WO2022027625A1

WO2022027625A1 - Frequency domain precoding for fdd reciprocity

Info

Publication number: WO2022027625A1
Application number: PCT/CN2020/107920
Authority: WO
Inventors: Rui Hu; Liangming WU; Chenxi HAO; Yu Zhang; Hao Xu; Qiaoyu Li; Kangqi LIU
Original assignee: Qualcomm Incorporated
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2022-02-10

Abstract

Aspects of the disclosure relate to precoding a wireless transmission based on frequency division duplex (FDD) carrier reciprocity. A base station transmits a reference signal over a plurality of ports, employing an initial precoding based on FDD reciprocity. A user equipment (UE) receives the reference signal, where there is a known association between a first set of ports and a first frequency domain basis vector, and between a second set of ports and a second frequency domain basis vector. The UE generates a channel estimate based on the reference signal, generates information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector, and transmits the generated information as a feedback signal. The base station generates an updated frequency domain basis vector based on the feedback message and transmit a subsequent message with precoding corresponding to the updated frequency domain basis vector.

Description

FREQUENCY DOMAIN PRECODING FOR FDD RECIPROCITY

TECHNICAL FIELD

The technology discussed below relates generally to wireless communication systems, and more particularly, to determining a precoding matrix to employ in a wireless transmission.

INTRODUCTION

In wireless communication systems, the use of multiple antennas at a transmitter and/or at a receiver can provide improved functionality beyond the use of a single antenna at each endpoint. For example, beamforming, or the directional transmission or reception of a wireless signal, can be achieved by applying a suitable precoding matrix to a signal transmission. That is, 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 another example, sometimes referred to as spatial multiplexing or multiple-input multiple-output (MIMO) , a transmitter can transmit multiple different streams of data, also referred to as layers, simultaneously on the same wireless resources. Similar to beamforming, for MIMO, the transmitter applies a suitable beamforming matrix to a signal transmission.

For beamforming and for MIMO, generation of a suitable precoding matrix generally corresponds to sophisticated processing of a timely channel estimate, where a reference signal transmitted over the channel is received and measured. In many cases, with bidirectional (duplex) communication, a channel estimate corresponding to a reference signal transmitted in one direction can be used to generate a precoding matrix for transmissions in the other direction. In general, this is referred to in the art as channel or carrier reciprocity. 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 some examples, a method, apparatus, and computer-readable medium for precoding a transmission over a plurality of ports is disclosed. In these examples, a user equipment (UE) receives a port association signal configured to indicate an association between a first set of the ports and a first frequency domain basis vector, and an association between a second set of the ports and a second frequency domain basis vector. The base station further generates a channel estimate based on a reference signal received over the plurality of ports, and transmits a feedback message based on the channel estimate, the feedback message including information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector.

In further examples, a method, apparatus, and computer-readable medium for updating a precoder for precoding a transmission over a plurality of ports is disclosed. In these examples, a base station generates a channel estimate based on a received first reference signal. The base station further generates an initial frequency domain basis vector for precoding the transmission, based on the channel estimate, and determines a dominant set and a complementary set of a frequency domain representation of the initial frequency domain basis vector. The base station further precodes a second reference signal for transmission on the first set of the ports based on the dominant set, and precodes the second reference signal for transmission on the second set of the ports based on the complementary set. The base station then transmits a port association signal configured to indicate an association between the first set of the ports and the dominant set, and an association between the second set of the ports and the complementary set. The base station then transmits the second reference signal over the plurality of ports, and receives a feedback message in response to the second reference signal, the feedback message comprising information for updating at least one of the dominant set or the complementary set. The base station then transmits an updated message with precoding updated based on the feedback message.

These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and embodiments will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments in conjunction with the accompanying figures. While the following description may discuss various advantages and features relative to certain embodiments and figures, all embodiments can include one or more of the advantageous features discussed herein. In other words, while this description may discuss one or more embodiments as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments discussed herein. In similar fashion, while this description may discuss exemplary embodiments as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a wireless communication system according to some aspects.

FIG. 2 is a conceptual illustration of an example of a radio access network according to some aspects.

FIG. 3 is a schematic illustration of an organization of wireless resources in an air interface utilizing orthogonal frequency divisional multiplexing (OFDM) according to some embodiments.

FIG. 4 is a block diagram illustrating a wireless communication system supporting multiple-input multiple-output (MIMO) communication.

FIG. 5 is a schematic illustration of a base station-generated portion of a precoder according to some examples.

FIG. 6 is a schematic illustration of a base station-generated portion of a precoder according to further examples.

FIG. 7 is a schematic illustration of a representation of a frequency domain basis vector in terms of a dominant set and a complementary set according to some aspects.

FIG. 8 is a schematic illustration of a representation of a frequency domain basis vector showing non-ideal FDD reciprocity according to some aspects.

FIG. 9 is a block diagram conceptually illustrating an example of a hardware implementation for a scheduling entity according to some aspects of the disclosure.

FIG. 10 is a block diagram conceptually illustrating an example of a hardware implementation for a scheduled entity according to some aspects of the disclosure.

FIG. 11 is a flow chart illustrating an exemplary process for employing an updated frequency domain basis vector for precoding according to some aspects of the disclosure.

FIG. 12 is a schematic illustration of an example association between ports and frequency domain basis vectors according to some aspects of the disclosure.

DETAILED DESCRIPTION

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.

The disclosure that follows presents various concepts that may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. Referring now to FIG. 1, as an illustrative example without limitation, this schematic illustration shows various aspects of the present disclosure with reference to a wireless communication system 100. The wireless communication system 100 includes three interacting domains: a core network 102, a radio access network (RAN) 104, and a user equipment (UE) 106. 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 104 may implement any suitable wireless communication technology or technologies to provide radio access to the UE 106. As one example, the RAN 104 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, many other examples may be utilized within the scope of the present disclosure.

As illustrated, the RAN 104 includes a plurality of base stations 108. Broadly, a base station is a network element in a radio access network 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 radio access network 104 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 104 and a UE 106 may be described as utilizing an air interface. Transmissions over the air interface from a base station (e.g., base station 108) to one or more UEs (e.g., UE 106) 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 (described further below; e.g., base station 108) . Another way to describe this scheme may be to use the term broadcast channel multiplexing. Transmissions from a UE (e.g., UE 106) to a base station (e.g., base station 108) 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 (described further below; e.g., UE 106) .

In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station 108) allocates resources for communication among some or all devices and equipment within its service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more scheduled entities. That is, for scheduled communication, UEs 106, which may be scheduled entities, may utilize resources allocated by the scheduling entity 108.

Base stations 108 are not the only entities that may function as scheduling entities. That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more scheduled entities (e.g., one or more other UEs) .

As illustrated in FIG. 1, a scheduling entity 108 may broadcast downlink traffic 112 to one or more scheduled entities 106. Broadly, the scheduling entity 108 is a node or device responsible for scheduling traffic in a wireless communication network, including the downlink traffic 112 and, in some examples, uplink traffic 116 from one or more scheduled entities 106 to the scheduling entity 108. On the other hand, the scheduled entity 106 is a node or device that receives downlink control information 114, including but not limited to scheduling information (e.g., a grant) , synchronization or timing information, or other control information from another entity in the wireless communication network such as the scheduling entity 108.

In general, base stations 108 may include a backhaul interface for communication with a backhaul portion 120 of the wireless communication system. The backhaul 120 may provide a link between a base station 108 and the core network 102. Further, in some examples, a backhaul network may provide interconnection between the respective base stations 108. 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.

The core network 102 may be a part of the wireless communication system 100, and may be independent of the radio access technology used in the RAN 104. In some examples, the core network 102 may be configured according to 5G standards (e.g., 5GC) . In other examples, the core network 102 may be configured according to a 4G evolved packet core (EPC) , or any other suitable standard or configuration.

