According to one or more embodiments, a network node configured to communicate with a wireless device is provided. The network node includes processing circuitry configured to: receive multilayer feedback; determine a beamformer for transmission of a first quantity of transmission layers where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers, where the first quantity of transmission layers is a less than the second quantity of transmission layers; and cause the transmission using the beamformer.

TECHNICAL FIELD

Wireless communication and in particular, a low rank beamforming based at least on multi-layer feedback.

BACKGROUND

A wireless network including a network node (e.g., gNB) or a transmitter may send the control data (e.g., physical downlink control channel (PDCCH)) over a single logical port (e.g., one layer), or a few ports using a beamformer is considered. When information regarding the wireless device's direction or channel is not available at the network node, the network node may prefer to employ common beamforming optimized for the cell shape. On the other hand, it is also possible to employ a wireless device specific beamformer. Third Generation Partnership Project (3GPP) Release 15+ (also referred to as New Radio (NR) or 5′ Generation (5G)) allows for wireless device-specific beamforming for some of the control channel information transmission. Determining a suitable beamformer for such channels (e.g., PDCCH) using available feedback information can significantly improve the system performance as it may allow for simultaneously utilizing both multiplexing and diversity gains offered by multi-path propagation.

However, existing systems disadvantageously rely on a randomized beamformer. For example, when the network node attempts to perform wireless device specific beamforming to transmit data, if a codebook based Single User-Multiple Input Multiple Output (SU-MIMO) transmission is employed using Type-1 feedback, the Channel State Information-Reference Signal (CSI-RS) feedback contains (among others) a precoder matrix index (PMI) that indicates the wireless device's preference on the precoder to be used by network node. In case of rank>1 feedback, the PMI corresponds to a N_ports×RI precoder matrix where RI is the rank indicator. So, in 3GPP Release 15+ codebook, each column of the precoder in the codebook indicates a preferred direction for the corresponding layer. Since this precoder is evaluated with the specific constraint of sending RI layers, it may not directly indicate the best direction for a single-layer transmission or cases where it may be desired to overwrite the wireless device's desired/requested RI with a smaller value due to, for example, unprecedented channel conditions. In particular, PDCCH is transmitted using a single layer and if a wireless device specific beamforming is to be employed, existing systems attempt to randomize the beamformer among the directions indicated by the PMI. However, this may reduce the gains for some of the transmission instances since some of the directions may not be able to fully utilize the channel between the network node and the wireless device in a satisfactory manner.

Further, randomizing beamforming may also cause a flashlight effect in other cells. In addition, it may also create a non-stable PDCCH channel transmission for the wireless device when the PDCCH is being transmitted over a beam that is not suitable for single-layer transmission even though that direction may be suitable in case of multi-layer transmission. In other words, insufficient knowledge on the strength of the multipaths in the directions indicated by the wireless device may disadvantageously lead to mechanisms that perform wireless device specific beamforming without sufficient knowledge of the multipaths.

SUMMARY

Some embodiments advantageously provide a method and system for a low rank beamforming based at least on multi-layer feedback.

In one or more embodiments, a low-complexity and agile beam-former calculation method that may only require the knowledge of a precoder (or PMI) that is fedback from the wireless device to network node. It may be assumed that the feedback indicates multiple layer transmissions, e.g., RI>1. In this case, each column of the precoder contains a suitable beamformer for the corresponding layer. However, unlike existing system that simply randomly select a beamformer from among the directions, one or more embodiments described herein uses information on all the directions indicated by the precoder columns and determines a single or (a few if needed) beamformer that can generate a radiation pattern suitable for a single-layer (or lower-rank) transmission.

Further, based on, for example, the power requirements and tapering efficiencies, the precoder may be converted to a constant-modulus phased array beamformer. One or more embodiments described herein allows for a layer-weighting algorithm that is adaptable to the time-varying channels observed by the wireless device and that can dynamically determine the significance of each layer's direction to a multi-directional transmission carrying a single-layer data. Layer partitioning may be applied to one or more embodiments to groups of layers to create more than one stream if low-rank transmission having a rank larger than 1 is desired.

Further, in one or more embodiments, a dynamic beam-broadening method is applied to low-rank precoder to compensate the CSI feedback delays due to loss or incorrect reception of feedback. Also, one or more embodiments described herein can be combined with selective nulling techniques to avoid undesired interference creations towards interference-prone directions.

