Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for uplink and downlink beam selection.
Wireless communications systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcasts, or other similar types of services. These wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available wireless communications system resources with those users.
Although wireless communications systems have made great technological advancements over many years, challenges still exist. For example, complex and dynamic environments can still attenuate or block signals between wireless transmitters and wireless receivers. Accordingly, there is a continuous desire to improve the technical performance of wireless communications systems, including, for example: improving speed and data carrying capacity of communications, improving efficiency of the use of shared communications mediums, reducing power used by transmitters and receivers while performing communications, improving reliability of wireless communications, avoiding redundant transmissions and/or receptions and related processing, improving the coverage area of wireless communications, increasing the number and types of devices that can access wireless communications systems, increasing the ability for different types of devices to intercommunicate, increasing the number and type of wireless communications mediums available for use, and the like. Consequently, there exists a need for further improvements in wireless communications systems to overcome the aforementioned technical challenges and others.
One aspect provides a method for wireless communication at a user equipment (UE). The method includes measuring channel state information (CSI) reference signals (CSI-RS) associated with a plurality of beams; determining an uplink rank and a downlink rank; selecting, from the plurality of beams, a downlink beam for processing downlink transmissions, based on the CSI RS measurements and the downlink rank; and selecting, from the plurality of beams, an uplink beam for processing uplink transmissions, based on the CSI RS measurements, the uplink rank, and the downlink rank.
Other aspects provide: an apparatus operable, configured, or otherwise adapted to perform any one or more of the aforementioned methods and/or those described elsewhere herein; a non-transitory, computer-readable media comprising instructions that, when executed by a processor of an apparatus, cause the apparatus to perform the aforementioned methods as well as those described elsewhere herein; a computer program product embodied on a computer-readable storage medium comprising code for performing the aforementioned methods as well as those described elsewhere herein; and/or an apparatus comprising means for performing the aforementioned methods as well as those described elsewhere herein. By way of example, an apparatus may comprise a processing system, a device with a processing system, or processing systems cooperating over one or more networks.
The following description and the appended figures set forth certain features for purposes of illustration.
The appended figures depict certain features of the various aspects described herein and are not to be considered limiting of the scope of this disclosure.
Aspects of the present disclosure provide apparatuses, methods, processing systems, and computer-readable mediums for uplink and downlink beam selection.
In wireless communications, a beam generally refers to a focused radio frequency (RF) signal transmitted or received by an antenna array. Beam selection generally refers to a process of selecting an optimal beam for communication between a network entity/base station (e.g., a gNB) and a user equipment (UE), such as a smartphone or a wireless modem. Beam selection is a technique associated with beamforming, which is a signal processing technique employed in wireless systems to improve the performance and efficiency of communication links by concentrating signal power in a specific direction.
In wireless communication systems that employ beamforming, multiple antennas may be used to transmit and receive signals. By dynamically adjusting the direction of the transmit beam, the transmitted energy may be focused towards the intended receiver, which may mitigate interference from other directions while enabling higher signal quality, improved coverage, increased data rates, and improved overall system capacity.
In some cases, a UE may use measured channel quality to determine an uplink (UL) serving beam (e.g., UL_SUB) and a downlink (DL) serving beam (e.g., DL_SUB). Channel quality metrics as measured on gNB transmitted reference signals (e.g., SSB, CSI-RS, etc.) may include various metrics, such as reference signal receive power (RSRP), Signal to Interference and Noise Ratio (SINR), spectral efficiency (e.g., measured in bits per second per hertz (bps/Hz)).
In some cases, UE beam selection may be fully based on SSB RSRP measurements. However, this approach may have some weaknesses. For example, an SSB beam may not be the same as a traffic beam, meaning UE beam selection based on an SSB beam may not be optimized for downlink traffic. Additionally, an SSB beam has an inherent rank-1 precoder, which may be different from a precoding matrix indicator (PMI) on a traffic beam for both rank-1 and rank-2.
Aspects of the present disclosure provide techniques for CSI-RS based UE per-rank UL and DL beam selection. For example, when UL and DL beam de-coupling is supported, aspects of the present disclosure may enable a UE to select optimal UL and DL beams separately, per-rank. This may be advantageous, since the best DL beam may not the best UL beam, especially when there is a PMI/rank mismatch. Selecting the most optimal beams (e.g., decoupled) for UL and DL may provide higher signal quality, improved coverage, increased data rates, and improved overall system capacity.
The techniques and methods described herein may be used for various wireless communications networks. While aspects may be described herein using terminology commonly associated with 3G, 4G, and/or 5G wireless technologies, aspects of the present disclosure may likewise be applicable to other communications systems and standards not explicitly mentioned herein.
