Uplink MIMO reference signals and data transmission schemes

Certain aspects of the present disclosure relate to methods and apparatus for Uplink MIMO reference signals and data transmission schemes communications systems operating according to 5G technologies. For example, one or more techniques for enabling PRG selection and conveying that selection are provided. In some cases, precoder selection techniques may be provided. Further, in some cases, techniques may be provided to distinguish OFDM and DFT-s-OFDM by using different ports.

BACKGROUND

Field of the Disclosure

The present disclosure relates generally to communication systems, and more particularly, to methods and apparatus for Uplink MIMO reference signals and data transmission schemes communications systems operating according to 5G technologies.

Description of Related Art

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is new radio (NR), for example, 5G radio access. NR is a set of enhancements to the LTE mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) as well as support beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues to increase, there exists a desire for further improvements in 5G technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

Devices in a wireless network may communicate using SRS transmissions. In some cases, SRS may be precoded differently for different subbands, and different precoders may use a different physical resource group (PRG) selection of the SRS allocated bandwidth. However, precoder selection can be challenging. Also, defining techniques for determining a PRG selection for SRS transmission can be challenging. In some cases, both OFDM and DFT-s-OFDM waveforms may be supported in uplink. However, the precoder matrix, Tx power scaling factor, and/or modulated coding scheme (MCS) for OFDM and DFT-s-OFDM may be different.

Thus, aspects of the present disclosure present techniques for enabling PRG selection and conveying that selection. In some cases, precoder selection techniques may be provided. Further, in some cases, techniques may be provided to distinguish OFDM and DFT-s-OFDM by using different ports.

Certain aspects provide a method for wireless communication by a user equipment (UE). The method generally includes determining a physical resource block group (PRG) size for the UE to use for sounding reference signal (SRS) transmission, wherein the SRS transmission is allocated over a bandwidth including a plurality of PRGs, and transmitting the SRS transmission to a base station (BS) in accordance with the determination, wherein at least two of the plurality of PRGs have different precoding.

Certain aspects provide a method for wireless communication by a base station. The method generally includes determining a physical resource block group (PRG) size for a user equipment (UE) to use for sounding reference signal (SRS) transmission, and receiving an SRS transmitted from the UE in accordance with the determination.

Certain aspects provide a method for wireless communication by an apparatus. The method generally includes precoding a first sequence for a sounding reference signal (SRS) transmission on a first subband resource using a first precoder, precoding a second sequence for the sounding reference signal (SRS) transmission on a second subband resource using a second precoder, transmitting the first precoded sequence of the reference signal SRS transmission on the first subband resource in a first transmission time interval, and transmitting the second precoded sequence of the reference signal SRS transmission on the second subband resource in a second transmission time interval.

Certain aspects provide a method for wireless communication by an apparatus. The method generally includes receiving a first portion of a reference signal an SRS transmission from a user equipment (UE)transmitting apparatus on a first subband resource in a first transmission time interval, wherein the first portion was precoded by the UE transmitting apparatus using a first precoder, receiving a second portion of the reference signal SRS transmission from the UE transmitting apparatus on a second subband resource in a second transmission time interval, wherein the second portion was precoded by the UE transmitting apparatus using a second precoder, and processing the first portion and the second portions of the reference signal SRS transmission based on the first precoder and the second precoders.

Certain aspects provide a method for wireless communication by a user equipment. The method generally includes determining whether an uplink transmission is to be sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal, and select one or more ports for sending the uplink transmission based on the determination.

Certain aspects provide a method for wireless communication by a base station. The method generally includes determining, based on one or more ports used by a user equipment (UE) for sending an uplink transmission, whether the uplink transmission was sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal, and processing the uplink transmission based on the determination.

Aspects generally include methods, apparatus, systems, computer readable mediums, and processing systems, as substantially described herein with reference to and as illustrated by the accompanying drawings.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for new radio (NR) (new radio access technologies or 5G technologies).

Example Wireless Communications System

FIG. 1illustrates an example wireless network100, such as a 5G network, in which aspects of the present disclosure may be performed.

As illustrated inFIG. 1, the wireless network100may include a number of BSs110and other network entities. A BS may be a station that communicates with UEs. Each BS110may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a Node B and/or a Node B subsystem serving this coverage area, depending on the context in which the term is used. In 5G systems, the term “cell” and eNB, Node B, 5G NB, AP, NR BS, NR BS, or TRP may be interchangeable. In some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile base station. In some examples, the base stations may be interconnected to one another and/or to one or more other base stations or network nodes (not shown) in the wireless network100through various types of backhaul interfaces such as a direct physical connection, a virtual network, or the like using any suitable transport network.

While aspects of the examples described herein may be associated with LTE technologies, aspects of the present disclosure may be applicable with other wireless communications systems, such as 5G. 5G may utilize OFDM with a CP on the uplink and downlink and include support for half-duplex operation using time division duplex (TDD). A single component carrier bandwidth of 100 MHz may be supported. 5G resource blocks may span 12 sub-carriers with a sub-carrier bandwidth of 75 kHz over a 0.1 ms duration. Each radio frame may consist of 50 subframes with a length of 10 ms. Consequently, each subframe may have a length of 0.2 ms. Each subframe may indicate a link direction (i.e., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for 5G may be as described in more detail below with respect toFIGS. 6 and 7. Beamforming may be supported and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells. Alternatively, 5G may support a different air interface, other than an OFDM-based. 5G networks may include entities such CUs and/or DUs.

