Patent Publication Number: US-11382050-B2

Title: Methods and apparatus for user equipment to differentiate human grip from protective covers

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of and priority to U.S. Provisional Application No. 62/986,528, filed Mar. 6, 2020, which is herein incorporated by reference in its entirety for all applicable purposes. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     Certain aspects of the present disclosure generally relate to wireless devices and, more particularly, to differentiating between human grip and a protective cover on a wireless device. 
     Description of Related Art 
     Modern wireless devices (such as cellular phones) are generally required to meet radio frequency (RF) exposure limits set by domestic and international standards and regulations. To ensure compliance with the standards, such devices must currently undergo an extensive certification process prior to being shipped to market. To ensure that a wireless device complies with an RF exposure limit, techniques have been developed to enable the wireless device to assess RF exposure from the wireless device in real time and adjust the transmission power of the wireless device accordingly to comply with the RF exposure limit. 
     SUMMARY 
     The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description,” one will understand how the features of this disclosure provide advantages that include improved systems and methods for assessing RF exposure from a wireless device. 
     Certain aspects of the present disclosure provide a method for wireless communications by a user equipment (UE). The method generally includes receiving a plurality of signals at the UE, determining values for at least two different types of parameters based on the received plurality of signals, determining an environmental scenario for the UE based on the values for the at least two different types of parameters, and transmitting a signal using a transmission power based on the determined environmental scenario. 
     Certain aspects of the present disclosure provide a method for wireless communications by a UE. The method generally includes receiving a plurality of signals at the UE; determining a value for each of one or more parameters based on the received plurality of signals; determining a type of a cover adjacent an antenna array of the UE based on the value for each of the one or more parameters; selecting an antenna array codebook based on the determined type of the cover; and transmitting a signal according to the selected antenna array codebook. 
     Certain aspects of the present disclosure provide a method for wireless communications by UE. The method generally includes receiving a plurality of cross-polarization captures from multiple antenna arrays of the UE; detecting that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first open space (OS) circle in an in-phase/quadrature (IQ) plane out of a set of possible OS circles for the UE; based on the detection, assigning the first OS circle as an active OS circle for the UE and deactivating other possible OS circles in the set; determining an environmental scenario corresponding to the active OS circle; and transmitting a signal using a transmission power based on the determined environmental scenario. 
     Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a receiver, a transmitter, a memory, and a processor. The receiver is configured to receive a plurality of cross-polarization captures from multiple antenna arrays. The processor is coupled to the memory, and the processor and the memory are configured to: detect that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first OS circle in an IQ plane out of a set of possible OS circles for the apparatus; assign the first OS circle as an active OS circle for the apparatus and deactivate other possible OS circles in the set, based on the detection; and determine an environmental scenario corresponding to the active OS circle. The transmitter is configured to transmit a signal using a transmission power based on the determined environmental scenario. 
     Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for receiving a plurality of cross-polarization captures from multiple antenna arrays of the apparatus; means for detecting that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first OS circle in an IQ plane out of a set of possible OS circles for the apparatus; means for assigning the first OS circle as an active OS circle for the apparatus and deactivating other possible OS circles in the set, based on the detection; means for determining an environmental scenario corresponding to the active OS circle; and means for transmitting a signal using a transmission power based on the determined environmental scenario. 
     Certain aspects of the present disclosure provide a computer-readable medium having instructions stored thereon for receiving a plurality of cross-polarization captures from multiple antenna arrays of the UE; detecting that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first open OS circle in an IQ plane out of a set of possible OS circles for the UE; based on the detection, assigning the first OS circle as an active OS circle for the UE and deactivating other possible OS circles in the set; determining an environmental scenario corresponding to the active OS circle; and transmitting a signal using a transmission power based on the determined environmental scenario. 
     To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. 
         FIG. 1  is a block diagram conceptually illustrating an example telecommunications system, in accordance with certain aspects of the present disclosure. 
         FIG. 2  is a block diagram conceptually illustrating a design of an example base station (BS) and an example user equipment (UE), in accordance with certain aspects of the present disclosure. 
         FIG. 3  is a block diagram showing an example transceiver front-end, in accordance with certain aspects of the present disclosure. 
         FIG. 4A  illustrates millimeter wave (mmW) sensing by a UE, in accordance with certain aspects of the present disclosure. 
         FIG. 4B  illustrates mmW sensing using cross-polarization (Xpol), in accordance with certain aspects of the present disclosure. 
         FIG. 4C  illustrates mmW sensing using frequency-modulated continuous-wave (FMCW) radar, in accordance with certain aspects of the present disclosure. 
         FIG. 5  illustrates example fast Fourier transform (FFT) symbol values from Xpol detection, in accordance with certain aspects of the present disclosure. 
         FIG. 6  is an example plot of cross-polarization ratios (K) in the in-phase/quadrature (IQ) plane for detection of an object in front of an antenna, in accordance with certain aspects of the present disclosure. 
         FIG. 7  is a flow diagram of example operations for wireless communications, in accordance with certain aspects of the present disclosure. 
         FIG. 8  is an example plot of signal-to-noise ratio (SNR) in decibels (dB) of vertical and horizontal polarization components for different scenarios, in accordance with certain aspects of the present disclosure. 
         FIG. 9  illustrates an example correlation between standard deviation of K values (σ K ) and the mean signal-to-noise ratio (SNR m ) of the vertical and horizontal polarization components for different scenarios, in accordance with certain aspects of the present disclosure. 
         FIG. 10  illustrates an example linear relationship between σ K  and SNR m  for different scenarios, where the line represents a boundary between open space (OS) and objection detection regions, in accordance with certain aspects of the present disclosure. 
         FIG. 11  is a flow chart for determining parameters for OS based on σ K  and SNR m , in accordance with certain aspects of the present disclosure. 
         FIG. 12  is a flow diagram of example operations for wireless communications based on antenna array codebook selection, in accordance with certain aspects of the present disclosure. 
         FIG. 13  is a flow diagram of example operations for wireless communications, in accordance with certain aspects of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation. 
     DETAILED DESCRIPTION 
     Certain aspects of the present disclosure provide techniques and apparatus for distinguishing between an antenna of a user equipment (UE) being blocked by a cover (e.g., a protective rubber or plastic cover) or by human tissue (e.g., a finger or palm). The transmission power of uplink (UL) signals may be adjusted accordingly, with relatively higher transmission power for open space or a cover and relatively lower transmission power for human tissue. 
     The following description provides examples, and is not limiting of the scope, applicability, or examples set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to some examples may be combined in some other examples. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to, or other than, the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. 
     The techniques described herein may be used for various wireless communication technologies, such as LTE, CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as NR (e.g. 5G RA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 
     New Radio (NR) is an emerging wireless communications technology under development in conjunction with the 5G Technology Forum (5GTF). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, while aspects may be described herein using terminology commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later, including NR technologies. 
     NR access (e.g., 5G technology) may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHz or beyond), millimeter wave (mmW) targeting high carrier frequency (e.g., 25 GHz or beyond), massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC). These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTI) to meet respective quality of service (QoS) requirements. In addition, these services may co-exist in the same subframe. 
     Example Wireless Communications System 
       FIG. 1  illustrates an example wireless communications network  100  in which aspects of the present disclosure may be performed. Wireless devices in the wireless network  100  may perform the methods for determining an environmental scenario for an antenna (or antenna array) of the wireless device as further described herein. As used herein, an environmental scenario generally refers to the antenna (or antenna array) of the wireless device being blocked by an object (such as a protective cover or human grip) or not being blocked by an object (a condition referred to as “open space”). 
     As illustrated in  FIG. 1 , the wireless network  100  may include a number of base stations (BSs)  110  and other network entities. A BS may be a station that communicates with user equipments (UEs). Each BS  110  may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB) and/or a Node B subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term “cell” and next generation Node B (gNB), new radio base station (NR BS), 5G NB, access point (AP), or transmission reception point (TRP) may be interchangeable. In some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile BS. In some examples, the base stations may be interconnected to one another and/or to one or more other base stations or network nodes (not shown) in wireless communication network  100  through various types of backhaul interfaces, such as a direct physical connection, a wireless connection, a virtual network, or the like using any suitable transport network. 
     In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular radio access technology (RAT) and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, etc. A frequency may also be referred to as a carrier, a subcarrier, a frequency channel, a tone, a subband, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs. In some cases, NR or 5G RAT networks may be deployed. 
     A base station (BS) may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having an association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs for users in the home, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In the example shown in  FIG. 1 , the BSs  110   a ,  110   b , and  110   c  may be macro BSs for the macro cells  102   a ,  102   b , and  102   c , respectively. The BS  110   x  may be a pico BS for a pico cell  102   x . The BSs  110   y  and  110   z  may be femto BSs for the femto cells  102   y  and  102   z , respectively. A BS may support one or multiple (e.g., three) cells. 
     Wireless communication network  100  may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., a BS or a UE) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE or a BS). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in  FIG. 1 , a relay station  110   r  may communicate with the BS  110   a  and a UE  120   r  in order to facilitate communication between the BS  110   a  and the UE  120   r . A relay station may also be referred to as a relay BS, a relay, etc. 
     Wireless network  100  may be a heterogeneous network that includes BSs of different types, e.g., macro BS, pico BS, femto BS, relays, etc. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless network  100 . For example, a macro BS may have a high transmit power level (e.g., 20 watts (W)) whereas a pico BS, a femto BS, and relays may have a lower transmit power level (e.g., 1 W). 
     Wireless communication network  100  may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operation. 
     A network controller  130  may couple to a set of BSs and provide coordination and control for these BSs. The network controller  130  may communicate with the BSs  110  via a backhaul. The BSs  110  may also communicate with one another (e.g., directly or indirectly) via wireless or wireline backhaul. 
