WO2016036270A1

WO2016036270A1 - Transceiver arrangement and method for transmitting and receiving electromagnetic signals in a mimo system

Info

Publication number: WO2016036270A1
Application number: PCT/RU2014/000661
Authority: WO
Inventors: Sergey Nikolaevich DUDOROV; Yanxing Zeng; Jianqiang Shen; Igor Mihailovich PUNKOV
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2014-09-04
Filing date: 2014-09-04
Publication date: 2016-03-10
Also published as: CN106537689B; CN106537689A

Abstract

The present invention refers to a transceiver arrangement (20, 30, 40) for transmitting and receiving electromagnetic signals in a multiple-input-multiple-output, MIMO, system, comprising antenna elements (10, 11, 16) arranged in rotational symmetry on a circular line (12, 13) in a common plane, wherein said antenna elements (10, 11, 16) are respectively identical in shape, said shape being axial symmetric, and encoding means (21) adapted to encode electromagnetic signals to be transmitted via said antenna elements (10, 11, 16) with orthogonal vectors, and decoding means (22) adapted to decode electromagnetic signals received via said antenna elements (10, 11, 16) with said orthogonal vectors, said orthogonal vectors being selected to reduce interference caused by parasitic coupling between said antenna elements. The present invention further refers to a corresponding method.

Description

TRANSCEIVER ARRANGEMENT AND METHOD FOR TRANSMITTING AND RECEIVING ELECTROMAGNETIC SIGNALS IN A MIMO SYSTEM

TECHNICAL FIELD

The present invention refers to a transceiver arrangement and method for transmitting and receiving electromagnetic signals in a multiple-input-multiple-output, MIMO, system. The present invention particularly refers to a MIMO system, in which the front end of the communication system, i.e. the antenna elements and related circuitry, can be operated in a full duplex configuration in which electromagnetic signals can be transmitted and received simultaneously and at the same time as well as at the same frequency band or at least similar or overlapping frequency bands.

BACKGROUND

Typically, in transceiver arrangements of wireless communication systems with at least one transmitting antenna element and one receiving antenna element with identical transmission and reception frequencies, there is the problem of parasitic coupling between the transmitting and the receiving antenna elements. One possibility to overcome this problem is by increasing the physical distance between the transmitting and the receiving parts. However, this means an increase of the overall size of the transceiver arrangement and specifically the antenna array, which is not acceptable for modern compact devices.

In the prior art, it has been proposed, in order to overcome the mentioned problem of parasitic coupling, to branch off the signal on the transmitting side before it is transmitted and to couple this signal to the receiving side. This coupling is done at the radio frequency level. In the receiving branch, the signal from the transmitting side then is received by the receiving antenna in two ways, namely through the mentioned branched-off transmission signal and through the antenna coupling. By adjusting the attenuation level and the delay or the phase shift of the branched-off signal, a signal can be formed which cancels the parasitic coupling between the antennas.

However, in case of N transmitting and N receiving antennas, i.e. in a multiple-input- multiple-output, MIMO, case (N being an integer larger than 1 , N² of such branched- off or coupling circuits have to be introduced, one between each transmission branch and receiving branch, in order to isolate each possible or potential coupling between a transmitting and a receiving antenna element. The consequence is that the system becomes very complex and complicated. There is therefore a need to propose a transceiver arrangement which allows the reduction of the number of necessary compensation circuits and elements.

SUMMARY The object of the present invention is therefore to provide a transceiver arrangement and a method for transmitting and receiving electromagnetic signals in a multiple- input-multiple-output, MIMO, system which allow a reduction of interference between antenna elements in a simple manner. The aim of the present invention is also to propose a way to transmit and simultaneously receive MIMO data streams at the same time through independent MIMO channels in a wireless telecommunication system.

The above object is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations are defined in the respective dependent claims.

A first aspect of the present invention provides a transceiver arrangement for transmitting and receiving electromagnetic signals in a multiple-input-multiple-output, MIMO, system, comprising antenna elements arranged in rotational symmetry on a circular line in a common plane, wherein said antenna elements are respectively identical in shape, said shape being axial symmetric, and encoding means adapted to encode electromagnetic signals to be transmitted via said antenna elements with orthogonal vectors, and decoding means adapted to decode electromagnetic signals received via said antenna elements with said orthogonal vectors, said orthogonal vectors being selected to reduce interference caused by parasitic coupling between said antenna elements.

The transceiver arrangement of the present invention provides the advantages of reducing the interference between the antenna elements e.g. caused by parasitic coupling between said antenna elements in a simple way. A further specific advantage is that the invention allows to provide an inventive transceiver arrangement with a simple and compact structure, while at the same time reducing interference and providing compensation between the antenna elements, specifically in a duplex mode in which electromagnetic signals are transmitted and received at the same time and optional even in the same or at least similar/overlapping frequency bands. In a first implementation form of the transceiver arrangement according to the first aspect, said orthogonal vectors form a beam forming matrix which enables the generation of electromagnetic signal beams with different Orbital Angular Momentum, OAM, states. Advantageously, the orthogonal vectors form a beam forming matrix which enables the generation of electromagnetic signal beams with two or four OAM states.

