WO2022266871A1

WO2022266871A1 - Multiplexing reference signal transmission in orbital angular momentum (oam) communication systems

Info

Publication number: WO2022266871A1
Application number: PCT/CN2021/101718
Authority: WO
Inventors: Min Huang; Chao Wei; Hao Xu
Original assignee: Qualcomm Incorporated
Priority date: 2021-06-23
Filing date: 2021-06-23
Publication date: 2022-12-29

Abstract

Aspects of the disclosure relate to transmitting, via a transceiver and a first antenna of a plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; transmitting, via the transceiver and a second antenna of the plurality of antennas, a second reference signal on a second OAM mode using the same first resources; and transmitting, via the transceiver and a third antenna of the plurality of antennas, a third reference signal on a third OAM mode using second resources. Other aspects, embodiments, and features are also claimed and described.

Description

MULTIPLEXING REFERENCE SIGNAL TRANSMISSION IN ORBITAL ANGULAR MOMENTUM (OAM) COMMUNICATION SYSTEMS

TECHNICAL FIELD

The technology discussed below relates generally to wireless communication systems, and more particularly, to modulation of transmission waveforms and multiplexing of data streams. For example, some aspects of the disclosed technology can provide and enable techniques for multiplexing reference signal transmissions using orbital angular momentum (OAM) multiplexing.

INTRODUCTION

In wireless communication, information is transmitted over electromagnetic radiation by modulating a carrier signal with one or more information signals. Many techniques for modulating a carrier signal are used in the art, including various analog and digital modulation techniques such as frequency modulation (FM) , amplitude modulation (AM) , phase-shift keying (PSK) , and quadrature amplitude modulation (QAM) , among numerous others. In a typical cellular wireless communication system, many such signals can be multiplexed (e.g., combined) onto a suitable carrier or band to enable simultaneous communication between multiple devices. Once again, many techniques for multiplexing and multiple access are used in the art, including frequency-division multiplexing (FDM) , time-division multiplexing (TDM) , and orthogonal frequency-division multiplexing (OFDM) , among many others.

As the demand for mobile broadband access continues to increase, research and development continue to advance wireless communication technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

BRIEF SUMMARY OF SOME EXAMPLES

The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

In one example, an apparatus configured for wireless communication is disclosed. In a more particular example, the apparatus includes: a processor; a plurality of antennas; a transceiver coupled to the processor and to plurality of antennas; and a memory coupled to the processor, wherein the processor and the memory are configured to: transmit, via the transceiver and a first antenna of the plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; transmit, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and transmit, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.

In another example, another apparatus configured for wireless communication is disclosed. In a more particular example, the apparatus includes: a processor; a plurality of antennas; a transceiver coupled to the processor and to plurality of antennas; and a memory coupled to the processor, wherein the processor and the memory are configured for: receive, via the transceiver and a first antenna of the plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; receive, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and receive, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.

In yet another example, a method for wireless communication is disclosed. In a more particular example, the method includes: transmitting, via a transceiver and a first antenna of a plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; transmitting, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and transmitting, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.

In still another example, another method for wireless communication is disclosed. In a more particular example, the method includes: receiving, via a transceiver and a first antenna of a plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; receiving, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and receiving, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a radio access network according to some aspects of this disclosure.

FIG. 2 is a schematic illustration of wireless communication between multi-antenna devices according to some aspects of this disclosure.

FIG. 3 is a block diagram conceptually illustrating an example of a hardware implementation for a transmitting device according to some aspects of the disclosure.

FIG. 4 is a block diagram conceptually illustrating an example of a hardware implementation for a receiving device according to some aspects of the disclosure.

FIG. 5 is a schematic illustration of wireless communication via a spiral phase plate (SPP) configuration that supports the use of orbital angular momentum (OAM) modes for multiplexing communications in accordance with some aspects of this disclosure.

FIG. 6 is a schematic illustration of wireless communication via a uniform circular array (UCA) configuration that supports the use of orbital angular momentum (OAM) modes for multiplexing communications in accordance with some aspects of this disclosure.

FIG. 7 is a schematic illustration of a coaxial multi-circle OAM configuration that supports two-dimensional index modulation according to some aspects of this disclosure.

FIG. 8 is a call flow diagram illustrating an exemplary process for multiplexing reference signals on shared resources using different OAM modes in accordance with some aspects of this disclosure.

FIG. 9 is a call flow diagram illustrating an exemplary process for grouping OAM modes for transmission using shared resources in accordance with some aspects of this disclosure.

FIG. 10 is a schematic illustration of groupings of OAM modes for concurrent transmission of multiplexed reference signals on shared resources using different OAM modes an organization of wireless resources in accordance with some aspects of the disclosure.

FIG. 11 is a schematic illustration of transmission of reference signals using different OAM modes using non-overlapping resources useable to determine a mode orthogonality distance threshold in accordance with some aspects of the disclosure.

FIG. 12 is a schematic illustration of channel gain and inter-mode interference that may be calculated from reference signals received in three groups on shared resources in accordance with some aspects of the disclosure.

DETAILED DESCRIPTION

In some aspects, this disclosure provides for a wireless communication technique that exploits an orbital angular momentum (OAM) property of electromagnetic (EM) waves for modulating a carrier to carry information, and/or for multiplexing information streams onto a common wireless resource. In particular, a coaxial multi-circle uniform circular array (UCA) -based antenna may be utilized to transmit reference signals for multiple OAM modes using shared resources, such that the reference signals may be used to perform channel estimation and/or estimate channel characteristics (e.g., channel gain) . Other aspects, embodiments, and features are also described and claimed.

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, those skilled in the art will readily recognize that these concepts may be practiced without these specific details. In some instances, this description provides well known structures and components in block diagram form in order to avoid obscuring such concepts.

While this description describes aspects and embodiments by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, packaging arrangements. For example, embodiments and/or uses may come about via integrated chip embodiments and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, AI-enabled devices, etc. ) . While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or OEM devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also necessarily include additional components and features for implementation and practice of claimed and described embodiments. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processor (s) , interleaver, adders/summers, etc. ) . It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, end-user devices, etc. of varying sizes, shapes and constitution.

In communication systems, modulation is a technique for systematically varying a carrier signal in such a way that the transmitted signal contains information. Many techniques for modulating a carrier signal are used in the art, including various analog and digital modulation techniques. Modern wireless communication devices often employ quadrature amplitude modulation (QAM) , where a pair of quadrature (orthogonal) carrier signals have their amplitudes controlled to represent a desired location in a complex plane (sometimes referred to as a Gauss plane) .

And relatedly, multiplexing and multiple access are techniques for enabling simultaneous communication of multiple signals and/or devices on the same channel. For example, 5G New Radio (NR) specifications provide multiple access for uplink transmissions from mobile devices to base stations, and for multiplexing for downlink transmissions from base stations to mobile devices, utilizing orthogonal frequency division multiplexing (OFDM) with a cyclic prefix (CP) . In addition, for uplink transmissions, 5G NR specifications provide support for discrete Fourier transform-spread-OFDM (DFT-s-OFDM) with a CP (also referred to as single-carrier FDMA (SC-FDMA) ) . However, within the scope of the present disclosure, multiplexing and multiple access are not limited to the above schemes. For example, a mobile device may provide for uplink multiple access utilizing time division multiple access (TDMA) , code division multiple access (CDMA) , frequency division multiple access (FDMA) , sparse code multiple access (SCMA) , resource spread multiple access (RSMA) , orbital angular momentum (OAM) multiple access, coaxial multi-circle antenna multiple access, and/or other suitable multiple access schemes. Further, a base station may multiplex DL transmissions to UEs utilizing time division multiplexing (TDM) , code division multiplexing (CDM) , frequency division multiplexing (FDM) , orthogonal frequency division multiplexing (OFDM) , sparse code multiplexing (SCM) , orbital angular momentum (OAM) multiplexing, coaxial multi-circle antenna multiplexing, and/or other suitable multiplexing schemes.

OAM

An EM transmission can be characterized as a wave that carries momentum. In some examples, this momentum can include angular momentum, which includes a spin angular momentum (SAM) component, and an orbital angular momentum (OAM) component. In some cases, the SAM of the EM wave may be associated with the polarization of the EM wave. For example, an EM wave may be associated with different polarizations, such as left, right, and circular polarizations. Accordingly, the SAM of an EM wave may have multiple (e.g., two) degrees of freedom.

In some cases, the OAM of the EM wave may be associated with a field spatial distribution of the EM wave, which may be in the form of a helical or twisted wavefront shape. For example, an EM wave or light beam may be in a helical mode, which may also be referred to as an OAM mode; and such helical mode may be characterized by a wavefront that is shaped as a helix with an optical vortex in the center (e.g., at the beam axis) , where each helical mode is associated with a different helical wavefront structure. The helical modes (e.g., OAM modes) may be defined or referred to by a mode index l, where a sign of the mode index l corresponds to a ‘handedness’ (e.g., left or right) of the helix or helices; and a magnitude of the mode index l (e.g., |l|) corresponds to a quantity of distinct but interleaved helices of the EM wave.

For example, for an EM wave associated with an OAM mode index of l = 0, the EM wave is not helical, and the wavefronts of the EM wave are multiple disconnected surfaces (e.g., the EM wave is a sequence of parallel planes) . For an EM wave associated with an OAM mode index of l = +1, the EM wave may propagate in a right-handed sense (e.g., the EM wave may form a right helix that rotates about the beam axis in a clockwise direction) and the wavefront of the EM wave may be shaped as a single helical surface with a step length equal to a wavelength λ of the EM wave. Likewise, the phase delay over one revolution of the EM wave may be equal to 2π. Similarly, for an OAM mode index of l = -1, the EM wave may propagate in a left-handed sense (e.g., the EM wave may form a left helix that rotates about the beam axis in a counter-clockwise direction) and the wavefront of the EM wave may be also be shaped as a single helical surface with a step length equal to the wavelength λ of the EM wave. Likewise, the phase delay over one revolution of the EM wave may be equal to -2π.

In a further example, for an OAM mode index of l = ±2, the EM wave may propagate in either a right-handed sense (if l = +2) or in a left-handed sense (if l = -2) and the wavefront of the EM wave may include two distinct but interleaved helical surfaces. In such examples, the step length of each helical surface may be equal to λ/2. Likewise, the phase delay over one revolution of the EM wave may be equal to ±4π. In general terms, a mode-l EM wave may propagate in either a right-handed sense or a left-handed sense (depending on the sign of l) and may include l distinct but interleaved helical surfaces with a step length of each helical surface equal to π/|l|. Likewise, the phase delay over one revolution of the EM wave may be equal to 2lπ. In some cases, an EM wave may be indefinitely extended to provide for a theoretically infinite number of degrees of freedom of the OAM of the EM wave (e.g.,

where

is the unbounded set of integers) . As such, the OAM of the EM wave may be associated with an infinite number of degrees of freedom.

OAM modulation

In some examples, the OAM mode index l of an EM wave may correspond to or otherwise function as (e.g., be defined as) an additional dimension for signal or channel multiplexing. For example, each OAM mode or state (of which there may be an infinite number) may function similarly (or equivalently) to a communication channel, such as a sub-channel. In other words, an OAM mode or state may correspond to a communication channel, and vice–versa. For instance, a transmitting device or a receiving device may communicate separate signals using EM waves having different OAM modes or states similar to how a transmitting device or receiving device may communicate separate signals over different communication channels. In some aspects, such use of the OAM modes or states of an EM wave to carry different signals may be referred to as the use of OAM beams.

Additionally, in some examples, EM waves with different OAM modes (e.g., OAM states) may be mutually orthogonal to each other (e.g., in a Hilbert sense, in which a space may include an infinite set of axes and sequences may be come infinite by way of always having another coordinate direction in which next elements of the sequence can go) . Likewise, in a Hilbert sense, orthogonal OAM modes or states may correspond to orthogonal communication channels (e.g., orthogonal sequences transmitted over a communication channel) and, based on the potentially infinite number of OAM modes or states, a wireless communication system employing the use of OAM beams may theoretically achieve infinite capacity. Here, due to the mutual orthogonality among OAM modes, the waveform of one OAM mode generally cannot be received by a receiver aperture configured for a different OAM mode. In theory, an infinite number of OAM states or modes may be twisted together for multiplexing, and the capacity of the OAM link can approach infinity while preserving orthogonality between signals carried by different OAM modes (e.g., indices l) . In practice, however, due to non-ideal factors (e.g., Tx/Rx axial and/or position placement error, propagation divergence, and the like) , there may be crosstalk among OAM modes at the receiver, and thus a reduced number of concurrent OAM modes may be implemented between wireless devices. In some cases, a transmitting device may generate such OAM beams using spiral phase plate (SPP) or uniform circular array (UCA) configurations, such as discussed with reference to FIGs. 5 and 6.

The disclosure that follows presents various concepts that may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. FIG. 1 illustrates an example of a radio access network (RAN) 100 operating in a wireless communication system that supports one-and/or two-dimensional index modulation in connection with coaxial multi-circle OAM transmissions. By virtue of the wireless communication system 100, the UE 106 may be enabled to carry out data communication with an external data network 110, such as (but not limited to) the Internet.

The RAN 100 may implement any suitable wireless communication technology or technologies to provide radio access to one or more UEs. As one example, the RAN 100 may operate according to 3 ^rd Generation Partnership Project (3GPP) New Radio (NR) specifications, often referred to as 5G. As another example, the RAN 104 may operate under a hybrid of 5G NR and Evolved Universal Terrestrial Radio Access Network (eUTRAN) standards, often referred to as LTE. The 3GPP refers to this hybrid RAN as a next-generation RAN, or NG-RAN. Of course, the RAN 100 may operate according to any suitable 6G or other technology, and many other examples may be utilized within the scope of the present disclosure.

In FIG. 1, two

base stations

110 and 112 are shown in

cells

102 and 104; and a third base station 114 is shown controlling a remote radio head (RRH) 116 in cell 106. That is, a base station can have an integrated antenna or can be connected to an antenna or RRH by feeder cables. Broadly, a base station is a network element in a RAN responsible for radio transmission and reception in one or more cells to or from a UE. In different technologies, standards, or contexts, a base station may variously be referred to by those skilled in the art as a base transceiver station (BTS) , a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , an access point (AP) , a Node B (NB) , an eNode B (eNB) , a gNode B (gNB) , or some other suitable terminology.