     The UEs  120  (e.g.,  120   x ,  120   y , etc.) may be dispersed throughout the wireless network  100 , and each UE may be stationary or mobile. A UE may also be referred to as a mobile station (MS), a terminal, an access terminal, a subscriber unit, a station, a Customer Premises Equipment (CPE), a cellular phone, a smartphone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet computer, a camera, a gaming device, a netbook, a smartbook, an ultrabook, an appliance, a medical device or medical equipment, a biometric sensor/device, a wearable device such as a smart watch, smart clothing, smart glasses, a smart wrist band, or smart jewelry (e.g., a smart ring, a smart bracelet, etc.), an entertainment device (e.g., a music device, a video device, a satellite radio, etc.), a vehicular component or sensor, a smart meter/sensor, industrial manufacturing equipment, a Global Positioning System (GPS) device, or any other suitable device that is configured to communicate via a wireless or wired medium. Some UEs may be considered machine-type communication (MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, etc., that may communicate with a BS, another device (e.g., remote device), or some other entity. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT) devices. 
     Certain wireless networks (e.g., LTE) utilize orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, the spacing of the subcarriers may be 15 kHz, and the minimum resource allocation (called a “resource block” (RB)) may be 12 subcarriers (or 180 kHz). Consequently, the nominal fast Fourier transform (FFT) size may be equal to 128, 256, 512, 1024, or 2048 for a system bandwidth of 1.25, 2.5, 5, 10, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz (i.e., 6 resource blocks), and there may be 1, 2, 4, 8, or 16 subbands for a system bandwidth of 1.25, 2.5, 5, 10, or 20 MHz, respectively. 
     While aspects of the examples described herein may be associated with LTE technologies, aspects of the present disclosure may be applicable with other wireless communications systems, such as NR. NR may utilize OFDM with a cyclic prefix (CP) on the uplink and downlink and include support for half-duplex operation using time-division duplexing (TDD). Beamforming may be supported, and beam direction may be dynamically configured. Multiple-input, multiple-output (MIMO) transmissions with precoding may also be supported. MIMO configurations in the downlink (DL) may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Aggregation of multiple cells may be supported with up to 8 serving cells. 
     In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station) allocates resources for communication among some or all devices and equipment within its service area or cell. The scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. Base stations are not the only entities that may function as a scheduling entity. In some examples, a UE may function as a scheduling entity and may schedule resources for one or more subordinate entities (e.g., one or more other UEs), and the other UEs may utilize the resources scheduled by the UE for wireless communication. In some examples, a UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may communicate directly with one another in addition to communicating with a scheduling entity. 
     In  FIG. 1 , a solid line with double arrows indicates desired transmissions between a UE and a serving BS, which is a BS designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and a BS. 
       FIG. 2  illustrates example components of BS  110  and UE  120  (as depicted in  FIG. 1 ), which may be used to implement aspects of the present disclosure. For example, antennas  252 , transceiver (TX/RX) front-end circuits  254 , processors  258 ,  264 , and/or controller/processor  280  of the UE  120  may be used to perform the various techniques and methods described herein (e.g., operations  700  of  FIG. 7 , operations  1200  of  FIG. 12 , or operations  1300  of  FIG. 13 ). 
     At the BS  110 , a transmit processor  220  may receive data from a data source  212  and control information from a controller/processor  240 . The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical hybrid ARQ indicator channel (PHICH), physical downlink control channel (PDCCH), group common PDCCH (GC PDCCH), etc. The data may be for the physical downlink shared channel (PDSCH), etc. The processor  220  may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The processor  220  may also generate reference symbols, e.g., for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell-specific reference signal (CRS). A transmit (TX) multiple-input multiple-output (MIMO) processor  230  may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the transmit (TX) front-end circuits  232   a  through  232   t . Each TX front-end circuit  232  may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each TX front-end circuit  232  may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from TX front-end circuits  232   a  through  232   t  may be transmitted via the antennas  234   a  through  234   t , respectively. 
     At the UE  120 , the antennas  252   a  through  252   r  may receive the downlink signals from the BS  110  and may provide received signals to the receive (RX) front-end circuits  254   a  through  254   r , respectively. Each RX front-end circuit  254  may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each RX front-end circuit  254  may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector  256  may obtain received symbols from all the RX front-end circuits  254   a  through  254   r , perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor  258  may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE  120  to a data sink  260 , and provide decoded control information to a controller/processor  280 . Memory  282  may store data and program codes for the UE  120  and may interface with the controller/processor  280 . 
     On the uplink, at UE  120 , a transmit processor  264  may receive and process data (e.g., for the physical uplink shared channel (PUSCH)) from a data source  262  and control information (e.g., for the physical uplink control channel (PUCCH) from the controller/processor  280 . The transmit processor  264  may also generate reference symbols for a reference signal (e.g., for the sounding reference signal (SRS)). The symbols from the transmit processor  264  may be precoded by a TX MIMO processor  266  if applicable, further processed by the RX front-end circuits  254   a  through  254   r  (e.g., for SC-FDM, etc.), and transmitted to the BS  110 . At the BS  110 , the uplink signals from the UE  120  may be received by the antennas  234 , processed by the TX front-end circuits  232 , detected by a MIMO detector  236  if applicable, and further processed by a receive processor  238  to obtain decoded data and control information sent by the UE  120 . The receive processor  238  may provide the decoded data to a data sink  239  and the decoded control information to the controller/processor  240 . Memory  242  may store data and program codes for the BS  110  and may interface with the controller/processor  240 . 
     The controllers/processors  240  and  280  may direct the operation at the BS  110  and the UE  120 , respectively. The processor  240  and/or other processors and modules at the BS  110  may perform or direct the execution of processes for the techniques described herein. The memories  242  and  282  may store data and program codes for BS  110  and UE  120 , respectively. A scheduler  244  may schedule UEs for data transmission on the downlink and/or uplink. 
       FIG. 3  is a block diagram of an example transceiver front-end  300 , such as TX/RX front-end circuits  232 ,  254  in  FIG. 2 , in accordance with certain aspects of the present disclosure. The transceiver front-end  300  includes at least one transmit (TX) path  302  (also known as a transmit chain) for transmitting signals via one or more antennas and at least one receive (RX) path  304  (also known as a receive chain) for receiving signals via the antennas. When the TX path  302  and the RX path  304  share an antenna  303 , the paths may be connected with the antenna via an RF interface  306 , which may include any of various suitable RF devices, such as a duplexer, a switch, a diplexer, and the like. 
     Receiving in-phase (I) or quadrature (Q) baseband analog signals from a digital-to-analog converter (DAC)  308 , the TX path  302  may include a baseband filter (BBF)  310 , a mixer  312 , a driver amplifier (DA)  314 , and a power amplifier (PA)  316 . The BBF  310 , the mixer  312 , and the DA  314  may be included in a radio frequency integrated circuit (RFIC), while the PA  316  may be included in the RFIC or external to the RFIC. The BBF  310  filters the baseband signals received from the DAC  308 , and the mixer  312  mixes the filtered baseband signals with a transmit local oscillator (LO) signal to convert the baseband signal of interest to a different frequency (e.g., upconvert from baseband to RF). This frequency conversion process produces the sum and difference frequencies between the LO frequency and the frequencies of the baseband signal of interest. The sum and difference frequencies are referred to as the beat frequencies. The beat frequencies are typically in the RF range, such that the signals output by the mixer  312  are typically RF signals, which may be amplified by the DA  314  and/or by the PA  316  before transmission by the antenna  303 . 
     The RX path  304  may include a low noise amplifier (LNA)  322 , a mixer  324 , and a baseband filter (BBF)  326 . The LNA  322 , the mixer  324 , and the BBF  326  may be included in a radio frequency integrated circuit (RFIC), which may or may not be the same RFIC that includes the TX path components. RF signals received via the antenna  303  may be amplified by the LNA  322 , and the mixer  324  mixes the amplified RF signals with a receive local oscillator (LO) signal to convert the RF signal of interest to a different baseband frequency (i.e., downconvert). The baseband signals output by the mixer  324  may be filtered by the BBF  326  before being converted by an analog-to-digital converter (ADC)  328  to digital I or Q signals for digital signal processing. 
     Some systems may employ frequency synthesizers with a voltage-controlled oscillator (VCO) to generate a stable, tunable LO with a particular tuning range. Thus, the transmit LO may be produced by a TX frequency synthesizer  318 , which may be buffered or amplified by amplifier  320  before being mixed with the baseband signals in the mixer  312 . Similarly, the receive LO may be produced by an RX frequency synthesizer  330 , which may be buffered or amplified by amplifier  332  before being mixed with the RF signals in the mixer  324 . 
     Example RF Exposure Assessment 
     RF exposure may be expressed in terms of a specific absorption rate (SAR), which measures energy absorption by human tissue per unit mass and may have units of watts per kilogram (W/kg). Alternatively, RF exposure may be expressed in terms of power density (PD), which measures energy absorption per unit area and may have units of mW/cm 2 . 
     SAR may be used to assess RF exposure for transmission frequencies less than 6 GHz, which cover wireless communication technologies such as 3G (e.g., CDMA), 4G (e.g., LTE), 5G (e.g., NR in 6 GHz bands), IEEE 802.11ac, etc. PD may be used to assess RF exposure for transmission frequencies higher than 10 GHz, which cover wireless communication technologies such as IEEE 802.11ad, 802.11ay, 5G, etc. Thus, different metrics may be used to assess RF exposure for different wireless communication technologies. 
     A wireless device (e.g., UE  120 ) may simultaneously transmit signals using multiple wireless communication technologies. For example, the wireless device may simultaneously transmit signals using a first wireless communication technology operating at or below 6 GHz (e.g., 3G, 4G, 5G, etc.) and a second wireless communication technology operating above 6 GHz (e.g., 5G in 24 to 60 GHz bands, IEEE 802.11ad or 802.11ay). In certain aspects, the wireless device may simultaneously transmit signals using the first wireless communication technology (e.g., 3G, 4G, 5G in 6 GHz bands, IEEE 802.11ac, etc.) in which RF exposure is measured in terms of SAR, and the second wireless communication technology (e.g., 5G in 24 to 60 GHz bands, IEEE 802.11ad, 802.11ay, etc.) in which RF exposure is measured in terms of PD. 
     To assess RF exposure from transmissions using the first technology (e.g., 3G, 4G, 5G in 6 GHz bands, IEEE 802.11ac, etc.), the wireless device may include multiple SAR distributions for the first technology stored in memory (e.g., memory  282  of  FIG. 2  or memory  336  of  FIG. 3 ). Each of the SAR distributions may correspond to a respective one of multiple transmit scenarios supported by the wireless device for the first technology. The transmit scenarios may correspond to various combinations of antennas (e.g., antennas  252   a  through  252   r  of  FIG. 2  or antenna  303  of  FIG. 3 ), frequency bands, channels and/or body positions, as discussed further below. 
     The SAR distribution (also referred to as a SAR map) for each transmit scenario may be generated based on measurements (e.g., E-field measurements) performed in a test laboratory using a model of a human body. After the SAR distributions are generated, the SAR distributions may be stored in the memory to enable a processor (e.g., processor  266  of  FIG. 2 ) to assess RF exposure in real time. Each SAR distribution includes a set of SAR values, where each SAR value may correspond to a different location (e.g., on the model of the human body). Each SAR value may comprise a SAR value averaged over a mass of 1 g or 10 g at the respective location. 
     The SAR values in each SAR distribution correspond to a particular transmission power level (e.g., the transmission power level at which the SAR values were measured in the test laboratory). Since SAR scales with transmission power level, the processor may scale a SAR distribution for any transmission power level by multiplying each SAR value in the SAR distribution by the following transmission power scaler: 
                     T   ⁢     x   c         T   ⁢     x   SAR               (   1   )               
where Tx c  is a current transmission power level for the respective transmit scenario, and Tx SAR  is the transmission power level corresponding to the SAR values in the stored SAR distribution (e.g., the transmission power level at which the SAR values were measured in the test laboratory).
 
