Channel calibration using parameter perturbation

Abstract

Methods, systems, and devices for channel calibration based on parameter perturbation are described. An example wireless communication method includes determining a current precoding operational point (OP) for transmissions to one or more wireless devices, performing a first (and second) set of measurement transmissions having a first (and second) precoding OP that is positively (negatively) perturbed from the current precoding OP by a first (second) perturbation value, and estimating, based on one or more feedback signals received from the one or more wireless devices in response to the first set of measurement transmissions and the second set of measurement transmissions, a next precoding OP to be used for transmissions from the network device to the one or more wireless devices.

Description

PCT Patent Application Attorney Docket No.119314.8118.WO00 CHANNEL CALIBRATION USING PARAMETER PERTURBATION CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application No.63 / 518,657, filed August 10, 2023, the disclosure of which is hereby incorporated by reference herein in its entirety. TECHNICAL FIELD

[0002] The present document relates to wireless communication. BACKGROUND

[0003] Due to an explosive growth in the number of wireless user devices and the amount of wireless data that these devices can generate or consume, current wireless communication networks are fast running out of bandwidth to accommodate such a high growth in data traffic and provide high quality of service to users.

[0004] Various efforts are underway in the telecommunication industry to come up with next generation of wireless technologies that can keep up with the demand on performance of wireless devices and networks. Many of those activities involve situations in which a large number of user devices may be served by a network. SUMMARY

[0005] This document discloses techniques that may be used by wireless networks to achieve several operational improvements.

[0006] In an example aspect, a wireless communication method is disclosed. The method includes (a) determining, by a network device, a current precoding operational point (OP) for transmissions to one or more wireless devices, (b) performing a first set of measurement transmissions from the network device to the one or more wireless devices, and (c) performing a second set of measurement transmissions from the network device to the one or more wireless devices. In this example method, the first set of measurement transmissions have a first precoding OP that is positively perturbed from the current precoding OP by a first perturbation value, and the second set of measurement transmissions has a second precoding OP that is negatively perturbed from the current precoding OP by a second perturbation value. The method 1 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 lastly includes (d) estimating, based on one or more feedback signals received from the one or more wireless devices in response to the first set of measurement transmissions and the second set of measurement transmissions, a next precoding OP to be used for transmissions from the network device to the one or more wireless devices.

[0007] In another example aspect, a wireless communication apparatus that implements the above-described method is disclosed.

[0008] In yet another example aspect, a wireless system in which the above-described method is implemented is disclosed.

[0009] In yet another example aspect, a computer-readable storage medium that stores processor-executable code for the above-described method is disclosed.

[0010] These, and other, features are described in this document. DESCRIPTION OF THE DRAWINGS

[0011] Drawings described herein are used to provide a further understanding and constitute a part of this application. Example embodiments and illustrations thereof are used to explain the technology rather than limiting its scope.

[0012] FIG.1 shows an example communication network.

[0013] FIG.2 shows a simplified example of a wireless communication system in which uplink and downlink transmissions are performed.

[0014] FIG.3A–3C show examples of beamforming achieved by various embodiments.

[0015] FIG.4 is a block diagram of an example implementation of channel calibration.

[0016] FIG.5 is a block diagram of another example implementation of channel calibration.

[0017] FIG.6 shows details of an example channel calibration implementation.

[0018] FIG.7 shows additional details of the example channel calibration implementation.

[0019] FIG.8 is a flowchart for an example method of wireless communication.

[0020] FIG.9 is a block diagram of an example hardware platform. DETAILED DESCRIPTION

[0021] To make the purposes, technical solutions and advantages of this disclosure more apparent, various embodiments are described in detail below with reference to the drawings. Unless otherwise noted, embodiments and features in embodiments of the present document may be combined with each other. 2 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0022] Section headings are used in the present document to improve readability of the description and do not in any way limit the discussion or the embodiments to the respective sections only. Furthermore, certain standard-specific terms are used for illustrative purpose only, and the disclosed techniques are applicable to any wireless communication systems.

[0023] 1. Introduction to the wireless communication environment

[0024] The wireless or time-variant nature of the communication channel poses several challenges in designing a transmission protocol suitable for wireless communication scenarios. These days, users expect their wireless devices to work everywhere and in a variety of mobile or stationary situations.

[0025] The time-variant nature of a wireless network and the expectation by users of a reliable, high-bandwidth network connection at any time and in any place creates a tension between the required amount of transmission resources a wireless network needs for overhead signal communications (e.g., for calibrating a wireless channel) and allocating as much transmission bandwidth to user data as possible. Deployments of user devices and network devices having multiple antennas makes this problem becomes even more challenging because wireless networks may need to calibrate wireless channel to / from each antenna of a multi-antenna device.

