MIMO communication between wireless communication nodes TECHNICAL FIELD

The present disclosure relates to wireless communication systems, and in particular to MIMO communication between wireless communication nodes.

BACKGROUND

Wireless communication systems today often utilize spatial multiple-input multiple-output (MIMO) technology for increasing transmission capacity by utilizing multiple physical paths between a transmitter and a receiver, which are commonly available in indoor and urban environments by means of reflections and diffraction in obstacles. Such systems often operate in non- line-of-sight (NLOS) in order to provide multiple spatial paths between transmitter and receiver. Today, MIMO is utilized in e.g. wireless local area network (WLAN) standards such as Wi-Fi and mobile data systems such as long term evolution (LTE). Access systems such as Wi-Fi and LTE operate by varying the number of spatial paths over time, where the maximum MIMO capacity is rarely reached.

Opposed to this, conventional microwave point to point (PtP) usually operates with line-of-sight (LOS) between transmitter and receiver, i.e., with a minimum of reflections and a dominant line-of-sight propagation path, and MIMO is therefore difficult to achieve. However, by separating multiple radio antennas properly in vertical and/or horizontal dimension the requirements of orthogonally between paths can be created in order to allow MIMO for capacity increase. This type of system is often referred to as a LOS-MIMO system. A fundamental difference between communication links for access systems and PtP links for transport systems is that a PtP link must operate with its designed capacity during almost all conditions, e.g. during rain and snow, where this design capacity normally is very high, sometimes exceeding 99.9% of its required capacity.

However, the required antenna separation for optimal LOS-MIMO capacity is often impractically large, especially for horizontal separation of antennas. Vertical separation can be obtained by putting antennas on top of each other on a high mast while horizontal separation is obtained by having multiple masts or mounting locations separated horizontally. Multiple masts require redundant active equipment which increases cost and maintenance. Furthermore, all antenna signals must be wired to a central location for signal processing and data recovery, which also increases cost and maintenance.

There is thus a need for obtaining MIMO communication between two nodes that has a high capacity and at the same time a relatively low cost and uncomplicated maintenance. SUMMARY

An object of the present disclosure is to provide a wireless communication node that is arranged for high capacity MIMO communication with at least one other wireless communication node while keeping cost and maintenance at a relatively low level.

This object is achieved by means of a wireless communication node comprising an antenna arrangement with at least two antenna devices having corresponding main radiation beams and respective antenna radiation beam reflectors spatially separated from the wireless communication node. Each of the main radiation beams is directed towards its respective antenna radiation beam reflector. The radiation beam reflectors are positioned to configure the wireless communication node for multiple-input multiple-output (MIMO) communication at a carrier centre frequency with at least one other wireless communication node via the antenna radiation beam reflectors.

This object is also achieved by means of a wireless communication system comprising a first wireless communication node and a second wireless communication node. The first wireless communication node comprises a first node antenna arrangement with at least two antenna devices having corresponding main radiation beams and respective antenna radiation beam reflectors spatially separated from the wireless communication node. Each of the main radiation beams is directed towards its respective antenna radiation beam reflector. The radiation beam reflectors are positioned to configure the wireless communication node for multiple-input multiple-output (MIMO) communication at a centre frequency with the second wireless communication node via the antenna radiation beam reflectors.

According to an example, each antenna radiation beam reflector is positioned as function of effective node distances between effective antenna devices of the wireless communication node and corresponding other antenna devices of the other wireless communication node via corresponding antenna radiation beam reflectors, and of the centre frequency. Each effective antenna device is formed by a corresponding antenna device together with its corresponding antenna radiation beam reflector.

According to another example, the radiation beam reflectors are positioned to satisfy system requirements on spectral efficiency in terms of bits/sec/Hz beyond that of a single-input single-output (SISO) system.

According to another example, a channel between the wireless communication node and said other wireless communication node is represented by a channel matrix. The radiation beam reflectors are positioned such that a conditional number of the channel matrix falls below a conditional number threshold. According to another example, the radiation beam reflectors are positioned to increase a capacity in terms of bits/sec/Hz of said MIMO communication beyond that of a corresponding single-input multiple-output (SIMO) or a corresponding multiple-input single-output (MISO) or a SISO communication between the wireless communication node and the at least one other wireless communication node. According to another example, the wireless communication node is configured for 2x2 MIMO, or 4x4 dual polarization MIMO, communication, where the radiation beam reflectors are positioned such that the condition

(L + L _r ) ^■ c

d ^{Ae - dB =} 2 - f _c is satisfied, where L+L _r is the shortest distance between each effective antenna device and a corresponding opposing other antenna device of said other wireless communication node, 0B is the distance between adjacent other antenna devices of said other wireless communication node, c is the speed of light in air and dAe is the distance between adjacent effective antenna device.

According to another example, the antenna devices of each antenna arrangement are positioned along a corresponding horizontal extension. According to another example, the antenna devices of each antenna arrangement are positioned along a corresponding vertical extension.