     As discussed above, the wireless device may support multiple transmit scenarios for the first technology. In certain aspects, the transmit scenarios may be specified by a set of parameters. The set of parameters may include one or more of the following: an antenna parameter indicating one or more antennas used for transmission (i.e., active antennas), a frequency band parameter indicating one or more frequency bands used for transmission (i.e., active frequency bands), a channel parameter indicating one or more channels used for transmission (i.e., active channels), a body position parameter indicating the location of the wireless device relative to the user&#39;s body location (head, trunk, away from the body, etc.), and/or other parameters. In cases where the wireless device supports a large number of transmit scenarios, it may be very time-consuming and expensive to perform measurements for each transmit scenario in a test setting (e.g., test laboratory). To reduce test time, measurements may be performed for a subset of the transmit scenarios to generate SAR distributions for the subset of transmit scenarios. In this example, the SAR distribution for each of the remaining transmit scenarios may be generated by combining two or more of the SAR distributions for the subset of transmit scenarios, as discussed further below. 
     For example, SAR measurements may be performed for each one of the antennas to generate a SAR distribution for each one of the antennas. In this example, a SAR distribution for a transmit scenario in which two or more of the antennas are active may be generated by combining the SAR distributions for the two or more active antennas. 
     In another example, SAR measurements may be performed for each one of multiple frequency bands to generate a SAR distribution for each one of the multiple frequency bands. In this example, a SAR distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the SAR distributions for the two or more active frequency bands. 
     In certain aspects, a SAR distribution may be normalized with respect to a SAR limit by dividing each SAR value in the SAR distribution by the SAR limit. In this case, a normalized SAR value exceeds the SAR limit when the normalized SAR value is greater than one, and is below the SAR limit when the normalized SAR value is less than one. In these aspects, each of the SAR distributions stored in the memory may be normalized with respect to a SAR limit. 
     In certain aspects, the normalized SAR distribution for a transmit scenario may be generated by combining two or more normalized SAR distributions. For example, a normalized SAR distribution for a transmit scenario in which two or more antennas are active may be generated by combining the normalized SAR distributions for the two or more active antennas. For the case in which different transmission power levels are used for the active antennas, the normalized SAR distribution for each active antenna may be scaled by the respective transmission power level before combining the normalized SAR distributions for the active antennas. The normalized SAR distribution for simultaneous transmission from multiple active antennas may be given by the following: 
                     S   ⁢   A   ⁢     R     n   ⁢   o   ⁢   r   ⁢     m   -     ⁢   c   ⁢   o   ⁢   m   ⁢   b   ⁢   i   ⁢   n   ⁢   e   ⁢   d         =       ∑     i   =   1       i   =   K       ⁢         T   ⁢     x   i         T   ⁢     x     S   ⁢   A   ⁢   R   ⁢   i           ·       S   ⁢   A   ⁢     R   i         S   ⁢   A   ⁢     R   lim                     (   2   )               
where SAR lim  is a SAR limit, SAR norm_combined  is the combined normalized SAR distribution for simultaneous transmission from the active antennas, i is an index for the active antennas, SARI is the SAR distribution for the i th  active antenna, Tx i  is the transmission power level for the i th  active antenna, Tx SARi  is the transmission power level for the SAR distribution for the i th  active antenna, and K is the number of the active antennas.
 
