Dynamic sounding reference signal (SRS) resource allocation

Abstract

Wireless communications systems and methods related to dynamic sounding reference signal (SRS) resource allocation for channel sounding are provided. A base station (BS) determines a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), where a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources. The BS transmits a configuration to the first UE indicating the plurality of SRS resources.

Description

TECHNICAL FIELD

[0001] The technology described below relates generally to wireless communication systems, and more particularly to dynamic sounding reference signal (SRS) resource allocation.

[0002] INTRODUCTION

[0003] Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems can be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). A wireless multiple-access communication system can include a number of base stations (BSs), each simultaneously supporting communications for multiple communication devices, e.g., user equipment (UE).

[0004] To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the long-term evolution (LTE) technologies to next generation new radio (NR) technologies, which can be referred to as 5thGeneration (5G). For example, NR is designed to provide lower latency, higher bandwidth, or higher throughput, and more reliable communications than LTE. NR is designed to operate over a wide range of spectrum bands, such as low-frequency bands below about 1 gigahertz (GHz), mid-frequency bands from about 1 GHz to about 6 GHz, and high-frequency bands, such as mmWave frequency bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed and shared spectrum.

[0005] NR can further extend multiple-input multiple-output (MIMO) technologies to massive MIMO to achieve high spectral efficiency and high throughput. For example, a BS can utilize a large number of antenna elements to spatially multiplex a large number of UEs while providing large beamforming gains. One important operation in massive MIMO is the acquisition of channel state information. Such acquisition procedures can rely on the use of reference signals. For example, a BS can configure each connected UE to transmit one or more SRSs to assist the BS in determining uplink (UL) channel characteristics, e.g., for UL scheduling, link adaptation, and / or UL precoder selection. In a time division duplex (TDD) system with channel reciprocity, the BS can also determine downlink (DL) channel characteristics from the UL SRSs, e.g., for DL scheduling, link adaptation, and / or DL precoder selection.

[0006] BRIEF OVERVIEW OF SOME EXAMPLES

[0007] The following presents a simplified summary of some aspects of the present disclosure in order to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated aspects of the present disclosure, and is intended to neither identify key or critical elements of all aspects of the present disclosure nor delineate the scope of any or all aspects of the present disclosure. Its sole purpose is to present some concepts of one or more aspects of the present disclosure in a simplified form as a prelude to the more detailed description that is presented later.

[0008] For example, in an aspect of the disclosure, a method of wireless communication includes determining, by a base station (BS), a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and transmitting, by the BS to the first UE, a configuration indicating the plurality of SRS resources.

[0009] In an additional aspect of the disclosure, a method of wireless communication includes receiving, by a user equipment (UE) from a base station (BS), a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and transmitting, by the UE to the BS, a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources.

[0010] In an additional aspect of the disclosure, a base station (BS) includes a processor configured to determine a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and a transceiver configured to transmit, to the first UE, a configuration indicating the plurality of SRS resources.

[0011] In an additional aspect of the disclosure, a user equipment (UE) includes a transceiver configured to receive, from a base station (BS), a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and transmit, to the BS, a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources.

[0012] In an additional aspect of the disclosure, a non-transitory computer- readable medium has program code recorded thereon, the program code comprising: code for causing a base station (BS) to determine a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and code for causing the BS to transmit, to the first UE, a configuration indicating the plurality of SRS resources.

[0013] In an additional aspect of the disclosure, a non-transitory computer- readable medium has program code recorded thereon, the program code comprising: code for causing a user equipment (UE) to receive, from a base station (BS), a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and code for causing the UE to transmit, to the BS, a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources.

[0014] In an additional aspect of the disclosure, a base station (BS) comprises: means for determining a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and means for transmitting, to the first UE, a configuration indicating the plurality of SRS resources.

[0015] In an additional aspect of the disclosure, a user equipment (UE) comprises: means for receiving, from a base station (BS), a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; and means for transmitting, to the BS, a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources.

[0016] After studying the following description of specific exemplary embodiments in conjunction with the accompanying drawings, other aspects, features and embodiments will be apparent to those of ordinary skill in the art. Although each feature may be discussed below with respect to certain embodiments and drawings, all embodiments may include one or more of the advantageous features discussed herein. In other words, although one or more embodiments may be discussed as having certain advantageous features, one or more such features may also be used according to the various embodiments discussed herein. In a similar manner, although exemplary embodiments may be discussed below as device, system or method embodiments, it should be appreciated that such exemplary embodiments may be implemented in various devices, systems, and methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1

[0014] Illustrated is a wireless communication network in accordance with some aspects of the present disclosure.

[0019] Figure 2 Illustrated is a radio frame structure in accordance with some aspects of the present disclosure.

[0020] Figure 3A is a signaling diagram of a sounding reference signal (SRS) resource configuration and a channel sounding method according to some aspects of the present disclosure.

[0021] Figure 3B An SRS resource configuration scheme according to some aspects of the present disclosure is illustrated.

[0022] Figure 3C An SRS resource activation scheme according to some aspects of the present disclosure is illustrated.

[0023] Figure 4 is a block diagram of an exemplary base station (BS) according to some aspects of the present disclosure.

[0024] Figure 5 is a block diagram of an example user equipment (UE) according to some aspects of the present disclosure.

[0025] Figure 6A is a signaling diagram for dynamic SRS resource configuration and channel sounding according to some aspects of the present disclosure.

[0026] Figure 6B A dynamic SRS resource configuration scheme according to some aspects of the present disclosure is illustrated.

[0027] Figure 6C An SRS resource activation scheme according to some aspects of the present disclosure is illustrated.

[0028] Figure 7 is a flow chart of a method of wireless communication according to some aspects of the present disclosure.

[0029] Figure 8 is a flow chart of a method of wireless communication according to some aspects of the present disclosure.

[0030] Detailed description

[0031] The detailed description set forth below in conjunction with the accompanying 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. This detailed description includes specific details in order to provide a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0032] The present disclosure generally relates to wireless communication systems (also referred to as wireless communication networks). In various embodiments, various techniques and devices can be used for wireless communication networks, such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single carrier FDMA (SC-FDMA) networks, LTE networks, global system for mobile communications (GSM) networks, fifth generation (5G) or new radio (NR) networks, and other communication networks. As described herein, the terms "network" and "system" can be used interchangeably.

[0033] OFDMA networks can implement radio technologies such as Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM, etc. UTRA, E-UTRA, and GSM are part of the Universal Mobile Telecommunications System (UMTS). Specifically, Long Term Evolution (LTE) is a version of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS, and LTE are described in documents provided by an organization called the "3rd Generation Partnership Project" (3GPP), while cdma2000 is described in documents from an organization called the "3rd Generation Partnership Project 2" (3GPP2). These various radio technologies and standards are either known or under development. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between a group of telecommunications associations that aims to define globally applicable third generation (3G) mobile phone specifications. 3GPP Long Term Evolution (LTE) is a 3GPP project aimed at improving the UMTS mobile phone standard. 3GPP may define specifications for next generation mobile networks, mobile systems, and mobile devices. This disclosure focuses on the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond, with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

[0034] Specifically, 5G networks envision diverse deployments, diverse spectrum, and diverse services and devices that can be implemented using a unified air interface based on OFDM. To achieve these goals, in addition to developing new radio technologies for 5G NR networks, further enhancements to LTE and LTE-A are also being considered. 5G NR will be able to scale to: (1) serve networks with ultra-high density (e.g., approximately 1M nodes / km) 2 (1) providing coverage for the Massive Internet of Things (IoT) with ultra-low complexity (e.g., on the order of tens of bits / second), ultra-low energy (e.g., on the order of 10+ years of battery life), and deep coverage capable of reaching challenging locations; (2) providing coverage including mission-critical control with strong security to protect sensitive personal, financial, or confidential information, ultra-high reliability (e.g., on the order of 99.9999% reliability), ultra-low latency (e.g., on the order of 1 ms), and for users with a wide range of mobility or lack thereof; and (3) providing coverage with enhanced mobile broadband, including very high capacity (e.g., on the order of 10 Tbps / km 2 ), extreme data rates (e.g., multi-Gbps rates, 100+Mbps user experience rates), and deep cognition with advanced discovery and optimization.

[0035] 5G NR communication systems can be implemented to use optimized OFDM-based waveforms with scalable parameter sets and transmission time intervals (TTIs). Additional features may also include a common, flexible framework for efficiently multiplexing services and features using dynamic, low-latency time division duplex (TDD) / frequency division duplex (FDD) designs; and the use of advanced wireless technologies such as massive multiple-input multiple-output (MIMO), robust millimeter wave (mmWave) transmission, advanced channel coding, and device-centric mobility. The scalability of parameter design in 5G NR (and the scaling of subcarrier spacing) can efficiently address the operation of diverse services across diverse spectrums and diverse deployments. For example, in various outdoor and macro coverage deployments implemented with less than 3 GHz FDD / TDD, subcarrier spacing can occur at 15 kHz, such as on bandwidths (BWs) of 5, 10, 20 MHz, etc. For other various outdoor and small cell coverage deployments with TDD greater than 3 GHz, subcarrier spacing can occur at 30 kHz on 80 / 100 MHz BWs. For various other indoor broadband implementations, using TDD on the unlicensed portion of the 5 GHz band, subcarrier spacing can occur at 60 kHz over 160 MHz BW. Finally, for various deployments transmitting using the mmWave component with TDD at 28 GHz, subcarrier spacing can occur at 120 kHz over 500 MHz BW.

[0036] The scalable parameter design of 5G NR facilitates scalable TTI to meet diverse latency and quality of service (QoS) requirements. For example, shorter TTIs can be used for low latency and high reliability, while longer TTIs can be used for higher spectral efficiency. Efficient multiplexing of long and short TTIs allows transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with UL / downlink scheduling information, data, and acknowledgments in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, and supports adaptive UL / downlink that can be flexibly configured on a per-cell basis to dynamically switch between UL and downlink to meet current traffic needs.

[0037] Various other aspects and features of the present disclosure are further described below. It should be apparent that the teachings herein can be embodied in a variety of forms, and any specific structure, function, or both disclosed herein are representative and non-limiting. Based on the teachings herein, it will be appreciated by those of ordinary skill in the art that the aspects disclosed herein can be implemented independently of any other aspects and that two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement a device or practice a method. In addition, other structures, functionality, or structure and functionality that supplement or differ from one or more aspects set forth herein can be used to implement such a device or practice such a method. For example, the method can be implemented as a part of a system, device, apparatus, and / or as an instruction stored on a computer-readable medium for execution on a processor or computer. Not only that, an aspect can include at least one element of a claim.

[0038] In a specific wireless communication network, a base station (BS) may configure each connected UE with one or more SRS resource sets. Each SRS resource set may include one or more SRS resources. Each SRS resource may be associated with one or more SRS ports. An SRS port may be mapped to a UE's transmit antenna port, which may be used to sound for SRS transmission and may correspond to a certain transport layer. In 3GPP Release 15, a BS may configure a connected UE with SRS resources for SRS transmission. The BS may configure the number of SRS ports used for SRS resources based on the number of transmit antenna ports and / or receive antenna ports supported by the corresponding UE. For example, if a UE has four transmit antenna ports and four receive antenna ports, the BS may configure the UE to transmit SRS using four SRS ports. However, in some scenarios, it may be sufficient for the UE to sound for a subset of the configured SRS ports rather than all configured SRS ports. For example, in some instances, in addition to UL sounding, SRS transmission may be used for estimation. For example, in channel reciprocity operations, SRS may be used for DL ​​CSI acquisition. In some other scenarios, the UE may not be able to concurrently sound all configured SRS ports, for example, due to power limitations at the UE. When the number of SRS ports is exclusively provided to the UE based on the number of transmit antenna ports and / or receive antenna ports supported by the UE, the BS may not be able to reclaim SRS resources or SRS ports not utilized by the UE for use by other UEs.

