TECHNICAL FIELD

Embodiments of the invention relate to a client device and a network access node for determining a transmit beam of the network access node for the client device during beam sweeping. Furthermore, embodiments of the invention also relate to corresponding methods and a computer program.

BACKGROUND

In the initial beam sweeping phase in 3GPP 5G new radio (NR), which is also referred to as the P-1 phase, the next generation eNode B (gNB) periodically sends a synchronization signal (SS) burst to the idle user equipments (UEs) in the cell. The SS burst consists of different beam transmissions from the gNB chosen from a predefined beam codebook at the gNB. Each UE receives the SS burst with beams from its own beam codebook. In this way, the UE is able to find a best pair of transmit and receive beam for its own radio link. During the beam reporting phase, the UE feeds back the index of the best transmit beam to the gNB, which the gNB can later use when transmitting to the UE.

After the P-1 phase, the gNB and the UE enter a connected mode by using the best beam pair found during the P-1 phase. In the connected mode, the gNB and UE perform a P-2 phase for further refinement of the best beam pair from the P-1 phase to increase signal-to-noise-ratio (SNR) of the radio link. Typically, this refinement is made around the best beam pair (in angular domain) from the P-1 phase, which means that a good initial beam pair is important.

SUMMARY

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

Another objective of embodiments of the invention is to provide a solution to determine an optimal transmit beam during beam sweeping in an efficient way.

The above and further objectives are solved by the subject matter of the independent claims.

Further embodiments of the invention can be found in the dependent claims. According to a first aspect of the invention, the above mentioned and other objectives are achieved with a client device for a communication system, the client device being configured to: receive a SS burst set in a radio channel from a network access node, the SS burst set being associated with a set of transmit beams of the network access node; estimate the radio channel based on the received SS burst set and beam information associated with the set of transmit beams of the network access node; determine a transmit beam of the network access node based on the estimated radio channel; and transmit a control signal to the network access node, the control signal indicating the determined transmit beam.

An advantage of the client device according to the first aspect is that the beam information enables the client device to determine a very good estimate of an optimal transmit beam of the network access node during an initial beam sweeping phase. The client device can then feedback the determined transmit beam to the network access node, enabling the network access node to improve a data transmission to the client device using the determined transmit beam.

In an implementation form of a client device according to the first aspect, the beam information comprises angular information about the set of transmit beams of the network access node and/or an antenna array configuration of the network access node.

An advantage with this implementation form is that the angular information and the antenna array configuration enables the client device to improve the estimation of the optimal transmit beam and can further be signaled with low overhead.

In an implementation form of a client device according to the first aspect, the client device is configured to: receive the SS burst set during a first time period, the first time period being a P-1 phase; and transmit the control signal during a second time period following the first time period.

An advantage with this implementation form is that the solution is compatible with and can easily be implemented as part of the initial beam sweeping phase according to the 3GPP standard. In an implementation form of a client device according to the first aspect, the second time period is a P-2 phase.

An advantage with this implementation form is that the optimal transmit beam determined by the client device can be indicated to the network access node as part of reporting in the P-2 phase according to the 3GPP standard.

In an implementation form of a client device according to the first aspect, the client device is configured to: receive the beam information in a synchronization signal block, SSB, of the received SS burst set.

An advantage with this implementation form is that it enables the client device to obtain the beam information during the initial beam sweeping phase in an efficient way.

In an implementation form of a client device according to the first aspect, estimating the radio channel comprises: determine measurements for the set of transmit beams of the network access node based on the SS burst set; and estimate the radio channel based on the measurements.

An advantage with this implementation form is that it enables the client device to estimate the radio channel based on measurements already performed by the client device according to the 3GPP standard. Thereby, simplifying the implementation of the invention and improving the estimation of the optimal transmit beam.

In an implementation form of a client device according to the first aspect, the measurements comprise amplitude and phase information.

An advantage with this implementation form is that the amplitude and phase information allow the client device to improve the estimation of the optimal transmit beam.

