Switching between rank two and rank four operating modes for analog beamforming

Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a first wireless communication device may receive, from a second wireless communication device, a set of beamformed reference signals for analog beam training. The first wireless communication device may transmit, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents a phase between a first beamforming vector and a second beamforming vector, and an angle between the first beamforming vector and the second beamforming vector. Numerous other aspects are described.

FIELD OF THE DISCLOSURE

Aspects of the present disclosure generally relate to wireless communication and to techniques and apparatuses for switching between rank two and rank four operating modes for analog beamforming.

BACKGROUND

SUMMARY

In some aspects, a first wireless communication device for wireless communication includes a memory; and one or more processors coupled to the memory, the memory and the one or more processors configured to: receive, from a second wireless communication device, a set of beamformed reference signals for analog beam training; and transmit, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, a first wireless communication device for wireless communication includes a memory; and one or more processors coupled to the memory, the memory and the one or more processors configured to: transmit, to a second wireless communication device, a set of beamformed reference signals for analog beam training; and receive, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the second wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, a method of wireless communication performed by a first wireless communication device includes receiving, from a second wireless communication device, a set of beamformed reference signals for analog beam training; and transmitting, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, a method of wireless communication performed by a first wireless communication device includes transmitting, to a second wireless communication device, a set of beamformed reference signals for analog beam training; and receiving, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the second wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, a non-transitory computer-readable medium storing a set of instructions for wireless communication includes one or more instructions that, when executed by one or more processors of a first wireless communication device, cause the first wireless communication device to: receive, from a second wireless communication device, a set of beamformed reference signals for analog beam training; and transmit, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, a non-transitory computer-readable medium storing a set of instructions for wireless communication includes one or more instructions that, when executed by one or more processors of a first wireless communication device, cause the first wireless communication device to: transmit, to a second wireless communication device, a set of beamformed reference signals for analog beam training; and receive, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the second wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, an apparatus for wireless communication includes means for receiving, from a wireless communication device, a set of beamformed reference signals for analog beam training; and means for transmitting, to the wireless communication device, feedback that indicates a first complex correlation coefficient associated with the apparatus that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the apparatus based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the apparatus based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

In some aspects, an apparatus for wireless communication includes means for transmitting, to a wireless communication device, a set of beamformed reference signals for analog beam training; and means for receiving, from the wireless communication device, feedback that indicates a first complex correlation coefficient associated with the wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

DETAILED DESCRIPTION

Controller/processor240of base station110, controller/processor280of UE120, and/or any other component(s) ofFIG. 2may perform one or more techniques associated with switching between rank two and rank four operating modes for analog beamforming, as described in more detail elsewhere herein. In some aspects, the wireless communication device described herein is the base station110, is included in the base station110, or includes one or more components of the base station110shown inFIG. 2. In some aspects, the wireless communication device described herein is the UE120, is included in the UE120, or includes one or more components of the UE120shown inFIG. 2. For example, controller/processor240of base station110, controller/processor280of UE120, and/or any other component(s) ofFIG. 2may perform or direct operations of, for example, process600ofFIG. 6, process700ofFIG. 7, and/or other processes as described herein. Memories242and282may store data and program codes for base station110and UE120, respectively. In some aspects, memory242and/or memory282may include a non-transitory computer-readable medium storing one or more instructions (e.g., code and/or program code) for wireless communication. For example, the one or more instructions, when executed (e.g., directly, or after compiling, converting, and/or interpreting) by one or more processors of the base station110and/or the UE120, may cause the one or more processors, the UE120, and/or the base station110to perform or direct operations of, for example, process600ofFIG. 6, process700ofFIG. 7, and/or other processes as described herein. In some aspects, executing instructions may include running the instructions, converting the instructions, compiling the instructions, and/or interpreting the instructions, among other examples.

In some aspects, the first wireless communication device includes means for receiving, from a second wireless communication device, a set of beamformed reference signals for analog beam training; or means for transmitting, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; or an angle between the first beamforming vector and the second beamforming vector. In some aspects, the means for the first wireless communication device to perform operations described herein may include, for example, one or more of transmit processor220, TX MIMO processor230, modulator232, antenna234, demodulator232, MIMO detector236, receive processor238, controller/processor240, memory242, or scheduler246. In some aspects, the means for the first wireless communication device to perform operations described herein may include, for example, one or more of antenna252, demodulator254, MIMO detector256, receive processor258, transmit processor264, TX MIMO processor266, modulator254, controller/processor280, or memory282.

In some aspects, the first wireless communication device includes means for receiving, from the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on a signal strength threshold, wherein the signal strength threshold is based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

In some aspects, the first wireless communication device includes means for receiving, from the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

In some aspects, the first wireless communication device includes means for transmitting, to a second wireless communication device, a set of beamformed reference signals for analog beam training; or means for receiving, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; or an angle between the first beamforming vector and the second beamforming vector. In some aspects, the means for the first wireless communication device to perform operations described herein may include, for example, one or more of transmit processor220, TX MIMO processor230, modulator232, antenna234, demodulator232, MIMO detector236, receive processor238, controller/processor240, memory242, or scheduler246. In some aspects, the means for the first wireless communication device to perform operations described herein may include, for example, one or more of antenna252, demodulator254, MIMO detector256, receive processor258, transmit processor264, TX MIMO processor266, modulator254, controller/processor280, or memory282.

