TECHNICAL FIELD

The present disclosure relates generally to the field of wireless communication. More particularly, it relates to approaches for multiple-input multiple-output (MIMO) transmission.

BACKGROUND

A general problem in relation to wireless communication is how to achieve as high throughput as possible under given channel conditions. This problem is also applicable for multiple-input multiple-output (MIMO) transmission.

Although various approaches exist that aim for increased throughput, there are communication scenarios (e.g., defined by channel conditions and/or by which devices are involved in the communication) where the capacity of the given channel conditions is not fully exploited.

Therefore, there is a need for alternative approaches to MIMO transmission. Preferably, such approaches should - in one or more communication scenarios - provide increased throughput compared to other approaches.

SUMMARY

It should be emphasized that the term "comprises/comprising" (replaceable by "includes/including") when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Generally, when an arrangement is referred to herein, it is to be understood as a physical product; e.g., an apparatus. The physical product may comprise one or more parts, such as controlling circuitry in the form of one or more controllers, one or more processors, or the like. It is an object of some embodiments to solve or mitigate, alleviate, or eliminate at least some of the above or other disadvantages.

A first aspect is a method for a radio access node. The method is for communicating with a plurality of users by multiple-input multiple-output (MIMO) transmission. The radio access node is configured to receive user feedback, and to use uplink channel estimates for downlink beamforming of the MIMO transmission.

The method comprises estimating a user-specific signal quality value, wherein the signal quality value is a signal-to-interference ratio (SIR) value and/or a signal-to-interference-and-noise ratio (SINR) value, and performing or causing downlink MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value.

Estimating the signal quality value comprises combining a desired power component and a total power component, wherein the desired power component is determined from an extended downlink channel model, wherein the total power component is determined from the extended downlink channel model, and is compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user, and wherein the extended downlink channel model is a combination of a downlink beamforming precoder, an estimation of a downlink radio channel, and a receiver model of the one or more user determined based on the user feedback.

In some embodiments, the estimation of the downlink radio channel comprises a reciprocity version of uplink channel estimates, wherein uplink channel estimates used for the estimation of the downlink radio channel relate to one or more frequency sub-band and/or sub-carrier, which is different than a frequency sub-band and/or sub-carrier related to uplink channel estimates used for the downlink beamforming precoder.

In some embodiments, uplink channel estimates used for the estimation of the downlink radio channel and uplink channel estimates used for the downlink beamforming precoder relate to different sub-carriers within a sub-carrier group.

In some embodiments, the receiver model of the one or more user matches a combination of the downlink beamforming precoder and the estimation of the downlink radio channel, as compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user. In some embodiments, the total power component comprises inter-layer interference power and/or inter-user interference power, as derived from the extended downlink channel model.

In some embodiments, compensation of the total power component comprises a combination of the receiver model of the one or more user with uncertainties of the uplink channel estimate and/or estimated disturbances at the user.

In some embodiments, the uncertainties of the uplink channel estimate are determined from the downlink beamforming precoder and a variance relating to the uncertainties of the uplink channel estimates.

In some embodiments, estimated disturbances at the user comprises inter-user interference caused by using the uplink channel estimates for downlink beamforming.

In some embodiments, estimated disturbances at the user is determined based on the user feedback.

In some embodiments, the estimated disturbances at the user is determined from one or more of: a reciprocity version of uplink channel estimates used for downlink beamforming, beamforming indicated by the user feedback, and signal quality value and rank indicated by the user feedback.

In some embodiments, the estimated disturbances at the user is determined from an effect of a combination of the beamforming indicated by user feedback and the reciprocity version of uplink channel estimates used for downlink beamforming, as biased by the signal quality value and rank indicated by user feedback.

In some embodiments, estimating the user-specific signal quality value comprises estimating intermediate user-specific signal quality values per sub-carrier group, transforming (for each of a plurality of modulation order hypotheses) each intermediate user-specific signal quality value to a spectrum efficiency value, accumulating (for each of the plurality of modulation order hypotheses) the spectrum efficiency values over a plurality of sub-carrier groups, selecting (based on the accumulated spectrum efficiency values) a modulation order from the plurality of modulation order hypotheses, and transforming the accumulated spectrum efficiency values of the selected modulation order to the estimated user-specific signal quality value. In some embodiments, the MIMO transmission comprises using the estimated user-specific signal quality value for controlling transport formal selection of an upcoming transmission occasion.

In some embodiments, the MIMO transmission comprises using the estimated user-specific signal quality value for link adaptation.

In some embodiments, using the estimated user-specific signal quality value for link adaptation comprises selecting a modulation and coding scheme (MCS) that is associated with the estimated user-specific signal quality value.

In some embodiments, the MIMO transmission comprises one or more of: a multi-user (MU) MIMO transmission, and a single-user (SU) MIMO transmission.

In some embodiments, the MU MIMO transmission comprises dynamic MU grouping overtime, or un-dynamic MU grouping.

In some embodiments, the user feedback comprises one or more of: channel quality information (CQI), precoding matrix index (PMI), and rank indicator (Rl).

In some embodiments, the uplink channel estimates are determined by the radio access node based on one or more user transmission of at least one type of uplink signal.

In some embodiments, the at least one type of uplink signal comprises sounding reference signal (SRS) and/or demodulation reference signal (DMRS).

A second aspect is a computer program product comprising a non-transitory computer readable medium, having thereon a computer program comprising program instructions. The computer program is loadable into a data processing unit and configured to cause execution of the method according to the first aspect when the computer program is run by the data processing unit.

A third aspect is an apparatus for a radio access node configured for communication with a plurality of users by multiple-input multiple-output (MIMO) transmission, wherein the radio access node is configured to receive user feedback, and wherein the radio access node is configured to use uplink channel estimates for downlink beamforming of the MIMO transmission. The apparatus comprises controlling circuitry configured to cause estimation of a user-specific signal quality value, wherein the signal quality value is a signal-to-interference ratio (SIR) value and/or a signal-to-interference-and-noise ratio (SINR) value, and downlink MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value.

Estimation of the signal quality value comprises combination of a desired power component and a total power component, wherein the desired power component is determined from an extended downlink channel model, wherein the total power component is determined from the extended downlink channel model, and is compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user, and wherein the extended downlink channel model is a combination of a downlink beamforming precoder, an estimation of a downlink radio channel, and a receiver model of the one or more user determined based on the user feedback.

A fourth aspect is a radio access node comprising the apparatus of the third aspect.

A fifth aspect is a server node comprising the apparatus of the third aspect, wherein the server node is configured to control the radio access node.

A sixth aspect is a control node comprising the apparatus of the third aspect, wherein the control node is configured to control a plurality of access points of a distributed MIMO system, and wherein the radio access node is one of the access points.

In some embodiments, any of the above aspects may additionally have features identical with or corresponding to any of the various features as explained above for any of the other aspects.