In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station) allocates resources for communication among some or all devices and equipment within the scheduling entity's service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. Base stations are not the only entities that may function as a scheduling entity. That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more subordinate entities (e.g., one or more other UEs). In this example, the UE is functioning as a scheduling entity, and other UEs utilize resources scheduled by the UE for wireless communication. A UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may optionally communicate directly with one another in addition to communicating with the scheduling entity.

FIG. 2illustrates an example logical architecture of a distributed radio access network (RAN)200, which may be implemented in the wireless communication system illustrated inFIG. 1. A 5G access node206may include an access node controller (ANC)202. The ANC may be a central unit (CU) of the distributed RAN200. The backhaul interface to the next generation core network (NG-CN)204may terminate at the ANC. The backhaul interface to neighboring next generation access nodes (NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs208(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, or some other term). As described above, a TRP may be used interchangeably with “cell.”

The architecture may share features and/or components with LTE. According to aspects, the next generation AN (NG-AN)210may support dual connectivity with 5G. The NG-AN may share a common fronthaul for LTE and 5G.

The architecture may enable cooperation between and among TRPs208. For example, cooperation may be preset within a TRP and/or across TRPs via the ANC202. According to aspects, no inter-TRP interface may be needed/present.

According to aspects, a dynamic configuration of split logical functions may be present within the architecture200. As will be described in more detail with reference toFIG. 5, the Radio Resource Control (RRC) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, Medium Access Control (MAC) layer, and a Physical (PHY) layers may be adaptably placed at the DU or CU (e.g., TRP or ANC, respectively). According to certain aspects, a BS may include a central unit (CU) (e.g., ANC202) and/or one or more distributed units (e.g., one or more TRPs208).

FIG. 3illustrates an example physical architecture of a distributed RAN300, according to aspects of the present disclosure. A centralized core network unit (C-CU)302may host core network functions. The C-CU may be centrally deployed. C-CU functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU)304may host one or more ANC functions. Optionally, the C-RU may host core network functions locally. The C-RU may have distributed deployment. The C-RU may be closer to the network edge.

FIG. 4illustrates example components of the BS110and UE120illustrated inFIG. 1, which may be used to implement aspects of the present disclosure. As described above, the BS may include a TRP. One or more components of the BS110and UE120may be used to practice aspects of the present disclosure. For example, antennas452, Tx/Rx222, processors466,458,464, and/or controller/processor480of the UE120and/or antennas434, processors460,420,438, and/or controller/processor440of the BS110may be used to perform the operations described herein and illustrated with reference toFIG. 13.

FIG. 4shows a block diagram of a design of a BS110and a UE120, which may be one of the BSs and one of the UEs inFIG. 1. For a restricted association scenario, the base station110may be the macro BS110cinFIG. 1, and the UE120may be the UE120y. The base station110may also be a base station of some other type. The base station110may be equipped with antennas434athrough434t, and the UE120may be equipped with antennas452athrough452r.

At the UE120, the antennas452athrough452rmay receive the downlink signals from the base station110and may provide received signals to the demodulators (DEMODs)454athrough454r, respectively. Each demodulator454may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator454may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector456may obtain received symbols from all the demodulators454athrough454r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. For example, MIMO detector456may provide detected RS transmitted using techniques described herein. A receive processor458may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE120to a data sink460, and provide decoded control information to a controller/processor480. According to one or more cases, CoMP aspects can include providing the antennas, as well as some Tx/Rx functionalities, such that the CoMP aspects reside in distributed units. For example, some Tx/Rx processings can be done in the central unit, while other processing can be done at the distributed units. For example, in accordance with one or more aspects as shown in the diagram, the BS mod/demod432may be in the distributed units.

The controllers/processors440and480may direct the operation at the base station110and the UE120, respectively. The processor440and/or other processors and modules at the base station110may perform or direct, e.g., the execution of the functional blocks illustrated inFIG. 12, and/or other processes for the techniques described herein. The processor480and/or other processors and modules at the UE120may also perform or direct processes for the techniques described herein. The memories442and482may store data and program codes for the BS110and the UE120, respectively. A scheduler444may schedule UEs for data transmission on the downlink and/or uplink.

FIG. 5illustrates a diagram500showing examples for implementing a communications protocol stack, according to aspects of the present disclosure. The illustrated communications protocol stacks may be implemented by devices operating in a in a 5G system (e.g., a system that supports uplink-based mobility). Diagram500illustrates a communications protocol stack including a Radio Resource Control (RRC) layer510, a Packet Data Convergence Protocol (PDCP) layer515, a Radio Link Control (RLC) layer520, a Medium Access Control (MAC) layer525, and a Physical (PHY) layer530. In various examples the layers of a protocol stack may be implemented as separate modules of software, portions of a processor or ASIC, portions of non-collocated devices connected by a communications link, or various combinations thereof. Collocated and non-collocated implementations may be used, for example, in a protocol stack for a network access device (e.g., ANs, CUs, and/or DUs) or a UE.

A second option505-bshows a unified implementation of a protocol stack, in which the protocol stack is implemented in a single network access device (e.g., access node (AN), new radio base station (NR BS), a new radio Node-B (NR NB), a network node (NN), or the like). In the second option, the RRC layer510, the PDCP layer515, the RLC layer520, the MAC layer525, and the PHY layer530may each be implemented by the AN. The second option505-bmay be useful in a femto cell deployment.

