the grid according to the directions And of the spherical reference RSRA.

be And the number of beams according to the directions And of the spherical reference RSRA respectively, we then have:

(6)

with (7)

From equations (6) and (7), we get:

(8)

The value is then rounded to the nearest divisor of so as to obtain .

It follows:

(9)

In the example described with reference to Figure 4, is 32 which gives:

Thus, the grid G comprises 32 subdivisions distributed as follows: 4 subdivisions along the axis and 8 subdivisions along the axis , since Consequently .

During a step E6, the size of each subdivision SD _nbbeam of the grid G is determined so that each subdivision SD _nbbeam contains the same number of possible positions of the user equipment UE. Thus, the probability of selection of each _nbbeam SD subdivision, and therefore of each beam, is almost uniform.

Determining the size of each subdivision SD _nbbeam of the grid G amounts to determining the angular aperture of the corresponding beam. Consequently, the higher the probability density of angular presence of the user equipment UE for a given subdivision SD _nbbeam , the lower the angular aperture of the corresponding beam. Conversely, the lower the probability density of angular presence of the user equipment UE for a given subdivision SD _nbbeam , the greater the angular aperture of the corresponding beam. In the general reference RG, which is a Cartesian reference, the present method leads to a degradation of the power received from the sectors of the zone to be covered ZC associated with a low angular probability density to the benefit of a majority of them.

Thus, knowing that each point corresponding to a possible position of the user terminal UE is associated, in the RSRA reference frame, with an elevation value and in azimuth , an algorithm defines the splitting of the different SD _nbbeam subdivisions of the grid G according to the following example implementation.

In a step E6 ₁ , the points are sorted according to their azimuthal value associated such as:

- each point belongs to exactly 1 azimuth zone

- each azimuthal zone contains the same number of points to within 1 point (if the number of points is not a multiple of ):

- for everything

In a step E6 ₂ , for each azimuthal zone defined in step E6 ₁ , the points are then sorted according to their elevation value such as :

- each point belongs to exactly 1 zone in elevation

- each zone contains the same number of points to within 1 point (if the number of points is not a multiple of :

- for everything

In a step E6 ₃ , we then obtain point subgroups . The bounds of the _nbbeam SD subdivision corresponding to each subgroup are determined by And . The minimums and the maximum do not necessarily belong to the same point.

The determination of the amplitude and phase modulation coefficients that each antenna of the antenna array applies to a signal for which it provides processing to form each beam consists in calculating Fourier coefficients for a linear array oriented according to and for a linear array oriented along .

As a reminder, radiation produced by a linear array of antennas composed of 2K antennas is given by the following formula:

with

(11)

And or corresponds to the wave number.

The corresponding Fourier coefficients are then obtained by applying the following formulas:

(12)

Or corresponds to a period of the radiation . Here the radiation is defined via the function since the beams are rectangular in shape as can be seen in the , so we get:

(13)

For a linear array oriented along , the width of the radiation desired according to direction having been determined during step E6 for each beam making up the grid G, we then have for a given beam:

(14)

Or And define the angular range in elevation for which power is emitted for a given beam, and represents the spacing between the antennas making up the antenna array RA. Knowing that the antenna array RA includes in the chosen example 4NM antennas where N and M are even numbers, in the case where , we obtain :

(16)

and so

(17)

Thus, after application of a Fourier transform during a step E7, an excitation vector is thus obtained for the antenna array RA in the direction in the following form:

(18)

For a linear array oriented along , the width of the radiation desired according to having been determined during step E6 for each beam making up the grid G, we then have for a given beam:

(19)

(20)

Or And define the angular range in azimuth for which the power is emitted for a given beam. Knowing that the antenna array RA includes in the chosen example 4NM antennas where N and M are even numbers, in the case where , we obtain :

(21)

and so

Thus, after application of a Fourier transform during a step E8, an excitation vector is thus obtained for the antenna array RA in the direction in the following form:

(23)

Finally, the excitation vector to be applied to the antenna array RA to form a grid beam G is expressed as follows:

(24)

Which give :

(25)

Or

(26)

Thus, the number of vectors to be calculated depends directly on the number of beams composing the grid G.

During a step E9, each constituent antenna of the antenna array RA modulates a signal in amplitude and in phase from the vector . Excitation coefficients vector can be rewritten in an exponential form which makes it possible to dissociate the control in amplitude phase control :

(27)

with

(28)

And

Or And correspond respectively to a command at the level of an amplifier and at the level of a phase shifter for the antenna of the RA antenna array according to and the antenna according to .

For example, the excitation vector is calculated for each beam of the grid of beams G and is applied by the constituent antennas of the array of antennas RA in order to generate the beams corresponding to the grid of beams G. The gain provided by the array of antennas RA for each beam is represented on the . On this , the SDnbbeam subdivisions with the largest areas are those with the lowest gain. They correspond to the regions of the zone to be covered ZC by the antenna array in which the probability density of angular presence of the user equipment UE is the lowest.