In a second implementation form of the transceiver arrangement according to the first implementation form of the first aspect, the beam forming matrix B is

1 1 1 1

i j - i - j

B

i - j - i j

1 - 1 1 - 1

In a third implementation form of the transceiver arrangement according to the first aspect as such or according to any of the previous implementation forms of the first aspect, said antenna elements comprise four first antenna elements arranged in rotational symmetry on a first circular line in said comment plane and having said identical shape, and four second antenna elements arranged in rotational symmetry on a second circular line in said common line and having said identical shape, wherein said second circular line is concentric to said first circular line.

In a fourth implementation form of the transceiver arrangement according to the third implementation form of the first aspect, each of said four first and four second antenna elements comprises (only) a single feeding point and said four first antenna elements are exclusively adapted to transmit electromagnetic signals and said four second antenna elements are exclusively adapted to receive electromagnetic signals.

In a fifth implementation form of the transceiver arrangement according to the third or fourth implementation form of the first aspect, the four second antenna elements are respectively arranged at 45 degree angles to the four first antenna elements in relation to a common center of the first and the second circular line.

In a sixth implementation form of the transceiver arrangement according to the third, fourth or fifth implementation form of the first aspect, the four first and second antenna elements are respectively adapted to radiate with linear polarization in a same direction.

In a seventh implementation form of the transceiver arrangement according to one of the third to sixth implementation forms of the first aspect, the encoding means comprises four inputs, each input corresponding to a different Orbital Angular Momentum, OAM, state and the decoding means comprises four outputs, each output corresponding to a different one of said OAM states. Advantageously, said four different OAM states are "0", "+1 ", "-1 " and "2".

In an eighth implementation form of the transceiver arrangement according to the first aspect as such or according to the first or second implementation form of the first aspect, said antenna elements comprise four third antenna elements arranged in rotational symmetry on said circular line in said common plane and having said identical shape.

In a ninth implementation form of the transceiver arrangement according to the eighth implementation form of the first aspect, said four antenna elements respectively comprise (only) two feeding points and are adapted to transmit and to receive electromagnetic signals.

In a tenth implementation form of the transceiver arrangement according to the eighth or ninth implementation form of the first aspect, the encoding means comprises two inputs, each input corresponding to a different Orbital Angular Momentum, OAM, state and the decoding means comprises two outputs, each output corresponding to a different one of said OAM states. Advantageously, these two different OAM states are "0" and "1 ". In an eleventh implementation form of the transceiver arrangement according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the transceiver arrangement further comprises baseband cancellation circuitry adapted to perform baseband interference cancellation and/or radio frequency band cancellation circuitry adapted to perform radio frequency band interference cancellation. These additional cancellation circuitries provide additional interference cancellation in order to further enhance the performance of the present invention in relation to reduction of interference.

In a twelfth implementation form of the method according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the transceiver arrangement further comprises a parabolic reflector having a focal plane in which said antenna elements are located. Such an implementation allows a larger communication distance, specifically in line of sight, LOS, implementations. The second aspect of the present invention provides a method for transmitting and receiving electromagnetic signals in a multiple-input-multiple-output, MIMO, system, in which antenna elements are arranged in rotational symmetry on a circular line in a common plane, wherein said antenna elements are respectively identical in shape, said shape being axial symmetric, comprising the steps of encoding electromagnetic signals to be transmitted via said antenna elements with orthogonal vectors, and decoding electromagnetic signals received via said antenna elements with said orthogonal vectors, wherein said orthogonal vectors are selected to reduce interference caused by parasitic coupling between said antenna elements.

Generally, the method according to the second aspect of the invention is embodied by the functionalities of the transceiver arrangement of the first aspect of the present invention.

In a first implementation form of the method according to the second aspect of the present invention, said orthogonal vectors form a beam forming matrix which enables the generation of electromagnetic signal beams with different Orbital Angular Momentum, OAM, states.

In a second implementation form of the method according to the first implementation form of the second aspect of the invention, said beam forming matrix B is l l

i j - i - j

B =

i - j - i J

The above-described first and second aspects of the present invention solve the above-described object in an advantageous way. Specifically, the first and the second aspect of the present invention provide an advantageous and efficient way to reduce interference between the antenna elements in a simple and effective manner. Further advantageous but optional implementations are defined in the various above-described implementation forms.

The present invention provides a specifically advantageous way to reduce or even completely cancel interference between transmitting and receiving antenna elements, which transmit and receive MIMO data streams simultaneously in the same or at least similar/overlapping frequency bands.