In some aspects, the first wireless communication device includes means for determining a signal strength threshold based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

In some aspects, the first wireless communication device includes means for determining an occurrence of a rank switch trigger event based at least in part on determining that an operating signal strength satisfies the signal strength threshold.

In some aspects, the first wireless communication device includes means for transmitting, to the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on determining the occurrence of the rank switch trigger event.

In some aspects, the first wireless communication device includes means for transmitting, to the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

In some aspects, the first wireless communication device includes means for determining a realizable data rate associated with the second rank operating mode; or means for scheduling the second wireless communication device and at least a third wireless communication device based at least in part on the realizable data rate.

FIG. 3is a diagram illustrating an example beamforming architecture300that supports beamforming for millimeter wave (mmW) communications, in accordance with the present disclosure. In some aspects, architecture300may implement aspects of wireless network100. In some aspects, architecture300may be implemented in a transmitting device (e.g., a first wireless communication device, UE, or base station) and/or a receiving device (e.g., a second wireless communication device, UE, or base station), as described herein.

Broadly,FIG. 3is a diagram illustrating example hardware components of a wireless communication device in accordance with the present disclosure. The illustrated components may include those that may be used for antenna element selection and/or for beamforming for transmission of wireless signals. There are numerous architectures for antenna element selection and implementing phase shifting, only one example of which is illustrated here. The architecture300includes a modem (modulator/demodulator)302, a digital to analog converter (DAC)304, a first mixer306, a second mixer308, and a splitter310. The architecture300also includes multiple first amplifiers312, multiple phase shifters314, multiple second amplifiers316, and an antenna array318that includes multiple antenna elements320.

Transmission lines or other waveguides, wires, and/or traces are shown connecting the various components to illustrate how signals to be transmitted may travel between components. Reference numbers322,324,326, and328indicate regions in the architecture300in which different types of signals travel or are processed. Specifically, reference number322indicates a region in which digital baseband signals travel or are processed, reference number324indicates a region in which analog baseband signals travel or are processed, reference number326indicates a region in which analog intermediate frequency (IF) signals travel or are processed, and reference number328indicates a region in which analog radio frequency (RF) signals travel or are processed. The architecture also includes a local oscillator A330, a local oscillator B332, and a controller/processor334. In some aspects, controller/processor334corresponds to controller/processor240of the base station described above in connection withFIG. 2and/or controller/processor280of the UE described above in connection withFIG. 2.

Each of the antenna elements320may include one or more sub-elements for radiating or receiving RF signals. For example, a single antenna element320may include a first sub-element cross-polarized with a second sub-element that can be used to independently transmit cross-polarized signals. The antenna elements320may include patch antennas, dipole antennas, or other types of antennas arranged in a linear pattern, a two dimensional pattern, or another pattern. A spacing between antenna elements320may be such that signals with a desired wavelength transmitted separately by the antenna elements320may interact or interfere (e.g., to form a desired beam). For example, given an expected range of wavelengths or frequencies, the spacing may provide a quarter wavelength, half wavelength, or other fraction of a wavelength of spacing between neighboring antenna elements320to allow for interaction or interference of signals transmitted by the separate antenna elements320within that expected range.

The modem302processes and generates digital baseband signals and may also control operation of the DAC304, first and second mixers306,308, splitter310, first amplifiers312, phase shifters314, and/or the second amplifiers316to transmit signals via one or more or all of the antenna elements320. The modem302may process signals and control operation in accordance with a communication standard such as a wireless standard discussed herein. The DAC304may convert digital baseband signals received from the modem302(and that are to be transmitted) into analog baseband signals. The first mixer306upconverts analog baseband signals to analog IF signals within an IF using a local oscillator A330. For example, the first mixer306may mix the signals with an oscillating signal generated by the local oscillator A330to “move” the baseband analog signals to the IF. In some cases, some processing or filtering (not shown) may take place at the IF. The second mixer308upconverts the analog IF signals to analog RF signals using the local oscillator B332. Similar to the first mixer, the second mixer308may mix the signals with an oscillating signal generated by the local oscillator B332to “move” the IF analog signals to the RF or the frequency at which signals will be transmitted or received. The modem302and/or the controller/processor334may adjust the frequency of local oscillator A330and/or the local oscillator B332so that a desired IF and/or RF frequency is produced and used to facilitate processing and transmission of a signal within a desired bandwidth.

In the illustrated architecture300, signals upconverted by the second mixer308are split or duplicated into multiple signals by the splitter310. The splitter310in architecture300splits the RF signal into multiple identical or nearly identical RF signals. In other examples, the split may take place with any type of signal, including with baseband digital, baseband analog, or IF analog signals. Each of these signals may correspond to an antenna element320, and the signal travels through and is processed by amplifiers312,316, phase shifters314, and/or other elements corresponding to the respective antenna element320to be provided to and transmitted by the corresponding antenna element320of the antenna array318. In one example, the splitter310may be an active splitter that is connected to a power supply and provides some gain so that RF signals exiting the splitter310are at a power level equal to or greater than the signal entering the splitter310. In another example, the splitter310is a passive splitter that is not connected to power supply, and the RF signals exiting the splitter310may be at a power level lower than the RF signal entering the splitter310.