Regardless of whether a network access device implements part or all of a protocol stack, a UE may implement an entire protocol stack (e.g., the RRC layer510, the PDCP layer515, the RLC layer520, the MAC layer525, and the PHY layer530).

FIG. 6is a diagram600showing an example of a DL-centric subframe. The DL-centric subframe may include a control portion602. The control portion602may exist in the initial or beginning portion of the DL-centric subframe. The control portion602may include various scheduling information and/or control information corresponding to various portions of the DL-centric subframe. In some configurations, the control portion602may be a physical DL control channel (PDCCH), as indicated inFIG. 6. The DL-centric subframe may also include a DL data portion604. The DL data portion604may sometimes be referred to as the payload of the DL-centric subframe. The DL data portion604may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE). In some configurations, the DL data portion604may be a physical DL shared channel (PDSCH).

The DL-centric subframe may also include a common UL portion606. The common UL portion606may sometimes be referred to as an UL burst, a common UL burst, and/or various other suitable terms. The common UL portion606may include feedback information corresponding to various other portions of the DL-centric subframe. For example, the common UL portion606may include feedback information corresponding to the control portion602. Non-limiting examples of feedback information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of information. The common UL portion606may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information. As illustrated inFIG. 6, the end of the DL data portion604may be separated in time from the beginning of the common UL portion606. This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the subordinate entity (e.g., UE)) to UL communication (e.g., transmission by the subordinate entity (e.g., UE)). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 7is a diagram700showing an example of an UL-centric subframe. The UL-centric subframe may include a control portion702. The control portion702may exist in the initial or beginning portion of the UL-centric subframe. The control portion702inFIG. 7may be similar to the control portion described above with reference toFIG. 6. The UL-centric subframe may also include an UL data portion704. The UL data portion704may sometimes be referred to as the payload of the UL-centric subframe. The UL portion may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, the control portion702may be a physical DL control channel (PDCCH).

As illustrated inFIG. 7, the end of the control portion702may be separated in time from the beginning of the UL data portion704. This time separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). The UL-centric subframe may also include a common UL portion706. The common UL portion706inFIG. 7may be similar to the common UL portion706described above with reference toFIG. 7. The common UL portion706may additional or alternative include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

Example Physical Resource Block Group Size Selection for Srs Transmission

FIG. 8illustrates example operations for wireless communications by a UE, in accordance with aspects of the present disclosure.

Operations800begin, at block802, with the UE determining a physical resource block group (PRG) size for the UE to use for sounding reference signal (SRS) transmission, wherein the SRS transmission is allocated over a bandwidth including a plurality of PRGs. In one or more cases the determination may be based on signaling from the base station. In other cases, the determination may be based a number of ports used for the SRS transmission. The PRG size may correspond to a whole operating bandwidth if the number of layers is below a predetermined number. In one example, the predetermined number is 4. In one or more cases the determination may be based on power headroom of the UE. According to one or more other aspects the PRG size may correspond to a whole operating bandwidth if the UE is transmitting at full power such that there is no longer any UE power headroom available. The PRG size or a number of layers for the SRS transmission may be reused for the downlink. For example, the PRG size or a number of layers for the SRS transmission may be used for transmitting one or more downlink reference signals from the BS to the UE.

The UE may also include, at block804, transmitting the SRS transmission to a base station (BS) in accordance with the determination, wherein same precoding is used within a PRG. For example, the UE may transmit the SRS to a base station based on the PRG size determined in a preceding operation. As shown at806, the method may optionally also include transmitting an indication of a recommended at least one of PRG size or a number of layers for the SRS transmission to the base station. Providing the indication to the BS helps inform the BS of the determination made by the UE regarding, for example, a determined PRG size. Having the indication may therefore help the BS process that which is transmitted to the BS from the UE in the form of an SRS transmission based on the determination.

FIG. 8Aillustrates a communications device800A that may include various means-plus-function components configured to perform the operations illustrated inFIG. 8. For example, at802A, the communications device800A includes means for performing the operations illustrated at802inFIG. 8. Particularly, in one or more cases, the purpose of the means802A is to serve as a processing element for the UE for determining one or more properties for use when transmitting reference signals. For example, the means802A may be configured to determine a PRG size for the UE to use for SRS transmission. In some cases, the SRS transmission may be allocated over a bandwidth including a plurality of PRGs. Additionally, at804A, the communications device800A includes means for performing the operations illustrated at804inFIG. 8. Particularly, the purpose of the means804A, in one or more cases, is to serve as a transmitter for the UE for transmitting one or more reference signals to a base station. For example, the means804A may be configured to transmit the SRS transmission to a base station (BS) based on the PRG size determined by the means802A. In some cases, a same precoding is used within a PRG. In one or more cases, at least two of the plurality of PRGs may have different precoding. Optionally, at806A, the communications device800A may further include means for performing the operations illustrated at806inFIG. 8. Particularly, the communication device800A may include means for transmitting an indication of a recommended at least one of PRG size or a number of layers for the SRS transmission to the base station.

FIG. 9illustrates example operations for wireless communications by a base station, in accordance with aspects of the present disclosure. For example, the base station may be configured to determine the PRG size the UE will use for SRS transmissions that the BS may then use when receiving SRS transmission from the UE.

