Polarization handling of beam-formed signals

TECHNICAL FIELD

0001Embodiments presented herein relate to methods, radio transceiver devices, computer programs, and a computer program product for polarization handling of beam-formed signals.

BACKGROUND

0002In communications systems, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications system is deployed.

0003For example, for future generations of mobile communications systems frequency bands at many different carrier frequencies could be needed. For example, low such frequency bands could be needed to achieve sufficient network coverage for users (e.g. wireless devices) and higher frequency bands (e.g. at millimeter wavelengths (mmW), i.e. near and above 30 GHz) could be needed to reach required network capacity. In general terms, at high frequencies the propagation properties of the radio channel are more challenging and beamforming both at the network-side (e.g. at transmission points or access nodes) and at the user-side might be required to reach a sufficient link budget.

0004In mobile communications systems having a beam centric design, users may be operatively connected to the network by, and perform handover between, narrow beams instead of cells. At high frequencies, where high-gain beamforming will be needed due to more challenging radio channel propagation properties, each such narrow beam will only be optimal within a small area covered by the narrow area and the link budget for a user using the narrow beam but being located outside the small area will deteriorate quickly. Hence, a frequent and fast beam switching method is needed to maintain high performance, so called beam management.

0005The purpose of beam management is to keep track of users communicating with the network using narrow beams in order to increase the network coverage and throughput. Due to rotation, movement and blockage of the users, the beam (at the network-side and/or at the user-side) needs to be updated dynamically in order to maintain good channel quality between the network and the user. In case a user loses beam connection with the network, for example due to blockage, a beam recovery procedure can be initiated to re-establish the beam connection. Such beam recovery procedure can for example involve all beam combinations of the beams used at the user-side and the beams used at the network-side to be swept through in order for the best combination to be selected. When there are many candidate beams at both the network-side and the user-side, such a beam sweeping procedure (also referred to as beam training procedure) can be very costly in terms of time consumption and overhead signaling.

0006<patcit id="pcit0001" dnum="US9214981B1"><text>US 9 214 981 B1</text></patcit> discloses a switching device and a method and medium for using the switching device. The switching device is associated with a remote radio unit (RRU) and an antenna of a base station and comprises a plurality of switching cables arranged in predetermined configurations including a single-layer beam forming configuration, a dual-layer beam forming configuration, and a MIMO configuration. In response to inputs received from UEs served by the base station, the switching device can implement the configuration best-suited to target the UEs

0007<patcit id="pcit0002" dnum="US2012052828A1"><text>US 2012/052828 A1</text></patcit> discloses a method that includes scanning beams of a multiple beam antenna to collect metrics associated with the beams; selecting a best beam based on the collected metrics or based on a manual selection received from an operator; retrieving thresholds associated with the metrics; comparing the collected metrics, associated with the selected best beam, to the retrieved thresholds; and determining whether the antenna unit is in an acceptable location based on the comparison.

0008Hence, there is still a need for mechanisms enabling the beam sweeping procedure to be improved.

SUMMARY

0009An object of embodiments herein is to provide mechanisms that enable efficient beam sweeping handling in a beam sweeping procedure. The invention is defined by the independent claims. The following aspects present the invention in general terms. Detailed aspects of the invention are highlighted as such in the later parts of the description.

0010According to a first aspect there is presented a method for polarization handling of received beam-formed signals. The method is performed by a receiving radio transceiver device. The method comprises collecting statistics of received power of a beam-formed signal transmitted in two orthogonal polarizations from a transmitting radio transceiver device. The method comprises determining a similarity measure value of the beam-formed signal between the two orthogonal polarizations using the collected statistics. The method comprises signalling to the transmitting radio transceiver device, when the similarity measure value is equal to, or larger than, a similarity threshold value, to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0011According to a second aspect there is presented a radio transceiver device acting as a receiving radio transceiver device for polarization handling of received beam-formed signals. The radio transceiver device comprises processing circuitry. The processing circuitry is configured to cause the radio transceiver device to collect statistics of received power of a beam-formed signal transmitted in two orthogonal polarizations from a transmitting radio transceiver device. The processing circuitry is configured to cause the radio transceiver device to determine a similarity measure value of the beam-formed signal between the two orthogonal polarizations using the collected statistics. The processing circuitry is configured to cause the radio transceiver device to signal to the transmitting radio transceiver device, when the similarity measure value is equal to, or larger than, a similarity threshold value, to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0012According to a third aspect there is presented a radio transceiver device acting as a receiving radio transceiver device for polarization handling of received beam-formed signals. The radio transceiver device comprises processing circuitry and a storage medium. The storage medium stores instructions that, when executed by the processing circuitry, cause the radio transceiver device to perform operations, or steps. The operations, or steps, cause the radio transceiver device to collect statistics of received power of a beam-formed signal transmitted in two orthogonal polarizations from a transmitting radio transceiver device. The operations, or steps, cause the radio transceiver device to determine a similarity measure value of the beam-formed signal between the two orthogonal polarizations using the collected statistics. The operations, or steps, cause the radio transceiver device to signal to the transmitting radio transceiver device, when the similarity measure value is equal to, or larger than, a similarity threshold value, to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0013According to a fourth aspect there is presented a radio transceiver device acting as a receiving radio transceiver device for polarization handling of received beam-formed signals. The radio transceiver device comprises a collect module configured to collect statistics of received power of a beam-formed signal transmitted in two orthogonal polarizations from a transmitting radio transceiver device. The radio transceiver device comprises a determine module configured to determine a similarity measure value of the beam-formed signal between the two orthogonal polarizations using the collected statistics. The radio transceiver device comprises a signal module configured to signal to the transmitting radio transceiver device, when the similarity measure value is equal to, or larger than, a similarity threshold value, to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0014According to a fifth aspect there is presented a computer program for polarization handling of received beam-formed signals, the computer program comprises computer program code which, when run on processing circuitry of a radio transceiver device acting as a receiving radio transceiver device, causes the radio transceiver device to perform a method according to the first aspect.

