Patent Description:
A wireless communication network may include a number of base stations (BSs) that can support communication for a number of user equipments (UEs). In Long Term Evolution (LTE), BSs are referred to as evolved NodeBs (eNBs). In recent years, the carrier frequencies at which BSs and UEs communicate have continued to increase and include larger bandwidths. To take advantage of these higher frequencies, more antennas in the same physical aperture have been used. For these higher frequency bands to be useful and approximate the same coverage radius as prior technologies (such as <NUM>, <NUM>, or <NUM>), however, more beam forming gain (and more accurate) beamformed transmissions are becoming necessary.

Reciprocity describes the ability for a wireless device to use information (such as angles-of-arrival and delays) from one channel (e.g., the DL) in making determinations regarding another channel (e.g., the UL). In time-division duplexing (TDD) systems, after circuit mismatches have been compensated, the physical UL channel and the physical DL channel are identical (or transpositions of each other from a matrix algebra perspective) since UL and DL operate in the same frequency band. For example, BSs may compute UL channel estimates based on UL reference signals such as sounding reference signals (SRSs) transmitted by UEs and use the UL channel estimates for DL beamforming. In another example, the UE may compute DL channel estimates based on secondary synchronization block (SSB) or channel state information -reference signals (CSI-RS) transmissions transmitted from the BS and use this information for UL channel estimates in UL transmissions. However, in practice, a communication channel between a pair of nodes (e.g., a BS and a UE) includes not only the physical channel, but also radio frequency (RF) transceiver chains, for example, including antennas, low-noise amplifiers (LNAs), mixers, RF filters, and analog-to-digital (A/D) converters or digital-to-analog (D/A) converters, and in-phase quadrature-phase (I/Q) imbalances, which may be different between different nodes and/or different antennas. Thus, each node can introduce a mismatch, for example, in amplitude and/or phase, to transmitted and/or received signals. The mismatch may impact performance of channel reciprocity-based transmissions.

<CIT> relates to an AP which may position or orient antennas in an antenna array in a particular configuration, apply different beamforming weights to different antennas in the array, and/or use different amplitudes or phases for different antennas in the array. Each particular configuration may be associated with one or more transmit chains of AP. In some cases, an AP may select a fraction of the antennas in an antenna array for a communication.

<CIT> discloses that an aircraft receiver may measure the Signal to Interference plus Noise Ratio (SINR) and send an index of the measured SINR to a ground base station. In one aspect, the ground base station adjusts the transmit power on the forward link beam to maintain the SINR received at the aircraft above a target value.

Advantageous embodiments are subject to the dependent claims.

In the following, each of the described methods, apparatuses, systems, examples and aspects, which does not fully correspond to the invention as defined in the appended claims, is thus not according to the invention and is, as well as the whole following description, present for illustration purposes only or to highlight specific aspects or features of the appended claims.

The present disclosure provides mechanisms for mitigation calibration errors. Implementations can occur from both network perspectives (e.g., at the base station (BS)-side) or non-network perspectives (e.g., UEs, relays, nodes, etc.). Calibration is the procedure by which phase and amplitude at every antenna are ensured to replicate the desired response with a certain excitation. Without calibration, receive beam weights may not produce the correct behavior as intended. Calibration helps correct the phase and amplitude mismatches between transmit and receive circuitry (e.g., due to mismatches in amplifiers, mixers, filters, couplers, etc.). Transmit and receive beam weights are typically assumed to be reciprocal. Accordingly, without calibration, the receive beam weights may not be reused for the transmission. Mitigation of phase and amplitude calibration errors involves modifying the array size, and transmission power levels, optionally also a beam codebook at the BS-side.

This disclosure relates generally to providing or participating in authorized shared access between two or more wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, <NUM>th Generation (<NUM>) or new radio (NR) networks, as well as other communications networks. As described herein, the terms "networks" and "systems" may be used interchangeably.

In particular, <NUM> networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of the new radio technology for <NUM> NR networks. The <NUM> NR will be capable of scaling to provide coverage (<NUM>) to a massive Internet of things (IoTs) with a ULtra-high density (e.g., ~<NUM> nodes/km<NUM>), ultra-low complexity (e.g., ~<NUM> of bits/sec), ultra-low energy (e.g., ~<NUM>+ years of battery life), and deep coverage with the capability to reach challenging locations; (<NUM>) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ~<NUM>% reliability), ultra-low latency (e.g., ~ <NUM>), and users with wide ranges of mobility or lack thereof; and (<NUM>) with enhanced mobile broadband including extreme high capacity (e.g., ~ <NUM> Tbps/km<NUM>), extreme data rates (e.g., multi-Gbps rate, <NUM>+ Mbps user experienced rates), and deep awareness with advanced discovery and optimizations.