     Equation (2) may be rewritten as follows: 
                     S   ⁢   A   ⁢     R     nor   ⁢     m   -     ⁢   c   ⁢   o   ⁢   m   ⁢   b   ⁢   i   ⁢   ned         =       ∑     i   =   1       i   =   K       ⁢         T   ⁢     x   i         T   ⁢     x     S   ⁢   A   ⁢   R   ⁢   i           ·     SAR     nor   ⁢     m   -     ⁢   i                   (     3   ⁢   a     )               
where SAR norm_i  is the normalized SAR distribution for the i th  active antenna. In the case of simultaneous transmissions using multiple active antennas at the same transmitting frequency (e.g., multiple in multiple out (MIMO)), the combined normalized SAR distribution is obtained by summing the square root of the individual normalized SAR distributions and computing the square of the sum, as given by the following:
 
     
       
         
           
             
               
                 
                   
                     
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     In another example, normalized SAR distributions for different frequency bands may be stored in the memory. In this example, a normalized SAR distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the normalized SAR distributions for the two or more active frequency bands. For the case where the transmission power levels are different for the active frequency bands, the normalized SAR distribution for each of the active frequency bands may be scaled by the respective transmission power level before combining the normalized SAR distributions for the active frequency bands. In this example, the combined SAR distribution may also be computed using Equation (3a) in which i is an index for the active frequency bands, SAR norm_i  is the normalized SAR distribution for the i th  active frequency band, Tx i  is the transmission power level for the i th  active frequency band, and Tx SARi  is the transmission power level for the normalized SAR distribution for the i th  active frequency band. 
     To assess RF exposure from transmissions using the second technology (e.g., 5G in 24 to 60 GHz bands, IEEE 802.11ad, 802.11ay, etc.), the wireless device may include multiple PD distributions for the second technology stored in the memory (e.g., memory  282  of  FIG. 2  or memory  336  of  FIG. 3 ). Each of the PD distributions may correspond to a respective one of multiple transmit scenarios supported by the wireless device for the second technology. The transmit scenarios may correspond to various combinations of antennas (e.g., antennas  252   a  through  252   r  of  FIG. 2  or antenna  303  of  FIG. 3 ), frequency bands, channels and/or body positions. 
     The PD distribution (also referred to as PD map) for each transmit scenario may be generated based on measurements (e.g., E-field measurements) performed in a test laboratory using a model of a human body. After the PD distributions are generated, the PD distributions may be stored in the memory to enable the processor (e.g., processor  266  of  FIG. 2 ) to assess RF exposure in real time, as discussed further below. Each PD distribution includes a set of PD values, where each PD value may correspond to a different location (e.g., on the model of the human body). 
     The PD values in each PD distribution correspond to a particular transmission power level (e.g., the transmission power level at which the PD values were measured in the test laboratory). Since PD scales with transmission power level, the processor may scale a PD distribution for any transmission power level by multiplying each PD value in the PD distribution by the following transmission power scaler: 
                     T   ⁢     x   c         T   ⁢     x     P   ⁢   D                 (   4   )               
where Tx c  is a current transmission power level for the respective transmit scenario, and Tx PD  is the transmission power level corresponding to the PD values in the PD distribution (e.g., the transmission power level at which the PD values were measured in the test laboratory).
 
     As discussed above, the wireless device may support multiple transmit scenarios for the second technology. In certain aspects, the transmit scenarios may be specified by a set of parameters. The set of parameters may include one or more of the following: an antenna parameter indicating one or more antennas used for transmission (i.e., active antennas), a frequency band parameter indicating one or more frequency bands used for transmission (i.e., active frequency bands), a channel parameter indicating one or more channels used for transmission (i.e., active channels), a body position parameter indicating the location of the wireless device relative to the user&#39;s body location (head, trunk, away from the body, etc.), and/or other parameters. In cases where the wireless device supports a large number of transmit scenarios, it may be very time-consuming and expensive to perform measurements for each transmit scenario in a test setting (e.g., test laboratory). To reduce test time, measurements may be performed for a subset of the transmit scenarios to generate PD distributions for the subset of transmit scenarios. In this example, the PD distribution for each of the remaining transmit scenarios may be generated by combining two or more of the PD distributions for the subset of transmit scenarios, as discussed further below. 
     For example, PD measurements may be performed for each one of the antennas to generate a PD distribution for each one of the antennas. In this example, a PD distribution for a transmit scenario in which two or more of the antennas are active may be generated by combining the PD distributions for the two or more active antennas. 
     In another example, PD measurements may be performed for each one of multiple frequency bands to generate a PD distribution for each one of the multiple frequency bands. In this example, a PD distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the PD distributions for the two or more active frequency bands. 
     In certain aspects, a PD distribution may be normalized with respect to a PD limit by dividing each PD value in the PD distribution by the PD limit. In this case, a normalized PD value exceeds the PD limit when the normalized PD value is greater than one, and is below the PD limit when the normalized PD value is less than one. In these aspects, each of the PD distributions stored in the memory may be normalized with respect to a PD limit. 
     In certain aspects, the normalized PD distribution for a transmit scenario may be generated by combining two or more normalized PD distributions. For example, a normalized PD distribution for a transmit scenario in which two or more antennas are active may be generated by combining the normalized PD distributions for the two or more active antennas. For the case in which different transmission power levels are used for the active antennas, the normalized PD distribution for each active antenna may be scaled by the respective transmission power level before combining the normalized PD distributions for the active antennas. The normalized PD distribution for simultaneous transmission from multiple active antennas may be given by the following: 
                     P   ⁢     D     n   ⁢   o   ⁢   r   ⁢     m   -     ⁢   c   ⁢   o   ⁢   m   ⁢   b   ⁢   i   ⁢   n   ⁢   e   ⁢   d         =       ∑     i   =   1       i   =   L       ⁢         T   ⁢     x   i         T   ⁢     x     P   ⁢   D   ⁢   i           ·       P   ⁢     D   i         P   ⁢     D   lim                     (   5   )               
where PD lim  is a PD limit, PD norm_combined  is the combined normalized PD distribution for simultaneous transmission from the active antennas, i is an index for the active antennas, PD i  is the PD distribution for the i th  active antenna, Tx i  is the transmission power level for the i th  active antenna, Tx PDi  is the transmission power level for the PD distribution for the i th  active antenna, and L is the number of the active antennas.
 
     Equation (5) may be rewritten as follows: 
                     P   ⁢     D     nor   ⁢     m   -     ⁢   c   ⁢   o   ⁢   m   ⁢   b   ⁢   i   ⁢   ned         =       ∑     i   =   1       i   =   L       ⁢         Tx   i       T   ⁢     x     P   ⁢   D   ⁢   i           ·     PD     nor   ⁢     m   -     ⁢   i                   (     6   ⁢   a     )               
where PD norm_i  is the normalized PD distribution for the i th  active antenna. In the case of simultaneous transmissions using multiple active antennas at the same transmitting frequency (e.g., MIMO), the combined normalized PD distribution is obtained by summing the square root of the individual normalized PD distributions and computing the square of the sum, as given by the following:
 
     
       
         
           
             
               
                 
                   