Referring now to FIG. 2, by way of example and without limitation, a schematic illustration of a RAN 200 is provided. In some examples, the RAN 200 may be the same as the RAN 104 described above and illustrated in FIG. 1. The geographic area covered by the RAN 200 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. 2 illustrates

macrocells

202, 204, and 206, and a small cell 208, 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 FIG. 2, two base stations 210 and 212 are shown in

cells

202 and 204; and a third base station 214 is shown controlling a remote radio head (RRH) 216 in cell 206. That is, a base station can have an integrated antenna or can be connected to an antenna or RRH by feeder cables. In the illustrated example, the

cells

202, 204, and 126 may be referred to as macrocells, as the

base stations

210, 212, and 214 support cells having a large size. Further, a base station 218 is shown in the small cell 208 (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 208 may be referred to as a small cell, as the base station 218 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 radio access network 200 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

210, 212, 214, 218 provide wireless access points to a core network for any number of mobile apparatuses. In some examples, the

base stations

210, 212, 214, and/or 218 may be the same as the base station/scheduling entity 108 described above and illustrated in FIG. 1.

FIG. 2 further includes a quadcopter or drone 220, 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 220.

Within the RAN 200, the cells may include UEs that may be in communication with one or more sectors of each cell. Further, each

base station

210, 212, 214, 218, and 220 may be configured to provide an access point to a core network 102 (see FIG. 1) for all the UEs in the respective cells. For example, UEs 222 and 224 may be in communication with base station 210;

UEs

226 and 228 may be in communication with base station 212;

UEs

230 and 232 may be in communication with base station 214 by way of RRH 216; UE 234 may be in communication with base station 218; and UE 236 may be in communication with mobile base station 220. In some examples, the

UEs

222, 224, 226, 228, 230, 232, 234, 236, 238, 240, and/or 242 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 220) may be configured to function as a UE. For example, the quadcopter 220 may operate within cell 202 by communicating with base station 210.

In a further aspect of the RAN 200, 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 226 and 228) may communicate with each other using peer to peer (P2P) or sidelink signals 227 without relaying that communication through a base station (e.g., base station 212) . In a further example, UE 238 is illustrated communicating with

UEs

240 and 242. Here, the UE 238 may function as a scheduling entity or a primary sidelink device, and

UEs

240 and 242 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

240 and 242 may optionally communicate directly with one another in addition to communicating with the scheduling entity 238. 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.

The air interface in the radio access network 200 may utilize one or more duplexing algorithms. Duplex refers to a point-to-point communication link where both endpoints can communicate with one another in both directions. Full duplex means both endpoints can simultaneously communicate with one another. Half duplex means only one endpoint can send information to the other at a time. In a wireless link, a full duplex channel generally relies on physical isolation of a transmitter and receiver, and suitable interference cancellation technologies. Full duplex emulation is frequently implemented for wireless links by utilizing frequency division duplex (FDD) or time division duplex (TDD) . In FDD, transmissions in different directions operate at different carrier frequencies. In TDD, transmissions in different directions on a given channel are separated from one another using time division multiplexing. That is, at some times the channel is dedicated for transmissions in one direction, while at other times the channel is dedicated for transmissions in the other direction, where the direction may change very rapidly, e.g., several times per slot.

The air interface in the radio access network 200 may utilize one or more multiplexing and multiple access algorithms to enable simultaneous communication of the various devices. For example, 5G NR specifications provide multiple access for UL transmissions from UEs 222 and 224 to base station 210, and for multiplexing for DL transmissions from base station 210 to one or more UEs 222 and 224, utilizing orthogonal frequency division multiplexing (OFDM) with a cyclic prefix (CP) . In addition, for UL 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 UE may provide for UL 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) , or other suitable multiple access schemes. Further, a base station 210 may multiplex DL transmissions to UEs 222 and 224 utilizing time division multiplexing (TDM) , code division multiplexing (CDM) , frequency division multiplexing (FDM) , orthogonal frequency division multiplexing (OFDM) , sparse code multiplexing (SCM) , or other suitable multiplexing schemes.

Various aspects of the present disclosure will be described with reference to an OFDM waveform, schematically illustrated in FIG. 3. It should be understood by those of ordinary skill in the art 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) . On a given carrier, there may be one set of frames in the UL, and another set of frames in the DL. Referring now to FIG. 3, an expanded view of an exemplary DL subframe 302 is illustrated, showing an OFDM resource grid 304. However, as those skilled in the art will readily appreciate, the PHY transmission structure for any particular application may vary from the example described here, depending on any number of factors. Here, time is in the horizontal direction with units of OFDM symbols; and frequency is in the vertical direction with units of subcarriers or tones.

The resource grid 304 may be used to schematically represent time–frequency resources for a given antenna port. That is, in a MIMO implementation with multiple antenna ports available, a corresponding multiple number of resource grids 304 may be available for communication. The resource grid 304 is divided into multiple resource elements (REs) 306. An RE, which is 1 subcarrier × 1 symbol, is the smallest discrete part of the time–frequency grid, and contains 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) 308, 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. Within the present disclosure, it is assumed that a single RB such as the RB 308 entirely corresponds to a single direction of communication (either transmission or reception for a given device) .

A UE generally utilizes only a subset of the resource grid 304. An RB may be the smallest unit of resources that can be allocated 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.

In this illustration, the RB 308 is shown as occupying less than the entire bandwidth of the subframe 302, with some subcarriers illustrated above and below the RB 308. In a given implementation, the subframe 302 may have a bandwidth corresponding to any number of one or more RBs 308. Further, in this illustration, the RB 308 is shown as occupying less than the entire duration of the subframe 302, although this is merely one possible example.

Each subframe 302 (e.g., a 1ms subframe) may consist of one or multiple adjacent slots. In the example shown in FIG. 3, one subframe 302 includes four slots 310, as an illustrative example. In some examples, a slot may be defined according to a specified number of OFDM symbols with a given cyclic prefix (CP) length. For example, a slot may include 7 or 14 OFDM symbols with a nominal CP. Additional examples may include mini-slots having a shorter duration (e.g., 1, 2, 4, or 7 OFDM symbols) . These mini-slots may in some cases be transmitted occupying resources scheduled for ongoing slot transmissions for the same or for different UEs.

An expanded view of one of the slots 310 illustrates the slot 310 including a control region 312 and a data region 314. In general, the control region 312 may carry control channels (e.g., PDCCH) , and the data region 314 may carry data channels (e.g., PDSCH or PUSCH) . Of course, a slot may contain all DL, all UL, or at least one DL portion and at least one UL portion. The simple structure illustrated in FIG. 3 is merely exemplary in nature, and different slot structures may be utilized, and may include one or more of each of the control region (s) and data region (s) .

Although not illustrated in FIG. 3, the various REs 306 within an RB 308 may be scheduled to carry one or more physical channels, including control channels, shared channels, data channels, etc. Other REs 306 within the RB 308 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 308.

In a DL transmission, the transmitting device (e.g., the scheduling entity 108) may allocate one or more REs 306 (e.g., within a control region 312) to carry DL control information 114 including one or more DL control channels that generally carry information originating from higher layers, such as a physical broadcast channel (PBCH) , a physical downlink control channel (PDCCH) , etc., to one or more scheduled entities 106. In addition, DL REs may be allocated 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.

The synchronization signals PSS and SSS (collectively referred to as SS) , and in some examples, the PBCH, may be transmitted 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 106) may utilize one or more REs 306 to carry UL control information 118 (UCI) . The UCI can originate from higher layers via one or more UL control channels, such as a physical uplink control channel (PUCCH) , a physical random access channel (PRACH) , etc., to the scheduling entity 108. 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 118 may include a scheduling request (SR) , i.e., a request for the scheduling entity 108 to schedule uplink transmissions. Here, in response to the SR transmitted on the control channel 118, the scheduling entity 108 may transmit downlink control information 114 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 the integrity of packet transmissions may be checked at the receiving side for accuracy, e.g., utilizing any suitable integrity checking mechanism, such as a checksum or a cyclic redundancy check (CRC) . If the integrity of the transmission confirmed, an ACK may be transmitted, whereas if not confirmed, a NACK may be transmitted. 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 306 (e.g., within the data region 314) 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) .

