Linear calculation of radio frequency exposure for coherent transmission

Abstract

Certain aspects of the present disclosure provide techniques and apparatus for radio frequency (RF) exposure compliance for coherent transmission. An example method of wireless communication includes obtaining a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode. The method further includes transmitting, in the coherent transmission mode, the first signal via the plurality of antennas at a first transmit power determined based at least in part on the first transmit power limit.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 18 / 593,190, filed on March 1, 2024, which claims the benefit of U.S. provisional patent application serial No. 63 / 449,896, filed on March 3, 2023, each of which is hereby incorporated by reference in its entirety for all applicable purposes. Background Art Technical Field

[0003] Aspects of the present disclosure relate to wireless communications, and more particularly, to radio frequency (RF) exposure compliance.

[0004] Related technical description

[0005] Wireless communication systems are widely deployed to provide a variety of telecommunication services, such as telephony, video, data, messaging, and broadcasting. Modern wireless communication devices, such as cellular phones, are often required to meet radio frequency (RF) exposure limits set by certain government and international standards and regulations. To ensure compliance with the standards, such devices currently undergo an extensive certification process before being shipped to the market. To ensure that wireless communication devices comply with RF exposure limits, technologies have been developed that enable wireless communication devices to assess RF exposure from wireless communication devices and adjust the transmit power of the wireless communication devices accordingly to comply with the RF exposure limits. Summary of the Invention

[0006] Certain aspects of the subject matter described in this disclosure may be implemented in a method for wireless communication by a wireless device. The method generally includes obtaining a first transmit power limit associated with a coherent transmit mode. The first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode. The method also includes transmitting a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0007] Certain aspects of the subject matter described in this disclosure may be implemented in an apparatus for wireless communication. The apparatus generally includes one or more memories that collectively store executable instructions; and one or more processors coupled to the one or more memories. The one or more processors are collectively configured to execute the executable instructions to cause the apparatus to: obtain a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; and transmit a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0008] Certain aspects of the subject matter described in this disclosure may be implemented in an apparatus for wireless communication. The apparatus generally includes means for obtaining a first transmit power limit associated with a coherent transmit mode. The first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode. The apparatus further includes means for transmitting a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0009] Certain aspects of the subject matter described in this disclosure may be implemented in a computer-readable medium. The computer-readable medium has instructions stored thereon that, when executed by an apparatus, cause the apparatus to perform operations. The operations generally include obtaining a first transmit power limit associated with a coherent transmit mode. The first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode. The operations also include transmitting a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0010] Certain aspects of the subject matter described in this disclosure may be implemented in a method for determining a transmit power limit for radio frequency (RF) exposure compliance. The method generally includes obtaining a first RF exposure level associated with transmitting a signal using only a first antenna. The method also includes obtaining a second RF exposure level associated with transmitting the signal using only a second antenna. The method also includes obtaining a third RF exposure level associated with transmitting the signal using multiple antennas in a coherent transmit mode. The multiple antennas include the first antenna and the second antenna. The method also includes determining a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level. The method also includes storing the first transmit power limit in one or more wireless communication devices.

[0011] Certain aspects of the subject matter described in this disclosure may be implemented in an apparatus for wireless communication. The apparatus generally includes: one or more memories that collectively store executable instructions; and one or more processors that are coupled to the one or more memories. The one or more processors are collectively configured to execute the executable instructions to cause the apparatus to: obtain a first RF exposure level associated with transmitting a signal using only a first antenna; obtain a second RF exposure level associated with transmitting the signal using only a second antenna; obtain a third RF exposure level associated with transmitting the signal using multiple antennas in a coherent transmit mode, wherein the multiple antennas include the first antenna and the second antenna; determine a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level; and store the first transmit power limit in one or more wireless communication devices.

[0012] Certain aspects of the subject matter described in this disclosure may be implemented in an apparatus for wireless communication. The apparatus generally includes components for obtaining a first RF exposure level associated with transmitting a signal using only a first antenna. The apparatus also includes components for obtaining a second RF exposure level associated with transmitting the signal using only a second antenna. The apparatus also includes components for obtaining a third RF exposure level associated with transmitting the signal using multiple antennas in a coherent transmit mode. The multiple antennas include the first antenna and the second antenna. The apparatus also includes components for determining a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level. The apparatus also includes components for storing the first transmit power limit in one or more wireless communication devices.

[0013] Certain aspects of the subject matter described in this disclosure may be implemented in a computer-readable medium. The computer-readable medium has instructions stored thereon that, when executed by a device, cause the device to perform operations. The operations generally include obtaining a first RF exposure level associated with transmitting a signal using only a first antenna. The operations also include obtaining a second RF exposure level associated with transmitting the signal using only a second antenna. The operations also include obtaining a third RF exposure level associated with transmitting the signal using multiple antennas in a coherent transmit mode. The multiple antennas include the first antenna and the second antenna. The operations also include determining a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level. The operations also include storing the first transmit power limit in one or more wireless communication devices.

[0014] Other aspects provide: an apparatus operable to, configured to, or otherwise adapted to perform any one or more of the aforementioned methods and / or those described elsewhere herein; a non-transitory computer-readable medium comprising instructions that, when executed by a processor of the apparatus, cause the apparatus to perform the aforementioned methods and those described elsewhere herein; a computer program product embodied on a computer-readable storage medium comprising code for performing the aforementioned methods and those described elsewhere herein; and / or an apparatus comprising components for performing the aforementioned methods and those described elsewhere herein. By way of example, an apparatus may comprise a processing system, a device having a processing system, or processing systems cooperating through one or more networks.

[0015] To achieve the foregoing and related ends, one or more aspects include the features fully described below and particularly pointed out in the claims. The following description and the accompanying drawings set forth in detail certain illustrative features of these one or more aspects. However, these features are indicative of only some of the various ways in which the principles of the various aspects can be employed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order that the above-mentioned features of the present disclosure may be understood in detail, a more particular description, briefly summarized above, may be obtained by reference to some aspects illustrated in the accompanying drawings. It should be noted, however, that the drawings illustrate only certain typical aspects of the present disclosure and are therefore not to be considered limiting of its scope, as the description may admit to other equally effective aspects.

[0017] Figure 1 is a block diagram conceptually illustrating an example wireless communication network exhibiting radio frequency (RF) exposure to humans, in accordance with certain aspects of the present disclosure.

[0018] Figure 2 is a block diagram conceptually illustrating a design of an example wireless communication device that communicates with another device in accordance with certain aspects of the present disclosure.

[0019] Figure 3 is a graph illustrating an example of transmit power over time in compliance with RF exposure limits in accordance with certain aspects of the present disclosure.

[0020] Figure 4 is a diagram illustrating an example system for measuring RF exposure levels or distributions associated with wireless communication devices, in accordance with certain aspects of the present disclosure.

[0021] Figure 5 is a flow chart illustrating example operations for ensuring compliance with time-averaged RF exposure regulatory limits, in accordance with certain aspects of the present disclosure.

[0022] Figure 6 is a flow diagram illustrating example operations for wireless communications by a wireless device in accordance with certain aspects of the present disclosure.

[0023] Figure 7 is a flow diagram illustrating example operations for determining a transmit power limit in accordance with certain aspects of the present disclosure.

[0024] Figure 8 Illustrated are communications devices that may include various components configured to perform operations for the techniques disclosed herein, in accordance with certain aspects of the present disclosure.

[0025] 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

[0026] Aspects of the present disclosure provide apparatus, methods, processing systems, and computer-readable media for complying with radio frequency (RF) exposure limits for related transmissions.

[0027] In some cases, wireless communication devices may perform time-averaged evaluations to ensure that transmissions comply with RF exposure limits. For incoherent transmissions (e.g., signals that are not synchronized in terms of frequency, phase, transmit power, etc.), the wireless device may use a linear calculation (such as the sum of past transmit powers over time) to evaluate the time-averaged RF exposure. For coherent transmissions (e.g., signals that are synchronized in terms of frequency, phase, transmit power, etc.), the time-averaged evaluation may apply a nonlinear operation to account for RF transmissions associated with the coherent signal. As an example, coherent transmissions may involve multiple-input, multiple-output (MIMO) transmissions. For certain devices, such as portable computing devices including smartphones or tablets, nonlinear operations may be computationally intensive. Because the time-averaged evaluation may be repeatedly updated on a rolling basis (e.g., every 500 milliseconds), the wireless device may not be able to complete the nonlinear operation in each iteration associated with the time-averaged evaluation. In some cases, the nonlinear operation may use additional power and / or excessive computational resources that could be allocated to other signal processing operations, such as digital signal processing, automatic gain control, precoding, and forward error correction, as illustrative, non-limiting examples.

[0028] Aspects of the present disclosure provide apparatus and methods for RF exposure compliance for coherent transmission using calculations with reduced complexity (e.g., linear calculations rather than nonlinear calculations involving square roots). Transmit power limits (e.g., P) for individual antennas can be scaled. limit) to account for the nonlinear effects of coherent transmission, as further described herein. The wireless device may apply a linear operation using the scaled transmit power limit when determining the time-averaged exposure for coherent transmission. This time-averaged evaluation may avoid computationally intensive nonlinear operations for coherent transmission.

[0029] The apparatus and methods for RF exposure compliance for coherent transmission described herein can provide various advantages. For example, RF exposure compliance for coherent transmission can improve wireless communication performance, including, for example, increasing throughput, reducing latency, and / or increasing transmission range. This improved performance can be attributed to the increased transmit power allocated for coherent transmission. In some cases, RF exposure compliance for coherent transmission can promote computational efficiency, for example, due to the application of less intensive linear operations being performed. Such computational efficiency can allow the wireless device to dedicate resources to other signal processing operations, such as digital signal processing, automatic gain control, pre-coding, and forward error correction, as illustrative, non-limiting examples.

[0030] The following description provides examples of RF exposure compliance in communication systems and does not limit the scope, applicability, or examples set forth in the claims. The functions and arrangements of the elements discussed may be changed without departing from the scope of this disclosure. Various examples may omit, replace, or add various processes or components as appropriate. For example, the methods described may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with respect to some examples may be combined in some other examples. For example, a device or method may be implemented using any number of aspects set forth herein. In addition, the scope of this disclosure is intended to cover such devices or methods that are practiced using other structures, functionalities, or structures and functionalities that supplement or replace 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 the present claims. The word "exemplary" is used herein to mean "used as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or having advantages over other aspects.

[0031] Generally speaking, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a specific radio access technology (RAT) and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, air interface, etc. A frequency may also be referred to as a carrier, subcarrier, frequency channel, tone, subband, etc. Each frequency may support a single RAT in a given geographic area to avoid interference between wireless networks of different RATs, or may support multiple RATs.

[0032] As used herein, a radio may refer to a physical or logical transmission path associated with one or more frequency bands (carriers, channels, etc.), transceivers, and / or RATs (e.g., wireless wide area network (WWAN), wireless local area network (WLAN), short-range communication (e.g., Bluetooth), non-terrestrial communication, vehicle-to-everything (V2X) communication, etc.) used for wireless communication. For example, for uplink carrier aggregation (or multi-connectivity) in WWAN communication, each of the active component carriers used for wireless communication may be considered a separate radio. Similarly, multi-band transmission in IEEE 802.11 may be considered a separate radio for each frequency band (e.g., 2.4 gigahertz (GHz), 5 GHz, or 6 GHz).

