Determining a number of symbols for sounding reference signal transmission

Apparatuses, methods, and systems are disclosed for determining a number of symbols for sounding reference signal transmission. One apparatus (200) includes a processor (202) that determines (602) a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. The apparatus (200) includes a transmitter (210) that transmits (604) an indication of the number to a base unit.

FIELD

The subject matter disclosed herein relates generally to wireless communications and more particularly relates to determining a number of symbols for sounding reference signal transmission.

BACKGROUND

The following abbreviations are herewith defined, at least some of which are referred to within the following description: Third Generation Partnership Project (“3GPP”), Positive-Acknowledgment (“ACK”), Binary Phase Shift Keying (“BPSK”), Clear Channel Assessment (“CCA”), Cyclic Prefix (“CP”), Channel State Information (“CSI”), Common Search Space (“CS S”), Discrete Fourier Transform Spread (“DFTS”), Downlink Control Information (“DCI”), Downlink (“DL”), Downlink Pilot Time Slot (“DwPTS”), Enhanced Clear Channel Assessment (“eCCA”), Enhanced Mobile Broadband (“eMBB”), Evolved Node B (“eNB”), European Telecommunications Standards Institute (“ETSI”), Frame Based Equipment (“FBE”), Frequency Division Duplex (“FDD”), Frequency Division Multiple Access (“FDMA”), Guard Period (“GP”), Hybrid Automatic Repeat Request (“HARQ”), Internet-of-Things (“IoT”), Key Performance Indicators (“KPI”), Licensed Assisted Access (“LAA”), Load Based Equipment (“LBE”), Listen-Before-Talk (“LBT”), Long Term Evolution (“LTE”), Medium Access Control (“MAC”), Multiple Access (“MA”), Modulation Coding Scheme (“MCS”), Machine Type Communication (“MTC”), Massive MTC (“mMTC”), Multiple Input Multiple Output (“MIMO”), Multi User Shared Access (“MUSA”), Narrowband (“NB”), Negative-Acknowledgment (“NACK”) or (“NAK”), Next Generation Node B (“gNB”), Non-Orthogonal Multiple Access (“NOMA”), Orthogonal Frequency Division Multiplexing (“OFDM”), Primary Cell (“PCell”), Physical Broadcast Channel (“PBCH”), Physical Downlink Control Channel (“PDCCH”), Physical Downlink Shared Channel (“PDSCH”), Pattern Division Multiple Access (“PDMA”), Physical Hybrid ARQ Indicator Channel (“PHICH”), Physical Random Access Channel (“PRACH”), Physical Resource Block (“PRB”), Physical Uplink Control Channel (“PUCCH”), Physical Uplink Shared Channel (“PUSCH”), Quality of Service (“QoS”), Quadrature Phase Shift Keying (“QPSK”), Radio Resource Control (“RRC”), Random Access Procedure (“RACH”), Random Access Response (“RAR”), Reference Signal (“RS”), Resource Spread Multiple Access (“RSMA”), Round Trip Time (“RTT”), Receive (“RX”), Sparse Code Multiple Access (“SCMA”), Scheduling Request (“SR”), Sounding Reference Signal (“SRS”), Single Carrier Frequency Division Multiple Access (“SC-FDMA”), Secondary Cell (“SCell”), Shared Channel (“SCH”), Signal-to-Interference-Plus-Noise Ratio (“SINR”), System Information Block (“SIB”), Transport Block (“TB”), Transport Block Size (“TBS”), Time-Division Duplex (“TDD”), Time Division Multiplex (“TDM”), Transmission Time Interval (“TTI”), Transmit (“TX”), Uplink Control Information (“UCI”), User Entity/Equipment (Mobile Terminal) (“UE”), Uplink (“UL”), Universal Mobile Telecommunications System (“UMTS”), Uplink Pilot Time Slot (“UpPTS”), Ultra-reliability and Low-latency Communications (“URLLC”), and Worldwide Interoperability for Microwave Access (“WiMAX”). As used herein, “HARQ-ACK” may represent collectively the Positive Acknowledge (“ACK”) and the Negative Acknowledge (“NAK”). ACK means that a TB is correctly received while NAK means a TB is erroneously received.