In order for a UE to gain initial access to a cell, the RAN may provide system information (SI) characterizing the cell. This system information may be provided utilizing minimum system information (MSI) , and other system information (OSI) . The MSI may be periodically broadcast over the cell to provide the most basic information a UE requires for initial cell access, and for acquiring any OSI that may be broadcast periodically or sent on-demand. In some examples, a network may provide MSI over two different downlink channels. For example, the PBCH may carry a master information block (MIB) , and the PDSCH may carry a system information block type 1 (SIB1) . Here, the MIB may include a UE with parameters for monitoring a control resource set. The control resource set may thereby provide the UE with scheduling information corresponding to the PDSCH, e.g., a resource location of SIB1. In the art, SIB1 may be referred to as remaining minimum system information (RMSI) .

OSI may include any SI that is not broadcast in the MSI. In some examples, the PDSCH may carry a plurality of SIBs, not limited to SIB1, discussed above. Here, the OSI may be provided in these SIBs, e.g., SIB2 and above.

The channels or carriers described above and illustrated in FIGs. 1 and 3 are not necessarily all the channels or carriers that may be utilized between a scheduling entity 108 and scheduled entities 106, 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.

In some examples, a physical layer may generally multiplex and map these physical channels described above to transport channels for handling at a medium access control (MAC) layer entity. Transport channels carry blocks of information called transport blocks (TB) . The transport block size (TBS) , which may correspond to a number of bits of information, may be a controlled parameter, based on the modulation and coding scheme (MCS) and the number of RBs in a given transmission.

In some aspects of the disclosure, the scheduling entity and/or scheduled entity may be configured with multiple antennas for beamforming and/or multiple-input multiple-output (MIMO) technology. FIG. 4 illustrates an example of a wireless communication system 400 with multiple antennas, supporting beamforming and/or MIMO. The use of such multiple antenna technology enables the 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 402 includes multiple transmit antennas 404 (e.g., N transmit antennas) and a receiver 406 includes multiple receive antennas 408 (e.g., M receive antennas) . Thus, there are N × M signal paths 410 from the transmit antennas 404 to the receive antennas 408. Each of the transmitter 402 and the receiver 406 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, as shown in FIG. 4, 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 404. The signal from each transmit antenna 404 reaches each receive antenna 408 along a different signal path 410. The receiver 406 may then reconstruct the data streams using the received signals from each receive antenna 408.

In some examples, a transmitter may send multiple data streams to multiple receivers. This may be referred to as multi-user MIMO (MU-MIMO) . In this way, a MU-MIMO system exploits multipath signal propagation to increase the overall network capacity by increasing throughput and spectral efficiency, and reducing the required transmission energy. This is achieved by spatially precoding (i.e., multiplying the data streams with different weighting and phase shifting) each data stream (in some examples, based on known channel state information) and then transmitting each spatially precoded stream through multiple transmit antennas to the receiving devices using the same allocated time-frequency resources. The receiver may transmit feedback including a quantized version of the channel so that the transmitter can schedule the receivers with good channel separation. The spatially precoded data streams arrive at the receivers with different spatial signatures, which enables the receiver (s) (in some examples, in combination with known channel state information) to separate these streams from one another and recover the data streams destined for that receiver. In the other direction, multiple transmitters can each transmit a spatially precoded data stream to a single receiver, which enables the receiver to identify the source of each spatially precoded data stream.

The number of data streams or layers in a MIMO or MU-MIMO (generally referred to as 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

404 or 408, 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; and/or a sounding reference signal, or SRS) that the receiving device may measure. In some cases, 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 Time Division Duplex (TDD) systems, the UL and DL may be reciprocal, in that each uses different time slots of the same frequency bandwidth. Therefore, in TDD systems, a base station may assign a rank for DL MIMO transmissions based on an UL SINR measurement (e.g., based on a sounding reference signal (SRS) or other pilot signal transmitted from the UE) . Based on the assigned rank, the base station may then transmit a channel state information reference signal (CSI-RS) with separate sequences for each layer to provide for multi-layer channel estimation. From the CSI-RS, the UE may measure the channel quality across layers and resource blocks. The UE may then transmit a CSI report (including, e.g., CQI, RI, and PMI) to the base station for use in updating the rank and assigning resources for future downlink transmissions.

While the use of such TDD reciprocity is relatively straightforward, there has recently been increased interest in FDD reciprocity. In an FDD carrier, because the UL component carrier and DL component carrier operate at different frequencies, even in different bands, the reciprocity of the respective UL and DL component carriers is less straightforward. Still, although some portions of the UL and DL carriers might be irretrievably distinct, there remain features or characteristics of UL and DL carriers in an FDD system that nevertheless exhibit useful reciprocity. For example, since both carriers provide communication between the same endpoints, the angle of departure and angle of arrival of the different paths can be considered reciprocal. Furthermore, larger-scale fadings can often be the same, or similar, between UL and DL carriers. Broadly, according to various aspects of this disclosure, FDD reciprocity refers to a set of channel characteristics, parameters, or features that may be considered reciprocal between UL and DL carriers, even if other characteristics, parameters, or features of the respective carriers may not exhibit such reciprocity. And further, based on this FDD reciprocity, useful information for configuring a DL transmission may be obtained based on channel characteristics, parameters, or features of a corresponding UL carrier; and useful information for configuring an UL transmission may be obtained based on channel characteristics, parameters, or features of a corresponding DL carrier.

As one example, according to release-16 of 3GPP specifications for 5G NR, a base station may employ a certain Type II precoder to a CSI-RS transmission on a subband designated subband n. For example, a release-16 Type II precoder for subband n may be described according to the following equation.

Here, b _i represents a spatial domain basis vector, or the spatial domain portion of a precoder. For example, b _i may correspond to the i-th column of a spatial domain basis W ₁;L represents a number of spatial domain basis vectors in the spatial domain basis W ₁. In various examples, the spatial domain basis W ₁ may represent a singular-value decomposition (SVD) of the reciprocal (e.g., UL) channel, based on a measurement of one or more suitable reference signals such as the SRS. However, within the scope of this disclosure a spatial domain basis W ₁ may be a discrete Fourier transform (DFT) basis or any other suitable matrix that generally matches the spatial domain of the channel.

Further,

represents a frequency domain basis vector. For example,

may correspond to a row vector, e.g., being the m-th row of a frequency domain basis

In various examples,

may represent a frequency domain basis of size M by N, where M is a number of frequency domain basis vectors, and N is a number of subbands (e.g., a number of columns in the frequency domain basis

) . The superscript H represents a conjugate transform. While the discussion that follows assumes that the frequency domain basis vector

is m-th row of

within the scope of this disclosure, a frequency domain basis vector may generally correspond to a linear combination of a set of any suitable number of selected rows of

In this example,

represents the element at the m-th row and n-th column of

Still further, c _i, m represents a set of linear combination coefficients corresponding to UE feedback based on UE beam measurements. For example, when a UE receives a reference signal (e.g., CSI-RS) over the precoded channel (e.g., over a plurality of ports) , the UE can compare the different ports with one another, e.g., in terms of received signal power. Based on these channel measurements, the UE may rank and rate the different ports, and/or may select a subset of the ports that has a relatively strong power. Thus, the UE can provide feedback to the base station corresponding to the linear coefficients associated with the selected ports. Thus, the base station can utilize this linear coefficient information to update a precoder for a subsequent transmission.

With this release-16 type II precoder, the UE may provide the base station with feedback from which the base station can obtain the linear combination coefficients c _i, m and the frequency domain basis vector

Thus, according to the release-16 precoder, the base station calculates the spatial domain basis vector b _i (e.g., based on an UL reference signal from the UE) , while the UE calculates the frequency domain basis vector

(e.g., based on a DL reference signal from the base station) . The base station then precodes a DL transmission based on this combination of information.

Referring now to FIG. 5, this illustration is a grid that schematically shows one example of a base station-generated part of a release-16 Type II precoder, applied to two ports (Port 0 and Port 1) for transmission of a CSI-RS. In the illustrated table, each row shows a portion of a precoder the base station generates for a corresponding port; and each column n (where n = [0, …, N-1] ) shows the precoder the base station generates for a corresponding frequency domain (FD) unit. In the discussion above, the notation n was discussed in relation to a particular FD unit called a 'subband. ' In the discussion that follows, for generality, n will refer to a FD unit; and any reference to a subband may be inferred to be generalized to an FD unit.