[0033] The techniques described herein can be used for various wireless networks and radio technologies. Although various aspects may be described herein using terms typically associated with 3G, 4G, and / or New Radio (NR) (e.g., 5G NR) wireless technologies, various aspects of the present disclosure may be applied to communication systems based on other generations and / or to wireless technologies such as 802.11, 802.15, etc.

[0034] Example Wireless Communication Networks and Devices

[0035] Figure 1 An example wireless communication network 100 in which various aspects of the present disclosure may be implemented is illustrated. For example, the wireless communication network 100 may include a wireless wide area network (WWAN) and / or a wireless local area network (WLAN). For example, the WWAN may include a new radio (NR) system (e.g., a fifth generation (5G) NR network), an evolved universal terrestrial radio access (E-UTRA) system (e.g., a fourth generation (4G) network), a universal mobile telecommunications system (UMTS) (e.g., a second generation (2G) / third generation (3G) network), a code division multiple access (CDMA) system (e.g., a 2G / 3G network), any future WWAN system, or any combination thereof. A WLAN may include a wireless network configured for communication according to an Institute of Electrical and Electronics Engineers (IEEE) standard, such as one or more of the 802.11 standards. In some cases, the wireless communication network 100 may include a device-to-device (D2D) communication network or a short-range communication system, such as Bluetooth communication.

[0036] like Figure 1As illustrated in FIG, the wireless communication network 100 may include a first wireless device 102 communicating with any of various second wireless devices 104a-f (second wireless device 104) via any of various RATs, where a wireless device may refer to a wireless communication device. The RATs may include, for example, WWAN communication (e.g., E-UTRA and / or 5G NR), WLAN communication (e.g., IEEE 802.11), vehicle-to-everything (V2X) communication, non-terrestrial network (NTN) communication, and / or short-range communication (e.g., Bluetooth).

[0037] The first wireless device 102 may transmit RF signals in proximity to a human 108, who may be a user of the first wireless device 102 and / or a bystander. By way of example, the first wireless device 102 may be held in the hand of the human 108 and / or positioned against or near the head of the human 108. In some cases, the first wireless device 102 may be positioned in a pocket or bag of the human 108. In some cases, the first wireless device 102 may be positioned in proximity to the human 108 as a mobile hotspot. To ensure that the human 108 is not overexposed to RF transmissions from the first wireless device 102, the first wireless device 102 may control the transmit power associated with the RF signals according to RF exposure limits, as further described herein, where the RF exposure limits may depend on the corresponding exposure scenario (e.g., head exposure, hand (limb) exposure, body (body-worn) exposure, hotspot exposure, etc.).

[0038] The first wireless device 102 may include any of a variety of wireless communication devices, including user equipment (UE), a wireless station, an access point, customer premises equipment (CPE), etc. In certain aspects, according to aspects of the present disclosure, the first wireless device 102 includes an RF exposure manager 106 that uses linear operations to ensure RF exposure compliance for coherent transmissions.

[0039] The second wireless devices 104a-f may include, for example, a base station 104a, an aircraft 104b, a satellite 104c, a vehicle 104d, an access point (AP) 104e, and / or a UE 104f. Furthermore, the wireless communication network 100 may include terrestrial aspects, such as ground-based network entities (e.g., base stations 104a and / or access points 104e), and / or non-terrestrial aspects, such as aircraft 104b and satellite 104c. These non-terrestrial aspects may include onboard network entities (e.g., one or more base stations) capable of communicating with other network elements (e.g., ground base stations) and / or user equipment.

[0040] The base station 104a may generally include: a NodeB (NB), an enhanced NodeB (eNB), a next-generation enhanced NodeB (ng-eNB), a next-generation NodeB (gNB or gNodeB), an access point, a base transceiver station, a radio base station, a radio transceiver, transceiver functionality, a transmit / receive point, and / or the like. The base station 104a may provide communication coverage for a corresponding geographic coverage area, which may sometimes be referred to as a cell and may overlap in some cases (e.g., a small cell may have a coverage area that overlaps with the coverage area of ​​a macro cell). For example, the base station may provide communication coverage for a macro cell (covering a relatively large geographic area), a pico cell (covering a relatively small geographic area, such as a stadium), a femto cell (covering a relatively small geographic area (e.g., a home)), and / or other types of cells.

[0041] The first wireless device 102 and / or UE 104f may generally include: a cellular phone, a smart phone, a Session Initiation Protocol (SIP) phone, a laptop computer, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player, a camera, a game console, a tablet computer, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor / actuator, a display, an Internet of Things (IoT) device, an always-on (AON) device, an edge processing device, or other similar devices. A UE may also be more generally referred to as a mobile device, a wireless device, a wireless communication device, a wireless station (STA), a mobile station, a subscriber station, a mobile subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a remote device, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, and other terms.

[0042] In some cases, the first wireless device 102 may control the transmit power used to transmit RF signals to comply with RF exposure limits. RF exposure may be expressed in terms of specific absorption rate (SAR), which measures energy absorption per unit mass of human tissue and may have units of watts per kilogram (W / kg). RF exposure may also be expressed in terms of power density (PD), which measures energy absorption per unit area and may have units of milliwatts per square centimeter (mW / cm 2 In some cases, a maximum permissible exposure (MPE) limit (in the form of PD) may be imposed on wireless communication devices using transmit frequencies above 6 GHz. MPE limits are area-based exposure regulatory metrics, such as energy density limits, which are defined as the number X (Watts per square meter (W / m2) averaged over a defined area and time-averaged over a frequency-dependent time window). 2)) to prevent hazardous human exposure indicated by changes in tissue temperature. Certain RF exposure limits may be specified based on a maximum RF exposure metric (e.g., SAR or PD) averaged over a specified time window (e.g., 100 seconds or 360 seconds for sub-6 GHz bands, or 2 seconds for 60 GHz bands).

[0043] SAR can be used to assess RF exposure for transmission frequencies less than 6 GHz, which encompass wireless communication technologies such as 2G / 3G (e.g., CDMA), 4G (e.g., E-UTRA), 5G (e.g., NR in bands below 6 GHz), IEEE 802.11 (e.g., a / b / g / n / ac), etc. PD can be used to assess RF exposure for transmission frequencies above 6 GHz, which encompass wireless communication technologies such as IEEE 802.11ad, 802.11ay, 5G in mmWave bands, etc. Note that the frequency band from 24 GHz to 71 GHz is sometimes referred to as "millimeter wave" ("mmW" or "mmWave"). Therefore, different metrics can be used to assess RF exposure for different wireless communication technologies.

[0044] A wireless device (e.g., the first wireless device 102) may be capable of transmitting signals using multiple wireless communication technologies and / or frequency bands, and in some cases, may be capable of transmitting such signals simultaneously. For example, a wireless device may transmit signals using a first wireless communication technology (e.g., 3G, 4G, 5G, 802.11a / b / g / n / ac, etc.) operating at or below 6 GHz and a second wireless communication technology (e.g., mmWave 5G in the 24 GHz to 60 GHz band, IEEE 802.11ad, or 802.11ay) operating above 6 GHz. In some aspects, a wireless device may transmit signals using a first wireless communication technology (e.g., 3G, 4G, 5G, IEEE 802.11ac in the sub-6 GHz band, etc.) where RF exposure may be measured in terms of SAR and a second wireless communication technology (e.g., 5G in the 24 GHz to 71 GHz band, IEEE 802.11ad, 802.11ay, etc.) where RF exposure may be measured in terms of PD. As used herein, in some examples, sub-6 GHz frequency bands may include frequency bands from 300 megahertz (MHz) to 6000 MHz, and in some examples may include frequency bands in the 6000 MHz and / or 7000 MHz ranges.

[0045] Figure 2 Illustrated are example components of a first wireless device 102 that may be used to communicate with any of the second wireless devices 104 that are, in some cases, in proximity to human tissue, as represented by a person 108 .

[0046] The first wireless device 102 may be or include a chip, system on chip (SoC), chipset, package, or device that includes one or more modems 212. In some cases, the modem 212 may include, for example, any of a WWAN modem (e.g., a modem configured to communicate via E-UTRA and / or 5G NR standards), a WLAN modem (e.g., a modem configured to communicate via 802.11 standards), a Bluetooth modem, an NTN modem, or the like. In certain aspects, the first wireless device 102 also includes one or more radio components (collectively, "radio component 250"). In some aspects, the first wireless device 102 also includes one or more processors, processing blocks, or processing elements (collectively, "processor 210") and one or more memory blocks or elements (collectively, "memory 240").

[0047] In some aspects, the processor 210 may comprise a processor representing an application processor that generates information for transmission (e.g., application data, such as a content request) and / or receives information (e.g., requested content) via the modem 212. In some cases, the processor 210 may comprise a microprocessor associated with the modem 212 that may implement the RF exposure manager 106 and / or process any of certain protocol stack layers associated with the RAT. For example, the processor 210 may process any of the application layer, the packet layer, the WLAN protocol stack layer (e.g., the link or MAC layer), and / or the WWAN protocol stack layer (e.g., the radio resource control (RRC) layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, and the MAC layer). In some cases, at least one of the modems 212 (e.g., the WWAN modem) may communicate with one or more of the other modems 212 (e.g., the WLAN modem and / or the Bluetooth modem). For example, the processor 210 may represent at least one of the modems 212 that communicates with one or more of the other modems 212.

[0048] The modem 212 may include an intelligent hardware block or device (such as an application specific integrated circuit (ASIC) and other possibilities). The modem 212 may generally be configured to implement a physical (PHY) layer. For example, the modem 212 may be configured to modulate packets and output the modulated packets to the radio 250 for transmission over a wireless medium. The modem 212 is similarly configured to obtain modulated packets received by the radio 250 and demodulate the packets to provide demodulated packets. In addition to the modulator and demodulator, the modem 212 may also include digital signal processing (DSP) circuitry, automatic gain control (AGC), a decoder, a decoder, a multiplexer, and a demultiplexer (not shown).

[0049] As an example, when in transmit mode, the modem 212 may obtain data from the processor 210. The data obtained from the processor 210 may be provided to a decoder, which encodes the data to provide coded bits. The coded bits may be mapped (e.g., using a selected modulation and coding scheme) to points in a modulation constellation to provide modulated symbols. The modulated symbols may be mapped to, for example, spatial streams or space-time streams. The modulated symbols may be multiplexed, transformed via an inverse fast Fourier transform (IFFT) block, and then provided to a DSP circuit for transmit windowing and filtering. The digital signal may be provided to a digital-to-analog converter (DAC) 222. In certain aspects related to beamforming, the modulated symbols in the corresponding spatial streams may be pre-decoded via a steering matrix before being provided to the IFFT block.