After being split by the splitter310, the resulting RF signals may enter an amplifier, such as a first amplifier312, or a phase shifter314corresponding to an antenna element320. The first and second amplifiers312,316are illustrated with dashed lines because one or both of them might not be necessary in some aspects. In some aspects, both the first amplifier312and second amplifier316are present. In some aspects, neither the first amplifier312nor the second amplifier316are present. In some aspects, one of the two amplifiers312,316is present but not the other. By way of example, if the splitter310is an active splitter, the first amplifier312may not be used. By way of further example, if the phase shifter314is an active phase shifter that can provide a gain, the second amplifier316might not be used.

The amplifiers312,316may provide a desired level of positive or negative gain. A positive gain (positive dB) may be used to increase an amplitude of a signal for radiation by a specific antenna element320. A negative gain (negative dB) may be used to decrease an amplitude and/or suppress radiation of the signal by a specific antenna element. Each of the amplifiers312,316may be controlled independently (e.g., by the modem302or the controller/processor334) to provide independent control of the gain for each antenna element320. For example, the modem302and/or the controller/processor334may have at least one control line connected to each of the splitter310, first amplifiers312, phase shifters314, and/or second amplifiers316that may be used to configure a gain to provide a desired amount of gain for each component and thus each antenna element320.

The phase shifter314may provide a configurable phase shift or phase offset to a corresponding RF signal to be transmitted. The phase shifter314may be a passive phase shifter not directly connected to a power supply. Passive phase shifters might introduce some insertion loss. The second amplifier316may boost the signal to compensate for the insertion loss. The phase shifter314may be an active phase shifter connected to a power supply such that the active phase shifter provides some amount of gain or prevents insertion loss. The settings of each of the phase shifters314are independent, meaning that each can be independently set to provide a desired amount of phase shift or the same amount of phase shift or some other configuration. The modem302and/or the controller/processor334may have at least one control line connected to each of the phase shifters314and which may be used to configure the phase shifters314to provide a desired amount of phase shift or phase offset between antenna elements320.

In the illustrated architecture300, RF signals received by the antenna elements320are provided to one or more first amplifiers356to boost the signal strength. The first amplifiers356may be connected to the same antenna arrays318(e.g., for time division duplex (TDD) operations). The first amplifiers356may be connected to different antenna arrays318. The boosted RF signal is input into one or more phase shifters354to provide a configurable phase shift or phase offset for the corresponding received RF signal to enable reception via one or more Rx beams. The phase shifter354may be an active phase shifter or a passive phase shifter. The settings of the phase shifters354are independent, meaning that each can be independently set to provide a desired amount of phase shift or the same amount of phase shift or some other configuration. The modem302and/or the controller/processor334may have at least one control line connected to each of the phase shifters354and which may be used to configure the phase shifters354to provide a desired amount of phase shift or phase offset between antenna elements320to enable reception via one or more Rx beams.

The outputs of the phase shifters354may be input to one or more second amplifiers352for signal amplification of the phase shifted received RF signals. The second amplifiers352may be individually configured to provide a configured amount of gain. The second amplifiers352may be individually configured to provide an amount of gain to ensure that the signals input to combiner350have the same magnitude. The amplifiers352and/or356are illustrated in dashed lines because they might not be necessary in some aspects. In some aspects, both the amplifier352and the amplifier356are present. In another aspect, neither the amplifier352nor the amplifier356are present. In other aspects, one of the amplifiers352,356is present but not the other.

In the illustrated architecture300, signals output by the phase shifters354(via the amplifiers352when present) are combined in combiner350. The combiner350in architecture300combines the RF signals into a combined signal. The combiner350may be a passive combiner (e.g., not connected to a power source), which may result in some insertion loss. The combiner350may be an active combiner (e.g., connected to a power source), which may result in some signal gain. When combiner350is an active combiner, it may provide a different (e.g., configurable) amount of gain for each input signal so that the input signals have the same magnitude when they are combined. When combiner350is an active combiner, the combiner350may not need the second amplifier352because the active combiner may provide the signal amplification.

The output of the combiner350is input into mixers346and348. Mixers346and348generally downconvert the received RF signal using inputs from local oscillators370and372, respectively, to create intermediate or baseband signals that carry the encoded and modulated information. The output of the mixers346and348are input into an analog-to-digital converter (ADC)344for conversion to analog signals. The analog signals output from ADC344is input to modem302for baseband processing, such as decoding, de-interleaving, or similar operations.

The architecture300is given by way of example only to illustrate an architecture for transmitting and/or receiving signals. In some cases, the architecture300and/or each portion of the architecture300may be repeated multiple times within an architecture to accommodate or provide an arbitrary number of RF chains, antenna elements, and/or antenna panels. Furthermore, numerous alternate architectures are possible and contemplated. For example, although only a single antenna array318is shown, two, three, or more antenna arrays may be included, each with one or more of their own corresponding amplifiers, phase shifters, splitters, mixers, DACs, ADCs, and/or modems. For example, a single UE may include two, four, or more antenna arrays for transmitting or receiving signals at different physical locations on the UE or in different directions.