Generally, wireless communications network 100 includes various network entities (alternatively, network elements or network nodes). A network entity is generally a communications device and/or a communications function performed by a communications device (e.g., a user equipment (UE), a base station (BS), a component of a BS, a server, etc.). For example, various functions of a network as well as various devices associated with and interacting with a network may be considered network entities. Further, wireless communications network 100 includes terrestrial aspects, such as ground-based network entities (e.g., BSs 102), and non-terrestrial aspects, such as satellite 140 and aircraft 145, which may include network entities on-board (e.g., one or more BSs) capable of communicating with other network elements (e.g., terrestrial BSs) and user equipments.
In the depicted example, wireless communications network 100 includes BSs 102, UEs 104, and one or more core networks, such as an Evolved Packet Core (EPC) 160 and 5G Core (5GC) network 190, which interoperate to provide communications services over various communications links, including wired and wireless links.
BSs 102 wirelessly communicate with (e.g., transmit signals to or receive signals from) UEs 104 via communications links 120. The communications links 120 between BSs 102 and UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a BS 102 and/or downlink (DL) (also referred to as forward link) transmissions from a BS 102 to a UE 104. The communications links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity in various aspects.
BSs 102 may generally include: a NodeB, enhanced NodeB (eNB), next generation enhanced NodeB (ng-eNB), next generation NodeB (gNB or gNodeB), access point, base transceiver station, radio base station, radio transceiver, transceiver function, transmission reception point, and/or others. Each of BSs 102 may provide communications coverage for a respective geographic coverage area 110, which may sometimes be referred to as a cell, and which may overlap in some cases (e.g., small cell 102′ may have a coverage area 110′ that overlaps the coverage area 110 of a macro cell). A BS may, for example, provide communications coverage for a macro cell (covering relatively large geographic area), a pico cell (covering relatively smaller geographic area, such as a sports stadium), a femto cell (relatively smaller geographic area (e.g., a home)), and/or other types of cells.
While BSs 102 are depicted in various aspects as unitary communications devices, BSs 102 may be implemented in various configurations. For example, one or more components of a base station may be disaggregated, including a central unit (CU), one or more distributed units (DUs), one or more radio units (RUs), a Near-Real Time (Near-RT) RAN Intelligent Controller (RIC), or a Non-Real Time (Non-RT) RIC, to name a few examples. In another example, various aspects of a base station may be virtualized. More generally, a base station (e.g., BS 102) may include components that are located at a single physical location or components located at various physical locations. In examples in which a base station includes components that are located at various physical locations, the various components may each perform functions such that, collectively, the various components achieve functionality that is similar to a base station that is located at a single physical location. In some aspects, a base station including components that are located at various physical locations may be referred to as a disaggregated radio access network architecture, such as an Open RAN (O-RAN) or Virtualized RAN (VRAN) architecture.
Different BSs 102 within wireless communications network 100 may also be configured to support different radio access technologies, such as 3G, 4G, and/or 5G. For example, BSs 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC 160 through first backhaul links 132 (e.g., an S1 interface). BSs 102 configured for 5G (e.g., 5G NR or Next Generation RAN (NG-RAN)) may interface with 5GC 190 through second backhaul links 184. BSs 102 may communicate directly or indirectly (e.g., through the EPC 160 or 5GC 190) with each other over third backhaul links 134 (e.g., X2 interface), which may be wired or wireless.
Wireless communications network 100 may subdivide the electromagnetic spectrum into various classes, bands, channels, or other features. In some aspects, the subdivision is provided based on wavelength and frequency, where frequency may also be referred to as a carrier, a subcarrier, a frequency channel, a tone, or a subband. For example, 3GPP currently defines Frequency Range 1 (FR1) as including 410 MHZ-7125 MHz, which is often referred to (interchangeably) as “Sub-6 GHz”. Similarly, 3GPP currently defines Frequency Range 2 (FR2) as including 24,250 MHZ-52,600 MHZ, which is sometimes referred to (interchangeably) as a “millimeter wave” (“mmW” or “mm Wave”). A base station configured to communicate using mmWave/near mmWave radio frequency bands (e.g., a mmWave base station such as BS 180) may utilize beamforming (e.g., 182) with a UE (e.g., 104) to improve path loss and range.
The communications links 120 between BSs 102 and, for example, UEs 104, may be through one or more carriers, which may have different bandwidths (e.g., 5, 10, 15, 20, 100, 400, and/or other MHz), and which may be aggregated in various aspects. Carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL).
Communications using higher frequency bands may have higher path loss and a shorter range compared to lower frequency communications. Accordingly, certain base stations (e.g., 180 in
Wireless communications network 100 further includes a Wi-Fi AP 150 in communication with Wi-Fi stations (STAs) 152 via communications links 154 in, for example, a 2.4 GHz and/or 5 GHz unlicensed frequency spectrum.
Certain UEs 104 may communicate with each other using device-to-device (D2D) communications link 158. D2D communications link 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), a physical sidelink control channel (PSCCH), and/or a physical sidelink feedback channel (PSFCH).
