WO2021053370A1

WO2021053370A1 - Pmi distance (pmid) assisted mu-mimo transmission

Info

Publication number: WO2021053370A1
Application number: PCT/IB2019/057872
Authority: WO
Inventors: Yongquan Qiang; Auon AKHTAR; Chaocheng TU; Hai Wang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2019-09-18
Filing date: 2019-09-18
Publication date: 2021-03-25

Abstract

A method, system and apparatus for precoder matrix indicator (PMI) distance assisted multiple user multiple input multiple output (MU-MIMO) transmission are disclosed. According to one aspect, a network node is configured to, for each of a plurality of pairs of wireless devices, WDs, determine a distance between PMI of the pair of WDs. The network node is also configured to group WDs for MU-MIMO transmission according to the PMI distances of WD pairs and sort the PMI distances according to a rule. The network node is further configured to assign demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned 1029640

Description

PMI DISTANCE (PMID) ASSISTED MU-MIMO TRANSMISSION

TECHNICAL FIELD

The present disclosure relates to wireless communications, and in particular, to Precoder Matrix Indicator (PMI) distance (PMID) assisted multiple user multiple input multiple output (MU-MIMO) transmission.

BACKGROUND

An active antenna system (AAS) is one of technologies adopted by 3^rd Generation Partnership Project (3GPP) as part of its 4^th Generation (4G) Long Term Evolution (LTE) and 5^th Generation (5G) New Radio (NR) standards to enhance the wireless network performance and capacity by using full dimension MIMO (FD-MIMO) and massive MIMO. A typical AAS may have a two-dimensional antenna array with M rows, N columns and K polarizations (K=2 in case of cross -polarization) as shown in FIG. 1.

In the 3GPP Technical Release 15 (Rel-15) for NR, the “Typel-SinglePanel” codebook was introduced for single user (SU)-MIMO. A two-dimensional discrete Fourier transform (DFT) codebook is defined for configured channel state information reference signal (CSI-RS) ports. The precoding matrix W is further described as a two-stage precoding structure as follow:

W= W₁W₂ where W₁ consists of a group of 2D grid-of-beams (GoB) denoted by

(i)

where, v₁ and v_m are precoding vectors selected from over-sampled DFT matrix for horizontal direction and vertical direction, expressed by:

where, N₁, N₂ are configured CSI-RS ports in horizontal and vertical direction, with corresponding over-sampling rate of O_1, O₂. W₂ is used for beam selection within W₁ and co-phasing between two polarizations. For single layer transmission:

For dual layer transmission:

where f_n is co-phasing factor determined by the wireless device (WD) reported wideband or subband co-phasing index n , denoted by f_n = e^jpn/2

The 2 dimensional precoder matrix indicator (PMI) ( l,m ) and co-phasing index n are obtained from a wireless device (WD) PMI report with “Typel” codebook.

A typical application of AAS is to perform MU-MIMO. This allows the frequency resources to be shared by multiple WDs with co-channel transmissions at the same time. Referring to FIG. 2., as a result, the co-channel interference from co-scheduled WDs suffers. This is one of the biggest challenges for wireless communication system developers and providers, especially for downlink (DL) MU-MIMO. So, a multiple-users (MU) pairing algorithm may be useful at the base station (e.g., gNB) to determine separation among WDs to be co-scheduled with minimized co-channel interference.

For data transmission on the physical downlink shared channel (PDSCH), a demodulation reference signal (DMRS) is used to perform channel estimation and demodulation. Each layer may have an associated DMRS port. Single or multiple DMRS symbols are reserved to form multiple DMRS ports as shown in FIG. 3. In FIG. 3, the X- axis represents the symbol number and the Y-axis is divided into slots. Thus, FIG. 3 shows the OFDM symbol number per slot. With “1 + 1” DMRS configuration, four DMRS ports can be formed. In the case of MU-MIMO, the number of DMRS ports might be less than the co-scheduled layers. For example, four co-scheduled WDs with two layers per WD can support 8-layers of transmission in total. Ideally, for better channel estimation, orthogonal DMRS ports are preferred for WDs not well separated. For WDs with good separation, the DMRS ports can be reused. So, allocation of a limited number of DMRS ports among co scheduled layers is another challenge of MU-MIMO transmission. MU-MIMO pairing

Traditionally, multi-user (MU) pairing is done at the network node, e.g., gNB, based on pair-wise orthogonality (correlation) of the channel response, expressed by

where, is the uplink (UL) channel response or the transposition of the downlink (DL) channel response of WDi, denoted by is the UL channel response

or the transposition of DL channel response of WD₂, denoted by

denotes the dot product between vector x and y, expressed by

where denotes the amplitude of vector x, expressed by

The WDs with pair-wise correlation below a threshold will be paired, expressed by r < Th

There are two approaches to obtain the DL channel response of the WD.