[0050] The modem 212 can be coupled to a radio 250 that includes a transmit (TX) path 214 (also referred to as a transmit chain) for transmitting signals via one or more antennas 218 and a receive (RX) path 216 (also referred to as a receive chain) for receiving signals via the antenna 218. When the TX path 214 and the RX path 216 share an antenna 218, these paths can connect to the antenna via an interface 220, which can include any of various suitable RF devices, such as switches, duplexers, diplexers, multiplexers, etc. As an example, the modem 212 can output digital in-phase (I) baseband signals and / or quadrature (Q) baseband signals representing corresponding symbols to a DAC 222.

[0051] Receive the I baseband analog signal or the Q baseband analog signal from the DAC 222. The TX path 214 may include a baseband filter (BBF) 224, a mixer 226, and a power amplifier (PA) 228. The BBF 224 filters the baseband signal received from the DAC 222, and the mixer 226 mixes the filtered baseband signal with a transmit local oscillator (LO) signal to convert the baseband signal to a different frequency (e.g., upconvert from baseband to RF). In some aspects, the frequency conversion process generates sum and difference frequencies between the LO frequency and the baseband signal's frequency. These sum and difference frequencies are referred to as beat frequencies. Some beat frequencies are in the RF range, so the signal output by the mixer 314 is typically an RF signal, which may be amplified by the PA 228 before being transmitted by the antenna 218. The antenna 218 may transmit RF signals, which may be received at the second wireless device 104. Although one mixer 226 is illustrated, several mixers may be used to upconvert the filtered baseband signal to one or more intermediate frequencies and thereafter upconvert the intermediate frequency signal to a frequency for transmission.

[0052] In certain aspects, the first wireless device 102 can communicate via multiple-input, multiple-output (MIMO) signals. The first wireless device 102 can transmit more than one signal to the second wireless device 104 via multiple antennas 218a, 218b (collectively, "antennas 218") via multipath propagation. As an example, a first signal can be transmitted via the first antenna 218a, and a second signal can be transmitted via the second antenna 218b via a different propagation path than the first signal. The MIMO signal can facilitate increased communication link capacity (e.g., throughput) between the first wireless device 102 and the second wireless device 104. The MIMO signal can be coherent, e.g., synchronized in terms of phase, frequency, and / or transmit power. In some cases, the MIMO signal can exhibit nonlinear transmission characteristics, as further described herein.

[0053] The RX path 216 may include a low noise amplifier (LNA) 230, a mixer 232, and a BBF 234. An RF signal received via the antenna 218 (e.g., from the second wireless device 104) may be amplified by the LNA 230, and the mixer 232 may mix the amplified RF signal with a receive local oscillator (LO) signal to convert the RF signal to a baseband frequency (e.g., downconvert). The baseband signal output by the mixer 232 may be filtered by the BBF 234 before being converted to a digital I signal or Q signal by an analog-to-digital converter (ADC) 236 for digital signal processing. The modem 212 may receive the digital I signal or Q signal and further process the digital signal, for example, demodulate the digital signal.

[0054] Some transceivers may employ a frequency synthesizer with a voltage-controlled oscillator (VCO) to generate a stable, tunable LO frequency with a specific tuning range. Thus, the transmit LO frequency may be generated by frequency synthesizer 238, which may be buffered or amplified by an amplifier (not shown) before being mixed with the baseband signal in mixer 226. Similarly, the receive LO frequency may be generated by frequency synthesizer 238, which may be buffered or amplified by an amplifier (not shown) before being mixed with the RF signal in mixer 232. Separate frequency synthesizers may be used for TX path 214 and RX path 216.

[0055] When in receive mode, modem 212 may obtain a digitally converted signal via ADC 236 and RX path 216. For example, within modem 212, the digital signal may be provided to a DSP circuit configured to acquire the received signal, for example, by detecting the presence of a signal and estimating initial timing and frequency offset. The DSP circuit may also be configured to digitally condition the digital signal, for example, using channel (narrowband) filtering, analog impairment conditioning (such as correcting I / Q imbalance), and applying digital gain to ultimately obtain a narrowband signal. The output of the DSP circuit may be fed to an AGC, which may be configured to use information extracted from the digital signal (e.g., in one or more received training fields) to determine an appropriate gain. The output of the DSP circuit may also be coupled to a demodulator configured to extract the modulated symbols from the signal and, for example, calculate a log-likelihood ratio (LLR) for each bit position of each subcarrier in each spatial stream. The demodulator may be coupled to a decoder, which may be configured to process the LLRs to provide decoded bits. The decoded bits from all spatial streams may be fed to a demultiplexer for demultiplexing. The demultiplexed bits may be descrambled and provided to a medium access control layer (eg, processor 210) for processing, evaluation, or interpretation.

[0056] The processor 210 and / or the modem 212 may control the transmission of signals via the TX path 214 and / or the reception of signals via the RX path 216. In some aspects, the processor 210 and / or the modem 212 may be configured to perform various operations, such as those associated with any of the methods described herein. The processor 210 and / or the modem 212 may include a microcontroller, a microprocessor, an application processor, a baseband processor, a MAC processor, a neural network processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic components, discrete hardware components, or any combination thereof. In some cases, aspects of the processor 210 may be integrated with (incorporated into and / or shared with) the modem 212, such as the RF exposure manager 106, a microcontroller, a microprocessor, a baseband processor, a media access control (MAC) processor, a digital signal processor, etc. The memory 240 may store data and program code (e.g., computer-readable instructions) for performing wireless communications as described herein. The memory 240 may be external to (as shown) and / or incorporated into the processor 210 and / or modem 212. In some cases, the RF exposure manager 106 (e.g., as implemented via the processor 210 and / or modem 212) may determine a transmit power (e.g., corresponding to certain gain levels applied to the TX path 214, including the BBF 224, the mixer 226, and / or the PA 228) that complies with RF exposure limits set by country-specific regulations and / or international guidelines (e.g., the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines) as described herein.

[0057] Notice Figure 2 A reference example of a transceiver design is shown. It will be understood that other transceiver designs or architectures may be applied in conjunction with aspects of the present disclosure. For example, while the examples discussed herein utilize I and Q signals (e.g., quadrature modulation), those skilled in the art will understand that the components of the transceiver may be configured to utilize any other suitable modulation, such as polar modulation. As another example, the circuit blocks may be coupled to Figure 2 The configuration shown may be arranged differently, and / or in addition to or in place of the blocks depicted, the blocks depicted may be implemented. Figure 2 Other circuit blocks not shown.

[0058] In some cases, compliance with RF exposure limits can be performed as a time-averaged RF exposure assessment within a specified operating (mobile) time window associated with the RF exposure limit. The RF exposure limit can specify a time-averaged RF exposure metric (e.g., SAR and / or PD) within the operating time window. As an example, the U.S. Federal Communications Commission (FCC) stipulates that for frequency bands below 6 GHz, certain SAR limits (general public exposure) are 0.08 W / kg, as averaged over the entire body, and a peak spatially averaged SAR of 1.6 W / kg averaged over any 1 gram of tissue (defined as a cubic-shaped tissue volume), while certain PD limits are 1 mW / cm 2 , as averaged over the entire body, and at any 1 cm 2 Averaged 4mW / cm 2 The FCC also specifies that for sub-6 GHz bands, the corresponding averaging time may be six minutes (360 seconds), while for mmWave bands (e.g., 60 GHz bands), the averaging time may be 2 seconds.

[0059] The RF exposure limit and / or the corresponding averaging time window may vary based on the frequency band. In some aspects, the RF exposure limit and / or the corresponding averaging time window (if applicable) may be specific to a particular geographic region or country, such as the United States, Canada, China, or the European Union, as illustrative examples. In some cases, the RF exposure limit may specify the maximum allowable RF exposure that may be encountered without time averaging. In such cases, the maximum allowable RF exposure may correspond to the maximum output or transmit power that may be used by the wireless device.

[0060] Figure 3 3. Graph 300 of transmit power (P(t)) over time within a running (e.g., rolling or moving) time window (T) associated with an RF exposure limit. A wireless device (e.g., first wireless device 102) may evaluate RF exposure compliance within the running time window 302 (T) based on past RF exposure (e.g., transmit power reports) in past time intervals 304 of the time window 302 and future time intervals 306. The wireless device may determine a maximum allowable transmit power for the future time interval 306 that satisfies the time-averaged RF exposure limit based on the past RF exposure used in the past time intervals 304. The wireless device may perform this time-averaged evaluation as the time window 302 moves over time, for example, to a next future time interval 308, where the past time interval 304 now includes the previous future time interval 306.

[0061] Maximum time average transmit power limit (P limit) represents the maximum transmit power that the wireless device can continuously transmit within the duration of the operating time window 302(T) to comply with the RF exposure limit. For example, the wireless device transmits at P in the third time window 302c. limit Transmission is continuously performed such that the time-averaged transmission power over a time window (eg, the third time window 302c) is equal to P , which complies with the time-averaged RF exposure limit. limit .

[0062] In some cases, the instantaneous transmit power may exceed P in some transmit opportunities. limit , for example, as shown in the first time window 302a and the second time window 302b. In some cases, the wireless device may P max (It may be the maximum instantaneous transmit power supported by the wireless device, the maximum instantaneous transmit power that the wireless device can output, or the maximum instantaneous transmit power allowed by a standard or regulatory body (e.g., maximum output power P CMAX In some cases, the wireless device may transmit at a rate less than or equal to P in certain transmission opportunities. limit The transmission is performed with a transmission power of , for example, as shown in the first time window 302a.

[0063] In some cases, the reserved power can be used to achieve the following when the power is higher than P in the time window (T) limit When transmitting, the transmission power can be changed from P to P, or from P to ... max Fall back to the reserved power (P reserve ), so that the wireless device can maintain continuous transmission during the time window (e.g., maintain a radio connection with the receiving entity) in compliance with the time average RF exposure limit. In the third time window 302c, the wireless device can increase the transmit power to P that complies with the time average RF exposure limit. limit In some cases, P reserve A specific transmission quality level may be allowed for certain transmissions (e.g., control signaling). reserve It can be used to reserve transmit power for certain transmissions (e.g., control signaling) during at least a portion of the time window 302. reserve May also be called "control power level" or "control level".

[0064] In the second time window 302b, at P max The duration of sending is between P max With P reserve The area between can be equal to the area between P and limit With P reserveThe area between them makes the total area of ​​the transmission power (P(t)) in the second time window 302b equal to P in the time window T limit This area can be considered to use 100% of the energy (transmitted power or exposure) to maintain compliance with the time-averaged RF exposure limit. reserve In the case of max The transmission is performed and the transmitter is turned off for the remainder of the time window to ensure compliance with the time-averaged RF exposure limits.

[0065] In some aspects, the wireless device may operate at a higher frequency than P in the time averaging mode illustrated in the second time window 302b. limit But less than P max While a single transmit burst is illustrated in the second time window 302b, it will be understood that the wireless device may instead utilize multiple transmit bursts within the time window (T), wherein the transmit bursts are transmitted during which the transmit power is maintained at or below P reserve Furthermore, it will be understood that the transmit power of each transmit burst may vary (within a burst and / or compared to other bursts), and that at least a portion of a burst may be higher than P limit of power is sent.