It has to be noted that the present invention can be adapted and implemented in any kind of wireless communication or telecommunication system. Specifically, the transceiver arrangement according to the first aspect of the invention can be implemented in any kind of means, device, element, unit or the like in any kind of communication or telecommunication system in which electromagnetic signals are wirelessly transmitted and received. The common plane in which the antenna elements are arranged according to the first and the second aspect of the invention could be represented by any suitable element, on which said antenna elements are fixed, located, implemented or arranged in any other suitable way. For example, said antenna elements could be arranged on one surface side of a substrate, said surface side having a two-dimensional extension and being essentially flat in nature. The term common plane thus refers to an arrangement of the antenna elements in an essentially two-dimensional, flat and even surface. Further, the shape of .the antenna elements according to the first and second aspect of the invention could be represented by any suitable shape, for example but not limited to circular shape, quadratic shape and so forth. The only requirement is that the shape is axial symmetric, i.e. the shape is unchanged if rotated around an axis of the respective antenna element. This axis around which the axial symmetry exists is the center or middle axis of the respective antenna element, which extends perpendicular to said mentioned common plane through the center or middle of the respective antenna element. Further, the orientation of all antenna elements in said common plane is identical. The number of antenna elements is arbitrary, but an integer larger than 2. The encoding means and the decoding means of the first aspect of the present invention and its implementations could be implemented and realized in any kind of suitable software or hardware implementation and could be reflected in any kind of suitable device, unit, element and so forth. Also, the encoding means and the decoding means could be part of the same software or hardware structure or could be represented in physically separate software or hardware structures. Generally, it has to be noted that all arrangements, devices, elements, units and means and so forth described in the present application could be implemented by software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionality described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if in the following description of specific embodiments, a specific functionality or step to be performed by a general entity is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is in the following explained in detail in relation to embodiments of the invention in reference to the enclosed drawings, in which

Fig. 1 shows a general arrangement of antenna elements according to a first embodiment of the invention,

Fig. 2 shows an example of a more specific implementation of the first embodiment of Fig. 1 ,

Fig. 3 shows a visualization of the coupling coefficients of the arrangement of antenna elements of Fig. 2,

Fig. 4 shows a schematic circuit representation of the transceiver arrangement of the first embodiment,

Fig. 5 shows a schematic view of a transceiver arrangement according to the first embodiment of the present invention,

Fig. 6 shows a schematic representation of an arrangement of antenna elements of a second embodiment of the present invention,

Fig. 7 shows a schematic representation of a transceiver arrangement according to the second embodiment,

Fig. 8 shows a specific implementation example of the second embodiment of the invention,

Fig. 9 shows a specific implementation example of the first embodiment of the invention, and

Fig. 10 shows an implementation example of the present invention with parabolic reflectors.

DESCRIPTION OF EMBODIMENTS

Fig. 1 schematically visualizes the general idea underlying the invention. The present invention is generally directed to a transceiver arrangement and a method for transmitting and receiving electromagnetic signals in a multiple-input-multiple-output, MIMO, system, as explained above in the summary of the invention. The transceiver arrangement of the invention comprises a number of antenna elements, wherein the number is an integer number equal to or larger than 4. At least two of the antenna elements are adapted to transmit electromagnetic signals in the wireless communication system, and at least two of the antenna elements are adapted to receive electromagnetic signals in the wireless communication system. The antenna elements can either be exclusively adapted to transmit or receive signals, or can be adapted to transmit as well as receive signals in the wireless communication system, as will be explained in more detail in relation to the embodiments below.

As shown in Fig. 1 , the antenna elements 10, 1 1 of the transceiver arrangement of the present invention are generally arranged in rotational symmetry on a respective circular line 12, 13 in a common plane. In the general example shown in Fig. 1 , a number N of first antenna elements 10 are arranged in rotational symmetry on a circular line 12 and a number N' of second antenna elements 1 1 are arranged in rotational symmetry on a circular line 13 in a common plane. Hereby, in the example shown in Fig. 1 , the first circular line 12 and the second circular line 13 are concentric. It has to be understood that the general idea of the invention, however, is not restricted to two groups of antenna elements on two respective concentric circular lines. In a very basic and general implementation, as explained in relation to the second embodiment, the invention can be realized by a number of antenna elements which are located in rotational symmetry on a single circular line in a common plane. However, the arrangement of Fig. 1 with antenna elements on two concentric circular lines 12, 13 makes the basis of the present invention more clear.

As visualized by the arrows extending from each of the first antenna elements 10 towards two neighboring second antenna elements 1 1, isolation between transmitting antenna elements, for example antenna elements 10, and receiving antenna elements, for example antenna elements 1 1, is an important issue because normally the transmitted power is much higher than the received power. If a radio frequency leakage appears from the transmitting to the receiving antenna element, the received signal level may exceed the saturation level of the receiver and/or produce a strong interference, thus degrade the performance of the communication system. According to the general idea of the present invention as visualized in Fig. 1, in order to overcome or at least reduce the cross-talk problem, antenna elements are arranged in rotational symmetry on a single circular line in a common plane, or on two concentric circular lines in a common plane. The antenna elements in the single circular line, or in the two concentric circular lines, are respectively identical in shape, wherein the shape is axial symmetric. The transmitting antenna elements 10 are excited with a uniform phase delay increment along the circular line 12. The signals coupled to every receiving antenna element 1 1 are delayed in the same way along the circular line 12. One can show that if the signals from every receiving antenna element 1 1 are multiplied by complex coefficients in the same way again and combined, they cancel one another. In the example of Fig. 1 , transmitting antenna elements 10 are arranged in rotational symmetry on the first circular line 12, in a common plane, and receiving antenna elements 1 1 are arranged in a rotational symmetry on a second circular line 13 in the same common plane, wherein the first and second circular line are concentric, and wherein the transmitting and receiving antenna elements 10, 1 1 are respectively identical in shape, the shape being axial symmetric. Also, all antenna elements 10, 1 1 are oriented in the same direction. The number N of transmitting antenna elements 10 and the number N' of receiving antenna elements 1 1 is arbitrary, wherein N, N' are respectively equal to or larger than 2.