0015According to a sixth aspect there is presented a method for polarization handling of transmitted beam-formed signals. The method is performed by a transmitting radio transceiver device. The method comprises transmitting a beam-formed signal in two orthogonal polarizations. The method comprises receiving signalling from a receiving radio transceiver device, the signalling indicating for the transmitting radio transceiver device to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0016According to a seventh aspect there is presented a radio transceiver device acting as a transmitting radio transceiver device for polarization handling of transmitted beam-formed signals. The radio transceiver device comprises processing circuitry. The processing circuitry is configured to cause the radio transceiver device to transmit a beam-formed signal in two orthogonal polarizations. The processing circuitry is configured to cause the radio transceiver device to receive signalling from a receiving radio transceiver device, the signalling indicating for the transmitting radio transceiver device to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0017According to an eighth aspect there is presented a radio transceiver device acting as a transmitting radio transceiver device for polarization handling of transmitted beam-formed signals. The radio transceiver device comprises processing circuitry and a storage medium. The storage medium stores instructions that, when executed by the processing circuitry, cause the radio transceiver device to perform operations, or steps. The operations, or steps, cause the radio transceiver device to transmit a beam-formed signal in two orthogonal polarizations. The operations, or steps, cause the radio transceiver device receive signalling from a receiving radio transceiver device, the signalling indicating for the transmitting radio transceiver device to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0018According to a ninth aspect there is presented a radio transceiver device acting as a transmitting radio transceiver device for polarization handling of transmitted beam-formed signals. The radio transceiver device comprises a transmit module configured to transmit a beam-formed signal in two orthogonal polarizations. The radio transceiver device comprises a receive module configured to receive signalling from a receiving radio transceiver device, the signalling indicating for the transmitting radio transceiver device to use rank one for subsequent transmission of the beam-formed signal to the receiving radio transceiver device.

0019According to a tenth aspect there is presented a computer program for polarization handling of transmitted beam-formed signals, the computer program comprising computer program code which, when run on processing circuitry of a radio transceiver device acting as a transmitting radio transceiver device, causes the radio transceiver device to perform a method according to the sixth aspect.

0020According to an eleventh aspect there is presented a computer program product comprising a computer program according to at least one of the fifth aspect and the tenth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

0021Advantageously these methods, these radio transceiver devices, and these computer programs can be used to streamline a beam sweeping procedure.

0022Advantageously these methods, these radio transceiver devices, and these computer programs allow the receiving radio transceiver device to quicker perform a beam training procedures in some scenario where rank one beam sweeping is sufficient.

0023It is to be noted that any feature of the first, second, third, fourth, fifth, sixth seventh, eighth, ninth, tenth and eleventh aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, and/or eleventh aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

0024Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

0025The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li><figref idref="f0001">Fig. 1</figref> is a schematic diagram illustrating a communications system according to embodiments;</li><li><figref idref="f0001">Fig. 2</figref> is a schematic illustration of part of the communications system in <figref idref="f0001">Fig. 1</figref> according to embodiments;</li><li><figref idref="f0002">Figs. 3, 4</figref>, <figref idref="f0003">5, 6</figref>, <figref idref="f0004">7</figref>, and <figref idref="f0005">8</figref> are flowcharts of methods according to embodiments;</li><li><figref idref="f0006">Fig. 9</figref> is a schematic diagram showing functional units of a radio transceiver device acting as a receiving radio transceiver device according to an embodiment;</li><li><figref idref="f0006">Fig. 10</figref> is a schematic diagram showing functional modules of a radio transceiver device acting as a receiving radio transceiver device according to an embodiment;</li><li><figref idref="f0006">Fig. 11</figref> is a schematic diagram showing functional units of a radio transceiver device acting as a transmitting radio transceiver device according to an embodiment;</li><li><figref idref="f0006">Fig. 12</figref> is a schematic diagram showing functional modules of a radio transceiver device acting as a transmitting radio transceiver device according to an embodiment; and</li><li><figref idref="f0003">Fig. 13</figref> shows one example of a computer program product comprising computer readable means according to an embodiment.</li></ul>