The <NUM> NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI); having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD)/frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO), robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in <NUM> NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than <NUM> FDD/TDD implementations, subcarrier spacing may occur with <NUM>, for example over <NUM>, <NUM>, <NUM>, <NUM>, and the like BW. For other various outdoor and small cell coverage deployments of TDD greater than <NUM>, subcarrier spacing may occur with <NUM> over <NUM>/<NUM> BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the <NUM> band, the subcarrier spacing may occur with <NUM> over a <NUM> BW. Finally, for various deployments transmitting with mmWave components at a TDD of <NUM>, subcarrier spacing may occur with <NUM> over a <NUM> BW.

Beam management operations are based on the control messages that are periodically exchanged between transmitter and receiver nodes. Beamforming may be used to bridge the link budget, which may be quite pessimistic at mmWave frequencies due to the heavy propagation loss. The BS and UE may communicate information using beams, and each of the BS and the UE may steer its energy in a particular direction, reaping array gains in the process and bridging the link budget. In particular, the BS transmits DL information and the UE receives the DL information using the beams. Subsequently, when the UE transmits UL information, the UE may set the beam weight corresponding to the same direction as the previously mentioned beam and transmit UL data with the same beam weights, assuming it has reciprocity.

Beamforming may rely on the design of good beamforming codebooks. These codebooks, however, may perform as designed when the amplitude and phase at the antennas are reasonably well calibrated. The BS may have a large amount of antennas, and near-perfect amplitude and phase calibration may demand a lot of time, complexity, and effort. It may be desirable to mitigate phase and amplitude calibration errors at the BS.

The present disclosure provides techniques for mitigating phase and amplitude calibration errors in communications between a user equipment (UE) and a base station (BS). Due to various factors, the DL and UL channels may lack reciprocity. With calibration, the adjusted beam weights may be used for receiving and transmitting data. Calibration is the procedure by which phase and amplitude at every antenna are ensured to replicate the desired response with a certain excitation. Without calibration, receive beam weights may not produce the correct behavior as intended. Calibration helps correct the phase and amplitude mismatches between transmit and receive circuitry (e.g., due to mismatches in amplifiers, mixers, filters, couplers, etc.). Transmit and receive beam weights are typically assumed to be reciprocal. Accordingly, without calibration, the receive beam weights may not be reused for the transmission.

While per-antenna calibration can be performed, it can be time-consuming, complex, and manually intensive. Even assuming it is performed on a per-antenna basis, residual errors in phase and amplitude for each antenna (e.g., due to measurement precision and time spent on calibration) may occur. Additionally, with regard to time-varying calibration error, calibration is typically done on a per-frequency/subcarrier and per-temperature (value) basis. Due to complexity, only a finite number of points may be sampled across frequency and temperature. Once an operating frequency or a number of component carriers is determined, the only variation(s) come from temperature drifts. Due to finite sampling, time-varying phase and amplitude calibration errors may occur.

Aspects of the technology discussed herein can provide several benefits. For example, mitigation of phase and/or amplitude calibration errors at the BS-side may result in better performance. NR frequency bands may have high path loss and may be less stable than the LTE frequency bands due to high frequencies. Thus, mitigation of phase and/or amplitude calibration errors can improve NR network coverage. These benefits and other features are recognized and discussed below.

<FIG> illustrates a wireless communication network <NUM> according to some embodiments of the present disclosure. The network <NUM> may be a <NUM> network. The network <NUM> includes a number of base stations (BSs) <NUM> and other network entities. A BS <NUM> may be a station that communicates with UEs <NUM> and may also be referred to as an evolved node B (eNB), a next generation eNB (gNB), an access point, and the like. Each BS <NUM> may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to this particular geographic coverage area of a BS <NUM> and/or a BS subsystem serving the coverage area, depending on the context in which the term is used.

In the example shown in <FIG>, the BSs 105d and 105e may be regular macro BSs, while the BSs 105a-105c may be macro BSs enabled with one of <NUM> dimension (3D), full dimension (FD), or massive MIMO.

The UEs <NUM> are dispersed throughout the wireless network <NUM>, and each UE <NUM> may be stationary or mobile. A UE <NUM> may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE <NUM> may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. In one aspect, a UE <NUM> may be a device that includes a Universal Integrated Circuit Card (UICC). In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs <NUM> that do not include UICCs may also be referred to as internet of everything (IoE) devices. The UEs 115a-115d are examples of mobile smart phone-type devices accessing network <NUM> A UE <NUM> may also be a machine specifically configured for connected communication, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. The UEs 115e-<NUM> are examples of various machines configured for communication that access the network <NUM>. A UE <NUM> may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In <FIG>, a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE <NUM> and a serving BS <NUM>, which is a BS designated to serve the UE <NUM> on the downlink and/or uplink, or desired transmission between BSs, and backhaul transmissions between BSs.