For simplicity, in the example shown in Fig. 1 , only two coupling coefficients between a transmitting antenna element 10 and a receiving antenna element 11 are considered to be present, as visualized by the arrows pointing from each transmitting element 10 to its respectively adjacent receiving antenna elements 11. Further, it is assumed that all possible coupling elements are rotational symmetric. If the transmitting antenna elements 10 are each fed with signals of the same absolute value but with a uniform phase increment of 2π/Ν radians, or 360 deg/N, the complex

f 2π Λ

amplitudes of the input signals are A, = exp j *— * / , where j is the imaginary part.

N j

It can be shown that if the received signals are combined with the same weighting coefficients, the resulting signal will be zero. This means that it is possible to transmit and receive electromagnetic beams independently with the arrangement shown in Fig. 1 .

As stated above, the number of antenna elements 10, 11 on the first and second circular lines 12, 13 are arbitrary but equal or larger than 2. However, a number of four antenna elements 10, 1 1 on each of the first and second circular lines 12, 13 is an advantageous choice in view of the simplified mathematics. Each of the four antenna elements 10, 1 1 on each of the first and second circular lines 12, 13 is excited with 90 degree phase shifts in relation to each other. According to the invention, the antenna elements 10, 1 1 on each circular line 12, 13 are respectively identical in shape, the shape being axial symmetric. Hereby, the axial symmetry, as explained above, is provided in relation to the axis through the center or middle of each antenna element perpendicular to the common plane. The arrangement shown in Fig. 2 with the advantageous implementation of respective four antenna elements 10 on the first circular line 12 and four receiving antenna elements 1 1 on the second circular line 13 implies 4x4 MIMO, i.e. four communication channels between the transmitting antenna elements 10 and the receiving antenna elements 11. In this example with transmitting antenna elements 10 on the first circular line and receiving antenna elements 1 1 on the second circular line 13, each of the antenna elements 10, 1 1 only has a single feeding point for transmitting and reception, respectively. However, it is possible, as will be explained in relation to the second embodiment, to implement the antenna elements on a single circular line only and as being adapted to transmit as well as receive signals. In this case, each antenna element has two feeding points. In such an implementation, this applies also a 4x4 MIMO communication. In another potential implementation, one part of the antenna elements on the single circular line could be adapted to only transmit, and the other part of the antenna elements on the single circular line could be adapted to only receive signals. For example, in case of four antenna elements on a single circular line, two of the antenna elements could be adapted to transmit and the other two antenna elements could be adapted to only receive electromagnetic signals.

Fig. 2 shows, in a first embodiment of the invention, the more specific implementation example of the arrangement shown in Fig. 1. As shown in Fig. 2, four first antenna elements 10 are arranged in rotational symmetry on a first circular line 12. Four second antenna elements 1 1 are arranged in rotational symmetry on a second circular line 13. The first circular line 12 and the second circular line 13 are concentric, but have a respectively different radius. In the example shown in Fig. 2, the first circular line 12 has a smaller radius than the second circular line 13. All antenna elements 10 and 1 1 are respectively identical in shape, wherein the shape is axial symmetric. In the shown example, the shape is quadratic. Each of the antenna elements 10 and 1 1 comprises the single feeding point 14 or 15. The four first antenna elements 10 as well as the four second antenna elements 1 1 are arranged in the same common plane and they are all oriented in the same direction. As shown in Fig. 2, the first antenna elements 10 are arranged in respective 90 degree angles in respect to each other and the second antenna elements 1 1 are respectively arranged at 45 degree angles in relation to the four first antenna elements 10 in relation to the common center of the first and the second circular lines 12 and 13.

The first antenna elements 10 are exclusively adapted to transmit electromagnetic signals, whereas the second antenna elements 1 1 are exclusively adapted to receive electromagnetic signals. In order to reduce the interference between the transmitting and receiving antenna elements 10, 1 1 , according to the invention, the electromagnetic signals transmitted from the first antenna elements 10 are encoded with orthogonal vectors. Similarly, the signals received by the receiving antenna elements 1 1 are decoded with the same orthogonal vectors. The orthogonal vectors are hereby selected to reduce the interference caused by parasitic coupling between the transmitting and receiving elements 10, 1 1.