[0026] The techniques described in the present application allow for calibration of uplink or downlink wireless network connections using various techniques that provide operational advantages as further described throughout the present document.

[0027] 2. Example wireless systems

[0028] FIG.1 shows an example of a wireless communication system 100 in which a transmitter device 102 transmits signals to a receiver 104. The signals may undergo various wireless channels and multipaths, as depicted. Some reflectors such as buildings and trees may be static, while others such as cars, may be moving scatterers. The transmitter device 102 may be, for example, a user device, a mobile phone, a tablet, a computer, or another Internet of Things (IoT) device such as a smartwatch, a camera, and so on. The receiver device 104 may be a network device such as the base station. The signals transmitted from the base station to the transmitter 102 may experience similar channel degradations produced by static or moving scatterers. The techniques described in the present document may be implemented by the devices in the wireless communication system 100. The terms “transmitter” and “receiver” are simply used for convenience of explanation and as further described herein, depending on the direction of 3 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 transmission (uplink or downlink), the network station may be transmitting or receiving, and user device may be receiving or transmitting.

[0029] FIG.2 shows a simplified wireless network to highlight certain aspects of the disclosed technology. A transmitter transmits wireless signals to a receiver in the wireless network. Some transmissions in the network, variously called as downlink or downstream transmissions, a network-side node such as a base station acts as a transmitter of wireless signals and one or more user devices act as the receiver of these wireless signals. For some other transmissions, as depicted in FIG.2, the direction of transmission may be opposite. Such transmissions are often called uplink or upstream transmissions. For such transmissions, one or more user devices act as transmitters of the wireless signals and a network-side node such as the base station acts as the receiver of these signals (as depicted in FIG.2). Other type of transmissions in the network may include device-to-device transmissions, sometimes called direct or sideband transmissions. While the present document primarily uses the terms “downlink” and “uplink” for the sake of convenience, similar techniques may also be used for other situations in which transmissions in two directions are performed - e.g., inbound or incoming transmissions that are received by a wireless device and outbound or outgoing transmissions that are transmitted by a wireless device. For example, downlink transmissions may be inbound transmissions for a user device, while outbound transmissions for a network device. Similarly, uplink transmission may be inbound transmissions for a network device while outbound transmissions from a wireless device. Therefore, for some embodiments, the disclosed techniques may also be described using terms such as “inbound” and “outbound” transmission without importing any 3GPP-specific or other wireless protocol-specific meaning to the terms “uplink” and “downlink.”

[0030] In frequency division multiplexing (FDM) networks, the transmissions to a base station and the transmissions from the base station may occupy different frequency bands (each of which may occupy continuous or discontinuous spectrum). In time division multiplexing (TDM) networks, the transmissions to a base station and the transmissions from the base station occupy a same frequency band but are separated in time domain using a TDM mechanism such as time slot-based transmissions. Other types of multiplexing are also possible (e.g., code division multiplexing, orthogonal time frequency space, or OTFS, multiplexing, spatial multiplexing, etc.). In general, the various multiplexing schemes can be combined with each other. For example, in spatially multiplexed systems, transmissions to and from two different user devices 4 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 may be isolated from each other using directional or orientational difference between the two end points (e.g., the user devices and a network station such as a base station).

[0031] 3. Network alignment functions

[0032] Most modern networks implement a network alignment functionality. This functionality refers to aligning timing, phase, and / or gain across transmit and / or receive paths at both sides of a communication channel, e.g., between a base station and user devices (UEs), between UEs in a sidelink, or between devices in direct communication. The alignment may include aligning timing and communication parameters used for transmission. Aligning timing at the transmitter and the receiver allows for error-free transmissions without having to use time gaps for allowing time for receivers to absorb communication propagation delays, thereby improving channel transmission efficiency (e.g., bits per hertz per second). Aligning timing, phase, and gain at the transmitter and the receiver enables signals to interact with each other and the channel in a coherent manner. This improves network capacity by reducing the probability-of-error when spatial-multiplexing data transmissions to a single (SU) or multiple users (MU).

[0033] In some embodiments, automated calibration of downlink (DL) and uplink (UL) may be performed using a communication protocol that allows exchange of related information.

[0034] In some embodiments, the alignment operation may exchange information about whether and how the transmitter is able to send, or the receiver is able to receive one or more Multi-user (MU) modulation and code (MCS) values. To be able to obtain this information, an MU-MCS estimation operation may be performed based on transmitted signals.

[0035] FIG.3A–3C show beamforming achieved by various embodiments. FIG.3A shows a case in which “ideal” beamforming may occur where the weights w0 and w1 are selected to form a beam in a desired direction. As depicted, transmission energy is directed spatially with an intended beam-pattern. A main lobe of energy may point in a desired direction (e.g., 15 degrees) while minimal energy may be directed in another desired direction (e.g., –50 degrees). Here, it is assumed that the angle of arrival (AoA) for the target user device has been estimated as disclosed in the present document.