One or more embodiments advantageously use the information directly provided by the wireless device feedback such as not to require extra information to determine the beamformer for single layer transmission. One or more embodiments advantageously generate suitable single-layer or low-rank beamformers regardless of the underlying multipath propagation medium. The network node does not need to predict the channel realizations to determine the precoder as the network node may only require the knowledge of the precoder provided by the wireless device. One or more embodiments allows for constant modulus schemes (just employing the resulting phase-taper) and the transmitter does not suffer from array tapering loss. One or more embodiments provide a dynamic beam-broadening method that can be applied to low-rank precoders. In case of a rank−1 multi-lobe pattern, the beam-broadening scheme gradually expands the beam-width of individual lobes in each layer. One or more embodiments are extensible to different channel state information feedbacks available from a wireless device (e.g., Type-1/2 CSI feedback, SRS based channel estimation).

According to one embodiment of this aspect, a network node configured to communicate with a wireless device is provided. The network node includes processing circuitry configured to: receive multilayer feedback; determine a beamformer for transmission of a first quantity of transmission layers where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers and where the first quantity of transmission layers is a less than the second quantity of transmission layers; and cause the transmission using the beamformer.

According to one or more embodiments of this aspect, the multilayer feedback includes information associated with beam directions of the first quantity of transmission layers and information associated with directions of the second quantity of transmission layers. According to one or more embodiments of this aspect, the determining of the beamformer for the transmission of the first quantity of transmission layers includes: combining the information, in the multilayer feedback, associated with the second quantity of transmission layers, with the information associated with the first quantity of transmission layers; generating matrices based at least on the combined information; and performing one of a single value decomposition and weight mean vector function based on the matrices to obtain the beamformer for the transmission of the first quantity of transmission layers. According to one or more embodiments of this aspect, the weighted mean function includes applying weighting coefficients to the matrices.

According to one or more embodiments of this aspect, the first quantity of transmission layers is n, n being greater than 1, where the generating of matrices includes generating n matrices, where the single value decomposition being performed for each of n matrices; and where the processing circuitry being further configured to: select a singular vector for each single value decomposition to obtain a plurality of singular vectors; and the beamformer for the transmission of the first quantity of transmission layers being based at least on the plurality of singular vectors. According to one or more embodiments of this aspect, the beamformer for the transmission of the first quantity of transmission layers is a constant modulus beamformer. According to one or more embodiments of this aspect, the multilayer feedback is a Pre-coding Matrix Indicator, PMI. According to one or more embodiments of this aspect, the transmission using the beamformer is a single layer transmission in a physical downlink control channel.

According to another aspect of the disclosure, a method implemented by a network node that is configured to communicate with a wireless device is provided. Multilayer feedback is received. A beamformer for transmission of a first quantity of transmission layers is determined where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers where the first quantity of transmission layers is a less than the second quantity of transmission layers, and the transmission using the beamformer is caused.

According to one or more embodiments of this aspect, the multilayer feedback includes information associated with beam directions of the first quantity of transmission layers and information associated with directions of the second quantity of transmission layers. According to one or more embodiments of this aspect, the determining of the beamformer for the transmission of the first quantity of transmission layers includes: combining the information, in the multilayer feedback, associated with the second quantity of transmission layers, with the information associated with the first quantity of transmission layers; generating matrices based at least on the combined information; and performing one of a single value decomposition and weight mean vector function based on the matrices to obtain the beamformer for the transmission of the first quantity of transmission layers.

According to one or more embodiments of this aspect, the weighted mean function includes applying weighting coefficients to the matrices. According to one or more embodiments of this aspect, the first quantity of transmission layers is n, n being greater than 1, where the generating of matrices includes generating n matrices, where the single value decomposition being performed for each of n matrices; and where the processing circuitry is further configured to: select a singular vector for each single value decomposition to obtain a plurality of singular vectors; and the beamformer for the transmission of the first quantity of transmission layers being based at least on the plurality of singular vectors.

According to one or more embodiments of this aspect, the beamformer for the transmission of the first quantity of transmission layers is a constant modulus beamformer. According to one or more embodiments of this aspect, the multilayer feedback is a Pre-coding Matrix Indicator, PMI. According to one or more embodiments of this aspect, the transmission using the beamformer is a single layer transmission in a physical downlink control channel.

