Antenna impedance detection and tuning

Abstract

A user equipment (UE) is provided that includes an antenna conversion array for sequentially demultiplexing reference signals to each of a plurality of antennas. When the antenna conversion array selects an antenna, the UE measures a reflection coefficient for the antenna. The UE then tunes the antenna in response to the reflection coefficient measurement.

Description

Technical Field

[0001] The present disclosure relates generally to wireless communications, and more particularly to antenna impedance detection and tuning. Background Art

[0002] In order to achieve higher and higher data rates in modern wireless communication systems such as fifth generation (5G) systems, cellular handsets have evolved to include antenna arrays. The use of antenna arrays has several advantages over a single antenna. For example, as received signal strength decreases, the signal-to-noise ratio becomes a limiting factor on the achievable data rate. However, the use of multiple receive antennas enables multiple-input multiple-output (MIMO) and beamforming techniques to increase received signal strength, thereby increasing the achievable data rate. Similarly, the use of multiple transmit antennas allows the transmitter to beamform and / or beamsteer the transmit signal to achieve higher data rates.

[0003] The use of distinct transmit and receive antennas in a user equipment (UE) complicates antenna characterization and impedance matching because the UE has no direct way to characterize the impedance matching of the receive antenna during normal operation. Regarding this impedance matching, the UE may include a radio frequency front end circuit (RFFE) that is coupled to the transmit antenna via an RFFE output impedance. Optimal power transfer occurs when this RFFE output impedance matches the impedance of the transmit antenna. Similarly, the RFFE is coupled to the receive antenna via an RFFE input impedance, which should match the impedance of the receive antenna. The RFFE output and input impedances may be controlled by design to equal certain desired values, such as 50Ω. However, each transmit antenna and receive antenna in the UE may have a unique direction and position within the UE that changes their impedance. In addition, the antenna impedance may change depending on how the user handles the UE. In addition, coupling to the transmit antenna and / or receive antenna changes their impedance. Therefore, matching the RFFE impedance to the antenna impedance is problematic. Summary of the invention

[0004] The following summary discusses some aspects of the present disclosure to provide a basic understanding of the discussed technology. This overview is not a general review of all expected features of the present disclosure, and is neither intended to identify key or important elements of all aspects of the present disclosure, nor is it intended to describe the scope of any or all aspects of the present disclosure. Its sole purpose is to give some concepts of one or more aspects of the present disclosure in a summarized form as a prelude to more specific embodiments given later.

[0005] According to one aspect of the present disclosure, there is provided an apparatus for wireless communication, comprising: a plurality of antennas, including at least one transmitting antenna and at least one receiving antenna; an amplifier; an antenna switching array, coupled to the plurality of antennas; a directional coupler, coupled between the amplifier and the antenna switching array; and a controller, configured to: control the antenna switching array to sequentially select each of the plurality of antennas so as to transmit a reference signal amplified by the amplifier from the antenna, and to cause the directional coupler to generate a reflected signal from the antenna; and determine a reflection coefficient for each antenna in response to the reflected signal from the antenna.

[0006] According to another aspect of the present disclosure, a user equipment (UE) for wireless communication is provided, comprising: a transmitting antenna; a receiving antenna; a transceiver configured to generate one or more sounding reference signals (SRS) for wireless channel estimation; an antenna switching array configured to respectively select the transmitting antenna and the receiving antenna to send the one or more SRS in sequence; a first tuner coupled between the transmitting antenna and the antenna switching array; a second tuner coupled between the receiving antenna and the antenna switching array; a directional coupler coupled between the transceiver and the antenna switching array; and a controller configured to adjust the first tuner and the second tuner based on a signal from the directional coupler during a sequence.

[0007] According to another aspect of the present disclosure, a method for wireless communication is provided, comprising: sequentially selecting each of a plurality of antennas of the UE through an antenna switching array; and when each antenna is selected by the antenna switching array: amplifying a reference signal through an amplifier to provide an amplified reference signal; transmitting the amplified reference signal through the antenna so that a reflected signal is reflected back to the amplifier; evaluating the impedance matching of the antenna based on samples of the amplified reference signal and samples of the reflected signal; and tuning the impedance matching of the antenna based on the evaluation of the impedance matching.

[0008] When the following specific, exemplary implementations of the present disclosure are reviewed in conjunction with the accompanying drawings, other aspects, features, and implementations of the present disclosure will become apparent to those of ordinary skill in the art. Although the features of the present disclosure may be discussed below with respect to certain implementations and accompanying drawings, all implementations of the present disclosure may include one or more of the advantageous features discussed herein. In other words, although one or more implementations may be discussed as having certain advantageous features, one or more of such features may also be used according to the various implementations of the disclosure discussed herein. In a similar manner, although exemplary implementations may be discussed below as device, system, or method implementations, it should be understood that such exemplary implementations may be implemented in various devices, systems, and methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings are used to further illustrate various implementations and explain various principles and advantages according to the present disclosure. Like reference numerals in the accompanying drawings refer to identical or functionally similar elements throughout the separate views, and are incorporated into the specification together with the specific embodiments or form a part of the specification.

[0010] Figure 1

[0013] An example system for wireless communications in accordance with aspects of the present disclosure is shown.

[0011] Figure 2

[0013] An example system for supporting wireless communications of sounding reference signals in accordance with aspects of the present disclosure is shown.

[0012] Figure 3 An example subframe structure including a sounding reference signal is shown in accordance with aspects of the present disclosure.

[0013] Figure 4 An example wireless communication device supporting sounding reference signals in accordance with aspects of the present disclosure is shown.

[0014] Figure 5 Another example wireless communication device supporting sounding reference signals in accordance with aspects of the present disclosure is shown.

[0015] Figure 6 Another example wireless communication device supporting sounding reference signals in accordance with aspects of the present disclosure is shown.

[0016] Figure 7 is a flow chart of a method for antenna impedance detection using a sounding reference signal according to aspects of the present disclosure. DETAILED DESCRIPTION

[0017] The following detailed description is intended as a description of various configurations and is not intended to represent the only configuration in which the concepts described herein can be practiced. For the purpose of providing a comprehensive understanding of the various concepts, the specific embodiments include specific details. However, it will be apparent to those skilled in the art that these concepts can be practiced without these specific details. In some cases, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0018] If the antenna is operating ideally, the guided electromagnetic waves generated and amplified by the transceiver will be completely converted into free space electromagnetic waves by the antenna. But in real-world antennas, some of the guided electromagnetic waves are reflected back to the transceiver instead of being converted into free space electromagnetic waves. The ratio of this reflected signal to the transmitted or forward signal defines the reflection coefficient Γ for the antenna. It is advantageous for the transceiver to characterize this parameter so that user interaction conditions can be determined, and so that the antenna impedance can be tuned to optimize power transfer.

