TECHNICAL FIELD

Embodiments presented herein relate to methods, a network node, a user equipment, computer programs, and a computer program product for determining a reciprocity- based precoder for the user equipment.

BACKGROUND

One component in Release 15 of the third generation partnership project (3GPP) New Radio (NR) standard is the support of multiple-input multiple-output (MIMO) antenna deployments and MIMO related techniques. MIMO systems can significantly increase the data carrying capacity of wireless systems. So-called massive MIMO generally refers to MIMO systems where hundreds of antennas are used at the transmitter side and/or the receiver side. Typically, the peak data rate in MIMO systems multiplies with a factor of N _t over single antenna systems in rich scattering environment, where N _t is the number of antennas at the transmitter side.

Precoding is a generalization of beamforming to support multi-stream transmission in multi-antenna wireless communications, such as in MIMO systems.

Before giving a brief introduction to how precoding is performed, it could be of benefit to disclose some details of message exchange between a network node and a UE in an NR system. Reference is therefore made to the signalling diagram of Fig. 1 which shows a typical sequence of message exchange between a network node 200 and a UE 300 for downlink data transfer in an NR system. From pilots or reference signals (such as cell specific reference signals or UE specific reference signals) as transmitted from the network node 200 in step Si, the UE 300 in step S2 computes channel estimates and then from the channel estimates computes parameters needed for channel state information (CSI) reporting. The CSI report comprises, for example, channel quality indicator (CQI), precoding matrix index (PMI), rank information (RI) and channel state information reference signal (CSI-RS) Resource Indicator (CRI; the same as beam indicator), etc. The CSI report is by the UE 300 in step S3 sent to the network node 200 over a feedback channel, such as on an uplink control channel, either a-periodically on request from the network node 200 or periodically according to configuration. The uplink control channel carries channel state information as well as information about hybrid automatic repeat request (hybrid ARQ or HARQ) acknowledgment (ACK) information corresponding to downlink data transmissions. The channel state information typically consists of CRI, RI, CQI, PMI and Layer Indicator etc. The network node 200 can indicate whether the UE 300 should report all the listed parameters, such as CRI, RI, PMI, and CQI or only a subset of these parameters, such as CQI and RI, CQI, RI and PMI etc. The network node 200 in step S4 uses the information in the CSI report when selecting scheduling parameters for the UE 300. The network node 200 in step S5 sends the scheduling parameters to the UE 300 over a downlink control channel. The downlink control channel thus carries information about the scheduling grants. Typically, information such as the number of MIMO layers scheduled, transport block sizes, modulation for each codeword, parameters related to HARQ, sub band locations, etc. is signalled on the downlink control channel. In general, which information to signal on the downlink control channel depends on transmission mode and the used downlink control information (DCI) format. In step S6 actual data transfer takes place from the network node 200 to the UE 300 in accordance with the scheduling parameters.

Precoding is applied at the network node to achieve a beamforming gain. When the channel is not known, such as in a system operating using frequency division duplex (FDD), the network node obtains a PMI value from the UE (as disclosed above), whilst in in a system operating using time division duplex (TDD) the uplink channel can be estimated at the network node through measurements on uplink reference signals, such as sounding reference signals. When reciprocity is assumed, the downlink channel is equal to the uplink channel, and hence the precoding matrix/vector can be obtained from the channel estimation at the network node.

In reciprocity-based precoding, mathematically, the received signal at the UE can be written as

Y = HWx + n, where H is the channel matrix between the transmitter antenna elements of dimensions (iV _r -by-iV _t ), W the digital precoding matrix of dimensions (iV _t -by- R), where x is the signal vector of size (R- by-1) as transmitted from the network node, and where R is the transmission rank of the system. For reciprocity-based systems W = V, where V is computed from

SVD(tf) = UDV, where SVD(H) is the singular value decomposition of the channel matrix H. In reciprocity-based precoding the precoder is computed at the network node. However, the modulation and coding scheme (MCS) needed for scheduling is obtained from the CQI measurements provided from the UE in the CSI report. This is because the downlink interference is assumed to be different from the uplink interference. Hence, even though the channel is reciprocal and the network node can estimate the channel, the network node cannot schedule the UE without channel state information. If the network node obtains the CQI from the UE and use the computed precoder at the network node, the performance can be improved over conventional codebook-based precoding where the CSI is computed only at the UE. However, this may not achieve optimal gains because part of the scheduling parameters (such as precoding weights to be used by the precoder) are computed at the network node, whilst some other parameters (such as CQI, RI) are computed at the UE, and the CQI reported by the UE does not consider the precoding weights computed at the network node.