In an implementation form of a client device according to the first aspect, determining the transmit beam of the network access node comprises: determine a transmit beam of the network access node providing the highest received power in dependency on the estimated radio channel. An advantage with this implementation form is that the optimal transmit beam is strongly dependent on the received power.

In an implementation form of a client device according to the first aspect, the control signal is a channel state information, CSI, report.

An advantage with this implementation form is that the control signal can be implemented in an existing reporting procedure according to the 3GPP standard.

In an implementation form of a client device according to the first aspect, the client device is configured to: receive a data transmission in the determined transmit beam from the network access node.

An advantage with this implementation form is that the data transmission can be received in a transmit beam that has been determined by the client device to be optimal. Thereby, increasing the quality of the data transmission.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a network access node for a communication system, the network access node being configured to: transmit a SS burst set in a radio channel to a client device, the SS burst set being associated with a set of transmit beams of the network access node; transmit beam information associated with the set of transmit beams of the network access node to the client device; receive a control signal from the client device, the control signal indicating a transmit beam of the network access node; and perform a data transmission in the indicated transmit beam to the client device.

An advantage of the network access node according to the second aspect is that the beam information enables the client device to determine a very good estimate of an optimal transmit beam of the network access node during an initial beam sweeping phase. The client device can then feedback the determined transmit beam to the network access node, enabling the network access node to improve a data transmission to the client device using the determined transmit beam. In an implementation form of a network access node according to the second aspect, the beam information comprises angular information about the set of transmit beams of the network access node and/or an antenna array configuration of the network access node.

An advantage with this implementation form is that the angular information and the antenna array configuration enables the client device to improve the estimation of the optimal transmit beam and can further be signaled with low overhead.

In an implementation form of a network access node according to the second aspect, the network access node is configured to: transmit the SS burst set during a first time period, the first time period being a P-1 phase; and receive the control signal during a second time period following the first time period.

An advantage with this implementation form is that the solution is compatible with and can easily be implemented as part of the initial beam sweeping phase according to the 3GPP standard.

In an implementation form of a network access node according to the second aspect, the second time period is a P-2 phase.

An advantage with this implementation form is that the optimal transmit beam determined by the client device can be indicated to the network access node as part of reporting in the P-2 phase according to the 3GPP standard.

In an implementation form of a network access node according to the second aspect, the network access node is configured to: transmit the beam information in a SSB of the SS burst set.

An advantage with this implementation form is that it enables the client device to obtain the beam information during the initial beam sweeping phase in an efficient way.

In an implementation form of a network access node according to the second aspect, the control signal is a CSI report.

An advantage with this implementation form is that the control signal can be implemented in an existing reporting procedure according to the 3GPP standard. According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method for a client device, the method comprises receiving a SS burst set in a radio channel from a network access node, the SS burst set being associated with a set of transmit beams of the network access node; estimating the radio channel based on the received SS burst set and beam information associated with the set of transmit beams of the network access node; determining a transmit beam of the network access node based on the estimated radio channel; and transmitting a control signal to the network access node, the control signal indicating the determined transmit beam.

The method according to the third aspect can be extended into implementation forms corresponding to the implementation forms of the client device according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the client device.

The advantages of the methods according to the third aspect are the same as those for the corresponding implementation forms of the client device according to the first aspect.

According to a fourth aspect of the invention, the above mentioned and other objectives are achieved with a method for a network access node, the method comprises transmitting a SS burst set in a radio channel to a client device, the SS burst set being associated with a set of transmit beams of the network access node; transmitting beam information associated with the set of transmit beams of the network access node to the client device; receiving a control signal from the client device, the control signal indicating a transmit beam of the network access node; and performing a data transmission in the indicated transmit beam to the client device.

The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the network access node according to the second aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network access node. The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the network access node according to the second aspect.

Embodiments of the invention also relate to a computer program, characterized in program code, which when run by at least one processor causes the at least one processor to execute any method according to embodiments of the invention. Further, embodiments of the invention also relate to a computer program product comprising a computer readable medium and the mentioned computer program, wherein the computer program is included in the computer readable medium, and may comprises one or more from the group of: read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), flash memory, electrically erasable PROM (EEPROM), hard disk drive, etc.