[0019] Such characterization is hindered by bifurcating the antenna of the transceiver into a transmitting antenna and a receiving antenna. The system disclosed in this article overcomes this problem by utilizing the use of reference signals that are periodically sent through each transmitting antenna and each receiving antenna, respectively. The following discussion will assume that the reference signal is a sounding reference signal (SRS), but it will be understood that other types of reference signals can be used. In order to characterize the impedance of the transmitting antenna and the receiving antenna, the user equipment sends a reference signal sequentially on each antenna. The reference signal transmission is continuously sequenced through the antenna (through the transmitting antenna and through both the receiving antenna). During the transmission of the reference signal through each antenna, the user equipment drives the reference signal to the antenna through a directional coupler. The directional coupler samples the reflected signal from the selected antenna during the transmission of the reference signal. By comparing the amplitude and phase of the incident (forward) signal with the amplitude and phase of the reflected signal as sampled by the directional coupler, the user equipment can characterize the (real or complex) impedance of the antenna. In this way, by sending the reference signal sequentially through each antenna, the UE can characterize the impedance of both the transmitting antenna and the receiving antenna. As used herein, the terms "antenna impedance characterization" and "antenna reflection coefficient" characterization are used interchangeably.

[0020] Since the antenna impedance is characterized for the antenna, the UE can then adjust the antenna tuning circuit coupled to the antenna to better match the antenna to the UE's RFFE. The antenna tuning circuit can intervene between the RFFE and the corresponding antenna. If the impedance of the antenna tuning circuit is the complex conjugate of the antenna impedance, then maximum power transfer occurs between the antenna and the RFFE. For example, assume that the antenna impedance is determined to be equal to R+jX, where R is resistance, X is reactance, and j is the square root of -1. The UE can then adjust the impedance of the antenna tuning circuit to be equal to R–jX for maximum power transfer.

[0021] The technology discussed in this article allows the UE to use reference signal transmission to detect the antenna impedance of both the transmit (TX) antenna and the receive (RX) antenna. Although the following discussion will assume that the reference signal is a sounding reference signal, other types of reference signals may be used, such as an uplink demodulation reference signal (DM-RS) specific to each UE. Taking SRS as an example, the UE may send SRS to the base station in sequence through each of its antennas (including TX and RX antennas). The base station may then characterize the uplink channel for each antenna based on the received SRS. A window is provided for the transmission of SRS to detect the antenna impedance by comparing the incident power and the reflected power during the transmission. As the SRS transmission cycles through the antenna, the corresponding antenna impedance may be detected in sequence. In some implementations, the reference signal may be sent at a power level determined by the user.

[0022] In order to provide a better understanding of the advantageous properties of this characterization of the antenna impedance of the UE in both the TX antenna and the RX antenna by sequentially sending reference signals, some example wireless communication systems that support this impedance characterization will first be discussed. In addition, the frame structure of the example reference signal (particularly SRS) will also be discussed.

[0023] Figure 1 An example wireless communication system 100 supporting SRS for wireless channel estimation according to various aspects of the present disclosure is shown. The wireless communication system 100 includes a base station 105, a UE 115, and a core network 130. In some implementations, the wireless communication system 100 may be a long term evolution (LTE) network, an advanced LTE (LTE-A) network, an LTE-A Pro network, or a new radio (NR) network. In other implementations, the wireless communication system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission-critical) communications, low-latency communications, or communications with low-cost and low-complexity devices.

[0024] The base station 105 may communicate wirelessly with the UE 115 via one or more base station antennas. The base station 105 may include or may contain a base station transceiver, a radio base station, an access point, a radio transceiver, a NodeB (Node B), an eNodeB (eNB), a next generation NodeB or a giga NodeB (any of which may be referred to as a gNB), a home NodeB, a home eNodeB, or other suitable components. The wireless communication system 100 may include different types of base stations 105 (e.g., macro cell base stations or small cell base stations). The UE 115 described herein may be able to communicate with various types of base stations 105 and network devices (including macro eNBs, small eNBs, gNBs, relay base stations, etc.), and / or may be able to communicate directly with each other.

[0025] Each base station 105 may be associated with a geographic coverage area 110 in which communications with respective UEs 115 are supported. Each base station 105 may provide communications coverage for the respective geographic coverage area 110 via a communications link 125, and the communications link 125 between the base station 105 and the UE 115 may utilize one or more carriers. The communications link 125 shown in the wireless communication system 100 may include an uplink transmission from the UE 115 to the base station 105, or a downlink transmission from the base station 105 to the UE 115. Downlink transmissions may also be referred to as forward link transmissions, and uplink transmissions may also be referred to as reverse link transmissions.

[0026] UE 115 can be dispersed throughout the wireless communication system 100, and each UE 115 can be stationary or mobile. UE 115 can also be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a user device, or some other appropriate term, in which "device" can also be referred to as a unit, a station, a terminal, or a client. UE 115 can also be a personal electronic device, such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, UE 115 can be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communication (MTC) device, etc., which can be implemented in various items such as electrical appliances, or vehicles, meters, etc.

[0027] Some UEs 115 may be configured to employ a mode of operation that reduces power consumption, such as half-duplex communication (e.g., a mode that supports one-way communication via transmission or reception, rather than transmission and reception simultaneously). In some examples, half-duplex communication may be performed at a reduced peak rate. Other power conservation techniques for UE 115 include entering a power conservation "deep sleep" mode when not engaged in active communications, or operating over limited bandwidth (e.g., based on narrowband communications). In some cases, UE 115 may be designed to support critical functions (e.g., mission-critical functions), and the wireless communication system 100 may be configured to provide ultra-reliable communications for these functions.

[0028] The base stations 105 may communicate with the core network 130 and with each other. For example, the base stations 105 may interface with the core network 130 via a backhaul link 132 (e.g., via an S1, N2, N3, or other interface). The base stations 105 may communicate with each other directly (e.g., directly between the base stations 105) or indirectly (e.g., via the core network 130) via a backhaul link 134 (e.g., via an X2, Xn, or other interface).