According to another example, at least two antenna radiation beam reflectors are positioned at two different relative heights. Other examples are evident from the dependent claims.

A number of advantages are obtained by means of the present disclosure. Mainly, all MIMO antennas and active equipment can be mounted in the same location/mast at both side of a link, significantly simplifying deployment and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where: shows a schematic side view of a first example of a communication node arrangement; shows a schematic perspective top view of a first example of the communication node arrangement; shows a further schematic perspective top view of a first example of the communication node arrangement; shows a schematic perspective top view of a second example of the communication node arrangement; shows a schematic perspective top view of a third example of the communication node arrangement;

Figure 6 shows a schematic front view illustrating a fourth example of the communication node arrangement; and Figure 7 shows a further schematic perspective top view of a fifth example of the communication node arrangement. DETAILED DESCRIPTION

Figure 1 shows a side view of a wireless communication system 21 , while Figure 2 and Figure 3 show a top perspective view of the wireless communication system 21 . Figure 2 and Figure 3 are in fact showing the same configuration, but due to a plurality of details two figures have been used for improving clarity.

With reference to Figure 1 , Figure 2 and Figure 3, showing a first example, there is a first wireless communication node 1 comprising a first antenna arrangement 2 that comprises four antenna devices 3, 4, 5, 6 with corresponding main radiation beams 7, 8, 9, 10. A first antenna device 3 is separated from an adjacent second antenna device 4 with a first antenna device distance di, the second antenna device 4 is separated from an adjacent third antenna device 5 with a second antenna device distance 02, and the third antenna device 5 is separated from an adjacent fourth antenna device 6 with a third antenna device distance d3.

The first wireless communication node 1 comprises a first antenna radiation beam reflector 12, a second antenna radiation beam reflector 13, a third antenna radiation beam reflector 14 and a fourth antenna radiation beam reflector 15, where the antenna radiation beam reflectors 12, 13, 14, 15 are spatially separated from the first antenna arrangement 2.

The antenna radiation beam reflectors and their function in enabling MIMO communication between the first 1 and the second 1 1 wireless communication node will be further elaborated on below.

According to the present disclosure, each of the main radiation beams 7, 8, 9, 10 is directed towards one respective antenna radiation beam reflector 12, 13, 14, 15, where the radiation beam reflectors are positioned to configure the first wireless communication node 1 for multiple-input multiple-output, (MIMO) communication at a centre frequency fc with a second wireless communication node 1 1 via the antenna radiation beam reflectors 12, 13, 14, 15. The antenna radiation beam reflectors 12, 13, 14, 15 are oriented to reflect signals incoming from the first wireless communications node 1 in the direction of the second wireless communications node 1 1 , and to reflect signals incoming from the second wireless communications node 1 1 in the direction of the first wireless communications node 1 , thus enabling communication between the first and second wireless communication node via respective antenna radiation beam reflectors 12, 13, 14, 15. The antenna radiation beam reflectors 12, 13, 14, 15 are furthermore positioned such that at least one certain predetermined condition is satisfied, enabling spatial multiplexing.

The second wireless communication node 1 1 is positioned at a node distance L from the first wireless communication node 1 , where the second wireless communication node 1 1 comprises a second antenna arrangement 16 that comprises four antenna devices 29, 30, 31 , 32. A fifth antenna device 29 is separated from an adjacent sixth antenna device 30 with a fourth antenna device distance d ₄ , the sixth antenna device 30 is separated from an adjacent seventh antenna device 31 with a fifth antenna device distance d ₅ , and the seventh antenna device 31 is separated from an adjacent eighth antenna device 32 with a sixth antenna device distance d6.

The antenna devices 3, 4, 5, 6 of the first antenna arrangement 2 are positioned along a corresponding horizontal extension Hi . Between the horizontal extension Hi and the antenna radiation beam reflectors 12, 13, 14, 15 there is a height difference Ah that in this example is the same for all antenna radiation beam reflectors 12, 13, 14, 15. The height difference Ah may vary for the antenna radiation beam reflectors 12, 13, 14, 15 in order to obtain certain advantages, as will be discussed later.

From the first antenna device 3 a first main radiation beam 7 is directed towards the first antenna radiation beam reflectors 12, and is reflected towards the fifth antenna device 29 as indicated with a solid radiation beam indicating line 33. The first main radiation beam 7 is reflected towards the three other antenna devices 30, 31 , 32 of the second wireless communication node 1 1 as indicated with corresponding dash-dotted radiation beam indicating lines 34, 35, 36.

In the same way, each one the second main radiation beam 8, the third main radiation beam 9 and the fourth main radiation beam 10 of the corresponding second antenna device 4, the third antenna device 5 and the fourth antenna device 6 is also reflected towards each one of the antenna devices 29, 30, 31 , 32 of the second wireless communication node 1 1 .