The geographic area covered by the RAN 100 may be divided into cellular regions (cells) that can be uniquely identified by a user equipment (UE) based on an identification broadcasted from one access point or base station. FIG. 1 illustrates

macrocells

102, 104, and 106, and a small cell 108, each of which may include one or more sectors (not shown) . A sector is a sub-area of a cell. All sectors within one cell are served by the same base station. A radio link within a sector can be identified by a single logical identification belonging to that sector. In a cell that is divided into sectors, the multiple sectors within a cell can be formed by groups of antennas with each antenna responsible for communication with UEs in a portion of the cell.

In the illustrated example, the

cells

102, 104, and 126 may be referred to as macrocells, as the

base stations

110, 112, and 114 support cells having a large size. Further, a base station 118 is shown in the small cell 108 (e.g., a microcell, picocell, femtocell, home base station, home Node B, home eNode B, etc. ) which may overlap with one or more macrocells. In this example, the cell 108 may be referred to as a small cell, as the base station 118 supports a cell having a relatively small size. Cell sizing can be done according to system design as well as component constraints.

It is to be understood that the RAN 100 may include any number of wireless base stations and cells. Further, a relay node may be deployed to extend the size or coverage area of a given cell. The

base stations

110, 112, 114, 118 provide wireless access points to a core network for any number of mobile apparatuses.

The RAN 100 supports wireless communication for multiple mobile apparatuses. A mobile apparatus may be referred to as user equipment (UE) in 3GPP standards, but may also be referred to by those skilled in the art as a mobile station (MS) , a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal (AT) , a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. A UE may be an apparatus (e.g., a mobile apparatus) that provides access to network services.

Within the present document, a “mobile” apparatus need not necessarily have a capability to move, and may be stationary. The term mobile apparatus or mobile device broadly refers to a diverse array of devices and technologies. UEs may include a number of hardware structural components sized, shaped, and arranged to help in communication; such components can include antennas, antenna arrays, RF chains, amplifiers, one or more processors, etc. electrically coupled to each other. For example, some non-limiting examples of a mobile apparatus include a mobile, a cellular (cell) phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal computer (PC) , a notebook, a netbook, a smartbook, a tablet, a personal digital assistant (PDA) , and a broad array of embedded systems, e.g., corresponding to an “Internet of things” (IoT) . A mobile apparatus may additionally be an automotive or other transportation vehicle, a remote sensor or actuator, a robot or robotics device, a satellite radio, a global positioning system (GPS) device, an object tracking device, a drone, a multi-copter, a quad-copter, a remote control device, a consumer and/or wearable device, such as eyewear, a wearable camera, a virtual reality device, a smart watch, a health or fitness tracker, a digital audio player (e.g., MP3 player) , a camera, a game console, etc. A mobile apparatus may additionally be a digital home or smart home device such as a home audio, video, and/or multimedia device, an appliance, a vending machine, intelligent lighting, a home security system, a smart meter, etc. A mobile apparatus may additionally be a smart energy device, a security device, a solar panel or solar array, a municipal infrastructure device controlling electric power (e.g., a smart grid) , lighting, water, etc.; an industrial automation and enterprise device; a logistics controller; agricultural equipment; military defense equipment, vehicles, aircraft, ships, and weaponry, etc. Still further, a mobile apparatus may provide for connected medicine or telemedicine support, e.g., health care at a distance. Telehealth devices may include telehealth monitoring devices and telehealth administration devices, whose communication may be given preferential treatment or prioritized access over other types of information, e.g., in terms of prioritized access for transport of critical service data, and/or relevant QoS for transport of critical service data.

Wireless communication between a RAN 100 and a UE may be described as utilizing an air interface. The UEs and the base stations may wirelessly communicate with one another via one or more communication links utilizing one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting the communication links. Transmissions over the air interface from a base station to one or more UEs may be referred to as downlink (DL) transmission. In accordance with certain aspects of the present disclosure, the term downlink may refer to a point-to-multipoint transmission originating at a scheduling entity (e.g., a base station) . Another way to describe this scheme may be to use the term broadcast channel multiplexing. Transmissions from a UE to a base station may be referred to as uplink (UL) transmissions. In accordance with further aspects of the present disclosure, the term uplink may refer to a point-to-point transmission originating at a scheduled entity (e.g., a UE) .

In general, base stations may include a backhaul interface (not illustrated) for communication with a backhaul portion of the wireless communication system. The backhaul may provide a link between a base station and a core network. Further, in some examples, a backhaul network may provide interconnection between the respective base stations. Various types of backhaul interfaces may be employed, such as a direct physical connection, a virtual network, or the like using any suitable transport network. In some aspects, a portion of a backhaul network may be implemented using OAM transmitters and receivers, each associated with a respective base station.

In some examples, one or more base stations in the RAN 100 may be configured as integrated access and backhaul (IAB) nodes, where the wireless spectrum may be used both for access links (i.e., wireless links with UEs) , and for backhaul links. This scheme is sometimes referred to as wireless self-backhauling. By using wireless self-backhauling, rather than requiring each new base station deployment to be outfitted with its own hard-wired backhaul connection, the wireless spectrum utilized for communication between the base station and UE may be leveraged for backhaul communication, enabling fast and easy deployment of highly dense small cell networks. Additionally or alternatively, OAM transmissions may be leveraged for backhaul communication, which reduce an impact of wireless backhaul communications on wireless spectrum utilized for communication between the base station and UE when communications with UEs utilizes a different technology.

FIG. 1 further includes a quadcopter or drone 120, which may be configured to function as a base station. That is, in some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile base station such as the quadcopter 120.

Each

base station

110, 112, 114, 118, and 120 may be configured to provide an access point to a core network for all the UEs in the respective cells. For example,

UEs

122 and 124 may be in communication with base station 110;

UEs

126 and 128 may be in communication with base station 112;

UEs

130 and 132 may be in communication with base station 114 by way of RRH 116; UE 134 may be in communication with base station 118; and UE 136 may be in communication with mobile base station 120. In some examples, the

UEs

122, 124, 126, 128, 130, 132, 134, 136, 138, 140, and/or 142 may be the same as the UE/scheduled entity 106 described above and illustrated in FIG. 1.

In some examples, a mobile network node (e.g., quadcopter 120) may be configured to function as a UE. For example, the quadcopter 120 may operate within cell 102 by communicating with base station 110.

In a further aspect of the RAN 100, sidelink signals may be used between UEs without necessarily relying on scheduling or control information from a base station. For example, two or more UEs (e.g., UEs 126 and 128) may communicate with each other using peer to peer (P2P) or sidelink signals 127 without relaying that communication through a base station (e.g., base station 112) . In a further example, UE 138 is illustrated communicating with

UEs

140 and 142. Here, the UE 138 may function as a scheduling entity or a primary sidelink device, and

UEs

140 and 142 may function as a scheduled entity or a non-primary (e.g., secondary) sidelink device. In still another example, a UE may function as a scheduling entity in a device-to-device (D2D) , peer-to-peer (P2P) , or vehicle-to-vehicle (V2V) network, and/or in a mesh network. In a mesh network example,

UEs

140 and 142 may optionally communicate directly with one another in addition to communicating with the scheduling entity 138. Thus, in a wireless communication system with scheduled access to time–frequency resources and having a cellular configuration, a P2P configuration, or a mesh configuration, a scheduling entity and one or more scheduled entities may communicate utilizing the scheduled resources.

In some examples, The RAN 100 may operate in a super high frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also known as the centimeter band, in an extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz) , also known as the millimeter band, or in even higher frequency bands reaching into the terahertz (THz) range. And in some examples, the RAN 100 may support millimeter wave (mmW) communications between the UEs and the base stations, and EHF antennas of the respective devices may be smaller and more closely spaced than UHF antennas. In some examples, this may facilitate use of antenna arrays within a device. The propagation of EHF transmissions, however, may be subject to even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. The techniques disclosed herein may be employed across transmissions that use one or more different frequency regions, and designated use of bands across these frequency regions may differ by country or regulating body.

Multi-Antenna Arrays Generally

In some aspects of the disclosure, a wireless communication node or device may be configured with multiple antennas, e.g., for beamforming, multiple-input multiple-output (MIMO) , and/or orbital angular momentum (OAM) modulation technology. FIG. 2 illustrates an example of wireless communication utilizing multiple antennas, supporting beamforming, MIMO, and OAM. In some examples, the system of FIG. 2 may implement aspects of RAN 100. The use of such multiple antenna technology enables a wireless communication system to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity.

Beamforming generally refers to directional signal transmission or reception. For a beamformed transmission, the amplitude and phase of each antenna in an array of antennas may be precoded, or controlled to create a desired (e.g., directional) pattern of constructive and destructive interference in the wavefront. In a MIMO system, a transmitter 202 includes multiple transmit antennas 204 (e.g., N transmit antennas) and a receiver 206 includes multiple receive antennas 208 (e.g., M receive antennas) . Thus, there are N × M signal paths 210 from the transmit antennas 204 to the receive antennas 208. Each of the transmitter 202 and the receiver 206 may be implemented, for example, within a scheduling entity 108, a scheduled entity 106, or any other suitable wireless communication device.

In a MIMO system, spatial multiplexing may be used to transmit multiple different streams of data, also referred to as layers, simultaneously on the same time-frequency resource. In some examples, a transmitter may send multiple data streams to a single receiver. In this way, a MIMO system takes advantage of capacity gains and/or increased data rates associated with using multiple antennas in rich scattering environments where channel variations can be tracked. Here, the receiver may track these channel variations and provide corresponding feedback to the transmitter. In the simplest case, a rank-2 (i.e., including 2 data streams) spatial multiplexing transmission on a 2x2 MIMO antenna configuration will transmit two data streams via two transmit antennas 204. The signal from each transmit antenna 204 reaches each receive antenna 208 along a different signal path 210. The receiver 206 may then reconstruct the data streams using the received signals from each receive antenna 208.

The number of data streams or layers in a MIMO system corresponds to the rank of the transmission. In general, the rank of a MIMO system is limited by the number of transmit or receive

antennas

204 or 208, whichever is lower. In addition, the channel conditions at the receiving device, as well as other considerations, such as the available resources at the transmitting device, may also affect the transmission rank. For example, a base station in a cellular RAN may assign a rank (and therefore, a number of data streams) for a DL transmission to a particular UE based on a rank indicator (RI) the UE transmits to the base station. The UE may determine this RI based on the antenna configuration (e.g., the number of transmit and receive antennas) and a measured signal-to-interference-and-noise ratio (SINR) on each of the receive antennas. The RI may indicate, for example, the number of layers that may be supported under the current channel conditions. The base station may use the RI along with resource information (e.g., the available resources and amount of data to be scheduled for the UE) to assign a DL transmission rank to the UE.

The transmitting device determines the precoding of the transmitted data stream or streams based, e.g., on known channel state information of the channel on which the transmitting device transmits the data stream (s) . For example, the transmitting device may transmit one or more suitable reference signals (e.g., a channel state information reference signal, or CSI-RS) that the receiving device may measure. The receiver may then report measured channel quality information (CQI) back to the transmitting device. This CQI generally reports the current communication channel quality, and in some examples, a requested transport block size (TBS) for future transmissions to the receiver. In some examples, the receiver may further report a precoding matrix indicator (PMI) back to the transmitting device. This PMI generally reports the receiving device's preferred precoding matrix for the transmitting device to use, and may be indexed to a predefined codebook. The transmitting device may then utilize this CQI/PMI to determine a suitable precoding matrix for transmissions to the receiver.

In some cases, the RAN 100 may be an example of or otherwise support an OAM-based communication system and a transmitting device 202 or a receiving device 206 may communicate via OAM beams. In some examples, a transmitting device 202 or a receiving device 206 may generate and steer an OAM beam based on selecting a set of antenna elements from a planar array of antenna elements (e.g., a planar array on the transmitting device 202 or a receiving device 206 that may be used for MIMO communications) based on which antenna elements fall within a determined area on the planar array associated with a uniform circular array (UCA) for OAM communications. Additionally or alternatively, one or more transmitting devices 202 or receiving devices 206 may include components that provide for spiral phase plate (SPP) -based OAM communications.

In various examples, some or all of the wireless resources of the RAN 100 may be scheduled to carry one or more physical channels, including control channels, shared channels, data channels, etc. Other resources of the RAN 100 may also carry pilots or reference signals. These pilots or reference signals may provide for a receiving device to perform channel estimation of the corresponding channel.

In a DL transmission, the transmitting device (e.g., a base station or scheduling entity) may allocate a set of wireless resources to carry DL control information including one or more DL control channels that generally carry information originating from higher layers to one or more receiving devices (e.g., a UE or scheduled entity) . In addition, DL resources may be allocated to carry DL physical signals that generally do not carry information originating from higher layers. These DL physical signals may include synchronization signals, demodulation reference signals (DM-RS) , phase-tracking reference signals (PT-RS) , channel-state information reference signals (CSI-RS) , etc.

In an UL transmission, a transmitting device (e.g., a UE or scheduled entity) may utilize a set of designated wireless resources to carry UL control information (UCI) to a receiving device (e.g., a base station or scheduling entity) . The UCI can originate from higher layers via one or more UL control channels. Further, UL wireless resources may carry UL physical signals that generally do not carry information originating from higher layers, such as demodulation reference signals (DM-RS) , phase-tracking reference signals (PT-RS) , sounding reference signals (SRS) , etc.

In a sidelink (SL) transmission, a transmitting device (e.g., a UE or scheduled entity, or a base station of scheduling entity) may utilize a set of designated wireless resources to carry SL control information (SCI) to a receiving device (e.g., another UE or scheduled entity, or another base station of scheduling entity) . Further, SL wireless resources may carry SL physical signals that generally do not carry information originating from higher layers, such as demodulation reference signals (DM-RS) , phase-tracking reference signals (PT-RS) , sounding reference signals (SRS) , etc.

In addition to control information, wireless resources may be allocated for user data or traffic data, which may be carried on one or more traffic channels.

Wireless Resources

Those of ordinary skill in the art should understand that the various aspects of the present disclosure may be applied to a DFT-s-OFDMA waveform in substantially the same way as described herein below. That is, while some examples of the present disclosure may focus on an OFDM link for clarity, it should be understood that the same principles may be applied as well to DFT-s-OFDMA waveforms.