1. “Typell” codebook based approach:

In 3GPP Rel-15 for NR, the “Typell” codebook is introduced, which allows the WD to report up to L (L= 4) orthogonal beams per polarization per layer with quantized amplitude and phase, expressed as follows:

With the multi-beam CSI report, the quantized DL channel is known by the gNB. The problems with this approach include: The “Typell” CSI feedback is dependent on WD capability and is not supported by WD in an early phase of NR commercial deployment.

The overhead of “Typell” CSI report is too high.

2. Reciprocity based approach: In a time division duplex (TDD) AAS system, the channel response can be measured by UL reference signals (e.g., sounding reference signals (SRS) or DMRS). According to reciprocity of channel response, the DL channel response can be estimated by

The problems with this approach include:

It requires UL reference signals (e.g. SRS or DMRS) and huge memory to store the channel response.

The computation complexity is to calculate the averaged orthogonality across whole bandwidth. - In a frequency division duplex (FDD) system, it is not straightforward to get DL channel response estimation from UL reference signals.

DMRS ports assignment

Traditionally, there are two options to assign DMRS ports to paired WDs. Identical DMRS ports assignment: all paired WDs are assigned with the same DMRS ports as shown in Table 1. A problem is that DMRS ports collide for paired WDs, which will degrade the channel estimation if WDs are not well-separated. As used herein, separation is referenced in the spatial domain such that well-separated WDs will cause less co-channel interference among WDs. Furthermore, the DMRS ports are not fully utilized.

Table 1

2. DMRS ports assignment based on WD priority: all WDs are paired with different DMRS ports blindly based on WD priority. WD separation is not considered for DMRS port assignment. A problem is that the WDs with bad separation might be assigned with the same DMRS ports as shown in Table 2. For example, in this case, WD1 and WD2 are assigned with the orthogonal DMRS ports, while, WD1 and WD3 are assigned with the same DMRS port. However, the separation between WD1 and WD3 are worse than that between WD1 and WD2.

Table 2

SUMMARY

Some embodiments advantageously provide methods and network nodes for PMI distance assisted MU-MIMO transmission. According to one aspect, a method includes determining of PMI distance (PMID) assisted MU paring and DMRS ports assignment for DL MU-MIMO. In some embodiments, a method performed by a network node such as a gNB, does the following:

Obtaining PMI from a WD CSI report or UL reference signals.

Calculating the pair-wise PMI distance for WDs to be paired with obtained PMI

Performing MU pairing based on calculated pair-wise PMI distance.

Assigning DMRS ports for paired WDs based on calculated pair-wise PMI distance.

Methods described herein may be applied for UL and DL MU-MIMO.

According to one aspect, a method in a network node for precoder matric indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission. The method includes, for each of a plurality of pairs of wireless devices, WD, determining a distance between PMIs of the pair of wireless devices, WD. The method includes grouping WDs for MU-MIMO transmission according to the PMI distances of WD pairs. The method further includes sorting the PMI distances of WD pairs in MU group according to a rule, assigning demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

According to this aspect, in some embodiments, when a number of WD pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD pairs are assigned DMRS ports. In some embodiments, the PMI for each WD in a pair is obtained from the WD in a channel state information, CSI, report or from uplink reference signals. In some embodiments, a PMI distance is compared to a threshold to determine a measure of separation between WDs in a pair. In some embodiments, a PMI distance in a first direction is compared to a first threshold, and a PMI distance in a second direction orthogonal to the first direction is compared to a second threshold. In some embodiments, two WDs are grouped into a pair when one or both of the first and second threshold are exceeded by a respective PMI distance. In some embodiments, two WDs are grouped into a pair only when both the first and second threshold are exceeded by a respective PMI distance. In some embodiments, DMRS ports are assigned first to a WD with the smallest PMI.