In certain wireless communications networks, a high carrier frequency (e.g., >6 GHz) may be used, such as millimeter wave (“mmW”). In such networks, transmission in the mmW range may suffer from higher path loss than the microwave range (e.g., typically with an additional loss of 20 to 30 dB). Without increasing the transmission power, the additional path loss may be compensated by deploying a large number of antenna elements and transmission and reception beamforming at a gNB and a UE. The number of antenna elements at the gNB may be in the order of one hundred or more. Transmission beamforming with a large number of antenna elements may focus the transmission energy in a certain direction (e.g., with a narrow angle) to compensate for additional path loss. In various configurations, a large directional gain may be achieved in the transmission. In some configurations, a large number of antenna elements may be used for transmission in the microwave range in a massive-MIMO system in order to achieve high system capacity.

In certain configurations, because of a large number of antenna elements, a cost of implementing an all-digital transceiver may be high. For example, a separate RF chain may be used for each antenna element (e.g., either TX or RX) and the associated cost and power consumption may be prohibitive. In some configurations, a compromise may be to use hybrid analog/digital beamforming in which a small number of radio frequency (“RF”) chains may be used to power a large number of antenna elements. Relative phases between certain antenna elements may be controlled by a separate power distribution (at the TX side)/combining (at the RX side) and phase shift network (e.g., RF precoder).

In some networks, on a TX side, a baseband signal XRFtransmitted by the antenna array may be represented by XRF=FRFFBBXINwhere XIN, FBB, FRFare the baseband input signal, baseband TX precoder, and RF TX precoder respectively. A transmitter may control its TX beam with the combination of an analog precoder FRFand a digital precoder FBB. Pure analog beamforming may be considered a special case of hybrid beamforming with FBB=I. As used herein, there may be no difference between pure analog beamforming and hybrid beamforming.

In various networks, UL beam management may be supported. UL beam management may refer to the process that a UE and a gNB search and find suitable TX beam (e.g., UE) and RX beam (e.g., gNB) through beam selection, measurement, and/or refinement.

In some configurations, an important UL RS for UL beam management may be SRS. In various configurations, SRS may not be associated with UL data or control transmission, and may not primarily be used for a gNB to manage an UL beam, estimate an UL channel quality, determine an UL MIMO transmission codeword used for a UE, and for frequency selective scheduling.

In certain networks, different UEs may have different antenna configurations, including beamforming circuitry. For a UE which does not employ transmission beamforming, it may simply transmit SRS in designated resources for a gNB to estimate the UL channel from its antenna elements. For a UE with full digital beamforming, it may be capable of generating different digital TX beams, transmitted as different ports, using baseband precoding processing. Different TX beams may be generated in the same OFDM symbol, possibly multiplexed in the frequency domain as different comb. For a UE with hybrid TX beamforming, multiple beams may be generated with different baseband precoders based on a same analog beam. This may be because of a limitation of an analog phase shifter (e.g., only one wide band analog beam may be generated at a given time). If a UE needs to transmit SRS through multiple analog beams, the SRS resources corresponding to different analog beams may be in different OFDM symbols.

BRIEF SUMMARY

Apparatuses for determining a number of symbols for sounding reference signal transmission are disclosed. Methods and systems also perform the functions of the apparatus. In one embodiment, the apparatus includes a processor that determines a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. In various embodiments, the apparatus includes a transmitter that transmits an indication of the number to a base unit.

In some embodiments, the number of orthogonal frequency-division multiplexing symbols includes 1, 2, 3, or 4. In various embodiments, the number of orthogonal frequency-division multiplexing symbols corresponds to a number of sounding reference signal ports. In certain embodiments, in response to the number of sounding reference signal ports being 1, the number of orthogonal frequency-division multiplexing symbols is 1. In one embodiment, in response to the number of sounding reference signal ports being 2, the number of orthogonal frequency-division multiplexing symbols is 1 or 2. In some embodiment, in response to the number of sounding reference signal ports being 4, the number of orthogonal frequency-division multiplexing symbols is 1, 2, 3, or 4.

