Patent Description:
Wireless communications systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources (e.g., time, frequency, power, and/or spectrum). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA).

An example telecommunication standard is Long Term Evolution (LTE) or LTE-Advanced (LTE-A). However, although newer multiple access systems, such as an LTE or LTE-A system, deliver faster data throughput than older technologies, such increased downlink rates have triggered a greater demand for higher-bandwidth content, such as high-resolution graphics and video, for use on or with mobile devices. As such, demand for bandwidth, higher data rates, better transmission quality as well as better spectrum utilization, and lower latency on wireless communications systems continues to increase.

The 5th Generation (<NUM>) New Radio (NR) communications technology, used in a wide range of spectrum, is envisaged to expand and support diverse usage scenarios and applications with respect to current mobile network generations. In an aspect, <NUM> NR communications technology includes, for example: enhanced mobile broadband (eMBB) addressing human-centric use cases for access to multimedia content, services and data; ultra-reliable low-latency communications (URLLC) with strict requirements, especially in terms of latency and reliability; and massive machine type communications (mMTC) for a very large number of connected devices and typically transmitting a relatively low volume of non-delay-sensitive information. As the demand for mobile broadband access continues to increase, there exists a need for further improvements in <NUM> communications technology and beyond. Accordingly, due to the requirements for increased data rates, higher capacity and reliability, and better cell coverage, new approaches may be desirable to improve beam discovery and beamforming, in order to satisfy consumer demand and improve user experience in wireless communications.

<NPL>) relates to dedicated CSI-RS resource per UE. <CIT> relates to a method for reporting channel state information (CSI) in a wireless communication system.

Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

Aspects of the present invention are set out in the accompanying claims. In the following, each of the described methods, apparatuses, systems, examples and aspects which does not correspond to the invention as defined in the claims is thus not according to the invention and is, as well as the whole following description, present for illustration purposes or to highlight specific aspects or features of the claims. According to an example, a method related to signaling for channel state information reference signals (CSI-RS) in a wireless communications system is provided. The method includes receiving, by a user equipment (UE), a channel state information reference signal (CSI-RS) beam of a set of CSI-RS beams, and the CSI-RS beam includes a change indication message. The method further includes determining, by the UE, whether the set of CSI-RS beams has changed based on a value of the change indication message.

In another aspect, an apparatus for wireless communications is provided that includes a receiver, a memory configured to store instructions, and one or more processors communicatively coupled with the receiver and the memory. For example, the apparatus may include a receiver configured to receive a CSI-RS beam of a set of CSI-RS beams, and the CSI-RS beam may include a change indication message. The apparatus may also include a memory configured to store instructions, and at least one processor communicatively coupled with the receiver and the memory, and the at least one processor is configured to execute the instructions to determine whether the set of CSI-RS beams have changed based on a value of the change indication message.

In another aspect, an apparatus for wireless communication is provided that includes means for receiving a CSI-RS beam of a set of CSI-RS beams, the CSI-RS beam includes a change indication message, and means for determining whether the set of CSI-RS beams have changed based on a value of the change indication message.

In yet another aspect, a computer-readable medium (e.g., a non-transitory computer-readable medium) is provided. The computer-readable medium stores or comprises code, executable by at least one processor, to receive a CSI-RS beam of a set of CSI-RS beams and the CSI-RS beam includes a change indication message, and to determine whether the set of CSI-RS beams have changed based on a value of the change indication message.

In order to facilitate a fuller understanding of aspects described herein, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be illustrative only.

In a wireless communications system (e.g., a millimeter wave (mmW) communications system), a user equipment (UE) may need to find a suitable beam from a periodic channel state information reference signals (CSI-RS) signal, which is sent from a base station and provides a beam sweep. A challenge is that the base station may insert or remove one or more beams from the beam sweep without notice to the UE. In some cases, the base station may also remap beams to different time and/or frequency resources. As such, a hierarchical beam search may be impossible or very difficult. Therefore, new approaches to improve beam discovery and beamforming may be desirable. In an aspect, an indicator, such as but not limited to a single bit, in the CSI-RS waveform is used to indicate to the receiving UEs that the base station has modified a set of beams involved in the beam sweep. For example, the bit may be conveyed through a choice of a scrambling sequence customarily used for the CSI-RS. In some implementations, system performance may be improved by restricting the times at which the base station can execute a modification of the set of beams.

In some examples, a next generation NodeB (a gNodeB or a gNB) in a <NUM> NR system may provide the indication (e.g., a single-bit indication) to indicate one or more beam sweep changes, for example, through the choice of a scrambling sequence customarily used for the CSI-RS. In some aspects, the time durations at which the one or more changes in the CSI-RS beam sweep may be restricted to allow for a more robust beam discovery by the UE. In some cases, the indication may help to reduce the amount of time used by the beam search process. In some implementations, the UE in a mmW communications system is able to perform beam search based on the CSI-RS beam sweep, and the gNB may modify, insert, and/or delete one or more beam directions, and indicate the beam change(s) through the indication to the UE.