It has been observed that a base station can obtain better precoding performance if the base station, rather than the UE, generates the frequency-domain basis vector

In this manner, the base station can consider frequency-selective characteristics of the channel in its determination of a precoder to employ. For example, a base station may freely generate a frequency domain basis vector based on, e.g., the SVD of the reciprocal channel, a discrete cosine transform (DCT) basis, or any other kind of basis that matches the frequency domain of the channel. In some examples, e.g., when FDD reciprocity is good, an SVD basis may perform better, while in other examples, another frequency domain basis might perform better. Thus, moving generation of the frequency-domain basis vector to the base station provides more flexibility in precoding, as well as alleviating the burden of calculating this parameter for the UE.

Accordingly, in the more recent release-17 of 3GPP specifications for 5G NR, when it employs a Type II precoder the base station generates the frequency-domain basis vector

as well as the spatial-domain basis vector b _i. In this example, the UE may provide the base station with feedback representing the linear combination coefficients c _i, m, omitting UE feedback corresponding to the frequency-domain basis vector

Here, while the release-17 Type II precoder can be expressed with the same equation as provided above for the release-16 Type II precoder, the parameters within that equation may have a different origin.

Referring now to FIG. 6, this illustration is a grid that schematically shows one example of a base station-generated part of a release-17 Type II precoder, applied to four ports (Port 0, Port 1, Port 2, and Port 3) for transmission of a CSI-RS. In this grid, each row shows the portion of the precoder that the base station generates for a corresponding port; and each column n shows the portion of the precoder that the base station generates for a corresponding FD unit, where n = [0, …, N-1] . Thus, in the illustrated example, for Port 0, the base station generates a spatial domain precoder b ₀ as well as a frequency domain basis vector

The particular combination of spatial domain basis vector and frequency domain basis vector shown in FIG. 6 is merely illustrative in nature. In general, each spatial domain basis vector may be paired with a different frequency domain basis vector. That is, the spatial domain beam may be observed at different taps. In the illustrated example, Port 0 and Port 1 both have the same spatial domain basis vector, but different frequency domain basis vectors. But other combinations of spatial domain basis vectors and frequency domain basis vectors may be employed in a given implementation.

According to some aspects of the present disclosure, a base station operating in FDD may take advantage of an FDD reciprocity feature, and generate a DL precoder at least in part based on an UL channel estimate. For example, a base station may receive an UL reference signal, such as a sounding reference signal (SRS) or any other suitable signal, transmitted from a UE. Based on this UL reference signal, the base station may generate an UL channel estimate. And further, based on the UL channel estimate, the base station may generate an UL precoder based on an UL spatial domain basis vector

and an UL frequency domain basis vector

In the present disclosure, certain aspects, features, and operations upon a frequency domain basis vector are discussed. For ease of discussion, the spatial domain basis vector may be considered as an ideal precoder, and thus, is not specifically addressed in the following discussion. However, such an ideal spatial domain basis vector is not a requirement, and any suitable ideal or non-ideal spatial domain basis vector may be utilized in a given example in association with the frequency domain basis vectors as discussed herein.

According to an aspect of this disclosure, as illustrated in FIG. 7, a base station may represent the UL frequency domain basis vector

as a vector having M elements, each element corresponding to a different frequency domain basis vector. Equivalently, the base station may represent the UL frequency domain basis vector

as a product of a basis matrix D and a sparse vector

as illustrated, where the sparse vector corresponds to a delay-domain representation of the UL frequency domain basis vector. Here, the basis matrix D may, for example, correspond to a DFT matrix, or an oversampled DFT matrix, representing the UL frequency domain basis vector

in the frequency domain. The basis matrix D may have a size of (N-1) ×G. Here, once again, N represents a number of FD units. G represents a number of columns in basis matrix D. In an example where D is a DFT matrix, then G = N-1. But in an example where D is an oversampled DFT matrix, then G > N-1.

For example, the channel between the base station and the UE may be modeled as a multipath channel, wherein a line-of-sight signal and a number of signal reflections may arrive at a receiver over different paths, having different respective propagation times or delays. In general, the receiving device observes signals from a small number of taps. This is a characteristic of a sparse channel in the delay domain. When such a channel is projected into the delay domain, e.g., using a DFT matrix, a sparse set of relatively few columns of the frequency-domain channel matrix have any value, while other columns are zeros.

Accordingly, in an aspect of this disclosure, when the UL frequency domain basis vector

is represented by a basis matrix D and a sparse vector

due to channel sparsity, relatively few columns of the basis matrix D have values. Similarly, the sparse vector

may only carry any value in rows corresponding to the nonzero columns of the basis matrix D, while other rows are zeros, as illustrated in FIG. 7.

In a still further aspect, such a basis matrix D may be segmented into two matrices, referred to herein as a dominant set D _dom and a complementary set D _comp. Here, the dominant set may include the set of columns of the basis matrix D having nonzero values, while the complementary set may include the set of columns of the basis matrix D having zero values. In the particular example shown in this illustration, the basis matrix D includes 8 columns, with only 4 of those columns including the information of the UL frequency domain basis vector

and the other 4 columns having zero values. Like the basis matrix D, each one of these dominant and complementary sets can be multiplied by a suitable vector and added together, to recover the UL frequency domain basis vector

Of course, this half-and-half example is merely provided for ease of description. In a particular implementation, a basis matrix D may have a dominant set D _dom and a complementary set D _comp that include any suitable number of columns. And furthermore, it is not necessary that the complementary set include all zero values, and one or more columns of the complementary set may include nonzero values in some examples.

As discussed above, due to certain reciprocal properties of the respective UL and DL carriers in FDD, a base station may in some examples generate a DL frequency domain basis vector

based on the UL frequency domain basis vector

and its corresponding dominant and complementary sets. As one example, a base station may simply apply the UL frequency domain basis vector without change as a DL frequency domain basis vector. And with ideal, or at least reasonably good channel reciprocity, this reuse of the UL frequency domain basis may be suitable. That is, the UL and DL channels may share at least some columns that have nonzero values.

However, a more conventional DL precoder generated based on UE measurements of a DL reference signal may provide improved performance over one based on such reuse of the UL frequency domain precoder. For example, as illustrated in FIG. 8, a DL frequency domain basis vector

processed in the same way as described above may result in the same dominant set D _dom, but its complementary set D _comp may have one or more columns with nonzero values. In other words, if the UL frequency domain basis vector

were fully reused in the DL, the DL precoder may cause a loss of information or signal power corresponding to other channel paths, having different propagation times or delays. Especially in a case where FDD reciprocity is low, reuse of the UL frequency domain basis vector for the DL precoder can result in poor performance, and may potentially require updating based on UE feedback (e.g., based on a UE measurement of a DL reference signal) .

For example, as illustrated in FIG. 8, an initial DL frequency domain basis vector

may be represented by a DFT or oversampled DFT basis matrix D, which may then be separated or segmented into a dominant set D _dom and a complementary set D _comp. In an example with ideal FDD reciprocity, the UL and DL frequency domain precoders are in the same subset of the DFT basis. And thus, use of the dominant set D _dom as the frequency domain basis may suitably precode both the UL and the DL. However, in an example where FDD reciprocity is less than ideal, use of the same DL precoder as for the UL may result in poor or reduced performance.