In some examples, a frame may refer to a predetermined duration of time (e.g., 10 ms) for wireless transmissions. And further, each frame may consist of a set of subframes (e.g., 10 subframes of 1 ms each) . A given carrier may include one set of frames in the UL, and another set of frames in the DL.

A resource grid may represent time–frequency resources for a given antenna port. For example, in a MIMO implementation with multiple antenna ports available, a corresponding multiple number of resource grids may be available for communication. For example, as described below, different OAM modes may be orthogonal when transmitted using the same time, frequency, and/or code resources, and thus may be associated with independent resource grids.

A resource grid may be divided into multiple resource elements (REs) . An RE, which is 1 subcarrier × 1 symbol, is the smallest discrete part of the time–frequency grid, and may contain a single complex value representing data from a physical channel or signal. Depending on the modulation utilized in a particular implementation, each RE may represent one or more bits of information. In some examples, a block of REs may be referred to as a physical resource block (PRB) or more simply a resource block (RB) , which contains any suitable number of consecutive subcarriers in the frequency domain. In one example, an RB may include 12 subcarriers, a number independent of the numerology used. In some examples, depending on the numerology, an RB may include any suitable number of consecutive OFDM symbols in the time domain. The present disclosure assumes, by way of example, that a single RB entirely corresponds to a single direction of communication (either transmission or reception for a given device) .

A UE generally utilizes only a subset of a resource grid. An RB may be the smallest unit of resources that a scheduler can allocate to a UE. Thus, the more RBs scheduled for a UE, and the higher the modulation scheme chosen for the air interface, the higher the data rate for the UE.

Description of Channels and Signals

Various REs within an RB may carry one or more physical channels, including control channels, shared channels, data channels, etc. Other REs within the RB may also carry pilots or reference signals. These pilots or reference signals may provide for a receiving device to perform channel estimation of the corresponding channel, which may enable coherent demodulation/detection of the control and/or data channels within the RB.

In a DL transmission, the transmitting device (e.g., a base station or a UE) may allocate one or more REs (e.g., within a control region) to carry one or more DL control channels. These DL control channels include DL control information (DCI) that generally carries information originating from higher layers, such as a physical broadcast channel (PBCH) , a physical downlink control channel (PDCCH) , etc., to one or more receiving devices (e.g., a UE) . In addition, the transmitting device may allocate one or more DL REs to carry DL physical signals that generally do not carry information originating from higher layers. These DL physical signals may include a primary synchronization signal (PSS) ; a secondary synchronization signal (SSS) ; demodulation reference signals (DM-RS) ; phase-tracking reference signals (PT-RS) ; channel-state information reference signals (CSI-RS) ; etc.

A base station may transmit the synchronization signals PSS and SSS (collectively referred to as SS) , and in some examples, the PBCH, in an SS block that includes 4 consecutive OFDM symbols, numbered via a time index in increasing order from 0 to 3. In the frequency domain, the SS block may extend over 240 contiguous subcarriers, with the subcarriers being numbered via a frequency index in increasing order from 0 to 239. Of course, the present disclosure is not limited to this specific SS block configuration. Other nonlimiting examples may utilize greater or fewer than two synchronization signals; may include one or more supplemental channels in addition to the PBCH; may omit a PBCH; and/or may utilize nonconsecutive symbols for an SS block, within the scope of the present disclosure.

The PDCCH may carry downlink control information (DCI) for one or more UEs in a cell. This can include, but is not limited to, power control commands, scheduling information, a grant, and/or an assignment of REs for DL and UL transmissions.

In an UL transmission, a transmitting device (e.g., a scheduled entity) may utilize one or more REs to carry one or more UL control channels, such as a physical uplink control channel (PUCCH) , a physical random access channel (PRACH) , etc. These UL control channels include UL control information (UCI) that generally carries information originating from higher layers. Further, UL REs may carry UL physical signals that generally do not carry information originating from higher layers, such as demodulation reference signals (DM-RS) , phase-tracking reference signals (PT-RS) , sounding reference signals (SRS) , etc. In some examples, the control information may include a scheduling request (SR) , i.e., a request for the scheduling entity to schedule uplink transmissions. Here, in response to the SR transmitted on the control channel, the scheduling entity may transmit downlink control information that may schedule resources for uplink packet transmissions.

UL control information may also include hybrid automatic repeat request (HARQ) feedback such as an acknowledgment (ACK) or negative acknowledgment (NACK) , channel state information (CSI) , or any other suitable UL control information. HARQ is a technique well-known to those of ordinary skill in the art, wherein a receiving device can check the integrity of packet transmissions for accuracy, e.g., utilizing any suitable integrity checking mechanism, such as a checksum or a cyclic redundancy check (CRC) . If the receiving device confirms the integrity of the transmission, it may transmit an ACK, whereas if not confirmed, it may transmit a NACK. In response to a NACK, the transmitting device may send a HARQ retransmission, which may implement chase combining, incremental redundancy, etc.

In addition to control information, one or more REs may be allocated for user data or traffic data. Such traffic may be carried on one or more traffic channels, such as, for a DL transmission, a physical downlink shared channel (PDSCH) ; or for an UL transmission, a physical uplink shared channel (PUSCH) .

The channels or carriers described above are not necessarily all the channels or carriers that may be utilized between a scheduling entity and one or more scheduled entities, and those of ordinary skill in the art will recognize that other channels or carriers may be utilized in addition to those illustrated, such as other traffic, control, and feedback channels.

Block Diagrams

FIG. 3 is a block diagram illustrating an example of a hardware implementation for a transmitting device 300 employing a processing system 314. For example, the transmitting device 300 may be a user equipment (UE) , a base station, or any other wireless communication node, e.g., as illustrated in any of FIGs. 1 and/or 2.

The transmitting device 300 may be implemented with a processing system 314 that includes one or more processors 304. Examples of processors 304 include microprocessors, microcontrollers, digital signal processors (DSPs) , field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , application specific integrated circuits (ASICs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. In various examples, the transmitting device 300 may be configured to perform any one or more of the functions described herein. That is, the processor 304, as utilized in a transmitting device 300, may be configured (e.g., in coordination with the memory 305) to implement any one or more of the processes and procedures described below and illustrated in FIGs. 8 and/or 9.

In this example, the processing system 314 may be implemented with a bus architecture, represented generally by the bus 302. The bus 302 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 314 and the overall design constraints. The bus 302 communicatively couples together various circuits including one or more processors (represented generally by the processor 304) , a memory 305, and computer-readable media (represented generally by the computer-readable medium 306) . The bus 302 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. A bus interface 308 provides an interface between the bus 302 and a transceiver 310.

The transceiver 310 provides a communication interface or means for communicating with various other apparatus over a transmission medium. In some aspects, the transceiver 310 includes (or is coupled to) a plurality of antennas 311. The plurality of antennas 311 may be configured similar to the spiral phase plate (SPP) antennas described below and illustrated in FIG. 5; similar to the uniform circular array (UCA) antennas described below and illustrated in FIG. 6; similar to the coaxial multi-circle UCA configuration described below and illustrated in FIG. 7; or some combination of two or more of the above. In some aspects, any structures that enable OAM multiplexing of electromagnetic signals (e.g., RF signals, light signals, etc. ) may apply, including but not limited to UCA antennas and SPP antennas, which are described as examples. The plurality of antennas 311 may include or otherwise be configured using any other suitably configured phase plates, spatial modulators, integrated circuits, any other suitable components, and/or any suitable combination thereof, for transmission over any suitable medium including a wireless air interface, an optical fiber, etc.

Depending upon the nature of the transmitting device 300, a user interface 312 (e.g., keypad, display, speaker, microphone, joystick) may also be provided. Of course, such a user interface 312 is optional, and may be omitted in some examples, such as a base station.

In some aspects of the disclosure, the processor 304 may include communication circuitry 341 configured (e.g., in coordination with the memory 305) for various functions, including, e.g., coordinating with a transceiver controller circuit 342 and/or transceiver controller instructions 362 to transmit suitable waveform to communicate information and/or transmit reference signals using one or more OAM modes. For example, the communication circuitry 341 may be configured to implement one or more of the functions described below in relation to FIG. 8, including, e.g., blocks 802 and/or 808; in relation to FIG. 9, including, e.g., blocks 902, 922, and/or 928.

In some further aspects of the disclosure, the processor 304 may include a transceiver controller 342 configured (e.g., in coordination with the memory 305 and/or the transceiver 310) for various functions, including, e.g., transmitting a suitable waveform (e.g., information or data stream) and/or reference signal (e.g., DM-RS, CSI-RS, etc. ) as disclosed herein. For example, the transceiver controller 342 may be configured to implement one or more of the functions described below in relation to FIG. 8, including, e.g., blocks 802 and/or 808; in relation to FIG. 9, including, e.g., blocks 902, 922, and/or 928.

In some further aspects of the disclosure, the processor 304 may include OAM mode grouping circuitry 343 configured (e.g., in coordination with the memory 305) for various functions, including, e.g., receiving a mode orthogonality distance threshold T (e.g., as described below in connection with block 914) from a receiving device, and calculating an inter-mode interval based on the mode orthogonality distance threshold T. In some examples, the OAM mode grouping circuitry 343 may group OAM modes based on the inter-mode interval, such that the mode order between any two OAM modes in a group is no smaller than the inter-mode interval; in some additional examples, the OAM mode grouping circuitry 343 may cause the transceiver (e.g., in coordination with the transceiver controller 342) to transmit group configuration information indicative of which OAM modes are grouped together; and in some other examples, the OAM mode grouping circuitry 343 may cause the transceiver (e.g., in coordination with the transceiver controller 342) to transmit each group of reference signals using shared resources. For example, the OAM mode grouping circuitry 343 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 920, 922, and/or 928..

The processor 304 is responsible for managing the bus 302 and general processing, including the execution of software stored on the computer-readable medium 306. The software, when executed by the processor 304, causes the processing system 314 to perform the various functions described below for any particular apparatus. The computer-readable medium 306 and the memory 305 may also be used for storing data that is manipulated by the processor 304 when executing software.

One or more processors 304 in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium 306. The computer-readable medium 306 may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip) , an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD) ) , a smart card, a flash memory device (e.g., a card, a stick, or a key drive) , a random access memory (RAM) , a read only memory (ROM) , a programmable ROM (PROM) , an erasable PROM (EPROM) , an electrically erasable PROM (EEPROM) , a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium 306 may reside in the processing system 314, external to the processing system 314, or distributed across multiple entities including the processing system 314. The computer-readable medium 306 may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

In some aspects, the transmitting device 300 may include (or otherwise be associated with) an alignment detection system 316 that may include a light source (e.g., a laser) and/or a photodetector (e.g., an image sensor) . In some aspects, the alignment detection system 316 may emit a beam of light parallel to a central axis of the antennas 311 (e.g., a central axis of a UCA antenna) configured to transmit OAM signals. The beam may be detected by a photodetector associated with a receiving device (e.g., the receiving device 400 described below in connection with FIG. 4) , such that the receiving device may determine a misalignment between the antennas 311 and antennas associated with the receiving device based on a location of the beam.

Additionally or alternatively, in some aspects, the alignment detection system 316 may detected a beam of light emitted by a laser associated with a receiving device (e.g., the receiving device 400 described below in connection with FIG. 4) , and may determine a misalignment between the antennas 311 and antennas associated with the receiving device based on a location of the beam. In some examples, the alignment detection system 316 may be omitted, for example, in cases when alignment is detected using other techniques (e.g., based on interference between adjacent OAM modes, as described below in connection with FIGs. 9 and 12) .

In one or more examples, the computer-readable storage medium 306 may store computer-executable code that includes communication instructions 361 that configure a transmitting device 300 for various functions, including, e.g., receiving an information stream (e.g., a sequence of bits) for transmission, and coordinating with a transceiver controller circuit 342 and/or transceiver controller instructions 362 to transmit a suitable waveform. For example, the communication instructions 361 may be configured to cause a transmitting device 300 to implement one or more of the functions described below in relation to FIG. 8, including, e.g., blocks 802 and/or 808; in relation to FIG. 9, including, e.g., blocks 902, 922, and/or 928.

In one or more further examples, the computer-readable storage medium 306 may store computer-executable code that includes transceiver controller instructions 362 that configure a transmitting device 300 for various functions, including, e.g., transmitting a suitable waveform (e.g., information or data stream) and/or reference signal (e.g., DM-RS, CSI-RS, etc. ) as disclosed herein. For example, the transceiver controller instructions 362 may be configured to cause a transmitting device 300 to implement one or more of the functions described below in relation to FIG. 8, including, e.g., blocks 802 and/or 808; in relation to FIG. 9, including, e.g., blocks 902, 922, and/or 928.

In one or more further examples, the computer-readable storage medium 306 may store computer-executable code that includes OAM mode grouping instructions 363 that configure a transmitting device 300 for various functions, including, e.g., receiving a mode orthogonality distance threshold T (e.g., as described below in connection with block 914) from a receiving device, and calculating an inter-mode interval based on the mode orthogonality distance threshold T. In some examples, the OAM mode grouping instructions 363 may group OAM modes based on the inter-mode interval, such that the mode order between any two OAM modes in a group is no smaller than the inter-mode interval; in some additional examples, the OAM mode grouping instructions 363 may cause the transceiver to transmit group configuration information indicative of which OAM modes are grouped together; and in some other examples, the OAM mode grouping instructions 363 may cause the transceiver to transmit each group of reference signals using shared resources. For example, the OAM mode grouping instructions 363 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 920, 922, and/or 928.

In one configuration, the transmitting device 300 for wireless communication includes means for transmitting a first reference signal on a first OAM mode using first resources, means for transmitting a second reference signal on a first OAM mode using the first resources, and means for transmitting a third reference signal on a third OAM mode using second resources, means for receiving information indicative of inter-mode interference, and/or means for grouping OAM modes into groups based on inter-mode interference. In one aspect, the aforementioned means may be the processor 304 shown in FIG. 3 configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a circuit or any apparatus configured to perform the functions recited by the aforementioned means.

Of course, in the above examples, the circuitry included in the processor 304 is merely provided as an example, and other means for carrying out the described functions may be included within various aspects of the present disclosure, including but not limited to the instructions stored in the computer-readable storage medium 306, or any other suitable apparatus or means described in any one of the FIGs. 1, 2, 5, 6, and/or 7, and utilizing, for example, the processes and/or algorithms described herein in relation to FIGs. 8 and/or 9.