According to another aspect of the disclosure, a computer readable medium is provided. The computer readable medium is configured to store instructions, which when executed by a processor, cause the processor to: receive multilayer feedback; determine a beamformer for transmission of a first quantity of transmission layers where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers, and where the first quantity of transmission layers is a less than the second quantity of transmission layers; and cause the transmission using the beamformer.

According to one or more embodiments of this aspect, the multilayer feedback includes information associated with beam directions of the first quantity of transmission layers and information associated with directions of the second quantity of transmission layers. According to one or more embodiments of this aspect, the determining of the beamformer for the transmission of the first quantity of transmission layers includes: combining the information, in the multilayer feedback, associated with the second quantity of transmission layers, with the information associated with the first quantity of transmission layers; generating matrices based at least on the combined information; and performing one of a single value decomposition and weight mean vector function based on the matrices to obtain the beamformer for the transmission of the first quantity of transmission layers. According to one or more embodiments of this aspect, the multilayer feedback is a Pre-coding Matrix Indicator, PMI; and the transmission using the beamformer is a single layer transmission in a physical downlink control channel.

DETAILED DESCRIPTION

Transmitting in downlink may pertain to transmission from the network or network node to the terminal. Transmitting in uplink may pertain to transmission from the terminal to the network or network node. Transmitting in sidelink may pertain to (direct) transmission from one terminal to another. Uplink, downlink and sidelink (e.g., sidelink transmission and reception) may be considered communication directions. In some variants, uplink and downlink may also be used to described wireless communication between network nodes, e.g. for wireless backhaul and/or relay communication and/or (wireless) network communication for example between base stations or similar network nodes, in particular communication terminating at such. It may be considered that backhaul and/or relay communication and/or network communication is implemented as a form of sidelink or uplink communication or similar thereto.

Some embodiments provide a low rank beamforming based at least on multi-layer feedback.

A network node16is configured to include a node beamformer unit32which is configured to perform one or more network node16functions as described herein such as with respect to a low rank beamforming based at least on multi-layer feedback. A host computer is configured to include a central beamformer unit34which is configured to perform one or more host computer functions as described herein such as with respect to a low rank beamforming based at least on multi-layer feedback.

The software48may be executable by the processing circuitry42. The software48includes a host application50. The host application50may be operable to provide a service to a remote user, such as a WD22connecting via an OTT connection52terminating at the WD22and the host computer24. In providing the service to the remote user, the host application50may provide user data which is transmitted using the OTT connection52. The “user data” may be data and information described herein as implementing the described functionality. In one embodiment, the host computer24may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider. The processing circuitry42of the host computer24may enable the host computer24to observe, monitor, control, transmit to and/or receive from the network node16and or the wireless device22. The processing circuitry42of the host computer24may include a central beamformer unit54configured to enable the service provider to perform one or more host computer functions as described herein such as with respect to a low rank beamforming based at least on multi-layer feedback.

Thus, the network node16further has software74stored internally in, for example, memory72, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node16via an external connection. The software74may be executable by the processing circuitry68. The processing circuitry68may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node16. Processor70corresponds to one or more processors70for performing network node16functions described herein. The memory72is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software74may include instructions that, when executed by the processor70and/or processing circuitry68, causes the processor70and/or processing circuitry68to perform the processes described herein with respect to network node16. For example, processing circuitry68of the network node16may include node beamformer unit32configured to perform one or more network node16functions as described herein such as with respect to a low rank beamforming based at least on multi-layer feedback.

The communication system10further includes the WD22already referred to. The WD22may have hardware80that may include a radio interface82configured to set up and maintain a wireless connection64with a network node16serving a coverage area18in which the WD22is currently located. The radio interface82may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers.

The processing circuitry84may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD22. The processor86corresponds to one or more processors86for performing WD22functions described herein. The WD22includes memory88that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software90and/or the client application92may include instructions that, when executed by the processor86and/or processing circuitry84, causes the processor86and/or processing circuitry84to perform the processes described herein with respect to WD22.

In some embodiments, the inner workings of the network node16, WD22, and host computer24may be as shown inFIG.2and independently, the surrounding network topology may be that ofFIG.1.

In some embodiments, the host computer24includes processing circuitry42and a communication interface40that is configured to a communication interface40configured to receive user data originating from a transmission from a WD22to a network node16. In some embodiments, the WD22is configured to, and/or comprises a radio interface82and/or processing circuitry84configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the network node16, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the network node16.