However, for the sake of clarity, only one corresponding radiation beam indicating line 37, 38, 39 is indicated for each one these antenna devices 4, 5, 6, here the radiation beam indicating lines 37, 38, 39 that run between opposing corresponding first and fifth antenna devices 3, 29, second and sixth antenna devices 4, 30, third and seventh antenna devices 5, 31 and fourth and eighth antenna devices 6, 32 of the corresponding wireless communication nodes 1 , 1 1 . For the same reason, in the rest of the Figures only these radiation beam indicating lines running between opposing antenna devices are shown, although each antenna radiation beam 7, 8, 9, 10 of the first wireless communication node 1 reaches all antenna devices 29, 30, 31 , 32 of the second wireless communication node 1 1 via the corresponding antenna radiation beam reflectors 12, 13, 14, 15.

By means of the antenna radiation beam reflectors 12, 13, 14, 15, there is provided a first effective antenna device 3 _e corresponding to the first antenna device 3, a second effective antenna device 4 _e corresponding to the second antenna device 4, a third effective antenna device 5 _e corresponding to the third antenna device 5 _e and a fourth effective antenna device 6 _e corresponding to the third antenna device 6, where the effective antenna devices 3 _e , 4 _e , 5 _e , 6 _e are indicated by circles. The first effective antenna device 3 _e is fornned by the first antenna device 3 together with the first antenna radiation beam reflector 12, the second effective antenna device 4 _e is formed by the second antenna device 4 together with the second antenna radiation beam reflector 13, the third effective antenna device 5 _e is formed by the third antenna device 5 together with the third antenna radiation beam reflector 14 and the fourth effective antenna device 6 _e is formed by the fourth antenna device 6 together with the fourth antenna radiation beam reflector 15. In the same direction as the horizontal extension Hi , there is a first effective antenna device distance di _e between the first effective antenna device 3 _e and the second effective antenna device 4 _e , a second effective antenna device distance d2e between the second effective antenna device 4 _e and the third effective antenna device 5 _e , and a third effective antenna device distance d3 _e between the third effective antenna device 5 _e and the fourth effective antenna device 6 _e .

It is appreciated, that by means of the antenna radiation beam reflectors, the spatial relationship between resulting effective antenna devices 3e, 4e, 5e, 6e, can be such as to allow for MIMO communication between the first wireless communication node 1 and the second wireless communication node 1 1 , for a wide variety of antenna device mountings. Thus, the presence of the antenna radiation beam reflectors enable MIMO communication in scenarios where such MIMO communication was previously not possible due to, e.g., constraints on antenna separation.

There is a first node distance l_i between the first antenna radiation beam reflector 12 and the opposing fifth antenna device 29, a second node distance L ₂ , between the second antenna radiation beam reflector 13 and the opposing sixth antenna device 30, a third node distance L ₃ between the third antenna radiation beam reflector 14 and the opposing seventh antenna device 31 and fourth node distance L between the fourth antenna radiation beam reflector 15 and the opposing eighth antenna device 32.

There is a first reflector distance l_i _r between the first antenna device and the first antenna radiation beam reflector 12, and also between the first antenna radiation beam reflector 12 and the first effective antenna device 3 _e . In the same way, there is a reflector distance L _2r between the second antenna device 4 and the second antenna radiation beam reflector 13, and also between the second antenna radiation beam reflector 13 and the second effective antenna device 4 _e ; a third reflector distance L _3r between the third antenna device 5 and the third antenna radiation beam reflector 14, and also between the third antenna radiation beam reflector 14 and the third effective antenna device 5 _e ; and a fourth reflector distance L _r between the fourth antenna device 6 and the fourth antenna radiation beam reflector 15, and also between the fourth antenna radiation beam reflector 15 and the fourth effective antenna device 6 _e .

There is thus a corresponding effective node distance between each effective antenna device 3 _e , 4 _e , 5 _e , 6 _e and the corresponding opposing antenna device 29, 30, 31 , 32 of the second wireless communication node 1 1 that equals the sum of the corresponding node distance l_i , L ₂ , L ₃ , L and reflector distance

It is thus evident that the effective antenna device distances d i _e , d2e, d3 _e can be made arbitrarily large by placing the antenna radiation beam reflectors 12, 13, 14, 15 in appropriate positions. In order to obtain MIMO communication at a centre frequency f _c , the antenna radiation beam reflectors 12, 13, 14, 15 should be positioned such that predetermined conditions are satisfied. For example, the effective node distances Li+I_i _r , L ₂ +L _2r , L ₃ +L _3r , L ₄ +L _4r should satisfy predetermined phase requirements for a four-channel MIMO wireless communication system 21 . The wireless communication system 21 can of course be designed in the same way for arbitrary numbers of MIMO channels.

Generally, each antenna radiation beam reflector 12, 13, 14, 15 may be positioned as function of the effective node distances Li+I_i _r , L ₂ +L _2r , L ₃ +L _3r , L +L _r and the centre frequency f _c . Equivalently, each antenna radiation beam reflector 12, 13, 14, 15 may be positioned as function of the effective node distances Li+I_i _r , L ₂ +L ₂ r, L ₃ +L _3r , L +L _r and of the wavelengths at which communication is performed.