These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements").

Accordingly, in one or more aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), and floppy disk where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

In wireless communications systems (e.g., mmW communications systems), beamforming may be used to overcome high-path losses. In some aspects, both a base station (e.g., a gNB) and a user equipment (UE) may have to find and maintain suitable beams to enable a communication link between each other. For instance, for connected UEs, to find and maintain suitable beams, a procedure is typically involved that the base station (e.g., a gNB) periodically (or semi-persistently) sending a CSI-RS signal that contains a beam sweep over all relevant spatial directions. For example, a CSI-RS burst may include several orthogonal frequency division multiplexing (OFDM) symbols. For each OFDM symbol, in an aspect, the signals of several gNB beams pointing in different directions may be frequency multiplexed. In an aspect, gNB beams of different symbols may also point into different spatial directions. In some implementations, the base station (e.g., a gNB) may time division multiplexed (TDMed) or frequency division multiplexed (FDMed) the beams.

In an aspect, the transmission of a signal (e.g., an OFDM signal, or a CSI-RS) requires electric energy. To use the electric energy wisely, a beam sweep is typically restricted to those spatial directions that are relevant to the UEs (e.g., a limited number of UEs) in a cell. In an example, if there are only a few UEs in the cell, the beam sweep may consist of only a few gNB beams. In an aspect, the number of beams used during the sweep may grow or increase with the number of the UEs in the cell, in a condition that the beams are uniformly (or partial-uniform) spatially distributed. In an aspect, when the UEs may be found in all spatial directions, the beam sweep may contain the maximum number of beams. As such, a set of beams used during the beam sweep may change over time. For example, one or more UEs may enter or leave the cells at a certain time, therefore, one or more beams may be added or removed from the beam sweep. Additionally, the existing gNB beams may be reshuffled and/or reassigned to different time-frequency resources for the purpose of consolidating the gNB beams in a small number of symbols.

In some aspects, to discover new beams, the UE may apply a hierarchical search, which aims to find the strongest gNB beams first. In an example, the beam search may be conducted in parallel independently for several or all symbols of a CSI-RS. For example, in a first step, the UE may apply sequentially all of the antenna sub-arrays of the UE, employing an omnidirectional or pseudo-omnidirectional receive directivity pattern (e.g., a UE beam). The UE may determine the maximum Reference Signal Received Power (RSRP) over all frequency resources over all sub-arrays. In some examples, if the maximum RSRP is above a threshold, the UE may apply during the next iterations the best (or a better) antenna sub-array and may try out sequentially different directivity patterns (e.g., UE beams) pointing into different spatial directions. After the best pattern (e.g., a UE beam) has been found, a third round of iterations may be entered where sharper UE beams are applied.

In an aspect, due to analog beamforming, each iteration of the search algorithm may require the reception of a new CSI-RS burst with a different sub-array or a different UE beam. In some examples, the entire search may stretch over several CSI-RS bursts, and may only be successful when the UE has one or more indications indicate that the set of beams does not change during the search.

In another aspect, a gNB may communicate the change discussed herein (e.g., add or remove a UE beam or a gNB beam) to all the UEs. However, in mmW, a broadcast message is prohibitively expensive since the broadcast message may have to be transmitted in a beam-swept manner.

Described herein are various aspects related to a wireless communications system (e.g., an mmW system), in particular, signaling for CSI-RS with time varying cell-specific beam training. In an aspect, the waveform for each CSI-RS beam may convey a bit which is toggled by the gNB whenever the set of beams of CSI-RS changes. In an aspect, this bit may be called as a change indication bit. In an example, the change indication bit may determine the scrambling sequence of the beams. For example, when bit = <NUM>, the waveform of the beams is scrambled using a scrambling sequence A, otherwise a scrambling sequence B is used. In some examples, the sequence A and/or the sequence B may be used depending on a respective cell identification (ID) and/or a symbol number within a radio frame. Then, the UE may test upon reception of the CSI-RS for hypothesis A versus B through descrambling and channel estimation. In an aspect, the hypothesis with the higher likelihood yields the detected change indication bit.

In some aspects, the beam search may use a serving beam pair, which is used for accessing the system, since both the UE and the gNB may need to establish a beam. In an aspect, the serving beam pair may be maintained throughout the connection or a communication link. By evaluating a CSI-RS, the UE may discover alternate serving beam pairs as a fall back for the case that the serving beam fades away. Accordingly, in some examples, the UE may extract the change indication bit from the waveform of the serving beam or any of the alternate beams.