The performance can be further improved if the network node computes the precoding weights based on the channel estimate from the uplink reference signals. The network node then beamforms the downlink reference signals with the computed precoder and obtains. From the user equipment, the CQI corresponding to the beamformed downlink reference signals. However, whilst this improves the performance, there is still a need for improved reciprocity-based precoding.

SUMMARY An object of embodiments herein is to provide efficient reciprocity-based precoding where the above-mentioned issued are resolved, mitigated, or at least reduced.

According to a first aspect there is presented a method for determining a reciprocity- based precoder for a user equipment. The method is performed by a network node. The method comprises signalling configuration to the user equipment according to which a precoding processing technique is specified for the user equipment to use for determining rank information. The method comprises transmitting downlink reference signals towards the user equipment. The method comprises receiving uplink reference signals and the rank information from the user equipment. The method comprises determining the reciprocity-based precoder from channel information and the rank information. The network node uses the precoding processing technique for obtaining channel information from channel estimates of the uplink reference signals.

According to a second aspect there is presented a network node for determining a reciprocity-based precoder for a user equipment. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to signal configuration to the user equipment according to which a precoding processing technique is specified for the user equipment to use for determining rank information. The processing circuitry is configured to cause the network node to transmit downlink reference signals towards the user equipment. The processing circuitry is configured to cause the network node to receive uplink reference signals and the rank information from the user equipment. The processing circuitry is configured to cause the network node to determine the reciprocity-based precoder from channel information and the rank information. The network node uses the precoding processing technique for obtaining channel information from channel estimates of the uplink reference signals. According to a third aspect there is presented a network node for determining a reciprocity-based precoder for a user equipment. The network node comprises a signal module configured to signal configuration to the user equipment according to which a precoding processing technique is specified for the user equipment to use for determining rank information. The network node comprises a transmit module configured to transmit downlink reference signals towards the user equipment. The network node comprises a receive module configured to receive uplink reference signals and the rank information from the user equipment. The network node comprises a determine module configured to determine the reciprocity-based precoder from channel information and the rank information. The network node uses the precoding processing technique for obtaining channel information from channel estimates of the uplink reference signals. According to a fourth aspect there is presented a computer program for determining a reciprocity-based precoder for a user equipment. The computer program comprises computer program code which, when run on processing circuitry of a network node, causes the network node to perform a method according to the first aspect. According to a fifth aspect there is presented a method for assisting a network node for determining a reciprocity-based precoder for a user equipment. The method is performed by the user equipment. The method comprises receiving downlink reference signals and signalling of a configuration from the network node. According to the configuration a precoding processing technique is specified for the user equipment to use for determining rank information. The method comprises determining the rank information from channel information. The user equipment uses the precoding processing technique for obtaining channel information from channel estimates of the downlink reference signals. The method comprises transmitting uplink reference signals and the rank information towards the network node.

According to a sixth aspect there is presented a user equipment for determining a reciprocity-based precoder for the user equipment. The user equipment comprises processing circuitry. The processing circuitry is configured to cause the user equipment to receive downlink reference signals and signalling of a configuration from the network node. According to the configuration a precoding processing technique is specified for the user equipment to use for determining rank information. The processing circuitry is configured to cause the user equipment to determine the rank information from channel information. The user equipment uses the precoding processing technique for obtaining channel information from channel estimates of the downlink reference signals. The processing circuitry is configured to cause the user equipment to transmit uplink reference signals and the rank information towards the network node.