The network <NUM> may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE 115e, which may be a drone. Redundant communication links with the UE 115e may include links from the macro BSs 105d and 105e, as well as links from the small cell BS 105f. Other machine type devices, such as the UE 115f (e.g., a thermometer), the UE <NUM> (e.g., smart meter), and UE <NUM> (e.g., wearable device) may communicate through the network <NUM> either directly with BSs, such as the small cell BS 105f, and the macro BS 105e, or in multi-hop configurations by communicating with another user device which relays its information to the network, such as the UE 115f communicating temperature measurement information to the smart meter, the UE <NUM>, which is then reported to the network through the small cell BS 105f. The network <NUM> may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as in a vehicle-to-vehicle (V2V).

In some implementations, the network <NUM> utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable.

In an embodiment, the BSs <NUM> can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB)) for downlink (DL) and uplink (UL) transmissions in the network <NUM>. DL refers to the transmission direction from a BS <NUM> to a UE <NUM>, whereas UL refers to the transmission direction from a UE <NUM> to a BS <NUM>. The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes, for example, about <NUM>. Each subframe can be divided into slots, for example, about <NUM>. Each slot may be further divided into mini-slots. In a frequency-division duplexing (FDD) mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a time-division duplexing (TDD) mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions.

The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs <NUM> and the UEs <NUM>. For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS <NUM> may transmit cell specific reference signals (CRSs) and/or channel state information - reference signals (CSI-RSs) to enable a UE <NUM> to estimate a DL channel. Similarly, a UE <NUM> may transmit sounding reference signals (SRSs) to enable a BS <NUM> to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some embodiments, the BSs <NUM> and the UEs <NUM> may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than UL communication. A UL-centric subframe may include a longer duration for UL communication than DL communication.

In some embodiments, the BS <NUM> can coordinate with the UE <NUM> to cooperatively schedule, beamform, and/or transmit data in the network <NUM>. Substantial gain may be achieved through greater use of a multiple antenna system. In mm Wave access, for example, a large number of antenna elements may be used to take advantage of shorter wavelengths, and to enable beamforming and beam-tracking. The higher the frequencies, the greater the propagation and penetration losses may be.

Beamforming techniques may be used to increase the signal level received by a device and to avoid transmission losses when using, for example, mm Wave frequencies. A beamformer enhances energy over its targeted/intended direction(s), obtaining a certain antenna gain in a given direction while having attenuation in others. Beamforming combines signals from multiple antenna elements in an antenna array, so that the combined signal level increases when several signal phases align (constructive interference). Each antenna array may include a plurality of antenna elements. The signals from each antenna element are transmitted with a slightly different phase (delay) to produce a narrow beam directed towards the receiver.

Due to various factors, the DL and UL channels may lack reciprocity for various reasons. Example scenarios in which the DL and UL channels may lack reciprocity include use of poor RF components on either the DL or the UL, poor calibration efforts to adjust the DL/UL circuitry, drift of component behavior with time, temperature, and other parameters, etc. The calibration procedure may involve determining nominal differences between the DL and UL circuitry.

While per-antenna calibration can be performed, it can be time-consuming, complex, and manually intensive. Even assuming it is performed on a per-antenna basis, residual errors in phase and amplitude for each antenna (e.g., due to measurement precision and time spent on calibration) may occur. Additionally, with regard to time-varying calibration errors, calibration is typically done on a per-frequency/subcarrier and per-temperature (value) basis. Due to complexity, only a finite number of points may be sampled across frequency and temperature. Once an operating frequency or number of common carriers is determined, the only variation(s) may come from temperature drifts.

Due to finite sampling, time-varying phase and amplitude calibration errors may occur. In terms of phase calibration error, it may be reasonable to assume that the phase at the i-th antenna at any point in time satisfies the following equation: <MAT> where φi represents a measured phase, φ̂i represents a true phase, and εi represents a phase error in calibration.

The phase calibration error may be uniformly distributed in +/- q degrees in accordance with the following equation: <MAT>.

The phase calibration error may be uniformly distributed with some small angular resolution of +/- q degrees. In an example, q is <NUM>°, which may be reasonable based on low calibration, but may result in an approximate error of +/- <NUM>° for low-complexity calibration.

In terms of amplitude calibration error, it may be reasonable to assume that the amplitude at the i-th antenna at any point in time satisfies the following equation: <MAT> where αi represents a measured amplitude, α̂i represents a true amplitude, and ϑi represents an amplitude calibration error in calibration.

The amplitude calibration error may be uniformly distributed in +/- A amplitude units in accordance with the following equation: <MAT>.

The amplitude calibration error may be uniformly distributed with some small angular resolution of
+/- A amplitude units.