According to some aspects, other predetermined conditions are satisfied by the positioning of the antenna radiation beam reflectors 12, 13, 14, 15. Between the first wireless communication node 1 and the second wireless communication node 11 , there is a channel 28 that is represented by a channel matrix H. A received vector of symbol samples y is then given by, or modelled as, y=Hx+n, where n is a vector of distortion samples and x is a vector of transmitted symbols samples.

The radiation beam reflectors 12, 13, 14, 15 may be positioned such that a conditional number of the channel matrix H falls below a conditional number threshold, where an example of such a conditional number threshold is 10. In essence, having a channel matrix H with conditional number sufficiently low implies that the channel matrix can be inverted with maintained signal quality, and thus MIMO communication is enabled. This means that an estimate of the transmitted symbol samples x is given by H ^~1 y

Furthermore, the antenna radiation beam reflectors 12, 13, 14, 15 may be positioned to satisfy system requirements on spectral efficiency in terms of bits/sec/Hz beyond that of a single-input single-output, SISO, system. This means that with a preferred placement of the antenna radiation beam reflectors 12, 13, 14, 15, MIMO communication between the first wireless communication node 1 and the second wireless communication node 11 is enabled for a wide variety of antenna device mountings, which gives rise to a spectral efficiency in terms of bits/sec/Hz beyond that of a SISO system. The antenna radiation beam reflectors 12, 13, 14, 15 may also be positioned to increase a capacity in terms of bits/sec/Hz of said MIMO communication beyond that of a corresponding single-input multiple-output, SIMO, or a corresponding multiple-input single-output, MISO, or a single-input single- output, SISO, communication between the first wireless communication node 1 and the second wireless communication node 1 1 .

The use of antenna radiation beam reflectors 12, 13, 14, 15 will cause antenna beam radiation to be directed in different directions than the LOS direction of first wireless communication node 1 , and the antenna devices 29, 30, 31 , 32 at the second wireless communication node 1 1 may also spread antenna beam radiation in a wider angle than in the conventional LOS system. In order to reduce risk of interference with other systems in the vicinity operating at the same frequency, it is beneficial to mount the antennas and the reflectors on site A at different heights with a varying height difference Ah as indicated previously. This will cause energy in the non LOS direction to radiate up in the sky and down in the ground, which will be beneficial from an interference point of view.

In order not introduce significant transmission loss, the size of each antenna radiation beam reflectors 12, 13, 14, 15 may for example exceed 60% of the width of the first Fresnel zone, but can of course be larger or smaller. A small reflector is in reality preferred in order to simplify deployment and therefore a high loss can sometimes be acceptable.

The first wireless communication node 1 may in addition comprise a direct antenna arrangement 18 that comprises at least one antenna device 19 with a direct main radiation beam 20, where the direct main radiation beam 20 is arranged to propagate directly towards the second wireless communication node 1 1 . A corresponding direct antenna arrangement 40 that comprises at least one antenna device 41 is thus positioned at the second wireless communication node 1 1 . Each wireless communication node 1 , 1 1 may of course comprise several such direct antenna arrangement which thus are arranged for LOS communication.

According to a second example, if the first wireless communication node can accommodate the required antenna separation in the vertical direction for two antenna arrangements, the antenna radiation beam reflectors 12, 13, 14, 15 can be used to scale the system in both vertical and horizontal direction as will be discussed below.

As illustrated in Figure 4, there is a wireless communication system 21 ' where the first wireless communication node V comprises a first upper antenna arrangement 2' and a first lower antenna arrangement 2 that corresponds to the first antenna arrangement 2 in the first example. The antenna arrangements 2, 2' are positioned along a vertical extension V, and are separated by an antenna arrangement distance dAv that fulfils the required MIMO path differences for a desired conditional number, as discussed previously. Provided that the antenna arrangement distance dAv is sufficient, the antenna radiation beam reflectors 12', 13', 14', 15' can be used for both antenna arrangements 2, 2'. However, the antenna radiation beam reflectors 12', 13', 14', 15' should then be mounted at different relative heights hi, h ₂ , h ₃ , h in order to provide orthogonality between all MIMO channels.