EPC 160 may include various functional components, including: a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and/or a Packet Data Network (PDN) Gateway 172, such as in the depicted example. MME 162 may be in communication with a Home Subscriber Server (HSS) 174. MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, MME 162 provides bearer and connection management.
Generally, user Internet protocol (IP) packets are transferred through Serving Gateway 166, which itself is connected to PDN Gateway 172. PDN Gateway 172 provides UE IP address allocation as well as other functions. PDN Gateway 172 and the BM-SC 170 are connected to IP Services 176, which may include, for example, the Internet, an intranet, an IP Multimedia Subsystem (IMS), a Packet Switched (PS) streaming service, and/or other IP services.
BM-SC 170 may provide functions for MBMS user service provisioning and delivery. BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN), and/or may be used to schedule MBMS transmissions. MBMS Gateway 168 may be used to distribute MBMS traffic to the BSs 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and/or may be responsible for session management (start/stop) and for collecting eMBMS related charging information.
5GC 190 may include various functional components, including: an Access and Mobility Management Function (AMF) 192, other AMFs 193, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. AMF 192 may be in communication with Unified Data Management (UDM) 196.
AMF 192 is a control node that processes signaling between UEs 104 and 5GC 190. AMF 192 provides, for example, quality of service (QOS) flow and session management.
Internet protocol (IP) packets are transferred through UPF 195, which is connected to the IP Services 197, and which provides UE IP address allocation as well as other functions for 5GC 190. IP Services 197 may include, for example, the Internet, an intranet, an IMS, a PS streaming service, and/or other IP services.
In various aspects, a network entity or network node can be implemented as an aggregated base station, as a disaggregated base station, a component of a base station, an integrated access and backhaul (IAB) node, a relay node, a sidelink node, to name a few examples.
Each of the units, e.g., the CUS 210, the DUs 230, the RUs 240, as well as the Near-RT RICs 225, the Non-RT RICs 215 and the SMO Framework 205, may include one or more interfaces or be coupled to one or more interfaces configured to receive or transmit signals, data, or information (collectively, signals) via a wired or wireless transmission medium. Each of the units, or an associated processor or controller providing instructions to the communications interfaces of the units, can be configured to communicate with one or more of the other units via the transmission medium. For example, the units can include a wired interface configured to receive or transmit signals over a wired transmission medium to one or more of the other units. Additionally or alternatively, the units can include a wireless interface, which may include a receiver, a transmitter or transceiver (such as a radio frequency (RF) transceiver), configured to receive or transmit signals, or both, over a wireless transmission medium to one or more of the other units.
In some aspects, the CU 210 may host one or more higher layer control functions. Such control functions can include radio resource control (RRC), packet data convergence protocol (PDCP), service data adaptation protocol (SDAP), or the like. Each control function can be implemented with an interface configured to communicate signals with other control functions hosted by the CU 210. The CU 210 may be configured to handle user plane functionality (e.g., Central Unit-User Plane (CU-UP)), control plane functionality (e.g., Central Unit-Control Plane (CU-CP)), or a combination thereof. In some implementations, the CU 210 can be logically split into one or more CU-UP units and one or more CU-CP units. The CU-UP unit can communicate bidirectionally with the CU-CP unit via an interface, such as the E1 interface when implemented in an O-RAN configuration. The CU 210 can be implemented to communicate with the DU 230, as necessary, for network control and signaling.
The DU 230 may correspond to a logical unit that includes one or more base station functions to control the operation of one or more RUs 240. In some aspects, the DU 230 may host one or more of a radio link control (RLC) layer, a medium access control (MAC) layer, and one or more high physical (PHY) layers (such as modules for forward error correction (FEC) encoding and decoding, scrambling, modulation and demodulation, or the like) depending, at least in part, on a functional split, such as those defined by the 3rd Generation Partnership Project (3GPP). In some aspects, the DU 230 may further host one or more low PHY layers. Each layer (or module) can be implemented with an interface configured to communicate signals with other layers (and modules) hosted by the DU 230, or with the control functions hosted by the CU 210.
Lower-layer functionality can be implemented by one or more RUs 240. In some deployments, an RU 240, controlled by a DU 230, may correspond to a logical node that hosts RF processing functions, or low-PHY layer functions (such as performing fast Fourier transform (FFT), inverse FFT (IFFT), digital beamforming, physical random access channel (PRACH) extraction and filtering, or the like), or both, based at least in part on the functional split, such as a lower layer functional split. In such an architecture, the RU(s) 240 can be implemented to handle over the air (OTA) communications with one or more UEs 104. In some implementations, real-time and non-real-time aspects of control and user plane communications with the RU(s) 240 can be controlled by the corresponding DU 230. In some scenarios, this configuration can enable the DU(s) 230 and the CU 210 to be implemented in a cloud-based RAN architecture, such as a vRAN architecture.