Further applications and advantages of embodiments of the invention will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are intended to clarify and explain different embodiments of the invention, in which:

- Fig. 1 shows a client device according to an embodiment of the invention;

- Fig. 2 shows a flow chart of a method for a client device according to an embodiment of the invention;

- Fig. 3 shows a network access node according to an embodiment of the invention;

- Fig. 4 shows a flow chart of a method for a network access node according to an embodiment of the invention;

- Fig. 5 shows a communication system according to an embodiment of the invention;

- Fig. 6 shows signaling for determining a transmit beam according to an embodiment of the invention; and

- Fig. 7 shows estimation of a radio channel according to an embodiment of the invention.

DETAILED DESCRIPTION

In the current P-1 phase in 5G NR, the gNB will only know which one of its transmit beams used in the P-1 phase were best towards a specific UE. It will then search around this beam during the P-2 phase to further refine it for improving the signal-to-noise ratio (SNR) of the radio link toward the UE. However, it could very well happen that the optimal beam toward the UE is far away from all the beams transmitted during the P-1 phase. Due to this, the P-2 phase may result in a highly suboptimal radio link with the current way of reporting the best transmit beam in 5G NR.

Essentially, a good beam pair means that the beams are well “aligned” with the underlying multiple input multiple output (MIMO) channel between the gNB and UE antenna arrays. The P-1 phase is searching for this optimal alignment, but due to the finite number of transmitted beams, the true optimum could be far away from any of the beams transmitted. An obvious remedy to this is to increase the number of transmitted beams, but this leads to a waste of resources. Consequently, there is a need to be able to obtain a better transmit beam for the gNB after the P-1 phase than currently possible without increasing the number of transmitted beams.

According to embodiments of the invention a solution is therefore provided which enables the UE to more accurately estimate the best transmit beam during the P-1 phase. This estimated transmit beam may be different to any of the transmit beams transmitted by the gNB during the P-1 phase. The best transmit beam estimated by the UE may then be provided to the gNB and used by the gNB when later transmitting to the UE.

Fig. 1 shows a client device 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1 , the client device 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The client device 100 further comprises an antenna or antenna array 110 coupled to the transceiver 104, which means that the client device 100 is configured for wireless communications in a communication system.

The processor 102 may be referred to as one or more general-purpose central processing units (CPUs), one or more digital signal processors (DSPs), one or more application-specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, or one or more chipsets. The memory 106 may be a read-only memory, a random access memory (RAM), or a non-volatile RAM (NVRAM). The transceiver 104 may be a transceiver circuit, a power controller, or an interface providing capability to communicate with other communication modules or communication devices. The transceiver 104, memory 106 and/or processor 102 may be implemented in separate chipsets or may be implemented in a common chipset. That the client device 100 is configured to perform certain actions can in this disclosure be understood to mean that the client device 100 comprises suitable means, such as e.g., the processor 102 and the transceiver 104, configured to perform the actions.

According to embodiments of the invention the client device 100 is configured to receive a synchronization signal (SS) burst set 510 in a radio channel h from a network access node 300, the SS burst set 510 being associated with a set of transmit beams f , of the network access node 300; and estimate the radio channel h based on the received SS burst set 510 and beam information associated with the set of transmit beams .. ,,f _K of the network access node 300. The client device 100 is further configured to determine a transmit beam f _x of the network access node 300 based on the estimated radio channel h, and transmit a control signal 520 to the network access node 300, the control signal 520 indicating the determined transmit beam f _x .

Furthermore, in an embodiment of the invention, the client device 100 for a communication system 500 comprises: a transceiver configured to: receive a SS burst set 510 in a radio channel h from a network access node 300, the SS burst set 510 being associated with a set of transmit beams .. ,,f _K of the network access node 300; a processor configured to: estimate the radio channel h based on the received SS burst set 510 and beam information associated with the set of transmit beams .. ,,f _K of the network access node 300; and determine a transmit beam f _x of the network access node 300 based on the estimated radio channel h, the transceiver configured to: transmit a control signal 520 to the network access node 300, the control signal 520 indicating the determined transmit beam f _x .