An advantage of some embodiments is that alternative approaches to MIMO transmission are provided.

An advantage of some embodiments is that increased throughput is provided compared to other approaches.

An advantage of some embodiments is that improved link adaptation is provided compared to other approaches (e.g., selection of a modulation and coding scheme, MCS, that is more appropriate for the communication scenario at hand). An advantage of some embodiments is that a radio access node is enabled to predict downlink SINR for link adaptation in MU-MIMO transmission. This enables the radio access node to select a proper MCS, which matches not only the downlink channel conditions but also the dynamic pairing of multiple UEs, so that the total throughput can be improved compared to other approaches.

Generally, being more appropriate for a communication scenario may be defined as achieving higher throughput in the communication scenario.

Also generally, throughput may refer to throughput for an individual user and/or to accumulated throughput for two or more users.

It should be noted that, even though described in the context of terminology from Third Generation Partnership (3GPP) standardization, embodiments may be equally applicable for other types of communication (e.g., communication according to IEEE802.il standardization).

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages will appear from the following detailed description of embodiments, with reference being made to the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments.

Figure 1 is a flowchart illustrating example method steps according to some embodiments;

Figure 2A is a schematic block diagram illustrating example functions according to some embodiments;

Figure 2B is a schematic drawing illustrating an example sub-carrier group according to some embodiments;

Figure 3 is a schematic block diagram illustrating an example apparatus according to some embodiments;

Figures 4A-C are schematic drawings illustrating example communication scenarios according to some embodiments;

Figure 5 is a schematic drawing illustrating an example computer readable medium according to some embodiments; Figure 6 schematically illustrates a telecommunication network connected via an intermediate network to a host computer;

Figure 7 is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection; and

Figures 8 and 9 are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment.

DETAILED DESCRIPTION

As already mentioned above, it should be emphasized that the term "comprises/comprising" (replaceable by "includes/including") when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Embodiments of the present disclosure will be described and exemplified more fully hereinafter with reference to the accompanying drawings. The solutions disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the embodiments set forth herein.

In the following, various approaches to MIMO transmission will be disclosed and exemplified. At least some of the approaches provide increased throughput in one or more communication scenarios; compared to other approaches.

Generally, the term "user" is meant to encompass a user equipment (UE), as well as any other suitable wireless communication device (e.g., a station - STA - compliant with an IEEE802.il standard, an Internet-of-Things - loT- device, etc.), and the term "radio access node" is meant to encompass a base station (BS; e.g., a gNB), as well as any other suitable wireless communication node (e.g., an access point - AP - compliant with an IEEE802.il standard, an access point of a distributed MIMO system, etc.). In the following description, a user is often exemplified with a UE and a radio access node is often exemplified by a gNB. These exemplifications are not to be construed as limiting. Also generally, the term "channel" may refer to the transfer conditions only (i.e., conditions between transmitter antenna(s) and reception antenna(s)), or may also include the impact of one or more components of the transmitter and/or the impact of one or more components of the receiver.

MIMO communication in a wireless communication network is a technique wherein spatial diversity is exploited for using the same time and frequency resource to serve several users simultaneously, or to serve one user with multiple information streams. This is also referred to as spatial multiplexing. When MIMO is applied between a gNB and a UE, the gNB and/or the UE are equipped with multiple antennas. Spatial diversity typically enables more efficient utilization of the frequency spectrum compared to other communication techniques. Moreover, MIMO can reduce inter-cell interference and/or intra-cell interference, which may improve the possibilities for frequency re-use.

In spatial multiplexing, two or more data streams (MIMO layers) are transmitted over respective (ideally independent) channels that are spatially separated in space. The throughput increases when the number of simultaneously transmitted parallel MIMO layers increases.

Single user (SU) MIMO refers to a situation when the spatial layers are utilized for transmission to a single UE and multi user (MU) MIMO refers to a situation when the spatial layers are utilized for transmission to two or more UEs (each UE being associated with one or more of the layers).

Spatial channel separation may be efficiently utilized (e.g., to provide high throughput) via transmission and/or reception beamforming. DL transmission beamforming is a technique where a weighted coherent phase shift is added to each base station antenna element with the effect of creating a concentrated beam of energy from the base station antenna array towards a UE. The phase shifts are often collectively referred to as a pre-coder. There are various approaches for beamforming. For example, a Minimum Mean Square Estimator (MMSE) criterion or a Singular Value Decomposition (SVD) criterion may be used for computation of beam weights. For MU-MIMO, beamforming enables reduction of inter-user interference as well as energy concentration towards each UE, which typically improves throughput.

Efficient utilization of spatial channel separation (e.g., to provide high throughput) is typically also related to how well the number of MIMO layers are matched to the rank of the channel and/or to how well link adaptation (e.g., selection of modulation and coding scheme - MCS) is performed for the channel. If the selected number of MIMO layers and MCS are not well suited for the selected pre-coder, the throughput will typically not reach the full potential of the channel. For example, when the selected pre-coder can support a specific number (e.g., four) MIMO layers with the highest MCS index, while the gNB transmits a lower number of (e.g., only three) MIMO layers and/or uses a lower MCS index, the throughput will be restricted by the conservative selection of the gNB.

Thus, to properly configure MIMO communication (e.g., beamforming, selection of number of MIMO layers, link adaptation, etc.), it is beneficial to have information regarding the channel responses between the gNB and the users (e.g., in the form of downlink - DL - channel estimates). Such information is often called channel state information (CSI), and that exemplifying term will be used herein without limiting purposes. Information regarding these channel responses is useful for beamforming transmissions from the gNB towards the intended UE(s).

Generally, the UE(s) may be configured to perform measurements on reference signals (e.g., CSI reference signal - CSI-RS) transmitted by the gNB to determine DL channel estimates, and send user feedback (e.g., in the form of CSI reports) indicating the DL channel estimates to the gNB.

Also generally, the gNB may be configured to perform measurements on reference signals (e.g., sounding reference signal - SRS) transmitted by the UE(s) to determine uplink (UL) channel estimates.

In some situations, UL channel estimates are used by the gNB for DL beamforming. For example, it may be assumed that the DL channel is so similar to the reverse UL channel (possibly except for a power scaling factor) that beamforming based on the UL channel estimates can be applied for DL transmission instead of beamforming based on the DL channel estimates. This may be referred to as reciprocity based beamforming. One example, where reciprocity based beamforming may be applied is in time division duplex (TDD) systems.

It should be noted that, even though problems and solutions are exemplified herein in the context where uplink channel estimates are used for reciprocity based beamforming, embodiments are equally applicable in the context of any uplink channel estimate based beamforming.

In some typical wireless communication systems (e.g., fifth generation new radio - 5G NR), the gNB is configured to receive user feedback from UE(s) (e.g., in the form of CSI reports; typically including channel quality information - CQI, precoding matrix index - PM I, and rank indicator - Rl). The gNB is typically configured to use the user feedback for part of the configuration of downlink transmission (e.g., use the CQI for MCS selection, and/or use the Rl for selection of number of MIMO layers).