[0036] FIG.3B shows another example where calibration impairments produce uneven distortion in each transmit or receive chain, and the resulting uncalibrated beam may be formed in a direction that is different from the desired direction as shown in FIG.3A. 5 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0037] FIG.3C shows an embodiment in which transmit path distortions are calibrated and corresponding compensatory timings, gains, and phases are applied in order to produce a beam pattern that is close to the ideal beam pattern as shown in FIG.3A. In the depicted embodiment, a calibration coefficient alignment is performed by applying an inverse ratio factor of the ratio between two different processing chains of two antenna ports. Alternatively, the calibration coefficient alignment may be applied to each signal processing path to match each path’s signal distortions to a uniform level. Additionally, or alternatively, the uniform level may be scaled to a predetermined gain value (e.g., based on a bit width of an analog-to-digital converter (ADC) or a digital-to-analog converter (DAC) in the respective signal processing paths.

[0038] In some embodiments, link capacity of a communication link between a transmitter and one or more receivers may be optimized using the alignment operation. Here, a “transmitter” may represent an antenna, an antenna port or a transmission reception point (TRP), as it is variously called for an entity that emanates or receives an electromagnetic wavefront.

[0039] Another operation that may be performed during alignment includes alias detection and correspondingly aligning transmitter and receiver operations in the frequency domain. Another operation that may be performed during alignment includes spatial-alias detection, aligning transmitter and / or receiver relative to a direction vector. The various embodiments disclosed in the present document are further explained using examples from well-understood communication protocols such as Third Generation Partnership Project’s (3GPP) Long Tern Evolution (LTE) protocol, LTE-Advanced (LTE-A) protocol or the Fifth Generation (5G) protocol.

[0040] In Release 10 LTE-Advanced, Channel State Information (CSI) was decoupled from LTE's broadcast Cell-specific Reference Signal (CRS) with Channel State Information – Reference Signals (CSI-RS). One of the advantages of such a decoupling is to allow flexible, UE-specific scheduling and precoding of the CSI-RS enabling calibration and alignment of individual transmission / reception points, thereby allowing multi-user multiple-input multiple- output (MU-MIMO) configuration support.

[0041] 4. Brief introduction to CSI-RS

[0042] One example of CSI-RS is a downlink (DL) reference signal measured by UE for CSI reporting. CSI-RS is supported in 5G and LTE-A with TM9 (introduced in LTE release 10) or TM10 (introduced in LTE release 11).5G-NR and later LTE-A releases allow for many orthogonal CSI-RS configurations. 6 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0043] In 5G-NR and LTE-A networks, nearby cells can be configured with non-zero-power (NZP)-CSI-RS and zero-power (ZP)-CSI-RS to mitigate measurement interference. Some of the later LTE-A releases add capabilities giving more flexibility to CSI-RS and the entire CSI framework, similar to 5G-NR.

[0044] 5. Using reference data vs CSI-RS for network alignment or calibration

[0045] In a legacy (pre- LTE-A) LTE system, because CSI-RS was not available, transport blocks are used as a reference to estimate link capacity in the form of block error rate BLER with a particular modulation and coding scheme (MCS) and rank. Typical measurements performed using reference data involve two steps:

[0046] (1) Estimate the appropriate MCS for desired BLER range

[0047] (2) Estimate BLER corresponding to MCS estimated in the previous step

[0048] In 5G and LTE-A, the concept of CSI-RS was expanded to use for measuring a channel quality indicator (CQI) representative of quality of the channel between a transmitting and a receiving point. At a receiver, the CSI-RS is received and is used to measure link capacity in the form of (CQI, rank). A CSI report is generated by the receiving device and provided to the transmitting device.

[0049] 6. Examples of calibration using reference data

[0050] FIG.4 shows an example flowchart of a process of calibrating a channel using reference data transmissions. At 402, resource may be allocated for transmission of reference data. The allocation of resources may be performed explicitly (e.g., through signaling or indications in control channel transmissions) or implicitly (e.g., by predefined rules about locations of time- frequency resources). In parallel with 402, or after 402, at 404, the MCS of the reference data transmission is adjusted or determined according to a calibration algorithm. In parallel with or after 402 and 404, perturbation used for perturbing a precoder used for precoding the reference data transmissions may be updated (406) to a new value. The process of updating the precoder operational parameters is described throughout the present document. In some embodiments, the precoder may be defined by a precoding gain (gi) and a precoding phase (φi). For MIMO cases, the precoding gain / phase may be represented by a matrix. In some embodiments, subsequent to determination of the perturbation value(s) to be used, these values may be used in two different measurement steps. In the first measurement step (comprising 408, 412), the precoder value is changed by increasing (or biasing) its value in one direction using the perturbation values 7 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 determined in 406. In the second measurement step (410, 414), the precoder value is changed by decreasing or biasing its value in a second direction using the perturbation values determined in 406. In a simplistic case, the two directions may simply be opposite of each other, that is, the perturbation used in the first step (408, 412) may include increasing precoding values and the perturbation used in the second step (410, 414) may include reducing precoding values. In other words, the magnitudes of the two perturbation values (used in 408 / 412 and 410 / 414) are equal and their signs are opposite to each other.