A method for determining a number of symbols for sounding reference signal transmission, in one embodiment, includes determining a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. In various embodiments, the method includes transmitting an indication of the number to a base unit.

One apparatuses for determining sounding reference port assignments includes a receiver that receives an indication of a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. The apparatus includes a processor that determines sounding reference signal port and resource assignments based on the indication. The apparatus also includes a transmitter that transmits information indicating the sounding reference signal port and resource assignments.

In some embodiments, the number of orthogonal frequency-division multiplexing symbols includes 1, 2, 3, or 4. In various embodiments, the number of orthogonal frequency-division multiplexing symbols depends on a number of sounding reference signal ports. In certain embodiments, in response to the number of sounding reference signal ports being 1, the number of orthogonal frequency-division multiplexing symbols is 1. In one embodiment, in response to the number of sounding reference signal ports being 2, the number of orthogonal frequency-division multiplexing symbols is 1 or 2. In some embodiment, in response to the number of sounding reference signal ports being 4, the number of orthogonal frequency-division multiplexing symbols is 1, 2, 3, or 4.

A method for determining sounding reference port assignments, in one embodiment, includes receiving an indication of a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. In certain embodiments, this indication may be transmitted as an uplink RRC message. The method also includes determining sounding reference signal port and resource assignments based on the indication. The method includes transmitting information indicating the sounding reference signal port and resource assignments.

DETAILED DESCRIPTION

FIG. 1depicts an embodiment of a wireless communication system100for determining a number of symbols for sounding reference signal transmission. In one embodiment, the wireless communication system100includes remote units102and base units104. Even though a specific number of remote units102and base units104are depicted inFIG. 1, one of skill in the art will recognize that any number of remote units102and base units104may be included in the wireless communication system100.

The base units104may be distributed over a geographic region. In certain embodiments, a base unit104may also be referred to as an access point, an access terminal, a base, a base station, a Node-B, an eNB, a gNB, a Home Node-B, a relay node, a device, or by any other terminology used in the art. The base units104are generally part of a radio access network that includes one or more controllers communicably coupled to one or more corresponding base units104. The radio access network is generally communicably coupled to one or more core networks, which may be coupled to other networks, like the Internet and public switched telephone networks, among other networks. These and other elements of radio access and core networks are not illustrated but are well known generally by those having ordinary skill in the art.

In one implementation, the wireless communication system100is compliant with the LTE of the 3GPP protocol, wherein the base unit104transmits using an OFDM modulation scheme on the DL and the remote units102transmit on the UL using a SC-FDMA scheme or an OFDM scheme. More generally, however, the wireless communication system100may implement some other open or proprietary communication protocol, for example, WiMAX, among other protocols. The present disclosure is not intended to be limited to the implementation of any particular wireless communication system architecture or protocol.

The base units104may serve a number of remote units102within a serving area, for example, a cell or a cell sector via a wireless communication link. The base units104transmit DL communication signals to serve the remote units102in the time, frequency, and/or spatial domain.

In one embodiment, a base unit104may receive an indication of a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission from a remote unit102. The base unit104may also determine sounding reference signal port and resource assignments based on the indication. The base unit104may transmit information indicating the sounding reference signal port and resource assignments to the remote unit102. Accordingly, a base unit104may be used for determining sounding reference port assignments.

In another embodiment, a remote unit102may determine a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. In various embodiments, the remote unit102may transmit an indication of the number to a base unit104. Accordingly, a remote unit102may be used for determining a number of symbols for sounding reference signal transmission.

The transmitter210is used to provide UL communication signals to the base unit104and the receiver212is used to receive DL communication signals from the base unit104. In some embodiments, the transmitter210transmits an indication of a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission to a base unit104. Although only one transmitter210and one receiver212are illustrated, the remote unit102may have any suitable number of transmitters210and receivers212. The transmitter210and the receiver212may be any suitable type of transmitters and receivers. In one embodiment, the transmitter210and the receiver212may be part of a transceiver.