However, when the user feedback from UE(s) is based on an assumption of codebook based transmission (e.g., an assumption of SU-MIMO codebook based transmission), while the gNB applies reciprocity based beamforming (i.e., not codebook based beamforming) and possibly MU-MIMO, the downlink transmission configuration (e.g., MCS) will typically not be optimal for the beamforming that the gNB applies.

One solution to address such mismatches between downlink transmission configuration based on user feedback and reciprocity based beamforming is outer-loop adjustment (OLA; also referred to outer-loop link adaptation - OLLA) at the gNB. OLA approaches are well known and will not be elaborated on further herein. Some problems with OLA approaches is that they converge relatively slowly, that they are typically unable to follow rapidly varying channel conditions and/or dynamic MU pairing/grouping, and that they are unsuitable for scenarios with sporadic traffic.

Thus, it is a problem with reciprocity based beamforming that, when the DL channel (at the time of transmission) is not exactly equal to the UL channel (at the time of measurement), the reciprocity based beamforming may be less than optimal. Furthermore, it is a problem that MCS selection does not match the applied beamforming when it is based on an assumption of codebook based transmission, while the gNB applies reciprocity based beamforming.

Some embodiments address these and/or other problems by providing approaches in which the gNB (or another node) estimates a user-specific signal quality value (e.g., a signal-to- interference ratio, SIR, value and/ora signal-to-interference-and-noise ratio, SINR, value), which may then be used for the downlink MIMO transmission (e.g., for selection of MCS). Compared to approaches that relies on direct use of user feedback, the suggested approaches may provide improved selection of MCS, which can more fully exploit the benefits of the gNB beamforming. Compared to approaches that relies on direct use of user feedback together with OLA, the suggested approaches may provide faster convergence, and/or ability to follow rapidly varying conditions (e.g., of the channel and/or MU grouping), and/or suitability for scenarios with sporadic traffic.

In an ideal scenario, it is typically possible for the gNB to accurately predict the downlink transmission conditions for an upcoming downlink MU-MIMO transmission Such a predication may be based on the downlink beamforming precoder to be applied for the transmission, the downlink radio channel from gNB to UE, the interference plus noise (IpN) as experienced by the UE, and receiver particulars of the UE (e.g., spatial de-multiplexing, equalization, channel estimation, etc.). The prediction may, for example, comprise prediction of UE downlink reception behavior, which may enable the gNB to find an optimal number of layers and/or an optimal MCS for the UE.

In practical scenarios, however, it may be cumbersome (or even impossible) to accurately acquire the above-mentioned information in full (i.e., the downlink beamforming precoder to be applied for the transmission, the downlink radio channel from gNB to UE, the interference plus noise (IpN) as experienced by the UE, and receiver particulars of the UE).

Regarding the downlink radio channel from gNB to UE, it is possible to use the UL reference signaling to estimate the uplink radio channel and apply channel reciprocity assumption to estimate the downlink radio channel. However, the estimated uplink channel will include imperfections such as uplink noise and interference experienced at gNB when performing the uplink channel estimation. Thus, the estimated downlink channel derived by reciprocity will not be an accurate estimation of the actual downlink radio channel. This will be referred to as uplink channel estimation error. Using the downlink channel derived by reciprocity might lead to an erroneous estimation (e.g., overestimation) of the signal quality value (e.g., SIR, SINR, etc.), which in turn may lead to a sub-optimal MCS selection.

The precoder applied at the gNB may have a coarse granularity (e.g., to save computational complexity). For example, the precoder may be based on sub-band granularity (e.g., sub-carrier group granularity) rather than being based on sub-carrier granularity. A sub-band granularity precoder may be use the channel estimation for one of the sub-carriers in the sub-band for precoder calculation, and apply that precoder for all of the sub-carriers in the sub-band. Consequently, when the channel estimation for sub-carrier used for precoder calculation differs from the channels of other sub-carriers (which may occur, for example, for scenarios with strong frequency selectivity), the precoder is not optimal for all sub-carriers. This situation may also contribute to an erroneous situation (e.g., overestimation) of the signal quality value (e.g., SIR, SINR, etc.), which in turn may lead to a sub-optimal MCS selection.

As indicated above, the gNB typically does not have information available regarding the IpN experienced by the UE, nor information regarding UE reception behavior. The gNB may estimate the IpN experienced by the UE based on feedback from UE (e.g., CQI, PMI, Rl) together with the uplink radio channel estimation, and make some assumptions regarding UE reception behavior. Some embodiments provide approaches suitable for these purposes.

According to various embodiments, it is suggested to utilize information gathered (acquired) at the gNB to predict the downlink per-SCG SINR experienced at each UE for MIMO transmission (e.g., MU-MIMO). The acquired information typically includes one or more of: CSI feedback from the UE (user feedback), uplink channel estimation based on SRS (uplink channel estimates), downlink precoder applied by the gNB for beamforming (downlink beamforming precoder), scheduled UEs, number of layers for each scheduled UE, estimation of interference plus noise (IpN) experienced at the UE (estimated disturbances at the user), uplink channel estimation error (uncertainties discrepancies of the uplink channel estimate), and outer loop adjustment.

Taking account of the uplink channel estimation error, the SINR estimation can become more accurate. Furthermore, some embodiments suggest application of a frequency shift between the channel used for SINR estimation and the channel used for precoder calculation, which improves the accuracy in scenarios with frequency selective channels.

Figure 1 illustrates an example method 100 according to some embodiments. The method 100 is for a radio access node configured to communicate with a plurality of users by multiple-input multiple-output (MIMO) transmission.

The method 100 may be performed by the radio access node. Alternatively or additionally, the method 100 may be performed by a server node (e.g., a central network node or a cloud server) controlling the radio access node. Yet alternatively or additionally, the method 100 may be performed by a control node configured to control a plurality of access points of a distributed MIMO system.

The method 100 may be performed by a single node (e.g., a radio access node). Alternatively, the method 100 may be distributedly performed; i.e., two or more nodes (e.g., cloud computing nodes) each performing one or more steps, or part of a step, or the method 100.

In any case, the radio access node is configured to receive user feedback, which is typically indicative of downlink channel estimates. For example, the user feedback may be in the form of channel state information (CSI) reports, and/or the downlink channel estimates may be based on user measurements on channel state information reference signals (CSI-RS) transmitted by the radio access node. In some embodiments, the user feedback comprises one or more of: channel quality information (CQI), precoding matrix index (PMI), and rank indicator (Rl). In some embodiments, the user feedback is derived by the corresponding UE under a single-user SU assumption.