[0051] The BLER estimates obtained at 412 and 414 may be used (at 416) to determine updated phase and gain estimate values that are can be used for subsequent transmissions from the transmitter to the receiver and also for a next measurement cycle for achieving and / or maintaining calibration between the transmitter and the receiver. In some examples, the updated phase and gain estimate values are part of the feedback signal shown in FIG.4.

[0052] As depicted in FIG.4, in some embodiments, the calibration by precoding gain and / or phase perturbation may be repeated with N reference data transmissions per iteration. Typically, N is 20 to 40, with reference data transmissions spanning about 20% of physical resource blocks (PRBs) per subframe, occurring every 5 to 20 milliseconds, resulting in a duration of 100 to 800 milliseconds per iteration with reference data using 1 to 4 percent of data transmissions.

[0053] 7. Examples of calibration using CSI-RS

[0054] FIG.5 shows a process implemented in 5G and similar technologies where CSI-RS transmissions are used for CQI estimation. The overall structure of the process in FIG.5 is similar to that shown in FIG.4, and the details for certain blocks will not be repeated in this section. At 502, CSI-RS resources are allocated. At 504, perturbation values are updated. At 506, 510, precoder is biased in one direction and corresponding CQI estimate is obtained. At 508, 512, precoder is biased in a second direction and corresponding CQI estimate is obtained. At 514, based on the two CQI estimates, the values of gain and phase estimates are updated for next iteration. In some examples, the values of phase and gain estimate values are part of the feedback signal shown in FIG.5. In this scenario, calibration performed using CSI-RS results in a duration of 8 to 100 milliseconds per iteration.

[0055] 8. Additional implementation examples

[0056] In some examples, using LTE-like protocols (e.g., FIG.4), the following parameters in an example configuration may be used. 8 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0057] N_0: # grants for MCS adaption

[0058] N_1: # grants per precoder parameter

[0059] P: periodicity of reference grants (milliseconds, ms)

[0060] N = N_0 + 2*N_1

[0061] Latency = N*P (ms)

[0062] In an example, and for { N_0 = 20; N_1 = 10; P = 15ms }, the number of reference data transmissions per iteration is N = 40 with Latency = 600ms.

[0063] In some examples, using 5G-like protocol (e.g., FIG.5), the following parameters in an example configuration may be used.

[0064] N_0: # CQI Reports for avg / parameter

[0065] P: periodicity of CSI-Report (ms)

[0066] N = 2*N_0

[0067] Latency = N*P (ms)

[0068] In an example, and for { N_0 = 2; P = 10ms }, the number of CSI-Reports per iteration is N = 4 with Latency = 40ms.

[0069] In these examples, the overhead may include ZP-CSI-RS overhead (e.g., for 7 orthogonal sets) and typically consumes less than 2% of all resources.

[0070] 9. Additional perturbation examples

[0071] In various embodiments, a perturbation may be an additive or a multiplicative operation applied to transmit or receive paths along with nominal precoding coefficients. Typically, perturbations are interpreted as multiplicative, complex-valued coefficients applied across some coherent bandwidth. The perturbation coefficients may typically have a gain within a range of –3 dB to +3 dB, a phase within a range of –30 degrees to +30 degrees, and are applied over a bandwidth of 0.5 MHz to 50 MHz.

[0072] For example, when a base station has determined a current precoding OP for transmissions to a particular UE, such a precoder can be written as ^^^^^^, a complex-valued matrix over some frequency band (e.g., the downstream bandwidth being used for the signal transmission). The perturbation operation in this case is the following Hadamard product with perturbation matrix ^^^ ^^^ ^ᇣ^ᇤ^ ^ᇥ^^ ∘ ^ถ^^ ^^^ .^^ ^୰^ୡ୭^^୰ ^^୰^^୰ୠୟ^୧୭୬9 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0073] The perturbed precoder may need to be normalized due to power or phase constraints, so the resulting perturbed precoder OP can be written as follows, ^ᇣ^ᇧ ^ᇤ^^ᇧ^ᇥ^^ ൌ ^ᇣ^ᇤ^ ^ᇥ^^ ∘ ^ถ^^ ^^^ ∘ ^ᇣ^ᇤ^ ^ᇥ^^ .^^୰^^୰ୠ^^ ^୰^ୡ୭^^୰ ^^ ^୰^ୡ୭^^୰ ^^ ^^୰^^୰ୠୟ^୧୭୬ ^୭୰୫ୟ୪୧^^ ^୭୮^୧୭୬ୟ୪^