AlthoughFIGS.1and2show various “units” such as node beamformer unit32, and central beamformer unit34as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

FIG.7is a flowchart of an example process in a network node16according to one or more embodiments of the present disclosure. One or more Blocks and/or functions performed by network node16may be performed by one or more elements of network node16such as by node beamformer unit32in processing circuitry68, processor70, radio interface62, etc. In one or more embodiments, network node16such as via one or more of processing circuitry68, processor70, node beamformer unit32, communication interface60and radio interface62is configured to receive (Block S134) multilayer feedback, as described herein. In one or more embodiments, network node16such as via one or more of processing circuitry68, processor70, node beamformer unit32, communication interface60and radio interface62is configured to determine (Block S136) a beamformer for transmission of a first quantity of transmission layers where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers, and where the first quantity of transmission layers is less than the second quantity of transmission layers, as described herein. In one or more embodiments, network node16such as via one or more of processing circuitry68, processor70, node beamformer unit32, communication interface60and radio interface62is configured to cause (Block S138) the transmission using the beamformer, as described herein.

According to one or more embodiments, the multilayer feedback includes information associated with beam directions of the first quantity of transmission layers and information associated with directions of the second quantity of transmission layers. According to one or more embodiments, the determining of the beamformer for the transmission of the first quantity of transmission layers includes: combining the information, in the multilayer feedback, associated with the second quantity of transmission layers, with the information associated with the first quantity of transmission layers, generating matrices based at least on the combined information, and performing one of a single value decomposition and weight mean vector function based on the matrices to obtain the beamformer for the transmission of the first quantity of transmission layers.

According to one or more embodiments, the weighted mean function includes applying weighting coefficients to the matrices. According to one or more embodiments, the first quantity of transmission layers is n, n being greater than 1. The generating of matrices includes generating n matrices. The single value decomposition is performed for each of n matrices. The processing circuitry68is further configured to: select a singular vector for each single value decomposition to obtain a plurality of singular vectors; and the beamformer for the transmission of the first quantity of transmission layers being based at least on the plurality of singular vectors.

According to one or more embodiments, the beamformer for the transmission of the first quantity of transmission layers is a constant modulus beamformer. According to one or more embodiments, the multilayer feedback is a Pre-coding Matrix Indicator, PMI. According to one or more embodiments, the transmission using the beamformer is a single layer transmission in a physical downlink control channel.

FIG.8is a flowchart of another example process in a network node16according to one or more embodiments of the present disclosure. One or more Blocks and/or functions performed by network node16may be performed by one or more elements of network node16such as by node beamformer unit32in processing circuitry68, processor70, radio interface62, etc. In one or more embodiments, network node16such as via one or more of processing circuitry68, processor70, node beamformer unit32, communication interface60and radio interface62is configured to receive (Block S140) multilayer feedback, as described herein. In one or more embodiments, network node16such as via one or more of processing circuitry68, processor70, node beamformer unit32, communication interface60and radio interface62is configured to determine (Block S142) a beamformer for transmission of a first quantity of transmission layers where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers, and the first quantity of transmission layers is a less than the second quantity of transmission layers, as described herein.

In one or more embodiments, network node16such as via one or more of processing circuitry68, processor70, node beamformer unit32, communication interface60and radio interface62is configured to cause (Block S142) the transmission of the beamformer for use in uplink transmission, as described herein. For example, the wireless device22may use/apply the beamformer for multi-antenna transmission from the wireless device22to the network node16such as for uplink transmission such as on the physical uplink control channel (PUCCH). While the wireless device22may be equipped with a various antenna arrays, the wireless device22may be limited to rank 1 or low rank transmissions due to power restrictions such that the teachings here are equally applicable to various types of wireless devices22.

In one or more embodiments, a computer readable medium (e.g., memory72) is configured to store instructions, which when executed by a processor, cause the processor to: receive multilayer feedback, determine a beamformer for transmission of a first quantity of transmission layers where the beamformer is based at least on information, in the multilayer feedback, that is associated with a second quantity of transmission layers, and where the first quantity of transmission layers is a less than the second quantity of transmission layers, and cause the transmission using the beamformer.