[0029] The wireless communication system 100 may operate using one or more frequency bands, such as in the range of 300 megahertz (MHz) to 300 gigahertz (GHz) or higher. The region from 300 MHz to 3 GHz is referred to as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from about one decimeter to one meter in length. UHF waves may be blocked or redirected by buildings and environmental features. However, the waves may penetrate structures enough for a macro cell to provide service to a UE 115 located indoors. Transmissions on UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 km) than transmissions using the lower frequencies and longer wavelengths of the high frequency (HF) or very high frequency (VHF) portions of the spectrum below 300 MHz.

[0030] The wireless communication system 100 may also operate in the Super High Frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also referred to as centimeter bands. The SHF region includes frequency bands such as the 5 GHz Industrial, Scientific, and Medical (ISM) band, which may be used from time to time by devices that may be able to tolerate interference from other users.

[0031] The wireless communication system 100 may also operate in the extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz or higher), also referred to as the millimeter band (which in some systems may also include some frequencies in the 20 GHz range). In some examples, the wireless communication system 100 may support millimeter wave (mmW) communications between the UE 115 and the base station 105, and the EHF antennas of the respective devices may be even smaller and more closely spaced than UHF antennas. In some examples, this may facilitate the use of antenna arrays within the UE 115. However, the propagation of EHF transmissions may suffer from even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. The techniques disclosed herein may be employed across transmissions using one or more different frequency regions, and the designated use of frequency bands across these frequency regions may vary by country or regulatory agency.

[0032] In some cases, the wireless communication system 100 can utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communication system 100 can adopt license assisted access (LAA), LTE unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band (such as a 5GHz ISM band). When operating in an unlicensed radio frequency spectrum band, wireless devices (such as base stations 105 and UE 115) can use LBT procedures to ensure that the frequency channel is idle before sending data. In some cases, operations in unlicensed bands can be based on carrier aggregation configurations (e.g., LAA) in conjunction with component carriers operating in licensed bands. Operations in unlicensed spectrum can include downlink transmissions, uplink transmissions, peer-to-peer transmissions, or a combination of these items. Duplexing in unlicensed spectrum can be based on frequency division duplexing (FDD), time division duplexing (TDD), or a combination of both.

[0033] Beamforming (which may also be referred to as spatial filtering, directional transmission, or directional reception) is a signal processing technique that can be used at a transmitting device or a receiving device (e.g., a base station 105 or a UE 115) to shape or direct an antenna beam (e.g., a transmit beam or a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming can be achieved by combining signals transmitted via antenna elements of an antenna array so that signals propagating in some directions relative to the antenna array experience constructive interference, while other signals experience destructive interference. Adjustments to signals transmitted via antenna elements may include the transmitting device or the receiving device applying one or more amplitude offsets and phase offsets to signals carried via each of the antenna elements associated with the device. The adjustments associated with each of these antenna elements may be defined by a set of beamforming weights associated with a direction (e.g., relative to the antenna array of the transmitting device or the receiving device or relative to some other direction).

[0034] Figure 2 A portion of an example wireless communication system 200 that supports the use of SRS for wireless channel estimation is shown. In some examples, the wireless communication system 200 can implement aspects of the wireless communication system 100. In this example, the wireless communication system 200 includes a base station 105 and a UE 115, which can be as shown with respect to Figure 1 For the purpose of simplifying the discussion, Figure 2 One base station 105 and one UE 115 are shown, however, it will be appreciated that embodiments of the present disclosure may be extended to more UEs 115 and / or base stations 105. The UE 115 and the base station 105 may communicate with each other at various frequencies. For example, in one embodiment, the UE 115 and the base station 105 may communicate at sub-6 GHz (below 6 GHz) frequencies, and in another embodiment, at 6 GHz (or higher) frequencies, to name just two examples. The base station 105 may send data and control information to the UE 115 via a downlink 205, and the UE 115 may send data and control information to the base station 105 via an uplink 210.

[0035] In this example, the base station 105 may send SRS configuration information to the UE 115, and the SRS configuration information may configure one or more SRS transmissions 220 performed by the UE 115 via the uplink 210. After receiving the SRS configuration information from the base station 105, the UE 115 broadcasts the SRS 220 to the base station 105. The UE 115 may include multiple antennas, such as one TX antenna and two RX antennas (1T2R), one TX antenna and four RX antennas (1T4R), two TX antennas and four RX antennas (2T4R), four TX antennas and four RX antennas (4T4R), or other suitable TX and RX antenna combination configurations. For a UE 115 with multiple antennas, each antenna is selected in turn to transmit an SRS in a corresponding time slot within the uplink portion of the subframe structure (e.g., as Figure 3 2 and further discussed herein). Upon receiving the SRS 220, the base station 105 may determine channel information for an uplink channel between the UE 115 and the base station 105. The base station 105 may then use the uplink channel information to train its antennas to beamform the downlink 205 to the UE 115. The base station 105 may also use the uplink channel information to determine which frequency band or which of the multiple RX antennas of the UE 115 may provide better use of the available bandwidth in the wireless communication channel, and send the antenna configuration 215 to the UE 115 accordingly. The antenna configuration 215 may select one (or more) RX antennas of the UE 115 for subsequent data reception.

[0036] For ease of explanation, Figure 3 A single subframe 300 is shown; as will be appreciated, the structure of the SF 300 may be extendable to any number of subframes as needed or desired. Each SF 300 includes a plurality of time slots 306, wherein each time slot 306 includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols. Each time slot 306 in the SF 300 may be divided into an uplink portion 302 and a downlink portion 304, separated by a transition portion U / D. As part of the uplink portion 302, the UE 115 may send various types of signals to the base station 105. For example, these may include SRS, uplink data, and optionally a request for information (e.g., in an uplink burst). The transition portion U / D is provided between the uplink portion 302 and the downlink portion 304. During the downlink portion 304, the base station 105 sends various types of signals to the UE 115, including, for example, a user equipment reference signal (UERS) and downlink data (e.g., in a downlink burst).