[0074] In this example, ^^^ ^^^, ^^^ ^^^ and ^^^ ^^^ are matrices with a number of rows equal to the number of antenna and a number of columns equal to a number of layers:^^^^^^, ^^^^^^∈ ℂ^୬^୫^୬^^୬୬ୟ^୭୰^^,୬^୫^ୟ^^୰^^.

[0075] Then, the⋯ ^^^ ^^^ ൌ ^ ⋮ ⋱ ⋮^

[0076] Herein, fof physical resource blocks (PRBs).

[0077] One example construction for the perturbation matrix is: ^^గఝ i ൌ port^s^ of intere^^୧,୨^ ^^, ^^, ^^^ ൌ ^10^ଶ^^ ∙ ^^^଼^ when st, andjൌ layer^s^ of interest1 otherwise,

[0078] spans first N physical resource blocks (PRBs), where ^^ and ^^ have units in dB (gain) and degrees (phase), respectively.

[0079] This results in the positively perturbed precoder OP ^ᇣ^ᇧ ^ᇧ^^ᇧ^ᇧ^,ᇤ^ ^ᇧ^ᇧ,ᇧ^ᇧ^ᇥ^^ ൌ ^ᇣ^ᇤ^ ^ᇥ^^ ∘ ^ᇣ^^ᇧ^ᇧ^,ᇧ^ᇤ^^ᇧ,ᇧ^ᇧ^ᇥ^^ ,^^ ^^

[0080] along with^ᇣ^ᇧ ^ᇧ^^ᇧ^ᇧ^,ᇤെ ^ᇧ^ᇧ,ᇧെᇧ^ᇥ^^ ൌ ^ᇣ^ᇤ^ ^ᇥ^^ ∘ ^ᇣ^^ᇧ^ᇧ^,ᇧെᇤ^^ᇧ,ᇧെᇧ^ᇥ^^ .

[0081] Although theof gain and phase values for convenience, in general these values may be different in the positive and negative directions.

[0082] FIG.6 shows additional details of embodiments that perform the calibration based on reference data. As depicted in FIG.6, reference data intended for reception by UEx (x here represents an index to a particular UE) is depicted in a resource grid 602. Resource grid 604 depicts transmissions for other UEs, or generic data for no UE, uncorrelated to reference data in grid 602 acting as interference to UEx. The two transmissions are precoded using precoder 606 10 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 and the resulting combined signal is transmitted using multiple antenna (or transmission points). Graph 608 represents an example of radiation beamwidths used for various signal types that make up the combined signal transmission.

[0083] As depicted in resource grid 602, reference data may be multiplexed with other reference signals such as cell specific reference signal CRS and control transmissions such as a physical downlink control channel (which occupies the first two symbols in LTE). As depicted in resource grid 604, a reference data subframe for interference may comprise reference data on data symbols and blank or zero power resource elements at RE that avoid interference with the reference transmissions from subframe 602.

[0084] As depicted in the beam patterns of graph 608, CRS may be transmitted using an omnidirectional beam pattern. Physical Downlink Control Channel (PDCCH) transmissions may use the same beam pattern as CRS. The reference data transmissions to UEx may have a main lobe in the direction of UEx (estimated direction) and remaining lobes suppressed to a practically negligible amount. The beam pattern of the interfering reference data transmissions to other UEs may include one or more other lobes in the direction of other UEs, with a null point in the direction of UEx.

[0085] For simplicity, the precoder 606 is shown as a 2×2 precoder with precoding coefficients p00, p01, p10, p11, which in general are complex numbers and also effectuate a phase precoding.

[0086] FIG.7 shows details of a calibration scheme in which CSI-RS transmissions are used for calibration. As depicted in FIG.7, CSI-RS intended for reception by UEx (x here represents an index to a particular UE) is depicted in a resource grid representing a subframe 702. Resource grid 704a depicts self-generated interference or transmissions intended for other UEs, uncorrelated to CSI-RS in grid 702. Resource grid 704b depicts NZP-CSI-RS for interference measurement. NZP-CSI-RS in 704b may be used by other UEs for signal measurement. The two subframe resources are precoded using precoder 706 and the resulting combined signal is transmitted using multiple antennas (or transmission reception points). Graph 708 represents an example of radiation beamwidths used for various signal types that make up the combined signal transmission.