The SMO Framework 205 may be configured to support RAN deployment and provisioning of non-virtualized and virtualized network elements. For non-virtualized network elements, the SMO Framework 205 may be configured to support the deployment of dedicated physical resources for RAN coverage requirements which may be managed via an operations and maintenance interface (such as an O1 interface). For virtualized network elements, the SMO Framework 205 may be configured to interact with a cloud computing platform (such as an open cloud (O-Cloud) 290) to perform network element life cycle management (such as to instantiate virtualized network elements) via a cloud computing platform interface (such as an O2 interface). Such virtualized network elements can include, but are not limited to, CUs 210, DUs 230, RUS 240 and Near-RT RICs 225. In some implementations, the SMO Framework 205 can communicate with a hardware aspect of a 4G RAN, such as an open eNB (O-eNB) 211, via an O1 interface. Additionally, in some implementations, the SMO Framework 205 can communicate directly with one or more RUs 240 via an O1 interface. The SMO Framework 205 also may include a Non-RT RIC 215 configured to support functionality of the SMO Framework 205.
The Non-RT RIC 215 may be configured to include a logical function that enables non-real-time control and optimization of RAN elements and resources, Artificial Intelligence/Machine Learning (AI/ML) workflows including model training and updates, or policy-based guidance of applications/features in the Near-RT RIC 225. The Non-RT RIC 215 may be coupled to or communicate with (such as via an A1 interface) the Near-RT RIC 225. The Near-RT RIC 225 may be configured to include a logical function that enables near-real-time control and optimization of RAN elements and resources via data collection and actions over an interface (such as via an E2 interface) connecting one or more CUs 210, one or more DUs 230, or both, as well as an O-eNB, with the Near-RT RIC 225.
In some implementations, to generate AI/ML models to be deployed in the Near-RT RIC 225, the Non-RT RIC 215 may receive parameters or external enrichment information from external servers. Such information may be utilized by the Near-RT RIC 225 and may be received at the SMO Framework 205 or the Non-RT RIC 215 from non-network data sources or from network functions. In some examples, the Non-RT RIC 215 or the Near-RT RIC 225 may be configured to tune RAN behavior or performance. For example, the Non-RT RIC 215 may monitor long-term trends and patterns for performance and employ AI/ML models to perform corrective actions through the SMO Framework 205 (such as reconfiguration via O1) or via creation of RAN management policies (such as A1 policies).
Generally, BS 102 includes various processors (e.g., 320, 330, 338, and 340), antennas 334a-t (collectively 334), transceivers 332a-t (collectively 332), which include modulators and demodulators, and other aspects, which enable wireless transmission of data (e.g., data source 312) and wireless reception of data (e.g., data sink 339). For example, BS 102 may send and receive data between BS 102 and UE 104. BS 102 includes controller/processor 340, which may be configured to implement various functions described herein related to wireless communications.
Generally, UE 104 includes various processors (e.g., 358, 364, 366, and 380), antennas 352a-r (collectively 352), transceivers 354a-r (collectively 354), which include modulators and demodulators, and other aspects, which enable wireless transmission of data (e.g., retrieved from data source 362) and wireless reception of data (e.g., provided to data sink 360). UE 104 includes controller/processor 380, which may be configured to implement various functions described herein related to wireless communications.
In regards to an example downlink transmission, BS 102 includes a transmit processor 320 that may receive data from a data source 312 and control information from a controller/processor 340. The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical HARQ indicator channel (PHICH), physical downlink control channel (PDCCH), group common PDCCH (GC PDCCH), and/or others. The data may be for the physical downlink shared channel (PDSCH), in some examples.
Transmit processor 320 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. Transmit processor 320 may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), PBCH demodulation reference signal (DMRS), and channel state information reference signal (CSI-RS).
Transmit (TX) multiple-input multiple-output (MIMO) processor 330 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) in transceivers 332a-332t. Each modulator in transceivers 332a-332t may process a respective output symbol stream to obtain an output sample stream. Each modulator may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from the modulators in transceivers 332a-332t may be transmitted via the antennas 334a-334t, respectively.
In order to receive the downlink transmission, UE 104 includes antennas 352a-352r that may receive the downlink signals from the BS 102 and may provide received signals to the demodulators (DEMODs) in transceivers 354a-354r, respectively. Each demodulator in transceivers 354a-354r may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator may further process the input samples to obtain received symbols.
MIMO detector 356 may obtain received symbols from all the demodulators in transceivers 354a-354r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. Receive processor 358 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 104 to a data sink 360, and provide decoded control information to a controller/processor 380.
In regards to an example uplink transmission, UE 104 further includes a transmit processor 364 that may receive and process data (e.g., for the PUSCH) from a data source 362 and control information (e.g., for the physical uplink control channel (PUCCH)) from the controller/processor 380. Transmit processor 364 may also generate reference symbols for a reference signal (e.g., for the sounding reference signal (SRS)). The symbols from the transmit processor 364 may be precoded by a TX MIMO processor 366 if applicable, further processed by the modulators in transceivers 354a-354r (e.g., for SC-FDM), and transmitted to BS 102.