FIG. 4 is a conceptual diagram illustrating an example of a hardware implementation for an exemplary receiving device 400 employing a processing system 414. In accordance with various aspects of the disclosure, an element, or any portion of an element, or any combination of elements may be implemented with a processing system 414 that includes one or more processors 404. For example, the receiving device 400 may be a user equipment (UE) , a base station, or any other suitable wireless communication node, e.g., as illustrated in any of FIGs. 1 and/or 2.

In some aspects, the transceiver 410 includes (or is coupled to) a plurality of antennas 411. The plurality of antennas 411 may be configured similar to the spiral phase plate (SPP) antennas described below and illustrated in FIG. 5; similar to the uniform circular array (UCA) antennas described below and illustrated in FIG. 6; similar to the coaxial multi-circle UCA configuration described below and illustrated in FIG. 7; or some combination of two or more of the above. In some aspects, any structures that enable OAM multiplexing of electromagnetic signals (e.g., RF signals, light signals, etc. ) may apply, including but not limited to UCA antennas and SPP antennas, which are described as examples. The plurality of antennas 411 may include or otherwise be configured using any other suitably configured phase plates, spatial modulators, integrated circuits, any other suitable components, and/or any suitable combination thereof, for transmission over any suitable medium including a wireless air interface, an optical fiber, etc.

The processing system 414 may be substantially the same as the processing system 314 illustrated in FIG. 3, including a bus interface 408, a bus 402, memory 405, a processor 404, and a computer-readable medium 406. Furthermore, the receiving device 400 may include a user interface 412, a transceiver 410, and an alignment detection system 416 substantially similar to those described above in FIG. 3. That is, the processor 404, as utilized in a receiving device 400, may be configured (e.g., in coordination with the memory 405) to implement any one or more of the processes described below and illustrated in FIGs. 8 and/or 9.

In some aspects of the disclosure, the processor 404 may include a transceiver controller 441 configured (e.g., in coordination with the memory 405) for various functions, including, for example, receiving and sampling a waveform (in some examples, including one or more reference signals) , and storing samples of the received waveform in memory 405. For example, the transceiver controller 441 may be configured to implement one or more of the functions described below in relation to FIG. 8, including, e.g., block 804 and/or 810; in relation to FIG. 9, including, e.g., blocks 906, 926, and/or 932.

In some further aspects of the disclosure, the processor 404 may include direction misalignment circuitry 442 configured (e.g., in coordination with the memory 405) for various functions, including, for example, configured (e.g., in coordination with the memory 405) for various functions, including, for example, determining a magnitude of misalignment based on a detected position at which light impinges a photodetector of alignment detection system 416. In some examples, the direction misalignment circuitry 442 may determine a mode orthogonality distance threshold (e.g., as described below in connection with block 914 of FIG. 9) ; and in some other examples, the direction misalignment circuitry 442 may cause the transceiver (e.g., in coordination with the transceiver controller 441) to transmit the mode orthogonality distance threshold to a transmitting device. For example, the direction misalignment circuitry 442 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 912, 914, and/or 916.

In some further aspects of the disclosure, the processor 404 may include channel modeling circuitry 443 configured (e.g., in coordination with the memory 405) for various functions, including, for example, configured (e.g., in coordination with the memory 405) for various functions, including, for example, estimating properties of channels associated with OAM modes used to transmit reference signals received from a transmitting device (e.g., DM-RS, CSI-RS, etc. ) , and in some examples, providing an indication of channel properties associated with the OAM modes to the transmitting device. For example, the channel modeling circuitry 443 may be configured to implement one or more of the functions described below in relation to FIG. 8, including, e.g., block 814; and/or in relation to FIG. 9, including, e.g., block 932.

And further, the computer-readable storage medium 406 may store computer-executable code that includes transceiver controller instructions 461 that configure a receiving device 400 for various functions, including, e.g., receiving and sampling a waveform (in some examples, including one or more reference signals) , and storing samples of the received waveform in memory 405. For example, the transceiver controller instructions 461 may be configured to cause a receiving device 400 to implement one or more of the functions described below in relation to FIG. 8, including, e.g., block 804 and/or 810; in relation to FIG. 9, including, e.g., blocks 906, 926, and/or 932.

In some further examples, the computer-readable storage medium 406 may store computer-executable code that includes direction misalignment instructions 462 that configure a receiving device 400 for various functions, including, e.g., direction misalignment instructions 462 that configure a receiving device 400 for various functions, including, e.g., determining a magnitude of misalignment based on a detected position at which light impinges a photodetector of alignment detection system 416. In some examples, the direction misalignment instructions 462 may determine a mode orthogonality distance threshold (e.g., as described below in connection with block 914 of FIG. 9) ; and in some other examples, the direction misalignment instructions 462 may cause the transceiver to transmit the mode orthogonality distance threshold to a transmitting device. For example, the direction misalignment instructions 462 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 912, 914, and/or 916.

In some further examples, the computer-readable storage medium 406 may store computer-executable code that includes channel modeling instructions 463 that configure a receiving device 400 for various functions, including, e.g., estimating properties of channels associated with OAM modes used to transmit reference signals received from a transmitting device (e.g., DM-RS, CSI-RS, etc. ) , and in some examples, providing an indication of channel properties associated with the OAM modes to the transmitting device. For example, the channel modeling instructions 463 may be configured to implement one or more of the functions described below in relation to FIG. 8, including, e.g., block 814; and/or in relation to FIG. 9, including, e.g., block 932.

In one configuration, the receiving device 400 for wireless communication includes for receiving a first reference signal on a first OAM mode using first resources, means for receiving a second reference signal on a first OAM mode using the first resources, and means for receiving a third reference signal on a third OAM mode using second resources, means for transmitting information indicative of inter-mode interference, means for determining a degree of direction misalignment between the plurality of antennas and a plurality of antennas associated with an OAM transmitter apparatus based on the reference signals received using the different resources, means for determining an orthogonality distance threshold, means for determining a channel gain of an OAM mode, and/or means for determining inter-mode interference between two OAM modes. In one aspect, the aforementioned means may be the processor 404 shown in FIG. 4 configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a circuit or any apparatus configured to perform the functions recited by the aforementioned means.

Of course, in the above examples, the circuitry included in the processor 404 is merely provided as an example, and other means for carrying out the described functions may be included within various aspects of the present disclosure, including but not limited to the instructions stored in the computer-readable storage medium 406, or any other suitable FIGs. 1, 2, 5, 6, and/or 7, and utilizing, for example, the processes and/or algorithms described herein in relation to FIGs. 8 and/or 9.

In some aspects, this disclosure provides for a wireless communication technique that exploits an orbital angular momentum (OAM) property of electromagnetic (EM) waves for modulating a carrier to carry information, and/or for multiplexing reference signals onto a common wireless resource. Systems and devices that employ OAM are currently under intense development due to its improved communication spectrum efficiency, its capability to provide high-order spatial multiplexing (e.g., as described further below) , potentially resulting in higher data rates, and the possibility to enable low receiver complexity, OAM is regarded as a strong candidate for future 6G communication technology or as an enhancement to existing 5G technology.

SPP Configuration

FIG. 5 illustrates an example of a spiral phase plate (SPP) OAM configuration that supports information transmission by OAM mode selection and detection in accordance with some aspects of the present disclosure. In some examples, the illustrated SPP OAM configuration may implement aspects of RAN 100, and may be employed by the transmitting device 202/300 and receiving device 206/400. In this example, a transmitting device (e.g., UE or base station) may include transmitter OAM components 505 and a receiving device (e.g., UE or base station) may include receiver OAM components 510.

In cases in which wireless devices use an SPP methodology, a transmitting device may convert an EM wave 515 associated with an OAM mode index l = 0 (e.g., a non-helical EM wave associated with mode-zero OAM) into an EM wave associated with an OAM mode index l ≠ 0 (e.g., a helical EM wave associated with a non-zero OAM mode) by passing the EM wave through an aperture 520 and an SPP 525. Such an SPP 525 may have a suitable structure and/or configuration, known to those skilled in the art, such as to generate an EM wave associated with a single OAM mode. Thus, the wireless device may use one SPP 525 to generate one OAM mode of an OAM beam 535. As such, a wireless device may implement a different SPP 525 for each OAM mode of an OAM beam 535.

In the example of FIG. 5, two OAM modes may be used (e.g., l = +1 and -1) . In the transmitter OAM components, a first EM wave 515-a may be provided to a first aperture 520-a and a first SPP 525-a, and a second EM wave 515-b may be provided to a second aperture 520-b and a second SPP 525-b. A beam splitter/combiner 550 may combine the output of the first SPP 525-a and the second SPP 525-b to generate OAM beam 535. The receiver OAM components 510 may receive the OAM beam 535 at a beam splitter/combiner 540 to provide instances of the OAM beam 535 to a third SPP 525-c and a fourth SPP 525-d that provide output to a first receiver aperture 520-c and a second receiver aperture 520-d, respectively. In general, a receiving device includes a separate SPP and receiver aperture for each OAM mode. Thus, the third SPP 525-c may be configured recover the OAM mode corresponding to the first SPP 525-a, and thus, the output of the first receiver aperture 520-c may correspond to the first EM wave 515-a (e.g., for OAM Mode l = 1) . Likewise, the fourth SPP 525-d may be configured to recover the OAM mode corresponding to the second SPP 525-b, and thus, the output of the second receiver aperture 520-d may correspond to the second EM wave 515-b (e.g., for OAM Mode l = 2) . In devices that use an SPP methodology, separate SPPs 525-a may thus be used for each OAM mode, and the number of SPPs 525 at a device may constrain the number of usable OAM modes. As described below, wireless devices may also use a UCA methodology for OAM communications, an example of which is discussed with reference to FIG. 6.

UCA Configuration

FIG. 6 illustrates an example of a uniform circular array (UCA) OAM configuration that supports information transmission by OAM mode selection and detection in accordance with some aspects of the present disclosure. In some examples, the illustrated UCA OAM configuration may implement aspects of RAN 100, and may be employed by the transmitting device 202/300 and receiving device 206/400. In this example, a transmitting device (e.g., UE or base station) may include OAM transmitter UCA antennas 605 and a receiving device (e.g., UE or base station) may include OAM receiver UCA antennas 610.

In some aspects, one or both of the OAM transmitter UCA antennas 605 or the OAM receiver UCA antennas 610 may be implemented as a planar array of antenna elements, which may be an example of or otherwise function as a (massive or holographic) MIMO array or an intelligent surface. In some cases, the transmitting device may identify a set of antenna elements 615 of the planar array that form a transmitter UCA, and a receiving device may identify a set of antenna elements 645 of the planar array that form a receiver UCA.

Upon selecting the set of antenna elements from the planar array, the OAM transmitter may apply a weight 635 to each of the selected antenna elements 615 based on the OAM mode index l of the transmitted OAM beam and one or more spatial parameters associated with each antenna element. In cases in which a UCA methodology is used to generate an OAM beam, the transmitting device may identify the set of antenna elements 615 on a circular array of antenna elements and may load a first set of weights 620 to each of the identified antenna elements based on a first OAM mode index (e.g., l = 0) . Further, for other OAM mode indices, other weights may be used for the set of antenna elements 615, such as a second OAM mode index (e.g., l = +1) that may use a second set of weights 625 and a third OAM mode index (e.g., l = –1) that may use a third set of weights 630.

For example, to generate an OAM beam with a selected OAM mode index (e.g., l = 0) , an OAM transmitter may load a weight 635 to each antenna element 615 on the UCA based on an angle 640 measured between a reference line on the UCA (e.g., the x-axis of the plane on which the UCA is located, where the origin is at the center of the UCA) and the antenna element, the OAM mode index l, and i (e.g., for complex-valued weights, which may alternatively be denoted as j in some cases) . In some cases, for instance, the weight for an antenna element n may be proportional to

where

is equal to the angle 640 measured between the reference line on the UCA and the antenna element n. By multiplying respective beamforming weights 635 of each set of weights 620–730 (e.g., for first set of weights 620, w ₁ = [w _1, 1, w _1, 2, …, w _1, 8 ^T) onto each antenna, a signal port may be generated. If the weight 635 of each antenna 615 is equal to

where

is the angle of antenna 615 in the circle (e.g., angle 640 for antenna element 615-g) , and l is the OAM mode index, then each set of weights 620–730 provides a beamformed port that is equivalent OAM mode l. By using different beamforming weights

where l’≠ l, multiple OAM modes are thus generated.

At the OAM receiver UCA antennas 610, the receiving device may have receive antenna elements 645 equipped in a circle. The channel matrix may be denoted from each transmit antenna to each receive antenna as H, and then for the beamformed channel matrix

any two columns of

are orthogonal, which means the beamformed ports have no crosstalk. This may allow OAM-based communication to efficiently realize a high-level spatial multiplexing degree. Further, the eigen-based transmit precoding weights and receive combining weights of UCA-based OAM are equal to a discrete Fourier transform (DFT) matrix, which is independent of communication parameters (e.g., distance, aperture size, and carrier frequency) . Thus, UCA-based OAM may be implemented at relatively low cost. In some cases, the receiving device may test multiple different OAM modes to determine the OAM mode that was used in a transmission (e.g., based on whether a particular OAM mode yields a successfully demodulated transmission) , which may be used to identify one or more information bits of a transmission.

In some aspects, as described below in connection with FIGs. 8 to 10, when the central axes of the transmitter antennas (e.g., the antennas 311) and receiver antennas (e.g., the antennas 411) are closely aligned (e.g., with less than 0.1 milliradians (mrad) of misalignment) , each OAM mode is orthogonal to each other OAM mode. However, as the antennas become misaligned, neighboring OAM modes may cause interference. For example, at 1 mrad of misalignment, an adjacent OAM mode may cause significant interference, and at larger misalignments, OAM modes that are father from a particular OAM mode may also cause interference.

Multiple Coaxial UCA Configuration

FIG. 7 illustrates an example of a coaxial multi-circle UCA OAM configuration that supports multiplexing and modulating wireless transmissions by controlling OAM modes and coaxial UCA circles in accordance with some aspects of the present disclosure. In some examples, the illustrated coaxial multi-circle UCA OAM configuration may implement aspects of RAN 100, and may be employed by the transmitting device 202/300 and receiving device 206/400. In this example, a transmitting device (e.g., UE or base station) may include OAM transmitter UCA antennas 705 and a receiving device (e.g., UE or base station) may include OAM receiver UCA antennas 710.