According to one or more embodiments, the multilayer feedback includes information associated with beam directions of the first quantity of transmission layers and information associated with directions of the second quantity of transmission layers. According to one or more embodiments, the determining of the beamformer for the transmission of the first quantity of transmission layers includes: combining the information, in the multilayer feedback, associated with the second quantity of transmission layers, with the information associated with the first quantity of transmission layers, generating matrices based at least on the combined information, and performing one of a single value decomposition and weight mean vector function based on the matrices to obtain the beamformer for the transmission of the first quantity of transmission layers. According to one or more embodiments, the multilayer feedback is a Pre-coding Matrix Indicator, PMI, and the transmission uses the beamformer is a single layer transmission in a physical downlink control channel.

Having generally described arrangements for a low rank beamforming based at least on multi-layer feedback, details for these arrangements, functions and processes are provided as follows, and which may be implemented by the network node16, wireless device22and/or host computer24.

Some embodiments provide a low rank beamforming based at least on multi-layer feedback.

A single-user MIMO communication system where network node16employs a Nv×Nh2D antenna array is considered. It may be assumed that the network node16, such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., estimates the precoder and/or receives feedback to calculate a precoder to transmit to wireless device22. For 3GPP, Type-1 CSI-RS feedback can be used to collect the precoder information from one or more wireless devices22. For example, the PMI in 3GPP Rel 15+ contains indices: (i11, i12, i13, i2, RI), where i11and i12are the indices for the layer-0's directions in dimension 1 and dimension 2 of the 2D array prototype. Further, i13contains the information regarding the directions of the layers other than the 0thlayer. Let u0and v0denote the N1×1 and N2×1 dimensional steering vectors for layer-0 transmission, respectively. Here, the (N1, N2) tuple indicates the codebook configuration of Type-1 as defined in wireless communication standards such as 3GPP Technical Specification (TS) 38.314. The scenario with RI>1 is considered. RI=1 is a case where the feedback precoder can be directly used. The final precoder for each dimension can be obtained by the underlying CSI-RS port to antenna mapping denoted by Wp2a,hand Wp2a,v, for horizontal and vertical dimension of the array, respectively.

Matrices U[i11,i3]=Wp2a,h[u0u1. . . uRI-1] and V[i12,i3]=Wp2a,v[v0v1. . . vRI-1] are defined where each column indicates the steering vector for layer-l, l=0, 1, . . . , RI−1 for dimension 1 and 2, respectively. For each dimension, the SVD is obtained as

Note that the matrices A=[a0. . . aRI-1] and C=[c0. . . cRI-1] correspond to the eigenvectors of UUHand VVH, respectively. Assuming that the r and A contains the singular values in descending order along the diagonal, the beamformer for single layer transmission may be

for azimuth and elevation, respectively.

An alternative beamformer is to employ a constant modulus beamformer by using only the phase tapering information from a0and c0such that

where ej<x=[ej<x0. . . ej<xN-1]Twith x=[x0. . . xN-1]T. One advantage of using constant modulus beamformer in this method is that the radio frequency (RF) branches such as at the wireless device22can be operated at full power while at the same time the resulting constant modulus beamformer can attain a very similar radiation pattern to the target radiation pattern.

An extension to the above method can be made by suitably weighting the beams for individual layer directions. To that end, the scaled precoders are obtained for dimension 1 and 2, respectively, as

The beamformer for the single-layer transmission is then given by eigenvectors of USUSHand VSVSHcorresponding to largest singular value. The network node16, such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., can utilize any adaptive or non-adaptive heuristics to determine suitable layer weighting coefficients α=(α0. . . αRI-1) and β=(β0. . . βRI-1) providing desirable PDCCH reception quality. If a feedback from the wireless device22is available through Type-2 CSI-RS feedback, these weight scales can also be used for the corresponding beams. If no feedback related to relative strength of the beams are available, multiple weighting options can be employed such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., to create single beams with different beam strength for each direction corresponding to ranks ∈{0, 1, . . . , RI−1}.

In cases where a beamformer for a L′<L layers, e.g., a smaller number of layers than RI (feedback from the wireless device22) is to be generated, L′ block matrices are created, each with li, i=0, . . . L′−1, non-overlapping layers such that Σi=0L′-1li, and apply the single-layer approach defined above to each block separately, and select left singular vector corresponding to strongest singular value from each block. For rank−1 blocks, the beamformer in that partition (e.g., no need to get the singular values since they are the same) is used.