DETAILED DESCRIPTION

0026The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

0027<figref idref="f0001">Fig. 1</figref> is a schematic diagram illustrating a communications system 100 where embodiments presented herein can be applied. The communications system 100 comprises at least one radio transceiver device 300 acting as a transmitting radio transceiver device 300. The transmitting radio transceiver device 300 is operatively connected to a transmission and reception point (TRP) 305 for transmission and receptions of signals 140. Further functionality of the transmitting radio transceiver device 300 and how it interacts with other entities, nodes, and devices in the communications system 100 will be further disclosed below.

0028The transmitting radio transceiver device 300 could either be part of a radio access network 110 and be operatively connected to a core network 120 or be part of the core network 120. The core network 120 is in turn operatively connected to a service network 130. The transmitting radio transceiver device 300 provides network access in the radio access network 110 by transmitting and receiving signals 140. A radio transceiver device 200 acting as a receiving radio transceiver device served by the transmitting radio transceiver device 300 is thereby enabled to access services and exchange data with the core network 120 and the service network 130.

0029For ease of notation, the radio transceiver device 200 will hereinafter be referred to as a receiving radio transceiver device 200 and the radio transceiver device 300 will hereinafter be referred to as a transmitting radio transceiver device 300. However, as the skilled person understands, the radio transceiver device 200 may selectively act as either a receiving radio transceiver device or a transmitting radio transceiver device, and the radio transceiver device 300 may selectively act as either a transmitting radio transceiver device or a receiving radio transceiver device.

0030<figref idref="f0001">Fig. 2(a)</figref> schematically illustrates part of the communications system 100 of <figref idref="f0001">Fig. 1</figref>. In more detail, <figref idref="f0001">Fig. 2(a)</figref> schematically illustrates a transmitting radio transceiver device 300 that, via the TRP 305, transmits a beam-formed signal 140 to a receiving radio transceiver device 200. The beam-formed signal 140 is transmitted in beams B1, B2, B3. As the skilled person understands, although only three beams B1, B2, B3 are illustrated, the beam-formed signal 140 could be transmitted in a plurality of beams. The beam-formed signal 140 is in each beam Bi, B2, B3 transmitted using two orthogonal polarizations P1, P2.

0031As illustrated in <figref idref="f0001">Figs. 2(b) and 2(c)</figref> the received power at the receiving radio transceiver device 200 of beam Bx, where x=1, 2, 3, using polarization Py, where y=1, 2, is denoted P_Bx,Py. The transmitting radio transceiver device 300 and/or the receiving radio transceiver device 200, for example during a beam training procedure, sweeps through each beam B1, B2, B3 for each polarization P1, P2.

0032The transmitting radio transceiver device 300 and/or the receiving radio transceiver device 200 could implement beamforming by means of analog beamforming, digital beamforming, or hybrid beamforming. Each implementation has its advantages and disadvantages. A digital beamforming implementation is the most flexible implementation of the three but also the costliest due to the large number of required radio chains and baseband chains. An analog beamforming implementation is the least flexible but cheaper to manufacture due to a reduced number of radio chains and baseband chains compared to the digital beamforming implementation. A hybrid beamforming implementation is a compromise between the analog and the digital beamforming implementations. As the skilled person understands, depending on cost and performance requirements of different wireless devices, different implementations will be needed.

0033Different antenna architectures for different frequency bands are being discussed for wireless devices. At high frequency bands (e.g. above 15 GHz) something called "panels" of antenna arrays are being discussed. These panels of antenna array may be uniform linear/rectangular arrays (ULAs/URAs), for example steered by using analog phase shifters. A panel is an antenna array with (typically) one transmit/receive radio chain per polarization and where an analog distribution network with phase shifters is used to steer the beam of each panel. Multiple panels can be stacked next to each other and digital beamforming can be used to generate beams also between the panels. At high frequencies panels are expected to be used both at the network-side and at the user-side.

0034Panels typically have two polarizations with one radio per polarization per panel. Hence, when performing beam sweeping procedures, either each beam is transmitted (and received) in one polarization (so-called rank one beam sweeping) or each beam is transmitted (and received) in two orthogonal polarizations (so-called rank two beam sweeping). One potential drawback with rank one beam sweeping is that it is less reliable due to that different polarizations experience different channels, so the best beam for one polarization might not be the best beam for the other polarization. One benefit with rank one beam sweeping is that it only requires half the overhead compared to rank two beam sweeping, and hence can be performed twice as quick. Thus, for some scenarios it could be unnecessary for the receiving radio transceiver device 200 to sweep through all beams B1, B2, B3 using both polarizations P1, P2.