According to another aspect, a network node for precoder matric indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission is provided. The network node includes processing circuitry configured to, for each of a plurality of pairs of wireless devices, WD, determine a distance between PMI of the pair of wireless devices, WD. The network node is further configured to group WDs for MU-MIMO transmission according to the PMI distances of WD pairs, sort the PMI distances according to a rule, and assign demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

According to this aspect, in some embodiments, when a number of WD pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD pairs are assigned DMRS ports. In some embodiments, the PMI for each WD in a pair is obtained from the WD in a channel state information, CSI, report or from uplink reference signals. In some embodiments, a PMI distance is compared to a threshold to determine a measure of separation between WDs in a pair. In some embodiments, a PMI distance in a first direction is compared to a first threshold, and a PMI distance in a second direction orthogonal to the first direction is compared to a second threshold. In some embodiments, two WDs are grouped into a pair when one or both of the first and second threshold are exceeded by a respective PMI distance. In some embodiments, two WDs are grouped into a pair only when both the first and second threshold are exceeded by a respective PMI distance. In some embodiments, DMRS ports are assigned first to a WD with the smallest PMI. According to yet another aspect, a method in a network node for precoder matrix indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission, includes for each of a plurality of pairs of wireless devices, WD, determining a distance between PMI of the pair of wireless devices, WD, in a first direction and a second direction orthogonal to the first direction. The method further includes grouping WDs for MU-MIMO transmission according to the PMI distances of WD pairs. The method further includes sorting the PMI distances according to a rule and comparing the distance between the pairs to a threshold. The method further includes, when the distance exceeds the threshold, assigning demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

According to this aspect, in some embodiments, when a number of WD pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD pairs are assigned DMRS ports. In some embodiments, the PMI for each WD in a pair is obtained from the WD in a channel state information, CSI, report or from uplink reference signals. In some embodiments, DMRS ports are assigned first to a WD with the smallest PMI.

According to yet another aspect, a network node for precoder matrix indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission. The network node comprising processing circuitry configured to, for each of a plurality of pairs of wireless devices, WD, determine a distance between PMI of the pair of wireless devices,

WD, in a first direction and a second direction orthogonal to the first direction. The network node 16 is further configured to group WDs for MU-MIMO transmission according to the PMI distances of WD pairs, sort the PMI distances according to a rule, compare the distance between the pairs to a threshold, when the distance exceeds the threshold, assign demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is an array of cross -polarized antenna elements;

FIG. 2 illustrates transmission between a network node and wireless devices;

FIG. 3 illustrates reservation of DMRS symbols to form multiple DMRS ports;

FIG. 4 is a schematic diagram of an exemplary network architecture illustrating a communication system according to the principles in the present disclosure;

FIG. 5 is a block diagram of a network node in communication with a wireless device over a wireless connection according to some embodiments of the present disclosure;

FIG. 6 is a flowchart of an exemplary process in a network node for PMI distance assisted MU-MIMO transmission; and

FIG. 7 is a flowchart of an exemplary process in a wireless device for PMI distance assisted MU-MIMO transmission.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to Precoder Matrix Indicator (PMI) distance (PMID) assisted multiple user multiple input multiple output (MU-MIMO) transmission. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Like numbers refer to like elements throughout the description.

As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. 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. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication.

In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections.

The term “network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.

In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The WD herein can be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD). The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device etc.

Also, in some embodiments the generic term “radio network node” is used. It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH).

Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure.

Note further, that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

A method, system and apparatus for precoder matrix indicator (PMI) distance assisted multiple user multiple input multiple output (MU-MIMO) transmission are disclosed. According to one aspect, a network node is configured to for each of a plurality of pairs of wireless devices, WDs, determine a distance between PMI of the pair of WDs. The network node is also configured to group WDs for MU-MIMO transmission according to the PMI distances of WD pairs and sort the PMI distances according to a rule. The network node is further configured to assign demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned

Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in FIG. 4 a schematic diagram of a communication system 10, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14. The access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18). Each network node 16a,

16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b and 22d (collectively referred to as wireless devices 22) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD 22 is in the coverage area or where a sole WD 22 is connecting to the corresponding network node 16. In the example of FIG. 4, WD 22b and WD 22d are shown in the same coverage area (coverage area 18b) and are in communication with network node 16b. Note that although only three WDs 22 and three network nodes 16 are shown for convenience, the communication system may include many more WDs 22 and network nodes 16.