[0039] The present disclosure describes mechanisms for dynamic SRS resource allocation. For example, a BS can configure a pool of SRS resources for sharing among a group of UEs. The BS can configure different SRS resources in the pool of SRS resources with different numbers of SRS ports. The BS can configure each UE in the group with one or more sets of SRS resources each formed from one or more SRS resources from the pool of SRS resources. Each set of SRS resources can have an aperiodic or semi-persistent resource type. In some aspects, the BS can determine a number of SRS resources for a UE based on a number of transmit antenna ports and / or receive antenna ports supported by the UE. For example, if a UE supports T transmit antenna ports, the BS can configure the UE with at least M SRS resources, where T and M are positive integers and M can be less than or equal to T. Each of the M SRS resources can be associated with a different m SRS ports, where m is a positive integer and can vary from 1 to M. In some instances, the BS can configure the UE to have one SRS resource for each number of SRS ports. For example, if the UE supports four transmit antenna ports (e.g., T = 4), the BS can configure the UE with a first SRS resource associated with one SRS port, a second SRS resource with two SRS ports, a third SRS resource with three SRS ports, and a fourth SRS resource with four SRS ports. In some aspects, each UE in the group can be configured with the same SRS resources of different numbers of SRS ports. The UE can not use the SRS resources for SRS transmissions until the BS activates a particular SRS resource for the UE to transmit SRS transmissions. The activation can be via medium access control-control element (MAC-CE) signaling or downlink control information (DCI) signaling.

[0040] In some aspects, the BS can select a subset of SRS resources for the UE to probe for SRS transmissions based on a transmission rank of the UE. For example, to activate SRS transmissions at the UE, the BS can select an SRS resource with a number of SRS ports that matches a transmission rank of the UE. In other words, if the UE has a transmission rank of 2, the BS can activate an SRS resource associated with two SRS ports for the UE to probe for SRS transmissions, even though the UE can support four transmit antenna ports. In some aspects, the UE can report a rank indicator (RI) and the BS can select and activate SRS resources for the UE based on the reported rank information.

[0041] To avoid using outdated RI reports from the UE, the BS can set a certain time threshold to filter out outdated RI reports. For example, if the gap between the time the BS receives the RI report and the UE's next SRS transmission opportunity lasts longer than a certain threshold, the BS can determine that the RI report is invalid. If the BS determines that there are no valid RI reports, the BS can activate SRS resources with the maximum number of SRS ports (e.g., equal to the number of transmit antenna ports at the UE).

[0042] In some instances, when no SRS resources with a number of SRS ports matching the UE's transmission rank are available, the BS may activate the UE with SRS resources having a number of SRS ports greater than the UE's transmission rank. The UE may repeat SRS transmissions on the remaining SRS ports or silence the remaining SRS ports. For example, the UE may have a transmission rank of R (e.g., equal to 1, 2, 3, 4, or more), but may be activated with SRS resources having L SRS ports, where L is greater than R. The UE may transmit SRS transmissions using R of the L SRS ports and repeat SRS transmissions on the remaining (LR) SRS ports or remain silent on the (LR) SRS ports.

[0043] Various aspects of the present disclosure can provide several benefits. For example, using a common SRS resource pool with different numbers of SRS ports to share among a group of UEs allows the BS to dynamically activate SRS resources with an appropriate number of SRS ports based on the current operating conditions of the UE for the UE to sound out SRS transmissions. Using a common SRS resource pool with different numbers of SRS ports can cater to the needs of different UEs to sound out different numbers of SRS ports at different times (for example, due to changing operating conditions (such as power usage) and / or different numbers of spaces or transmission layers). Selecting an SRS resource with an appropriate number of SRS ports for UEs to sound out SRS transmissions can reduce resource waste (for example, reducing unused SRS ports). Accordingly, the present disclosure can support sounding with a reduced amount of SRS resources.

[0044] While aspects and embodiments are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases can come about in many different arrangements and scenarios. Innovations described herein can be implemented across many differing platform types, devices, systems, form factors, and packaging arrangements. For example, embodiments and / or uses can 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.). Some examples can be or can not be specifically intended for consumer use, and the like. The scope of solutions as described herein can come about from a wide variety of motivations. The breadth and wide applicability of innovations described herein can come about from the recognition of a wide variety of

[0045] Figure 1 A wireless communication network 100 according to some aspects of the present disclosure is illustrated. The network 100 can be a 5G network. The network 100 includes a number of base stations (BSs) 105 (labeled as Bs 105a, 105b, 105c, 105d, 105e, and 105f) and other network entities. A BS 105 can be a station that communicates with UEs 115 and can also be referred to as an evolved node B (eNB), a next generation eNB (gNB), an access point, and the like. Each BS 105 can provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS 105 and / or a BS subsystem serving the coverage area, depending on the context in which the term is used.

[0046] BS 105 may provide communication coverage for macro cells or small cells (such as pico cells or femto cells), and / or other types of cells. Macro cells generally cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs that have a service subscription with a network provider. Small cells (such as pico cells) generally cover a relatively small geographic area and may allow unrestricted access by UEs that have a service subscription with a network provider. Small cells (such as femto cells) generally also cover a relatively small geographic area (e.g., a residence) and, in addition to unrestricted access, may also provide restricted access to UEs associated with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs of users in the residence, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS, or a home BS. In Figure 1 In the example shown in FIG, BS 105d and 105e may be conventional macro BSs, while BSs 105a-105c may be macro BSs enabled with one of three-dimensional (3D), full-dimensional (FD), or massive MIMO. BSs 105a-105c may utilize their higher-dimensional MIMO capabilities to utilize 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. BS 105f may be a small cell BS, which may be a home node or a portable access point. BS 105 may support one or more (e.g., two, three, four, etc.) cells.

[0047] Network 100 may support synchronous or asynchronous operation. For synchronous operation, each BS may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, each BS may have different frame timing, and transmissions from different BSs may not be aligned in time.

[0048] The UEs 115 can be dispersed throughout the wireless network 100, and each UE 115 can be stationary or mobile. The UEs can be referred to as mobile devices, mobile stations, subscriber units, stations, etc. A UE 115 can be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, etc. In one aspect, a UE 115 can be a device that includes a Universal Integrated Circuit Card (UICC). In another aspect, a UE can be a device that does not include a UICC. In some aspects, UEs 115 that do not include a UICC can also be referred to as IoT devices or Internet of Everything (IoE) devices. UEs 115a-115d are examples of mobile smart phone-type devices accessing network 100 A UE can also be a machine specifically configured to perform communications, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. UEs 115e-115h are examples of various machines configured to access the network 100 configured to perform communications. UEs 115i- 115k are examples of vehicles equipped with wireless communication devices configured to access network 100 configured to perform communications. A UE can be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In Figure 1 In general, a lightning bolt (e.g., a communication link) indicates a wireless transmission between a UE 115 and a serving BS 105, which is a BS to which the UE 115 is currently assigned for services, a desired transmission between BSs 105, a backhaul transmission between BSs, or a sidelink transmission between UEs 115.

[0049] In operation, BSs 105a- 105c can serve UEs 115a and 115b using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. Macro BS 105d can perform backhaul communications with BSs 105a- 105c, as well as small cell BS 105f. Macro BS 105d can also transmit multicast services which are subscribed to and received by UEs 115c and 115d. Such multicast services can include mobile television or stream video, or can include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

[0050] The BSs 105 may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs 105 (e.g., which may be examples of gNBs or access node controllers (ANCs)) may interface with the core network via a backhaul link (e.g., NG-C, NG-U, etc.) and may perform radio configuration and scheduling for communications with the UEs 115. In various examples, the BSs 105 may communicate with each other directly or indirectly (e.g., through the core network) over a backhaul link (e.g., X1, X2, etc.), which may be a wired or wireless communication link.

[0051] The network 100 may also support mission-critical communications with ultra-reliable and redundant links for mission-critical devices, such as UE 115e, which may be a drone. The redundant communication links with UE 115e may include links from macro BSs 105d and 105e, as well as a link from small cell BS 105f. Other machine-type devices, such as UE 115f (e.g., a thermometer), UE 115g (e.g., a smart meter), and UE 115h (e.g., a wearable device), may communicate directly with a BS (e.g., small cell BS 105f and macro BS 105e) via the network 100, or in a multi-step configuration by communicating with another user device that relays its information to the network (e.g., UE 115f conveys temperature measurement information to smart meter UE 115g, which is then reported to the network via small cell BS 105f). The network 100 may also provide additional network efficiency through dynamic, low latency TDD / FDD communications, such as V2V, V2X, C-V2X communications between UE 115i, 115j, or 115k and other UEs 115, and / or vehicle-to-infrastructure (V2I) communications between UE 115i, 115j, or 115k and BS 105.

[0052] In some implementations, network 100 utilizes OFDM-based waveforms for communication. OFDM-based systems can divide the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, frequency tones, frequency bins, etc. Each subcarrier can be modulated with data. In some examples, the subcarrier spacing between adjacent subcarriers can be fixed, and the total number of subcarriers (K) can depend on the system BW. The system BW can also be divided into subbands. In other examples, the subcarrier spacing and / or the duration of the TTI can be scalable.

[0053] In some aspects, BS 105 may assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RBs)) for downlink (DL) and uplink (UL) transmissions in network 100. DL refers to the transmission direction from BS 105 to UE 115, while UL refers to the transmission direction from UE 115 to BS 105. This communication may take the form of radio frames. A radio frame may be divided into a plurality of subframes or time slots, e.g., approximately 10. Each time slot may be further divided into subslots. In FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in the UL frequency band and a DL subframe in the DL frequency band. In TDD mode, UL and DL transmissions occur in different time periods using the same frequency band. For example, a subset of subframes in a radio frame (e.g., DL subframes) may be used for DL ​​transmissions, and another subset of subframes in the radio frame (e.g., UL subframes) may be used for UL transmissions.

[0054] DL subframes and UL subframes can be further divided into several regions. For example, each DL or UL subframe may have a predefined region for the transmission of reference signals, control information, and data. Reference signals are predetermined signals that facilitate communication between BS 105 and UE 115. For example, the reference signal may have a specific pilot pattern or structure, wherein the pilot tones may span the operating BW or frequency band, and each pilot tone is positioned at a predefined time and a predefined frequency. For example, BS 105 may transmit a cell-specific reference signal (CRS) and / or a channel state information-reference signal (CSI-RS) to enable UE 115 to estimate the DL channel. Similarly, UE 115 may transmit a sounding reference signal (SRS) to enable BS 105 to estimate the UL channel. Control information may include resource assignments and protocol control. Data may include protocol data and / or operational data. In some aspects, BS 105 and UE 115 may communicate using self-contained subframes. A self-contained subframe may include a portion for DL ​​communication and a portion for UL communication. A self-contained subframe may be DL-centric or UL-centric. A DL-centric subframe may include a duration for DL ​​communication that is longer than a duration for UL communication. A UL-centric subframe may include a duration for UL communication that is longer than a duration for DL ​​communication.

[0055] In some aspects, network 100 may be an NR network deployed on a licensed spectrum. BS 105 may transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)) in network 100 to facilitate synchronization. BS 105 may broadcast system information associated with network 100 (e.g., including a master information block (MIB), residual system information (RMSI), and other system information (OSI)) to facilitate initial network access. In some instances, BS 105 may broadcast the PSS, SSS, and / or MIB in the form of a synchronization signal block (SSB) on a physical broadcast channel (PBCH), and may broadcast the RMSI and / or OSI on a physical downlink shared channel (PDSCH).

[0056] In some aspects, a UE 115 attempting to access the network 100 may perform an initial cell search by detecting the PSS from the BS 105. The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE 115 may then receive the SSS. The SSS may enable radio frame synchronization and may provide a cell identity value that may be combined with the physical layer identity value to identify the cell. The PSS and SSS may be located in the center portion of the carrier or at any suitable frequency within the carrier.