A lower complexity alternative to the SVD approach is to employ a weighted mean vector to get the low-rank precoder. In this case, if the correlations between the precoder among different layers is less than a predefined threshold, e.g., |<ui,uj>|2≤Dth, the precoders obtained are

where α and β denote the RI×1 weight vectors for azimuth and elevation beams, respectively. These values can be different from those used for SVD weighting method above. In cases of large tapering loss, constant modulus weights can be used in this case as well. Sub-grouping can also be applied in case more than one rank is required to send the data.

The selection of weighted SVD and weighted-mean vector methods can be decided by the network node16, such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., depending on (i) the angular separation between the directions of the layers, (ii) knowledge of per layer signal strength, and (iii) the resulting tapering loss of the low rank precoder. If strength of each layer are similar to each other and the spatial separation between layers is larger than a threshold, weighted-mean sum can be employed to generate the low-rank precoder. Alternatively, if the angular separation between different layers is smaller than some threshold, weighted SVD can be employed.

In some scenarios, the feedback (i.e., multi-layer feedback) may not be available in a periodic manner. In this case, due to potential variations in spatial positions of the receivers/wireless devices22, the beam pattern of PDCCH can be gradually transformed to ensure receiver of the wireless device22is covered properly. The low-rank precoder is updated as follows:

where

is a design parameter to control the pace of beam pattern change, and ⊙ denotes the element-wise product. The time index t represents the delay from the most recent precoder feedback instant. The network node16, such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., can employ location and speed context of the wireless device22to suitably select the values at for each transmission instance t. ϕmaxindicates the largest phase adjustment value at the edge elements of the array and can be selected independently for vertical and horizontal dimensions of the array to achieve desired beam widening in elevation and azimuth, respectively. wAZand wELprecoders can be replaced by wAZCMor wELCM, respectively, to reduce the tapering loss. αtcan be gradually increased from0to the maximum value allowed over different transmission instances if a CSI-RS feedback is missed, and can be reset to 0 when a reliable CSI-RS feedback or precoder estimate is available for the next transmission.

In cases where the directions corresponding to the precoders for different layers are widely separated from each other, the beam broadening approach can be adjusted for αt≥αthreshold, by re-employing SVD or weighted-mean onto low-rank precoders using auxiliary beam directions in between the layers. To that end, the following is obtained

and then the quadratic phase adjustment is applied on the resulting SVD or weighed-mean (or their constant-modulus alternatives) using U′ and V′. Here, waux,azand waux,eldenote the Nh×Laux,azand Nv×Laux,elauxiliary spatial DFT sub-matrices corresponding to the sampled directions in between the layers. Note that wAZand wELcan be replaced by constant modulus alternatives if desired or needed.

If the time from the most recent precoder feedback exceeds some threshold value, e.g., t≥τth, the beam weights can be replaced by a common beamforming weight.

FIG.9is a flow diagram of an example process for PDCCH beamformer calculation using precoder feedback according to the principles of the disclosure. In general, layer weighting can be enabled or disabled such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., based on the availability of PDCCH reception quality over time. The generalized beamformer is based on either left-singular vector or weighted-mean vector. A constant modulus scheme can be enabled such as via one or more of processing circuitry68, processor70, radio interface62, node beamformer unit32, etc., in case of, for example, high-EIRP transmissions. In case feedback is intermittently available, beam-broadening module can be enabled.

In particular, PMI feedback (e.g., i11, i12, i13, i2, RI) is received where RI is greater than 1, as discussed herein (Block S146). A codebook based precoder is generated based at least on the PMI feedback, as described herein (Block S148). Layer partitioning for a low rank (i.e., a rank lower than RI from the PMI) with more than 1 layer may optionally be performed, as described herein (Block S150). Weighted SVD (left-singular vector) or weighted mean may be performed, as described herein (Block S152).

Feedback for PDCCH reception quality may be optionally received, as described herein (Block S154). The weight calculator may optionally be configured to generate (Blocks S156) layer weighting, as described herein. In one example, the weight calculator is initialized to all is. Referring back to Block S152, the layer weighting generated by the weight calculator may optionally be considered or used for the weighted SVD determine or weighted mean determination. In one or more embodiments, the a generalized beamformer or a constant modulus beamformer are generated, as described herein (Blocks S158-S160). In one or more embodiments, beam broadening is optionally performed (Block S162). The result/output of the flow diagram ofFIG.9is a low-rank precoder for transmission, as described herein. In one or more embodiments, the low-rank precoder is associated with a rank of 1 or a rank lower than the RI in the PMI, as described herein.