Also, it is contemplated that a WD 22 can be in simultaneous communication and/or configured to separately communicate with more than one network node 16 and more than one type of network node 16. For example, a WD 22 can have dual connectivity with a network node 16 that supports FTE and the same or a different network node 16 that supports NR. As an example, WD 22 can be in communication with an eNB for FTE/E-UTRAN and a gNB for NR/NG-RAN.

A network node 16 is configured to include a grouping unit 32 which is configured to group WDs for MU-MIMO transmission according to the PMI distances of WD pairs.

Example implementations, in accordance with an embodiment, of the WD 22, network node 16 and host computer 24 discussed in the preceding paragraphs will now be described with reference to FIG. 5.

The communication system 10 includes a network node 16 provided in a communication system 10 and includes hardware 38 enabling the network node 16 to communicate with the WD 22. The hardware 38 may include a radio interface 42 for setting up and maintaining at least a wireless connection 46 with a WD 22 located in a coverage area 18 served by the network node 16. The radio interface 42 may 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 radio interface 42 includes an array of antennas 43 to radiate and receive signal carrying electromagnetic waves.

In the embodiment shown, the hardware 38 of the network node 16 further includes processing circuitry 48. The processing circuitry 48 may include a processor 50 and a memory 52. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 48 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 50 may be configured to access (e.g., write to and/or read from) the memory 52, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the network node 16 further has software 44 stored internally in, for example, memory 52, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node 16 via an external connection. The software 44 may be executable by the processing circuitry 48. The processing circuitry 48 may 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 node 16. Processor 50 corresponds to one or more processors 50 for performing network node 16 functions described herein. The memory 52 is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 44 may include instructions that, when executed by the processor 50 and/or processing circuitry 48, causes the processor 50 and/or processing circuitry 48 to perform the processes described herein with respect to network node 16. For example, processing circuitry 48 of the network node 16 may include a grouping unit 32 which is configured to group WDs for MU-MIMO transmission according to the PMI distances of WD pairs.

The communication system 10 further includes the WD 22 already referred to. The WD 22 may have hardware 60 that may include a radio interface 62 configured to set up and maintain a wireless connection 46 with a network node 16 serving a coverage area 18 in which the WD 22 is currently located. The radio interface 62 may 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 radio interface 62 includes an array of antennas 63 to radiate and receive signal carrying electromagnetic waves.

The hardware 60 of the WD 22 further includes processing circuitry 64. The processing circuitry 64 may include a processor 66 and memory 68. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 64 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 66 may be configured to access (e.g., write to and/or read from) memory 68, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the WD 22 may further comprise software 70, which is stored in, for example, memory 68 at the WD 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD 22. The software 70 may be executable by the processing circuitry 64. The software 70 may include a client application 72. The client application 72 may be operable to provide a service to a human or non-human user via the WD 22.

The processing circuitry 64 may 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 WD 22. The processor 66 corresponds to one or more processors 66 for performing WD 22 functions described herein. The WD 22 includes memory 68 that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 70 and/or the client application 72 may include instructions that, when executed by the processor 66 and/or processing circuitry 64, causes the processor 66 and/or processing circuitry 64 to perform the processes described herein with respect to WD 22. .

In some embodiments, the inner workings of the network node 16 and WD 22 may be as shown in FIG. 5 and independently, the surrounding network topology may be that of FIG. 4.

The wireless connection 46 between the WD 22 and the network node 16 is in accordance with the teachings of the embodiments described throughout this disclosure. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. In some embodiments, 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.

Although FIGS. 4 and 5 show various “units” such as grouping unit 32 as 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. 6 is a flowchart of an exemplary process in a network node 16 for PMI distance assisted MU-MIMO transmission. One or more blocks described herein may be performed by one or more elements of network node 16 such as by one or more of processing circuitry 68 (including the grouping unit 32), processor 70, radio interface 62 and/or communication interface 60. Network node 16 such as via processing circuitry 68 and/or processor 70 and/or radio interface 62 and/or communication interface 60 is configured to, for each of a plurality of pairs of WDs, determine a distance between PMI of the pair of wireless devices, WD (Block S100). The process also includes grouping WDs for MU-MIMO transmission according to the PMI distances of WD pairs (Block S 102). The process also includes sorting the PMI distances according to a rule (Block S104). The process further includes, assigning demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned (Block S106).