As depicted at , it appears that the previously described method leads to an improvement in the overall gain of an array of RA antennas for two main reasons:

• The gain is degraded for some SD _nbbeam subdivisions of the beam grid G in favor of a majority of them,
• Each beam covers an SD _nbbeam subdivision where the user equipment UE is potentially present unlike the solutions in which the grid of beams G is uniformly cut out as shown in [fig. 7].

Indeed, always with reference to the , it appears that in approximately 90% of the cases, that is to say for 90% of the positions of the user equipment UE in the zone to be covered ZC by the antenna array RA, the method proposed in the present application is superior to a solution in which the grid of beams G is uniformly cut.

There represents a device 10 capable of implementing the method for generating beams according to the .

A device 10 can comprise at least one hardware processor 11, a storage unit 12, and at least one network interface 13 which are connected together through a bus 14. Of course, the constituent elements of the device 10 can be connected by means of a connection other than a bus.

The processor 11 controls the operations of the device. The storage unit 12 stores at least one program for implementing the method according to one embodiment to be executed by the processor 11, and various data, such as parameters used for calculations performed by the processor 11, intermediate data of calculations performed by the processor 11, etc. Processor 11 may be any known and suitable hardware or software, or a combination of hardware and software. For example, the processor 11 may be formed by dedicated hardware such as a processing circuit, or by a programmable processing unit such as a Central Processing Unit which executes a program stored in a memory of this one.

Storage unit 12 may be formed by any suitable means capable of storing the program or programs and data in a computer readable manner. Examples of storage unit 12 include non-transitory computer-readable storage media such as semiconductor memory devices, and magnetic, optical, or magneto-optical recording media loaded into a read-and-write unit. 'writing.

At least one network interface 13 provides a connection between the device 10 and a signal phase modulator connected to an antenna of the antenna array.

There represents the device 10 connected to a phase modulator MP and an amplitude modulator MA of an antenna of the antenna array. The phase modulator MP and the amplitude modulator MA are also connected to a radio frequency chain CRF whose role is to convert the signal after baseband processing into a useful transposed signal, amplified and transposed at the S _RF frequency. The phase modulator MP and amplitude modulator MA then supply a modulated radio signal S _RF ( ), the value of the phase shift applied having been calculated according to the method previously described.

Claims (8)

Method for generating beams of a network of radio communication antennas, a beam corresponding to a subdivision of a grid of beams of the network of radio communication antennas consisting of a given number of subdivisions, the method comprising the steps following:
- determination of an angular aperture of at least one beam of said beam grid as a function of a probability density of presence, in the corresponding subdivision of said beam grid, of a user terminal to be served,
- determination, as a function of the angular aperture of said at least one beam of said beam grid, of modulation coefficients of a signal in amplitude and in phase,
- modulation of at least one signal feeding an antenna of the network of radio communication antennas by means of said amplitude and phase modulation coefficients. Method for generating beams of a network of radio communication antennas according to claim 1, further comprising a step of distributing the constituent subdivisions of said grid of beams according to a geometry of a zone to be covered by the network radio communication antennas. A method of generating beams of a radio communication antenna array according to claim 2, wherein the geometry of an area to be covered by the radio communication antenna array is a function of a position and an orientation of the radio communication antenna array in an environment where the radio communication antenna array is located. A method of generating beams of a radio communication antenna array according to claim 1, wherein the number of constituent subdivisions of the beam grid is determined as a function of a value of a signal-to-noise ratio of the radio signals transmitted by the antenna network and a latency time to serve said user terminal. Method for generating beams of a network of radio communication antennas according to claim 1, in which the modulation coefficients of a signal in amplitude and in phase are obtained by applying a Fourier transformation to the radiation emitted by at least one radio communication antenna array. Device configured to generate beams, a beam corresponding to a subdivision of a grid of beams of a network of radio communication antennas consisting of a given number of subdivisions, the device comprising means for:
- determining an angular aperture of at least one beam of said beam grid as a function of a probability density of presence of a user terminal to be served in the corresponding subdivision of said beam grid,
- determining, as a function of the angular aperture of said at least one beam of said beam grid, modulation coefficients of a signal in amplitude and in phase,
- Interface with means for modulating at least one signal supplying an antenna of the network of radio communication antennas. Radio communication antenna array adapted to interface with at least one device configured to generate beams, a beam corresponding to a subdivision of a beam grid of the radio communication antenna array consisting of a number of subdivisions given, the antenna array comprising means for:
- modulating at least one signal to supply an antenna of the network of radio communication antennas by means of amplitude and phase modulation coefficients determined by the device. computer program product comprising program code instructions for implementing a method of generating beams of a radio communication antenna array according to claim 1, when executed by a processor.