As an advantageous example, the orthogonal vectors form a beam forming matrix B which enables the generation of electromagnetic signal beams with different Orbital Angular Momentum, OAM, states. In the shown example, for transmitting a beam with an OAM state of for example "+1", the transmitting antenna elements 10 can be fed with the same signal amplitudes, but phase distributed along the first circular line 12 as 0, 90, 180 and 270 degrees. In terms of complex amplitudes, this may be written as (l ,y, -1 , These are the weighting coefficients. Each receiving antenna element 1 1 at the receiving side has a parasitic coupling to each antenna element 10 on the transmitting side. This means that there is a parasitic signal from the transmitting antenna elements 10 at the receiving antenna elements 1 1. In order to receive a beam which is coded with an OAM state, the signals at each receiving antenna element 1 1 have to be combined again with similar coefficients. Therefore, the same procedure is performed automatically with the coupled transmitting signals in view of radio frequency leakage or self-interference.

In the following, the self-interference signal using a matrix notation is calculated. First, the coupling matrix M has to be obtained. The coupling with coefficients from the transmitting antenna elements 10 to the receiving antenna elements 1 1 is shown in the schematic representation of Fig. 3, which shows the arrangement of the antenna elements 10 and antenna elements 1 1 of the embodiment shown in Fig. 2 in a schematic view with the respective coupling coefficients from each transmitting antenna element 10 to each receiving antenna element 1 1 as ky, where y are integer numbers between 1 and 4. Fig. 4 shows a schematic circuit representation of the transceiver arrangement 20 according to the first embodiment of the present invention. It comprises an encoding means 21 adapted to encode electromagnetic signals to be transmitted via the transmitting antenna elements 10 with orthogonal vectors, and decoding means 22 adapted to decode electromagnetic signals received via the receiver antenna elements 1 1 with the same orthogonal vectors. The orthogonal vectors are being selected to reduce interference between the transmitting and receiving elements 10 and 1 1 in the manner described below. The encoding means 21 has 4 input ports, wherein each input port corresponds to one OAM state. The OAM states are "0", "+1 ", and "2". The encoding means 21 encodes electromagnetic signals received via one or more of these input ports with orthogonal vectors. The orthogonal vectors are represented by a beam forming matrix B which enables the generation of electromagnetic signal beams with the different OAM states. The correspondingly encoded electromagnetic signals are then transmitted in corresponding signal beams via the transmitting antenna elements 10. The parasitic coupling of these transmitted signal beams, which are received at the receiving antenna elements 1 1 , is represented by the coupling matrix M indicated with the reference number 23 in Fig. 4. On the receiving side, the received signal beams are decoded by the decoding means 22 which decodes the received signals with the same orthogonal vectors used by the encoding means, in form of the beam forming matrix B, and then outputs received signals in one or more of the four output ports which respectively correspond to one of the four mentioned OAM states "0", "+1 ", "- 1 " and "2".

The coupling matrix M can be written as:

Since the structure geometry is symmetric, some matrix components are equal or approximately equal: k = k_{4 i} ~ &₃₃ = k_2i := k_] k_n = k₄₄ ~ k₂₂ = &₃₄ ,:= k₂

i- ⁼ ^4 ^{¾ = : =} ^3 , and &i 4 ⁼ ^42 ^¾ ^32 ⁼ ^24 ^{: =} ^4 . "Approximately equal" signs are written here because, in an antenna element 10, 1 1 with a single feeding point 14, 15, the field distribution in the resonant mode, strictly speaking, is not symmetrical. However, one can accept it or, say, use differential feeds and "symmetrise" the field distribution. Thus, the coupling matrix can be rewritten as

Any non-symmetry like a reflecting object nearby will disturb that balance, but the rewritten matrix M is a good approximation. This matrix M can be used for calculating the parasitic signal in all the receiving antenna elements 1 1 , if the signals at the transmitting antenna elements 10 are known. Simply take the transmitted signal vector x , which is a column of signal complex amplitudes at the transmitting antenna elements 1 1 , and multiply it from the left side with the matrix M, to obtain the signal vector at the receiver side y . That is, the parasitic signal vector y = M * x .

For generating electromagnetic beams with the mentioned four different OAM states,

1 1 1 1

1 j - i - j

the beam forming matrix B = can be used as an advantageous

1 - j - i J

1 - 1 1 - 1

example. Other suitable matrices could also be used. The rows in this matrix correspond to signals at the transmitting antenna elements 10 needed to generate beams with the mentioned four possible Orbital Angular Momentum, OAM, states. Further, the orthogonality of these rows is being used as explained below.

Multiplying M by B^T gives - k₂ + k₃ - k₂ + k₃

' k₂ -f~ k k₄

k₂ 4~ k₃ k_{4 j}

Columns of the obtained matrix are the self-interference signals when transmitting beams with different OAM states.