FIG. 7 is a flowchart of an alternative exemplary process in a network node 16 according to some embodiments of the present disclosure. The process includes, for each of a plurality of pairs of WDs determining a distance between PMI of the pair of WDs in a first direction and a second direction orthogonal to the first direction (Block S108). The process further includes grouping WDs for MU-MIMO transmission according to the PMI distances of WD pairs (Block S110). The process further includes sorting the PMI distances according to a rule (Block S 112) and comparing the distance between the pairs to a threshold (Block S114). When the distance exceeds the threshold, the process includes assigning demodulation reference signal, DMRS, ports to WD pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned (Block S116).

Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for Precoder Matrix Indicator (PMI) distance (PMID) assisted multiple user multiple input multiple output (MU-MIMO) transmission.

In NR Rel-15, WDs 22 configured with “Typel-SinglePanel” codebook will report, such a via for example processing circuitry 64 and/or radio interface 62, two dimensional PMI (e. g., i _{, ,}i_1,2)· Then, the 2D PMI ( l,m ) can be obtained at the network node 16 by:

(l,m) = ( i _{, ,}i_1,2 ) In a TDD system, the two dimensional (2D) PMI can also be obtained by the network node 16 through UL reference signals (e.g., SRS or DMRS). For two WDs 22, with PMI₁ = ( and PMI₂ = (l₂,m₂), the pair-wise PMI distance (PMID) may be defined as a Euclidean distance in a given circular 2D PMI space, expressed by

where

Similarly, the one-dimensional (ID) PMID can be obtained separately in a given direction. The PMID in the horizontal direction is given by:

The PMID in the vertical direction is given by:

For WDs 22 to be paired for co-scheduling, the pair-wise PMID may be used as a metric of orthogonality or separation. For example:

2D PMID is no less than a predefined threshold:

PMID(PMI₁, PMI₂) ³ Th

PMID in either direction is no less than a predefined threshold:

PMID_h((PMI₁, PMI₂) ³ Th₁, OR, PMID_v((PMI₁, PMI₂) ³ Th₂ PMID in both directions is no less than a predefined threshold:

PMID_h((PMI₁, PMI₂) ³ Th₁, AND, PMID_v((PMI₁, PMI₂) ³ Th₂ PMID in horizontal direction is no less than a predefined threshold, OR, PMID in vertical direction equal to a predefined threshold:

PMID_h((PMI₁, PMI₂) ³ Th₁, OR, PMID_v((PMI₁, PMI₂) ³ Th₂,

Given a number of DMRS ports, the DMRS ports may be assigned based on PMI distance of paired WDs 22, e.g., WD 22b and WD 22d. In some embodiments, DMRS ports may be assigned first for WDs 22 with smallest PMI distance. First, the pair-wise PMI distances may be sorted according to a rule, such as in ascending order. Then, DMRS ports are assigned to WD 22 pairs based on the sorted order until all WDs get DMRS ports assigned. If DMRS ports run out of resources, the DMRS ports are reused. For WDs with DMRS assigned in previous steps, the DMRS ports assignment may be skipped. For example, there are four DMRS ports (0, 1, 2, 3) available for 4 WDs 22 paired and two layers per WD 22. First, the pair-wise PMI distance is ordered as shown in the example of Table 3. Table 3

Then, the DMRS ports are assigned based on sorted order as shown in the example of Table

4.

Table 4

The final DMRS ports assignment is obtained as shown in the example of Table 5. Table 5

According to one aspect, a method in a network node 16 for precoder matric indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission. The method includes, for each of a plurality of pairs of wireless devices, WD 22, determining (S 100) a distance between PMIs of the pair of wireless devices, WD 22. The method includes grouping (S102) WDs 22 for MU-MIMO transmission according to the PMI distances of WD 22 pairs. The method further includes sorting (S104) the PMI distances of WD 22 pairs in MU group according to a rule, assigning (S106) demodulation reference signal, DMRS, ports to WD 22 pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

According to this aspect, in some embodiments, when a number of WD 22 pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD 22 pairs are assigned DMRS ports. In some embodiments, the PMI for each WD 22 in a pair is obtained from the WD 22 in a channel state information, CSI, report or from uplink reference signals. In some embodiments, a PMI distance is compared to a threshold to determine a measure of separation between WDs 22 in a pair. In some embodiments, a PMI distance in a first direction is compared to a first threshold, and a PMI distance in a second direction orthogonal to the first direction is compared to a second threshold. In some embodiments, two WDs (22) are grouped into a pair when one or both of the first and second threshold are exceeded by a respective PMI distance. In some embodiments, two WDs (22) are grouped into a pair only when both the first and second threshold are exceeded by a respective PMI distance. In some embodiments, DMRS ports are assigned first to a WD 22 with the smallest PMI.