In some examples, while the change indication bit does not toggle, the UE may conduct a hierarchical beam search on all symbols of the CSI-RS burst. In an aspect, when the search algorithm investigates a symbol that contains the serving beam, the search algorithm may try out different sub-arrays or beams, and the serving beam may then not be received, hence the change indication bit may not be extracted from the serving beam. In an aspect, when one or more alternate serving beams are available on different symbols, the change indication bit may be extracted from the one or more alternate serving beams. Otherwise a stipulation may be needed that the gNB may not change the beam set arbitrarily fast or at arbitrary times. For example, a beam set may only be changed at the start of every fourth radio frame. In an aspect, a condition like the one discussed herein may introduce a protection interval during which the UE does not have to monitor the change indication bit and may try out different antenna sub-arrays/ beams on the symbol that usually carries the serving beam. In some examples, the UE may use the protection interval to reduce the probability of misdetection of the change indication bit.

In some examples, when the change indication bit signifies a beam change while a hierarchical beam search is ongoing, a simple approach may include discarding the results of the search, and another approach is provided in <FIG> discussed later.

One or more of the aspects described above may be performed or implemented by the apparatus and methods described below in connection with <FIG>.

Referring to <FIG>, in an aspect, a wireless communication system <NUM> includes at least one UE <NUM> or UE <NUM> in communication coverage of at least one network entity <NUM> (e.g., a base station or a gNB, or a cell thereof, in an mmW system or a <NUM> NR system). UE <NUM> and/or UE <NUM> may communicate with a network via the network entity <NUM>. In some aspects, multiple UEs including UE <NUM> and/or UE <NUM> may be in communication coverage with one or more network entities, including network entity <NUM>. In an aspect, the network entity <NUM> may be a base station such a gNB in a <NUM> NR network, and/or in an LTE network. Although various aspects are described in relation to the Universal Mobile Telecommunications System (UMTS), LTE, or <NUM> NR networks, similar principles may be applied in other wireless wide area networks (WWAN). The wireless network may employ a scheme where multiple base stations may transmit on a channel.

In some examples, UE <NUM> and/or UE <NUM> may transmit and/or receive wireless communications (e.g., beamforming) to and/or from network entity <NUM>. For example, the UE <NUM> and/or UE <NUM> may be actively communicating with network entity <NUM>. In some implementations, each of the UE <NUM> and/or UE <NUM> and network entity <NUM> (e.g., a gNB) may establish a beam, as such, a serving beam pair may be established between the UE <NUM>, <NUM> and the network entity <NUM>. In an aspect, the serving beam pair may be maintained throughout the connection or communication links <NUM>. By evaluating a CSI-RS, the UE <NUM>, <NUM> may discover alternate serving beam pairs as a fall back for the case that the serving beam fades away. Accordingly, in some examples, the UE may extract a change indication bit from a waveform of the serving beam and/or any of the alternate beams.

In some implementations, the network entity <NUM> may be an mmW base station or an mmW gNB, and may operate in mmW frequencies and/or near mmW frequencies. In some examples, extremely high frequency (EHF) may be part of the radio frequency (RF) in the electromagnetic spectrum. Radio waves in the band/range may be referred to as a millimeter wave. Communications using the mmW and/or near mmW radio frequency band has extremely high path loss and a short range. The network entity <NUM> and/or the UE <NUM>, <NUM> may utilize beamforming <NUM> to compensate for the extremely high path loss and short range.

In some aspects, UE <NUM> and/or UE <NUM> may also be referred to by those skilled in the art (as well as interchangeably herein) as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. A UE <NUM> and/or UE <NUM> may 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, a global positioning system (GPS) device, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a wearable computing device (e.g., a smart-watch, smart-glasses, a health or fitness tracker, etc.), an appliance, a sensor, a vehicle communication system, a medical device, a vending machine, a device for the Internet-of Things, or any other similar functioning device.

In some examples, the network entity <NUM> may be referred to as a base transceiver station, a radio base station, a radio transceiver, a basic service set (BSS), an extended service set (ESS), NodeB, eNodeB, Home NodeB, Home eNodeB, gNB, macrocell, picocell, femtocell, relay, small cell box, or some other suitable terminology. The coverage area for a base station may be divided into sectors making up only a portion of the coverage area (not shown). The wireless communications system <NUM> may include a network entity <NUM> of different types (e.g., macro, micro, and/or pico base stations). The network entity <NUM> may utilize different radio technologies, such as cellular and/or Wireless Local Area Network (WLAN) radio access technologies (RAT). The network entity <NUM> may be associated with the same or different access networks or operator deployments. The coverage areas of the network entity <NUM>, including the coverage areas of the same or different types of the network entity <NUM>, utilizing the same or different radio technologies, and/or belonging to the same or different access networks, may overlap. Furthermore, the network entity <NUM> may be substantially any type of component that may communicate with UE <NUM> and/or <NUM> to provide wireless network access at the UE <NUM> and/or <NUM>.