Furthermore, mixers, splitters, amplifiers, phase shifters and other components may be located in different signal type areas (e.g., represented by different ones of the reference numbers322,324,326,328) in different implemented architectures. For example, a split of the signal to be transmitted into multiple signals may take place at the analog RF, analog IF, analog baseband, or digital baseband frequencies in different examples. Similarly, amplification and/or phase shifts may also take place at different frequencies. For example, in some aspects, one or more of the splitter310, amplifiers312,316, or phase shifters314may be located between the DAC304and the first mixer306or between the first mixer306and the second mixer308. In one example, the functions of one or more of the components may be combined into one component. For example, the phase shifters314may perform amplification to include or replace the first and/or or second amplifiers312,316. By way of another example, a phase shift may be implemented by the second mixer308to obviate the need for a separate phase shifter314. This technique is sometimes called local oscillator (LO) phase shifting. In some aspects of this configuration, there may be multiple IF to RF mixers (e.g., for each antenna element chain) within the second mixer308, and the local oscillator B332may supply different local oscillator signals (with different phase offsets) to each IF to RF mixer.

The modem302and/or the controller/processor334may control one or more of the other components304through372to select one or more antenna elements320and/or to form beams for transmission of one or more signals. For example, the antenna elements320may be individually selected or deselected for transmission of a signal (or signals) by controlling an amplitude of one or more corresponding amplifiers, such as the first amplifiers312and/or the second amplifiers316. Beamforming includes generation of a beam using multiple signals on different antenna elements, where one or more or all of the multiple signals are shifted in phase relative to each other. The formed beam may carry physical or higher layer reference signals or information. As each signal of the multiple signals is radiated from a respective antenna element320, the radiated signals interact, interfere (constructive and destructive interference), and amplify each other to form a resulting beam. The shape (such as the amplitude, width, and/or presence of side lobes) and the direction (such as an angle of the beam relative to a surface of the antenna array318) can be dynamically controlled by modifying the phase shifts or phase offsets imparted by the phase shifters314and amplitudes imparted by the amplifiers312,316of the multiple signals relative to each other. The controller/processor334may be located partially or fully within one or more other components of the architecture300. For example, the controller/processor334may be located within the modem302in some aspects.

As indicated above,FIG. 3is provided as an example. Other examples may differ from what is described with regard toFIG. 3.

FIG. 4is a diagram illustrating examples400,405, and410of analog beamforming, in accordance with the present disclosure. As shown inFIG. 4, examples400,405, and410include a UE420in communication with a base station425in a wireless network (e.g., wireless network100). However, the devices shown inFIG. 4are provided as examples, and the wireless network may support communication and beam management between other devices (e.g., between a UE420and a base station425or TRP, between a mobile termination node and a control node, between an integrated access and backhaul (IAB) child node and an IAB parent node, and/or between a scheduled node and a scheduling node). In some aspects, the UE420and the base station425may be in a connected state (e.g., a radio resource control (RRC) connected state). As is further shown inFIG. 4, the UE420may include a first antenna module430and a second antenna module435. In some aspects, the UE420may include any number of additional antenna modules.

As shown inFIG. 4, example400may be an example of rank two (which may be indicated, interchangeably, as “rank-2”) beamforming. As shown, the UE420may identify a best beam440over two polarizations from a codebook maintained at the UE420. Similarly, the base station425may identify a best beam445over two polarizations from a codebook maintained at the base station425. In a rank two operating mode, beamforming is performed using two RF chains for polarization-based transmissions.

In a rank four operating mode, a device may use four RF chains for polarization-based transmissions over two beams (spatial directions). In some aspects, as shown by example405, the RF chains may be used within one antenna module. This may be referred to as intra-module beamforming. As shown, for example, the UE420may determine, using the first antenna module430, a best beam450over two polarizations and a second best beam455over two polarizations. Similarly, the base station425may determine a best beam460(corresponding to the best beam450) and a second best beam465(corresponding to the second best beam455). These best beams may be chosen to maximize signal strength (e.g., reference signal received power (RSRP)), whereas the second best beams may be second best from a signal strength perspective.

In some aspects, as shown by example410, the RF chains may be used across more than one antenna module. This may be referred to as inter-module beamforming. As shown, for example, the UE420may determine, using the second antenna module435, a best beam470over two polarizations and, using the first antenna module430, a second best beam475over two polarizations. Similarly, the base station425may determine a best beam480(corresponding to the best beam470) and a second best beam485(corresponding to the second best beam475).

In some cases, a UE may transmit feedback indicating a rank indicator (RI), a precoding matrix indicator (PMI) and a CQI for precoding operations. For precoding, a fixed codebook of a finite number of precoders of different ranks may be considered. The UE may evaluate the realizable rate with these different (but finite number of) precoders and transmit feedback indicating an RI and a PMI (e.g., best rank and best precoder matrix from the class) as well as a MCS that is useful as CQI. In practice, a wireless communication device may not necessarily be constrained in terms of its precoding matrix choice, which may lead to a non-codebook operation. However, without an agreement in terms of the precoders, it becomes difficult for another wireless communication device to determine which precoder to use.

Some aspects of the subject matter disclosed herein may provide a generalized rank indication for non-codebook operations. To facilitate the generalized rank indication, some aspects involve the feedback of a complex correlation coefficient associated with beams in the codebook. In some aspects, a rank switch trigger event is provided so that a wireless communication device may determine when to switch between a rank two operation mode and a rank four operation mode (or vice versa). Dynamic switching to the higher rank transmissions may lead to better data rates and diversity. By determining an occurrence of the rank switch trigger event based at least in part on the complex correlation coefficient, some aspects may facilitate improving spectral efficiency and data rates.