Moreover, in yet another example of the invention, the client device 100 for a communication system 500 comprises a processor and a memory having computer readable instructions stored thereon which, when executed by the processor, cause the processor to: receive a SS burst set 510 in a radio channel h from a network access node 300, the SS burst set 510 being associated with a set of transmit beams f , of the network access node 300; estimate the radio channel h based on the received SS burst set 510 and beam information associated with the set of transmit beams f , of the network access node 300; determine a transmit beam f _x of the network access node 300 based on the estimated radio channel h, and transmit a control signal 520 to the network access node 300, the control signal 520 indicating the determined transmit beam f _x . Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a client device 100, such as the one shown in Fig. 1. The method 200 comprises receiving 202 a SS burst set 510 in a radio channel h from a network access node 300, the SS burst set 510 being associated with a set of transmit beams .. , , f _K of the network access node 300; and estimating 204 the radio channel h based on the received SS burst set 510 and beam information associated with the set of transmit beams f , of the network access node 300. The method 200 further comprises determining 206 a transmit beam f _x of the network access node 300 based on the estimated radio channel h, and transmitting 208 a control signal 520 to the network access node 300, the control signal 520 indicating the determined transmit beam f _x .

Fig. 3 shows a network access node 300 according to an embodiment of the invention. In the embodiment shown in Fig. 3, the network access node 300 comprises a processor 302, a transceiver 304 and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 by communication means 308 known in the art. The network access node 300 may be configured for wireless and/or wired communications in a communication system. The wireless communication capability may be provided with an antenna or antenna array 310 coupled to the transceiver 304, while the wired communication capability may be provided with a wired communication interface 312 e.g., coupled to the transceiver 304.

The processor 302 may be referred to as one or more general-purpose CPU, one or more DSPs, one or more ASICs, one or more FPGAs, one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, one or more chipsets. The memory 306 may be a read-only memory, a RAM, or a NVRAM. The transceiver 304 may be a transceiver circuit, a power controller, or an interface providing capability to communicate with other communication modules or communication devices, such as network nodes and network servers. The transceiver 304, the memory 306 and/or the processor 302 may be implemented in separate chipsets or may be implemented in a common chipset.

That the network access node 300 is configured to perform certain actions can in this disclosure be understood to mean that the network access node 300 comprises suitable means, such as e.g., the processor 302 and the transceiver 304, configured to perform the actions.

According to embodiments of the invention the network access node 300 is configured to transmit a SS burst set 510 in a radio channel h to a client device 100, the SS burst set 510 being associated with a set of transmit beams f _r , of the network access node 300; and transmit beam information associated with the set of transmit beams f , of the network access node 300 to the client device 100. The network access node 300 is further configured to receive a control signal 520 from the client device 100, the control signal 520 indicating a transmit beam f _x of the network access node 300; and perform a data transmission 530 in the indicated transmit beam f _x to the client device 100.

Furthermore, in an embodiment of the invention, the network access node 300 for a communication system 500 comprises: a transceiver configured to: transmit a SS burst set 510 in a radio channel h to a client device 100, the SS burst set 510 being associated with a set of transmit beams .. ,,f _K of the network access node 300; transmit beam information associated with the set of transmit beams f , of the network access node 300 to the client device 100; receive a control signal 520 from the client device 100, the control signal 520 indicating a transmit beam f _x of the network access node 300; and perform a data transmission 530 in the indicated transmit beam f _x to the client device 100.

Moreover, in yet another example of the invention, the network access node 300 for a communication system 500 comprises a processor and a memory having computer readable instructions stored thereon which, when executed by the processor, cause the processor to: transmit a SS burst set 510 in a radio channel h to a client device 100, the SS burst set 510 being associated with a set of transmit beams .. ,,f _K of the network access node 300; transmit beam information associated with the set of transmit beams f , of the network access node 300 to the client device 100; receive a control signal 520 from the client device 100, the control signal 520 indicating a transmit beam f _x of the network access node 300; and perform a data transmission 530 in the indicated transmit beam f _x to the client device 100.