[0087] As depicted in resource grid of subframe 702, CSI-RS transmissions may be used along with PDCCH and CRS transmission, with the remaining RE having zero energy. As depicted in resource grid of subframe 704a, one possible way to simulate interference is to use same RE as 11 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 subframe 702 for carrying CSI-RS transmissions for other UEs. As depicted in resource grid of subframe 704b, alternatively, or in addition, CSI-RS transmissions for other UEs may be allocated orthogonal or non-overlapping resources than CSI-RS for UEx.

[0088] As depicted in the beam patterns of graph 708, CRS may be transmitted using an omnidirectional beam pattern. PDCCH transmissions may use the same beam pattern as CRS. The reference data transmissions to UEx may have a main lobe in the direction of UEx (estimated direction) and remaining lobes suppressed to a practically negligible amount. The beam pattern of the interfering reference data transmissions to other UEs may include one or more other lobes in the direction of other UEs, with a null point in the direction of UEx.

[0089] For simplicity, the precoder 706 is shown as a 2×2 precoder with precoding coefficients p00, p01, p10, p11, which in general are complex numbers and also effectuate a phase precoding.

[0090] 10. Example methods and implementations of the disclosed technology

[0091] FIG.8 is a flowchart for an example method 800 of wireless communication. The method 800 includes, at operation 802, determining, by a network device, a current precoding operational point (OP) for transmissions to one or more wireless devices.

[0092] The method 800 includes, at operation 804, performing a first set of measurement transmissions from the network device to the one or more wireless devices, with the first set of measurement transmissions having a first precoding OP that is positively perturbed from the current precoding OP by a first perturbation value.

[0093] The method 800 includes, at operation 806, performing a second set of measurement transmissions from the network device to the one or more wireless devices, with the second set of measurement transmissions having a second precoding OP that is negatively perturbed from the current precoding OP by a second perturbation value.

[0094] The method 800 includes, at operation 808, estimating, based on one or more feedback signals received from the one or more wireless devices in response to the first set of measurement transmissions and the second set of measurement transmissions, a next precoding OP to be used for transmissions from the network device to the one or more wireless devices.

[0095] FIG.9 is a block diagram representation of a wireless hardware platform 900 which may be used to implement the various methods described in the present document. The hardware platform 900 may be incorporated within a base station or a user device. The hardware platform 900 includes at least one processor 902, a memory 904 and a transceiver circuitry 906. The at 12 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 least one processor may execute instructions, e. g., by reading from the memory 904, and control the operation of the transceiver circuitry 906 and the hardware platform 900 to perform the methods described herein. In some embodiments, the memory 904 and / or the transceiver circuitry 906 may be partially or completely contained within the at least one processor 902 (e.g., same semiconductor package).

[0096] The following examples highlight some preferred embodiments and technical solutions that use one or more of the techniques described herein.

[0097] 1. A method of wireless communication (e.g., method 800 in FIG.8), comprising: (a) determining (802), by a network device, a current precoding operational point (OP) for transmissions to one or more wireless devices; (b) performing (804) a first set of measurement transmissions from the network device to the one or more wireless devices, the first set of measurement transmissions having a first precoding OP that is positively perturbed from the current precoding OP by a first perturbation value; (c) performing (806) a second set of measurement transmissions from the network device to the one or more wireless devices, the second set of measurement transmissions having a second precoding OP that is negatively perturbed from the current precoding OP by a second perturbation value; and (d) estimating (808), based on one or more feedback signals received from the one or more wireless devices in response to the first set of measurement transmissions and the second set of measurement transmissions, a next precoding OP to be used for transmissions from the network device to the one or more wireless devices. Further measurement signal transmissions may be performed by applying the next precoding OP.

[0098] In some examples, operations 804 and 806 correspond to at least one of steps {406, 408, 412} and {406, 410, 414} in FIG.4, respectively, and operation 808 corresponds to at least one of steps {416, feedback, 402-406}. In other examples, operations 804 and 806 correspond to at least one of steps {504, 506, 510} and {504, 508, 512} in FIG.5, respectively, and operation 808 corresponds to at least one of steps {514, feedback, 502-504}.

[0099] 2. The method of solution 1, including: iterating (a) to (d) by setting the next precoding OP to the current precoding OP.

[0100] 3. The method of solution 2, including: modifying the first perturbation value and / or the second perturbation value according to a rule. 13 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0101] 4. The method of solution 3, wherein the rule specifies that the first perturbation value and / or the second perturbation value are modified according to a change in the one or more feedback signals during the iterating. In some examples, the one or more feedback signals include the feedback signal in FIG.4 and / or FIG.5.

[0102] 5. The method of solution 3 or 4, wherein the rule specifies that the first perturbation value is equal in magnitude as the second perturbation value.