[0066] In certain aspects, a wireless device may transmit at a power less than or equal to a fixed power limit (e.g., P ) without regard to past exposure and / or past transmit power in terms of time-averaged RF exposure. limit For example, the wireless device may use (depending on the RF exposure scenario to include P limit One or more values ​​of the lookup table with a value less than or equal to P limit The lookup table may provide P depending on the transmit frequency, transmit antenna, radio configuration (single radio or multi-radio), and / or RF exposure scenario (e.g., device state index corresponding to head exposure, body or torso exposure, limb or hand exposure, and / or hotspot exposure) encountered by the wireless device. limit Examples of RF exposure scenarios include situations where the wireless device is transmitting RF signals near human tissue (such as the user's head, hands, or body (e.g., torso)), or where the wireless device is being used as a hotspot away from human tissue. Therefore, RF exposure can be managed as a time-averaged RF exposure assessment (e.g., Figure 3 ), managed using a lookup table or a flat or maximum value, or managed using another strategy or algorithm, where the particular process of managing RF exposure may be referred to herein as an RF exposure control scheme.

[0067] For certain aspects, a wireless device may exhibit or be configured with a transmit duty cycle. The wireless device may determine a transmit power level and / or a reserved power level for compliance with a time-averaged RF exposure limit based on the duty cycle. The transmit duty cycle may indicate a fraction (e.g., 5 ms) of a specific time period (e.g., 500 ms) in which the wireless device transmits an RF signal. The duty cycle may be a ratio of the fraction to the specific time period (e.g., 100 ms / 500 ms), where the duty cycle may be represented as a number from zero to one. For example, in a first time window 302a, the duty cycle may be greater than 50% of the duration of the time window (T), while in a second time window 302b, the duty cycle may be equal to 100% of the duration of the time window (T). In some cases, the duty cycle may be standardized (e.g., predetermined) for a specific RAT and / or may change over time, for example, due to changes in radio conditions, mobility, and / or user behavior. As an example, some RATs may specify an uplink duty cycle in the form of a time division duplex (TDD) configuration, such as a TDD uplink-downlink (UL-DL) slot pattern in 5G NR or a similar TDD pattern in E-UTRA or UMTS. In 5G NR, a TDD UL-DL slot pattern may specify the number of uplink time slots and the corresponding time positioning associated with the uplink time slots in a sequence of time slots, such that the total number of uplink time slots relative to the total number of time slots in the sequence indicates the duty cycle. In certain aspects, the duty cycle may correspond to the actual duration of past transmissions scheduled or used within, for example, the TDD UL-DL slot pattern. For example, although a wireless device may be configured with a TDD UL-DL slot pattern, the wireless device may use a portion or subset of the UL time slots to transmit RF signals. As a result, the duty cycle of the wireless device may be less than the maximum available duty cycle corresponding to the TDD UL-DL slot pattern.

[0068] Example RF Exposure Measurement

[0069] In some cases, the RF exposure of wireless devices may be certified by a regulatory body (e.g., the FCC in the United States or Innovation, Science, and Economic Development (ISED) in Canada). Spatial measurements may be made relative to a model representing the human body (a phantom), where the model may be filled with a liquid that simulates human tissue. As discussed above, a first wireless device 102 may simultaneously transmit signals using a first technology (e.g., 3G, 4G, IEEE 802.11ac, etc.) and a second technology (e.g., 5G, IEEE 802.11ad, etc.), where RF exposure is measured using different metrics for the first and second technologies (e.g., SAR for the first technology and PD for the second technology). RF exposure measurements may be performed differently for each transmission scenario and include, for example, electric field measurements using a phantom. RF exposure values ​​and / or distributions (simulated and / or measured) may then be generated for each transmit antenna / configuration (beam) on various evaluation surfaces / positionings at various locations.

[0070] Figure 4 is a diagram illustrating an example system 400 for measuring RF exposure levels (e.g., values ​​and / or distributions) associated with a wireless communication device (e.g., first wireless device 102). As shown, RF exposure measurement system 400 includes a processing system 402, a (robotic) RF probe 404, and a human body model 406. RF exposure measurement system 400 can take RF measurements at various transmission scenarios (e.g., frequency bands, antennas, and / or beams) and / or exposure scenarios (e.g., head exposure, body-worn exposure, limb (hand) exposure, and / or hotspot exposure) associated with first wireless device 102. In some examples, these measurements can be used to generate an RF exposure map and assess appropriate scaling factors for the transmit power of antenna 218 for complying with one or more RF exposure limits, as further described herein. First wireless device 102 can transmit electromagnetic radiation at various transmit powers via antenna 218, and RF exposure measurement system 400 can take RF measurements via robotic RF probe 404 (e.g., to determine an RF exposure map and / or scaling factors for antenna 218). The transmit power limits (eg, P) for various transmit scenarios and / or exposure scenarios associated with the first wireless device 102 may be determined based on RF measurements and / or exposure maps or scaling factors. limit Note that while the measurements are described as being performed relative to the wireless device 102, the measurements may be performed relative to a (different) representative device (e.g., a sample device for testing purposes) and then the transmit power limit value may be loaded into the first wireless device 102 (e.g., a device manufactured for an end user) or otherwise provided or communicated to the first wireless device.

[0071] In some cases, the test separation distance 420 (or spacing) may be adjusted (increased or decreased) depending on the transmit scenario and / or exposure scenario, where the test separation distance 420 may be the distance between the radiating structure (e.g., antenna 218) and any part of the human body (in this example, the human body model 406). For example, the test separation distance 420 may be set to 14 millimeters (mm) for body-worn exposure, 0 mm for head exposure, 10 mm for hotspot exposure, and so on. In some cases, the test separation distance 420 may be different between regions. For example, the test separation distance 420 may be set to 0 mm for body-worn exposure in a particular region and 14 mm for body-worn exposure in another region, and in some cases, the same RF exposure limit (e.g., 1.6 W / kg averaged over 1 gram) may be used. Because the test separation distance 420 may be different between some regions, the corresponding transmit power limits (e.g., P limit ) may differ between these areas regardless of whether the same RF exposure limits apply.

[0072] The processing system 402 may include a processor 408 coupled to a memory 410 via a bus 412. The processing system 402 may be a computing device, such as a computer. The processor 408 may include a microprocessor, a central processing unit (CPU), a graphics processing unit (GPU), a neural network processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic components, discrete hardware components, or any combination thereof, designed to perform the functions described herein. For example, the processor 408 may communicate with the robotic RF probe 404 via an interface 414 (such as a computer bus interface) so that the processor 408 can obtain RF measurements taken by the robotic RF probe 404 and control the positioning of the robotic RF probe 404 relative to the mannequin 406.

[0073] The memory 410 may be configured to store instructions (e.g., computer executable code) that, when executed by the processor 408, cause the processor 408 to perform various operations. For example, the memory 410 may store instructions for obtaining RF exposure values ​​or distributions associated with various RF exposure / transmission scenarios and / or adjusting the positioning of the robotic RF probe 404.

[0074] The robotic RF probe 404 may include an RF probe 416 coupled to a robotic arm 418. In various aspects, the RF probe 416 may be a dosimetry probe capable of measuring RF exposure at various frequencies, such as sub-6 GHz and / or mmWave bands. The RF probe 416 may be positioned by the robotic arm 418 in various positions (as indicated by the dashed arrows) to capture electromagnetic radiation emitted by the antenna 218 of the first wireless device 102. The robotic arm 418 may be a six-axis robot capable of performing precise movements to position the RF probe 416 at a location (on the mannequin 406) of maximum electromagnetic field generated by the first wireless device 102. In other words, the robotic arm 418 may provide six degrees of freedom when positioning the RF probe 416 relative to the antenna 218 of the first wireless device 102 and / or the mannequin 406.

[0075] Mannequin 406 may be a specific anthropomorphic mannequin having simulated human tissue. For example, mannequin 406 may include one or more fluids that simulate human tissue of the head, body, and / or limbs. Mannequin 406 may simulate human tissue to determine the maximum permissible transmit power of antenna 218 in compliance with various RF exposure limits implemented in various regions.

[0076] In some aspects, the RF exposure level associated with the first wireless device 102 can be measured without the human body model 406. For example, the RF probe 416 can be an electric field or magnetic field probe capable of estimating the SAR and / or PD exposure encountered by human tissue in free space surrounding the first wireless device 102. Although this document describes obtaining RF exposure levels using a robotic RF probe, Figure 4 The examples depicted in 406 are provided to facilitate understanding, but aspects of the present disclosure may also be applied to other suitable RF probe architectures, such as using multiple fixed RF probes positioned at various locations along the mannequin 406 or in free space.

[0077] For wireless devices, a specific P can be defined for each RAT, frequency band (or carrier, channel, etc.), antenna (or antenna group), and / or RF exposure scenario (e.g., head exposure, body-worn exposure, hand exposure, hotspot exposure, etc.). limit In some cases, an RF exposure scenario may correspond to a device state index (DSI) or a specific operating state of a device, where the DSI may indicate the device positioning relative to a human body (e.g., head, hand, body, etc.). limit Can correspond to a specific RF exposure target (e.g., SAR or PD), where a separate P can be determined for each RF exposure profile. limit , for example, as this article on Figure 4 As an example of SAR exposure, the P for the kth SAR distribution islimitk It can be given by the following formula:

[0078] P limitk =Tx SARk *SAR_design_target / max(SAR k )(1)where max(SAR k ) is the maximum SAR value in the kth SAR distribution, Tx SARk is the transmit power applied at the antenna when collecting the SAR distribution, and SAR_design_target may be a target SAR limit. In some cases, SAR_design_target may be lower than the regulatory SAR limit to account for device uncertainties and / or to budget sufficient SAR margin to comply with the total RF exposure in simultaneous transmission scenarios with other transmitters that are not included in the RF exposure time averaging operation. Regulatory exposure limits may include RF exposure limits set by regulatory agencies (e.g., FCC) and / or provided by standards bodies (e.g., IEEE or ICNIRP). Therefore, by keeping the time-averaged transmit power for the kth SAR distribution less than or equal to P limitk , so that the time-averaged SAR exhibited by the wireless device remains in compliance with the corresponding regulatory RF exposure limits. limitk It may vary with technology, operating frequency band, transmitting antenna, and / or device positioning relative to the human body (which device positioning may be referred to as a "device state index").

[0079] Since RF exposure (e.g., SAR and / or PD) is proportional to the transmitted power, the time-averaged estimate can be obtained by scaling the stored P limit To perform RF exposure averaging based on past transmit power, as provided in the following expression:

[0080]

[0081] SAR k (t) is the instantaneous SAR value of the kth transmitter (e.g., the maximum value in the SAR distribution), SAR total (t) is the instantaneous total SAR exhibited by the m transmitters, and P limitk Is with Tx k The instantaneous transmission power of the kth transmitter is P corresponding to limit Because P limitk Definition based on max(SAR k ), for example, the maximum SAR value in the kth SAR distribution, so SAR total (t) is to press The maximum SAR values ​​among the scaled active m transmitters are summed regardless of the differences in the location of the maximum SAR in the SAR distribution among the m active transmitters. In other words, expression (2b) provides an example estimate of the total SAR from the m transmitters because it only considers the maximum SAR value of the SAR distribution and does not consider the distribution of the SAR of these transmitters in space. The time-averaged SAR can be given by the following expression:

[0082]

[0083] Where T is the time-averaged (moving) time window associated with the RF exposure limit, e.g., as described herein for Figure 3 described.