[0057] After receiving the PSS and SSS, the UE 115 may receive the MIB. The MIB may include system information for initial network access and scheduling information for RMSI and / or OSI. After decoding the MIB, the UE 115 may receive the RMSI and / or OSI. The RMSI and / or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource sets (CORESETs) for physical downlink control channel (PDCCH) monitoring, physical UL control channel (PUCCH), physical UL shared channel (PUSCH), power control, and SRS.

[0058] After obtaining the MIB, RMSI, and / or OSI, the UE 115 may perform a random access procedure to establish a connection with the BS 105. The random access procedure (or RACH procedure) may be a single-step or multi-step process. In some examples, the random access procedure may be a four-step random access procedure. For example, the UE 115 may transmit a random access preamble, and the BS 105 may respond with a random access response. The random access response (RAR) may include a detected random access preamble identifier (ID) corresponding to the random access preamble, timing advance (TA) information, an UL grant, a temporary cell radio network temporary identifier (C-RNTI), and / or a backoff indicator. Upon receiving the random access response, the UE 115 may transmit a connection request to the BS 105, and the BS 105 may respond with a connection response. The connection response may indicate a contention resolution method. In some examples, the random access preamble, RAR, connection request, and connection response may be referred to as message 1 (MSG 1), message 2 (MSG 2), message 3 (MSG 3), and message 4 (MSG 4), respectively. In some examples, the random access procedure may be a two-step random access procedure, in which the UE 115 may transmit a random access preamble and a connection request in a single transmission, and the BS 105 may respond by transmitting a random access response and a connection response in a single transmission.

[0059] After establishing the connection, the UE 115 and the BS 105 can enter a normal operation phase, in which operational data can be exchanged. For example, the BS 105 can schedule the UE 115 for UL and / or DL ​​communications. The BS 105 can transmit an UL and / or DL ​​scheduling grant to the UE 115 via the PDCCH. The scheduling grant can be transmitted in the form of DL control information (DCI). The BS 105 can transmit a DL communication signal (e.g., carrying data) to the UE 115 via the PDSCH based on the DL scheduling grant. The UE 115 can transmit an UL communication signal to the BS 105 via the PUSCH and / or PUCCH based on the UL scheduling grant.

[0060] In some aspects, the network 100 may operate on a system BW or a component carrier (CC) BW. The network 100 may divide the system BW into multiple BWPs (e.g., multiple portions). The BS 105 may dynamically assign the UE 115 to operate on a certain BWP (e.g., a certain portion of the system BW). The assigned BWP may be referred to as an active BWP. The UE 115 may monitor the active BWP for signaling information from the BS 105. The BS 105 may schedule the UE 115 to conduct UL or DL ​​communications in the active BWP. In some aspects, the BS 105 may assign a BWP pair within a CC to the UE 115 for UL and DL communications. For example, the BWP pair may include one BWP for UL communications and one BWP for DL ​​communications.

[0061] In some aspects, network 100 may utilize massive MIMO technology for communications. For example, BS 105 may have a large number of transmit antenna elements and receive antenna elements. BS 105 may serve multiple UEs 115, each having one or more transmit antenna elements and / or one or more receive antenna elements. BS 105 may multiplex multiple UEs 115 for simultaneous communication on different spatial layers. The use of a large number of transmit and receive antenna elements may allow BS 105 to provide large beamforming gain while spatially multiplexing multiple UEs 115 for simultaneous transmission and / or reception. To assist BS 105 in determining UL channel characteristics, BS 105 may configure each UE 115 to sound on one or more transmit antenna ports of the corresponding UE 115. Sounding may refer to the transmission of an SRS via one or more antenna ports. The SRS may include a predetermined waveform sequence known to BS 105 and UE 115. For example, the SRS may be a Zadoff-Chu sequence or any suitable waveform sequence. In some instances, the transmit antenna ports at UE 115 may be mapped to physical transmit antenna elements of UE 115. In some other instances, the transmit antenna ports at UE 115 may be virtual antenna ports or logical ports created by UE 115, for example, via precoding. Precoding may include applying different amplitude weights and / or different phase adjustments to signals output by the physical transmit antenna elements of UE 115 to produce signals pointed in a certain spatial direction. In some aspects, network 100 may operate in TDD mode. BS 105 may also estimate DL channel characteristics from UL SRS received from UE 115 based on TDD channel reciprocity.

[0062] In some aspects, the BS 105 may configure an SRS resource pool for sharing among a group of connected UEs 115. The SRS resource pool may include multiple SRS resources with different numbers of SRS ports. The BS 105 may dynamically trigger or activate a subset of the multiple SRS resources for the connected UEs 115 to transmit SRS. In some aspects, the BS 105 may activate the number of SRS ports for the connected UEs 115 based on the transmission rank (e.g., the number of spatial layers) currently used by the UEs 115. Mechanisms for dynamic SRS resource allocation and channel sounding are described in more detail herein.

[0063] Figure 2 Illustrated is a radio frame structure 200 according to some aspects of the present disclosure. Radio frame structure 200 may be employed by a BS (such as BS 105) and a UE (such as UE 115) in a network (such as network 100) for communication. In particular, the BS may communicate with the UE using the time-frequency resources configured as shown in radio frame structure 200. Figure 2 In FIG. 2 , the x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. Transmission frame structure 200 includes radio frame 201. The duration of radio frame 201 may vary depending on various aspects. In one example, radio frame 201 may have a duration of approximately 10 milliseconds. Radio frame 201 includes M number of time slots 202, where M may be any suitable positive integer. In one example, M may be approximately 10.

[0064] Each time slot 202 includes a number of subcarriers 204 in frequency and a number of symbols 206 in time. The number of subcarriers 204 and / or the number of symbols 206 in a time slot 202 may vary depending on various aspects, such as the channel bandwidth, subcarrier spacing (SCS), and / or CP pattern. One subcarrier 204 in frequency and one symbol 206 in time form one resource element (RE) 212 for transmission. A resource block (RB) 210 is formed from a number of consecutive subcarriers 204 in frequency and a number of consecutive symbols 206 in time.

[0065] In one example, a BS (e.g., Figure 1 The BS 105 in the embodiment may schedule the UE (e.g., Figure 1UL and / or DL communications with the UE 115 in the network 100. Each slot 202 can be time divided into a number K of mini-slots 208. Each mini-slot 208 can include one or more symbols 206. The mini-slots 208 in a slot 202 can have variable lengths. For example, when a slot 202 includes a number N of symbols 206, the mini-slots 208 can have lengths between 1 symbol 206 and (N-1) symbols 206. In some aspects, the mini-slots 208 can have lengths of about 2 symbols 206, about 4 symbols 206, or about 7 symbols 206. In some examples, a BS can schedule a UE at a frequency granularity of a resource block (RB) 210 (e.g., including about 12 subcarriers 204).

[0066] Figure 3A With respect to Figure 3B and Figure 3C SRS resource allocation and channel sounding mechanisms that can be employed by BSs (such as the BSs 105) and UEs (such as the UEs 115) in a network (such as the network 100) are discussed to illustrate. Figure 3A is a signaling diagram of a SRS resource configuration and channel sounding method 300 in accordance with some aspects of the present disclosure. Figure 3B illustrates a SRS resource configuration scheme 380 in accordance with some aspects of the present disclosure. Figure 3C illustrates a SRS resource activation scheme 360 in accordance with some aspects of the present disclosure. The method 300 and the schemes 360 and 380 can be used in conjunction with the radio frame structure 200 of Figure 2

[0067] Referring to Figure 3A , the method 300 can be implemented between a BS 302 located in a network (such as the network 100) and four communicating or attached UEs 304 (shown as 304a, 304b, 304c, and 304d). The BS 302 can correspond to the BSs 105. The UEs 304 can correspond to the UEs 115. While the method 300 is illustrated with four UEs 304, the method 300 can be applied to a larger number of UEs 304 or a smaller number of UEs 304. As illustrated, the method 300 includes a number of enumerated actions, but embodiments of the method 300 can include additional actions before, after, and in between the enumerated actions. In some embodiments, one or more of the enumerated actions can be omitted or performed in a different order.

[0068] ​Method 300 is implemented after BS 302 establishes a connection (e.g., an RRC connection) with each of UEs 304a, 304b, 304c, and 304d. In action 310, UE 304a transmits a UE capability report A to BS 302. UE 304a may include a transmit / receive antenna port configuration in UE capability report A. For example, UE 304a may support four transmit antenna ports and four receive antenna ports, and thus the transmit / receive antenna port configuration may indicate four transmit antenna ports and four receive antenna ports. In some instances, the transmit antenna ports and / or receive antenna ports may be mapped to physical antenna elements of UE 340a. In some other instances, the transmit antenna ports and / or receive antenna ports are virtual ports or logical ports created by UE 304a by applying precoding, as discussed above.

[0069] In some aspects, the UE 304a may transmit a UE capability report A via RRC signaling (e.g., in the form of an RRC message). The RRC message may include a supportedSRS-TxPortSwitch information element (IE). The supportedSRS-TxPortSwitch IE may indicate the number of transmit antenna ports (denoted as t) and / or the number of receive antenna ports (denoted as r) supported by the UE 304a. For example, the UE 304a may set the supportedSRS-TxPortSwitch IE to "t4r4" to indicate four transmit antenna ports and four receive antenna ports. In another example, the supportedSRS-TxPortSwitch IE may be set to "t2r2" to indicate two transmit antenna ports and two receive antenna ports. In general, the supportedSRS-TxPortSwitch IE can be set to "t1r1", "t1r2", "t2r4", "t1r4", or "t1r4-t2r4" to indicate various combinations of transmit / receive antenna port configurations. The various settings (e.g., "t1r1", "t1r2", "t2r4", "t1r4", and "t1r4-t2r4") can be enumerated from 0 to P, where P can represent the number of allowable transmit / receive antenna configurations.

[0070] At action 312, UE 304b transmits a UE capability report B to BS 302. At action 314, UE 304c transmits a UE capability report C to BS 302. At action 316, UE 304c transmits a UE capability report C to BS 302. At action 318, UE 304d transmits a UE capability report D to BS 302. Each of UEs 304b, 304c, and 304d can transmit the corresponding UE capability report using substantially similar mechanisms as UE 304a. For example, each of UEs 304b, 304c, and 304d can support four transmit antenna ports and four receive antenna ports, and thus can include a supportedSRS-TxPortSwitch IE indicating "t4r4" in the corresponding UE capability report.

[0071] At action 320, BS 304 determines SRS resources based on the UE capability reports received from UEs 304a, 304b, 304c, and 304d. BS 302 can allocate and configure each of UEs 304a, 304b, 304c, and 304d with one or more SRS resource sets (e.g., as shown in FIG. 3) for SRS transmission. Figure 3B

[0072] Referring to Figure 3B , scheme 380 includes multiple SRS resource sets 370 (shown as SRS resource set 0 through SRS resource set N). Each SRS resource set 370 can include one or more SRS resources 372. Each SRS resource 372 can include time-frequency resources. For example, each SRS resource 372 can span one or more symbols (e.g., symbol 206) within a slot (e.g., slot 202) and can include one or more subcarriers (e.g., subcarriers 204) or REs (e.g., REs 212) within each SRS symbol. Additionally, each SRS resource 372 can be configured with one or more SRS ports 374. For example, each SRS port 374 can be associated with one or more REs within an SRS symbol. UE 304 can transmit an SRS via a transmit antenna port (e.g., denoted as Pl). UE 304 can transmit the SRS in SRS REs associated with SRS port 374 corresponding to transmit antenna port Pl. The SRS can be a predetermined waveform sequence (e.g., a Zadoff-Chu sequence). The SRS can assist BS 302 in determining UL CSI and / or DL CSI associated with UE 304.