Specifically, operations900begin, at block902, with the base station determining a physical resource block group (PRG) size for a user equipment (UE) to use for sounding reference signal (SRS) transmission. The determination may be based a number of ports used for the SRS transmission. The PRG size may correspond to a whole operating bandwidth if the number of layers is below a predetermined number. The determination may be based on power headroom of the UE. The PRG size may correspond to a whole operating bandwidth if there is no UE power headroom available because the UE is transmitting at full power.

The base station also may include, as shown at block904, receiving an SRS transmitted from the UE in accordance with the determination. For example, the base station may have a receiver that receives a transmission. The transmission may originate from the UE and may include the SRS transmission that is sent in accordance with the determined PRG size. For example, the SRS transmission may be precoded differently depending on the subband of the SRS transmission. Further, as shown at906, the method may optionally include receiving, from the UE, an indication of a recommended at least one of PRG size or a number of layers for the SRS transmission. The BS may take this indication into consideration when determining the PRG size. In one or more cases, the BS may use the indication when received and may otherwise use a calculated value in other cases were such an indication is not received.

FIG. 9Aillustrates a communications device900A that may include various means-plus-function components configured to perform the operations illustrated inFIG. 9. For example, at902A, the communications device900A includes means for performing the operations illustrated at902inFIG. 9. Particularly, in one or more cases, the purpose of the means902A is to serve as a processing element for the BS for determining one or more properties for use on received reference signals from a UE. For example, the means902A may be configured to determine a PRG size for a UE to use for SRS transmission. Additionally, at904A, the communications device900A includes means for performing the operations illustrated at904inFIG. 9. Particularly, the purpose of the means904A, in one or more cases, is to serve as a receiver for the BS for receiving one or more reference signals in one or more subbands from a UE. For example, the means904A may be configured to receive an SRS transmission from a UE based on the PRG size determined by the means902A. Optionally, at906A, the communications device900A may further include means for performing the operations illustrated at906inFIG. 9. Particularly, the communication device900A may include means for receiving, from the UE, an indication of a recommended at least one of PRG size or a number of layers for the SRS transmission

In some cases, the method may include signaling information regarding the PRG size to the UE. In some cases, the PRG size or a number of layers for the SRS transmission may be reused for the downlink. For example, the PRG size or a number of layers for the SRS transmission may be used for transmitting one or more downlink reference signals from the BS to the UE. At least one factor that may contribute to this reuse includes channel reciprocity. Particularly, because of channel reciprocity, the DL channel may be estimated from the UL measurements.

For SRS transmission, SRS may be precoded differently for different subbands. For example,FIG. 10illustrates subband precoding, in accordance with aspects of the present disclosure. According to some aspects, an SRS bandwidth1001is shown that spans a number of subbands1002,1003, and1004. In this example there are three subbands1002,1003, and1004which correspond to the three shown precoders and physical resource groups (PRGs). Specifically, the SRS bandwidth corresponds to PRG1, PRG2, and PRG3as shown. Further, PRG1, PRG2, and PRG3are precoded using the corresponding precoders Precoder1, Precoder2, and Precoder3, respectively.

According to one or more cases, the units that define the parameters and size for different subbands of a PRG (Physical Resource Group) may vary. For example, a PRG may be 2{circumflex over ( )}n*PRB (Physical Resource Block) and the PRB may be 12 tones. In one or more cases, the PRG may be any number of sizes such as, but not limited to 1, 2, 4, 8, and so on, which corresponds to 2{circumflex over ( )}n*PRB, where n=0, 1, 2, 3. and so on. Further, the PRG is not limited to a specific number of tones and may therefore be any number of tones depending on the specific embodiment.

The PRG size may be configured by a UE and/or a gNB. In accordance with one or more aspects, the PRG size may also be configured based on number of layers (ports). According to one or more cases, the PRG may be a whole band and no subband precoding may be applicable if a number of layers is less than a predetermined number, for example 4.

According to one or more aspects, in addition to the PRG size being configurable by a UE and/or a gNB, the PRG size may also be configured based on UE power headroom. Take for instance, in accordance with one or more aspects, a case when there is no UE power headroom available because the UE is transmitting at full power. In this case with no UE power headroom a full band precoding may be chosen. For example, the UE may be transmitting at full power if there is no UE power headroom. In this case the PRG may be equal to a whole SRS band.

In accordance with one or more aspects, in a case where there is UE power headroom then one may then be free to use subband precoding. In this example, when there is UE power headroom the PRG size may therefore be less than the whole SRS band.

FIG. 11illustrates an example of a wireless system transmitting in accordance with aspects of the present disclosure. Particularly,FIG. 11shows a gNB1101transmitting to a UE1102and then shows the UE1102responding to the gNB1101.

Specifically, the gNB1101may configure the number of layers for SRS and/or a PRG size for SRS, which may be determined by the number of layers. The gNB1101then transmits the number of layers and/or a PRG size to the UE1102. The UE1102then generates a Precoded SRS based on the received transmissions from the gNB1101. The UE1102may then transmit the Precoded SRS with configured layers and PRG size. In accordance with one or more cases, a precoding matrix for SRS may be configured such that the precoding matrix remains constant for each PRG.

FIG. 12illustrates another example of a wireless system transmitting in accordance with aspects of the present disclosure. Particularly,FIG. 12shows a UE1202transmitting a number of layers and/or a PRG size to a gNB1201and then shows the UE1202also transmitting to the gNB1201a precoded SRS.