At BS 102, the uplink signals from UE 104 may be received by antennas 334a-t, processed by the demodulators in transceivers 332a-332t, detected by a MIMO detector 336 if applicable, and further processed by a receive processor 338 to obtain decoded data and control information sent by UE 104. Receive processor 338 may provide the decoded data to a data sink 339 and the decoded control information to the controller/processor 340.
Memories 342 and 382 may store data and program codes for BS 102 and UE 104, respectively.
Scheduler 344 may schedule UEs for data transmission on the downlink and/or uplink.
In various aspects, BS 102 may be described as transmitting and receiving various types of data associated with the methods described herein. In these contexts, “transmitting” may refer to various mechanisms of outputting data, such as outputting data from data source 312, scheduler 344, memory 342, transmit processor 320, controller/processor 340, TX MIMO processor 330, transceivers 332a-t, antenna 334a-t, and/or other aspects described herein. Similarly, “receiving” may refer to various mechanisms of obtaining data, such as obtaining data from antennas 334a-t, transceivers 332a-t, RX MIMO detector 336, controller/processor 340, receive processor 338, scheduler 344, memory 342, and/or other aspects described herein.
In various aspects, UE 104 may likewise be described as transmitting and receiving various types of data associated with the methods described herein. In these contexts, “transmitting” may refer to various mechanisms of outputting data, such as outputting data from data source 362, memory 382, transmit processor 364, controller/processor 380, TX MIMO processor 366, transceivers 354a-t, antenna 352a-t, and/or other aspects described herein. Similarly, “receiving” may refer to various mechanisms of obtaining data, such as obtaining data from antennas 352a-t, transceivers 354a-t, RX MIMO detector 356, controller/processor 380, receive processor 358, memory 382, and/or other aspects described herein.
In some aspects, a processor may be configured to perform various operations, such as those associated with the methods described herein, and transmit (output) to or receive (obtain) data from another interface that is configured to transmit or receive, respectively, the data.
In particular,
Wireless communications systems may utilize orthogonal frequency division multiplexing (OFDM) with a cyclic prefix (CP) on the uplink and downlink. Such systems may also support half-duplex operation using time division duplexing (TDD). OFDM and single-carrier frequency division multiplexing (SC-FDM) partition the system bandwidth (e.g., as depicted in
A wireless communications frame structure may be frequency division duplex (FDD), in which, for a particular set of subcarriers, subframes within the set of subcarriers are dedicated for either DL or UL. Wireless communications frame structures may also be time division duplex (TDD), in which, for a particular set of subcarriers, subframes within the set of subcarriers are dedicated for both DL and UL.
In
In certain aspects, the number of slots within a subframe is based on a slot configuration and a numerology. For example, for slot configuration 0, different numerologies (μ) 0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots, respectively, per subframe. For slot configuration 1, different numerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, per subframe. Accordingly, for slot configuration 0 and numerology μ, there are 14 symbols/slot and 2μ slots/subframe. The subcarrier spacing and symbol length/duration are a function of the numerology. The subcarrier spacing may be equal to 2μ×15 kHz, where u is the numerology 0 to 5. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=5 has a subcarrier spacing of 480 kHz. The symbol length/duration is inversely related to the subcarrier spacing.
As depicted in
As illustrated in
A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE (e.g., 104 of
A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing.
Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI). Based on the PCI, the UE can determine the locations of the aforementioned DMRS. The physical broadcast channel (PBCH), which carries a master information block (MIB), may be logically grouped with the PSS and SSS to form a synchronization signal (SS)/PBCH block. The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN). The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs), and/or paging messages.
As illustrated in
In mmWave systems, beam forming may be important to overcome high path-losses. As described herein, beamforming may refer to establishing a link between a BS and UE, wherein both of the devices form a beam corresponding to each other. Both the BS and the UE find at least one adequate beam to form a communication link. BS-beam and UE-beam form what is known as a beam pair link (BPL). As an example, on the DL, a BS may use a transmit beam and a UE may use a receive beam corresponding to the transmit beam to receive the transmission. The combination of a transmit beam and corresponding receive beam may be a BPL.
As a part of beam management, beams which are used by BS and UE have to be refined from time to time because of changing channel conditions, for example, due to movement of the UE or other objects. Additionally, the performance of a BPL may be subject to fading due to Doppler spread. Because of changing channel conditions over time, the BPL should be periodically updated or refined. Accordingly, it may be beneficial if the BS and the UE monitor beams and new BPLs.
At least one BPL has to be established for network access. As described above, new BPLs may need to be discovered later for different purposes. The network may decide to use different BPLs for different channels, or for communicating with different BSs (TRPs) or as fallback BPLs in case an existing BPL fails.
The UE typically monitors the quality of a BPL and the network may refine a BPL from time to time.
For successful reception of at least a symbol of this “P1-signal”, the UE has to find an appropriate receive beam. It searches using available receive beams and applying a different UE-beam during each occurrence of the periodic P1-signal.