[0073] ​In some aspects, each SRS resource set 370 can be associated with a certain resource type. For example, an SRS resource set 370 can have a periodic, semi-persistent, or aperiodic resource type. An SRS resource set 370 with a periodic resource type can have a configured periodicity, and each periodic SRS resource 372 can have a configured symbol offset within a slot. The UE 304 can use a periodic SRS resource 372 for periodic SRS transmissions. An SRS resource set 370 with a semi-persistent resource type can have a similar configured periodicity as a periodic SRS resource set 370, and each semi-persistent resource 372 can have a similar configured symbol offset within a slot as a periodic SRS resource 372. However, the UE 304 can not transmit an SRS in a semi-persistent SRS resource 372 until the BS 302 triggers activation of the SRS resource 372 (e.g., via a MAC-CE). An SRS resource 372 in an SRS resource set 370 with an aperiodic resource type can be utilized by the UE 304 when the UE 304 receives an explicit trigger from the BS 302 (e.g., via DCI).

[0074] In some aspects, each SRS resource set 370 can be configured for a certain use case, such as for UL CSI acquisition, DL CSI acquisition (assuming TDD channel reciprocity), and / or beam management. For example, the BS 302 can determine an UL transmission scheme and / or UL precoding based on acquired UL CSI. The BS 302 can determine antenna switching or selection based on DL CSI. In an example, for DL CSI acquisition, the BS 302 can configure the UE 304 with up to two SRS resource sets 370, each with a different resource type. In some instances, the BS 302 can configure the UE 304 with zero or one SRS resource set 370 configured with a periodic or semi-persistent resource type. In some other instances, the BS 302 can configure the UE 304 with zero or two SRS resource sets 370, each configured with an aperiodic resource type.

[0075] In some aspects, the BS 302 can determine a number of SRS ports 374 for each SRS resource 372 configured for each UE 304 according to a number of transmit antenna ports supported by the UE 304. For example, if the UE 304 supports four transmit antenna ports, the BS 302 can configure the UE 304 with one or more SRS resources 372 each with four SRS ports 374, as Figure 3BIn general, if the UE 304 supports T transmit antenna ports, the BS 302 may configure the UE 304 with one or more SRS resources 372 each having T SRS ports 374, where T is a positive integer (eg, 1, 2, 3, or 4).

[0076] In some aspects, for a UE 304 with one transmit antenna port and two receive antenna ports (e.g., "t1r2"), two transmit antenna ports and four receive antenna ports (e.g., "t2r4"), one transmit antenna port and four receive antenna ports (e.g., "t1r4"), or one transmit antenna port and four receive antenna ports - two transmit antenna ports and four receive antenna ports (e.g., "t1r4-t2r4"), the BS 302 may determine the total number of SRS resources 372 per SRS resource set 370 for the UE 304 based on the number of receive antenna ports supported by the UE 304 divided by the number of transmit antenna ports. Additionally, the BS 302 may not configure more than one SRS resource set 370 for the UE 304 for DL ​​purposes (e.g., for DL ​​CSI estimation) in the same timeslot.

[0077] In some aspects, for a UE 304 having one transmit antenna port and one receive antenna port (e.g., "t1r1"), two transmit antenna ports and two receive antenna ports (e.g., "t2r2"), or four transmit antenna ports and four receive antenna ports (e.g., "t4r4"), the BS 302 may configure the UE 304 with one SRS resource 372 per SRS resource set 370. Additionally, the BS 302 may not configure more than one SRS resource set 370 for the UE 304 for DL ​​purposes (e.g., for DL ​​CSI acquisition) in the same symbol. Referring to an example in which each of the UEs 304a, 304b, 304c, and 304d supports four transmit antenna ports and four receive antenna ports, the BS 302 may configure each of the UEs 304a, 304b, 304c, and 304d with one SRS resource 372 having four SRS ports 374 (e.g., as shown in FIG. Figure 3C ).

[0078] Reference Figure 3AIn action 330, BS 302 configures UEs 304a, 304b, 304c, and 304d with SRS resources based on the corresponding UE capability reports. For example, BS 302 may transmit an SRS configuration to each UE 304a, 304b, 304c, and 304d, for example, via RRC configuration. A first SRS configuration for UE 304a may indicate a first SRS resource set (e.g., SRS resource set 370) including a single SRS resource 374a having four SRS ports 374. A second SRS configuration for UE 304b may indicate a second SRS resource set including a single SRS resource 374b having four SRS ports 374. A third SRS configuration for UE 304c may indicate a third SRS resource set including a single SRS resource 374c having four SRS ports 374. A fourth SRS configuration for the UE 304 d may indicate a fourth SRS resource set including a single SRS resource 374 d having four SRS ports 374 .

[0079] As an example, the first, second, third, and fourth SRS resource sets configured for UEs 304a, 304b, 304c, and 304d are semi-persistent or aperiodic. Thus, in action 340, BS 304 may activate SRS resources 372a, 372b, 372c, 372d for UEs 304a, 304b, 304c, and 304d, respectively (e.g., Figure 3C ). In some examples, BS 302 may activate each of UEs 304a, 304b, 304c, and 304d via MAC-CE or DCI.

[0080] Reference Figure 3C , BS 302 may activate SRS resource 372a for UE 304a to transmit SRS, as indicated by arrow 362. BS 302 may activate SRS resource 372b for UE 304b to transmit SRS, as indicated by arrow 364. BS 302 may activate SRS resource 372c for UE 304c to transmit SRS, as indicated by arrow 366. BS 302 may activate SRS resource 372d for UE 304d to transmit SRS, as indicated by arrow 368.

[0081] Reference Figure 3AIn action 350, upon receiving activation for SRS resource 372a, UE 304a transmits an SRS to BS 302 using SRS resource 372a. Similarly, in action 352, UE 304b transmits an SRS to BS 302 using SRS resource 372b. In action 354, UE 304c transmits an SRS to BS 302 using SRS resource 372c. In action 356, UE 304d transmits an SRS to BS 302 using SRS resource 372d.

[0082] As can be observed from the method 300 and / or scheme 360, the number of SRS ports 374 in the SRS resources 372 used by the UE 304 for SRS transmission is configured by the BS 302 based on the number of transmit and / or receive antenna ports reported by the UE 304. In other words, once the BS 302 configures the UE 304 with one, two, or four SRS ports 374, the UE 304 will use all of the configured one, two, or four SRS ports 374 to transmit SRS. However, in some scenarios, it may be sufficient for the UE 304 to transmit SRS using a subset of the configured SRS ports 374 rather than all of the configured SRS ports 374. In some other scenarios, the UE 304 may not be able to support full SRS port transmission.

[0083] For example, in Figure 3C In the illustrated example, UE 304a may operate with a transmission rank of 2 (e.g., RI=2 for two spatial transmission layers), and thus, it may be sufficient for UE 304a to transmit SRS using two SRS ports 374 instead of all four SRS ports. Similarly, UE 304c may operate with a transmission rank of 1 (e.g., RI=1 for a single spatial transmission layer), and thus, it may be sufficient for UE 304c to transmit SRS using one SRS port 374 instead of all four SRS ports. In another example, UE 304 may not use SRS for UL sounding. For example, SRS may be used to sound a linear receiver (e.g., at a BS), which may be represented by the matrix U CQI UE 304 can determine the matrix U from singular value decomposition (SVD) based on the DL channel state information reference signal (CSI-RS) CQI The DL CSI-RS may be a reference signal configured for the UE 304 to determine a channel quality indicator (CQI) and / or RI. CQI Instead of the matrix U, we can have a subset of columns that will be probed using SRS CQI Therefore, UE 304 can use the same matrix U CQISRS on SRS ports corresponding to a subset of the columns to be sounded. In yet another example, the UE 304 can be power limited and thus can not be able to support full SRS port transmission. The UE 304 can be able to transmit SRS in a portion or subset of the configured SRS ports 374, but not all of the configured SRS ports 374.

[0084] While the UE 304 can not use all of the configured SRS ports 374 for SRS transmission in various scenarios or use cases, the SRS resources 372 are exclusively provided for the UE 304. Thus, the BS 302 cannot easily reuse or recycle SRS ports 374 that are not utilized or sounded by the UE 304 for other UEs.

[0085] Accordingly, the present disclosure provides techniques for a BS (e.g., the BS 105 and / or 302) to dynamically allocate and / or activate SRS resource(s) with a number of SRS ports as needed by a UE, e.g., based on a current transmission rank and / or current operating conditions.

[0086] Figure 4 is a block diagram of an exemplary UE 400 in accordance with some aspects of the present disclosure. The UE 400 can be a UE 115 in the network 100 as discussed above Figure 1 in the network 100 as discussed above

[0087] The processor 402 can have various features as a specific-type processor. For example, these can include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 402 can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0088] Memory 404 can include cache memory (e.g., of processor 402), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, solid state memory devices, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, memory 404 can comprise a non-transitory computer-readable medium. Memory 404 can store instructions 406. Instructions 406 can include instructions that, when executed by processor 402, enable processor 402 to perform the operations described herein (e.g., with regard to various aspects of FIGS. 1-8). Instructions 406 can also be referred to as program code. The program code can be for causing a wireless communication device to perform these operations, e.g., by causing one or more processors, such as processor 402, to control or command the wireless communication device to do so. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” can refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” can include a single computer-readable statement, or many computer-readable statements. Figure 2 , 6A Processor 402 can also include memory 404 and / or other storage. Memory 404 can include a cache area for the temporary storage of data and a

[0089] SRS module 408 can be implemented via hardware, software, or combinations thereof. For example, SRS module 408 can be implemented as a processor, circuit, and / or instructions 406 stored in memory 404 and executed by processor 402. In some examples, SRS module 408 can be integrated within modem subsystem 412. For example, SRS module 408 can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within modem subsystem 412.

[0090] SRS module 408 can be used in various aspects of the present disclosure, for example, Figure 2 , 6AAspects of 6C and 8. For example, the SRS module 408 is configured to receive, from a BS (e.g., BS 105, 302, 500, and / or 602), a configuration indicating a plurality of SRS resources configured for the UE, where a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources. The SRS module 408 can also be configured to receive, from the BS, a request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission. The one or more SRS ports can be associated with one or more SRS resources of the plurality of SRS resources. The request can be in the form of a MAC-CE or DCI. The SRS module 408 can also be configured to transmit, to the BS, the first SRS transmission using the one or more SRS ports within the configured plurality of SRS resources.

[0091] In some aspects, the SRS module 408 is further configured to transmit, to the BS, a UE capability report indicating a number of transmit antenna ports supported by the UE 400. In some aspects, a number of SRS resources of the plurality of SRS resources configured for the UE is equal to or greater than the number of transmit antenna ports supported by the UE 400. In some aspects, a transmit antenna port can correspond to a transmit antenna element at the antenna 416. In some aspects, a transmit antenna port can be a logical antenna port created by the UE 400 by applying precoding to the transmit antenna elements.

[0092] In some aspects, the SRS module 408 is further configured to transmit, to the BS, a RI report including transmission rank information. In some aspects, a number of the one or more SRS ports activated can be based at least in part on the transmission rank information associated with the UE 400. In some aspects, the number of the one or more SRS ports can be less than a number of transmit antenna ports supported by the UE 400. For example, the UE 400 can support four transmit antenna ports, but can operate with a transmission rank of two. Thus, the BS can activate a SRS resource with two SRS ports for the UE 400 to sound the SRS transmission.

[0093] In some aspects, the SRS module 408 is further configured to receive a further request from the BS to activate multiple SRS ports within the multiple SRS resources for a second SRS transmission. When the number of activated SRS ports is greater than the number of spatial layers currently supported by the UE 400, the SRS module 408 is further configured to transmit the second SRS transmission to the BS using a first subset of the multiple SRS ports, wherein the number of SRS ports in the first subset of the multiple SRS ports corresponds to the number of spatial layers currently supported by the UE; and transmit repetitions of the second SRS transmission to the BS using a second subset of the multiple SRS ports that do not overlap with the first subset of the multiple SRS ports. In some other aspects, when the number of activated SRS ports is greater than the number of spatial layers currently supported by the UE 400, the SRS module 408 is further configured to transmit the second SRS transmission to the BS using the first subset of the multiple SRS ports, wherein the number of SRS ports in the first subset of the multiple SRS ports corresponds to the number of spatial layers currently supported by the UE; and refrain from transmitting SRS on remaining SRS ports in the multiple SRS ports. Mechanisms for utilizing dynamically allocated and / or activated SRS resources for channel sounding are described in greater detail herein.