The complex correlation coefficient may be determined as an approximation to a solution of an analysis that identifies an optimal transition signal to noise ratio (SNR). For example, if H denotes the Nr×Ntchannel matrix between a base station and a UE with a total Tx power constraint of ρ, the analysis seeks to identify a transition from rank-1 spatial MIMO to rank-2 spatial MIMO (which gets scaled up over two polarizations as rank-2 to rank-4). Under a perfect channel state information (CSI) assumption at both ends of the communication, the data rate with rank-1 spatial MIMO is given as
R1=log2(1+ρ·λ1(HHH)),
where λ1(HHH) denotes the dominant squared singular value of H. The data rate with rank-2 spatial MIMO is given as

R2=log2(1+ρ2·λ1(HH⁢H)·D1)+log2(1+ρ2·λ2(HH⁢H)·D2),
where λ1(HHH) and λ2(HHH) denote the dominant and second dominant squared singular values of H and, and Diis the waterfilling power allocation (v is the water level and optimized) which is given as

Di=(v-1λi(HH⁢H))+,
where v is chosen such that D1+D2≤2.

The analysis is configured to identify a ρ such that R2≥R1. This is the smallest SNR (denoted as the transition SNR) at which rank-2 spatial MIMO becomes optimal. Solving for the transition SNR leads to a quadratic equation in ρ which results in

This mathematical result is not easily practically implementable. Some aspects of the subject matter disclosed herein provide a relatively simple way in which the transition SNR can be estimated in closed-form. For example, the case in which H is dominated by two clusters (other clusters have weaker power and can be assumed to not contribute much to channel matrix) may be considered. This scenario captures many practical mmW deployments such a dominant line of sight (LOS) and a dominant non line of sight (NLOS) path. For example, this scenario may include an indoor hotspot with a LOS path and a NLOS reflection.

In this scenario, the channel matrix H may be characterized as:
H≈α1·uiv1H+α2·u2v2H,
where α1is the complex gain of the dominant cluster, u1is the dominant array steering vector at Rx, v1is the dominant array steering vector at Tx, α2is the complex gain of the sub-dominant cluster, u2is the sub-dominant array steering vector at Rx, and v2is the sub-dominant array steering vector at Tx.

If the following inner products of array steering vectors are denoted in this manner:
u1Hu2=ejθ·cos(ϕ) andv1Hv2=ejμ·cos(γ),
then, application of linear algebra may show that switching from rank-1 to rank-2 spatial MIMO is optimal if

This expression is given in terms of channel parameters but may still be too cumbersome to be evaluated in practice. To approximate the threshold for the SNR, some aspects may include a two stage approximation scheme. In a first approximation, since α1and α2capture the complex gains of the dominant and sub-dominant clusters, the wireless communication device may approximate |α1|2by the RSRP of the best beam pair and |α2|2by the RSRP of the second best beam pair (in the beam training process used over synchronization signal blocks (SSBs) in initial acquisition). In the second approximation, φ and γ denote the angle/direction between the best and second best beams at both sides of the communication, whereas θ and μ denote the phase in the complex correlation between the best and second best beams at both sides of the communication. Computing φ, γ, θ and μ requires knowledge of the best and second best beams at both sides, which also supposes knowledge of the beamforming codebooks used at both sides, however, each device is unaware of the other device's codebook. On the other hand, one of the devices can compute the corresponding angle/direction and phase of the complex correlation coefficient and feed it back to the other device, allowing that device to make an estimate of the threshold to the SNR.

As described above, in some aspects, a first wireless communication device receives reference signals from a second wireless communication device and feeds back a complex correlation coefficient between the best beam and second best beam as seen from the perspective of the first wireless communication device. Based on the second wireless communication device's knowledge of RSRPs of best and second best beams, as well as the complex correlation of the best and second best beam from the perspective of the second wireless communication device (μ and γ) which it is aware of based on the feedback of the best beam indices to be used at the second device. Transmission Configuration Indicator (TCI) state feedback, the second wireless communication device may compute the transition SNR and may indicate a switch from rank-2 transmissions to rank-4 transmissions (or vice versa).

As indicated above,FIG. 4is provided as an example. Other examples may differ from what is described with regard toFIG. 4.

FIG. 5is a diagram illustrating an example500associated with switching between rank two and rank four operating modes for analog beamforming, in accordance with the present disclosure. As shown, a wireless communication device505and a wireless communication device510may communicate with one another. In some aspects, the wireless communication device505and/or the wireless communication device510may be, or include, a UE, a CPE, a base station, a relay node, an IAB node, or a repeater node with configurable beamforming capabilities.

As shown by reference number515, the wireless communication device510may transmit, and the wireless communication device505may receive, a set of beamformed reference signals for analog beam training. As shown by reference number520, the wireless communication device505may determine reference signal feedback based at least in part on the set of beamformed reference signals. For example, in some aspects, the wireless communication device505may determine a first signal strength associated with a first beam pair and a second signal strength associated with a second beam pair. The first beam pair may include a beam associated with the wireless communication device505and a beam associated with the wireless communication device510that correspond to a first beamformed reference signal. The second beam pair may include a beam associated with the wireless communication device505and a beam associated with the wireless communication device510that correspond to a second beamformed reference signal. In some aspects, the wireless communication device505may determine any number of signal strengths associated with any number of beam pairs and may identify two beam pairs for reporting.