Specifically,FIG. 12shows the UE1202transmitting one or more indication that may contain suggestions of the number of layers for SRS and/or also the PRG size for SRS, which may be determined by the number of layers. The UE1202may then transmit a precoded SRS that is configured based on the suggested layers and/or PRG size. In accordance with one or more cases, a precoding matrix for SRS may be configured such that the precoding matrix remains constant for each PRG.

In one or more cases, the wireless system may be configured such that the number of layers and/or the PRG size may be reused for downlink transmissions as well as the uplink transmissions as described above. In particular the SRS (uplink) may be also used for downlink channel estimation based on channel reciprocity.

Example of Time Splitting Symbols

FIG. 13illustrates example operations1300for wireless communications by an apparatus, in accordance with aspects of the present disclosure. Particularly, as shown inFIG. 13, the operations1300may include precoding multiple sequences of a reference signal with different precoders and then transmitting the precoded sequences of the reference signal.

Specifically, operations1300begin, at block1302, with the apparatus precoding a first sequence for a reference signal transmission on a first resource using a first precoder. In one or more cases, the apparatus may be at least one of a user equipment (UE) or a base station (BS). Further, the reference signal may at least be one of a sounding reference signal (SRS) when the apparatus is a UE and a downlink (DL) reference signal when the apparatus is a BS. Additionally, in some cases, the first resource may be at least one of a first subband and/or a first port.

The operations1300also include, at block1304, precoding a second sequence for the reference signal transmission on a second resource using a second precoder. In one or more cases, the second resource may be at least one of a second subband and/or a second port. In accordance with one or more aspects, the first and second precoders may be different. In one or more cases, different physical resource block groups (PRG) sizes may be used for the first and second SRS transmissions.

Operations1300further include, at block1306, transmitting the first precoded sequence of the reference signal transmission on the first resource in a first transmission time interval. In one or more cases, the apparatus that precodes and transmits the first sequence may be a user equipment (UE). In these cases the reference signal may be a sounding reference signal (SRS). In accordance with other cases, the apparatus that precodes and transmits the first sequence may be a base station (BS). In these cases the reference signal may be a downlink (DL) reference signal. In accordance with one or more cases, the first resource is at least one of a first subband or a first port.

Further, operations1300includes, at block1308, transmitting the second precoded sequence of the reference signal transmission on the second resource in a second transmission time interval. In one or more cases, the first transmission time interval is different from the second transmission time interval. In one or more cases, the apparatus that precodes and transmits the second sequence may be a user equipment (UE). In these cases the reference signal may be a sounding reference signal (SRS). In accordance with other cases, the apparatus that precodes and transmits the second sequence may be a base station (BS). In these cases the reference signal may be a downlink (DL) reference signal. In accordance with one or more cases, the second resource is at least one of a second subband or a second port.

FIG. 13Aillustrates a communications device1300A that may include various means-plus-function components configured to perform the operations illustrated inFIG. 13. For example, at1302A, the communications device1300A includes means for performing the operations illustrated at1302inFIG. 13. Particularly, in one or more cases, the purpose of the means1302A is to serve as a processing element of the apparatus for precoding a first sequence of a reference signal that may be transmitted later. For example, according to one or more cases, an IDFT size may be used for the first sequence and may scale with a number of tones in the first subband. In one or more cases, the means1302A may add at least one cyclic prefix to the first precoded sequence. Further, the IDFT size may be scaled by one half and the number of tones in the first subband may also be scaled by half.

Additionally, at1304A, the communications device1300A includes means for performing the operations illustrated at1304inFIG. 13. Particularly, in one or more cases, the purpose of the means1304A is to serve as a processing element of the apparatus for precoding a second sequence of a reference signal that may be transmitted later. For example, according to one or more cases, an IDFT size may be used for the second sequence and may scale with a number of tones in the second subband. In one or more cases the means1304A may add at least one cyclic prefix to at least the second precoded sequence. Further, the IDFT size may be scaled by one half and the number of tones in the second subband may also be scaled by half.

Further, at1306A, the communications device1300A includes means for performing the operations illustrated at1306inFIG. 13. Particularly, the purpose of the means1306A, in one or more cases, is to serve as a transmitter for the apparatus for transmitting one or more portions of a reference signal. For example, the means1306A may be configured to transmit the first precoded sequence of an SRS transmission precoded by the means1302A. Additionally, at1308A, the communications device1300A includes means for performing the operations illustrated at1308inFIG. 13. Particularly, the purpose of the means1308A, in one or more cases, is to serve as a transmitter for the apparatus for transmitting one or more portions of a reference signal. For example, the means1308A may be configured to transmit the second precoded sequence of an SRS transmission precoded by the means1304A.

FIG. 14illustrates example operations1400for wireless communications by an apparatus, in accordance with aspects of the present disclosure. Particularly, as shown inFIG. 14, the operations1400include receiving a first and second portion of a reference signal during different time intervals and processing the received portions.

Specifically, operations1400begin, at block1402, with the apparatus receiving a first portion of a reference signal transmission from a transmitting apparatus on a first resource in a first transmission time interval, wherein the first portion was precoded by the transmitting apparatus using a first precoder. In one or more cases, the apparatus that receives the first portion may be a base station (BS) and the transmitting apparatus may be a user equipment (UE). In these cases, the reference signal transmission may be a sounding reference signal (SRS) transmission. In other cases, the apparatus that receives the first portion may be a user equipment (UE) and the transmitting apparatus may be a base station (BS). In these cases, the reference signal transmission may be a downlink (DL) reference signal transmission. In some cases, the first resource may be at least one of a first subband or a first port.