The radio access node is also configured to use uplink channel estimates for (e.g., reciprocity based) downlink beamforming of the MIMO transmission. For example, the uplink channel estimates may be based on radio access node measurements on uplink signals transmitted by the user(s).

One example of such uplink signal is sounding reference signals (SRS) transmitted by the user(s). The SRS is an uplink only signal. Generally, the SRS is transmitted by the user(s) to help the gNB obtain channel state information for each user.

Other uplink signals and/or uplink reference signals may -alternatively or additionally - be used to obtain uplink channel estimates. For example, when a user is scheduled for uplink data transmission, the Demodulation Reference Signal (DMRS) can be used to obtain uplink channel estimates.

The uplink channel estimate based (e.g., reciprocity based) beamforming may be determined by the radio access node (or by another suitable node, such as a server node; e.g., a central network node or a cloud server) based on the uplink channel estimates. As illustrated by optional step 110, the method may comprise acquiring information. In some embodiments, part/all of this information is already available when/where the method 100 is performed.

For example, step 110 may comprise acquiring user feedback (e.g., receiving a CSI report), as illustrated by sub-step 112.

Alternatively or additionally, step 110 may comprise performing - or otherwise acquiring - UL measurements (e.g., SRS measurements), as illustrated by sub-step 114.

Yet alternatively or additionally, step 110 may comprise retrieving the beamforming (BF) setting (i.e., the downlink beamforming precoder), as illustrated by sub-step 116. The BF setting may comprise the BF setting used when the DL measurements were made and/or the BF setting that will be used for the upcoming MIMO transmission.

Yet alternatively or additionally, step 110 may comprise estimating disturbances at the user 8^, as illustrated by sub-step 117. The estimated disturbances may comprise inter-user interference (experienced at the user) caused by using the uplink channel estimates for downlink beamforming. In some embodiments, the estimate of disturbances at the user is determined based on the user feedback. Alternatively or additionally, the estimate of disturbances at the user may be determined from one or more of: a reciprocity version of uplink channel estimates used for downlink beamforming H^ ^coder , beamforming indicated by the user feedback W ^M/ , and signal quality value S1NR^ _B and rank Rl^ ^b indicated by the user feedback. For example, the estimated disturbances at the user may be determined from an effect of a combination H™ ¹ of the beamforming indicated by user feedback and the reciprocity version of uplink channel estimates used for downlink beamforming, as biased by the signal quality value and rank indicated by user feedback.

Yet alternatively or additionally, step 110 may comprise determining a variance (and/or other relevant uncertainties/discrepancies) for the uplink channel measurements, as illustrated by sub-step 118. In some embodiments, uncertainties of the uplink channel estimate are determined from the downlink beamforming precoder and a variance 8 , _{srs h t} (b,p~) relating to the uncertainties of the uplink channel estimates. Yet alternatively or additionally, step 110 may comprise retrieving the current OLA setting, as illustrated by sub-step 119.

In step 120, a user-specific signal quality value (e.g., an SIR value or an SINR value) is estimated. For example, the user-specific signal quality value may be determined based on spectrum efficiency (e.g., throughput) as illustrated by sub-step 140.

In any case, the signal quality value y _{u fc} (Z) is estimated by combining a desired power component P ^s ^ _k (/) and a total power component

The desired power component is determined (as illustrated by sub-step 134) from an extended downlink channel model H^ _k . The extended downlink channel model is a combination of a downlink beamforming precoder an estimation of a downlink radio channel H ^s ^ _k ^t , and a receiver model V _{u k} of the one or more user determined (as illustrated by sub-step 132) based on the user feedback.

The total power component P^(Z) is also determined (as illustrated by sub-step 136) from the extended downlink channel model H^ _k , and is compensated for uncertainties of the uplink channel estimate R^ _k and/or estimated disturbances at the user For example, the total power component may comprise inter-layer interference power : ) || and/or inter- user interference power ) || , as derived from the extended downlink channel model. Alternatively or additionally, the compensation of the total power component may comprise a combination of the receiver model of the one or more userwith uncertainties of the uplink channel estimate and/or estimated disturbances at the user.

As illustrated by 130, sub-steps 132, 134, 136 are typically performed per sub-carrier group.

According to some embodiments, the receiver model of the one or more user matches a combination of the downlink beamforming precoder and the estimation of the downlink radio channel, as compensated for uncertainties of the uplink channel estimate R^ _k and/or estimated disturbances at the user

The estimation of the downlink radio channel may comprise a reciprocity version of uplink channel estimates, wherein uplink channel estimates used for the estimation of the downlink radio channel relate to one or more frequency sub-band and/or sub-carrier, which is different than a frequency sub-band and/or sub-carrier related to uplink channel estimates used for the downlink beamforming precoder (i.e., implementing a frequency shift; see also Figure 2B). For example, uplink channel estimates used for the estimation of the downlink radio channel and uplink channel estimates used for the downlink beamforming precoder may relate to different sub-carriers within a sub-carrier group.

In some embodiments, estimating the user-specific signal quality value in step 120 comprises estimating intermediate user-specific signal quality values per sub-carrier group (as illustrated by sub-step 138), and transforming S1NR21CC (for each of a plurality of modulation order hypotheses) each intermediate user-specific signal quality value to a spectrum efficiency value (e.g., throughout).

The spectrum efficiency values may be accumulated (for each of the plurality of modulation order hypotheses) over a plurality of sub-carrier groups, a modulation order mod _max may be selected from the plurality of modulation order hypotheses (based on the accumulated spectrum efficiency values), and the accumulated spectrum efficiency values of the selected modulation order may be transformed 1CC2S1NR to the estimated user-specific signal quality value (possibly after averaging over layers).

In step 160, downlink (DL) MIMO transmission to one or more user of the plurality of users is performed (e.g., when the method 100 is performed by a radio access node) or caused (e.g., when the method 100 is performed by a server node or a control node). The DL MIMO transmission to the one or more user is based on the respective estimated signal quality value. The DL MIMO transmission may be a single-user (SU) MIMO transmission or a multi-user (MU) MIMO transmission.

In some embodiments, DL MIMO transmission may comprise using the estimated signal quality value for controlling the MIMO configuration (e.g., a transport formal selection) of an upcoming transmission occasion, as illustrated by optional sub-step 150. For example, the estimated signal quality value may be used for link adaptation, as illustrated by 152. When the estimated signal quality value is used for link adaptation, the link adaptation may comprise selecting a modulation and coding scheme (MCS) that is associated with the estimated signal quality value. For example, any suitable mapping from SIR/SINR to MCS may be applied.

Generally, it should be noted that any embodiment may be combined with other techniques for MIMO transmission control, as suitable. For example, OLA may be applied in combination with link adaptation based on the respective estimated signal quality values.

Some various ways to implement various embodiments will now be presented through an example of MU-MIMO transmission with M scheduled UEs, where the gNB to calculates MU- MIMO SINR and uses the calculated MU-MIMO SINR for MCS selection.