[0084] Since RF exposure is proportional to transmit power, the time averaging algorithm can be used in normalized terms (e.g., relative to P limit ) tracks the time-averaged RF exposure as provided in the following expression:

[0085]

[0086] For non-coherent signals (e.g., signals transmitted at different frequencies, or where there is no phase lock to signals transmitted at the same frequency), the total SAR (SAR total (t)) can be expressed as the sum of the SAR of each antenna (k), as provided in the following expression:

[0087]

[0088] Expressions (5) and (4) may represent characteristics of exposure associated with non-coherent signals (e.g., single-input single-output (SISO) transmissions). As further described herein, Expressions (4) and (5) may also be applied to coherent signals using a specific scaling factor that compensates for nonlinear components of exposure exhibited by coherent signals (e.g., MIMO transmissions).

[0089] For coherent signals (e.g., signals transmitted at the same frequency and phase-locked), in the case of a MIMO transmitter where multiple antennas transmit at the same frequency, the total SAR (SAR total (t)) can be given by the following expression:

[0090]

[0091] SAR i (t) and SAR j Each of (t) is the instantaneous SAR associated with antenna i and antenna j, respectively.

[0092] Likewise, for coherent signals, the time averaging algorithm can be used in normalized terms (e.g., relative to P limit ) tracks the time-averaged RF exposure of the coherent signal, as provided in the following expression:

[0093]

[0094] The exponential and square root operations involve nonlinear operations. For some devices, such as portable computing devices including smartphones or tablets, nonlinear operations can be computationally intensive. Because the time-averaged evaluation can be repeatedly updated on a rolling basis (e.g., every 500 milliseconds), the wireless device may not be able to complete the nonlinear operation in every iteration associated with the time-averaged evaluation. In some cases, the nonlinear operation may use additional power and / or excessive computational resources that could be allocated to other signal processing operations, such as digital signal processing, automatic gain control, precoding, forward error correction, etc.

[0095] Example linear calculation of RF exposure for coherent transmission

[0096] Aspects of the present disclosure provide apparatus and methods for RF exposure compliance for coherent transmission using linear calculations. Transmit power limits (e.g., P) for individual antennas can be scaled. limit ) to account for the nonlinear effects of coherent transmission on RF exposure, as described herein with respect to expressions (6) and (7). The wireless device may apply a linear operation using the scaled transmit power limit when determining the time-averaged exposure for coherent transmission. For example, the wireless device may determine the time-averaged exposure based on the sum of the transmit power over time for each of the antennas without the nonlinear components described herein with respect to expressions (6) and (7). This time-averaged evaluation may avoid computationally intensive nonlinear operations for coherent transmission.

[0097] The apparatus and methods for RF exposure compliance for coherent transmission described herein can provide various advantages. For example, RF exposure compliance for coherent transmission can improve wireless communication performance, including, for example, increasing throughput, reducing latency, and / or increasing transmission range. This improved performance can be attributed to the increased transmit power allocated for coherent transmission. In some cases, RF exposure compliance for coherent transmission can promote computational efficiency, for example, due to the application of less intensive linear operations being performed. Such computational efficiency can allow the wireless device to dedicate resources to other signal processing operations, such as digital signal processing, automatic gain control, pre-decoding, forward error correction, as illustrative, non-limiting examples.

[0098] As described herein with respect to expressions (6) and (7), the total SAR and time-averaged SAR encountered for coherent transmission may exhibit nonlinear components, such as square root operations and / or exponentials. For a coherent signal in a 2×2 MIMO transmission, the total instantaneous SAR based on expression (6) may be expressed as:

[0099] MIMO.SAR(t)=SAR1(t)+SAR2(t)+2*sqrt[SAR1(t)*SAR2(t)]

[0100] (8a) where SAR1(t) and SAR2(t) are the instantaneous SAR exhibited by the first antenna (e.g., the first antenna 218a) and the second antenna (e.g., the second antenna 218b), respectively (e.g., the maximum SAR value associated with the corresponding distribution, or a single SAR value or measurement when the distribution is not utilized or considered). Therefore, the MIMO.SAR(t) calculated using expression (8a) may produce a higher value than the sum of SAR1(t) and SAR2(t). However, if expression (8a) is performed using a SAR distribution (which varies with position (x, y, z)), the maximum value among all positions of the SAR distribution may be expressed as:

[0101] MIMO.SAR(t)=max{MIMO.SAR(x,y,z,t)}=

[0102] max{SAR1(x,y,z,t)+SAR2(x,y,z,t)+2*sqrt[SAR1(x,y,z,t)*SAR2(x,y,z,t)]}

[0103] (8b) Given the relationship in expression (8b), MIMO.SAR(t) can be higher, lower, or equal to the sum of SAR1(t) and SAR2(t), depending on the location of the maximum SAR value in the corresponding SAR distributions SAR1(x,y,z,t) and SAR2(x,y,z,t).

[0104] In some aspects, a scaling factor (backoff_for_MIMO, e.g., P limit The scaling factor is abbreviated as back-off (in the example), to compensate for the nonlinear component of RF exposure encountered in MIMO transmission, as further described herein. It will be understood that although the scaling factor is abbreviated as back-off, the scaling factor can represent an adjustment (e.g., an increase or decrease). For example, the total SAR of a 2×2 MIMO transmission can be expressed as follows based on the scaling factor:

[0105] MIMO.SAR(t)=[SAR1(t)+SAR2(t)] / backoff_for_MIMO (9)

[0107] In certain aspects, the scaling factor may be determined using SAR measurements obtained in various transmission modes (e.g., MIMO mode and single transmitter mode), as described herein with respect to Figure 4 As described above. For example, SAR measurements may be obtained for each antenna associated with MIMO transmission when used individually and for each antenna when used in MIMO mode. Thus, in 2×2 MIMO mode, at least three SAR measurements may be obtained: a measurement for each antenna and a measurement for MIMO transmission. In certain aspects, the SAR measurement may correspond to a SAR distribution and / or a particular SAR level associated with the SAR distribution (e.g., the highest SAR value in the SAR distribution).

[0108] In some cases, the wireless device may apply a suitable backoff (e.g., including the scaling factors described herein) to the P determined using the SAR design target. limit Afterwards, P limit Applies to both non-coherent transmission and coherent transmission (e.g., MIMO), as described herein with respect to expressions (3) and (4). For a given SAR design target, P in expression (4) (corresponding to the SAR design target) limit Can be scaled by P limit Replace, where the scaled P limit can be equal to P associated with the SAR design goal limit and the backoff factor (e.g., scaled_P limit =P limit *backoff, where backoff≤1.0) to ensure RF exposure compliance for both non-coherent transmission and coherent transmission (e.g., MIMO). In certain aspects, this scaled P limit It can be used for both non-coherent and coherent transmission.

[0109] In certain aspects, a scaling factor may be applied when certain conditions are met. For example, the scaling factor (backoff_for_MIMO) may only be less than or equal to 1.0 to ensure that non-coherent (e.g., SISO) transmissions are also followed when using expression (4). Thus, the scaling factor may be applied when the SAR exhibited by the MIMO transmission exceeds the sum of the individual RF exposures associated with the antennas in the MIMO transmission. In some cases, the scaling factor may be applied to antennas in the same antenna group, as further described herein. The scaling factor (backoff_for_MIMO) may be applied when (for a 2×2 MIMO scenario) the following conditions are met:

[0110] meas.MIMO.SAR>meas.SAR1+meas.SAR2

[0111] Wherein meas.MIMO.SAR represents the SAR measured when both Tx1 and Tx2 transmit at the P_test level (e.g., in MIMO transmission), meas.SAR1 represents the SAR measured when only Tx1 transmits at the P_test level (e.g., in SISO transmission), and meas.SAR2 represents the SAR measured when only Tx2 transmits at the P_test level (e.g., in SISO transmission).

[0112] The scaling factor (backoff_for_MIMO) can be determined according to the following expression:

[0113] backoff_for_MIMO=(meas.SAR1+meas.SAR2) / (meas.MIMO.SAR) (10)

[0115] When (for 2×2 MIMO scenarios) the following conditions are met, no scaling factor may be applied (or the scaling factor is equal to 1):

[0116] meas.MIMO.SAR≤meas.SAR1+meas.SAR2 (11)

[0118] In certain aspects, the scaling factor may be determined according to the following expression (for a 2×2 MIMO example):

[0119] backoff_for_MIMO(i,j)=

[0120] min{(meas.SARi+meas.SARj) / (meas.MIMO.SARij),1} (12)

[0122] The scaling factor may be determined for all (or some) antenna pair combinations that support 2×2 MIMO. For example, if antenna “k” supports MIMO transmission on a device with N other antennas, the scaling factor for antenna “k” may be determined as:

[0123] backoff_for_MIMO_antenna_k=

[0124] min{backoff_for_MIMO(k,j),j=1 to N,j≠k} (13)

[0126] In scenarios where MIMO.SAR(t) in expression (8b) is less than the sum of the SAR1(t) and SAR2(t) of the individual transmitters, the scaling factor may not be applied or may be set to 1. This may occur in scenarios where the MIMO antennas are physically far enough apart on the device (e.g., when the antennas are in different antenna groups). In such cases, the RF exposure for MIMO transmission is equivalent to the maximum SAR on the device, e.g., In such cases, the scaling factor may not be applied or may be set to 1, since for antennas that are far enough apart, there is less overlap in the SAR distributions.

[0127] In some cases, the scaling factor can be applied to antennas in the same antenna group. If the MIMO antennas are distributed in different antenna groups, the scaled P limit Applied separately to a subset of each antenna group. In a 4×4 MIMO example, three antennas may be in the same antenna group and the fourth antenna may be in a different antenna group. If the SAR exhibited by the MIMO transmission exceeds the sum of the individual RF exposures associated with the antennas in the MIMO transmission as described herein, the three antennas in the same antenna group may have scaled P applied. limit , and the fourth antenna may apply P determined according to expression (1), for example limit An antenna group can be a group of one or more antennas, where the RF exposure associated with such antennas can be tracked and evaluated as a group. The RF exposure associated with an antenna group can be considered mutually exclusive within the antenna group. This RF exposure treatment for an antenna group can be attributed to the physical arrangement of the antennas in the antenna group.

[0128] While the examples provided herein are described with respect to 2×2 MIMO to facilitate understanding, aspects of the present disclosure may also be applied to any MIMO configuration or multi-output transmission mode, such as 4×4 MIMO or any other number (m) of MIMO pairs, as illustrative, non-limiting examples. For example, the scaling factor may be determined according to the following expression:

[0129]

[0130] After determining the scaling factor for each antenna supporting the MIMO transmission mode, the scaled transmit power limit (backed.off.Plimit k ) can be determined as follows:

[0131] backed.off.Plimit k =Plimit k *backoff_for_MIMO_antenna_k(15) Here, after scaling Plimit (by backed.off.Plimit k denoted) may be determined for each combination of RAT, frequency band, antenna (or antenna group), and / or exposure scenario supporting MIMO transmission, and may be always used or selectively used (e.g., when in a coherent transmission scenario, as described below). For antennas to which the scaling factors described above are not applied, the corresponding P limit may remain unchanged such that, for example, only one P is used for each combination of RAT, frequency band, antenna (or antenna group) and / or exposure scenario. limit Can be stored or made available.