According to the present aspects, the UE <NUM> and/or UE <NUM> may include one or more processors <NUM> and a memory <NUM> that may operate in combination with a beam management component <NUM> to control a beam search component <NUM>, a CSI-RS beam management component <NUM> (and/or sub-components of the CSI-RS beam management component <NUM> which may include a change indication component <NUM> and/or a mode selection component <NUM>) for performing beamforming management, transmissions and/or receptions as described herein. The network entity <NUM> may include one or more processors <NUM> and a memory <NUM> that may operate in combination with a beam management component <NUM> to control a CSI-RS beam management component <NUM> (and/or one or more of the sub-components <NUM> and <NUM>) for performing beamforming management, transmissions and/or receptions as described herein. In some examples, some of the components and/or sub-components are shown in dashed line boxes because some of the components and/or sub-components may be not part of the UE <NUM> / UE <NUM> or the network entity <NUM> implementation (or may be optional), as applicable.

For example, the beam management component <NUM> may perform beamforming management, transmissions and/or receptions as described herein. In an aspect, the term "component" as used herein may be one of the parts that make up a system, may be hardware, firmware, and/or software, and may be divided into other components. The beam management component <NUM> may be communicatively coupled with a transceiver <NUM>, which may include a receiver <NUM> for receiving and processing RF or beam signals and a transmitter <NUM> for processing and transmitting RF or beam signals. In some examples, the beam management component <NUM> may include the beam search component <NUM> and/or the CSI-RS beam management component <NUM> (and/or its sub-components) for performing CSI-RS signaling/beamforming with time varying cell-specific beam training. The processor <NUM> may be coupled with the transceiver <NUM> and memory <NUM> via at least one bus <NUM>.

The receiver <NUM> may include hardware, firmware, and/or software code executable by a processor for receiving data, the code comprising instructions and being stored in a memory (e.g., computer-readable medium). The receiver <NUM> may be, for example, an RF receiver. In an aspect, the receiver <NUM> may monitor or receive beam signals transmitted by UE <NUM> and/or UE <NUM> or network entity <NUM>. The receiver <NUM> may obtain measurements of or indications in the signals. For example, the receiver <NUM> may determine Ec/Io, SNR, etc..

The transmitter <NUM> may include hardware, firmware, and/or software code executable by a processor for beamforming and transmitting data, the code comprising instructions and being stored in a memory (e.g., computer-readable medium). The transmitter <NUM> may be, for example, an RF transmitter.

In an aspect, the one or more processors <NUM> can include a modem <NUM> that uses one or more modem processors. The various functions related to the beam management component <NUM> may be included in modem <NUM> and/or processors <NUM> and, in an aspect, can be executed by a single processor, while in other aspects, different ones of the functions may be executed by a combination of two or more different processors. For example, in an aspect, the one or more processors <NUM> may include any one or any combination of a modem processor, or a baseband processor, or a digital signal processor, or a transmit processor, or a transceiver processor associated with transceiver <NUM>. In particular, the one or more processors <NUM> may implement components included in the beam management component <NUM>, including the beam search component <NUM> and/or the CSI-RS beam management component <NUM> (and/or its sub-components).

The beam management component <NUM>, the beam search component <NUM>, and/or the CSI-RS beam management component <NUM> (and/or its sub-components) may include hardware, firmware, and/or software code executable by a processor for performing random access management and operations. For example, the hardware may include, for example, a hardware accelerator, or specialized processor.

Moreover, in an aspect, UE <NUM> and/or UE <NUM> and/or network entity <NUM> may include an RF front end <NUM> and a transceiver <NUM> for receiving and transmitting radio transmissions including beamforming, for example, communication links <NUM> (e.g., beam signals). In some examples, the communication links <NUM> may use spatial multiplexing, beamforming, transmit diversity, and/or a multiple-input multiple-output (MIMO) antenna technology. The communication links <NUM> may be through one or more carriers. In an example, transceiver <NUM> of network entity <NUM> may transmit or receive a signal, such as beam signals (e.g., a CSI-RS beam) or messages generated by beam management component <NUM>, and/or including a pilot signal (e.g., common pilot channel (CPICH). The transceiver <NUM> of UE <NUM>, <NUM> may measure the received beam signals (e.g., a CSI-RS beam) and/or pilot signals in order to determine signal quality and for providing feedback to the network entity <NUM>.

RF front end <NUM> may be connected to one or more antennas <NUM> and can include one or more low-noise amplifiers (LNAs) <NUM>, one or more switches <NUM>, <NUM>, one or more power amplifiers (PAs) <NUM>, and one or more filters <NUM> for transmitting and receiving RF signals. In an aspect, components of RF front end <NUM> can connect with transceiver <NUM>. Transceiver <NUM> may connect to one or more modems <NUM> and processor <NUM>.

In an aspect, RF front end <NUM> may use one or more switches <NUM>, <NUM> to select a particular LNA <NUM> and its specified gain value based on a desired gain value for a particular application. In an aspect, the RF front end <NUM> may provide measurements (e.g., Ec/Io) and/or applied gain values to the beam management component <NUM>.