0035The embodiments disclosed herein thus relate to mechanisms for polarization handling of received beam-formed signals 140 and polarization handling of transmitted beam-formed signals 140. In order to obtain such mechanisms there is provided a receiving radio transceiver device 200, a method performed by the receiving radio transceiver device 200, a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the receiving radio transceiver device 200, causes the receiving radio transceiver device 200 to perform the method. In order to obtain such mechanisms there is further provided a transmitting radio transceiver device 300, a method performed by the transmitting radio transceiver device 300, and a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the transmitting radio transceiver device 300, causes the transmitting radio transceiver device 300 to perform the method.

0036<figref idref="f0002">Figs. 3 and 4</figref> are flow charts illustrating embodiments of methods for polarization handling of received beam-formed signals 140 as performed by the receiving radio transceiver device 200. <figref idref="f0003">Figs. 5 and 6</figref> are flow charts illustrating embodiments of methods for polarization handling of transmitted beam-formed signals 140 as performed by the transmitting radio transceiver device 300. The methods are advantageously provided as computer programs 1320a, 1320b.

0037Reference is now made to <figref idref="f0002">Fig. 3</figref> illustrating a method for polarization handling of received beam-formed signals 140 as performed by the receiving radio transceiver device 200 according to an embodiment.

0038As will be further disclosed below, the transmitting radio transceiver device 300 transmits a beam-formed signal 140. It is assumed that the beam-formed signal 140 is received by the receiving radio transceiver device 200. Thus, the receiving radio transceiver device 200 is configured to perform step S102: S102: The receiving radio transceiver device 200 collects statistics of received power of a beam-formed signal 140. The beam-formed signal 140 is transmitted in two orthogonal polarizations P1, P2 from the transmitting radio transceiver device 300. Examples of the beam-formed signal 140 will be disclosed below.

0039In this respect, the receiving radio transceiver device 200 measures received power of the beam-formed signal 140 as transmitted using rank two (i.e. where the beam-formed signal 140 is transmitted from two orthogonal polarizations P1, P2). It might be so that the receiving radio transceiver device 200 only requires reception of the beam-formed signal 140 in one of the polarizations P1, P2 in order to adequately process the beam-formed signal 140. Hence, the receiving radio transceiver device 200 compares the beam-formed signal 140 received in one of the two orthogonal polarizations P1, P2 to the beam-formed signal 140 received in the other one of the two orthogonal polarizations P1, P2. Particularly, the receiving radio transceiver device 200 is configured to perform step S104: S104: The receiving radio transceiver device 200 determines a similarity measure value of the beam-formed signal 140 between the two orthogonal polarizations P1, P2 using the collected statistics. Examples of how the similarity measure value can be determined will be disclosed below.

0040If the similarity measure value is equal to, or larger than, a similarity threshold value then the receiving radio transceiver device 200 need only receive the beam-formed signal in one of the polarizations P1, P2. Hence, the receiving radio transceiver device 200 is configured to perform step S106: S106: The receiving radio transceiver device 200 signals to the transmitting radio transceiver device 300, when the similarity measure value is equal to, or larger than, a similarity threshold value, to use rank one for subsequent transmission of the beam-formed signal 140 to the receiving radio transceiver device 200.

0041It will below be disclosed how the receiving radio transceiver device 200 could be configured to act when the similarity measure value is smaller than the similarity threshold value.

0042Embodiments relating to further details of polarization handling of received beam-formed signals 140 as performed by the receiving radio transceiver device 200 will now be disclosed.

0043As mentioned above, the similarity measure value is equal to, or larger than, a similarity threshold value then the receiving radio transceiver device 200 needs only to receive the beam-formed signal in one of the polarizations P1, P2. Therefore, according to an embodiment, when signalled to use rank one, the transmitting radio transceiver device 300 is in step S106 signalled to only use one of the two orthogonal polarizations P1, P2 for the subsequent transmission of the beam-formed signal 140 to the receiving radio transceiver device 200.

0044In general terms, if rank one or rank two should be used for the beam-formed signal 140 depends largely on the antenna implementation at the receiving radio transceiver device 200. For example, if the receiving radio transceiver device 200 has dual-polarized receive antennas, it could be that only rank one is needed. Further, in scenarios where there is a line of sight radio propagation channel between the TRP 305 of the transmitting radio transceiver device 300 and the receiving radio transceiver device 200, rank one could be sufficient, as long as the receiving radio transceiver device 200 has dual-polarized antennas.