[0132] Since the scaled P limit The nonlinear component of the RF exposure for coherent transmission is compensated so that the time-averaged RF exposure can be determined in normalized terms according to the following expression:

[0133]

[0134] Where backed.off.Plimit can be determined according to expression (15).

[0135] In some aspects, the scaled P limit Can be applied to both coherent and incoherent signals. limit Compared to the scaled P limit can be reduced, so the scaled P limit Ensures RF exposure compliance regardless of scaled P limit Whether it is applied to coherent and incoherent signals.

[0136] For certain aspects, the wireless device may select a scaled P for a coherent signal depending on whether a coherent signal or a non-coherent signal is being transmitted. limit and P for incoherent signals limit Wireless devices can store P limit and selects the corresponding P in response to whether the transmission type is coherent or non-coherent limit The time averaging algorithm can convert the incoherent P limit Applied to active antennas that transmit incoherent signals, and the scaled P limit Active antennas used to transmit coherent signals (e.g., MIMO). In certain aspects, the wireless device may store scaled P for each of the supported MIMO antenna configurations (e.g., all or some supported antenna pairs in a 2×2 MIMO scenario, all or some supported antenna quads in a 4×4 MIMO scenario, etc.). limitThe scaling factor may be applied during coherent transmission, and in such aspects, there may be no restrictions on the value of the scaling factor (eg, the scaling factor may be greater than, less than, or equal to 1.0).

[0137] In certain aspects, a wireless device may apply a transmit power limit to antennas belonging to a MIMO combination. For example, a MIMO transmit power limit may be expressed as:

[0138] mimoPlimit(i,j)=Tx SAR(i,j) *SAR design target / max(meas.MIMO.SAR (i,j) )

[0139] In such cases, the sum of the transmit powers of each antenna is can be Instead, Tx(1,2,..,m) is the transmit power for all "m" MIMO transmitters in an mXm MIMO configuration belonging to the same antenna group. In some cases, mimoPlimit may be determined for all supported antenna combinations in all supported MIMO configurations. In some aspects, instead of using P for a MIMO configuration, limit A separate set of limit (as for SISO), but the scaling factor (e.g., backoff_for_MIMO) may be selectively applied in response to whether a coherent signal or an incoherent signal is being transmitted. This implementation may reduce storage size and complexity because P limit A single set of can be used with an appropriate scaling factor.

[0140] For certain aspects, there may be situations where, even if MIMO or other coherent transmission is being used, it may be possible to not apply backoff (with backoff P) when, for example, expression (11) is satisfied. limit The form or will be consistent with P limit Multiplied by the backoff factor). Therefore, whether to use P limit The determination of the back-off factor may not only be based on whether MIMO (or other coherent transmission) is being used, but may also be based on whether a triggered scaled P is being used. limit or unscaled P limit Specific MIMO (or other coherent transmission) scenarios. limit In such cases, the backoff can be set to 1, or the MIMO P limit Set to the same SISO P for this specific MIMO scenario limit The same value allows the device to perform similar operations each time (eg, instead of determining whether to apply a fallback, the device applies a specific fallback each time, and the fallback may be 1 or another value).

[0141] While the examples provided herein are described with respect to SAR to facilitate understanding, aspects of the present disclosure may also be applied to other suitable measures of RF exposure, such as PD.

[0142] Figure 5 is a flow diagram illustrating example operations 500 for ensuring compliance with time-averaged RF exposure regulatory limits. Operations 500 may be performed, for example, by a wireless device (eg, the first wireless device 102).

[0143] Operations 500 may optionally begin at block 502, where the wireless device may obtain transmit power for a particular time interval (e.g., time interval 306) in a time window (T) associated with a time-averaged RF exposure limit. The wireless device may determine the transmit power relative to P limit The normalized power report of the past transmit power of , for example, as described herein with respect to expression (16) In certain aspects, the wireless device may apply the scaled P in response to transmitting the coherent signal. limit , or a backoff may be applied to the past transmit power when transmitting with or with a coherent signal. For certain aspects, the wireless device may limit Applicable to both incoherent and coherent signals.

[0144] The transmit power may be obtained from the radio (e.g., radio 250) that applied the transmit power in the time interval. In certain aspects, the processor 210 and / or the modem 212 may obtain (or access) the transmit power for a particular time interval from the radio 250. For example, the processor 210 and / or the modem 212 may track the transmit power used by the transmit (TX) path 214 over time, as reported by the radio 250 to the processor 210 and / or the modem 212 in a transmit power report. The transmit power report of past transmit power (e.g., past transmit power used in time interval 306) may represent the actual transmit power within an expected device uncertainty.

[0145] At block 504, the wireless device may limit Or the use of scaling factors to perform time averaging operations. For example, due to the scaled P limitor application of a scaling factor that compensates for nonlinear effects of the coherent signal, so the wireless device may determine the time-averaged RF exposure using, for example, a linear operation according to expression (16). The wireless device may determine a normalized exposure margin allowed for the next time interval (e.g., time interval 308) in the time window (T) such that the time-averaged value of the normalized power report and the exposure margin for the next time interval meet the RF exposure limit or design target. In some aspects, the exposure margin may be a maximum RF exposure that the wireless device can produce and meet the RF limit or design target. The normalized exposure margin may be a percentage of the exposure remaining relative to the normalized power report and the scaled RF exposure limit or design target. For example, when the time-averaged value of the normalized power report and the exposure margin for the next time interval is less than or equal to one (e.g., the normalized RF exposure limit or design target), the normalized scaled RF exposure design target may be met.

[0146] At block 506, the wireless device may determine the maximum allowed transmit power (P max_allowed For example, the maximum allowed transmit power (P max_allowed ) can be equal to the normalized exposure margin and P limit The product of .

[0147] At block 508, the wireless device may provide the maximum allowed transmit power to the transceiver circuitry (e.g., radio 250). For example, radio 250 may obtain the maximum allowed transmit power as digital RF information (e.g., a particular gain index associated with the output power of TX path 214), and radio 250 may control the gain applied to the circuitry in the transmit path to output a signal (e.g., an analog RF signal) at the transmit power associated with the digital RF information. Radio 250 may provide the actual transmit power as a transmit power report to processor 210 and / or modem 212 for use in determining the transmit power to be used in the next time interval.

[0148] Figure 6 6 is a flow diagram illustrating example operations 600 for wireless communication. Operations 600 may be performed, for example, by a wireless device (e.g., the first wireless device 102 in the wireless communication network 100). Operations 600 may be implemented as a processor on one or more processors (e.g., Figure 2 Furthermore, the transmission and / or reception of signals by the wireless device in operation 600 may be performed by, for example, one or more antennas (e.g., Figure 2In some aspects, the transmission and / or reception of signals by the wireless device may be implemented by obtaining and / or outputting signals for reception or transmission via a bus interface of one or more processors (e.g., processor 210 and / or modem 212).

[0149] Operations 600 may optionally begin at block 602, where the wireless device may obtain a first transmit power limit value (e.g., backed.off.Plimit) associated with a coherent transmit mode. k ), wherein the first transmit power limit is adjusted by a scaling factor associated with a coherent transmit mode (e.g., backoff_for_MIMO). The first transmit power limit may include a maximum time-averaged transmit power associated with an RF exposure limit. The scaling factor may be a ratio of a sum of RF exposure levels associated with single-antenna transmissions to an RF exposure level associated with MIMO transmissions. The coherent transmit mode may include a MIMO transmit mode. In certain aspects, to obtain the first transmit power limit, the wireless device may select the first transmit power limit from among a plurality of transmit power limits in response to detecting that the wireless device is transmitting a coherent signal.

[0150] At block 604, the wireless device may transmit a first signal via a plurality of antennas in a coherent transmit mode at a first transmit power determined at least in part based on a first transmit power limit. The plurality of antennas may be in an antenna group among a plurality of antenna groups. RF exposures associated with the antenna groups may be considered mutually exclusive of one another among the antenna groups.

[0151] The wireless device may transmit a second signal via at least one of the plurality of antennas in a non-coherent transmit mode at a second transmit power determined at least in part based on the first transmit power limit. The non-coherent transmit mode may be a SISO transmit mode.

[0152] The wireless device may obtain a second transmit power limit associated with a non-coherent transmit mode. The wireless device may transmit a second signal via at least one of the plurality of antennas in the non-coherent transmit mode at a second transmit power determined at least in part based on the second transmit power limit, wherein the second transmit power limit is different from the first transmit power limit. The first transmit power limit may be equal to a product of the second transmit power limit and a scaling factor.

[0153] The wireless device may determine a time-averaged exposure based on the one or more transmit powers and a first transmit power limit. The wireless device may determine the first transmit power based on whether the time-averaged exposure satisfies the RF exposure limit. To determine the time-averaged exposure, the wireless device may perform a linear calculation of the time-averaged exposure based on the first transmit power limit, for example, according to Expression (16). To determine the time-averaged exposure, the wireless device may determine a sum of the one or more transmit powers normalized by the first transmit power limit.

[0154] Figure 7 is a flow diagram illustrating example operations 700 for determining a transmit power limit for RF exposure compliance. Operations 700 may be performed, for example, by a processing system including an RF exposure measurement system (e.g., RF exposure measurement system 400) and / or one or more computing devices (such as one or more computers).

[0155] Operations 700 may optionally begin at block 702, where a processing system may obtain a first RF exposure level associated with transmitting signals using only a first antenna.

[0156] At block 704 , the processing system may obtain a second RF exposure level associated with using only the second antenna to transmit signals.

[0157] At block 706 , the processing system may obtain a third RF exposure level associated with transmitting a signal using a plurality of antennas in a coherent transmit mode, where the plurality of antennas includes a first antenna and a second antenna.

[0158] At block 708 , the processing system and / or another computing device may determine a back-off factor and / or a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level.

[0159] At block 710, a processing system and / or another computing device may store a back-off factor and / or a first transmit power limit in one or more wireless communication devices. The first transmit power limit may include a maximum time-averaged transmit power associated with an RF exposure limit. The first transmit power limit may be adjusted by a scaling factor associated with a coherent transmit mode. The first transmit power limit may be determined as a product of a second transmit power limit and the scaling factor.

[0160] The processing system may configure one or more wireless communication devices to apply a first transmit power limit when transmitting via the multiple antennas in a coherent transmit mode to ensure compliance with RF exposure limits.

[0161] To determine the first transmit power limit, the processing system may determine a sum of at least a first RF exposure level and a second RF exposure level. The processing system may determine a ratio of the sum to a third RF exposure level. The processing system may determine the first transmit power limit as the product of the ratio and a second transmit power limit associated with at least one of the plurality of antennas. To determine the first transmit power limit, the processing system may determine the first transmit power limit in response to determining that the third RF exposure level satisfies criteria associated with the first RF exposure level and the second RF exposure level. The criteria may be satisfied when the third RF exposure level is greater than the sum.