FIG.10is a block diagram of a cloud implementation according to the principles of the disclosure.FIG.11is a flowchart of an example process in a host computer24according to some embodiments of the present disclosure. One or more Blocks and/or functions performed by host computer24may be performed by one or more elements of host computer24(i.e., central unit) such as by central beamformer unit31in processing circuitry42, processor44, communication interface40, etc. In one or more embodiments, host computer24such as via one or more of processing circuitry42, processor44, central beamformer unit31, and communication interface40is configured to collect PMI feedback information and resulting signal reception qualities for channels of interest and any other auxiliary information to estimate directional information of nearby network nodes16that may be exposed to interference resulting from the network node16transmission. The technique described herein can weigh the precoder columns to suppress the signal propagation towards unintended directions.

In one or more embodiments, host computer24such as via one or more of processing circuitry42, processor44, central beamformer unit31, and communication interface40is configured to performs the following set of steps to determine the precoder:1. Receive the list of PMIs per wireless device22(Block S164).2. Determine the geographic directions of main beams from each network node16(Block S166).3. For each network node16, the host computer24is configured to:a. Determine the main beams that may be needed by each network node16to cover the desired area in that network node16(Block S168). Set their weights α and β to 1. In one or more embodiments, “main beams” may refer the beams have at least one beam characteristic meet a criterion such as meeting a threshold or having a beam direction toward the wireless device22, etc.b. Determine the beam directions that may need to be suppressed to reduce interference to neighbor coverage area. Set their weights α and β to 0 (Block S170).c. Determine the low-rank precoder as described above such as with respect toFIG.7(Block S172).d. Use the low-rank precoder or the constant modulus weight derived from this low-rank precoder (Block S174).e. If more than one layer is needed for transmission, employ the partitioning method and obtain a single beamformer for each partition (Block S176).4. Apply projection based nulling as needed, i.e., this step is optional (Block S178).a. The host computer24may observe that the neighboring network node16may end-up with beamformers for low-rank transmissions that may create partially overlapping beams. In those cases, the beams can be selectively nulled in desired nulling directions using

Pnull,dim=(IMdim−w(wHw)−1wH)where w is the Mdim×Lnprecoding matrix weights (for the dimension 1 or 2) that creates the beams in the overlapping directions, Lnis the number of beams to be nulled, and Mdimis the number of antennas in dimension-dim, dim∈{1,2}
In one or more embodiments, the host computer24may be a central network node16.

Therefore, one or more embodiments described herein create one or more beamformer weights that can be used for single layer transmissions (e.g., PDCCH transmissions) or low-rank transmissions, whether the beamforming and diversity gains obtained through codebook based SU-MIMO via CSI-RS feedback is able to be cultivated. In other words, single or low-rank transmission are configured using multi-layer feedback, thereby advantageously using the beamforming and diversity gains.

One or more embodiments described herein advantageously have a low-computation complexity since they may require determining only the eigen vector corresponding to the largest singular value, or eigen-vectors corresponding to a few of largest eigenvalues as opposed to, for example, full matrix processing.

In one or more embodiments, since the PMI indicates the suitable directions considering the multi-path propagation, the radiation pattern resulting from the one or more embodiments can continue utilizing all the propagation paths according to their contribution to overall performance as observed by the wireless device22.

One or more embodiments described herein can be extended to the case where there is CSI-RS feedback for RI layers and a transmission with L layers such that 1<L<RI is performed. In order to transmit L layers, two alternatives are proposed: (i) evaluate L eigenvectors corresponding to largest L singular values, or (ii) partition the directions of interest into L groups and create a single direction for each partition.

One or more embodiments described herein can dynamically increase the beam width of low-rank multi-beam pattern. This capability can be used to compensate the lack of precoder feedback information in case network load or reliability prevents accurate reception of feedback information.

One or more embodiments described herein can utilize any additional feedback or information that provides the relative strength or significance of the desired beam directions and determine suitable beamforming weights for the low-rank transmissions.

Abbreviations that may be used in the preceding description include:

CSI-RS Channel State Information-Reference Signal UE

gNB Base station for New Radio, i.e., a type of network node16

PDCCH Physical Downlink Control Channel

PMI Precoding Matrix Index

RI Rank Indicator

User Equipment, i.e., a type of wireless device22