In various embodiments, the receiver312is used to receive an indication of a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. In some embodiments, the processor302is used to determine sounding reference signal port and resource assignments based on the indication. In certain embodiments, the transmitter310is used to transmit information indicating the sounding reference signal port and resource assignments. Although only one transmitter310and one receiver312are illustrated, the base unit104may have any suitable number of transmitters310and receivers312. The transmitter310and the receiver312may be any suitable type of transmitters and receivers. In one embodiment, the transmitter310and the receiver312may be part of a transceiver.

FIG. 4is a schematic block diagram illustrating one embodiment of sounding reference port assignments400. In certain embodiments, a remote unit102may signal to a base unit104a number of OFDM symbols it needs to transmit SRS. In various embodiments, a remote unit102may only signal to a base unit104a number of OFDM symbols it needs to transmit SRS in response to a number of SRS ports being more than 1. The potential number of OFDM symbols used to transmit different numbers of SRS ports may be, in certain embodiments, as listed in Table 1.

TABLE 1Number of SRS PortsMinimum Number of OFDM Symbols Needed1121 or 241, 2, 3, or 4

In certain embodiments, a default number of OFDM symbols is 1 for any given number of SRS ports. In some embodiments, for a given remote unit102, a number of OFDM symbols used to transmit a certain number of SRS ports may change over time. For example, in a first phase (e.g., U1) of an UL beam management process, before a remote unit102has a good indication of a direction of a base unit104, the remote unit102may choose to transmit SRS in multiple directions, with more than one analog beams and/or with each analog beam coupled with multiple digital beams, to enable the base unit104to search for the direction of the remote unit102transmission. Doing this the remote unit102may use multiple OFDM symbols to transmit on the number of SRS ports used. After beam measurement and selection of initial SRS beams, the base unit104may instruct the remote unit102to, in a second phase (e.g., next phase, phase two, U2), transmit SRS further based on one of the received beams. Therefore, in the second phase the remote unit102may transmit multiple digital beams all based on the analog beam selected in the first phase. Accordingly, there may be no constraint on a minimum number of OFDM symbols used in the second phase.

In some embodiments, a remote unit102may signal a minimum number of OFDM symbols used for SRS transmission to a base unit104in an RRC message or an UL control message (e.g., UCI) if the number is different from a default value of 1. When the base unit104receives the number of OFDM symbols that the remote unit102uses to transmit in a given number of ports, the base unit104may allocate SRS resources accordingly.

In certain embodiments, a remote unit102may signal to a base unit104the number of SRS ports it can transmit in a single OFDM symbol. This number of SRS ports may be a number of SRS ports that can be transmitted in a single OFDM symbol during a specific stage of an initialization process. This may also be a maximum number of SRS ports that can be transmitted in a single OFDM symbol by the remote unit102such that every SRS port is transmitted in a different analog beam.

In some embodiments, a remote unit102may signal a number of SRS ports used for SRS transmission to a base unit104. a maximum number of orthogonal SRS ports that it can transmit with a single OFDM symbol.

In one embodiment illustrated inFIG. 4, a base unit104assigns SRS resources to two remote units102(e.g., UE1 and UE2), each with 4 SRS ports with a comb of 4. A first remote unit102has SRS ports402,404,406, and408. Moreover, a second remote unit102has SRS ports410,412,414, and416. Each of the first and second remote units102may use hybrid beamforming and may go through first and second phases of beam management with SRS. The base unit104assigns 4 SRS ports to each remote unit102for the beam management process. For beam management, it may be sufficient to transmit wideband SRS signal with relative low density in the frequency domain, with comb of 4.

Initially the first and second remote units102may use two analog beams to send SRS in the first phase. Accordingly, the base unit104may allocate SRS resources to the remote units102as illustrated inFIG. 4in which the first and second remote units102use two symbols to transport in 4 SRS ports. For example, in a first OFDM symbol418, the first remote unit102uses SRS ports402and406and the second remote unit102uses SRS ports412and416. Moreover, in a second OFDM symbol420, the first remote unit102uses SRS ports404and408and the second remote unit102uses SRS ports410and414. Furthermore, in a third OFDM symbol422, the first remote unit102uses SRS ports402and406and the second remote unit102uses SRS ports412and416. Moreover, in a fourth OFDM symbol424, the first remote unit102uses SRS ports404and408and the second remote unit102uses SRS ports410and414. In addition, in a fifth OFDM symbol426, the first remote unit102uses SRS ports402and406and the second remote unit102uses SRS ports412and416. Moreover, in a sixth OFDM symbol428, the first remote unit102uses SRS ports404and408and the second remote unit102uses SRS ports410and414. It should be noted that OFDM symbols418,420,422,424,426, and428allocated to SRS transmissions may or may not be adjacent.