The apparatus also includes, as shown at block1404, receiving a second portion of the reference signal transmission from the transmitting apparatus on a second resource in a second transmission time interval, wherein the second portion was precoded by the transmitting apparatus using a second precoder. In one or more cases, the apparatus that receives the second portion may be a base station (BS) and the transmitting apparatus may be a user equipment (UE). In these cases, the reference signal transmission may be a sounding reference signal (SRS) transmission. In other cases, the apparatus that receives the second portion may be a user equipment (UE) and the transmitting apparatus may be a base station (BS). In these cases, the reference signal transmission may be a downlink (DL) reference signal transmission. In some cases, the second resource may be at least one of a second subband or a second port.

The apparatus also includes, at block1406, processing the received portions of a reference signal transmission. Specifically, the apparatus may process the first portion of the reference signal transmission based on the first precoder. Further, the apparatus may also process the second portion of the reference signal transmission based on the second precoder. In one or more cases the apparatus may be a BS that is configured to process a first and second portion of an SRS transmission from a UE based on the first and second precoders. In other cases, the apparatus may be a UE that is configured to process a first and second portion of a DL reference signal transmission from a BS based on the first and second precoders.

FIG. 14Aillustrates a communications device1400A that may include various means-plus-function components configured to perform the operations illustrated inFIG. 14. For example, at1402A, the communications device1400A includes means for performing the operations illustrated at1402inFIG. 14. Particularly, the purpose of the means1402A, in one or more cases, is to serve as a receiver of the apparatus for receiving one or more portions of reference signals from a transmitting apparatus. For example, the means1402A may be configured to receive a first portion of a reference signal transmission from a transmitting apparatus on a first resource in a first transmission time interval, wherein the first portion was precoded by the transmitting apparatus using a first precoder.

Additionally, at1404A, the communications device1400A includes means for performing the operations illustrated at1404inFIG. 14. Particularly, the purpose of the means1404A, in one or more cases, is to serve as a receiver of the apparatus for receiving one or more other portions of reference signals from a transmitting apparatus. For example, the means1404A may be configured to receive a second portion of a reference signal transmission from a transmitting apparatus on a second resource in a second transmission time interval, wherein the second portion was precoded by the transmitting apparatus using a s precoder.

Further, at1406A, the communications device1400A includes means for performing the operations illustrated at1406inFIG. 14. Particularly, in one or more cases, the purpose of the means1406A is to serve as a processing element for the apparatus for processing one or more portions of a reference signal transmission. For example, the means1406A may be configured to process the first portion and the second portion of the references signal transmission based on the first and second precoders.

According to one or more aspects, the processing may include removing at least one cyclic prefix from at least one precoded sequence of at least one of the first or second portions of the SRS transmission. In some cases the first and second precoders may be different. According to one or more cases, different physical resource block groups (PRG) sizes may be used for the first and second SRS transmissions. In some cases, an IDFT size may be used for the first and second sequence and may scale with a number of tones in the first and second subbands. The IDFT size may scale by one half and the number of tones in the first and second subbands that may scale by half.

FIG. 15illustrates an example of using multiple precoders, p1and p2, at the same time, in accordance with aspects of the present disclosure. Specifically,FIG. 15shows a pilot sequence1502transmitting at time ‘a’ in parts a1through a16. As shown, the sequence a1-a16is input to a DFT1504and the output of the DFT is precoded using p1and p2before being provided to the IDFT1506.

Particularly, as shown inFIG. 15, a different precoder (Precoder p1and Precoder p2) are each used for a different frequency band at the same time. This use of a precoder for a particular frequency band may be called subband precoding. However, in this example, by using a different precoder for different subbands at the same time, the reference signal may not fit within a single carrier even for the logical port.

FIG. 16illustrates an example of using different precoders p1and p2at different times, in accordance with aspects of the present disclosure. A waveform with large PAPR results from using different precoders for different subbands compared to using one precoder over the whole bandwidth. One solution is to divide an SRS symbol into multiple parts. This division may reduce the IDFT by half, and the corresponding number of tones may also scale by half.

Specifically, in order to reduce the size of the overall reference signal, one or more cases are able to provide a time split when applying the precoder which provides for a size reduction as shown inFIG. 16. As shown a pilot sequence1601A and pilot sequence1601B are shown where each is at a different time ‘a’ and ‘b’ respectively. Particularly, pilot sequence1601A is at time ‘a’ transmitting at a1-a4and pilot sequence1601B transmits b1-b4at time V. As shown, by implementing a time splitting (TDM) approach, size reductions are provided to the other elements. For example, as shown inFIG. 16, by time splitting one or more cases may also reduce the IDFT size by half and the corresponding number of tones also scales by half, e.g., downsampled by half. With these size reductions it may be appreciated that in one or more cases the reference signal may now fit in a single carrier. In accordance with one or more cases, using a TDM approach may provide a Peak-to-Average Power Ratio (PAPR) reduction.

Turning now toFIG. 17examples of SRS transmissions are illustrated, in accordance with aspects of the present disclosure.

Particularly,FIG. 17shows examples of PRG Size selection for SRS transmissions. As shown in the upper portion ofFIG. 17, when different precoders are applied at different times (as done inFIG. 16) a resulting split is provided. Specifically, a CP1702is provided along with the sequence a1-a41704that was precoded with precoderp1that is split from a subsequent CP1706that is provided along with the sequence b1-b41708that were precoded with precorderp2as shown. Thus, as shown by introducing TDM across precoders, the resulting SRS is single carrier.