Once the UE has succeeded in receiving a symbol of the P1-signal it has discovered a BPL. The UE may not want to wait until it has found the best UE receive beam, since this may delay further actions. The UE may measure the reference signal receive power (RSRP) and report the symbol index together with the RSRP to the BS. Such a report will typically contain the findings of one or more BPLs.
In an example, the UE may determine a received signal having a high RSRP. The UE may not know which beam the BS used to transmit; however, the UE may report to the BS the time at which it observed the signal having a high RSRP. The BS may receive this report and may determine which BS beam the BS used at the given time.
The BS may then offer P2 and P3 procedures to refine an individual BPL. The P2 procedure refines the BS-beam of a BPL. For example, the BS may transmit a few symbols of a reference signal with different BS-beams that are spatially close to the BS-beam of the BPL (the BS performs a sweep using neighboring beams around the selected beam). In P2, the UE keeps its beam constant. Thus, while the UE uses the same beam as in the BPL (as illustrated in P2 procedure in
The P3 procedure refines the UE-beam of a BPL (see P3 procedure in
Over time, the BS and UE establish several BPLs. When the BS transmits a certain channel or signal, it lets the UE know which BPL will be involved, such that the UE may tune in the direction of the correct UE receive beam before the signal starts. In this manner, every sample of that signal or channel may be received by the UE using the correct receive beam. In an example, the BS may indicate for a scheduled signal (e.g., SRS, CSI-RS) or channel (e.g., PDSCH, PDCCH, PUSCH, PUCCH) which BPL is involved. In NR, this information may be referred to as a quasi co-location (QCL) indication.
Two antenna ports are quasi co-located (QCL) if properties of the channel over which a symbol on one antenna port is conveyed may be inferred from the channel over which a symbol on the other antenna port is conveyed. QCL supports, at least, beam management functionality, frequency/timing offset estimation functionality, and radio resource management (RRM) functionality.
The BS may use a BPL which the UE has received in the past. The transmit beam for the signal to be transmitted and the previously-received signal both point in a same direction or are QCL. The QCL indication may be needed by the UE (in advance of signal to be received) such that the UE may use a correct receive beam for each signal or channel. Some QCL indications may be needed from time to time when the BPL for a signal or channel changes and some QCL indications are needed for each scheduled instance. The QCL indication may be transmitted in the downlink control information (DCI), which may be part of the PDCCH channel. Because DCI is needed to control the information, it may be desirable that the number of bits needed to indicate the QCL is not too big. The QCL may be transmitted in a medium access control-control element (MAC-CE) or radio resource control (RRC) message.
According to one example, whenever the UE reports a BS beam that it has received with sufficient RSRP, and the BS decides to use this BPL in the future, the BS assigns it a BPL tag. Accordingly, two BPLs having different BS beams may be associated with different BPL tags. BPLs that are based on the same BS beams may be associated with the same BPL tag. Thus, according to this example, the tag is a function of the BS beam of the BPL.
As noted above, wireless systems, such as millimeter wave (mmW) systems, bring gigabit speeds to cellular networks, due to availability of large amounts of bandwidth. However, the unique challenges of heavy path-loss faced by such wireless systems necessitate new techniques such as hybrid beamforming (analog and digital), which are not present in 3G and 4G systems. Hybrid beamforming may enhance link budget/signal to noise ratio (SNR) that may be exploited during the RACH.
In such systems, the node B (NB) and the user equipment (UE) may communicate over active beam-formed transmission beams. Active beams may be considered paired transmission (Tx) and reception (Rx) beams between the NB and UE that carry data and control channels such as PDSCH, PDCCH, PUSCH, and PUCCH. As noted above, a transmit beam used by a NB and corresponding receive beam used by a UE for downlink transmissions may be referred to as a beam pair link (BPL). Similarly, a transmit beam used by a UE and corresponding receive beam used by a NB for uplink transmissions may also be referred to as a BPL.
Since the direction of a reference signal is unknown to the UE, the UE may evaluate several beams to obtain the best Rx beam for a given NB Tx beam. However, if the UE has to “sweep” through all of its Rx beams to perform the measurements (e.g., to determine the best Rx beam for a given NB Tx beam), the UE may incur significant delay in measurement and battery life impact. Moreover, having to sweep through all Rx beams is highly resource inefficient. Thus, aspects of the present disclosure provide techniques to assist a UE when performing measurements of serving cells and neighbor cells when using Rx beamforming.
As noted above, in certain wireless communications systems, a UE may use measured channel quality (e.g., metrics such as RSRP, SINR, Spectral efficiency) to determine an uplink (UL) serving beam (e.g., UL_SUB) and a downlink (DL) serving beam (e.g., DL_SUB).