Another impairment aside from the phase and amplitude calibration errors may involve the failure of a certain fraction of the antennas. Random antenna failures may occur, where αi may be assumed to be zero for some indices. In an example, if a certain percentage of antennas in a 32x4 antenna array at the BS-side are dropped or failed (e.g., one, two, five, ten, fifteen, and twenty percent), the worst-case performance may degrade dramatically. In this example, the smallest percentage drop may be one percent. If five percent of the antennas are dropped, the worst-case gain in coverage area may go from about -<NUM> dB to about -<NUM> dB. In an example, an antenna is "dropped" if it is excluded from being used for transmitting a communication signal, thus decreasing the number of antennas used for transmitting the communication signal. Conversely, an antenna is "added" if it is included (and was previously excluded) for use in transmitting a communication signal, thus increasing the number of antennas used for transmitting the communication signal. The array is reconfigured for optimal phase/amplitude or for compensating the phase/amplitude calibration errors for one or more beams in a particular sector.

Additionally, the aforementioned errors may be time-varying. For example, at one point in time, the errors may be between +/- <NUM>°, but if the array at the BS <NUM> heats up and the temperature drifts, the expected nominal temperature may drift away by about <NUM>°. If the calibration is not performed using that actual temperature (rather than the expected temperature), a +/- <NUM>° error may result. Moreover, if the size of the BS <NUM>'s antenna array is large, a large amount of net accumulation due to the above-mentioned impairments may occur.

A codebook includes beam weights for a collection of beams used to cover the BS <NUM>'s coverage area. A codebook may be designed a priori, and the BS may use the codebook to apply a specific set of beam weights to point signals in a certain direction. For example, an array that covers <NUM>° in azimuth and <NUM>° in elevation may use four beams. Each beam may include a collection of beam weights applied to the antennas. A first beam may point in a first direction, a second beam may point in a second direction, a third beam may point in a third direction, and a fourth beam may point in a fourth direction. Each of these four beams covers a distinct region of the coverage area, and in particular, the BS may use the four beams to cover the <NUM>°×<NUM>° coverage area. The latency associated with the initial acquisition, refinement, or other beamforming procedure may be dependent on the codebook size (e.g., four, eight, sixteen, thirty-two). The greater the codebook size, the more refined the link may be, resulting in a better beamforming gain.

With regard to codebooks, even a small phase calibration error +/- <NUM>° may result in substantial worst-case gain deterioration for a small codebook size. Additionally, a moderate phase calibration error +/- <NUM>° can result in significantly large performance deterioration. Significant deterioration in performance may result from poor amplitude calibration or from a substantial fraction of antennas being lost. The above impairments may have a larger effect on small-sized codebooks compared to large-sized codebooks due to more redundancy in beam weights in the latter. For example, for a size four codebook, a worst-case gain over a <NUM>°×<NUM>° coverage area may be poor because a large array size is used to cover a huge area with small number of beams. For good coverage, the latency may be reduced. If the size four codebook entry has a +/- <NUM>° error uniformly distributed, the cumulative distribution function (CDF) of the worst-case gain may range from about -<NUM> to about -<NUM> dB. If the size four codebook entry has a +/- <NUM>° error uniformly distributed, the worst-case gain may range from about -<NUM> to about -<NUM> dB. The greater the calibration error, the worse the performance may be in terms of worst-case gain for the coverage area. The BS is unware of where the UE may be located and may be interested in improving the performance, even for the worst-case scenario.

It may be desirable to mitigate phase and amplitude calibration errors at the BS. In some examples, mitigation of phase and amplitude calibration errors may involve modifying the array size, transmission power levels, and/or a beam codebook at the BS-side.

<FIG> illustrates a communication method <NUM> according to some embodiments of the present disclosure. As shown in diagram <NUM>, a set of input parameters <NUM> and a set of control inputs <NUM> are associated with a BS <NUM>. A set of input parameters <NUM> and set of control inputs <NUM> may be used to modify the antenna array size or codebook size for transmitting data. Set of input parameters <NUM> may include a size of antenna array <NUM>, a coverage area of array <NUM>, and a codebook size <NUM>, among other input parameters. Set of control inputs <NUM> may include a maximal phase calibration error q <NUM>, a maximal amplitude calibration error A <NUM>, and a fraction of antennas lost <NUM>, among other control inputs.

The BS <NUM> includes a plurality of antenna elements <NUM>. In an example, the plurality of antenna elements includes <NUM> antenna elements (32x4 antenna array), and the codebook size is four. A codebook size of four is small and constrained compared to larger sizes (e.g., eight, sixteen, or thirty-two). Rather than use the 32x4 array, the BS <NUM> may use a reduced size array (e.g., 16x4 antenna array) to cover the same coverage area <NUM> and with the same codebook size <NUM>. The BS <NUM> may increase the transmit power to be within the effective isotropic radiated power (EIRP)/total radiated power (TRP) limit for transmission due to the lost peak array gain from the antenna array size reduction.