                     
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     In another example, normalized PD distributions for different frequency bands may be stored in the memory. In this example, a normalized PD distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the normalized PD distributions for the two or more active frequency bands. For the case where the transmission power levels are different for the active frequency bands, the normalized PD distribution for each of the active frequency bands may be scaled by the respective transmission power level before combining the normalized PD distributions for the active frequency bands. In this example, the combined PD distribution may also be computed using Equation (6a) in which i is an index for the active frequency bands, PD norm_i  is the normalized PD distribution for the i th  active frequency band, Tx i  is the transmission power level for the i th  active frequency band, and Tx PDi  is the transmission power level for the normalized PD distribution for the i th  active frequency band. 
     Example Method to Distinguish Between Cover and Human Grip 
     As noted above, in wireless communication, there is a maximum permissible exposure (MPE) limit from international regulators, including the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Federal Communications Commission (FCC) in the United States, that specifies the highest power or energy density (in W/cm 2  or J/cm 2 ) of an electromagnetic source that is considered safe. In some cases, the MPE limit(s) may be converted into a constraint related to the maximum transmission power by one or more devices (e.g., depending on the implementation of each of the devices) and, thus, an uplink (UL) signal transmitted by a device may be limited due to MPE compliance. 
     Some UEs may include sensors (e.g., millimeter wave (mmW) sensors) that allow for higher UL transmission power levels if the sensor output shows no detection of an object blocking the UE antenna(s), potentially boosting UL throughput with transmission at such higher power levels. For example,  FIG. 4A  illustrates mmW sensing by a UE  120  using such object-detection sensors. In  FIG. 4A , the UE  120  includes at least one antenna array  400  with multiple antennas  402   a - d  (collectively referred to herein as “antennas  402 ”). To detect an object  404  (shown in  FIGS. 4B and 4C ) or an open space (OS) condition, the UE  120  may output a signal (e.g., a continuous wave (CW), out-of-band signal) from one of the antennas  402  in the array  400  (e.g., from antenna  402   a ) with a particular detection angle  406 , and another antenna (e.g., antenna  402   d ) in the array may receive signals reflected from the surface of a nearby object  404 , such as a protective cover or a human hand or finger. With the reflected signals, the UE  120  may utilize cross-polarization (Xpol) as illustrated in  FIG. 4B  with two polarized receive paths (one for the horizontal polarization component (labeled “H-pol”) in the circuit diagram  420  and another for the vertical polarization component (labeled “V-pol”) to determine a cross-polarization ratio (K=k V /k H ) and detect whether an object  404  is present. Additionally or alternatively, the UE  120  may employ frequency-modulated continuous-wave (FMCW) radar for object detection, as illustrated in  FIG. 4C  with the example frequency sweep and the circuit diagram  460 . As illustrated in  FIG. 4A , Xpol may have an object detection radius  408  ranging from 0 to about 4 cm from the UE  120 , whereas FMCW radar may have an objection detection radius ranging from about 4 cm to about 60 cm from the UE. 
     As explained above,  FIG. 4B  illustrates mmW sensing using cross-polarization (Xpol) to detect an object  404  near a UE or to detect an OS condition, in accordance with certain aspects of the present disclosure. In  FIG. 4B , the antenna array  400  comprises four antennas  402 , although any suitable number of antennas may be used. In the circuit diagram  420 , the transmit path (e.g., transmit path  302 ) includes a frequency synthesizer (e.g., the TX frequency synthesizer  318 ) and an amplifier  421 . The frequency synthesizer is used to generate a CW signal having a frequency (f CW ) that is out of band, for example, between a first component carrier band (CC 1 ) and a second component carrier band (CC 2 ). In this example, f CW  is 28 GHz. The amplifier  421  may amplify the CW signal and drive the antenna  402   a  to wirelessly transmit the signal (e.g., with a particular detection angle  406 ). 
     If there is an object  404  near the UE, a surface of the object may reflect the transmitted signal, and another antenna (e.g., antenna  402   d ) in the antenna array  400  may receive signals reflected from the surface of the object. For Xpol detection, the receive path (e.g., receive path  304 ) may include two polarized receive paths (one for the horizontal polarization component (labeled “H-pol”) in the circuit diagram  420  and another for the vertical polarization component (labeled “V-pol”). The H-pol receive path includes an amplifier (e.g., a low noise amplifier  332 H), a mixer  324   H , a filter (e.g., baseband filter  326   H ), and an ADC  328   H . Similarly, the V-pol receive path includes an amplifier (e.g., a low noise amplifier  332   V ), a mixer  324   V , a filter (e.g., baseband filter  326   V ), and an ADC  328   V . A frequency synthesizer (e.g., an RX frequency synthesizer  330 ) may generate a local oscillator (LO) signal (e.g., having a frequency of 28.001 GHz, offset 100 MHz from the transmitted signal) as an input to each of the H-pol and V-pol mixers  324   H ,  324   V . These receive chain components in  FIG. 4B  may function as described above with respect to  FIG. 3 , amplifying received RF signals, mixing the amplified RF signals with the LO signal to downconvert the signals, filtering the mixed signals to focus on the baseband signals, and digitizing the baseband signals. 
     The H-pol and V-pol digitized signals from the ADCs may be sent to a processor  422 , which may be implemented by a digital signal processor (DSP) or any other suitable processing system. The processor  422  may include a fast Fourier transform (FFT) module  424  and a frequency-domain in-phase/quadrature (FD-IQ) module  426 . The FFT module  424  may be used to convert the time-domain digitized signals to frequency-domain data, which may yield a maximum H-pol FFT value (k H ) and a maximum V-pol FFT value (k V ), as explained below with respect to  FIG. 5 . Using the frequency-domain data, the FD-IQ module  426  may be used to plot the cross-polarization ratio (K=k V /k H ) in the I/Q plane, as illustrated in the graph  430 . Open space (i.e., no nearby object) may have a different location in the I/Q plane than various objects, and in this manner, Xpol may be used to determine whether an object is present. 
     As explained above,  FIG. 4C  illustrates mmW sensing using FMCW radar to detect an object  404  near a UE or to detect an OS condition, in accordance with certain aspects of the present disclosure. In  FIG. 4C , the antenna array  400  comprises four antennas  402 , although any suitable number of antennas may be used. In the circuit diagram  460 , the transmit path (e.g., transmit path  302 ) includes a DAC  308 , a baseband filter  310 , a mixer  312 , and the amplifier  421 , which may represent the DA  314  and/or the PA  316 . A frequency synthesizer  462  may be used to generate an LO signal for inputting to the mixer  312 . The frequency synthesizer  462 , in conjunction with the other components of the transmit path, may be used to generate a frequency sweep (e.g., from 25 to 29 GHz), which may include CC 1  and CC 2  bands as shown, in a wirelessly transmitted signal output from the antenna  402   a , for example. 
     If there is an object  404  near the UE, a surface of the object may reflect the transmitted signal, and another antenna (e.g., antenna  402   d ) in the antenna array  400  may receive signals reflected from the surface of the object. For FMCW radar detection, the receive path (e.g., receive path  304 ) may include a low noise amplifier  332 , a mixer  324 , a baseband filter  326 ), and an ADC  328 . These receive path components in the circuit diagram  460  of  FIG. 4C  may function as described above with respect to  FIG. 3 , amplifying received RF signals, mixing the amplified RF signals with the LO signal from the frequency synthesizer  462  to downconvert the signals, filtering the mixed signals to focus on the baseband signals, and digitizing the baseband signals. The FMCW digitized signals from the ADC  328  may be sent to a processor  464 , which may be implemented by a DSP or any other suitable processing system. The processor  464  may process the FMCW digitized signals to detect an object or an open space condition. 
       FIG. 5  illustrates example FFT symbol values from Xpol detection, in accordance with certain aspects of the present disclosure. The FFT symbol values include horizontal polarization FFT values  510  based on digitized signals from the H-pol receive path and vertical polarization FFT values  520  based on digitized signals from the V-pol receive path. The maximum value of the horizontal polarization FFT values  610  indicates k H , whereas the maximum value of the vertical polarization FFT values  620  indicates k V . The cross-polarization ratio (K) is determined by K=k V /k H . 
     The complex value of K (I+jQ) provides an indication of the presence of an object in front of the antenna. k V /k H  division (which may be implemented as k V k H *) may eliminate calibration of the transmit gain/phase randomness during each measurement.  FIG. 6  is an example plot  600  of multiple samples of K in the in-phase/quadrature (IQ) plane for two different scenarios: open space and a finger grip (or protective case). 