[0103] Some preferred embodiments or technical solutions that are fully compatible with the LTE protocol include the following:

[0104] 6. The method of any of solutions 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions include reference data transmissions, and wherein the estimating the next precoding OP includes: receiving a first block error rate estimated using a first feedback signal for the first set of measurement transmissions; receiving a second block error rate estimated using a second feedback signal for the second set of measurement transmissions; and estimating the next precoding OP as a function of the first block error rate and the second block error rate.

[0105] 7. The method of any of solutions 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions are performed by adjusting a modulation and coding index according to the one or more feedback signals.

[0106] 8. The method of any of solutions 1 to 7, wherein the first set of measurement transmissions and the second set of measurement transmissions are performed using transmission resources in a data portion of downlink subframes.

[0107] 9. The method of solution 8, wherein the first set of measurement transmissions and the second set of measurement transmissions comprise multiple-input, multiple-output (MIMO) transmissions in which corresponding beamforming precoding matrices are applied to transmissions to the one or more wireless devices.

[0108] Some preferred embodiments or technical solutions that are fully compatible with the LTE protocol include the following:

[0109] 10. The method of any of solutions 1 to 9, wherein the first set of measurement transmissions and the second set of measurement transmissions include channel state information reference signal (CSI-RS) transmissions, and wherein the estimating the next precoding OP includes: receiving a first channel quality indicator (CQI) and / or a first rank estimated using a 14 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 first feedback signal for the first set of measurement transmissions; estimating a second CQI and / or a second rank estimated using a second feedback signal for the second set of measurement transmissions; and estimating the next precoding OP as a function of the first CQI, and / or first rank and the second CQI and / or the second rank.

[0110] 11. The method of any of solutions 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions are performed using CSI-RS transmission resources in downlink subframes.

[0111] 12. The method of solution 11, wherein the first set of measurement transmissions and the second set of measurement transmissions comprise multiple-input, multiple-output (MIMO) transmissions in which corresponding beamforming precoding matrices are applied to transmissions to the one or more wireless devices.

[0112] 13. The method of any of solutions 10 to 12, wherein the CSI-RS transmissions are performed using interference on co-located resource elements (REs).

[0113] 14. The method of any of solutions 10 to 12, wherein the CSI-RS transmissions are performed using orthogonal resource element (RE) assignments to the one or more wireless devices.

[0114] 15. The method of any of solutions 1 to 14, wherein the first perturbation value comprises a first gain perturbation value, a first phase perturbation value or a combination thereof.

[0115] 16. The method of any of solutions 1 to 15, wherein the second perturbation value comprises a second gain perturbation value, a second phase perturbation value or a combination thereof.

[0116] 17. A wireless communication apparatus comprising one or more processors and a transceiver, wherein the one or more processors cause the wireless communication apparatus to perform the method recited in any of solutions 1 to 16.

[0117] 18. A system comprising a plurality of wireless communication apparatus, each apparatus comprising one or more processors that are configured to implement the method recited in any of solutions 1 to 16.

[0118] In the above-described solutions, the operational point (OP) may include, for example, a precoder used for communication, a codebook used for communication, other communication parameters such as a modulation and coding index, layer information, and so on. In some solutions, the network device may monitor the progression of the iterative process that includes 15 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 the above-recited determining-performing-performing-estimating operations, and adjust the accuracy and rate of convergence of the iteration to a stable state by modifying the amount of perturbation introduced by the first and second perturbations. For example, the network device may start an iteration cycle using equal values of perturbation in the positive direction (the first perturbation value) and the perturbation in the opposite direction (the second perturbation value). The network device may then estimate the change in network performance based on the respective feedback received from positive and negative perturbations. In case that the network performance changes are equal or comparable (within a predefined value of each other), the network device may use a same amount of change in both perturbation values in the next iteration. In some embodiments, the network device may reduce a perturbation value in one direction if the measured performance change in that direction is larger than the other direction. For example, smaller changes to feedback may be indicative that the perturbation value has neared a steady-state optimum value in a particular direction, whereas a large change to the network performance may indicate that the perturbation value should be increased because the operational point is not near convergence. In some embodiments, the size calibration perturbations may be a function of a current state of the network. For example, if the network is relatively busy (e.g., if network is reaching capacity above a threshold), smaller values of perturbation may be used to ensure that the iterative calibration does not cause detrimental impacts on the network performance. For example, size of the calibration magnitude and phase perturbations may be inversely proportional to network capacity utilization.

[0119] It will be appreciated by one of skill in the art that various techniques are described to find precoding weights to maximize estimated link capacity, as measured by the UE’s CSI- Report, in the presence of inter-beam interference caused by MU-MIMO. These measurements may be performed in a fully compatible manner with existing protocols such as LTE with Reference-Data or 5G with CSI-RS transmissions.