[0037] Within each slot 306, the SRS may span one, two, or four consecutive OFDM symbols, which are located within the last six OFDM symbols of the slot 306. Each antenna may transmit its own SRS, so that the sounding reference signal is multiplexed across the antennas of the UE, each antenna having its own SRS in the corresponding slot 306. Each slot 306 may include a first cyclic prefix (CP) appended to the front of the OFDM symbol of the multiplexed SRS. Each slot 306 may also include a second CP appended to the front of the guard period. The guard period may ensure sufficient time for the UE 115 to perform SRS antenna switching.

[0038] Figure 3 Also shown is the timing of SRS antenna switching and antenna impedance detection. At the beginning of each time slot 306, the antenna switching array (discussed further herein) is configured to couple an amplifier that amplifies the SRS to the selected antenna. When the selected antenna transmits the demultiplexed SRS as routed through the antenna switching array, antenna impedance detection is also performed (as indicated by the "ON" duration). The duration of the antenna impedance detection may be shorter than the transmission time of the demultiplexed SRS through the selected antenna pair, so that the detection is completed before the start of the second CP attached to the front of the protection period ("OFF"). During the transmission of the SRS from the selected antenna pair, the SRS can be transmitted at a single carrier frequency, which allows the antenna impedance to be detected at a fixed frequency point; or, the SRS can be hopped in the carrier frequency, which allows the antenna impedance to be detected at multiple frequencies. When the transmission of the SRS through the selected antenna pair is completed, the antenna switching array is configured to disconnect the selected antenna from the amplifier. Note that antenna impedance detection does not need to be performed for each SRS transmission.

[0039] In SF 300, the UE has four antennas, ranging from antenna 0 (ANT0) to antenna 3 (ANT3). Therefore, there are four time slots 306 corresponding to the selection of the respective antennas. As long as each antenna is selected for the desired reflection coefficient characterization, the order of antenna selection is arbitrary. In the first time slot 306, antenna 0 is selected by the antenna switching array and its reflection coefficient characterized. In the second time slot 306, the antenna switching array is selected for the first antenna (ANT1) so that its reflection coefficient can be characterized. In the third time slot 306, the antenna switching array is selected for the second antenna (ANT2) so that its reflection coefficient can be characterized. Finally, in the fourth time slot 306, the antenna switching array is selected for the third antenna (ANT3) so that its reflection coefficient can be characterized. Therefore, the UE advantageously characterizes the reflection coefficients of its antennas (both receiving and transmitting) in the SRS portion of the uplink burst 302 of the subframe 300. Since the reflection coefficient is also represented as gamma (Γ), the characterization obtained by the UE can be represented as SRS speed gamma detection, because it can be done within the relatively brief SRS portion of the uplink burst 302. The SRS speed gamma detection disclosed herein allows the UE to tune its antenna impedance to provide reductions in dropped calls and / or reductions in power consumption.

[0040] Figure 3 The four time slots 306 shown in correspond to a UE with four antennas. Depending on the number of antennas to be characterized in the UE, the SRS portion may contain more or fewer time slots 306. Since the antenna impedance will change, such as through user interaction with the UE, the sequence of SRS transmissions may be repeated periodically so that the antenna impedance characterization may be updated accordingly. The SRS may be identical for each antenna transmission. Alternatively, the SRS may be unique for each antenna so that the base station 105 can identify which antenna is transmitting the respective SRS.

[0041] Further, the SF 300 may be provided as part of a synchronization system such that the SF 300 is provided repeatedly over time so that the base station 105 can adjust its antenna beam to accommodate the UE 115 motion and channel decorrelation (and / or other effects) associated with the movement. Channel reciprocity may allow the base station 105 to apply information about the channel in the uplink direction to estimate one or more channel properties in the downlink direction, which may be used to beamform the downlink transmission. In this manner, the base station 105 may direct its antenna beam based on the SRS from the UE 115. The SRS may also include information that allows the base station 105 to demodulate data received from the UE 115 during the uplink portion 302 of the SF 300. The base station 105 may additionally determine scheduling information based on the SRS that allows the base station 105 to schedule future SFs 300 (e.g., frequency bands, etc.) for communication with the UE 115 or instruct the UE 115 which RX antenna provides higher efficiency of bandwidth usage to select for subsequent data reception. Furthermore, repeated transmissions of the SRS sequence allow the UE 115 to collect antenna impedance values ​​for the same antenna multiple times and average the values ​​with improved accuracy. An example UE 115 will now be discussed in more detail.

[0042] Figure 4 4 is a circuit diagram 400 of an example UE 115. In this exemplary design, UE 115 includes a data processor (or controller) 410, a transceiver 420, an antenna switching array 450, and multiple antennas including antenna 462, antenna 464, and antenna 466. Data processor 410 may be implemented as a modem. Transceiver 420 includes a transmitter 430 and a receiver 440 that support two-way wireless communication. Data processor 410 processes (e.g., encodes and modulates) data to be transmitted, and provides an output signal to transmitter 430. Memory 412 in data processor 410 may store program code and data for data processor 410. Transmit power controller 414 controls the transmit power of transceiver 420. Switch controller 416 controls antenna selection via antenna switching array 450. Each of memory 412, transmit power controller 414, and switch controller 416 may be internal to data processor 410 (e.g., Figure 44) or outside the data processor 410. Within the transmitter 430, the TX circuit 432 amplifies, filters and up-converts the output signal from the baseband to the RF, and provides a modulated signal. The TX circuit 432 may include an amplifier, a filter, a mixer, an oscillator, a local oscillator (LO) generator, a phase-locked loop (PLL), etc. The power amplifier (PA) 434 receives and amplifies the modulated signal to provide an amplified RF signal with an appropriate output power level. During normal operation (non-SRS transmission), the amplified RF signal is provided to the corresponding TX antenna (such as antenna 462) through selection by the antenna switching array 450. In this normal operation, each RX antenna (such as antennas 464 and 466) in the RX antenna receives a signal from the base station 105 and / or other transmitter stations, and provides a received RF signal. The received RF signal is routed through the antenna switching array 450 and provided to a corresponding low noise amplifier (LNA), such as LNA 442 and 444 in the receiver 440. LNA 442 amplifies the RF signal received from RX antenna 464 and provides an LNA output signal. Similarly, LNA 444 amplifies the RF signal received from RX antenna 466 and provides an LNA output signal. RX circuit 446 downconverts the LNA output signal from RF to baseband, amplifies and filters the downconverted signal, and provides an input signal to data processor 410. RX circuit 446 may include amplifiers, filters, mixers, oscillators, LO generators, PLLs, and other suitable components.