Fig. 4 shows a flow chart of a corresponding method 400 which may be executed in a network access node 300, such as the one shown in Fig. 3. The method 400 comprises transmitting 402 a SS burst set 510 in a radio channel h to a client device 100, the SS burst set 510 being associated with a set of transmit beams .. ,,f _K of the network access node 300; and transmitting 404 beam information associated with the set of transmit beams f , of the network access node 300 to the client device 100. The method 400 further comprises receiving 406 a control signal 520 from the client device 100, the control signal 520 indicating a transmit beam f _x of the network access node 300; and performing 408 a data transmission 530 in the indicated transmit beam f _x to the client device 100. Fig. 5 shows a communication system 500 according to an embodiment of the invention. The communication system 500 in the disclosed example comprises a client device 100 and a network access node 300 configured to communicate and operate in the communication system 500. The network access node 300 may be connected to a network (NW) such as e.g., a core network over a communication interface. The communication system 500 may be a communication system according to the 3GPP standard such as e.g., a 5G system in which case the client device 100 may be a UE and the network access node 300 may be a gNB but the invention is not limited thereto.

The network access node 300 may periodically transmit SS burst sets 510 associated with a set of transmit beams f , of the network access node 300, as shown in Fig. 5. The SS burst sets 510 enables each client device 100 in a cell to determine/identify a best pair of transmit and receive beam for its own radio link to the network access node 300. Conventionally, the client device 100 can only determine the best transmit beam from among the set of transmit beams f , However, according to embodiments of the invention a solution is provided which enables the client device 100 to determine an even better transmit beam possibly outside the set of transmit beams f , transmitted by the network access node 300.

To achieve this the network access node 300 according to embodiments of the invention transmits the SS burst sets 510 and further beam information associated with the set of transmit beams to the client device 100. The beam information allows the client device 100 to identify the set of transmit beams f , of the network access node 300 and thereby to make a more accurate estimate of the best transmit beam at the client device 100. The client device 100 determines the best transmit beam by estimating a radio channel h based on the received SS burst set 510 and the beam information and then determines a transmit beam f _x of the network access node 300 based on the estimated radio channel h, as will be further described with reference to Fig. 6 and 7.

With reference to Fig. 5, the client device 100 further indicates the determined transmit beam f _x to the network access node 300 by transmitting a control signal 520 to the network access node 300. In this way, the network access node 300 is informed about the transmit beam f _x determined to be the best transmit beam according to the client device 100 and can use this transmit beam f _x for further beam refinement, e.g., in a P-2 phase, and/or for data transmissions to the client device 100. Fig. 6 shows signaling between the client devices 100 and the network access nodes 300 for determining a transmit beam f _x of the network access node 300 according to an embodiment of the invention. The client device 100 may be a UE and the network access node 300 may be a gNB but is not limited thereto.

In step I in Fig. 6, the network access node 300 transmits a SS burst set 510 in a radio channel h to the client device 100 and the client device 100 receives the SS burst set 510 in the radio channel h from the network access node 300. The SS burst set 510 is associated with a set of transmit beams f , of the network access node 300.

With reference to Fig. 6, the network access node 300 may transmit and the client device 100 may receive the SS burst set 510 during a first time period T1. The first time period T1 may in embodiments be a P-1 phase, i.e. , an initial beam sweeping phase used to identify a suitable beam pair for communication between the network access node 300 and the client device 100.

The network access node 300 further transmits beam information associated with the set of transmit beams f , of the network access node 300 to the client device 100. The beam information may comprise angular information about the set of transmit beams f , ... , f _K of the network access node 300 and/or an antenna array configuration of the network access node 300. The beam information hence allows the client device 100 to identify the set of transmit beams f , of the network access node 300 and thereby to make a good estimate of the best transmit beam at the client device 100.

The network access node 300 may transmit the beam information in a synchronization signal block (SSB) of the SS burst set 510. The beam information may e.g., be comprised in the SSB by defining bits that signals the angular information and/or the antenna array configuration. The new bits may e.g., be included in the physical broadcast channel (PBCH) part of the SSB. In embodiments, the network access node 300 may instead transmit the beam information in another existing or new broadcast signal, or in a unicast signal to the client device 100 such as e.g., in downlink control information (DCI).