More in detail, as shown in Figure 4, the first upper antenna arrangement 2' comprises four antenna devices 3', 4', 5', 6' with corresponding main radiation beams 7', 8', 9', 10', as indicated with dashed lines. Although not explicitly indicated, all antenna device are separated from adjacent antenna devices with corresponding antenna device distance as in the first example, and due to the antenna radiation beam reflectors 12', 13', 14', 15' corresponding effective antenna device distance will occur. In the same way as the first wireless communication node 1 ', there is a second wireless communication node 1 1 ' that here comprises a second lower antenna arrangement 16 and a second upper antenna arrangement 16' with corresponding antenna devices 29, 30, 31 , 32; 29', 30', 31 ', 32'. Solid radiation beam indicating lines 33, 34, 35, 36 indicate how the main radiation beams 7, 8, 9, 10 of the lower antenna arrangement 2 are directed towards the corresponding antenna radiation beam reflectors 12', 13', 14', 15' and are reflected towards the antenna devices 29, 30, 31 , 32; 29', 30', 31 ', 32' of the second wireless communication node 1 1 '. Dashed radiation beam indicating lines 33', 34', 35', 36' indicate how the main radiation beams 7', 8', 9', 10' of the upper antenna arrangement 2' are directed towards the corresponding antenna radiation beam reflectors 12', 13', 14', 15' and are reflected towards the antenna devices 29, 30, 31 , 32; 29', 30', 31 ', 32' of the second wireless communication node 1 1 ' via a channel 28'.

As mentioned previously, for reasons of clarity, only these radiation beam indicating lines running between opposing antenna devices are shown, although each antenna radiation beam 7, 8, 9, 10; 7', 8', 9', 10' of the first wireless communication node 1 ' reaches all antenna devices 29, 30, 31 , 32; 29', 30', 31 ', 32' of the second wireless communication node 1 1 ' via the corresponding antenna radiation beam reflectors 12', 13', 14', 15'.

With reference to Figure 5, showing a third example, there is a wireless communication system 21 " where the first wireless communication node 1 " comprises an antenna arrangement 22 which in turn comprises a first antenna device 23, having a first main radiation beam 7", and a second antenna device 24, having a second main radiation beam 8". The antenna devices 23, 24 are separated by a first antenna device distance dA.

The first wireless communication node 1 " is arranged for 2x2 MIMO communication with the second wireless communication node 1 1 " which comprises a second antenna arrangement 25. The second antenna arrangement 25 comprises a third antenna device 26 and a fourth antenna device 27 which are separated by a second antenna device distance 0B- Each of the main radiation beams 7", 8" is directed towards its respective antenna radiation beam reflector 12", 13", wherein the radiation beam reflectors are positioned to configure the wireless communication node 1 " for multiple-input multiple-output, MIMO, communication at the centre frequency f _c with the second wireless communication node 1 1 " via the antenna radiation beam reflectors 12", 13", via a channel 28".

The first main radiation beam 7" is thus arranged to propagate towards the second wireless communication node 1 1 " only via the first antenna radiation beam reflector 12" and, the second main radiation beam 8" is thus arranged to propagate towards the second wireless communication node 1 1 " only via the second antenna radiation beam reflector 13".

By means of the antenna radiation beam reflectors 12", 13", there is provided a first effective antenna device 23 _e corresponding to the first antenna device 23 and a second effective antenna device 24 _e corresponding to the second antenna device 24, where the effective antenna devices 23 _e , 24 _e are indicated by circles. The first effective antenna device 23 _e is formed by the first antenna device 23 together with the first antenna radiation beam reflector 12" and the second effective antenna device 24 _e is formed by the second antenna device 24 together with the second antenna radiation beam reflector 13".

In the same way as in the first example, there is horizontal extension Hi, and in the same direction as the horizontal extension Hi, there is an effective antenna device distance dAe between the first effective antenna device 23 _e and the second effective antenna device 24 _e . There is a node distance L between the first antenna radiation beam reflector 12" and the opposing third antenna device 26 and between the second antenna radiation beam reflector 13" and the opposing fourth antenna device 27. Between the first antenna radiation beam reflector 12" and the fourth antenna device 27 there is an additional distance ΔΙ_, forming a total distance of Ι_+ΔΙ_. The same total distance Ι_+ΔΙ_ is of course formed between the second antenna radiation beam reflector 13" and the third antenna device 26. There is a reflector distance L _r between the first antenna device 23 and the first antenna radiation beam reflector 12", and also between the first antenna radiation beam reflector 12" and the first effective antenna device 23 _e . In the same way, due to symmetry in this example, the same reflector distance L _r is also present between the second antenna device 24 and the second antenna radiation beam reflector 13", and also between the second antenna radiation beam reflector 13" and the second effective antenna device 24 _e .

There is thus a corresponding effective node distance between each effective antenna device 23 _e , 24 _e and the corresponding opposing antenna device 26, 27 of the second wireless communication node 1 1 " that equals the sum of the node distance L and the reflector distance L _r .

In order to obtain MIMO communication, the radiation beam reflectors 12", 13" are positioned such that the condition r

2 - f, is satisfied. As follows from the above, L+L _r is the shortest distance between one of the first effective antenna device 23 _e and the second effective antenna device 24 _e , and the corresponding opposing antenna device 26, 27 of the second wireless communication node 1 1 ", 0B is the second antenna device distance, c is the speed of light in air, f _c is the carrier centre frequency and dAe is the effective antenna device distance between the first effective antenna device 23 _e and the second effective antenna device 24 _e . The above is also applicable for 4x4 dual polarization MIMO, in which case each polarization is seen as having separate antenna devices. The principles of MIMO communication discussed above still apply, with an addition of a polarization attenuation between differently polarized antenna devices.