The two beam pairs may include a best beam pair and a second best beam pair. A best beam pair may be a beam pair associated with a signal strength that is greater than a signal strength associated with any other evaluated beam pair. A second best beam pair may be a beam pair associated with a signal strength that is greater than a signal strength of any other beam pair except the best beam pair. In some aspects, the signal strength may include an RSRP, an RSRQ, an RSSI, a signal to interference plus noise ratio (SINR), and/or an SNR, among other examples. In some aspects, the wireless communication device510also may determine a third signal strength associated with the first beam pair and a fourth signal strength associated with the second beam pair.

In some aspects, the wireless communication device505may determine a first complex correlation coefficient. The complex correlation coefficient may be associated with the wireless communication device505and may be based at least in part on the set of beamformed reference signals. The complex correlation coefficient may represent a phase between a first beamforming vector used for beamforming at the wireless communication device505based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the wireless communication device505based at least in part on a second beamformed reference signal of the set of beamformed reference signals. The complex correlation coefficient may also represent an angle between the first beamforming vector and the second beamforming vector and may be determined as described above in connection withFIG. 4.

In some aspects, the wireless communication device510may determine a second complex correlation coefficient. The second complex correlation coefficient may be associated with the wireless communication device510and may be based at least in part on the set of beamformed reference signals. The second complex correlation coefficient may represent a phase between a first beamforming vector used for beamforming at the wireless communication device510based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the wireless communication device510based at least in part on a second beamformed reference signal of the set of beamformed reference signals. The second complex correlation coefficient may also represent an angle between the first beamforming vector and the second beamforming vector and may be determined as described above in connection withFIG. 4.

As shown by reference number525, the wireless communication device505may transmit, and the wireless communication device510may receive, the determined feedback. The feedback may indicate the first complex correlation coefficient. The feedback may further indicate the first signal strength associated with the first beam pair and the second signal strength associated with the second beam pair. In some aspects, the feedback may further indicate beam information associated with the first beam pair and the second beam pair. The beam information may include, for example, one or more transmission configuration indicators (TCIs), one or more PMIs, one or more beam directions, one or more beam phases, and/or codebook information, among other examples.

As shown by reference number530, the wireless communication device510may determine a signal strength threshold for determining an occurrence of a rank switch trigger event. In some aspects, the wireless communication device510may determine the signal strength threshold based at least in part on the first complex correlation coefficient, the second complex correlation coefficient, the first signal strength, the second signal strength, and/or the beam information, among other examples.

As shown by reference number535, the wireless communication device510may determine an occurrence of a rank switch trigger event based at least in part on determining that an operating signal strength satisfies the signal strength threshold. In some aspects, the signal strength threshold may include, or be referred to as, a transition SNR. The wireless communication device510may switch from a rank two operating mode to a rank four operating mode, or vice versa, based on determining the occurrence of the rank switch trigger event. In some aspects, the rank switch may be further based at least in part on a determination that an operating signal strength satisfies the signal strength threshold. In some aspects, the rank switch may be based at least in part on at least one codebook indicated by a wireless communication standard.

As shown by reference number540, the wireless communication device510may transmit, and the wireless communication device505may receive, an indication of a rank switch from a first rank operating mode to a second rank operating mode. The first rank operating mode may correspond to rank two transmissions and the second rank operating mode may correspond to rank four transmissions, or the first rank operating mode may correspond to rank four transmissions and the second rank operating mode may correspond to rank two transmissions. In some aspects, the rank two transmissions may correspond to transmissions over two polarizations with a single beam, and rank four transmissions may

As shown by reference number545, the wireless communication device510may transmit, and the wireless communication device505may receive an enhanced beam training configuration. The enhanced beam training configuration may indicate an additional set of beamformed reference signals for beam training associated with the second rank operating mode. In some aspects, the wireless communication device510may determine a realizable data rate associated with the second rank operating mode. The wireless communication device510may schedule the wireless communication device505and one or more additional wireless communication devices based at least in part on the realizable data rate.

As indicated above,FIG. 5is provided as an example. Other examples may differ from what is described with regard toFIG. 5.

FIG. 6is a diagram illustrating an example process600performed, for example, by a first wireless communication device, in accordance with the present disclosure. Example process600is an example where the first wireless communication device (e.g., wireless communication device505) performs operations associated with switching between rank two and rank four operating modes for analog beamforming.

As shown inFIG. 6, in some aspects, process600may include receiving, from a second wireless communication device, a set of beamformed reference signals for analog beam training (block610). For example, the first wireless communication device (e.g., using reception component802, depicted inFIG. 8) may receive, from a second wireless communication device, a set of beamformed reference signals for analog beam training, as described above.

As further shown inFIG. 6, in some aspects, process600may include transmitting, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector (block620). For example, the first wireless communication device (e.g., using transmission component804, depicted inFIG. 8) may transmit, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector, as described above.

In a first aspect, the feedback further indicates a first signal strength associated with a first beam pair and a second signal strength associated with a second beam pair, wherein the feedback further indicates beam information associated with the first beam pair and the second beam pair.