For the purpose of illustration, FIG. 8 provides an example corresponding to non-ideal FDD reciprocity. In the illustrated example, the base station generates a UL frequency domain basis vector

e.g., based on an UL reference signal. And for the purpose of explanation, assume that the base station generates a DL frequency domain basis vector

e.g., based on a DL reference signal transmitted to a UE, and corresponding feedback from the UE. As discussed above, both the UL frequency domain basis vector and the DL frequency domain basis vector can be represented according to a DFT or oversampled DFT basis matrix D. And further, either basis matrix D may be separated or segmented into a dominant set D _dom and a complementary set D _comp. In the illustrated example, all of the information of the UL matrix D ^UL may be represented in the dominant set, and the complementary set may include all zero values. However, in this example, while dominant set of the DL matrix

is the same as the dominant set of the UL matrix

due to non-ideal FDD reciprocity their complementary sets differ. That is, while the complementary set of the UL matrix

may have all zero values, the complementary set of the DL matrix

may indicate one or more delay paths in the DL direction that were small or unmeasured in the UL direction. Thus, at least one column of the complementary set of the DL matrix

may include nonzero values for the DL frequency domain precoder.

Therefore, according to some aspects of this disclosure, a base station may generate an initial DL frequency domain basis vector by reusing an UL frequency domain basis vector. Further, the base station may update the DL frequency domain basis vector based on UE feedback. Here, the base station may transmit a precoded DL reference signal over a plurality of ports, with the precoder being applied at respective ports being based on either the dominant set D _dom or the complementary set D _comp. The base station may further signal to the UE to indicate the port association between dominant set ports and complementary set ports. After a UE receives these DL reference signals and generates a DL channel estimate, the UE may generate a channel report corresponding to a set of ports corresponding to a selected subset among the dominant set and/or the complementary set. The base station may utilize this channel report to update its DL frequency domain basis vector for improved performance. In some examples, this process may be repeated any number of times to dynamically maintain a suitable level of DL performance.

By employing some of the aspects described herein, a UE may reduce or limit the size of its port selection overhead, achieving improved DL performance with a relatively small cost in UL signaling overhead. For example, with an updated DL precoder based on certain features herein, a UE can capture more power in receiving a DL transmission.

FIG. 9 is a block diagram illustrating an example of a hardware implementation for a scheduling entity 900 employing a processing system 914. For example, the scheduling entity 900 may be a user equipment (UE) as illustrated in any one or more of FIGs. 1, 2, and/or 4. In another example, the scheduling entity 900 may be a base station as illustrated in any one or more of FIGs. 1, 2, and/or 4.

The scheduling entity 900 may be implemented with a processing system 914 that includes one or more processors 904. Examples of processors 904 include microprocessors, microcontrollers, digital signal processors (DSPs) , field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , 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 scheduling entity 900 may be configured to perform any one or more of the functions described herein. That is, the processor 904, as utilized in a scheduling entity 900, may be configured (e.g., in coordination with the memory 905) to implement any one or more of the processes and procedures described below and illustrated in FIG. 11.

In this example, the processing system 914 may be implemented with a bus architecture, represented generally by the bus 902. The bus 902 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 914 and the overall design constraints. The bus 902 communicatively couples together various circuits including one or more processors (represented generally by the processor 904) , a memory 905, and computer-readable media (represented generally by the computer-readable medium 906) . The bus 902 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 908 provides an interface between the bus 902 and a transceiver 910. The transceiver 910 provides a communication interface or means for communicating with various other apparatus over a transmission medium. Depending upon the nature of the apparatus, a user interface 912 (e.g., keypad, display, speaker, microphone, joystick) may also be provided. Of course, such a user interface 912 is optional, and may be omitted in some examples, such as a base station.

In some aspects of the disclosure, the processor 904 may include communication circuitry 940 configured (e.g., in coordination with the memory 905 and the transceiver 910) for various functions, including, e.g., transmitting and/or receiving data, control signaling, and reference signals over a wireless air interface. The processor 904 may further include precoding circuitry 942 configured (e.g., in coordination with the memory 905 and the transceiver 910) for various functions, including, e.g., determining and applying a precoding matrix to a transmission.

The processor 904 is responsible for managing the bus 902 and general processing, including the execution of software stored on the computer-readable medium 906. The software, when executed by the processor 904, causes the processing system 914 to perform the various functions described below for any particular apparatus. The computer-readable medium 906 and the memory 905 may also be used for storing data that is manipulated by the processor 904 when executing software.

One or more processors 904 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 906. The computer-readable medium 906 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 906 may reside in the processing system 914, external to the processing system 914, or distributed across multiple entities including the processing system 914. The computer-readable medium 906 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 one or more examples, the computer-readable storage medium 906 may store computer-executable code that includes communication instructions 960 that configure a scheduling entity 900 for various functions, including, e.g., transmitting and/or receiving data, control signaling, and reference signals over a wireless air interface. The computer-readable storage medium 906 may store computer-executable code that includes channel characterization instructions 962 that configure a scheduling entity 900 for various functions, including, e.g., determining and applying a precoding matrix to a transmission.

Of course, in the above examples, the circuitry included in the processor 904 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 906, or any other suitable apparatus or means described in any one of the FIGs. 1, 2, and/or 4, and utilizing, for example, the processes and/or algorithms described herein in relation to FIG. 11.

FIG. 10 is a conceptual diagram illustrating an example of a hardware implementation for an exemplary scheduled entity 1000 employing a processing system 1014. 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 1014 that includes one or more processors 1004. For example, the scheduled entity 1000 may be a user equipment (UE) as illustrated in any one or more of FIGs. 1, 2, and/or 4.

The processing system 1014 may be substantially the same as the processing system 914 illustrated in FIG. 9, including a bus interface 1008, a bus 1002, memory 1005, a processor 1004, and a computer-readable medium 1006. Furthermore, the scheduled entity 1000 may include a user interface 1012 and a transceiver 1010 substantially similar to those described above in FIG. 9. That is, the processor 1004, as utilized in a scheduled entity 1000, may be configured (e.g., in coordination with the memory 1005) to implement any one or more of the processes described below and illustrated in FIG. 11.

In some aspects of the disclosure, the processor 1004 may include communication circuitry 1040 configured (e.g., in coordination with the memory 1005 and the transceiver 1010) for various functions, including, for example, transmitting and/or receiving data, control signaling, and reference signals over a wireless air interface. The processor 1004 may further include channel characterization circuitry 1042 configured (e.g., in coordination with the memory 1005 and the transceiver 1010) for various functions, including, for example, receiving and performing suitable measurements on a signal such as a reference signal.

And further, the computer-readable storage medium 1006 may store computer-executable code that includes communication instructions 1060 that configure a scheduled entity 1000 configured (e.g., in coordination with the memory 1005 and the transceiver 1010) for various functions, including, for example, transmitting and/or receiving data, control signaling, and reference signals over a wireless air interface. The computer-readable storage medium 1006 may further store computer-executable code that includes channel characterization instructions 1062 that configure a scheduled entity 1000 configured (e.g., in coordination with the memory 1005 and the transceiver 1010) for various functions, including, for example, receiving and performing suitable measurements on a signal such as a reference signal.

Of course, in the above examples, the circuitry included in the processor 1004 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 1006, or any other suitable apparatus or means described in any one of the FIGs. 1, 2, and/or 4, and utilizing, for example, the processes and/or algorithms described herein in relation to FIG. 11.

As discussed above, in some aspects of this disclosure, a network may exploit FDD reciprocity by basing a DL frequency domain basis vector

upon its generated UL frequency domain basis vector

For example, FIG. 11 is a flow chart illustrating an exemplary process 1100 for MIMO communication utilizing a DL frequency domain basis vector based on FDD reciprocity in accordance with some aspects of the present 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 1100 may be carried out by the scheduling entity 900 illustrated in FIG. 9 and the scheduled entity 1000 illustrated in FIG. 10. In some examples, the process 1100 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

At block 1102, a base station may receive an UL reference signal (e.g., SRS) transmitted from a UE. For example, at block 1152, a UE may transmit an UL reference signal (e.g., SRS) to a base station. Based on the UL reference signal, the base station may generate a UL channel estimate.

At block 1104, based on the UL channel estimate, the base station may generate an UL precoder. For example, the base station may calculate a spatial domain basis of the UL channel

and from this spatial domain basis, the base station may select a UL spatial domain basis vector

Further, the base station may calculate a frequency domain basis of the UL channel

and from this frequency domain basis, the base station may select a frequency domain basis vector

Based on the UL precoder, the base station may determine an initial DL frequency domain basis vector

at least in part by relying on FDD reciprocity. For example, in some cases, the base station may set the initial DL frequency domain basis vector

as equal to the determined UL frequency domain basis vector

Further, the base station may represent the initial DL frequency domain basis vector

by basis matrix D and sparse vector s. Here, as discussed above, the basis matrix D may correspond to a DFT or oversampled DFT basis.