Information collection (compare with step 110 of Figure 1)

In relation to the scheduled UEs - each UE with an associated number of MIMO layers -the gNB acquires the following information for UE u:

1) CSI feedback from UE, including CQI, PMI, and Rl (compare with sub-step 112), wherein: RI^ ^b denotes Rl of the feedback from UE with index u, denotes the pre-coder based on PMI of the feedback from UE with index u, at sub-carriergroup (SCG) index k, wherein N _t denotes the number of antennas of the gNB, and

CQI denotes CQI index of the feedback from UE with index u, wherein the CQI index can indicate wideband CQI or sub-band CQI (e.g., in accordance with 3GPP standardization).

2) gNB channel estimation based on SRS (compare with sub-step 114), wherein:

H^ ^coder g C(7 _t , / _r ) denotes a channel matrix estimated based on SRS for UE with index u, at sub-carriergroup (SCG) index k, wherein N _r denotes the number of antennas at the UE, and

^G C(AT _t , N _r ) denotes a channel matrix estimated based on SRS for UE with index u, at sub-carrier group (SCG) index k, wherein a sub-carrier used for H^^ ^coder j _s different from a sub-carrier used for H ^s ^ ^t (see Figure 2B for illustration).

3) gNB pre-coder for beamforming based on the SRS based channel estimation (compare with sub-step 116), wherein: - rming pre-coder for UE with index u, at subcarrier group (SCG) index k, wherein L _u denotes the number of layers for the UE.

4) OLA value (compare with sub-step 119), wherein:

OLA[L _U ] denotes the outer loop adjustment value in dB for L _u . It should be noted that the OLA values for different number of layers can be different or can be identical.

5) Estimation of the interference plus noise (IpN) as experienced at the UE (compare with sub-step 117), wherein: denotes the IpN covariance for UE with index u.

6) Uncertainties of the uplink channel estimate (compare with sub-step 118), wherein: p) denotes the variance of the SRS channel estimation error for the Z?-th gNB antenna or beam and the p-th UE antenna port of UE u. This variance may be achieved in any suitable way. Examples may be found in section 5.3 of "Channel Estimation Error Model for SRS in LTE" by Pontus Arvidson, 2011, Master Thesis, KTH Electrical Engineering, Stockholm, Sweden, XR-EE-SB 2011:006.

One example for calculating is the method in "A vector-perturbation technique for nearcapacity multiantenna multi-user communication - Part I: channel inversion and regularization" by B. C. B. Peel, B. M. Hochwald, and A. L. Swindlehurst, in IEEE Transactions on Communications, vol. 53, no. 1, pp. 195-202, 2005. Other examples can also be found in the literature. According to some embodiments, a general principle is that is calculated to minimize the inter-user and/or inter layer interference; i.e., it provides orthogonalization or nulling between the users and/or different MIMO layers. For more details about possible principles of choosing please see the discussion in Chapters 9 and 11 of the book "5G NR: The Next Generation Wireless Access Technology" by Erik Dahlman, Stefan Parkvall, and Johan Skbld, 2018 Elsevier Ltd, ISBN: 978-0-12-814323-0.

The IpN covariance 8^ may be determined based on H^^ ^coder and the UE feedback. For example, a wideband IpN value may be provided based on the Shannon capacity with a SINR compensation factor as follows. It should be noted that this IpN covariance approach is merely an example and that other IpN estimations may be equally applicable.

Based on W™ ¹ and H^ ^coder , a PMI precoded channel matrix for UE u at sub-carrier group (SCG) index k may be determined as = (Hy ^r _fe ^ecoder ) ⁷ ’l4/'u ^M/ G ^(N _r , RIu ^b )- The CQI CO! index of the UE feedback may be related to a corresponding SINR va\ue SINR _{u dB} through a CQI- to-SINR mapping, wherein SINR^ ^Q _B denotes a wideband SINR based on CQI for UE u in dB. Then, the wideband IpN covariance may be estimated through: wherein the first term may represent the power experienced at the UE, and the second term may represent compensation. The regularization factor A _ipn may be applied to stabilize the matrix inversion, wherein a _ipn is a pre-configured value (an example typical setting is a _ipn = 0.001). N _scg denotes the number of SCGs in the channel bandwidth.

Per-SCG SINR calculation and link adaptation (compare with steps 120 and 150 of Figure 1)

The SINR is calculated for each UE and for each SCG. When the gNB transmits multiple layers to one or more of the scheduled UEs, the SINR is first calculated for each layer, and then converted to get the per-SCG SINR.

A model of the UE receiver is determined (compare with sub-step 132) by assuming, for example, MMSE reception and taking account of and the uplink channel estimation error. The corresponding receiver model for UE u, at sub-carrier group (SCG) index k, may be represented as: where R ^s _k ^G ^(N _r , N _r ~) is a diagonal matrix corresponding to inter-user interference caused by the uplink channel estimation error, wherein the p-th diagonal element may be expressed as The signal power for the Z-th layer of UE u at the Zc-th SCG may be estimated (compare with sub-step 134) as :

P3® = I«3('.O| ² , where |- 1 ² is the norm operation of a complex number, is an equivalent channel matrix for UE u after receiver processing.

The total signal power experienced at UE u, for the Z-th layer, at the Zc-th SCG may be represented (compare with sub-step 136) as: where ||-|| ² is the square of Euclidean norm of a vector, is an inter-user interference matrix for UE u after receiver processing, and R^ _k is diagonal matrix corresponding to the inter-user interference caused by the uplink channel estimation error, with

The per-layer per-SCG downlink SINR for the Z-th layer of the UE u, at the Zc-th SCG may be estimated (compare with sub-step 138) as:

The per-layer per-SCG downlink SINR may be converted to per-SCG SINR. The conversions may be performed according to any suitable approach, and an example is provided as follows.

For each SCG k, the information carried per carrier (ICC; e.g., spectrum efficiency or throughput) may be calculated for each layer I of UE u using a conversion function S1NR21CC as: wherein represents the set of available modulation orders. Then, the total ICC over all SCGs and all layers may be determined as: and the modulation order mod _max that maximizes the total ICC (or satisfies some other suitable criterion, e.g., leading to the total ICC exceeding an ICC threshold) may be determined through:

Then, the total ICC may be calculated over multiple layers for each SCG - normalized by the number of layers: and the inverse of the conversion function S1NR21CC may be used to convert from ICC to SINR to get the per-SCG SINR (compare with sub-step 140):

The per-SCG SINR y _{u k} calculated in Step 1 can be used in combination with OLA to provide an adjusted SINR value SINR _{u k} = y^ ^B _k + OLA _U [L _U ] for the Zc-th SCG of the UE u. Either y _{u k} or SlNR _{u k} may be used for link adaptation (compare with sub-step 152).