0045There could be different ways to set the similarity threshold value. The similarity threshold value could be a pre-configured, or pre-set, value implemented in the receiving radio transceiver device 200. Further, the similarity threshold value could be based on a previous beam training procedure as performed by the receiving radio transceiver device 200. The similarity threshold value could then be set such that the receiving radio transceiver device 200 has a high probability (such that a probability over 0.50, preferably over 0.75, and most preferably over 0.90) of successfully receiving and decoding the beam-formed signal 140 when being transmitted using only rank one. Further, the similarity threshold value could be based on a pre-configured, or pre-set, value that is updated during a beam training procedure.

0046There could be different ways for the receiving radio transceiver device 200 to determine the similarity measure value in step S104. According to an embodiment the similarity measure value is determined to indicate a correlation between the beam-formed signal 140 in a first (say, P1) of the two orthogonal polarizations P1, P2 and the beam-formed signal 140 in a second (say, P2) of the two orthogonal polarizations P1, P2.

0047As in <figref idref="f0001">Fig. 2(a)</figref>, the beam-formed signal 140 could by the transmitting radio transceiver device 300 be transmitted in at least two beams B1, B2, B3. Hence, according to an embodiment the beam-formed signal 140 for each of the two orthogonal polarizations P1, P2 is in step S102 received in at least two beams B1, B2, B3.

0048According to one embodiment of the present invention, the similarity measure is based on a comparison between the polarizations P1, P2 according to the order in which the strongest received power is received for the different beams B1, B2, B3. Hence, according to an embodiment the similarity measure value is determined based on an ordering of the at least two beams B1, B2, B3 according to received power P_B1,P1, P_B2,P1, P_B3,P1, P_B1,P2, P_B2,P2, P_B3,P2 in each of the at least two beams B1, B2, B3 for each of the two orthogonal polarizations P1, P2. As an example the combination P_B1,P1 > P_B3,P1 > P_B2,P1, and P_B1,P2 > P_B3,P2 > P_B2,P2 would indicate a high similarity measure value, whereas the combination P_B1,P1 > P_B2,P1 > P_B3,P1, and P_B3,P2 > P_B2,P2 > P_B1,P2 would indicate a low similarity measure value.

0049According to one embodiment of the present invention, the similarity measure is based on a comparison between the polarizations P1, P2 of the beams B1, B2, B3 in which the strongest power is received. Hence, according to an embodiment the similarity measure value is determined based on in which of the at least two beams B1, B2, B3 the received power P_B1,P1, P_B2,P1, P_B3,P1, P_B1,P2, P_B2,P2, P_B3,P2 is strongest for the two orthogonal polarizations P1, P2. As an example the combination P_B1,P1 > P_B3,P1 > P_B2,P1, and P_B1,P2 > P_B2,P2 > P_B3,P2 would indicate a high similarity measure value, whereas the combination P_B1,P1 > P_B2,P1 > P_B3,P1, and P_B3,P2 > P_B1,P2 > P_B2,P2 would indicate a low similarity measure value.

0050As disclosed above, the receiving radio transceiver device 200 could, for example during a beam training procedure, sweep through each beam B1, B2, B3 for each polarization P1, P2. Hence, according to an embodiment the statistics of the received power P_B1,P1, P_B2,P1, P_B3,P1, P_B1,P2, P_B2,P2, P_B3,P2 is collected during at least one beam training procedure. In some scenarios, multiple beam training procedures may be needed in order for the receiving radio transceiver device 200 to collect enough statistics (such that the statistics have a variation (variance, or standard deviation) being smaller than a threshold variation value).

0051Reference is now made to <figref idref="f0002">Fig. 4</figref> illustrating methods for polarization handling of received beam-formed signals 140 as performed by the receiving radio transceiver device 200 according to further embodiments. It is assumed that steps S102, S104, S106 are performed as described above with reference to <figref idref="f0002">Fig. 3</figref> and a thus repeated description thereof is therefore omitted.

0052There may be different ways for the receiving radio transceiver device 200 to act if the similarity measure value is smaller than the similarity threshold value. According to some aspects the receiving radio transceiver device 200 keeps using rank two. Particularly, according to an embodiment the receiving radio transceiver device 200 is configured to perform step S108 when the similarity measure value is smaller than the similarity threshold value: S108: The receiving radio transceiver device 200 continues to collect statistics of received power P_B1,P1, P_B2,P1, P_B3,P1, P_B1,P2, P_B2,P2, P_B3,P2 of the beam-formed signal 140 in the two orthogonal polarizations Pi, P2.

0053Reference is now made to <figref idref="f0003">Fig. 5</figref> illustrating a method for polarization handling of transmitted beam-formed signals 140 as performed by the transmitting radio transceiver device 300 according to an embodiment.

0054S202: The transmitting radio transceiver device 300 transmits a beam-formed signal 140 in two orthogonal polarizations P1, P2.