In the ideal case of no phase calibration error, use of the 16x4 antenna array by the BS <NUM> in terms of performance may be poorer than using the 32x4 antenna array. However, by reducing the antenna array size from 32x4 to 16x4, the performance may be more robust to phase calibration errors. For example, if the BS <NUM> performed with a +/- <NUM>° error with the 32x4 array size, the use of the 16x4 array size with the same +/-<NUM>° error may not cause the worst-case scenario to suffer too much. In the presence of a phase calibration error, the 16x4 antenna array provides better performance than the 32x4 antenna array by a <NUM> dB boost. In this example, the peak powers for these two arrays may match, but the 16x4 antenna array provides more robustness to the worst-case power scenario.

If the BS <NUM> uses a codebook that is small in size, the design may not provide for robustness to phase and amplitude calibration errors. If the BS <NUM> uses a large array, a number of antennas from the array may be left unused (e.g., <NUM>% of the antennas), resulting in the loss of <NUM> dB in terms of peak array gain. The loss may be compensated by increasing the EIRP by <NUM> dB such that the net power steered in a particular direction stays the same.

The BS <NUM> receive feedback <NUM> from one or more UEs <NUM> to determine whether to modify the antenna array size and/or the power transmit level. Modification may occur to support changing an effective array size (e.g., for broadened beams). The feedback <NUM> may be an indication to the BS <NUM> to modify the first number and the first transmission power level for subsequent signal transmissions. The feedback <NUM> from one or more UEs may guide the BS <NUM> in its determination of whether to modify the number antenna elements and/or the transmission power level for future signal transmissions. In an example, the feedback <NUM> is a measurement report including at least one of a reference signal received power (RSRP), a reference signal received quality (RSRQ), a received signal strength indicator (RSSI), a signal-to-interference-plus-noise ratio (SINR), or a signal-to-noise ratio (SNR) from one or more UEs <NUM>. It may be advantageous for a UE to provide this type of information in a measurement report that is sent to the BS because it provides the BS with feedback the UE's experience. For example, if the BS is provided with an indication (via measurement reports) that multiple UEs are experiencing poor RSRP levels, the BS may determine that the poor performance is due to phase and/or amplitude calibration errors. To mitigate these calibration errors, the BS may modify the array size and/or the transmission power level for future signal transmissions.

With reference to <FIG>, the BS <NUM> may have sufficient processing power to determine a mitigation strategy <NUM>. A mitigation strategy includes determining whether to modify the array size and the transmission power level for future signal transmissions. The BS modifies the transmission power level and the array size (e.g., by decreasing the array size and increasing the transmission power level if the error estimate is large or by increasing the array size and decreasing the transmission power level if the error estimate is small) based on the feedback from one or more UEs.

The BS may modify the transmission power level and the array size based on an aggregate of power reports of multiple UEs (e.g., UE action requests and phase/amplitude calibration error information). The BS may adjust/refine the codebook based on the feedback. For example, the BS may go from using a size four codebook to a size eight or a size sixteen codebook. Using information from the UEs in the coverage area, the BS may perform a codebook adjustment at the BS. Thus, codebook changes can be done as a function of information contained in aggregated UE reports. If the net performance at the UEs improve, the BS codebook adjustment is in the correct direction and iterates this process to improve the codebook. Additionally, the BS may improve the calibration accuracy with a built-in test mode (e.g., an online/mission mode calibration or self-test).

A self-test may include reviewing operational characteristics and adjusting antenna array usage parameters based on reviewing results of the self-test. By performing a self-test, a BS can improve operational performance or perform in accordance with desired network design conditions. Self-test details may be stored in a memory at the BS and/or periodically updated throughout operations as desired.

<FIG> illustrates a communication method <NUM> according to some embodiments of the present disclosure. <FIG> includes the BS <NUM>, the set of input parameters <NUM>, and the set of control inputs <NUM>. The BS <NUM> is coupled to a transmission point <NUM> via a link <NUM>. The transmission point <NUM> includes the plurality of antenna elements <NUM>. In some examples, the link <NUM> is an optical fiber link between the BS and the transmission point <NUM>. The BS <NUM> may forward feedback <NUM> from one or more UEs to the transmission point <NUM>.

With reference to <FIG>, the BS <NUM> may have little in terms of computational intelligence. For example, the BS may be small and a large antenna array (e.g., 32x4) may be unable to fit in the BS. In this example, the BS may forward to a transmission point (e.g., server) the feedback (e.g., measurement report) from the UE and instantaneous information on phase and/or amplitude calibration errors (e.g., temperature estimate and a lookup table for calibration interpolation error). The transmission point <NUM> processes the information forwarded by the BS and feeds the mitigation strategy <NUM> back to the BS. Although not shown, the transmission point <NUM> may be used by one or more BS for mitigating amplitude and phase calibration errors. The transmission point <NUM> may be, for example, a server, a network-level device, or other device.