In an aspect, each PA <NUM> may have a specified minimum and maximum gain values. In an aspect, RF front end <NUM> may use one or more switches <NUM>, <NUM> to select a particular PA <NUM> and its specified gain value based on a desired gain value for a particular application.

In an aspect, RF front end <NUM> can use one or more switches <NUM>, <NUM>, <NUM> to select a transmit or receive path using a specified filter <NUM>, LNA, <NUM>, and/or PA <NUM>, based on a configuration as specified by transceiver <NUM> and/or processor <NUM>.

Transceiver <NUM> may be configured to transmit and receive wireless signals (e.g., beam signals) through one or more antennas <NUM> via RF front end <NUM>. In an aspect, transceiver may be tuned to operate at specified frequencies such that UE <NUM> and/or UE <NUM> can communicate with, for example, network entity <NUM>. In an aspect, for example, modem <NUM> may configure transceiver <NUM> to operate at a specified frequency and power level based on the UE configuration of the UE <NUM> and/or UE <NUM> and communication protocol used by modem <NUM>.

In an aspect, modem <NUM> can control one or more components of UE <NUM> and/or UE <NUM> or network entity <NUM> (e.g., RF front end <NUM>, transceiver <NUM>) to enable transmission and/or reception of signals based on a specified modem configuration. In another aspect, the modem configuration can be based on UE configuration information associated with UE <NUM> and/or UE <NUM> as provided by the network during cell selection and/or cell reselection.

UE <NUM> and/or UE <NUM>, or network entity <NUM> may further include memory <NUM>, such as for storing data used herein and/or local versions of applications or beam management component <NUM> and/or one or more of its subcomponents being executed by processor <NUM>. Memory <NUM> may include any type of computer-readable medium usable by a computer or processor <NUM>, such as random access memory (RAM), read only memory (ROM), tapes, magnetic discs, optical discs, volatile memory, non-volatile memory, and any combination thereof. In an aspect, for example, memory <NUM> may be a computer-readable storage medium that stores one or more computer-executable codes defining beam management component <NUM> and/or one or more of its subcomponents, and/or data associated therewith, when UE <NUM> and/or UE <NUM> and/or network entity <NUM> is operating processor <NUM> to execute beam management component <NUM> and/or one or more of its subcomponents. In another aspect, for example, memory <NUM> may be a non-transitory computer-readable storage medium.

Referring to <FIG>, a diagram illustrates an example of a wireless communications system <NUM>, in accordance with aspects described herein. In some examples, the wireless communications system <NUM> may be the same as or include the wireless communications system <NUM> in <FIG>, and may include a plurality of network entities <NUM> (e.g., base stations, gNBs, or WLAN network entities), a number of UEs <NUM> and/or <NUM>, and one or more core networks <NUM>. In an aspect, one or more UEs <NUM> and/or <NUM> may include a beam management component <NUM> configured to perform beamforming management, transmissions and/or receptions as described herein. The beam management component <NUM> may be configured to perform at least some aspects of the techniques or methods described above in wireless communications, including LTE or <NUM> NR. Some of the network entity <NUM> may communicate with the UEs <NUM> and/or <NUM> under the control of a base station controller (not shown), which may be part of the core network <NUM> or the network entity <NUM> (e.g., a base station or a gNB) in various examples.

In an aspect, the network entity <NUM> may communicate control or system information and/or user data with the core network <NUM> through backhaul links <NUM>. In some cases, the network entity <NUM> may communicate, either directly or indirectly, with each other over backhaul links <NUM>, which may be wired or wireless communication links. The wireless communications system <NUM> may support operation on multiple carriers (waveform signals of different frequencies). Multi-carrier transmitters may transmit modulated signals simultaneously on the multiple carriers. For example, each communication link <NUM> (e.g., wireless communications <NUM> in <FIG>) may be a multi-carrier signal modulated according to the various radio technologies described above. Each modulated signal or beam may be sent on a same or different carrier and may carry control or system information (e.g., reference signals, control channels, etc.), overhead information, data, etc..

In some examples, the network entity <NUM> may wirelessly communicate with the UEs <NUM> and/or <NUM> via one or more antennas. Each of the network entity <NUM> may provide communication coverage for a respective coverage area <NUM>. In some examples, the network entity <NUM> may be referred to as a base station, a NodeB, an eNodeB, a Home NodeB, a Home eNodeB, a gNB, or an access point. In some cases, at least a portion of the wireless communications system <NUM> may be configured to operate on a spatial multiplexing (e.g., multiple-input and multiple-output (MIMO)) scheme in which one or more of the UEs <NUM> and/or <NUM> and one or more of the network entity <NUM> may be configured to support transmissions on closed-loop MIMO and/or open-loop MIMO scheme.