Further at the receiving side, the signals from each of the antenna element 1 1 are combined again with the same beam forming matrix B. That is, if multiplying this from the left side by the beam forming matrix B, the following is obtained:

That is, only 6 of the possible 16 couplings need to be isolated with corresponding radio frequency and/or baseband cancellation circuiting as explained below. Thus, if port 1 is activated (OAM=0), signals with OAM=l , -1 and 2 in duplex regime (simultaneous transmission and receipt) can be received. Similarly, activated port 4 (OAM^) does not give interference when receiving signals with OAM=0, 1 , and -1. However, each active port corresponding to OAM=l or -1 gives an interference at two ports at the receiving side. This situation is schematically summarized in Fig. 5. The arrows show all possible couplings among the antenna elements 10 and 1 1. The transmitting and receiving antenna elements 10, 1 1 are connected to the corresponding encoding or decoding circuit 21 and 22. If measuring transmission coefficients from each input port to all output ports, several port pairs with non-zero transmission coefficients will be found, which are shown by the dashed lines. The long arrow coming from the top right come ("signal to be received") shows the signal with an OAM state coming from a remote host. This signal is not compensated and is expected to be properly received at one of the output ports. A further advancement may be compensating the remaining non-zero parasitic transmission coefficients. Nevertheless, duplex operation (i.e. simultaneous transmission and reception in the same frequency band) is already possible. For example, when one beam with OAM=0 is used for transmission, while 3 beams with OAM=l , -1 , and 2 are received (1TX and 3RX). Alternatively, one can radiate beams with OAM=l and -1 , and receive beams with OAM=0 and 2 (2TX and 2 RX). One can also notice that if coupling coefficients k_\=ki and ky=kn, each single input port will interfere only one output port. All antenna elements 10, 1 1 radiate with the same linear polarization. Adding the orthogonal polarization will double the number of channels.

Fig. 6 shows a schematic arrangement of antenna elements 16 in a second embodiment of the invention. In this embodiment, only a specific number of antenna elements, in the shown example four antenna elements 16, are arranged on a single circular line in the common plane in rotational symmetry. The antenna elements 16 are respectively identical in shape, the shape being axial symmetric, and the orientation of each antenna element 16 is the same. In the shown example, the shape is quadratic. In this embodiment, the antenna elements 16 are respectively adapted to transmit as well as receive electromagnetic signals in the wireless communication system. Hereby, each antenna element 16 has an input feeding point 16 for transmitting signals and the receiving feeding port 17 to receive electromagnetic signals. In Fig. 6, the coupling coefficients kj, i being an integer number between 1 and 4, are shown. These coupling coefficients are already simplified in view of the structural geometry (rotational symmetry of the antenna element 16 and identical shape of antenna element 16 and the shape being axial symmetric to the center or middle axis of each antenna element 16 in relation to the common plane). The same applies as explained above in relation to Figs. 3 and 4 of the first embodiment and the simplification of the coupling matrix M into the re-written coupling matrix M.

It can be shown that such an arrangement of four antenna elements 16 as shown in Fig. 6 radiates eigen MIMO modes, one with horizontal polarization with OAM=l, one vertical polarization with OAM=l , and left-and- right handed circularly polarized beams with OAM=0. This system may be useful for long range line-of-sight, LOS, MIMO systems. In case of a long-distance LOS scenario, one can show that, if an OAM state not more than 1 is used, it attenuates relatively slowly compared to higher OAM states. This structure is rotationally symmetric. Therefore, if there are no reflecting objects next to the structure, which would destroy the balance, it is not needed to "symmetrise" antenna elements. The coupling matrix can be written as

Similar operations with the beam forming matrix B as explained in relation to the first embodiment gives the following:

It_] ~i^~

M * B'

) and

That is, when one transmitting port is active, only one port is interfered at the receiving side, and 3 remaining ports can be used for independent reception.

Fig. 7, which is directed to the second embodiment but corresponds in nature to Fig. 5 of the first embodiment, visualizes the number of critical couplings between the transmitting and receiving antenna element 16 of the second embodiment, where only four connections need to be isolated (with corresponding baseband and/or radio frequency cancellation circuitry as explained below), which is less than 16 connections, so that the complexity is significantly reduced. The overall circuitry and implementation requirements are therefore much simplified.