[0043] To perform demultiplexing of the SRS from the power amplifier 434 to the antenna, the antenna switching array 450 may include a "1" pole "N" throw (1PNT) switch 452 (N is an integer equal to the number of TX and RX antennas of the UE 115) to couple the PA 434 to any of the antennas. The antenna switching array 450 may also include a plurality of "1" pole "1" throw (1P1T or single pole single throw) switches 454 (the number of 1P1T switches is equal to the number of RX antennas) to provide a one-to-one connection between each of the RX antennas and a respective LNA. When the UE 115 is in data transmission or reception (e.g., in Figure 3 4 (e.g., during an uplink data portion in SF 300 in RF 300 or a downlink data portion in SF 300 in RF 300), antenna switching array 450 may couple PA 434 to TX antenna 462, LNA 442 to RX antenna 464, and LNA 444 to RX antenna 466. When UE 115 is transmitting SRS (e.g., during an uplink data portion in SF 300 in RF 300 or a downlink data portion in SF 300 in RF 300), antenna switching array 450 may couple PA 434 to TX antenna 462, LNA 442 to RX antenna 464, and LNA 444 to RX antenna 466. Figure 34. During the SRS portion of the SF 300 in the antenna switching array 450, the antenna switching array 450 may disconnect the LNA from the RX antenna and connect the PA 434 to each of the antennas in sequence. The data processor 410 generates a baseband SRS, which is then converted to RF in the TX circuit 432 and amplified by the PA 434 before being converted by the antenna switching array 450 for sequencing through the antennas. Although multi-throw and several single-throw switches are described as being included in the antenna switching array 450, other switches, combinations of components, or connections may be included in the antenna switching array 450. Further, it will be understood that although the terms "TX antenna" and "RX antenna" are used herein, there may be times, modes, or configurations in which the TX antenna may operate to receive and / or there may be times, modes, or configurations in which the RX antenna may operate to transmit.

[0044] The voltage standing wave ratio (VSWR) is a figure of merit that can be derived from the reflection coefficient. The VSWR indicates how well the antenna is impedance matched to its transceiver. Since the VSWR and the reflection coefficient are related, the VSWR may vary based on external factors. For example, the VSWR for an antenna may vary depending on the way a user holds the UE. If the wireless unit is being held, the antenna may be blocked by a part of the holder's body. For example, if a mobile phone handset is placed on a person's head, the person's head may block the antenna. The antenna of a mobile phone handset may be blocked by a person's hand or another body part.

[0045] Reference again Figure 4 , measurement circuitry (not shown) may be included in UE 115 to measure the reflection coefficient for each antenna. The measurement circuitry may be part of transceiver 420, part of other circuitry in UE 115, or some combination of circuitry in transceiver 420 and other circuitry. For example, in transceiver 420, a high power detector (HDET) may be used to detect incident power to an antenna and reflected power (amplitude only) from the antenna. In some examples, a sophisticated detector may detect both the amplitude and phase of the incident and reflected signals. For example, if transceiver 420 supports both in-phase and quadrature-phase signaling, the phase may be derived. The measurement circuitry will now be discussed in more detail.

[0046] Figure 5A circuit diagram 500 of an exemplary UE 115 including measurement circuit 470 is shown. In this exemplary design, UE 115 includes data processor (controller) 410, transceiver 420, antenna switching array 450, and multiple antennas including antenna 462, antenna 464, and antenna 466, as discussed with respect to circuit diagram 400. Measurement circuit 470 is coupled between PA 434 and antenna switching array 450. Measurement circuit 470 may be external to transceiver 420 (e.g., Figure 5 ) or inside the transceiver 420. The operation of the measurement circuit 470 may be controlled by the impedance measurement controller 418 in the data processor 410.

[0047] The measurement circuit 470 may include a directional coupler 472, a switch 474, and a signal detector 476. The directional coupler 472 may receive an input RF signal at a first port P1, provide an output RF signal at a second port P2, and provide a forward (coupled) RF signal at a third port P3. The directional coupler 472 may also provide a reflected RF signal at a fourth port P4. Therefore, the directional coupler 472 functions to sample the SRS amplified from the PA 434 to provide a forward signal. Due to non-ideality, the amplified SRS is not completely converted into free space propagation by the selected antenna, but a portion is reflected back to the PA 434. The directional coupler 472 also functions to sample the reflection to form a reflected signal at the fourth port P4. The signal detector 476 may be a square-law power detector, a phase and amplitude signal detector, or other suitable types of signal detectors. The signal detector 476 may receive RF signals at different ports of the directional coupler 472, and may measure the voltage, current, power, and / or other characteristics of the RF signal. The measurement circuit 470 can then characterize the real and imaginary parts (or only the amplitude) of the reflection coefficient for the selected antenna. The switch 474 can be a "2"-pole "2"-throw (DPDT) switch. In one state, the switch 474 connects port 4 (P4) of the directional coupler 472 to a terminal impedance (such as ground) through a matched load, and connects port 3 (P3) to a signal detector 476 so that the forward signal can be sampled. In another state, the switch 474 connects port 4 to the signal detector 476, and connects port 3 to a terminal impedance (such as ground) through a matched load so that the reflected signal can be sampled. In this way, the directional coupler 472 can be used to sample both the forward signal and the reflected signal. In other implementations, one directional coupler can be used to sample the forward signal, and another (separate) directional coupler can be used to sample the reflected signal.

[0048] During transmission of the SRS from the selected antenna, when the switch 474 is set in the first state, the signal detector 476 can detect a voltage V indicative of a forward signal. f When the switch 474 is set in the second state, the signal detector 476 can detect a voltage V indicating a reflected signal. r Since power is a function of voltage and current, the voltage V f is proportional to the forward power. Similarly, the voltage V r Proportional to reverse power.