At block 1106, the base station may separate or segment the matrix D into a dominant set D _dom and a complementary set D _comp. Here, the base station may determine a set of ports projected to have a generally higher received signal power for the dominant set, and a set of ports projected to have a generally lower received signal power for the complementary set.

At block 1108, according to a further aspect of the present disclosure, the base station may transmit a signal (e.g., a port association signal) to the UE to indicate a port association between dominant set ports and complementary set ports. That is, the base station may schedule DL transmissions to a given UE such that a first set of DL ports will employ a frequency domain basis based on the dominant set, and a second set of DL ports will employ a frequency domain basis based on the complementary set. Accordingly, the base station may provide a suitable information signal to the UE, to inform the UE which port (s) correspond to a precoder from the dominant set, and which port (s) correspond to a precoder from the complementary set.

For example, FIG. 12 illustrates an example of a portion of a joint spatial domain (SD) and frequency domain (FD) precoder for a DL transmission from a base station according to an aspect of this disclosure, utilizing a two-SD, two-FD basis. For example, a spatial domain basis vector may include (b ₀, b ₁) , and a frequency domain basis vector may include

As described above, each of these frequency domain basis vectors may be separated or segmented into a dominant set and a complementary set. In the illustrated example, there are K ₀+K ₁ ports, divided into two sets: a first set including Port 0 through Port K ₀, and a second set including Port K ₀+1 through Port K ₀+K ₁. Further, for the illustrated example, the base station may apply a first spatial domain basis vector b ₀ to the first set from Port 0 to Port K ₀, and the base station may apply a second spatial domain basis vector b ₁ to the second set from Port K ₀+1 to Port K ₀+K ₁.

According to an aspect of the present disclosure, a base station may employ a known association between ports and frequency domain precoders, to enable a UE receiving the DL transmission to evaluate the DL transmission and provide useful updates for improving the DL precoder at the base station. For example, for the first set of ports from Port 0 to port K ₀, the base station may employ the first frequency domain basis vector

which may be represented by a dominant set D _{dom_0} and a complementary set D _{comp_0}. Here, the base station may apply the dominant set D _{dom_0} as the frequency domain precoder on Port 0; and the base station may apply the complementary set D _{comp_0} to Ports 1 through K ₀. Thus, while all of the first set of ports from Port 0 to Port K ₀ utilize the first SD basis vector b ₀, a subset of those ports (e.g., Port 0) utilizes the dominant set D _{dom_0} as the FD basis vector

and another subset of those ports (e.g., Ports 1 through K ₀) utilizes the complementary set D _{comp_0} as the FD basis vector

Similarly, for the second set of ports from Port K ₀+1 to Port K ₀+K ₁, the base station may employ the second frequency domain basis vector

which may be represented by a dominant set D _{dom_1} and a complementary set D _{comp_1}. Here, the base station may apply the dominant set D _{dom_1} as the frequency domain basis vector on Port K ₀+1; and the base station may apply the complementary set D _{comp_1} to Ports K ₀+2 through K ₀+K ₁. Thus, while all of the second set of ports from Port K ₀+1 to Port K ₀+K ₁ utilize the second SD basis vector b ₁, a subset of those ports (e.g., Port K ₀+1) utilizes the dominant set D _{dom_1} as the FD basis vector

and another subset of those ports (e.g., Ports K ₀+2 through K ₀+K ₁) utilizes the complementary set D _{comp_1} as the FD basis vector

Thus, returning to block 1108, the base station may transmit a signal to the UE to indicate, e.g., that Port 0 and Port K _{0_1} utilize the dominant set for a FD basis vector, while other ports (Ports 1 through K ₀ and Ports K ₀+1 through K ₀+K ₁) utilize the complementary set for a FD basis vector. Correspondingly, at block 1154, the UE may receive a signal indicating the port association of dominant set ports and complementary set ports.

Those skilled in the art will recognize that the specific allocation of dominant set and complementary set among ports as described above and illustrated in FIG. 12 is merely illustrative in nature, and not intended to be limiting. In a given implementation, any suitable association between ports and dominant/complementary set may be utilized. As another example, a DL CSI-RS being transmitted over 16 ports may associate 12 ports (e.g., the first through twelfth ports) with a dominant set, and may associate 4 ports (e.g., the thirteenth through sixteenth ports) with a complementary set. Other associations or distributions can be utilized as appropriate.

At block 1110, the base station may transmit a precoded DL reference signal (e.g., CSI-RS) , applying a precoder based in part on the initial frequency domain basis vector. Here, the precoder the base station applies may be as described above and illustrated in FIG. 12, with a subset of ports being precoded utilizing a dominant set, and a subset of ports being precoded utilizing a complementary set. And at block 1156, the UE may receive a DL reference signal (e.g., CSI-RS) and generate a corresponding channel estimate.

At block 1158, based on the DL channel estimate, the UE may generate a PMI report corresponding to a selected subset of ports associated with the dominant set and/or the complementary set. For example, referring once again to FIG. 12, assume that the base station transmits a CSI-RS over a set of K ₀+K ₁ ports, applying the precoding illustrated in this figure. In this example, as discussed above in connection with block 1154, the UE can determine whether a CSI-RS received over a particular port was precoded utilizing dominant set FD precoding, or complementary set FD precoding. In an example with ideal, or relatively good FDD reciprocity, the CSI-RS received over the complementary set ports (Ports 1 through K ₀, and Ports K ₀+2 through K ₀+K ₁) may only provide a very low energy signal, and the CSI-RS received over the dominant set ports (Ports 0 and K ₀+1) may provide a relatively high energy signal. In this example, at block 1160, the UE may prepare a CSI report including PMI feedback only corresponding to the dominant set ports.

However, as discussed above, in an example with a non-ideal FDD reciprocity, the DL carrier may exhibit one or more delay paths that differ from those seen in the UL carrier. In this example, the CSI-RS received over one or more of the complementary set ports may provide a substantial energy signal in relation to the CSI-RS received over the dominant set ports. Accordingly, at block 1160 the UE may prepare a feedback message (e.g., a CSI report including information (e.g., PMI) ) corresponding to one or more of the complementary set ports. That is, in an aspect of the present disclosure, the UE may selectively report feedback relating to the precoded channel for the dominant set and/or for the complementary set, based on the respective sets' known port associations.

By providing for a UE to signal such update information to a base station, and enabling a base station to update its DL precoder as described herein based on the UL feedback, a DL performance can be improved relative to simple reuse of an UL precoder for a DL based on FDD reciprocity. While some other examples may employ conventional a DL precoder that does not rely on FDD reciprocity, those examples may suffer from increased latency caused by their need to employ direct estimates of the UL and DL channels and send feedback for a full precoder.

In an example where the UE provides feedback corresponding to one or more of the complementary set ports, according to a further aspect of this disclosure, the UE may provide feedback relating to a precoding for the complementary set, to enable the UE received signal to capture power that DL precoding based on the UL FD precoder alone would fail to capture.

In a still further aspect of the disclosure, when the UE determines the parameters to provide the base station in the CSI report at block 1160, the UE may select a subset of the dominant set ports, and/or a subset of the complementary set ports, for reporting. Selection of the set of ports to include in a CSI report according to an aspect of this disclosure may be made in accordance with a suitable given rule or algorithm. Here, the base station may provide the UE with the port selection rule or algorithm in any suitable signaling or information message, or in other examples, the UE may determine the port selection rule or algorithm based on any other suitable information (e.g., information stored in memory) .