0055As disclosed above, the beam-formed signal 140 is received by the receiving radio transceiver device 200 that collects statistics of received power of the beam-formed signal 140 in the polarizations P1, P2. The receiving radio transceiver device 200 the signals to the transmitting radio transceiver device 300 as in step S106, when the similarity measure value is equal to, or larger than, the similarity threshold value, to use rank one for subsequent transmission of the beam-formed signal 140 to the receiving radio transceiver device 200. It is assumed that this signalling is received by the transmitting radio transceiver device 300. Hence, the transmitting radio transceiver device 300 is configured to perform step S204: S204: The transmitting radio transceiver device 300 receives signalling from the receiving radio transceiver device 200. The signalling indicates for the transmitting radio transceiver device to use rank one for subsequent transmission of the beam-formed signal 140 to the receiving radio transceiver device 200.

0056Embodiments relating to further details of polarization handling of transmitted beam-formed signals 140 as performed by the transmitting radio transceiver device 300 will now be disclosed.

0057As disclosed above, according to an embodiment, when the signalling indicates for the transmitting radio transceiver device 300 to use rank one, the transmitting radio transceiver device 300 is indicated to only use one of the two orthogonal polarizations P1, P2 for the subsequent transmission of the beam-formed signal 140 to the receiving radio transceiver device 200.

0058As disclosed above, in some embodiments the beam-formed signal 140 is for each of the two orthogonal polarizations P1, P2 transmitted in at least two beams B1, B2, B3.

0059As disclosed above, in some embodiments the beam-formed signal 140 is transmitted during a beam training procedure.

0060Reference is now made to <figref idref="f0003">Fig. 6</figref> illustrating methods for polarization handling of transmitted beam-formed signals 140 as performed by the transmitting radio transceiver device 300 according to further embodiments. It is assumed that steps S202, S204 are performed as described above with reference to <figref idref="f0003">Fig. 5</figref> and a thus repeated description thereof is therefore omitted.

0061There may be different ways for the transmitting radio transceiver device 300 to act once having been signalled to use rank one for subsequent transmission of the beam-formed signal 140 to the receiving radio transceiver device 200. In some aspects the transmitting radio transceiver device 300 uses rank one at least temporarily before going back to using rank two. Particularly, according to an embodiment the transmitting radio transceiver device 300 is configured to perform step S206: S206: The transmitting radio transceiver device 300 transmits the beam-formed signal 140 in only one of the two orthogonal polarizations P1, P2 during a time period before returning to transmitting the beam-formed signal 140 in both the two orthogonal polarizations P1, P2.

0062That is, according to this embodiment the transmitting radio transceiver device 300 changes from rank two beam sweeping to rank one beam sweeping for a predefined period of time, and then goes automatically back to rank-two again.

0063Embodiments applicable to both the methods performed by the receiving radio transceiver device 200 and the transmitting radio transceiver device 300 will now be disclosed.

0064There could be different examples of beam-formed signals 140. In some aspects the beam-formed signal 140 is a reference signal. Particularly, according to an embodiment the beam-formed signal 140 is a downlink reference signal and according to another embodiment the beam-formed signal 140 is an uplink reference signal. In general terms, the particular type of reference signal would depend on the type of transmitting radio transceiver device 300 and receiving radio transceiver device 200. For example, where the transmitting radio transceiver device 300 acts as, is implemented in, or is implemented to perform the functionality of, an access node and the receiving radio transceiver device 200 acts as, is implemented in, or is implemented to perform the functionality of, a wireless device the beam-formed signal 140 is a downlink reference signal. The downlink reference signal could be a beam reference signal for rank two beam sweeping, or channel state information reference signals used for closed loop polarization precoding. For example, where the transmitting radio transceiver device 300 acts as, is implemented in, or is implemented to perform the functionality of, a wireless device and the receiving radio transceiver device 200 acts as, is implemented in, or is implemented to perform the functionality of, an access node the beam-formed signal 140 is an uplink reference signal. The uplink reference signal could be a sounding reference signal.

0065A first particular embodiment for polarization handling of received beam-formed signals 140 as performed by the receiving radio transceiver device 200 based on at least some of the above disclosed embodiments will now be disclosed in detail.

0066This is a typical scenario where the receiving radio transceiver device 200 is implemented in a user device, such as in a wireless device.

0067S301: The receiving radio transceiver device 200 collects statistics of received power of a beam-formed signal 140 for both transmitted polarizations P1, P2 for different beams B1, B2, B3. One way to implement step S301 is to perform step S102.

0068S302: The receiving radio transceiver device 200 evaluates the correlation between the two polarizations P1, P2 of the beam-formed signal 140 based on the statistics. When enough statistics has been collected, the receiving radio transceiver device 200 evaluates, based on the statistics, if the correlation of the received signal power between the two transmit polarizations P1, P2 are stronger than a given threshold. One way to implement step S302 is to perform step S104.