With reference to Figure 6, showing a fourth example, the first wireless communication node 1 "' comprises a first vertical antenna arrangement 42 and a second vertical antenna arrangement 43. The antenna arrangements 42, 43 are positioned along a horizontal extension H and are separated by an antenna arrangement distance dAH - The antenna devices 44, 45, 46, 47; 48, 49, 50, 51 of each antenna arrangement 42, 43 are positioned along a corresponding vertical extension Vi, V ₂ . Figure 6 only illustrates the first wireless communication node 1 "', and it is to be noted that a similar antenna arrangement configuration is apparent at a corresponding second wireless communication node, and where antenna radiation beam reflectors are used to obtain desired effective antenna device distances as in the first three examples. Figure 6 is merely showing an alternative antenna arrangement configuration without repeating all details.

Figure 7 shows a further schematic perspective top view of a fifth example of the wireless communication node 1 "", wherein the wireless communication node 1 "" comprises an antenna arrangement 52, schematically indicated in Figure 7. The antenna arrangement 52 in turn comprises four antenna devices 53, 54, 55, 56. The antenna devices 53, 54, 55, 56 are mounted in an irregular geometrical relationship, i.e., not on a line or otherwise regular layout. The antenna devices 53, 54, 55, 56 have corresponding main radiation beams 57, 58, 59, 60, where each main radiation beams 57, 58, 59, 60 is directed towards one corresponding antenna radiation beam reflector 12"", 13"", 14"", 15"", and is reflected towards a second wireless communication node (not shown) in the same way as in the previous examples. This is schematically indicated with corresponding dashed radiation beam indicating lines 61 , 62, 63, 64.

It is thus appreciated that in general antenna devices that are comprised in a wireless communication node according to the present disclosure are not necessarily mounted on a straight line, horizontal or vertical, as shown in Figures 2-6, but that such antenna devices can be mounted according to any regular or irregular spatial distribution, e.g., in a rectangular configuration, a circle, or a more irregular fashion. However, the above discussion on MIMO and conditions for MIMO communication holds true regardless of relative geometry of antenna devices, which geometry can be compensated for by means of the above-mentioned antenna radiation beam reflectors.

The present disclosure is not limited to the above example, but may vary freely within the scoop of the appended claims. For example, the symmetry in the third example is not necessary, but that would affect the condition above. The examples shown are only for conveying an understanding of the present disclosure; other configurations and number of antenna arrangements is possible, and naturally the number of antenna devices in each antenna arrangement may vary. There is at least one other node, in the examples above the second node. The antenna devices may be identical or of different types, for example there may be different antenna devices in different antenna arrangements.

Each antenna device may comprises one or more antenna elements, where the antenna elements for example may be in the form of reflector antennas, slot antenna elements or microstrip patch antenna elements. An antenna device may be formed by an array of slot antenna elements or microstrip patch antenna elements. An antenna device may comprise sub-arrays in an antenna array. The representation of the antenna devices in the Figures is only schematical, and should not be regarded as limiting. An antenna device may for example have a circular, elliptical or square appearance and/or antenna aperture.

The height differences and the relative heights may also vary in any suitable way.

The antenna radiation beam reflector mounted at outside locations may be passive, e.g. a flat metal plate, and then require no network cabling, electricity, or other supporting infrastructure. Spreading of energy in unwanted directions can be avoided by mounting the antenna devices and antenna radiation beam reflectors at different heights above ground, thus reducing risk of interfering with other links since energy from the site close to the antenna radiation beam reflectors will either go into the ground or up in the sky.

The antenna radiation beam reflectors can be implemented in many different ways. An uncomplicated alternative is a metal sheet that can be adjusted in appropriate angles in order to fulfil the law of reflection, i.e. input angle equals output angle of energy. Other alternatives include having two coupled antennas, which avoid the angle requirements stipulated by the law of reflection. The present disclosure is scalable to aby suitable number of MIMO channels, e.g. 6, 8, 10 ... channels.

All antennas at a node do not have to reside in the same enclosure but may have individual alignment control, e.g. by means of motors. One or more direct antenna arrangements 18, 19 as described above may be applied for all examples described above, and further for any type of configuration within the scope of the present disclosure. The present disclosure relates to a wireless communication node 1 , V, 1 ", 1 "', 1 "" as well as a wireless communication system 21 , 21 ', 21 " comprising a first wireless communication node 1 , 1 ', 1 ", 1 "', 1 "" and a second wireless communication node 1 1 , 1 1 ', 1 1 ". Expressions such as satisfied symmetry and identical are not intended to be interpreted literally, but within what is practically obtainable with in this field of technology, for example a condition is normally approximately satisfied.