According to another aspect, a network node 16 for precoder matric indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission is provided. The network node 16 includes processing circuitry 48 configured to, for each of a plurality of pairs of wireless devices, WD 22, determine a distance between PMI of the pair of wireless devices, WD 22. The network node 16 is further configured to group WDs 22 for MU-MIMO transmission according to the PMI distances of WD 22 pairs, sort the PMI distances according to a rule, and assign demodulation reference signal, DMRS, ports to WD 22 pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

According to this aspect, in some embodiments, when a number of WD 22 pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD 22 pairs are assigned DMRS ports. In some embodiments, the PMI for each WD 22 in a pair is obtained from the WD 22 in a channel state information, CSI, report or from uplink reference signals. In some embodiments, a PMI distance is compared to a threshold to determine a measure of separation between WD 22s in a pair. In some embodiments, a PMI distance in a first direction is compared to a first threshold, and a PMI distance in a second direction orthogonal to the first direction is compared to a second threshold. In some embodiments, two WDs 22 are grouped into a pair when one or both of the first and second threshold are exceeded by a respective PMI distance. In some embodiments, two WDs 22 are grouped into a pair only when both the first and second threshold are exceeded by a respective PMI distance. In some embodiments, DMRS ports are assigned first to a WD 22 with the smallest PMI. According to yet another aspect, a method in a network node 16 for precoder matrix indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission, includes for each of a plurality of pairs of wireless devices, WD 22, determining (S108) a distance between PMI of the pair of wireless devices, WD 22, in a first direction and a second direction orthogonal to the first direction. The method further includes grouping (SI 10) WDs 22 for MU-MIMO transmission according to the PMI distances of WD 22 pairs. The method further includes sorting (SI 12) the PMI distances according to a rule and comparing (S 114) the distance between the pairs to a threshold. The method further includes, when the distance exceeds the threshold, assigning (SI 16) demodulation reference signal, DMRS, ports to WD 22 pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

According to this aspect, in some embodiments, when a number of WD 22 pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD 22 pairs are assigned DMRS ports. In some embodiments, the PMI for each WD 22 in a pair is obtained from the WD 22 in a channel state information, CSI, report or from uplink reference signals. In some embodiments, DMRS ports are assigned first to a WD 22 with the smallest PMI.

According to yet another aspect, a network node 16 for precoder matrix indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission. The network node 16 comprising processing circuitry 48 configured to, for each of a plurality of pairs of wireless devices, WD 22, determine a distance between PMI of the pair of wireless devices, WD 22, in a first direction and a second direction orthogonal to the first direction. The network node 16 is further configured to group WDs (22) for MU-MIMO transmission according to the PMI distances of WD 22 pairs, sort the PMI distances according to a rule, compare the distance between the pairs to a threshold, when the distance exceeds the threshold, assign demodulation reference signal, DMRS, ports to WD 22 pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and/or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and/or functionality described herein may be performed by, and/or associated to, a corresponding module, which may be implemented in software and/or firmware and/or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++.

However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.

Abbreviations that may be used in the preceding description include:

Abbreviation Explanation

AAS Active Antenna System

CSI-RS Channel State Information Reference Signal

DFT Discrete Fourier Transform

DMRS Demodulation Reference Signal

FD-MIMO Full Dimension MIMO

GoB Grid-of-beams

PMI Precoding Matrix Indicator

SRS Sounding Reference Signal It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims

What is claimed is:

1. A method in a network node (16) for precoder matric indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission, the method comprising: for each of a plurality of pairs of wireless devices, WD (22), determining (S100) a distance between PMIs of the pair of wireless devices, WD (22); grouping (S102) WDs 22 for MU-MIMO transmission according to the PMI distances of WD (22) pairs; sorting (S104) the PMI distances of WD (22) pairs in MU group according to a rule; and assigning (S106) demodulation reference signal, DMRS, ports to WD (22) pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

2. The method of Claim 1, wherein, when a number of WD (22) pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD (22) pairs are assigned DMRS ports.

3. The method of any of Claims 1 and 2, wherein the PMI for each WD (22) in a pair is obtained from the WD (22) in a channel state information, CSI, report or from uplink reference signals.