According to a seventh aspect there is presented a user equipment for determining a reciprocity-based precoder for the user equipment. The user equipment comprises a receive module configured to receive downlink reference signals and signalling of a configuration from the network node. According to the configuration a precoding processing technique is specified for the user equipment to use for determining rank information. The user equipment comprises a determine module configured to determine the rank information from channel information. The user equipment uses the precoding processing technique for obtaining channel information from channel estimates of the downlink reference signals. The user equipment comprises a transmit module configured to transmit uplink reference signals and the rank information towards the network node.

According to an eighth aspect there is presented a computer program for determining a reciprocity-based precoder for a user equipment. The computer program comprises computer program code which, when run on processing circuitry of the user equipment, causes the user equipment to perform a method according to the fifth aspect.

According to a ninth aspect there is presented a computer program product comprising a computer program according to at least one of the fourth aspect and the eighth 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.

Advantageously, these aspects provide efficient reciprocity-based precoding where the above-mentioned issued are resolved.

Advantageously, these aspects provide a significant performance improvement to conventional reciprocity-based precoding since the uplink overhead is significantly saved. The reason for this is that, since the precoder is determined at the network node, the user equipment does not need to report the precoder to the network node.

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.

Generally, 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

The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. l is a signalling diagram of a method according to an example;

Fig. 2 is a schematic diagram illustrating a communication network according to embodiments;

Figs. 3 and 4 are flowcharts of methods according to embodiments; Fig. 5 is a signalling diagram of a method according to embodiments;

Fig. 6 show simulation results according to embodiments;

Fig. 7 is a schematic diagram showing functional units of a network node according to an embodiment;

Fig. 8 is a schematic diagram showing functional modules of a network node according to an embodiment;

Fig. 9 is a schematic diagram showing functional units of a user equipment according to an embodiment;

Fig. 10 is a schematic diagram showing functional modules of a user equipment according to an embodiment; and Fig. 11 shows one example of a computer program product comprising computer readable means according to an embodiment.

DETAILED DESCRIPTION

The 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.

Fig. 2 is a schematic diagram illustrating a communication network loo where embodiments presented herein can be applied. The communication network 100 could be a third generation (3G) telecommunications network, a fourth generation (4G) telecommunications network, a fifth generation (5G) telecommunications network, a sixth generation (6G) telecommunications network, or any evolvement thereof, and support any 3GPP, IEEE, or other telecommunications standard, where applicable. In some examples, the communication network 100 represents part of a MIMO system.

The communication network 100 comprises a network node 200 configured to provide network access to user equipment, as represented by user equipment 300, in a radio access network no. The radio access network no is operatively connected to a core network 120. The core network 120 is in turn operatively connected to a service network 130, such as the Internet. The user equipment 300 is thereby enabled to, via the network node 200, access services of, and exchange data with, the service network 130.

The network node 200 comprises, is collocated with, is integrated with, or is in operational communications with, at least one transmission and reception point (TRP) 140. The network node 200 (via its at least one TRP 140) and the user equipment 300 are configured to communicate with each other over a wireless link, as illustrated at reference numeral 150.

Examples of network nodes 200 are radio access network nodes, radio base stations, base transceiver stations, Node Bs, evolved Node Bs (eNBs), gNBs, access points, access nodes, and integrated access and backhaul nodes. Examples of user equipment 300 are wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, smartphones, laptop computers, tablet computers, network equipped sensors, network equipped vehicles, and so-called Internet of Things (IoT) devices.

As noted above, there is still a need for improved reciprocity-based precoding. In this respect, the inventor has, as part of developing the inventive concept of the present disclosure, realized that even if the network node 200 computes the precoder and beamforms the downlink reference signals with the computed precoder and obtains the CQI, the following limitations still apply. Firstly, there is a latency between the precoder computation at the network node 200 and the CQI computation at the user equipment 300. Hence, the CSI obtained from the user equipment 300 may not reflect the actual link quality experienced by the user equipment 300. Hence, if the user equipment 300 is moving even with a small speed, the performance might be severely impacted. Secondly, separate uplink reference signal resources are needed for computing the precoder at the network node 200. In general, transmission of uplink reference signals from the user equipment 300 requires frequent transmission of uplink resources. When the load of the cell is high, transmitting uplink reference signals from the user equipment 300 is cumbersome and frequent transmission of uplink reference signals reduces the uplink throughput.