In some aspects, one or both of the OAM transmitter coaxial multi-circle UCA antennas 705 or the OAM receiver coaxial multi-circle UCA antennas 710 may be implemented as a planar array of coaxial UCA antenna elements as described above and illustrated in FIG. 6. In various examples, an OAM transmitter may include the same number of UCA circles as an OAM receiver, but this is not necessarily the case. That is, a transmitting device 202/300 can communicate with a receiving device 206/400 with the same number and with a different number of UCA circles.

According to a further aspect of the present disclosure, a transmitting device may employ a subset (e.g., one or more) of its UCA circles from its transmitter UCA antennas 705 for a given transmission. For example, a transmitting device may multiplex a plurality of beams, streams, or waveforms onto a given wireless resource by transmitting each such stream with a different respective set of one or more UCA circles. Theoretically, streams transmitted via different sets of UCA circles can be orthogonal, such that a receiving device can receive and separately recover these streams received over the same radio resource (e.g., overlapping in the time-and frequency-domains, using the same code, etc. ) .

In a further aspect, a transmitting device may independently select or control an OAM mode for each of the plurality of multiplexed OAM beams. That is, a transmitting device may utilize a first set of one or more UCA circles to transmit a first OAM beam having a first OAM mode, and a second set of one or more UCA circles to transmit a second OAM beam having a second OAM mode. Here, the first OAM mode (i.e., from the first set of one or more UCA circles) may be the same as, or different from the second OAM mode (i.e., from the second set of one or more UCA circles) . Various options and further details of such a system are provided in the discussion that follows.

In the description that follows, for ease of description, reference is made to a UCA configuration such as the ones illustrated in FIGs. 6 and 7. However, it is to be understood that the present disclosure is not limited thereto. That is, according to another aspect of this disclosure, reference signal multiplexing using multiple OAM modes may be implemented utilizing an SPP configuration as described above and illustrated in FIG. 5. Additionally, according to other aspects of this disclosure, reference signal multiplexing using multiple OAM modes may be implemented using any structures that enable OAM multiplexing of electromagnetic signals (e.g., RF signals, light signals, etc. ) may apply, including but not limited to UCA antennas and SPP antennas, which are described as examples. Signals transmitted (e.g., multiplexed) using multiple OAM modes may be transmitted and/or received using any suitable transmitting components and/or receiving components, which may include or otherwise be configured using any suitably configured phase plates, spatial modulators, integrated circuits, any other suitable components, and/or any suitable combination thereof, for transmission over any suitable medium including a wireless air interface, an optical fiber, etc.

Multiplexing Reference Signals Using Different OAM Modes

FIG. 8 is a call flow diagram illustrating an exemplary process for multiplexing reference signals on shared resources using different OAM modes in accordance with some aspects of this disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In some examples, the process illustrated in FIG. 8 may be carried out by the transmitting device 300 illustrated in FIG. 3 and the receiving device 400 illustrated in FIG. 4. In some examples, the process of FIG. 8 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

At block 802, a transmitting device (e.g., transmitting device 300) may transmit a signal 804 (e.g., a waveform) that includes multiple reference signals (which may be referred to as multiplexed reference signals) using a first group of orbital angular momentum (OAM) modes that otherwise share resources. For example, in some aspects, the transmitting device may transmit the reference signals on any suitable channel (e.g., any suitable physical layer channel, such as the physical downlink control channel (PDCCH) , the physical uplink control channel (PUCCH) , or the physical sidelink control channel (PSCCH) ) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via a device-to-device (D2D) connection, , using one or more downlink (DL) slots, one or more uplink (UL) slots, one or more sidelink (SL) slots, etc. ) . In some aspects, the transmitting device can transmit the multiplexed reference signals using any suitable communication interface, such as a transceiver (e.g., transceiver 310) and antennas (e.g., antennas 311) .

As described above, in some aspects, the transmitting device may transmit the multiplexed reference signals using shared resources (e.g., shared time-frequency resources using a shared resource element) . Additionally, the transmitting device may transmit the multiplexed reference signals using a shared code (e.g., a single code division multiplexing (CDM) code) . In such examples, the transmitting device may transmit the signal 804 including multiple reference signals using relatively few wireless resources, freeing resources for other uses (e.g., for the transmitting device to transmit reference signals for other OAM modes, for the transmitting device to transmit information, for the transmitting device to receive data, etc. ) .

In some aspects, the multiplexed reference signals may be any suitable reference signals. For example, the multiplexed reference signals may include one or more demodulation reference signals (DM-RS) . As another example, the multiplexed reference signals may include one or more channel state information reference signals (CSI-RS) .

In some aspects, signal 804 may be represented as a signal x=∑ _i∈mf _ir _i, where f _i is a function associated with the i ^th OAM mode (e.g., a discrete Fourier transform (DFT) vector) used to encode a signal onto the i ^th OAM mode, r _i, is a reference signal associated with the i ^th OAM mode, and m is a group of OAM modes to be transmitted using shared resources. For example, if OAM modes l=1, 4, and 7 are in group m (e.g., a first group) , the signal can be expressed as x=f ₁r ₁+f ₄r ₄+f ₇r ₇.

In some aspects, the transmitting device may transmit a first reference signal associated with a first OAM mode (e.g., a mode associated with l=1, or any other mode) via the transceiver and at least a first antenna. For example, the transmitter device may use multiple antennas configured as a UCA antenna to transmit the first reference signal (e.g., as described above in connection with FIGs. 6 and 7) . As another example, the transmitter device may use a first aperture and SSP to transmit the first reference signal (e.g., as described above in connection with FIG. 5) . Additionally, in some aspects, the transmitting device may transmit a second reference signal associated with a second OAM mode (e.g., a mode associated with l=3, or any other suitable mode) via the transceiver and at least a second antenna. For example, the transmitter device may use the multiple antennas configured as a UCA antenna to transmit the second reference signal, where the UCA antenna includes the first antenna and the second antenna. As another example, the transmitter device may use a second aperture and SSP to transmit the second reference signal.

At block 806, a receiving device (e.g., receiving device 400) may receive the signal 804 that includes multiple reference signals using the first group of OAM modes. For example, in some aspects, the receiving device may receive the reference signals on any suitable channel (e.g., any suitable physical layer channel, such as PDCCH, PUCCH, or PSCCH) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D connection, using one or more DL slots, one or more UL slots, one or more SL slots, etc. ) . In some aspects, the receiving device can receive the multiplexed reference signals using any suitable communication interface, such as a transceiver (e.g., transceiver 410) and antennas (e.g., antennas 411) . In some aspects, the receiving device can receive the reference signals by sampling and buffering a received wireless signal on an appropriate channel, and applying suitable processing to the buffered signal such as energy detection, demodulation (e.g., using a demodulation function

associated with the i ^th OAM mode, and based on the channel matrix H) , decoding, etc.

In some aspects, the received signal 804 may be represented as a signal Z=Hx+noise (represented using ∈) . In some aspects, the receiving device can use a demodulation function associated with a particular OAM mode (e.g.,

) to generate a received reference signal for the i ^th OAM mode. For example, a received signal y _i can be expressed as

where

is a demodulation function associated with the i ^th OAM mode (e.g., an inverse discrete Fourier transform (iDFT) vector) used to decode a signal transmitted on the i ^th OAM mode For example, if OAM modes l=1, 4, and 7 are in group m (e.g., a first group) , the transmitted signal can be expressed as x=f ₁r ₁+f ₄r ₄+f ₇r ₇, and the received signal for mode l=1 can be expressed as

as

where λ _i is the ith singular value of H.

In some aspects, the receiving device may receive the first reference signal associated with the first OAM mode (e.g., a mode associated with l=1, or any other mode) via a transceiver and at least a first antenna associated with the receiving device. For example, the receiving device may use multiple antennas configured as a UCA antenna to receive the first reference signal (e.g., as described above in connection with FIGs. 6 and 7) . As another example, the receiver device may use a first aperture and SSP to receive the first reference signal (e.g., as described above in connection with FIG. 5) . Additionally, in some aspects, the receiving device may receive the second reference signal associated with the second OAM mode (e.g., a mode associated with l=3, or any other suitable mode) via the transceiver and at least a second antenna associated with the receiving device. For example, the receiver device may use the same antennas configured as a UCA antenna to receive the second reference signal, where the UCA antenna includes the first antenna and the second antenna. As another example, the transmitter device may use a second aperture and SSP to transmit the second reference signal.

At block 808, the transmitting device (e.g., transmitting device 300) may transmit a signal 810 (e.g., a waveform) that includes multiple reference signals (which may be referred to as multiplexed reference signals) using a second group of orbital angular momentum (OAM) modes that otherwise share resources. For example, in some aspects, the transmitting device may transmit the reference signals using techniques described above in connection with block 802. In some aspects, the OAM modes in the second group may be different than the OAM modes in the first group used to transmit reference signals at block 802. For example, as described below in connection with FIG. 9, the first group may include OAM modes that are orthogonal to each other, and the second group may include OAM modes that may interfere with the OAM modes in the first group.

In some aspects, the transmitting device may transmit a third reference signal associated with a third OAM mode (e.g., a mode associated with l=2, or any other suitable mode) via the transceiver and at least a third antenna. For example, the transmitter device may use multiple antennas configured as a UCA antenna to transmit the first reference signal (e.g., as described above in connection with FIGs. 6 and 7) . As another example, the transmitter device may use a third aperture and SSP to transmit the third reference signal (e.g., as described above in connection with FIG. 5) . Additionally, in some aspects, the transmitting device may transmit other reference signals associated with other OAM modes via the transceiver and at least a fourth antenna (e.g., the UCA antenna, a fourth aperture, etc. ) .

At block 812, the receiving device (e.g., receiving device 400) may receive the signal 810 that includes multiple reference signals using the second group of OAM modes. For example, in some aspects, the receiving device may receive the reference signals using techniques described above in connection with block 806.

In some aspects, the receiving device may receive the third reference signal associated with the second OAM mode (e.g., a mode associated with l=2, or any other suitable mode) via a transceiver and at least a third antenna associated with the receiving device. For example, the receiving device may use the antennas configured as a UCA antenna to receive the third reference signal (e.g., as described above in connection with FIGs. 6 and 7) . As another example, the receiver device may use a third aperture and SSP to receive the third reference signal (e.g., as described above in connection with FIG. 5) . Additionally, in some aspects, the receiving device may receive other reference signals associated with other OAM modes via the transceiver and at least a fourth antenna (e.g., the UCA antenna, a fourth aperture, etc. ) .

At block 814, the receiving device (e.g., receiving device 400) may estimate one or more properties of channels associated with the OAM modes in the first and second groups. For example, the receiving device may estimate a channel using the reference signals. As another example, the receiving device may estimate a channel gain of a channel associated with an OAM mode based on the received signal and the reference signal. In a more particular example, the receiving device may estimate the channel gain g _i associated with an i ^th OAM mode based on the received signal y _i and the reference signal r _i using the expression

As yet another example, the receiving device may estimate inter-mode interference between OAM modes (e.g., between adjacent OAM modes) . In a more particular example, the receiving device may attempt to demodulate the received signal for a first group for an OAM mode that is not included in the group. If x includes reference signals for OAM mode i, but not OAM mode i+1, the receiving device may attempt to extract a signal y _i+1 from z using a demodulation function

associated with OAM mode i+1, and can use the signal to estimate inter-mode interference from OAM mode i+1 on OAM mode i. In such an example, if

then inter-mode interference I _i+1, i can be estimated using the expression

In some aspects, the receiving device may provide an indication of channel properties associated with the OAM modes to the transmitting device. For example, the transmitting device may use information about channel properties associated with OAM modes to determine which modes may be multiplexed using shared resources to transmit information to the receiving device, and/or to allocate resources for transmission using the OAM modes. Additionally or alternatively, in some aspects, if the receiving device is configured to allocate resources to the transmitting entity (e.g., the receiving device may act as a scheduling entity) , the receiving device may use information about channel properties associated with OAM modes to determine which modes may be multiplexed using shared resources to transmit information to the receiving device, and/or to allocate resources for transmission by the transmitting device using the OAM modes.

FIG. 9 is a call flow diagram illustrating an exemplary process for grouping OAM modes for transmission using shared resources in accordance with some aspects of this disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In some examples, the process illustrated in FIG. 9 may be carried out by the transmitting device 300 illustrated in FIG. 3 and the receiving device 400 illustrated in FIG. 4. In some examples, the process of FIG. 9 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

At block 902, a transmitting device (e.g., transmitting device 300) may transmit multiple different signals 904 (e.g., waveforms) that each includes a single reference signal using a first orbital angular momentum (OAM) mode. In some aspects, the transmitting device may transmit the different reference signals using non-overlapping resources (e.g., different along at least one degree of freedom, other than OAM mode) . For example, the transmitting device may map each reference signal to different time-frequency resources. As another example, the transmitting device may associate multiple reference signals with orthogonal codes (e.g., {1, 1} and {1-1} ) , and may map each set of reference signals to different time-frequency resources.

In some aspects, the transmitting device may transmit the reference signals using any suitable channel (s) (e.g., any suitable physical layer channel, such as the physical downlink control channel (PDCCH) , the physical uplink control channel (PUCCH) , or the physical sidelink control channel (PSCCH) ) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D communications, using one or more downlink (DL) slots, one or more uplink (UL) slots, one or more sidelink (SL) slots, etc. ) . In some aspects, the transmitting device may transmit the non-overlapping reference signals using any suitable communication interface, such as a transceiver (e.g., transceiver 310) and antennas (e.g., antennas 311) . For example, the non-overlapping resources may be share the same time-frequency resources, and use different codes (e.g., the non-overlapping resources may not use the same code) . As another example, the non-overlapping resources may be different same time-frequency resources, and may use the same code (e.g., the non-overlapping resources may not share the same time-frequency resources) . As yet another example, the non-overlapping resources may be different time-frequency resources, and may use different codes (e.g., the non-overlapping resources may not use the same code or the same time-frequency resources) .