[0120] It will also be appreciated that such measurements may be considered to be a link optimization when a single transmitter single receiver pair is used for the measurements (e.g., a single UE as a receiver). In the case that multiple receivers are used (e.g., multiple UEs), the measurements may be considered to be a calibration of the network to achieve a maximal transmission efficiency. 16 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0121] The disclosed and other embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, which is generated to encode information for transmission to suitable receiver apparatus.

[0122] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0123] The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be 17 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0124] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read -only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0125] While this patent document contains many specifics, these should not be construed as limitations on the scope of an invention that is claimed or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub- combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. 18 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00

[0126] Only a few examples and implementations are disclosed. Variations, modifications, and enhancements to the described examples and implementations and other implementations can be made based on what is disclosed. 19 167995293.2

Claims

PCT Patent Application Attorney Docket No.119314.8118.WO00 WHAT IS CLAIMED IS:

1. A method of wireless communication, comprising: (a) determining, by a network device, a current precoding operational point (OP) for transmissions to one or more wireless devices; (b) performing a first set of measurement transmissions from the network device to the one or more wireless devices, the first set of measurement transmissions having a first precoding OP that is positively perturbed from the current precoding OP by a first perturbation value; (c) performing a second set of measurement transmissions from the network device to the one or more wireless devices, the second set of measurement transmissions having a second precoding OP that is negatively perturbed from the current precoding OP by a second perturbation value; and (d) estimating, based on one or more feedback signals received from the one or more wireless devices in response to the first set of measurement transmissions and the second set of measurement transmissions, a next precoding OP to be used for transmissions from the network device to the one or more wireless devices.

2. The method of claim 1, including: iterating (a) to (d) by setting the next precoding OP to the current precoding OP.

3. The method of claim 2, including: modifying the first perturbation value and / or the second perturbation value according to a rule.

4. The method of claim 3, wherein the rule specifies that the first perturbation value and / or the second perturbation value are modified according to a change in the one or more feedback signals during the iterating.

5. The method of claim 3, wherein the rule specifies that the first perturbation value is equal in magnitude as the second perturbation value.

6. The method of any of claims 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions include reference data transmissions, and wherein the estimating the next precoding OP includes: 20 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 receiving a first block error rate estimated using a first feedback signal for the first set of measurement transmissions; receiving a second block error rate estimated using a second feedback signal for the second set of measurement transmissions; and estimating the next precoding OP as a function of the first block error rate and the second block error rate.

7. The method of any of claims 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions are performed by adjusting a modulation and coding index according to the one or more feedback signals.

8. The method of any of claims 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions are performed using transmission resources in a data portion of downlink subframes.

9. The method of claim 8, wherein the first set of measurement transmissions and the second set of measurement transmissions comprise multiple-input, multiple-output (MIMO) transmissions in which corresponding beamforming precoding matrices are applied to transmissions to the one or more wireless devices.

10. The method of any of claims 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions include channel state information reference signal (CSI-RS) transmissions, and wherein the estimating the next precoding OP includes: receiving a first channel quality indicator (CQI) and / or a first rank estimated using a first feedback signal for the first set of measurement transmissions; estimating a second CQI and / or a second rank estimated using a second feedback signal for the second set of measurement transmissions; and estimating the next precoding OP as a function of the first CQI, and / or first rank and the second CQI and / or the second rank.

11. The method of any of claims 1 to 5, wherein the first set of measurement transmissions and the second set of measurement transmissions are performed using CSI-RS transmission resources in downlink subframes. 21 167995293.2PCT Patent Application Attorney Docket No.119314.8118.WO00 12. The method of claim 11, wherein the first set of measurement transmissions and the second set of measurement transmissions comprise multiple-input, multiple-output (MIMO) transmissions in which corresponding beamforming precoding matrices are applied to transmissions to the one or more wireless devices.

13. The method of claim 11, wherein the CSI-RS transmissions are performed using interference on co-located resource elements (REs).

14. The method of claim 11, wherein the CSI-RS transmissions are performed using orthogonal resource element (RE) assignments to the one or more wireless devices.

15. The method of any of claims 1 to 5, wherein the first perturbation value comprises a first gain perturbation value, a first phase perturbation value or a combination thereof.

16. The method of any of claims 1 to 5, wherein the second perturbation value comprises a second gain perturbation value, a second phase perturbation value or a combination thereof.

17. A wireless communication apparatus comprising one or more processors and a transceiver, wherein the one or more processors cause the wireless communication apparatus to perform the method recited in any of claims 1 to 16.

18. A system comprising a plurality of wireless communication apparatus, each apparatus comprising one or more processors that are configured to implement the method recited in any of claims 1 to 16. 22 167995293.2

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