[0049] At the voltage V f and voltage V r After the determination of the ratio V r / V f It may be determined, for example, by the impedance measurement controller 418. The voltage V r and V f Proportional to the forward power and reflected power respectively. Ratio V r / V f Define the voltage reflection coefficient Γ. The voltage reflection coefficient Γ can then be used to determine the VSWR such as given by the following formula (1):

[0050] VSWR=(1+│Γ│) / (1-│Γ│) Formula (1)

[0051] A smaller value of VSWR indicates less reflection and a better match between the antenna and the radio unit (or the antenna and the transmission line). As can be determined from formula (1) above, the lowest possible value for VSWR is 1. For example, if there is no reflection, so that the reflection coefficient is 0, the result of formula (1) is 1. When the reflection coefficient is 0, no reflection occurs, i.e., the antenna and the radio unit or the antenna and the transmission medium are perfectly matched. When VSWR is 1, no power is reflected. As reflection increases, VSWR increases accordingly. Performance may decrease as VSWR increases. Therefore, a lower value of VSWR may be more appropriate.

[0052] In some implementations, the signal detector 476 can be configured to detect the f and V r The signal detector 476 calculates VSWR and / or other quality factors (e.g., return loss) based on the measurement results, and reports the calculated results to the data processor 410. In some implementations, the signal detector 476 includes an analog-to-digital converter (ADC) that digitizes the measurement results from the signal detector 476 and provides a voltage V r and V f The digitized measured value of the voltage V r and V fThe digitized value of may be sent to the data processor 410 so that the impedance measurement controller 418 may calculate the desired quality factor.

[0053] Another figure of merit related to how well the antenna is matched is the return loss. The return loss (RL) expressed in decibels may be as defined in the following formula (2):

[0054] RL dB =20log(V f / V r )=20log(1 / Γ) formula (2)

[0055] Therefore, return loss is related to VSWR as indicated in the following equation (3):

[0056] RL dB =20log((VSWR+1) / (VSWR-1)) Formula (3)

[0057] Formulas (1)-(3) can be calculated using the measurement results described above. Therefore, VSWR and return loss can be calculated based on V f and V r The impedance of the antenna is calculated by the measurement results of the antenna. Using formulas (1)-(3), a value indicating how well the impedance is matched between the antenna and the transceiver can be generated. Therefore, in some implementations, the UE 115 includes an antenna tuning network (e.g., a tuner) coupled to the antenna, and the value indicating how well the impedance is matched to the antenna can be compared to adjust the antenna tuning network to improve the antenna impedance matching. Using both the real component and the imaginary component of the reflection coefficient can improve the tuning process. In other implementations, only the magnitude of the reflection coefficient can be used in the tuning process. The tuning process will now be discussed in more detail.

[0058] Figure 6 A circuit diagram 600 is shown of an exemplary design of a UE 115 including an antenna tuning network 480. The circuit diagram 600 is generally similar to Figure 5 The circuit diagram 500 and Figure 44. Circuit diagram 400 in FIG. 4. In this exemplary design, UE 115 includes a data processor (controller) 410, a transceiver 420, an antenna switching array 450, a plurality of antennas including antenna 462, antenna 464, and antenna 466, and a measurement circuit 470. An antenna tuning network 480 is coupled between antenna switching array 450 and the antennas. Antenna tuning network 480 may include a tuner for each antenna. For example, tuner 482 is coupled to TX antenna 462, tuner 484 is coupled to RX antenna 464, and tuner 486 is coupled to RX antenna 466. In general, a UE may include any number of tuners for any number of TX / RX antennas. The operation of antenna tuning network 480, and accordingly each of tuners 482, 484, and 486 may be controlled by a tuner controller 419 in data processor 410. Each of the tuners performs impedance and / or power matching for an antenna and may also be referred to as a matching circuit, a tunable matching circuit, or an antenna tuning circuit. In one implementation, tuners 482, 484, 486 are impedance tuners that may be configured to adjust an impedance load to respective antennas 462, 464, and 466, respectively. In another example, tuners 482, 484, 486 are aperture tuners that may be configured to adjust the effective aperture of antennas 462, 464, and 466, which in turn adjusts the impedance and / or power matching of antennas 462, 464, and 466.

[0059] like Figure 6 As shown in , the antenna switching array 450 can sequentially connect antennas 462, 464, 466 and their respective tuners 482, 484, 486 to a directional coupler 472. The directional coupler 472, along with the switch 474 and the signal detector 476, can be used to measure a value indicating how well the antenna impedance is matched. Depending on the antenna selected by the antenna switching array 450, the reflection coefficient can be measured accordingly.

[0060] Note that each tuner may be initially set to a certain default value and then periodically updated through the SRS speed gamma detection process to better match the corresponding antenna. For example, each tuner may be configured to provide an adjustable capacitance and / or an adjustable inductance. In addition, each tuner may be configured to provide an adjustable resistance. Taking tuner 486 as an example, tuner 486 and RX antenna 466 may be selected by antenna switching array 450 so that measurement circuit 470 may measure the corresponding reflection coefficient during the transmission of SRS by RX antenna 466. Subsequently, tuner 486 may be configured by tuner controller 419 to achieve a better match for RX antenna 466, such as by adjusting the tuner capacitance and / or adjusting the tuner inductance or resistance. Note that antenna impedance measurement may be performed within a frequency band, but the resulting tuning may be applied to other frequency bands. For example, it may be determined how impedance varies with frequency, for example, based on a previous characterization operation performed on UE 115 or on a representative device. Such a relationship may be stored by the UE 115, for example, in the memory 412. In some configurations, antenna impedance measurements performed in one frequency band or subset of frequency bands may be used, for example, by the impedance measurement controller 418 or another component of the data processor 410 to determine antenna impedance at other frequency bands. Methods of SRS velocity gamma detection will now be discussed in more detail.

[0061] Figure 77 is a flow chart of a method for SRS speed gamma detection according to the present disclosure. The method begins with act 700, and sequentially selects each of a plurality of antennas in a UE by an antenna switching array. The plurality of antennas may be each antenna in the UE, or may be a subset of antennas in the UE, such as a subset of antennas configured for a particular RAT or a particular frequency band. The sequential selection of antennas 462, 464, and 466 by the antenna switching array 450 is an example of act 700. The following acts of the method occur during the selection of a given antenna, and include an act 705 of amplifying a reference signal by an amplifier to provide an amplified reference signal. Amplification of the SRS for the selected antenna by the PA 434 is an example of act 705. In addition, the method includes an act 710 of transmitting the amplified reference signal by the antenna so that the reflected signal is reflected back to the amplifier. The transmission of the amplified SRS by the selected antenna and the formation of the reflected signal at the directional coupler 472 are examples of act 710. The method also includes an act 715 of evaluating an impedance match for the antenna based on the samples of the amplified reference signal and the samples of the reflected signal. Evaluation of a reflection coefficient for the selected antenna by measurement circuit 470 is an example of act 715. Finally, the method includes an act 720 of tuning an impedance match for the antenna based on the evaluation of the impedance match. Tuning of any one of tuners 482, 484, or 486 by tuner controller 419 is an example of act 720.