As one example, the UE may follow a rule or algorithm configured such that the UE selects a greater number of dominant set ports than complementary set ports. Here, the number of selected ports for the UE to include in its CSI report may be preconfigured or established as part of the rule or algorithm. For example, if a UE were configured to select a set of 5 dominant set ports and 2 complementary set ports, the UE may identify the 2 complementary set ports with the best characteristics (e.g., the highest received power) among the complementary set ports. Accordingly, the UE may provide a CSI report with PMI information corresponding to the 5 dominant set ports and the 2 selected complementary set ports.

In another example, the port selection rule or algorithm may provide for the UE to include in its CSI report PMI information corresponding to all of the dominant set ports, and to report any complementary set port or ports that the UE determines to include based on one or more suitable factors or parameters. For example, a UE may be configured to include in its CSI report PMI information corresponding to those complementary set ports, if any, which have greater than a suitable threshold received power level.

In still another example, the port selection rule or algorithm may provide for the UE to include in its CSI report PMI information corresponding to all complementary set ports. Here, the UE may omit from its CSI report PMI information corresponding to any of the dominant set ports. In this example, the network may rely on FDD reciprocity for the part of the FD precoder corresponding to the dominant set. But based on a CSI report including PMI information for the complementary set ports, the base station may determine suitable modification, if any, to the part of the FD precoder corresponding to the complementary set.

And in yet another example, the port selection rule or algorithm may provide for a UE to report all observations it makes of the complementary set ports. Here, the UE may omit PMI information corresponding to the complementary set ports, and in some examples, also corresponding to the dominant set ports, in a CSI report. (However, in other examples, such a UE may report to the base station selected information relating to the dominant set ports, such as PMI information, a received power, or other suitable information. ) Rather than providing the base station with PMI information corresponding to the complementary set ports, or selected complementary set ports, in this example a UE may report to the base station its observations of the received DL signal itself. These observations may correspond to a sequence of complex numbers indicating samples of a received signal. Here, the UE may quantize the sample or measurement information, and then transmit information (e.g., a set of complex numbers) corresponding to samples of the received signal. Those of ordinary skill in the art will recognize that in this example, a UE transmitting feedback to a base station corresponding to its observations of the received DL signal may result in an increase to the feedback overhead. Accordingly, here, the UE may receive an allocation of a greater set of resources for transmission of its feedback than conventionally allocated for a CSI report. In other examples, the UE may utilize any suitable UL resources to provide the feedback to the base station, including resources on a control channel and/or a data channel.

At block 1112, the base station receives the UE feedback (e.g., CSI report) as described above.

At block 1114, according to some aspects of the disclosure, a base station may generate a modified FD basis vector based in part on the dominant set and the UE feedback. For example, based on the UE feedback, a base station may design an updated FD precoder

such that the updated FD precoder

can also cover the spatial area of D _comp. Here, K _m represents the number of ports (e.g., in the example illustrated in FIG. 12, K _m = K ₀+K ₁) . And further, each element

in the FD precoder

corresponds to an FD basis vector for a given port. For example, the base station may employ a technique known in the art as compressive sensing. That is, the base station may design the updated FD precoder

in part, with an aim to reduce or minimize the mutual coherence of matrix A, where

Here, calculation of the mutual coherence of matrix A is well-known in the art and for reasons of clarity is not provided here.

At block 1116, the base station may transmit a subsequent DL transmission, applying a precoder based in part on the modified FD precoder described above. That is, the base station may apply an update to its DL precoder with an aim to improve DL performance compared to a DL precoder directly corresponding to an UL precoder based on FDD reciprocity.

Further Examples Having a Variety of Features:

Example 1: A method, apparatus, and non-transitory computer-readable medium for precoding a transmission over a plurality of ports. A UE receives a port association signal configured to indicate an association between a first set of the ports and a first frequency domain basis vector, and an association between a second set of the ports and a second frequency domain basis vector. The UE then generates a channel estimate based on a reference signal received over the plurality of ports and transmits a feedback message based on the channel estimate, the feedback message comprising information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector.

Example 2: A method, apparatus, and non-transitory computer-readable medium of Example 1, where the UE further selects a subset of the second set of ports based on the channel estimate, and generates the feedback message including a precoding matrix indicator (PMI) corresponding to each port of the selected subset of the second set of the ports.

Example 3: A method, apparatus, and non-transitory computer-readable medium of any of Examples 1 to 2, where the UE further generates the feedback message including information indicating observation values corresponding to the reference signal received over the plurality of ports.

Example 4: A method, apparatus, and non-transitory computer-readable medium of any of Examples 1 to 3, where the UE further generates first precoder feedback information corresponding to a predetermined subset of at least some of the first set of the ports, and generates second precoder feedback information corresponding to a predetermined subset of at least some of the second set of the ports. Here, the information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector includes the first precoder feedback information and the second precoder feedback information.

Example 5: A method, apparatus, and non-transitory computer-readable medium of any of Examples 1 to 4, where the UE further selects a subset of at least some of the second set of ports based on one or more port-specific channel parameters. The UE generating precoder feedback information corresponding to the subset of at least some of the second set of the ports. Here, the information for updating at least one of the first frequency domain basis vector or the second frequency basis vector precoder includes the precoder feedback information.

Example 6: A method, apparatus, and non-transitory computer-readable medium for precoding a transmission over a plurality of ports. A base station generates a channel estimate based on a received first reference signal, and generates an initial frequency domain basis vector for precoding the transmission, based on the channel estimate. The base station then determines a dominant set and a complementary set of a frequency domain representation of the initial frequency domain basis vector. The base station precodes a second reference signal for transmission on the first set of the ports based on the dominant set, and precodes the second reference signal for transmission on the second set of the ports based on the complementary set. The base station additionally transmits a port association signal configured to indicate an association between the first set of the ports and the dominant set, and an association between the second set of the ports and the complementary set. The base station then transmits the second reference signal over the plurality of ports. The base station then receives a feedback message in response to the second reference signal, the feedback message including information for updating at least one of the dominant set or the complementary set. The base station may then transmit an updated message with precoding updated based on the feedback message.

Example 7: A method, apparatus, and non-transitory computer-readable medium of Examples 6, where the base station further generating an updated frequency domain basis vector based on the feedback message by utilizing compressive sensing in relation to the channel estimate.

Several aspects of a wireless communication network have been presented with reference to an exemplary implementation. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and communication standards.

By way of example, various aspects may be implemented within other systems defined by 3GPP, such as Long-Term Evolution (LTE) , the Evolved Packet System (EPS) , the Universal Mobile Telecommunication System (UMTS) , and/or the Global System for Mobile (GSM) . Various aspects may also be extended to systems defined by the 3rd Generation Partnership Project 2 (3GPP2) , such as CDMA2000 and/or Evolution-Data Optimized (EV-DO) . Other examples may be implemented within systems employing IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Ultra-Wideband (UWB) , Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system.

Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration. ” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another-even if they do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly physically in contact with the second object. The terms “circuit” and “circuitry” are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure.

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

A method for precoding a transmission over a plurality of ports, the method comprising:

receiving a port association signal configured to indicate an association between a first set of the ports and a first frequency domain basis vector, and an association between a second set of the ports and a second frequency domain basis vector;

generating a channel estimate based on a reference signal received over the plurality of ports; and

transmitting a feedback message based on the channel estimate, the feedback message comprising information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector.
The method of claim 1, further comprising:

selecting a subset of the second set of ports based on the channel estimate; and

generating the feedback message comprising a precoding matrix indicator (PMI) corresponding to each port of the selected subset of the second set of the ports.
The method of claim 1, further comprising:

generating the feedback message comprising information indicating observation values corresponding to the reference signal received over the plurality of ports.
The method of claim 1, further comprising

generating first precoder feedback information corresponding to a predetermined subset of at least some of the first set of the ports; and

generating second precoder feedback information corresponding to a predetermined subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector comprises the first precoder feedback information and the second precoder feedback information.
The method of claim 1, further comprising:

selecting a subset of at least some of the second set of ports based on one or more port-specific channel parameters; and

generating precoder feedback information corresponding to the subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency basis vector precoder comprises the precoder feedback information.
A method for updating a precoder for precoding a transmission over a plurality of ports, the method comprising:

generating a channel estimate based on a received first reference signal;