Fig. 8 shows a schematic block diagram of a third embodiment of the present invention, which is represented by a transceiver arrangement 30 for transmitting and receiving electromagnetic signals in a MIMO system and comprises four antenna elements 26, 27 which are arranged in rotational symmetry on a circular line in a common plane. The antenna elements 26, 27 are respectively identical in shape, wherein the shape is axial symmetric (and are oriented in the same direction). The shape, as shown in Fig. 8, is quadratic. In this embodiment, the two antenna elements 26 are exclusively adapted to transmit electromagnetic signals, whereas the two antenna elements 27 are exclusively adapted to receive electromagnetic signals. In other words, the shown transceiver arrangement 30 is an example of a 2x2 MIMO full-duplex structure. Two transmitting signals streams S i(t) and s₂(t) are shown, which go into respective digital-to-analog converters, DAC, 31 and at the same time are fed into a digital signal processor, DSP, 40 at the receiving side, namely the baseband side of the receiving side, on the right side of the picture, for an additional baseband interference cancellation. Thus, the signal lines guiding the signal streams Si(t) and s₂(t) to the DSP 40 on the receiving side and the respective processing part of the DSP 40 represent baseband interference cancellation circuitry. Further, the analog signals output from the DACs 31 in the respective signal streams on the transmitting side are fed into respective circuitry 32 adapted to transform the baseband signals into radio frequency signals. The generated radio frequency signals are fed into a respective balun 33, which respectively generate two output signals. One signal goes into the encoding means 34 which encodes the radio frequency electromagnetic signal with orthogonal vectors (1 , 1) and (1 , -1), from which the encoded signals are then fed to the transmitting antenna elements 26 from which the signal beams are transmitted. The other output signal from the two baluns 33 is used for radio frequency interference cancellation at the receiving side. Hereby, this respective second output signal from each balun 33 is respectively fed to an attenuation and delay circuitry 36 which attenuates and delays (or phase shifts) the signal which is then added to the received signal output from the decoding means 35 coupled to the two receiving antenna elements 27 in order to cancel the parasitic coupling between the transmitter antenna element 26 and the receiving antenna element 27 in the radio frequency band. These signal lines and circuitry elements, i.e. the two balun elements 33, the attenuation and delay circuitry 36 as well as the summation means 37 adding the attenuated and delayed signals to the received signals, form radio frequency interference cancellation circuitry. The decoding means 35 and the encoding means 34 can for example be implemented with magic-T junctions as known in the art. Consequently, in the radio frequency part of the system, these magic-T junctions and the symmetry of the antenna elements 26, 27 as explained allows to isolate the first input port TXl of the encoding means 34 from the second output port RX2 of the decoding means 35 and to isolate the second input port TX2 of the encoding means 34 from the first output port RXl of the decoding means 35. The remaining two port pairs, namely TXl ' RXl and TX2' RX2 can be isolated in a conventional manner, for example as indicated with the radio frequency interference cancellation circuitry using the two balun elements 33, the attenuation and delay circuits 36 and the summation means 37. It can be shown that only two port pairs have to be isolated (by radio frequency and/or baseband cancellation circuitry as explained), not four, as in other possible implementation and embodiments, which makes the transceiver arrangement of the present embodiment much less complex. The magic-T junction of the encoding means 34 excites the two transmitting antenna elements 26 either in phase or in counter-phase, depending on which of the input ports TXl or TX2 is active. If, for example, the transmitting antenna elements 26 are fed in phase, the receiving antenna elements 27 have in-phase signals. The magic-T junction of the decoding means 35 at the receiver side outputs the sum signal at one output port and the differential signal at the other output port, which is zero in this case. The case in which the transmitting antenna elements 26 are fed in counter-phase can be considered in a similar way, wherein a zero signal at the sum output port and the non-zero signal at the difference output port on the receiving side are obtained. Fig. 9 shows a schematic block diagram of a possible implementation of a transceiver arrangement 40 which corresponds to the general first embodiment of the transceiver arrangement 20 explained above in relation to Figs. 2, 3, 4 and 5. Consequently, in this implementation example, four transmitting antenna elements 10 and four receiving antenna elements 1 1 are provided in respective concentric circular lines 12 and 13 in rotational symmetry on a common plane as explained above. The specific circuitry elements of the transceiver arrangement 40 shown in Fig. 9 are similar to the ones of Fig. 8, whereby the example of Fig. 9 has four signal streams arriving at the transmitting side identified with si(t) to s₄(t) (some elements have identical reference numbers). For the sake of simplicity, the signal lines s₂(t) and s₃(t) are not shown but have the same structure and the same elements as the signal lines si(t) and s₄(t) as explained in the following. Similar to the example of Fig. 8, each signal line is fed to a DAC 31 and a baseband-to-radio-frequency converter 32. For the sake of simplicity, these elements are combined in the single block in Fig. 9. The radio frequency signals are then processed in a respective balun element, from which one output is fed through a respective input port to an encoding means 41. The other output port is fed through a radio frequency interference cancellation circuitry to the receiving side via a respective attenuation and delay element 36 and a summation means 37. Also, each of the signal lines si(t) to s₄(t) is directly fed from the baseband level into the DSP 43 on the receiving side. Hereby, a baseband interference cancellation circuitry is provided and enabled. The encoding means 41 of the example shown in Fig. 9 corresponds in its functionalities identically to the ones of the encoding means 21 explained in relation to Figs. 4 and 5 of the first embodiment. Correspondingly, the encoding means 41 has four input ports, each one for one of the signal streams si(t) to s₄(t), respectively, and each one corresponding to one of the four mentioned OAM states "0", "+1", "-1" and "2". The encoding means 41 applies the beam forming matrix B as explained in relation to the first embodiment to the input signals and feeds the resulting signals to be transmitted to the transmitting antenna elements 10. Similarly, the decoding means 42 decoding the received signals from the receiving antenna elements 11 on the receiving side applies the same beam forming matrix B and outputs the decoded signals in a respective one of four output lines, each one corresponding to one of the OAM states "0", "+1", "-1" and "2". The functionalities of the decoding means 42 of Fig. 9 correspond identically to the functionalities of the decoding means 42 explained in relation to Figs. 4 and 5 of the first embodiment. The signals output from the output ports of the decoding means 42 are then radio frequency interference cancellation processed by means of the summation means 37 and then fed to corresponding radio-to-baseband converter and ADC 38 and 39, respectively, in the same way as the signals on the receiving side of this transceiver arrangement 30 shown in Fig. 8. The digitalized signals are then fed into the digital signal processor 43 for further processing, including baseband interference cancellation.