Thirdly, separate UE-specific downlink reference signal resources are needed for beamforming the downlink reference signals for obtaining the CQI. Hence with the beamformed downlink reference signals, downlink resources are wasted.

Hence there is a need to improve the downlink performance and at the same time optimize the resource allocation in downlink and uplink when using reciprocity- based precoding.

The embodiments disclosed herein thus relate to mechanisms for determining a reciprocity-based precoder for a user equipment 300. In order to obtain such mechanisms there is provided a network node 200, a method performed by the network node 200, a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the network node 200, causes the network node 200 to perform the method. In order to obtain such mechanisms there is further provided a user equipment 300, a method performed by the user equipment 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 user equipment 300, causes the user equipment 300 to perform the method.

Reference is now made to Fig. 3 illustrating a method for determining a reciprocity- based precoder for a user equipment 300 as performed by the network node 200 according to an embodiment.

In short, the method is based on that the network node 200 configures the user equipment 300 to use a certain precoding processing technique when determining rank information and then the network node 200 uses the same precoding processing technique when determining its precoder. S104: The network node 200 signals configuration to the user equipment 300 according to which a precoding processing technique is specified for the user equipment 300 to use for determining rank information.

S106: The network node 200 transmits downlink reference signals towards the user equipment 300. S108: The network node 200 receives uplink reference signals and the rank information from the user equipment 300.

S110: The network node 200 determines the reciprocity-based precoder from channel information and the rank information. The network node 200 uses the same precoding processing technique for obtaining channel information from channel estimates of the uplink reference signals as the user equipment 300 was configured with in step S104.

Embodiments relating to further details of determining a reciprocity-based precoder for a user equipment 300 as performed by the network node 200 will now be disclosed. There could be different precoding processing technique that the user equipment 300 is to use for determining the rank information. In some non-limiting examples, the precoding processing technique is any of: SVD, zero-forcing (ZF), maximum ratio transmission (MRT) and weighted minimum mean squared error (MMSE). There could be different ways for the network node 200 to signal the configuration to the user equipment 300 in step S104. In some embodiments, the configuration is signalled as part of configuring the user equipment 300 with CSI report settings. In some embodiments, the configuration is signalled using radio resource control (RRC) or medium access control element (MAC-CE) signalling.

There could be additional information in the configuration that is signalled to the user equipment 300 in step S104. In some embodiments, according to the configuration, the user equipment 300 is configured with a PMI-less transmission. In some embodiments, according to the configuration, the user equipment 300 is configured to determine the rank information from channel information that is based on either subband or wideband measurements on the downlink reference signals. In some embodiments, according to the configuration, the user equipment 300 is configured to use the precoding processing technique when determining a CQI and a layer indicator (LI). The CQI and the LI are then received together with the rank information in step S108.

In some aspects, the network node 200 checks that the user equipment 300 is capable of using the precoding processing technique before the user equipment 300 is informed, by means of the configuration in step S104, of the precoding processing technique. Particularly, in some embodiments, the network node 200 is configured to perform (optional) step S102:

S102: The network node 200 verifies that the user equipment 300 supports using the precoding processing technique when determining rank information before signalling the configuration to the user equipment 300.

There could be different ways for the network node 200 to perform the verifying in step S102. In some examples, the network node 200 queries a database for information indicating whether or not the user equipment 300 supports using the precoding processing technique. In some examples, the network node 200 queries the user equipment 300 itself whether or not the user equipment 300 supports using the precoding processing technique. In some aspects, the network node 200 applies the determined precoder when transmitting downlink signals towards the user equipment 300. Particularly, in some embodiments, the network node 200 is configured to perform (optional) step S112:

S112: The network node 200 transmits signals towards the user equipment 300 whilst using the reciprocity-based precoder.

Reference is now made to Fig. 4 illustrating a method for determining a reciprocity- based precoder for a user equipment 300 as performed by the user equipment 300 according to an embodiment.

This method is based on that the user equipment 300 is by the network node 200 configured to use a certain precoding processing technique when determining rank information.