[0162] Aspects of the present disclosure may be applied to any of a variety of wireless communication devices (wireless devices), such as base stations and / or CPE, that may transmit RF signals that may cause exposure to human tissue, thereby implementing the RF exposure compliance described herein.

[0163] Example Communication Device

[0164] Figure 8 Depicted are aspects of an example communication device 800. In some aspects, the communication device 800 is a wireless communication device, such as described above with respect to Figure 1 and Figure 2 A first wireless device 102 is depicted.

[0165] The communication device 800 includes a processing system 802 coupled to a transceiver 808 (e.g., a transmitter and / or receiver). The transceiver 808 is configured to transmit and receive signals for the communication device 800, such as the various signals described herein, via an antenna 810. The processing system 802 can be configured to perform processing functions for the communication device 800, including processing signals received by the communication device 800 and / or to be transmitted by the communication device.

[0166] The processing system 802 includes one or more processors 820. In various aspects, the one or more processors 820 may represent Figure 2 The one or more processors 820 are coupled to a computer readable medium / memory 830 via a bus 806. In some aspects, the computer readable medium / memory 830 is configured to store instructions (e.g., computer executable code) that, when executed by the one or more processors 820, cause the one or more processors 820 to perform operations related to the processing of the data. Figure 6 The described operations 600, or any aspects related to the operations described herein. Note that references to a processor performing a function of the communication device 800 may include one or more processors performing that function of the communication device 800.

[0167] In the depicted example, the computer-readable medium / memory 830 stores code (e.g., executable instructions) for obtaining 831, code for sending 832, code for determining 833, code for executing 834, or any combination thereof. Processing of the codes 831-834 may cause the communication device 800 to perform operations related to Figure 6 The described operations 600, Figure 7 The operations 700 described herein, or any aspect related to the operations described herein.

[0168] The one or more processors 820 include circuits configured to implement (e.g., execute) code stored in the computer-readable medium / memory 830, including circuitry for obtaining 821, circuitry for sending 822, circuitry for determining 823, circuitry for executing 824, or any combination thereof. Processing using circuits 821-824 may enable the communication device 800 to perform operations related to Figure 6 The described operations 600, Figure 7 The operations 700 described herein, or any aspect related to the operations described herein.

[0169] The various components of the communication device 800 may provide for performing Figure 6 The described operations 600, Figure 7 The described operations 700 or any aspect related to the operations described herein may include means for sending, transmitting, or outputting for sending. For example, means for sending, transmitting, or outputting for sending may include Figure 2 TX path 214 and / or antenna 218 of the first wireless device 102 as illustrated in FIG. 1 , and / or Figure 8 The transceiver 808 and antenna 810 of the communication device 800 in FIG. Components for receiving or obtaining may include Figure 2 RX path 216 and / or antenna 218 of the first wireless device illustrated in FIG. 1 , and / or Figure 8 The transceiver 808 and antenna 810 of the communication device 800 in FIG. The means for obtaining, the means for determining, the means for storing, and / or the means for executing may include a processor, such as Figure 2 The processor 210 and / or the modem 212 depicted in FIG. Figure 8 The processor 820 in the embodiment of the present invention. The means for storing may additionally or alternatively include one or more memories, such as Figure 2 Memory 240 depicted in FIG, and / or Figure 8 Computer readable media / memory 830 in.

[0170] Example aspects

[0171] Specific implementation examples are described in the following numbered clauses:

[0172] Aspect 1: A method for wireless communication by a wireless device, the method comprising: obtaining a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; and transmitting a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0173] Aspect 2: The method of aspect 1, wherein: the plurality of antennas are in an antenna group among a plurality of antenna groups; and a radio frequency (RF) exposure associated with the antenna group is considered mutually exclusive with an RF exposure associated with each other antenna group among the plurality of antenna groups.

[0174] Aspect 3: The method according to aspect 1 or 2 further includes transmitting a second signal via at least one antenna of the multiple antennas in a non-coherent transmission mode at a second transmission power determined at least in part based on the first transmission power limit.

[0175] Aspect 4: The method according to Aspect 1 or 2 further includes: obtaining a second transmit power limit associated with a non-coherent transmit mode; and transmitting a second signal via at least one of the multiple antennas in the non-coherent transmit mode at a second transmit power determined at least in part based on the second transmit power limit, wherein the second transmit power limit is different from the first transmit power limit.

[0176] Aspect 5: The method according to aspect 3 or 4, wherein the first transmit power limit is equal to the product of the second transmit power limit and the scaling factor.

[0177] Aspect 6: The method of any one of aspects 1 to 5, wherein the scaling factor is a ratio of a sum of radio frequency (RF) exposure levels associated with single antenna transmission to an RF exposure level associated with multiple input multiple output (MIMO) transmission.

[0178] Aspect 7: The method according to any one of aspects 3 to 6, wherein the non-coherent transmission mode comprises a single-input single-output (SISO) transmission mode.

[0179] Aspect 8: The method according to any one of aspects 1 to 7, wherein the coherent transmission mode comprises a multiple-input multiple-output (MIMO) transmission mode.

[0180] Aspect 9: According to the method described in any one of Aspects 1 to 8, the method further includes: determining the time-averaged exposure based on one or more transmit powers and the first transmit power limit; and determining the first transmit power based on the time-averaged exposure satisfying the radio frequency (RF) exposure limit.

[0181] Aspect 10: The method of aspect 9, wherein determining the time-averaged exposure comprises performing a linear calculation of the time-averaged exposure based on the first transmit power limit.

[0182] Aspect 11: The method of aspect 9 or 10, wherein determining the time average exposure comprises determining a sum of the one or more transmit powers normalized by the first transmit power limit.

[0183] Aspect 12: The method of any one of aspects 1 to 11, wherein the first transmit power limit comprises a maximum time-averaged transmit power associated with an RF exposure limit.

[0184] Aspect 13: The method according to any one of aspects 1 to 2 and 4 to 12, wherein obtaining the first transmit power limit comprises selecting the first transmit power limit among a plurality of transmit power limits in response to detecting that the wireless device is transmitting a coherent signal.

[0185] Aspect 14: A method according to any one of Aspects 1 to 2 and 4 to 12, wherein obtaining the first transmit power limit includes selecting the first transmit power limit from multiple transmit power limits in response to detecting that the wireless device is transmitting in the coherent transmit mode.

[0186] Aspect 15: A method for determining a transmit power limit for radio frequency (RF) exposure compliance, the method comprising: obtaining a first RF exposure level associated with using only a first antenna to transmit a signal; obtaining a second RF exposure level associated with using only a second antenna to transmit the signal; obtaining a third RF exposure level associated with using multiple antennas to transmit the signal in a coherent transmit mode, wherein the multiple antennas include the first antenna and the second antenna; determining a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level; and storing the first transmit power limit in one or more wireless communication devices.

[0187] Aspect 16: The method according to aspect 15, further comprising configuring the one or more wireless communication devices to apply the first transmit power limit when transmitting via the multiple antennas in the coherent transmit mode to ensure compliance with RF exposure limits.

[0188] Aspect 17: A method according to Aspect 15 or 16, wherein determining the first transmit power limit includes: determining the sum of at least the first RF exposure level and the second RF exposure level; determining the ratio of the sum to the third RF exposure level; and determining the first transmit power limit as the product of the ratio and a second transmit power limit associated with at least one of the multiple antennas.

[0189] Aspect 18: A method according to any one of Aspects 15 to 17, wherein determining the first transmit power limit includes determining the first transmit power limit in response to determining that the third RF exposure level satisfies criteria associated with the first RF exposure level and the second RF exposure level.

[0190] Aspect 19: The method of aspect 18, wherein the criterion is satisfied when the third RF exposure level is greater than the sum.

[0191] Aspect 20: The method of any one of aspects 15 to 19, wherein the first transmit power limit comprises a maximum time-averaged transmit power associated with an RF exposure limit.

[0192] Aspect 21: The method according to any one of aspects 15 to 20, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode.

[0193] Aspect 22: The method according to aspect 21, wherein the first transmit power limit value is determined as a product of the second transmit power limit value and the scaling factor.

[0194] Aspect 23: A device for wireless communication, the device comprising: one or more memories, the one or more memories collectively storing executable instructions; and one or more processors, the one or more processors coupled to the one or more memories, the one or more processors collectively configured to execute the executable instructions so that the device: obtains a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; and controls the transmission of a first signal via multiple antennas in the coherent transmit mode with a first transmit power determined at least in part based on the first transmit power limit.

[0195] Aspect 24: An apparatus for determining a transmit power limit for radio frequency (RF) exposure compliance, the apparatus comprising: one or more memories that collectively store executable instructions; and one or more processors coupled to the one or more memories, the one or more processors being collectively configured to execute the executable instructions so that the apparatus: obtains a first RF exposure level associated with using only a first antenna to transmit a signal; obtains a second RF exposure level associated with using only a second antenna to transmit the signal; obtains a third RF exposure level associated with using multiple antennas to transmit the signal in a coherent transmit mode, wherein the multiple antennas include the first antenna and the second antenna; determines a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level; and stores the first transmit power limit in one or more wireless communication devices.

[0196] Aspect 25: An apparatus for wireless communication, the apparatus comprising: a component for obtaining a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; and a component for transmitting a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0197] Aspect 26: An apparatus for determining a transmit power limit for radio frequency (RF) exposure compliance, the apparatus comprising: a component for obtaining a first RF exposure level associated with transmitting a signal using only a first antenna; a component for obtaining a second RF exposure level associated with transmitting the signal using only a second antenna; a component for obtaining a third RF exposure level associated with transmitting the signal using multiple antennas in a coherent transmit mode, wherein the multiple antennas include the first antenna and the second antenna; a component for determining a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level; and a component for storing the first transmit power limit in one or more wireless communication devices.

[0198] Aspect 27: A computer-readable medium having instructions stored thereon, the instructions being for: obtaining a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; and transmitting a first signal via multiple antennas in the coherent transmit mode at a first transmit power determined at least in part based on the first transmit power limit.

[0199] Aspect 28: A computer-readable medium having instructions stored thereon, the instructions being used to: obtain a first RF exposure level associated with using only a first antenna to transmit a signal; obtain a second RF exposure level associated with using only a second antenna to transmit the signal; obtain a third RF exposure level associated with using multiple antennas to transmit the signal in a coherent transmit mode, wherein the multiple antennas include the first antenna and the second antenna; determine a first transmit power limit associated with the coherent transmit mode based at least in part on the first RF exposure level, the second RF exposure level, and the third RF exposure level; and store the first transmit power limit in one or more wireless communication devices.

[0200] Aspect 29: A device comprising: one or more memories that collectively store executable instructions; and one or more processors that are coupled to the one or more memories, the one or more processors being collectively configured to execute the executable instructions and cause the device to perform a method according to any one of Aspects 1 to 22.

[0201] Aspect 30: An apparatus comprising means for performing the method according to any one of aspects 1 to 22.

[0202] Aspect 31: A non-transitory computer-readable medium comprising computer-executable instructions that, when executed by one or more processors of a processing system, cause the processing system to perform the method of any one of aspects 1 to 22.