In some aspects, signal 904 may be represented as multiple signals x _i=f _ir _i, where f _i is a function associated with the i ^th OAM mode (e.g., a discrete Fourier transform (DFT) vector) used to encode a signal onto the i ^th OAM mode, r _i, is a reference signal associated with the i ^th OAM mode. For example, if OAM modes l=1, 4, and 7 are transmitted using non-overlapping signals, the signals can be expressed as x ₁=f ₁r ₁, x ₄=f ₄r ₄, and x ₇=f ₇r ₇.

In some aspects, the transmitting device may transmit a first reference signal associated with a first OAM mode (e.g., a mode associated with l=1, or any other mode) via the transceiver and at least a first antenna and first resources (e.g., first time-frequency resources, first time-frequency resources and a first code, etc. ) . For example, the transmitter device may use multiple antennas configured as a UCA antenna to transmit the first reference signal (e.g., as described above in connection with FIGs. 6 and 7) . As another example, the transmitter device may use a first aperture and SSP to transmit the first reference signal (e.g., as described above in connection with FIG. 5) . Additionally, in some aspects, the transmitting device may transmit a second reference signal associated with a second OAM mode (e.g., a mode associated with l=3, or any other suitable mode) via the transceiver and at least a second antenna and second resources (e.g., second time-frequency resources, second time-frequency resources and the first code, the first time-frequency resources and a second code, etc. ) . For example, the transmitter device may use the multiple antennas configured as a UCA antenna to transmit the second reference signal, where the UCA antenna includes the first antenna and the second antenna. As another example, the transmitter device may use a second aperture and SSP to transmit the second reference signal.

In some aspects, the transmitting device may transmit the reference signals at block 902 periodically (e.g., at regular intervals) and/or periodically (e.g., in response to a trigger) . Transmitting the reference signals separately (e.g., using non-overlapping resources) at regular and/or irregular intervals may facilitate estimation of channel properties of associated with OAM modes with a lower likelihood of interference (e.g., from another OAM mode) disrupting estimation of channel properties.

In some aspects, the transmitting device may transmit a subset of reference signals at block 902 (e.g., associated with a subset of OAM modes that the transmitting device is configured to generate) . For example, if the transmitting device is configured to generate 12 modes, the transmitting device may transmit fewer than 12 reference signals at 902, which can reduce the amount of resources dedicated to transmission of reference signals. In a particular example, the transmitting device may transmit a subset of the reference signals (e.g., half of the reference signals) , and may concurrently transmit information sing the other OAM modes using shared resources with the reference signals. Transmitting fewer reference signals may reduce the amount of resources dedicated to reference signals, and may increase resources available for transmission of information.

At block 906, a receiving device (e.g., receiving device 400) may receive the signals 904 that each includes a reference signal using an OAM mode. For example, in some aspects, the receiving device may receive the reference signals on any suitable channel (e.g., any suitable physical layer channel, such as PDCCH, PUCCH, or PSCCH) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D communications, , using one or more DL slots, one or more UL slots, one or more SL slots, etc. ) . In some aspects, the receiving device may receive the reference signals using any suitable communication interface, such as a transceiver (e.g., transceiver 410) and antennas (e.g., antennas 411) . In some aspects, the receiving device may receive the reference signals by sampling and buffering a received wireless signal on an appropriate channel, and applying suitable processing to the buffered signal such as energy detection, demodulation (e.g., using a demodulation function

In some aspects, the received signals 904 may be represented as a signal Z _i=Hx _i+∈. In some aspects, the receiving device can use a demodulation function associated with a particular OAM mode (e.g.,

where

is a demodulation function associated with the i ^th OAM mode (e.g., an inverse discrete Fourier transform (iDFT) vector) used to decode a signal transmitted on the i ^th OAM mode For example, if OAM modes modes l=1, 4, and 7 are transmitted using non-overlapping signals, the signals can be expressed as x ₁=f ₁r ₁, x ₄=f ₄r ₄, and x ₇=f ₇r ₇, and the received signals can be expressed as

and

In some aspects, the receiving device may estimate channel gain and/or inter-mode interference associated with one or more OAM modes at block 906. For example, as described above in connection with block 814, the receiving device may estimate channel gain

for channel i, and may estimate inter-mode interference between channel i and one or more neighboring OAM modes j (e.g., interference from modes i-2, i-1, i+1, and mode i+2) . For example, the receiving device may attempt to extract a signal y _j≠i from z _i using a demodulation function

associated with OAM mode j, and may use the signal to estimate inter-mode interference from OAM mode j on OAM mode i. In such an example, if

then inter-mode interference I _j, i can be estimated using the expression

In some aspects, the receiving device may infer a degree of misalignment between antennas used to transmit the reference signals and antennas used to receive the reference signals based on the channel gain and/or inter-mode interference associated with one or more OAM modes. For example, as the antennas become misaligned, interference between neighboring OAM modes may increase. In some aspects, estimation of a degree of misalignment by the receiving device at block 906 may be omitted (e.g., if a laser alignment system is used to measure a degree of misalignment) .

At block 908, a transmitting device (e.g., transmitting device 300) may output light 910 from a light source associated with an alignment system. For example, the transmitting device may cause a laser beam to be output from a laser alignment system that may be used to measure alignment between the antenna (s) associated with the transmitting device and a corresponding antenna (s) associated with the receiving device. In some aspects, the light 910 may be encoded using a particular encoding scheme that may be used to identify the light as originating from the transmitting device.

At block 912, a receiving device (e.g., receiving device 400) may detect the light 910, and determine a position at which the light 910 impinges a photodetector. For example, the receiving device can detect light (e.g., at a specific wavelength, encoded using a particular encoding scheme, etc. ) .

In some aspects, the receiving device may determine a degree of misalignment between antennas used to transmit the reference signals and the antennas used to receive the reference signals based on the position of at which the light 910 is detected. For example, the receiving device may determine an offset (sometimes referred to a subtension) between a reference point (e.g., a center of a photodetector, a position at which the light 910 is detected when the antennas are aligned, etc. ) . Based on a distance between the transmitting antennas and the receiving antennas, the receiving device may determine an angle of misalignment (e.g., misalignment angle = arctan (offset/distance) in degrees, which is approximately equal to the offset/range in milliradians) .

At block 914, the receiving device may determine a mode orthogonality distance threshold T that indicates a minimum distance, in mode order, between two orthogonal OAM modes. For example, when the antennas are perfectly aligned, a mode orthogonality distance threshold may be T=0, indicating that all OAM modes are orthogonal to every other OAM mode. As described above, this property of OAM modes may be leveraged to increase the amount of data that may be transmitted between a transmitting device and a receiving device. However, as the transmitting and receiving antennas become misaligned, the orthogonality distance threshold may increase. For example, at a misalignment of 0.1 mrad the orthogonality distance threshold increased to T=1, and at a misalignment of 1 mrad the orthogonality distance threshold increased to T=2.

In some aspects, the receiving device may determine the orthogonality distance threshold based on received reference signals. For example, the receiving device may determine an inter-mode distance that yield a signal to interference ratio of at least 20 dB based on calculated signal gain and inter-mode interference.

Additionally or alternatively, in some aspects, the receiving device may determine the orthogonality distance threshold based on a misalignment measured by an alignment system. For example, the receiving device may calculate an angular misalignment (e.g., in mrads) , and compare the angular misalignment to stored values to determine a mode orthogonality distance threshold. In such an example, the receiving device may use a look up table to determine a mode orthogonality distance threshold associated with the angular misalignment. The lookup table may be based on empirical measurements of SIR.

In some aspects, the receiving device 400 may also act as a transmitting device (e.g., when two-way communication is carried out between the transmitting device and the receiving device) , and may execute may execute block 902 and/or block 908. The transmitting device 300 may determine a mode orthogonality distance based on reference signals transmitted by the receiving device (not shown) , and/or based on a position at which the light output by a light source associated with an alignment system of the receiving device 400 impinges a photodetector (e.g., transmitting device 300 may execute blocks 906 and/or 912, and 914. In examples in which both the transmitting device 300 and the receiving device 400 execute block 914, one or both of transmitting device 300 and receiving device 400 may omit block 916, which may reduce consumption of radio resources.

At block 916, the receiving device may transmit a signal 918 encoded with information indicative of inter-mode interference between N OAM modes (e.g., where N > 2) . For example, the receiving device may transmit the orthogonality distance threshold T. In such an example, the receiving device may associate the orthogonality distance threshold T with a subset of OAM modes. For example, if the orthogonality distance threshold T varies with OAM mode order, the receiving device may calculating multiple orthogonality distance thresholds T associated with different subsets of OAM modes, and may transmit each orthogonality distance threshold T in connection with information identifying OAM modes associated with the threshold. For example, the receiving device may transmit a first orthogonality distance threshold T associated with a first subset of N OAM modes, and may transmit a second orthogonality distance threshold T′ associated with a second subset of N′ OAM modes.

In some aspects, the receiving device may transmit the information indicative of inter-mode interference between OAM modes (e.g., threshold T) using any suitable technique or combination of techniques. For example, in some aspects, the receiving device may transmit the information on any suitable channel (e.g., any suitable physical layer channel, such as the physical downlink control channel (PDCCH) , the physical uplink control channel (PUCCH) , or the physical sidelink control channel (PSCCH) , the physical uplink shared channel (PUSCH) , the physical downlink shared channel (PDSCH) , the physical sidelink shared channel (PSSCH) , one or more transport channels, one or more logical channels, etc. ) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D communications, using one or more downlink (DL) slots, one or more uplink (UL) slots, one or more sidelink (SL) slots, etc. ) . In some aspects, the receiving device may transmit the multiplexed reference signals using any suitable communication interface, such as a transceiver (e.g., transceiver 410) and antennas (e.g., antennas 411) .

In some aspects, the receiving device may transmit the signal 910 using any suitable message. For example, the receiving device may transmit the signal 910 via a radio resource control (RRC) message. In such an example, the message may be transmitted via RRC signaling. As another example, the receiving device may transmit the signal 910 via a medium access control (MAC) control element (CE) message. In such an example, message may be transmitted via MAC CE signaling. As yet another example, the receiving device may transmit the signal 910 via a physical layer message, such as a control information message (e.g., via one or more of downlink control information (DCI) , uplink control information (UCI) , or sidelink control information (SCI) ) .

At block 920, the transmitting device may receive the information indicative of inter-mode interference between OAM modes (e.g., one or more thresholds T associated with the OAM modes or a subset of the OAM modes) using any suitable technique or combination of techniques. For example, in some aspects, the transmitting device may receive the information indicative of inter-mode interference between OAM modes on any suitable channel (e.g., any suitable physical layer channel, any suitable transport layer channel via MAC CE signaling, any suitable logical channel via RRC signaling, etc. ) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D communications, using one or more DL slots, one or more UL slots, one or more SL slots, etc. ) . In some aspects, the transmitting device may receive the information indicative of inter-mode interference between OAM modes (e.g., in an RRC message, a MAC CE message, a control information message, etc. ) using any suitable communication interface, such as a transceiver (e.g., transceiver 310) and antennas (e.g., antennas 311) . In some aspects, the transmitting device may receive the message by sampling and buffering a received wireless signal on an appropriate channel, and applying suitable processing to the buffered signal such as energy detection, demodulation (e.g., using a demodulation function

associated with the i ^th OAM mode used to transmit the message, and based on the channel matrix H) , decoding, etc.

In some aspects, the transmitting device may calculate an inter-mode interval D, that the transmitting device may use to group OAM modes for transmission of reference signals using overlapping resources. In some aspects, the transmitting device may calculate D based on the orthogonality distance threshold T. For example, the transmitting device may set the inter-mode interval D to be in range from 1 to at least twice the orthogonality distance threshold T (e.g., such that D≥2T+1) . As another example, the transmitting device may set the inter-mode interval D to be at least one larger than T (e.g., (e.g., such that D≥T+1) .

In some aspects, the transmitting device may group N OAM modes into M modes, such that any two modes in a group are separated by at least D. For example, if D is three, than a first group may include modes associated with l=1 and 4, and may exclude modes associated with l=2, 3, 5, and 7, as those modes fall within the distance D from the modes present in the first group. As another example, if D is three for modes 1 to 10, and five for modes 11 to 20, the transmitting device may include modes associated with l=1, 4, 7, 10, 15, and 20 in a first group, and may exclude other OAM modes based on the interval D.

At block 922, the receiving device may transmit a signal 924 encoded with information indicative of OAM mode groupings to be used to transmit reference signals using overlapping signals. In some aspects, the transmitting device may transmit the information indicative of OAM mode groupings using any suitable technique or combination of techniques. For example, in some aspects, the transmitting device may transmit the information on any suitable channel (e.g., any suitable physical layer channel, such as the physical downlink control channel (PDCCH) , the physical uplink control channel (PUCCH) , or the physical sidelink control channel (PSCCH) , the physical uplink shared channel (PUSCH) , the physical downlink shared channel (PDSCH) , the physical sidelink shared channel (PSSCH) , one or more transport channels, one or more logical channels, etc. ) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D communications, using one or more downlink (DL) slots, one or more uplink (UL) slots, one or more sidelink (SL) slots, etc. ) . In some aspects, the transmitting device may transmit the multiplexed reference signals using any suitable communication interface, such as a transceiver (e.g., transceiver 310) and antennas (e.g., antennas 311) .

In some aspects, the transmitting device may transmit the signal 924 using any suitable message. For example, the transmitting device may transmit the signal 924 via a radio resource control (RRC) message. In such an example, the message may be transmitted via RRC signaling. As another example, the transmitting device may transmit the signal 924 via a medium access control (MAC) control element (CE) message. In such an example, message may be transmitted via MAC CE signaling. As yet another example, the transmitting device may transmit the signal 924 via a physical layer message, such as a control information message (e.g., via one or more of downlink control information (DCI) , uplink control information (UCI) , or sidelink control information (SCI) ) .

In some aspects, the information indicative of OAM mode groupings may include any suitable information in any suitable format. The information indicative of OAM mode groupings may be group configuration information that includes an indication of which OAM modes are included in each group. For example, the group configuration information may include a number of groups M. As another example, the group configuration information may include information indicative of the OAM modes associated with the M groups (e.g., formatted as a starting mode and an ending mode, formatted as a list of modes, formatted as a value associated with a set of modes in a lookup table, etc. ) . In some aspects, the group configuration information may include any suitable information that identifies specific modes includes in each group. For example, the group configuration information may include an explicit indication of each OAM mode order that is included in each mode. In a more particular example, information indicative of OAM modes included in an m ^th group of the M groups may include a set of OAM mode orders

where the m ^th group includes n _m OAM modes, and i _m, n is a mode order of an OAM mode in the m ^th group.