In network communication systems using LTE/LTE-A, <NUM> NR, or similar communication technologies, the terms eNodeB, eNB or gNB may be used to describe the network entity <NUM>, though concepts described herein may be applied to other types of network entity in other types of communication technologies. For example, the wireless communications system <NUM> may be an LTE or a <NUM> NR network in which different types of network entity provide coverage for various geographical regions. For example, each network entity <NUM> may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. Small cells such as pico cells, femto cells, and/or other types of cells may include low power nodes or LPNs. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs <NUM> and/or <NUM> with service subscriptions with the network provider. A small cell may cover a relatively smaller geographic area and may allow unrestricted access by UEs <NUM> and/or <NUM> with service subscriptions with the network provider, for example, and in addition to unrestricted access, may also provide restricted access by UEs <NUM> and/or <NUM> having an association with the small cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). A base station for a macro cell may be referred to as a macro base station. A base station for a small cell may be referred to as a small cell base station. A base station may support one or multiple (e.g., two, three, four, and the like) cells.

In some aspects, the core network <NUM> may communicate with the base stations or other network entity <NUM> via one or more backhaul links <NUM> (e.g., S1 interface, etc.). The network entity <NUM> may also communicate with one another, e.g., directly or indirectly via backhaul links <NUM> (e.g., X2 interface, etc.) and/or via backhaul links <NUM> (e.g., through core network <NUM>).

In some examples, the UEs <NUM> and/or <NUM> may be dispersed throughout the wireless communications system <NUM>, and each UE <NUM> or <NUM> may be stationary or mobile. The UE <NUM> or <NUM> may be referred to by those skilled in the art as a suitable terminology discussed herein. The UE <NUM> or <NUM> may be able to communicate with macro base stations, small cell base stations, relays, and the like. The UE <NUM> or <NUM> may be able to communicate over different access networks, such as cellular or other WWAN access networks, or WLAN access networks.

The communication links <NUM> (e.g., wireless communications <NUM> in <FIG>) shown in wireless communications system <NUM> may include uplink transmissions from the UE <NUM> or <NUM> to the network entity <NUM>, and/or downlink transmissions (e.g., one or more CSI-RS beams) from the network entity <NUM> to the UE <NUM> or <NUM>. The downlink transmissions may also be called forward link transmissions while the uplink transmissions may also be called reverse link transmissions. The communication links <NUM> may carry transmissions of each hierarchical layer which, in some examples, may be multiplexed in the communication links <NUM>. The UEs <NUM> and/or <NUM> may be configured to collaboratively communicate with multiple network entity <NUM> through, for example, MIMO, carrier aggregation (CA), Coordinated Multi-Point (CoMP), or other schemes. MIMO techniques use multiple antennas on the network entity <NUM> and/or multiple antennas on the UE <NUM> or <NUM> to transmit multiple data streams. The MIMO techniques may include closed-loop MIMO and/or open-loop MIMO scheme. Carrier aggregation (CA) may utilize two or more component carriers (CCs) on a same or different serving cell for data transmission. CoMP may include techniques for coordination of transmission and reception by a number of network entity <NUM> to improve overall transmission quality for UEs <NUM> and/or <NUM> as well as increasing network and spectrum utilization.

Referring to <FIG>, in an aspect, a flow chart outlines a beam discovery scheme <NUM> executable by, for example, UE <NUM> (or UE <NUM>) for CSI-RS (e.g., periodic CSI-RS) discovery with a cell-specific time varying beam sweep, including a potential procedure labeled as a restore mode for salvaging information from one or more identified beams once the UE <NUM> has determined that the beam set has changed.

In an aspect, after the UE <NUM> initially establishes communication with the network entity <NUM>, the UE <NUM> may have knowledge of at least a serving beam. As such, the beam discovery scheme <NUM> starts at block <NUM> with the UE <NUM> waiting for a next CSI-RS burst at block <NUM>. For example, in an aspect, the beam search component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to wait for a CSI-RS burst, or monitor beam signals for a CSI-RS burst transmitted by the network entity <NUM>.

In an aspect, at block <NUM>, upon the next CSI-RS burst, the UE <NUM> determines whether at least one beam from the network entity <NUM> has been detected. In an aspect, for example, the beam search component <NUM>, CSI-RS beam management component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to detect and receive one or more CSI-RS beams of a set of CSI-RS beams from the network entity <NUM> (e.g., a gNB).

In one alternative, if no beam from the network entity <NUM> has been detected, at block <NUM>, the UE <NUM> may start or continue a synchronized hierarchical search over all symbols. In an aspect, for example, the beam search component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to start or continue a synchronized hierarchical search. The details of this alternative are described below with reference to the "no" option stemming from block <NUM> that triggers the actions at block <NUM>.

In another alternative, if at least one beam from the network entity <NUM> has been detected at block <NUM>, then, at block <NUM>, the UE <NUM> may extract a change indication bit to see if the beam set has changed. For example, the UE <NUM> may jointly extract the change indication bit from all identified beams using maximal ration combining. In an aspect, for example, the CSI-RS beam management component <NUM>, and/or change indication component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to determine whether the CSI-RS beam includes a change indication message (e.g., in or via a change indication bit). If a change indication message is found or detected, the CSI-RS beam management component <NUM>, and/or change indication component <NUM> may extract the change indication message or bit.