In a second aspect, alone or in combination with the first aspect, process600includes receiving, from the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on a signal strength threshold, wherein the signal strength threshold is based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

In a third aspect, alone or in combination with the second aspect, the first rank operating mode corresponds to rank two transmissions and the second rank operating mode corresponds to rank four transmissions, or the first rank operating mode corresponds to rank four transmissions and the second rank operating mode corresponds to rank two transmissions.

In a fourth aspect, alone or in combination with the third aspect, the rank switch is further based at least in part on a determination that an operating signal strength satisfies the signal strength threshold.

In a fifth aspect, alone or in combination with one or more of the third through fourth aspects, the signal strength threshold comprises a transition signal-to-noise ratio.

In a sixth aspect, alone or in combination with one or more of the third through fifth aspects, process600includes receiving, from the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

In a seventh aspect, alone or in combination with one or more of the third through sixth aspects, the rank switch is based at least in part on at least one codebook indicated by a wireless communication standard.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the first wireless communication device comprises a UE, a CPE, a base station, a relay node, an IAB node, or a repeater node with configurable beamforming capabilities.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, the second wireless communication device comprises a UE, a CPE, a base station, a relay node, an IAB node, or a repeater node with configurable beamforming capabilities.

AlthoughFIG. 6shows example blocks of process600, in some aspects, process600may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted inFIG. 6. Additionally, or alternatively, two or more of the blocks of process600may be performed in parallel.

FIG. 7is a diagram illustrating an example process700performed, for example, by a first wireless communication device, in accordance with the present disclosure. Example process700is an example where the first wireless communication device (e.g., wireless communication device510) performs operations associated with switching between rank two and rank four operating modes for analog beamforming.

As shown inFIG. 7, in some aspects, process700may include transmitting, to a second wireless communication device, a set of beamformed reference signals for analog beam training (block710). For example, the first wireless communication device (e.g., using transmission component804, depicted inFIG. 8) may transmit, to a second wireless communication device, a set of beamformed reference signals for analog beam training, as described above.

As further shown inFIG. 7, in some aspects, process700may include receiving, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector (block720). For example, the first wireless communication device (e.g., using reception component802, depicted inFIG. 8) may receive, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector, as described above.

In a first aspect, the feedback further indicates a first signal strength associated with a first beam pair and a second signal strength associated with a second beam pair, wherein the feedback further indicates beam information associated with the first beam pair and the second beam pair.

In a second aspect, alone or in combination with the first aspect, process700includes determining a signal strength threshold based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

In a third aspect, alone or in combination with the second aspect, process700includes determining an occurrence of a rank switch trigger event based at least in part on determining that an operating signal strength satisfies the signal strength threshold.

In a fourth aspect, alone or in combination with the third aspect, the signal strength threshold comprises a transition signal-to-noise ratio.

In a fifth aspect, alone or in combination with one or more of the third through fourth aspects, process700includes transmitting, to the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on determining the occurrence of the rank switch trigger event.

In a sixth aspect, alone or in combination with fifth aspect, the first rank operating mode corresponds to rank two transmissions and the second rank operating mode corresponds to rank four transmissions, or the first rank operating mode corresponds to rank four transmissions and the second rank operating mode corresponds to rank two transmissions.

In a seventh aspect, alone or in combination with one or more of the fifth through sixth aspects, process700includes transmitting, to the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

In an eighth aspect, alone or in combination with one or more of the fifth through seventh aspects, process700includes determining a realizable data rate associated with the second rank operating mode, and scheduling the second wireless communication device and at least a third wireless communication device based at least in part on the realizable data rate.

In a ninth aspect, alone or in combination with one or more of the third through eighth aspects, determining the occurrence of the rank switch triggering event comprises determining the occurrence of the rank switch triggering event based at least in part on at least one codebook indicated by a wireless communication standard.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the first wireless communication device comprises a UE, a CPE, a base station, a relay node, an IAB node, or a repeater node with configurable beamforming capabilities.

In an eleventh aspect, alone or in combination with one or more of the first through tenth aspects, the second wireless communication device comprises a UE, a CPE, a base station, a relay node, an IAB node, or a repeater node with configurable beamforming capabilities.

AlthoughFIG. 7shows example blocks of process700, in some aspects, process700may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted inFIG. 7. Additionally, or alternatively, two or more of the blocks of process700may be performed in parallel.

The reception component802may receive, from a second wireless communication device, a set of beamformed reference signals for analog beam training. The determination component808may determine a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector. In some aspects, the determination component808may include one or more antennas, a modulator, a transmit MIMO processor, a transmit processor, a controller/processor, a memory, or a combination thereof, of the wireless communication device described above in connection withFIG. 2. In some aspects, the determination component808may include the reception component802and/or the transmission component804.

The transmission component804may transmit, to the second wireless communication device, feedback that indicates the first complex correlation coefficient. The reception component802may receive, from the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on a signal strength threshold, wherein the signal strength threshold is based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

The reception component802may receive, from the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

The transmission component804may transmit, to a second wireless communication device, a set of beamformed reference signals for analog beam training. The reception component802may receive, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents a phase between a first beamforming vector used for beamforming at the second wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

The determination component808may determine a signal strength threshold based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information. The determination component808may determine an occurrence of a rank switch trigger event based at least in part on determining that an operating signal strength satisfies the signal strength threshold.