[0062] The present disclosure will now be summarized in the following example clauses.

[0063] Clause 1. An apparatus for wireless communication, comprising:

[0064] a plurality of antennas, comprising at least one transmit antenna and at least one receive antenna;

[0065] Amplifier;

[0066] an antenna switching array coupled to the plurality of antennas;

[0067] a directional coupler coupled between the amplifier and the antenna switching array; and

[0068] A controller configured to:

[0069] controlling the antenna switching array to sequentially select each of the plurality of antennas so that a reference signal amplified by the amplifier is transmitted from the antenna and causing the directional coupler to generate a reflected signal from the antenna; and

[0070] A reflection coefficient for each antenna is determined in response to reflected signals from the antenna.

[0071] Clause 2. The apparatus of clause 1, wherein the reference signal is configured to estimate a wireless channel.

[0072] Clause 3. The apparatus of clause 2, wherein the reference signal is a sounding reference signal (SRS).

[0073] Clause 4. An apparatus according to any one of clauses 1-3, wherein the controller is also configured to control the amplifier to send the reference signal at intervals separated by protection periods, and wherein the reflection coefficient for each antenna is determined over the duration of the interval in which the antenna sends the reference signal.

[0074] Clause 5. An apparatus according to any of clauses 1-4, wherein the directional coupler is configured to receive the reference signal from the amplifier at a first port, pass the reference signal from the first port to the antenna switching array at a second port, provide a coupled signal at a third port, and a reflected signal at a fourth port, and the apparatus further comprises:

[0075] A signal detector is coupled to the directional coupler and is configured to measure at least an amplitude of the coupled signal and an amplitude of the reflected signal.

[0076] Clause 6. The apparatus of clause 5, wherein the signal detector is further configured to measure a phase of the coupled signal and a phase of the reflected signal.

[0077] Clause 7. An apparatus according to any one of clauses 1 to 6, further comprising:

[0078] a plurality of tuners corresponding to the plurality of antennas,

[0079] The controller is further configured to adjust each tuner to improve impedance matching with a corresponding one of the antennas.

[0080] Clause 8. The apparatus of clause 7, wherein one or more of the plurality of tuners each comprises an impedance tuner. Clause 9. The apparatus of clause 7, wherein one or more of the plurality of tuners each comprises an antenna aperture tuner.

[0081] Clause 10. The apparatus of any of clauses 1-9, wherein the controller is further configured to determine a voltage standing wave ratio (VSWR) of each antenna.

[0082] Clause 11. Apparatus according to any of clauses 1-10, wherein the amplifier is a power amplifier.

[0083] Clause 12. A user equipment (UE) for wireless communication, comprising:

[0084] Transmitting antenna;

[0085] Receiving antenna;

[0086] a transceiver configured to generate one or more sounding reference signals (SRS) for wireless channel estimation;

[0087] an antenna switching array configured to respectively select the transmit antenna and the receive antenna for sequentially transmitting the one or more SRSs;

[0088] a first tuner coupled between the transmit antenna and the antenna switching array;

[0089] a second tuner coupled between the receiving antenna and the antenna switching array;

[0090] a directional coupler coupled between the transceiver and the antenna switching array; and

[0091] A controller is configured to adjust the first tuner and the second tuner based on a signal from the directional coupler during a sequence.

[0092] Clause 13. The UE of clause 12, further comprising: a signal detector coupled to the directional coupler and configured to detect the signal from the directional coupler during the sequence.

[0093] Clause 14. A UE according to clause 13, wherein the directional coupler has a first port for receiving the one or more SRSs, a second port for relaying the one or more SRSs to the antenna switching array, a third port for providing a forward signal, and a fourth port for providing a reflected signal.

[0094] Clause 15. A UE according to clause 13, wherein the signal detector is configured to determine the reflection coefficient of the transmitting antenna in response to a ratio of a first forward signal from the directional coupler to a first reflected signal from the directional coupler when the antenna switching array is selected for the transmitting antenna, and wherein the signal detector is also configured to determine the reflection coefficient of the receiving antenna in response to a ratio of a second forward signal from the directional coupler to a second reflected signal from the directional coupler when the antenna switching array is selected for the receiving antenna.

[0095] Clause 16. The UE of clause 15, further comprising an amplifier configured to amplify the one or more SRSs.

[0096] Clause 17. The UE of clause 16, wherein the controller is configured to adjust the first tuner in response to a reflection coefficient of the transmit antenna and to adjust the second tuner in response to a reflection coefficient of the receive antenna.

[0097] Clause 18. A UE as set forth in any of clauses 12-17, wherein the first tuner comprises a first impedance tuner and the second tuner comprises a second impedance tuner.

[0098] Clause 19. A UE as set forth in any of clauses 12-17, wherein the first tuner comprises a first antenna aperture tuner and the second tuner comprises a second antenna aperture tuner.

[0099] Clause 20. A method for wireless communication of a user equipment (UE), comprising:

[0100] sequentially selecting each of the plurality of antennas of the UE through an antenna switching array; and

[0101] When each antenna is selected by the antenna switching array:

[0102] amplifying the reference signal by an amplifier to provide an amplified reference signal;

[0103] transmitting the amplified reference signal through the antenna so that a reflected signal is reflected back to the amplifier;

[0104] evaluating impedance matching of the antenna based on samples of the amplified reference signal and the reflected signal; and

[0105] The impedance match of the antenna is tuned based on the evaluation of the impedance match.

[0106] Clause 21. The method of clause 20, wherein sequentially selecting each antenna comprises selecting a transmit antenna and comprises selecting a receive antenna.

[0107] Clause 22. The method of any of clauses 20-21, further comprising sampling the amplified reference signal and the reflected signal in a directional coupler.

[0108] Clause 23. The method of any of clauses 20-22, wherein the reference signal is a sounding reference signal (SRS). Clause 24. The method of any of clauses 20-23, wherein tuning the impedance match for each antenna comprises tuning an impedance tuner coupled to the antenna.