Then, after extracting the change indication bit, at block <NUM>, the UE <NUM> determines whether the beam set has changed. For example, the UE identifies the value of the change indication bit (e.g., "<NUM>" or "<NUM>") in order to determine whether the bit indicates a change or no change. In an aspect, for example, the change indication component <NUM> may be configured to determine whether the set of CSI-RS beams have changed based on the value of the change indication (e.g., a change indication bit = "<NUM>" or "<NUM>"). In some cases, the change of the set of CSI-RS beams may be that a beam or beams in the set of CSI-RS beams have been added or removed by the network entity <NUM>.

In one alternative, if the beam set has not changed, at block <NUM>, the UE <NUM> may determine whether the UE <NUM> is in a restore mode. In an aspect, for example, the mode selection component <NUM> may be configured to determine whether the UE <NUM> is in a restore mode. In an example, if the processing related to a prior restore mode was not completed before a time threshold to end the restore mode operations, or if a timing for a next CSI-RS burst has arrived, the UE <NUM> (e.g., via the mode selection component <NUM>) may have partially performed the restore mode operations and may determine to return to finish the restore mode at block <NUM>. This alternative related to block <NUM> will be discussed in more detail below.

In the other alternative, if the UE <NUM> determines that it is not in the restore mode, then at block <NUM>, the UE <NUM> may start or continue an independent hierarchical beam search on all symbols. In an aspect, for example, the mode selection component <NUM> may be configured to determine whether the UE <NUM> is in a restore mode, and if not, the beam search component <NUM> may be configured to start or continue an independent hierarchical beam search on all symbols. In an implementation, the speed of the search might be reduced on symbols which have already one beam identified. Once completed or once a time threshold has been reached, the UE <NUM> may return to the beginning of the beam discovery scheme <NUM> to wait for the next CSI-RS (e.g., at block <NUM>) and repeat the process.

Alternatively, if the UE <NUM> determines that the beam set has changed (at block <NUM>), or if the UE <NUM> has determined that it was in the restore mode (at block <NUM>), the UE <NUM> may respectively start a new restore mode at block <NUM>, or continue a pending restore mode where it left off (at block <NUM>). In an aspect, for example, the beam management component <NUM> and/or mode selection component <NUM> may be configured to start a new restore mode or continue a pending restore mode as shown in <FIG>.

In some aspects of a restore mode, at block <NUM>, the UE <NUM> (e.g., via the beam management component <NUM>, beam search component <NUM>, CSI-RS beam management component <NUM>, and/or mode selection component <NUM>) may attempt to find the time-frequency locations of one or more previously identified beams (e.g., most or all of the previously identified beams), which is independent from a determination of whether the best UE beam has been found. As such, most of the prior efforts for the time-frequency locations discovery may be salvaged. In some examples, the UE <NUM> may first test which of the beams still show up in their usual symbol. For the beams that cannot be found in their usual symbol, the UE <NUM> may search other symbols during future CSI-RS bursts. For the search, the beams may be ordered in descending RSRP. In some examples, the UE <NUM> may require an entire CSI-RS burst per beam. During the burst, the UE <NUM> may apply the same beam specific sub-array or directivity pattern for all CSI-RS symbols, and the UE <NUM> may identify or determine which symbol the RSRP is the highest, excluding the time-frequency resources of the beams that has already been processed. As such, excluding the time-frequency resources of the beams that has already been processed will be successful provided that the beam is still in the set. In contrast, if not excluding the time-frequency resources of the beams that has already been processed, the search may not provide a useful result, and the UE <NUM> may discard the beam. In an example, the entire search may be terminated early, because the UE <NUM> may consider that it is not worth to delay any longer the resumption of beam monitoring and the ordinary hierarchical search. In this case, the mode may be set back to normal.

Returning to the alternative stemming from block <NUM> where no beam from the network entity <NUM> has been detected, in an example, there may be a situation that all serving beams are lost. In this case, referring to block <NUM>, a hierarchical search may be conducted, where the UE <NUM> may always use the same sub-array and the UE beam for all CSI-RS symbols of the burst (e.g., a synchronous hierarchical search). In some examples, a hierarchical search may work as long as the beam (that the UE hunts for) stays within the beam set. In an aspect, the beam may change the time-frequency resource on which the beam is transmitted, but this change may not influence the performance of the synchronous search. If, however, the network entity <NUM> happens to remove the beam during the search, the search may end with any useful result. The beam removal, however, may typically not happen, as the network entity <NUM> sends all beams required for any of the UEs in the cell. In any case, for example, the UE <NUM> may start a new search (e.g., via the beam management component <NUM>, and/or beam search component <NUM>).