In step 2 in Fig. 6, the client device 100 estimates the radio channel h based on the received SS burst set 510 and the beam information associated with the set of transmit beams f , of the network access node 300. As mentioned above, the beam information allows the client device 100 to identify the set of transmit beams f , of the network access node 300 and the client device 100 may receive the beam information in a SSB of the received SS burst set 510. The client device 100 may further receive the beam information in another existing or new broadcast signal, or in a unicast signal to the client device 100 such as e.g., in DCI.

Estimating the radio channel h may comprise determine measurements for the set of transmit beams f , of the network access node 300 based on the SS burst set 510 and estimate the radio channel h based on the determined measurements, as will be further described below with reference to Fig. 7. In embodiments, the measurements comprise amplitude and phase information derived from the received SS burst set 510.

In step 3 in Fig. 6, the client device 100 determines a transmit beam f _x of the network access node 300 based on the estimated radio channel h. Determining the transmit beam f _x of the network access node 300 may comprise determine a transmit beam of the network access node 300 providing the highest received power in dependency on the estimated radio channel h.

In step 4 in Fig. 6, the client device 100 transmits a control signal 520 to the network access node 300, the control signal 510 indicating the determined transmit beam f _x . The network access node 300 receives the control signal 520 from the client device 100 and hence obtains the indicated transmit beam f _x of the network access node 300. In embodiments, the control signal 520 is a channel state information (CSI) report such as e.g., the CSI report following the P-2 phase in connected mode according to the 3GPP standard. The CSI report may e.g., be a CSI report with CSI-reference signal (RS) resource indicator (CRI) or SS/PBCH resource block indicator (SSBRI) and layer 1 reference signal received power (L1-RSRP) or layer 1 signal to interference noise ratio (L1-SINR) as reporting quantities. The control signal 520 may further be implemented as one or more new fields in another existing report or message, as well as in a new report or message.

When the SS burst set 510 is transmitted and received during the first time period T1 , the client device 100 may transmit and the network access node 300 may receive the control signal 520 during a second time period T2 following the first time period T1. The second time period T2 may e.g., be a beam reporting phase following an initial beam sweep sweeping phase. In embodiments, the second time period T2 is a P-2 phase.

In step 5 in Fig. 6, the network access node 300 perform a data transmission 530 in the indicated transmit beam f _x to the client device 100 and the client device 100 receives the data transmission 530 in the determined transmit beam f _x from the network access node 300. The network access node 300 may further use the indicated transmit beam f _x to perform refinement of the transmit beam to the client device 100. The network access node 300 may e.g., search around (in the angular domain) the indicated transmit beam f _x during a P-2 phase to further refine the transmit beam and thereby improve the SNR of the radio link toward the client device 100.

Further details related to the estimation of the radio channel h and the determination of the transmit beam f _x of the network access node 300 performed by the client device 100 will now be described. An objective of the estimation and determination is to find a transmit beam f _x of the network access node 300 that is well aligned with the best receive beam r of the client device 100. Generally, the best beam pair is the one aligned optimally with the underlying multiple input multiple output (MIMO) channel matrix H. For a given receive beam r, r e R, that belongs to a beam codebook R at the client device 100, the resulting multiple input single output (MISO) channel from the network access node 300 to the client device 100 equals the row vector /i(r) = r ^H H. Hence, for this MISO channel, the best transmit beam under a power constraint P is simply the matched filter (MF) beam f = V h(r)/| |h(r)| |, since this beam choice maximizes the received power at the client device 100 which then equals \h(r) ^H f\ ² = P| |h(r)| | ² . Therefore, for the specific receive beam r used at the client device 100, the client device 100 should estimate the radio channel /i(r) as accurately as possible. From the estimated radio channel h(r), the client device 100 may know in advance that using the receive beam r will result in the maximum received power being P\ \h(r) 11 ² .