Fig. 10 shows a further example of an implementation of a transceiver arrangement according to the invention in a respective focal plane of a parabolic reflector 50. In this example, a respective antenna array 51 and 52 comprising antenna elements 10, 1 1 , 16 according to the present invention and being part of a transceiver arrangement of the present invention is arranged in the focal plane of a corresponding parabolic reflector. The result is that a larger effective aperture is obtained and a larger line of sight communication distance is feasible.

The invention has been described in conjunction with various embodiments herein. However, other variations to disclose the embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the wording "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in the mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

Transceiver arrangement (20, 30, 40) for transmitting and receiving electromagnetic signals in a multiple-input-multiple-output, MIMO, system, comprising antenna elements (10, 11 , 16) arranged in rotational symmetry on a circular line (12, 13)in a common plane, wherein said antenna elements (10, 1 1, 16) are respectively identical in shape, said shape being axial symmetric, and encoding means (21) adapted to encode electromagnetic signals to be transmitted via said antenna elements (10, 1 1, 16) with orthogonal vectors, and decoding means (22) adapted to decode electromagnetic signals received via said antenna elements (10, 1 1 , 16) with said orthogonal vectors, said orthogonal vectors being selected to reduce interference caused by parasitic coupling between said antenna elements.

Transceiver arrangement (20, 30, 40) according to claim 1, wherein said orthogonal vectors form a beam forming matrix which enables the generation of electromagnetic signal beams with different Orbital Angular Momentum, OAM, states.

Transceiver arrangement (20, 30, 40) according to claim 2, wherein said beam

forming matrix B is B

Transceiver arrangement (20, 40) according to one of the claims 1 to 3, wherein said antenna elements (10, 1 1) comprise four first antenna elements (10) arranged in rotational symmetry on a first circular line (13) in said common plane and having said identical shape, and four second antenna elements (1 1) arranged in rotational symmetry on a second circular line (13) in said common plane and having said identical shape, wherein said second circular line (13) is concentric to said first circular line (12).

Transceiver arrangement (20, 40) according to claim 4, wherein each of said four first (10) and four second (12) antenna elements comprises a single feeding point (14, 15)and wherein said four first antenna elements (10) are exclusively adapted to transmit electromagnetic signals and said four second antenna elements (1 1) are exclusively adapted to receive electromagnetic signals.

6. Transceiver arrangement (20, 40) according to claim 4 or 5, wherein the four second antenna elements (1 1) are respectively arranged at 45 degree angles to the four first antenna elements (10) in relation to a common center of the first (12) and the second (13) circular line.

7. Transceiver arrangement (20, 40) according to claim 4, 5 or 6, wherein the four first and second antenna elements (10, 1 1) are respectively adapted to radiate with linear polarization in a same direction.

8. Transceiver arrangement (20, 40) according to one of the claims 4 to 7, wherein the encoding means (21) comprises four inputs, each input corresponding to a different Orbital Angular Momentum, OAM, state and the decoding means comprises four outputs, each output corresponding to a different one of said OAM states.

9. Transceiver arrangement (20, 30) according to one of the claims 1 to 3, wherein said antenna elements (16) comprise four third antenna elements (10) arranged in rotational symmetry on said circular line in said common plane and having said identical shape.

10. Transceiver arrangement (20, 30) according to claim 9, wherein said four third antenna elements (10) respectively comprise two feeding points (16, 17) and are adapted to transmit and to receive electromagnetic signals.

1 1 . Transceiver arrangement (30) according to claim 9 or 10, wherein the encoding means comprises two inputs, each input corresponding to a different Orbital Angular Momentum, OAM, state and the decoding means comprises two outputs, each output corresponding to a different one of said OAM states.

12. Transceiver arrangement (20, 30, 40) according to one of the claims 1 to 1 1, further comprising baseband cancellation circuitry adapted to perform baseband interference cancellation and radio frequency band cancellation circuitry adapted to perform radio frequency band interference cancellation.

13. Transceiver arrangement (20, 30, 40) according to one of the claims 1 to 12, further comprising a parabolic reflector (50) having a focal plane in which said antenna elements (10, 1 1 , 16) are located.

14. Method for transmitting and receiving electromagnetic signals in a multiple-input- multiple-output, MIMO, system, in which antenna elements are arranged in rotational symmetry on a circular line in a common plane, wherein said antenna elements are respectively identical in shape, said shape being axial symmetric, comprising the steps of encoding electromagnetic signals to be transmitted via said antenna elements with orthogonal vectors, and decoding electromagnetic signals received via said antenna elements with said orthogonal vectors, wherein said orthogonal vectors are selected to reduce interference caused by parasitic coupling between said antenna elements.