[0094] As shown, transceiver 410 may include a modem subsystem 412 and an RF unit 414. Transceiver 410 may be configured to communicate bidirectionally with other devices, such as UE 115 and / or 300 and / or another core network element. Modem subsystem 412 may be configured to modulate and / or encode data according to an MCS (e.g., an LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc.). RF unit 414 may be configured to process (e.g., perform analog-to-digital conversion or digital-to-analog conversion, etc.) modulated / encoded data (e.g., PDSCH signals, PDCCH signals, SRS resource configurations, SRS resource activations, SRS resource deactivations) from modem subsystem 412 (on out-of-band transmissions) or from another source, such as UE 115. RF unit 414 may further be configured to perform analog beamforming in conjunction with digital beamforming. Although shown as being integrated together in the transceiver 410, the modem subsystem 412 and the RF unit 414 may be separate devices that are coupled together at the UE 400 to enable the UE 400 to communicate with other devices.

[0095] The RF unit 414 can provide the modulated and / or processed data, e.g., data packets (or, more generally, data messages that can contain one or more data packets and other information), to the antennas 416 for transmission to one or more other devices. This can include, for example, information transmission for completing attachment to a network and communication with a camped UE 115 or 300 in accordance with some aspects of the present disclosure. The antennas 416 can further receive data messages transmitted from other devices and provide the received data messages for processing and / or demodulation at the transceiver 410. The transceiver 410 can provide demodulated and decoded data (e.g., PUSCH signals, UL data, SRS, UE capability report, RI report) to the SRS module 408 for processing. The antennas 416 can include multiple antennas of similar or different designs in order to sustain multiple transmission links.

[0096] In an aspect, the UE 400 can include multiple transceivers 410 implementing different RATs (e.g., NR and LTE). In an aspect, the UE 400 can include a single transceiver 410 implementing multiple RATs (e.g., NR and LTE). In an aspect, the transceiver 410 can include various components, where different combinations of components can implement different RATs.

[0097] Figure 5 is a block diagram of an exemplary BS 500 in accordance with some aspects of the present disclosure. The BS 500 can be a BS 105 as discussed above in connection with FIG. 1. As shown, the BS 500 can include a processor 502, a memory 504, an SRS module 508, a transceiver 510 (including a modem subsystem 512 and a radio frequency (RF) unit 514), and one or more antennas 516. These elements can be in direct or indirect communication with one another over one or more buses. The transceiver 510 can communicate bi-directionally with one or more devices, another BS, one or more UEs 115, one or more network devices, and / or one or more other devices. The transceiver 510 can include a modem subsystem 512 and a RF unit 514. The modem subsystem 512 can process packets, user data, and / or other data according to various protocols and / or techniques. The RF unit 514 can condition and / or otherwise process data for transmission. The RF unit 514 can include one or more amplifiers and / or filters to condition signals for transmission. The RF unit 514 can also include one or more antennas to transmit and / or receive signals. Figure 1

[0098] The processor 502 can include a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device that

[0099] ​Memory 504 can include cache memory (e.g., of processor 502), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable Figure 2 , 6A -6C and 7), instructions for the operations described with reference to the UE 115. The instructions 506 can also be referred to as program code and, broadly Figure 4 ,

[0100] The SRS module 508 can be implemented via hardware, software, or combinations thereof. For example, the SRS module 508 can be implemented as a processor, circuit, and / or instructions 506 stored in the memory 504 and executed by the processor 502. In some examples, the SRS module 508 can be integrated within the modem subsystem 512. For example, the SRS module 508 can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem 512.

[0101] The SRS module 508 can be used for various aspects of the present disclosure, for example, Figure 2 , 6A- Aspects of 6C and 7. The SRS module 508 is configured to determine one or more SRS resource sets for a group of UEs (e.g., UEs 115, 304, and / or 400) including the first UE. The SRS resource sets can include a plurality of SRS resources, where a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources. The one or more SRS resource sets can be semi-persistent or aperiodic. The SRS module 508 can also be configured to transmit, to the first UE, a configuration indicating the plurality of SRS resources. The SRS module 508 can also be configured to transmit, to the first UE, a request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission, and receive, from the first UE, the first SRS transmission from the one or more SRS ports within the plurality of SRS resources. The request can be carried in a MAC-CE or DCI. The one or more SRS ports can be associated with one or more SRS resources of the plurality of SRS resources.

[0102] In some aspects, the SRS module 508 is further configured to receive, from the first UE, a UE capability report indicating a number of transmit antenna ports supported by the first UE. The SRS module 508 can also be configured to determine a plurality of SRS resources for the first UE such that a number of the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the UE.

[0103] In some aspects, the SRS module 508 is further configured to receive, from the first UE, a RI report indicating a number of spatial layers currently supported by the first UE. The SRS module 508 can also be configured to select, for the first UE, a subset of the plurality of SRS resources having one or more SRS ports based on the number of spatial layers indicated by the first UE. The SRS module 508 can be configured to select the subset of the SRS resources such that a number of the one or more SRS ports of the subset of the SRS resources matches the number of spatial layers supported by the first UE. Thus, in some instances, the number of the one or more SRS ports can be less than the number of transmit antenna ports supported by the first UE. For example, the first UE can support four transmit antenna ports but can operate with a transmission rank of two. Thus, the SRS module 508 can be configured to activate an SRS resource having two SRS ports for the first UE to probe for a SRS transmission.

[0104] In some aspects, the SRS module 508 is further configured to determine whether a valid RI report is received from the second UE. The SRS module 508 can be configured to transmit, based on a number of transmit antenna ports supported by the second UE, a request for activation of multiple SRS ports for a second SRS transmission if no valid RI report is received from the second UE. In some aspects, the SRS module 508 can be further configured to determine whether an RI report is received from the second UE based on whether a gap duration between a most recent RI report received from the second UE and a transmission occasion of the second SRS transmission satisfies a threshold.

[0105] In some instances, the SRS module 508 is further configured to transmit, to the second UE, a request for activation of multiple SRS ports for a second SRS transmission, and receive, from the second UE, a second SRS transmission from a first subset of the multiple SRS ports that is fewer than all of the multiple SRS ports. The SRS module 508 can be further configured to receive, from the second UE, a repetition of the second SRS transmission from a second subset of the multiple SRS ports that is non-overlapping with the first subset of the multiple SRS ports. Mechanisms for performing dynamic SRS resource allocation and activation for UE channel sounding are described in greater detail herein.

[0106] As shown, the transceiver 510 can include the modem subsystem 512 and the RF unit 514. The transceiver 510 can be configured to communicate bi-directionally with other devices, such as the BS 105. The modem subsystem 512 can be configured to modulate and / or encode data from the memory 504 and / or configured transmissions module 407, according to a modulation and coding scheme (MCS), e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit 514 can be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated / encoded data from the modem subsystem 512 (on out-of-band transmissions) or transmissions originating from another source such as a UE 115 or a BS 105 (e.g., PUSCH signals, UL data, SRS, UE capability reports, RI reports). The RF unit 514 can be further configured to perform analog beamforming in combination with digital beamforming. Although shown as integrated together in transceiver 510, the modem subsystem 512 and the RF unit 514 can be separate devices that are coupled together at the BS 500 to enable the BS 500 to communicate with other devices.

[0107] The RF unit 514 can provide the modulated and / or processed data, e.g., data packets (or, more generally, data messages that can contain one or more data packets and other information), to the antennas 516 for transmission to one or more other devices. The antennas 516 can further receive data messages transmitted from other devices. The antennas 516 can provide the received data messages for processing and / or demodulation at the transceiver 510. The transceiver 510 can provide demodulated and decoded data (e.g., PDSCH signals, PDCCH, DL data, SRS resource configuration, SRS resource activation, SRS resource deactivation) to the configured transmission module 407 for processing. The antennas 516 can include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit 514 can configure the antennas 516.

[0108] In an aspect, the BS 500 can include multiple transceivers 510 implementing different RATs (e.g., NR and LTE). In an aspect, the BS 500 can include a single transceiver 510 implementing multiple RATs (e.g., NR and LTE). In an aspect, the transceiver 510 can include various components, where different combinations of components can implement different RATs.

[0109] Figure 6A With respect to Figure 6B and Figure 6C are discussed to illustrate dynamic SRS resource allocation and channel sounding mechanisms that can be employed by BSs (such as the BSs 105, 302, and / or 500) and UEs (such as the UEs 115, 304, and / or 400) in a network, such as the network 100. Figure 6A is a signaling diagram of a dynamic SRS resource configuration and channel sounding method 600 according to some aspects of the disclosure. Figure 6B illustrates a dynamic SRS resource configuration scheme 680 according to some aspects of the disclosure. Figure 6C illustrates an SRS resource activation scheme 660 according to some aspects of the disclosure. The methods 600 and the schemes 660 and 680 can be used in conjunction with Figure 2 the radio frame structure 200 of

[0110] Referring to Figure 6AMethod 600 can be implemented between a BS 602 located in a network, such as network 100, and four communicating or attached UEs 604, shown as 604a, 604b, 604c, and 604d. BS 602 can be similar to BSs 105, 302, and / or 600. UEs 604 can correspond to UEs 115, 304, and / or 500. While method 600 is illustrated with four UEs 604, method 600 can be applied to a larger number of UEs 604 or a smaller number of UEs 604. As illustrated, method 600 includes a number of enumerated actions, but embodiments of method 600 can include additional actions before, after, and in between the enumerated actions. In some embodiments, one or more of the enumerated actions can be omitted or performed in a different order.

[0111] Similar to method 300, method 600 can begin with UEs 604a, 604b, 604c, and 604d reporting UE capabilities to BS 602 at actions 610, 612, 614, and 616, respectively. Actions 610, 612, 614, and 616 are similar to actions 310, 312, 314, and 316 of method 300, respectively. Accordingly, the details of these steps will not be repeated here for the sake of brevity.

[0112] At action 620, BS 602 determines SRS resources based on the UE capability reports received from UEs 604a, 604b, 604c, and 604d. In some aspects, BS 602 can allocate or configure a pool of SRS resources for sharing among a group of UEs, including UEs 604a, 604b, 604c, and 604d, for example. The pool of SRS resources can include one or more sets of SRS resources (e.g., as shown in Figure 6B

[0113] Referring to Figure 6B BS 602 can configure a pool of SRS resources 682 including one or more sets of SRS resources 670 (shown as set of SRS resources 0 through set of SRS resources N) for the group of UEs 604. Each set of SRS resources 670 can have an aperiodic or semi-persistent resource type. BS 602 can further configure a periodicity for the sets of SRS resources 670 having a semi-persistent resource type. Generally, the semi-persistent sets of SRS resources 670 and the aperiodic sets of SRS resources 670 can be configured with different periodicities, as described above with reference to Figure 3B ​The semi-persistent SRS resource sets 370 and the aperiodic SRS resource sets 370 under discussion operate substantially similar mechanisms. Each SRS resource set 670 can include multiple SRS resources 672 (shown as 672a, 672b, 672c, and 672d). The BS 602 can determine the number of SRS resources 672 for each SRS resource set 670 based on the number of transmit antenna ports supported by the UE 604. The SRS resources 672 in an SRS resource set 670 can include different numbers of SRS ports 674 (e.g., SRS ports 374). For example, if the UE 604 in a group of UEs supports four transmit antenna ports (e.g., T = 4) and four receive antenna ports, the BS 602 can configure at least four SRS resources 672 for the SRS resource set 670, where a first SRS resource 672a can have one SRS port 674, a second SRS resource 672b can have two SRS ports 674, a third SRS resource 672c can have three SRS ports 674, and a fourth SRS resource 672d can have four SRS ports 674, as shown.