In some examples, if a sufficient number of UEs report a power metric (e.g., RSRP, RSRQ, RSSI, SINR, or SNR) below a particular threshold, the BS may modify the array size and the transmission power level (e.g., by decreasing the array size and increasing the transmission power level or by increasing the array size and decreasing the transmission power to improve the BS's worst-case coverage). In some examples, the transmission point may suggest a codebook adjustment (e.g., increase or decrease the codebook size) or refinement. In some examples, the transmission point improves calibration accuracy with a built-in test mode (e.g., an online mode/mission mode calibration).

<FIG> is a block diagram of an exemplary BS <NUM> according to embodiments of the present disclosure. The BS <NUM> may be a BS <NUM> as discussed above. As shown, the BS <NUM> may include a processor <NUM>, a memory <NUM>, a calibration module <NUM>, a report module <NUM>, a transceiver <NUM> including a modem subsystem <NUM> and a RF unit <NUM>, and one or more antennas <NUM>. These elements may be in direct or indirect communication with each other, for example via one or more buses.

Instructions <NUM> may also be referred to as code. The terms "instructions" and "code" should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms "instructions" and "code" may refer to one or more programs, routines, sub-routines, functions, procedures, etc. "Instructions" and "code" may include a single computer-readable statement or many computer-readable statements.

Each of calibration module <NUM> and report module <NUM> may be implemented via hardware, software, or combinations thereof. For example, each of calibration module <NUM> and report module <NUM> may be implemented as a processor, circuit, and/or instructions <NUM> stored in the memory <NUM> and executed by the processor <NUM>.

Each of calibration module <NUM> and report module <NUM> may be used for various aspects of the present disclosure. For example, the calibration module <NUM> may be configured to transmit, via an antenna array including a plurality of antenna elements, a first communication signal using a first number of the plurality of antenna elements and a first transmission power level. The report module <NUM> may be configured to receive, from at least one UE, a measurement report based on the first communication signal. The calibration module <NUM> may perform calibration for the mismatch based on the measurement report. For example, the calibration module <NUM> may increase the number of antenna elements and decrease the transmission power level for future communication signal transmissions. In another example, the calibration module <NUM> may decrease the number of antenna elements and increase the transmission power level for future communication signal transmissions.

The calibration module <NUM> may be further configured to transmit a second communication signal using a second number of the plurality of antenna elements and a second transmission power level based on the measurement report. At least one of the first number of the plurality of antenna elements is different from the second number of the plurality of antenna elements, or at least one of the first transmission power level is different from the second transmission power level. The calibration module <NUM> may be further configured to transmit the first communication signal beam, a beam codebook, adjust or refine the beam code book based on the measurement report, and transmit the second communication signal based on the adjusted beam code book. Mechanisms for mitigating phase and amplitude calibration errors for communications between a BS and a UE are described in greater detail herein.

As shown, the transceiver <NUM> may include the modem subsystem <NUM> and the RF unit <NUM>. The transceiver <NUM> can be configured to communicate bi-directionally with other devices, such as the UEs <NUM> and/or another core network element. The modem subsystem <NUM> may be configured to modulate and/or encode data from the memory <NUM>, the calibration module <NUM>, and/or the report module <NUM> according to a modulation and coding scheme (MCS), e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit <NUM> may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data from the modem subsystem <NUM> (on outbound transmissions) or of transmissions originating from another source such as a UE <NUM>. The RF unit <NUM> may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver <NUM>, the modem subsystem <NUM> and the RF unit <NUM> may be separate devices that are coupled together at the BS <NUM> to enable the BS <NUM> to communicate with other devices.

The RF unit <NUM> may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas <NUM> for transmission to one or more other devices. The antennas <NUM> may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver <NUM>. The antennas <NUM> may include multiple antennas of similar or different designs in order to sustain multiple transmission links.

<FIG> is a block diagram of an exemplary UE <NUM> according to embodiments of the present disclosure. The UE <NUM> may be a UE <NUM> as discussed above. As shown, the UE <NUM> may include a processor <NUM>, a memory <NUM>, a calibration module <NUM>, a report module <NUM>, a transceiver <NUM> including a modem subsystem <NUM> and a radio frequency (RF) unit <NUM>, and one or more antennas <NUM>. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The memory <NUM> may include a cache memory (e.g., a cache memory of the processor <NUM>), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In an embodiment, the memory <NUM> includes a non-transitory computer-readable medium. The instructions <NUM> may include instructions that, when executed by the processor <NUM>, cause the processor <NUM> to perform the operations described herein with reference to the UEs <NUM> in connection with embodiments of the present disclosure.

Each of calibration module <NUM> and report module <NUM> may be used for various aspects of the present disclosure. For example, the calibration module <NUM> may be configured to receive a first communication sign from a BS (e.g., the BSs <NUM>). The report module <NUM> may be configured to transmit to the BS, a request to change at least one of an antenna array size at the base station, a transmit power level at the base station, and/or a beam codebook based on the first communication signal. The calibration module <NUM> may be configured to receive from the base station, a second communication signal in response to the request.