For example, DL_SUB may define a UE beam used to serve DL control and data channels (e.g., PDCCH and PDSCH). DL_SUB may also be used for CSI-RS acquisition, synchronization signal block (SSB)/tracking reference signal (TRS)-based loop tracking (e.g., frequency tracking loops (FTL), time tracking loops (TTL), and/or power tracking loops (e.g., automatic gain control (AGC)). UL_SUB may define a UE beam used to serve UL control and data channels (e.g., PUCCH and PUSCH). UL_SUB may also be used for SRS. SSB/TRS-based loop tracking (e.g., for TTL/FTL/AGC) if it's de-coupled from DL SUB.
In some cases, UE beam selection may be fully based on SSB RSRP. In some cases, a VSB based on a serving cell SSB transmission (e.g., quasi co-located (QCLed) to active TCI) may be determined to be a (coupled) UL and DL UE beam. For example, on a per-SSB basis, the best UE beams may be selected based on an SSB RSRP metric (e.g., collapsing between 2 receive ports where the collapsing rule may be based on an average, max, etc.) with certain hysteresis maintained as a virtual serving UE beam (VSB), which may be used for a layer 1 (L1) SSB RSRP report. In some cases, a VSB on a serving SSB (e.g., quasi co-located (QCLed) to active TCI) may be determined to be a (coupled) UL and DL UE beam.
However, as noted above, an SSB beam may not be the same as a traffic beam, so UE beam selection based on an SSB beam may be suboptimal for traffic. Additionally, an SSB beam has an inherent rank-1 precoder, which may be different from a precoding matrix indicator (PMI) on a traffic beam for both rank-1 and rank-2.
Aspects of the present disclosure provide for what may be considered more advanced UE beam selection techniques (e.g., based on CSI-RS rather than solely SSB-based). For example, in some cases, beam selection may be based on beam dithering with spectral efficiency (SPEFF)/RSRP, CSI-RS P3 procedures, and/or UL and DL beam de-coupling.
Aspects of the present disclosure provide techniques for CSI-RS based UE UL and DL beam selection on a per-rank basis. For example, when UL and DL beam de-coupling is supported, aspects of the present disclosure may enable a UE to select optimal UL and DL beams separately for a given rank. This approach may be advantageous, since the best DL beam may not be the best UL beam, especially when there is a PMI/rank mismatch. Selecting optimal beams (e.g., separately selecting decoupled beams) for UL and DL in this manner may provide higher signal quality, improved coverage, increased data rates, and improved overall system capacity.
As illustrated at 602, a network entity may transmit CSI-RS on a plurality of different beams. As illustrated at 604, a UE may measure the CSI-RS associated with a plurality of different beams. For example, in some aspects, UE beam sweeping may be performed on a CSI-RS resource (e.g., per a P3 procedure described above with reference to
As illustrated at 606, the UE may determine an uplink (UL) rank and a downlink (DL) rank.
As illustrated at 608, the UE may select, from the plurality of different beams, a DL beam (e.g., DL_SUB), based on the CSI-RS measurements and the DL rank. In some aspects, for example, DL_SUB may be determined as the best DL serving beam based on CSI-RS measurements and/or a downlink rank. For example, DL-SUB may be determined in terms of the best wideband (WB) SPEFF on the PMI aligned with the DL_rank.
As illustrated at 610, the UE may select, from the different beams, a UL beam (e.g., UL_SUB), based on the CSI-RS measurements, the UL rank, and the downlink rank. In some aspects, for example, UL_SUB may be determined based on the various CSI-RS measurements discussed above, an uplink rank, and/or a downlink rank.
As illustrated at 612, the UE may communicate with the network entity using the selected UL beam and the selected DL beam.
As noted above with reference to 606 of
According to certain aspects, the UL Rank and DL Rank may be determined using a mechanism involving filtering, which may be slower than the grant-based mechanism. For example, such a mechanism may involve accumulating (e.g., averaging or summing) a rank in each UL and DL grant, and applying deep filtering (e.g. with filter length of 20 ms). In some aspects, the rank may be changed (flipped) only if the filtered rank exceeds a threshold. Such a mechanism may avoid frequent beam toggling, but may result in delays associated with beam switching.
As illustrated in table 700 of
As illustrated in
If port-1 is used for the CSI-RS, UL_SUB may be determined by the following equation:
If port diversity or port switch diversity (PsDiv) is used for the CSI-RS, UL_SUB may be determined by the following equation:
If transmit antenna port virtualization (TAV) or cyclic delay diversity (CDD) is used for the CSI-RS, UL_SUB may be determined by the following equation:
In such cases, UL_SUB is not selected to be the same as DL_SUB, because when using DL_SUB with a maximum DL Rank of 2, SPEFF does not necessarily improve for UL communications with a UL Rank of 1, as rank-1 PMI operates on row of a channel matrix, where the UL channel is a conjugate of the DL channel.