[0114] By configuring SRS resources 672 with different numbers of SRS ports 674, the BS 602 can dynamically activate SRS resources 672 with a suitable number of SRS ports 674 for the UE 604 to sound SRS transmissions based on current operating conditions. Generally, the BS 602 can configure at least M SRS resources 672 in one or more SRS resource sets 670, where M is less than or equal to T, and each SRS resource 672 can have m SRS ports 674, where m can vary from 1 to M. Referring to the example where the UE 604 includes four transmit antenna elements, the BS 602 can configure a first SRS resource 672a with one SRS port 674, a second SRS resource 672b with two SRS ports 674, a third SRS resource 672c with three SRS ports 674, and a fourth SRS resource 672d with four SRS ports 674 in a single SRS resource set 670, as shown. In another example, the BS 602 can configure a first SRS resource 672 with one SRS port 674 and a second SRS resource 672 with two SRS ports 674 in a first SRS resource set 670, and can configure a third SRS resource 672 with three SRS ports 674 and a fourth SRS port 672 with four SRS ports 674 in a second SRS resource set 670. In some instances, the first SRS resource set 670 and the second SRS resource set 670 can have the same resource type (e.g., aperiodic or semi-persistent). In some other instances, the first SRS resource set 670 and the second SRS resource set 670 can have different resource types.

[0115] Referring to Figure 6A At act 630, the BS 602 configures the UEs 604a, 604b, 604c, and 604d with SRS resources based on the corresponding UE capability reports. For example, the BS 602 can transmit an SRS configuration to each of the UEs 604a, 604b, 604c, and 604d, e.g., via RRC configuration. The SRS configuration for each of the UEs 604a, 604b, 604c, and 604d can be the same, as the BS 602 configures the SRS resource pool for sharing among the UEs 604a, 604b, 604c, and 604d. The SRS configuration can indicate the SRS resource pool (e.g., the SRS resource pool 682). The SRS configuration can also indicate the SRS resource sets within the SRS resource pool (e.g., the SRS resource sets 670). The SRS configuration can also indicate the SRS resources within each SRS resource set (e.g., the SRS resources 672). For example, the SRS configuration can indicate the symbol locations and / or REs allocated for each SRS resource, the number of SRS ports (e.g., the SRS ports 674) within each SRS resource, and / or the association between the SRS ports and the SRS REs.

[0116] At act 640, the UE 604a transmits an RI report A to the BS 602 indicating that the UE 604a is currently operating with a transmission rank of 2 (e.g., an RI = 2 with two spatial layers). The UE 604a can determine the transmission rank based on various reference signal measurements and / or interference measurements. Similarly, at act 642, the UE 604b transmits an RI report B to the BS 602 indicating that the UE 604b is currently operating with a transmission rank of 4 (e.g., an RI = 4 with four spatial layers). At act 644, the UE 604c transmits an RI report C to the BS 602 indicating that the UE 604c is currently operating with a transmission rank of 2 (e.g., an RI = 1 with one spatial layer). At act 646, the UE 604d transmits an RI report D to the BS 602 indicating that the UE 604d is currently operating with a transmission rank of 3 (e.g., an RI = 3 with three spatial layers).

[0117] At act 650, the BS 602 activates the SRS resources for the UEs 604a, 604b, 604c, and 604d to transmit SRS. The BS 602 can determine which SRS resource 672 in the SRS resource pool 682 to activate for each UE 604 based on the current transmission rank of the UE 604, e.g., as described above with respect to FIG. 6. For example, the BS 602 can activate the SRS resource 672-1 in the SRS resource pool 682 for the UE 604a, the SRS resource 672-2 in the SRS resource pool 682 for the UE 604b, the SRS resource 672-3 in the SRS resource pool 682 for the UE 604c, and the SRS resource 672-4 in the SRS resource pool 682 for the UE 604d. Figure 6C). The BS 602 may select a subset of the configured SRS resources 672 for the UE 604 such that the number of SRS ports 674 associated with the subset of the configured SRS resources 672 is equal to or greater than the RI reported by the UE 604. The BS 602 may indicate SRS resource activation via MAC-CE or DCI.

[0118] Reference Figure 6C , BS 602 may activate SRS resource 672b having two SRS ports 674 based on the RI indicated by UE 304a as 2 for UE 304a to sound for SRS transmission (as indicated by arrow 662). BS 602 may activate SRS resource 672d having four SRS ports 674 based on the RI indicated by UE 304b as 4 for UE 304b to sound for SRS transmission (as indicated by arrow 664). BS 602 may activate SRS resource 672a having one SRS port 674 based on the RI indicated by UE 304c as 1 for UE 304c to sound for SRS transmission (as indicated by arrow 666). BS 602 may activate SRS resource 672c having three SRS ports 674 based on the RI indicated by UE 304d as 3 for UE 304d to sound for SRS transmission (as indicated by arrow 668).

[0119] Back to Figure 6A In act 650, upon receiving activation for SRS resource 672b, UE 604a transmits an SRS to BS 602 using SRS resource 672b having two SRS ports 674. Similarly, in act 652, in response to the activation of BS 602, UE 604b transmits an SRS to BS 602 using SRS resource 672d having four SRS ports 674. In act 654, in response to the activation of BS 602, UE 604c transmits an SRS to BS 602 using SRS resource 672a having one SRS port 674. In act 656, in response to the activation of BS 602, UE 604d transmits an SRS to BS 602 using SRS resource 672c having three SRS ports 674.

[0120] In some aspects, BS 602 may determine whether a valid RI report exists from UE 604 to avoid using outdated RI reports for SRS resource selection. BS 602 may set a time threshold to filter out outdated RI reports for SRS resource selection. The time threshold may have any suitable time unit. In some instances, the time threshold may be in units of time slots (e.g., time slot 202). For example, BS 602 may determine whether the gap duration between the most recent RI report received from UE 604 and an upcoming SRS transmission opportunity of UE 604 is longer than the time threshold. If the gap duration is longer than the time threshold, BS 602 may determine that there is no valid RI report from UE 604. When there is no valid rank information for UE 604, BS 602 may activate an SRS resource 672 (e.g., SRS resource 672d) with the maximum number of SRS ports 674 (e.g., corresponding to the number of transmit antenna ports supported by UE 604) for UE 604 to sound for SRS transmission. If the gap duration meets the time threshold, the BS 602 may use the transmission rank in the most recent RI report to select an SRS resource 672 with a number of SRS ports that matches the transmission rank of the UE 604. Figure 6A In the illustrated example, the gap duration 606 between the most recent RI report received from UE 604a (at action 640) and the upcoming SRS transmission (at action 660) meets the time threshold. Accordingly, BS 602 selects an SRS resource 672b having two SRS ports 674 that match the rank of 2 as reported by UE 604a (at action 640).

[0121] In some aspects, when there are no SRS resources 672 in the SRS resource pool 682 having a number of SRS ports 674 that matches the RI of the UE 604, the BS 602 can activate the UE 604 with an SRS resource 672 having a number of SRS ports 674 that is greater than the RI of the UE 604 (e.g., L). When the UE 604 is activated with an SRS resource 672 having a number of SRS ports 674 that is greater than the RI of the UE 604, the UE 604 can repeat the SRS transmission in the remaining (L-RI) SRS ports 674. As an example, the UE 604 can have an RI of 2. If the UE 604 receives an activation for an SRS resource 672 having four SRS ports 674, the UE 604 can transmit an SRS transmission using two SRS ports 674 and can repeat the SRS transmission in the remaining two SRS ports 674. Alternatively, the UE 604 can mute the (L-RI) SRS ports 674. Referring to the same example, if the UE 604 receives an activation for an SRS resource 672 having four SRS ports 674 when the UE is operating with an RI of 2, the UE 604 can transmit an SRS transmission using two SRS ports 674 and can mute or remain mute in the remaining two SRS ports 674. In some aspects, the UE 604 can select the first two SRS ports 674 for SRS transmission and mute the other two SRS ports 674. For example, the four SRS ports 674 can be identified by SRS port numbers (e.g., SRS port 1, SRS port 2, SRS port 3, and SRS port 4), and the UE 604 can transmit an SRS using SRS port 1 and SRS port 2. In some other instances, the UE 604 can select any two of the four SRS ports 674 for SRS transmission, and the BS 602 can perform blind decoding to detect the SRS ports 674 used by the UE 604 to transmit an SRS. In some aspects, the BS 602 can configure the UE 604 to mute the remaining two (e.g., L-RI) SRS ports 674 and can reclaim the two unused SRS ports 674 for another UE 604 to sound SRS transmissions. For example, another UE 604 can have an RI of 2 and can thus use the two unused SRS ports 674 to transmit an SRS transmission.

[0122] In some aspects, the BS 602 may deactivate one or more SRS resources 672 previously activated for the UE 604, for example, by sending a MAC-CE or DCI indicating deactivation. Upon receiving the deactivation, the UE 604 may not transmit SRS in the one or more deactivated SRS resources 672. In some aspects, the UE 602 may transmit an SRS resource activation (e.g., a MAC-CE) for the UE 604 before the activated SRS resources. For example, there may be a minimum time interval between the activation signaling (e.g., a MAC-CE) in time slot x and the earliest subframe or time slot (e.g., time slot 202) for transmission of the activated SRS resources. In some aspects, the BS 602 may transmit a deactivation command to the UE during subframe or time slot n (e.g., time slot 202). The UE 604 may not transmit in the deactivated SRS resources after time slot n+Y.

[0123] Figure 7 700 is a flow chart of a wireless communication method 700 according to some aspects of the present disclosure. Aspects of the method 700 may be performed by a computing device (e.g., a processor, processing circuitry, and / or other suitable components) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device (such as BS 105, 302, 500, and / or 602) may utilize one or more components (such as processor 502, memory 504, SRS module 508, transceiver 510, modem 512, and one or more antennas 516) to perform the steps of the method 700. The method 700 may be implemented as described above with reference to Figure 3A and 6A The methods 300 and 600 discussed above refer to Figure 3B 、 3C , 6B, and 6C. As illustrated, method 700 includes several enumerated steps, but aspects of method 700 may include additional steps before, after, and between these enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

[0124] At block 710, a BS (e.g., BS 105, 302, 500, and / or 602) determines a plurality of SRS resources (e.g., SRS resources 672) for at least a first UE (e.g., UE 115, 304, 400, and / or 604), wherein a first SRS resource in the plurality of SRS resources includes a different number of SRS ports (e.g., SRS ports 674) than a second SRS resource in the plurality of SRS resources. In some examples, the BS may utilize one or more components (e.g., processor 502, memory 504, SRS module 508, transceiver 510, modem 512, and one or more antennas 516) to determine the plurality of SRS resources for at least the first UE.

[0125] In some aspects, determining the plurality of SRS resources includes determining, by the base station, one or more SRS resource sets (e.g., SRS resource set 670) for a group of UEs including the first UE, the one or more SRS resource sets including the plurality of SRS resources. In some aspects, the one or more SRS resource sets are at least one of semi-persistent or aperiodic.

[0126] At block 720, the BS transmits a configuration indicating the plurality of SRS resources to the first UE. In some examples, the BS may utilize one or more components, such as the processor 502, the memory 504, the SRS module 508, the transceiver 510, the modem 512, and one or more antennas 516, to transmit the configuration indicating the plurality of SRS resources.

[0127] At block 730, the BS transmits a request to the first UE to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission. In some examples, the BS may utilize one or more components, such as the processor 502, the memory 504, the SRS module 508, the transceiver 510, the modem 512, and one or more antennas 516, to transmit the request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission.

[0128] In some aspects, the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.In some aspects, transmitting the request comprises transmitting, by the BS to the first UE, at least one of a MAC-CE or a DCI.