[0109] Clause 25. A method as set forth in any of clauses 20-24, wherein the plurality of antennas comprises a subset of antennas for the UE.

[0110] Clause 26. A method as set forth in any of clauses 20-24, wherein the plurality of antennas comprises each antenna in the UE.

[0111] It should be noted that the methods described herein describe possible implementations, and that operations and steps may be rearranged or otherwise modified, and that other implementations are possible. Furthermore, aspects from two or more of the methods may be combined.

[0112] The descriptions set forth in conjunction with the accompanying drawings herein describe example configurations, and do not represent all examples that can be implemented or within the scope of the claims. For the purpose of providing an understanding of the described technology, the specific embodiments include specific details. However, these technologies can be practiced without these specific details. In some cases, well-known structures and devices are shown in block diagram form to avoid obscuring the concepts of the described examples. The descriptions herein are provided to enable those of ordinary skill in the art to implement or use the present disclosure. It will be apparent to those skilled in the art that various modifications to the present disclosure will be apparent, and the general principles defined herein may be applicable to other variants without departing from the scope of the present disclosure. Therefore, the present disclosure is not limited to the examples and designs described herein, but is given the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for wireless communication, comprising: a plurality of antennas, comprising at least one transmit antenna and at least one receive antenna; Amplifier; an antenna switching array coupled to the plurality of antennas; a directional coupler coupled between the amplifier and the antenna switching array; as well as A controller configured to: controlling the antenna switching array to sequentially select each of the plurality of antennas so that a reference signal amplified by the amplifier is transmitted from the antenna and causing the directional coupler to generate a reflected signal from the antenna; as well as A reflection coefficient for each antenna is determined in response to reflected signals from the antenna.

2. The device according to claim 1, wherein: The reference signal is configured to estimate a wireless channel.

3. The device according to claim 2, wherein: The reference signal is a sounding reference signal (SRS).

4. The device according to claim 1, wherein: The controller is further configured to control the amplifier to transmit the reference signal at intervals separated by a guard period, and wherein the reflection coefficient for each antenna is determined over the duration of the interval in which the antenna transmits the reference signal.

5. The device according to claim 1, wherein: The directional coupler is configured to receive the reference signal from the amplifier at a first port, pass the reference signal from the first port to the antenna switching array at a second port, provide a coupled signal at a third port, and a reflected signal at a fourth port, the device further comprising: A signal detector is coupled to the directional coupler and is configured to measure at least an amplitude of the coupled signal and an amplitude of the reflected signal.

6. The device according to claim 5, wherein: The signal detector is further configured to measure a phase of the coupled signal and a phase of the reflected signal.

7. The apparatus according to claim 1, further comprising: a plurality of tuners corresponding to the plurality of antennas, The controller is further configured to adjust each tuner to improve impedance matching with a corresponding one of the antennas.

8. The device according to claim 7, wherein: One or more of the plurality of tuners each include an impedance tuner.

9. The device according to claim 7, wherein: One or more of the plurality of tuners each comprises an antenna aperture tuner.

10. The device according to claim 1, wherein: The controller is also configured to determine a voltage standing wave ratio (VSWR) of each antenna.

11. The device according to claim 1, wherein: The amplifier is a power amplifier.

12. A user equipment (UE) for wireless communication, comprising: Transmitting antenna; Receiving antenna; a transceiver configured to generate one or more sounding reference signals (SRS) for wireless channel estimation; an antenna switching array configured to respectively select the transmit antenna and the receive antenna for sequentially transmitting the one or more SRSs; a first tuner coupled between the transmit antenna and the antenna switching array; a second tuner coupled between the receiving antenna and the antenna switching array; a directional coupler coupled between the transceiver and the antenna switching array; as well as A controller is configured to adjust the first tuner and the second tuner based on a signal from the directional coupler during a sequence.

13. The UE according to claim 12, further comprising: A signal detector is coupled to the directional coupler and is configured to detect the signal from the directional coupler during the sequence.

14. The UE according to claim 13, wherein: The directional coupler has a first port for receiving the one or more SRSs, a second port for relaying the one or more SRSs to the antenna switching array, a third port for providing a forward signal, and a fourth port for providing a reflected signal.

15. The UE according to claim 13, wherein: The signal detector is configured to determine the reflection coefficient of the transmitting antenna in response to a ratio of a first forward signal from the directional coupler to a first reflected signal from the directional coupler when the antenna switching array is selected for the transmitting antenna, and wherein the signal detector is further configured to determine the reflection coefficient of the receiving antenna in response to a ratio of a second forward signal from the directional coupler to a second reflected signal from the directional coupler when the antenna switching array is selected for the receiving antenna. The UE of claim 15 , further comprising an amplifier configured to amplify the one or more SRSs.

17. The UE according to claim 15, wherein: The controller is configured to adjust the first tuner in response to a reflection coefficient of the transmit antenna and to adjust the second tuner in response to a reflection coefficient of the receive antenna.

18. The UE according to claim 12, wherein: The first tuner includes a first impedance tuner, and the second tuner includes a second impedance tuner.

19. The UE according to claim 12, wherein: The first tuner includes a first antenna aperture tuner and the second tuner includes a second antenna aperture tuner.

20. A method for wireless communication of a user equipment (UE), comprising: sequentially selecting each of the plurality of antennas of the UE through an antenna switching array; as well as When each antenna is selected by the antenna switching array: amplifying the reference signal by an amplifier to provide an amplified reference signal; transmitting the amplified reference signal through the antenna so that a reflected signal is reflected back to the amplifier; evaluating impedance matching of the antenna based on samples of the amplified reference signal and the reflected signal; as well as The impedance match of the antenna is tuned based on the evaluation of the impedance match.

21. The method according to claim 20, wherein: Selecting each antenna sequentially includes selecting a transmit antenna and includes selecting a receive antenna.

22. The method of claim 20, further comprising sampling the amplified reference signal and the reflected signal in a directional coupler.

23. The method according to claim 20, wherein: The reference signal is a sounding reference signal (SRS).

24. The method according to claim 20, wherein: Tuning the impedance match for each antenna includes tuning an impedance tuner coupled to the antenna.

25. The method according to claim 20, wherein: The plurality of antennas comprises a subset of antennas for the UE.

26. The method of claim 20, wherein: The plurality of antennas includes each antenna in the UE.

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