The transmission component804may transmit, to the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on determining the occurrence of the rank switch trigger event. The transmission component804may transmit, to the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

The determination component808may determine a realizable data rate associated with the second rank operating mode. The determination component808may schedule the second wireless communication device and at least a third wireless communication device based at least in part on the realizable data rate.

Aspect 1: A method of wireless communication performed by a first wireless communication device, comprising: receiving, from a second wireless communication device, a set of beamformed reference signals for analog beam training; and transmitting, to the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the first wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the first wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the first wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

Aspect 2: The method of Aspect 1, wherein the feedback further indicates a first signal strength associated with a first beam pair and a second signal strength associated with a second beam pair, wherein the feedback further indicates beam information associated with the first beam pair and the second beam pair.

Aspect 3: The method of Aspect 2, further comprising receiving, from the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on a signal strength threshold, wherein the signal strength threshold is based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

Aspect 4: The method of Aspect 3, wherein the first rank operating mode corresponds to rank two transmissions and the second rank operating mode corresponds to rank four transmissions, or the first rank operating mode corresponds to rank four transmissions and the second rank operating mode corresponds to rank two transmissions.

Aspect 5: The method of Aspect 4, wherein the rank switch is further based at least in part on a determination that an operating signal strength satisfies the signal strength threshold.

Aspect 6: The method of either of Aspects 4 or 5, wherein the signal strength threshold comprises a transition signal-to-noise ratio.

Aspect 7: The method of any of Aspects 4-6, further comprising receiving, from the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

Aspect 8: The method of any of Aspects 4-7, wherein the rank switch is based at least in part on at least one codebook indicated by a wireless communication standard.

Aspect 9: The method of any of Aspects 1-8, wherein the first wireless communication device comprises a user equipment, a customer premises equipment, a base station, a relay node, an integrated access and backhaul node, or a repeater node with configurable beamforming capabilities.

Aspect 10: The method of any of Aspects 1-9, wherein the second wireless communication device comprises a user equipment, a customer premises equipment, a base station, a relay node, an integrated access and backhaul node, or a repeater node with configurable beamforming capabilities.

Aspect 11: A method of wireless communication performed by a first wireless communication device, comprising: transmitting, to a second wireless communication device, a set of beamformed reference signals for analog beam training; and receiving, from the second wireless communication device, feedback that indicates a first complex correlation coefficient associated with the second wireless communication device that is based at least in part on the set of beamformed reference signals and that represents: a phase between a first beamforming vector used for beamforming at the second wireless communication device based at least in part on a first beamformed reference signal of the set of beamformed reference signals and a second beamforming vector used for beamforming at the second wireless communication device based at least in part on a second beamformed reference signal of the set of beamformed reference signals; and an angle between the first beamforming vector and the second beamforming vector.

Aspect 12: The method of Aspect 11, wherein the feedback further indicates a first signal strength associated with a first beam pair and a second signal strength associated with a second beam pair, wherein the feedback further indicates beam information associated with the first beam pair and the second beam pair.

Aspect 13: The method of Aspect 12, further comprising determining a signal strength threshold based at least in part on the first complex correlation coefficient, a second complex correlation coefficient associated with the second device, the first signal strength, the second signal strength, and the beam information.

Aspect 14: The method of Aspect 13, further comprising determining an occurrence of a rank switch trigger event based at least in part on determining that an operating signal strength satisfies the signal strength threshold.

Aspect 15: The method of Aspect 14, wherein the signal strength threshold comprises a transition signal-to-noise ratio.

Aspect 16: The method of either of Aspects 14 or 15, further comprising transmitting, to the second wireless communication device, an indication of a rank switch from a first rank operating mode to a second rank operating mode, wherein the rank switch is based at least in part on determining the occurrence of the rank switch trigger event.

Aspect 17: The method of Aspect 16, wherein the first rank operating mode corresponds to rank two transmissions and the second rank operating mode corresponds to rank four transmissions, or the first rank operating mode corresponds to rank four transmissions and the second rank operating mode corresponds to rank two transmissions.

Aspect 18: The method of either of Aspects 16 or 17, further comprising transmitting, to the second wireless communication device, an enhanced beam training configuration that indicates an additional set of beamformed reference signals for beam training associated with the second rank operating mode.

Aspect 19: The method of any of Aspects 16-18, further comprising: determining a realizable data rate associated with the second rank operating mode; and scheduling the second wireless communication device and at least a third wireless communication device based at least in part on the realizable data rate.

Aspect 20: The method of any of Aspects 14-19, wherein determining the occurrence of the rank switch triggering event comprises determining the occurrence of the rank switch triggering event based at least in part on at least one codebook indicated by a wireless communication standard.

Aspect 21: The method of any of Aspects 11-20, wherein the first wireless communication device comprises a user equipment, a customer premises equipment, a base station, a relay node, an integrated access and backhaul node, or a repeater node with configurable beamforming capabilities.

Aspect 22: The method of any of Aspects 11-21, wherein the second wireless communication device comprises a user equipment, a customer premises equipment, a base station, a relay node, an integrated access and backhaul node, or a repeater node with configurable beamforming capabilities.