As another example, the group configuration information may include information from which group membership may be derived. For example, the information indicative of OAM modes included in each of the M groups may include, for each of the M groups: a starting OAM mode order associated with the group; an inter-mode interval D; and an ending OAM mode order associated with the group. In a more particular example, if the first mode order in a first group is 1, and the last is 7, with D=3, this may indicate that

modes

1, 4, and 7 are included in the first group.

As another example, the information indicative of OAM modes included in each of the M groups may include: a starting OAM mode order; an inter-mode interval D; the number of groups M; and an ending OAM mode order. In a more particular example, if the first mode is 1, the last mode is 12 and the number of groups is 3, with D=3, this may indicate that the four groups each include three OAM modes (e.g., {1, 4, 7, 10} , {2, 5, 8, 11} , and {3, 6, 9, 12} ) .

At block 926, the receiving device may receive the signal 924 that includes the group configuration information. For example, in some aspects, the receiving device may receive the group configuration information on any suitable channel (e.g., any suitable physical layer channel, any suitable transport layer channel via MAC CE signaling, any suitable logical channel via RRC signaling, etc. ) via any suitable communication network (e.g., via a RAN, such as RAN 200, and/or via D2D communications, using one or more DL slots, one or more UL slots, one or more SL slots, etc. ) . In some aspects, the receiving device may receive the information indicative of inter-mode interference between OAM modes (e.g., in an RRC message, a MAC CE message, a control information message, etc. ) using any suitable communication interface, such as a transceiver (e.g., transceiver 410) and antennas (e.g., antennas 411) . In some aspects, the receiving device may receive the message by sampling and buffering a received wireless signal on an appropriate channel, and applying suitable processing to the buffered signal such as energy detection, demodulation (e.g., using a demodulation function

At block 928, the transmitting device may transmit reference signals 930 associated with various groups of OAM modes using overlapping resources using any suitable technique or combination of techniques. For example, the transmitting device may transmit the groups of OAM reference signals using techniques described above in connection with

blocks

802 and 808 of FIG. 8.

At block 932, the receiving device may receive the reference signals 930 associated with various groups of OAM modes using overlapping resources using any suitable technique or combination of techniques. For example, the receiving device may receive the groups of OAM reference signals using techniques described above in connection with

blocks

806 and 812 of FIG. 8.

In some aspects, the receiving device may estimate properties associated with the OAM modes, such as channel gain and inter-mode interference, using any suitable technique or combination of techniques. For example, the receiving device may estimate the properties associated with the OAM modes using techniques described above in connection with block 814 of FIG. 8. In a particular example, if the orthogonality distance threshold T is 1, then the inter-mode interference between adjacent modes may be expected to be about zero, as only adjacent modes should be capable of causing significant interference. In such an example,

and

where f _i is OAM mode generation vector (e.g., a DFT vector) . When T = 1, the inter-mode interference should only potentially exist between two adjacent OAM modes, because

when |i-j|＞1.

FIG. 10 is a schematic illustration of groupings of OAM modes for concurrent transmission of multiplexed reference signals on shared resources using different OAM modes an organization of wireless resources in accordance with some aspects of the disclosure. As shown in FIG. 10, reference signals associated with at least nine different OAM modes may be transmitted using resources that may otherwise be used to transmit reference signal associated with just three ports. For example, transmitting the reference signals of three groups, the an OAM receiver device may obtain channel gains and inter-mode interference of many more OAM modes (e.g., at least nine modes, twelve modes, etc. ) . This has the potential to greatly reduce radio consumption for reference signal transmission compared to mapping the reference signals of all of the OAM modes into non-overlapping radio resources, which may facilitate increased spectrum efficiency. The specific reduction degree may depend on the direction alignment status between the OAM transmitter and the OAM receiver, as greater misalignment may be associated with more crosstalk between OAM modes at the receiver device.

FIG. 11 is a schematic illustration of transmission of reference signals using different OAM modes using non-overlapping resources useable to determine a mode orthogonality distance threshold in accordance with some aspects of the disclosure. As shown in FIG. 11, a transmitter device may transmit non-overlapping reference signals periodically (e.g., as described above in connection with blocks 902 to 906 of FIG. 9) , which may be used to determine a mode orthogonality distance threshold (e.g., which may depend on how closely aligned the transmitting and receiver antennas are) . During other times, the transmitter device may transmit the reference signals in groups using overlapping resources, which may reduce the resources dedicated to transmitting reference signals.

For example, consider an OAM system with two OAM devices (e.g., a transmitter device and a receiver device) that includes a 16-antenna UCA with a panel radius of 0.3 meters 30 meters apart, that communicates using a single polarization, and a carrier frequency of 100 gigahertz (GHz) . As described above, with no misalignment, every OAM mode is theoretically orthogonal. Depending on the panel radius, carrier frequency, separation distance, and environmental noise, UCA-base OAM may support from a mid-single digits to dozens of OAM modes when the antennas are aligned.

At a misalignment of 0.1 mrad (～3.3 mm at 30 meters) , the signal to interference ratio (SIR) between adjacent modes may be about 30 dB at the receiver device. If 20 dB is used as a threshold for acceptable SIR, the OAM orthogonality distance threshold T for such a system with a misalignment of 0.1 mrad is 0, as the adjacent modes (at a distance of -1 and 1) do not significantly interfere with the center OAM mode (in this example, OAM mode 1) .

At a misalignment of 1 mrad (～3 cms at 30 meters) , the SIR between adjacent modes may be about 10 dB at the receiver device, and the SIR with the next neighboring modes (i.e., modes at a distance of -2 and 2) may be about 25 dB. Using the same 20 dB threshold for acceptable SIR, the OAM orthogonality distance threshold T for such a system with a misalignment of 1 mrad is 1, as the adjacent modes (at a distance of -1 and 1) significantly interfere with the center OAM mode (in this example, OAM mode 1) , but the next closest modes (at a distance of -2 and 2) do not significantly interfere with the center OAM mode.

In some aspects, simulations may be used to establish a relationship between misalignment and orthogonality distance threshold, which may be used by an OAM receiving device to estimate a mode orthogonality distance threshold T based on a measured misalignment (e.g., using an alignment detection system) .

FIG. 12 is a schematic illustration of channel gain and inter-mode interference that may be calculated from reference signals received in three groups on shared resources in accordance with some aspects of the disclosure. A shown in FIG. 12, using techniques described herein, by receiving the reference signals of three groups (the OAM modes in one group share the radio resource) , an OAM receiver device (e.g., receiver device 400) may obtain channel gains and inter-mode interference associated with twelve OAM modes. For example, if a first group of reference signals is transmitted using four modes (e.g.,

modes

1, 4, 7, and 10) , the receiver device may estimate channel gain for those four modes, and may estimate inter-mode interference on those four modes from adjacent modes. This may dramatically reduce radio resource utilization for the purposes of calculating channel gain and inter-mode interference when compared to mapping the reference signals of the same OAM modes into non-overlapping radio resources. For example, using techniques described herein, channel gain and inter-mode interference may be obtained for twelve modes using a quarter of the radio resources. Note that this is merely an example, and the reduction in radio resource consumption may vary based on system configuration (e.g., UCA panel radius, UCA panel size in antennas, carrier signal frequency, etc. ) , environmental conditions (e.g., environmental noise) , and misalignment.

Further Examples Having a Variety of Features:

Implementation examples are described in the following numbered clauses:

1. A method for wireless communication, comprising: transmitting, via a transceiver and a first antenna of a plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; transmitting, via the transceiver and a second antenna of the plurality of antennas, a second reference signal on a second OAM mode using the same first resources; and transmitting, via the transceiver and a third antenna of the plurality of antennas, a third reference signal on a third OAM mode using second resources.

2. The method of clause 1, wherein the first antenna comprises a first aperture associated with a first spiral phase plate.

3. The method of clause 1, wherein the first antenna, the second antenna, and the third antenna are included in a uniform circular array (UCA) .

4. The method of clause 3, wherein the UCA comprises a plurality of co-axial circles, a first circle of the plurality of circles comprising: the first antenna, the second antenna, and the third antenna.

5. The method of clause 3, wherein the UCA comprises a plurality of co-axial circles, wherein a first circle of the plurality of circles comprises the first antenna, a second circle of the plurality of circles comprises the second antenna, and plurality of circles comprises the third antenna.

6. The method of any one of clauses 1 to 5, wherein the first resources comprise time-frequency resources and a code.

7. The method of any one of clauses 1 to 6, wherein the first reference signal comprises a demodulation reference signal (DM-RS) .

8. The method of any one of clauses 1 to 6, wherein the first reference signal comprises a CSI-RS.

9. The method of any one of clauses 1 to 8, wherein the second reference signal comprises a channel state information reference signal (CSI-RS) .

10. The method of any one of clauses 1 to 8, wherein the second reference signal comprises a DM-RS.

11. The method of any one of clauses 1 to 10, further comprising: transmitting, via the transceiver, reference signals on the first OAM mode and the second OAM mode using different resources.

12. The method of clause 11, further comprising: transmitting the reference signals on the first OAM mode and the second OAM mode using the different resources periodically at regular intervals.

13. The method of any one of

clauses

11 or 12, further comprising: transmitting the reference signals on the first OAM mode and the second OAM mode using the different resources aperiodically in response to a trigger.

14. The method of any one of clauses 11 to 13, wherein the different resources share the same time-frequency resources, and use different codes.

15. The method of any one of clauses 11 to 13, wherein the different resources share the same code, and use different time-frequency resources.

16. The method of any one of clauses 1 to 15, further comprising: receiving, via the transceiver, information indicative of inter-mode interference between N OAM modes, wherein N > 2; grouping the set of N OAM modes into M groups based on the information indicative of inter-mode interference, wherein the first mode and the second mode are included in a first group of the M groups, and the third mode is included in a second group of the M groups; transmit, via the transceiver, a reference signal on each OAM mode in the first group of the M groups using the first resources; and transmit, via the transceiver, a reference signal on each OAM mode in a second group of the M groups using the second resources.

17. The method of clause 16, wherein the information indicative of inter-mode interference between the N OAM modes comprises an OAM mode orthogonality distance threshold from the OAM receiver.

18. The method of clause 17, wherein the orthogonality distance threshold comprises a value T indicative of a minimum order distance at which OAM modes transmitted using shared resources are orthogonal. 19. The method of any one of clauses 16 to 18, further comprising: receiving the information indicative of inter-mode interference between the N OAM modes from an OAM receiving method.

20. The method of any one of clauses 16 to 19, further comprising: receiving the information indicative of inter-mode interference between the N OAM modes via one or more of: radio resource control (RRC) signaling, medium access control (MAC) control element (CE) signaling, or physical layer signaling using at least one of downlink control information (DCI) , uplink control information (UCI) , or sidelink control information (SCI) .

21. The method of any one of clauses 16 to 20, further comprising: receiving, via the transceiver, second information indicative of inter-mode interference between a set of N' OAM modes, wherein N' > 2, where inter-mode interference varies with the OAM mode order; and grouping the set of N' OAM modes into M' groups based on the second information indicative of inter-mode interference.

22. The method of any one of clauses 16 to 21, further comprising: transmitting, via the transceiver, information indicating group membership of the N OAM modes within the M groups.

23. The method of any one of clauses 16 to 22, further comprising: determinign an inter-mode interval D; and grouping the set of N OAM modes such that the mode order between any two OAM modes in a group is no smaller than D.

24. The method of any one of clauses 16 to 23, wherein D≥2T+1.

25. The method of any one of clauses 23 or 24, further comprising: transmitting the reference signal on each OAM mode in the first group of the M groups using the first resources via a signal x=∑ _k∈mr _i, where ri is a reference signal of OAM mode k in the first group, and m includes the OAM modes in the first group.

26. The method of any one of clauses 16 to 25, further comprising: transmitting, via the transceiver, group configuration information indicative of OAM modes included in each of the M groups.

27. The method of clause 26, wherein the group configuration information comprises the number of groups M.

28. The method of any one of clauses 26 or 27, wherein the group configuration information comprises information indicative of the OAM modes included in the N OAM modes.

29. The method of any one of clauses 26 to 28, wherein the group configuration information comprises identifying information of OAM modes included in each of the M groups.

30. The method of clause 29, wherein identifying information of OAM modes included in an m ^th group of the M groups comprises a set of OAM mode orders

31. The method of clause 30, wherein information indicative of OAM modes included in each of the M groups comprises, for each of the M groups: a starting OAM mode order associated with the group; an inter-mode interval D; and an ending OAM mode order associated with the group. 32. The method of clause 30, wherein information indicative of OAM modes included in each of the M groups comprises: a starting OAM mode order; an inter-mode interval D; the number of groups M, an inter-mode interval D; and an ending OAM mode order.

33. The method of any one of clauses 26 to 32, further comprising: transmitting the group configuration information via one or more of: RRC signaling, MAC CE signaling, or physical layer signaling using at least one of DCI, UCI, or SCI.

34. A method configured for wireless communication, comprising: receiving, via the transceiver and a first antenna of the plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources; receiving, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and receiving, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.

35. The method of clause 34, wherein the first antenna comprises a first aperture associated with a first spiral phase plate.

36. The method of clause 34, further comprising a uniform circular array (UCA) that includes the first antenna, the second antenna, and the third antenna.

37. The method of any one of clauses 34 to 36, wherein the first resources comprise time-frequency resources and a code.

38. The method of any one of clauses 34 to 37, wherein the first reference signal comprises a demodulation reference signal (DM-RS) .

39. The method of any one of clauses 34 to 38, wherein the second reference signal comprises a channel state information reference signal (CSI-RS) .

40. The method of any one of clauses 34 to 39, the method further comprising receive, via the transceiver, reference signals on the first OAM mode and the second OAM mode using different resources.

41. The method of clause 40, the method further comprising receive the reference signals on the first OAM mode and the second OAM mode using the different resources periodically at regular intervals.

42. The method of any one of clauses 40 or 41, the method further comprising receive the reference signals on the first OAM mode and the second OAM mode using the different resources aperiodically in response to a trigger.