0069S303: The receiving radio transceiver device 200 checks if the correlation is stronger than a predefined threshold value. If yes, step S304 is entered, and if no, step S305 is entered. One way to implement step S303 is to perform step S104.

0070S304: The receiving radio transceiver device 200 signals to the transmitting radio transceiver device 300 to switch to rank one beam sweeping (i.e., to transmit the beam-formed signal 140 in only one of the polarizations P1, P2). One way to implement step S304 is to perform step S106.

0071S305: The receiving radio transceiver device 200 signals to the transmitting radio transceiver device 300 to keep rank two beam sweeping (i.e., to transmit the beam-formed signal 140 in both the polarizations Pi, P2).

0072A second particular embodiment for polarization handling of received beam-formed signals 140 as performed by the receiving radio transceiver device 200 based on at least some of the above disclosed embodiments will now be disclosed in detail. This is a typical scenario where the receiving radio transceiver device 200 is implanted in an access node.

0073S401: The receiving radio transceiver device 200 collects statistics of received power of a beam-formed signal 140 for both transmitted polarizations P1, P2 for different beams B1, B2, B3. One way to implement step S401 is to perform step S102.

0074S402: The receiving radio transceiver device 200 evaluates the correlation between the two polarizations P1, P2 of the beam-formed signal 140 based on the statistics. One way to implement step S402 is to perform step S104.

0075S403: The receiving radio transceiver device 200 checks if the correlation is stronger than a predefined threshold value. If yes, step S404 is entered, and if no, step S405 is entered. One way to implement step S403 is to perform step S104.

0076S404: The receiving radio transceiver device 200 causes the transmitting radio transceiver device 300 to switch to rank one beam sweeping (i.e., to transmit the beam-formed signal 140 in only one of the polarizations P1, P2). One way to implement step S404 is to perform step S106

0077S405: The receiving radio transceiver device 200 keeps using rank two beam sweeping (receiving the beam-formed signal 140 in both the polarizations P1, P2). One way to implement step S405 is to perform step S108.

0078<figref idref="f0006">Fig. 9</figref> schematically illustrates, in terms of a number of functional units, the components of a radio transceiver device acting as a receiving radio transceiver device 200 according to an embodiment. Processing circuitry 210 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1310a (as in <figref idref="f0003">Fig. 13</figref>), e.g. in the form of a storage medium 230. The processing circuitry 210 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

0079Particularly, the processing circuitry 210 is configured to cause the receiving radio transceiver device 200 to perform a set of operations, or steps, S102-S108, S301-S305, S401-S405, as disclosed above. For example, the storage medium 230 may store the set of operations, and the processing circuitry 210 may be configured to retrieve the set of operations from the storage medium 230 to cause the receiving radio transceiver device 200 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 210 is thereby arranged to execute methods as herein disclosed.

0080The storage medium 230 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

0081The receiving radio transceiver device 200 may further comprise a communications interface 220 for communications with other entities, devices, and nodes of the communications system 100. As such the communications interface 220 may comprise one or more transmitters and receivers, comprising analogue and digital components.

0082The processing circuitry 210 controls the general operation of the receiving radio transceiver device 200 e.g. by sending data and control signals to the communications interface 220 and the storage medium 230, by receiving data and reports from the communications interface 220, and by retrieving data and instructions from the storage medium 230. Other components, as well as the related functionality, of the receiving radio transceiver device 200 are omitted in order not to obscure the concepts presented herein.

0083<figref idref="f0006">Fig. 10</figref> schematically illustrates, in terms of a number of functional modules, the components of a radio transceiver device acting as a receiving radio transceiver device 200 according to an embodiment. The receiving radio transceiver device 200 of <figref idref="f0006">Fig. 10</figref> comprises a number of functional modules; a collect module 210a configured to perform step S102, a determine module 210b configured to perform step S104, and a signal module 210c configured to perform step S106. The receiving radio transceiver device 200 of <figref idref="f0006">Fig. 10</figref> may further comprise a number of optional functional modules, such as a collect module 210d configured to perform step S108. In general terms, each functional module 210a-210d may be implemented in hardware or in software. Preferably, one or more or all functional modules 210a-210d may be implemented by the processing circuitry 210, possibly in cooperation with the communications interface 220 and/or the storage medium 230. The processing circuitry 210 may thus be arranged to from the storage medium 230 fetch instructions as provided by a functional module 210a-210d and to execute these instructions, thereby performing any steps of the receiving radio transceiver device 200 as disclosed herein.