S204: The user equipment 300 receives downlink reference signals and signalling of a configuration from the network node 200. According to the configuration a precoding processing technique is specified for the user equipment 300 to use for determining rank information.

S206: The user equipment 300 determines the rank information from channel information. The user equipment 300 uses the precoding processing technique for obtaining channel information from channel estimates of the downlink reference signals. S208: The user equipment 300 transmits uplink reference signals and the rank information towards the network node 200.

Embodiments relating to further details of determining a reciprocity-based precoder for a user equipment 300 as performed by the user equipment 300 will now be disclosed. As disclosed above, there could be different precoding processing technique that the user equipment 300 is to use for determining the rank information. As disclosed above, in some non-limiting examples, the precoding processing technique is any of: SVD, ZF, MRT and weighted MMSE. As disclosed above, there could be different ways for the network node 200 to signal the configuration to the user equipment 300 in step S104. In some embodiments, the configuration is received as part of the user equipment 300 being configured with CSI report settings. In some embodiments, the configuration is signalled using RRC or MAC-CE signalling.

As above, could be additional information in the configuration than is signalled to the user equipment 300 in step S104. In some embodiments, according to the configuration, the user equipment 300 is configured with a PMI-less transmission. In some embodiments, according to the configuration, the user equipment 300 is configured to determine the rank information based on either subband or wideband measurements on the downlink reference signals. In some embodiments, according to the configuration, the user equipment 300 is configured to use the precoding processing technique when determining a CQI and a LI, where the CQI and the LI are determined by the user equipment 300, and where the CQI and the LI are transmitted together with the rank information.

As disclosed above, in some aspects, the network node 200 checks that the user equipment 300 is capable of using the precoding processing technique. Particularly, in some embodiments, the user equipment 300 is configured to perform (optional) step S202: S202: The user equipment 300 verifies to the network node 200 that the user equipment 300 supports using the precoding processing technique when determining rank information before receiving the signalling of the configuration from the network node 200.

There could be different ways for the user equipment 300 to verify to the network node 200 that the user equipment 300 supports using the precoding processing technique. In some embodiments, the verifying is part of providing UE capability information to the network node 200.

There could be different ways for the user equipment 300 to determine the rank information from channel information in step S206. In some aspects the rank information is determined to yield as high system capacity has possible. In particular, in some embodiments, the user equipment 300 is configured to perform (optional) steps S2o6a and S2o6b as part of determining the rank information in step S206:

S2o6a: The user equipment 300 determines a system capacity value for each possible rank value r = i:R (i.e., for each value of r from 1 to R). S2o6b: The user equipment 300 selects as rank information the rank value r yielding highest system capacity value, Cr.

There could be different ways for the user equipment 300 to determine the system capacity value in step S2o6a. In some aspects, the system capacity value is based on a signal to interference plus noise ratio value (SINR). There will be one SINR value for each rank value. Denote by SINR(r) the SINR value for rank r, i.e., the SINR value if r layers are used (i.e., all layers 1 to r are used). In particular, in some embodiments, the user equipment 300 is configured to perform (optional) steps S2o6aa, S2o6ab and S2o6ac for each r = i:R as part of determining the system capacity value for each possible rank value in step S206: S2o6aa: The user equipment 300 computes an SINR value, SINR(r), from the channel information as if all layers 1 to r were used.

S2o6ab: The user equipment 300 maps SINR(r) to a CQI value, CQI(r).

S2o6ac: The user equipment 300 determines the system capacity value, C(r), as C(r)

= r · CQI(r). One particular embodiment for determining a reciprocity-based precoder for a user equipment 300 based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the signalling diagram of Fig. 5.

S301: The network node 200 signals configuration to the user equipment 300 according to which a precoding processing technique is specified for the user equipment 300 to use for determining rank information. The configuration is received by the user equipment 300. Further, the network node 200 might in step S301 configure the user equipment 300 with a single or multiple downlink reference signal resource configuration with fixed number of antenna ports. Further, the network node 200 might in step S301 configure the user equipment 300 with CSI report settings where the reporting quantities and their time domain properties are indicated. Further, the network node 200 might in step S301 configure the user equipment 300 to not transmit the PMI as part of the CSI reporting, but however to report CQI/RI/LI/CRI based on the SVD of the channel. Further, the network node 200 might in step S301 inform the user equipment 300 whether the user equipment

300 is to use subband or wideband precoding when computing the CSI.