generating an initial frequency domain basis vector for precoding the transmission, based on the channel estimate;

determining a dominant set and a complementary set of a frequency domain representation of the initial frequency domain basis vector;

precoding a second reference signal for transmission on the first set of the ports based on the dominant set;

precoding the second reference signal for transmission on the second set of the ports based on the complementary set;

transmitting a port association signal configured to indicate an association between the first set of the ports and the dominant set, and an association between the second set of the ports and the complementary set;

transmitting the second reference signal over the plurality of ports;

receiving a feedback message in response to the second reference signal, the feedback message comprising information for updating at least one of the dominant set or the complementary set; and

transmitting an updated message with precoding updated based on the feedback message.
The method of claim 6, further comprising:

generating an updated frequency domain basis vector based on the feedback message by utilizing compressive sensing in relation to the channel estimate.
An apparatus for precoding a transmission over a plurality of ports, comprising:

means for receiving a port association signal configured to indicate an association between a first set of the ports and a first frequency domain basis vector, and an association between a second set of the ports and a second frequency domain basis vector;

means for generating a channel estimate based on a reference signal received over the plurality of ports; and

means for transmitting a feedback message based on the channel estimate, the feedback message comprising information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector.
The apparatus of claim 8, further comprising:

means for selecting a subset of the second set of ports based on the channel estimate; and

means for generating the feedback message comprising a precoding matrix indicator (PMI) corresponding to each port of the selected subset of the second set of the ports.
The apparatus of claim 8, further comprising:

means for generating the feedback message comprising information indicating observation values corresponding to the reference signal received over the plurality of ports.
The apparatus of claim 8, further comprising

means for generating first precoder feedback information corresponding to a predetermined subset of at least some of the first set of the ports; and

means for generating second precoder feedback information corresponding to a predetermined subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector comprises the first precoder feedback information and the second precoder feedback information.
The apparatus of claim 8, further comprising:

means for selecting a subset of at least some of the second set of ports based on one or more port-specific channel parameters; and

means for generating precoder feedback information corresponding to the subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency basis vector precoder comprises the precoder feedback information.
An apparatus for updating a precoder for precoding a transmission over a plurality of ports, the apparatus comprising:

means for generating a channel estimate based on a received first reference signal;

means for generating an initial frequency domain basis vector for precoding the transmission, based on the channel estimate;

means for determining a dominant set and a complementary set of a frequency domain representation of the initial frequency domain basis vector;

means for precoding a second reference signal for transmission on the first set of the ports based on the dominant set;

means for precoding the second reference signal for transmission on the second set of the ports based on the complementary set;

means for transmitting a port association signal configured to indicate an association between the first set of the ports and the dominant set, and an association between the second set of the ports and the complementary set;

means for transmitting the second reference signal over the plurality of ports;

means for receiving a feedback message in response to the second reference signal, the feedback message comprising information for updating at least one of the dominant set or the complementary set; and

means for transmitting an updated message with precoding updated based on the feedback message.
The method of claim 13, further comprising:

means for generating an updated frequency domain basis vector based on the feedback message by utilizing compressive sensing in relation to the channel estimate.
A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a base station to:

receive a port association signal configured to indicate an association between a first set of ports of a plurality of ports, and a first frequency domain basis vector, and an association between a second set of ports of the plurality of ports, and a second frequency domain basis vector;

generate a channel estimate based on a reference signal received over the plurality of ports; and

transmit a feedback message based on the channel estimate, the feedback message comprising information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector.
The non-transitory computer-readable medium of claim 15, wherein the code is further for causing the base station to:

select a subset of the second set of ports based on the channel estimate; and

generate the feedback message comprising a precoding matrix indicator (PMI) corresponding to each port of the selected subset of the second set of the ports.
The non-transitory computer-readable medium of claim 15, wherein the code is further for causing the base station to:

generate the feedback message comprising information indicating observation values corresponding to the reference signal received over the plurality of ports.
The non-transitory computer-readable medium of claim 15, wherein the code is further for causing the base station to

generate first precoder feedback information corresponding to a predetermined subset of at least some of the first set of the ports; and

generate second precoder feedback information corresponding to a predetermined subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector comprises the first precoder feedback information and the second precoder feedback information.
The non-transitory computer-readable medium of claim 15, wherein the code is further for causing the base station to:

select a subset of at least some of the second set of ports based on one or more port-specific channel parameters; and

generate precoder feedback information corresponding to the subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency basis vector precoder comprises the precoder feedback information.
A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a user equipment to:

generate a channel estimate based on a received first reference signal;

generate an initial frequency domain basis vector for precoding the transmission, based on the channel estimate;

determine a dominant set and a complementary set of a frequency domain representation of the initial frequency domain basis vector;

precode a second reference signal for transmission on the first set of the ports based on the dominant set;

precode the second reference signal for transmission on the second set of the ports based on the complementary set;

transmit a port association signal configured to indicate an association between the first set of the ports and the dominant set, and an association between the second set of the ports and the complementary set;

transmit the second reference signal over the plurality of ports;

receive a feedback message in response to the second reference signal, the feedback message comprising information for updating at least one of the dominant set or the complementary set; and

transmit an updated message with precoding updated based on the feedback message.
The non-transitory computer-readable medium of claim 20, wherein the code is further for causing the user equipment to:

generate an updated frequency domain basis vector based on the feedback message by utilizing compressive sensing in relation to the channel estimate.
An apparatus for precoding a transmission over a plurality of ports, comprising:

a processor;

a transceiver communicatively coupled to the processor; and

a memory communicatively coupled to the processor,

wherein the processor and the memory are configured to:

receive a port association signal configured to indicate an association between a first set of the ports and a first frequency domain basis vector, and an association between a second set of the ports and a second frequency domain basis vector;

generate a channel estimate based on a reference signal received over the plurality of ports; and

transmit a feedback message based on the channel estimate, the feedback message comprising information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector.
The apparatus of claim 22, wherein the processor and the memory are further configured to:

select a subset of the second set of ports based on the channel estimate; and

generate the feedback message comprising a precoding matrix indicator (PMI) corresponding to each port of the selected subset of the second set of the ports.
The apparatus of claim 22, wherein the processor and the memory are further configured to:

generate the feedback message comprising information indicating observation values corresponding to the reference signal received over the plurality of ports.
The apparatus of claim 22, wherein the processor and the memory are further configured to

generate first precoder feedback information corresponding to a predetermined subset of at least some of the first set of the ports; and

generate second precoder feedback information corresponding to a predetermined subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency domain basis vector comprises the first precoder feedback information and the second precoder feedback information.
The apparatus of claim 22, wherein the processor and the memory are further configured to:

select a subset of at least some of the second set of ports based on one or more port-specific channel parameters; and

generate precoder feedback information corresponding to the subset of at least some of the second set of the ports,

wherein the information for updating at least one of the first frequency domain basis vector or the second frequency basis vector precoder comprises the precoder feedback information.
An apparatus for updating a precoder for precoding a transmission over a plurality of ports, the apparatus comprising:

a processor;

a transceiver communicatively coupled to the processor; and

a memory communicatively coupled to the processor,

wherein the processor and the memory are configured to:

generate a channel estimate based on a received first reference signal;

generate an initial frequency domain basis vector for precoding the transmission, based on the channel estimate;

determine a dominant set and a complementary set of a frequency domain representation of the initial frequency domain basis vector;

precode a second reference signal for transmission on the first set of the ports based on the dominant set;

precode the second reference signal for transmission on the second set of the ports based on the complementary set;

transmit a port association signal configured to indicate an association between the first set of the ports and the dominant set, and an association between the second set of the ports and the complementary set;

transmit the second reference signal over the plurality of ports;

receiving a feedback message in response to the second reference signal, the feedback message comprising information for updating at least one of the dominant set or the complementary set; and

transmit an updated message with precoding updated based on the feedback message.
The apparatus of claim 6, wherein the processor and the memory are further configured to:

generate an updated frequency domain basis vector based on the feedback message by utilizing compressive sensing in relation to the channel estimate.