Generally, the present disclosure relates to a wireless communication node 1 comprising an antenna arrangement 2 with at least two antenna devices 3, 4, 5, 6; 3', 4', 5', 6' having corresponding main radiation beams 7, 8, 9, 10; 7', 8', 9', 10' and respective antenna radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' spatially separated from the wireless communication node 1 , each of the main radiation beams 7, 8, 9, 10 being directed towards its respective antenna radiation beam reflector 12, 13, 14, 15; 12', 13', 14', 15', wherein the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned to configure the wireless communication node 1 , 1 ' for multiple- input multiple-output (MIMO) communication at a carrier centre frequency f _c with at least one other wireless communication node 1 1 , 1 1 ' via the antenna radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15'.

According to an example, each antenna radiation beam reflector 12, 13, 14, 15 is positioned as function of effective node distances Li+I_i _r , L ₂ +L _2r , L ₃ +L _3r , L +L _r between effective antenna devices 3 _e , 4 _e , 5 _e , 6 _e of the wireless communication node 1 and corresponding other antenna devices 29, 30, 31 , 32 of the other wireless communication node 1 1 via corresponding antenna radiation beam reflectors 12, 13, 14, 15, and of the centre frequency f _c , where each effective antenna device 3 _e , 4 _e , 5 _e , 6 _e is formed by a corresponding antenna device 3, 4, 5, 6 together with its corresponding antenna radiation beam reflector 12, 13, 14, 15. According to an example, the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned to satisfy system requirements on spectral efficiency in terms of bits/sec/Hz beyond that of a single-input single-output (SISO) system. According to an example, wherein a channel 28, 28' between the wireless communication node 1 , 1 ' and said other wireless communication node 1 1 , 1 1 ' is represented by a channel matrix H, where the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned such that a conditional number of the channel matrix H falls below a conditional number threshold.

According to an example, the conditional number threshold is 10.

According to an example, the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned to increase a capacity in terms of bits/sec/Hz of said MIMO communication beyond that of a corresponding single-input multiple-output (SIMO) or a corresponding multiple-input single-output, (MISO) or a single-input single-output (SISO) communication between the wireless communication node 1 , 1 ' and the at least one other wireless communication node 1 1 , 1 1 '.

According to an example, the wireless communication node 1 " is configured for 2x2 MIMO, or 4x4 dual polarization MIMO, communication, where the radiation beam reflectors are positioned such that the condition r) «-

2 - f, is satisfied, where L+L _r is the shortest distance between each effective antenna device 23 _e , 24 _e and a corresponding opposing other antenna device 26, 27 of said other wireless communication node 1 1 ", 0B is the distance between adjacent other antenna devices 26, 27 of said other wireless communication node 1 1 ", c is the speed of light in air and dAe is the distance between adjacent effective antenna device 23 _e , 24 _e , where each effective antenna device 23 _e , 24 _e is formed by a corresponding antenna device 23, 24 together with its corresponding antenna radiation beam reflector 12", 13". According to an example, the wireless communication node 1 " comprises one antenna arrangement 22 which in turn comprises a first antenna device 23, having a first main radiation beam 7", and a second antenna device 24, having a second main radiation beam 8", the antenna devices 23, 24 being separated by an antenna device distance dA, where the first effective antenna device 23 _e is formed by the first antenna device 23 together with the first antenna radiation beam reflector 12" and the second effective antenna device 24 _e is formed by the second antenna device 24 together with the second antenna radiation beam reflector 13". According to an example, the antenna devices 3, 4, 5, 6; 3', 4', 5', 6' of each antenna arrangement 2, 2' are positioned along a corresponding horizontal extension Hi, H ₂ .

According to an example, the wireless communication node 1 comprises at least two antenna arrangements 2, 2', where the antenna arrangements 2, 2' are positioned along a vertical extension V, neighbouring antenna arrangements 2, 2' being separated by a corresponding antenna arrangement distance dAv- According to an example, the antenna devices 44, 45, 46, 47; 48, 49, 50, 51 of each antenna arrangement 42, 43' are positioned along a corresponding vertical extension Vi, V ₂ . According to an example, the wireless communication node 1 "' comprises at least two antenna arrangements 42, 43, where the antenna arrangements 42, 43 are positioned along a horizontal extension H, neighbouring antenna arrangements 42, 43 being separated by a corresponding antenna arrangement distance dAH -

According to an example, the wireless communication node 1 comprises at least one direct antenna arrangement 18, each direct antenna arrangement comprising at least one antenna device 19 with a corresponding direct main radiation beam 20, where each direct main radiation beam 20 is arranged to propagate directly towards said other wireless communication node 1 1 .

According to an example, at least two antenna radiation beam reflectors 12', 13', 14', 15' are positioned at two different relative heights hi, h ₂ , h ₃ , h .