S302: The network node 200 transmits downlink reference signals, such as CSI-RS, towards the user equipment 300. The downlink reference signals are received by the user equipment 300. S303: The user equipment 300 determines the rank information from channel information. The user equipment 300 uses the precoding processing technique for obtaining channel information from channel estimates of the downlink reference signals.

S304: The user equipment 300 transmits a CSI report comprising the rank information, but no PMI, towards the network node 200. The rank information is received by the network node 200. Examples of how the rank information might be reported to the network node 200 have been disclosed above.

S305: The user equipment 300 transmits uplink reference signals towards the network node 200. The uplink reference signals are received by the network node 200. The network node 200 estimates the uplink channel from the uplink reference signals so as to obtain channel information.

S306: The network node 200 determines the reciprocity-based precoder from channel information and the rank information. The network node 200 uses the same precoding processing technique for obtaining the channel information from the channel estimates of the uplink reference signals as the user equipment 300 was configured with in step S301.

S307: The network node 200 determines scheduling parameters for downlink data transmission towards the user equipment 300. S308: The network node 200 indicates the scheduling parameters with signalling on a downlink control channel to the user equipment 300. The user equipment 300 receives the scheduling parameters.

S309: The network node 200 transmits downlink reference signals, such as demodulation reference signals (DMRS) towards the user equipment 300. The user equipment 300 receives the downlink reference signals.

S310: The network node 200 transmits signals, such as data signals on a downlink shared channel, towards the user equipment 300 whilst using the reciprocity-based precoder. The user equipment 300 receives the signals. S311: The user equipment 300 transmits feedback of the signals on a feedback channel towards the network node 200. The network node 200 receives the feedback.

To verity benefits of the herein disclosed embodiments, the performance of an NR massive MIMO system was evaluated with link level simulations. A MIMO system with 32 antenna ports at the network node 200 a user equipment 300 capable of receiving 32 antenna ports are considered with link adaptation. Parameters relating to rank information, precoding information, modulation and coding scheme, and transport block size are dynamically updated for each slot. For link adaptation using CSI, the user equipment 300 is configured to select the PMI, RI and CQI based on maximization of mutual information. The feedback reported from the user equipment to the network node 200 from the user equipment 300 is assumed to have 4 slots delay and is assumed to be error free. Simulation results are in Fig. 6 shown in terms of throughput (in megabits per second; MBPS) as a function of SNR (in decibel; dB). In Fig. 6 the link throughput as obtained using the herein disclosed embodiments is compared to conventional beamformed CSI-RS transmission and the conventional precoding (in accordance with Fig. 1). It can be observed that significant gains can be achieved as the precoder and the CQI are exactly matched to each other.

In view of the above, at least some of the herein disclosed embodiments enable an improvement to the performance of a reciprocity-based massive MIMO system using a single step process, where the network node 200 informs the user equipment 300 to in its CSI report not to transmit PMI but when computing the CQI and RI, LI, to use a precoding processing technique (such as SVD, ZF, MRT or weighted MMSE) specified by the network node 200. The configuration can be part of RRC signalling or MAC-CE signalling. Hence, there is no overhead on the uplink control channel as the user equipment 300 does not need to report the PMI. The network node 200 determines its precoder based on channel estimate of uplink reference signals and rank information received from the user equipment 300. Hence, proper link adaptation can be achieved without any significant delay between the determination of the precoder at the network node 200 and the reception of the rank information from the user equipment 300.

Fig. 7 schematically illustrates, in terms of a number of functional units, the components of a network node 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 1110a (as in Fig. 11), 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).

Particularly, the processing circuitry 210 is configured to cause the network node 200 to perform a set of operations, or steps, 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 network node 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.

The 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.