     The standard deviation of consecutive K measurements over time (σ K ) provides a metric of stability of an object in front of the antenna. In other words, a relatively larger σ K  means less object stability (i.e., more object movement), whereas a relatively smaller σ K  indicates greater stability (i.e., less object movement). Open space (i.e., no reflector) provides a relatively smaller σ K . A human finger or hand not gripping the UE in front of an antenna provides a relatively larger σ K , but a finger gripping the UE provides a relatively smaller σ K  because a finger does not move as much when part of a grip. Similar to a finger with grip, protective cases (e.g., made of plastic and/or glass) also provide smaller σ K , thereby making it difficult to differentiate a protective cover from a human grip using only σ K . For example, as illustrated in the example plot  600  of  FIG. 6 , the σ K  for open space may be similar to the σ K  for a protective case (or a finger grip). 
     A higher transmission power may be used by a UE when the antenna is blocked by a protective case, but a lower transmission power should be used when the antenna is blocked by a finger or other human tissue, due to MPE limits, as described above. Therefore, what is needed are techniques and apparatus for differentiating between a protective cover and human grip by object-detection sensors of a UE. 
     Furthermore, different protective cases may provide different cross-polarization ratio centers {mean(K)} in the IQ plane. An algorithm for determining transmission power may periodically adapt the open space parameters for a UE, which, when combined with the different K centers for different protective cases, may also make it more difficult to differentiate a protective case from finger grip. 
     Certain aspects of the present disclosure provide techniques and apparatus for distinguishing between an antenna of a UE being blocked by a cover (e.g., a protective rubber or plastic case) or by human tissue (e.g., a finger or palm) using at least two different types of parameters, as described in greater detail below. 
       FIG. 7  is a flow diagram illustrating example operations  700  for wireless communications, in accordance with certain aspects of the present disclosure. The operations  700  may be performed, for example, by a wireless device (e.g., UE  120  of  FIG. 1 ), and more particularly, by a receiver, processor, and transmitter of the wireless device. 
     The operations  700  may begin, at block  701 , with the wireless device transmitting a first signal (e.g., with the TX front-end circuits  254   a - 254   r  or the transmit path  302  of the UE  120 ) and, at block  702 , receiving a plurality of signals (e.g., with the RX front-end circuits  254   a - 254   r  or the receive path  304  of a UE  120 ) based on the transmitted first signal (e.g., reflections of the transmitted first signal). At block  704 , the wireless device determines values for at least two different types of parameters based on the received plurality of signals (e.g., with the receive processor  258 , the control/processor  280 , and/or the transmit processor  264  or with the processor  422  of the UE  120 ). At block  706 , the wireless device determines an environmental scenario for the device based on the values for the at least two different types of parameters (e.g., with the receive processor  258 , the control/processor  280 , and/or the transmit processor  264  or with the processor  422  of the UE  120 ). At block  708 , the wireless device transmits a second signal using a transmission power based on the determined environmental scenario (e.g., with the TX front-end circuits  254   a - 254   r  or the transmit path  302  of the UE  120 ). The operations  700  are described in greater detail below and illustrated in the various drawings. 
     As presented above, σ K  may be insufficient to distinguish between a protective cover and human grip. Therefore, certain aspects of the present disclosure provide another dimension of information in addition to σ K . For certain aspects, this additional information may be determined from the FFT data already provided by the two polarized receive paths. 
     For example, empirical studies show the signal-to-noise ratio (SNR) of FFTs from H-pol and V-pol fluctuate with different types of objects. The SNR of the vertical polarization component (SNR V ) may be expressed as SNR V =10*log 10 (k V /σ 2   FFTV ), where σ 2   FFTV  is the variance of the vertical polarization FFT values (e.g., FFT values  520 ). The SNR of the horizontal polarization component (SNR H ) may be expressed as SNR H =10*log 10 (k H /σ 2   FFTH ), where σ 2   FFTH  is the variance of the horizontal polarization FFT values (e.g., FFT values  510 ). The mean SNR (SNR m ) of these two SNRs may be expressed as SNR m =SNR V −(SNR H −SNR V ). The processor (e.g., processor  422 ) calculating the FFT values may calculate the noise power of a number of bins adjacent to the k H  or k V  peak (e.g.,  20  adjacent bins, 10 bins on either side of the peak). For certain aspects, the processor may remove or otherwise effectively ignore bins that have spurs. 
     Electromagnetic (EM) simulations show that the near-field coupled electric field changes with the dielectric that mimics a human finger. The hypothesis for observed SNR fluctuations is that coupled signal power fluctuates relative to a fixed receiver noise floor (e.g., according to kTBFG, where k is Boltzmann&#39;s constant, T is absolute temperature, F is the noise figure, B is the reception bandwidth, and G is the gain) and has a correlation to the type of material due to the reflection coefficient of the material. 
       FIG. 8  is an example plot  800  of SNR in decibels (dB) of vertical and horizontal polarization components for different scenarios, including open space (OS), grip, and protective case. Thus, with this additional information, different environmental scenarios that produce the same σ K  can be differentiated by also looking at SNR m . 
       FIG. 9  illustrates an example plot  900  of K for different scenarios in the IQ plane. In the IQ plot  900 , an orthogonal human finger pressed against the UE has a relatively very large σ K , as shown by the spread of the K values. In contrast, open space and a human palm pressed against the UE have similar, relatively small σ K , and a rubber protective case and a vertical human finger pressed on the UE have a similar, albeit noticeably larger σ K . Therefore, considering only σ K  may make it difficult to distinguish between open space, a protective case, or a human tissue condition. 
       FIG. 9  also illustrates a graph  950  showing an example correlation between σ K  and SNR m  for the same scenarios presented in the IQ plot  900 , in accordance with certain aspects of the present disclosure. Using regression or any of various other suitable techniques, a linear equation can be found to separate scenarios that may be categorized as OS (e.g., OS or protective cover) and scenarios that may be categorized as object detection (e.g., presence of human tissue), for the purposes of determining transmission power. The line  952  represented by this linear equation in the graph  950  may be considered as a boundary separating the two regions: an OS region versus an object detection region. The threshold standard deviation (σ TH ) of this OS/detection boundary line  952  may be expressed as σ TH =m*SNR m +c, where m is the slope of the line and c is the σ K  offset. 
       FIG. 10  is a graph  1000  illustrating an example linear relationship between σ K  and SNR m  for different scenarios (e.g., different materials), where the line  1002  with equation σ TH =m*SNR m +c represents a boundary between open space (OS) and object detection regions, in accordance with certain aspects of the present disclosure. Note how air, the rubber protective case, and the plastic phone back housing are in the OS region, whereas the pressed horizontal human finger, the pressed human palm, the pressed orthogonal human finger, and the pressed vertical human finger are in the detection region. The linear equation may be frequency or band dependent. Additionally or alternatively, the linear equation may be dependent on the specific UE, varying between types, brands, and models. 
       FIG. 11  is a flow chart  1100  for determining parameters for OS based on σ K  and SNR m , in accordance with certain aspects of the present disclosure. The parameters for OS may include the radius (R OS ) and the center (C OS ) of the OS. As shown in the flow chart  1100 , if σ K &lt;σ TH  (indicating the OS region), then the OS parameters may be updated, where R OS =3*σ K  and where C OS =mean (K). Otherwise, the OS parameters are not updated, and more samples are captured. More specifically, samples (e.g., Xpol samples) are captured at block  1102 , and an FFT is performed on the captured samples at block  1104  to convert the sampled data from the time domain to the frequency domain. From the FFT, σ K  may be determined at block  1106 , and the SNR m  may be determined at block  1108 , as described above. At block  1110 , the variables (e.g., m and c) of the linear equation for the boundary between open space and object detection regions (e.g., line  952  or line  1002 ) may be determined (e.g., read from memory, such as from memory  282 ). At block  1112 , σ TH  may be calculated using the variables for the linear equation and SNR m . If σ K &lt;σ TH  (indicating the OS region) as determined at block  1114 , then the OS parameters are updated at block  1116 , where R OS =3*σ K  and where C OS =mean (K). Otherwise, if σ K ≥σ TH  as determined at block  1114 , the OS parameters are not updated, and more samples are captured at block  1102 . 
     As described above, certain aspects of the present disclosure are directed to a method for wireless communications by a UE. The method generally includes receiving a plurality of signals at the UE, determining values for at least two different types of parameters based on the received plurality of signals, determining an environmental scenario for the UE based on the values for the at least two different types of parameters, and transmitting a signal using a transmission power based on the determined environmental scenario. 