With reference to Fig. 7, the client device 100 therefore, based on the SS burst set 510 with the set of transmit beams f , estimates the MISO channel /i(r) = r ^H H as the estimated radio channel h(r) from the measurements y _x (r), ... ,y _K (r) for a given receive beam r. The client device 100 uses a receive beam r from its the beam codebook R, during the SS burst set 510 to obtain up to K measurements y _x (r), ... , y _K (r) for that receive beam r. From the K measurements y _x (r), ...,y _K (r), the client device 100 then estimates the MISO channel /i(r) = r ^H H as the estimated radio channel h(r). By switching receive beam r to another beam in the beam codebook R, while the network access node 300 transmits the SS burst set 510 with the set of transmit beams f , the client device 100 is able to sweep the received beams across its beam codebook R and obtain the estimated radio channel h(r) for each receive beam r and in this way find the highest received power maxP| | (r)| | ² . The client device 100 then feeds back the estimated radio channel (r) that gives the highest received power maxP| | (r)| | ² to the network access node 300, as shown in Fig. 7. From the reR estimated radio channel (r) provided by the client device 100, the network access node 300 may then derive the corresponding transmit beam f _x of the network access node 300. In the shown embodiment, the client device 100 hence indicates the transmit beam f _x of the network access node 300 determined to be optimal to the network access node 300 by providing the estimated radio channel (r) with the highest received power to the network access node 300.

To estimate the radio channel /i(r) as accurately as possible, for any receive beam r e R, the client device 100 according to the invention is made aware of the set of transmit beams fi, transmitted from the network access node 300 in the SS burst set 510, e.g., during the P-1 phase. Hence, the client device 100 gain knowledge about e.g., the antenna configuration of the network access node 300. For example, if the transmit beams f _1; are analog/discrete Fourier transform (DFT) beams and the client device 100 is made aware of the phases and dimensions of the set of transmit beams f _1; then the client device 100 can obtain a good estimate of the radio channel /i(r) with an advanced estimation algorithm. In case of a uniform linear array (ULA) at the transmitter, the dimension of the beams is simply the antenna size. In case of a uniform planar array (UPA), the dimensions would be the number of antennas in the vertical and horizontal directions, respectively.

Consequently, to improve the accuracy of the estimation of the radio channel h(r), r e R at the client device 100, the network access node 300 according to the invention provides its antenna array dimensions and/or the transmit beams f _1; it uses during e.g., the P-1 phase. The beam information may be provided with the SSB that carries each transmit beam f _1; As previously described, bits that indicate the transmit beam angle in case of analog/DFT beams and or the dimensions of the transmit beams may be included in the SSB., e.g., in the PBCH part of the SSB.

The client device herein may be denoted as a user device, a user equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, and is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in this context may be, for example, portable, pocket-storable, hand-held, computer- comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via a radio access network (RAN), with another communication entity, such as another receiver or a server. The UE may further be a station, which is any device that contains an IEEE 802.11- conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM). The UE may be configured for communication in 3GPP related long term evolution (LTE), LTE-advanced, fifth generation (5G) wireless systems, such as new radio (NR), and their evolutions, as well as in IEEE related Wi-Fi, worldwide interoperability for microwave access (WiMAX) and their evolutions.

The network access node herein may also be denoted as a radio network access node, an access network access node, an access point (AP), or a base station (BS), e.g., a radio base station (RBS), which in some networks may be referred to as transmitter, “gNB”, “gNodeB”, “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the standard, technology and terminology used. The radio network access nodes may be of different classes or types such as e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby the cell size. The radio network access node may further be a station, which is any device that contains an IEEE 802.11 -conformant MAC and PHY interface to the WM. The radio network access node may be configured for communication in 3GPP related LTE, LTE- advanced, 5G wireless systems, such as NR and their evolutions, as well as in IEEE related Wi-Fi, WiMAX and their evolutions.

Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as previously mentioned a ROM, a PROM, an EPROM, a flash memory, an EEPROM, or a hard disk drive.

Moreover, it should be realized that the client device and the network access node comprise the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing or implementing embodiments of the invention. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution. Therefore, the processor(s) of the client device and the network access node may comprise, e.g., one or more instances of a CPU, a processing unit, a processing circuit, a processor, an ASIC, a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like. Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.