Figure 2A schematically illustrates example functions according to some embodiments in the form of a functional arrangement 200. For example, the functional arrangement 200 may be seen as an exemplification of the method 100 of Figure 1. Alternatively or additionally, the functional arrangement 200 may be seen as an exemplification of an architecture for the apparatus 300 of Figure 3 (to be described later herein).

According to Figure 2A, a function 210 uses scheduling information (SCH) 206, user feedback (UFB) 201, uplink channel estimation (ULCE) 202, downlink transmitter pre-coder (PC) 203, an uplink channel estimation error (CEE) 207, estimated IpN 205 experienced at the UE, and outer loop adjustment values (OLA) 204 to perform SINR estimation (SINR EST) 211. The downlink transmitter pre-coder may be based on the uplink channel estimation. The estimated SINR is used for link adaptation (LA) 213.

Referring to Figure 1, block 201 may be compared to 112, block 202 may be compared to 114, block 203 may be compared to 116, block 204 may be compared to 119, block 205 may be compared to 117, and block 207 may be compared to 118. Block 211 may be compared to 120, and block 213 may be compared to 152. Figure 2B schematically illustrates an example sub-carrier group (SCG) 270 according to some embodiments. The sub-carrier group 270 comprises first and second physical resource blocks (PRB1, PRB2) 280, 290. The first and second physical resource blocks 280, 290 each comprises twelve sub-carriers (scl-scl2).

To exemplify how the estimation of the downlink radio channel H^ ^coder , may be based on a reciprocity version of uplink channel estimates, the uplink channel estimates used for the estimation of the downlink radio channel may relate to a sub-carrier (e.g., the first sub-carrier 281) of PRB1, when the uplink channel estimates used for the downlink beamforming precoder relate to a sub-carrier (e.g., the first sub-carrier 291) of PRB2. Thus, H^^ ^coder may relate to subcarrier 291 and H^ ^L ^ ^t may relate to sub-carrier 281.

Thereby, there is a frequency shift between the uplink channel estimates used for the estimation of the downlink radio channel and the uplink channel estimates used for the downlink beamforming precoder. As already mentioned, this typically improves the signal quality value estimation - and thereby the link adaptation - for frequency selective channels.

Figure 3 schematically illustrates an example apparatus 300 according to some embodiments. The apparatus 300 is for a radio access node configured for communication with a plurality of users by multiple-input multiple-output (MIMO) transmission.

For example, the apparatus 300 may be comprised in the radio access node 310 as illustrated in Figure 3, in a server node (e.g., a central network node or a cloud server) controlling the radio access node, or in a control node configured to control a plurality of access points of a distributed MIMO system.

Alternatively or additionally, the apparatus 300 may be configured to execute, or cause execution of, one or more method steps as described in connection with the method 100 of Figure 1.

In any case, the radio access node is configured to receive user feedback. The radio access node is also configured to use uplink channel estimates for downlink beamforming of the MIMO transmission. The apparatus 300 comprises a controller (CNTR; e.g., controlling circuitry or a control module)

320.

The controller 320 is configured to cause estimation of a user-specific signal quality value (compare with step 120 of Figure 1).

To this end, the controller 320 may comprise, or be otherwise associated with (e.g., connected, or connectable, to) an estimator (EST; e.g., estimating circuitry or an estimation module) 322. The estimator 322 may be configured to estimate the user-specific signal quality value.

The controller 320 is also configured to cause DL MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value (compare with step 160 of Figure 1).

To this end, the controller 320 may comprise, or be otherwise associated with (e.g., connected, or connectable, to) a transmitter (TX; e.g., transmitting circuitry or a transmission module) 330 of the radio access node. The transmitter 330 may be configured to perform the DL MIMO transmission. It should be noted that, when the apparatus 300 is comprised in another node than the radio access node, the controller 320 may be associated with the transmitter via a connection between the node comprising the controller 320 and the radio access node.

In some embodiments, the controller 320 may be configured to cause the respective estimated signal quality value to be used for controlling MIMO configuration of an upcoming transmission occasion (compare with step 150 of Figure 1). For example, the controller 320 may be configured to cause the respective estimated signal quality value to be used for link adaptation.

To this end, the controller 320 may comprise, or be otherwise associated with (e.g., connected, or connectable, to) a transmission controller (TC; e.g., transmission controlling circuitry or a transmission control module) 324. The transmission controller 324 may be configured to control MIMO configuration of an upcoming transmission occasion based on the respective estimated signal quality value.

In some embodiments, the controller 320 may be configured to cause acquisition of information such as - for example - user feedback, UL measurements, BF setting, and OLA setting (compare with step 110 of Figure 1). To this end, the controller 320 may comprise, or be otherwise associated with (e.g., connected, or connectable, to) an acquirer (ACQ; e.g., acquiring circuitry or an acquisition module) 321. The acquirer 321 may be configured to acquire the information.

It should be noted that features and/or advantages described herein in connection with any of Figures 1, 2A, and 2B are generally equally applicable (mutatis mutandis) for the apparatus 300 of Figure 3, even if not explicitly mentioned in connection thereto.

Figure 4A schematically illustrates an example communication scenario according to some embodiments. The scenario of Figure 4A comprises a radio access node in the form of a base station (BS) 410 and a plurality of users in the form of UEs 411, 412, 413.

The BS 410 may be configured to communicate with the UEs 411, 412, 413 by MIMO transmission. To this end, the BS 410 may comprise the apparatus 300 of Figure 3. Alternatively or additionally, the BS 410 may be configured to execute one or more steps of the method 100 of Figure 1.

Figure 4B schematically illustrates an example communication scenario according to some embodiments. The scenario of Figure 4B comprises a radio access node in the form of a base station (BS) 420 and a plurality of users in the form of UEs 421, 422, 423. The scenario of Figure 4B also comprises a server node (SN) 425. For example, the SN 425 may be a central network node or a cloud server.

The BS 420 may be configured to communicate with the UEs 421, 422, 423 by MIMO transmission; under the control of the SN 425. To this end, the SN 425 may comprise the apparatus 300 of Figure 3. Alternatively or additionally, the SN 425 may be configured to execute one or more steps of the method 100 of Figure 1.

Referring to Figure 1, the SN 425 may, for example, be configured to perform step 120 and provide the user-specific signal quality value(s) to the BS 420, while the BS 420 is configured to perform step 160.

Figure 4C schematically illustrates an example communication scenario according to some embodiments. The scenario of Figure 4C comprises a plurality of radio access nodes in the form of access points (AP) 435, 436, 437 of a distributed MIMO system, and a plurality of users in the form of UEs 431, 432, 433. The scenario of Figure 4C also comprises a control node (CN) 430 of the distributed MIMO system, which is configured to control the APs 435, 436, 437.

The distributed MIMO system may be configured to communicate with the UEs 431, 432, 433 by MIMO transmission; under the control of the CN 430. To this end, the CN 430 may comprise the apparatus 300 of Figure 3. Alternatively or additionally, the CN 430 may be configured to execute one or more steps of the method 100 of Figure 1.