43. The method of any one of clauses 40 to 42, wherein the different resources share the same time-frequency resources, and use different codes.

44. The method of any one of clauses 40 to 42, wherein the different resources share the same code, and use different time-frequency resources.

45. The method of any one of clauses 34 to 44, the method further comprising transmit, via the transceiver, information indicative of inter-mode interference between a set of N OAM modes, wherein N > 2; receive, via the transceiver, a reference signal on each OAM mode in a first group of M groups using the first resources; and receive, via the transceiver, a reference signal on each OAM mode in a second group of the M groups using the second resources.

46. The method of clause 45, wherein the information indicative of inter-mode interference between the set of N OAM modes comprises an OAM mode orthogonality distance threshold from the OAM receiver.

47. The method of clause 46, wherein the orthogonality distance threshold comprises a value T indicative of a minimum order distance at which OAM modes transmitted using shared resources are orthogonal.

48. The method of any one of clauses 45 to 47, the method further comprising transmit the information indicative of inter-mode interference between the set of N OAM modes to an OAM transmitting method.

49. The method of any one of clauses 45 to 48, the method further comprising transmit the information indicative of inter-mode interference between the set of N OAM modes via one or more of: radio resource control (RRC) signaling; medium access control (MAC) control element (CE) signaling; or physical layer signaling using at least one of downlink control information (DCI) , uplink control information (UCI) , or sidelink control information (SCI) .

50. The method of any one of clauses 45 to 49, the method further comprising transmit, via the transceiver, second information indicative of inter-mode interference between N' OAM modes, wherein N'> 2, where inter-mode interference varies with the OAM mode order.

51. The method of any one of clauses 45 to 50, the method further comprising receive, via the transceiver, information indicating group membership of the set of N OAM modes within the M groups.

52. The method of any one of clauses 46 to 51, the method further comprising receive, via the transceiver, reference signals on the first OAM mode and the second OAM mode using different resources; determine a degree of direction misalignment between the plurality of antennas and a plurality of antennas associated with an OAM transmitter method based on the reference signals received using the different resources; and transmit the information indicative of inter-mode interference based on the degree of direction misalignment.

53. The method of any one of clauses 45 to 48, wherein the method further comprises a photodetector, and wherein processor and the memory are further configured to:detect, using the photodetector, a position at which light emitted from a laser associated with an OAM transmitter method is received; determine a degree of direction misalignment between the plurality of antennas and a plurality of antennas associated with the OAM transmitter method based on the position; and transmit the information indicative of inter-mode interference based on the degree of direction misalignment.

54. The method of any one of clauses 52 or 53, the method further comprising determine the orthogonality distance threshold based on the degree of direction misalignment.

55. The method of any one of clauses 45 or 54, the method further comprising receive the reference signal on each OAM mode in the first group of the M groups using the first resources via a signal z=Hx+∈, where H is a channel matrix associated with channel used to transmit the reference signals, ∈ is noise, and x=∑ _i∈mr _i, where r _i is a reference signal of OAM mode i in the first group, and m includes the OAM modes in the first group.

56. The method of any one of clauses 34 to 55, the method further comprising receive, via the transceiver, group configuration information indicative of OAM modes included in each of the M groups.

57. The method of clause 56, wherein the group configuration information comprises the number of groups M.

58. The method of any one of clauses 56 or 57, wherein the group configuration information comprises information indicative of the OAM modes included in the set of N OAM modes.

59. The method of any one of clauses 56 to 58, wherein the group configuration information comprises identifying information of OAM modes included in each of the M groups.

60. The method of clause 59, wherein information indicative of OAM modes included in an m ^th group of the M groups comprises a set of OAM mode orders

61. The method of clause 59, wherein information indicative of OAM modes included in each of the M groups comprises, for each of the M groups: a starting OAM mode order associated with the group; an inter-mode interval D; and an ending OAM mode order associated with the group.

62. The method of clause 59, wherein information indicative of OAM modes included in each of the M groups comprises: a starting OAM mode order; an inter-mode interval D; the number of groups M, an inter-mode interval D; and an ending OAM mode order.

63. The method of any one of clauses 56 to 58, the method further comprising receive the group configuration information via one or more of: RRC signaling; MAC CE signaling, or physical layer signaling using at least one of DCI, UCI, or SCI.

64. The method of any one of clauses 34 to 63, the method further comprising receive, via the transceiver, a signal z=Hx+∈, where H is a channel matrix associated with channel used to transmit the reference signals, ∈ is noise, and x=∑ _i∈mr _i, where r _i is a reference signal of OAM mode i in the first group, and m includes the OAM modes in the first group; determine, based on z, a channel gain g _i of OAM mode i, where i is an OAM mode order in m.

65. The method of clause 64, the method further comprising determine, based on z, a mutual interference I _i, j from OAM mode i to OAM mode j, where i is an OAM mode order in m, and j is an OAM mode order not in m.

66. The method of any one of clauses 34 to 64, the method further comprising receive, via the transceiver, a signal z=Hx+∈, where H is a channel matrix associated with a channel used to transmit the reference signals, ∈ is noise, and x=∑ _i∈mr _i, where r _i is a reference signal of OAM mode i in the first group, and m includes the OAM modes in the first group; and determine, based on z, a mutual interference I _i, j from OAM mode i to OAM mode j, where i is an OAM mode order in m, and j is an OAM mode order not in m.

67. The method of any one of clauses 34 to 64, the method further comprising receive, via the transceiver, a signal z=Hx+∈, where H is a channel matrix associated with a channel used to transmit the reference signals, ∈ is noise, and x=∑ _i∈mr _i, where r _i is a reference signal of OAM mode i in the first group, and m includes the OAM modes in the first group; demodulate z based on the first OAM mode to yield a signal

where

is a demodulation function associated with the first OAM mode; and determine a channel gain

68. The method of any one of clauses 34 to 64, the method further comprising receive, via the transceiver, a signal z=Hx+∈, where H is a channel matrix associated with a channel used to transmit reference signals in a first group using the first resources and reference signals in a second group using the second resources, ∈ is noise, and x=∑ _i∈mr _i, where ri is a reference signal of OAM mode i _k in the first group, and m includes the OAM modes in the first group; demodulate z based on the first OAM mode to yield a signal

where

is a demodulation function associated with the first OAM mode; demodulate z based on the third OAM mode to yield a signal

where

is a demodulation function associated with the first OAM mode; and determine a mutual interference I _2, 1 between the first OAM mode and the second OAM mode channel

where r ₁ is the transmitted first reference signal.

69. An apparatus for wireless communication, comprising: a processor; and a memory communicatively coupled to the at least one processor, wherein the processor and memory are configured to: perform a method of any of clauses 1 to 68.

70. A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a computer to cause a processor to: perform a method of any of clauses 1 to 68.

71. An apparatus for wireless communication, comprising: at least one means for carrying out a method of any of clauses 1 to 68.

One or more of the components, steps, features and/or functions illustrated in FIGs. 1–12 may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in FIGs. 1–12 may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware.

It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

Claims

An apparatus configured for wireless communication, comprising:

a processor;

a plurality of antennas;

a transceiver coupled to the processor and to plurality of antennas; and

a memory coupled to the processor,

wherein the processor and the memory are configured to:

transmit, via the transceiver and a first antenna of the plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources;

transmit, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and

transmit, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.
The apparatus of claim 1, further comprising a uniform circular array (UCA) that includes the first antenna, the second antenna, and the third antenna.
The apparatus of claim 1, wherein the first resources comprise time-frequency resources and a code.
The apparatus of claim 1, wherein the first reference signal comprises a demodulation reference signal (DM-RS) .
The apparatus of any one of claims 1 to 4, wherein the second reference signal comprises a channel state information reference signal (CSI-RS) .
The apparatus of any one of claims 1 to 4, wherein the processor and the memory are further configured to:

transmit, via the transceiver, reference signals on the first OAM mode and the second OAM mode using different resources.
The apparatus of any one of claims 1 to 4, wherein the processor and the memory are further configured to:

receive, via the transceiver, information indicative of inter-mode interference between a set of N OAM modes, wherein N > 2;

group the set of N OAM modes into M groups based on the information indicative of inter-mode interference,

wherein the first OAM mode and the second OAM mode are included in a first group of the M groups, and

the third OAM mode is included in a second group of the M groups;

transmit, via the transceiver, a reference signal on each OAM mode in the first group of the M groups using the first resources; and

transmit, via the transceiver, a reference signal on each OAM mode in a second group of the M groups using the second resources.
The apparatus of claim 7, wherein the information indicative of inter-mode interference between the set of N OAM modes comprises an OAM mode orthogonality distance threshold from an OAM receiver wherein the orthogonality distance threshold comprises a value T indicative of a minimum order distance at which OAM modes transmitted using shared resources are orthogonal.
The apparatus of claim 7, wherein the processor and the memory are further configured to:

receive the information indicative of inter-mode interference between the set of N OAM modes via one or more of:

radio resource control (RRC) signaling,

medium access control (MAC) control element (CE) signaling, or

physical layer signaling using at least one of downlink control information (DCI) , uplink control information (UCI) , or sidelink control information (SCI) .
The apparatus of claim 7, wherein the processor and the memory are further configured to:

transmit, via the transceiver, information indicating group membership of the set of N OAM modes within the M groups.
The apparatus of claim 7, wherein the processor and the memory are further configured to:

determine an inter-mode interval D; and

group the set of N OAM modes such that a mode order between any two OAM modes in a group is no smaller than D.
The apparatus of claim 7, wherein D≥2T+1.
An apparatus configured for wireless communication, comprising:

a processor;

a plurality of antennas;

a transceiver coupled to the processor and to plurality of antennas; and

a memory coupled to the processor,

wherein the processor and the memory are configured for:

receive, via the transceiver and a first antenna of the plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources;

receive, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and

receive, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.
The apparatus of claim 13, further comprising a uniform circular array (UCA) that includes the first antenna, the second antenna, and the third antenna.
The apparatus of claim 13, wherein the first resources comprise time-frequency resources and a code.
The apparatus of claim 13, wherein the first reference signal comprises a demodulation reference signal (DM-RS) .
The apparatus of any one of claims 13 to 16, wherein the second reference signal comprises a channel state information reference signal (CSI-RS) .
The apparatus of any one of claims 13 to 16, wherein the processor and the memory are further configured to:

receive, via the transceiver, reference signals on the first OAM mode and the second OAM mode using different resources.
The apparatus of any one of claims 13 to 16, wherein the processor and the memory are further configured to:

transmit, via the transceiver, information indicative of inter-mode interference between a set of N OAM modes, wherein N > 2;

receive, via the transceiver, a reference signal on each OAM mode in a first group of M groups using the first resources; and

receive, via the transceiver, a reference signal on each OAM mode in a second group of the M groups using the second resources.
The apparatus of claim 19, wherein the information indicative of inter-mode interference between the set of N OAM modes comprises an OAM mode orthogonality distance threshold, wherein the mode orthogonality distance threshold comprises a value T indicative of a minimum order distance at which OAM modes transmitted using shared resources are orthogonal.
The apparatus of claim 20, wherein the processor and the memory are further configured to:

determine the orthogonality distance threshold based on the degree of direction misalignment.
The apparatus of claim 19, wherein the processor and the memory are further configured to:

transmit the information indicative of inter-mode interference between the set of N OAM modes to an OAM transmitting apparatus.
The apparatus of claim 19, wherein the processor and the memory are further configured to:

transmit the information indicative of inter-mode interference between the set of N OAM modes via one or more of:

radio resource control (RRC) signaling;

medium access control (MAC) control element (CE) signaling; or

physical layer signaling using at least one of downlink control information (DCI) , uplink control information (UCI) , or sidelink control information (SCI) .
The apparatus of claim 19, wherein the processor and the memory are further configured to:

receive, via the transceiver, reference signals on the first OAM mode and the second OAM mode using different resources;

determine a degree of direction misalignment between the plurality of antennas and a plurality of antennas associated with an OAM transmitter apparatus based on the reference signals received using the different resources; and

transmit the information indicative of inter-mode interference based on the degree of direction misalignment.
The apparatus of claim 19, wherein the apparatus further comprises a photodetector, and

wherein processor and the memory are further configured to:

detect, using the photodetector, a position at which light emitted from a laser associated with an OAM transmitter apparatus is received;

determine a degree of direction misalignment between the plurality of antennas and a plurality of antennas associated with the OAM transmitter apparatus based on the position; and

transmit the information indicative of inter-mode interference based on the degree of direction misalignment.
The apparatus of any one of claims 13 to 16, wherein the processor and the memory are further configured to:

receive, via the transceiver, a signal z=Hx+ε, where H is a channel matrix associated with channel used to transmit the reference signals, ε is noise, and x=∑ _i∈m r _i, where r _i is a reference signal of OAM mode i in the first group, and m includes the OAM modes in the first group; and

determine, based on z, a channel gain g _i of OAM mode i, where i is an OAM mode order in m.
The apparatus of claim 26, wherein the processor and the memory are further configured to:

determine, based on z, a mutual interference I _i, j from OAM mode i to OAM mode j, where i is an OAM mode order in m, and j is an OAM mode order not in m.
The apparatus of any one of claims 13 to 16, wherein the processor and the memory are further configured to:

receive, via the transceiver, a signal z=Hx+ε, where H is a channel matrix associated with a channel used to transmit reference signals in a first group using the first resources and reference signals in a second group using the second resources, ε is noise, and x=∑ _i∈m r _i, where r _i is a reference signal of OAM mode i _k in the first group, and m includes the OAM modes in the first group;

demodulate z based on the first OAM mode to yield a signal
where
is a demodulation function associated with the first OAM mode;

demodulate z based on the third OAM mode to yield a signal
where
is a demodulation function associated with the first OAM mode; and

determine a mutual interference I _2, 1 between the first OAM mode and the second OAM mode channel
where r ₁ is the transmitted first reference signal.
A method for wireless communication, comprising:

transmitting, via a transceiver and a first antenna of a plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources;

transmitting, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and

transmitting, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.
A method for wireless communication, comprising:

receiving, via a transceiver and a first antenna of a plurality of antennas, a first reference signal on a first orbital angular momentum (OAM) mode using first resources;

receiving, via the transceiver and a second antenna, a second reference signal on a second OAM mode using the same first resources; and

receiving, via the transceiver and a third antenna, a third reference signal on a third OAM mode using second resources.