As shown, the transceiver <NUM> may include the modem subsystem <NUM> and the RF unit <NUM>. The transceiver <NUM> can be configured to communicate bi-directionally with other devices, such as the BSs <NUM>. The modem subsystem <NUM> may be configured to modulate and/or encode the data from the memory <NUM>, the calibration module <NUM>, and/or the report module <NUM> according to a MCS, e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit <NUM> may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data from the modem subsystem <NUM> (on outbound transmissions) or of transmissions originating from another source such as another UE or a BS <NUM>. The RF unit <NUM> may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver <NUM>, the modem subsystem <NUM> and the RF unit <NUM> may be separate devices that are coupled together at the UE <NUM> to enable the UE <NUM> to communicate with other devices.

The RF unit <NUM> may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas <NUM> for transmission to one or more other devices. The antennas <NUM> may further receive data messages transmitted from other devices. The antennas <NUM> may provide the received data messages for processing and/or demodulation at the transceiver <NUM>. The antennas <NUM> may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit <NUM> may configure the antennas <NUM>.

<FIG> illustrates a signaling diagram of a method <NUM> for mitigating calibration errors according to some embodiments of the present disclosure. Steps of the method <NUM> can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of wireless communication devices, such as the BSs <NUM> and <NUM> and the UEs <NUM> and <NUM>. The method <NUM> can be better understood with reference to <FIG> and <FIG>. As illustrated, the method <NUM> includes a number of enumerated steps, but embodiments of the method <NUM> may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. The method <NUM> illustrates one BS and one standalone UE for purposes of simplicity of discussion, though it will be recognized that embodiments of the present disclosure may scale to many more UEs and/or BSs.

At step <NUM>, a BS <NUM> transmits a first communication signal using a first number of a plurality of antenna elements and a first transmission power level to a UE <NUM>. The BS <NUM> includes an antenna array including the plurality of antenna elements. In this example, the BS <NUM> determines the first number of the plurality of antenna elements and/or the first transmission power level based on at least one of a size of the antenna array, a coverage area for the antenna array, a codebook size, a latency, a phase calibration error, an amplitude calibration error, or a fraction of failed antenna elements. In another example, a transmission point (e.g., transmission point <NUM> in <FIG>) includes an antenna array including the plurality of antenna elements and is remote from the BS. In this example, the BS transmits the first communication signal to a UE via the transmission point.

The UE <NUM> receives the first communication signal from the BS <NUM>. At step <NUM>, the UE <NUM> transmits feedback based on the received first communication signal, the feedback including an indication to modify the first number and the first transmission power level for a subsequent signal transmission. The feedback includes a request to change at least one of an antenna array size at the BS <NUM> and a transmit power level at the BS <NUM> based on the first communication signal. In an example, the feedback includes a measurement report including at least one of a RSRP, a RSRQ, a RSSI, a SINR, or a SNR corresponding to a best beam pair from one or more UEs.

The BS <NUM> may compare the measurement report to a threshold. In an example, the measurement report includes a RSRP, RSRQ, RSSI, SINR, or SNR metric corresponding to the best beam pair from the UE. If a certain fraction of the UE's power level reports satisfies the threshold (e.g., is below or above the threshold), the BS <NUM> may modify the number of the plurality of antenna elements and/or the transmission power level for future signal transmissions. The BS <NUM> may determine the second number of the plurality of antenna elements and/or the second transmission power level based on a comparison between the measurement report and the threshold.

At step <NUM>, the BS <NUM> transmits a second communication signal based on the feedback to the UE <NUM>, the second communication signal using a second number of the plurality of antenna elements and a second transmission power level. The BS <NUM> may use a combination of the feedback from one or more UEs, phase calibration error information, and/or amplitude calibration error information in its decision to modify the number of antenna elements and the transmission power level for future communication signal transmissions.

The BS <NUM> determines the second number of the plurality of antenna elements and the second transmission power level based on the feedback. The BS <NUM> decreases the array size and increases the transmission power level such that the first number of the plurality of antenna elements is less than the second number of the plurality of antenna elements and the first transmission power level is greater than the second transmission power level. In another example, not covered by the claims, the BS <NUM> increases the array size and decreases the transmission power level such that the first number of the plurality of antenna elements is greater than the second number of the plurality of antenna elements and the first transmission power level is less than the second transmission power level. Additionally, the BS <NUM> may transmit the second communication signal by applying a codebook including beamforming weights. The BS <NUM> may adjust the beamforming weights in the codebook based on the feedback (e.g., measurement report).