Referring to Figure 1, the CN 430 may, for example, be configured to perform step 120 and provide the user-specific signal quality value(s) to the relevant AP(s) 435, 436, 437, which are configured to perform step 160. Alternatively, the CN 430 may be configured to perform step 120 and the link adaptation of 160 and provide the selected MCS to the relevant AP(s) 435, 436, 437, which are configured to perform the actual transmission of step 160.

It should be noted that features and/or advantages described herein in connection with any of the Figures is equally applicable (as suitable) for any other Figure, even if not explicitly mentioned in connection thereto.

The described embodiments and their equivalents may be realized in software or hardware or a combination thereof. The embodiments may be performed by general purpose circuitry. Examples of general purpose circuitry include digital signal processors (DSP), central processing units (CPU), co-processor units, field programmable gate arrays (FPGA) and other programmable hardware. Alternatively or additionally, the embodiments may be performed by specialized circuitry, such as application specific integrated circuits (ASIC). The general purpose circuitry and/or the specialized circuitry may, for example, be associated with or comprised in an apparatus such as a radio access node, a server node, or a distributed MIMO control node.

Embodiments may appear within an electronic apparatus (such as a radio access node, a server node, or a distributed MIMO control node) comprising arrangements, circuitry, and/or logic according to any of the embodiments described herein. Alternatively or additionally, an electronic apparatus (such as a radio access node, a server node, or a distributed MIMO control node) may be configured to perform methods according to any of the embodiments described herein. According to some embodiments, a computer program product comprises a non-transitory computer readable medium such as, for example, a universal serial bus (USB) memory, a plugin card, an embedded drive, or a read only memory (ROM). Figure 5 illustrates an example computer readable medium in the form of a compact disc (CD) ROM 500. The computer readable medium has stored thereon a computer program comprising program instructions. The computer program is loadable into a data processor (PROC; e.g., a data processing unit) 520, which may, for example, be comprised in a device 510 (e.g., a radio access node, a server node, or a distributed MIMO control node). When loaded into the data processor, the computer program may be stored in a memory (MEM) 530 associated with, or comprised in, the data processor. According to some embodiments, the computer program may, when loaded into, and run by, the data processor, cause execution of method steps according to, for example, the method illustrated in Figure 1, or as otherwise described herein.

With reference to Figure 6, in accordance with an embodiment, a communication system includes a telecommunication network 610, such as a 3GPP-type cellular network, which comprises an access network 611, such as a radio access network, and a core network 614. The access network 611 comprises a plurality of base stations 612a, 612b, 612c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 613a, 613b, 613c. Each base station 612a, 612b, 612c is connectable to the core network 614 over a wired or wireless connection 615. A first user equipment (UE) 691 located in coverage area 613c is configured to wirelessly connect to, or be paged by, the corresponding base station 612c. A second UE 692 in coverage area 613a is wirelessly connectable to the corresponding base station 612a. While a plurality of UEs 691, 692 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 612.

The telecommunication network 610 is itself connected to a host computer 630, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 630 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 621, 622 between the telecommunication network 610 and the host computer 630 may extend directly from the core network 614 to the host computer 630 or may go via an optional intermediate network 620. The intermediate network 620 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 620, if any, may be a backbone network or the Internet; in particular, the intermediate network 620 may comprise two or more sub-networks (not shown).

The communication system of Figure 6 as a whole enables connectivity between one of the connected UEs 691, 692 and the host computer 630. The connectivity may be described as an over-the-top (OTT) connection 650. The host computer 630 and the connected UEs 691, 692 are configured to communicate data and/or signaling via the OTT connection 650, using the access network 611, the core network 614, any intermediate network 620 and possible further infrastructure (not shown) as intermediaries. The OTT connection 650 may be transparent in the sense that the participating communication devices through which the OTT connection 650 passes are unaware of routing of uplink and downlink communications. For example, a base station 612 may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 630 to be forwarded (e.g., handed over) to a connected UE 691. Similarly, the base station 612 need not be aware of the future routing of an outgoing uplink communication originating from the UE 691 towards the host computer 630.

Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to Figure 7. In a communication system 700, a host computer 710 comprises hardware 715 including a communication interface 716 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 700. The host computer 710 further comprises processing circuitry 718, which may have storage and/or processing capabilities. In particular, the processing circuitry 718 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer 710 further comprises software 711, which is stored in or accessible by the host computer 710 and executable by the processing circuitry 718. The software 711 includes a host application 712. The host application 712 may be operable to provide a service to a remote user, such as a UE 730 connecting via an OTT connection 750 terminating at the UE 730 and the host computer 710. In providing the service to the remote user, the host application 712 may provide user data which is transmitted using the OTT connection 750. The communication system 700 further includes a base station 720 provided in a telecommunication system and comprising hardware 725 enabling it to communicate with the host computer 710 and with the UE 730. The hardware 725 may include a communication interface 726 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 700, as well as a radio interface 727 for setting up and maintaining at least a wireless connection 770 with a UE 730 located in a coverage area (not shown in Figure 7) served by the base station 720. The communication interface 726 may be configured to facilitate a connection 760 to the host computer 710. The connection 760 may be direct or it may pass through a core network (not shown in Figure 7) of the telecommunication system and/orthrough one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 725 of the base station 720 further includes processing circuitry 728, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station 720 further has software 721 stored internally or accessible via an external connection.

The communication system 700 further includes the UE 730 already referred to. Its hardware 735 may include a radio interface 737 configured to set up and maintain a wireless connection 770 with a base station serving a coverage area in which the UE 730 is currently located. The hardware 735 of the UE 730 further includes processing circuitry 738, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE 730 further comprises software 731, which is stored in or accessible by the UE 730 and executable by the processing circuitry 738. The software 731 includes a client application 732. The client application 732 may be operable to provide a service to a human or non-human user via the UE 730, with the support of the host computer 710. In the host computer 710, an executing host application 712 may communicate with the executing client application 732 via the OTT connection 750 terminating at the UE 730 and the host computer 710. In providing the service to the user, the client application 732 may receive request data from the host application 712 and provide user data in response to the request data. The OTT connection 750 may transfer both the request data and the user data. The client application 732 may interact with the user to generate the user data that it provides. It is noted that the host computer 710, base station 720 and UE 730 illustrated in Figure 7 may be identical to the host computer 630, one of the base stations 612a, 612b, 612c and one of the UEs 691, 692 of Figure 6, respectively. This is to say, the inner workings of these entities may be as shown in Figure 7 and independently, the surrounding network topology may be that of Figure 6.

In Figure 7, the OTT connection 750 has been drawn abstractly to illustrate the communication between the host computer 710 and the use equipment 730 via the base station 720, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE 730 or from the service provider operating the host computer 710, or both. While the OTT connection 750 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).