As the beams are selected in the first phase and the fine tuning of second phase starts, the first and second remote units102may transmit on 4 SRS ports with a single analog beam. In such embodiments, the number of OFDM symbols required may be 1. After the base unit104receives this indication from the remote unit102, the base unit104may re-assign the SRS resources to the first and second remote units102so that each remote unit102may multiplex all its 4 SRS ports in the same OFDM symbol as illustrated inFIG. 5, thereby reducing the latency in the second phase.

Specifically,FIG. 5is a schematic block diagram illustrating another embodiment of sounding reference port assignments500. As illustrated, in a first OFDM symbol502, the first remote unit102uses SRS ports402,404,406, and408. Moreover, in a second OFDM symbol504, the second remote unit102uses SRS ports410,412,414, and416. Furthermore, in a third OFDM symbol506, the first remote unit102uses SRS ports402,404,406, and408. Moreover, in a fourth OFDM symbol508, the second remote unit102uses SRS ports410,412,414, and416. In addition, in a fifth OFDM symbol510, the first remote unit102uses SRS ports402,404,406, and408. Moreover, in a sixth OFDM symbol512, the second remote unit102uses SRS ports410,412,414, and416. It should be noted that OFDM symbols502,504,506,508,510, and512allocated to SRS transmissions may or may not be adjacent.

FIG. 6is a schematic flow chart diagram illustrating one embodiment of a method600for determining a number of symbols for sounding reference signal transmission. In some embodiments, the method600is performed by an apparatus, such as the remote unit102. In certain embodiments, the method600may be performed by a processor executing program code, for example, a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or the like.

The method600may include determining602a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. The method600may also include transmitting604an indication of the number to a base unit.

In some embodiments, the number of orthogonal frequency-division multiplexing symbols includes 1, 2, 3, or 4. In various embodiments, the number of orthogonal frequency-division multiplexing symbols corresponds to a number of sounding reference signal ports. In certain embodiments, in response to the number of sounding reference signal ports being 1, the number of orthogonal frequency-division multiplexing symbols is 1. In one embodiment, in response to the number of sounding reference signal ports being 2, the number of orthogonal frequency-division multiplexing symbols is 1 or 2. In some embodiment, in response to the number of sounding reference signal ports being 4, the number of orthogonal frequency-division multiplexing symbols is 1, 2, 3, or 4.

FIG. 7is a schematic flow chart diagram illustrating another embodiment of a method700for determining sounding reference port assignments. In some embodiments, the method700is performed by an apparatus, such as the base unit104. In certain embodiments, the method700may be performed by a processor executing program code, for example, a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or the like.

The method700may include receiving702an indication of a number of orthogonal frequency-division multiplexing symbols for sounding reference signal transmission. The method700may also include determining704sounding reference signal port and resource assignments based on the indication. The method700may include transmitting706information indicating the sounding reference signal port and resource assignments.

In some embodiments, the number of orthogonal frequency-division multiplexing symbols includes 1, 2, 3, or 4. In various embodiments, the number of orthogonal frequency-division multiplexing symbols corresponds to a number of sounding reference signal ports. In certain embodiments, in response to the number of sounding reference signal ports being 1, the number of orthogonal frequency-division multiplexing symbols is 1. In one embodiment, in response to the number of sounding reference signal ports being 2, the number of orthogonal frequency-division multiplexing symbols is 1 or 2. In some embodiment, in response to the number of sounding reference signal ports being 4, the number of orthogonal frequency-division multiplexing symbols is 1, 2, 3, or 4.