In contrast, in the lower portion ofFIG. 17, when precoders are applied at the same time (as done inFIG. 15) a single resulting transmission is provided as shown. Specifically, a single larger CP1703is provided along with both the a1-a41705and b1-b41707which were precoded with precoderp1and precorderp2at the same time. Although a single split into two parts is shown inFIG. 17, it can be appreciated that aspects and cases in accordance with disclosure are not limited to this example. Particularly, there is not a limit to doing a half split, for example there could be a provided split into 3 or 4 or more by splitting into multiple times using multiple precoders. The idea is the precoder is being split over time.

FIG. 18illustrates an example of using a single precoder at a single time, in accordance with aspects of the present disclosure. As shown the same precoder p1is used to precode the pilot sequence1801that is made up of a1-a16.

Specifically, precoder p1is used to precode a1-a8and then the same precoder p1is used to precode a9-a16in a second subband. Thus, what is shown is multiband precoding using a single port and single precoder. However, similar to what occurred inFIG. 15, the resulting output may not fit in a single carrier. Specifically, even though a single precoder is used, if SRS is allocated over multiple frequency bands, the final SRS is not a single carrier any more.

Therefore, looking atFIG. 19a time split when applying the same precoder can be provided that allows for the output to fit into a single carrier. Specifically,FIG. 19illustrates an example of using a single precoder p1at different times, in accordance with aspects of the present disclosure.

Particularly,FIG. 19shows a pilot sequence1901with parts a1, . . . , a4transmitting at time ‘a’ and pilot sequence1902with b1, . . . , b4transmitting at later time V. This time splitting and application of the precoder p1provides a size reduction to other elements as shown. Specifically, a reduction in the IDFT size by half may be provided. Further, the corresponding number of tones also scales by half, e.g., downsampled by half.

FIG. 20illustrates an example of antenna transmission of precoded SRS, in accordance with aspects of the present disclosure.

However, an issue is present in this arrangement using precoded SRS as shown. Specifically, due to the precoding, even though pilot sequences (s1, s2) at the logical ports are single carriers, pilot sequences at the physical antennas (Ant1and Ant2) are not single carrier because the signals were added in the time domain and transmitted.

This issue is further explained with reference toFIG. 21that illustrates an example FDM of precoded SRS, in accordance with aspects of the present disclosure.

As shown a pilot sequence2101made up of a1-a8is precoded using port1and a second pilot sequence2102made up of b1-b8is precoded using port2at the same time. The outputs of these ports are then provided to a physical antenna for transmission. However, as shown, the antenna (Ant1) transmission of the precoded sequences will not fit on a single carrier. Accordingly, similar toFIG. 20, the transmitted pilot sequences at the physical antennas are not single carrier.

FIG. 22illustrates a solution in the form of an example of time splitting precoding of SRS, in accordance with aspects of the present disclosure.

As shown a pilot sequence2201a1-a4is precoded at a time1at port1. Further, a pilot sequence2202b1-b4is precoded at a time2at port2. In the time domain, these pilot sequences don't add together. By precoding at different times the sequences are reduced in size and as a result other elements are also reduced in size. For example, as shown, a reduction of the IDFT size by half is provided in this example. Further, the corresponding number of tones also scales down by half. This reduction in size provides a precoded sequence that may fit on one carrier. In some cases, frequency domain sequences2201and2202may be chosen to have low-PAPR in the time-domain (e.g., as an extension or truncation of Zadoff-Chu Sequences).

Example of Separate Port for DFT-S-OFDM

FIG. 23illustrates example operations2300for wireless communications by a UE, in accordance with aspects of the present disclosure.

Operations2300begin, at block2302, with the UE determining whether an uplink transmission is to be sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal. In one example, the uplink transmission may be sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal or an orthogonal frequency division multiplexed (OFDM) signal.

The UE also, at block2304, selects one or more ports for sending the uplink transmission based on the determination. According to other aspects, a first set of ports may be selected if the uplink transmission is configured as a DFT-s-OFDM signal versus sending the UL transmission as an ODFM signal. Also, a second set of ports may be selected if the uplink transmission is not configured as DFT-s-OFDM signal, i.e., an OFDM signal. In one example, if a UE selects port10for UL transmission, DFT-s-OFDM will be used. If the BS configures the UE to use ports11=18, OFDM will be used.

FIG. 23Aillustrates a communications device2300A that may include various means-plus-function components configured to perform the operations illustrated inFIG. 23. For example, at2302A, the communications device2300A includes means for performing the operations illustrated at2302inFIG. 23. Additionally, at2304A, the communications device2300A includes means for performing the operations illustrated at2304inFIG. 23.