[0129] At block 740, the BS receives a first SRS transmission from the first UE from the one or more SRS ports within the plurality of SRS resources. In some examples, the BS may utilize one or more components, such as the processor 502, the memory 504, the SRS module 508, the transceiver 510, the modem 512, and one or more antennas 516, to receive the first SRS transmission from the one or more SRS ports within the plurality of SRS resources.

[0130] In some aspects, the number of the one or more SRS ports is based at least in part on transmission rank information associated with the first UE. In some aspects, the BS may further select a subset of the plurality of SRS resources for the first UE based on the number of spatial layers indicated by the transmission rank information associated with the first UE, wherein the one or more SRS ports are associated with the subset of the plurality of SRS resources. In some aspects, the BS may further receive an RI report from the first UE indicating the number of spatial layers currently supported by the first UE.

[0131] In some aspects, the number of SRS resources in the plurality of SRS resources determined at block 710 is equal to or greater than the number of transmit antenna ports supported by the first UE. In some aspects, the BS may also receive a UE capability report from the first UE indicating the number of transmit antenna ports supported by the first UE. In some aspects, the number of the one or more SRS ports activated at block 730 is less than the number of transmit antenna ports supported by the first UE.

[0132] In some aspects, the BS may also transmit a request to the second UE to activate the plurality of SRS ports for the second SRS transmission. The BS may also receive, from the second UE, a second SRS transmission from a first subset of the plurality of SRS ports that is less than all of the plurality of SRS ports. In some aspects, the BS may also receive, from the second UE, a repetition of the second SRS transmission from a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

[0133] In some aspects, the BS may determine whether a rank indicator (RI) report has been received from the second UE. In response to determining that the RI report has not been received from the second UE, the BS may also transmit to the second UE a request to activate a plurality of SRS ports for a second SRS transmission based on the number of transmit antenna ports supported by the second UE. In some aspects, determining whether the RI report has been received from the second UE includes determining, by the BS, whether a gap duration between a most recent RI report received from the second UE and a transmission opportunity for the second SRS transmission satisfies a threshold.

[0134] Figure 8800 is a flow chart of a wireless communication method 800 according to some aspects of the present disclosure. Aspects of the method 800 may be performed by a computing device (e.g., a processor, processing circuitry, and / or other suitable components) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device (such as UE 115, 304, 500, and / or 604) may utilize one or more components (such as processor 402, memory 404, SRS module 408, transceiver 410, modem 412, and one or more antennas 416) to perform the steps of the method 800. The method 800 may be implemented as described above with reference to Figure 3A and 6A The methods 300 and 600 discussed above refer to Figure 3B 、 3C , 6B, and 6C. As illustrated, method 800 includes several enumerated steps, but aspects of method 800 may include additional steps before, after, and between these enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

[0135] At block 810, a UE (e.g., UE 115, 304, 400, and / or 604) receives a configuration indicating a plurality of SRS resources (e.g., SRS resources 672) configured for the UE from a BS (e.g., BS 105, 302, 500, and / or 602), wherein a first SRS resource in the plurality of SRS resources includes a different number of SRS ports (e.g., SRS ports 674) than a second SRS resource in the plurality of SRS resources. In some examples, the BS may utilize one or more components (e.g., processor 502, memory 504, SRS module 508, transceiver 510, modem 512, and one or more antennas 516) to receive the configuration indicating the plurality of SRS resources configured for the UE.

[0136] At block 820, the UE receives a request from the BS to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission. In some examples, the BS may utilize one or more components (such as the processor 502, the memory 504, the SRS module 508, the transceiver 510, the modem 512, and the one or more antennas 516) to receive the request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission.

[0137] In some aspects, the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.In some aspects, receiving the request may include receiving at least one of a MAC-CE or a DCI from the BS.

[0138] At block 830, the UE transmits a first SRS transmission to the BS using one or more SRS ports within the configured plurality of SRS resources. In some examples, the BS may utilize one or more components (such as the processor 502, the memory 504, the SRS module 508, the transceiver 510, the modem 512, and the one or more antennas 516) to transmit the first SRS transmission using one or more SRS ports within the configured plurality of SRS resources.

[0139] In some aspects, the number of the one or more SRS ports is based at least in part on transmission rank information associated with the UE.In some aspects, the UE may also transmit an RI report including the transmission rank information to the BS.

[0140] In some aspects, the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the UE. In some aspects, the UE may also transmit a UE capability report to the base station indicating the number of transmit antenna ports supported by the UE. In some aspects, the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the UE.

[0141] In some aspects, the UE may also receive a further request from the BS to activate multiple SRS ports within the multiple SRS resources for a second SRS transmission, wherein the number of the multiple SRS ports is greater than the number of spatial layers currently supported by the UE. The UE may also transmit the second SRS transmission to the BS using a first subset of the multiple SRS ports, wherein the number of SRS ports in the first subset of the multiple SRS ports corresponds to the number of spatial layers currently supported by the UE. In some aspects, the UE may also transmit a repetition of the second SRS transmission to the BS using a second subset of the multiple SRS ports that does not overlap with the first subset of the multiple SRS ports. In some aspects, the UE may also refrain from transmitting SRS on remaining SRS ports in the multiple SRS ports.

[0142] Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0143] The various illustrative blocks and modules described herein can be implemented or performed with a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0144] The functions described herein can be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations thereof. Features implementing functions can also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, "or" as used in a list of items prefaced by "comprising" or "including" indicates an inclusive list such that, for example, a list of [A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

[0145] As will be appreciated by those of ordinary skill in the art to which this application pertains, many modifications, alternative constructions, and equivalent substitutions can be made in the devices, apparatus, configurations, and methods of use of the present disclosure without departing from the spirit and scope of the present disclosure. Accordingly, the scope of the present disclosure should not be limited to the specific embodiments illustrated and described herein (as these are merely examples of some of the embodiments of the present disclosure), but rather the scope of the present disclosure is to be accorded the complete scope consistent with the claims and functional equivalents thereof.

Claims

1. A wireless communication method, comprising: determining, by a network entity, a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; transmitting, by the network entity, a configuration indicating the plurality of SRS resources; determining, by the network entity, whether a rank indicator (RI) report is received from a second UE; as well as In response to determining that the RI report is not received from the second UE, a request is transmitted by the network entity to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the second UE.

2. The method of claim 1, further comprising: transmitting, by the network entity, a request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission; as well as The first SRS transmission is received by the network entity from the one or more SRS ports within the plurality of SRS resources. 3 . The method of claim 2 , wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the first UE.

4. The method of claim 3, further comprising: A subset of the plurality of SRS resources is selected by the network entity for the first UE based on a number of spatial layers indicated by the transmission rank information associated with the first UE, wherein the one or more SRS ports are associated with the subset of the plurality of SRS resources.

5. The method of claim 4, further comprising: A rank indicator (RI) report is received by the network entity indicating the number of spatial layers currently supported by the first UE. 6 . The method of claim 1 , wherein the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the first UE.

7. The method of claim 6, further comprising: A UE capability report is received by the network entity indicating the number of transmit antenna ports supported by the first UE.

8. The method of claim 2, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the first UE.

9. The method of claim 2, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

10. The method of claim 1 , wherein determining the plurality of SRS resources further comprises: One or more SRS resource sets for a group of UEs including the first UE are determined by the network entity, where the one or more SRS resource sets include the multiple SRS resources.

11. The method of claim 10, wherein the one or more SRS resource sets are at least one of semi-persistent or aperiodic.

12. The method of claim 1, further comprising: transmitting, by the network entity, a request to activate a plurality of SRS ports for a second SRS transmission; as well as The second SRS transmission is received by the network entity from a first subset of the plurality of SRS ports that is less than all of the plurality of SRS ports.

13. The method of claim 12, further comprising: Repetitions of the second SRS transmissions from a second subset of the plurality of SRS ports that do not overlap with the first subset of the plurality of SRS ports are received by the network entity.

14. The method of claim 1 , wherein determining whether an RI report is received from the second UE comprises: Determining, by the network entity, whether a gap duration between a most recent RI report received from the second UE and a transmission opportunity of the second SRS transmission satisfies a threshold.

15. The method of claim 1, further comprising: At least one of a Medium Access Control-Control Element (MAC-CE) or Downlink Control Information (DCI) is transmitted by the network entity.

16. A wireless communication method, comprising: Receiving, by a user equipment (UE), a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources includes a different number of SRS ports than a second SRS resource of the plurality of SRS resources; transmitting, by the UE, a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources; as well as A request is received by the UE to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the UE.

17. The method of claim 16, further comprising: A request is received by the UE to activate the one or more SRS ports within the plurality of SRS resources for the first SRS transmission.

18. The method of claim 16, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the UE.

19. The method of claim 18, further comprising: A rank indicator (RI) report including the transmission rank information is transmitted by the UE.

20. The method of claim 16, wherein the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the UE.

21. The method of claim 20, further comprising: A UE capability report is transmitted by the UE indicating the number of transmit antenna ports supported by the UE.

22. The method of claim 20, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the UE.

23. The method of claim 16, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

24. The method of claim 16, further comprising: receiving, by the UE, a further request to activate a plurality of SRS ports within the plurality of SRS resources for a second SRS transmission, wherein the number of the plurality of SRS ports is greater than a number of spatial layers currently supported by the UE; as well as The second SRS transmission is transmitted by the UE using a first subset of the plurality of SRS ports, wherein a number of SRS ports in the first subset of the plurality of SRS ports corresponds to the number of spatial layers currently supported by the UE.

25. The method of claim 24, further comprising: A repetition of the second SRS transmission is transmitted by the UE using a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

26. The method of claim 25, further comprising: Transmission of the SRS in the remaining SRS ports of the plurality of SRS ports is suppressed by the UE.

27. The method of claim 16, further comprising: At least one of a Medium Access Control-Control Element (MAC-CE) or Downlink Control Information (DCI) is received by the UE.

28. A network entity comprising: a processor configured to determine a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources comprises a different number of SRS ports than a second SRS resource of the plurality of SRS resources; a transceiver configured to transmit a configuration indicating the plurality of SRS resources, in: The processor is further configured to: determine whether a rank indicator (RI) report is received from a second UE; and The transceiver is further configured to, in response to determining that the RI report is not received from the second UE, transmit a request to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the second UE.

29. The network entity of claim 28, wherein the transceiver is further configured to: transmitting a request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission; and The first SRS transmission is received from the one or more SRS ports within the plurality of SRS resources.

30. The network entity of claim 29, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the first UE.

31. The network entity of claim 30, wherein the processor is further configured to: A subset of the plurality of SRS resources is selected for the first UE based on a number of spatial layers indicated by the transmission rank information associated with the first UE, wherein the one or more SRS ports are associated with the subset of the plurality of SRS resources.

32. The network entity of claim 31 , wherein the transceiver is further configured to: A rank indicator (RI) report indicating the number of spatial layers currently supported by the first UE is received.

33. The network entity of claim 28, wherein the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the first UE.

34. The network entity of claim 33, wherein the transceiver is further configured to: A UE capability report is received indicating the number of transmit antenna ports supported by the first UE.

35. The network entity of claim 29, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the first UE.

36. The network entity of claim 29, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

37. The network entity of claim 28, wherein the processor configured to determine the plurality of SRS resources is further configured to: One or more SRS resource sets for a group of UEs including the first UE are determined, the one or more SRS resource sets including the plurality of SRS resources.

38. The network entity of claim 37, wherein the one or more SRS resource sets are at least one of semi-persistent or aperiodic.

39. The network entity of claim 28, wherein the transceiver is further configured to: transmitting a request to activate a plurality of SRS ports for a second SRS transmission; and The second SRS transmission is received from a first subset of the plurality of SRS ports that is less than all of the plurality of SRS ports.