The wireless connection 770 between the UE 730 and the base station 720 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 730 using the OTT connection 750, in which the wireless connection 770 forms the last segment. More precisely, the teachings of these embodiments may improve the throughput and thereby provide benefits such as one or more of: reduced user waiting time, relaxed restriction on file size, and better responsiveness.

A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 750 between the host computer 710 and UE 730, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 750 may be implemented in the software 711 of the host computer 710 or in the software 731 of the UE 730, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 750 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 711, 731 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 750 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the base station 720, and it may be unknown or imperceptible to the base station 720. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer's 710 measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the software 711, 731 causes messages to be transmitted, in particular empty or 'dummy' messages, using the OTT connection 750 while it monitors propagation times, errors etc.

FIGURE 8 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figures 6 and 7. For simplicity of the present disclosure, only drawing references to Figure 8 will be included in this section. In a first step 810 of the method, the host computer provides user data. In an optional sub-step 811 of the first step 810, the host computer provides the user data by executing a host application. In a second step 820, the host computer initiates a transmission carrying the user data to the UE. In an optional third step 830, the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional fourth step 840, the UE executes a client application associated with the host application executed by the host computer.

FIGURE 9 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figures 6 and 7. For simplicity of the present disclosure, only drawing references to Figure 9 will be included in this section. In a first step 910 of the method, the host computer provides user data. In an optional sub-step (not shown) the host computer provides the user data by executing a host application. In a second step 920, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step 930, the UE receives the user data carried in the transmission. Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used.

Reference has been made herein to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the claims.

For example, the method embodiments described herein discloses example methods through steps being performed in a certain order. However, it is recognized that these sequences of events may take place in another order without departing from the scope of the claims. Furthermore, some method steps may be performed in parallel even though they have been described as being performed in sequence. Thus, the steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step.

In the same manner, it should be noted that in the description of embodiments, the partition of functional blocks into particular units is by no means intended as limiting. Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. Furthermore, functional blocks described herein as being implemented as two or more units may be merged into fewer (e.g. a single) unit.

Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever suitable. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa.

Hence, it should be understood that the details of the described embodiments are merely examples brought forward for illustrative purposes, and that all variations that fall within the scope of the claims are intended to be embraced therein. Some numbered embodiments

1. A base station configured to communicate with a user equipment ( U E), wherein the base station is a radio access node configured for communication with a plurality of users by multiple-input multiple-output, MIMO, transmission, wherein the UE is one of the plurality of users, wherein the radio access node is configured to receive user feedback, and wherein the radio access node is configured to use uplink channel estimates for downlink beamforming of the MIMO transmission, the base station comprising a radio interface and processing circuitry configured to: estimate a user-specific signal quality value, wherein the signal quality value is a signal-to- interference ratio, SIR, value and/or a signal-to-interference-and-noise ratio, SINR, value; and perform or cause downlink MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value, wherein estimating the signal quality value comprises combining a desired power component and a total power component, wherein the desired power component is determined from an extended downlink channel model, wherein the total power component is determined from the extended downlink channel model, and is compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user, and wherein the extended downlink channel model is a combination of a downlink beamforming precoder, an estimation of a downlink radio channel, and a receiver model of the one or more user determined based on the user feedback.

2. A communication system including a host computer comprising: processing circuitry configured to provide user data; and a communication interface configured to forward the user data to a cellular network for transmission to a user equipment (UE), wherein the cellular network comprises a base station configured to communicate with the UE, wherein the base station is a radio access node configured for communication with a plurality of users by multiple-input multiple-output, MIMO, transmission, wherein the UE is one of the plurality of users, wherein the radio access node is configured to receive user feedback, and wherein the radio access node is configured to use uplink channel estimates for downlink beamforming of the MIMO transmission, the base station having a radio interface and processing circuitry, the base station's processing circuitry configured to: estimate a user-specific signal quality value, wherein the signal quality value is a signal-to- interference ratio, SIR, value and/or a signal-to-interference-and-noise ratio, SINR, value; and perform or cause downlink MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value, wherein estimating the signal quality value comprises combining a desired power component and a total power component, wherein the desired power component is determined from an extended downlink channel model, wherein the total power component is determined from the extended downlink channel model, and is compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user, and wherein the extended downlink channel model is a combination of a downlink beamforming precoder, an estimation of a downlink radio channel, and a receiver model of the one or more user determined based on the user feedback.

3. The communication system of embodiment 2, further including the base station.

4. The communication system of embodiment 3, further including the UE, wherein the UE is configured to communicate with the base station.

5. The communication system of embodiment 4, wherein: the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application.

6. A method implemented in a base station configured to communicate with a user equipment (UE), wherein the base station is a radio access node configured for communication with a plurality of users by multiple-input multiple-output, MIMO, transmission, wherein the UE is one of the plurality of users, wherein the radio access node is configured to receive user feedback, and wherein the radio access node is configured to use uplink channel estimates for downlink beamforming of the MIMO transmission, the method comprising: estimating a user-specific signal quality value, wherein the signal quality value is a signa I- to-interference ratio, SIR, value and/or a signal-to-interference-and-noise ratio, SINR, value; and performing or causing downlink MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value, wherein estimating the signal quality value comprises combining a desired power component and a total power component, wherein the desired power component is determined from an extended downlink channel model, wherein the total power component is determined from the extended downlink channel model, and is compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user, and wherein the extended downlink channel model is a combination of a downlink beamforming precoder, an estimation of a downlink radio channel, and a receiver model of the one or more user determined based on the user feedback.

7. A method implemented in a communication system including a host computer, a base station and a user equipment (UE), wherein the base station is configured to communicate with the UE, wherein the base station is a radio access node configured for communication with a plurality of users by multiple-input multiple-output, MIMO, transmission, wherein the UE is one of the plurality of users, wherein the radio access node is configured to receive user feedback, and wherein the radio access node is configured to use uplink channel estimates for downlink beamforming of the MIMO transmission, the method comprising: estimating a user-specific signal quality value, wherein the signal quality value is a signa I- to-interference ratio, SIR, value and/or a signal-to-interference-and-noise ratio, SINR, value; and performing or causing downlink MIMO transmission to one or more user of the plurality of users based on respective estimated signal quality value, wherein estimating the signal quality value comprises combining a desired power component and a total power component, wherein the desired power component is determined from an extended downlink channel model, wherein the total power component is determined from the extended downlink channel model, and is compensated for uncertainties of the uplink channel estimate and/or estimated disturbances at the user, and wherein the extended downlink channel model is a combination of a downlink beamforming precoder, an estimation of a downlink radio channel, and a receiver model of the one or more user determined based on the user feedback. The method of embodiment 7, further comprising: at the base station, transmitting the user data. The method of embodiment 8, wherein the user data is provided at the host computer by executing a host application, the method further comprising: at the UE, executing a client application associated with the host application.