It should be noted that, for purposes of simplicity of explanation, the schemes and methods discussed herein are shown and described as a series of acts, and it is to be understood and appreciated that the scheme and method (and further methods related thereto) is/are not limited by the order of acts, as some acts may, in accordance with one or more aspects, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, it is to be appreciated that a method could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a method in accordance with one or more features described herein.

Referring to <FIG>, in an operational aspect, a UE such as UE <NUM> and/or UE <NUM> (<FIG>) may perform one or more aspects of a method <NUM> for CSI-RS beamforming. For example, one or more of the processors <NUM>, the memory <NUM>, modem <NUM>, transceiver <NUM>, beam management component <NUM>, beam search component <NUM>, CSI-RS beam management component <NUM>, change indication component <NUM>, and/or mode selection component <NUM>, may be configured to perform one or more aspects of the method <NUM>.

In an aspect, at block <NUM>, the method <NUM> may include determining, by the UE from a message received from a base station, time intervals during which the set of CSI-RS beams does not change. In an aspect, for example, the beam management component <NUM>, the CSI-RS beam management component <NUM>, the change indication component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to determine a time interval during which the UE does not determine whether the CSI-RS beam includes the change indication. In an example, the UE may be configured to determine a protection interval during which the UE <NUM> or <NUM> does not have to monitor a change indication message or bit, and may try out different antenna sub-arrays or beams on the symbol that may carry a serving beam. In some examples, the UE may use the protection interval to reduce the probability of misdetection of the change indication bit.

At block <NUM>, the method <NUM> includes receiving, by a user equipment (UE), a channel state information reference signal (CSI-RS) beam of a set of CSI-RS beams, wherein the CSI-RS beam includes a change indication message. In an aspect, for example, the beam management component <NUM>, the CSI-RS beam management component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to receive one or more CSI-RS beams of a set of CSI-RS beams.

At block <NUM>, the method <NUM> includes determining, by the UE, whether the set of CSI-RS beams have changed based on a value of the change indication message. In an aspect, for example, the CSI-RS beam management component <NUM> and/or the change indication component <NUM> (<FIG>), e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to determine whether the CSI-RS beam includes a change indication message (e.g., in or via a change indication bit), and the change indication may indicate whether the set of CSI-RS beams have changed (e.g., a beam or beams in the set of CSI-RS beams have been added or removed by the network entity <NUM>). For example, the UE may be configured to determine whether the set of CSI-RS beams have changed based on a value of the change indication (e.g., a change indication bit = "<NUM>" or "<NUM>"), as described herein.

In an aspect, at block <NUM>, the method <NUM> may include interrupting, by the UE, a hierarchical beam search in response to the value of the change indication message indicating that the set of CSI-RS beams have changed. In an aspect, for example, the beam search component <NUM>, the CSI-RS beam management component <NUM>, the change indication component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to interrupt the hierarchical beam search in response to the value of the change indication message indicating that the set of CSI-RS beams have changed, as described herein.

In an aspect, at block <NUM>, the method <NUM> may include entering, at the UE, a restore mode to search time-frequency locations of one or more previously identified or processed CSI-RS beams. In an aspect, for example, the CSI-RS beam management component <NUM>, the mode selection component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to enter a restore mode to search time-frequency locations of one or more previously identified or processed CSI-RS beams, as described herein.

In another aspect, the method <NUM> may optionally include conducting a hierarchical beam search on all symbols associated with the CSI-RS beam. In an aspect, for example, the beam search component <NUM>, the CSI-RS beam management component <NUM>, e.g., in conjunction with one or more of the processors <NUM>, the memory <NUM>, the modem <NUM>, and/or the transceiver <NUM>, may be configured to conduct one or more hierarchical beam search on at least a portion or all of the symbols associated with the CSI-RS beam or burst, as described herein. In some examples, the hierarchical beam search may be used to find a symbol that contains a serving beam, or to find one or more different symbols that include one or more alternate serving beams, and the change indication may be extracted from one or more of the serving beams.

Several aspects of a telecommunications system have been presented with reference to an LTE/LTE-A or a <NUM> communication system.

By way of example, various aspects may be extended to other communication systems such as High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), High Speed Packet Access Plus (HSPA+) and TD-CDMA. Various aspects may also be extended to systems employing Long Term Evolution (LTE) (in FDD, TDD, or both modes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000, Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB), IEEE <NUM> (Wi-Fi), IEEE <NUM> (WiMAX), IEEE <NUM>, Ultra-Wideband (UWB), Bluetooth, and/or other suitable systems.

Claim 1:
A method of wireless communications, comprising:
receiving (<NUM>), by a user equipment UE, a channel state information reference signal, CSI-RS, beam of a set of CSI-RS beams, wherein a waveform of a CSI-RS of the CSI-RS beam includes a change indication message; and
determining (<NUM>), by the UE, whether the set of CSI-RS beams has changed based on a value of the change indication message.