Generally, the present disclosure also relates to a wireless communication system 21 , 21 ' comprising a first wireless communication node 1 , 1 ' and a second wireless communication node 1 1 , 1 1 ', where the first wireless communication node 1 , 1 ' comprises a first node antenna arrangement 2, 2' with at least two antenna devices 3, 4, 5, 6; 3', 4', 5', 6' having corresponding main radiation beams 7, 8, 9, 10; 7', 8', 9', 10' and respective antenna radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' spatially separated from the wireless communication node 1 , 1 ', each of the main radiation beams 7, 8, 9, 10, 7', 8', 9', 10' being directed towards its respective antenna radiation beam reflector 12, 13, 14, 15; 12', 13', 14', 15', wherein the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned to configure the wireless communication node 1 , 1 ' for multiple-input multiple- output (MIMO) communication at a centre frequency f _c with the second wireless communication node 1 1 , 1 1 ' via the antenna radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15'. According to an example, each antenna radiation beam reflector 12, 13, 14, 15 is positioned as function of effective node distances Li+I_i _r , L ₂ +L _2r , L ₃ +L _3r , L +L _r between effective antenna devices 3 _e , 4 _e , 5 _e , 6 _e of the first wireless communication node 1 , 1 ' and corresponding other antenna devices 29, 30, 31 , 32 of the second wireless communication node 1 1 via corresponding antenna radiation beam reflectors 12, 13, 14, 15, and of the carrier centre frequency f _c , where each effective antenna device 3 _e , 4 _e , 5 _e , 6 _e is formed by a corresponding antenna device 3, 4, 5, 6 together with its corresponding antenna radiation beam reflector 12, 13, 14, 15.

According to an example, the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned to satisfy system requirements on spectral efficiency in terms of bits/sec/Hz beyond that of a single-input single-output (SISO) system.

According to an example, a channel 28, 28' between the wireless communication node 1 , 1 ' and said other wireless communication node 1 1 , 1 1 ' is represented by a channel matrix H, where the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned such that a conditional number of the channel matrix H falls below a conditional number threshold.

According to an example, the conditional number threshold is 10.

According to an example, the radiation beam reflectors 12, 13, 14, 15; 12', 13', 14', 15' are positioned to increase a capacity in terms of bits/sec/Hz of said MIMO communication beyond that of a corresponding single-input multiple-output (SIMO) or a corresponding multiple-input single-output (MISO) or a single-input single-output (SISO) communication between the wireless communication node 1 , 1 ' and the at least one other wireless communication node 1 1 , 1 1 '. According to an example, the wireless communication node 1 " is configured for 2x2 MIMO, or 4x4 dual polarization MIMO, communication, where the radiation beam reflectors are positioned such that the condition

(L + L _r ) ^■ c

d ^{Ae - dB =} 2 - f _c is satisfied, where L+L _r is the shortest distance between each effective antenna device 23 _e , 24 _e and a corresponding opposing other antenna device 26, 27 of said other wireless communication node 1 1 ", 0B is the distance between adjacent other antenna devices 26, 27 of said other wireless communication node 1 1 ", c is the speed of light in air and dAe is the distance between adjacent effective antenna device 23 _e , 24 _e , where each effective antenna device 23 _e , 24 _e is formed by a corresponding antenna device 23, 24 together with its corresponding antenna radiation beam reflector 12", 13". According to an example, the wireless communication node 1 " comprises one antenna arrangement 22 which in turn comprises a first antenna device 23, having a first main radiation beam 7", and a second antenna device 24, having a second main radiation beam 8", the antenna devices 23, 24 being separated by an antenna device distance dA, where the first effective antenna device 23 _e is formed by the first antenna device 23 together with the first antenna radiation beam reflector 12" and the second effective antenna device 24 _e is formed by the second antenna device 24 together with the second antenna radiation beam reflector 13". According to an example, the antenna devices 3, 4, 5, 6; 3', 4', 5', 6' of each antenna arrangement 2, 2' are positioned along a corresponding horizontal extension Hi, H ₂ .

According to an example, the wireless communication node 1 comprises at least two antenna arrangements 2, 2', where the antenna arrangements 2, 2' are positioned along a vertical extension V, neighbouring antenna arrangements 2, 2' being separated by a corresponding antenna arrangement distance dAv- According to an example, the antenna devices 44, 45, 46, 47; 48, 49, 50, 51 of each antenna arrangement 42, 43' are positioned along a corresponding vertical extension Vi, V ₂ .

According to an example, the wireless communication node 1 "' comprises at least two antenna arrangements 42, 43, where the antenna arrangements 42, 43 are positioned along a horizontal extension H, neighbouring antenna arrangements 42, 43 being separated by a corresponding antenna arrangement distance dAH - According to an example, the wireless communication node 1 comprises at least one direct antenna arrangement 18, each direct antenna arrangement comprising at least one antenna device 19 with a corresponding direct main radiation beam 20, where each direct main radiation beam 20 is arranged to propagate directly towards said other wireless communication node 1 1 .

According to an example, at least two antenna radiation beam reflectors 12', 13', 14', 15' are positioned at two different relative heights hi, h ₂ , h ₃ , h .