     According to certain aspects, the received plurality of signals includes a vertical polarization component signal and a horizontal polarization component signal. For certain aspects, the at least two different types of parameters comprise a statistic of a cross-polarization ratio between the vertical polarization component signal and the horizontal polarization component signal. For example, the statistic of the cross-polarization ratio may be a standard deviation of the cross-polarization ratio. For certain aspects, the at least two different types of parameters further include a statistic of a signal-to-noise ratio based on the vertical polarization component signal and the horizontal polarization component signal. For example, the statistic of the signal-to-noise ratio may be a mean of the signal-to-noise ratio calculated based on a variance of the vertical polarization component signal and on a variance of the horizontal polarization component signal. 
     According to certain aspects, the at least two different types of parameters include a statistic of a signal-to-noise ratio based on the vertical polarization component signal and the horizontal polarization component signal. 
     According to certain aspects, receiving the plurality of signals entails receiving the vertical polarization component signal via a vertically polarized receive path of the UE and receiving the horizontal polarization component signal via a horizontally polarized receive path of the UE. 
     According to certain aspects, the method further involves transmitting a test signal from the UE. In some cases, the test signal may be a continuous wave (CW) signal or a frequency-modulated continuous-wave (FMCW) radar signal. For certain aspects, the test signal is transmitted from an antenna in an antenna array of the UE, and the plurality of signals is received by another antenna in the antenna array. 
     According to certain aspects, determining the environmental scenario entails distinguishing between an antenna of the UE being blocked by a cover or by human tissue. For example, the cover may include a protective case for the UE. 
     According to certain aspects, determining the environmental scenario involves determining a center and a radius of an open space from an antenna of the UE. 
     According to certain aspects, determining the environmental scenario includes determining a line (e.g., a line, such as line  952  or line  1002 ) based on a linear relationship between the at least two types of parameters and determining whether one of the at least two types of parameters is above the line. In this case, the signal may be transmitted using a relatively lower transmission power if the one of the at least two types of parameters is above the line, whereas the signal may be transmitted using a relatively higher transmission power if the one of the at least two types of parameters is not above the line. For certain aspects, parameters of the line (e.g., the slope and the offset) may be stored in memory. 
     According to certain aspects, determining the environmental scenario involves determining a boundary based on a relationship between the at least two types of parameters and determining whether one of the at least two types of parameters is on a first side of the boundary or a second side of the boundary. In this case, the signal may be transmitted using a relatively lower transmission power if the one of the at least two types of parameters is on the first side of the boundary, whereas the signal may be transmitted using a relatively higher transmission power if the one of the at least two types of parameters is on the second side of the boundary. 
     According to certain aspects, determining the environmental scenario involves determining a material of a protective case covering the UE. For certain aspects, the received plurality of signals includes a vertical polarization component signal and a horizontal polarization component signal, and the at least two different types of parameters comprise a statistic of a cross-polarization ratio between the vertical polarization component signal and the horizontal polarization component signal. In this case, determining the material of the protective case covering the UE may be based, at least in part, on the statistic of the cross-polarization ratio. For example, the statistic may be a standard deviation of the cross-polarization ratio. 
     Example Automatic Cover Detection 
     As explained above, millimeter wave (mmWave) transmissions present a potential safety hazard because such transmissions can cause localized heating on the skin or the eye surface. To protect the public from this hazard, government regulators set an RF exposure limit (e.g., in terms of maximum power per square centimeter area). For mmWave, this limit is called the maximum permissible exposure (MPE) limit. For example, the Federal Communications Commission (FCC) in the United States has set the MPE limit for all transmissions at frequencies greater than 3 GHz. For transmissions between 30 and 300 GHz, for example, the FCC MPE limit is set at 1 mW/cm 2 . The MPE limit tightens the link budget of 5G mmWave uplink (UL) transmissions. 
     One solution is the use of proximity sensors that determine whether there is a human body near the mmWave module. When the proximity sensor indicates open space (OS), the UE may transmit at a higher power, but if the sensor indicates the presence of an object, then the UE may back off its UL transmission power to remain in compliance with MPE limits. One shortcoming of many proximity sensors is their inability to distinguish between the human body and other objects. Accordingly, when an end-user installs a protective cover on the UE, the cover may trigger a persistent detection, making the proximity sensor unusable. Therefore, a mechanism for sensing through protective covers is desirable. 
     As described above, cross-polarization (Xpol) sensors may rely on the near-field coupling property between transmit and receive antenna elements within a mmWave antenna array to detect the present of an object in the vicinity of the antenna array. With Xpol, a transmitter may transmit a single tone (e.g., at a mmWave frequency), and two receivers may receive back the transmitted tone. The two receivers may be attached to antenna ports with different polarization (e.g., vertical and horizontal polarization). The phase and amplitude of the ratio of the two received signals (K=k V /k H ) serve as a signature to identify an OS from an object. 
     With the Xpol algorithm, the OS signature may be defined as an OS circle whose center and radius are plotted on an in-phase/quadrature (IQ) plane, for example, as described herein with respect to  FIG. 6 . The OS signature of each antenna array (at each frequency or each band) may be characterized or calibrated per device. Once this OS circle is established for a given antenna array, the Xpol algorithm may detect objects by classifying captures that land outside the OS circle in the IQ plane as detection of an object and by classifying captures that land inside the OS circle as open space. OS circles may be characterized or generated for the antenna arrays and various states of the UE, such as a state when the UE is uncovered and multiples states corresponding to various cases or covers. For example, an OS circle may be characterized for a given antenna array when the UE is uncovered, and another OS circle may characterized for that antenna array when the UE is covered with a specific case or cover. 
     Single-shot Xpol sensing may have difficulty distinguishing between a human body part and other objects, which is typically the case with most other sensors, as well. Accordingly, when an end-user installs a protective cover on the UE (e.g., a smartphone), the cover may trigger a persistent detection, which is problematic. One potential solution to this problem is to have multiple active OS circles. For example, one OS circle may be associated with a naked (i.e., uncovered) UE, and another OS circle may correspond to a characterized cover. In such cases, the Xpol algorithm may classify a capture as OS if the capture lands in either of these OS circles. The issue with this approach is that it is possible to find a particular finger-touching position on top of a naked UE that leads to a capture incorrectly landing in the OS circle of a cover. Such a finger-touching position may most likely be mis-detected on a naked UE because the capture will be interpreted as an OS over a cover. 
     Certain aspects of the present disclosure provide an Xpol-based algorithm and sensors that support multiple OS circles, but allow only one of these OS circles to be active at a time. In this manner, when the algorithm determines that the UE is naked, the algorithm deactivates OS circles of all covers, and when the algorithm determines that a particular cover is installed, the algorithm deactivates OS circles of the naked UE and of any other covers (other than the OS circle of the installed cover). Thus, certain aspects of the present disclosure relate to an Xpol algorithm that determines when a cover is installed and which kind of cover is installed. This Xpol algorithm relies on the very low likelihood of holding a naked UE in such a manner that the particular holding scenario appears like OS of a cover across multiple antenna arrays. For certain aspects, the Xpol algorithm may determine that a cover is installed by observing Xpol captures across multiple antenna arrays. When an OS corresponding to a given cover is detected across multiple antenna arrays, the algorithm assigns the given cover&#39;s OS circle to be the only active OS circle. Similarly, when the end-user removes the cover, the algorithm may eventually observe that the naked UE&#39;s OS is detected across multiple antenna arrays, and thus, the algorithm may reassign the naked UE&#39;s OS circle as the only active OS circle. 
     As illustrated in Table 1, the nominal value of OS circles may not be the same for a given environmental condition (e.g., a particular cover) observed by different antenna arrays. In Table 1, the rows correspond to the antenna arrays in the UE, and the columns correspond to the environmental conditions. The algorithm disclosed herein may pick a single column in Table 1 at one time, rather than a single OS at a time. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Env. 
                 Env. 
                 Env. 
                 Env. 
               