The network node 200 may further comprise a communications interface 220 for communications with other entities, functions, nodes, and devices of the communication network 100 as well as entities, functions, nodes, and devices served by the communication network 100, such as the user equipment 300. As such the communications interface 220 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 210 controls the general operation of the network node 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 network node 200 are omitted in order not to obscure the concepts presented herein.

Fig. 8 schematically illustrates, in terms of a number of functional modules, the components of a network node 200 according to an embodiment. The network node 200 of Fig. 8 comprises a number of functional modules; a signal module 210b configured to perform step S104, a transmit module 210c configured to perform step S106, a receive module 2iod configured to perform step S108, and a determine module 2ioe configured to perform step S110. The network node 200 of Fig. 8 may further comprise a number of optional functional modules, such as any of a verity module 210a configured to perform step S102, and a transmit module 2iof configured to perform step S112. In general terms, each functional module 210a: 2iof may be implemented in hardware or in software. Preferably, one or more or all functional modules 210a: 2iof 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: 2iof and to execute these instructions, thereby performing any steps of the network node 200 as disclosed herein.

The network node 200 may be provided as a standalone device or as a part of at least one further device. For example, the network node 200 may be provided in a node of the radio access network or in a node of the core network. Alternatively, functionality of the network node 200 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 (such as the radio access network or the core network) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell than instructions that are not required to be performed in real time. Thus, a first portion of the instructions performed by the network node 200 may be executed in a first device, and a second portion of the instructions performed by the network node 200 may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node 200 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node 200 residing in a cloud computational environment. Therefore, although a single processing circuitry 210 is illustrated in Fig. 7 the processing circuitry 210 maybe distributed among a plurality of devices, or nodes. The same applies to the functional modules 210a: 2iof of Fig. 8 and the computer program 1120a of Fig. 11.

Fig. 9 schematically illustrates, in terms of a number of functional units, the components of a user equipment 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 1110b (as in Fig. 11), 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). Particularly, the processing circuitry 310 is configured to cause the user equipment 300 to perform a set of operations, or steps, 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 user equipment 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.

The 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. The user equipment 300 may further comprise a communications interface 320 for communications with other entities, functions, nodes, and devices, such as the network node 200. As such the communications interface 320 may comprise one or more transmitters and receivers, comprising analogue and digital components.

The processing circuitry 310 controls the general operation of the user equipment 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 user equipment 300 are omitted in order not to obscure the concepts presented herein.

Fig. 10 schematically illustrates, in terms of a number of functional modules, the components of a user equipment 300 according to an embodiment. The user equipment 300 of Fig. 10 comprises a number of functional modules; a receive module 310b configured to perform step S204, a determine module 310c configured to perform step S206, and a transmit module 3101 configured to perform step S208. The user equipment 300 of Fig. 10 may further comprise a number of optional functional modules, such as any of a verity module 310a configured to perform step S202, a determine module 3iod configured to perform step S2o6a, a compute module 3ioe configured to perform step S2o6aa, a map module 3iof configured to perform step S2o6ab, a determine module 3iog configured to perform step S2o6ac, and a select module 3ioh configured to perform step S2o6b. In general terms, each functional module 3ioa:3ioi may be implemented in hardware or in software. Preferably, one or more or all functional modules 3ioa:3ioi maybe 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 3ioa:3ioi and to execute these instructions, thereby performing any steps of the user equipment 300 as disclosed herein.

Fig. 11 shows one example of a computer program product 1110a, 1110b comprising computer readable means 1130. On this computer readable means 1130, a computer program 1120a can be stored, which computer program 1120a 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 1120a and/or computer program product 1110a may thus provide means for performing any steps of the network node 200 as herein disclosed. On this computer readable means 1130, a computer program 1120b can be stored, which computer program 1120b 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 1120b and/or computer program product 1110b may thus provide means for performing any steps of the user equipment 300 as herein disclosed. In the example of Fig. 11, the computer program product 1110a, 1110b 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 1110a, 1110b 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 1120a, 1120b is here schematically shown as a track on the depicted optical disk, the computer program 1120a, 1120b can be stored in any way which is suitable for the computer program product 1110a, 1110b.

The 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.