As also illustrated in
For example, UL_SUB may be selected to be the best beam in terms of WB SPEFF (e.g., the beam having the greatest WB SPEFF) on rank-2 PMI. In such cases, UL_SUB is not selected to be the same as DL_SUB, because when using DL_SUB with a maximum DL Rank of 1, SPEFF does not necessarily improve for UL communications with a UL Rank of 2.
Method 800 begins at step 805 with measuring channel state information (CSI) reference signals (CSI-RS) associated with a plurality of beams. In some cases, the operations of this step refer to, or may be performed by, circuitry for measuring and/or code for measuring as described with reference to
Method 800 then proceeds to step 810 with determining an uplink rank and a downlink rank. In some cases, the operations of this step refer to, or may be performed by, circuitry for determining and/or code for determining as described with reference to
Method 800 then proceeds to step 815 with selecting, from the plurality of beams, a downlink beam for processing downlink transmissions, based on the CSI RS measurements and the downlink rank. In some cases, the operations of this step refer to, or may be performed by, circuitry for selecting and/or code for selecting as described with reference to
Method 800 then proceeds to step 820 with selecting, from the plurality of beams, an uplink beam for processing uplink transmissions, based on the CSI RS measurements, the uplink rank, and the downlink rank. In some cases, the operations of this step refer to, or may be performed by, circuitry for selecting and/or code for selecting as described with reference to
In some aspects, the method 800 further includes determining, based on the CSI-RS measurements, precoding matrix indicators (PMIs) for the plurality of beams, corresponding to the downlink rank. In some cases, the operations of this step refer to, or may be performed by, circuitry for determining and/or code for determining as described with reference to
In some aspects, the method 800 further includes determining wideband spectrum efficiency (SPEFF) values for the PMIs, wherein the downlink beam is selected based on the wideband SPEFF values. In some cases, the operations of this step refer to, or may be performed by, circuitry for determining and/or code for determining as described with reference to
In some aspects, selecting the uplink beam comprises selecting a same beam for the downlink beam and the uplink beam if the downlink rank and uplink rank are a same rank that is greater than 1.
In some aspects, if the uplink rank is 1, selecting the uplink beam is based on which of one or more ports is used for the CSI-RS.
In some aspects, if the uplink rank is 1, selecting the uplink beam is based on whether port diversity is used for the CSI-RS.
In some aspects, if the uplink rank is 1, selecting the uplink beam is based on whether at least one of transmit antenna port virtualization (TAV) or cyclic delay diversity (CDD) is used for the CSI-RS.
In some aspects, determining at least one of the uplink rank or the downlink rank is based on at least one of: a rank value indicated in at least one uplink grant; or a rank value indicated in at least one downlink grant.
In some aspects, determining at least one of the uplink rank or the downlink rank is based on at least one of: an accumulation of rank values indicated in multiple uplink grants; or an accumulation of rank values indicated in multiple downlink grants.
In one aspect, method 800, or any aspect related to it, may be performed by an apparatus, such as communications device 900 of
Note that
The communications device 900 includes a processing system 905 coupled to the transceiver 955 (e.g., a transmitter and/or a receiver). The transceiver 955 is configured to transmit and receive signals for the communications device 900 via the antenna 960, such as the various signals as described herein. The processing system 905 may be configured to perform processing functions for the communications device 900, including processing signals received and/or to be transmitted by the communications device 900.
The processing system 905 includes one or more processors 910. In various aspects, the one or more processors 910 may be representative of one or more of receive processor 358, transmit processor 364, TX MIMO processor 366, and/or controller/processor 380, as described with respect to
In the depicted example, computer-readable medium/memory 930 stores code (e.g., executable instructions), such as code for measuring 935, code for determining 940, and code for selecting 945. Processing of the code for measuring 935, code for determining 940, and code for selecting 945 may cause the communications device 900 to perform the method 800 described with respect to
The one or more processors 910 include circuitry configured to implement (e.g., execute) the code stored in the computer-readable medium/memory 930, including circuitry such as circuitry for measuring 915, circuitry for determining 920, and circuitry for selecting 925. Processing with circuitry for measuring 915, circuitry for determining 920, and circuitry for selecting 925 may cause the communications device 900 to perform the method 800 described with respect to
Various components of the communications device 900 may provide means for performing the method 800 described with respect to
Implementation examples are described in the following numbered clauses:
The preceding description is provided to enable any person skilled in the art to practice the various aspects described herein. The examples discussed herein are not limiting of the scope, applicability, or aspects set forth in the claims. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects. For example, changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various actions may be added, omitted, or combined. Also, features described with respect to some examples may be combined in some other examples. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method that is practiced using other structure, functionality, or structure and functionality in addition to, or other than, the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.
The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an ASIC, a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may 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, a system on a chip (SoC), or any other such configuration.
As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).
As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.
The methods disclosed herein comprise one or more actions for achieving the methods. The method actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of actions is specified, the order and/or use of specific actions may be modified without departing from the scope of the claims. Further, the various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor.
The following claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims. Within a claim, reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for”. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.