40. The network entity of claim 39, wherein the transceiver is further configured to: Repetitions of the second SRS transmission are received from a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

41. The network entity of claim 28, wherein the processor configured to determine whether an RI report is received from the second UE is further configured to: It is determined whether a gap duration between a most recent RI report received from the second UE and a transmission opportunity of the second SRS transmission satisfies a threshold.

42. The network entity of claim 28, wherein the transceiver is further configured to: At least one of a medium access control-control element (MAC-CE) or downlink control information (DCI) is transmitted.

43. A user equipment (UE), comprising: A transceiver configured to: receiving a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources comprises a different number of SRS ports than a second SRS resource of the plurality of SRS resources; transmitting a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources; as well as A request is received to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the UE.

44. The UE of claim 43, wherein the transceiver is further configured to: A request is received to activate the one or more SRS ports within the plurality of SRS resources for the first SRS transmission.

45. The UE of claim 43, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the UE.

46. ​​The UE of claim 45, wherein the transceiver is further configured to: A rank indicator (RI) report including the transmission rank information is transmitted.

47. The UE of claim 43, wherein the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the UE.

48. The UE of claim 47, wherein the transceiver is further configured to: A UE capability report is transmitted indicating the number of transmit antenna ports supported by the UE.

49. The UE of claim 47, wherein the number of the one or more SRS ports is less than the number of the transmit antenna ports supported by the UE.

50. The UE of claim 43, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

51. The UE of claim 43, wherein the transceiver is further configured to: receiving a further request to activate a plurality of SRS ports within the plurality of SRS resources for a second SRS transmission, wherein the number of the plurality of SRS ports is greater than a number of spatial layers currently supported by the UE; and The second SRS transmission is transmitted using a first subset of the plurality of SRS ports, wherein a number of SRS ports in the first subset of the plurality of SRS ports corresponds to the number of spatial layers currently supported by the UE.

52. The UE of claim 51 , wherein the transceiver is further configured to: Repetitions of the second SRS transmission are transmitted using a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

53. The UE of claim 52, further comprising: A processor is configured to refrain from transmitting an SRS in remaining SRS ports of the plurality of SRS ports.

54. The UE of claim 43, wherein the transceiver is further configured to: At least one of a medium access control-control element (MAC-CE) or downlink control information (DCI) is received.

55. A non-transitory computer-readable medium having program code recorded thereon, the program code comprising: code for causing a network entity to determine a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources comprises a different number of SRS ports than a second SRS resource of the plurality of SRS resources; code for causing the network entity to transmit a configuration indicating the plurality of SRS resources; code for causing the network entity to determine whether a rank indicator (RI) report is received from a second UE; as well as Code for causing the network entity to transmit, in response to determining that an RI report is not received from the second UE, a request to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the second UE.

56. The non-transitory computer readable medium of claim 55, further comprising: code for causing the network entity to transmit a request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission; as well as Code for causing the network entity to receive the first SRS transmission from the one or more SRS ports within the plurality of SRS resources.

57. The non-transitory computer-readable medium of claim 56, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the first UE.

58. The non-transitory computer readable medium of claim 57, further comprising: Code for causing the network entity to select a subset of the plurality of SRS resources for the first UE based on a number of spatial layers indicated by the transmission rank information associated with the first UE, wherein the one or more SRS ports are associated with the subset of the plurality of SRS resources.

59. The non-transitory computer readable medium of claim 58, further comprising: Code for causing the network entity to receive a rank indicator (RI) report indicating the number of spatial layers currently supported by the first UE.

60. The non-transitory computer-readable medium of claim 55, wherein a number of SRS resources in the plurality of SRS resources is equal to or greater than a number of transmit antenna ports supported by the first UE.

61. The non-transitory computer readable medium of claim 60, further comprising: Code for causing the network entity to receive a UE capability report indicating the number of transmit antenna ports supported by the first UE.

62. The non-transitory computer-readable medium of claim 56, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the first UE.

63. The non-transitory computer-readable medium of claim 56, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

64. The non-transitory computer-readable medium of claim 55, wherein the code for causing the network entity to determine the plurality of SRS resources is further configured to: One or more SRS resource sets for a group of UEs including the first UE are determined, the one or more SRS resource sets including the plurality of SRS resources.

65. The non-transitory computer-readable medium of claim 64, wherein the one or more SRS resource sets are at least one of semi-persistent or aperiodic.

66. The non-transitory computer readable medium of claim 55, further comprising: code for causing the network entity to transmit a request to activate a plurality of SRS ports for a second SRS transmission; as well as Code for causing the network entity to receive the second SRS transmission from a first subset of the plurality of SRS ports that is less than all of the plurality of SRS ports.

67. The non-transitory computer readable medium of claim 66, further comprising: Code for causing the network entity to receive a repetition of the second SRS transmission from a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

68. The non-transitory computer-readable medium of claim 55, wherein the code for causing the network entity to determine whether an RI report is received from the second UE is further configured to: It is determined whether a gap duration between a most recent RI report received from the second UE and a transmission opportunity of the second SRS transmission satisfies a threshold.

69. The non-transitory computer readable medium of claim 55, further comprising: The method is configured to cause the network entity to transmit at least one of a medium access control-control element (MAC-CE) or downlink control information (DCI).

70. A non-transitory computer-readable medium having program code recorded thereon, the program code comprising: code for causing a user equipment (UE) to receive a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources comprises a different number of SRS ports than a second SRS resource of the plurality of SRS resources; code for causing the UE to transmit a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources; as well as Code for causing the UE to receive a request to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the UE.

71. The non-transitory computer readable medium of claim 70, further comprising: Code for causing the UE to receive a request to activate the one or more SRS ports within the plurality of SRS resources for the first SRS transmission.

72. The non-transitory computer-readable medium of claim 70, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the UE.

73. The non-transitory computer readable medium of claim 72, further comprising: Code for causing the UE to transmit a rank indicator (RI) report including the transmission rank information.

74. The non-transitory computer-readable medium of claim 70, wherein a number of SRS resources in the plurality of SRS resources is equal to or greater than a number of transmit antenna ports supported by the UE.

75. The non-transitory computer readable medium of claim 74, further comprising: Code for causing the UE to transmit a UE capability report indicating the number of transmit antenna ports supported by the UE.

76. The non-transitory computer-readable medium of claim 74, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the UE.

77. The non-transitory computer-readable medium of claim 70, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

78. The non-transitory computer readable medium of claim 70, further comprising: code for causing the UE to receive a further request to activate a plurality of SRS ports within the plurality of SRS resources for a second SRS transmission, wherein the number of the plurality of SRS ports is greater than a number of spatial layers currently supported by the UE; as well as Code for causing the UE to transmit the second SRS transmission using a first subset of the plurality of SRS ports, wherein a number of SRS ports in the first subset of the plurality of SRS ports corresponds to the number of spatial layers currently supported by the UE.

79. The non-transitory computer readable medium of claim 78, further comprising: Code for causing the UE to transmit a repetition of the second SRS transmission using a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

80. The non-transitory computer readable medium of claim 79, further comprising: Code for causing the UE to refrain from transmitting SRS in remaining SRS ports of the plurality of SRS ports.

81. The non-transitory computer readable medium of claim 70, further comprising: The method is configured to enable the UE to receive at least one of a medium access control-control element (MAC-CE) or downlink control information (DCI).

82. A network entity comprising: means for determining a plurality of sounding reference signal (SRS) resources for at least a first user equipment (UE), wherein a first SRS resource of the plurality of SRS resources comprises a different number of SRS ports than a second SRS resource of the plurality of SRS resources; means for transmitting a configuration indicating the plurality of SRS resources; means for determining whether a rank indicator (RI) report is received from a second UE; as well as Means for transmitting, in response to determining that no RI report is received from the second UE, a request to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the second UE.

83. The network entity of claim 82, further comprising: means for transmitting a request to activate one or more SRS ports within the plurality of SRS resources for a first SRS transmission; as well as means for receiving the first SRS transmission from the one or more SRS ports within the plurality of SRS resources.

84. The network entity of claim 83, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the first UE.

85. The network entity of claim 84, further comprising: means for selecting a subset of the plurality of SRS resources for the first UE based on a number of spatial layers indicated by the transmission rank information associated with the first UE, wherein the one or more SRS ports are associated with the subset of the plurality of SRS resources.

86. The network entity of claim 85, further comprising: Means for receiving a rank indicator (RI) report indicating the number of spatial layers currently supported by the first UE.

87. The network entity of claim 82, wherein the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the first UE.

88. The network entity of claim 87, further comprising: Means for receiving a UE capability report indicating the number of transmit antenna ports supported by the first UE.

89. The network entity of claim 83, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the first UE.

90. The network entity of claim 83, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

91. The network entity of claim 82, wherein the means for determining the plurality of SRS resources is further configured to: One or more SRS resource sets for a group of UEs including the first UE are determined, the one or more SRS resource sets including the plurality of SRS resources.

92. The network entity of claim 91, wherein the one or more SRS resource sets are at least one of semi-persistent or aperiodic.

93. The network entity of claim 82, further comprising: means for transmitting a request to activate a plurality of SRS ports for a second SRS transmission; as well as Means for receiving the second SRS transmission from a first subset of the plurality of SRS ports that is less than all of the plurality of SRS ports.

94. The network entity of claim 93, further comprising: Means for receiving a repetition of the second SRS transmission from a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

95. The network entity of claim 82, wherein the means for determining whether an RI report is received from the second UE is further configured to: It is determined whether a gap duration between a most recent RI report received from the second UE and a transmission opportunity of the second SRS transmission satisfies a threshold.

96. The network entity of claim 82, further comprising: Means for transmitting at least one of a Medium Access Control - Control Element (MAC-CE) or Downlink Control Information (DCI).

97. A user equipment (UE), comprising: means for receiving a configuration indicating a plurality of sounding reference signal (SRS) resources configured for the UE, wherein a first SRS resource of the plurality of SRS resources comprises a different number of SRS ports than a second SRS resource of the plurality of SRS resources; means for transmitting a first SRS transmission using one or more SRS ports within the configured plurality of SRS resources; as well as Means for receiving a request to activate a plurality of SRS ports for a second SRS transmission based on a number of transmit antenna ports supported by the UE.

98. The UE of claim 97, further comprising: Means for receiving a request to activate the one or more SRS ports within the plurality of SRS resources for the first SRS transmission.

99. The UE of claim 97, wherein the number of the one or more SRS ports is based at least in part on transmission rank information associated with the UE.

100. The UE of claim 99, further comprising: Means for transmitting a rank indicator (RI) report including the transmission rank information.

101. The UE of claim 97, wherein the number of SRS resources in the plurality of SRS resources is equal to or greater than the number of transmit antenna ports supported by the UE.

102. The UE of claim 101, further comprising: Means for transmitting a UE capability report indicating the number of transmit antenna ports supported by the UE.

103. The UE of claim 101, wherein the number of the one or more SRS ports is less than the number of transmit antenna ports supported by the UE.

104. The UE of claim 97, wherein the one or more SRS ports are associated with one or more SRS resources of the plurality of SRS resources.

105. The UE of claim 97, further comprising: means for receiving a further request to activate a plurality of SRS ports within the plurality of SRS resources for a second SRS transmission, wherein the number of the plurality of SRS ports is greater than a number of spatial layers currently supported by the UE; as well as means for transmitting the second SRS transmission using a first subset of the plurality of SRS ports, wherein a number of SRS ports in the first subset of the plurality of SRS ports corresponds to the number of spatial layers currently supported by the UE.

106. The UE of claim 105, further comprising: means for transmitting a repetition of the second SRS transmission using a second subset of the plurality of SRS ports that does not overlap with the first subset of the plurality of SRS ports.

107. The UE of claim 106, further comprising: means for refraining from transmitting SRS in remaining SRS ports of the plurality of SRS ports.

108. The UE of claim 101, further comprising: Means for receiving at least one of a Medium Access Control - Control Element (MAC-CE) or Downlink Control Information (DCI).

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