In one or more cases, the method may further include determining a transmit power scaling factor configured by the UE, based on whether the uplink transmission is to be sent as a DFT spread orthogonal frequency division multiplex (DFT-s-OFDM) signal. According to another aspect, a first matrix may be selected if the uplink transmission is to be sent as a DFT-s-OFDM signal, and a second precoding matrix is selected if the uplink transmission is not to be sent as DFT-s-OFDM signal. According to one or more cases, elements of the first and second precoding matrix may have different amplitudes. In other cases, elements of the first and second precoding matrix may have same amplitudes, but different phases. For DFT-s-OFDM, precoding matrices are limited to CM (cubic metric) preserving matrices. In one or more cases, the uplink transmission may be sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal or an orthogonal frequency division multiplexed (OFDM) signal. Further, the (DFT-s-OFDM) signal may support one layer, while the (OFDM) signal may support a plurality of layers. In one or more cases, different ports may be used for SRS transmitted using a DFT-s-OFDM signal and/or CP-OFDM signal. Further, at least one of SRS transmission power, bandwidth, or cluster in frequency bands may be different depending on whether SRS is transmitted using a DFT-s-OFDM or CP-OFDM signal.

FIG. 24illustrates example operations2400for wireless communications by a base station, in accordance with aspects of the present disclosure.

Operations2400begin, at block2402, with the base station determining, based on one or more ports used by a user equipment (UE) for sending an uplink transmission, whether the uplink transmission was sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal. According to one or more aspects, a first set of ports may be selected by the UE if the uplink transmission is configured as a DFT-s-OFDM signal, and a second set of ports is selected by the UE if the uplink transmission is not configured as DFT-s-OFDM signal. In one or more cases, the first set of ports may be different from the second set of ports. For example, the first set of ports may include port10while the second set of ports may include one or more of ports11through18.

Further, operations2400also include, at block2404, processing the uplink transmission based on the determination.

FIG. 24Aillustrates a communications device2400A that may include various means-plus-function components configured to perform the operations illustrated inFIG. 24. For example, at2402A, the communications device2400A includes means for performing the operations illustrated at2402inFIG. 24. Additionally, at2404A, the communications device2400A includes means for performing the operations illustrated at2404inFIG. 24.

The method may include determining a transmit power scaling factor configured by the UE, based on whether the uplink transmission is to be sent as a DFT spread orthogonal frequency division multiplexed (DFT-s-OFDM) signal. A difference between a transmit power scaling factor for the (DFT-s-OFDM) signal and the (OFDM) signal is less than a fixed amount, and the difference is configurable by the UE. In one or more cases, a first matrix is selected for the processing if the uplink transmission is sent as a DFT-s-OFDM signal, and a second matrix is selected for the processing if the uplink transmission is not sent as a DFT-s-OFDM signal. In some examples, elements of the first and second precoding matrix have different amplitudes. In some examples, elements of the first and second precoding matrix have same amplitudes, but different phases.

According to one or more examples, aspects of the present disclosure provide techniques and apparatus for distinguishing OFDM and DFT-s-OFDM by different ports (UL Data). It can be appreciated that both OFDM and DFT-s-OFDM waveforms may support uplink data transmission. However, a precoder matrix and transmission (Tx) power scaling factor, MCS for OFDM and DFT-s-OFDM may be different.

Thus, in accordance with one or more aspects of the present disclosure, different ports (layer) are assigned to OFDM and DFT-s-OFDM waveforms. By providing these different ports (layers) OFDM and DFT-s-OFDM waveforms may be distinguished. For example, Port10may be assigned for DFT-s-OFDM and one or more of Ports11-18may be assigned for OFDM. Thus, in an example, if UE selects Port10for UL transmission, the selection means that a DFT-s-OFDM will be used. Further, in another example, if a BS configures UE to use Port10for UL transmission, it means that DFT-s-OFDM will be used.

In accordance with one or more cases, Tx power scaling factors for OFDM and DFT-s-OFDM may be different by a fixed factor. For example, a OFDM power scaling factor=b may be provide, while a DFT-s-OFDM power scaling factor=b*2 may be provided that is different the OFDM power scaling factor. In one or more cases, the Tx power scaling for OFDM and DFT-s-OFDM may be independently configured by UE or gNB.

Configuring OFDM and DFT-s-OFDM port may also be provided in accordance with one or more cases. For example, a precoder for OFDM and DFT-s-OFDM may be different. In one or more cases, for an OFDM waveform, elements in a precoding matrix may have different amplitudes. For DFT-s-OFDM, elements in a precoding matrix may have the same amplitude and may only have different phases. For DFT-s-OFDM, precoding matrices may be limited to CM (cubic metric) preserving matrices.

Rank selection for OFDM and DFT-s-OFDM Ports may also be provided in accordance with one or more cases. For example, an OFDM waveform may support multi-rank/multi-layer transmission. Thus, multiple ports may be selected among multiple OFDM Ports. An DFT-s-OFDM waveform may only support 1-layer transmission. Thus, only one DFT-s-OFDM Port may exist, and may not be selected together with OFDM Ports.

Aspects of configuring OFDM and DFT-s-OFDM ports can be provided in accordance with one or more cases. For example, it is possible to assign different Ports to SRS for OFDM and SRS for DFT-s-OFDM. Particularly, making a one-to-one correspondence between Data port (OFDM/DFT-s-OFDM port) and SRS Port may be provided.

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. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components, for example, as illustrated inFIGS. 8A, 9A, 13A, 14A, 23A, and 24A.

For example, means for transmitting and/or means for receiving may comprise one or more of a transmit processor420, a TX MIMO processor430, a receive processor438, or antenna(s)434of the base station110and/or the transmit processor464, a TX MIMO processor466, a receive processor458, or antenna(s)452of the user equipment120. Additionally, means for generating, means for multiplexing, and/or means for applying may comprise one or more processors, such as the controller/processor440of the base station110and/or the controller/processor480of the user equipment120.