[0203] Aspect 32: A computer program product embodied on a computer-readable storage medium, the computer program product comprising code for executing the method according to any one of aspects 1 to 22.

[0204] Additional Notes

[0205] 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). For example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other ordering of a, b, and c).

[0206] As used herein, "processor," "at least one processor," or "one or more processors" generally refers to a single processor configured to perform one or more operations or multiple processors configured to collectively perform one or more operations. In the case of multiple processors, execution of one or more operations may be divided among different processors, but a processor may perform multiple operations, and multiple processors may collectively perform a single operation. Similarly, "memory," "at least one memory," or "one or more memories" generally refers to a single memory configured to store data and / or instructions or multiple memories configured to collectively store data and / or instructions.

[0207] As used herein, the term "determining" encompasses a wide variety of actions. For example, "determining" may include calculating, computing, processing, deriving, investigating, searching (e.g., searching in a table, database, or another data structure), ascertaining, and the like. Furthermore, "determining" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Furthermore, "determining" may include resolving, selecting, identifying, searching, choosing, establishing, and the like.

[0208] The method disclosed herein includes one or more actions for implementing the method. Method actions can be interchangeable with each other without departing from the scope of the claims. In other words, unless a specified order of actions is specified, the order and / or use of specific actions can be modified without departing from the scope of the claims. In addition, the various operations of the method described above can be performed by any appropriate component that can perform the corresponding function. The component may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs) or processors.

[0209] The foregoing description is provided to enable anyone skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects. Accordingly, the claims are not intended to be limited to the aspects shown herein, but should be given the full scope consistent with the language of the claims, wherein, unless specifically stated otherwise, references to elements in the singular are not intended to mean "one and only one," but rather "one or more." Unless otherwise specifically stated, the term "some" refers to one or more. All structural and functional equivalents of the elements of the various aspects described throughout this disclosure that are known or later become known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be covered by the claims. In addition, nothing disclosed herein is intended to be dedicated to the public, regardless of whether such disclosure is explicitly stated in the claims. No claim element should be interpreted under the provisions of 35 U.S.C. § 112(f) unless the element is explicitly stated using the phrase "means for..." or, in the case of a method claim, the phrase "step for..."

[0210] The various operations of the methods described above may be performed by any suitable component capable of performing the corresponding functions. The component may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs), or processors. Generally speaking, where there are operations illustrated in the accompanying drawings, those operations may have corresponding corresponding components plus functional components with similar numbers. A hardware module may include several electrical components packaged together, such as one or more dies and / or other components.

[0211] The various illustrative logical blocks, modules, and circuits described in conjunction with this disclosure may be implemented or executed using a general-purpose processor, a digital signal processor (DSP), a neural network processor, a system on a chip (SoC), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic components, discrete hardware components, or any combination thereof, designed to perform the functions described herein. Although a general-purpose processor may be a microprocessor, in an alternative embodiment, the processor may be any commercially available processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

[0212] If implemented in hardware, an example hardware configuration may include a processing system in a wireless node. The processing system may be implemented using a bus architecture. Depending on the specific application and overall design constraints of the processing system, the bus may include any number of interconnecting buses and bridges. The bus may link various circuits together, including a processor, a machine-readable medium, and a bus interface. The bus interface may be used to connect a network adapter, etc., to the processing system via the bus. The network adapter may be used to implement signal processing functions at the physical (PHY) layer. In the UE (see Figure 1 ), a user interface (e.g., a 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 further. The processor may be implemented using one or more general-purpose processors and / or special-purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuits that execute software. Those skilled in the art will recognize how best to implement the described functionality of the processing system depending on the specific application and the overall design constraints imposed on the entire system.

[0213] If implemented in software, the functionality may be stored or transmitted as one or more instructions or codes on a computer-readable medium. Software should be broadly interpreted to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Computer-readable media include both computer storage media and communication media, including any medium that facilitates the transfer of computer programs from one location to another. The processor may be responsible for managing the bus and general processing, including executing software modules stored on a machine-readable storage medium. A computer-readable storage medium may be coupled to the processor so that the processor can read information from and write information to the storage medium. In an alternative, the storage medium may be integral to the processor. For example, the machine-readable medium may include a transmission line, a carrier modulated by data, and / or a computer-readable storage medium having instructions stored thereon, separate from the wireless node, all of which may be accessed by the processor via a bus interface. Alternatively or in addition, the machine-readable medium or any portion thereof may be integrated into the processor, such as in the case of a cache and / or general register file. By way of example, examples of machine-readable storage media may include RAM (random access memory), flash memory, ROM (read-only memory), PROM (programmable read-only memory), EPROM (erasable programmable read-only memory), EEPROM (electrically erasable programmable read-only memory), registers, magnetic disks, optical disks, hard drives, or any other suitable non-transitory storage media, or any combination thereof. The machine-readable medium may be embodied in a computer program product.

[0214] A software module may include a single instruction or perhaps multiple instructions and may be distributed across several different code segments, between different programs, and across multiple storage media. A computer-readable medium may include multiple software modules. A software module includes instructions that, when executed by a device such as a processor, cause a processing system to perform various functions. A software module may include a sending module and a receiving module. Each software module may reside in a single storage device or be distributed across multiple storage devices. By way of example, when a triggering event occurs, a software module may be loaded from a hard drive into RAM. During execution of the software module, the processor may load some of the instructions into a cache to increase access speed. One or more cache lines may then be loaded into a general register file for execution by the processor. When reference is made to the functionality of a software module below, it will be understood that such functionality is implemented by the processor when executing instructions from the software module.

[0215] Moreover, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology such as infrared (IR), radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technology such as infrared, radio, and microwave are included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Optical disks, where magnetic disks typically reproduce data magnetically, and optical disks, which use lasers to reproduce data optically. Thus, in some aspects, computer-readable media may include non-transitory computer-readable media (e.g., tangible media). Furthermore, for other aspects, computer-readable media may include transient computer-readable media (e.g., signals). Combinations of the above should also be included within the scope of computer-readable media.

[0216] Thus, certain aspects may include a computer program product for performing the operations presented herein. For example, such a computer program product may include a computer-readable medium having instructions stored (and / or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein, such as for performing the operations described herein and in Figure 6 and / or Figure 7 Instructions for the operations shown in .

[0217] In addition, it should be understood that the modules and / or other appropriate components for performing the methods and techniques described herein can be downloaded and / or otherwise obtained by the user terminal and / or base station where applicable. For example, such a device can be coupled to a server to facilitate the transfer of components for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage component (e.g., RAM, ROM, or other physical storage media such as a compact disc (CD) or a floppy disk) so that the user terminal and / or base station can obtain the various methods when the storage component is coupled to or provided to the device. In addition, any other appropriate technology for providing the methods and techniques described herein to a device can be used.

[0218] 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.

Claims

1. A method for wireless communication by a wireless device, the method comprising: obtaining a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; and A first signal is transmitted via multiple antennas in the coherent transmission mode at a first transmission power determined at least in part based on the first transmission power limit.

2. The method according to claim 1, wherein: The plurality of antennas are in an antenna group among a plurality of antenna groups; and A radio frequency (RF) exposure associated with the antenna group is considered mutually exclusive from an RF exposure associated with each other antenna group among the plurality of antenna groups.

3. The method of claim 1 , further comprising transmitting a second signal via at least one of the plurality of antennas in a non-coherent transmit mode at a second transmit power determined at least in part based on the first transmit power limit.

4. The method according to claim 1, further comprising: obtaining a second transmit power limit associated with a non-coherent transmit mode; as well as A second signal is transmitted via at least one antenna of the plurality of antennas in the non-coherent transmission mode at a second transmit power determined at least in part based on the second transmit power limit, wherein the second transmit power limit is different from the first transmit power limit.

5. The method of claim 4, wherein the first transmit power limit is equal to a product of the second transmit power limit and the scaling factor.

6. The method of claim 5, wherein the scaling factor is a ratio of a sum of radio frequency (RF) exposure levels associated with single antenna transmission to an RF exposure level associated with multiple input multiple output (MIMO) transmission.

7. The method of claim 4, wherein the non-coherent transmission mode comprises a single-input single-output (SISO) transmission mode.

8. The method of claim 1, wherein the coherent transmission mode comprises a multiple-input multiple-output (MIMO) transmission mode.

9. The method according to claim 1, further comprising: determining a time-averaged exposure based on one or more transmit powers and the first transmit power limit; as well as The first transmit power is determined based on the time-averaged exposure satisfying a radio frequency (RF) exposure limit.

10. The method of claim 9, wherein determining the time-averaged exposure comprises performing a linear calculation of the time-averaged exposure based on the first transmit power limit. The method of claim 9 , wherein determining the time-averaged exposure comprises determining a sum of the one or more transmit powers normalized by the first transmit power limit.

12. The method of claim 1, wherein the first transmit power limit comprises a maximum time-averaged transmit power associated with a radio frequency (RF) exposure limit.

13. The method of claim 1, wherein obtaining the first transmit power limit comprises selecting the first transmit power limit among a plurality of transmit power limits in response to detecting that the wireless device is transmitting a coherent signal.

14. The method of claim 1, wherein obtaining the first transmit power limit comprises selecting the first transmit power limit among a plurality of transmit power limits in response to detecting that the wireless device is transmitting in the coherent transmit mode.

15. An apparatus for wireless communication, the apparatus comprising: one or more memories that collectively store executable instructions; as well as one or more processors coupled to the one or more memories, the one or more processors being collectively configured to execute the executable instructions to cause the apparatus to: obtaining a first transmit power limit associated with a coherent transmit mode, wherein the first transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode, and Transmission of a first signal via a plurality of antennas in the coherent transmission mode is controlled at a first transmission power determined at least in part based on the first transmission power limit.

16. An apparatus according to claim 15, wherein the one or more processors are collectively configured to execute the executable instructions to further cause the apparatus to: control the transmission of a second signal via at least one antenna of the multiple antennas in a non-coherent transmission mode with a second transmission power determined at least in part based on the first transmission power limit.

17. The apparatus of claim 15, wherein the one or more processors are collectively configured to execute the executable instructions to further cause the apparatus to: obtaining a second transmit power limit associated with a non-coherent transmit mode; and Controlling transmission of a second signal via at least one antenna of the plurality of antennas in the non-coherent transmit mode at a second transmit power determined at least in part based on the second transmit power limit, wherein the second transmit power limit is different from the first transmit power limit.

18. The apparatus of claim 17, wherein the first transmit power limit is equal to a product of the second transmit power limit and the scaling factor.

19. The apparatus of claim 18, wherein the scaling factor is a ratio of a sum of radio frequency (RF) exposure levels associated with single antenna transmission and an RF exposure level associated with multiple-input multiple-output (MIMO) transmission.

20. An apparatus for wireless communication, the apparatus comprising: means for obtaining a transmit power limit associated with a coherent transmit mode, wherein the transmit power limit is adjusted by a scaling factor associated with the coherent transmit mode; as well as means for transmitting signals via a plurality of antennas in the coherent transmit mode at a transmit power determined based at least in part on the transmit power limit.

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