4. The method of any of Claims 1-3, wherein a PMI distance is compared to a threshold to determine a measure of separation between WDs (22) in a pair.

5. The method of any of Claims 1-3, wherein a PMI distance in a first direction is compared to a first threshold, and a PMI distance in a second direction orthogonal to the first direction is compared to a second threshold.

6. The method of Claim 5, wherein two WDs (22) are grouped into a pair when one or both of the first and second threshold are exceeded by a respective PMI distance.

7. The method of Claim 5, wherein two WDs (22) are grouped into a pair only when both the first and second threshold are exceeded by a respective PMI distance.

8. The method of any of Claims 1-7, wherein DMRS ports are assigned first to a WD (22) with the smallest PMI.

9. A network node (16) for precoder matric indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission, the network node (16) including processing circuitry configured to: for each of a plurality of pairs of wireless devices, WD (22), determine a distance between PMI of the pair of wireless devices, WD (22); group WDs (22) for MU-MIMO transmission according to the PMI distances of WD (22) pairs; sort the PMI distances according to a rule; and assign demodulation reference signal, DMRS, ports to WD (22) pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

10. The network node (16) of Claim 9, wherein, when a number of WD (22) pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD (22) pairs are assigned DMRS ports.

11. The network node (16) of any of Claims 9 and 10, wherein the PMI for each WD (22) in a pair is obtained from the WD (22) in a channel state information, CSI, report or from uplink reference signals.

12. The network node (16) of any of Claims 9-11, wherein a PMI distance is compared to a threshold to determine a measure of separation between WD (22)s in a pair.

13. The network node (16) of any of Claims 9-11, wherein a PMI distance in a first direction is compared to a first threshold, and a PMI distance in a second direction orthogonal to the first direction is compared to a second threshold.

14. The network node (16) of Claim 13, wherein two WDs (22) are grouped into a pair when one or both of the first and second threshold are exceeded by a respective PMI distance.

15. The network node (16) of Claim 13, wherein two WDs (22) are grouped into a pair only when both the first and second threshold are exceeded by a respective PMI distance.

16. The network node (16) of any of Claims 9-15, wherein DMRS ports are assigned first to a WD (22) with the smallest PMI.

17. A method in a network node (16) for precoder matrix indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission, the method comprising: for each of a plurality of pairs of wireless devices, WD (22), determining (S108) a distance between PMI of the pair of wireless devices, WD (22), in a first direction and a second direction orthogonal to the first direction; grouping (S110) WDs (22) for MU-MIMO transmission according to the PMI distances of WD (22) pairs; sorting (S 112) the PMI distances according to a rule; comparing (S114) the distance between the pairs to a threshold; and when the distance exceeds the threshold, assigning (SI 16) demodulation reference signal, DMRS, ports to WD (22) pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

18. The method of Claim 17, wherein, when a number of WD (22) pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD (22) pairs are assigned DMRS ports.

19. The method of any of Claims 17 and 18, wherein the PMI for each WD (22) in a pair is obtained from the WD (22) in a channel state information, CSI, report or from uplink reference signals.

20. The method of any of Claims 17-19, wherein DMRS ports are assigned first to a WD (22) with the smallest PMI.

21. A network node (16) for precoder matrix indicator, PMI, distance assisted multiple user multiple input multiple output, MU-MIMO, transmission, the network node (16) comprising processing circuitry configured to: for each of a plurality of pairs of wireless devices, WD (22), determine a distance between PMI of the pair of wireless devices, WD (22), in a first direction and a second direction orthogonal to the first direction; group WDs (22) for MU-MIMO transmission according to the PMI distances of WD (22) pairs; sort the PMI distances according to a rule; compare the distance between the pairs to a threshold; and when the distance exceeds the threshold, assign demodulation reference signal, DMRS, ports to WD (22) pairs based at least in part on the sorted PMI distances until all DMRS ports are assigned.

22. The method of Claim 21, wherein, when a number of WD (22) pairs exceeds a number of DMRS ports, reusing DMRS ports until a remainder of WD (22) pairs are assigned DMRS ports.

23. The method of any of Claims 21 and 22, wherein the PMI for each WD (22) in a pair is obtained from the WD (22) in a channel state information, CSI, report or from uplink reference signals.

24. The method of any of Claims 21-23, wherein DMRS ports are assigned first to a WD (22) with the smallest PMI.