               
                   
                 Condition 1 
                 Condition 2 
                 Condition 3 
                 Condition 4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Antenna 
                 OS11 
                 OS12 
                 OS13 
                 OS14 
               
               
                 array 1 
               
               
                 Antenna 
                 OS21 
                 OS22 
                 OS23 
                 OS24 
               
               
                 array 2 
               
               
                 Antenna 
                 OS31 
                 OS32 
                 OS33 
                 OS34 
               
               
                 array 3 
               
               
                 Antenna 
                 OS41 
                 OS42 
                 OS43 
                 OS44 
               
               
                 array 4 
               
               
                   
               
            
           
         
       
     
       FIG. 13  is a flow diagram of example operations  1300  for wireless communications, in accordance with certain aspects of the present disclosure. The operations  1300  may be performed, for example, by a wireless device (e.g., UE  120  of  FIG. 1 ), and more particularly, by a receiver, processor, and transmitter of the wireless device. 
     The operations  1300  may begin, at block  1301 , with the wireless device transmitting at least one test signal (e.g., with the TX front-end circuits  254   a - 254   r  or the transmit path  302  of the UE  120 ), and at block  1302 , receiving a plurality of cross-polarization captures from multiple antenna arrays (e.g., with the RX front-end circuits  254   a - 254   r  or the receive path  304  of the UE  120 ). In aspects, the received plurality of cross-polarization captures may be indicative of reflections of the transmitted test signal. At block  1304 , the wireless device may detect that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first open space (OS) circle in an in-phase/quadrature (IQ) plane out of a set of possible OS circles for the wireless device. Based on the detection at block  1304 , the wireless device may, at block  1306 , assign the first OS circle as an active OS circle for the wireless device. The wireless device may also deactivate (e.g., ignore) other possible OS circles in the set, based on the detection at block  1304 . At block  1308 , the wireless device may determine an environmental scenario corresponding to the active OS circle. At block  1310 , the wireless device may transmit a signal using a transmission power based on the determined environmental scenario (e.g., with the TX front-end circuits  254   a - 254   r  or the transmit path  302  of the UE  120 ). 
     In certain aspects, as the first OS circle may be associated with a particular state of the wireless device (e.g., uncovered or covered with a particular case/cover), the wireless device may update the active OS circle to a second OS circle among the set of possible OS circles and associated with another state of the wireless device, for example, due to a change in the wireless device being uncovered or covered with a different case/cover. With respect to the operations  1300 , the wireless device may transmit another test signal and receive another plurality of cross-polarization captures from the multiple antenna arrays of the wireless device. The wireless device may detect that the other plurality of cross-polarization captures from the multiple antenna arrays correspond to a second OS circle in the IQ plane out of the set of possible OS circles, the second OS circle being different from the first OS circle. The wireless device may assign, based on the detection of correspondence to the second OS circle, the second OS circle as the active OS circle for the wireless device and deactivate other possible OS circles in the set, including the first OS circle. As an example, the first OS circle may correspond to when the wireless device is uncovered, and the second OS circle may correspond to when the wireless device is covered with a particular case or cover. 
     In aspects, the set of possible OS circles may correspond or be associated with various states of the wireless device. For example, the set of possible OS circles may correspond to the wireless device being uncovered and/or to the wireless device being covered with one or more different types of covers or cases. 
     In certain aspects, the transmission of the test signal at block  1302  may involve using one of the antennas in one of the antenna arrays. The test signal may include a continuous wave signal or a FMCW radar signal. The test signal may be transmitted from an antenna in one of the multiple antenna arrays of the wireless device, and a vertical polarization component signal and a horizontal polarization component signal may be received by another antenna in the same one of the multiple antenna arrays. 
     In aspects, the determination of the environmental scenario at block  1308  may entail identifying whether the human tissue is in proximity to the wireless device. For example, the determination of the environmental scenario may include the wireless device distinguishing between an antenna of the wireless device being blocked by a cover or by human tissue. 
     According to certain aspects, the cover may include a protective case for the wireless device. For example, the cover may be a case for a mobile phone or smartphone. The cover may include various materials, such as plastic, rubber, or leather. 
     In certain aspects, the cross-polarization captures may be indicative of cross-polarization component signals received at block  1302 . For example, each of the plurality of cross-polarization captures may be based on a cross-polarization ratio between a vertical polarization component signal and a horizontal polarization component signal. 
     According to certain aspects, the cross-polarization captures associated with multiple antenna arrays may be used to detect the OS circle associated with the current covered/uncovered state of the wireless device. For example, the detection at block  1304  may include the wireless device detecting that a first cross-polarization capture from a first antenna array corresponds to the first OS circle and to a second OS circle and detecting that a second cross-polarization capture from a second antenna array corresponds to the first OS circle, but not to the second OS circle. Based on the first OS circle corresponding to the first and second antenna arrays, the wireless device may identify that the first OS circle is the OS circle corresponding to the current covered/uncovered state of the wireless device. 
     While various examples are described herein with respect to an OS circle being used to identify an environmental scenario or correspond to an uncovered or covered state of a wireless device to facilitate understanding, aspects of the present disclosure may also be applied to other suitable areas (e.g., a polygon) in an IQ plane. For example, a specific polygon in the IQ plane may be indicative of the OS state of a wireless device. 
     The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application-specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function. For example, means for receiving may include the RX front-end circuits  254   a - 254   r  and/or antennas  252   a - 252   r  of  FIG. 2  or the receive path  304  and/or antenna  303  of  FIG. 3 . Means for transmitting may include the TX front-end circuits  254   a - 254   r  and/or antennas  252   a - 252   r  of  FIG. 2  or the transmit path  302  and/or antenna  303  of  FIG. 3 . Means for detecting, means for determining, and/or means for assigning (and deactivating) may include at least one processor, such as the receive processor  258 , the controller/processor  280 , and/or the transmit processor  264  of  FIG. 2  or the processor  422  of  FIG. 4B . 
     EXAMPLE ASPECTS 
     In addition to the various aspects described above, specific combinations of aspects are within the scope of the disclosure, some of which are detailed below: 
     Aspect 1. A method for wireless communications by a user equipment (UE), comprising: receiving a plurality of cross-polarization captures from multiple antenna arrays of the UE; detecting that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first open space (OS) circle in an in-phase/quadrature (IQ) plane out of a set of possible OS circles for the UE; based on the detection, assigning the first OS circle as an active OS circle for the UE and deactivating other possible OS circles in the set; determining an environmental scenario corresponding to the active OS circle; and transmitting a signal using a transmission power based on the determined environmental scenario. 
     Aspect 2. The method of Aspect 1, further comprising: receiving another plurality of cross-polarization captures from the multiple antenna arrays of the UE; detecting that the other plurality of cross-polarization captures from the multiple antenna arrays correspond to a second OS circle in the IQ plane out of the set of possible OS circles, the second OS circle being different from the first OS circle; and based on the detection of correspondence to the second OS circle, assigning the second OS circle as the active OS circle for the UE and deactivating other possible OS circles in the set, including the first OS circle. 
     Aspect 3. The method according to Aspect 1 or 2, wherein the set of possible OS circles corresponds to the UE being uncovered and to one or more different types of covers for the UE. 
     Aspect 4. The method according to Aspects 1-3, further comprising transmitting at least one test signal from the UE. 
     Aspect 5. The method of Aspect 4, wherein the at least one test signal comprises a continuous wave signal or a frequency-modulated continuous-wave (FMCW) radar signal. 
     Aspect 6. The method of Aspect 4, wherein the at least one test signal is transmitted from an antenna in one of the multiple antenna arrays of the UE and wherein a vertical polarization component signal and a horizontal polarization component signal are received by another antenna in the same one of the multiple antenna arrays. 
     Aspect 7. The method according to any of Aspects 1-6, wherein determining the environmental scenario comprises distinguishing between an antenna of the UE being blocked by a cover or by human tissue. 
     Aspect 8. The method of Aspect 7, wherein the cover comprises a protective case for the UE. 
     Aspect 9. The method according to any of Aspects 1-8, wherein each of the plurality of cross-polarization captures is based on a cross-polarization ratio between a vertical polarization component signal and a horizontal polarization component signal. 
     Aspect 10. The method according to any of Aspects 1-9, wherein the detecting comprises: detecting that a first cross-polarization capture from a first antenna array corresponds to the first OS circle and to a second OS circle; and detecting that a second cross-polarization capture from a second antenna array corresponds to the first OS circle, but not to the second OS circle. 
     Aspect 11. An apparatus for wireless communications, comprising: multiple antenna arrays; a receiver configured to receive a plurality of cross-polarization captures from the multiple antenna arrays; a memory; a processor coupled to the memory, the processor and the memory being configured to: detect that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first open space (OS) circle in an in-phase/quadrature (IQ) plane out of a set of possible OS circles for the apparatus, assign the first OS circle as an active OS circle for the apparatus and deactivate other possible OS circles in the set, based on the detection, and determine an environmental scenario corresponding to the active OS circle; and a transmitter configured to transmit a signal using a transmission power based on the determined environmental scenario. 
     Aspect 12. The apparatus of Aspect 11, wherein: the receiver is configured to receive another plurality of cross-polarization captures from the multiple antenna arrays of the apparatus; and the processor and the memory are further configured to: detect that the other plurality of cross-polarization captures from the multiple antenna arrays correspond to a second OS circle in the IQ plane out of the set of possible OS circles, the second OS circle being different from the first OS circle, and assign the second OS circle as the active OS circle for the apparatus and deactivate other possible OS circles in the set, including the first OS circle, based on the detection of correspondence to the second OS circle. 
     Aspect 13. The apparatus according to Aspect 11 or 12, wherein the set of possible OS circles corresponds to the apparatus being uncovered and to one or more different types of covers for the apparatus. 
     Aspect 14. The apparatus according to any of Aspects 11-13, wherein the transmitter is further configured to transmit at least one test signal. 
     Aspect 15. The apparatus of Aspect 14, wherein an antenna in one of the multiple antenna arrays of the apparatus is configured to transmit the at least one test signal and wherein another antenna in the same one of the multiple antenna arrays is configured to receive a vertical polarization component signal and a horizontal polarization component signal. 
     Aspect 16. The apparatus according to any of Aspects 11-15, wherein the processor and the memory are further configured to distinguish between an antenna of the apparatus being blocked by a cover or by human tissue. 
     Aspect 17. The apparatus of Aspect 16, wherein the cover comprises a protective case for the UE. 
     Aspect 18. The apparatus according to any of Aspects 11-17, wherein each of the plurality of cross-polarization captures is based on a cross-polarization ratio between a vertical polarization component signal and a horizontal polarization component signal. 
     Aspect 19. The apparatus according to any of Aspects 11-18, wherein the processor and the memory are further configured to: detect that a first cross-polarization capture from a first antenna array corresponds to the first OS circle and to a second OS circle; and detect that a second cross-polarization capture from a second antenna array corresponds to the first OS circle, but not to the second OS circle. 
     Aspect 20. An apparatus for wireless communications, comprising: means for receiving a plurality of cross-polarization captures from multiple antenna arrays of the apparatus; means for detecting that the plurality of cross-polarization captures from the multiple antenna arrays correspond to a first open space (OS) circle in an in-phase/quadrature (IQ) plane out of a set of possible OS circles for the apparatus; means for assigning the first OS circle as an active OS circle for the apparatus and deactivating other possible OS circles in the set, based on the detection; means for determining an environmental scenario corresponding to the active OS circle; and means for transmitting a signal using a transmission power based on the determined environmental scenario. 
     As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database, or another data structure), ascertaining, and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, “determining” may include resolving, selecting, choosing, establishing, and the like. 
     As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c). 
     The various illustrative logical blocks, modules, and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an ASIC, a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     The functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in hardware, an example hardware configuration may comprise a processing system in a wireless node. The processing system may be implemented with a bus architecture. The bus may include any number of interconnecting buses and bridges depending on the specific application of the processing system and the overall design constraints. The bus may link together various circuits including a processor, machine-readable media, and a bus interface. The bus interface may be used to connect a network adapter, among other things, to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the physical (PHY) layer. In the case of a user terminal, a user interface (e.g., keypad, display, mouse, joystick, etc.) may also be connected to the bus. The bus may also link various other circuits such as timing sources, peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further. 
     The processing system may be configured as a general-purpose processing system with one or more microprocessors providing the processor functionality and external memory providing at least a portion of the machine-readable media, all linked together with other supporting circuitry through an external bus architecture. Alternatively, the processing system may be implemented with an ASIC with the processor, the bus interface, the user interface in the case of an access terminal), supporting circuitry, and at least a portion of the machine-readable media integrated into a single chip, or with one or more FPGAs, PLDs, controllers, state machines, gated logic, discrete hardware components, or any other suitable circuitry, or any combination of circuits that can perform the various functionality described throughout this disclosure. Those skilled in the art will recognize how best to implement the described functionality for the processing system depending on the particular application and the overall design constraints imposed on the overall system. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatus described above without departing from the scope of the claims.