0084<figref idref="f0006">Fig. 11</figref> schematically illustrates, in terms of a number of functional units, the components of a radio transceiver device acting as a transmitting radio transceiver device 300 according to an embodiment. Processing circuitry 310 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1310b (as in <figref idref="f0003">Fig. 13</figref>), e.g. in the form of a storage medium 330. The processing circuitry 310 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

0085Particularly, the processing circuitry 310 is configured to cause the transmitting radio transceiver device 300 to perform a set of operations, or steps, S202-S206, as disclosed above. For example, the storage medium 330 may store the set of operations, and the processing circuitry 310 may be configured to retrieve the set of operations from the storage medium 330 to cause the transmitting radio transceiver device 300 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 310 is thereby arranged to execute methods as herein disclosed.

0086The storage medium 330 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

0087The transmitting radio transceiver device 300 may further comprise a communications interface 320 for communications with other entities, devices, and nodes of the communications system 100. As such the communications interface 320 may comprise one or more transmitters and receivers, comprising analogue and digital components. For example, the communications interface 320 may comprise, or be operatively connected to, at least one TRP 305.

0088The processing circuitry 310 controls the general operation of the transmitting radio transceiver device 300 e.g. by sending data and control signals to the communications interface 320 and the storage medium 330, by receiving data and reports from the communications interface 320, and by retrieving data and instructions from the storage medium 330. Other components, as well as the related functionality, of the transmitting radio transceiver device 300 are omitted in order not to obscure the concepts presented herein.

0089<figref idref="f0006">Fig. 12</figref> schematically illustrates, in terms of a number of functional modules, the components of a radio transceiver device acting as a transmitting radio transceiver device 300 according to an embodiment. The transmitting radio transceiver device 300 of <figref idref="f0006">Fig. 12</figref> comprises a number of functional modules; a transmit module 310a configured to perform step S202 and a receive module 310b configured to perform step S204. The transmitting radio transceiver device 300 of <figref idref="f0006">Fig. 12</figref> may further comprise a number of optional functional modules, such as a transmit module 310c configured to perform step S206. In general terms, each functional module 310a-310d may be implemented in hardware or in software. Preferably, one or more or all functional modules 310a-310d may be implemented by the processing circuitry 310, possibly in cooperation with the communications interface 320 and/or the storage medium 330. The processing circuitry 310 may thus be arranged to from the storage medium 330 fetch instructions as provided by a functional module 310a-310d and to execute these instructions, thereby performing any steps of the transmitting radio transceiver device 300 as disclosed herein.

0090The receiving radio transceiver device 200 and/or the transmitting radio transceiver device 300 may be provided as a standalone device or as a part of at least one further device. For example, the receiving radio transceiver device 200 or the transmitting radio transceiver device 300 may be provided in a node of the radio access network or in a node of the core network whereas the other of the receiving radio transceiver device 200 or the transmitting radio transceiver device 300 may be provided in a wireless device. Alternatively, functionality of the receiving radio transceiver device 200 and/or the transmitting radio transceiver device 300 may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part or may be spread between at least two such network parts.

0091Thus, a first portion of the instructions performed by the receiving radio transceiver device 200 and/or transmitting radio transceiver device 300 may be executed in respective first devices, and a second portion of the of the instructions performed by the receiving radio transceiver device 200 and/or transmitting radio transceiver device 300 may be executed in respective second devices; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the receiving radio transceiver device 200 / transmitting radio transceiver device 300 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a receiving radio transceiver device 200 / transmitting radio transceiver device 300 residing in a cloud computational environment. Therefore, although a single processing circuitry 210, 310 is illustrated in <figref idref="f0006">Figs. 9 and 11</figref> the processing circuitry 210, 310 may be distributed among a plurality of devices, or nodes. The same applies to the functional modules 210a-210d, 310a-310d of <figref idref="f0006">Figs. 10 and 12</figref> and the computer programs 1320a, 1320b of <figref idref="f0003">Fig. 13</figref> (see below).

0092<figref idref="f0003">Fig. 13</figref> shows one example of a computer program product 1310a, 1310b comprising computer readable means 1330. On this computer readable means 1330, a computer program 1320a can be stored, which computer program 1320a can cause the processing circuitry 210 and thereto operatively coupled entities and devices, such as the communications interface 220 and the storage medium 230, to execute methods according to embodiments described herein. The computer program 1320a and/or computer program product 1310a may thus provide means for performing any steps of the receiving radio transceiver device 200 as herein disclosed. On this computer readable means 1330, a computer program 1320b can be stored, which computer program 1320b can cause the processing circuitry 310 and thereto operatively coupled entities and devices, such as the communications interface 320 and the storage medium 330, to execute methods according to embodiments described herein. The computer program 1320b and/or computer program product 1310b may thus provide means for performing any steps of the transmitting radio transceiver device 300 as herein disclosed.

0093In the example of <figref idref="f0003">Fig. 13</figref>, the computer program product 1310a, 1310b is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 1310a, 1310b could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 1320a, 1320b is here schematically shown as a track on the depicted optical disk, the computer program 1320a, 1320b can be stored in any way which is suitable for the computer program product 1310a, 1310b.

0094The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.