<FIG> is a flow diagram of a communication method <NUM> according to embodiments of the present disclosure. Steps of the method <NUM> can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device, such as the BSs <NUM> and <NUM>. The method <NUM> may employ similar mechanisms as in the methods <NUM> and <NUM> described with respect to <FIG> and <FIG>, respectively. As illustrated, the method <NUM> includes a number of enumerated steps, but embodiments of the method <NUM> may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order.

At step <NUM>, the method <NUM> includes transmitting, by a base station via an antenna array including a plurality of antenna elements, a first communication signal using a first number of the plurality of antenna elements and a first transmission power level. In an example, the BS includes an antenna array including the plurality of antenna elements. In this example, the BS determines the first number of the plurality of antenna elements and/or the first transmission power level based on at least one of a size of the antenna array, a coverage area for the antenna array, a codebook size, a latency, a phase calibration error, an amplitude calibration error, or a fraction of failed antenna elements. In another example, a transmission point (e.g., transmission point <NUM> in <FIG>) includes an antenna array including the plurality of antenna elements and is remote from the BS. In this example, the BS transmits the first communication signal to a UE via the transmission point.

At step <NUM>, the method <NUM> includes receiving, by the base station from at least one user equipment, a measurement report based on the first communication signal. In an example, the measurement report includes at least one of a RSRP, a RSRQ, a RSSI, a SINR, or a SNR metric corresponding to a best beam pair from a UE. The BS may receive multiple measurement reports from multiple UEs.

At step <NUM>, the method <NUM> includes transmitting, by the base station, a second communication signal using a second number of the plurality of antenna elements and a second transmission power level based on the one or more measurement reports, where the first number of the plurality of antenna elements is different from the second number of the plurality of antenna elements and the first transmission power level is different from the second transmission power level. The BS may determine the second number of the plurality of antenna elements and/or the second transmission power level based on a comparison between the measurement report and a threshold. In an example, the BS determines to modify the number of plurality of antenna elements used for transmitting the second communication signal from the first number to the second number and determines to modify the transmission power level used for transmitting the second communication signal from the first the first transmission power level to the second transmission power level.

The BS may compare the data included in the one or more measurement reports to the threshold. In an example, a measurement report includes at least one of a RSRP, RSRQ, RSSI, SINR, or SNR metric corresponding to the best beam pair from the UE. If a certain fraction of the UE's power level reports satisfies the threshold (e.g., is below or above the threshold), the BS may modify the number of the plurality of antenna elements and/or the transmission power level for future signal transmissions. In an example not covered by the claims, the BS may increase the number of antenna elements and decrease the transmission power level for future communication signal transmissions. The BS decreases the number of antenna elements and increases the transmission power level for future communication signal transmissions.

In some examples, a plurality of UEs sends the BS a measurement report. Accordingly, the BS receives a plurality of measurement reports. The BS may aggregate the plurality of measurement reports and determine, based on the aggregated measurement reports, to transmit the second communication signal using the second number of the plurality of antenna elements and the second transmission power level. The changes made to adjust the antenna element array size may happen at any time and may be based on feedback from one or more UEs (e.g., based on a measurement report).

<FIG> is a flow diagram of a communication method <NUM> according to embodiments of the present disclosure. Steps of the method <NUM> can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device, such as the UEs <NUM> and <NUM>. The method <NUM> may employ similar mechanisms as in the methods <NUM> and <NUM> described with respect to <FIG> and <FIG>, respectively. As illustrated, the method <NUM> includes a number of enumerated steps, but embodiments of the method <NUM> may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order.

At step <NUM>, the method <NUM> includes receiving, by a user equipment from a base station, a first communication signal. In an example, the UE receives the first communication signal from the BS via a link that connects the UE and the BS. In another example, the UE receives the first communication signal from the BS via the transmission point.

At step <NUM>, the method <NUM> includes transmitting, by the user equipment to the base station, a request to change at least one of an antenna array size at the base station or a transmit power level at the base station based on the first communication signal. The UE transmits a request to change the antenna array size at the BS based on the first communication signal. Further, the UE transmits a request to change the transmit power level at the base BS based on the first communication signal.

At step <NUM>, the method <NUM> includes receiving, by the user equipment from the base station, a second communication signal in response to the request. The BS modifies the antenna array size and the transmit power level at the base station in accordance with the request and transmits the second communication signal using the modified antenna array size and the transmit power level.

Claim 1:
A method of wireless communication, comprising:
transmitting (<NUM>), by a base station, BS, via an antenna array including a plurality of antenna elements, a first communication signal using a first number of the plurality of antenna elements and a first transmit power level;
receiving (<NUM>), by the BS from at least one user equipment, UE, one or more measurement reports based on the first communication signal; and
transmitting (<NUM>), by the BS, a second communication signal using a second number of the plurality of antenna elements and a second transmit power level based on the one or more measurement reports,
wherein the first number of the plurality of antenna elements is greater than the second number of the plurality of antenna elements, and the first transmit power level is less than the second transmit power level.